Ignition apparatus for internal combustion engine

In an ignition apparatus, a deterioration determination circuit performs a deterioration determination task of (i) monitoring an absolute increase in a temperature parameter during a predetermined deterioration detection period that has been started since an energization command signal being inputted to a control circuit, and (ii) performing a comparison between the absolute increase in the temperature parameter and a predetermined deterioration detection threshold to thereby determine whether a level of deterioration of a switching circuit is within an acceptable level.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and claims the benefit of priority from Japanese Patent Application Publication No. 2020-073600 filed on Apr. 16, 2020, the disclosure of which is incorporated in its entirety herein by reference.

TECHNICAL FIELD

The present disclosure relates to ignition apparatuses for internal combustion engines.

BACKGROUND

Ignition apparatuses for an internal combustion engine include an igniter comprised of a switch. The igniter controls the switch for applying a high voltage to an ignition plug of the internal combustion engine.

SUMMARY

According to an exemplary aspect of the present disclosure, there is provided an ignition apparatus. The ignition apparatus includes a deterioration determination circuit that performs a deterioration determination task. The deterioration determination task monitors an absolute increase in a temperature parameter during a predetermined deterioration detection period that has been started since an energization command signal being inputted to a control circuit. Then, the deterioration determination task performs a comparison between the absolute increase in the temperature parameter and a predetermined deterioration detection threshold to thereby determine whether a level of deterioration of a switching circuit is within an acceptable level.

DETAILED DESCRIPTION OF EMBODIMENTS

Typical ignition apparatuses for an internal combustion engine include an ignition coil and an igniter serving as an ignition controller. The igniter controls energization of the ignition coil, so that the energized ignition coil outputs a high voltage for igniting an ignition plug of the internal combustion engine.

The igniter includes, for example, a switch, such as an insulated gate bipolar transistor (IGBT), and a control circuit for controlling on-off switching operations of the switch. The ignition coil is comprised of a primary coil and a secondary coil, and the switch is connected to the primary coil. The secondary coil is connected to the ignition plug. The control circuit turns on the switch to energize the primary coil, and thereafter turns off the switch to deenergize the primary coil to accordingly induce a high voltage across the secondary coil based on electromagnetic induction. The generated high voltage is applied across the ignition plug, so that the high voltage applied across the ignition plug causes the ignition plug to generate a spark discharge.

Such a control circuit included in an igniter can have an overtemperature protection function of preventing the switch from overtemperature.

For example, Japanese Patent Application Publication No. 2006-19700 discloses such an igniter, which is an example of a semiconductor apparatus, having such an overtemperature protection function.

The igniter disclosed in the patent publication includes first and second lead frames that are separately arranged from each other. The igniter includes a semiconductor switch that is frequently switched for energization of an ignition coil and mounted on the first lead frame. The igniter includes a comparative semiconductor device mounted on the second lead frame; the comparative semiconductor device has an operating temperature that is lower than that of the semiconductor switch.

Additionally, a thermal resistance member is arranged between the first lead frame and the second lead frame to reduce thermal transfer from the first lead frame to the second lead frame.

The comparative semiconductor device serves as a comparator and performs such an overtemperature protection function of protecting the semiconductor switch against overtemperature.

Specifically, the comparative semiconductor device performs the overtemperature protection function to thereby

(1) Compare a temperature of the semiconductor switch with a reference temperature

(2) Determine that the semiconductor switch is likely to be in an overtemperature state upon determination that the temperature of the semiconductor switch is higher than the reference temperature

(3) Shut off energization of the semiconductor switch, i.e. turn off the semiconductor switch, in response to determination that the temperature of the semiconductor switch is higher than the reference temperature to accordingly prevent the semiconductor switch from being in the overtemperature state, making it possible to protect the semiconductor switch against deteriorations due to its overtemperature

(4) Permit energization of the semiconductor switch, i.e. permit turn-on of the semiconductor switch in response to determination that the temperature of the semiconductor switch is maintained to be lower or equal to the reference temperature

Such a comparative semiconductor device, which has the overtemperature protection function, is usually designed not to perform the overtemperature protection function while the semiconductor switch is in a normal operation state. Note that the semiconductor switch is determined to be in the normal operation state as long as the semiconductor switch is switched on or off with its on duration maintained within a predetermined normal on-duration threshold.

That is, the comparative semiconductor device is designed to perform the overtemperature protection function in response to determination that the semiconductor switch is in a specific operation state, in other words, the on duration of the semiconductor switch has exceeded the predetermined normal on-duration threshold. Note that a switch, which is in a state where its on duration has exceeded the predetermined normal on-duration threshold, will be referred to as the switch being locked, i.e. frozen, in the on state.

How the temperature of a switch increases depends on not only its energized time but also its mounted state on a circuit board, such as a lead frame set forth above. In particular, how the temperature of a switch increases is likely to be susceptible to its heat-dissipation change with age.

A switch, such as a semiconductor switch for energization of an ignition coil, is usually mounted on a circuit board with adhesive, such as solder paste. This configuration enables heat generated from the switch to be dissipated to the circuit board via the adhesive. A progression of deterioration of the adhesive with long-term use of the switch may cause cracks in the adhesive to increase, resulting in the heat dissipation of the switch becoming deteriorated.

Such deterioration of the heat dissipation of the semiconductor switch disclosed in the patent publication may cause the temperature of the semiconductor switch to be likely to increase even if the semiconductor switch is in the normal operation state. This may result in the temperature of the semiconductor switch exceeding the reference temperature, causing unexpected execution of the overtemperature protection function. This unexpected execution of the overtemperature protection function may cause unscheduled shutdown of energization of the semiconductor switch.

This unscheduled shutdown of energization of the semiconductor switch may result in turn-off of the semiconductor switch being earlier than a proper turn-off timing, resulting in the ignition plug being ignited earlier than properly scheduled, in other words, resulting in preignition of the ignition plug. This preignition of the ignition plug may result in damage to components constituting the internal combustion engine.

From the above viewpoints, the present disclosure seeks to provide ignition devices, each of which is capable of reducing unexpected execution of such an overtemperature protection function.

An ignition apparatus according to an exemplary aspect of the present disclosure aims to control energization of a primary winding of an ignition coil to accordingly generate an ignition voltage across a secondary winding of the ignition coil. The ignition apparatus includes a switching circuit including a switch connected to the primary winding, and a control circuit. The control circuit includes a driver configured to control energization of the switch in response to an energization command signal inputted thereto. The control circuit includes an overtemperature protection circuit.

The overtemperature protection circuit is configured to (i) monitor a temperature parameter representing a temperature of the switch, (ii) cause the driver to energize the switch upon determination that the temperature of the switch obtained based on the monitored temperature parameter is lower than or equal to a predetermined prevention temperature, and (iii) cause the driver to shut down the energization of the switch upon determination that the temperature of the switch obtained based on the monitored temperature parameter is higher than the predetermined prevention temperature.

The control circuit includes a deterioration determination circuit configured to perform a deterioration determination task.

The deterioration determination task monitors an absolute increase in the temperature parameter signal during a predetermined deterioration detection period that has been started since the energization command signal being inputted to the control circuit. The deterioration determination task performs a comparison between the absolute increase in the temperature parameter signal and a predetermined deterioration detection threshold to thereby determine whether a level of deterioration of the switching circuit is within an acceptable level.

The overtemperature protection circuit of the ignition apparatus according to the exemplary embodiment causes the driver to shut down the energization of the switch upon determination that the temperature of the switch obtained based on the monitored temperature parameter is higher than the predetermined prevention temperature. This configuration therefore protects the switch against overtemperature.

Additionally, the deterioration determination circuit of the ignition apparatus according to the exemplary embodiment is configured to

1. Monitor the absolute increase in the temperature parameter during the predetermined deterioration detection period that has been started since the energization command signal being inputted to the control circuit

2. Perform a comparison between the absolute increase in the temperature parameter and a predetermined deterioration detection threshold to thereby determine whether the level of deterioration of the switching circuit is within the acceptable level.

This configuration makes it possible to determine whether the level of deterioration of the switching circuit is within the acceptable level before the switch is shut down by the overtemperature protection circuit. This therefore reduces execution of the ignition operation at an unscheduled timing.

The following describes exemplary embodiments of the present disclosure with reference to the accompanying drawings. In the embodiments, like parts between the embodiments, to which like reference characters are assigned, are omitted or simplified to avoid redundant description.

