GB2592239A - Method of controlling and monitoring spark ignition systems - Google Patents

Abstract

Disclosed is a method of monitoring and/or controlling the operation of a spark ignition system for an internal combustion engine. The system includes at least a first primary winding L1, coupled to a corresponding first secondary winding L2 via a first common core K1. The secondary winding is connected to a spark plug U1. The method comprises the steps of obtaining a signal indicative of current Ip/Is through the primary and/or secondary winding during an operational spark cycle of the system, integrating the current over one or more time periods, comparing the integrated current value with a threshold and indicating an error in the system based on the comparison and/or subsequently controlling the system dependent on the comparison. The system may be a multi-spark system. The method eliminates problems caused by noise in the current signal when assessing failure of the spark system.

Description

Method of Controlling and Monitoring Spark Ignition Systems

TECHNICAL FIELD

The present invention relates to an ignition system and method of controlling spark plugs and monitoring sparking. It has particular, but not exclusive, application to systems which are adapted to provide a continuous spark, such as a multi-spark ignition system.

BACKGROUND OF THE INVENTION

Ignition engines that use very lean air-fuel mixtures have been developed, that is, having a higher air composition to reduce fuel consumption and emissions. In order to provide a safe ignition, it is necessary to have a high energy ignition source. Prior art systems generally use large, high energy, single spark ignition coils, which have a limited spark duration and energy output. To overcome this limitation and to reduce the size of the ignition system multi-charge ignition systems have been developed. Multi-charge systems produce a fast sequence of individual sparks, so that the output is a long quasi-continuous spark. Multi-charge ignition methods have the disadvantage that the spark is interrupted during the recharge periods, which has negative effects, particularly noticeable when high turbulences are present in the combustion chamber. For example, this can lead to misfire, resulting in higher fuel consumption and higher emissions.

A problem for both single spark and multi-spark is that often the operating parameters will fall outside an acceptable range, e.g. will be unusually high which can damage the apparatus; i.e. the coil spark plugs or associated circuitry.

In order to detect such instances operating parameters such as primary and/or secondary currents can be monitored and compared with a threshold.

During operation of spark cycle, the primary current for a primary coil will be ramped up to a peak, and thereafter will operate for a period at a nominal level before falling to zero (For CIVIC (multi-spark) operation, after the ramp-up phase, the operating current in a single coil may oscillate, i.e. have a rectangular waveform) during multi-sparking, Thus the primary current against time can be recorded and can be viewed as a plot; i.e. a signal of primary current against time.

In prior art methodology refined embodiments a "mask" is provided such that a boundary is drawn around a nominal operating plot e.g. having an approximate, e.g. similar, but larger shape. During operation if the current signal extends beyond the mask then a problem is flagged, and appropriate action may be taken. So, in prior art methods, a mask is used to determine if the Ip signal is correct. The mask is large enough to be able to cover the signal depending on temperature variation.

However, there are problems with using a mask. For example, the mask is not able to detect if the coil is activated in single charge mode when coil is supposed to work on CIVIC mode.

It is an object of the invention to provide an improved method of monitoring coil operation which also overcomes such problems

SUMMARY OF THE INVENTION

In aspect if provided a method of monitoring and or controlling the operation of a spark ignition system, said system including at least a first primary winding Li, coupled to a corresponding first secondary winding L2 via a first common core Kl, said secondary winding connected to a spark plug (U1) ; said method including the following steps: a) obtaining a signal indicative of current (Ip/ls) through the primary andJor secondary winding during an operational spark cycle of said system; b) integrating the said current over one or more time periods; c) comparing the value determine in step b) with a threshold, d) indication an error in said system dependent on said comparison step c); and/or subsequently controlling said system dependent on the comparison step c).

The current may be primary current Ip Said system is a single spark system.

Said system is a multi-spark (multi-charge) system comprising least a further second primary winding L3, coupled to a corresponding second secondary winding 10 L4 via a second common core K2, Said value determined in step b) for comparison may be obtained by integrating the value of the current between the start of an initial ramp-up phase and the end of the initial ramp-up phase The value determined in step b) for comparison may be obtained by integrating the value of the current from the end of the ramp up phase to the end of the spark cycle.

Said spark cycle may be a multi-spark or operated in CMC mode Current Ip may be the value of the current through the first and/or second primary coil(s).

