Piston pump

Abstract

A piston pump (20), in particular a fuel pump such as a high-pressure fuel pump of a common rail system, comprises a pump cylinder (21), a pump piston (22) movably mounted in a recess (23) of the pump cylinder (21), the pump piston being movable upward and downward in the recess (23), and a leakage groove (24) introduced into the pump cylinder (21) in the region of the recess (23), the leakage groove being connected to a leakage line (25) for discharging fuel leakage, wherein mating gaps of different sizes are formed in different parts (28, 29) between the pump cylinder (21) and the pump piston (22).

Description

Technical Field

[0001] The present invention relates to piston pumps, and more particularly to fuel pumps, such as high pressure fuel pumps for common rail fuel systems. Background Art

[0002] Fuel pumps known from practice include a pump cylinder in which a pump piston is movably mounted. Preferably, the pump piston is moved up and down in the pump cylinder by one or more cams, through which the fuel is sucked in and supplied from the fuel pump to a consumer, such as an injection valve of a fuel system.

[0003] Figure 1 A schematic cross section through a fuel pump 10 known from the prior art and designed as a piston pump is shown, wherein the fuel pump 10 comprises a pump cylinder 11 and a pump piston 12. The pump piston 12 is guided displaceably upward and downward in a recess 13 in the pump cylinder 11, wherein the upward and downward movement of the pump piston 12 in the pump cylinder 11 is preferably controlled by a cam (not shown).

[0004] Specifically, when Figure 1 Compression of the fuel occurs when the pump piston 12 moves upward in the recess 13. In the opposite direction of movement of the pump piston 12, there is a suction phase of the fuel pump 10. The fuel can be sucked in by the fuel pump 10 via at least one bore 17a in the pump cylinder 11 and, after compression, supplied to a consumer such as an injection valve via at least one bore 17b in the pump cylinder 11.

[0005] In the pump cylinder 11, a leakage groove 14 is introduced to discharge fuel leakage that may form during operation of the fuel pump. For this purpose, the leakage groove 14 is connected to a leakage line 15, through which the final fuel leakage can be discharged into a leakage tank, where a low pressure (especially ambient pressure) exists.

[0006] The fuel leakage that develops in the region of the fuel pump 10 depends on the size of the spacing 16 between the pump piston 12 and the pump cylinder 11. In order to ensure the lowest possible fuel leakage, this spacing 16 should be as small as possible, which can be provided by a very small mating clearance between the pump cylinder 11 and the pump piston 12. During the operation of such a fuel pump, there is the problem of so-called piston jamming or plunger jamming, i.e. the pump piston 22 jams in the pump cylinder 21. This leads to malfunctions of the fuel pump. This is a disadvantage. Summary of the invention

[0007] There is a need to reduce the risk of such piston seizures occurring in piston pumps, in particular fuel pumps. Starting from this, the present invention is based on the object of creating a piston pump.

[0008] This object is solved by a piston pump according to the invention. A piston pump, in particular a fuel pump such as a high-pressure fuel pump of a common rail system, has a pump cylinder; a pump piston movably mounted in a recess of the pump cylinder, the pump piston being movable upward and downward in the recess; a leakage groove introduced into the pump cylinder in the region of the recess, the leakage groove being connected to a leakage line for draining fuel leakage. Between the pump cylinder and the pump piston, mating gaps of different sizes are formed in different parts.

[0009] In the piston pump according to the present invention, between the pump cylinder and the pump piston, matching gaps of different sizes are formed in different portions. A larger matching gap is formed in a portion where the pump piston passes through the leakage groove during its upward and downward movement than in a portion where the pump piston does not pass through the leakage groove during its upward and downward movement.

[0010] With the piston pump according to the present invention, between the pump cylinder and the pump piston, mating gaps of different sizes are formed in different portions. The mating gap is designed to be larger in the portion where the pump piston passes the leakage groove in the pump cylinder during its movement than in the portion where the pump piston does not pass the leakage groove in the pump cylinder during its movement. In this way, on the one hand, low fuel leakage can be ensured by a low mating gap, while on the other hand, there is no risk of so-called piston sticking or plunger sticking.

[0011] The invention is based on the recognition that the risk of so-called piston or plunger sticking is primarily due to the fact that in the region of the leakage groove the pump cylinder is subject to a lower thermal expansion than the pump piston. This can lead to a reduction in the mating clearance in the region of the leakage groove, as a result of which, in the prior art, piston or plunger sticking can result. However, since, according to the invention, a larger mating clearance is provided in the section of the pump piston that passes through the leakage groove of the pump cylinder, there is no risk of a loss of mating clearance due to different thermal expansions of the pump piston and pump cylinder. In this way, the risk of piston or plunger sticking can ultimately be significantly reduced compared to fuel pumps known from the prior art.

