Thrust sliding bearing and mounting structure of a strut-type suspension using the thrust sliding bearing

A thrust sliding bearing 1 includes a synthetic resin-made lower casing 2, a synthetic resin-made upper casing 3 superposed on the lower casing 2, and a synthetic resin-made thrust sliding bearing piece 4 interposed between said upper casing 3 and the lower casing 2.

This application is the U.S. national phase of International Application No. PCT/JP2011/007110 filed 20 Dec. 2011 which designated the U.S. and claims priority to JP Patent application No. 2011-002510 filed 7 Jan. 2011, the entire contents of each of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a synthetic resin-made thrust sliding bearing, and more particularly to a thrust sliding bearing which is suitably incorporated as a thrust sliding bearing of a strut-type suspension (Macpherson type) in a four-wheeled motor vehicle, as well as a mounting structure of a strut-type suspension using the thrust sliding bearing.

BACKGROUND ART

In general, a strut-type suspension is mainly used for a front wheel of a four-wheeled motor vehicle, and has a construction in which a strut assembly incorporating a hydraulic shock absorber in an outer cylinder formed integrally with a main shaft is combined with a coil spring. Among such suspensions, (1) there is a type of structure in which the axis of the coil spring is actively offset with respect to the axis of the strut, so as to allow the sliding of a piston rod of the shock absorber incorporated in that strut to be effected smoothly, and (2) there is another type of structure in which the axis of the coil spring is arranged in alignment with the axis of the strut. In the suspension of either structure, a bearing is disposed between a mounting member for a motor vehicle body and an upper spring seat of the coil spring to allow the rotation to be effected smoothly when the strut assembly rotates together with the coil spring by the steering operation.

Further, this bearing is required to have a performance which supports the vehicle body load (thrust load) and concurrently smoothly allows for the radial load due to the above-described suspension structure, i.e., in the case of the former structure, the radial load produced by the restoring force of the coil spring in the axial direction of the strut even in a stationary state since the axis of the coil spring is offset with respect to the axis of the strut, and in the case of the latter structure, the radial load occurring due to misalignment attributable to the difficulty in fabrication that the axis of the strut and the axis of the coil spring must be arranged in alignment with each other.

PRIOR ART DOCUMENTS

Patent Documents

SUMMARY OF THE INVENTION

Problems that the Invention is to Solve

As a thrust sliding bearing which smoothly allows for the thrust load and radial load described above, a thrust sliding bearing has been proposed which is comprised of a synthetic resin-made lower casing, a synthetic resin-made upper casing superposed on this lower casing, a synthetic resin-made disk-shaped thrust sliding bearing piece interposed between the upper and lower casings, and a synthetic resin-made radial bearing piece interposed between the upper and lower casings (Patent Document 1 and Patent Document 2).

However, there are cases where it is impossible to secure a space for radially outward mounting between a vehicle body-side mounting member and an upper spring seat where the thrust sliding bearing is disposed. In addition, there is an economic problem in that an increase in cost is entailed as the two bearings, the thrust sliding bearing and the radial sliding bearing, are used.

The present invention has been devised in view of the above-described aspects, and its object is to provide a thrust sliding bearing which is capable of overcoming the problem of the mounting space and also overcoming the economic problem by making the radial dimension small by forming a radial sliding bearing portion within the upper and lower casings without using a radial sliding bearing.

