Position measuring device and steering actuator

Abstract

Position measuring device, comprising a permanent magnet (10) and a Hall sensor (11) which interacts with the permanent magnet and is displaceable relative to the permanent magnet (10), characterized in that the Hall sensor (11) is fixedly connected to a housing (3) in which a rod (4) is displaceably guided, wherein a single permanent magnet (10) is connected to the rod (4), which is designed to detect the position of the rod (4) over its entire displacement range, and wherein the permanent magnet (10) is designed asymmetrically with respect to at least one of the axes: the longitudinal axis, i.e. the axis predetermined by the displacement direction of the rod (4), and the transverse axis, i.e. the axis orthogonal to the displacement direction, wherein the permanent magnet (10) is shaped as a triangle (12) whose two poles (S, N) are located at the base (14) and the apex (13) of the triangle (12).

Description

The invention relates to a position measuring device having a permanent magnet and a Hall sensor according to the preamble of claim 1.A position measuring device of the generic type is known, for example, from DE 101 24 760 A1. The known position measuring device comprises two components that can be moved linearly with respect to one another, wherein a magnetic sensor is located on one of the components and a permanent magnet is located on the other component. The magnetic sensor is to be capable of outputting a maximum value, a minimum value, or an arbitrary intermediate value. According to DE 101 24 760 A1, the difference between the maximum value and the minimum value is defined as the signal swing. A normalized signal can be calculated from a signal output by the magnetic sensor by means of division by the signal swing, which normalized signal can be evaluated for contactless, linear position measurement. The permanent magnet used in the device according to DE 101 24 760 A1 is oriented with its magnetization axis parallel to the longitudinal direction of the device, i.e. to the displacement direction of one of the components. Insofar as it is required from the size of the working range, i.e. displacement range, a plurality of magnetic field sensors, namely Hall sensors, can be arranged one behind the other in the longitudinal direction.DE 10 2016 106 779 A1 discloses a travel sensor device which, in addition to a magnet and a sensor, has a reference guide plate and two measurement guide plates. This forms two magnetic circuits, namely a first magnetic circuit as reference circuit and a second magnetic circuit as measurement circuit.DE 10 2017 104 875 A1 discloses a sensor device for detecting the displacement position of a motor vehicle seat. This sensor device comprises a Hall sensor and a bias magnet. Shielding plates, on the other hand, are not provided.As regards the use of Hall sensors in vehicle steering systems, reference is made by way of example to the documents DE 10 2011 017 335 A1 and DE 103 58 009 B3.DE 10 2015 115 247 A1 describes a measuring arrangement which comprises a plurality of Hall sensors and an associated magnetic target. The magnetic target is designed as a magnetic multipole. With the aid of the plurality of Hall sensors, it should be possible to detect radial, axial and tangential field components.A rotor position transducer described in DE 10 2013 203 388 B3 is provided for use in an electronically commutated electric machine. A plurality of permanent magnets are located on a rotor of the electric machine. The rotor position sensor comprises a rotor position sensor designed as a Hall sensor and a reference sensor, which is likewise a Hall sensor. The reference transmitter is provided in particular for detecting a zero crossing of the flux density or for detecting minima and maxima.DE 10 2011 115 566 A1 describes a Hall sensor which is constructed from a plurality of individual Hall sensor elements. The Hall sensor elements are arranged here within a defined surface shape, which can be, inter alia, a rectangular shape, a cross shape, a circular shape or the shape of a straight polygon, in particular a hexagon or an octagon.EP 3 559 602 B1 describes an absolute value measuring device which operates with an array of Hall effect sensors. The Hall effect sensors cooperate with a reference track and a high resolution track, each track having a plurality of north / south pole pairs. In addition, there may be a third track having only a single north / south pole pair.DE 100 10 042 A1 discloses linear displacement pickup for motor vehicles, which comprises a displaceable element 4, 5, 7 and a stator (1, 2, 3). The displaceable element comprises a magnetic encoder. Sensor modules are connected to the stator in a fixed manner, which operate according to the AMR principle, the GMR principle or the Hall principle. The slidable element is carried by a bearing 11 connected to the stator, which engages around the slidable element and axially guides it. The sensor module or modules are connected