METHOD AND SYSTEM FOR DETERMINING A WHEEL LOAD ACTING ON A TIRE OF A VEHICLE

Abstract

The invention relates to a method for determining a wheel load (WL) acting on a tire (1) of a vehicle, comprising: a) determining a footprint (L) of the tire (1), b) receiving a tire information (ti) that identifies a type of the tire (1) and/or characterizes physical properties of the tire (1) as such, c) receiving tire operation conditions (toe) based on a measurement, d) selecting one of a plurality of predetermined calculation models (mod(ti)) based on the received tire information (ti), wherein each of the predetermined calculation models (mod(ti)) defines the wheel load (WL) as a function of the footprint (L) and the tire operation conditions (toe) for a respective tire type and/or respective physical properties of the tire (1) as such, e) calculating the wheel load (WL) based on the determined footprint (L) and the received tire operation conditions (toe), using the selected calculation model (mod(ti)). Further, a corresponding system (10) for determining a wheel load (WL) is proposed. Advantageously, the invention can be employed very universally and can deal with the problem of varying tire characteristics.

Claims

1. A method for determining a wheel load acting on a tire of a vehicle, comprising: a) determining a footprint of the tire, b) receiving tire information that at least one of identifies a type of the tire and characterizes physical properties of the tire, c) receiving tire operation conditions based on a measurement, d) selecting one of a plurality of predetermined calculation models based on the received tire information, wherein each of the predetermined calculation models defines the wheel load as a function of the footprint and tire operation conditions for at least one of respective tire type and respective physical properties of the tire, e) calculating the wheel load based on the determined footprint and the received tire operation conditions using the selected calculation model.

2. The method according to claim 1, wherein in step a) the footprint is determined as a length of a footprint area of the tire.

3. The method according to claim 1, wherein step a) is performed in a wheel unit disposed at the tire and comprising a sensor for measuring a deformation of the tire and a determining unit for determining the footprint based on the measured deformation of the tire.

4. The method according to claim 1, wherein the tire information received in step b) comprises data related to at least one of: tire type, tire dimension, season stipulated for the tire, material, material properties, tread depth, age, and manufacturing date.

5. The method according to claim 1, wherein the tire information in step b) is received at least partially from a digital store disposed at the tire.

6. The method according to claim 1, wherein the tire information in step b) is received at least partially from a digital store disposed in a control unit of the vehicle.

7. The method according to claim 1, wherein the tire operation conditions received in step c) comprise at least one of: tire pressure, tire temperature, vehicle velocity, tire rotational speed, vehicle acceleration, and tire rotational acceleration.

8. The method according to claim 1, wherein the measurement upon which the receiving of the tire operation conditions in step c) is based comprises a measurement by a measurement unit disposed at the tire.

9. The method according to claim 1, wherein each of the predetermined calculation models used in step d) is represented by a respective set of digitally stored model parameters.

10. The method according to claim 1, wherein in step e) the wheel load is calculated based on the formula
WL=f1(TP,FPAn) wherein WL is the wheel load, TP is the tire pressure, FPAn is a normalized footprint area of the tire, and f1 is a first function in the calculation models, wherein the normalized footprint area is calculated based on the formula
FPAn=f2(FPA,ti,toc) wherein FPA is a footprint area determined based on the determined footprint in step a) taking into account the tire information received in step b), ti is the tire information received in step b), and toc are the tire operation conditions received in step c).

11. The method according to claim 1, wherein at least one of step d) and step e) is performed by a control unit of the vehicle executing software.

12. The method according to claim 1, wherein the performance of step b) and step d) is initiated at the beginning of each driving period of the vehicle that follows a standstill period of at least a predetermined minimum standstill duration of the vehicle.

13. The method according to claim 1, wherein the predetermined calculation models are determined based on a fitting of previously recorded experimental data.

