GB2501980A

GB2501980A - Estimating load distribution using vehicle motion, particularly in tyre monitor autolocation

Info

Publication number: GB2501980A
Application number: GB1305289.9A
Authority: GB
Inventors: John Greer; Michael Byberg
Original assignee: Schrader Electronics Ltd
Current assignee: Schrader Electronics Ltd
Priority date: 2012-03-22
Filing date: 2013-03-22
Publication date: 2013-11-13
Anticipated expiration: 2033-03-22
Also published as: GB201205000D0; GB2501980B; GB201305289D0; WO2013139977A1

Abstract

A wheel monitoring system 102 monitors movement, for example acceleration or steering angle, of a vehicle 100 and estimates or predicts changes in the distribution of vehicle load, for example load on wheels 104, 106, 108, 110, from the detected changes in the vehicle's movement. Preferably each wheel 104, 106, 108, 110 has a tyre comprising a tyre monitor 124, 126, 128, 130 which measures tyre pressure or another parameter indicative of tyre load, allowing system 102 to automatically assign locations to tyre monitors 124, 126, 128, 130 by correlating the estimated or predicted change in the load distribution with measured load data from tyre monitors 124, 126, 128, 130. Confirming that auto-location of the locations of all wheel monitors 124, 126, 128, 130 is successful may be delayed until they have been repeatedly identified consistently.

Description

System and Method for Monitoring Vehicle Load Dynamics

Field of the Invention

The present invention relates to monitoring vehicle load dynamics. The invention also relates to wheel monitoring systems, especially Tire Pressure Monitoring Systems (TPMS).

Background to the Invention

Systems have been developed for monitoring characteristics, such as tire pressure, tire (air) temperature and/or acceleration of the wheels of a vehicle, or the battery voltage of a battery in a wheel mounted unit. A wheel mounted unit comprising one or more appropriate sensor(s) is located at each wheel, typically inside the tire, which measures the relevant characteristic(s) and transmits corresponding information to a remote central monitoring station.

One problem associated with such systems is automatically determining which wheel unit is associated with which wheel (known as "auto-location"). Conventional solutions to this problem tend to be relatively complex and therefore expensive, and are not suitable for all vehicles.

It would be desirable to provide a better solution to this problem.

Summary of the Invention

A first aspect of the invention provides a system for monitoring changes in vehicle load, the system comprising a controller configured to monitor at least one aspect of a vehicle's movement and to determine at least one aspect of a change in the distribution of said vehicle load from one or more detected changes in said at least one aspect of said vehicle's movement.

In typical applications, the vehicle load comprises the weight of the vehicle (including the weight of any occupants and cargo) acting through the vehicle's wheels.

In preferred embodiments, said at least one aspect of a change in the distribution of said vehicle load comprises whether the vehicle load is shifting towards the front of the vehicle or towards the rear of the vehicle. Preferably, said at least one aspect of a change in the distribution of said vehicle load comprises whether the vehicle load is shifting towards the right side of the vehicle or towards the left side of the vehicle.

In preferred embodiments, said at least one aspect of the vehicle's movement comprises acceleration, said controller being configured to detect changes in acceleration of the vehicle. Typically, the controller is configured to detect changes in acceleration in a measurement period. The controller may be configured to detect the rate of change of acceleration. In particular, the controller may be configured to determine if, in respect of a measurement period, acceleration has increased (typically by an amount more than an acceleration threshold amount) or decreased, i.e. deceleration, (typically by an amount more than a deceleration threshold amount).

In preferred embodiments, said at least one aspect of the vehicle's movement comprises steering angle (including any data or other means that can be used to obtain an indication thereof, e.g. pitch and yaw data), said controller being configured to detect changes in steering angle of the vehicle. Typically, the controller is configured to detect changes in steering angle in a measurement period. The controller may be configured to detect the rate of change of steering angle. The controller may be configured to determine if, in respect of a measurement period, a left turn is effected (typically by an amount more than a left turn threshold amount) or a right turn (typically by an amount more than a right turn threshold amount).

Typically, said controller is configured to determine at least one parameter having a value indicative of said at least one aspect of a vehicle's movement. In the preferred embodiment, said at least one parameter comprises an acceleration parameter having a value that is indicative of a change in acceleration of the vehicle. Typically, the acceleration parameter has a value that is indicative of a change in acceleration in a measurement period. The value of said acceleration parameter may be indicative of rate of change of acceleration. In the preferred embodiment, said at least one parameter comprises a steering angle parameter having a value that is indicative of a change in steering angle of the vehicle. Typically, the steering angle parameter has a value that is indicative of a change in steering angle in a measurement period. The value of said steering angle parameter may be indicative of rate of change of acceleration.

In the preferred embodiment, the controller is configured to determine that the vehicle load is shifting towards the front of the vehicle in response to determining that the vehicle's acceleration in a forward direction is increasing (typically by an amount more than an acceleration threshold amount), and that the vehicle load is shifting towards the rear of the vehicle in response to determining that the vehicle's acceleration in a forward direction is decreasing (typically by an amount more than a deceleration threshold amount).

In the preferred embodiment, the controller is configured to determine that the vehicle load is shifting towards the left side of the vehicle in response to determining that a right turn is effected (typically by an amount more than a right turn threshold amount), and that the vehicle load is shifting towards the right side of the vehicle in response to determining that a left turn is effected (typically by an amount more than a left turn threshold amount).

