JP2003335249A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device eliminating such a risk that muddy water having eventually intruded into a boot in the case of its breakage reaches the moor to damage it. <P>SOLUTION: In a gear housing 11, both ends of the shaft 32 of the motor 30 are supported rotatably by shield bearings 33 and 34, and a stator 31 of the motor 30 fixed inside the gear housing 11 is installed between the shield bearings. <P>COPYRIGHT: (C)2004,JPO

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 device.

[0002]

2. Description of the Related Art Generally, an electric power steering system transmits the rotation of a steering wheel to a rack shaft via an input shaft and a pinion shaft, and steers left and right front wheels through tie rods connected to both ends of the rack shaft. The steering torque applied to the steering wheel is detected by the torque sensor, the electric motor arranged on the rack shaft is driven based on this detected torque, and the output torque of this electric motor is passed through the ball screw device. The steering force is assisted by transmitting it to the rack shaft.

By the way, in an electric power steering apparatus having a structure in which an electric motor for assisting is arranged around a rack shaft, a nut constituting a ball screw device is connected to a motor shaft of the electric motor, and an inner periphery of the nut is formed. The screw groove formed on the rack shaft is engaged with the formed screw groove via a ball.

In this type of rack-assist type electric power steering apparatus, boots provided between both ends of the gear housing and the tie rods cover the openings at both ends of the gear housing, so that muddy water and flying stones inside the gear housing. It is designed to protect you from the like.

In the conventional rack-assist type electric power steering apparatus, if the boot is damaged, foreign matter may enter the boot and damage the ball screw or the like.

As a countermeasure against such damage to the boot, the technique disclosed in Japanese Patent Laid-Open No. 2001-278080 has been proposed.

According to the technique described in this publication, a ball screw device is installed in a gear housing at a substantially intermediate portion between a pinion meshing portion and an electric motor installation portion, and a screw groove of a rack shaft meshing with the ball screw device is formed. Even when the boot is damaged, the screw groove of the rack shaft is prevented from being damaged from the outside even if the boot is damaged, even when the steering wheel is steered from side to side.

[0008]

However, in the technique described in the above-mentioned publication, when the boot is damaged, damage to the thread groove of the rack shaft due to flying stones or the like can be prevented, but muddy water enters the boot due to the damage to the boot. Then, the muddy water may reach the electric motor and damage the electric motor.

[0009]

According to a first aspect of the present invention, there is provided a gear housing, a rack shaft movably supported by the gear housing and meshing with a pinion connected to the input shaft side, and a gear housing. An electric motor arranged around a rack shaft in the gear housing, and a ball screw device arranged around the rack shaft in the gear housing and transmitting torque of the electric motor to the rack shaft. In an electric power steering device in which a ball screw device is installed between a pinion meshing part and an electric motor installation part in an axial direction along the, a motor shaft of the electric motor is provided with shield bearings at both ends thereof in the gear housing. An electric motor stator, which is rotatably supported and fixed in the gear housing, is arranged between these shield bearings. Than it is.

According to a second aspect of the present invention, in the electric power steering apparatus according to the first aspect, one of the inner ring and the outer ring of the shield bearing is press-fitted into the motor shaft or the gear housing, and the inner ring and The other of the outer rings is fluid-tightly fitted to the motor shaft or gear housing via a seal.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

In FIGS. 1 and 2, reference numeral 10 denotes an electric power steering apparatus, and a gear housing 11 of the electric power steering apparatus 10 has a first hollow cylindrical shape.
Rack housing 12 and second rack housing 13
And a motor housing 14 provided between these rack housings 12 and 13, each housing 12,
13, 14 are coaxially connected by a bolt.

A rack shaft 15 is penetrated through the gear housing 11 so as to be movable in the axial direction, and both ends of the rack shaft 15 protruding from the first and second rack housings 12 and 13 are provided with tie rods 17 and 18, respectively. It is connected to the left and right front wheels. The first and second rack housings 12, 1
Extendable and bendable boots 19 and 20 are mounted between the end of 3 and each of the tie rods 17 and 18, and these boots 19 and 20 shield the inside of the gear housing 11 from the outside.

