WO2009036547A1

WO2009036547A1 - A method of calculating tire cold inflation pressure in a moving vehicle and system for same

Info

Publication number: WO2009036547A1
Application number: PCT/CA2007/001690
Authority: WO
Inventors: Vlad Ardelean; Sean Boyle; Scott Feagan
Original assignee: Tirestamp Inc.
Priority date: 2007-09-21
Filing date: 2007-09-21
Publication date: 2009-03-26

Abstract

The present invention relates to a system and method for determining more accurately a cold tire inflation pressure of at least one tire on a vehicle. The present invention provides a system for determining a cold inflation pressure value of a tire mounted on a vehicle, by recording an internal pressure reading of the tire while in motion, and adjusting the reading to take into account the altitude at which the reading took place, the difference between the internal temperature of the tire and the ambient temperature and the pressure change due to volume expansion and increase in the number of molecules as determined by the tire's characteristics such as tire brand, tire model, wheel size, tire profile, sidewall elasticity and tire air humidity. The present invention is advantageous in that the present invention is able to continuously generate accurate cold inflation pressure values for each tire of a vehicle in motion.

Description

A METHOD OF CALCULATING TIKE COLD INFLATION PRESSURE IN A MOVING VEHICLE AND SYSTEM FOR SAME

Field of Invention

The present invention relates to a method for an improved, approximated calculation of a cold tire inflation pressure whether or not a vehicle is in motion.

Background

While there are a variety of factors that can jeopardize the safety, performance and life expectancy of a tire, none has more impact than incorrect inflation pressure.

Tire inflation pressure is the level of air (or other gas) in a tire that provides the tire with load-carrying capacity. Proper tire inflation pressure permits a tire to deliver its handling, traction and durability features properly. Proper inflation results in the correct contact profile with the road for traction, braking capability and safety.

Under-inflation may cause abnormal tire deflection, which can build up heat and cause irregular wear. An under- inflated tire may build up excessive heat due to over- deflection because the tire does not maintain its shape and therefore becomes flatter than intended while in contact with the road. A tire's internal structure may also weaken and eventually lead to failure if under-inflated. The additional internal heat caused by deflection can increase rolling resistance, thereby causing an increase in fuel consumption, reducing a tire's tread life while increasing the probability of irregular tread wear. In addition, a loss of steering precision and cornering stability may result .

Over-inflation may cause tires to be stiffer and more vulnerable to impacts in addition to causing irregular wear. An over-inflated tire is stiff and unyielding in addition to causing rapid center tread wear, reduced traction and a harsher ride because the size of its contact footprint on the road is smaller.

While the importance of maintaining proper inflation of a tire is evident, the manner in which to do so is complicated.

Most tires naturally lose air over time through the process of permeation. Changes in outdoor temperature can also affect the rate at which a tire loses air. Since air is a gas, it expands when heated and contracts when cooled. The air pressure inside a tire can therefore be theoretically calculated based on the principles of the Ideal Gas Law, which states that:

pV = nRT (1)

More specifically, to find a pressure at any given temperature, the following formula becomes:

nRT _m

V where : p = pressure V = volume

T = temperature

R = ideal gas constant n = number of moles of gas

Unfortunately, this formula applies to ideal gases and not to real-life situations. For example, the foregoing equation assumes that pressure and volume are independent. In the real world, a tire behaves more like a balloon with the result that the volume (V) will change with the amount of pressure (p) . In addition, the air within a tire is not an ideal gas, as it contains moisture. Further, the number of gas molecules n changes as a result of any change in the temperature (T) . Due to these factors, formulae relating the pressure, volume, temperature and number of moles of a gas in real life are much more complex.

A tire manufacturer determines tire inflation pressure, referred to as the "recommended cold inflation pressure", based on the greatest amount of weight a tire can safely carry for a given speed. This pressure reflects the proper pressure, stated in units of pounds per square inch (PSI) required to inflate a tire when it is "cold".

A generally accepted rule for passenger vehicle tires is that for every 10° Fahrenheit change in air temperature, a tire's inflation pressure will change by about 1 PSI (the pressure will increase with higher temperatures and decrease with lower temperatures) . At various times in the year, the difference between cold nighttime temperatures and hot daytime temperatures can be 20° Fahrenheit or more. Thus, if one sets a tire's pressure in the morning, the actual tire pressure could be almost 2 PSI higher when measured in the afternoon. If one set a tire's pressure in the heat of the day, the cold inflation pressure could be 2 PSI lower the following morning. If a vehicle is parked in a heated garage, a tire will lose pressure as it ventures outside during winter, in light of the almost 100° Fahrenheit temperature variation it could easily encounter.

Therefore, generally speaking, inflation pressure should be checked regularly, particularly in the fall and early winter months as the days get shorter and ambient temperatures get colder.

