FR2674918A1 - Sliding bearing - Google Patents

Abstract

The subject of the invention is a sliding bearing comprising a tubular body (1; 1') forming, at its ends, an annular row of strips (3; 3') projecting in the axial direction. According to the invention, the said strips are relatively flexible in the radial direction and it comprises, at least around the said strips, a sleeve (5; 5'; 15) made of an elastic material, exerting a radial load on the strips tending to flex them towards the axis, the said sheath having an outside diameter greater than that of the said body.

Description

The present invention relates to a sliding bearing arranged to support any sliding cylindrical part and in particular the smooth part of a steering rack of a motor vehicle.

Metal sliding bearings have the drawback when they are force-fitted into the housing to require precise machining of the latter and not to be able to be easily assembled automatically, and when they are mounted slightly, to require additional fastenings . In the latter case, the functional play is also at the origin of vibrations, clicks and parasitic noises.

The plastic bearings are mounted slightly tightened with additional fixings, but the assembly is complex.

These are the reasons why sliding bearings have been proposed comprising a tubular body forming at its ends an annular row of blades projecting in the axial direction. These bearings settle to a certain extent the problem of vibrations and parasitic noise, but on the other hand pose the problem of the level of the sliding force which must be neither too strong nor too weak, and which must moreover be stable during of the life of the bearing. However, this sliding force tends to vary within very large measures, due to the aging of the material, in particular of the blades of these bearings.

In addition, the existing bearings do not take into account in their design the geometric variations due to the manufacturing tolerances of the bearing and its environment.

Another disadvantage of the bearings of the prior art is that they always have a continuous path of hard material between the sliding part and the casing, so that the vibrations of this part are not filtered.

In addition, unwanted noises and squeaks may occur under certain climatic conditions.

The present invention aims to overcome these drawbacks.

To this end, the subject of the invention is a sliding bearing comprising a tubular body, forming at its ends an annular array of blades projecting in an axial direction, characterized in that the said blades are relatively flexible in the radial direction and that it comprises, at least around said blades, a sheath of elastic material, for example rubber, exerting on the blades a radial force tending to bend them in the direction of the axis, said sheath having an outside diameter greater than that of said body.

Such a structure has a number of advantages.

First of all, the fact that the end blades undergo on the part of the elastic sheath a radial force in the direction of the axis, results in the bearing according to the invention having a substantially constant sliding force throughout its lifespan.

Furthermore, only the elastic sheath bears on the bore of the bearing, thus opposing an obstacle to the propagation of vibrations originating from the sliding shaft. In the case of several sheaths, the bearing body is located in the areas between these sheaths, bearing on the latter, so that again the vibrations are not transmitted.

In addition, by a suitable adjustment of the elastic modulus of the sheath, the mechanical characteristics of the bearing according to the invention can be determined with precision.

It will also be noted that when the bearing is mounted, the ends of the blades are supported on the shaft, so that no functional play is introduced at the level of the bearing. The vibrations and clicks which existed in the prior art are therefore suppressed.

The sheath and possibly the body can also be toothed externally or have any other equivalent form.

In a particular embodiment, the sheath has an annular groove at its periphery, in which is engaged a ring whose outside diameter is greater than that of the sheath.

Such an arrangement makes it possible to position the bearing axially in its bore, forming in the latter an annular groove in which the outer periphery of the ring engages.

Maintaining the sheath on the body can be ensured by forming in the central part of the latter an annular rib engaged in a corresponding annular groove, formed at the inner periphery of the sheath.

Also in a particular embodiment of the invention, the bearing comprises a part of sheath at each of its ends around each of said annular rows of blades.

In the latter case, the body may comprise at its periphery between the sheath parts an annular groove in which is engaged a ring whose outside diameter is greater than that of the body, also for the purpose of ensuring axial maintenance of the bearing in its bore.

The ring itself can also be toothed externally.

Advantageously, the transverse section of the ring has, at least in its outer part, a dimension in the axial direction which decreases away from the axis, this arrangement making it possible, by giving a shape corresponding to the centering groove, to ensure the latter without play, without requiring hard-to-reach tolerances.

In the case where the bearing has a sheath part at each of its ends, these parts may include an inner peripheral rib engaged in a corresponding groove in the body in order to maintain them.

We will now describe, by way of non-limiting example, particular embodiments of the invention, with reference to the accompanying drawings in which - Figure 1 is a perspective view of the body of a
sliding bearing according to the invention - Figure 2 is a sectional view along the line II-II
of Figure 3 - Figure 3 is a partial front view of a bearing
according to a first embodiment of the invention - Figure 4 is a sectional view along the line IV-IV
of Figure 5 - Figure 5 is a partial front view of a bearing
according to a second embodiment of the invention i - Figure 6 is a half sectional view of a bearing
according to a third embodiment of
the invention; ; - Figure 7 is a partial front view of the ring
of the bearing of Figure 6 - Figure 8 is a sectional view along the line
VIII-VIII of Figure 7 and; - Figure 9 is a half cross-sectional view
of one of the sheath parts of the bearing of FIG. 6.

If we now refer to FIG. 1, we see the body 1 of a sliding bearing, formed essentially, of a rigid ring 2 at each axial end of which is formed an annular row of flexible blades 3.

