GB2088298A

GB2088298A - Twin Axle Suspensions

Info

Publication number: GB2088298A
Application number: GB8038054A
Authority: GB
Original assignee: MOGFORD ALAN KEITH; MOGFORD MELVILLE JAMES
Current assignee: MOGFORD ALAN KEITH; MOGFORD MELVILLE JAMES
Priority date: 1980-11-27
Filing date: 1980-11-27
Publication date: 1982-06-09

Abstract

In a spring suspension unit for road vehicles, such as heavy trailers having twin axles, on each side of the vehicle a rocker beam (5) pivotally interconnecting the two axles, (2, 3) supports centrally a pivoted spring support plate (8). A row of helical springs (12) is interposed between the main frame (1) of the vehicle and the spring support plate (8). The springs may be graded in height, so that only the outermost springs (12a) are under load when the vehicle is unladen. <IMAGE>

Description

SPECIFICATION Spring Suspension Unit for Road Vehicles This invention relates to spring suspension units for road vehicles having twin road wheel axles, with particular, but not exclusively, reference to heavy goods vehicles including trailers of articulated vehicles.

The commonestform of spring suspension for road vehicles, particularly heavy duty transport vehicles, utilises semi-elliptical leaf springs. Such leaf springs are prone to expensive failure in use, since failure of a leaf spring on an axle of a heavy transport vehicle such as a trailer frequently leads to coilapse of one side of the vehicle, sufficiently to result in the vehicle's shedding its load. The replacement of broken leaf springs is, moreover, an expensive and time-consuming operation.

In U.K. Patent Specification No. 1,31 6,1 34 a spring suspension unit for road vehicles is described in which an assembly of helical springs is employed for the suspension of a vehicle from an axle or axles and an alternative to the conventional leaf spring. This spring suspension unit has been found to offer many practical advantages compared with the leaf spring, not least of which is the relatively small deflection of the spring suspension unit in the event of spring failure, resulting in considerably reduced dropping of one side of the vehicle fitted in the event of failure of the suspension unit on that side, so that the vehicle remains at least sufficiently stable to retain its load and to be driven with safety.

The present invention is a further improvement in spring suspension units specifically adapted for use in twin axle road vehicles.

According to the present invention there is provided a spring suspension unit for a road vehicle having twin axles, comprising, for each side of the vehicle, a rocker beam adapted to be pivotally connected at opposite ends to the two axles, a spring support plate pivotally connected to the centre of the rocker beam and a number of helical springs supported by the support plate and arranged in a longitudinally extending row with their axes substantially vertical, the springs in use of the suspension unit bearing against and supporting the frame of the vehicle.

The invention has particular application to heavy goods vehicles. The suspension unit is ideally suited for twin axle trailers or articulated vehicles. The pivotal movement of the spring support plate relative to the rocker beam in use of the spring suspension unit accommodates relative movement between the axles when the vehicle moves over uneven ground.

Preferably the spring support plate has two depending walls along its opposite longitudinal edges, the rocker beam having a central portion which is located between said walls and pivotally connected to the latter by a transverse pivot pin extending through said central portion and the two walls.

The helical springs of the unit are preferably carried on the support plate by at least one tray which can be slid longitudinally relative to the support plate when the suspension unit is unloaded to facilitate withdrawal and replacement of the springs. Preferably the springs are arranged in two sets carried on two trays supported on the said spring support plate and removable by longitudinal sliding movement from opposite ends of said support plate. This arrangement facilitates removal and replacement of individual springs of the spring suspension unit easily and quickly. The opposite ends of the support plate may be closed by removable end walls secured to one of the housings and preventing, when in position, removal of the tray or trays supporting the springs.

In a preferred embodiment of the invention guide pins project laterally from the spring support plate and are located in vertical slots in guide plates adapted to be attached to the vehicle frame to guide movement of the support plate relative to said frame in use of the suspension device.

