Steering actuator and method for operating rear axle steering system

Abstract

A steering actuator (1) comprising: an electric motor (2); a tappet (6) which can be linearly adjusted by the electric motor (2) via the gear assembly (3) and which is guided in a housing (15); and a sensor unit (12) which is designed to at least indirectly detect the position of the tappet (6). The sensor unit comprises two different sensors (7, 8), a rotation sensor (7) and a linear sensor (8), said linear sensor (8) being designed to directly detect the position of the tappet (6). The push rod (6) is movable between two stops (23, 24) fixed to the housing, in which each of the two stop positions of the push rod (6) is assigned a position value (FW, SW) of the linear sensor (8) and defines a mechanical center (MC = (FW + SW) / 2). An actuating unit (9) interacting with the two sensors (7, 8) is provided, which is designed to calculate the difference between the output value (RSLS = 0) of the rotation sensor (7) and the machine center (MC) when the linear sensor (8) indicates zero, and to use this difference in order to actuate the electric motor (2).

Description

Technical Field

[0001] This invention relates to an electromechanical steering actuator according to the preamble of claim 1, the electromechanical steering actuator comprising a gear assembly, a sensor unit, and a pushrod. The invention also relates to a method for operating a rear-axle steering system used in a motor vehicle. Background Technology

[0002] For example, a steering actuator of the type discussed is known from DE 10 2008 032 046 A1. Known steering actuators intended for use in rear axle steering systems include a position determination system that operates via two distinct sensors: a linear sensor and a rotary sensor. Within the scope of the calibration method described in DE 10 2008 032 046 A1, calibration information is generated, including zero-point information for the linear sensor and sector information associated with the rotary sensor. For this purpose, the measurement range of the rotary sensor is divided into at least two sectors. The sector information is intended to determine the angle at which the angular position of the steering actuator rotor, detected by the rotary sensor, lies when the movable actuator element of the steering actuator is positioned at its geometric center. According to an advantageous embodiment as described in DE 10 2008 032 046 A1, the angular range covered by the sector is greater than the angular resolution of the rotary sensor.

[0003] Another steering actuator with the features of the preamble of claim 1, also intended for use in a rear axle steering system, is known from DE 10 2018 129 119 A1. This steering actuator includes a two-stage gear assembly and a sensor assembly designed to detect the setting of the gear assembly, and the steering actuator has two spatially separated, independently operating sensors. According to DE 10 2018 129 119 A1, the two sensors of the steering actuator are located on a linearly displaceable element on the same output side of the gear assembly of the steering actuator.

[0004] The chassis actuator disclosed in DE 10 2015 206 678 A1 includes an electric motor, a spindle driver having a threaded spindle and a spindle nut, and a gear with a fixed transmission ratio connected between the electric motor and the spindle nut. The electric motor has a first rotation angle sensor. Furthermore, a second rotation angle sensor is arranged on the output gear of the gear connected to the spindle nut.

[0005] DE 10 2021 121 869 A1 relates to the calibration and linearization of position sensors used in rear axle steering systems. The intent is to calibrate and linearize the first portion of the position sensor's measurement range using a higher grid point density compared to the second portion of the position sensor's measurement range. According to DE 10 2021 121 869 A1, the position sensor can be arranged on a printed circuit board. Summary of the Invention

[0006] The purpose of this invention is to increase the effectiveness of measurements of the rear axle steering system of a vehicle compared to the aforementioned prior art, wherein a particularly favorable ratio between equipment workload and accuracy is sought.

[0007] According to the present invention, this objective is achieved by a steering actuator having the features of claim 1. This objective is also achieved by a method for operating a rear-axle steering system of a motor vehicle designed according to claim 7. The embodiments and advantages of the invention explained below in conjunction with the operating method, with necessary modifications, are equally applicable to the device, i.e., the steering actuator, the entire rear-axle steering system, and the motor vehicle equipped with the rear-axle steering system; and the embodiments and advantages of the invention explained below in conjunction with the device, i.e., the steering actuator, the entire rear-axle steering system, and the motor vehicle equipped with the rear-axle steering system, with necessary modifications, are equally applicable to the operating method.

[0008] In its basic concept, a steering actuator includes: an electric motor; a pushrod, which is linearly adjustable via a gear assembly by means of the electric motor and guided within the housing of the steering actuator; and a sensor unit for detecting the position of the pushrod, the sensor unit comprising two different sensors. The sensors include a rotational sensor and a linear sensor, the linear sensor being designed for direct, i.e., gearless, detection of the pushrod position.

