Patent Application
20110284312
The present invention relates to an electric power steering device which is built-in to the steering device of an automobile, and achieves a reduction in the force required for the driver to operate the steering wheel, by utilizing an electric motor as an auxiliary force.
The steering device of an automobile, by means of the construction shown in
An electric power steering device to which an electric motor 8 is built-in is well-known. As one example of an electric power steering device of such a construction, the construction disclosed in Patent Document 1 is shown in
In regard to the cylindrical steering column 9 through which the steering shaft 3 is inserted, the front end portion (left end portion of
The steering force auxiliary device 10 is provided with; the steering shaft 3 serving as an input shaft, the output shaft 13, the torsion bar 12, the electric motor 8 (refer to
That is to say, when torque is applied to the steering shaft 3, the torsion bar 12 that connects the steering shaft 3 and the output shaft 13 elastically deforms such that it twists depending on the torque that is transmitted between the steering shaft 3 and the output shaft 13. Then, accompanying this elastic deformation, the steering shaft 3 and the output shaft 13 relatively rotate. There is a correlation between the relative rotation amount (relative displacement amount) between the steering shaft 3 and the output shaft 13, and the direction and the magnitude of the torque. Consequently, the torque sensor 15 detects the direction and the magnitude of the torque applied to the steering shaft 3, based on this relative rotation amount between the steering shaft 3 the output shaft 13.
Specifically, the direction and the magnitude of the torque are detected in the following manner. That is to say, as mentioned above, when the steering shaft 3 and the output shaft 13 relatively rotate, there is a phase shift in the circumferential direction generated between the sleeve 18 and the torque detecting concave and convex portions 28. As a result, a change in the impedance of the detecting coil corresponding to the direction and the magnitude of this phase shift is generated. Consequently, the torque sensor 15 detects the direction and the magnitude of the torque based on such a change (increase and decrease from a reference value) in the impedance. Then, the control device sends a signal to the electric motor 8 to drive according the signal that represents the detected value of this torque, and other signals that represent the vehicle speed, or the like, and generates an auxiliary force in a predetermined direction and at a predetermined magnitude.
In the case of an electric power steering device configured in this manner, the torque output from the output shaft 13 of the steering force auxiliary device 10 can be made larger than the torque applied from the steering wheel 1 to the steering shaft 3. That is to say, the torque output from the output shaft 13 can be made larger by the amount of the auxiliary force applied from the electric motor 8 which constitutes the steering force auxiliary device 10, via the worm reducer 14. Accordingly, the force required by the driver for operating the steering wheel 1 in order to impart a steering angle to the steered vehicle wheels can be made smaller by the amount of the auxiliary force of the steering force auxiliary device 10.
Incidentally, in the case of the construction shown in
Together with the increased output of electric power steering devices in recent years, the force (load) applied to the output shaft 13 has become large, and together with this, the force applied to the rolling bearings 19 has also increased. More specifically, the following three types of forces are applied to the output shaft 13 as shown in
(1) a force (reaction force) F1 based on the meshing between the worm wheel 16 and the worm 17
(2) a moment M that is applied around a yoke 23 of the universal joint 4a
(3) an axial direction load (sliding load) F2 of the intermediate shaft 5
For example, in the case of a high output electric power steering device in which the output torque of the electric motor 8 is of the order of 6 Nm, the force F1 becomes approximately 600 to 1500 N in the three axial directions (XYZ directions), the moment M becomes approximately 80 to 90 Nm, and the axial direction load F2 becomes approximately 1500 N.
When such forces are applied to the output shaft 13, the output shaft 13 distorts, and as shown exaggeratively in
The present invention takes the above circumstances into consideration, with an object of providing an electric power steering device that is provided with a construction that can suppress the generation of stick slip where fixing and sliding is repeated between the outer peripheral face of the output shaft serving as the rotation shaft, and the inner peripheral face of the inner ring of the rolling bearings, and can reduce or prevent the generation of vibrations and abnormal noise, such as “chattering”, arising from this stick slip.
The electric power steering device of the present invention is, in the same manner as the conventional construction, provided with a housing, a rotation shaft, a worm wheel, a worm, and an electric motor.
