Bơm ECD-V - P - Outline of Injection Timing Control

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

The engine ECU judges the engine conditions and driving status of the vehicle based on the information received from the sensors This is used to calculate the optimum fuel injection timing for the engine The ECU then sends a signal 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 it

is possible to control injection timing with a far greater accuracy than with the distributor type pump of conventional mechanical types

.

• Starting advance control • Cold temperature advance control

• Engine speed injection timing control • Load condition injection timing control

• Intake pressure injection timing control

In order to change the injection timing, the amount of fuel pressure added to the timer piston of the injection pump is controlled, and the position of the piston is varied The movement of the timer piston rotates the roller ring via the slide pin As a result, the position of the roller relative to the cam plate is changed, which varies the timing of the start of injection

The control of injection timing when the timing control valve is ON is explained below The control when the timing control valve is switched between ON/OFF is explained in section 3-2 Timing Control Valve (TCV)

When the pressure is low in the high pressure chamber side, the timer piston is pushed in the direction of injection retard by the timer spring

Timing Control Valve

Roller Ring

R e ta rd T im in g : Timing Control Valve is widely open.

Timer Piston

Timer Spring

Low Pressure

Side

High Pressure Chamber (Inside Pump Chamber)

ON Time: Long

Retard

Slide Pin

Engine ECU

Cam Plate

When the pressure is increased in the high pressure chamber it overcomes the strength of the spring and moves in the advance direction

A d va n ce T im in g : Timing Control Valve is almost closed.

ON Time: Short

Advance

Low Pressure

Side

Engine

The crankshaft position sensor is an electromagnetic pick-up type sensor for detecting the crankshaft position of the engine It is installed on the engine cylinder block, and through the projection installed on the crankshaft, it generates a pulse for every revolution of the engine This pulse is used as a "standard crankshaft position" signal

in order to control injection timing

One pulse of the crankshaft position signal is generated for every revolution of the engine (360° CA) On the other hand during the same period the injection pump completes 1/2 a revolution (180° PA), and if the engine has 4 cylinders a pulse equivalent to 2 cylinders is output by the engine speed sensor (The position of the engine speed sensor 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 target injection timing

With the crankshaft position sensor signal as a standard, the angle (°CA) up to the position of the certain pulse of the engine speed sensor signal determined by each engine is calculated as the actual injection timing

3-1 Crankshaft Position Sensor

Projection

Crankshaft Position Sensor

Relationship between the crankshaft position sensor signal and the engine speed sensor signal

Engine Speed Sensor

Crankshaft Position Sensor

The timing control valve is an electromagnetic valve that opens and closes the fuel passages to the high pressure and low pressure side of the timer piston, according to actuating signals from the engine ECU The opening degree

of these passages is controlled by the ON/OFF rate (duty ratio) of the current energized by the coil When the current is ON for a long time, the open time of the TCV becomes longer This causes a lot of fuel to leak from the high pressure chamber side to the low pressure chamber side The pressure of the high pressure chamber side

is 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 calculated

from the following formula, dividing the length of the

ON time (t) by the unit of time (T)

.

In the figure on the left, the ON time is longer so the TCV passage is open for a long period, and the timer piston moves to the retard side

3-2 Timing Control Valve (TCV)

Timer Piston

Timing Control Valve

High Pressure Chamber

Timer Spring

Coil Low Pressure Side

Moving Core Spring

High Pressure Chamber

(Inside Pump Chamber)

Coil

Low Pressure Side

Moving Core Spring

Fuel Valve

High Pressure Chamber (Inside Pump Chamber)

Fuel Valve

Duty Ratio =   × 100 (%)t

T