JP2001158368A - Motor-driven power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor-driven power steering device having a compact arrangement and capable of securing collapse stroke more. SOLUTION: A sensor shaft 32 is freely rotatably supported by a sealed needle bearing 14 disposed inward of the mutually fitting portions of a housing 10 and a lower column tube 102, so that the inside diameter of the lower column tube 102 and the inside diameter of an axial opening 10b in the housing 10 can be made smaller than when the sensor shaft 32 is supported by use of, e.g. ball bearings, resulting in the compacting of the motor-driven power steering device. Also, the needle bearing 14 is equipped with a seal to eliminate the need for disposing independent seals axially in series and secure the collapse stroke.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electric power steering apparatus, and more particularly to an electric power steering apparatus having a compact structure.

[0002]

2. Description of the Related Art As an electric power steering device for a vehicle, the rotational force 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, and the steering force applied to a steering wheel is assisted. Then, there is known one configured to steer wheels. In such an electric power steering device, a power transmission mechanism provided in a housing is used to transmit power to an output shaft while reducing the rotation of an electric motor.

[0003]

By the way, when assembling the electric power steering apparatus according to the prior art,
After fitting the column tube to the housing,
An input shaft directly attached to the steering wheel is connected to a sensor shaft extending from the torque sensor unit.

Here, there is a problem how to rotatably support the sensor shaft. That is, since parts related to the vehicle are arranged around the electric power steering apparatus, it is necessary to keep the housing diameter and the like as small as possible. On the other hand, in the housing, it is necessary to provide a seal to prevent foreign substances from entering through the column tube, but if the bearing and the seal are arranged in series,
There is also a problem that the collapse stroke for reducing the impact at the time of the secondary collision of the vehicle is shortened accordingly.

Accordingly, the present invention has a compact configuration in view of the problems of the prior art, and
It is an object of the present invention to provide an electric power steering device that can secure a more collapsed stroke.

[0006]

In order to achieve the above object,
An electric power steering apparatus according to the present invention includes a housing, an input shaft for inputting a steering force, a column tube supporting the input shaft, an electric motor for generating a rotational force, the input shaft, and a steering mechanism. A worm wheel mechanism including a worm and a worm wheel, which transmits the rotational force from the electric motor to the sensor shaft,
And the sensor shaft is rotatably supported by a sealed needle bearing disposed inside a fitting portion between the housing and the column tube.

[0007]

According to the electric power steering apparatus of the present invention, the housing, the input shaft for inputting the steering force, the column tube for supporting the input shaft, the electric motor for generating the rotational force, the input shaft, A sensor shaft connected to a steering mechanism, and a detection unit that detects torque of the sensor shaft,
Transmitting the rotational force from the electric motor to the sensor shaft, a worm wheel mechanism including a worm and a worm wheel, wherein the sensor shaft is provided inside a fitting portion between the housing and the column tube. Placed,
Since it is rotatably supported by a needle bearing with a seal, the inner diameter of the column tube and the inner diameter of the housing of the housing can be suppressed smaller than in a case where the sensor shaft is supported using, for example, a ball bearing. ,
This makes it possible to reduce the size of the electric power steering device. Further, by providing the needle bearing with a seal, it is not necessary to arrange a separate seal in series in the axial direction, and a collapse stroke can be secured.

Further, if a collar is provided between the sensor shaft and the needle bearing, the inner diameter of the needle bearing can be increased by the thickness of the collar.
Even in the case where a large-diameter portion for attaching a key lock collar is provided around the input shaft, it becomes easy to pass the input shaft through the inside of the needle bearing and incorporate the input shaft.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a partial cross-sectional view of an electric power steering apparatus 100 according to a first embodiment of the present invention. FIG. 2 shows the configuration II of FIG.
It is a figure which expands and shows a part. FIG. 3 shows the configuration of FIG.
It is the figure seen in the III direction.

Referring to FIG. 1, an electric power steering apparatus 100 includes a bracket 101 mounted on a vehicle body (not shown).
(a), an inner column tube (102), which is fitted to and contained in the outer column tube (102) and extends leftward, and an outer column tube (101) connected to the left end of the inner column tube (102). And a housing 10 supported by a vehicle body (not shown). As shown in FIGS. 1 and 2, a torque sensor unit 30 is disposed in the housing 10.

