Steering device

Abstract

The present invention relates to a steering device (100), which includes: a motor (110) configured to generate a driving force for independently steering a steering wheel (200); a speed reducer (120) connected to the rotating shaft body of the motor (110); and a brake (150) configured to inhibit the transmission of torque between the motor (110) and the speed reducer (120).

Description

Technical Field

[0001] The present invention relates to a steering device that independently steers the steering wheels of a vehicle. Background Art

[0002] Hitherto, there has been a so-called steer-by-wire system as a steering system for an automobile. In this steer-by-wire system, the steering wheels are steered based on information indicating the steering angle without a mechanism mechanically connecting the steering wheel and the steering wheels or without a mechanism mechanically transmitting torque between the steering wheel and the steering wheels. There has also been proposed a steer-by-wire system in which the left and right steering wheels are connected to each other by a mechanical connection member, and a left and right independent steering type steer-by-wire system in which the left and right steering wheels are steered by separate motors without inserting a mechanical connection member between the left and right steering wheels, as described in Japanese Unexamined Patent Application Publication No. 2018-58484 (JP 2018-58584A). Summary of the Invention

[0003] When using a motor as a drive source to independently steer the steering wheels, the steering wheels are steered by the output torque from the motor increased by a speed reducer. Depending on the conditions of the road surface on which the vehicle travels, the steering conditions, etc., a so-called reverse input, i.e., a torque input from the steering wheels to the speed reducer, may occur.

[0004] The present invention provides a steering device in which the speed reducer is protected from reverse input from the steering wheels.

[0005] One aspect of the present invention provides a steering device including: a motor configured to generate a driving force for independently steering the steering wheels; a speed reducer connected to the rotating shaft body of the motor; and a brake configured to inhibit torque transmission between the motor and the speed reducer.

[0006] With the above configuration, a steering device can be provided in which even when reverse input occurs, damage to the speed reducer can be avoided by using the brake to inhibit the rotation of the motor. Brief Description of the Drawings

[0007] The features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the drawings, in which like reference numerals indicate like elements, and in the drawings:

[0008] Figure 1 A steering device, a suspension mechanism, and a steering wheel according to an embodiment are shown;

[0009] Figure 2 is a cross-sectional view showing a steering device according to an embodiment;

[0010] Figure 3 is a block diagram showing a functional configuration of a brake control unit according to an embodiment; and

[0011] Figure 4 is a cross-sectional view showing another example of a steering device. Detailed Embodiments

[0012] The steering device according to an embodiment of the present invention will be described below with reference to the accompanying drawings. Numerical values, shapes, materials, components, positional relationships between components, connection states, steps, the order of steps, etc. are exemplary and are not intended to limit the present invention. Multiple inventions may be described with respect to one of the following embodiments. Components not described in the claims are described as optional components of the inventions according to the claims. The drawings are schematic diagrams, which include appropriate exaggerations, omissions, and scale adjustments for explaining the present invention and may be different from the actual shapes, positional relationships, or scales.

[0013] Figure 1 The steering wheel and the suspension are shown. The steering device 100 is a device capable of independently steering a plurality of steering wheels 200. In the case of the present embodiment, the steering device 100 steers the steering wheels 200 via a suspension mechanism, for example. Figure 1 A strut-type suspension mechanism is shown, which is a type of suspension mechanism. The steering device 100 is provided between the strut suspension mechanism and the vehicle body 210, such as a wheel housing, and the steering device 100 steers the steering wheels 200 by rotating the steering wheels 200 about the strut shaft 230 and the shock absorber 220 and the spring 240. The strut suspension mechanism also includes a knuckle 250 attached to the steering wheel 200, a lower arm 260 coupled to the lower portion of the knuckle 250, a hinge member for connecting the respective parts to enable hinge operation, and the like.

[0014] Figure 2 is a cross-sectional view showing the internal structure of the steering device 100. As shown in the figure, the steering device 100 includes a motor 110, a speed reducer 120, and a brake 150. In the case of the present embodiment, the steering device 100 includes a first rotation sensor 141, a second rotation sensor 142, and a brake control unit 181.

