Steer-by-Wire Steering Device

Abstract

To provide a steer-by-wire type steering device which allows a steering actuator to change a direction of a steering part according to an operation amount of the steering wheel detected by the steering sensor, and allows a driver to surely sense a situation where the direction of the steering part reaches a stroke end through a steering wheel when the direction reaches the stroke end.SOLUTION: A steer-by-wire type steering device includes: a shaft 4 which is connected to a steering wheel 1 so as to be rotated integrally with the steering wheel 1; an outer ring 21 having an inner periphery arranged in the periphery of the shaft 4; an engagement element 24 arranged between the shaft 4 and the inner periphery of the outer ring 21; a holder 25 which is arranged so as to be movable in a circumferential direction between an engagement position where the engagement element 24 is held and the engagement element 24 is engaged with the shaft 4 and the inner periphery of the outer ring 21 and a release position where the engagement is released; a centering spring 26 which elastically holds the holder 25 at a release position and stops rotation in the shaft 4 and the holder 25 so as to be rotated integrally with the shaft 4; and an excitation operating electromagnetic brake 27 for braking the holder 25.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a steer-by-wire steering device that steers in a state mechanically separated from a steering wheel.

Background Art

[0002] As a steering device that changes the direction of a steering part such as a vehicle's steered wheels (generally the front wheels) or a ship's rudder in response to a rotational operation of a steering wheel by a driver, a steer-by-wire type is known.

[0003] A steer-by-wire steering device has a steering sensor that detects the operation amount of a steering wheel and a steering actuator provided so as to be mechanically separated from the steering wheel. The steering actuator operates according to the operation amount of the steering wheel detected by the steering sensor and changes the direction of the steering part.

[0004] This type of steer-by-wire steering device can once convert the operation amount of the steering wheel by the driver into an electric signal and control the operation of the steering actuator based on the electric signal. Therefore, for example, it is possible to optimize the correspondence relationship between the operation amount of the steering wheel and the operation amount of the steering actuator according to the driving state of a vehicle, a ship, etc., such as adjusting the amount of change in the direction of the steering part when the steering wheel is operated according to the moving speed of the vehicle, ship, etc.

[0005] On the other hand, in a steer-by-wire steering device, since the steering wheel rotated by the driver and the steering actuator that changes the direction of the steering part are mechanically separated, even when the direction of the steering part reaches its movement limit (stroke end), the driver can further rotate the steering wheel. Therefore, a vehicle steer-by-wire steering device has been proposed that enables the driver to sense that situation through the steering wheel when the direction of the steering part reaches the stroke end (Patent Document 1).

[0006] The steer-by-wire type steering device for a vehicle disclosed in Patent Document 1 includes a reaction force motor that applies a steering reaction force calculated based on the vehicle speed, the operation amount of the steering wheel, etc. to the steering wheel, and a reaction force controller that controls the reaction force motor. Then, when the direction of the steered wheels reaches the stroke end, the reaction force controller performs control to correct and increase the magnitude of the steering reaction force generated by the reaction force motor. Thereby, the driver can sense through the steering wheel that the direction of the steered wheels has reached the stroke end.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] When control is performed to correct and increase the magnitude of the steering reaction force generated by the reaction force motor when the direction of the steered wheels reaches the stroke end as in Patent Document 1, the control of the reaction force motor becomes complicated. Also, since the rotation of the steering wheel is not blocked and only the steering reaction force of the steering wheel becomes larger, there is a possibility that some drivers may not notice that the direction of the steered wheels has reached the stroke end and continue the rotation operation of the steering wheel as it is.

[0009] Therefore, the problem to be solved by this invention is to provide a steer-by-wire type steering device that can surely make the driver sense the situation through the steering wheel when the direction of the steering section reaches the stroke end.

Means for Solving the Problems

[0010] In order to solve the above problems, the present invention provides a steer-by-wire type steering apparatus including a steering wheel, a steering sensor that detects an operation amount of the steering wheel, and a steering actuator that changes the direction of a steering section according to the operation amount of the steering wheel detected by the steering sensor. In the steer-by-wire type steering apparatus, a shaft connected to the steering wheel so as to rotate integrally with the steering wheel, an outer ring having an inner circumference disposed around the shaft, an engaging element disposed between the shaft and the inner circumference of the outer ring, a retainer that holds the engaging element and is disposed so as to be movable in the circumferential direction between an engaging position where the engaging element is engaged with the shaft and the inner circumference of the outer ring and a release position where the engagement is released, a centering spring that elastically holds the retainer at the release position and is prevented from rotating relative to the shaft and the retainer so as to rotate integrally with the shaft, and an excitation-operated electromagnetic brake that brakes the retainer are further provided.

[0011] According to the above configuration, when the excitation-operated electromagnetic brake is in a non-excited state, the retainer is not braked. At this time, when the shaft rotates, the centering spring that is non-rotatably fixed to the shaft so as to rotate integrally with the shaft transmits the rotational force of the shaft to the retainer and holds the retainer at the release position with respect to the shaft. Therefore, the engaging element cannot engage with the shaft and the inner circumference of the outer ring. That is, when the electromagnetic brake is in the non-excited state, the rotation of the steering wheel is permitted. On the other hand, when the excitation-operated electromagnetic brake is in the excited state, the retainer is braked. At this time, when the steering wheel is rotated, since the retainer that receives the rotational force of the shaft from the centering spring is braked by the electromagnetic brake, the shaft rotates relative to the retainer. Due to this relative rotation, when the retainer that moves in the circumferential direction with respect to the shaft reaches the engagement position against the centering spring, the engaging element engages with the shaft and the inner circumference of the outer ring, so that further rotation of the shaft is reliably blocked. When the electromagnetic brake is switched from the excited state to the non-excited state, the retainer is returned to the release position by the elastic restoring force of the centering spring. Therefore, by switching the electromagnetic brake from the non-excited state to the excited state, it is possible to reliably prevent the steering wheel from rotating by more than the circumferential movement amount between the release position and the engagement position of the retainer, and through the steering wheel, the driver can be reliably made aware that the direction of the steering section has reached the stroke end.