Means for Solving the Problems

A thrust sliding bearing in accordance with the present invention comprises: a synthetic resin-made lower casing, a synthetic resin-made upper casing superposed on the lower casing, and a synthetic resin-made thrust sliding bearing piece interposed between the upper casing and the lower casing, wherein the lower casing includes an annular base portion which has an annular upper surface and an annular lower surface, as well as a tubular small-diameter inner surface, a tubular large-diameter inner surface, and a cylindrical outer surface which are arranged between the annular upper surface and the annular lower surface and has a first annular recessed portion provided on the annular upper surface; a small-diameter hole which is defined by the tubular small-diameter inner surface of the annular base portion and is open at the annular lower surface of the annular base portion; a large-diameter hole which is defined by the tubular large-diameter inner surface of the annular base portion and is open at the annular upper surface of the annular base portion; an annular shoulder surface which is continuous from the tubular small-diameter inner surface at its annular inner peripheral end and is continuous from the tubular large-diameter inner surface at its annular outer peripheral end; an annular projecting portion which projects radially outward from a lower end portion of the cylindrical outer surface; a tubular projecting portion which is provided on an annular upper surface of the annular projecting portion and defines a second annular recessed portion by its tubular inner surface in cooperation with the cylindrical outer surface and the annular upper surface of the annular projecting portion; and an annular engaging projecting portion which projects radially outward from a tubular outer surface of the tubular projecting portion, wherein the upper casing includes an annular baseplate portion; an inner tubular suspended portion which is integrally provided on a tubular inner surface of the annular baseplate portion in such a manner as to be suspended downward from an annular upper surface of the annular baseplate portion and defines a central hole concentric with the small-diameter hole by its tubular inner surface; a thick-walled outer tubular suspended portion which is integrally provided on a tubular outer surface of the annular baseplate portion in such a manner as to be suspended from the annular upper surface of the annular baseplate portion and to extend downwardly of an annular lower end surface of the inner tubular suspended portion, and which has a cylindrical inner surface; a third annular recessed portion which is defined by an annular lower surface of the annular baseplate portion, a tubular outer surface of the inner tubular suspended portion, and the cylindrical inner surface of the outer tubular suspended portion; an inner tubular vertical wall portion and an outer tubular vertical wall portion which are provided vertically downward from an annular lower end surface of the outer tubular suspended portion; a fourth annular recessed portion which is defined by the annular lower end surface of the outer tubular suspended portion, a tubular outer surface of the inner tubular vertical wall portion, and a tubular inner surface of the outer tubular vertical wall portion; an annular engaging portion which projects downward from an annular lower end surface of the outer tubular vertical wall portion; and an annular hook portion which projects radially inward from a tubular inner surface of the annular engaging portion, and wherein the thrust sliding bearing piece is disposed in the third annular recessed portion with its annular upper surface brought into slidable contact with the annular lower surface of the annular baseplate portion defining the third annular recessed portion, and is disposed in the first annular recessed portion with its annular lower surface brought into slidable contact with an annular recessed portion bottom surface of the annular base portion defining the first annular recessed portion, such that the annular lower surface of the annular baseplate portion of the upper casing and the annular upper surface of the annular base portion of the lower casing are spaced apart from each other, the upper casing being superposed on the lower casing, such that the annular lower end surface of its inner tubular suspended portion is opposed to the annular shoulder surface with a gap therebetween, the cylindrical inner surface of its outer tubular suspended portion having a greater wall thickness than the inner tubular suspended portion concerning a radial direction is brought into slidable contact with the cylindrical outer surface of the annular base portion of the lower casing, its inner tubular vertical wall portion is disposed in the second annular recessed portion, and its annular hook portion is resiliently fitted to the annular engaging projecting portion, whereby a sealing portion based on labyrinth action is formed between the resiliently fitted portion and the slidably contacting portion of the cylindrical outer surface of the annular base portion with respect to the cylindrical inner surface of the outer tubular suspended portion by the inner tubular vertical wall portion disposed in the second annular recessed portion and the tubular projecting portion and the annular engaging projecting portion disposed in the fourth annular recessed portion.

According to the thrust sliding bearing in accordance with the present invention, the relative rotation between the upper casing and the lower casing in the direction of the thrust load is allowed by the smooth sliding between the annular upper surface of the thrust sliding bearing piece disposed in the first and third annular recessed portions and the annular lower surface of the annular baseplate portion of the upper casing, whereas the relative rotation between the upper casing and the lower casing in the direction of the radial load is allowed by the smooth sliding between the cylindrical inner surface of the outer tubular suspended portion of the upper casing and the cylindrical outer surface of the annular base portion of the lower casing.

