AIR AND THE CAR

Taranaki Daily News, 21 March 1935, Page 13

AIR AND THE CAR

FRIEND AND ENEMY OF MOTOR. MANY IMPORTANT USES. Modern motorists take many things for granted, among them being the very important part played in the presentday car by air. - The “breath of fresh air” that means so much to the jaded Worker eager to jump, into the driving seat and seek the open country, means—metaphorically speaking—just as much to the vehicle in which he rides. Without air a pneumatic tyre is a sorry spectacle, although to appreciato the advantages of low-pressure tyres is difficult in these days of good roads, and only the dimmest—if any—recollections of “solids.” Pneumatic upholstery works on much the same principle as a tyre, but with this difference that it can be run fairly soft. Air and petrol form, as we know, the combustible mixture that enters the cylinders and does all the hard work when ignited by the spark across the plug points. The temperature of the air which has a distinct bearing on the maintenance of tyre pressures, has also a marked effect on the performance of the car in general. When the temperature is very low, the petrol drawn from the jet is not fully vaporised, the cylinders are fed with an incorrect mixture and the running of the car as a whole is unsatisfactory until things have warmed up sufficiently under the bonnet to effect a partial cure. Nowadays problems of this kind have been very carefully tackled, however, with the advent of radiator thermostats and other devices controlling temperatures. Most engines are fitted with what appropriately enough, called a breather, but novices particularly often are puzzled to know why a vent of this kii.» is necessary, arguing that the air displaced by the pistons coming dowii is. surely accommodated in the space provided as the remaining pistons travel upwards. Actually, however, the pistons. do not maintain equilibrium of air pressure within the crankcase, a bellows effect resulting, which, although small, would be sufficient to cause fluctuation of pressure in the crankcase and exudence of oil from bearings, etc., if a vent were not provided. There are on the modern car a number of interesting gadgets relying upon air or its exhaustion for their operation, notable amongst them being the vacuum fuel supply tank and. the suction-operated windscreen wiper. By means of valve mechanism connected to the induction pipe the air is exhausted from an auxiliary fuel tank, the vacuum created being sufficient to draw petrol from the rear main tank A float then closes the induction valve and opens an air valve, which, by destroying the vacuum, releases the petrol on its way to the carburettor, when the process of replenishment arid discharge is repeated. The suction-operated windscreen wiper consists in the main of a piston working backwards and forwards in a cylinder. Via the familiar rubber tubing, first one side of the piston and then the other comes under the influence of Induction, so that an alternating movement is obtained, which is transmitted to the wiper arm. AUTOMATIC CLUTCHES. Similar principles govern induction devices for automatic clutch operation and for engine-operated servo brake mechanisms. In the supercharger employed on Graham cars vanes revolving at high speed feed a constant supply of gas undei- pressure to the cylinders. There is only one part of a motor car depending for its ?<ictioning entirely on the total exclusion of air, this being, of course, the electric bulb of the vacuum type for lighting purposes, although nowadays gas-filled bulbs are more common. Finally we come to one of the most im-

portant considerations of the subject under discussion, as evidenced by the attention which at the moment body designers are giving to stream-lining for the reduction of air resistance to the car in motion. Even when there is no wind, a large proportion of the engine’s power is absorbed in* overcoming resistance of /the air. Against a head-on wind, blowing at, say, 30 miles an hour the extra work which the engine is called upon trj do is enormous, air resistance increasing as the square of the car’s speed.