THE DE RAM SHOCK ABSORBER FULL DETAILS OF AN ACCESSORY WHICH HAS ALTERED PREVIOUS THEORIES ON SPORTS AND RACING CAR SPRINGING
WITH the first appearance of the new 750 Kg formula racing cars, 1934 will always remain a redletter year for the followers of motorracing, and particularly a year of triumph for the German racing cars with their independant suspension, which undoubtedly has given them a great part of their superiority over the orthodox Monoposto Alfas. Bugatti however stuck to the rigid axle lay-out, and much to the surprise of the critics these cars proved themselves in road-holding little if at all inferior to those built according to the new ideas. The familiar Bugatti suspension system, half elliptics in front and reversed quarter elliptics at the rear was still retained. How then had it been adapted to deal with speeds in the neighbourhood of 170 m.p.h. ? Simply by changing over to De Ram shockabsorbers, the merits of which have come to be appreciated fairly generally on the Continent and which have several times been referred to in these pages. Monsieur De Ram has been for many years engaged in research in connection with springing, and after exhaustive tests on touring cars and a close study of racing conditions, a state of affairs made easier through his personal friendship with Monsieur Bugatti, came to the conclusion that the only satisfactory type of shock absorber, especially on a car intended for high speeds, was the friction type. Unfortunately as is well known, with these adjusted to make the car hold the road at high speeds, riding at low speeds is harsh, as the shocks are not sufficient to ” unstick” the friction surfaces and allow the springs to flex. A partial solution of this difficulty is found in those types controlled from the dashboard, where the friction can be reduced for slow speed travel and increased when the car is
being driven fast. Unfortunately it is the speed at which the axle moves, and not the speed of the car which determines the shock transmitted to the car, and also the way in which the car wheels are displaced, and this can be the same whether a car hits a pot-hole at 30 m.p.h. or a minor ripple in the road surface at 100 m.p.h.
The problem which confronted the inventor was to produce an appliance which would check the axle according to the shock received, and this has been achieved by having a friction damper in which the power of the mechanical brake is controlled by a hydraulic arrangement acting as a servomotor. The suspension thus remains comparatively free when dealing with slight movements, but hardens up to racing stiffness when severe shocks are met with. How this object has been attained will be appreciated from sectional drawings and from the description which follows. Various patterns of De Ram shockabsorber have been made, one of which had two arms of round section and an enlargement at their junction which contains the mechanism, making the whole interchangeable with the Hartford
pattern. The most ingenious type is that used on the 3.3-litre racing Bugattis in which a circular casing is bolted on to the chassis. From this a straight arm projects and this is connected to the axle through the usual type of link, the joints working on silentbloc bushes.
Referring to the diagrams, the device consists of a casing (1) filled with special liquid. In this casing a shaft (3) is mounted and on this is keyed the operating lever (4). This shaft is supported at its two extremities on needle bearings (21) and (31).
A piston (5) carried in the shaft (4) is maintained in contact with the cam (8). by means of the roller (7). The cam controls the movement of the piston in accordance with the movement of the lever, and the liquid displaced by the former is forced into the chamber (33). This latter is closed by a plate (11) in which are fitted a series of little pistons (20), and these act in turn through a system of links on the friction discs (14) and (15), which constitute the mechanical brake. The friction of the mechanical brake thus depends on the pressure existing in the chamber (33), which is in turn proportional to the speed of displacement of the piston (5). The movement of the shaft being decided directly by the speed of the axle movement, the movement of the piston is also proportional, though some modification is possible by altering the shape of the cam (8). The pressure
existing in the chamber (33) is however proportional to the square of the movement of the piston (5), so that the braking effect rises as the square of the axle speed.
In order that the shock-absorbers shall act at full efficiency it is necessary to prevent friction between the spring leaves, and when fitting them to existing cars, the inventor interposes strips of aluminium or in the case of touring cars, brass leaves with holes filled with graphite. Another essential factor is that the chassis of the car should be stiff, and that is one reason why the De Ram is so successful on the racing Bfigattis. Other racing manufacturers such as Auto-Union have also become aware of the advantages of the device. Unfortunately the chassis of this car is not stiff enough to allow it to be used, but Monsieur De Ram is submitting an amended design of his own which would provide the necessary rigidity. He is nothing if not enthusiastic and accompanied Caracciola, presumably in a car fitted with a two-seater body, round the Montlhery road circuit a short time ago, but considers that owing to the excessive flexing which took place at high speeds his shock-absorber were not likely in this case to bring about any substantial improvement in road-holding. The first set of these shock-absorbers to be used in England are fitted to a 3.3-litre Bugatti saloon belonging to Mr. Noel Rees, to whom we are indebted for much of the foregoing information. He tells us that good as was the suspension before the De Rams were fitted, it is now improved out of all recognition. Roads like that pave section leading out of Paris via Beaumont, on which the average car does well to exceed 25 m.p.h., can be taken at 70, and the same applies to wavy sections, pot holes or any other form of road surface, and purely as an experiment, the hands may be removed from the wheel when traversing the roughest of them, at 50 to 60 m.p.h., without the car tending to deviate from the straight. ” When you corner on an adverse camber,” Mr. Rees told us, ” the car is just as steady as if
a fifth wheel were put out to support it.” He has just returned from a visit to Paris to get the shock absorbers adjusted to suit English roads which differ from those encountered on the continent by containing many more wavy sections. This alteration is carried out by changing the control cams (8) for others of a different shape. Another important matter is to run the tyres at a pre-determined pressure.
Once the correct setting is found, the devices may be left without further attention for two or three years, according to the inventor. Those used last year on the racing Bugattis were found to be in perfect condition after a season’s work.
There is usually a drawback to the most successful piece of apparatus, and in the case of the De Ram shock-absorbers this is found in the price. Every part is made by hand, and a set costs £170, with an extra £30 for fitting. Produced in limited quantities in a factory they could be made for about £90, and proportionally less in accordance with the output. An attempt is being made to get the French railway companies to fit them, and a number of engines and carriages so equipped have given good results. If they should be adopted as standard equipment on trains, of course, the price of automobile dampers will be much reduced. Meanwhile we shall await with interest their first appearance on the racing cars other than the Bugatti. In these days of £100 motor cars there use is not likely to become general for some time yet.