End stop for vehicle steering - reset function

Abstract

The invention relates to a control device (30) and a method for controlling a vehicle steering actuator (20) which is coupled to a steering gear (14), the method comprising: providing an end stop-reset function (40) by means of which a first control variable (S1) for the vehicle steering actuator (20) can be determined, based on which a force can be generated at least in part by means of the vehicle steering actuator (20) for resetting the steering gear (14) in the direction of a defined position (0); determining whether the steering gear (14) falls below a limit distance (D) from an end stop (E); and if this is the case: controlling the vehicle steering actuator (20) based on the first control variable (S1) determined by means of the end stop-reset function (40), the first control variable having a value above a threshold value; wherein, if the limit distance (D) is not fallen below, the end stop-reset function (40) is used to not determine the control variable (S1) or to determine a control variable (S1) having a value that does not exceed the threshold value.

Description

Technical Field

[0001] The invention relates to a method and a control device for controlling a vehicle steering actuator by means of an end stop reset function. In particular, the invention relates to the field of vehicle technology and furthermore in particular to the field of motor vehicle technology. In particular, the invention is directed to a motor vehicle, such as a passenger car or a truck. Background Art

[0002] It is known that a so-called reset function is provided in a steering system that generates the steering force of the actuator. The reset function generally has the following task: reset the steering gear to a predetermined position. This position usually corresponds to straight-line driving. Such a reset function is usually arranged in a control device of a motor vehicle steering device and preferably continuously determines the control parameters for the vehicle steering actuator (especially an electric motor or a general servomotor). The vehicle steering actuator can also obtain control parameters from other functions and determine the force to be applied by it from the control parameters obtained as a whole. The function of transmitting the control parameters to the vehicle steering actuator is usually optimized for its corresponding task (such as the generation of the reset force), especially in view of the safety limits to be followed, the steering feel that can be perceived by the driver or the interaction with other functions.

[0003] Furthermore, it is known that motor vehicle steering systems and in particular steering gears have so-called end stops. The end stops can be mechanical end stops which limit the maximum deflection of the steering system in two directions (steering to the left and steering to the right) or in other words the maximum steering angle. However, so-called software end stops are also known. These usually define the movement limits of the steering gear and in particular a possible rack or other deflectable gear element, beyond which driver-independent forces arise which make further deflection in the direction of the mechanical end stops difficult.

[0004] For example, a software end stop is provided as a function of the control device, which outputs a control variable to the vehicle steering actuator at a certain distance before the mechanical end stop. Based on the control variable, a force can be generated which acts against the force applied by the driver, i.e., prevents further displacement in the direction of the mechanical end stop.

[0005] It is also desirable to provide the described reset function near the (mechanical or software) end stop of the steering system, for example in order to ensure a familiar steering feel for the driver. However, it has been shown that, in particular, in the vicinity of the end stop, increased steering forces occur in the case of certain axle and / or steering system configurations. These forces cannot be easily overcome by conventional reset functions for producing a reset effect. In other words, in certain steering system configurations and / or axle configurations, it is possible that, in particular at low driving speeds and large steering angles (i.e., in particular during maneuvering or parking procedures), conventional reset functions no longer exert an adequate reset effect. In these operating conditions, the steering may be perceived by the driver as unnatural and stiff.

[0006] In principle, there is the possibility of identifying such an operating state and generating an increased restoring force there (i.e. in the area of ​​the mechanical and / or software end stop of the steering device) using a conventional restoring function limited to the area of ​​the end stop. For example, US 2019 / 0344823 A1 discloses a solution in which the restoring force can be adapted in a speed-dependent manner, especially in the vicinity of the end stop, adapted to the situation where the vehicle is moving from a standstill. In this case, the initial increase in the restoring force should be smaller than the subsequent acceleration in order to avoid a sudden increase in the restoring force and the resulting distortion of the steering feel.

[0007] US Pat. No. 10,214,234 B2 discloses adapting the amplification factor of the reset function in a similar manner in a speed-dependent manner.

[0008] Such solutions have in common that even the reset function used next to the end stop can be changed, so to speak, locally in the region of the end stop in order to react to the characteristics present there. However, this requires a comprehensive adaptation to the characteristics of the specific steering gear in the region of its end stop. In addition to the development effort that is associated with this, this can also impair the transferability to other steering devices or steering gears.

