EP0309501B1 - Fuel injection pump for combustion engines - Google Patents

Abstract

A process and a device for quantity control of fuel injection by means of a fuel injection pump are proposed. With the process or with the device, the noise of a diesel engine during idling and partial loading can be reduced. The fuel injection pump includes at least one pump piston (3) which produces the pressure for the injection and delimits a pump working chamber (5), as well as a valve (26) which is opened by the element pressure in the pump working chamber (5) and closed by an electromagnetic device (34, 37). When the valve (26) is open, some of the fuel supply in the pump working chamber (5) is conveyed away through a discharge channel (29) without being injected. As this reduces the quantity of fuel injected in unit time, the overall delivery time must be prolonged. By prolonging the duration of injection, the noise of the combustion is reduced. During partial loading of the internal combustion machine, the valve (26) is closed by means of the electromagnetic device (34, 37) after a time-interval (DELTA) has elapsed since the valve was opened. The fuel which is conveyed thereafter is is injected. The magnitude of the time-interval (DELTAt) between opening and closing of the valve is determined in an electronic control unit (52) in function of load parameters (59, 62) of the internal combustion engine. During full-load operation of the internal combustion engine, the valve (26) remains closed.

Description

The invention is based on a fuel injection pump according to the preamble of claim 1. A fuel injection pump of this type is known from FR-A-2 299 523. There, the relief duct leads away from the pump cylinder in the effective area of the pump piston and is distributed by one of several filling grooves, which are distributed around the circumference of the pump piston, which is driven back and forth and rotates at the same time, and also serve to supply the pump work space with fuel. steered on. The control takes place in the known fuel injection pump shortly after the pressure stroke or delivery stroke of the pump piston has begun. In the known fuel injection pump, the solenoid valve that controls the relief channel is opened during idling and in the low speed range, in each case over the entire pump piston delivery stroke. This fuel injection pump has the disadvantage that a fixed throttle is provided to reduce the fuel injection delivery rate, which is either always open or always closed, depending on the operating range of the internal combustion engine. In transitions, there is a sudden change in the fuel injection rate or the fuel injection duration, which is to be extended by the outflow via the throttle in idle mode and in part-load mode. The advantageous effect in this area consists in a lower combustion noise of the internal combustion engine, although the effect cannot be optimally adapted to the various load conditions of the internal combustion engine.

In a fuel injection pump of this type known from DE-OS 35 07 853, an electric valve is used which is in the de-energized state State that the bypass is fully open and which closes the bypass with increasing electrical excitation. In a first operating state, the valve for fixing the injection phase is completely closed and in a second operating state, in idle mode, is only partially closed over the entire duration of the injection with the result that the fuel injection rate is reduced. To compensate for this, the duration of the partially closed state compared to an injection with a high injection rate must be extended accordingly in order to bring the same amount of fuel to the injection. In this fuel injection pump, the start and end of delivery are determined solely by the closing or opening movement of the valve, which requires precise coordination between the delivery movement of the pump piston and the electrical control of the valve. Even slight irregularities in the mutual coordination of these movements can lead to major changes in the fuel quantities reaching the injection valves and thus to irregularities in the fuel metering of the internal combustion engine.

Advantages of the invention

The device according to the invention with the characterizing features of the independent claim has the advantage that precise coordination between the delivery movement of the pump piston and the electrical control of the valve for determining the start of delivery can be eliminated and thus a possible source of error can be eliminated. With the pressure-actuated opening of the valve, an initial signal is generated, which forms the basis for the further control of the electric valve.

It is particularly advantageous that the course of the injection can be designed in such a way that the one reaching the injection valves Fuel quantity towards the end of delivery is injected with a high injection rate, but at the beginning of injection with a reduced injection rate that takes into account the still low combustion rate. This increases the combustion efficiency and reduces the combustion noise, these advantages also being achieved above the idling speed and idling quantity.

drawing

Embodiments of the invention are shown in simplified form in the drawing and explained in more detail in the following description. FIG. 1 shows a fuel injection pump in a simplified representation with a ring slide valve for controlling the fuel quantity, FIG. 2 shows a diagram that shows the course of the pump piston stroke over time, FIG. 3 shows a diagram that shows the course of the stroke of the valve closing member over time, FIG 4 shows a further diagram which shows the course of the element pressure in the pump working chamber over time. Figure 5 shows a fuel injection pump with an additional solenoid valve instead of the ring slide to control the total duration of injection per pump piston stroke.

