DE102018211647A1 - Piston pump, in particular high-pressure fuel pump for an injection system of an internal combustion engine - Google Patents

Abstract

A piston pump (10), in particular a high pressure fuel pump for an injection system of an internal combustion engine, with a piston (22) and a working space (24), which is delimited by the piston (22), is designed and developed in such a way that the piston (22 ) has in its interior a cavity (40) which is closed to the outside and which is filled with a medium (42) which has a higher thermal conductivity than the piston (22).

Description

State of the art

The invention relates to a piston pump, in particular a high-pressure fuel pump for an injection system of an internal combustion engine according to the preamble of claim 1.

Such a piston pump is from the DE 10 2014 211 591 A1 known. This comprises a piston running in a pump housing for the delivery and compression of fuel.

Disclosure of the invention

The problem underlying the invention is solved by a piston pump with the features of claim 1.

In the suction phase of the piston pump (piston moves away from the work area), the piston ensures that the medium, e.g. fuel, which has already been pumped to low pressure, can flow into the work area (delivery chamber) from a tank line. In the delivery phase (piston moves towards the work area), the medium is compressed and brought to a higher pressure level. The medium can then be conveyed into the rail under high pressure and made available to the injection unit. The high compression causes comparatively high temperatures on the side of the piston (high-pressure side) facing the working area.

On the part of the applicant it has been recognized that the pistons heat differently over their length due to the high temperatures during compression. This leads to a different thermal expansion along the longitudinal axis of the piston. In areas subject to higher thermal stress, the piston increases more in cross-section due to the thermal expansion than in areas subject to less thermal stress. This influences the play between the piston and the guide element, which must always be greater than the maximum thermal expansion of the piston at the most thermally stressed point.

The conflict of objectives between the smallest possible play, which is positive for the reduction of leakage, and the pinching of the piston is solved by an optimized heat transfer on the piston. This can reduce the expansion of the piston cross-section in the areas subjected to higher thermal loads. It is proposed that the inside of the piston have a cavity which is closed to the outside and is filled with a medium (transmission medium) which has a higher thermal conductivity than the piston or the material from which the piston is formed.

The cavity in the interior of the piston can initially save weight on the piston. The lower piston mass has a positive effect on the piston drive, since the mass to be accelerated and decelerated is lower. Due to the up and down movement of the piston in relation to the working space, the medium in the cavity of the piston is also moved up and down due to the inertia (relative movement of the medium in relation to the piston). This accelerates the heat transfer. Due to the more uniform temperature distribution over the entire piston, the cross section of the piston, in particular its diameter, expands more evenly and with smaller amounts. The piston play can thereby be reduced. This increases the efficiency and the running time of the piston pump, since particularly large expansions at the points of highest thermal stress can be avoided on the piston (piston has fewer "edge supports").

The medium can be a solid or liquid material under normal conditions, which in any case becomes liquid when the piston pump is operating, for example as a result of the piston heating. The medium is designed in such a way that it also reciprocates in the cavity of the piston due to the reciprocating movement of the piston. As already indicated, the medium has a high thermal conductivity, preferably at least 100 W / (m * K).

The piston of the piston pump can be a reciprocating piston for compressing a medium (fluid), for example fuel. The piston pump can be a high-pressure pump for direct fuel injection.

The piston can be guided on or in the pump housing of the piston pump via its tread portion, which can also be referred to as a tread or guide portion.

The piston can have several piston sections. For example, at the end facing the working area, the piston can have a compression section for compressing the fuel in the working area. This can be followed by the running surface section (running surface or guide section) of the piston, via which the piston is guided on a guide element of the pump housing. At the end facing away from the working space, the piston can have an actuating section via which the piston can be driven by means of a drive device (for example a camshaft). The compression section and / or the The actuating section can have a reduced cross section compared to the tread section. The piston can be rotationally symmetrical (several sections with different diameters). The piston can be formed from a metallic material, for example from a suitable steel.

