Advance arrangement

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

• an advance piston which is slidable within a first bore 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 being exposed to fuel pressure within a first 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 first control chamber, the servo piston being responsive to speed dependent fuel pressure variations within a servo control chamber, thereby to permit adjustment of the timing in response to engine speed;
• a light load piston moveable relative to the advance piston against the action of a light load control spring in response to fuel pressure variations within a light load control chamber;
• and
• an arrangement for ensuring the servo piston is substantially unresponsive to speed dependent fuel pressure variations within the servo control chamber, in circumstances in which fuel pressure within the light load control chamber is increased beyond a predetermined amount;
• wherein the light load control chamber is provided with a restricted outlet arrangement to permit fuel within the list load control chamber to flow to a low pressure fuel reservoir at a restricted rate, and further comprising further adjuster for adjusting the effective restriction to fuel flow provided by the restricted outlet arrangement;
• and
• wherein the further adjuster comprises a valve member arranged within an additional bore, whereby adjustment of the position of the valve member within the additional bore permits the diameter of the first restricted outlet to be varied.

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

• an advance piston which is slidable within a first bore 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 being exposed to fuel pressure within a first control chamber, a piston moveable relative to the advance piston against the action of a control spring in response to fuel pressure variations within a control chamber, a supply passage for supplying fuel at a signal pressure to the control chamber, wherein the supply passage communicates with a flow path between a source of fuel at transfer pressure and a low pressure drain;
• an adjuster to permit adjustment of the extent of travel of the piston;
• and
• a control valve arrangement, operable to vary the rate of flow of fuel through the flow path and, hence, to vary the signal pressure, wherein the control valve arrangement is arranged in the flow path at a position upstream of the supply passage.