Method and system for determining a pressure deviation between a setpoint tire pressure and an actual tire pressure for a tire of a vehicle as well as for determining a wheel load

Abstract

A pressure deviation between a setpoint tire pressure and an actual tire pressure for a tire of a vehicle is determined by the following steps: Ascertaining a wheel load for the tire. Ascertaining a dynamic tire radius of the tire. Determining the pressure deviation as a function of the wheel load and the dynamic tire radius.

Claims

1. A method for indicating a vehicle tire pressure, the vehicle including a control device, a force sensor, wheel sensor, and a display, the method comprising: ascertaining, by the force sensor, a wheel load for the tire; ascertaining, by the wheel sensor, a dynamic tire radius of the tire; and determining, by the control device, a pressure deviation as a function of the wheel load and the dynamic tire radius; wherein a non-loaded tire radius of the tire is specified in a non-loaded state, and the actual tire pressure is calculated, by the control device, as a function of the wheel load, the non-loaded tire radius, and the dynamic tire radius using a tire rigidity function; wherein the tire rigidity function is specified, and the control device is configured to calculate a tire rigidity of the tire as a function of the wheel load, the actual tire pressure, and a velocity, at which the vehicle is currently traveling; and wherein constants of the tire rigidity function are learned in that measured values for the velocity and the wheel load are ascertained for multiple points in time and in that for these measured values the constants are determined such that an estimation error is minimized; and displaying, on the display, a setpoint tire pressure and the actual tire pressure.

2. The method according to claim 1, wherein the setpoint tire pressure is determined as a function of the wheel load using a setpoint tire pressure function.

3. The method according to claim 1, wherein the actual tire pressure is regarded as a constant and is also learned when the constants are learned.

4. The method according to claim 1, wherein: the tire rigidity (m) is determined using the tire rigidity function; and the non-loaded tire radius (r.sub.0) is ascertained by the following equation as a function of the dynamic tire radius (r.sub.dyn), the wheel load (f), and the tired rigidity (m):
r.sub.0=r.sub.dyn+m*f.

5. The method according to claim 1, wherein: an ideal dynamic tire radius is specified; and the setpoint tire pressure is determined as a function of the ideal dynamic tire radius using the tire rigidity function.

6. A system for indicating a vehicle tire pressure, comprising: a control device adapted to ascertain, by a wheel sensor, a dynamic tire radius of the tire, to ascertain, by a force sensor, a wheel load for the tire, and to determine the pressure deviation as a function of the wheel load and the dynamic tire radius; and a display; wherein a non-loaded tire radius of the tire is specified in a non-loaded state, and the control device is configured to calculate the actual tire pressure as a function of the wheel load, the non-loaded tire radius, and the dynamic tire radius using a tire rigidity function; wherein the tire rigidity function is specified, and the control device is configured to calculate a tire rigidity of the tire as a function of the wheel load, the actual tire pressure, and a velocity, at which the vehicle is currently traveling; and wherein the control device is configured to learn constants of the tire rigidity function in that measured values for the velocity and the wheel load are ascertained for multiple points in time and in that for these measured values the constants are determined such that an estimation error is minimized; and wherein the control device is adapted to display, on the display, a set point tire pressure and the actual tire pressure.

7. A method for indicating a vehicle tire pressure, the vehicle including a control device, a pressure sensor, a wheel sensor, and a display, the method comprising: ascertaining, by the pressure sensor, an actual tire pressure; ascertaining, by the wheel sensor, a dynamic tire radius of the tire; specifying a non-loaded tire radius of the tire in a non-loaded state; and determining, by the control device, the wheel load for the tire as a function of the actual tire pressure, the dynamic tire radius, and the non-loaded tire radius using a tire rigidity function; wherein the tire rigidity function is specified, and the control device is configured to calculate a tire rigidity of the tire as a function of the wheel load, the actual tire pressure, and a velocity, at which the vehicle is currently traveling; and wherein constants of the tire rigidity function are learned in that measured values for the velocity and the wheel load are ascertained for multiple points in time and in that for these measured values the constants are determined such that an estimation error is minimized; and determining, by the control device, a tire rigidity (m) by the following equation as a function of the dynamic tire radius (r.sub.dyn), the non-loaded tire radius (r.sub.0), and the determined wheel load (f): $m=\frac{r_0-r_{dyn}}{f}$ determining, the pressure deviation as a function of the determined wheel load and the dynamic tire radius; and displaying, on the display, a setpoint tire pressure and the actual tire pressure.

8. A vehicle, comprising the system recited in claim 6.

9. The method according to claim 1, further comprising: displaying a warning signal on the display if the set point tire pressure exceeds a threshold value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is used to explain the terms static, dynamic and unloaded tire radius.

(2) FIG. 2 shows examples of the tire rigidity (ratio between the difference between dynamic and unloaded tire radius and the wheel load).

(3) FIG. 3 shows the flow chart of an example embodiment of the present invention for determining the pressure deviation between the setpoint tire pressure and the actual tire pressure.

(4) FIG. 4 schematically shows a vehicle having a system according to an example embodiment of the present invention.

DETAILED DESCRIPTION

(5) FIG. 1 shows a tire 5, which has a static tire radius r.sub.stat, a dynamic tire radius r.sub.dyn and a non-loaded tire radius r.sub.0. Static tire radius r.sub.stat defines the shortest distance between center axis 6 of tire 5 and the road on which the vehicle is standing. Dynamic tire radius r.sub.dyn may be calculated on the basis of the rolling circumference of the tire. The non-loaded tire radius r.sub.0 is the largest radius measurable on tire 5 and corresponds to the tire radius that tire 5 assumes in the non-loaded state (i.e., no wheel load is acting on the tires). In summary, the following in equation (10) applies:
r.sub.stat<r.sub.dyn<r.sub.0(10)

(6) Reference symbol d denotes the difference or the separation between non-loaded tire radius r.sub.0 and dynamic tire radius r.sub.dyn.

