JP2009056906A - Motor-driven power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a small-sized motor-driven power steering device with a structure easy in the adjustment of buffering performance at a low cost, which can effectively prevent the generation of noise called a rattle sound and vibration at a torque joint section 19 provided between the tip of an output shaft 10 and the base end of a worm shaft 6. <P>SOLUTION: A sleeve 24 of an elastic material is externally fitted to a rugged part 23 which has the same rugged phase as that of a male spline tooth 21 and is formed at the tip of a spline shaft 12a provided at the tip of the output shaft 10 and at a portion projecting more than a portion where the male spline tooth 21 in the axial direction is formed. The sleeve 24 is pressed elastically and radially inward with the blade tip of the female spline tooth 22 formed on the inner circumferential surface of a spline hole 11a formed at the base end of the worm shaft 6. This structure makes the sleeve 24 withstand relative displacement in the rotary direction between the output shaft 10 and the worm shaft 6, thus solving the problem. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The electric power steering apparatus according to the present invention is used as a steering apparatus for an automobile, and uses an electric motor as auxiliary power to reduce the force required for the driver to operate the steering wheel. is there. The present invention suppresses the generation of unpleasant noise called rattling noise at the spline engaging portion between the output shaft of the electric motor and the worm shaft of the speed reducer constituting such an electric power steering apparatus. It was invented with the intention of realizing such a structure.

  A power steering device is widely used as a device to reduce the force required for the driver to operate the steering wheel when giving a steering angle to the steered wheels (usually the front wheels except for special vehicles such as forklifts) Has been. In addition, an electric power steering apparatus that uses an electric motor as an auxiliary power source in such a power steering apparatus has begun to spread in recent years. Various structures of the electric power steering apparatus are known. In any structure, the electric motor is attached to the rotating shaft that is rotated by the operation of the steering wheel and gives a steering angle to the steered wheel as the wheel rotates. Auxiliary power is applied through a speed reducer. In general, a worm reducer is used as the reducer. In the case of an electric power steering device using a worm speed reducer, a worm that is rotationally driven by the electric motor and a worm wheel that rotates together with the rotating shaft are engaged with each other, and auxiliary power of the electric motor is applied to the rotating shaft. Communicate freely.

  For example, Patent Document 1 describes an electric power steering device as shown in FIGS. A front end portion of a steering shaft 2 that is a rotating shaft that is rotated in a predetermined direction by the steering wheel 1 is rotatably supported inside the housing 3, and the worm wheel 4 is fixed to this portion. Worm teeth 5 meshing with the worm wheel 4 are provided in the axial direction intermediate portion of the worm shaft 6, and both ends of the worm 8 driven to rotate by the electric motor 7 are paired with a pair of rolling bearings 9 a such as a deep groove ball bearing, 9b is rotatably supported in the housing 3.

  In order to rotationally drive the worm 8 by the output shaft 10 of the electric motor 7, a spline hole 11 is formed in the proximal end portion of the worm shaft 6 so as to open to the proximal end surface of the worm shaft 6. A spline shaft 12 is formed at the tip of the output shaft 10. The spline shaft portion 12 and the spline hole 11 are spline-engaged so that the output shaft 10 and the worm shaft 6 are freely coupled to transmit rotational force.

  Further, in the case of the conventional structure shown in FIG. 8, in order to eliminate backlash at the meshing portion between the worm wheel 4 and the worm tooth 5, the tip portion (the right end portion in FIG. 8) of the worm shaft 6 is connected to the worm shaft. The wheel 4 is elastically pressed toward the wheel 4. That is, the pressing piece 13 is externally fitted to a portion protruding from the leading end side rolling bearing 9 a at the tip of the worm shaft 6, and an elastic member such as a coil spring 14 is provided between the pressing piece 13 and the housing 3. Provided. The worm teeth 5 are pressed against the worm wheel 4 by the coil spring 14 through the pressing piece 13. With such a configuration, backlash between the worm teeth 5 and the worm wheel 4 is suppressed, and the meshing portion of the worm wheel 4 and the worm teeth 5 is activated when the electric motor 7 is started or when the rotation direction is changed. The occurrence of rattling noise is suppressed. When the structure for eliminating the backlash is provided, the center axis of the worm shaft 6 and the center axis of the output shaft 10 are deviated from each other, but this deviation is very slight. Virtually concentric.