[0012] The excitation-operated electromagnetic brake preferably includes, for example, an armature that is prevented from rotating around the cage and is arranged to be axially movable, a friction surface portion fixed at a position axially facing the armature, an electromagnet axially facing the armature, and a separation spring arranged to accumulate potential energy in response to the axial movement of the armature that is supported at a position axially separated from the electromagnet and the friction surface portion when the electromagnet is de-energized and is attracted by the electromagnet to the friction surface portion when the electromagnet is energized. In this way, when the electromagnet is in a de-energized state without being energized, the separation spring can support the armature to keep it at a position separated from the friction surface portion, keeping the cage in an unbraked state, and a predetermined magnetic gap can be formed between the armature and the electromagnet. When the electromagnet is switched from the de-energized state to the energized state, the electromagnet attracts the armature against the separation spring to the friction surface portion, applying an operating pressure between the friction surface portion and the armature, thereby braking the cage and moving it circumferentially relative to the shaft. Since the separation spring accumulates potential energy in response to the axial movement of the armature during this attraction, when the electromagnet is switched from the energized state to the de-energized state, the elastic restoring force of the separation spring can separate the armature from the electromagnet and the friction surface portion, releasing the braking of the cage.

[0013] The electromagnet has a field core that faces the armature in the axial direction and a solenoid coil wound around the field core. The friction surface portion is integrally formed with the field core, and the armature may be a movable member that is directly adsorbed to the friction surface portion of the field core when the electromagnet is excited. By doing so, it is possible to eliminate the rotor that serves as the contact partner of the armature between the electromagnet and the armature. As a result, the size and the number of parts of the excitation-operated electromagnetic brake can be reduced. Further, since there is no rotor between the electromagnet and the armature, compared with the case where there is a rotor, the magnetic flux efficiently circulates between the electromagnet and the armature, the attractive force of the electromagnet on the armature can be strengthened, and the braking torque on the holder can be strengthened. As a result, the resistance of the centering spring can be strongly set for the relative rotation of the holder and the shaft during braking. Therefore, immediately after the excitation of the electromagnet, the rotation operation of the steering wheel can be quickly made heavier than usual, and the driver can be made aware that the direction of the steering part is near the stroke end.

[0014] More preferably, it is further provided with a control unit that switches the excitation-operated electromagnetic brake to an excited state at a predetermined stroke position before the direction of the steering part reaches the stroke end. Since it is possible to quickly make the rotation operation of the steering wheel heavier after switching the electromagnet to the excited state as described above, when the electromagnet is switched to the excited state at a predetermined stroke position near the stroke end of the steering part, for the driver who further turns the steering wheel after this switching, the rotation operation of the steering wheel can be made heavier than usual until it reaches the stroke end, and the driver can be made aware that the direction of the steering part is approaching the stroke end.

[0015] Further provided is a cylindrical brake case that houses the outer ring and the excitation-operated electromagnetic brake, the brake case being formed of a non-magnetic material separate from the outer ring, and the outer ring being preferably prevented from rotating relative to the brake case. In this way, when the excitation-operated electromagnetic brake is in an excited state, it is possible to prevent magnetic flux generated from the excitation-operated electromagnetic brake from leaking into the brake case.

[0016] Also, further provided is a cylindrical brake case that houses the excitation-operated electromagnetic brake, and the outer ring is preferably integrally formed with the brake case. In this way, the axial positioning and anti-rotation process of the outer ring with respect to the brake case can be eliminated, and the number of components can be reduced.

[0017] Further provided is a reaction force motor that applies a steering reaction force to the steering wheel, the steering portion being a pair of left and right steering wheels, and the outer ring, the engaging element, the retainer, and the excitation-operated electromagnetic brake being preferably provided between the steering wheel and the reaction force motor or on the axially opposite side of the reaction force motor from the steering wheel. In this way, as a steer-by-wire type steering device for a vehicle, when the steering wheel reaches the stroke end, the driver can surely perceive through the steering wheel that the steering wheel has reached the stroke end.

Advantages of the Invention

[0018] As described above, by adopting the above configuration, the steer-by-wire type steering device according to the present invention can surely make the driver perceive the situation through the steering wheel when the steering portion reaches the stroke end.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Mode for Carrying Out the Invention

[0020] FIGS. 1 and 2 show a steer-by-wire type steering device (hereinafter simply referred to as "steering device") according to a first embodiment as an example of the present invention.

[0021] This steering device can change the directions of a pair of left and right steering wheels 3 as a steering part by converting the operation amount of a steering wheel 1 by a driver into an electric signal and controlling a steering actuator 2 based on the electric signal.

[0022] This steering device includes a steering wheel 1 steered by a driver, a shaft 4 connected to the steering wheel 1, a steering sensor 5 for detecting the operation amount of the steering wheel 1, a reaction force motor 6 for applying a steering reaction force to the steering wheel 1, a brake unit 7 for preventing the rotation of the steering wheel 1 in a non-excited state and allowing the rotation of the steering wheel 1 in an excited state, a steering actuator 2 mechanically separated from the steering wheel 1, and a control unit 8.

[0023] Shaft 4 is connected to the steering wheel 1 so as to rotate integrally with the steering wheel 1 when the steering wheel 1 is steered. The steering sensor 5 is attached to the shaft 4. Examples of the steering sensor 5 include a steering angle sensor that detects the steering angle of the steering wheel 1, and a steering torque sensor that detects the steering torque input to the steering wheel 1 by the driver.

[0024] The reaction force motor 6 is an electric motor that generates a rotational torque when energized. The reaction force motor 6 is connected to the end of the shaft 4. The reaction force motor 6 applies a steering reaction force to the steering wheel 1 via the shaft 4 by inputting a rotational torque to the shaft 4.

