JP3458867B2 - Electric power steering device - Google Patents

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 As an electric power steering device for a vehicle, the rotational output of an electric motor, which is an auxiliary steering torque, is reduced by a gear device and transmitted to an output shaft of a steering mechanism to assist the manual force of a steering wheel. It is known that the wheel is steered by reciprocating the shaft within a predetermined range. During operation of such an electric power steering apparatus, a sudden force received by a wheel from a road surface may oppose the output of the electric motor to generate an impact force. Such impact force may cause damage to the electric motor and the power transmission mechanism.

[0003]

In order to reduce or eliminate this impact force, in the prior art, measures such as disposing an electromagnetic clutch on the rotating shaft of an electric motor have been taken.
However, such an electromagnetic clutch is generally high in cost, and it is not preferable from the viewpoint of energy saving because it is necessary to always supply electric power during operation. If the rated output of the electric motor increases, There is a problem in that the coil and the like must be made considerably large.

On the other hand, it is conceivable to provide a separate torque limiter in the reduction gear portion, but there are problems such as high cost and limited mounting space.

It is an object of the present invention to provide an electric power steering device which has a simple structure and can prevent damage to an electric motor and a power transmission system.

[0006]

In order to achieve the above object, an electric power steering apparatus according to a first aspect of the present invention comprises a housing, a motor mounted on the housing for rotating a rotary shaft, and a wheel steering wheel. Output shaft for transmitting a steering force, an input shaft for connecting the steering wheel and the output shaft, a driving means attached to the rotating shaft, and a driven means for engaging the driving means in a power-transmittable manner. And a torque limit provided between the driven means and the output shaft, which transmits torque less than a predetermined value but does not transmit torque exceeding the predetermined value. Means, the torque limit means comprising:
Elasticity that is fixedly attached to one of the driven means or the output shaft and that includes a ring member that gives an elastic force to the other when assembled, and elasticity given to the other. The force can be adjusted by the ring member alone. An electric power steering apparatus according to a second aspect of the present invention includes a housing, a motor attached to the housing for rotating a rotating shaft, an output shaft for transmitting a steering force for steering wheels, and a steering wheel. And an input shaft connecting the output shaft with the output shaft,
A power transmission mechanism including a drive unit attached to the rotary shaft and a driven unit engaged with the drive unit so as to be capable of transmitting power, and provided between the driven unit and the output shaft. And a torque limit means for transmitting torque equal to or less than a predetermined value but not transmitting torque exceeding the predetermined value, wherein the torque limit means is fixed to one of the driven means and the output shaft. And a ring member selected so that a predetermined elastic force can be applied to the other when attached to the other. An electric power steering apparatus according to a third aspect of the present invention includes a housing, a motor attached to the housing for rotating a rotating shaft, an output shaft for transmitting a steering force for steering wheels, and a steering wheel. An input shaft connecting the output shaft and the output shaft, and a drive unit attached to the rotary shaft,
A power transmission mechanism including a driven unit that engages with the drive unit so as to transmit power, and a torque provided below the predetermined value, which is provided between the driven unit and the output shaft. And a torque limit unit that does not transmit torque exceeding the predetermined value, the torque limit unit being fixedly attached to one of the driven unit and the output shaft, and the other unit when assembled. It is configured to include a ring member that applies an elastic force via a plurality of projections that abut against. The ring member can be selected so that a predetermined elastic force can be applied to the other.

[0007]

According to the electric power steering apparatus of the present invention, since the torque limit means is provided between the driven means and the output shaft, the conventional structure can be obtained even if the torque limit means is attached. On the other hand, a ring member that is separate from the output shaft or the driven means is used to generate the frictional force necessary for torque transmission without increasing the size of the device. Because you can
Manufacturing costs are low.

[0008]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a partial sectional view in the axial direction of an electric power steering device 100 that is an embodiment of the present invention.

