STEER-BY-WIRE STEERING SYSTEM FOR A MOTOR VEHICLE

Description

[0001] The invention relates to a steer-by-wire steering system for a motor vehicle according to the preambles of independent claims 1 and 2.

[0002] Steer-by-wire steering systems are becoming increasingly popular in motor vehicles. This is largely due to the growing importance of autonomous driving, which is naturally easier to achieve with steer-by-wire systems than with conventional steering systems. Furthermore, steer-by-wire systems offer the advantage of allowing for relatively flexible responses to steering wheel movements. This makes it possible, for example, for the steering to react differently to steering wheel inputs depending on the vehicle's driving conditions, such as whether maneuvering into a parking space at walking speed or traveling at high speed on a highway.

[0003] Steering systems of the type in question comprise an electric motor to effect the steering movement and a steering linkage to transmit the steering movement to the wheels. The steering linkage is typically connected to steering knuckles where the wheels are mounted.

[0004] The electric motor is mechanically coupled to the steering linkage via a steering gear. This mechanical coupling is designed such that a steering movement across the entire possible steering angle range requires a multiple of motor shaft revolutions. Typically, 70 to 90 motor revolutions are necessary for a steering movement across the entire steering angle range.

[0005] For the implementation of a steer-by-wire steering system, it is crucial, particularly from a control engineering perspective and especially for regulating the steering system's position, to be able to detect the current steering angle using sensors. In other words, the steering system's control unit must know at all times how far the wheels are turned in one direction or the other.

[0006] Several methods are known for this purpose according to the current state of the art. For example, sensors can detect the position of the steering linkage. However, the angle sensors typically used for this purpose do not measure absolute values, but only changes in angle. As a result, if the sensors lose their power supply, they "lose" their position. Therefore, measures must be taken to calibrate the sensors with regard to the current absolute steering angle each time the vehicle is started.

[0007] Another disadvantage of angle sensors is that they require the installation of corresponding electronic sensors in the steering linkage. This necessitates measures such as connecting them via cable harnesses, which also have to be routed in the steering linkage area, thus making the entire steering system vulnerable, especially to environmental influences.

[0008] WO 2020 / 104593 A2 discloses a steering angle sensor that operates using a multi-pole magnetic ring and multiple sensors. It can be connected to a steering shaft and detect its absolute position. Such a sensor would be overwhelmed by the task of detecting the steering angle on an electric motor in a steer-by-wire steering system, due to the high number of motor revolutions relative to the angle ratio, just like the rotary angle sensors often used for motor control on electric motors.

[0009] A method for measuring the steering angle that eliminates the need for such wiring would therefore be desirable. For example, electric motors typically have rotary encoders used to control the motor. However, due to the high number of rotations involved in a steering movement, using these encoders to deduce the steering angle from the motor shaft position would be problematic. In a typical steering system, 70 to 90 possible steering angles can correspond to a single rotary position on the motor shaft. If such an encoder loses its steering angles, which may be determined by summing up full rotations—for example, due to a power failure—the correlation is no longer unambiguous.

[0010] From generic German patent DE 10 2018 213 112 A1, an actuating device that can be used in motor vehicle steering systems is known. The actuating device has a rotor position sensor for determining the rotor position and a multiturn sensor for counting the number of rotor revolutions.

[0011] EP 3 907 473 A1 discloses an angle measuring device for single- and multi-turn measurement. A field element is rotatably mounted about a first axis of rotation, which in turn is rotatably mounted about a second axis of rotation offset from the first. A sensor array is configured to determine the position of the field element in the plane of rotation and its orientation with respect to its north-south pole by measuring the magnetic field generated by the field element.

[0012] The object of the present invention is therefore to demonstrate a steering system of the type mentioned at the outset, which enables a reliable determination of the steering angle that is insensitive to environmental influences.

[0013] The problem is solved by a steering system having the features of claim 1, the features of the dependent claims relating to advantageous embodiments.

