GB2188096A

GB2188096A - Fuel injection pumps for internal combustion engines

Info

Publication number: GB2188096A
Application number: GB08706854A
Authority: GB
Inventors: Karl Konrath
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1986-03-22
Filing date: 1987-03-23
Publication date: 1987-09-23
Also published as: FR2596103B1; DE3609758A1; IT1204925B; GB2188096B; JPS62225725A; FR2596103A1; IT8719676A0; GB8706854D0

Abstract

The maximum quantity of fuel supplied by a fuel injection pump to an internal combustion engine operable with or without pressure-charging is set by limiting the travel of a fuel quantity adjusting member (2) by means of an adjusting device (11) which is subjected in a first direction to a force derived from a pressure (in chamber 14) which varies in dependence upon speed and in the opposite direction to a force derived from a control pressure (in chamber 23) which varies in dependence upon both speed and the density or pressure of the air fed to the engine. The speed dependence is provided by fuel supplied by a pump 18 to a suction chamber (17) of the fuel injection pump and used to pressurise chambers (14), (34) and (23). The dependence upon inlet air pressure is determined by a diaphragm 44 which adjusts the position of a control edge 30 to vary a discharge cross section 31 to control fuel flow from a line 25 to a return line 33. <IMAGE>

Description

SPECIFICATION Fuel injection pumps four internal combustion engines The invention relates to a method for controlling the maximum quantity of injected fuel supplied by a fuel injection pump to an internal combustion engine operated with super-charging.

In the case ofthe fuel injection pump described in German Offenlegungsschrift No. 31 46 499, the travel of the fuel quantity adjusting member is limited by a piston which is subjected on the one hand to the speed-dependent pressure ofthe fuel in the suction chamber of the fuel injection pump against the force of a return spring, and, on the other hand, in support of the return spring, to a control pressure which is controlled according tothe density of the charged air fed to the combustion chambers ofthe internal combustion engine. The pressure medium for generating the control pressure is drawn from a constant pressure source and is modulated by allowing the discharge of partial quantities thereof.This method servesto limitthe maximum quantityofinjected fuel in internal combustion engines operated with supercharging. The maximum injected fuel quantity is adapted to the characteristic of the fuel requirement of the internal combustion engine atwhich optimum combustion can take place without detrimental side effects with respect to exhaust gas emission, soot and hydrocarbon (HC) emission.

The invention resides in a method of controlling the maximum quantity of injected fuel supplied by a fuel injection pump to an internal combustion engine by limiting the travel of a fuel quantity adjusting member ofthefuel injection pump in a direction to increase the quantityoffuel injected, in which this limitation is altered in dependence upon operating parameters by an adjusting device, which is subjected in a first direction to a force derived from a pressure which varies in dependence on speed, and in a second, opposite direction to a force derived from a control pressure and to the bore of a return spring, and in which the airfed to the combustion chambers ofthe internal combustion engine is charged by means of a chargerwhich can be connected and disconnected, and the control pressure varies in dependence upon the density ofthe air fed to the combustion chambers ofthe internal combustion engine and in dependence upon the speed ofthe internal combustion engine.

This has the advantage that operation ofthe internal combustion engine can be divided into two types, that is, operation with super-charging and operation without super-charging, with corresponding ada ptation of the maximum injected fuel quantity orfull-load injected fuel quantity to the fuel requirement ofthe internal combustion engine in each case. Adaptation in one operating range can take place independently of adaptation in the other operating range.

Advantageously, possibilities for influencing this can befound, for example, in the fact that the speed-dependent control pressure increases with increasing speed and the force acting in the first direction is increasingly reduced. In super-charged operation, the control pressure, in addition to the example with increasing load pressure, which in turn can increase with increasing speed, can be modified in such a waythat, for example, a characteristic of constant injected fuel quantity over operating speed is obtained.By means of corresponding adaptation of the speed-dependent modification and the loadpressure-dependent modification ofthe control pressure, any other curve of injected fuel quantity with respect to speed can be obtained as required, whereby the upward or downward slope ofthe injection characteristic for operation without super-charging can be independent ofthe shape of the characteristic for operation with super-charging.

