GB2165501A - Air suspended vehicles - Google Patents

Abstract

When a trailer has two or more axles, at least one of which has air suspension, substantial restraint strops are provided to prevent excess travel of the air suspended axle(s) away from the trailer chassis which can otherwise occur in certain modes of operation. One such mode occurs in roll on-roll off operations of the trailer. When the trailer 2 passes over the top of a gradient 3 the rear axle drops to a free in air position, forced downwardly by pressure of air in its associated air springs. This pressure may be enhanced if the leading axles are also air suspended and the air springs on each side of the trailer are pneumatically interconnected. The invention obviates the need for restraint strops by replacing the conventional shock absorbers and their mountings by strengthened shock absorbers and mountings able to withstand the applied loads in the modes of operation referred to. <IMAGE>

Description

SPECIFICATION Air suspended vehicles This invention relates to trailer vehicles fitted with two or more axles and having air suspension for at least one of the axles and a shock absorber or shock absorbers associated therewith. Such a vehicle is hereafter referred to as a vehicle of the type described.

When a vehicle of the type described is used in what is termed a roll-on roll-off operation, that is from ship to shore and vice-versa, there is frequently a gradient to be negotiated over a bridging section between the shore and the ship. In this situation the trailing axle on the trailer can hang free in air for a short period before it reaches the high point on an up gradient or passes over the high point on a down gradient. It is customary for the trailer builder to provide substantial restraint strops to support the trailing axle in this situation.

When more than one axle on a trailer is carried by air suspension the air springs on each side of the trailer are interconnected to provide load equalisation. Since the air springs for the hanging axle are at the same pressure as those for the axles which are bearing load very large down forces can be generated on the hanging axle and these are not reacted by the ground, consequently they have to be reacted by the strops. Because of the magnitude of the down force which can be generated the strops and their attachments to the trailer chassis have to be substantial and so represent significant extra work and expense for the trailer builder.

Such strops are also needed in other applications.

For example, in container operations. Modern container handling equipment can enable a fully laden container to be lifted clear of a trailer chassis much more quickly than a trailer air suspension control system can dump air from the air springs. Strops are needed for each axle to react the resulting lift force on the trailer chassis arising from removal of the laden container.

Special tractors are now available with elevating fifth wheel couplings which are used to lift and move parked semi-trailers without the need to retract the landing legs because these are lifted clear of the ground by the fifth wheel coupling. Frequently the leading axle of the trailer is also lifted off the ground and the resulting down load from the air suspension requires reacting by strops.

According to one aspect of the present invention in a vehicle of the type described at least one telescopic shock absorber is provided acting between the air suspended axle and a chassis of the vehicle, said shock absorber and the mountings therefor being constucted in such a manner as to be capable of reacting the loading imposed by the air suspension when the axle hangs free in air and thereby avoiding a requirement for restraint strops acting between the vehicle and the axle.

According to a further aspect of the present invention an air suspension for a trailer vehicle comprises a member or members adapted to be secured to the vehicle, two arms, each arm having one end pivotally carried buy a or the member and an axle (or separate stub axles) secured to the other end of each arm, a platform associated with each arm and adapted to receive one end of an air spring (whose other end is secured to the vehicle chassis) and at least one telescopic shock absorber pivotally mounted to act between the axle (or stub axles) and the member or members wherein the shock absorber(s) and the mountings therefor are constructed in such a manner as to be capable of reacting the loading imposed by the air springs, thereby avoiding a requirement for restraint strops acting between the axle (or stub axles) and the trailer vehicle.

The invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows in outline a tractor and semi-trailer at the top of a gradient with the rear wheels of the semi-trailer hanging free in air, and Figure 2 is a perspective view of an air suspension for a trailer vehicle, some parts being omitted.

Referring to Figure 1, a tractor 1 has drawn a semi-trailer 2 up a gradient 3. The rear wheels 4 of the trailer are clear of the gradient surface because the air suspension for the axle carrying the wheels 4 has reached the limit of its extension. This drawing illustrates one of the conditions to which reference has already been made.

Referring now to Figure 2 a member comprising a hollow beam 5 has an upstanding bracket 6 at each end adapted for securing to a trailer vehicle, as by welding, so the beam 5 is transverse of the trailer vehicle.

Outer brackets 7 (part only of one of which is shown) and an inner bracket 8 depend from beam 5.

Arms 9, 11 are pivotally mounted at their front ends between the brackets 7, 8. Stub axles 12, 13 are secured, as by welding, to the respective arms 9, 11.

Platforms 14, 15 (shown in part only) are secured to and extend rearwardlyfrom the respective stub axles 12, 13. The platforms 14, 15 have bolt holes for securing the lower end of respective air springs (not shown) thereto.

