Tappets for high-pressure fuel pumps

Abstract

A tappet (1) of a high-pressure fuel pump is proposed, wherein the tappet (1) comprises a housing (2), two diametrically opposed holes (4) are arranged in the end (3) of the housing on the drive side, a pin (5) is provided in the holes, a cam roller (7) moves on the pin via an intermediate ring (6), wherein a bridge (8) is located in the tappet (1) axially below the cam roller (7), and the lower side (10) of the end (9) of the bridge facing the driven side of the housing (2) is ) has a contact portion (11) for a follower, wherein the pin (5) which is not coated on the outer surface (12) and the intermediate ring (6) which is not coated on its hole (13) are engaged with each other by a press fit, and wherein the pin (5) can rotate freely relative to the hole (4) of the housing (2), and the axial fixing of the roller assembly is only carried out by the intermediate ring (6) with its outer end face (14) thrust on the inner wall (15) of the housing (2).

Description

Technical Field

[0001] The present invention relates to a tappet with a slidingly supported cam roller, which is provided for a high-pressure fuel pump of an internal combustion engine and has a housing, in which two diametrically opposed holes are arranged at the drive-side end of the housing, and in which there are pins, on which the cam roller moves via an intermediate ring, wherein a bridge is located axially below the cam roller in the tappet, and the lower side of the bridge, which end faces the driven side of the housing, has an abutment portion for a follower. Background Art

[0002] By DE 10 2018 120 265 A1 Figure 2 Paragraph

[0013] discloses a tappet of the type described above with a slidingly supported roller assembly having an intermediate ring between a pin and a cam roller. The components are capable of relative rotational movement, wherein a hydrodynamic sliding bearing is provided in the annular gap between a) the pin and the intermediate ring and b) the annular gap between the intermediate ring and the cam roller during operation. The mating surfaces at the two annular gaps are provided with a friction- and wear-reducing hard material layer (DLC layer), which is subsequently subjected to a brushing process. The pin is axially secured by enlarging its ends via radial point riveting or caulking, with retaining ring fastening also known.

[0003] DE 10 2009 013 130 A1 discloses a tappet as described above, but with a needle-roller-mounted cam roller. Summary of the Invention

[0004] The object is to design a tappet which is suitable for the very high loads and high rotational speeds in pump drives and which can at the same time be produced inexpensively.

[0005] According to the invention, this object is achieved in that a pin which is not coated on its outer surface and an intermediate ring which is not coated in its bore are joined to one another by a press fit, wherein the pin can freely rotate relative to the bore of the housing and the axial fixing of the roller assembly is achieved solely by the thrust of the intermediate ring with its outer end face against the inner wall of the housing.

[0006] The hydrodynamic plain bearing thus moves only on the radially outer annular gap between the intermediate ring and the cam roller, while on the radially inner annular gap a permanent press fit is now achieved between the pin and the intermediate ring and no relative rotation can therefore occur.

[0007] From a purely functional perspective, the advantages of this are that, due to the plain bearing being designed only on a relatively large diameter, higher peripheral speeds can be achieved, significantly improving elastohydrodynamic lubrication. The proportion of solid and mixed friction is reduced. This type of bearing can effectively withstand the continuously increasing pump pressures and speeds of the drive (camshaft, crankshaft, balance shaft, or auxiliary shaft).

[0008] At the same time, in press-fit composites, which in terms of surface quality are only considered "standard rolling bearing composites," pins with smaller diameters can be installed, so that, for example, the two pin holes in the housing can be relatively close to the upper annular end of the housing. At the same time, thinner annular cam rollers can now be used, which, due to their low mass, are relatively "easy to rotate" and exhibit little slippage during operation, such as during starting / acceleration, due to known wear patterns. The stepped pins with thin cam rings known from the prior art can be dispensed with; the pins can simply be installed without problems in the U-shaped pocket of the housing.

[0009] Furthermore, the manufacturing costs are reduced by eliminating the previously essential hard material coating between the outer surface of the pin and the hole in the intermediate ring and the subsequent painting of the surface. Although the assembly process can be automated on the coating chamber, the manual feeding (threading) and removal are still the main tasks.

[0010] The pin to be pressed against the intermediate ring is guided laterally into one of the holes in the housing, wherein the intermediate ring, together with the rollers mounted thereon, is held in the interior of the housing. The pin is then pressed against the intermediate ring by a punch or the like.

[0011] The present invention also has the advantage that the laborious securing methods currently predominantly employed, such as caulking or radial point riveting on fully hardened pins, which carry the risk of, for example, impacting the housing or even its ground raceways (outer surfaces) or loosening the connection, can be dispensed with. The axial securing of the roller assembly and pin is thus achieved solely by the thrust of the intermediate ring, via its outer end face, against the inner surface of the housing. The outer end face of the cam roller is slightly retracted relative to the outer end face of the intermediate ring.