This is particularlythe case in a method in which, when the charger is disconnected, the control pressure changes only in dependence upon speed, and, when the charger is connected, itvaries in dependence upon speed and upon the density of the air fed to the combustion chambers. It is particularly advan tageous that in this way, given chargers provided for super-charging which are driven in synchronism with the speed ofthe internal combustion engine, or chargers which are driven by a separate drive unit, when the charger is connected, and there is hence a sudden increase in combustion chamberfilling,there is also a sudden changeoverto anothervalue or curve ofthe limitation of the maximum injected fuel quantity.In addition, the high working capacity of the fuel inthesuction chamberofthefuel injection pump, which is already under a pressure which is controlled in dependence on speed, is advantageously available.

The forces required to produce the control pressure are no longerdependentontheforceswhich occuron mechanical sensing of the adjusting piston, which forces are mentioned, for example in German Offenlegungsschrift No. 2847 572forthe adjustment of the limitation ofthe maximum quantity of fuel injected.

Advantageously, the charger can then be connected in a load-dependent manner withoutthis having any negative effecton the quality ofthe airandfuel charge in the combustion chamber.

For an internal combustion engine, the invention includes the combination of a super-charger, a fuel injection pump which hasafuel quantity adjusting member and a means associated therewith for limiting the possible travel ofthe quantity adjusting member, said means comprising an adjusting device, which has an adjusting piston which is adjustable against a return spring, the possible travel ofthe quantity adjusting member being alterablebywayofa transmission device according to the position of the adjusting piston, the adjusting piston defining a working chamber which can be connected to a pressure source whose pressure can be altered in dependence upon the speed ofthe fuel injection pump, and the rear ofthe adjusting piston remote from the working chamber defining a pressurecham- ber, which, in support of a return spring, is subjected to a control pressure which is controllable in dependence upon an operating parameter of the internal combustion engine, such as the density of the airfed to the combustion chambers ofthe internal combustion engine, and can also be connected by way of a decoupling throttle to a pressure source as well as by way of a pressure control valve to a relief chamber, the pressure control valve having a valve closure element, such as a control spool controlling a discharge cross section to the relief chamber, which control spool is subjected byway of an adjusting memberto a force which acts againsta returnforceandwhich varies in dependence upon the air pressure generated by the charger, the pressure chamber being connected by way ofthedecoupling throttleto the pressure source whose pressure varies in dependence upon speed, and the return force being generated by pressure from this pressure source acting on a pressure surface of the control spool.

Such a combination is a modification which is simple to implement of a known device for adjusting the possible travel of a quantity-adjusting member.

Preferably a valve closure element is subjected to the pressure from the pressure source acting on the pressure surface with the object of reducing the discharge flow cross section.

Advantageously, the valve closure element is in the form of a control spool which is sealinglydisplaceble in a bore and whose end face defines a pressure chamberwhich is permanently connected to the pressure source, and whose other end face is subjected to the force of a spring whose other end rests on a support which is adjustable in dependence upon the density ofthe air fed to the combustion chambers of the internal combustion engine.

This produces a particularly accurately controllable device.

The invention isfurther described, by way of example with reference to the accompanying drawings, in which Fig. lisa schematic view of a first embodiment of an adjusting device having a pressure control valve whose control spool closesthedischarge cross section during operation without super-charging; Fig. 2 is a characteristic of the curve ofthe quantity of fuel injected plotted against speed for an internal combustion engine operated with and without supercharging, and Fig. 3 shows a variant of the embodiment of the pressure control valve in Fig. 1, in which asthe pressure ofthe pressure source increases, the discharge cross section is enlarged, or reduced, by way of a controllable recess in the control spool.

Fig. 1 shows a part of a fuel injection pump which may, for example, be a distributor-type fuel injection pump. This pump is provided in a known mannerwith afuel quantity adjusting member2 intheform ofa leverwhich actuates an annular slider (notshown) to control the quantity of fuel injected. In the full-load position, it abuts, possibly with the interposition of a bell-crank lever3, against an adjustable stop which is in the form of a sensing pin 5which is guided in a bore 8 and projects at right angles into a cylinder 9 disposed in the housing ofthe fuel injection pump. An adjusting piston 11 is guided in this cylinder and one of its end faces 12 defines a working chamber 14inthis cylinder 9.This working chamber 14 is connected, if necessary with the interposition ofdamping throttle 16 in the end face ofthe cylinder 9, to a pressure source whose pressure is controlled in dependence on speed. In the embodiment shown, this pressure source is the fuel-filled suction chamber 17 ofthefuel injection pump, the suction chamber being supplied with fuel by a fuel pump 18 which sucks in fuel from a fuel supply tank 19 and whose delivery side can be relieved by way of a pressure control valve 20.