[0015] The motor 110 is a drive source that generates a driving force for steering the steering wheels 200. In the case of the present embodiment, the motor 110 is a servo motor including a rotating shaft body 111, a rotor 112, a magnet 113, and a coil 114.

[0016] The rotating shaft body 111 is a rod-shaped rigid body that outputs the rotational driving force of the motor 110. The rotating shaft body 111 is a member having a length longer than the lengths of the rotor 112, the magnet 113, and the coil 114 in the axial direction (the Z-axis direction in the figure). Specifically, the rotating shaft body 111 extends from near the output-side member 171 that is connected to the external gear 124 (to be discussed later) of the speed reducer 120, and the rotating shaft body 111 passes through the central portion of the wave generator 121 and the brake 150. In the case of the present embodiment, the rotating shaft body 111 has a tubular shape penetrated by a hollow portion 115 in the axial direction.

[0017] The rotor 112 is a member that transmits the torque generated between the magnet 113 and the coil 114 to the rotating shaft body 111. The shape of the rotor 112 is not particularly limited. In the case of the present embodiment, the rotor 112 includes a holding portion 116 and a connecting portion 117, where the holding portion 116 has a short cylindrical shape for holding the magnet 113, and the connecting portion 117 is connected between the holding portion 116 and the outer peripheral surface of the rotating shaft body 111. The holding portion 116 is arranged coaxially with the rotating shaft body 111. The connecting portion 117 is integrally attached to one end portion of the holding portion 116 in the axial direction. The rotor 112 has a container shape. At least a part of the brake 150 for braking the rotating shaft body 111 is accommodated in the rotor 112. Therefore, the length of the steering device 100 in the axial direction can be suppressed.

[0018] The magnet 113 is a member that generates a torque for rotating the rotating shaft body 111 by interacting with the magnetic force generated by the coil 114, and the magnets 113 are attached side by side in the circumferential direction to the outer peripheral surface of the holding portion 116 of the rotor 112. The magnets 113 are arranged such that the N poles and S poles of the magnets 113 are arranged in a predetermined pattern.

[0019] The coil 114 is a member obtained by winding a wire material constituting an electromagnet that generates a magnetic field acting on the magnet 113. The direction of the winding axis of the coil 114 extends along the radial direction around the axis of the rotating shaft body 111. The coil 114 is provided at a position slightly outside the region that rotates relative to the magnet 113, and the coils 114 are arranged side by side in the circumferential direction to surround the magnet 113. The coil 114 is fixed to the inner peripheral surface of a housing 160 having a cylindrical shape. The coil 114 may include a core that concentrates the magnetic field.

[0020] The speed reducer 120 is a device that is connected to the rotary shaft body 111 of the motor 110 to amplify the rotational torque generated by the motor 110 into a rotational torque capable of steering the steering wheel 200. The type of the speed reducer 120 is not particularly limited. In the case of the present embodiment, a harmonic speed reducer with a coaxial input shaft and output shaft is employed as the speed reducer 120. The harmonic speed reducer includes a rigid cylindrical internal gear 123, an external gear 124, and a wave generator 121. The external gear 124 has external teeth that mesh with the internal teeth of the internal gear 123, and the external gear 124 is tubular and flexible in the radial direction. The wave generator 121 is elliptical, and the wave generator 121 deforms the external gear 124 relative to the internal gear 123 into an elliptical shape to cause the two gears to mesh with each other at multiple positions and cause these meshing positions to circulate along the internal gear 123.

[0021] In the case of the present embodiment, the external gear 124 is of a so-called top hat type, and the external gear 124 includes a cylindrical portion 125 and a flange portion 126. The external teeth are formed at one end portion of the cylindrical portion 125, and the flange portion 126 projects radially outward at the other end portion of the cylindrical portion 125. The flange portion 126 is disposed on the input side with respect to the external teeth. The outer peripheral end portion of the flange portion 126 is fixed to the housing 160, and the coil 114 is fixed to the housing 160. By arranging the external gear 124 in this way, a first bearing 127, such as a crossed roller bearing, for fixing the internal gear 123 so that the internal gear 123 can rotate relative to the housing 160 can be provided outside the cylindrical portion 125 between the external teeth and the flange portion 126, and a part of the brake 150 and the like can be provided inside the cylindrical portion 125. Therefore, the length of the steering device 100 in the axial direction can be suppressed.

