Rack-and-pinion type steering apparatus

A rack-and-pinion type steering apparatus 1 includes a housing 3 having a cylindrical holding hole 2 in its interior; a pinion 6 which is disposed in the housing 3 rotatably in a direction R about an axis O by means of bearings 4 and 5; a rack bar 8 which has rack teeth 7 meshing with the pinion 6 and is movable in a direction A; a rack guide 9 which is disposed in the holding hole 2 within the housing 3 movably in a direction C, and which guides and supports the rack bar 8 movably in the direction A; and a coil spring 10 for resiliently pressing the rack teeth 7 of the rack bar 8 against the pinion 6 by means of the rack guide 9.

TECHNICAL FIELD

The present invention relates to a rack-and-pinion type steering apparatus.

BACKGROUND ART

Patent Document 1: microfilm of Japanese Utility Model Application No. 56-115067

A rack-and-pinion type steering apparatus generally has a configuration such as the one shown inFIG. 15, and a rack-and-pinion type steering apparatus1shown inFIG. 15is comprised of a pinion6which is rotatably disposed in a housing3by means of bearings4and5so as to be rotated by steering; a rack bar8having rack teeth7meshing with the pinion6so as to be moved in a direction perpendicular to the plane of the drawing by the rotation of the pinion6; a rack guide9which is movably disposed in a cylindrical holding hole2extending in a lateral direction inside the housing3(in a perpendicular direction to the movement of the rack bar8); and a coil spring10which is disposed between the housing3and the rack guide9to resiliently press the rack teeth7of the rack bar8against the pinion6by means of the rack guide9. An annular clearance Δ for allowing the movement of the rack guide9toward the pinion6is provided between an outer peripheral surface31of a rack guide body22of the rack guide9and an inner peripheral surface15of the housing3for defining the holding hole2.

DISCLOSURE OF THE INVENTION

Problems that the Invention is to Solve

In such a rack-and-pinion type steering apparatus1, runout occurs in the rack bar8about its axis owing to a reaction force acting from a road surface through wheels. If the annular clearance Δ between the outer peripheral surface31of the rack guide body22and the inner peripheral surface15of the housing3is large, the movement of the rack guide9along the radial direction of the holding hole2becomes large. Hence, there is a problem in that the noise of collision between the outer peripheral surface31of the rack guide body22and the inner peripheral surface15of the housing3and the noise of collision between the rack teeth7and the teeth of the pinion6become large.

Incidentally, in the rack-and-pinion type steering apparatus1, the housing3is formed of aluminum or an aluminum alloy because of their light weight and ease of fabrication. In addition, the rack guide body22, which is disposed in a cylindrical holding hole2, is also formed of aluminum or an aluminum alloy because of their low cost in addition to their light weight and ease of fabrication.

In the case where the housing3and the rack guide body22are formed of aluminum or an aluminum alloy, the runout occurs in the rack bar8about its axis owing to the annular clearance Δ provided between the outer peripheral surface31of the rack guide body22and the inner peripheral surface15of the housing3. If the rack guide body22is strongly pressed against the inner peripheral surface15side of the housing3, coupled with the action of the pressing force due to the coil spring10, the two members of the rack guide body22and the housing3are in the state of the so-called “metals of similar composition,” so that the frictional resistance therebetween increases, and adhesive wear is hence brought about therebetween. Thus there arises the problem that the movement of the rack guide9in the direction toward the rack bar8is hampered.

To overcome the above-described problem, a proposal (contained in patent document 1) has been made in which an O-ring constituted by a rubber elastomer is interposed between the rack guide body22and the housing3, and that O-ring is sandwiched between the outer peripheral surface31of the rack guide body22and the inner peripheral surface15of the housing3, to thereby restrict the movement of the rack guide9along its radial direction. Also, a proposal (contained in patent document 2) has been made in which an elongated elastic member in the axial direction is sandwiched between the outer peripheral surface31of the rack guide body22and the inner peripheral surface15of the housing3, to thereby restrict the movement of the rack guide9along its radial direction.

