Renault Megane Technical Review: System operation

The high-pressure injection system is designed to deliver a precise quantity of diesel to the engine at a specific moment.

DESCRIPTION

DELPHI 112-way ECU, type "DDCR".

The system consists of:

a priming bulb on the low-pressure circuit,
a diesel fuel filter,
a high-pressure pump incorporating a feed pump (transfer pump),
a pressure regulator fitted to the pump,
an injection rail,
a pressure sensor mounted on the rail,
four solenoid injectors,
a diesel temperature sensor,
a coolant temperature sensor,
a cylinder reference sensor,
an engine speed sensor,
an accelerometer,
an exhaust gas recirculation solenoid valve,
an accelerator pedal potentiometer,
an atmospheric pressure sensor,
and an ECU.

The "common rail" direct high-pressure injection system operates in sequential mode (based on the operation of multipoint injection for petrol engines).

Thanks to the pre-injection process, this injection system reduces operating noise, lowers particulate and polluting gas emissions, and delivers high engine torque even at low engine speeds.

The high-pressure pump generates the high pressure, which it directs to the injection rail. The actuator located on the pump controls the quantity of diesel supplied according to the demand determined by the ECU. The rail supplies each injector through a steel pipe.

The ECU:

determines the injection pressure value required for correct engine operation, then controls the pressure regulator. It checks that the pressure value is correct by analysing the value transmitted by the pressure sensor located on the rail,
determines the injection time required to deliver the correct quantity of diesel and the moment at which injection must start,
electrically controls each injector individually after determining these two values.

The fuel flow injected into the engine is determined by:

the injector drive duration,
the opening and closing speed of the injector,
the needle lift (determined by a constant for each injector type),
the nominal hydraulic flow rate of the injector (unique to each injector),
of the high-pressure rail pressure regulated by the ECU.

The ECU manages:

idle speed control,
exhaust gas recirculation (EGR) flow to the intake,
fuel supply control (timing, quantity and rail pressure),
control of the cooling fan unit (GCTE function: Centralised Coolant Temperature Management),
air conditioning (cold loop function),
cruise control / speed limiter function,
glow plug pre- and post-heating control.

The high-pressure pump is supplied at low pressure by an integrated booster pump (transfer pump).

It supplies the rail, whose pressure is controlled for charging by the flow actuator and for discharging by the injector valves. Pressure drops can thus be compensated. The flow actuator allows the high-pressure pump to supply only the quantity of diesel needed to maintain pressure in the rail.

Thanks to this component, heat generation is minimised and engine efficiency is improved.

To discharge the rail through the injector valves, the valves are controlled with short electrical pulses:

small enough not to open the injector (flow returns through the return circuit from the injectors),
long enough to open the valves and relieve the rail.

Control of the cooling fan unit and the coolant temperature warning light on the instrument panel by the injection ECU (GCTE function: Centralised Coolant Temperature Management).

Multiplexed network link between the vehicle's various ECUs. As a result, the fault warning lights on the instrument panel are illuminated via the multiplexed network.

Removal of the vehicle speed sensor on the gearbox. The vehicle speed information for the instrument panel is sent by the ABS ECU or the wheel speed UCE unit via a wired link, then broadcast on the multiplexed network by the instrument panel. The main users of the vehicle speed information are the injection ECU and the airbag ECU.

Some vehicles use a water-in-diesel detection sensor, located in the filter. If water is present in the diesel, the injection and pre/post-heating warning light (orange) comes on.

IMPORTANT

The engine must not be run with:

diesel containing more than 10 % diester,
even small quantities of petrol.

The system can inject diesel into the engine at pressures up to 1400 bar. Before each intervention, check that the injection rail is no longer pressurised and that the fuel temperature is not too high.

During any work on the high-pressure injection system, observe the cleanliness and safety instructions given in this document.

Do not disassemble the inside of the pump or the injectors. Only the flow actuator, the diesel temperature sensor and the venturi may be replaced.

For safety reasons, it is strictly forbidden to loosen a high-pressure pipe connection while the engine is running.

To avoid contamination of the circuit, it is forbidden to remove the fuel rail pressure sensor. If the pressure sensor fails, replace the pressure sensor, the rail and all five high-pressure pipes.

It is strictly forbidden to remove any injection pump pulley marked 070 575. If the pump is replaced, the pulley must be replaced as well.

Do not supply any system component directly with 12 V.

Decarbonising and ultrasonic cleaning are forbidden.

Never start the engine unless the battery is reconnected correctly.

Disconnect the injection ECU before carrying out any welding on the vehicle.

Always replace any plastic air intake pipes that have been disconnected.

HOSTED FUNCTIONS

Air conditioning management aid:

On air-conditioned models, the DDCR system allows the air conditioning to be switched off under certain operating conditions:

Voluntary request by the driver.
During engine start-up phases.
In case of overheating (to reduce the power the engine has to deliver).
When engine speed is held at a very high level (compressor protection).
During transient phases (such as strong acceleration demands for overtaking, stall prevention and pulling away). These conditions are only taken into account when they do not occur repeatedly, to avoid system instability (unwanted deactivations).
When certain faults are cleared.

