Method for adjusting a control system for power steering and control system for power steering.

Abstract

Method for adjusting a control system for power steering in a vehicle, wherein the power steering assistance is reduced from a defined steering angle (S0) until a maximum steering angle (S1, S2, S3) is reached, characterized in that the power steering assistance is reduced to an individual value (F1, F2, F3) depending on the hardness and / or the position of a buffer (20) arranged at an end stop (18).

Description

[0001] The invention relates to a method for adjusting a control system for steering assistance in a vehicle, wherein the steering assistance is reduced from a defined steering angle until a maximum steering angle is reached. The invention further relates to a control system for steering assistance in a vehicle.

[0002] Such a generic method is known from DE 197 13 576 A1.

[0003] The maximum steering range of a vehicle is limited by stops that the steering linkage, such as the rack, hits when a maximum steering angle is reached. Buffers are usually provided at the stops to slow the steering movement before the maximum steering angle is reached in order to prevent the vehicle from hitting the stops too hard. If the steering linkage hits the buffer, it is compressed and provides a restoring force that counteracts the steering force. This force increases as the buffer becomes more compressed. The maximum steering angle is reached when the restoring force and the steering force provided by the driver and / or any power steering are equal in magnitude (at least when neglecting mass inertia forces, which can play a role when the vehicle approaches the stop very quickly). The increasing resistance also provides the driver with feedback that the maximum steering angle has been reached.

[0004] In addition, controls are often provided that reduce the steering force assistance before the maximum steering angle is reached, so that full steering force assistance is no longer available before the buffer or maximum steering angle is reached. This provides the driver with early feedback that the maximum steering angle has been reached. Furthermore, the reduced steering force results in a softer stop at the buffers or end stops, which can reduce the load on the steering linkage.

[0005] The simplest control systems reduce steering assistance from a defined steering angle, with a constant ratio to the steering angle. However, these control systems do not take into account manufacturing-related variations in the hardness or installation-related positioning inaccuracies of the buffer, resulting in a very large variation in the maximum steering angle depending on the hardness and position of the buffer.

[0006] To solve this problem, control systems are known that determine the steering angle at which a reduction in steering assistance occurs, depending on the position or hardness of the buffer. For this purpose, the maximum steering angle is determined at a defined steering force. The control system then defines the steering angle at which a reduction in steering assistance occurs, at a predetermined angular distance from the measured maximum steering angle. While such control systems allow for a more precise setting of the desired maximum steering angle, even these control systems still exhibit very large differences in the maximum steering angle.

[0007] The object of the invention is to provide a method for adjusting a control system for steering assistance in a vehicle, which enables a more precise adjustment of the reduction in steering assistance to the position and hardness of a buffer in order to achieve a smaller deviation of the actual maximum steering angle from a desired ideal steering angle. The object of the invention is further to provide a control system for steering assistance using such a method.

[0008] To achieve this objective, a method for adjusting a control system for steering assistance in a vehicle, wherein the steering assistance is reduced from a defined steering angle until a maximum steering angle is reached, provides that the steering assistance is reduced to an individual value depending on the hardness and / or position of a buffer arranged at an end stop. Previously known control systems measure the maximum steering angle in order to determine the position or hardness of the buffer and adjust the starting point of the steering force reduction to this value. However, the steering force assistance is always reduced to the same value, so that the remaining, always constant steering force compresses, for example, a soft buffer more than a hard buffer, which can lead to deviations in the maximum steering angle.

[0009] The method according to the invention, on the other hand, reduces the steering force assistance to a value that is specific to the hardness and / or position of the buffer. For example, with a soft buffer, the steering force assistance is reduced to a lower value, so that significantly less steering force is provided. The soft buffer is thus less compressed. Accordingly, with a hard buffer, the steering force assistance is set to a higher value, so that the available "braking distance" can be fully utilized even with this buffer.

[0010] By reducing the value to an individual value, a much more precise adjustment of the steering force assistance to the installation conditions of the buffer in the vehicle is possible, so that after carrying out the process, a much smaller deviation of the maximum steering angle or a better approximation of the ideal desired maximum steering angle is possible. The value to which the steering force assistance is reduced can, for example, be set so that the buffer is compressed to the same extent regardless of the hardness or so that the increase in steering force has the same characteristics in each case. The control system can determine the buffer hardness and / or the buffer position once at the beginning of the control process by means of a measurement. However, this can also be an iterative process, so that by repeating the process the closest possible approximation to the desired ideal steering angle is possible or the buffer hardness can be checked.

