JP4051998B2 - Reduction mechanism of electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a speed reduction mechanism for an electric power steering apparatus.
[0002]
[Prior art]
As a conventional key lock mechanism for a steering shaft, for example, Japanese Utility Model Laid-Open No. 3-24959 discloses the one shown in FIG. In the figure, a lock bracket 21 formed by pressing a metal plate into an elliptical cylinder shape and having an engagement hole 21a with which an inner end portion of a lock pin 22 can be engaged is provided at a part of the steering shaft 20. Is fixed to the outer peripheral surface of the intermediate portion by welding. Reference numeral 23 is an ignition switch, 24 is a key, and 25 is a steering column.
[0003]
In Japanese Patent Laid-Open No. 2001-163187, the steering shaft is relatively rotated about the column axis in a lock member that is inserted into the steering column so as to be relatively movable in the column axis direction and prevented from rotating relative to the column axis. Steering shaft key that is inserted in such a way that it is displaced in the column axis direction between the locked position and unlocked position by interlocking with the transmission mechanism that operates in accordance with the opening / closing operation of the ignition switch by the opening / closing mechanism. A locking mechanism is disclosed. The lock member in this lock position is connected to a receiving part that can rotate together with the steering shaft so that it cannot rotate relative to the center of the column axis. By releasing the unlocked position, the locking member is rotated relative to the center of the column axis. It is the structure to do.
[0004]
[Problems to be solved by the invention]
However, in the conventional key lock mechanism for the steering shaft, the lock bracket 21 is welded and fixed to the steering shaft, or the steering shaft is provided with a lock bracket and a torque limiter so as to be relatively rotatable. The lock mechanism and the surrounding structure are complicated and the number of parts increases, thereby occupying space and limiting the collapse stroke of the steering shaft.
[0005]
In particular, in the case of an electric power steering device, since a speed reduction mechanism including a worm and a worm wheel is equipped, if a key lock mechanism is provided on a steering shaft (or a transmission shaft connected to the shaft), the shaft It was difficult to secure enough space.
[0006]
The present invention improves the disadvantages of the conventional example described above, includes a key lock mechanism, and has a simple configuration that can sufficiently secure a space on a steering shaft (or a transmission shaft connected to the shaft). It is an object to provide an electric power steering apparatus.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, a worm that is connected to a motor shaft as a drive shaft and a steering shaft that engages the worm as a driven gear and transmits the rotation from the worm to the steering shaft. And a worm wheel, wherein a mandrel portion on the inner diameter side of the tooth portion of the worm wheel is disposed on the steering shaft output side to prevent transmission of the steering force of the steering shaft. A plurality of lock holes provided in the side surface at equal intervals in the circumferential direction; and a lock unit provided in a housing of the speed reduction mechanism and having a lock pin that moves in the housing in the axial direction and engages one of the lock holes. When the worm wheel is less than a predetermined limit torque value on the steering shaft Integrally rotated, it provides a speed reduction mechanism of the electric power steering apparatus characterized by being fitted through the annular member to cause relative rotation by sliding it exceeds the predetermined limit torque value.
[0008]
With the above configuration, there is no need to provide a key lock mechanism on the steering shaft (or the transmission shaft connected to the shaft), a sufficient space can be ensured on the shaft, and the collapse stroke is sufficient. Can be taken to.
[0011]
According to the configuration of the present invention, since the take relatively large distance from the axial center of the locking hole position of the worm wheel, in relation to the moment of the force, and can be locked in less strength for the same input torque.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Reference examples and embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view of a reduction mechanism of an electric power steering apparatus showing a reference example of the present invention, FIG. 2 is a view of the worm wheel of FIG. 1 viewed from the direction of arrow A, and FIG. 3 is a first embodiment of the present invention. cross-sectional view of a reduction gear mechanism of the electric power steering apparatus shown, FIG. 4 is a diagram of the worm wheel as viewed from the direction of arrow B in FIG 3, FIG 5 is a perspective view showing a tolerance ring, FIG. 6 illustrates the second reference example It is sectional drawing of the deceleration mechanism of the electric power steering apparatus for this.