  In the electric power steering apparatus as described above, it is possible to suppress the occurrence of rattling noise at the meshing portion between the worm wheel 4 and the worm tooth 5, but the spline engagement between the spline shaft portion 12 and the spline hole 11. Generation of rattling noise at the joint cannot be suppressed. In particular, it is necessary to provide a certain gap in the spline engaging portion. This is because the spline hole 11 and the spline shaft 12 need to be easily engaged in spline engagement, and backlash between the worm wheel 4 and the worm teeth 5 is further reduced. In order to suppress this, it is necessary to swing and displace the tip of the worm shaft 6 toward the worm wheel 4. Based on the clearance between the spline engaging portions provided as described above, when the electric motor 7 is started up or when the rotation direction is changed, the spline engaging portions use the side surfaces of the male spline teeth and the female spline teeth. Noise and vibration are generated based on the collision with the side.

  A torque joint for transmitting torque between the output shaft of the electric motor and the worm shaft of the worm speed reducer, and has been patented as a structure to prevent the generation of noise and vibration called rattling noise. Structures described in documents 2 to 6 are known. Among these, the structure described in Patent Document 2 is formed by sandwiching an elastic body between the end surfaces of a pair of shafts that are coupled so as to be able to transmit torque to each other. In the case of such a structure, even if shakiness in the axial direction can be prevented, shakiness in the rotational direction cannot be prevented. Therefore, noise generated when the electric motor 7 is started or when the rotational direction is changed. And vibration cannot be suppressed.

  Further, Patent Document 3 describes a structure in which a pair of connecting members 15a and 15b are engaged with each other through an elastic member 16 as shown in FIG. In this conventional structure, the connecting members 15a and 15b and the elastic member 16 are engaged with each other with respect to the torque transmission direction. According to such a structure described in Patent Document 3, it is possible to suppress noise and vibration generated when the electric motor 7 is started up and when the rotation direction is changed. However, the structure is complicated, both parts production and assembly work become troublesome, and not only costs increase, but also the radial and axial dimensions of the joints increase, making it difficult to assemble in a limited installation space. Become. In addition, in order to adjust the shock absorbing performance to mitigate the impact in the rotational direction, it is necessary to replace all the parts 15a, 15b, and 16, so that the parts can be shared between the electric power steering devices having different specifications. There are also problems such as difficulty in drawing. Such a problem also occurs in the structures of the inventions described in Patent Documents 4 to 6.

JP 2004-306898 A JP 2002-255047 A JP 2006-177505 A Special table 2002-518242 gazette JP-A-2005-306141 JP 2006-183676 A

  In view of the circumstances as described above, the present invention devised the state of assembly of the elastic member to the torque joint portion provided between the tip end portion of the output shaft and the base end portion of the worm shaft. The present invention has been invented to achieve a low-cost structure that can effectively prevent the generation of noise and vibration called rattling noise, and that is small in size and easy to adjust the buffering performance.

The electric power steering apparatus of the present invention includes a housing, a rotating shaft, a worm wheel, a worm, an electric motor, and a torque joint portion, as in the case of a conventionally known electric power steering apparatus.
Of these, the housing is supported by a fixed portion and does not rotate.
The rotating shaft is provided so as to be rotatable with respect to the housing, and is rotated by an operation of a steering wheel, and gives a steering angle to the steered wheels as it rotates. As such a rotating shaft, in addition to the steering shaft 2 shown in FIG. 7, the intermediate shaft 17, the input shaft (pinion shaft) of the steering gear unit 18 and the like can be adopted. Of course, the fixed portion for supporting the housing differs depending on which of the rotating shafts.
The worm wheel is supported on a part of the rotating shaft inside the housing and concentrically with the rotating shaft, and rotates together with the rotating shaft.
The worm is provided with worm teeth at an intermediate portion in the axial direction of the worm shaft. Then, in a state where the worm teeth are engaged with the worm wheel, the axial end portion of the worm shaft is rotatably supported with respect to the housing by a bearing.
The electric motor has an output shaft concentric with the worm shaft for rotationally driving the worm.

