JP4773653B2 - Electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric power steering apparatus.
[0002]
[Prior art]
As an electric power steering apparatus, a rack shaft having a ball screw supported by a housing, a nut screwed to the ball screw and rotatably supported by a housing via a bearing, and a steering assist force applied to the nut Some have an electric motor and transmit the steering assist force of the electric motor to the nut through a reduction gear train. In this electric power steering device, the input shaft pinion to which the nut and the ball screw are engaged and the steering wheel is coupled when the rotation of the electric motor is started or when the rotation of the electric motor is reversed. The rack meshing portion of the rack shaft may collide due to the backlash movement of the existing racks and generate a hitting sound.
[0003]
In the prior art, as described in JP-A-2-254057, in order to reduce the above-described hitting sound, the nut and the bearing are integrally movable in the axial direction, and the thrust of the rack shaft is absorbed between the bearing and the housing. What provides an elastic body is disclosed. Thereby, the impact force applied to the electric motor or the rack shaft is absorbed by the nut and the bearing compressing the elastic body and moving in the axial direction.
[0004]
[Problems to be solved by the invention]
The prior art has the following problems.
(1) The movable part that moves based on the impact force applied to the electric motor or the rack shaft and compresses the elastic body includes a bearing in addition to the nut, and the inertial mass of the movable part increases. Need to be large.
[0005]
(2) The reduction gear train that transmits the rotational force of the electric motor to the nut consists of meshing of a small gear fixed to the output shaft of the electric motor and a large gear fixed to the nut, and the impact force due to axial movement of the nut At the time of absorption, a resistance force of tooth surface sliding that increases in proportion to the transmission torque of the large gear and the small gear is generated. Therefore, the resistance force of the tooth surface sliding changes with the fluctuation of the rotational force of the electric motor, and the impact force absorption characteristic by the elastic body becomes unstable.
[0006]
An object of the present invention is to absorb an impact force in a torque transmission path of an electric motor by using a compact elastic body in an electric power steering apparatus.
[0007]
Another object of the present invention is to stabilize the absorption characteristics of impact force due to elasticity.
[0008]
[Means for Solving the Problems]
According to the first aspect of the present invention, a rack shaft having a ball screw supported by a housing, a nut screwed to the ball screw and rotatably supported via a bearing fixed to the housing, and a steering assist to the nut In an electric power steering apparatus having an electric motor for applying a force, a sleeve integrated on the inner periphery of the rotor of the electric motor is coaxially disposed on the nut, and coupled to the nut via a torque limiter. One end extension of the sleeve protruding to one side is supported so as to be slidable in the axial direction with respect to the bearing provided in the housing, and the above-mentioned nut connected to the other end extension of the sleeve protruding to the other of the rotor is provided in the housing It is slidably supported in the axial direction relative to the bearing, and the nut, between the opposite end surfaces in the axial direction of the bearing for supporting the nut, rack To absorb the impact force from is provided with a resilient member.
[0009]
According to a second aspect of the present invention, in the first aspect of the invention, the elastic body provided on the one end surface of the bearing is provided on the other end surface of the bearing between the stepped portion provided on the nut and the one end portion of the bearing. Elastic bodies are inserted between the other ends of the bearings by being pre-compressed, and the pre-compression load of these elastic bodies can be adjusted by adjusting the tightening position of the lock nut. .
[0010]
[Action]
(1) There is no place in which the movable part which compresses an elastic body contains bearings other than a nut. Therefore, the inertial mass of the movable part can be reduced, the response can be improved, and the elastic body for absorbing the impact force including the inertial force can be miniaturized.
[0011]
(2) Absorption of impact force by an elastic body without causing a change in the resistance force of sliding of the gear teeth of the reduction gear train when absorbing the impact force due to the axial movement of the nut in the normal range of the electric power steering device The characteristics can be stabilized.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
1 is a partially cutaway front view of the electric power steering apparatus, FIG. 2 is a cross-sectional view of the main part of FIG. 1, and FIG.