A hollow input shaft 11 connected to a steering wheel (not shown) at the right end extends from the right inside the outer column tube 101, and penetrates the torque sensor unit 30 near the left end of the outer column tube 101. The right end of the extending sensor shaft 32 is fitted. More specifically, a female serration 11 a is formed on the inner periphery of the left end of the input shaft 11, and a male serration 32 b is formed on the outer periphery of the right end of the sensor shaft 32.
The input shaft 11 and the sensor shaft 32 are integrally connected in the rotational direction by being engaged with each other, and are connected so as to be relatively movable in the axial direction. The input shaft 11 is rotatably supported by the outer column tube 101 by a ball bearing 13.

On the other hand, the sensor shaft 32 is formed in the axial opening 1 of the housing 10 by the needle bearing 14 having a seal.
It is rotatably supported with respect to the inner column tube 102 fitted to Ob so as to secure a collapse stroke. This will be described specifically. For example, if the sensor shaft 32 is to be supported by a ball bearing, the axial opening 10b of the housing 10 must be increased in diameter. Axial opening 10
There is a limit in increasing the diameter of b. On the other hand, since it is necessary to provide a seal in order to prevent foreign substances from entering the housing 10, the ball bearing and the seal must be arranged in series in the axial direction.

However, when the ball bearing and the seal are arranged in series in the axial direction, the input shaft 11 pushed by the driver via the steering wheel (not shown) during the secondary collision of the vehicle causes the input shaft 11 of the sensor shaft 32 to move. The distance that can be entered (collapsed) as much as possible while sliding around, that is, the so-called collapse stroke, becomes shorter. Therefore, in the present embodiment, the collapse stroke is achieved by rotatably supporting the sensor shaft 32 on the inner column tube 102 fitted in the axial opening 10b of the housing 10 by the needle bearing 14 with a seal. Is to be secured.

FIG. 8 is an axial sectional view of the torque sensor unit 30. In FIG. 8, a sensor shaft 32 penetrating the main body 1 having a housing shape is disposed. The sensor shaft 32 is provided near the both ends of the main body 31 with ball bearings 34, 3
5 rotatably supported. A pair of helical groove groups 32c and 32d extending in directions intersecting with each other are formed on the center outer periphery of the main body 1 of the sensor shaft 32. On the inner periphery of the main body 1, coils 36 arranged so as to correspond to the helical groove groups 32c and 32d, respectively.
A coil unit 36 as a detection unit including the components a and b and a circuit board 36c is disposed. Circuit board 36c
Is connected to a wiring 33.

The torque sensor unit 30 includes a sensor shaft 3
The torsion stress generated according to the torque applied to the helical groove group 32c, 32d
6a and 36b, and a corresponding signal can be output to an external CPU (not shown) via the wiring 33.

When the sensor shaft 32 is bent when detecting the torsional stress of the sensor shaft 32, the helical groove group 32
Since the intervals between c and 32d and the coils 36a and 36b partially change, an erroneous value may be detected. In view of this, the sensor shaft 32 is so-called floating supported at equal distances from the helical groove groups 32c and 32d via the ball bearings 34 and 35.
2, even if bending occurs, helical groove groups 32c and 32d,
The distance between the coils 36a and 36b does not change.

As shown in FIG. 2, the wiring 33 extends outward through a hole 10a formed in the side surface of the housing 10. Outside the hole 10a, a bracket 15
Is provided.

As shown in FIGS.
The housing 1 has four bolts 12a to 12d.
Attached to 0. The bracket 15 is attached to the housing 10, and includes a holding portion 15 a separated from the outer periphery by a distance slightly smaller than the outer diameter of the wiring 33, and a raised attachment portion 15 b. The pressing portion 15a has a function of blocking the opening 10 of the housing 10 and a contact with the wiring 33, and the wiring 33 is pulled from the outside by applying a predetermined frictional force by pressing the wiring 33 against the outer periphery of the housing 10. Sometimes, it has a function of preventing the wiring from being peeled off from the circuit board 36c (FIG. 8).

