Engine Starting System — General Information and Precautions (BMW 7 Series E38)

General information

The sole purpose of the engine starting system is to ensure that the engine rotates at a speed sufficient to start it.

The starting system consists of a starter, battery, ignition switch, traction relay and connecting electrical wiring.

The starter is a DC electric motor with mixed excitation and an externally mounted electromagnetic traction relay. The starter consists of a housing or stator with excitation windings, an anchor with an overrunning clutch, a cover with brush holders and a traction relay.

When the starter is turned on, current from the battery begins to flow through the winding of the traction relay. The relay anchor is pulled in and the contacts are closed. At the same time, the relay anchor, through the drive lever, ensures the extension of the gear with the overrunning clutch, while the hub of the clutch rotates on the helical splines of the starter anchor shaft and also rotates the gear, which facilitates the entry of the latter into engagement with the toothed ring of the flywheel. Current flows through the closed contacts of the traction relay, feeding the stator and anchor windings, and the starter anchor begins to rotate together with the hub and the overrunning clutch.

After the engine is started, the rotation speed of the pinion exceeds the rotation speed of the starter anchor. In this case, the overrunning clutch rotates freely, and the torque is not transmitted from the engine flywheel to the starter anchor shaft. After releasing the ignition key, the power supply circuit of the traction relay windings through the ignition switch is opened, the anchor of the traction relay is pressed back to its original position by the spring, the relay contacts are opened and the drive pinion disengages from the flywheel ring gear.



The starter with a solenoid relay is located parallel to the engine crankshaft and is fixed to the power unit.

Precautionary measures

When performing any work on the engine starting system, observe the following requirements:

• To avoid failure of the electric motor due to overheating, do not turn on the starter for more than 15 seconds - wait at least 1 minute before turning it on again. Long cranking of the engine that does not start with the starter leads to the accumulation of unburned fuel in the catalytic converter, which is fraught with failure of the latter due to ignition during starting;
• The starter is connected directly to the battery and careless handling may cause a fire due to a short circuit;
• Always disconnect the negative battery cable before servicing the starter.