Fuel System
- Connector.
- Fuel rail
- Sensor, fuel pressure high pressure circuit
- High pressure line
- High pressure pump
- Fuel pump
- Fuel pump module
- Low pressure line
- Sensor, fuel pressure low pressure circuit
- Injector
Overview
The main components of the fuel system are:
- High pressure pump with control valve, fuel flow
- Fuel rail
- Sensor, fuel pressure high pressure circuit
- Injector
- Sensor, fuel pressure low pressure circuit
- Fuel pump, low pressure
The fuel pressure in the fuel rail is approx. 11 MPa (110 bar) at idle and varies at other loads between 2 MPa to 20 MPa (200 bar).
To accurately control injection at idle, relatively high pressure is required. This is to obtain a correct predetermined injection amount at short injection times under 1 ms.
If the fuel pressure in the fuel rail exceeds 23 MPa (230 bar), a safety valve opens in the high pressure pump and the fuel is routed to the inlet side (low pressure side).
In general, the greater the load the higher the fuel pressure. The principle of regulation is based on a calculation model in the engine control module (ECM). Based on the driver's torque request, the following occurs: Air request → measured quantity of air → desired fuel quantity → desired fuel pressure → measured fuel pressure → gives desired fuel quantity through injection timing.
Sensor, fuel pressure, high pressure side
The sensor is included as a unit in the fuel rail. The seal against the fuel rail is a "metal against metal" seal.
The pressurized fuel acts on a diaphragm, which in turn, via the oil, acts against a "sensor chip". The "chip" converts pressure into an electrical variable of 5 V that informs the engine control module (ECM) about the current fuel pressure. The sensor must not be removed from the fuel pipe. In the event of a faulty probe, the fuel rail must be replaced.
Sensor, fuel pressure, low pressure side
The sensor is a piezoresistive sensor that is powered with 5 V by the engine control module (ECM). The signal to the engine control module (ECM) is an analogue voltage signal between 0.5 - 4.5 V. The signal is a feedback to the engine control module (ECM) stating that control of the fuel pump via the fuel pump module is correct. The pressure to the high pressure pump is approx. 300-620 kPa (3 to 6.2 bar) relative pressure, depending on driving conditions and fuel temperature.
PEM (Pump Electronic Module)
The engine control module (ECM) sends a request to the fuel pump module about the desired fuel pressure as a 12 V PWM signal. The fuel pump module then controls the pump's rotation speed as well via the 12 V PWM signal.
High pressure pump
- Camshaft
- Cam followers
- Cam, high pressure pump
- Vacuum pump
- O-ring
- Control valve, fuel flow
- Inlet
- Exhaust
The high pressure pump is installed on the vacuum pump housing. The high pressure pump's pumping action is achieved by a reciprocating piston. The piston rolls against a cam with four lobes. The cam is driven by the exhaust camshaft, which also operates the vacuum pump. A camshaft revolution thus gives four strokes. The cam lobes' lift height is 4 mm. The capacity per stroke is 0.283 cm3 (283 mm3).
The function of the high pressure pump is to control and create a pressure as high as is needed to enable the injectors to inject correct fuel volume in the combustion chamber during a certain time. Thus, the high pressure pump pressurizes the fuel to the fuel rail and then via injectors injects fuel into the combustion chamber. The high pressure pump is all stainless steel and does not have internal O-ring seals, which makes it even more durable. The pump can handle a system pressure of up to 20 MPa (200 bar).
Control valve, fuel flow
- Return spring
- Coil
- Anchor
- Cover
- Pulsation damper
- Outlet valve
- Piston
- Return spring
- PRV (Pressure Relief Valve), safety valve
- Return spring
- Inlet valve
The effective pump stroke is regulated through the control valve, fuel flow, on the high pressure pump in order to supply the correct amount of fuel to the fuel rail. The valve is controlled by the engine control module (ECM) via a 12 V PWM signal. The pump piston position is calculated by the engine control module (ECM) based on the signals from the exhaust camshaft and crankshaft position sensor. The fuel pump in the tank supplies the high-pressure pump with a pressure of approx. 300-620 kPa (3 to 6.2 bar) relative pressure. The pulsation damper contains a gas that compensates the fuel volume changes and pressure shocks through the pulsation damper's corresponding change in volume.
Inlet phase
- Control valve, fuel flow
- Piston
- Outlet valve
The piston (2) moves down through the spring. The area above the piston increases in volume, whereupon, by the fuel pump in the tank, the pressurized fuel flows in through the open control valve (1). The outlet valve (3) is closed. The control valve, fuel flow, consists of an electric coil that axially moves a bar, which, in turn, affects a valve. No power when the valve is open. When the engine control module (ECM) powers the coil, the valve closes.
Pressure phase, step 1
The cam lobes push the piston up. The area above the piston reduces in volume. As long as the control valve, fuel flow, is open, the fuel flows back to the fuel inlet. The surplus fuel is taken care of by the pulsation damper. The outlet valve is closed since the fuel pressure in the fuel rail is greater than the fuel pressure in the pump.
Pressure phase, step 2
When the engine control module (ECM) closes the control valve, fuel flow, the pressure rises above the piston. When the pressure exceeds the pressure in the fuel rail, the outlet valve opens and the fuel flows into the fuel rail. By regulating the effective pump stroke, the fuel rail supplies the amount of fuel required to keep the pressure at the desired level.