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Tất cả tài liệu về bơm ECD-V (tài liệu đào tạo của Denso ECD): -Composition and Construction of ECD-V3 Pump System -Determining the Injection Timing -ECD-V Series -ECD-V4 Outline -ntake Restriction Control -Outline of Injection Ti
9SERVICE TECH Vol.469 03-12 The engine ECU judges the engine conditions and driving status of the vehicle based on the information receivedfrom the sensors. This is used to calculate the optimum fuel injection timing for the engine. The ECU then sends asignal to the timing control valve (TCV) of the injection pump. The main injection timing items are: The engine ECU calculates the injection timing based on the information from the sensors (computer control), so itis possible to control injection timing with a far greater accuracy than with the distributor type pump of conventionalmechanical types • Starting advance control • Cold temperature advance control• Engine speed injection timing control • Load condition injection timing control• Intake pressure injection timing control11Outline of Injection Timing Control 10SERVICE TECH Vol.469 03-12 In order to change the injection timing, the amount of fuel pressure added to the timer piston of the injection pump iscontrolled, and the position of the piston is varied. The movement of the timer piston rotates the roller ring via the slidepin. As a result, the position of the roller relative to the cam plate is changed, which varies the timing of the start ofinjection. The control of injection timing when the timing control valve is ON is explained below. The control when the timingcontrol valve is switched between ON/OFF is explained in section 3-2 Timing Control Valve (TCV).22Basic Control Method for Injection Timing When the pressure is low in the high pressure chamber side, the timer piston is pushed in the direction ofinjection retard by the timer spring.Timing ControlValveRoller RingRetard Tim ing : Timing Control Valve is widely open.Timer PistonTimer SpringLow PressureSideHigh Pressure Chamber(Inside Pump Chamber)ON Time: LongRetardSlide PinEngine ECUCam Plate When the pressure is increased in the high pressure chamber it overcomes the strength of the spring andmoves in the advance direction.A dvance Tim ing : Timing Control Valve is almost closed.ON Time: ShortAdvanceLow PressureSideEngine ECU 11SERVICE TECH Vol.469 03-12 The crankshaft position sensor is an electromagnetic pick-up type sensor for detecting the crankshaft position ofthe engine. It is installed on the engine cylinder block, and through the projection installed on the crankshaft, itgenerates a pulse for every revolution of the engine. This pulse is used as a "standard crankshaft position" signalin order to control injection timing. One pulse of the crankshaft position signal is generated for every revolution of the engine (360° CA). On the otherhand during the same period the injection pump completes 1/2 a revolution (180° PA), and if the engine has 4cylinders a pulse equivalent to 2 cylinders is output by the engine speed sensor. (The position of the engine speedsensor changes according to the injection timing, so the actual relative position varies with the engine conditions.)The actual injection timing is calculated from these two signals, which the engine ECU compares with the targetinjection timing. With the crankshaft position sensor signal as a standard, the angle (°CA) up to the position of the certain pulse ofthe engine speed sensor signal determined by each engine is calculated as the actual injection timing.33Construction and Operation of Components3-1 Crankshaft Position SensorProjectionCrankshaft Position SensorRelationship between the crankshaft position sensor signal and the engine speed sensor signalEngine Speed SensorCrankshaft Position Sensor 12SERVICE TECH Vol.469 03-12 The timing control valve is an electromagnetic valve that opens and closes the fuel passages to the high pressureand low pressure side of the timer piston, according to actuating signals from the engine ECU. The opening degreeof these passages is controlled by the ON/OFF rate (duty ratio) of the current energized by the coil. When thecurrent is ON for a long time, the open time of the TCV becomes longer. This causes a lot of fuel to leak from thehigh pressure chamber side to the low pressure chamber side. The pressure of the high pressure chamber sideis reduced so the timer piston loses out to the strength of the timer spring, and it moves to the retard side.Duty Ratio Expresses the ratio between energized (ON) and non-energized (OFF) electricity. The ratio is calculatedfrom the following formula, dividing the length of theON time (t) by the unit of time (T) In the figure on the left, the ON time is longer so theTCV passage is open for a long period, and the timerpiston moves to the retard side.3-2 Timing Control Valve (TCV)Timer PistonTiming Control ValveHigh Pressure ChamberTimer SpringON Duty Ratio: Minimum AdvanceON Duty Ratio: Maximum RetardCoilLow Pressure SideMoving CoreSpringHigh Pressure Chamber(Inside Pump Chamber)CoilLow Pressure SideMoving CoreSpringFuel ValveHigh Pressure Chamber(Inside Pump Chamber)Fuel ValveDuty Ratio = × 100 (%)tT . the timing of the start ofinjection. The control of injection timing when the timing control valve is ON is explained below. The control when the timingcontrol. change the injection timing, the amount of fuel pressure added to the timer piston of the injection pump iscontrolled, and the position of the piston is