GB2140099A - Injection system for an internal combustion engine - Google Patents

Abstract

An injection quantity metering device (3) meters fuel to a pumping nozzle (4) for pumping and injection into the combustion chamber of an internal combustion engine. The pumping nozzle (4) has a pump cylinder (8), a main piston (9) which enters the pump cylinder and is driven by a cam (62), and an auxiliary piston (10) which is displaceable within the pump cylinder (8) and defines a pump working chamber (8a). The pump cylinder (8) surrounds between the main piston (9) and the auxiliary piston (10) a compensating chamber (74) which serves to receive a liquid column of adjustable length, the said column driving the auxiliary piston (10) during downward movement of the main piston (9) during the injection operation. The injection operation only takes place when a control port (48) disposed in the main piston (9) and communicating with the compensating chamber (74) is closed by means of a hydraulically adjustable control sleeve (49). The commencement of injection can be advanced or retarded by varying the adjusting pressure acting upon the control sleeve (49). <IMAGE>

Description

SPECIFICATION Injection system for an internal combustion engine The invention relates to an injection system for an internal combustion engine.

German Utility Model No. 81 33 716 describes an internal combustion engine injection system having a pumping nozzle. The pumping nozzle has a pump cylinder, a camdriven main piston which enters the pump cylinder, an auxiliary piston which is disposed in axial alignment with the main piston and defines a pump working chamber, a compensating chamber which is enclosed by the pump cylinder between the main piston and the auxiliary piston and which accommodates a liquid column of adjustable length, so that the liquid column forms a hydraulic linkage between the main piston and the auxiliary piston, an injection nozzle disposed in axial alignment with the auxiliary piston, and an inlet valve for pre-metered quantities of fuel which are delivered to the injection nozzle by means of the auxiliary piston. An injection quantity metering device is disposed upstream of the inlet valve.The injection quantity metering device has a fuel source which supplies liquid fuel at a predetermined pressure, and a solenoid vaive. During the suction strokes of the main piston, the solenoid valve is opened for periods of time which are sufficiently long to allow the injection quantity required at any given time to flow through the inlet valve to a location below the two-part auxiliary piston provided with a relief piston. The main piston is rotatable by means of a control rod by way of a coaxially aligned adjusting pinion, and its end directed towards the auxiliary piston incorporates an upwardly sloping, so-called oblique control edge. The pump cylinder has a control port which is associated with the control edge.According to the chosen angular position of the main piston, the latter travels distances of differing lengths from the commencement of its pumping stroke until the control edge has passed the control port, and the main piston thereby closes the control port. Before the control port is closed, a portion of a liquid, such as fuel located between the main piston and the auxiliary piston, flows out through the control port. The main piston then drives the auxiliary piston by way of the remaining column of liquid acting like a mechanical plunger, so that the auxiliary piston forces a pre-metered quantity of fuel through the injection nozzle. By selective rotation of the main piston, its control edge advances or retards the commencement of injection .

An injection system described in U.S.A.

Patent Specification No. 4 092 964 also has at least one main piston which has an oblique control edge and which is rotatable by means of a control rod by way of an adjusting piston for the purpose of timing the commencement of injection. In this instance, the associated auxiliary piston driven by a liquid column is of a one-piece construction. The quantities of fuel to be injected are metered by means of a detering pump and are fed by way of an inlet valve to the pump working chamber located below the auxiliary piston.

These known injection systems have the disadvantage that the adjusting movements of, for example, an electric adjusting motor, first have to be transmitted to the control rod then by the control rod to the adjusting pinion and finally from the latter to the main piston by way of angular displacement means. This requires a large number of individual parts which have to co-operate with a minimum of play and which are therefore particularly expensive to manufacture.

It is an object of the present invention to improve injection systems of the type described, such that it is possible to time the commencement of injection with less technical expense and sufficient accuracy.

In accordance with the invention, there is provided an injection system comprising an injection quantity metering device for supplying a metered quantity of fuel, and at least one pumping nozzle for pumping and injecting metered quantities of fuel into a combustion chamber of an internal combustion engine, the pumping nozzle having a pump cylinder, a main piston and an auxiliary piston which enter the pump cylinder, and a compensating chamber located between the auxiliary piston and the rnain piston for receiving a pressure-transmitting liquid column of ad adjustable length, an injection nozzle and a control means for adjusting the length of the liquid column for the purpose of timing the commencement of injection, which control means includes a control sleeve which is guided in an adjusting cylinder and which surrounds the main piston and which is directly adjustable in the directions of the stroke of the main piston by means of a hydraulic pressure medium which acts upon the adjusting cylinder, the control edge liying in a plane normal to the longitudinal axis of the main piston .

