Drive system of a motor vehicle steering system, in particular a steer-by-wire steering system, and steer-by-wire steering system

Abstract

Drive system of a motor vehicle steering system comprising an electric motor (29) for the indirect or direct displacement of a steering rod (24), wherein the electric motor (29) has a rotor with a rotor shaft (29A) to which a pinion (301) is rotatably connected at one end of which a magnet (50) is non-rotatably connected at the other end of which a magnet (50) is non-rotatably connected, wherein a measuring device (40, 80) is further provided at a distance (A) from the magnet (50), which comprises a printed circuit board (80) and a rotor position sensor (40) arranged thereon, which is arranged such that it generates position information for the rotor based on the respective current position of the magnet (50), characterized in that at least a first and a second measuring coil (70A, 70B) are provided at a distance (A) from the magnet (50), which are arranged at an angle of approximately 90 degrees or exactly 90 degrees,arranged in relation to each other and designed to detect induced voltage signals of sine and cosine angles (Uindsin, Uindcos) due to the changing magnetic flux of the magnet (50) during operation, and furthermore a control unit (60) is provided which is connected to the measuring device (40, 80) and the measuring coils (70A-70D) such that the control unit (60) , - receives the position information from the rotor position sensor (40) and processes it in such a way that the control unit (60) determines rotor position voltage signals of sine and cosine angles (U_RPSsin, U_RPScos), and - receives the induced voltage signals (Uindsin, Uindcos) of the measuring coils (70A-70D) and combines them with the rotor position voltage signals (U_RPSsin, U_RPScos) in such a way that the control unit (60) determines an output signal (X) which is directly proportional to the speed of the electric motor (29).

Description

[0001] The present invention relates to the field of controlling electric motors for steering systems of vehicles, in particular rear axle steering systems with steer-by-wire technology.

[0002] Steering systems in motor vehicles are known to include a steering wheel, a steering shaft, a steering gear, and a steering linkage for converting the steering angle specified by the driver into a steering angle of the steerable wheels. So-called steer-by-wire steering systems are also known, which are used, for example, in rear-axle steering systems. In these systems, the steering movement is converted electromechanically by means of an electric motor that adjusts the steering angle. DE 10 2014 206 934 A1 discloses an actuator with a spindle drive with a trapezoidal thread for a rear-wheel steering system in a motor vehicle.

[0003] Permanent magnet synchronous motors (PSMs) are frequently used as electric motors to drive steering systems, particularly steer-by-wire systems. A problem with these PSMs is that they generate torque fluctuations due to a non-sinusoidal (magnetic) flux distribution, the cogging torque of the electric motor, and magnetic saturation effects. Such torque fluctuations lead to speed variations of the electric motor and can cause vibrations in the drive unit or steering gear. This can affect the durability of the components used.

[0004] To measure motor oscillations of an electric motor, it is necessary to measure torque or speed fluctuations and feed these fluctuations as input to a control algorithm. For this to work, the fluctuations must be recorded as accurately as possible.

[0005] The problem is that torque fluctuations can only be detected with an additional sensor. The rotor position of electric motors is often measured using AMR (Anisotropic Magnetoresistance) or GMR (Giant Magnetoresistance) position sensors. This involves measuring the sine and cosine angles based on resistance, i.e., generating a sine / cosine voltage output. The rotor speed (rotational speed) is then determined using the time derivative of the position signal. The issue is that speed fluctuations are difficult to detect with these sensors due to low harmonic signal amplitudes, low resolution of the analog-to-digital converter, and poor signal-to-noise ratio (SNR).

[0006] From DE 10 2018 204 901 A1, a sensor device for detecting at least one position information of a movable rotor of an electric motor, in particular of a steering system, is known, with at least two position sensor units operatively connected to the rotor for detecting the position information of the rotor, wherein the position sensor units have different measuring principles for detecting the position information.

