Steering actuator and method for operating a rear-axle steering system

Abstract

Steering actuator (1) with an electric motor (2), a push rod (6) that is linearly adjustable by means of the electric motor (2) via a gear arrangement (3), and a sensor system (12) provided for detecting a position of the push rod (6), which sensor system comprises two different sensors (7, 8), and wherein one of the two sensors (8) covers a wide measuring range (M2) in which the position of the push rod (6) can be detected, whereas the other sensor (7) is designed to detect the position of the push rod (6) in narrow, adjacent measuring ranges (M1) lying within the wide measuring range (M2), and wherein there is a control unit (9) that interacts with both sensors (7, 8), characterized in that it is designed, in interaction with the electric motor (2),if necessary, in each of the narrow measuring ranges (M1), to move the push rod (6) into a neutral position (NR) located centrally in the said narrow measuring range (M1) without approaching a reference position located outside the respective narrow measuring range (M1).

Description

[0001] The invention relates to an electromechanical steering actuator according to the preamble of claim 1. Furthermore, the invention relates to a method for operating a rear axle steering system of a motor vehicle.

[0002] A steering actuator of this type is known, for example, from DE 10 2008 032 046 A1. The known steering actuator, intended for use in a rear-axle steering system, comprises a position determination system that operates with two different sensors, namely a linear sensor and a rotary sensor. Within the framework of a calibration procedure described in DE 10 2008 032 046 A1, calibration information is generated, which includes zero-point information from the linear sensor and sector information relating to the rotary sensor. For this purpose, the measuring range of the rotary sensor is divided into at least two sectors. The sector information is intended to identify the angle at which the angular position of a rotor of the steering actuator, as detected by the rotary sensor, lies when a movable actuator element of the steering actuator is arranged in its geometric center position.According to an embodiment described as advantageous in DE 10 2008 032 046 A1, the angular range covered by each sector is larger than the angular resolution of the rotary sensor.

[0003] Another steering actuator is known from DE 10 2018 129 119 A1. This steering actuator comprises a two-stage gear arrangement and a sensor arrangement designed to detect the setting of the gear arrangement and having two spatially separated, independently functioning sensors. Both sensors of the steering actuator according to DE 10 2018 129 119 A1 are located on one and the same output-side, linearly displaceable element of the gear arrangement of the steering actuator.

[0004] A landing gear actuator disclosed in DE 10 2015 206 678 A1 comprises an electric motor, a spindle drive having a threaded spindle and a spindle nut, and a gearbox with a fixed gear ratio connected between the electric motor and the spindle nut. The electric motor has a first angle sensor. Furthermore, a second angle sensor is arranged on an output gear of the gearbox, which is connected to the spindle nut.

[0005] WO 2018 / 233849 A1 discloses a steering system comprising a steering rod measuring system, a steering gear, an electric motor, and an electronic control unit. The steering rod measuring system has a linear position sensor that can determine the absolute position of the pushrod by means of markings on a pushrod of the steering system.

[0006] German patent application DE 10 2021 132 392 A1 discloses a steering system comprising a steering column measuring system, a steering gear, an electric motor, and an electronic control unit. The steering column measuring system includes a linear displacement sensor system and a position sensor. The linear displacement sensor is configured to measure in at least two outer areas. The position sensor is configured to measure an intermediate area located between the outer areas.

[0007] From DE 10 2021 132 394 A1, a steering system is known which discloses a steering rod measuring system, a steering gear, an electric motor, and an electronic control unit. The steering rod measuring system has a magnetic field sensor for determining the direction of a steering rod deflection relative to a reference position and a rotor position sensor for determining the rotational position of the electric motor.

[0008] The invention is based on the objective of further developing electromechanical actuators suitable for adjusting the steering angle of the rear wheels of a motor vehicle compared to the aforementioned prior art, whereby a particularly favorable ratio between equipment effort and operational reliability should be given and at the same time good comfort, especially in the starting phase of the vehicle, is sought.

[0009] This problem is solved according to the invention by a steering actuator having the features of claim 1. Likewise, the problem is solved by a method designed according to claim 8 for operating a rear axle steering system of a motor vehicle. The embodiments and advantages of the invention explained below in connection with the operating method also apply mutatis mutandis to the devices, i.e., the steering actuator, the entire rear axle steering system, and the motor vehicle equipped therewith, and vice versa.

[0010] In a basic concept known per se, the steering actuator comprises an electric motor, a push rod which is linearly adjustable by means of the electric motor via a gear arrangement, and a sensor system for detecting the position of the push rod, which includes two different sensors.