(7) FIG. 2 shows the approximately linear relationship or ratio m between difference d and wheel load f acting on the respective wheel 5 for a specific tire or tire type. Ratio m or the relationship between d and f depends on the actual tire pressure and on the velocity at which the vehicle is traveling. FIG. 2 shows ratio m for pressures 1.7 bar, 2.2 bar and 2.7 bar and respectively for a velocity of 0 km/h (i.e., for standstill), and for a velocity of 200 km/h.

(8) FIG. 3 shows a flow chart of a method according to an example embodiment of the present invention for determining the pressure deviation.

(9) In first step S1, dynamic tire radius r.sub.dyn is determined. In general, it holds true that the lower the tire pressure and the higher the wheel load, the more the respective tire will be deformed in the area in which the tire contacts the road surface (i.e., the greater is the difference between dynamic tire radius r.sub.dyn and non-loaded tire radius r.sub.0, and thus difference d).

(10) In second step S2, wheel load f acting on the respective tire is determined. Wheel load f may be detected by suitable sensors, which in case of an air suspension, for instance, measure the air pressure within the corresponding suspension element. In a conventional suspension system of the vehicle, wheel load f may be detected based on the deflection of the corresponding suspension element.

(11) If no suitable sensors exist, wheel load f acting on the respective tire may be entered manually by the driver of the vehicle, for example. Simplifications are possible in that for example only one load per axle of the vehicle is specified and a symmetrical load distribution is presupposed, so that half of the specified axle load is acting on the respective tire.

(12) In third step S3, the actual tire pressure of the respective tire is detected by pressure sensors installed in the tire, for example. This step S3 is optional and supports in particular the automatic calibration of the tire constants or tire parameters in subsequent step S4. Moreover, a directly measured value for the actual tire pressure is to be preferred over the value calculated in step S9.

(13) In fourth step S4, a tire rigidity function is determined, by which the tire rigidity, i.e. the ratio between m between the difference between dynamic tire radius r.sub.dyn and non-loaded tire ratio r.sub.0 and the wheel load f acting on the respective tire is able to be determined as a function of the wheel load and the tire pressure.

(14) For this purpose, measured values are detected or ascertained for each tire of the vehicle over a certain time span for the wheel load, the velocity and the dynamic tire radius. If the actual tire pressure is also available, corresponding measured values are additionally detected.

(15) For example, using a Kalman filter (or a similar approach), it is possible to determine the parameters of the tire rigidity function m=func(f, p, v) in advance using the previously detected measured values (see FIG. 2). The constants or parameters estimated with the aid of the Kalman filter describe specific characteristics of the respective tire or tire type and define the tire rigidity function, so that it is possible to determine the tire rigidity m for the variables of tire pressure p, wheel load f and velocity v.

(16) Alternatively, the function may also be provided in the form of a database in which the previously described tire rigidity function, by which it is possible to calculate the tire rigidity as a function of the tire pressure, the wheel load and the vehicle velocity are stored for the various types of tires. Furthermore, there is the option of storing the data, by which the tire rigidity function is described, on an RFID tag in or on the tire, for example, and of reading out these data in a contactless manner.

(17) In step S5, the tire rigidity is calculated using the previously completely determined or learned tire rigidity function.

(18) In subsequent step S6, difference d results from the product of tire rigidity m and wheel load f. Using difference d, it is possible to calculate in subsequent step S7 the non-loaded tire radius r.sub.0 by an addition of dynamic tire radius r.sub.dyn and difference d.

(19) Using an optimization criterion, the tire pressure or setpoint tire pressure that is optimized for the actually applied wheel load is calculated in subsequent step S8. This criterion is either present explicitly in the tire database as a map (function or characteristic curve), or it is used in a generally useable approximation (for example a predefined ratio r.sub.ideal/r.sub.0). By solving the previously determined tire rigidity function for p, it is possible to determine the setpoint tire pressure as a function of the wheel load using the rearranged tire rigidity function.

(20) If the actual tire pressure p.sub.actual is not measured in step S3, it is possible to calculate it in step S9. For this purpose, the tire rigidity is calculated as a function of the dynamic tire radius r.sub.dyn and the wheel load f. The tire rigidity function is then solved for p such that using the rearranged function it is possible to calculate the actual tire pressure as a function of the wheel load, the velocity and the tire rigidity.

(21) In step S10, the pressure deviation is calculated as the difference between the setpoint pressure p.sub.ideal and the actual tire pressure p.sub.actual. This pressure deviation is monitored and the driver is informed or warned if necessary, or the actual pressure is adapted accordingly by an automatic pressure adaptation device.

(22) Steps S5 through S10 may be repeated periodically.

(23) FIG. 4 schematically shows a vehicle having a system 20 according to an example embodiment of the present invention. System 20 includes a control 1, a tire pressure sensor 2, a force sensor 3, and a velocity sensor 4.

LIST OF REFERENCE CHARACTERS

(24) 1 control 2 tire pressure sensor 3 force sensor 4 velocity sensor 5 tire 6 tire center axis 10 vehicle 20 system d difference (r.sub.0r.sub.dyn) f wheel load m tire rigidity p.sub.actual actual tire pressure p.sub.ideal setpoint tire pressure r.sub.0 tire radius in the non-loaded state r.sub.dyn dynamic tire radius r.sub.stat static tire radius S.sub.1-S.sub.10 method step