This has the advantage that the main piston no longer has to be rotated and thus obviates the use of transmission elements which were hitherto required to convert a linear movement to a rotary movement and to transmit this rotary movement to the main piston. The manufacture of the main piston is thereby also simplified. Furthermore, in the case of an injection system designed for a multi-cylinder internal combustion engine, there is the advantage that means for adjusting the angular alignment of the main piston relative to the gear wheels are not required, and a linkage between the toothed racks is not required.

This considerably simplifies manufacture and particularly the instailation of injection systems in multi-cylinder engines and avoids time-consuming adjustment.

In an advantageous development of the injection system of the present invention the control edge is formed by a boundary edge of an annular groove which commences from a bore which passes through the control sleeve and surrounds the main piston, the annular groove having at least one associated controi port which is located in the main piston and which communicates with the cornpensating chamber by way of a transverse bore, located in the main piston, and a longitudinai bore.

This has the advantage that the rnain piston only has one transverse bore in the region of the control sleeve and is ithereby satisfactoriiy dispiaceable within the control sleeve.

In a further development. the adjusting cyl- inder is aligned coaxially of the purnp cylinder and is contiguous thereto, and the control sleeve is a piston which is hydraulically displaceable within the adjusting cylinder against the force of a return spring.This has the advantage of a particularly space-saving type of construction. As a result of the hydraulic timing of the commencement of injection, it is aiso possible, in multi-cylina'er internal com- bustion engines, and in contrast to the conventional parallel alignment of the pumping nozzles, to align the pumping nozzles arbitrarily in a row, in a manner advantageously resulting from predetermined arrangements of the inlet and exhaust valves of intenal com- bustion engines chosen for the purpose of, for example, obtaining favourable ignition oper- ations.

Preferably, means are provided by which the compensating chamber can be filled and partially emptied in a technically advan- tageous manner. To this end sealing rings are fitted in two grooves incorporated in the peri- phery of the control sleeve in the region of the ends thereof, and an additional groove is disposed between the two grooves, and at least one transverse bore is disposed between the additional groove and she inner annular groove.The adjusting cylinder has at least one port which is Located opposite tile addi- tional groove and through which the hydraulic pressure medium can be fed to, and conducted from the compensating chamber.

Advantageously, a one-way valve opening under pressure is connected to the port of the adjusting cylinder and opens towards a tank, and the main piston and the auxiliary piston are interconnected by way o, a draw linicage which performs an idle stroke and Alien pulls the auxiliary piston along behind the rnain piston.This has the advantage that the hydraualic column located in the compensating chamber is subjected to biasing pressure and thereby faultlessly transmits the lifting move- ment of the main piston to the auxiliary piston even when the pump cylinder is hot.There is the additional advantage that the auxiliary piston is forced to perform suction strokes by means of the draw linkage, and thereby facili Taxes the filling of the pump chamber with metered quantities of fuel which are to be injected. The draw linkage has an advantageous effect on the accuracy of metering particularly when the fuel is metered by means of a solenoid valve or the like.

In a preferred embodiment the draw linkage comprises two hooks, one of which is formed on the main piston and the other of which is formed on the auxiliary piston.

In a further embodiment the port located opposite the control sleeve is connected by way of a one-way valve, opening towards the control sleeve, to a line through which the pressure medium, subjected to adjusting pressure, is admitted to the adjusting cylinder from a hydraulic adjuster. This has the advantage that a pump, which is in any case required for adJusting the control sleeve, also personas the task of filling the compensating chamber.The arrangement of the one-wave valve directly on the adjusting cylinder results in the saving of lines.

The invention will now be described further hereinafter, by way of example only, with reference to the accompanying drawing, which is a sectional view ort a pumping type fuei injection nozzle in a fuel injection system.

The embodiment of the injection system 2 shown in the drawing has an inJection quan tity metering device 3 for liquid fuel, and at least one pumping nozzle 4. The injection quantity metering device 3 has a fuel source 5 subjected to a predetermined pressure, a solenoid valve 6 connected to the fuel source, and a non-return valve 7 which is disposed between the solenoid valve and the pumping nozzle 4 and which opens towards a pump working chamber 8a of the pumping nozzle 4.

By way of example, and as is described in German Utility Model No. 81 33 716, the fuel source 5 comprises a fuel tank, a feed pump an a pressure-limiting valve for main- taining the pressure constant at the outlet of the feed pump. The injection quantities are metered by the solenoid valve 6 being opened for longer or shorter periods of time during the suction strokes Of the pumping nozzle 4.

