GB2050559A

GB2050559A - Shock Absorbers for Use in Self- levelling Vehicle Suspensions

Info

Publication number: GB2050559A
Application number: GB8012669A
Authority: GB
Original assignee: IAO Industrie Riunite SpA
Current assignee: IAO Industrie Riunite SpA
Priority date: 1979-05-04
Filing date: 1980-04-17
Publication date: 1981-01-07
Also published as: DE3015959A1; FR2455696A1; ES250422Y; IT1118500B; DE3015959C2; IT7967937A0; FR2455696B3; ES250422U

Abstract

The annular space 36, 38 between the inner 34 and outer 32 tubes of a bi-tubular shock absorber is sub-divided by an annular sealing diaphragm 70. The outer tube 32 is provided with an oil supply union 82 communicating with the annular space 36 below the diaphragm, and with an oil bleed union 84 communicating with the annular space 38 above the diaphragm 70. The supply union 82 is adapted to be connected to the outlet of the height control valve of the self-levelling suspension system, whilst the bleed union 84 is adapted to be connected to the oil reservoir of the system. Oil which is drawn up along the shock absorber rod 52 returns to the space 38 above the diaphragm, via space 64 and passages 66, and is returned to the oil reservoir, thus permitting the use of bi-tubular shock absorbers in self-levelling suspension systems. <IMAGE>

Description

SPECIFICATION Shock Absorbers; Self-Levelling Suspensions For Motor Vehicles The present invention relates to motor vehicle suspensions having telescopic hydraulic shock absorbers.

In particular, the invention is concerned with a motor vehicle suspension having a bi-tubular telescopic hydraulic shock absorber of the type comprising inner and outer coaxial tubes defining between them a cavity, the outer tube being closed at one end (the lower end when installed) by a base and the inner tube opening into the cavity, the inner tube constituting a cylinder housing a valved piston fixed to a piston rod which projects from the other end (the upper end when installed), the upper end of the outer tube being closed by a terminal metal ring and the two tubes being provided with a common head in the form of bush, the piston rod extending through the head and the metal ring with respective interposed sealing gaskets, such that between the head and the metal ring, surrounding the rod, there is defined an annular chamber which communicates with the cavity through at least one side passage made in the head, the inner tube and the cavity being adapted to contain oil and the annular chamber being adapted to receive the oil drawn through the head by the rod and to return it to the cavity through the side passage or passages.

Bi-tubular hydraulic shock absorbers are generally used in MacPherson-type suspensions.

These suspensions include a strut which, essentially, is constituted by a wheel-bearing member and the shock absorber itself, the external tube of which is fixed to the wheelbearing member.

MacPherson-type suspensions have been used increasingly in recent years due to the fact that they impart optimum road hoiding characteristics to a motor vehicie, and that they have a limited size which enables better use to be made of the internal space of the vehicle.

On the other hand, self-levelling suspensions are becoming increasingly common in motor vehicles. These suspensions have a power-driven oil pump having an intake which is connected to an oil reservoir and an outlet which is selectively connectible with the interior of a pair of hydraulic shock absorbers and with respective pneumatic plenum chambers through a common regulating valve sensitive to the level of one part of the motor vehicle body relative to the wheels, in order to maintain such level constant upon variation of the load on the suspension.

The main purpose of self-levelling suspensions, especially when applied to the rear wheels, is to remedy the variation in angle of incidence of the headlights, and to give the motor vehicle greater stability, even when overloaded.

According to one aspect of the present invention there is provided a bi-tubular shock absorber, for a motor vehicle suspension, comprising inner and outer coaxial tubes defining between them a cavity, the outer tube being closed at one end (the lower end when installed) by a base and the inner tube opening into the cavity, the inner tube constituting a cylinder housing a valved piston fixed to a piston rod which projects fr6m the other end (the upper end when installed), the upper end of the outer tube being closed by a terminal metal ring and the two tubes being provided with a common head in the form of a bush, the piston rod extending through the head and the metal ring with respective interposed sealing gaskets, such that between the head and the metal ring, surrounding the rod, there is defined an annular chamber which communicates with the cavity through at least one side passage made in the head, the inner tube and the cavity being adapted to contain oil and the annular chamber being adapted to receive the oil drawn through the head by the rod and to return it to the cavity through the side passage or passages, and wherein the cavity is divided intermediate its length by an annular, pressuresealed diaphragm, wherein the outer tube is provided with a supply union communicating with the part of the cavity enclosed between the diaphragm and the base, and wherein there is a bleed union communicating with the part of the cavity enclosed between the head and the diaphragm, the supply union being adapted to be connected to a source of oil of regulatable pressure, and the bleed union being adapted for connection with a supply reservoir for the source of oil.