[0022] The wave generator 121 is coaxially penetrated by the rotary shaft body 111, and the wave generator 121 directly receives the rotational torque from the rotary shaft body 111. In addition, the rotation axis of the wave generator 121 is determined by the rotary shaft body 111.

[0023] The internal gear 123 is fixed to the housing 160 via the first bearing 127 so as to be rotatable relative to the housing 160, and the internal gear 123 serves as a member on the output side. The coil 114 is fixed to the housing 160. An output side member 171 is fixed to the internal gear 123 to cover the output side. In addition, a universal joint 172 is attached to the output side member 171. The internal gear 123 is connected to the strut shaft 230 of the suspension mechanism via the output side member 171 and the universal joint 172, and outputs a rotational torque for steering the steering wheel 200.

[0024] The brake 150 is a device that inhibits torque transmission between the motor 110 and the speed reducer 120. Specifically, the brake 150 can inhibit and stop the rotation of the rotation shaft body 111 by friction, where the rotation shaft body 111 is the output shaft body of the motor 110. In the case of this embodiment, the brake 150 is a non-energized actuation type that engages the brake when not energized and disengages the brake when energized, and the brake 150 is provided between the motor 110 and the speed reducer 120. Specifically, the brake 150 is a non-energized actuation type whose operation is controlled by an electromagnet 155 (see Figure 3 ), and a biasing member (not shown), and the brake 150 includes a brake disc 151, a brake lining 152, an armature 153, and an operating device 154.

[0025] The brake disc 151 is an annular member having a rectangular cross-sectional surface, and the brake disc 151 is firmly attached to the rotation shaft body 111 to project in the radial direction of the rotation shaft body 111. The brake disc 151 rotates together with the rotation shaft body 111 and is sandwiched between the brake lining 152 and the armature 153 to generate torque in the direction opposite to the rotation direction of the rotation shaft body 111 by friction.

[0026] The brake lining 152 is a member provided on the side of the brake disc 151 opposite to the operating device 154 and fixed to the operating device 154. The brake lining 152 is an annular member having a rectangular cross-sectional surface. The brake lining 152 is arranged to extend in the radial direction of the rotation shaft body 111 to surround the rotation shaft body 111, and the brake lining 152 is arranged parallel to the brake disc 151.

[0027] The armature 153 is a member provided on the side of the brake disc 151 opposite to the brake lining 152, and the armature 153 is configured to move in the direction of clamping the brake disc 151 and the brake lining 152 together by the biasing force of the biasing member of the operating device 154 and move in the direction approaching the operating device 154 against the biasing force of the biasing member when the electromagnet 155 of the operating device 154 is energized. The armature 153 is an annular member having a rectangular cross-sectional surface. The armature 153 is arranged to extend in the radial direction of the rotation shaft body 111 to surround the rotation shaft body 111, and the armature 153 is arranged parallel to the brake disc 151.

[0028] The operating device 154 is a cylindrical member fixed to the housing 160, and includes a biasing member that reciprocally moves the armature 153 in the axial direction of the rotation shaft body 111 and an electromagnet 155. Examples of the biasing member include a helical spring. The operating device 154 includes a plurality of helical springs arranged in the circumferential direction.

[0029] The first rotation sensor 141 is a sensor that detects the rotation angle of the output side of the speed reducer 120. The type of the first rotation sensor 141 is not particularly limited. The first rotation sensor 141 may be an optical rotary encoder. In the case of the present embodiment, the first rotation sensor 141 includes a detection shaft body 143. One end portion of the detection shaft body 143 penetrates the undulator 121 of the speed reducer 120 and is connected to the rotation center of the output side member 171 located on the output side of the speed reducer 120. In addition, the detection shaft body 143 also penetrates the hollow portion 115 of the rotary shaft body 111. The other end portion of the detection shaft body 143 protrudes from the rotary shaft body 111. The first rotation sensor 141 detects the rotation angle of the output side of the speed reducer 120 based on the rotation of the detection shaft body 143 by detecting the rotation angle of a disk portion 144 provided at the other end portion of the rotary shaft body 111 on the input side of the speed reducer 120 and on the side opposite to the speed reducer 120 of the motor 110. The first rotation sensor 141 is disposed farther from the speed reducer 120 than the brake 150 and the second rotation sensor 142.

