GB2292423A - Pump for fuel injection - Google Patents

Abstract

A fuel supply pump of the rotary distributor fuel-injection type is provided with an electromagnetically operable control valve (30) which when opened allows fuel at high pressure to trigger the operation of a spill valve member (22, 23) to terminate delivery of fuel by the pump. The control valve includes a multipart body (32, 33), which is held in assembled relationship by bolts and the body is held in position against a location in a housing part of the pump by means of a coiled compression spring (38) which acts between the body and a further part of the housing. <IMAGE>

Description

PUMP This invention relates to a pump, and particularly to a fuel pump for use in the distribution of fuel to the cylinders of a diesel engine.

A known type of pump for supplying fuel to an internal combustion engine comprises a plunger reciprocable within a bore, a cam for imparting inward movement to the plunger, an outlet from the bore and through which fuel can flow through a delivery passage to an outlet port of the apparatus, a valve seating defined about a spill passage connected to the bore, a piston slidable within a cylinder, a valve member defined on the piston, the valve member being shaped for cooperation with the seating and being urged into engagement therewith by resilient means, and means for applying fluid pressure to said piston to lift the valve member from the seating thereby to spill fuel from the bore, the spilled fuel flowing into said cylinder to assist the movement of the valve member away from the seating.

In order to apply fluid pressure to the piston to spill fuel from the bore, a control valve is provided controlling communication between a first passage arranged to receive fluid from the delivery passage at high pressure and a second passage arranged to communicate such high pressure fluid to the piston. The control valve commonly comprises an electromagnetically operated valve including a reciprocable control valve member arranged to move within a bore extending within the housing of the control va!ve, although other types of control valve may be used. !n order to prevent undesired spilling of fuel from the bore, the control valve member must be a very good fit within the bore, leakage of fuel around the valve member possibly resulting in the application of a sufficient pressure to the piston in order to cause spilling of fuel.

The control valve is commonly secured in position by means of bolts extending through the housing of the control valve and engaging in threaded bores provided in the pump housing. If the end face of the control valve housing or the mating portion of the pump housing are not constructed accurately, or if the bolts are not tightened to the correct torque, the bore of the control valve tends to distort resulting in poor performance of the valve. In addition, since the bolts used to secure the control valve to the pump housing also secure the various parts of the control valve to one another, the control valve must be assembled during assembly of the pump rather than separately.

According to the present invention there is provided a pump of the type described above wherein the control valve is secured in position by spring means arranged to engage with the control valve.

The control valve preferably comprises an electromagnetically operated valve.

Conveniently, the spring means comprises a helical compression spring arranged to engage with the control valve and with a further part of the housing of the pump.

The invention will further be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a cross sectional view of a pump in accordance with an embodiment of the invention, and Figure 2 is a perspective view of the control valve used in the pump of Figure 1.

Referring to Figure 1 the pump comprises a rotary distributor member 10 which is journaled in a fixed sleeve 11 forming part of a body 12. The distributor member in use, is driven in timed relationship with the associated engine. A portion of the distributor member extends from the sleeve and there is formed therein a transverse bore 13 in which is mounted a pair of pumping plungers 14. In the particular example, which shows a pump for supplying fuel to a four cylinder engine, a further transverse bore is provided and a further pair of plungers are located therein in order to increase the pumping capacity of the apparatus. The bores are disposed at right angles to each other and the inner portions of the bores communicate with a longitudinal passage 15 extending within the distributor member and communicating with an outwardly extending delivery passage 16.Four equi-angularly spaced, radially extending inlet passages 16A also communicate with the longitudinal passage 15.

The plungers 14 are arranged to be moved inwardly by the action of cam lobes formed on the internal peripheral surface of a cam ring which surrounds the distributor member and during the inward movement of the plungers 14, the delivery passage 16 registers with one of a plurality of outlet ports 17 which communicate with outlets 18 in the body, the outlets 18 in use being connected to the injection nozzles of the associated engine.

Axially spaced from the outlet ports 17 is an inlet port 1 7A which communicates with a source of fuel under pressure, conveniently the outlet of a vane pump 1 7B the rotary part of which is coupled to the distributor member. In use, during the whole time the plungers are moved inwardly, the delivery passage 16 is in register with an outlet port 17 and fuel can be supplied to the associated engine. As the distributor member rotates, the delivery passage 16 moves out of register with an outlet port 17 and one of the inlet passages 1 6A moves into register with the inlet port 1 7A so that fuel can now flow to the bores 13 to urge the plungers outwardly by an amount which is determined by the base circle of the cam ring or by stop plates not shown, it being appreciated that cam followers including rollers are interposed between the plungers 14 and the cam lobes.Instead of using separate inlet passages to fill the bores with fuel, the delivery passage may be used in which case four inlet ports are provided in the sleeve axially aligned with the outlet ports and arranged so that the delivery passage alternately registers with an inlet port and then an outlet port.

Formed in the distributor member is a cylinder 19 having an end wall 20 in which is formed a spill passage 21 which communicates with the bores 13. Surrounding the spill passage is a seating which is engaged by a shaped projection 22 extending from an end face of a piston 23 which is slidable within the cylinder. The projection forms a valve member and the piston is biased so that the valve member engages with the seating, by means of a coiled compression spring 24. Formed in the piston is an axially disposed blind drilling 5 which extends towards said end face of the piston and the inner end of the drilling communicates by way of a passage 26 formed in the valve member 22, with the bores 13.