14. A system for determining a wheel load acting on a tire of a vehicle comprising: a) means for determining a footprint of the tire, b) means for receiving a tire information that at least one of identifies a type of the tire and/or characterizes physical properties of the tire, c) means for receiving tire operation conditions based on a measurement, d) means for selecting one of a plurality of predetermined calculation models based on the received tire information, wherein each of the predetermined calculation models defines the wheel load as a function of the footprint and the tire operation conditions for at least one of a respective tire type and respective physical properties of the tire, e) means for calculating the wheel load based on the determined footprint and the received tire operation conditions, using the selected calculation model.

15. A non-transitory computer readable medium containing program instructions for determining a wheel load acting on a tire of a vehicle, wherein execution of the program instructions by one or more processors of a computer system causes the one or more processors to carry out the steps of: a) determining a footprint of the tire, b) receiving tire information that at least one of identifies a type of the tire and characterizes physical properties of the tire, c) receiving tire operation conditions based on a measurement, d) selecting one of a plurality of predetermined calculation models based on the received tire information, wherein each of the predetermined calculation models defines the wheel load as a function of the footprint and tire operation conditions for at least one of respective tire type and respective physical properties of the tire, e) calculating the wheel load based on the determined footprint and the received tire operation conditions using the selected calculation model.

16. The non-transitory computer readable medium according to claim 15, wherein in step a) the footprint is determined as a length of a footprint area of the tire.

17. The non-transitory computer readable medium according to claim 15, wherein step a) is performed in a wheel unit disposed at the tire and comprising a sensor for measuring a deformation of the tire and a determining unit for determining the footprint based on the measured deformation of the tire.

18. The non-transitory computer readable medium according to claim 15, wherein the tire information received in step b) comprises data related to at least one of: tire type, tire dimension, season stipulated for the tire, material, material properties, tread depth, age, and manufacturing date.

19. The non-transitory computer readable medium according to claim 15, wherein the tire information in step b) is received at least partially from a digital store disposed at the tire.

20. The non-transitory computer readable medium according to claim 15, wherein the tire information in step b) is received at least partially from a digital store disposed in a control unit of the vehicle.

Description

[0072] The invention will now be described in more detail by way of example embodiments with reference to the accompanying drawings, in which

[0073] FIG. 1 illustrates a schematic block diagram of a system for determining a wheel load according an embodiment,

[0074] FIG. 2 illustrates a schematic block diagram of a wheel unit used in the system of FIG. 1,

[0075] FIG. 3 illustrates a schematic flow-chart of essential steps conducted in a method for determining a wheel load according to the invention, and

[0076] FIG. 4 illustrates a flow-chart of a method for determining a wheel load according to an embodiment.

[0077] FIG. 1 illustrates an embodiment of a system 10 for determining a wheel load acting on a tire 1 of a wheel 3 of a vehicle.

[0078] The system 10 comprises: [0079] a) means for determining a footprint of the tire 1, [0080] b) means for receiving a tire information that identifies a type of the tire and/or characterizes physical properties of the tire as such, [0081] c) means for receiving tire operation conditions based on a measurement, [0082] d) means for selecting one of a plurality of predetermined calculation models based on the received tire information, wherein each of the predetermined calculation models defines the wheel load as a function of the footprint and the tire operation conditions for a respective tire type and/or respective physical properties of the tire as such, [0083] e) means for calculating the wheel load based on the determined footprint and the received tire operation conditions, using the selected calculation model.

[0084] The above mentioned means of the system 10 can be described more detailed as follows:

a) Means for Determining a Footprint

[0085] The footprint is determined as a length L (FIG. 1) of a footprint area of the tire 1 by means of a wheel unit 12 disposed at the tire 1. The wheel unit 12 is illustrated in more detail in FIG. 2 and comprises a sensor 14 for measuring a local deformation of the tire 1 at a predetermined location 5 at the tire (corresponding to the location of the wheel unit 12) and a determining unit 20, implemented as a microcontroller, for determining the footprint length L (alternatively: e.g. footprint area) based on the measured deformation of the tire 1. In FIG. 2, the sensor signal provided by the sensor 14 is designated as “def”.

