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. Advance Required characteristics Required characteristics . Coolant A :Sub Port Improving cold startability C : Thermo -element Injection Timing At cold start B : Sub Lead Main Port At no load Main Lead Piston At full load Rated Barrel Reduction of noise & NOx Plunger Retard Reduction of white smoke Pump speed 20 Hydraulic control device of injection timing (Speed timer,Load timer,Cold start timer) Timing Control Device