GB2165500A - Vehicle with air suspension - Google Patents

Abstract

Trailer vehicles fitted with two or more axles provided with air suspension frequently have provision for lifting one axle together with its associated wheels to reduce rolling resistance and tyre scrub when the trailer is running lightly laden. Such vehicles are usually fitted with a levelling valve operated by rise or fall of one axle to admit pressure air to or release it from the air springs to maintain a constant ride height. The tyres on a lifted axle lose their deflection when load is removed from them, reducing their clearance from the road surface. An extensible member 49 is provided in the operating linkage for levelling valve 47. Extension of member 49 as or when an axle is lifted causes operation of valve 47 to admit pressure air to the air springs of the laden axle(s). These springs extend and in so doing neutralise valve 47 so that trailer then runs at an increased ride height. <IMAGE>

Description

SPECIFICATION Vehicle with air suspension This invention relates to a vehicle fitted with pneumatic suspension for a plurality of axles and having provision for lifting one of such axles and its associated wheels to enable rolling resistance and tyre scrub to be reduced when the vehicle is running lightly laden. When one such axle is lifted the loading previously borne by that axle is transferred to the other axle or axles. It is customary to interconnect the air springs on each side of the vehicle to equalise axle loading and to fit a levelling valve for each set of interconnected air springs. The levelling valve is generally fitted in a fixed position relative to the vehicle chassis and it has operating lever means which is pivotally, or pivotally and slidably, connected between the levelling valve and a moving part of the suspension for one axle. These locations may be reversed.Each levelling valve is pneumatically connected to an air reservoir on the vehicle which is fed buy a compressor. A variation in ride height of the vehicle, that is to say the distance between the vehicle chassis and the road surface, will cause actuation of one or more of the levelling valves to either admit air to or release air from the corresponding air springs so as to restore the original ride height. Such a vehicle will hereafter be referred to as a vehicle of the type described.

According to the present invention in a vehicle of the type described an extensible link is included in the or each operating lever means for the levelling valve or valves and means are provided to change the length of said extensible link or links whereby the respective levelling valve or valves are actuated to cause the ride height of the vehicle to be increased.

The increased ride height allows increased road clearance for the tyres on an axle which is lifted.

The extensible link may be a telescopic fluid pressure operated member the extension or contraction of which, as the case may be, causes actuation of the respective levelling valve whereby the ride height of the vehicle is increased, said member being connected to a source of fluid pressure on the vehicle to effect said extension or contraction thereof.

The fluid pressure operated member may conveniently be a single acting piston and cylinder assembly which is caused to extend (or retract) by admission of pressure air. Retraction (or extension) following release of pressure air may be caused or assisted by spring means. Such spring means may be external or may be incorporated in the piston and cylinder assembly. Pressure air is preferred as the operating medium because this is already available for brake operation and the air springs on a vehicle of the type described, however hydraulic pressure operation may be used if desired.

Pressure air may be admitted to such a piston and cylinder assembly by control valve means simultaneously with admission of pressure air to an air bag for lifting an axle. In an alternative construction the supply of pressure air may be sequenced, for example so that the axle is lifted first and then the ride height is increased. When air is released from the air bag to allow the raised axle to be lowered by its associated air springs the air may also be released from the piston and cylinder assembly allowing it to retract (or extend) whereby the original ride height is restored. The release from the cylinder may be simultaneous with release of air from the air bag or the releases may be sequenced if desired.

It will be appreciated that instead of a single acting piston and cylinder assembly a double acting piston and cylinder assembly can be used if desired. The latter has the disadvantage of requiring an additional fluid pressure line to the assembly and a more complex control valve means.

In a further example of an alternative construction the extensible link may comprise an electrically operated linear actuator, operated by an electrical power supply under the control of switch means.

The fluid pressure operated member, in another alternative construction, may be an hydraulically operated piston and cylinder assembly. Conveniently, where sequenced operation is required whereby the axle is first lifted and the ride height is then increased, an hydraulically connected master cylinder and slave cylinder assembly may be used. Lifting of the axle can be arranged to cause operation of the master cylinder whereby the slave cylinder (being the, or part of the, extensible link) causes actuation of the respective levelling valve.

The invention will now be described by way of example with reference to the accompanying drawings in which: Figure lisa schematic view partly in plan and partly in elevation showing the air springs for a three axle trailer and their levelling valves and a pneumatic circuit therefor, Figure 2 is a schematic side view of a semi-trailer with three air suspended axles with lift on the leading axle, Figure 3 is a schematic side view of one air suspended axle, a levelling valve and an extensible link, Figure 4 is similar to Figure 3 but having a different arrangement of levelling valve and extensible link, and FigureS is a scrap view similar to Figure 1 showing inclusion of a valve of sequencing inflation of air bag and an extensible link.