[0009] Furthermore, it is not trivial that the reset function used over the entire steering range is adapted only in the end stop region when interactions with other steering functions are to be taken into account. Nonlinearities must also be taken into account, since the driver usually applies the maximum hand torque both in the end stop and when deflecting from the neutral position. This means that there is no linear increase or decrease in the hand torque over the range of motion of the steering gear. This also makes it difficult to adjust the reset function appropriately for the entire range of motion of the steering gear.

[0010] Another solution used in practice is to adapt the software end stop mentioned above. In the case of the described steering devices which make resetting difficult in the end stop region, the end stop region can be adapted in such a way that the force acting against the driver in this end stop region is higher and thus has a resetting effect and / or the force acting against the driver in this end stop region is generated in the vicinity of the actual mechanical end stop region. However, it has also been shown here that this cannot be easily achieved taking into account the steering feel to be followed and in the case of nonlinearities and interactions with other functions. Summary of the invention

[0011] There is therefore a need to improve the control, in particular the control of a vehicle steering actuator, also in the region of an end stop of a motor vehicle steering device with regard to a regulating steering feel and / or a restoring effect of the steering device.

[0012] This object is achieved by a control device and a method for actuating a steering actuator of a vehicle.

[0013] The present invention is generally arranged to provide an additional reset function in order to compensate for the excessively high steering force (acting against reset) occurring in the end stop region. The steering force can be transmitted, for example, from the wheel to the steering gear. This compensation-reset function is referred to as the end stop-reset function below. This compensation-reset function is based on the following concept, that is, the reset function is basically limited to the end stop region, that is to say, preferably only used there. It is preferably arranged that the end stop-reset function is provided in addition to the reset function for normal operation that is provided anyway (hereinafter referred to as the normal operation-reset function). In other words, the end stop-reset function is specifically supplemented for producing the desired reset effect in the end stop region. And the normal operation-reset function can be operated in a familiar manner over the entire steering region and preferably also in the end stop region in parallel with the end stop-reset function.

[0014] This makes it possible that the normal operating reset function does not have to be adapted so extensively to a steering device which, unlike conventional steering types, does not have a self-aligning effect in the end stop region, for example. In particular, a conventional steering gear with limited adaptation that has a normal operating reset function can be used, and the end stop reset function can be provided in addition to compensate for the lack of self-aligning effect of the special steering gear. This reduces the development effort and, in particular, the adaptation effort for the normal operating reset function.

[0015] In addition, it is achieved that the normal operation-reset function is optimized for the operating state that often occurs in the driving operation. And the end stop-reset function is optimized only for the special operating state of steering and rarely occurring in the vehicle operation near the end stop and preferably even in the case of only a small driving speed. Therefore, the task separation of the definition of the reset function can be set. This generally improves the compatibility of each function with the corresponding use scenario or operating state set for it and generally leads to the separation of these functions in the end stop area and outside the end stop or in view of the different requirements of the reset action provided. In addition, this realizes the improved processing of the nonlinearity of the type described above. In addition, safety is improved thereby, because then different reset functions can be monitored individually and in view of the conditions or operating limits to be followed for the reset function respectively.

[0016] A method is proposed for controlling a vehicle steering actuator, in particular an electric motor and further in particular a servomotor, which is coupled to a steering gear (for example, is engaged with the steering gear via a pinion or a lever driven by the actuator), the method comprising:

[0017] - providing an end stop reset function, by means of which a first control variable for a vehicle steering actuator can be determined, based on which a force can be generated at least partially and by means of the vehicle steering actuator to move the steering gear in the direction of a defined position;

[0018] - determining whether the steering gear, in particular the optional rack or another movable gear element of the steering gear, has fallen below a limit distance to a (preferably mechanical) end stop;

[0019] And when this is the case:

[0020] - actuating a vehicle steering actuator based on a first control variable, the first control variable having a value above a threshold value;

[0021] In this case, when the limit distance is not fallen below, a control variable (in particular a first control variable) is not determined using the end stop reset function, based on which a force can be generated using the vehicle steering actuator, which resets the steering gear into a defined position, or only a control variable with a value that does not exceed a threshold value is determined.

[0022] In other words, the control variable for producing a reset effect can be selectively generated and outputted using the end stop reset function only when the limit distance is undershot. Outside the limit distance or when the limit distance is not undershot, this determination and / or outputting of the control variable does not take place. However, the control variable can then be outputted as before with a zero value or with a value below a threshold value, wherein the reset effect is preferably only possible when the threshold value is exceeded.