An input shaft 21 connected to a steering wheel is provided in the first rack housing 12 as a rack shaft 15.
A pinion shaft 22 having pinion teeth that mesh with rack teeth 15A formed on the rack shaft 15 is rotatably supported around an axis that intersects with the input shaft 21 and is input through a torsion bar (not shown). It is connected to the shaft 21 so as to be rotatable relative thereto.

A cylinder hole 23 is formed in the first rack housing 12 at a position facing the pinion shaft 22 with the rack shaft 15 interposed therebetween in a direction orthogonal to the axis of the rack shaft 15. A rack guide 24 joined to the peripheral surface of the rack shaft 15 is slidably accommodated. The rack guide 24 presses the rack shaft 15 toward the pinion shaft 22 by the spring force of a spring 25 provided on the back side thereof.

A torque sensor is provided between the input shaft 21 and the pinion shaft 22 for detecting the torsional torque of the torsion bar based on the steering torque applied to the steering wheel. The torque sensor detects the torque detected by the torque sensor. The electric motor, which will be described later, is controlled.

An electric motor 30, which is a brushless DC motor, is provided in the motor housing 14 which constitutes the gear housing 11.
Includes a drive stator 31 forming a motor stator and a motor shaft 32 forming a motor rotor.

The drive stator 31 is fitted on the inner circumference of the motor housing 14 and has a coil 31A wound around it. The motor shaft 32 has a hollow cylindrical shape and is coaxially and loosely fitted around the rack shaft 15. One end of the motor shaft 32 extends to a position where the motor shaft 32 projects into the first rack housing 12, and the other end of the motor shaft 32 has a second end. It is extended to a position where it projects into the rack housing 13. One end of the motor shaft 32 is rotatably supported by the axial end of the first rack housing 12 via an angular shield bearing 33, and the other end of the motor shaft 32 is interposed by a radial shield bearing 34. Is rotatably supported on the axial end of the motor housing 14.

As shown in FIGS. 2, 3 and 4, the inner ring of the shield bearing 33 is press-fitted into the outer periphery of one end of the motor shaft 32, and the outer ring of the shield bearing 33 is fitted into the inner periphery of the first rack housing 12. The outer ring of the shield bearing 33 and the first rack housing 12
A seal ring 35, which is an O-ring, is interposed between the inner periphery of the bearing and the inner periphery of the bearing to seal the fitting surface on the outer periphery of the bearing in a liquid-tight manner. On the other hand, the outer ring of the shield bearing 34 is press-fitted into the inner periphery of the motor housing 14, the inner ring of the shield bearing 34 is fitted into the outer periphery of the motor shaft 32, and the inner ring of the shield bearing 34 and the inner periphery of the motor housing 14 are joined together. A seal ring 36, which is an O-ring, is interposed therebetween to liquid-tightly seal the fitting surface on the inner peripheral side of the bearing.

As a result, both ends of the motor shaft 32 are liquid-tightly sealed by the shield bearings 33, 34 and the seal rings 35, 36, and the drive stator 3
The space 40 in which 1 and the coil 31A are disposed is liquid-tightly shielded from the outside.

A nut 38 of a ball screw device 37 is mounted on the inner circumference of the other end of the motor shaft 32 which is rotatably supported by the motor housing 14 via the shield bearing 34. A thread groove 38A is formed on the inner circumference of the nut 38, and a thread groove 15B is formed on the outer circumference of the rack shaft 15 corresponding to this thread groove 38A.
A ball 39 is interposed between A and 15B. As a result, the rotational movement of the nut 38 of the ball screw that rotates together with the motor shaft 32 is converted into the axial movement of the rack shaft 15.

As described above, the rack shaft 15 has rack teeth 15A meshing with the pinion shaft 22 and screw grooves 15B screwed into the nut 38 at both ends, and the motor of the electric motor 30 is provided on the outer periphery of the rack shaft 15 between them. With the configuration in which the shaft 32 is arranged, the rack teeth 15A and the screw grooves 15B do not protrude from the gear housing 11 even when the rack shaft 15 is axially moved, and the shield bearings 33 and 34 that support both ends of the motor shaft 32 are provided. Thus, the electric motor 30 can be shut off from the outside.

