JP3613696B2 - Electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric power steering apparatus using an electric motor as a generation source of steering assist force, and in particular, an electric power configured to transmit the rotational force of the motor to a steering mechanism via a worm gear type reduction device. The present invention relates to a steering device.
[0002]
[Prior art]
The electric power steering device is configured to drive a steering assist motor based on the detection result of the steering torque applied to the steering wheel, and to assist the steering by adding the rotational force of the motor to the steering mechanism. In recent years, the use of the assisting force characteristic according to the running state such as the level of the vehicle speed and the steering frequency can be easily performed by the energization control of the motor.
[0003]
As a difficulty of the electric power steering device, there is a problem that it is difficult to obtain a small motor capable of generating sufficient rotational force for steering assistance, and it is difficult to secure a space for arranging the motor. This is solved by a configuration in which a speed reduction device is interposed in the middle of the transmission system from the steering assist motor to the steering mechanism, and the rotational force of the motor is increased by deceleration and applied to the steering mechanism. It is desirable that the speed reducer can be compactly configured to avoid an increase in the size of the entire transmission system and that a high speed reduction ratio can be obtained. In order to meet this requirement, the speed reducer is coaxial with the output shaft connected to the steering mechanism. 2. Description of the Related Art A worm gear type reduction device is widely used in which a worm connected to the output side of a steering assist motor is engaged with a worm wheel that is attached to the worm wheel.
[0004]
FIG. 4 is a front sectional view showing a conventional electric power steering apparatus. In the figure, 1 is an input shaft and 2 is an output shaft. These are coaxially connected via a torsion bar 3 and are rotatably supported in a common housing having a cylindrical shape. The housing includes a first housing H ₁ of the input shaft side, a second configuration in which are integrated with the housing of H ₂ output shaft side, to the interior of the first housing H _1, the input shaft 1 and output shaft 2 A torque sensor 4 for detecting a steering torque according to the relative angular displacement amount between the input shaft 1 and the output shaft 2 is installed outside the facing portion. Extraction of the feed and output to the torque sensor 4 are made respectively through the terminal box 5 which protrude outside the first housing H _1.
[0005]
The upper end portion of the input shaft 1 protrudes from the first housing H _1, as the steering torque applied to a steering wheel (not shown) acts on the input shaft 1, the steering wheel via the upper shaft 10 It is connected. On the other hand, the lower end portion of the output shaft 2 so protrudes, is steered is transmitted the rotation of the output shaft 2 is a rack and pinion steering mechanism (not shown) is performed from the second housing H _2, a universal joint It connects with the steering mechanism via appropriate connection means, such as.
[0006]
The input shaft 1 is supported at both ends by a bearing (not shown) that supports the integrally connected upper shaft 10 and a bearing bush 8 that is fitted inside the output shaft 2. Ball On the other hand, the output shaft 2, the second housing H ball bearing 22 which is fitted and fixed to the opening of the input shaft _2, which is fitted in and fixed to the second opening of the steering mechanism of the housing H ₂ Both ends of the worm wheel 6 are supported by a bearing 21, and a short cylindrical worm wheel 6 is mounted between these supporting positions as described later, and the worm 7 is engaged with the outer periphery of the worm wheel 6.
[0007]
FIG. 5 is a cross-sectional view taken along line VV in FIG. In correspondence to the position of the worm wheel 6, the motor M is fixed to the outside of the second housing H _2. The rotating shaft 70 of the motor M is positioned in a direction orthogonal to the axis of the worm wheel 6, and the worm 7 is coaxially connected at the tip thereof. The worm 7 is placed inside the second housing H _2, by a ball bearing 23 and the ball bearing 24 is fitted to the second housing H _2, it is supported across the intersection with the worm wheel 6 Yes.
[0008]
FIG. 6 is an enlarged front sectional view in the vicinity of the position where the worm wheel 6 is attached. The worm 7 is a screw gear geared like a trapezoidal screw. On the other hand, the worm wheel 6 includes a metal annular boss portion 6a and a synthetic resin gear portion 6b integrally formed on the outer side of the boss portion 6a. To engage with the worm 7, the teeth 6c are cut. The worm wheel 6 and the worm 7 are meshed with each other so that the rotational axis of the worm 7 is positioned at the approximate center in the axial direction of the worm wheel 6.
