JP3869973B2 - Electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric power steering device that applies a steering assist force by rotating a ball nut screwed to a ball screw shaft integrated with a rack by a motor.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as an electric power steering device, a ball nut screwed to a ball screw shaft integrated with a rack that meshes with a pinion rotated by steering is rotationally driven by a steering assisting force applying motor.
[0003]
The motor has a rotor into which the rack is inserted, and a convex portion formed on one of the rotor and the ball nut is fitted into a concave portion formed on the other via a gap. The rotation is transmitted from the rotor to the ball nut via the outer surface of the convex portion and the inner side surface of the concave portion that are in contact with each other in the rotational circumferential direction of the rotor.
[0004]
[Problems to be solved by the invention]
In the conventional configuration, at the beginning of transmission of rotation from the rotor to the ball nut, a hitting sound is generated when the outer surface of the convex portion and the inner side surface of the concave portion are in metal contact. Therefore, it is considered that an elastic member such as rubber is interposed between the convex portion and the concave portion. However, since the elastic member receives a large rotational torque, it has a short life and deteriorates early.
[0005]
An object of the present invention is to provide an electric power steering apparatus that can solve the above-described problems.
[0006]
[Means for Solving the Problems]
An electric power steering apparatus according to the present invention includes a pinion that rotates by steering, a rack that meshes with the pinion, a ball screw shaft that is integrated with the rack, a ball nut that is screwed to the ball screw shaft, and the ball nut. A steering assisting force applying motor that rotationally drives the motor, and the motor has a rotor into which the rack is inserted, and a first rotation transmission surface and a second rotation transmission surface are formed on the rotor side, A first rotation receiving surface that faces the first rotation transmission surface via an elastic member and a second rotation transmission surface that faces the second rotation transmission surface via a gap in the rotational circumferential direction of the rotor on the ball nut side. When the rotational torque transmitted from the motor to the ball nut is less than a certain value, the rotation of the rotor is the first rotational transmission. When the rotational torque transmitted from the motor to the ball nut is greater than a certain level via the elastic member through the first rotation receiving surface, the gap is eliminated by elastic deformation of the elastic member. The second rotation transmission surface and the second rotation receiving surface are in metal contact, and the rotation of the rotor is transmitted from the second rotation transmission surface to the ball nut through the second rotation receiving surface . One has a convex portion, and the other of the rotor and the ball nut has a concave portion in which the convex portion is fitted from the rack axis direction, and the elastic member is fitted in the concave portion so as to be parallel to the convex portion. And the insertion portion integrated on the convex portion side is inserted into the elastic member, and the first rotation transmission surface is constituted by one of the outer side surface of the insertion portion and the inner side surface of the concave portion, and the other The first Rolling receiving surface is configured and the second rotation transmitting surface by one in the inner surface of the outer surface and the concave portion of the convex portion is formed, and features that you have configured the second rotating receiving surface by the other To do.
According to the configuration of the present invention, at the beginning of transmission of rotation from the rotor to the ball nut, the rotation of the rotor is transmitted from the first rotation transmission surface to the first rotation receiving surface via the elastic member. Thereafter, when the rotational torque transmitted from the motor to the ball nut increases, the elastic member is elastically deformed by the gap, and the second rotation transmission surface and the second rotation receiving surface come into metal contact, and the rotation of the rotor Is transmitted from the second rotation transmitting surface to the second rotation receiving surface. Thereby, at the beginning of the transmission of the rotation from the rotor to the ball nut, the metal contact between the rotor and the ball nut can be prevented by the elastic member. When the rotational torque is increased, the second rotation transmission surface and the second rotation receiving surface are in metal contact with each other so that the elastic member is not elastically deformed and receives a torque exceeding a certain level. Since rotation can be transmitted through the surface and the metal contact surface of the second rotation receiving surface, the load on the elastic member can be reduced and the life can be extended. In addition, it is possible to achieve the prevention of the hitting sound by the elastic member and the improvement of the life of the elastic member with a compact configuration.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
A rack and pinion type electric power steering apparatus 1 shown in FIG. 1 includes a pinion 3 that rotates by steering a steering wheel (not shown) coupled to an input shaft 2, and a rack 4 that meshes with the pinion 3. Wheels (not shown) are connected to both ends of the motor. The rudder angle of the vehicle changes as the rack 4 moves in the longitudinal direction along the vehicle width direction by the rotation of the pinion 3.
