JP2006082663A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device generating little noise with a good steering feeling. <P>SOLUTION: The electric power steering device 1 applies power of an electric motor 16 to a steering mechanism A including a rack bar 8 as a steering shaft moved to the axial direction according to operation of a steering member 2 through reduction gears 17 including gears to assist the steering. A piston 20 moves in a hydraulic cylinder 21 along with the movement of the rack bar 8 in the axial direction, and oil flows through a orifice 24 of the piston 20. Comparatively high-speed vibration (15-20 Hz, for example) by reverse input from a road surface is attenuated by damping force composed of viscous resistance of the oil flowing through the orifice 24 to reduce noise of tooth striking sounds. As the movement speed of the piston 20 by normal steering of operating the steering member is low at of 1-2 Hz, for example, the damping force by the orifice 24 hardly works and the steering feeling is not deteriorated. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electric power steering apparatus that obtains a steering assist force by an electric motor.

Conventionally, in a hydraulic power steering device for an automobile, a communication hole that is opened and closed by a valve is provided in the piston of the power cylinder, and by opening the communication hole when the steering is neutral, the pressure receiving area of the piston of the power cylinder is reduced. There is a hydraulic power steering device that gives a driver a sense of responsiveness (see, for example, Patent Document 1).
On the other hand, a reduction gear using a gear mechanism is generally used in an electric power steering apparatus for an automobile. That is, the rotation of the output shaft of the motor is decelerated through a reduction gear, so that the output of the motor is amplified and transmitted to the steering mechanism, and the steering operation is torque-assisted.

In the gear mechanism used for the speed reducer in the electric power steering device described above, an appropriate backlash is necessary for the meshing of the teeth. For example, when driving on a rough road, the tooth strike caused by the backlash is caused by the reverse input from the road surface. Sound (rattle sound) may be generated.
Japanese Patent No. 2668032

In the electric power steering apparatus, the noise due to the rattling noise is reduced by reducing the backlash, but the steering feeling is deteriorated particularly in the vicinity of the steering neutral position due to the increase of the fllink.
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 apparatus with low noise and good steering feeling.

  In order to solve the above-described problems, the present invention provides a steering mechanism including a steered shaft that is moved in the axial direction in accordance with an operation of a steering member by applying power of an electric motor via a reduction gear including a gear to perform steering. In the assisting electric power steering apparatus, a piston that moves as the steering shaft moves, a hydraulic cylinder having a pair of oil chambers partitioned by the piston, and a pair of oil chambers that are formed in the piston communicate with each other. And an orifice.

  Since relatively high-speed vibration (for example, about 15 to 20 Hz) due to reverse input from the road surface is attenuated by a damping force composed of viscous resistance of oil flowing through the orifice, noise due to rattling noise can be reduced. On the other hand, since the movement of the piston by normal steering by operating the steering member is low, for example, at 1 to 2 Hz, the damping force by the orifice hardly acts and the steering feeling is not deteriorated. Thereby, an electric power steering device with low noise and good steering feeling can be realized.

  If the cylinder diameter of the hydraulic cylinder is smaller than the remaining region in the region near the steering neutral position, the piston orifice can be used in the region near the steering neutral position to obtain a sense of steering rigidity. Moreover, since the oil flow between the pair of oil chambers is free in the remaining region, the resistance of the piston to the steering can be reduced, and the steering feeling can be improved. The region near the steering neutral position is a region in the range of −θ1 ≦ θ ≦ θ1 with the steering angle θ of the steering member at the steering neutral position being zero. The angle θ1 is set according to the vehicle in the range of 5 degrees to 10 degrees. That is, the neighborhood region is set to a region in the range of −10 degrees ≦ θ ≦ 10 degrees, for example.

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 width direction of the 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 steering mechanism A including a rack and pinion 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 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 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 (Electronic 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 output shaft 3b of the steering shaft 3, and further converted into a linear motion of the rack bar 8 via the pinion shaft 7, thereby assisting steering. .

The speed reducer 17 includes a worm 18 as a drive gear that is rotationally driven by an electric motor 16, and a worm wheel 19 as a driven gear that meshes with the worm 18 and is connected to the output shaft 3 b of the steering shaft 3 so as to be integrally rotatable. Prepare.
The features of the electric power steering apparatus 1 of the present embodiment are as follows. That is, the rack bar 8 is provided with a piston 20 that moves integrally with the rack bar 8, and a hydraulic cylinder 21 that accommodates the piston 20 is formed in a part of the housing 9.

