8/12/2019 Denso Avance

1/4

8/12/2019 Denso Avance

2/410SERVICE 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 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).

22 Basic Control Method for Injection Timing

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 etard 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 vance T im ing : Timing Control Valve is almost closed.

ON Time: Short

Advance

Low Pressure

Side

Engine

ECU

8/12/2019 Denso Avance

3/411 SERVICE 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, 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 otherhand 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.

33 Construction and Operation of Components

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

8/12/2019 Denso Avance

4/412SERVICE TECH Vol.469 03-12

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 theON 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

ON Duty Ratio: Minimum AdvanceON Duty Ratio: Maximum Retard

Coil

Low Pressure Side

Moving Core SpringHigh 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