[0007] From DE 103 34 869 B3 a rotary angle sensor is known with a rotatable shaft, as well as a magnet coupled to the rotatable shaft and a magnetically sensitive sensor element, which generates a sinusoidal and a cosinusoidal output signal depending on the relative angle of rotation between the magnet and the sensor, and with an evaluation unit that generates a signal corresponding to the angle of rotation from the output signals.

[0008] Further state of the art can be found in documents DE 600 34 471 T2, DE 10 2019 125 883 A1, DE 10 2009 027 191 A1, KR 10 2009 0 035 844 A, DE 10 2019 204 913 A1 or DE 10 2019 207 070 A1.

[0009] It is therefore an object of the invention to provide an improved drive system for a steering system of a motor vehicle, in particular a steer-by-wire steering system, which brings about an improvement in the steer-by-wire steering.

[0010] This task is solved by the features of independent claims. Advantageous embodiments are the subject of dependent claims.

[0011] A drive system for the steering of a motor vehicle, in particular a steer-by-wire steering system, is proposed, comprising an electric motor for the indirect or direct displacement of a steering rod. The electric motor has a rotor with a rotor shaft, to one end of which a pinion is rotatably connected, and to the other end of which a magnet is non-rotatably connected. A measuring device is also provided at a distance from the magnet, comprising a printed circuit board and a rotor position sensor arranged thereon, which is positioned such that it generates position information for the rotor based on the current position of the magnet. At least a first and a second measuring coil are provided at a distance from the magnet, arranged at an angle of approximately 90 degrees, preferably exactly 90 degrees, to each other.They are designed to detect induced voltage signals of sine and cosine angles due to the changing magnetic flux of the magnet during operation.

[0012] The proposed arrangement of the measuring coils results in improved determination of the rotor position.

[0013] In one version, a third and a fourth measuring coil are provided, which are arranged at an angle of 90 degrees to each other.

[0014] In one embodiment, the first and third measuring coils and the second and fourth measuring coils each detect the same angle and are arranged on opposite sides of the rotor position sensor.

[0015] In one embodiment, the measuring coils covering one angle overlap, at least partially, the measuring coils covering the other angle.

[0016] In one version, the measuring coils are arranged on the circuit board and adjacent to the rotor position sensor.

[0017] In one embodiment, the measuring coils are arranged on the circuit board and adjacent to the rotor position sensor, with the first and third measuring coils arranged in a first plane and the second and fourth measuring coils arranged in a parallel second plane.

[0018] In one version, the measuring coils are formed as air coils or as windings integrated into a circuit board.

[0019] In one embodiment, a control unit is further provided which is connected to the measuring device and the measuring coils in such a way that the control unit receives the position information of the rotor position sensor and processes it in such a way that the control unit determines rotor position voltage signals of sine and cosine angles and receives the induced voltage signals of the measuring coils and combines them with the rotor position voltage signals in such a way that the control unit determines an output signal which is directly proportional to the speed of the electric motor.

[0020] In one embodiment, the output signal is obtained by the control unit multiplying the rotor position voltage signal of the sine angle with the induced voltage signal of the cosine angle and subtracting from this the rotor position voltage signal of the cosine angle multiplied by the induced voltage signal of the sine angle: X=U_RPSsin*U_indcos-U_RPScos*UVU_indsin.

[0021] Furthermore, a steer-by-wire steering system for a motor vehicle is proposed, comprising the drive system.

[0022] A steering system in a motor vehicle must generally be able to handle the high forces in the vehicle's chassis that act on the steered axle and thus on the wheel steering due to lateral forces, for example, during cornering or lateral acceleration. These high forces, such as 5 to 15 kN, act equally on a steer-by-wire steering system and the associated actuator, which initiates the steering movement. A wheel steering system is required to be designed to guide the wheel so that the set steering angle, and therefore the intended driving path, can be maintained. This means that a steering angle must always be maintained when high lateral and / or transverse forces, and the resulting forces and moments, act on the steering system. This is particularly the case while driving. The spindle of an actuator is therefore designed as a wheel-guiding component.In the event of an actuator failure, it must have a way to maintain the wheel steering angle in its current position. For example, in a steer-by-wire system, which is an auxiliary steering system on the rear axle in addition to the standard front axle steering, a return to a steering angle of 0 degrees (i.e., in the direction of the vehicle's longitudinal axis) may be necessary in the event of a malfunction. This steering angle must then also be maintained after the return, because otherwise the steering angle at the rear axle could change uncontrollably due to dynamic influences, making the vehicle more difficult to control.

