JP2007186009A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To install a worm to keep balance in a lift state, by supporting the worm with an elastic supporting member changed in stiffness on a circumference. <P>SOLUTION: Though a pre-load of the worm 11 varies according to the stiffness of rubber dampers 18a, 18b (the elastic supporting members), the worm 11 is supported by the rubber dampers 18a, 18b (the elastic supporting members) varied in its stiffness on the circumference, thereby installing the worm while keeping balance in a lifted state. Namely, the stiffness in a lifting direction is lowered, on the other hand, the axial stiffness can be kept at high to a certain degree. Therefore, the pre-load of the worm 11 can be lowered, and rotation torque can be reduced. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention detects a steering torque applied to a steering wheel by a torque sensor, generates an auxiliary steering torque from an electric motor corresponding to the detected steering torque, decelerates it by a reduction gear, and transmits it to an output shaft of a steering mechanism. The present invention relates to an electric power steering apparatus.

  In a steering system of an automobile, a so-called power steering device that performs steering assist using an external power source is widely adopted. Conventionally, vane type hydraulic pumps have been used as power sources for power steering devices, and many of these hydraulic pumps are driven by an engine. However, this type of power steering device has a large engine drive loss due to the constant drive of the hydraulic pump (several horsepower to about 10 horsepower at the maximum load), so it can be used in light vehicles with small displacement. It was difficult, and it was unavoidable that the fuel consumption of a car with a relatively large displacement was reduced to a level that could not be ignored.

  In order to solve these problems, an electric power steering device (Electric Power Steering, hereinafter referred to as EPS) using an electric motor as a power source has attracted attention in recent years. The EPS uses an in-vehicle battery as a power source for the electric motor, so there is no direct engine drive loss, and since the electric motor is started only at the steering assist time, a decrease in driving fuel consumption is suppressed, and electronic control is performed. It has the feature that it can be done very easily.

  In EPS, an auxiliary steering torque is generated from an electric motor in response to a steering torque applied to a steering wheel, and is decelerated by a power transmission mechanism (reduction gear) and transmitted to an output shaft of the steering mechanism. Yes.

  In EPS using a worm reducer as the power transmission mechanism (reduction gear), a worm wheel meshes with a worm on the drive shaft side of the electric motor, and this worm wheel is connected to the output shaft (for example, the steering mechanism) It is fitted to the pinion shaft and column shaft).

By the way, in the electric power steering device disclosed in Patent Document 1, a housing, a motor attached to the housing and transmitting auxiliary operation capability to the rotating shaft via the motor shaft, and formed or externally fitted to the rotating shaft, A worm having a gear portion made of metal or resin, a rolling bearing disposed in the housing and disposed on both sides of the worm, and rotatably supporting the rotating shaft, and for steering the axle An output shaft that is pivotally supported at a predetermined position of the housing, a worm wheel that is formed or externally fitted to the output shaft so as to mesh with the worm, and a gear portion is formed of resin. The backlash is provided by providing a preload mechanism for applying a preload toward the worm wheel at the shaft end of the rotating shaft far from the motor. Eliminate the presence of Yoo, without impairing the transmission performance of the power, it is possible to reduce the rattling noise.
International Publication Number WO 03/047948 A1

  However, since the worm preload mechanism for eliminating backlash loads preload against the worm wheel, the rotational torque of the shaft into which the worm wheel is press-fitted is higher than that without the preload mechanism. There is.

  The present invention has been made in view of the circumstances as described above, and can be installed so as to be balanced in a lift state by worm support by an elastic support member whose rigidity is changed on the circumference. An object of the present invention is to provide an electric power steering device that can be used.

In order to achieve the above object, an electric power steering apparatus according to the present invention detects a steering torque applied to a steering wheel by a torque sensor, and generates an auxiliary steering torque from an electric motor corresponding to the detected steering torque. In the electric power steering device that decelerates by the worm reducer and transmits to the output shaft of the steering mechanism,
The worm speed reducer includes a preload mechanism that applies a preload by pressing the worm against the worm wheel by an elastic force,
The worm is supported by an elastic support member at one end thereof,
The elastic support member is characterized in that its rigidity is changed in the circumferential direction.

  Preferably, the elastic support member is changed in thickness in the circumferential direction, and the rigidity in the circumferential direction is changed.

  Preferably, the elastic support member has a circumferential shape changed by changing a shape in the circumferential direction.

  Further preferably, the elastic support members are paired to support one end of the worm.

  The pre-pressure of the worm varies depending on the rigidity of the elastic support member. According to the present invention, the worm is supported by the elastic support member whose rigidity is changed on the circumference, so that it can be installed so as to be balanced in the lift state. That is, while the rigidity in the lift direction is lowered, the rigidity in the axial direction can be kept high to some extent. Therefore, the pre-pressure of the worm can be reduced and the rotational torque can be reduced.

  Hereinafter, an electric power steering apparatus according to an embodiment of the present invention will be described with reference to the drawings.

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

  As shown in FIG. 1, the worm 11 is rotatable at both ends by a motor-side bearing 15 on the side close to the electric motor 10 and an anti-motor-side bearing 23 on the side far from the electric motor 10. I support it.

  The worm 11 is splined to the drive shaft 10 a of the electric motor 10.