[0011] Preferably, this method compares the actual maximum possible steering angle with a desired ideal steering angle to determine the stiffness and position of the buffer and / or to determine the amount of steering assistance reduction. The desired ideal steering angle serves as a reference, and the value to which the steering assistance is reduced is selected so that the actual maximum steering angle is as close as possible to this ideal steering angle.

[0012] The defined steering angle at which the steering assistance is reduced can, for example, be independent of the hardness and / or position of the buffer. This means that the reduction in steering assistance always begins at the same, fixed steering angle. In this case, the ratio between the reduction in steering assistance and the further steering angle is adjusted so that the steering assistance is reduced to the desired, individual value when the maximum steering angle is reached.

[0013] However, it is also conceivable that the steering angle at which the steering assistance is reduced depends on the measured maximum steering angle, the stiffness, and / or the position of the buffer. For example, the starting point for reducing the steering assistance can be selected so that the reduction always occurs with approximately the same ratio between steering force reduction and steering angle, but due to the different starting points, it is reduced to the desired individual value, which depends on the position of the buffer.

[0014] For example, the steering force assistance can be reduced linearly with the steering angle, at least in sections, so that the steering force assistance is constantly reduced as the steering angle increases.

[0015] However, the ratio of the reduction in steering force assistance to the steering angle can also be selected so that, for example, a progressive or degressive reduction in steering force assistance occurs. The reduction can therefore also occur in proportion to the steering angle, at least in sections, along a curve.

[0016] Regardless of the type of reduction in steering force assistance, the defined steering angle from which the steering force assistance is reduced is preferably selected such that at this steering angle, regardless of the position of the buffer or the hardness of the buffer, no contact with the buffer occurs, so that at this point no restoring force is provided by the buffer.

[0017] According to the invention, a control for a steering force assistance in a vehicle is further provided, wherein the control is adjusted using a method according to the invention.

[0018] Further advantages can be found in the following description in conjunction with the attached drawings. These show: Fig. 1 a detailed view of a stop of a steering linkage in a vehicle, Fig. 2 a representation of the steering force in relation to the steering angle in the area of ​​the stop of the steering linkage from Fig. 1, and Fig. 3 a representation of the method according to the invention for reducing the steering force assistance.

[0019] In Fig. Figure 1 shows a section of a steering linkage 10 for a motor vehicle. The steering linkage 10 has a piston rod 12, which is mounted in a guide 14 fixed to the vehicle for displacement in an adjustment direction A. An end stop 18 is provided on the guide 14, which limits the displacement of the piston rod 12. For this purpose, an annular counter-stop 16 is provided on the piston rod 12.

[0020] Piston rod 12 is coupled to the rest of the steering linkage 10 and is moved in guide 14 when the vehicle is steered in or against the direction of travel A. The force required to move the piston rod is provided by the vehicle occupant and an additional steering force assist. In some steering systems, the steering force is also provided entirely by corresponding systems or motors.

[0021] At the end stop 18, a buffer 20 made of a reversibly deformable material, for example plastic, is provided, against which the counter-stop 16 is guided, so that a movement of the piston rod 12 against the end stop 18 is braked by deformation of the buffer 20.

[0022] If the piston rod 12 is moved in the actuating direction A, the counter-stop 16 comes into contact with the buffer 20 and is reversibly deformed upon further movement of the piston rod 12. The compression of the buffer 20 provides a restoring force that is directed against the actuating direction A or the steering force F. Fig. 2 shows various restoring forces R1, R2, R3 in relation to the steering angle L, which is approximately proportional to the displacement of the piston rod 12.

[0023] The functionality is explained below using curve R1. As the steering angle L increases, the restoring force R1 increases until its magnitude equals the steering force F, i.e., a force equilibrium is established between the restoring force R1 and the steering force F. This intersection point P defines the maximum steering angle S for the steering force F at a constant steering force. Further steering would only be possible by increasing the steering force.

[0024] In Fig. 2 shows the maximum steering angles S', S'', S''' for a buffer 20, its restoring force R1, and various values ​​F', F'', F''' of the steering force assistance. The maximum steering angles S', S', S''' are each defined by the steering angle at which the values ​​F', F'', F''' of the steering force assistance are equal in magnitude to the restoring force R1. These points are marked by the intersection points P', P'', P'''.

[0025] To prevent the counter-stop 16 from striking the buffer 20 too hard, the steering force or the steering force assistance provided by the power steering is usually reduced by a control system before reaching the maximum steering angle starting at a steering angle S0. Such a steering force curve is shown in Fig. 2 represented by curve K'. The corresponding steering angle is designated S1', the value of the steering assistance is designated F1', and the intersection point is designated P1'. In addition, the increase in resistance provides the driver with feedback that the maximum steering angle is almost reached.