[0011] According to claim 1, one of the two sensors covers the entire measuring range in which the position of the pushrod can be detected, whereas the other sensor is designed to detect the position of the pushrod in smaller, adjacent measuring ranges located within the entire measuring range. Furthermore, the steering actuator according to the application comprises a control unit that interacts with both sensors and, in conjunction with the electric motor and the transmission arrangement, is designed to move the pushrod, as required, in each of the smaller measuring ranges to a neutral position located centrally within the respective narrow measuring range, without moving to a reference position located outside the relevant narrow measuring range.

[0012] Thus, there exists a number of neutral positions corresponding to the number of smaller, i.e., narrow, measuring ranges, which can be used for calibration. These neutral positions can take over the function of reference positions, which in older, unused positioning systems are provided, for example, by stop positions.

[0013] When using the steering actuator in a rear-axle steering system of a motor vehicle, this means that no calibration procedure is required after starting the vehicle, which would involve turning the rear wheels to one of their extreme positions. Likewise, it is not necessary to force the rear wheels to return to their center position if they are turned. Instead, it is possible to drive off directly with the rear wheels turned, for example, when pulling out of a parking space. Eliminating the need to return the rear wheels to the center position, i.e., the straight-ahead position, which is not required for driving dynamics reasons, significantly increases comfort.

[0014] According to one possible embodiment, the steering actuator's sensor, designed to acquire measured values ​​in the smaller measuring range, is configured as a rotary sensor. This can be, in particular, a rotary sensor designed for absolute value measurement. The rotary sensor can, for example, detect the angular position of the steering actuator's electric motor shaft. Variants are also possible in which the rotary sensor detects the angular position of a component of the steering actuator's gear assembly that rotates at a lower speed compared to the electric motor shaft. In both cases, the rotary sensor is, in particular, a multi-turn sensor, meaning a sensor that detects a rotational angle over several revolutions.The multi-turn functionality can be implemented electronically in a manner known per se, or with the aid of a reduction gear that serves purely metrological purposes and converts the rotation of the shaft on which the measurement is to be carried out into a slower rotary motion.

[0015] The sensor that covers the entire measuring range is specifically designed as a linear sensor. This sensor detects, for example, displacements of the push rod or movements of an output-side element of the gear assembly that is rigidly connected to the push rod. In any case, the linear sensor can be designed as an incremental sensor.

[0016] Regardless of the design of the two sensors, the wider measuring range corresponds, for example, to at least four times and at most twenty times the narrower measuring range, which is equivalent to the wider measuring range being subdivided into four or twenty narrower measuring ranges, respectively. The width of the narrower measuring range can, in particular, be defined by one full revolution of an input-side element of the gear assembly, whereby the input-side element of the gear assembly can be rotationally fixed to or identical with the motor shaft of the electric motor. Alternatively, the narrower measuring range can correspond to one full revolution of an element of the gear assembly rotating at a reduced speed compared to the motor shaft of the electric motor.

[0017] The steering actuator's transmission arrangement includes, for example, a wrap-around drive, particularly in the form of a belt or chain drive, and a rotary-linear drive downstream of the wrap-around drive, 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 linear drive, i.e., a spindle drive without rolling elements, can also be used.

[0018] The steering actuator is generally suitable for use in an electromechanically operated steering system of a motor vehicle. In particular, such a steering system can also be a steer-by-wire system for steering the front wheels of a motor vehicle. Therefore, designs that refer to rear-axle steering are also applicable to front-wheel steering systems.

[0019] Besides steering configurations where the measuring range, achieved primarily with the aid of the linear sensor, covers the entire travel range of the pushrod, configurations are also possible where the physically possible travel range—that is, the entire range from stop to stop—extends beyond the entire measuring range, which is subdivided into numerous smaller measuring ranges. In such a case, at least one signal must be present indicating the direction in which the pushrod has been displaced beyond the entire measuring range. This signal is sufficient as a minimum to allow the pushrod to be moved back into the range where its position can be determined using both sensors.

[0020] The patented method for operating a rear-axle steering system generally assumes that a pushrod, by means of which the steering angle of the rear wheels can be varied, is adjusted electromechanically via a gear arrangement. The position of the pushrod is determined using a combination of two sensors, one of which covers the entire measuring range in which the position of the pushrod can be detected, while the other, particularly higher-resolution, sensor is used to detect the position of the pushrod in smaller, non-overlapping measuring ranges located within the entire measuring range.With the aid of a control unit that interacts with both sensors, the push rod is moved, in conjunction with the electric motor, to a neutral position located centrally within each of the smaller measuring ranges without moving to a reference position outside the small measuring range.

[0021] Within the framework of the operating procedure as described in the application, the position of the push rod is directly scanned by means of one of the two sensors, whereas a change in the angular position of a rotatable element of the gear assembly is detected by means of the second sensor. The shaft of the electric motor can also constitute an element of the gear assembly.

