Patent Application
20060130794
The invention concerns a valve train of an internal combustion engine comprising a tappet and a tappet pushrod that is actuated by said tappet, said tappet pushrod being at least partly hollow and comprising on one end, a first support for an at least indirectly contacting pressure piston of a hydraulic lash adjuster of said tappet that follows a periodic driving element, typically a cam, a second support for a follower member, typically a rocker arm, being arranged on a further end of the tappet pushrod, said first support comprising a passage for hydraulic medium that can be routed out of the pressure piston during operation of the internal combustion engine into an interior of the tappet pushrod.
A valve train of the pre-cited type is disclosed in U.S. Pat. No. 6,196,175 B1. The tappet of this valve train is configured as a switchable roller tappet and is installed in a relatively strongly restricted mounting space, so that only an inadequate quantity of hydraulic medium can be contained in its pressure piston. However, in various situations such as upon re-firing of the internal combustion engine after a longer standstill, “taxi operation” etc., this hydraulic medium proves to be insufficient for a proper lash adjusting operation of the lash adjuster. Therefore, a relatively high risk of a re-aspiration of air into the high pressure chamber of the lash adjuster exists with all the drawbacks, like rattling noises, wear etc., known in the technical field.
Moreover, it is usual in OHV trains comprising a roller tappet and a tappet pushrod to lubricate further components like rocker arms, cam-contacting surfaces etc. that are situated at a high geodetic level, through a hollow tappet pushrod. This is also disclosed in the pre-cited U.S. Pat. No. 6,196,175, while U.S. Pat. No. 3,908,615 likewise discloses a hollow tappet pushrod. Further, U.S. Pat. No. 5,351,662 shows a tappet configured as a roller tappet in which it can be seen that, for design reasons, the hydraulic lash adjuster can contain only a very small quantity of hydraulic medium.
It is an object of the invention to provide a valve train of the pre-cited type in which the aforesaid drawbacks are eliminated.
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 pipette means is installed in the tappet pushrod for retaining, during a standstill of the internal combustion engine, a hydraulic medium column which, as viewed in gravity direction, is situated under the pipette means.
In this way, the initially mentioned drawbacks are effectively eliminated. Thus, when the internal combustion engine is switched off, the oil accumulated in the interior of the tappet pushrod is retained after the principle of a pipette as an additional reserve. When the internal combustion engine is started, this hydraulic medium can flow into the reservoir of the pressure piston.
The corresponding one-way valve body, such as, for example, a ball, a plate, a cone or the like opens immediately upon re-firing of the internal combustion engine due to the then occurring vibrations. Thus, from the very beginning, an adequate quantity of hydraulic medium is available for avoiding the aforesaid rattling noises. Even during so-called “taxi operation”, i.e. during extreme short-distance driving, it is guaranteed that a sufficient quantity of hydraulic medium always accumulates in the reservoir, so that a re-aspiration of air is avoided.
According to a further feature of the invention, the second support of the tappet pushrod, i.e. the support on the rocker arm side also comprises a passage for the hydraulic medium. The pipette means of the invention is preferably intended to simultaneously act as a choke for limiting the flow of hydraulic medium to this passage. Thus only a defined small quantity of hydraulic medium flows to the higher-lever lubrication points while a larger part of the hydraulic medium is available for lash adjustment.
According to still another feature of the invention, a bushing (solid or thin-walled, for example, of sheet metal) comprising the pipette means on one of its collars and the choke on its other collar can be installed in the tappet pushrod. It is clear that the bushing may be arranged at any height in the tappet pushrod, preferably, however, it is arranged at a very high geodetic level so that, after the internal combustion engine is shut off, a sufficiently high hydraulic medium column, retained after the principle of a pipette, is formed under the bushing.
The through-openings on the second support of the bushing may be formed, for instance, by leaf spring-like tongues or by rib-like circumferential projections or the like. It is also conceivable to simply perforate the collar in this region.
It is further proposed to make the tappet pushrod of at least two separate, fabricated sections with a cylindrical part situated therebetween in which the pipette means and the choke are configured. This fabricated embodiment has, for example, the advantage that the tappet pushrod as a whole is simpler to integrate in different surrounding structures. According to a further feature of the invention, a connection between the fabricated sections is achieved through the aforesaid two-piece cylindrical part whose one end comprises the sealing valve seat and whose other end comprises the stop for the closing body which is arranged for slight axial displacement between these ends and is configured, for example, as a ball, a double-taper cone, a plate of the like.
It is clear that such a fabricated tappet pushrod, i.e. a pushrod made up of a plurality of inter-inserted sections can also be generally used even if it does not comprise the pipette means or the choke of the invention.
According to a final proposition of the invention, the supports of the tappet pushrod are configured as ball heads. These can be made separately, but a one-piece configuration with the tappet pushrod is also within the scope of the invention. In place of the ball heads, supports of other configurations such as pan-like or cylindrical shapes etc. will also occur to a person skilled in the art.
The invention will now be described more closely with reference to the appended drawing.
As can be seen from the figures, the tappet pushrod 1 has a generally hollow configuration, so that hydraulic medium can be routed through its interior 11 to the follower member 2. The hydraulic medium is routed out of the space enclosed by the pressure piston 5, through a first passage 10 in the region of the one end 3 of the tappet pushrod 1, the interior 11 of the tappet pushrod 1 and a second passage 13 in the region of the other end 8, to lubrication points on the follower member 2.
As already described above, when the internal combustion engine is turned off, the hydraulic medium column in the pressure piston 5 sinks, under certain circumstances, below an adequate minimum, so that when the engine is re-fired, not enough hydraulic medium for lash adjustment can be re-suctioned into a high pressure chamber of the hydraulic lash adjuster 6. In the most unfavorable of cases, a re-aspiration of air then takes place.
To avoid these serious drawbacks, precisely as can be encountered in the case of very small hydraulic medium reservoirs in confined mounting spaces, it is proposed to arrange a pipette means 12 in the tappet pushrod 1 to retain the hydraulic medium column during a standstill of the internal combustion engine.
As best seen in
As shown in
A closing body 30, configured in the present embodiment as a ball, extends for slight axial displacement between the two parts of the cylindrical part 27. A sealing valve seat 32 for the closing body 30 is formed on an inner end face 31 of the (lower) extension 28. The pipette means 12 is thus created.
A stop 34 comprising a plurality of circumferentially spaced through-openings 35 for the hydraulic medium is formed in the region of an inner end face 33 of the upper part of the two-piece cylindrical part 27. This results in the formation of the choke 14 in this region.
During the operation of the internal combustion engine, i.e. under prevailing hydraulic medium pressure, the closing body 30 is pressed against the stop 34 of the upper part of the cylindrical part 27, so that a small quantity of hydraulic medium can flow past this toward the follower member 2. When the internal combustion engine is shut off, the closing body 30 drops onto its valve seat on the inner end face 31. With this, as already mentioned above, the pipette means 12 becomes effective and the hydraulic medium accumulated in the interior 11 of the tappet pushrod 1 is retained and is available for a rapid re-filling of the reservoir in the pressure piston 5 of the lash adjuster 6 when the internal combustion engine is re-started. The hydraulic medium is released when the closing body 30 lifts off its valve seat 32 as a result of the vibrations that set in as soon as the internal combustion engine is started.
According to
According to
| Number | Date | Country | |
|---|---|---|---|
| 60637273 | Dec 2004 | US |
