Steering gear with a highly integrated steering angle sensor, and method for operating the same

Abstract

The invention relates to a steering gear (100) having a highly integrated steering angle sensor (102), wherein an annular, multi-pole magnetic transmitter (136) of the steering angle sensor (102) is provided on a surface (200) of a rotational component (106) of the steering gear (100), and a magnetic field direction sensor (140) of the steering angle sensor (102) is rotationally fixed in the steering gear (100) so as to form an air gap (204) between the sensor and the transmitter (136). The transmitter (136) consists of at least one layer of a magnetizable material provided on the surface (200), and the magnetic poles of the transmitter (136) are formed by a surface magnetization (300) of the material when the material is solidified. A controller (146) of the steering angle sensor (102) is configured to determine, using a signal (144) of the magnetic field direction sensor (140), the angular position (104) of the rotational component (106) and, using the angular position (104) and the transmission ratio (108) between the rotational component (106) and a translational component (110) of the steering gear (100), the current steering angle (116) of the steering gear (100).

Description

[0001] Description

[0002] title

[0003] Steering gear with a highly integrated steering angle sensor and method for operating it

[0004] Field of invention

[0005] The invention relates to a steering gear with a highly integrated steering angle sensor, a method for operating a corresponding steering gear, and a corresponding computer program product.

[0006] State of the art

[0007] The steering angle of a vehicle's steered wheels can be detected by a steering angle sensor. The steering angle sensor can be mounted on the vehicle's steering column. The sensor detects the angular position of the vehicle's steering wheel, and the actual steering angle can be calculated using a known gear ratio of the vehicle's steering system.

[0008] Since the steering wheel can usually be turned more than a full rotation to achieve maximum wheel lock, the steering column's angle cannot be unambiguously converted into the steering angle, especially after a power interruption. To address this, the steering angle sensor can incorporate a revolution counter. This counter provides additional information that allows for a clear correlation between the steering angle and the steering column's angle.

[0009] Disclosure of the Invention Against this background, the approach presented here comprises a steering gear with a highly integrated steering angle sensor, a method for operating such a steering gear, and a corresponding computer program product according to the independent claims. Advantageous further developments and improvements of the approach presented here will become apparent from the description and are described in the dependent claims.

[0010] Advantages of the invention

[0011] In a steer-by-wire vehicle, i.e., a vehicle without a steering column or a mechanical connection between the steering wheel and the steering gear, it is not possible to determine the steering angle via the angular position of the steering column. In this case, for example, the linear position of a steering tie rod can be detected using a linear sensor.

[0012] In the approach presented here, the linear position of the tie rod is determined via the angular position of a rotatable component of the steering gear and a rotational-translational transmission ratio between the component and the tie rod. To detect the angular position, the field direction of a magnetic field emanating from the component is measured and evaluated. The magnetic field exhibits several changes between north and south poles over one rotation of the component.

[0013] The magnetic field is generated by a sensor mounted on the component. This sensor only becomes a multipole magnet during its manufacturing process. External magnetic fields are applied to a magnetizable material within the sensor, causing particles in the material to align with the magnetic fields. The material solidifies or hardens while the magnetic fields are applied. During solidification or hardening, an image of these magnetic fields is "frozen" within the sensor.

[0014] The approach presented here eliminates the need for an additional linear sensor on the tie rod. The rotatable component is an existing part of the steering system, and its angular position is directly coupled to the linear position of the tie rod via the rotational-translational transmission ratio. As a first step, a steering gear with a highly integrated steering angle sensor is proposed. A ring-shaped, multipole magnetic sensor of the steering angle sensor is arranged on the surface of a rotating component of the steering gear, and a magnetic field direction sensor of the steering angle sensor is fixedly mounted within the steering gear with an air gap to the sensor. The sensor consists of at least one layer of magnetizable material arranged on its surface, and the magnetic poles of the sensor are formed by surface magnetization of the material during solidification.wherein a control unit of the steering angle sensor is configured to determine an angular position of the rotating component using a signal from the magnetic field direction sensor and to determine a current steering angle of the steering gear using the angular position and a transmission ratio between the rotating component and a translational component of the steering gear.

[0015] According to a second aspect, a method for operating a steering gear according to the first aspect is proposed, wherein the angular position of the rotary component of the steering gear is determined using the signal of the magnetic field direction sensor, and the steering angle is determined using the angular position and the transmission ratio between the rotary component and the translational component.