In addition, according to the thrust sliding bearing in accordance with the present invention, since the thrust sliding bearing portion, which is constituted by the annular upper surface of the thrust sliding bearing piece and the annular lower surface of the annular baseplate portion of the upper casing and allows smooth sliding in the relative rotation between the upper casing and the lower casing with respect to the direction of the thrust load, is located upwardly of the sealing portion based on the labyrinth action and the annular upper surface of the lower casing, it is possible to prevent as practically as possible the ingress of foreign objects such as dust from the inner and outer peripheral surface sides into that thrust sliding bearing portion, thereby making it possible to obviate trouble such as the abnormal wear of the thrust sliding bearing portion ascribable to the ingress of such foreign objects. Furthermore, the ingress of foreign objects such as dust from the outer peripheral surface side into the radial sliding bearing portion, which is constituted by the cylindrical inner surface of the outer tubular suspended portion of the upper casing and the cylindrical outer surface of the annular base portion of the lower casing and allows smooth sliding in the relative rotation between the upper casing and the lower casing with respect to the direction of the radial load, is prevented as practically as possible by the sealing portion based on the labyrinth action, thereby also making it possible to obviate trouble such as the abnormal wear of the radial sliding bearing portion ascribable to the ingress of such foreign objects.

In the thrust sliding bearing in accordance with the present invention, the synthetic resin for forming the thrust sliding bearing piece interposed between the upper casing and the lower casing should preferably have self-lubricity, in particular, whereas the synthetic resin for forming upper casing and the lower casing should preferably excel in mechanical properties, such as wear resistance, shock resistance, sliding properties including creep resistance, and rigidity. Specifically, the upper casing and the lower casing should preferably be formed of a thermoplastic synthetic resin such as polyacetal resin, polyamide resin, and polyester resin. Meanwhile, the thrust sliding bearing piece should preferably be formed of such as polyethylene resin, fluororesin, or the like.

A mounting structure for mounting to a vehicle body through the above-described thrust sliding bearing a strut-type suspension for a motor vehicle equipped with a hydraulic shock absorber and a coil spring disposed in such a manner as to surround the hydraulic shock absorber, comprises: mounting means for mounting a piston rod of the hydraulic shock absorber to the vehicle body and an upper spring receiving means for receiving the coil spring, the thrust sliding bearing being interposed between the mounting means and the upper spring receiving means, wherein the mounting means includes: a vehicle body mounting member having an annular flat portion fixed to a vehicle body side and a cylindrical projecting portion projecting downwardly from an annular inner edge of the annular flat portion and defining a through hole by its inner peripheral surface; and a mounting member having an annular flat portion formed integrally on a lower surface of the annular flat portion of the vehicle body mounting member, as well as a cylindrical suspended portion extending downwardly from an annular outer edge of the annular flat portion, wherein the upper spring receiving means is constituted by an upper spring receiving member having an annular flat portion and a cylindrical projecting portion which projects upwardly from an annular inner edge of the annular flat portion and defines a through hole by its inner peripheral surface, a lower end surface of the cylindrical projecting portion of the vehicle body mounting member and an upper end surface of the cylindrical projecting portion of the upper spring receiving member being arranged in such a manner as to oppose each other, and wherein the thrust sliding bearing is interposed in an annular space which is formed by the cylindrical projecting portion of the vehicle body mounting member, the annular flat portion of the mounting member, the cylindrical suspended portion of the mounting member, the annular flat portion of the upper spring receiving member, and the cylindrical projecting portion of the upper spring receiving member, such that the inner tubular suspended portion of the annular baseplate portion of the upper casing is brought into contact with an outer surface of the cylindrical projecting portion of the vehicle body mounting member, the annular upper surface of the annular baseplate portion of the upper casing is brought into contact with the annular flat portion of the mounting member, and an outer peripheral surface of the outer tubular suspended portion is surrounded by an inner surface of the cylindrical suspended portion of the mounting member, and such that the annular lower surface of the annular base portion of the lower casing is brought into contact with an upper surface of the flat portion of the upper spring receiving member, and the tubular small-diameter inner surface of the annular base portion of the lower casing is surrounded by an inner surface of the cylindrical projecting portion of the upper spring receiving member.

