GB2202921A - Damper - Google Patents

Abstract

A damper for use with a motor cycle frame has a cylinder containing a liquid damping medium. A piston rod carries a piston assembly which is siidable along the cylinder. First communication means extends through the piston assembly to permit the flow of damping medium upon movement of the piston assembly in one direction, similarly second communication means permits the flow of damping medium in an opposite direction, and a one-way valve arrangement is associated with each of the communication means. The first communication means consists of first 1 and second 2 paths of lower and higher resistance to liquid flow, and a control pin 32 and pin holder are arranged to control routing of the liquid along the paths. The second communication means may also provide two paths of differing resistance which are selected by the control pin. In a separate embodiment the control pin travels with the piston assembly until it engages a fixed stop when it then carries out its routing function. <IMAGE>

Description

DAMPER This invention relates to a damper for mounting on a vehicle frame in order to damp up and down oscillations of a vehicle wheel relative to the frame.

As is well known, dampers and shock absorbers (a damper with a compression spring) are provided on vehicle frames in order to damp or cushion the impact of a surface irregularity in the ground or in a road, which is applied initially to the wheel and (in the absence of the damper) would then be transmitted directly to the main frame proper, via the mounting of the wheel on the main frame, and therefore also to the occupants of the vehicle.

In addition to cushioning the impact on the main frame of e.g. a bump in a road surface, the damper also has the function of providing controlled resistance to relative upward or downward movement of the wheel so as to tend to maintain the wheel in contact with the road after it has passed over the bump.

The invention has been developed primarily with a view to providing an improved form of damper for use with a rear wheel of a motorcycle which is carried by a trailing arm linkage, but it should be understood that a damper according to the invention is applicable generaly to multiwheeled vehicles (motorcyles and motorcars), in order to provide controlled resistance to up and down movement of a respective wheel of the vehicle.

For motorcycles used on normal roads, it is sufficient to provide relatively unsophisticated designs of dampers (and shock absorbers) which are designed to be able to absorb the type of shock loadings normally encountered e.g.

a manhole cover or pothole in a road, so that the rider can remain in control of the motorcycle after such an impact.

However, for scrambler or enduro type motorcycles, there is a demand for a more sophisticated type of damper arrangement which provides an acceptable damping action with minor impacts of the type encountered in normal roadwork, but which provide a "stiffer" response to more severe impacts of the type encountered in cross-country work.

Ideally, a damper arrangement capable of meeting this requiremen would have a "position sensitive" response to relative movement between the usual piston and cylinder components of the damper, in that an initial phase of relative movement (caused by moderate impacts) is met by a certain level of resistance, but further relative movement (caused by a more severe impact) is met by a greater level of resistance. However, to date, attempts to manufacture damper arrangements of this type have resulted in a product which is technically inadequate and also very bulky in space requirements.

Therefore, given the present inability to design an acceptable position sensitive damper, the designers of motorcycle frames have turned in another direction to solve this problem, by varying the manner by which the rear wheel is mounted, rather than by redesigning the damper. To this end, so-called VLRS (variable lever ratio suspensions) have been provided, in which the rear wheel is carried by a specially designed trailing arm linkage in conjunction with conventional designs of shock absorber, in which the suspension system itself is position sensitive, rather than the damper or shock absorber.The combined suspension / damper arrangement therefore can provide an increasingly "stiff" response to progressively larger applied impacts, but this is an expensive and complicated mechanical set-up, and which does not readily lend itself to adjustment in the response which a particular rider might require.

There is therefore a clear need to provide a position sensitive damper of simple but reliable form, and it is the objective of this invention to meet this need.

According to the invention there is provided a damper for mounting on a vehicle frame in order to damp the up and down oscillations of a vehicle wheel relative to the frame, the damper being intended to extend between two parts of the frame which are relatively movable when the vehicle wheel is subjected to an impact, and said damper comprising:: a cylinder connectable to one of said frame parts and arranged to contain a liquid damping medium; a piston rod connectable to the other of said frame parts; a piston assembly carried by said piston rod and slidable along the cylinder when relative movement takes place between said frame parts; a first communication means extending through the piston assembly to permit the flow of liquid damping medium through the piston assembly upon relative movement of the piston assembly in one direction; a second communication means extending through the piston assembly to permit the flow of liquid damping medium through the piston assembly upon relative movement of the latter in an opposite direction; and a respective one-way valve arrangement associated with each communication means; in which: the first communication means is defined by first and second paths of travel of respectively lower and higher resistance to liquid flow; and a control device is arranged to respond to relative movement of the piston assembly in said one direction from a datum position in order to control initial routing of the liquid along the first path of lower resistance and, when a predetermined relative movement is exceded, to route the liquid along the second path of higher resistance.

