Denso-Common Rail System – Fuel injectors
A Fuel injector nozzle
B Hydraulic servo system
C Solenoid valve
1 Combustion chamber seal
2 Electrical connection – solenoid valve
3 High pressure fuel line connection
NOTE: The combustion chamber sealing rings must not be reused.
The exact procedure for the correct installation of the fuel injectors can be found in the current service literature.
Start of injection and injected fuel quantity are adjusted via the fuel injectors.
In order to achieve the optimal injection timing and precise injected fuel quantity, special fuel injectors with a hydraulic servo system and electrical actuator unit (solenoid valve) are used.
The injectors are actuated directly by the PCM. The PCM specifies the injected quantity and the injection timing.
The fuel injectors are divided into different function blocks:
• injector nozzle,
• hydraulic servo system,
• solenoid valve.
Operating principle of the fuel injectors The operating principle of the fuel injectors is similar to that of the fuel injectors in the Bosch common rail system.
Denso-Common Rail System – Fuel rail (common rail)
1 Fuel pressure sensor
2 Pressure limiting valve
3 Fuel rail
The fuel rail performs the following functions:
• stores fuel under high pressure and
• minimizes pressure fluctuations.
Pressure fluctuations are induced in the high-pressure fuel system due to the operating movements in the high-pressure chambers of the high-pressure pump and the opening and closing of the solenoid valves on the fuel injectors.
Consequently, the fuel rail is designed in such a way that, on the one hand, it possesses sufficient volume to minimize pressure fluctuations, but, on the other hand, the volume in the fuel rail is sufficiently low to build up the fuel pressure required for a quick start in the shortest time possible.
Function
The fuel supplied by the high pressure pump passes through a high pressure line to the high pressure accumulator. The fuel is then sent to the individual fuel injectors via the four injector tubes which are all the same length.
When fuel is taken from the fuel rail for an injection process, the pressure in the fuel rail is kept almost constant.
Pressure limiting valve
The pressure limiting valve opens at a fuel pressure of approx. 2000 bar. It serves as a safety device in the case of malfunctions in the high-pressure system. Thus, damage due to excessive pressure in the high-pressure system is prevented.
The pressure limiting valve operates as a disposable valve. This means that it must be replaced after a single triggering, as the valve can no longer be guaranteed leak-free.
Triggering of the pressure limiting valve is detected by the PCM, whereupon a corresponding DTC is set and the MIL is actuated.
For removal and installation, please follow the instructions in the current service literature.
Denso-Common Rail System – Principle of high pressure generation
A Pump plunger 1
B Pump plunger 2
C To fuel rail
1 Inlet valve
2 Outlet valve
3 Eccentric cam
4 Eccentric cam ring
5 Fuel metering valve
6 Drive shaft
The rotary movement of the drive shaft is converted to a reciprocating movement by the eccentric cam. The eccentric cam ring transfers the reciprocating movement to the pump plungers.
The pump plungers are offset by 180 degrees. This means, that during a reciprocating movement, pump plunger 1 performs exactly the opposite movement to pump plunger 2.
The eccentric cam produces an “upward” stroke:
• Pump plunger 1 moves in the direction of TDC, thus compressing the fuel and delivering it to the fuel rail via the outlet valve. The inlet valve is pressed into its seat by the delivery pressure.
• Pump plunger 2 is moved by the tension spring force in the direction of BDC. Due to the high pressure in the fuel rail, the outlet valve is pressed into its seat. The pump internal pressure opens the inlet valve and fuel flows into the high pressure chamber.
The eccentric cam produces a “downward” stroke:
• The process is the reverse to that previously described.
Calibrating the high-pressure pump (fuel metering valve)
After replacing the high pressure pump and/or the PCM the fuel metering valve of the high pressure pump must be calibrated with the aid of WDS.
Denso-Common Rail System – High pressure pump
The diagram shows the high pressure pump in the 2.4L Duratorq-TDCi
A High pressure fuel to fuel rail
B Fuel return
C Fuel feed
1 High-pressure chamber outlet valve
2 High-pressure chamber inlet valve
3 Pump plunger
4 Fuel metering valve return spring
5 Fuel metering valve
6 Pre-pressurize control valve (pump interior pressure)
7 Transfer pump (rotor pump)
8 Fuel inlet
9 Fuel filter
10 Eccentric cam ring
11 Eccentric cam
12 Drive shaft
13 Fuel tank
14 Overflow throttle valve
Design
The high-pressure pump provides the interface between the low and the high pressure systems. Its function is to always provide sufficient compressed fuel under all operating conditions and for the entire service life of the vehicle.
