Electricity: electrical systems and devices – Control circuits for electromagnetic devices – Including compensation for thermal change of electromagnetic...
Reexamination Certificate
2000-12-15
2001-12-25
Ballato, Josie (Department: 2836)
Electricity: electrical systems and devices
Control circuits for electromagnetic devices
Including compensation for thermal change of electromagnetic...
C361S078000, C361S139000, C361S140000, C361S143000, C361S152000, C361S153000, C361S154000, C123S090110
Reexamination Certificate
active
06333843
ABSTRACT:
BACKGROUND OF THE INVENTION
An electromagnetic actuator for operating a cylinder valve in a piston-type internal-combustion engine essentially comprises two spaced electromagnets, whose pole faces are oriented toward one another. An armature connected to the cylinder valve to be actuated is guided back and forth between the pole faces against the force of restoring springs. When the armature is at rest, it is located in its center position between the two pole faces. As the two electromagnets are alternatingly energized, the armature arrives into contact with the pole face of the momentarily energized (capturing) electromagnet against the force of a restoring spring. If the holding current force of the restoring spring accelerates the armature in the direction of the other electromagnet which is energized with a capturing current during the armature movement. As a result, after overshooting the center position, the armature arrives into contact with the other, capturing electromagnet against the force of the restoring spring associated with the last-mentioned electromagnet. One of the electromagnets serves as a closing magnet holding the cylinder valve in a closed position against the force of the opening spring (that is, one of the restoring springs), while the other electromagnet serves as an opening magnet holding the cylinder valve in an open position against the force of the associated closing spring (that is, the other restoring spring).
To start an electromagnetic actuator of the above-described type, the two electromagnets are alternatingly supplied with current at the known resonant frequency of the spring-mass system which is composed of the restoring springs, the armature and the cylinder valve. The current supply at the resonant frequency is effected until the armature comes to rest at one of the electromagnets. By means of suitable data inputted in an engine control unit (ECU) which controls the energization of the two electromagnets, the oscillation-startup process may be terminated in such a manner that the armature comes to rest at a predetermined electromagnet, typically the closing magnet. In a multi-cylinder piston-type internal-combustion engine, the cylinder valves of the individual cylinder, or groups of cylinders, are brought into the closed position in this way by the oscillation startup, so that the individual cylinder valves can be actuated from the closed position to start the engine in the predetermined ignition- and work-cycle sequence.
To regulate the current supply, a sensor assembly responds as the armature approaches the capturing electromagnet, particularly to reduce the capturing current shortly before the armature impacts on the pole face of the capturing electromagnet. For this purpose a control signal may be emitted when the armature reaches a predetermined position relative to the pole face, or the traveled path is detected or, by derivation, the speed is determined or the speed is directly sensed. These approach-dependent values can be utilized by the engine control unit to reduce the capturing current such that the armature impacts the pole face gently, that is, with a speed slightly above “zero”. As a result, the respective electromagnet has to be supplied only with a low holding current.
The above-outlined normal oscillation-startup method and normal operation, however, cannot be performed if at the engine, and particularly at the electromagnetic actuator, a low temperature level prevails. Such a low temperature, for example, appreciably increases the viscosity of the lubricating oil and/or changes the fit and thus increases the friction between the moving parts of the spring-mass system due to the heat-caused expansion of materials. A low temperature level in terms of the invention would be, for example, 0° C.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE METHOD ACCORDING TO THE INVENTION
It is an object of the invention to provide a problem-free startup and operation of an electromagnetic actuator
According to an embodiment of the invention, this object is accomplished in that a reference temperature is detected for the electromagnets, and, in case of a normal temperature level, the armature is caused to start oscillation in the resonant frequency by an alternating energization of the electromagnets and is brought into engagement with a predeterminable pole face, preferably the pole face of the closing magnet. Or, in case of a low temperature level, a high current pulse is applied to one of the electromagnets, preferably the closing magnet.
The temperature of the cooling water or the oil of the piston-type internal-combustion engine can be predetermined as a reference temperature, or the solenoid temperature can be measured directly. Thus, it is feasible to use two different start strategies for engine startup, namely a startup oscillation at a normal temperature, or directly attracting the armature to the pole face of an electromagnet at a low temperature with a relatively high energy input.
To minimize the high current consumption in the cold-start strategy, an embodiment of the invention provides that the level of the high-current pulse is preset as a function of the level of the reference temperature. Such a procedure has the advantage that in an intermediate range between low and normal temperatures, in which the current supply is still controlled according to the cold-start strategy, not only the current consumption is reduced, but also the high impact energy can already be cut back.
A further embodiment of the invention provides that the current level of the electromagnet to which the high-current pulse is applied is controlled as a function of the approach of the armature toward the pole face in order to reduce the impact energy. Consequently, even in cold-start operation, despite the high current pulse and the associated high magnetic force that rapidly moves the armature toward the pole face, the impact energy can already be reduced during such approach by a reduction in the current level of the current pulse that is applied over a specific switching period. As a result, the restoring force of the restoring spring becomes more effective, and the armature impacts gently on the pole face. The method can also be modified such that the duration of the current pulse is controlled as a function of the armature approach, that is, the applied high-current pulse is cut off before the armature impacts the pole face. Such a moment can be ascertained based on the displacement and/or speed information of the sensor assembly.
A further embodiment of the invention provides that heat energy is supplied to at least one electromagnet of the electromagnetic actuator when a low temperature level is detected. The heat energy may be supplied to the electromagnet by a heating current. When a direct current is used as the heating current, however, ohmic losses must be taken into account. It is therefore advantageous to use a high-frequency alternating current as the heating current in order to generate eddy current-caused losses in the magnet yoke, the armature and the armature-guide bar, whereby the arrangement is heated by eddy currents. It is advantageous for the two electromagnets to be supplied alternatingly with a heating current to attain a uniform heating of the two electromagnets and to avoid local overheating.
Another embodiment of the invention provides that heat energy is alternatingly supplied to the two electromagnets as the armature moves slightly. In this procedure, an alternating current supply to the magnets causes the armature to move slightly, so that the guides heat up due to friction. The current supply may (but need not) be effected at the resonant frequency.
According to a further embodiment of the invention, at least one of the electromagnets is supplied with a current in the form of a start pulse. Further, depending on the initial movements of the armature as detected by the sensor, the subsequent supply of current to the electromagnets is controlled according to the normal startup-oscillation. Or, energization for th
Boie Christian
Feyerl Günter Rudolf
Kather Lutz
Schmitz Gunter
Staay Frank Van Der
Ballato Josie
FEV Motorentechnik GmbH
Kelemen Gabor J.
Marquis Vaughn
Venable
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