JP2009166684A - Electric assist mechanism for electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric assist mechanism for an electric power steering device capable of transmitting the required steering auxiliary torque in a fitting part of an output shaft to a worm wheel and preventing occurrence of reduction of the strength and abnormal noise. <P>SOLUTION: The apex angles of uneven ridges of an output shaft side uneven part 91 formed on an end face of an annular expanded stepped part 51 and a wheel side uneven part 95 formed on an end face of a boss part 79 of a worm wheel 77 which are engaged with each other to prevent their relative rotation are formed to be ≤90°. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electric assist mechanism for an electric power steering device that applies a steering assist torque to an output shaft in accordance with detected steering torque, and more particularly to an improvement in a fitting portion between an output shaft and a worm wheel.

  In an electric assist mechanism for an electric power steering device, a steering torque generated by a driver turning a steering wheel is detected by a torque detection mechanism, and an electric motor is driven by a control device in accordance with the detected steering torque. In some cases, a steering assist torque is generated and transmitted to an output shaft via a worm gear reduction mechanism. In the electric power steering apparatus incorporating such an electric assist mechanism, when the driver rotates the steering wheel, the generated steering torque is output from the steering shaft, the output shaft connected to the steering shaft via the torsion bar, and the output shaft. Are transmitted to a lower steering shaft and a rack and pinion type steering gear connected via a universal joint to steer the traveling wheels.

  Here, the worm wheel of the worm gear speed reduction mechanism is composed of a metal core part fitted on the output shaft and a resin gear part fixed to the metal core part. Various ideas have been made in the fitting part with the part.

  For example, in Patent Document 1 (see FIG. 2 in the same document), a boss portion extending in the axial direction for press-fitting an output shaft is formed at the center of the core metal portion, and the outer peripheral surface portion of this boss portion is a bearing. A device that can be reduced in size while having a sufficient press-fitting allowance is shown.

In Patent Document 2, serrations are formed on one of the inner peripheral surface of the boss portion of the worm wheel and the outer peripheral surface of the output shaft, and the worm wheel and the output shaft are fitted by fitting with the enamel formed on the other. A device capable of greater torque transmission, fitted and fixed, is shown.
Japanese Patent Laid-Open No. 2004-203212 JP 2000-95122 A

  In recent years, electric power steering devices have been installed in large vehicles, and the steering assist torque required has increased accordingly.

  Even in the invention that enables miniaturization as in the conventional electric power steering device of Patent Document 1 described above, if the steering assist torque is transmitted only by cylindrical press-fitting of the worm wheel and the output shaft, the press-fitting length may be increased. There is a need to increase the press-fit diameter. Therefore, when the press-fitting length and the press-fitting diameter are limited in layout, there is a problem that a necessary steering assist torque cannot be secured. In addition, when the cored bar is fixed to the housing via a bearing, for the axial load applied to the output shaft, the fitting state can be obtained only by managing the press-fit load between the cored bar and the output shaft. It must be guaranteed, and when the press-fitting length is short, there is a problem that its management is very difficult.

  In the configuration of Patent Document 2 described above, a large steering assist torque can be transmitted with a short press-fitting length, but since it is necessary to increase the hardness on the serration side, a heat treatment such as quenching is necessary, which causes a cost increase. Become. Further, in the case of serration press-fitting, since the counterpart side is plastically deformed, there is a concern that the eccentricity or the fall of the worm wheel after press-fitting becomes large.

  Further, in order to eliminate the above-described conventional problems, uneven portions that mesh with each other are formed on the end surface of the annular diameter-enlarged stepped portion formed on the output shaft and the end surface in the axial direction of the boss portion of the worm wheel that contacts this. It is conceivable to prevent relative rotation of the output shaft and the worm wheel by molding. In the case of such a configuration, the above-mentioned problem can be solved, but due to a phase error at the time of assembling, an uneven contact such as contact with only one side of the uneven crest occurs, resulting in strength reduction and abnormal noise. . In addition, there is a problem in that the unevenness of the pitch when forming the concavo-convex part causes a mountain that does not mesh, resulting in a decrease in strength. In addition, it is easiest to form the irregularities on the end face by forging, but a very large load is required to form a high peak height.

