GB2262133A

GB2262133A - I.c. engine fuel injection pumping apparatus

Info

Publication number: GB2262133A
Application number: GB9126039A
Authority: GB
Inventors: Kenneth Maxwell Harris; Mark Andrew Stead
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1991-12-07
Filing date: 1991-12-07
Publication date: 1993-06-09
Also published as: GB9126039D0

Abstract

A low pressure pump 11 supplies fuel at a pressure depending upon the engine speed to a high pressure pump 10. The pump 10 has a fuel control means 14 which is responsive to the movement of a piston 20 which is biased by a spring and is movable by the fuel pressure developed by the pump 11. When the cold engine is at rest the fuel control means allows an excess of fuel to be supplied to the engine for starting purposes but when the engine is started the piston is moved from the end of its cylinder 21 to reduce the amount of fuel which can be supplied. In order to prevent the supply of excess fuel when the engine is hot, a stop element 30 is movable by a temperature responsive memory spring 35 into the path of the piston 20 to prevent the return of the piston to the end of the cylinder when the engine is stopped. <IMAGE>

Description

FUEL PUMPING APPARATUS This invention relates to a fuel pumping apparatus for supplying fuel to an internal combustion engine and of the kind comprising a high pressure pump having an outlet from which fuel is displaced to the engine, a low pressure pump which supplies fuel to the high pressure pump and fuel control means including a fuel pressure actuated member which is responsive to the pressure of fuel developed by the low pressure pump and which moves in response to the speed of the engine to vary the maximum amount of fuel which can be supplied by the apparatus to the engine, said member when the engine is at rest, moving to a position so that an excess amount of fuel can be supplied to the engine for starting purposes.

The supply of excess fuel to a compression ignition engine is a well known measure to facilitate starting of the engine from cold. The supply of excess fuel in the type of apparatus set out above continues only until the output pressure of the low pressure pump has built up sufficiently to move the aforesaid member against the action of a spring. Thereafter the engine governor will determine the amount of fuel supplied to the engine in accordance with the demand set by the engine operator, with the aforesaid member determining the maximum amount of fuel which can be supplied to the engine.

When the engine is hot the supply of excess fuel to facilitate starting of the engine is not required and supplying excess fuel in this situation is not only wasteful of fuel but also produces excessive exhaust emissions.

The object of the present invention is to provide an apparatus of the kind specified in a simple and convenient form.

According to the invention an apparatus of the kind specified comprises a stop element movable from an inoperative position to an operative position in which it lies in the path of movement of said fuel pressure actuated member so as to prevent movement of the member to the position at which an excess of fuel can be supplied to the engine, and a temperature responsive memory spring which expands when a predetermined temperature is reached, said memory spring being coupled to said stop element so that when the temperature of the memory spring is below said predetermined temperature the stop element will be moved to the inoperative position.

An apparatus in accordance with the invention will now be described with reference to the accompanying drawing a portion of the apparatus being seen in diagrammatic form.

Referring to the drawing the apparatus comprises a high pressure pump 10 to which fuel is supplied by a low pressure pump 11 which is more generally known as the transfer pump. Both pumps are driven in timed relationship with the associated engine and the output pressure of the low pressure pump is controlled by a valve 12 which interconnects the inlet and outlet of the pump. The outlet pressure of the low pressure pump varies in accordance with the speed at which the associated engine is driven. The high pressure pump is provided with outlets 13 which are connected in use to the injection nozzles of the associated engine.

Moreover, a fuel control means 14 is provided the purpose of which is to spill at each delivery stroke, a predetermined volume of fuel from the pumping chamber of the high pressure pump 10. In this way the amount of fuel which is supplied to the associated engine can be carefully controlled.

An arm or follower 16 is provided which is pivotally mounted on a pivot 15 and which engages with a cam profile 17 which is formed on a fuel pressure actuated member 18 axially slidable within a bore 19 of the housing of the apparatus. The follower 16 is connected by a linkage 37 to the control means 14 and its position determines the maximum amount of fuel which can be supplied to the associated engine. The member 18 is movable by fuel under pressure from the low pressure pump 11 which acts upon the right hand end as seen in the drawing, of a piston 20 slidable within a bore 21 of a sleeve 22 which is secured in the housing.The initial movement of the piston 20 and the fuel pressure actuated member 18 is against the action of a first coiled compression spring 23 which is partly accommodated within a recess in the member 18 and which engages a movable abutment plate 24 which is urged into contact with a step 25 in the housing, by means of a further coiled compression spring 26.