According to another aspect of the present invention there is provided a self-levelling suspension having a power-driven oil pump the inlet of which is connected to an oil reservoir and the outlet of which is selectively connectible with the interior of a pair of hydraulic shock absorbers and with respective pneumatic plenum chambers, through a common regulating valve sensitive to the level of the motor vehicle body relative to the wheels, in order to maintain such level constant while the load on the suspension varies, wherein each of the shock absorbers is of a bi-tubular type as referred to in the preceding paragraph and its supply union is connected to the outlet of the regulating valve, whilst its bleed union is connected to the oil reservoir.

In a self-levelling suspension, particularly of MacPherson type, provided with shock absorbers according to the invention, the oil under pressure completely fills that part of the cavity beneath the diaphragm, as well as the interior of the inner tube, above and below the piston. Since the lower surface of the piston, on which the oil pressure acts, is greater than the upper surface, which is reduced by the presence of the rod, the pressure tends to urge the piston and the rod upwards, in co-operation with a spring associated with the shock absorber. The thrust exerted increases with the pressure. In shock absorbers of bi-tubular type the rod traditionally has a very large section, on account of which the difference in area between the two surfaces is appreciable and the pressures required to raise the piston, so as to restore the normal trim of the motor vehicle, are modest.This results in the cost of the hydraulic suspension system being lower, since use may be made of a pump with a smaller head in relation to those of traditional systems. With a lower delivery pressure the other elements of the hydraulic circuit may also be more economical, the delivery pressure being lower.

In a shock absorber of a suspension according to the invention, the oil which is inevitably drawn upwards along the rod returns to the cavity above the diaphragm and from there is returned to the oil reservoir, from which it is again taken up by the pump.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Fig. 1 is a schematic representation of a selflevelling suspension; Fig. 2 is a longitudinal section of one shockabsorber of the suspension of Fig. 1; Fig. 3 is a partial section, on an enlarged scale, of the part encircled Ill in Fig. 2, showing details of the diaphragm, and Figs. 4 and 5 are views similar to Fig. 3, showing two alternative embodiments of the diaphragm.

With reference to Fig. 1, a motor M, which may be the engine of a motor vehicle itself or an electric motor fed from the battery of the motor vehicle, drives a pump 10 which, by means of an intake pipe 14, takes up oil from a reservoir 1 2.

The outlet pipe 1 6 of the pump 10 terminates at the inlet of a regulating valve 1 8. The body of the valve 18 is fixed to a part of the bodywork C of the motor vehicle.

The valve 18 may be one of many known types and has a control member in the form of an arm 20 adapted to rock as shown by the double arrow F. The control arm 20 is connected, in a manner not shown, to an unsprung part of the suspension.

The valve 1 8 has two outlets: one of these is connected to a pipe 22 returning to the reservoir 12; the other is connected to a supply pipe 24 and is bifurcated into two branches, each of which terminates in one of the hydraulic shock absorbers 26 of the suspension. A respective bleeder line 28, branches off from each shock absorber 26. The two bleeder lines 28 unite as a pipe which discharges into the reservoir 12.

A plenum chamber 30 of known type is connected to an offtake from each branch of the feed pipe 24.

The plenum chamber 30 has a spherical container with a hemispherical internal membrane fixed sealingly in an equatorial plane.

The interior of the container communicates, beneath the membrane, with the supply pipe 24.

The construction of the shock absorbers 26 will now be described in detail.

Referring to Fig. 2, each shock absorber has two coaxial tubes, outer tube 32 and inner tube 34. The two tubes 32 and 34 define a cavity between them. For reasons which will be clarified below, a lower part of the cavity is shown as 36 and an upper part of the cavity is shown as 38.

