GB2192157A

GB2192157A - Pneumatic system for trailer units

Info

Publication number: GB2192157A
Application number: GB08615731A
Authority: GB
Inventors: Brian W Clay
Original assignee: LODGE TRAILERS
Current assignee: LODGE TRAILERS
Priority date: 1986-06-27
Filing date: 1986-06-27
Publication date: 1988-01-06
Also published as: GB8615731D0; GB2192157B

Abstract

A pneumatic system for a vehicle trailer having air brakes (76) and inflatable air springs (54 to 60) for raising and lowering a load bearing body relative to the chassis, wherein a valve means (V1 ,V2) are provided for venting the air springs when a road tractor unit is decoupled and for preventing repressurisation of said air springs when only an emergency brake line (50) is pressurised due to the coupling of a dock-spotter vehicle (Figure 2). Repressurisation of the air springs may only occur when the service line is pressurised by the road tractor when connected to both the service line 48 and the emergency line 50, with the service brakes applied. <IMAGE>

Description

SPECIFICATION Pneumatic system for trailer units Field ofinvention This invention concerns pneumatic systems by which trailer bodies can be raised and lowered relative to a road wheel chassis.

Background to the invention In conventional trailer units the body is elevated by inflating airsprings and lowered by venting the springs. lfthetrailer is unhooked from its tractor unit and left in a trailer park in the normal elevated position used in transit, it is found that creep can occur and the trailer body will drop slightly from the transit height. This can be a problem if the body has been left over a loading platform since the drop can result in the body settling ontothe platform.

Typically a special tractor unit (often known as a dock spotter) is used for moving trailers around a docking area to assist in loading and unloading, movement onto a ship or railway rolling stock and the like. Such tractor units are normally only provided with emergency airline braking and no provision is made for supplying air to the airsprings to allowfor elevation ofthetrailer body. To this end, where creep and resulting drop has occurred the special tractor unit can not be used to lift the body to allowittocleara loading bay or the like.

The problem can be obviated if the trailer body is dropped when its road tractor unit is first detatched.

However, this can only be achieved by positively venting the air springs atthe time of detatchment whilst the original trailer unit is still in service and the delay occasioned by such a procedure is unattractive to the operator.

It is therefore an object ofthe present invention to provide a modified pneumatic system for raising and lowering the body of a trailer and controlling braking thereon, which automatically operates in a desired mannerwhereverthe trailer is detatched from or attached to a road tractor unit.

Summary of the invention According to the present invention in a pneumatic system for a trailerfitted with air brakes and with inflatable air springs for raising and lowering a load carrying body relative to a chassis, and which includes a first airline connection (known as the emergency line) and a second airline connection (known as the service line), for respectively receiving airfrom a road tractor unit but in which onlythe emergency line is energised when the trailer is connected to a special purpose tractor unit ofthe type used for relocating trailers around a trailer park or the like, there is provided a first valve means which when a road tractor unit is uncoupled, causes the airspring suspension units to vent to atmosphere and deflate to lower the trailer body from its transit height to its lower parked height, and a second valve means which prevents air passing to the air spring suspension units if the emergency line only is pressurised (as when connected to a special purpose tractor unit as aforesaid), the second valve means being operable to pressurise the airsprings upon pressurisation ofthe service airline as will only occur when the service brake is applied from a tractor unit which supplies air to both emergency and service lines on the trailer.

The invention will now be described byway of example with reference to the accompanying drawings, in which Figure 1 illustrates a tractor and trailer unit ofthe type described, and Figure2 is a schematic diagram of the airline connections and pneumatic units on the trailer, constructed as an embodiment of the present invention.

Figure 1 illustrates an articulated vehicle comprising tractor unit 10 with driving cab and a trailer 12 connected to the tractor unit by way of a conventional fifth wheel coupling (notshown in detail). The tractor unit has two sets of road wheels 14,16 and the trailer unit includes telescopic (or otherwise adjustable) legs (not shown) at its front end -forsupporting it when detached from the tractor unit) and two sets of road wheels 18,20 on transverse axles.

The load bearing body 12 is supported byfour airsprings ofthe type manufactured and sold by Dunlop Limited between transverse axles having the road wheels mounted therein. Relative displacement of the body 12 and chassis 22 is effected by inflating ordeflatingthefourairsprings.