Low-pressure zone:
• The transfer pump draws fuel out of the fuel tank via the fuel inlet.
• The pump internal pressure is adjusted via the admission-pressure control valve. This ensures that sufficient lubrication and cooling are always provided for the high pressure pump components.
Excess fuel is transferred to the inlet side of the transfer pump via the admission-pressure control valve.
• A portion of the fuel is transferred to the fuel metering valve from the transfer pump. The fuel quantity delivered to the high pressure chambers is determined by the opening cross-section of the fuel metering valve.
• The small restriction bore in the overflow throttle valve provides for automatic bleeding of the high pressure pump. The entire low-pressure system is designed to allow a defined quantity of fuel to flow back into the fuel tank via the overflow throttle valve. This assists cooling of the high pressure pump.
High-pressure zone:
– A total of two high pressure chambers, each with one pump plunger, are used for high pressure generation.
– The drive for the pump plungers is via an eccentric cam, which is in turn driven by the drive shaft (principle similar to the Bosch common rail system, see relevant section in this Student Information).
– The high pressure pump permanently generates the high system pressure for the fuel rail.
Denso-Common Rail System – High-pressure system
The illustration shows the system in the 2.4L Duratorq-TDCi
1 High pressure line
2 Leak-off pipe
3 Fuel injection line
4 Fuel injector
5 Pressure limiting valve
6 Fuel rail
7 Fuel metering valve
8 Fuel pressure sensor
9 Fuel temperature sensor
10 High pressure pump
11 Fuel return
High-pressure line and injector tubes
NOTE: The bending radii are exactly matched to the system and must not be changed.
NOTE: After disconnecting one or more high pressure fuel lines, these must always be replaced. Reason: The reason for this is that leaks can occur when re-tightening, due to distortion of the connections of the old lines.
The high-pressure fuel lines connect the high-pressure pump to the fuel rail and the fuel rail to the individual fuel injectors.
Fuel pressure sensor
The fuel pressure sensor must not be replaced separately in the event of a fault. The whole fuel rail must always be replaced in the event of a fault.
Fuel injectors
When replacing one (or more) fuel injector(s) this must be signaled to the PCM through the input of a 16-digit code. This code is located in the head area of the fuel injector.
High pressure system leak test
After working on the high-pressure system (e.g. after replacing a fuel injector or after replacing the high pressure pump or the injector tubes) a high-pressure system leak test must be conducted with the aid of WDS.
Denso-Common Rail System – Fuel filter
1 Fuel return (to the fuel filter)
2 Fuel return (to the fuel tank)
3 Fuel feed (to the high-pressure pump)
4 Air cleaner element minder gauge
5 Water-in-fuel sensor (certain markets only)
6 Water drain screw
7 Water-in-fuel sensor wiring harness
8 Fuel feed (from the fuel tank)
The fuel heater functions in a similar way to that in the Delphi common rail system via a bi-metal controlled control valve.
Denso-Common Rail System – Fuel system
A Fuel return from high-pressure pump
B High pressure line
C Fuel injection line
D Leak-off pipe
E Fuel return to fuel tank
F Fuel feed
1 High pressure pump
2 Fuel rail
3 Fuel injector
4 Pressure limiting valve
5 T-piece
6 Fuel tank
7 Fuel pump and filling level sensor unit
8 Fuel filter
Function
The fuel is drawn from the fuel tank via the fuel filter by means of the transfer pump integrated in the high pressure pump. The high-pressure pump compresses the fuel and forces it into the fuel rail. The fuel pressure required for any given situation is available for the fuel injectors for each injection process. Oil leaking from the fuel injectors and/or returning fuel from the high pressure pump are fed back into the fuel tank.
Possible causes of defects in fuel pipes and the fuel tank
Fuel lines may be blocked due to foreign bodies or bending. In addition, blocked parts and lines of the low-pressure system can cause air to enter the low-pressure system on account of the increased vacuum in the system. Air can also enter the low pressure system through loose or leaking pipe connections. Faulty valves or pipes in the tank venting system can impair the flow of fuel through the low-pressure system.
Effects in case of faults (low pressure system contains air or is blocked)
Poor engine starting when warm or cold
Irregular idling
Engine does not start.