First Embodiment

The following describes an ignition apparatus1for an internal combustion engine100with an ignition plug P according to the first embodiment of the present disclosure with reference toFIGS.1to6.

The internal combustion engine100, which will be referred to simply as an engine100, is a vehicular engine installed in, for example, a vehicle, and the ignition plug P is provided in a combustion chamber of the engine100.

Referring toFIG.1, the ignition apparatus1has a main power supply terminal +B to which electrical power, i.e. a drive voltage, VB is supplied from an unillustrated power source, and has a ground terminal GND. The ignition apparatus1aims to apply, based on the supplied drive voltage VB, a high voltage to the ignition plug P to thereby generate a spark discharge in the ignition plug P. This results in a gas mixture, such as an air-fuel mixture, in the combustion chamber igniting.

FIG.1also illustrates an electronic control unit (ECU)200for controlling operations of the engine100. The ECU200cyclically outputs an ignition signal IGt serving as an energization command signal to the ignition apparatus1, and the ignition apparatus1controls, based on the ignition signal IGt inputted thereto, the timing to cause a spark discharge in the ignition plug P.

The ignition apparatus1includes an ignition coil2comprised of (i) a primary winding21and a secondary winding22, and (ii) an igniter10comprised of a switching circuit30and a control circuit4.

Each of the primary and secondary windings21and22has a first end, i.e. a high-voltage end, and a second end, i.e. a ground-side end, opposite to each other, and the first end of the secondary winding22is connected to the ignition plug P. The primary and secondary windings21and22can be magnetically coupled with each other.

Note that, in the specification, a connection between components represents at least an electrical connection therebetween or both an electrical connection and a mechanical connection.

The ignition apparatus1has a power supply line Lv and a ground line Lg, each of which has opposing first and second ends, and the first end of the power supply line Lv is connected to the main power supply terminal +B, and the second end thereof is connected to the first end of the primary winding21. This enables the main electrical power, i.e. drive voltage VB, supplied from the unillustrated power source to be applied to the first end of the primary winding21via the power supply line Lv. The first end of the ground line Lg is connected to a ground terminal GND of the ignition apparatus1.

As described later, the igniter10controls the amount of a current flowing through the primary winding21to thereby induce, based on the main electrical power, i.e. drive voltage VB, supplied from the unillustrated power source, a high voltage through the secondary winding22for generation of a spark discharge in the spark plug P.

The switching circuit30of the control circuit4has plural terminals that include a coil terminal IGC, a power terminal12, a ground terminal33, a gate terminal34, and a current detection terminal35.

The switching circuit30is for example designed as a single semiconductor chip with a circuit board, and is comprised of, for example, a switch3and a temperature sensor32mounted on the circuit board in the single semiconductor chip with adhesive, such as solder paste. The temperature sensor32aims to measure the temperature of the switch3.

The control circuit4aims to control on-off switching operations of the switch3, in other words, to control energization or de-energization of the switch3.

For example, the switch3has a first input/output (I/O) terminal, a second I/O terminal, and a control terminal. The first embodiment uses an insulated gate bipolar transistor (IGBT)31as the switch3. Specifically, the IGBT31has a collector as the first I/O terminal, an emitter as the second I/O terminal, and a gate as the control terminal. The IGBT31also has a sense terminal31a.

The collector of the IGBT31is connected to the second end of the primary winding21, and the emitter of the IGBT31is connected to the ground terminal GND of the ignition apparatus1via the ground terminal33and the ground line Lg. The IGBT31includes diodes whose cathodes are connected to each other; the diodes are provided between the collector and emitter of the IGBT31.

The control circuit4is configured to receive the ignition signal IGt sent from the ECU200, and control, based on the ignition signal IGt, on-off switching operations of the IGBT31to thereby control how the ignition plug P generates a spark discharge.

Specifically, the ignition signal IGt is, for example, a pulse signal having a high level indicative of turn-on of the IGBT31or a low level indicative of turn-off of the IGBT31.

Specifically, the control circuit4has plural terminals that include an input terminal11, a detection terminal TSD, and a ground terminal GND, and includes, for example, a switch control circuit module M comprised of a lock prevention circuit5serving as an overheat prevention circuit and a deterioration determination circuit6.

Referring toFIG.2, a detection voltage Vs, which serves as a switch-temperature parameter, i.e. an electrical signal of the switch-temperature parameter indicative of the temperature of the IGBT31(switch3), is inputted to the lock prevention circuit5of the control circuit4. The lock prevention circuit5aims to prevent, based on the detection voltage Vs, the IGBT31from overtemperature to accordingly protect the IGBT31against overtemperature.

Specifically, the lock prevention circuit5of the first embodiment is designed as a thermal-shutdown lock prevention circuit5to

1. Monitor the detection voltage Vs

2. Determine whether the monitored detection voltage Vs has exceeded a predetermined energization prevention temperature threshold T1

3. Output, to a driver41described later, an overtemperature detection signal S upon determination that the monitored detection voltage Vs has exceeded the predetermined energization prevention temperature threshold T1for shutdown of energization of the IGBT31

The temperature sensor32is configured to measure the temperature of the IGBT31(switch3), and output, to each of the lock prevention circuit5and the deterioration determination circuit6, the switch-temperature parameter signal that includes the detection voltage Vs that serves as a parameter representing the temperature of the IGBT31(switch3).

As illustrated inFIG.4, the energization prevention temperature threshold T1represents an upper limit temperature for the IGBT31, i.e., the switch3, so that energization of the IGBT31is enabled as long as the temperature of the IGBT31is maintained to be lower than or equal to the energization prevention temperature threshold T1. Specifically, the lock prevention circuit5is configured to estimate, based on the detection voltage Vs, a value of the temperature of the IGBT31, and control energization of the IGBT31to thereby maintain the estimated value of the temperature of the IGBT31to be lower than or equal to the energization prevention temperature threshold T1. For example, a value of the energization prevention temperature threshold T1can be set to be lower than an upper-temperature limit of the IGBT31; the upper-temperature limit of the IGBT31is determined beforehand based on the specifications of the IGBT31.

Like the lock prevention circuit5, the detection voltage Vs, which serves as the switch-temperature parameter signal indicative of the temperature of the IGBT31(switch3), is inputted to the deterioration determination circuit6.

The deterioration determination circuit6is configured to monitor, based on the detection voltage Vs, how the temperature of the IGBT31(switch3) increases to accordingly detect a level of deterioration of the switching circuit30.

Specifically, the deterioration determination circuit6is configured to

1. Calculate, in response to the input of the ignition signal IGt to the control circuit4, an initial value of the detection voltage Vs at the input of the ignition signal IGt at the input of the ignition signal IGt; the initial value of the detection voltage Vs corresponds to an initial value of the temperature of the IGBT31(switch3) at the input of the ignition signal IGt

2. Cyclically monitor the detection voltage Vs during a predetermined deterioration detection period Ta that has been started since the input of the ignition signal IGt to the control circuit4to accordingly calculate, for each cycle, an absolute increase ΔVs in the detection voltage Vs relative to the initial value of the detection voltage Vs; the absolute increase ΔVs in the detection voltage Vs relative to the initial value of the detection voltage Vs corresponds to an absolute increase in the temperature of the IGBT31(switch3) relative to the initial value of the temperature of the IGBT31(switch3).

The absolute increase ΔVs in the detection voltage Vs will be referred to as a temperature-parameter increase ΔVs.

The deterioration determination circuit6is also configured to

1. Perform a comparison of the temperature-parameter increase ΔVs calculated for each cycle with a deterioration detection threshold Vth previously determined for the switching circuit30

2. Determine, based on the comparison result for each cycle, whether to output a deterioration detection signal S1to the driver41via a filter circuit described later

As illustrated inFIGS.5and6, the deterioration detection period Ta is set within a high-level duration of the ignition signal IGt. Additionally, as illustrated inFIGS.5and6, the deterioration detection period Ta is preferably set such that the deterioration detection signal S1is outputted before the temperature of the IGBT31(switch3) estimated based on the detection voltage Vs reaches a predetermined energization prevention temperature T1. This setting of the deterioration detection period Ta enables an estimated temperature of the IGBT31(switch3) based on the deterioration detection threshold Vth to be lower than the energization prevention temperature T1, making it possible to detect an abnormal increase in the temperature of the IGBT31(switch3) due to, for example, a partial deterioration of the switching circuit30before the lock prevention circuit5shuts down energization of the IGBT31, i.e., the switch3.