Cold Inflation Pressure (CIP) is a measurement made on a stationary vehicle when the tire's inside temperature roughly equals the outside, or ambient, temperature (i.e. the tire is "cold") . Recommended industry practice considers a tire to be "cold" if it has not been driven on for at least three hours, thereby theoretically allowing the. tire temperature to reach the ambient temperature.

The temperature of the air within a tire will change, as a result of use, which in turn may change the tire pressure. Even driving short distances at reduced speeds can impose significant changes in the pressure.

This implies that if a tire is adjusted to its recommended inflation pressure when it is still hot, it will be significantly under-inflated once it finally cools down. Therefore, in order to get as accurate a tire pressure reading as possible, one would like to measure tire pressure only when the tire has not been driven on for at least three hours and the temperature inside the tire is considered equivalent to ambient temperature.

Traditionally, tire manufacturers have developed recommended inflation pressure tables. Such tables are created by evaluating inflation pressure at a given ambient temperature, load and speed values. With these values, a tire manufacturer relies on the basic physical principles to correlate temperature and pressure in order to arrive at a tire's baseline performance characteristics. Tire manufacturers also research the effects of different ambient temperatures, loads and rotational speeds within a controlled environment in order to create such recommended inflation pressure tables for their tires. Tires are typically inflated according to the tire manufacturer' s specification tables.

Table 1 provides an example of load and inflation specifications for certain Michelin™ built tires. First, the axle configuration is determined by reviewing whether a tire will be part of a single application (2 tires per axle) or a dual application (4 tires per axle) . Once determined, the appropriate CIP value may be obtained by finding the closest weight per axle to the proposed scenario in the row corresponding to the selected applicant . Table 1: Sample Load & Inflation Table 1S' = single application and ¹D' = dual application

However, a Load and Inflation Table, such as in Table 1, only specifies the appropriate cold inflation pressure at a tire's rated maximum speed. The faster a tire rolls, the smaller the load it can carry. Therefore, by reducing the maximum speed at which a tire will actually operate and adjusting the inflation pressure, a tire's carrying capacity can be increased. The amount of capacity increase and the amount of passage increase called for to permit such load increase may be obtained by applying multiplication factors set out in a coefficient table (such as the exemplary load and pressure coefficients table shown in Table 2) to the load and pressure values taken from a Load and Inflation Table (such as Table 1) . Table 2 is an exemplary coefficient table providing pressure and load correction factors for a given speed for the Michelin™ built tires of Table 1.

Table 2: Static & Low Speed Load & Pressure Coefficients Table

Since air pressure inside a tire will decrease when a vehicle is driven from a warm environment to a cold one, adjustment of tire pressure is appropriate when operating in a colder ambient environment. To make it easier for tire technicians, additional tables have been generated using scientific algorithms for tire pressure normalization.

Table 3 is an exemplary tire pressure normalization chart for cold climate temperature changes, for the Michelin™ built tires of Table 1.

Table 3

Adjusted Inflation Pressure (psi)

(when inflating indoors atSS'F [18"CJ)

Such tables permit the determination of cold inflation pressure for only the recommended inflation pressure and the anticipated outside ambient temperature at mid-day, assuming that a tire technician is working within a heated garage. The intersection of the recommended pressure's row and the outside ambient temperature's column provides the inflation pressure that will suitably make allowance for the outside ambient temperature.

The problems associated with this methodology are numerous First, the environment never totally matches the ambient temperature chosen for application of the adjusted inflation pressure table. Thus, inevitably, one may be making under-adjustments or over-adjustments.

Second, tires are only usually checked and corrected periodically, for example once a week. As a result, a tire could undergo significant over-inflation or under-inflation between such periodic checks. The effects of such incorrect inflation are cumulative, such that with each successive period of incorrect inflation, the tire may be further irrevocably damaged.

Third, this methodology relies on the accuracy of individual pressure gauges. Many pressure gauges are inaccurate due to a lack of proper re-calibration against an accurate master gauge. As a result, instead of inflating a tire to its correct cold inflation pressure, inadvertent over- and under-inflation may be occurring routinely.

Fourth, since vehicles coming in for service typically have been in recent operation, it is often difficult to check "cold" tires in a servicing environment. For this reason, tire technicians often develop guidelines to compensate for inaccurate readings, such as adding 4 (PSI) to the recommended inflation pressure when checking a hot tire. The use of such guidelines does not produce good approximations and as such, often the net result is the improper management of a tire's inflation pressure resulting in permanent damage to the tire.

Fifth, typically, the CIP is determined only once for an axle on a given vehicle. More preferably adjustments may be made seasonally for the extreme temperatures of winter and summer, and most preferably on a weekly basis.