[0009] According to claim 1, the push rod of the steering actuator is movable between two stops fixed to the housing. Each of the two stop positions of the push rod, determined by the positions of the stops, is assigned a position value from a linear sensor, typically expressed in mm (with a positive or negative sign). Without limitation, these two stop positions are referred to, for example, as the left stop position and the right stop position. The mechanical center of the steering actuator is defined as the sum of the left and right stop positions divided by two (considering the sign). The steering actuator is equipped with an actuation unit designed to calculate the difference between the value output by the rotary sensor when the linear sensor indicates zero and the mechanical center, and to use this difference to control the electric motor.

[0010] Therefore, steering actuators are particularly suitable for metering compensation for geometric errors occurring within a range of variations, which may affect, for example, the dimensions of the actuator's pushrod and / or housing. Steering actuators can also compensate for the effects of sensor aging. This is equally applicable to any compensation for eccentricity or manufacturing-related air gaps.

[0011] The rotation sensor of the steering actuator is specifically designed as a multi-turn sensor for absolute value measurement. A multi-turn sensor is a rotation sensor that provides absolute angular information for multiple rotations, for example, in the form of (n x 360°) + α, where n is the number of complete rotations and α is the angle between zero and 360°. The multi-turn sensor can, for example, convert angles exceeding 360° into angles within the range of zero to 360° by means of gears. The number of complete rotations can also be detected electronically.

[0012] Unlike rotary sensors, linear sensors are designed as, for example, incremental sensors. Implementations with multiple linear sensors are possible; these linear sensors can be of different types and / or cover different measurement ranges. Specifically, the linear sensors assigned to the steering actuator may only cover a portion of the total adjustment range of the pushrod, limited by the two stops. The portion of the total adjustment range covered by the linear sensors particularly includes the mechanical center, wherein this portion extends over less than half of the total adjustment range of the pushrod.

[0013] In terms of the functional principle of the sensor, all known principles in length and angle measurement techniques, such as optical or magnetic measurement methods, can be used.

[0014] The gear assembly of the steering actuator includes, for example, a belt gear, particularly in the form of a belt or chain drive, and a rotary linear gear connected downstream of the belt gear, particularly in the form of a spindle drive. The spindle drive is designed, for example, as a ball screw drive or a planetary roller screw drive. In principle, a simple moving thread, i.e., a spindle drive without rolling elements, can also be used.

[0015] A patented method for operating a rear-axle steering system of a motor vehicle assumes electromechanical adjustment of a pushrod that is movable between two stops fixed to a housing and guided within the housing of the rear-axle steering system, via a single-stage or multi-stage, particularly two-stage, gear assembly. The position of the pushrod is determined by means of a sensor unit including a rotary sensor and a linear sensor. Once the pushrod is in the relevant stop position, a position value of the linear sensor is determined at each of the two stops provided by or rigidly connected to the housing. A mechanical center is calculated based on the position values, defined as half the sum of the two position values. The difference between the output value of the rotary sensor and the mechanical center when the linear sensor indicates zero is determined, and this difference is used to electromechanically actuate the gear assembly.

[0016] The difference mentioned is referred to as the deviation value. This deviation value can be stored in a non-volatile data storage device and used in multiple subsequent adjustment operations of the step, i.e., electromechanical changes in the position of the push rod.

[0017] Steering actuators are particularly suitable for use in rear-axle steering systems of motor vehicles. Furthermore, these actuators are also suitable for use in electromechanical front-axle steering systems designed as steer-by-wire systems. Generally, steering actuators can be used in vehicles with two or more axles. Attached Figure Description

[0018] In the following, exemplary embodiments of the present invention will be explained in more detail with reference to the accompanying drawings. In the drawings: Figure 1 The rear axle steering system of the vehicle, i.e., the passenger car, is shown. The rear axle steering system includes an electromechanical steering actuator. Figure 2 and Figure 3 It shows that according to Figure 1 The characteristics of signal processing in the rear axle steering system; Figure 4 The operation is shown according to Figure 1 The flowchart shows the method for the rear axle steering system. Detailed Implementation

[0019] The steering actuator, generally indicated by reference numeral 1 in the accompanying drawings, is intended for use in a rear axle steering system 10 of a motor vehicle (not shown in detail). Regarding the main functions of the rear axle steering system 10 including the steering actuator 1, refer to the prior art cited at the beginning.

