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ENERGY SAVING DEFOG/DEVICE
OPERATION STRATEGY AND CONTROL
SCHEME FOR VEHICLES
The present invention is related to an automobile defrost/ 5 deice operation.
Passenger comfort and fuel efficiency have set forth increasing demands on automotive heating, ventilating and 10 air-conditioning (HVAC) systems. It is a primary goal of most HVAC systems to detect and avoid internal climate conditions that will result in windshield/window fogging.
As a result, newer and improved automotive HVAC systems are configured to communicate with a plurality of 15 sensors and control actuators. For example, an automotive HVAC system may have a plurality of temperature sensors for measuring the internal temperature of the automobile, the outside temperature and the temperature at various locations within the ductwork of the HVAC system. 20
In addition, the system will also have user manipulated control settings for varying air temperature, fan speed, direct airflow, vary air recirculation ratio and other relevant settings.
Accordingly, and in order to prevent undesired fogging conditions, the HVAC system must be able to prevent and/or rectify such a condition. Moreover, the relationship of the factors causing such a condition varies significantly.
SUMMARY OF THE INVENTION 30
An object of the present invention is to provide an operational protocol for an automotive HVAC system.
Another object of the present invention is to provide an energy-saving defrost/deice operation for use in automobile. ^
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will now be described, by way of example only, with reference to the accompanying drawings in which:
FIG. 1 is a graph illustrating condensation and non- 40 condensation zones;
FIG. 2 is a graph illustrating possible air manipulation scenarios for providing heated air in response to a defog request; 45
FIG. 3 is a graph illustrating a fogging prediction algorithm;
FIG. 4 is a graph illustrating an application of the fogging prediction algorithm illustrated in FIG. 3;
FIG. 5 is an illustration of a schematic for a climate 50 control system utilizing the fogging prediction algorithm of FIG. 4;
FIG. 6 is a block diagram of the automatic defog control loop illustrated in FIG. 5;
FIG. 7 is a graph illustrating refrigeration and nonrefrig- 55 eration operating zones for a defog control system;
FIG. 8 is a block diagram of the energy-saving defog control loop employed by the climate control system illustrated in FIG. 5; and
FIG. 9 is a flowchart illustrating an exemplary embodi- 60 ment of a command sequence for the climate control system illustrated in FIG. 5.
DETAILED DESCRIPTION OF THE
PREFERRED EMBODIMENTS 65
The fogging of the interior surfaces of an automobile's windshield and/or windows is a result of moisture condens
ing on the interior surfaces of the windows. Water vapor will condensate on a surface whose temperature is below the dew point of the air.
The dew point is the temperature of saturated moist air at the same pressure and humidity ratio as the given mixture.
Referring now to FIG. 1, a graph 10 illustrates the relationship between surface temperature, air moisture or humidity and points where the moisture will condensate on the surface creating fog.
Graph 10 defines a "saturation line" 12 the limits or boundary defining a fogging situation for a given temperature and humidity. Graph 10 defines a condensation zone 14 and a non-condensation zone 16.
Accordingly, and in order to prevent or rectify a fogging situation, the temperature and/or the humidity must be manipulated to a point which will avoid and reduce the occurrence of an undesired fogging situation.
The heating ventilating and air conditioning system (HVAC) and climate control system of current automobiles are arranged to alter the air temperature, humidity and air flow direction in response to a defog request.
In response to a defog request, incoming air is first cooled and then heated prior to directing it to the windshield surface. This process may lead to unnecessary cooling and subsequent re-heating of the air which results in an increased load upon the vehicles HVAC system, namely, the unneeded activation of the air-conditioning system and subsequent reheating of the cooled air.
Referring now to FIG. 2, an example of such a situation is illustrated by a graph 18. In a first scenario, air at point A is 32 degrees Fahrenheit with a 100 percent relative humidity. The air is then heated to 90 degrees Fahrenheit which changes its relative humidity to 12 percent. This is illustrated by point B. Note point B is now in the non-condensation zone 16.
In a second scenario, the air at point A is cooled by the vehicles HVAC system to a temperature of to 25 degrees Fahrenheit with a relative humidity of 100 percent. This air is illustrated by point C. Then the air at point C is heated to 90 degrees Fahrenheit, which changes its relative humidity to 9 percent which and illustrated by point D.
In comparing scenario 1 to scenario 2 there is only a 3% difference in the relative humidity of the air at points B and D. However, scenario 2 requires the activation of the airconditioning system as well as an additional heating requirement to reach 90 degrees. This results in a higher energy load upon the vehicles HVAC system that also affects the vehicles fuel efficiency.
Moreover, if the automobile is an electric vehicle or hybrid electric vehicle (HEV) where energy conservation is critical, the needless activation of the air-conditioning system adversely affects the vehicles energy load.
Currently, automobile control systems are configured to activate the cooling system in response to a defog/deice request in order to reduce the humidity of the air.
