15.9.
Starter Installation
Generally starters are installed in a horizontal position next to the engine crankcase, so that the drive pinion is in a position to mesh with the flywheel or drive plate ring gear. The starters are either flange or cradle mounted. Flange mounting is the most common on small and medium sized vehicles. In some cases this technique uses an additional support bracket at the rear of the starter to reduce its vibration. Starters on larger vehicle are often cradle mounted but also use the flange mounting technique for fixing usually with at least three large bolts. In both cases the starters must use some kind of pilot, often in the form a ring machined on the drive end bracket, to ensure correct meshing with the ring gear. This ensures correct gear backlash and a suitable out of mesh clearance. The flange and cradle mountings method used for many starter motors is illustrated in Fig. 15.32.
Fig. 15.32. Starter mountings. A. Flange mounting. B. Cradle mounting.
A cable carrying a current experiences power loss (/ R loss) and hence to reduce this loss the current or the resistance must be reduced. The main load on the vehicle battery is the starter and hence with a starter the high current is inhabitable as it is the only way of delivering the high torque. Therefore heavy conductors are used to the starter to ensure low resistance so that voltage drop and power loss are reduced. The maximum voltage drop of 0.5 V is allowed on a 12 V system and 1 V on a 24 V system. For a typical car starter the short circuit (initial) current is up to 500 A and for very heavy applications can be up to 3000 A.
The starter system is normally controlled by spring loaded key switch, which controls the current to the starter solenoid, generally through a relay. On vehicles with automatic transmission an inhibitor switch interrupts this circuit to prevent the engine from starting in gear.
The starter circuit controls the glow plugs in a diesel engine powered vehicle. This may also use a timer relay. The glow plugs, in some vehicles, are activated by a switch positioned just before the start position.
