Rack guide and rack-and-pinion type steering apparatus having the rack guide

A rack and pinion steering device has a pinion rotatable in the R-direction, a rack bar having rack teeth meshing with the pinion and rectilinearly movable in the A-direction, a housing for rotatably supporting the pinion, a rack guide for slidably supporting the rack bar, and an elastic means for pressing the rack guide toward the pinion.

This application is the U.S. national phase of International Application No. PCT/JP2006/309865 filed 17 May 2006 which designated the U.S. and claims priority to Japanese Application No. 2005-146102 filed 18 May 2005, the entire contents of each of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a rack guide for supporting a rack bar of an automotive steering mechanism and a rack-and-pinion type steering apparatus having the rack guide.

BACKGROUND ART

A rack-and-pinion type steering apparatus is generally comprised of a housing, a pinion rotatably supported by this housing, a rack bar having rack teeth meshing with this pinion, a rack guide disposed in the housing to slidably support the rack bar, and a resilient means such as a spring for pressing this rack guide toward the rack bar.

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

In such a rack-and-pinion type steering apparatus, the rack guide for slidably supporting the rack bar which linearly moves in the steering operation is slidably fitted in the housing with a very small gap (clearance) with the inner peripheral surface of the housing movably in a direction perpendicular to the linearly moving direction of the rack bar, so as to avoid the swinging motion of the rack guide itself. However, since the rack guide and the housing are generally formed of metal, the so-called “metal of similar composition” can possibly occur between the rack guide and the housing when the rack guide slides with respect to the housing. If such a “metal of similar composition” occurs, there arises the problem that the movement of the rack guide toward the rack bar is hampered due to an increase in the frictional resistance and adhesive wear.

Accordingly, it has been proposed to eliminate the direct contact of the rack guide with the housing by fitting a resilient ring on the rack guide. With the rack-and-pinion type steering apparatus based on such a proposal, it is possible to overcome the drawbacks due to the “metal of similar composition.” However, as a result of the fact that the resilient ring fitted on the rack guide completely closes the very small gap which functions as an air passage between the inner peripheral surface of the housing and the rack guide, the circulation of air, which is effected through the very small gap as the rack guide moves with respect to the housing, becomes difficult, and the space between the housing and the end face of the rack guide becomes a closed air chamber. Owing to this closed air chamber, there arises the possibility that the speedy movement of the rack guide with respect to the housing is hampered.

The present invention has been devised in view of the above-described aspects, and its object is to provide a rack guide which makes it possible to overcome the drawbacks caused by the “metal of similar composition,” and which makes it possible not to produce the closed air chamber between the housing and the end face of the rack guide and which makes it possible to thereby allow the rack guide to speedily move in the axial direction with respect to the housing and instantly respond to the displacement in the direction perpendicular to the linearly moving direction of the rack bar, as well as a rack-and-pinion type steering apparatus having the rack guide.

Means for Solving the Problems

The rack guide in accordance with the present invention comprises: a slider having a slidable surface which is adapted to slidably contact a rack bar; a rack guide base body which supports the slider at one axial end face thereof and has an annular groove at an outer peripheral surface thereof; an annular resilient member which is fitted to the annular groove of the rack guide base body and is adapted to contact an inner peripheral surface of a housing of a rack-and-pinion type steering apparatus at an outer peripheral surface projecting from the outer peripheral surface of the rack guide base body; and communicating means which is disposed in the rack guide base body and has one end portion opened to an interior of the housing at the outer peripheral surface or the one axial end face of the rack guide base body and another end portion opened thereto at another axial end face of the rack guide base body, so as to allow the interior of the housing on a side of the outer peripheral surface or the one axial end face of the rack guide base body to communicate with the interior of the housing on a side of the other axial end face of the rack guide base body, wherein the annular resilient member is disposed so as to contact the inner peripheral surface of the housing between the one end portion of the communicating means which is open at the outer peripheral surface or the one axial end face of the rack guide base body and the other end portion of the communicating means which is open at the other axial end face of the rack guide base body, as viewed in an axial direction.