[0014] A steer-by-wire steering system for a motor vehicle comprises an electric motor to effect the steering movement and a steering linkage to transmit the steering movement to the wheels of the motor vehicle. The steering linkage can, for example, be an arrangement consisting of a rack and / or threaded rod extending transversely to the motor vehicle, which is slidable in the transverse direction of the vehicle and can be connected at its ends, in particular by means of tie rods, to the steering knuckles of the motor vehicle.

[0015] Furthermore, the steer-by-wire steering system incorporates an electric motor. This motor is mechanically coupled to the steering linkage via a steering gear. The steering gear can, for example, be a type where the motor shaft's movement is initially transferred to a wheel by means of a traction element, such as a toothed belt. This wheel can then be mechanically coupled to the steering linkage, for example, by means of a ball screw drive. In this way, the rotary motion of the motor shaft can be converted into a translational motion of the steering linkage, at least predominantly.

[0016] The electric motor is coupled to the steering linkage via the steering gear in such a way that a steering movement across the entire possible steering angle range requires a multiple rotations of the motor shaft. Specifically, this can amount to 70 to 90 rotations of the motor shaft for a steering movement across the entire possible steering angle range.

[0017] The steering system also includes a sensor array for detecting the movement of the motor shaft, comprising a sensor and a target that the sensor can detect. The sensor can be, in particular, a magnetoresistive sensor and / or an inductive sensor. Accordingly, the target can be a magnet and / or a target made of an electrically conductive material. Alternatively and / or additionally, it can be, for example, an optical sensor.

[0018] The invention provides, in particular, that the sensor arrangement is coupled to the motor shaft via a transmission such that the motor shaft causes a relative movement between the sensor and the target, enabling a unique correlation between the relative position of the target to the sensor and the steering angle of the steering system. This unique correlation is enabled, in particular, over the entire possible steering angle range of the steering system, or in other words, over the entire steering travel of the steering system.

[0019] The coupling of the sensor assembly to the motor shaft via a gearbox results in the relative movement between the target and the sensor occurring at a significantly lower speed, particularly a significantly lower angular velocity, than the movement of the motor shaft. Consequently, the path or angle swept by the movement through the gearbox is reduced. This makes it possible to avoid ambiguous relative positions between the target and the sensor, thus unambiguously assigning the target's relative position to the steering angle of the steering system.

[0020] In particular, the electric motor, sensor array, and gearbox can form a drive unit housed in a single unit. This allows the housing already required for the electric motor to be used to protect the sensor array and gearbox from environmental influences. The result is a compact and cost-effective design overall.

[0021] The steering system can include an evaluation unit for determining the steering angle from the measurement results of the sensor array. The evaluation unit, in particular, can also be arranged in the same housing as the electric motor, sensor array, and gearbox. This results in a compact design that minimizes exposed wiring.

[0022] The steering system, in particular, cannot have any mechanical connection between the steering wheel and the steering linkage for transmitting the steering movement. With such "pure" steer-by-wire systems, there is no longer any mechanical coupling between the steering wheel and the steering linkage. Therefore, especially with such systems, precise knowledge of the absolute steering angle at any given time is essential for controlling the steering system.

[0023] The gearbox can be located relative to the electric motor's rotor on the side of the B-bearing of the motor's mounting. The B-bearing of an electric motor is the bearing that faces away from the output shaft, specifically the connection between the electric motor and the steering gear, relative to the electric motor's rotor. The gearbox can be advantageously positioned on this side of the rotor.

[0024] In particular, the gearbox is located between the rotor and the B-bearing of the electric motor. This arrangement has the advantage that a design in which the gearbox, sensor assembly, and electric motor are enclosed in a common housing can be implemented in a particularly cost-effective and compact manner.

[0025] The gearbox can be a multi-stage gearbox. A multi-stage gearbox offers the advantage of achieving high gear ratios. Furthermore, a multi-stage arrangement allows for a compact design while maintaining a given gear ratio.