According to the mounting structure in accordance with the present invention, when the strut assembly is rotated by a steering operation, the lower casing is rotated with respect to the upper casing, and the rotation of this lower casing is smoothly allowed by the thrust sliding bearing piece interposed between the upper casing and the lower casing, thereby allowing the steering operation to be performed smoothly. In addition, when a radial load has been applied, the radial load is smoothly allowed by mutual sliding between the synthetic resins in the radial sliding bearing portion which is formed while holding a bearing clearance between the cylindrical inner surface of the outer tubular suspended portion of the annular baseplate portion of the upper casing and the cylindrical outer surface of the annular base portion of the lower casing and is constituted by that cylindrical inner surface and that cylindrical outer surface.

Advantages of the Invention

According to the present invention, it is possible to provide a low-cost thrust sliding bearing whose radial dimension can be made small by forming the radial sliding bearing portion between the upper and lower casings without using a radial sliding bearing, as well as a mounting structure of a strut-type suspension using this thrust sliding bearing.

MODE FOR CARRYING OUT THE INVENTION

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

A thrust sliding bearing1in accordance with the present invention is comprised of a synthetic resin-made lower casing2, a synthetic resin-made upper casing3superposed on the lower casing2, and a synthetic resin-made thrust sliding bearing piece4interposed between the upper casing3and the lower casing2.

The lower casing2includes an annular base portion11which has an annular upper surface5and an annular lower surface6, as well as a tubular small-diameter inner surface7, a tubular large-diameter inner surface8, and a cylindrical outer surface9which are arranged between the annular upper surface5and the annular lower surface6and has a wide annular recessed portion10provided on the annular upper surface5; a small-diameter hole12which is defined by the tubular small-diameter inner surface7of that annular base portion11and is open at the annular lower surface6of the annular base portion11; a truncated cone-shaped large-diameter hole13which is defined by the truncated cone-shaped tubular large-diameter inner surface8which is gradually enlarged in diameter toward the annular upper surface5of the annular base portion11and is open at the annular upper surface5of the annular base portion11; an annular shoulder surface which is continuous from the tubular small-diameter inner surface7at its annular inner peripheral end and is continuous from the tubular large-diameter inner surface8at its annular outer peripheral end; an annular projecting portion15which projects radially outward from a lower end portion of the cylindrical outer surface9; a tubular projecting portion19which is provided on an annular upper surface16of that annular projecting portion15and defines an annular recessed portion18by its tubular inner surface17in cooperation with the cylindrical outer surface9and the annular upper surface16of the annular projecting portion15; an annular engaging projecting portion20which projects radially outward from a tubular outer surface of the tubular projecting portion19; and two wall thickness-reducing annular recessed portions21which are formed in the annular lower surface6of the annular base portion11in such a manner as to extend from the annular lower surface6toward the annular upper surface5side and to surround the small-diameter hole12, so as to make the wall thickness of the annular base portion11uniform.

The upper casing3includes an annular baseplate portion25; an inner tubular suspended portion29which is integrally provided on a tubular inner surface of the annular baseplate portion25in such a manner as to be suspended downward from an annular upper surface26of that annular baseplate portion25and defines a central hole28concentric with the small-diameter hole12by its tubular inner surface27; a thick-walled outer tubular suspended portion32which is integrally provided on a tubular outer surface of the annular baseplate portion25in such a manner as to be suspended from the annular upper surface26of the annular baseplate portion25and to extend downwardly of an annular lower end surface30of the inner tubular suspended portion29, and which has a cylindrical inner surface31; an annular recessed portion36which is defined by an annular lower surface33of the annular baseplate portion25, a tubular outer surface34constituted by a truncated cone-shaped surface of the inner tubular suspended portion29, and the cylindrical inner surface31of the outer tubular suspended portion32; an inner tubular vertical wall portion38and an outer tubular vertical wall portion39which are provided vertically downward from an annular lower end surface37of the outer tubular suspended portion32; an annular recessed portion42which is defined by the annular lower end surface37of the outer tubular suspended portion32, a tubular outer surface40of the inner tubular vertical wall portion38, and a tubular inner surface41of the outer tubular vertical wall portion39; an annular engaging portion43which projects downward from an annular lower end surface of the outer tubular vertical wall portion39; and an annular hook portion44which projects radially inward from a tubular inner surface of the annular engaging portion43.

