EP2137402B1 - High-pressure pump for delivering fuel comprising a torsion-decoupled compression spring element in the plunger unit - Google Patents

Abstract

The invention relates to a high-pressure pump, especially for delivering fuel for a common rail fuel injection system. The pump includes at least one cam drive having a feeler element which can be set moving in direction of a stroke axis by a cam geometry introduced into the camshaft, the stroke movement being transmittable to a plunger unit. The plunger unit and the feeler element are impinged upon with a force by a compression spring element in the direction of the cam geometry and the plunger unit has at least one contact surface which adjoins the compression spring element. The at least one contact surface and/or the surface of the compression spring element adjoining the same has a friction-reduced surface coating to bring about a torsion decoupling of the compression spring element.

Description

The present invention relates to a high-pressure pump, in particular for conveying fuel for a common-rail fuel injection system according to the type defined in more detail in the preamble of claim 1 (US Pat. DE-A-4 227 853 ).

State of the art

High pressure pumps for the promotion of fuel, which are used for common rail fuel injection systems, are generally known. The high-pressure pumps are used to provide a high-pressure fuel within the common rail, which are acted upon by service bridges up to 2 Kbar and more. Therefore, special requirements are placed on the high-pressure pumps in order to promote the fuel in an efficient manner to the said pressures. The high-pressure pumps are usually driven via a coupling with the crankshaft of the internal combustion engine, wherein the high-pressure pump can be designed according to the principle of a cam drive. These include a camshaft having a cam geometry which displaces a picking element into a lifting movement in the direction of a lifting axis, and thus a pump piston connected to the picking element is set in a lifting movement. Via a valve train introduced in a cylinder head, the pump piston can cooperate with this to promote the fuel. The pump piston is guided in a liftable manner in the pump body or in the cylinder head, and communicates with the tapping element at least via a roller shoe. The tapping element is usually designed as a roller, which rolls over the cam geometry. The arrangement of the roller in operative connection with the cam geometry is advantageous, since forms a line contact between the roller and the cam geometry, which has a high load capacity. In addition, only rolling movements take place, which are wear-minimized compared to sliding movements. The tapping element in the form of the roller is pressed to guide it on the cam geometry by means of a compression spring element against this, whereby at the same time the return stroke of the pump piston is ensured. Such compression spring elements are designed as coil springs and extend between a collar within the cylinder head and the so-called roller shoe in which the roller is received.

In such an arrangement, a high-pressure pump for the promotion of fuel according to the principle of cam drive, however, the problem arises that when using a compression spring element in the form of a coil spring by the compression of the compression spring element torsion on the composite of the roller shoe, the plunger guide, the pump piston and thus also on the tapping element, ie the role is exercised. Therefore, there is a Verdrehneigung the roller shoe and the Abgriffselementes, so that the line contact between the Abgriffselement and the cam geometry is not ensured closer. Although this against rotation between the plunger device and the pump body in the form of linear guides are known, however, a sufficient accuracy is often not achievable. Also, linear guides have minimal play, which is comparatively large, and the line contact between the pick-off element and the cam geometry also remains unaffected. This circumstance leads to premature wear of the high pressure pump, which is undesirable in view of the required operating time and reliability of the high pressure pump.

Furthermore, it is necessary to build such lifting devices from a few components and to ensure a simple construction. Arrangements of torsion-minimized compression spring elements, which differ from the design of a simple coil spring, are often designed very expensive and yet do not cause the torsion-free compression of the spring portion.

It is therefore the object of the present invention to provide a high pressure pump for delivering fuel for an internal combustion engine, which allows for obtaining the line contact between the Abgriffselement and the cam geometry rotational guidance of the plunger device.

Disclosure of the invention

This object is achieved on the basis of a high-pressure pump for conveying fuel for an internal combustion engine according to the preamble of claim 1 in conjunction with its characterizing features. Advantageous developments of the invention are specified in the dependent claims.

The invention provides the technical teaching that the at least one contact surface between the compression spring element and the plunger device and / or the adjoining surface of the compression spring element comprises a frictional force minimized surface coating to create a Torsionsentkopplung the compression spring element.

The advantage of the solution according to the invention lies in a decoupling of the torsional movement of the compression spring element from the plunger device. The rotation accompanying the compression of the compression spring element can not be transferred further to the plunger device in the case of a contact surface with a friction-minimized surface coating, so that rotation of the plunger device, and thus rotation of the pick-off element on the cam geometry, are no longer caused by the torsion of the compression spring element can. The compression spring element is received between the cylinder head and the plunger guide, so that one end of the compression spring element is supported against a receiving contour in the plunger guide. This Aufnahmcstruktur within the ram guide forms the contact surface, which includes the frictional force minimized surface coating. However, this may also be formed on the part of the compression spring element, so that the surface of the compression spring element, which is adjacent to the tappet guide, having the friction-minimized surface coating.

