JP2014210465A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device which achieves good steering feeling during initial steering and inhibits noise occurring during the initial steering.SOLUTION: A motor shaft 24 and a worm shaft 18 are coaxially connected through a joint 33. The joint 33 includes: a first member 34 connected with the motor shaft 24; a second member 35 connected with the worm shaft 18 through spline fitting; and an elastic member 36 disposed between the first and second members 34, 35. A first spline of a spline shaft 41 and a second spline of a spline hole 42 provided at the second member 35 fit with each other on tooth surfaces inclined in an axial direction Y. The second member 35 moves in the axial direction to the first member 34 side during initial steering when the motor shaft 24 is stopped.

Description

  The present invention relates to an electric power steering apparatus.

In the electric power steering apparatus, the rotational output of the electric motor is decelerated via the worm and the worm wheel and transmitted to the steering mechanism, thereby assisting the steering operation with torque.
In Patent Document 1, the worm shaft is elastically supported in the axial direction by a cylindrical member such as rubber disposed on both sides of the inner ring of the bearing that supports the worm shaft, and the worm shaft is movable in the axial direction with respect to the bearing. Power steering devices have been proposed.

  On the other hand, Patent Document 2 proposes a joint including an elastic member that transmits torque by being interposed between a motor shaft and a worm shaft of an electric motor.

JP 2012-111457 A JP 2002-145083 A

In Patent Document 1, the worm shaft moves in the axial direction without rotating in the initial stage of steering immediately after the driver starts operating the steering member. Therefore, since the electric motor that is stopped before the start of driving does not become a resistance of the steering operation at the initial stage of steering, there is an advantage that the steering feeling at the initial stage of steering can be improved.
However, since the entire worm shaft moves in the axial direction, for example, noise due to rattling noise at the meshing portion between the worm shaft and the worm wheel and noise due to rattling noise of the bearing supporting the worm shaft are generated. There is a risk.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an electric power steering apparatus that has good steering feeling at the initial stage of steering and can suppress the generation of abnormal noise at the initial stage of steering.

  In order to achieve the object, the invention of claim 1 has a motor housing (21) and a motor shaft (24; 124) supported by the motor housing so as to be immovable and rotatable in the axial direction (X). Worm shaft (18; 118) which is supported so as to be immovable and rotatable in the axial direction (Y) by an electric motor (16) for assisting steering and bearings (27, 28) held in gear housing (20). And a worm wheel (19) meshing with the worm shaft, a speed reducer (17) for decelerating the rotation of the motor shaft and transmitting it to the steering mechanism (A), and the motor shaft and the worm shaft are coaxial. A coupling (33; 133; 233) coupled to the motor shaft so as to be capable of transmitting torque, the coupling including a first member (34; 134; 234) coupled to the motor shaft so as to transmit torque. A shaft interposed between the first member and the second member, and a second member (35; 135; 235) coupled to the worm shaft so as to transmit torque and coupled to the first member so as to transmit torque. Elastic members (36; 136; 236, 60) that are elastically compressible in a direction, wherein at least one of the first member and the second member is moved in the axial direction by a corresponding motor shaft or worm shaft The at least one of the first member and the second member, and the corresponding motor shaft or worm shaft, which are supported so as to be inclined with respect to the axial direction (44a, 44b; 45a, 45b; 144a) , 144b; 145a, 145b) The electric power steer connected via the first spline (44; 144) and the second spline (45; 145) which are engaged with each other. Providing; (100 1) ring system.

  In addition, although the alphanumeric character in a parenthesis represents the corresponding component etc. in embodiment mentioned later, this does not mean that this invention should be limited to those embodiment as a matter of course. The same applies hereinafter.

  According to the first aspect of the present invention, when the worm shaft is slightly rotated by the worm wheel when the electric motor is not driven at the initial stage of steering, for example, the second member spline-fitted to the worm shaft is The first spline and the second spline that are fitted to each other with the tooth surfaces inclined with respect to the direction do not rotate and compress the elastic member interposed between the first member and the second member from the worm shaft. It moves in the axial direction to move away (that is, to approach the first member). Therefore, the steering feeling in the initial stage of steering can be improved. In addition, it suppresses the generation of unusual noise (for example, rattling noise at the meshing portion of the worm shaft and the worm wheel, rattling noise of the bearing that supports the worm shaft) as in the case of moving the worm shaft in the axial direction. be able to.

