WO2007140500A1

WO2007140500A1 - Pump element for a high-pressure pump

Info

Publication number: WO2007140500A1
Application number: PCT/AT2007/000270
Authority: WO
Inventors: Theodor Stipek; Christian Meisl
Original assignee: Robert Bosch Gmbh
Priority date: 2006-06-02
Filing date: 2007-06-04
Publication date: 2007-12-13
Also published as: AT503697A1; AT503697B1

Abstract

In a pump element for a high-pressure pump having a pump cylinder (2), a pump piston (3), an upstroke valve (5) and a pressure valve (7), medium is sucked out of a pump suction space (6) via the upstroke valve (5) during the downward stroke of the pump piston (3) and medium is ejected via the pressure valve (7) during the upward stroke of the pump piston (3). The pump piston (3) has a hole (15) which connects the pump suction space (6) to the upstroke valve (5) and bears cylindrical sealing faces which interact with the inner wall of the pump cylinder (2) in the region of the hollow space (32) which adjoins the valve seat (13) of the upstroke valve (5) and communicates with the pump space (14).

Description

Pump element for a high-pressure pump

The invention relates to a pump element for a high-pressure pump with a pump cylinder, a pump piston, a suction valve and a pressure valve, wherein in the downwards gear of the pump piston medium via the suction valve is sucked from a pump suction and medium is discharged via the pressure valve during the upward movement of the pump piston.

High pressure pumps are used, for example, in internal combustion engines to bring fuel to a suitable for injection into the combustion chamber pressure. In the case of diesel engines with common-rail injection system, the high-pressure pump ensures that the pressure required for the respective operating state in the rail is maintained. To allow a quick engine start, the maximum delivery of the high-pressure pump must be well above the full load required by the engine. On the other hand, however, only a small flow rate of the high-pressure pump is required at part load or idling of the engine. The regulation of the flow rate of the high-pressure pump in the rail via an electronically controlled metering unit, which determines the inflow to the high-pressure pump in dependence on the fuel pressure in the rail. Thus, only the respectively required amount of high-pressure fuel is replenished in the rail and not generated an excess of high-pressure fuel, which would then be relieved via a pressure control valve and returned to the tank. Such a procedure would be associated with high energy losses, which would also lead to an undesirable high heating of the fuel.

A high-pressure pump consists of at least one pump element which is driven by a roller tappet or directly by a camshaft. On the suction side delivers a feed pump, such as a gear pump, the fuel at low pressure from the tank. On the pressure side of the compressed fuel passes through a collector into the rail. As a rule, the high-pressure pump operates in such a way that during the downward movement of the pump piston the quantity of fuel determined by the metering unit is sucked out of the pump suction chamber via the suction valve and then pressed into the rail via the pressure valve during the upward movement of the pump piston. Care must be taken in particular in the area of the valve unit to ensure that the pressure losses caused by the flow are kept as low as possible and that a design that is particularly susceptible to wear is selected. In valve units according to the prior art, as shown for example in Fig. 1, but due to the flow path within the valve unit, which is characterized by frequent large-angle deflections of the fuel, resulting significant flow losses and unevenness in the promotion. The invention therefore aims to provide a valve unit in which the flow-related pressure losses can be kept to a minimum and which is characterized by a compact design and by a small number of components.

To achieve this object, the invention consists essentially in that the pump piston has a bore connecting the pump suction with the suction valve, that the valve seat of the suction valve is formed on or in the pump piston, that the valve body of the suction valve in the pump piston in communicating with the pump room, to the suction valve seat adjoining cavity of the pump piston is displaceably guided and that the pump piston carries in the region of the cavity with the inner wall of the pump cylinder cooperating cylindrical sealing surfaces. Due to the fact that the suction of the medium to be pumped to the suction valve via a bore of the pump piston connecting the pump suction with the suction valve, there is a central inflow of the medium to the suction valve, wherein the medium passes in this area substantially without deflections to the suction valve, so that give optimal flow conditions. It is thus the occurrence of flow-related pressure losses largely avoided, and prevents caused by the flow losses fuel heating. Likewise cavitation phenomena, as they can occur in the otherwise necessary deflections of the medium, avoided and thus reduces the wear. Further advantages are the reduction of dead volumes, the reduction of the number of sealing points, the reduction of the construction space and the improvement of the durability.

In order to achieve a particularly simple and compact design, the valve seat of the suction valve is formed on or in the pump piston, wherein the valve body of the suction valve is guided displaceably in the pump piston. This allows a complete integration of the suction valve into the pump piston.

