GB2117448A - Hydraulic ram assembly - Google Patents

Abstract

A hydraulic tipping ram assembly 10 such as is employed for tipping a load-carrying body of a heavy goods vehicle has a cylinder 14 which carries on its external surface a resilient pressure pad 22 for contacting the inner rim 18 surface of a bell-shaped cover 17 coupled to the or a terminal piston 12. With the ram assembly in the position it assumes with the load body fully lowered, the pressure pad 22 is in compression and the bell cover is subject to a corresponding reaction force F with components parallel to and transverse to the longitudinal axis of the cylinder 14 which components are effective to damp vibrations between components of the ram assembly parallel to the longitudinal axis thereof, and vibrational contact between the bell cover 17 and a guard ring 20 on the exterior of the cylinder 14. <IMAGE>

Description

SPECIFICATION Hydraulic ram assembly The present invention relates to an hydraulic ram assembly and more particularly is concerned with a hydraulic tipping ram assembly such as is employed for tipping a load-carrying body of a heavy goods vehicle relative to a chassis thereof.

It is usual, in heavy goods vehicles with tipping load bodies, to employ a hydraulic, piston and cylinder, ram assembly mounted in an upright disposition in front of the load body for tipping the body. The ram in the assembly is usually a multistage ram. A first pair of trunnions located at the base of the assembly is pivotally mounted to the chassis. A second pair of trunnions which moves with the terminal piston of the multi-stage ram assembly is pivotally connected to the load body. It is convenient to provide a bell-shaped cover for the ram assembly which is connected to the terminal piston of the assembly at the apex of the bell cover, and to mount the second pair of trunnions to the bell cover near the rim thereof.

To ensure that the rim of the bell cover does not foul the upper end of the cylinder in use of the assembly, it is necessary to leave a gap between those surfaces of the cylinder over which the cover moves in use, and the internal wall surface of the cover itself. However, if the gap is made unduly large there is a danger that sideways forces on the cover near the rim thereof will move it transverse to the line of action of the ram assembly by a distance sufficiently large to cause permanent deformation of the cover, or other damage to the ram assembly.

The present Applicants have found that these constraints on the size of the gap between the cover and the cylinder, together with the inevitable vibration to which components of vehicles are subject during use of the vehicle, leads to metal-to-metal vibrational contact between the cylinder and the cover during use of the vehicle to which the assembly is fitted, and such vibrational contact is not only noisy but can be harmful to the assembly.

When the tipping load body is fully lowered, it rests on supporting members of the vehicle chassis.

It is arranged that the body contacts the supporting members before the ram assembly attains a fully nested and stopped minimum length so that, when the vehicle is travelling, no part of the weight of the lowered load body is carried by the ram assembly.

The difference in length of the ram assembly between that when it is mounted in a vehicle as aforesaid, and the tipping body is fully lowered, and that when it is in its fully nested and stopped disposition, is referred to herein as the "pull out" distance.

The present Applicants have appreciated that relieving the ram assembly of the weight of the load body will tend to lead to vibration of component parts of the ram assembly relative to one another and through the trunnions by which the assembly is mounted to the chassis and load body. This vibration is undesirable.

The present invention has as one object to mitigate or avoid the above-mentioned disadvantages.

According to the present invention there is provided an hydraulic tipping ram assembly comprising a single or multi-stage piston and cylinder hydraulic actuator which includes a first pair of trunnions for mounting the actuator to a vehicle chassis and a bell-shaped cover with a flared rim attached at its apex to the end of the, or the terminal, piston which projects from the cylinder, the cover surrounding the cylinder and extending at least part of the way along the length of the cylinder when the said piston is fully retracted into the cylinder and carrying a second pair of trunnions for mounting the cover to a tipping body of a vehicle, characterised in that the cylinder carries on its external cylindrical wall surface a resilient pressure pad which includes a surface for contacting the inner surface of the rim of the bell-shaped cover whereby, when the ram assembly is a pull out distance from its fully nested, stopped disposition, the pressure pad is placable in compression by the contact of the rim therewith and there is imposed on the bell-shaped cover a corresponding reaction force which has a component parallel to the longitudinal axis of the bell-shaped cover and a component transverse to the said longitudinal axis.

