Valve assembly for a fuel pump
A valve assembly for a fuel pump for a fuel system, the fuel pump comprising a pump chamber and the valve assembly comprising a solenoid winding; and an electromagnetically controlled armature operable under the influence of an electromagnetic field generated by applying a current to the solenoid winding. The armature is coupled to a valve member cooperable with a valve seat to control fuel flow, and the armature is movable within an armature bore and is exposed to fuel within an armature chamber defined within the armature bore. The valve assembly includes a clearance defined between the armature and the armature bore which defines a variable restriction to the fuel flow, whereby during armature movement in use the fuel is displaced from the armature chamber through the variable restriction so that the speed of movement of the armature is reduced as the armature moves further into the armature chamber.
1 . A valve assembly for a fuel pump for a fuel system, the fuel pump comprising a pump chamber, and the valve assembly comprising:
a solenoid winding;
an electromagnetically controlled armature operable under the influence of an electromagnetic field generated by applying a current to the solenoid winding, the armature being shaped to have an outer surface of variable diameter including a tapered region, and the armature being coupled to a valve member which is cooperable with a valve seat to control fuel flow into and out of the pump chamber,
an armature chamber defined within an armature bore; and
an armature lift stop defined within the armature chamber;
wherein:
the armature is movable within the armature bore towards and away from the armature lift stop and is exposed to fuel within the armature chamber,
the armature lift stop serves to limit the extent of movement of the armature into the armature chamber,
the tapered region of the armature and the armature bore defining a variable clearance flow path out of the armature chamber which varies through the range of travel of the armature within the armature chamber so as to define a variable restriction to the fuel flow out of the armature chamber, and
the variable clearance flow path reduces in size as the armature moves towards the armature lift stop,
whereby during armature movement in use the fuel is displaced from the armature chamber through the variable clearance flow path so that the speed of movement of the armature is reduced as the armature moves further into the armature chamber towards the armature lift stop.
2 . The valve assembly as claimed in claim 1 , wherein the tapered region reduces the diameter of the armature from a smaller diameter at one end of the armature to a larger diameter in a central region of the armature.
3 . The valve assembly as claimed in claim 2 , including a tapered region on each side of the central region so that the upper and lower ends of the armature are of reduced diameter compared to the central region.
4 . The valve assembly as claimed in claim 3 , wherein the outer surface of the armature includes a central region of enlarged diameter.
5 . The valve assembly as claimed in claim 4 , wherein the outer surface of the armature is of reduced diameter on both upper and lower sides of the central region.
6 . The valve assembly as claimed in claim 1 , wherein the armature has an outer surface of constant diameter and wherein the armature bore is shaped to have a variable internal diameter.
7 . The valve assembly as claimed in claim 1 , wherein the armature bore is shaped to have a variable internal diameter.
8 . A fuel pump comprising a valve assembly as claimed in claim 1 .