JP2010064562A - Electric power steering device - Google Patents

Abstract

An electric power steering device further suppresses backlash between a worm gear and a worm wheel.
An electric power steering apparatus includes a pinion shaft connected to a handle, a rack shaft that meshes with the pinion shaft and steers a steered wheel, and a housing that supports the pinion shaft and the rack shaft. And an electric motor for generating an auxiliary torque on the pinion shaft 31, a worm gear 61 connected to the electric motor, and a worm wheel 62 for transmitting the auxiliary torque to the pinion shaft 31. The housing 5 is disposed below the rack shaft 32, and a first bearing 71 that supports the pinion shaft 31 and a second bearing that is disposed between the handle and the first bearing 71 and supports the pinion shaft 31. 72 and a first elastic member 81 provided in the first bearing 71 so as to bias the pinion shaft 31 in a direction opposite to the rack shaft 32.
[Selection] Figure 2

Description

  The present invention relates to an electric power steering apparatus driven by an electric motor.

  2. Description of the Related Art Conventionally, an electric power steering device using an electric motor (electric motor) as a power source is known as a power steering device for compensating for steering force of the steering wheel (see, for example, Patent Document 1). An electric power steering device generally assists a driver's steering operation by boosting the rotational torque of an electric motor by a speed reduction mechanism composed of a worm gear and a worm wheel and applying the boosted torque to a rack shaft via a rack and pinion mechanism. .

  In the conventional electric power steering device, the steering feeling given to the driver is reduced due to the backlash of the meshing portion between the rack and the pinion, and the steering feeling is reduced due to the deflection and vibration of the rack shaft due to the reaction force of the road surface. There was a problem.

For this reason, in the electric power steering apparatus described in Patent Document 1, the elasticity that biases the rolling shaft toward the rack shaft between the rolling bearing that supports the vicinity of the pinion of the pinion shaft and the inner surface of the housing. By interposing a member, backlash is suppressed and the operational feeling is improved.
Japanese Patent No. 3862897 (Claims, paragraph 0025)

  However, the elastic member of the electric power steering apparatus described in Patent Document 1 biases the rolling bearing that supports the vicinity of the pinion of the pinion shaft connected to the rack shaft on which the electric motor is installed to the rack side. To suppress deflection of the rack shaft due to the reaction force of the road surface, vibration, and backlash of the pinion rack mechanism. In order to suppress the deflection of the rack shaft, vibration, and backlash of the pinion rack mechanism, it is necessary to make the spring force of the elastic member strong, and the strength of the elastic member over a long period of time. Improvement of durability to maintain is required.

  Conventional electric power steering devices include a rack assist type device in which an electric motor is installed on the rack shaft side and a pinion assist type device in which an electric motor is installed on the pinion shaft side as described in Patent Document 1. In particular, in a pinion assist type electric power steering device, the driving force of the electric motor is transmitted to the pinion shaft via a worm gear and a worm wheel. For this reason, when the elastic member described in Patent Document 1 is provided on the pinion shaft, the pinion shaft must have a structure that also has a spring force that suppresses backlash between the worm gear and the worm wheel. There was a problem that strength and durability had to be improved.

  Accordingly, the present invention has been made to solve the above-described problems, and an object thereof is to provide an electric power steering device that can further suppress backlash between the worm gear and the worm wheel.

  In order to solve the above-mentioned problems, an electric power steering apparatus according to claim 1 is provided with a pinion shaft connected to a handle and rotated by the handle, and a rack that meshes with the pinion shaft and steers a steered wheel of a vehicle. A shaft, a housing that supports the pinion shaft and the rack shaft, an electric motor that generates an auxiliary torque on the pinion shaft, a worm gear connected to the electric motor, and a gear connected to the pinion shaft and meshing with the worm gear. An electric power steering apparatus comprising: a worm wheel that transmits the auxiliary torque to the pinion shaft, wherein the housing is disposed below the rack shaft with respect to the handle and rotatably supports the pinion shaft A first bearing that is disposed between the handle and the first bearing; A second bearing that rotatably supports the shaft, and a first elastic member provided on the first bearing so as to bias the pinion shaft in a direction opposite to the rack shaft. It is characterized by being.

  According to this configuration, in the housing, the first bearing disposed below the rack shaft and supporting the pinion shaft, and the second bearing disposed between the handle and the first bearing and supporting the pinion shaft. A bearing and a first elastic member provided on the first bearing so as to be urged in a direction opposite to the rack shaft with respect to the pinion shaft are disposed. The pinion shaft is arranged on the second bearing side with the meshing portion meshing with the rack shaft as a fulcrum by the first bearing below being biased by the first elastic member in the opposite direction to the rack shaft. The worm wheel is tilted in the direction in which it engages with the worm gear and presses the worm gear. For this reason, the backlash between a worm gear and a worm wheel can be suppressed.