[0026] However, the position of the buffer 20 varies slightly due to assembly. Furthermore, there are manufacturing-related tolerances in the hardness of the buffer 20. However, by changing the position of the buffer, with a constant starting point S0, the steering stop shifts, from which the counter-stop 16 rests on the buffer 20, and thus also the progression of the restoring force R in relation to the steering angle S. This is shown in Fig. 2 represented by the curves R2 and R3.

[0027] This results in the intersection points P2' and P3', at which the restoring force R2 or R3 and the steering force assistance are in equilibrium, and thus also the maximum steering angles S2' and S3', shifting.

[0028] A change in hardness also results in a change in the increase in the restoring force R. A softer buffer 20, for example, results in a flatter increase in the restoring force, whereby a force equilibrium with the steering force is only achieved at a larger steering angle, so that a shift in the maximum steering angles can also occur.

[0029] In order to compensate for these tolerances, the control according to the invention measures the actual maximum steering angle S at the beginning of the method at a defined steering force F. The control then compares the measured actual maximum steering angle with an ideal maximum steering angle and from this determines the value F to which the steering force assistance is reduced, as well as the starting point S0 and the ratio of the reduction to the steering angle.

[0030] In Fig. Figure 3 illustrates this process for various hardnesses of the buffer 20. Curve R1 represents the restoring force curve of an ideal buffer with the desired hardness and the ideal installation position. Accordingly, curve K1 represents the ideal steering force curve over the steering angle, F1 represents the ideal desired value of the steering force assistance, and S1 represents the ideal maximum steering angle.

[0031] If a soft buffer 20 is installed (curve R2), the steering force F is reduced more significantly from the same level as with an ideal buffer 20 at the same steering angle S0, so that the force equilibrium at the intersection point P2 is reached at a significantly lower value F2 of the steering force assistance (curve K2). The remaining steering force is preferably selected so that the steering angle S2 corresponds as closely as possible to the ideal steering angle S1.

[0032] Analogously, with a hard buffer (curve R3), the steering force assistance is reduced to a lesser extent (K3). The value F3 is therefore higher than the ideal value F1, so that a higher steering force F3 is applied here compared to the ideal buffer 20, which also allows the hard buffer 20 to be compressed more strongly.

[0033] The key to the function of this procedure is the reduction of the steering force assistance, i.e. the remaining steering force, to an individual value F depending on the buffer hardness and / or the buffer position. The steering force assistance does not have to be reduced linearly to the steering angle, as is the case in Fig. 3. The reduction of the steering force assistance can also take place, at least in part, along a trajectory curve or be a mixture of a linear reduction and a trajectory curve, so that, for example, a progressive or degressive reduction of the steering force assistance takes place.

[0034] In the exemplary embodiment shown here, the steering force assistance is reduced starting at a fixed steering angle S0. However, this starting point of the steering force assistance can also be individually adjusted to the respective buffer 20. Ideally, the steering angle S0 is selected such that there is no contact between the piston rod 12 and the stop 18 or the buffer 20.

[0035] For example, the procedure can be performed once after mounting the buffer 20 to determine the position and hardness of the buffer 20. However, the procedure can also be performed repeatedly to check the buffer hardness or to obtain a more precise adjustment to the ideal, desired maximum steering angle.

Claims

[1] Method for setting a control for a steering force assistance in a vehicle, wherein the steering force assistance is reduced from a defined steering angle (S0) until a maximum steering angle (S1, S2, S3) is reached, characterized by that the steering force assistance is reduced to an individual value (F1, F2, F3) depending on the hardness and / or the position of a buffer (20) arranged at an end stop (18). [2] Method according to claim 1, characterized by that the actual maximum steering angle is compared with a desired ideal steering angle in order to determine the hardness and position of the buffer (20) and / or to determine the value (F1, F2, F3) to which the steering force assistance is reduced. [3] Method according to claim 1 or 2, characterized by that the steering angle (S0) from which the steering force assistance is reduced is independent of the hardness and / or the position of the buffer (20). [4] Method according to claim 1 or 2, characterized by that the steering angle (S0) above which the steering force assistance is reduced depends on the actual maximum steering angle and / or on the hardness and position of the buffer. [5] Method according to claim 3 or 4, characterized by that the steering force assistance is reduced linearly with the steering angle, at least in sections. [6] Method according to claim 3 or 4, characterized by that the steering assistance is provided at least in sections on a curved path. [7] Method according to claim 5 or 6, characterized by that the defined steering angle (S0), from which the steering force assistance is reduced, is selected such that a reduction in the steering force assistance occurs independently of the buffer hardness before contact with the buffer (20). [8] Control system for power steering in a vehicle, characterized bythat the control is adjusted using a method according to one of the preceding claims.

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