  The present invention has been made in view of the above problems, and can transmit a steering assist torque required in a small size at a fitting portion between an output shaft and a worm wheel, and does not cause a decrease in strength or generation of abnormal noise. An object of the present invention is to provide an electric assist mechanism for an electric power steering device.

  In order to solve the above-described problems, in the present invention, the steering torque generated by the rotation of the steering wheel is detected by the torque detection mechanism, and the steering assist torque generated from the electric motor according to the detected steering torque is converted into the worm gear deceleration. In order to transmit to the output shaft through the mechanism, the output shaft is press-fitted into a boss portion formed at the center of the worm wheel of the worm gear reduction mechanism, and the end surface of the annular enlarged diameter step portion formed on the output shaft Further, in the electric assist mechanism for an electric power steering apparatus in which one axial end surface of the boss portion is in contact with the end surface of the annular diameter-expanded stepped portion, the output shaft side unevenness formed by radially extending protrusions And the one end face in the axial direction of the boss portion meshes with the output shaft side uneven portion, and the phase between the worm wheel and the output shaft is Molded wheel side uneven portion for preventing rotation of said output shaft uneven portion and the wheel-side uneven portion crest angle of the unevenness of the is characterized by being molded together below 90 degrees.

  In a preferred aspect of the present invention, the peak angle of the ridges of the unevenness is different between the output shaft side and the wheel side.

  According to the present invention, the steering assist torque required in a small size can be transmitted at the fitting portion between the output shaft and the worm wheel, and even if there is a slight phase error, the force in the phase correction direction due to the press-fitting load is reduced. It works strongly and is set at a regular position without causing a drop in strength or abnormal noise. Furthermore, it is easy to produce a peak height of the unevenness, and the molding load can be kept low.

  Moreover, according to the preferable aspect of this invention, even if there exists a pitch error, it can mesh | engage reliably in all the peaks, and does not cause a strength fall.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  First, an overall configuration of an electric power steering apparatus incorporating an electric assist mechanism for an electric power steering apparatus according to an embodiment of the present invention will be described with reference to FIG.

  FIG. 1 is a side view showing an example of a compartment side portion of an electric power steering apparatus incorporating an electric assist mechanism for an electric power steering apparatus according to an embodiment of the present invention.

  The electric power steering apparatus 1 is provided at a steering shaft 5 having a steering wheel 3 attached to a rear end portion, a hollow steering column 7 that rotatably supports the steering shaft 5 inside, and a front end portion of the steering column 7. And an electric assist mechanism 9 for assisting the steering force of the steering wheel 3. On the vehicle compartment side, the electric power steering device 1 is attached to the vehicle body side structural members 15 and 17 via a known bracket mechanism 11 that supports the steering column 7 and a pivot pin 13 provided in the electric assist mechanism 9. ing. In addition, the front-back direction of each member in description in this specification shall respond | correspond to the front-back direction of a vehicle.

  The bracket mechanism 11 includes a vehicle body side bracket 19 fixed to the vehicle body side structural member 15 and a column side bracket (not shown) fixed to the steering column 7. The bracket mechanism 11 includes a known mechanism (not shown) that can adjust the tilt position of the steering wheel 3 by operating the adjustment lever 21 to lock or unlock the column side bracket with respect to the vehicle body side bracket 19. Is provided. The pivot pin 13 forms a tilt pivot that becomes a swing fulcrum when the tilt position of the steering wheel 3 is adjusted. When adjusting the tilt position, the adjustment lever 21 is unlocked, the steering wheel 3 is swung together with the steering column 7 and the like, and the adjustment lever 21 is locked at a desired position. Fix the tilt position.