[0016] Ideas for embodiments of the present invention can be considered to be based, among other things, on the thoughts and findings described below.

[0017] A rotary-translational transmission ratio of a steering gear is defined, for example, by the thread pitch. The thread can be coupled to the tie rod or mounted directly on it. The thread pitch establishes a direct relationship between a change in the angle of a nut engaging the thread and a change in the thread's position. The nut is driven by a steering gear's drive motor. The rotary-translational transmission ratio can also be determined by the dimensions of a pinion engaging a rack. The rack can be coupled to the tie rod or mounted directly on it. Here, too, a direct relationship exists between a change in the pinion's angle and a change in the rack's position.

[0018] A magnetic field direction sensor can represent the direction of a magnetic field passing through it as an electrical signal. The sensor can output this direction as a multidimensional vector. Preferably, the angle of the (differential) magnetic field direction is determined and output as an angle signal to a control unit.

[0019] An air gap can be defined as a path consisting of a material with low magnetic permeability, such as air. The air gap can also be a partition made of plastic. Furthermore, the air gap can run through different materials.

[0020] The arrangement of ferromagnetic material on the back of the magnetized material can increase the useful field on the other side and have a beneficial effect on the amplitude of the difference field.

[0021] The magnetic field direction sensor can have at least two sensor elements arranged at a predefined distance from each other. Due to their distance, the sensor elements can each detect slightly different magnetic field directions. The control unit can be configured to compensate for a homogeneous interference field at the sensor elements by differentially evaluating the detected magnetic field directions. Differential evaluation calculates the difference between the vectors output by the sensor elements. A homogeneous magnetic field can be an external interference field. This interference field alters the magnetic field direction equally at both sensor elements. By calculating the difference, the equal components of the vectors cancel each other out, leaving only the difference between the vectors. This difference is then directly dependent on the difference between the detected magnetic field directions.The difference in magnetic field directions depends on the angular position of the sensor. The steering angle sensor can be mounted on another rotating component of the steering gear with a fixed rotational speed ratio to the first rotating component. This position sensor has a rotationally fixed position sensor. The control unit can be configured to further determine the steering angle using the rotational speed ratio and a vernier calculation between the position of the position sensor and the angular position of the first rotating component. The rotating component, i.e., the nut on the thread or the pinion on the rack, can complete a multitude of revolutions along the length of the thread or rack. Without additional information, only a change in the steering angle, i.e., a relative steering angle, can be detected. An absolute steering angle can be determined, for example, by observing the relative steering angle.This means that the absolute steering angle cannot be determined after an interruption of the power supply. The power supply is interrupted, for example, when the vehicle is switched off. Only when a reference point on the thread or rack is detected can the absolute steering angle be determined again by observing the relative steering angle.

[0022] Here, the additional information recorded is the current rotation of the nut or pinion. This information remains available even after a power interruption. This detection is performed using the vernier principle. The vernier principle involves detecting the position of another rotatable component of the steering gear. This component is coupled to the nut or pinion via a fixed rotational ratio. This rotational ratio, combined with the position of the other component and its angular position, results in a unique combination of values ​​that can be unambiguously assigned to the respective rotation of the nut or pinion.

[0023] The position sensor can be a rotor position sensor of the steering gear's drive motor. The rotor position sensor is required for the operation of the drive motor and is therefore already present. The drive motor is coupled to the rotating component via a reduction gear. The reduction gear defines a speed ratio between the two components. A suitable design of the reduction gear results in a unique sequence of value combinations that allows for the determination of the absolute steering angle.

[0024] The sensor can be located on the surface of a pulley to drive a tie rod nut that engages in a thread of the steering gear's tie rod. A pulley can be part of a reduction gear between the drive motor and the drive nut. The pulley can be rotationally fixed to the drive nut. For example, the pulley can have internal teeth that engage with corresponding external teeth on the drive nut. The drive nut can be a ball screw nut, and the thread can then be a ball screw. The drive nut and the thread can form a ball screw drive.