[0009]
With the configuration as described above, when the steering wheel is rotated, the rotational force is transmitted from the input shaft 1 to the output shaft 2 via the torsion bar 3, and is transmitted to the steering mechanism connected to the output shaft 2. Steering is performed. At this time, road surface resistance acting on the wheels acts on the output shaft 2 via the steering mechanism, and the torsion bar 3 connecting the input shaft 1 and the output shaft 2 corresponds to the steering torque applied to the steering wheel. Torsion occurs, and the torque sensor 4 generates an output corresponding to the relative angular displacement between the input shaft 1 and the output shaft 2.
[0010]
The output of the torque sensor 4 is given to a control unit (not shown) and used to control the drive current of the motor M. As a result, the motor M generates a rotational force according to the magnitude and direction of the steering torque applied to the steering wheel, and the rotational force is decelerated by the worm 7 and the worm wheel 6 and transmitted to the output shaft 2. It is transmitted to the steering mechanism to assist steering in the direction of returning the torsion bar 3 torsion.
[0011]
[Problems to be solved by the invention]
In the conventional electric power steering apparatus as described above, noise is generated when the backlash amount of the worm wheel and the worm is not appropriate, and the radius of the worm wheel between the worm wheel and the worm is used to adjust the backlash amount. Had to adjust the direction distance. The backlash can be adjusted by changing the relative position of the steering shaft to which the worm wheel is attached and the rotating shaft of the electric motor to which the worm is connected in the radial direction of the worm wheel. Is a direction orthogonal to the axial length direction of each of the steering shaft and the rotating shaft of the electric motor, and in order to change the relative position of the steering shaft and the rotating shaft of the electric motor in the above-mentioned direction, a bearing supporting each of them Therefore, it is very difficult to make a structure capable of adjusting the backlash after assembling the electric power steering apparatus. Therefore, in order to obtain an appropriate backlash, it is necessary to measure the finished dimensions of the worm wheel, worm, and housing, and combine them to obtain an appropriate backlash, and a backlash failure has occurred. In some cases, it took a lot of work, such as reassembling and reassembling the parts that can be reassembled to obtain an appropriate backlash.
[0012]
The present invention has been made in view of such circumstances, and an object thereof is to provide an electric power steering device that can easily adjust the backlash between the worm wheel and the worm during the assembly of the electric power steering device. And
[0013]
[Means for Solving the Problems]
An electric power steering apparatus according to the present invention includes a steering shaft having one end connected to a steering wheel and the other end connected to a steering mechanism, a worm wheel coaxially attached to the steering shaft, and the worm A worm meshed with a wheel and connected to a rotating shaft of an electric motor for assisting steering, and the rotational force of the electric motor driven based on a detection result of a steering torque applied to the steered wheel is converted to the worm and the worm. In the electric power steering apparatus configured to transmit to the steering shaft via a wheel, the steering shaft has an axial length of the steering shaft with respect to the rotation shaft of the electric motor by ball bearings on both sides of the mounting position of the worm wheel. is supported by the relatively movable in a direction, the worm wheel has name a tapered outer peripheral surface of the tooth is formed with respect to the axis of the steering shaft The ball bearing is positioned by a separate lock nut so that backlash adjustment between the worm and the worm wheel can be performed. Further, the steering shaft is arranged at both ends of the support position by the ball bearing. And the backlash adjustment is performed by assembling the steering shaft, worm wheel, electric motor, worm, ball bearing, and lock nut to the housing. It is made to perform in the state of the unit which becomes .
[0014]
According to the electric power steering apparatus of the present invention, the backlash can be adjusted by adjusting the distance between the worm wheel and the worm in the axial direction of the worm wheel by making the worm wheel tapered. Therefore, the backlash can be adjusted by changing the relative position in the axial direction of the steering shaft between the steering shaft to which the worm wheel is attached and the rotating shaft of the electric motor to which the worm is connected. It is possible to easily adjust the backlash during the assembly of the steering device.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings illustrating embodiments thereof. FIG. 1 is a front sectional view showing a configuration of a main part of an embodiment of an electric power steering apparatus according to the present invention. In the figure, 1 is an input shaft and 2 is an output shaft. These are coaxially connected via a torsion bar 3 and are rotatably supported in a common housing having a cylindrical shape. The housing includes a first housing H ₁ of the input shaft side, a second configuration in which are integrated with the housing of H ₂ output shaft side, to the interior of the first housing H _1, the input shaft 1 and output shaft 2 A torque sensor 4 for detecting a steering torque according to the relative angular displacement amount between the input shaft 1 and the output shaft 2 is installed outside the facing portion. Extraction of the feed and output to the torque sensor 4 are made respectively through the terminal box 5 which protrude outside the first housing H _1.