[0023] The end stop reset function is not limited to direct operation at the end stop. Instead, the end stop reset function can generate a reset force above a threshold value in a defined angle range between the end stop and the limit distance. Alternatively, it is also possible to speak purely of a reset function or a compensation reset function or a first reset function compared to a second (normal operation) reset function.

[0024] The steering gear can include a toothed rack. However, the present invention is not limited to a specific type of steering gear. In particular, the present invention can also be used in steering gears without a toothed rack and in particular in steering gears with ball circulation.

[0025] In principle, it can be provided that the end stop reset function is only selectively activated and / or switched on when the limit distance is undershot. Preferably, however, the end stop reset function is permanently activated, but only when the limit distance is undershot, a first control variable is generated with which a reset action can be achieved and in particular only when the limit distance is undershot with a control variable having a value different from zero. In other words, the control variable output by the end stop reset function outside the limit distance cannot cause the vehicle steering actuator to generate a force and / or at least does not generate a force with which the steering gear can be moved but or with which the steering gear can be moved in the region of the end stop.

[0026] All functions described here and in particular the reset function can be implemented as a software component of a control device for a motor vehicle steering device. The software component can acquire or determine movement parameters of the steering device and in particular the steering gear. In the first case, the movement parameters can be detected by sensors. For the determination, these movement parameters can be indirectly inferred, for example, from the rotational speed and / or angular position of the vehicle steering actuator when the transmission ratio between the actuator and the steering gear (for example an optional rack of the steering gear) is known.

[0027] The control variable generated by the reset function can be output by the control device to the actuator and in particular to the control device of the actuator. For example, the control device of the vehicle steering actuator can adapt the electrical power supply of the vehicle steering actuator according to the requirements of the control variable, so as to generate a force according to the requirements of the current control variable and in particular thereby move the steering gear.

[0028] In order to generate a force based on the control variable with the vehicle steering actuator, with which the steering gear can be reset to a defined position even when the limit distance (i.e. in the area of ​​the end stop) is below, the control variable is preferably above a threshold value. The threshold value can be determined by tests, by simulations and / or by calculations. The threshold value can be determined in such a way that the control variable controls the vehicle steering actuator to generate a force that is equal to or exceeds the steering force applied to the steering gear, for example, by the vehicle wheels. However, it is not necessarily necessary that the reset effect can be achieved in the area of ​​the end stop using only the first control variable. Instead, only a certain portion of the force can be generated based on the control variable, in order to generate a reset force, for example, together with the normal operating reset function mentioned and the control variable determined by the normal operating reset function.

[0029] One extension provides that an additional condition for the control of the vehicle steering actuator is determined based on the end stop reset function (or based on the first control variable determined by the end stop reset function) whether a criterion related to the operating state of the vehicle including the steering gear is met. This criterion can be met, for example, when the vehicle speed is below a predetermined limit value. The criterion can thus relate to the driving state as the operating state. Only when the vehicle speed is correspondingly low can the vehicle steering actuator be controlled by the end stop reset function or the first control variable determined by the end stop reset function. More precisely, only the first control variable can be determined using the end stop reset function, which has a value above the threshold value in the manner described. Then, above the limit value of the vehicle speed, the control variable cannot be determined using the end stop reset function or only a control variable with a value that does not exceed the threshold value is determined.

[0030] This embodiment additionally specifies the use scenario of the end stop reset function and restricts it to the area in which the conventional normal operating reset function does not generate sufficient reset force as expected. The invention recognizes that in special types of designs, a lack of self-steering effect of the steering gear occurs primarily when the steering device is in the end stop area, but at a low driving speed at the same time. By means of the end stop reset function, which is only used at correspondingly low driving speeds, it can be ensured that an additional reset force can be generated particularly in accordance with the requirements.

[0031] Another operating state-related criterion, which can be provided in addition or alternatively, relates to the activation of an assistance function. In particular in the case of at least partially driver-autonomous assistance functions and in particular in the case of such assistance functions which at least partially autonomously control the (driving) operation of the vehicle, the requirements for the exact adjustment of the desired steering feel can be lower. Accordingly, if the assistance function at least partially controls the operation of the vehicle and in particular the steering, it can be dispensed with to generate significant forces with the end stop return function. An example of such an assistance function is the parking function, which is discussed further below.