1 is a schematic diagram of an electric power steering apparatus according to a first embodiment of the present invention, and shows a schematic configuration of the electric power steering apparatus. It is a schematic sectional drawing of the electric motor and reduction gear of 1st Embodiment. It is a disassembled perspective view of the coupling of 1st Embodiment and its peripheral part. It is sectional drawing of the coupling of 1st Embodiment, and is equivalent to sectional drawing which follows the IV-IV line of FIG. It is a schematic diagram which shows the meshing state of the 1st spline and 2nd spline of 1st Embodiment. It is sectional drawing of the coupling of 1st Embodiment, and its peripheral structure, (a) shows the state at the time of non-steering, (b) has shown the state at the initial stage of steering. It is a schematic sectional drawing of the electric motor and the reduction gear in the electric power steering apparatus of 2nd Embodiment of this invention. It is sectional drawing of the coupling of 2nd Embodiment, and its peripheral structure, (a) has shown the state at the time of non-steering, (b) has shown the state of steering initial stage. It is a schematic diagram which shows the meshing state of the 1st spline and 2nd spline of 2nd Embodiment. It is sectional drawing of the coupling in 3rd Embodiment of this invention.

Preferred embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic configuration diagram of an electric power steering apparatus according to a first embodiment of the present invention. Referring to FIG. 1, an electric power steering device 1 includes a steering shaft 3 connected to a steering member 2 such as a steering wheel, an intermediate shaft 5 connected to the steering shaft 3 via a universal joint 4, A rack as a steered shaft extending in the left-right direction of an automobile, having a pinion shaft 7 connected to the shaft 5 via a universal joint 6 and a rack 8a meshing with the pinion 7a provided in the vicinity of the end of the pinion shaft 7 Bar 8. The pinion shaft 7 and the rack bar 8 constitute a steering mechanism A including a rack and pinion mechanism.

The rack bar 8 is supported in a housing 9 fixed to the vehicle body so as to be capable of linear reciprocation through a plurality of bearings (not shown). Both end portions of the rack bar 8 protrude to both sides of the housing 9, and tie rods 10 are coupled to the respective end portions. Each tie rod 10 is connected to a corresponding steered wheel 11 via a corresponding knuckle arm (not shown).
When the steering member 2 is operated and the steering shaft 3 is rotated, this rotation is converted into a linear motion of the rack bar 8 along the left-right direction of the automobile by the pinion 7a and the rack 8a. Thereby, the turning of the steered wheel 11 is achieved.

The steering shaft 3 includes an input-side first steering shaft 3a having a steering member 2 connected to one end thereof, an output-side second steering shaft 3b connected to the pinion shaft 7, a first steering shaft 3a, and a second steering shaft 3b. And a torsion bar 12 connected to be rotatable relative to each other on the same axis.
A torque sensor 13 is provided for detecting a steering torque based on a relative rotational displacement amount between the first steering shaft 3a and the second steering shaft 3b via the torsion bar 12. The torque detection result of the torque sensor 13 is given to an ECU (Electronic Control Unit) 14. The ECU 14 drives and controls the steering assisting electric motor 16 via the drive circuit 15 based on a torque detection result or a vehicle speed detection result given from a vehicle speed sensor (not shown).

  The output rotation of the electric motor 16 is decelerated via a speed reducer 17 as a transmission device and transmitted to the pinion shaft 7 and converted into a linear motion of the rack bar 8 to assist steering. The speed reducer 17 is a worm shaft 18 as a drive gear that is rotationally driven by the electric motor 16, and a driven gear that meshes with the worm shaft 18 and is connected to the second steering shaft 3b of the steering shaft 3 so as to be integrally rotatable. And a worm wheel 19.