[0022] The operating procedure is characterized in particular by the possibility that, immediately after starting a vehicle equipped with rear-axle steering, the position of the pushrod is calibrated by driving to one of those neutral positions which do not correspond to the center position of the pushrod, i.e. the setting for straight-ahead driving.

[0023] As far as the operating principle of the sensors is concerned, all principles known in length and angle measurement technology can be used, for example optical or magnetic measurement methods.

[0024] An embodiment of the invention is explained in more detail below with reference to a drawing. The drawing shows, in some cases roughly schematically: Fig. 1 a rear axle steering system including an electromechanical steering actuator, Fig. 2 a control loop of the steering actuator, Fig. 3. In a flowchart, a procedure for operating the rear axle steering according to Fig. 1.

[0025] A steering actuator, designated in its entirety by reference numeral 1, is intended for use in a rear axle steering system 10 of a motor vehicle not shown. Regarding the fundamental function of the rear axle steering system 10, including the steering actuator 1, reference is made to the prior art cited above.

[0026] The steering actuator 1 comprises an electric motor 2 as an electromechanical actuator and, in this case, a two-stage transmission arrangement 3. The transmission arrangement 3 includes a belt drive 4, i.e., a wrap-around drive, as a rotary-rotary transmission, and a spindle drive 5 as a rotary-linear transmission. A push rod 6 is provided as the output element of the spindle drive 5, which is connected to forked sections 16. Further chassis elements (not shown) are articulated to these forked sections, enabling adjustment of the steering angle of the vehicle's rear wheels. The housing of the steering actuator 1 is designated 15.

[0027] The sensor system 12 comprises a small or narrow measuring range M1 and a comparatively wide measuring range M2. The wide measuring range M2 covers the entire adjustment range of the push rod 6. The position of the push rod 6 can only be determined as an absolute value measurement within the narrow measuring range M1. In contrast, only incremental measurements of the change in the position of the push rod 6 are possible within the wide measuring range M2. In this embodiment, it is assumed that the linear sensor 8 covers the wide measuring range M2. The absolute value measurement in the narrow measuring range M1, which lies within the wide measuring range M2, is achieved using the sensor 7, which detects the angular position of the rotor of the electric motor 2 and thus the setting of a rotatable input element of the gearbox assembly 3. Alternatively, it is also conceivable that both sensors 7 and 8 detect the angular position or rotation of a rotatable element.Likewise, configurations are possible in which both sensors 7, 8 detect the position or displacement of a linearly movable element of the steering actuator 1. The number of narrow measuring ranges M1, into which the wide measuring range M2 is subdivided, is greater than in . Fig. 1 simplified representation.

[0028] Steering actuator 1 is designed to implement a control procedure which is in Fig. Figure 2 illustrates this. A setpoint SW of the position of the push rod 6 is processed using a processing module 17, which in this case is designed as a ramp generator, and fed to a comparator 13.

[0029] The comparator 13 is responsible for comparing the value supplied by the processing unit 17 with a measured value MW obtained using the sensor 12, whereby in the cases considered, measured values ​​MW from both sensors 7 and 8 are always available. The result of the comparison between the setpoint SW and the measured value MW is fed to a controller 14, which, like the comparator 13, is part of the control unit 9. The controlled system of the control loop comprises the mechanical components of the steering actuator 1. In this case, the pushrod 6 is adjustable in a range of at least -25 mm to +25 mm, with the linear sensor 8 covering the entire adjustment range, i.e., the wide measuring range M2.

[0030] In the sketched case, the wide measuring range M2 is completely divided into a multitude of smaller, equally sized narrow measuring ranges M1. It is also possible to divide only a portion of the wide measuring range M2 into smaller narrow measuring ranges M1. In either case, the center position of the push rod 6 lies within a range encompassed by both the wide measuring range M2 and the narrow measuring ranges M1. One full rotation of the shaft of the electric motor 2 corresponds to the width of each of the narrow measuring ranges M1.

[0031] As in Fig. Figure 1, which only shows a part of the narrow measurement ranges M1, shows that within each narrow measurement range M1 a signal SR is generated, which is in Fig. Figure 1 is visualized as a linearly rising curve. A neutral position within each narrow measuring range M1, which is sampled using sensor 7, is designated NR. Thus, there is a total number of neutral positions NR of the sensor 12, corresponding to the number of narrow measuring ranges M1. Each of these neutral positions NR can be used as a reference position for calibrating the sensor 12.