As shown in Figure 2, air is supplied to the trailer from a compressor (not shown) on the tractor unit 10 via flexible hoses (not shown). Afoot operated valve (not shown) controls the supply of air along a service braking pipeline 48. Airis also supplied along the emergency pipeline 50, in known manner, all the time the tractor unit is coupled to the trailer and air pressure is available.

A control valve 52 is positioned at the rear ofthe trailer chassis 22 (see Figure 1) and this has different positions for venting or inflating the four airsprings to adjust the height of the body 12.

As shown in Figure 2 airtothefourairsprings54, 56,58,60 is obtainable via bistable valve V2 from a levelling valve V3 when V2 is in one of its two states (its drive state). This state is determined by there having previously been air pressure applied to one of its two control inputs 62 the other of which is denoted by 64. Input 62 is pressurised whenever air pressure is supplied along the service braking line 48, via line 66. Thus, after hitching to a conventional road tractor unit (which delivers air along both emergency line 50 and service line 48) the valve V2 is changed to its drive state on the first application of the service brake.

Airforthe brakes is supplied via valve V4 in known manner, the system including a brake reservoir 70 and protection valve 72 which supplies air to the levelling valveV3 and an air suspension reservoir74.

On uncoupling a road tractor unit the lines 48 and 50 depressurise and allow reservoirs 74to vent via valve V1 and V2 as soon as 50 depressurises. This causes the springs 54 - 60to vent via V2 and the body 12 settles into the parked level. The valve V2 is now in its other state (having been operated into this condition by the venting of 74therethrough), and the springs remain deflated.

On the subsequent hitching of a tractor unit having only "emergency air", only line 50 is pressurised.

This closes valve V1 to prevent reservoir 74from communicating with valve V2 but does not affectthe state of V2. Valve V4 is of course operated to supply airto the braking system which includes inter alia brake chamber 76, to release the brakes as is normal.

In this condition, no aircan pass to the airsprings 54 -60 and the body therefore remains in its low state, whilst being shunted around a park the like, by a dock-spotter vehicle.

Ifsubsequently connected to a tractor unitwith both emergency and service air supplies, both 48 and 50 are energised. Thefirst operation ofthe footbrakepedal pressurises the service line 48 and changesthe state of V2to allowairto pass from the levelling valve V3 via V2 to the airsprings 54-56 thus raising the body as determined by the valve V3.

The invention thus allows trailers to be manipulated by dockspotterorroadtractorunits without any additional steps over and above those previously required.

Claims

1. A pneumatic system for a trailer fitted with air brakes and with inflatable air springs for raising and lowering a load carrying body relative to a chassis, which includes a first airline connection (known as the emergency line) and a second airline connection (known as the service line);; for respectively receiving airfrom a road tractor unit but in which onlythe emergency line is energised when the trailer is connected to a special purpose tractor unit ofthe type used for relocating trailers around a trailer park orthe like, a firstvalve means which, when a road tractor unit is uncoupled, causes the airspring suspension units to vent to atmosphere and deflate to lowerthetrailer bodyfrom its transit height to its lower parked height, and a second valve means which prevents air passing to the air spring suspension units if the emergency line only is pressurised (as when connected to a special purpose tractor unit as aforesaid),the second valve means being operable to pressurise the airsprings upon pressurisation ofthe service airline, as will only occur when the service brake is applied from a tractorunitwhich supplied air to both emergency and service lines on the trailer.

2. Asystem according to claim 1, having an air suspension reservoir which is depressu rised via the first valve means when the tractor unit is uncoupled, the venting ofthe reservoir causing operation ofthe second valve means, thereby to allow the suspension units to vent to atmosphere.

3. A system according to claim 2, wherein pressurisation ofthe emergency line only restores the first valve means to isolate the reservoirfrom the second valve means.

4. A system according to claim 3,wherein pressurisation of both the emergency and service lines restores the second valve means to allow air to pass to the air springs via a leveling valve.

5. A pneumatic system for a trailer substantially as herein before described with reference to the accompanying drawings.

6. Atrailer incorporating the pneumaticsystem of any of claims 1 to 5.