However, if such an O-ring or an elongated elastic member in the axial direction is sandwiched between the outer peripheral surface31of the rack guide body22and the inner peripheral surface15of the housing3, the smooth axial movement of the rack guide9is hampered by the friction between that O-ring or the elastic member and the inner peripheral surface15of the housing3. Hence, there arises the problem that the pinion6and the rack teeth7of the rack bar8cannot be meshed smoothly.

The present invention has been devised in view of the above-described circumstances, and its object is to provide a rack-and-pinion type steering apparatus which is capable of avoiding the collision between the outer peripheral surface of the rack guide body and the inner peripheral surface of the housing ascribable to the runout of the rack bar about its axis owing to the reaction force acting from the road surface through the wheels, and which is constantly capable of smoothly moving the rack guide in the direction toward the rack bar without causing the adhesive wear which is ascribable to the so-called “metals of similar composition” and can possibly occur frequently in the case where the housing and the rack guide body are formed of aluminum or an aluminum alloy.

Means for Solving the Problems

A rack-and-pinion type steering apparatus in accordance with the present invention comprises: a housing having a cylindrical holding hole in its interior; a pinion which is disposed rotatably in the housing and is rotated by steering; a rack bar which has rack teeth meshing with the pinion and is movable; a rack guide which is disposed movably in the holding hole within the housing, and which guides and supports the rack bar movably; and resilient means which is disposed between the housing and the rack guide to resiliently press the rack teeth of the rack bar against the pinion by means of the rack guide. Here, the rack guide includes: a rack guide body having a cylindrical outer peripheral surface, a wide annular recessed portion formed in the outer peripheral surface, and at least one narrow annular groove formed in a bottom surface of the wide annular recessed portion and having a narrower width than a width of the wide annular recessed portion; a sliding plate piece which is secured to the rack guide body and is brought into contact with an outer surface of the rack bar so as to support the rack bar movably; an endless annular elastic member fitted and secured in the narrow annular groove of the rack guide body in such a manner as to project from an opening of the narrow annular groove; and a cylindrical bush which has a split groove and is fitted and secured in the wide annular recessed portion, such that the cylindrical bush on an outer peripheral surface side thereof projects from an opening of the wide annular recessed portion of the rack guide body, while an inner peripheral surface of the cylindrical bush abuts against an outer surface of the endless annular elastic member, the cylindrical bush being fitted in the holding hole of the housing with an interference, an outer peripheral surface of the cylindrical bush being movably in contact with a cylindrical inner peripheral surface of the housing defining the holding hole of the housing.

According to the rack-and-pinion type steering apparatus in accordance with the invention, the endless annular elastic member is fitted and secured in the narrow annular recessed portion formed in the bottom surface of the wide annular recessed portion, and the cylindrical bush abutting against the outer peripheral surface of the endless annular elastic member is fitted and secured in the wide annular recessed portion. Therefore, it is possible to prevent collision between the outer peripheral surface of the rack guide body and the inner peripheral surface of the housing defining the holding hole, making it possible to eliminate the occurrence of collision noise. Moreover, it is possible to absorb the noise of collision between the rack teeth and the teeth of the pinion, thereby making it possible to reduce that collision noise. In addition, it is possible to reduce the sliding frictional resistance between the inner peripheral surface of the housing and the outer peripheral surface of the cylindrical bush fitted and secured to the outer peripheral surface of the rack guide body without causing adhesive wear which is ascribable to the “metals of similar composition” in the case where the housing and the rack guide body are formed of aluminum or an aluminum alloy. As a result, it is possible to constantly allow the movement of the rack guide in the direction toward the rack bar to be effected smoothly.

In the rack-and-pinion type steering apparatus in accordance with the invention, the wide annular recessed portion may have an annular recessed portion formed in the cylindrical outer peripheral surface of the rack guide body over its entire circumferential area, and the cylindrical bush may have a cylindrical portion which has one split groove and is fitted and secured in the annular recessed portion. Furthermore, the wide annular recessed portion may further have, in addition to the annular recessed portion, a pair of circular arc-shaped recessed portions continuous to the annular recessed portion and formed on mutually opposing outer peripheral surface portions in the cylindrical outer peripheral surface of the rack guide body, and the cylindrical bush may further have, in addition to the cylindrical portion, a pair of circular arc-shaped projecting portions which are formed integrally on the cylindrical portion in face-to-face relation to each other with the split groove located therebetween and which are respectively fitted and secured to the pair of circular arc-shaped recessed portions.

