Feedback actuator and steer-by-wire system for a motor vehicle

Abstract

The present invention relates to a feedback actuator (5) for a steering system (1) of a motor vehicle, comprising a drive wheel (53) rotatable about a drive axis (M) by an electric motor (51) and a driven wheel (54) engaged with the drive wheel by a surrounding belt (55), the driven wheel being connected to a steering shaft (22) spaced apart from the drive axis (M) and rotatably supported about the steering axis (L), and the feedback actuator comprising a rotation angle detection device (7) having a first electrical position sensor (72) corresponding to the drive wheel (53), a second position sensor (75) corresponding to the driven wheel (54), and a circuit board (73, 76) carrying the position sensors (72, 75). In order to achieve an improved and less interference-resistant rotation angle detection device, the present invention proposes that the circuit board (73, 76) has a first circuit board section (73) carrying a first position sensor (72), which is spatially displaceable and electrically connected to a second circuit board section (76) carrying a second position sensor (75) by means of a flexible conductor element (77).

Description

Technical Field

[0001] This invention relates to a feedback actuator for a motor vehicle steering system, comprising a drive wheel rotatable about a drive axis by an electric motor, and a driven wheel engaged with the drive wheel via a surrounding belt. The driven wheel is connected to a steering shaft, which is spaced from the drive axis and supported in a manner rotatable about the steering axis. The feedback actuator includes a rotation angle detection device and / or a torque detection device, having a first electrical position sensor corresponding to the drive wheel, a second position sensor corresponding to the driven wheel, and a circuit board carrying the position sensors. Steer-by-wire systems for motor vehicles having such a feedback actuator are also the subject of this invention. Background Technology

[0002] A steer-by-wire system for motor vehicles can receive manual steering commands from the driver through the rotation of a steering wheel attached to the driver's side rear end of a steering shaft (steering spindle) supported in the steering column, similar to a conventional mechanical steering system. However, instead of being mechanically connected to the wheels to be steered via a steering transmission, the steering shaft works in conjunction with a rotation angle sensor or torque sensor. This sensor detects the input steering command and generates an electrical control signal, which is then output to a steering adjuster. The steering adjuster, via an electrically adjustable actuator, adjusts the wheel steering angle according to the steering command.

[0003] Due to the lack of mechanical coupling, in a drive-by-wire system, the driver does not receive direct physical feedback from the steering wheels through the steering system. In traditional mechanically coupled steering systems, this physical feedback is transmitted back to the steering wheel as a reaction torque or return torque, based on lane conditions, vehicle speed, current steering angle, and other operating conditions. The lack of tactile feedback makes it difficult for the driver to reliably perceive the current driving conditions and perform appropriate steering maneuvers, thereby impairing the vehicle's steerability and consequently compromising driving safety.

[0004] To generate a realistic driving feel, it is known in the prior art to detect or calculate parameters, such as vehicle speed, steering angle, and steering reaction torque, from actual instantaneous driving conditions, and to generate feedback signals from these parameters, which are then input into a feedback actuator. The feedback actuator is preferably integrated into the vehicle's steering column and has a manual torque or steering wheel adjuster, which includes an electric motor drive unit that couples a return torque or feedback torque corresponding to the actual reaction torque to the steering wheel via the steering shaft, based on the feedback signal. This "force feedback" system gives the driver the impression of a real driving situation, similar to that in conventional steering, making intuitive responses easier.

[0005] An example of this type of feedback actuator is known from EP 3 521 136 A1, in which an electric motor is coupled to a steering shaft via a belt drive, specifically a toothed belt drive. The motor torque is transmitted via a wrapped belt or toothed belt from a drive pulley mounted on the motor shaft (the drive side) to a driven pulley mounted on the steering shaft (the driven side). The feedback of the coupled input can be measured and adjusted using a rotation angle detection device. Here, sensors configured as angle or rotor position sensors are respectively provided for the drive and driven pulleys, so that the angular position or rotation of the drive and driven pulleys is detected independently of each other. This provides the advantage that redundant measurements can be performed so that disturbances in torque transmission, such as those caused by slippage or belt breakage, can be reliably detected.

[0006] These two sensors are constructed as non-contact sensors, for example, as Hall effect sensors arranged on a circuit board that also serves as a mechanical carrier and has electrical conductor circuitry for powering the sensors and transmitting signals. On one or both sides of this mechanically rigid circuit board, the sensors are positioned such that they have defined, small measuring distances from signal generators, such as encoder magnets or another preferred non-contact encoder element, mounted on the driven and driven wheels, respectively. Advantageously, the sensors are fixed relative to the belt drive on the circuit board. However, if the position of the driven or driven wheel relative to each other or relative to the circuit board changes, for example due to relative displacement of the driven and driven wheels for adjusting the defined belt tension—either during assembly or operation, or due to alternating load responses—the measuring distance between the sensor and the corresponding signal generator on the driven or driven wheel may change, potentially interfering with the measurement signal. Summary of the Invention

[0007] To address the aforementioned problems, the purpose of this invention is to provide a feedback actuator with an improved rotation angle detection device that is less prone to failure.

