This invention relates to air suspension means for a trailer.

It is known to provide air suspension means for a trailer incorporating air bags which are interposed between the loaded trailer body and the axle(s) in use. In normal running, the air supply to the suspension is automatically controlled by load sensitive valve means, hereinafter called a "levelling valve" for convenience.

Where air suspension is provided, it is usual to provide a manual "lift and lower valve" to enable the trailer level to be lifted or lowered when the trailer is stationary at a loading bay for example, so that it can be aligned with the loading bay.

Clearly, this facility is only required when the trailer is stationary and it is undesirable that the lift and lower valve should remain in operation at other times when the trailer is moving. There is therefore a problem that, if the driver forgets to switch off the manual lift and lower valve, the trailer can be towed off while the air bags are over-inflated or under-inflated. If the air bags are over-inflated, the air bags or shock absorbers can become overstretched and damaged. If they are under-inflated, the load can rest on the bump stops provided below the suspension and this will cause damage and vibration.

The conventional system also has a disadvantage if the lift and lower valve is operated when the trailer air brakes are on. As the air bag suspension is inflated, the lifting of the trailer takes place about a pivotal axis somewhat spaced from the axle. Hence there is tendency during lifting for the trailer wheels to move somewhat, perhaps up to 150mm for a

large diameter wheel, since the axle moves on an arc relative to the pivotal axis.

Under these circumstances, the tyres may be scrubbed along the ground by the action of lifting because the wheels are unable to rotate relative to the axle. Alternatively, the resistance to lifting by the locked tyre/axle combination may be sufficient to prevent the air bags from lifting the load. A loaded semi-trailer detached from its tractor unit and having its forward end supported on legs may even topple forwards under these conditions.

It is an object of the present invention to provide a control apparatus for connection to an air suspension means of a trailer which overcomes or reduces the disadvantages set out above. It is a further object of the invention to provide air suspension means incorporating such control apparatus.

The present invention provides a control apparatus for connection to the air suspension means of a trailer wherein a single valve is provided having first port means connected to a main air supply;

second port means connected to levelling valve means (as defined) ;

third port means connected to one or more air bags of the air suspension means;

fourth port means comprising an exhaust port;

and a manually operable multi-position operating member, the single valve also including control override means adapted to override the multi-position manual operating member.

The manually operated multi-position operating member may have a first "drive" condition in which the second and third port

means are connected. In this case, the air bags are connected through the valve to the normal levelling valve means operated during running of the vehicle.

Operation of the control override means is arranged to place the multi-position operating member in the normal "drive" condition. ("Out") .

The multi-position operating member may have a second position providing a "lift" condition in which the first and third port means are connected, whereby the main air supply is connected to the air bags to cause lifting.

The multi-position operating member may have a third position providing a "hold" condition in which the first, second and third port means are all closed, whereby the condition of the air bags remains constant.

The multi-position operating member may have a fourth position affording a "lower" condition in which the third and fourth port means are connected, whereby air is exhausted from the air bags.

The single valve may include a first auxiliary port arranged for connection with the fourth port means when the operating member is in the first "drive" and third "hold" conditions and with the first port means when the operating member is in the second "lift" and fourth "lower" conditions.

The first auxiliary port may comprise a brake release port.

Alternatively, or in addition, the single valve may include a second auxiliary port which is arranged for connection with the fourth port means in all conditions of the operating member except for the third "hold" condition, the second auxiliary port being then connected to the first port means.

The second auxiliary port may comprise a suspension lock operating port.

The control override means may comprise a further port means providing a pneumatic signal in accordance with the condition of the brakes of the trailer. Alternatively, it may comprise an electrical override means operating for example a solenoid adapted to return the manually operable multi-position operating member to its first normal "drive" condition.

The electrical signal of the control override means may be derived from application of the vehicle footbrake. Alternatively, it may be derived from the condition of rotation or otherwise of the wheels, or from an electrical pressure switch connected to the brake system.

The second arrangement may use an exciter ring for example of the type provided in a vehicle wheel hub for use in anti-skid brake systems which is arranged to provide electrical pulses to a sensor when the wheels are rotating.

A single valve unit embodying the invention will now be described in more detail by way of example only with reference to the accompanying drawings in which

Figure 1 is a diagrammatic view of a single valve control apparatus applied to a trailer in a first "drive" condition;

Figure 2 is a similar diagram of the valve in a second "lift" condition;

Figure 3 is a similar view of the valve in a third "hold" condition and

Figure 4 is a similar view of the valve in a fourth "lower" condition.

Figures 5 to 8 represent a second embodiment of valve in the same four conditions of operation;

Figures 9 to 12 represent a third embodiment of valve of the present invention in the same four conditions of operation.

