(57) A fuel pump comprising a plurality of radially spaced pumping arrangements (10a,
10b, 10c), each of which includes a pumping plunger (20a, 20b, 20c) which is reciprocable
within a plunger bore (19a, 19b, 19c) formed in a pump housing (18) under the influence
of a respective driven tappet member (24a, 24b, 24c) which acts to transmit a force
to the pumping plunger (20a, 20b, 20c) during a forward stroke thereof. The plunger
bore (19a, 19b, 19c) defines a pumping chamber (22a, 22b, 22c) within which pressurisation
of fuel to a relatively high level occurs upon reciprocal movement of the pumping
plunger within the plunger bore. An end region of the tappet member (24a, 24b, 24c)
is provided with a further bore (70a, 70b, 70c), a surface associated with the end
region of the tappet member (24a, 24b, 24c) defining, in part, an annular auxiliary
pumping chamber (40a, 40b, 40c) for fuel, the further bore (70a, 70b, 70c) defining
a working chamber (51a, 51b, 51c) arranged to receive fuel to generate a force on
the tappet member (24a, 24b, 24c) which acts in a return direction so as to increase
the volume of the pumping chamber (22a, 22b, 22c) during a return stroke of the pumping
plunger. The fuel pump further comprises a transfer pressure flow path (43) providing
communication between the auxiliary pumping chamber (40a, 40b, 40c) of a first pumping
arrangement (10a) and the pumping chamber (22b, 22c) of at least one of the other
pumping arrangements (10a, 10b) such that fuel displaced from the auxiliary pumping
chamber (40a, 40b, 40c), in use, can be supplied through the transfer pressure flow
path (43) to said at least one of the other pumping chambers (22b, 22c). The auxiliary
pumping chambers (40a, 40b, 40c) and the transfer pressure flow path (43) are constructed
and adapted to ensure fuel flows through the transfer pressure flow path (43) at a
substantially constant flow rate for a given speed of rotation of the pump.
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