JP2003112635A - Electric power steering unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that a gear of a speed reduction mechanism generates a tooth hitting sound caused by backlash due to a road surface when a vehicle runs on a bad road, thereby generating noise, in an electric power steering system decelerating the rotation of an electric motor by the speed reduction mechanism and amplifying an output to perform torque assist. SOLUTION: An input shaft 3 and an output shaft 5 continuous to a steering wheel 2 are mutually connected through a first torsion bar 4. A pinion shaft 7 engaged with a rack bar 9 and the output shaft 5 are mutually connected through a second torsion bar 6. The transmission of vibration given to the pinion shaft 7 through wheels and the rack bar 9 to the output shaft 5 is suppressed. A tooth hitting sound between a worm shaft 15 and a worm wheel 16 can be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering apparatus for obtaining a steering assist force by an electric motor.

[0002]

2. Description of the Related Art In an electric steering device for an automobile, for example, a pinion type EPS, the rotational force of a motor is transmitted to a worm, and further transmitted to a worm wheel to decelerate the rotation of the motor to amplify the output of the motor. , The steering operation is torque assisted.

[0003]

By the way, an appropriate backlash is required for the meshing of the worm and the worm wheel as the reduction mechanism, but when traveling on a bad road such as a stone pavement, the reaction force from the tire causes Rattle noise (dentation noise) may be generated due to the backlash. When these sounds are transmitted as noise in the passenger compartment,
This will make the driver uncomfortable.

Therefore, it is conceivable to improve the meshing accuracy of the worm and the worm wheel of the reduction gear mechanism to reduce the backlash, but if the backlash is reduced too much, the friction resistance increases and the rotational resistance of the steering shaft increases. A new defect occurs. In recent years, synthetic resin is often used for worm wheels as a noise countermeasure, but in pinion type EPSs where the mounting position is in the engine room and in a relatively high temperature environment, backlash is reduced due to temperature expansion of the worm wheel. Tend to do. Therefore, the backlash cannot be set too small in the first place.

The present invention has been made in view of the above problems, and an electric power steering system capable of reducing the noise generated due to the backlash of the reduction mechanism during traveling on a rough road without causing other problems. It is to provide a taking device.

[0006]

In order to achieve the above object, the present invention according to claim 1 is connected to an input shaft connected to a steering wheel, and is rotatably connected via an input shaft and a torsion bar. An output shaft, a pinion shaft that engages with a rack bar connected to the wheels, and a reduction mechanism that reduces the rotation of an electric motor for steering assistance and transmits the rotation to the output shaft,
An elastic body for transmitting the rotation of the output shaft to the pinion shaft is provided.

In the present invention, since the output shaft and the pinion shaft are connected via the elastic body, the vibration transmitted from the road surface to the pinion shaft via the wheels and the rack bar during traveling on a bad road (for example, vibration of about 15 Hz). However, it can be further suppressed from being transmitted to the output shaft. Therefore, it is possible to suppress generation of rattle noise between the worm shaft and the worm wheel of the reduction mechanism due to the influence of road surface vibration, and it is possible to suppress noise. It is not necessary to set the backlash to an extremely small value, and the rotational resistance of the steering shaft does not increase.

According to a second aspect of the present invention, in the first aspect, the elastic body includes a torsion bar that coaxially connects the output shaft and the pinion shaft.
Conventionally, the output shaft and the pinion shaft were usually formed of an integral member, but noise is suppressed by a simple structural change of simply dividing the output shaft into two and connecting them with a coaxial torsion bar. be able to. According to a third aspect of the present invention, in the second aspect, the stopper mechanism includes a pair of opposed portions that come close to each other with the relative rotation of the output shaft and the pinion shaft and restrict the relative rotation amount of the output shaft and the pinion shaft. It is characterized by that. In the present invention, by controlling the twist amount of the torsion bar, it is possible to prevent damage to the torsion bar.

According to a fourth aspect of the present invention, in the third aspect, an elastic body interposed between the pair of opposed portions is provided. According to the present invention, it is possible to prevent the tapping sound from being generated by the contact between the facing portions of the stopper mechanism. According to a fifth aspect of the present invention, in the first aspect, a shaft body that integrally rotates with any one of the output shaft and the pinion shaft is inserted into a connection hole formed in the other, and the elastic body is a shaft body. It is characterized in that it is interposed between the outer circumference and the inner circumference of the connecting hole. According to the present invention, it is possible to transmit torque between both shafts while suppressing noise with a simple structure in which an elastic body is interposed in the connecting portion between the output shaft and the pinion shaft.