In FIG. 1, an electric power steering apparatus 100 has a housing body 101 and a rack column 110 extending from the housing body 101. Housing body 101
The rack column 110 is fixed to a vehicle body (not shown) by brackets (not shown), and these form a housing integrally. Inside the housing body 101, an input shaft 111, which is adapted to connect one end to a steering shaft and a steering wheel (not shown), extends obliquely from above, while inside the housing body 101 and the rack column 110. The rack shaft 112, which is an output shaft, extends. A pinion (not shown) is formed at the lower end of the input shaft 111, meshes with the rack of the rack shaft 112, and the rack shaft 1 is rotated by the rotation of the input shaft 111.
12 is designed to move left and right. The rack shaft 112 is formed by connecting a hollow shaft 112a and a solid shaft 112b having a rack formed on the outer surface thereof.

The torque detecting device 113 is the housing body 1.
It is provided in 01. This torque detection device 113
Is to detect the torque applied to the input shaft 111 by using a torsion bar and output a signal value corresponding thereto.

Further, a power transmission mechanism (hypoid gear train described later) connected to the input shaft 111 is provided in the housing body 101, and the rotation shaft (FIG. 2) of the electric motor 114 mounted on the housing body 101 is connected to the power transmission mechanism. Is decelerated and transmitted to the input shaft 111.
The torque detection device 113 and the electric motor 114 are
It is connected to a control device (not shown).

Ball joints 115 and 116 are attached to both ends of the rack shaft 112, and tie rods 117 and 1 are attached to the ball joints 115 and 116, respectively.
Eighteen ends are pivotally mounted. Around the ball joints 115 and 116, dust-proof boots 11
9, 120 are attached.

FIG. 2 is an enlarged partial sectional view of a portion II of the electric power steering apparatus of FIG. In FIG. 2, the housing 101 includes a cover 101a and a base 101b. The input shaft 111 extends inside the cover 101a. The hollow input shaft 111 is rotatably supported by the bearing 122 with respect to the cover 101a. Input shaft 1
A torsion bar 123, of which one end is connected to the input shaft 111 and the other end is connected to the output shaft 121, extends inside 11.

A detection device 113 for detecting the steering torque is provided around the center of the input shaft 111 based on the torsion bar 123 twisting in proportion to the received torque. The detection device 113 has a slider 124 externally fitted to the input shaft 111 so as to be rotatable relative to the input shaft 111 and movable in the axial direction, and has an inner end fitted to a hole formed at an upper end of the output shaft 121 and externally fitted. The pin 125 inserted in the vertical groove formed at the lower end of the slider 124 at the side end and the input shaft 1
11 and the spiral groove formed on the outer periphery of the lower end of the slider 124.
Ball 1 which can roll freely in the space formed by the recess of
26 and the spring 1 for urging the slider 124 upward.
27 and the slider 12 connected to the outer circumference of the slider 124.
4 potentiometer 128 for measuring the amount of movement in the axial direction
It consists of and. Incidentally, such a detecting device is publicly known as represented by, for example, Japanese Utility Model Application Laid-Open No. 60-179944, and therefore its configuration will not be described in detail below.

A large hypoid gear 129 is attached to the upper end of the output shaft 121 as described later.
Large hypoid gear 129 at the upper end of the output shaft 121
The upper bearing 131 is fitted in the vicinity of. Output shaft 121
A lower bearing 132 is fitted to the lower end of the. The outer circumference of the lower bearing 132 is supported by the base 101b via a first sleeve 133 screwed to the base 101b.
Between the outer rings of the upper bearing 131 and the lower bearing 132, a second
A sleeve 134 is provided. A nut 135 is screwed into the male screw at the lower end of the output shaft 121.

Large hypoid gear 129 which is a driven means
Engages with a small hypoid gear 136 which is a drive means formed on a rotary shaft connected to the electric motor 114. By rotating the first sleeve 133 with respect to the base 101b, the first sleeve 133 can freely move in and out of the base 101b, whereby the tooth surface distance between the large hypoid gear 129 and the small hypoid gear 136, that is, backlash can be adjusted. .

