Patent Description:
Generally, the combustion of a mixture of fuel and air in a cylinder of a spark-ignited internal combustion engine, e.g., an Otto engine, is initiated using an ignition device including a spark plug. For example, the ignition device may include an ignition coil comprising a primary winding and a secondary winding. The secondary winding is connected to the spark plug, and a current is selectively supplied to the primary winding to induce a magnetic field in the secondary winding. This results in an increase in the voltage across the spark plug, and eventually the spark plug is discharged. Upon discharge, the mixture of fuel and air in the combustion chamber of the cylinder is ignited and the combustion energy pushes down the piston to rotate the internal combustion engine. The rotation speed is varied by controlling the frequency of reciprocation of the piston, for example, by varying the fuel content while the torque is constant. As a consequence, the discharge frequency of the spark plug has to be changed.

In spark-ignited internal combustion engines, the spark plugs are members that are subject to considerable wear, resulting in a reduced service life and high failure rates. As a result of such failures, an emergency stop of the internal combustion engine may have to be initiated, which may result in further thermal stress on the spark plugs of the engine and potential further damage to the same. This may negatively affect the operation and/or productivity of the facilities including the internal combustion engine, for example, power plants, construction machines, etc..

<CIT>discloses a device and a method for ignition of an internal combustion engine. The device includes a central control unit and peripheral units, digital control signals being sent from the central control unit to the peripheral units, triggering the peripheral units to ignition of the respective cylinder, measured values describing the states in the peripheral units being determined by the peripheral units and sent to the central control unit as a function of the measured values, at least one time difference between the control signals and the diagnostic signals being determined by the central control unit for analysis of the diagnostic signals.

<CIT> relates to the detection of short circuits in ignition coils. The duration times of the spark discharge signals in the primary winding of the coil are compared to a threshold spark duration time, and a low impedance short circuit is indicated if the threshold spark duration time is exceeded. Short circuits in the secondary may also be detected by applying pairs of signals to the primary and monitoring current flow in the primary for each of the applied signals.

<CIT> discloses a high voltage ignition system monitoring circuit.

The present disclosure is directed, at least in part, to improving or overcoming one or more aspects of prior systems.

According to one aspect of the disclosure, a method for determining a defect in a spark plug associated with a cylinder of a spark-ignited internal combustion engine comprises the steps of claim <NUM>.

According to another aspect of the present disclosure, a spark-ignited internal combustion engine includes the features of claim <NUM>.

In yet another aspect of the present disclosure, a computer program comprises computer-executable instructions which, when run on a computer, cause the computer to perform the steps of the method of the above aspect.

Other features and aspects of the present disclosure will become apparent from the following description and the accompanying drawings.

The following is a detailed description of exemplary embodiments of the present disclosure. The exemplary embodiments described herein are intended to teach the principles of the present disclosure, enabling those of ordinary skill in the art to implement and use the present disclosure in many different environments and for many different applications. Therefore, the exemplary embodiments are not intended to be, and should not be, considered as a limiting description of the scope of protection. Instead, the scope of protection shall be defined by the appended claims.

The present disclosure may be based in part on the realization that, although it may be conceivable to determine whether a spark plug is defective or reaches the end of its service life (i.e., becomes defective due to wear) based on a secondary voltage of an ignition coil, it may be very difficult to continuously measure the secondary voltage during operation of the internal combustion engine. Therefore, according to the present disclosure, it is determined from the primary current flowing through the primary winding of the ignition coil whether a spark plug becomes defective, i.e., has been damaged or reaches the end of its service life due to wear. Accordingly, as used herein, the term "defect" also includes wear of the spark plug due to operation of the same over extended periods of time. In this respect, the present disclosure may be based in part on the realization that a rise time of the primary current, i.e., a time from starting supply of the primary current to reaching a first global maximum of the primary current, may be used as an indicator for the secondary voltage and therefore the condition of the spark plug. This rise time (also referred to as pull-in time or ignition delay) may be compared to a reference time in order to predict the remaining service life of the spark plug.

The present disclosure may also be based, at least in part, on the realization that the reference time may be empirically determined for a given type of spark plug and/or depending on the current supply, for example, the maximum value for the primary current or the power supply voltage.