  The invention according to claim 2 is the electric power steering apparatus according to claim 1, wherein a second elastic member is interposed between the pinion shaft and the second bearing.

  According to such a configuration, the backlash between the pinion shaft and the second bearing can be eliminated by the second elastic member being interposed between the pinion shaft and the second bearing.

  A third aspect of the present invention is the electric power steering apparatus according to the first or second aspect, wherein a third elastic member is interposed at a connecting portion between the pinion shaft and the worm wheel. And

  According to such a configuration, the backlash between the pinion shaft and the worm wheel can be eliminated by interposing the third elastic member at the connecting portion between the pinion shaft and the worm wheel. As a result, backlash between the worm gear and the worm wheel is suppressed, and the worm gear and the worm wheel are engaged with each other at an appropriate height.

  The invention according to claim 4 is the electric power steering apparatus according to claim 2 or claim 3, wherein the pinion shaft is a meshing portion in which a pinion provided on the pinion shaft meshes with a rack of the rack shaft. The distance from the installation part where the worm wheel is installed on the pinion shaft to the meshing part is longer than the distance from the position to the first bearing.

  According to such a configuration, the pinion shaft is formed so that the distance from the installation portion of the worm wheel to the engagement portion is longer than the distance from the engagement portion of the pinion and the rack to the first bearing, and thus the engagement portion is used as a fulcrum. Tilt toward the worm gear with a small force. For this reason, it is possible to prevent the second elastic member interposed between the pinion shaft and the second bearing from being loaded with a strong external force, and to make it possible to cope with the elastic member having a low spring force and strength. (2) The durability of the elastic member can be improved.

  According to the electric power steering device of the present invention, it is possible to further suppress the backlash between the worm gear and the worm wheel and improve the strength and durability of the spring of the elastic member.

Hereinafter, an electric power steering apparatus according to an embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a schematic configuration diagram showing an electric power steering apparatus according to an embodiment of the present invention. FIG. 2 is a central enlarged cross-sectional view showing an installation state of the speed reduction mechanism, the rack and pinion mechanism, the bearing and the elastic member of the electric power steering apparatus according to the embodiment of the present invention. 3 is an enlarged cross-sectional view taken along line XX in FIG. 4 is an enlarged YY sectional view of FIG. FIG. 5 is an enlarged view of a portion Z in FIG. FIG. 6 is an explanatory diagram showing an electric power steering apparatus according to an embodiment of the present invention.

≪Configuration of electric power steering device≫
As shown in FIG. 1, the electric power steering apparatus 1 drives the electric motor M according to the steering input when the driver operates the handle 2, and transmits the power of the electric motor M to the steering system via the speed reduction mechanism 6. This is a device that assists in turning the vehicle. The electric power steering device 1 includes a handle 2, a pinion shaft 31, a steering torque sensor T, a vehicle speed sensor S, an electric motor M, a drive control device 11, a worm gear 61, and a worm wheel 62, which will be described later. Mechanism 6, rack and pinion mechanism 3, rack shaft 32, housing 5 (see FIG. 2), bearing 7 (see FIG. 2), elastic member 8 (see FIG. 2), tie rod 12, and steering wheel 4 And is configured. This device comprises a so-called column-type electric power steering device 1.

≪Composition of the handle≫
The handle 2 is an operation member for steering the vehicle. In the electric power steering apparatus 1, the steering wheel 2 is connected in order of a steering shaft 21, a universal joint 22, a pinion shaft 31, a rack and pinion mechanism 3, a rack shaft 32, a tie rod 12, a knuckle (not shown), and a steering wheel 4. ing.

≪Configuration of pinion shaft and pinion≫
The pinion shaft 31 is a shaft that is connected to the handle 2 via the steering shaft 21 and the universal joint 22 and is rotated by a rotation operation of the handle 2. The pinion shaft 31 is integrally provided with a worm wheel 62 of the speed reduction mechanism 6 and a pinion 33 of the rack and pinion mechanism 3. As shown in FIG. 2, the pinion shaft 31 is supported by the housing 5 through bearings 7 installed at three locations, an upper portion, a central portion, and a lower portion in the housing 5.
In the pinion shaft 31, the pinion 33 is integrally formed at a position between the second bearing 72 disposed substantially at the center and the first bearing 71 disposed at the lower end.
In the pinion shaft 31, the worm wheel 62 is installed on the pinion shaft 31 from the distance a (see FIG. 6) from the position of the meshing portion 3a where the pinion 33 and the rack 34 of the rack shaft 32 mesh with each other. Further, the distance b (see FIG. 6) from the installation portion 6a to the meshing portion 3a is increased.

