GB2134051A

GB2134051A - Suspension locking device

Info

Publication number: GB2134051A
Application number: GB08301642A
Authority: GB
Inventors: Peter Farrer; David Arthur Buckley
Original assignee: Fairey Engineering Ltd
Current assignee: WFEL Ltd
Priority date: 1983-01-21
Filing date: 1983-01-21
Publication date: 1984-08-08
Also published as: GB8301642D0

Abstract

A suspension locking device 19 comprises a piston 23, which is attached by means of a piston rod 29 to an axle casing of a vehicle, and a cylinder 21, which is attached to a frame of the vehicle. A passageway 31 having a valve 33 allows the two chambers 25 and 27 of the cylinder defined by the piston to communicate with each other. Closing the valve prevents hydraulic fluid flow between the chambers and therefore locks the piston with respect to the cylinder thereby locking the vehicle suspension. <IMAGE>

Description

SPECIFICATION Suspension locking device This invention relates to suspension locking device suitable for selectively locking an axle of a vehicle to a frame of the vehicle.

There are many situations in which it is necessary or desirable for vehicle suspensions to be locked. It is particularly envisaged that a device in accordance with the present invention can be used on vehicles whose load can be transferred over the back of the vehicle. Examples of such vehicles are those with demountable bodies. Such vehicles often require stabilization, and this is frequently achieved by mechanically locking the rear suspension or by hydraulic jacks.

According to a first aspect of the present invention, there is provided a device suitable for selectively locking an axle of a vehicle to a frame of the vehicle, the device compr;sing a piston, a cylinder in which the piston and cylinder define a first chamber and a second chamber, a passageway communicating with the first chamber and the second chamber to form a closed circuit for hydraulic fluid and a valve operable selectively to allow hydraulic fluid to flow and to prevent hydraulic fluid from flowing through the passageway, one of the piston and cylinder being connected to an axle of the vehicle and the other of the piston and cylinder being connected to a frame of the vehicle.

A device in accordance with the first aspect of the invention can be said to be a "passive" device as no external power source is required other than for operating the valve. Further, it may be found that it is easier to maintain the equilibrium of the vehicle when the suspension is locked as no initial load transfer occurs, as can be the case when using conventional hydraulic jacks.

By means of a device in accordance with the first aspect of this invention the suspension of a vehicle may be locked at any suspension position, including full articulation and when one of a multiplicity of wheels of the vehicle is at a level different from the other wheels, such as when a wheel is on a bump or in a depression in the ground.

The two chambers may have the same crosssectional area. In such a case a displacement of the piston of a unit length will cause the same volume of hydraulic fluid to be displaced in the two chambers. Alternatively, the two-chambers may have different cross-sectional areas, in which case the device comprises means for compensating for the different volumes of hydraulic fluid displaced in the two chambers per unit length displacement of the piston. The compensating means desirably comprises an accumulator.

At least a portion of the passageway may be sufficiently restricted to cause the device to function as a suspension damping unit or shock absorber. This is achieved in the following way.

When the valve is closed, hydraulic fluid is prevented from flowing from one of the chambers to the other and so the position of the piston with respect to the cylinder will be fixed. This locks the suspension. However, when the valve is open, hydraulic fluid may flow between the first and second chambers through the passageway and so the piston can move in the cylinder. Relative movement between vehicles axles and the frame will tend to cause the piston to move, but this movement may be curtailed by a restriction in the passageway; the suspension will thus be damped.

The passageway is preferably located in a wall of the cylinder. This is envisaged as being the optimum location for ease of access to the valve and compactness. On the other hand, the valve and passageway could be in the piston itself or outside the cylinder wall.

According to a second aspect of the present invention, there is provided a vehicle having a device in accordance with the first aspect of the invention.

For a better understanding of the present invention, and to show how it may be put into effect, reference is now made, by way of example, to the accompanying drawings, in which: FIGURE 1 shows a schematic side view of the suspension of a vehicle having a device in accordance with this invention; FIGURE 2 shows a schematic sectional view through the device which appears in Figure 1; and FIGURE 3 shows a schematic sectional view through a second embodiment of the present invention.