According to the rack guide in accordance with the present invention, since the annular resilient member fitted in the annular groove of the rack guide base body is adapted to contact the inner peripheral surface of the housing of the rack-and-pinion type steering apparatus at its outer peripheral surface projecting from the outer peripheral surface of the rack guide base body, it is possible to eliminate the direct contact of the rack guide base body with respect to the housing. Further, the communicating means, which allows the interior of the housing on the side of the outer peripheral surface or the one axial end face of the rack guide base body to communicate with the interior of the housing on the side of the other axial end face of the rack guide base body, is disposed in the rack guide base body and has one end portion opened to the interior of the housing at the outer peripheral surface or the one axial end face of the rack guide base body and another end portion opened thereto at the other axial end face of the rack guide base body. Moreover, the annular resilient member is disposed so as to contact the inner peripheral surface of the housing between the one end portion of the communicating means which is open at the outer peripheral surface or the one axial end face of the rack guide base body and the other end portion of the communicating means which is open at the other axial end face of the rack guide base body, as viewed in an axial direction. Therefore, the interior of the housing on the side of the outer peripheral surface or the one axial end face of the rack guide base body and the interior of the housing on the side of the other axial end face of the rack guide base body divided by the annular resilient member can be communicated with each other, thereby making it possible not to produce a closed air chamber between the housing and the other axial end face of the rack guide. Thus, the rack guide in accordance with the present invention is able to instantly respond to the displacement in the direction perpendicular to the linearly moving direction of the rack bar.

In a preferred example, the slider includes a slider body having the slidable surface on one surface and a cylindrical projecting portion provided integrally on another surface of the slider body, and the rack guide base body includes a supporting surface provided on the one axial end face and adapted to support the slider body, a large-diameter recessed portion which is open at a central portion of the supporting surface and has a larger diameter than the diameter of the projecting portion of the slider, and a fitting hole which communicates with the large-diameter recessed portion and in which the projecting portion of the slider is fitted. Further, the communicating means includes a transverse groove which is covered by the slider body and is open at the outer peripheral surface or the one axial end face of the rack guide base body, a vertical groove which is covered by the projecting portion of the slider and is provided on an annular wall surface of the rack guide base body defining the fitting hole, an annular space which communicates with the transverse groove on one side and with the vertical groove on another side, and which is defined by an annular wall surface of the rack guide base body defining the large-diameter recessed portion and by an outer peripheral surface of the projecting portion of the slider, and a communicating passage which communicates with the fitting hole and is open at the other axial end face of the rack guide base body.

According to the rack guide of such an example, in a case where the rack guide base body is manufactured from, for example, aluminum or the like by the die casting process, the communicating means can be easily formed by only preparing a die having a shape capable of simultaneously forming the transverse groove and the vertical groove in addition to the large-diameter recessed portion and the fitting hole. Therefore, it is possible to substantially lower the manufacturing cost.

The projecting portion of the slider may be a bottomed cylindrical one having a hollow cylindrical portion and a bottom portion provided integrally on one end of the hollow cylindrical portion. Alternatively, however, the projecting portion of the slider may comprise only the hollow cylindrical portion which does not have the bottom portion. In the case of the bottomed hollow cylindrical projecting portion, the interior of the hollow cylindrical portion can be favorably used as a reservoir for a lubricant.

The communicating means may further include a cavity disposed between the communicating passage and a bottom portion of the projecting portion of the slider, in which case the cavity may communicate with the vertical groove on one side and with the communicating passage on another side.

Preferably, the rack guide base body has at least two annular grooves spaced apart in the axial direction, in which case annular resilient members may be respectively fitted in the annular grooves. If the rack guide base body has such at least two annular grooves, the swinging motion of the rack guide base body can be favorably suppressed.

The rack-and-pinion type steering apparatus in accordance with the present invention comprises: a rotatable pinion; the rack bar which has rack teeth meshing with the pinion and is linearly movable; the housing for rotatably supporting the pinion; the rack guide according to any one of the above-described aspects for slidably supporting the rack bar; and resilient means for pressing the rack guide toward the pinion.