≪Configuration of steering torque sensor and vehicle speed sensor≫
The steering torque sensor T is a sensor that detects the direction and magnitude of the steering torque that acts on the pinion shaft 31 when the steering torque from the handle 2 acts on the pinion shaft 31, and includes, for example, a magnetostrictive torque sensor. . The steering torque sensor T, for example, opposes the magnetostrictive film (not shown) provided on the pinion shaft 31 and changes the magnetic characteristics of the magnetostrictive film according to the twist generated on the pinion shaft 31 with a predetermined distance from the magnetostrictive film. And a coil (not shown) for detecting the torque applied to the pinion shaft 31.
The vehicle speed sensor S is a sensor that detects the vehicle speed.

≪Configuration of electric motor≫
As shown in FIG. 1, the electric motor M is an electric motor that applies a steering assist force to the pinion shaft 31 via the speed reduction mechanism 6, and includes, for example, a resolver (not shown) that detects the rotation angle of the rotor. It consists of a brushless DC motor. The electric motor M is accommodated in, for example, a housing 5 (see FIG. 2) that accommodates the speed reduction mechanism 6, the rack and pinion mechanism 3, and the like. In the electric motor M, a worm gear shaft 61a (see FIG. 2) is coupled to a rotor shaft Ma that rotates integrally with the rotor of the electric motor M via a coupling (not shown) such as an elastic body such as rubber or serrations. The rotation and torque of the electric motor M are transmitted to the worm gear 61.

≪Configuration of drive control device≫
The drive control device 11 is a device that controls the drive of the electric motor M according to detection signals from the steering torque sensor T, the vehicle speed sensor S, and the like, and includes an ECU (Electrical Control Unit).

≪Deceleration mechanism configuration≫
The speed reduction mechanism 6 shown in FIG. 2 includes a gear speed reduction mechanism having a function of boosting the rotational torque of the electric motor M and transmitting it to the pinion shaft 31. The speed reduction mechanism 6 meshes with a worm gear 61 that is connected to the rotor shaft Ma (see FIG. 1) of the electric motor M and rotates therewith, and a worm wheel 62 provided on the pinion shaft 31 to reduce the rotation of the electric motor M. And transmitted to the pinion shaft 31.

<Configuration of worm gear>
As shown in FIG. 2, the worm gear 61 has a worm gear shaft 61a and a tooth profile portion integrally formed with the worm gear shaft 61a. The worm gear 61 is pivotally supported by bearings (not shown) such as ball bearings installed at both ends of the worm gear shaft 61a. The worm gear 61 is disposed on the same side as the rack shaft 32 with respect to the pinion shaft 31.

<Configuration of worm wheel>
The worm wheel 62 is a gear that meshes with the worm gear 61 to reduce and transmit the rotation (auxiliary torque) of the worm gear 61 to the pinion shaft 31. The worm wheel 62 is fitted with a flanged cylindrical cored bar 63 on the shaft insertion hole 62a side into which the pinion shaft 31 is inserted. The worm wheel 62 is mounted on the core metal mounting portion 31b of the second bearing 72 via the third elastic member 83 and the core metal 63 below the stepped portion 31a of the pinion shaft 31. And so as to rotate together.

≪Configuration of rack and pinion mechanism≫
As shown in FIG. 2, the rack and pinion mechanism 3 is a gear transmission that converts the rotation of the pinion shaft 31 into a linear movement of the rack shaft 32 in the vehicle width direction. The rack and pinion mechanism 3 includes a pinion 33 provided on the pinion shaft 31, a rack 34 provided on the rack shaft 32 and meshing with the pinion 33, and a rack guide 9 that urges the rack 34 toward the pinion 33. It is prepared for.
The rack shaft 32 is coupled to the pinion shaft 31 via the rack and pinion mechanism 3, and the pinion 33 of the pinion shaft 31 and the rack 34 are engaged with each other to linearly move in the vehicle width direction to steer the steered wheels 4. . The rack 34 is integrally formed with the rack shaft 32, for example.

≪Configuration of housing≫
The housing 5 is a member that supports and covers the pinion shaft 31 and the rack shaft 32. The housing 5 is configured by continuously arranging an upper housing 51 disposed on the upper side, a middle housing 52 disposed on the center portion, and a lower housing 53 disposed on the lower side in the vertical direction. The housing 5 is provided with the speed reduction mechanism 6, the rack and pinion mechanism 3, a bearing 7, an elastic member 8, a rack guide 9, an oil seal 10, a cap nut 13, and the like.

