Function
The components of the system can be divided into three groups:
· Control unit.
· Sensors.
· Actuators.
The sensors provide input signals to the control unit, which contains microprocessors and fixed program data. The control unit calculates the required output variables, which are applied to the actuators.
If the control unit detects a malfunction in the system that will not cause damage to the engine or uncontrolled operation, a replacement value is substituted for the malfunctioning parameter. These replacement values allow limited operation to be maintained, enabling the vehicle to still be driven. The replacement values are available for coolant temperature, start of injection, pedal position, injection timing and engine speed.
As an example, should the engine speed sensor malfunction, a replacement value is determined from the intervals between the injection signals from the start of injection sensor.
Malfunctions that could result in damage to the engine or uncontrolled operation cause the control unit to switch off the injection system, stopping the engine.
The replacement values are immediately suspended and the actual parameters re - instated if the malfunction disappears or is corrected.
Start of injection regulation
The start of injection is regulated by the injection adjuster in the injection pump. A solenoid valve modulates the inner pump pressure on one side of the injection adjuster, leading to the setting of a defined start of injection. When not powered, the solenoid valve is closed, which leads to early start of injection.
The actual start of injection value is reported to the EDC control unit by the start of injection sensor.
Injection quantity regulation
Injection quantity regulation is made possible by the quantity actuator in the injection pump. The quantity actuator is operated by a variable width pulse from the control unit. An electro - magnetic rotary actuator is operated to move an eccentrically arranged ball pin. The rotary motion is converted into a linear movement, which acts on the control valve, varying the effective stroke of the pump piston (injection quantity).
The position of the control valve is reported to the control unit by the position sensor. If necessary, it can be adapted until the voltage quantity nominal value is attained.
When not powered, the quantity actuator is reset to zero output.
The start quantity regulation controls the injection amount required for starting and for engine speed increase, depending on the engine temperature, time and engine speed.
The amount of fuel injected in operation depends on the position of the pedal sensor and the engine temperature and speed.
Engine speed regulation
After starting (pedal position sensor in idle position), the idle speed regulation goes into operation when a certain engine speed is exceeded. This is calculated by the control unit depending on the coolant temperature and thus is kept to a constant value. The idle speed can be regulated using TECH 1.
The engine maximum speed limitation is performed by the control unit by reducing the injection quantity.
Idle stabilizer
The idle stabilizer counteracts the irregularities in power output of individual cylinders caused by deviations in fuel injection quantities. The deviations are remedied by regulated injection quantity correction to produce a stable idle speed.
Judder dampening
When the accelerator pedal position is changed spontaneously or there is a sudden
change in the road resistance, vibrations arise, which, in conjunction with the regulation frequency of the injection hydraulics, can lead to juddering.
The engine speed signal is a series of pulses, which can also be used to evaluate rotational irregularities at the flywheel. These irregularities, which cause the vibrations, are counteracted by adjustments to the quantity actuator.
Smoke limitation
At high ambient air temperatures or at low atmospheric density, the full load amount is reduced to limit smoke emissions.
Overheating protection
If the permitted coolant temperature is exceeded when travelling at high speeds, the full load quantity is reduced (engine protection).
Exhaust gas recirculation (EGR system)
The return of a proportion of the exhaust gas in the partial load range lowers the combustion temperature to reduce the formation of nitrogen oxides.
Self - diagnosis
The self - diagnosis recognizes faults in the EDC system, accesses replacement values and emergency programs, subsequently stores the fault, and allows readout via TECH 2.
In addition, trouble - shooting can be facilitated by calling up current inputs and outputs from the EDC control unit.
The EDC is checked with TECH 2 in conjunction with the "Checking Procedures".