  FIG. 2 is a cross-sectional view of the electric motor 16 and the speed reducer 17. As shown in FIG. 2, the electric motor 16 includes a motor housing 21 that is formed in a bottomed cylindrical shape and is fixed to the gear housing 20, and a stator 22 that is fixed to the inner periphery of the motor housing 21 and generates a rotating magnetic field. The rotor 23 rotates according to the rotating magnetic field, and the motor shaft 24 is press-fitted coaxially to the rotor 23. The motor shaft 24 is rotatably supported by the worm side bearing 25 and the anti-worm side bearing 26 held by the motor housing 21 in a state where movement in the axial direction X is restricted.

  The worm shaft 18 is disposed coaxially with the motor shaft 24 of the electric motor 16. The worm shaft 18 includes a first end 18a and a second end 18b that are separated from each other in the axial direction Y, and a tooth portion 18c at an intermediate portion between the first end 18a and the second end 18b. A positioning step 18d is provided between the first end 18a and the tooth 18c. A positioning step 18e opposite to the positioning step 18d is provided between the second end 18b and the tooth 18c. The worm wheel 19 is coupled to an intermediate portion in the axial direction of the second steering shaft 3b of the steering shaft 3 so as to be integrally rotatable and immovable in the axial direction.

The first end 18 a of the worm shaft 18 is rotatably supported by the gear housing 20 via the first bearing 27. The second end 18 b of the worm shaft 18 is rotatably supported by the gear housing 20 via the second bearing 28. The first bearing 27 and the second bearing 28 are constituted by ball bearings, for example.
The gear housing 20 includes a worm shaft housing portion 20 a that houses the worm shaft 18, and a worm wheel housing portion 20 b that is connected to the worm shaft housing portion 20 a so as to intersect with the worm wheel 19. The worm shaft accommodating portion 20 a has an opening 29 that opens on the opposite side to the electric motor 16. A screw member 30 is screwed into a screw portion in the opening 29 and is locked by a lock nut 31.

  One end face of the outer ring 27 a of the first bearing 27 is in contact with a positioning step 32 provided in the worm shaft housing portion 20 a of the gear housing 20. The screw member 30 biases one end face of the outer ring 28a of the second bearing 28 toward the first bearing 27 side. Accordingly, the outer rings 27 a and 28 a of the first bearing 27 and the second bearing 28 are positioned and fixed to the gear housing 20.

  On the other hand, the end surface of the inner ring 27 b of the first bearing 27 is in contact with the positioning step portion 18 d of the worm shaft 18. Further, the end face of the inner ring 28 b of the second bearing 28 is in contact with the positioning step portion 18 e of the worm shaft 18. Therefore, the preload by the screw member 30 causes the outer ring 28a of the second bearing 28, the inner ring 28b of the second bearing 28, the positioning step 18e of the worm shaft 18, the positioning step 18d of the worm shaft 18, and the first bearing. 27 is provided to the positioning step 32 of the gear housing 20 through the inner ring 27b of the first bearing 27 and the outer ring 27a of the first bearing 27 sequentially. That is, axial preload is applied to the first bearing 27 and the second bearing 28 at once. Further, the movement of the worm shaft 18 in the axial direction Y is restricted by the first bearing 27 and the second bearing 28.

A spline shaft 41 is connected to the first end portion 18a of the worm shaft 18 to be connected to a joint 33 described later. The first end portion 18 a of the worm shaft 18 and the end portion of the motor shaft 24 (output shaft) of the electric motor 16 opposed to the first end portion 18 a are connected via a joint 33 so that torque can be transmitted.
Specifically, the joint 33 is moved in the axial direction to the first member 34 that is connected to the motor shaft 24 of the electric motor 16 so as to be integrally rotatable and non-movable in the axial direction, and to the first end 18 a of the worm shaft 18. Between the first member 34 and the second member 35, the second member 35 is connected so as to be able to transmit torque in a possible state and is connected to the first member 34 so as to be able to transmit torque, and is elastically compressed in the axial direction. And an elastic member 36 interposed therebetween.

