GB2268997A

GB2268997A - Fluid damper

Info

Publication number: GB2268997A
Application number: GB9315141A
Authority: GB
Inventors: Richard Martin Weatherley
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-07-25
Filing date: 1993-07-21
Publication date: 1994-01-26
Also published as: GB9315141D0; GB9215897D0

Abstract

A damper for use in a suspension system of a model car comprises an apertured piston and a member carried on the piston rod movable between a position spaced from the face of the piston when the piston moves in one direction to a position in which it abuts the face of the piston and closes one or more of the apertures when the piston moves in the other direction. The member may comprise a flexible membrane 50 fixed adjacent the face of the piston or a cup-shaped washer (66, Fig 3A) slidably fitted on the piston rod. The damper chamber wall is at least in part formed by a fluid tight diaphragm 52 to accomodate movement of the damper fluid as it is compressed, the diaphragm being located in a housing provided with one or more vent holes 64 communicating with atmosphere - a seal being formed by trapping the edges of the diaphragm between a shoulder in the housing and an end wall of a cylindrical chamber. <IMAGE>

Description

DAMPERS DESCRIPTION The invention relates to dampers for use in the suspension systems of model cars, more particularly the suspension systems of radio controlled model racing cars.

Radio controlled model cars are widely known, inter alia, as toys in the developed world. They are also used for the fast growing sport of radio controlled model car racing.

Within this area relatively small design changes can increase a car's performance and have a large effect on the competitive results obtained when racing cars.

The more successful radio controlled model racing cars have fully moving suspension systems including oiled springs and oil filled dampers (or shock absorbers).

The function of the coil springs within a suspension system is to accomodate movement of a wheel of a car as it passes over a bump or irregularity in the road upon which it is racing. The function of a damper, or shock absorber, is to control the rate at which the spring reacts to movement of a vehicles wheel - generally slowing down the rate at which the spring will react and holding the wheel more firmly in contact with the road.

Dampers in current use are of a design generally as shown in Figure 1 of the accompanying drawing and comprise a cylindrical chamber 10 housing a viscous fluid 12 and a piston 14 movable along the chamber, the piston being carried on a piston rod 16 extending through a seal in one end of the chamber, the piston being provided with one or more small holes 20 allowing passage therethrough of the fluid as the piston moves.

Such an arrangement works reasonably well but has the draw back of providing equal "bump" and "rebound" damping rates - in such an arrangement it is equally difficult to push the piston rod into the damper body (in the direction of the arrow shown in Figure 1) as it is to pull it out.

The suspension systems of radio controlled model racing cars fitted with this type of damper cannot be optimally tuned as it has been experimentally shown that bump: rebound rates in excess of 1:2 are desired.

A first object of the present invention is to provide a damper for use in the suspension system of a model car which alleviates and/or overcomes this difficulty.

Another drawback of the prior art arrangement arises from the volume of trapped air 22 within the sealed body of the damper.

This air must necessarily be provided to accomodate the changing volumes to either side of the piston within the damper body as the piston moves in and out of the damper in response to movements of the car's suspension system.

It will be appreciated that the viscous fluid has difficulty in passing through the holes provided in the piston and thus as the piston shown in Figure 1 moves in the direction of the arrow the volume of fluid above it will be compressed. Air is a more compressible fluid than the generally viscous fluids used in model car dampers and therefore must be included in the known arrangements to enable the piston to move upwardly until such time as sufficient fluid has passed through the apertures in the piston to the lower part of the chamber (as viewed in the Figure).

When a car fitted with such a damper encounters a bump the piston rod is pushed into the body the trapped air 22 within the damper is compressed. The compression rate of the air within the damper is greater than that of the fluid which is in the damper. The compressed air stores energy which exerts a force on the piston tending to push the piston rod out of the damper body.

A dampers main function is, as noted, to control the stored energy in the spring within the suspension system and the effect of the compressed, trapped, air adversely effects this function. As a result a car fitted with a damper as shown in Figure 1 will tend to bounce from bumps instead of absorbing them.

