INDUCTIVE ANGLE SENSOR FOR A VEHICLE STEERING SYSTEM

Description

[0001] The present invention relates to a torque sensor unit having the features of the preamble of claim 1, an electromechanical power steering system for a motor vehicle comprising the torque sensor unit and a method for determining a torque introduced into an upper steering shaft of a motor vehicle steering system having the features of the preamble of claim 12.

[0002] Torque sensors are used in motor vehicles to measure the torque applied by a driver to the steering wheel. Currently used torque sensors are magnetic sensors, whose measurements are easily disrupted by external magnetic fields. Motor vehicles will be fully or partially electrically powered in the future, and some already are, which can lead to significant external field interference measurements from high-current cables, which are often located near the steering system. Furthermore, currently used magnetic sensors have low accuracy.

[0003] A combined angle of rotation and torque sensor unit for measuring the angle of rotation of a steering shaft and the torque applied to the steering shaft, the sensor unit comprising a first inductive sensor with a first coil arrangement and a second inductive sensor with a second coil arrangement, is known in the prior art from US 2008 / 0007251 A1. Furthermore, US 2017 / 0144703 A1 discloses an electromechanical power steering system with multiple sensors, which include multiple inductive sensors that are also used to determine torque. An inductive torque sensor, which is also designed for use in steering systems, is furthermore known from WO 2018 / 108783 A2. Furthermore, US 3,812,481 A discloses an inductive rotary encoder that can be used in the control system, for example in engine control.

[0004] It is an object of the present invention to provide a torque sensor which has increased accuracy and a reduced influence of an existing magnetic interference field on the determination of the torque value.

[0005] This object is achieved by a torque sensor unit having the features of claim 1 and a method for determining a torque having the features of claim 12.

[0006] Accordingly, a torque sensor unit is provided for measuring a torque introduced into an upper steering shaft of a motor vehicle, wherein the upper steering shaft is connectable to a lower steering shaft via a torsion bar, wherein the torque sensor unit has two inductive sensors, wherein a first inductive sensor is connectable to the upper steering shaft for measuring the rotational position of the upper steering shaft and a second inductive sensor is connectable to the lower steering shaft for measuring the rotational position of the lower steering shaft, and wherein an evaluation unit is designed to process the signals of the two inductive sensors and to calculate the torque therefrom by means of the angular difference between the rotational positions of the two steering shafts.The inductive sensing technology underlying the torque sensor is a short-range, non-contact sensor technology that enables cost-effective, high-resolution detection of conductive objects in the presence of dust, dirt, oil, and moisture, making it extremely reliable.

[0007] According to the invention, an inductive sensor has a carrier plate which can be connected in a rotationally fixed manner to the corresponding steering shaft and a printed circuit board which is spatially fixed relative to the carrier plate, wherein at least one electrically conductive track is arranged on the carrier plate and a scanning device with two coils which are part of an oscillating circuit is arranged on the printed circuit board, and wherein the scanning device is designed to scan the at least one electrically conductive track in order to generate an angle-dependent sensor signal during rotational movement of the corresponding steering shaft.

[0008] Preferably, the one electrically conductive track is self-contained and extends around the center of the carrier plate.

[0009] Preferably, the at least one electrically conductive track has a wave pattern that enables absolute angle determination over one steering shaft rotation.

[0010] A single electrically conductive track is provided for each sensor, which is scanned by the two corresponding coils, with the two coils arranged at a 90-degree angle to each other. In this case, the scanning device preferably comprises an electronic control unit configured to determine the angle of rotation of the steering shaft using a Cordic algorithm.

[0011] It is advantageous if the circuit board is arranged asymmetrically to the center of the steering shaft, since this design enables a particularly compact construction.

[0012] It is preferred that the at least one electrically conductive track is formed from copper.

[0013] It can also be provided that the two coils are configured to be used independently of each other. This allows, for example, counting the revolutions of the respective steering shaft or detecting a sector.

[0014] In a preferred embodiment, the coils of the first inductive sensor are located longitudinally on one side of the scanning devices, and the coils of the second inductive sensor are located on the other side. This ensures that the inductive sensors detect a signal with as little interference as possible. It is advantageous if an electromagnetic shield is provided on the side of the scanning devices facing away from the coils, ensuring that the coils of the respective scanning device only read the assigned track. Furthermore, it can be provided that the scanning devices of the two inductive sensors are preferably located circumferentially on opposite sides of the torsion bar to further minimize interference.

[0015] Furthermore, an electromechanical power steering system for a motor vehicle is provided, comprising an upper steering shaft connected to a steering wheel and a lower steering shaft connected to the upper steering shaft via a torsion bar, a torque sensor unit as described above and an electric motor for assisting a steering movement introduced into the steering wheel by a driver as a function of the torque measured by the torque sensor unit.