  The electric assist mechanism 9 includes an electric motor 23, a housing 25, an output shaft 27 extending through the inside of the housing 25, and the like. The detailed configuration will be described later. 27 is connected via a torsion bar, and a torque detection mechanism and a worm gear reduction mechanism are provided around both axes. The output shaft 27 is connected to a lower steering shaft 31 through a universal joint 29 at the front end, and the lower steering shaft 31 is connected to a rack and pinion type steering gear in front of the vehicle (not shown). Reference numeral 33 denotes a column cover that covers the electric power steering apparatus 1, and reference numeral 35 denotes a dashboard that partitions the vehicle compartment and the engine room.

  Steering torque generated when the driver rotates the steering wheel 3 is input from the steering shaft 5 to the electric assist mechanism 9, is increased inside the electric assist mechanism 9, and is transmitted to the output shaft 27 as steering assist torque. Further, it is transmitted from the output shaft 27 to the steering gear via the universal joint 29 and the lower steering shaft 31. In this way, the driver can steer the traveling wheels.

  Next, the configuration of the electric assist mechanism will be described with reference to FIG.

  2 is an enlarged cross-sectional view of the electric assist mechanism of the electric power steering apparatus of FIG. The illustration of the electric motor is omitted.

  The housing 25 of the electric assist mechanism 9 includes a gear housing 37 and a cover 39 fixed on the front side thereof. The gear housing 37 stores a worm gear reduction mechanism 41 described later in a space defined with the cover 39 on the front side, and stores a torque detection mechanism 43 described later on the rear side. At the rear end portion of the gear housing 37, a flange portion 45 that is formed by bending the front end of the steering column 7 and is outward in the radial direction of the column is fixed by a bolt 47. Further, in the vicinity of the rear end portion of the gear housing 37, there is a front end portion of the steering shaft 5 extending inside the steering column 7, and the steering shaft 5 serves as an input shaft for inputting steering torque to the electric assist mechanism 9. (Hereinafter, the steering shaft 5 is referred to as an input shaft).

  A hollow output shaft 27 extends inside the gear housing 37, and the front end portion of the output shaft 27 protrudes outside the housing 25. An annular diameter-enlarged stepped portion 51 is formed at a substantially central portion between the front and rear ends of the output shaft 27 by slightly expanding the outer peripheral surface portion of the output shaft in the radial direction. A rolling bearing 53 is interposed between the outer peripheral surface of the motor and the gear housing 37. Further, a rolling bearing 55 is interposed between the outer peripheral surface of the output shaft 27 in front of the annular diameter expanding step portion 51 and the cover 39. The output shaft 27 is rotatably supported with respect to the housing 25 and coaxially with the input shaft 5 via the pair of rolling bearings 53 and 55.

  The front end portion of the input shaft 5 has a diameter-expanded end portion (hereinafter referred to as a diameter-expanded end portion) 57 having an internal space where the front end surface side is open, and is drilled rearward in the axial direction continuously to the internal space. The bottomed hole 59 is provided. The rear end portion of the output shaft 27 is loosely fitted in the internal space of the enlarged diameter end portion 57. A base end portion of the torsion bar 61 is press-fitted and fixed to the bottomed hole 59. The torsion bar 61 extends forward in the inner space of the output shaft 27 formed in a hollow shape, and the tip end portion thereof is the output shaft. It is fixed to the front end portion of this by a fixing pin 63.

  A seal member 65 is attached to a position where the outer peripheral surface of the front end portion of the input shaft 5 and the inner peripheral surface of the steering column 7 are opposed to prevent dust and the like from entering the electric assist mechanism 9.

  The torque detection mechanism 43 provided in the gear housing 37 on the rear side of the rolling bearing 53 extends in the axial direction formed at equal intervals on the outer peripheral surface portion of the output shaft 27 on the rear side of the annular diameter enlarged step portion 51. Torque detection groove 67, sleeve 69 disposed radially outward of these torque detection grooves 67, torque detection coil 71 disposed radially outward of sleeve 69, and connection to this coil 71 The circuit board 73 for torque detection and a harness (not shown) for electrical connection with the outside are configured.

