DE102010042295A1 - High pressure pump and engine for a high pressure pump - Google Patents

Abstract

The invention relates to a high-pressure pump for a fuel injection device of an internal combustion engine, which has at least one pump piston, which by rotating a drive shaft about an axis of rotation via at least one cam arranged on the drive shaft and a tappet assembly arranged on the pump piston in a stroke movement in a substantially radial direction is driven to an axis of rotation of the drive shaft, wherein the tappet assembly has a roller with a roller surface that is in contact with a tread of the cam, the cam on its tread and / or the roller surface is at least partially provided with a coating that is an elastomer having. The invention further relates to an engine for a high-pressure pump, which has a drive shaft provided with at least one cam and a roller arranged in a roller shoe, wherein a roller surface of the roller is in rolling contact with a tread of the cam, the tread of the cam and / or The roller surface of the roller is at least partially provided with a coating which has an elastomer.

Description

The present invention relates to a high pressure pump for a fuel injection device of an internal combustion engine according to the preamble of claim 1 and an engine for a high pressure pump according to the preamble of claim 10.

State of the art

For pressurizing the fuel at high pressure in a fuel injection system, such as in a common rail system, among other high pressure pumps with radial piston with one or more pump pistons are used, which are indirectly offset by a drive shaft, for example via a cam or an eccentric in a stroke to perform a suction stroke and a pressure stroke. During the suction stroke, fuel is sucked into a pump working space of the high pressure pump, and during the pressure stroke, the sucked fuel is compressed and output to the high pressure accumulator of the common rail system.

In the known high pressure pumps usually a roller cam drive is used with a arranged in a roller shoe roller.

For example, in DE 10 2008 043 429 A1 a radial piston pump with a camshaft drive described. There, a drive shaft is rotatably mounted in a pump housing. The drive shaft has between two bushings on a cam track which drives a pump piston in a lifting movement. The pump piston is displaceably guided in the pump housing in a cylinder bore extending radially to the axis of rotation of the drive shaft and is supported on the cam track with a piston foot via a roller rotatably mounted in a roller shoe. The roller shoe is in turn pressed into a plunger body, which is guided in a ram guide bore of the pump housing in a liftable and freely rotatable about its longitudinal axis. A compression spring pushes the roller against the drive shaft via the plunger body and the roller shoe, whereby the roller is held in contact with the cam track.

However, the ever higher pressures in the diesel common rail technology, in particular, put the engines of high-pressure pumps of a high load in terms of fatigue or wear. The engines described above, which consist of cam or drive shaft, cam, roller and roller shoe are exposed to different tribological loads.

Typically, the cam and roller are each made of very hard steel, with fuel forming an intermediate layer in the form of a lubricating film between the cam and the roller. Condition for an ideal operation of the engine is that there is always a small but not too large lubricating film between the cam and roller. Since the roller itself is guided in a sliding bearing in the roller shoe, it is necessary that the so-called "adhesion" between the roller and the cam against the sliding resistance is large enough to maintain a permanent rotation. If a permanent rotation is provided, then also the lubricating film, which is a kind of protective layer against the direct metal-metal contact, which can lead to wear, for example in the form of adhesion damage, permanently generated between the Wälzpartnern. If the lubricating film protective layer is too large, however, the rolling motion can no longer be ensured by the lack of adhesion. This would lead to a standstill of the roller ("aquaplaning effect"), which in turn abruptly degrades the lubricating film by the lack of rolling motion and leads to a turning of the roller on the camshaft with subsequent Adhäsionsverschleiß. Particularly problematic are fuels of inferior quality. Here it can happen that the lubricating gap does not build up properly and increasingly metal-metal contacts come about, which ultimately lead to wear and failure of the engine.

The increasing demand for higher pressures and fuel temperatures and the servicing of markets with poorly lubricating or low viscosity fuels therefore requires optimization of the existing system.

In order to avoid a failure of the high pressure pump due to a lack of lubricant supply, it is known in the art to subject the contact surfaces on the rolling contact of the engine, for example, a surface treatment such as nitriding or to coat the contact surfaces with a coating.

In DE 103 48 140 A1 a radial piston pump for fuel high pressure generation is described in a fuel injection system, which has a polygonal rotor whose sliding surfaces are at least partially provided with a surface covering of a ductile or viscoelastic material. In this case, molybdenum, tungsten carbide, cermet or alloys of these materials are used as the preferred coating material.

Due to their ductility, a coating with the above-mentioned materials prevents so-called pittings on the sliding surfaces due to material brittleness. A guarantee of reliable rolling of the cam and the roller for ensuring the necessary lubricating film on the rolling contact can not be achieved thereby.