The said parallel and transverse components of the reaction force will have the effect of damping the undesirable vibrations mentioned above. It will be appreciated that the invention provides a simple and inexpensive way of damping vibrations which, by making use of the previously provided flared rim of the bell cover, avoids the need for design modification of large metal components of the ram assembly.

It is convenient to provide the pressure pad in the form of a resilient ring which extends around the circumference of the cylinder like a belt. Slackening the belt allows it to be moved up and down on the cylinder. Such a ring is prevented from slipping along the cylinder, to relieve the compression in the ring, by arranging for it to press tightly onto the surface of the cylinder, and it is to be noted that the pressure of the rim of the bell cover on the ring is to press it more tightly against the cylinder.

Preferably, the resilient ring is in the form of a strap which can be fastened around the cylinder at a time when the bell-shaped cover is in position.

Preferably, the shape of the outer surface of the cylinder where the resilient ring or other pad is located and the nature of the resilient ring or pad are such that the position of the ring or pad along the length of the cylinder is smoothly adjustable so that any wear of the pad material caused by rubbing contact between it and the cover can be taken up by appropriate movement of the ring or pad along the cylinder, and such small differences from onevehi- cle to another in the gap between the mounting points of the first and second pairs of trunnions of the ram assembly can be taken up by re-positioning of the ring or pad.

In one preferred embodiment, the ring comprises an extruded length of a tough, rubber material which, in cross-section, has the form of a "D". The flat face of the extruded section abuts against the external wall surface of the cylinder, the curved surface thereby being outwardly-directed and adapted to abut the rim surface of the cover, and the central aperture in the extruded section providing a passage all the way round the ring for accommodation of a securing band, which may be a "Jubilee" or other clip in which the band carries surface formations which co-operate with a threaded member for tensioning of the band by manual rotation of the threaded member.

The pressure pad need not be a resilient ring but could be, for example, a small number of strips of resilient material, say four, arranged parallel to the longitudinal axis of the ram assembly and regularly spaced around the circumference of the cylinder.

The strips might be held in position by a metal strap extending around the cylinder.

For a better understanding of the present invention, and to show more clearly how the same may be carried into effect, reference will now be made to the accompanying drawings, in which Figure 1 is an elevation of a multi-stage hydraulic ram assembly which includes a bell-shaped outer cover shown for clarity in section; Figure 2 is a detail of Figure 1, shown art a larger scale; and Figure 3 is a plan view at a smaller scale of the resilient ring shown in Figures 1 and 2.

Referring to Figure 1, a ram assembly 10 has a first pair of trunnions 11 by which the assembly may be pivotally mounted to the chassis of a heavy goods vehicle. To the smallest one 12 of the series of pistons 13 within a cylinder 14 is secured by an end nut 15 an annular end plate 16 to which is welded a cylindrical cover 17, the end plate 16 and cover 17 together forming a bell-shaped cover secured at its apex to the piston 12 and extending downwardly over the upper part of cylinder 14. Near the rim 18 of the outer cover 17 there is a provided a second pair of trunnions 19 which are for pivotal mounting on the pivoting load-carrying body of the vehicle to which the ram assembly is to be secured. For economy of presentation, part of the length of the ram assembly, that is to say, that between chain dotted lines XX and YY, is not shown.

Thetrunnions 19 are carried on a ring 19A loosely captivated between a lower seating ring 19B and a stop ring 1 9C spaced above the top of the trunnion ring 19A. When the ram is actuated to lift the vehicle load body the lifting force is transmitted to the trunnions 19 through the interaction oftherings 19A and 19B.

To avoid permanent distortion of the outer cover 17 of the ram assembly, by excessive movement thereof transverse to the line of action of the hydraulic actuator, a steel guard ring 20 is secured around the cylinder 14 at a position where it is level with the trunnions 19 when the ram assembly is fully retracted.

The gap 21 between the guard ring 20 and the internal surface of the outer cover 17 is small enought to prevent permanent distortion of the cover but large enough to allow the cover to move back and forth over the guard ring 20 during operation of the ram assembly.

