HYDRAULIC LASH ADJUSTER FOR AN INTERNAL COMBUSTION ENGINE

Abstract

A hydraulic lash adjuster for a valve train of an internal combustion engine is provided, with the hydraulic lash adjuster including a circular cylindrical housing in which a piston (22) is arranged for axial displacement, and further including a one-way valve (31) with a closing body (32) that can be brought to bear against a valve seat (28) of the piston (22) for sealing a through-opening (24). The closing body is surrounded by a valve cap (35) and loaded by a compression spring (33 that is supported with a first end on the closing body (32) and with a second end on the valve cap (35). The closing body (32) has an approximately spherical, convexly vaulted bearing surface (34) for sealing contact on the valve seat (28) and deviates in shape from a ball shape.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application 60/802,929, filed May 24, 2006, which is incorporated by reference herein as if fully set forth.

FIELD OF THE INVENTION

The invention relates to a hydraulic lash adjuster for the valve train of an internal combustion engine, said hydraulic lash adjuster comprising a circular cylindrical housing, in which a piston is arranged for axial displacement, and further comprising a one-way valve comprising a closing body that can be brought to bear against a valve seat of said piston for sealing a through-opening, said closing body being surrounded by a valve cap and loaded by a compression spring that is supported with a first end on the closing body and with a second end on the valve cap.

BACKGROUND OF THE INVENTION

For a plurality of technical reasons, it is desirable to reduce the size of a hydraulic lash adjuster (HLA) used in the components of a valve train. This would be apparent, for example, for the development of a switchable tappet for a tappet push rod motor. One of the factors determining the minimum height of an adjuster is the height of the one-way valve, which typically contains a ball as a closing body. If this height can be reduced, then the entire height of the adjuster can also be reduced.

In the publication DE 40 23 885 A1, which concerns a roller tappet with hydraulic lash adjustment, the disadvantage is mentioned that roller tappets known up until then were constructed with relative large volumes and had an increased overall height especially compared with conventional cup tappets. Accordingly, measures should already have been disclosed there, with whose help the dimensions of roller tappets with hydraulic lash adjustment could be reduced. For achieving this goal, in this publication it is proposed, e.g., for the one-way valve device, through which a hydraulic high-pressure chamber connects to a hydraulic storage chamber, to use several one-way valves, which are then arranged one next to the other. In this way, the associated storage chamber with a typical, relatively large volume can be divided into several sub-chambers, which can then be arranged in a construction, which has been optimized in the sense of installation space, at suitable free spaces in the roller tappet.

A hydraulic lash adjuster of the type noted above is known from the publication DE 198 44 202 A1. This adjuster constructed as a roller tappet features the mentioned disadvantage of the large-volume construction with increased overall height relative to conventional cup tappets.

SUMMARY OF THE INVENTION

The invention is based on the objective of reducing the installation size of a hydraulic lash adjuster to be used in a valve train of an internal combustion engine.

This objective is met according to the invention in that the closing body features an approximately spherical, convexly vaulted bearing surface for the sealing contact on the valve seat and, incidentally, deviates in shape from a ball shape. In this way, in the minimum installation height of the adjuster, the entire diameter of a ball is not included, as was used in previously known elements as a closing body. Instead, in contrast to these previously known elements, the support point of the compression spring can be located significantly closer to the valve seat in the arrangement according to the invention. Consequently, the length dimension of the installation space, which is determined by the closing body and the compression spring, can be smaller.

The closing body can have, for example, a mushroom shape. In this case, the compression spring, when it is constructed as a cylindrical, helical compression spring, can partially surround the shaft of the closing body mushroom concentrically and can be supported on the bottom side of the mushroom head of the closing body in the vicinity of the valve seat.

It is also possible for the closing body to have a dome shape. Then the compression spring can project partially into the hollow space of the closing body dome and can be supported there on the closing body in the area of the vaulting in the vicinity of the valve seat.

The invention thus offers two solutions leading to the reduction of the height of the one-way valve unit and thus also to the reduction of the height of the overall lash adjuster. Here, one of the factors determining the minimum size of the element is the size and shape of the closing body of the one-way valve.