Description of the embodiments

In the fuel injection pump shown in FIG. 1, for example, a socket 2 is arranged in a housing 1, in which a pump piston 3 executes a reciprocating and simultaneously rotating movement. The pump piston 3 is driven in a manner known per se by a cam drive via a shaft which rotates synchronously with the speed of the internal combustion engine supplied with fuel by the injection pump. The pump piston 3 is mounted in a pump cylinder 4 within the bushing 2. The pump piston 3 encloses the pump cylinder 4 with a pump working space 5 which Via a filling groove 6 in the outer surface of the pump piston 3 during the suction stroke thereof, it is connected to a fuel supply line 8 which opens laterally on the pump piston 3 into the pump cylinder 4. This branches off from a suction chamber 9 which is filled with fuel-controlled pressure levels by means not shown.

A relief channel 10 runs axially in the pump piston 3, from which a radial bore 11 leads and opens into a distributor groove 12. This is connected in the course of the pump piston working movement during each pressure stroke of the pump piston 3 to one of a plurality of fuel delivery lines 14 which, in an axial plane corresponding to the number and distribution of the cylinders of the associated internal combustion engine to be supplied by the fuel injection pump, around the pump piston 3 from the pump cylinder 4 branch. Each of the fuel delivery lines 14 leads to a pressure-actuated injection nozzle known per se.

The relief channel 10 merges in a part of the pump piston 3 projecting into the suction chamber 9 into a transverse bore 15, the mouth of which is controlled on the outer surface of the pump piston 3 by a ring slide 16 which can be moved tightly on the pump piston 3. By a controller, of which only one eccentric 18 is shown in the drawing, the ring slide 16 is adjusted in a known manner in its axial position in order to change that lifting point of the pump piston 3 at which the delivery of fuel to the injection nozzles by opening the Relief channel 10 is ended. A mechanical or hydraulic as well as an electrical signal box can be used to adjust the ring slide 16.

A removal duct 20 branches off from the pump work chamber 5, which is followed by a constriction designed as a throttle 22. After the throttle 22, the extraction channel 20 merges into a valve seat 23, which cooperates with an axially movable valve closing member 25 of an electrically controllable valve 26, so that when the valve closing member 25 rests on the valve seat 23, the removal channel 20 is blocked off. When the valve closing member 25 is lifted from the valve seat 23, part of the pressurized fuel passes from the pump working chamber 5 via the extraction channel 20 into a collecting chamber 27 partially surrounding the valve closing member 25, which is connected via a relief channel 29 either to the suction chamber 9 or to a fuel storage container . The valve 26 thus controls a bypass for the fuel.

The valve closing member 25 is guided axially by a soft magnetic core 31 arranged inside a valve housing 30. The core 31 forms the inner part of a soft magnetic pole housing 35 which almost completely surrounds a magnetic coil 34 and which is embedded in the valve housing 30. The valve closing member 25 is fixedly connected to an armature 37 at its end facing away from the valve seat 23, with a first magnetic gap between the armature 37 and an end face of the core 31 and a second magnetic gap between the armature 37 and an outer end face of the pole housing 35. If electrical current is applied to the solenoid 34 when the valve closing member 25 is lifted off the valve seat 23, the armature 37 is pulled towards the pole housing 35 while simultaneously reducing the thickness of the magnetic gaps, as a result of which the valve closing member 25 moves towards the valve seat 23; the valve 26 closes.

On the flat side of the armature 37 facing away from the valve closing member 25, a spring 38 acts on pressure, which on the other hand is supported on the bottom of a pot-shaped adjusting sleeve 40. The adjusting sleeve 40 can slide axially in a shoulder 41 of reduced diameter of the valve housing 30. Averted from the spring 38, the adjusting sleeve 40 is supported on an adjusting screw 43, which means its thread within the valve housing 30 is axially adjustable. By turning the adjusting screw 43, the axial position of the adjusting sleeve 40 can be changed, which directly changes the pretension of the spring 38 acting on the armature 37. The adjusting screw 43 thus serves to set that opening pressure in the pump work chamber 5 at which the valve closing member 25 lifts off the valve seat 23, ie the valve 26 opens.

