Procedure for adjusting a steer-by-wire steering system of a motor vehicle

Abstract

The invention relates to a method for adjusting a steer-by-wire steering system of a motor vehicle, wherein the front axle of the motor vehicle is pre-assembled, pre-adjusted separately from the body of the motor vehicle and mounted to the body in the pre-adjusted state, wherein after mounting the pre-adjusted front axle to the body, the steering wheel is paired with the front axle by electronically adjusting the steering wheel position with the steering angle of the front axle, wherein the straight-ahead position of the steering wheel is assigned to the steering angle leading to straight-ahead driving.

Description

[0001] The invention relates to a method for adjusting a steer-by-wire steering system of a motor vehicle.

[0002] In a motor vehicle, the steering system must be adjusted to ensure that the straight-ahead position of the steering wheel actually results in the vehicle traveling straight ahead. This is primarily determined by the adjustment of the vehicle's axles. Vehicle axles can be adjusted for precise wheel alignment to compensate for manufacturing tolerances and thus achieve the best possible alignment of the wheels connected to the vehicle body by the axles.

[0003] In practice, the front axle is often adjusted depending on the rear axle. The rear axle can be pre-adjusted before the rear axle is mounted on the vehicle. This type of pre-adjustment ideally results in a rear axle adjustment of such quality that further adjustment of the rear axle after it has been mounted on the vehicle body is unnecessary. In practice, this leads to considerable savings because the adjustment elements are easily accessible and the pre-adjustment of an axle before it is mounted on the vehicle can be carried out automatically. However, once the axle is mounted on the vehicle, automated adjustment usually fails because the adjustment elements are difficult to reach. Previous attempts to enable automated adjustment have been associated with economic disadvantages.For example, automated adjustments can be made if the vehicle is mounted on a suspension system. However, suspension systems represent an expensive solution in the automotive manufacturing process, particularly in terms of the conveyor technology used to transport vehicle bodies during assembly.

[0004] Approaches to automatically adjust the axles of motor vehicles in conventional axle adjustment stations require complex robot technology and are therefore not economically viable.

[0005] DE 196 36 427 A1 discloses a method in which the measurement and adjustment of the axles during vehicle assembly is not performed on an axle alignment station, but rather in the respective assembly areas for the front and rear axles. For this purpose, the rear axle is measured after assembly, and the measurement results are stored. Using the stored data from the measured rear axle, the front axle is adjusted after assembly.

[0006] However, the overhead work required to adjust the front axle based on the rear axle's measurement, which must be performed manually, still occurs with this method. The efficiency benefits during production are minimal.

[0007] FR 3 117 986 A1 discloses a method in which the position of the steering wheel in a steer-by-wire steering system is adjusted to the actual steering behavior while the vehicle is moving. However, this requires minimum speeds of 70-80 km / h so that any yaw rate that may occur can be measured as a function of the steering wheel position and the assignment of the steering wheel position to the steering angle applied on the front axle can be corrected such that the straight-ahead position of the steering wheel actually results in the vehicle traveling straight ahead. A disadvantage of such a method, however, is that a multitude of potential interference factors affect the vehicle when adjusted under real-world driving conditions. Furthermore, the correct steering adjustment only occurs "over time" during use of the vehicle.However, the correct adjustment of the steering is beyond the manufacturer's quality control and the buyers of the vehicles are initially confronted with suboptimally adjusted steering systems.

[0008] DE 10 2005 003 993 A1 relates to an adjustment device for vehicle axles. This device comprises a clamping device for securing a vehicle axle in a defined position on a frame of the adjustment device, a device for generating a laser beam in a defined position relative to the frame, wherein the laser beam is directed toward a reference position on the vehicle axle, and a screen for intercepting the laser beam reflected from the reference position. A target position for the laser beam is defined on the screen, which corresponds to a predetermined camber and / or toe adjustment of the vehicle axle.