[0032] As mentioned, a preferred further development provides that a (preferably conventional) normal operation reset function is additionally provided. With this normal operation reset function, a second control variable for the vehicle steering actuator can be determined independently of the undershooting of the limit distance. With the aid of this second control variable, the vehicle steering actuator can cause at least a proportion of the force to be generated for resetting the steering gear into a defined position. In the case of exceeding the limit distance to the end stop, this force can preferably be sufficient alone to achieve a reset effect. During the undershooting of the limit distance, such a force is preferably generated, which, in addition to the force generated according to the requirements of the first control variable of the end stop reset function, jointly exerts a sufficient reset effect.

[0033] Accordingly, it is preferably provided that the vehicle steering actuator is controlled both on the basis of the first control variable and on the basis of the second control variable when the limit distance is undershot. In general, the normal operation reset function is thus also maintained in the end stop region (i.e. when the limit distance is undershot). The end stop reset function, however, preferably generates an additional reset force only selectively in the end stop region in order to take into account the characteristics of a specific motor vehicle steering device in the end stop region and in particular the lack of self-steering of the motor vehicle steering device.

[0034] In this regard, it can be provided that the end stop reset function and the normal operation reset function are each based on a characteristic line. The characteristic lines can be different from one another. In a manner known per se, the characteristic line can define the value of the corresponding control variable as a function of the movement variable. The movement variable can be a movement variable of the steering gear and in particular a movement variable of an optional rack of the steering gear.

[0035] For example, it can be provided that the characteristic curve of the mentioned reset function has different courses. Preferably, the end stop reset function (also independently of its ratio to the characteristic curve of the normal operation reset function) is not linear. Particularly preferably, the end stop reset function has a progressive and / or exponential course.

[0036] The use of characteristic lines enables the reset force to be provided in accordance with the requirements. The use of different characteristic lines enables the end stops and the normal operating reset function to be specifically adapted to their respective (main) use scenario.

[0037] An extension is provided that the vehicle steering actuator can also be controlled based on a third control variable, which is generated by a steering force support function. In a manner known per se, the steering force support function can be used to apply a force supporting the driver to the steering transmission in order to achieve the steering desired by the driver.

[0038] In this context, it is preferably provided that a first maximum force can be generated as a result of the third control variable (for example for normal operation outside the region of the end stop).

[0039] Additionally or alternatively, in the case of being below the limit distance and in order to (manually) oversteer the end stop-reset function, a second maximum force can also be generated based on the third control variable. The second maximum force can therefore be limited to the end stop area. Preferably, the second maximum force corresponds at least to the sum of the first maximum force and the (preferred numerical value) of the reset force generated based on the first control variable. This ensures the reliable oversteerability of the force generated autonomously by the driver in the end stop area. In particular, this is for the following scenario, that is, the driver first steers with maximum reset in the end stop area and the maximum reset force is also generated by the end stop-reset function. But if the driver then wants to steer in the opposite direction spontaneously, he must be able to oversteer again the steering force generated autonomously by the driver that is then in effect. This is ensured by the above-mentioned embodiment and thus improves the driving safety and the controllability of the general steering system from the driver's perspective.

[0040] According to one embodiment, a monitoring function is provided, by means of which the first control variable can be checked with respect to at least one criterion. The monitoring function can again be provided as a function of the control device, i.e., for example, generally implemented on the basis of a computer and / or in a computer-supported manner. The monitoring function is preferably configured to prevent the control of the vehicle steering actuator based on the first control variable in the event of a violation (i.e., non-fulfillment) of the criterion. In particular, the monitoring criterion can ensure that only values ​​of the first control variable that are consistent with the situation are output and actually used to control the vehicle steering actuator. For this purpose, the first control variable can, for example, perform a type of plausibility check or ensure compliance with safety limits.

[0041] In particular, it can be provided that the criterion checked by the monitoring function defines a reliable value of the control variable as a function of a movement variable of the steering gear, in particular a possible rack or other movable gear element of the steering gear. For example, the monitoring function can be predefined such that, starting from a minimum movement of the steering gear, from a neutral position of the steering gear (for example, after at least 50% of the maximum distance between the neutral position and the end stop has been traveled), the control variable can have a value above the mentioned threshold value. The value of the control variable that is reliable from the perspective of the monitoring function can then increase with the displacement travel of the steering gear. In particular, the value can increase linearly to a maximum value. The maximum value can correspond to a value of the control variable with which a force of, for example, up to 4 kN can be generated by the vehicle steering actuator.