Therefore, it is desirable to provide a high pressure pump with an engine that will provide permanent adhesion and thus permanent rotation in the area of rolling contact between the roller and the cam to reduce engine wear and fatigue.

Disclosure of the invention

Advantages of the invention

According to the invention, a high-pressure pump is provided for a fuel injection device of an internal combustion engine, which has at least one pump piston, which by the rotation of a drive shaft about an axis of rotation about at least one arranged on the drive shaft cams and arranged on the pump piston plunger assembly in a lifting movement in a substantially radial direction is driven to an axis of rotation of the drive shaft, wherein the plunger assembly has a roller with a roller shell surface, which is in contact with the cam, wherein the cam is provided on its tread and / or the roller shell surface at least partially with a coating having an elastomer. By providing the elastomer on the tread of the cam or on the roller skirt surface, the rolling contact between the roller and the cam, at which forces of approximately 8000 N occur, is significantly improved. It is an optimal operation allows in which a rolling of the roller body takes place on the cam with low slip. The coating has a high adhesion, which means that it is able to reliably drive the roller and has the additional advantage that the coating usually only elastically deformed, so restores its original shape and thus no direct wear plastic deformation allows. Adhäsionsverschleiß in the engine and premature failure of the high-pressure pump are effectively avoided by the configuration of the invention. Particularly in fuel-critical markets or at high loads, the elastomer coating in the area of rolling contact is particularly helpful.

According to a preferred embodiment, the coating is provided at a run-up of the cam. The run-up of the cam is a highly stressed point in the engine, where slipping of the caster can cause massive damage. A coating especially in this area effectively prevents these possible damages.

According to yet a preferred embodiment, at least one adhesion promoter layer is arranged between the coating and the running surface of the cam.

According to yet another preferred embodiment, the coating comprises at least one of the materials selected from the group consisting of silicone rubber, silicone, rubber, rubber or latex. Important when choosing the right material is that it is fuel-resistant, flexible and highly adhesive. It is also possible to use silicone-containing, rubber-containing, rubber-containing, latex-containing or other elastic materials for the coating, which as a rule are in liquid, solid or pulverulent form.

Preferably, at least one additive and / or at least one filler is added to the elastomer, in particular the rubber and the rubber. Preferably, the filler is a fumed silica, precipitated silica or carbon black. In a preferred embodiment, in which silicone rubber is used as the coating material, the filler preferably comprises diatomaceous earth, quartz or carbon black. Preferably, a crosslinking chemical, in particular peroxide or a platinum catalyst, is added to the silicone rubber as additive.

According to yet another preferred embodiment, a plasticizer, in particular a silicone polymer-based plasticizer, is added to the elastomer.

Preferably, an additional substance for improving the elongation properties and the crack resistance, in particular silica, is added to the coating material. Particularly preferred is the addition of silica in silicone-containing materials.

It is also preferred if the admixed silica is admixed with a weight percentage ranging between 1% by weight (weight percent) and 30% by weight, especially between 5% and 15% by weight.

According to a preferred embodiment, the elastomer is colorless and has a density in a range of 1.05 to 1.14 g / cm ³ , a hardness in a range of 20 to 55 Shore A, a tear strength in a range of 6.0 to 12.0 N / mm ² , an elongation at break in a range of 500 to 1300%, a tear resistance in a range of 15 to 30 N / mm, a rebound resilience in a range of 50 to 70% and a compression set resistance (22 h / 175 ° C) in a range of 10 to 30%.

According to a further preferred embodiment, the at least partial coating is produced by immersion with subsequent drying and polymerization.

According to yet another preferred embodiment, the at least partial coating is applied by means of injection molding, steaming or rolling on the running surface of the cam and / or the roller surface area.

Moreover, it is particularly preferred if the coating has a layer thickness which is in a range of 50 nm to 5 μm, in particular in a range of 2 μm to 3 μm.

According to the invention, there is further provided an engine for a high-pressure pump which has a drive shaft provided with at least one cam and a roller arranged in a roller shoe, wherein a roller surface of the roller is in rolling contact with a running surface of the cam, the running surface of the cam and / or or the roller shell surface of the roller is at least partially provided with a coating of an elastomer. Due to the rolling contact optimized by the elastomer layer, the engine according to the invention has no adhesion wear and thus does not cause premature failure of the high-pressure pump, even when using low-viscosity or poorly lubricating fuels.