In addition, the present disclosure may be based in part on the realization that, when it is detected that a spark plug becomes defective, an emergency stop of the engine may be avoided by reducing the load of the engine. In this manner, the engine can be shut down in a controlled manner before the spark plug fails. This may allow continuing operation of the internal combustion engine for several days or even weeks before exchanging the defective spark plug. For example, as the rise time is load-dependent, the engine load may be limited by the associated control unit outputting a derate pulse in response to the detection of the defect in the spark plug.

Further, the present disclosure may be based in part on the realization that, while generally a defective spark plug will lead to increased rise times, there may also be defects that result in a significantly lower rise time. For example, when a mechanical defect results in a reduced distance between the parts of the spark plug where the discharge occurs, this may lead to a significant decrease of the rise time. According to the present disclosure, a rise time window may be defined in order to detect different types of defects in a spark plug by checking whether the determined rise time is within said window.

Referring now to the drawings, an exemplary embodiment of an internal combustion engine <NUM> is illustrated in <FIG>. Internal combustion engine <NUM> may include features not shown, such a fuel systems, air systems, cooling systems, drive train components, etc. For the purpose of the present disclosure, internal combustion engine <NUM> is a gas engine. One skilled in the art will recognize, however, that internal combustion engine <NUM> may be any type of spark-ignited internal combustion engine, for example, a dual fuel engine or any other Otto engine that utilizes a spark plug for igniting a mixture of gaseous fuel and air for combustion.

Internal combustion engine <NUM> may be of any size, with any number of cylinders and in any configuration ("V", "in-line", etc.). Internal combustion engine <NUM> may be used to power any machine or other device, including ships or other marine applications, locomotive applications, on-highway trucks or vehicles, off-highway machines, earth-moving equipment, generators, pumps, stationary equipment such as power plants, or other engine-powered applications.

Still referring to <FIG>, internal combustion engine <NUM> comprises an engine block <NUM> including a bank of cylinders. In <FIG>, only a single exemplary cylinder <NUM> is shown. A piston (not shown) may reciprocate in cylinder <NUM> to rotate a crank shaft (not shown) of internal combustion engine <NUM>. The crank shaft may in turn drive a flywheel <NUM> of internal combustion engine <NUM>.

A spark plug <NUM> is associated with cylinder <NUM> and configured to ignite the mixture of gaseous fuel and air within the combustion chamber of cylinder <NUM> at a desired timing. A cylinder pressure sensor <NUM> may be provided for cylinder <NUM> and configured for detecting a cylinder pressure of cylinder <NUM>, for example, for detecting knock or the like. Cylinder pressure sensor <NUM> is operatively connected to a charge amplifier <NUM> for amplifying the associated measurement signal. Charge amplifier <NUM> is connected to a cylinder pressure data acquisition unit <NUM> configured to determine the cylinder pressure based on the measurement signal output by cylinder pressure sensor <NUM>. As shown in <FIG>, for example, during testing of the internal combustion engine and the associated systems, charge amplifier <NUM> may also be connected to an oscilloscope <NUM> for displaying the detected cylinder pressure signals.

A shaft encoder <NUM> may be associated with the crank shaft of internal combustion engine <NUM> and configured to detect the rotational position of the crank shaft, i.e., the position of the piston reciprocating in cylinder <NUM>. An output of shaft encoder <NUM> may also be connected to oscilloscope <NUM>, for example, during testing of engine <NUM>.

Spark plug <NUM> is connected to an ignition coil <NUM> associated with the same. A control unit <NUM> is also connected to ignition coil <NUM> and configured to operate the same in order to generate a spark at spark plug <NUM> with a desired ignition timing for igniting the mixture of gaseous fuel and air in cylinder <NUM>. Control unit <NUM> may include a single microprocessor or plural microprocessors that include means for controlling, among others, an operation of various components of internal combustion engine <NUM>. In the present embodiment, control unit <NUM> is a general engine control module (ECM) capable of controlling internal combustion engine <NUM> and/or its associated components. Control unit <NUM> may include all components required to run an application, such as, for example, a memory, a secondary storage device, and a processor such as a central processing unit or any other means known in the art for controlling internal combustion engine <NUM> and its components. Various other known circuits may be associated with control unit <NUM>, including power supply circuitry, signal conditioning circuitry, communication circuitry and other appropriate circuitry. Control unit <NUM> may analyze and compare received and stored data, and, based on instructions and data stored in memory or input by a user, determine whether action is required. For example, control unit <NUM> may compare received values with target values stored in memory and transmit signals to one or more components based on the results of the comparison to alter the operation status of the same.

