Advance arrangements

An advance arrangement for use in controlling timing of fuel delivery by a fuel pump for use in an engine comprising;

• 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) being exposed to fuel pressure within a first control chamber (38) and the advance piston (12) being slidable within the first bore (14) in either an advance or a retard direction to advance or retard, respectively, the timing of the fuel pump delivery,
• a servo piston (24) which is slidable within a further bore (22) provided in the advance piston (12) to control the pressure of fuel within the first control chamber (38), the servo piston (24) being 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, and
• a light load piston (26) moveable relative to the advance piston (12) against the action of a light load control spring (28) in response to fuel pressure variations within a light load control chamber (60),
• wherein the light load piston (26) is carried within a cold cranking sleeve (120), the cold cranking sleeve (120) being 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) such that 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.