Page 64 - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

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Figure 1.69 A hydraulic system like this
Figure 1.68 Gears in a car gearbox
one is sometimes called a liquid lever

the speed ratio – the speed of the output shaft compared with the speed of
●
the input shaft.
Gears with the ratio 2:1 (say 20 teeth input and 10 teeth output) will have an
output twice the speed and half the torque of the input.
A common type of gear for parallel shafts is the spur gear, with straight teeth
parallel to the shaft axis. The helical gear as shown in Fig. 1.68 (most common in
car gear boxes) has teeth cut at an angle in a corkscrew shape.

1.4.22 Hydraulics

Hydraulics means using the properties of liquids to transmit pressure and
Defi nition
movement ( Fig. 1.69 ). The best known machines of this type are the hydraulic

press and the hydraulic jack. The principle of pressurized liquid and increasing Hydraulics
mechanical effi ciency is also ideal for use on vehicle braking systems. Using the properties of liquids to
transmit pressure and movement.
A basic hydraulic system consists of two liquid-connected pistons in cylinders,
one of narrow bore, one of large bore. A force applied to the narrow piston
applies a certain pressure to the liquid, which is transmitted to the larger piston.
Because the area of this piston is larger, the force exerted on it is larger. The
original force has been increased, although the smaller piston has to move a
greater distance to move the larger piston only a small distance. Mechanical
advantage is gained in force, but movement is lost.

1.4.23 Materials and properties

Different materials are used in different places on motor vehicles because of
their properties. For example, cast iron is a fairly obvious choice for use as an
exhaust manifold because of the very high temperatures ( Fig. 1.70 ). Plastic would
probably melt so would not be used. However, perhaps aluminium could be used
instead? This time it is not obvious and more thought is required to decide the
most suitable material.
In Table 1.22 are listed several types of material together with important
properties. As a very rough guide these are given as a number from 1 (best) to 5
(worst) in a kind of league table. This makes the table easier to use for comparing