An important practical advantage of the spring suspension unit of the present invention is that it can easily be adapted to give a progressive loading characteristic, that is to say, an increased resistance to deflection with increasing vehicle loads. For this purpose at least two of the helical springs, preferably the extreme springs of each longitudinal row, may have a greater unloaded length than the remaining springs, such that when the unit is in use on an unladen or partially unladen vehicle only these longer springs are compressively loaded. The spring suspension unit is less stiff when the vehicle is unladen than when the vehicle is fully laden.

This is an important feature from the standpoints of safety and roadway damage, since it is well known that heavy goods vehicles, particularly the trailers of articulated vehicles, are prone to exhibit 'axle hop' when unladen, because of the stiffness of their heavy duty suspensions, a phenomenon which can lead to loss of control and which also causes severe impact damage to roadway surfaces. Thus the suspension unit when unladen, by using only two or a small number of the total number of springs in the unit ensures a firm but resilient suspension for the vehicle when unladen, and minimises any tendency towards axle hopping or suspension bounce when the vehicle is unladen, while at the same time giving the vehicle much smoother 'ride' characteristics from the driver's viewpoint.

The invention also comprehends a road vehicle having twin axles which support each side the vehicle frame by means of respective spring suspension units as herein defined.

The invention will be further described, by way of example, with reference to the accompanying purely diagrammatic drawings, in which: Figure 1 is a side elevational view of a spring suspension unit according to one embodiment of the invention fitted to twin axles of a vehicle; Figure 2 is a vertical cross-section on line Il-li in Figure 1, and Figure 3 is a plan view of part of a twin axle heavy transport vehicle, in this case a trailer of an articulated vehicle, incorporating spring suspension units as shown in Figures 1 and 2.

The spring suspension unit illustrated in the drawings is shown fitted to a trailer of an articulated goods vehicle. Parts of the longitudinal frame members 1 of the trailer, consisting of two I-section beams, are shown, the frame members 1 being supported by two pairs of road wheels (not shown) carried by twin axles 2, 3 which are connected to the frame members 1 by respective spring suspension units 4 according to the invention, disposed one on each side of the vehicle.

Each spring suspension unit 4 comprises a rocker beam 5 of steel box construction pivotally connected by respective pins and rubber bush assemblies, 6, 7 at its opposite ends to the respective housings of the axles 2, 3. A central portion of the rocker beam 5 is located between parailel depending longitudinal walls 8, 9 of a spring support plate 10 of inverted U-section (Figure 2) and is pivotally connected to said plate 10 by a transverse pivot pin 11 passing through bushes located on said longitudinal walls 8, 9.

The spring support plate 10 extends longitudinally and is parallel to and directly beneath the associated longitudinal frame member 1 of the trailer.

The trailer frame member 1 is supported from the support plate 10 by a number of helical suspension springs 12 arranged in a longitudinally extending row with their axes substantially vertical and interposed between the upper surface of the spring support plate 10 and the lower surface of the frame member 1. The springs 12 are located on the spring support plate 10 by locating bosses, retaining screw-clamps, welding or other convenient means (not shown). Only three of the springs 12 are shown in Figure 1 , for clarity.

The two outermost springs 1 2A of the row of springs 12 have a longer unloaded length than the other springs, so that when the trailer is unladen, only these outermost springs 1 2A are loaded, as shown in Figure 1. The remaining springs 12 of the row may have lengths when reiaxed which are graded so that the springs come into play successively as the trailer is progressively loaded.

The spring support plate 10 is constrained for limited travel vertically, that is, towards and away from the trailer frame member 1, by guide plates 1 3 which are welded to the each longitudinal edge of the frame member 1 and depend from the latter on opposite sides of the spring support plate 10. Atransverse guide pin 14 extends between the two walls 8, 9 ofthe support plate 10 and projects laterally from the plate 10, the projecting ends of the pin 14 being located in respective vertical slots 1 5 in the respective guide plates 13.

Each laterally projecting end of the pin 14 carries a respective roller 1 6 which runs freely in the slot 15 of the respective guide plate 13.