[0086] The determining unit 20 generates data D, which are transferred to a transmitter 22 of the wheel unit 12, which transmits the data D by means of a wireless signal preferably an RF signal 24 to a vehicle unit 30 configured to receive the RF signal 24 and to transfer the data D via a digital bus system 32 to a central control unit 34 (in-vehicle computer) of the vehicle.

[0087] The central control unit 34 comprises an electronic control unit (ECU) 36, implemented as a microcontroller for conducting calculations, and a digital store 38.

[0088] Thus, in the illustrated embodiment, the means for determining a footprint (footprint length L) are constituted by the deformation sensor 14 and the determining unit 20 in the wheel unit 12.

b) Means for Receiving a Tire Information

[0089] The tire information is received e.g. at least partially from a digital store 26 arranged in the wheel unit 12. The digital store 26 is connected to the determining unit 20, so that tire information can be transmitted by transmitter 22 via wireless communication, preferably via RF communication. A receiver 28 has functionality for receiving new and/or modified tire information via wireless communication, preferably via LF communication by user inputs (e.g. by service personal) via a trigger tool (not shown). These received tire information are transferred via the determining unit 20 into the digital store 26. The wheel unit 12 is configured to incorporate tire information from the digital store 26 into the data D, which are transmitted to the central control unit 34.

[0090] A further possibility for storing tire information is provided by the digital store 38 of the central control unit 34, which is also accessible by the ECU 36. In this case, the tire information components stored in the digital store 38 can be defined by user inputs (e.g. by service personal) via a (not shown) human machine interface (HMI) of the central control unit 34.

[0091] Thus, in the illustrated embodiment, the means for receiving a tire information are constituted by the digital store 26 of the wheel unit 12 and/or the digital store 38 of the vehicle's central control unit 34.

[0092] The received tire information comprises data related to: tire type, tire dimension, season stipulated for the tire, material and/or material properties, tread depth, age and/or manufacturing date.

c) Means for Receiving Tire Operation Conditions

[0093] The measurement upon which the receiving of the tire operation conditions is based comprises a measurement conducted by means of two additional sensors integrated within the wheel unit 12, namely a pressure sensor 16 for measuring a tire pressure TP in the tire 1 and a temperature sensor 18 for measuring a temperature T of the tire 1.

[0094] The respective measurement results TP and T are also incorporated into the data D to be transmitted to the central control unit 34.

[0095] Further, the wheel unit 12 can be configured to further incorporate a tire rotational speed (and/or based thereon a tire rotational acceleration) into these data D. This additional information can be determined by the determining unit 20 by way of an analysis of the sensor signal “def” provided by the deformation sensor 14. Further, if the determining unit 20 knows the diameter of the tire 1, it can e.g. also calculate vehicle velocity.

[0096] Such components of the tire operation conditions, here at least the tire pressure TP and the tire temperature T, which are provided by the wheel unit 12, are incorporated into the data D to be transmitted to the central control unit 34. Alternatively, or in addition, components of the tire operation conditions can be received from other systems (e.g. ESP) of the vehicle's control system. Such information component(s) may be available e.g. from the central control unit 34.

[0097] Thus, in the illustrated embodiment, the means for receiving tire operation conditions are constituted by the wheel unit 12 and corresponding functionalities of the central control unit 34.

[0098] The received tire operation conditions comprise: tire pressure, tire temperature, vehicle velocity and/or tire rotational speed, vehicle lateral and longitudinal accelerations and/or tire rotational acceleration.

d) Means for Selecting a Calculation Model

[0099] The store 38 of the central control unit 34 stores not only software code for operating the ECU 36, but also a digital representation of the plurality of predetermined calculation models (e.g. mathematical modelling functions represented by digitally stored equation parameters). Based on the received tire information, the ECU 36 selects one of the stored calculation models by retrieving corresponding equation parameters etc. from the store 38.

