JPH0428583B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an electric power steering device that generates auxiliary torque by a steering force booster using an electric motor.

(Prior Art) Conventionally, as an electric power steering device that generates auxiliary torque using an electric motor, there is one disclosed in, for example, Japanese Patent Laid-Open No. 59-206259. This electric power steering device includes a rack shaft (shaft-shaped member) that axially displaces the rotation of the steering wheel and transmits it to the steered wheels. A ball screw is provided at one end of the rack shaft, and includes a nut member encircled around the outer periphery of the groove and having a spiral groove on the inner periphery, and a ball interposed between the spiral grooves.
Furthermore, an electric motor for generating auxiliary torque is installed around the ball screw and is fixed to the rack case.
A rotor of this electric motor is integrally formed with the nut member. Therefore, the rotational torque of the electric motor is transmitted to the rack shaft via the ball screw,
The structure uses a ball screw with low friction loss to transmit data with high transmission efficiency.

(Problems to be Solved by the Invention) However, in the conventional electric power steering device described above, the stator of the electric motor is fixed to the rack case, while the rotor of the electric motor is integrally formed with the nut member of the ball screw. Because of this structure, the shock loads and vibrations that the wheels receive from the road surface while the vehicle is running are transmitted to the electric motor via the rack shaft and ball screw, and the field parts of the electric motor, such as permanent magnets and field There was a risk of damage to the windings, breakage of the rotor windings, etc., and there were problems that reduced durability and reliability. Furthermore, since the electric motor has a built-in ball screw structure, it has the disadvantage that the entire electric motor becomes large in size.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an electric power steering device that maintains high transmission efficiency of a ball screw and has improved durability and reliability.

(Means for Solving Problems) The electric power steering device of the present invention includes a shaft-like member that displaces the rotation of the steering wheel in the axial direction and transmits it to the steered wheels, and a shaft-like member provided at one end of the shaft-like member. The apparatus includes a ball screw and an electric motor that generates an auxiliary torque corresponding to the steering torque of the steering system, and has a structure in which the electric motor and the nut member of the ball screw are connected by a belt, and the shaft-shaped member Shock loads and vibrations transmitted to the belt are absorbed by the belt and are not transmitted to the electric motor.

(Embodiment) A preferred embodiment of the present invention will be described below based on the accompanying drawings.

FIG. 1 shows the electric power steering device of this embodiment.

In FIG. 1, 1 is an input shaft, 2 is a steering speed detection section, 3 is a steering torque detection section, 4 is a rack shaft (shaft-like member), 5 is a ball recirculating nut (ball screw), 7 is an electric motor, 8 is a control device.

One end of the input shaft 1 is connected to a steering wheel via a universal joint (not shown), and a pinion gear 1b is integrally attached to the other end. Furthermore, pinion holders 12 are attached to both sides of the pinion gear 1b of the input shaft 1 via bearings 10a and 11a. This pinion holder 12 consists of cylindrical plates 10 and 11 and a support 13 that integrally connects these plates, and the cylindrical plates 10 and 11 are provided on the bearings 10a and 11a at positions eccentric from the center thereof. Also,
The pinion holder 12 is rotatably supported by a rack case (not shown) by a needle bearing 14, while
One end of a torsion bar 15 is fixed to the center of rotation of the cylindrical plate 11.
The other end is fixed to the rack case.

Furthermore, a pin 11b is protruded from a position eccentric from the center of rotation of the cylindrical plate 11, and a movable iron core 16 made of a non-magnetic material and having a cylindrical magnetic material 16a at the end is fitted to the tip of this pin 11b. ing. The movable iron core 16 is loosely inserted into a cylindrical coil portion 17 that is integrally fixed to the rack case so as to be movable in the axial direction, and together with the coil portion 17 constitutes a differential transformer. Therefore, the pinion holder 12
As the movable iron core 16 rotates, the displacement is converted into an axial displacement of the movable iron core 16, and this axial displacement is outputted from the differential transformer as an electric signal.

The rack shaft 4 is connected to the pinion 1 as shown in FIG.
b, and converts the rotational displacement of the input shaft 1 into the axial displacement of the rack shaft 4. Both ends of the rack shaft 4 are connected to ball joints, tie rods, and knuckles (not shown), respectively, to change the steering of the wheels. Here, a load is applied to the rack shaft 4, and when the load is large, the pinion 1b rotates around the meshing portion with the rack shaft 4. For example, when the input shaft 1 is rotated by applying torque in the direction of arrow X, the torsion bar 15 is twisted in accordance with the magnitude of the torque, and the pinion holder 12 is
Rotate in the direction of The rotational displacement at this time is proportional to the torque applied to the input shaft 1, that is, the steering torque. Therefore, the movable iron core 16 is
is converted into an axial displacement Z. That is, the steering torque is proportional to the axial displacement of the movable iron core 16, and this axial displacement is detected by the coil portion 17. In this way, the torque detection section 3 is composed of the pinion 1b, the rack shaft 4, the pinion holder 12, the pin 11b, the movable section 16, and the differential transformer 17, and detects the magnitude and direction of the steering torque.

