TECHNICAL FIELD

This invention relates to shock absorbers and particularly, but not solely, relates

to telescopic shock absorbers for use with vehicle suspension systems. BACKGROUND ART

Although there are only limited sizes of telescopic shock absorbers, diameter wise, there are many different lengths required for various vehicles, meaning that many hundreds of different shock absorbers usually need to be held in stock. This is

disadvantageous in that production schedules are complex and the stock inventory for

manufacturers and distributors is necessarily very high.

Amongst others, there are two known types of telescopic shock absorber.

A. The DE CARBON Mono-Tube shock absorber:

This shock absorber consists of a single seamless tube or cylinder containing a

piston rod and piston with guide and seal at one end and a floating piston and cylinder end plug at the other. The area between the rod guide and seal and the floating piston contains the piston and is filled with oil. The area between the floating piston and cylinder end plug contains gas under pressure.

The operation of the DE CARBON shock absorber is as follows:

As the piston rod and piston moves upward toward the guide and seal the oil contained in the area between the seal and piston is forced through the piston rebound valves thereby giving the required rebound resistance. At the same time the pressurized

floating piston moves upward to compensate for the diminished piston rod displacement.

When the piston rod and piston moves down the cylinder oil is forced back through the piston against the resistance of the compression valves thereby giving compression resistance. At the same time the floating piston is forced down the cylinder against the

gas pressure to accommodate the increased piston rod displacement as it enters the

cylinder.

The disadvantages of this construction are:

1. The stroke is somewhat restricted due to the area taken up by floating piston and gas chamber.

2. The piston rod is necessarily kept to as small a diameter as possible to minimize the size of gas chamber required.

3. The piston rod is subject to bending due to small diameter.

4. If the cylinder tube becomes damaged shock absorber becomes in-operable. 5. The unit is difficult to service, necessitating special equipment.

B. Twin Tube Hydraulic Shock Absorber:

This shock absorber consists of an inner pressure tube enclosed by a larger outer tube with the area between the tubes being used as an oil reservoir. Fitted inside the inner pressure tube is a piston rod and piston with a rod guide and seal at the upper end and a base and valves at the lower end. As the piston rod and piston move longitudinally in the inner cylinder oil passes through the piston and in and out the base valve. A further explanation of the action is as follows:

As the piston rod and piston move up the cylinder towards the rod guide and seal, oil contained in the area above the piston is forced through the piston rebound valve which offers resistance thereby giving rebound control at the same time the piston rod is partially exiting the inner cylinder leaving space and creating a vacuum so oil is sucked

in through the base valve to fill this space. When the piston rod and piston moves in the opposite direction, that is down towards the base valve, oil moves through the piston via a lightly seated piston plate valve to fill the increasing area above the piston. At the same time, because the piston rod is now re-entering the inner cylinder through the rod and

guide, the piston rod displacement forces oil out through the base compression valve which offers resistance thereby giving compression or bump control.

The disadvantages of the construction are:

1. At high speed oil must be sucked very quickly from the reservoir to refill the inner cylinder as the piston rod moves upward.

2. Only the diameter of the piston rod is used to force oil out the base valve on the compression stroke, if, as is the case in most telescopic shock absorbers of this type, the piston rod is of small diameter, the pressure on the oil to give the required compression

resistance is very high which can shorten the oil's useful life.

3. In this design foaming of the oil and consequent fade become a problem, especially at high speed.

DISCLOSURE OF THE INVENTION It is an object of the present invention to provide a shock absorber which will at least go

some way toward overcoming the above disadvantages, or to at least provide the public with a useful choice.

In one aspect the invention consists in a shock absorber comprising an inner cylinder having a piston rod containing end and a non-piston rod containing end. A first piston is disposed within the inner cylinder and a piston rod is attached to the first piston. The piston rod exits the cylinder from the piston rod containing end and a floating piston

is provided between the first piston and the non-piston rod containing end of the cylinder so that the floating piston divides the cylinder into a first piston containing compartment and a non- piston containing compartment. The first piston containing compartment contains a liquid, and the non-piston containing compartment contains a gas under pressure. An outer cylinder is also provided in fluid connection with the non-piston

containing compartment.

