EP0971123B1 - Fuel injection pump - Google Patents

Abstract

A high pressure fuel pump for an IC engine, e.g. for a diesel engine, has a piston (2) driven by a camshaft and with its upper end (5) bounded by the high pressure chamber (3). A duct through the piston links input control ducts (4a,4b) to control the timing of the fuel pulses. The duct has an upper edge (6) and a sloping lower edge (7a) to define the start and closing points of the fuel timing. The rotational setting of the piston varies the closing setting of the pump. A bypass duct (20) provides a controlled bypass flow at the bottom of the sloping duct to provide a controlled termination of the fuel pulse, and hence a reduction in cavitation.

Description

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

A common fuel injection pump for an internal combustion engine contains one in one Pump cylinder guided pump piston and a limited by the pump piston Pressure chamber and at least one control hole. The pump piston has a upper control edge on the pressure chamber side and at least one lower, sloping one Control edge, which is the beginning and end of the Determine the fuel delivery of the injection pump. The pump piston has one in the pressurized piston head located in the pressure chamber. A such a fuel injection pump is known for example from DE 43 04 084 C2.

From DE 38 04 843 A1 a fuel injection pump emerges as known, at the other in a cylinder axially and rotatably guided pump piston a control edge and a pre-control is formed, which essentially follows the course of the Control edge follows. The Vorabsteuemut stands with a longitudinal groove in the lateral surface of the Pump piston in connection, which in turn in connection with the pump work space stands. The pre-tax groove arrives in the immediately before the control edge Area of the control opening, which causes high-pressure fuel in metered Quantity flows into the tax openings immediately before the start of taxation, thereby Cavitation damage to the outer surface of the pump piston can be avoided.

To avoid cavitation, a pump element is used Injection pump according to DE 40 06 899 A1 during a delivery process Leakage from the pressure chamber of the pump cylinder to the control holes, to push vacuum bubbles away from the control edge of the pump piston. To achieve A constant leak is sufficient play between the guide surfaces of Pump pistons and cylinders provided. In one embodiment, a circumferential groove is used in the Pistons in a horizontal plane to guide the leakage to the control bores.

The fuel injection pump, which is shown in EP 0 270 519 A1, is also used constant leakage to convey away in the suction and overflow holes located gas bubbles. For this purpose, exiting on the circumference of the pump piston radial bores that are throttled via a longitudinal bore in the pump piston Connect to the working area of the pump piston.

In the fuel injection pump according to DE 43 47 430 A1 is used over a part of the External groove running around the circumference of the pump piston for speed-dependent Influencing the fuel delivery rate and the start of delivery. The outer groove is over Radial holes and an axial hole in the pump piston with the pump work space connected and is only effective at the beginning of the delivery stroke of the pump piston.

In such injection pumps, as used in particular in diesel engines are, pump pressures of up to 2000 bar occur in the pressure chamber, the Fuel with outflow speeds of 500m / s and above from the pressure chamber escapes when the control edge clears the control hole. Because of these conditions the components repeatedly appear on the control edges and the control bores destructive cavitation.

The object of the invention is to provide a fuel injection pump for a Specify internal combustion engine in which the occurrence of cavitation is essential is reduced or even avoided altogether.

This object is achieved by a fuel injection pump with the Features of claim 1 solved.

Advantageous developments of the invention are specified in the subclaims.

The fuel injection pump according to the invention for an internal combustion engine comprises a pump piston guided in a pump cylinder and one of the Pump piston limited pressure space, and at least one control bore, the Pump piston an upper control edge on the pressure chamber side and at least one has lower, oblique control edge, which is covered by sweeping over the control bore (s) Determine the start and end of fuel delivery for the injection pump, with the Pump piston a the fuel in the pressure chamber has pressurizing piston head. According to the invention, it is provided that A pre-control groove is formed on the pump piston in the region of the lower control edge which is earlier than the lower, sloping one when the control bore (s) are covered Control edge releases the control hole in the sense of ending the fuel delivery, and that a flow connection leading from the piston head to the pre-control groove is provided which has means for limiting the flow. It is provided that the pre-control groove essentially the course of the lower, oblique control edge is subsequently formed in the outer surface of the pump piston. Here is the Advance control groove by spacing against the lower, oblique control edge subsequent high pressure area sealed. It is also envisaged that the Flow connection at least one from the piston head in the axial direction into the interior of the pump piston and at least one bore in the radial direction of the pilot control groove running into the interior of the pump piston, the axial bore intersecting bore.