[0012] Preferably, the matching gap is formed to be approximately 25% to 125%, particularly preferably 30% to 100% larger in the portion where the pump piston passes through the leakage groove during its upward and downward movement than in the portion where the pump piston does not pass through the leakage groove during its upward and downward movement. This is particularly preferred in order to reduce the risk of piston sticking or plunger sticking of the fuel pump.

[0013] According to an advantageous further development, the pump piston has a smaller outer diameter in the section where the pump piston passes through the leakage groove during its upward and downward movement than in the section where the pump piston does not pass through the leakage groove during its upward and downward movement. In this way, different mating clearances between the pump cylinder and the pump piston in different sections can be easily and reliably adjusted. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] According to the following description, preferred further improvements of the present invention are obtained. Exemplary embodiments of the present invention are explained in more detail by the accompanying drawings, but are not limited thereto. Therein are shown:

[0015] Figure 1 shows a schematic section through a fuel pump according to the prior art,

[0016] Figure 2 A schematic section through a fuel pump according to the invention is shown. DETAILED DESCRIPTION

[0017] The present invention relates to a piston pump.Preferably, the present invention relates to a fuel pump, in particular a high-pressure fuel pump for a common rail fuel system of an internal combustion engine, such as a marine internal combustion engine.

[0018] Figure 2 A schematic cross section through an exemplary embodiment of a fuel pump 20 according to the invention is shown. Figure 2 The fuel pump 20 further comprises a pump cylinder 21 and a pump piston 22 , wherein the pump piston 22 is guided displaceably up and down in a recess 23 of the pump cylinder 21 , in particular by means of a cam (not shown).

[0019] During the upward movement of the pump piston 22 in the recess 23 towards the top, compression of the fuel occurs in order to supply the compressed fuel to the consumer via the at least one hole 27b. In the opposite movement direction downward, the pump piston 22 sucks in fuel via the at least one hole 27a.

[0020] Introduced in the recess 23 of the pump cylinder 21 is a leakage groove 24 which is connected to a leakage line 25 for discharging fuel leakage which can flow between the pump cylinder 21 and the pump piston 22 via the interval 26 formed between the pump cylinder 21 and the pump piston 22. Via the leakage line 25, this fuel leakage is usually discharged into a leakage tank (not shown) in which an underpressure or ambient pressure prevails.

[0021] According to the invention, it is provided that between the pump cylinder 21 and the pump piston 22 , mating gaps of different sizes are formed in different sections 28 and 29 .

[0022] In the portion 28 where the pump piston 22 passes through the leakage groove 24 of the pump cylinder 21 during its upward and downward movement, a larger mating gap is formed between the pump cylinder 21 and the pump piston 22 than in the portion 29 where the pump piston 22 does not pass through the leakage groove 24 during its upward and downward movement. This means that Figure 2 In the embodiment, between the pump piston 22 and the pump cylinder 21 , a relatively small mating gap is formed in the upper portion 29 , and a relatively large mating gap is formed in the lower portion 28 .

[0023] Due to the relatively small mating gap in the upper region 29 , any leakage of fuel which occurs via the space 26 between the pump cylinder 21 and the pump piston 22 can be kept as low as possible.

[0024] By means of the larger mating gap in the lower part 28 , the different thermal expansions of the pump piston 20 and the pump cylinder 21 in the region of the leakage groove 24 , which are caused by the discharge of the fuel leakage, can be taken into account, so that the mating gap is not lost in this part 28 and so-called piston jamming or plunger jamming of the pump piston 22 in the pump cylinder 21 can be prevented.

[0025] It is preferably provided that the mating gap is formed to be 25% to 125% larger, preferably 30% to 100% larger, in a portion 28 of the pump piston 22 which passes through the leakage groove 24 of the pump cylinder 21 during its movement in the pump cylinder 21, than in a portion 29 of the pump piston 22 which does not pass through the leakage groove 24 of the pump cylinder 21 during its movement in the pump cylinder 21.

[0026] It is preferable to provide portions 28 and 29 with different mating clearances between the pump piston 22 and the pump cylinder 21 because the pump piston 22 has outer diameters of different sizes in these portions 28 and 29 .