[0016] Furthermore, a method for determining a torque introduced into an upper steering shaft of a motor vehicle steering system is provided, wherein the upper steering shaft is connected to a lower steering shaft via a torsion bar, and a first inductive sensor is connected to the upper steering shaft for measuring the rotational position of the upper steering shaft and a second inductive sensor is connected to the lower steering shaft for measuring the rotational position of the lower steering shaft, the method comprising the following steps: Measuring the absolute rotational position of the upper steering shaft using the first inductive sensor, measuring the absolute rotational position of the lower steering shaft using the second inductive sensor, calculating the angular difference between the two absolute rotational positions, determining the torque introduced into the upper steering shaft using the equation: T STW = c*δ , where c is the spring constant of the torsion bar and δ is the angular difference.

[0017] In the method according to the invention, an inductive sensor has a carrier plate which is connected in a rotationally fixed manner to the corresponding steering shaft and a printed circuit board which is spatially fixed relative to the carrier plate, wherein at least one electrically conductive track is arranged on the carrier plate and a scanning device with two coils which are part of an oscillating circuit is arranged on the printed circuit board, wherein the coils scan at least one electrically conductive track which rotates with the corresponding steering shaft and extends around the respective steering shaft and is closed in itself, in which a change in a resonance frequency of the oscillating circuit is detected.

[0018] It is preferred that the at least one electrically conductive track has a wave pattern that enables absolute angle determination over one steering shaft rotation.

[0019] ItIn each case, a single electrically conductive track is provided, which is scanned by two associated coils, whereby the two coils are arranged at an angle of 90 degrees to each other, and the angle of rotation of the corresponding steering shaft is determined from the two coil signals by means of a Cordic algorithm.

[0020] A preferred embodiment of the invention is explained in more detail below with reference to the drawings. Identical or functionally identical components are provided with the same reference numerals throughout the figures. They show: Fig. 1: a schematic representation of an electromechanical motor vehicle steering system, and Fig. 2: a schematic representation of a steering system of a motor vehicle with an inductive torque sensor.

[0021] In the Figure 1An electromechanical motor vehicle power steering system 1 is shown schematically, comprising a steering wheel 2 that is rotationally fixedly coupled to an upper steering shaft 3. Via the steering wheel 2, the driver applies a corresponding torque as a steering command to the steering shaft 3. The torque is then transmitted via the upper steering shaft 3 and lower steering shaft 4 to a steering pinion 5. The pinion 5 meshes in a known manner with a toothed segment of a rack 6. The rack 6 is mounted in a steering housing so that it can be displaced in the direction of its longitudinal axis. At its free end, the rack 6 is connected to tie rods 7 via ball joints (not shown). The tie rods 7 themselves are each connected in a known manner via steering knuckles to a steered wheel 8 of the motor vehicle. A rotation of the steering wheel 2, via the connection between the steering shaft 3 and the pinion 5, leads to a longitudinal displacement of the rack 6 and thus to a pivoting of the steered wheels 8.The steered wheels 8 experience a reaction via a roadway 80 that counteracts the steering movement. Consequently, a force is required to pivot the wheels 8, necessitating a corresponding torque on the steering wheel 2. An electric motor 9 of a servo unit 10 is provided to assist the driver in this steering movement. The upper steering shaft 3 and the lower steering shaft 4 are torsionally elastically coupled to one another via a torsion bar (not shown). A torque sensor unit 11 detects the rotation of the upper steering shaft 3 relative to the lower steering shaft 4 as a measure of the torque manually applied to the steering shaft 3 or the steering wheel 2. Depending on the torque measured by the torque sensor unit 11, the servo unit 10 provides steering assistance to the driver.The servo unit 10 can be coupled as an auxiliary power assistance device 10, 100, 101 either to a steering shaft 3, the steering pinion 5, or the rack 6. The respective auxiliary power assistance device 10, 100, 101 applies an auxiliary power torque to the steering shaft 3, the steering pinion 5, and / or the rack 6, thereby assisting the driver in steering. The three different ones in . Figure 1 The auxiliary power assistance devices 10, 100, 101 shown show alternative positions for their arrangement. Typically, only one of the positions shown is occupied by an auxiliary power assistance device.

[0022] In the Figure 21 shows a steering system with a torque sensor unit 11. The torque sensor unit 11 is arranged between the upper steering shaft 3, which is connected to the steering wheel 2, and the lower steering shaft 4, which is torsionally elastically connected to the upper steering shaft 3 via a torsion bar 12. The torque sensor unit 11 has a first inductive sensor 13 and a second inductive sensor 14, wherein the first inductive sensor 13 measures the angle of rotation of the upper steering shaft 3 and the second inductive sensor 14 measures the angle of rotation of the lower steering shaft 4.

