EP0971122B1 - Fuel injection pump for an internal combustion engine - Google Patents

Abstract

A high pressure fuel pump, e.g. for a diesel engine, has a control duct through the pump piston to control the start and end points of the fuel pulse. The end point is controlled by a sloping duct (7) and is variable through the rotational setting of the piston. A controlled delay in the start of the fuel pulse is provided by a control piston (12) in a control cylinder (10) on the input duct of the fuel pump. The control piston (12) is linked to a drive piston (11) by a control spring (13) for a simple mode of control.

Description

The invention relates to a fuel injection pump for an internal combustion engine according to the Preamble of claim 1.

Such a fuel injection pump comprises a one that is guided in a pump cylinder Pump piston and a pressure chamber delimited by the pump piston, from which the fuel delivered by the pump piston via a delivery channel for delivery in the combustion chamber of the internal combustion engine is released. The pump piston has an upper control edge on the pressure chamber side and at least one lower one Control edge, which by sweeping at least one with a suction chamber Fuel injection pump connected, opening into the pressure chamber Determine the control bore for the start and end of fuel delivery for the injection pump.

While with such a fuel injection pump the end and thus the time period the fuel injection is adjustable by the lower control edge of the pump piston which is inclined with respect to the axis of the pump piston and by rotation brought into a different position to the control hole or holes can be the start of injection with a fuel injection pump of this type initially not adjustable.

One way to adjust the start of fuel injection is under the Aspect of a reduction of the consumption and emission values of the Internal combustion engine, however, particularly desirable for diesel engines.

There are already systems for adjusting the start of the injection Fuel injection pumps of the type assumed become known, which a electronically controlled solenoid valve, with the help of which the Pump piston acted upon the pressure chamber of the fuel injection pump for the purpose of Delay in the start of injection compared to the suction space of the fuel injection pump can be relieved of pressure. A disadvantage of this, however, is the great effort involved.

A fuel injection pump is known to be known from JP abstract 59077046 A, in which an escape piston which is arranged displaceably in a bore is provided, which is connected to the pressure chamber of the fuel injection pump Alternative space limited. The escape piston works with one of an adjustment rod formed stop together, the adjusting rod by means of a hydraulic actuatable piston is adjustable to the evasive stroke for the evasive piston adjust. The start of injection can be controlled by the device.

By an increase in the injection pressure depending on the speed and also to achieve a variable injection start, according to the DE 38 01 929 A1 one of the injection pressure against the action of springs adjustable control piston arrangement may be provided. The control piston arrangement has a first, from the injection pressure in the pressure chamber of the injection pump directly acted upon control piston and a second with this with the interposition of one Compression spring coupled control piston to form the first control piston a valve cooperates, which is designed to block a throttle bore, that connects the pressure chamber with an outlet space.

The object of the invention is therefore to provide a fuel injection pump Art in such a way that a relatively simple way to adjust the beginning of Fuel injection is possible.

This task is performed by a fuel injection pump with the characteristics of Claim 1 solved.

Advantageous developments of the fuel injection pump according to the invention are in the Subclaims marked.

According to the invention, a fuel injection pump for an internal combustion engine created that a pump piston guided in a pump cylinder and one of the pump piston has limited pressure space, from which the Pump piston delivered fuel via a delivery channel for delivery into the Combustion chamber of the internal combustion engine is released. The pump piston has a upper control edge on the pressure chamber side and at least one lower control edge, which by painting over at least one with a suction chamber of the Fuel injection pump connected, opening into the pressure chamber Determine the control bore for the start and end of fuel delivery for the injection pump. To adjust the start of the fuel injection is in a hole slidably arranged escape piston provided which one with the Pressure room related alternative space limited and in the sense of a Enlargement of the evasive space via an evasive stroke s between an initial position and an end position is displaceable. Furthermore, means for adjusting the Dodge stroke s of the dodge piston provided. The means of adjusting the Dodge strokes s of the dodge piston are operated by a hydraulically operated one Adjustment device formed in the form of a displaceable in a bore by one pressurized fluid pressurized control piston, the location of which is the size of the Dodge stroke of the dodge piston determined. A control device is used to feed and Switching off the hydraulic pressure actuating the control piston.