The concept of normalized cold inflation pressure presently assumes or demands that the vehicle not be moved for at least three hours. Even so, the accuracy of measurements and inflation is poor due to the reasons mentioned above. The underlying problem has always centered on the fact that the real values for any of the instantaneous parameters are not readily available. In addition, such instantaneous parameters are continuously changing with time, and in potentially significant ways.

A number of prior art attempts at providing such information have been made. U.S. Pat. No. 4,909,074 discloses a method of detecting, evaluating and displaying tire pressure. The detected pressure is then compared to a range of pressure values defined at the ambient temperature and the inner tire temperatures (as well as the ambient pressure, as the case may be) . A signal is produced when the actual tire air pressure falls outside the range. Further, the detected pressure is compared with a desired tire pressure that is associated with a predetermined maximum speed. A maximum safe speed is specified based on the result of the comparison.

This method suffers from a series of drawbacks. First, the inner tire temperature is not necessarily the actual temperature of the gas in the tire, since the sensor is situated in the valve, and actually measures the wheel rim temperature. In addition, the algorithm used does not account for tire specifics such as the tire gas volume and the humidity level inside the tire.

U.S. Patent Application 2005/0162263 Al discloses a method for temperature compensation in a system for tire pressure monitoring. The temperature compensation is established by determining the gas temperature in the tire by way of measuring at least two temperature values. This method does not incorporate tire specifics, nor does it provide a means for determining the cold inflation pressure while the vehicle is in motion.

In addition, current methods do not cover a wide range of tires, or neglect tire specifics (e.g. tire gas volume, humidity inside the air used to inflate the tire, etc.) altogether. Furthermore, many methods do not include key elements such as the ambient temperature and atmospheric pressure (altitude), when calculating the CIP. Presently, there is no method that takes historical data into account to determine correction points where the tire temperature is equal to the ambient temperature.

Given the above drawbacks of accurately determining the CIP, there is presently a need to more accurately calculate an instantaneous cold tire inflation pressure value. In particular, there is a need to calculate a cold tire inflation value while a vehicle is in motion that is more accurate than determining a tire's inflation pressure when the vehicle is stationary.

Summary of Invention

The present invention relates to a system and method for determining more accurately a cold tire inflation pressure of at least one tire on a vehicle. The system has a number of on-board sensors that take periodic readings of conditions relevant to the pressure in the tires mounted on the vehicle. These readings are communicated to either an on-board data processing system or a remote back-end infrastructure which computes a cold inflation pressure (CIP) for at least one of the tires on the vehicle based on the readings. The CIP may then be compared to desired tire pressures based on the conditions under which the tire is operating. Depending on the configuration of the system, alerts may be generated if the CIP is outside a desired range of pressures.

In a first aspect, the present invention provides a system for gathering data for calculating a cold inflation pressure value for a tire mounted on a vehicle, the system comprising :

a plurality of sensors for determining an internal pressure reading for said tire, an internal gas temperature for said tire, and an ambient temperature for said tire a data collection unit for receiving data from said plurality of sensors; and communication means for communicating with a data processing means; wherein said communication means receives data from said data collection unit and sends data to said data processing means, said data processing means calculates said cold inflation pressure value based on data from said plurality of sensors.

In a second aspect, the present invention provides a method for determining a corrective action based on a cold inflation pressure value of a tire mounted on a vehicle, the method comprising: a) receiving data from a data gathering system which gathers data related to conditions regarding said tire, said data comprising an instantaneous pressure reading of said tire, an internal gas temperature of said tire, and an external ambient temperature reading for said vehicle; b) calculating a cold inflation pressure value of said tire based on data received in step a) c) retrieving an optimal pressure range for said tire from a database, said optimal pressure range being based on conditions specific to said tire and characteristics of said tire d) comparing said cold inflation pressure value from step b) with said optimal pressure range retrieved in step c) e) in the event said cold inflation pressure is outside said optimal pressure range, generating an alert and selecting a corrective action based on an amount by which said cold inflation pressure is outside said optimal pressure range.

In another aspect, the present invention provides a system for determining a cold inflation pressure value of a tire mounted on a vehicle, comprising: a tire pressure sensor adapted to generate an internal pressure reading of the tire; a tire temperature sensor adapted to generate an internal gas temperature reading of the tire; an ambient temperature sensor adapted to generate an external ambient temperature reading of the vehicle; a vehicle altitude data source adapted to provide a vehicle altitude reading; a data collection unit adapted to receive readings from the vehicle altitude data source and sensors including the tire pressure sensor, the tire temperature sensor and the ambient temperature sensor; a data processing unit adapted to receive and process data collected by the data collection unit and to access data records relating to characteristics of the tire selected from a group consisting of tire brand, tire model, wheel size, tire profile, sidewall elasticity and tire air humidity; whereby the cold inflation pressure may be obtained from the internal pressure reading of the tire, a ratio of the external ambient temperature reading to the internal gas temperature reading, the vehicle altitude reading and the characteristics of the tire.

