Machine element or mechanism – Control lever and linkage systems – Hand operated
Reexamination Certificate
1998-07-30
2001-01-30
Hannon, Thomas R. (Department: 3682)
Machine element or mechanism
Control lever and linkage systems
Hand operated
C074S3880PS, C074S422000, C384S276000, C384S279000, C384S291000
Reexamination Certificate
active
06178843
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a rack guide in a rack and pinion type steering system, which supports a rack bar, and more specifically to the rack guide whose sliding frictional resistance against the rack bar is reduced.
Conventionally, a rack and pinion type steering system comprises a pinion provided at an end of a steering shaft and a rack bar having rack teeth which engage with the pinion through which rotation of the steering shaft or the pinion is transformed into reciprocating motion of the rack bar.
In such rack and pinion type steering system, the pinion is rotatably supported in a housing through bearings, while the rack bar is supported in such a manner that a hemi-cylindrical back surface thereof opposite to the teethside is slidable on a rack guide disposed in the housing. The rack guide is formed by mounting a slide bearing member on a supporting base. The slide bearing member usually comprises a backing metal having an arc shape and a synthetic resin layer coated on the backing metal as an inner surface layer so as to support the rack bar on the surface of the synthetic resin layer.
High sliding frictional resistance between the rack guide and the rack bar makes the efficiency of the steering system to be deteriorated, so as to affect on the steering characteristics. To cope with this, it is proposed, for example, in JP-Y2-1-27984 to reduce the contact area between a rack bar and a synthetic resin layer of a slide bearing member in order to reduce the sliding frictional resistance between a rack guide and the rack bar.
According to a specific structure of JP-Y2-127984 for reducing the contact area between the rack bar and the slide bearing member, as shown in the attached drawing of
FIG. 6
, the rack bar
2
is partially in contact with a synthetic resin layer
1
of the slide bearing member at two restricted linear zones of the surface of the synthetic resin layer
1
. The linear zones are located within two surface sections, respectively, which are defined by a symmetrical center line corresponding to the curvature center (line) of the hemi-cylindrical back surface of the rack bar
2
being received in the slide bearing member, the symmetrical center line dividing the hemi-cylindrical back surface of the rack bar
2
to the two surface sections
3
and
4
. In
FIG. 6
, a reference character “LS” means a phantom line which includes the curvature center “O” of the hemi-cylindrical back surface of the rack bar
2
and the above symmetrical center line on the surface of the synthetic resin layer
1
. The surface of the synthetic resin layer
1
consists of the two cylindrical surface sections
3
and
4
which have curvature centers “Oa” and “Ob”, respectively. The curvature centers “Oa” and “Ob” are located above the curvature center “O” in FIG.
6
. Thus, the radii of curvature “Ra” and “Rb” of the two cylindrical surface sections
3
and
4
are greater than that of the radius of curvature “Ro” of the rack bar.
In such structure, however, the hemi-cylindrical back surface of the rack bar
2
is almost in linear contact with the synthetic resin layer
1
at the respective two surface sections
3
and
4
. This means that the synthetic resin layer
1
bears the rack bar
2
by small areas. Thus, the bearing load per unit area is considerably large resulting in that the slide bearing member has an inferior durability. Further, the synthetic resin layer
1
is elastically deformed during supporting the rack bar
2
so as to be dented in a circular-arc form along the respective two linear zones being in contact with the hemi-cylindrical back surface of the rack bar
2
. Such deformation amount is different from one steering system to another due to variance errors in size of components, the variance errors occurring in assembling the steering systems, and so on. Consequently, the contact area between the synthetic resin layer
1
and the hemi-cylindrical back surface of the rack bar
2
varies from one steering system to another. Thus, the sliding frictional resistance between the synthetic resin layer
1
and the rack bar
2
is different from one steering system to another resulting in a problem that the fabrication quality is unstable in producing such steering systems.
SUMMARY OF THE INVENTION
The present invention is proposed under such technical background and an object thereof is to provide a rack guide in a rack and pinion type steering system, whose slide bearing member can have a long lifetime and a constant load bearing area.
Thus, there is provided a rack guide in a rack and pinion type steering system, in which the rack guide is mounted in a casing of the steering system to slidably support a rack bar which is reciprocatingly driven by a pinion being rotatably supported in the casing, the rack guide consisting of a supporting base and a slide bearing member which is mounted on the supporting base and which has a cross-sectional circular-arc profile, wherein
the slide bearing member comprises a backing metal layer and a liner formed on the backing metal, the liner comprising a synthetic resin layer which forms an inner surface of the rack guide and which is brought into sliding contact with the rack bar;
the inner surface of the rack guide consists of sliding-contact surface portions and remaining surface portions, all of which are elongated longitudinally and which are circumferentially distinguished from one another;
the sliding-contact surface portions which are entirely in sliding contact with the rack bar and have a cross sectional circular-arc profile with a predetermined circumferential length, respectively and which are continuous to the adjacent remaining surface portions; and
the remaining surface portions are radially more recessed or dented than the sliding-contact surface portions.
According to such structure, since the synthetic resin layer of the rack guide bears the rack bar at the sliding-contact surface portions partially formed in the inner surface of the rack guide, the contact area between the rack bar and the synthetic resin layer is comparatively small so that the sliding frictional resistance can be reduced. Moreover, the sliding-contact surface portions have a predetermined circumferential length, respectively so that the rack bar is in band-zone contact with the synthetic resin layer but not be in linear contact therewith. Thus, the bearing load per unit area is small resulting in a long lifetime of the steering system. Besides, the remaining surface portions adjacent to the sliding-contact surface portions are more recessed from the latter, therefore even if the sliding-contact surface portions are elastically deformed radially outwardly under a load from the rack bar, the contact area between the rack bar and the sliding-contact surface portions will never increase so that the fabrication quality becomes stable in producing such steering systems.
Alternatively, a porous sintered alloy layer may be coated on the inner surface of a back metal and a synthetic resin layer is formed on the porous sintered alloy layer by way of impregnating the resin into the alloy layer. According to such structure, frictional heat generated between the synthetic resin layer and the rack bar is easily transmitted to the backing metal through the porous sintered alloy layer so that the rack guide has excellent heat radiation property.
The backing metal may be made from a metal having excellent heat conductivity such as bronze. Since bronze is hard to be corroded and has high thermal conductivity, frictional heat produced between the synthetic resin layer and the rack bar is easily dissipated.
According to one embodiment of the invention, a cylindrical hollow protrusion with a bottom may be provided to the backing metal, which protrudes radially outwardly to be fitted into a positioning opening formed in the supporting base. The inner space of the hollow protrusion can be used as a reservoir for a lubricant so that the lubricant is stably supplied to the sliding-contact surface between the synthetic resin layer and
Ido Yasuo
Mabuchi Nobumitsu
Machida Katsuhiro
Browdy and Neimark
Daido Metal Company LTD
Hannon Thomas R.
Joyce William C
LandOfFree
Rack guide in rack and pinion type steering system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Rack guide in rack and pinion type steering system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Rack guide in rack and pinion type steering system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2516552