A HYDRO-PNEUMATIC SHOCK ABSORBER.
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Recent Modifications in the Newton Device which Make for Easy Adjustment to Suit the Vehicle to which it is Fitted.
TNURING the past two years we have followed IL/ very closely the development of the Newton hydropneumatic shock absorber, the invention of Mr. Noel Newton, son of Mr. John Newton, of Newton and Bennett, Ltd., Manchester aid London. Mr. Noel Newton has had a very extensive experience of motor driving over some of the roughest roads in Italy and was led thereby to study the absorption of shocks imposed on motor vehieles by inequalities of the road. The result. has been that the Newton shock absorber, -which is the outcome of many years' experiments, has proved highly satisfactory and successful in this country, and not least of any, in its application to the fast passenger-carrying vehicle. To such a vehicle and, in particular, to the sleeper coach, a satisfactory shock absorber would -appear to be an absolutely essential fitting.
.We have already, as our readers will be aware, described the Newton device, and wish now to refer to certain modifications which it has undergone in the past twelve months, the chief of these being the incorporation of an outside adjustmeat, both for the compression and for the return of the road
spring, enabling the adjustment to be carried out
readily in the matter of a few minutes, without the need for disturbing the shock absorber in any way. So far as commercial vehicles are concerned, definite advantages are thereby offered, because, the essential units are so much heavier to handle than in the case of a private car.
Undue. oscillations of the road-spring are absorbed in the Newton device by a piston connected to an outer cylinder, working through a hydraulic gland in an inner cylinder and there displacing "the fluid, which takes the form of a special emulsion which is free from the defects and objectiOns attaghing to the use of oil. There is a central hole in the base of the inner cylinder which communicates with two valves, which transfer the Ilquid through an annular space between the cylinders and, thence, through perforations in the top of the inner cylinder, to the top of the piston. Of the two valves, one is a needle valve giving freedom of passage each way, and the second is a non-return ball valve which acts on compression only. Up to a certain speed, the needle valve only is working both for compression and for the return, but when a big bump is encountered the ball valve lifts and allows a freer compression thee if all the liquid had to pass through the needle valve. The ball valve is of such dimensions that it does not, when once lifted, give a progressive action of tightening up. It The Newton hydropneumatic shock absorber shown in section. Emulsion fills the to w e r cylinder, its displacement by the piston, controlled by the valve setting, serving to damp excessive r o a dspring oscillation.
GLAND NUT LOCKING RING FELT
oiStorcE alma
WASHERS GLAND PLATE SOLID PISTON OUTER CYLINDER SASS ADJUSTING SCREW
LOCK NUT
NEEDLE VALVE
can be set at whatever weight is desired and so long as the pressure is maintained by the movement of the piston, the ball valve will remain open. From zero up to the opening of the ball valve, the resistance is increasing, and after the ball valve is opened the given pressure. is maintained. The return stroke is resisted by the liquid passing through the needle valve only and the faster the piston tries to move, so does the resistance increase.
There is, of course, always a risk that an absorber of this character may introduce harshness through the sudden resistance offered by it. This is overcome in the Newton device by the introduction of a volute spring within the outer cylinder, so that the brackets on the vehicle do not compress the absorber directly, but through the medium of the volute spring.
A very subtle point in connection with the employment of a piston in a cylinder arises from the fact that provision must be nuide for the displacement effect of the piston rod itself, for not only does the piston move in the cylinder, but the piston rod enters it and occupies space that is really required by the fluid. This situation is very cleverly met in the Newton absorber by the incorporation of a small chamber at the top of the main cylinder, but isolated from it. In this chamber a certain amount of air is left and it is the compression of this small volume of air which is employed to counteract the intrusion of the piston rod. The presence of this air, however, introduces other troubles, and these have been met in the form of a hanging plate valve which admits emulsion to the air chamber. The passage being small, quick upward oscillations of the pistons are resisted.
The liquid used is, as we have said, an emulsion of oil and water, the use of which is patented; it overcomes all the difficulties associated with the use of Ordinary oils, and with them, the difficulty of making an absorber thoroughly proof against leakage, because the emulsion is not prone to capillary action, which is the usual cause of creepage past glands and washers, whilst it is impervious to oxidization and maintains a uniform consistency despite wide changes in temperature. Emulsions of this sort are, of course, well known and experience suggests that their use should be quite satisfactory.
The two adjusting screws at the bottom of the absorber are employed to give the initial setting to the &Mee of the needle valve and to load the spring of the ball valve to snit the particular vehicle to which the absorber is fitted. CAP NUT LOCKING WASHER
JOINT COVER RUBBER SUFFERS OUST COVER VOLUTE SPRING SPRING PLATE PISTON ROD CREASE PACKING GLAND HAT LEATHER HAT LEATHER PORTS INNER CYLINDER OUTER CYLINDER INNER CYLINDER ADJUSTING SCREW BALL VALVE