[0026] The gearbox was either a cycloidal gearbox or a planetary gearbox. Cycloidal and planetary gearboxes allow for comparatively high gear ratios to be achieved in a small space. The planetary gearbox in question is specifically a double planetary gearbox. In a double planetary gearbox, the ring gear and the sun gear are connected by pairs of meshing planet gears. This allows for even higher gear ratios.

[0027] In this context, it is advantageous if the ring gear of the planetary gear set, or of the respective stage of the planetary gear set, is fixed, for example, connected to the housing. The sun gear of the planetary gear set, or of the first stage of the planetary gear set, is in particular arranged on the motor shaft and, in particular, non-rotatably connected to it.

[0028] The planetary gear is a multi-stage planetary gear. A multi-stage planetary gear can be implemented, for example, by coupling the planet carrier of one gear stage with the sun gear of the next gear stage in terms of its rotational movement. In particular, if, in such a case, the sun gear of the first gear stage rotates with the motor shaft, the sun gears of subsequent gear stages can be rotatably arranged on and / or around the motor shaft relative to it.

[0029] The gearbox can be arranged around the motor shaft. In particular, when the gearbox is arranged around the motor shaft, a component of the sensor assembly can be moved around the shaft by the gearbox. This component of the sensor assembly is, in particular, the target. Moving the target around the shaft has the advantage that, unlike the sensor, the target does not usually need to be connected to an evaluation unit via cables.

[0030] This arrangement has the advantage that the target can be moved along a comparatively long path, while the target's path of movement still allows for a compact arrangement of the sensor array within the housing. The steering system, particularly the gearbox, is designed such that the sensor assembly component can move around the shaft through an angular range of less than 360°. This enables the unambiguous assignment of each point on the path to a possible steering angle. The path of movement is, in particular, circular.

[0031] The sensor can be a sensor ring. The sensor ring can be designed to detect the position of the target along the ring. Using such a ring-shaped sensor offers the advantage that, in particular, a target that can be moved in a circular path around the shaft can be detected at any of its positions.

[0032] The steering system may include an additional sensor arrangement. The steering system, in particular the evaluation unit, may be designed to evaluate the measurement results of the sensor arrangement and the additional sensor arrangement in relation to each other in order to improve the resolution when determining the steering angle.

[0033] By using two sensor arrays, measurement results from two sensors can be used to calculate the steering angle. The sensor array connected to the motor shaft via the gearbox exhibits only relatively small relative movements of the target to the sensor during small steering movements due to the comparatively high gear ratio required for unambiguous assignment. Therefore, a further sensor array with another sensor and another target, in which the relative movement between the further sensor and another target is caused directly by the motor shaft or indirectly through a lower gear ratio than in the case of the first sensor array, can be used. In other words, the further sensor array relates to the first sensor array like the minute hand of a clock relates to the hour hand.This means, in particular, that in the further sensor arrangement, the unambiguous assignment of the relative position of target and sensor to a specific steering angle can be dispensed with.

[0034] In this context, the additional sensor arrangement can be, in particular, a rotor position sensor arrangement for measuring the rotor position of the electric motor. Such rotor position sensor arrangements are often already integrated into electric motors. With such rotor position sensor arrangements, the additional target is advantageously attached directly to the motor shaft. By additionally using such rotor position sensor arrangements to determine the steering angle, the resolution can be significantly increased in a cost-effective manner.

[0035] Alternatively and / or additionally, it is possible, for example, that the further sensor arrangement is coupled to a gear stage of the gearbox with regard to the relative position of the target to the sensor.

[0036] Further practical embodiments of the invention are described below in connection with the drawings. They show: Fig. 1 a schematic diagram of an exemplary steering system, Fig. 2 a perspective sectional view of an exemplary drive unit consisting of an electric motor, gearbox and sensor arrangement of an exemplary steering system, Fig. 3 a longitudinal sectional view of a part of the drive unit from figure two.

