JP2006290237A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily perform assembling of a deceleration mechanism and a rack housing with good working efficiency and to increase freedom of a fastening position of the deceleration mechanism and the rack housing. <P>SOLUTION: A fastening part of a gear housing GH and a cover housing CH and a fastening part of the deceleration part assembling body (GH, CH) and the rack housing RH are set such that screw diameters are different. Namely, since a bolt 14 has a screw (large diameter screw part 14a) for fastening the cover housing CH and a screw (small diameter screw part 14b) for fastening the rack housing RH, difference is provided in a loosening torque and a fastening torque, thereby, the firstly fastened screw (large diameter screw part 14a) can be prevented from being loosened. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electric power steering device that generates an auxiliary steering torque from an electric motor in accordance with a steering torque applied to a steering wheel, decelerates by a speed reduction mechanism, and transmits it to an output shaft of the steering mechanism. The present invention relates to an improvement in an assembly method of a pinion assist type electric power steering device.

  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.

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

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

  By the way, as disclosed in Patent Document 1, in a pinion assist type electric power steering apparatus, there is one in which a pinion shaft is integrated with an output shaft of a speed reduction mechanism. The integrated output shaft and pinion shaft are configured to be detachable from the rack housing of the rack portion.

On the other hand, the cover housing and the gear housing are fastened with bolts, and the gear housing and the rack housing are fastened with separate bolts.
JP-A-8-175403

  However, since it is necessary to provide the fastening part of the cover housing and the fastening part of the rack housing separately, when the fastening part is arranged on the outer periphery of the gear housing, the degree of freedom of setting is limited. There is a case that the phase of the speed reduction mechanism is restricted and the position of the electric motor is restricted, which is disadvantageous in terms of layout.

  Also, when using multiple bolts of the same type and the same size for the fastening part of each cover housing and the fastening part of the rack housing, in order to fasten the fastening part of the rack housing with a nut after fastening the fastening part of the cover housing, When the nut is tightened, the fastening portion of the cover housing may be loosened.

  The present invention has been made in view of the above-described circumstances, and is easy to assemble the speed reduction mechanism and the rack housing, has high working efficiency, and has a degree of freedom in the fastening position between the speed reduction mechanism and the rack housing. In other words, an object of the present invention is to provide an electric power steering apparatus that can increase the degree of freedom of the electric motor, that is, can increase the degree of freedom of the position of the electric motor, and is advantageous in terms of layout.

In order to achieve the above object, an electric power steering apparatus according to claim 1 of the present invention generates an auxiliary steering torque from an electric motor in accordance with a steering torque applied to a steering wheel and decelerates it by a reduction mechanism. In the pinion assist type electric power steering device that transmits to the pinion shaft of the steering mechanism,
The output shaft of the speed reduction mechanism and the pinion shaft are separable,
The gear housing, the cover housing, and the rack housing are fastened by the same bolt,
The fastening parts of the gear housing and the cover housing and the fastening parts of the speed reduction part assembly and the rack housing are set to have different screw diameters.

  In the electric power steering apparatus according to claim 2 of the present invention, the fastening portions of the gear housing and the cover housing and the fastening portions of the speed reduction portion assembly and the rack housing are set with different screw twist directions. It is characterized by being.

  According to the present invention, since the output shaft of the speed reduction mechanism and the pinion shaft can be separated, the speed reduction mechanism and the rack and pinion mechanism can be made independent of each other, and the performance can be easily guaranteed. It is simple.

  In addition, since the cover housing and gear housing for storing the output shaft of the speed reducer and the rack housing for storing the pinion shaft are fastened by the same bolt, the fastening position between the speed reduction unit assembly and the rack housing The degree of freedom of the electric motor can be increased, that is, the degree of freedom of the position of the electric motor can be increased.

  Furthermore, according to the present invention, since the fastening portions of the gear housing and the cover housing and the fastening portions of the speed reduction unit assembly and the rack housing are set with different screw diameters, the loosening torque and the fastening portion are set. It is possible to prevent the screw that was initially tightened from loosening by providing a difference in the applied torque.

  Therefore, when the speed reduction unit assembly and the rack housing are fastened with screws, the fastening portion of the speed reduction unit assembly (gear housing and cover housing) does not loosen, and there is no need to hold the screw to work. , Work efficiency can be improved.

  In addition, the same effect can be obtained when the fastening portions of the gear housing and the cover housing and the fastening portions of the speed reducer assembly and the rack housing are set to have different screw twist directions.

  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 longitudinal sectional view of a pinion-assisted electric power steering apparatus according to an embodiment of the present invention, and is an exploded view.

  FIG. 2 is a longitudinal sectional view of the pinion-assist type electric power steering apparatus according to the embodiment of the present invention, and is an assembled view.

  FIG. 3 is a side view of a bolt used for assembling the pinion-assisted electric power steering apparatus according to the embodiment of the present invention.

  In the present embodiment, the housing includes a rack housing RH on the lower side of the vehicle, a gear housing GH on the upper side of the vehicle, and a cover housing CH that covers the gear housing GH.