Advantageous further developments are specified in the subclaims. Features important to the invention can also be found in the following description and in the drawings.

Specifically, the medium used can be sodium. Due to the high thermal conductivity and the positive material properties for the present application, the heat transport is further optimized. Sodium melts at 97.5 ° C, has a density of 0.97 g / cm ³ and is a very good heat conductor. During operation, the sodium becomes liquid and is moved back and forth due to the inertia due to the inertial forces in the cavity of the piston.

In the context of a preferred embodiment, the central longitudinal axis of the cavity can extend parallel to the central longitudinal axis of the piston. The omission of shear force components hereby promotes the back and forth movement of the medium in the cavity of the piston and thus also the heat transfer.

The central longitudinal axis of the cavity can advantageously be arranged congruent to the central longitudinal axis of the piston. In other words, the preferably rotationally symmetrical cavity can be formed centrally with respect to the central longitudinal axis of the piston. In this way, uniform heat transport on the piston can be achieved in relation to the circumference.

The cavity can expediently extend over all sections of the piston. In this way, comparatively large amounts of heat can be transported and uniform heating over the entire piston is promoted. This leads to a more even piston expansion. The cavity can extend over the compression section facing the working area, the adjoining tread section (guide section) and over the actuating section on the side of the tread section facing away from the working area.

Specifically, the cavity can be partially filled with the medium, in particular between 30 and 70 percent (volume fraction of the medium in the volume of the cavity). As a result of the piston movement, a sufficient back and forth movement of the medium is achieved with a sufficient amount of transported thermal energy. This favors heat transfer.

The piston can advantageously be formed by a generative manufacturing process, for example by a 3D printing process, a stereolithography process or the like. This allows the piston to be manufactured in a profitable manner even with small quantities, undercuts are also possible. In this context, but also regardless of the selected manufacturing process, the configuration of the inner wall of the cavity of the piston with a structure is conceivable that increases the surface of the inner wall of the cavity, for example a structure with ribs or waves.

As an alternative to this, the piston can be formed by an original manufacturing process, for example by casting. This means that the piston can be reliably manufactured in large quantities using proven technology. The piston can be formed in one piece and also have the cavity in the interior of the piston. This can be filled with the medium during further production and then closed.

It is also conceivable that the piston is formed by a forming or a machining manufacturing process. The piston can also be reliably manufactured using proven technology. For example, the piston can be forged as a forming manufacturing process. When using a cutting manufacturing process, the piston can be manufactured by turning.

A further production possibility can consist in the piston being formed from a plurality of separate piston sections (for example sleeves), the adjacent piston sections being integrally connected to one another, in particular by gluing or welding, for example friction welding. The piston can thus be designed as a built-in piston, the individual components of the piston being able to be designed more individually before being joined together due to good accessibility than in the case of a one-piece design.

• 1 eine Ausführungsform einer Kolbenpumpe in einer schematischen und teilweise geschnittenen Seitenansicht;
• 2 den Kolben und das Führungselement der Kolbenpumpe aus 1 in einer geschnittenen Seitenansicht;
• 3 in einer vergrößerten und geschnittenen Seitenansicht den Kolben mit Hohlraum der Kolbenpumpe aus 1;
• 4 in einer vergrößerten und geschnittenen Seitenansicht den Kolben mit Hohlraum der Kolbenpumpe aus 1 bei einer Bewegung zum Arbeitsraum der Kolbenpumpe hin; und
• 5 in einer vergrößerten und geschnittenen Seitenansicht den Kolben mit Hohlraum der Kolbenpumpe aus 1 bei einer Bewegung vom Arbeitsraum der Kolbenpumpe weg.

Particularly preferred exemplary embodiments of the present invention are explained in more detail below with reference to the accompanying drawing. The drawing shows:

• 1 an embodiment of a piston pump in a schematic and partially sectioned side view;
• 2 the piston and the guide element of the piston pump 1 in a sectional side view;
• 3 in an enlarged and sectioned side view of the piston with the cavity of the piston pump 1 ;
• 4 in an enlarged and sectioned side view of the piston with the cavity of the piston pump 1 when moving towards the working area of the piston pump; and
• 5 in an enlarged and sectioned side view of the piston with the cavity of the piston pump 1 when moving away from the working area of the piston pump.