  Referring to FIG. 3 which is an exploded perspective view of the joint 33 and its peripheral structure and FIG. 6A which is a schematic sectional view, the first member 34 is a disc having a first end face 37a and a second end face 37b. A worm shaft 18 extending from the second end surface 37b of the main body 37, a press-fitting hole 38 provided in the center of the first end surface 37a of the main body 37, and a press-fitting hole 50 at the end of the motor shaft 24. And a plurality of engaging protrusions 39 which are formed to protrude toward the side and are arranged at equal intervals in the circumferential direction.

  The second member 35 is provided at the center of the disc-shaped main body 40 having the first end surface 40 a and the second end surface 40 b, and the second end surface 40 b of the main body 40, and the second member 35 of the first end 18 a of the worm shaft 18. A spline hole 42 into which the spline shaft 41 is spline-fitted, and a plurality of engaging protrusions 43 that protrude from the first end surface 40a of the main body 40 toward the electric motor 16 and are arranged at equal intervals in the circumferential direction. ing.

The elastic member 36 is a rubber member having a cylindrical shape, for example. The elastic member 36 is interposed between the second end surface 37 b of the main body 37 of the first member 34 and the first end surface 40 a of the main body 40 of the second member 35, and the second end surface 37 b of the main body 37 of the first member 34. The second member 35 can be elastically compressed in the axial direction between the first end surface 40 a of the main body 40 of the second member 35.
As shown in FIG. 4, which is a cross-sectional view taken along the line IV-IV in FIG. 2, the engagement protrusions 39 of the first member 34 and the engagement protrusions 43 of the second member 35 are alternately engaged in the circumferential direction. Torque is transmitted between the first member 34 and the second member 35. The elastic member 36 is accommodated in a space surrounded by the engagement protrusions 39 and 43.

Referring again to FIG. 2, the spline shaft 41 of the worm shaft 18 is fitted into the spline hole 42 of the second member 35, so that the second member 35 can be moved in the axial direction Y by the spline shaft 41. It is supported.
Further, as shown in FIG. 5 which is a schematic diagram, the first spline 44 (male spline) provided on the spline shaft 41 of the worm shaft 18 is rotated in the rotation direction (first rotation direction Z1, second rotation direction Z2). It has a pair of opposing tooth surfaces 44a and 44b. The second spline 45 (female spline) provided in the spline hole 42 of the second member 35 has a pair of tooth surfaces 45 a and 45 b that face the pair of tooth surfaces 44 a and 44 b of the first spline 44, respectively. .

  The tooth surfaces 45a and 45b of the second spline 45 facing the tooth surfaces 44a and 44b of the first spline 44 are inclined at the same angle opposite to each other in the axial direction Y. In other words, the tooth thickness t1 of the first spline 44 of the spline shaft 41 is made thinner toward the electric motor 16 side. The tooth thickness t2 of the second spline 45 of the spline hole 42 is made thinner toward the worm shaft 18 side.

When the first spline 44 rotates in the first rotation direction Z1, one tooth surface 44a of the first spline 44 engages with one tooth surface 45a of the second spline 45, and the rotational force is converted into an axial force. Thus, the second spline 45 moves to one Y1 in the axial direction Y (on the electric motor 16 side).
Although not shown, when the first spline 44 rotates in the second rotational direction Z2, the other tooth surface 44b of the first spline 44 engages with the other tooth surface 45b of the second spline 45, and the rotational force is increased. Converted into axial force, the second spline 45 moves to one Y1 in the axial direction Y (on the electric motor 16 side).

  According to the present embodiment, when the worm shaft 18 is slightly rotated by the worm wheel 19 while the electric motor 16 is not driven at the initial stage of steering, as shown in FIG. The spline-fitted second member 35 does not rotate due to the action of the first spline 44 and the second spline 45 that are fitted between the tooth surfaces 44a and 45a inclined with respect to the axial direction Y (see FIG. 5). Thus, one Y1 in the axial direction Y1 (electrically driven) moves away from the worm shaft 18 while compressing the elastic member 36 interposed between the first member 34 and the second member 35 (that is, closer to the first member 34). To the motor 16 side).