A substantially disk-shaped bearing holder 16 and a substantially cylindrical housing lid 17 are attached to the left end of the substantially cylindrical housing 10 so as to include the bearing holder 16. That is, the outer periphery of the bearing holder 16 is fitted to the flange portion 10c of the housing 10, and is fitted to the flange portion 17b of the housing lid 17 facing the flange portion 10c. The bearing holder 16 and the housing lid 17 are connected to each other with a bolt (not shown) separate from a bolt for attaching to the housing 10.

An electric motor 20 is attached to the housing lid 17. Central opening 1 of bearing holder 16
A ball bearing 18 with a seal is fitted in 6a, and a ball bearing with a seal is provided in the reduced diameter portion 17a on the left end of the housing lid 17 so that it cannot be displaced in the axial direction by retaining rings 21 and 22. The bearing 19 is fitted. In other words, the ball bearing 19 closer to the steering mechanism performs axial positioning.

The ball bearings 18, 19 rotatably support both ends of the cylindrical member 23. A worm wheel 24 composed of a core metal 24a and a ring gear portion 24b made of resin is attached to a substantially central outer periphery of the cylindrical member 23 by press-fitting or the like. The worm wheel 24 is connected to the electric motor 20.
And the worm 20a formed on the rotating shaft 20b.

On the inner periphery of the cylindrical member 23, a radially reduced portion 23a is provided radially inward of the worm wheel 24, and on the inner periphery of the reduced diameter portion 23a, a female serration 2 is provided.
3b is formed. On the other hand, a male serration 32a is formed on the outer periphery of the sensor shaft 32 penetrating the cylindrical member 23 so as to face the female serration 23b. By engaging the female serrations 23b and the male serrations 32a, the cylindrical member 23 and the sensor shaft 32 rotate integrally. A steering mechanism (not shown) is connected to the left end of the sensor shaft 32. In this embodiment, the male serrations 32a and the female serrations 23a are used.
b constitutes a power transmission means.

Next, the operation of this embodiment will be described below. If the vehicle is in a straight running state and no steering force is input to the input shaft 11 and the sensor shaft 32 via a steering wheel (not shown), since the sensor shaft 32 does not twist, the torque sensor unit 30 is substantially Therefore, the electric motor 21 does not generate an auxiliary steering force.

When the driver steers a steering wheel (not shown) when the vehicle is going to make a curve, the steering torque transmitted via the input shaft 11 and the sensor shaft 32 causes the sensor shaft 32 to twist. Thus, the torque sensor unit 30 outputs a detection signal corresponding to the direction and amount of rotation of the torque sensor unit 30 to the CPU (not shown) via the wiring 33 in a known manner. The electric motor 20 driven and controlled by the CPU based on this signal rotates the rotating shaft 20b to generate an auxiliary steering force (rotational force). The rotation of the electric motor 20 is transmitted to the cylindrical member 23 via the worm 20a and the worm wheel 24, and further transmitted to the sensor shaft 32.

According to the present embodiment, even when the female serration 23b is formed in the reduced diameter portion 23a of the cylindrical member 23, the tool can be penetrated in the axial direction, so that more efficient processing such as broaching can be performed. Can do
Thereby, productivity can be improved. In addition, by using the sensor shaft 32 also as an output shaft of the electric power steering device, the electric power steering device is downsized. Therefore, at the time of a secondary collision of the vehicle, it is possible to secure a collapse stroke that is an amount by which the input shaft 11 can slide along the sensor shaft 32.

Further, the sensor shaft 32 is connected to the housing lid 17.
Ball bearing 19 mounted on the
Since the sensor shaft 32 is supported by the ball bearings 18 attached to the sensor shaft 32, the sensor shaft 32 is maintained in a supported state even when the housing 10 is removed, thereby facilitating assembly and maintenance.

Further, the bracket 15 is connected to the housing 10.
Has a function of blocking the opening 10a and a function of applying a predetermined frictional force by contacting the wiring 33, so that the bracket 15 can also be used as a cover member that blocks the opening 10a, for example, thereby omitting the cover member. The bracket 15 can be connected to the wiring 3
By applying a predetermined frictional force by contacting the wire 3, for example, a fastener for the wiring 33 can be omitted, so that cost can be reduced.

