Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
2002-01-15
2004-08-10
Huynh, Hai (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel injection system
C123S090110, C251S129180, C239S585100
Reexamination Certificate
active
06772737
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and a circuit system for operating a solenoid valve, particularly for actuating an electrohydraulic gas-exchange valve control, an injection valve, or an intake or exhaust valve of an internal combustion engine.
BACKGROUND INFORMATION
The electrohydraulic gas-exchange valve control of an internal combustion engine for the camshaft-free actuation of the gas-exchange valves of the internal combustion engine is conventional. Each gas-exchange valve of an electrohydraulic gas-exchange valve control has a separate actuator for the opening and closing. The actuator has a control element which is subdivided in the interior by a hydraulic differential piston into a first chamber and a second chamber. A first solenoid valve is arranged on the intake side of the first chamber, and a second solenoid valve is arranged on the outlet side of the first chamber. Three phases are differentiated in response to the actuation of the electrohydraulic gas-exchange valve control:
In a first phase, the second solenoid valve is initially closed. Directly after that, the first solenoid valve is opened. Oil can flow with a high pressure from the supply side via the first solenoid valve into the first chamber of the control element. The closed second solenoid valve prevents the oil from flowing out of the first chamber toward a tank. A comparable pressure prevails in the first chamber as in the second chamber. The side of the differential piston facing the first chamber has a substantially larger effective area than the side facing the second chamber. A resulting force causes an opening movement of the gas-exchange valve.
In a second phase, the gas-exchange valve is held statically open at full stroke or partial stroke. To that end, the first solenoid valve is closed, so that both solenoid valves are closed for the inlet or outlet of oil.
In a third phase, the second solenoid valve is opened while the first solenoid valve continues to be closed, so that the oil which has flowed into the first chamber can flow off again. The pressure in the first chamber diminishes very sharply compared to the pressure in the second chamber, resulting in a closing movement of the gas-exchange valve.
It is also conventional to provide a plurality of intake and exhaust valves per cylinder of an internal combustion engine. For example, when working with 4-valve technology, each cylinder has two intake valves and two exhaust valves for the gas exchange. Therefore, given one actuator per gas-exchange valve and two solenoid valves per actuator, eight solenoid valves are needed for each cylinder. Thus, in the case of a four-cylinder internal combustion engine,
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solenoid valves result, which must be electrically driven.
For the electrical driving of the solenoid valves, German Published Patent Application No. 40 24 496 describes applying a pull-up voltage to a solenoid valve in a pull-up phase and to apply a lower holding voltage in a subsequent holding phase. So that the holding current in the holding phase does not exceed a specific limiting value, arranged in the holding-current circuit is a current sensing element which adjusts the level of the holding voltage as a function of the ascertained actual value of the holding current and a setpoint value of the holding current.
In addition to the actual current value detection, a current regulator is also necessary for each current control loop. This relatively high circuitry expenditure for regulating current would have to be provided for each individual solenoid valve of an electrohydraulic gas-exchange valve control. This would result in an enormously high circuitry expenditure for actuating an electrohydraulic gas-exchange valve control of an internal combustion engine.
It is therefore an object of the present invention to simplify the triggering of a solenoid valve without thereby impairing the performance reliability of the solenoid valve.
SUMMARY
To achieve this objective, the method for operating a solenoid valve according to the present invention provides that the solenoid valve is acted upon in a controlled manner in a cycle including three phases: in a pull-up phase, the solenoid valve is connected for a predefined time duration to a first voltage of predetermined magnitude for generating a pull-up current; in a holding phase, the solenoid valve is connected to a second voltage of predefined magnitude for generating a holding current; and in a de-energize phase, the solenoid valve is separated from both voltages.
In the pull-up phase, the armature of the solenoid valve may be pulled up as quickly as possible. This is achieved by a current overshoot. To that end, the magnetic coil of the solenoid valve is connected for a predefined time duration to the first voltage. The first voltage is considerably higher than, for example, a system voltage of a motor vehicle, e.g., than the voltage of the vehicle battery, for instance. Therefore, the operation of the solenoid valve during the pull-up phase with the high first voltage is a so-called boost operation. The high first voltage produces a particularly rapid buildup of the pull-up current in the magnetic coil. The time duration is selected so that the armature current necessary for rapidly and reliably pulling up the armature is reached.
During the holding phase, the pulled-up armature of the solenoid valve is retained by a reduced, constant holding current. Because of the magnetic-field characteristic, a considerably smaller force, and therefore a smaller current than for pulling up the armature is sufficient for holding the armature. During the holding phase, the magnetic coil of the solenoid valve is connected to the second voltage of predefined magnitude. The second voltage has a lower magnitude than the first voltage. The supply of the electromagnet by the second voltage ensures a constant holding current through the magnetic coil (regardless of fluctuations in the voltage of the vehicle electrical system).
In the de-energize phase, the electromagnet of the solenoid valve is separated from both voltages. As a result, after a decay phase, no current flows any longer through the electromagnet, and the armature returns to its starting position. During the decay phase, the current may be allowed to decay in different ways (e.g., diode extinction, Zener diode extinction, R-C extinction). In addition, the energy decayed during the decay phase may be recovered in various manners.
The method of the present invention does not provide a closed-loop control, but merely an open-loop control of the current of the solenoid valve. The current of the solenoid valve results by applying a voltage of predefined magnitude to the solenoid valve, because of the resistance of the magnetic coil of the solenoid valve. This holds true both in the pull-up phase and in the holding phase of the solenoid valve.
According to the present invention, it is possible to dispense with a current measurement, directly via a current-measuring element or indirectly via a voltage divider, which is formed by a measuring resistance and the resistance of the magnetic coil of the solenoid valve, and to dispense with a closed-loop current control by a current regulator. The operation of the solenoid valve is thereby simplified. In a simple manner, the method according to the present invention permits exact triggering of all solenoid valves of an electrohydraulic gas-exchange valve control of an internal combustion engine. A closed-loop current control for each of the solenoid valves is replaced in the method according to the present invention by an exact triggering as a function of time, at precisely defined supply voltages.
A voltage correction may be used to compensate for the effects of relevant changes in the branch circuits on the current flowing through the magnetic coils. Relevant changes in the branch circuits are, for example, the change of the coil resistance of the magnetic coil of a solenoid valve because of temperature changes in the magnetic coil. However, such a temperature compensati
Beuche Volker
Diehl Udo
Gaessler Hermann
Grosse Christian
Liskow Uwe
Huynh Hai
Kenyon & Kenyon
Robert & Bosch GmbH
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