WO2013086386A1 - Control algorithm for temperature control system for vehicle cabin - Google Patents

Control algorithm for temperature control system for vehicle cabin Download PDF

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Publication number
WO2013086386A1
WO2013086386A1 PCT/US2012/068534 US2012068534W WO2013086386A1 WO 2013086386 A1 WO2013086386 A1 WO 2013086386A1 US 2012068534 W US2012068534 W US 2012068534W WO 2013086386 A1 WO2013086386 A1 WO 2013086386A1
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WO
WIPO (PCT)
Prior art keywords
controller
electric heater
heat exchanger
temperature
air
Prior art date
Application number
PCT/US2012/068534
Other languages
French (fr)
Inventor
Guangning GAO
Neil Carpenter
Original Assignee
Magna E-Car Systems Of America, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Magna E-Car Systems Of America, Inc. filed Critical Magna E-Car Systems Of America, Inc.
Publication of WO2013086386A1 publication Critical patent/WO2013086386A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60H—ARRANGEMENTS OF HEATING, COOLING, VENTILATING OR OTHER AIR-TREATING DEVICES SPECIALLY ADAPTED FOR PASSENGER OR GOODS SPACES OF VEHICLES
    • B60H1/00—Heating, cooling or ventilating [HVAC] devices
    • B60H1/22—Heating, cooling or ventilating [HVAC] devices the heat being derived otherwise than from the propulsion plant
    • B60H1/2215—Heating, cooling or ventilating [HVAC] devices the heat being derived otherwise than from the propulsion plant the heat being derived from electric heaters
    • B60H1/2218—Heating, cooling or ventilating [HVAC] devices the heat being derived otherwise than from the propulsion plant the heat being derived from electric heaters controlling the operation of electric heaters
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60H—ARRANGEMENTS OF HEATING, COOLING, VENTILATING OR OTHER AIR-TREATING DEVICES SPECIALLY ADAPTED FOR PASSENGER OR GOODS SPACES OF VEHICLES
    • B60H1/00—Heating, cooling or ventilating [HVAC] devices
    • B60H1/00357—Air-conditioning arrangements specially adapted for particular vehicles
    • B60H1/00385—Air-conditioning arrangements specially adapted for particular vehicles for vehicles having an electrical drive, e.g. hybrid or fuel cell
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60H—ARRANGEMENTS OF HEATING, COOLING, VENTILATING OR OTHER AIR-TREATING DEVICES SPECIALLY ADAPTED FOR PASSENGER OR GOODS SPACES OF VEHICLES
    • B60H1/00—Heating, cooling or ventilating [HVAC] devices
    • B60H1/22—Heating, cooling or ventilating [HVAC] devices the heat being derived otherwise than from the propulsion plant
    • B60H1/2215—Heating, cooling or ventilating [HVAC] devices the heat being derived otherwise than from the propulsion plant the heat being derived from electric heaters
    • B60H1/2221—Heating, cooling or ventilating [HVAC] devices the heat being derived otherwise than from the propulsion plant the heat being derived from electric heaters arrangements of electric heaters for heating an intermediate liquid
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D23/00—Control of temperature
    • G05D23/19—Control of temperature characterised by the use of electric means
    • G05D23/1919—Control of temperature characterised by the use of electric means characterised by the type of controller
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60H—ARRANGEMENTS OF HEATING, COOLING, VENTILATING OR OTHER AIR-TREATING DEVICES SPECIALLY ADAPTED FOR PASSENGER OR GOODS SPACES OF VEHICLES
    • B60H1/00—Heating, cooling or ventilating [HVAC] devices
    • B60H1/22—Heating, cooling or ventilating [HVAC] devices the heat being derived otherwise than from the propulsion plant
    • B60H2001/2228—Heating, cooling or ventilating [HVAC] devices the heat being derived otherwise than from the propulsion plant controlling the operation of heaters
    • B60H2001/224—Heating, cooling or ventilating [HVAC] devices the heat being derived otherwise than from the propulsion plant controlling the operation of heaters automatic operation, e.g. control circuits or methods
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60H—ARRANGEMENTS OF HEATING, COOLING, VENTILATING OR OTHER AIR-TREATING DEVICES SPECIALLY ADAPTED FOR PASSENGER OR GOODS SPACES OF VEHICLES
    • B60H1/00—Heating, cooling or ventilating [HVAC] devices
    • B60H1/22—Heating, cooling or ventilating [HVAC] devices the heat being derived otherwise than from the propulsion plant
    • B60H2001/2246—Heating, cooling or ventilating [HVAC] devices the heat being derived otherwise than from the propulsion plant obtaining information from a variable, e.g. by means of a sensor
    • B60H2001/225—Heating, cooling or ventilating [HVAC] devices the heat being derived otherwise than from the propulsion plant obtaining information from a variable, e.g. by means of a sensor related to an operational state of another HVAC device
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60H—ARRANGEMENTS OF HEATING, COOLING, VENTILATING OR OTHER AIR-TREATING DEVICES SPECIALLY ADAPTED FOR PASSENGER OR GOODS SPACES OF VEHICLES
    • B60H1/00—Heating, cooling or ventilating [HVAC] devices
    • B60H1/22—Heating, cooling or ventilating [HVAC] devices the heat being derived otherwise than from the propulsion plant
    • B60H2001/2259—Heating, cooling or ventilating [HVAC] devices the heat being derived otherwise than from the propulsion plant output of a control signal
    • B60H2001/2265—Heating, cooling or ventilating [HVAC] devices the heat being derived otherwise than from the propulsion plant output of a control signal related to the quantity of heat produced by the heater

Definitions

  • the present disclosure relates to temperature control systems for vehicles and more particularly to temperature control systems for vehicles that are powered at least sometimes solely by an electric motor.
  • Electric and hybrid vehicles offer the promise of powered transportation through the use of electric motors while producing little or no emissions. Some vehicles are powered by electric motors only and rely solely on the energy stored in an on-board battery pack. Others are powered by electric motors but have an internal combustion engine to boost the performance of the vehicle or to extend the range of the vehicle.
  • a necessary task in any vehicle is to heat cabin.
  • this task is carried out using an electric heater, and can thus consume a lot of energy, and so it is important to carry out this task efficiently.
  • another necessary task in any vehicle is to cool the cabin, and it is desirable to do so efficiently but without sending uncomfortably cold air into the cabin.
  • Some control schemes that exist for controlling heating or cooling systems for vehicles operate well enough under steady state conditions, but are easily upset during transient conditions, which can lead to overshoot or undershoot of the desired cabin temperature, and/or to situations where uncomfortably hot or cold air is sent to the cabin, which can lead to passenger discomfort. It is desirable to provide a system that is less upset by such transient conditions. Such a system may be applicable to vehicles that are powered solely by internal combustion engines also, in some embodiments.
  • the present disclosure is directed to a controller for a system for controlling the temperature of a cabin in a vehicle having an electric traction motor.
  • the system includes an electric heater and a liquid-to-air heat exchanger positioned to heat an air flow that is directed to the cabin using coolant that is heated by the electric heater.
  • the controller is programmed to: a) select an output level for the electric heater based on the value of the difference between an actual cabin air temperature and a target cabin air temperature, and based on at least one parameter selected from the group of parameters consisting of the temperature of the air flow entering the heat exchanger and the flow rate of the air flow, and b) operate the electric heater at the output level selected in step a).
  • the present disclosure is directed to a controller for a system for controlling the temperature of a cabin in a vehicle having an electric traction motor.
  • the system includes an electric heater and a liquid-to-air heat exchanger positioned to heat an air flow that is directed to the cabin using coolant that is heated by the electric heater.
  • the controller is operatively connected to the electric heater and is programmed to: a) select an output level for the electric heater based on the difference between an actual coolant inlet temperature to the heat exchanger and a target coolant inlet temperature to the heat exchanger, and based on at least one parameter selected from the group of parameters consisting of the air inlet temperature to the heat exchanger and the air flow rate to the heat exchanger, and b) operate the electric heater at the output level selected in step a).