Control unit <NUM> may include any memory device known in the art for storing data relating to operation of internal combustion engine <NUM> and its components. The data may be stored in the form of one or more maps that describe and/or relate, for example, the detection results from associated sensors to reference values stored in the memory of the same. Each of the maps may be in the form of tables, graphs and/or equations, and may include a compilation of data collected from lab and/or field operation of internal combustion engine <NUM>. The maps may be generated by performing instrumented tests on internal combustion engine <NUM> under various operating conditions via varying parameters associated therewith or performing various measurements. Control unit <NUM> may reference these maps and control one component in response to the desired operation of another component. For example, the maps may contain data on the normal rise times of the primary current of ignition coil <NUM> for different engine loads and/or different types of spark plugs when spark plug <NUM> is operating normally.

Ignition coil <NUM> includes a primary winding <NUM> and a secondary winding <NUM>. Primary winding <NUM> is connected to control unit <NUM> and configured to receive current supplied by control unit <NUM>, for example, by actuating a switch disposed in the current path between control unit <NUM> and primary winding <NUM>. A current detector <NUM> is provided in the current path between control unit <NUM> or a power supply (not shown) and primary winding <NUM> to detect the current flowing through primary winding <NUM>. Current detector <NUM> is connected to control unit <NUM>, which may receive the output form current detector <NUM> to determine the instantaneous value of the current flowing through primary winding <NUM>. In the exemplary embodiment, the output of current detector <NUM> is also connected to oscilloscope <NUM>. In addition, further probes are connected to respective power supply lines connected to both primary winding <NUM> and secondary winding <NUM> to detect the voltage across primary winding <NUM> and across secondary winding <NUM>, which probes are also connected to oscilloscope <NUM>. In this manner, during testing of internal combustion engine <NUM>, the instantaneous values of the primary current, the primary voltage and the secondary voltage may be detected and displayed on oscilloscope <NUM>.

<FIG> shows a graphical illustration of the primary current IP, the secondary current IS and the secondary voltage US measured during an ignition event for a spark plug that is defective. In <FIG>, the dashed line shows the primary current IP, the dotted line shows the secondary current IS, and the dot-dashed line shows the secondary voltage US.

As shown in <FIG>, when an ignition event is initiated, control unit <NUM> initiates a supply of current to primary winding <NUM> at a timing t<NUM>. Accordingly, the primary current in primary winding <NUM> increases. Ideally, the primary current IP increases in a linear manner, with the slope of the increase being defined by the ratio of the power supply voltage U divided by the inductance L of primary winding <NUM>. This is illustrated by the solid line Iref in <FIG>.

As shown in <FIG>, however, when spark plug <NUM> is defective, the primary current IP increases in a non-linear manner, i.e., slower than in the ideal case Iref. Simultaneously, the secondary voltage US also increases more slowly due to the magnetic field induced by the primary current IP. At a certain point, when the secondary voltage US reaches a given value (in the example, about <NUM> kV), a discharge occurs at spark plug <NUM>, and the mixture of gaseous fuel and air in cylinder <NUM> is ignited. The secondary voltage US breaks down, and the primary current IP continues to increase linearly, in accordance with the ideal behavior Iref. At the same time, the secondary current IS increases. When the primary current IP reaches a predetermined maximum value, for example, about -<NUM> A, this is detected by control unit <NUM> via current detector <NUM>, and the supply of current to primary winding <NUM> is stopped. Subsequently, in order to assure that ignition occurs, additional current pulses are output by control unit <NUM>, resulting in the behaviour of the primary current, the secondary current and the secondary voltage shown in <FIG>.

As shown in <FIG>, a time interval TD lapses between the timing t<NUM> of starting the supply of current to primary winding <NUM> and a timing t<NUM> of reaching the predetermined current value. It can be seen from <FIG> that the time interval TD, which is also referred to as pull-in time or ignition delay, is longer than the corresponding time interval (t<NUM>-t<NUM>) in case of a strictly linear increase as shown by Iref. Accordingly, control unit <NUM> may detect the time interval TD and compare the same to a predetermined reference interval for a normal spark plug <NUM> that may be stored in the memory of the same, for example, as a map relating the reference interval to the engine load. When the detected time interval TD is significantly larger than the reference interval, control unit <NUM> may determine that spark plug <NUM> is defective.

