Patent Application
20060180110
The invention concerns a hydraulic lash adjuster, typically for a valve train of an internal combustion engine, said hydraulic lash adjuster comprising a hollow cylindrical housing and a pressure piston that are axially inter-inserted for axial displacement relative to each other, a bottom of the pressure piston comprising a central passage for hydraulic medium from a reservoir enclosed by the pressure piston into a high pressure chamber situated between the bottom of the pressure piston and an opposing bottom of the housing, said passage comprising, on an end oriented toward the high pressure chamber, a one-way valve that opens toward the high pressure chamber.
A lash adjuster of a generic type is disclosed in U.S. Pat. No. 6,196,175 B1. This lash adjuster is installed in a switchable roller tappet of a valve train of an internal combustion engine. Through a roller arranged on its housing, the roller tappet is in contact at one end with a cam. At its other end, the roller tappet acts through a support of its pressure piston on a tappet push rod.
A drawback of this prior art roller tappet is that its pressure piston encloses only a relatively small reservoir for hydraulic medium. During a re-suction of hydraulic medium during a base circle phase of the cam and, thus, a lash adjusting phase of the lash adjuster, the partial vacuum forming in the high pressure chamber causes the hydraulic medium column to collapse in the shape of a funnel toward the one-way valve. The lower the height of the hydraulic medium column, the more clearly does this phenomenon manifest itself. In the worst case, it is possible for the air funnel to “sink” completely into the one-way valve. As a result, an undesired re-aspiration of air into the high pressure chamber takes place. These effects occur more frequently after a longer standstill of the internal combustion engine because of the emptying of the reservoir. Such a “break-through” of air into the high pressure chamber is, however, also encountered in so-called “taxi operation” of the internal combustion engine, i.e. during an extreme short-distance operation of the engine.
The undesired accumulation of air in the high pressure chamber of the lash adjuster, which air, moreover, can only be re-evacuated with some amount of difficulty out of the high pressure chamber, results not only in rattling noises but also in wear. Besides this, the air can have a detrimental effect on the gas exchange process.
It is an object of the invention to provide a lash adjuster of the pre-cited type in which a penetration of air from the reservoir into the high pressure chamber can be avoided by simple measures.
This and other objects and advantages of the invention will become obvious from the following detailed description.
The invention achieves the above objects by the fact that a flexible disk-shaped body, that is capable of floating on the hydraulic medium, extends within the reservoir.
This disk-shaped body is made preferably of a thin-walled plastic. It is clear that to guarantee the floating ability of this body, its density must be lower than the density of the hydraulic medium.
The body preferably has a circular geometry. However, it is also conceivable to use general polygonal, rectangular or rounded shapes or edge configurations. The claimed flexibility of the body is not an indispensable condition for implementing the invention. If necessary, it is also possible to use a body that is more or less inflexible.
If the inventive body is used and the hydraulic medium column accumulated in the reservoir tends to collapse in a funnel-shape in the direction of the one-way valve, the body follows the funnel that is being formed and counteracts this.
A person skilled in the art will choose the geometry and the flexibility etc. of the body, so that an undesired re-aspiration of air, as described in the introduction, does not take place. Thus, the undesired effects such as rattling noises, wear etc. are also eliminated.
According to a further feature of the invention, the body itself may also be pre-shaped to have a slight resemblance to a funnel. Thus, in the case of a possible abutment of the body against the upper side of the bottom of the pressure piston, an excellent seal is created for the passage, to that a re-aspiration of air is prevented.
It goes without saying that a criterion for the choice of the material of which the body is made is that this material, for example plastic, must be oil resistant and, at the same time, must be able to resist the prevailing oil temperatures.
As mentioned above, according to a further and particularly advantageous feature of the invention, if the hydraulic medium column in the reservoir happens to sink down completely, the body provided by the invention guarantees a disk valve-type sealing of the passage at its end oriented toward the reservoir. Because the body is closed at all events in the region of its center, at least the re-aspiration of air into the high pressure chamber is avoided despite an absence or deficiency of hydraulic medium in the reservoir.
Preferably, the body extends with its edge near a wall of the reservoir. The body is thus guided by the wall. If necessary, the body may also comprise circumferentially spaced recesses starting from its edge, for example in the shape of fractional cylinders, so that a good transfer of oil is guaranteed in this region.
According to a further feature of the invention, the lash adjuster is installed, for instance, in a switchable or non-switchable roller tappet. The undesired phenomenon of re-aspiration of air into the high pressure chamber can be encountered particularly in switchable elements because of their restricted design space conditions and the resulting relatively small reservoir in the pressure piston.
The measures of the invention are conceivable and intended for use in many types of hydraulic lash adjusters, for example, also in such adjusters as are installed in cup tappets or support elements or are designed as insert elements for lever-type cam followers, or for use in any type of hydraulic length compensators in valve trains, in belt or chain tensioners or the like. If the case arises, any oil foam that may be formed can also be “squeezed away” by means of the inventive body.
The invention will now be described more closely with reference to the appended drawing.
The reservoir 6 communicates with a high pressure chamber 8 situated thereunder through a passage 5 in the region of a bottom 4 of the pressure piston 3. In the direction leading away from the reservoir 6, the high pressure chamber 8 is likewise defined by a bottom 7. This bottom 7 must not necessarily form a part of the housing 2. On a side 9 turned away from the reservoir 6, the bottom 4 comprises a one-way valve 10, configured in the present case as a ball valve. The one-way valve 10 opens in a known manner toward the high pressure chamber 8.
As described in the introductory part of the description, when the amount of hydraulic medium accumulated in the reservoir 6 is insufficient, it is possible (s.
At this point, the measures of the invention, that can be implemented very economically, become effective. To prevent the aforesaid undesired “break-through” of air in the direction of the high pressure chamber 8, it is proposed to let a disk-shaped body 11 float on the hydraulic medium column in the reservoir 6. The body 11 preferably has a flexible configuration and advantageously extends with its outer peripheral surface at a slight distance from a wall 14 of the reservoir 6, so that its centered positioning is assured. If the hydraulic medium column shows a tendency to form a funnel during re-suction, the center of the thin, flexible body 11 follows, so to speak, this funnel, so that re-aspiration of air is effectively prevented.
In the case of an almost complete absence of hydraulic medium in the reservoir 6, the body 11, as disclosed in
| Number | Date | Country | |
|---|---|---|---|
| 60652667 | Feb 2005 | US |
