Engine fuel metering system

Claim 1

A fuel metering system for varying the supply of fuel to an engine comprising a fuel tank, a first fuel pump having an inlet connected to the fuel tank and an outlet connected to an inlet of a second fuel pump, the second fuel pump being of the fixed displacement type, delivery control means being connected to an outlet of the second fuel pump to control the amount of fuel supplied to the engine and to divert fuel in excess to the engine requirements back to the inlet of the second pump, the second pump being driven at a speed proportional to the speed of the engine, the first pump being selectively driven by either a mechanical drive between the first and second pumps or by a variable drive, automatic clutch means being provided which operates in response to the difference between the rotational speeds of the first and second pumps to selectively connect the mechanical drive between the first and second pumps, whereby in operation if the delivery control means detects that the fuel delivered by the first and second fuel pumps is required by the engine the automatic clutch means engages to provide a direct mechanical drive between the first and second pumps so that the first pump is driven at the same speed as the second pump, however if the delivery control means detects that the first and second pumps are delivering fuel in excess to the engine requirement the automatic clutch means disengages and the fuel in excess to the engine requirements is diverted, the energy of the diverted fuel being used to drive the variable drive of the first pump at a speed higher than the speed of the second pump.