JP2005240959A - Electric power steering unit and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering unit which is small size and low in cost and has less noise. <P>SOLUTION: The electric power steering unit comprises connecting a worm shaft 18 as an output shaft 20 of an electric motor 16 and an input shaft of a reduction gear 17 by a tubular joint 21. It comprises press-fitting the output shaft 20 into a press-fit part 41 of inner peripheral surface 21a of the joint 21. It comprises fitting an engagement part 42 of a spline on the worm shaft 18 into an engagement part 43 of the spline of inner peripheral surface 21a of the joint 21. It comprises filling a resin P between the engagement parts 42, 43 of the spline and lessening play between the engagement parts 42, 43 of the spline. It comprises inserting a nozzle for fusion resin injection in inserted-through hole 40 penetrating shaft core of the worm shaft 18 and after injecting fusion resin from the nozzle between the engagement parts 42, 43 in the joint 21, and obtaining the resin P filled between the engagement parts 42, 43 of the spline without clearance by cooling and solidifying. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electric power steering apparatus that obtains a steering assist force by an electric motor and a method for manufacturing the same.

A reduction gear is used in an electric power steering system (EPS) for automobiles. For example, in the column type EPS, the rotation of the output shaft of the electric motor is decelerated through the worm shaft and the worm wheel, so that the output of the electric motor is amplified and transmitted to the steering mechanism, and the steering operation is torque-assisted. Yes.
Typically, a cylindrical joint that connects the output shaft of the electric motor and the worm shaft has a spline fit at the end of the worm shaft. This spline fitting portion has some backlash, and there is a problem that abnormal noise accompanying the rattling noise is generated due to this backlash.

As a measure for preventing abnormal noise, it is conceivable to improve the dimensional accuracy of each part and reduce the play of the spline fitting portion. However, the improvement of the dimensional accuracy of each component is accompanied by a great increase in cost.
In addition, it is conceivable to use a so-called elastic coupling as a joint for connecting the output shaft of the electric motor and the worm shaft, but there is a problem that the apparatus becomes large.

On the other hand, the end of the worm shaft is supported to be radially deflectable, and the end of the deflectable worm shaft is elastically biased toward the worm wheel using a spring, so that the worm shaft and the worm wheel are There is a technique for removing the backlash between them (for example, Patent Document 1).
JP 2001-233225 A

However, although Patent Document 1 is effective in removing the backlash at the meshing portion of the worm shaft and the worm wheel, the effect of killing backlash at the spline fitting portion of the joint cannot be expected so much. Therefore, it is not possible to suppress noise caused by spline fitting play.
The present invention has been made in view of the above problems, and an object of the present invention is to provide an electric power steering device that is small, inexpensive, and has low noise, and a method for manufacturing the same.

  In order to solve the above problems, the present invention provides an electric motor for assisting steering, a speed reducer for decelerating the rotation of the output shaft of the electric motor and transmitting it to the steering mechanism, an output shaft of the electric motor, and a speed reducer. A cylindrical joint that couples the input shaft to each other so that power can be transmitted, and the inner peripheral surface of the joint and the outer peripheral surface of the input shaft of the speed reducer include spline fitting portions that are spline-fitted to each other. Provided is an electric power steering device characterized in that a resin is filled in between.

In the present invention, the gap between the spline fitting portion of the joint and the input shaft is filled with resin, so that the spline fitting backlash can be removed. Can be prevented. It is not necessary to improve the dimensional accuracy of each part and is inexpensive. Further, the gap is only filled with resin, and the apparatus does not increase in size.
In the present invention, the input shaft may include a hollow shaft having an insertion hole penetrating in the axial direction. In this case, it can contribute to weight reduction of an electric power steering device. Moreover, it can use suitably for the following manufacturing method.

  That is, the present invention is a method for manufacturing the electric power steering apparatus, wherein after the molten resin is injected between the spline fitting portions from the nozzle for injection of the molten resin inserted through the insertion hole of the input shaft, the spline fitting is performed. Provided is a method for manufacturing an electric power steering device, characterized in that molten resin injected between joint portions is cooled and solidified. In this case, a nozzle for injection of molten resin is inserted into the insertion hole of the input shaft of the speed reducer incorporated in the joint, and the resin is injected between the spline fitting parts using this nozzle to form the spline fitting part. The gaps between them can be easily filled with resin.

  Further, the present invention is a method of manufacturing the electric power steering device, wherein a heater is inserted through the insertion hole of the input shaft, and the cylindrical resin member disposed in advance between the spline fitting portions is heated by the heater. Provided is a method for manufacturing an electric power steering device, wherein after melting, the molten resin between spline fitting portions is cooled and solidified. In this case, a spline fitting part is obtained by inserting a heater into the insertion hole of the input shaft incorporated in the joint and solidifying the resin melted by heating with the heater in a shape that follows the gap shape between the spline fitting parts. The gaps between them can be easily filled with resin.