  In the rack housing RH, the lower part of the pinion shaft 1 is rotatably supported by the lower bearing 2 (needle bearing), and the upper part thereof is rotatably supported by the upper bearing 3.

  A worm reduction gear is accommodated in the gear housing GH and the cover housing CH. The worm wheel 5 includes a cored bar (7) and gear teeth 6. In the present embodiment, the cored bar (7) and the output shaft 7 are integrally formed.

  The gear teeth 6 are driven by a worm 9 connected to an electric motor 8.

  The upper end portion 10 (male fitting portion) of the pinion shaft 1 and the lower end portion 11 (female fitting portion) of the output shaft 7 are configured to be separable, but will be described in detail later with reference to FIG. To do.

  A rack 21 is engaged with the pinion 1 a of the pinion shaft 1. In the rack guide 22, a roller 23 is constantly pressed against the back surface of the rack 21 by an adjust cover 24. The roller 23 is rotatably supported on a shaft 25 by a needle bearing 26.

  The adjusting cover 24 has a roller 23 pressed against the back surface of the rack 21 via a spring. As a result, the backlash of the meshing portion between the pinion 20 and the rack 21 is eliminated, and the rack 21 moves smoothly.

  An input shaft 30 is rotatably supported in the gear housing GH via a bearing 31.

  The input shaft 30 is connected to the steering wheel via a steering shaft (not shown). The torsion bar 33 whose upper end is connected to the input shaft 30 by a pin 32 is connected to the upper end portion of the output shaft 7 by press fitting.

  A torque sensor 34 that detects torque acting on the torsion bar 33 includes a sensor shaft portion 35, detection coils 36 and 37, and a cylindrical member 38. The sensor shaft portion 35 is formed at the lower end of the input shaft 30, and detection coils 36 and 37 are arranged in a yoke 39 press-fitted inside the sensor box. The cylindrical member 38 is disposed between the sensor shaft portion 35 and the detection coils 36 and 37.

  The cylindrical member 38 is fixed to the output shaft 7, and a plurality of ridges extending in the axial direction on the sensor shaft portion 35 are formed at equal intervals in the circumferential direction. In the cylindrical member 38, a plurality of rectangular windows are formed at equal intervals in the circumferential direction at positions facing the detection coils 36 and 37.

  When the input wheel 30 is rotated by operating the steering wheel, the rotational force is transmitted to the output shaft 7 via the torsion bar 33. At this time, the torsion bar 33 connecting the input shaft 30 and the output shaft 7 is twisted due to the resistance on the steering wheel side, and a relative rotation occurs between the protrusion on the surface of the sensor shaft portion 35 and the window of the cylindrical member 38. . With this relative rotation, the magnetic flux generated in the sensor shaft portion 35 increases and decreases, and the increase and decrease of the magnetic flux is detected by the detection coils 36 and 37 as a change in inductance. From this detection result, a torque acting on the torsion bar 33 is detected, and the electric motor 8 is driven to rotate the worm 9 with a required steering assist force. The rotation of the worm 9 is transmitted to the rack 21 via the worm wheel 5, the output shaft 7, and the pinion 1 a of the pinion shaft 1, and changes the direction of the steering wheel via a tie rod (not shown) connected to the rack 21.

  As shown in FIG. 1, the upper end portion 10 (male fitting portion) of the pinion shaft 1 and the lower end portion 11 (female fitting portion) of the output shaft 7 are configured to be separable.

  The output shaft 7 is preferably forged. The output shaft 7 is supported by two bearings 18 and 19, and is supported by at least one bearing so as not to be axially displaceable and rotatable.

  The cover housing CH is provided with a screw thread, and is fixed with a gear housing GH and a bolt 14 and has an inlay recess 12.

  As a result, the upper speed reduction part assembly itself can measure performance such as friction and assist torque.

  The bolt 14 is further extended by fastening the cover housing CH (small-diameter screw portion 14b described later), and penetrates the fastening portion of the rack housing RH. After the speed reduction part assembly (GH, CH) and the rack part are assembled, the small-diameter screw part 14b, which will be described later, is fastened by the nut 15 to be completely fixed.

  In addition, the rack portion includes the rack 21, the rack housing RH, the pinion shaft 1, and the bearings 2 and 3, as described above. The rack housing RH is provided with a fastening part for fixing the speed reduction part assembly (GH, CH) and an inlay convex part 13.

  One end of the pinion shaft 1 is fixed by an upper bearing 3 (four-point contact bearing) so as not to be axially displaceable and rotatable. The bearing 3 is also fixed to the rack housing RH so as not to be axially displaceable in the axial direction. . The other end is rotatably supported by the lower bearing 2 (needle bearing).

  The rack part has a function by itself, and can measure performances such as friction and adjustment backlash.

  The speed reduction part assembly (GH, CH) and the rack part are assembled on the basis of the in-loose uneven parts 12 and 13 provided in the respective parts to ensure the coaxial and airtightness of the shaft.