[0023] The first inductive sensor 13 has a first carrier plate 15 that is connected to the upper steering shaft 3 in a rotationally fixed manner, and an associated first stationary scanning device 16 that is arranged on a first circuit board 18 connected to a first electronic control unit 17. The first carrier plate 15 has a track 19 made of an electrically conductive material, preferably copper. The track 19 is self-contained and has no beginning or end. The pattern of the track 19 is preferably a wave pattern that has curved triangular shapes that extend around the center of the first carrier plate 15. The wave pattern has wave crests and wave troughs and repeats periodically. The pattern of the track 19 is not concentric with the upper steering shaft 3. It is designed such that an absolute angle determination is possible over one shaft revolution.

[0024] Two coils 80, 81 of the first scanning device 16 are arranged on the first circuit board 18. The first circuit board 18 is preferably designed as a PCB (printed circuit board) and carries all electronic components, in particular an evaluation circuit and the coils 80, 81. The first circuit board 18 with the coils 80, 81 is located directly below the first copper track 19. The first circuit board 18 is not arranged concentrically to the center axis of the upper steering shaft 3.

[0025] The rotation angle of the upper steering shaft 3 is estimated by the first inductive sensor 13, which scans the copper track 19 on the first carrier plate 15. The first coils 80, 81 are part of an oscillating circuit. They 80, 81 generate a high-frequency magnetic field. When the track 19 moves in the magnetic field, an induced current begins to flow due to electromagnetic induction. Based on the mutual inductance coupling, the resonant frequency of the oscillating circuit changes. When a non-ferrous metal object, such as the copper track, approaches, the resonant frequency of the electrical oscillating circuit increases. The mutual inductance coupling thus changes when the copper track 19 rotates over the coils 80, 81. The first sensor 13 monitors the movement of the conductive track 19 with the first carrier plate 15 or the rotating upper steering shaft 3 and thereby calculates an absolute angular position.Two coils 80, 81 are sufficient to calculate the angle when arranged at 90 degrees to each other. In the case of the previously described triangular pattern, the output of the two coils 80, 81 is a sine signal and a cosine signal. The angle calculation is based on the industry-standard Coordinate Rotation Digital Computer (Cordic) algorithm. This algorithm allows for the efficient calculation of basic trigonometric and hyperbolic functions using almost exclusively fast operations, such as additions and multiplications by powers of two.

[0026] The second inductive sensor 14 has the same components as the first inductive sensor 13 and the same functionality. The components of the second inductive sensor 14 are identified by primed reference numerals of the first inductive sensor 13.

[0027] The first scanning device 16 and the second scanning device 16' are arranged within the first carrier plate 15 and the second carrier plate 15'. The coils of the scanning devices 80, 81, 80', 81' are thus located longitudinally on opposite sides of the scanning device 16, 16' and the electronic control units 17, 17', respectively. An electromagnetic shield 20, 20' is provided on the other side of the electronic control unit 17, 17', ensuring that the coils of the respective scanning device 80, 81, 80', 81' only read the assigned track 19, 19' and are not disturbed in the process. The scanning devices 16, 16' are therefore preferably located circumferentially on opposite sides of the torsion bar 12.

[0028] The torque acting on the upper steering shaft 3 is calculated from the angle difference between the angles measured by the two inductive sensors 13,14: T STW = c ∗ δ , where c is the spring constant of the torsion bar and δ is the angle difference.

[0029] Multiple circuit boards, each with two coils, can be used to provide high redundancy and electronic error compensation (misalignment, mechanical errors). The coil pairs can be arranged in pairs on separate PCBs or on a common PCB.

[0030] The two inductive sensors 13, 14 can be used independently of each other, for example, to count the revolutions of the steering shafts or to detect a sector. They can also be used together, for example, in a steering angle sensor with a reduction gear that operates according to the vernier principle.

Claims

1. Torque sensor unit (11) for measuring a torque introduced into an upper steering shaft (3) of a motor vehicle, wherein the upper steering shaft (3) can be connected to a lower steering shaft (4) via a torsion bar (12), wherein the torque sensor unit (11) has two inductive sensors (13, 14), wherein a first inductive sensor (13) can be connected to the upper steering shaft (3) for measuring the rotational position of the upper steering shaft (3) and a second inductive sensor (14) can be connected to the lower steering shaft (4) for measuring the rotational position of the lower steering shaft (4), and wherein an evaluation unit is designed to process the signals of the two inductive sensors (13, 14) and to calculate the torque therefrom by means of the angular difference existing between the rotational positions of the two steering shafts (3, 4), characterized in that the inductive sensors (13, 14) has in each case a carrier plate (15, 15') which can be connected to the corresponding steering shaft (3, 4) in a rotationally fixed manner and a printed circuit board (18, 18') which is spatially fixed with respect to the carrier plate (15, 15'), a single electrically conductive track (19, 19') being provided on the carrier plate (15, 15') and a sensing device (16, 16') with two coils (80, 81, 80', 81') being provided on the printed circuit board (18, 18') with two coils (80, 81, 80', 81'), which are part of a resonant circuit, are arranged on the printed circuit board (18, 18'), the two coils (80, 81, 80', 81') being arranged at an angle of 90 degrees to one another, and the sensing device (16, 16') being designed to sense the electrically conductive track (19, 19') in order to generate an angle-dependent sensor signal when the corresponding steering shaft (3, 4) rotates.