to the stator in a fixed manner. Along the longitudinal axis of the displaceable element, the field generating means or the field generating means are connected to the displaceable element in a form-transmitting manner. The use of the linear displacement sensor for measuring the pedal or lever position in a brake actuating device of motor vehicles is also described.DE 199 62 378 A1 discloses a method and a device for monitoring the direction of movement (R) of a moving component, such as a bending wheel of a motor vehicle heating unit, conveyor belt or the like, in which, using signal transmitter(s) and signal receiver(s), a control unit (1) monitors signals correlated with the direction of movement of the component and switches off the movement of the component if the component has the wrong direction of movement, it is proposed to form the signal transmitter with a magnetic field that is asymmetrical with respect to the direction of movement (R) of the component, wherein a Hall sensor (2) and / or an inductive sensor (3) is used as signal receiver for detecting the asymmetry of the magnetic field. The asymmetry of the magnetic field is significantly more for the direction of movement and can be correspondingly utilized for detecting the direction of the moving component.DE 101 50 305 A1 discloses a device for measuring the steering rod path of a motor vehicle steering system, which has a steering actuator and a steering rod operatively connected thereto, which steering rod can be moved substantially linearly and, via further elements, such as a track rod and a track rod lever, pivots the wheel into a desired position, one or more field generating means are provided in the region of the steering rod, which field generating means have a permanent magnetic material with a circular magnetic field line course and / or magnetic field line course extending in the longitudinal direction of the steering rod, and in that one or more sensor modules are arranged in a fixed manner adjacent to the steering rod, which sensor modules have at least one magnetic field sensor and optionally at least one sensor circuit and which convert the magnetic field line course or magnetic field line course completely or partially into output signals which can be processed further, indicating a linear displacement or position of the steering rod in the direction of its longitudinal axis.DE 102 44 703 A1 discloses a displacement and / or position measuring device ( 1) having a magnet ( 2) and having a sensor ( 3) detecting the magnetic field state. The magnet (2) and / or the sensor (3) cooperate with a movable element (4), wherein a relative movement between the sensor (3) and the magnet (2) can be effected by means of the movable element (4). Furthermore, the magnet ( 2) has such a shape that the magnetic field width along an axis ( 5) of the magnet ( 2) has a varying, non-constant course. The relative movement occurs substantially in the direction of this axis (5) of the magnet (2). On the basis of the magnetic field state detected by the sensor (3), the path and / or the position of the movable element (4) can be determined.US 2009 / 0 121 708 A1 discloses a method for designing a sensor arrangement, having a housing, a first magnet and a second magnet. The method includes forming the first magnet and the second magnet into a wedge shape. The method further includes tilting the first and second magnets at an angle within the housing.DE 10 2010 053 217 A1 discloses a sensor arrangement ( 1) designed for detecting the position of a linearly movable element ( 3), wherein the sensor arrangement has a magnet ( 5) and a sensor element ( 4) detecting the position of the magnet ( 5). A stationary carrier is provided which is designed to receive the sensor element (4) and to receive the movable element (3) which is linear and relative to the magnet (5)The invention is based on the object of further developing a position sensor system based on Hall sensors, which is suitable in particular for a steering actuator, compared to the aforementioned prior art, wherein a particularly favorable relationship between apparatus complexity, measurement accuracy and functional reliability is sought.This object is achieved according to the invention by a position measuring device having the features of claim 1. The position measuring device is suitable in particular for use in a steering actuator of a motor vehicle, wherein the steering actuator can be part of a rear axle steering system. Also, the steering actuator may be provided for steering front wheels of a vehicle.The position measuring device is provided for detecting the relative positioning of two elements that can be displaced relative to one another, wherein the longitudinal direction of the device is given by the displacement direction. The elements that are linearly movable relative to one another are firstly a housing and secondly a rod, in particular a push rod, which is guided in the housing in a linearly movable manner. The central axis of the rod is aligned