Hydraulic bucket tappet

Abstract

A hydraulic tappet for internal combustion engines with overhead camshaft has hollow cylindrical housing that is sealed at one end by a tappet floor that is mechanically linked to a cam of a camshaft. Longitudinally borne in the housing is a hydraulic play compensation unit, the pressure chamber of which, for exchanging fluid, can be connected to a fluid reservoir that is sealed to the outside. For compensating volume from the fluid reservoir, a largely circular compensation element that limits the fluid reservoir is provided and that is provided with at least one undulation and/or fold. The compensation element is arranged such that the center region is freely movable and the undulation and/or fold opens or closes depending on the required volume compensation.

Description

[0001] The invention relates to a hydraulic tappet for an internal combustion engine with an overhead camshaft in accordance with the preamble to claim 1.

[0002] A generic hydraulic tappet is known from DE 41 36 746 A1.

[0003] The generic document illustrates a hydraulic tappet for internal combustion engines with a housing in which is arranged a play compensation element joined concentrically to at least one fluid reservoir. The fluid reservoir is completely sealed to the outside and the hydraulic tappet consequently works with an internal oil supply.

[0004] Automatic hydraulically adjusting play compensation elements, in particular those in tappets of internal combustion engines, are constructed such that during the lift phase of the cam, due to a piston displacement hydraulic fluid is pressed out of a pressure chamber in the play compensation element through a choke channel into a reservoir. A spring restores the piston in the base circle phase of the cam, whereby a non-return valve in a channel opens and hydraulic fluid flows back from the reservoir into the pressure chamber. In the lift phase the piston displacement generally reduces the size of the reservoir. Volume compensation elements are necessary in order, nevertheless, to be able to receive the hydraulic fluid exiting the pressure chamber.

[0005] Known from DE 41 25 568 A1 is the arrangement of spring-loaded elements in the fluid reservoir.

[0006] Elastomer membranes that are employed for volume compensation are known from DE 39 10 666 C2. The membranes are curved and are arranged between an exterior surface of the play compensation element and an interior surface of the housing. However, due to contact with oil, the membranes have substantial disadvantages in terms of permeation and changes in hardness and associated poor cold flexibility. It is also disadvantageous that leaks can occur, since the membranes are also subject to stretching due to the annular embodiment and the limited space for volume compensation. In addition, the membranes also seal the movable components, and failure due to tears occurs over the service life under vehicle conditions.

[0007] The function of the hydraulic tappet is negatively affected by the support of the membranes on the play compensation element. First of all, this can lead to the hydraulic tappet becoming jammed, and, secondly, it can mean that tolerance compensation is not assured.

[0008] Another hydraulic tappet with an integrated reservoir is known from DE 41 30 529 A1. One membrane element constituting two layers is employed. The membrane element is arranged analogous to the membrane element described in DE 39 10 666 C2, radially on the interior surface of the housing and on the exterior surface of the play compensation element. The disadvantages cited with respect to DE 39 10 666 C2 in terms of being leak-proof, the stress of stretching, and the negative effect of the hydraulic tappet apply similarly.

[0009] The generic document, DE 41 36 746 A1, provides that the total volume from the pressure chamber and reservoir remains constant without fluid forces having to act on the volume compensation elements. When the piston moves, the volume of the pressure chamber decreases/increases by the same amount as the volume of the reservoir increases/decreases. Thus, actual volume compensation is not necessary. In one illustrated embodiment, two partial reservoirs are provided that are arranged axially on either side of the pressure chamber. Flexible membranes that seal these are provided at each axially exteriorly situated end of the partial reservoirs. Also provided in this embodiment is that the volume of the pressure chamber decreases/increases by the same amount as the volume of the two partial reservoirs increases/decreases. The membranes make it possible for the play compensation element to be employed even when it is expected that there will be thermally-caused changes in the density of the hydraulic fluid in the pressure chamber and reservoir (column 5, lines 4-8).