The present invention provides significant advantages over known shock absorbers.

The provision of the outer cylinder allows a large diameter (heavy duty) piston

rod to be used, as the displacement of liquid caused by introduction of the piston into the inner cylinder can be compensated for by the relatively large volume of gas provided in the outer cylinder. Furthermore, because the outer cylinder is provided, the floating piston can travel to the base of the inner cylinder, thus permitting a full range of movement.

The non-piston containing compartment can also contain a liquid as well as the gas. The liquid allows heat transfer to occur, therefore increasing the efficiency of the shock absorber, and can also be used to adjust the volume of gas provided in the outer cylinder so that the change in gas pressure of the outer cylinder as the piston rod enters the inner cylinder can be selected.

The first piston has a valve therein for allowing transfer of the liquid from one side of the first piston to the other. This provides a damping or shock absorbing effect, and together with the gas between the floating piston and the outer cylinder allows the shock absorber to also act as a gas spring, so that a separate shock absorber and spring arrangement is not necessary.

The inner and outer cylinders are concentric with each other, the walls of the inner cylinder being disposed within the walls of the outer cylinder. This adds to the mechanical strength of the overall construction and also provides the advantage that the outer tube can be damaged, for example by being dented, without preventing the shock absorber from functioning properly.

A valve is provided in a wall of the outer cylinder or in the non-piston rod

containing end. This allows the gas in the outer cylinder to be charged, recharged, emptied or replaced.

The outer cylinder may also be provided as part of a strut. This allows the shock absorber to be used directly as part of a vehicle suspension system.

In a further aspect the invention consists in a shock absorber having at at least one end an attachment fixing fitting which in use enables selected attachments to be fixed to the shock absorber. The attachments are fixed by a complementary attachment fitting to

enable the shock absorber to be adapted for use in a variety of motor vehicles. The

attachments are selected to suit a particular motor vehicle in that series of motor vehicles. This provides the advantage that a single shock absorber may be used in a number of different vehicles so that the stock or inventory which needs to be held by suppliers or distributors is significantly reduced, leading to a corresponding reduction in costs.

Each attachment fixing fitting comprises a male or female threaded screw fitting fixed to the shock absorber.

The attachments comprise couplings having at one end the complementary attachment fitting to co-act with the attachment fixing fitting on the shock absorber and at the other end a connection for connecting to the shock absorber connection fitting of a motor vehicle.

Alternatively the other end is mounted in a case carrying a wheel stud, a selected one of a plurality of packing pieces being provided, if required, between the other end of the shock absorber and the base of the case.

To those skilled in the art to which the invention relates, many changes in

construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the

appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting.

The invention consists in the foregoing and also envisages constructions of which

the following gives examples only. The invention consists in the foregoing and also envisages constructions of which the following gives examples.

DESCRIPTION OF THE DRAWING FIGURES

One preferred form of the present invention will now be described with reference to the accompanying drawings in which; Figure 1 is a diagrammatic cross section of a shock absorber having one form of attachment fixing fitting at each end thereof;

Figure 2 shows a shock absorber having an alternative form of attachment fixing fitting fitted thereto;

Figures 3 to 6 show different shock absorber attachments suited to particular vehicles and for association with the shock absorber of figure 1;

Figures 7 to 10 show different shock absorber attachments for association with the shock absorber of Figure 2;

Figure 11 is a diagrammatic cross section of a shock absorber in the form of a McPHERSON strut; Figure 12 is an elevation in partial cross-section of a shock absorber in accordance with the present invention; and

Figure 13 is a front elevation in partial cross-section showing a shock absorber of the type shown in figure 12 fitted to a McPHERSON strut.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to the drawings there is shown in figure 1 one form of shock absorber

1 having a piston rod 2 and attached to the piston rod so as to move therewith is a dust cover 3.

The internal operation of the shock absorber is in accordance with known practice

or is described further below with reference to figures 12 and 13.

The upper end of the piston rod 2 is provided with a male thread 5 and a male threaded member 6 is fixed, for example by welding, to the lower end of the shock

absorber casing 7. The threaded members 5 and 6 provide attachment fixing fittings.