Inside the cover 101a of the housing 101, there is provided an inner cylindrical portion 101c whose lower end extends near the upper surface of the large hypoid gear 129. The upper surface of the large hypoid gear 129 is an annular flat surface 129a, and the flat surface 129a is in sealing contact with a seal 137 attached to the lower end of the inner cylindrical portion 101c. A hole 101d coaxial with the small hypoid gear 136 is formed on the side wall of the inner cylindrical portion 101c, and the tip of the small hypoid gear 136 is formed by a needle bearing 150.
It is rotatably supported in the hole 101d. In addition,
The axes of the large and small hypoid gears are offset from the orthogonal state.

FIG. 3 is a partial sectional view obtained by cutting the electric power steering system of FIG. 2 along the line III-III. FIG. 4 is an enlarged partial cutaway perspective view of the ring member 201. In FIG. 2, two circumferential grooves 121a are formed near the upper end of the output shaft 121. The ring member 201 has a circumferential projection 201a (FIG. 4) on the inner circumference,
The ring member 201 is fixedly attached to the output shaft 121 by engaging the circumferential projection 201a with the circumferential groove 121a. On the other hand, the large hypoid gear 129
A circumferential groove 129b is formed on the inner circumference. Ring member 20
1 has a large number of axial protrusions 201b (FIGS. 3 and 4) extending in the axial direction on the outer periphery. The axial projection 201b elastically abuts the bottom of the circumferential groove 129b of the large hypoid gear 129 during assembly to apply an appropriate frictional force to the large hypoid gear. In addition, the circumferential groove 1
29b and the ring member 201 constitute a torque limit means.

Next, the operation of the electric power steering system according to this embodiment will be described below with reference to FIG. When the driver rotates a steering wheel (not shown), the input shaft 111 rotates and torque is transmitted to the rack shaft 112 via the output shaft 121. In this case, the value of the torque detected by the torque detection device 113 is
It is sent to a control circuit (not shown) and compared there with a predetermined value. When the torque exceeds a predetermined value, it is a case where the auxiliary steering force is required, and therefore a drive command is issued to drive the electric motor 114. The electric motor 114 driven by the drive command outputs the output shaft 12 via the hypoid gear.
1 is rotated to move the rack shaft 112 in the axial direction. When the value of the torque detected by the torque detection device 113 is lower than the predetermined value, the auxiliary steering force is unnecessary,
The electric motor 114 is not driven.

By the way, in such an electric power steering apparatus, when the steering gear reaches the stroke end while rotating at a high speed, the electric motor 114 rotating at a speed that is twice the speed reduction ratio of the rotation of the large hypoid gear 129. Will suddenly stop, and a large impact force generated by the inertia of the electric motor will be transmitted to the reduction mechanism, which may result in damage to the power transmission system or functional deterioration in the future. However, since the impact force that causes a problem in strength is much larger than the torque that is normally used, and the frequency of occurrence of such an excessive impact force is extremely low, slippage occurs between the large hypoid gear 129 and the output shaft 121. It is possible to absorb this impact force by generating. That is, in the present embodiment, the frictional force generated based on the elastic force applied from the axial projection 201b of the ring member 201 to the circumferential groove 129b of the large hypoid gear 129 is taken into consideration during normal use in consideration of a change with time such as wear. The inner diameter of the circumferential groove 129b and the protrusion amount of the axial projection 201b are set so as to be larger than the transmitted torque and lower than the impact force. Therefore, during normal operation, the circumferential groove 12
Since slippage does not occur between 9b and the axial projection 201b, power transmission from the large hypoid gear 129 to the output shaft 121 can be performed without any trouble. On the other hand, when the impact force is generated, the axial projection 201b is slid with respect to the circumferential groove 129b so that the power transmission between the large hypoid gear 129 and the output shaft 121 is prevented.

The circumferential projection 2 of the ring gear member 201
01a is intended for ease of incorporation. That is, the ring member 201 is assembled together with the large hypoid gear 129, but when the relative position in the vertical direction with respect to the output shaft 121 becomes appropriate, the circumferential protrusion 201a engages with the circumferential groove 121b of the output shaft 121 with the snap. As a result, the relative positional relationship between the output shaft 121 and the large hypoid gear 129 can be uniquely determined. Furthermore,
By providing a large number of axial protrusions 201b, the elastic force applied from the ring member 201 to the large hypoid gear 129 is made insensitive to variations in dimensional tolerance. That is, even if the amount of protrusion of the axial protrusion 201b changes to some extent, the applied elastic force does not change significantly.