It is essential for the invention that the point in time is recorded at which the valve closing member 25 lifts off the valve seat 23 with increasing pressure in the pump work chamber 5. This is done by sensors, three of which are shown in the drawing and are briefly explained below:
The sensors can be designed, for example, as position, speed or acceleration sensors or as switches 50a and arranged in the valve 26 in such a way that the latter generates a signal at the same time that the valve closing member 25 lifts off the valve seat 23. This signal is assigned to an electronic control unit 52.

An indirectly working method for generating an opening signal to be assigned to the electronic control unit 52 consists in attaching a pressure sensor 50b, which detects the pressure in the pump workspace 5 and which generates a measurement signal as soon as the pressure in the pump workspace 5 at which the valve 26 opens is reached.

Another method for generating an opening signal consists in detecting the axial movement of the pump piston 3 by means of a displacement sensor 50c. This is also an indirect method for detecting the opening time of the valve 26.

This is only intended to reflect a selection of methods for determining the start of opening of the valve 26 and in this way establishing a start and reference time. Ultimately, it is crucial to receive an electrical signal that reports to the electronic control unit 52 the time at which the valve closing member 25 lifts off the valve seat 23, and consequently a portion of the fuel from the pump work chamber 5 via the extraction channel 20, the throttle 22 and the relief channel 29 can flow off.

The electronic control unit 52 is also assigned further electrical signals which, above all, describe the position of an accelerator pedal 58, determined, for example, via a further travel sensor 59 and the speed 62 of the internal combustion engine.

The pump piston 3 is moved axially in the direction of the pump working chamber 5 by the cam drive, as is described in FIG. 2. As a result of the reduction in the volume of the pump work chamber 5 with simultaneous back pressure of the pressure-actuated injection valves connected to the fuel delivery line 14, the element pressure p _EL in the pump work chamber 5 increases, as shown in FIG. 4. The element pressure p _EL in the pump work chamber 5 is equal to the pressure in the extraction channel 20 immediately before the valve seat 23. If this element pressure increases with increasing compression, the counter pressure of the spring 38 rises, the valve closing member 25 lifts off the valve seat 23, fuel can thus be throttled by the Throttle 22 via the collecting space 27 in the relief channel 29 and flow from there into the suction space 9 or in the fuel tank. After opening the valve 26, only part of the fuel delivered by the pump piston 3 reaches the injection valves, while the other part can flow out at least temporarily via the opened valve 26. In FIGS. 3 and 4, the reference time at which the valve closing member is detected by one of the transmitters 50a, b, c and assigned to the electronic control unit 52 is 25 lifts off the valve seat 23, designated t₀. Up to this point in time, the valve 26, which is still completely currentless, opens like a check valve only due to the force of the element pressure p _EL . At the time t 1, the valve 26 is fully open, fuel can reach the respective injection valve via the relief duct 10 and the fuel delivery line 14 as well as flow out via the throttle 22 and the relief duct 29.

kann also kein Kraftstoff mehr über den Entlastungskanal 29 entweichen, sämtlicher fortan geförderter Kraftstoff gelangt zum Einspritzventil. Der Elementdruck im Pumpenarbeitsraum unterliegt nur noch dem Gegendruck der Einspritzdüsen, ein Druckabbau über den Entnahmekanal 20, die Drossel 22 und den Entlastungskanal 29 ist nicht mehr möglich, wodurch sich der Elementdruck p_EL und damit die Kraftstoffeinspritzrate schlagartig erhöht. Diese Erhöhung nach dem Zeitpunkt t_s ist in Figur 4 durch die strichpunktierte Linie dargestellt. Führt die axiale Bewegung des Pumpenkolbens 3 in den Bereich der Aufsteuerung de: Querbohrung 15 durch den Ringschieber 16, so fällt der Elementdruck p_EL stark ab, die Kraftstofförderung zu den Einspritzventilen ist beendet.Depending on the accelerator pedal position determined by the further travel sensor 59 and the speed 62 of the internal combustion engine, a time difference .DELTA.t (see FIG. 4) is determined within the electronic control unit 52, after the end of which the magnetic coil 34 is acted upon by the electronic control unit 52 with electrical current. As a result, the armature 37 is pulled in the direction of the pole housing 35, the valve closing member 25 closes the valve seat 23 ${\text{t}}_{\text{s}}\text{= t₀ + Δ t}$