The rack guide body may be formed of aluminum, an aluminum alloy, or an iron-based sintered body, and the endless annular elastic member may be constituted by an O-ring made of rubber.

The cylindrical bush may be formed of a thermoplastic synthetic resin such as polyacetal resin, polyamide resin, and polybutylene terephthalate resin which exhibit self-lubricity. A lubricating substance such as lubricating oil, graphite, molybdenum disulfide, tetrafluoroethylene resin, or the like may be incorporated in such a synthetic resin. In addition, as the cylindrical bush, it is possible to use a winding bush which is formed such that a plate-like body, which is comprised of a backing plate formed of a steel plate, a porous sintered alloy layer formed integrally on the surface of that metal backing, and a synthetic resin layer filled in the pores of, and coated on the surface of, the porous sintered alloy layer, is convoluted into a cylindrical form with the synthetic resin layer facing the outer side.

In the rack-and-pinion type steering apparatus in accordance with the invention, an annular clearance between a bottom surface of the wide annular recessed portion of the rack guide body and the inner peripheral surface of the cylindrical bush may have a radial width which is smaller than a radial width of an annular clearance between the outer peripheral surface of the rack guide body and the inner peripheral surface of the housing defining the cylindrical holding hole.

In the state in which the rack guide is fitted in the cylindrical holding hole of the housing, if the annular clearance between the bottom surface of the wide annular recessed portion of the rack guide body and the inner peripheral surface of the cylindrical bush, which is fitted and secured in that wide annular recessed portion in such a manner as to cover the endless annular elastic member, has a radial width which is smaller than the radial width of the annular clearance between the outer peripheral surface of the rack guide body and the inner peripheral surface of the housing defining the cylindrical holding hole of the housing, it is possible to effectively avoid the collision between the outer peripheral surface of the rack guide body and the inner peripheral surface of the housing defining the cylindrical holding hole of the housing, as well as the occurrence of collision noise due to that collision. In particular, in the case where the housing and the rack guide body are formed of aluminum or an aluminum alloy, it is possible to reliably achieve the constant smooth movement of the rack guide in the direction toward the rack bar without causing adhesive wear which is ascribable to the “metals of similar composition” in addition to the above description.

ADVANTAGES OF THE INVENTION

According to the invention, it is possible to provide a rack-and-pinion type steering apparatus which is capable of avoiding the collision between the outer peripheral surface of the rack guide body and the inner peripheral surface of the housing ascribable to the runout of the rack bar about its axis owing to the reaction force acting from the road surface through the wheels, and which is constantly capable of smoothly moving the rack guide in the direction toward the rack bar without causing the adhesive wear which is ascribable to the so-called “metals of similar composition” and can possibly occur frequently in the case where the housing and the rack guide body are formed of aluminum or an aluminum alloy.

Hereafter, a more detailed description will be given of the present invention and the mode for carrying out the invention with reference to the preferred embodiment illustrated in the drawings. It should be noted that the invention is not limited by this embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

InFIGS. 1 to 8, a rack-and-pinion type steering apparatus1in accordance with this embodiment is comprised of a housing3having a cylindrical holding hole2in its interior; a pinion6which is disposed in the housing3rotatably in a direction R about an axis O by means of bearings4and5and is rotated in the direction R by steering; a rack bar8which has rack teeth7meshing with the pinion6so as to be moved in the direction A perpendicular to the plane of the drawing ofFIG. 1by the rotation of the pinion6in the direction R and is movable in a direction A; a rack guide9which is disposed in the holding hole2within the housing3movably in a direction C perpendicular to the direction A and an axial direction B of the pinion6, respectively, and which guides and supports the rack bar8movably in the direction A; and a coil spring10serving as a resilient means which is disposed between the housing3and the rack guide9to resiliently press the rack teeth7of the rack bar8against the pinion6by means of the rack guide9.