Said at least one aspect of a vehicle's movement, and as applicable said at least one parameter indicative of same, may be calculated from a respective one or more input signals received by the controller during use. The input signals are conveniently received from a respective one or more sensors that may be included in the system. For example, the vehicle's acceleration may be determined from an input signal indicative of the vehicle's speed. The steering angle may be determined from an input signal indicative of the steering angle of the vehicle's steering system.

In typical embodiments, the controller is included in the vehicle's communication network, and may for example be implemented by a vehicle ECU, BCU or any other convenient processor(s) included in the vehicle's communication network. The system may comprise one or more sensor devices for monitoring one or more aspects of the vehicle's movement (e.g. vehicle speed and steering angle) and providing corresponding signals to the controller.

In preferred embodiments, the system includes a respective tyre monitorfor each (typically four) wheel of the vehicle, each lyre monitor being configured to monitor one or more characteristics of the respective tyre and to transmit data indicative of the monitored characteristics to a tyre monitor controller: which is typically included in the vehicle's communication network, and may for example be implemented by a vehicle ECU, BCU or any other convenient processor(s) included in the vehicle's communication network.

Most conveniently, said controller for determining changes in the distribution of said vehicle load is integrated with said tyre monitor controller, i.e. the same controller is configured to perform both functions.

Typically, each tyre monitor is configured to measure tyre pressure. In preferred embodiments, therefore, the system comprises a tyre pressure monitoring system.

Advantageously, each tyre monitor is configured to monitor the tyre load, i.e. the load experienced by the tyre as a result of the vehicle's weight (including any occupants and cargo) acting on the tyre, or to monitor one or more characteristics of the tyre from which tyre load can be determined, and to transmit data to the tyre monitor controller indicative of the tyre load or from which tyre load can be determined (e.g. by the controller for determining changes in the distribution of said vehicle load or the tyre monitor controller), or indicative of changes in the tyre load or from which changes in tyre load can be determined (e.g. by the controller for determining changes in the distribution of said vehicle load or the tyre monitor controller).

For example, each tyre monitor may be configured to measure or monitor a "footprint" of the tyre (i.e. the size of an area of the tyre that is in contact with the ground) during a road strike once per wheel revolution. The size of the footprint increases with a larger load applied to the tyre and decreases with a smaller load applied to the tyre. Alternatively, where the tyre monitor comprises a pressure sensor, variations in pressure in the tyre can be used as an indication of an increase or decrease in tyre load (an increase in pressure corresponds to an increase in load and a decrease in pressure corresponds to a decrease in load).

Vehicle load shifting towards the front of the vehicle corresponds with an increase in load applied through the wheels of the front axle and a decrease in load applied through the wheels of the rear axle. Vehicle load shifting towards the rear of the vehicle corresponds with an increase in load applied through the wheels of the rear axle and a decrease in load applied through the wheels of the front axle. Vehicle load shifting towards the right side of the vehicle corresponds with an increase in load applied through the wheels at the right side of the vehicle and a decrease in load applied through the wheels at the left side of the vehicle. Vehicle load shifting towards the left side of the vehicle corresponds with an increase in load applied through the wheels at the left side of the vehicle and a decrease in load applied through the wheels at the right side of the vehicle.

Hence, in a preferred application of the invention, auto-location of tyre monitors can be performed by correlating a determined change in the distribution of vehicle load with respective tyre load data obtained from each tyre monitor.

In preferred embodiments, the controller is configured to make any one or more of the following determinations in respect of each tyre monitor: i) if the vehicle load is shifting to the front and the respective tyre load is increasing, then the respective tyre monitor is located at the front of the vehicle; U) if the vehicle load is shifting to the rear and the respective tyre load is increasing, then the respective tyre monitor is located at the rear of the vehicle; Ui) if the vehicle load is shifting to the front and the respective tyre load is decreasing, then the respective tyre monitor is located at the rear of the vehicle; iv) if the vehicle load is shifting to the rear and the respective tyre load is decreasing, then the respective tyre monitor is located at the front of the vehicle; v) if the vehicle load is shifting to the right and the respective tyre load is increasing, then the respective tyre monitor is located at the right hand side of the vehicle; vi) if the vehicle load is shifting to the left and the respective tyre load is increasing, then the respective tyre monitor is located at the left hand side of the vehicle; vii) if the vehicle load is shifting to the right and the respective tyre load is decreasing, then the respective tyre monitor is located at the left hand side of the vehicle; viii) if the vehicle load is shifting to the left and the respective tyre load is decreasing, then the respective tyre monitor is located at the right hand side of the vehicle.

The relevant one or more determinations are preferably made in respect of a measurement period, preferably a measurement period in respect of which a corresponding load shifting determination is made, which may be the same measurement period or a measurement period after the corresponding load shifting measurement is made. The controller may be configured to assign a respective location (e.g. front-left, front-right, rear-left, rear-right) to each tyre monitor based on said determination(s).

Advantageously, the relevant one or more determinations are made in respect of a plurality of measurement periods, after which the controller assigns locations to each tyre monitor. Preferably, the controller assigns locations only after a plurality of consistent determinations are made in respect of the tyre monitor, preferably in respect of all tyre monitors.

