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The
generator is located at the front RH side of the engine, on the cylinder block.
The generator has an output of 85/150 Amps and is manufactured by Denso. A
six-ribbed polyvee belt drives the generator pulley, which in turn is driven
from the engine crankshaft pulley.
The generator comprises a stator, a
rotor, a rectifier pack and a regulator. There is a three-pin connector (C0053)
on the generator:
- Pin 1 – Voltage reference line to the battery via the Battery Junction Box
(BJB)
- Pin 2 – Pulse Width Modulated (PWM) signal from the Engine Control Module
(ECM) to the generator (generator control)
- Pin 3 – PWM signal from the generator to the ECM (generator monitoring)
The generator is connected to earth via its mountings.
The
rotor comprises a field winding, wound around an iron core and mounted on a
shaft. The iron core has extensions at each end, which form North and South
poles as current flows through the field winding. The rotor is located inside
the stator and is mounted on bearings for smooth running and to support the
rotor due to the high side loading applied by the drive belt tension.
The
stator has three sets of coils made from copper wire. The three coil windings
are connected in a 'star' connection, where one end of the winding is connected
to the other two windings. The output current is supplied from the opposite end
of each winding. Rotation of the rotor causes ac current to be produced in the
coils.
The rectifier converts the ac current produced in the stator coils
into dc (rectified) current required by the vehicle electrical system. The
rectifier comprises semi-conductor diodes mounted on a heatsink to dissipate
heat. An equal number of the diodes are on the negative and positive side, an
additional diode in the regulator to control feedback through the battery
voltage signal line. The rectifier also prevents current flow from the battery
to the generator when the output voltage is less than the battery
voltage.
The 'smart' regulator controls the output voltage from the
generator to protect the battery; at low temperatures battery charge acceptance
is very poor so the voltage needs to be high to maximise any re-chargeability,
but at high temperatures the charge voltage must be restricted to prevent
excessive gassing with consequent water loss. The EMS, which controls the
regulator, will calculate the voltage set point required for the ensuing
conditions. The 'traditional' regulator controls voltage against generator
temperature, which means the battery temperature will lag a long way behind so
there will be significant periods of operation when battery charging is
compromised. With this system, the EMS can set the voltage by inferring the
battery temperature from information received from it's various sensors, hence
voltage will follow the battery's needs a lot more accurately.
The
regulator has transistors, which rapidly switch on and off to regulate the
voltage output according to the voltage sensed internally. The regulator also
provides a PWM signal output to the ECM, which uses the signal to adjust the
idle speed under varying electrical loads.
Initially, the ignition switch
supply provides an excitation current to the rotor at low generator speeds via
brushes, which contact slip rings at the end of the rotor shaft. As the
generator speed increases the generator becomes self-exciting.
The charge
warning lamp function is transmitted to the EMS and then on to the Controller
Area Network (CAN) bus to the instrument pack.
LOAD MANAGEMENT SYSTEM
The load management system comprises software
resident in the Automatic Temperature Control Module (ATCM).
Control Components (412-04 Control Components)
Its
purpose is to protect battery state-of-charge during abnormal usage of the
vehicle. The system will request the Media Orientated System Transport (MOST)
ring and the air suspension to go into 'power save' mode, and will modulate
features such as seat heating and screen heating to prevent the battery being
dragged down to a point where the car becomes unoperational. A 'WARNING - LOW
BATTERY' message will be displayed in the message centre.