Referring toFIG.2, the deterioration determination circuit6preferably includes a deterioration detection period generator7, a switch SW1, a differential amplifier61serving as a temperature increment calculator, a comparator62, a filter circuit63, a counter64, a capacitor65, and a voltage source66.

The deterioration detection period generator7triggers generation of the deterioration detection period Ta in response to the input of the ignition signal IGt to the control circuit4. The differential amplifier61calculates, in response to the input of the ignition signal IGt to the control circuit4, the initial value of the temperature of the IGBT31at the input of the ignition signal IGt, and calculates, for each cycle, the temperature-parameter increase ΔVs relative to the initial value of the detection voltage Vs.

The comparator62compares the temperature-parameter increase ΔVs with the deterioration detection threshold Vth to accordingly determine whether the temperature-parameter increase ΔVs becomes higher than the deterioration detection threshold Vth. Then, the comparator62outputs the deterioration detection signal S1to the filter circuit63upon determination that the temperature-parameter increase ΔVs becomes higher than the deterioration detection threshold Vth.

The filter circuit63is configured to enable the deterioration detection signal S1to be passed therethrough to the counter64upon a signal representing the deterioration detection period Ta being outputted from the deterioration detection period generator7to the control circuit4. Operations of the counter64will be described later.

This configuration of the control circuit4generates the deterioration detection period Ta, which has a predetermined length, immediately in response to the input of the ignition signal IGt to the control circuit4, calculates the temperature increase ΔV, and compares the temperature increase ΔV with the deterioration detection threshold Vth.

This configuration of the control circuit4enables output of warning information representing that the switching circuit3has deteriorated upon determination that the temperature increase ΔV becomes higher than the deterioration detection threshold Vth within the generated deterioration detection period Ta.

In other words, this configuration of the control circuit4disables output of warning information representing that the switching circuit3has deteriorated even upon determination that the temperature increase ΔV becomes higher than the deterioration detection threshold Vth after termination of the generated deterioration detection period Ta.

This configuration of the control circuit4therefore makes it possible to immediately detect deterioration of the switching circuit3, and notify one or more occupants in the vehicle of the warning information about the deterioration of the switching circuit3.

The following describes the configuration and operations of the ignition apparatus1according to the first embodiment in more detail.

As described above, the igniter10of the ignition apparatus1is configured to perform on-off switching operations of the IGBT31(switch3) in response to the ignition signal IGt send from the ECU200and inputted to the input terminal11of the control circuit4of the igniter10.

The second end of the primary winging21is connected to the collector (first I/O terminal) of the IGBT31via the coil terminal IGC.

The first embodiment uses a vehicular battery installed in the vehicle as the unillustrated power source.

The ignition plug P has a center electrode and a ground electrode with a gap therebetween.

The first end of the secondary winding22is connected to the center electrode of the ignition plug P, and the ground electrode of the ignition plug P is connected to a ground of the engine100. The second end of the secondary winding22is also connected to the ground of the engine100via a diode23for prevention of flying sparks.

The ignition coil2is configured such that shutting down energization of the primary winding21induces a high voltage across the secondary winding22based on electromagnetic induction, and applies the high voltage across the center and ground electrodes of the ignition plug P, thus causing a spark discharge to be generated therebetween.

The anode of the diode23is connected to the second end of the secondary winding22, and the cathode of the diode23is connected to the ground of the engine100. In other words, the diode23is connected between the secondary winding22and the predetermined ground of the engine100with its forward direction being directed from the secondary winding22to the ground of the engine100. That is, the diode23disables a current generated due to energization of the primary winding21from flowing toward the second end of the secondary winding22from the ground of the engine100, thus preventing flying sparks in the ignition plug P due to energization of the primary winding21.

The temperature sensor32according to the first embodiment is comprised of a temperature-sensitive sensor including, for example, at least a first temperature-sensitive diode D1and a second temperature-sensitive diode D2connected in series to each other.

For example, the temperature sensor32according to the first embodiment is arranged to be adjacent to the IGBT31, so that the temperature of the IGBT31is substantially identical to that of the temperature sensor32.

The temperature sensor32is comprised of a temperature-sensitive sensor including, for example, at least a first temperature-sensitive diode D1and a second temperature-sensitive diode D2. Specifically, the anode of the first temperature-sensitive diode D1is connected to the cathode of the second temperature-sensitive diode D2, so that they are connected in series to each other. The cathode of the first temperature-sensitive diode D1is connected to the ground terminal GND of the control circuit4, and the anode of the second temperature-sensitive diode D2is connected to the detection terminal TSD of the control circuit4. This results in the direction from the anode of the second temperature-sensitive diode D2toward the ground terminal GND of the control circuit4corresponding to the forward direction of each of the first and second temperature-sensitive diodes D1and D2.

Each of the first and second temperature-sensitive diodes D1and D2is configured to generate a forward voltage thereacross upon a forward current is flowing therethrough; the forward voltage generated across each of the first and second temperature-sensitive diodes D1and D2correlates with the temperature thereof. That is, the higher the temperature of each of the first and second temperature-sensitive diodes D1and D2, the lower the forward voltage across the corresponding one of the first and second temperature-sensitive diodes D1and D2. This enables the control circuit4to measure, based on the forward voltage, which serves as the detection voltage Vs, of each of the first and second temperature-sensitive diodes D1and D2, the temperature of the corresponding one of the first and second temperature-sensitive diodes D1and D2, thus measuring the temperature of the IGBT31(switch3).

The control circuit4is for example designed as a monolithic integrated circuit (IC), and is comprised of a single semiconductor chip with a circuit board, the lock prevention circuit5, and the deterioration determination circuit6mounted on the circuit board in the single semiconductor chip. The lock prevention circuit5preferably includes the driver41, a filter circuit42, an overvoltage protection circuit43, an overcurrent protection circuit44, and a switch45.

The filter circuit42is configured to shape the waveform of the ignition signal IGt transmitted from the ECU200to remove noise therefrom, thus outputting, to the driver41, a binary signal with one of the high level and low level as the ignition signal IGt. The binary signal outputted from the filter circuit42can also be referred to as the ignition signal IGt. Note that an input of the ignition signal IGt to a given component represents that the ignition signal IGt with the high level is inputted to the given component, and shut down of the ignition signal IGt to a given component represents that the ignition signal IGt with the low level is inputted to the given component.

For example, a bipolar transistor is used as the switch45. Specifically, the switch45has a collector as a first I/O terminal, an emitter as a second I/O terminal, and a base as a control terminal.

The driver41has an output terminal connected to the base, i.e. control terminal, of the switch45, and the collector (first I/O terminal) of the switch45is connected to the power supply line Lv via the overvoltage protection circuit43, a resistor R1, and the power terminal12of the control circuit4. The emitter (second I/O terminal) of the switch45is connected to the ground terminal GND via the ground line Lg.

The collector (first I/O terminal) of the switch45is connected to the gate (control terminal) of the IGBT31via the gate terminal34of the switching circuit30and a resistor R2.

The driver41is configured to output, to the base of the switch45, an energization signal, i.e. a turn-on signal, in response to the on duration of the ignition signal IGt inputted thereto from the filter circuit42. This turns off the switch45to thereby apply the drive voltage VB supplied from the unillustrated power source to the gate of the IGBT31, thus turning on the IGBT31.

In contrast, the driver41is configured to output, to the base of the switch45, a shutdown signal, i.e. a turn-off signal, in response to the off duration of the ignition signal IGt inputted thereto from the filter circuit42. This turns on the switch45to thereby shut down the drive voltage VB from the unillustrated power source to the gate of the IGBT31, thus turning on the IGBT31.

That is, alternately controlling the high level or low level of the ignition signal IGt enables the IGBT31to be alternately turned on or off.

The overvoltage protection circuit43is connected between the power supply line Lv and the ground line Lg, and also connected between the power supply line Lv and the driver41. The overvoltage protection circuit43is configured to monitor how the drive voltage VB supplied from the unillustrated power source via the power supply line Lv is changed, and to forcibly shut down the drive voltage VB from the unillustrated power source to the driver41upon detecting an overvoltage based on change of the drive voltage VB. This makes it possible to protect the switching circuit3against the overvoltage.