A second object of the present invention is to provide a damper for use in a suspension system of a model car which will alleviate and/or overcome this difficulty of the known prior art arrangements.

In one aspect the invention provides a damper for use in a suspension system of a model car, which damper comprises a cylindrical chamber housing a fluid and a piston movable along the chamber, the piston being mounted on a piston rod extending through a seal in one end of the chamber, means being provided allowing passage of fluid from a first face to an opposed second face of the piston, wherein said fluid passage means is adapted to allow flow of fluid from between said faces at differing rates depending upon the direction of movement of the piston along the cylindrical chamber.

The fluid passage means may comprise one or more apertures extending between the first and second faces of the piston and flow control means operable to open said at least one aperture when the piston moves in a first direction and to at least partially close said at least one aperture when the piston moves in a second direction.

The flow control means is preferably mounted on the piston rod.

The flow control means advantageously may comprise a flexible member forced by pressure of fluid movement to open said at least one aperture in the piston when the piston moves in said first direction and forced by pressure of the fluid to at least partially close said at least one aperture when the piston moves in said second direction.

The flexible member may be held on the piston rod by a clip holding the piston on the rod.

Alternatively the flow control means may comprise a rigid plate mounted for movement axially along the piston rod between a first position in which it is spaced from the piston and a second position in which abuts the piston and at least partially closes said at least one aperture extending therethrough.

Desirably the extent of movement of the rigid plate from the face of the piston is constrained by a clip member mounted on the piston rod.

The rigid plate may be cup shaped and edges of the plate are adapted, in use, to overlie and at least partially close said at least one aperture extending through the piston when the piston moves in said second direction.

Dampers embodying the invention may be provided with a plurality of apertures extending between the first and second faces of the piston, the flow control means being operable to close one or more of those apertures when the piston moves in said second direction.

With advantage the flow control means is of a plastics material.

Preferably, at least part of the chamber wall is flexible to accomodate movement of fluid as it is compressed by movement of the piston.

The flexible wall part of the chamber desirably comprises the end wall of the chamber opposed to that end through which the piston rod passes.

The flexible wall part of the chamber may be provided by a flexible diaphragm; advantageously, the outer surface of which is in contact with the atmosphere.

The flexible wall part of the cylindrical chamber may be located in a housing provided with one or more vent holes communicating with atmosphere.

If this is the case the housing may be fixed to side walls of the cylindrical chamber and edges of a flexible diaphragm be trapped between surfaces of the housing and the ends of the side walls of the cylindrical chamber.

In a second aspect the invention provides a damper for use in a suspension system of a motor car, which damper comprises a cylindrical chamber housing a fluid and a piston movable along with the chamber, the piston being mounted on a rod extending through a seal in an end wall of the chamber, means being provided allowing passage of fluid from a first to an opposed second face of the piston, wherein at least part of the chamber wall is flexible to accomodate movement of fluid as it is compressed by movement of the piston.

The above aspects, features and advasntages of the present invention will become more apparent from the description of embodiments of the invention now made with reference to Figures 2 and 3 of the accompanying drawings, in which: Figure 2 shows at A and B a damper embodying the invention in two operative conditions respectively, and Figure 3 shows at A and B a modified form of the damper shown in Figure 2 in the same two operative conditions.

The damper shown in Figure 2 comprises a generally cylindrical body 30 (typically of aluminium or a rigid plastics material) which is filled with a viscous fluid 32 (for example an oil or silicon). Passing through a seal 34 at one end of the damper body there is a piston rod 36 (usually made from a hard metal) carrying a piston 38 (usually of a plastics material) attached to the piston rod 38 by clips 40 and 42 as shown within the cylindrical body 30 of the damper.

The piston 38 is provided with a particular configuration of holes and or slots 44 which extend between opposed faces 46 and 48 of the piston.

The slots and/or holes may be varied in size and/or disposition to achieve different bump and rebound damping rates.

Fitted between the face 48 of the piston 38 and its retaining clip 42 is a flexible membrane member 50 (a member made of a thin, tough plastics material such as polythene or nylon).