  The sleeve 69 is externally fitted and secured to the outer periphery of the enlarged diameter end portion 57 of the input shaft 5 on the rear end side by caulking or the like. The sleeve 69 has a plurality of rectangular shapes opposed to the torque detection groove 67 in the radial direction. A window 75 is formed. The torque detection coil 71 faces these windows 75 in the radial direction, and is attached to the gear housing 37 together with the circuit board 73 and the like.

  A worm wheel 77 is fitted on the output shaft 27 at a position between the rolling bearings 53 and 55. The worm wheel 77 includes a substantially disc-shaped cored bar part 81 integrally having a boss part 79 for press-fitting the output shaft 27 at the center, and a resin gear part 83 fixed to the outer peripheral part of the cored bar part 81. ing. The boss part 79 of the cored bar part 81 is formed thicker in the axial direction than the outer peripheral part of the cored bar part 81, and has a cylindrical hole inside. The boss 79 is fastened to the annular diameter enlarged step 51 of the output shaft 27 by the nut 85 via the rolling bearing 55, so that the worm wheel 77 is fixed to the output shaft 27 and rotates together with the output shaft 27. It has become. The resin gear portion 83 of the worm wheel 77 meshes with a worm 87 connected to the drive shaft of the electric motor 23. The worm 87 and the worm wheel 77 constitute a worm gear reduction mechanism 41 of the electric assist mechanism 9.

  The electric assist mechanism 9 is configured as described above, and the steering torque generated when the driver rotates the steering wheel 3 is transmitted from the input shaft 5 to the torsion bar 61 and the output shaft 27. At this time, the steering torque is detected by the torque detection mechanism 43, and an appropriate drive signal is output by a control device (not shown) according to the detected torque to rotate the electric motor 23, and the rotational force of the electric motor 23 is converted to the worm gear reduction mechanism 41. To the output shaft 27 as steering assist torque. Appropriate steering assist torque can be applied to the output shaft 27 by appropriately controlling the rotational force and the rotational direction of the electric motor 23.

  Next, a coupling method between the output shaft of the electric assist mechanism and the worm wheel will be described with reference to FIGS.

  FIG. 3A is an exploded perspective view showing an output shaft of the electric assist mechanism of FIG. 2, and FIG. 3B is an enlarged view of the rotation stopping means. 4A is an exploded perspective view showing a worm wheel of the electric assist mechanism of FIG. 2, and FIG. 4B is an enlarged view of the rotation stopping means. FIG. 5 is a perspective view showing a state where the output shaft of FIG. 3 and the worm wheel of FIG. 4 are fitted together and assembled.

  As shown in FIGS. 3A and 3B, the output shaft 27 has a cylindrical portion 89 for fixing the worm wheel 77 at a substantially central portion between the front and rear ends, and a rear adjacent portion of the cylindrical portion 89. The above-described annular diameter expanding step portion 51 and the above-described torque detecting groove 67 are disposed in the rear portion of the annular diameter expanding step portion 51. When the output shaft 27 and the worm wheel 77 are fitted together, the cylindrical portion 89 of the output shaft 27 is press-fitted into the boss portion 79 of the metal core portion 81 of the worm wheel 77, and the axial direction rear end surface of the boss portion 79 is pressed. The front end surface in the axial direction of the annular enlarged diameter step portion 51 is brought into contact. On the front end surface in the axial direction of the annular diameter-enlarged stepped portion 51, an output shaft side uneven portion 91 is formed which is formed of a radially extending protrusion, and is formed in a tooth shape that is repeatedly uneven in the circumferential direction.

  On the other hand, as shown in FIGS. 4A and 4B, the rear end surface in the axial direction of the boss portion 79 of the cored bar portion 81 projects rearward in the axial direction to form an annular projecting portion 93. On the radially inner side of the annular projecting portion 93, the wheel side is opposed to and meshed with the output shaft side uneven portion 91 formed on the axial front end surface of the annular enlarged stepped portion 51 of the output shaft 27. An uneven portion 95 is formed.