Brief description of the drawings

Hereinafter, embodiments of the invention will be described in detail with reference to the accompanying drawings. It shows:

1 a section through a high pressure pump according to the prior art;

2 a schematic partially sectioned side view through an engine according to the prior art; and

3A . 3B each a cam according to an embodiment of the invention.

Embodiments of the invention

In 1 is a section through a high pressure pump 1 for a fuel injection device of an internal combustion engine according to the prior art. The high pressure pump shown here 1 is a radial piston pump and is used in a common rail system.

The high pressure pump 1 According to the prior art has a housing 2 in which a rotationally driven drive shaft 3 is arranged, which is designed as a camshaft. The high pressure pump 1 has at least one or more in each case a cylinder head 8th arranged pump elements 4 each with a pump piston 5 on that by a cam 6 the drive shaft 3 indirectly in a lifting movement in at least approximately radial direction to a rotation axis 7 the drive shaft 3 is driven. The pump piston 5 is in a cylinder bore 9 in a shaft section 10 of the cylinder head 8th guided tightly displaceable and limited with its the drive shaft 3 opposite end face in the cylinder bore 9 a pump workroom 11 , Around the shaft section 10 There is a feather around 12 arranged.

The pump workroom 11 has one in the housing 2 extending fuel inlet channel (not shown) to connect to a fuel inlet, for example, a feed pump. At the mouth of the fuel inlet duct into the pump workspace 11 is one in the pump work space 11 opening inlet valve 13 arranged. The pump workroom 11 also has one in the cylinder head 8th extending fuel drain channel 14 a connection with an outlet, for example, with a high-pressure accumulator 15 connected is. With the high-pressure accumulator 15 are one or preferably a plurality of arranged on the cylinders of the internal combustion engine injectors 16 is connected, is injected through the fuel into the cylinders of the internal combustion engine. At the mouth of the fuel drainage channel 14 into the pump workroom 11 is one out of the pump workroom 11 opening exhaust valve 17 arranged.

The pump element 4 is a ram assembly 24 assigned over which the pump piston 5 on the cam 6 the drive shaft 3 supported. The ram assembly 24 comprises a hollow cylindrical tappet body 18 in a hole 19 slidably guided. At his the pump workroom 11 opposite end, the pump piston 5 a piston foot 20 on.

The ram assembly 24 and the pump piston 5 be through the preloaded spring 12 to the cam 6 the drive shaft 3 pressed down. The feather 12 is as the pump piston 5 surrounding and in the ram body 18 protruding helical compression spring formed. The feather 12 supported on the one hand on the cylinder head 8th and on the other hand on a spring plate 21 from. The spring plate 21 is with the pump piston 5 connected and lies on a roller shoe 22 opposite side of a ring land (not shown here in detail) on. The feather 12 thus acts on the spring plate 21 both on the pump piston 5 as well as on the tappet body 18 to this as described above, against the cam 6 the drive shaft 3 to press. In the ram body 18 is of which the drive shaft 3 facing side of the roller shoe 22 inserted. In the roller shoe 22 is in a cylinder-section-shaped receptacle on the cam 6 the drive shaft 3 facing side of the roller shoe 22 a cylindrical roller 23 rotatably mounted.

Upon rotation of the drive shaft 3 around the axis of rotation 7 her the rotary motion thus over the cam 6 and the plunger assembly on the pump piston 5 transferred to move it up and down, whereby a suction stroke for conveying the fuel into the pump element accordingly 4 and a compression stroke for compressing into the pump element 4 subsidized fuel is carried out. The compressed fuel is then delivered via the exhaust valve 17 the high-pressure accumulator 15 fed.

2 is a schematic partially sectioned side view through an engine 25 according to the prior art, which one on a drive shaft 3 arranged cams 6 with a tread 27 and one in a roller shoe 22 mounted roller 23 with a roller cover surface 26 includes.

Both the cam 6 as well as the roller 23 are made of a hard steel. When the cam 6 by a rotation of the drive shaft 3 around its axis of rotation 3 turns around, is at the rolling contact 28 between the caster surface 26 and the tread 27 of the cam 6 formed a lubricating layer of fuel, which can be abruptly degraded in the absence of rolling motion, resulting in a knocking of the roller 23 on the cam 6 leads. This danger also exists in the case of using low-viscosity or low-grade fuel.

