JP2830992B2 - Electric power steering device - Google Patents

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 having a worm speed reduction mechanism for supplying a motor torque to a steering system.

[0002]

2. Description of the Related Art There is known an electric power steering apparatus for supplementing a steering force by an electric motor. FIG. 6 is an overall configuration diagram of an electric power steering device according to the related art. The electric power steering device 101 includes a steering sensor 103 that detects a steering torque applied to a steering wheel 102, and a control device 104 controls the steering torque. , And the generated torque assists the steering system 108 via the electromagnetic clutch 106 for connecting and disconnecting the rotational force and the speed reduction mechanism 107.

When the speed reducing mechanism 107 is a worm gear (for example, Japanese Patent Application Laid-Open No. 1-249575), the worm wheel is made of a synthetic resin material. On the other hand, the base of the worm wheel is a metal member. It is necessary to integrally mold a worm wheel made of a synthetic resin material, the disadvantages of cost are inevitable due to the complicated manufacturing process, and the torque transmission capacity is small and the strength of the member at the time of temperature rise is greatly reduced. Therefore, the increase in the torque transmission capacity leads to an increase in the size of the gear mechanism. Therefore, improvements in both manufacturing cost and strength are expected.

[0004]

However, when the worm wheel of the worm gear reduction mechanism is formed of a metal material, the load acting on the steering system when the vehicle is not assisted due to frictional resistance acting between the worm wheel and the metal worm. As a result, the steering environment is degraded as a noise source of the steering system.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electric power steering apparatus which can reduce the manufacturing cost and reduce the size by solving the problems of frictional resistance and noise accompanying the metalization of the worm gear reduction mechanism. .

[0006]

In order to solve the above problems, a control device drives an electric motor based on a steering torque,
In an electric power steering apparatus configured to transmit an auxiliary torque generated by the electric motor to an output shaft of a steering system via a worm gear reduction mechanism, the worm gear reduction mechanism is configured by a metal gear and arranged outside the vehicle compartment. Further, an electric power steering apparatus is configured by interposing a clutch mechanism having a dead zone between the worm gear reduction mechanism and the output shaft of the steering system.

In the electric power steering apparatus having the above-described structure, the worm gear reduction mechanism is constituted by a metal gear, so that the gear can be downsized by improving the material strength and the structure can be simplified by integrating the shaft member. In addition, since it is located outside the cabin to eliminate noise interference, the cabin environment is not impaired, and a clutch mechanism having a dead zone is interposed between the worm gear reduction mechanism and the output shaft of the steering system. Therefore, within the dead zone,
Since the power assist system such as the electric motor 7 and the worm gear mechanism is cut off from the steering system, the steering by the steering torque acting on the steering wheel can be performed without causing the power assist system to have a steering resistance.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an overall configuration diagram of an electric power steering device according to the present invention. The electric power steering device 1 includes a steering system from a steering wheel 2 to turning wheels 4 and 4 via a steering shaft 3, and is provided in the steering system. A steering torque sensor 5 for detecting the steering torque, a control device 6 for determining an assist torque based on the output of the steering torque sensor 5, a motor 7 driven by the control device 6, and a reduction in the output of the motor. The worm gear reduction mechanism 8 includes a clutch mechanism 9 for connecting and disconnecting torque transmission from the worm gear reduction mechanism 8 to the steering system.

The worm gear reduction mechanism 8 is constituted by a worm gear mechanism made of metal and disposed outside the vehicle compartment, and the dashboard 10 defining the vehicle compartment is constituted by a sound insulating material, so that the noise generated by the speed reducer and the like is reduced. Intrusion into the cabin is suppressed, and the cabin environment can be maintained.

FIG. 2 is a sectional view of a main part of the electric power steering apparatus according to the present invention. The electric power steering apparatus 1 is engaged with a cylindrical input shaft 11 connected to the steered wheels and a rack shaft 4a. The output shaft 12 and the input shaft 1
1, a rotating shaft composed of a torsion bar 13 serving as a torque displacement member that allows relative angular displacement due to an action torque between the output shaft 12 and a relative angular difference between the input shaft 11 and the output shaft 12 of the rotating shaft. An operation converter 14 for converting the displacement into an axial displacement
An output conversion unit 15 that converts the displacement into an electric signal, a control device 6, an electric motor 7, a worm gear reduction mechanism 8,
The clutch mechanism 9 is integrally formed. Operation conversion unit 1
4 and the output converter 15 constitute a steering torque sensor 5 that operates according to the relative angle difference between the differential shafts corresponding to the acting torque.

