Injection timing control device for distributor-type fuel injection pumps

An injection timing control device for combination with a fuel injection pump of the type including a pumping and distributing plunger, and a roller holder carrying a plurality of rollers circumferentially arranged and disposed in camming engagement with an end face of said plunger, said injection timing control device comprising:

• a cylinder;
• a timer piston slidably received within said cylinder, said timer piston being coupled to said roller holder such that displacement thereof causes a corresponding change in the circumferential position of said roller holder;
• a first chamber defined at one end of said timer piston;
• a second chamber defined at another opposite end of said timer piston, said second chamber communicating with a zone under lower pressure;
• a timer spring accommodated within said second chamber and axially urging said timer piston;
• a passageway formed in said timer piston for supplying said first chamber with fuel pressure variable as a function of the rotational speed of an internal combustion engine associated with said fuel injection pump;
• and
• servo valve means arranged within said timer piston and across said passageway, said servo valve means being actuatable in response to said fuel pressure variable as a function of the rotational speed of said engine;
• said servo valve means being automatically displaceable relative to said timer piston in response to a change in said fuel pressure, to open said passageway at a first predetermined position thereof to allow feeding of said fuel pressure to said first chamber for displacement of said timer piston in an injection timing advancing direction, to open said passageway at a second predetermined position thereof to allow escape of fuel pressure in said first chamber to said zone under lower pressure for displacement of said timer piston in an injection timing retarding direction, and to close said passageway at a third predetermined position thereof to hold said timer piston stationary;
• said servo valve means comprising:
• a valve bore axially formed in said timer piston;
• a valve body slidably fitted in said valve bore, said valve bore having end faces, an outer peripheral surface formed with a land and first and second annular grooves arranged in axial juxtaposition, said valve body being arranged to be urged at one of said end faces thereof by said fuel pressure variable as a function of the engine rotational speed, said first annular groove being disposed to communicate with a suction chamber of said fuel injection pump to be supplied with fuel pressure variable as a function of the engine rotational speed, said second annular groove communicating with said second chamber;
• a servo spring disposed to urge another of said end faces of said valve body against said fuel pressure variable as a function of the engine rotational speed;
• a spring seat on which said servo spring is seated, said spring seat having an axis and a spirally extending end face remote from said servo spring;
• and
• an adjusting member arranged rotatably and eccentrically with respect to the axis of said spring seat and having an end disposed in urging contact with said spiral end face of said spring seat;
• whereby said adjusting member, when rotated about said axis of said spring seat, causes a change in the axial position of said spring seat to thereby vary the setting load of said servo spring;
• said valve body being disposed such that said passageway encounters said first annular groove at said first predetermined position of said servo valve means, said second annular groove at said second predetermined position of said servo valve means, and said land at said third predetermined position of said servo valve means, respectively.