The overcurrent protection circuit44is connected between the current detection terminal35of the switching circuit30and the ground line Lg; the current detection terminal35of the switching circuit30is connected to the sense terminal31aof the IGBT31via a resistor R3. The sense terminal31aof the IGBT31enables a minute current, i.e. a sense current, to flow upon a collector current flowing through the IGBT31.

Specifically, as illustrated inFIG.1, the drive voltage VB applied to the first end of the primary winding21with the IGBT31being on enables a primary current to flow through the primary winding21and flow through the IGBT31as a collector current to the ground terminal GND. This enables the sense current to flow from the sense terminal31aof the IGBT31into the overcurrent protection circuit44. The overcurrent protection circuit44is connected to the driver41.

The overcurrent protection circuit44is therefore configured to monitor how the primary current flowing through the primary winding21is changed, and to output, to the driver41, information indicative of the occurrence of an overcurrent upon detecting the overcurrent based on change of the primary current. This enables the driver41to control on-off switching operations of the switch45, i.e. the IGBT31, to thereby limit the level of the primary current flowing through the primary winding21. This makes it possible to protect the switching circuit3against the overcurrent.

The control circuit3additionally includes a capacitor13connected between the main power supply terminal +B and the ground terminal GND for preventing high-frequency noise components from flowing into the control circuit4.

The lock prevention circuit5performs an overtemperature protection task that prevents an excessive increase in the temperature of the IGBT31(switch3) due to its overtemperature while the IGBT3is driven in a selected one of prepared lock drive modes in which the IGBT31is locked in the on state for a certain amount of time. The prepared lock drive modes of the IGBT31in which the IGBT31is locked in the on state for a certain amount of time include, for example, a lock-on mode in which the ignition signal IGt is locked in the high level for a certain amount of time, and a high-rotation high-duty mode in which the ignition signal IGt has a relatively high duty so that the IGBT31is turned on with a relatively long on-duration every predetermined short period, so that the RPM of the engine100is relatively high.

That is, when detecting the IGBT3is in an overtemperature state in a selected one of the lock drive modes, the lock prevention circuit5is configured to output, to the driver41, the overtemperature prevention signal S that causes the driver41to forcibly perform shutdown, i.e. thermal shutdown, of energization of the IGBT31.

This prevents the IGBT31from being deteriorated, such as thermally damaged, due to its overtemperature.

Referring toFIGS.2and3, the lock prevention circuit5includes, for example, a constant current source51, an overtemperature detector52, and a voltage source53with positive and negative terminals.

The overtemperature detector52is comprised of, for example, a hysteresis comparator, and has a non-inverting terminal (a positive terminal), an inverting input terminal (a negative terminal), and an output terminal.

The detection terminal TSD of the control circuit4and the non-inverting input terminal of the overtemperature detector52are connected to each other via a signal line SL. The constant current source51has an input terminal connected to the power terminal12of the control circuit4, and an output terminal connected to both the detection terminal TSD of the control circuit4and the non-inverting input terminal of the overtemperature detector52.

Note thatFIG.2schematically illustrates selected components of the lock protection circuit5and selected components of the deterioration determination circuit6and their selected components; these components are used to perform energization control of the IGBT31.

The non-inverting input terminal of the overtemperature detector52is connected to the detection terminal TSD of the control circuit4, and the inverting input terminal of the overtemperature detector52is connected to the positive terminal of the voltage source53. The negative terminal of the voltage source53is connected to the ground terminal GND of the ignition apparatus1. The output terminal of the overtemperature detector52is connected to the driver41.

The detection terminal TSD of the control circuit4is connected to the non-inverting input terminal of the overtemperature detector52. As described above, the temperature sensor32outputs the detection voltage Vs as a parameter indicative of the temperature of the IGBT32across the detection terminal32and the ground terminal GND of the control circuit4. This results in the detection voltage Vs being inputted to the non-inverting input terminal of the overtemperature detector52.

The voltage source53is configured to apply, to the inverting input terminal of the overtemperature detector52, a predetermined first threshold voltage Vth1; the predetermined first threshold voltage Vth1corresponds to the predetermined energization prevention temperature T1. That is, when the temperature of the IGBT31has reached the energization prevention temperature T1, a value of the first threshold voltage Vth1is detected by the temperature sensor32as the detection voltage Vs.

The constant current source51is connected between the non-inverting input terminal of the overtemperature detector52and the detection terminal TSD of the control circuit4, and configured to apply, based on the drive voltage VB supplied from the unillustrated power source, a detection current to the first and second temperature-sensitive diodes D1and D2for detecting the temperature of the IGBT31.

The overtemperature detector52of the lock prevention circuit5is configured to

1. Output the overtemperature prevention signal S to the driver41upon the detection voltage Vs inputted to the non-inverting input terminal of the overtemperature detector52being lower than the first threshold voltage Vth1

2. Disable output of the overtemperature prevention signal S to the driver41upon the detection voltage Vs inputted to the non-inverting input terminal of the overtemperature detector52being higher or equal to the first threshold voltage Vth1

While the overtemperature prevention signal S is disabled from being outputted from the overtemperature detector52to the driver41, the lock prevention circuit5is operating in an energization permission mode. In contrast, while the overtemperature prevention signal S is outputted from the overtemperature detector52to the driver41, the lock prevention circuit5is operating in an energization prevention mode.

Referring toFIG.4, if the ignition signal IGt is locked in the high level for control of energization of the IGBT31, the IGBT31is locked in the on state from time to, so that the temperature of the IGBT31rises with the energization time, i.e. the on duration, of the IGBT31to have reached the energization prevention temperature T1.

As described above, the higher the temperature of each of the first and second temperature-sensitive diodes D1and D2, the lower the forward voltage across the corresponding one of the first and second temperature-sensitive diodes D1and D2. For this reason, the detection voltage Vs inputted to the non-inverting input terminal of the overtemperature detector52is higher than the first threshold voltage Vth1until the temperature of the IGBT31reaches the energization prevention temperature T1, so that the overtemperature prevention signal S is disabled from being outputted from the overtemperature detector52to the driver41during the energization permission mode of the lock prevention circuit5. This enables the driver41and the switch45to output the drive voltage VB to the gate of the IGBT31, thus turning on the IGBT31to thereby energize the ignition coil2.

While the temperature of the IGBT31rises with the energization time, i.e. the on duration, of the IGBT31, the detection voltage Vs decreases, and when the temperature of the IGBT31has reached the energization prevention temperature T1, a value of the detection voltage Vs becomes lower than the detection threshold voltage Vgth1at the time t1.

In response to the value of the detection voltage Vs becoming lower than the detection threshold voltage Vgth1at the time t1, the overtemperature detector52determines that the IGBT31is in an overtemperature condition, thus outputting the overtemperature prevention signal S to the driver41, so that the operation mode of the lock prevention circuit5is switched from the energization permission mode to the energization prevention mode at the time t1.

In response to receiving the overtemperature prevention signal S, the driver41and the switch45shut down application of the drive voltage VB to the gate of the IGBT31, thus turning off the IGBT31. This results in shutdown of energization of the ignition coil2at the time t1.

Next, the following describes how the lock prevention circuit5works with reference toFIG.4.

As illustrated inFIG.4, at the time t1, energization of the IGBT31is shut down, so that the temperature of the IGBT31gradually decreases after the time t1whereas the detection voltage Vs gradually increases after the time t1.

Previously determining the first threshold voltage Vth1corresponding to the predetermined energization prevention temperature T1enables overtemperature of the IGBT31to be detected based on comparison between the first threshold voltage Vth1and the detection voltage Vs, making it possible to protect the IGBT31against overtemperature.

It is preferable to previously determine an energization permission temperature T2that enables, after shutdown of energization of the IGBT31in response to the overtemperature detection signal S, energization of the IGBT31at time t2if the temperature of the IGBT31has decreased down to a second threshold voltage Vth2previously determined to correspond to the energization permission temperature T2.

That is, as described above, the overtemperature detector52of the first embodiment is configured to control energization of the IGBT31in accordance with predetermined hysteresis characteristics. That is, the overtemperature detector52of the first embodiment is configured to

1. Shut down energization of the IGBT31upon the detection voltage Vs being lower than the first threshold voltage Vth1

2. Hold the shutdown even if the detection voltage Vs being higher or equal to the first threshold voltage Vth1

3. Energize the IGBT31upon the detection voltage Vs being higher than the second threshold voltage Vth2that is set to be higher than the first threshold voltage Vth1

Specifically, the lock prevention circuit5prevents energization of the IGBT31from the time t1to the time t2at which the temperature of the IGBT31has reached the energization permission temperature T2even upon the ignition signal IGt with the high level being input to the lock prevention circuit5. This results in the IGBT31being maintained in the off state.

