EP0309501A1

EP0309501A1 - Fuel Injection Pump for Combustion engines.

Info

Publication number: EP0309501A1
Application number: EP19880902423
Authority: EP
Inventors: Helmut Laufer
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1987-04-07
Filing date: 1988-03-26
Publication date: 1989-04-05
Anticipated expiration: 2008-03-26
Also published as: KR890700752A; US4974564A; JP2818175B2; JPH01502768A; WO1988008080A1; DE3711744A1; EP0309501B1; DE3877302D1; KR960013108B1

Abstract

Sont décrits un procédé et un dispositif pour réguler la quantité d'injection de carburant au moyen d'une pompe d'injection de carburant. Ce procédé et ce dispositif permettent de réduire le bruit d'un moteur diesel pendant le ralenti et en charge partielle. La pompe d'injection de carburant comprend au moins un piston (3) produisant la pression nécessaire à l'injection et délimitant une chambre de travail (5) dans la pompe, ainsi qu'une soupape (26) qui s'ouvre par la pression de l'élément dans la chambre de travail (5) et se ferme au moyen d'un dispositif électromagnétique (34, 37). Lorsque la soupape (26) est ouverte, une partie du carburant refoulé dans la chambre de travail de la pompe (5) est évacuée par l'intermédiaire d'un canal de décharge (29) sans être injecté. La quantité de carburant parvenant à l'injection par unité de temps étant réduite, il faut allonger la durée globale de refoulement. L'allongement de la durée de l'injection permet une diminution du bruit de combustion. Lors de la charge partielle du moteur, la soupape (26) est fermée au moyen d'un dispositif électromagnétique(34, 37) après écoulement, depuis l'ouverture de la soupape, d'un intervalle de temps (DELTAt). Le carburant encore refoulé par la suite parvient pleinement à l'injection. L'ordre de grandeur de l'intervalle de temps (DELTAt) entre l'ouverture et la fermeture de la soupape est déterminé dans une unité de commande électronique (52) en fonction des paramètres de charge (59, 62) du moteur. Pendant la pleine charge du moteur, la soupape (26) reste fermée.A method and a device are described for regulating the amount of fuel injection by means of a fuel injection pump. This method and this device make it possible to reduce the noise of a diesel engine during idling and at partial load. The fuel injection pump comprises at least one piston (3) producing the pressure necessary for injection and delimiting a working chamber (5) in the pump, as well as a valve (26) which opens through the element pressure in the working chamber (5) and closes by means of an electromagnetic device (34, 37). When the valve (26) is open, part of the fuel discharged into the working chamber of the pump (5) is discharged via a discharge channel (29) without being injected. As the quantity of fuel arriving at the injection per unit of time is reduced, the overall delivery time must be extended. Extending the duration of the injection allows a reduction in combustion noise. When the engine is partially loaded, the valve (26) is closed by means of an electromagnetic device (34, 37) after a time interval (DELTAt) has elapsed from the opening of the valve. The fuel still pumped afterwards fully reaches the injection. The order of magnitude of the time interval (DELTAt) between the opening and closing of the valve is determined in an electronic control unit (52) according to the load parameters (59, 62) of the engine. During full engine load, the valve (26) remains closed.

Description

Method and device for controlling the fuel injection quantity

State of the art

The invention is based on a method and a device for controlling the fuel injection quantity by means of a fuel injection pump for internal combustion engines according to the type of the independent claims. As is known, most diesel engines have uncomfortably hard combustion noises when idling or in the low partial load range, which can be reduced by extending the injection duration in this speed range. It is already known to provide for this purpose in the case of fuel injection pumps a bypass opening into the pump work space and adjustable by an electric valve. In particular at low engine speeds, this bypass allows part of the fuel delivered in the pump work chamber to flow out into the suction chamber or into the fuel tank, bypassing the fuel injection nozzles. In this way, the injection duration can be extended. The amount of fuel sprayed off is the balance between the amount of fuel delivered by the pump workspace and the amount of fuel flowing out via the bypass.