[0025] The steering actuator 2 includes a steering shaft 10, a steering shaft housing 11, a steering motor 12 that moves the steering shaft 10 in the left - right direction of the vehicle, and a steering sensor 13 that detects the position of the steering shaft 10. The steering shaft 10 is supported by the steering shaft housing 11 so as to be movable in the left - right direction of the vehicle. The steering shaft housing 11 houses the central portion of the steering shaft 10 such that both the left and right ends of the steering shaft 10 protrude from the steering shaft housing 11.

[0026] The steering motor 12 and the steering sensor 13 are attached to the steering shaft housing 11. A motion conversion mechanism (not shown) that converts the rotation output by the steering motor 12 into the linear motion of the steering shaft 10 is incorporated between the steering motor 12 and the steering shaft 10. Both the left and right ends of the steering shaft 10 are connected to a pair of left and right steering wheels 3 via tie rods 14, and when the steering shaft 10 moves in the axial direction, the directions of the pair of left and right steering wheels 3 change in conjunction with this movement.

[0027] As shown in Fig. 1, the reaction force motor 6 has a motor case 15 and a motor shaft 16 that protrudes from the motor case 15 to the side opposite to the steering wheel 1 (the lower side in the figure). The motor shaft 16 is rotatably supported by a rolling bearing (not shown) incorporated inside the motor case 15. Further, the motor shaft 16 is a component of the shaft 4 and is connected to the shaft portion on the steering column side of the shaft 4 so as to rotate integrally with the steering wheel 1. The motor case 15 is fixed to the vehicle body (not shown) so as not to rotate.

[0028] The brake unit 7 has an inner ring 20 connected to the motor shaft 16, an outer ring 21 having an inner circumference disposed around the inner ring 20, a plurality of cam surfaces 22 (see Fig. 3) formed on the outer circumference of the inner ring 20, a cylindrical surface 23 formed on the inner circumference of the outer ring 21, engagement elements 24 disposed between each cam surface 22 and the cylindrical surface 23, a retainer 25 that holds these engagement elements 24, a centering spring 26 that is prevented from rotating with respect to the inner ring 20 and the retainer 25, an excitation-operated electromagnetic brake 27 that brakes the retainer 25, and a brake case 28 connected to the motor case 15.

[0029] The inner ring 20 shown in Fig. 1 is a component of the shaft 4 and is spline-fitted onto the outer circumference of the motor shaft 16. By this spline fitting, the motor shaft 16 is connected to the inner ring 20 without play so as not to rotate relative to the inner ring 20 at all.

[0030] Note that the entire inner ring 20 is integrally formed by forging. The inner ring 20 and the motor shaft 16 are made separate because it becomes easier to form the plurality of cam surfaces 22 with high precision by forging. The shaft 4 may be configured by connecting a plurality of members such as the inner ring 20, the motor shaft 16, and a steering shaft directly connected to the steering wheel 1 as shown in Figs. 1 and 2, or may be configured appropriately with a single or a plurality of members such as integrally forming the motor shaft and the steering shaft or integrally forming the motor shaft and the inner ring.

[0031] The outer ring 21 and the brake case 28 shown in FIG. 1 are formed separately from each other. The brake case 28 is a cylindrical member that collectively houses the components of the brake unit 7 (inner ring 20, engaging element 24, cage 25, magnetically actuated electromagnetic brake 27, etc.). The brake case 28 is made of a non-magnetic material (such as aluminum alloy, copper, etc.). At one axial end of the brake case 28, a flange portion extending radially outward is formed, and the flange portion is fixed to the axial end face of the motor case 15 with bolts (not shown).

[0032] On the other hand, the outer ring 21 is made of steel. The outer ring 21 is fitted into the cylindrical brake case 28 and is prevented from coming off the brake case 28 by a retaining ring 29 attached to the inner circumference of the brake case 28. A bearing 30 that rotatably supports the inner ring 20 is disposed between the inner circumference of the outer ring 21 and the outer circumference of the inner ring 20.

[0033] As shown in FIG. 3, a common key member 33 is fitted into a key groove 31 formed on the inner circumference of the brake case 28 and a key groove 32 formed on the outer circumference of the outer ring 21, and the outer ring 21 is prevented from rotating relative to the brake case 28 by this key member 33.

[0034] The cam surface 22 on the outer circumference of the inner ring 20 faces the cylindrical surface 23 on the inner circumference of the outer ring 21 in the radial direction. A wedge-shaped space that gradually narrows from the center in the circumferential direction toward both ends in the circumferential direction is formed between the cam surface 22 and the cylindrical surface 23.

[0035] The cage 25 is an annular member in which a plurality of pockets 34 penetrating in the radial direction are formed at intervals in the circumferential direction. The engaging element 24 is housed in each of the pockets 34.

[0036] As shown in FIG. 1, the cage 25 has an inward flange portion 35. The flange portion 35 is located between a retaining ring 36 attached to the outer circumference of the inner ring 20 and a shoulder 37 formed on the outer circumference of the inner ring 20. The axial movement of the cage 25 is restricted by the flange portion 35, the retaining ring 36, and the shoulder 37.

[0037] The engaging element 24 is composed of a roller having a circular rolling surface that rotates once around the engaging element central axis.

[0038] The retainer 25 is supported so as to be movable in the circumferential direction with respect to the inner ring 20 between an engaging position where the engaging element 24 is engaged with the cam surface 22 and the cylindrical surface 23 by moving the engaging element 24 shown in FIG. 3 in the circumferential direction from the center in the circumferential direction of the cam surface 22, and a release position where the engagement of the engaging element 24 with respect to the cam surface 22 and the cylindrical surface 23 is released by moving the engaging element 24 to the center in the circumferential direction of the cam surface 22. In FIG. 3, the retainer 25 is shown in the release position, particularly when it is in the neutral release position A where the engaging element 24 is arranged on the center in the circumferential direction of the cam surface 22.