Thereafter, the lock prevention circuit5cancels the output of the overtemperature detection signal S upon the temperature of the IGBT31exceeding the energization permission temperature T2at the time t2, so that the operation mode of the lock prevention circuit5is switched from the energization prevention mode to the energization permission mode. After the time t2, the lock prevention circuit5energizes the IGBT31in response to input of the ignition signal IGt with the high level thereto to thereby turn on the IGBT31at time t3. After the time t3, the temperature of the IGBT31gradually increases due to the IGBT31being in the on state whereas the detection voltage Vs gradually decreases after the time t3.

As described above, the lock prevention circuit5is configured such that the overtemperature detection circuit52determines whether to output the overtemperature detection signal S to the driver41in accordance with the detection voltage Vs, the first threshold voltage Vth1, and the second threshold voltage Vth2. This configuration enables the temperature of the IGBT31to be adjusted within a predetermined temperature range.

As described above, the ignition coil2is configured to perform an ignition operation based on shutdown of energization of the primary coil21. This configuration therefore may result in the occurrence of a spark discharge in the ignition plug P at an unscheduled timing due to forcible turn-off of the IGBT31by the above overtemperature protection task. Additionally, the rate of increase in the temperature of the IGBT31depends on how the IGBT31is mounted on the circuit board of the switching circuit30. In particular, a decrease in the heat dissipation characteristics of the IGBT31may cause the IGBT31to be likely to increase.

For example, the IGBT31(switch3) is configured to dissipate heat generated therefrom to the circuit board via the adhesive, such as the solder paste interposed between the IGBT31and the circuit board. A progression of deterioration of the adhesive, such as the solder pate, may cause cracks in the adhesive to increase, resulting in the heat dissipation of the IGBT31becoming deteriorated.

Such deterioration of the heat dissipation of the IGBT31may cause the temperature of the IGBT31to be likely to increase even if the IGBT31is operated normally. This may cause the lock prevention circuit5to operate to output the overtemperature detection signal S to the driver41although the ignition signal IGt is driven normally without being unlocked in the high level. This operation of the lock prevention circuit5may result in the ignition plug P being ignited earlier than properly scheduled, in other words, resulting in preignition of the ignition plug P. This preignition of the ignition plug P may result in damage to components constituting the engine100.

From this viewpoint, the control circuit4includes the deterioration determination circuit6in addition to the lock prevention circuit5.

The deterioration determination circuit6is configured to detect an increase in the temperature of the IGBT31due to the deterioration of the switching circuit30to thereby output the deterioration detection signal S1to the filter circuit63before the lock protection circuit5outputs the overtemperature detection signal S based on the increase in the temperature of the IGBT31due to the deterioration of the switching circuit30.

As described above, as illustrated inFIG.2, the deterioration determination circuit6of the first embodiment includes the deterioration detection period generator7, the switch SW1, the differential amplifier61, the comparator62, the filter circuit63, the counter64, the capacitor65, and the voltage source66.

The deterioration detection period generator7generates the deterioration detection period Ta in response to the input of the ignition signal IGt to the control circuit4.

The differential amplifier61calculates, in response to the input of the ignition signal IGt to the control circuit4, an initial value of the detection voltage Vs at the input of the ignition signal IGt; the initial value of the detection voltage Vs corresponds to the initial value of the temperature of the IGBT31at the input of the ignition signal IGt. The differential amplifier61additionally calculates, for each cycle, the temperature-parameter increase ΔVs relative to the initial value of the detection voltage Vs.

Specifically, the differential amplifier61has a pair of first and second differential input terminals and an output terminal.

A pair of signal lines L1and L2are branched from the signal line SL connecting between the detection terminal TSD of the control circuit4and the non-inverting input terminal of the overtemperature detector52. The signal line L1branched from the signal line SL is connected to the first differential input terminal of the differential amplifier61, and the signal line L2branched from the signal line SL is connected to the second differential input terminal of the differential amplifier61. This enables the detection voltage Vs to be inputted to both the first and second differential input terminals of the differential amplifier61.

The switch SW1is provided on the signal line L1; the switch SW1is configured to disconnect the first differential input terminal of the differential amplifier61from the detection terminal TSD when turned off.

The capacitor65is connected between a portion of the signal line L1and the ground line Lg; the portion of the signal line L1is located between the differential amplifier61and the switch SW1.

Referring toFIG.5, the switch SW1has an unillustrated control terminal to which the ignition signal IGt is inputted. This enables the switch SW1to be alternately turned on, i.e. closed, upon the ignition signal IGt being in the low level, and turned off, i.e. opened, upon the ignition signal IGt being in the high level. The on state of the switch SW1enables the first differential input terminal of the differential amplifier61and the detection terminal TSD to be connected to each other, enabling the detection voltage Vs to be inputted to the first differential input terminal of the differential amplifier61. The on state of the switch SW1additionally enables the capacitor65to be charged based on the detection voltage Vs via the signal line L1, so that a voltage A1across the capacitor65, which will be referred to as a capacitor voltage A1, becomes equivalent to the detection voltage Vs inputted to the signal line L1.

Next, the following describes how the deterioration determination circuit6works with a level of the deterioration of the switching circuit30being within an acceptable level, i.e., an acceptable range, which represents an acceptable deterioration condition, with reference toFIG.5A.

Before time t11illustrated inFIG.5A, the ignition signal IGt is in the low level, so that the capacitor voltage A1across the capacitor65is equivalent to the detection voltage Vs inputted to the second differential input terminal of the differential amplifier61from the signal line L2. This results in a constant value of the temperature-parameter increase ΔVs being outputted from the differential amplifier61based on a differential value between the detection voltage Vs at the first differential input terminal and the detection voltage Vs at the second differential input terminal.

When the ignition signal IGt is inputted to the control circuit4at the time t11, the switch SW1is turned off, so that the capacitor voltage A1is maintained as a value of the detection voltage Vs at the time t11.

Because the switch SW1is in the off state, the capacitor voltage A1inputted to the first differential input terminal of the differential amplifier41is fixed to the value of the detection voltage Vs at the input of the ignition signal IGt to the control circuit4at the time t11; the value of the detection voltage Vs is referred to as the reference voltage set forth above.

The turn-on of the IGBT31in response to the input of the ignition signal IGt to the control circuit4causes the detection voltage Vs to gradually decreases after the time t11. The turn-on of the IGBT31causes an energization current I1flowing through the primary winding21of the ignition coil2to increase, resulting in the temperature of the IGBT31increasing with the increase of the energization current I1after the time t11. However, because the level of the deterioration of the switching circuit30being within the acceptable level so that the rate of decrease in the detection voltage Vs is small, an absolute value of the voltage difference between the capacitor voltage A1and the detection voltage Vs is relatively small.

Next, the following describes how the deterioration determination circuit6works with the level of the deterioration of the switching circuit30being higher than the acceptable level, which represents an unacceptable deterioration condition, with reference toFIG.5B.

Before time t11aillustrated inFIG.5B, the ignition signal IGt is in the low level, so that the capacitor voltage A1across the capacitor65is equivalent to the detection voltage Vs inputted to the second differential input terminal of the differential amplifier61from the signal line L2. This results in the constant value of the temperature-parameter increase ΔVs being outputted from the differential amplifier61based on the differential value between the detection voltage Vs at the first differential input terminal and the detection voltage Vs at the second differential input terminal.

When the ignition signal IGt is inputted to the control circuit4at the time t11a, the switch SW1is turned off, so that the capacitor voltage A1is maintained as a value of the detection voltage Vs at the time t11a.

Because the switch SW1is in the off state, the capacitor voltage A1inputted to the first differential input terminal of the differential amplifier41is fixed to the initial value of the detection voltage Vs at the input of the ignition signal IGt to the control circuit4at the time t11a.

Due to the level of the deterioration of the switching circuit30being higher than the acceptable level, the turn-on of the IGBT31in response to the input of the ignition signal IGt to the control circuit4causes the detection voltage Vs in the unacceptable deterioration condition to decrease after the time t11ain a shorter time than the detection voltage Vs in the acceptable deterioration condition. This results in the absolute value of the voltage difference between the capacitor voltage A1and the detection voltage Vs becomes larger as that in the acceptable deterioration condition.