Referring to Figure 2, a semi-trailer 1 is fitted with three axles each having a wheel at each end, the wheels 2, 3,4 at one end of each axle being shown.

Two air springs (shown in plan) 5, 5A, 6, 6A and 7, 7A (Figure 1) are interposed between each axle and the trailer chassis and the axles are carried by trailing arms 8, 9, 11 which are pivotally connected, forward of the respective axles, to the chassis of the trailer.

The trailing arms 8 are pivoted at 14 adjacent the bottom of brackets 15 depending from the trailer chassis. A lever 10 is pivoted to a depending bracket below arms 8. The rear end of lever 10 engages the underside of both arms 8 when an air bag 13 arranged between the trailer chassis and a forward end 12 of lever 10 is inflated. In consequence the axle and wheels 2 are raised as shown in Figure 2.

Referring now to Figure 1, the semi-trailer has an air reservoir 16 which is supplied with air under pressure from a compressor on a tractor when the latter is coupled to the semi-trailer. Pipes 17,18 connect the reservoir 16to levelling valves 19,21 (shown in side elevation) down-stream of a pressure protection valve 16A. The pressure protection valve 1 6A ensures there is adequate pressure for braking (say 41/2 to 6 Bar) before air can be admitted to the suspension system. The levelling valve 19 is connected by pipes 22,23,24 to the air springs 5, 6,7 respectively. The levelling valve 21 is connected by pipes 25, 26 to the air springs 5A, 6A, 7A. Each levelling valve also has an atmospheric exhaust port shown at 27.

Each levelling valve is operated by a lever 28 so as to seal the air in the air springs, orto connect them to reservoir 16 or to exhaust them to atmosphere. Each lever 28, at its end remote from the levelling valve, is connected to a movable part of the suspension for the centre axle, for example the trailing arms 9, by an extensible link 29. In this case each link 29 comprises a single acting spring closed air cylinder and piston pivotally connected between a trailing arm 9 and a lever 28. Air under pressure can be admitted to the cylinder via a pipe 31 to extend the piston. This causes lever 28 to be moved so extra air is admitted to the air springs, extending them and so increasing the ride height.As the air springs extend the levelling valves 19,21 are raised because they are carried by the trailer chassis and the levers 28 pivot about their connections to links 29 to neutralise valves 19, 21 when the new increased ride height (corresponding to the extension of the links 29) is attained.

As shown in Figure 1 the pipes 31 are connected to reservoir 16 via pipes 34,35, a selector valve 32, a pipe 33 and pressure protection valve 16A. The selectorvalve 32 may, for example, be manually operated or electrically operated and also has a connection to atmosphere. Pilot operated 3 way valves 36, 37 are connected in pipes 22,26 with their pilots connected to pipes 34, 35 respectively, as is the bag 13.

When selector valve 32 is operated air from reservoir 16 is admitted to air bag 13, links 29 and the pilots of valves 36, 37. The pilots operate the valves 36,37 to close the pipes 22,26 and connect air springs 5, 5A to atmosphere, thus permitting the inflating bag 13 to cause lifting of the axle and wheels 2. At the same time the extension of links 29 causes operation of levelling valves 19,21 to increase inflation and extension of the air springs 6, 7, 6A, 7A to increase the ride height.

When selector valve 32 is reverted the pipes 34, 35 are connected to atmosphere allowing valves 36,37 to revert whereby air springs 5, 5A are re-inflated whilst air bag 13 and links 29 are connected to atmosphere. Links 29 close under the bias of their internal springs causing operation of levelling valves 19,21 to reduce the ride height to its original value. A spring or springs (not shown) connected between the trailer chassis and end 12 of lever 10 may assist closure of air bag 13 to pull lever 10 clear of arms 8.

It will be appreciated that the diameter of the tyres on wheels 2 increases as the load on them is released when the axle is lifted. This increase is compensated for by the extensible links 29. In a tandem axle trailer the levelling valve or valves are usually fitted to the rear axle suspension. Axle lift may of course be provided on an axle otherthan the leading axle.

Referring now to the drawing Figure 3, the trailer chassis is referenced 41. Brackets 42 (one on each side of the trailer) depending from chassis 41 pivotally mount trailing arms as 43 which carry an axle (or respective stub axles in the case of independently suspended wheels) on which wheels as 44 are rotatably mounted. Rearward extensions 45 of arms 43 have platforms. Air springs as 46 are mounted between the platforms and the chassis 41. A levelling valve 47 carried by chassis 41 has a lever 48 whose free end is pivotally connected to the piston rod of a single acting spring return piston and cylinder assembly 49, the cylinder of which is pivotally connected to arm 43. This is substantially as has been described with reference to Figures 1 and 2. Extension of assembly 49 actuates levelling valve 47 to admit air to springs 46 to increase the ride height.

