GRADUAL DETECTION OF THE APPEARANCE OF TORQUE STEER

Abstract

A method for the gradual activation and deactivation of a steering return function in a vehicle, the vehicle including at least two wheels, a steering wheel, an assist motor applying an assist torque to a steering rack, and a drive motor applying a wheel torque to the wheels, the method including a step of calculating an application gain including a first phase of determining a first gain dependent on the wheel torque of at least one of the two wheels, a step of estimating the assist torque associated with the return function, and a step of multiplying the assist torque associated with the return function and the application gain, wherein during the application gain calculation step the method also includes a second phase of determining a second gain dependent on the angle of the steering wheel and the difference in the rotation speeds of the at least two wheels.

Claims

1. A method for gradually activating and deactivating a steering return function in a vehicle, the vehicle comprising, at least two wheels, a steering wheel, an assist motor applying an assist torque to a steering rack and a driving motor applying a wheel torque on the at least two wheels, the method comprising a step of calculating an application gain including a first phase of determining a first gain depending on the wheel torque of at least one of the two wheels, a step of estimating the assist torque associated with the return function, and a step of multiplying the assist torque associated with the return function and the application gain, wherein the method also includes during the calculation step of the application gain, a second phase of determining a second gain depending on an angle of the steering wheel, and a difference in the rotational speeds of the at least two wheels.

2. The method according to claim 1, wherein the second phase of determination depends on the angle of the steering wheel multiplied by the sign of a difference in the rotational speeds of the at least two wheels.

3. The method according to claim 1, wherein the second phase of determination depends on an absolute value of the difference in rotational speeds of the at least two wheels.

4. The method according to claim 1, wherein the second gain is comprised between 0 and 1.

5. The method according to claim 1, wherein the first gain is comprised between 0 and 1.

6. The method according to claim 1, wherein the step of calculating the application gain consists of multiplying the first gain and the second gain.

7. The method according to claim 1, wherein the wheel torque is determined as a function of the rotational speed of at least one of the two wheels, an engine speed and a driving torque supplied by the driving motor.

8. The method according to claim 1, comprising a step of evaluating a compensation gain depending on a lateral acceleration, a longitudinal acceleration of the vehicle, a yaw rate and the angle of the steering wheel.

9. The method according to claim 8, wherein the step of evaluating the compensation gain comprises a third phase of determining a third gain depending on the lateral acceleration, a fourth phase of determining a fourth gain depending on the longitudinal acceleration, and a fifth phase of determining a fifth gain depending on the absolute value of the yaw rate, or a theoretical angle calculated from the yaw rate and a vehicle speed, or a theoretical lateral acceleration calculated from the yaw rate and vehicle speed, and the angle of the steering wheel or a theoretical yaw rate calculated from the angle of the steering wheel and vehicle speed.

10. The method according to claim 9, wherein the fifth gain depends on the angle of the steering wheel multiplied by the sign of the yaw rate, or a theoretical yaw rate multiplied by the sign of the yaw rate calculated from the angle of the steering wheel and the vehicle speed.

11. A power steering device of a vehicle comprising at least two wheels, a steering wheel, an assist motor applying an assist torque on a rack, a driving motor applying a wheel torque on the at least two wheels and implementing a method for progressively activating and deactivating a steering return function in a vehicle according to claim 1.

Description

[0043] The invention will be better understood, thanks to the description below, which relates to an embodiment according to the present invention, given by way of non-limiting example and explained with reference to the accompanying schematic drawings, in which:

[0044] FIG. 1 is a schematic representation of the steps of a method according to the invention

[0045] FIG. 2 is a three-dimensional graph representing a second gain according to the invention as a function of an angle of the steering wheel multiplied by the sign of a difference in the rotational speeds of two wheels of the vehicle and an absolute value of the difference in rotational speeds of the two wheels.

[0046] FIG. 3 is a three-dimensional graph representing a fifth gain according to the invention as a function of the steering wheel angle multiplied by the sign of a vehicle yaw rate and the absolute value of the yaw rate.

[0047] In the remainder of the description, a vehicle is considered comprising a steering wheel allowing a driver to modify a trajectory followed by the vehicle as a function of an angle of the steering wheel α.sub.D. The steering wheel is connected to a steering column, itself linked to a rack transforming the angle of the steering wheel α.sub.D into a translational movement making it possible to modify the orientation of two steered and drive wheels of the vehicle, and thus perform a right bend or a left bend.