The housing3includes a housing body14having a cylindrical portion13as well as a cover member16threadedly secured to an inner peripheral surface15of the cylindrical portion13. The cover member16for closing one end face of the holding hole2formed in the cylindrical portion13is fixed to the cylindrical portion13by a lock nut17so that its state of threaded engagement with the cylindrical portion13will not loosen.

The rack bar8which is passed through the housing3and extends in the direction A has a circular arc-shaped convex surface19on its side opposite to its side where the rack teeth7are formed.

As shown in detail inFIGS. 2 to 7, the rack guide9includes a rack guide body22which has a circular arc-shaped concave surface21on one end face20thereof and is formed of aluminum or an aluminum alloy; a sliding plate piece24which is secured to the circular arc-shaped concave surface21of the rack guide body22and has a circular arc-shaped inner surface23for being brought into contact with the circular arc-shaped convex surface19of the rack bar8relatively movably in the direction A, so as to support the rack bar8movably in the direction A; a pair of O-rings25made of rubber and serving as endless annular elastic members provided on the rack guide body22; and a cylindrical bush26made of synthetic resin and similarly provided on the rack guide body22.

The rack guide body22has, in addition to the circular arc-shaped concave surface21, a cylindrical outer peripheral surface31; a wide annular recessed portion32formed in the outer peripheral surface31; at least one, in this embodiment two, narrow annular grooves34formed in a cylindrical bottom surface33of the annular recessed portion32and each having a narrower width in the axial direction of the rack guide body22, i.e., in the direction C, than the width of the wide annular recessed portion32; a cylindrical recess36provided in another end face35opposing the one end face20where the circular arc-shaped concave surface21is disposed; and a through hole37which is disposed in a center of the circular arc-shaped concave surface21in such a manner as to communicate with the recess36on one side and to be open at the circular arc-shaped concave surface21on the other side.

The annular recessed portion32comprises by a circular ring-shaped recessed portion41formed in the outer peripheral surface31of the rack guide body22over its entire circumferential area.

The sliding plate piece24supports the rack bar8movably in the direction A, is comprised of a backing plate formed of a steel plate, a porous sintered alloy layer formed integrally on the surface of that metal backing, and a synthetic resin layer filled in the pores of, and coated on the surface of, the porous sintered alloy layer. The sliding plate piece24has the circular arc-shaped inner surface23on the synthetic resin layer side. In addition to the inner surface23having a shape complementary to the circular arc-shaped convex surface19of the rack bar8, the sliding plate piece24has a circular arc-shaped outer surface42having a shape complementary to the circular arc-shaped concave surface21of the rack guide body22as well as a bottomed cylindrical portion43formed on a central portion of the outer surface42. The sliding plate piece24at its bottomed cylindrical portion43is fitted in the through hole37of the rack guide body22, and is seated at its outer surface42on the circular arc-shaped concave surface21of the rack guide body22.

The O-ring25is provided on the rack guide body22by being fitted and secured in each of the narrow annular grooves34in such a manner as to radially project from an opening of each of these narrow annular grooves34.

The cylindrical bush26has a cylindrical portion48which is formed of a thermoplastic synthetic resin such as polyacetal resin, polyamide resin, and polybutylene terephthalate resin which exhibit self-lubricity, or a thermoplastic synthetic resin in which a lubricating substance such as lubricating oil, graphite, molybdenum disulfide, tetrafluoroethylene resin, or the like is incorporated. The cylindrical portion48has a split groove45and is provided on the rack guide body22by being fitted and secured in the recessed portion41of the wide annular recessed portion32, such that the cylindrical portion48on an outer peripheral surface46side thereof projects radially from the opening of the recessed portion41of the annular recessed portion32, while an inner peripheral surface47of the cylindrical portion48abuts against the outer surface of the O-ring25.

Before the rack guide9is fitted in the holding hole2, a clearance is secured between end faces of the cylindrical portion48at the split groove45, and a degree of freedom of deformation is hence imparted to the cylindrical bush26in its radially inward and outward directions.

The cylindrical bush26is fitted in the holding hole2with an interference, and its outer peripheral surface46is in contact with the inner peripheral surface15of the cylindrical portion13defining the holding hole2movably in the direction C.

