Timer Mechanism; Structure And Functions; Pump Speed - Takeuchi TB 175 Handbuch

2.6. Timer Mechanism

When the engine is used in a wide range from low to high speeds, it is necessary to change the fuel injection timing
according to the engine speeds for always keeping the optimum firing timing. It is also necessary to optimize the
injection timing for reducing noise and exhaust gas emissions.
This pump has the timer mechanism for revolutions, load and cold starting.

2.6.1. Structure and Functions

The engine speed timer is the mechanical timer which uses the oil leakage from the small diameter sub spill port installed
slightly upper side of the main spill port of the jerk pump. When the engine speed is high, pressure rises before oil leaks
from the small diameter port and injection is started. But when the engine speed is low, pressure does not rise until the
port blocked by the plunger and the injection start is delays. Usually, the lower the engine speed, further the injection
timing advances. But this engine speed timer prevents the injection timing from advancing during the low engine speed
ranges and thus the noise and Nox. emissions can be controlled.
The fewer the injection amount, the earlier the load timer causes the main port to close by the plunger's upper lead for
advancing the injection timing. This feature is instrumental in preventing misfire or emission of bluish white smoke during
low load operation.
The cold start timer causes the sub port to be blocked only under cold temperatures for accelerating injection timing and
facilitating in cold starting. The timer houses the thermo element and cooling water circulates around the temperature
sensing section. The thermo-element senses the coolant temperature for adjusting the control piston. The sub-port is
blocked when the temperature is lower than the set temperature and the pressure is raised earlier than in the normal
temperature for advancing the injection timing. When the temperature exceeds the set temperature, the sub-port is
opened and the regular injection characteristics are recovered.
Hydraulic control device of injection timing
Hydraulic control device of injection timing
(Speed timer,Load timer,Cold start timer)
(Speed timer,Load timer,Cold start timer)
Advance
Retard
Required characteristics
Required characteristics
Improving cold startability
At cold start
At no load
At full load
Reduction of noise & NOx
Reduction of white smoke

Pump speed

A :Sub Port
B : Sub Lead
Main Port
Main Lead
Rated
20
Timing Control
Device
Coolant
.
C : Thermo
-element
Piston
Barrel
Plunger