Internal-combustion engines – Poppet valve operating mechanism – Hydraulic system
Reexamination Certificate
2000-02-14
2001-11-27
Lo, Weilun (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
Hydraulic system
Reexamination Certificate
active
06321703
ABSTRACT:
PRIOR ART
The invention is based on device for controlling a gas exchange valve for internal combustion engines as set forth here in after. In a control device of this kind, which has been disclosed by DE 195 11 320, a piston-shaped valve member is guided so that the valve member can be axially moved in a housing, wherein on an end close to the combustion chamber, the valve member has a disk-shaped valve sealing face which cooperates with a valve seat fixed to the housing, in order to control an inlet or outlet cross section on the combustion chamber of the engine to be fed. On a shaft end remote from the combustion chamber, the valve member has a hydraulic piston which axially separates two hydraulic working chambers from each other. The lower working chamber closer to the combustion chamber acts on the valve member of the gas exchange valve in the closing direction and an upper working chamber further from the combustion chamber acts on the valve member in the opening direction. In this connection, the lower working chamber continuously communicates with a high pressure source by way of a high pressure supply line and is consequently acted on with high pressure. The upper working chamber can be alternatingly filled with high pressure by way of a high pressure supply line containing an electric control valve and discharged by way of a discharge line that contains another electric control valve. The gas exchange valve is then actuated by means of the controlled filling of the upper working chamber. When the control valve in the high pressure supply line is open, a highly pressurized pressure fluid flows into the upper working chamber. The pressure engagement area on the piston of the valve member of the gas exchange valve is greater than the pressure engagement area in the lower working chamber so that the piston and the valve member together are moved downward in the opening direction and thus open the opening cross section at the valve member seat. The discharge line of the upper working chamber is closed in the meantime by the second control valve. Through the deliberate opening of the control valves in the high pressure supply line and the discharge line at the upper working chamber of the gas exchange valve member, it is then possible to produce different opening positions and to move the gas exchange valve member back onto its valve seat again by opening the control valve in the discharge line.
The known control device for gas exchange valves, however, has the disadvantage that in the event of a failure of the pressure supply system, the valve member can remain in its open valve member position so that there is the danger of the gas exchange valve member colliding with the piston of the engine in the top dead center of this piston. This can lead to the jamming of the entire valve assembly and to extremely serious mechanical damage to the engine itself and also jeopardizes the safety of the vehicle passengers due to the possible locking of the drive axles in the driven vehicle.
ADVANTAGES OF THE INVENTION
The device according to the invention for controlling a gas exchange valve for internal combustion engines has an advantage over the prior art that a hydraulically actuatable valve adjuster concept is produced which, even in the event of a failure of the pressure supply device or the electrical triggering of the control valves, reliably prevents the gas exchange valve member from jamming in the open position and assures a return of the valve member to its closed position. According to the invention, three safety measures that are independent of one another are proposed, which can be realized individually, but for safety reasons, only represent an optimal safety concept when they are used together.
A first measure is realized according to the invention by virtue of the fact that the electric control valves, which are disposed in the high pressure supply line and in the discharge line of the upper working chamber that produces the opening movement of the gas exchange valve member, are switched into the currentless state so that the upper working chamber against the piston of the gas exchange valve member is pressure relieved. When the lower working chamber, which acts on the gas exchange valve member in the closing direction, is continuously connected to the high pressure supply line, it is consequently assured that the valve member is held securely in contact with the valve seat when the control valves are without current. The hydraulic working chamber responsible for the opening stroke motion of the gas exchange valve member can be filled with high pressure only when the electric control valves are supplied with current so that the gas exchange valve can only be triggered when the on-off valves are functioning perfectly. When there are electrical problems, for example in the event of a cable deterioration with regard to the actuator, short circuits in the control lines, etc., it is sufficient to switch the control valves or their triggering devices into the currentless state. It is particularly advantageous that two independent actions are required to move the gas exchange valve member into the critical open position, namely the active closing of the electric control valve in the discharge line and the opening of the electric control valve in the high pressure supply line. Since the working chamber responsible for the closing motion of the valve member of the gas exchange valve continuously communicates with the high pressure supply line, there is no electric component that can fail in the path responsible for the closing.
The electric control valves are advantageously embodied as solenoid valves, which are triggered by an electric control unit as a function of operating parameters of the engine to be fed.
Another possibility according to the invention for moving the gas exchange valve member into its closed position in the event of a failure of the control device is achieved through the provision of an emergency reservoir that is connected directly to the lower hydraulic working chamber responsible for the closing motion. This emergency reservoir, which is preferably embodied as a spring reservoir, only stores the volume of high pressure fluid required to move the gas exchange valve member into its closed position. The valve control device can also be provided with another working chamber, which is likewise preferably embodied as a spring pressure reservoir and is particularly used to maintain a preset standing pressure in the control device. This working pressure reservoir is preferably intended to compensate for a possible leakage loss during the shutting off of the engine to be fed and also to maintain a standing pressure which assures a reliable function of the control device immediately with the beginning of the operation of the engine. Furthermore, the working pressure reservoir produces a smoothing of the pressure fluctuations in the system during operation so that the working pressure reservoir requires a stronger restoring moment than the emergency reservoir and therefore has a higher spring force than the emergency reservoir so that the two spring reservoirs operate at different pressure levels.
In order to prevent a drainage of reservoir pressure in the high pressure supply of the control device, a check valve is also provided in a high pressure supply line from a pressure supply device. The valve opens in the direction of the gas exchange valve member and is followed in the flow direction by the pressure reservoir and a branch line into the lower working chamber.
Another check valve is advantageously inserted into the discharge line.
Another measure for reliably restoring and holding the gas exchange valve member in the non-critical closed position is achieved through the provision of a mechanically acting restoring element, preferably an emergency spring on the gas exchange valve member. In the event of a failure of the entire pressure supply system and a pressure drop as well in the hydraulic working chambers against the piston of the valve member, this v
Beuche Volker
Diehl Udo
Franzl Stefan
Mischker Karsten
Reimer Stefan
Greigg Ronald E.
Lo Weilun
Robert & Bosch GmbH
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