Referring now to figure 2 the shock absorber 1 in that figure is provided with a

piston rod 2 and moving with that piston rod is a dust cover 3 this arrangement being as with the construction in figure 1 but the attachment fixing fitting 10 at the upper end of the piston rod 2 and 11 at the lower end of the shock absorber body 12 are provided with female threads.

To . enable the shock absorber of figure 1 to be fitted to various motor vehicles different forms of attachment are provided as separate members and are shown in figures

3 to 6. Thus in figure 3, a ring 15 is provided with a female complementary attachment fitting 16 comprising a female threaded member which engages with the male threaded member 5. Similarly in figure 4 the complementary attachment fitting 16 is associated with a male screw 17. In figure 5, the complementary attachment fitting 16 is associated

with a ring 18 and in figure 6 the complementary attachment fitting 16 is associated with a male threaded member 19. Similarly in figures 7 to 10 a complementary attachment fixing fitting 20 is associated with the ring 21 in figure 7, with a male threaded member

22 in figure 8 with a ring 23 in figure 9 and a male threaded member 24 in figure 10.

The male complementary fitting 20 is engageable with the female attachment fixing fitting 10 or 11 of figure 2.

It will be apparent from the foregoing that the attachment fixing fittings shown in figure 1 and figure 2 are alternatives and generally speaking only one such alternative would be provided.

Thus by the provision of a shock absorber having the attachment fixing fittings associated therewith and by providing a plurality of attachments having complementary attachment fittings such as those in figures 3 to. 6, or if the fittings of figure 2 are selected, those shown in figures 7 to 10 a considerable number of combined shock

absorbers and attachments can be provided to enable varying motor vehicle requirements to be met. As a consequence of this a stockist may considerably reduce the amount and value of the stock required to be held to enable a demand for a considerable number of specific shock absorber sizes or specifications to be met.

Referring now to figure 11 this shows a McPHERSON strut assembly. The shock absorber 30 has a piston rod 2 extending therefrom which is provided with a interchangeable end piece substantially as previously described. The piston rod 2 may be provided with a female threaded depression at 32 and an interchangeable bearing stud 31 may be provided having a thread at 33 onto which a fitting may be mounted. To allow variation in extended length of the construction, attachment spacing means are provided including a range of extension members 31 having appropriate threaded portions at each end. The dimension A of each of the extension members 31 varies so as to provide varying lengths.

At the other end of the shock absorber 30 the shock absorber is contained within a case in the form of strut case 34. The strut case 34 may be threaded on its surface at 35 so that a threaded apertured securing cap 36 may be positioned therein if required. To

allow for further variation in length of the shock absorber 30 the attachment spacing means if required include a plurality of packing pieces 37, a selected one of which is

positionable between end 38 of the shock absorber and the end 39 of the strut case 34.

A wheel mounting assembly 40 including an axle is provided on the strut case 34. The strut case 34 also carries the spring saddle 41.

There are generally four or five sizes of telescopic shock absorbers, diameter wise in common use. Taking one size of shock absorber for example, by manufacturing a range of 10 lengths in stages of say 25mm increase would give sufficient range lengthwise to cover most requirements for this size. A selection of three valve setting

combinations would cover most requirements for the replacement shock absorber market.

Accordingly ten lengths by three valve settings gives 30 models to be held in stock by

using constructions according to the present invention.

The required attachment can be readily selected for a required motor vehicle and thus the range of 30 replacement shock absorbers can be magnified many times as compared with the present system where the mountings or attachments are welded in

place during manufacture and it is believed that the above 30 models of shock absorber with appropriate mountings or attachments would cover the requirements of 100 to 200 different shock absorbers as at present required. Thus production schedules would be simplified and the stock inventory for both manufacturer and distributor would be much lower.

In relation to the McPHERSON strut construction shown in figure 11 to date it is necessary to provide a satisfactory repair service to manufacture stock and distribute something in excess of 80 different model cartridges. This can be reduced by the use of

the present invention to shock absorber cartridges of two different diameters for example 38mmOD 3/4 inch piston rod and 41mmOD 7/8 inch piston rod and two or three different lengths. Allowing for five valve setting options for each size means a substantial reduction in the number of cartridges that must be carried in stock.