[0039] The centering spring 26 shown in FIGS. 1 and 3 is an elastic member that elastically holds the retainer 25 in the release position and transmits the rotational force of the shaft 4 to the retainer 25. As shown in FIG. 3, the centering spring 26 is composed of a C-shaped annular portion 38 formed by winding a steel wire in a C shape, and a pair of extending portions 39 extending radially outward from both ends of the C-shaped annular portion 38.

[0040] A recess 40 and a radial groove 41 for holding the centering spring 26 are formed on the axial end surface of the inner ring 20. The recess 40 is in the shape of an arc groove extending along the circumferential direction. The radial groove 41 penetrates radially outward from the recess 40 to the outer circumference of the inner ring 20.

[0041] The C-shaped annular portion 38 of the centering spring 26 is fitted into the recess 40. The pair of extending portions 39 are inserted into the radial groove 41. Further, the extending portion 39 protrudes from the radially outer end of the radial groove 41, and the protruding portion of the extending portion 39 from the radial groove 41 is inserted into the cage groove 42 formed in the cage 25. The radial groove 41 and the cage groove 42 are formed to have the same circumferential width. The extending portion 39 is in contact with the groove inner surfaces at both circumferential ends of the radial groove 41 and the groove inner surfaces at both circumferential ends of the cage groove 42, respectively. Thereby, the centering spring 26 is prevented from rotating relative to the inner ring 20 so as to rotate integrally with the inner ring 20, and is also prevented from rotating relative to the cage 25. The cage 25 can be elastically held in the release position by the circumferential force acting on the contact portion between the extending portion 39 and the cage groove 42.

[0042] As shown in FIGS. 1 and 4, the centering spring 26 is axially restricted by an annular cover member 43 fitted on the outer periphery of the inner ring 20 so as not to come out of the recess 40 or the like. The axial movement of the cover member 43 is restricted by a retaining ring 44 attached to the outer periphery of the inner ring 20 and the axial end face of the inner ring 20. Note that the cover member may be omitted, and a flange portion for preventing the centering spring from coming out may be formed on the cage.

[0043] The excitation-operated electromagnetic brake 27 includes an armature 51 arranged to be axially movable between an inner ring shaft portion 50 provided integrally with the inner ring 20 and the inner periphery of a brake case 28, a friction surface portion 52 fixed at a position axially opposed to the armature 51, an electromagnet 53 axially opposed to the armature 51, and a separating spring 54 for separating the armature 51 from the electromagnet 53 and the friction surface portion 52.

[0044] The armature 51 is supported on the outer periphery of the inner ring shaft portion 50 so as to be axially movable. The armature 51 is composed of a disk-shaped movable member formed of a magnetic material (such as iron or silicon steel). Note that a bearing 55 for rotatably supporting the inner ring 20 is arranged between the inner ring shaft portion 50 and the inner periphery of the brake case 28.

[0045] The armature 51 has an engaging recess 56 formed on the side surface on the cage 25 side. The cage 25 has an engaging projection 57 axially inserted into the engaging recess 56. The engaging projection 57 and the engaging recess 56 can engage with each other in the circumferential direction. Thereby, the armature 51 is prevented from rotating relative to the cage 25 so as to move circumferentially integrally with the cage 25 and is arranged to be axially movable relative to the cage 25.

[0046] In the illustrated example, the armature 51 is directly prevented from rotating relative to the cage 25. However, by preventing the cover member from rotating relative to the cage and the armature, the armature may be indirectly prevented from rotating relative to the cage via the cover member.

[0047] The electromagnet 53 has an annular field core 58 having a C-shaped cross section that opens axially toward the armature 51, and a solenoid coil 59 wound around the field core 58. The electromagnet 53 is attached inside the brake case 28 so as not to move in either the axial direction or the circumferential direction. A retaining ring 60 for restricting the axial movement of the electromagnet 53 is attached to the inner circumference of the brake case 28.

[0048] The brake case 28 is formed with a through hole through which a lead wire for supplying power to the solenoid coil 59 passes, and a rubber grommet for filling the gap between the lead wire and the inner circumference of the through hole is attached.

[0049] The friction surface portion 52 is formed integrally with the field core 58. The friction surface portion 52 constitutes the end portion of the field core 58 on the armature 51 side. By attaching the electromagnet 53 to the brake case 28 as described above, the friction surface portion 52 of the field core 58 is fixed at a position axially opposed to the armature 51.

[0050] The separation spring 54 is composed of an annular spring such as a wave washer. The separation spring 54 is disposed between an annular groove portion extending in the circumferential direction on the end face of the armature 51 on the side of the electromagnet 53 and the end face of the field core 58 on the side of the armature 51. Note that it is also possible to change the separation spring to another non-annular spring such as a compression coil spring and arrange them dispersedly at a plurality of locations in the circumferential direction.

[0051] When the solenoid coil 59 is de-energized, the electromagnet 53 is in a non-excited state. At this time, the separation spring 54 supports the armature 51 at a position axially separated from the friction surface portion 52 and the electromagnet 53. When the solenoid coil 59 is energized, the electromagnet 53 becomes an excited state generating a magnetic circuit passing through the field core 58 and the armature 51, and axially attracts the armature 51 to the friction surface portion 52 of the field core 58 against the separation spring 54. By this attraction, the armature 51 can be axially attracted to the friction surface portion 52 which is a stationary system, and an operating pressure can be applied to the friction contact portion between the two 51, 52 to brake the rotation of the retainer 25. Further, when the electromagnet 53 is switched from the non-excited state to the excited state, the separation spring 54 sandwiched between the attracted armature 51 and the field core 58 which is a stationary system is elastically axially compressed and deformed according to the axial movement of the armature 51, so that a spring force in the direction of axially separating the armature 51 from the electromagnet 53 including the friction surface portion 52 is stored. When the electromagnet 53 is switched from the excited state to the non-excited state, due to the elastic restoring force of the separation spring 54, the armature 51 is axially separated from the electromagnet 53 including the friction surface portion 52, so that the rotation of the retainer 25 cannot be braked. The armature 51 separated from the separation spring 54 is received by the retainer 25, and the space between the armature 51 and the electromagnet 53 is restored to a predetermined magnetic gap.

