PLUNGER ASSEMBLY FOR A HIGH-PRESSURE FUEL PUMP, AND HIGH-PRESSURE FUEL PUMP

Abstract

The invention relates to a plunger assembly for a high-pressure fuel pump for supporting a reciprocating pump piston (1) of a pump element on a cam (2) of a drive shaft (3), comprising a supporting element (4) with a recess (5), in which a running roller (6) is mounted rotatably. According to the invention, it is provided that, furthermore, a holding element (7) is provided for holding the running roller (6) in the recess (5) of the supporting element (4), which holding element (7) is connected to the supporting element (4) in a positively locking manner, wherein the positively locking connection brings about an anti-rotation safeguard of the holding element (7) with respect to a longitudinal axis A of the pump piston (1).

Description

BACKGROUND OF THE INVENTION

The present invention relates to a plunger assembly for a high-pressure fuel pump for supporting a reciprocatingly movable pump piston of a pump element on a cam of a drive shaft, comprising a support element with a recess in which a running roller is rotatably mounted . The invention furthermore relates to a high-pressure fuel pump having a plunger assembly of said type.

A plunger assembly of the above-mentioned type emerges for example from DE 10 2008 000 699 A1. Said plunger assembly comprises a hollow cylindrical plunger body in which a roller shoe for the rotatable mounting of a running roller is accommodated. Via the running roller, a pump piston of a pump element can be supported on a cam of a drive shaft, such that the pump piston is driven in a reciprocating movement when the drive shaft rotates. A restoring spring ensures the restoring movement of the pump piston by virtue of the restoring spring being supported on a spring plate which is connected to the pump piston in a form-fitting manner. The form fit is realized by virtue of the spring plate engaging behind a piston foot of the pump piston.

To prevent the running roller from rotating about the longitudinal axis of the pump piston during the operation of the high-pressure pump, it is proposed in DE 10 2008 000 699 A1 that one end of the restoring spring be connected to the roller shoe in a form-fitting manner. The prevention of rotation results in a uniform load on the running roller, such that wear is reduced.

It is not only the running roller, but also those surfaces of the other components of the plunger assembly that are in frictional contact with the running roller, that are subject to wear. The present invention is therefore based inter alia on the object of specifying a plunger assembly with increased wear resistance.

SUMMARY OF THE INVENTION

The proposed plunger assembly comprises a support element with a recess in which a running roller is rotatably mounted. According to the invention, it is provided that, to hold the running roller in the recess of the support element, provision is also made of a retention element which is connected to the support element in a form-fitting manner. Here, the form fit has the effect of preventing rotation of the retention element with respect to a longitudinal axis A of the pump piston.

The support and retention functions are conventionally performed by the roller shoe by virtue of the recess for the rotatable mounting of the roller having a wraparound angle of >180°. For the insertion of the roller into the roller shoe, said roller is pushed in from the side. After the roller shoe has been inserted into the hollow cylindrical plunger body, the running roller is securely held in the roller shoe, wherein the tips of the running roller bear against the inner wall of the plunger body. The inner wall of the plunger body accordingly forms axial run-on surfaces for the running roller.

By contrast, in the plunger assembly according to the invention, the support and retention functions of the running roller are divided between two elements, specifically the support element and the retention element. The wraparound angle of the recess of the support element may accordingly be selected to be <180°. The running roller is prevented from falling out of the recess of the support element by the retention element, wherein, to partially receive the running roller, the retention element has a recess whose width is selected to be smaller, at at least one point, than the diameter of the running roller. The cross section of the recess is preferably matched to the cross section of the running roller.

To prevent the retention element from rotating relative to the support element during the operation of the high-pressure pump, which in turn could lead to the running roller becoming jammed, the retention element is connected to the support element in a form-fitting manner.

If it is thus ensured that the axial run-on surfaces for the running roller are formed by the support element and/or the retention element, a sleeve-shaped plunger body can be omitted. The running roller accordingly bears by way of its tips against delimiting surfaces of the support element and/or of the retention element. All of the surfaces that are subjected to dynamic loading by the running movement of the running roller are accordingly formed on the support element and/or on the retention element, which may accordingly be produced from a wear-resistant material and/or provided with a wear-resistant coating. Owing to the omission of the plunger body, the need for pressing the support element into the plunger body is also omitted. Since, during the pressing-in process, there is the risk of deformation of the support element and of the recess, formed therein, for receiving the running roller, said risk is counteracted by dispensing with a plunger body. This has an advantageous effect on the running characteristics of the running roller and thus the wear. The omission of the plunger body furthermore results in a reduction of the weight of the plunger assembly, which has likewise proven to be expedient. This is because, owing to the weight reduction, it is firstly possible for the restoring spring to be of smaller dimensions, and secondly, the spacing between the camshaft and the top side of the cylinder head can be reduced if the plunger assembly is used in a high-pressure fuel pump. This leads to further weight savings in the cylinder head and/or in the pump housing.