  • the present disclosure is directed to a method for controlling the temperature of a cabin in a vehicle having an electric traction motor, an electric heater, and a liquid-to-air heat exchanger positioned to heat an air flow that is directed to the cabin using coolant that is heated by the electric heater.
  • the method comprising: a) selecting an output level for the electric heater based on the value of the difference between an actual coolant inlet temperature to the heat exchanger and a target coolant inlet temperature to the heat exchanger, and based on at least one parameter selected from the group of parameters consisting of the air inlet temperature to the heat exchanger and the air flow rate to the heat exchanger, and b) operating the electric heater at the output level selected in step a).
  • the present disclosure is directed to a system for controlling the temperature of a cabin in a vehicle that has an electric traction motor.
  • the system includes an electric heater, a liquid- to-air heat exchanger positioned to heat an air flow that is directed to the cabin using coolant that is heated by the electric heater, and a controller operatively connected to the electric heater.
  • the controller is programmed to: a) select an output level for the electric heater based on the difference between an actual coolant inlet temperature to the heat exchanger and a target coolant inlet temperature to the heat exchanger, and based on at least one parameter selected from the group of parameters consisting of the air inlet temperature to the heat exchanger and the air flow rate to the heat exchanger, and b) operate the electric heater at the output level selected in step a).
  • the present disclosure is directed to a controller for a system for controlling the temperature of a cabin in a vehicle.
  • the system includes a compressor, a condenser, a thermal expansion valve, and an evaporator positioned to cool an air flow that is directed to the cabin using refrigerant that is compressed by the compressor.
  • the controller is operatively connected to the compressor and is programmed to: a) select an output level for the compressor based on the difference between an actual air temperature at the evaporator and a target air temperature at the evaporator, and based on at least one parameter selected from the group of parameters consisting of the ambient air temperature and the air flow rate at the evaporator, and b) operate the compressor at the output level selected in step a).
  • the controller may control the output level of the heater by controlling the duty cycle of the heater.
  • the controller may control the output level of the heater using a P-l control algorithm.
  • the invention is directed to a controller that is like any of the controllers described above, except that the controller controls a compressor instead of a heater.
  • FIG. 1 is a perspective view of a vehicle that includes an electric traction motor in accordance with an embodiment of the present invention
  • FIG. 2 is a schematic illustration of a portion of a temperature control system for the vehicle shown in FIG. 1 ;
  • FIG. 3A is a flow diagram of an algorithm used for the control of the temperature of the cabin based on the air flow rate through the heater used to heat air for the cabin of the vehicle shown in FIG. 1 ;
  • FIG. 3B is a flow diagram of an algorithm used for the control of the temperature of the cabin based on the air inlet temperature to the heater used to heat air for the cabin of the vehicle shown in FIG. 1 ;
  • FIG. 4 is a first graph relating to the actual and target temperatures for the air flow leaving the heater, and a second graph relating to the duty cycle of an electric heater used to heat coolant that is in turn used to heat the air flow through the heater, which result from using either of the temperature control algorithms shown in FIGS. 3A or 3B;
  • FIG. 5 is a graph showing the fluctuation in the air outlet temperature that would result from a drop in fan speed or that would result from an increase in air inlet temperature to the heater, using a standard P-l control algorithm;
  • FIG. 6 is a flow diagram of another algorithm that can be used for the control of the temperature of the cabin, according to another embodiment of the present invention.
  • FIG. 2 shows a schematic illustration of a portion of a cabin temperature control system 10 for a vehicle 12 shown in FIG. 1 .
  • the vehicle 12 includes wheels 13, an electric traction motor 14 for driving the wheels 13, first and second battery packs 16a and 16b, a cabin 18, and, among other things, the cabin temperature control system 10 (FIG. 2).
  • the motor 14 may have any suitable configuration for use in powering the electric vehicle 12.
  • the motor 14 may be mounted in a motor compartment that is forward of the cabin 18 and that is generally in the same place an engine compartment is on a typical internal combustion powered vehicle.
  • the vehicle may include one or more hub motors which are mounted directly at the driven wheel(s) 13.
  • the battery packs 16a and 16b provide power that is used by the motor 14 to drive the vehicle 12.
  • the battery packs 16a and 16b may be any suitable types of battery packs.
  • the battery packs 16a and 16b are each made up of a plurality of lithium polymer, Nickel metal hydride or any other type of cells. While two battery packs 1 6a and 16b are shown, it is possible to provide the vehicle 12 with any other suitable number of battery packs, such as, for example, one battery pack.
  • the cabin temperature control system 10 includes a pump 20, an electric heater 22, a liquid-to-air heat exchanger 24 and a controller 26.
  • the pump 20 pumps liquid coolant through the electric heater 22, through the liquid-to-air heat exchanger 24 and on to a destination. While the destination may be controlled through the use of valves, in a scenario where the electric heater 22 is being used to heat coolant that will be used to heat air going to the cabin 18, the coolant will be pumped in a closed loop so that the destination after passing through the heat exchanger 24 will be the inlet of the pump 20.
  • the closed loop or circuit around which the coolant flows is shown at 27.
  • the electric heater 22 heats coolant flowing therethrough and may be any suitable type of electric heater.
  • the electric heater 22 may be a PTC heater and may be sized to consume about 6 kW of power.
  • the heater 22 draws power from the battery packs 16a and 16b.
  • the electric heater 22 may be controlled by several IGBTs, which can be used to adjust the amount of heat that is emitted by the heater 22 to the coolant flowing through it by controlling the duty cycle of the heater 22.
  • the liquid-to-air heat exchanger 24 is used to transfer heat from the coolant to an air flow that is ultimately directed to the vehicle cabin 18 for heating the cabin 18.
  • the liquid-to-air heat exchanger 24 may be any suitable type of liquid-to-air heat exchanger.
  • the controller 26 controls the operation of the electric heater 22 for the purpose of achieving a cabin temperature that is selected by a vehicle occupant via a temperature selector shown at 28.
  • the control algorithm 100 determines which mode to operate in from a plurality of possible modes based on such inputs as the fan speed setting selected by the vehicle occupant using the fan speed selector shown at 30, the target cabin temperature selected using the temperature selector 28, the ambient temperature is sensed by an ambient temperature sensor shown at 32. Examples of different modes include a MAX mode, a FAST mode and a SLOW mode. Each mode represents a different weighting of priorities. For example, in the MAX mode, the highest priority is placed on achieving the selected target cabin temperature as quickly as possible with essentially no regard for energy consumption.
  • the controller 26 attempts to reach the selected target cabin temperature quickly, but with some regard for energy efficiency.
  • the higher priority is on energy efficiency for the vehicle 12 and the controller 26 heats the cabin with little or no compromise in energy efficiency.
  • the controller 26 may attempt to interpret the level of desire of the vehicle occupant based on the settings selected by the occupant on the selectors 28 and 30, and then set the mode accordingly. For example, if the user selects a relatively high target cabin temperature and has selected the highest fan speed setting, the controller 26 may interpret these inputs as an indication of a high level of desire and may operate in the MAX mode.
  • the controller 26 may select or adjust a control algorithm that is applied to the operation of the electric heater 22, based on the mode that the controller 26 is operating in.
  • a P-l control algorithm is used in all three modes.
  • the P-l control algorithm is used to determine a duty-cycle for the electric heater 22 based on a comparison of a target coolant inlet temperature for the heat exchanger 24 with an actual coolant inlet temperature for the heat exchanger 24.
  • the target coolant inlet temperature is selected based on the target cabin temperature. This may be carried out using a lookup table or some other suitable means.
  • the lookup table may be established during vehicle testing, and/or may be based generally on a heat transfer efficiency associated with the heat exchanger 24, among other things.
  • OUTPUT P- D + l-J (from T i to T 2) D-d(t)
  • some terms used in the calculation are: the offset ' (which is the difference between the target and actual coolant inlet temperatures of the heat exchanger), the P-value 'P' (a constant) and the l-value T (another constant).