However, and as illustrated in FIG. 2, the more efficient response is to only heat the fresh air without activating the air-conditioning system (scenario 1). Moreover, and in most cases, the ambient air in winter conditions is very dry.
In accordance with the present invention, a criterion y for determining whether or not to activate the automobiles air-conditioning system in response to a defog or deice request, has been developed. Criterion y can be defined as a
Finally, an empirical equation can be applied as follows:
Equation 1 can be further simplified if there is only one humidity sensor in the HVAC air duct wherein a fogging prediction algorithm is utilized.
Referring now to FIGS. 3-6, a fogging prediction algorithm for use with the instant application is illustrated. Here, the humidity ratio is defined as 00, the degree of saturation is defined as fi, and the saturation humidity ratio is defined as ws.
A dew point prediction model yields the following equations:
The saturation humidity ratio (co^) with respect to temperature is defined using predetermined reference values. For example, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) provides a 25 publication wherein the thermodynamic properties of moist air are available.
In addition, and for the convenience of programming, the following correlation between the saturation humidity ratio (ws) and temperature (T) was developed for use in the instant 30 application:
Referring now to FIGS. 3 and 4, the air humidity ratio is determined by measuring the temperature T and the humidity (j). Then using the above equations the ratio at saturation is calculated. The degree of saturation fi is derived and the humidity ratio 00 is determined. 40
Then the temperature at the windshield must be determined. FIGS. 5 and 6 illustrate one possible implementation of a HVAC system employing the dew point prediction model previously discussed wherein a temperature sensor 50 is positioned on the inside surface of the windshield. 45
Alternatively, an approximate algorithm of estimating windshield temperature Tw can be defined as follows: Tvv=g
For example, and using a constant value of 0.8, y = l defines a fogging zone, 0.8<y<l defines a fogging warning zone and y<0.8 defines a no fogging zone.
Referring now to FIGS. 5 and 6, an automotive HVAC system 20 using the above fogging prediction algorithm is illustrated. Here system 20 receives an air input from a fresh air passage 22 and a recycled air passage 24. An air circulation door 26 controls the mixture of the fresh to recycled air that is inputted into the system. A blower or fan 28 forces the fresh and or recycled air into a main HVAC unit 30 that contains an evaporator 32 for cooling the air. Blower 28 is controlled by either a user manipulated control switch or command signals received from a controller.
A heating element 34 is positioned down stream from evaporator 32. A blend door 35 is positioned to direct the air to and/or away from heating element 34.
A temperature sensor 36 and a humidity sensor 38 are positioned to take air temperature and humidity readings. The location of humidity sensor 38 may vary in order to provide the most accurate humidity reading of the passenger compartment of an automobile. A mode door 40 is positioned to direct the air or a portion thereof to a defog pathway 42, a panel pathway 44 or a floor pathway 46.
Defog pathway 42 is positioned to deliver forced air to an automobile windshield 48.
A second temperature sensor 50 is positioned to take temperature readings at or around the windshield surface. Alternatively, and as previously discussed, the temperature of the windshield may be estimated using an empirical equation wherein sensor 50 is no longer necessary. An ambient air temperature sensor 52 is positioned to provide exterior or fresh air temperature readings.
Sensors 36, 38, 50 and 52 provide readings to a thermal controller 54. Thermal controller 54 controls the positioning of air circulation door 26, blend door 35 and mode door 40. In addition, thermal controller 54 also activates evaporator 32 and heating unit 34.
A humidity set point 56 also provides an input into controller 54. In addition, a defog/deice request 58 is also inputted into thermal controller 54.
Accordingly, and once a defog or deice request is received, controller 54 determines through the application of criterion y whether to activate the air-conditioning 32 and heating system 34 or the heating system only. As discussed, y is determined by a control algorithm and accordingly, the activation of the heating and/or refrigeration systems is based upon the ambient condition, namely, heating of air and or dehumidification of the air. Once y is determined, a control algorithm of controller 54 manipulates system 20.
If y = l controller 54 actuates mode door 40 into a defog position. If, 0.8>y<l, controller 54 actuates mode door 40 into a defog and floor position. Moreover, and in response to the value of y, controller 54 will also adjust recirculation door 26 and, if necessary, adjust the speed of blower 28.
Referring back now to Equation 2: y=w's/(a it is noted that If y>0.8 then the air-conditioning system of the automobile needs to be activated to cool the air prior to its being heated and directed towards the windshield surface.
On the other hand, if y<0.8 then the air-conditioning system of the automobile is not required and the air only needs to be heated prior to it being directed to the windshield surface.
As an alternative, Equation 1 can also be simplified if there is no humidity sensor in the system yielding the following equation:
Tair=0.5Tambient+55 (all temperatures are in Fahrenheit) Equation 4
Accordingly, equation 4 provides a graph 60 as illustrated in FIG. 7. Graph 60 defines a criterion line Beta that defines 5 a boundary, based upon ambient and discharge air temperatures, between a non-refrigeration or no AC operating zone 62 and a refrigeration or AC operating zone 64.