A major advantage of the fuel injection pump according to the invention is that before the control edge of the pump piston sweeps over the control bore, by means of the In advance control groove there is a significant reduction in the pressure in the pressure chamber and thus flow processes in the area of the control edge and Control bore can be reduced.

An advantageous embodiment of the fuel pump according to the invention provides that the pump cylinder has two diametrically opposite control bores and the pump piston each have two diametrically opposite lower control edges and pilot control grooves, and that the bores extending in the radial direction open diametrically opposite in the axial bore. The diametrical arrangement of the Openings of the radial bores in the axial bore bring the advantageous Effect that the fuel flows entering the radial bores are directed in the opposite direction and thus as much pressure energy as possible is destroyed.

According to an advantageous development, it is provided that for each pre-tax groove several radial bores are provided, which are angularly offset from one another run, with two holes diametrically opposite each other at the same height in the axial bore open. On the one hand, this leads to a splitting of the piston head fuel flows entering the pre-tax groove with the effect of a strong reduction of pressure energy, as well as the opposite occurring in the pre-tax grooves Fuel flows through which further energy degradation takes place.

Advantageously, two radial bores are provided for each pilot control, which each lead into the vicinity of the ends of the pre-tax grooves. This leads to two opposite currents in the pre-tax grooves, whose energies Remove each other from entering the control holes.

The means for limiting the flow are advantageously by at least one Small cross-sectional area of the one running through the interior of the pump piston Holes formed. It is advantageously provided that the cross section of the axial bore is smaller than the sum of the cross sections of the radial bores opening into these.

In the embodiments in which there are several radial for each pilot control Holes are provided, it is advantageously provided that the cross section the axial bore from the piston head between the confluent radial bores reduced.

In particular, it is in the embodiments in which there are two for each pilot control groove radial bores are provided, particularly preferable to that of the piston head outgoing axial bore before the first radial bore a first cross section A and has a second cross section B in front of the second radial bore, the second cross section B is smaller than the first cross section A. In particular, the first cross section A advantageously about twice the second cross section B.

The cross section of the radial bore is advantageously smaller or approximately small the cross-section of the pre-tax groove.

It is the case with all exemplary embodiments of the fuel injection pump according to the invention an advantage if the pilot groove on its sole is rounded with a radius R having.

The following is a preferred embodiment of the invention with reference to FIG the attached drawing described in more detail.

Fig. 1)

eine Querschnittsansicht eines Pumpenelements einer Einspritzpumpe gemäß einer Ausführungsform der Erfindung;

Fig. 2a)

eine vergrößerte Seitenansicht des mit dem Druckraum und den Steuerbohrungen zusammenwirkenden Teils des Pumpenkolbens;

Fig. 2b)

eine Draufsicht auf den Pumpenkolben;

Fig. 2c)

eine Abwicklung um 360° des mit dem Druckraum und den Steuerbohrungen zusammenwirkenden Teils des Pumpenkolbens;

Fig. 3a)

eine nochmals vergrößerte Draufsicht auf den Kopf des Pumpenkolbens;

Fig. 3b)

eine Schnittansicht der durch den Pumpenkolben als Strömungsverbindung führenden Bohrungen bei dem dargestellten Ausführungsbeispiel; und

Fig. 3c)

eine vergrößerte Schnittansicht entlang der Linie A-B in Fig. 2c), welche den Querschnitt der Vorabsteuernut zeigt.

Show it:

Fig. 1)

a cross-sectional view of a pump element of an injection pump according to an embodiment of the invention;

Fig. 2a)

an enlarged side view of the part of the pump piston interacting with the pressure chamber and the control bores;

Fig. 2b)

a plan view of the pump piston;

2c)

a 360 ° development of the part of the pump piston which interacts with the pressure chamber and the control bores;

3a)

another enlarged plan view of the head of the pump piston;

3b)

a sectional view of the holes leading through the pump piston as a flow connection in the illustrated embodiment; and

3c)

an enlarged sectional view taken along line AB in Fig. 2c), which shows the cross section of the pilot valve groove.

In Fig. 1, reference numeral 1 means the pump cylinder Fuel injection pump for an internal combustion engine, in particular a diesel engine. in a pump piston 2 is displaceably guided in the axial direction of the pump cylinder 1, which of a camshaft acting on a piston foot of the pump piston is cyclically driven. The camshaft and piston foot are not shown in FIG. 1. The Pump piston 2 is provided at its lower end with a piston vane 11, which in cooperation with, for example, a rack a twist around Piston axis allows over a predetermined angular range. The pump piston 2 delimits on its upper side a pressure chamber 3 which is in the pump cylinder 1 is provided. At the top of the pressure chamber 3, an inlet channel 10 and open Drain channel 9 for the fuel.

