Piston pump

Abstract

A piston pump as a high-pressure fuel pump of a common rail system includes: a pump cylinder; a pump piston moveably mounted in a recess of the pump cylinder, the pump piston being moveable up and down in the recess; and a leakage groove arranged in the pump cylinder in a region of the recess, the leakage groove being coupled with a leakage line configured to discharge a fuel leakage. Between the pump cylinder and the pump piston a different size pairing clearance is formed in first and second portions of the pump cylinder.

Claims

1. A piston pump (20) as a high-pressure fuel pump of a common rail system, comprising: a pump cylinder (21); a pump piston (22) moveably mounted in a recess (23) of the pump cylinder (21), the pump piston (22) being moveable up and down in the recess (23); and a leakage groove (24) arranged in the pump cylinder (21) in a region of the recess (23), the leakage groove (24) being coupled with a leakage line (25) configured to discharge a fuel leakage, wherein between the pump cylinder (21) and the pump piston (22) a different size pairing clearance is formed in first and second portions (28, 29) of the pump piston, wherein in the first portion (28) of the pump piston, in which the pump piston (22) during its up-and-down movement passes over the leakage groove (24), a larger pairing clearance is formed than in the second portion (29) of the pump piston, in which the pump piston (22) during its up-and-down movement does not pass over the leakage groove (24), wherein the pump piston (22), in the first portion (28), has a smaller outer diameter than in the second portion (29), and wherein portions of the pump piston (22) having different size outer diameters are separated from one another by a circumferential groove (30) in the pump piston (22).

2. The pump piston according to claim 1, wherein in the first portion (28), the pairing clearance is formed 25% to 125% larger than in the second portion (29).

3. The pump piston according to claim 1, wherein in the first portion (28), the pairing clearance is formed larger by 30% to 100% than in the second portion (29).

4. The pump piston according to claim 1, wherein the leakage line (25) discharges the fuel leakage in a low-pressure region of the common rail fuel system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Preferred further developments of the invention are obtained from the following description. Exemplary embodiments of the invention are explained in more detail by way of the drawings without being restricted to this. There it shows:

(2) FIG. 1: is a schematic cross section through a fuel pump according to the prior art; and

(3) FIG. 2: is a schematic cross section through a fuel pump according to the invention.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

(4) The invention relates to a piston pump. Preferentially, the invention relates to a fuel pump, in particular a high-pressure fuel pump of a common rail fuel system of an internal combustion engine such as an internal combustion engine of a ship.

(5) FIG. 2 shows a schematic cross section through an exemplary embodiment of a fuel pump 20 according to an aspect of the invention. The fuel pump 20 of FIG. 2 in turn comprises a pump cylinder 21 and a pump piston 22, wherein the pump piston 22 is moveably guided up and down in a recess 23 of the pump cylinder 21, in particular by way of a cam which is not shown.

(6) During the upward movement of the pump piston 22 in the recess 23 towards the top, a compression of the fuel takes place in order to feed the compressed fuel to a consumer via at least one bore 27b. In the opposite movement direction downwards, the pump piston 22 draws in fuel via at least one bore 27a.

(7) Into the recess 23 of the pump cylinder 21, a leakage groove 24 is introduced, which is coupled with a leakage line 25 for discharging a fuel leakage, which can flow between the pump cylinder 21 and the pump piston 22 via a gap 26 formed between the the pump cylinder 21 and the pump piston 22. By way of the leakage line 25, this fuel leakage is typically discharged into a leakage tank which is not shown, in which low pressure or ambient pressure is present.

(8) According to the invention it is provided that between the pump cylinder 21 and the pump piston 22 a different size pairing clearance is formed in different portions 28 and 29.

(9) In a portion 28, in which the pump piston 22, during its up-and-down movement, passes over the leakage groove 24 of the pump cylinder 21, a larger pairing clearance between pump cylinder 21 and pump piston 22 is formed than in a portion 29, in which the pump piston 22, during its up-and-down movement does not pass over the leakage groove 24. This means that in FIG. 2 in the upper portion 29 a relatively small pairing clearance and in the lower portion 28 a relatively large pairing clearance between the pump piston 22 and the pump cylinder 21 is formed.

(10) Through the relatively small pairing clearance in the upper region 29, the fuel leakage that forms, which flows via the gap 26 between pump cylinder 21 and pump piston 22, can be kept as low as possible.

(11) By way of the larger pairing clearance in the lower portion 28, a different heat expansion of pump piston 20 and pump cylinder 21 in the region of the leakage groove 24, which is caused by the discharge of the fuel leakage, can be taken into account so that in this portion 28 the pairing clearance is not lost and a so-called piston seizure or plunger seizure of the pump piston 22 in the pump cylinder 21 can be prevented.

(12) Preferentially it is provided that in the portion 28, in which the pump piston 22 during its movement in the pump cylinder 21 passes over the leakage groove 24 of the pump cylinder 21, the pairing clearance is formed larger by 25% to 125%, preferentially by 30% to 100% than in the portion 29 in which the pump piston 22, during its movement in the pump cylinder 21, does not pass over the leakage groove 24 of the pump cylinder 21.

(13) The portions 28 and 29 with different pairing clearance between pump piston 22 and pump cylinder 21 are preferentially provided in that in these portions 28 and 29 the pump piston 22 has a different size outer diameter.

(14) In the portion 28, with which the pump piston 22 during its movement passes over the leakage groove 24, a smaller outer diameter on the pump piston 22 is formed than in that portion 29, in which the pump piston 22 during its movement in the pump cylinder 21 does not pass over the leakage groove 24 of the pump cylinder 21.

(15) The recess 23 in the pump cylinder 21 preferentially has a continuously same inner diameter. The smaller the outer diameter of the pump piston 22, the larger is the pairing clearance.

(16) The two portions 28 and 29 of the pump piston 22 with the different size outer diameters are separated from one another in FIG. 2 by a circumferential groove 30 in the pump piston 22. This is preferred in order to avoid a step-like diameter shoulder between the two different portions 28 and 29 of the pump piston 22.

(17) Accordingly it is provided with the invention to embody a different pairing clearance between the pump cylinder 21 and the pump piston 22 in the portions 28 and 29. In the region of the leakage groove 24, a comparatively large pairing clearance is provided for avoiding so-called plunger seizures as a consequence of different heat expansions. Accordingly, the pairing clearance in the lower portion 28, with which the pump piston 22 passes over the leakage groove 24, is larger in the upper portion 29 in which the pump piston 22, during its movement, does not pass over the leakage groove 24. This serves to ensure a low fuel leakage while avoiding the risk of a plunger seizure at the same time. Ultimately, the efficiency of the fuel pump 20 can be increased. The operational safety of the fuel pump 20 can be increased. Should gumming-up form on the pump piston 22, the risk of a plunger seizure can nevertheless be reduced.

(18) The fuel pump 20 is preferentially a high-pressure fuel pump of a common rail fuel system of an internal combustion engine, in particular of a ship diesel internal combustion engine. However, the invention can also be employed with other fuel pumps and piston pumps.

(19) Thus, while there have been shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.

LIST OF REFERENCE NUMBERS

(20) 10 Fuel pump 11 Pump cylinder 12 Pump piston 13 Recess 14 Leakage groove 15 Leakage line 16 Gap 17a Bore 17b Bore 20 Fuel pump 21 Pump cylinder 22 Pump piston 23 Recess 24 Leakage groove 25 Leakage line 26 Gap 27a Bore 27b Bore 28 Portion 29 Portion 30 Circumferential groove