General information — starting and charging systems (Audi Q7-4L-D)

Table of contents: Engine starting system ↓ Charging system ↓

The electrical system of the vehicles discussed in this manual operates at 12 V. The ground connection is made through the negative terminal of the battery. The battery is located under the driver's seat.

Engine starting system

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 and connecting wiring.

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

The starter switch is an integral part of the ignition switch and is designed to excite the traction relay installed on the starter. When the starter is turned on, current from the battery begins to flow through the traction relay winding. The relay armature is pulled in and the contacts are closed. At the same time, the relay armature, through the drive lever, ensures the extension of the gear with the overrunning clutch, while the clutch hub rotates on the helical splines of the starter armature shaft and also rotates the gear, which facilitates the engagement of the latter with the flywheel ring gear. Current flows through the closed contacts of the traction relay, supplying power to the stator and armature windings, and the starter armature begins to rotate together with the hub and overrunning clutch.

After the engine starts, the pinion speed exceeds the starter armature speed. In this case, the overrunning clutch rotates freely, and torque is not transmitted from the engine flywheel to the starter armature shaft. After the ignition key is released, the power supply to the traction relay windings via the ignition switch is disconnected, the traction relay armature is pressed back to its original position by a spring, the relay contacts open, 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 secured to the power unit.

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

To prevent starter failure due to overheating, do not crank the engine for more than 15 seconds. Wait at least 1 minute before cranking it again. Cranking an engine that won't start for long periods of time with the starter causes unburned fuel to accumulate in the catalytic converter, which can cause it to fail due to fuel 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.

Charging system

The vehicles in question use an alternator. When installing additional electrical equipment, check that the generator capacity is sufficient to provide new consumers with electricity.

The generator is driven by a belt from the engine crankshaft.

The generator is a three-phase synchronous electric machine with electromagnetic excitation. To convert alternating current to direct current, a diode rectifier is built into the generator. The output voltage is regulated by a built-in regulator. The generator has a ground connection.

When the generator is running, the electric current flowing through the excitation winding creates a magnetic flux around the rotor poles. When the rotor rotates, its magnetic poles periodically change under each stator tooth. As a result, the magnetic flux passing through the teeth continuously changes in magnitude and voltage. This alternating magnetic flux generates an electromotive force (EMF) in the stator winding. The wedge-shaped rotor pole pieces are designed to produce a nearly sinusoidal EMF waveform.

At high rotor speed, when the generator output voltage begins to exceed 13.6 + 14.6 V, the voltage regulator is locked and no current flows through the excitation winding. When the voltage drops, the regulator opens again, allowing current to flow freely through the excitation winding. The higher the rotor speed, the longer the regulator remains locked and, accordingly, the more the voltage at the generator output decreases. The process of locking and unlocking the regulator occurs at a high frequency, so the output oscillations remain virtually unnoticeable and the generator voltage can be considered constant.

The charging system does not require periodic maintenance, however, the condition of the alternator drive belt, battery and its wiring should be checked and replaced on a regular basis in accordance with the maintenance schedule (see sections 17 and 18 Chapters 1).

When the ignition is turned on, the charge indicator on the instrument cluster should light up briefly (see chapter "Governing bodies"). If the lamp does not turn off after starting the engine or lights up during its operation, check the condition of the charging system components. Failure of the lamp to activate when the ignition is turned on indicates that it is faulty, the corresponding electrical wiring is damaged, or the generator is not functioning properly (including a broken drive belt).

When servicing your generator, take the following safety precautions:

Do not disconnect the battery or voltage regulator while the engine is running.
Do not short the generator excitation terminal or the cable attached to it to ground.
Do not confuse the order of connecting the voltage regulator wiring.
Remember that turning on a voltage regulator shorted to ground will cause it to fail immediately.
Never remove the generator while the battery is connected.
Do not confuse the polarity of the battery connection.
Never use voltage meters or test lamps connected to the household power supply (110/220 V) when testing on-board electrical equipment.
When checking the condition of the diodes, do not apply a voltage greater than 12 V to them and do not use megohmmeters that also have a high output voltage - breakdown of the diodes will lead to a short circuit.
Remember that when checking the insulation of electrical wiring with a megohmmeter, it is necessary to disconnect all electrical wiring from the generator.
When charging the battery without removing it from the car, make sure that both cables are disconnected from it; do not confuse the polarity of the charger connection.
Before performing any electric welding work on the vehicle, do not forget to disconnect the electrical wiring from the generator and battery.
Any checks of the circuits and components of the on-board electrical wiring should be carried out with the engine not running and the battery disconnected.
Remember that reversing the polarity of any connections carries the risk of irreversible damage to the rectifier and voltage regulator of the generator.