in the longitudinal direction of the position measuring device. A Hall sensor of the position measuring device is rigidly connected to the housing, while a permanent magnet cooperating with the Hall sensor is connected to the displaceable rod. Instead of a separate permanent magnet, a magnetization of the rod which can be displaced along its own central axis, i.e. in the axial direction of the entire device, can also be provided.In the simplest case, the position measuring device has only a single Hall sensor. Embodiments with a second Hall sensor are likewise possible, which represents a "second track" in the sense of a redundant solution. The second Hall sensor is provided to increase safety, not to improve the resolution of the position measuring device.In any case, it is possible, by means of the permanent magnet, to detect the position of the rod over its entire displacement range. The permanent magnet is designed asymmetrically with respect to the longitudinal axis predefined by the displacement direction and / or with respect to the transverse axis orthogonal thereto. This is associated with an asymmetry of the magnetic field lines, which is of substantial importance for the desired spatial resolution. The longitudinal axis and the transverse axis define a plane to which the central axis of the displaceable rod is arranged parallel.In the longitudinal direction of the position measuring device, the permanent magnet, which is generally also referred to as a magnetic target, is, according to various possible configurations, more extended than the Hall sensor. In particular, at least one triangle is described by the permanent magnet. In the transverse direction, on the other hand, the Hall sensor can be more extended than the permanent magnet.. . According to the invention, the permanent magnet is shaped as a whole as a triangle. In this case, the permanent magnet can have the basic shape of an isosceles triangle, the axis of symmetry of which is oriented in the axial direction of the position measuring device. The two poles of the permanent magnet are located in this case at the base or tip of the triangle.A steering actuator for a motor vehicle, which is designed according to Claim 2, comprises a drive unit, a rod which is displaceable by means of the drive unit, that is to say a push rod, and a position measuring device according to Claim 1, which is designed to detect the position of the rod. The drive unit can in particular be an electromechanical drive unit, wherein said drive unit can comprise a multistage transmission, in particular a combination of a rotational-rotational transmission and a rotational-linear transmission. In principle, the position measuring device can also be used in hydraulically assisted steering.Two exemplary embodiments of the invention are explained in more detail below with reference to a drawing. Shown herein are: FIG. 1 shows a first exemplary embodiment of a steering actuator in a simplified, partially cut-away illustration, FIG. 2 shows components of a position measuring device of the steering actuator according to FIG. 1, FIGS. 3 and 4 show a second exemplary embodiment of a steering actuator with position measuring device in representations analogous to FIGS. 1 and 2.Unless stated otherwise, the following explanations relate to both exemplary embodiments. Parts corresponding to one another or having the same effect in principle are identified by the same reference sign in all figures.A rear axle steering system, denoted overall by the reference symbol 1, of a motor vehicle, which is not shown in greater detail, operates with an electromechanical steering actuator 2.The steering actuator 2 comprises a push rod 4 which is displaceable in a housing 3. The displacement direction of the push rod 4, which is also referred to as a rod for short, is defined as the longitudinal direction LR of the actuator 2. The actuator longitudinal direction LR thus corresponds to the vehicle transverse direction. Fork-shaped connecting elements 5 are connected to the push rod 4, which connecting elements are provided in a manner known per se for coupling to chassis elements, not shown, in order to enable steering of the rear wheels of the vehicle. Bellows between the connection elements 5 and the housing 3 are denoted 6.The shaft of an electric motor, designated 7, of the steering actuator 2 is arranged parallel to the push rod 4, wherein the electric motor 7 is mounted on the housing 3 in the present case. The electric motor 7 is operatively connected to the push rod 4 via a multi-stage transmission arrangement 8. The arrangement, which is designated overall as drive unit 18, comprises the electric motor 7 and the transmission arrangement 8. In the present cases, the transmission arrangement 8 is constructed from a belt drive or chain drive, that is to say a belt drive, as a rotary-rotary transmission and a rotary-linear transmission connected downstream thereof in the form of a planetary rolling screw drive, a ball screw drive or another screw drive.To