The outer tube 32 is closed by a base 40 and a bracket 42 is welded on to its exterior as shown in Fig. 1. The bracket 42 is for the attachment of a wheel-bearing member 44, as shown in Fig. 1.

ach wheel-bearing member 44 supports a respective wheel R.

A washer 46 is welded to the outer tube adjacent to its upper part, as shown in Fig. 1, and serves as an abutment shoulder for the lower end of a spring 48 (Fig. 1) of the suspension. The upper end of the spring reacts against a part of the body C.

The inner tube 34 constitutes a cylinder in which a valved piston 50 slides. Integral with the piston 50 is a piston rod 52 the upper end of which projects from the shock absorber 26, as shown in Fig. 1, and is fixed to the body C.

At the upper end of the shock absorber, the two tubes 32 and 34 are closed by a common head 54 in the form of a bush. Above the head 54, the outer tube 32 is closed by a terminal metal ring 56.

The upper part of the rod 52 extends through the head 54 and the metal ring 56 with the interpositioning of gasket seals, shown as 58, 60 and 62. These seals are preferably made from a plastics material with a low coefficient of friction, such as polytetrafluorethylene.

An annular chamber 64 is defined between the head 54 and the metal ring 56, surrounding the rod 52. This chamber communicates with the upper part 38 of the cavity through one or more side passages 66, made in the head 54.

The lower part 36 of the cavity communicates with the interior space of the inner tube or cylinder 34, beneath the piston 50, by means of a compression valve or foot valve 68.

The structure in Fig. 2 which has been described up to now is, it will be appreciated, the structure of a typical bi-tubular shock absorber.

Moreover, the assembly of a shock absorber 26, with its respective bracket 42 and wheel-bearing member 44 constitutes a typical strut for a MacPherson-type suspension.

According to the present invention, the cavity is subdivided intermediate its length by a pressure-sealed annular diaphragm shown in the assembly as 70 and better visible in Fig. 3.

The diaphragm 70 comprises a toroidal sealing ring 72 and a rebated collar 74. The sealing ring 72 is located on the side of the collar 74 which faces towards the lower part 36 of the cavity. The cross-section of the ring 72 is such as to fill the cavity completely, effecting a seal.

The inner tube 34 is made with an annular groove 76 which houses a wire ring (for example a "Seeger" ring 78). The ring 78 projects from the groove 76. The radially inner surface of the rebated collar 74 has a shoulder 80 which faces the projecting part of the ring 76 and forms an abutment for the said ring.

The diaphragm may be embodied differently.

For example; in the variant shown in Fig. 4, the sealing ring 172, identical to the ring 72 of Fig. 3, abuts a collar 174 formed by a simple metal ring which is fixed to the inner tube 34 by means of an annular bead weld 176.

In the variant of Fig. 5, the diaphragm 270 again comprises a toroidal sealing ring 272. The cellar 274 is again metallic and is welded to inner tube 34 by an annular bead 276. The sealing ring 272 is however, housed in a peripheral annular groove 280 of the collar 274 and abuts the inner surface of the outer tube 32.

As will be seen, in every case the diaphragm 70, 1 70 or 270 is adapted to provide a seal which prevents the transfer of oil under pressure, as will be seen later, from the lower part 38 to the upper part 38 of the cavity.

Referring again to Fig. 2, the outer tube 32 is provided with a supply union 82 which communicates with the lower part 36 of the cavity enclosed between the diaphragm 70 and the base 40. The union 82 is adapted to be connected to the supply pipe 24 of Fig. 1.

The outer tube 32 is provided with a bleed union 84 which communicates with the upper part 38 of the cavity enclosed between head 54 and diaphragm 70. The bleed union 84 is adapted to be connected to the bleeder line 28 of Fig. 1.

The arrangement of the two unions 82 and 84 and of diaphragm 70 in the longitudinal direction of the shock absorber is not critical but is simply dictated by the need for convenient assembly.

Thus it is convenient to arrange the two unions 82 and 84 one beneath the other immediately below the washer 46. In fact, however, installation above the washer would be impossible due to the presence of the spring 48, whilst being arranged too low would bring the unions and their respective pipes too close to the ground and would render them more susceptible to damage.