According to a sixth aspect of the present invention, in the fifth aspect, a pair of facing portions are provided on the outer periphery of the shaft body and the inner periphery of the connecting hole, the pair of facing portions being close to each other as the output shaft and the pinion shaft are relatively rotated. The elastic body is characterized by being interposed between a pair of facing portions and including any one of a compression coil spring, rubber and synthetic resin which are compressed when the facing portions approach each other. In the present invention, torque is transmitted between the output shaft and the pinion shaft by using the reaction force of compression. Since the reaction force of compression of the compression coil spring, rubber or synthetic resin is used, a sufficient torque can be transmitted even with a small size.

According to a seventh aspect of the present invention, in the first aspect, the first shaft extends from the output shaft and the pinion shaft, respectively.
And the second shaft body is fitted into a fitting hole formed in an elastic body made of rubber or synthetic resin, and the elasticity interposed between the facing portions of the first and second shaft bodies during relative rotation of the output shaft and the pinion shaft. It is characterized in that the body part is compressed. In the present invention, torque can be transmitted between both shafts while suppressing noise with a simple structure in which the shaft bodies from the output shaft and the pinion shaft are fitted to the elastic body.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic sectional view of an electric power steering apparatus according to an embodiment of the present invention. Referring to FIG. 1, the electric power steering apparatus 1 includes an input shaft 3 that rotates integrally with a steering wheel 2, and an output that is coaxially connected to the input shaft 3 via a first torsion bar 4. It has a shaft 5 and a pinion shaft 7 which is coaxially connected to the output shaft 5 via a second torsion bar 6.
A steering shaft 8 is configured by the input shaft 3, the output shaft 5, and the pinion shaft 7 which are coaxially connected. In the following, the upper and lower sides in FIG. 1 are referred to as the upper and lower sides.

The pinion shaft 7 meshes with a rack bar 9 extending in the vehicle width direction of a vehicle body (not shown), and although not shown, both ends of the rack bar 9 are connected to steering wheels via tie rods. There is. The gear housing 10 that supports the steering shaft 8 is made of, for example, an aluminum alloy and is attached to the vehicle body. Gear housing 10
Is composed of a first housing 11 and a second housing 12. The second housing 12 houses a speed reduction mechanism 13 including a worm gear mechanism.

The deceleration mechanism 13 serves as a reduction gear that meshes with the worm shaft 15 that is integrally rotatably connected to the rotation shaft of the electric motor 14 for generating steering assist force, and that meshes with the worm shaft 15 and rotates integrally with the output shaft 5. And a worm wheel 16. The worm wheel 16 includes a core metal 16a that is fitted onto the output shaft 5 so as to be integrally rotatable, and a synthetic resin member 16b that is fixed to the core metal 16a so as to be integrally rotatable and forms teeth on the outer circumference.
Including and The input shaft 3 is inserted into the first housing 11,
The upper end of the input shaft 3 projects above the first housing 11. The upper portion of the input shaft 3 is supported by the first housing 11 via a rolling bearing 17 formed of, for example, a ball bearing.

The output shaft 5 is rotatably supported via a pair of upper and lower rolling bearings 18 and 19 which are formed by sandwiching the worm wheel 16 and are composed of, for example, ball bearings. The upper rolling bearing 18 is held by the first housing 11, and the lower rolling bearing 19 is held by the second housing 12. Further, one end of the pinion shaft 7 is rotatably supported by the second housing 12 via a rolling bearing 20, and the other end of the pinion shaft 7 is in the second housing via a rolling bearing 21 which is, for example, a needle roller bearing. 12 is rotatably supported.

A reduced diameter portion 22 is provided at the lower end of the input shaft 3, and the reduced diameter portion 22 is housed in a hole 23 provided in the output shaft 5. Outer peripheral surface of reduced diameter portion 22 and hole 23
The inner peripheral surface of is a cross-sectional shape with a width across flats,
The input shaft 3 and the output shaft 5 are in contact with each other in order to regulate the relative rotation of the input shaft 3 and the output shaft 5 within a predetermined range. The first torsion bar 4 penetrates the input shaft 3 in the axial direction and has a lower end 4a.
Penetrates into the inner part of the hole 23 of the output shaft 5 and is integrally rotatably connected by, for example, serration connection. on the other hand,
The upper end 4b of the torsion bar 4 is connected to the input shaft 3 by a dowel pin 24 so as to be rotatable integrally therewith.

