Method for controlling an electromechanical feedback actuator in a steering system and low-pass filter for the signal of a lateral acceleration sensor of a vehicle

Abstract

Method for controlling an electromechanical feedback actuator in a steering system of a motor vehicle without a force or torque transmitting connection between a steering handle and the steerable wheels, wherein, when controlling the electric motor of the feedback actuator, the current lateral acceleration of the motor vehicle is taken into account in the form of a low-pass filtered signal, characterized in that the low-pass filtering of the lateral acceleration signal is carried out with a corner frequency that varies depending on the current steering angle and / or the current steering angle speed and / or the current driving speed of the vehicle.

Description

[0001] The invention relates to a method for controlling an electric feedback actuator in a steering system of a motor vehicle without a force- or torque-transmitting connection between a steering handle and the steerable wheels, wherein, in controlling the electric motor of the feedback actuator, the current lateral acceleration of the motor vehicle is taken into account, among other things, in the form of a low-pass filtered signal. For the prior art, reference is made, by way of example, to DE 199 12 169 A1 and DE 103 36 818 A1. Furthermore, the invention relates to a low-pass filter for the signal of a vehicle's lateral acceleration sensor.

[0002] In today's standard vehicle steering systems, the driver's steering wheel (steering handle) is mechanically connected to the steerable wheels via the steering column or steering spindle, which leads to a steering gear. From this gear, the vehicle's steerable wheels are steered, i.e., turned, according to the driver's steering input. This mechanical connection, which transmits forces and torques, also provides the driver with feedback at the steering wheel about the forces transmitted between the road surface and the wheels during steering, which is very helpful for the driver's sense of control.

[0003] As is well known, so-called steer-by-wire systems are currently under development. These are steering systems that do not have a mechanical connection between the steering wheel and the steerable wheels, meaning there is no connection that transmits forces or torques. Instead, the steerable wheels are steered by an actuator, which is controlled directly or indirectly by an electronic control unit that evaluates the driver's steering input at the steering wheel. Naturally, with such a steer-by-wire system, or any other steering system without a connection that transmits forces or torques between the steering wheel and the steerable wheels, the driver receives no direct feedback about the forces transmitted between the road surface and the wheels when steering. This is a disadvantage of such steering systems (which otherwise offer advantages).

[0004] As a remedy for this problem, so-called feedback actuators, preferably in the form of appropriately controlled electric motors, have already been proposed. These actuators apply a force or torque to the steering wheel corresponding to the respective steering maneuver, which is essentially comparable to the force or torque that the driver experiences during the same steering maneuver with a conventional steering system. In particular, such a feedback actuator can also generate a suitable restoring torque that attempts to return the steering wheel, when it has been turned relative to its neutral position, to its neutral position. Appropriate control of such a feedback actuator takes into account suitable current boundary conditions, especially the current wheel steering angle and the current lateral acceleration acting on the vehicle. The latter is measured using a conventional accelerometer.

[0005] As is well known, the electrical signal of a lateral acceleration sensor of a motor vehicle is a relatively noisy signal, caused among other things by road surface irregularities, which is why this sensor signal is subjected to low-pass filtering in order to be able to use it effectively in the electronic determination of the control of the feedback actuator of a vehicle steering system.

[0006] This low-pass filtering has the disadvantage of causing a phase shift, and furthermore, valuable feedback or information can be lost through low-pass filtering, especially through low-pass filtering with a relatively low corner frequency or cutoff frequency, which significantly dampens the signal amplitudes.

[0007] The aim here is therefore to demonstrate an improved method according to the preamble of claim 1 (= object of the present invention).

[0008] The solution to this problem is characterized by the fact that the low-pass filtering of the lateral acceleration signal is performed with a corner frequency that varies depending on the current steering angle and / or the current steering angle velocity and / or the current vehicle speed. Preferably, the corner frequency is constant up to a certain limiting steering angle and increases with increasing vehicle speed and / or steering angle velocity for steering angles whose magnitude is greater than the limiting steering angle, wherein a preferred range of values ​​for the corner frequency of the low-pass filter for typical passenger cars is on the order of 2 Hertz to 8 Hertz.

[0009] Furthermore, it was recognized that the adaptation of the corner frequency of the low-pass filtering of the lateral acceleration signal according to the invention and found for controlling the feedback actuator of a steering system without a force or moment transmitting connection between the steering handle and the steerable wheels is also beneficial for other vehicle dynamics control systems of a motor vehicle which evaluate the lateral acceleration of the vehicle measured by means of a sensor.By transferring the quasi-adaptive low-pass filter found herein, protection is further claimed according to claim 4 for a low-pass filter for the signal of a lateral acceleration sensor provided in a vehicle, in particular a motor vehicle, for controlling an electric motor of an electromechanical feedback actuator in a steering system of the vehicle, and thus, after appropriate filtering, is supplied to a vehicle dynamics control system of the motor vehicle, wherein the low-pass filtering of the lateral acceleration signal is carried out with a corner frequency that varies depending on the current steering angle and / or the current steering angle speed and / or the current driving speed of the vehicle.Examples of vehicle dynamics control systems that evaluate the signal from a lateral acceleration sensor include (longitudinal dynamic) slip control systems such as ESP, (DSC) and ABS, but also lateral dynamic systems, with which, for example, another controlled steering angle is added to the steering angle specified by the driver (= so-called superimposed steering systems) or vertical dynamic control systems, such as a roll stabilization system.