Control bores 4a and 4b are provided laterally in the pump cylinder 1. A that the upper end of the pump piston 2 forming piston head 5 is on a circumference with a upper, pressure chamber-side control edge 6 and lower, oblique control edges 7a, 7b provided, of which only one control edge 7a is visible in Fig. 1. The top control edge 6 and the lower control edge 7a together limit a connection of the Pressure chamber 3 with the underside of the lower, oblique control edge 7a, 7b producing Piston groove 8 is a control triangle, which by sweeping the control holes 4a, 4b Determines the start and end of fuel delivery for the injection pump. In the illustrated Fuel injection pump are two such control triangles, each of which cooperate with the control bores 4a and 4b.

By turning the pump piston 2 by means of the piston vane 11 is by Change the mutual position of the lower control edge 7a, 7b and control bore 4a, 4b set the end of fuel delivery and thus the injection duration. in this respect corresponds to the known fuel injection pump known.

As can be seen from Fig. 1 and Fig. 2a) to c), is in the range of the lower one Control edge 7a, 7b on the pump piston 2 a pre-control groove 20a, 20b in the form of a the routing of the lower control edge 7a, 7b provided. The Pre-control groove 20a, 20b is formed by a formed in the interior of the pump piston 2 Flow connection with the piston head 5 and thus with the pressure chamber in Connection. The flow connection is through a in the center of the pump piston 2 extending axial bore 23 and two for each pilot valve groove 7a, 7b provided radially extending bores 21a, 22a and 21b, 22b. At hers The upper side of the axial bore 23 is expanded by a cone 24.

The pre-control groove 20a, 20b sweeps as the pump piston moves upward 2 earlier during the delivery stroke of the injection pump, the respective control bore 4a, 4b than the lower, oblique control edge 7a, 7b, so that an earlier pressure relief of the Pressure chamber 3 via the bores 23 and 21a, 22a, 21b, 22b and the pilot valve grooves 20a, 20b in the sense of ending fuel delivery.

The cross section of the through the axial bore 23 and the radial bores 21a, 22a, 21b, 22b formed flow connection is chosen so that a substantial degradation of the pressure energy stored in the printing space 3 takes place, so that in the final Pressure relief of the pressure chamber 3 via the lower control edge 7a, 7b no cavitation no longer occurs, but on the other hand, there is still no cavitation in the pilot control groove 20a, 20b occurs.

As can be seen from FIG. 2c), this is a development of the upper part of the pump piston 2 shows by 360 °, the pre-control grooves 20a, 20b each sweep over the Control bores 4a, 4b, which are shown in dashed lines in Fig. 2c). The pre-tax mutes 20a, 20b are against that adjoining the lower control edge 7a, 7b High pressure area sealed by a distance S by spacing.

The radial bores 21a, 22a and 21b, 22b each open near the ends of the Pre-tax grooves 20a, 20b in this. As can be seen from Fig. 2b), the radial Bores 21a, 22a and 21b, 22b angularly offset and open each in pairs diametrically opposite each other in the axial bore 23. Die mutual position of the radial bores 21a, 22a and 21b, 22b is again in Fig. 3a) shown enlarged.

As can be seen from Fig. 3b), the axial bore 23 has between the mouths of the radial bores 21a, 21b and 22a, 22b a reduction in the cross section. In the illustrated embodiment, the cross sections of the axial bore 23 chosen so that the first cross section at the first radial bore 21a, 21b approximately is twice as large as the second cross section at the second radial bore 22a, 22b. This reduction in the flow limiting in the axial bore 23 Cross section should be achieved that the flow from the pressure chamber 3 to the Pre-control grooves 20a, 20b approximately equal to the first radial bore 21a, 21b and the second radial bore 22a, 22b distributed. Furthermore, the cross sections of the holes chosen so that the cross section of the axial bore 23 is smaller than the sum of the Cross sections of the radial bores 21a, 21b or 22a, 22b opening into these.

Fig. 3c) shows a further enlarged section along the line A-B in Fig. 2c) in Pre-tax groove area 20b. As can be seen, the edges of the pre-control groove are on rounded their sole with a radius R, which on the one hand improves the Flow behavior within the pre-control groove 20a, 20b and the other Strength of the pump piston 2 in the area of the pre-control groove 20a, 20b and serves in particular the heavily loaded lower control edges 7a, 7b. With regard to the Strength is the measure of the distance S between the pre-control groove 20a, 20b and lower control edge 7a, 7b of importance. This dimension S is to be chosen so that on the one hand the beginning of the pre-control when the pre-control groove 20a, 20b arrives at the Control bore 4a, 4b in an appropriate relationship to the end of fuel delivery when the lower control edge 7a, 7b arrives at the control bore 4a, 4b and on the other hand, the occurrence of damage in this highly stressed area of the Pump piston 2 is reliably excluded.