In 1 a piston pump, which is designed as a high-pressure fuel pump for a fuel injection system of an internal combustion engine, not shown, bears the overall reference number 10 , The piston pump 10 has a pump housing 12 and a mounting flange 14 on. Via the mounting flange 14 is the piston pump 10 on a cylinder head indicated only schematically here 16 attached to an internal combustion engine.

Via one on the pump housing 12 arranged connection 18 can the piston pump 10 are connected to a rail of an injection unit (not shown), so that a medium, for example fuel, can be made available to the injection unit under high pressure. The one through the rectangle 20 area marked as high pressure area of the piston pump 10 be designated.

The piston pump 10 has a piston 22 and a work space 24 on that on one side of the piston 22 is limited. Walls and entrances limit the work area 24 on further sides of the work space 24 , By - related to the work space 24 - Up and down movement of the piston 22 can be a medium in the work space 24 sucked in and compressed, thus brought to a higher pressure level and then fed to a rail of an injection unit.

The piston 22 has a tread portion 26 on which the piston 22 by means of the guide element 28 on the pump housing 12 is led. The guide element 28 has a circular cylindrical inner surface 30 on which the piston 22 with its tread section 26 is led. The guide element 28 is in the present embodiment as one in the housing 12 the piston pump 10 arranged, ie in the housing 12 inserted, socket trained. It is also conceivable that the guide element 28 than one in the case 12 the piston pump 10 trained bore is executed (not shown).

In 2 are the piston 22 and the guide element 28 shown enlarged on its own (for the sake of clarity, without showing the piston cavity). The guide element 28 (Socket) and the piston 22 are arranged coaxially to one another, being between the outer surface of the tread portion 26 and the inner surface 30 of the guide element 28 a game S results. The area of the piston which is subject to the greatest thermal stress during operation 22 is through the circle 29 characterized.

The piston 22 points to the workspace 24 facing end 32 (in 2 right end) a compression section 34 on. The compression section 34 borders on the tread section 26 and has a smaller diameter than the tread portion 26 on. Between the compression section 34 and the tread portion 26 there is a paragraph 42 ,

At his by the work room 24 opposite end 36 (in 2 left end) has the piston 22 an operating section 38 on which the piston 22 can be actuated and thus driven, for example by means of a camshaft of an internal combustion engine. The operating section 38 borders on the tread section 26 and has a smaller diameter than the tread portion 26 on. Between the operating section 38 and the tread portion 26 there is a paragraph 43 , The piston 22 is rotationally symmetrical (several piston sections with different diameters).

The piston 22 has a cavity closed inside 40 on that with a medium 42 is filled, which has a higher thermal conductivity than the material of the piston 22 exhibits (see 3 ). The medium 42 can also be referred to as a transport medium (heat transport medium).

As a medium 42 For example, sodium can be used. Sodium has a high thermal conductivity and is well suited for the present application. Sodium melts at 97.5 ° C. During operation, the sodium becomes liquid and is caused by the mass forces in the cavity 40 of the piston 22 back and forth (relative movement of the medium 42 based on the piston 22 ).

The central longitudinal axis 44 of the cavity 40 can be parallel to the central longitudinal axis 46 of the piston 22 extend. In the present exemplary embodiment, the central longitudinal axis is 44 of the cavity 40 congruent to the central longitudinal axis 46 arranged of the piston 22 , In other words, the cavity 40 related to the central longitudinal axis 46 of the piston 22 centered.