A first cylinder 26 made of a magnetic material is fixed to the outer periphery of the axially intermediate portion of the input shaft 2 via a sleeve 25 made of a non-magnetic material. A second cylinder 27 made of a magnetic material is fixed to the outer periphery of the upper portion of the output shaft 5. Although not shown, a large number of rectangular tooth portions are formed at equal intervals in the circumferential direction on the end faces of the two cylinders 26, 27 that face each other. A predetermined space is maintained between the teeth. On the other hand, inside the housing, a cylindrical body 2 for a coil, which has a U-shaped cross section and is made of a sintered metal that is a magnetic material.
8 and 29 are fixed. The tubular body 28 is disposed so as to straddle the facing portion of the first cylinder 26 and the second cylinder 27. A temperature compensation coil 30 and a torque detection coil 31 as a torque sensor are housed in the cylinders 28 and 29. The cylinder 28 is the first cylinder 26, and the cylinder 29 is the first cylinder 26 and the second cylinder. 27 and a magnetic circuit, respectively.

The signals from the torque detecting coil 31 and the temperature compensating coil 30 are given to the control section mounted on the control board 33 mounted on the board housing section 32 in the first housing 11. The direction and magnitude of the steering torque applied to the steering wheel 1 is recognized from the signals received from the sensors 30 and 31 via the sensor circuit. Although not shown, the control unit outputs a signal for rotating the steering assisting motor, which is connected to the output side thereof via the drive circuit, in the direction corresponding to the operating direction of the steering wheel 2.

Referring to FIG. 1 and FIG. 2 which is an enlarged view of the main part of FIG. 1, a cylindrical diameter reducing portion 34 is provided at the lower end of the output shaft 5, and the diameter reducing portion 34 is It is accommodated in a hole 35 provided at the upper end of the pinion shaft 7. The upper end 6a of the second torsion bar 6 is inserted into a connecting hole 36 that axially penetrates the reduced diameter portion 34 of the output shaft 5, and is integrally rotatably connected by, for example, serration coupling. The lower end 6b of the second torsion bar 6 is inserted into a connecting hole 37 formed in the inner portion of the hole 35 of the pinion shaft 7, and is connected integrally rotatably by, for example, serration connection. Reference numeral 45 is an elastic body such as an O-ring that interferes with the collision between the output shaft 5 and the pinion shaft 7 when the relative rotation of the output shaft 5 and the pinion shaft 7 is restricted within a predetermined range.

2 and FIG. 3, which is a sectional view taken along the line III--III of FIG. 1, the outer peripheral surface 42 of the reduced diameter portion 34 and the hole 3 are shown.
5, the stopper mechanism 3 for restricting the relative rotation amount of the output shaft 5 and the pinion shaft 7 within a predetermined range.
8 are provided. Specifically, the inner peripheral surface 39 of the hole 35
Pinion stoppers 40 and 41 as a pair of abutting portions which are parallel to each other are formed on the outer peripheral surface 42 of the reduced-diameter portion 34.
3, 44 are formed.

Adjacent stopper engaging portions 43, 44 are inclined with respect to each other. A pair of stopper engaging portions 43, 43
Engage with the corresponding pinion stoppers 40 and 41, respectively, and regulate the rotation range of the output shaft 5 in the clockwise direction in FIG. The other pair of stopper engaging portions 44, 44 engages with the corresponding pinion stoppers 40, 41, respectively, and regulates the rotation range of the output shaft 5 in the counterclockwise direction in FIG. The elastic body 4 including the above-mentioned O-ring and the like
5 is wound around the outer peripheral surface 42 of the reduced diameter portion 34 of the output shaft 34, for example, so as to soften the impact at the time of contact between the stopper engaging portions 43, 44 and the pinion stoppers 40, 41 so as not to generate a tapping sound. To The elastic body 45 may be attached to the inner peripheral surface 39 of the hole 35.

According to the present embodiment, since the output shaft 5 and the pinion shaft 7 are connected via the second torsion bar 6 as an elastic body, the wheels and the rack bar 9 from the road surface during traveling on a rough road. To the pinion shaft 7 via the
Even if a vibration of about Hz) propagates, it is possible to prevent the vibration from further propagating to the output shaft 5. Therefore, it is possible to suppress the generation of rattle noise between the worm shaft 15 and the worm wheel 16 of the speed reduction mechanism 13 due to the influence of road surface vibration, and it is possible to suppress noise.

Moreover, this can be achieved only by a simple structural change in which the output shaft 5 and the pinion shaft 7 which are conventionally integrated members are separated from each other and connected by the second torsion bar 6. Further, the backlash between the worm shaft 15 and the worm wheel 16 does not have to be made too small.
The rotation resistance of is not increased.