A second aspect of the invention provides a controller configured to monitor at least one aspect of a vehicle's movement and to determine at least one aspect of a change in the distribution of vehicle load from one or more detected changes in said at least one aspect of said vehicle's movement.

A third aspect of the invention provides a method of monitoring changes in vehicle load, the method comprising monitoring at least one aspect of a vehicle's movement, and determining at least one aspect of a change in the distribution of said vehicle load from one or more detected changes in said at least one aspect of said vehicle's movement.

A fourth aspect of the invention comprises a computer program product comprising computer usable code configured to cause a computer to perform the method of the third aspect of the invention.

A fifth aspect of the invention provides a wheel monitoring system, especially a tyre pressure monitoring system, comprising a respective tyre monitor for each wheel being configured to monitor one or more characteristics of the respective tyre and to transmit data indicative of the monitored characteristics to a tyre monitor controller, said system being configured to monitor at least one aspect of a vehicle's movement and to determine at least one aspect of a change in the distribution of vehicle load from one or more detected changes in said at least one aspect of said vehicle's movement, wherein said data transmitted from said tyre monitors is indicative of tyre load, and wherein said system is further configured to assign locations to said tyre monitors by correlating a determined change in the distribution of vehicle load with respective tyre load data obtained from the respective tyre monitors.

A sixth aspect of the invention provides a method of assigning locations to tyre monitors in a wheel monitoring system, the method comprising monitoring at least one aspect of a vehicle's movement, and determining at least one aspect of a change in the distribution of said vehicle load from one or more detected changes in said at least one aspect of said vehicle's movement, and assigning locations to said tyre monitors by correlating a determined change in the distribution of vehicle load with respective tyre load data obtained from the respective tyre monitors.

A seventh aspect of the invention comprises a computer program product comprising computer usable code configured to cause a computer to perform the method of the sixth aspect of the invention.

In an alternative application, said first, second, third and fourth aspects of the invention may be used to provide an input signal, being indicative of at least one determined aspect of a change in the distribution of said vehicle load, to an Electronic Stability Programme (ESP) system, which determines how much driving/braking force should be applied to each wheel on a vehicle. In embodiments where the absolute level of load on each wheel is not measured, the input signal may be indicative of the relative level of load on each wheel, the ESP system being configured to determine ratiometrically a corresponding amount of driving/braking force to apply to each wheel.

Other aspects of the invention therefore include an ESP system including or otherwise co-operable with a system of the first aspect of the invention, or a controller of the second aspect of the invention, or a computer program product of the fifth aspect of the invention, or configured to perform the method of the third aspect of the invention.

Further advantageous aspects of the invention will become apparent to those ordinarily skilled in the art upon review of the following description of a specific embodiment and with reference to the accompanying drawings.

Brief Description of the Drawings

An embodimentof the invention is nowdescribed bywayof exampleand with reference to the accompanying drawings in which like numerals are used to denote like parts and in which: Figure 1 is a block diagram of an embodiment of a tyre monitoring system (TMS) shown in conjunction with parts of a vehicle; Figure 2 is a block diagram of a tyre monitoring apparatus included in the TMS of Figure 1; and Figure 3 is a flow chart illustrating an embodiment of a method of monitoring wheel loads.

Detailed description of the Drawings

Referring now to Figure 1 of the drawings, there is shown, generally indicated as 102, a system that monitors vehicle load dynamics shown in situ on a vehicle 100, the system taking the preferred form of tyre monitoring system (TMS) for the purposes of illustration.

For reasons of clarity, only those portions of the vehicle 100 and TMS 102 that are helpful in understanding the present invention are shown.

The vehicle 100, typically a 4-wheeled vehicle, includes wheels 104, 106, 108, 110, each wheel including a tyre mounted on a rim. The TMS 102 includes a control unit 112 and tyre monitors 124, 126, 128, 130, typically generally referred to as sensors, transmitters, wheel units, or the like. The tyre monitors 124, 126, 128, 130 measure tyre characteristics, typically including tyre pressure and temperature, and transmit corresponding tyre data for reception and processing by the control unit 112. Typically, a respective tyre monitor is associated with each wheel of the vehicle 100.

In typical embodiments, the tyre monitors are capable of measuring at least tyre pressure and of transmitting data to the control unit 112, including data representing the measured tyre pressure and usually also identification information uniquely identifying the respective tyre monitor. Each of the tyre monitors 124, 126, 128, 130 includes a suitably powered wireless transmitter, conveniently a battery (or otherwise) powered radio frequency (RF) transmitter, and a pressure sensor for measuring the pressure of the gas (usually air) within the tyre. In such embodiments, the system 102 may be referred to as a tyre pressure monitoring system (TPMS).

Any suitable control unit may be used in the system 102. By way of example, in the illustrated embodiment, the control unit 112 includes a controller 132 (e.g. a vehicle ECU and/or a BCU, or other processor (typically a suitably programmed microprocessor or microcontroller)), a memory device 134 and a receiver 136 for receiving wireless transmissions from the tyre monitors. More generally, the vehicle 100 may include one or more controllers, each typically comprising a suitably programmed microprocessor or microcontroller, e.g. the controller 112, one or more ECUs and/or one or more BCUs, and one or more other electronic units, such as the memory device 134 or receiver 136 and one or more sensors. These components are capable of communication with one another as required, usually by means of a vehicle communications bus, e.g. a CAN (controller area network) bus and/or LIN (local interconnect network), and together may be said to comprise the vehicle's communication network, referred to generally in Figure las 115.