[0030] As described above, by using the detection shaft body 143 to dispose the first rotation sensor 141 at a position farther from the speed reducer 120 than the motor 110, a plurality of rotation sensors can be concentrated at one position, which is advantageous for implementing dust suppression measures for these rotation sensors and the like. In addition, the output signals from the rotation sensors can be concentrated at one position to be led out from the housing 160, which is advantageous for processing the signal lines outside the housing 160. Furthermore, the processing of the electric wires can be made more convenient by concentrating the electric wires for supplying power to the motor 110 and the power lines for the brake 150 at the same position as the signal lines and leading these lines out from the housing 160. The use of a connector (not shown) penetrating the housing 160 is advantageous for connecting to and disconnecting from the electric wires outside the housing 160 and can also suppress dust.

[0031] The second rotation sensor 142 is a sensor attached to the rotary shaft body 111 of the motor 110 to detect the rotation angle of the motor 110. The type of the second rotation sensor 142 is not particularly limited. In the case of the present embodiment, a resolver is employed as the second rotation sensor 142. The resolver can accurately sense the rotation angle of the rotary shaft body 111 rotating at a high speed.

[0032] As described above, by using the first rotation sensor 141 to obtain the rotation angle of the output side and using the second rotation sensor 142 to obtain the rotation angle of the input side, the second rotation sensor 142 can be calibrated using the information based on the first rotation sensor 141 when the information based on the second rotation sensor 142 is not in a predetermined relationship with the information based on the first rotation sensor 141.

[0033] The housing 160 is a box-shaped member that sequentially houses at least the input side of the motor 110, the brake 150, the speed reducer 120, the second rotation sensor 142, and the first rotation sensor 141 in this order. The shape of the housing 160 is not particularly limited. In the case of the present embodiment, the housing 160 has a cylindrical shape, and the portion of the housing 160 near the first rotation sensor 141 is closed by a cover member 161. The housing 160 is fixed to the vehicle body 210 such that at least the input side of the motor 110, the brake 150, the speed reducer 120, the second rotation sensor 142, and the first rotation sensor 141 are disposed outside a portion of the vehicle body 210 that forms a so-called fender that houses the steering wheel 200 and the suspension mechanism. In the case of the present embodiment, the housing 160 also houses a part of the internal gear 123 provided on the output side of the speed reducer 120 and the output side member 171, and the internal gear 123 is disposed outside the vehicle body 210. Although the housing 160 is attached to protrude outward from the vehicle body 210, since the housing 160 is covered by the engine hood of the vehicle, the housing 160 is not exposed to the outside and cannot be visually recognized.

[0034] As described above, in the steering device 100 according to the present embodiment, the brake 150 is connected between the motor 110 and the speed reducer 120. Therefore, the rotational torque or moment of inertia of the motor 110 is resisted before being input to the speed reducer 120, and damage to the steering device 100 due to the occurrence of reverse input can be suppressed.

[0035] The torque is suppressed against the rotational torque or moment of inertia of the motor 110 before being amplified by the speed reducer 120, and thus the torque generated by friction can be set to be low. Therefore, a smaller brake 150 can be employed, and the size of the steering device 100, particularly the thickness in the axial direction, can be reduced.

[0036] By using the detection shaft body 143 to sense the rotation angle of the output side of the speed reducer 120 with the first rotation sensor 141 provided at the position on the input side, the length of the steering device 100 in the axial direction can be shortened compared to the case where the rotation angle sensor is provided on the output side of the speed reducer 120.

[0037] A relatively high dust suppression performance can be obtained because the motor 110, the brake 150, the speed reducer 120, the first rotation sensor 141, and the second rotation sensor 142 are accommodated in a housing 160 attached to the vehicle body 210 and disposed above the vehicle body 210 defining a tire cover, wherein the steering wheel 200 is disposed in the tire cover.

[0038] The wiring harness can be easily handled because the electric wires for exchanging electrical signals and power between the inside and the outside of the housing 160 can be concentrated at one location.

