Fuel pump relay
The V8 engine uses a closed fuel supply system. Regardless of the intake manifold pressure, the fuel system maintains a constant fuel pressure of 4 bar. Fuel is supplied to the injectors by means of a fuel priming pump located in the fuel tank. Power is supplied to the fuel priming pump controlled by the ECM (the engine control unit) through a power relay and an inertial switch that cuts off the fuel supply in the event of a collision. Fuel system pressure builds up immediately after ECM power is turned on (the engine control unit) , then the fuel priming pump is turned off until the engine starts.
Viscous fan control
ECM block (the engine control unit) regulates engine cooling by controlling a viscous fan. To control fan performance, the ECM (the engine control unit) uses PWM (pulse width modulation) -signals by controlling the coefficient of clutch slippage. The EMS fan speed is determined by a Hall effect sensor. For more information refer to Engine Cooling (303-03B Engine Cooling - 4.4L)
Valve timing mechanism (VVT)
To improve the performance of the engine in the zone of low and high speeds and increase the stability of idling, the engine uses variable valve timing.
The single intake camshaft timing mechanism consists of the following components:
- Clutch mechanism VVT
- Phase control solenoid valve
The VVT system reverses the intake valve timing with respect to the fixed exhaust valve timing in order to regulate:
- Weight filling of engine cylinders.
- Engine torque.
- OG toxicity.
A vane-type hydraulic clutch is used to change the camshaft angle. The angular position of the shaft can vary in the range of 48 degrees. The shaft phases change in the direction of delay or advance, taking the optimal value in the specified range.
ECM block (the engine control unit) controls the VVT system based on engine load, engine speed, and engine oil temperature.
Using the VVT system provides the following benefits:
- Reduced exhaust emissions and reduced fuel consumption, which in turn improves the efficiency of internal EGR recirculation (exhaust gas recirculation) over a wider range of engine operation.
- Improved external torque characteristic.
- Reduced fuel consumption due to improved torque characteristics across the entire speed range.
Clutch mechanism VVT
To control the position of the intake camshaft, a hydraulic clutch is used, mounted on its toe. The clutch moves the camshaft forward or backward relative to the crankshaft. To control the VVT clutch, the ECM (the engine control unit) uses electromagnetic hydraulic valve. A spool type solenoid valve directs pressurized oil into either the advanced or retard chambers of the clutch.
The VVT clutch is driven by the primary timing chain and can change its position relative to the exhaust camshaft. When the ECM (the engine control unit) requires to reduce the timing of the camshaft, the solenoid valve is turned on, moving the spool to a position in which the oil leaves the advance chambers and at the same time oil under pressure enters the retard chambers.
ECM block (the engine control unit) adjusts the advance or retard of the shaft based on engine load and crankshaft speed. ECM block (the engine control unit) keeps the solenoid valve energized until the camshaft reaches its desired position. When the camshaft reaches a predetermined position, the valve supply is limited to the level of maintaining the reached position. This process occurs in closed-loop control mode when the ECM (the engine control unit) «recognizes» about all changes in oil pressure in the spool valve according to the signals of the camshaft position sensor and regulates the power of the electromagnet to maintain the set position.
The operation of the VVT mechanism is affected by the temperature of the oil and its properties. At low oil temperatures, due to its high viscosity, the VVT mechanism will slowly adjust the shaft position. At high oil temperatures, the quality of the VVT mechanism can be adversely affected by a decrease in oil viscosity. The oil pump output is large enough to fend off changes in oil properties, and the oil temperature sensor constantly tells the ECM (the engine control unit) data for the necessary correction. When the ECM oil temperature is extremely high (the engine control unit) can impose a limit on the amount of phase advance so that the engine does not stall when idling.
The VVT mechanism stops working if the oil pressure does not exceed 1.25 bar. This is because the pressure is not high enough to release the VVT clutch from the inner locking pin. This happens when the engine is turned off and the clutch returns to its most retarded position. The locking pin secures the position of the clutch so that the camshaft maintains a stable position during the next start. For more information refer to Engine (303-01B Engine - 4.4L)
Phase control solenoid valve
The phase control solenoid valve controls the position of the spool relative to the sleeve. The solenoid valve stem extends when power is turned on and retracts when power is turned off.
When the solenoids are de-energized, coil springs in the bushings hold the spools in position to drain oil from the hydraulic couplings. Return springs located in the hydraulic couplings hold the camshafts in the retarded position. When the ECM (the engine control unit) supplies power to the solenoid valves, their stems set the spools in the position of supplying engine oil to the hydraulic couplings. The oil pressure overcomes the resistance of the return springs in the couplings and displaces the annular piston in the advance direction. The system enters the lead position in no more than 1.0 s, and in the retard position - no more than 0.7 s. When the clutches are in the retard position, the ECM (the engine control unit) periodically gives orders to perform lubrication. In this case, a short-term power pulse is applied to the solenoid valve, which causes a short injection of oil into the clutch. Such pulsating lubrication is performed every five minutes.
Exhaust gas Recirculation valve (EGR)
EGR valve (exhaust gas recirculation) is an electrically controlled valve that is designed to bypass the exhaust gas back into the engine. EGR valve (exhaust gas recirculation) opens and closes with a stepper motor. Since exhaust gases contain very little free oxygen, they are practically inert. Exhaust gas takes the place of air in the combustion chamber, which reduces the maximum combustion temperature. Reducing the maximum combustion temperature leads to a decrease in the formation of nitrogen oxides (NOx).
EGR valve (exhaust gas recirculation) located on the intake manifold and connected by a tube to the exhaust manifold. The connection to the wiring harness is made via a 6-pin connector. For more information refer to Engine Emission Control (303-08B)
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