The housing is supported by a fixed part such as the frame of the vehicle body, the steering column, or the like, and does not rotate. The rotation shaft is freely rotatably provided with respect to the housing, and rotates as a result of the operation of the steering wheel, and together with this rotation, imparts a steering angle to a steered wheel. The worm wheel is supported by a portion of the rotation shaft in the interior of the housing, concentric with the rotation shaft, and rotates together with the rotation shaft. The worm, in a state meshed with the worm wheel, is freely rotatably supported with respect to the housing. The electric motor rotationally drives the worm. Moreover, by means of at least one pair of rolling bearings respectively provided on both axial direction sides of the worm wheel, the rotation shaft is freely rotatably supported with respect to the housing.
In particular, in the electric power steering device of the present invention, a lubricant is interposed between the inner peripheral face of at least one of the inner rings of the inner rings, or more preferably all of the inner rings, which constitute the rolling bearings, and the outer peripheral face of the rotation shaft.
Preferably, prior to externally fitting the inner rings of the rolling bearings onto the rotation shaft, lubricant is applied between, at the very least, one of the peripheral faces of the inner peripheral face of one of the inner rings, and the outer peripheral face of the rotation shaft.
In a case of implementing the electric power steering device of the present invention as mentioned above, for example, the following configuration can be employed. That is to say, among the pair of rolling bearings, one of the rolling bearings which is present on the front end side of the rotation shaft sandwiching the worm wheel, is made a single row deep groove-type ball bearing. Furthermore, one part in the axial direction of the outer peripheral face of the rotation shaft is provided with torque detecting concave and convex portions which are alternately arranged with respect to the circumferential direction, and are formed with concave portions and convex portions respectively extending in the axial direction. Moreover, in relation to the axial direction, a large diameter portion that has a larger diameter than the torque detecting concave and convex portions is provided on a part adjacent to the front end side of the torque detecting concave and convex portions. In addition, among the pair of rolling bearings, in regard to the inner ring that constitutes the other rolling bearing, which is present on the rear end side of the rotation shaft sandwiching the worm wheel, only one part on the front end side with respect to the axial direction is externally fitted onto the large diameter portion, and the engaged state between the inner peripheral face of the inner ring and the large diameter portion is a clearance fit. Furthermore, among the pair of rolling bearings, lubricant is interposed, at least between the inner peripheral face of the inner ring that constitutes the other rolling bearing, and the outer peripheral face of the rotation shaft.
In this case, preferably, of the outer peripheral face of the rotation shaft, the part in which lubricant is interposed between it and the inner peripheral face of the inner ring which constitutes the rolling bearing, is configured by a face in which plurality of concave portions, or a groove, is formed. Furthermore, alternatively, of the outer peripheral face of the rotation shaft, the part in which lubricant is interposed between it and the inner peripheral face of the inner ring which constitutes the rolling bearing, is made a Plateau surface (a face with flat convexities and that has deep concavities). The skewness Rsk, which is the surface roughness parameter relating to this Plateau surface, is made Rsk<0. Such a Plateau surface can be obtained by various conventionally known processing methods, such as carrying out a finish honing after performing a rough honing on the processed face. However, the shape for retaining the lubricant is in no way limited to these, and in addition, may be a concave groove that extends in the circumferential direction, a plurality of dimples (fine concavities), other shapes thereof, and furthermore, it is possible to apply a combination of these.
The lubricant that is interposed between the inner peripheral face of the inner ring which constitutes the rolling bearing, and the outer peripheral face of the rotation shaft, can be the same as the lubricant that is used for the meshing portion between the worm and worm wheel.
On the other hand, in an alternative aspect of the electric power steering device of the present invention, an elastic material, for example, an elastomer such as rubber, synthetic resin, or the like, is interposed between the inner peripheral face of at least one of the inner rings among the inner rings, or more preferably all of the inner rings which constitute the rolling bearings, and the outer peripheral face of the rotation shaft.
