Internal-combustion engines – Poppet valve operating mechanism – Tappet
Reexamination Certificate
2000-10-17
2001-11-20
Lo, Weilun (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
Tappet
C123S090370, C123S090460
Reexamination Certificate
active
06318325
ABSTRACT:
The invention relates to a hydraulic valve-play compensation element (HVC). In connection with hydraulic valve play compensation elements, the re-adjustment or an increase in length is accomplished in the presence of play by means of the pressure of the lubricating oil, and a reduction in length caused by a minor flow of leakage oil in conjunction with the cam of the camshaft that compresses the compensating element.
Such a valve-play compensation element is known from DE-OS 38 19 927, where provision is made in connection with a hydraulic valve-play compensation element of the commonly employed type for an additional check valve which, when the engine is at a standstill, is expected to prevent draining of the oil-filled supply chamber located upstream of the high-pressure chamber. However, what is not prevented in this connection is that as long as the play compensation element is loaded by the cam of the camshaft, with the valve in the open condition and the engine standing still, the oil filling of the operating or high-pressure chamber is reduced due to the leakage oil passing through between the cylinder part and the piston part, and the length of the play compensation element is reduced accordingly. This is undesirable in the standstill condition because it leads to increased valve play when the engine is subsequently started.
Another hydraulic valve-play compensation element is known from EP 324085, where during the braking operation of the engine, the re-setting function of the hydraulic valve-play compensation element is to be shut down. For this purpose, the hydraulic valve-play compensation element has a sealed high-pressure chamber and a capillary overflow bore, by way of which the “leakage oil” can drain so as to assure that the length of the hydraulic valve-play compensation element is reduced. During the braking operation of the engine, a valve body actuated by a piston is pressed into the valve seat, whereby both the feed to the high-pressure chamber and also the opening of the capillary overflow bore disposed in the surface of the valve seat are closed. Owing to the fact that the capillary overflow bore feeds directly into the seating surface of the valve, the intention presumably is to prevent the pressure effective in the high-pressure chamber from acting also on the valve body as a whole, and from opening the valve in that way. However, it seems uncertain whether or not this goal is achieved.
The invention is dealing with the problem of providing a hydraulic valve-play compensation element that will not change the adjusted length in the idle position even in the presence of high active forces. Said problem is solved by a hydraulic valve-play compensation element according to the present invention
The basic idea of the invention is to prevent the loss of leakage oil—which is required in connection with valve-play compensation elements for such elements to function from occurring between the cylinder part and the piston part when the engine is at a standstill. According to the invention, this is accomplished in that the leakage oil is admitted into the space located between the check valve of the high-pressure chamber and a second valve. When the engine is at a standstill, this leads to a self-reinforcing sealing function of the second valve. The precondition that needs to be satisfied for this to occur is that the leakage oil cannot drain by any other passageway. Therefore, the gap between the cylinder part and the piston part of the valve-play compensation element has to be sealed in a special way on the other side of the overflow bore, for example by providing for particularly narrow play or for a special seal.
Since the play compensation function would be obstructed if a sealed space were created from which the leakage oil cannot escape, it has to be assured for the operation of the engine that the leakage oil is capable of escaping. This is accomplished according to the invention in that the second valve on the supply side is opened and kept open during the operation of the engine by means of a piston that is actuated by a defined force.
By designing the actuating piston as a component through which the lubricating oil is flowing, it is possible to achieve a space-saving design as compared to the hydraulic valve-play compensation element shown in EP 324085.
REFERENCES:
patent: 4633827 (1987-01-01), Buente
patent: 4977867 (1990-12-01), Rhoads
patent: 12 36 857 (1967-03-01), None
patent: 36 35 110 (1987-04-01), None
patent: 38 19 927 (1989-01-01), None
patent: 42 25 012 (1993-07-01), None
patent: 93 18 108 (1994-01-01), None
patent: 03 24 085 (1989-07-01), None
patent: 01 232103 (1989-09-01), None
Collard & Roe P.C.
Lo Weilun
Mahle Ventiltrieb GmbH
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