Land Rover Common Rail System Crs Denso Manual
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Operation Section1–46 4. RAIL DESCCRIPTION 4.1 Rail Functions and Composition zThe function of the rail is to distribute fuel pressurized by the supply pump to each cylinder injector. zThe shape of the rail depends on the model and the component parts vary accordingly. zThe component parts are the rail pressure sensor (Pc sensor), pressure limiter, and for some models a flow damper and pressure discharge valve. 4.2 Component Part Construction and Operation Component PartsFunctions Rail Stores pressurized fuel that has been pumped from the supply pump and distrib- utes the fuel to each cylinder injector. Pressure Limiter Opens the valve to release pressure if the pressure in the rail becomes abnormally high. Rail Pressure Sensor (Pc Sensor) Detects the fuel pressure in the rail. Flow Damper Reduces the pressure pulsations of fuel in the rail. If fuel flows out excessively, the damper closes the fuel passage to prevent further flow of fuel. Mostly used with engines for large vehicles. Pressure Discharge Valve Controls the fuel pressure in the rail. Mostly used with engines for passenger cars. Rail Rail Pressure LimiterPressure Limiter Rail Pressure Sensor (Pc Sensor) Rail Pressure Sensor (Pc Sensor)Flow Damper Pressure Discharge Valve Q000854E
Operation Section1–47 (1) Pressure Limiter • The pressure limiter opens to release the pressure if abnormally high pressure is generated. If pressure within the rail becomes abnormally high, the pressure limiter operates (opens). It resumes operation (closes) after the pressure falls to a certain level. Fuel released by the pressure limiter returns to the fuel tank. < NOTE > The operating pressures for the pressure limiter depend on the vehicle model and are approximately 140-230MPa for the valve opening pressure, and approximately 30-50MPa for the valve closing pressure. (2) Rail Pressure Sensor (Pc Sensor) • The rail pressure sensor (Pc sensor) is installed on the rail. It detects the fuel pressure in the rail and sends a signal to the engine ECU. This is a semi-conductor sensor that uses the piezo-electric effect of the electrical resistance vary- ing when pressure is applied to a silicon element. • There are also rail pressure sensors that have dual systems to provide a backup in case of breakdown. The output voltage is offset. Pressure LimiterLeak (To Fuel Tank) Valve Open Valve Close Rail PressureAbnormally High Pressure Return Q000855E GNDVout Sensor Wiring Diagram Common Rail Pressure Characteristic Output Voltage - Rail PressureOutput Voltage Vcc +5V ECU PcVout Vcc=5V GND VoutVcc Q000856E Q000857E E2S PR2 VCS VC PR E2 Pc Sensors VC VCS PR2PR E2 E2S+5V ECU ECUVout/Vcc Vcc=5V Rail Pressure Output Voltage 1 Output Voltage 2
Operation Section1–48 (3) Flow Damper • The flow damper reduces the pressure pulsations of the fuel in the pressurized pipe and supplies fuel to the injectors at a stabilized pressure. The flow damper also presents abnormal discharge of fuel by shutting off the fuel passage in the event of excess fuel discharge, for example due to fuel leaking from an injection pipe or injector. Some flow dampers combine a piston and ball, and some have only a piston. Operation of Piston-and-Ball Type - When a pressure pulse occurs in a high-pressure pipe, the resistance of it passing through the orifice disrupts the balance between the rail side and injector side pressures, so the piston and ball move to the injector side, absorbing the pressure pulse. With normal pressure pulses, since the rail side and injector side pressures are soon balanced, the piston and ball are pushed back to the rail side by the spring. If there is an abnormal discharge, for example due to an injector side fuel leak, the amount of fuel passing through the orifice cannot be balanced out and the pis- ton presses the ball against the seat, so the passage for fuel to the injector is shut off. Operation of Piston-Only Type - The piston contacts the seat directly and the piston shuts off the fuel passage directly. Operation is the same as for the piston-and-ball type. Q000858E Piston Ball SeatSpring Piston Spring Seat Type Combining Piston and Ball Piston-Only Type Q000859E · During Pressure Pulse Absorption · Fuel Cut-Off Piston Ball SeatSpring Q000860E · During Pressure Pulse Absorption · Fuel Cut-Off Piston SpringSeat
Operation Section1–49 (4) Pressure Discharge Valve • The pressure discharge valve controls the fuel pressure in the rail. When rail fuel pressure exceeds the target injection pressure, or when the engine ECU judges that rail fuel pressure exceeds the target value, the pressure discharge valve solenoid coil is energized. This opens the pressure discharge valve passage, allowing fuel to leak back to the fuel tank, and reducing rail fuel pressure to the target pressure. Q000861E Pressure Discharge Valve Rail ON ECU To Fuel tank Operating Solenoid Coil
Operation Section1–50 5. INJECTOR DESCRIPTION 5.1 General Description zThe injector injects the pressurized fuel in the rail into the engine combustion chamber at the optimal injection timing, injection quantity, injection rate, and injection pattern, in accordance with signals from the ECU. zInjection is controlled using a TWV (Two-Way Valve) and orifice. The TWV controls the pressure in the control chamber to control the start and end of injection. The orifice controls the injection rate by restraining the speed at which the nozzle opens. zThe command piston opens and closes the valve by transmitting the control chamber pressure to the nozzle needle. zWhen the nozzle needle valve is open, the nozzle atomizes the fuel and injects it. zThere are three types of injectors: the X1, X2, and G2. Q000862E ECU Supply Pump Nozzle Command PistonControl Chamber Portion OrificeTWV Rail Rail Pressure SensorNozzle Needle