In certain suspensions in which the spring is not of a helical type and is without the washer, the two unions and the diaphragm may obviously be placed higher.

The working of the shock absorber and the self-levelling suspension according to the invention is as follows:- When the pump 10 is operating, and if the trim of the motor vehicle is correct, the arm 20 a the valve 18 is in an intermediate position in which the outlet pipe 1 6 is connected with the discharge pipe 22, blocking communication with supply pipe 24. In the two branches of the pipe 24, in the two plenum chambers 30 and in the two shock absorbers 26 there exists a predetermined pressure which depends on a preceding inlet of pressure from the pipe 1 6 to the pipe 24, in a preceding adjustment phase, of which more will be said below, The suspension oscillates due to the effect of bumps in the road and the shock absorbers 26 extend and retract correspondingly in the usual manner.The extension and retraction movements are dampened by restricting passages in the valved piston 50 and the foot valve 68.

In known bi-tubular shock absorbers, the cavity between the two tubes serves to compensate for differences in the volume of the internal chamber of cylinder 34. When the rod 52 descends, the volume of the chamber decreases and some of the oil contained in the cavity flows into the chamber itself. When the rod 52 ascends, the reverse occurs. In the upper part of the cavity, away from the diaphragm, a certain quantity of air is present which is compressed and expands as the oil ascends and descends.

In a suspension according to the present invention, the oil completely fills the lower part 36 of the cavity and the presence of air is not necessary, in that the same function is fulfilled by the plenum chamber 30. In connection with this, it should be noted that the flow cross-section of the pipes which connect the supply union 82 with the plenum chamber 30 should be sufficiently large (6-8 mm in diameter) so as not to influence the oscillations, or so that the column of oil therein should not undergo excessive accelerations and decelerations, influencing the behaviour of the shock absorbers.

In the known bi-tubular shock absorbers, the oil which is inevitably drawn along the rod through the gap between the latter and the sealing rings, such as those shown as 58 and 60 in Fig. 2, reaches the collection chamber 64, from which it is returned to the cavity.

In a shock absorber according to the present invention, the drawn oil which descends from the collection chamber 64, through the passage or passages 66, to the cavity 38 obviously cannot return to the lower part 36 of the cavity and flows away, instead, through the union 84 and the .bleeder line 28 returning to the reservoir 12, where it is taken up again by the pump 10.

According to a preferred characteristic, the head 54 is of a porous material which is permeable to gases but substantially impermeable to oil. Out of the various porous materials, sintered materials are most suitable and, in particular, sintered iron that is not vaporised or not subject to vapour treatment during sintering since this treatment would eliminate its porosity.

The porosity of the head 54 enables any gases or vapours which collect under the head to pass to the upper part 38 of the cavity. As is known, the presence of gases or vapours in the inner cylinder of a shock absorber is harmful, since it gives rise to jerky extension and retraction movements.

Returning to the operation of the suspension, when the bodywork C of the motor vehicle falls below a certain limit through the effect of excess overloading, the arm 20 rotates upwardly and puts the regulating valve 1 8 into the position which blocks communication from the outlet pipe 16 to the discharge pipe 22 and opens communication of the outlet pipeline 1 6 to the supply pipe 24. In this manner, the pump 10 sends a certain volume of oil into the pipe 24 which goes in part to supply the shock absorbers 26 through the unions 82, raising the rods 52 upwards and recovering the trim of the body.

Another part of the oil goes to compress the gas contained in the plenum chamber 30.

When, in the opposite manner, the body tends to rise through the effect of a reduction in weight, the arm 20 rotates downwardly and puts the regulating valve 1 8 into a position in which the supply pipe 24 is placed in communication with the discharge pipe 22, always maintaining the communication between the latter and the outlet pipe 1 6. In this manner, the rods 52 lower again and the gas in the plenum chambers 30 reexpands until the arm 20 returns to the neutral position in which the pipe 24 is blocked.

The self-levelling force which is exerted on the rods 52 depends on the pressure existing in the plenum chambers 30 at any given moment, and is equal to this pressure divided by the section of the rod.