Brackets 16, 17 are provided for the conventional air brake actuators and an "S" camshaft 18 for connection to each actuator to operate the brakes is carried at its inner end by a bearing 19 depending from the stub axle. The outer end of each stub axle carries a conventional brake and brake drum and a hub, mounted on bearings, to which a wheel is attached. A brake dust cover 21 secured to a brake anchor bracket 22 is shown to represent the brake and hub assembly on the stub axle 12.

Upwardly and rearwardly extending brackets 23 are secured to beam 5, as by welding, in alignment with corresponding forward facing brackets 24 carried by the inner end of each stub axle. A telescopic shock absorber 25 is pivotally connected between each pair of brackets 23, 24.

The shock absorbers 25 may be of conventional construction except that the piston and piston rod, cylinder and gland and the cylinder and rod end attachments and bushes are strengthened, as compared with a conventional shock absorber, as as to withstand and react the tension loads imposed by the air springs when the wheels on the stub axles are hanging free in air. The brackets 23, 24 and their attachment to the beam 5 and stub axles respectively are also designed to withstand and react these loads.

It will be appreciated that the upper ends of the shock absorbers may be pivotally secured to the trailer chassis instead of to the beam 5. The latter is a preferred construction as the trailer builder has merely to align and secure the suspension unit which has been described to the trailer chassis.

Separate mountings on the chassis for the shock absorbers are not required and the need for restraint strops has been obviated.

The suspension unit described provides independent suspension for the wheels. Howeverthe invention is equally applicable where a complete axle is provided comprising an axle beam secured, for example, to arms such as 9, 11 and having a brake, hub and wheel assembly at each end in substitution for the stub axles, and air springs similarly acting between the axle and the vehicle chassis.

it will be appreciated that the member 5 with upstanding brackets 6 for attachment to a vehicle may be substituted by separate attachment members for each arm 9, 11 and associated parts. Such a construction involves additional work in aligning the wheel where these are carried by stub axles as in Figure 2 but is not necessarily disadvantageous where a complete axle is substituted as the latter locates the wheels in alignment with one another.

The conventional shock absorbers which have been mentioned are provided to prevent bouncing of the sprung mass of the trailer chassis and its load and of the unsprung mass of the wheels and axle which may occur because of the very low stiffness of air suspension systems. However they are not designed to, or able to react the air suspension imposed loads which have been described. It will be appreciated that a further benefit of using specially designed shock absorbers as has been described instead of the customary strops is that due to the characteristics of the shock absorber impact loads are reduced when an axle drops to a free in air suspended position.

Claims (9)

1. A vehicle of the type described having at least one telescopic shock absorber acting between the air suspended axle and a chassis of the vehicle, said shock absorber and the mountings therefor being constructed in such a manner as to be capable of reacting the loading imposed by the air suspension when the axle hangs free in air and thereby avoiding a requirement for restraint strops acting between the vehicle and the axle.

2. A vehicle as claimed in Claim 1 wherein the air suspended axle comprises a through axle beam and two telescopic shock absorbers and mountings therefor are provided acting between the axle beam and the chassis of the vehicle.

3. A vehicle as claimed in Claim 1 or Claim 2 wherein each axle has two air springs acting between the axle and the vehicle chassis arranged one on either side of the longitudinal centre line through the vehicle and on each side of the vehicle the air springs for the axles are interconnected pneumatically.

4. An air suspension for a trailer vehicle comprising a member or members adapted to be secured to the vehicle, two arms, each arm having one end pivotally carried by a or the member and an axle secured to the other end of each arm, a platform associated with each arm and adapted to receive one end of an air spring whose other end is adapted to be secured to the vehicle and at least one telescopic shock absorber pivotally mounted to act between the axle and the or a member and wherein the shock absorber or shock absorbers and the mountings therefor are constructed in such a manner as to be capable of reacting the loading imposed by the air springs thereby avoiding a requirement for a restraint strop acting between the axle and the trailer.

5. An air suspension as claimed in Claim 4 modified by the substitution of a stub axle connected to said other end of each arm instead of the axle and wherein two shock absorbers and associated mountings are provided arranged so that one shock absorber acts between each stub axle and the or a member and an air spring acts between each stub axle and the vehicle.

6. Avehicle incorporating a suspension as claimed in Claim 4 or Claim 5.

7. A vehicle incorporating a suspension as claimed in Claim 4 or Claim 5 and at least one other axle or pair of aligned stub axles, an air spring on each side of the vehicle acting between the axle, or the stub axles, and the vehicle and wherein said air springs on each side of the vehicle are pneumatically interconnected.

8. An air suspension for a vehicle substantially as described herein with reference to Figure 2.

9. A vehicle fitted with an air suspension substantially as described herein with reference to Figure 2.