Turning now to Figure 4, this is similar to Figure 3 except that arm 43 now has a forward extension 51 to which the cylinder is pivoted. In the normal condition the piston and cylinder assembly 49 is extended. Admission of pressure air to retract the piston into the cylinder causes actuation of the levelling valve 47 to cause the ride height to be increased.

Figure 5 reproduces the upper part of Figure 1 and the same reference numerals are used. A component 52 has been added in pipe 31 leading to the extensible link 29. In one embodiment of the invention this component 52 may be a plunger operated pneumatic valve arranged to be operated by an axle during, or at the completion of, lifting so as to allow pressure air to pass to the link 29 (or 49) to extend or retract it as the case may be, thus sequencing operation of the extensible link.

In another embodiment (not illustrated) a conventional hydraulic master cylinder may be mounted on the trailer chassis to be operated by an axle while it is being lifted. The master cylinder is hydraulically connected in the usual way to a slave cylinder which constitutes, or is part of, the extensible link 29, thus sequencing operation of the extensible link. Such a slave cylinder can replace the piston and cylinder assembly 49 seen in Figures 3 and 4.

The extensible link may alternately comprise an electrically operated linear actuator. An electrical supply from the tractor or the trailer may be connected via a switch to the actuator to cause its extension and retraction as required for variation of the ride height. Operation may be sequenced by arranging for the (or a) switch in circuit with the actuator to be operated by an axle whilst it is being lifted and again during lowering. Separate switches may be provided with associated electrical wiring so that one is operated during axle lifting and the other is operated during axle lowering for respectively causing the ride height to be increased and reverted to normal.

This invention has been described primarily with reference to a trailer having through axles but is equally applicable to a trailer having wheels which are independently suspended, for example on stub axles. The term axle is to be understood to include a stub axle and also aligned stub axles.

Claims (11)

1. A vehicle of the type described having an extensible linkin the or each operating lever means for the levelling valve or valves and means to change the length of said extensible link or links wherebythe respective levelling valve or valves is/are actuated to cause the ride height of the vehicle to be increased.

2. A vehicle as claimed in Claim 1 wherein the extensible link comprises a telescopic fluid pressure operated member the extension or contraction of which, as the case may be, causes actuation of the respective levelling valve whereby the ride height of the vehicle is increased, said member being connected to a source of fluid pressure on the vehicle to effect said extension or contraction thereof.

3. A vehicle as claimed in Claim 2 including a pressure air bag adapted, when pressurised, to act between the vehicle chassis and a wheel axle thereof to raise said axle and control valve means to admit pressure air from the supply to said air bag and wherein said control valve means also controls admission of pressure air to said fluid pressure operated member whereby said member extends (or contracts) to cause the ride height of the vehicle to be increased as said axle is raised.

4. A vehicle as claimed in Claim 3 wherein the control valve means also controls release of pressure air from said air bag and said member whereby the ride height of the vehicle is caused to be reduced when said axle is lowered.

5. A vehicle as claimed in Claim 3 or Claim 4 including a pilot operated valve in the air supply line to each air spring of said axle, said pilot operated valves connected in pneumatic circuit with the control valve means to be actuated upon operation of the control valve means to release pressure air from said air springs.

6. A vehicle as claimed in any one of Claims 3,4 or 5 modified by the inclusion of sequencing means actuated upon raising of the axle to allow operation of the fluid pressure operated member under the control of the control valve means to cause actuation of the respective levelling valve to effect increase of the ride height of the vehicle on raising of said axle.

7. A vehicle as claimed in Claim 1 including an electrical power supply and wherein the extensible link comprises an electrically operated linear actuator connected to the electrical power supply under the control of switch means, the extension or contraction of which actuator, as the case may be, causes actuation of the respective levelling valve.

8. A vehicle as claimed in Claim 7 including sequencing means actuated during or upon raising of an axle to allow operation of said actuator under the control of said switch means to cause actuation of the respective levelling valve to effect increase of the ride height of the vehicle on raising of said axle.

9. A vehicle as claimed in Claim 2 wherein the extensible link comprises a telescopic hydraulic pressure operated member.

10. A vehicle as claimed in Claim 9 wherein the fluid pressure source comprises as hydraulic master cylinder hydraulically connected to the hydraulic pressure operated member and adapted to be operated by an axle on the raising thereof.

11. A vehicle substantially as described herein with reference to Figures 1,2,3 or 4 or Figures 1,2,3 or 4 as modified by Figure 5.