  • the P-l calculation includes a P- term (the 'proportional' term, which is made up of P multiplied by D) which is summed with an l-term (the Integral' term, which is made up of I multiplied by the integral of the offset over a selected time period from a first point in time T to a second point in time T 2 ).
  • Time is represented here generally by the variable t.
  • T 2 typically represents the present.
  • Ti represents a selected time in the past, such as 10 seconds prior to time T 2 .
  • the P-l control algorithm is shown at 100 in FIG. 3A.
  • the values of P and I are selected for use in the P-l control calculation, optionally based on the mode (e.g. MAX, FAST, SLOW), the selected fan speed, the ambient air temperature, and/or other factors.
  • These P and I values may be determined using a lookup table that is derived based on testing of a prototype of the vehicle 12 during vehicle development and/or based on a software model of the temperature control system.
  • the controller 26 determines the actual coolant inlet temperature T A CT (obtained from a coolant inlet temperature sensor 103) and compares it to the target coolant inlet temperature T T GT, to determine the offset D.
  • T A CT obtained from a coolant inlet temperature sensor 103
  • T GT target coolant inlet temperature
  • the climate control system of the vehicle 1 2 may include an automatic setting for the fan speed, whereby the fan speed is controlled by the vehicle 1 2.
  • a controller in the vehicle 1 2 may take over control of the fan and reduce the fan speed.
  • the vehicle occupants may themselves lower the fan speed for one reason or another, such as to hear a conversation or music on the vehicle's radio.
  • a reduction in the fan speed results of course in a reduction in the air flow rate through the liquid-to-air heat exchanger 24.
  • a reduction in the air flow rate through the heat exchanger 24 means that there is less air to absorb heat from the coolant flow passing through the heat exchanger 24, which means that the outlet temperature of the coolant leaving the heat exchanger 24 would be higher than it would be if the air flow rate were higher.
  • the coolant passes around the circuit 27 it enters the electric heater 22 again, except the coolant is at a higher inlet temperature now because not as much heat was extracted from it at the heat exchanger 24 due to the reduced air flow there.
  • a standard P-l control algorithm responds only to the difference between the actual coolant inlet temperature T A CT and the target coolant inlet temperature T T GT and would therefore not change the duty cycle of the electric heater 22 yet, even though the coolant is at a higher inlet temperature to the electric heater 22 than it was at during its prior entry to the electric heater 22. Thus, the coolant would leave the electric heater 22 hotter than it did during its prior discharge from the electric heater 22.
  • the standard P-l control algorithm can then adjust the duty cycle of the electric heater 22.
  • a graph shown in FIG. 5 shows the performance of a standard P-l control algorithm in relation to T A CT and T T GT in the above scenario. At time T c , the fan speed is reduced.
  • the P-l control algorithm 100 in accordance with an embodiment of the present disclosure, shown in FIG. 3A, takes into account the new, lower, fan speed when determining the duty cycle to use for the electric heater 22.
  • the algorithm determines a saturation value I M AX for the l-term.
  • the saturation value I M AX is the upper limit on the value of the l-term that is permitted by the algorithm 100.
  • the algorithm when calculating the value of the l-term, if the value of I x the integral of the offset D over time exceeds the saturation value I MAX; then the algorithm simply sets it to be equal to the saturation value I M AX- A saturation value for the l-term limits the impact of the l-term on the overall result of the calculation, thereby preventing the control of the electric heater 22 from becoming unstable under certain conditions.
  • the algorithm multiples the saturation value I M AX by an air flow rate adjustment factor that is selected based on the current fan speed.
  • the value of the air flow rate adjustment factor that is used when the climate control system is operating at a high fan speed may be 1 , for example, which means that a high fan speed results in no change to the value of the saturation value I MAX-
  • the air flow rate adjustment factor may be some lower value, such as 0.8.
  • the saturation value I M AX is multiplied by 0.8, and that resulting value (which may be referred to as a modified saturation value I MAX) is then used as the upper limit for the l-term in the P-l control calculation.
  • the air flow rate adjustment factor may be a value that is lower again, such as, for example, 0.7.
  • the values of the air flow rate adjustment factor can be tuned during testing of a prototype of the vehicle 12 (and/or during development using modeling software) so that the response of the temperature control system can be as desired over all levels of air flow.
  • the duty cycle that was determined in step 106 in FIG. 3A is applied to the electric heater 22. The algorithm flow then returns to step 102.
  • FIG. 4 shows two related graphs relating to use of the algorithm 100.
  • the first graph is the target coolant temperature T T GT and the actual coolant temperature TACT in relation to time.
  • the second graph is the electric heater duty cycle in relation to time.
  • the target coolant temperature TTGT is set to some value, (e.g. by a control unit based on a request for a particular cabin temperature by a vehicle occupant).
  • the controller 26 increases the duty cycle to its maximum value to bring the actual coolant inlet temperature TACT up to the target coolant inlet temperature T T GT- At time T 2 , the controller 26 begins decreasing the duty cycle as TACT approaches T T GT- At time T 3 , the fan speed is decreased significantly (manually by a user in the vehicle in this particular instance). As can be seen, the controller 26 responds to this by dropping the duty cycle on the heater 22. This reduces or eliminates the overshoot that would have occurred in T A CT with a standard P-l control algorithm, and reduces the likelihood in an uncomfortably hot flow of air being sent to the cabin. Instead it can be seen in the upper graph that TACT remains relatively close to T T GT-
  • the air inlet temperature to the heat exchanger 24 i.e. the inlet temperature of the air flow to the liquid-to-air heat exchanger 24.
  • the air inlet temperature can change significantly in several scenarios. For example, when the vehicle 12 is turned on while in a relatively cool parking garage and is then driven out of the garage on a warm day, the ambient air temperature can rise by 10 - 20 degrees Fahrenheit relatively abruptly. This would hold true on a sunny winter morning when the ambient air temperature outside may be warmer than the air inside an unheated parking garage.
  • the ambient air temperature is of course directly related to the air inlet temperature to the liquid- to-air heat exchanger 24.
  • Another scenario that would generate an increase in the air inlet temperature would be when some cabin air is being recirculated to the inlet of the liquid-to-air heat exchanger 24 (i.e. the climate control system is being operated in 'recirc' mode). In such an instance the air inlet temperature may increase quickly from an initial temperature as the heat exchanger 24 heats the air flowing therethrough.
  • a standard P-l control algorithm responds only to the difference between the actual coolant inlet temperature TACT and the target coolant inlet temperature T T GT- Thus it would not change the duty cycle of the electric heater 22 in response to a change in ambient air temperature in fresh mode or a change in the air inlet temperature when in recirc mode.
  • the air inlet temperature is increased by some amount, while holding the air flow rate, the coolant flow rate and the coolant inlet temperature constant, there will be less heat transfer from the coolant to the air flow in the heat exchanger.
  • the temperature of the coolant passing through the heat exchanger 24 would not drop as much when the air flow is at an elevated temperature, and so the coolant, when it passes around to the electric heater 22 would be heated to an elevated temperature.
  • An algorithm 150 is shown in FIG. 3B, which is similar to the algorithm 100, but which is configured to compensate for situations where the air inlet temperature to the heat exchanger 24 rises.
  • the algorithm starts at step 151 .
  • the controller 26 determines the actual coolant inlet temperature T A CT (obtained from the coolant inlet temperature sensor 103) and compares it to the target coolant inlet temperature T T GT to determine the offset D.
  • the algorithm 150 multiplies the offset D by an air inlet temperature adjustment factor that is selected based on the current air inlet temperature. The value of the air inlet temperature adjustment factor that is used when the air inlet temperature is relatively low, (e.g.
  • -10 degrees Celsius may be 1 , for example, which means that a low air inlet temperature results in no change to the value of the offset that is used as input for the P-l control calculation.
  • the air inlet temperature adjustment factor may be some lower value, such as 0.8.