So no more fuel can escape via the relief channel 29, all fuel that is now being delivered reaches the injection valve. The element pressure in the pump work space is only subject to the back pressure of the injection nozzles, a pressure reduction via the extraction channel 20, the throttle 22 and the relief channel 29 is no longer possible, as a result of which the element pressure p _EL and thus the fuel injection rate suddenly increases. This increase after the time t _s is shown in FIG. 4 by the dash-dotted line. If the axial movement of the pump piston 3 leads into the area of the opening de: transverse bore 15 through the ring slide 16, the element pressure p _EL drops sharply, the fuel delivery to the injection valves has ended.

With Δ t _ö in Figure 3, the opening time of the valve 26 is designated, that is the time difference t₁ - t₀, which the valve closing member 25 needs to open completely due to the element pressure. With Δ t _s is the pull-in delay time of the armature 37 and thus denotes the closing time of the valve 26, that is to say that period of time between the electrical closing signal of the electronic control unit 52 and the actual contact of the valve closing member 25 on the valve seat 23.

ist, desto geringer ist die über die Drossel 22 abströmende Kraftstoffmenge und desto größer ist die von den Einspritzventilen abgespritzte Menge Brennstoffs.The simply dashed line in FIGS. 3 and 4 represents the axial movement of the valve closing member 25 (h _V ) or the element pressure (p _EL ) for a higher load state of the internal combustion engine. In this case, the time difference .DELTA.t 'when it expires electronic control unit 52 causes valve 26 to close. Due to the early closing of the bypass, a higher element pressure is built up earlier in the pump work chamber 5 than in the previous example, as a result of which the fuel quantity emitted by the injection valve increases. The smaller the time difference formed within the electronic control unit 52 ${\text{Δ t = t}}_{\text{s}}\text{- t₀}$

is, the smaller the amount of fuel flowing out through the throttle 22 and the greater the amount of fuel sprayed off by the injection valves.

When the internal combustion engine is operating at full load, the solenoid 34 is continuously energized, the valve 26 remains closed.

The other limit case is formed by the lowest idling mode of the internal combustion engine. In Figures 3 and 4, this load case is shown with a solid line. If the internal combustion engine is idling, which is transmitted to the electronic control unit 52 via the speed sensor 62 and the further travel sensor 59, the energization of the solenoid 34 can be completely omitted. The valve 26 therefore opens due to the increasing element pressure p _EL at the start of delivery of the pump piston 3, remains in this open position and closes due to pressure when the pump working chamber 5 is relieved by opening the relief channel 10 by means of the ring slide 16. In certain cases, For example, when the engine is cold, in order to achieve a larger injection quantity, it may also be necessary to prematurely close the valve 26 by energizing the solenoid 34 even when idling.

Since a part of the fuel flows out via the throttle 22 during the conveying movement of the pump piston 3, only a small amount of fuel, namely exactly the amount of fuel which is sufficient for the idle operation of the internal combustion engine, reaches the injection valves. By opening the bypass, the amount of fuel reaching the injection valves per unit of time is less than it would be if the bypass was closed. To compensate, the funding period must be extended. This is achieved by the ring slide 16 controlling the cross bores 15 very late or not at all. The ring slide 16 is thus in the vicinity of the full load position even when idling. When the load is taken from the above operating state, the valve 26 is closed increasingly earlier before the end of delivery, that is to say the time interval Δ t is reduced.

The necessary extension of the delivery duration and injection duration due to the temporary opening of the bypass results in a particularly soft combustion. The combustion noise of a diesel engine operated with the aid of this method is less than would be the case with only a short injection duration. This advantage is particularly noticeable in idle operation, but the combustion noise can also be reduced in partial load operation by controlled gradation of the injection rate combined with a lengthening of delivery and injection duration. It is particularly advantageous in the method described that the greatest fuel delivery rate is only reached after the time interval Δ t has elapsed and thus towards the end of the injection. This is beneficial for a quiet engine.