  The upper housing 51 is a cylindrical case body into which the upper part of the pinion shaft 31 is inserted. In the upper housing 51, a third bearing 73, an oil seal 10, and a steering torque sensor T are provided. The upper housing 51 is fixed to the middle housing 52 with bolts B1 with the sealing material 14 interposed therebetween.

  The middle housing 52 includes a substantially ring-shaped lid member interposed between the upper housing 51 and the lower housing 53. The middle housing 52 is fitted into the upper opening 53a of the lower housing 53, and is fixed to the upper surface of the lower housing 53 by a bolt B2.

  As shown in FIG. 2, the lower housing 53 has an installation space into which the portion from the center to the lower end of the pinion shaft 31, the rack shaft 32, and the rack guide 9 are inserted. And a substantially T-shaped cylindrical case body extending in the vehicle width direction. The lower housing 53 includes a worm gear 61, a worm wheel 62, a third elastic member 83, a core metal 63, a second bearing 72, a second elastic member 82, a pinion 33, a first bearing 71, A first elastic member 81, a nut N1, and a cap nut 13 are provided internally.

On the upper opening 53a side of the lower housing 53, there are a transmission mechanism installation space 53c for installing the worm gear 61 and the worm wheel 62, and a second bearing mounting portion 53d to which the second bearing 72 is mounted. Are formed in order.
On the lower opening 53 b side of the lower housing 53, a female screw portion 53 e into which the cap nut 13 is screwed, an annular first bearing mounting portion 53 f to which an outer ring of the first bearing 71 is mounted, and a first elastic member 81. Are formed in order on the upper back side.
The first bearing mounting portion 53f is provided on an inner wall formed in a circular shape along the axis O1 of the pinion shaft 31.

  The first elastic member installation portion 53g includes an annular groove that is continuously adjacent to the upper back side of the first bearing attachment portion 53f. The first elastic member installation portion 53g is a strain that is largely eccentric to the side where the rack shaft 32 and the worm gear 61 are arranged around the axis O1 of the pinion shaft 31 in accordance with the shape of the first elastic member 81 described later. It is formed on the inner cylinder surface. That is, the first elastic member installation portion 53g has a depth D1 on the rack shaft 32 (see FIG. 2) and worm gear 61 (see FIG. 2) side from the first bearing mounting portion 53f, as shown in FIG. It is formed deeper than the depth D2 of the opposite portion. The outer elastic pressing portions 81d, 81e, 81f of the first elastic member 81 are fitted into the first elastic member installation portion 53g in a state where they are elastically pressed.

≪Bearing configuration≫
As shown in FIG. 2, the bearing 7 is a rolling bearing that rotatably supports the pinion shaft 31 and includes, for example, a ball bearing composed of an inner ring, an outer ring, and a steel ball. The bearing 7 is provided in the lower part of the housing 5 to support the lower part of the pinion shaft 31, and the first bearing 71 is provided in the central part of the housing 5 to support the central part of the pinion shaft 31. 2 bearings 72 and a third bearing 73 installed in the upper part of the housing 5 and pivotally supporting the upper part of the pinion shaft 31.

<Configuration of the first bearing>
The first bearing 71 is a bearing that is disposed below the rack shaft 32 with respect to the handle 2 and rotatably supports the pinion shaft 31. The first bearing 71 is fitted into the pinion shaft 31 adjacent to the lower side of the pinion 33, and the inner ring is fixed to the pinion shaft 31 by screwing a nut N1 made of a seated nut to the lower end portion of the pinion shaft 31. The The outer ring of the first bearing 71 is supported by the lower housing 53 with the first elastic member 81 interposed therebetween, and is internally provided in the lower housing 53 by screwing the cap nut 13 into the female screw portion 53e. The first bearing 71 is installed at a position separated from the meshing portion 3a by a distance a (see FIG. 6).

<Configuration of second bearing and third bearing>
The second bearing 72 is disposed between the handle 2 (see FIG. 1) and the first bearing 71, and is a bearing that rotatably supports the pinion shaft 31. The second bearing 72 has an outer ring attached to the second bearing mounting portion 53 d of the lower housing 53, and an inner ring held by the pinion shaft 31 with the second elastic member 82 interposed therebetween. The 2nd bearing 72 is installed between the pinion 33 and the worm wheel 62, and is installed in the position away from the meshing part 3a to the distance c (refer FIG. 6) upper side.
A third bearing 73 shown in FIG. 2 is a bearing that is disposed between the handle 2 (see FIG. 1) and the second bearing 72 and supports the upper part of the pinion shaft 31.