2. Torque sensor unit according to claim 1, characterized in that the electrically conductive track (19, 19') is closed in itself and extends around the center point of the carrier plate (15, 15').

3. Torque sensor unit according to claim 1 or claim 2, characterized in that the electrically conductive track (19, 19') has a wave pattern that enables an absolute angle determination over a revolution of the steering shaft.

4. Torque sensor unit according to one of the preceding claims, characterized in that the respective sensing device (16, 16') in each case has an electronic control unit (17, 17') which is set up to determine the angle of rotation of the corresponding steering shaft (3, 4) by means of a Cordic algorithm.

5. Torque sensor unit according to one of the preceding claims, characterized in that the respective printed circuit board (18, 18') is arranged asymmetrically to the center of the corresponding steering shaft (3, 4).

6. Torque sensor unit according to one of the preceding claims, characterized in that the electrically conductive track (19, 19') is formed from copper.

7. Torque sensor unit according to one of the preceding claims, characterized in that the two coils (80, 81, 80', 81') are each set up to be used independently of one another.

8. Torque sensor unit according to one of the preceding claims, characterized in that the coils (80, 81, 80', 81') of the first inductive sensor (13, 14) are located in the longitudinal direction on one side of the sensing devices (16, 16') and the coils (80, 81, 80', 81') of the second inductive sensor (13, 14) are located on the other side.

9. Torque sensor unit according to claim 8, characterized in that an electromagnetic shielding (20, 20') is provided on the side of the sensing devices (16, 16') facing away from the coils (80, 81, 80', 81'), which ensures that the coils (80, 81, 80', 81') of the respective sensing device (16, 16') only read out the associated track (19, 19').

10. Torque sensor unit according to one of the preceding claims, characterized in that the sensing device (16, 16') of the two inductive sensors (13, 14) are located on opposite sides of the torsion bar (12) preferably in the circumferential direction.

11. Electromechanical power-assisted steering system for a motor vehicle, comprising an upper steering shaft (3) connected to a steering wheel (2) and a lower steering shaft (4) connected to the upper steering shaft (3) via a torsion bar (12), a torque sensor unit (11) according to one of claims 1 to 10 and an electric motor (9) for assisting a steering movement introduced into the steering wheel (2) by a driver in dependence on the torque measured by the torque sensor unit (11).

12. Method for determining a torque introduced into an upper steering shaft (3) of a motor vehicle steering system, the upper steering shaft (3) being connected to a lower steering shaft (4) via a torsion bar (12), and a first inductive sensor (13) is connected to the upper steering shaft (3) for measuring the rotational position of the upper steering shaft (3), and a second inductive sensor (14) is connected to the lower steering shaft (4) for measuring the rotational position of the lower steering shaft (4), characterized in that the inductive sensors (13, 14) each have a carrier plate (15, 15') connected in a rotationally fixed manner to the corresponding steering shaft (3, 4) and a printed circuit board (18,18') which is spatially fixed with respect to the carrier plate (15,15'), a single electrically conductive track (19, 19') being arranged on the carrier plate (15, 15') and a sensing device (16, 16') with two coils (80, 81, 80', 81'), which are part of a resonant circuit, being arranged on the printed circuit board (18, 18'), the coils (80, 81, 80', 81') being arranged at an angle of 90 degrees with respect to one another and sense an electrically conductive track (19, 19'), which rotates with the corresponding steering shaft (3, 4), extends around the respective steering shaft (3, 4) and is closed on itself, in that a change in a resonant frequency of the resonant circuit is detected, and the method comprising the following further steps: • Measuring the absolute rotational position of the upper steering shaft (3) using the first inductive sensor (13), • Measuring the absolute rotational position of the lower steering shaft (4) using the second inductive sensor (14), • Calculating the angular difference between the two absolute rotational positions, • Determining the torque introduced into the upper steering shaft (3) by means of the equation: TSTW= c*δ, where c is the spring constant of the torsion bar (12) and δ is the angular difference , • Determining the angle of rotation of the corresponding steering shaft (3, 4) from the two coil signals by means of a Cordic algorithm.

13. Method according to claim 12, characterized in that the electrically conductive track (19, 19') has a wave pattern which enables absolute angles to be determined over a revolution of the steering shaft.