[0042] By using the described monitoring function, an additional level of safety is provided in order to ensure that the steering forces generated autonomously by the driver by means of the end stop return function are actually measured for the current operating state.

[0043] According to another embodiment, the criteria related to the operating state discussed above relate to the parking function. More precisely, when the driver's autonomous parking function (or parking in function) is activated, the control of the vehicle steering actuator can be at least temporarily deactivated due to (or by) the end stop reset function and / or the criteria related to the operating state are not met. The idea is that the driver's autonomous parking function does not have to overcome any forces generated by the end stop reset function. It is therefore not important within the scope of the driver's autonomous parking function which possible steering feel is adjusted, especially when it comes to so-called hands-free parking assistance (hands-of-Parking assistance), in which the driver does not operate the steering control. If the driver's autonomous parking function is interrupted, for example because the driver grips the steering control, the end stop reset function can be selectively switched on again. This enables the appropriate use of the end stop return function and a simplified design of a driver-independent parking function, for example across a large number of different vehicle types, without the driver-independent parking function having to be adapted to an end stop return function that is provided only for a specific vehicle or steering device variant.

[0044] The present invention also relates to a control device for controlling a vehicle steering actuator, which is connected to a steering gear, wherein the (generally digital and / or electronically operable) control device includes an end stop-reset function, by means of which at least one first control parameter for the vehicle steering actuator can be determined, and based on the first control parameter, a force can be generated by the vehicle steering actuator to reset the steering gear in the direction of a defined position; wherein the control device is configured to determine whether the steering gear is below a limit distance from the end stop; and when this is the case, the vehicle steering actuator is controlled based on the first control parameter determined by means of the end stop-reset function, the first control parameter having a value above a threshold value; wherein the control device is further configured to, when the limit distance is not below, not determine the control parameter or determine a control parameter with a value that does not exceed the threshold value by means of the end stop-reset function.

[0045] The control device may include at least one processor device and / or at least one memory device. Program instructions may be stored on the memory device, which, when implemented by the processor device, cause the control device to implement each function and / or measure described herein. Generally, the control device may implement a method according to each of the aspects mentioned herein. For this purpose, the control device may have all other features and functions in order to provide such a method. In particular, all implementation schemes for method features and extension schemes of method features may also be applicable to the same features of the control device or be provided in the same features of the control device.

[0046] In general, it is self-evident that a vehicle can have two end stops or end stop regions for two steering directions. The invention can be used and function in the same manner in both end stops or end stop regions. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] An exemplary embodiment of the invention is explained below with reference to the schematic drawings:

[0048] Figure 1 A schematic diagram of a vehicle steering system with a control device according to an exemplary embodiment of the present invention is shown, which implements a method according to an exemplary embodiment of the present invention.

[0049] Figure 2 Show Figure 1 Flowchart of the method. DETAILED DESCRIPTION

[0050] exist Figure 11 shows a schematic vehicle steering system 10. The vehicle steering system is a front axle steering device for a passenger car. Two front wheels 12 are shown, which can be steered via a steering gear 14. For this purpose, the wheels 12 are connected to a rack 18 of the steering gear 14 via a connecting link 16, which is not shown in more detail. The rack 18 is linearly displaceable, as indicated by the double-headed arrow. This linear displacement can be converted into a rotation of the wheels 12 about the steering gear 14 in a manner known per se via the connecting link 16. Figure 1 Rotational movement about a vertical axis.

[0051] The steering system 10 also includes a vehicle steering actuator 20. The vehicle steering actuator is designed in the form of an electric motor. The vehicle steering actuator 20 drives a pinion 22, which is engaged with the rack 18. Similarly, a steering shaft 24 (for example, via a schematically shown worm gear 26) is engaged with the rack 18. The steering shaft 24 is connected to a steering control member 28 (steering wheel) and can therefore be manually operated. Therefore, a torque can be generated via the steering control member 28 and the vehicle steering actuator 20, which acts as a force on the rack 18 and more precisely as a displacement force on the rack according to the double-headed arrow shown. As a result, the steering system 10 shown by way of example is an electromechanical steering device.