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

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

The steering shaft 3 is divided into an input shaft 3a connected to the steering member 2 and an output shaft 3b connected to the pinion shaft 7. These input and output shafts 3a and 3b are on the same axis line via a torsion bar 12. They are connected to each other so as to be relatively rotatable.
A torque sensor 13 is provided for detecting a steering torque based on a relative rotational displacement amount between the input and output shafts 3a and 3b via the torsion bar 12, and the torque detection result of the torque sensor 13 is an ECU (Electric Control Unit: electronic). Control unit) 14. The ECU 14 drives and controls the steering assisting electric motor 16 via the drive circuit 15 based on a torque detection result or a vehicle speed detection result given from a vehicle speed sensor (not shown). The output rotation of the electric motor 16 is decelerated via the speed reducer 17 and transmitted to the pinion shaft 7 and converted into a linear motion of the rack bar 8 to assist steering.

The speed reducer 17 is a worm shaft 18 as a drive gear that is rotationally driven by the electric motor 16, and a worm wheel as a driven gear that meshes with the worm shaft 18 and is connected to the output shaft 3 b of the steering shaft 3 so as to be integrally rotatable. 19 is provided.
Referring to FIG. 2, worm shaft 18 is arranged coaxially with output shaft 20 of electric motor 16. The worm shaft 18 has first and second end portions 18a and 18b that are separated from each other in the axial length direction, and has a tooth portion 18c at an intermediate portion between the first and second end portions 18a and 18b. The worm shaft 18 is constituted by a hollow shaft having an insertion hole 40 penetrating the worm shaft 18.

  The worm wheel 19 is connected to an intermediate portion in the axial direction of the output shaft 3b of the steering shaft 3 so as to be integrally rotatable and immovable in the axial direction. The worm wheel 19 includes an annular cored bar 19a coupled to the output shaft 3b so as to be integrally rotatable, and a synthetic resin member 19b surrounding the cored bar 19a and having teeth 9c formed on the outer periphery. The core metal 19a is inserted into the mold when the synthetic resin member 19b is molded with resin, for example.

A region including the tooth meshing portion B of the worm shaft 18 and the worm wheel 19 is filled with a lubricant such as grease. The first end 18a of the worm shaft 18 and the output shaft 20 of the electric motor 16 are connected to each other coaxially via a cylindrical joint 21 so that power can be transmitted.
The first and second end portions 18a and 18b of the worm shaft 18 are rotatably supported by the housing 17a of the speed reducer 17 via corresponding first and second bearings 22 and 23, respectively. The first and second bearings 22 and 23 are ball bearings, for example.

  Inner rings 24, 25 of the first and second bearings 22, 23 are fitted to the first and second end portions 18a, 18b of the worm shaft 18 so as to be integrally rotatable. Each of the inner rings 24 and 25 is in contact with a corresponding positioning step portion of the worm shaft 18 opposite to each other. The outer ring 26 of the first bearing 22 is held in the bearing holding hole 27 of the housing 17a of the speed reducer 17 so as not to rotate. The outer ring 28 of the second bearing 23 is held in the bearing holding hole 29 of the housing 17a of the speed reducer 17 so as not to rotate.

  In addition, the preload adjusting screw member 31 is screwed into a screw hole 32 formed continuously to the bearing holding hole 27 to apply preload to the first and second bearings 22 and 23 collectively, The outer ring 28 of the second bearing 23 contacts the annular positioning portion 33 of the end wall 17b of the housing 17a, whereby the worm shaft 18 is positioned in the axial direction. The adjusted screw member 31 is fixed by the lock member 34.

The end wall 17b of the housing 17a has an opening 35 in a region inside the annular positioning portion 33, and the opening 35 is closed by a lid member 36.
With reference to FIG. 2 and FIG. 3 which is an enlarged view, one end portion 18a of the worm shaft 18 and the output shaft 20 of the electric motor 16 are fitted from the pair of end portions of the joint 21 to be coupled to the joint 21. . That is, the inner peripheral surface 21 a of the joint 21 is connected to a press-fit portion 41 into which the output shaft 20 of the electric motor 16 is press-fitted and a spline fitting portion 42 formed on the outer peripheral surface of the first end portion 18 a of the worm shaft 18. And a spline fitting portion 43 fitted.

Referring to FIGS. 2, 3, and 4, resin P is filled between the spline fitting portions 42 and 43 that are fitted to each other. Thereby, the play between the spline fitting parts 42 and 43 can be closed, and the generation of noise due to the play of the spline fitting can be prevented.
In addition, since it is not necessary to improve the dimensional accuracy of each component, the cost is not increased, and only the resin P is filled in the gap, and the apparatus is not enlarged.

As the resin P, for example, it is preferable to use a thermoplastic elastomer resin because it has high flexibility and is excellent in impact relaxation properties and followability.
In addition, since a hollow shaft is used as the worm shaft 18, there is an advantage that the filling of the resin P can be easily achieved by the following manufacturing method.
First, the 1st manufacturing method which carries out the injection molding of resin P in the coupling 21 is demonstrated based on FIG. As shown in FIG. 5A, in the state of the subassembly including the speed reducer 17 of the electric motor 16 and before the cover member 36 is assembled, the molten resin is injected into the insertion hole 40 penetrating the shaft center of the worm shaft 18. Nozzle 44 is inserted, and molten resin MP is injected from this nozzle 44.