[0013]
As shown in FIG. 1, the electric power steering apparatus 10 supports a steering input shaft 12 on a housing 11, and an output shaft 14 (not shown) is connected to the input shaft 12 via a torsion bar 13. A pinion is provided, and a rack shaft 15 having a rack that meshes with the pinion is supported by the housing 11 so as to be movable in the left-right direction. A steering torque sensor 16 (not shown) is provided between the input shaft 12 and the output shaft 14. The steering torque sensor 16 applies a steering torque applied to the steering wheel to the output shaft 14, and determines the steering torque based on the relative rotational displacement generated between the input shaft 12 and the output shaft 14 due to elastic torsional deformation of the torsion bar 13. To detect.
[0014]
The electric power steering apparatus 10 has both end portions of the rack shaft 15 projecting on both sides of the housing 11, tie rods 17A and 17B are connected to the end portions, and the left and right movements of the rack shaft 15 via the tie rods 17A and 17B. The wheels can be snaked. Note that one end of the rack shaft 15 is supported by the housing 11 by a rack guide (not shown) and the other end by a bearing 25 described later.
[0015]
The electric power steering apparatus 10 is provided with an electric motor 20 around the rack shaft 15 in the housing 11. The electric motor 20 includes a stator 21 that is fixed to the inner periphery of the housing 11 and a rotor 22 that is disposed with a gap around the outer periphery of the rack shaft 15 and transmits a rotational force to a nut 32 described later. The sleeve 23 integrated with the inner periphery of the rotor 22 is coaxially arranged with the rack shaft 15 with a gap on the outer periphery of the rack shaft 15, and one end extension portion protruding to one side of the rotor 22 is protruded to the other side by the bearing 24. The other end extension is supported by the bearing 25 via a nut 32 described later.
[0016]
In the electric motor 20, a brush 26 is held inside the housing 11, and this brush 26 is in contact with a commutator 27 on the end face of the rotor 22. When the electric motor 20 is supplied with power to the rotor 22 through the brush 26 and the commutator 27, the magnetic lines of the rotor 22 cut off the magnetic field of the stator 21, thereby rotating the rotor 22.
[0017]
In the electric power steering apparatus 10, a ball screw 30 is provided on the rack shaft 15, and a nut 32 and a sleeve 23 that are engaged with the ball screw 30 via a ball 31 are coaxially arranged, and an outer periphery of the extension portion of the sleeve 23 described above. The nut 32 is coupled to the housing 11 via a torque limiter 40, and the nut 32 is rotatably supported on the housing 11 via the bearing 25 described above. Note that the sleeve 23 and the nut 32 are integrally connected in the axial direction. The bearing 25 is pressed and held by a lock nut 33 screwed into the housing 11 against the inner circumferential step portion of the housing 11 via a washer 34.
[0018]
In the torque limiter 40, the outer peripheral surface of the extension portion of the sleeve 23 is fitted into an insertion hole provided in the inner periphery of the nut 32, and a corrugated elastic ring 41 is inserted into a ring groove provided in the outer peripheral surface of the sleeve 23. Is built in. With the torque in the normal range of the electric power steering device 10 (torque smaller than the limit torque), the elastic force of the elastic ring 41 keeps the sleeve 23 and the nut 32 connected without slipping and transmits the torque generated by the electric motor 20. On the other hand, the stroke of the rack shaft 15 is suddenly stopped, for example, when the tire rides on the curb during steering, and the inertial force of the electric motor 20 that is rotating at a high speed with the ratio of the lead of the ball screw 30 causes the thread groove of the ball screw 30 to rotate. For an impact torque (limit torque) exceeding the elastic force of the elastic ring 41 caused by exerting a large impact force on the sleeve, a slip is generated between the sleeve 23 and the nut 32, and this impact torque is transmitted. It is possible to prevent the thread groove of the ball screw 30 from being damaged.
[0019]
Hereinafter, the operation of the electric power steering apparatus 10 will be described.
(1) When the steering torque detected by the steering torque sensor 16 is lower than a predetermined value, the steering assist force is unnecessary and the electric motor 20 is not driven.
[0020]
(2) Since the steering assist force is required when the steering torque detected by the steering torque sensor 16 exceeds a predetermined value, the electric motor 20 is driven. The generated torque of the electric motor 20 is applied as a steering assist force from the rotor 22 to the nut 32 via the sleeve 23, and the rotation of the nut 32 is converted into a linear motion of the rack shaft 15 by the ball screw 30 and interlocked with the rack shaft 15. Snake the wheels.