In yet another aspect, the present invention provides a method for determining a cold inflation pressure value of a tire mounted on a vehicle, comprising the steps of: (a) generating an internal pressure reading of the tire while the tire is in motion; (b) generating a vehicle altitude reading; (c) generating an internal gas temperature reading of the tire while the tire is in motion; (d) generating an external ambient temperature reading of the vehicle; (e) retrieving data records relating to characteristics of the tire selected from a group consisting of tire brand, tire model, wheel size, tire profile, sidewall elasticity and tire air humidity; (f) adjusting the internal pressure reading as a function of the vehicle altitude reading; and (g) adjusting the internal pressure reading as a function of a ratio of the external ambient temperature reading to the internal gas temperature reading; (h) adjusting the internal pressure reading as a function of the characteristics of the tire; and (i) outputting the adjusted internal reading based on steps based adjustments made in steps (f) through (h) .

The present invention is advantageous in that it can be operated while a vehicle is in motion, so that data may be obtained when it is most appropriate to do so. Through the use of sensor data, the method of the present invention is able to continuously generate accurate cold inflation pressure values for each tire of a vehicle.

The method relies on a tire's instantaneous temperature and pressure values, while enhancing the sensitivity of these calculations by interpreting additional sensor data such as ambient temperature and altitude. The result is a novel mechanism to accurately calculate the resulting tire- specific cold inflation pressure continuously over time, based on how a tire actually performs within an environment, as opposed to a tire manufacturer's artificially controlled lab environment.

The method of the present invention further relates to the communication of under-inflation and over-inflation issues through highly accurate tire alerts, thereby preserving the overall condition and thus protecting the monetary value of the tire and increasing the overall safety of the vehicle. More specifically, the method of the present invention will permit a fleet to continuously monitor the CIP of every tire without having to physically handle the tires and ensure that each is continuously monitored at its optimal recommended pressure. The present invention also provides improved measurement accuracy of the tire pressure. Radial tires, in particular, are very difficult to determine through visual inspection whether they are under-inflated and the issues associated with manually gauging a tire's pressure have previously been discussed.

The present invention accepts complex data over time and simplifies it into communicable and understandable messages that are inherently extremely accurate. By removing potential measurement errors from the data, the normalization calculations of the present invention facilitate automated tire alerts and reports based on the CIP. The present invention permits determinations of exactly how much pressure is to be added or removed from a tire in order to bring it back into its optimal range while the tires are still hot.

One additional advantage of being able to instantaneously determine CIP is that the vehicle under test need no longer sit idle in a service bay to wait until the tire is cold enough to determine if the tire inflation is correct. With knowledge of the ambient temperature to which the tire will cool off, it is now easy to accurately predict what the CIP will be for readings taken while the tire is still in operation.

The present invention also relates to a sensor-driven system and method of measuring cold inflation pressure that enhances traditional cold inflation pressure values by making use of the accuracy and native abilities of sensors continuously over time. By constantly taking pressure, temperature, ambient temperature and altitude readings, the present invention is able to adjust and report the accurate CIP throughout a given day while the vehicle is either moving or stationary. It also takes into account the history of this digital data and as a result is better enabled to make timely adjustments for seasonal changes in addition to abnormal and unusual seasonal temperature spikes in either direction, regardless of their duration. In so doing, the system and method of the present invention are self-adapting, constantly changing the baseline for the CIP calculation. This is not something that can be achieved using the traditional approaches to tire pressure management .

Brief description of Figures

Figure 1 is a block diagram of a tire monitoring system according to an embodiment of the present invention.

Figure 2 is a flowchart illustrating the data processing steps according to an embodiment of the method of the present invention.

Figure 3 is a graph illustrating actual pressure, temperature and ambient temperature values measured from an exemplary truck tire.

Figure 4 is a graph illustrating pressure, temperature, ambient temperature measurements and CIP calculated for the exemplary truck tire referred to in Figure 3 according to an embodiment of the present invention. Detailed Description of the Invention

Referring now to Figure 1, a block diagram of the tire monitoring system 10, according to the present invention, is shown. The tire monitoring system 10 of the present invention is embodied in two units 20, 30. The first unit is a data collecting unit 20, and the second unit is a data processing unit 30. Both the data collecting unit 20 and the data processing unit 30 may be located on the vehicle under test (not shown) . However, according to an alternative embodiment, the data processing unit 30 may also be located remotely.