Further, since the relative rotation amount of the output shaft 5 and the pinion shaft 7 can be regulated within a predetermined range by the stopper mechanism 38, the second torsion bar 6 will not be excessively twisted, and accordingly, the second torsion bar 6 will not be twisted. It is possible to prevent the second torsion bar 6 from being damaged. Further, since the elastic body 45 can mitigate the collision between the pinion stoppers 40 and 41 and the stopper engaging portions 43 and 44 when the stopper mechanism 38 operates, a tapping sound or the like does not occur, which is preferable.

FIG. 4 shows another embodiment of the present invention. Referring to FIG. 4, the present embodiment differs from the embodiment of FIG. 2 in that in the embodiment of FIG. 2, a second torsion bar 6 is provided between output shaft 5 and pinion shaft 7. Although torque is transmitted, instead of this, in the present embodiment, the point is that torque is transmitted via the compression coil spring 51 (52) as an elastic body. Specifically, with reference to FIG. 5, stopper engaging portions 49 and 50 as opposed portions that are parallel to each other and are formed on the outer peripheral surface 48 of the reduced diameter portion 47 as the shaft body at the lower end of the output shaft 5. The pinion stopper 4 as a corresponding facing portion of the inner peripheral surface 39 of the hole 35 of the pinion shaft 7.
The compression coil springs 51 and 52 as a pair of elastic bodies are interposed between the compression coil springs 0 and 41.

The compression coil springs 49, 50 are arranged on both sides of the corresponding stopper engaging portions 49, 50 with the central portion sandwiched therebetween, and urge the output shaft 5 to rotate in opposite directions. Specifically, the compression coil springs 51 and 5 are arranged diagonally.
1 transmits the torque in the clockwise direction of the output shaft 5 in FIG. 5, and the compression coil springs 52 are also arranged diagonally,
52 transmits the counterclockwise torque of the output shaft 5 in FIG. A holding hole 53 for holding one end of the compression coil springs 51 and 52 is formed in each of the stopper engaging portions 49 and 50.

The pinion stoppers 40, 41 and the stopper engaging portions 49, 50 are in substantial contact with each other so that the relative rotation amount generated between the output shaft 5 and the pinion shaft 7 is regulated within a predetermined range. Function as. When the pinion stoppers 40 and 41 of the stopper mechanism 38A collide with the stopper engaging portions 49 and 50, the compression coil springs 51 and 52
Since it can be mitigated by, noise suppression can be achieved. According to the present embodiment, compression coil springs 51 and 52 as elastic bodies that expand and contract according to the twist between both shafts 5 and 7 are provided in the so-called fitting portion between output shaft 5 and pinion shaft 7.
With a simple structure intervening, the torque can be transmitted between both shafts 5 and 7, and noise can be suppressed.

In particular, the compression coil springs 51 and 52 are preferable because they can transmit a sufficient amount of torque even if they are small in size, without causing an increase in the size of the electric power steering apparatus 1. Next, FIG. 6 shows a cross section of a main part of still another embodiment of the present invention. Referring to FIG.
The feature of this embodiment is that the shaft 55 integrally formed at the lower end of the output shaft 5 has a cross-shaped cross section, and
5 is accommodated in the connecting hole 56 having a cross-shaped cross section of the pinion shaft 7,
The facing portion 57 provided on the outer periphery of the shaft body 55 and the connecting hole 56
An elastic body 59 made of rubber or synthetic resin is interposed between the elastic body 59 and the facing portion 58 provided on the inner circumference of the.

In the present embodiment, a simple structure is allowed while allowing a predetermined twist between the shafts 5 and 7 through the elastic body 59 such as rubber interposed between the output shaft 5 and the pinion shaft 7. Torque can be transmitted. Since the relative rotation amount between the two shafts 5 and 7 is regulated via the elastic body 59, noise can be suppressed. Next, FIGS. 7 (a) and 7 (b) show a cross section of a main part of still another embodiment of the present invention. With reference to FIGS. 7A and 7B, the feature of the present embodiment lies in that one or a plurality of first shaft bodies 60 integrally extending from the output shaft 5 and the pinion shaft 7 integrally extend. One or more second shaft bodies 61 are provided, and these shaft bodies 60, 61 are provided.
Are alternately arranged at equal intervals on the circumference centered on the central axis C of the output shaft 5 and the pinion shaft 7, and each shaft body 60, 61
Is fitted into corresponding fitting holes 63 and 64 provided in the elastic body 62 made of rubber or synthetic resin.