[0048] The driver is assisted in his intention to change the angle of the steering wheel α.sub.D by an assist motor applying an assist torque on the steering rack.

[0049] FIG. 1 illustrates a method, according to the invention, for gradually activating and deactivating a steering return function in a vehicle.

[0050] The return function makes it possible to apply an assist torque C.sub.R so as to compensate for a deviation of the angle of the steering wheel α.sub.D imposed by a torque steer phenomenon which appears in certain travel situations of the vehicle.

[0051] The return function determines during a estimation step 2 of the assist torque associated with the return function C.sub.R, the assist torque C.sub.R making it possible to compensate for the deviation of the angle of the steering wheel α.sub.D imposed by the torque steer phenomenon. The estimation step 2 receives as input a vehicle speed V.sub.V, the angle of the steering wheel α.sub.D, and a rotational speed V.sub.D of the steering wheel.

[0052] Furthermore, the method determines an application gain G.sub.A during a step 1 of calculating the application gain G.sub.A comprising a first phase 11 of determining a first gain G.sub.1 and a second phase 12 of determining a second gain G.sub.2.

[0053] The first phase 11 receives as input a driving torque C.sub.M supplied by a driving motor of the vehicle making it possible to propel the vehicle, an engine speed E.sub.RPM, that is to say the number of rotations performed by the driving motor per unit of time, and the rotational speed V.sub.R of the two wheels. The first phase 11 thus determines the first gain G.sub.1 which is represented by a two-dimensional graph with on the x-axis a wheel torque, that is to say the fraction of the driving torque C.sub.M received by the wheel, and on the y-axis, the first gain G.sub.1. The first gain G.sub.1 represents an intensity of the torque steer phenomenon. It is comprised between 0 and 1.

[0054] The second phase 12 receives as input the rotational speed V.sub.R of the two wheels and the angle of the steering wheel α.sub.D. The second phase 12 thus determines the second gain G.sub.2 which is represented by a three-dimensional graph, as illustrated in FIG. 2, comprising on an x-axis, an absolute value of the difference of the rotational speeds |ΔV.sub.R| of the two wheels in kilometers per hour km/h, and on a dimension axis the angle of the steering wheel α.sub.D multiplied by the sign of a difference in the rotational speeds of the two wheels (signΔV.sub.R), which will hereinafter be called the angle of the signed steering wheel α.sub.D, in degrees deg.

[0055] More precisely, the second gain G.sub.2 has, in a first zone 21, a value substantially equal to 0 when the vehicle is in a travel situation in which there is no risk of the appearance of torque steer phenomenon.

[0056] Thus, it is determined that when the difference in the rotational speed ΔV.sub.R between the wheels is important (greater than 3 km/h) and the angle of the signed steering wheel α.sub.D is negative, there is no risk of appearance of the phenomenon of pulling torque. This first zone 21 represents a travel situation in which the vehicle makes a bend in one direction, for example a left bend in a travel direction of the vehicle, with the left wheel which has a rotational speed V.sub.R greater than the right wheel. Indeed, the transfer of the driving torque C.sub.M on the wheel having the lowest rotational speed V.sub.R, that is to say the right wheel in our example, will promote the bend to the left of the vehicle.

[0057] The second gain G.sub.2 has, in a second zone 22, a value substantially equal to 0 when the angle of the signed steering wheel α.sub.D is substantially equal to 0 and has a value substantially equal to 1 when the angle of the signed steering wheel α.sub.D is substantially equal to 1. In the second zone 22, the second gain G.sub.2 increases continuously. The second zone 22 represents the vehicle travel situations in which there is a risk of the appearance of the torque steer phenomenon. Indeed, the more the angle of the signed steering wheel α.sub.D increases, that is to say the more the vehicle makes a curved trajectory, the more the risk of the appearance of the torque steer phenomenon is important.

[0058] Furthermore, in a third zone 23, the second gain G.sub.2 has a value substantially equal to 0 when the difference in the rotational speed ΔV.sub.R between the wheels is small (less than 3 km/h) and the angle of the signed steering wheel α.sub.D is negative, and has an increasing value up to 0.8 when the difference in the rotational speed ΔV.sub.R between the wheels is equal to 0 km/h and the signed steering wheel angle α.sub.D is equal to −90°. The third zone 23 represents the vehicle traffic situations in which there is an average risk of the appearance of the torque steer phenomenon. In fact, the smaller the difference in speed between the wheels, the more the torque steer phenomenon can appear.