detect the position of the push rod 4, a position measuring device 9 is provided, which comprises a permanent magnet 10 and a Hall sensor 11. In this case, the permanent magnet 10 is fixedly connected to the push rod 4 and the Hall sensor 11 is fixedly connected to the housing 3, which is shown partially open in FIGS. 1 and 3. The single Hall sensor 11 is capable, in cooperation with the single permanent magnet 10, of detecting the setting of the steering actuator 2 in the entire range of setting of the push rod 4. In both exemplary embodiments, the permanent magnet 10 has an elongate basic shape extending in the longitudinal direction LR. The transverse direction orthogonal thereto is denoted by QR. MA denotes the transverse direction of the magnet 10, and the Hall sensor 11 extends substantially in the transverse direction QR, as can be seen from FIGS. 2 and 4. The extent of the Hall sensor 11 in the longitudinal direction LR is less than the maximum displacement travel of the push rod 4.In the exemplary embodiment according to FIGS. 1 and 2, the permanent magnet 10 has, in the top view shown, viewed in the direction orthogonal to the push rod 4, the shape of an isosceles, acute-angled triangle 12, the tip of which is denoted by 13 and the base of which is denoted by 14. In this case, a triangular shape of the north pole N is given, while the south pole S of the same magnet 10 describes a trapezoid. The transverse direction MA of the magnet corresponds to the transverse direction QR in the case of FIGS. 1 and 2. With respect to a mirror plane which is placed between the south pole S and the north pole N and to which the central axis of the rod 4 represents a surface normal, the permanent magnet 10 is asymmetrically shaped. This asymmetry acts directly on the magnetic field lines and facilitates the precise detection of the position of the push rod 4 in the entire actuating range of the steering actuator 2 without requiring any further magnet or sensor. Optionally, an additional sensor system, not shown, is provided on the electric motor 7, with which the angular position of the rotor of the electric motor 7 can be detected.The exemplary embodiment according to FIGS. 3 and 4 differs from the exemplary embodiment according to FIGS. 1 and 2 in the shape of the permanent magnet 10. The transverse direction MA of the magnet is inclined by the angle α relative to the longitudinal direction LR. In the case of FIGS. 3 and 4, this results in an asymmetry of the permanent magnet 10 both with respect to a mirror plane which is placed through the central axis of the push rod 4 and with respect to a mirror plane which is orthogonal thereto, that is to say a plane to which the push rod 4 represents a surface normal.Both in the exemplary embodiment according to FIGS. 1 and 2 and in the exemplary embodiment according to FIGS. 3 and 4, the permanent magnet 10 is in each case a separate component. Alternatively, the corresponding function of position measuring device 9 can also be realized with a magnetization of push rod 4.List of reference characters1 Rear axle steering system 2 Steering actuator 3 Housing 4 Push rod 5 Connecting element 6 Bellows 7 Electric motor 8 Transmission arrangement 9 Position measuring device 10 Permanent magnet 11 Hall sensor 12 Triangle, isosceles acute angle 13 Tip 14 Base 15 Trapezoid 16 Triangle, right angle 17 Rectangle 18 Drive unit α Angle LR Longitudinal direction, displacement direction MA Magnet transverse direction N North pole QR Transverse direction of the position measuring device S South pole

Claims

Position measuring device, comprising a permanent magnet (10) and a Hall sensor (11) interacting therewith and displaceable relative to the permanent magnet (10), characterized in that the Hall sensor (11) is firmly connected to a housing (3) in which a rod (4) is displaceably guided, wherein a single permanent magnet (10) is connected to the rod (4) and is designed for detecting the position of the rod (4) over its entire displacement range, and wherein the permanent magnet (10) is designed asymmetrically with respect to at least one of the axes longitudinal axis, that is to say the axis predetermined by the displacement direction of the rod (4), and transverse axis, that is to say the axis orthogonal to the displacement direction, wherein the permanent magnet (10) is shaped overall as a triangle (12), the two poles (S) of which, n) are located at the base (14) and the apex (13) of the triangle (12).Steering actuator, comprising a drive unit (18), a rod (4) displaceable by means of the drive unit (18), i.e. a push rod, and a position measuring device (9) according to claim 1 designed for detecting the position of the rod (4).Steering actuator according to Claim 2, characterized in that an electromechanical unit is provided as the drive unit (18).Steering actuator according to Claim 2 or 3, characterized in that it is designed as an actuator of a rear-axle steering system (1) of a motor vehicle.

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