  • the offset is multiplied by 0.8 and that resulting value (which may be referred to as a modified offset) is then used as the input to the P- I control calculation, at step 156 to determine a duty cycle for the electric heater 22.
  • the duty cycle that was determined in step 156 is applied to the electric heater 22.
  • Flow of the algorithm control is then returned to step 152.
  • reducing the value of the offset D reduces the aggressiveness of the algorithm in its attempt to bring the actual coolant inlet temperature TACT to the target coolant inlet temperature T T GT.
  • an increase in the air inlet temperature will result in a reduction in the duty cycle of the electric heater 22, which results in a lower air temperature leaving the liquid-to-air heat exchanger 24 and entering the cabin 18 than would occur if the duty cycle of the heater 22 was left unchanged.
  • the values of the air inlet temperature adjustment factor can be tuned during testing of a prototype of the vehicle 12 and/or during development using modeling software so that the response of the temperature control system can be as desired over all air inlet temperatures.
  • the response of the temperature control system in terms of the air outlet temperature from the heat exchanger 24 in relation to an increase in air inlet temperature may be similar to the response in relation to a decrease in fan speed. Accordingly, the upper graph in FIG. 4 is also representative of the response of the temperature control system in relation to an increase in air inlet temperature at time T 3.
  • the controller 26 may account for the air inlet temperature to the heat exchanger using several inputs. For example, the controller 26 may incorporate the temperature read from an ambient air temperature sensor 120, and a value corresponding to the recirc setting (i.e. a value corresponding to what fraction of the inlet air to the heat exchanger 24 is coming from the cabin 18).
  • the algorithm 100 or 150 takes into account changes in either the air flow rate or the air inlet temperature. It is alternatively possible to combine the algorithms 100 and 150 into a single algorithm that took into account changes in both air flow rate and air inlet temperature. This could essentially be algorithm 150 but with steps 104 and 105 from algorithm 100 inserted between steps 152 and 154, or between steps 154 and 156.
  • an algorithm 200 is provided that takes into account parameters such as the air flow rate and/or the air inlet temperature by adjusting the P and I values used in the P-l control calculation instead of by adjusting the offset used in the calculation.
  • P and I values may be generated by testing a prototype vehicle for changes in the particular parameter or group of parameters being accounted for.
  • step 204 assigns new P and I values to be used in the P-l control calculation, in the place of step 104.
  • the P and I values that are selected may change depending on the mode that the temperature control system is operating in (i.e. MAX, FAST, SLOW).
  • the mode is a parameter that controls the P and I values selected by the controller 26.
  • control algorithms 100 and 150 have been described in relation to controlling the output level of the electric (PTC) heater 22 by controlling the duty cycle of the heater 22.
  • controlling the duty cycle of the heater 22 is just one way to control the output level of the heater 22.
  • the output level of the heater 22 may alternatively be controlled by adjustment of the current to the heater 22.
  • the control algorithm 100 has been described as accounting for a change in the air flow rate to the heat exchanger 24 by changing the saturation value for the l-term from the P-l control calculation. It is alternatively possible to account for a change in the air flow rate by changing something else, such as by changing the offset D used in the P-l control calculation.
  • control algorithm 150 has been described as accounting for a change in the air inlet temperature to the heat exchanger 24 by changing the offset D. It is alternatively possible to account for a change in the air inlet temperature by changing something else, such as by changing the saturation value for the l-term from the P-l control calculation.
  • control algorithm according to the present invention was described in relation to controlling an electric heater for the vehicle 12. It will be understood that a control algorithm in accordance with the present invention could be used to control the operation of a compressor as part of an air conditioning system for the vehicle cabin 18, instead of a heater.
  • FIGS. 3A, 3B and 6 show the air conditioning system components, including the aforementioned compressor shown at 300, a condenser 302, a thermal expansion valve 303 and an evaporator 304.
  • a control algorithm may be very similar to the control algorithms shown in FIGS. 3A, 3B and 6, except for the following differences.
  • the controller 26 determines a target refrigerant inlet temperature to the evaporator 304, and controls the compressor 300 in order to achieve that target refrigerant inlet temperature.
  • the control algorithm may be used to control some aspect of the compressor 300 other than duty cycle, such as the speed in a variable speed compressor or the displacement in a variable displacement compressor.
  • the control algorithm used in this embodiment may again be a P-l control algorithm.
  • the input to the P-l control calculation is based on the difference between the actual air temperature at the evaporator and the target air temperature at the evaporator.
  • a control algorithm can, in at least some embodiments, account for changes in the air flow rate through the evaporator 304. If the air flow rate over the evaporator 300 were reduced, it is understood that it would extract less heat from the evaporator, and so the inventive P-l control algorithm may be configured to compensate for that by adjusting some aspect of the P-l control calculation such as the saturation value for the I term, which will potentially reduce the output of the compressor 300. If the ambient air temperature drops, the P-l control algorithm may be configured to compensate for that by adjusting an aspect of the P-l control calculation such as the offset.
  • control of the compressor as described above need not only be used to advantage in a vehicle having an electric traction motor.
  • Many vehicles today that use internal combustions engines either solely, or in combination with an electric traction motor could benefit from such a control scheme as described herein.

Abstract

A controller for a system for controlling the temperature of a cabin in a vehicle having an electric traction motor. The system includes an electric heater and a liquid-to-air heat exchanger positioned to heat an air flow that is directed to the cabin using coolant that is heated by the electric heater. The controller is programmed to: a) select an output level for the electric heater based on the value of the difference between an actual cabin air temperature and a target cabin air temperature, and based on at least one parameter selected from the group of parameters consisting of: the temperature of the air flow entering the heat exchanger, and the flow rate of the air flow, and b) operate the electric heater at the output level selected in step a).

Description

Title: CONTROL ALGORITHM FOR TEMPERATURE CONTROL SYSTEM
FOR VEHICLE CABIN
CROSS-REFERENCE
[0001] This application claims the benefit of U.S. Provisional Patent Application No. 61 /569,043, filed December 9, 201 1 , which is incorporated herein by reference in its entirety.
FIELD OF THE INVENTION
[0002] The present disclosure relates to temperature control systems for vehicles and more particularly to temperature control systems for vehicles that are powered at least sometimes solely by an electric motor.
BACKGROUND OF THE INVENTION
[0003] This section provides background information related to the present disclosure which is not necessarily prior art.
[0004] Electric and hybrid vehicles offer the promise of powered transportation through the use of electric motors while producing little or no emissions. Some vehicles are powered by electric motors only and rely solely on the energy stored in an on-board battery pack. Others are powered by electric motors but have an internal combustion engine to boost the performance of the vehicle or to extend the range of the vehicle.
[0005] A necessary task in any vehicle is to heat cabin. When the electric motor is not producing waste heat, this task is carried out using an electric heater, and can thus consume a lot of energy, and so it is important to carry out this task efficiently. Furthermore, it is important to provide the vehicle occupants with a comfortable temperature in the cabin quickly but without sending uncomfortably hot air into the cabin. Similarly, another necessary task in any vehicle is to cool the cabin, and it is desirable to do so efficiently but without sending uncomfortably cold air into the cabin. [0006] Some control schemes that exist for controlling heating or cooling systems for vehicles operate well enough under steady state conditions, but are easily upset during transient conditions, which can lead to overshoot or undershoot of the desired cabin temperature, and/or to situations where uncomfortably hot or cold air is sent to the cabin, which can lead to passenger discomfort. It is desirable to provide a system that is less upset by such transient conditions. Such a system may be applicable to vehicles that are powered solely by internal combustion engines also, in some embodiments.
SUMMARY OF THE INVENTION
[0007] This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
[0008] In a first aspect, the present disclosure is directed to a controller for a system for controlling the temperature of a cabin in a vehicle having an electric traction motor. The system includes an electric heater and a liquid-to-air heat exchanger positioned to heat an air flow that is directed to the cabin using coolant that is heated by the electric heater. The controller is programmed to: a) select an output level for the electric heater based on the value of the difference between an actual cabin air temperature and a target cabin air temperature, and based on at least one parameter selected from the group of parameters consisting of the temperature of the air flow entering the heat exchanger and the flow rate of the air flow, and b) operate the electric heater at the output level selected in step a).
