Piston pump, in particular fuel pump for a fuel system for an internal combustion engine

Abstract

Piston pump (10), in particular fuel pump for a fuel system for an internal combustion engine, with an inlet (28), an inlet-side low-pressure area (20), a piston (32) and a working chamber (30) which is bounded by the piston (32), wherein a section of the piston (32) pointing away from the working chamber (30) is arranged in a fluid chamber (48) which is at least temporarily hydraulically connected to the low-pressure area (20), wherein downstream of the inlet (28) at least a first connecting channel (50) branches off to the inlet-side low-pressure area (20) and at least a second connecting channel (52) branches off to the fluid chamber (48), and wherein the fluid chamber (48) is connected to the inlet-side low-pressure area (20) by means of at least a third connecting channel (54), characterized in that the first and the second connecting channels (50, 52) are sections of a through-bore into which the inlet (28) leads to,or that the first and second connecting channels (50, 52) are blind bores that open into the inlet (28).

Description

State of the art

[0001] The invention relates to a piston pump according to the preamble of claim 1.

[0002] Piston pumps for fuel systems for internal combustion engines are well known on the market. These pumps allow a piston to move axially by means of a drive formed by a cam or an eccentric disc. The required restoring force of the piston is generated by a compression spring. During operation, the piston pump sometimes becomes extremely hot, which can adversely affect its properties and / or its fatigue strength.

[0003] Another piston pump is known from US 2011 / 0 247 488 A1. Disclosure of the invention

[0004] The problem underlying the invention is solved by a piston pump according to claim 1. Advantageous further developments are specified in the subclaims. Important features of the invention can also be found in the following description and the drawings, whereby the features may be important for the invention both individually and in various combinations, without this being explicitly referred to again.

[0005] The invention relates to a piston pump, in particular a fuel pump for a fuel system for an internal combustion engine, having an inlet, an inlet-side low-pressure region, a piston and a working chamber which is delimited by the piston, wherein a section of the piston facing away from the working chamber is arranged in a fluid chamber which is at least temporarily hydraulically connected to the low-pressure region.

[0006] The piston can be designed as a stepped piston with sections of different diameters. This creates a diameter step, and the exact section of the piston in which this diameter step is located can be located in the fluid chamber. This is therefore also referred to as the "step chamber." The cyclical axial piston movement leads to a corresponding cyclical volume change in this step chamber, whereby fuel is drawn into and expelled from the fluid chamber.

[0007] According to the invention, at least one first connecting channel branches off to the inlet-side low-pressure region downstream of the inlet, and at least one second connecting channel branches off to the fluid chamber. Furthermore, the fluid chamber is connected to the inlet-side low-pressure region by means of at least one third connecting channel. This allows a portion of the fuel flowing in via the inlet to flow through the fluid chamber, thereby significantly reducing the temperature in the fluid chamber. Depending on an embodiment of the piston pump, the flow through the fluid chamber can even be a "circular flow" and thus encompass a comparatively large fluid volume in the piston pump.

[0008] The invention has the advantage, among others, that wear on a piston seal (“sealing lips”) that seals the piston or the fluid chamber to the outside (towards a drive of the piston pump), as well as wear on a cylinder liner that guides the piston, can be reduced. Furthermore, the reduction in temperature described above makes it possible to reduce the hydraulic pressure required at the inlet of the piston pump (so-called “pre-pressure”) without impairing the lubrication required for piston operation. This can also reduce so-called “vapor lock” in the piston pump and the risk of potential “piston seizure.” Furthermore, undesired mixing of fuel and oil can be reduced or even prevented, particularly in an area of ​​the piston seal.

[0009] In one embodiment of the piston pump, the first and second connecting channels have at least approximately the same flow resistance, such that part of the inflowing fuel flows to the inlet-side low-pressure region and another part of the inflowing fuel flows to the fluid chamber. The third connecting channel has a hydraulic flow resistance such that the fuel flows out of the fluid chamber via the third connecting channel. This allows the flows according to the invention to be implemented in a simple manner. Preferably, said flow resistances can be adapted by selecting a cross-section of the respective connecting channel. If the connecting channels are designed as bores, this can advantageously be achieved by appropriately dimensioning the bore diameter.

[0010] In a further embodiment of the piston pump, a hydraulic pressure damper is arranged in the inlet-side low-pressure area. Taking into account the hydraulic resistance caused by the pressure damper, further advantageous possibilities arise for achieving a desired hydraulic flow through the fluid chamber.

[0011] The piston pump according to the invention is simplified according to a first of two alternatives according to the invention in that the first and the second connecting channel are sections of a through-bore into which the inlet opens. In this way, both connecting channels can be produced in one work step, thus saving costs. In one embodiment of the piston pump, a length at which the inlet opens into the through-bore produced in this way is structurally dimensioned in such a way that a desired relative flow resistance of the first to the second connecting channel is predetermined. As a result, the two connecting channels can optionally have different lengths and thus different flow resistances, whereby a proportion of the fuel flowing through the fluid space can be influenced.