[0020] The steering actuator 1 includes an electromechanical actuator, an electric motor 2, and, in this case, a two-stage gear assembly 3. The gear assembly 3 is equipped with a belt drive 4 (i.e., a belt gear) as a rotary-rotary gear, and a spindle drive 5 as a rotary-linear gear. A pushrod 6 is configured as an output element of the spindle drive 5, and is hinged to other chassis elements (not shown), thereby enabling adjustment of the steering angle of the rear wheels of the motor vehicle. The housing of the steering actuator 1 is generally indicated by reference numeral 15.

[0021] To detect the position of push rod 6, a sensor unit, designated 12, is provided, comprising a rotary sensor 7 and a linear sensor 8. In this case, the rotary sensor 7 detects the angular position of the motor shaft of electric motor 2 and is designed as a multi-turn sensor. Alternatively, it is conceivable that the rotary sensor 7 detects the angular position or rotation of a rotatable element of gear assembly 3, which has a reduced rotational speed compared to electric motor 2.

[0022] Linear sensor 8, acting as an incremental sensor, detects changes in the position of push rod 6. Actuation unit 9 works in conjunction with the two sensors 7 and 8. The wire is typically indicated by 11. Measuring devices supplied directly or indirectly by push rod 6 are not shown.

[0023] The adjustment range of push rod 6 is limited on one side by a first stop 23 fixed to the housing, and on the other side by a second stop 24 fixed to the housing. For the two stops 23 and 24, the names FW (first wall) and SW (second wall) are also used to refer to the measured values, i.e., the position values, detected by the sensor unit 12. The stops on the side of push rod 6 that mate with the housing-side stops 23 and 24 are referred to as spindle-side stops 25 and 26.

[0024] Figure 2 The characteristics of actuation unit 9, which functions during the operation of steering actuator 1, are illustrated. Adding element 14 forms the sum of two position values, FW and SW, detected by linear sensor 8 at the two stop positions of push rod 6. In this case, a divider 16 divides this sum by two, typically referred to as the divisor DW. The fraction determined by divider 16 is defined as the mechanical center MC.

[0025] If it is still possible Figure 2 As seen in the diagram, in the parallel processing step, comparator 13 is used to determine when the measured value output by the linear sensor 8 corresponds to the reference value RW. In this case, the reference value RW is set to zero. Processing module 17 is designed to process both the output signal from comparator 13 and the measured value from the rotation sensor 7. Therefore, processing module 17 outputs the value RS. LS=0This value indicates the reading of the rotation sensor 7 when the linear sensor 8 displays zero.

[0026] The described and Figure 2 The two processing lines shown are combined via a differential generator 19. The differential generator 19 provides a deviation value AW, which is written to the data storage device 19. Figure 2 The allocation of the functions of the different components 14, 16, 17, 18, and 19 shown in the figure is illustrative and does not imply any statement relating to the possible physical separation or aggregation of the different functions of the actuation unit 9 to which the aforementioned components 14, 16, 17, 18, and 19 belong.

[0027] Regarding Figure 2 Further processing of the deviation value AW obtained and stored in data storage device 19, refer to Figure 3 In this context, N7 represents the number of revolutions of the shaft of the electric motor 2 detected by means of the rotation sensor 7. The value N7 is fed to the link module 21 through the transmission ratio GR including the gear assembly 3. On the output side, the link module 21 is linked to the data processing device 22.

[0028] The data processing device 22, to which the data storage device 19 is connected, also receives signals from the differential generator 20, which compares the measured angular position of the shaft of the electric motor 2 with the calculated mechanical center MC. A value P6 representing the corrected position of the push rod 6 is set as the initial value for the data processing device 22. The corrected value P6 is used to control the electric motor 2 during further operation of the steering actuator 1.

[0029] According to Figure 4 In the flowchart, the start of the entire process is indicated as step S1. The correction procedure, performed as part of the entire process, begins at step S2. (Refer to...) Figure 1 The arrangement structure is assumed to initially move push rod 6 to the left. In step S3, the system continuously checks whether push rod 6 has reached the left stop position. If so, the stop position FW is saved, and push rod 6 is moved to the right. In step S4, the steps already performed in step S3 are repeated, this time at the right stop position.

