| 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. The light load piston ( 26 ) is carried within a cold cranking sleeve ( 120 ) which is slidable within the first bore ( 14 ) against the action of a cold cranking control spring ( 128 ) in response to fuel pressure variations within a cold cranking control chamber ( 134 ). Thus, the cranking control spring ( 128 ) acts, in use, to slide the cold cranking sleeve ( 120 ) a predetermined distance in the advance direction and fuel pressure variations within the control chamber ( 134 ) serve to slide the cold cranking sleeve ( 120 ) back in the retard direction.
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