[0025] The magnetic field direction sensor can comprise a first sensor arrangement with at least one sensor element and at least one redundant second sensor arrangement with at least one further sensor element. The sensor arrangements can be spatially separated from each other. One sensor arrangement can be housed in its own enclosure. The sensor arrangement can be in the form of a chip or an integrated circuit. The magnetic field direction sensor can be distributed across multiple redundant chips or integrated circuits. The sensor arrangements can, for example, be spaced so far apart that one sensor arrangement is positioned above a boundary between two magnetic poles of the sensor, while the other sensor arrangement is positioned centrally above a magnetic pole of the sensor. In this case, the sensor arrangements detect maximally different magnetic field directions.By comparing the signals from both sensor arrays, a fault can be easily detected. For example, a fault can be detected if the spatially separated sensor arrays detect magnetic field directions that are too similar.

[0026] The magnetizable material can be a polymer-bonded magnetic material. The material can be thermoplastic and injection-molded onto the component's surface. For this purpose, the component can, for example, be placed in an injection mold containing strong magnets. The magnets can be electromagnets or permanent magnets. As the mold cavity of the injection mold is filled, the magnets magnetize the magnetizable material to the alternating magnetic poles. When the component with the molded-on sensor is removed from the injection mold, the magnetic material is no longer plastically deformable, and the magnetic poles are permanently fixed within the material.

[0027] The penetration depth of the surface magnetization can be less than the thickness of the magnetizable material. This allows a large magnetic amplitude to be achieved close to the side of the material facing the measuring elements. Additionally, the component's substrate material can remain non-magnetic and unaffected by the surface magnetization.

[0028] Alternatively, surface magnetization can penetrate the magnetizable material almost completely. In this case, the substrate material, which is typically a ferromagnetic material, can allow magnetic feedback through the component. This magnetic feedback can increase the magnetic flux density.

[0029] The method is preferably computer-implemented and can be implemented, for example, in software or hardware or in a hybrid form of software and hardware, for example, in a control unit.

[0030] Also advantageous is a computer program product or computer program with program code that can be stored on a machine-readable carrier or storage medium such as a semiconductor memory, a hard disk memory or an optical memory and is used to carry out, implement and / or control the steps of the method according to one of the embodiments described above, in particular if the program product or program is executed on a computer or device.

[0031] It is noted that some of the possible features and advantages of the invention are described herein with reference to different embodiments. A person skilled in the art will recognize that the features of the control unit and the method can be suitably combined, adapted, or exchanged to arrive at further embodiments of the invention. Brief description of the drawings

[0032] Embodiments of the invention are described below with reference to the accompanying drawings, whereby neither the drawings nor the description are to be interpreted as limiting the invention.

[0033] Fig. 1 shows a representation of a steering gear according to an embodiment example;

[0034] Fig. 2 shows a representation of a component with a steering angle sensor of a steering gear according to an exemplary embodiment; and

[0035] Figures 3 and 4 show representations of magnetizations of a sensor for a steering gear according to exemplary embodiments.

[0036] The figures are schematic only and not to scale. Identical reference symbols denote identical or equivalent features.

[0037] Embodiments of the invention

[0038] Fig. 1 shows a representation of a steering gear 100 according to an embodiment. The steering gear 100 is therefore a rotary-translator transmission. The steering gear 100 has a highly integrated steering angle sensor 102. The steering angle sensor 102 detects an angular position 104 of a rotary component 106 of the steering gear 100. Using a rotary-translator transmission ratio 108 of the steering gear 100, a linear position 112 of a translational component 110 of the steering gear 100 is derived from the angular position 104. Using the linear position 112 and a steering kinematic 114 of a connected steering system, a steering angle 116 of the steering system is determined.

[0039] In the steering gear 100, a rotary motion of a drive motor 118 is transmitted to the rotary component 106 and converted into a linear motion of the translational component 110. Here, the translational component 110 is directly a tie rod 120 of the steering system. Alternatively, the translational component 110 can be coupled to the tie rod 120 at a different point. The steering gear 100 has no rotatable mechanical connection to a steering wheel of the vehicle. The steering gear 100 can therefore be described as a steer-by-wire steering gear.

[0040] In one embodiment, the steering gear 100 has a nut 122 as the rotary component 106, which engages in a thread 124 of the translational component 110. The nut 122 is a ball screw nut, and the thread 124 is a ball screw. The nut 122 is driven by a pinion 126. The pinion 126 is another rotary component 106. The pinion 126 is mounted on a shaft 128 of the drive motor 118. The drive motor 118 is arranged axially parallel to the translational component 110.

