WHAT CAN PRIVATE CAR DESIGN TEACH US?
Page 56
Page 57
If you've noticed an error in this article please click here to report it so we can fix it.
The Trend and Influence on the Design of the Commercial Motor.
TT was interesting to walk round the Motor Show, which has been such a great success this year, and to endeavour to learn from the chassis and the vehicles and equipment on view whether there were any lessons to be learnt which could be applied to the designing of the commercial motor vehicle. Taken as a whole, the Show was a grand one, and a careful examination of all the models exhibited revealed the fact that the general tendency leans more towards the embodiment of well-tried details rather than towards the introduction of startling novelties in design.
One hears it remarked that there is , very little in the way of novelties to he seen nowadays, but this
need not necessarily be taken as a sign hat designers are idle or indifferent to irnprovejients. In our opinion, it may be taken as a sign that the motorcar is approaching a point where but little improvement is urgently called for.
Motorcar Comfort Expected by Coach Passengers.
With but few exceptions, the design of the private car should have little influence on the design of the commercial motor, the conditions under which the two operate being so widely different ; but an outstanding Instance where the private car may be copied with advantage is in the motor coach. This vehicle is intended for carrying passengers only, and, consequently, the passengers look for the same graceful lines, comfortable seating, protection from weather and silent running that are found in the modern private car. •For those machines that are designed especially for carrying goods the requirements are so entirely different that to copy the private car design might mean a reduction of efficiency for the purpose for which they will be employed. As an instance, the construction of engine and gearbox as a unit gives to a private car that neat, clean appearance which is desired in that class of vehicle, but we know of many users of commercial vehicles who have yet to be convinced of the merits (which are undoubted) of this form of construction.
Tendencies in Car Design.
The general trend of the Olympia Show was towards neatness and a clean design of the chassis—even, in some cases, we thought, to the detriment of the ear. Engines and gearbox combined may be said to be general, the transmission brake has almost disappeared, the torque tube is replaced on many of the best models by two universal joints and a floating propeller shaft, and only on very few models can there be found anything in the nature of a torque rod when the torque tube is not employed. It would seem that the use of the springs to resist all stresses due to driving and braking is gaining ground. Fabric universal joints are decidedly to the fore. We noticed that on many models the error of having rear springs with shackles at one end only, working in conjunction with a torque tube, has been corrected, shackles being provided at both ends of the spring. In the matter of suspension, we certainly did expect to have seen more novelty, but the old half-elliptical spring seems to hold its own against most other designs. In one case, flexible fibre was used instead of a shackle between the spring end and the bracket.
A Curious but Effective Damper of Vibration.
Amongst the novelties that have not been shown before, perhaps the most outstanding is the Cardine Moderator, shown by Cardine Accessories, Ltd., Locksbrook Road, Bath. This is an accessory which can be made to fit any make of vehicle and can be added to existing vehicles. Unfortunately, only a small model is shown, but judging from the effects produced in this model by first trying its periodicity without the moderator in action, and then trying it with the moderator in action, its effect should be most beneficial. Between two ball-ended brackets on the frame (one on each side) and a ball bolted to the differential case are two coil springs encased in a telescopic tube. The springs are in compression and, therefore, exert a balanced pressure on the back-axle casing, so that it will be seen that it is not in any way a shock absorber (as the term is generally understood), that is to say, there is no damping by friction, the damping probably coming about by an alteration of the periodicity of the vibrations. We have not space here in which to give a detailed description of this very interesting device, but will do so after having made a trial on the road.
A very interesting device was shown by J. A. Ryley, of 73, Weaman Street, Birmingham, for compressing the springs of valves and holding them in a compressed
state whilst they are being introduced into their place in the engine. This consists of a small lever compressor and an adjustable c,ge in which the spring can be held whilst being put in its place. Another interesting novelty is the Len servo brake, shown by T. B. Andre and Co. Ltd., 5, Dering Street, W. From our illustration it will be seen that two -shoes are expanded in the usual manner by means of a cam. One of these shoes is of ordinary type, whilst the other shoe has the part which carries the lining made in a separate piece, and supported from its shoe by a number of rollers so that it is free to follow the drum in One direction when applied, and by so doing to exert a pressure on the cam in a direction that helps to revolve it so that it tends to apply the brake and thus produce the self-energizing effect. The figures on the drawing indicate the relative pressures in pounds at the various points.
A Piston which is Largely Free from Slapping.
For the first time the now well-known B.H.B. piston which has done so much to reduce piston slap is shown. This piston is of the split-skirt type, the skirt being separated from the part bearing the rings, just below the lowest ring, by a groove which entirely cuts through the outer wall. The only connections between the head and the split skirt are two arms that extend at an angle from the centre of the head to the bosses of the gudgeon pin, thus producing a slight spreading
effect, which, as a result of careful research, the makers have so arranged that a piston can be placed into a cylinder in which it is an appreciably slack fit, and after working for a time it will become a perfectly correct and workable fit in the cylinder. This piston is now used on many leading cars and is being manufactured in thousands, and we think we may say that piston slap is fast becoming a thing of the past.