[0059] The second gain G.sub.2, varying between 0 and 1, represents a probability of being in a traffic situation that could lead to the appearance of the torque steer phenomenon.

[0060] The calculation step 1 of the application gain G.sub.A consists of multiplying the first gain G.sub.1 and the second gain G.sub.2.

[0061] Thus, when the first gain G.sub.1 and/or the second gain G.sub.2 has a value of 0, the application gain G.sub.A is zero, that is to say that a torque steer phenomenon is not detected, and when the first gain G.sub.1 and the second gain G.sub.2 have a value of 1, the application gain G.sub.A is equal to 1, that is to say that the torque steer phenomenon is applied on the vehicle.

[0062] The method also determines a compensation gain G.sub.C during a step 3 of evaluating a compensation gain G.sub.C comprising a third phase of determining 33 a third gain G.sub.3, a fourth phase of determining 34 a fourth gain G.sub.4 and a fifth phase 35 of determining a fifth gain G.sub.5.

[0063] The third phase 33 receives as input a value of the lateral acceleration A.sub.lat of the vehicle. The third phase 33 thus determines the third gain G.sub.3 which is represented by a two-dimensional graph with on the x-axis, the lateral acceleration A.sub.lat and on the y-axis, the third gain G.sub.3 which varies between 0 and 1.

[0064] The lateral acceleration corresponds to the vehicle acceleration when it makes a trajectory in a bend.

[0065] The fourth phase 34 receives as input a value of the longitudinal acceleration A.sub.lon of the vehicle. The fourth phase 34 thus determines the fourth gain G.sub.4 which is represented by a two-dimensional graph with on the x-axis, the longitudinal acceleration A.sub.lon and on the y-axis, the fourth gain G.sub.4 which varies between 0 and 1.

[0066] The longitudinal acceleration A.sub.lon corresponds to the vehicle acceleration when it performs a straight line trajectory.

[0067] The fifth phase 35 receives as input the angle of the steering wheel α.sub.D and a yaw rate V.sub.L of the vehicle. The fifth phase 35 thus determines the fifth gain G.sub.5 which is represented by a three-dimensional graph, as illustrated in FIG. 3, comprising on an x-axis the angle of the steering wheel α.sub.D multiplied by the sign of the yaw rate, which will be called the angle of the signed steering wheel α.sub.D and on a dimension axis the absolute value of the vehicle yaw rate |V.sub.L|. The yaw rate V.sub.L corresponds to the speed of a rotational movement of the vehicle about a vertical axis.

[0068] More precisely, the fifth gain G.sub.5 has, in a first zone 24, a value substantially equal to 1 when the angle of the signed steering wheel α.sub.D is negative and has, in a second zone 25, a value substantially equal to 0 when the angle of the signed steering wheel α.sub.D is positive.

[0069] The fifth gain G.sub.5 illustrates a consistency between the angle of the steering wheel α.sub.D and the yaw rate V.sub.L.

[0070] The compensation gain G.sub.C is the multiplication of the third gain G.sub.3, the fourth gain G.sub.4 and the fifth gain G.sub.5. The compensation gain G.sub.C is comprised between 0 and 1.

[0071] During a multiplication step 4, the assist torque associated with the return function C.sub.R is multiplied with the application gain G.sub.A and the compensation gain G.sub.C so as to obtain a weighted return torque C.sub.RP.

[0072] Thus, the application gain G.sub.A modulates the application of the return function as a function of the intensity of the torque steer phenomenon applied to the vehicle and the compensation gain G.sub.C modulates the application of the return function as a function of a dynamic situation of the vehicle, that is to say an understeering, or oversteering situation so as to take into account the conditions of the vehicle grip on the road surface.

[0073] The weighted return torque C.sub.RP allows a progressive application of the steering return function on the steering system only when a torque steer phenomenon occurs. Thus, the method performs a continuous transition between a state in which the return function is completely active, that is to say when the application gain G.sub.A and the compensation gain G.sub.C are equal to 1, and a state in which the return function is inactive, that is to say when the application gain G.sub.A and/or the compensation gain G.sub.C are equal to 0. In this way, a driver does not feel the activation or deactivation of the return function.

[0074] Of course, the invention is not limited to the embodiment described and represented in the accompanying figures. Modifications remain possible, in particular from the point of view of the constitution of the various elements or by substitution of technical equivalents, without departing from the scope of protection of the invention.