  The hydraulic cylinder 21 has a pair of oil chambers 22 and 23 partitioned by the piston 20. The piston 20 is formed with one or more orifices 24 that communicate with each other between the pair of oil chambers 22 and 23. A circumferential groove provided on the outer periphery of the piston 20 accommodates a seal member 25 for sealing between the outer periphery of the piston 20 and the inner periphery of the hydraulic cylinder 21. In addition, a pair of seal members 26 that seal between the pair of end portions and the rack bar 8 are provided at the pair of end portions of the hydraulic cylinder 21.

When the rack bar 8 moves in the axial direction, the piston 20 moves in the hydraulic cylinder 21 along with this, and the oil passes through the orifice 24. The viscous resistance associated with the passage of oil in the orifice 24 serves as a damping force that suppresses the movement of the piston 20.
As shown in FIG. 2, the viscous resistance of the orifice 24 acting as a damping force is proportional to the square of the moving speed in the axial direction of the rack bar 8 serving as a steered shaft. That is, the damping force by the orifice 24 is speed dependent.

According to the present embodiment, the reverse input from the road surface given through the wheels 11 is high speed, for example, about 15 to 20 Hz, and is therefore attenuated by the damping force due to the viscous resistance of the oil flowing through the orifice 24, Noise due to rattling noise can be reduced.
On the other hand, the movement of the piston 20 by normal steering by operating the steering member 2 is, for example, about 1 to 2 Hz and low speed, so that the damping force by the orifice 24 hardly acts and the steering feeling is not deteriorated. Thereby, the electric power steering apparatus 1 with low noise and good steering feeling can be realized.

  Next, FIG. 3 shows a main part of an electric power steering apparatus according to another embodiment of the present invention. Referring to FIG. 3, the present embodiment is characterized in that the cylinder diameter D1 of the hydraulic cylinder 21 is in the vicinity region B1 (−) of the steering neutral position C (the position where the steering angle θ = 0 of the steering member 2). The angle is smaller than the remaining region B2 in θ1 ≦ θ ≦ θ1), and the damping force by the orifice 24 depends on the position of the piston 20 as shown in FIG.

The vicinity region B1 (−θ1 ≦ θ ≦ θ1) can be appropriately set according to the vehicle, and a value of 5 degrees to 10 degrees is employed as θ1. For example, θ1 = 10 degrees, and the region is set to −10 degrees ≦ θ ≦ 10 degrees.
Further, as the sealing member 27 on the outer periphery of the piston 20, an O-ring 28 and a fluororesin ring 29 backed up by the O-ring 28 are used to reduce friction when the piston 20 moves relative to the hydraulic cylinder 21. is there.

According to the present embodiment, it is possible to obtain a steering rigidity feeling by the action of the orifice 24 of the piston 20 in the vicinity region B1 of the steering neutral position. Further, in the remaining region B2, the flow of oil between the pair of oil chambers 22 and 23 can be made free, the resistance given to the steering by the piston 20 can be reduced, and the steering feeling can be improved.
In addition, this invention is not limited to the said embodiment, The bevel gear with which a drive gear and a driven gear mutually mesh | engage as a reduction gear may be sufficient. Further, the drive gear and the driven gear may be a helical gear or a hypoid gear.

It is a mimetic diagram showing a schematic structure of an electric power steering device of one embodiment of the present invention. It is a graph which shows the correlation with the moving speed of a rack bar, and the damping force by an orifice. It is sectional drawing of the principal part of the electric power steering apparatus of another embodiment of this invention. FIG. 4 is a diagram showing a correlation between a steering angle and a damping force in the embodiment of FIG. 3.

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 (steering shaft)
10 Tie Rod 11 Wheel A Steering Mechanism 16 Electric Motor 17 Reducer 18 Worm (Gear)
19 Worm wheel (gear)
20 Piston 21 Hydraulic cylinders 22, 23 Oil chamber 24 Orifice C Steering neutral position B1 Area near steering neutral position B2 Remaining area D1 Cylinder diameter

Claims (2)

In an electric power steering device for assisting steering by applying power of an electric motor to a steering mechanism including a steered shaft that is moved in an axial direction according to an operation of a steering member via a reduction gear including a gear,
A piston that moves as the steering shaft moves,
A hydraulic cylinder having a pair of oil chambers partitioned by a piston;
An electric power steering device comprising an orifice formed in the piston and communicating between a pair of oil chambers. 2. The electric power steering apparatus according to claim 1, wherein a cylinder diameter of the hydraulic cylinder is smaller than a remaining region in a region near the steering neutral position.

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