To realize the form fit between the retention element and the support element, it is proposed in one preferred embodiment of the invention that the retention element is at least partially inset into the support element. It may alternatively or additionally be provided that the support element has at least one axial projection which engages with the retention element. The form fit must be realized such that a rotation of the retention element with respect to the support element about the longitudinal axis of the pump piston is counteracted.

As a refining measure, it is proposed that the axial projection is formed in the shape of a segment of a circle, and surrounds a partial circumferential region of the retention element. Here, the axial projection need not imperatively have been attached to the support element but rather may also have been produced by way of milling operations. To produce multiple projections formed in the shape of segments of a circle, it is possible for the support element to have initially been milled out in circular form, for example, and for the milled-out portion to have been connected to the outer circumferential surface via radially running grooves. The grooves may interact with lugs, formed correspondingly thereto, of the retention element, such that a form fit is realized.

It is furthermore preferable for the retention element to be pressed into the support element. In this way, the retention element is secured so as to be prevented from falling out if the form fit between the retention element and the support element serves merely for rotation prevention.

The retention element advantageously forms axial run-on surfaces for the running roller. The running roller is accordingly secured in position primarily by the retention element. The wraparound angle of the running roller may accordingly also be considerably less than 180°, for example 140°.

In one refinement of the invention, it is proposed that the running roller has planar tip surfaces by which the running roller bears against the retention element and/or against the support element. Owing to the areal contact instead of the conventional punctiform contact, it is possible for much higher lateral run-on forces to be absorbed. Wear can be further reduced in this way. Furthermore, a running roller with flat tips is easier and accordingly cheaper to produce.

The high-pressure fuel pump which is also proposed for achieving the object stated in the introduction and which has a plunger assembly according to the invention is characterized in that the support element of the plunger assembly is inserted directly into a housing bore of the high-pressure fuel pump. The support element is thus not received in a hollow cylindrical plunger body. The advantages associated with the omission of the plunger body have already been described above, such that reference is made to said part of the description.

It is also proposed that the retention element has a lug which protrudes radially in relation to the support element and which interacts with a groove of the housing bore so as to prevent rotation of the plunger assembly.

It is furthermore preferable for the plunger assembly to be connected to the pump piston by means of a spring plate, wherein the spring plate is pressed onto the pump piston. In this way, the pump piston can be formed without a piston foot, which simplifies production.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention will be explained in more detail below on the basis of the appended drawings, in which:

FIG. 1 is a partial perspective sectional view of a known high-pressure pump in the region of a plunger assembly,

FIG. 2 shows a longitudinal section through a plunger assembly according to the invention,

FIG. 3 shows a view of the plunger assembly of FIG. 2 from below, and

FIG. 4 shows a longitudinal section through the support element, the retention element and the running roller of the plunger assembly of FIGS. 2 and 3, the section plane having been rotated through 90° with respect to the section plane of FIG. 2.

DETAILED DESCRIPTION

The high-pressure pump illustrated as a detail in the region of a plunger assembly in FIG. 1 comprises at least one pump element with a reciprocatingly guided pump piston 1 which is supported, via a plunger assembly, on a cam 2 of a drive shaft 3. The plunger assembly is received in an axially displaceable manner in a housing bore 11 of a housing part 20 of the high-pressure pump.

The illustrated plunger assembly comprises a sleeve-shaped plunger body 13 and, received therein, a support element 4 with a recess 5 for the rotatable mounting of a running roller 6. Via the running roller 6, the plunger assembly is supported directly on the outer circumference of the cam 2 of the drive shaft 3. A restoring spring 14 ensures the abutment of the plunger assembly against the cam 2.