According to an advantageous development of the arrangement of the plunger device comprises a Andruekscheibenelement, against which the compression spring element is brought into abutment, wherein at least one flat surface of the Andruckscheibenelementes forms the contact surface with the frictional force minimized surface coating. The Andruckscheibenelement is annular and has two opposing planar surfaces, so that a planar surface of the contact surface in the tappet guide and the other planar surface to the end of the compression spring elements, adjacent. To minimize the frictional force and thus to decouple the torsion between the Druekfederelement and the tappet guide either the first planar surface, the opposite plane surface or both planar surfaces of Andruekscheibenelementes be provided with a frictional force minimized surface coating. However, the Andruckscheibenelement can also be connected on one side rotationally fixed to the compression spring element, so that a defined sliding movement of the opposite plane surface of the Andruckscheibenelementes can take place relative to the plunger guide. If the compression spring element is compressed, then a torsion in the compression spring element can be caused, which is compensated between the Andruckscheibenelement and the tappet guide.

It is advantageous that the tapping element is designed as a roller element and the tappet device further comprises a tappet guide with a roller shoe inserted into it, on which the contact surface is formed with the friction-minimized surface coating itself. This shows a further possibility that the contact surface with the friction-minimized surface coating can be formed both on the pressure disk element and on the tappet guide itself, whereby a combination of the respective contact surfaces with a respective friction-minimized surface coating is possible. Here in particular the advantage can be used to select different surface coatings, which slide on each other, so that a tribologically optimized friction pairing is formed.

It is also advantageous that at the end of the compression spring element, a spring disk element is arranged rotationally fixed thereto, which is flush with the contact surface of the tappet guide. The spring disk element can be cohesively, positively or by means of connecting elements attached to the compression spring element, so that the spring disk element is likewise designed as a planar ring contour, and forms an annular contact surface. Advantageously, the adjacent to the contact surface of the tappet guide contact surface of the spring disk element comprises the frictional force minimized surface coating. An even more advantageous embodiment of the present invention comprises both a spring disk element arranged on the end side of the compression spring element and a pressure disk element, so that the pressure disk element is arranged between the spring disk element and the tappet guide, and the contact surface of the compression spring element adjoins the contact surface of the spring disk element. According to the last-mentioned arrangement, four contact surfaces with a respective friction-minimized surface coating in a stack arrangement can adjoin one another, wherein the pressure-disk element is located between the spring-disk element and the tappet guide.

Advantageously, the friction-minimized surface coating is applied to the at least one contact surface by means of a PVD process, a CVD process, a galvanic process or a chemical process. Furthermore, there is the possibility that the friction-minimized surface coating comprises a bonded coating and / or a dry lubricant applied to the contact surface. The friction-minimized Surface coating may also be a hard coating, such as a titanium oxide coating, a zirconium oxide coating, a silicon oxide coating, a titanium carbide coating or a titanium nitride coating. Furthermore, it is possible to provide innovative PVD hard coatings such as TiMgN coatings. A combination of friction-minimized surface coatings and a surface-layer treatment of the respective contact surface should also be provided as an advantageous possibility within the scope of the present invention. Particularly advantageous are titanium carbide coatings, which are characterized by a very high hardness, coupled with a low coefficient of friction and highest adhesion. Titanium nitrite coatings, on the other hand, are characterized by high hardness, high toughness and a very low tendency to weld on, so that seizing and deposit formation can be avoided. Furthermore, good corrosion and oxidation properties are advantageous.

The plunger device, which comprises the compression spring element, is located inside the pump body, which is filled with fuel. Therefore, the fuel may act as a lubricant, so that the surface coating cooperates with the lubricating effect of the fuel. Therefore, the surface coating should have a corresponding resistance to the fuel, which is particularly a diesel fuel. As a further surface coating may be mentioned a titanium-aluminum nitride coating, wherein a chromium nitride coating is also a possible hard material coating. These coatings are characterized in particular by a very high chemical and thermal stability, in which case the chromium nitrite coating has a low tendency to adhesion, since the arrangement of the compression spring element can have locally high surface pressures in operative connection with the pressure disk element or the spring disk element Adhesion tendency is advantageous.