Alternatively, control unit <NUM> may determine an ignition delay difference ΔTD, for example, based on the slope Iref and the timing of reaching the maximum of the primary current at time t<NUM>. For example, the slope Iref may be calculated in advance based on the voltage applied to primary winding <NUM> and the inductance of the same. Based on the maximum value of the primary current, the timing t<NUM> may be calculated, at which the supply of the primary current would have to be started in case of an ideal, i.e., non-defective behavior of spark plug <NUM> to reach the maximum value of the primary current at time t<NUM>. The reference timing t<NUM> obtained in this manner may then be subtracted from the ignition delay TD to obtain ΔTD for spark plug <NUM>. Similar to the above, when ΔTD is substantially larger than a reference value for the same, control unit <NUM> may determine that spark plug <NUM> is defective.

<FIG> shows the behavior of the determined ignition delay for three cylinders, where one of the cylinders has a defective spark plug. The upper half of <FIG> shows the ignition delays of the three cylinders as a function of time, with the engine load increasing over time and the engine speed increasing to a desired engine speed. As shown by the dotted line TD2,<NUM> for the two cylinders having normally functioning spark plugs, the ignition delay is substantially constant with varying engine load and engine speed. On the other hand, the solid line indicating the ignition delay TD1 for the cylinder having a defective spark plug shows that the ignition delay increases with increasing engine load. In particular, as the ignition delay TD1 increases past a threshold Th1 with increasing engine load, misfiring may occur in the associated cylinder. This can be seen from the measured cylinder pressure ICPM for the associated cylinder, which is shown in the lower half of <FIG> (indicated by the region A in <FIG>). Control unit <NUM> may therefore determine the ignition delay for each cylinder, and may determine that one of the spark plugs is defective when the ignition delay associated with the same increases beyond the threshold Th1. In this case, control unit <NUM> may further be configured to operate internal combustion engine <NUM> under limited load conditions. For example, control unit <NUM> may be configured to activate a derate pulse to hold mode in order to prevent any power increase and operate the engine under stable conditions for a predetermined amount of time. The derate pulse is a signal output by the ECM and indicating that maximum power has been reached and no further increase in power is possible. At the same time, a warning can be output to an operator of internal combustion engine <NUM> to notify the same that an exchange of a spark plug should be scheduled. In some embodiments, internal combustion engine <NUM> may be operated under the limited load conditions for several days or weeks before the spark plug has to be exchanged.

As previously mentioned, control unit <NUM> may also use the ignition delay difference ΔTD in order to determine that a spark plug is defective. ΔTD can be determined in the above-described manner, and an appropriate threshold may be defined for determining whether a spark plug is defective. For example, in the embodiment, ΔTD may be between around <NUM> and around <NUM>, depending on the power output by internal combustion engine <NUM>. For example, at <NUM>% power, ΔTD may be around <NUM>, with the secondary voltage reaching about <NUM> kV prior to the discharge in spark plug <NUM>.

In some embodiments, a second threshold Th2 may be defined to determine whether the ignition delay TD1 is below a lower time limit determined in advance for spark plug <NUM>. This is shown in <FIG>. Accordingly, control unit <NUM> may determine ignition delay TD1 in the above-described manner, and determine that spark plug <NUM> is defective when ignition delay TD1 is higher than first threshold Th1 and/or lower than second threshold Th2. The behavior of the ignition delays with three cylinders shown in <FIG> is the same as that in <FIG>.

It will be readily appreciated that control unit <NUM> may determine whether spark plug <NUM> is defective or nearing the end of its service life based on the ignition delay determined for the same in various manners. Generally, control unit <NUM> is configured to determine a time interval based on a timing of starting a supply of current and a timing of reaching a predetermined current value for a given spark plug. As described above, the time interval may be the ignition delay TD, i.e., the difference between the timing of reaching the predetermined current value t<NUM> and the timing of starting the supply of current t<NUM>. In other embodiments, the time interval may be the ignition delay difference ΔTD, which is defined by the difference between the reference timing t<NUM> determined based on the known behavior for a non-defective spark plug and the timing of starting the supply of current t<NUM>.