[0009]
A pinion housing 30 that covers the pinion 3 and the rack 4 is provided. A torque sensor 7 that detects a steering torque transmitted to the pinion 3 by steering of the steering wheel is provided in the pinion housing 30. A known sensor can be used as the torque sensor 7.
[0010]
As shown in FIGS. 2 and 3, a ball screw shaft 61 is integrated with the rack 4, and a metal ball nut 63 is screwed onto the ball screw shaft 61 via a circulation ball 62. On the outer periphery of the ball nut 63, a protruding portion 63a that constitutes a circulation path of the circulation ball 62 is provided.
[0011]
A brushless motor 8 that rotationally drives the ball nut 63 is provided. The brushless motor 8 includes a stator 8a that is fixed to the inner peripheral side of a cylindrical rack housing 31 that covers the rack 4, a cylindrical metal rotor 8b that is inserted into the stator 8a, and a rotational phase of the rotor 8b. It has a sensor 8c for detection and a magnet 8d integrated on the outer peripheral side of the rotor 8b. One end of the rack housing 31 is connected to the pinion housing 30. The rotor 8b is rotatably supported by the inner peripheral side of the rack housing 31 at one end side through a bearing 32b and the other end side through a bearing 32a. The rack 4 is inserted into the rotor 8b through the gap so as to be movable in the axial direction.
[0012]
One end side of the ball nut 63 is connected to the other end side of the rotor 8b.
That is, as shown in FIG. 4, recesses 82a and 82b that open at the other end and the inner periphery of the rotor 8b are formed at two positions 180 degrees apart in the circumferential direction.
Further, as shown in FIG. 5, a pair of convex portions 83a and 83b project along the rack axis direction from two positions that are 180 degrees apart in the circumferential direction of one end surface of the ball nut 63.
As shown in FIG. 2, FIG. 3 and FIG. 6 (1), the convex portions 83a and 83b of the ball nut 63 are fitted into the concave portions 82a and 82b of the rotor 8b from the rack axis direction.
As shown in FIGS. 2, 3, and 6 (1), (2), and (1), (2) in FIG. 8, the elastic members 81a, 81b are formed in the concave portions 82a, 82b and the convex portions 83a, 83b. They are mated in parallel. In this embodiment, the elastic members 81a and 81b are parallel to the convex portions 83a and 83b in the radial direction of the rotor 8b, and are prevented from falling off by being sandwiched between the outer surfaces of the convex portions 83a and 83b and the inner surfaces of the concave portions 82a and 82b. Has been. The elastic members 81a and 81b may be prevented from falling off by being parallel to the convex portions 83a and 83b in the axial direction of the rotor 8b and press-fitted into the concave portions 82a and 82b. The elastic members 81a and 81b are molded from rubber or synthetic resin, which is richer in elasticity than the metal rotor 8b or the metal ball nut 63. As shown in FIG. 7, the elastic members 81 a and 81 b have a substantially rectangular parallelepiped shape and have a notch 81 ′ that opens at an end surface facing the one end surface of the ball nut 63.
A pin-shaped metal insertion portion 84 having an axis positioned on the diameter of the ball nut 63 is integrated with each of the convex portions 83a and 83b by press-fitting. Each insertion portion 84 is inserted into the notch 81 ′ of the elastic members 81a and 81b.