[0030] In step S5, the second stop position SW is stored, and the mechanical center MC is calculated in the aforementioned manner. Then, push rod 6 is adjusted toward its central position. In step S6, monitoring is performed to see if the linear sensor 8 outputs a zero value. If this is the case, step S7 detects the angular position of the motor shaft of electric motor 2 and thus determines the value RS. LS=0 In step S8, the deviation value AW is calculated. The deviation value is defined as the difference between the mechanical center MC and the value RS. LS=0The difference between them. Step S9 marks the end of the method.

[0031] List of reference numerals in the attached figures 1. Steering actuator 2 electric motors 3-gear assembly 4 with driver 5 spindle drives 6 putters 7. Sensors on electric motors, rotation sensors 8 linear sensors 9 Actuation Units 10 Rear Axle Steering System 11 wires 12 sensor units 13 comparators 14 Adding Elements 15 housing 16 divider 17 processing modules 18 Differential Generator 19 Non-volatile data storage devices 20 differential generator 21 Link Module 22 Data Processing Equipment 23. Side stop of the housing, FW position 24. Side stop of the housing, SW position 25 First spindle side stop 26 Second spindle side stop AW deviation value DW divisor FW first stop position GR transmission ratio MC Mechanical Center N7 RPM Position of P6 push rod RS LS=0 When the linear sensor 8 displays zero, the measurement value of the rotary sensor 7... RW reference value, zero value S1…S9 Method Steps SW Second Stop Position WS Angle Position

Claims

1. A steering actuator (1) comprising: an electric motor (2); a push rod (6) linearly adjustable by the electric motor (2) via a gear assembly (3), and the push rod being guided in a housing (15); and a sensor unit (12) designed to detect the position of the push rod (6) at least indirectly, the sensor unit comprising two different sensors (7, 8), namely a rotation sensor (7) and a linear sensor (8), the linear sensor (8) being designed to directly detect the position of the push rod (6), characterized in that, The push rod (6) is movable between two stops (23, 24) fixed to the housing, wherein each of the two stop positions of the push rod (6) is assigned a position value (FW, SW) of the linear sensor (8), and a mechanical center (MC = (FW + SW) / 2) is defined, and wherein an actuation unit (9) is provided to interact with the two sensors (7, 8), the actuation unit being designed to calculate the output value (RS) of the rotation sensor (7) when the linear sensor (8) indicates zero. LS=0 The difference between the center of mass (MC) and the mechanical center (MC) is used to actuate the electric motor (2).

2. The steering actuator according to claim 1, characterized in that, The rotation sensor (7) is designed as a multi-turn sensor for absolute value measurement.

3. The steering actuator according to claim 2, characterized in that, The linear sensor (8) is designed as an incremental sensor.

4. The steering actuator according to any one of claims 1 to 3, characterized in that, The linear sensor (8) only covers a portion of the total adjustment range of the push rod (6).

5. The steering actuator according to claim 4, characterized in that, The partial area covered by the linear sensor (8) includes the mechanical center (MC) and corresponds to less than half of the total adjustment range of the push rod (6).

6. The steering actuator according to any one of claims 1 to 5, characterized in that, The gear assembly (3) includes a belt gear (4) and a spindle drive (5) connected downstream of the belt gear, particularly in the form of a ball screw drive.

7. A method for operating a rear axle steering system (10) of a motor vehicle, wherein, Electromechanical adjustment is performed on the push rod (6), which is movable between two stops (23, 24) fixed to the housing and guided within the housing (15), via the gear assembly (3), and the position of the push rod (6) is determined by means of a sensor unit (12) including a rotation sensor (7) and a linear sensor (8), wherein the position value (FW, SW) of the linear sensor (8) is determined at each of the two stops (23, 24) of the push rod, and the mechanical center (MC = (FW + SW) / 2) is calculated based on the position value, and wherein the output value (RS) of the rotation sensor (7) is determined when the linear sensor (8) indicates zero. LS=0 The difference between the gear assembly (3) and the mechanical center (MC), and the difference is used to actuate the gear assembly (3).

8. The method according to claim 7, characterized in that, The aforementioned difference is stored as an offset value (AW) in a non-volatile data storage device (19) and used in multiple subsequent adjustment operations, i.e., electromechanical changes in the position of the push rod (6).

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