Air conditioning management in cold loop:

The air conditioning is of the cold loop type; its control is shared between several ECUs. The injection ECU is responsible for:

Managing the cooling demand based on the cabin controls and the pressure value.
Determining the power absorbed by the compressor from the pressure.
Determining the GMV commands based on vehicle speed and pressure.

The driver requests air conditioning via the fan selector combined with a switch. This cooling request is allowed or not depending on the measured pressure. If this pressure is outside the operating limits, the cold loop strategy is not activated.

Note: Cooling fan unit control requests can be made from the injection ECU, but these are transmitted over the CAN network. These requests depend on the air conditioning, but also on the engine coolant temperature and vehicle speed.

Thermal regulation of the cabin heating circuit:

A direct injection engine is characterised by fuel being injected directly into the combustion chamber. This results in reduced heat losses from the upper part of the engine and, consequently, the cylinder head cooling circuit is smaller.

The effect of this reduction is that the temperature of the water circulating in it rises more slowly. However, this water is used by the cabin heating system. In cold weather, it therefore becomes difficult to quickly reach a comfortable temperature in the cabin.

To reduce the warm-up time, resistive air heating elements called RCH (cabin heating resistors) are added to the cabin heating circuit. The UCH determines whether the RCH need to be activated, the UPC physically controls the RCH, and the injection ECU determines, on the one hand, the power control limitation of the RCH based on alternator load and, on the other hand, the RCH inhibition based on engine speed, load and vehicle speed.

Speed limiter - cruise control management:

When activated, the vehicle speed regulation function keeps the vehicle at a preselected speed whatever the driving conditions encountered. Using the control buttons, the driver can increase or decrease the vehicle speed.

The speed regulation function can be deselected either by the control buttons, by switching off the cruise control function selector, or by detection of system events such as brake or clutch pedal application, or by detection of system faults such as inconsistent vehicle speed or excessive vehicle deceleration.

The regulation function can also be temporarily inhibited when the driver, by pressing the accelerator pedal beyond the regulation flow rate, wishes to take back control of the vehicle and exceed the selected set speed. Speed regulation resumes when the driver releases the accelerator pedal.

It is possible to reactivate the vehicle speed control and resume the last set speed following deactivation of the function for any reason during the same vehicle operating cycle (ECU power not switched off). The vehicle will then attempt to reach the set speed using a controlled speed ramp.

The vehicle speed limiter function, when activated (using the selector switch), limits the vehicle speed to a preset value. The driver controls the vehicle normally using the accelerator pedal up to the set speed. If the driver attempts to exceed this speed, the system will disregard the pedal demand and control the vehicle speed as the cruise control would, provided the accelerator pedal is pressed sufficiently.

As with the cruise control, the set speed can be changed using the control buttons, either by a short press or by a continuous press.

For safety reasons, it is possible to exceed the set speed by pressing the accelerator pedal beyond a pedal position limit value; control is then fully handled by the accelerator pedal until the vehicle speed drops back below the set speed, at which point the limiter becomes active again.

The driver has the following controls for the cruise control / speed limiter function:

Accelerator pedal.
Brake pedal.
Clutch pedal.
Function selector switch used to select the cruise control or speed limiter operating mode.

Instrument panel display:

The ECU manages the instrument panel display of certain information relating to engine operation.

This concerns 5 functions: the MIL (Malfunction Indicator Lamp) of the EOBD (European On Board Diagnostic), glow plug preheating/post-heating, coolant temperature and engine faults: Severity 1 (non-critical fault) and Severity 2 (emergency stop). These five functions are represented by 3 warning lamps or messages displayed by the on-board computer.

Glow plug indicator lamp:

This lamp is used both as an operating indicator and as a system fault indicator:

Steady illumination with + APC: indicates glow plug preheating.

After preheating has ended and after an automatic timed switch-off of 3 s, the lamp lighting up indicates a Severity 1 fault (implies reduced operation and limited safety level. The user must carry out repairs as soon as possible).

Temperature / emergency stop warning lamp:

This lamp is used both as an operating indicator and as a system fault indicator. It lights up for 3 s when the ignition is switched on (automatic test procedure managed by the instrument panel).

Steady illumination: indicates engine overheating or a Severity 2 fault.

In the case of a critical fault, fuel injection is automatically cut off after a few seconds. In the case of overheating, the driver remains free to stop the vehicle or not.

FAULT WARNING LAMP ILLUMINATION STRATEGIES ON THE INSTRUMENT PANEL:

Orange SERVICE warning lamp (severity 1):

Illumination of this lamp accompanied by the message "injection fault".

The user must have the repairs carried out as soon as possible.

Red STOP warning lamp (severity 2):