FIG. 3 is a sectional view taken along line AA of FIG. 2. The worm gear reduction mechanism 8 includes a worm 22 formed integrally with a main shaft 21 of the electric motor 7 and a worm wheel 24 formed on an outer peripheral member 23 of the clutch mechanism 9. And both gears are formed of a metal material such as carbon steel.

The worm gear reduction mechanism 8 made of metal
According to the material strength, downsizing of the gear and simplification of the configuration of the worm wheel 24 can be achieved. Also, the worm wheel 24 side is formed in a ring shape with a bronze material,
In the case of press-fitting the outer peripheral member 23, the friction with the worm 22 side can be reduced to suppress the generation of noise.

The clutch mechanism 9 includes a worm wheel 24
An inner peripheral member 25 that forms a substantially triangular cross section of a tapered shape with the outer peripheral member 23 that forms the output shaft 12 side, a roller 26 that forms an engagement member engageable with both members, and the rollers 26. , And a fork member 28 for regulating the roller position. This fork member 28 is integral with the input shaft 11.

A wedge-shaped space is formed by opposing the inner peripheral surface 23a of the outer peripheral member 23 and the outer peripheral surface 25a of the inner peripheral member 25, and a one-way clutch is formed when the roller 26 is engaged with a corner of the wedge-shaped space. Is done. The central portion of the inner peripheral member 25 forms a rotation restricting portion 29 in which the input shaft 11 is fitted with a play at a predetermined angle and restricts excessive relative rotation between the two.

FIG. 4 is a diagram for explaining the operation of the clutch unit shown in FIG. 3. In the range (a) where the relative rotation angle of the fork member 28 is small, the fork member 28 causes the roller 26 to be positioned at the corner of the wedge-shaped space. This roller 26
Does not engage between the outer peripheral member 23 and the inner peripheral member 25 and therefore does not transmit torque. That is, since the power assist system on the worm gear reduction mechanism 8 side and the steering system on the output shaft 12 side are shut off, the power assist system has no effect on the steering system, and is not affected by the steering torque from the steering wheel. Steering becomes possible.

As shown in (b), the fork member 28 retreats from the corner of the wedge-shaped space, and the roller 26
When the outer peripheral member 23 is rotated to the position where it can be engaged between the inner peripheral member 25 and the inner peripheral member 25 (rotation angle θ), torque is applied to the inner peripheral member 25 only when the outer peripheral member 23 rotates in the same direction as the fork member 28 by the one-way clutch action. Is transmitted. Therefore, the rotation of the fork member 28 controls the torque transmission of the clutch mechanism 9 in accordance with the magnitude of the steering torque applied to the input shaft 11 and the direction of the rotation.

As described above, the torque range smaller than the steering torque Tc when the fork member 28 forms the above-mentioned rotation angle θ with respect to the inner peripheral member 25 forms a dead zone of the clutch, and includes a motor, a worm gear reduction mechanism, and the like. Manual steering operation can be performed independently of the power assist system of the above. On the other hand, when the steering torque exceeds Tc, the assist force is supplied via the clutch mechanism only when the assist force is supplied in the steering torque direction. Supplied. Excessive rotation of the fork member 28 is restricted by the rotation restricting portion 29.

FIG. 5 is a functional block diagram of the control device. The control device 6 includes a steering torque sensor 5, a target current determination unit 32 for determining a target current according to a steering torque and a vehicle speed obtained from a vehicle speed sensor 31, A comparison unit 33 that calculates a deviation between the output and the actual assist force, a drive control unit 34 that outputs a control signal so as to quickly converge to a target current according to the deviation, and drives an electric motor according to the control signal. The motor drive unit 35 includes an actual assist force detection unit 36 that detects or calculates an assist force that is actually applied to the steering system by the motor and sends the calculated assist force to the comparison unit 33, and controls the electric motor 7 according to the steering torque and the vehicle speed. And generates a target torque by feedback control. The specific configuration of the actual assist force detecting unit is described in Japanese Patent Application Nos. Hei 5-279706 and Hei 5-79706 filed earlier by the present applicant.
No. 282782, so the description is omitted.