[0041] In one embodiment, the pinion 126 indirectly drives the nut 122 via a toothed belt 130. Alternatively, the nut 122 can be driven directly by the pinion 126. Here, the nut 122 is coupled to a pulley 132. The pulley 132 is positively connected to the nut 122. The toothed belt 130 runs around the pinion 126 and the pulley 132.

[0042] Alternatively, the steering gear 100 can have a rack as the translational component 110, into which the pinion 126 engages as the rotational component 106. In this case, the drive motor 118 would be arranged transversely to the tie rod 120.

[0043] The pinion 126 has a smaller diameter than the pulley 132 or the nut 122. A ratio of the diameters defines a speed ratio 134 between the pinion 126 and the nut 122. The speed of the drive motor 118 is thus reduced to a speed of the nut 122.

[0044] A multipole magnetic encoder 136 of the steering angle sensor 102 is arranged on the rotating component 106. In one embodiment, the encoder 136 is arranged on the pulley 132. Alternatively, the encoder 136 can also be arranged on the pinion 126. A magnetic field direction sensor 140 is arranged on a housing 138 of the steering gear 100 such that the magnetic fields emanating from the encoder 136 penetrate it. The magnetic field direction sensor 140 is arranged to be rotationally fixed. The magnetic field direction sensor 140 is arranged close to the encoder 136 and separated from it only by a small air gap. The magnetic field direction sensor 140 detects a field direction 142 of the magnetic field penetrating it and represents the field direction 142 in an electrical signal 144. The signal 144 is in particular a vector of at least two dimensions which represents a radial component and a tangential component of the field direction 142 as numerical values.

[0045] Signal 144 is read and evaluated by a control unit 146 of the steering gear 100. A relationship 148 stored in the control unit 146 between the measured field direction 142 and an angular position 104 of the sensor 136 determines the angular position 104 of the rotary component 106. The linear position 112 of the translational component 110 is derived from the angular position 104 using the rotary-translational transmission ratio 108, which is also stored in the control unit 146. The steering angle 116 of the steering system is then determined from the linear position 112 using the steering kinematics 114 stored in the control unit 146.

[0046] In one embodiment, the steering angle sensor 102 has a position sensor 150 on a further rotary component 106. In the illustrated embodiment, the position sensor 150 is coupled to the pinion 126, or the shaft 128, of the drive motor 118. A position sensor 152 detects a position 154 of the position sensor 150 and represents the position 154 in a further electrical signal 144. The control unit 146 also reads the further signal 144. Since the further rotary component 106 is coupled to the first rotary component 106 via the rotational speed ratio 134, the position 154 changes faster than the angular position 104. Over several revolutions of the rotary components 106, unique pairs of values ​​156 result from position 154 and angular position 104. The pairs of values ​​156 are stored in the control unit 146.By comparing the current values ​​of position 154 and angular position 104 with the stored value pairs 156, the rotation of the first rotary component 106 is determined. Thus, the linear position 112 and the steering angle 116 can be uniquely determined over several rotations of the rotary component 106 using the stored rotary-translational transmission ratio 108 and the stored steering kinematics 114. This determination also works after an interruption of the power supply to the control unit 146 and even if the steering angle 116 changes during the interruption of the power supply, for example, due to external forces.

[0047] Fig. 2 shows a representation of a rotary component 106 with a steering angle sensor 102 of a steering gear according to an exemplary embodiment. The rotary component 106 essentially corresponds to the first rotary component in Fig. 1. Here, the rotary component 106 is also a pulley 132. On a surface 200 of the rotary component 106, the sensor 136 is formed by a layer of surface-magnetized magnetizable material 202. The sensor 136 is applied to the component 106 in the circumferential direction. The magnetic field direction sensor 140 is arranged spaced apart from the sensor 136 by the air gap 204.

[0048] In one embodiment, the magnetic field direction sensor 140 has two sensor elements 208 spaced apart from each other by a distance 206. Each sensor element 208 represents the penetrating magnetic field of the encoder 136 as a vector with at least one tangential component 210 and one radial component 212 in its signal 144.

