Fuel System Component Description
Fuel System Component DescriptionInjector
Electronic control type injectors controlled by the engine control module (ECM) are used. Compared with conventional injection nozzles, a command piston, solenoid valve, etc. are added.
ID codes displaying various injector characteristics are laser marked in the plate, and 10 codes showing these in numeric form (30 alphanumeric figures are displayed and only 24 are used) are laser marked in the plate. This system uses fuel injector flow rate information (10 codes) to optimize injection quantity control. When an injector is newly installed in a vehicle, it is necessary to input the 10 codes in the ECM.
QR (Quick Response) codes or fuel injector flow rate (10 codes) have been adopted to enhance the injection quantity precision of the injectors. The adoption of codes enables injection quantity dispersion control throughout all pressure ranges, contributing to improvement in combustion efficiency, reduction in exhaust gas emissions and consistent horsepower throughout the vehicle built.
1. Non-injection state
The two way valve (TWV) closes the outlet orifice by means of a spring force, when no current is supplied from the engine control module (ECM) to the solenoid. At this time, the fuel pressure applied to the nozzle leading end is equal to the fuel pressure applied to the control chamber through the inlet orifice. As for the force competition in this state, the pressure on the command piston upper surface + nozzle spring force defeat the pressure on the nozzle leading end, and consequently the nozzle is pushed downward to close the injection holes.
2. Injection start
The TWV is pulled up to open the outlet orifice, and thus the fuel leaks toward the return port, when the current is supplied from the ECM to the solenoid. As a result, the nozzle is pushed up together with the command piston by the fuel pressure applied to the nozzle leading end, and then the nozzle injection holes open to inject the fuel.
3. Injection end
The TWV lowers to close the outlet orifice, when the ECM shuts off a current supply to the solenoid. As a result, the fuel cannot leak from the control chamber, and thus the fuel pressure in the control chamber rises abruptly and then the nozzle is pushed down by the command piston to close the nozzle injection holes, resulting in the end of fuel injection.
Fuel Supply Pump
The fuel supply pump is the heart of the common rail type electronic fuel injection system. The fuel supply pump is installed at the same location as the conventional injection type pump, which spins at a 1 to 1 ratio of fuel supply pump to crankshaft speed. A fuel rail pressure (FRP) regulator and fuel temperature sensor are part of the fuel supply pump assembly.
Fuel is drawn from the fuel tank via the fuel supply pump by the use of an internal feed pump (trochoid type). This feed pump pumps fuel into a 2-plunger chamber also internal to the fuel supply pump. Fuel into this chamber is regulated by the FRP regulator solely controlled by current supplied from the engine control module (ECM). No current to the solenoid results in maximum fuel flow whereas full current to the solenoid produces no fuel flow. As the engine spins, these two plungers produce high pressure in the fuel rail. Since the ECM controls the flow of fuel into this 2-plunger chamber, it therefore controls the quantity and pressure of the fuel supply to the fuel rail. This optimizes performance, improves economy and reduces NOx emissions.
Fuel Rail (Common Rail)
Along with the employment of a common rail type electronic control fuel injection system, the fuel rail is provided to store high pressure fuel between supply pump and injectors. A pressure sensor and a pressure limiter are installed on the fuel rail. The pressure sensor detects the fuel pressure inside the fuel rail and sends its signal to the engine control module (ECM). Based on this signal, the ECM controls the fuel pressure inside the fuel rail via the fuel rail pressure (FRP) regulator of the fuel supply pump. The pressure limiter opens the valve mechanically to relieve the pressure when the fuel pressure inside the fuel rail is excessive.
Flow Damper
The flow dampers are installed at the outlet of the fuel rail to dumper the pulsation of fuel pressure inside the fuel rail or to cut off the fuel supply when the fuel leaks downstream of the flow damper. The fuel is supplied to the injectors through an orifice of the piston. The pressure pulsation occurring in the fuel rail is dampered by a resistive force of the return spring and a passing resistance of the orifice, wherein the piston acts as a damper. Also, the leading end of the piston closes the fuel supply port to cut off the fuel supply, if the fuel leak occurs in the injection pipe or injectors. Since the fuel pressure on the downstream side of the flow damper supplied through an orifice + resistive force of return spring do not balance, the fuel pressure applied on the piston surface prior to the orifice will allow the fuel to be cut off. The piston will return when the fuel pressure inside the fuel rail is less than 145 psi (1.0 MPa).
Fuel Rail Pressure Sensor
Refer to Engine Control Component Description.
Pressure Limiter
The pressure limiter relieves pressure by opening the valve if abnormally high pressure is generated. The valve opens when pressure in the rail reaches approximately 29000 psi (200 MPa), and closes when pressure falls to approximately 8700 psi (60 MPa). Fuel leakage through the pressure limiter re-turns to the fuel tank.
Fuel Rail Pressure (FRP) Regulator
The engine control module (ECM) controls the duty ratio of the linear type fuel rail pressure (FRP) regulator (the length of time that the current is applied to the FRP regulator), in order to control the quantity of fuel that is supplied to the high-pressure plungers. Since only the quantity of fuel that is required for achieving the target rail pressure is drawn in, the drive load of the supply pump is decreased.
When current flows to the FRP regulator, variable electromotive force is created in accordance with the duty ratio, moving the armature to the left side. The armature moves the cylinder to the left side, changing the opening of the fuel passage and thus regulating the fuel quantity. With the FRP regulator OFF, the return spring contracts, completely opening the fuel passage and supplying fuel to the plungers (Full quantity intake and full quantity discharge). When the FRP regulator is ON, the force of the return spring moves the cylinder to the right, closing the fuel passage (normally opened). By turning the FRP regulator ON/OFF, fuel is supplied in an amount corresponding to the actuation duty ratio, and fuel is discharged by the plungers.