[0009] The invention is therefore based on the object of providing a method for adjusting a steer-by-wire steering system of a motor vehicle which enables cost-effective yet reliable adjustment of the steering system.

[0010] The object is achieved by a method for adjusting a steer-by-wire steering system having the features of claim 1. The features of the dependent claims relate to advantageous embodiments.

[0011] The motor vehicle whose steering system is adjusted using the described method is a motor vehicle with a steer-by-wire steering system. A steer-by-wire steering system is understood, in particular, to be a steering system in which there is no mechanical connection between the steering wheel and the steerable front axle of the motor vehicle to transmit the steering movement. The steering movement of the steerable front axle is effected, in particular, by an electromechanical actuator of the steering system.

[0012] The procedure involves pre-adjusting the front axle separately from the vehicle body and mounting it on the body in the pre-adjusted state. This allows for good accessibility to the front axle adjustment elements that must be operated to adjust the front axle during pre-adjustment.

[0013] After the pre-adjusted and pre-assembled front axle is mounted on the body, the steering wheel is married to the front axle by electronically matching the steering wheel position with the front axle's steering angle. The straight-ahead position of the steering wheel is assigned to the steering angle that leads to straight-ahead driving. This takes advantage of the steer-by-wire steering system's lack of a mechanical connection between the steerable front axle and the steering wheel.

[0014] It has been shown that pre-adjustment prior to assembly makes it possible to adjust the axle so precisely before assembly that it is "coherent" after being fitted to the vehicle body. The steer-by-wire steering system makes it possible to assign the steering angle that results in straight-ahead travel through purely electronic adjustment and kinematic calculation of the straight-ahead position of the steering wheel. After measurement, the driving axle angle can be taken into account in the kinematic calculation. It has been shown that in the vast majority of vehicles in production, after installation of the pre-adjusted front axle in this way, all that remains is to adjust the steering wheel position and steering angle, taking the driving axle angle into account, in order to ensure straight-ahead travel of the vehicle with the steering wheel in the "center" position.This largely eliminates the need for manual adjustment work on axles already mounted on the vehicle body, resulting in significant time and cost savings.

[0015] Electronic coordination of the steering wheel position with the steering angle of the front axle, particularly taking the driving axle angle into account, is understood to mean any assignment that has a corresponding effect on the subsequent operation of the steering system. In particular, storing corresponding information in a memory of a control device for controlling an electromechanical actuator for moving the front axle and / or for reading a corresponding sensor to determine the steering wheel position is understood in this context as electronic coordination of the steering wheel position with the steering angle of the front axle.

[0016] The method can in particular provide that during pre-adjustment of the front axle, the steering angle of the front axle is set to a steering angle of 0° by means of an electromechanical actuator of the steering system. In other words, a central position of the front axle is selected during pre-adjustment of the wheels by means of the actuator. Selecting a central setting corresponds to the desired ideal state in which, with a "perfect" adjustment of all axles, the steering angle of 0° on the front axle is the steering angle that leads to straight-ahead travel. With statistically distributed tolerances, it can be assumed that any deviations from the steering angle leading to straight-ahead travel in the actual steering system are equally distributed in both steering directions. Pre-adjustment with a centrally selected steering angle therefore allows for the least need for correction orexpect the smallest deviations of the steering angle leading to straight-ahead driving from the steering angle of 0° on the front axle.

[0017] The front axle is pre-adjusted primarily by manipulators controlled by a measurement of the front axle engaging adjustment elements on the front axle and actuating the adjustment elements to pre-adjust the front axle. The adjustment elements can be, for example, adjustment screws that are turned by the manipulators to pre-adjust the front axle. The front axle is measured primarily while the pre-adjustment is being performed using the manipulators. In this way, highly precise pre-adjustment can be achieved in the shortest possible time.

[0018] Pre-adjusting the front axle can, in particular, be automated. Automated adjustment can be achieved, for example, by controlling the manipulators acting on the adjustment elements based on the results of a front axle measurement performed during pre-adjustment.