[0039] By adopting a non-powered actuation type brake, in the case where no power is supplied to the steering device 100, such as when the vehicle is stationary, the rotation of the steering wheel 200 can be adjusted by fixing the rotation shaft body 111 by the brake 150.

[0040] In the case where it is determined based on the information from the first rotation sensor 141 that the behavior of the steering wheel 200 is abnormal, the brake control unit 181 generates a torque that resists the rotation of the rotation shaft body 111 by actuating the brake 150. Examples of the state where the behavior of the steering wheel 200 is abnormal include the case where the steering wheel 200 steers in an unexpected direction when the steering wheel 200 contacts the curb due to vehicle skidding during driving.

[0041] Figure 3 is a block diagram showing the functions of the brake control unit 181. As shown in the figure, the brake control unit 181 is a part of the steering electronic control unit (ECU) 180, and includes a rotation angle acquisition unit 182, a time measurement unit 183, an angular velocity calculation unit 184, an abnormality determination unit 185, an electromagnet control unit 186, and a vehicle state acquisition unit 187.

[0042] The rotation angle acquisition unit 182 is a processing unit that acquires the rotation angle from the first rotation sensor 141. Specifically, the rotation angle acquisition unit 182 can only count the number of pulse signals from the first rotation sensor 141, and calculate the rotation angle based on the number of pulses.

[0043] The time measurement unit 183 is a processing unit that measures time. The time measurement method of the time measurement unit 183 is not particularly limited, and the time measurement unit 183 can measure time based on, for example, the sampling period of the brake control unit 181. For example, one sampling period can be determined as time 1. Alternatively, the number of sampling periods can be multiplied by the sampling period to calculate the actual time.

[0044] The angular velocity calculation unit 184 calculates the angular velocity based on the rotation angle obtained from the rotation angle acquisition unit 182 and the time obtained from the time measurement unit 183. Specifically, the angular velocity calculation unit 184 may determine the difference in rotation angle for one sampling period of the brake control unit 181 as the number of pulses obtained from the first rotation sensor 141, and obtain this value as the angular velocity. Also, in this case, the angular velocity is calculated by dividing the rotation angle by the time obtained from the time measurement unit 183.

[0045] The abnormality determination unit 185 determines an abnormality by estimating that reverse input is caused when the angular velocity obtained from the angular velocity calculation unit 184 is equal to or greater than a predetermined angular velocity threshold.

[0046] When the abnormality determination unit 185 outputs a signal indicating an abnormality, the electromagnet control unit 186 applies a braking torque to the rotary shaft body 111 by controlling the electromagnet 155 of the brake 150. In the case of the present embodiment, the brake 150 is a non-excited actuation type, and thus, the braking torque is applied to the rotary shaft body 111 by preventing power supply to the electromagnet 155 by the electromagnet control unit 186.

[0047] With the above configuration, it is possible to suppress the inertial torque of the motor 110 by braking the rotary shaft body 111 when reverse input is caused. Therefore, damage to the speed reducer 120 caused by reverse input from the output side and torsional inertia moment from the input side can be suppressed.

[0048] The vehicle state acquisition unit 187 acquires the state of the vehicle to which the steering wheel 200 is attached, such as whether the vehicle is running or stationary, from a higher-level ECU, such as a steering ECU, and controls the brake 150 according to the state of the vehicle. In the case of the present embodiment, when information indicating that the vehicle is parked is acquired, the vehicle state acquisition unit 187 outputs a signal to cause the electromagnet control unit 186 to prevent power supply to the electromagnet 155. Therefore, even when the vehicle is rear-ended while the vehicle is stationary or the like, it is possible to suppress the steering of the steering wheel 200.

[0049] The present invention is not limited to the above-described embodiment. For example, the constituent elements described herein may be combined as needed, or some of the constituent elements may be excluded to implement different embodiments of the present invention. Additionally, the present invention also includes variants obtained by making various conceivable changes to the above-described embodiment by those skilled in the art without departing from the scope and spirit of the present invention, that is, the meaning of the language used in the claims.

[0050] For example, although the steering device 100 according to the above-described embodiment is described as a device that steers the steering wheel 200 via a suspension mechanism including a shock absorber 220 and a strut shaft 230, the steering device 100 may steer the steering wheel 200 via a different type of suspension mechanism, or the steering device 100 may steer the steering wheel 200 via a steering operation mechanism separate from the suspension mechanism.