[0009] In another aspect, the present disclosure is directed to a controller for a system for controlling the temperature of a cabin in a vehicle having an electric traction motor. The system includes an electric heater and a liquid-to-air heat exchanger positioned to heat an air flow that is directed to the cabin using coolant that is heated by the electric heater. The controller is operatively connected to the electric heater and is programmed to: a) select an output level for the electric heater based on the difference between an actual coolant inlet temperature to the heat exchanger and a target coolant inlet temperature to the heat exchanger, and based on at least one parameter selected from the group of parameters consisting of the air inlet temperature to the heat exchanger and the air flow rate to the heat exchanger, and b) operate the electric heater at the output level selected in step a).
[0010] In accordance with another aspect, the present disclosure is directed to a method for controlling the temperature of a cabin in a vehicle having an electric traction motor, an electric heater, and a liquid-to-air heat exchanger positioned to heat an air flow that is directed to the cabin using coolant that is heated by the electric heater. The method comprising: a) selecting an output level for the electric heater based on the value of the difference between an actual coolant inlet temperature to the heat exchanger and a target coolant inlet temperature to the heat exchanger, and based on at least one parameter selected from the group of parameters consisting of the air inlet temperature to the heat exchanger and the air flow rate to the heat exchanger, and b) operating the electric heater at the output level selected in step a).
[0011] In accordance with yet another aspect, the present disclosure is directed to a system for controlling the temperature of a cabin in a vehicle that has an electric traction motor. The system includes an electric heater, a liquid- to-air heat exchanger positioned to heat an air flow that is directed to the cabin using coolant that is heated by the electric heater, and a controller operatively connected to the electric heater. The controller is programmed to: a) select an output level for the electric heater based on the difference between an actual coolant inlet temperature to the heat exchanger and a target coolant inlet temperature to the heat exchanger, and based on at least one parameter selected from the group of parameters consisting of the air inlet temperature to the heat exchanger and the air flow rate to the heat exchanger, and b) operate the electric heater at the output level selected in step a). [0012] In accordance with a further aspect, the present disclosure is directed to a controller for a system for controlling the temperature of a cabin in a vehicle. The system includes a compressor, a condenser, a thermal expansion valve, and an evaporator positioned to cool an air flow that is directed to the cabin using refrigerant that is compressed by the compressor. The controller is operatively connected to the compressor and is programmed to: a) select an output level for the compressor based on the difference between an actual air temperature at the evaporator and a target air temperature at the evaporator, and based on at least one parameter selected from the group of parameters consisting of the ambient air temperature and the air flow rate at the evaporator, and b) operate the compressor at the output level selected in step a). [0013] In accordance with these and other aspects, the controller may control the output level of the heater by controlling the duty cycle of the heater.
[0014] In accordance with these and other aspects, the controller may control the output level of the heater using a P-l control algorithm.
[0015] In accordance with these and other aspects, the invention is directed to a controller that is like any of the controllers described above, except that the controller controls a compressor instead of a heater.
[0016] Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The present invention will now be described, by way of example only, with reference to the attached drawings, in which: [0018] FIG. 1 is a perspective view of a vehicle that includes an electric traction motor in accordance with an embodiment of the present invention;
[0019] FIG. 2 is a schematic illustration of a portion of a temperature control system for the vehicle shown in FIG. 1 ; [0020] FIG. 3A is a flow diagram of an algorithm used for the control of the temperature of the cabin based on the air flow rate through the heater used to heat air for the cabin of the vehicle shown in FIG. 1 ;
[0021] FIG. 3B is a flow diagram of an algorithm used for the control of the temperature of the cabin based on the air inlet temperature to the heater used to heat air for the cabin of the vehicle shown in FIG. 1 ;
[0022] FIG. 4 is a first graph relating to the actual and target temperatures for the air flow leaving the heater, and a second graph relating to the duty cycle of an electric heater used to heat coolant that is in turn used to heat the air flow through the heater, which result from using either of the temperature control algorithms shown in FIGS. 3A or 3B;
[0023] FIG. 5 is a graph showing the fluctuation in the air outlet temperature that would result from a drop in fan speed or that would result from an increase in air inlet temperature to the heater, using a standard P-l control algorithm; and
[0024] FIG. 6 is a flow diagram of another algorithm that can be used for the control of the temperature of the cabin, according to another embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0025] Example embodiments will now be described more fully with reference to the accompanying drawings. However, the example embodiments are solely provided so that this disclosure will be thorough and fully convey the scope to those skilled in the art. [0026] Reference is made to FIG. 2, which shows a schematic illustration of a portion of a cabin temperature control system 10 for a vehicle 12 shown in FIG. 1 . The vehicle 12 includes wheels 13, an electric traction motor 14 for driving the wheels 13, first and second battery packs 16a and 16b, a cabin 18, and, among other things, the cabin temperature control system 10 (FIG. 2). [0027] The motor 14 may have any suitable configuration for use in powering the electric vehicle 12. The motor 14 may be mounted in a motor compartment that is forward of the cabin 18 and that is generally in the same place an engine compartment is on a typical internal combustion powered vehicle. Alternatively, the vehicle may include one or more hub motors which are mounted directly at the driven wheel(s) 13.
[0028] The battery packs 16a and 16b provide power that is used by the motor 14 to drive the vehicle 12. The battery packs 16a and 16b may be any suitable types of battery packs. In an embodiment, the battery packs 16a and 16b are each made up of a plurality of lithium polymer, Nickel metal hydride or any other type of cells. While two battery packs 1 6a and 16b are shown, it is possible to provide the vehicle 12 with any other suitable number of battery packs, such as, for example, one battery pack.
[0029] Referring to FIG. 2, the cabin temperature control system 10 includes a pump 20, an electric heater 22, a liquid-to-air heat exchanger 24 and a controller 26. The pump 20 pumps liquid coolant through the electric heater 22, through the liquid-to-air heat exchanger 24 and on to a destination. While the destination may be controlled through the use of valves, in a scenario where the electric heater 22 is being used to heat coolant that will be used to heat air going to the cabin 18, the coolant will be pumped in a closed loop so that the destination after passing through the heat exchanger 24 will be the inlet of the pump 20. The closed loop or circuit around which the coolant flows is shown at 27.
[0030] The electric heater 22 heats coolant flowing therethrough and may be any suitable type of electric heater. In an embodiment, the electric heater 22 may be a PTC heater and may be sized to consume about 6 kW of power. The heater 22 draws power from the battery packs 16a and 16b. The electric heater 22 may be controlled by several IGBTs, which can be used to adjust the amount of heat that is emitted by the heater 22 to the coolant flowing through it by controlling the duty cycle of the heater 22. [0031] The liquid-to-air heat exchanger 24 is used to transfer heat from the coolant to an air flow that is ultimately directed to the vehicle cabin 18 for heating the cabin 18. The liquid-to-air heat exchanger 24 may be any suitable type of liquid-to-air heat exchanger. [0032] The controller 26 controls the operation of the electric heater 22 for the purpose of achieving a cabin temperature that is selected by a vehicle occupant via a temperature selector shown at 28. The control algorithm 100 determines which mode to operate in from a plurality of possible modes based on such inputs as the fan speed setting selected by the vehicle occupant using the fan speed selector shown at 30, the target cabin temperature selected using the temperature selector 28, the ambient temperature is sensed by an ambient temperature sensor shown at 32. Examples of different modes include a MAX mode, a FAST mode and a SLOW mode. Each mode represents a different weighting of priorities. For example, in the MAX mode, the highest priority is placed on achieving the selected target cabin temperature as quickly as possible with essentially no regard for energy consumption. In the FAST mode, the controller 26 attempts to reach the selected target cabin temperature quickly, but with some regard for energy efficiency. In the SLOW mode, the higher priority is on energy efficiency for the vehicle 12 and the controller 26 heats the cabin with little or no compromise in energy efficiency. The controller 26 may attempt to interpret the level of desire of the vehicle occupant based on the settings selected by the occupant on the selectors 28 and 30, and then set the mode accordingly. For example, if the user selects a relatively high target cabin temperature and has selected the highest fan speed setting, the controller 26 may interpret these inputs as an indication of a high level of desire and may operate in the MAX mode. The controller 26 may select or adjust a control algorithm that is applied to the operation of the electric heater 22, based on the mode that the controller 26 is operating in.