As shown in Figure 1, the data collecting unit 20 is operatively connected to tire sensors 5OA, 5OB, 5OC, 50D, an ambient sensor 60, and a vehicle altitude source 65. Any type of tire or ambient sensor may be used by the present invention. Each tire sensor is mounted inside a tire (not shown) . Alternatively, the tire sensors may be mounted on the wheel bearing of the tire (not shown) . The tire sensors may be mounted at the end of a wheel valve or be strap-mounted to the wheel. As well, each tire sensor 5OA, 5OB, 5OC, 5OD includes an individual tire pressure sensor and an individual tire temperature sensor (neither individual sensor is shown) . In an alternative embodiment, the tire pressure sensors and the tire temperature sensors may be mounted as separate sensor units inside the tire. The ambient sensor 60 is operatively connected to the data collecting unit 20. The ambient sensor 60 is adapted to measure both the atmospheric pressure and the ambient temperature. The altitude data source 65 is also operatively connected to the data collecting unit 20 and is adapted to provide altitude readings. According to alternative embodiments of the present invention, the altitude data source may be a Global Positioning System (GPS) receiver or an altimeter (not shown, but well known in the art to the skilled artisan) . Should the vehicle be driven at a relatively constant altitude, the altitude data source can also be fixed at a constant altitude value. Depending upon where the ambient sensor 60 and the altitude data source 65 are located on the vehicle, they may be operatively connected to the data collecting unit 20 through wireless or wired means.

The data collecting unit 20 includes a tire pressure monitoring system (TPMS) receiver 70. The TPMS receiver 70 is both operatively connected to the data processing unit 30 and operatively connected to the tire sensors 5OA, 5OB, 5OC, 50D, the ambient sensor 60, and the altitude data source 65.

In Figure 1, the dashed line box 75 encloses elements that form part of the alternative embodiment mentioned wherein the data processing unit 30 is located remotely. The data collecting unit 20 may include a telematic device 80 that is operatively connected to the data processing unit 30 via the Internet 90. However, as mentioned above, the data processing unit may be directly connected to the TPMS receiver 70, and thus to the data collecting unit 20. Accordingly, the system of the present invention may be situated entirely on the vehicle.

According to the present invention, each tire sensor 50A, 5OB, 50C, 5OD wirelessly transmits, at a pre-determined time interval, pressure and temperature readings from its corresponding tire to the TPMS receiver 70. The ambient sensor 60 also transmits, at a pre-determined time interval, both an atmospheric pressure reading and a temperature reading to the TPMS receiver 70. For its part, the TPMS receiver 70 continuously monitors for these wireless or wired transmissions from both types of sensors and then processes their data in the data processing unit 30.

The data processing unit 30 includes specialized data processing capability to decode and feed the sensor data into a relational database (not shown) within the data processing unit 30. The relational database associates a particular sensor's data to a particular tire on a particular vehicle in a particular position at a particular moment in time. According to the method of the present invention, these database records are harvested in order to understand a tire's current pressure status in relation to its historical context, as it relates to cold inflation pressure .

Figure 2 is a flowchart 200 illustrating the data collecting and processing steps according to the method of the present invention. The data collecting process step 210 generates an internal pressure of the tire under test, a vehicle altitude reading, and an internal temperature reading for the same tire under test. These readings may generated either simultaneously or in a different sequence altogether. The data processing steps follow the data collecting step 210 and begin by retrieving data records relating to tire characteristics at step 220. Next, step 230 adjusts the internal pressure reading based on the altitude reading, and the tire temperature reading (each of which were generated in step 210) and as a function of the tire characteristics (retrieved in step 220) . Finally, step 240 outputs an adjusted internal pressure reading.

More specifically, step 230, shown in Figure 2, involves calculating an Anytime Anywhere CIP (AACIP) formula to adjust the internal tire pressure reading to obtain an approximated cold tire inflation pressure value. The ACCIP is calculated using the following formula:

AACIP - V a_re C_altιtude )^χ- C_gas ^χ C_temperatun; ' ^{y )}

wherein

AACIP is the CIP calculated according to the method of the present invention,

P_ti_re is the instantaneous pressure of the tire (in PSI), and is derived from a tire sensor,

Caititude is the Calculated Altitude Correction,

Cgas is the Calculated Gas Correction Coefficient, and

Ctemperature is the Calculated Temperature Correction.

The altitude at which a tire is operating within at a particular moment in time has a minor effect on air pressure. This effect can be quantified as the air pressure will increase by approximately 0.5 PSI for every 1,000 feet increase in altitude above sea level. Expressed mathematically, it takes on the form:

._, altitude

^C— = 7^7T-- x 0 - 5 PSI ( 4 ) l,000Feet The altitude can either be preset for vehicles that are always operating at the same height, it can be continuously passed as a value from an electronic device such as a GPS receiver over a predetermined time period, or it can be read from an altimeter (atmospheric pressure sensor) .

The calculated gas correction coefficient (C_gas) is based on the volume correction coefficients associated with tire size and the number of gas molecules (n) for an initial amount of gas at a given pressure, temperature, humidity and volume at a given moment in time.