As the slider, it is suitable to use a synthetic resin material such as a polyacetal resin or a polyamide resin, or a multilayered material consisting of a steel sheet, a porous sintered metal layer formed integrally on this steel sheet, and a synthetic resin layer impregnating and coated on this porous sintered metal layer and formed of a synthetic resin such as a polyacetal resin or a polyamide resin. In particular, as the slider having the slider body and the bottomed hollow cylindrical projecting portion, it is preferable to use one which is formed integrally by subjecting a plate-like material consisting of such a multilayered material to press forming.

Advantageous Effect of the Invention

According to the present invention, it is possible to provide a rack guide which makes it possible to overcome the drawbacks caused by the “metal of similar composition,” and which makes it possible not to produce the closed air chamber between the housing and the end face of the rack guide and which makes it possible to thereby allow the rack guide to speedily move in the axial direction with respect to the housing and instantly respond to the displacement in the direction perpendicular to the linearly moving direction of the rack bar, as well as a rack-and-pinion type steering apparatus having the rack guide.

BEST MODE FOR CARRYING OUT THE INVENTION

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

DESCRIPTION OF THE PREFERRED EMBODIMENTS

InFIGS. 1 to 8, a rack-and-pinion type steering apparatus1in accordance with this embodiment is comprised of a pinion2which is rotatable in an R direction, a rack bar4which has rack teeth3meshing with the pinion2and is linearly movable in an A direction (a direction perpendicular to the plane of the drawing inFIG. 1), a housing5for rotatably supporting the pinion2, a rack guide6for slidably supporting the rack bar4, and a resilient means7for pressing the rack guide6toward the pinion2.

A pinion shaft11on which the pinion is integrally provided is supported in the housing5by means of a pair of ball bearings12so as to be rotatable in the R direction, and is adapted to be rotated in the R direction in the steering operation.

The rack bar4, which is moved linearly in the A direction through the meshing between the pinion2and the rack teeth3by the rotation of the pinion2in the R direction, has a sliding surface15which is provided on the opposite side to the surface where the rack teeth3are provided and which is constituted by a semicylindrical convex surface.

The housing5through which the rack bar4is passed includes a housing body portion16to which the ball bearings12are attached; a hollow cylindrical portion18formed integrally on the housing body portion16and having a cylindrical inner peripheral surface17; and a cover portion20threadedly secured to one end portion of the hollow cylindrical portion18by means of a threaded portion19. The cover portion20is fixed to the hollow cylindrical portion18by a lock nut21threadedly secured to the cover portion20.

The rack guide6includes a slider26which is adapted to slidably contact the sliding surface15of the rack bar4and has a slidable surface25constituted by a semicylindrical concave surface; a rack guide base body30which supports the slider26at one end face27in an axial direction B perpendicular to the A direction and which has two annular grooves29formed at an outer peripheral surface28and spaced apart in the axial direction B; a pair of annular resilient members32which are constituted by O-rings or the like and which are respectively fitted to the annular grooves29of the rack guide base body30and are adapted to contact the inner peripheral surface17of the hollow cylindrical portion18of the housing5at their outer peripheral surfaces31projecting from the outer peripheral surface28of the rack guide base body30; and a communicating means34which is disposed in the rack guide base body30which has one end portion35open to the interior of the housing5at the outer peripheral surface28of the rack guide base body30and the other end portion36open thereto at the other end face33in the axial direction B of the rack guide base body30, so as to allow the interior of the housing5on the outer peripheral surface28side of the rack guide base body30to communicate with the interior of the housing5on the other end face33side in the axial direction B of the rack guide base body30. Thus, the both annular resilient members32are disposed so as to contact the inner peripheral surface17of the hollow cylindrical portion18of the housing5between the one end portion35of the communicating means34which is open at the outer peripheral surface28of the rack guide base body30and the other end portion36of the communicating means34which is open at the other end face in the axial direction B of the rack guide base body30, as viewed in the axial direction B.

The slider26, which is formed of a thin steel plate, a porous sintered metal layer integrally formed on this thin steel plate, and a synthetic resin layer with which this porous sintered metal layer is impregnated and coated and whose synthetic resin layer side constitutes the slidable surface25, includes a slider body41formed in the shape of a curved plate and having the slidable surface25on one surface, as well as a bottomed cylindrical projecting portion43provided integrally on the other surface42which is the opposite surface to the slidable surface25of the slider body41. The projecting portion43has a hollow cylindrical portion44and a bottom portion45provided integrally on one end of the hollow cylindrical portion44.