[0023] A steer-by-wire steering system is a mostly electromechanical unit decoupled from a mechanical steering handle, such as a steering wheel. Based on steering signals and one or more parameters, such as vehicle speed, steering wheel angle, current steering angles at the front and / or rear axles, yaw acceleration, and / or lateral acceleration of the vehicle, etc., steering signals are generated in a control unit. The steering movement is carried out by at least one actuator of the steer-by-wire system, which receives steering signals from the control unit. For example, a spindle or steering rod can be axially displaced in the actuator by means of a spindle drive, which is directly or indirectly articulated to wheel carriers.

[0024] Further features and advantages of the invention will become apparent from the following description of exemplary embodiments of the invention and from the figures, which illustrate details of the invention. The individual features can be implemented individually or in any combination in a variant of the invention.

[0025] Preferred embodiments of the invention are explained in more detail below with reference to the accompanying figures. Fig. Figure 1 shows a schematic top view of a rear axle of a vehicle. Fig. Figure 2 shows a schematic side view of a drive system for operating a steering system according to an embodiment of the invention. Fig. Figure 3 shows a schematic top view of an end region of the electric motor of the drive system according to one embodiment of the invention. Fig. Figure 4 shows a diagram with rotor position signals. Fig. Figure 5 shows a diagram with induced voltage signals through the measuring coils. Fig. Figure 6 schematically shows the logical connection of the induced voltage signals and the rotor position signals to the output signal according to one embodiment of the invention.

[0026] In the following figure descriptions, identical elements or functions are marked with the same reference symbols.

[0027] In the schematic representation according to Fig. Figure 1 shows a vehicle axle in plan view, here depicted as a rear axle with a subframe 2, which is attached to or forms part of a vehicle body and is connected to the body of a motor vehicle. However, the invention is not limited to a rear axle. The wheels 5 and 6 are articulated to the subframe 2 by means of links 3, 4 as part of a wheel suspension. An actuator 10 of a steer-by-wire steering system 12 is arranged on the subframe 2. The actuator 10 is attached to the subframe 2 by its housing 22. In the present embodiment, the actuator 10 has a continuous steering rod 24, which passes through the housing 22 of the actuator 10. The drive motor, in the form of an electric motor 29, is arranged parallel to the steering rod 24, but can also be designed in another way, e.g., as a hollow shaft motor.At the ends of the steering rod 24, tie rods 23, 25 are articulated via joint connections 27, 28, which are articulated at their ends furthest from the actuator 10 to a wheel carrier 7 of the wheels 5 and 6. The axial displacement of the steering rod 24 is achieved by a rotary / translational converter, which can, for example, be designed as a lead screw of a spindle drive. When the electric motor or drive motor 29 rotates, a spindle nut, which is rotatably mounted in the housing 22, is set into slip-free rotation about its longitudinal axis by means of a drive belt. The spindle nut has an internal thread that engages with the external thread of a spindle (= steering rod 24) and forms a lead screw.Depending on the direction of rotation of the spindle nut, the steering rod 24, which is secured against rotation, is linearly displaced in one direction or the other along its longitudinal axis, depending on the direction of rotation of the electric motor 29. Ideally, the longitudinal axes of the spindle nut and the spindle coincide. It is obvious that an axial displacement, i.e., a displacement of the steering rod 24 along its longitudinal axis in one direction or the other, results in a change in the wheel steering angle 8, 9, because the tie rods 23, 25 form a positive connection between the wheel 5, 6 or wheel carrier 7 and the actuator 10. For steering the wheels 5, 6, these are pivotally connected to the wheel suspension 3, 4 via the wheel carrier 7 so as to be rotatable about their vertical axis. In other words, the actuator 10 is a device that enables the operation of the steering 12.

