EP0525401A1 - Fuel injection pump for internal combustion engines - Google Patents

Abstract

In a fuel injection pump with a reciprocating and at the same time rotationally driven pump piston (14), on the suction stroke of which fuel is drawn in by way of filling apertures (16) on the pump piston and a fuel feed duct (17) containing a solenoid valve (45) serving to switch off the fuel injection pump, and at a delivery stroke of which fuel is injected through an annular slide valve (37) until a relief line (40, 39) of the pump working chamber (15) in the pump piston (14) opens, an annular groove (48) connected to the pump working chamber is provided on the pump piston, which groove, after the last delivery end stroke hFE, is connected in a stroke hN to the fuel feed duct (17, 49), so that, when the solenoid valve (45) is closed, the pressure of the pump working chamber (15) can gradually be relieved towards the feed duct without abruptly loading the solenoid valve (45) and encouraging it to open. <IMAGE>

Description

State of the art

The invention is based on a fuel injection pump according to the preamble of the main claim. In such a fuel injection pump, known from DE-A 38 06 669, when the highest fuel injection quantity is delivered, i.e. when the fuel injection pump is operating at full load, the ring slide is brought into a position in which the outlet of the longitudinal channel opens during a pump piston stroke in which the annular groove occurs has already come into connection with the confluence of the fuel supply channel. In this known fuel injection pump at full load operation and controlled by the annular groove on the pump piston, there is always a constant delivery end. If the fuel injection quantity of the fuel injection pump is regulated by the controller when the maximum speed is reached, the ring slide is then adjusted in order to open the outlet of the longitudinal channel earlier and thus reduce the fuel injection quantity to drastically reduce the speed of the internal combustion engine. The aim is for the ring slide to travel a certain adjustment path before the actual regulation traffic, which is effected by a centrifugal speed sensor against the force of a control spring. It is avoided that the ring slide executes an oscillating movement at the beginning of the reduction in the fuel injection quantity, which is due to the beginning change in the balance of forces at the regulator between the centrifugal speed sensor and the force in the control spring. With this solution an exact start of the maximum fuel injection quantity control is achieved and thus a maximum of the power in the limit speed range.

It is also known from DE-A 25 03 345 a fuel injection pump, in which a solenoid valve of the generic type is also provided in the fuel supply channel. In the de-energized state, in this solenoid valve, a valve member is pressed by a closing spring onto a valve seat formed in the fuel supply channel and the fuel supply channel is closed in the process. When the ignition key is actuated to start the internal combustion engine, the solenoid valve is excited, so that the valve member lifts off the valve seat while the fuel supply channel is released. To shut off the internal combustion engine, the valve closing member then returns to the closed position after being de-energized after the power supply has been interrupted by the ignition key.

Under certain conditions, it can happen that the valve member of the solenoid valve, which is brought into the closed position, is acted upon by a pressure surge from the work space if the connection between the pump work space and the fuel supply channel is established through the filling opening in the pump piston during the remaining delivery stroke of the pump piston. This pressure surge can then result in the valve member lifting off the valve seat and a brief refilling of the pump work space via the fuel supply channel. This amount of fuel flowing into the pump work chamber is then injected during the next delivery stroke of the pump piston. The internal combustion engine cannot be brought to a standstill as desired and continues to run.

If, as also provided, the solenoid valve is also to be used as an emergency stop device if errors occur in the fuel injection quantity control that can lead to the internal combustion engine going through, in this case the shutdown of the internal combustion engine by the solenoid valve cannot take place to a sufficiently reliable degree.

