EP0971122A2 - 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 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 related, 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 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.

The object of the invention is therefore to provide a fuel injection pump Art in such a way that an adjustment of the beginning of the 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 covering at least one with a suction chamber of the Fuel injection pump related, opening into the pressure chamber Determine the control bore for the start and end of fuel delivery for the injection pump. According to the invention for adjusting the start of the fuel injection is one in one Bore 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 over an evasive stroke s between an initial position and an end position is displaceable. Furthermore, means for adjustment are according to the invention of the evasive stroke s of the evasive piston.

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 to 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 one embodiment of the invention, it is provided that the evasive piston is arranged in the housing of the fuel injection pump and in with the pressure chamber Connection is established.

According to a 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 this 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 his 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 in addition, it can be provided that the escape 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 im Suction chamber of the fuel pump pre-pressure.

According to an advantageous embodiment of the fuel injection pump according to the invention it provided that the means for adjusting the evasive stroke s of the evasive piston are formed by a hydraulically operated adjusting device.

In particular, the hydraulically actuated adjusting device can be operated by means of a Bore movable, pressurized by a fluid under pressure Control piston formed, the location of the size of the evasive stroke of the Dodge piston determined.

A particularly advantageous development of this is that the control piston and the escape piston are slidably mounted in a common bore, the Control piston an abutment surface that limits the evasive stroke s of the evasive piston having.

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 is 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 under pressure in the pressure chamber standing fuel area of the evasive piston smaller than that of the is 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.

A control device for switching the on and off is advantageous Control piston actuating hydraulic pressure provided.

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 adjusting device and Figure 1c) show the actuating 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 Slidably mounted in the axial direction, which one at the top of the pump cylinder 1b trained pressure space 3 limited. 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 to 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 supplied 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 evasive piston 12 is in the sense of increasing the Alternative space 18 between an initial position and an end position over one Dodge stroke s displaceable, see Figure 1a).

At the rear of the escape 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 escape piston 12 forces towards its initial position closer to the pressure chamber 3. Furthermore is a volume enclosed between the escape piston 12 and the control piston 11 Coupled with the suction chamber 20 via a connecting channel 14. The room above the Control piston 11 is connected to a hydraulic connection 16 via a hydraulic channel 17 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), on the underside of the evasive piston 12 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 rests 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 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 evasive piston 12 with its flat seat 12a on it Sealing surface 12b is present. The suction chamber pressure P _s typically takes 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.

With the upward movement of the pump piston 12 rises after the upper control edge 6 is swept past the control bores 4a, 4b, the pressure in the pressure chamber 3 and this is transferred via the connecting channel 19 to that of the flat seat 12a Cleared area on the underside of the evasive piston 12. If the caused force from the spring force of the auxiliary spring 13 and from the suction chamber 20 the pressure force transmitted to the connecting channel 14 exceeds the resulting force, the evasive piston 12 begins to evade the stroke s and thus removes it Pump pressure chamber 3 through the cross section of the bore 10 and the evasive stroke s defined volume. This delays the further increase in the pressure chamber 3 Fuel injection pump until the end of the evasive piston 12, if it bears against the control piston 11. Because of the then increasing Pressure in the pressure chamber 3, the opening pressure of the pressure valve 21 is exceeded and so that the delivery of fuel from the pump pressure chamber 3 to Fuel injection valve of the internal combustion engine released. This state in which the Dodge piston 12 bears against control piston 11 at the end of its dodge movement, is shown in Figure 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 Effect of the connection channel 14 to the rear of the evasive piston 12 transferred suction chamber pressure 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 Ensuring that the evasive piston 12 is held 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.