According to the invention, the control piston and the escape piston are in one Bore slidably mounted, the control piston a the evasive stroke s of Dodge piston limiting contact surface.

An advantage of the fuel injection pump according to the invention is that the start of the Fuel injection in a simple manner by means of shifting the Dodge piston required fuel volume can be delayed, the Means for adjusting the evasive stroke of the evasive piston in a simple manner can be designed so that they allow displacement of the evasive piston or not, i.e. an adjustment of the start of injection from early to late or from late to early.

According to a further development of this, the evasive piston is at the end on the pressure chamber side arranged to the pump housing connecting piece, one of the the alternate piston delimiting the alternate space with the pressure chamber Connection channel opens at the front of the pressure chamber. This means one space-saving design of the fuel injection pump according to the invention, whereby it can also be used in confined spaces.

According to one embodiment of the fuel injection pump according to the invention, it is provided that the escape piston by an auxiliary spring for return to its Initial position is spring-loaded. This is an easy measure to use the backup piston return to its initial position after the end of fuel injection.

Alternatively or additionally, it can be provided that the evasive piston to Purposes of returning to its initial position on its back over one Connection channel is coupled to the suction chamber of the fuel pump. In this case the return piston is returned to its initial position by the Suction chamber of the fuel pump pre-pressure.

Advantageously, the control piston has a larger one than the one under pressure Area to which fluid can be applied than that in the pressure chamber of the fuel injection pump the pressurized fuel surface of the escape piston. This allows a lower pressure to be used to operate the Control piston than the high supplied by the fuel injection pump Fuel injection pressure.

An advantageously simple embodiment of this consists in that on the Dodge piston with a connecting channel leading to the pressure chamber surrounding sealing surface cooperating flat seat is formed, the at the sealing surface of the flat seat adjacent to that in the pressure chamber under pressure standing fuel area of the evasive piston smaller than that of the is the pressurized fluid pressurized surface of the control piston.

The lubricating oil of the internal combustion engine advantageously becomes hydraulic Actuation of the control piston used.

The control piston is preferably between an initial position and one through one Stop limited end position movable.

An advantageous development of this is that the end position of the Control piston limiting stop is adjustable, and that means for adjusting the Stop are provided.

According to an advantageous embodiment, it is provided that the means for Adjustment of the stop by means of a threaded spindle that can be rotated by means of a servomotor are formed.

There is an alternative way of hydraulically adjusting the evasive stroke in that the means for adjusting the evasive stroke of the evasive piston by a rotatable threaded spindle are formed by means of an actuator, which a Displacement of a limit of the starting or end position of the evasive piston Cause attack.

Figuren 1a) bis 1c) jeweils eine teilweise Schnittdarstellung einer Kraftstoffeinspritzpumpe gemäß einem Ausführungsbeispiel der Erfindung, bei welchem die Mittel zur Verstellung des Ausweichhubs des Ausweichkolbens durch eine hydraulisch betätigte Verstelleinrichtung gebildet sind, wobei die Figuren 1a) und 1b) die im Sinne eines späteren Einspritzbeginns betätigte Verstelleinrichtung und Figur 1c) die im Sinne eines früheren Einspritzbeginns betätigte Verstelleinrichtung zeigen.

An exemplary embodiment of the fuel injection pump according to the invention is explained below with reference to the drawing. Show it:

Figures 1a) to 1c) each a partial sectional view of a fuel injection pump according to an embodiment of the invention, in which the means for adjusting the evasive stroke of the evasive piston are formed by a hydraulically operated adjusting device, with the figures 1a) and 1b) in the sense of a later start of injection actuated adjustment device and Figure 1c) show the adjustment device actuated in the sense of an earlier start of injection.

In Figures 1a) to 1c), reference numeral 1a denotes a connector on a Pump housing 1c of the fuel injection pump, being in the pump housing 1c Pump cylinder 1b is formed. A pump piston 2 in is in the pump cylinder 1b Axially displaceably mounted, which one at the top of the pump cylinder 1b designed pressure chamber 3 limits the end face of the pressure chamber 3 Pump piston 2 forms a piston head 5. The pump piston 2 has at its in the figures no longer shown lower end via a piston foot through which he by means of a cam driven by the internal combustion engine in an oscillating manner is driven. Furthermore, one is also in at the lower end of the pump piston 2 arranged in the figures not shown piston flag, by means of which Pump piston 2 for controlling the injection duration and quantity via a predetermined one Angular range is rotatable about its axis.

