GB2219773A - Tandem axle suspension - Google Patents

Abstract

A multi-axled vehicle 1 with at least one driven axle 3 and an adjacent non-driven axle 4 which is located on beams 7 which extend substantially parallel to the vehicle centre line and which are mounted on the vehicle chassis 2. The mounting of at least one of the beams 7 on the chassis includes a linkage arrangement 11 pivotably openable and closable to permit relative movement of the beam towards and away from the respective side frame member and having sufficient rigidity to transmit side loads from the axle tyres to the chassis. The linkage is in the form of a double shackle with two links 12 and 13 each of which comprises inner and outer arms to provide the required rigidity. The arrangement obviates the need for a horizontal transverse linkage to transmit sideways forces to the chassis. <IMAGE>

Description

A VEHICLE The present invention relates to a vehicle particularly but not exclusively to a road going vehicle for carrying or hauling freight.

In such vehicles there is generally a requirement that side loads from the axle tyres be transmitted to the chassis frame. However, it is not always possible to provide a horizontal linkage between the axle and the chassis. A particular example of vehicle in which this problem occurs if of the "dead axle" or "pusher axle" type in which there is a rearmost driven axle (the 'first' axle) a non-driven axle (the 'second' axle) just ahead of the first axle, and one or more non-driven front axles.

Traction requirements for such vehicles demand that as much load as is legally permissible is available at the rear driven axle, any excess being carried on the adjacent non-driven axle, ie. the 'second' axle. This means that under certain conditions of vehicle loading, the second axle may be without an imposed load. It is convenient to use an air suspension system for the second axle, air pressure being fed to load carrying diaphragms when the imposed load on the suspension of the rearmost driven axle reaches a predetermined value.

As the first and second axles are close together, the non-driven axle is normally of a "dropped bed" construction to permit the centrally disposed propellor shaft from the gearbox to the driven axle to pass over it. The presence of the shaft normally prevents or discourages the use of a horizontal linkage between the chassis sidemember and the dropped axle for transmission of the aforementioned side loads.

This problem is not however confined to the "dead axle" or "pusher axle" vehicles described above. The problem may for example exist for any dropped bed axle of a vehicle in which the space above the axle is already occupied by other necessary parts of the vehicle, such as an engine, precluding the use of a horizontal linkage between the axle and the frame.

It is therefore an object of the present invention to obviate or mitigate the abovementioned disadvantage.

According to the present invention there is provided a multi-axled vehicle with at least one driven axle and an adjacent non-driven axle which is located on beams which extend substantially parallel to the vehicle centre line and which are mounted on the vehicle chassis wherein the mounting of at least one of the beams on the chassis includes a linkage arrangement pivotably openable and closable to permit relative movement of the beam towards and away from the respective side frame member and having sufficient rigidity to transmit side loads from the axle tyres to the chassis.

Preferably there are two such linkage arrangements for the non-driven axle provided one towards each end thereof.

Preferably, also the or each linkage arrangement comprises first and second link members pivotably connected together and with the first link member being pivotably mounted on the vehicle chassis and the second link member being pivotably mounted on the beam.

Preferably the beams on which the non-driven axle is mounted are flexible beams, particularly springs.

The or each linkage arrangement serves to transmit sideways loads to the vehicle chassis and for this purpose should be such as to preclude twisting or side-to-side movement.

A suitable linkage arrangement comprises a first shackle pivotably connected at one of its ends to the beam and at its other end to one end of a second shackle the other end of which is pivotably connected to the vehicle chassis.

Furthermore the linkage arrangement(s) inherently permit sideways location of the axle without additional linkages.

The axle with which the or each linkage is associated may be an axle (eg. a dropped bed axle) over which a propellor shaft of the vehicle passes.

A preferred vehicle in accordance with the invention is one in which the or each linkage arrangement is associated with a non-driven axle which is adjacent (eg. immediately forward of) a driven axle of the vehicle and on which there is only an imposed load when that on the driven axle exceeds a predetermined maximum. Preferably the suspension system of the non-driven axle includes an air bellows which are only charged with compressed air when the predetermined load on the driven axle is exceeded.

Alternatively any type of suspension medium may be used to carry vehicle loads. In such a vehicle the or each linkage arrangement permits the tyres of the nondriven axle to remain on the road whether the axle is loaded or not.

A further example of vehicle to which the invention is applicable is a twin-steer vehicle in which there is a driven axle and an adjacent nondriven axle, with the wheels on the driven and nondriven axles being simultaneously steerable.