The rack guide base body30disposed in the hollow cylindrical portion18of the housing5and formed integrally of aluminum or the like includes, in addition to the annular grooves29, a supporting surface51provided on the one end face27in the axial direction B and adapted to support the slider body41; a large-diameter recessed portion52which is open at a central portion of the supporting surface51and has a larger diameter than the diameter of the hollow cylindrical portion44of the projecting portion43; a fitting hole53which communicates with the large-diameter recessed portion52and in which the hollow cylindrical portion44of the projecting portion43of the slider26is closely fitted; a small-diameter hole54communicating with the fitting hole53and having a smaller diameter than the fitting hole53; a recessed portion55which communicates with the small-diameter hole54and is open at the other end face33in the axial direction B of the rack guide base body30; and four holding projections56provided integrally on both edge portions in the A direction of the supporting surface51.

The supporting surface51constituted by a semicylindrical concave surface is in contact with the surface42which is a semicylindrical convex surface of the slider body41.

The four holding projections56surrounding the slider body41are adapted to engage edges of the slider body41so as to prevent the positional offset of the slider body41with respect to the supporting surface51.

The one end face27of the rack guide base body30has, in addition to the supporting surface51, a pair of crescent-shaped end faces57continuing to that supporting surface51. The outer peripheral surface28of the rack guide base body30has a pair of flat outer surfaces61opposed to each other in the A direction, as well as a pair of cylindrical surfaces62continuing to the flat outer surfaces61and each disposed between the pair of flat outer surfaces61. Each of the pair of flat outer surfaces61is divided by the annular grooves29in the axial direction B, and each flat outer surface61has an edge portion flat outer surface63continuing to the supporting surface51, and the edge portion flat outer surface63is located inwardly (on the large-diameter recessed portion52side) of the remaining portions of the flat outer surface61through a stepped portion64. Each of the pair of cylindrical surfaces62is also divided by the annular grooves29in the axial direction B. In each cylindrical surface62, a cylindrical surface65between the annular groove29and the end face27has a trapezoidal cylindrical surface67in which a plurality of retaining grooves66extending in parallel to the annular groove29to retain a lubricating oil such as grease are formed, as well as an edge portion cylindrical surface69located inwardly of the cylindrical surface67through a stepped portion68. The end face33of the rack guide base body30has an annular shape.

The communicating means34includes a pair of transverse grooves75which are covered by the slider body41and is open to the interior of the housing5at each of the edge portion flat outer surfaces63of the outer peripheral surface28of the rack guide base body30; a pair of vertical grooves77which are covered by the hollow cylindrical portion44of the projecting portion43of the slider26and are provided on an annular wall surface76of the rack guide base body30defining the fitting hole53; an annular space80which communicates with the transverse grooves75on one side and with the vertical grooves77on the other side, and which is defined by an annular wall surface78of the rack guide base body30defining the large-diameter recessed portion52and by an outer peripheral surface79of the hollow cylindrical portion44of the projecting portion43; a communicating passage81which communicates with the fitting hole53and is open to the interior of the housing5at the other end face33in the axial direction B of the rack guide base body30; and a cavity82disposed between the communicating passage81and the bottom portion45of the projecting portion43of the slider26in the fitting hole53.

One transverse groove75is provided in the supporting surface51of the rack guide base body30such that its one end portion35in the A direction is open to the interior of the housing5at the one edge portion flat outer surface63, and such that its other end portion in the A direction is open to the annular space80at the annular wall surface78. The other transverse groove75is provided in the supporting surface51of the rack guide base body30such that its one end portion35in the A direction is open to the interior of the housing5at the other edge portion flat outer surface63, and such that its other end portion in the A direction is open to the annular space80at the annular wall surface78. The pair of vertical grooves77are arranged in face-to-face relation to each other in the A direction. The cavity82formed between the small-diameter hole54and the bottom portion45of the projecting portion43of the slider26in the fitting hole53communicates with the vertical grooves77on one side and with the communicating passage81on the other side. The communicating passage81is constituted by the small-diameter hole54communicating with the cavity82and by the recessed portion55communicating with the small-diameter hole54and having the end portion36.

