GB2132706A

GB2132706A - Fuel-injection pump for i.c. engines

Info

Publication number: GB2132706A
Application number: GB08332931A
Authority: GB
Inventors: Wilfred Hofken
Original assignee: LOrange GmbH
Current assignee: LOrange GmbH
Priority date: 1982-12-24
Filing date: 1983-12-09
Publication date: 1984-07-11
Also published as: GB8332931D0; JPS59120777A; DE3248086A1; FR2538456A1; DE3248086C2; GB2132706B; FR2538456B1; JPH0351901B2

Abstract

The start of injection of a fuel- injection pump is continuously varied by controlling a rapidly closing valve (20) disposed in an outlet or relief bore (16) leading from the pump chamber (12). The closing body (23) of the valve is maintained in its open rest position by an interlock means such as an electromagnet (30) and after release of this interlock means is rapidly moved into its closed operating position by the pressure of the discharging fuel. In this operating position the discharge of fuel through the outlet bore (16) is stopped and delivery past a valve (13) into a fuel injection pipe (14) starts. <IMAGE>

Description

SPECIFICATION Fuel-injection pump This invention relates to a fuel-injection pump, especiallyfora diesel-powered internal-combustion engine, ofthe kind comprising a piston, which is movably mounted in a piston guide body and which, in the area of the bottom dead centre ofthe piston, is provided with at least one inlet bore opening into the pump chamber and, with a small spacing staggered towardsthe innerdeadsentre,with an additional outlet bore, wherein the piston is provided with appropriate control edges and controls the quantity of fuel to be injected.

An injection pump ofthis kind has been described in published German specificatioin 130 873. In this case the additional outlet bore has relatively small crosssection and acts as a throttle through which, when the supply begins, part of the fuel can flow off from the pump chamber The intention is a steeper descent of the supply characteristic with falling rotational speed ofthe camshaft.

In contrast thereto an object ofthe present invention is to solve the problem ofdevelopingafuel-injection pump ofthis kind comprising an additional outlet bore with means as simple as possible and susceptible to trouble tothe smallest possible extent so as to enable a continuous variation of the beginning of injection.

According to the invention in its broadest aspect, a fuel-injection pump ofthe kind referred to is characterised in thatthe discharge ofthefuel stream through this outlet bore is controllablethrough a valve, wherein in a rest position releasing the discharge the valve closing body may be blocked by an interlock means and is, when this interlock means is released, changed over by the discharging fuel into its operating position thus stopping the fuel discharge.

The invention is thereby based on the idea thatthe start of injection can be continuouslyvaried within wide limits, ifthis outlet bore is controlled by a rapidly-closing valve. Thereby the valve-closing time is assumed to be in the order of magnitude of 0.5 m sec. According to the invention, a valve of this kind, which closes very rapidly, is realised in that, in orderto close the valve, whose closing body is held by an interlock means in the rest position, the pressure of the fuel flowing offfrom this bore is utilised.

The interlock means which maintains the valve closing body in the rest position in which this outlet bore is opened can be controlled pneumatically or hydraulically. However, it is preferredthatthevalve- closing body be maintained in its rest position by the force of an energized electromagnet. It is also preferredthatthecurrenttothe electromagnet be interruptedforthe release ofthe interlock means and/orthatthe electromagnet be acted upon by a counter-current surge. In this way the valve-closing time is reduced further.

Any other desired positioning element can be used to reset the valve-closing body into the rest position.

Due to the fact that during the suction stroke ofthe pump piston a vacuum comes into existence in the pumpchamberwhichsupportstheopening move- ment of the valve-closing body and because there is sufficienttimeto open the valve during the suction stroke, recuperating springs may serve as a positioning elementfor resetting the valve-closing body.

In the interest of straining the valve as little as possible, the distance between the inlet bore and the outlet bore should be chosen in such a way that the pump piston almost reaches the outlet bore or partly covers it, when with the latest possible start of injection the valve-closing body is changed over into its operating position. In this way the high pump pressure is prevented from acting upon the valveclosing body.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawing in the form of a partial section through those parts of a fuel-injection pump which are essential for the invention.

In a piston guide body 10 is movably mounted a pump piston 11 which during its working stroke supplies the fuel from the pump chamber 12 into a fuel-injection pipe 14via avalve 13.