If the tire has a fixed volume (V) and the air inside the tire is an ideal gas containing a constant number of molecules n, the tire pressure variation with temperature would be easy to calculate using the ideal gas equation:

_PV = nRT (5)

A change in temperature from Ti to T₂ would lead to a change in pressure from Pi to P₂. Hence, to determine the new pressure P₂ after a change in temperature between the initial temperature of the tire Tl and a new temperature T2, one applies the mathematical expression of Gay Lussac' s Law derived from the Ideal Gas Law:

(⁶)

In reality, because the tire is made out of a flexible/elastic material, the volume (V) is changing with pressure change, from V₁ to V₂. In addition, since the gas inside the tire is in most cases air, which contains a certain amount of moisture, the number of gas molecules will change with temperature, from ni to n₂, thus making the calculation of the new pressure after temperature variation even more complicated.

Given the two pressure values Pi and P₂, where Pi is the tire pressure before the temperature change and P₂ is the tire pressure after the temperature change:

and

R = n, xRx-¹ (8)

V₁

These formulas can be rearranged as

Thus, the calculated gas correction coefficient C_gas depends on the amount of tire volume ratio change (Vi/V₂) due to pressure change with temperature and the amount of gas molecules ratio changing (n₂/n_x) due to temperature changes and moisture in the tire. These calculations are based on different tires, wheel sizes, profiles, sidewall elasticities, tire air humidity ratios, etc. resulting in a set of tables of coefficients to be used on different types of tires.

The calculated gas correction coefficient C_gas can also be determined experimentally for different types and brands of tires under different air humidity conditions.

Even if the vehicle is not driven before a tire's pressure is checked, the ambient temperature is taken into account. This is due to the fact that the tire pressure will change between 1 and 2 PSI for every 10° Fahrenheit change in air temperature. As a result, multiple ambient and tire temperature sensor readings are taken over a defined time period in order to be determine the most appropriate ambient and tire temperature values.

The tire is considered to be cold at the point in time where tire temperature equals ambient temperature, referred to as T_Coi_d- In later equations, T_coi_d can be referred to as T_ambient to reflect that it is also the changing ambient temperature. The calculated temperature correction is then derived by dividing this cold temperature value by the associated tire temperature value, as follows:

C, _ ^Λ cold temperature rp (8)

^ tire

It should be noted that, per the above explanation, si T ambient temperature rp tire Once the tire pressure has been accurately determined in accordance with the AACIP measurement, if it is found that a tire has lost a certain amount of pressure, signs of penetrations, valve leakage, or wheel/rim damage may then be checked on the vehicle. More importantly, if a tire is 20% below the recommended inflation pressure according to AACIP, it can be considered flat.

As an example of the calculation undertaken using AACIP, the following is provided:

For this example, the given parameters are: Ambient temperature (Ta) , Tire Temperature (Tt) and tire Pressure (Pt) . Also, all temperature measurements are converted to ⁰K:

Temp [K] = Temp [C] + 273

For simplification it is assumed that the altitude = 0, hence C_ai_ti_tud_e = (altitude/1000) x 0.5 = 0 (from Equation (4)) .

The formula for AACIP therefore becomes:

AACI P = Pt X C_gas X C_temperature O )

The method uses a starting seed where the ambient and tire temperature are equal. At this point (Tt = Ta), AACIP = Pt. In other words, when the tire temperature is equal to the ambient temperature, the pressure reported by the pressure sensors mounted inside the tire, Pt, is the cold inflation pressure, AACIP. For this example, we assume that the tire is cold at ambient temperature of 27⁰C or 300⁰K:

Ta = Tt = 300⁰K at which point the pressure is measured to be

Ptcold = AACIP = 114 psi (10)

In this example, after the vehicle has started to move, the sensors report a pressure of Pt = 118 psi and a tire temperature Tt = 318⁰K. One can now calculate AACIP using equation (3) .

While it is clear that C_gas = n₂Vi/niV₂ this coefficient does not necessarily need to be calculated directly as will be shown below. C_temp_eratur_e can be directly calculated given the data from the sensors.

Experiments have shown that, when establishing the C_gas coefficients, there is a direct interdependency between the Cgas coefficients (n₂Vi/niV₂) , temperature coefficients (C_temperature = Ta/Tt) and the actual physical characteristics of the tires and the amount of moisture in the air. Using a coefficients table that is specific to each type and brand of tires, the C_gas x C_temperature part of the equation can be re-written as:

Cgas X Ctemperature — J- ~ JA + i\ X Ctemperature \ 1 -L /

where K is tire pressure dependent and can be written as: K = Cl + C2 /Pt ( 12 )

Where Cl and C2 are coefficients from the table and Pt is the actual tire pressure measured by the tire sensor.