[0028] The steering gear 300 is preferably designed as a spindle drive for the actuator 10. The electric motor 29 drives a pinion 301 of the steering gear 300, which in turn drives a pinion 302 without slippage by means of a toothed belt 303, as shown in Fig. Figure 2 is shown schematically. The pinion 302 is rotationally fixed (pressed onto) a spindle nut 304, which is mounted stationary in a housing 322. The spindle, in the form of a steering rod 24, is axially displaceable along its longitudinal axis within the housing 322 and its internal thread engages with the external thread of a spindle, thus forming a drive thread. When the spindle nut is rotated, the rotational movement is converted into a translational movement by means of the drive thread of the spindle drive, and the spindle, which is secured against rotation and functions as a steering rod 24, is displaced axially, i.e., along its longitudinal axis. The steering rod 24 is articulated at at least one end to a wheel carrier by means of a steering linkage, such as a tie rod. The axial displacement of the steering rod or spindle causes the wheel carrier to rotate about its vertical axis.The wheel, which is rotatably mounted on at least one wheel carrier of an axle, can thus be steered, whereby a change in the position of the steering rod causes a change in the steering angle of the wheel or the vehicle axle. The actuator 10, which enables the steering to be operated, is a rotary / translational converter.

[0029] As mentioned in the introduction, in automotive applications the rotor position of electric motors is often detected using AMR (Anisotropic Magnetoresistance) or GMR (Giant Magnetoresistance) position sensors (resistance-based measurement of sine and cosine angles, i.e., sine / cosine voltage output) by means of an actuator that effects the positioning or steering movement. Such sensors are also referred to as rotor position sensors.

[0030] Steering refers specifically to a steer-by-wire steering system for an axle, where the axle can be a front axle, a rear axle, or an axle located between the front and rear axles of a motor vehicle. The steering system can be used for a motor vehicle intended, for example, for transporting people and, additionally or alternatively, goods.

[0031] A steer-by-wire steering system according to Fig. 1 has a steering rod 24 and a in Fig. Figure 2 schematically depicts a steering gear 300 (rotational / translational gear) which is operatively connected to the electric motor 29 and, in a known manner, converts the rotational force output by the electric motor 29 into a translational force to the steering rod 24 and thus to the wheels 5, 6 to change the wheel steering angle 8, 9 by means of a toothed belt drive or spindle drive. The electric motor 29 has a stator (not shown) and a rotor (not shown) with a rotor shaft 29A. Fig. Figure 2 shows a detailed view of the electric motor 29 according to Fig. 1, whose rotor position (rotor angle) can be determined by means of a rotor position sensor 40, which is in signal communication with a control unit 60 of the motor vehicle. The rotor position can be stored, for example, as sine and cosine values, which are then transmitted to the control unit 60 for calculating the position. However, it can also be provided that the rotor position sensor 40 determines the position itself and then transmits it to the control unit 60.

[0032] The rotor position is determined by connecting a magnet 50 to the rotor shaft 29A at one end of the shaft in a rotationally fixed manner. A measuring device is also provided at a distance from the magnet 50. This device comprises a printed circuit board 80 and a rotor position sensor 40 arranged thereon. The rotor position sensor 40 is positioned such that it generates position information for the rotor based on the current position of the magnet 50, as is known from the prior art. The flat side of the printed circuit board 80 is therefore advantageously arranged orthogonally to the rotor shaft 29A.