[0052] When the brake unit 7 shown in Fig. 1 is in a non-excited state where no current is applied to the electromagnet 53 of the excitation-operated electromagnetic brake 27, the inner ring 20 is in a free-wheeling state where it can freely rotate in either the forward or reverse direction with respect to the outer ring 21. That is, when the armature 51 is separated from the friction surface portion 52 of the field core 58 by the support of the return spring 54 and the holder 25 cannot be braked by the armature 51 and the friction surface portion 52, no matter whether the inner ring 20 rotates forward or reverse, the holder 25 is carried along by the centering spring 26 that rotates integrally with the inner ring 20 and is held at the release position (usually, the neutral release position A shown in Fig. 3) by the elastic restoring force of the centering spring 26. Therefore, the engaging element 24 held by the holder 25 does not engage with the cam surface 22 on the outer periphery of the inner ring 20 and the cylindrical surface 23 on the inner periphery of the outer ring 21, and the inner ring 20 and the motor shaft 16 can freely rotate in both the forward and reverse directions.

[0053] Fig. 5 shows the state when the holder 25 is at the intermediate release position B (the engaging element 24 is in a non-engaged state with the cam surface 22 and the cylindrical surface 23) during the movement from the neutral release position A in Fig. 3 to the engaging position, and Fig. 6 shows the state when the holder 25 is at the engaging position C (the engaging element 24 is in an engaged state with the cam surface 22 and the cylindrical surface 23).

[0054] When the brake unit 7 is in an excited state where current is supplied to the electromagnet 53 of the excitation-operated electromagnetic brake 27, it enters a locked state capable of preventing rotation of the inner ring 20 in either the forward or reverse direction with respect to the outer ring 21. That is, when current is supplied to the electromagnet 53 to switch to the excited state, the armature 51 is attracted against the return spring 54 to the friction surface portion 52 of the field core 58 and comes into a friction contact state with the friction surface portion 52. At this time, as shown in FIG. 5, when the inner ring 20 rotates in either the forward or reverse direction (in FIG. 5, the case where the inner ring 20 rotates in the direction of the arrow L is illustrated), the rotational force of the inner ring 20 is transmitted from the centering spring 26 that rotates integrally therewith to the cage 25. However, since the braking force due to the friction contact between the armature 51 (see FIG. 1) that is prevented from rotating in the cage 25 and the friction surface portion 52 belonging to the stationary system acts on the cage 25 via the armature 51, the inner ring 20 rotates relative to the cage 25. As a result, the cage 25 that moves in the circumferential direction (in the direction of the arrow R in the example of FIG. 5) with respect to the inner ring 20 elastically deflects one of the pair of extending portions 39 of the centering spring 26 by pushing it in the circumferential direction on the groove inner surface of the cage groove 42, and thus moves in the circumferential direction from the neutral release position A in FIG. 3 to the intermediate release position B in FIG. 5 against the centering spring 26. When this circumferential movement reaches a predetermined angular amount, the cage 25 reaches the engagement position C shown in FIG. 6, and the engaging element 24 held by the cage 25 engages with the cam surface 22 on the outer periphery of the inner ring 20 and the cylindrical surface 23 on the inner periphery of the outer ring 21, so that the rotation of the inner ring 20 is blocked and the rotation of the motor shaft 16 connected to the inner ring 20 is blocked.

[0055] The control unit 8 shown in FIG. 2 controls the reaction force motor 6, the brake unit 7, and the steering motor 12. On the input side of the control unit 8, an external sensor 61, a steering sensor 5, and a steering angle sensor 13 are electrically connected. The external sensor 61 is a vehicle speed sensor or the like that detects the traveling speed of the vehicle. On the output side of the control unit 8, the reaction force motor 6, the brake unit 7, and the steering actuator 2 are electrically connected.

[0056] The control unit 8 operates the steering motor 12 according to the operation amount of the steering wheel 1 detected by the steering sensor 5 and the running state of the vehicle (such as vehicle speed) detected by the external sensor 61, and controls to change the directions of the pair of left and right steering wheels 3. Also, at this time, the control unit 8 controls to operate the reaction force motor 6 so that a steering reaction force of a magnitude corresponding to the operation amount of the steering wheel 1 and the running state of the vehicle is generated.

[0057] Furthermore, the control unit 8 determines whether or not the direction of the steering wheel 3 has reached the stroke end based on the position of the steering shaft 10 detected by the steering sensor 13. Here, when it is determined that the direction of the steering wheel 3 has not reached the stroke end, the electromagnetic brake 27 of the excitation operation type is de-energized by de-energizing the electromagnet 53 shown in FIG. 1, and the brake unit 7 is kept in the above-described free rotation state. On the other hand, when it is determined that the direction of the steering wheel 3 shown in FIG. 2 has reached the stroke end, the electromagnetic brake 27 of the excitation operation type is energized by energizing the electromagnet 53 shown in FIG. 1, and the brake unit 7 is kept in the above-described locked state.

[0058] In the example of FIG. 2, the brake unit 7 including the outer ring 21, the engaging element 24, the retainer 25, and the electromagnetic brake 27 of the excitation operation type is provided on the side opposite to the steering wheel 1 in the axial direction with respect to the reaction force motor 6. However, it is also possible to provide the brake unit 7 between the steering wheel 1 and the reaction force motor 6. In this case, the motor shaft 16 shown in FIG. 1 is extended above the reaction force motor 6, a through hole facing the inner ring shaft portion 50 in the axial direction is added to the brake case 28, the brake unit 7 is attached to the side of the reaction force motor 6 facing the steering wheel 1 in a configuration where the up and down directions are reversed from FIGS. 1 and 2, and the inner ring shaft portion 50 is simply connected to the shaft portion on the steering column side of the shaft 4.