[0049] In control unit 146, differences 214 are calculated between the two tangential components 210 and the two radial components 212. These differences 214 result in a new vector that only represents the difference in the magnetic field directions at the two sensor elements 208. Components of magnetic fields that are represented identically in the signals 144 at both sensor elements 208 cancel each other out through the calculation of the difference and therefore do not affect the measurement of the magnetic field direction sensor 140.

[0050] Fig. 3 shows a representation of the surface magnetization 300 of a sensor 136 for a steering gear according to an exemplary embodiment. The sensor 136 essentially corresponds to the sensor 136 in Fig. 2. As in Fig. 2, the sensor 136 is arranged on the surface 200 of the rotating component 106 of the steering gear. The sensor 136 consists of a plastic material filled with magnetizable, magnetized, or magnetic particles. The plastic material thus forms a matrix for the particles. As long as the plastic material is plastically deformable, i.e., liquid, viscous, plasticized, or molten, the particles can move within the plastic material and thus orient themselves as desired. When the plastic material has solidified, i.e., is hard and no longer plastically deformable without external influences, the particles are fixed in the orientation they assumed before solidification.

[0051] The plastic material was applied to surface 200 in a plastically deformable state. The particles were then exposed to strong external magnetic fields and aligned themselves with the field lines of these fields. The plastic material solidified in this alignment. This alignment caused the particles themselves to become magnets, forming the magnetization 300 of the sensor 136.

[0052] Here, the particles have aligned themselves along essentially uninterrupted field lines. The field lines have essentially not penetrated the surface 200. As a result, the material of the rotating component 106 does not influence the magnetization 300, or only to a negligible extent.

[0053] The magnetic field direction sensor 140 is arranged above the encoder 136 and is penetrated by the magnetic fields of the encoder 136. The sensor elements 208 are thereby penetrated by field lines with different directions.

[0054] Fig. 4 shows a representation of the continuous magnetization 300 of a sensor 136 for a steering gear according to an exemplary embodiment. The sensor 136 essentially corresponds to the sensor in Fig. 3. In contrast, the layer of plastic material is significantly thinner. As a result, the magnetizable particles could not align themselves as continuous field lines. The magnetic fields of the sensor 136 penetrate the surface 200. This results in a magnetic feedback 400 in the rotating component 106.

[0055] Possible embodiments of the invention are summarized below or presented using slightly different wording.

[0056] A disturbance-field-robust, highly integrated magnetic measurement of the rack position of a steer-by-wire steering system is presented. Conventionally, the position of the rack or steering rod in a steer-by-wire (SbW) system is measured using a steering angle sensor. This sensor employs the vernier principle and a gear drive to measure the absolute steering angle (i.e., rack position) over several revolutions.

[0057] Here, the absolute steering angle is measured in a highly integrated SbW system using the existing mechanical components. This measurement is robust against interference fields, so that external fields of, for example, 4000 A / m can occur without affecting the measurement.

[0058] The approach presented here makes it possible in particular to reuse the mechanical components already present in an axis-parallel (APA) SbW system, especially the pulley, as an element for magnetic differential measurement.

[0059] Since this is an FE sintered metal, the influence of the FE metal is minimized, or even used to advantage, by means of surface magnetization of an injection-molded, polymer-bonded magnetic material.

[0060] The measurement is preferably performed using a Hall- or XMR-based differential ASIC. To increase availability, this can be implemented redundantly in a dual-die package, which also reduces package costs. Preferably, the magnetic field components in the air gap direction and tangential direction are evaluated at each pair of measuring elements of a die, with the measuring elements spaced tangentially around the circumference (e.g., 2 mm). The field components of the two measuring elements are subtracted from each other to ensure robustness against homogeneous external fields. A differential magnetic angle is calculated from the resulting differential field components using the atan2 operation.

[0061] To increase functional safety, two ASICs can be used, arranged circumferentially at a predetermined angular distance. Preferably, the angle is chosen such that there is a fixed relationship between the signals of the first and second ASICs, e.g., zero crossing at the first ASIC and maximum signal at the second ASIC, in order to maximize diagnostic coverage for comparing the two channels. This becomes necessary, for example, when a single ASIC is only ASIL-C capable, but redundant ASIL-D channels are required.

[0062] Advantageously, several magnetic pole pairs are created during the magnetization of the magnetic material to increase the accuracy of the measurement, e.g. 5 to 15 pole pairs.