[0010] The membranes described in DE 41 36 746 A1 are attached analogous to the membranes known from DE 39 10 666 C2 and DE 41 30 529 A1, and the same disadvantages apply. Although the stress on the membranes is lower since the membranes are not employed for compensating volume, the membranes still also seal the moving parts and are therefore correspondingly stressed. The thermally-caused change in density in the hydraulic fluid is received by the membranes in accordance with DE 41 36 746 A1 by stretching. In one embodiment that is not illustrated, it is provided that one of the membranes is just placed loose on the end face of a compensation rod so that when there is thermally induced fluid expansion, the compensation rod lifts the membrane. This reduces stretching of the membrane. However, a corresponding stress or even damage to the membrane results due to impacts or the like result, depending on the movement of the compensation rod upon which the membrane is situated.

[0011] None of the known hydraulic tappets with a fluid reservoir that is sealed to the outside has proved itself in practice, since leaks could not be reliably prevented over the service life under vehicle conditions. In general the membranes are stressed the most at the connecting points and consequently leak there.

[0012] An object of the present invention is to provide a hydraulic tappet for internal combustion engines with a fluid reservoir that is sealed to the outside, which tappet overcomes the aforesaid disadvantages of the prior art, in particular, is sealed for the provided service life, provides optimal functioning, and is simple and cost-effective to produce.

[0013] This object is achieved inventively by the characterizing portion of claim 1.

[0014] The undulation and/or fold in the inventive compensation element advantageously receives and then releases the corresponding fluid volume with almost no pressure. The center region is freely movable and is not joined to the play compensation element or to a piston, as in the hydraulic tappet known from prior art. Thus the compensation element merely receives the volume compensation role and does not also seal the moving components. These two functions are thus separated. Thus, proven movement seals such as for instance O-rings, rod seals, O-ring supported sealing rings, V-rings, or the like can be employed for sealing the moving components.

[0015] As was determined in trials, the inventive hydraulic tappet is particularly suitable for employment in practice. Leaks at the connection points to the compensation element do not occur, since no movement has to be sealed thereby. In addition, since volume compensation occurs when the undulation and/or fold opens or closes, the compensation element is not or is largely not stressed by stretching, which means that the service life clearly increases. Since the center region of the compensation element is freely movable and consequently is not in contact with the play compensation unit or a piston, the functioning of the hydraulic tappet is not negatively affected. The hydraulic tappet cannot be jammed, therefore. Tolerance compensation is assured at all times.

[0016] Advantageously, the compensation element has only one circumferential sealing site which simultaneously represents the attachment.

[0017] It is advantageous when the compensation element is embodied as a bellows.

[0018] In trials, it was demonstrated that an embodiment as bellows is particularly suited for opening or closing the undulation and/or fold with almost no pressure. In one preferred embodiment it can be provided that the bellows is made of rubber or synthetic rubber.

[0019] In accordance with the invention, it can furthermore be provided that the housing is sealed in the direction of the camshaft by a tappet floor and a bushing, whereby the tappet floor and the bushing are displaceably arranged in the housing and whereby the bellows is clamped between the bushing and the tappet floor. Advantageously, the bellows can be dimensioned like an O-ring in this region.

[0020] With respect to attaching the bellows in the most simple and most lasting possible manner, such an arrangement has proved particularly suitable. Thus, the bellows merely accomplishes the volume compensation function and no movement seal is required. Due to the O-ring-type cross-section of the bellows on the exterior circumference, it can be easily pressed in or compressed between the bushing and the tappet floor. A lasting and sealed connection is thus provided.

[0021] In one alternative embodiment of the invention, it can be provided that the bellows is vulcanized at the bushing and/or at the tappet floor.

[0022] In trials it was demonstrated that vulcanizing the bellows at the tappet floor or bushing can likewise provide a secure attachment that seals lastingly. Naturally other joining or attaching methods can be employed alternative to vulcanization, such as e.g. adhesives, soldering, or welding.

[0023] Advantageous embodiments and further developments of the invention result from the additional subordinate claims and from the following exemplary embodiment, the principles of which are illustrated using the drawing.

[0024] The only figure in the drawing illustrates an inventive hydraulic tappet with a play compensation element.