In the region in which the sensing pin 5 penerates into the cylinder9, the surface ofthe adjusting piston 11 is provided with a contour 21 which changes in the direction of displacement, which contour determines the position ofthe sensing pin and hence the maximum quantity offuel injected, which is set by the fuel quantity adjusting member. The rear 22 ofthe adjusting piston 11 defines in the cylinder 9 a pressure chamber 23 in which is disposed an adjustable return spring 24 acting on the rear 22 ofthe adjusting piston 1 1.A pressure line 25 leadsfrom the pressure chamber 23 to a cylinder bore 27 in a pressure control valve26 which controls the control pressure in the pressure chamber 23.A control spool 28 is displaceably disposed in the bore 27 and is provided with an annular groove 29, one of whose limiting edges 30 controls a discharge cross section 31 with the mouth ofthe pressure line 25 opening into the cylinder bore 27. Furthermore, the annular groove 29 is permanently connected byway of a relief line 33 to a relief chamber, the fuel supply tank 19. The end ofthe control spool 28to the side of the limiting edge 30 projects into a pressure chamber34which is permanently connected to the pressure side ofthe fuel pump 18 orto the suction chamber 17.Stops 35 are located in this pressure chamberto limit the extent of projection ofthecontrol spool 28 into the pressure chamber 34. Said pressure chamber 34 isfurthermore permanently connected to the pressure line 25 by way of a decoupling throttle 37.

The other end of the control spool 28 projects into a pressure-relieved chamber 38 and its end face 39 is subjected to the bore of a pressure spring 40 which is disposed in the chamber 38 and whose other end rests on a displaceable support 42. Said support42 is connected to a plunger 43, which is secured to a movablewall,which in this case is an adjusting diaphragm 44. This movable wall or adjusting diaphragm separates a control chamber 46 from a reference pressure chamber47 in a housing 45.A return spring 48 is disposed in the reference pressure chamber, is fixed between the housing 45 and the adjusting diaphragm 44, and attempts to move the adjusting diaphragm against an adjustable stop 50, at which point the support 42 is furthest away from the control spool 28. The control chamber46 is subjectto the same pressure as the air which is fed to the combustion chambers of the internal combustion engine, that is, given charger operation, to the charging pressure, which is greaterthan the air pressure exposed to atmospheric pressure in the reference pressure chamber 47, and causes the support 42 to be displaced towards the control spool 28. Depending on the charging pressure, the spring 40 is prestressed to a greater or lesser degreefor a given position of the control spool 28. From a particular movementofthe control spool 28 relative to the support42 onwards, the control spool comes into abutment against a pin 51 projecting from the support 42, sothatthe control spool 28 then directly follows the adjusting movement of the support 42. The control spool is moved into abutment against the pin 51 by the speed-dependent fuel pressure acting on the end face 53 ofthe end ofthe control spool 28 projecting into the pressure chamber 34.

In the device described with respect to Fig. 1, the speed-dependent pressure in the suction chamber7 and the working chamber 14 is built up when the internal combustion engine is started. The adjusting piston 11 is then displaced in accordance with this pressure againsttheforce ofthe return spring 24, the sensing pin 5 being displaced in conformity with the contour 21.The bell-crank lever3 orthe final position ofthe quantity adjusting member 2 are this adjusted accordingly. However, a hydraulic control pressure, which is determined by the pressure control valve 26, continues to acton the rear 22 against the pressure in the working chamber 14. This pressure effectively limits the displaceability ofthe adjusting piston 11.In the case described, in which the adjusting diaphragm 44 abuts against the adjustable stop 50, that is, in an operating condition in which there is no supercharging or in which the pressure ofthe airfed in exerts a smaller force component on the adjusting diaphragm than the sum of the forces of the atmospheric pressure and the return spring 48, the control edge 30 ofthe control spool 28 partially closes the discharge cross section 31,so that fuel may flow from the line 25 into the chamber 29 and the line 33. As a result, a control pressure is obtained in the chamber 23 which is lower than the pressure in the working chamber 14.As the speed, and hence the pressure in the working chamber 14, increases,the piston 11 moves againstthe spring 24 andthe control pressure in the chamber 23, the control pressure also being variable, if intended or necessary, in dependance upon the pressure in the suction chamber 17. In this way, it is possible to obtain, as a variation of characteristic A, a characteristic which falls as speed increases.