Referring now to Figure 2, there is shown a block diagram of an embodiment of a tyre monitor 200, suitable for us as monitors 124, 126, 128, 130. The tyre monitor 200 includes a controller 202, a power source such as a battery 204, a pressure sensor 208, a wireless transmitter 214 and an antenna 216. It will be apparent that the monitor 200 may use any convenient power source instead of or as well as a battery, e.g. thermoelectric and/or piezoelectric generators and/or electromagnetic induction. The monitor 200 usually also includes a transponder coil 206 and commonly one or more piezoelectric motion sensors 210, 212. The tyre monitor 200 typically also includes a temperature sensor 209 for measuring the temperature of the tyre and/or of the gas within the tyre. In this illustration, the motion sensors 210, 212 each comprise a respective shock sensor of the type that produces an electrical signal in response to being subjected to acceleration (typically shock sensors are responsive to changes in acceleration, the electrical signal being indicative of, typically proportional to, the experienced acceleration or change in acceleration, especially the rate of change of acceleration). Alternatively, the sensors 210, 212 may each comprise an accelerometer or a microelectromechanical systems (MEM5) sensor. The main difference between an accelerometer and a shock sensor is that the output signal from a shock sensor is related to a change of force applied to the shock sensor, whereas the output signal from an accelerometer is proportional to the absolute force applied.

The controller 202 may be implemented by any suitable means, for example a microprocessor, microcontroller or other suitable data processing device programmed to perform the functions described herein.

In the illustrated embodiment, the pressure sensor 208 detects the pneumatic air pressure of the tyre with which the tyre monitor 200 is associated. The temperature sensor 209 measures the temperature of the tyre and/or of the air within the tyre. In alternative embodiments, the pressure sensor 208 may be supplemented with or replaced by other devices for detecting tyre data. An indication of the tyre data is provided to the controller 202 at an input 220.

A sensor interface 213 is provided between the sensors 208, 209 and the controller 202 and is configured to allow the controller 202 to measure parameter values from the electrical signals that emanate from the sensors 208, 209 during use.

A shock sensor interface 207 is provided in the tyre monitor 200 and is configured to provide the necessary control signals and detect the electrical signals from the shock sensors 210, 212.

Auto-location involves the identification of each tyre monitor 124, 126, 128, 130 and determination of its position on the vehicle 100, automatically and without human intervention. Auto-location may be done initially upon installation and subsequently in the event of tyre rotation or replacement. Performing auto-location typically involves determining the identity or serial number of the tyre monitor in each of the wheels. In premium vehicles, knowing the identity of the tyre monitor in each wheel allows a pressure by position display to be implemented and shown to the driver. In base vehicles with different placard tire pressures for front and rear axles, it is desirable to know tyre monitor identities and positions in order to check pressure against a correct threshold for an applicable axle.

In arriving at the present invention, it is recognised that by monitoring changes in vehicle load as a result of the vehicle's movement, and in particular the effect of load changes at the vehicle's wheels, auto-location can be performed, as is described in more detail below in the context of a preferred embodiment. It will be understood, however, that the invention is not limited to use in auto-location of tyre monitors. For example, embodiments of the invention may be used in conjunction with a vehicle's an Electronic Stability Programme (ESP) system.

In use, the vehicle's communication network 115 gathers data concerning the operation of the vehicle 100 from at least one, but typically a plurality of, sensor devices provided on the vehicle. The sensor devices may include respective sensor(s) configured to determine any one or more of the following: vehicle speed; vehicle acceleration; steering angle; whether or not (a) reverse gear is selected. In Figure 1, respective sensor devices 117, 119 for determining vehicle speed and steering angle are shown by way of example.

Any suitable conventional sensors may be used for this purpose. It will be understood that an indication of steering angle may be obtained by means other than conventional steering angle sensors, for example by sensor(s) or other means for determining pitch and yaw data. Hence, the control unit 112, or more particularly ECU 132 or a BCU, is provided with data indicative of one or more of these parameters. In preferred embodiments, one or more of these parameters, preferably comprising or including vehicle speed and steering angle, are used to predict if load in the vehicle is shifting, and if so, to what location in the vehicle the load is shifting. Advantageously, information concerning the change in load can be used in conjunction with information from tyre monitors 124, 126, 128, 130 to auto-locate each tyre monitorwith respect to the vehicle.

In the present embodiment, it is assumed that the controller 132 is configured to monitor vehicle load (i.e. the load on the wheels caused by the weight of the vehicle (including any occupants and cargo)), and in particular to predict, or determine, changes in the distribution of the vehicle's load based on one or more parameters relating to the vehicle's movement. In this example, the parameters include vehicle speed and vehicle steering angle, although one or more alternative or additional parameters may be used.

In any event, to this end the controller 132 is provided with the relevant parameter measurements directly or indirectly from the sensors 117, 119, or other relevant sensors.

In alternative embodiments, any one or more other components of the vehicle communication network 115 may be used to monitor the vehicle load as is convenient, e.g. an ECU, BCU or other suitably programmed processor, and the following descriptions apply equally to such alternative embodiments as would be apparent to a skilled person.