[0033] In the embodiment shown, a P-l control algorithm is used in all three modes. The P-l control algorithm is used to determine a duty-cycle for the electric heater 22 based on a comparison of a target coolant inlet temperature for the heat exchanger 24 with an actual coolant inlet temperature for the heat exchanger 24. The target coolant inlet temperature is selected based on the target cabin temperature. This may be carried out using a lookup table or some other suitable means. The lookup table may be established during vehicle testing, and/or may be based generally on a heat transfer efficiency associated with the heat exchanger 24, among other things.
[0034] A generalized P-l control calculation, which is the core element of the P-l control algorithm, is shown as follows:
[0035] OUTPUT = P- D + l-J(from Ti to T2)D-d(t) [0036] For the purposes of this disclosure, some terms used in the calculation are: the offset ' (which is the difference between the target and actual coolant inlet temperatures of the heat exchanger), the P-value 'P' (a constant) and the l-value T (another constant). The P-l calculation includes a P- term (the 'proportional' term, which is made up of P multiplied by D) which is summed with an l-term (the Integral' term, which is made up of I multiplied by the integral of the offset over a selected time period from a first point in time T to a second point in time T2). Time is represented here generally by the variable t. T2 typically represents the present. Ti represents a selected time in the past, such as 10 seconds prior to time T2. [0037] The P-l control algorithm is shown at 100 in FIG. 3A. At step 101 , the values of P and I are selected for use in the P-l control calculation, optionally based on the mode (e.g. MAX, FAST, SLOW), the selected fan speed, the ambient air temperature, and/or other factors. These P and I values may be determined using a lookup table that is derived based on testing of a prototype of the vehicle 12 during vehicle development and/or based on a software model of the temperature control system. At step 102, the controller 26 determines the actual coolant inlet temperature TACT (obtained from a coolant inlet temperature sensor 103) and compares it to the target coolant inlet temperature TTGT, to determine the offset D. [0038] In a typical P-l control algorithm of the prior art, the duty cycle of the controlled device would be selected based entirely on the offset. However, it has been discovered that certain events can upset the performance of a standard P-l control algorithm when used to control the duty cycle of the electric heater 22 to reach the target temperature TTGT-
[0039] Such events can occur in many scenarios. For example, in some embodiments the climate control system of the vehicle 1 2 may include an automatic setting for the fan speed, whereby the fan speed is controlled by the vehicle 1 2. There may also be other situations in which a controller in the vehicle 1 2 may take over control of the fan and reduce the fan speed. In another scenario, the vehicle occupants may themselves lower the fan speed for one reason or another, such as to hear a conversation or music on the vehicle's radio. A reduction in the fan speed results of course in a reduction in the air flow rate through the liquid-to-air heat exchanger 24. A reduction in the air flow rate through the heat exchanger 24 means that there is less air to absorb heat from the coolant flow passing through the heat exchanger 24, which means that the outlet temperature of the coolant leaving the heat exchanger 24 would be higher than it would be if the air flow rate were higher. As the coolant passes around the circuit 27 it enters the electric heater 22 again, except the coolant is at a higher inlet temperature now because not as much heat was extracted from it at the heat exchanger 24 due to the reduced air flow there. A standard P-l control algorithm responds only to the difference between the actual coolant inlet temperature TACT and the target coolant inlet temperature TTGT and would therefore not change the duty cycle of the electric heater 22 yet, even though the coolant is at a higher inlet temperature to the electric heater 22 than it was at during its prior entry to the electric heater 22. Thus, the coolant would leave the electric heater 22 hotter than it did during its prior discharge from the electric heater 22. Upon reaching the inlet to the heat exchanger 24 where the temperature of the coolant is sensed, the standard P-l control algorithm can then adjust the duty cycle of the electric heater 22. However, depending on several factors, including for example the proximity of TACT to TTGT prior to the reduction in fan speed, there is the potential for the coolant temperature TACT to overshoot the target temperature TTGT, possibly significantly when a reduction in the air flow rate occurs.
[0040] This overshoot can increase the amount of time it takes for a standard P-l control algorithm to bring the temperature of the cabin to the desired temperature. Additionally, this overshoot in coolant temperature, combined with the reduced air flow rate through the heat exchanger 24 can result in an uncomfortably hot air flow leaving the heat exchanger 24 and entering the cabin 18. [0041 ] A graph shown in FIG. 5 shows the performance of a standard P-l control algorithm in relation to TACT and TTGT in the above scenario. At time Tc, the fan speed is reduced. As can be seen, the result of this reduction in fan speed is that TACT overshoots TTGT significantly, as shown at 36, before the standard P-l controller will set a new (lower) target coolant inlet temperature and will reduce the electric heater's duty cycle accordingly.
[0042] However, the P-l control algorithm 100 in accordance with an embodiment of the present disclosure, shown in FIG. 3A, takes into account the new, lower, fan speed when determining the duty cycle to use for the electric heater 22. As shown in FIG. 3A, at step 104 the algorithm determines a saturation value IMAX for the l-term. The saturation value IMAX is the upper limit on the value of the l-term that is permitted by the algorithm 100. In other words, when calculating the value of the l-term, if the value of I x the integral of the offset D over time exceeds the saturation value I MAX; then the algorithm simply sets it to be equal to the saturation value IMAX- A saturation value for the l-term limits the impact of the l-term on the overall result of the calculation, thereby preventing the control of the electric heater 22 from becoming unstable under certain conditions. At step 105, the algorithm multiples the saturation value IMAX by an air flow rate adjustment factor that is selected based on the current fan speed. The value of the air flow rate adjustment factor that is used when the climate control system is operating at a high fan speed may be 1 , for example, which means that a high fan speed results in no change to the value of the saturation value I MAX- However, for a certain fan speed that is lower than the high fan speed the air flow rate adjustment factor may be some lower value, such as 0.8. Thus, for the lower fan speed, the saturation value IMAX is multiplied by 0.8, and that resulting value (which may be referred to as a modified saturation value I MAX) is then used as the upper limit for the l-term in the P-l control calculation. For an even lower fan speed, the air flow rate adjustment factor may be a value that is lower again, such as, for example, 0.7. In general, reducing the value of saturation value IMAX limits the impact of the l-term on the overall resulting value of the P-l calculation and thus somewhat limits or dampens the aggressiveness of the algorithm in its attempt to bring the actual coolant inlet temperature TACT to the target coolant inlet temperature TTGT- In practical terms, in a situation where the actual coolant inlet temperature TACT is below the target coolant inlet temperature TTGT, a drop in fan speed (and therefore air flow rate) may result in a reduction in the duty cycle of the electric heater, so as to inhibit the large overshoot in TACT that resulted from use of the standard P-l control algorithm. The values of the air flow rate adjustment factor can be tuned during testing of a prototype of the vehicle 12 (and/or during development using modeling software) so that the response of the temperature control system can be as desired over all levels of air flow. [0043] At step 108 the duty cycle that was determined in step 106 in FIG. 3A is applied to the electric heater 22. The algorithm flow then returns to step 102.