As for the outer tubular suspended portion32having the cylindrical inner surface31for forming the radial sliding bearing portion together with the cylindrical outer surface9of the lower casing2, its wall thickness is formed to be greater than the wall thickness of the inner tubular suspended portion29in order to enhance the strength with respect to the radial load.

The thrust sliding bearing piece4includes an annular plate-like portion53having a cylindrical inner surface52defining a central hole51; a pair of annular recessed grooves56which are adapted to accommodate a lubricant such as grease and are respectively formed on an annular upper surface54and an annular lower surface55of the annular plate-like portion53and surround the central hole51; and a plurality of radial recessed grooves58which are adapted to accommodate a lubricant such as grease and are formed on the annular upper surface54and the annular lower surface55of the annular plate-like portion53, with one ends thereof being open to the annular recessed groove56and other ends thereof being open to the outside at a cylindrical outer surface57of the annular plate-like portion53.

The cylindrical inner surface52defining the central hole51of the thrust sliding bearing piece4has a greater inside diameter dimension than the outside diameter dimension of an annular inner vertical wall surface61of the annular base portion11defining the annular recessed portion10, whereas the cylindrical outer surface57of the thrust sliding bearing piece4has a smaller outside diameter dimension than the inside diameter dimension of an annular outer vertical wall surface62of the annular base portion11defining the annular recessed portion10. A lubricant such as grease is filled in the annular recessed grooves56and the radial recessed grooves58formed on the annular upper surface54and the annular lower surface55of the annular plate-like portion53.

The thrust sliding bearing piece4is disposed in the annular recessed portion36with its annular upper surface54brought into slidable contact with the annular lower surface33of the annular baseplate portion25defining the annular recessed portion36, and is disposed in the annular recessed portion10with its annular lower surface55brought into slidable contact with an annular recessed portion bottom surface63of the annular base portion11defining the annular recessed portion10in cooperation with the annular inner vertical wall surface61and the annular outer vertical wall surface62, such that the annular lower surface33of the annular baseplate portion25of the upper casing3and the annular upper surface5of the annular base portion11of the lower casing2are spaced apart from each other. Thus, the annular upper surface54of the annular plate-like portion53is located upwardly of the opening plane of the wide annular recessed portion10.

With the thrust sliding bearing1having the above-described construction, the upper casing3is superposed on the lower casing2, such that the tubular outer surface34of the inner tubular suspended portion29of the annular baseplate portion25is opposed to the tubular large-diameter inner surface8of the annular base portion11of the lower casing2with a gap therebetween, while the annular lower end surface30of the inner tubular suspended portion29is opposed to the annular shoulder surface14of the annular base portion11of the lower casing2with a gap therebetween, the cylindrical inner surface31of the outer tubular suspended portion32having a greater wall thickness than the inner tubular suspended portion29concerning the radial direction is brought into slidable contact with the cylindrical outer surface9of the annular base portion11of the lower casing2, the inner tubular vertical wall portion38is disposed in the annular recessed portion18, and the annular hook portion44is resiliently fitted to the annular engaging projecting portion20, whereby a sealing portion based on labyrinth action is formed between the resiliently fitted portion and the slidably contacting portion of the cylindrical outer surface9of the annular base portion11with respect to the cylindrical inner surface31of the outer tubular suspended portion32by the inner tubular vertical wall portion38disposed in the annular recessed portion18and the tubular projecting portion19and the annular engaging projecting portion20disposed in the annular recessed portion42.