≪Configuration of elastic member≫
The elastic member 8 is a member having a spring force for suppressing the bending, vibration, backlash of the rack and pinion mechanism 3, and backlash of the speed reduction mechanism 6. The elastic member 8 includes three members, a first elastic member 81, a second elastic member 82, and a third elastic member 83, which will be described later.

<Configuration of first elastic member>
As shown in FIG. 2, the first elastic member 81 is made of an elastic body provided on the first bearing 71 so as to bias the pinion shaft 31 in the direction opposite to the rack shaft 32. As shown in FIG. 3, the first elastic member 81 generates, for example, a tensile force that presses the first bearing 71 in the radial direction by forming a strong metal plate spring material in a substantially wave shape. And a tolerance ring that applies preload from the outside of the outer ring of the first bearing 71 on which the rack guide 9 and the rack shaft 32 are arranged toward the pinion shaft 31 side. The first elastic member 81 includes inner pressing portions 81a, 81b, 81c that press the outer ring 71a of the first bearing 71 and outer pressing portions 81d, 81e, 81f that press the first elastic member installation portion 53g of the lower housing 53. And inclined portions 81g formed between the inner pressing portions 81a, 81b, 81c and the outer pressing portions 81d, 81e, 81f, respectively.

The inner pressing portions 81a, 81b, and 81c are formed between the outer pressing portions 81d, 81e, and 81f, and are formed of five expanded recesses that are recessed from the outer pressing portions 81d, 81e, and 81f. It has elasticity to press the first bearing 71 in the direction of the center O1 (inner diameter direction). Each inner pressing portion 81a, 81b, 81c is formed along a circle centered on the axis O1, and is formed in an arc shape when viewed in cross section.
The inner pressing portion 81a is formed at the center of the first elastic member 81 having a substantially C-shaped cross section, and is disposed on the rack shaft 32 and the worm gear 61 side (see FIG. 2). The inner pressing portion 81a is in a state of being deeply recessed toward the axis O1 side from the inner wall (the adjacent outer pressing portion 81d) of the first elastic member installation portion 53g, as compared with the other inner pressing portions 81b and 81c. Is formed.

The inner pressing portions 81b and 81b are formed at positions adjacent to both sides of the inner pressing portion 81a via an inclined portion 81g and an outer pressing portion 81d. The inner pressing portions 81b and 81b are gradually shallower from the inner wall of the first elastic member installation portion 53g (adjacent outer pressing portions 81d and 81e) toward the axis O1 than the inner pressing portion 81a. It is formed so as to be recessed.
The inner pressing portions 81c and 81c are formed at positions adjacent to both end sides of the inner pressing portions 81b and 8b via the inclined portions 81g and the outer pressing portions 81e and 81e. The inner pressing portions 81c and 81c are shallower than the inner pressing portions 81b and 81b, and are shallower from the inner wall of the first elastic member installation portion 53g (adjacent outer pressing portions 81e and 81f) toward the axis O1. Is formed.

The outer pressing portions 81d, 81e, and 81f are convex portions that are formed so as to protrude in a trapezoidal shape from the inner pressing portions 81a, 81b, and 81c to the outside via the inclined portions 81g. Each outer pressing portion 81d, 81e, 81f is substantially arcuate in a cross-sectional view of its outer surface so as to come into surface contact with the inner wall of the first elastic member installation portion 53g formed eccentrically about the axis O1. Is formed.
The outer pressing portions 81d and 81d are formed on both sides of the inner pressing portion 81a at the center of the first elastic member 81 via inclined portions 81g. The outer pressing portions 81d and 81d are formed so as to protrude higher from the outer ring of the first bearing 71 than the other outer pressing portions 81e and 81f.
The outer pressing portions 81e and 81e are formed between the inner pressing portion 81b and the inner pressing portion 81c via an inclined portion 81g. The outer pressing portions 81e, 81e are formed at a height intermediate between the large outer pressing portion 81d and the small outer pressing portion 81f, with the height protruding outward from the outer ring of the first bearing 71.
The outer pressing portions 81f and 81f are formed at both ends of the first elastic member 81 via the inclined portion 81g so as to support both end sides of the inner pressing portion 81c with the inclined portion 81g.
Each inclined portion 81g is formed so as to elastically support the inner pressing portions 81a, 81b, 81c and the outer pressing portions 81d, 81e, 81f by providing elasticity outward and inward in the radial direction.