[0052] Furthermore, a control device 30 is shown. The control device outputs a control signal S to the vehicle steering actuator 20 and receives state parameters Z from the vehicle steering actuator. From the state parameters, movement parameters of the steering gear 14 and in particular the rack 18 can be determined in a known manner. For example, the position of the rack along its linear movement path or its linear movement axis B can be inferred from the angular position of the pinion 22 or the output shaft of the vehicle steering actuator 20.

[0053] exist Figure 1 The axis of motion B of the rack 18 is shown. The rack 18 can be linearly displaced along the axis of motion. The neutral position zero is shown. If the center point of the rack 18 covers the neutral position zero, the steering gear 14 is not deflected, i.e. straight-line travel occurs. In addition, the end stop E is shown. Figure 1 The left and right end regions or outer regions can be displaced up to the end stop E, which is achieved via mechanical elements (not shown) near the corresponding connecting link 16. A further displacement beyond the end stop E in the direction away from the neutral position zero is mechanically / structurally blocked.

[0054] Furthermore, the movement limits G1, G2 determined on the basis of the software are shown. If these movement limits are reached by the corresponding end region of the toothed rack 18, then the limit distance D of the toothed rack 18 from the end stop E is undershot. Whether these limits G1, G2 have been reached can in turn be determined by the control device 30 based on the toothed rack position, which is acquired by the state parameter Z.

[0055] The control device 30 is also connected to a hand torque sensor 34. Via the hand torque sensor, the control device 30 obtains information about the hand torque H currently applied.

[0056] Furthermore, a processor device 36 and a memory device 38 are shown as components of the control device. Program instructions are stored on the memory device 38, which are executed by the processor device 36. As a result, steering functions 40-44 are implemented, which are schematically shown in an enlarged manner in the dashed box. The steering function is an end stop reset function 40 explained below, which outputs a first control variable S1. In addition, a normal operation reset function 42 is provided, which outputs a second control variable S2. In addition, there is a steering support function 44, which outputs a third control variable S3.

[0057] In the example shown, it is provided that all of the steering functions 40-44 are run in parallel, i.e., their control variables S1-S3 are also output continuously or simultaneously. The control variables are then added to form a control variable or control signal S which is output as a whole to the vehicle steering actuator 20. The control variable S causes the vehicle steering actuator 20 to apply a force to the rack 18 via the rotation of the pinion 22, so that the rack is displaced in a desired manner along the axis of movement B. In particular, the control variables S1-S3 or at least the control variable S can be a rack target force, which is applied by the vehicle steering actuator 20. Alternatively, an electrical variable representing such a rack target force can also be provided as the control variable S or the control variables S1-S3, wherein these electrical variables are, for example, operating variables of a power input part (e.g., a rectifier) ​​of the vehicle steering actuator 20, with which the desired rack target force can be adjusted.

[0058] The control variable S or the control variables S1-S3 are therefore characterized by a value. The value preferably also has a sign in order to predetermine Figure 1 The rack 18 in the middle is to be moved to the left or to the right, i.e., in which direction it is to be turned. Here, the reset functions 40, 42 generally predetermine the following control variables S1, S2 or forces, which shift the rack 18 or its center point back toward the neutral position 0. With knowledge of the current rack position (the rack position is transmitted to the functions 40, 42 by the control device 30), the control variables S1, S2 or the signs of the forces to be generated thereby can be determined appropriately here.

[0059] Steering support function 44 generates a force component which acts in the direction of the rack movement specified by the driver via steering element 28. The sign of the corresponding control variable S3 or the force generated on the basis of the control variable can be selected as a function of the hand torque H obtained.

[0060] In the example shown, the control device 30 operates as follows: During the operation of the steering system 10, as soon as a deflection from the neutral position 0 of the toothed rack 18 occurs, a restoring force is continuously determined by means of a normal operation restoring function 42 or output via a control variable S2. The restoring force S2 as a force component determines the force applied by the vehicle steering actuator 20 to the toothed rack 18 and thus also the steering feel perceivable by the driver at the steering control element 28 coupled to the toothed rack 18. If the driver additionally applies a hand torque H, the steering support function 44 generates a control variable S3, with which a force component acting in the direction desired by the driver can be generated by the vehicle steering actuator 20.