BRIEF DESCRIPTION OF THE DRAWINGS

Two embodiments of the invention are shown in the drawing and are described in more detail below in comparison with a previously known valve train. Shown in each of the Figures in a longitudinal section are:

FIG. 1 is a longitudinal cross-sectional view of a lash adjuster according to the invention in a first construction;

FIG. 2 is a longitudinal cross-sectional view of a lash adjuster according to the invention in a second construction;

FIG. 3 is a longitudinal cross-sectional view of a valve train installed in an internal combustion engine with a previously known lash adjuster;

FIG. 4 is a partial representation in a longitudinal cross-sectional view of the previously known lash adjuster enlarged relative to FIG. 3;

FIG. 5 and FIG. 6 are longitudinal cross-sectional views of the one-way valve of the lash adjuster shown in FIG. 3 and FIG. 4, respectively, in an enlarged representation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The hydraulic lash adjuster 1 shown in FIGS. 3 and 4 according to the previously known state of the art is installed in a valve train 2 of an internal combustion engine 3, which can be actuated via tappet push rods 4. The adjuster 1 is constructed as a switchable cam follower and is comprised of an outer cylindrical section 5, which encloses in its interior 6 an inner cylindrical section 7. The section 7 can move axially relative to the outer section 5 and forms with this outer section a circular cylindrical housing.

The outer section 5 is closed with one end facing a cam 8 of a camshaft and by a base 9. In the area of the base 9 there is a roller 10, whose outer surface is used as a contact surface for the cam 8. The roller 10 is supported on a pin via a roller bearing. This pin is led in the area of the base 9 diametrically through the outer section 5 and fixed there with its end in the outer section 5 by stamping. With its end located outside of the outer section 5, the inner section 7 faces the tappet push rod 4, which here is supported with its end 12 on a dome-shaped bearing surface 11 of the inner section 7.

Hydraulic medium can be led to an outer end of a switching element 13 causing the switching process of the adjuster 1. For this purpose, a channel 14 is provided in the internal combustion engine 3. For achieving a large stroke of a gas-exchange valve 15 of the internal combustion engine 3, wherein said gas-exchange valve is connected to the adjuster 1 via a valve lifter 16 and the tappet push rod 4, the coupling of the outer section 5 to the inner section 7 of the element 1 is required. The switching element 13 is produced as a piston-like slide, which is held in the coupling position by a compression spring.

If it is desired to disconnect the gas-exchange valve 15, then hydraulic medium is led out of the channel 14 in front of the outer end of the switching element 13. If the adjuster 1 is located in its base-circle phase, in which the outer section 5 and the inner section 7 are not fixed relative to each other, then for sufficient pressure of the hydraulic means, the switching element 13 can be displaced radially completely into the inner section 7 against the force of its compression spring. In the subsequent cam stroke, the outer section 5 is then displaced relative to the inner section 7 against the force of a compression spring 17 arranged in the outer section 5. In this case, the tappet push rod 4 and the gas-exchange valve 15 are not displaced, because the force of the compression spring 17 of the outer section 5 is smaller than the counteracting force of a compression spring 20 of the gas-exchange valve 15.

As a hydraulic lash adjuster, the adjuster 1 requires the supply of oil as the hydraulic medium. For this purpose, a feed line 18 is arranged in the tappet push rod 4. Instead of this feed line, however, a feed line for hydraulic medium is also conceivable, which leads in the internal combustion engine 3 into the receptacle space 19 for the outer cylindrical section 5.

The inner cylindrical section 7 of the lash adjuster 1 is a rotationally symmetric housing part. It has a pocket hole, which forms a high-pressure chamber 21. A hollow cylindrical piston 22 is guided with seal lash in the housing part. This has a lower piston head and an upper piston head. Underneath the lower piston head is the high-pressure chamber 21. Above the lower piston head is a low-pressure chamber 23, which is formed by the interior of the piston 22 and which is used as an oil storage space.

The high-pressure chamber 21 is connected to the low-pressure chamber 23 via a central through-opening 24 (FIGS. 5 and 6), which is arranged in the lower piston head. It is part of a one-way valve 27 provided with a closing body 25 and a compression spring 26. This extends into the high-pressure chamber 21 underneath the lower piston head, wherein the through-opening 24 ends at a valve seat 28 of the piston 22 for a sealing contact on the closing body 25 in the closed state of the one-way valve 27. Another compression spring 29 is supported in the high-pressure chamber 21 at its base. It applies force to the piston 22 via a valve cap 30 surrounding the closing body 25 with its compression spring 26.

