Method for detecting ions in a combustion chamber of an internal combustion engine with a capacitive discharge ignition system

Abstract

A method for ion detection in a capacitive discharge ignition system for an internal combustion engine, comprising a storage capacitor connected to a power supply connected in series with the capacitor, an ignition transformer with a primary and a secondary winding, an adjustable switch connected in series with the storage capacitor and the primary winding of the ignition transformer, an electronic circuit for controlling the adjustable switch, and a spark plug with electrodes connected in series with the secondary winding of the ignition transformer, comprising the following steps: a) First, the closing of the adjustable switch synchronously with the internal combustion engine for a period of time to transfer energy to the primary side of the ignition coil so that a spark jump is caused across the spark plug; b) After the initial closing phase, repeated opening and closing of the switch, adjustment or adaptation of the ratio of opening and closing periods to achieve a desired constant preload across the spark plug electrodes; and c) Observing the current in the secondary winding circuit, which indicates ionization in the vicinity of the spark plug electrodes.

Description

Field of the invention

[0001] This invention relates to a method for ion detection in internal combustion engines and, as shown in one embodiment, the use of pulse width modulation to bias the secondary winding circuit during the detection period. Description of the state of the art

[0002] Ion sensing, or more correctly ionization current sensing, is a technique for determining the condition within a cylinder of an internal combustion engine, including, for example, misfire, ignition knock, and peak pressure. Misfire is the failure of the ignition system to ignite the air and fuel mixture near the end of the compression stroke, resulting in a loss of power. Knock indicates vibrations within the cylinder, often the result of premature ignition during the compression stroke. Peak pressure is the highest pressure within the cylinder, ideally occurring near the top of the compression stroke. Ion sensing enables correction or adjustment of the ignition to improve the performance of the internal combustion engine.

[0003] After the air and fuel mixture is ionized, an electric current flows between the center and ground electrodes of the spark plug. During the spark for ignition, ionization is the result of the intense electric field across the electrodes. However, ionization is also a result of the chemical reactions that occur at the flame front as it propagates through the cylinder. To detect flame front ions, an electrical potential must be maintained across the spark plug electrodes during non-ignition periods. Current flow in the secondary winding circuit of the ignition transformer or coil is an indication of ionization at the spark plug.

[0004] Ion detection has traditionally been implemented in induction systems with ignition interruption. It is well known that the current flowing in the primary winding of the ignition transformer in such an ignition system is interrupted due to a detected camshaft position in order to induce high voltage in the secondary winding of the ignition transformer, which is connected in series with the spark plug electrodes. To provide a bias voltage for ion detection, it is necessary to insert diodes and a capacitor into the secondary winding, for example, according to the teachings of the US patents US 6,118,276 A and US 6,498,490 B2. In such systems, only a small, if any, adjustment of the bias voltage stored during the initial ignition process can be made. Inductive breaker ignition systems are typically used in automotive engines.

[0005] Capacitive discharge ignition systems store energy on a storage capacitor and build up a voltage across the capacitor. A switch connected in series with the capacitor and the primary winding of the ignition transformer is closed based on the detected camshaft position to initiate ignition by inducing a large voltage in the secondary winding, which is connected in series with the spark plug electrodes. The switch is known to open and close during the compression stroke to generate a series of pulses to the primary winding to amplify the oscillation of the ignition transformer, as described in US patent US 7,401,603 B1.

[0006] US 2002 / 0 066 444 A1 discloses a method for ion detection in an ignition system in which the current meanders through the spark plug after the sparkover.

[0007] Further relevant procedures are known from US 2005 / 0 093 549 A1 and US 2002 / 0 145 429 A1.

[0008] The object of the invention is to provide a method for ion detection in a capacitive discharge ignition system. This eliminates the need to add a circuit element to the secondary winding to maintain a bias voltage across the spark plug electrodes. Furthermore, the bias voltage can be adjusted instantaneously to provide spark ignition and / or secondary current control in real time. It is not necessary to add a capacitor or diode to the secondary winding circuit.

[0009] The problem is solved by the features of the independent patent claim. Advantageous developments of the invention are described in the subclaims.

[0010] According to a further aspect, the method according to the invention, in contrast to other ion detection methods that only function within a time window clearly separated from the ignition phase, provides that the change in ionization caused by the onset of combustion in the spark gap of the spark plug during the ignition phase can be used to determine the onset of ignition. The increased current flow through the secondary winding, in addition to the normal ignition current, occurs due to the reduced impedance of the ionized gases between the electrodes, which is brought about by the onset of combustion. SUMMARY OF THE INVENTION

[0011] Briefly, the invention provides a method for ion detection in a capacitive discharge ignition system for an internal combustion engine comprising a storage capacitor for connection to a power supply connected in series with the capacitor, an ignition transformer having a primary and a secondary winding and a controllable switch connected in series with the storage capacitor and the primary winding of the ignition transformer, an electronic circuit for controlling the controllable switch, and a spark plug having electrodes connected in series with the secondary winding of the ignition transformer.