Thus, the damper according to the invention provides a position sensitive facility, in that the relative movement of the piston assembly from the datum position has an initial lower resistance followed by a higher resistance.

Usually, the relative movement of the piston assembly will be such as is caused by relative upward movement of the vehicle wheel following an impact.

Desirably, also the second communication means is similarly provided with respective first and second paths of travel for the liquid which is controlled by the control device, upon relative movement of the piston assembly in an opposiite direction from the datum position.

Thus, the damper can provide an increasing level of resistance, after a predetermined amount of movement of the piston assembly from the datum position, for both upward and downward (rebound) movement of the vehicle wheel.

Preferably, the piston assembly comprises first and second pistons spaced apart along the length of the piston rod and having suitable passages formed therein to define the first and second paths of travel.

The control device may take the form of a control valve which controls the routing of the liquid along the appropriate paths of travel, and may comprise a control rod secured at one end of the cylinder and engaging at its other end internally of the piston assembly to block, or allow, communication with the appropriate passages.

Alternatively, the control rod may be coupled with the piston assembly for movement therewith, but being arranged to be arrested in its movement by engagement with one end of the housing, when the piston assembly moves a predetermined distance towards said one end, so as to alter the routing of the damping liquid.

The one-way valve arrangements associated with each communication means may take any convenient and simple form, such as washers or shims arranged on both sides of the piston so as to block entry to the respective passages.

These washers or shims are preferably made of resilient material, so as to block access to the respective passages for one direction of movement, but to be moved by the pressure action of the liquid to allow the liquid to pass through the piston assembly for the opposite direction of movement.

Preferably, a gas accumulator or reservoir is coupled with the cylinder to communicate with the space above the piston assembly, so as to apply a predetermined biasing force which can at least partly serve to hold the wheel in a datum position.

A damper according to the invention is especially suitable for mounting on a motorcycle frame to control the up and down oscillation of a rear wheel mounting carried by a swinging arm assembly. If the rider wishes to alter the sensitivity of the response of the damper, to suit either his own weight, and / or the terrain over which he intends to travel, the washers or shims can readily be replaced or modified. Thus, by simply increasing the number of washers in a stack, the greater can be the resistance to liquid flow provided by the stack. Alternatively, replacement washers of different resilience may readily be mounted in position.

One embodiment of position-sensitive damper according to the invention will now be described in detail, by way of example only, with reference to the accompany drawings, in which:' Figure 1 is a schematic illustration of a damper mounted on a motorcycle frame for controlling the movement of the rear wheel thereof; Figure 2 is a diagramatic illustration of a piston rod of the damper; Figure 3 is an exploded view of a control device in the form of a circuit control pin for controlling the response of the damper; Figure 4 is an exploded view of a piston assembly carried by the piston rod; Figure 5 shows the upper and lower sides of each of the two pistons of the piston assembly shown in Figure 4; Figure 6 illustrates shims or washers for use with the pistons; Figure 7 is a schematic illustration of different paths of travel for liquid damping medium contained in the damper; and, Figure 8 shows alternative porting through the pistons of the damper.

Referring first to Figure 1 of the drawings, there is shown schematically a motorcycle frame having a main or first part 10, and a second part 11, and a rear wheel 12 mounted on the trailing end of the part 11. A damper 13 extends between the frame parts 10 and 11, such parts being relatively moveable when the wheel 12 is subjected to an impact, and such impact being cushioned or absorbed by the damper 13. The damper 13 is shown only schematically, and has a cylinder 14 connected to the frame part 10, and containing any suitable liquid damping medium 15. A piston rod 16 is connected to the frame part 11 and carries a piston assembly 17 which is slidable along the cylinder 14 when relative movement takes place between the frame parts 10 and 11.

As will be described in more detail below with reference to Figures 2 to 7, first communication means extends through the piston assembly to permit the flow of liquid damping medium through the piston assembly upon relatively movement of the latter in one direction from a datum position, and second communication means extend through the piston assembly to permit the flow of liquid damping medium upon relative movement of the piston assembly in an opposite direction. Further, respective one-way valve arrangements are associated with each communication means.