[0033] As already mentioned, absolute positioning accuracy in actuators for steering systems, such as steer-by-wire systems, and especially for rear-wheel steering, is a crucial requirement, since the steering rod 24 can only be adjusted via the electric motor 29 and its associated gearbox, as there is no mechanical connection to a steering wheel in a steer-by-wire system. Accurate measurement of the zero position of the actuator, and thus of the steering rod 24, is therefore of central importance. Even after a system failure (error or power outage) or a (regular) restart, the absolute position of the rotor of the electric motor 29, and thus of the steering rod 24, must be reliably detected to enable precise position control of the steering rod 24 and, consequently, the associated wheel steering angles 8, 9 on the respective axle during continued operation. The exact position can be calculated from the rotor position and the gearbox ratio.notice.

[0034] One problem with the currently used rotor position sensors 40 is that speed fluctuations are difficult to detect due to low harmonic signal amplitudes, low resolution of the analog / digital converter ADC and weak SNR (signal-to-noise ratio).

[0035] To solve this problem, it is proposed to provide at least two measuring coils 70A-70D, as described below, in addition to the rotor position sensors 40. These coils enable the direct measurement of speed fluctuations of the electric motor 29 based on the induced voltage Uindsin, Uindcos generated by the magnet 50. The induced voltage Uind (Uindsin, Uindcos, depending on the angle considered) can be measured due to the varying magnetic flux linkage, which is represented as: Uind=dψdt

[0036] Here, ψ is the magnetic flux of magnet 50.

[0037] To measure the rotor position, a magnet 50 is provided at the end of the rotor shaft 29A of the electric motor 29. This magnet is advantageously designed as a permanent magnet. It is further advantageously designed as a disc magnet. The magnet 50 has at least one north pole N and at least one south pole S. Fig. Figure 2 shows a north pole and a south pole. Furthermore, a measuring device is provided at a distance A from magnet 50, which is located in the Fig. In the embodiment shown in Figure 2, the rotor position sensor 40 is formed as a printed circuit board 80 with a rotor position sensor 40 mounted on it. The rotor position sensor 40 points towards the magnet 50 and, as is known in the prior art, can detect the orientation of an existing magnetic field by resistance-based measurement of the sine and cosine angles and output them as voltage signals U_RPSsin and U_RPScos. The rotor position sensor 40 is operatively connected via the printed circuit board 80 to a control unit 60, which receives the voltage signals U_RPSsin and U_RPScos from the rotor position sensor 40 and processes them in such a way as to determine a rotor position (in the form of an angle φ), as is also known in the prior art.

[0038] The rotor angle φ is calculated using formula (1): φ=arctan(URPSsinURPScos)

[0039] As already mentioned, the harmonic amplitudes of the voltage signals U_RPSsin and U_RPScos of the rotor position sensor 40 are very small, which in Fig. Figure 4 is shown as an example. Furthermore, the SNR (signal-to-noise ratio) is weak and the analog-to-digital converter (ADC) (in Fig. (shown in Figure 6), which converts the analog voltage signals U_RPSsin and U_RPScos into digital voltage signals U_RPSsin and U_RPScos, has a limited resolution. All of this means that the harmonic amplitudes of the voltage signals U_RPSsin and U_RPScos, and thus the speed fluctuations (more precisely, rotational speed fluctuations of the electric motor) of the electric motor 29, are difficult to detect and measure.

[0040] In order to better measure the existing speed fluctuations of the electric motor 29, at least two measuring coils 70A-70D arranged at a 90-degree angle to each other are provided in addition to the rotor position sensor 40, as indicated above, as shown in Fig. Figure 3 shows how to obtain two induced voltage signals with a 90-degree offset. These 70A-70D measuring coils measure induced voltages due to varying magnetic flux linkage. Fig. Figure 5 shows a diagram representing the induced voltages Uindsin and Uindcos. Here, it can be seen that the fluctuations are more pronounced than in the curves in [reference missing]. Fig. 4. The angle is preferably exactly 90 degrees, but can also be approximately 90 degrees. In the following description, an angle of exactly 90 degrees is assumed, as shown in the figures.