[0013]
As shown in FIG. 2, the other end side of the ball nut 63 is supported by a ball bearing 65 fitted to the inner peripheral side of the rack housing 31. The ball bearing 65 has an inner ring 65a, an outer ring 65b, and a bearing ball 65c. The inner ring 65 a is integrated with the outer periphery on the other end side of the ball nut 63. The outer ring 65b is composed of a pair of annular members 65b 'and 65b "arranged in parallel in the rack axis direction so as to sandwich the bearing ball 65c. The ball bearing 65 is a four-point contact type, and each bearing ball 65c is an inner ring. It contacts 65a at two points, and contacts each of the annular members 65b 'and 65b "at one point. The retaining member 50 of the bearing 65 is attached to the other end portion of the rack housing 31.
[0014]
As shown in (2) of FIG. 6 and (2) of FIG. 8, each of the recesses 82a and 82b on the rotor 8b side has an inner surface along the axial direction of the rotor 8b and facing each other in the circumferential direction. The first rotation transmission surface S1 and the second rotation transmission surface S2 are constituted by the inner surfaces. The first rotation transmission surface S1 is opposed to the elastic members 81a and 81b in the rotational circumferential direction of the rotor 8b, and the second rotation transmission surface S2 is opposed to the convex portions 83a and 83b in the rotational circumferential direction of the rotor 8b. To do.
[0015]
Due to the outer surface of the insertion portion 84 on the ball nut 63 side, a pair of first rotation receiving surfaces R1 facing the first rotation transmission surface S1 via the elastic members 81a and 81b in the rotational circumferential direction of the rotor 8b. It is configured. Further, the projections 83a and 83b on the ball nut 63 side are along the axial direction of the rotor 8b and are opposed to the second rotation transmission surface S2 with a gap δ in the rotational circumferential direction of the rotor 8b. The second rotation receiving surface R2 is constituted by each outer surface.
[0016]
The torque sensor 7 and the sensor 8c are connected to a control device (not shown), and the control device rotates according to the steering torque detected by the torque sensor 7 and the rotational phase of the rotor 8b detected by the sensor 8c. Driving AC current is input to the brushless motor 8. Accordingly, the ball nut 63 is rotationally driven by the brushless motor 8, and the steering assist force along the longitudinal direction of the rack 4 is applied according to the steering torque by the rotational drive of the ball nut 63. A known control device can be used.
[0017]
When the rotational torque transmitted from the motor 8 to the ball nut 63 is less than a certain value, the rotation of the rotor 8b passes through the first rotation receiving surface R1 from the first rotation transmitting surface S1 via the elastic members 81a and 81b. It is transmitted to the nut 63.
When the rotational torque transmitted from the motor 8 to the ball nut 63 is above a certain level, the elastic members 81a, 81b are elastically deformed by the gap δ, so that there is no gap δ corresponding to the direction of the rotational torque. Then, the second rotation transmission surface S2 and the second rotation receiving surface R2 are in metal contact, and the rotation of the rotor 8b is transmitted from the second rotation transmission surface S2 to the ball nut 63 via the second rotation receiving surface R2. .
[0018]
According to the above configuration, at the beginning of transmission of rotation from the rotor 8b to the ball nut 63, rotation of the rotor 8b is transmitted from the first rotation transmission surface S1 to the first rotation receiving surface R1 via the elastic members 81a and 81b. The Thereafter, when the rotational torque transmitted from the motor 8 to the ball nut 63 increases, the elastic members 81a and 81b are elastically deformed so that the second rotation transmission surface S2 and the second rotation receiving surface R2 are in metal contact, The rotation of the rotor 8b is transmitted from the second rotation transmission surface S2 to the second rotation receiving surface R2. Thereby, at the beginning of the transmission of the rotation from the rotor 8b to the ball nut 63, the elastic member 81a, 81b can prevent the rotor 8b and the ball nut 63 from coming into metal contact, so that it is possible to prevent the occurrence of hitting sound. When the rotational torque is increased, the elastic members 81a and 81b are not subjected to a certain amount of torque due to the elastic deformation of the elastic members 81a and 81b due to the metal contact between the second rotation transmission surface S2 and the second rotation receiving surface R2. Since the rotation can be transmitted through the metal contact surface of the second rotation transmission surface S2 and the second rotation receiving surface R2, the load on the elastic members 81a and 81b can be reduced and the life can be extended. Further, it is possible to realize the prevention of hitting sound by the elastic members 81a and 81b and the improvement of the life of the elastic members 81a and 81b with a compact configuration.