[0008] According to the present invention, this objective is achieved by the steering column of the present invention.

[0009] In this type of feedback actuator for a motor vehicle steering system, the feedback actuator includes a drive wheel that can be driven by an electric motor to rotate about a drive axis and a driven wheel that is driven and meshed with the drive wheel via a surrounding belt. The driven wheel is connected to a steering shaft that is spaced apart from the drive axis and supported in a manner rotatable about a steering axis. The feedback actuator includes a rotation angle detection device and / or a torque detection device having a first electrical position sensor corresponding to the drive wheel, a second position sensor corresponding to the driven wheel, and a circuit board carrying the position sensors. According to the invention, the circuit board has a first circuit board section carrying the first position sensor, which is spatially displaceable and electrically connected to a second circuit board section carrying the second position sensor by a flexible conductor element.

[0010] The belt drive is preferably designed as a toothed belt drive, wherein the drive pulley and driven pulley are designed as toothed pulleys or toothed belt discs, around which the toothed belt rotates. The toothed pulleys are aligned with each other, corresponding to a substantially parallel arrangement of a motor shaft extending along the drive axis on the drive side and a steering shaft extending along the driven axis or steering axis on the driven side, the steering shaft forming the driven shaft. Here, the drive pulley and driven pulley are respectively mounted torsionally in the regions of the free ends of the motor shaft and steering shaft, such that they have a common free axial end side in front of which a circuit board extends perpendicular to its axial direction. The position sensor, also synonymously referred to simply as a sensor, can therefore be mounted on the same side of the circuit board axially opposite the two toothed pulleys, so that they are at a defined axial measuring distance relative to an encoder element disposed on the pulley, the encoder element having, for example, an encoder magnet that rotates with it. Electronic position sensors and corresponding encoders can, in principle, operate according to different, preferably non-contact, physical measurement principles known in the prior art, such as magnetic, capacitive, optical, acoustic, or similar principles, as long as the angular position or rotor position of the drive and driven wheels can be detected. Advantageously, magnetic sensors, such as Hall effect sensors, are combined with rotating encoder magnets.

[0011] As an alternative to or supplement to the rotation angle detection device, a torque detection device can be installed. This torque detection device is used to determine the transmitted torque. This can be determined from the electrical signal provided by the position sensor.

[0012] Alternatively, the free ends of the drive wheel and driven wheel can be axially opposite each other, and the sensors assigned to them can be arranged on opposite sides of the circuit board.

[0013] According to the invention, the circuit board is not constructed as a rigid, continuous, one-piece unit as in the prior art, but is divided into at least two flexibly interconnected circuit board sections, which are also referred to below as circuit board components, sub-boards, or sub-elements. This flexible connection allows for relative movement of the two circuit board sections, preferably in a direction parallel to a common circuit board plane perpendicular to the axial directions of the drive and driven axes, and the circuit board sections are arranged parallel to this plane, preferably at the same spacing. The advantage of this relative mobility is that the position sensor can, for example, follow the relative movement between the drive wheel and the driven shaft when the belt is tensioned by increasing the axial spacing between the drive and driven axes. Here, one circuit board section, along with one sensor, is fixed relative to the drive wheel, and the other circuit board section is fixed relative to the driven wheel. The advantage here is that the measurement spacing between the respective sensors and the corresponding encoder elements remains constant regardless of the relative position of the pulleys, and the reliability of rotation angle detection is improved. Furthermore, calibration costs during installation can be advantageously reduced, and the belt can be easily re-tensioned by changing the axial spacing without impairing the rotation angle measurement.

[0014] Advantageously, the first circuit board segment is fixed relative to the drive wheel, and the second circuit board segment is fixed relative to the driven wheel. At least two first and second conductor circuit segments can, in principle, be constructed of the same type. By spatially defining the fixation relative to the drive or driven wheel, the corresponding distances of the position sensors relative to the drive and driven wheels can be predefined and fixed, thereby fixing the measurement distance. When the drive and driven wheels shift relative to each other, the conductor circuit segments also move together, wherein the relative movement can be compensated by the flexible connecting element according to the invention. The flexible connecting element forms a mechanical and conductive connection, which can include current supply and signal lines. By maintaining the same measurement distance in all assembly and operating states, interference is avoided as much as possible. The first circuit board segment can also be fixed relative to the driven wheel, and the second circuit board segment can also be fixed relative to the drive wheel.