Advantages of the invention

The fuel injection pump according to the invention with the characterizing features of claim 1 has the advantage that when the fuel supply channel is blocked by the solenoid valve and when there is a residual amount of fuel in the pump work space, which is brought to a high fuel pressure during the pump piston delivery stroke, the pump work space already during the delivery stroke the pump piston is connected to the fuel supply channel between the solenoid valve and the pump cylinder via the annular groove, so that the pressure in the pump working chamber can gradually be relieved in the course of the pump piston delivery retraction stroke in this part of the fuel supply channel and there is no pressure shock wave, as is otherwise the case when the connection is made Filling opening during the suction stroke of the pump piston. This means that no further fuel is drawn in due to an unwanted reopening of the solenoid valve and the solenoid valve can safely prevent the internal combustion engine from being supplied with fuel.

And by the measures listed in the further claims, advantageous developments and improvements of the fuel injection pump specified in claim 1 are possible. The configuration according to claim 5 results, in particular, in a throttled connection between the pump work chamber and the fuel supply channel part between the solenoid valve and the pump cylinder during the pump piston retraction stroke. This enables an even better time-delayed reduction of the pressure in the pump work space during the remaining stroke of the pump piston. The design according to Patentan saying 6 results in an advantageous embodiment of the throttle connection.

drawing

The invention is explained in more detail in the following description with reference to two exemplary embodiments shown in the drawing.

• Fig. 1 einen Längsschnitt durch eine Kraftstoffeinspritzpumpe, der Verteilerpumpenbauart in schematischer Darstellung.
• Fig. 2 einen Schnitt längs der Linien 11-11 in Fig. 1,
• Fig. 3 ein Diagramm des Hubes h des Pumpenkolbens der Kraftstoffeinspritzpumpe in Fig. 1 in Abhängigkeit vom Drehwinkel des Pumpenkolbens und
• Fig. 4 ein zweites Ausführungsbeispiel der Erfindung mit der Füllöffnung vorgelegter Ringnut.

Show it:

• Fig. 1 shows a longitudinal section through a fuel injection pump, the distributor pump type in a schematic representation.
• 2 shows a section along lines 11-11 in FIG. 1,
• Fig. 3 is a diagram of the stroke h of the pump piston of the fuel injection pump in Fig. 1 depending on the angle of rotation of the pump piston and
• Fig. 4 shows a second embodiment of the invention with the filling opening presented annular groove.

Description of the embodiment

1, a pump cylinder 12 is inserted in a pump housing 11, in its cylinder bore 13 a pump piston 14 by a drive shaft, not shown, and a cam gear known per se into a rotating one and at the same time back and forth movement is offset, as indicated by the arrows in Fig. 1. The pump piston 14 delimits a pump working space 15 in the cylinder bore 13, which is supplied with fuel during the suction stroke of the pump piston 14 via longitudinal grooves 16 which start from the front side of the pump piston and serve as filling openings. As can be seen from the sectional view in FIG. 2, the suction slits 16 are distributed around the circumferential surface of the pump piston 14 at uniform angular intervals. Corresponding to the four-cylinder internal combustion engine, four suction slots 16 are provided for four suction strokes of the pump piston 14 per pump piston revolution. During the suction stroke of the pump piston 14, one of the suction slots 16 is connected to a fuel supply channel 17 opening laterally into the cylinder bore 13, which leads to a pump suction chamber 18 , which is enclosed in the pump housing 11, communicates. The pump suction chamber 18 is supplied with fuel from a fuel reservoir 20 by a fuel delivery pump 19. The fuel in the pump suction chamber 18 is under speed-dependent pressure, which is additionally set by a pressure control valve 21.

Within the pump suction chamber 18, a ring slide 37 serving for injection quantity control sits axially displaceably on a part of the pump piston 14 projecting into the pump suction chamber, which is actuated in a known manner by a regulator of known type, not shown here, via a regulator lever 38 and thereby the outlet opening of a transverse bore 39 in Pump piston 14 controls. The transverse bore 39 is connected to an axial longitudinal channel 40 in the pump piston 14, which enters the end of the pump piston 14 that delimits the pump working space 15 and ends as a blind bore.