An inlet bore 15 extends into the piston guide body 10 and opens into the pump chamber 12 in the area of the bottom dead centre ofthe piston shown in the drawing. Moreoverthe piston guide body 10 has an additional outlet bore 16 which is staggered in the direction towards the top dead centre.

This outlet bore may be controlled by a valve designated as a whole 20. The housing 21 of this valve 20 is directly mounted onto the piston guide body 10 in such a waythatthetapered valveseat22 opening towards the outlet bore 16 is co-axially arranged in relation to the outlet bore 16. Avalve conserves as a closing body 23 of the valve, on which closing body is formed a stem 24, which extends into a bore in the valve housing 21. In the drawing this valve-closing body 23 is shown in its rest position in which the outlet bore 16 is practically opened, because the fuel can be discharged from the pump chamber 12 via this outlet bore 16 and the opening cross-section 26 ofthe valve, the bore 25 and the ducts 27.

Thevalve-closing body23 is maintained inthis rest position by an interlock means designated as a whole 30. This interlock means 30 comprises an electromagnet 31 with an iron core 32 and a solenoid 33 as well as an armature 34. To this armature 34 is secured an adjustng screw which projects into a bore 36 in the iron core 32 and serves as a stop forthe stem 24 ofthe valve-closing body 23. Two recuperating springs 37 supported in a firm manner on the base hold the armature 34 in the position shown, even if the electromagnet31 is not energized.

The mode of operation ofthefuel-injection pump shown in the drawing is described below in detail, wherein it is assumed, thatthe valve-closing body 23 occupies the rest position shown and is maintained in this position by the force of the energized electromagnet 31. During the delivery stroke of the pump piston 11 the inlet bore 15 is atfirst closed. However, at first, there is no fuel delivered into the fuel-injection pipe 14, even if the inlet bore 15 is closed, because the fuel from the pump chamber 12 can flow off via the outlet bore 16 thereby passing the valve cone 23. The flow of the discharging fuel exerts a closing force onto the valve cone in the closing direction F. Howeverthis closing force is not sufficient to overcome the force of the magnet 31. Thus the valve 20 continues to be opened at first.

In dependence on the rotational speed or other relevant parameters the electromagnet31 isthen de-energized at a given time. The interlock means maintaining the valve-closing body in the rest position is thereby released. Then the magnetic force dimi nishes rapidly and becomes smallerthan the closing force F acting upon the valve-closing body 23, which closing force thus displaces the valve cone in the closing direction againsttheforce ofthe recuperating springs 37. The opening cross-section 26 is thereby diminished and the fall of pressure in this area increases, so thatthe closing force F is consequently also increased. Thusthe valve-closing body23 is changed over into its operating position, in which it rests upon the valve seat 22 in such a way as to seal it.

Then no more fuel can flow off from the pump chamber 12 through the outlet bore 76 and the injection starts. The outlet bore 16which is continued in the valve housing 21 is thus closed.

The pump piston 11 terminates its working stroke, wherebythevalve 13 is opened andthefuel is pressed from the pump chamber 12 into the fuel-injection pipe 14-rheend ofthe injection is realised in conventional mannerviacontrol edges onthe pump piston 11 and control bores in the piston guide body 10. When the injection is terminated, there is only a low pressure in the pump chamber 12, sothatthe recuperating springs 37 resetthe armature 34 and thus also the valve-closing body 23 from the operating position into the rest position.Moreoverthis resetting movements supported by the force ofthe electromagnet 31 energized again and bythefactthat during the downstroke ofthe pump piston 11 a vacuum comes into existence in the pump chamber 12. Thus after each injection the valve-closing body 23 is again blocked in its rest position. This electromagneticallyacting interlock means is only released in the following working stroke of the pump piston 11 by de energizing the electromagnet or acting upon itwith a counter-currentsurge, so thatthe valve closing time is diminished further.

The distance A between the inlet bore 15 and the outletbore 16 is chosen in suchawaythatthe pump piston 11 almost reaches the outlet bore 16 or partly covers it, when with the latest possible start of injection the valve-closing body is changed over into the operating position. In this manneritis achieved thatthevalve-closing body 23 is not acted upon bythe high pump pressurefortoo long atime. Moreover in this case the latest start of injection is not determined bythe rim ofthe outlet bore 16, but exclusivelybythe closing action ofthe valve 20.