[0015] Each circuit board segment can be fixed to a support element, in which a drive shaft or driven shaft is rotatably supported. During relative movement of the axes, these support elements move relative to the circuit board segments, and this relative movement can be compensated for by their flexible connections.

[0016] Advantageously, the first and second circuit board sections can be rigidly constructed. The circuit board sections can each resemble a one-piece continuous circuit board in the prior art, having a rigid carrier plate made of an insulating material, such as fiber-reinforced plastic, on which conductive circuitry is applied in one, two, or more layers. The application of such multilayer circuit boards is known for printed circuit boards (PCBs). According to the invention, the circuit board sections are less flexible than the flexible conductive elements connecting these sections. This rigid, shape-stable design offers the advantage of enabling persistent and accurate spatial positioning and fixation of the sensor.

[0017] In a preferred embodiment, the flexible conductive element has a bendable printed circuit board. This bendable printed circuit board is, in principle, a thin, film-like circuit board that can be bent laterally across its surface; it is also called a flexible printed circuit board or flexible circuit board, and it is thinner than a rigid circuit board segment. The flexible printed circuit board can have an insulating plastic film as a carrier, such as a polyimide film with a thickness of approximately 0.02 mm to 0.2 mm, having electrical conductive circuitry printed on one or both sides. This flexible printed circuit board can be conductively inserted between the conductive circuitry of a rigid circuit board segment, and variable spatial spacing compensation is achieved through its variable bendability perpendicular to the plane of the circuit board.

[0018] By combining rigid conductor circuit segments with flexible printed circuit boards, the conflict between the goals of persistent and accurate positioning of the sensor relative to the pulley and variable positioning of the pulleys relative to each other can be advantageously resolved for the first time.

[0019] The design scheme of two rigid conductor circuit sections and flexible conductor elements makes it easy to economically automate the manufacturing of the electronic circuitry for the rotation angle detection device.

[0020] It can be specified that circuit board segments are arranged in a plane and spaced relative to each other, with flexible conductor elements extending through the gap and capable of bending laterally across the plane. This plane forms the circuit board plane, within which the circuit board segments can be displaced relative to each other. The flexible conductor elements may preferably have at least one arcuate or wavy connecting segment that arches perpendicular to the circuit board plane and spans the gap, bending more strongly or less strongly as the circuit board segments move toward or away from each other. Therefore, mechanical stress on the flexible connection can be minimized, which is beneficial for trouble-free operation and a long service life.

[0021] An advantageous embodiment of the invention may specify that a belt tensioning device is effectively provided between the drive axis and the steering axis. The belt tensioning device is used to adjust the distance between the drive axis and the driven axis such that the belt extending between the pulleys is tensioned in a defined manner, for example, by applying a tension force that loads the drive pulley and the driven pulley away from each other. This may result in relative displacement of the drive pulley and the driven pulley, thereby changing the distance from the sensor in the prior art. The advantage of the present invention is that even if the pulleys move relative to each other, the measured distance is independent of the adjustment of the belt tensioning device.

[0022] The belt tensioning device can have an adjustment mechanism to adjust the spacing of the axes when manufacturing the actuator to calibrate the belt tension. Alternatively, a persistent force-generating device can be used, which automatically maintains the belt tension within the optimal operating range even when changes occur during operation, such as belt elongation, or material expansion due to load variations or temperature fluctuations. The advantages of this invention are simplified manufacturing and uninterrupted functionality of the rotation angle detection device throughout its service life.

[0023] To achieve a belt tensioning device with sustained automatic operation, it can be specified that the belt tensioning device has a resilient preload mechanism. The preload mechanism can, for example, have a preloaded spring element that loads the drive and driven pulleys separately with a resilient spring force. Alternatively or additionally, other types of force-generating or preload mechanisms can be used, such as electrical, hydraulic, etc.

[0024] Preferably, the drive shaft and steering shaft are supported in a single housing, preferably in a common housing. This allows for a closed, compact feedback drive system, where the belt drive, along with the rotation angle detection device and / or torque detection device, can be protected within the preferably enclosed housing from external influences. The motor can be mounted on the housing or integrated therein. The drive shaft and driven shaft are preferably parallel to each other and, more preferably, adjustable relative to each other with a variable axial spacing, supported in bearings within the housing.

[0025] The housing may be made of metal and alternatively or additionally include plastic materials, and has an externally sealed internal space in which the belt drive is protected. Metal shielding provides protection against electrical interference.