[0014]
In FIG. 1, a torsion bar 7 is internally fitted, and a worm wheel 2 is externally fitted and fixed to a transmission shaft 1 that is coaxially connected to a steering shaft (not shown). 4 is rotatably provided.
[0015]
The worm wheel 2 is engaged with a worm (9 in FIG. 6) that is a drive gear connected to an output shaft of a motor for assisting power (M in FIG. 6), and is a driven gear that receives power transmission from the motor. And constitutes a part of the speed reduction mechanism. The configuration of the speed reduction mechanism itself is conventionally known and will not be described in detail.
[0016]
In the present embodiment, as shown in FIG. 2, a large number of lock holes 2 b are arranged at equal intervals in the circumferential direction of the core metal part 2 a of the worm wheel 2.
[0017]
On the other hand, a lock unit 5 having a cylinder (lock pin) 6 that is arbitrarily movable in the axial direction is disposed on the cover 3 side. The cylinder 6 of the lock unit 5 moves in the axial direction, and the tip of the cylinder 6 is locked by engaging with the lock hole 2b of the worm wheel 2. The lock hole 2b, the lock unit 5, and the cylinder 6 constitute a key lock mechanism.
When the steering shaft is connected to a universal joint (cross shaft joint) (not shown), the lock unit 5 is disposed at a position avoiding the joint swing circle.
[0018]
In the above configuration, the distance from the center of the transmission shaft 1 of the lock hole 2b of the worm wheel 2 can be at least 40 mm. Compared to the case where the distance from the shaft center (column center) is 25 to 30 mm as in the case of the lock hole of the conventional key lock mechanism, this is less proof against the input torque due to the moment force. Since it can be locked, it becomes easy to clear the regulations that require the lock to withstand a predetermined input torque.
[0019]
In addition, unlike the prior art, there is no need to provide a lock bracket on the steering shaft (or the transmission shaft connected to the shaft), so that a sufficient space can be secured on the shaft.
[0020]
Next, a first embodiment will be described with reference to FIGS. This embodiment is substantially the same as the reference example, and the same members are denoted by the same reference numerals. The difference is that the worm wheel 2 is externally fitted to the transmission shaft 1 via a tolerance ring 8 which is a torque limiter.
[0021]
As shown in FIG. 5, the tolerance ring 8 is formed by integrally forming a large number of protrusions 8a protruding radially outward at equal intervals along the circumferential direction on a metal ring body having a split groove. A radial force corresponding to the radial deformation amount of each projecting portion 8 a is applied to the outer peripheral surface of the transmission shaft 1 and the shaft hole of the core metal portion 2 a of the worm wheel 2.
[0022]
The friction between the outer periphery of the tolerance ring 8 and the inner periphery of the shaft hole of the cored bar 2a and the friction between the inner periphery of the tolerance ring 8 and the outer periphery of the transmission shaft 1 cause the core from the transmission shaft 1. Since torque can be transmitted to the metal part 2a, the transmission shaft 1 and the core metal part 2a can be integrally rotated up to a preset limit torque. When torque exceeding the limit torque acts on the cored bar part 2a from the transmission shaft 1, it is between the outer peripheral part of the tolerance ring 8 and the inner periphery of the shaft hole of the cored bar part 2a or between the inner peripheral part of the tolerance ring 8 and the transmission shaft. Slip occurs in at least one of the outer periphery of the core 1 and the cored bar 2 a rotates relative to the transmission shaft 1.
[0023]
The limit torque value may be set so that the cored bar 2a and the lock unit 5 are not damaged by the action, and the press-fitting squeeze management of the tolerance ring 8 may be performed according to the limit torque value.