According to the thrust sliding bearing1, the relative rotation between the upper casing3and the lower casing2in the direction of the thrust load is allowed by the smooth sliding of the thrust sliding bearing involving, on the one hand, the annular upper surface54of the thrust sliding bearing piece4disposed in the annular recessed portions10and36and, on the other hand, the annular lower surface33of the annular baseplate portion25of the upper casing3, whereas the relative rotation between the upper casing3and the lower casing2in the direction of the radial load is allowed by the smooth sliding of the radial sliding bearing portion involving, on the one hand, the cylindrical inner surface35of the outer tubular suspended portion32of the upper casing3and, on the other hand, the cylindrical outer surface9of the annular base portion11of the lower casing2.

In addition, with the thrust sliding bearing1, since the thrust sliding bearing portion, which is constituted by the annular upper surface54of the thrust sliding bearing piece4and the annular lower surface33of the annular baseplate portion25of the upper casing3and allows smooth sliding in the relative rotation between the upper casing3and the lower casing2with respect to the direction of the thrust load, is located upwardly of the sealing portion based on the labyrinth action and the annular upper surface5of the lower casing2, it is possible to prevent as practically as possible the ingress of foreign objects such as dust from the inner and outer peripheral surface sides of the thrust sliding bearing1into that thrust sliding bearing portion, thereby making it possible to obviate trouble such as the abnormal wear of the thrust sliding bearing portion ascribable to the ingress of such foreign objects. Furthermore, the ingress of foreign objects such as dust from the outer peripheral surface side of the thrust sliding bearing1into the radial sliding bearing portion, which is constituted by the cylindrical inner surface31of the outer tubular suspended portion32of the upper casing3and the cylindrical outer surface9of the annular base portion11of the lower casing2and allows smooth sliding in the relative rotation between the upper casing3and the lower casing2with respect to the direction of the radial load, is prevented as practically as possible by the sealing portion based on the labyrinth action, thereby also making it possible to obviate trouble such as the abnormal wear of the radial sliding bearing portion ascribable to the ingress of the foreign objects.

A strut-type suspension72for a motor vehicle, which is equipped with a hydraulic shock absorber (not shown) and a coil spring71disposed in such a manner as to surround the hydraulic shock absorber, is mounted to a vehicle body through the above-described thrust sliding bearing1by means of a mounting structure73, as shown inFIG. 8.

The mounting structure73for mounting the strut-type suspension72to the vehicle body through the thrust sliding bearing1includes a mounting means75for mounting a piston rod74of the hydraulic shock absorber to the vehicle body as well as an upper spring receiving means76for receiving the coil spring71, and the thrust sliding bearing1is interposed between the mounting means75and the upper spring receiving means76.

The mounting means75includes a vehicle body mounting member78which is secured to the vehicle body through bolts77; a mounting member80which is integrally coupled to that vehicle body mounting member78and surrounds the annular upper surface26of the annular baseplate portion25and a cylindrical outer surface79of the outer tubular suspended portion32of the upper casing3of the thrust sliding bearing1; and a coupling and fixing means82for coupling and fixing an upper end portion81of the piston rod74of the hydraulic shock absorber to the vehicle body mounting member78.

The vehicle body mounting member78includes an annular flat portion83which is fixed to the vehicle body side and a cylindrical projecting portion85which integrally projects downwardly from an annular inner edge of that annular flat portion83and defines a through hole84by its inner peripheral surface.

The mounting member80includes an annular flat portion87having a through hole86and formed integrally on a lower surface of the annular flat portion83of the vehicle body mounting member78, as well as a cylindrical suspended portion89which integrally extends downwardly from an annular outer peripheral edge of that annular flat portion87. This mounting member80is integrally coupled to the vehicle body mounting member78such that the annular flat portion87is fitted over an outer peripheral surface of the cylindrical projecting portion85of the vehicle body mounting member78through the through hole86, and such that the annular flat portion87is joined to the lower surface of the annular flat portion83of the vehicle body mounting member78.

