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AIR SUSPENSION FOR THE CHASSIS.

3rd November 1925
Page 58
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Page 58, 3rd November 1925 — AIR SUSPENSION FOR THE CHASSIS.
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Details of a Remarkable Development in Air-springing, by which Each Suspension Cylinder Automatically Adjusts Itself to the Load, and the Vehicle Always Remains Level with the Road.

IT HAS always surprised us that more use is not made on Motor vehicles of air as a medium for springing. Its elasticity is almost perfect, it does not possess periods which are the inherent fault of what may be -Called the mechanical spring, and if used correctly it forms a perfect cushion between wheel and vehicle. Some years ago there was a system of air suspension known as the Cowey. In this the ordinary springs were replaced by cylinders-provided with suitable pistons, and the air pressure to the cylinders was regulated by valves controlled from the dash and supplied from a central reservoir. In this way the air springs could be adjusted to suit the load, the one disadvantage being that the system was not automatic. • The usual type Of laminated spring, however well arranged, is not equally effective under all conditions of loading and road surface. The load may be light or heavy, uneqiielly distributed, or the road surf4e may be good or very had, and,' so far, it has proved almost impossible to provide springs. which will automatically adjust themselves to the varying circumstanees. , In addition, ordinary springs arc. heavy and -their inertia prevents the Wheels from following correctly the contours of the road, and where the surface is rough the wheels bounce and spin, causing shocks and rapid tyre wear. Air springs have much lighter moving parts and enable a wheel to hold the road in a remarkable manner.

William Beardmore and Co., Ltd., of Glasgow, were convinced that a welldesigned system of air springing which would automatically adjust itself to lead and road conditions would prove

ideal on all types of motor vehicle, and as a result of experimentri which they have carried out they have produced an sir suspension which Would appear to possess wonderful potentialities.

The Beardmore suspension is. not merely in the theoretical stage, but has been applied to light vehicles and others up to ii tons weight, but the system is not restricted in its applicaeion.

During a recent visit to the Beardmore works We Were afforded an opportunity for a short run: on a vehicle equipped with the new s-ieepension, and although we were taken over some ex

tol tremely rough roads we found that the riding with air , suspension compared very favourEttily with_ what would have been felt in a vehicle sprung in the ordinary manner.

The chief advantage of the Beardmore system is that the air pressure in each cylinder is automatically adjusted to the load on that particular cylinder, and, although a central reservoir is provided, the pressure in any particular cylinder may vary to a considerable degree from those in the others.

The pressure required in the. main reservoir is between SO lb. and 100 lb. per sq. in., according to the size of the cylinders,' and it is supplied from an air 'compressor, driven from the engine through the medium of a clutch, but which is very seldom required to work, runs of 60 miles or more having beenmade without any necessity for the compressor to operate.

In the vehicle which we tested 'two: of the ordinary spring leaves had been retained merely to act as radius and torque members, but other methods of taking these stresses can be utilised. At present universal and ball and socket joints are used in connection' with the air ..cylinders. to suit the movement e of these springs but if a vertical movement only be required the air cylinders, can be fixed and supplementary springs of any type employed, these coming into action nnoh baa roads or when running without air pressure.

The method of obtaining automatic compensation in the cylinders is far more simple than might appear to be the case. It involves the use in each cylinder of two valves—au inlet valve in the cylinder proper end an exhaust valve in the Piston portion. The inlet valve forms part of a rod carried in the centre ef the cylinder, and the method of construction can easily be followed by referring to the diagram of a cylinder which we reproduce.

Clearly to understand the compensating action we will take a hypothetical instance. With an equally distributed load on the platform supported by the cylinders, and assuming an air pressure of 100 lb. as being sufficient to bear that load, then the pressure in the air reservoir should be a few pounds more, Now, when air is admitted to the cylinders they eise on their pistons from the closed-in position until the inlet valve in each comes into contact with its seating. The pressure inside each cylinder is then 100 lb.

As the vehicle moves forward and a wheel encounters an obstacle the piston is pushed farther into the cylinder for that wheel and raises the inlet valve momentarily off its seat. Some air at the higher pressure in the reservoir then passes in and so takes the extra load.

Once the obstacle is passed over, the piston again descends in .the cylinder and closes the valve. The higher pressure in the inside then causes the cylinder to be raised higher than it was in the first instance, until the increase in the volume permits the pressure to be 100 lb. Repeated shocks cause the same

action to occur until, with a longer' rebound from a severe shock, the button on the lower. end of the inlet-valve spindle engliges with and raises the &inst valve. from its seat. with a consetMent slight escape of air, the pressure then being reduced and the cylinder and piston returning to the positions occupied :before the shock with pressure again at 100 lb. After a few shocks a normal working level is reached and. a certain amount of travel is possible without opening either valve ; this .distance.may be long or short to suit the requirements.

It will be obvious that the load en the vehicle need not be equally

buted to ensure it remaining level, as each cylinder will rise until, the inlet valve closes, however it be loaded, provided that the pressure in the reservoir is sufficient, with the area of the piston, to balance that load. Another feature of the system is that the height of the platform from the ground does not vary under any conditions of load.

It will• be quite understood that the air in the reservoir can be made use of for other purposes, such as filling pneumatic tyres or operating brakes, and in the case of four-wheel brakes it is particularly easy to arrange for lag in the operation of those on the front wheels.

Runs have been made on the test vehicle at 10 m.p.h., advancing by 5 m.p.h. at a time up to a maximum of 40 m.p.h, over bad roads, and it is stated that the air springing permits rough roads to be travelled at a much higher speed and with more comfort than would be possible with ordinary springs.

The power required by the air corn

pressor is less than h.p., and, as previously mentioned, it is very seldom in action. In the case of a private car equipped with these springs it was found possible to run the ear with five men standing on the running board on one side and still the vehicle remained absolutely level.

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Locations: Glasgow

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