Furthermore, at least the first communications means is defined by first and second paths of travel of respectively lower and higher resistance to liquid flow, and a control device is arranged to respond to relative movement of the piston assembly in one direction from a datum position in order to control initial routing of the liquid along the first path of lower resistance and, when a predetermined relative movement is exceded, to route the liquid along the second path of high resistance.

Referring now to Figures 2 to 4, there is shown the internal components of the damper in more detail, and comprising a damper rod 21, a piston carrier 22, a platform 23, and a piston assembly in the form of a first piston 24 and a second piston 25 spaced apart along the damper rod 21. A spacer 26 is arranged between the first and second pistons, and a lock nut 27 retains the assembly in position on the damper rod. Compression shims or washers 28 function as a one-way valve permitting the compression stroke of the first piston 24, and shims 29 act as a oneway valve permitting rebound movement of the first piston 24. Similarly, there are compression shims 30 and rebound shims 31 arranged one on either side of the second piston 25.

The control device for controlling the routing of the liquid damping medium along high or low resistance paths takes the form of circuit control pin 32 which is mounted in pin holder 33 and which also forms a hydraulic bump stop. Spring cap 35 retains a compression spring 34 within the control pin 32, to apply downward biasing to the latter.

Figure 5 shows the opposite sides of the first piston 24 and 25, the first piston 24 having compression damping feed ports 1A and rebound damping feed ports lB, whereas the second piston 25 has compression damping feed ports 2A and rebound damping feed ports 2B. As shown in Figure 6, reference 30 designates a primary shim or washer, and reference 30A designates additional shims which may be placed behind the primary shim, to be added to or subtracted from the stack, thereby to increase or decrease the damping rate. The shims 30 and 30A are used on each side of both pistons (compression and rebound) in varying numbers and combinations, to give a required damping rate.

Figure 7 shows schematically the different routing of liquid damping medium through the piston assembly, path 1 being the first compression damping circuit and path 2 being the second compression damping circuit of higher resistance, whereas path 3 represents the first rebound damping circuit and path 4 represents the second and more resistant rebound damping circuit. The first compression damping circuit is the first to operate, and is set up to give a light damping resistance, but the second compression damping circuit comes into operation when the control pin 32 enters the piston carrier 22 and closes the first compression damping circuit. The first rebound damping circuit operates in the same travel range as the first compression damping circuit, and the second rebound damping circuit operates in the same travel range as the second compression damping circuit. The length of the control pin 32 dictates the range of each damping circuit.

Alternative internal passages and porting for the pistons is shown in Figure 8.

The control pin controls the merging and change-over of damping circuits, and the length and taper of the pin can be varied to suit when and how the change-over of the circuits occurs. This may be arranged such as to have substantially instantaneous change-over, or else progressive change-over from one circuit to the other, and at a variety of different travel stages of the piston assembly along the cylinder.

In addition to possible modification of the control pin, the "tuning" of the damper may be adjusted by including two pistons and four shim stacks (two compression and two rebound), and four damping circuits (two compression and two rebound).

The first piston (the lower piston) controls the initial travel, and the compression and rebound. A damping rate that is considered ideal for the initial travel can be chosen, without the need to consider any compromise to prevent excessive "bottoming".

The second piston (the upper piston) works in conjunctions with the first piston when the control pin closes-off the first damping circuit. This second piston, together with the first piston, controls damping (compression and rebound) at the bottom end of travel and therefore can be set up to give a heavy damping rate to arrest wheel speed and to prevent bottoming.

Both pistons may be set up with any combination of speed sensitive valving, but it should be borne in mind that when the first damping circuit is closed, the second circuit operates through both shim stacks, there being one on each piston. This doubling-up effect should be borne in mind when initially setting up the damper.

If it should be required to increase initial damping resistance, but to keep the damping rate at the bottom end of the travel as it is, all that is required is to move a shim or shims from the second piston to the first piston.

This will increase the initial damping and at the same time the heavy damping on the second circuit will remain substantially the same as before.

If it is desired to decrease the initial damping rate and to keep the heavy damping as it is, then a shim or shims can be moved from the first piston to the second piston.

If it is required to increase or decrease the heavy damping rate, then it is only necessary to increase or decrease the number of shims on the second piston. This will not affect the initial light damping set on the first piston.

If it is required to increase damping resistance overall (compression or rebound) this can be done with the external adjusters, or by adding or subtracting shims from the first piston.

After the second circuit has been put into operation, and near the end of the limit of relative travel of the piston assembly, an hydraulic bump stop comes into operation and progressively closes this circuit.