In this aspect, preferably, an inwardly concave portion is provided on the outer peripheral face of the rotation shaft at a position facing the inner peripheral face of the inner ring, which is concave inwards in the radial direction. Moreover, the elastic material mentioned above is provided in this inwardly concave portion, and is preferably integrated with the rotation shaft. Alternatively, an outwardly concave portion which is concave outwards in the radial direction is provided on one axial direction part of the inner peripheral face of at least one of the inner rings. Moreover, the elastic material is provided in this outwardly concave portion, and is preferably integrated with the rotation shaft.
The configurations of both of the two aspects mentioned above can also be employed simultaneously. That is to say, both a lubricant and an elastic material can also be interposed between the inner peripheral face of at least one of the inner rings among the inner rings, or more preferably all of the inner rings, that constitute the rolling bearings, and the outer peripheral face of the rotation shaft.
According to the electric power steering device of the present invention, which is configured as described above, the occurrence of stick slip between the outer peripheral face of the rotation shaft and the inner peripheral face of the inner ring of the rolling bearings can be reduced or prevented.
That is to say, in the present invention, a lubricant, an elastic material, or the like, is interposed between the inner peripheral face of the inner rings of the rolling bearings and the outer peripheral face of the rotation shaft, and the friction coefficient between these peripheral faces is changed. Consequently, even if this rotation shaft becomes likely to be displaced in the axial direction, as a result of these lubricants, elastic materials, or the like, the sliding or axial displacement between these peripheral faces can be made smooth, and the occurrence of stick slip can be reduced or prevented. As a result, a reduction or elimination of vibrations and abnormal noise such as “chattering” can be achieved, a smooth and comfortable steering sensation can be assured, and the situation where the driver is subjected to discomfort, unpleasant sensations, and the like, can be prevented.
In particular, there is a case which employs a configuration where, of the pair of rolling bearings that are provided on both axial direction sides of the worm wheel and which freely rotatably support the rotation shaft with respect to the housing, as the one rolling bearing present on the front end side of the rotation shaft sandwiching the worm wheel, a single row deep groove-type ball bearing is utilized instead of a four-point contact-type ball bearing, due to demands of cost reduction and torque reduction. Whereas, in regard to the other rolling bearing present on the rear end side of the rotation shaft, of the outer peripheral face of the rotation shaft, only one part of the front end side of the inner ring is externally fitted with respect to the large diameter portion adjacent to the front end side of the torque detecting concave and convex portions, and this is installed in a state with the fit between the inner peripheral face of the inner ring and the large diameter portion as a clearance fit. In this configuration, it becomes easier for stick slip to occur between the inner ring of the other rolling bearing and the large diameter portion, which is attributable to the rotation shaft becoming easily displaced at the time of usage, and the central axes of the inner ring of the other rolling bearing and the rotation shaft becoming easily tilted. As a result of the present invention, even in such a configuration, it is possible to reduce or prevent the occurrence of stick slip between the inner peripheral face of the inner ring of the other rolling bearing and the outer peripheral face of the rotation shaft.
Furthermore, in the present invention, by devising the face shape of the part of the outer peripheral face of the rotation shaft, where the lubricant is interposed between the rotation shaft and the inner peripheral face of the inner ring which constitutes the rolling bearing, the lubricant collects on this face. Therefore the lubricated state between these can be well maintained over a long period. As a result, the effect of reducing or preventing the occurrence of stick slip, which occurs between the outer peripheral face of the rotation shaft and the inner peripheral face of the inner ring, can be maintained over a long period.
Also in the case of the present example, in the same manner as the construction shown in
In the case of the present example which is configured in this manner, the occurrence of stick slip between the outer peripheral face of the output shaft 13 and the inner peripheral face of the inner rings 20a and 20b of the rolling bearings 19a and 19b can be reduced or prevented.
That is to say, even if the output shaft 13 becomes likely to be displaced in the axial direction, as a result of the lubricant 24 interposed between the inner peripheral face of the inner rings 20a and 20b of the rolling bearings 19a and 19b and the outer peripheral face of the output shaft 13, the sliding between the peripheral faces can be made smooth, and the occurrence of stick slip can be reduced or prevented. As a result, a reduction or elimination of vibrations and abnormal noise, such as “chattering”, can be achieved, a smooth and comfortable steering sensation can be assured, and the situation where the driver is subjected to discomfort, unpleasant sensations, and the like, can be prevented.