Referring now to the drawings, Figure 1 shows the frame or chassis 1 of a vehicle. Depending from the frame 1 is a lug 3, pivotally mounted at the lower most end of which is the mid point of a suspension arm 5. Mounted on each end of the suspension arm 5 is a respective axle casing 7 or 9. Journalled through each of the axle casings 7 and 9 is a respective axle 11 or 13 bearing a respective wheel 1 5 or 17.

Extending between the frame 1 and the axle casing 9 associated with the wheel 1 7 is a device 19 in accordance with the invention. The device 19 is shown in greater detail in Figure 2.

The device 1 9 comprises a cylinder 21 which in use is attached to the frame 1 of the vehicle.

Located within the cylinder 21 is a piston 23 which divides the cylinder into a first chamber 25 and a second chamber 27. A piston rod 29 extends from the piston 23 through the second chamber 27 and is attached to the axle casing 9 associated with the wheel 17.

Allowing the first chamber 25 to communicate with the second chamber 27 is a passageway 31 in which is located a valve 33. Communicating with the passageway at a point between the first chamber 25 and the valve 33 is an accumulator 35.

In use the device 21 operates as follows. When the valve 33 is in the open position, fluid can flow through the passageway 31 between the first and second chambers 25 and 27. A given linear displacement of the piston 23 will displace a greater volume of fluid in the first chamber 25 than in the second chamber 27 because the first chamber 25 has a greater effective cross-sectional area because of the absence of the piston rod 29.

The differential volumes per unit length of the two chambers 25 and 27 are compensated for by the accumulator 35.

When it is desired to lock the suspension of a vehicle to which the device 21 is fitted, the valve 33 is simply closed. This ensures that no fluid can flow between the first and second chambers 25 and 27 and so the piston is effectively locked in position, thereby preventing relative movement between the frame 1 and the axle casing 9 of Figure 1. Figure 3 shows a second embodiment of the invention. A device 11 9 comprises a cylinder 121 in which is located a piston 1 23. The piston 123 divides the cylinder 1 21 in to a first chamber 125 and a second chamber 127. Piston rods 128 and 129 extend from opposite faces of the piston 123 through the first chamber 125 and the second chamber 127 respectively. The cylinder 121 is connected to the frame 1 of a vehicle and one or both of the piston rods 128 and 129 is connected to an axle casing 9. A passageway 1 31 extends between the first and second chambers 125 and 1 27. Located in the passageway is a valve 133.

The principle of operation of the device illustrated in Figure 3 is the same as for the device illustrated in Figure 2, except that, because the volumes per unit length of the chambers 1 25 and 127 are identical, there is no need for the presence of an accumulator or other means for compensating for differential volumes per unit length of the chambers.

Claims

1. A device suitable for selectively locking an axle of a vehicle to a frame of the vehicle, the device comprising a piston, a cylinder in which the piston and cylinder define a first chamber and a second chamber, a passageway communicating with the first chamber and the second chamber to form a closed circuit for hydraulic fluid and a valve operable selectively to allow hydraulic fluid to flow and to prevent hydraulic fluid from flowing through the passageway, one of the piston and cylinder being connected to an axle of the vehicle and the other of the piston and cylinder being connected to a frame of the vehicle.

2. A device as claimed in Claim 1, wherein the two chambers have the same cross-sectional area.

3. A device as claimed in Claim 1, wherein the two chambers have different cross-sectional areas and wherein the device comprises means for compensating for the different volumes of hydraulic fluid displaced in the two chambers per unit length displacement of the piston.

4. A device as claimed in Claim 3, wherein the compensating means comprises an accumulator.

5. A device as claimed in any one of claims 1 to 4, in which at least a portion of the passageway is restricted to cause the device to function as a suspension damping unit.

6. A device as claimed in any one of Claims 1 to 5, wherein the passageway is located in a wall of the cylinder.

7. A device as claimed in any one of Claims 1 to 5, wherein the valve and passageway are located in the piston.

8. A device substantially as described herein with reference to Figures 1 and 2 or to Figure 3 of the accompanying drawings.

9. A vehicle having a device as claimed in any one of Claims 1 to 8.