A radial bore 41 branches off from this longitudinal channel 40 and leads to a distributor opening 42 in the lateral surface of the pump piston 14 in the form of a longitudinal groove. At the level of this distributor opening 42, four pressure lines 43, which are each connected to an injection valve 44, open into the cylinder bore 13 of the pump cylinder 12 offset by the same angle of rotation. Of the four pressure lines 43 and four injection valves 44, only one pressure line 43 and one injection valve 44 can be seen in FIG. 1.

As already mentioned, the pump piston 14 sucks fuel from the pump suction chamber 18 during the respective suction strokes via a longitudinal groove 16 which is then covered with the suction channel 17, so that the pump working chamber 15 is fuel-filled at the beginning of the subsequent delivery stroke of the pump piston 14. The start of the delivery stroke is defined by the pump piston 14 being closed by the pump piston 14 as a result of the longitudinal groove 16 emerging from the mouth of the suction channel 17. The ring slide 37 has closed the outlet openings of the transverse bore 39, so that the fuel located in the pump work chamber 15 is brought to high pressure and is then supplied via the longitudinal channel 40, the radial bore 41 and the distributor opening 42 to one of the pressure lines 43 and the corresponding injection valve 44. The delivery stroke of the pump piston is ended when, after a stroke of the pump piston 14 predetermined by the axial position of the ring slide 37, the transverse bore 39 emerges from the overlap with the ring slide, the front-side limits of the ring slide inner bore serving as the control edge. The pump work chamber 15 is then relieved via the longitudinal channel 40 and the transverse bore 39 to the pump suction chamber 18. The delivery pressure of the pump piston 14 falls below the opening pressure of the injection valve 44, and the high-pressure injection is interrupted.

The internal combustion engine is general High-pressure injection stopped. For this purpose, a solenoid valve 45 designed as a seat valve is provided in the fuel supply channel 17, the valve member 46 of which, when the solenoid valve 45 is de-energized, is pressed onto a valve seat 47 formed in the fuel supply channel 17 by a closing spring. The solenoid valve 45 is excited when the ignition is switched on, as a result of which the valve member 46 lifts off the valve seat 47 and releases the fuel supply channel 17 and remains excited during the entire operating period of the internal combustion engine. If the internal combustion engine is to be stopped, where the ignition is interrupted, so that the valve member 46 is pressed again by the closing spring onto the valve seat 47 and the suction channel 17 is blocked. The pump piston 14 can no longer suck in fuel in the following suction stroke and the internal combustion engine stops.

In the event of faults in the fuel injection pump of the known type described above and also in the transition from normal operation of the fuel injection pump or internal combustion engine to switching off the fuel supply by closing the solenoid valve, it can happen that when connecting the pump work space 15 through one of the filling openings 16 during the suction stroke of the pump piston, a pressure surge reaches the solenoid valve 45 from the pump working space 15 brought to high pressure and pushes it open. Such a malfunction can occur, for example, when the ring slide 37 comes to an extreme position, e.g. B. by clamping on the pump piston 14 and loosening the regulator lever 38, and thereby the transverse bore 39 does not emerge from the ring slide 37 at the predetermined delivery end before the filling opening 16 with the mouth of the fuel supply channel 17 overlaps. This pressure surge leads to the valve member 46 lifting off the valve seat 47 and a brief refilling process of the pump work space 15 taking place via the fuel supply channel 17. This amount of fuel flowing into the pump work chamber 15 is brought to the injection on the next delivery stroke of the pump piston 14 and the shutdown of the internal combustion engine by the solenoid valve is not achieved.

In order to avoid this and to reliably stop the internal combustion engine when the ignition is switched off and the associated de-energization of the solenoid valve 45, an annular groove is arranged in the outer surface of the pump piston 14, which is arranged in front of the filling openings 16 on the side of the pump piston drive. In the exemplary embodiment shown, the filling openings 16 are continuously connected to the annular groove 48.