In a fuel injection pump of this type known from DE-OS 35 07 853, an electric valve is used which flows into loose state keeps the bypass fully open and which closes the bypass with increasing electrical excitation. In a first operating state, the valve for defining 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 actuation 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 method according to the invention and the device according to the invention with the characterizing features of the independent claims have 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 a possible source of error can thus 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 is injected towards the end of delivery 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 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. FIG. 5 shows a fuel injection pump with an additional magnetic valve instead of the ring slide for controlling the total duration of the 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 lateral 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 supply 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 supply lines 14 leads to a pressure-actuated injection nozzle which is 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 its axial position in a known manner 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. When the valve closing member 25 is lifted from the valve seat 23, part of the fuel under pressure passes from the pump working chamber 5 via the extraction channel 20 into a collecting chamber 27 which partially surrounds the valve closing member 25 and which is connected via a relief channel 29 either to the suction chamber 9 or to a fuel reservoir . 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, a first magnetic gap being located between the armature 37 and one end face of the core 31 and a second magnetic gap being located between the armature 37 and an outer end face of the pole housing 35. If, when the valve closing member 25 is lifted from the valve seat 23, the solenoid 34 is supplied with electric current, the armature 37 is pulled towards the pole housing 35 while reducing the thickness of the magnetic gaps, whereby 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 pressure spring 38 acts, which on the other hand is supported on the bottom of a cup-shaped adjusting sleeve 40. The adjusting sleeve 40 can slide axially in a shoulder 41 of reduced diameter of the valve housing 30. The adjusting sleeve 40 is averted from the spring 38 and is supported by an adjusting screw 43 means of 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 entered 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 work chamber 5 and which generates a measurement signal as soon as the pressure in the pump work chamber 5 is reached at which the valve 26 opens.

Another method for generating an opening signal is to detect 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 part of the fuel via the extraction channel 20, the throttle 22 and the relief channel 29 from the pump work chamber 5 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. By reducing 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 space 5, as shown in Figure 4. The element pressure p _EL in the pump work chamber 5 is equal to the pressure in the extraction channel 20 immediately in front of 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 Throttle 22 via the collecting space 27 in the relief channel 29 and from there flow into the suction space 9 or in the fuel tank. After opening the valve 26, only a 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 closes is detected by one of the transmitters 50a, b, c and assigned to the electronic control unit 52 member 25 lifts off the valve seat 23, denoted by t ₀ . Up to this point in time, the valve 26, which is completely currentless, opens like a check valve only due to the force of the element pressure p _EL . At time t ₁ , valve 26 is fully open,

Fuel can both reach the respective injection valve via the relief duct 10 and the fuel delivery line 14 and also flow out via the throttle 22 and the relief duct 29.

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 supplied with electrical current by the electronic control unit 52. 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. From the point in time t _s = t ₀ + Δ t, fuel can no longer escape via the relief channel 29, and all fuel that is now 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 of the transverse bore 15 through the ring slide 16, the element pressure p _EL drops sharply, the fuel delivery to the injection valves has ended.

The opening time of the valve 26 is denoted by Δ t _ö in FIG. 3, that is to say that time difference t ₁ -t ₀ which the valve closing member 25 requires in order 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.

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, during which the electronic control unit 52 causes the 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 A t = t _s - t ₀ formed within the electronic control unit 52, 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 when the pump piston 3 begins to deliver, 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 in idle operation.

Since 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 therefore also in the idle mode in the vicinity of the full load position. 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 lower than would be the case with only a short injection duration. This advantage is particularly noticeable in idle mode, but the combustion noise can also be reduced in partial load mode by controlled grading of the injection rate combined with a lengthening of the delivery and injection duration. It is particularly advantageous in the described method 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 duct 10 into the suction chamber 9 or into the fuel reservoir.