[0037] Figure 1Figure 1 shows a schematic representation of an exemplary steer-by-wire steering system 10. For the movement of the steering linkage 12 of the exemplary steering system 10 in the transverse direction X of the vehicle, a drive unit 14 can be provided, as in the example shown. The drive unit 14 is coupled to the steering linkage 12 via the steering gear 16 in such a way that a steering movement of the steering system 10 over the entire possible steering angle range of the steering system 10 requires a multiple revolutions of the motor shaft 18 of an electric motor 20 of the drive unit 14.

[0038] As in the example shown, the steering system 10 can be designed such that it has no mechanical connection between the steering wheel (not shown) and the steering linkage 12 for transmitting the steering movement. The steering linkage 12 is movably mounted, particularly along the transverse direction X of the vehicle, by means of a suitable bearing 22.

[0039] As in the example shown, the steering gear 16 can, for example, have a belt 24 which transmits the movement of the motor shaft 18 from a belt wheel 26 arranged on the motor shaft 18 to a belt wheel 28 which transmits the steering movement, for example by means of a ball screw drive 30, to the steering linkage 12.

[0040] The drive unit 14 can, as in the example shown, comprise an electric motor 20 for effecting the steering movement, a gearbox 32, and a sensor arrangement 34. These can be arranged in a common housing 36, as in the example shown.

[0041] The sensor arrangement 34 is coupled to the motor shaft 18 via the gearbox 32 such that the motor shaft 18 causes a relative movement between the sensor 38 and the target 40 of the sensor arrangement 34. As in the example shown, the stator 42 and the rotor 44 of the electric motor 20, the gearbox 32, and the sensor arrangement 34 can be arranged between the A-bearing 46 and the B-bearing 48 of the electric motor. Advantageously, as in the example shown, the gearbox 32 and the sensor arrangement 34 can be arranged between the B-bearing 48 and the rotor 44. In particular, as shown by way of example, the gearbox 32 can be located between the sensor arrangement 34 and the rotor 44.

[0042] The gearbox 32 is a multi-stage planetary gearbox. The ring gears 50 of the three gearbox stages shown in the example can be fixed relative to the housing 36 of the drive unit 14. As in the example shown, the sun gear 52 of the first stage of the gearbox 32 can be non-rotatably connected to the motor shaft 18. The sun gears 54 of the subsequent gearbox stages are, in particular as in the example shown, non-rotatably connected to the planet carriers 56 of the respective preceding gearbox stage. Relative to the motor shaft 18, the sun gears 54 of the subsequent gearbox stages are preferably rotatable about the motor shaft 18. The target 40 is attached to the planet carrier 58 of the last gearbox stage.

[0043] The steering system 10 is designed such that, during a steering movement over the full steering angle range of the steering system 10, the target 40 describes a circular movement in which the swept angle range is less than 360°, i.e., the arc described by the movement of the target 40 is smaller than a full circle. This allows a steering angle to be uniquely assigned to each position of the target 40.

[0044] The sensor 38 can, in particular, be a sensor ring, as is the case in the example shown. To improve the resolution, an evaluation device (not shown) for determining the steering angle can also evaluate the measurement results of the sensor arrangement 34 in relation to measurement results from another sensor arrangement, of which, in the example shown, a further target 60, which is rotationally fixed to the motor shaft 18, is shown as an example. The further target 60 is, in particular, as shown, a component of a rotor position sensor arrangement. The invention can be varied within the scope of the claims and taking into account the knowledge of the person skilled in the art. Reference symbol list

[0045] 10 Steer-by-wire steering system 12 Steering linkage 14 Drive unit 16 Steering gear 18 Motor shaft 20 Electric motor 22 Bearing 24 Belt 26 Pulley 28 Pulley 30 Ball screw drive 32 Gearbox 34 Sensor assembly 36 Housing 38 Sensor 40 Target 42 Stator 44 Rotor 46 A-bearing 48 B-bearing 50 Ring gears 52 Sun gear 54 Sun gear 56 Planetary gear 58 Planetary gear 60 Additional target