The four conditions of operation are respectively "drive";

"raise"; "hold"; and "lower";

Figure 13 is a diagrammatic layout of the first embodiment of valve shown in use with a wheel movement sensor;

Figure 14 is a similar view of the second embodiment of valve shown in Figures 5 to 8;

Figure 15 is a similar view of the third embodiment of valve shown in Figures 9 to 12.

Referring to Figure 1 of the drawings, a valve generally indicated at 10 comprises a plurality of ports 11-17 which can be selectively linked or isolated by an internal valve body of any conventional design (not shown) . The condition of the valve is changed, that is the internal connections are changed, by a manually operated multi-position operating member 18.

The port 11 is an exhaust port. The port 12 is connected to a supply of compressed air and is the main inlet port of the valve 10.

Ports 13 and 14 are connected to a conventional levelling valve 19 which is provided on a vehicle trailer and operates in a conventional manner to introduce air into, or exhaust air from, a plurality of air bags provided between the trailer road wheels and the trailer body. Since the levelling valve is conventional, no further description will be given. However, it is to be noted that the levelling valve 19 is operational while the vehicle is travelling so as to maintain the suspension of the chassis/load in response to changes in load conditions.

The ports 15 and 16 are connected respectively tc the left- hand and right-hand air bags 20 and 21 of the trailer.

In the normal operating condition of the trailer while it is travelling along a road, the multi-position operating member

18 is in its outermost "drive" condition shown in Figure 1. To assist in interpreting the diagrams, a scale has been indicated at the left-hand side of the operating member 18.

In this "drive" condition, the ports 13 and 14 are connected to the ports 15 and 16 as indicated by the chain-dotted lines in Figure 1. Thus, the conventional levelling valve 19 is connected to the air bags 20 and 21 at the left and right-hand sides of the trailer, so that automatic levelling of the trailer takes place in response to the load conditions.

When the vehicle has been brought to a halt and it is desired for example to lift the trailer so as to bring it level with a loading platform, the manually operable multi-position operating member 18 can be moved into its second "lift" condition as shown in Figure 2 of the drawings. In this condition, the ports 15 and 16 are connected to port 12 as indicated in chain-dotted lines in Figure 2. The automatic conventional levelling valve 19 has been bypassed because its connnections have been closed off and the air inlet 12 has been connected directly to the air bags 20 and 21 so as to lift the trailer relative to the ground.

When the trailer has been lifted sufficiently, the multi- position operating member 18 is moved inwardly to a third "hold" condition shown in Figure 3 of the drawings. In this condition the valve closes off all of the ports 12, 13, 14, 15 and 16. The air bags 20 and 21 are therefore held in their condition of inflation.

When it is desired to lower the trailer, the multi-position operating member 18 is pushed inwardly into the fourth "lower" condition shown in Figure 4 of the drawings. In this condition, the ports 15 and 16 are connected to the exhaust port 11 so that air contained in the air bags 20 and 21 can be exhausted, causing the trailer to be lowered relative to the ground.

Having briefly described the normal lifting and lowering of the trailer while it is stationary, the function of the control port 17 will now be described.

Irrespective of the position of the multi-position operating member 18, a signal at the port 17 will cause the operating member 18 to be thrust outwardly to the Figure 1 "drive" condition.

The control port 17 may be actuated by a pneumatic signal from the trailer brakes. This may be derived from the delivery side of the brake system such that, when the footbrake is applied, an air pressure signal is delivered to the port 17, causing the operating member 18 to be thrust out to the Figure 1 condition. Alternatively, a pneumatic signal may be provided from the supply side of the trailer braking system from the service line leading to the relay valve which operates the brakes.

It is important that the manual operating member cannot be operated while the trailer brakes are on (while the trailer is parked, disconnected from the tractor towing unit) . This is prevented by the emergency part of the brake system supplying an air signal to port 17 which resists inward manual movement of the operating member 18.

As an alternative to a pneumatic signal entering at the control port 17, electrical return of the valve body may be arranged by means of a solenoid which is operated by an electrical signal derived from either the movement of the vehicle wheels or the operation of a vehicle brake.

Anti-skid braking systems are conventionally provided in trailers and include an exciter ring which is of steel and which is mounted inside the brake drum or hub to which the wheel is attached. This exciter ring may have a plurality of windows or openings in its surface or may be solid having

castellated teeth. The exciter ring rotates with the hub and drum of the wheel brake and a fixed sensor on the axle detects the passage of the windows or castellations, which induce small voltage peaks in the sensor due to electromagnetic interaction. Currently, these voltage pulses are used to detect a condition where the wheel stops rotating due to being in a skid. However, a sensor could be used to produce an electrical signal which, when the wheel is moving, would cause the manually operated multi-position operating member to be returned to the Figure 1 condition, thereby overriding any manual setting of the operating member and automatically reconnecting the air bags 20 and 21 to the levelling valve 19, that is the normal condition for running of the trailer.