The deterioration determination circuit6is designed to perform determination of whether the deterioration of the switching circuit30is within the acceptable level using the difference between

(i) Change of the detection voltage Vs in the acceptable deterioration condition

(ii) Change of the detection voltage Vs in the unacceptable deterioration condition

Specifically, the deterioration determination circuit6calculates, for each cycle, the temperature-parameter increase ΔVs relative to the initial value of the detection voltage Vs during the deterioration detection period Ta. Then, the deterioration determination circuit6compares the temperature-parameter increase ΔVs calculated for each cycle with the deterioration detection threshold Vth previously determined for the switching circuit30to accordingly determine, based on the comparison result for each cycle, whether the level of the deterioration of the switching circuit30is higher than the acceptable level.

The deterioration detection period Ta is a period with a predetermined length; the period has been started since the input of the ignition signal IGt to the control circuit4. The differential amplifier61is configured to amplify an absolute of the differential value between the capacitor voltage A1at the first differential input terminal and the detection voltage Vs at the second differential input terminal, thus outputting the amplified absolute of the differential value as the temperature-parameter increase ΔVs.

The comparator62has a non-inverting terminal (a positive terminal), an inverting input terminal (a negative terminal), and an output terminal. The non-inverting terminal of the comparator62is connected to the output terminal of the differential amplifier61, and the inverting terminal of the comparator62is connected to the positive terminal of the voltage source66. The negative terminal of the voltage source66is connected to the ground terminal GND of the ignition apparatus1. The output terminal of the comparator62is connected to the filter circuit63.

As described above, the differential amplifier61outputs the temperature-parameter increase ΔVs from the output terminal thereof, so that the temperature-parameter increase ΔVs is inputted to the non-inverting input terminal of the comparator62.

The voltage source66is configured to apply, to the inverting input terminal of the comparator62, a predetermined deterioration detection threshold Vth.

The comparator62is configured to

1. Disable output of the deterioration detection signal S1to the filter circuit63upon the temperature-parameter increase ΔVs inputted to the non-inverting input terminal of the comparator62being lower than or equal to the deterioration detection threshold Vth

2. Output the deterioration detection signal S1to the filter circuit63upon the temperature-parameter increase ΔVs inputted to the non-inverting input terminal of the comparator62being higher than the deterioration detection threshold Vth

The deterioration determination circuit6is configured such that, in the acceptable deterioration condition, the temperature-parameter increase ΔV has not reached the deterioration detection threshold Vth, resulting in no output of the deterioration detection signal S1from the comparator62(seeFIG.5).

The deterioration detection signal S1outputted from the comparator62is inputted to the counter64through the filter circuit63.

The filter circuit63is configured to

1. Receive the signal representing the deterioration detection period Ta being outputted from the deterioration detection period generator7to the control circuit4

2. Enable the deterioration detection signal S1to be passed therethrough to the counter64upon the signal representing the deterioration detection period Ta being inputted to the control circuit4

For example, the deterioration detection period generator7is comprised of a timer circuit. The deterioration detection period generator7generates the deterioration detection period Ta in response to the input of the ignition signal IGt to the filter circuit63, and outputs the deterioration detection period Ta to the filter circuit63.

The deterioration detection period Ta is preferably set to be shorter than a predetermined normal input period Ts of the ignition signal IGt to the control circuit4. As illustrated inFIG.5B, in the unacceptable deterioration condition, the heat dissipation characteristics of the IGBT31decrease so that the rate of increase in the temperature of the IGBT31is sharper than that in the acceptable deterioration condition. We therefore experimentally measured the rate of increase in the temperature of the IGBT31in the acceptable deterioration condition. The deterioration detection period Ta is therefore preferably set, based on the measured rate of increase in the temperature of the IGBT31, to an appropriate value such that the deterioration detection signal S1is outputted before the temperature of the IGBT31(switch3) reaches the energization prevention temperature T1in the unacceptable deterioration condition.

In other words, the deterioration detection period Ta and the overtemperature detection threshold Vth1are preferably set, based on the measured rate of increase in the temperature of the IGBT31, to appropriate values such that the deterioration detection signal S1is outputted before the detection voltage Vs reaches the overtemperature detection threshold Vth1in the unacceptable deterioration condition.

Comparing the temperature-parameter increase ΔV with the deterioration detection threshold Vth enables the deterioration determination circuit6to promptly determine whether the level of the deterioration of the switching circuit30is higher than the acceptable level before the lock prevention circuit5operates to output the overtemperature detection signal S to the driver41.

The filter circuit63is configured to output, to the counter64, an output signal A2with a low level upon no deterioration detection signal S1being inputted thereto, and switch the low level of the signal A2to the high level upon the deterioration detection signal S1being inputted thereto while the signal indicative of the deterioration detection period Ta is inputted thereto. That is, the filter circuit63is configured to maintain, even if the deterioration detection signal S1is inputted thereto, the low level of the output signal A2upon no signal indicative of the deterioration detection period Ta being inputted thereto, that is, upon the deterioration detection period Ta being terminated.

The deterioration of the switching circuit30gradually proceeds over time, so that the detection voltage Vs is likely to decrease due to the deterioration of the heat dissipation characteristics of the IGBT31. This may result in, as illustrated inFIG.6, an arrival of the temperature-parameter increase ΔV at the deterioration detection threshold Vth at time t13bafter the termination of the deterioration detection period Ta at time t12bin the acceptable deterioration condition.

Even if the temperature-parameter increase ΔV has arrived at the deterioration detection threshold Vth, because of the termination of the deterioration detection period Ta, the filter circuit63maintains the low level of the output signal A2even if the deterioration detection signal S1is inputted thereto, the low level of the output signal A2upon no signal indicative of the deterioration detection period Ta being inputted thereto, that is, upon the deterioration detection period Ta being terminated.

The counter64is configured to count the number of switching of the output signal A2from the low level to the high level, and store the counted number therein. The counter64has an output terminal connected to the driver41, and sends, to the driver41, a count signal indicative of the number of switching of the output signal A2from the low level to the high level.

This enables the driver41to limit energization of the IGBT31in response to receiving the count signal.

For example, the driver41can turn off the IGBT31in response to receiving the count signal.

As described above, the control circuit4is configured to, in response to, for example, the input of the ignition signal IGt to the control circuit4, perform

1. A first determination of whether the IGBT31is in the overtemperature condition using the overtemperature detection circuit52to thereby output, to the driver41, the overtemperature detection signal S upon the first determination being affirmative, i.e., the IGBT31being determined to be in the overtemperature condition

2. A second determination of whether the level of the deterioration of the switching circuit30is higher than the acceptable level using the deterioration determination circuit6to thereby output, to the driver41, the deterioration detection signal S1upon determination that, before the first determination being affirmative, the level of the deterioration of the switching circuit30is higher than the acceptable level

This configuration therefore makes it possible to output, to the driver41, the deterioration detection signal S1upon determination that the level of the deterioration of the switching circuit30is higher than the acceptable level before outputting of the overtemperature detection signal S to the driver41. This configuration prevents unexpected execution of the overtemperature protection task.

The deterioration determination circuit6of the first embodiment can have

1. A first function of sending the deterioration detection signal S1to an external ECU located outside the ignition apparatus1for instructing the external ECU to determine whether the level of the deterioration of the switching circuit30is higher than the acceptable level, and/or

2. A second function of storing, in a storage previously installed therein, information indicative of the outputting of the deterioration detection signal S1to the driver41

If the deterioration determination circuit6includes the first function, the counter64can be eliminated from the deterioration determination circuit6.

The filter circuit63can be configured to output, to the driver41, the deterioration detection signal S1, thus causing the driver41to turn off the IGBT31. This enables the counter64to be eliminated from the deterioration determination circuit6.

The counter64can be configured to output, to the driver41, a definitive deterioration signal S2with a high level upon the counted number having reached a predetermined threshold number, and thereafter the counter64resets the counted number.

This preferably causes the driver41to continuously energize the IGBT31in response to receiving the definitive deterioration signal S2for a current ignition signal IGt currently inputted to the control circuit4, and to prevent energization of the IGBT31for the following ignition signals IGt after the current ignition signal IGt.