[0044] FIG. 4 shows two related graphs relating to use of the algorithm 100. The first graph is the target coolant temperature TTGT and the actual coolant temperature TACT in relation to time. The second graph is the electric heater duty cycle in relation to time. At time T-i , the target coolant temperature TTGT is set to some value, (e.g. by a control unit based on a request for a particular cabin temperature by a vehicle occupant). As can be seen in the second graph, the controller 26 increases the duty cycle to its maximum value to bring the actual coolant inlet temperature TACT up to the target coolant inlet temperature TTGT- At time T2, the controller 26 begins decreasing the duty cycle as TACT approaches TTGT- At time T3, the fan speed is decreased significantly (manually by a user in the vehicle in this particular instance). As can be seen, the controller 26 responds to this by dropping the duty cycle on the heater 22. This reduces or eliminates the overshoot that would have occurred in TACT with a standard P-l control algorithm, and reduces the likelihood in an uncomfortably hot flow of air being sent to the cabin. Instead it can be seen in the upper graph that TACT remains relatively close to TTGT-
[0045] Another factor that could upset a typical P-l control algorithm if not accounted for is the air inlet temperature to the heat exchanger 24 (i.e. the inlet temperature of the air flow to the liquid-to-air heat exchanger 24). The air inlet temperature can change significantly in several scenarios. For example, when the vehicle 12 is turned on while in a relatively cool parking garage and is then driven out of the garage on a warm day, the ambient air temperature can rise by 10 - 20 degrees Fahrenheit relatively abruptly. This would hold true on a sunny winter morning when the ambient air temperature outside may be warmer than the air inside an unheated parking garage. In a situation where the vehicle 12 is pulling fresh ambient air into the liquid-to-air heat exchanger 24, the ambient air temperature is of course directly related to the air inlet temperature to the liquid- to-air heat exchanger 24. Another scenario that would generate an increase in the air inlet temperature would be when some cabin air is being recirculated to the inlet of the liquid-to-air heat exchanger 24 (i.e. the climate control system is being operated in 'recirc' mode). In such an instance the air inlet temperature may increase quickly from an initial temperature as the heat exchanger 24 heats the air flowing therethrough. As noted above, a standard P-l control algorithm responds only to the difference between the actual coolant inlet temperature TACT and the target coolant inlet temperature TTGT- Thus it would not change the duty cycle of the electric heater 22 in response to a change in ambient air temperature in fresh mode or a change in the air inlet temperature when in recirc mode. [0046] If the air inlet temperature is increased by some amount, while holding the air flow rate, the coolant flow rate and the coolant inlet temperature constant, there will be less heat transfer from the coolant to the air flow in the heat exchanger. The temperature of the coolant passing through the heat exchanger 24 would not drop as much when the air flow is at an elevated temperature, and so the coolant, when it passes around to the electric heater 22 would be heated to an elevated temperature. A similar situation occurs here as it would with a reduced air flow rate through the heat exchanger 24, in the sense that under certain conditions (e.g. if TACT were close to TTGT) the coolant inlet temperature could wind up overshooting the target temperature TTGT if a standard P-l control algorithm were used. Similarly, a result could be that the temperature of the air flow into the cabin 18 from the liquid-to-air heat exchanger 24 could become uncomfortable in such an event.
[0047] An algorithm 150 is shown in FIG. 3B, which is similar to the algorithm 100, but which is configured to compensate for situations where the air inlet temperature to the heat exchanger 24 rises. The algorithm starts at step 151 . At step 152, the controller 26 determines the actual coolant inlet temperature TACT (obtained from the coolant inlet temperature sensor 103) and compares it to the target coolant inlet temperature TTGT to determine the offset D. At step 154, the algorithm 150 multiplies the offset D by an air inlet temperature adjustment factor that is selected based on the current air inlet temperature. The value of the air inlet temperature adjustment factor that is used when the air inlet temperature is relatively low, (e.g. -10 degrees Celsius), may be 1 , for example, which means that a low air inlet temperature results in no change to the value of the offset that is used as input for the P-l control calculation. However, for air inlet temperatures that are higher, (e.g. +2 degrees Celsius) the air inlet temperature adjustment factor may be some lower value, such as 0.8. Thus, for that air inlet temperature the offset is multiplied by 0.8 and that resulting value (which may be referred to as a modified offset) is then used as the input to the P- I control calculation, at step 156 to determine a duty cycle for the electric heater 22. At step 158, the duty cycle that was determined in step 156 is applied to the electric heater 22. Flow of the algorithm control is then returned to step 152. In general, reducing the value of the offset D reduces the aggressiveness of the algorithm in its attempt to bring the actual coolant inlet temperature TACT to the target coolant inlet temperature TTGT. In practical terms, in a situation where the cabin has not yet been heated up to TTGT, an increase in the air inlet temperature will result in a reduction in the duty cycle of the electric heater 22, which results in a lower air temperature leaving the liquid-to-air heat exchanger 24 and entering the cabin 18 than would occur if the duty cycle of the heater 22 was left unchanged. The values of the air inlet temperature adjustment factor can be tuned during testing of a prototype of the vehicle 12 and/or during development using modeling software so that the response of the temperature control system can be as desired over all air inlet temperatures. The response of the temperature control system in terms of the air outlet temperature from the heat exchanger 24 in relation to an increase in air inlet temperature may be similar to the response in relation to a decrease in fan speed. Accordingly, the upper graph in FIG. 4 is also representative of the response of the temperature control system in relation to an increase in air inlet temperature at time T3.
[0048] The controller 26 may account for the air inlet temperature to the heat exchanger using several inputs. For example, the controller 26 may incorporate the temperature read from an ambient air temperature sensor 120, and a value corresponding to the recirc setting (i.e. a value corresponding to what fraction of the inlet air to the heat exchanger 24 is coming from the cabin 18).
[0049] In the embodiments shown in FIGS. 3A and 3B, the algorithm 100 or 150 takes into account changes in either the air flow rate or the air inlet temperature. It is alternatively possible to combine the algorithms 100 and 150 into a single algorithm that took into account changes in both air flow rate and air inlet temperature. This could essentially be algorithm 150 but with steps 104 and 105 from algorithm 100 inserted between steps 152 and 154, or between steps 154 and 156.
[0050] Also, it is alternatively possible for the algorithm to take into account a completely different parameter or a different combination of parameters instead of air inlet temperature or air flow rate. [0051] In an alternative embodiment, shown in FIG. 6, an algorithm 200 is provided that takes into account parameters such as the air flow rate and/or the air inlet temperature by adjusting the P and I values used in the P-l control calculation instead of by adjusting the offset used in the calculation. Thus, during vehicle development a look up table of P and I values may be generated by testing a prototype vehicle for changes in the particular parameter or group of parameters being accounted for. As can be seen in FIG. 6, the primary difference between the algorithm 200 and the algorithm 100 in FIG. 3A is that step 204 is provided, which assigns new P and I values to be used in the P-l control calculation, in the place of step 104. As noted above, the P and I values that are selected may change depending on the mode that the temperature control system is operating in (i.e. MAX, FAST, SLOW). Thus, the mode is a parameter that controls the P and I values selected by the controller 26.