According to the present embodiment, the bearing holder 16, the housing lid 17, and the cylindrical member 23 supported via the ball bearings 18 and 19 can be a sub-assembly. That is, such a sub-assembly is pre-assembled in a separate process from the assembly on the housing 10 side, and the outer periphery of the bearing holder 16 is used as
If it is set to 0, the electric power steering apparatus can be assembled in a shorter time.

Further, in this embodiment, the sensor shaft 32 is rotatably supported by the inner column tube 102 fitted in the axial opening 10b of the housing 10 by the needle bearing 14 with the seal. , To ensure a collapse stroke.

FIG. 3 is a view similar to FIG. 2 showing the second embodiment. The embodiment shown in FIG. 3 differs from the first embodiment in the mode of coupling between the cylindrical member and the sensor shaft. Description of other common points is omitted. The difference will be described more specifically.
A tolerance ring 133 is interposed between the inner circumference of the sensor shaft 3 and the outer circumference of the sensor shaft 132. Tolerance ring 1
Numeral 33 denotes a ring-shaped plate material wavy in the circumferential direction.
Elastically deformed by being incorporated between the outer circumference of
A predetermined frictional force is applied to the cylindrical member 123 and the sensor shaft 132. In the present embodiment, tolerance ring 133 constitutes a power transmission unit.

During normal operation, the worm wheel 24
The auxiliary steering force from the electric motor 20 through the cylindrical member 1
When transmitted to the sensor 23, the frictional force causes the sensor shaft 132 to rotate integrally with the cylindrical member 123, whereby the auxiliary steering force is transmitted to the sensor shaft 132. On the other hand, when the sensor shaft 132 rotates vigorously to the rotation end and abuts against a stopper (not shown) to prevent further rotation, the cylindrical member 123 is about to rotate due to the auxiliary steering force of the electric motor 20. Therefore, a large relative rotational force is generated between the sensor shaft 132 and the cylindrical member 123. Therefore, when the cylindrical member and the sensor shaft are serrated and connected as in the first embodiment, a large stress may be generated in each part. Therefore, the cross-sectional area of the member is increased to reduce the stress. It is necessary to take measures such as making the materials high-grade.

On the other hand, according to the present embodiment, the large relative rotational force generated by the contact with the stopper causes the frictional force between the tolerance ring 133 and the sensor shaft 132 or the cylindrical shaft 123 (that is, the predetermined value). ), The tolerance ring 133 slides with respect to the inner circumference of the cylindrical member 123 or the outer circumference of the sensor shaft 132 to allow the relative rotation between the cylindrical member 123 and the sensor shaft 132. The applied stress can be reduced. That is, tolerance ring 133 limits the torque transmitted between cylindrical member 123 and sensor shaft 132,
It will function as a so-called torque limiter.

FIG. 5 is a view similar to FIG. 2 showing the third embodiment. The embodiment shown in FIG. 5 differs from the first embodiment in the mode of coupling between the cylindrical member and the sensor shaft. Description of other common points is omitted. The difference will be described more specifically.
The large-diameter portion 232a of the sensor shaft 232 is press-fitted into 3 and connected to each other. In the present embodiment, according to the coupling by press-fitting constituting the power transmission means, it is not necessary to form serrations and the like, so that a lower cost configuration can be provided.

FIG. 6 is a view similar to FIG. 1 showing a fourth embodiment. The embodiment shown in FIG. 6 differs from the first embodiment in the manner of supporting the lower input shaft. Description of other common points is omitted. More specifically, the collar 401 is fitted to the outer periphery of the left end of the sensor shaft 32 by press fitting or the like, and the collar 401 is rotatably supported by the needle bearing 14 with respect to the inner column tube 102. ing.

When assembling the electric power steering device, the input shaft 11 connected to the sensor shaft 32 must be inserted into the assembly of the outer column tube 101 and the inner column tube 102. It is convenient to insert from the open end (left end) side of 102. However, as shown in the embodiment of FIG. 1, if the open end of the inner column tube 102 is narrowed according to the outer diameter of the end of the sensor shaft 32, the key lock collar (not shown) on the input shaft 12 at the time of insertion. ) There is a possibility that the portion having the maximum diameter A such as the mounting portion cannot pass.