Since the voltage peaks generated by rotation of the wheel are typically of the order of 2-6 volts, the effect needs to be amplified in any convenient manner to operate the return of the valve. This may be achieved by the use of a relay or by microprocessor signalling means linked with the main 24 volt power supply of the trailer.

In the arrangements shown in Figures 13,14 and 15 of the drawings, the multi-position operating member 18 is capable of being moved outwardly to the first or "drive" condition by control override means which are electrically operated by a solenoid valve 25. An electronic control unit 26 is connected to the solenoid valve by a cable 35, the control unit 26 being provided a 24 volt electrical supply from the vehicle electrical system.

A signal may be passed to the control unit 26 via a sensor cable 33 which passes through a vehicle axle 32 and hub 31 to a sensor 28. The sensor 28 faces an exciter ring 27 which is provided within the hub cap 29 of the vehicle wheel, bolted to the hub 31 at 30.

In the arrangement shown, any rotation of the vehicle wheel

will cause the exciter ring 27 to rotate relative to the sensor 28 and will thereby produce a series of electro magnetic pulses. These pulses are passed through the cable 33 and amplified by the control unit 26, in order to provide a signal to operate the solenoid valve 25. On operation of the valve 25, an air signal is passed from the air reservoir 40 to the control port 17, operating the automatic control override and thereby thrusting the manual operating member outwardly to the "drive" condition.

It will therefore be understood that, so long as the trailer is stationary, the trailer can be raised or lowered or held at a preselected loading condition by means of the manual operating member 18.

Should any significant rotational movement of the vehicle wheel and hub occur, as a result of the towing vehicle being driven, the control override means will operate and the valve will be returned to the "drive" condition in which the levelling valve 19 is connected to the air bag suspension system.

Turning to Figures 5 to 8 of the drawings, it will be seen that an additional port 50 is provided, referred to as the first auxiliary port or brake release port 50. During normal driving conditions, the port 50 is connected to the exhaust port 11 so that the trailer brakes are automatically returned to the control of the main hand brake system to enable the vehicle to be driven.

When the trailer is stationary at a loading bay and it is desired to raise the trailer, the multi-position operating member 18 is moved to the "raise" condition shown in Figure 6 and the internal porting of the valve then connects the port 50 to the air supply port 12. By so doing, the trailer brakes are supplied with an air signal which releases them. The trailer brakes continue to be released until the multi-

position operating member 18 is either returned to the "drive" condition or is moved further to the "hold" condition shown in Figure 7. At this point, when the trailer has been elevated to the correct height, the exhaust port 11 is connected to the port 50, preventing the release signal from being given to the brakes which return to normal condition. If it is desired to lower the trailer, the operating member 18 is further depressed to the condition shown in Figure 8 and the brake release port 50 is again connected to the air supply port 12, automatically releasing the trailer brakes.

The valve shown in Figures 9 to 12 of the drawings operates in a precisely similar manner so far as the port 50 is concerned. However, a second auxiliary port 51 is also provided which, throughout most phases of the operation of the valve, is connected to the exhaust port 11. The second auxiliary port 51 is intended to be used to actuate a locking strut which prevents mechanical depression of the trailer during loading. However, it may be used to operate some other system which is required to be operated only during the stationary loading condition. For example, it may be used as a safety interlock to prevent tanker discharge outlets being opened, or to prevent the movement of internal hydraulic lifting floors, or to prevent trailer doors being opened or to switch on internal trailer lights. Similarly, a tail lift hydraulic system could be activated by the port 51 during the stationary loading condition. To achieve this, the port 51 is arranged to communicate with the air inlet port 12 only when the multi- position operating member 18 is in the "hold" condition shown in Figure 11 at which time both the levelling valve ports 13 and 14 and the air bag ports 15 and 16 are isolated.

Referring to Figures 14 and 15 of the drawings, it will be seen that connections are made with the brake release port 50 by means of the line 36 and with the auxiliary port 51 by means of the line 37 to convey the appropriate signals to the trailer brakes and to the auxiliary apparatus such as the

loading strut arrangement.

Viewed from one aspect, the invention seeks to provide additional safety features for an air suspension. However, viewed from a broader aspect, the control apparatus described provides an integrated valve system for an air suspension, replacing the rotary lift and lower valve. This integrated valve system further includes the desirable safety features outlined, including automatic return to control by the levelling valve.