On the piston head 5, the pump piston 2 has an upper pressure chamber side Control edge 6. Furthermore, there are two lower, sloping ends on the pump piston 2 Control edges 7 formed. The upper control edge 6 and the lower control edge 7 limit together with a connection of the pressure chamber 3 with the bottom of the oblique control edges 7 producing piston groove 8 each a control triangle, which by painting each one with a suction space 20 outside the Pump cylinder 1b connected, opening into the pressure chamber 3 Control bore 4a, 4b start and end of fuel delivery of the injection pump certainly. By rotating the pump piston 2 by means of the aforementioned Piston flag is created by changing the mutual position of the lower control edge 7 and control bore 4a, 4b the end of fuel delivery and thus the injection duration set. In contrast, the beginning of fuel delivery through the mutual Position of the upper control edge 6 and the control holes 4a, 4b fixed invariably. In this respect, the fuel injection pump described corresponds to the known.

The fuel displaced from the pressure chamber 3 by the pump piston 2 is transferred via a a delivery valve 9 containing a pressure valve 21 and via a pressure connection 22 for Delivery to a fuel injector for injection into the combustion chamber Internal combustion engine delivered.

In the connection piece 1 a, the pump piston 2 is upstream of the pressure chamber Dodge piston 12 slidably disposed in a bore 10. The escape piston 12 delimits an escape space 18 on its underside, compare FIG a connecting channel 19 with the pressure chamber 3 of the fuel injection pump in Connection is established The escape piston 12 is in the sense of an enlargement of the Alternative room 18 between an initial position and an end position over one Dodge stroke s displaceable, see Figure 1a).

At the back of the evasive piston 12 is also in the bore 10 Control piston 11 slidably mounted. Between the escape piston 12 and the control piston 11, an auxiliary spring 13 is provided which the evasive piston 12 Forces towards its starting position closer to the pressure chamber 3. Furthermore is a Volume enclosed between the escape piston 12 and the control piston 11 coupled to the suction space 20 via a connecting channel 14. The room above the Control piston 11 is via a hydraulic channel 17 with a hydraulic connection 16th connected, which with a control hydraulics not shown in the figure in Connection is established. A stop 15 is formed at the upper end of the bore 10, which serves to limit the displacement path of the control piston 12 upwards. The control piston 11 slidably mounted in the bore 10 forms a hydraulic one actuated adjusting device for adjusting the evasive stroke s of the evasive piston 12th

As can be seen in detail in FIG. 1b), there is 12 on the underside of the escape piston a flat seat 12a is formed, which with one leading to the pressure chamber 3 Connection channel 19 surrounding sealing surface 12b cooperates. If the flat seat 12a bears on the sealing surface 12b, that of the one in the pressure chamber 3 is Fuel injection pump pressurized fuel Area of the evasive piston 12 is smaller than the area of the control piston 11, which over the hydraulic channel 17 is pressurized by the control hydraulics. That is, it is a smaller pressure supplied via the hydraulic channel 17 sufficient to the Dodge piston 12 to hold the flat seat 12a on the sealing surface 12b as the pressure of the fuel in the pressure chamber 3. This allows, for example, the use of a Lubricating oil pressure of 300 bar for the hydraulic actuation of the control piston 11.

The control piston 11 is thus by means of the pressure supplied via the hydraulic channel 17 between an initial position, which is given when the evasive piston 12 with its flat seat 12a abuts the sealing surface 12b and the control piston 12 in turn abuts on the evasive piston 12, and an end position that can be moved by the The control piston 11 bears against the stop 15.

Now the function of the evasive piston 12 and its shall be based on Figures 1a) to 1c) Effect on the timing of the start of fuel injection in detail to be discribed.