[0012] In order to increase the load resistance and wear resistance of the roller assembly, a particularly preferred development of the invention provides that at least one of the annular gap fits of the “remaining” plain bearing is provided with a hard material layer, such as a DLC layer.

[0013] Likewise or independently of this, the annular section of the pin extending in the bore region of the housing can also be coated with a hard material, so that friction and wear in the region of the rotatable pin are minimized. If necessary, the pin can also move on the bushing in the hole.

[0014] Likewise, either alone or together with the last-mentioned design measure, the outer end face of the intermediate ring which abuts against the inner surface of the housing can be formed with a coated hard material layer or the inner surface can also be formed with a coated hard material layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] For the attached pictures:

[0016] Figure 1 The tappet is shown in an overall perspective view;

[0017] Figure 2 shows a longitudinal section of the tappet along the roller axis, and

[0018] Figure 3 Shows the tappet relative to Figure 2 Cross-section rotated 90°. DETAILED DESCRIPTION

[0019] Figure 1 The tappet 1, also known as a roller tappet or pump tappet, is shown in its basic known construction. The tappet 1 has a hollow cylindrical housing 2, with two diametrically opposed bores 4 in a recessed flattened portion 24 in its drive-side end 3. A pin 5 is positioned in the bore 4, rotatable relative to the bore and slightly axially movable, and carries a cam roller 7 via an intermediate ring 6. A thin-walled bridge 8 (see FIG. 1 ) is mounted axially below the cam roller 7. Figure 2 、 Figure 3 ), the lower side 10 of the end 9 of the bridge facing the output side of the housing 2 has a contact portion 11 for the follower (pump piston).

[0020] The pin 5, which is preferably completely hardened, is permanently pressed against the hole 13 of the intermediate ring 6 via its outer surface 12. Therefore, there is no sliding bearing in this radially inner annular area. The surface quality of the contact area is reduced to that of a "standard rolling bearing."

[0021] Only the thin-walled cam roller 7 is kept rotatably movable relative to the now fixed intermediate ring 6, wherein, needless to say, the hydrodynamic sliding bearing is formed only between the outer surface 23 of the intermediate ring 6 and the inner surface 16 of the cam roller 7. The outer surface 23 and the inner surface 16 are provided with a DLC layer.

[0022] The roller assembly is axially fixed by the intermediate ring 6 , whose outer end face 14 abuts against the inner wall 15 of the housing 2 .

[0023] Reference Signs List

[0024] 1 tappet

[0025] 2 Shell

[0026] 3 ends

[0027] 4 holes

[0028] 5 pins

[0029] 6 Intermediate ring

[0030] 7 Cam roller

[0031] 8 Bridge

[0032] 9 ends

[0033] 10 Lower side

[0034] 11. Adhesion

[0035] 12 External surface

[0036] 13 holes

[0037] 14 outer end face

[0038] 15 inner wall

[0039] 16 Inner surface

[0040] 17 Hard material layer

[0041] 18 hard material layer

[0042] 19 ring sections

[0043] 20 hard material layer

[0044] 22 hard material layer

[0045] 23 outer surface

[0046] 24 Flattening

Claims

1. A tappet (1) with a slidingly mounted cam roller (7), the tappet (1) being provided for a high-pressure fuel pump of an internal combustion engine and comprising a housing (2), in the drive-side end (3) of which two diametrically opposed holes (4) are arranged, in which there are pins (5), on which the cam roller (7) moves via an intermediate ring (6), wherein: Axially below the cam roller (7), a bridge (8) is located in the tappet (1), and the lower side (10) of the end (9) of the bridge facing the driven side of the housing (2) has an abutment portion (11) for the follower, characterized in that the pin (5) which is not coated on the outer surface (12) and the intermediate ring (6) which is not coated on its hole (13) are engaged with each other by a press fit, wherein the pin (5) can rotate freely relative to the hole (4) of the housing (2), and the axial fixing of the roller assembly including the pin (5), the intermediate ring (6) and the cam roller (7) is only carried out by the intermediate ring (6) with its outer end face (14) thrusting on the inner wall (15) of the housing (2).

2. The tappet according to claim 1, characterized in that The outer surface (23) of the intermediate ring (6) and / or the inner surface (16) of the cam roller (7) have a coated hard material layer (17, 18).

3. The tappet according to claim 1, wherein: The pin (5) is completely hardened and only the annular section (19) of the pin, whose outer surface (12) is located in the bore (4) of the housing (2), is provided with a coated hard material layer (20).

4. The tappet according to claim 1, wherein: A hard material layer (22) is applied to the outer end face (14) of the intermediate ring (6).

Images