[0026] It can be specified that the circuit board sections are axially arranged in front of the drive wheel and / or driven wheel, wherein the position sensor is arranged coaxially with the drive axis and / or driven axis or steering axis. Here, the two circuit board sections can be arranged perpendicular to the axis direction on the end sides in front of the free ends of the drive shaft and driven shaft, on which the drive wheel and driven wheel are arranged torsionally. This results in a compact and easy-to-assemble assembly, which can be installed in a housing with minimal cost. The conductor circuit sections can be connected to the shaft supporting the axis in the housing, so as to translate with the shaft during relative movement.

[0027] On one or two circuit board sections, an electronic control circuit (ECU) can preferably be constructed, which at least partially performs the electrical signal preparation and processing of the electrical signals from the position sensor. This enables an advantageously compact structural form, and allows the control device to be shielded from interference when mounted in a housing.

[0028] The invention also includes a steering column for a steer-by-wire system in a motor vehicle, the steering column comprising a rotatably supported steering shaft having a fixed section for mounting a steering wheel and coupled to a feedback actuator for introducing feedback torque, wherein the feedback actuator is constructed according to the invention. As described above, the steering column includes electronic sensing and feedback devices for detecting steering input generated by manually turning the steering wheel. Reliability and accuracy can be improved by the configuration of the feedback actuator according to the invention. The foregoing features can be implemented individually or in combination herein. Attached Figure Description

[0029] Advantageous embodiments of the invention will now be explained in detail with reference to the accompanying drawings. Details are shown below:

[0030] Figure 1 A schematic diagram of the steer-by-wire system according to the present invention is shown.

[0031] Figure 2 A schematic diagram of a feedback actuator according to the present invention is shown. Detailed Implementation

[0032] In different accompanying drawings, the same parts are always given the same reference numerals, and therefore are usually named or mentioned only once each.

[0033] Figure 1A steer-by-wire system 1, including a steering column 2, is schematically shown. This steer-by-wire system has a carrier unit 21 that can be mounted on a vehicle body (not shown), and a steering shaft 22 (also synonymously referred to as the steering master shaft 22) is rotatably supported by the carrier unit about its steering axis L (also referred to as the longitudinal axis or driven axis). The steering shaft 22 has a fixed section, not visible here, at its rearward, driver-side end with respect to the direction of travel, on which a steering wheel 23 is torsionally mounted.

[0034] A rotation angle and torque detection sensor (not shown in detail) is installed in the steering column 2, which converts the steering command introduced into the steering shaft 22 as rotation of the steering wheel 23 into an electric steering signal. This steering signal is transmitted to the electric steering drive unit 4 via the electric control circuit 3.

[0035] The steering drive unit 4 includes a servo motor 41 that introduces steering servo torque into the steering transmission unit 42. There, the steering servo torque is converted into translational motion of the steering tie rod 45 via a pinion 43 and a rack 44, as indicated by the double arrows, thereby causing the steering wheels 46 to steer relative to the road surface 47.

[0036] At the leading edge region in the direction of travel, the steering column has a feedback actuator 5 according to the invention, which in... Figure 2 It is shown schematically in the diagram.

[0037] The feedback actuator 5 has an electric motor 51, the motor shaft 52 of which extends along the drive axis M, which is parallel to the steering axis L at an axial spacing x.

[0038] The toothed belt drive includes a drive wheel 53, which is configured as a toothed pulley and is torsionally mounted on a motor shaft 52; a driven wheel 54, which is also configured as a toothed pulley and is torsionally mounted on a steering shaft 22; and a toothed belt 55 that wraps around the toothed pulleys 53 and 54.

[0039] The steering shaft 22 is rotatably supported in the housing 56, and the motor 51 is adjustablely mounted relative to the steering axis L on the belt tensioner 6, as indicated by the double arrows. The belt tensioner 6 may have a force generating device 61, such as a pre-tensioned spring element, thereby applying a tension force that directionally loads the motor 51 relative to the housing 56 away from the steering axis L, thus tensioning or maintaining the tension of the toothed belt 55.

[0040] The axial spacing can be changed by the relative movement during the tensioning of the toothed belt during assembly or by re-tensioning during operation, for example by a belt tensioning device 6 that automatically acts by spring force.

[0041] The rotation angle detection device and / or torque detection device 7 according to the present invention includes a first encoder magnet 71 mounted on the front end of the steering shaft 22 at one end and a second encoder magnet 74 mounted on the front end of the motor shaft 52 at one end. A first position sensor 72 is axially mounted on a first circuit board section 73 in front of the first encoder magnet 71 at a measuring interval, and a second position sensor 75 is axially mounted on a second circuit board section 76 in front of the second encoder magnet 74 at a measuring interval. Circuit board sections 73 and 76 can be implemented as printed circuits with rigid printed circuit boards on which electronic components are interconnected.