Further, as outlined above, in case of a defective spark plug, the determined ignition delay varies with varying engine load. Accordingly, in other embodiments, it may be determined that a spark plug is defective when the time interval or ignition delay determined for the same varies by more than a predetermined amount with varying engine loads. For example, control unit <NUM> may be configured to monitor the ignition delay of each spark plug as the engine load increases, and determine that the spark plug is defective when the ignition delay increases or decreases by more than the predetermined amount, for example, <NUM> or <NUM> %, <NUM> to <NUM> %, <NUM> to <NUM> %, <NUM> to <NUM> %, or <NUM> % to <NUM>% with varying engine load. In other embodiments, control unit <NUM> may determine a rate of change of the ignition delay, and determine whether the spark plug is defective based on said rate of change being greater than a predetermined reference rate. It will be readily appreciated that there are many other possibilities for determining whether a spark plug is defective based on a variation of the measured ignition delay with varying engine load.

In other embodiments, control unit <NUM> may be configured to continuously monitor the ignition delay of each spark plug during operation of internal combustion engine <NUM>. As outlined above, as the ignition delay will generally increase or decrease when a defect occurs, control unit <NUM> may also be configured to determine that a spark plug has become defective when the associated ignition delay changes significantly during operation of internal combustion engine <NUM>. For example, control unit <NUM> may determine that a spark plug has become defective when an absolute value of the variation of the ignition delay from an initial value is greater than a threshold value as internal combustion engine <NUM> is operated, or when a change is greater than, for example, <NUM> or <NUM> %, or up to <NUM> % to <NUM> %. It should be noted that the normal end of the lifetime of a spark plug can also be detected using this method.

In some embodiments, control unit <NUM> may further be configured to estimate a remaining service life of a defective spark plug <NUM> based on the duration of the determined time interval or ignition delay, for example, for a given engine load. In other words, a corresponding map may be stored in the memory of control unit <NUM>, said map establishing a relationship between the duration of the time interval and the expected remaining service life before spark plug <NUM> fails. The time stored in the map may be based on experiments and/or knowledge obtained during operation or testing of internal combustion engine <NUM>. Further, the map may also include a relationship between the estimated remaining service life and the engine load at which internal combustion engine <NUM> is operated. This may allow control unit <NUM> to determine the power limit for internal combustion engine <NUM> that will likely allow reaching a desired remaining operating time before spark plug <NUM> has to be exchanged. Of course, an operator may also be able to specify the engine load at which internal combustion engine <NUM> is to be operated, depending on the determined ignition delay and/or the desired time for which the engine is to be operated before the spark plug is to be exchanged.

As shown in <FIG> and <FIG>, the ignition delay is different for a defective spark plug when compared to the ignition delay for non-defective spark plugs. Accordingly, in some embodiments, control unit <NUM> may be configured to determine the ignition delay for a plurality of cylinders, compare the ignition delay for the plurality of cylinders, and determine that a spark plug associated with one cylinder has become defective when the ignition delay of the same differs by more than a predetermined amount from the ignition delay determined for the other spark plugs. Again, it will be appreciated that there are many possibilities for defining appropriate thresholds for determining that one of the plurality of spark plugs is defective due to the ignition delay of the same being significantly different from the ignition delays of the other spark plugs. In some embodiments, control unit <NUM> may also be configured to determine an average of the ignition delays for the spark plugs, and to determine that one or more of the spark plugs are defective when the ignition delays determined for the same differ from the average by more than a predetermined amount.

As also shown in <FIG> and <FIG>, in case a spark plug is defective and the engine load increases towards maximum load, misfires occur in the associated cylinder, as shown by the region A in <FIG>. Therefore, in order to improve the reliability of the determination of a defective a spark plug, control unit <NUM> may also be configured to receive the cylinder pressures measured for the cylinders of internal combustion engine <NUM> as inputs, and determine that the spark plug, for which an increased or decreased ignition delay has been determined, is defective when, in addition, a measured cylinder pressure of the associated cylinder shows irregularities, i.e., differs from the measured cylinder pressures of the other cylinders or is above or below respective thresholds and indicates misfiring.