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BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is now described by way of example with reference to the accompanying drawings in which: Figure la shows the circuitry of a prior art coupled-multi-charge (CMC) ignition system; Figure lb shows simpler circuitry which can be used to provide a single spark; Figure 2 illustrates a prior art method of monitoring spark operation; Figure 3 illustrates a method of monitoring spark operation according to an example of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure I a shows the circuitry of a prior art coupled-multi-charge (CMC) ignition system for producing a continuous ignition spark over a wide area of burn voltage servicing a single set of gapped electrodes in a spark plug Ul, such as might be associated with a single combustion cylinder of an internal combustion engine (not shown). The CMC system uses fast charging ignition coils (Li-L3), including primary windings, Li, L3 to generate the required high DC-voltage. Coils Li and L2 are wound on a common core K1 forming a first transformer and secondary windings L3, L4 wound on another common core K2 are forming a second transformer. The two coil ends of the first and second primary windings Li, L3 may be alternately switched to a common ground such as a chassis ground of an automobile by electrical switches Ql, Q2. These switches Ql, Q2 are preferably Insulated Gate Bipolar Transistors. Resistor RI for measuring the primary current Ip that flows from the primary side is connected between the switches Ql, Q2 and ground, while resistor R2 (25) for measuring the secondary current Is that flows from the secondary side is connected between the diodes D1, D2 and ground.

The low-voltage ends of the secondary windings L2, L4 may be coupled to a common ground or chassis ground of an automobile through high-voltages diodes D1, D2. The high-voltage ends of the secondary ignition windings L2, L4 are coupled to one electrode of a gapped pair of electrodes in a spark plug Ul through conventional means. The other electrode of the spark plug Ul is also coupled to a common ground, conventionally by way of threaded engagement of the spark plug to the engine block. The primary windings Ll, L3 are connected to a common energizing potential which in the present embodiment is assumed to correspond to conventional automotive system voltage in a nominal 12V automotive electrical system and is in the figure the positive voltage of battery. The charge current can be supervised by an electronic control circuit 13 that controls the state of the switches Ql, Q2. The control circuit 13 is for example responsive to engine spark timing (EST) signals, supplied by the ECU, to selectively couple the primary windings Ll and,-L3 to system ground through switches Q1 and Q2 respectively controlled by signals Igbtl and Igbt2, respectively. Measured primary current Ip and secondary current Is are sent to control unit 13. Advantageously, the common energizing potential of the battery 1 is coupled by way of an ignition switch MI to the primary windings L I, L3 at the opposite end that the grounded one. Switch M1 is preferably a MOSFET transistor. A diode D3 or any other semiconductor switch (e.g. MOSFET) is coupled to transistor MI so as to form a step-down converter. Control unit 13 is enabled to switch off switch Ml by means of a signal FET. The diode D3 or any other semiconductor switch will be switched on when MI is off and vice versa. It should be noted that the circuitry of figure la can be operated in single or multi-spark mode.

It should be noted that the aspects of the invention can be applied to single spark systems and systems having just one primary winding Li couple via a single core to one secondary winding. Thus, winding L3 an L4, as well as Q2 and DI can be dispensed with in the figure. Figure lb shows simpler circuitry which can be used to provide a single spark; reference numerals denote the like components as in Figure I a. This can be used in aspects of the invention.

The important point is that the primary current (Ip) that is the current through Li in a single spark system (e.g. of figure lb) or the combined primary current Ip in a CNTC system (e.g. of figure la) can be measured and monitored; i.e a signal or plot obtained.

Figure 2 illustrates a prior art method of monitoring spark operation e.g. of the above circuitry. The figure shows a plot of primary current Ip during a typical operational cycle.

During an initial period 2, the circuitry is switched to ramp up the primary current Ip to a peak value Ipeak. Thereafter during operation in single spark mode, the b value of Ip is generally around a nominal value which is usually somewhat lower than the peak value after the ramp. After sparking the value of Ip falls to zero.

The plot shows the primary current Ip for CIVIC operation. As can be seen, after the initial ramp, the current falls to zero at breakdown, whereupon current is discharged through the corresponding secondary coil to produce the spark, so primary current fall to a low value e.g. around zero. Afterwards the primary col is recharged to a nominal voltage level, before the cycle is repeated.

Reference numeral 6 shows successive charge/discharge periods during multi-charge operational cycle. These periods are controlled by appropriate switching of the appropriate switches shown in figures la. Advantageously the control of charge/discharge periods is done by monitoring i.e. dependent on the measured values of primary/secondary currents The whole operation sparking period/control in relation to a combustion event takes place over the time span 7, during which there is multi-sparking.

Typically, a mask 3 is provided which here comprises an upper boundary 4 and a lower boundary 5. In prior art system the Ip is monitored to see if the current Ip extends above or below the boundaries, during the rap up period and/or the subsequent (remaining) operation period Detection of errors in operation occurs when the signal crosses the mask.

This methodology does not allow for the detection of errors in single charge mode when CIVIC mode is activated.

Invention The problem of ignition coil default detection, together with the problem of potential destruction of the coil if coil over-current or heating is not stopped in time, is solved by methodology which monitors (e.g. continuously) the primary current (Ip) (and/or secondary current Is) and integrates the value over one or more appropriate time period(s).

