State of the art.

A known practice is to arrange gas springs between the cab and frame of road freight vehicles. These springs allow the cab to move between upper and lower limit stops. Gas springs serve to increase comfort while the vehicle is in motion but may give rise to problems while it is parked. Passing traffic may in particular result in air currents which may cause the cab of the parked vehicle to rock. The larger the vehicle which is passing, the more the cab will rock. As the sleeping accommodation in a modern driving cab is often situated relatively high in the cab, cab movements may be perceived as disturbing the comfort of a person lying in the sleeping accommodation. It is also the case that when the vehicle is lined up for loading, the cab may be subjected to severe oscillations when heavy loads are applied. These oscillations may be so great that the cab impinges powerfully against the limit stops.

The object of the present invention is therefore to provide a solution, which will eliminate the above-mentioned disadvantages. This is achieved by means of the characteristics of the invention, which are indicated in the patent claims below.

Using the invention makes it possible to lower or raise the cab from a resilient operating position of the vehicle to a position in which the cab abuts against the upper or lower limit stop. When the cab abuts against either limit stop, it has no possibility of springing relative to the vehicle frame,

thereby eliminating the aforesaid problems.

The invention will now be described below in two preferred embodiments with reference to the attached drawings.

Figure 1 shows a driving cab balanced on forward and rear gas springs.

Figure 2 shows the driving cab lowered against a lower limit- position stop.

Figure 3 shows the driving cab raised to abut against an upper limit-position stop.

Description of the invention.

Figures 1 to 3 show schematic side views of a driving cab 1 for a road freight vehicle together with the structure which supports the driving cab on a chassis or frame 2 of the road freight vehicle. The forward pair of wheels is designated by reference 3. The driving cab 1 is kept balanced by means of a number of gas springs, comprising in this embodiment two forward gas springs 4 and two rear gas springs 5. Both the rear and the forward gas springs are arranged approximately at the respective corners of the cab 1. The gas springs 4 and 5 are thus arranged between the floor of the cab 1 and the frame 2. There is usually a stabiliser (not depicted) arranged between the cab and the frame, thereby making it possible for the number of gas springs to be reduced to three or two.

Forward and rear support brackets 6 and 7 are installed in the cab floor close to the gas springs. Forward and rear bearers 8 and 9 are arranged on the frame 2 centrally opposite the support brackets. These bearers have upper limit-position stops in the form of stop pads 10 and 11. Lower limit-position stops in the form of stop cushions 12 and 13 are arranged on the frame centrally below the support brackets 6 and 7. As may

be seen in the drawings, the support brackets 6 and 7 are thus able to move between the respective stop pads 10,11 and stop cushions 12,13. The stop pads 10,11 and the stop cushions 12,13 thus limit the driving cab's springing movements upwards and downwards relative to the chassis. While the vehicle is in motion, the pressure in the gas springs 4 and 5 is maintained so that the support brackets 6 and 7 are always kept in a position of equilibrium approximately centrally between the stop pads and the stop cushions. This is effected by a number of level controllers 14,15, which adjust the gas supply to the gas springs 4,5. Each level controller consists of a valve housing fastened to the cab. An air duct (not depicted) extends through the valve housing. A valve element is arranged in the air duct. The valve element is adjustable between two limit positions. At one limit position the air duct is fully open and at the other limit position it is closed. Between the limit positions the air duct is more or less open. The valve element is connected to one end of an arm 26 which has its other end connected to the frame. When the cab springs relative to the frame, the arm swings up or down and influences the movement of the valve element between the two limit positions and thus controls the air supply to the air springs, since the air duct is more or less constricted depending on the position of the arm 26. In this embodiment two forward level controllers 14 and two rear level controllers 15 are used.

The device includes a gas pressure reservoir 16, which by means of a compressor (not depicted) is supplied with air at a pressure of, for example, 8 kilopond per cm2. This pressure is fed to the respective gas springs via a line 17 (feed line), an adjusting valve 18 hereinafter called the solenoid valve 18, two branch lines 19 and 20 (feed lines), the level controllers 14 and 15 and connecting lines 21 and 22 (feed lines). During normal motion of the vehicle, the gas springs are supplied with an air pressure of about 5 kilopond per cm2

by means of a reducing valve (not depicted). If the vehicle encounters a strong headwind, the cab will tend to lean backward relative to the vehicle frame 2. In such cases the rear level controllers 15 ensure that more compressed air is supplied to the rear gas springs 5 and the cab is kept upright.

Now it may be found desirable that the cab should rest not on the gas springs but on their lower stop cushions 12 and 13.

This is achieved by the solenoid valve 18 being set in a closing position so that the branch lines 19 and 20 receive no air pressure while at the same time these lines are vented, e.g. via a venting line 23 on the solenoid valve. The design of the solenoid valve 18 will not be described in further detail but its function will be indicated. The solenoid valve may be operated electrically, e.g. by means of the starting key 31 or a circuit breaker 30. Both of the alternatives 30,31 are depicted in parallel in the drawings but in practice only one of the alternatives is preferably used. Thus if no compressed air is supplied to the branch lines 19 and 20 and the lines are at the same time vented, the weight of the cab will cause the support brackets 6 and 7 (four brackets) to sink down against the stop cushions 12,13 on the vehicle frame 2 and the cab will rest firmly on the frame (see Figure 2).

As mentioned in the introduction, it may also be found desirable or necessary for the vehicle cab to be raised relative to the frame 2 so that the support brackets 6 and 7 abut against the stop pads 10 and 11 on the undersides of the bearers 8 and 9. In such a position, increased pressure has to be supplied to the gas springs 4 and 5, i.e. all four gas springs. This may be effected by eliminating the action of the level controllers 14,15. According to Figure 3, this is effected by the solenoid valve 18 having a further control position whereby two bypass lines 24 and 25 between the solenoid valve and the respective forward connecting lines 21

and rear connecting lines 22 receive increased pressure directly without the air passing through the level controllers. An increased pressure will thus be supplied to all four gas springs directly from the solenoid valve and this pressure may be that prevailing in the pressure reservoir 16.

Consequently the support brackets 6 and 7 will be pressed upwards against the stop pads 10 and 11 and the cab will thus be pressed firmly upwards against these latter. If the vehicle is subjected to powerful lowering or rocking as a result of loading, the cab will follow the movement of the vehicle chassis 2 without the occurrence of movements impinging against the stop cushions or the stop pads.

As an alternative to the bypass lines 24 and 25, the level controllers 14 and 15 may have an (undepicted) disconnecting mechanism (electrically operated) which disconnects the connections (the arms 26) to the bearers 8,9 whereby compressed air always passes through the level controllers.

When the level controllers have subsequently to be put back into operation, the first step is to release the gas pressure from the lines so that the vehicle cab sinks down, after which the function of the arms 26 can be reconnected. An adjusting valve has also been described but it may be seen that the device may include two or more valves which effect the function described.

The description above is of an embodiment in which an adjusting valve 18 is used. It is of course possible to use a system of valves in order to locate the cab against the lower stop cushions or against the upper stop pads.