Vibrational contact between the internal surface of the cover 17 and the guard ring 20 is prevented by the presence of a resilient ring 22 of tough, natural or synthetic rubber fitted around the cylinder 14 at the level of the rim 18 of the outer cover 17. As seen also in Figures 2 and 3, the ring 22 comprises a length of an extruded section fitted around the cylinder 14 and held in place by a "Jubilee" clip 23. The steel band 24 of the clip extends along the whole length of the ring 22 in an aperture 25 of the extruded section.

Tension in the band 24 is adjusted manually by rotation of the hexagonal headed screw 26 of the clip, and installation of the clip 23 within the rubber extruded section strap 22 is made easier by cutting one of the ends of the rubber strip 22 at an angle of 45Q to the length of the strip, as seen in Figure 3.

To take up wear of the rubber ring 22 in the zone 27 of contact between it and the rim 18 of the cover 17, the tension in the band 24 of the clip 23 may be slackened by rotation of the screw 26, and the ring 22 shifted upwardly on the surface of the cylinder 14 until the ring is once more firmly in contact with the rim 18.

Preferably the ring 22 is so shaped around its lower surfaces that it can be turned upside down when zone 27 has worn away, so that a further zone 28 may be used before the ring 22 need be replaced.

The force of reaction on the bell cover 20 which results from compression of the resilient ring in the zone 18 is indicated in Figure 2 as F. This force can be divided into componentsfxandfy. It will be appreciated that fx serves to resist vibration of the bell cover 20 transverse to the ram assembly 36 and fy serves to resist vibrations between components of the ram assembly parallel to the assembly. With a sufficiently resilient ring 12 held tightly enough against the cylindrical external surface of the cylinder 23, the compression of the ring can resist such vibrations of the trunnions 11 and 19 in their mountings on the vehicle as occur when the load body is fully lowered and the vehicle is travelling with the weight of the load body not carried by the ram assembly, in particular, vibrations in the nature of rattling between the trunnion ring 1 9A and the seating ring 19B.

Claims (9)

1. An hydraulic tipping ram assembly compris- ing a single or multi-stage piston and cylinder hydraulic actuator which includes a first pair of trunnions for mounting the actuator to a vehicle chassis and a bell shaped cover with a flared rim attached at its apex to the, or the terminal, piston which projects from the cylinder, the cover surrounding the cylinder and extending at least part of the way along the length of the cylinder when the said piston is fully retracted into the cylinder and carrying a second pair of trunnions for mounting the cover to a tipping body of a vehicle, characterised in that the cylinder carries on its external cylindrical wall surface a resilient pressure pad which includes a surface for contacting the inner surface of the rim of the bell-shaped cover whereby, when the ram assembly is a pull out distance from its fully nested, stopped disposition, the pressure pad is placeable in compression by the contact of the rim therewith and there is imposed on the bell-shaped cover a corresponding reaction force which has a componenent parallel to the longitudinal axis of the bell-shaped cover and a component transverse to the said axis.

2. An assembly as claimed in claim 1 wherein the pressure pad takes the form of a ring of resilient material extending around the circumference of the cylinder.

3. An assembly as claimed in claim 2 wherein the ring is in the form of a strap which can be fastened around the cylinder while the bell-shaped cover remains in its position surrounding the cylinder.

4. An assembly as claimed in claim 2 or 3 wherein the ring is formed from an extruded, D-shaped section, the flat face of the section being for abutment with the cylindrical surface of the cylinder.

5. An assembly as claimed in claim 4wherein the ring is removable from the cylinder and replaceable on the cylinder, for further service, in a disposition which is upside down relative to its disposition prior to said removal.

6. An assembly as claimed in any one of claims 2 to 5, wherein the ring is hollow and contains a securing band for holding it pressed against the cylinder.

7. An assembly as claimed in claim 6 wherein the band carries surface formations which co-operate with a threaded memberfortensioning of the band by manual rotation of the threaded member.

8. An assembly as claimed in any one of the preceding claims wherein the shape of the outer surface of the cylinder and the nature of the pressure pad are such that the position of the pad along the length of the cylinder is smoothly adjustable.

9. An hydraulic tipping ram assemblysubstantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.