  The motor-side bearing 15 is fixed so as to be concentric with the worm 11 between a flange 16 provided integrally with the worm 11 and a nut or a caulking spacer 17 fixed to the end of the worm 11. . Further, the motor side bearing 15 is elastically supported between the C-shaped retaining ring 28 and the gear box 29 via a pair of compressed rubber dampers 18a and 18b. Thus, the worm 11 can move in the axial direction with respect to the motor-side bearing 15 within the elastic range of the rubber damper 18.

  A preload mechanism 20 is provided for preloading the worm 11 by pressing the non-motor side end of the worm 1 in the direction in which the worm 11 approaches the worm wheel 12.

  That is, the bush 22, the non-motor-side bearing 23, and the holder 24 are fitted to the large diameter portion 21 of the worm 11, and the preload pad 26 is provided on the small diameter portion 25 of the worm 11. A torsion coil spring 27 is wound.

  Therefore, the non-motor side end portion (small diameter portion 25) of the worm 11 can be elastically pressed with a constant load in the direction in which the worm 11 approaches the worm wheel 12, and the rattling of the meshing portion can be adjusted. it can.

  2 (a), (b), and (c) are cross-sectional views of the lower rubber damper (elastic support member) in FIG. 1, and (d), (e), and (f) are respectively in FIG. It is sectional drawing of an upper rubber damper (elastic support member).

  In the present embodiment, the rubber dampers 18a and 18b (elastic support members) have their rigidity changed in the circumferential direction. As will be described later, the rubber dampers 18a and 18b (elastic support members) may be changed in thickness in the circumferential direction to change the rigidity in the circumferential direction, and the shape in the circumferential direction may be changed. Thus, the circumferential rigidity may be changed.

  In addition, the code | symbol 18a is a lower rubber damper (elastic support member) in FIG. 1, and the code | symbol 18b is an upper rubber damper (elastic support member) in FIG.

  In addition, phasing slits 30 are formed in the outer housings of the rubber dampers (elastic support members) 18a and 18b, and phasing is provided in a part of each rubber damper (elastic support member) 18a and 18b. A protrusion 31 is formed. Thereby, the high and low phases of the rigidity of the rubber dampers (elastic support members) 18a and 18b can be matched.

  2 (a) and 2 (d), the rubber dampers 18a and 18b (elastic support members) have their rigidity changed in the circumferential direction. The part is configured to have high rigidity. Specifically, the thicknesses of the rubber dampers 18a and 18b (elastic support members) are changed in the circumferential direction.

  2B and 2E, similarly, the rubber dampers 18a and 18b (elastic support members) have their rigidity changed in the circumferential direction, and the part L is low in rigidity. The portion H is configured to have high rigidity. Specifically, it is formed so that the thickness in the radial direction is slightly reduced in the portion (L) having low rigidity.

  2C and 2F, similarly, the rubber dampers 18a and 18b (elastic support members) have their rigidity changed in the circumferential direction, and the portion indicated by the symbol L has low rigidity. The part of the symbol H is configured to have high rigidity. Specifically, a hole (cavity) is formed at a low rigidity portion (L) so that the rigidity is lowered.

  From the above, the preload of the worm 11 varies depending on the rigidity of the rubber dampers 18a and 18b (elastic support members). However, according to the present embodiment, the rubber dampers 18a and 18b (with the rigidity varied on the circumference) By supporting the worm 11 by the elastic support member), it can be installed so as to be balanced in the lifted state. That is, while the rigidity in the lift direction is lowered, the rigidity in the axial direction can be kept high to some extent. Therefore, the preload of the worm 11 can be reduced and the rotational torque can be reduced.

  In addition, this invention is not limited to embodiment mentioned above, A various deformation | transformation is possible.

1 is a cross-sectional view of an electric power steering device according to an embodiment of the present invention. (A), (b), and (c) are sectional views of the lower rubber damper (elastic support member) in FIG. 1, and (d), (e), and (f) are respectively the upper side in FIG. It is sectional drawing of a rubber damper (elastic support member).

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Electric motor 10a Drive shaft 11 Worm 12 Worm wheel 15 Motor side bearing 16 Flange 17 Nut 17
18a, 18b Rubber damper (elastic support member)
DESCRIPTION OF SYMBOLS 20 Preload mechanism 21 Large diameter part 22 Bush 23 Anti-motor side bearing 24 Holder 25 Small diameter part 26 Preload pad 27 Torsion coil spring 28 C-type retaining ring 29 Gear box 30 Phase determination slit 31 Phase determination protrusion 31

Claims (4)

The steering torque applied to the steering wheel is detected by a torque sensor, an auxiliary steering torque is generated from the electric motor in response to the detected steering torque, decelerated by the worm reducer, and transmitted to the output shaft of the steering mechanism. In the power steering device,
The worm speed reducer includes a preload mechanism that applies a preload by pressing the worm against the worm wheel by an elastic force,
The worm is supported by an elastic support member at one end thereof,
The electric power steering apparatus according to claim 1, wherein the elastic support member has a rigidity changed in a circumferential direction.   The electric power steering apparatus according to claim 1, wherein the elastic support member is changed in thickness in the circumferential direction to change in rigidity in the circumferential direction.   The electric power steering apparatus according to claim 1, wherein the elastic support member has a circumferential rigidity changed by changing a circumferential shape thereof.   4. The electric power steering apparatus according to claim 1, wherein a pair of the elastic support members support one end of the worm. 5.

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