[0059] This steering device is as described above (hereinafter, refer to FIGS. 1 to 6 as appropriate), and includes a steering wheel 1, a steering sensor 5 that detects the operation amount of the steering wheel 1, a steering actuator 2 that changes the direction of the steering wheel 3 as a steering unit according to the operation amount of the steering wheel 1 detected by the steering sensor 5, a shaft 4 connected to the steering wheel 1 so as to rotate integrally with the steering wheel 1, an outer ring 21 having an inner circumference disposed around the shaft 4, an engaging element 24 disposed between the shaft 4 and the inner circumference of the outer ring 21, a holder 25 that holds the engaging element 24 and is disposed so as to be movable in the circumferential direction with respect to the shaft 4 between an engaging position where the engaging element 24 is engaged with the inner circumferences of the shaft 4 and the outer ring 21 and a release position where the engagement is released, a centering spring 26 that elastically holds the holder 25 at the release position and is rotationally locked to the shaft 4 and the holder 25 so as to rotate integrally with the shaft 4, and an excitation-operated electromagnetic brake 27 that brakes the holder 25. Thus, when the excitation-operated electromagnetic brake 27 is de-energized and the holder 25 is not braked, the centering spring 26 rotationally locked to the shaft 4 so as to rotate integrally with the shaft 4 transmits the rotational force of the shaft 4 to the holder 25 and holds the holder 25 at the release position with respect to the shaft 4. Therefore, the engaging element 24 cannot engage with the inner circumferences of the shaft 4 and the outer ring 21, and the rotation of the steering wheel 1 is allowed. On the other hand, when the excitation-operated electromagnetic brake 27 is energized and the holder 25 is braked, even if the steering wheel 1 is rotationally operated, the holder 25 that receives the rotational force of the shaft 4 from the centering spring 26 is braked by the excitation-operated electromagnetic brake 27. Therefore, the shaft 4 rotates relative to the holder 25, and when the holder 25 that moves in the circumferential direction with respect to the shaft 4 reaches the engaging position against the centering spring 26, the engaging element 24 engages with the inner circumferences of the shaft 4 and the outer ring 21, and further rotation of the shaft 4 is reliably blocked. When the excitation-operated electromagnetic brake 27 switches from the energized state to the de-energized state, the holder 25 is returned to the release position by the elastic restoring force of the centering spring 26.

[0060] Therefore, by switching the electromagnetic brake 27 of the excitation operation type from the non-excited state to the excited state, this steering device surely prevents the steering wheel 1 from rotating more than the circumferential movement amount between the release position and the engagement position of the retainer 25, and through the steering wheel 1, the driver can surely be made aware that the direction of the steering wheel 3 has reached the stroke end.

[0061] Note that the circumferential movement amount between the release position and the engagement position of the retainer 25 can be appropriately set based on the engagement element 24, the wedge space formed by the cam surface 22 and the cylindrical surface 23, and the dimensional setting of the engagement element 24. Therefore, when the circumferential movement amount between the release position and the engagement position of the retainer 25 is small and the brake unit 7 quickly shifts to the locked state, it is possible for the control unit 8 to slightly reduce the amount of rotation allowed for the steering wheel 1 after switching the electromagnetic brake 27 of the excitation operation type from the non-excited state to the excited state. In such a case, when the control unit 8 determines that the direction of the steering wheel 3 has reached the stroke end, there are no practical problems even if the electromagnetic brake 27 of the excitation operation type is switched from the non-excited state to the excited state. For example, the circumferential movement amount between the release position and the engagement position of the retainer 25 can be set to 20° or less in terms of the rotation angle between the release position and the engagement position of the retainer 25.

[0062] Also, when the control unit 8 can allow the steering wheel 1 to rotate by a predetermined amount after switching the electromagnetic brake 27 of the excitation operation type from the non-excited state to the excited state, when the control unit 8 determines that the direction of the steering wheel 3 has reached a predetermined stroke position, the electromagnetic brake 27 of the excitation operation type may be switched from the non-excited state to the excited state. The predetermined stroke position allows a predetermined amount of rotation of the steering wheel 1 corresponding to the circumferential movement amount between the release position and the engagement position of the retainer 25 (corresponding to the rotation angle θ from the neutral release position A to the engagement position C of the retainer 25 shown in FIG. 6) after switching the electromagnetic brake 27 of the excitation operation type from the non-excited state to the excited state, and when the direction of the steering wheel 3 reaches the stroke end due to the change in the direction of the steering wheel 3 corresponding to the rotation operation of the steering wheel 1 for the allowed amount, the retainer 25 may be set to reach the engagement position.

[0063] As described above, when setting the timing for switching the excitation-operated electromagnetic brake 27 from the non-excited state to the excited state either when it is determined that the direction of the steering wheel 3 has reached the stroke end or when it is determined that a predetermined stroke position has been reached, a resistance (reaction force from the centering spring 26) is applied to the shaft 4 when the centering spring 26 is elastically deformed while the retainer 25 moves from the release position to the engagement position, and this resistance increases as the retainer 25 approaches the engagement position. For the driver, the rotation operation of the steering wheel 1 becomes heavier due to the above-described increase in resistance. That is, in the examples of FIGS. 5 and 6, the torque (reaction force from the centering spring 26) for deflecting the extending portion 39 of the centering spring 26 increases, and this torque is received by the driver holding the steering wheel 1 in FIG. 2. Therefore, when the excitation-operated electromagnetic brake 27 is switched to the excited state, the driver feels that the steering torque required for the rotation operation of the steering wheel 1 is greater than that during the normal rotation operation of the steering wheel 1 (when the excitation-operated electromagnetic brake 27 is non-excited), that is, the rotation operation has become heavier. Thereby, the driver can be made to sense that the direction of the steering wheel 3 is near the stroke end.