[0061] If the toothed rack 18 now reaches the end stop region due to exceeding the limits G1, G2 (i.e. falling below the limit distance D to one of the end stops E), the end stop reset function 40 determines and outputs a first control variable S1 in such a way that an additional resetting force component can be generated (in addition to the normal operation reset function 42). Preferably, the end stop reset function 40 is also in operation before reaching the limits G1, G2, but until then outputs a control variable S1 with the value zero or a control variable S1 that generates a force component with the value zero. Whether the limits G1, G2 will be exceeded can again be determined by the control device 30 and / or the end stop reset function 40.

[0062] Not shown separately, each of the steering functions 40-44 can operate based on a characteristic line. Depending on the current movement variables of the steering gear 14, which can be the rack position 18 in particular, the corresponding values ​​of the control variables S1-S3 can be determined via the characteristic line. In the case of the end stop reset function 40, the characteristic variable is preferably defined as a value of zero until the limits G1, G2 are reached. The characteristic variable can then increase gradually and / or exponentially.

[0063] Furthermore, an optional monitoring function 50 is also shown. This monitoring function can receive the value of the control variable S1 from the end stop reset function 40 and check it with respect to predetermined criteria explained in the general description. Only when these criteria are met can the control variable S1 be output as a component of the control variable S (e.g. as an addend) to the vehicle steering actuator 20.

[0064] As a further preferred feature, it is provided that at least one of the control device 30 and the monitoring function 50 also receives information about the current driving speed V. This information can be obtained, for example, via a conventional speed sensor of the vehicle (not shown) or generally via a communication bus of the vehicle (also not shown). The control variable S1 can only be evaluated as reliable by the monitoring function 50 when the speed V is below a threshold value, for example, less than 10 km / h or less than 5 km / h. In other words, not exceeding the corresponding limit speed can be a criterion checked by the monitoring function 50. Alternatively or additionally, the control device 30 can check itself or the end stop reset function can check itself whether the limit speed is followed. If this is not the case, the first control variable S1 cannot be output, but the value of the control variable S1 can be set to zero. It is therefore also possible that the end stop reset function 40 includes a characteristic line family in which the speed V is introduced as a further axis or as a further parameter in addition to the motion variable-control variable-characteristic lines explained above.

[0065] The illustrated embodiment ensures that a sufficient reset effect can be achieved even in a steering device that is possibly not completely self-steering in the end stop region. For this purpose, it is not necessary to adapt the normal operation reset function 42 separately. In particular, the characteristic line of the normal operation reset function can remain continuous even when the limits G1, G2 are exceeded. The characteristic line does not have to rise in a jumpy manner in order to compensate for the lack of self-steering effect of the steering system 10. Instead, such an additional compensation force value can be provided by the end stop reset function 40. This achieves a functional separation between the reset functions 40, 42, each of which can be optimized separately for its corresponding operating scenario.

[0066] exist Figure 2, a flow chart of the method described above is shown in FIG. 1 . In step S1, it is determined that the toothed rack 18 is below a limit distance D from one of the end stops E, i.e., is located in the end stop region or close to a mechanical end stop E. In step S2 (which can also be carried out before step S1 or simultaneously with step S1), it is determined that the vehicle currently has a driving speed V below a predetermined limit value. In step S3, the end stop reset function 40 then outputs a control variable S1. The control variable can be checked for plausibility by the monitoring function 50 in an optional step S4. In step S5, the control variable S1 is output to the vehicle steering actuator 20, possibly in addition to other control variables and in particular control variables S2 and S3. The vehicle steering actuator drives the pinion 22 based on the control variable and thus adjusts the toothed rack 18 along the movement axis B in step S5 according to the requirements of the control variable S. As soon as this has resulted in the limit distance D being met again, the end stop reset function 40 no longer generates the control variable S1 with which the toothed rack 18 can be displaced. However, any reset forces that could affect the steering feel are still generated by the normal operation reset function 42 as before.

[0067] Reference numerals list

[0068] 10 Steering system

[0069] 12 front wheels

[0070] 14 Steering transmission mechanism

[0071] 16 Connection links

[0072] 18 rack

[0073] 20Vehicle Steering Actuator

[0074] 22 small gear

[0075] 24 Steering Axle

[0076] 26 Worm gear

[0077] 28 Steering control parts

[0078] 30 Control devices

[0079] 34-hand torque sensor

[0080] 36 processor devices

[0081] 38 memory device

[0082] 40 End stop - reset function

[0083] 42 Normal operation - reset function

[0084] 44 Steering support function

[0085] 50 monitoring functions

[0086] S1-S3 The first to third control parameters

[0087] S (accumulated) control parameter / control signal

[0088] Z state parameters

[0089] H hand torque

[0090] D Limit distance

[0091] G1, G2 limit

[0092] E end stop

[0093] B axis of motion

[0094] 0 Neutral position / zero position.

