Internal-combustion engines – Poppet valve operating mechanism – Electrical system
Reexamination Certificate
2001-07-10
2002-11-19
Denion, Thomas (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
Electrical system
C123S090560, C251S129150
Reexamination Certificate
active
06481395
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a device for actuating a gas exchange of an internal combustion engine including a hydraulic compensating structure.
Electromagnetic actuators for actuating the gas exchange valves generally have two operating magnets—one opening magnet and one closing magnet between whose pole faces an armature is arranged such that it can be displaced coaxially with the valve axis. The armature acts on a valve stem of the gas exchange valve either directly or via an armature tappet. In the case of actuators according to the principle of the mass oscillator, a prestressed spring mechanism acts on the armature. Usually, two prestressed valve springs, an upper valve spring of which biases the gas exchange valve in the opening direction and a lower valve spring of which biases the gas exchange valve in the closing direction, are used as the spring mechanism. When the magnets are not energized, the armature is held by the valve springs in a position of equilibrium between the two magnets. The valve springs can be arranged together on one side or separately from each other on opposite sides of the actuator.
When the actuator is first activated, either the closing magnet or the opening magnet is briefly overexcited or the armature is excited at its resonance frequency by an oscillation excitation routine, in order to move the armature out of the position of equilibrium. In the closed position of the gas exchange valve, the armature bears against the pole face of the energized closing magnet and is held by it. The closing magnet compresses further the valve spring, which acts in the opening direction. In order to open the gas exchange valve, the closing magnet is deenergized and the opening magnet is energized. The valve spring which acts in the opening direction then accelerates the armature beyond the position of equilibrium, with the result that the latter is attracted by the opening magnet. The armature impacts against the pole face of the opening magnet and is held firmly by the pole face. In order to close the gas exchange valve again, the opening magnet is deenergized and the closing magnet is energized. The valve spring which acts in the closing direction accelerates the armature beyond the position of equilibrium toward the closing magnet. The armature is attracted by the closing magnet, impacts on the pole face of the closing magnet and is held firmly by the latter. The two valve springs are compressed to such an extent that, when the operating magnets are deenergized, the armature moves to an approximately central position between the pole faces of the operating magnets, and that at the same time, in, or shortly before, the closing position of the gas exchange valve a residual closing force from the lower valve spring acts on the gas exchange valve.
Variables which have not been taken into consideration from the beginning or which change over time, for example manufacturing tolerances of individual components, thermal expansions of different materials, differing spring stiffnesses of the upper and lower valve springs on account of manufacturing tolerances, and also settling phenomena because of aging of the valve springs etc, may result in a position of equilibrium not coinciding with an energetic central position between the pole faces or not having a predetermined position, as this position is determined by the valve springs. Furthermore, variables of this type and wear on the valve seats may lead to the armature not bearing with a constant closing force against the pole face of the closing magnet or already bearing against it before the gas exchange valve is completely closed. Hot combustion gases, which escape past valves that are not tightly closed, destroy the valve seats. Also, different thermal expansions may cause the armature to no longer bear completely against the pole face of the closing magnet when the gas exchange valve is closed. As a result, the energy requirement of the closing magnet sharply increases. Furthermore, this process is generally associated with a reduced opening stroke of the gas exchange valve, with the result that the throttling losses increase during the charge cycle and the efficiency deteriorates.
If the gas exchange valves are actuated by a camshaft, thermal expansions, seat-ring deflection, settling phenomena because of aging of the valve springs etc. may likewise lead to the gas exchange valve not closing completely.
An earlier application DE 19 647 305 C1, illustrates an electromagnetic actuator which is mounted in a floating manner in a cylinder head. The said actuator opens and closes a gas exchange valve, while an armature is moved between two electromagnets and, in the process, acts on a valve stem of the gas exchange valve. A spring mechanism is arranged between the actuator and the valve disc of the gas exchange valve, with the upper opening spring being supported on the actuator and the lower closing spring on the cylinder head. A play-adjusting element which compensates for both a positive and a negative valve play is situated between a cover plate, which is connected to the cylinder head and the actuator on the side which faces away from the gas exchange valve.
The play-adjusting element has a piston in a cylinder. The piston separates a first pressure space, which faces away from the gas exchange valve and is controlled as a function of the internal combustion engine from a second pressure space, which faces the gas exchange valve. When there is excessive pressure in the first pressure space, a non-return valve in the piston opens in the direction of the second pressure space counter to the force of a holding spring. The holding spring is designed in such a manner that the non-return valve does not open if there is no play.
The gas exchange valve should always close securely. In order to achieve this, the play-adjusting element has the tendency to constantly slowly become shorter. This is achieved by a leakage area, which is formed by a defined play between the piston and the cylinder. When load is applied, pressure medium flows from the second pressure space into the first pressure space via the leakage area. If the armature no longer comes sufficiently close to the closing magnet or if a play arises between the armature tappet and the gas exchange valve because the play-adjusting element has become far too short, rapid adjustment in the opposite direction has to take place, which is achieved by the non-return valve opening. The pressure in the second pressure space drops below that of the first pressure space, so that the non-return valve opens towards the holding spring and pressure medium flows from the first pressure space into the second pressure space until the play has been compensated. This process may last for a number of working cycles of the valve.
The iterative process providing for rapid and slow adjustment has the effect that the gas exchange valve moves continuously within an optimum play-setting range. However, when the actuator is switched off, the armature is set by the valve springs to a position of equilibrium between the two magnets. In this case, a force of the valve springs acts on the second pressure space via the actuator. The pressure in the upper pressure space, which is controlled as a function of the internal combustion engine, drops and pressure medium is discharged from the second pressure space via the leakage area between the piston and the cylinder. The play-adjusting element collapses and the actuator is displaced upwards in the direction facing away from the gas exchange valve. As a result, the position of equilibrium of the valve springs is changed. After a renewed start of the actuator, the second pressure space of the play-adjusting element has to be filled, the actuator has to be displaced in the direction of the gas exchange valve and the position of equilibrium of the valve springs set to its correct value. This process may last for a number of working cycles of the gas exchange valve and may, in particular, lead to noises, unnecessary wear and
Gaisberg Alexander von
Kreitmann Fritz
Müller Hagen
Bach Klaus J.
Chang Ching
Daimler Chrysler A.G.
Denion Thomas
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