[0019] The automated pre-adjustment of the front axle particularly includes the adjustment of the camber. The adjustment of the front axle camber can be automated. Camber, also known as wheel camber or axle camber, is one of the parameters typically adjusted on motor vehicle axles, and it has been shown that the camber can usually be pre-adjusted so precisely during pre-assembly using the proposed method that this pre-adjustment can be adopted as the final setting after assembly of the front axle.

[0020] This refers to the camber that is adjusted via the front axle's pre-adjustment, specifically the basic camber. Basic camber refers specifically to the camber in the design position. Since camber can change over the axle's spring travel depending on the axle's kinematics, especially with independent suspensions, it is advisable to adjust it with reference to the basic camber.

[0021] The method can in particular provide that the pre-adjustment of the front axle includes the adjustment of the track of the wheels on the front axle. The adjustment of the track of the front axle can in particular be carried out automatically. The subsequent electronic coordination of steering wheel position and steering angle makes it possible to adjust the track as part of the pre-adjustment, in particular without taking the adjustment of the rear axle after assembly into account. If the adjustment of the tracks of the axles in the assembled state does not result in straight-line running, this can usually be corrected by adjusting the steering wheel position with the steering angle of the front axle. In this case, a certain "dachshund run" (driving axle angle) of the motor vehicle is mathematically taken into account via the kinematic relationship.

[0022] The method can, in particular, provide for the rear axle of the motor vehicle to be pre-adjusted separately from the body of the motor vehicle and mounted to the body in the pre-adjusted state. In the case of the rear axle, pre-adjusting the rear axle before its mounting to the body of the motor vehicle also leads to a corresponding saving in working time. Pre-adjusting the rear axle can, in particular, be carried out automatically.

[0023] The front axle is pre-adjusted primarily by manipulators controlled by a measurement of the front axle engaging adjustment elements on the front axle and actuating the adjustment elements to pre-adjust the front axle. The adjustment elements can be, for example, adjustment screws that are turned by the manipulators to pre-adjust the front axle. The front axle is measured primarily while the pre-adjustment is being performed using the manipulators. In this way, highly precise pre-adjustment can be achieved in the shortest possible time.

[0024] Alternatively and / or additionally, pre-adjustment can be performed on the steering gear, including the mounted ball joints. By measuring the screw length, which is particularly accurate to within a hundredth of a millimeter, a sufficiently precise pre-adjustment can be achieved. The theoretical default values ​​can be adjusted, particularly via a control loop with the measurement of the mounted front axle, to ensure a sufficiently precise pre-adjustment.

[0025] The pre-adjustment of the rear axle can, in particular, be automated. Automated adjustment can be achieved, for example, by controlling the manipulators acting on the adjustment elements based on the results of a rear axle measurement performed during pre-adjustment.

[0026] The automated pre-adjustment of the rear axle particularly includes the adjustment of the camber. The adjustment of the rear axle camber can be automated. Camber, also known as wheel camber or axle camber, is one of the parameters typically adjusted on motor vehicle axles, and it has been shown that the camber can usually be pre-adjusted so precisely during pre-assembly using the proposed method that this pre-adjustment can be adopted as the final setting after the rear axle is installed.

[0027] This refers to the camber that is adjusted via the rear axle's pre-adjustment, specifically the basic camber. Basic camber refers specifically to the camber in the design position. Since camber can change over the axle's spring travel depending on the axle's kinematics, especially with independent suspensions, it is advisable to adjust it with the basic camber in mind.

[0028] The method can, in particular, provide that the pre-adjustment of the rear axle includes adjusting the track of the rear axle wheels. The adjustment of the rear axle track can, in particular, be carried out automatically. It has been shown that, using the proposed method, the track can usually be pre-adjusted so precisely during pre-assembly that this pre-adjustment can be adopted as the final adjustment after the rear axle is assembled.