It is also possible to use a frictional force-minimized surface coating in the form of a monolayer, wherein also binary layers (Ti (C, N)), multilayer coatings (TiC / TiN) or graded coatings (TiC / Ti (C, N) / TiN) represent a possible variant. Thus, the friction-minimized surface coating according to the invention is not limited to a specific layer system, but comprises several different layer systems.

In order to use the advantages of the inventive solution of friction-minimized surface coating for other claimed surfaces, can in Be provided within the scope of the present invention, to provide the entire compression spring element and the entire plunger guide and also the entire Andruckscheibenelement and the spring washer element completely with a surface coating. Especially the plunger guide slides within the pump body or the cylinder head in a guide bore, so that a holistic coating of the components is also beneficial.

Further, measures improving the invention will be described in more detail below together with the description of a preferred embodiment of the invention with reference to FIGS.

embodiments

• Fig. 1 eine quergeschnittene Ansicht einer Hochdruckpumpe mit einer Stößeleinrichtung sowie einem Druckfederelement, einer Stößelführung mit einem eingesetzten Rollenschuh und einem zwischen dem Druckfederelement und der Stößelführung angeordneten Andruckscheibenelement;
• Fig. 2 eine quergeschnittene Ansicht des erfindungsgemäßen Andruckscheibenelementes mit einer ersten sowie einer zweiten Kontaktfläche; und
• Fig. 3 eine quergeschnittene Ansicht der Anordnung der Stößeleinrichtung mit jeweiligen erfindungsgemäßen Kontaktflächen, wobei das Druckfederelement, das Andruckscheibenelement sowie ein Federscheibenelement jeweils in einer voneinander gelösten Anordnung dargestellt ist.
• Fig. 1 zeigt eine quergeschnittene Seitenansicht einer Hochdruckpumpe 1, wie sie bei Common-Rail- Kraftstoffeinspritzsystemen für Dieselmotoren zum Einsatz kommt. Die Hochdruckpumpe 1 dient zur Förderung von Dieselkraftstoff, um diesen mit einem hohen Druck einem Common-Rail zur Verfügung zu stellen. Die Hochdruckpumpe 1 umfasst ein Abgriffselement 2, welches über einer auf einer Nockenwelle 3 angeordneten Nockengeometrie 4 abwälzt. Die Nockenwelle 3 wird motorseitig angetrieben, und umfasst wenigstens eine Nockengeometrie 4, wobei diese eine oder mehrere auf den Umfang gleichverteilt angeordnete Nocken umfasst. Dadurch übt das Abgriffselement 2 eine Hubbewegung in Richtung einer Hubachse 5 aus, wobei die Hubbewegung des Abgriffselementes 2 auf eine Stößeleinrichtung 6 übertragen wird. Die Stößeleinrichtung 6 umfasst ein Druckfederelement 7 sowie einen Pumpenkolben 12, wobei das Abgriffselement 2 innerhalb einer Stößelführung 10 aufgenommen ist, welche gemeinsam mit dem Rollenschuh 15 ebenfalls Bestandteil der Stößeleinrichtung 6 ist. Zwischen dem Druckfederelement 7 und der Stößelführung 10 ist ein Andruckscheibenelement 9 angeordnet, welches quergeschnitten dargestellt und in Gestalt einer Planscheibe ausgeführt ist. Mittig aus dem Rollenschuh 10 erstreckt sich der Pumpenkolben 12, welcher innerhalb eines Zylinderkopfes 13 geführt ist, und mit einer Ventileinrichtung im Zylinderkopf 13 zur Förderung des Kraftstoffes zusammenwirkt. Die Hochdruckpumpe 1 umfasst im Wesentlichen einen Pumpenkörper 14, wobei der Zylinderkopf 13 auf den Pumpenkörper 14 dichtend aufgesetzt ist. Daher bildet sowohl der Pumpenkörper 14 als auch der Zylinderkopf 13 die Führungseinrichtung der Hubbewegung der Stößeleinrichtung 6 in Richtung der Hubachse 5, wobei eine Verdrehsicherung der Stößeleinrichtung 6 zur Vermeidung einer Verdrehung um die Hubachse 5 nicht näher dargestellt ist.
• Fig. 2 zeigt eine vergrößerte Darstellung der Andruckscheibenelementes 9, welche sich - mit Blick auf Fig. 1 - zwischen dem Druckfederelement und der Stößelführung befindet. Das Andruckscheibenelement 9 umfasst eine erfindungsgemäße Kontaktfläche 8a sowie eine gegenüberliegende weitere Kontaktfläche 8b, welche eine reibkraftminimierte Oberflächenbeschichtung aufweist. Das Andruckscheibenelement 9 erstreckt sich ringförmig um die Hubachse 5, so dass sich durch das Andruckscheibenelement 9 der Pumpenkolben erstrecken kann. Die reibkraftminimierten Kontaktflächen 8a und 8b grenzen jeweils an das Druckfederelement sowie an die Stößelführung an, so dass entweder die erste Kontaktfläche 8a oder die zweite Kontaktfläche 8b oder beide Kontaktflächen die erfindungsgemäße reibkraftminimierte Oberflächenbeschichtung aufweisen.
• Fig. 3 zeigt eine mögliche Anordnung einer erfindungsgemäßen Stößeleinrichtung 6 mit einem Andruckscheibenelement 9, welches zwischen der Stößelführung 10 sowie einem Federscheibenelement 11 angeordnet ist, wobei in der Stößelführung 10 der Rollenschuh 15 zur Aufnahme des Abgriffselementes 2 eingesetzt ist. Das Federscheibenelement 11 ist mit dem Druckfederelement 7 in Verbindung gebracht, wobei die Verbindung entweder stoffschlüssig (Schweißen, Löten, Kleben) oder formschlüssig (Verpressen, Verkeilen oder Verstemmen) mit dem Druckfederelement verbunden ist. Das Federscheibenelement 11 kann eine weitere erfindungsgemäße Kontaktfläche 8d umfassen, welche ebenfalls eine reibkraftminimierte Oberflächenbeschichtung aufweist. Ferner befindet sich auf der Stößelführung 10 eine Kontaktfläche 8c, welche ebenfalls eine reibkraftminimierte Oberflächenbeschichtung aufweisen kann. Gemäß Fig. 3 ist ein Andruckscheibenelement 9 zwischen dem Federscheibenelement 11 und der Stößelführung 10 eingebracht, wobei das Andruckscheibenelement 9 auch entfallen kann, so dass die Kontaktfläche 8d des Federscheibenetementes 11 direkt auf der Kontaktfläche 8c der Stößelführung 10 angrenzt, und auf dieser abgleiten kann.

