Patent ID: 12227234

The invention relates to a method for managing a power steering system1for a vehicle2, and more particularly for a motor vehicle2intended for the transport of persons.

In a manner known per se, and as shown inFIG.1, said power steering system1comprises a steering wheel3which enables a driver to maneuver said power steering system1by exerting a force, called “steering wheel torque” T3, on said steering wheel3. The steering wheel torque T3is measured by means of a torque sensor23.

Said steering wheel3is preferably mounted on a steering column4, guided in rotation on the vehicle2, and which meshes, by means of a steering pinion5, on a rack6, which is itself guided in translation in a steering casing7fastened to said vehicle2.

Preferably, each of the ends of said rack6is connected to a tie rod8,9connected to the steering knuckle of a steered wheel10,11, such that the translational longitudinal displacement of the rack6allows modifying the steering angle of the steered wheels. An amplitude of the displacement of the rack6is limited by two mechanical stops B respectively positioned at a right end and a left end of the steering casing7.

Moreover, the steered wheels10,11could preferably also be drive wheels.

The power steering system1also comprises an assist motor12intended to provide a motor torque T12, to assist the maneuver of said power steering system1.

The assist motor12will preferably be an electric motor, with two directions of operation, and preferably a rotary electric motor, of the brush or brushless type.

The assist motor12can come into engagement, where necessary via a reducer of the gear reducer type, either on the steering column4itself, to form a so-called “single pinion” mechanism, or directly on the steering rack6, for example by means of a second pinion13distinct from the steering pinion5which enables the steering column4to mesh with the rack6, so as to form a so-called “double pinion” mechanism, as illustrated inFIG.1, or else by means of a ball screw which cooperates with a corresponding thread of said rack6, at a distance from said steering pinion5.

The power steering system1also comprises a steering computer20which receives the steering wheel torque T3from the torque sensor23and which determines a setpoint supply current CM of the assist motor12.

In addition, a rotational speed {umlaut over (θ)}12of the assist motor12is determined by a motor speed24or position sensor.

A control method50according to the invention, implemented by the steering computer20, is described more specifically inFIG.2.

The control method50comprises a determination step E1in which the steering computer20determines a setpoint torque Cc. The setpoint torque Cc corresponds to an assist torque, and therefore to the motor torque T12, which normally has to be applied by the assist motor12.

The control method50comprises a drive step E2in which the steering computer20determines the setpoint supply current CM of the assist motor12.

From the setpoint supply current CM and the constraints exerted on the assist motor12, the latter consumes a physical supply current CA. When the physical supply current CA of the assist motor12is greater than a maximum physical supply current CAmax, the steering computer20is degraded and/or disturbed.

The control method50comprises a detection step E3in which the steering computer20detects an impact X between the rack6and a mechanical stop B. For this purpose, the detection step E3comprises a phase P1of computing the absolute value of the acceleration |{umlaut over (θ)}12| of the assist motor12from the differentiation of the rotational speed {umlaut over (θ)}12of the assist motor12. Then the detection step E3comprises a tracking phase P2in which the absolute value of the acceleration |{umlaut over (θ)}12| of the assist motor12is compared with a predefined threshold. When the absolute value of the acceleration |{umlaut over (θ)}12| of the assist motor12exceeds the predefined threshold, the method50according to the invention considers that an impact X has taken place between the rack6and a mechanical stop B. The detection step E3then emits an impact signal S.

The control method50also comprises a timing step E4which emits an application signal SA from the impact signal S so as to guarantee the safety of the control method50. More specifically, the timing step E4emits the application signal SA for an application time Ta when an impact X is detected by the detection step E3, in other words when the impact signal S is emitted. The application time Ta is less than 50 ms and preferably less than 10 ms. In addition, the timing step E4prevents an emission of the application signal SA during an exclusion time Te after the end of the application time Ta. The exclusion time is less than 10 s and preferably less than 5 s.