Ifthe internal combustion engine is now operated with super-charging, a pressure is obtained in the control chamber 46 which is large enough to displace the su p port 42 towa rds the control spool 28. If the device according to Fig. 1 has been arranged in such a waythatthe discharge cross section 31 was initially partially closed before commencement of charging operation, said discharge cross section will be opened even further bytheforce component exerted by the plunger43 orthe adjusting diaphragm 44 on the control spool 28 in dependence upon the pressure in the control chamber46, and the control pressure in the pressure chamber 23 is reduced with respect to the original pressure with the cooperation ofthe decoupling throttle 37.Using this device, it is possible to achieve a characteristic ofthe injected fuel quantity plotted against speed such as Curve B in Fig. 2. This curve lies on values of high injected fuel quantity, this being achieved by the factthatthe pressure in the pressure chamber 23 was reduced by a considerable amount sothatthe control spool 11 could be correspondingly further displaced against the spring 24. This displacement causes the maximum injected fuel quantity to be altered to highervalues. Starting from such a pressure, charging pressure will increase with increasing speed, provided it is not limited to a particular value. This causes a displacement of the support 42.At the same time, however, the pressure level in the suction chamber 17 rises with increasing speed, which results in an increasing force component on the end face 53. The resulting position of the control spool 28 can be adjusted as required by adapting the end face 53, the design of the return spring 40 and the return spring 48, as well as the area of pressure acting upon the adjusting diaphragm 44.

In accordance with this adjustment, it is possible to obtain any characteristic desired in accordance with Characteristic B in Fig. 2 for operation with supercharging or pressure-charging, the characteristics of type A being independent ofthe characteristics of type B.

Fig. 3 shows a variant of the embodiment of the pressure control valve 26 in Fig. 1 with a control spool 28'. In this case, for example, the pressure line 25 opens into the cylinder bore 27 in the region ofthe annular groove 29 and cannot be closed. The outflow fromtheannularchamberformed between the two parts is then controlled in accordance with the position ofthe control spool 28'. This embodiment should initially be regarded as being equivalenttothe embodimentin Fig. 1. In deviation therefrom,the limiting edge 30' can be a V-shaped recess in one limiting edge ofthe annular groove 29, which in turn cooperates with a limiting edge 55 of an annular groove 56 provided in the cylinder bore 27.Like the annular groove 29 in Fig. 1,this annular groove is relieved in the direction of a relief chamber by way of a relief line 33. With the aid of the V-shaped recess 30', the discharge cross section 31 ' can be sensitively controlled, the cross section becoming smaller as the speed-dependent pressure increases and the charging pressure decreases. Using the decoupling throttle 37 provided in the connection between the pressure line 25 and the pressure chamber34 or suction chamber 17, an increasing control pressure in the pressure chamber 23 can be achieved with increasing speed using a control spool ofthistypeforan internal combustion engine operated without super-charging.

The dotted lines in Fig. 3 indicate an alternative solution in which, given increasing speed-dependent pressure,the discharge cross section 31", in contrast to the above-described solution, will become larger, as a result ofwhich the control pressure in the pressure chamber 23 decreases with increasing speed. To this end, in place ofthe V-shaped recess 30', a V-shaped recess 30" is provided on the opposite side oftheannulargroove29andcooperateswith an annular groove 26' disposed accordingly in the cylinder bore 27.

Using the above-described embodiments, any re quired curves of maximum injected fuel quantity over speed can be obtained, which take into account, in particular, the operation of an internal combustion engine in which a charger can be connected or disconnected in order to pressure-chargethe combustion air. This applies in particularto chargers which are driven in synchronism with the speed ofthe internal combustion engine or are moved by a separate drive. When connected, such chargers, for example so-called G-chargers, cause a spontaneous rise in pressure, to which the fuel quantity to be injected mustthen be adapted. Furthermore, different fuel injection curves for induction operation on the one hand and charging operation on the other are often required.This can be done for reasons of improving exhaust gas emission or optimizing performance or consumption. Using the described solution according to the invention, such improvements can be made at no great expense.