Figure 1a) shows the fuel injection pump in a state in which the pump piston 2 is at its bottom dead center. The control piston 11 is not pressurized via the hydraulic channel 17, so that due to the spring force of the auxiliary spring 13 and the pressure of the suction chamber 20 applied via the connecting channel 14, the control piston 11 is located at the upper stop 15 and the escape piston 12 with its flat seat 12a on it Sealing surface 12b is present. The suction chamber pressure P _s typically assumes a value of up to 15 bar before the start of each injection. In this state, the evasive piston 12 is prepared for an evasive movement by the evasive stroke s in the direction of the control piston 11.

During the upward movement of the pump piston 12, after the upper control edge 6 has passed the control bores 4a, 4b, the pressure in the pressure chamber 3 rises and this is transferred via the connecting channel 19 to the area on the underside of the evasive piston 12 that is released by the flat seat 12a If the force caused thereby exceeds the force resulting from the spring force of the auxiliary spring 13 and the pressure force transmitted from the suction chamber 20 via the connecting channel 14, the evasive piston 12 begins to evade the stroke s and thus takes the pump pressure chamber 3 through the cross section of the bore 10 and the evasive stroke s defined volume. As a result, the further increase in the pressure chamber 3 of the fuel injection pump is delayed until the evasive piston 12 stops evading when it contacts the control piston 11. Due to the then further increasing pressure in the pressure chamber 3, the opening pressure of the pressure valve 21 is exceeded and thus the delivery of the fuel from the pump pressure chamber 3 to
Fuel injection valve of the internal combustion engine released. This state, in which the evasive piston 12 bears against the control piston 11 at the end of its evasive movement, is shown in FIG. 1b).

If the pumping process is then ended by the lower control edge 7 Control bores 4a, 4b releases, the pressure in the pump pressure chamber 3 drops suddenly, whereby the evasive piston 12 due to the spring force of the auxiliary spring 13 and the Effect of the connection channel 14 to the rear of the evasive piston 12 transferred suction chamber pressure moved back to the starting position shown in Figure 1a) becomes. After reversing the movement of the pump piston 2 and returning to the lower one Dead center is again the starting position shown in FIG. 1a) for a new one Pumping process reached.

Figure 1c) shows the state in which the control piston 11 and the evasive piston 12 are in their lower position for an earlier start of injection. Because of the over the hydraulic channel 17 on the control piston 11 applied hydraulic pressure, which is, for example, 300 bar, the evasive piston 12 because of the Size ratio between the area of the hydraulic pressure Control piston 11 and located within the flat seat 12a, via the Connection channel 19 of the fuel pressure prevailing in the pressure chamber 3 acted upon surface of the evasive piston 12 with its flat seat 12a reliably held on the sealing surface 12b and thus an evasive movement the same made impossible, although the fuel pressure in the pressure chamber 3 one reached much higher value. For example, at a maximum fuel pressure in the pump pressure chamber 3 of 2250 bar and a hydraulic pressure of 250 bar To keep the evasive piston 12 in its lower position is sufficient Size ratio of 9: 1 of the pressurized surfaces of the control piston 11 or the escape piston 12.

Thus, when the control bores 4a, 4b are blocked by the upper control edge 6 an immediate increase in pressure, which without delay when the Opening pressure of the pressure valve 21 leads to the beginning of the injection process.

In the embodiment shown in Figures 1a) to 1c) Fuel injection pump according to the invention takes place by means of the control piston 11 Switching between two states, namely one in which the evasive piston 12 is released and thus a delay of the evasive movement Injection is started at a later time, and a state in which prevents an evasive movement of the evasive piston 12 and thus a Injection takes place at an earlier point in time without delay.

If, in addition to being able to choose between these two states, still the size of the time delay due to the evasive movement of the evasive piston 12 should be adjustable, this can be done by means of adjusting the evasive stroke s Dodge piston 12 happen. These can either be such that they are under Maintaining the control possibility of the control piston 11 by a to and Hydraulic pressure that can be switched off is an adjustment of the stop 15 of the control piston 11 cause, or they can instead of the control piston 11 directly on the escape piston 12 act and thus form the means for adjusting the evasive stroke s.

Such means for creating the stop 15 of the control piston 11 or for direct Adjustment of the evasive stroke s of the evasive piston 12 can be achieved by means of a Servomotor rotatable threaded spindle can be formed, which then a variable Federal start adjustment is possible.