Operation Section1–51 5.2 Injector Construction and Features zThe injector consists of a nozzle similar to the conventional nozzle & nozzle holder, an orifice that controls the injection rate, the command piston, and a TWV (two-way solenoid valve). The basic construction is the same for the X1, X2, and G2 types. (1) X1 Type • Precision control is attained through electronic control of the injection. The TWV comprises two valves: the inner valve (fixed) and the outer valve (movable). Q000863E Nozzle Command Piston TWV Solenoid Orifice 1 Orifice 2 Inner Valve Outer Valve
Operation Section1–52 (2) X2 Type • By reducing the injector actuation load, the injector has been made more compact and energy efficient, and its injec- tion precision has been improved. The TWV directly opens and closes the outlet orifice. Control Chamber Solenoid Va l v e Hollow Screw with Damper O-ring Command Piston Nozzle Spring Pressure Pin Nozzle Needle Seat High-Pressure Fuel Leak PassageFrom Rail Q000864E
Operation Section1–53 (3) G2 Type • To ensure high pressure, the G2 type has improved pressure strength, sealing performance and pressure wear re- sistance. It also has improved high-speed operability, enabling higher-precision injection control and multi-injection. < NOTE > Multi-injection means that for the purpose of reducing exhaust gas emissions and noise, the main injection is accom- plished with one to five injections of fuel without changing the injection quantity. Q000865E Connector Solenoid Valve Command Piston Nozzle Spring Pressure Pin Nozzle Needle SeatLeak Passage From Rail To Fuel Tank Example : Pattern with Five Injections Time Pre-Injection Pilot InjectionAfter-Injection Main Injection Post-Injection Injection Quantity Q000866E
Operation Section1–54 5.3 Injector Operation zThe injector controls injection through the fuel pressure in the control chamber. The TWV executes leak control of the fuel in the control chamber to control the fuel pressure within the control chamber. The TWV varies with the injector type. Non-Injection • When the TWV is not energized, the TWV shuts off the leak passage from the control chamber, so the fuel pressure in the control chamber and the fuel pressure applied to the nozzle needle are both the same rail pressure. The nozzle needle thus closes due to the difference between the pressure-bearing surface area of the command piston and the force of the nozzle spring, and fuel is not injected. For the X1 type, the leak passage from the control chamber is shut off by the outer valve being pressed against the seat by the force of the spring, and the fuel pressure within the outer valve. For the X2/G2 types, the control chamber outlet orifice is closed directly by the force of the spring. Injection • When TWV energization starts, the TWV valve is pulled up, opening the leak passage from the control chamber. When this leak passage opens, the fuel in the control chamber leaks out and the pressure drops. Because of the drop in pressure within the control chamber, the pressure on the nozzle needle overcomes the force pressing down, the nozzle needle is pushed up, and injection starts. When fuel leaks from the control chamber, the flow quantity is re- stricted by the orifice, so the nozzle opens gradually. The injection rate rises as the nozzle opens. As current continues to be applied to the TWV, the nozzle needle eventually reaches the maximum amount of lift, which results in the max- imum injection rate. Excess fuel is returned to the fuel tank through the path shown. End of Injection • When TWV energization ends, the valve descends, closing the leak passage from the control chamber. When the leak passage closes, the fuel pressure within the control chamber instantly returns to the rail pressure, the nozzle closes suddenly, and injection stops. Q000867E Outer Valve Injection Rate Control Chamber PressureControl Chamber PressureControl Chamber Pressure Solenoid TWV Outlet Orifice Inlet Orifice Command Piston Nozzle Injection RateInjection Rate Non-Injection Injection End of Injection Rail X1 X2 · G2 Outlet OrificeActuating CurrentActuating Current Actuating CurrentInner Valve To Fuel Tank Leak Passage Leak Passage TWV
Operation Section1–55 5.4 Injector Actuation Circuit zIn order to improve injector responsiveness, the actuation voltage has been changed to high voltage, speeding up both solenoid magnetization and the response of the TWV. The EDU or the charge circuit in the ECU raises the respective battery voltage to approximately 110V, which is supplied to the injector by signal from the ECU to actuate the injector. Q000868E INJ#1 (No.1 Cylinder) ECU InjectorINJ#2 (No.3 Cylinder) INJ#3 (No.4 Cylinder) INJ#4 (No.2 Cylinder) Charging Circuit IJt IJf EDU Actuating Current ECU Actuating Current ECU Direct Actuation EDU Actuation 2WV#3 (No.3 Cylinder) 2WV#4 (No.6 Cylinder) 2WV#5 (No.2 Cylinder) 2WV#6 (No.4 Cylinder) InjectorCommon 2 Common 1 2WV#1 (No.1 Cylinder) 2WV#2 (No.5 Cylinder) Constant Amperage Circuit High Voltage Generation Circuit Control Circuit Constant Amperage Circuit Constant Amperage Circuit High Voltage Generation Circuit