Although the present invention has been described with reference to the embodiments, the present invention should not be construed as being limited to the above embodiments, and it goes without saying that appropriate modifications and improvements can be made. For example, the axial protrusion of the ring member 201 may be provided inside instead of outside. Further, in this electric power steering device, the bottom surface of the circumferential groove 129b of the large hypoid gear 129 is a cylindrical surface.
It is possible to increase the torque when the relative slip of 1. Further, the hypoid gear may be a bevel gear or a friction transmission element.

[0023]

As described above, according to the electric power steering apparatus of the present invention, since the torque limit means is provided between the driven means and the output shaft, the torque limit means is attached. In addition, since the size of the device is not increased compared to the conventional configuration, and the ring member that is separate from the output shaft or the driven means is used to generate the frictional force necessary for torque transmission. Manufacturing costs are low because adjustments such as these can be made separately.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view in the axial direction of an electric power steering device 100 that is an embodiment of the present invention.

FIG. 2 is an enlarged partial sectional view of a II portion of the electric power steering device of FIG.

FIG. 3 is a III-II of the electric power steering device of FIG.
It is a fragmentary sectional view obtained by cutting along the line I.

FIG. 4 is an enlarged partial cutaway perspective view of a ring member 201.

[Explanation of symbols]

101 ……… Housing body 101c ......... Inner cylindrical part 111 ... Input axis 112 ... Rack rack 114 ... Electric motor 121 ... Output shaft 121a ......... circumferential groove 129 ………… Large hypoid gear 129b ……… Circumferential groove 136 ………… Small hypoid gear 201 ... Ring member

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) B62D 5/04 F16D 7/02

Claims (4)

(57) [Claims] 1. A housing, a motor attached to the housing for rotating a rotating shaft, an output shaft for transmitting a steering force for steering a wheel, and an input shaft for connecting a steering wheel and the output shaft. A power transmission mechanism including drive means attached to the rotary shaft and driven means engaged with the drive means so as to be capable of transmitting power; and provided between the driven means and the output shaft. A torque limit means for transmitting a torque equal to or less than a predetermined value but not transmitting a torque exceeding the predetermined value, the torque limit means being fixed to one of the driven means and the output shaft. Is configured to include a ring member that applies elastic force to the other when assembled, and the ring member alone adjusts the elastic force applied to the other. Electric power steering apparatus characterized by the playable manner. 2. A housing, a motor attached to the housing for rotating a rotating shaft, an output shaft for transmitting a steering force for steering a wheel, and an input shaft for connecting the steering wheel and the output shaft. A power transmission mechanism including drive means attached to the rotary shaft and driven means engaged with the drive means so as to be capable of transmitting power; and provided between the driven means and the output shaft. A torque limit means for transmitting a torque equal to or less than a predetermined value but not transmitting a torque exceeding the predetermined value, the torque limit means being fixed to one of the driven means and the output shaft. An electric power steering device including a ring member that is selected so that a predetermined elastic force can be applied to the other one when it is attached and assembled. 3. A housing, a motor attached to the housing for rotating a rotating shaft, an output shaft for transmitting a steering force for steering wheels, and an input shaft for connecting the steering wheel and the output shaft. A power transmission mechanism including drive means attached to the rotary shaft and driven means engaged with the drive means so as to be capable of transmitting power; and provided between the driven means and the output shaft. A torque limit means for transmitting a torque equal to or less than a predetermined value but not transmitting a torque exceeding the predetermined value, the torque limit means being fixed to one of the driven means and the output shaft. Electrically-powered steering device including a ring member that applies elastic force through a protrusion that is attached to the other and abuts against the other when assembled. . 4. The electric power steering device according to claim 3, wherein the ring member is selected so that a predetermined elastic force can be applied to the other.