The pumping nozzle 4 has a pump cylinder S, a main piston 9 which enters the pump cylinder 8, an auxiliary piston 10 which is displacealble within the pump cylinder 8 in iine with the main piston 9 and defines the pump working chamber 8, a valve plate 11 disposed contiguously to the pump cylinder 8 and below the pump working chamber 8a, an intermediate member 12 disposed below the valve plate 1 1, an injection nozzle 13 contiguous to the intermediate member 12, and an injection timing device 14 serving as a control means tror timing the commencement of injec tion.

The injection nozzle 1 3 has a hollow nozzle body 1 5 incorporating nozzle orifices 16, a valve seat 17, a nozzle needle 1 8 which is associated with the valve seat 1 7 and which has a larger diameter load piston 1 9 which is displaceably guided in the nozzle body 1 5.

The nozzle body 1 5 has a pressure chamber 20 in the region of the transition from the load piston 1 9 to the nozzle needle 18. The nozzle body 15 has a pressure passage 21 leading from the pressure chamber 20 towards the intermediate member 1 2. The intermediate member 1 2 is also provided with a passage 22 in line with the pressure passage 21. An additional passage 23 passing through the valve plate 11 is in alignment with the passage 22 and communicates with the pump working chamber 8a by way of an angled passage 24 below the piston 10.A centering lug 25 is formed on the load piston 1 9 and extends into a spring chamber 26 located within the intermediate member 1 2 between the nozzle body 1 5 and the valve plate 11.

One end of a prestressed valve closing spring 27 abuts against the valve plate 11, and the other end of the spring 27 embraces the centering lug 25.

The valve plate 11 incorporates a valve port 28a having a conical valve seat surface 28 which widens towards the pump working chamber 8a. A valve member 30 extending partially into the spring chamber 26 carries a spring abutment plate 31 and has a valve cone 29 which rests on the valve seat surface 28. A closing spring 32 is fitted between the spring abutment plate 31 and the valve plate 11. The valve plate 11 together with the valve cone 29, the valve member 30 and the closing spring form an inlet valve 33.

A passage 34 leads from the non-return valve 7 into the pump working chamber 8a. A passage 35 branches from the passage 34 and has contiguous thereto an additional passage 36 which passes through the valve plate 11 and which opens into the spring chamber 26. Quantitites of fuel metered by means of the injection quantity metering device 3 are fed to the pump working chamber 8a by way of the passages 34, 35, 36, the spring chamber 26 and the inlet valve 33. These metered quantities of fuel subsequently flow through the passages 24, 23, 22 and 21 and the pressure chamber 20 to leave the nozzle orifices 1 6 and thereby enter a combustion chamber (not illustrated) of an internal combustion engine.

The auxiliary piston 10 is located within that portion of the cylinder 8 which forms the pump working chamber 8a and to which the inlet valve 33 is contiguous. The auxiliary piston 10 has a longitudinal bore 41 commencing from the underside 40 thereof. A transverse bore 42 passing through the auxiliary piston 10 communicates with the longitudinal bore 41. The periphery of the auxiliary piston 10 has a control groove 43 which is on a level with the transverse bore 42 and which communicates with the latter. A hook or lug 44 is formed on the auxiliary piston 10 towards the main piston 9.

That region of the main piston 9 which enters the pump cylinder 8 also has a hook 45 which engages below the hook 44. The two hooks 44, 45 form a draw or tension linkage whhich performs an idle stroke until the hooks 44, 45 abut against one another.

The main piston 9 has above the hook 44 a longitudinal bore 46 which is substantially half as long as the main piston 9. The longitudinal bore 46 opens into a transverse bore 47 which forms two control ports 48 on the periphery of the main piston 9. These control ports 48 form part of the device 1 4 for timing the commencement of injection. The device 1 4 for timing the commencement of injection also has a control sleeve 49 which is directed coaxially of the main piston 9 and which is displaceable relative to the main piston 9, an adjusting cylinder 50 which surrounds the control sleeve 49 and which is directed coaxially of the pump cylinder 8 and is contiguous thereto, a return spring 51 which presses against the control sleeve 49, and a hydraulic adjuster 52.The control sleeve 49 is displaceably guided within the adjusting cylinder 50 and is sealed relative thereto by means of two sealing rings 53. The sealing rings 53 are located in grooves 54 which are disposed in the periphery of the control sleeve 49 in the region of the respective ends thereof. The periphery of the control sleeve 49 incorporates an additional groove 55 which is located between the grooves 54 and which communicates by way of transverse bores 56 with an annular groove 57 incorporated within the control sleeve 49. A port 57a is connected to the hydraulic adjuster 52 by way of lines 58, 59, 60 and opens into that portion of the adjusting cylinder 50 which is contiguous to the pump cylinder 8. The return spring 51 presses against that end of the control sleeve 49 which is furthest from the port 57. The adjusting spring 51 abuts against a spring abutment plate 61.