  Therefore, the stopped electric motor 16 does not become a resistance to the rotation of the worm wheel 19 (rotation by the steering operation by the driver), and the steering feeling at the initial stage of steering can be improved. In addition, it suppresses the generation of unusual noise (for example, rattling noise at the meshing portion of the worm shaft and the worm wheel, rattling noise of the bearing that supports the worm shaft) as in the case of moving the worm shaft in the axial direction. be able to.

7 and 8 show a second embodiment of the present invention. The second embodiment is mainly different from the first embodiment of FIG. That is, in the first embodiment of FIG. 2, the first member 34 of the joint 33 is fixed to the motor shaft 24, and the second member 35 is splined so as to be movable in the axial direction with respect to the first end portion 18 a of the worm shaft 18. It is mated.
On the other hand, referring to FIG. 7 and FIG. 8A which is an enlarged view, in the second embodiment, a spline shaft 141 is provided at the end of the motor shaft 124 and the first member 134 of the joint 133 is provided. A spline hole 142 for spline fitting to the spline shaft 141 is provided in the first end surface 137 a of the main body 137. Thus, the first member 134 is supported by the motor shaft 124 so as to be movable in the axial direction X.

A press-fit portion 150 is provided at the first end portion 118 a of the worm shaft 118, and a press-fit hole 138 into which the press-fit portion 150 is press-fit is provided at the second end surface 140 b of the main body 140 of the second member 135. Thereby, the axial movement of the second member 135 is restricted.
As shown in FIG. 9, which is a schematic diagram, the first spline 144 (male spline) provided on the spline shaft 141 of the motor shaft 124 has a pair of tooth surfaces 144a and 144b facing each other in the rotational direction. Yes. The second spline 145 (female spline) provided in the spline hole 142 of the first member 34 has a pair of tooth surfaces 145a and 145b that face the pair of tooth surfaces 144a and 144b of the first spline 144, respectively. ing.

  The tooth surfaces 145a and 145b of the second spline 145 facing the tooth surfaces 144a and 144b of the first spline 144 are inclined at equal angles in opposite directions with respect to the axial direction Y. In other words, the tooth thickness t10 of the first spline 144 of the spline shaft 141 is made thinner toward the worm shaft 118 side. The tooth thickness t20 of the second spline 145 of the spline hole 142 is made thinner toward the electric motor 16 side.

When the first spline 144 rotates in the first rotational direction Z1, one tooth surface 144a of the first spline 144 and one tooth surface 145a of the second spline 145 are engaged, and the rotational force is converted into an axial force. Thus, the first spline 144 moves to one side X1 (the worm shaft 118 side) in the axial direction X.
Although not shown, when the first spline 144 rotates in the second rotational direction Z2, the other tooth surface 144b of the first spline 144 and the other tooth surface 145b of the second spline 145 are engaged, and the rotational force is increased. Converted into the axial force, the first spline 144 moves to one side X1 in the axial direction X (the worm shaft 118 side).

  In the constituent elements of the second embodiment, the same constituent elements as those of the first embodiment are denoted by the same reference numerals as those of the constituent elements of the first embodiment. Further, in the second embodiment of FIGS. 7 and 8A and 8B, the elastic member 136, the second end surface 137b, the engagement protrusion 139, the first end surface 140a, and the engagement protrusion 143 are shown in FIG. This corresponds to the elastic member 36, the second end face 37b, the engagement protrusion 39, the first end face 40a, and the engagement protrusion 43 of the first embodiment shown in FIGS.

  According to the present embodiment, when the worm shaft 118 is slightly rotated by the worm wheel 19 when the electric motor 16 is not driven at the initial stage of steering, as shown in FIG. The spline-fitted first member 134 does not rotate, and compresses the elastic member 136 interposed between the first member 134 and the second member 135 while moving away from the motor shaft 124. Move to (worm shaft 18 side).

  Therefore, the stopped electric motor 16 does not become a resistance to the rotation of the worm wheel 19 (rotation by the steering operation by the driver), and the steering feeling at the initial stage of steering can be improved. Therefore, the generation of abnormal noise (for example, rattling noise at the meshing portion of the worm shaft and the worm wheel, rattling noise of the bearing supporting the worm shaft, etc.) that occurs when the conventional worm shaft is moved in the axial direction is generated. Can be suppressed.