The lash adjusters according to the invention shown in FIGS. 1 and 2 differ from this previously known element by the modified construction of each one-way valve.

In FIG. 1, the one-way valve 31 has a mushroom-shaped closing body 32. This contacts the valve seat 28 of the piston 22 due to the effect of its compression spring 33 with an approximately spherical, convexly vaulted bearing surface 34 and therefore closes the through-opening 24 of the piston. The compression spring 33, which is arranged with the mushroom-shaped closing body 32 in a corresponding valve cap 35 contacting the piston 22 and which is supported on this cap with one end, surrounds the shaft of the closing body 32 coaxially over part of its length. It has a cylindrical, helical compression spring construction and is supported with its other end on the bottom side of the mushroom head of the closing body 32. In this way, the overall height h₂ of the one-way valve 31 in FIG. 1 is less than the overall height h₁ of the previously known one-way valve 27 in FIG. 5 by the difference h₃.

In FIG. 2, the one-way valve 36 has a dome-shaped closing body 37, which contacts the valve seat 28 of the piston 22 due to the effect of its compression spring 38 with a similarly approximately spherical, convexly vaulted bearing surface 39 and therefore closes the through-opening 24 of the piston. The compression spring 38 is arranged together with the dome-shaped closing body 37 in a corresponding valve cap 40 contacting the piston 22. It is supported on this cap with one end and projects with a part of its length into the dome-shaped closing body 37, with which it is arranged coaxially. With its other end, the compression spring 38 is supported on the inside of the closing body 37 in the area of its vaulted bearing surface 39. In this way, the overall height h₄ of the one-way valve 36 in FIG. 2 is less than the overall height h₁ of the previously known one-way valve 27 in FIG. 6 by the difference h₅.

The present solution was designed as one possible construction for the installation of a switchable tappet for a tappet push-rod motor, but can also be applied in the development of other lash adjusters.

LIST OF REFERENCE SYMBOLS

• 1 Lash adjuster
• 2 Valve train
• 3 Internal combustion engine
• 4 Tappet push rod
• 5 Outer cylindrical section
• 6 Interior
• 7 Inner cylindrical section
• 8 Cam
• 9 Base
• 10 Roller
• 11 Bearing surface
• 12 End of tappet push rod
• 13 Switching element
• 14 Channel
• 15 Gas-exchange valve
• 16 Valve lifter
• 17 Compression spring
• 18 Feed line
• 19 Receptacle space
• 20 Compression spring
• 21 High-pressure chamber
• 22 Piston
• 23 Low-pressure chamber
• 24 Through-opening
• 25 Closing body
• 26 Compression spring
• 27 One-way valve
• 28 Valve seat
• 29 Additional compression spring
• 30 Valve cap
• 31 One-way valve
• 32 Closing body
• 33 Compression spring
• 34 Bearing surface
• 35 Valve cap
• 36 One-way valve
• 37 Closing body
• 38 Compression spring
• 39 Bearing surface
• 40 Valve cap
• h₁ Overall height
• h₂ Overall height
• h₃ Difference
• h₄ Overall height
• h₅ Difference

Claims

1. Hydraulic lash adjuster for a valve train of an internal combustion engine, said hydraulic lash adjuster comprising a circular cylindrical housing in which a piston is arranged for axial displacement, and further comprising a one-way valve comprising a closing body that can be brought to bear against a valve seat of said piston for sealing a through-opening, said closing body being surrounded by a valve cap and loaded by a compression spring that is supported with a first end on the closing body and with a second end on the valve cap, and the closing body has an approximately spherical, convexly vaulted bearing surface for a sealing contact on the valve seat and deviates in shape from a ball shape.

2. Adjuster according to claim 1, wherein the closing body has a mushroom-shaped construction.

3. Adjuster according to claim 1, wherein the closing body has a dome-shaped construction.

4. Adjuster according to claim 1, wherein the compression spring applying a force on the closing body is constructed as a helical compression spring.