Also in this embodiment, when the output shaft 5 and the pinion shaft 7 rotate relative to each other, for example, in FIG. 7B, the output shaft 5 with the first shaft body 60 rotates clockwise relative to the pinion shaft 7 ( If the shafts 60 and 61 are rotated relative to each other, the peripheral surfaces of the adjacent shaft bodies 60 and 61 become the facing portions 60a and 61a, and the elastic body 62 interposed between the facing portions 60a and 61a. The portion 62a and its periphery are compressed, and the reaction force of this compression can be used to transmit torque between the two shafts 5, 7. Further, since the relative rotation amount between the shafts 5 and 7 is regulated via the elastic body 62, noise can be suppressed.

The present invention is not limited to the above-mentioned embodiments, and in short, the output shaft 5 and the pinion shaft 7
It suffices to connect and via an elastic body so that torque can be transmitted,
Various modifications can be made within the scope of the claims of the present invention.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of an electric power steering apparatus according to an embodiment of the present invention.

FIG. 2 is an enlarged view of a main part of FIG.

FIG. 3 is a sectional view taken along the line III-III in FIG.

FIG. 4 is a sectional view of a main part of an electric power steering apparatus according to another embodiment of the present invention.

5 is a cross-sectional view taken along the line VV of FIG.

FIG. 6 is a cross-sectional view of a main part of an electric power steering apparatus according to still another embodiment of the present invention.

7 (a) is a cross-sectional view of a main part of an electric power steering apparatus according to still another embodiment of the present invention, and FIG. 7 (b) is a line 7B-7B in FIG. 7 (a). FIG.

[Explanation of symbols]

1 Electric power steering device 2 steering wheel 3 input axes 4 First Torsion Bar 5 output shafts 6 Second torsion bar (elastic body) 7 pinion shaft 9 rack bars 13 Reduction mechanism 14 Electric motor 15 Worm shaft 16 worm wheel 34 Reduced diameter part 36, 37 Connection hole 38, 38A stopper mechanism 39 Inner surface 40,41 Pinion stopper (opposing part) 42 outer peripheral surface 43,44 Stopper engaging part (opposing part) 45 Elastic body 47 Reduced diameter part 48 outer peripheral surface 49,50 Stopper engaging part (opposing part) 51,52 Compression coil spring (elastic body) 55 axis 56 Connection hole 57,58 Opposing part 59 Elastic body 60 First shaft 61 Second shaft 60a, 61a Opposing part 62 elastic body 63, 64 fitting holes

Claims (7)

[Claims] 1. An input shaft connected to a steering wheel, an output shaft rotatably connected to the input shaft via a torsion bar, a pinion shaft engaging with a rack bar connected to wheels, and an electric motor for steering assistance. An electric power steering apparatus comprising: a reduction mechanism that reduces the rotation of a motor and transmits it to an output shaft; and an elastic body that transmits the rotation of the output shaft to a pinion shaft. 2. The electric power steering apparatus according to claim 1, wherein the elastic body includes a torsion bar that coaxially connects the output shaft and the pinion shaft. 3. The stopper mechanism according to claim 2, further comprising a pair of opposed portions that come close to each other with the relative rotation of the output shaft and the pinion shaft and restrict the relative rotation amount of the output shaft and the pinion shaft. The electric power steering device. 4. The electric power steering apparatus according to claim 3, further comprising an elastic body interposed between the pair of facing portions. 5. The shaft body according to claim 1, wherein a shaft body that rotates integrally with one of the output shaft and the pinion shaft is inserted into a connecting hole formed in the other, and the elastic body is connected to the outer periphery of the shaft body. An electric power steering apparatus characterized in that it is interposed between the inner circumference of the hole and the inner circumference. 6. A pair of opposed portions, which are arranged close to each other as the output shaft and the pinion shaft rotate relative to each other, are provided on the outer periphery of the shaft body and the inner periphery of the coupling hole, and the elastic body is composed of a pair of opposed portions. An electric power steering apparatus comprising: a compression coil spring, a rubber, and a synthetic resin, which are interposed between the facing portions and are compressed when the facing portions approach each other. 7. The first and second shaft bodies extending from the output shaft and the pinion shaft, respectively, according to claim 1, fitted into fitting holes formed in an elastic body made of rubber or synthetic resin,
An electric power steering apparatus characterized in that a portion of an elastic body interposed between opposed portions of the first and second shaft bodies is compressed when the output shaft and the pinion shaft rotate relative to each other.