In preferred embodiments, in order to monitor vehicle load, the controller 132, or other designated component(s) of the system 102, monitors changes in acceleration, conveniently the rate of change of acceleration, of the vehicle 100, and changes in steering angle, conveniently the rate of change of steering angle. The changes in acceleration can be calculated from the vehicle speed, e.g. as indicated by sensor 117, and changes in steering angle can be determined from the output of sensor 119. With regard to acceleration, the controller 132, or other designated component(s) of the system 102 may be configured to determine if, in respect of a measurement period, acceleration has increased (typically by an amount more than an acceleration threshold amount) or decreased, i.e. deceleration, (typically by an amount more than a deceleration threshold amount). With regard to steering angle, the controller 132, or other designated component(s) of the system 102 may be configured to determine if, in respect of a measurement period, a left turn is effected (typically by an amount more than a left turn threshold amount) or a right turn (typically by an amount more than a right turn threshold amount).

In order to perform auto-location, the system 102 is also configured to monitor the individual load experienced by the tyre of each wheel 104, 106, 108, 110, and in particular to detect an increase or decrease in tyre load. This may be achieved by any suitable means. For example, data received from the respective tyre monitors 124, 126, 128, 130 may be used for this purpose. In one option, for example where the tyre monitors 124, 126, 128, 130 each comprises a tyre mounted sensors (TMS), the tyre monitors 124, 126, 128, 130 are configured to measure or monitor a "footprint" of the tyre (i.e. the size of an area of the tyre that is in contact with the ground) during a road strike once per wheel revolution. The size of the footprint increases with a larger load applied to the tyre and decreases with a smaller load applied to the tyre. Alternatively, where the tyre monitors 124, 126, 128, 130 each comprises a pressure sensor, variations in pressure in the tyre can be used as an indication of an increase or decrease in tyre load (an increase in pressure corresponds to an increase in load and a decrease in pressure corresponds to a decrease in load). Typically, no special activation of pressure sensors would be required for this purpose -pressure sensors normally sample and transmit pressure data in a manner compatible for use for this purpose. By way of example, International PCT patent application W02011162962 discloses suitable methods of detecting changes in tyre load.

In respect of a vehicle load transfer occurring during a detected vehicle event (accelerating/decelerating or cornering), the tyre monitors 124, 126, 128, 130 are configured to transmit tyre load data to the control unit 112, and in particular to the controller 132. Typically, the tyre load data is indicative of an increase in load, a decrease in load or no significant change in load. The controller 202 of the respective monitor 124, 126, 128, 130 may be configured to analyse the pressure or footprint data generated within the tyre and transmit only an indication of tyre load increase, decrease or no significant change. Alternatively, the relevant raw data may be sent from the tyre monitors 124, 126, 128, 130 and a determination of tyre load increase, decrease or no significant change may be made by the controller 132.

The system 102, e.g. by means of the controller 132, based upon the aforementioned vehicle parameters, detects vehicle events (accelerating/decelerating and/or cornering) and determines the direction of load shift in the vehicle. The detected vehicle events are then correlated with the tyre load data received from the tyre monitors 124, 126, 128, 130 to determine where on the vehicle each monitor is located.

For example, when the tyre monitors transmit to the controller 132, part of each transmission frame may include tyre load information applied to each tyre and optionally when it occurred (although this is not necessary if for example the transmission of tyre load data is synchronised with the detection of vehicle events). In any event, the controller 132 correlates each vehicle event with the respective tyre load data from each tyre monitor 124, 126, 128, 130 and makes a decision as to whether the tyre is FRONT, REAR, LEFT and/or RIGHT depending on its programming logic. Typically, the process is repeated until enough information has been received to determine with reasonable certainty that a tyre monitor is located in a particular location, upon which the controller 132 assigns the tyre monitor to the determined location. Conveniently, the controller 132 can distinguish between tyre monitors using a respective monitor ID.

Figure 3 shows a flow chart illustrating a preferred method by which the system 102 can monitor changes in the vehicle's load distribution. The flow chart also illustrates how this can be used to perform auto-location of the tyre monitors 124, 126, 128, 130. As previously indicated, this method may be performed by the controller 132, and/or any other convenient component of the system 102, and in particular of the vehicle communication network 115.

At the beginning of a drive, a timer is initiated (300), auto-location being performed until the timer times out (301, 302). The duration of the timer may be specified by, for example, government legislation or the vehicle's manufacturer.

While the vehicle is in motion, vehicle parameters, which in this example comprise vehicle speed and steering angle, are obtained from the relevant components of the vehicle communication network 115 (303). Typically, the vehicle speed and steering angle are measured continuously and so the measured values may be buffered and averaged over a suitable time period, e.g. 1 second (304). Next, respective values for an acceleration parameter and a steering angle parameter are calculated. The value of the acceleration parameter is indicative of the change in acceleration of the vehicle, and may conveniently be determined as the rate of change of acceleration. The steering angle parameter is indicative of the change in steering angle, and may conveniently be calculated as the rate of change of steering angle. The acceleration parameter and steering angle parameter are conveniently calculated in respect of the same time period for which the vehicle speed and steering angle were averaged (305).