The present invention is not limited to the above-described embodiments. For example, the first member of the joint is spline-fitted to the first end of the worm shaft so as to be movable in the axial direction, and the motor shaft The second member of the joint may be spline fitted to the end portion so as to be movable in the axial direction.
Moreover, in each said embodiment, as shown, for example in FIG. 4, the engagement protrusions 39 and 43 of the 1st member 34 of the coupling 33 and the 2nd member 35 are directly engaging in the rotation direction. On the other hand, like the joint 233 of the third embodiment shown in FIG. 10, the engagement protrusions 239 and 243 of the first member 234 and the second member 235 are rotated via the interposition member 60 made of an elastic member. You may engage indirectly in the direction. The interposition member 60 includes an annular main body 61 that surrounds the elastic member 236 corresponding to the elastic member 36 of FIG. 4 and a plurality of engagement arms that extend radially from the main body 61 and are respectively interposed between the corresponding engagement protrusions 239 and 243. 62.

  Although not shown, the interposed member 60 is interposed between the main body of the first member 234 and the main body of the second member 235 in the axial direction. When both the elastic member 236 and the interposed member 60 made of an elastic member are used in combination, at least one of them is elastically compressed in the axial direction between the main body of the first member 234 and the main body of the second member 235. What is necessary is just to exhibit the same function as the elastic member 36 of 1st Embodiment. Further, either one of the elastic member 236 and the interposition member 60 may be eliminated, and the same function as that of the elastic member 36 of the first embodiment may be exhibited only by the other.

  In addition, the present invention can be variously modified within the scope of the claims.

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus, 2 ... Steering member, 3 ... Steering shaft, 16 ... Electric motor, 17 ... Reduction gear, 18; 118 ... Worm shaft, 19 ... Worm wheel, 20 ... Gear housing, 21 ... Motor housing, 24 124 ... motor shaft, 27 ... first bearing, 28 ... second bearing, 33; 133; 233 ... joint, 34; 134; 234 ... first member, 35; 135; 235 ... second member, 36; 136; 236 ... elastic member, 37; 137 ... main body, 38; 138 ... press-fitting hole, 39; 139; 239 ... engagement protrusion, 40; 140 ... main body, 40a; 140a ... first end face, 40b; 140b ... second end face, 41; 141 ... spline shaft, 42; 142 ... spline hole, 43; 143; 243 ... engagement protrusion, 44; 144 ... first spline, 44a, 44b; 1 4a, 144b ... tooth surface, 45a, 45b; 145a, 145b ... tooth surface, 50; 150 ... press-fitting part, 60 ... interposition member (elastic member), 61 ... main body, 62 ... engagement arm, A ... steering mechanism, X ... Axis direction (motor shaft), Y ... Axis direction (worm shaft), Z1 ... First rotation direction, Z2 ... Second rotation direction

Claims (1)

An electric motor for assisting steering having a motor housing and a motor shaft supported by the motor housing so as not to move in the axial direction and to be rotatable;
Deceleration including a worm shaft that is supported so as to be axially immovable and rotatable by a bearing held in the gear housing, and a worm wheel that meshes with the worm shaft, and that decelerates the rotation of the motor shaft and transmits it to the steering mechanism Machine,
A coupling that coaxially connects the motor shaft and the worm shaft so that torque can be transmitted;
The joint includes a first member connected to the motor shaft so as to be able to transmit torque, a second member connected to the worm shaft so as to be able to transmit torque, and connected to the first member so as to be able to transmit torque, and the first member An elastic member interposed between the member and the second member and elastically compressible in the axial direction,
At least one of the first member and the second member is supported so as to be movable in the axial direction by a corresponding motor shaft or worm shaft,
The at least one of the first member and the second member and the corresponding motor shaft or worm shaft are interposed via a first spline and a second spline that are fitted with tooth surfaces inclined with respect to the axial direction. The electric power steering device connected.

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