In the state in which the rack guide9is fitted in the cylindrical holding hole2of the housing3with an interference, an annular clearance50between the bottom surface33of the recessed portion41and the inner peripheral surface47of the cylindrical portion48has a radial width δ which is smaller than a radial width Δ of an annular clearance51between the outer peripheral surface31of the rack guide body22and the inner peripheral surface15of the cylindrical portion13.

According to the above-described rack-and-pinion type steering apparatus1, the O-rings25are respectively fitted and secured in the annular grooves34formed in the bottom surface33of the recessed portion41, and the cylindrical bush26having the cylindrical portion48abutting against the outer peripheral surface of the O-rings25is fitted and secured in the recessed portion41. Furthermore, in particular, the annular clearance50has the radial width δ which is smaller than the radial width Δ of the annular clearance51. Therefore, it is possible to prevent collision between the outer peripheral surface31of the rack guide body22and the inner peripheral surface15of the cylindrical portion13defining the holding hole2, making it possible to eliminate the occurrence of collision noise. In addition, it is possible to constantly move the rack guide9smoothly in the direction toward the rack bar8without causing adhesive wear which is ascribable to the “metals of similar composition” between the rack guide body22and the cylindrical portion13. Moreover, it is possible to absorb the noise of collision between the rack teeth7and the teeth of the pinion6, thereby making it possible to reduce that collision noise as well.

In addition, according to the rack-and-pinion type steering apparatus1, since the synthetic resin-made cylindrical portion48is fitted and secured to the outer peripheral surface31of the rack guide body22, the sliding frictional resistance between the outer peripheral surface46of the cylindrical portion48and the inner peripheral surface15of the cylindrical portion13can be reduced, with the result that it is possible to constantly allow the movement of the rack guide9in the direction toward the rack bar8to be effected more smoothly.

The above-described rack guide9includes the annular recessed portion32constituted by the circular ring-shaped recessed portion41formed in the outer peripheral surface31of the rack guide body22over its entire circumferential area; the cylindrical bush26constituted by the cylindrical portion48fitted and secured in the recessed portion41of the annular recessed portion32; the two narrow annular grooves34; and the O-rings25respectively disposed in the annular grooves34. Alternatively, as shown inFIGS. 9 to 13, the rack guide9may include: the wide annular recessed portion32further having, in addition to the recessed portion41, a pair of circular arc-shaped recessed portions52continuous to the recessed portion41and formed on mutually opposing outer peripheral surface portions60in the outer peripheral surface31of the rack guide body22; the cylindrical bush26further having, in addition to the cylindrical portion48, a pair of synthetic resin-made circular arc-shaped projecting portions53which are formed integrally on the cylindrical portion48in face-to-face relation to each other with the split groove45located therebetween and which are respectively fitted and secured to the pair of circular arc-shaped recessed portions52; the one narrow annular groove34; and the one O-ring25disposed in the annular groove34.

The above-described rack guide9further includes the rack guide body22having the circular arc-shaped concave surface21, as well as the slider24having the inner surface23having a shape complementary to the circular arc-shaped convex surface19of the rack bar8and the outer surface42having a shape complementary to the circular arc-shaped concave surface21. Alternatively, as shown inFIG. 14, the rack guide9may include the rack guide body22provided on the one end face20side with a recessed surface64having a pair of flat surfaces61mutually opposing to each other, a pair of inclined surfaces62extending integrally in such a manner as to oppose each other from the pair of flat surfaces61, respectively, and a bottom flat surface63extending integrally from the pair of flat surfaces61and having the through hole37disposed in the center; and the sliding plate piece24having an outer surface71and an inner surface72having shapes similar to that of the recessed surface64. In this case, the sliding plate piece24at its bottomed cylindrical portion43is fitted in the through hole37of the rack guide body22, and is seated at its outer surface71on the recessed surface64of the rack guide body22. The sliding plate piece24at a pair of inclined surfaces73of its inner surface72is adapted to be brought into contact with the circular arc-shaped convex surface19of the rack bar8relatively movably in the direction A.

In the case where the rack guide9having the rack guide body22and the sliding plate piece24such as those shown inFIG. 14is used, it is possible to use the rack bar8having inclined surfaces corresponding to the pair of inclined surfaces73instead of the rack bar8having the circular arc-shaped convex surface19.