The main piston 9 is moved towards the auxiliary piston 10 by way of a cup-type plunger 63 by means of a cam 62 driven by the internal combustion engine, and towards the cam 62 by means of a spring 64 by way of an additional spring abutment plate 65 which is slotted in a fork-like manner and which acts upon the main piston 9. The spring 64 located opposite the return spring 51 abuts against the spring abutment plate 61. A one-way valve 66 opening towards the adjusting cylinder 50 is connected to the line 58. The one-way valve 66 is connected by way of a line 67 to a port 68 which opens into the adjusting cylinder 50 opposite to the groove 55. A second port 69, which also opens into the adjusting cylinder 50, is connected by way of a line 70 to an additional one-way valve 71 which communicates with a tank 73 by way of a line 72.The one-way valve 71 opens when a pressure of, for example, 6 bar is reached between the groove 55 and the tank 73.

The hydraulic adjuster 52 produces a hydraulic pressure of variable value which is applied to the adjusting cylinder 50 by way of the lines 58, 59, 60 and which acts upon the control sleeve 49 and, in dependence upon its value, compresses the return spring 51 to a greater or lesser extent. Hence, according to the value of this adjusting pressure, the control sleeve 49 will assume a different position or vertical adjustment relative to the pump cylinder 8. Accordingly, the control ports 48 will pass the annular groove 57 downwardly at an earlier or later instant during a downward movement of the main piston 9, effected by means of the cam 62, and are then closed by the control sleeve 49.As long as the control ports 48 are in alignment with the annular groove 57, as is illustrated in the drawing, the hydraulic adjuster 52 also forces fluid to the control ports 48 by way of the line 58, the one-way valve 56, the line 67, the port 68, the groove 55 and t & &commat; the transverse ports 56 and, by way of the transverse bore 47 and the longitudinal bore 46, into a compensating chamber 74 in which the hooks 44 and 45 are located and which is surrounded by the pump cylinder 8 between the pistons 9, 10. The hydraulic pressure prevailing in the compensating chamber 74 acts upon the auxiliary piston 10 and causes pressurization of a quantity of fuel located below the auxiliary piston 10 in the pump cylinder 8.During further downward movement of the main piston 9, the pressure within the compensating chamber 78 finally increases to an extent that this pressure opens the one-way valve 71 by way of the longitudinal bore 46 and the transverse bore 47 and finally through the control sleeve 49 and through the line 70 and causes fluid to flow off into the tank 73. As already mentioned, the control ports 48 finally pass the annular groove 57 upon further downward movement of the main piston 9 effected by means of the cam 62, and are closed by the control sleeve 49. Consequently, fluid can no longer escape from the compensating chamber 74.The fluid still enclosed thereby forms between the main piston 9 and the auxiliary piston 1 0 a hydraulic pressure linkage whose length, as already described above, is dependent upon the vertical alignment of the control sleeve 49 and transmits pressure forces to the auxiliary piston 10. A greatly increasing pressure thereby develops below the auxiliary piston 10 and finally acts upon the load piston 1 9 by way of the passages 24, 22, 21 and the pressure chamber 20 and removes the nozzle needle 1 8 from its valve seat 1 7. Fuel thereby flows along the nozzle needle 1 8 to the nozzle orifices 1 6 and flows therethrough in the form of fine jets into the combustion chamber of the associated internal combustion engine.

During further downward movement of the pistons 9, 10, the control groove 43 of the auxiliary piston 10 finally comes into register with the passage 34. The pressure of the fuel built up below the auxiliary piston 10 is thereby relieved through the longitudinal bore 41, the transverse bore 42, the control groove 43 and the passages 34, 35 and 36 into the spring chamber 26 into which the load piston 1 9 extends. The pressure thereby increasing in the spring chamber 26 loads the load piston 1 9 in addition to the valve closure spring 24 towards the valve seat 17, so that the injection nozzle 1 3 is abruptly closed and after-injection is avoided.

During further rotation of the cam 62, the main piston 9 finally assumes its bottommost position and is then raised by means of the spring 54. After the main piston 9 has covered an idle stroke of independent length, its hook 45 finally engages the hook 44 of the auxiliary piston 10 to pull the latter upwardly.