Membrane 50 is readily pushed away from the face 48 of piston 38 by the viscous fluid 32 when the piston is moved into the chamber 30 (as shown in Figure 2A) but is held firmly against that face 38, by the pressure of the viscous fluid 32, when the piston moves in the sense shown in Figure 2B. When held against the face 48 of piston 38 the membrane 50 will block one or more of the positioned holes or slots 44 reducing the rate at which fluid may flow through the piston.

As a result the damping rate provided by the damper is different depending upon the direction of movement of the piston 38 within the cylinder 32 it will be seen that there is a lower resistance to movement of the piston rod 36 when the piston moves in the direction shown in Figure 2A than when the piston rod moves in the direction shown in Figure 2B.

That end of the cylindrical body of the damper opposed to the seal 34 is closed by a flexible diaphragm 52 held in position by a screw on cap or housing 54.

The cap or housing 54 has a skirt 56 the lower edge of which is threaded for female screw engagement with a thread 58 formed on the upper (as viewed) end of the cylinder 32.

The flexible diaphragm is of an elastic material and can flex from the position shown in Figure 2A to the position shown in Figure 2B and thus accomodate different positions within the cylindrical body of the damper.

The diaphragm 52 is generally circular and its edges are trapped between the ends 60 of the walls of the cylindrical housing 30 and a shoulder 62 in the housing 54.

The housing 54 has a specific volume and is shaped to ensure the diaphragm 52 does not become damaged when displaced into the cap or housing 54 (see Figure 2A) by movement of the piston 38 into the damper. The housing 54 is provided with a vent 64 to atmosphere.

It will be appreciated that this arrangement and the damper piston is driven from the position shown in Figure 2A to the position shown in Figure 2B atmospheric air can enter the volume between the housing 54 and the diaphragm 52 - which air will be driven from the volume between the diaphragm and the housing should the piston move in the direction shown in Figure 2A.

The vent hole is relatively small but sufficiently large to allow the passage of air therethrough without a significant build up in pressure in volume between the diaphragm and housing (as the piston moves in the direction indicated in Figure 2A - or cause a negative pressure above the diaphragm (as the piston moves in the direction indicated in Figure 2B).

A modified form of the arrangement shown in Figure 2 is illustrated in Figure 3 in which Figure parts common to the arrangement of Figure 2 are given the same reference numerals.

It will be appreciated that the flexible membrane 50 provided in Figure 2A and B has been replaced in the arrangement of Figure 3 by a rigid, cup-shaped washer 66 (of a rigid hard plastics material) loosely mounted on the piston rod 36 and movable towards and away from the piston 38 independent upon the direction of motion of the piston within the chamber of the damper.

The rigid, cup-shaped washer 66 is constrained to move between a position in which it is spaced from the piston and held on the piston rod 36 and by a clip 68 (as shown in Figure 3A) and a position in which the flat faces 70 of its raised edges abut the face 48 of piston 38 and cover one or more of the apertures or slots 34 formed therein (as shown when the piston moves in the direction indicated in Figure 3B).

It will be seen that in this position the cup shaped washer 66 is shaped to overlie the clip 42 holding piston 38 on piston rod 38.

As with the arrangement shown in Figure 2, the damper shown in Figure 3 is provided with a diaphragm at its upper end 52 and which may be driven between the position shown in Figures 3A and 3B as the piston moves in the direction indicated.

It will be appreciated that the number, size and disposition of the apertures 54 in the piston 38 may be varied to vary the bump: rebound rates provided by the damper. These rates may be further varied by varying the size of the member 50 or 66 such that it covers (when the piston rod is being drawn out of the damper) more or less of the holes or slots formed in the piston. It is also possible to vary the bump: rebound rates provided by the damper by replacing the viscous fluid 36 within the damper by another having a higher or lower viscosity.

Furthermore it will be appreciated that the provision of the diaphragm 52 above the fluid within the damper will have the result that no air is directly compressed as the damper is actuated. Furthermore none of the air notionally within the damper will become mixed with the viscous fluid (it is separated from the fluid by the diaphragm seal) and will not act to store energy as the damper is driven to compress the fluid above (as viewed in the Figures) the piston 38.