For a specific type of tire (brand "X" model "Y"), the coefficients Cl and C2 may be given as:

Cl = 0.974 and C2 = 18.5 (13)

Applying the formula (12) and using the measured Pt from equation (10) :

K = 0.974 + 18.5/122 = 1.1256

Next, using the calculated K in equation (11) the result is :

Cgas X Ctemperature = 1 " 1 . 125 6 + 1 . 12 56 X ( 300 / 318 ) = 0 . 9362

Referring back to equation (9), AACIP = Pt x C_gas x C_temperature = 122 * 0.9362 = 114.2 psi, close to the initial measured value at equation (10) when the tire was cold. In other words, the sensor is showing 122 psi instantaneous pressure on a hot tire, but what is desired is the cold inflation pressure. Thus, if the tire were allowed to cool down to the ambient temperature of 300⁰K (27°C) it would show 114 psi. Hence, when the method above is applied, one can determine the cold inflation pressure on a hot tire.

Regarding the coefficients Cl and C2, these can be found experimentally by gathering data regarding specific tires. By gathering data on temperature and pressure over time as a specific tire is used, a correlation between the temperature and the pressure can be found. Once such data is plotted, by comparing a theoretical model (assuming an ideal gas and a fixed volume) to the data collected, the correlation was found to be that in equation (11) . Since C_temp_erature is known, it was found that the constant K changed with absolute pressure P_t. The value for K was found to be represented by the relationship in equation (12) where Cl and C2 were tire model specific. Cl and C2 can therefore be found experimentally.

In Figure 3, the tire pressure variation of a commercial truck tire is shown daily for a period of one half month. The tire pressure variation over time is shown as the top line 300 and the measurement units are in PSI. The middle line 310 shows the instantaneous tire temperature values during the day with the measurement units in degrees Celsius (left axis) . The correlation between tire temperature 310 and tire pressure 300 at a moment in time may be readily observed. The bottom line 320 shows the variation of the ambient temperature during the day.

Figure 3 shows that it is very difficult to select one pressure value and decide that this would be the proper inflation pressure at that moment in time. Due to pressure variation with temperature, the industry's recommended best practice is to take a tire's pressure reading only when the tire is cold. The two lower readings in the graph illustrate that there is always one moment in time where the temperature inside a tire reaches the ambient temperature (shown in Figure 3 as contact points where the two lines meet) . That is the correct moment to take a pressure reading under conventional methods. Therefore, according to conventional methods, one is forced to wait for an average of three hours in order for the tire to cool .

By contrast, Figure 4 graphically illustrates that the CIP value calculated over time and shown as a line 430 just below the top line 400, which illustrates the tire pressure variation, in accordance with Eq. (3) of the present invention, is extremely close to the correct CIP value that corresponds to the point where the ambient and tire temperatures are equal. To achieve maximum accuracy, the intersection points where the ambient and tire temperatures are equal are tracked continuously and applied to the AACIP calculation.

True tire visibility and pressure accuracy is now achievable continuously over time and facilitates advanced analysis that can make use of this knowledge, in order to properly monitor under-inflation, over-inflation, and overheating.

In addition to driver safety, being able to accurately maintain correct tire inflation pressure over time helps optimize tire performance, comfort and durability. A tire will wear longer, save fuel by reducing rolling resistance, improve traction on all road surfaces and help prevent accidents. Proper tire inflation pressure also stabilizes the tire's structure, blending the tire's responsiveness, traction and handling. Once the tire pressure has been determined according to the method outlined above, the adjusted pressure can be used for various ends. As an example, based on the adjusted tire pressure, an alarm may be generated to signal the need for corrective measures such as replacement of the tire, adding more air to the tire, or other similar measures.

An example of the end-to-end process for retrieving data and calculating the adjusted tire pressure would begin with the on-board system (on-board the vehicle) communicating with the back-end computing infrastructure (e.g. the DPU 130 in Fig 1) via the telematics subsystem. Once the data from the on-board sensors are communicated to the back-end infrastructure, a cold inflation pressure for each tire on the vehicle is calculated. The data from the vehicle, as well as the cold inflation pressure, are stored in a relational database which forms part of the back-end infrastructure .

At the back-end infrastructure, the cold inflation pressure for each vehicle' s tire is compared to a predetermined standard or template - an optimal range of cold inflation pressures that takes into account that tire' s wheel position, vehicle type, and other vehicle attributes, as well as the individual fleet operator' s policies regarding the tire. The optimal range for each specific tire on each specific vehicle is stored in the relational database and is retrieved by the relevant section of the back-end infrastructure when required. If the calculated cold inflation pressure for that tire is within the optimal range, then no alert is generated. However, once the cold inflation pressure for a specific tire deviates from the predetermined optimal range, then an alert is generated. Depending on the reading (i.e. how far off from the optimal range the calculated CIP is), the relevant corrective measure is communicated to the operator of the vehicle.