In the second exemplary embodiment of a fuel injection pump shown in FIG. 5, parts having the same effect are provided with the same reference symbols. In contrast to the first exemplary embodiment, the relief duct 10 is located in the housing 1. It opens into the pump working chamber 5 on the one hand, and into the suction chamber 9 on the other hand and can be closed by means of a further solenoid valve 72. The solenoid valve 72, which, in contrast to the valve 26, has no upstream throttle, replaces the ring slide 16 of the first exemplary embodiment and, like this, determines the start and end of delivery. The start of delivery is determined by the closing and the end of delivery by opening the solenoid valve 72. After opening the solenoid valve 72, the fuel delivered by the pump piston 3 no longer reaches the injection valves, but flows out via the relief channel 10 into the suction chamber 9 or into the fuel storage container.

The solenoid valve 72 can also be used instead of the transmitters 50a, b, c to determine the reference point in time, in that the point in time at which the solenoid valve 72 closes (for example by electromagnetic actuation) and thus the fuel delivery to the injection valves begins in the electronic control unit 52 is stored as the initial time t₀, from which the time difference Δt for closing the valve 26 is then calculated. Valve 26 and solenoid valve 72 are therefore components of a common control concept, which is defined within the electronic control unit 52. The start and end of delivery is determined by solenoid valve 72, and the delivery rate by valve 26.

Claims (6)

1. Fuel injection pump for internal combustion engines, having a pump piston (3) driven in a reciprocating manner in a pump cylinder (4) to produce a suction stroke and a delivery stroke, which pump piston (3) encloses, in the pump cylinder (4), a pump working space (5) which is connected during the suction stroke of the pump piston to a fuel reservoir (9) via a fuel supply conduit (8) controlled by the pump piston and can be connected, during the delivery stroke, to a fuel injection valve via a fuel delivery conduit (10, 14) and simultaneously to a relief space (9) via a relief passage (29) which contains an electric valve (26), controlled as a function of load, and a drain throttle (22), and which pump working space can be relieved via a valve (15, 16; 72) controlled as a function of load in order to end the delivery stroke effective for injection, the electrically controlled valve having a valve closing element (25) actuated by a spring (38) in the closing direction, which valve closing element (25) can be actuated by an electromagnet (31, 34, 35, 37) and is subject to the pressure in the pump working space in the opening direction against the force of the spring (38), characterised in that the valve closing element (25) can be brought into the closed position by the electromagnet and the relief passage (29) is permanently connected to the pump working space (5) and the electrically controlled valve is opened, controlled by a control device (52), in the idling and part-load range of the internal combustion engine during each delivery stroke of the pump piston by the pressure in the pump working space when the electromagnet (31, 34, 35, 37) is not excited and, with increasing load, is closed earlier during the course of the delivery stroke of the pump piston by the controlled excitation of the electromagnet, the opening time (t₀) of the electrically controlled valve (26) being recorded as a control signal by a device (50a, 50b, 50c) recording the motion of the valve closing element (25), which control signal is supplied to the control device (52) to control the closing time, variable as a function of load, of the electrically controlled valve (26).
2. Fuel injection pump according to Claim 1, characterised in that the electrically controlled valve is permanently closed by the electromagnet (31, 34, 35, 37) during full-load operation of the internal combustion engine.
3. Fuel injection pump according to Claim 1, characterised in that the starting signal representing the time (t₀) of the opening of the valve (26) is generated by a displacement sensor, velocity sensor or acceleration sensor or switch (50a) recording the position or the motion of the valve closing element (25).
4. Fuel injection pump according to Claim 1, characterised in that the starting signal representing the time (t₀) of the opening of the valve (26) is generated by a pressure sensor (50b) recording the element pressure in the pump working space (5).
5. Fuel injection pump according to Claim 1, characterised in that the starting signal representing the time (t₀) of the opening of the valve (26) is generated by a displacement sensor (50c) recording the position of the pump piston (3).
6. Fuel injection pump according to one of the preceding claims, characterised in that the preload on the spring (38) can be changed by means of an adjustment device (40, 43).

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