<Configuration of second elastic member>
As shown in FIG. 4, the second elastic member 82 is an elastic body interposed between the pinion shaft 31 and the second bearing 72, and is made of, for example, a resin bush that is elastically deformed. The second elastic member 82 is a leaf spring having a substantially C-shaped cross section that fits into an annular elastic member installation groove 31c formed near the lower side of the cored bar mounting portion 31b (see FIG. 2) of the pinion shaft 31. . This 2nd elastic member 82 consists of a wave-like thing which formed many inner side press parts 82a and the outer side press parts 82b alternately.
The inner pressing portion 82a is formed in a concave shape curved toward the axis O1 direction of the pinion shaft 31, and is provided so as to press the bottom surface of the elastic member installation groove 31c of the pinion shaft 31.
The outer pressing portion 82b is formed in an arc shape centering on the axis O1 of the pinion shaft 31, and is formed in a convex shape protruding outward with respect to the inner pressing portion 82a. The outer surface of the outer pressing portion 82 b is provided so as to elastically press against the inner ring of the second bearing 72, and the inner ring is fixed to the pinion shaft 31.

<Configuration of third elastic member>
As shown in FIG. 5, the third elastic member 83 is an elastic body that is interposed in the connecting portion between the pinion shaft 31 and the worm wheel 62, and is made of, for example, a rubber washer-like member that is elastically deformed. The third elastic member 83 is made of a flat plate material having a ring shape like a flat washer disposed between the lower surface of the stepped portion 31 a of the pinion shaft 31 and the upper surface of the core metal 63.

≪Configuration of rack guide≫
As shown in FIG. 2, the rack guide 9 is a device for pressing the rack 34 against the pinion 33, and is installed in a lateral hole 53 h drilled in the side surface of the lower housing 53. The rack guide 9 includes a guide portion 91, a compression coil spring 92, an adjustment bolt 93, a contact member 94, and a lock nut 95, which will be described later.
The guide portion 91 is a member for pressing the abutting member 94 against the back side of the rack shaft 32, and is inserted into the lateral hole 53h so as to be movable back and forth in the direction of the rack shaft 32.
The compression coil spring 92 is a spring that presses and biases the guide portion 91 and the abutting member 74 toward the rack shaft 32 side.
The adjustment bolt 93 is a spring receiver that can adjust the pressing force of the compression coil spring 92 by moving the positions of the guide portion 91 and the compression coil spring 92 by rotating the adjustment bolt 93.
The abutting member 94 is an elastic contact member that presses the back surface of the rack shaft 32 so as to be slidable.
The lock nut 95 is a member for fixing the position adjusted by the adjustment bolt 93.

≪Configuration of tie rod and steering wheel≫
The tie rods 12 are rod-like members installed at both ends of the rack shaft 32, respectively. The rudder wheel 4 is composed of a front wheel disposed at the tip thereof via a tie rod 12, a knuckle (not shown), and the like.

≪Action≫
Next, the operation of the electric power steering apparatus 1 according to the embodiment of the present invention will be described with reference to FIG.
1, when the driver steers the handle 2, the rack shaft 32 linearly reciprocates via the rack and pinion mechanism 3 by the steering torque applied to the pinion shaft 31, and the tie rod 12 and the like. The steered wheel 4 is steered via

  At this time, the drive control device 11 sets a target current value to be supplied to the electric motor M based on the steering torque signal input from the steering torque sensor T and the vehicle speed signal input from the vehicle speed sensor S, and this target current value The motor M is driven by current feedback control so that the deviation between the motor current value input from the motor current sensor (not shown) and the motor current value is zero. Accordingly, the electric motor M generates an appropriate steering assist force (assist force), and this steering assist force is decelerated and rotated by the worm gear 61 and the worm wheel 62 to be applied to the pinion shaft 31, whereby the driver's handle The steering force during operation can be reduced.

Next, the operation of the elastic member 8 of the electric power steering apparatus 1 according to the embodiment of the present invention will be described with reference mainly to FIGS. 2 and 6.
As shown in FIG. 2, the pinion shaft 31 is inserted into the upper opening 53a of the lower housing 53 from above, and the upper opening 53a is closed by the middle housing 52 and the upper housing 51, and bolts B1 and B2 are used. And assembled to the housing 5. The lower end portion of the pinion shaft 31 is supported by the lower housing 53 with the first bearing 71 and the first elastic member 81 interposed therebetween.