[0029] It has been demonstrated that this pre-adjustment method can create a "coherent" rear axle, which, for the vast majority of vehicles, requires no further adjustment after the rear axle has been mounted on the vehicle body. The axle angle resulting from the rear axle's installation, which is currently taken into account when adjusting the front axle mounted on the vehicle, can be compensated for using the proposed method by electronically coordinating the steering wheel position with the steering angle of the front axle, thus ensuring the vehicle's straight-ahead travel when the steering wheel is in the straight-ahead position.

[0030] The method can provide that the steering angle leading to straight-ahead running is determined on the basis of the setting of the front axle and / or the rear axle achieved with the pre-setting of the respective axle when the respective axle is mounted on the body. For this purpose, in particular, a corresponding measurement of the front axle and / or the rear axle is carried out when the respective axle is mounted on the body. In this case, in particular, the setting of a defined steering angle, in particular a steering angle of 0°, can also be carried out using an electromechanical actuator of the steering system. The steering angle leading to straight-ahead running determined in this way can then be assigned to the straight-ahead position of the steering wheel.

[0031] The method can, in particular, provide for the actual steering wheel position to be determined, in particular by means of a steering wheel measuring scale and / or a camera, and taken into account when adjusting the steering wheel position with the steering angle of the front axle. By determining the steering wheel position, a sensor of the steering system can, in particular, be calibrated to determine the steering wheel position within the framework of the proposed method. This ensures that the steering wheel position assigned to the steering angle leading to straight-ahead travel is actually the straight-ahead position or the center position of the steering wheel. Any tolerances that may arise during installation of the steering wheel with regard to its position can thus also be compensated for.

[0032] The method can provide that after checking the pre-adjustment of the axles when mounted on the body, the front axle and / or the rear axle are readjusted depending on the result of the check if a predetermined tolerance value is exceeded by the adjustment achieved with the pre-adjustment of the respective axle. This measure can ensure that errors that may arise during assembly of the axles on the body of the motor vehicle do not lead to inadequate adjustment of the axles. It has been shown that the quality of the adjustment can be significantly improved if, after checking the adjustment of the axles mounted on the body of the motor vehicle, the axles are readjusted in only some of the motor vehicles produced.In this way, a good compromise between cost-effectiveness and quality can be achieved.

[0033] In particular, the method can provide that after the respective axle has been installed, no further mechanical adjustment is carried out on the front axle and / or the rear axle if the specified tolerance values, in particular all specified tolerance values, are complied with by the adjustment achieved with the pre-adjustment of the respective axle when checking them after the respective axle has been installed on the body of the motor vehicle. In other words, this means that all mechanical adjustments on the front axle and / or the rear axle are already carried out during pre-assembly with the aim of conclusively completing all adjustments necessary for adjusting the respective axle during pre-assembly.Ideally, in cases where specified tolerance values ​​are maintained by the adjustment achieved with the pre-adjustment of the respective axle when checking this after the respective axle has been mounted on the body of the vehicle, only the electronic adjustment of the steering wheel position with the steering angle of the front axle is necessary to ensure the correct steering wheel position when driving straight ahead.

[0034] Further practical embodiments of the invention are described below in connection with the Fig. 1 described. Fig. 1 shows a simplified process diagram of a method for adjusting a steer-by-wire steering system of a motor vehicle.

[0035] The method for adjusting a steer-by-wire steering system of a motor vehicle provides for the front axle of the motor vehicle to be pre-assembled in a method step 10. The pre-assembled front axle is pre-adjusted in a further method step 12, which takes place separately from the body of the motor vehicle.

[0036] The method can also provide for the rear axle to be pre-assembled in a method step 14 and for the rear axle to be pre-adjusted in a further method step 16. Pre-adjustment 16 is also carried out separately from the body of the motor vehicle.