Engine starts, but cuts out again immediately afterwards.
Engine has insufficient power.
Note: At a certain residual fuel amount, the PCM causes the engine to judder. The intention is to draw the driver’s attention to the fact that the vehicle must urgently be refueled.
Diagnostic information: If the system causes the engine to judder because the fuel tank is empty, the EOBD is deactivated during this phase. This prevents apparent faults from being displayed.
Denso-Common Rail System – Fuel injector solenoid valve
1 PCM
2 Coil
3 Solenoid armature
4 Solenoid valve
The fuel injectors are each fitted with one solenoid valve. Actuation for fuel metering is carried out by the PCM.
Current is applied to the solenoid valves in two stages. At the beginning of an injection process, the solenoid valve is actuated with a higher pick-up current so that it opens quickly.
After a short period of time, the pick-up current is reduced to a low holding current.
Effects of faults
rough engine running,
increased emissions of black smoke,
loud combustion noise
reduced power output
Diagnosis
The monitoring system is able to identify two types of malfunctions via several electrical tests.
• Fuel metering fault of all fuel injectors,
• Fuel metering fault of a single fuel injector.
The PCM detects malfunctions based on the power consumption of the solenoid valves.
Deviations from the tolerance range result in uncontrollable fuel metering. This means that the injected quantity and the injection timing cannot be determined exactly (see Possible consequences of faults).
In addition, the fuel injectors are checked for short circuit and open circuit.
Components significant for emissions:
• Yes (MIL-active), if engine continues to run.
• No (Non MIL active), if the engine is stopped.
Denso-Common Rail System – Fuel metering valve
A Fuel metering valve opened to maximum
B Fuel metering valve opened to minimum
V Voltage
a Low duty cycle
b High duty cycle
1 Transfer pump
2 Fuel metering valve
3 Fuel flow to the high-pressure chambers
Function
NOTE: The fuel metering valve operates together with the fuel pressure sensor (on the fuel rail) in a closed control loop.
NOTE: The fuel metering valve is fully open when de-energized.
The fuel quantity that passes to the high pressure chambers of the high pressure pump is dependent on the opening cross section of the fuel metering valve.
The opening cross-section is determined by the PCM via the duty cycle of the PWM signal:
• Low duty cycle: large aperture cross-section
• High duty cycle: small aperture cross-section
Effects of faults
In the event of malfunctions: Injected quantity = 0 (engine cuts out or cannot be started.)
Diagnosis
The monitoring system checks:
• the circuit for short circuits and open circuit.
• the fuel metering valve for correct function; the values of the fuel pressure sensor are used for this purpose. The currently measured values from the fuel pressure sensor are continuously compared with the map data. Slight deviations are indicated as control faults whereupon:
– the quantity of fuel injected is reduced and
– the pilot injection is deactivated.
• whether serious deviations exist. They are indicated as a malfunction whereupon
– the quantity injected is set to 0 and the engine is stopped.
Note: Control faults do not necessarily mean a defective fuel metering valve or a defective high pressure pump. A blocked fuel low pressure system or defective fuel injectors could (among other things) also be the cause.
Emissions-related component (vehicles with EOBD):
• Yes (MIL-active), with control faults
• No (Non MIL active), with malfunctions.
Denso-Common Rail System – Electrical turbocharger guide vane adjustment actuator
1 Electrical turbocharger guide vane adjustment actuator
2 Variable geometry turbocharger
In this system, a simplified electrical turbocharger guide vane adjustment actuator is used. The integral electronics in the actuator unit are no longer required.
This means
• that the DC motor is actuated directly by the PCM.
• that the position of the guide vanes is detected directly via the position sensor by the PCM.
1 Connection 1: DC motor (+)
2 Connection 2: DC motor (–)
3 Connection 3: Position sensor (–)
4 Connection 4: PWM position sensor output signal
5 Connection 5: Position sensor reference voltage
6 PCM
7 DC motor
8 Position sensor (breakerless)
9 Electrical turbocharger guide vane adjustment actuator
The inductive (breakerless) position sensor transmits PWM signals to the PCM. The duty cycle is determined by the position of the guide vanes.
Duty cycle of the position sensor:
• with minimum opening of the guide vanes (maximum boost pressure): approx. 90 %
• with maximum opening of the guide vanes (minimum boost pressure): approx. 10 %