  Further, the torque joint portion is provided between the distal end portion of the output shaft and the proximal end portion of the worm so as to freely transmit torque from the output shaft to the worm. And the said torque coupling part is the bottomed spline hole provided in the state opened to the end surface of the said edge part in one edge part of the front-end | tip part of this output shaft, and the base end part of the said worm shaft. And a spline shaft portion that is provided at the other end portion of the tip end portion of the output shaft and the base end portion of the worm shaft and engages with the spline hole so as to transmit torque.

In particular, in the electric power steering apparatus according to the present invention, an elastic sleeve is externally fitted to a portion protruding in the axial direction from the portion where the male spline teeth are formed at the tip of the spline shaft portion. ing. The sleeve is elastically pressed toward the inside in the radial direction by the cutting edge of the female spline teeth.
In order to elastically press the sleeve in this way, as described in claim 2, the outer diameter of the sleeve before fitting into the spline shaft portion and being pushed into the spline hole is set to the male diameter. It is less than the diameter of the cutting edge circle of the spline teeth and larger than the diameter of the cutting edge circle of the female spline teeth. The inner diameter of the sleeve is made smaller than the diameter of the cutting edge circle of the female spline teeth.

Further, when the present invention as described above is carried out, preferably, a male spline-shaped concavo-convex portion is formed at a portion of the spline shaft portion where the sleeve is externally fitted, as described in claim 3. . The concave and convex portions are smaller in diameter than the male spline teeth, and have the same pitch and the same phase as the male spline teeth.
Further, when the present invention as described above is carried out, as described in claim 4, between the tip end surface in the axial direction of the spline shaft portion where the male spline teeth are formed and the back end surface of the spline hole. Thus, the sleeve can be elastically compressed in the axial direction.
Further, when carrying out the invention described in claim 4, for example, as described in claim 5, a sleeve having a cylindrical portion, a closing portion, and a projecting piece is used as the sleeve. You can also do things. Among these, the cylindrical portion is pressed in the radial direction between the outer peripheral surface of the tip end portion of the spline shaft portion and the cutting edge of the female spline teeth. Further, the closing portion closes one axial end opening of the cylindrical portion. Further, the projecting piece is provided on the opposite side surface in the axial direction of the cylindrical portion of the both side surfaces in the axial direction of the closing portion so as to protrude to the opposite side to the cylindrical portion. Then, the end of the cylindrical portion is abutted against the tip end surface in the axial direction of the portion where the male spline teeth are formed, and the end of the projecting piece is abutted against the back end surface of the spline hole.

According to the electric power steering device of the present invention having the above-described configuration, noise or vibration called rattling noise is generated at the torque joint portion provided between the distal end portion of the output shaft and the proximal end portion of the worm shaft. It is possible to effectively prevent the occurrence of this, and to realize a small structure that can easily adjust the buffer performance at a low cost.
First, the noise and vibration are caused by the resistance of the sleeve, which is elastically pressed radially inward by the blade edge of the female spline teeth, to the relative displacement of the female spline teeth and the male spline teeth in the rotational direction. It is planned by generating. That is, the cutting edge of the female spline teeth bites into the outer peripheral surface of the sleeve as the sleeve is pressed inward in the radial direction. Therefore, resistance against the displacement of the female spline teeth with respect to the rotational direction is generated with respect to the sleeve. Further, the inner peripheral surface of the sleeve frictionally engages with the outer peripheral surface of the portion protruding in the axial direction from the portion where the male spline teeth are formed at the tip end portion of the spline shaft portion. For this reason, resistance against rotation of this portion with respect to the sleeve is also generated. As a result, this sleeve creates resistance against the relative displacement of the two spline teeth in the rotational direction, preventing the circumferential side surfaces of the two spline teeth from colliding with each other vigorously, thereby preventing the noise and vibration. Can be suppressed.