The integrated values can be analyzed and compared with e.g. expected values or thresholds. If the values are higher than respective thresholds, then an error may be determined/flagged, or used to adjust the subsequent control of the system. The results may also be analyzed together in conjunction with known techniques such as monitoring the peak current Ip after the ramp up phase Ipeak, The methodology can be applied to single or multi-spark systems or modes.

Such methodology allows the detection of problems under different working conditions, for both single charge mode or Coupled Multi-Charge (CMC), i.e. multi-spark mode.

Activation of coil may be modified or stopped after one or more of errors e.g. defined at the start to avoid losing the first ignition defect. The methodology can be applied to whatever number of coils under consideration. In aspects the methodology allows other coils to continue to be activated to avoid losing time during durability.

Examples

Example will now be given with reference to figure 3 which shows the same plot as in figure 2; i.e. the value of primary current, Ip, with time for a sparking (operational) cycle

Example 1

In this example, the value of Ip is integrated from the start of the ramp up (initial) phase to the end of this phase; i.e. the phase 2 of figure 2. The phase starts at timepoint To and end at time point T1 when the peak ramp-up phase current Ipeak is achieved. The integrated value is shown by the area 8 in figure 3. The integrated value may be compared with a threshold. The threshold may be dependent on various other parameters, and so may be varied according to operating conditions.

Example 2

In this example, the value of Ip is integrated in the period of operation following the end of the (initial) ramp up phase; during the period 9 of figure 3 which is the time period between Ti (end of the ramp-up phase) and T2 which is the end of the spark cycle, or to any time point when the current in the primary (finally) reaches a value of zero towards the end of the spark cycle. This integrated value is shown by the area 10 in figure 3. The integrated value may be compared with a threshold. The threshold may be dependent on various other parameters, and so may be varied according to operating conditions.

The term "end of the spark cycle-should be interpreted as designated (pre-determined/ predefined) (control time) time when the spark cycle is finished or any within the spark cycle when the vaule of Ip falls and stays at a level generally zero.

Further Examples

One or more of each coil may have either or both the integrated values (designated 8 and 10) checked (compared with thresholds) as well as optionally also checking whether the values of Ipeak is within a further threshold value So the three major parameters (e.g. for ignition coils with CMC) can be checked: the Ip initial charge value, Ip x time area before Ipeak (during initial charge) and after Ip x time area after initial charge.

In other words the checking for errors may be based on the detection on three main primary current characteristics. The Ip pulse area (8) in figure3, and the peak value for single charge mode and system is adding Ip pulse area total for CMC mode (10 in figure 3) There may testing where before a durability testing start, one or more of the three parameters of test are checked, and the three comparison values are calculated to define their operating limits The three values are calculated for each activation per coil, these values are timely saved inside a file to follow the evolution of the signal during all the durability. If the signal is going outside the limits during an amount of time defined before the test, the coils is stop by the system to protect the defect coil to be destroyed.

Then failure analysis can be conduct based on the evolution of the key parameters In the prior art, continuous monitoring was done on Ip signal with a comparison of a mask that was very large to compensate the temperature variation. The advantages of invention are the following: it improves the accuracy of the error detection. and by providing e.g., continuous monitoring on the Ip Initial charge; continuous monitoring on the 1p Area before initial charge; and/or continuous monitoring on the Ip area after initial charge; error detected when the parts is not doing CIVIC (Ip Area2 at 0).

Claims (8)

1. CLAIMS1. A method of monitoring and or controlling the operation of a spark ignition system, said system including at least a first primary winding Li, coupled to a corresponding first secondary winding L2 via a first common core K1, said secondary winding connected to a spark plug (UI) ; said method including the following steps: a) obtaining a signal indicative of current (Ip/Is) through the primary and/or secondary winding during an operational spark cycle of said system; b) integrating the said current over one or more time periods; c) comparing the value determine in step b) with a threshold; d) indication an error in said system dependent on said comparison step c); and/or subsequently controlling said system dependent on the comparison step c).
2. 2. A method as claimed in claim 1 wherein the current is primary current Ip.
3. 3. A method as claimed in claim I wherein said system is a single spark system.
4. 4. A method as claimed in claim I wherein said system is a multi-spark system comprising least a further second primary winding L3, coupled to a corresponding second secondary winding L4 via a second common core 1(2,
5. 5. A method as claimed in claim Ito 4 where said value determined in step b) for comparison, is obtained by integrating the value of the current between the start of an initial ramp-up phase and the end of the initial ramp-up phase.
6. 6 A method as claimed in claim 1 to 5 value determined in step b) for comparison, is obtained by integrating the value of the current from the end of the ramp up phase to the end of the spark cycle.
7. 7 A method as claimed in claim 6 where said spark cycle is a multi-spark or operated in CMC mode
8. 8. A method as claimed in claims 1 to 7 where current lp is the value of the current through the first and/or second primary coil(s).