Slidable within the drilling 25 is a plug 27 which is engaged by a stem 28.

The end area of the plug 27 is substantially equal to the area embraced by the line of contact between the seating and the valve member 22 so that the piston is substantially pressure balanced and will be maintained in the position shown in which the valve member is in engagement with the seating, by the force exerted by the spring 24. In use, in order to effect movement of the piston 23 against the action of the spring and thereby to lift the valve member 22 from the seating so as to permit further fuel displaced by the plungers to flow into the annular space surrounding the extension, fuel under pressure is admitted to the aforesaid annular space so that the pressure acting on the end face of the piston which in part defines the annular space, will move the piston against the action of the spring.The flow of fuel into the annular space is conveniently controlled by a control valve assembly generally indicated at 30.

The control valve assembly 30 (See also Figure 2) comprises a valve stem 31 which is slidable in a blind bore provided in a spigot 32. The spigot 32 is shaped so as to engage in a bore provided in the pump housing, the clearance between the spigot 32 and the pump housing being such as to form a substantially fluid tight seal. An electromagnetic actuator for the valve stem 31 is mounted upon the spigot 32, the actuator comprising an E-core 33 having a central bore through which the valve stem 31 extends and a pair of terminals 34 (not shown in Figure 2) for the connection of leads for supplying a current to a winding associated with the core, and an armature 35 which is reciprocable with respect to the core 33 the armature 35 being connected to the valve stem 31 in order to transmit movement of the armature 35 to the valve stem 31.

The control valve assembly 30 further comprises a helical spring 36 arranged to bias the valve stem 31 to its open position, lifting the armature 35 away from the core 33. It will be understood that on applying a current to the core 33, the armature 35 is attracted towards the core 33 against the action of the spring 36, closing the valve, and on removing the current, the valve opens under the action of the spring 36.

The control valve assembly 30 includes a pair of bolts 37 (Figure 2) which extend through the core 33 and into the spigot 32 in order to secure the various parts of the assembly 30 together. It will therefore be understood that the control valve assembly 30 can be constructed completely separately from the assembly of the pump.

In order to secure the control valve assembly 30 to the remainder of the pump, a helical compression spring 38 is provided, the spring 38 engaging in a shallow cylindrical recess provided on the control valve assembly 30, and with an oil cover forming part of the housing of the pump. The use of the spring 38 to secure the control valve assembly 30 allows the forces applied to the control valve assembly 30 to be accurately controlled. Further, the accuracy with which the mating surfaces of the control valve assembly 30 and the pump housing need to be constructed is reduced, simplifying construction of the pump.

Extending from the aforesaid annular space is in the particular example, an axially disposed passage 40 which has a radially disposed portion 41 opening into a peripheral annular passage of the distributor member at a position so that it registers with a first connecting passage 42 formed in the body and sleeve. Also formed in the body and sleeve is a second connecting passage 43 which extends from the periphery of the distributor member and the two connecting passages can be placed in communication with each other by the valve 30. The second connecting passage 43 is positioned to communicate with one of the inlet passages 16A formed in the distributor member which in turn communicates with the longitudinal passage 15.Within the valve assembly 30, the second connecting passage 43 is closed by a valve member 39 provided at the end of the valve stem 31 when the actuator is energised and the spring 36 lifts the valve stem 31 and hence the valve member 39 from its seating to permit flow of fuel into the first connecting passage 42 and through the passage 40 into the annular space when the actuator is deenergised. The flow of electric current to the actuator is controlled by an electronic control system and the actuator is arranged to be de-energised when a pre-determined inward movement of the pumping plungers has taken place. When the actuator is de-energised fuel at high pressure is supplied to the annular space and this acts upon the end face of the piston to move the piston against the action of the spring 24. The initial movement lifts the valve member 22 from the seating and substantially unrestricted flow of fuel can then take place into the annular space by way of the port 21. This flow of fuel results in a reduction in the pressure of fuel and termination of the flow of fuel to the associated engine.

When the crests of the cam lobes are reached the plungers are allowed to move outwardly and the spring 24 urges the piston towards the position in which it is shown. This movement results in displacement of the fuel spilled into the aforesaid space back into the bores 13 to effect outward movement of the plungers. Such fuel as is lost by leakage together with the fuel delivered to the associated engine, is made up by a flow of fue! from the fue! supply pump by way of the inlet port 1 7A and one of the inlet passages.

Claims (2)

1. A fuel supply pump for supplying fuel to an internal combustion engine and comprising a plunger reciprocable within a bore, a cam for imparting inward movement to the plunger an outlet from the bore through which fuel can flow through a delivery passage to an outlet port of the apparatus, a valve seating defined about a spill passage connected to the bore, a piston slidable within a cylinder, a valve member defined on the piston and shaped for cooperation with the seating, resilient means urging the valve member into engagement with the seating, a control valve operable to apply fuel under pressure from said bore to the piston to lift the valve member from the seating and thereby spill fuel from the bore, and spring means acting to retain the body of the control valve in position relative to the housing of the fuel pump.

2. A fuel supply pump according to Claim 1 in which said spring means comprises a helical compression spring interposed between the body of the control valve and a part of said housing.