When the auxiliary piston 10 is being pulled upwardly or, preferably, subsequently when the auxiliary piston 1 0 has reached its highest possible position, an injection quantity of fuel is metered by the injection quantity metering device 3 and is fed into the pump working chamber 8a by way of the passages 34, 35, the spring chamber 26 and the inlet valve 33 below the auxiliary piston 10. During this suction stroke movement of the main piston 9, the volume of the compensating chamber 74 increases until the hooks 44, 45 abut against one another. The suction action of the auxiliary piston 1 0 then occurring assists the inflow of the quantity of fuel to be metered into the pump cylinder 8.Accuracy of metering is at its greatest when the injection quantity metering device only supplies the quantity of fuel to be injected when the auxiliary piston 10 is raised, since the difference between the pressure in the pump working chamber 8a defined by the auxiliary piston 10 and the pressure of the fuel source 5 then has a value dependent upon the vapour pressure of the fuel. This value then fluctuates only as a result of the effects of temperature. However, the temperature-dependent pressure differences affecting the accuracy of metering are negligible particularly when the internal combustion engine and the pumping nozzle 4 are suitably cooled, and even without cooling.

When a known metering pump having lifting pistons or the like is used instead of the injection quantity metering devices comprising the fuel source 5 and the solenoid valve 6 or another valve such as a piezoelectric valve assuming the function of the solenoid valve 6, the draw linkage formed by the hooks 44, 45 and permitting an idle stroke can be dispensed with when the lifting pistons exert an adequately strong pressure.

Furthermore, instead of connecting the oneway valve 66 to the hydraulic adjuster 55 it is possible to connect the one-way valve 66 to a prefeed pump (not illustrated) which is disposed upstream of the fuel source 5 or the hydraulic adjuster. Fluctuations of the adjusting pressure below the control sleeve 49 are thereby avoided, this being advantageous particularly in the case of injection systems designed for multi-cylinder internal combustion engines.

Claims (8)

1. An injection system comprising an injection quantity metering device for supplying a metered quantity of fuel, and at least one pumping nozzle for pumping and injecting metered quantities of fuel into a combustion chamber of an internal combustion engine, the pumping nozzle having a pump cylinder, a main piston and an auxiliary piston which enter the pump cylinder, and a compensating chamber located between the auxiliary piston and the main piston for receiving a pressuretransmitting liquid column of adjustable length, an injection nozzle and a control means for adjusting the length of the liquid column for the purpose of timing the commencement of injection, which control means includes a control sleeve which is guided in an adjusting cylinder and which surrounds the main piston and which is directly adjustable in the directions of the stroke of the main piston by means of a hydraulic pressure medium which acts upon the adjusting cylinder, the control edge lying in a plane normal to the longitudinal axis of the main piston.

2. An injection system as claimed in claim 1, wherein the control means comprises a control edge which co-operates with a control port and which is formed by a boundary edge of an annular groove which commences from a bore which passes through the control sleeve and surrounds the main piston, and wherein the annular groove has at least one associated control port which is located in the main piston and which communicates with the compensating chamber by way of a transverse bore located in the main piston, and a longitudinal bore.

3. An injection system as claimed in claim 1 or 2, wherein the adjusting cylinder is aligned coaxially of the pump cylinder and is contiguous thereto, and wherein the control sleeve comprises a piston which is hydraulically displaceable within the adjusting cylinder against the force of a return spring.

4. An injection system as claimed in claim 3, wherein sealing rings are fitted in two grooves incorporated in the periphery of the control sleeve in the region of the ends thereof, and an additional groove is disposed between the grooves, and wherein at least one transverse bore is disposed between the additional groove and the inner annular groove, and the adjusting cylinder has at least one port which is located opposite the additional groove and through which the hydraulic pressure medium can be fed to, and conducted from the compensating chamber.

5. An injection system as claimed in claim 4, wherein a one-way valve opening under pressure is connected to the port of the adjusting cylinder and opens towards a tank, and the main piston and the auxiliary piston are interconnected by way of a draw linkage which performs an idle stroke and then pulls the auxiliary piston along behind the main piston.

6. An injection system as claimed in claim 5, wherein the draw linkage comprises two hooks, one of which hooks is formed on the main piston and the other hook is formed on the auxiliary piston.

7. An injection system as claimed in claim 5 or 6, wherein the port located opposite the control sleeve is connected by way of a oneway valve, opening towards the control sleeve, to a line through which the pressure medium, subjected to adjusting pressure, is admitted to the adjusting cylinder from a hydraulic adjuster.

8. An injection system constructed and adapted to operate substantially as herein described, with reference to and as illustrated in the accompanying drawing.