The outer surface of the ring 1 is cylindrical with a circular section while its inner surface has, between the blades 3, longitudinal grooves 4, giving the body 1 a certain flexibility, facilitating the establishment of the bearing.

The body 1 is preferably produced in a rigid self-lubricating thermoplastic material having good physicochemical characteristics. In particular, this thermoplastic material must hold well in temperature, resist abrasion and have a low coefficient of friction. This material may in particular be that sold by the company HOECHST under the brand Hostalen Gur.

Figures 2 and 3 show a bearing having a body 1 of the type of that of Figure 1, around which is disposed a flexible ring 5, made for example of rubber or thermoplastic material.

The sheath 5 has in its central part, and at its inner periphery, an annular groove 6 in which is engaged the projecting part towards the outside of the ring, this projecting part forming, as can be seen in FIG. 1, a rib annular at the outer periphery of the body 1.

The sheath 5 has on its outer surface teeth 7 whose geometry makes it possible to adjust the radial stiffness of the bearing. Due to the elasticity of the sheath 5, it presses on the flexible blades 3 and therefore tends to cause them to bend towards the axis of the bearing, which has the effect, when the shaft is mounted in the bearing, bring the ends of these blades to bear on the shaft.

If we now refer to Figures 4 and 5, we see a bearing always comprising a body 1 of the same type, on which is mounted an elastic sheath 5 ', this sheath being held axially as before by an annular groove cooperating with the ring 2 of body 1.

The sheath 5 'is also provided with teeth 7' at its outer periphery.

In the present case, the sheath 5 'further has an annular groove 8 at its outer periphery, this groove 8 receiving a ring 9 whose outside diameter is greater than the outside diameter of the sheath 5'.

The ring 9 is toothed externally and has a shape of the type which will be described below with reference to FIG. 7.

Figure 4 shows the bearing mounted in a bore 10, this bore having an annular groove 11 in which is engaged the ring 9, which allows to maintain the bearing axially.

This embodiment lends itself well to automatic assembly by robot. In fact, when the bearing begins to be inserted in its bore, the ring 9 is compressed axially, from which a relatively high insertion force results. When the ring 9 arrives in the groove 11 of the bore, it relaxes and the force is reduced, so that the robot knows that the bearing is correctly mounted.

If we now refer to Figures 6 to 9, we see that the body 1 'of the bearing has a central portion 12 of great length, this central portion comprising as previously blades 3' at its axial ends.

Between the part 12 and each of the rows of blades 3 ', the body 1' forms an annular rib 13 which is engaged in a corresponding annular groove 14 formed at the inner periphery of a flexible sheath 15 bearing on the blades 3 ' from the body.

It can be seen that these sheaths 15 have an outside diameter greater than the outside diameter of the part 12 of the body 1 ', so that, after assembly, only these sheaths 15 are supported on the bore, the body 1' being somehow suspended between the two sheaths 15, which prevents the transmission to the bore of the vibrations of the shaft supported by the bearing.

In its central zone, the part 12 of the body 1 ′ forms an annular groove 16, in which is engaged a ring 17 whose function is the same as that of the ring 9 of FIGS. 4 and 5.

The ring 17 has an accordion shape allowing it to be easily compressed radially. In addition, it has in its outermost part a trapezoidal shape 18 allowing it to easily cooperate with the groove of the bore in which it comes to engage during assembly, if this groove has a corresponding section.

The invention therefore provides a bearing whose sliding force is controlled, which does not present any aging problem, which can be easily mounted by a robot and which prevents the transmission of vibrations and the propagation of noise.
The radial rigidity, the radial saturation, the fitting and extraction force, as well as the detachment force are also controlled and easily adjustable during design.

In the case of a non-rotating bearing, a non-circular section can be provided. In the case of a sliding and rotating bearing, we can take into account the torque which is controlled and easily adjustable during design.

Claims (9)

Claims 1. Sliding bearing comprising a tubular body (1; 1 ') forming at its ends an annular row of blades (3; 3') projecting in the axial direction, characterized in that the said blades are relatively flexible in the radial direction and that it comprises, at least around said blades, a sheath (5; 5 '; 15) of elastic material exerting on the blades a radial force tending to bend them in the direction of the axis, said sheath having an outside diameter greater than that of said body. 2. A bearing according to claim 1, wherein said sheath is toothed externally. 3. A bearing according to any one of claims 1 and 2, wherein said sheath has a groove (8) annular at its periphery, in which is engaged a ring (9) whose outer diameter is greater than that of the sheath. 4. Bearing according to any one of claims 1 to 3, wherein the body forms, in its central part, an annular rib (2) engaged in an annular groove (6) formed at the inner periphery of the sheath. 5. A bearing according to any one of claims 1 and 2, comprising a sheath portion (15) at each of its ends around each of said annular rows of blades.  6. A bearing according to claim 5, wherein said body has at its periphery, between the sheath parts, an annular groove (16) at its periphery, in which is engaged a ring (17) whose outside diameter is greater than that from the body. 7. A bearing according to any one of claims 3 and 6, wherein said ring is toothed externally. 8. A bearing according to any one of claims 3, 6 and 7, wherein the cross section of the ring has, at least in its outer part, a dimension in the axial direction which decreases away from the axis. 9. A bearing according to any one of claims 5 and 6, wherein the sheath parts comprise an inner peripheral rib (14) engaged in a groove (13) corresponding to the body.