[0063] To determine the absolute steering angle, a combination with the measured rotor position angle on the "other side" of the belt using a vernier scale can be employed. In this case, the transmission ratio of the pulleys, the number of pole pairs on the pulley, and the periodicity of the rotor position measurement are all coordinated.

[0064] Fig. 3 shows a surface magnetization in a simplified linear flux line representation, which does not reach the depth to the FE metal.

[0065] Figure 4 shows an alternative magnetization in a simplified linear flux line representation, which is enhanced by the FE metal. Generally, for polymer-bonded isotropic materials, magnetization is preferably carried out using a coil, while for anisotropic materials, magnetization is preferably carried out using a master magnet in the tool.

[0066] Finally, it should be noted that terms such as "comprising," "encompassing," etc., do not exclude other elements or steps, and terms such as "a" or "an" do not exclude a plurality. Reference numerals in the claims are not to be considered as limitations.

Claims

Claims 1. Steering gear (100) with a highly integrated steering angle sensor (102), wherein an annular, multipole magnetic encoder (136) of the steering angle sensor (102) is arranged on a surface (200) of a rotating component (106) of the steering gear (100), and a magnetic field direction sensor (140) of the steering angle sensor (102) is arranged in the steering gear (100) with an air gap (204) to the encoder (136) in a rotationally fixed manner, wherein the encoder (136) consists of at least one layer of magnetizable material (202) arranged on the surface (200), and magnetic poles of the encoder (136) are formed by at least one surface magnetization (300) of the material, wherein a control unit (146) of the steering angle sensor (102) is configured toto determine an angular position (104) of the rotary component (106) using a signal (144) from the magnetic field direction sensor (140) and to determine an actual steering angle (116) of the steering gear (100) using the angular position (104) and a transmission ratio (108) between the rotary component (106) and a translational component (110) of the steering gear (100).

2. Steering gear (100) according to claim 1, wherein the magnetic field direction sensor (140) has at least two sensor elements (208) arranged at a predefined distance (206) from each other, which, due to their distance (206), are each penetrated by a magnetic field with different magnetic field directions (142), wherein the control unit (146) is configured to compensate for a homogeneous disturbance field at the sensor elements (208) by a differential evaluation of the detected magnetic field directions (142).

3. Steering gear (100) according to one of the preceding claims, wherein the steering angle sensor (102) is mounted on a further rotating component (106) of the steering gear (100) with a fixed rotational speed ratio (134) to the first rotating component (106) and a position sensor (150) with a rotationally fixed ten position sensor (152) wherein the control unit (146) is configured to determine the steering angle (116) further using the rotational speed ratio (134) and a vernier calculation between a position (154) of the position sensor (150) and the angle position (104) of the first rotary component (106).

4. Steering gear (100) according to claim 3, wherein the position sensor (150) is a rotor position sensor of a drive motor (118) of the steering gear (100).

5. Steering gear (100) according to one of the preceding claims, wherein the sensor (136) is arranged on the surface (200) of a pulley (132) for driving a drive nut (122) of the tie rod (120) engaging in a thread (124) of a tie rod (120) of the steering gear (100).

6. Steering gear (100) according to one of the preceding claims, wherein the magnetic field direction sensor (140) has a first sensor arrangement with at least one sensor element (208) and at least one redundant second sensor arrangement with at least one further sensor element (208), wherein the sensor arrangements are spatially separated from each other.

7. Steering gear (100) according to one of the preceding claims, wherein the magnetizable material (202) is a plastic-bonded magnetic material and is sprayed onto the surface (200) of the component (106).

8. Steering gear (100) according to one of the preceding claims, wherein the penetration depth of the surface magnetization (300) is less than the layer thickness of the magnetizable material (202).

9. Method for operating a steering gear (100) according to any one of claims 1 to 8, wherein the angular position (104) of the rotating component (106) of the steering gear (100) is determined using the signal (144) of the magnetic field direction sensor (140), wherein the steering angle (116) is determined using the angular position (104) and the gear ratio. The relationship (108) between the rotary component (106) and the translational component (110) is determined.

10. Computer program product configured to instruct a processor, upon execution of the computer program product, to execute, implement and / or control the method according to claim 9.

11. Machine-readable storage medium on which the computer program product according to claim 10 is stored.

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