[0016]
The upper end portion of the input shaft 1 protrudes from the first housing H _1, as the steering torque applied to a steering wheel (not shown) acts on the input shaft 1, a steering via the upper shaft 10 Wheel ( Connected to the steering wheel). On the other hand, the lower end portion of the output shaft 2 so protrudes, is steered is transmitted the rotation of the output shaft 2 is a rack and pinion steering mechanism (not shown) is performed from the second housing H _2, a universal joint It connects with the steering mechanism via appropriate connection means, such as.
[0017]
The input shaft 1 is supported at both ends by a bearing (not shown) that supports the integrally connected upper shaft 10 and a bearing bush 8 that is fitted inside the output shaft 2. On the other hand, the output shaft 2, the second housing H ball bearing 22 provided in the opening of the input shaft 1 side _2, a ball bearing 21 provided in the second opening of the steering mechanism of the housing H ₂ The tapered worm wheel 6 is mounted between these supporting positions as described later, and the worm 7 is engaged with the outer periphery of the worm wheel 6. The output shaft 2 is slidable in the axial length direction with respect to the ball bearings 21 and 22, and a male screw is formed on a part of the outer peripheral surface near the upper end and the lower end of the output shaft 2, Lock nuts 23 and 24 are screwed below the ball bearing 21 and above the ball bearing 22 to fix the ball bearings 21 and 22.
[0018]
2 is a cross-sectional view taken along line II-II in FIG. In correspondence to the position of the worm wheel 6, the motor M is fixed to the outside of the second housing H _2. The rotating shaft 70 of the motor M is positioned in a direction orthogonal to the axis of the worm wheel 6, and the worm 7 is coaxially connected at the tip thereof. The worm 7 is placed inside the second housing H _2, by a ball bearing 23 and the ball bearing 24 is fitted to the second housing H _2, it is supported across the intersection with the worm wheel 6 Yes.
[0019]
FIG. 3 is an enlarged front sectional view in the vicinity of the position where the worm wheel 6 is attached. The worm 7 is a screw gear geared like a trapezoidal screw. On the other hand, the worm wheel 6 includes a metal annular boss portion 6a and a synthetic resin gear portion 6b integrally formed on the outside of the boss portion 6a in a tapered shape, and the gear portion 6b has a tapered shape. On the outer peripheral surface, teeth 6c are cut out to mesh with the worm 7. The worm wheel 6 is attached to the output shaft 2 such that the diameter of the worm wheel 6 decreases downward and the worm wheel 6 and the worm 7 extend in the axial length direction on the outer peripheral surface of the worm wheel 6. Engage at approximately the center position.
[0020]
With the configuration as described above, when the steering wheel is rotated, the rotational force is transmitted from the input shaft 1 to the output shaft 2 via the torsion bar 3, and is transmitted to the steering mechanism connected to the output shaft 2. Steering is performed. At this time, road surface resistance acting on the wheels acts on the output shaft 2 via the steering mechanism, and the torsion bar 3 connecting the input shaft 1 and the output shaft 2 corresponds to the steering torque applied to the steering wheel. Torsion occurs, and the torque sensor 4 generates an output corresponding to the relative angular displacement between the input shaft 1 and the output shaft 2.
[0021]
The output of the torque sensor 4 is given to a control unit (not shown) and used to control the drive current of the motor M. As a result, the motor M generates a rotational force according to the magnitude and direction of the steering torque applied to the steering wheel, and the rotational force is decelerated by the worm 7 and the worm wheel 6 and transmitted to the output shaft 2. It is transmitted to the steering mechanism to assist steering in the direction of returning the torsion bar 3 torsion.