[0064] Further, this steering device includes an excitation-operated electromagnetic brake 27 having an armature 51 that is rotationally stopped by a retainer 25 and arranged to be axially movable, a friction surface portion 52 fixed at a position axially opposed to the armature 51, an electromagnet 53 axially opposed to the armature 51, and a separation spring 54 arranged to store energy in response to the axial movement of the armature 51 that is supported at a position axially separated from the electromagnet 53 and the friction surface portion 52 when the electromagnet 53 is de-energized and attracted to the friction surface portion 52 by the electromagnet 53 when the electromagnet 53 is energized. Therefore, when the electromagnet 53 is in a de-energized state where no current is passed through it, the armature 51 can be held at a position separated from the friction surface portion 52 by the support of the separation spring 54, keeping the retainer 25 in an unbraked state, and a predetermined magnetic gap can be provided between the armature 51 and the electromagnet 53. When the electromagnet 53 is switched from the de-energized state to the energized state, the electromagnet 53 attracts the armature 51 against the separation spring 54 to the friction surface portion 52, applying an operating pressure between the friction surface portion 52 and the armature 51, thereby enabling the retainer 25 to be braked and moved circumferentially with respect to the shaft 4. Since the separation spring 54 stores energy in response to the axial movement of the armature 51 during this attraction, when the electromagnet 53 is switched from the energized state to the de-energized state, the elastic restoring force of the separation spring 54 can separate the armature 51 from the friction surface portion 52 and the electromagnet 53, releasing the braking of the retainer 25.

[0065] In addition, this steering device has an electromagnet 53, a field core 58 that faces the armature 51 in the axial direction, and a solenoid coil 59 wound around the field core 58. The friction surface portion 52 is integrally formed with the field core 58, and the armature 51 is a movable member that is directly attracted to the friction surface portion 52 of the field core 58 when the electromagnet 53 is excited. Therefore, a rotor that serves as a contact partner for the armature 51 can be eliminated between the electromagnet 53 and the armature 51, and thus, the size and the number of components of the excitation operation type electromagnetic brake 27 can be reduced. Further, since there is no rotor between the electromagnet 53 and the armature 51, magnetic flux circulates more efficiently between the electromagnet 53 and the armature 51 than in the case where there is a rotor. Therefore, compared with the case where there is a rotor, when there is no rotor, the attractive force of the electromagnet 53 on the armature 51 is increased to enhance the braking performance of the holder 25, and thus, the reaction force of the centering spring 26 against the relative rotation of the holder 25 and the shaft 4 during braking can be increased to increase the steering torque.

[0066] Here, the relationship between the rotation angle of the steering wheel 1 and the shaft 4 and the increase in the steering torque, which is the reaction force from the centering spring 26 described above, is schematically shown in FIG. 7. The "centering spring torque generation region" in FIG. 7 corresponds to the case where, after switching the excitation operation type electromagnetic brake 27 to the excited state, the driver further turns the steering wheel 1 of FIG. 2 until the retainer 25 of FIG. 3 reaches the engagement position C of FIG. 6 from the neutral release position A. The "roller engagement region" in FIG. 7 corresponds to the case where, after the retainer 25 reaches the engagement position C as shown in FIG. 6, the rotation operation is blocked by the engagement of the cam surface 22 and the cylindrical surface 23 of the engaging element 24 even if the driver tries to further turn the steering wheel 1 of FIG. 2. As shown in FIG. 7, when the driver further turns the steering wheel 1 toward the stroke end side after switching the excitation operation type electromagnetic brake 27 of FIG. 1 to the excited state (centering spring torque generation region), the steering torque increases as the steering wheel 1 is further turned. This tendency is the same regardless of the presence or absence of the rotor. However, compared with the case where the rotor is present, when the rotor is absent, the steering torque in the centering spring torque generation region is clearly larger immediately after excitation, and the increase rate of the steering torque with respect to the increase in the rotation angle (amount of turn) also becomes larger.

[0067] Therefore, this steering device provided with the excitation operation type electromagnetic brake 27 without a rotor as described above can quickly make the rotation operation of the steering wheel 1 heavier than in the normal state (when the electromagnet 53 is not excited) immediately after excitation of the electromagnet 53, and can make the driver sense that the direction of the steered wheels 3 is near the stroke end.

[0068] Further, this steering device includes a control unit 8 that switches the excitation operation type electromagnetic brake 27 to an excited state at a predetermined stroke position before the direction of the steering wheel 3 as the steering unit reaches the stroke end. As a result, the electromagnet 53 is switched to an excited state at a predetermined stroke position near the stroke end of the direction of the steering wheel 3. For a driver who further turns the steering wheel 1 after this switching, the rotational operation of the steering wheel 1 is quickly made heavier than normal until the direction of the steering wheel 3 reaches the stroke end, and the driver can be made to sense that the direction of the steering wheel 3 is approaching the stroke end.

[0069] Further, this steering device includes a cylindrical brake case 28 that houses the excitation operation type electromagnetic brake 27 and the outer ring 21. The brake case 28 is formed of a non-magnetic material separate from the outer ring 21, and the outer ring 21 is prevented from rotating relative to the brake case 28. Therefore, when the excitation operation type electromagnetic brake 27 is in an excited state, leakage of the magnetic flux generated from the excitation operation type electromagnetic brake 27 to the brake case 28 can be prevented. For this reason, the size of the excitation operation type electromagnetic brake 27 can be reduced.

[0070] Further, this steering device further includes a reaction force motor 6 that applies a steering reaction force to the steering wheel 1. The steering unit is a pair of left and right steering wheels 3. The outer ring 21, engagement element 24, retainer 25, and excitation operation type electromagnetic brake 27 are provided between the steering wheel 1 and the reaction force motor 6 or on the side axially opposite to the steering wheel 1 with respect to the reaction force motor 6. Therefore, as a steer-by-wire type steering device for a vehicle, the driver can be surely made to sense through the steering wheel 1 that the direction of the steering wheel 3 has reached the stroke end.

[0071] FIG. 8 shows a second embodiment of the present invention. Hereinafter, differences from the first embodiment will be described, and the same element names will be used for the components corresponding to those in the first embodiment.