The restoring spring 14 and the support element 4 of the plunger assembly are supported in each case on opposite sides of an annular collar 16 of the plunger body 13, wherein the restoring spring 14 is supported indirectly on the annular collar 16 via a spring plate 12. The spring plate 12 serves for connecting the plunger assembly to the pump piston 1. For this purpose, the spring plate 12 has a central recess through which the pump piston 1 is guided such that the spring plate 12 engages behind a piston foot 15 of the pump piston 1. In this way, a form-fitting connection of the pump piston 1 to the plunger assembly is realized.

The plunger assembly according to the invention illustrated in FIGS. 2 to 4 differs from that in FIG. 1 in particular in that no plunger body 13 is provided. The support element 4 is received directly in the housing bore 11 of the housing part 20 of the high-pressure pump (see FIG. 2). Furthermore, the support element 4 has a central milled-out portion which extends, via grooves 18, to the outer circumference of the support element 4 (see FIG. 3). The milled-out portion is delimited by two projections 8 which are in the form of segments of a circle, said projections being of rotationally symmetrical form and being separated from one another by the grooves 18. Into the central milled-out portion there is pressed a retention element 7 which has lugs 17 which engage into the grooves 18 such that a form fit is produced (see FIGS. 3 and 4). The lugs that engage with the grooves 18 thus prevent a rotation of the retention element 7 with respect to the support element 4 about the longitudinal axis A of the pump piston 1.

By virtue of a lug 17 extending in a radial direction beyond the outer circumference of the support element 4 (see FIG. 4), said lug can be used for preventing rotation of the plunger assembly within the housing bore 11. For this purpose, a groove (not illustrated) which interacts with the lug 17 is formed in the housing bore 11.

As can also be seen from FIG. 4, the running roller 6 has planar tip surfaces 10, that is to say flat tips by which the running roller 6 bears against axial run-on surfaces 9 formed by the retention element 7 (see FIGS. 3 and 4).

It can also be seen from FIG. 2 that the support element 4, the retention element 7 and the spring plate 12 have throughflow openings 19 arranged to the sides of the running roller 6 (see also FIG. 3). Said throughflow openings ensure the throughflow of fuel.

Furthermore, the pump piston 1 is illustrated without a piston foot 15, from which it follows that the spring plate 12 is pressed onto the pump piston 1. This is however not imperatively necessary. The pump piston 1 may also be formed with a piston foot 15. That end of the pump piston 1 which faces away from the spring plate 12 is received in a cylinder head 21 of the high-pressure pump.

Claims

1. A plunger assembly for a high-pressure fuel pump for supporting a reciprocatingly movable pump piston (1) of a pump element on a cam (2) of a drive shaft (3), comprising a support element (4) with a recess (5) in which a running roller (6) is rotatably mounted, also comprising, to hold the running roller (6) in the recess (5) of the support element (4), a retention element (7) which is connected to the support element (4) in a form-fitting manner to prevent rotation of the retention element (7) with respect to a longitudinal axis of the pump piston (1).

2. The plunger assembly as claimed in claim 1, characterized in that, to realize a form fit, the support element (4) has at least one axial projection (8) which engages with the retention element (7).

3. The plunger assembly as claimed in claim 2, characterized in that the axial projection (8) is formed in the shape of a segment of a circle, and surrounds a partial circumferential region of the retention element (7).

4. The plunger assembly as claimed in claim 1, characterized in that the retention element (7) is pressed into the support element (4).

5. The plunger assembly as claimed in claim 1, characterized in that the retention element (7) forms axial run-on surfaces (9) for the running roller (6).

6. The plunger assembly as claimed in claim 1, characterized in that the running roller (6) has planar tip surfaces (10) by which the running roller (6) bears against at least one of the retention element (7) and the support element (4).

7. A high-pressure fuel pump having a plunger assembly as claimed in claim 1, wherein the support element (4) is inserted directly into a housing bore (11) of the high-pressure fuel pump.

8. The high-pressure fuel pump as claimed in claim 7, characterized in that the retention element (7) has a lug (17) which protrudes radially in relation to the support element (4) and which interacts with a groove of the housing bore (11) so as to prevent rotation of the plunger assembly.

9. The high-pressure fuel pump as claimed in claim 7, characterized in that the plunger assembly is connected to the pump piston (1) by means of a spring plate (12), wherein the spring plate (12) is pressed onto the pump piston (1).

10. The plunger assembly as claimed in claim 1, characterized in that, to realize a form fit, the retention element (7) is at least partially inset into the support element (4).

11. The plunger assembly as claimed in claim 1, characterized in that, to realize the form fit, the support element (4) has at least one axial projection (8) which engages with the retention element (7).