Since the rods of bi-tubular shock absorbers currently in use are of a minimum diameter of 22 mm to a maximum diameter of 25 mm, it can be seen that, with maximum delivery pressures of 50 bars, one may obtain self-levelling forces of the order of 1 50-200 daN per wheel. These forces are more than sufficient to integrate the load of a spring, such as 48, calculated with only the static load of a vehicle empty but for the driver.

The present invention therefore provides a hydraulic shock absorber of bi-tubular type suited to self-levelling suspensions which, in particular combines the advantages of self-levelling and MacPherson-type suspensions.

Claims

1. A bi-tubular shock absorber, for a motor vehicle suspension, comprising inner and outer coaxial tubes defining between them a cavity, the outer tube being closed at one end (the lower end when installed) by a base and the inner tube opening into the cavity, the inner tube constituting a cylinder housing a valved piston fixed to a piston rod which projects from the other end (the upper end when installed), the upper end of the outer tube being closed by a terminal metal ring and the two tubes being provided with a common head in the form of a bush, the piston rod extending through the head and the metal ring with respective interposed sealing gaskets, such that between the head and the metal ring, surrounding the rod, there is defined an annular chamber which communicates with the cavity through at least one side passage made in the head, the inner tube and the cavity being adapted to contain oil and the annular chamber being adapted to receive the oil drawn through the head by the rod and to return it to the cavity through the side passage or passages, and wherein the cavity is divided intermediate its length by an annular, pressure-sealed diaphragm, wherein the outer tube is provided with a supply union communicating with the part of the cavity enclosed between the diaphragm and the base, and wherein there is a bleed union communicating with the part of the cavity enclosed between the head and the diaphragm, the supply union being adapted to be connected to a source of oil of regulatable pressure, and the bleed union being adapted for connection with a supply reservoir for the source of oil.

2. A shock absorber as claimed in claim 1, wherein the annular diaphragm comprises a toroidal sealing ring restrained by a rebated collar which is itself held on the inner tube in such a manner as to prevent movement of the diaphragm at least towards the bleed union.

3. A shock absorber as claimed in claim 2, wherein an annular groove is formed on the external surface of the inner tube to house a wire ring which projects from the groove and abuts the rebated collar.

4. A shock absorber as claimed in claim 3, wherein the radially inner surface of the rebated collar has a step facing the projecting part of the wire ring and forming an abutment for the said ring.

5. A shock absorber as claimed in claim 2, wherein the rebated collar is metallic and is fixed to the inner tube by an annular weld bead.

6. A shock absorber as claimed in claim 5, wherein the rebated collar has a peripheral annular groove in its radially outer surface housing the toroidal sealing ring.

7. A shock absorber as claimed in claim 1, wherein the common head of the two tubes is made from a porous material permeable to gases and substantially impermeable to oil.

8. A shock absorber as claimed in claim 7, wherein the porous material is a sintered material.

9. A shock absorber as claimed in claim 8, wherein the head is made from sintered iron.

10. A self-levelling suspension having a powerdriven oil pump the inlet of which is connected to an oil reservoir and the outlet of which is selectively connectible with the interior of a pair of hydraulic shock absorbers and with respective pneumatic plenum chambers, through a common regulating valve sensitive to the level of the motor vehicle body relative to the wheels, in order to maintain such level constant while the load on the suspension varies, wherein each of the shock absorbers is of a bi-tubular type as claimed in any of claims 1 to 9 and its supply union is connected to the outlet of the regulating valve, whilst its bleed union is connected to the oil reservoir.

11. A suspension as claimed in claim 10, wherein each shock absorber forms part of a MacPherson-type suspension strut.

12. A bi-tubular shock absorber substantially as herein described with reference to and as illustrated in Figs.1,2 and 3, Figs.1,2 and 4, or Figs. 1, 2 and 5 of the accompanying drawings.

1 3. A self-levelling suspension substantially as herein described with reference to and as illustrated in Figs.1,2 and 3, Figs.1,2, and 4, or Figs.1,2 and 5, of the accompanying drawings.

14. A motor vehicle including a shock absorber or a self-levelling suspension as claimed in any one of the preceding claims.