[0012] In one embodiment, the method comprises the following steps: a) First, closing the adjustable switch synchronously with the internal combustion engine for a period of time to transfer energy to the primary winding of the ignition coil to cause a spark over the spark plug; b) After the initial closing phase, repeatedly opening and closing the switch, setting or adjusting the ratio of opening and closing periods to achieve a desired bias voltage across the spark plug electrodes; and c) Observe the current in the secondary winding circuit, which indicates ionization in the vicinity of the spark plug electrodes.

[0013] In a further embodiment, the method comprises the following steps: a) First, closing the controllable switch synchronously with the internal combustion engine for a period of time to transfer energy to the primary winding of the ignition coil to cause a spark over the spark plug; and b) Observe the current in the secondary winding circuit, which indicates ionization in the vicinity of the spark plug electrodes. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Further features, objectives and advantages of the invention will become apparent from the description which illustrates the drawings: Fig. Figure 1 is a schematic diagram of a typical capacitive discharge ignition system; Fig. 2 is a schematic diagram of the waveform of a secondary current for illustrating an embodiment of this invention; Fig. 3 is a schematic diagram of the waveform of a secondary current for illustrating another embodiment of this invention; Fig. Fig. 4 is a schematic diagram of the waveform of a secondary current for illustrating another embodiment of this invention; and Fig. 5 is a schematic diagram of the waveform of a secondary current for illustrating another embodiment of this invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] With a view to Fig. Figure 1 shows a basic capacitive discharge circuit for a high-voltage ignition system, in particular as essentially described in US Patent No. 7,401,603 B1, comprising a storage capacitor (C1), a diode (D1), and a power supply connected in series. An ignition transformer (TR1) has primary and secondary windings. The primary winding is connected in series with the storage capacitor and a controllable switch (S1). A spark plug is connected in series with the secondary winding of the ignition transformer. An electronic control circuit (EC1) drives the controllable switch.

[0016] The electronic control circuit operates synchronously with the engine and regulates the open (conductive) and closed (non-conductive) periods of the switch such that the switch (S1) is initially closed for a period (T1) to transfer energy in the form of pulses to the primary winding of the ignition coil; the switch (S1) is then opened for a second period (T2). The pulse duration and spacing are determined by the control circuit. It is possible to provide a measuring resistor (R) connected in series with the ignition electrodes; other current sensing means are also possible, such as the use of a Hall element or current measuring transformer, which can measure the secondary current instead of a resistor.

[0017] The electronic control circuit may comprise a programmable microcontroller with input ports for detecting one or more positions relative to the rotation of the crankshaft, such as top dead center of the first cylinder, an input for detecting current and / or voltage in the secondary circuit of at least one ignition transformer, and outputs for opening and closing one or more adjustable switches.

[0018] According to the present disclosure, a method for ion detection using the capacitive discharge circuit described above comprises: a) First, closing the adjustable switch synchronously with the internal combustion engine for a period of time to transfer energy to the primary winding of the ignition coil to cause a spark over the spark plug; b) After the initial closing phase, repeatedly opening and closing the switch, adjusting or adapting the ratio of opening and closing periods to obtain a desired bias voltage across the spark plug electrodes; and c) Observe the current in the secondary winding circuit, which indicates ionization in the vicinity of the spark plug electrodes.

[0019] With reference to Fig. 2, according to an embodiment of the invention, after an initial closing period of the adjustable switch to induce sparkover, a low bias voltage is maintained across the electrodes by controlling the ratio of open and closed periods sufficiently long to detect the passage of the flame font between the spark plug electrodes. After the initial closing period of the adjustable switch to generate a spark, the ratio between the open and closed periods is preferably controlled accordingly to provide a constant low voltage across the spark plug. The passage of the flame font is detected by means of a current increase in the secondary circuit.

[0020] With reference to Fig. 3, according to a second embodiment of the invention, it can be seen that the initial closing period of the adjustable switch to cause the arcing and a period for closing the adjustable switch to realize the second arcing are followed by maintaining a low bias voltage across the ignition electrodes by controlling the ratio of opening and closing periods sufficiently long to detect the passage of the flame front between the spark plug electrodes.

[0021] With reference to Fig. 4, according to a third embodiment of the invention, after the initial closing period of the controllable switch for generating the sparkover, a low bias voltage is maintained across the ignition electrodes by controlling the ratio of opening and closing periods in such a way that a second sparkover is only caused when the initial sparkover has brought about continuous combustion of the air and fuel mixture, after which a low bias voltage is maintained across the spark plugs by controlling the ratio of opening and closing periods for a sufficiently long time to detect the passage of the flame front between the spark plug electrodes.