In a typical practical embodiment the total vertical deflection of each spring suspension unit between its unloaded state and its fully loaded state, that is, the maximum permitted vertical displacement of the frame member 1 relative to the support member 10, corresponding to the length of the slot 1 5 in the guide plate 13, is relatively small, typically about 5 cm. This ensures that even in the event of 'bottoming' of the helical springs 12, or failure of individual springs, the spring suspension unit does not collapse by more, than a few inches, and insufficiently to cause the trailer to overturn or shed its load.

The twin axles 2, 3 are located relatively to each other by the rocker beams 5 of the two suspension units on each side of the trailer. Each of the axles is located relative to the trailer frame by a respective A-frame 17, 1 8 pivotally connected to a respective bracket upstanding from the centre of the respective axle 2 (Figure 3).

The two arms of each A- frame 17, 18 are interconnected by a respective transverse shaft 19, 20 which is pivotally supported at its opposite ends by respective bearing plates attached to a cross beam 21 which rigidly interconnects the two longitudinal I-beam frame members 1.

Each suspension unit has two associated shock absorbers 22, of conventional type, which interconnect the axles 2, 3 and the longitudinal frame members 1: one of these shock absorbers 22 is shown in Figure 1, the position of the axis of the other shock absorber being marked by a dashed line.

For convenience in the removal of the helical suspension springs 12 for inspection or replacement the row of springs 12 of each suspension unit may comprise two sets of equal numbers of springs (for example, two, three, four or five springs per set) arranged end to end. Each set of springs 12 may be supported on a sliding tray, the springs being spaced apart at equal intervals along the length of the tray and secured to the bottom of the tray by easily releasable fixing bolts or clips. Each tray may be slid longitudinally, for example on runners welded to the spring support plate 10, and removed with its set of springs 12, from one end of the plate 10 when the trailer is jacked up, with all the springs unloaded. At its outer end each tray may have an upstanding end cover.

Claims

1. A spring suspension unit for a road vehicle having twin axles, comprising, for each side of the vehicle, a rocker beam adapted to be pivotally connected at opposite ends to the two axles, a spring support plate pivotally connected to the centre of the rocker beam and a number of helical springs supported by the support plate and arranged in a longitudinally extending row with their axes substantially vertical, the springs in use of the suspension unit bearing against and supporting the frame of the vehicle.

2. A spring suspension unit as claimed in Claim 1, in which at least two of the helical springs have a greater unloaded length than the remaining springs such that when the unit is in use on an unladen vehicle or partially laden vehicle only these longer springs are compressively loaded.

3. A spring suspension unit according to Claim 2, in which the extreme springs of the longitudinal row of springs have a longer unloaded length than the other springs.

4. A spring suspension unit according to any of Claims 1 to 3, in which the spring support plate has two depending walls along its opposite longitudinal edges, the rocker beam having a central portion which is located between said walls and pivotally connected to the latter by a transverse pivot pin extending through said central portion and the two walls.

5. A spring suspension unit as claimed in any one of the preceding claims, in which the helical springs are carried on the support plate by at least one tray which can be slid longitudinally relative to the support plate when the suspension unit is unloaded to facilitate withdrawal and replacement of the springs.

6. A spring suspension unit as claimed in Claim 5, in which the helical springs are arranged in two sets carried on two trays supported by the said spring support plate and removable by longitudinal sliding movement from opposite ends of said support plate.

7. A spring suspension unit according to any one of the preceding claims, in which guide pins project laterally from the spring support plate and are located in vertical slots in guide plates adapted to be attached to the vehicle frame to guide movement of the support plate relative to said frame in use of the suspension unit.

8. A road vehicle having twin axles which support each side of the vehicle frame by means of respective spring suspension units according to any one of the preceding claims.

9. A road vehicle according to Claim 8, in which at least one of the axles has a pivoted link connection to the vehicle frame to locate the axle relative to the frame.