Therefore, when the motor is operating beyond the dead zone of the clutch, a predetermined assist force compensated for the power transmission loss by the worm gear reduction mechanism 8, the clutch mechanism 19 and the like is accurately supplied from the motor 7 to the steering system. Is done.

The electric power steering apparatus configured as described above can reduce the manufacturing cost and reduce the size by solving the problems of frictional resistance and noise accompanying the metalization of the worm reduction mechanism. Has a unique effect.

[0021]

As described above, in the electric power steering apparatus according to the first aspect, since the worm gear reduction mechanism is constituted by metal gears, the gears can be downsized by improving the material strength and integrated with the shaft member. The simplification of the configuration is possible, and it has been arranged outside the cabin to solve the noise disturbance without compromising the cabin environment.In addition, the clutch mechanism having a dead zone is replaced by the worm gear reduction mechanism and the steering system. Since the power assist system such as the electric motor 7 and the worm gear mechanism is cut off from the steering system in the range of the dead zone because the power assist system is interposed between the output shaft and the output shaft, the power assist system does not become a steering resistance, and thus the steering wheel is connected to the steering wheel. Steering by the acting steering torque becomes possible, and the friction caused by the worm gear reduction mechanism consisting of metal gears There is no effect of the increase in resistance,
It is possible to prevent a decrease in steering feeling.

Therefore, the electric power steering apparatus according to the present invention has a unique effect that the manufacturing cost can be reduced and the size can be reduced by solving the problems of frictional resistance and noise accompanying the metalization of the worm speed reduction mechanism. To play. In addition, the reduction ratio can be increased in response to the increase in the transmission capacity due to the metalization of the reduction mechanism, which allows the motor to be downsized. The mechanism can be installed in the engine room.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an electric power steering device according to the present invention.

FIG. 2 is a sectional view of a main part of the electric power steering device according to the present invention.

FIG. 3 is a sectional view taken along line AA of FIG. 2;

FIG. 4 is an explanatory diagram of an operation of the clutch unit in FIG. 3;

FIG. 5 is a functional configuration diagram of the control device of FIG. 1;

FIG. 6 is an overall configuration diagram of an electric power steering device according to the related art.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electric power steering device, 2 ... Steering wheel, 3 ... Steering shaft (steering system), 4 ... Turning wheel, 4a ... Rack shaft, 5 ... Steering torque sensor, 6 ... Control device, 7 ... Electric motor, 8 ... Worm gear reduction Mechanism, 9: clutch mechanism, 10: dashboard (sound insulation material), 11: input shaft, 12: output shaft, 13: torque displacement member (torsion bar), 14: motion converter, 1
5 ... Output conversion unit, 21 ... Spindle, 22 ... Warm, 23 ...
Outer peripheral member, 23a: inner peripheral surface, 24: worm wheel,
25 inner peripheral member, 25a outer peripheral surface, 26 roller, 2
7 ... Spring, 28 ... Fork member, 29 ... Rotation restricting unit, 31 ... Vehicle speed sensor, 32 ... Target current determining unit, 33 ...
Comparison section, 34: drive control section, 35: motor drive section, 36
... Actual assist force detection unit.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-64-32966 (JP, A) JP-A-2-256561 (JP, A) JP-A-1-233162 (JP, A) JP-A-1- 249575 (JP, A) JP-A-7-132846 (JP, A) JP-A-7-132839 (JP, A) JP-A-6-39664 (JP, U) JP-A-2-80070 (JP, U) (58) Field surveyed (Int. Cl. ⁶ , DB name) B62D 5/04

Claims (1)

(57) [Claims] 1. An electric power steering apparatus wherein a control device drives an electric motor based on a steering torque, and transmits an auxiliary torque generated by the electric motor to an output shaft of a steering system via a worm gear reduction mechanism. An electric power steering system comprising: a worm gear reduction mechanism formed of metal gears; and disposed outside the vehicle compartment; and a clutch mechanism having a dead zone between the worm gear reduction mechanism and an output shaft of a steering system. apparatus.