The cavity 40 extends over all sections of the piston 22 , The cavity 40 thus extends over the work area 24 facing compression section 34 , the adjoining tread section 26 and over the operating section 38 at the of the work room 24 opposite side of the tread portion 26 ,

The cavity 40 is partly with the medium 42 filled, especially between 30 and 70 percent (volume fraction of the medium 42 on the volume of the cavity 40 ). In the present embodiment, about 50 percent of the cavity is with the medium 42 filled

4 shows a state in which the piston 22 due to its drive, for example by means of a camshaft or between the camshaft and piston 42 arranged plunger, to the work area 24 moved there (in 4 up). This movement is through the arrow 50 illustrated. The medium moves 42 which on the work room 24 facing end 32 of the piston 22 Has absorbed thermal energy in the cavity 40 due to inertia to the work area 24 opposite end 36 of the piston 22 there (in 4 downward). So there is a relative movement of the medium 42 based on the piston 22 , The medium gives 42 Thermal energy on the pistons 22 down to a (lower) part of the tread section 26 and to the operating section 38 , These are in operation of the piston pump 10 thermally less stressed than the compression section 34 , From the tread section 26 and the operating section 38 can transfer thermal energy to the pump housing 12 are delivered, for example, via the guide element 28 ,

5 shows a state in which the piston 22 away from the work space due to its drive 24 moved away (in 5 downward). This movement is through the arrow 52 illustrated. The medium moves 42 which is from the work room 24 opposite end 36 of the piston 22 has already given off thermal energy in the cavity 40 due to inertia to the work area 24 facing end 32 of the piston 22 there (in 5 up). So there is a relative movement of the medium 42 based on the piston 22 , The medium takes 42 Thermal energy from the piston 22 on, from the compression section 34 and possibly from an (upper) part of the tread section 26 , These are in operation of the piston pump 10 thermally higher than a lower part of the tread section 26 and as the operating section 38 ,

The through the medium 42 absorbed heat energy can result in a subsequent movement of the piston 22 to the work room 24 there (in 5 upward) to the piston 22 are delivered to a (lower) part of the tread portion 26 and to the operating section 38 because the medium 42 due to inertia to the work area 24 opposite end 36 of the piston 22 moved as related to 4 explained. This optimized heat transfer leads to a more even temperature distribution over the entire piston 22 away so that the piston 22 expands in diameter more evenly and with a smaller amount, as explained above.

For further configuration of the piston 22 The measures described above can serve, in particular with regard to its manufacture and the manufacturing process used here.

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 102014211591 A1 [0002]

Claims (10)

Piston pump (10), in particular high-pressure fuel pump for an injection system of an internal combustion engine, with a piston (22) and a working space (24), which is delimited by the piston (22), characterized in that the piston (22) inside has a cavity (40) which is closed to the outside and is filled with a medium (42) which has a higher thermal conductivity than the material of the piston (22). Piston pump (10) after Claim 1 , characterized in that the medium (42) is sodium. Piston pump (10) after Claim 1 or 2 , characterized in that the central longitudinal axis (44) of the cavity (40) extends parallel to the central longitudinal axis (46) of the piston (22). Piston pump (10) according to one of the preceding claims, characterized in that the central longitudinal axis (44) of the cavity (40) is arranged congruent to the central longitudinal axis (46) of the piston (22). Piston pump (10) according to one of the preceding claims, characterized in that the cavity (40) extends over all sections (26, 34, 38) of the piston (22). Piston pump (10) according to one of the preceding claims, characterized in that the cavity (40) is partially filled with the medium (42), in particular between 30 and 70 percent. Piston pump (10) according to one of the preceding claims, characterized in that the piston (22) is formed by a generative manufacturing process. Piston pump (10) according to one of the Claims 1 to 6 , characterized in that the piston (22) is formed by an original manufacturing process. Piston pump (10) according to one of the Claims 1 to 6 , characterized in that the piston (22) is formed by a forming or a cutting manufacturing process. Piston pump (10) according to one of the Claims 1 to 6 , characterized in that the piston (22) is formed from a plurality of separate piston sections, the adjacent piston sections being integrally connected to one another.

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