In the space 40, a rotation angle sensor 41 is provided between the drive stator 31 of the electric motor 30 and one shield bearing 33. The rotation angle sensor 41 is composed of a known resolver, and has a detection stator 42 fixed to the inner circumference of the motor housing 14,
Detection rotor 43 fixed to the outer periphery of the motor shaft 32
It has and. A predetermined voltage is induced in the detection stator 42 according to the rotational position of the detection rotor 43, so that the rotation angle of the electric motor 30 can be detected.

In the space 40, the drive stator 31 of the electric motor 30 and the other shield bearing 3 are also provided.
3, a power feeding device 45 connected to the coil 31A of the driving stator 31 is provided.

With the above structure, a control device (E) to which signals from torque sensors, vehicle speed sensors, etc. (not shown) are input.
The electric power supplied to the electric motor 30 is controlled by (CU), and the electric motor 30 is driven. The motor shaft 32 is rotated by driving the electric motor 30, and the rack shaft 15 is moved in the left-right direction via the nut 51 of the ball screw device 50 integrated with the motor shaft 32 to assist the steering force.

When the boots 19 and 20 are damaged, muddy water and the like enter the boots 19 and 20, but shield bearings 33 and 34 and seal rings 45 and 4 that support both ends of the motor shaft 32 of the electric motor 30.
6 prevents entry into the space 40 and protects the electric motor 30 and the rotation angle sensor 41 from muddy water and the like.
With such a simple waterproofing measure, damage to the electric motor 30 and the rotation angle sensor 41 can be prevented.

In the above-described embodiment, the motor shaft 32 of the electric motor 30 is attached to the motor housing 14.
By simply press-fitting one of the inner ring and the outer ring of the shield bearings 33, 34 supported to the (gear housing 11) into the motor shaft 32 or the motor housing 14 and providing the seal rings 35, 36 on the other of the inner ring and the outer ring, Although the configuration has been described in which the space portion 40 accommodating the electric motor 30 and the rotation angle sensor 41 can be liquid-tightly sealed by various assembly, the seal ring is provided on both the inner ring and the outer ring. Alternatively, conversely, by tightly fitting both the inner ring and the outer ring, the seal ring can be eliminated.

[0028]

As described above, according to the present invention, the bearings for supporting the both ends of the motor shaft of the electric motor with respect to the gear housing are constructed in the shield type, and the space between the shield bearings is externally exposed. Since the space is tightly sealed, and the stator of the electric motor with the coil wound is housed in this space, the boots that cover the openings on both ends of the gear housing are damaged and mud etc. Even in this case, the muddy water does not reach the electric motor section, and the electric motor can be prevented from being damaged.

[Brief description of drawings]

FIG. 1 is an overall view of an electric power steering apparatus showing an embodiment of the present invention.

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

FIG. 3 is a cross-sectional view of a shield bearing portion in which a portion B of FIG. 2 is enlarged.

FIG. 4 is a cross-sectional view of a shield bearing portion in which a portion C of FIG. 2 is enlarged.

[Explanation of symbols]

11 gear housing 15 rack shafts 19 and 20 boots 30 electric motor 31 Stator 32 motor shaft 33, 34 sealed bearing 35, 36 Seal ring 37 Ball Screw Device 41 Rotation angle sensor

Claims (2)

[Claims] 1. A gear housing, a rack shaft that is movably supported by the gear housing and meshes with a pinion connected to the input shaft side, and an electric motor that is arranged around the rack shaft in the gear housing, A ball screw device which is arranged around the rack shaft in the gear housing and transmits the torque of the electric motor to the rack shaft, and the pinion meshing portion and the electric motor installation portion in the axial direction along the rack shaft in the gear housing. In an electric power steering device having a ball screw device installed between the two, both ends of a motor shaft of the electric motor are rotatably supported via shield bearings in the gear housing, and the gears are provided between the shield bearings. An electric power steering device characterized in that a stator of an electric motor fixed in a housing is arranged. . 2. One of the inner ring and the outer ring of the shield bearing is press-fitted into the motor shaft or the gear housing, and the other of the inner ring and the outer ring is liquid-tightly fitted to the motor shaft or the gear housing via a seal. The electric power steering apparatus according to claim 1, wherein