As a practical example, if it is assumed that a tire's target pressure on the left front wheel position of a vehicle is 100 psi with an optimal value range defined as 95 PSI to 105 PSI by the fleet in question, then values outside that range would trigger an alarm. If the left front wheel tire' s cold inflation pressure is measured at 98 PSI, then the tire is within its optimal range and no alert is triggered. If, later in the day, the same tire's cold inflation pressure drops to 85 PSI, then the tire is no longer within its optimal value range and an alert is triggered notifying the tire technician to inflate the tire back to its target pressure of 100 PSI. It should be noted that these optimal template values can be adjusted at any time and for whatever reason by the fleet or by the back- end infrastructure operator, and so should be thought of as dynamic bands. As a further example, if the history of the cold inflation pressure for the tire indicates that it consistently loses pressure, then an alert may be generated that instructs the tire technician to replace the tire at the next opportunity.

It should be understood that the preferred embodiments mentioned here are merely illustrative of the present invention. Numerous variations in design and use of the present invention may be contemplated in view of the following claims without straying from the intended scope and field of the invention herein disclosed.

Claims

Having thus described the invention, what is claimed as new and secured by Letters Patent is:

1. A system for gathering data for calculating a cold inflation pressure value for a tire mounted on a vehicle, the system comprising :

- a plurality of sensors for determining an internal pressure reading for said tire, an internal gas temperature for said tire, and an ambient temperature for said tire a data collection unit for receiving data from said plurality of sensors communication means for communicating with a data processing means; wherein said communication means receives data from said data collection unit and sends data to said data processing means, said data processing means calculates said cold inflation pressure value based on data from said plurality of sensors.

2. A system according to claim 1 wherein said plurality of sensors includes a vehicle altitude data source for providing a vehicle altitude reading, said vehicle altitude reading being used to calculate said cold inflation pressure.

3. A system according to claim 1 wherein said plurality of sensors is mounted on a wheel bearing said tire.

4. A system according to claim 2 wherein at least one of said plurality of sensors is in wireless communication with said data collection unit.

5. A system according to claim 1 wherein said system is mounted on said vehicle.

6. A system according to claim 1 wherein said data processing means calculates said cold inflation pressure based on a formula :

wherein

AACIP is the Cold Inflation Pressure for said tire

P_ti_re is said instantaneous pressure of the tire (in

PSI) ; ^-_alti_tude is a Calculated Altitude Correction based on said vehicle altitude reading;

Cg_as is a Calculated Gas Correction Coefficient based on characteristics of said tire and said data gathered by said system, and Ctemperatare is a Calculated Temperature Correction based on said internal gas temperature.

7. A method for determining a corrective action based on a cold inflation pressure value of a tire mounted on a vehicle, the method comprising : a) receiving data from a data gathering system which gathers data related to conditions regarding said tire, said data comprising an instantaneous pressure reading of said tire, an internal gas temperature of said tire, and an external ambient temperature reading for said vehicle; b) calculating a cold inflation pressure value of said tire based on data received in step a) c) retrieving an optimal pressure range for said tire from a database, said optimal pressure range being based on conditions specific to said tire and characteristics of said tire d) comparing said cold inflation pressure value from step b) with said optimal pressure range retrieved in step c) e) in the event said cold inflation pressure is outside said optimal pressure range, generating an alert and selecting a corrective action based on an amount by which said cold inflation pressure is outside said optimal pressure range

8. A method according to claim 7 wherein said data received in step a) further comprises a vehicle altitude reading.

9. A method according to claim 8 wherein said cold inflation pressure value is determined according to a formula :

^/P = (P,_re -C_flteWJxC gas x C temperature wherein

AACIP is the Cold Inflation Pressure for said tire

P_ti_re is said instantaneous pressure of the tire (in

PSI) ;

5 C_ai_ti_tude is a Calculated Altitude Correction based on said vehicle altitude reading;

C_gas is a Calculated Gas Correction Coefficient based on characteristics of said tire and said data gathered by said system, and

10 ^temperature is a Calculated Temperature Correction based on said internal gas temperature.

10. A method according to claim 9 wherein Wherein

Λ C /-> T ambient

^ temperature rp tire

T_ambi_ent is said external ambient temperature reading Tti_re is said internal gas temperature .

11 . A method according to claim 9 wherein

20 C_aa_ll_Λti_tt_uu_dd_ee = ~ _l ^a ₀ ^l _Q ^ti ₀ ^t _F ^ud _e^_et x0 . 5 PSI

wherein altitude is said vehicle altitude reading.

12. A method according to claim 9 wherein

1 - K + KC_temperαture gas .-, temperature

25 wherein K is pressure dependent variable.

13. A method according to claim 12 wherein K = Cl + C2/Pt

Wherein Cl and C2 are tire model dependent coefficients and Pt is said instantaneous pressure reading of said tire.