The control method50comprises a protection step E5which receives the setpoint torque Cc and the application signal SA and which emits a protected signal SP and the setpoint torque Cc to the drive step E2when the application signal SA is emitted. When the application signal SA is absent, the protection step E5does not interfere with the determination step E1and only transmits the setpoint torque Cc.

The protected signal SP comprises a setpoint torque C3limited to a predetermined value and a control parameter of the drive step E2.

TheFIGS.3to9illustrate some parameters of the steering system1upon an impact X occurring at 0.5 s.

FIG.3represents the rotational speed {umlaut over (θ)}12of the assist motor12as a function of time T. Upon the impact X, the rotational speed {umlaut over (θ)}12decreases significantly. Indeed, the rack6is stopped in its movement by the stop B. Then the rotational speed {umlaut over (θ)}12has a bounce before stabilizing at approximately 0.52 s. The bounce is linked to a nature of the mechanical stop, that is to say its elasticity.

FIG.4represents the acceleration {umlaut over (θ)}12of the assist motor12as a function of time T. This is the derivative of the rotational speed {umlaut over (θ)}12. Thus, the acceleration {umlaut over (θ)}12decreases significantly to a minimum before rising again, bouncing and stabilizing at around 0.52 s.

FIG.5represents a steering wheel angle θ3of the steering wheel3as a function of the time T. Before the impact X, the driver turns the steering wheel3, the steering wheel angle θ3increases. Upon the impact, the elasticity of the stop B enables the driver to turn the steering wheel further, the steering wheel angle θ3increases a little further up to a maximum elasticity value before stabilizing at a maximum rotation value of 540°.

FIG.6illustrates the motor torque T12and the setpoint torque Cc as a function of time T when the control method50according to the invention is not present in the steering computer20. InFIG.6, the assist motor12should achieve a motor torque T12equal to 5.2 N·m corresponding to the setpoint torque Cc. However, the motor torque T12supplied by the assist motor12has an increase then a decrease before stabilizing at the setpoint torque Cc. This phenomenon is linked to the impact X.

FIG.7illustrates the physical supply current CA of the assist motor12as a function of time T when the control method50according to the invention is not present in the steering computer20. The physical supply current CA has a curve substantially similar to that of the motor torque T12illustrated inFIG.6. In other words, after the impact X, the physical supply current CA increases sharply, exceeding the maximum physical supply current CAmaxand then decreases before stabilizing. When increasing, the physical supply current CA passes through a maximum exceeding the maximum physical supply current CAmax, which corresponds to an overcurrent phenomenon in the power steering system1.

FIG.8illustrates the motor torque T12as a function of time T when the control method50according to the invention is present in the steering computer20. In this case, the assist motor12should perform a motor torque T12having a profile as requested by the limited setpoint torque C3emitted by the protection step E5. In this way, the motor torque T12provided by the assist motor12has a very slight increase then a decrease before increasing again to stabilize at the limited setpoint torque C3.FIG.8also illustrates the application time Ta of the protected signal SP followed by the exclusion time Te during which the protected signal SP cannot be emitted.

FIG.9illustrates the physical supply current CA of the assist motor12as a function of time T when the control method50according to the invention is present in the steering computer20. The physical supply current CA has a curve substantially similar to that of the motor torque T12. In other words, after the impact X, the physical supply current CA has a very slight increase but decreases rapidly thanks to an almost simultaneous reduction in the setpoint supply current CM. In this way, the overrun of the maximum physical supply current CAmaxis almost non-existent and the overcurrent phenomenon does not appear.

The control method50according to the invention thus allows avoiding the apparition of an overcurrent phenomenon without requiring knowledge of the steering wheel angle θ3of the steering wheel3.

Of course, the invention is not limited to the embodiments described and shown in the appended figures. Modifications remain possible, in particular with regards to the constitution of the various elements or by substitution with technical equivalents, yet without departing from the scope of protection of the invention.