[0100] Thus, in the illustrated embodiment, the means for selecting a suitable calculation model are provided by the respective functionality of the ECU 36.

e) Means for Calculating the Wheel Load

[0101] The ECU 36 using software running thereon conducts not only the above mentioned selection of the calculation model, but also the calculation of the wheel load based on the determined footprint length L (or e.g. subsequently based on the length L determined footprint area FPA) and the received tire operation conditions, using the selected calculation model.

[0102] FIG. 3 summarizes the essential steps a) to e), which are necessary for the determination of the wheel load “WL” according to the invention.

[0103] The steps a), b) and c), i.e. the determining of footprint (step a), the receiving of tire information “ti” (step b) and the receiving of tire operation conditions “toc” (step c) are substantially independent from one another, i.e. can be conducted in sequence or parallel. In the case, however, that the determination of the tire operation conditions (step c) uses any result of the steps a) or b), the step c) should be conducted after a previous conduction of step a) or step b), respectively.

[0104] The step d), i.e. the selection of the suitable calculation model “mod(ti)”, has to be conducted upon a previous conduction of step b).

[0105] The step e), i.e. the calculation of the wheel load WL, necessitates a previous conduction of steps a) to d).

[0106] The conduction of the steps a) to e) can be continuously repeated during driving periods of the vehicle. For saving calculation resources, however, steps b) and d) can often be omitted in such repeated processing according to FIG. 3. Namely, taking into account that a change in the tire information “ti” necessitates a preceding change of one or more tires or wheels, respectively, the steps b) and d) can be omitted by simply using the corresponding most recently selected calculation model in step e).

[0107] FIG. 4 is a more concrete flow-chart of a method for determining a wheel load WL, as can be performed e.g. by the system 10 of FIG. 1, in accordance to the more general flow-chat of FIG. 3.

[0108] In a step S1 corresponding to the method step a), the footprint length L is determined.

[0109] In a step S2, it is determined whether a driving period of the vehicle that follows a standstill period of at least a predetermined minimum standstill duration of the vehicle has just begun. If so, a step S3 corresponding to the method step b) is conducted (i.e. the tire information “ti” is received), followed by the conduction of a step S4 corresponding to the method step c). Otherwise, step S3 is omitted and the process jumps to step S4.

[0110] In step S4 the tire operation conditions “toc” are received.

[0111] In a step S5 it is determined whether a driving period of the vehicle that follows a standstill period of at least predetermined minimum standstill duration of the vehicle has just begun (To this end, the algorithm may simply resort to the result of step S2). If so, the process continues with a step S6 corresponding to the method step d), in which the selection of a calculation model “mod(ti)” in accordance with the received tire information “ti” is conducted, followed by a step S7. Otherwise, the step S6 is omitted and the process jumps to step S7.

[0112] In step S7, which corresponds to the method step e) the wheel load WL is calculated based on the determined footprint length L and the received tire operation conditions, using the most recently selected calculation model “mod(ti)”.

[0113] In summary, the invention and the described embodiments provide a reliable method and system for determining a wheel load. The benefits of correct tire pressure at given tire load results in uniform tire wear, which means better usability of tire over its lifetime, reduction in fuel consumption, best safety, overload warning. In addition to that, the tire load information can be provided to different systems such as transmission control, engine control, power steering, vehicle dynamic control system for better driving experience and safety.

LIST OF REFERENCE SIGNS

[0114] 1 tire [0115] 3 wheel [0116] 5 measurement location [0117] L length of footprint [0118] 10 determining system [0119] 12 wheel unit [0120] 14 deformation sensor [0121] def deformation sensor signal [0122] 16 pressure sensor [0123] TP measured tire pressure [0124] 18 temperature sensor [0125] T measured temperature of tire [0126] 20 determining unit [0127] D data [0128] 22 transmitter [0129] 24 RF signal [0130] 26 digital store [0131] 28 receiver [0132] 30 vehicle unit [0133] 32 bus system [0134] 34 central control unit [0135] 36 ECU [0136] 38 digital store [0137] ti tire information [0138] toc tire operation conditions [0139] mod(ti) selected calculation model [0140] WL determined wheel load