CN-111629953-B - Power steering system

CN111629953BCN 111629953 BCN111629953 BCN 111629953BCN-111629953-B

Abstract

The invention relates to a power steering system (1) comprising a steering wheel (2) and a return function (REC) for automatically returning the steering wheel (2) to a given reference position (P0), for example a central position, for this purpose comprising a function (FK 1) for calculating a return speed set point (v_sw_set) from the difference between the steering wheel effective instantaneous position (p_sw) and the reference position (P0), i.e. a steering wheel position error (Δp), and a function (FK 2) for calculating a return assist, which defines a return assist set point (t_rec) from the difference between the steering wheel effective speed (v_sw) and the steering wheel speed set point (v_sw_set), i.e. a steering wheel speed error (AV), the system (1) comprising a dynamic saturation function (RDS) defining at least one saturation threshold (sat_hi, sat_w) from the steering wheel effective instantaneous position (p_sw) and a dynamic saturation function setting the return assist set point (t_w) to a dynamic saturation threshold value (d_w) from the steering wheel effective speed (v_sw_set) and then setting the return assist set point (t_rec_w) to a dynamic saturation threshold value (d_w_w).

Inventors

Dimitri Bart
Pascal mueller
Zhu Lian.pangte

Assignees

捷太格特欧洲公司
捷太格特欧洲公司

Dates

Publication Date: 20260421
Application Date: 20190104
Priority Date: 20180109

Claims (11)

1. A power steering system (1) comprising a steering wheel (2), and a return function (REC) designed to automatically return the steering wheel (2) to a given reference position (P0) when the steering wheel is in a position (p_sw) different from the reference position (P0), the return function (REC) comprising for this purpose a return speed setpoint calculation function (FK 1) which calculates a steering wheel speed setpoint (v_sw_set) as a function of the deviation between the instantaneous actual position (p_sw) of the steering wheel and the reference position (P0) called "steering wheel position error" (Δp), and a return assistance calculation function (FK 2) which defines a "assistance setpoint" (t_rec) as a function of the deviation between the actual speed (v_sw) of the steering wheel and the steering wheel speed setpoint (v_sw), the return assistance calculation function defining a dynamic speed (rds_3) of the steering wheel by at least one of the threshold values (saw) based on the actual speed (v_sw), the dynamic saturation function is adjusted according to the value of the steering wheel speed set point (v_sw_set) and then used for the calculation of the clip wave performed by the return assist calculation function (FK 2) in order to include the return assist set point (t_rec) in a field called "authorized return assist field" (d2_t), the range of which is related to the value of the steering wheel speed set point (v_sw_set).
2. A power steering system according to claim 1, characterized in that the dynamic saturation function (RDS) defines a high saturation threshold (sat_high) and a low saturation threshold (sat_low), which dynamic saturation function (RDS) is adjusted on the one hand in dependence on the vehicle speed (v_ vehic) and on the other hand in dependence on the value of the steering wheel set point (v_sw_set).
3. A power steering system according to claim 2, characterized in that one of the saturation thresholds of the high saturation threshold (SAT high) and the low saturation threshold (SAT low) is set to zero, while the other saturation threshold corresponds to a non-zero value, the sign of which depends on the sign of the steering wheel speed set point (v_sw_set).
4. A power steering system according to any one of the preceding claims, wherein the dynamic saturation function (RDS) acts on the input of the return assist calculation function (FK 2) to clip steering wheel speed error (av), which is taken into account when calculating the return assist setpoint (t_rec).
5. The power steering system according to claim 4, wherein the dynamic saturation function (RDS) chops the steering wheel speed error (Δv) such that the steering wheel speed error (Δv) is comprised between a first saturation threshold substantially equal to zero and a second saturation threshold substantially equal to the value of the steering wheel speed setpoint (v_sw_set).
6. A power steering system according to any one of claims 1 to 3, characterized in that the dynamic saturation function (RDS) acts on the output of the return assistance calculation function (FK 2) so as to clip the return assistance setpoint (T rec, T rec basic) calculated by the return assistance calculation function (FK 2).
7. The power steering system according to claim 6, characterized in that the dynamic saturation function (RDS) chops the return assistance setpoint (t_rec) such that the return assistance setpoint (t_rec) is comprised between a first saturation threshold substantially equal to zero and a second saturation threshold substantially equal to an image of the steering wheel speed error (Δv) obtained by the return assistance calculation function (FK 2), which is equal to the value of the steering wheel setpoint (v_sw_set).
8. A power steering system according to claim 1, characterized in that the saturation threshold (sat_high, sat_low) defined by the dynamic saturation function (RDS) is independent of the actual speed (v_sw) of the steering wheel (2).
9. Motor vehicle equipped with a power steering system (1) according to any one of claims 1 to 8.
10. A steering wheel return method allowing to return the steering wheel (2) to a given reference position (P0) automatically when the steering wheel (2) of a power steering system (1) is in a position (p_sw) different from said reference position (P0), in which method a steering wheel speed set point (v_sw_set) is first calculated from the deviation between the instantaneous actual position (p_sw) of the steering wheel and said reference position (P0), called "steering wheel position error" (Δp), and then a set point called "return assist set" (t_rec) is defined from the deviation between the actual speed (v_sw) of the steering wheel and said steering wheel speed set point (v_sw_set), said set point being used to control an assist motor (3) to converge the actual speed (v_sw) of the steering wheel to said steering wheel speed set point (v_sw_set), characterized in that it comprises a dynamic saturation step defined in accordance with at least one saturation threshold value in said dynamic saturation Step (SAT) to be applied in said saturation domain, said saturation threshold value (sat_reset) is then defined in accordance with said dynamic saturation step, the range of the field is related to the value of the steering wheel speed set point (v_sw_set).
11. A data medium which is computer readable and which contains code elements of a computer program which, when the medium is read by the computer, allow the method according to claim 10 to be implemented.