It shows:

• Fig. 1 a cross-sectional view of a high-pressure pump with a plunger device and a compression spring element, a plunger guide with a roller shoe inserted and arranged between the compression spring element and the plunger guide Andruckscheibenelement;
• Fig. 2 a cross-sectional view of the Andruckscheibenelementes invention having a first and a second contact surface; and
• Fig. 3 a cross-sectional view of the arrangement of the plunger device with respective contact surfaces according to the invention, wherein the compression spring element, the Andruckscheibenelement and a spring washer element is shown in each case in a disassembled arrangement.
• Fig. 1 shows a cross-sectional side view of a high pressure pump 1, as used in common rail fuel injection systems for diesel engines. The high-pressure pump 1 serves to deliver diesel fuel in order to provide it with a common rail at high pressure. The high-pressure pump 1 comprises a tapping element 2, which rolls over a cam geometry 3 arranged on a camshaft 3. The camshaft 3 is driven on the engine side, and comprises at least one cam geometry 4, wherein these includes one or more evenly distributed on the circumference arranged cams. As a result, the tapping element 2 exerts a lifting movement in the direction of a lifting axis 5, wherein the lifting movement of the tapping element 2 is transmitted to a tappet device 6. The tappet device 6 comprises a compression spring element 7 and a pump piston 12, wherein the tapping element 2 is received within a tappet guide 10, which together with the roller shoe 15 is also part of the tappet device 6. Between the compression spring element 7 and the tappet guide 10, a Andruckscheibenelement 9 is arranged, which is shown cross-cut and executed in the form of a face plate. Centrally from the roller shoe 10, the pump piston 12 extends, which is guided within a cylinder head 13, and cooperates with a valve device in the cylinder head 13 for conveying the fuel. The high-pressure pump 1 essentially comprises a pump body 14, wherein the cylinder head 13 is placed sealingly on the pump body 14. Therefore, both the pump body 14 and the cylinder head 13, the guide device of the lifting movement of the plunger device 6 in the direction of the lifting axis 5, wherein a rotation of the plunger device 6 to prevent rotation about the lifting axis 5 is not shown in detail.
• Fig. 2 shows an enlarged view of the Andruckscheibenelementes 9, which - with respect to Fig. 1 - Located between the compression spring element and the tappet guide. The Andruckscheibenelement 9 comprises a contact surface 8a according to the invention and an opposite further contact surface 8b, which has a frictional force-minimized surface coating. The Andruckscheibenelement 9 extends annularly around the lifting axis 5, so that can extend through the Andruckscheibenelement 9 of the pump piston. The friction-minimized contact surfaces 8a and 8b respectively adjoin the compression spring element and the tappet guide, so that either the first contact surface 8a or the second contact surface 8b or both contact surfaces have the friction-minimized surface coating according to the invention.
• Fig. 3 shows a possible arrangement of a plunger device 6 according to the invention with a Andruckscheibenelement 9, which is disposed between the plunger guide 10 and a spring washer element 11, wherein in the plunger guide 10 of the roller shoe 15 is used to receive the pick-off element 2. The spring disk element 11 is brought into contact with the compression spring element 7, wherein the connection either cohesively (welding, soldering, gluing) or form-fitting (pressing, wedging or caulking) with is connected to the compression spring element. The spring disk element 11 may comprise a further contact surface 8d according to the invention, which likewise has a friction-minimized surface coating. Further, located on the tappet guide 10, a contact surface 8c, which may also have a frictional force minimized surface coating. According to Fig. 3 a Andruckscheibenelement 9 is inserted between the spring disk element 11 and the tappet guide 10, wherein the Andruckscheibenelement 9 can also be omitted, so that the contact surface 8d of the Federscheibenetementes 11 directly adjacent to the contact surface 8c of the tappet guide 10, and can slide on this.