[0041] According to the invention, a signal, hereinafter referred to as output signal X, is provided which is directly proportional to the rotational speed of the electric motor 29. This output signal X is obtained by combining the voltage signals Uindsin, Uindcos of the measuring coils 70A-70D with the voltage signals U_RPSsin and U_RPScos detected by the rotor position sensor 40, which are processed by the analog-to-digital converter ADC (in Fig. 6) are converted into digital voltage signals U_RPSsin and U_RPScos, and combined as shown in Fig. 6 shown. The combination is carried out according to formula (2): X=URPSsin∗Uindcos−URPScos∗Uindsin

[0042] This yields an output signal X that is directly proportional to the rotational speed of the electric motor 29. The output signal X is used to determine the strength of harmonic oscillations on the rotor position voltage signals U_RPSsin and U_RPScos. The advantage of this output signal X is that the harmonic content in the signals is relatively high, resulting in a better signal-to-noise ratio (SNR) and improved signal resolution for the analog-to-digital converter. This allows for more accurate measurement of speed fluctuations.

[0043] The output signal X can be easily processed further, e.g. by applying an FFT (Fast Fourier Transform) to obtain the necessary information about the average speed of the electric motor 29 and the speed fluctuations. These are then used as input variables in the control algorithm for the subsequent control process.

[0044] The at least two measuring coils 70A-70D are arranged at a distance A from the magnet 50 and adjacent to the rotor position sensor 40, as shown in Fig. 2 schematically indicated by means of a preferred embodiment and in Fig. Figure 3 shows four measuring coils 70A-70D. The rotor position sensor 40 and measuring coils 70A-70D are arranged relative to the magnet 50 in such a way that they detect the magnetic field.

[0045] The measuring coils 70A-70D are arranged such that (each) two measuring coils 70A, 70B and 70C, 70D (more precisely, their windings) are arranged at an angle of 90 degrees to each other. Thus, two (or four) voltage signals of the voltage Uindsin, Uindcos induced in the measuring coils 70A-70D by the magnetic field are obtained with a 90-degree offset from each other, which are directly proportional to the rotational speed (angular velocity ω) of the electric motor 29, as can be seen from formula (3): Uind_sin=dψsindt=ωψcos(φ) Uind_cos=dψcosdt=−ωψsin(φ)

[0046] Here, ψ is the magnetic flux of magnet 50 and φ is the rotor position (in the form of an angle), also known as the rotor angle.

[0047] In an advantageous embodiment, the at least two measuring coils 70A-70D are arranged on the same circuit board 80 as the rotor position sensor 40 and are integrated into the circuit board 80 as conductor tracks (planar coils).

[0048] If four measuring coils 70A-70D are provided, measuring coils 70B and 70D are arranged oriented 180 degrees to measuring coils 70A and 70C. One pair of measuring coils 70A and 70C or 70B and 70D detects the sine angle, and the other pair of measuring coils 70B and 70D or 70A and 70C detects the cosine angle. The measuring coils 70A and 70C, and 70B and 70D, which detect the same angle (i.e., cosine or sine), are arranged next to each other (and on opposite sides of the rotor position sensor 40). Measuring coils 70A and 70C can at least partially overlap measuring coils 70B and 70D, as shown in [reference missing]. Fig. 3 is indicated, although this is not strictly necessary. Overlapping the measuring coils 70A-70D has the advantage that the largest possible area is covered by the measuring coils 70A-70D, thus capturing as much magnetic flux as possible. Since currently used printed circuit boards 80 are multilayered (typically 4, 6, or 8 layers), it is not a problem to place the measuring coils 70A-70D on different layers.

[0049] It is important that the rotor position sensor 40 is not covered. The measuring coils 70A, 70C and the measuring coils 70B, 70D can also be arranged in different parallel planes (one above the other), especially if they overlap.