The acceleration parameter and steering angle parameter are used to determine if one (or more) of the following scenarios exists in respect of the vehicle load: 1. load is shifting towards the front of the vehicle 2. load is shifting towards the rear of the vehicle 3. load is shifting towards the left side of the vehicle 4. load is shifting towards the right side of the vehicle 5. no significant amount of load is shifting in the vehicle By making a determination concerning changes in load distribution, the system may be said to be predicting load changes since the inertia of the vehicle may result in the actual load shift occurring after the determination is made. In the flowchart of Figure 3, in each cycle an appropriate one of the above scenarios is determined. In an alternative embodiment each cycle may decide that any one of the following scenario pairs is true: I & 3; 1 & 4; 2 & 3 012 & 4, or that scenario S is true.

Referring again to Figure 3, the steering parameter value is processed to determine if the detected change in steering angle corresponds to a right or left turn (it is noted that detecting a right or left turn does not necessarily mean that the vehicle is turning right and left respectively). This may be achieved by comparing the steering angle parameter value against a first steering angle parameter threshold in order to determine if a right turn is detected (306)-in which case it may be determined that the load is shifting left -and against a second steering angle parameter threshold to determine if a left turn is detected (307)-in which case it may be determined that the load is shifting right.

Normally, a right turn and a left turn can be distinguished by the sense (e.g. positive or negative) of the steering angle measurement provided by sensor 119. Conveniently, the sense is preserved when determining the change in steering angle (305). Hence, the first and second steering angle thresholds may have opposite senses (but optionally the same magnitude) and the distinction between a left and right turn may be made by determining whether or not the steering parameter angle value exceeds one of the first or second thresholds or is less than the other.

The acceleration parameter value is processed to determine if the vehicle is undergoing acceleration or deceleration in the forward direction of travel, i.e. the direction in which a properly seated driver faces. This may be achieved by comparing the acceleration parameter value against a first acceleration parameter threshold in order to determine if acceleration is detected (308)-in which case it may be determined that the load is shifting towards the rear -and against a second acceleration parameter threshold to determine if deceleration is detected (309) -in which case it may be determined that the load is shifting towards the front. Normally, acceleration and deceleration can be distinguished by the sense (e.g. positive or negative) of the change in vehicle speed measurement provided by sensor 117. Conveniently, the sense is preserved when determining the change in acceleration (305). Hence, the first and second acceleration thresholds may have opposite senses (but optionally the same magnitude) and the distinction between acceleration and deceleration may be made by determining whether or not the steering parameter angle value exceeds one of the first or second thresholds or is less than the other.

If the steering angle parameter or the acceleration parameter satisfies the relevant threshold criteria, then a vehicle event is detected and a determination on load shifting can be made as indicated above. If neither the steering angle parameter nor the acceleration parameter satisfy the relevant threshold criteria, then it is determined that there is no significant load shifting in the vehicle (310), i.e. no valid vehicle event is detected. Steps 303 to 310 may then be repeated. The timer is preferably decremented by one after each cycle of the assessment (312). Preferably, the timer is only decremented if the vehicle's speed exceeds a threshold value (311), e.g. 2okph.

If at step 306, it is determined that the steering angle parameter threshold is satisfied (indicating a load shift to the left in this example), then the respective tyre load data from each tyre monitor is checked (313). If the tyre load data indicates that tyre load is increasing, then a decision is made that the respective tyre monitor is on the left of the vehicle (314, 315). If the tyre load data indicates that tyre load is decreasing, then a decision is made that the respective tyre monitor is on the right of the vehicle (316, 317).

If the tyre load data indicates that there is no significant change in tyre load, then no decision is made for the respective tyre monitor (318).

If at step 307, it is determined that the steering angle parameter threshold is satisfied (indicating a load shift to the right in this example), then the respective tyre load data from each tyre monitor is checked (319). If the tyre load data indicates that tyre load is increasing, then a decision is made that the respective tyre monitor is on the right of the vehicle (320, 317). If the tyre load data indicates that tyre load is decreasing, then a decision is made that the respective tyre monitor is on the left of the vehicle (321, 315). If the tyre load data indicates that there is no significant change in tyre load, then no decision is made for the respective tyre monitor (318).

If at step 308, it is determined that the acceleration parameter threshold is satisfied (indicating a load shift to the rear in this example), then the respective tyre load data from each tyre monitor is checked (322). If the tyre load data indicates that tyre load is increasing, then a decision is made that the respective tyre monitor is on the rear axle of the vehicle (323, 324). If the tyre load data indicates that tyre load is decreasing, then a decision is made that the respective tyre monitor is on the front axle of the vehicle (325, 326). If the tyre load data indicates that there is no significant change in tyre load, then no decision is made for the respective tyre monitor (327).

If at step 309, it is determined that the acceleration parameter threshold is satisfied (indicating a load shift to the front in this example), then the respective tyre load data from each tyre monitor is checked (328). If the tyre load data indicates that tyre load is increasing, then a decision is made that the respective tyre monitor is on the front axle of the vehicle (329, 326). If the tyre load data indicates that tyre load is decreasing, then a decision is made that the respective tyre monitor is on the rear axle of the vehicle (330, 324). If the tyre load data indicates that there is no significant change in tyre load, then no decision is made for the respective tyre monitor (327).