[0010] According to the invention, the (generally known) low-pass filtering of the signal from the vehicle's lateral acceleration sensor is not performed with a constant, but with a variable corner frequency adapted to the current boundary conditions. The term "corner frequency" is synonymous with the term "cutoff frequency," so the term "cutoff frequency" can also be used instead.

[0011] According to the invention, a lower corner frequency, which smooths the lateral acceleration signal (i.e., the signal from a lateral acceleration sensor) more effectively through low-pass filtering, is only used if the signal actually contains significant disturbances, i.e., if it is highly noisy. This is the case at lower values ​​of the vehicle's speed and also at low values ​​of the steering angle velocity, i.e., the speed at which the driver turns the steering wheel or the angular velocity at which the steerable wheels are turned.

[0012] If, however, the (unfiltered) lateral acceleration signal is characterized by a relatively low noise component (with less interference), the low-pass filtering can be performed with a higher cutoff frequency, which smooths the signal less and thus retains more signal information. This can be implemented at higher values ​​of the vehicle's speed and also at higher values ​​of the steering angle velocity.

[0013] Although it would theoretically be advantageous to adapt the corner frequency to the actual noise component of the lateral acceleration sensor signal, this is not possible in practice. Therefore, according to the invention, the corner frequency is adapted based on the vehicle's speed and / or the current steering angle. It is assumed that at smaller steering angles and / or low steering angle speeds and / or low vehicle speeds, only relatively minor vehicle reactions are elicited, so that road information that could potentially be derived from the lateral acceleration sensor signal can be dispensed with.Instead of this road information (suppressed by low-pass filtering), more intensive filtering is preferred in such driving conditions in order to obtain a quasi-integrated and therefore consistent value for the lateral acceleration.

[0014] Furthermore, it has been shown that a lower corner frequency is generally preferable for smaller amounts of the steering angle specified by the driver in order to achieve acceptable signals for the aforementioned feedback actuator or another vehicle dynamics control system. This means that the corner frequency can be kept constant at a lower value (e.g., the aforementioned 2 Hz) up to a certain limit steering angle. Only at larger steering angles can the aforementioned adjustment, in the form of increasing the corner frequency to higher values ​​(up to, for example, the aforementioned 8 Hz), be made depending on the vehicle speed and the steering angle rate.Further improved results can be achieved if, for steering angles whose magnitude exceeds the limiting steering angle, the increase in corner frequency is dependent on the steering angle speed in such a way that the extent of the corner frequency increase is lower for steering angles with a larger magnitude than for steering angles with a smaller magnitude.

[0015] The precise dependence of the optimal corner frequency on the aforementioned boundary conditions—namely, vehicle speed (longitudinal speed), steering angular velocity, and steering angle—can be determined, for example, through a series of tests. These dependencies can indeed be linear at steering angles larger than the specified limiting steering angle.

Claims

[1] Method for controlling an electric motor feedback actuator in a steering system of a motor vehicle without a force or torque transmitting connection between a steering handle and the steerable wheels, wherein, when controlling the electric motor of the feedback actuator, the current lateral acceleration of the motor vehicle is taken into account in the form of a low-pass filtered signal, characterized by , that the low-pass filtering of the lateral acceleration signal is performed with a corner frequency that varies depending on the current steering angle and / or the current steering angle speed and / or the current vehicle speed. [2] Method according to claim 1, characterized by , that the corner frequency is constant up to a certain limit steering angle and increases with increasing vehicle speed and / or with increasing steering angle speed for steering angles whose magnitude is greater than the limit steering angle. [3] Method according to claim 2, characterized by , that for steering angles whose magnitude exceeds the limiting steering angle, the increase in the corner frequency is such that the extent of the corner frequency increase is lower for steering angles with a larger magnitude than for steering angles with a smaller magnitude. [4] Low-pass filter for the signal of a lateral acceleration sensor provided in a vehicle, in particular a motor vehicle, for controlling an electric motor of an electromechanical feedback actuator in a steering system of the vehicle, characterized by , that the low-pass filtering of the lateral acceleration signal is performed with a corner frequency that varies depending on the current steering angle and / or the current steering angle speed and / or the current vehicle speed. [5] Low-pass filter according to claim 4, characterized by, that the corner frequency is constant up to a certain limit steering angle and increases with increasing vehicle speed and / or with increasing steering angle speed for steering angles whose magnitude is greater than the limit steering angle. [6] Low-pass filter according to claim 5, characterized by , that for steering angles whose magnitude exceeds the limiting steering angle, the increase in the corner frequency is such that the extent of the corner frequency increase is lower for steering angles with a larger magnitude than for steering angles with a smaller magnitude.