Claims (11)

1. Fuel injection pump for an internal combustion engine, with a pump piston (2) guided in a pump cylinder (1), with a pressure space (3) delimited by the pump piston (2) and with at least one control bore (4a, 4b), the pump piston (2) having an upper control edge (6) located on the pressure-space side and at least one lower oblique control edge (7a, 7b), which control edges, by passing over the control bore or control bores (4a, 4b), define the start and end of fuel conveyance of the injection pump, the pump piston (2) having a piston head (5) acting upon the fuel located in the pressure space (3), there being formed in the region of the lower control edge or control edges (7a, 7b), on the pump piston (2), a pre-cut-off groove (20a, 20b) which, when it passes over the bore or bores (4a, 4b), opens the control bore (4a, 4b) earlier than the lower oblique control edge (7a, 7b) with the effect of ending fuel conveyance, and there being provided a flow connection which leads from the piston head (5) to the pre-cut-off groove (20a, 20b) and which has means for flow limitation, the pre-cut-off groove (20a, 20b) being formed, so as to essentially follow the run of the lower oblique control edge (7a, 7b), in the outer surface of the pump piston (2), and the pre-cut-off groove (20a, 20b) being sealed off by spacing (S) relative to the high-pressure region adjacent to the lower oblique control edge (7a, 7b), characterized in that the flow connection comprises at least one bore (23) running from the piston head (5) in the axial direction into the interior of the pump piston (2) and at least one bore (21a, 21b, 22a, 22b) running in the radial direction from the pre-cut-off groove (20a, 20b) into the interior of the pump piston (2) and intersecting the axial bore (23).
2. Fuel injection pump according to Claim 1, characterized in that the pump cylinder (1) has two diametrically opposite control bores (4a, 4b), and the pump piston (2) has in each case two diametrically opposite lower control edges (7a, 7b) and pre-cut-off grooves (20a, 20b), and in that the bores (21a, 21b, 22a, 22b) running in the radial direction issue, diametrically opposite one another, into the axial bore (23).
3. Fuel injection pump according to Claim 2, characterized in that, for each pre-cut-off groove (20a, 20b), a plurality of radial bores (21a, 22a and 21b, 22b) are provided, which run, offset angularly relative to one another, in each case two bores (21a, 21b and 22a, 22b) issuing, diametrically opposite one another, into the axial bore (23).
4. Fuel injection pump according to Claim 3, charaterized in that, for each pre-cut-off groove (20a, 20b), two radial bores (21a, 22a and 21b, 22b) are provided, which issue into the pre-cut-off grooves (20a, 20b) in each case in the vicinity of the ends of the latter.
5. Fuel injection pump according to one of Claims 1 to 4, characterized in that the means for flow limitation are formed by at least one region of small cross section of the bore or bores (21a, 21b, 22a, 22b, 23) running through the interior of the pump piston (2).
6. Fuel injection pump according to Claim 5, characterized in that the cross section of the axial bore (23) is smaller than the sum of the cross sections of the radial bore or bores (21a, 21b and 22a, 22b) issuing into the latter.
7. Fuel injection pump according to Claim 6, in conjunction with Claim 3 or 4, characterized in that the cross section of the axial bore (23) decreases from the piston head (5) between the radial bores (21a, 21b and 22a, 22b) issuing into the said axial bore.
8. Fuel injection pump according to Claim 7, in conjunction with Claim 4, characterized in that the axial bore (23) emanating from the piston head (5) has a first cross section upstream of the first radial bore (21a, 21b) and a second cross section upstream of the second radial bore (22a, 22b), the second cross section being smaller than the first cross section.
9. Fuel injection pump according to Claim 8, characterized in that the first cross section is about double the second cross section.
10. Fuel injection pump according to one of Claims 1 to 9, characterized in that the cross section of the radial bore or bores (21a, 21b, 22a, 22b) is smaller than or approximately equal to the cross section of the pre-cut-off groove (20a, 20b).
11. Fuel injection pump according to one of Claims 1 to 10, charaterized in that the pre-cut-off groove (20a, 20b) has on its floor edges which are rounded with a radius R.

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