A light shielding plate 18 having a large number of slits 18a in the circumferential direction is integrally provided on the input shaft 1.
A photo coupler 1 is installed at a position sandwiching this light shielding plate 18.
9 and 20 are integrally fixed to the pinion holder. The photo couplers 19 and 20 detect the light passing through the slit 18a of the light shielding plate 18, and output a pulsed electrical signal. Also,
The photocouplers 19 and 20 are installed at positions such that the pulse phases differ by approximately 90°. In this way, the steering speed detection section 2 is constituted by the light shielding plate 18 and the photo couplers 19, 20, and detects the magnitude of the steering speed and its rotation direction. Rack shaft 4
A helical groove 4a with a semicircular cross section is formed on the outer periphery of one end, and a nut member 21 having a helical groove with a semicircular cross section on the inner periphery is fitted around the outer periphery of the helical groove 4a. Balls are interposed between the spiral grooves, and the ball screw 5 is constituted by the spiral grooves 4a, the nut member 21, and the balls.

Further, a thrust bearing 22 fixed to the rack case is provided at one end of the nut member 21, and a pulley 23 having a V-groove cross section is integrally provided at the other end of the nut member 21. Furthermore, a thrust bearing (not shown) is provided on the end surface of the pulley 23 and is fixed to the rack case.
is axially fixed and rotatably supported. Further, a pulley 24 having a V-groove cross section is installed along the pulley 23 and is attached to the rotating shaft of the electric motor 7, and a V-belt 25 is stretched between the pulleys 23 and 24. . The electric motor 7 is supported by a vehicle body (not shown) via an elastic member. Therefore, the rotation of the electric motor 7 displaces the rack shaft 4 in the axial direction through the rotation of the ball screw 5.

On the other hand, the control device 8 includes a power supply circuit, a microcomputer unit, a motor drive circuit, etc., and supplies control power to the motor 7 based on the detection signals from the photocouplers 19 and 20 and the differential transformer 17. supply to. In conjunction with this, the electric motor 7 is driven, and the rotational torque of the electric motor 7 displaces the rack shaft 4 in the axial direction via the V-belt 25 and the ball screw 5, thereby reducing the steering force.

Therefore, since the rotational torque generated by the electric motor is transmitted to the rack shaft via the ball screw, the same high torque transmission efficiency as before can be maintained, and the V-belt absorbs the impact load and vibration that the wheels receive from the road surface. Since the energy is absorbed by the magnet, it is not transmitted to the electric motor, and it is possible to reliably prevent problems such as damage to the field part of the electric motor and disconnection of the rotating winding. Furthermore, since a ball screw is not built into the electric motor, the electric motor itself can be made smaller.

(Effects of the Invention) As is clear from the above description, according to the present invention, the rotational torque of the electric motor is transmitted to the shaft member (rack shaft) via the ball screw, so that the transmission efficiency can be maintained at a high level. Furthermore, by connecting the ball screw and the electric motor with a belt, it is possible to prevent damage to the field part of the electric motor and breakage of the rotor winding, thereby improving durability and reliability. Furthermore, since the ball screw is not built into the electric motor, there is an advantage that the electric motor can be made smaller.

[Brief explanation of drawings]

1 and 2 relate to an embodiment of the electric power steering device of the present invention, FIG. 1 is a schematic perspective view thereof, and FIG. 2 is a sectional view taken along the - arrow in FIG. 1. In the drawing, 1... input shaft, 4... easy shaft, 7...
...Electric motor, 5, 21...Ball screw and its nut member, 25...Belt.

Claims (1)

[Claims] 1. An electric power steering device that includes a steering system that transmits the rotation of the steering wheel to the steered wheels via a shaft-shaped member that is displaced in the axial direction, and an electric motor that generates an auxiliary torque corresponding to the steering torque of the steering system. A spiral groove formed on the outer periphery of one end of the shaft member, a nut member ringed around the outer periphery of the spiral groove and having a spiral groove on the inner periphery, and a ball interposed between these spiral grooves. What is claimed is: 1. An electric power steering device characterized in that a ball screw is provided, and a nut member of the ball screw and an electric motor are connected by a belt.