[0012] According to the second alternative of the invention, the first and second connecting channels are blind bores that open into the inlet. This allows the first and second connecting channels to be axially offset from one another, which can result in additional design options and a simplified design of the piston pump. In particular, the first and second connecting channels can be designed with different diameters.

[0013] Furthermore, the third connecting channel can be provided as a through-hole. This allows the third connecting channel to be manufactured particularly easily and thus cost-effectively.

[0014] In particular, it can be provided that the piston pump comprises an at least substantially cylindrical housing, and that the inlet is designed as a radial channel and the connecting channels as axial channels. This simplifies the geometry of the piston pump and thus saves costs.

[0015] In the following, exemplary embodiments of the invention are explained with reference to the drawing. In the drawing, the only Fig. 1 a longitudinal section through a piston pump of a fuel system for an internal combustion engine.

[0016] Fig. Figure 1 shows an axial sectional view of a high-pressure fuel pump, which in this case is designed as a piston pump 10. The piston pump 10 is an element of a fuel system (not shown), for example, for a common rail fuel system for an internal combustion engine (also not shown). The piston pump 10 is designed to be at least partially rotationally symmetrical about a longitudinal axis 12.

[0017] The piston pump 10 comprises a substantially cylindrical housing 14, which can be screwed to a - not shown - engine block of the internal combustion engine by means of a flange 16. In the Fig. 1 upper area, the piston pump 10 comprises an inlet-side chamber-like low-pressure area 20 formed between a curved cover 18 and an upper and essentially flat end face of the housing 14 in the figure, in which a hydraulic pressure damper 22 is arranged to dampen pressure pulsations occurring during operation of the piston pump 10.

[0018] In a left-hand area in the drawing, the piston pump 10 has an inlet nozzle 24 for connection to a low-pressure fuel line (not shown). In the present case, the inlet nozzle 24 is connected in the housing 14 to a cylindrical fluid chamber 26, which in turn is connected to a channel designated as inlet 28 and radially oriented with respect to the housing 14. In one embodiment of the piston pump 10, a quantity control valve for controlling a quantity of fuel supplied via the inlet 28 is provided on the inlet nozzle 24 in the area of ​​the fluid chamber 26. However, this is not explicitly shown or visible in the drawing.

[0019] Furthermore, the piston pump 10 comprises a working chamber 30, which is defined on one side by the housing 14 and on the other side by an upper end section of a piston 32 (in the figure). The piston 32 is arranged vertically movable in a bushing 34 (in the drawing). A section of the piston 32 facing away from the working chamber 30 and having a diameter step is arranged in a fluid chamber 48, which is at least temporarily hydraulically connected to the low-pressure region 20.

[0020] In a lower range of Fig. 1, the piston pump 10 further comprises: an approximately pot-shaped spring retainer 36 pressed into the housing 14 or otherwise firmly and fluid-tightly connected thereto, a compressively loaded piston spring 38, a piston seal 40, and a spring plate 42 pressed onto a lower end section of the piston 32 in the figure. In a lower section in the drawing, in particular in the area of ​​the fluid chamber 48 and the piston seal 40, the piston 32 has a smaller diameter than in a middle section, whereby the diameter step already mentioned above is formed and a hydraulic volume displaced by the piston 32 in the fluid chamber 48 is dependent on an axial position of the piston 32.

[0021] The working chamber 30 is in this case connected to two hydraulic channels 44 and 46, through which the working chamber 30 is hydraulically connected on the one hand to the inlet-side low-pressure region 20 and on the other hand to an outlet valve (not shown) of the piston pump 10.

[0022] Furthermore, the piston pump 10 comprises a first connecting channel 50, which branches off upwards downstream of the inlet 28 in the drawing to the inlet-side low-pressure region 20. Furthermore, the piston pump 10 comprises a second connecting channel 52, which branches off downwards downstream of the inlet 28 in the drawing to the fluid chamber 48. The second connecting channel 52 is highlighted in the drawing by a dashed border.

[0023] Furthermore, the piston pump 10 comprises, on the right in the drawing, a third connecting channel 54, by means of which the fluid chamber 48 is connected upwards to the inlet-side low-pressure region 20. The first connecting channel 50, the second connecting channel 52, and the third connecting channel 54 are each designed essentially parallel to the longitudinal axis 12.

[0024] In the present case, the three connecting channels 50, 52 and 54 are designed as axial channels, which are designed as axial bores in the housing 14. The first and second connecting channels 50 and 52 are designed as blind bores, which open into the inlet 28. Alternatively, the first and second connecting channels 50 and 52 can be sections of a through-bore, into which the inlet 28 opens. The third connecting channel 54 is in the Fig. 1 also designed as a through hole.