Claims

1. Steer-by-wire steering system (10) for a motor vehicle, comprising an electric motor (20) for effecting the steering movement of the steering system (10), and comprising a steering linkage (12) for transmitting the steering movement toward the wheels of the motor vehicle, the electric motor (20) being mechanically coupled to the steering linkage (12) via a steering gear (16) in such a way that a steering movement of the steering system (10) over the entire possible steering angle range of the steering system (10) requires a plurality of rotations of the motor shaft (18), and comprising a sensor arrangement (34) for detecting the movement of the motor shaft (18) with a sensor (38) and a target (40) detectable by the sensor (38), characterized in that the sensor arrangement (34) is coupled to the motor shaft (18) via a transmission (32) in such a way that the motor shaft (18) effects a relative movement between the sensor (38) and the target (40), which movement allows a unique assignment between the relative position of the target (40) to the sensor (38) and the steering angle of the steering system (10), in particular over the entire possible steering angle range of the steering system (10), the transmission being a cycloidal gear.

2. Steer-by-wire steering system (10) for a motor vehicle, comprising an electric motor (20) for effecting the steering movement of the steering system (10), and comprising a steering linkage (12) for transmitting the steering movement toward the wheels of the motor vehicle, the electric motor (20) being mechanically coupled to the steering linkage (12) via a steering gear (16) in such a way that a steering movement of the steering system (10) over the entire possible steering angle range of the steering system (10) requires a plurality of rotations of the motor shaft (18), and comprising a sensor arrangement (34) for detecting the movement of the motor shaft (18) with a sensor (38) and a target (40) detectable by the sensor (38), characterized in that the sensor arrangement (34) is coupled to the motor shaft (18) via a transmission (32) in such a way that the motor shaft (18) effects a relative movement between the sensor (38) and the target (40), which movement allows a unique assignment between the relative position of the target (40) to the sensor (38) and the steering angle of the steering system (10), in particular over the entire possible steering angle range of the steering system (10), the transmission being a multi-stage planetary gear train, the target (40) being fastened to the planet carrier (58) of the final gear train stage.

3. Steering system (10) according to claim 1 or 2, characterized in that the electric motor (20), the sensor arrangement (34) and the transmission (32) are arranged in a common housing (36).

4. Steering system (10) according to any of the preceding claims, characterized in that the steering system (10) does not have a mechanical connection for transmitting the steering movement between the steering wheel and the steering linkage (12).

5. Steering system (10) according to any of the preceding claims, characterized in that the transmission (32) is arranged on the side of the B-bearing (48) of the mounting of the electric motor (20) relative to the rotor (44) of the electric motor (20), in particular between the rotor (44) and the B-bearing (48).

6. Steering system (10) according to any of the preceding claims 1 or 3 to 5, characterized in that the transmission (32) is a multi-stage transmission.

7. Steering system (10) according to any of claims 2 to 6, characterized in that the transmission (32) is a double planetary gear train.

8. Steering system (10) according to any of the preceding claims, characterized in that the transmission (32) is arranged surrounding the motor shaft (18) and a component of the sensor arrangement (34), in particular the target (40), is moved around the shaft (18) by the transmission (32).

9. Steering system (10) according to any of the preceding claims, characterized in that the sensor (38) is a sensor ring designed to identify the position of the target (40) along the ring.

10. Steering system (10) according to any of the preceding claims, characterized in that the steering system (10) has an evaluation device for determining the steering angle from the measurement results of the sensor arrangement (34), the steering system (10) having a further sensor arrangement and the steering system (10), in particular the evaluation device, being designed to evaluate the measurement results of the sensor arrangement (34) and the further sensor arrangement in relation to each other in order to improve the resolution in determining the steering angle.

11. Steering system (10) according to any of the preceding claims, characterized in that the further sensor arrangement is a rotor position sensor arrangement for measuring the rotor position of the electric motor (20).