The advantages of the disclosed embodiment of position sensitive damper are as follows: 1. There is a saving in production costs of a motorcycle frame on which the damper is provided, as compared with motorcycle frames manufactured with a linkage system.

2. There is much less maintainence involved as compared with the known linkage system.

3. A motorcycle frame incorporating the damper can be manufactured with a lighter weight than the motorcycle frames provided with the linkage system.

4. The damping curve can be altered easily by changing a few low cost parts internally of the damper, which is much more simple than manufacturing an entire revised linkage.

5. Any part of the travel of the damper can be tuned separately from the rest of the travel, again by changing a few low cost parts inside the damper.

6. Various speed sensitive combinations can be used at different travel stages.

7. There are minimal frictional losses, unlike the linkage system.

8. With the embodiment of damper, an hydraulic bump stop can be used, which is advantageous over the usual crude type of rubber bump stop.

The disclosed embodiment of damper has a piston assembly provided with two spaced apart pistons. However, the first and second communication means providing different resistance paths of travel may readily be incorporated in a single design of piston. Furthermore, while the illustrated embodiment has a control device which is mounted at one end of the cylinder, so that the piston assembly moves relative to it, it should be understood that a control pin arrangement may be provided which is capable of travelling with the piston assembly for a predetermined distance, but then has its motion arrested by coming into engagement with a fixed stop on the cylinder, when it then carries out its control over the routing of the path of travel taken up by the damping liquid through the piston assembly.

Claims (11)

1. A damper for mounting on a vehicle frame in order to damp the up and down oscillations of a vehicle wheel relative to the frame, the damper being intended to extend between two parts of the frame which are relatively movable when the vehicle wheel is subjected to an impact, and said damper comprising:: a cylinder connectable to one of said frame parts and arranged to contain a liquid damping medium; a piston rod connectable to the other of said frame parts; a piston assembly carried by said piston rod and slidable along the cylinder when relative movement takes place between said frame parts; a first communication means extending through the piston assembly to permit the flow of liquid damping medium through the piston assembly upon relative movement of the piston assembly in one direction; a second communication means extending through the piston assembly to permit the flow of liquid damping medium through the piston assembly upon relative movement of the latter in an opposite direction; and a respective one-way valve arrangement associated with each communication means; in which: the first communication means is defined by first and second paths of travel of respectively lower and higher resistance to liquid flow; and a control device is arranged to respond to relative movement of the piston assembly in said one direction from a datum position in order to control initial routing of the liquid along the first path of lower resistance and, when a predetermined relative movement is exceded, to route the liquid along the second path of higher resistance.

2. A damper according to Claim 1, in which the second communication means is provided with respective first and second paths of travel for the liquid which is controlled by the control device, upon relative movement of the piston assembly in an opposite direction from the datum position.

3. A damper according to Claim 1 or 2, in which the piston assembly comprises first and second pistons spaced apart along the length of the piston rod and having passages formed therein to define said first and second paths of travel.

4. A damper according to any one of Claims 1 to 3, in which the control device takes the form of a control valve for controlling the routing of the liquid along the appropriate paths of travel.

5. A damper according to Claim 4, in which the control valve comprises a control rod secured at one end of the cylinder and engaging at its other end internally of the piston assembly to block, or to allow, communication with the appropriate passages.

6. A damper according to Claim 4, in which the control valve comprises a control rod coupled with the piston assembly for movement therewith, but being arranged to be arrested in its movement by engagement with one end of the housing, when the piston assembly moves a predetermined distance towards said one end, so as to alter the routing of the damping liquid.

7. A damper according to any one of the preceding Claims, in which the one-way valve arrangements associated with each communication means comprises washers or shims arranged on both sides of the piston so as to block entry to the respective passages.

8. A damper according to Claim 7, in which the washers or shims are made of resilient material, so as to block access to the respective passages for one direction of movement, but to be moved by the pressure action of the liquid to allow the liquid to pass through the piston assembly for the opposite direction of movement.

9. A damper according to any one of the preceding Claims, including a gas accumulator or reservoir coupled with the cylinder to communicate with the space above the piston assembly, so as to apply a predetermined biasing force which can at least partly serve to hold the wheel in a datum position.

10. A motor cycle frame having mounted thereon a damper according to any one of the preceding Claims, so as to control the up and down oscillation of a rear wheel mounting carried by a swinging arm assembly.

11. A damper according to Claim 1 and substantially as hereinbefore described with reference to, and as shown in the accompanying drawings.