[0021]
Here, in the electric power steering apparatus 10, the nut 32 can slide in the axial direction with respect to the bearing 25, and the sleeve 23 can slide in the axial direction with respect to the bearing 24. And between the nut 32 and the bearing 25, the elastic bodies 51 and 52 which absorb the impact force from the rack shaft 15 are provided. The elastic body 51 is between a step 53 provided on the nut 32 and one end of the inner ring of the bearing 25, and the elastic body 52 is a lock nut 54 screwed on the nut 32 and the other end of the inner ring of the bearing 25. In between, each is compressed and inserted. By adjusting the tightening position of the lock nut 54, the precompression load of the elastic bodies 51 and 52 can be adjusted.
[0022]
The elastic bodies 51 and 52 are used in the normal range of the electric power steering apparatus 10 and have an impact torque (which is relatively smaller than the limit torque of the torque limiter 40) at the start of the rotation of the electric motor 20 or when the rotation of the electric motor 20 is reversed. When an impact force such as per tooth surface acts on the electric motor 20 or the rack shaft 15, the nut 32 is moved in the axial direction by elastically compressing and deforming, and the impact force including the inertia force of the nut 32 is absorbed. To do.
[0023]
The elastic bodies 51 and 52 may be rubber, resin blocks or the like in addition to plate springs such as disc springs.
[0024]
According to this embodiment, there are the following operations.
(1) There is no place where the movable part that moves based on an impact force smaller than the torque limit load applied to the electric motor 20 or the rack shaft 15 and compresses the elastic bodies 51 and 52 includes the bearing 25 other than the nut 32. Therefore, the inertial mass of the movable part can be reduced to improve the responsiveness, and the elastic bodies 51 and 52 for absorbing the impact force including the inertial force can be reduced in size.
[0025]
(2) Although the torque limiter 40 is interposed between the sleeve 23 and the nut 32, which are the rotor side members of the electric motor 20, no reduction gear train is interposed. Accordingly, when the impact force due to the axial movement of the nut 32 is absorbed in the normal range of the electric power steering device 10, the elastic bodies 51 and 52 are not accompanied by the resistance force of the tooth surface sliding of the reduction gear train. It is possible to stabilize the shock absorption characteristics.
[0026]
Although the embodiment of the present invention has been described with reference to the drawings, the specific configuration of the present invention is not limited to this embodiment, and there are design changes and the like without departing from the scope of the present invention. Are also included in the present invention.
[0027]
【The invention's effect】
As described above, according to the present invention, in the electric power steering apparatus, the impact force in the torque transmission path of the electric motor can be absorbed by the compact elastic body configuration.
[0028]
Further, according to the present invention, it is possible to stabilize the absorption characteristics of impact force due to elasticity.
[Brief description of the drawings]
FIG. 1 is a front view showing a partially broken electric power steering apparatus.
FIG. 2 is a cross-sectional view of the main part of FIG.
FIG. 3 is an enlarged cross-sectional view of FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Electric power steering apparatus 11 Housing 15 Rack shaft 20 Electric motor 23 Sleeve
24 Bearing 25 Bearing 30 Ball screw 32 Nut 40 Torque limiter 51, 52 Elastic body

Claims (2)

A rack shaft having a ball screw supported by the housing, a nut screwed to the ball screw and rotatably supported via a bearing fixed to the housing, and an electric motor for applying a steering assist force to the nut In an electric power steering apparatus having
A sleeve in which a sleeve integrated with the inner periphery of the rotor of the electric motor is coaxially disposed on the nut, and is coupled to the nut via a torque limiter, and one end extension of the sleeve protruding to one side of the rotor is provided in the housing The nut, which is supported so as to be slidable in the axial direction and is coupled to the other end extension of the sleeve protruding to the other of the rotor, is supported so as to be slidable in the axial direction with respect to a bearing provided in the housing,
An electric power steering apparatus, characterized in that an elastic body that absorbs an impact force from a rack shaft is provided between a nut and opposite end faces in the axial direction of the bearing that supports the nut . The elastic body provided on one end surface of the bearing is between the step portion provided on the nut and the one end portion of the bearing, and the elastic body provided on the other end surface of the bearing is between the other end portion of the bearing, respectively. The electric power steering device according to claim 1, wherein the electric power steering device is pre-compressed and interposed, and the pre-compression load of the elastic bodies can be adjusted by adjusting the tightening position of the lock nut .

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