[0025] As can be seen from the figure, the hydraulic tappet 1 has a hollow cylindrical housing 2 that is sealed at one end by a tappet floor 5 that is mechanically linked to a cam 3 of a camshaft 4. The hydraulic tappet 1 is provided for a internal combustion engine (not shown) with the overhead camshaft 4. Longitudinally borne in the housing 2 is a hydraulic play compensation unit 6, the pressure chamber 7 of which, for exchanging fluid, can be connected to a fluid reservoir 8 that is sealed to the outside. The principle upon which the play compensation unit 6 functions is well-known from the prior art (see for instance DE 39 10 666 C2), for which reason it will not be described in greater detail in the following.

[0026] As can be seen from the figure, the hydraulic tappet 1, for compensating volume from the fluid reservoir 8, has a largely circular compensation element 9 that limits the fluid reservoir 8. The compensation element 9 is arranged such that it is not situated in the power force between the cam 3 and a valve lifter 21. The compensation element 9 is consequently situated outside of the power force.

[0027] The compensation element 9 in the exemplary embodiment is designed as a bellows 9 and has an undulation 10 which opens or closes depending on the required volume compensation. The opening and closing of the undulation 10 occurs with almost no pressure. In one alternative embodiment it can also be provided that the bellows 9 has a plurality of undulations and/or folds 10.

[0028] As can also be seen from the figure, the center region 11 of the bellows 9 is freely movable. In the exemplary embodiment, the center region 11 of the bellows 9 extends almost to the exterior circumference of the bellows 9.

[0029] The housing 2 has a housing floor 2a embodied integrally with the housing 2 at the side facing away from the tappet floor 5. The play compensation unit 6 stands on this housing floor 2a. The housing is sealed in the direction of the camshaft 4 by the tappet floor 5 and a bushing 12. The tappet floor 5 and the bushing 12 are displaceably arranged in the housing 2. In order to assure the mobility of the hydraulic tappet 1, the bushing 12 is supported by a spring 13 that is arranged between the bushing 12 and the housing floor 2a.

[0030] The fluid reservoir 8 is sealed by the housing 2, the bushing 12, and the bellows 9. The fluid is sealed in the housing 2 by a seal 14 between the bushing 12 and the housing 2. The seal 14 is preferably embodied as an O-ring. In the exemplary embodiment, the tappet floor 5 thus has no contact with the fluid of the fluid reservoir 8 and therefore also does not have to be sealed to the housing 2.

[0031] As can be seen from the figure, the bellows 9 is clamped between the bushing 12 and the tappet floor 5. The bellows 9 has on its exterior circumference an O-ring-shaped form 9a. This O-ring-shaped form 9a can be pressed in or compressed between the bushing 12 and the tappet floor 5. The O-ring-shaped form 9a, in which the bellows 9 terminates and which is illustrated in cross-section in the figure, is compressed by the difference in the diameters of the bushing 12 and the tappet floor 5, and thus seals. As can also be seen from the figure, the tappet floor 5 has a free space 15 for receiving the opened fold 10. Thus the required compensation volume is provided. The free space 15 can be maintained with no pressure by an opening or pressure compensation unit (not shown) in the tappet floor 5.

[0032] If the hydraulic tappet 1 moves apart, a spring 17 presses a piston 16 of the play compensation unit 6 away from the floor of the housing 18 of the play compensation element 6. Fluid is suctioned from the fluid reservoir 8 via a non-return valve 19 in a known manner.

[0033] As can be seen from the figure, the fluid reservoir 8 is situated in the interior of the housing 2, in which the housing 18 of the play compensation unit 6 is also situated.

[0034] When the hydraulic tappet 1 moves together, the bellows 9 receives the volume that derives both from the displaced fluid from the pressure chamber 7 and from the decrease in the size of the fluid reservoir 8. The fold 10 folds into the free space 15 below the tappet floor 5.

[0035] The power force between the cam 3 of the camshaft 4 and a valve lifter (not shown) is transferred as follows. The force is conducted via the tappet floor 5 onto the bushing 12 and from there to the piston 16 of the play compensation unit 6. From there the force travels via the tolerance-compensating non-compressible fluid (pressure chamber 7) enclosed in the play compensation element 6 to the housing 18 of the play compensation unit 6, which stands on the housing floor 2a of the housing 2. The force is introduced to the housing floor 2a directly by the housing 18.