Second Embodiment

The following describes the second embodiment of the present disclosure. The structures and/or functions of an ignition apparatus1A according to the second embodiment are different from those of the ignition apparatus1according to the first embodiment in the following points. The following therefore mainly describes the different points.

The ignition apparatus1A includes a deterioration determination circuit6A comprised of a deterioration detection period generator7A.

As illustrated inFIG.7A, the deterioration detection period generator7A of th deterioration determination circuit6A triggers generation of a timer signal B3in response to the input of the ignition signal IGt to the control circuit4; the timer signal B3is, for example, a pulse signal having a high-level width, i.e. pulse width that represents the deterioration determination period Ta. The deterioration detection period generator7A outputs the timer signal B3to the filter circuit63, so that both the deterioration detection signal S1and the timer signal B3are inputted to the filter circuit63.

Like the first embodiment, the output signal A2of the filter circuit63is inputted to the counter64.

The counter64is configured to

(i) Count the number of times the output signal A2is switched from the low level to the high level

(ii) Store the counted number therein

(iii) Output, to the driver41, the definitive deterioration signal S2upon the counted number having reached a predetermined threshold number

(iv) Reset the counted number upon the counted number having reached a predetermined threshold number

The deterioration detection period generator7A of the second embodiment is designed as, for example, an analog circuit.

Specifically, as illustrated inFIG.7A, the deterioration detection period generator7A designed as an analog circuit includes a constant current source71, a capacitor72, a comparator73, an inverter74, an AND gate75, a voltage source76with positive and negative terminals, a resistor R, and switches SW2and SW3.

The capacitor72has opposing first and second electrodes.

The constant current source71has an input terminal connected to the power terminal12via the switch SW2, and an output terminal connected to the ground line GND of the ignition apparatus1A via the first electrode of the capacitor72. The second electrode of the capacitor72is connected to the ground line GND of the ignition apparatus1A.

The comparator73has a non-inverting terminal (a positive terminal), an inverting input terminal (a negative terminal), and an output terminal. The non-inverting terminal of the comparator73is connected to the connection point between the output terminal of the constant current source71and the capacitor C. The inverting input terminal of the comparator73is connected to the positive terminal of the voltage source76, and the negative terminal of the voltage source76is connected to the ground terminal GND of the ignition apparatus1A.

The inverter74has an input terminal and an output terminal. The AND gate75has first and second input terminals and an output terminal. The output terminal of the comparator73is connected to the input terminal of the inverter74, and the output terminal of the inverter74is connected to the first input terminal of the AND gate75. To the second input gate of the AND gate75, the ignition signal IGt is inputted. The output terminal of the comparator75is connected to the filter circuit63.

A series circuit comprised of the switch SW3and the resistor R, which are connected in series to each other, is connected between the non-inverting input terminal of the comparator73and the ground terminal GND of the ignition apparatus1A to be parallel to the capacitor72.

The switch SW2has an unillustrated control terminal to which the ignition signal IGt is inputted. This enables the switch SW2to be alternately turned on, i.e. closed, upon the ignition signal IGt being in the high level, and turned off, i.e. opened, upon the ignition signal IGt being in the low level. The on state of the switch SW2enables the constant current source71to supply, based on the drive voltage VB, a constant current to the capacitor72and the non-inverting input terminal of the comparator73, thus storing electrical charge in the capacitor72.

A voltage B1based on the electrical charge stored in the capacitor72is applied to the non-inverting input terminal of the comparator73.

Additionally, the voltage source76is configured to apply, to the inverting input terminal of the comparator73, a predetermined reference voltage Vref.

As illustrated inFIG.7B, the above configuration of the deterioration detection period generator7A causes the voltage B1based on the electrical charge stored in the capacitor72, which is inputted to the non-inverting input terminal of the comparator73, to gradually increase with a predetermined time constant of the capacitor72with the input of the ignition signal IGt to the deterioration detection period generator7A.

Until the input voltage B1reaches the reference voltage Vref, the reference voltage Vref is higher than the input voltage B1, so that the comparator73outputs a low-level signal to the inverter74, so that a signal B2with the high level outputted from the inverter74is inputted to the first input terminal of the AND circuit75. That is, until the input voltage B1reaches the reference voltage Vref, the signal B2with the high level is inputted to the first input terminal of the AND circuit75.

To the second input terminal of the AND circuit75, the ignition signal IGt is directly inputted. This results in an output signal of the AND circuit75being switched from a low-level signal to a high-level signal at the time when the ignition signal IGt is inputted to the second input terminal of the AND circuit75.

The output signal with the high level is outputted from the AND circuit75to the filter circuit63as the timer signal B3. The switching of the timer signal B3from the low level to the high level starts the deterioration detection period Ta (seeFIG.7B).

The reference voltage Vref inputted to the inverting input terminal of the comparator73is set to correspond to the length of the deterioration detection period Ta. That is, the length of the deterioration detection period Ta is set to a period for which the input voltage B1has increased since the input of the ignition signal IGt to the deterioration detection period generator7A until the input voltage B1has exceeded the reference voltage Vref.

An increase in the input voltage B1over the reference voltage Vref results in the high level of the signal B2inputted to the first input terminal of the AND gate75being switched to the low level, so that the high-level timer signal B3from the AND gate75is switched to the low-level timer signal B3. The switching of the high-level timer signal B3to the low-level timer signal B3results in the deterioration detection period Ta being terminated (seeFIG.7B).

That is, the deterioration detection period generator7A is configured to continuously output the high-level timer signal B3to the filter circuit63during the deterioration detection period Ta.

As described above, the series circuit comprised of the switch SW3and the resistor R, which are connected in series to each other, is connected between the non-inverting input terminal of the comparator73and the ground terminal GND of the ignition apparatus1A to be parallel to the capacitor72.

For example, the switch SW3has an unillustrated control terminal to which an inversion of the ignition signal IGt is inputted. This enables the switch SW2and the switch SW3to be complementarily switched. Specifically, the switch SW2is turned on when the switch SW3is turned off, and vice versa.

Turning on the switch SW3immediately from turn-off of the switch SW2makes it possible to connect the capacitor72to the ground terminal GND of the ignition circuit1A, thus discharging the electrical charge stored in the capacitor72immediately.

The counter64of the second embodiment is configured to

1. Count the number of times the deterioration detection signal S1is inputted thereto

2. Store the counted number therein

3. Output, to the driver41, the definitive deterioration signal S2upon the counted number having reached a predetermined threshold number, and thereafter the counter64resets the counted number (seeFIG.8)

As described above, the high-level timer signal B3is outputted to the filter circuit63from the deterioration detection period generator7A in response to the input of the ignition signal IGt thereto. While the high-level timer signal B3is outputted to the filter circuit63from the deterioration detection period generator7A, when the temperature-parameter increase ΔV becomes higher than the deterioration detection threshold Vth, the deterioration detection signal S1is outputted from the comparator62to the filter circuit63. This enables the filter circuit63to increment, by one, a count value, whose initial value of zero, in response to detection of the deterioration detection signal S1.

Similarly, the filter circuit63increments, by one, the count value each time the deterioration detection signal S1is inputted thereto from the comparator62.

That is, the comparator62of the deterioration detection period generator7A of the second embodiment is configured to repeatedly perform a task of determining whether the level of the deterioration of the switching circuit30is higher than the acceptable level each time the ignition signal IGt is inputted thereto, and repeatedly output the deterioration detection signal S1to the counter64each time it is determined that the level of the deterioration of the switching circuit30is higher than the acceptable level.

The counter64is therefore configured to count the number of continuous deterioration detection signals S1input thereto as a continuous detection number in response to inputting continuous ignition signals IGt to the deterioration detection period generator7A. Then, the counter64is configured to determine that the level of the deterioration of the switching circuit30is higher than the acceptable level to accordingly determine that there is an unacceptable level of deterioration in the switching circuit30upon the continuous detection number having reached the predetermined threshold number, such as five times, and output, to the driver41, the definitive deterioration signal S2.

This configuration makes it possible to improve the accuracy of determining whether there is an unacceptable level of deterioration in the switching circuit30. This therefore enables proper energization of the IGBT31in accordance with how the deterioration of the switching circuit30proceeds while preventing erroneous determination that there is an unacceptable level of deterioration in the switching circuit30.