For the manufacturer of cartridges it would mean a greatly reduced stock inventory with long production runs of only a few part numbers. The stock would not

tend to become obsolete which has happened in the past as some stock has become

obsolete and therefore of little or no commercial value. Referring to figure 12, a shock absorber in accordance with a preferred embodiment of the present invention is shown generally referenced 50. The shock absorber has an inner cylinder or tube 52 which is concentrically mounted within an outer

cylinder or tube 54. The cylinders 52 and 54 have a piston rod guide 56 and top cap 58 at one end thereof which contain a piston rod 60 and through which the piston rod exits the cylinders. The piston rod guide 56 has an O-ring seal 62, sealing the piston rod guide against the inner walls of inner cylinder 52 and an O-ring seal 64 which makes the seal between the piston rod guide and the inner surfaces of outer cylinder 54. The piston rod 60 is longitudinally slidably moveable through aperture 66 in piston rod guide 56. End cap 58 has a thread 68 on the outer edge thereof for attachment to inner surfaces of outer cylinder 54 to aid assembly or disassembly of the shock absorber. Alternatively, or in addition, the upper edges 70 (as shown by the dashed lines) of outer cylinder 54 may be rolled over the upper edges of the top cap 58 to ensure a good connection. However this makes disassembly more difficult. The end cap 58 has an aperture 72 therein through which piston rod 60 can slidably move in a longitudinal direction and adjacent to aperture 62 a high pressure seal 74 is provided to substantially prevent transfer of liquid or air to or from the cylinders. A cylinder base and valve body 76 is provided at the other end of the cylinders 52 and 54. The cylinder base and valve body has an O-ring seal 78 which provides a seal between the cylinder base and the inner walls of outer cylinder 54. The cylinder base and valve body 76 has a valve member 80 therein and an O-ring seal 82 is provided between the valve member and the cylinder base valve body. A portion of the

valve member 80 is provided externally of the cylinder base and valve body and this portion has a thread 84 to provide a mounting stud. As described above, the cylinder base and valve body may be fixed to the outer cylinder 54 by rolling the ends 86 of cylinder

54 over outer edges of cylinder base and valve body 76 or alternatively welding ends 86 to the base 76. A first piston 88 is provided on an end of the piston rod 60, the piston preferably having a seal 90 about the outer edges thereof to make sealing contact with inner surfaces of the walls of the inner cylinder 52. Piston 88 also has apertures 92

therein and plate springs 94 either side of the apertures which provide compression valves

to allow a restricted flow of a hydraulic fluid such as oil through the piston so as to damp

movement of the piston. The piston is attached to the piston rod by threaded member 96. A floating piston 98 is provided having a seal 100 and is provided between piston 88 and cylinder base 76 to effectively divide the inner cylinder into two compartments, a first piston containing compartment containing piston 88, piston rod 60 and a liquid such as

oil, and a compartment 102 containing a gas under pressure. Apertures or ports 104 are provided in the base of inner cylinder 52 so that gas from compartment 102 is free to pass between compartment 102 and annular space 106 between the inner and outer cylinders.

The annular space 106 between the two cylinders provides a gas storage reservoir. Although, if desired, some liquid such as oil may be added to the space 106 between the

two cylinders to aid heat transfer from the inner cylinder to the outer cylinder. The level of the oil present is indicated by dashed lines 107. The provision of liquid or oil between the cylinders also allows the volume of gas provided in the outer chamber to be selected so that the increase or rate of increase of pressure in the outer cylinder as the piston rod

enters the inner cylinder, and therefore the change in the "gas spring" effect of the shock

absorber, can be selected in response to the introduction of the piston rod to the inner cylinder.

In operation, the action of the shock absorber shown in figure 12 is very different

from the prior art, in that the floating piston 98 is able to travel to the base 76 of the inner cylinder thus allowing a full stroke of the piston and piston rod to be achieved. This is not possible with the conventional shock absorber, unless a separate gas cylinder is used which is an awkward and untidy arrangement. The provision of twin cylinders adds

to the strength and robustness of the overall shock absorber construction.