  Since the sleeve is a small part and the space for assembling the sleeve is not bulky, the torque joint portion can be made compact even if a buffer mechanism for suppressing the noise and vibration is provided. Further, the buffering performance, which is the level of suppressing the noise and vibration by the buffer mechanism, can be adjusted by the thickness of the sleeve and the material (elasticity) of the sleeve. In other words, in order to adjust the cushioning performance, the diameter of the cutting edge circle of the female spline teeth and the outer diameter of the portion protruding in the axial direction from the portion where the male spline teeth are formed at the tip of the spline shaft portion are set. There is no need to change. For this reason, it is easy to make parts common between the electric power steering apparatuses having different specifications, and it is easy to reduce the cost of the electric power steering apparatus including the buffer mechanism.

[First example of embodiment]
1 to 5 show a first example of an embodiment of the present invention. The electric power steering apparatus according to the present embodiment is characterized in that the ratchet noise is generated by a torque joint portion 19 provided between the distal end portion of the output shaft 10 of the electric motor 7 and the proximal end portion of the worm shaft 6 of the worm 8. Assemble between the outer peripheral surface of the spline hole 11a and the outer peripheral surface of the spline shaft portion 12a in order to realize a compact and easy-to-adjust cushioning performance that can effectively prevent noise and vibration. The structure of the buffer mechanism 20 is devised. In addition, since the structure and operation of the entire electric power steering apparatus are the same as those of the conventional structure described above, illustrations and descriptions regarding the same parts as those of the conventional structure are omitted or simplified. The explanation will focus on the part. 7 to 8 and FIG. 1 (and FIG. 6 to be described later) are different in the mounting direction of the electric motor 7 with respect to the housing 3, but this point is appropriately changed in design according to the automobile to be installed. Therefore, it is not related to the characteristic part of the present invention.

  In the case of the structure of this example, as shown in FIGS. 1 to 3, a spline hole 11 a is opened at the base end portion of the worm shaft 6, and the worm shaft 6 is concentric with the base end surface. Is formed. Further, a spline shaft portion 12 a is formed concentrically with the output shaft 10 at the distal end portion of the output shaft 10 of the electric motor 7. Then, the male spline teeth 21 formed on the outer peripheral surface of the spline shaft portion 12a and the female spline teeth 22 formed on the inner peripheral surface of the spline hole 11a are spline-engaged, whereby the output shaft 10 and the worm are The shaft 6 is coupled so as to be able to transmit rotational force. The above configuration is a torque coupling portion that freely couples transmission of rotational force between the distal end portion of the output shaft of the electric motor and the proximal end portion of the worm shaft in the conventionally known electric power steering apparatus. The structure is the same.

In particular, in the case of this example, the male spline-like (or external gear-like) irregularities are formed at the tip end portion of the spline shaft portion 12a in the portion protruding in the axial direction from the portion where the male spline teeth 21 are formed. A portion 23 is formed. The uneven portion 23 has a smaller diameter than the male spline teeth 21 and is formed at the same pitch and the same phase as the male spline teeth 21. The maximum outer diameter (diameter of cutting edge circle) D ₂₃ of the concave-convex portion 23 is smaller (D ₂₃ <d ₂₁₎ than the diameter d ₂₁ of root circle of the male spline teeth 21.

A sleeve 24 made of an elastic material such as an elastomer such as rubber or vinyl is externally fitted to the uneven portion 23. The sleeve 24 has a round bowl shape including a cylindrical portion 25 and a closing portion 26. Such a sleeve 24 is attached to the distal end portion of the spline shaft portion 12a as shown in FIGS. The inner diameter of the cylindrical portion 25 in the free state is the same as or slightly smaller than the maximum outer diameter D _{23 of the} uneven portion 23 so that the cylindrical portion 25 can be externally fitted to the uneven portion 23 without rattling. I have to. In this manner, the outer diameter D ₂₅ of the cylindrical portion 25 is regulated as follows in a state in which the cylindrical portion 25 is externally fitted to the uneven portion 23 (before being pushed into the spline hole 11a). Yes. That is, the outer diameter D ₂₅ of the cylindrical portion 25 is equal to or less than the diameter D ₂₁ of the cutting edge circle of the male spline teeth 21 and larger than the diameter d ₂₂ of the cutting edge circle of the female spline teeth 22 (D ₂₁ ≧ D ₂₅ > d ₂₂ ). The inner diameter R ₂₅ of the cylindrical portion 25 is smaller than the diameter d ₂₂ of the cutting edge circle of the female spline teeth 22 (R ₂₅ <d ₂₂ ).