[0025] In an embodiment of the piston pump 10 (not shown), at least one of the connecting channels 50, 52, and 54 is designed as an “oblique” bore with respect to the longitudinal axis 12. In a further embodiment of the piston pump 10 (not shown), the housing 14 is manufactured using a metal powder injection molding (MIM) and / or ceramic powder injection molding (CIM) process, with the connecting channels 50, 52, and 54 being created simultaneously by means of the casting process. In a further embodiment of the piston pump 10 (not shown), at least one of the connecting channels 50, 52, and 54 is designed as an external hydraulic line, which is connected to ports of the piston pump 10, for example by means of a screw connection or welding.

[0026] In the present case, the first and second connecting channels 50 and 52 have at least approximately the same flow resistance. This occurs in such a way that a portion of the fuel flowing in via the inlet connection 24 and the inlet 28 flows to the inlet-side low-pressure region 20, and another portion of the inflowing fuel flows to the fluid chamber 48. The third connecting channel 54 has such a hydraulic flow resistance that the fuel can flow out of the fluid chamber 48 via the third connecting channel 54.

[0027] During operation of the piston pump 10, the piston 32 is periodically moved axially in the direction of the longitudinal axis 12 by a drive (not shown) via the spring plate 42. The piston seal 40 is lubricated by the fuel in the surrounding area. In an intake stroke, the piston 32 is moved downward in the drawing, allowing fuel to flow from the inlet-side low-pressure region 20 into the working chamber 30. In a working stroke, the piston 32 is moved upward in the drawing, allowing fuel to be pumped under pressure from the working chamber 30 via the outlet valve (not shown) into a high-pressure fuel reservoir (not shown).

[0028] As a result of the piston movement, as already described above, the hydraulic volume displaced by the piston 32 in the fluid chamber 48 is periodically reduced and increased. A first flow of fuel, indicated by an arrow 56, results from the inlet connection 24 through the fluid chamber 26, then through the inlet 28, and then through the first connecting channel 50 to the inlet-side low-pressure region 20 in the upper region of the piston pump 10 in the drawing.

[0029] Taking into account the hydraulic resistance caused by the pressure damper 22, a second flow of fuel, indicated by an arrow 58, results through the second connecting channel 52 - at least on average over time. Comparatively cool fuel flows from the inlet connection 24 through the fluid chamber 26, then through the inlet 28, then through the second connecting channel 52, then through the fluid chamber 48, and then through the third connecting channel 54 to the inlet-side low-pressure region 20 in the upper region of the piston pump 10. This allows the fluid chamber 48 to be cooled.

[0030] In particular, the described second fuel flow according to arrow 58 can reduce the operating temperature of the piston pump 10. This can prevent the formation of vapor bubbles in the piston pump 10 even with a comparatively low hydraulic pressure at the inlet connection 24. Consequently, lubrication of the piston 32 in the area of ​​the piston seal 40 can also be improved.

[0031] Depending on the properties of the piston pump 10 and, in particular, on the dimensions of the connecting channels 50, 52, and 54, the second flow indicated by arrow 58 can be optimized. This is possible, for example, by structurally adapting a respective hydraulic cross-section. It is also possible to structurally adapt the axial or vertical position of the inlet 28 with respect to the longitudinal axis 12, thereby providing an additional degree of freedom in optimizing the hydraulic flows.

Claims

[1] Piston pump (10), in particular a fuel pump for a fuel system for an internal combustion engine, having an inlet (28), an inlet-side low-pressure region (20), a piston (32), and a working chamber (30) delimited by the piston (32), wherein a portion of the piston (32) facing away from the working chamber (30) is arranged in a fluid chamber (48) which is at least temporarily hydraulically connected to the low-pressure region (20), wherein downstream of the inlet (28), at least one first connecting channel (50) branches off to the inlet-side low-pressure region (20) and at least one second connecting channel (52) branches off to the fluid chamber (48), and wherein the fluid chamber (48) is connected to the inlet-side low-pressure region (20) by means of at least one third connecting channel (54), characterized bythat the first and second connecting channels (50, 52) are sections of a through-bore into which the inlet (28) opens, or that the first and second connecting channels (50, 52) are blind bores which open into the inlet (28). [2] Piston pump (10) according to claim 1, characterized by that the first and the second connecting channel (50, 52) have an equal flow resistance, such that a part of the inflowing fuel flows to the inlet-side low-pressure region (20) and another part of the inflowing fuel flows to the fluid space (48), and that the third connecting channel (54) has such a hydraulic flow resistance that the fuel flows out of the fluid space (48) via the third connecting channel (54). [3] Piston pump (10) according to at least one of the preceding claims, characterized by that a hydraulic pressure damper (22) is arranged in the inlet-side low-pressure region (20). [4] Piston pump (10) according to one of the preceding claims, characterized by that the third connecting channel (54) is a through hole. [5] Piston pump (10) according to at least one of the preceding claims, characterized by that the piston pump (10) comprises a cylindrical housing (14), and that the inlet (28) is designed as a radial channel and the connecting channels (50, 52, 54) are designed as axial channels.

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