Description

Power steering system Technical Field The present invention relates to a power steering system that includes a return function to the center of the steering wheel. Background After the driver turns the steering wheel and then usually releases it to turn, the return function returns the steering wheel to a neutral central position, which corresponds to a straight-line trajectory, using an auxiliary motor in a manner known per se. In this way, it is particularly known to use a return function which servo-controls the rotational speed of the steering wheel. Such a return function determines a steering wheel speed set point based on the deviation of the actual angular position of the steering wheel from the central position of the steering wheel, which set point is intended to return the steering wheel to the central position, thereby adjusting the set point applied to the auxiliary motor so that the steering wheel attains the desired angular speed. However, the inventors have found that the implementation of such a return function may have some drawbacks. In fact, during certain maneuvers, the driver starts turning sharply, that is to say starts turning the steering wheel significantly in the first direction, then turning it in reverse rapidly, that is to say then turning it quickly to a central position, for example when the intersection changes direction (called "street corner" case) or makes a sharp turn (hairpin), when the driver turns said steering wheel to a central position, the driver may manually give the steering wheel an actual rotational speed that is greater than the steering wheel speed set point defined by the return function. By braking the steering wheel against manual operation, the return function will tend to inhibit return. This return suppression behavior is a source of artificial driving feel for the driver, which is inconsistent with the feel that the driver expects in this case. Similarly, when the driver turns the steering wheel in a direction that causes the steering wheel to be away from its central position, that is, when the driver aggravates the steering angle of the steering system, the known return function sometimes produces a viscous behavior that is opposite to the rotation of the steering wheel, and such viscous behavior is more noticeable and thus uncomfortable because the rotational speed that the driver imparts to the steering wheel is high. Disclosure of Invention The object assigned to the invention is therefore to overcome the above-mentioned drawbacks and to propose a new power steering system which ensures an efficient return of the steering wheel to the central position without causing viscous disturbances during steering of the steering wheel. The object assigned to the invention is achieved by a power steering system comprising a steering wheel and a return function designed to return the steering wheel automatically to a given reference position, for example a central position, when the steering wheel is in a position different from the reference position, the return function comprising a return speed setpoint calculation function for this purpose which calculates a steering wheel speed setpoint from the deviation between the instantaneous actual position of the steering wheel and the reference position, called "steering wheel position error", followed by a return assistance calculation function which defines a setpoint called "return assistance setpoint" from the deviation between the actual speed of the steering wheel and the steering wheel speed setpoint, called "steering wheel speed error", the setpoint being used to control an assistance motor to converge the actual speed of the steering wheel to the steering wheel speed setpoint, the system being characterized in that it comprises a dynamic saturation function defining at least one saturation threshold, the dynamic saturation function being adjusted according to the value of the steering wheel speed setpoint, and the dynamic saturation function being used to calculate by the assistance calculation function so as to include the return assistance value in the range of the return assistance threshold, called "assistance threshold". Advantageously, the dynamic saturation function according to the invention allows to define a saturation threshold that varies in real time to adapt to the steering situation of the vehicle, depending on whether the steering wheel is in a position to the left or vice versa with respect to its reference position, depending on whether the driver turns to move the steering wheel away from its driving position, or vice versa to bring the steering wheel closer to its reference position, and finally depending on the speed at which the driver shifts the steering wheel to perform its steering, in particular the rotational angular speed. In this way, the dynamically adjusted saturation threshold allows to clip at any time some components called "bad components" which may be present in the s