After each set of decisions on tyre location for the respective tyre monitors, it is decided if a sufficient number of decisions have been made allocating each tyre monitor to a given location to warrant assigning the tyre monitors to respective locations. If so, then each tyre monitor is assigned to a respective location (332). Preferably, a check is made to ensure that a unique ID is assigned to each wheel location (333). If so, then auto-location is complete (334), otherwise the process (in particular the event detection and load shift determination of 303 to 310 and the location decisions of 313 to 330) is repeated. If a sufficient number of location decisions have not been made at 331, then the process (in particular the event detection and load shift determination of 303 to 310 and the location decisions of 313 to 330) is repeated. The timer is preferably decremented by one after each cycle of the assessment (312). Preferably, the timer is only decremented if the vehicle's speed exceeds a threshold value (311), e.g. 20kph.

In the embodiment of Figure 3, each instant decision on tyre monitor location can determine either if it is left or right, or if it is front or rear. This is because each processing cycle determines either if the steering angle parameter satisfies the threshold criteria or if the acceleration parameter satisfies the threshold criteria, but not both (the two criteria are assessed in series). In alternative embodiments, both the steering angle parameter and the acceleration parameter may be examined with respect to their threshold criteria in each cycle, i.e. the two criteria are assessed in parallel. This allows a determination of load shifting to be made in respect of both "left or right" and "front or rear" in each cycle.

This in turn allows the respective location decisions to be made in respect of both "left or right" and "front or rear" in each cycle. Moreover, in the illustrated embodiment precedence is given to steering angle / side decisions. For example in Figure 3 the steering angle assessment takes precedence over the acceleration assessment in that if the steering angle exceeds a threshold, then acceleration is not assessed. In alternative embodiments, this precedence may be reversed. The respective threshold values may be determined empirically through testing and may be vehicle dependent.

Optionally, the system 102 may be configured to detect whether or not the vehicle is in reverse (by any convenient means, e.g. an appropriate sensor connected to the vehicle communication network 115). If the vehicle is determined to be in reverse, then the assessment of vehicle load and, if applicable, auto-location maybe suspended until the vehicle is determined to be moving forwards. Alternatively, different acceleration parameter threshold(s) may be used, e.g. acceleration parameter thresholds having a sense opposite to the sense of the acceleration parameter thresholds used for forward travel.

Three examples are outlined below, assuming that the steering angle is negative when turning right and positive when turning left, and assuming forward motion.

Example 1:

A vehicle travels through a right hand corner at constant speed. Initially, the steering angle parameter value is negative as the steering angle changes from roughly zero to something negative. In this case, the prediction is that load would shift to the left rear and left front wheels, and lift from the right front and right rear wheels. Now, when the vehicle is in the process of completing the turn, the steering angle changes from something negative to zero, thus there is a positive steering angle parameter value. In this case, the prediction is that load would lift from the left rear and left front wheels and shift to the right front and right rear wheels.

Example 2:

A vehicle decelerates from speed A to speed B. Initially, the acceleration parameter value is negative as the vehicle first decelerates from speed A. At this point, the prediction is that the load will shift to the front wheels (increase) and lift from the rear wheels (decrease). When the vehicle begins to approach speed B, the acceleration parameter value turns positive. At this point, the prediction would be that the load will lift from the front wheels (decrease) and shift to the rear wheels (increase).

Example 3:

A vehicle decelerates while making a right hand corner. Using the same logic as the two aforementioned examples, the prediction is that the load will shift to the left front (increase) and lift from the right rear (decrease) when the steering angle parameter value is negative and the acceleration parameter value is negative. When the vehicle completes the turn and eases into a lower speed than it was travelling before entering the turn, the prediction is that the load shall lift from the left front (decrease) and shift to the right rear (increase).

Hence, the system 102 performs load shift prediction by monitoring one or more vehicle parameters (e.g. speed and steering angle) and calculating the direction of load shift. This is an advantageous solution because it does not require ABS information from the vehicle's communication network and does not require a biased receiver ECU (thus allowing for an integrated solution which is lower cost compared to previous systems).

By way of example, when used for auto-location, the following advantages are obtained: relatively low cost; the relatively large integration effort required for ABS correlation auto-location TPM systems is avoided; it is viable on vehicles that do not have all necessary system components required to do ABS correlation (e.g. vehicles with only front or rear wheel pulse counters); and the system does not require a front or rear biased TPM receiver ECU.

By way of alternative application, detecting dynamic load shifts on the vehicle could also be used as a low-cost input to an Electronic Stability Programme (ESP) system, which determines how much driving/braking force should be applied to each wheel on a vehicle.

Although the preferred system described herein does not measure the absolute level of load on each wheel, it could determine the relative level of load on each wheel, and therefore allow a ratiometric amount of driving/braking force to apply to each wheel to be determined.

The invention is not limited to the embodiment described herein, which may be mified or varied without departing from the scope of the invention.