[0051] The harmonic gear mechanism is exemplarily described as the speed reducer 120 in which the input shaft and the output shaft are coaxially arranged. However, the speed reducer 120 is not limited thereto, and for example, the speed reducer 120 may utilize a planetary gear mechanism.

[0052] As Figure 4 shown, the steering device 100 may include an overload protection device 130. The overload protection device 130 is a so-called torque limiter that blocks torque transmission between the motor 110 and the speed reducer 120 in the event of an overload. The overload protection device 130 includes: a first member 131 that is coaxially arranged with the rotary shaft body 111 and fixed to the outer peripheral surface of the rotary shaft body 111; a second member 132 that is attached to the outer peripheral edge portion of the through hole 128 of the wave generator 121 on the input side of the speed reducer 120; a biasing member 133 that biases the second member 132 against the first member 131; and a spherical engagement member 134 that is disposed between the first member 131 and the second member 132 and firmly engages with the first member 131 and the second member 132 when the second member 132 is pressed against the first member 131 by the biasing member 133.

[0053] In the overload protection device 130, under normal conditions, the first member 131 and the second member 132 are firmly coupled to each other via the engagement member 134 by the biasing force of the biasing member 133, and thus, the rotational torque of the rotary shaft body 111 is transmitted to the wave generator 121 of the speed reducer 120. On the other hand, in a case where a sudden reverse input is generated, such as when the steering wheel 200 collides with a curb, and in a case where the rotational torque of the reverse input that has been attenuated by the speed reducer 120 from the strut shaft 230 exceeds the biasing force of the biasing member 133, the second member 132 idles relative to the first member 131, and the reverse input is not transmitted to the first member 131, the rotary shaft body 111, etc.

[0054] The overload protection device 130 is provided on the input side of the speed reducer 120 and thus operates according to the rotational torque of the reverse input that has been reduced by the speed reducer 120. That is, the threshold value of the rotational torque when the overload protection device 130 idles can be reduced, and a smaller overload protection device 130 can be employed. Therefore, the overall size of the steering device 100 can be suppressed.

[0055] As shown Figure 4 in the figure, the brake 150 may be provided on the side of the motor 110 opposite to the speed reducer 120. The brake 150 protects the speed reducer 120 by suppressing the inertial torque of the motor 110 in a state before the overload protection device 130 idles. The brake 150 can also protect the overload protection device 130 by reducing the number of times the overload protection device 130 idles.

[0056] Part or all of the steering device 100 may be provided inside the fender.

[0057] The present invention can be applied to vehicles such as those with independently steerable steering wheels, such as automobiles, construction machinery, and agricultural machinery.

Claims

1. A steering device (100), characterized in that, The steering device (100) includes: a motor (110) configured to generate a driving force for independently steering a steering wheel (200); a speed reducer (120) connected to a rotating shaft body of the motor (110); a brake (150) configured to resist a rotational torque or moment of inertia of the motor (110) before being input to the speed reducer (120), and inhibit transmission of torque between the motor (110) and the speed reducer (120), thereby inhibiting damage to the steering device (100) due to occurrence of reverse input; a first rotation sensor (141) configured to detect a rotation angle on an output side of the speed reducer (120); and a steering electronic control unit (180) configured to actuate the brake (150) when it is presumed that reverse input has occurred based on information from the first rotation sensor (141) and it is determined that the behavior of the steering wheel (200) is abnormal.

2. The steering device (100) according to claim 1, characterized in that, The steering electronic control unit (180) is configured to measure time, determine abnormality of the behavior of the steering wheel (200) based on the rotation angle obtained from the first rotation sensor (141) and an angular velocity calculated according to the measured time, and actuate the brake (150) when the behavior of the steering wheel (200) is determined to be abnormal.

3. The steering device (100) according to claim 2, characterized in that, The steering electronic control unit (180) is configured to actuate the brake (150) when the vehicle to which the steering wheel (200) is attached is stationary.

4. The steering device (100) according to claim 1 or 2, characterized in that, The brake (150) is a non - electrically - actuated brake configured to prevent rotation of the rotating shaft body of the motor (110) by friction when the brake (150) is not energized.

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