Improvements to advance arrangement

摘要

An advance arrangement for use in controlling timing of fuel delivery by a fuel pump for use in an engine comprises an advance piston (12) which is slidable within a first bore (14) and which cooperates, in use, with a cam arrangement of a fuel pump to adjust the timing of fuel delivery by the pump. A surface associated with the advance piston (12) is exposed to fuel pressure within a first control chamber (38). The pressure of fuel within the first control chamber (38) is controlled by means of a servo piston (24) which is slidable within a further bore (22) provided in the advance piston (12). The servo piston (24) is responsive to speed dependent fuel pressure variations within a servo control chamber (37), thereby to permit adjustment of the timing in response to engine speed. A light load piston (26) is moveable relative to the advance piston (12) against the action of a light load control spring (28) in response to load dependent fuel pressure variations within a light load control chamber (60), thereby to adjust the timing under light load conditions.