[0036] In the exemplary embodiment, the hydraulic tappet 1 is sealed by a retaining ring 20. Alternatively, any other known axial securing element, such as for instance a locking ring, crimping of the container, or the like can be employed.

[0037] The spring 13 between the housing 2 and the bushing 12, which compensates the increased friction in the system and is responsible for rapid and precise adjusting of the hydraulic tappet 1, can be omitted if the spring 17 between the piston 15 and the housing 18 of the play compensation unit 6 assumes this function.

[0038] Preferably the bellows 9 is produced from rubber or synthetic rubber. Alternatively, of course, the bellows 9 can also be produced from any other desired material that enables the fold 10 to open and close to the greatest extent possible with no pressure.

[0039] Legend

[0040] 1 Hydraulic tappet

[0041] 2 Housing

[0042] 2a Housing floor

[0043] 3 Cam

[0044] 4 Camshaft

[0045] 5 Tappet floor

[0046] 6 Play compensation unit

[0047] 7 Pressure chamber

[0048] 8 Fluid reservoir

[0049] 9 Compensation element

[0050] 9a Form

[0051] 10 Undulation/fold

[0052] 11 Center region

[0053] 12 Bushing

[0054] 13 Spring

[0055] 14 Seal

[0056] 15 Free space

[0057] 16 Piston

[0058] 17 Spring (play compensation unit)

[0059] 18 Housing (play compensation unit)

[0060] 19 Non-return valve

[0061] 20 Retaining ring

[0062] 21 Valve lifter

Claims

1. Hydraulic tappet for internal combustion engines with an overhead camshaft, comprising a hollow cylindrical housing that is sealed at one end by a tappet floor that is mechanically linked to a cam of the camshaft, a hydraulic play compensation unit in said housing, said hydraulic play compensation unit having a pressure chamber of which, for exchanging fluid, can be connected to a fluid reservoir that is sealed to the outside wherein for compensating the volume from said fluid reservoir, a compensation element that limits the fluid reservoir and provided with at least one undulation and/or folds is provided, whereby said compensation element being arranged such that the center region thereof is freely movable and said undulation and/or fold opens or closes depending on the required volume compensation.

2. Hydraulic tappet in accordance with claim 1, wherein said compensation element is arranged outside of the power force between said cam and a valve lifter.

3. Hydraulic tappet in accordance with claim 1 or 2, wherein said compensation element is embodied such that said undulation and/or fold opens and closes with almost no pressure.

4. Hydraulic tappet in accordance with claim 1 or 2 wherein said compensation element is a bellows.

5. Hydraulic tappet in accordance with claim 1 or 2, wherein said housing has a housing floor integral with said housing at the side facing away from said tappet floor.

6. Hydraulic tappet in accordance with claim 5, wherein said compensation element stands on said housing floor.

7. Hydraulic tappet in accordance with claim 1 or 2, wherein said housing is sealed in the direction of said camshaft by said tappet floor and a bushing.

8. Hydraulic tappet in accordance with claim 7, wherein said tappet floor and said bushing are displaceably arranged in said housing.

9. Hydraulic tappet in accordance with claim 7, comprising a spring is arranged between said bushing and said housing floor.

10. Hydraulic tappet in accordance with claim 7, wherein a seal is arranged between said bushing and said housing.

11. Hydraulic tappet in accordance with claim 7, wherein said bellows is clamped between said bushing and said tappet floor.

12. Hydraulic tappet in accordance with claim 11, wherein said bellows has on its exterior circumference an O-ring-shaped form that can be pressed in or compressed between said bushing and said tappet floor.

13. Hydraulic tappet in accordance with claim 7, wherein said bellows is vulcanized at said bushing and/or at said tappet floor.

14. Hydraulic tappet in accordance with claim 1 or 2, wherein said tappet floor has a free space for receiving said opened undulation and/or fold.

15. Hydraulic tappet in accordance with claim 14, wherein said free space is maintained with no pressure by an opening in said tappet floor.

16. Hydraulic tappet in accordance with claim 10, wherein said seal is an o-ring.