Reference list

1a

Connector

1b

Pump cylinder

1c

Pump housing

2nd

Pump piston

3rd

Pressure room

4a, b

Control drilling

5

Piston head

6

upper control edge

7

lower control edge

8th

Piston groove

9

Conveyor channel

10th

drilling

11

Control piston

12th

Alternative pistons

12a

Flat seat

12b

Sealing surface

13

Auxiliary spring

14

Connecting channel

15

attack

16

Hydraulic connection

17th

Hydraulic channel

18th

Alternative room

19th

Connecting channel

20th

Suction chamber

21

Pressure valve

22

Pressure connection

Claims (16)

Fuel injection pump for an internal combustion engine with a pump piston (2) guided in a pump cylinder (1b) and a pressure chamber (3) delimited by the pump piston (2), from which the fuel delivered by the pump piston (2) is supplied via a delivery channel (9) is emitted into the combustion chamber of the internal combustion engine, the pump piston (2) having an upper control edge (6) on the pressure chamber side and at least one lower control edge (7) which is connected by sweeping over at least one connection with a suction chamber (20) of the fuel injection pump , Determine in the pressure chamber (3) control bore (4a, 4b) the start and end of fuel delivery of the injection pump, characterized in that an adjustment piston (12) is provided in a bore (10) which is displaceably arranged to adjust the start of the fuel injection one with the pressure chamber (3) in connection with the alternative space (18) and in S within an enlargement of the escape space (18) can be displaced between an initial position and an end position via an escape stroke s, and that means for adjusting the escape stroke s of the escape piston (12) are provided. Fuel injection pump according to Claim 1, characterized in that the evasive piston (12) is arranged in the housing of the fuel injection pump and is connected to the pressure chamber (3). Fuel injection pump according to Claim 2, characterized in that the escape piston (12) is arranged at the end on the pressure chamber side in a connecting piece (1a) forming the pump head, and in that an escape chamber (18) delimited by the escape piston (12) with the pressure chamber (3) connecting connecting channel (19) opens at the end of the pressure chamber (3). Fuel injection pump according to Claim 1, 2 or 3, characterized in that the evasive piston (12) is spring-loaded by an auxiliary spring (13) for returning it to its initial position. Fuel injection pump according to one of claims 1 to 4, characterized in that the evacuation piston (12) is coupled to the suction chamber (20) of the fuel pump on its rear side via a connecting channel (14) for the purpose of returning it to its initial position. Fuel injection pump according to one of claims 1 to 5, characterized in that the means for adjusting the evasive stroke s of the evasive piston (12) are formed by a hydraulically actuated adjusting device. Fuel injection pump according to Claim 6, characterized in that the hydraulically actuated adjusting device is formed by a control piston (11) which is displaceable in a bore (10) and can be acted upon by a pressurized fluid, the position of which determines the size of the evasive stroke s of the evasive piston (12) . Fuel injection pump according to Claim 7, characterized in that the control piston (11) and the escape piston (12) are displaceably mounted in a common bore (10), the control piston (11) having a contact surface which limits the escape stroke s of the backup piston (12). Fuel injection pump according to Claim 7 or 8, characterized in that the control piston (11) has a larger area which can be acted upon by the pressurized fluid than the area of the evasive piston (12) which is pressurized in the pressure chamber (3) of the fuel injection pump ) having. Fuel injection pump according to Claim 9, characterized in that a flat seat (12a) cooperating with a sealing surface (12b) surrounding the connecting channel (19) leading to the pressure chamber (3) is formed on the evasive piston (12b), wherein the seat on the sealing surface (12b ) adjacent flat seat (12a) of the pressurized fuel area in the pressure chamber (3) of the evasive piston (12) is smaller than the area of the control piston (11) acted upon by the pressurized fluid. Fuel injection pump according to one of Claims 7 to 10, characterized in that the control piston (11) can be acted upon by the lubricating oil pressure of the internal combustion engine for hydraulic actuation. Fuel injection pump according to one of Claims 6 to 11, characterized in that a control device is provided for switching on and off the hydraulic pressure which actuates the control piston (11). Fuel injection pump according to one of Claims 7 to 12, characterized in that the control piston (11) can be displaced between an initial position and an end position limited by a stop (15). Fuel injection pump according to Claim 13, characterized in that the stop (15) delimiting the end position of the control piston (11) is adjustable, and in that means are provided for adjusting the stop (15). Fuel injection pump according to Claim 14, characterized in that the means for adjusting the stop (15) are formed by a threaded spindle which can be rotated by means of a servomotor. Fuel injection pump according to one of Claims 1 to 5, characterized in that the means for adjusting the evasive stroke s of the evasive piston (12) are formed by a threaded spindle which can be rotated by means of an actuating motor and which limits a displacement of the starting or end position of the evasive piston (12) Cause attack.

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