[0027] A smaller outer diameter is formed on the pump piston 22 in the portion 28 where the pump piston 22 passes through the leakage groove 24 during its movement than in the portion 29 where the pump piston does not pass through the leakage groove 24 of the pump cylinder 21 during its movement in the pump cylinder 21 .

[0028] The recess 23 in the pump cylinder 21 preferably has a continuously uniform inner diameter. The smaller the outer diameter of the pump piston 22, the greater the mating gap.

[0029] The two parts 28 and 29 of the pump piston 22 with different outer diameters are arranged in a Figure 2 The pump piston 22 is separated from each other by a circumferential groove 30 in the pump piston 22. This is preferred in order to avoid a stepped diameter shoulder between the two different parts 28 and 29 of the pump piston 22.

[0030] Therefore, the invention provides different mating gaps between the pump cylinder 21 and the pump piston 22, which are reflected in the parts 28 and 29. In the area of ​​the leakage groove 24, a relatively large mating gap is provided to avoid so-called plunger jamming due to different thermal expansions. Therefore, the mating gap in the lower part 28 of the pump piston 22 passing through the leakage groove 24 is larger than in the upper part 29 of the pump piston 22 not passing through the leakage groove 24 during its movement. This serves to ensure low fuel leakage and at the same time avoid the risk of plunger jamming. Ultimately, the efficiency of the fuel pump 20 can be increased. The operating safety of the fuel pump 20 can be increased. If glue forms on the pump piston 22, the risk of plunger jamming can be reduced.

[0031] The fuel pump 20 is preferably a high pressure fuel pump of a common rail fuel system of an internal combustion engine, in particular a marine diesel internal combustion engine. However, the present invention can also be used with other fuel pumps and piston pumps.

[0032] Reference Numbers List

[0033] 10 Fuel Pump

[0034] 11 Pump cylinder

[0035] 12 Pump piston

[0036] 13 Recessed part

[0037] 14 Leakage groove

[0038] 15 Leaking pipeline

[0039] 16 intervals

[0040] Hole 17a

[0041] 17b hole

[0042] 20 Fuel Pump

[0043] 21 Pump cylinder

[0044] 22 Pump piston

[0045] 23 recessed portion

[0046] 24 Leakage groove

[0047] 25 Leaking pipeline

[0048] 26 intervals

[0049] 27a hole

[0050] 27b hole

[0051] 28 parts

[0052] Part 29

[0053] 30 circumferential grooves.

Claims

1. A piston pump (20) comprising a pump cylinder (21), A pump piston (22) is movably mounted in a recess (23) of the pump cylinder (21), wherein the pump piston is movable upward and downward in the recess (23), having a leakage groove (24) introduced into the pump cylinder (21) in the region of the recess (23), the leakage groove being connected to a leakage line (25) for draining fuel leakage, It is characterized in that Between the pump cylinder (21) and the pump piston (22), matching gaps of different sizes are formed in different parts, wherein a larger mating gap is formed in a first portion (28) of the pump piston (22) passing through the leakage groove (24) during its upward and downward movement than in a second portion (29) of the pump piston (22) not passing through the leakage groove (24) during its upward and downward movement, wherein the pump piston (22) has a smaller outer diameter in the first portion (28) where the pump piston passes the leakage groove (24) during its upward and downward movement than in the second portion (29) where the pump piston does not pass the leakage groove (24) during its upward and downward movement, The first and second parts (28, 29) of the pump piston (22) having different outer diameters are separated from each other by a circumferential groove (30) in the pump piston (22) and a stepped diameter shoulder between the first and second parts (28, 29) of the pump piston (22) is avoided.

2. The piston pump according to claim 1, characterized in that The mating gap is formed to be 25% to 125% larger in the first portion (28) where the pump piston (22) passes the leakage groove (24) during its upward and downward movement than in the second portion (29) where the pump piston (22) does not pass the leakage groove (24) during its upward and downward movement.

3. The piston pump according to claim 1 or 2, characterized in that: The mating gap is formed to be 30% to 100% larger in the first portion (28) where the pump piston (22) passes the leakage groove (24) during its upward and downward movement than in the second portion (29) where the pump piston (22) does not pass the leakage groove (24) during its upward and downward movement.

4. The piston pump according to claim 1 or 2, characterized in that: The piston pump is a fuel pump.

5. The piston pump according to claim 1 or 2, characterized in that: The piston pump is a high-pressure fuel pump of a common rail fuel system, wherein the leakage line (25) discharges fuel leakage in the low-pressure area of ​​the common rail fuel system.

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