Claims

1. A method for controlling a vehicle steering actuator (20), the vehicle steering actuator being coupled to a steering transmission (14), the method comprising: - providing an end stop reset function (40), by means of which a first control variable (S1) for the vehicle steering actuator (20) can be determined, based on which a force can be generated at least in part by means of the vehicle steering actuator (20) for resetting the steering gear (14) in the direction of a defined position (0); - determining whether the steering transmission mechanism (14) is below a limit distance (D) from the end stop (E); And when this is the case: - actuating the vehicle steering actuator (20) based on a first control variable (S1) determined by means of the end stop reset function (40), the first control variable having a value above a threshold value; in, If the limit distance (D) is not fallen below, the control variable (S1) is not determined using the end stop reset function (40) or a control variable (S1) is determined with a value that does not exceed the threshold value; - providing a normal operating reset function (42), by means of which a second control variable (S2) for the vehicle steering actuator (20) can be determined independently of falling below the limit distance (D), based on which a force can be generated at least partially by means of the vehicle steering actuator (20) for resetting the steering gear (14) to the defined position (0); When the limit distance (D) is undershot, the vehicle steering actuator (20) is activated both on the basis of the first control variable (S1) and on the basis of the second control variable (S2).

2. The method according to claim 1, wherein: The threshold is zero.

3. The method according to claim 1 or 2, characterized in that: As an additional condition for the actuation of the vehicle steering actuator (20), it is determined based on the end stop reset function (40) whether a criterion related to the operating state of the vehicle including the steering gear (14) is met.

4. The method according to claim 3, characterized in that Deactivation of the at least partially driver-independent parking function and / or the fact that a limit value is not exceeded by the vehicle speed are defined as operating state-dependent criteria.

5. The method according to claim 1, characterized in that The end stop reset function (40) and the normal operation reset function (42) comprise mutually different characteristic lines, wherein the characteristic lines define the values ​​of the respective control variables (S1, S2) as a function of the movement variable.

6. The method according to claim 1 or 2, characterized in that: The vehicle steering actuator (20) can also be controlled by a steering force support function (44) based on a third control variable (S3), wherein a first maximum force can be generated based on the third control variable (S3) and a second maximum force can be generated when the limit distance (D) is below, the value of the second maximum force at least corresponding to the sum of the first maximum force and a maximum restoring force that can be generated based on at least the first control variable (S1).

7. The method according to claim 1 or 2, characterized in that A monitoring function (50) is provided, by means of which the first control variable (S1) can be checked with respect to at least one criterion and which is configured to prevent actuation of the vehicle steering actuator (20) based on the first control variable (S1) if the criterion is violated.

8. The method according to claim 7, characterized in that The criterion defines a reliable value for the first control variable (S1) as a function of a movement variable of the steering gear (14) and / or a vehicle speed (V).

9. A control device (30) for controlling a vehicle steering actuator (20), the vehicle steering actuator being coupled to a steering transmission (14), in, The control device (30) comprises an end stop reset function (40), by means of which at least one first control variable (S1) for the vehicle steering actuator (20) can be determined, based on which a force can be generated at least in part by means of the vehicle steering actuator (20) for resetting the steering gear (14) in the direction of a defined position (0); wherein the control device (30) is configured to determine whether the steering gear (14) is below a limit distance (D) from an end stop (E); and, if this is the case, to control the vehicle steering actuator (20) based on a first control variable (S1) determined using the end stop reset function (40), the first control variable having a value above a threshold value; The control device (30) is further configured to not determine the control variable (S1) or to determine the control variable (S1) with a value that does not exceed the threshold value by means of the end stop-reset function (40) when the limit distance (D) is not exceeded; wherein the control device (30) comprises a normal operating reset function (42), by means of which a second control variable (S2) for the vehicle steering actuator (20) can be determined independently of falling below the limit distance (D), based on which a force can be generated at least partially by means of the vehicle steering actuator (20) for resetting the steering gear (14) to the defined position (0); The control device (30) is further configured to control the vehicle steering actuator (20) both on the basis of the first control variable (S1) and on the basis of a second control variable (S2) when the limit distance (D) is undershot.

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