Since the insertion hole 40 communicates with the space in the joint 21, as shown in FIG. 5B, the molten resin MP is filled in the joint 21 without a gap between the spline fitting portions 42 and 43. After filling, the nozzle 44 is removed from the insertion hole 40.
When the filled molten resin MP is cooled and solidified, as shown in FIG. 5C, a resin P (molded resin) filled without a gap between the spline fitting portions 42 and 43 can be obtained. Further, the opening 35 is closed by the lid member 36.

According to the first manufacturing method, the injection nozzle 44 is inserted into the insertion hole 40 of the worm shaft 18 incorporated in the joint 21, and the molten resin MP is inserted between the spline fitting portions 42 and 43 using the injection nozzle 44. The gap between the spline fitting portions 42 and 43 can be easily filled with the resin P.
Next, a second manufacturing method in which the resin is once melted in the joint 21 and then solidified will be described with reference to FIG. As shown in FIG. 6A, in the state of the subassembly including the speed reducer 17 of the electric motor 16 and before the cover member 36 is assembled, a thin cylindrical shape is formed in the gap between the spline fitting portions 42 and 43 in advance. The resin member 45 is interposed.

For example, a rod-shaped heater 46 supported at the tip of the support rod 47 is inserted into the insertion hole 40 penetrating the shaft center of the worm shaft 18, and the heater 46 reaches the first end portion 18 a of the worm shaft 18. The first end 18 a of the worm shaft 18 is heated by the heater 46.
By this heating, the resin member 45 interposed between the spline fitting portions 42 and 43 is melted, and the molten resin MP follows the shape of the spline fitting portions 42 and 43 as shown in FIG. It is filled without gaps. After filling, the heater 46 is removed from the insertion hole 40.

Next, when the filled molten resin MP is cooled and solidified, as shown in FIG. 6C, the filled resin P can be obtained without a gap between the spline fitting portions 42 and 43. Further, the opening 35 is closed by the lid member 36.
According to the second manufacturing method, the heater 46 is inserted into the insertion hole 40 of the worm shaft 18 incorporated in the joint 21, and the gap shape between the spline fitting portions 42 and 43 is melted by heating with the heater 46. By solidifying with a conforming shape, the gap between the spline fitting portions 42 and 43 can be easily filled with resin.

  The present invention is not limited to the above embodiments, and various modifications can be made within the scope of the claims of the present invention.

It is a mimetic diagram showing a schematic structure of an electric power steering device of one embodiment of the present invention. It is sectional drawing of the principal part of an electric power steering device. It is an enlarged view of the principal part of FIG. It is an enlarged view of the principal part of FIG. It is sectional drawing of the principal part of the electric power steering apparatus which shows an example of the manufacturing method of an electric power steering apparatus. It is sectional drawing of the principal part of the electric power steering apparatus which shows another example of the manufacturing method of an electric power steering apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric power steering apparatus 2 Steering member 3 Steering shaft 5 Intermediate shaft 7 Pinion shaft 8 Rack bar 10 Tie rod 11 Steering wheel A Steering mechanism 16 Electric motor 17 Reducer 17a Housing 17b End wall 18 Warm shaft (input shaft)
18a first end 18b second end 19 worm wheel 20 output shaft 21 joint 21a inner peripheral surface 35 opening 36 lid member 40 insertion hole 41 press-fit portion 42 (for worm shaft) spline fitting portion 43 (for joint) ) Spline fitting portion 44 Injection nozzle 45 Resin member 46 Heater 47 Support rod P Resin MP Molten resin

Claims (4)

  An electric motor for assisting steering, a speed reducer for decelerating the rotation of the output shaft of the electric motor and transmitting it to the steering mechanism, and a cylinder for connecting the output shaft of the electric motor and the input shaft of the speed reducer so as to be able to transmit power And the inner peripheral surface of the joint and the outer peripheral surface of the input shaft of the speed reducer include spline fitting portions that are spline-fitted with each other, and resin is filled between these spline fitting portions. Electric power steering device.   2. The electric power steering apparatus according to claim 1, wherein the input shaft includes a hollow shaft having an insertion hole penetrating in the axial direction.   3. The method of manufacturing an electric power steering device according to claim 2, wherein after the molten resin is injected between the spline fitting portions from the nozzle for molten resin injection inserted through the insertion hole of the input shaft, the spline fitting portion A method for manufacturing an electric power steering apparatus, characterized by cooling and solidifying molten resin injected therebetween.   3. The method of manufacturing an electric power steering apparatus according to claim 2, wherein a heater is inserted through the insertion hole of the input shaft, and a cylindrical resin member previously disposed between the spline fitting portions is melted by the heat of the heater. Then, the molten resin between spline fitting parts is cooled and solidified, The manufacturing method of the electric power steering apparatus characterized by the above-mentioned.

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