Internal-combustion engines – Poppet valve operating mechanism – Hydraulic system
Reexamination Certificate
2000-05-11
2001-11-27
Lo, Weilun (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
Hydraulic system
C123S19800E
Reexamination Certificate
active
06321702
ABSTRACT:
PRIOR ART
The invention is based on a process for controlling a gas exchange valve for internal combustion engines. In a device of this kind, which has been disclosed by DE 195 11 320 and is for controlling a gas exchange valve, the gas exchange valve has an axially movable valve member which, on its end close to the combustion chamber, has a valve sealing face that it uses to cooperate with a stationary valve seat in order to control an inlet or outlet cross section at the combustion chamber of the engine. On its end remote from the combustion chamber, the valve member of the gas exchange valve has a working piston which, with its axial end faces, defines two hydraulic working chambers, of which an upper working chamber further from the combustion chamber can be alternatingly filled with a pressure fluid and discharged, and which consequently acts on the valve member of the gas exchange valve in the opening or closing direction counter to a constant closing force acting on the underside of the piston. The constant closing force on the valve member piston is assured through the fact that the lower working chamber close to the combustion chamber constantly communicates with a high pressure fluid source.
The known control device, however, has the disadvantage that it is operated with a constant pressure fluid supply pressure. This supply pressure must thereby be chosen to be at least high enough to achieve the necessary valve adjusting dynamics at the maximum speed and load of the engine as well as at low temperatures and consequently a low viscosity of the hydraulic fluid. These operating states in the engine to be fed, however, only occur temporarily in actual vehicle operation so that most of the time, an unnecessarily high pressure fluid supply pressure has to be maintained. However, since this pressure contributes directly to the power consumption of the overall vehicle system, it also impairs the overall efficiency of the engine to be fed.
Advantages of the Invention
The process according to the invention for controlling a gas exchange valve for internal combustion engines has the advantage over the prior art that the supply pressure of the valve control device is only brought to the maximum level required for the extreme boundary conditions when such a high supply pressure is actually required by the current operating parameters of the engine to be fed. The pressure fluid supply pressure produced to actuate the gas exchange valve member advantageously changes and adjusts as a function of the current operating parameters of the engine to be fed during its operation. In this manner, over broad operating cycles of the engine to be fed, it is possible to operate the valve control device with a reduced pressure that is sufficient for the normal everyday operation of vehicle engines. In this everyday operation, vehicle engines are for the most part operated at an operating temperature and in an average speed and load range in which the demands on the dynamics of the hydraulic valve control system are significantly lower than in high-stress operating states, e.g. at high speed, high load, and low temperatures. In this connection, however, the continuous variable adjustment of the supply pressure of the valve control system also assures the reliable operation of the valve control device even in the high-stress operating states of the engine that require a high pressure fluid supply pressure.
Since the supply pressure to be supplied by the high pressure pump for the valve control system contributes directly to the power consumption of the engine, a pressure reduction that is dependent on the current operating state of the engine leads directly to an energy savings in comparison to the known valve control system that has a constant supply pressure.
In this connection, the variable changing of the supply pressure level is alternatively possible by means of two strategies, wherein with a first strategy, the valve control system pressure is changed smoothly as a function of the operating parameters of the engine, e.g. the temperature, speed, and load. In this connection, it is particularly advantageous to execute the adjustment of the supply pressure level by way of a characteristic diagram stored in an electric control unit.
A second alternative strategy for the variable control of the supply pressure level is the smooth switching between different pressure levels as a function of the temperature, speed, and load of the engine to be fed. The number of pressure stages in this connection is initially variable, but an optimal design must be adapted to the respective engine. It is particularly advantageous to provide two pressure level stages, the first of which covers the lower to middle operating state of the engine and the second covers the high pressure level for the high-stress operating states. In order to prevent an excessively frequent switching back and forth between adjacent pressure levels, a hysteresis function is provided in their boundary regions.
A high pressure pump that can be regulated is advantageously used as a pressure supply device and this pump can be driven directly by the engine and at a speed synchronous to the engine so that the delivery volume of the pump already increases automatically with the speed of the engine. Alternatively, however, it is also possible to execute the regulation of the high pressure pump on the suction side, for example, by means of an adjustable suction throttle, or on the pressure side by means of corresponding pressure valves.
The valve control device advantageously has a hydraulic adjuster in which a piston connected to the gas exchange valve defines at least one hydraulic working chamber. This hydraulic working chamber can be alternately filled with a highly pressurized pressure fluid and discharged, wherein the filling and discharging of the working chamber takes place by means of control valves in a supply line or discharge line, as a function of operating parameters of the engine. The adjusting force acting on the piston of the hydraulic adjuster from the side of the hydraulic working chamber is counteracted by a constant opposing force directed in the closing direction of the gas exchange valve member. This constantly present closing force can be produced hydraulically or mechanically. The mechanical production of this force takes place by means of springs, while the hydraulic opposing force is produced through the provision of a second hydraulic working chamber which engages the adjusting piston of the gas exchange valve member in opposition to the first hydraulic working chamber. In the exemplary embodiment described, this second hydraulic working chamber that acts in the closing direction advantageously communicates continuously with the high pressure fluid supply line so that the high pressure of the hydraulic adjusting medium continuously prevails in this chamber. Alternatively, it is also possible to produce the adjusting motion in the piston of the gas exchange valve member by means of alternately filling the two hydraulic working chambers in the adjusting piston with a pressure fluid.
Other advantages and advantageous embodiments of the subject of the invention can be inferred from the specification, the claims, and the drawing.
REFERENCES:
patent: 4009695 (1977-03-01), Ule
patent: 4930464 (1990-06-01), Letsche
patent: 4930465 (1990-06-01), Wakeman et al.
patent: 5572961 (1996-11-01), Schechter et al.
patent: 05-202712 (1993-08-01), None
Beuche Volker
Diehl Udo
Franzl Stefan
Mischker Karsten
Reimer Stefan
Greigg Ronald E.
Lo Weilun
Robert & Bosch GmbH
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