[0032] Regarding the calibration of sensor 12, refer to the flowchart below. Fig. Reference is made to Section 3. The start of the calibration procedure is designated as step S1. In step S2, it is checked whether the push rod 6 is located within the area that can be detected by the linear sensor 8. If this is not the case, in step S7 a switch is made to a method described in patent application DE 10 2023 109 655 A1. This method makes it possible to move the push rod 6, even though it has left the detection range of the linear sensor 8, i.e., the wide measuring range M2, back into the narrow and wide measuring ranges M1, M2, in particular to its central position, as shown in the simplified flow diagram according to Fig. 3 is not shown.

[0033] If the test performed in step S2 shows that the pushrod 6 is within the wide measuring range M2, step S3 checks whether and, if so, in what way there is a deviation from the neutral position NR of the narrow measuring range M1, i.e., the rotary measuring range. In most cases, such a deviation will be detectable. If it is a positive deviation, the pushrod 6 is moved in the negative direction in step S4. If, on the other hand, a negative deviation is detected in step S3, the pushrod 6 is moved in the positive direction in step S5. In any case, the query performed in step S3 and the subsequent adjustment in step S4 or step S5 result in a calibration of the steering actuator 1, including the sensor 12, designated as step S6. Step S8 marks the completion of the calibration procedure. Reference symbol list 1 steering actuator 2 electric motors 3 Gear arrangement 4 Belt drive 5 Spindle drive 6 push rod 7 Sensor on the electric motor 8 Linear sensor 9 Control unit 10 Rear axle steering 11 electrical line 12 Sensors 13 comparators 14 controllers 15 cases 16 Fork piece 17 Processing module M1 narrow measuring range, rotary measuring range M2 extended measuring range, linear measuring range NR Neutral position within the rotary measuring range S1... S8 Process step SR signal within the rotary measurement range SW setpoint

Claims

[1] Steering actuator (1), comprising an electric motor (2), a push rod (6) which is linearly adjustable by means of the electric motor (2) via a gear arrangement (3), and a sensor system (12) for detecting a position of the push rod (6), which includes two different sensors (7, 8), wherein one of the two sensors (8) covers a wide measuring range (M2) in which the position of the push rod (6) can be detected, whereas the other sensor (7) is designed to detect the position of the push rod (6) in narrow, adjacent measuring ranges (M1) located within the wide measuring range (M2), and wherein a control unit (9) interacting with both sensors (7, 8) exists, characterized by, that in conjunction with the electric motor (2) it is designed to move the push rod (6) as required in each of the narrow measuring ranges (M1) to a neutral position (NR) located centrally in the said narrow measuring range (M1) without approaching a reference position located outside the relevant narrow measuring range (M1). [2] Steering actuator (1) according to claim 1, characterized by , that the sensor (7) intended for recording measured values ​​in the narrow measuring range (M1) is designed as a rotary sensor. [3] Steering actuator (1) according to claim 2, characterized by , that the rotation sensor (7) is designed for absolute value measurement. [4] Steering actuator (1) according to claim 3, characterized by , that the sensor (8) intended for recording measured values ​​in the wider measuring range (M2) is designed as a linear sensor. [5] Steering actuator (1) according to claim 4, characterized by, that the linear sensor (8) is designed as an incremental sensor. [6] Steering actuator (1) according to any one of claims 1 to 5, characterized by , that the wider measuring range (M2) corresponds to at least four times and at most twenty times the narrower measuring range (M1), wherein the width of the narrower measuring range (M1) is given by one full revolution of an input-side element of the gear arrangement (3). [7] Steering actuator (1) according to any one of claims 1 to 6, characterized by , that the gear arrangement (3) comprises a wrap-around gear (4) and a spindle drive (5) downstream of it, in particular in the form of a ball screw drive. [8] Method for operating a rear axle steering system (10), wherein a pushrod (6) is electromechanically adjusted via a gear arrangement (3) and a position of the pushrod (6) is determined by means of a combination of two sensors (7, 8), wherein one of the two sensors (8) covers a wide measuring range (M2) in which the position of the pushrod (6) can be detected, whereas the other sensor (7) is used to detect the position of the pushrod (6) in narrow, adjacent measuring ranges (M1) located within the wide measuring range (M2), characterized by , that with the aid of a control unit (9) cooperating with both sensors (7, 8) in conjunction with the electric motor (2) the push rod (6) is moved as required in each of the narrow measuring ranges (M1) to a neutral position (NR) located centrally in the said narrow measuring range (M1) without moving to a reference position located outside the relevant narrow measuring range (M1). [9] Method according to claim 8, characterized by , that by means of one of the two sensors (8) the position of the push rod (6) is directly scanned, whereas by means of the second sensor (7) a change in an angular position of a rotatable element of the gear arrangement (3) is detected. [10] Method according to claim 8 or 9, characterized by , that immediately after starting a vehicle equipped with rear axle steering (10), the position of the pushrod (6) is calibrated by driving to one of the neutral positions which do not correspond to the center position of the pushrod (6).

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