  The first bearing 71 is inserted into the lower opening 53b of the lower housing 53 from below and is accommodated in the first bearing mounting portion 53f. In the first bearing 71, the inner ring is clamped between the nut N1 and the pinion 33 by screwing the nut N1 to the lower end portion of the pinion shaft 31, and the outer ring is screwed to the female nut 53e. As a result, the cap nut 13 is sandwiched between the lower housing 53 and the movement in the axial direction is restricted. The outer diameter of the outer ring of the first bearing 71 is set slightly smaller than the inner diameter of the first bearing mounting portion 53 f so that the first bearing 71 can be inserted into the lower housing 53. For this reason, there is a small gap between the inner surface of the first bearing mounting portion 53 f of the lower housing 53 and the outer surface of the outer ring of the first bearing 71.

As shown in FIGS. 3 and 6, the first elastic member 81 is pivoted from the outside in the direction in which the rack shaft 32 and the worm gear 61 are arranged when the first bearing 71 is fitted in the lower housing 53. The outer ring of the first bearing 71 is pressed by the elastic force of the preload F1 toward the center O1.
As shown in FIG. 6, the pinion 33 of the pinion shaft 31 has an elastic force of a spring force F2 by the rack 34 biased by the compression coil spring 92 through the guide portion 91 and the abutting member 94 at the meshing portion 3a. The pressure is pressed in the same direction as the preload F1.

  As shown in FIG. 2, the central portion of the pinion shaft 31 is supported by the lower housing 53 with a second elastic member 82 and a second bearing 72 interposed therebetween. The second bearing 72 is inserted into the upper opening 53 a of the lower housing 53 from above with the second elastic member 82 interposed in the elastic member installation groove 31 c and inserted into the upper opening 53 a of the lower housing 53. It is stored in the bearing mounting portion 53d.

The outer diameter of the outer ring of the second bearing 72 is set slightly smaller than the inner diameter of the second bearing mounting portion 53 d so that the second bearing 72 can be inserted into the lower housing 53. For this reason, there is a small gap between the inner surface of the second bearing mounting portion 53 d of the lower housing 53 and the outer surface of the outer ring of the second bearing 72.
As shown in FIG. 4, when the second bearing 72 is fitted in the lower housing 53, the second elastic member 82 is separated from the outer surface of the pinion shaft 31 by the inner pressing portion 82 a and the outer pressing portion 82 b. The inner surface of the second bearing mounting portion 53d of the lower housing 53 is pressed in the radial direction with a substantially uniform elastic force.

  As shown in FIG. 6, the first bearing 71 and the second bearing 72 may be displaced in the radial direction by the amount of the gap between the first bearing 71 and the second bearing 72 and the lower housing 53. It is possible. The pinion shaft 31 pivotally supported by the bearings 7 is pressed in a direction opposite to the installation position of the worm gear 61 by the preload F1 by the first elastic member 81 and the spring force F2 by the compression coil spring 92, It is elastically supported in a state where it is tilted in the direction perpendicular to the axis (direction of arrow A) and moved eccentrically by the gap.

In other words, the pinion shaft 31 is positioned in the direction in which the worm gear 61 is located (in the direction of arrow A) around the fulcrum O3 where the engagement portion 3a of the pinion 33 of the pinion shaft 31 and the rack 34 is located by the preload F1 of the first elastic member 81 ) Is supported in a state of being slightly tilted and moved. The shaft center line O1-O1 of the pinion shaft 31 is obtained by elastically deforming the second elastic member 82 pressed against the pinion shaft 31 and the second bearing 72 into a distorted eccentric shape by the preload F1. It leans to the state of O2. The second elastic member 82 has a uniform elasticity in the radial direction so that the axis O2-O2 of the pinion shaft 31 is positioned on the axis O1-O1 of the shaft hole of the housing 5. The outer surface of the pinion shaft 31 is pressed to suppress excessive movement of the pinion shaft 31 tilting.
6 is exaggerated to show that the pinion shaft 31 is tilted.

  The worm wheel 62 attached to the pinion shaft 31 also moves in the same direction (arrow C direction) when the pinion shaft 31 tilts in the direction of the worm gear 61 (arrow A direction). For this reason, the gap between the worm gear 61 and the worm wheel 62 can be narrowed, and the occurrence of hitting sound due to backlash can be suppressed.

That is, the pinion shaft 31 is meshed with the rack shaft 32 when the lower first bearing 71 is urged by the first elastic member 81 in the direction opposite to the rack shaft 32 with respect to the pinion shaft 31. The worm wheel 62 disposed on the second bearing 72 side tilts in a direction to engage with the worm gear 61 around the fulcrum O3 where the portion 3a is located, and presses the worm gear 61. On the other hand, the second elastic member 82 is arranged at an upper position opposite to the lower side where the first elastic member 81 is arranged with respect to the fulcrum O3 of the pinion shaft 31, and the pinion shaft 31 is connected to the axis O1. It is pressing in the -O1 direction.
As described above, the first elastic member 81 and the second elastic member 82 restrict the movement of the pinion shaft 31 in the direction perpendicular to the axis. Therefore, by changing the spring force, The backlash between the worm gear 61 and the worm wheel 62 can be appropriately adjusted.