[0052] The control algorithms 100 and 150 have been described in relation to controlling the output level of the electric (PTC) heater 22 by controlling the duty cycle of the heater 22. However, controlling the duty cycle of the heater 22 is just one way to control the output level of the heater 22. For example, the output level of the heater 22 may alternatively be controlled by adjustment of the current to the heater 22. [0053] The control algorithm 100 has been described as accounting for a change in the air flow rate to the heat exchanger 24 by changing the saturation value for the l-term from the P-l control calculation. It is alternatively possible to account for a change in the air flow rate by changing something else, such as by changing the offset D used in the P-l control calculation. Analogously, the control algorithm 150 has been described as accounting for a change in the air inlet temperature to the heat exchanger 24 by changing the offset D. It is alternatively possible to account for a change in the air inlet temperature by changing something else, such as by changing the saturation value for the l-term from the P-l control calculation. [0054] Throughout this disclosure, the control algorithm according to the present invention was described in relation to controlling an electric heater for the vehicle 12. It will be understood that a control algorithm in accordance with the present invention could be used to control the operation of a compressor as part of an air conditioning system for the vehicle cabin 18, instead of a heater. FIG. 2 shows the air conditioning system components, including the aforementioned compressor shown at 300, a condenser 302, a thermal expansion valve 303 and an evaporator 304. Such a control algorithm may be very similar to the control algorithms shown in FIGS. 3A, 3B and 6, except for the following differences. The controller 26 determines a target refrigerant inlet temperature to the evaporator 304, and controls the compressor 300 in order to achieve that target refrigerant inlet temperature. The control algorithm may be used to control some aspect of the compressor 300 other than duty cycle, such as the speed in a variable speed compressor or the displacement in a variable displacement compressor. The control algorithm used in this embodiment may again be a P-l control algorithm. The input to the P-l control calculation is based on the difference between the actual air temperature at the evaporator and the target air temperature at the evaporator. Such a control algorithm can, in at least some embodiments, account for changes in the air flow rate through the evaporator 304. If the air flow rate over the evaporator 300 were reduced, it is understood that it would extract less heat from the evaporator, and so the inventive P-l control algorithm may be configured to compensate for that by adjusting some aspect of the P-l control calculation such as the saturation value for the I term, which will potentially reduce the output of the compressor 300. If the ambient air temperature drops, the P-l control algorithm may be configured to compensate for that by adjusting an aspect of the P-l control calculation such as the offset. It will be noted that a change in the ambient air temperature affects both the performance of the evaporator 304 and the performance of the condenser 302. As a result, the specific impact on the resulting value outputted by the P-l control calculation may be more complex.
[0055] It will be noted that the control of the compressor as described above need not only be used to advantage in a vehicle having an electric traction motor. Many vehicles today that use internal combustions engines either solely, or in combination with an electric traction motor could benefit from such a control scheme as described herein.
[0056] While the above description constitutes a plurality of embodiments of the present disclosure, it will be appreciated that the present disclosure is susceptible to further modification and change without departing from the fair meaning of the accompanying claims.

Claims

CLAIMS:
1 . A controller for a system for controlling the temperature of a cabin in a vehicle having an electric traction motor, the system including an electric heater and a liquid-to-air heat exchanger positioned to heat an air flow that is directed to the cabin using coolant that is heated by the electric heater, wherein the controller is operatively connected to the electric heater and is programmed to: a) select an output level for the electric heater based on the difference between an actual coolant inlet temperature to the heat exchanger and a target coolant inlet temperature to the heat exchanger, and based on at least one parameter selected from the group of parameters consisting of: the air inlet temperature to the heat exchanger, and the air flow rate to the heat exchanger, and
b) operate the electric heater at the output level selected in step a).
2. A controller as claimed in claim 1 , wherein the controller is programmed to select the output level of the electric heater according to a P-l control algorithm, and wherein the controller adjusts the P and I values used in the P-l control algorithm based on the at least one parameter.
3. A controller as claimed in claim 1 , wherein the controller is programmed to select the output level of the electric heater according to a P-l control calculation, and wherein the controller provides input to the P-l control calculation that is based on the value of the difference between the actual coolant inlet temperature and the target coolant inlet temperature and based on the at least one parameter.
4. A controller as claimed in claim 3, wherein the input to the P-l control calculation is the value of the difference between the actual coolant inlet temperature and the target coolant inlet temperature multiplied by an adjustment factor that is selected based on the at least one parameter.
5. A controller as claimed in claim 4, wherein the adjustment factor decreases as the air inlet temperature to the heat exchanger increases.
6. A controller as claimed in claim 1 , wherein the controller is programmed to select the output level of the electric heater according to a P-l control calculation that includes a P-term and an l-term, wherein the controller is further programmed to select a saturation value for the l-term, wherein the saturation value depends in part on the air flow rate into the heat exchanger.
7. A controller as claimed in claim 1 , wherein the controller is programmed to control the output level of the electric heater by controlling the duty cycle of the electric heater.
8. A method for controlling the temperature of a cabin in a vehicle having an electric traction motor, wherein the vehicle includes an electric heater, a liquid-to- air heat exchanger positioned to heat an air flow that is directed to the cabin using coolant that is heated by the electric heater, the method comprising:
a) selecting an output level for the electric heater based on the value of the difference between an actual coolant inlet temperature to the heat exchanger and a target coolant inlet temperature to the heat exchanger, and based on at least one parameter selected from the group of parameters consisting of: the air inlet temperature to the heat exchanger, and the air flow rate to the heat exchanger, and
b) operating the electric heater at the output level selected in step a).
9. A method as claimed in claim 8, wherein the output level of the electric heater is selected according to a P-l control algorithm, and wherein the P and I values of the P-l control algorithm are adjusted based on the at least one parameter.
10. A method as claimed in claim 9, wherein the output level of the electric heater is selected according to a P-l control calculation, and wherein input for the P-l control calculation is based on the value of the difference between the actual coolant inlet temperature and the target coolant inlet temperature and based on the at least one parameter.
1 1 . A method as claimed in claim 10, wherein the input to the P-l control calculation is the value of the difference between the actual coolant inlet temperature and the target coolant inlet temperature multiplied by an adjustment factor that is selected based on the at least one parameter.
12. A method as claimed in claim 1 1 , wherein the adjustment factor decreases as the air flow temperature into the heat exchanger increases.
13. A method as claimed in claim 8, wherein the controller is programmed to select the output level of the electric heater according to a P-l control calculation that includes a P-term and an l-term, wherein the controller is further programmed to select a saturation value for the l-term, wherein the saturation value depends in part on the air flow rate into the heat exchanger.
14. A method as claimed in claim 9, wherein the controller is programmed to control the output level of the electric heater by controlling the duty cycle of the electric heater.
15. A system for controlling the temperature of a cabin in a vehicle that has an electric traction motor, comprising:
an electric heater;
a liquid-to-air heat exchanger positioned to heat an air flow that is directed to the cabin using coolant that is heated by the electric heater; and
a controller operatively connected to the electric heater, wherein the controller is programmed to:
a) select an output level for the electric heater based on the difference between an actual coolant inlet temperature to the heat exchanger and a target coolant inlet temperature to the heat exchanger, and based on at least one parameter selected from the group of parameters consisting of: the air inlet temperature to the heat exchanger, and the air flow rate to the heat exchanger, and
b) operate the electric heater at the output level selected in step a).
16. A controller for a system for controlling the temperature of a cabin in a vehicle, the system including a compressor, a condenser, a thermal expansion valve and an evaporator positioned to cool an air flow that is directed to the cabin using refrigerant that is compressed by the compressor, wherein the controller is operatively connected to the compressor and is programmed to: a) select an output level for the compressor based on the difference between an actual air temperature at the evaporator and a target air temperature at the evaporator, and based on at least one parameter selected from the group of parameters consisting of: the ambient air temperature, and the air flow rate at the evaporator, and
b) operate the compressor at the output level selected in step a).
17. A controller as claimed in claim 16, wherein the controller is programmed to select the output level of the compressor according to a P-l control algorithm, and wherein the controller adjusts the P and I values used in the P-l control algorithm based on the at least one parameter.
18. A controller as claimed in claim 16, wherein the controller is programmed to select the output level of the compressor according to a P-l control calculation, and wherein the controller provides input to the P-l control calculation that is based on the difference between the actual air temperature at the evaporator and the target air temperature at the evaporator and based on the at least one parameter.
19. A controller as claimed in claim 18, wherein the input to the P-l control calculation is the value of the difference between the actual air temperature at the evaporator and the target air temperature at the evaporator multiplied by an adjustment factor that is selected based on the at least one parameter.
20. A controller as claimed in claim 19, wherein the adjustment factor decreases as the ambient temperature to the heat exchanger increases.
21 . A controller as claimed in claim 16, wherein the controller is programmed to select the output level of the compressor according to a P-l control calculation that includes a P-term and an l-term, wherein the controller is further programmed to select a saturation value for the l-term, wherein the saturation value depends in part on the air flow rate into the compressor.
PCT/US2012/068534 2011-12-09 2012-12-07 Control algorithm for temperature control system for vehicle cabin WO2013086386A1 (en)

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