  When the output shaft 27 is press-fitted into the worm wheel 77, the output shaft side uneven portion 91 and the wheel side uneven portion 95 mesh with each other, thereby constituting a rotation stop means for preventing relative rotation. The worm wheel 77 rotates integrally.

  When the output shaft 27 and the worm wheel 77 are assembled and assembled with each other, as shown in FIG. 5, first, output is performed using a jig or the like so that the output shaft side uneven portion 91 and the wheel side uneven portion 95 are engaged with each other. The shaft 27 is press-fitted into the worm wheel 77 from the front end side. After the press-fitting, a rolling bearing 55 for supporting the output shaft 27 is fitted from the front end side of the output shaft 27, and is fastened and fixed by a nut 85 screwed to the output shaft 27. In addition, although the screw | thread screwed together with the nut 85 is shape | molded by the outer peripheral surface part of the output shaft 27, illustration is abbreviate | omitted in Fig.3 (a). Here, the worm wheel 77 is also fastened to the annular diameter-enlarged stepped portion 51 of the output shaft 27 by the nut 85 via the rolling bearing 55, so that both concavo-convex portions of the rotation stopping means are rotated by the rotation of the worm wheel 77 and the output shaft 27. Even if an axial force is generated in 91 and 95, the engagement is not disengaged because it is regulated by the nut 85.

  Next, the shape of the unevenness of the output shaft side uneven portion and the wheel side uneven portion that mesh with each other will be described with reference to FIGS. 6 and 7.

  FIG. 6A is an enlarged view of a portion along the circumference of both concavo-convex portions viewed radially inward with the output shaft side concavo-convex portion of FIG. 3 and the wheel-side concavo-convex portion of FIG. 4 engaged. There is an example in which the peak angle of the uneven peak is 90 degrees or less. FIG. 6B is a reference example in which the apex angle of the uneven peak is larger than 90 degrees.

  FIG. 7A is an enlarged view of a portion along the circumference of both concavo-convex portions seen radially inward with the output shaft side concavo-convex portion of FIG. 3 and the wheel-side concavo-convex portion of FIG. 4 engaged. There is an example in which the apex angle of the uneven peak is changed between the output shaft side and the wheel side. FIG. 7B is a reference example in which the apex angles of the uneven peaks are the same on the output shaft side and the wheel side.

  6 (a) and 6 (b), symbol A indicates the apex angle of the mountain. An arrow F indicates a press-fit load, an arrow X indicates a force in a correction direction (that is, a circumferential direction) that acts on the output shaft side uneven portion due to the press-fit load, and an arrow Y indicates a correction direction that acts on the wheel-side uneven portion due to the press-fit load (that is, (Circumferential direction) force.

  In the present embodiment, as shown in FIG. 6 (a), the peak angle A of the concavo-convex portions of both the concavo-convex portions 91 and 95 is formed to be 90 degrees or less (A ≦ 90 °). Even if there is a phase error, the forces X and Y acting in the correction direction due to the press-fit load F are large, so that the concavo-convex portions are shifted from each other and set at the normal position. Further, when forging, the peak angle of the peak is an acute angle, so that the molding load can be kept low and the peak height can be increased.

  If the peak angle is larger than 90 degrees (A> 90 °) as in the reference example shown in FIG. 6B, the forces X and Y acting in the correction direction are small, so the position is corrected to the normal position. Hard to be done. In addition, since the peak angle of the peak is obtuse during forging, a very large load is required to form a high peak.

  Moreover, in this embodiment, as shown to Fig.7 (a), the peak angle of the uneven | corrugated peak of both the uneven parts 91 and 95 is changed on the output-shaft side and the wheel side. For example, as shown in FIG. 7A, by making the apex angle of the peak on the output shaft side slightly smaller than that on the wheel side, all the peaks on the output shaft side mesh with the trough on the wheel side, and the strength can be increased.

