Measuring and testing – Vehicle chassis – Steering
Reexamination Certificate
1999-06-09
2001-07-24
Oen, William (Department: 2855)
Measuring and testing
Vehicle chassis
Steering
Reexamination Certificate
active
06263727
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to a system for detecting a combustion condition in an internal combustion engine, and more particularly, to a system configured to develop a bias voltage for ion current measurement within a combustion chamber of the engine.
BACKGROUND OF THE INVENTION
It is desirable to detect a misfire condition during the operation of an internal combustion engine. One approach taken in the art to detect misfire involves assessing the degree of engine speed (RPM) variation. Although such an approach does not require additional circuit components, it does require relatively extensive software to perform the evaluation, and, further, is incapable of producing accurate and reliable results over the entire engine speed and load range on a higher number of cylinder engines.
Another approach involves the use of a so-called ion sense system. It is known that the combustion of an air/fuel mixture in an engine results in molecules in the cylinder being ionized. It is further known to apply a relatively high voltage across, for example, the electrodes of a spark plug just after the ignition operation to produce a current across the electrodes. Such current is known as an ion current. The ion current that flows is proportional to the number of combustion ions present in the area of, for example, the spark plug gap referred to above, and is consequently indicative of the ionization throughout the entire cylinder as combustion occurs. The level or amount of ion current is indicative of the quality of the combustion event, or whether in fact combustion has occurred at all (e.g., a misfire condition).
Known ion current sensing systems generally include, in addition to an ignition coil, a capacitor or the like configured to store a voltage. The stored voltage is thereafter used as a “bias” voltage which is applied to the spark plug to generate the ion current. These systems therefore require additional circuitry for the storing and biasing operation, which may be undesirable in certain circumstances.
U.S. Pat. No. 5,814,994 to Hohner et al. discloses a system to generate an ion current and purports to provide a control circuit configured to drive an ignition transistor such that a saw-toothed collector current, or alternatively, a triangle-shaped current, results as a primary current. Although the circuitry of such a control circuit is not disclosed in detail, it is believed that such circuitry would be relatively complicated, and further, would require that the ignition transistor dissipate a relatively increased amount of power. These aspects may also be undesirable in certain circumstances.
Moreover, known ion sense systems, while capable of producing results over the entire engine speed and load range, even on a higher number of cylinder engines, generally require a microprocessor or the like, and thus are more expensive.
There is therefore a need to provide an apparatus for detecting a combustion condition, such as a misfire condition, that minimizes or eliminates one or more of the shortcomings as set forth above.
SUMMARY OF THE INVENTION
This invention provides for accurate and reliable detection of a combustion condition, such as a misfire condition, without the need for extra hardware components, and can thus be provided at a lower cost. Moreover, an apparatus in accordance with this invention is full engine speed and load capable, and does not require extensive software overhead as do certain known misfire detection systems.
This invention advantageously makes use of a so-called “make” voltage. Historically, contact breaker points were used in ignition systems to alternatively establish and interrupt the flow of primary current through an ignition coil. Closure of the contact breaker points was known as a “make” condition. Notwithstanding technological advancements which have largely displaced contact breaker points with, for example, solid state devices, the term “make” continues to be used. During charging of the ignition coil, a positive voltage (i.e., a “make” voltage) is generated across the spark plug gap. When the make voltage is generated across the spark gap for the initial coil charging, combustion has not yet occurred and thus little if any ion current will flow. Therefore, in accordance with the present invention, after combustion has occurred, the ignition coil is recharged, preferably for a predetermined time, to reestablish the make voltage across the secondary winding. The make voltage bias causes an ion current to flow wherein a valid indication of combustion (or lack thereof) may be obtained.
An apparatus for detecting a combustion condition in accordance with the present invention therefor includes an ignition coil, a switch, means for closing the switch after an ignition control signal so as to establish a make voltage for biasing a spark plug, and an ion current sensing circuit. During the initial ignition coil charging, a make voltage is established across a secondary winding of the ignition. Charging is interrupted to generate the spark. During the initial spark operation, a spark current flows across the electrodes of the spark plug. Thereafter, an ion sense interval is commenced by activating the switch closing means to thereby begin recharging of the ignition coil. Recharging establishes the make voltage across the secondary winding. During this interval, however, if combustion has occurred, the cylinder will contain ionized molecules, which will also be present in the spark plug gap. The make voltage bias will cause an ion current to flow. During ion current flow, the sensing circuit generates an ion sense signal representative of the ion current.
In one embodiment, the sensing circuit includes a resistor between a low side end of the secondary winding and a ground node. The resistor produces the ion sense signal when the ion current flows therethrough.
In a further embodiment, the switch closing means includes a control circuit configured to generate an interrogation pulse signal in timed relation after the ignition control signal. The interrogation pulse signal is operative to close the switch to begin recharging of the ignition coil. During recharging, the make voltage is established for biasing the spark gap.
Other objects, features, and advantages of the present invention will become apparent to one skilled in the art from the following detailed description and accompanying drawings illustrating features of this invention by way of example, but not by way of limitation.
REFERENCES:
patent: 5675072 (1997-10-01), Yasuda et al.
patent: 5676113 (1997-10-01), Johansson et al.
patent: 5769049 (1998-06-01), Nytomt et al.
patent: 5775298 (1998-07-01), Haller
patent: 5803047 (1998-09-01), Rask
patent: 5814994 (1998-09-01), Hohner et al.
patent: 5866808 (1999-02-01), Ooyabu et al.
Delphi Technologies Inc.
Dobrowitsky Margaret A.
Oen William
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