The upper spring receiving means76is constituted by an upper spring receiving member93which includes an annular flat portion90and a cylindrical projecting portion92which integrally projects upwardly from an annular inner edge of the annular flat portion90and defines a through hole91by its inner peripheral surface. An upper end surface94of the cylindrical projecting portion92of the upper spring receiving member93is arranged in such a manner as to oppose a lower end surface95of the cylindrical projecting portion85of the vehicle body mounting member78.

The coupling and fixing means82includes an outer coupling member96which is fitted and secured at its outer surface to an inner surface of the vehicle body mounting member78; an annular elastic rubber body97bonded to the outer coupling member96; an inner coupling member98bonded to the annular elastic rubber body97; and a nut99which is threadedly secured to the upper end portion81of the piston rod74while clamping an inner edge portion of the inner coupling member98together with the upper end portion81.

The thrust sliding bearing1is interposed between the vehicle body mounting member78and the upper spring receiving member93, i.e., in an annular space101which is formed by the inner surface of the cylindrical projecting portion85of the vehicle body mounting member78, the lower surface of the annular flat portion87of the mounting member80, the inner surface of the cylindrical suspended portion89, the upper surface of the annular flat portion90of the upper spring receiving member93, and the outer surface of the cylindrical projecting portion92of the upper spring receiving member93, such that the tubular inner surface27of the inner tubular suspended portion29of the annular baseplate portion25of the upper casing3is brought into contact with the outer surface of the cylindrical projecting portion85of the vehicle body mounting member78, the annular upper surface26of the annular baseplate portion25of the upper casing3is brought into contact with the lower surface of the annular flat portion87of the mounting member80, and the cylindrical outer surface79of the outer tubular suspended portion32is surrounded by the inner surface of the cylindrical suspended portion89of the mounting member80in such a manner as to be in contact with the inner surface of that cylindrical suspended portion89, and such that the annular lower surface6of the annular base portion11of the lower casing2is brought into contact with the upper surface of the flat portion90of the upper spring receiving member93, and the tubular small-diameter inner surface7of the annular base portion11of the lower casing2is surrounded by the inner surface of the cylindrical projecting portion92of the upper spring receiving member93in such a manner as to be in contact with the inner surface of that cylindrical projecting portion92.

According to the mounting structure73, when the upper spring receiving means76is rotated with respect to the mounting means75by a steering operation, the lower casing2is rotated with respect to the upper casing3, and the rotation of this lower casing2is smoothly allowed by the thrust sliding bearing piece4interposed between the upper casing3and the lower casing2, thereby allowing the steering operation to be performed smoothly. In addition, when a radial load has been applied, the radial load is smoothly allowed by mutual sliding between the synthetic resins in the radial sliding bearing portion formed while holding a bearing clearance between the cylindrical inner surface31of the outer tubular suspended portion32of the annular baseplate portion25of the upper casing3and the cylindrical outer surface9of the annular base portion11of the lower casing2.

In addition, as for the mounting structure73as well, since the thrust sliding bearing portion in the thrust sliding bearing1disposed in the annular space101is located upwardly of the annular upper surface5and the sealing portion based on the labyrinth action, it is possible to prevent as practically as possible the ingress of foreign objects such as dust from the inner and outer peripheral surface sides of the thrust sliding bearing1into that thrust sliding bearing portion, thereby making it possible to obviate trouble such as the abnormal wear of the thrust sliding bearing portion ascribable to the ingress of the foreign objects. Furthermore, the ingress of foreign objects such as dust from the outer peripheral surface side of the thrust sliding bearing1into the radial sliding bearing portion, which is constituted by the cylindrical inner surface31of the outer tubular suspended portion32of the upper casing3and the cylindrical outer surface9of the annular base portion11of the lower casing2and allows smooth sliding in the relative rotation between the upper casing3and the lower casing2with respect to the direction of the radial load, is prevented as practically as possible by the sealing portion based on the labyrinth action, thereby also making it possible to obviate trouble such as the abnormal wear of the radial sliding bearing portion ascribable to the ingress of such foreign objects.

DESCRIPTION OF REFERENCE NUMERALS