[0022] With reference to a fourth embodiment of the invention, the total secondary current (spark plus ion current) detected after the arcing event is maintained at a substantially constant value for a fixed time sufficient to detect the ion current by controlling the ratio of the opening and closing periods of the primary switch. The total current, composed of the spark current plus ion current, would normally decrease rapidly after the arcing event, thus forming a triangular waveform. By forcing the total current value to be kept constant, the current waveform is rectangular for the duration of the fixed constant current period. In this embodiment, the higher the ion current present during this period, the less power the primary supply circuit must provide to maintain this constant total current value.The ratio of opening and closing periods of the primary switch can then be used to determine the relative ion concentration between the spark plug electrodes during individual ignition events by measuring this ON / OFF ratio of the switch controller.

[0023] According to a fifth embodiment of the invention, the total secondary current (spark plus ion current) built up after the arcing event is allowed to drop to a very low value and then held at a virtually constant value for a fixed period of time sufficient to detect the ion current by regulating the opening and closing times of the primary switch. The total current, composed of the ignition current plus ion current, would normally drop rapidly after the arcing event, thus forming a triangular waveform. By forcing the ion current value to be held constant, the ion current waveform is rectangular and fixed for the duration of the constant current period, occurring after the triangular waveform of the decreasing spark current occurs.In this embodiment, this means that the higher the ion current present during this period, the less energy the primary supply circuit must provide to maintain this constant ion current value. The ratio of the primary switch's open and closed periods can then be used to determine the relative ion concentration between the spark plug electrodes present after individual ignition events by measuring this ON / OFF ratio of the switch controller.

[0024] With reference now to Fig. In a sixth embodiment, relating to an engine with cylinders of sufficiently small bore size, it can be seen in Figure 5 that the reflected ionization wavefront occurs during the ignition phase itself, and the energy provided by the initial closure of the switch to discharge the storage capacitor creates a sufficient bias voltage to detect the increased current flow due to the ionization induced by the start of combustion. Fig. 5, the upper line represents the voltage across the secondary winding; the lower line represents the current flowing in the secondary winding. Fig. Figure 5 contains a schematic illustration of the fact that the current increase is detected by an abrupt increase in the current I during the ignition period.

[0025] Having defined the invention above in detail and particularly in accordance with the patent laws, the following claims define the desired scope of protection of the present disclosure.

Claims

[1] A method for ion detection in a capacitive discharge ignition system for an internal combustion engine, comprising a storage capacitor connected to a power supply connected in series with the capacitor, an ignition transformer having a primary and a secondary winding, and a controllable switch connected in series with the storage capacitor and the primary winding of the ignition transformer, an electronic circuit for controlling the controllable switch, a spark plug with electrodes connected in series with the secondary winding of the ignition transformer, comprising the following steps: a) First, closing the adjustable switch synchronously with the internal combustion engine for a period of time to transfer energy to the primary side of the ignition coil to cause a spark to arc across the spark plug; b) After the initial closing phase, repeatedly opening and closing the switch, adjusting or adapting the ratio of opening and closing periods to achieve a desired constant bias voltage across the spark plug electrodes; and c) Observe the current in the secondary winding circuit, which indicates ionization in the vicinity of the spark plug electrodes. [2] A method according to claim 1, wherein the current in the secondary winding circuit is detected as a voltage across a measuring resistor connected in series with the spark plug electrodes. [3] The method of claim 1, wherein the current in the secondary winding circuit is detected as an output of a Hall element sensor coupled to the secondary winding. [4] A method according to claim 1, wherein after the initial closing period of the controllable switch to cause arcing, a low bias voltage is maintained across the spark plug electrodes by maintaining the ratio of open and closed periods for a period sufficient to detect the passage of the flame front between the spark plug electrodes. [5] A method according to claim 1, wherein after the initial closing period of the controllable switch to cause a sparkover and a period for closing the controllable switch to realize a second sparkover, a constant low bias voltage is maintained across the spark plug electrodes by controlling the ratio of opening and closing times for a time sufficient to detect the passage of the flame front between the spark plug electrodes. [6] A method according to claim 1, wherein, after the initial closing period of the controllable switch to cause a spark over, a constant low bias voltage is maintained across the spark plug electrodes by controlling the ratio of opening and closing times to cause a second spark over only when the initial spark over has brought about continuous combustion of the air and fuel mixture, after which a constant low bias voltage is maintained across the spark plug electrodes by controlling the ratio of opening and closing times for a period sufficient to detect the passage of the flame front between the spark plug electrodes. [7] A method according to claim 1, wherein after the initial closing period of the controllable switch to cause a sparkover, the total secondary current, which is composed of the spark current plus the ion current, is maintained at a substantially constant value, and the measured energy required therefor is used as a relative inversely proportional measurement of the ion concentration between the electrodes of the spark plug during the ignition event. [8] A method according to claim 1, wherein after the initial closure period of the controllable switch to cause arcing, the secondary current is allowed to fall to a very low value where it is maintained at a substantially constant value, and the energy required to maintain this current is used as a relative inversely proportional measure of the ion concentration between the electrodes of the spark plug during the ignition event.

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