[0024]
As described above, when torque exceeding the limit torque acts on the cored bar portion 2a from the transmission shaft 1, the worm wheel 2 rotates relative to the transmission shaft 1, so that excessive bending input is applied to the cylinder 6 of the lock unit 5. Can be prevented.
[0025]
Next, a second reference example will be described with reference to FIG. In this embodiment, a worm shaft 10 integrally having a worm 9 is rotatably and integrally connected to an output shaft M1 of the motor M. The worm wheel 2 is engaged with the worm 9. A lock bracket 11 is integrally provided on the worm shaft 10. The lock bracket 11 is locked by being engaged with the lock hole 11a of the lock bracket 11 and the cylinder 6 of the lock unit 5 fixed to the housing Z.
[0026]
The lock bracket 11 can be externally fitted and fixed on the worm shaft 10, or can be joined by press-fitting, welding, or the like. However, the same tolerance ring as that of the first embodiment is attached and the lock bracket 11 has a limit torque. You can also
[0027]
In this configuration, when torque is applied to the transmission shaft 1 of the worm wheel 2, the worm shaft 10 tries to move in the circumferential direction due to the meshing relationship between the worm wheel 2 and the worm 9. Stop by match. At this time, the torque applied to the transmission shaft 1 of the worm wheel 2 can be supported with a proof stress of (1 / gear reduction ratio) as compared with the case where the worm wheel 2 is locked as in the above embodiment.
[0028]
In the above embodiment, the worm / worm wheel gear mechanism is exemplified as the speed reduction mechanism. However, the present invention is not limited to this, and can be applied to, for example, a hypoid gear mechanism, a spur gear mechanism, or a helical gear mechanism.
[0029]
【The invention's effect】
As described above, according to the present invention, since the speed reduction mechanism includes the key lock mechanism, a sufficient space can be secured on the steering shaft (or the transmission shaft connected to the shaft), and the telescopic mechanism. Etc. can be provided.
[0030]
Further, since the distance from the axis center of the lock position can be made larger than before, it is possible to easily clear the proof of the proof stress with respect to a predetermined input torque in relation to the moment of force.
[0031]
Moreover, since the fitting part length of an inner column or an outer column can be taken large, a collapse stroke can be taken sufficiently and it can contribute also to the advantageous characteristic at the time of a collision. Furthermore, it is not necessary to provide a key lock mechanism on the steering shaft, and column rigidity and column bending rigidity can be improved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a speed reduction mechanism of an electric power steering apparatus showing a first reference example of the present invention.
FIG. 2 is a view of the worm wheel of FIG. 1 as viewed from the direction of arrow A.
FIG. 3 is a cross-sectional view of a speed reduction mechanism of the electric power steering apparatus showing the first embodiment of the present invention.
4 is a view of the worm wheel of FIG. 3 as viewed from the direction of arrow B. FIG.
FIG. 5 is a perspective view showing a tolerance ring.
FIG. 6 is a cross-sectional view of a speed reduction mechanism of an electric power steering apparatus for explaining a second reference example .
FIG. 7 is a partial cross-sectional view showing a conventional key lock mechanism.

Claims (1)

A speed reduction mechanism comprising a worm that is connected to a motor shaft and serving as a drive shaft, and a worm wheel that is provided on the steering shaft and engages with the worm and transmits rotation from the worm to the steering shaft as a driven gear , the deceleration in the mechanism to prevent the steering force transmission of the steering shaft, the core metal portion in the tooth portion inner diameter side of the worm wheel, a number provided at equal intervals in the circumferential direction on the steering shaft output side of the side surface Provided with a lock hole and a lock unit having a lock pin provided in the housing of the speed reduction mechanism and having a lock pin that moves in the housing in the axial direction and engages with one of the lock holes. When the steering shaft is less than a predetermined limit torque value, the steering shaft is rotated integrally, and the predetermined limit torque is Reduction mechanism of the electric power steering apparatus characterized by being fitted through the annular member to cause relative rotation by sliding exceeds the value.

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