The guide of the valve member in the pump piston can in this case take place within a cavity or cage, resulting in a particularly simple design, if, as it corresponds to a preferred embodiment, the valve body of the suction valve is designed as a ball. The valve body of the suction valve is in this case arranged in a communicating with the pump chamber cavity of the pump piston, wherein preferably the cavity connects to the pump suction with the suction valve connecting the bore of the pump piston, is closed at the end of the piston by a filler and by radial openings in the piston wall is connected to the pump room.

A particular challenge in the design according to the invention is to ensure the required tightness between pump piston and cylinder inner wall. Because the suction valve seat is arranged on or in the pump piston in the constructions according to the invention, wherein the valve body of the suction valve is arranged in a cavity of the pump piston which communicates with the pump chamber and adjoins the suction valve seat, there is a risk Design-related reduction of the sealing and guiding length of the pump piston in the pump cylinder. Therefore, measures must be taken to ensure a sufficient tightness between pump piston and pump cylinder in the area of the suction valve. For this purpose, the embodiment of the invention is such that the pump piston in the region of the adjoining the valve seat cavity carries cooperating with the inner wall of the pump cylinder cooperating cylindrical sealing surfaces. In this context, it can be provided that the pump piston in the region of the adjoining the valve seat cavity has an outer diameter which substantially corresponds to the inner diameter of the pump cylinder. By virtue of such a design, the sealing gap between the cylinder inner wall and the pump piston, in particular from the upper edge of the piston, can be kept deliberately at a very low value over a relatively long range.

A particularly simple production and in particular the introduction of the valve member into the corresponding valve space succeeds according to a preferred embodiment in that the cavity is formed in an axial slot of the piston wall formed with the end portion of the piston and the front side has an opening for insertion of the valve member , As already known, a spring can act on the valve member in order to apply a corresponding restoring force. In this case, the design is preferably made such that a valve spring constructed as a compression spring is arranged in the cavity. The compression spring can be designed as a conical compression spring and be supported on inwardly jumping areas of the slotted piston wall.

Alternatively it can be provided as a tension spring valve spring, which is fixed on the one hand on the valve member and on the other hand, on or in the pump piston. It can the

Tension spring preferably arranged in the bore of the pump piston be, wherein the tension spring preferably engages the valve seat on the side facing away from the valve member.

The sealing gap between the cylinder inner wall and the pump piston is naturally dependent on the respective pressure in the cylinder, since an increased internal pressure causes a widening of the cylinder and thereby an enlargement of the sealing gap. In order to minimize the enlargement of the sealing gap, it is provided according to a preferred development of the construction according to the invention that the adjoining the Saugventilsitz cavity has a diameter corresponding to 50 to 90%, preferably about 65% of the outer diameter of the piston. In such a configuration, the pressure prevailing in the cavity of the pump piston causes a widening of the piston, the dimensioning being such that the widening of the outer diameter of the piston corresponds approximately to the widening of the inner cylinder diameter so that the sealing gap width is kept approximately constant within the desired range. Thus, the leakage can be reduced to the minimum required for lubrication.

In the uppermost region of the pump piston, an additional reduction of the sealing gap can be achieved in that the cavity has an expansion leading to the pump chamber. In this case, the widening of the cavity causes a corresponding reduction in the wall thickness of the piston in this area, so that the piston is widened more strongly in this area by the fluid pressure acting in the cavity of the piston.

In the region of the suction valve seat, it may be undesirable that the widening of the piston exerts an influence on the sealing gap, so that it is preferably provided that an annular groove is formed on the circumference of the pump piston in the area of the suction valve seat.

By extending the sealing surfaces from the area of the suction valve as far as the piston top edge is a radial Diverting the pumped medium after the suction valve not readily possible, but it remains the medium over a short distance in the adjoining the Saugventilsitz cavity of the pump piston, whereby the described radial expansion of the piston is effected. The outflow of the medium into the pump chamber should thus take place in the axial direction, for which purpose preferably an axial flow openings releasing filler is disposed within the cavity, wherein preferably a valve spring for the Saugventilglied engages the filling.

A preferred development finally provides that the pressure valve member at least partially protrudes into the cavity in the uppermost position of the pump piston. As a result, the dead volume can be reduced.