With each pump piston stroke, the annular groove comes towards the end of the pump piston stroke in connection with the orifice 49 of the fuel supply channel 17. With the solenoid valve open, i. H. during normal operation of the internal combustion engine and the fuel injection pump, the connection of the annular groove to the fuel supply channel 17 then relieves the pump work chamber towards the suction chamber 18 and ends the injection-effective pump piston stroke. The remaining fuel required by the pump piston flows out to the suction chamber. The filling openings have not yet come into direct connection with the mouth 49 of the fuel supply channel 17.

FIG. 3 shows the cam elevation curve of the pump piston drive or the stroke curve of the pump piston, from bottom dead center UT to top dead center OT via the rotation angle alpha of the pump piston. With the dashed line there is entered the stroke h, which corresponds to the stroke at which the annular groove 48 comes into connection with the mouth 49. This useful stroke is always greater than the largest stroke of the pump piston h in which, in the highest position of the ring slide 37, the transverse bore 39 is opened by the control edge on the end face of the ring slide in order to terminate a fuel injection controlled by the regulator of the fuel injection pump. This stroke h FE can be changed by the controller depending on the load of the internal combustion engine. Should, however, as described above, the ring slide clamp on the pump piston, there is no opening of the pump work space via the transverse bore 39 to the pump suction chamber 18. In this case, relief via the ring groove 48 is possible, which in itself does not function during normal operation of the fuel injection pump has, since the pump work space relief is controlled solely by the ring disc.

If the internal combustion engine is to be switched off, the solenoid valve 45 is cut off from the power supply, so that its closing member comes into the closed position and closes the fuel supply channel between the mouth 49 and the suction chamber 18. If the pump piston is currently in the delivery stroke, the pump high-pressure delivery to the injection valves via the distributor opening is ended by opening the transverse channel 39, as in normal operation. Nevertheless, a relatively high pump pressure arises in the pump work chamber, which is in particular higher than the suction chamber pressure but lower than the injection pressure. However, this pressure is not suddenly passed through the filling openings 16 to the closing element of the solenoid valve during the subsequent suction stroke, but rather slowly towards the end of the high-pressure delivery stroke through the annular groove gradually opening up the pump work chamber to the solenoid valve relieved. This avoids a pressure surge that strikes the solenoid valve again. If the pump piston is at the time of the closing of the solenoid valve during the suction stroke, a lower pressure than the suction chamber pressure is activated due to the lack of inflowing fuel, since at least once the cross bore 39 has been closed, no more fuel can flow in through the ring slide. But even if the cross bore 39 is still open, ie before immersion in the ring slide, the cross section of the cross bore 39 is not sufficiently large to fill the pump work space with fuel that is under the same pressure as the suction space pressure. From the closing of the bore 39 at the latest, there is a considerable reduction in the pump work space. This lowering is also effective in the area between the cylinder bore and the solenoid valve in the fuel supply channel. During the subsequent delivery stroke of the pump piston, the fuel supply channel is then separated from the pump work space by the rotation of the pump piston. The fuel that got into the pump work space during this time is then first brought to normal pressure and then compressed, so that it still comes to a relatively high pressure in the pump work space at the end of the pump piston stroke even after the transverse bore 39 has emerged from the ring slide, which then suddenly occurs without an annular groove provided according to the invention could in turn open the solenoid valve at the beginning of the suction stroke via a pressure surge. However, this sudden introduction of pressure is avoided by the annular groove according to the invention and the pump work chamber is gently relieved of the solenoid valve early on before the end of its delivery stroke.

In a second exemplary embodiment according to FIG. 4, the annular groove 148 is arranged upstream of the filling opening 16 and in this case is connected to the filling opening 16 via a longitudinal slot 50 in the lateral surface of the pump piston. It is also possible to provide a plurality of such slots which connect the plurality of filling openings to the annular groove 148. Such a longitudinal slot 50 can advantageously be designed as a throttle connection, so that pump work space relief when connected to the mouth 49 after the annular groove 148 is relieved via the throttling longitudinal slot 50 to the fuel supply channel in front of the solenoid valve. This advantageously delays the pressure drop and effectively prevents a pressure surge. Instead of the throttle connection shown here, a throttle bore 51 can also be provided between the annular groove and the longitudinal channel.