LIST OF REFERENCE NUMBERS

1a

connector

1b

pump cylinder

1c

pump housing

2

pump pistons

3

pressure chamber

4a, b

drillings

5

piston head

6

upper control edge

7

lower control edge

8th

piston groove

9

delivery channel

10

drilling

11

spool

12

bypass piston

12a

flat seat

12b

sealing surface

13

auxiliary spring

14

connecting channel

15

attack

16

hydraulic connection

17

hydraulic channel

18

alternative space

19

connecting channel

20

suction

21

pressure valve

22

pressure connection

Claims (10)

1. Fuel injection pump for an internal combustion engine, with a pump piston (2) guided in a pump cylinder (1b) and with a pressure space (3) which is delimited by the pump piston (2) and out of which the fuel conveyed by the pump piston (2) is discharged via a conveying duct (9) in order to be fed into the combustion space of the internal combustion engine, the pump piston (2) having an upper control edge (6) located on the pressure-space side and at least one lower control edge (7), which control edges, by passing over at least one control bore (4a, 4b) connected to a suction space (20) of the fuel injection pump and issuing into the pressure space (3), determine the start and end of the fuel conveyance of the injection pump, there being provided, for adjusting the start of fuel injection, a bypass piston (12) which is arranged displaceably in a bore (10) and which delimits a bypass space (18) connected to the pressure space (3) and is displaceable over a bypass stroke s between an initial position and an end position with the effect of enlarging the bypass space (18), means for adjusting the bypass stroke s of the bypass piston (12) being provided, the means for adjusting the bypass stroke s of the bypass piston (12) being formed by a hydraulically actuated adjusting device, the hydraulically actuated adjusting device being formed by a control piston (11) which is capable of being acted upon by a pressurized fluid and the position of which determines the size of the bypass stroke s of the bypass piston (12), and a control device for cutting in and cutting out the hydraulic pressure actuating the control piston (11) being provided, characterized in that the control piston (11) and the bypass piston (12) are mounted displaceably in a common bore (10), the control piston (11) having a bearing surface limiting the bypass stroke s of the bypass piston (12).
2. Fuel injection pump according to Claim 1, characterized in that the bypass piston (12) is arranged, at the end located on the pressure-space side, in a connection piece (1a) which forms the pump head, and in that a connecting duct (19) connecting the bypass space (18) delimited by the bypass piston (12) to the pressure space (3) issues on the end face of the pressure space (3).
3. Fuel injection pump according to Claim 1 or 2, characterized in that the bypass piston (12) is spring-loaded for return into its initial position by means of an auxiliary spring (13).
4. Fuel injection pump according to one of Claims 1 to 3, characterized in that the bypass piston (12), for the purpose of return into its initial position, is coupled on its rear side to the suction space (20) of the fuel pump via a connecting duct (14).
5. Fuel injection pump according to one of Claims 1 to 4, characterized in that the control piston (11) has a larger surface capable of being acted upon by the pressurized fluid than that surface of the bypass piston (12) which is acted upon by the pressurized fuel located in the pressure space (3) of the fuel injection pump.
6. Fuel injection pump according to Claim 5, characterized in that a flat seat (12a) co-operating with a sealing surface (12b) surrounding the connecting duct (19) leading to the pressure space (3) is formed on the bypass piston (12), that surface of the bypass piston (12) which is acted upon by the pressurized fuel located in the pressure space (3) when the flat seat (12a) comes to bear on the sealing surface (12b) being smaller than that surface of the control piston (11) which is acted upon by the pressurized fluid.
7. Fuel injection pump according to one of Claims 1 to 6, characterized in that, for hydraulic actuation, the control piston (11) can be acted upon by the lubricating-oil pressure of the internal combustion engine.
8. Fuel injection pump according to one of Claims 1 to 7, characterized in that the control piston (11) is displaceable between an initial position and an end position limited by a stop (15).
9. Fuel injection pump according to Claim 8, characterized in that the stop (15) limiting the end position of the control piston (11) is adjustable, and in that means for adjusting the stop (15) are provided.
10. Fuel injection pump according to Claim 9, characterized in that the means for adjusting the stop (15) are formed by a threaded spindle rotatable by means of a servomotor.

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