Claims

1. A method of controlling a maximum quantity of injected fuel supplied by a fuel injection pump an internal combustion engine by limiting the travel of a fuel quantity adjusting member ofthefuel injection pump in a direction to increase the quantity of fuel injected, in which this limitation is altered in dependence upon operating parameters by an adjusting device, which is subjected in a first direction to a force derived from a pressure which varies in dependence on speed, and in a second, opposite, direction to a force derived from a control pressure and to the bore of a return spring, and in which the airfed to the combustion chambers ofthe internal combustion engine is charged by means of a charger which can be connected and disconnected, and the control pressure varies in dependence upon the density of the airfed to the combustion chambers of the internal combustion engine and in dependence upon the speed ofthe internal combustion engine.

2. A method as claimed in claim 1, in which, when the charger is disconnected,the control pressure changes only in dependence upon speed, and, when the charger is connected, it varies in dependence upon speed and upon the density ofthe airfed to the combustion chambers.

3. A method as claimed in claim 2, in which the charger is connected in dependence upon load.

4. A method as claimed in anyoneofclaims 1 to 3, in which the control pressure increases with increasing speed, and this increase is reduced as the density ofthe air fed to the combustion chambers increases.

5. For an internal combustion engine, the com- bination of a super-charger, a fuel injection pump which has a fuel quantity adjusting member and means associated therewith for limiting the possible travel ofthe quantity adjusting member, said means comprising an adjusting device, which has an adjusting piston which is adjustable against a return spring, the possible travel ofthe quantity adjusting member being alterable byway of a transmission device according to the position ofthe adjusting piston, the adjusting piston defining a working chamber which can beconnectedto a pressure source whose pressure can be altered in dependence upon the speed ofthe fuel injection pump, and the rear of the adjusting piston remote from the working chamber defining a pressurechamber,which, in supportof a return spring, is subjected to a control pressure which is controllable in dependence upon an operating parameter of the internal combustion engine, such as the density of the air fed to the combustion chambers ofthe internal combustion engine, and can also be connected by way of a coupling throttleto a pressure source as well as by way of a pressure control valve to a relief chamber, the pressure control valve having a valve closure element, such as a control spool controlling a discharge cross section to the relief chamber, which control spool is subjected by way of an adjusting memberto a force which acts against a return force and which varies in dependence upon the air pressure generated by the charger, the pressure chamber being connected bywayofthedecoupling throttle to the pressure source whose pressure varies in dependence upon speed, and the return force being generated by pressure from this pressure source acting on a pressure surface ofthe control spool.

6. Acombination-as claimed in claim 5, in which the valve closure element is subjected to the pressure from the pressure source acting on the pressure surface with the object of reducing the discharge flow cross section.

7. Acombination as claimed in claim 5, in which the valve closure element is subjected to the pressure from the pressure source acting on the pressure surface with the aim of opening the discharge cross section.

8. A combination as claimed in claim 6 or7, in which the valve closure element is in theform of a control spool which is sealingly displaceable in a bore and whose end face defines a pressure chamber which is permanently connected to the pressure source and whose other end face is subjected to the force of a spring, whose other end rests on a support which is adjustable in dependence upon the density of the airfed to the combustion chamber of the internal combustion engine.

9. Acombination as claimed in anyofclaims 5to 8, in which the valve closure member is a control spool provided with an annular groove which is permanently connected to the pressure chamber byway of a pressure line orto the relief chamber by way of a relief line and one of whose limiting edges, together with a limiting edge of the cross section of the relief line or the pressure line, forms the discharge flow cross section.

10. Acombination as claimed in claim 9, inwhich the limiting edge defines a recess in the surface of the spool, said recess being permanently connected to the annular groove, the cross section of which recess varies in the direction of adjustment ofthe control spool and which recess cooperates with a control edge surrounding the control spool in an annular manner and defining the discharge flow cross section at one side.

11. Acombination as claimed in any of claims 5to 10, in which the coordination ofthe control spool with the discharge cross section is such that, if the charger is not operating, the control spool is moved by the adjusting force exerted by the pressure source on the control spool into a position in which the discharge flow cross section is small.

12. Acombination as claimed in claim 11, in which the displaceability ofthe control spool in the direction of opening of the discharge cross section is limited by an adjustable stop.

13. Afuel quantity control method substantially as herein described with reference to the accompanying drawings.

14. The combination of a super-charger, a fuel injection pump and meansforadjusting the max imum injected fuel quantity constructed and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.