Referring to figure 12 as the piston rod 60 and piston 88 move upward out of the

two cylinders in a direction away from base 76, the oil contained in the area between seal 74 and piston 88 is forced through apertures 92 iri the piston and the compression or rebound valves 94 on the lower side of the piston. The piston rebound valves give the required rebound resistance to provide the damper action of the shock absorber. At the same time as the piston is moving in the upward direction, the floating piston 98, under force of the pressurised gasses in regions 106 and 102, moves upward to compensate for the diminished piston rod displacement, thus maintaining substantially constant oil pressure within the chamber above the floating piston.

When the piston rod and piston move down the cylinder toward base 76, oil is forced back through the apertures 92 in the piston against the rebound valves 94 on the upper surface of the piston, thereby giving compression resistance to provide damping. At the same time the floating piston 100 is forced downwardly toward base 76 of the cylinder, against the force exerted by the gas pressure in regions 102 and 106, in order to accommodate the increased piston rod displacement as the piston rod enters the cylinder.

Because of the large gas storage area available in the shock absorber shown in

figure 12, a much larger piston rod can be used for greater strength, and, if required, for gas lift. Furthermore, the filling valve 80 and screw top 58 construction (without rolled

edges 70) enable easy assembly and disassembly. In particular, the following advantages can be identified in the shock absorber described with reference to figure 12;

(i) the twin tube or cylinder construction, which uses a heavy outer wall, gives

greater strength and in the event of disfigurement of the outer tube, the normal operation

of the shock absorber is unaffected.

(ii) the design, having screw top construction, allows easy, fast assembly and disassembly, without the need for complex equipment.

(iii) the floating piston may travel to the very bottom of the cylinder, giving full stroke to the piston. In the prior art shock absorbers which have a floating piston a pocket of gas must always be present between floating piston and the cylinder base unless a

separate gas cylinder is used which is an awkward and untidy arrangement.

(iv) a heavy duty piston rod may be used, to provide greater strength and optional gas lift. The heavy duty piston rod would have a greater diameter, and this diameter can be accommodated in the shock absorber of figure 12 because the increased liquid or oil displacement of the larger piston rod can be accommodated by the large volume of gasses

space 106 between the two cylinders.

(v) as a high pressure seal is used, then the gas pressure can be increased to provide a gas spring effect acting on the piston rod to provide lift to assist the vehicle springs. In some cases the gas spring effect can be used to provide total vehicle support without

normal springs such as coil or leaf springs.

(vi) As the oil in the inner pressure cylinder is totally separated from the gas chamber by the floating piston, aeration cannot take place which overcomes the problem of

aeration and fade experienced in twin tube shock absorbers as previously described,

(vi) the design of shock absorber illustrated in figure 12 lends itself to the construction of a range of shock absorbers of all sizes, for vehicle suspensions, McPHERSON strut cartridges, steering dampers, industrial dampers etc. In particular, the shock absorber shown in figure 12 can be used within a standard McPHERSON strut and interchangeable

bearing studs, piston rod attachments and base packers as described with reference to figures 1 to 11.

Referring to figure 13, a shock absorber substantially the same as the shock absorber described with reference to figure 12 is shown fitted to a McPHERSON strut. The reference numerals used in figure 13 for features which are common to shock absorbers shown in figures 12 and 13 are the same, and the general operation of these shock absorbers is the same. However, it will be seen that the outer tube or cylinder 54 comprises part of the McPHERSON strut in that the axle 106 and the spring collar 108 are provided directly attached to cylinder 54. The gas ports 104 are provided in the cylinder base and the gassing valve 80, rather than being provided within the cylinder base, is provided in a wall of cylinder 54. Furthermore, a piston rod stop 110 is provided to limit the upward movement of the piston. It will also be seen that the piston rod attachments and base packers described with reference to figures 1 to 11 could also be used in the shock absorber arrangement depicted in figure 13.

From the foregoing it will be seen that a series of fittings for shock absorbers are provided, and a new shock absorber is provided which provide considerable advantages

over previously known shock absorbers and shock absorber assemblies.