  By restricting the dimensions of the respective portions as described above, the cylindrical portion 25 is moved into the female spline as the cylindrical portion 25 of the sleeve 24 fitted on the concave and convex portion 23 is pushed into the spline hole 11a. The tooth 22 is elastically pressed inward in the radial direction by the cutting edge of the tooth 22. Further, the phase of the female spline teeth 22 (projection) and the phase of the projection of the concavo-convex part 23 are shifted by the opposite pitch. The cylindrical portion 25 is pressed radially inward by the protrusions of the female spline teeth 22 and radially outward by the protrusions of the uneven portion 23. As a result, the cross-sectional shape of the cylindrical portion 25 with respect to the virtual plane orthogonal to the central axis in a state where the cylindrical portion 25 is pushed into the concave portion of the spline hole 11a has a waveform as shown in FIG. When trying to relatively displace the female spline teeth 22 and the concavo-convex portion 23 in the rotational direction from the state shown in FIG. 5, a part of the cylindrical portion 25 is elastically compressed. . Accordingly, resistance against relative rotation of the female spline teeth 22 and the concave-convex portion 23 acts. For this reason, the circumferential side surface of the female spline teeth 22 and the circumferential side surface of the male spline teeth 21 rotating together with the concave and convex portion 23 do not collide with force. As a result, noise and vibration are generated at the spline engaging portion between the spline shaft portion 12a and the spline hole 11a at the moment when the output shaft 10 of the electric motor 7 is started or when the rotation direction is changed. Can be suppressed.

  Further, the sleeve 24 including the cylindrical portion 25 is a small part, and the space for assembling the sleeve 24 is not bulky. Therefore, even if a buffer mechanism for suppressing the noise and vibration is provided, the spline shaft portion 12a The torque joint portion 19 including the spline hole 11a can be configured in a small size. Further, the buffer performance, which is the level of suppressing the noise and vibration by the buffer mechanism, can be adjusted by the radial thickness of the cylindrical portion 25 constituting the sleeve 24 and the material (elasticity) of the sleeve 24. In other words, in order to adjust the buffering performance, the diameter of the cutting edge circle of the female spline teeth 22 or the portion protruding in the axial direction from the portion where the male spline teeth 21 are formed at the tip of the spline shaft portion 12a There is no need to change the outer diameter. For this reason, it is easy to make parts common between the electric power steering apparatuses having different specifications, and it is easy to reduce the cost of the electric power steering apparatus including the buffer mechanism.

In addition, the base half part of the sleeve whose axial direction length is longer than the case of illustration can also be externally fitted in the uneven | corrugated | grooved part 23 provided in the front-end | tip part of the said spline shaft part 12a. And the cylindrical part which comprises the said long sleeve makes the level | step difference surface 27 provided between the part which formed the male spline tooth | gear 21 in the said spline shaft part 12a, and the said uneven | corrugated | grooved part 23, and the back end surface of the said spline hole 11a. 29 can also be elastically compressed in the axial direction. In this case, the sleeve is composed of only the cylindrical portion, and both end edges in the axial direction of the cylindrical portion are elastically compressed between the step surface 27 and the back end surface of the spline hole 11a.
Alternatively, as shown by a chain line in FIG. 4, a protruding piece 28 is provided on the opposite side surface in the axial direction of the cylindrical portion 25 of both sides in the axial direction of the closing portion 26 so as to protrude to the opposite side of the cylindrical portion 25. You can also. And while the edge of this cylindrical part 25 is abutted on the said level | step difference surface 27, the front-end | tip part of the said protrusion 28 is abutted on the back end surface 29 of the spline hole 11a.
If these structures are employed, it is possible to prevent the spline shaft portion 12a and the worm shaft 6 from rattling in the axial direction.

[Second Example of Embodiment]
FIG. 6 shows a second example of the embodiment of the present invention. In the case of this example, a spline hole 11b is formed on the output shaft 10a side of the electric motor 7, and a spline shaft portion 12b is formed on the base end portion of the worm shaft 6a. Since the configuration and operation other than the point that the member for providing the spline hole and the spline shaft portion is the reverse of the first example of the above-described embodiment is the same as the case of the first example, overlapping illustrations and explanations are provided. Is omitted.