The industrial applicability of the systems and methods disclosed herein will be readily appreciated from the foregoing discussion. An exemplary machine suited to the disclosure is a large internal combustion engine such as the engines of the series M46DF, GCM46, GCM34, M32DF, M34DF, M3x manufactured by Caterpillar Motoren GmbH & Co. KG, Kiel, Germany. Similarly, the systems and methods described herein can be adapted to a large variety of internal combustion engines used for various different tasks. With the system and method disclosed herein, it is possible to determine an impending failure of a spark plug of an internal combustion engine by determining the ignition delay for the respective spark plugs of the engine. In this manner, a timely warning can be output for an operator of internal combustion engine <NUM> to warn the same that one or more spark plugs <NUM> are defective and should be replaced. In this manner, the operator of internal combustion engine <NUM> may schedule an exchange of the one or more spark plugs, while emergency stops of internal combustion engine <NUM> due to a failed spark plug can be avoided. As such, the reliability and productivity of internal combustion engine <NUM> can be increased. An exemplary control in accordance with the present disclosure is described in the following.

Internal combustion engine <NUM> may be operated by control unit <NUM> at a desired engine load or engine speed. While internal combustion <NUM> is operating at the desired engine speed, control unit <NUM> determines the ignition timing for each spark plug <NUM> of internal combustion engine <NUM> in the above-described manner. For example, control unit <NUM> determines the timing of starting a supply of current to primary winding <NUM> of each spark plug <NUM>, and determines a timing of reaching a predetermined maximum value of the primary current. From the two timings t<NUM> and t<NUM> (see <FIG>), control unit <NUM> may then determine ignition delay TD for each spark plug. Next, control unit <NUM> compares the determined ignition delay TD to threshold Th1 (see <FIG>). If it is determined that the ignition delay TD is greater than threshold Th1 in <FIG> (or less than threshold Th2 in <FIG>), control unit <NUM> determines that the associated spark plug <NUM> may be defective.

Accordingly, control unit <NUM> activates the derate pulse to limit the engine power. Further, control unit <NUM> outputs a warning to an operator on internal combustion engine <NUM> to indicate that spark plug <NUM> is defective. As a consequence, the operator of internal combustion engine <NUM> may schedule a downtime for internal combustion engine <NUM> to allow for replacement of spark plug <NUM>.

It will be appreciated that the foregoing description provides examples of the disclosed systems and methods. However, it is contemplated that other implementations of the disclosure may differ in detail from the foregoing examples. All references to the disclosure or examples thereof are intended to reference the particular example being discussed at that point and are not intended to imply any limitation as to the general disclosure.

Recitations of ranges of values herein are merely intended to serve as a shorthand method for referring individually to each separate value falling within the range, unless otherwise indicated, and each separate value is incorporated into the specification as if it were individually recited herein. All method steps described herein can be performed in any suitable order, unless otherwise indicated or clearly contradicted by the context.

Claim 1:
A method for determining a defect in a spark plug (<NUM>) associated with a cylinder (<NUM>) of a spark-ignited internal combustion engine (<NUM>), the method comprising:
starting a supply of current to a primary winding (<NUM>) of an ignition coil (<NUM>) associated with the spark plug (<NUM>);
measuring the current flowing through the primary winding (<NUM>);
determining that the current flowing through the primary winding (<NUM>) has reached a predetermined maximum current value;
stopping the supply of current to the primary winding (<NUM>) in response to determining that the current flowing through the primary winding (<NUM>) has reached the predetermined maximum current value;
determining a time interval (TD, ΔTD) based on a timing of starting the supply of current (t<NUM>) and a timing of reaching the predetermined maximum current value (t<NUM>); and
determining that the spark plug (<NUM>) is defective when the time interval (TD, ΔTD) is longer than an upper limit time interval (Th1) determined in advance for the spark plug (<NUM>),
the method further comprising:
determining a slope (Iref) of the current signal when the predetermined maximum current value is reached, based on the voltage applied to the primary winding (<NUM>) and the inductance of the same;
determining a reference timing (t<NUM>) at which the supply of current to the primary winding (<NUM>) would have to be started in case of an ideal behavior of the spark plug (<NUM>) to reach the maximum current value at the timing of reaching the predetermined maximum current value (t<NUM>), based on the determined slope (Iref); and
determining the time interval (ΔTD) from a time difference between the reference timing (t<NUM>) and the timing of starting the supply of current (t<NUM>).