[0050] The rotor position sensor 40, which is implemented as an integrated circuit (IC), and the measuring coils 70A-70D are advantageously arranged on the same circuit board 80, with the rotor position sensor 40 positioned in the center. Therefore, it is not possible to also place the measuring coils 70A-70D in the center. This area is therefore omitted.

[0051] In an alternative version, the measuring coils 70A-70D are not located on the same circuit board 80 as the rotor position sensor 40, but on separate circuit boards.

[0052] In another alternative version, the measuring coils 70A-70D are not integrated or printed as planar coils on the circuit board 80, but are attached to the circuit board 80 as coils wound with copper wire, or as additional components such as SMD components, e.g. soldered on. Each coil can be designed as either an air-core coil or a coil with a soft magnetic core.

[0053] The advantage of using four 70A-70D measuring coils is that it results in an increased induced voltage Uindsin, Uindcos, more precisely a doubling due to the arrangement. This, in turn, facilitates the measurement and determination of speed fluctuations. Furthermore, the symmetrical design, as in Fig. Figure 3 shows the reduced influence of mechanical tolerances between magnet 50 and measuring coils 70A-70D.

[0054] The proposed extension of known rotor position sensors 40 by at least two measuring coils 70A-70D, as described, and the described combination of input variables U_RPSsin, U_RPScos and Uindsin, Uindcos, enables accurate and robust measurement of speed fluctuations. This results in more precise input variables for the control algorithm for the electric motor 29, thereby improving the control and reducing vibration and noise generation due to torque fluctuations and thus speed fluctuations of the electric motor 29.

[0055] The electric motors 29 used for the proposed drive system are advantageously electric motors 29 with a high cogging torque, which is used to keep the electric motor 29 stationary even when external forces are applied to the steering rod 24 in the event of an interruption of the power supply. The magnitude of the cogging torque of the electric motor 29 is designed, depending on the overall system (i.e., vehicle, transmission, electric motor 29, and associated components), such that when the electric motor 29 is stationary, any movement of the system (displacement of the steering rod 24) caused by external forces can be reliably suppressed, i.e., no rotor movement occurs.

[0056] The cogging torque of an electric motor 29 is the force required to overcome the interaction or attractive force between the permanent magnets of the rotor and the stator slots (iron core of the motor winding). The cogging torque is also referred to as cogging torque in English.

[0057] A control unit 60 is a processing unit designed to receive signals such as voltage signals, position signals from sensor units and other components of the drive system or the vehicle, and to process them in such a way that a signal is output which can be used to control a component, in particular a steering system such as a steer-by-wire system. The control unit 60 can contain calculation programs as algorithms which are executed to generate the desired output signals from input signals.

[0058] The object of the invention is to utilize induced voltages resulting from a change in the magnetic field. A design objective is to maximize the induced voltage at the measuring coils 70A-70D. The induced voltage is measured to determine the angle change of the rotor. A high induced voltage is advantageous because it can then be measured more accurately by downstream electronics. By using planar coils, changes in the applied magnetic field are measured directly (without abrupt remagnetization) by measuring the proportional induced voltage at the measuring coils 70A-70D. This allows conclusions to be drawn about the rotational speed. The induced voltage is proportional to the size of the measuring coils 70A-70D (window area or "distance" A) and the flux ψ of the magnet 50 enclosed within them.By using two measuring coils 70A, 70B or 70C and 70D, the enclosed flux is doubled, as both poles of the magnet 50 are utilized. This also doubles the induced voltage. A further advantage is the symmetrical design with a total of four measuring coils 70A-70D, which utilize two coils arranged at 90 degrees to each other. These two coil pairs are used to generate two induced voltages for evaluation, similar to the sine / cosine signals. By combining both measurement signals, a speed fluctuation can be detected at any given time. Reference sign 2 subframes, vehicle body 3, 4 handlebars 5, 6 wheel 7 bike carriers 8, 9 Wheel steering angle 10 Actuator 12 Steering, steer-by-wire steering 22 cases 23, 25 tie rod 24 handlebar 27, 28 Joint connections 29 Electric motor 29A Rotor shaft 40 Rotor position sensor 50 Magnet North Pole, South Pole 60 Control unit 70A-70D measuring coils 80 circuit boards 300 spindle drive 301 sprocket 302 pinion 303 belts 304 Spindle nut 322 Cases A distance R axis of rotation RPS signal from the rotor position sensor U_RPSsin, U_RPScos Rotor position voltage signals (of 4) Uindsin, Uindcos induced voltage signals X output signal