The cam profile 17 includes an excess fuel portion 27 with which the follower 16 engages when the engine is at rest and as is illustrated in the drawing. The excess fuel portion 27 positions the follower 16 so that an excess of fuel can be supplied to the associated engine for starting purposes. When the engine has started the piston 20 under the action of the fuel under pressure delivered by the low pressure pump 11, moves the member 18 towards the left against the action of the spring 23 and in so doing the arm 16 follows the cam profile and moves in the anti-clockwise direction therefore reducing the maximum amount of fuel which can be supplied to the engine. A differential valve can be provided intermediate the outlet of the low pressure pump and the cylinder containing the piston 20 so as to ensure that the piston will not move whilst the engine is being cranked.The cam follower 16 then engages an intermediate portion 28 of the cam profile and this is shaped to provide what is known in the art as torque control. When the engine has started the piston 20 moves the member 18 into engagement with the abutment plate 24 and thereafter it is the force exerted by the spring 26 which has to be opposed by the piston to move the member 18. The piston 20 and the spring 26 together with the cam profile therefore provide torque control and the cam profile is chosen to ensure that at any given engine speed the maximum amount of fuel can be supplied to the associated engine without emission of smoke from the engine exhaust.

The supply of excess fuel is beneficial when the engine is cold in order to achieve starting of the engine. When the engine is hot however the provision of excess fuel is not necessary. Nevertheless, with the apparatus so far described, excess fuel will be supplied whether the engine is hot or cold. In order to prevent the supply of excess fuel when the engine is hot, a stop element 30 is provided and this is located in a bore 31 formed in the housing and which extends transversely to the axis of movement of the piston 20. The stop element 30 can move through an aperture 32 formed in the sleeve 22, into the path of the piston. The stop element is biased outwardly by a coiled compression spring 33 one end of which engages against a shoulder 34 secured to the stop element. The stop element is movable against the action of the spring 33 by a temperature responsive memory spring 35 one end of which engages the shoulder 34. When the temperature of the spring 35 is below a predetermined value, the spring contracts and this allows the stop element 30 to move under the action of the spring 33. On the other hand, when the temperature of the spring 35 exceeds a predetermined value the spring extends and will move the stop element against the action of the spring 33. As shown the spring 35 is in its contracted state and the stop element is in an inoperative position. When the engine starts the piston will move towards the left as described but as the temperature to which the spring 35 is subjected increases, and the predetermined temperature is attained, the stop element 30 will move into the path of the piston.This however does not prevent the piston and the member 18 providing the torque control function.

However, once the engine is hot and is stopped, the piston 20 will be unable to move under the action of the spring 23 to the excess fuel position so that excess fuel will not be supplied when the engine is started. On the other hand if the engine is halted for some considerable time, and cools down sufficiently so that the temperature of the spring 35 falls below the predetermined temperature, the spring 33 will move the stop element 30 out of the operative position thereby allowing the piston 20 to move under the action of the spring 23, thereby causing the portion 27 of the cam profile to engage and move the follower 16 so that an excess of fuel will be supplied to the engine on starting.

The springs 33 and 35 are located in a chamber 36 in the housing and this chamber is connected by means of a passage, with the end of the cylinder containing the piston, so that the pressure within the chamber is the same as the pressure which is applied to the piston. In this way the stop element 30 is pressure balanced.

Claims

1. A fuel pumping apparatus for supplying fuel to an internal combustion engine and comprising a high pressure pump having an outlet from which fuel is displaced to the engine, a low pressure pump which supplies fuel to the high pressure pump, fuel control means including a fuel pressure actuated member which is responsive to the pressure of fuel developed by the low pressure pump and which moves in response to the speed of the engine to vary the maximum amount of fuel which can be supplied by the apparatus to the engine, said member when the engine is at rest, moving to a position so that an excess amount of fuel can be supplied to the engine for starting purposes, a stop element movable from an inoperative position to an operative position in which it lies in the path of movement of said fuel pressure actuated member so as to prevent movement of the member to the position at which an excess of fuel can be supplied to the engine, and a temperature responsive memory spring which expands when a predetermined temperature is reached, said memory spring being coupled to said stop element so that when the temperature of the memory spring is below said predetermined temperature the stop element will be moved to the inoperative position.

2. An apparatus according to Claim 1, in which said stop element is biased by resilient means to the inoperative position.

3. An apparatus according to Claim 2, in which said fuel pressure actuated member comprises a piston slidable within a cylinder and said stop element is movable to its operative position through an aperture in the wall of said cylinder.