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 t ₀ , from which the time difference Δ t 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

Expectations

1. A method for controlling the fuel injection quantity by means of a fuel injection pump for internal combustion engines, in which a pump piston which is axially movable in a pump cylinder conveys a part of the fuel located in a pump working space, which is determined by controlling the injection effective delivery duration of the pump piston, to at least one injection valve, the other one Part of the fuel can flow out bypassing the injection valve via a relief channel and in which the amount of fuel flowing out can be influenced by an electrically controllable valve, the actuation of which is carried out by signals from an electronic control unit as a function of load parameters of the internal combustion engine, characterized by the following, one Process steps forming the funding cycle:

1. If the element pressure of the fuel in the pump work chamber (5) increases due to the axial movement of the pump piston (3), the valve (26) opens in a pressure-actuated manner against the closing force of a spring (38);

2. The time (t ₀ ) of the opening of the valve (26) is detected by an encoder (50a, b, c) and assigned to the electronic control unit (52) as an initial signal;

3. At a time (t), the valve (26) closes, the time difference (Δ t = t _s - t ₀ ) being determined within the electronic control unit (52).

2. The method according to claim 1, characterized in that the speed (62) of the internal combustion engine and / or the position of the accelerator pedal (58) or the throttle valve is used as the load parameter.

3. The method according to claim 2, characterized in that the time difference (Δt = t _s - t ₀ ) decreases with increasing load of the internal combustion engine and increases with decreasing load of the internal combustion engine.

4. The method according to claim 3, characterized in that the valve (26) remains closed at full load of the internal combustion engine.

5. The method according to claim 1, characterized in that the time (t ₀ ) of the opening of the valve (26) representing the initial signal by a position, movement of the valve closing member (25) detecting displacement, speed or acceleration sensor or switch ( 50a) is generated.

6. The method according to claim 1, characterized in that the time (t ₀ ) of the opening of the valve (26) representing the initial signal is generated by a pressure sensor (50b) sensing the element pressure in the pump work chamber (5).

7. The method according to claim 1, characterized in that the time (t ₀ ) of the opening of the valve (26) representing the initial signal is generated by a position sensor of the pump piston (3) detecting the encoder (50c).

8. A fuel injection pump for internal combustion engines, in particular for carrying out one of the methods according to the preceding claims, with a pump piston which is axially movable in a pump cylinder, a pump working space enclosed by the latter and a Relief channel which can be connected to the pump work space via an electrically controlled valve, characterized in that the valve (26) has a valve closing member (25) which is acted upon on the one hand by the pressure in the pump work space (5) and on the other hand by the pressure of a spring (38) and which, when the electrically controlled valve (26) is actuated, is moved in the direction of the force of the spring (38) against a fixed valve seat (23) and that the fuel injection pump has a fuel quantity control element (16, 72) by means of which the injection effective delivery duration of the pump piston ( 3) is controlled.

9. Fuel injection pump according to claim 8, characterized in that there is a throttle (22) for the fuel between the pump working chamber (5) and the valve seat (23).

10. Fuel injection pump according to claim 8, characterized by an adjusting device (40, 43) by means of which the bias of the spring (38) can be changed.

11. Fuel injection pump according to one of claims 8 to 10, characterized in that an electromagnetically actuated valve is used as the electrically controlled valve (26).

12. Fuel injection pump according to claim 8, characterized in that the fuel quantity control member is designed as a valve device which monitors a discharge channel (10) leading away from the pump work chamber (5).

13. A fuel injection pump according to claim 12, characterized in that the valve device is designed as a ring slide (16) which can be displaced on the pump piston (3) and through which the relief channel (10) emerging on the pump piston (3) can be opened in the course of the pump piston stroke (Figure 1 ).

14. Fuel injection pump according to claim 13, characterized in that the ring slide (16) is electrically adjustable.

15. Fuel injection pump according to claim 12, characterized in that the valve device is designed as a solenoid valve (72) through which the relief channel (10) can be opened in the course of the pump piston stroke (Figure 5).