  The connecting part (male / female fitting part 10, 11) of the output shaft 7 and the pinion shaft 1 of the speed reduction part assembly (GH, CH) has a plurality of engaging uneven parts, and each uneven part is engaged. Torque is transmitted by matching. In addition, since a slight gap is provided between them, the assembling property can be improved and misalignment can be absorbed.

  In addition, the coupling part (male / female fitting part 10, 11) is provided with an elastic body 16 and has rigidity in the rotation direction.

  A heat treatment is applied to the coupling portion (male fitting portion 10) of the pinion shaft 1 to improve the hardness. The joint part (female fitting part 11) of the output shaft 7 of the speed reduction part assembly (GH, CH) has improved hardness by plastic hardening by plastic working.

  By assembling the speed reducer assembly (GH, CH) and the rack portion each of which guarantees performance, it is possible to reduce the defect rate and man-hours.

  As described above, in this embodiment, since the output shaft 7 and the pinion shaft 1 can be separated, it is easy to guarantee the performance of the speed reducer assembly (GH, CH) and the rack portion independently. It is easy to assemble.

  Further, since the cover housing CH, the gear housing GH, and the rack housing RH, which store the pinion shaft 1, are fastened by the same bolt 14, housings CH, The degree of freedom of the fastening position between the GH and the rack housing RH can be increased, that is, the degree of freedom of the position of the electric motor 8 can be increased, which is advantageous in terms of layout.

  Further, in the present embodiment, the bolt 14 is fastened by making the size of the screw (small diameter screw portion 14b) for fastening the rack housing RH smaller than the screw (large diameter screw portion 14a) for fastening the cover housing CH. Due to the difference in torque, it is possible to prevent bolt rotation when the rack housing RH is fastened.

  Further, the small-diameter screw portion 14b can be used as a reference for assembling the rack housing RH.

  Since the screw processing length can be shortened, the cost can be reduced and the assembly time can be shortened because the screw length is short when the gear housing GH and the cover housing CH are fastened.

  According to the present embodiment, the fastening portions of the gear housing GH and the cover housing CH and the fastening portions of the reduction gear assembly (GH, CH) and the rack housing RH are set with different screw diameters. is there. That is, since the bolt 14 has a screw (large diameter screw portion 14a) for fastening the cover housing CH and a screw (small diameter screw portion 14b) for fastening the rack housing RH, the loosening torque and the tightening torque. Thus, it is possible to prevent the screw (large-diameter screw portion 14a) tightened at first from being loosened.

  Therefore, when fastening the speed reduction part assembly (GH, CH) and the rack housing RH with screws (small diameter screw part 14b), the screw (large diameter screw part 14a) of the fastening part of the speed reduction part assembly (GH, CH) is used. Since it does not loosen and it is not necessary to work by pressing the screw (small-diameter screw portion 14b), work efficiency can be improved.

  Further, the fastening portions of the gear housing GH and the cover housing CH, and the fastening portions of the speed reducer assemblies (GH, CH) and the rack housing RH are screw bolts (large diameter screw portions 14a and small diameter screw portions 14b). ) May be set differently. In this case, the same effect can be obtained.

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

BRIEF DESCRIPTION OF THE DRAWINGS It is a longitudinal cross-sectional view of the pinion assist type electric power steering device according to the embodiment of the present invention, and is an exploded view. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view of a pinion-assisted electric power steering device according to an embodiment of the present invention, and is an assembled view. It is a side view of the volt | bolt used for the assembly of the pinion assist type electric power steering device concerning an embodiment of the invention.

Explanation of symbols

CH cover housing GH gear housing RH rack housing 1 pinion shaft 2 lower bearing 3 upper bearing 5 worm wheel 6 gear teeth 7 output shaft (core metal)
DESCRIPTION OF SYMBOLS 8 Electric motor 9 Worm 10 Male fitting part 11 Female fitting part 12 Inner recessed part 13 Inner recessed part 14 Bolt 14a Large diameter screw part 14b Small diameter screw part 15 Nut 16 Elastic body 18, 19 Bearing 1a Pinion 21 Rack 22 Rack guide 23 Roller 24 Adjust cover 25 Shaft 26 Needle bearing 27 Upper bearing 30 Input shaft 31 Bearing 32 Pin 33 Torsion bar 34 Torque sensor 35 Sensor shaft portion 36, 37 Detection coil 38 Cylindrical member 39 Yoke

Claims (2)

In a pinion assist type electric power steering device that generates an auxiliary steering torque from an electric motor according to a steering torque applied to a steering wheel, decelerates by a speed reduction mechanism, and transmits it to a pinion shaft of the steering mechanism.
The output shaft of the speed reduction mechanism and the pinion shaft are separable,
The gear housing, the cover housing, and the rack housing are fastened by the same bolt,
The electric power steering apparatus, wherein the fastening portions of the gear housing and the cover housing and the fastening portions of the speed reduction unit assembly and the rack housing are set to have different screw diameters.   2. The electric motor according to claim 1, wherein the fastening portions of the gear housing and the cover housing and the fastening portions of the speed reducer assembly and the rack housing are set to have different screw twist directions. Power steering device.

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