[0022]
When the relative positions of the worm 7 and the worm wheel 6 are not in an appropriate amount of backlash, the output shaft 2, the worm wheel 6, the ball bearings 21, 22, the lock nuts 23, 24, the second housing H _{2. In} the state of the unit composed of the motor M, the worm 7 and the like, the lock nuts 23 and 24 are loosened, and the output shaft 2 is slid in the axial direction to obtain an appropriate amount of backlash positional relationship. The backlash can be adjusted by sometimes tightening the lock nuts 23 and 24 to fix the output shaft 2. The first Ujingu H ₁ and second housing H ₂ and the upper shaft 10 caused by the backlash adjusting individual differences of the relative position between the input shaft 1, and the output shaft 2, the first housing H ₁ and the second housing H ₂ It is absorbed by being attached to the vehicle body by adjusting the position through a long hole provided in the mounting bracket to be mounted.
[0023]
In the present embodiment, the output shaft 2 is slidable in the axial direction with respect to the ball bearings 21 and 22, and the position of the output shaft 2 in the axial direction is adjusted to reduce backlash between the worm wheel and the worm. Although the configuration is such that the adjustment can be performed, a configuration in which the motor M or its rotating shaft 70 can be moved in the axial direction of the output shaft 2 may be employed.
[0024]
【The invention's effect】
As described above in detail, according to the electric power steering apparatus of the present invention, since the worm wheel is tapered, the relative position in the axial direction of the steering shaft between the steering shaft and the rotating shaft of the electric motor is determined after assembly. By changing the position of the ball bearing that supports the steering shaft on both sides of the worm wheel with the lock nut , the backlash adjustment at the meshing part of the worm wheel and the worm can be easily performed, and each part to obtain the appropriate backlash There is no need to select and assemble, and there is no need for reassembly due to poor backlash, and the number of assembly steps for the electric power steering apparatus can be reduced .
[0025]
In addition, since the housing that supports the steering shaft by the ball bearings on both sides of the worm wheel and includes the fixed portion of the electric motor has the end portions on both sides of the ball bearing, the state in which the steering shaft and the electric motor are assembled to the housing Backlash adjustment can be performed with this, and other parts can be assembled to this unit to configure an electric power steering device. The possibility of reassembly requiring a great deal of labor is greatly reduced, and the number of assembly steps can be further reduced. The present invention has excellent effects, such as being able to achieve .
[Brief description of the drawings]
FIG. 1 is a front sectional view showing a configuration of a main part of an embodiment of an electric power steering apparatus according to the present invention.
FIG. 2 is a cross-sectional view taken along line II-II in FIG.
FIG. 3 is an enlarged front sectional view in the vicinity of a worm wheel mounting position.
FIG. 4 is a front sectional view showing a conventional electric power steering apparatus.
5 is a cross-sectional view taken along line VV in FIG.
FIG. 6 is an enlarged front sectional view in the vicinity of a worm wheel mounting position in a conventional electric power steering apparatus.
[Explanation of symbols]
1 Input shaft 2 Output shaft (steering shaft)
23, 24 Lock nut 6 Worm wheel 6a Boss part 6b Gear part 6c Teeth 7 Worm

Claims (2)

A steering shaft whose one end is connected to the steering wheel and the other end is connected to the steering mechanism, a worm wheel coaxially attached to the steering shaft, and an electric motor for assisting steering, which meshes with the worm wheel A worm coupled to the rotating shaft of the motor, and the rotational force of the electric motor driven based on the detection result of the steering torque applied to the steering wheel is transmitted to the steering shaft through the worm and the worm wheel. In the above-described electric power steering apparatus, the steering shaft is supported by ball bearings on both sides of the attachment position of the worm wheel so as to be movable relative to the rotation axis of the electric motor in the axial direction of the steering shaft , worm wheel has name a tapered shape with respect to the outer peripheral surface teeth are formed axis of the steering shaft, positioning the respective different locknut said ball bearing To an electric power steering apparatus characterized by you have to allow backlash adjustment between the worm and the worm wheel. The steering shaft has end portions on both sides of a support position by the ball bearing, and is supported inside a housing having a fixing portion of the electric motor, and the backlash adjustment is performed by adjusting the steering shaft, worm wheel, electric motor 2. The electric power steering apparatus according to claim 1, wherein the motor, the worm, the ball bearing and the lock nut are carried out in a unit assembled with the housing.

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