Claims

[1] Drive system of a steering system of a motor vehicle, comprising an electric motor (29) for the indirect or direct displacement of a steering rod (24), wherein the electric motor (29) has a rotor with a rotor shaft (29A) to which a pinion (301) is rotatably connected at one end of which a magnet (50) is non-rotatably connected at the other end of which a magnet (50) is connected, wherein a measuring device (40, 80) is further provided at a distance (A) from the magnet (50), which comprises a printed circuit board (80) and a rotor position sensor (40) arranged thereon, which is arranged such that it generates position information for the rotor based on the respective current position of the magnet (50), characterized by, that at a distance (A) from the magnet (50) at least a first and a second measuring coil (70A, 70B) are provided, which are arranged at an angle of approximately 90 degrees or exactly 90 degrees to each other and are intended for detecting induced voltage signals of sine and cosine angles (Uindsin, Uindcos) due to the changing magnetic flux of the magnet (50) during operation, and wherein a control unit (60) is further provided which is connected to the measuring device (40, 80) and the measuring coils (70A-70D) such that the control unit (60) - receives the position information from the rotor position sensor (40) and processes it in such a way that the control unit (60) determines rotor position voltage signals of sine and cosine angles (U_RPSsin, U_RPScos), and - receives the induced voltage signals (Uindsin, Uindcos) of the measuring coils (70A-70D) and combines them with the rotor position voltage signals (U_RPSsin, U_RPScos) in such a way that the control unit (60) determines an output signal (X) which is directly proportional to the speed of the electric motor (29). [2] Drive system according to claim 1, wherein a third and a fourth measuring coil (70C, 70D) are provided which are arranged at an angle of 90 degrees to each other. [3] Drive system according to claim 2, wherein the first and third measuring coils (70A, 70C) and the second and fourth measuring coils (70B, 70D) each detect the same angle and are arranged on opposite sides of the rotor position sensor (40). [4] Drive system according to one of the preceding claims, wherein the measuring coils (70A, 70C; 70B, 70D) covering one angle overlap at least partially the measuring coils (70A, 70C; 70B, 70D) covering the other angle. [5] Drive system according to one of the preceding claims, wherein the measuring coils (70A-70D) are arranged on the circuit board (80) and adjacent to the rotor position sensor (40). [6] Drive system according to one of claims 2, 3 or 4, wherein the measuring coils (70A-70D) are arranged on the circuit board (80) and adjacent to the rotor position sensor (40) and the first and third measuring coils (70A, 70C) are arranged in a first plane and the second and fourth measuring coils (70B, 70D) are arranged in a parallel second plane. [7] Drive system according to one of claims 1 to 4, wherein the measuring coils (70A-70D) are formed as air coils or as windings integrated in a circuit board. [8] Drive system according to one of the preceding claims, wherein the output signal (X) is obtained by the control unit (60) multiplying the rotor position voltage signal of the sine angle (U_RPSsin) with the induced voltage signal of the cosine angle (Uindcos) and subtracting from it the rotor position voltage signal of the cosine angle (U_RPScos) multiplied by the induced voltage signal of the sine angle (Uindsin): X=URPSsin∗Uindcos−URPScos∗Uindsin. [9] Drive system according to one of the preceding claims, configured to drive a steer-by-wire steering system (12). [10] Steer-by-wire steering (12) for a motor vehicle, comprising the drive system according to one of the preceding claims.

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