Experiments have shown that, bythis principle, valve-closing times smallerthan 0.5 m sec can be achieved. Onlytheseshortvalve closing times make possible a continuous variation ofthe start of injec tion,whilethe pump piston 11 moves between the upper rim ofthe inlet bore 15 and the upper rim ofthe outlet bore 16. Such shortvalve-closing times couid not be reached with an electromagnetically-operated slide, which closesthe outlet bore 16transversally to the direction of discharge. Systems ofthis kind comprising a slide for closing the outlet bore 16 are therefore rather intended for a twopoint adjustment ofthe start of injection.

In the embodiment shown, the valve 20 is directly mounted on the piston guide body 10. Of course, a solution can also be realised in which this valve 20 is connected with the outlet bore 16 via a duct; however the current losses in this ductwould increase the closing times ofthe valve. Thus the valve will be mounted as close as possible to the outlet bore.

In the embodimentshown, the recuperating springs 37 serve as a positioning elementfor resetting the valveclosing body 23 into the rest position. However, an additional electromagnet or another hydraulic or pneumatic positioning element could also be used.

Of course the interlock means could also be of a different design. In particular, an interlock means could be adopted which comprises a positioning element, which, transversally to the direction of motion ofthe valve-closing body, is moved into the motion path ofthe stem 24.

Finally it is pointed outthatthefuel-injection pump continues to be operable even if the valve 20 is defective. It would not, however, ofcourse,work underoptimal operating conditions. If the closing body 23 ofthe valve 20 remains in the rest position shown in which thefuel can discharge via the outlet core 1 6,the start of injection is controlled by the upper edge ofthis outlet bore 16. if, in contrastthereto,the valve 20 were to remain closed continuously, the start of injection would be controlled via the upper edge of the inlet bore 15.

Thus, by a utilisation ofthefiow pressure ofthefuel discharging via theoutet bore l6forclosing a valve a fuel-injection pump is created in which in a very simple way the start of injection is continuously rariable within wide limits. Thus a fuel-injection pump ofthis kind can be easilyadapted to differing operating conditionsofa diesel-powered internal combustion engine.

Claims

1. Afuel-injection pump, especiallyfora dieselpowered internal-combustion engine of the kind comprising a piston, which is movably mounted in a piston guide body and wnich, in the area ofthe bottom dead centre ofthe piston, is provided with at least one inlet bore opening into the pump chamber and, with a small spacing staggered towards the inner dead centre, with an additional outlet bore, wherein the piston is provided with appropriate control edges and controls the quantity of fuel to be injected, characterised in thatthe discharge ofthefuel stream through this outlet bore (16) is controllable through a valve (20), wherein in a rest position releasing the discharge the valve closing body (23) may be blocked by an interlock means (30) and is, when this interlock means is released, changed over by the discharging fuel into its operating position thus stopping the fuel discharge.

2. Afuel-injection pump according to claim 1, characterised in thatthe valve-closing body (23) is retained in its rest position bytheforce of an energized electromagnet (31).

3. Afuel-injection pump according to claim 2, characterised in thatthe currentto the electromagnet (31) is interrupted for the release ofthe interlock means (30) and/orthatthe electromagnet (31) is acted upon by a counter-currentsurge.

4. Afuel-injection pump according to anyone of the preceding claims, characterised in that during the downstroke of the pump piston (11) the valve-closing body (23) is changed over from the operating position into the rest position by a positioning element.

5. Afuel-injection pump according to claim 4, characterised inthatrecuperating springs (37) serve as a positioning element for resetting the valve closing body (23).

6. Afuel-injection pump according to any one of the preceding claims, characterised in that the distance (A) between the inlet bore (15) and the outlet bore (16) is chosen in such a waythatthe pump piston (11) almost reaches the outlet bore (16) or partly covers it, when with the latest possible start of injection the valve-closing body (23) is changed over into its operating position.

7. Afuel-injection pump according to any one of the preceding claims, characterised in that the housing (21) ofthe valve (20) is directly mounted on the piston guide body (10), thatthetapered valve seat (22) opening towards the outlet bore (16) is co-axially arranged relative to the outlet bore (16) and that the valve-closing body (23) designed as valve cone has a stem (24) which is entered in the valve housing (21) and is mechanically connected with the armature (34) of an electromagnet (31).

8. Afuel-injection pump substantially as described with reference to the accompanying drawings.