The configuration according to the invention is particularly effective also in the case of clamping ring slides on the pump piston, in the state in which the pump work space is no longer relieved and would continuously promote a maximum fuel injection quantity if the solenoid valve was not closed. If the solenoid valve is then brought into the closed position in the event of a fault detection, a certain amount of fuel can be drawn from the evacuation of the fuel supply part between the solenoid valve and the pump cylinder during the suction phase, which amount can no longer flow back after the mouth 49 is closed when the pump piston rotates and during the subsequent delivery stroke of the Pump piston would generate a corresponding high pressure in the pump work space, which would in turn cause the aforementioned shock on the solenoid valve closing member in the absence of annular groove 48. In addition to a fuel injection that actually takes place up to the opening of the pump work chamber to the solenoid valve in accordance with the delivered residual quantity, there would then be a refilling of the fuel supply channel between the solenoid valve and the pump cylinder or pump work chamber due to the opening process of the closing element of the solenoid valve. Additional fuel would then be supplied to the pump work space, which in turn could be injected during the next delivery stroke. The annular groove provided according to the invention prevents this reopening in the manner described above.

Claims (6)

1.Fuel injection pump for internal combustion engines with a pump piston (14) which delimits a pump working chamber (15) in a pump cylinder bore (13) and which is driven back and forth by a cam drive and at the same time rotates and thereby works as a distributor, with a fuel supply channel (17) running in the pump housing ), which contains a solenoid valve (45) and opens into the cylinder bore (13) and is connected there via a filling opening (16) which is arranged in the outer surface of the pump piston and is permanently connected to the pump working chamber during the suction stroke of the pump piston with the pump working chamber (15) a longitudinal channel (40) arranged in the pump piston, which is permanently connected to a distributor opening (42) on the outer surface of the pump piston, which alternates with the rotation of the pump piston and a delivery stroke of the pump piston with one of several pressure lines leading to an injection point on the internal combustion engine (43) in the pump n housing is connected with a ring slide (37) which can be adjusted on a part of the pump piston which projects into a fuel-filled suction chamber (18) of the fuel injection pump and through which a control edge can be used to open an outlet of the longitudinal channel on the lateral surface of the pump piston into the suction chamber (18) to end the injection stroke of the pump piston is and with an annular groove (48) on the circumference of the pump piston, which is in constant communication with the pump working chamber (15) and at the end of the injection-effective delivery stroke of the pump piston with the mouth (49) of the fuel supply channel (17), characterized in that the pump piston stroke h from the start of the pump piston stroke, at which the annular groove (48) comes into contact with the mouth (49), is greater than the pump piston stroke h, at which the outlet (52) of the longitudinal channel is opened by the control edge of the ring slide (37) when the ring slide controls one of the largest fuel injection quantities position. 2. Fuel injection pump according to claim 1, characterized in that outgoing longitudinal grooves (16) are provided as filling openings from the pump working chamber side end of the pump piston. 3. Fuel injection pump according to claim 2, characterized in that the annular groove (48) intersect the longitudinal grooves (16). 4. Fuel injection pump according to claim 2, characterized in that the annular groove (148) is arranged in front of the longitudinal grooves (16) and at least one of the longitudinal groove (16) is connected via at least one connecting slot (50) in the lateral surface of the pump piston. 5. Fuel injection pump according to claim 4, characterized in that the connecting slot (50) is designed as a throttle. 6. Fuel injection pump according to claim 2, characterized in that the annular groove (148) is the longitudinal grooves (16) upstream and is connected via a throttle (51) to the pump work chamber (15).

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