[0072] The steering device according to the second embodiment has an outer ring 71 integrally formed with a brake case 72. Among the inner circumference of the brake case 72, the part that functions as the outer ring 71 is the rib that forms a cylindrical surface for engaging an engaging element 73. A bearing 74 is disposed between an inner ring 75 and the inner circumference of the brake case 72. The inner circumferential portion of the brake case 72 from the open end of the brake case 72 to the electromagnet 53 has an inner diameter enlarged compared to the first embodiment, and corresponding to the enlargement of the inner diameter, dimensions of each part such as the outer diameter of a cage 76, a cover member 77, and the pitch circle diameter of the engaging element 73 are enlarged. Thereby, the electromagnet 53, the armature 78, etc. can be inserted from the opening of the brake case 72 into the inside of the brake case 72.

[0073] A separating spring 79 is interposed between a retaining ring 60 and the armature 78.

[0074] A notch 80 recessed axially is formed on the side surface of the cage 76 on the armature 78 side. Also, a slit 81 penetrating the armature 78 axially is formed. The cover member 77 has a first protrusion 82 inserted into the notch 80 in a circumferentially engageable and axially movable state, and a second protrusion 83 inserted into the slit 81 in a circumferentially engageable and axially movable state. The armature 78 is axially moved with respect to the cage 76 and the cover member 77 by switching between the non-excited state and the excited state of the electromagnet 53, but is prevented from rotating with respect to the cage 76 via the cover member 77 by the circumferential engagement between the first protrusion 82 and the notch 80 and between the second protrusion 83 and the slit 81.

[0075] The steering device according to the second embodiment includes a cylindrical brake case 72 that houses an excitation-operated electromagnetic brake 27. Since the outer ring 71 is integrally formed with the brake case 72, the steps of axially positioning the outer ring 71 with respect to the brake case 72 using a retaining ring or the like and preventing rotation using a key or the like are eliminated, and the number of parts can be reduced.

[0076] In each of the above-described embodiments, a roller has been described as an example of the engaging element, but it is also possible to use a ball or a sprag as the engaging element.

[0077] In each of the above-described embodiments, the motor case and the brake case of the reaction force motor are formed separately, but they may be formed integrally.

[0078] In each of the above-described embodiments, the friction surface portion is configured as a part of the field core of the electromagnet, but the friction surface portion may be provided as another member such as a rotor attached to the brake case.

[0079] In each of the above-described embodiments, the steer-by-wire type operation device for a vehicle is excited, but the present invention can also be applied to a steer-by-wire type operation device for a ship that does not have a reaction force motor and includes a rudder as a steering portion.

[0080] The embodiments disclosed this time should be considered as illustrative in all respects and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims are included.

Explanation of Reference Numerals

[0081] 1 Steering wheel 2 Steering actuator 3 Steering wheel (steering portion) 4 Shaft 5 Steering sensor 6 Reaction force motor 8 Control unit 16 Motor shaft 20, 75 Inner ring 21, 71 Outer ring 22 Cam surface 23 Cylindrical surface 24, 73 Engaging element 25, 76 Retainer 26 Centering spring 27 Excitation-operated electromagnetic brake 28, 72 Brake case 33 Key member 39 Extension part 41 Radial groove 42 Retainer groove 51, 78 Armature 52 Friction surface 53 Electromagnet 54, 79 Separation spring 58 Field core 59 Solenoid coil

Claims

1. In a steer-by-wire type steering device including a steering wheel, a steering sensor that detects an operation amount of the steering wheel, and a steering actuator that changes the direction of a steering section according to the operation amount of the steering wheel detected by the steering sensor, a shaft connected to the steering wheel so as to rotate integrally with the steering wheel, an outer ring having an inner circumference disposed around the shaft, an engaging member disposed between the shaft and the inner circumference of the outer ring, a retainer that holds the engaging member and is disposed so as to be movable in the circumferential direction between an engaging position where the engaging member is engaged with the shaft and the inner circumference of the outer ring and a release position where the engagement is released, a centering spring that elastically holds the retainer in the release position and is rotationally stopped on the shaft and the retainer so as to rotate integrally with the shaft, and an excitation-operated electromagnetic brake that brakes the retainer, the steer-by-wire type steering device being characterized by further comprising these components.

2. The excitation-operated electromagnetic brake includes an armature that is rotationally stopped on the retainer and is disposed so as to be axially movable, a friction surface portion fixed at a position axially opposed to the armature, an electromagnet axially opposed to the armature, and a separation spring disposed so as to accumulate energy according to the axial movement of the armature that is supported at a position axially separated from the electromagnet and the friction surface portion when the electromagnet is de-energized and is attracted to the friction surface portion by the electromagnet when the electromagnet is energized, the steer-by-wire type steering device according to Claim 1.

3. The electromagnet has a field core axially opposed to the armature and a solenoid coil wound around the field core, the friction surface portion is formed integrally with the field core, and the armature is a movable member that is directly adsorbed to the friction surface portion of the field core when the electromagnet is energized, the steer-by-wire type steering device according to Claim 2.

4. The steer-by-wire type steering device according to Claim 3 further includes a control unit that switches the excitation-operated electromagnetic brake to an excited state at a predetermined stroke position before the direction of the steering section reaches a stroke end.

5. The steer-by-wire type steering device further includes a cylindrical brake case that houses the outer ring and the excitation-operated electromagnetic brake. The brake case is formed of a non-magnetic body separate from the outer ring, The outer ring is prevented from rotating relative to the brake case. The steer-by-wire type steering apparatus according to any one of claims 1 to 4. **Claim 6** Further comprising a cylindrical brake case for housing the excitation-operated electromagnetic brake, The outer ring is integrally formed with the brake case. The steer-by-wire type steering apparatus according to any one of claims 1 to 4. **Claim 7** Further comprising a reaction force motor for applying a steering reaction force to the steering wheel, The steering wheel is a pair of left and right steering wheels, The outer ring, the engagement member, the retainer, and the excitation-operated electromagnetic brake are provided between the steering wheel and the reaction force motor or on the side axially opposite to the steering wheel with respect to the reaction force motor. The steer-by-wire type steering apparatus according to any one of claims 1 to 6.

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