Patent ID: 6883499
Filing Date: 2005-04-26
Classification: F02D,F02M

Abstract:
1. An advance arrangement for use in controlling timing of fuel delivery by a fuel pump, the advance arrangement comprising; an advance piston which is moveable within a first bore to adjust the timing of fuel delivery a surface associated with the advance piston being exposed to fuel pressure within an advance piston control chamber, a servo-piston which is slidable within a further bore provided in the advance piston to control the pressure of fuel within the advance piston control chamber, a surface associated with the servo-piston being exposed to fuel pressure within a servo control chamber, and a non-drift arrangement for preventing fuel pressure variations in the advance piston control chamber due to fuel leakage causing the advance piston to drift whilst the servo control piston remains in a substantially fixed position relative to the advance piston or the cam box housing; wherein the advance piston is provided with a fill passage which is brought into communication with the servo control chamber upon movement of the servo-piston in a direction to advance timing, thereby to permit fuel within the servo control chamber to flow into the advance piston control chamber; and wherein the non-drift arrangement is arrange to maintain a negative net leakage flow into the advance piston control chamber for any position of the servo-piston in which the servo control chamber communicates with the advance piston control chamber through the fill passage.