3A and 3B each show a cam 6 according to an embodiment made of a hard steel. In the in 3A illustrated embodiment is the cam 6 on his tread 27 with a coating 29 provided that the entire tread 27 covered. The coating 29 is a rubbery, fuel-resistant, flexible and highly adhesive layer of silicone rubber with a silica content of 10 wt .-%. Alternatively, the coating 29 also be formed from another elastomeric material such as silicone, rubber, rubber or latex or silicone-containing, rubber-containing, latex-containing or rubber-containing substances with or without addition of silica. The coating 29 has a high adhesion and is thus able to handle the roller 23 (please refer 2 ) to drive. Because the coating 29 is made of an elastomer, it has the advantage that it deforms elastically and restores its original shape, with no direct wear due to plastic deformation occurs. Between the surface or tread 27 of the cam 6 and the coating 29 In addition, one or more adhesion-promoting layers can be arranged. The coating 28 is by dipping and then drying and polymerizing the elastomer on the cam 6 applied. Alternatively, however, an injection molding, steaming or rolling is possible. The coating can take place both in vacuum or under normal pressure. Depending on the coating process, tempering may be necessary. Alternatively, or depending on the material used, however, a polymerization of the elastomer can also take place at room temperature. Also, an addition of organic or inorganic substances to promote the polymerization can take place. The layer thickness of the coating 28 is 5 μm in the embodiment. Thicker or thinner layer thicknesses are also possible. In the 3B illustrated embodiment differs from the in 3A shown embodiment in that the coating 28 only partially, namely only in the area of run-up 30 , on the tread 27 of the cam 6 is applied.

By means of the configuration according to the invention can effectively an engine 25 for a high pressure pump 1 be provided, in which adhesive wear is effectively avoided, which in turn premature failure of the high-pressure pump 1 prevented.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely 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.

Cited patent literature

• DE 102008043429 A1 [0004]
• DE 10348140 A1 [0009]

Claims (10)

High pressure pump ( 1 ) for a fuel injection device of an internal combustion engine, which at least one pump piston ( 5 ), which by the rotation of a drive shaft ( 3 ) about a rotation axis ( 7 ) about at least one on the drive shaft ( 3 ) arranged cam ( 6 ) and one on the pump piston ( 5 ) arranged plunger assembly ( 24 ) in a lifting movement in a substantially radial direction to a rotation axis ( 7 ) of the drive shaft ( 3 ), wherein the plunger assembly ( 24 ) a roller ( 23 ) with a roller shell surface ( 26 ), which in contact with a tread ( 27 ) of the cam ( 6 ), characterized in that the cam ( 6 ) on its tread ( 27 ) and / or the roller shell surface ( 26 ) at least partially with a coating ( 29 ) having an elastomer. High pressure pump ( 1 ) according to claim 1, characterized in that the coating ( 29 ) at a run-up ( 30 ) of the cam ( 6 ) is provided. High pressure pump ( 1 ) according to claim 1 or 2, characterized in that between the coating ( 29 ) and the tread ( 27 ) of the cam ( 6 ) at least one adhesion promoter layer is arranged. High pressure pump ( 1 ) according to one or more of claims 1 to 3, characterized in that the coating ( 29 ) comprises at least one of the materials selected from the group consisting of silicone rubber, silicone, rubber, rubber or latex. High pressure pump ( 1 ) according to claim 4, characterized in that the coating ( 29 ) an additive substance for improving the elongation properties and the crack resistance, in particular silica, is mixed. High pressure pump ( 1 ) according to claim 5, characterized in that the additional substance is silica, wherein the silica is admixed with a percentage by weight which is between 1 wt .-% and 30 wt .-%, in particular between 5 wt .-% and 15 wt .-% , lies. High pressure pump ( 1 ) according to one or more of claims 1 to 6, characterized in that the coating ( 29 ) is prepared by dipping with subsequent drying and polymerizing. High pressure pump ( 1 ) according to one or more of claims 1 to 6, characterized in that the coating ( 29 ) by injection molding, steaming or rolling on the tread ( 27 ) of the cam ( 6 ) and / or the roller shell surface ( 26 ) is applied. High pressure pump ( 1 ) according to one or more of claims 1 to 8, characterized in that the coating ( 29 ) has a layer thickness which is in a range of 50 nm to 5 μm, in particular in a range of 2 μm to 3 μm. Engine ( 25 ) for a high pressure pump ( 1 ), one with at least one cam ( 6 ) provided drive shaft ( 3 ) and one in a roller shoe ( 22 ) arranged roller ( 23 ), wherein a roller shell surface ( 26 ) of the roller ( 23 ) with a tread ( 27 ) of the cam ( 6 ) in rolling contact ( 28 ), characterized in that the tread ( 27 ) of the cam ( 6 ) and / or the roller shell surface ( 26 ) of the roller ( 23 ) at least partially with a coating ( 29 ) having an elastomer.

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