Internal-combustion engines – Spark ignition timing control – Electronic control
Reexamination Certificate
2004-05-18
2004-11-30
Mohanty, Bibhu (Department: 3747)
Internal-combustion engines
Spark ignition timing control
Electronic control
Reexamination Certificate
active
06823841
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
This application claims the priority of German patent document 101 21 993.8, filed 5 May 2001 (PCT International Application No.: PCT/EP02/04017), the disclosure of which is expressly incorporated by reference herein.
The invention relates to a hybrid ignition system for internal combustion engine having 14 V or 42 V on-board power system voltages with a timed and current-controlled ignition stage having two operating phases.
In ignition systems of this type, during a first phase, a self-induction voltage for the spark breakdown is generated from the energy stored in the magnetic field of the ignition transformer. In a second phase, the ignition system with timed control of the ignition stage and superimposed current limitation generates an alternating voltage for the ignition spark so that the ignition spark is fired without interruption even when there is an increased requirement for firing voltage due to gas flowing at the spark location. The hybrid ignition system does not require any intermediate power unit.
The invention is based on an ignition system such as is described, for example, in German patent document DE 197 00 179 C2 from Bosch, which operates according to the resonant converter principle. A typical design contains an intermediate power unit which steps up the on-board power system voltage of the on-board power system generator to values on the order of magnitude of 200 V on the primary side of the ignition transformer (which is embodied as a resonant converter). A semiconductor power output stage is actuated using a control device and the current on the primary side of the ignition transformer is interrupted when a predefined, variable switch-off current is reached. The current on the secondary side of the ignition transformer corresponds to the spark current and results from the transmission ratio of the ignition transformer, specifically essentially from the primary current, the coupling factor of the ignition transformer and the square root of the ratio of the inductances on the primary side and the secondary side.
Alternating current ignition systems have the advantage over capacitively or purely inductively operating ignition systems that the ignition energy from the intermediate power unit is transmitted continuously to the ignition spark. The maximum firing period of the ignition spark is determined by the maximum power of the intermediate power unit of the ignition system. By combining spark ignition and ion current measuring technologies, closed control circuits are obtained which make it possible for the entire ignition process including the spark plug and ignition spark to be continuously monitored and operated with the smallest possible spark current, and thus lowest possible degree of spark plug erosion.
Previously described alternating current ignition systems have the disadvantage of requiring a power unit, for generating an intermediate voltage of approximately 200 V, and a resonant converter as an ignition stage. The power unit and the resonant converter give rise to additional manufacturing and installation costs.
One object of the present invention therefore, is to provide a suitable ignition system that does not require an intermediate power unit or a resonant converter, and achieves the advantages of alternating current ignition systems.
German patent document DE 42 26 246 A1 discloses an ignition system for an internal combustion engine with subsequent spark ignition. Pure current control is carried out without timed control of the switch on and switch off times. In the process spark pauses and subsequent spark ignition occur.
German patent document DE 198 40 765 A1, on the other hand, discloses a method and a circuit arrangement for an ignition system of an internal combustion engine, in which resonant ignition with a preceding self induction phase is carried out without any mention of current control or timed control.
Finally, German patent document DE 24 44 242 A1 discloses an ignition system for an internal combustion engine which generates an ignition spark or a light arc of a predefined, relatively prolonged duration for each engine cylinder and has the capability of igniting again at successive times during such a period. In the process, timed control of the primary current is carried out with superimposed current control. The latter is carried out only in each case for the first time period, and is maintained without modification during the entire ignition enable time. 500 &mgr;s are provided for the first and second time periods (switch on and switch off times) so that the ignition can operate advantageously. In addition, the limiting resistance of 30 k&OHgr; is provided in the spark plug circuit owing to the long switch on time.
However, in such ignition systems, a long switch on time and a limiting resistance are necessary in the spark plug circuit, with the result that the circuit design is more complex and costly.
Accordingly, another object of the present invention is to provide an ignition system of the generic type which is of relatively simple design, and in which a switch-on time is significantly reduced.
These and other objects and advantages are achieved by the ignition system according to the invention for a 14 V or 42 V on-board power system voltage, which is applied directly to the ignition stage without an intermediate power unit. After an input signal from a superordinate engine control device, the semiconductor power output stage is switched on by an ignition control device. As a result, a current is built up on the primary side of the ignition transformer. After a predefined maximum current value is reached for the first time, the primary side of the ignition transformer is switched off for a predefined time period. In this time period, a high voltage for the spark breakdown builds up, according to the principle of self induction, at the electrodes of the spark plug which is connected at the secondary side to the ignition transformer. After the spark breakdown, the primary side of the ignition transformer is timed and current-controlled until the end of the ignition process which is predefined by the superordinate engine control device.
The timed control operates with selected, predefined time intervals in which the semiconductor power stage is alternately switched on and off. The switch-on time is selected to be so short that when the efficiency of the ignition plasma decreases owing to the limited voltage supply from the product of the on-board power system voltage and transmission ratio of the ignition transformer after a short time, a relatively high self-induction voltage is provided again during the switch-off time. The switch-on time is however selected to be of such a length that an intermittent buildup of the stored energy takes place if there is little energy stored. In order to build up high voltage for the first spark breakdown, a large amount of energy is required so that energy has to be recharged again. The switch-off time is also selected to be as short as possible so that the drop in the energy stored in the ignition transformer during the switch-off time is small. Typical values are 10-200 &mgr;s for the switch-on time, and 5-50 &mgr;s for the switch-off time. A current limitation is superimposed on the timed control and it switches off the primary side of the ignition transformer whenever the primary current reaches the predefined maximum value.
The maximum current limitation protects the components of the ignition system, and the on-board power system against overloading. In conjunction with a high coupling factor of the ignition transformer, the maximum current limitation also advantageously limits the ignition spark current during the switch-on time.
The following advantages are achieved with the invention:
The ignition transformer has a transmission ratio ü which is greater than 100 for an on-board power system voltage of 14 V, and greater than 50 for an on-board power system voltage of 42 V. The large transmission ratio of the ignition transformer
Crowell & Moring LLP
Daimler-Chrysler AG
Mohanty Bibhu
LandOfFree
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