MOTOR VEHICLE CONTROL MODULE AND METHOD, COMPRISING AN EVALUATION OF REAR WHEEL SPEED BASED ON THE FRON WHEELS ONLY

Abstract

An evaluation of the speed of movement of a rear wheel of a motor vehicle on the ground, in particular on the inside of a bend, is made exclusively according to the speeds of the front wheels, in situations in which a direct measurement is not possible or in order to accurately evaluate occurrences of wheel lock-up or wheel slip. The invention can be applied to improving the braking setpoints when cornering.

Claims

1-8. (canceled)

9) A module for evaluating a speed of a rear wheel (3G, 3D) of an automobile, wherein the module is fed by input parameters which comprise, as the only speed parameters, evaluations of speeds of the front wheels (2G, 2D) of the automobile, in that the speed of the rear wheel is evaluated by a formula $V_{\mathrm{eAR}}=\left(\frac{V_{\mathrm{moy}}}{3}+\frac{2}{3}\frac{V_{\min }^2}{V_{\max }}\right)K_{\mathrm{corr}},$ where V.sub.eAR is the rear wheel speed evaluation, V.sub.min and V.sub.max the front wheel speed evaluations with V.sub.min≤V.sub.max, V.sub.moy=½(V.sub.min+V.sub.max), and K.sub.corr is a correction coefficient, and in that K.sub.corr=1 for $\frac{V_{\max }}{V_{\min }}\le S_1,$ and K.sub.corr≤1 for $\frac{V_{\max }}{V_{\min }}>S_1,$ S1 being a fixed threshold.

10) The evaluation module according to claim 9, wherein K.sub.corr is decreasing when $\frac{V_{\max }}{V_{\min }}$ increases above S.sub.1.

11) The evaluation module according to claim 10, wherein K.sub.corr is constant when $\frac{V_{\max }}{V_{\min }}\ge S_2,$ S.sub.2 being a second fixed threshold with S.sub.2>S.sub.1.

12) The evaluation module according to claim 11, S.sub.1=1.15, S2=1.4, wherein K.sub.corr is linear between S.sub.1 and S.sub.2 and K.sub.corr=0.6 at S.sub.2.

13) A device for controlling braking of an automobile, comprising the evaluation module according to claim 9.

14) A method for controlling an automobile comprising a device for controlling braking of an automobile, the device comprising a module for evaluating a speed of a rear wheel (3G, 3D) of the automobile, wherein the module is fed by input parameters which comprise, as the only speed parameters, evaluations of speeds of the front wheels (2G, 2D) of the automobile, the speed of the rear wheel is evaluated by a formula $V_{eAR}=\left(\frac{V_{moy}}{3}+\frac{2}{3}\frac{V_{\min }^2}{V_{\max }}\right)K_{c\mathrm{orr}},$ where V.sub.eAR is the rear wheel speed evaluation, V.sub.min and V.sub.max the front wheel speed evaluations with V.sub.min≤V.sub.max, V.sub.moy=½(V.sub.min+V.sub.max), and K.sub.corr is a correction coefficient, and in that K.sub.corr=1 for $\frac{V_{\max }}{V_{\min }}\le S_1,$ and K.sub.corr≤1 for $\frac{V_{\max }}{V_{\min }}>S_1,$ S1 being a fixed threshold, and the method comprising a step of, after comparing evaluations of the speed of said rear wheel made by said module, applying a braking command or not, thereby imposing anti-lock braking of said rear wheel.

15) The method for controlling an automobile according to claim 14, wherein antilock braking is decided if said evaluations are lower than a reference speed of the automobile, multiplied by a constant coefficient of less than 1.

16) The method for controlling an automobile according to claim 15, wherein the reference speed is an average of the front wheel speed evaluations.

Description

[0014] Certain aspects, characteristics and advantages of the invention will now be described in detail by means of the following figures, appended for illustrative purposes only, which allow a detailed description of an embodiment thereof:

[0015] FIG. 1 is a schematic view of an automobile in the method of turning;

[0016] FIG. 2 is a diagram of wheel speeds;

[0017] FIG. 3 illustrates the environment of the control module, and

[0018] FIG. 4 represents a correction coefficient function.

[0019] FIG. 1 partially represents an automobile, especially its chassis 1 mounted onto left and right front wheels 2G and 2D and left and right rear wheels 3G and 3D. The drive front wheels 2D and 2G are represented with a turning angle A that induces a turning radius R. In the non-limiting example in FIG. 1, the rear wheels 3D and 3G are neither drive nor steering wheels, but are equipped with brakes, which are not represented in this figure, and can be used for parking, but also contribute to braking.