The resilient means7has a coil spring86which is disposed between the rack guide base body30and the cover portion20in such a manner as to be compressed with its one end in contact with an annular face85of the rack guide base body30defining the recessed portion55and with its other end in contact with the cover portion20. The coil spring86resiliently presses the slidable surface25of the slider26against the sliding surface15of the rack bar4by means of the rack guide base body30.

In the above-described rack-and-pinion type steering apparatus1, when the pinion shaft11is rotated in the R direction in the steering operation, the rack bar4is moved linearly in the A direction through the meshing between the pinion2and the rack teeth3. As a result, the steering operation can be transmitted to automobile wheels connected to the rack bar4. In the rack-and-pinion type steering apparatus1, the rack guide6is adapted to guide the linear motion in the A direction of the rack bar4by coming into contact with the sliding surface15of the rack bar4at its slidable surface25, and to secure the meshing between the pinion2and the rack teeth3by the resiliency of the resilient means7. Moreover, the rack guide6is adapted to move in the axial direction B by being accompanied by the extension and contraction of the resilient means7by following the very small displacement in the axial direction B of the rack bar4.

Incidentally, according to the above-described rack guide6, since the annular resilient members32fitted in the annular grooves29of the rack guide base body30are adapted to contact the inner peripheral surface17of the housing5at their outer peripheral surfaces31projecting from the outer peripheral surface28of the rack guide base body30, it is possible to eliminate the direct contact of the rack guide base body30with respect to the housing5. As a result, it is possible to overcome the drawback caused by the “metals of similar composition.” Further, the communicating means34allows the interior of the housing5on the outer peripheral surface28side of the rack guide base body30, i.e., an annular space91between the inner peripheral surface17and the cylindrical surface65, to communicate with the interior of the housing5on the end face33side in the axial direction B of the rack guide base body30, i.e., a space92between the end face33and the cover portion20. Furthermore, the both annular resilient members32are disposed so as to contact the inner peripheral surface17of the hollow cylindrical portion18of the housing5between the one end portion35of the communicating means34which is open at the outer peripheral surface28of the rack guide base body30and the other end portion36of the communicating means34which is open at the other end face33in the axial direction B of the rack guide base body30, as viewed in the axial direction B. Therefore, the annular space91and the space92in the housing5divided by the annular resilient members32can be communicated with each other, and it is possible not to produce a hermetically closed air chamber between the cover portion20of the housing5and the end face33in the axial direction B of the rack guide6. Hence, it becomes possible for the rack guide6to instantly move in the axial direction B with respect to the hollow cylindrical portion18of the housing5by following the very small displacement in the axial direction B of the rack bar4. In consequence, it is possible to constantly ensure the close meshing between the pinion2and the rack teeth3, thereby making it possible to eliminate the occurrence of abnormal noise due to the teeth collision between the pinion2and the rack teeth3.

In the rack guide6in accordance with this embodiment, the rack guide30is provided with the transverse grooves75and the vertical grooves77which are each provided in a pair, the transverse grooves75and the vertical grooves77may respectively be one or three or more. Further, although each transverse groove75is made open to the interior of the housing5at the edge portion flat outer surface63, in substitution for or in addition to it each transverse groove75may be made open to the interior of the housing5at the crescent-shaped end face57of one end face27in the axial direction B.

The outer peripheral surface28of the above-described rack guide base body30has the pair of flat outer surfaces61opposed to each other in the A direction, with the result that in a case where the rack guide base body30is manufactured from aluminum or the like by the die casting process, as runner channel ends are disposed at the portions of the die corresponding to such flat outer surfaces61, even if runners produced by the runner channels after the casting are cut with slight cut remnants (projections), such cut remnants can be made not to project from a phantom circle defined by the cylindrical surface62. In the present invention, however, the rack guide base body30may be one having the outer peripheral surface28which is not provided with the pair of flat outer surfaces61and is constituted by a circumferentially extending cylindrical surface62, as shown inFIG. 10.