[0042] A flexible conductor element 77 is installed between circuit board sections 73 and 76, preferably a thin-film, bendable flexible circuit board having a conductor circuit that electrically connects circuit board sections 73 and 76.

[0043] Circuit board segment 73 is fixed relative to the steering axis L, and circuit board segment 76 is fixed relative to the drive axis M. When the motor shaft 52 shifts relative to the steering shaft 22, the relative movement of the tensioning device 6 within the housing 56 changes the axial distance x, and accordingly displaces circuit board segments 73 and 76 relative to each other. This relative movement can be absorbed by the variable bending of the flexible conductor element 77. Thus, the measurement distance between the position sensors 72, 75 and the corresponding encoders 71, 74 remains the same in all adjustment and operating states, thereby avoiding interference.

[0044] Explanation of reference numerals in the attached figures

[0045] 1. Steer-by-wire system

[0046] 2 steering columns

[0047] 21 bearing units

[0048] 22 steering shaft

[0049] 23 steering wheel

[0050] 3 control circuits

[0051] 4. Steering drive unit

[0052] 41 servo motors

[0053] 42 Steering transmission

[0054] 43 small gears

[0055] 44 rack

[0056] 45 Steering Tie Bar

[0057] 46 wheels

[0058] 47 driving lanes

[0059] 5 Feedback Actuator

[0060] 51 motor

[0061] 52 motor shaft

[0062] 53 drive wheels

[0063] 54 driven wheels

[0064] 55-tooth belt

[0065] 56 shell

[0066] 6. Belt tensioning device

[0067] 61 Force generating device

[0068] 7. Rotation Angle Detection Device

[0069] 71 and 74 encoder magnets

[0070] 72, 75 position sensors

[0071] 73 and 76 circuit board sections

[0072] 77 Flexible Conductor Components

[0073] L-shaped steering axis

[0074] M drive axis

[0075] x-axis spacing

Claims

1. A feedback actuator (5) for a steering system (1) of a motor vehicle, comprising a drive wheel (53) rotatably driven by an electric motor (51) about a drive axis (M) and a driven wheel (54) driven by the drive wheel via a surrounding belt (55), the driven wheel being connected to a steering shaft (22) spaced apart from the drive axis (M) and rotatably supported about a steering axis (L), and the feedback actuator comprising a rotation angle detection device (7) and / or a torque detection device having an electrical first position sensor (72) corresponding to the drive wheel (53), a second position sensor (75) corresponding to the driven wheel (54), and an electrical circuit board (73, 76) carrying the position sensors (72, 75). Its features are, The circuit boards (73, 76) have a first circuit board section (73) that carries the first position sensor (72), the first circuit board section being spatially displaceable and electrically connected to a second circuit board section (76) that carries the second position sensor (75) via a flexible conductor element (77); the first circuit board section (73) is fixed relative to the steering axis (L), and the second circuit board section (76) is fixed relative to the drive axis (M); a belt tensioning device (6) is effectively arranged between the drive axis (M) and the steering axis (L).

2. The feedback actuator according to claim 1, characterized in that, The first and second circuit board sections (73, 76) are rigidly constructed.

3. The feedback actuator according to any one of claims 1-2, characterized in that, The flexible conductor element (77) has a bendable printed circuit board.

4. The feedback actuator according to any one of claims 1-2, characterized in that, The circuit board segments (73, 76) are arranged in a plane and are spaced apart from each other, and the flexible conductor element (77) extends flexibly across the plane at the spacing.

5. The feedback actuator according to any one of claims 1-2, characterized in that, The belt tensioning device (6) has an elastic pre-tensioning mechanism (61).

6. The feedback actuator according to any one of claims 1-2, characterized in that, The drive shaft (M) and the steering shaft (L) are supported in the housing (56).

7. The feedback actuator according to any one of claims 1-2, characterized in that, Circuit board sections (76, 73) are axially arranged in front of the drive wheel (53) and / or the driven wheel (54), wherein position sensors (72, 75) are coaxially arranged with the drive axis (M) and / or the steering axis (L).

8. A steering column (2) for a steer-by-wire system (1) of a motor vehicle, comprising a rotatably supported steering shaft (22) having a fixed section for mounting a steering wheel (23) and coupled to a feedback actuator (5) for introducing feedback torque, characterized in that, The feedback actuator (5) is constructed according to any one of claims 1 to 7.

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