The invention will be explained in more detail with reference to an embodiment schematically illustrated in the drawing. 1 shows the basic structure of a pump element according to the prior art, FIG. 2 shows a pump element according to the invention in a first position, FIG. 3 shows the pump element according to the invention according to FIG. 2 in a further position, FIG. 4 shows a partial view of the suction valve and FIGS. 5 to 10 each show further modified embodiments of the suction valve.

Fig. 1 shows the basic structure of a pump element according to the prior art. A pump element 1 consists of a cylinder 2 and a piston 3, which is guided longitudinally displaceably in the cylinder 2. A camshaft 4 driven by the internal combustion engine moves the piston 3 up and down in the cylinder 2, the piston spring 3 a maintaining contact between the piston 3 and the camshaft 4. During the downward movement of the piston 3, fuel is sucked out of the pump suction chamber 6 via a suction valve 5 and then pressed into the rail 8 during the upward gear via a pressure valve 7. Figs. 2, 3 and 4 show a pumping element according to the present invention. The piston 3 has in this case a valve ball 9, a valve spring 10, a filler 11 and a snap ring 12. The filler 11 is connected via the snap ring 12 fixed to the piston 3. When the piston 3, the pressure in the element chamber 14 decreases so far that the pressure in the pump suction 6, the valve ball 9 presses out of the Saugventilsitz 13 and thus fuel in the element space 14 flows. During the upward movement, the valve ball 9 is pressed by the valve spring 10 and the pressure of the fuel in the element space 14 into the suction valve seat 13 and the suction channel 15 is closed, while at the same time fuel is forced into the rail 8 via the pressure valve 7.

Fig. 5 shows an alternative embodiment of the suction valve. The piston 3 has a piston crown 20 with at least two slots 16, and a bore 17 of slightly smaller diameter than the valve ball 9. The bore 17 further has a Einführfase 18 with a very small angle. The valve ball 9 is pressed during assembly in the bore 17 with Einführfase 18, the slotted piston crown 20 expands elastically, and the valve ball 9 falls into the Saugventilraum 19 where it is trapped, as the piston crown 20 springs back to its original shape. As a valve spring 10, a conical compression spring is used in this case, which is supported on the valve ball 9 and on the piston crown 20. The valve spring 10 is inserted in a compressed state via one of the slots 16 in the Saugventilraum 19 and brought into position.

6 shows a second alternative embodiment of the suction valve. The piston 3 has, analogously to FIG. 5, at least two

Slots 16, a hole 17 with slightly smaller

Diameter than the valve ball 9 and a Einführfase 18. The valve spring 10 is formed as a tension spring, which is fixed to an attached to the valve ball 9 eyelet 21, and to a bracket 22.

FIG. 7 shows a further alternative embodiment of the suction valve analogously to FIG. 6. Instead of a valve ball 9, however, a flat cylindrical sealing plate 23 with eyelet 24 is used.

Fig. 8 shows an alternative embodiment with an elastic, provided with lateral slots 16 clip 28 which is positively connected to the piston 3. The clip 28 acts as a guide of valve spring 10 and valve ball 9, and as a stroke stop for the valve ball. 9

Fig. 9 shows an embodiment in which the maintenance of a defined sealing gap between the cylinder inner wall and the pump piston is made possible, wherein the construction of the head part of the pump piston is shown. During the downward movement of the pump piston 3, the fuel flows through the suction channel 15 on the valve ball 9 lifting away from its seat by several flow openings 33 on the filling piece 29 into the element space 14. During the upward movement of the pump piston 3, the valve ball 9 is sealed by the valve spring 10 and the fuel pressure pressed on its seat 13, the suction channel 15 thereby closed and pressed the fuel through the element space 14 and the pressure valve 7 in the rail direction.

The head region of the pump piston 3 between the suction valve seat 13 and the piston top edge 30 expands under the effect of the fuel pressure, so that the gap between the pump piston 3 and the cylinder 2 can be kept very small. The expansion of the outer diameter of the pump piston 3 is in an advantageous manner proportional to the expansion of the inner diameter of the cylinder 2. As a result, the leakage losses are minimized. In this case, the cavity 32 of the piston 3 adjoining the suction valve seat 13 should have substantially no radial openings, so that the fuel pressure can be fully filled. constantly comes in the sense of expansion of the piston to the effect. A conical widening 34 of the piston cavity 32 in the uppermost region can be used to reduce the piston clearance in this area.

By an annular groove 31 on the outer contour of the pump piston 3 in the region of the ball seat 13, the local expansion of the piston 3 in this area remains without influence on the piston clearance.