The sliding movement comprises an oscillating rotational movement in small angular ranges, since at each stroke of the roller shoe 15 there is a torsion of the compression spring element 7 relative to the tipping guide 10. This rotation of the compression spring element 7 is thus compensated between the contact surfaces 8a, 8b, 8c and 8d, since the contact surfaces are minimized friction and allow a sliding movement to each other, the sliding causes minimal or even in connection with the lubricating effect of the fuel no significant frictional force. Thus, the Verdrehneigung of the compression spring element 7 is not transmitted to the tappet guide 10 so that it does not transmit the rotational movement further to the tapping element 2, and the line contact between the tapping element 2 and the cam geometry 4 is maintained on the camshaft 3.

The invention is not limited in its execution to the above-mentioned preferred Auführungsbeispiel. Rather, a number of variants is conceivable, which makes use of the solution shown in the scope of claim 1.

Claims (8)

1. High-pressure pump (1), in particular for the conveyance of fuel for a common-rail fuel injection system, comprising at least one cam drive with a pick-off element (2) which can be set in a lifting movement in the direction of a lifting axis (5) by a cam geometry (4) introduced into a camshaft (3), the lifting movement being transmittable to a plunger device (6), the plunger device (6) and the pick-off element (2) being acted upon with force in the direction of the cam geometry (4) by means of a compression-spring element (7), and the plunger device (6) having at least one contact face (8a, 8b, 8c, 8d) to which the compression-spring element (7) is contiguous, characterized in that the at least one contact face (8a, 8b, 8c, 8d) and/or that surface of the compression-spring element (7) which is contiguous to this comprise/comprises a surface coating having minimized frictional force, in order to provide a torsional decoupling of the compression-spring element (7).
2. High-pressure pump (1) according to Claim 1, characterized in that the plunger device (6) comprises a pressure-washer element (9), against which the compression-spring element (7) is brought to bear, and at least one plane face of the pressure-washer element (9) forms the contact face (8a, 8b) with the surface coating having minimized frictional force.
3. High-pressure pump (1) according to Claim 1 or 2, characterized in that the pick-off element (2) is designed as a roller element, and the plunger device (6) comprises, furthermore, a plunger guide (10), on which is formed the contact face (8c) with the surface coating having minimized frictional force.
4. High-pressure pump (1) according to Claim 3, characterized in that a spring-washer element (11) is arranged on the end face of the compression-spring element (7) fixedly in terms of rotation on the latter and is continuous in a planar manner to the contact face (8c) of the plunger guide (10).
5. High-pressure pump (1) according to Claim 3 or 4, characterized in that that contact face (8d) of the spring-washer element (11) which is contiguous to the contact face (8c) of the plunger guide (10) comprises a surface coating having minimized frictional force.
6. High-pressure pump (1) according to Claim 4 or 5, characterized in that the pressure-washer element (9) is arranged between the spring-washer element (11) and the plunger guide (10), so that the contact face (8a, 8b) of the compression-spring element (7) is contiguous to the contact face (8d).
7. High-pressure pump (1) according to one of the abovementioned claims, characterized in that the surface coating having minimized frictional force is applied by means of a PVD method, a CVD method, an electroplating method or a chemical method to the at least one contact face (8a, 8b, 8c, 8d).
8. High-pressure pump (1) according to one of the abovementioned claims, characterized in that the surface coating having minimized frictional force comprises a slip lacquer and/or a dry lubricant applied to the contact face (8a, 8b, 8c, 8d).

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