  As described above, the pinion shaft 31 is tilted about the meshing portion 3a between the pinion 33 and the rack 34. Therefore, the meshing portion 6a of the worm wheel 62 is engaged with the meshing portion from the distance a from the meshing portion 3a to the first bearing 71. By forming the distance b to the part 3a long, the worm gear 61 is tilted with a small force with the meshing part 3a as a fulcrum. For this reason, the preload F1 of the first elastic member 81 that tilts the pinion shaft 31 can be set small. As a result, the spring strength and durability of the first elastic member 81 can be improved.

  The third elastic member 83 suppresses the worm wheel 62 integral with the core metal 63 from shifting upward by pressing the core metal 63 downward when the pinion shaft 31 is tilted. The worm wheel 62 can be adjusted to an appropriate height.

≪Modification≫
The present invention is not limited to the above-described embodiment, and various modifications and changes can be made within the scope of the technical idea. The present invention extends to these modifications and changes. Of course.

Next, a modification of the present invention will be described with reference to FIG.
FIG. 7 is an enlarged vertical sectional view of a main part showing a modification of the electric power steering apparatus according to the embodiment of the present invention.
For example, as shown in FIG. 7, the third elastic member 83 is installed at the lower end 63a of the core 63 of the worm wheel 62, and above the lower end 63a and the elastic member installation groove 31c of the pinion shaft 31A. It may be sandwiched between the adjacent flange portion 31Aa.
Thus, even if the third elastic member 83 is installed on the pinion shaft 31A, the vertical movement of the pinion shaft 31A can be suppressed as in the above embodiment.

  Note that the present invention also relates to a configuration (steer-by-wire) in which the steering wheel 2 and the steered wheel 4 are mechanically separated and the electric motor M generates all of the steering force for the steered wheel 4 (steer-by-wire). Any device having a worm wheel 62 can be used.

1 is a schematic configuration diagram illustrating an electric power steering apparatus according to an embodiment of the present invention. It is a center expanded sectional view which shows the installation state of the deceleration mechanism of the electric power steering device which concerns on embodiment of this invention, a rack and pinion mechanism, a bearing, and an elastic member. It is XX expanded sectional drawing of FIG. FIG. 3 is an enlarged YY sectional view of FIG. 2. FIG. 3 is an enlarged view of a Z part in FIG. 2. It is explanatory drawing which shows the electric power steering apparatus which concerns on embodiment of this invention. It is a principal part expanded vertical sectional view which shows the modification of the electric power steering apparatus which concerns on embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric power steering apparatus 2 Handle 3 Rack and pinion mechanism 3a Engagement part 4 Steering wheel 5 Housing 6 Reduction mechanism 6a Installation part 7 Bearing 8 Elastic member 31, 31A Pinion shaft 32 Rack shaft 33 Pinion 34 Rack 61 Worm gear 62 Worm wheel 71 1st Bearing 72 Second bearing 81 First elastic member 82 Second elastic member 83 Third elastic member a, b, c Distance M Electric motor

Claims (4)

A pinion shaft connected to the handle and rotated by the handle;
A rack shaft that meshes with the pinion shaft and steers the steering wheel;
A housing that supports the pinion shaft and the rack shaft;
An electric motor for generating an auxiliary torque on the pinion shaft;
A worm gear coupled to the electric motor;
A worm wheel coupled to the pinion shaft and meshing with the worm gear to transmit the auxiliary torque to the pinion shaft;
In the electric power steering apparatus with
The housing includes
A first bearing that is disposed below the rack shaft with respect to the handle and rotatably supports the pinion shaft;
A second bearing disposed between the handle and the first bearing and rotatably supporting the pinion shaft;
A first elastic member provided on the first bearing so as to urge the pinion shaft in a direction opposite to the rack shaft;
Is installed in the electric power steering device.   The electric power steering apparatus according to claim 1, wherein a second elastic member is interposed between the pinion shaft and the second bearing.   3. The electric power steering apparatus according to claim 1, wherein a third elastic member is interposed at a connection portion between the pinion shaft and the worm wheel. The pinion shaft is connected to the first bearing by a distance from the position of the meshing portion where the pinion provided on the pinion shaft meshes with the rack of the rack shaft to the meshing position from the installation portion where the worm wheel is installed on the pinion shaft. The electric power steering apparatus according to claim 2 or 3, wherein a distance to the portion is long.

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