[0020] FIG. 2 illustrates some of the wheel speed V curves as a function of the automobile's turning radius R. Speeds V are in arbitrary units. These speeds are ground travel speeds; the linear speeds of the wheels, which are proportional to their rotational speeds, may be different in the event of lock, skid, or other rolling faults. An average speed of the automobile V.sub.moy will be assumed to be the same regardless of the turning radius under consideration. The travel speed of the outer front wheel, here 2D, is thereby given by the curve V.sub.max, and the speed of the inner front wheel, here 2G, by the curve V.sub.min. The speed curve V.sub.AR of the inner rear wheel, here 3G, and V′.sub.AR the curve of the outer rear wheel, here 3D, are also represented.

[0021] A first purpose of the invention is to be able to evaluate the speed of the rear wheels 3G and 3D, and especially the speed (V.sub.AR) of the wheel inside a bend, using only the front wheel travel speed V.sub.max and V.sub.min information. A logic module 4 is used which is embedded into the vehicle control circuits and which has two inputs fed by the speeds V.sub.max and V.sub.min, which can be provided by rotation sensors 5 and 6 sensing rotation of the axes of these wheels 2D and 2G, or by any other means. Module 4 then performs the calculation

[00004]$V_{eAR}=\left(\frac{V_{moy}}{3}+\frac{2}{3}\frac{V_{\min }^2}{V_{\max }}\right)K_{c\mathrm{orr}},$

where V.sub.eAR is the evaluation of the speed of the rear wheel inside the bend, V.sub.min and V.sub.max are still the evaluations or measurements of the speeds of the front wheels and V.sub.moy is their average. K.sub.corr is a correction coefficient whose value is advantageously that of the function represented in FIG. 4, equal to 1 for

[00005]$\frac{V_{\max }}{V_{\min }}<1.15,$

to 0.6 for

[00006]$\frac{V_{\max }}{V_{\min }}>1.4,$

and being linear between these two values.

[0022] The curve V.sub.eAR thus obtained is also represented in FIG. 2; it can be seen that it is very close to the value V.sub.AR, except for extreme turning angles of the front wheels 2D and 2G.

[0023] The invention therefore makes it possible to evaluate the speed V.sub.AR with very good accuracy using only the speeds of the front wheels 2D and 2G. Module 4 can comprise other inputs to receive additional parameters, but information relating to direct measurement on the 3D and 3G rear wheels are not provided.

[0024] The result V.sub.eAR at the output of module 4 can be used for various applications. However, a particularly interesting method is the decision whether to control braking or reversely anti-lock braking of the rear wheels 3D and 3G, depending on situations. Back to FIG. 2 for explanation.

[0025] When a direct and reliable speed measurement of the rear wheels 3D and 3G is not available, it is usual to define a threshold speed Vs equal to, for example, 0.8 V.sub.moy. Indeed it is considered that the speeds V.sub.AR and V′.sub.AR of the rear wheels 3D and 3G should not deviate too far from the speed V.sub.moy and especially not drop too far below it, which would mean that these rear wheels would lock up. But in reality V.sub.AR is below the threshold speed Vs in tight bends, which means that traditional decision modules wrongly diagnose lock of the inside wheel, here 3G, and command its anti-lock braking system if braking the vehicle is requested.

[0026] In accordance with an application of the invention, the evaluation V.sub.eAR of the speed of the rear inner wheel obtained by module 4 is used to define a new decision threshold V's, deduced from V.sub.eAR by the same constant correction coefficient as previously. A new decision threshold V′.sub.s is thus obtained which increasingly sharply deviates from Vs for tighter bends, and which remains below the normal speed V.sub.AR of the inner wheel 3G, except possibly for the tightest bends. Anti-lock braking will therefore be imposed only if a decrease in rear wheel speed below these new threshold values V′.sub.s, and sharply below normal speeds VAR and V′.sub.AR, is detected.

[0027] The control system can comprise, downstream of module 4, a decision module 7 which receives the evaluation V.sub.eAR, calculates V's and compares its value to the speeds V.sub.AR and V′.sub.AR provided by other parameter providing modules 8 of the control system. Based on the result of the comparison, the command of a brake pedal 9 is applied (braking is allowed if V.sub.eAR≥V′.sub.s) or not (anti-lock braking is imposed if V.sub.eAR<V′.sub.s) to the actuator 10 of a brake 11, which may be a drum brake, also used for parking on the rear wheel 3G. A similar device also exists for the other rear wheel 3D.

[0028] The speed evaluation made here more precisely related to the inner rear wheel (here 3G) of the bend. An evaluation of the outer rear wheel (3D) could be made with an analogous module and a different generation function V.sub.eAR, but it is the inner wheel that raises the most difficulties in driving.

NOMENCLATURE

[0029] 1 Chassis [0030] 2G Front left wheel [0031] 2D Front right wheel [0032] 3G Rear left wheel [0033] 3D Rear right wheel [0034] 4 Module [0035] 5 Rotation sensor [0036] 6 Rotation sensor [0037] 7 Decision module [0038] 8 Parameter providing modules [0039] 9 Brake pedal [0040] 10 Actuator [0041] 11 Brake [0042] A Turning angle [0043] R Turning radius [0044] V Speed