HYDRAULIC MACHINES.
Vehicle Springs.— No adequate understand ing of the requirements in vehicle springs for motor cars can be gained without a compre hensive study including not only spring mate rials and spring design but also the relations of the spring action to the auxiliary action obtained from resilient wheel tires, to the length of the wheelbase of the vehicle (the dis tance between axles), to the distribution of weight between axles, to the average and maxi mum speeds required of the car, to the nature of the roads over which it is most likely to travel and to several minor factors. On the whole experimentation has dictated the develop ment, and all gspringing) is a compromise among more or less conflicting requirements. As the object of °springing" in general is to permit the wheels and axles to bounce over the inequalities of a road surface without com municating severe shocks or much up-and-down movement to the vehicle frame and body, and the springs for this purpose should be as flex ible as practicable, and as, on the other hand, very flexible springs oscillate with great ampli tude after a shock, and such oscillations in turn are liable to react upon the frame and body, the technical effort in spring design is largely concentrated upon the problem of moderating the rebounds and oscillations of vehicle springs which are flexible and lively. Flexibility, life and strength are combined in the springs by using special alloy steel for the spring leaves, by having each spring made of many thin leaves rather than a smaller number of thick ones (this permitting a reduction of. their
length) and often by using springs which do not only bend but also rock around a pivot near their middle (cantilever springs). The nature of the cantilever spring, being a type almost exclusively used for motor cars, is illustrated in Fig. 20.
The use of coil springs in lieu of leaf springs has often been attempted but has never yet become general, except for auxiliary purposes, mainly because this type of spring does not in itself possess lateral stability and therefore must be specially braced to prevent the motor car body and frame from swaying from side to side. The means adopted for moderating rebound and oscillations take the form of aux iliary devices which can be coil springs whose periods of oscillation differ from those of the leaf springs and thereby break up the harmonic sequence of movements, but usually they are based on mechanical or hydraulic friction and are called rebound checks or shock absorbers. But for motor cars intended for speeds higher than 20 miles per hour satisfac tory results, securing both comfort for occu pants and safety for the vehicle structure, are not considered to be obtained without the addi tional equipment of pneumatic tires for the vehicle wheels.
Most of the elements in the springing of motor cars are also used for other classes of motor vehicles and in part for ordinary horse drawn carriages and for railway cars and coaches. To avoid repetition more detailed information will therefore be found under