The figure equivalent to the expanded AA cross section of FIG. 7 which shows the 1st example of embodiment of this invention. The B section enlarged view of FIG. Sectional drawing similarly shown in the state before a combination. The perspective view which similarly takes out and shows a spline shaft and a sleeve. CC sectional drawing of FIG. The figure similar to FIG. 1 which shows the 2nd example of embodiment of this invention. The partial cutaway side view of the whole structure of the electric power steering device which shows the 1st example of conventional structure. The expanded AA sectional view of FIG. The disassembled perspective view of the joint part which shows the 2nd example of conventional structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering wheel 2 Steering shaft 3 Housing 4 Worm wheel 5 Worm tooth | gear 6, 6a Worm shaft 7 Electric motor 8 Worm 9a, 9b Rolling bearing 10, 10a Output shaft 11, 11a, 11b Spline hole 12, 12a, 12b Spline shaft part 13 Pressing piece 14 Coil springs 15 a and 15 b Connecting member 16 Elastic member 17 Intermediate shaft 18 Steering gear unit 19 Torque joint portion 20 Buffer mechanism 21 Male spline teeth 22 Female spline teeth 23 Concavity and convexity 24 Sleeve 25 Cylindrical portion 26 Closure portion 27 Stepped surface 28 Projection piece 29

Claims (5)

  A housing that is supported by a fixed portion and does not rotate; a rotating shaft that is rotatably provided to the housing and is rotated by an operation of a steering wheel; A worm wheel that is supported concentrically with the rotary shaft inside the housing and rotates together with the rotary shaft, and a worm tooth is provided at an axially intermediate portion of the worm shaft. In a state where the worm teeth are engaged with the worm wheel, the worm shaft is rotatably supported with respect to the housing by a bearing at the axial end portion of the worm shaft, and the output shaft is driven to rotate the worm. An electric motor arranged concentrically with the worm shaft, and between the distal end portion of these output shafts and the proximal end portion of the worm shaft, this warp A torque coupling portion that allows transmission of torque to the shaft, and the torque coupling portion is connected to one end of the distal end portion of the output shaft and the proximal end portion of the worm shaft. Provided at the other end of the spline hole formed with female spline teeth on the inner peripheral surface and the distal end of the output shaft and the proximal end of the worm shaft. In addition, in the electric power steering apparatus comprising a spline shaft portion formed on the outer peripheral surface with male spline teeth that are spline engaged with the spline hole so that torque can be transmitted, the tip portion of the spline shaft portion An elastic sleeve is externally fitted to the portion protruding in the axial direction from the portion where the male spline teeth are formed, and this sleeve is elastically pressed radially inward by the cutting edge of the female spline teeth. The Electric power steering apparatus according to claim that that.   The outer diameter of the sleeve before being fitted onto the spline shaft and being pushed into the spline hole is equal to or smaller than the diameter of the cutting edge circle of the male spline teeth, and larger than the diameter of the cutting edge circle of the female spline teeth, and The electric power steering apparatus according to claim 1, wherein an inner diameter of the sleeve is smaller than a diameter of a cutting edge circle of the female spline teeth.   The male spline-shaped uneven part which is smaller in diameter than the male spline teeth and has the same pitch and the same phase as the male spline teeth is formed in a portion of the spline shaft portion where the sleeve is externally fitted. The electric power steering apparatus described in any one of 1-2.   The sleeve is elastically compressed in the axial direction between the axial front end surface of the portion of the spline shaft portion where the male spline teeth are formed and the back end surface of the spline hole. The electric power steering apparatus described in any one of the items.   A cylindrical portion in which the sleeve is pressed in a radial direction between the outer peripheral surface of the tip end portion of the spline shaft portion and the cutting edge of the female spline tooth; a closing portion that closes one axial opening of the cylindrical portion; and an axis of the closing portion Of the two side surfaces in the direction of the cylindrical portion and the axially opposite side surface, and a protruding piece protruding to the opposite side of the cylindrical portion. 5. The electric power steering apparatus according to claim 4, wherein the electric power steering device is abutted against an axial front end surface and a front end portion of the projecting piece is abutted against a back end surface of the spline hole.

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