On the other hand, according to the present embodiment, since the collar 401 is fitted to the left end of the sensor shaft 32,
The open end of the inner column tube 102 can be widened by the thickness. That is, in FIG. 6, a relationship of B> A can be established between the inner diameter B of the needle bearing 14 and the maximum diameter A of the input shaft 11, whereby the needle bearing is provided at the open end of the inner column tube 102. 1
4 can be passed through the needle bearing 14 and the input shaft 11 can be incorporated.

FIG. 7 is a view similar to FIG. 1 showing a fifth embodiment. The embodiment shown in FIG. 7 differs from the first embodiment in the manner of supporting the lower input shaft. Description of other common points is omitted. Explaining the different point more specifically, the housing lid 517 is a large-diameter cylindrical portion 51 attached to the left end of the housing 10.
7b, a small-diameter cylindrical portion 517a having ball bearings 18 and 19 mounted on the inner periphery thereof, and a flange portion 517c connecting them in the radial direction.

Large-diameter cylindrical portion 517b of housing lid 517
Inside, a worm wheel 24 is arranged. The cylindrical member 523 to which the worm wheel 24 is attached near the outer periphery on the right end is supported by a ball bearing (not necessarily a seal) 18 on the outer periphery of the center and supported by a ball bearing 19 with a seal on the outer periphery near the left end. . The cylindrical member 5
A space between the right end of the housing 23 and the housing 10 is sealed by a seal 507, and a preload can be applied to the ball bearings 18 and 19 by a nut member 501 screwed to the left end of the cylindrical member 523.

Although the present invention has been described with reference to the embodiments, it should be understood that the present invention should not be construed as being limited to the above-described embodiments, and that modifications and improvements can be made as appropriate. is there. In the present embodiment, a torque sensor that obtains torque by directly detecting the torsional stress of the sensor shaft is used, but a torque sensor that detects torque by a mechanical or other method may be used.

[0040]

According to the electric power steering apparatus of the present invention, the housing, the input shaft for inputting the steering force,
A column tube that supports the input shaft, an electric motor that generates rotational force, a sensor shaft connected to the input shaft, a steering mechanism, a detection unit that detects torque of the sensor shaft, and the electric motor A worm wheel mechanism including a worm and a worm wheel, which transmits the rotational force from the sensor shaft to the sensor shaft, wherein the sensor shaft is disposed inside a fitting portion between the housing and the column tube. Since it is rotatably supported by a needle bearing with a seal, the inner diameter of the column tube and the inner diameter of the housing of the housing can be suppressed to be smaller than when the sensor shaft is supported using, for example, a ball bearing. Accordingly, the electric power steering device can be made more compact. Further, by providing the needle bearing with a seal, it is not necessary to arrange a separate seal in series in the axial direction, and a collapse stroke can be secured.

[Brief description of the drawings]

FIG. 1 is an axial partial cross-sectional view of an electric power steering device 100 according to a first embodiment of the present invention.

FIG. 2 is an enlarged view showing a part II of the configuration of FIG. 1;

FIG. 3 is a view of the configuration of FIG. 2 as viewed in the direction of arrow III.

FIG. 4 is a view similar to FIG. 2, showing a second embodiment.

FIG. 5 is a view similar to FIG. 2, showing a third embodiment.

FIG. 6 is a view similar to FIG. 1, showing a fourth embodiment.

FIG. 7 is a view similar to FIG. 1, showing a fifth embodiment.

8 is an axial sectional view of the torque sensor unit 30. FIG.

[Explanation of symbols]

 Reference Signs List 10 Housing 11 Input shaft 14 Needle bearing with seal 20 Electric motor 23, 123, 223, 523 Cylindrical member 24 Worm wheel 30 Torque sensor unit 32, 132, 232, 532 Sensor shaft

Claims (2)

[Claims] 1. A housing, an input shaft for inputting a steering force, a column tube supporting the input shaft, an electric motor for generating a rotational force, a sensor shaft connected to the input shaft, and a steering mechanism. And a worm wheel mechanism that includes a worm and a worm wheel that transmits the rotational force from the electric motor to the sensor shaft. An electric power steering apparatus rotatably supported by a needle bearing with a seal disposed inside a fitting portion between the housing and the column tube. 2. The electric power steering apparatus according to claim 1, wherein a collar is provided between the sensor shaft and the needle bearing.