[0037] In a further method step 18, the front axle and in particular the rear axle are mounted on the body of the motor vehicle.

[0038] The method can provide, as in the example shown, that a measurement 20 of the axles is carried out after assembly of the axles. Depending on the result of the measurement, a decision can be made, as in the example shown, whether a readjustment 22 of the front axle and / or the rear axle is carried out, or whether the settings of the front axle and in particular the rear axle achieved by the pre-adjustments 12 and in particular 16 are retained as the final setting of the axles. After the measurement 20 and in particular the further adjustment 22, the steering wheel position is adjusted 24 to the steering angle of the front axle. The straight-ahead position of the steering wheel is assigned to the steering angle leading to straight-ahead travel.

[0039] The features of the invention disclosed in the present description, the drawings, and the claims may be essential, both individually and in any combination, for the realization of the invention in its various embodiments. The invention may be varied within the scope of the claims and taking into account the knowledge of the person skilled in the art. List of reference symbols 10 Pre-assembly front axle 12 Pre-adjusting the front axle 14 Pre-assembly rear axle 16 Pre-adjusting the rear axle 18 Assembly front axle / rear axle 20 Measurement front axle / rear axle 22 Further adjustment of front axle / rear axle 24 Adjusting steering wheel position / steering angle

Claims

[1] Method for adjusting a steer-by-wire steering system of a motor vehicle, wherein the front axle of the motor vehicle is pre-assembled (10), pre-adjusted (12) separately from the body of the motor vehicle and mounted (18) to the body in the pre-adjusted state, wherein after mounting (18) of the pre-adjusted front axle to the body, the steering wheel is married to the front axle by electronically adjusting (24) the steering wheel position with the steering angle of the front axle, wherein the straight-ahead position of the steering wheel is assigned to the steering angle leading to straight-ahead travel. [2] Method according to claim 1, characterized by that during the pre-adjustment (12) of the front axle, the steering angle of the front axle is set to a steering angle of 0° by means of an electromechanical actuator of the steering system. [3] Method according to claim 1 or 2, characterized bythat the pre-setting (12) of the front axle is carried out in that, depending on a measurement of the front axle, controlled manipulators act on setting elements of the front axle and actuate the setting elements for pre-setting the front axle. [4] Method according to one of the preceding claims, characterized by that the pre-adjustment (12) of the front axle comprises the, in particular automated, adjustment of the camber, in particular the basic camber, of the wheels of the front axle. [5] Method according to one of the preceding claims, characterized by that the pre-adjustment (12) of the front axle comprises the, in particular automated, adjustment of the track of the wheels of the front axle. [6] Method according to one of the preceding claims, characterized bythat the rear axle of the motor vehicle is separated from the body of the motor vehicle, in particular automated, pre-adjusted (16) and mounted on the motor vehicle body in the pre-adjusted state (18). [7] Method according to one of the preceding claims, characterized by that the steering angle leading to straight-ahead running is determined on the basis of the setting of the front axle and / or the rear axle achieved with the presetting (12, 16) of the respective axle when the respective axle is mounted on the body. [8] Method according to one of the preceding claims, characterized by that the actual steering wheel position is determined, in particular by means of a camera and / or a steering wheel measuring scale, and is taken into account when adjusting (24) the steering wheel position with the steering angle of the front axle. [9] Method according to one of the preceding claims, characterized bythat after checking the pre-adjustment of the axles when mounted on the body, a further adjustment of the front axle and / or the rear axle is carried out depending on the result of the check if a predetermined tolerance value is exceeded by the adjustment achieved with the pre-adjustment of the respective axle. [10] Method according to one of the preceding claims, characterized by that after the assembly (10) of the respective axle, no further mechanical adjustment is carried out on the front axle and / or the rear axle if the specified tolerance values ​​are maintained by the adjustment achieved with the pre-adjustment of the respective axle when checking it after the assembly of the respective axle on the body of the motor vehicle.

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