[0019]
The present invention is not limited to the above embodiment. For example, in order to connect the rotor and the ball nut, a concave portion may be formed on the ball nut side, and a convex portion fitted to the concave portion may be formed on the rotor side. In this case, the first rotation transmission surface is constituted by the outer surface of the insertion portion, the second rotation transmission surface is constituted by the outer surface of the convex portion, and the first and second rotation receiving surfaces are constituted by the inner side surface of the concave portion. The Moreover, you may form both a recessed part and a convex part in the both sides of a rotor and a ball nut.
[0020]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, generation | occurrence | production of a striking sound can be prevented with an elastic member with a compact structure, and the electric power steering apparatus which can improve the lifetime of the elastic member can be provided.
[Brief description of the drawings]
FIG. 1 is a sectional view of an electric power steering apparatus according to an embodiment of the present invention. FIG. 2 is a partial sectional view of an electric power steering apparatus according to an embodiment of the present invention. FIG. 4 is a partial cross-sectional view of the ball nut rotated 90 degrees from the state shown in FIG. 2. FIG. 4 is a partial perspective view of the rotor in the electric power steering apparatus according to the embodiment of the invention. Partial perspective view of a ball nut in an electric power steering apparatus. [FIG. 6] (1) is a sectional view taken along line VI-VI in FIG. 2, (2) is a partially enlarged view of (1). [FIG. FIG. 8 is a perspective view of an elastic member in the electric power steering apparatus. FIG. 8 is a cross-sectional view of the main part of the electric power steering apparatus according to the embodiment of the present invention, and FIG. Description of the code]
3 Pinion 4 Rack 8 Motor 8b Rotor 61 Ball screw shaft 63 Ball nuts 81a, 81b Elastic members 82a, 82b Recesses 83a, 83b Protrusion 84 Insertion part R1 First rotation receiving surface R2 Second rotation receiving surface S1 First rotation transmission surface S2 Second rotation transmission surface

Claims (1)

A pinion rotating by steering,
A rack meshing with the pinion,
A ball screw shaft integrated into the rack;
A ball nut screwed to the ball screw shaft,
A steering assisting force applying motor that rotationally drives the ball nut;
The motor has a rotor into which the rack is inserted,
A first rotation transmission surface and a second rotation transmission surface are formed on the rotor side,
A first rotation receiving surface that faces the first rotation transmission surface via an elastic member and a second rotation transmission surface that faces the second rotation transmission surface via a gap in the rotational circumferential direction of the rotor on the ball nut side. A rotation receiving surface is formed,
When the rotational torque transmitted from the motor to the ball nut is less than a certain value, the rotation of the rotor is transmitted from the first rotation transmission surface to the ball nut through the elastic member through the first rotation receiving surface,
When the rotational torque transmitted from the motor to the ball nut is above a certain level, the gap is eliminated by elastic deformation of the elastic member, and the second rotation transmitting surface and the second rotation receiving surface are in metal contact, The rotation of the rotor is transmitted from the second rotation transmission surface to the ball nut through the second rotation receiving surface ,
One of the rotor and ball nut has a convex part,
The other of the rotor and the ball nut has a concave portion in which the convex portion is fitted from the rack axis direction,
The elastic member is fitted in the concave portion so as to be parallel to the convex portion,
The insertion part integrated on the convex side is inserted into the elastic member,
The first rotation transmission surface is configured by one of the outer surface of the insertion portion and the inner surface of the recess, and the first rotation receiving surface is configured by the other,
Part the second rotation transmitting surface by one in the inner surface of the outer surface and the concave portion of the convex portion is formed, an electric power steering apparatus wherein the second rotating receiving surface, characterized that you have been configured by the other.

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