Therefore, the temperature reading from sensor 36 can be utilized in the following manner. 10
If the temperature reading from sensor 36 (the air temperature at discharge) is less than or equal to 0.5TamWe„t+55, then the system is in refrigeration operating zone 64 and the air-conditioning system should be activated in response to a defog or deice operation request. 15
Conversely, if the temperature reading from sensor 36 is greater than 0.5Tami)je„t+55, then the system is in nonrefrigeration operating zone 62 and accordingly, there is no need for the air-conditioning system to be activated in response to a defog or deice request; therefore, only the 20 heating system should be activated.
Accordingly, a thermal controller of a climate control system in an automobile can be preprogrammed to activate or not activate the air-conditioning system in response to a defog or deice request. Moreover, the thermal controller is 25 programmed to utilize an energy-saving algorithm wherein activation of the air-conditioning system can be controlled in response to air temperature readings exclusively. Therefore, there is no need for humidity sensors in the energy-saving algorithm. 30
Moreover, since there is no requirement for a humidity sensor there is less sensor and electrical interface required between a controller and the HVAC system of an automobile. In addition, the software required to operate the controller is also made less complicated. Here a controller 35 algorithm simply applies two temperature readings to a simplistic equation to define a refrigeration and nonrefrigeration zones.
In accordance with the present invention, the climate control system operates under a criterion that determines 40 whether or not to activate the air-conditioning system in response to a defog or deice request. Moreover, the determination of the criterion is based upon two temperature readings.
Simply put, and based upon temperature input, if criterion 45 Y exceeds a given value, then the system will not activate the air-conditioning system in response to a defog or deice request. This prevents unnecessary cooling and subsequent reheating of the discharge air, which, in turn, prevents unnecessary power consumption. Similarly if criterion Y is 50 less than the given value, the air-conditioning system will be activated in response to such a request.
Referring now to FIG. 8, a block diagram 66 illustrates the energy-saving defog/deice operation strategy and control scheme in accordance with the present invention. Thermal 55 controller 54 receives temperature inputs (Tatnbient and
(FIG. 5); Tc the cabin temperature from sensor 50 (FIG. 5); Td the discharge temperature from sensor 36 (FIG. 5); vehicle speed in mph; and the relative humidity from sensor 38.
A second step or decision node 72 determines if the blower unit is on, if so, a third step 74 calculates uas (the saturated humidity ratio at temperature sensor 50 (Tc)) wherein w^^Tc).
A fourth step 76 calculates the humidity ratio w based upon uas and using the equations:
A fifth step 78 estimates the windshield temperature Wt. (Wt=(l-x)Ta+xTd). Wherein x is a weighted factor that can be calibrated, for example, if vehicle speed (V) is less than or equal to 5 mph x=0.5; if V is greater than 70 mph x=0.9; and if 5<V=<70 mph, then x=0.5+28/V. In addition, and at higher vehicle speeds the ambient air temperature has a greater effect upon windshield temperature.
Alternatively, the windshield temperature can be determined from a temperature sensor position on, in or near windshield 48.
A sixth step 80 calculates w's.
A seventh step 82 Calculates y=w'Jai
An eighth step 84 determines whether or not Y is less than 0.8. If so, a ninth step 86 determines whether the airconditioning has been manually activated. If so, the current status is maintained. If not, a next step 88 determines whether the auto defog is on. If so, a next step 90 turns auto defog off. If the auto defog is off already, status is maintained.
If on the other hand, gamma (y) is greater than or equal to 0.8 a decision node 92 determines whether or not the air-conditioning system is on. If yes, the current status is maintained. If not, an energy-saving algorithm 94, as contemplated for use in accordance with an exemplary embodiment of the present invention, is employed.
A first step 96 of energy-saving algorithm 124 calculates Beta the air-conditioning system actuation criterion that defines non-refrigeration operating zone 62 and refrigeration operating zone 64. (FIG. 7).
A next step 98 determines whether the temperature reading from sensor 50 is greater than Beta. If so, the non-AC operating zone is maintained. If on the other hand, the temperature rating from sensor 50 is less than or equal to Beta, then the AC operating zone is maintained.
Alternatively, and in order to alter the control characteristics and or software which is utilized to operate the control systems and or command sequences for automotive HVAC system 20, a disk drive 100 is coupled to thermal controller 54 wherein a software upgrade may be installed into the system of thermal controller 54. This will allow improvements to the operation strategy and or software to be easily installed into the vehicles operational system. Moreover, upgrades may be mailed to a consumer negating the need for the owner to bring their vehicle into an authorized dealer for a service upgrade. Such an implementation may also negate the need for the vehicle being brought in for factory recalls which are primarily due to new software and or control systems.
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and