The invention will be described by way of example only with reference to the accompanying drawings, in which: Fig. 1 is a side view of one embodiment of vehicle in accordance with the invention: Fig. 2 is a detail of Fig. 1; and Fig. 3 illustrates a linkage as used in the vehicle of Fig.

1.

The illustrated vehicle is a tractor unit 1 (for hauling an articulated trailer-not shown) with two parallel chassis side frame members 2 (only one shown), a rearmost driven axle 3, a non-driven axle 4 immediately forward thereof, and a non-driven front axle 5. The wheels 6 on axles 5 and 4 are steerable whereas those on axle 3 are non-steerable.

All of axles 3 to 5 are associated with respective suspension systems. That for axle 4 comprises, towards each end of the axle 4, an arrangement as shown in more detail in Fig.2. This arrangement comprises a flexible beam in the form of a stiff quarter elliptic spring 7 (to which the axle 4 is rigidly attached) pivotably mounted on a frame bracket 8 (itself affixed to a chassis side member 2) by a pin 9. Additionally an air bellows 10 is mounted between the spring 7 and the chassis side member 2.

Although the bellows 10 are shown as being behind the axle 4, they may be positioned over the axle or in front thereof.

Air bellows 10 are charged with air from an external source (not shown) which is operated when the imposed load on rearmost driven axle 3 exceeds a predetermined legal maximum. Upto this predetermined maximum, all imposed load is carried by the axle 3 (to ensure maximum traction). Above the predetermined maximum, the air pressure source provides air pressure to the bellows 10.

The excess load is thus now transmitted to the axle 4 through the frame bracket pin 9 and the air bellows 10.

Axle 4 is additionally associated with two collapsible linkage arrangements 11 (provided one at each side of the vehicle) in the form of knee joints (see also Fig. 3). Each such linkage is comprised of two link members 12 and 13 pivotally connected together by a pin 14, with link 12 being pivotably mounted on a frame bracket 15 by a pin 16 and link 13 being pivotably mounted on spring 7 by a pin 17. Pins 14, 16 and 17 are all parallel to each other.

The link 12 is comprised of two parallel arms 12a and 12b between which one end of link 13 is received.

The other end of link 13 has two lugs 13a and 13b between which the end of spring 7 is received. This arrangement of arms 12a, 12b and lugs 13a, 13b is such that the linkage arrangement 11 precludes twisting or side-to-side movement.

The linkage arrangements 11 are therefore of sufficient rigidity (in the direction transverse to the vehicle centre line) such that side loads may be transmitted from the axle 4 to the frame members 2 through the frame brackets 8 and 15 whilst avoiding undesirable skewing effects at the spring attachment to the axle.

Additionally, the linkage arrangements open and close as required (see arrows A-Fig. 2) to maintain the tyres of the wheels on axle 4 on the road surface regardless of the height relationship of the driven axle 3 to the frame members 2.

Claims (7)

1. A multi-axled vehicle with at least one driven axle and an adjacent non-driven axle which is located on beams which extend substantially parallel to the vehicle centre line and which are mounted on the vehicle chassis wherein the mounting of at least one of the beams on the chassis includes a linkage arrangement pivotably openable and closable to permit relative movement of the beam towards and away from the respective side frame member and having sufficient rigidity to transmit side loads from the axle tyres to the chassis.

2. A vehicle as claimed in Claim 1 wherein there are two such linkage arrangements for the nondriven axle provided one towards each end thereof.

3. A vehicle as claimed in Claims 1 or 2 wherein the or each linkage arrangement comprises first and second link members pivotably connected together and with the first link member being pivotably mounted on the vehicle chassis and the second link member being pivotably mounted on the beam.

4. A vehicle as claimed in Claims 1 to 3 wherein the beams on which is mounted are flexible beams, particularly springs.

5. A vehicle as claimed in any one of Claims 1 to 4 wherein the non-driven axle is adjacent a driven axle of the vehicle and the vehicle is such that there is an imposed load on the non-driven axle when that on the driven axle exceeds a predetermined maximum.

6. A vehicle as claimed in any one of Claims 5 wherein the suspension system of the non-driven axle includes air bellows which are only charged with compressed air when the predetermined load on the driven axle is exceeded.

7. A vehicle substantially as hereinbefore described with reference to Figs. 1 to 3 of the accompanying drawings.