  As in the reference example shown in FIG. 7B, when the apex angle of the uneven peak is the same on the output shaft side and the wheel side, it does not mesh as in the portion Z surrounded by the illustrated ellipse. Mountains are formed, and there is a concern about strength reduction.

  As described above, according to the present embodiment, the steering assist torque required in a small size can be transmitted at the fitting portion between the output shaft and the worm wheel, and is resistant to an axial load. Electric assist for electric power steering devices that does not require heat treatment such as load management or quenching, can suppress the eccentricity and collapse of the worm wheel and output shaft, and does not cause strength reduction or abnormal noise A mechanism can be realized.

  In addition, this invention is not limited to embodiment mentioned above, A various deformation | transformation is possible.

It is a side view showing an example of a compartment side portion of an electric power steering device incorporating an electric assist mechanism for an electric power steering device according to an embodiment of the present invention. It is sectional drawing which expands and shows the electric assist mechanism of the electric power steering apparatus of FIG. (A) is an exploded perspective view showing the output shaft of the electric assist mechanism of FIG. 2, (b) is an enlarged view of the rotation stop means. (A) is an exploded perspective view showing the worm wheel of the electric assist mechanism of FIG. 2, (b) is an enlarged view of the rotation stop means. FIG. 5 is a perspective view showing a state in which the output shaft of FIG. 3 and the worm wheel of FIG. 4 are fitted together and assembled. (A) is the enlarged view which looked at the part along the periphery of both uneven | corrugated | grooved parts in the radial direction in the state which meshed | engaged the output side uneven | corrugated | grooved part of FIG. 3, and the wheel side uneven | corrugated | grooved part of FIG. This is an example in which the apex angle of the uneven mountain is 90 degrees or less. (B) is a reference example in which the peak angle of the uneven peak is larger than 90 degrees. (A) is the enlarged view which looked at the part along the periphery of both uneven | corrugated | grooved parts in the radial direction in the state which meshed | engaged the output side uneven | corrugated | grooved part of FIG. 3, and the wheel side uneven | corrugated | grooved part of FIG. This is an example in which the apex angle of the uneven peak is changed between the output shaft side and the wheel side. (B) is a reference example in which the peak angles of the uneven peaks are the same on the output shaft side and the wheel side.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electric power steering device 3 ... Steering wheel 5 ... Steering shaft 7 ... Steering column 9 ... Electric assist mechanism 23 ... Electric motor 25 ... Housing 27 ··· Output shaft 41 ··· Worm gear reduction mechanism 43 ··· Torque detection mechanism 51 ··· Ring-shaped enlarged diameter stepped portions 53 and 55 · · · Rolling bearing 77 ··· Worm wheel 79 ··· Boss portion 87 ··· Worm 91 ··· Output shaft side uneven portion 95 ··· Wheel side uneven portion

Claims (2)

In order to detect the steering torque generated by the rotation of the steering wheel by the torque detection mechanism and transmit the steering assist torque generated from the electric motor according to the detected steering torque to the output shaft via the worm gear reduction mechanism. The output shaft is press-fitted into a boss portion formed at the center of the worm wheel of the worm gear speed reduction mechanism, and one axial end surface of the boss portion is formed on an end surface of an annular diameter expanding step portion formed on the output shaft. In the electric assist mechanism for the electric power steering device in contact,
On the end surface of the annular diameter-enlarging step portion, an output shaft side uneven portion including a radially extending protrusion is formed,
On the one axial end surface of the boss portion, a wheel side uneven portion is formed that meshes with the output shaft side uneven portion and prevents relative rotation between the worm wheel and the output shaft,
An electric assist mechanism for an electric power steering apparatus, wherein apex angles of the ridges of the output shaft side uneven portion and the wheel side uneven portion are each formed to be 90 degrees or less.   2. The electric assist mechanism for an electric power steering apparatus according to claim 1, wherein an apex angle of the uneven mountain is different between an output shaft side and a wheel side.

Images