Note that the counter64can be configured to count the number of times the discontinuous deterioration detection signals S1are inputted thereto as a discontinuous detection number in response to inputting discontinuous ignition signals IGt to the deterioration detection period generator7A. Then, the counter64is configured to determine that the level of the deterioration of the switching circuit30is higher than the acceptable level to accordingly determine that there is an unacceptable level of deterioration in the switching circuit30upon the discontinuous detection number having reached the predetermined threshold number, and output, to the driver41, the definitive deterioration signal S2. The threshold number can be freely determined. The counter64can be designed as an analog counter or a digital counter.

Third Embodiment

The following describes the third embodiment of the present disclosure. The structures and/or functions of an ignition apparatus1B according to the third embodiment are different from those of the ignition apparatus1A according to the second embodiment in the following points. The following therefore mainly describes the different points.

As illustrated inFIG.9A, a control circuit4B of the ignition apparatus1B has an external input terminal T to which the lock prevention circuit5and the deterioration determination circuit6of the switch control circuit module M are connected; the lock prevention circuit5and the deterioration determination circuit6are connected to the driver41like the first embodiment. The external input terminal T of the control circuit4B is connected to an external ECU, such as the ECU200, so that the deterioration determination circuit6is capable of outputting, to the ECU200, a deterioration information signal IGf based on the definitive deterioration signal S2.

As illustrated inFIG.9B, the deterioration information signal IGf is designed as a binary signal with one of the high level and low level, and the deterioration determination circuit6outputs, to the ECU200, the deterioration information signal IGf with the high level in synchronization with the definitive deterioration signal S2with the high level being outputted from the counter64to the driver41based on a present cycle of the ignition signal IGt that is outputted from the ECU200to the control circuit4(seeFIG.2).

In response to receiving the deterioration information signal IGf from the deterioration determination circuit6, the ECU200is configured to stop a next cycle of outputting the ignition signal IGt to the ignition apparatus1B, and perform a known task of reducing an increase in the temperature of the switching circuit30due to its deterioration.

The above configuration of the ignition apparatus1B, which outputs the deterioration information signal IGf to the ECU200in synchronization with the definitive deterioration signal S2, makes it possible to reduce the occurrence of a spark discharge in the ignition plug P at an unscheduled timing.

For example, the ECU200is capable of turning on one or more warning lamps mounted to the vehicle in response to receiving the deterioration information signal IGf, thus notifying the deterioration of the switching circuit30to one or more occupants of the vehicle. The one or more warning lamps can be directly connected to the external input terminal T, so that each of the one or more warning lamps is turned on in response to receiving the deterioration information signal IGf.

FIG.10Aschematically illustrates an ignition apparatus1C according to a first modification of the second embodiment. When generating the definitive deterioration signal S2at a present cycle of the ignition signal IGt that is outputted from the ECU200to the control circuit4, the deterioration determination circuit6A is configured not to output the definitive deterioration signal S2to the driver41during the energization operation of the IGBT31based on the present cycle of the ignition signal IGt, and output the definitive deterioration signal S2to the driver41after termination of the energization operation of the IGBT31based on the present cycle of the ignition signal IGt (seeFIG.10B).

This configuration of the ignition apparatus1C enables the energization current I1based on the present cycle of the ignition signal IGt to flow through the primary winding21of the ignition coil2until a spark discharge is generated in the ignition plug P, making it possible to prevent the occurrence of a spark discharge in the ignition plug P at an unscheduled timing.

This configuration of the ignition apparatus1C prevents energization of the IGBT31based on each of the subsequent cycles of the ignition signal IGt, thus preventing the energization current It from flowing through the primary winding21.

The above configuration of the ignition apparatus1C reduces an increase in the temperature of the IGBT31due to the deterioration of the switching circuit30while reducing an impact on the ignition operation of the ignition plug P due to execution of the deterioration determination task set forth above.

FIG.11Aschematically illustrates an ignition apparatus1D according to a second modification of the second embodiment. In place of having the external input terminal T, a control circuit4D of the ignition apparatus1D includes a storage circuit50. When generating the definitive deterioration signal S2at a present cycle of the ignition signal IGt, a deterioration determination circuit6D of the ignition apparatus1D is configured to output the definitive deterioration signal S2to the storage circuit50while outputting the definitive deterioration signal S2to the driver41during the energization operation of the IGBT31based on the present cycle of the ignition signal IGt. This enables information about a deterioration history indicative of how the definitive deterioration signal S2is outputted to be stored in the storage circuit50. The deterioration history indicative of how the definitive deterioration signal S2is outputted can include whether the definitive deterioration signal S2is outputted and/or how many times the definitive deterioration signal S2is outputted.

The storage circuit50can be freely designed. For example, a memory circuit comprised of a memory cell can be used as the storage circuit45, and the memory circuit can store the deterioration history in the memory cell. The storage circuit50can be comprised of Zener zap elements, and can mechanically store the deterioration history.

This configuration of the ignition apparatus1D, which has no functions of notifying information to other devices, enables users to check the deterioration history stored in the storage circuit50to thereby determine how the definitive deterioration signal S2is outputted. This therefore enables, during investigation of the ignition apparatus1D, uses to determine whether the cause of shutdown of the igniter10is due to the output of the definitive deterioration signal S2. The storage circuit50can be configured to store history information indicative of how the deterioration detection signal S1is outputted.

FIG.12schematically illustrates an ignition apparatus1E, which is a modification of the ignition apparatus1D. A lock prevention circuit5E of the ignition apparatus1E is configured to output the overtemperature detection signal S to the storage circuit50while outputting the definitive deterioration signal S2to the storage circuit50.

This enables (i) information about a deterioration history indicative of how the definitive deterioration signal S2is outputted and (ii) an overtemperature history of how the overtemperature detection signal S is outputted to be stored in the storage circuit50. The deterioration history indicative of how the overtemperature detection signal S is outputted can include whether the overtemperature detection signal S is outputted and/or how many times the overtemperature detection signal S is outputted.

This configuration of the ignition apparatus1E enables users to check the overtemperature history stored in the storage circuit50. This therefore enables, during investigation of the ignition apparatus1E, uses to check how the overtemperature history impacts on the lifetime of the IGBT31and/or on the deterioration of the IGBT31.

As described above, each of the ignition devices1and1A to1E is comprised of the corresponding lock prevention circuit5for determining whether the IGBT3is in the overtemperature state, and the corresponding deterioration determination circuit6,6A for determining whether the level of the deterioration of the switching circuit30is within the acceptable level.

Specifically, each of the ignition devices1and1A to1E is configured to

1. Determine whether the IGBT31is in the overtemperature condition using the overtemperature detection circuit52to thereby output, to the driver41, the overtemperature detection signal S upon determination that the IGBT31is in the overtemperature condition

2. Determine whether the level of the deterioration of the switching circuit30is higher than the acceptable level using the deterioration determination circuit6,6A to thereby output, to the driver41, the deterioration detection signal S1upon determination that, before the IGBT31is determined to be in the overtemperature condition, the level of the deterioration of the switching circuit30is higher than the acceptable level

This configuration therefore makes it possible to output, to the driver41, the deterioration detection signal S1upon determination that the level of the deterioration of the switching circuit30is higher than the acceptable level before outputting of the overtemperature detection signal S to the driver41. This configuration therefore prevents subsequent ignition operations based on subsequent ignition signals IGt inputted to the corresponding ignition apparatus after determination that the level of the deterioration of the switching circuit30is higher than the acceptable level. This therefore prevents preignition of the ignition plug10thus preventing damage to components constituting the engine100due to preignition.

The present disclosure is not limited to each embodiment, and therefore can be variously modified within the scope of the present disclosure. For example, the configuration of each of the control circuit and/or switching circuit of the igniter10can be appropriately modified. The internal combustion engine100is not limited to a vehicular engine, and can be appropriately modified for another machine. The configuration of each of the ignition apparatuses1and1A to1E can be appropriately modified for the configuration of an internal combustion engine to which the corresponding one of the ignition apparatuses1and1A to1E is applied.

While the illustrative embodiments and their modifications of the present disclosure have been described herein, the present disclosure is not limited to the embodiments and their modifications described herein. Specifically, the present disclosure includes any and all embodiments having modifications, omissions, combinations (e.g., of aspects across various embodiments), adaptations and/or alternatives as would be appreciated by those in the art based on the present disclosure. The limitations in the claims are to be interpreted broadly based on the language employed in the claims and not limited to examples described in the present specification or during the prosecution of the application, which examples are to be construed as non-exclusive.