Claims

CLAIMS: 1. A system for monitoring changes in vehicle load, the system comprising a controller configured to monitor at least one aspect of a vehicle's movement and to determine at least one aspect of a change in the distribution of said vehicle load from one or more detected changes in said at least one aspect of said vehicle's movement.
2. A system as claimed in claim 1, wherein said at least one aspect of a change in the distribution of said vehicle load comprises whether the vehicle load is shifting towards the front of the vehicle or towards the rear of the vehicle.
3. A system as claimed in claim 1 or 2, wherein said at least one aspect of a change in the distribution of said vehicle load comprises whether the vehicle load is shifting towards the right side of the vehicle or towards the left side of the vehicle.
4. A system as claimed in and preceding claim, wherein said at least one aspect of the vehicle's movement comprises acceleration, said controller being configured to detect changes in acceleration of the vehicle.
5. A system as claimed in claim 4, wherein the controller is configured to determine that the vehicle load is shifting towards the front of the vehicle in response to determining that the vehicle's acceleration in a forward direction is increasing, and that the vehicle load is shifting towards the rear of the vehicle in response to determining that the vehicle's acceleration in a forward direction is decreasing.
6. A system as claimed in any preceding claim, wherein said at least one aspect of the vehicle's movement comprises steering angle of the vehicle.
7. A system as claimed in any preceding claim, wherein the controller is configured to determine if, in respect of a measurement period, a left turn or a right turn is effected.
8. A system as claimed in claim 5 or 6, wherein the controller is configured to determine that the vehicle load is shifting towards the left side of the vehicle in response to determining that a right turn is effected, and that the vehicle load is shifting towards the right side of the vehicle in response to determining that a left turn is effected.
9. A system as claimed in any preceding claim, wherein the vehicle load comprises the weight of the vehicle acting through the vehicles wheels.
10. A system as claimed in any preceding claim, further including a respective tyre monitor for respective wheels of the vehicle, each tyre monitor being configured to monitor one or more characteristics of the respective wheel and to transmit data indicative of the monitored characteristics to a tyre monitor controller.
11. A system as claimed in claim 10, wherein each tyre monitor is configured to measure tyre pressure.
12. A system as claimed in claim 10 or 11, wherein each tyre monitor is configured to monitor tyre load, or to monitor one or more characteristics of the tyre from which tyre load can be determined, and to transmit data to the tyre monitor controller indicative of the tyre load or from which tyre load can be determined.
13. A system as claimed in claim 12, wherein each tyre monitor is configured to measure the size of an area of the respective tyre that is in contact with the ground during a road strike once per wheel revolution.
14. A system as claimed in claim 12 or 13, wherein each tyre monitor is configured to measure variations in pressure in the tyre for use as an indication of an increase or decrease in tyre load.
15. A system as claimed in any one of claims 10 to 14, configured to perform auto-location of said tyre monitors by correlating a determined change in the distribution of vehicle load with respective tyre load data obtained from each tyre monitor.
16. A system as claimed in claim 15, wherein the controller is configured to make any one or more of the following determinations in respect of each tyre monitor: i) if the vehicle load is shifting to the front and the respective tyre load is increasing, then the respective tyre monitor is located at the front of the vehicle; U) if the vehicle load is shifting to the rear and the respective tyre load is increasing, then the respective tyre monitor is located at the rear of the vehicle; UI) if the vehicle load is shifting to the front and the respective tyre load is decreasing, then the respective tyre monitor is located at the rear of the vehicle; iv) if the vehicle load is shifting to the rear and the respective tyre load is decreasing, then the respective tyre monitor is located at the front of the vehicle; v) if the vehicle load is shifting to the right and the respective tyre load is increasing, then the respective tyre monitor is located at the right hand side of the vehicle; vi) if the vehicle load is shifting to the left and the respective tyre load is increasing, then the respective tyre monitor is located at the left hand side of the vehicle; vii) if the vehicle load is shifting to the right and the respective tyre load is decreasing, then the respective tyre monitor is located at the left hand side of the vehicle; viii) if the vehicle load is shifting to the left and the respective tyre load is decreasing, then the respective tyre monitor is located at the right hand side of the vehicle.
17. A system as claimed in claim 16, wherein any one or more of said determinations are made in respect of a measurement period which may be the same measurement period, or a measurement period after, a corresponding load shifting measurement is made.
18. A system as claimed in claim 16 or 17, wherein the controller is configured to assign a respective location to each tyre monitor based on any one or more of said determinations.
19. A system as claimed in any one of claims 16 to 18, wherein said determinations are made in respect of a plurality of measurement periods, after which the controller is configured to assign a respective location to each tyre monitor.
20. A system as claimed in claim 19, wherein the controller is configured to assign said locations only after a plurality of consistent determinations are made in respect of the respective tyre monitor, preferably in respect of all tyre monitors.
21. A method of monitoring changes in vehicle load, the method comprising monitoring at least one aspect of a vehicle's movement, and determining at least one aspect of a change in the distribution of said vehicle load from one or more detected changes in said at least one aspect of said vehicles movement.
22. A wheel monitoring system comprising a respective tyre monitor for each wheel being configured to monitor one or more characteristics of the respective tyre and to transmit data indicative of the monitored characteristics to a tyre monitor controller, said system being configured to monitor at least one aspect of a vehicle's movement and to determine at least one aspect of a change in the distribution of vehicle load from one or more detected changes in said at least one aspect of said vehicle's movement, wherein said data transmitted from said tyre monitors is indicative of tyre load, and wherein said system is further configured to assign a respective locations to respective tyre monitors by correlating a determined change in the distribution of vehicle load with respective tyre load data obtained from the respective tyre monitors.
23. A method of assigning locations to tyre monitors in a wheel monitoring system, the method comprising monitoring at least one aspect of a vehicle's movement, and determining at least one aspect of a change in the distribution of said vehicle load from one or more detected changes in said at least one aspect of said vehicle's movement, and assigning a respective location to respective tyre monitors by correlating a determined change in the distribution of vehicle load with respective tyre load data obtained from the respective tyre monitors.