In practical experiments, the following results were achieved for the embodiment according to FIG. 9. The outer diameter (a) of the cylinder 2 was 25 mm. The inner diameter (b) of the cylinder 2, which corresponded to the outer diameter of the piston 3, was 10 mm. The cavity 32 of the piston 3 had a diameter (c) of 6 mm in a first attempt. In a second experiment, the cavity 32 of the piston 3 had an enlarged diameter (c) of 6.5 mm. It could be observed that the sealing gap between the inner wall of the cylinder 2 and the piston 3 in the first attempt was about 2 microns wide, while he was about zero in the second attempt. It could thus be shown that by increasing the cavity diameter or by reducing the piston wall thickness, better utilization of the delivery pressure in the sense of widening the piston to minimize the sealing gap could be achieved. A delivery pressure of 1500 bar was assumed.

To reduce the dead volume of the lower part of the pressure valve 7 can be carried out such that it protrudes into the cavity 32 of the pump piston 3.

In Fig. 10, the filling piece 29 is shown from above, wherein four bulges are visible along the circumference, which form the flow channels 33.

Claims

Claims:

1. Pump element for a high-pressure pump with a pump cylinder, a pump piston, a suction valve and a pressure valve, wherein medium is sucked through the suction valve from a pump suction during downwards movement of the pump piston and medium is ejected via the pressure valve during the upward movement of the pump piston, characterized the pump piston (3) has a bore (15) connecting the pump suction space (6) with the suction valve (5), that the valve seat (13) of the suction valve (5) is formed on or in the pump piston (3) Valve body (9) of the suction valve (5) in the pump piston (3) in a with the pump chamber (14) communicating, to the suction valve seat (13) adjoining cavity (32) of the pump piston is displaceably guided and that the pump piston (3) Area of the cavity (32) with the inner wall of the pump cylinder (2) cooperating cylindrical sealing surfaces carries.

2. Pump element according to claim 1, characterized in that the valve body (9) of the suction valve (5) is designed as a ball.

3. Pump element according to claim 1 or 2, characterized in that the cavity (32) connects to the pump suction chamber (6) with the suction valve (5) connecting bore (15) of the pump piston (3), on the end face of the piston (3) is closed by a filler (11) and is connected by radial openings (16) in the piston wall with the pump chamber (14).

4. Pump element according to one of claims 1 to 3, characterized in that the cavity (32) in an axial slots (16) of the piston wall formed end portion of the piston (3) is formed and frontally an opening for insertion of the valve member (9) having.

5. Pump element according to one of claims 1 to 4, characterized in that a pressure spring designed as a valve spring (10) in the cavity (32) is arranged.

6. Pump element according to claim 5, characterized in that the compression spring (10) is designed as a conical compression spring and is supported on inwardly jumping portions of the slotted piston wall.

7. Pump element according to one of claims 1 to 6, characterized in that a tension spring designed as a valve spring (10) on the one hand on the valve member (9) and on the other hand on or in the pump piston (3) is fixed.

8. Pump element according to claim 7, characterized in that the tension spring (10) in the bore (15) of the pump piston (3) is arranged.

9. Pump element according to claim 7 or 8, character- ized in that the tension spring (10) on the valve seat (13) facing away from the valve member (9) engages.

10. Pump element according to one of claims 1 to 9, characterized in that the pump piston (3) in the region of the valve seat (13) adjoining the cavity (32) has an outer diameter substantially to the inner diameter (b) of the pump cylinder ( 2) corresponds.

11. Pump element according to one of claims 1 to 10, characterized in that the suction valve seat (13) adjoining cavity (32) has a diameter (c) which is 50 to 90%, preferably about 65% of the outer diameter (b) of Piston (3) corresponds.

12. Pump element according to one of claims 1 to 11, characterized in that on the circumference of the pump piston (3) in the region of the suction valve seat (13) an annular groove (31) is formed.

13. Pump element according to one of claims 1 to 12, characterized in that the cavity (32) has a pump space to the (14) leading widening (34).

14. Pump element according to one of claims 1 to 13, characterized in that the pressure valve member in the uppermost position of the pump piston (3) at least partially protrudes into the cavity (32).

15. Pump element according to one of claims 1 to 14, characterized in that an axial flow openings (33) exposed filler (29) within the cavity (32) is arranged, wherein preferably the valve spring (10) for the Saugventilglied (9) on the filler (29) attacks.