. Springs and Springing
Tin: more effectively a car is sprung the greater the comfort Of the driver and his passengers, the less wear and tear upon the engine and the various working parts, and the smaller the quantity of petrol consumed. Everyone appreciates that good springing increases Comfort, but very few have ever given a thought to the fact that the less movement there is in the body of the car, especially when running over a bumpy road, the less petrol is used and the less wear and tear there is upon the tyres.
The wheels of a car sink into every pot-hole they encounter in their path, and, if the springs be working stiffly, the whole ear sinks with the wheels. On the other hand, if the springs are doing their work properly, the chassis and body of the ear only drop a fraction of the distance dropped by the wheels. Power is required to pull the wheel up the side of the pot-hole. If the weight of the chassis and body, with the occupants, be added to the weight of the wheel, axle and spring, considerably more power will be needed to get the machine out of the pot-hole. Thus it will be seen that the better the- springs the-less petrol is consumed. On a perfect road this saving would amount to very little indeed, but it must be remembered that many roads are anything but perfect. The Saving in the • course of a long day's run is considerable '
The type of spring commonly employed is that known as the leaf spring, and is composed of 'laminated -pieces of metal fastened together at a central. point, Springs of various forms are used, each one varying somewhat in its formation and its mode of attachment to the chassis. The great majority of cars are suspended at four points—that is, at each corner of the chassis. There are several advantages, however, in the three-point method of suspension. In the latter case, when one of the road wheels passes over an obstruction or drops into a pot-hole, the stresses are relieved and there is no tendency for the chassis to twist. This may easily happen in the case of the four-point suspension. A car that is suspended at three points only is fitted with an inverted half-elliptic spring in the front and two other springs at the rear.
Several different forms of spring are used on the modern car. These are the quarter-elliptic, which is attached to the chassis at one end and to the rear axle at the other end ; the half-elliptic, in which case both ends are attached to the chassis, with the axle in the Centre ; the cantilever, somewhat similar to the half-elliptic but with the centre and one end attached to the chassis, the rear axle being mounted on the other end ; the three-quarter-elliptic, which employs a -half- elliptic and inverted quarter-elliptic in place of the dumb iron of the chassis ; • and the full-elliptic, which consists of two half-elliptic springs, the upper one being inverted, the centre of the upper being attached to the chassis and the centre of the lower holding the axle, while the ends of the two are jointed together.
The value of a' leaf 'spring is strictly limited, and it does not eliminate all road shocks. For this reason a good many manufacturers fit-shock-absorbers to their cars as standard. Shock-absorbing devices may be classified into two groups , those which are placed between the axle and the chassis and those which are incorporated in the union between the rear ends of the upper and lower springs in the three-quarter and full-elliptic types. Shock-absorbers offer no resistance when the car springs are being compressed ; hence their full flexi- bility is available for absorbing the initial road shocks. But immediately *the springs rebound, the shock-absorbers at once check their movement, and the springs reach their former or normal position, but at a rate which is diminished progressively and to the extent desired through the hydraulic braking effect. Thus the springs no longer throw the chassis upwards, and travelling over bad surfaces, even at high speeds, is rendered quite comfortable.
Apart from increased comfort there is a saving in tyres, since these are kept in constant contact with the road. What damages a tyre more than anything else is when, travelling along a rough road, the wheels bound upwards, revolving at a much more rapid rate, and they receive incalculable damage when they touch the road again. Various types of shock- absorbers are employed, some being provided with stout springs, others working through the medium of a dash-pot ,filled with oil, while others are composed of a pair of hinged arms with friction discs between the working parts of the hinge
Unless there be a considerable quantity of grease between the leaves of the springs, the friction set up is excessive and they become squeaky, Liiiir• ultimately 'break. Grease- filled spring gaiters prove very valuable, these being fitted as standard in some cases. These gaiters only require repacking with grease every twelve months or so : hence the labour of looking after this part of the car is reduced to a minimum. If spring gaiters be not fitted, the springs should be greased about every three months. To grease the leaves of the springs the car should be jacked up by the chassis —not by the axles—so that the weight of the wheels and the axles will open the leaves. If leaf clips be fitted, these shotild be removed before the ear is jacked up. The grease can then be inserted between the leaves, a blunt knife being a useful instrument 'to use.
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