Fuel supply systems for internal combustion engines

Claim 2

A fuel supply system for an engine, comprising in combination a pump for supplying fuel to the engine, pump control means for controlling the output of the pump, a first summing amplifier to which are fed electrical signals representing the demanded and actual values of pump output, the first summing amplifier comparing the signals and producing an output for controlling the pump control means, a second summing amplifier to which are fed electrical signals representing engine speed, pump output, and a reference, and a discriminator coupling the first and second summing amplifiers to the pump control means, the output from the discriminator at any given instant being the output from the summing amplifier which demands the least fuel, so that the second summing amplifier limits the maximum speed of the engine but varies the maximum speed of the engine in accordance with the pump output, said summing amplifiers each having a feedback path incorporating a resistor, and each of said feedback paths being taken from the input to the pump control means.

Claim 3

A system as claimed in claim 1. including means for limiting the maximum output of the pump.

Claim 4

A system as claimed in claim 2, in which said means acts by restricting the demand signal to a predetermined level.

Claim 5

A system as claimed in claim 1, in which the discriminator comprises a pair of diodes through which the outputs of the amplifiers are fed to the pump control means, whereby at any given moment one of the diodes will be conducting and will reverse bias the other diode.

Claim 6

A system as claimed in claim 1 in which the maximum output of the pump is controlled, but the system includes circuit means having a first state and a second state, said circuit means when in its second state increasing the maximum output of the pump, said circuit means being driven to its second state when the engine speed is below cranking speed and being driven to its first state when the engine speed is above a datum speed, the datum speed being in excess of the cranking speed.

Claim 7

A system as claimed in claim 5, in which the datum speed at which excess pump output is terminated is set by a bistable circuit forming part of said circuit menas and the cranking speed at which excess pump output is permitted again is set by a control circuit which until the engine speed falls to cranking speed holds the bistable circuit in a state to prevent excess pump output.

Claim 8

A system as claimed in claim 6, in which said control circuit becomes operative when the engine speed is above cranking speed, and when operative is capable of holding the bistable circuit in a state to prevent excess pump output, but not of driving the bistable circuit to a state to prevent excess pump output.

Claim 9

A system as claimed in claim 5, in which the circuit means incorporates a bistable circuit switching to the first state at said datum speed, and by virtue of its own differential switching back to the second state at the cranking speed.

Claim 10

A system as claimed in claim 6, in which the engine drives a vehicle and an accelerator pedal is provided for setting said demand signal, said circuit means being driven to its second state only when the engine speed is below cranking speed and the accelerator pedal is depressed beyond a predetermined position, and the circuit means being driven to its first state when either the engine speed is above the datum speed, or the pedal is not depressed beyond said predetermined position.

Claim 11

A system as claimed in claim 11, in which excess pump output is permitted only if the engine temperature is below a predetermined value.

Claim 12

A system as clAimed in claim 1, including means for maintaining said circuit means in its first state between the datum and cranking speeds even if the supply to the circuit means becomes momentarily disconnected between the datum and cranking speeds.

Claim 13

A system as claimed in claim 11, in which said means includes a capacitor.

Claim 14

A system as claimed in claim 1, in which the engine has an air intake manifold and the maximum pump output is controlled but is modified in accordance with the pressure of the air in said intake manifold.

Claim 15

A system as claimed in claim 1, in which the first and second summing amplifiers are each operational amplifiers having an inverting input and a non-inverting input, and the signals fed to the summing amplifiers representing the demanded and actual values of pump output, engine speed and said reference are in the form of currents fed to the inverting input of the appropriate summing amplifier.

Claim 16

A system as claimed in claim 14 in which the feedback network of the amplifier includes a capacitor for modifying the d.c. gain of the amplifier.

Claim 17

A fuel injection system for a diesel engine, comprising in combination a pump for supplying fuel to the engine, an electromechanical actuator coupled to the pump to control the pump output, a drive circuit for controlling the electromechanical actuator, first, second and third transducers producing respectively output voltages representing engine speed, pump output and throttle position, a first operational amplifier connected as a summing amplifier and having its inverting input connected through resistors to the second and third transducers, said first amplifier producing an output representing the difference between the actual and demanded pump outputs, a second operational amplifier connected as a summing amplifier and having its inverting input connected through resistors to the first and second transducers, and a discriminator coupling the amplifier producing the greater output to the drive circuit, the arrangement being such that until a predetermined engine speed is attained, the discriminator couples the first amplifier to the drive circuit, but when said predetermined engine speed is reached, the discriminator couples the second amplifier to the drive circuit to limit the maximum engine speed, the maximum engine speed being varied with pump output by the second amplifier.

Claim 18

A fuel injection system for a diesel engine, comprising in combination a pump for supplying fuel to the engine, an electromechanical actuator coupled to the pump to control the pump output, a drive circuit for controlling the electromechanical actuator, first, second and third transducers producing respectively output voltages representing engine speed, pump output and throttle position, a first operational amplifier connected as a summing amplifier and having its inverting input connected through resistors to the second and third transducers, said first amplifier producing an output representing the difference between the actual and demanded pump outputs, a second operational amplifier connected as a summing amplifier and having its inverting input connected through resistors to the first and second transducers, and a discriminator coupling the amplifier producing the greater output to the drive circuit, the arrangement being such that until a predetermined engine speed is attained, the discriminator couples the first amplifier to the drive circuit, but when said predetermined engine speed is reached, the discriminator couples the second amplifier to the drive circuit to limit the maximum engine speed, the maximum engine speed being varied with pump output by the second amplifier.

Claim 19

A system as claimed in claim 16, in which the discriminator comprises a pair of diodes, one coupling each of the amplifiers to the drive circuit, and the resistive feedback paths of the two amplifiers are taken from the input to the drive circuit.

Claim 20

A fuel supply system for an engine as claimed in claim 1, a transistor which receives an input representing engine speed and conducts at a predetermined engine speed, and circuit means selectively connectible to said transistor so as alternatively to increase or decrease the maximum pump output when the transistor conducts.

Claim 21

A system as claimed in claim 18 in which the maximum pump output is modified above a predetermined engine speed.

Claim 22

A fuel supply system for an engine as claimed in claim 1, comprising means associated with said first summing amplifier for limiting the maximum pump output, and a control network to which an electrical signal dependent on engine speed is applied, said control network including a transistor which is turned on at a predetermined engine speed and when conductive modifies the input to the first summing amplifier to modify the maximum pump output.

Claim 23

A fuel system as claimed in claim 1, for a compression-ignition engine, in which each feedback circuit includes a capacitor in series with said resistor.