In the examples shown in the drawings, the lubricant 24 is interposed both between the inner peripheral face of the inner rings 20a and 20b of both rolling bearings 19a and 19b, and the outer peripheral face of the output shaft 13. However depending on the case, it is also possible for the lubricant 24 to be interposed between either one, for example, only the inner ring 20b of the rolling bearing 19b on the side (the right side of
As the lubricant 24 that is applied to either face, which is the inner peripheral face of the inner rings 20a and 20b or the outer peripheral face of the output shaft 13, it is possible to utilize the same substance as the lubricant used for the meshing portion between the worm 17 and the worm wheel 16. As a result, at the time of application of the lubricant, mistakes in coating can be prevented, and also the types of lubricants applied to the electric power steering device can be reduced, and the management thereof becomes easy. Furthermore, even in a case where one lubricant becomes mixed with the other due to utilization over a long period, there is the advantage that problems due to mixing do not occur.
A second embodiment of the present invention is described with reference to the same
Furthermore, as shown in
Furthermore, in the case of the present example, a single row deep groove-type ball bearing is utilized as the one rolling bearing 19a. However in a case where such a configuration is employed, compared to a case where a four-point contact-type ball bearing is utilized as one of the rolling bearings 19a, it becomes easier for the output shaft 13 to be displaced in the axial direction at the time of use. Accordingly, in a case where neither measure is carried out, it becomes easier for stick slip to occur between the inner peripheral face of the inner ring 20b which constitutes the other rolling bearing 19b, and the large diameter portion 30.
Consequently, in the case of the present example, in the same manner as the case of the first embodiment mentioned above, of the intervening space between the inner peripheral face of the inner rings 20a and 20b which constitute the pair of rolling bearings 19a and 19b, and the outer peripheral face of the output shaft 13, the lubricant 24 such as lubricant oil and grease, is interposed between at least the inner peripheral face of the inner ring 20b which constitutes the other rolling bearings 19b, and the outer peripheral face of the output shaft 13 (large diameter portion 30). As a result, despite the circumstances such as those mentioned above, at the very least, a reduction or prevention of stick slip that occurs between the inner peripheral face of the inner ring 20b which constitutes the other rolling bearings 19b, and the outer peripheral face of the output shaft 13 (large diameter portion 30) can be achieved.
In the case of the electric power steering device of the present example which possesses such a configuration, the lubricant 24 collects in the concave portions 31 (refer to
In the case of carrying out the present invention, it is possible to form a lubricant accumulating part, such as the concave portion 31 or the concave groove 32 mentioned above, on the section of the outer peripheral face of the output shaft that externally fits with the inner ring 20a of the one rolling bearing 19a (refer to
A seventh embodiment of the present invention is described with reference to, in addition to
In the case of the electric power steering device of the present example, which possesses such a configuration, the lubricant 24 (refer to
In the case of such a present example, in the same manner as the first embodiment, the occurrence of stick slip can be reduced or prevented. That is to say, the elastic material 25 is interposed between the inner peripheral face of the inner ring 20a of the rolling bearing 19a and the outer peripheral face of the output shaft 13c. Consequently, even if the output shaft 13e becomes likely to be displaced in the axial direction, as a result of this elastic material 25 being displaced in the axial direction, the displacement between the peripheral faces can be made smooth, and the reduction or elimination of the occurrence of stick slip can be achieved. As a result, a reduction of vibrations and abnormal noise such as “chattering” can be achieved, a smooth and comfortable steering sensation can be assured, and the situation where the driver is subjected to discomfort, unpleasant sensations, and the like at the time of driving can be prevented. The configuration and operation of the other parts are the same as the first embodiment, and hence illustration and explanation relating to the common sections are omitted.
As necessary, the lubricant 24 (refer to
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-269866 | Nov 2009 | JP | national |
| 2010-158381 | Jul 2010 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2010/071145 | 11/26/2010 | WO | 00 | 7/19/2011 |