Although particularly described for use with model racing cars it will be appreciated that the arrangements now described have advantage with all of the cars (whether or not they are radio controlled).

It will be appreciated that various modifications may be made to the described arrangements both in terms of the structure of the devices described, the sizes of those devices and the materials used, without departing from the scope of the present invention.

Claims

1. A damper for use in a suspension system of a model car, which damper comprises a cylindrical chamber housing a fluid and a piston movable along the chamber, the piston being mounted on a piston rod extending through a seal in one end of the chamber, means being provided allowing passage of fluid from a first face to an opposed second face of the piston, wherein said fluid passage means is adapted to allow flow of fluid from between said faces at differing rates depending upon the direction of movement of the piston along the cylindrical chamber.

2. A damper as claimed in Claim 1, wherein said fluid passage means comprises one or more apertures extending between the first and second faces of the piston and flow control means operable to open said at least one aperture when the piston moves in a first direction and to at least partially close said at least one aperture when the piston moves in a second direction.

3. A damper as claimed in Claim 2, wherein said flow control means is mounted on the piston rod.

4. A damper as claimed in Claim 3, wherein said flow control means comprises a flexible member forced by pressure of fluid movement to open said at least one aperture in the piston when the piston moves in said first direction and forced by pressure of the fluid to at least partially close said at least one aperture when the piston moves in said second direction.

5. A damper as claimed in Claim 4, wherein said flexible member is held on the piston rod by a clip holding the piston on the rod.

6. A damper as claimed in any one of claims 1 to 3, wherein said flow control means comprises a rigid plate mounted for movement axially along the piston rod between a first position in which it is spaced from the piston and a second position in which abuts the piston and at least partially closes said at least one aperture extending therethrough.

7. A damper as claimed in Claim 6, wherein the extent of movement of the rigid plate from the face of the piston is constrained by a clip member mounted on the piston rod.

8. A damper as claimed in Claim 6 or Claim 7, wherein said rigid plate is cup shaped and edges of the plate are adapted, in use, to overlie and at least partially close said at least one aperture extending through the piston when the piston moves in said second direction.

9. A damper as claimed in any one of claims 1 to 8, wherein there are provided a plurality of apertures extending between the first and second faces of the piston, the flow control means being operable to close one or more of those apertures when the piston moves in said second direction.

10. A damper as claimed in any one of claims 2 to 9, wherein said flow control means is of a plastics material.

11. A damper for use in a suspension system of a model car, which damper comprises a cylindrical chamber housing a fluid and a piston movable along with the chamber, the piston being mounted on a rod extending through a seal in an end wall of the chamber, means being provided allowing passage of fluid from a first to an opposed second face of the piston, wherein at least part of the chamber wall is flexible to accomodate movement of fluid as it is compressed by movement of the piston.

12. A damper as claimed in any one of claims 1 to 10, wherein at least part of the chamber wall is flexible to accomodate movement of fluid as it is compressed by movement of the piston.

13. A damper as claimed-in Claim 11 or Claim 12, wherein said flexible wall part of the chamber comprises the end wall of the chamber opposed to that end through which the piston rod passes.

14. A damper as claimed in any one of claims 11, 12 and 13, wherein said flexible wall part of the chamber is provided by a flexible diaphragm.

15. A damper as claimed in any one of claims 11 to 14, wherein the outer surface of the flexible wall part of the chamber is in contact with the atmosphere.

16. A damper as claimed in Claim 15, wherein the flexible wall part of the cylindrical chamber is located in a housing provided with one or more vent holes communicating with atmosphere.

17. A damper as claimed in Claim 16, wherein said housing is fixed to side walls of the cylindrical chamber and edges of a flexible diaphragm are trapped between surfaces of the housing and the ends of the side walls of the cylindrical chamber.

18. A damper as claimed in Claim 1, and substantially as herein described with reference to Figure 2 or Figure 3.

19. A damper as claimed in Claim 11, and substantially as herein described with reference to Figure 2 or Figure 3.

20. A damper as claimed in Claim 12, and substantially as herein described with reference to Figure 2 or Figure 3.