WO2017141820A1

WO2017141820A1 - Ignition device

Info

Publication number: WO2017141820A1
Application number: PCT/JP2017/004789
Authority: WO
Inventors: 規生加藤; 和紀笠井
Original assignee: 株式会社デンソー
Priority date: 2016-02-17
Filing date: 2017-02-09
Publication date: 2017-08-24
Also published as: CN108700015B; DE112017000858T5; JP2017145765A; CN108700015A; BR112018016669A2; JP6631304B2

Abstract

An ignition device (1) is provided with: an ignition switching element (2); a capacitor (3); a pre-drive switching element (5); and a turn-off constant current circuit (4_OFF). The ignition switching element (2) is connected to a primary winding (11) of an ignition coil (10). The capacitor (3) is connected to a control terminal (21) of the ignition switching element (2). The pre-drive switching element (5) is connected in parallel with the capacitor (3). The turn-off constant current circuit (4_OFF) is electrically connected between the control terminal (21) and the capacitor (3). The turn-off constant current circuit (4_OFF) discharges, at constant current, electric charge accumulated in the capacitor (3).

Description

Ignition device

Cross-reference of related applications

This application is based on Japanese Patent Application No. 2016-28248 filed on February 17, 2016, the contents of which are incorporated herein by reference.

The present disclosure relates to an ignition device for igniting a spark plug of an internal combustion engine.

As an ignition device for igniting an ignition plug of an internal combustion engine, an ignition device including an ignition switching element connected to a primary winding of an ignition coil and a predrive circuit connected to a control terminal of the ignition switching element is known. (See Patent Document 1 below). The ignition plug is connected to the secondary winding of the ignition coil.

When the ignition device ignites the ignition plug, the ignition switching element is turned off at high speed using a pre-drive circuit. As a result, the primary current flowing in the primary winding is interrupted at a high speed, and a high secondary voltage is generated in the secondary winding. The secondary plug is used to ignite the spark plug.

The ignition device is configured to turn off the ignition switching element while suppressing ignition of the ignition plug when an abnormality occurs. For this purpose, the ignition device is provided with an RC circuit (see FIG. 16) having a resistor and a capacitor. When any abnormality occurs, the ignition device gently turns off the ignition switching element using the discharge of the capacitor of the RC circuit. Thereby, a primary current is interrupted | blocked slowly and it suppresses that a high secondary voltage generate | occur | produces. Thus, when an abnormality occurs, the ignition switching element is turned off while suppressing the ignition plug from igniting and igniting the air-fuel mixture.

In the ignition device, when the primary current starts to flow in the primary winding, the ignition switching element is slowly turned on using the RC circuit. As a result, the primary current starts to flow slowly, the generation of a high secondary voltage is suppressed, and the ignition of the air-fuel mixture by the spark plug is suppressed.

Japanese Patent No. 5517686

Since the ignition device uses an RC circuit when interrupting the primary current when an abnormality occurs (hereinafter also referred to as a soft-off operation), a voltage applied to the control terminal of the ignition switching element (hereinafter referred to as a control voltage). ) Decreases exponentially. Therefore, the time change rate of the control voltage is relatively high, and the time change rate of the primary current is relatively high. Therefore, there is a possibility that a high secondary voltage is generated and the spark plug is ignited despite the soft-off operation.
In addition, it is desired to apply a high control voltage to the control terminal when the ignition switching element is turned on so that the ignition switching element can be operated in a saturation region with low loss. However, in the above ignition device, the control voltage decreases exponentially during the soft-off operation. Therefore, if the control voltage during the on-time is increased, the rate of time change of the control voltage when the soft-off operation starts increases. Easy (see FIG. 7). Therefore, the time change rate of the primary current is increased, and a high secondary voltage is easily generated. Therefore, there is a possibility that the spark plug may ignite despite the soft-off operation. Therefore, there is a problem that the control voltage has to be lowered, and the loss of the ignition switching element tends to increase.

Further, since the ignition device uses an RC circuit when the ignition switching element is turned on (hereinafter also referred to as a soft-on operation), the voltage applied to the control terminal of the ignition switching element (that is, the control voltage) ) Rises exponentially. Therefore, the time change rate of the control voltage is relatively high, and the time change rate of the primary current is relatively high. Therefore, there is a possibility that a high secondary voltage is generated and the spark plug is ignited even though the soft-on operation is performed.
Further, the threshold voltage of the ignition switching element has manufacturing variations. In the above ignition device, the control voltage rises exponentially when the soft-on operation is performed. Therefore, when the threshold voltage varies, the time rate of change of the control voltage when the control voltage reaches the threshold voltage is likely to vary. (See FIG. 13). Therefore, depending on the variation of the threshold voltage, when the soft-on operation is performed, there is a possibility that the temporal change rate of the primary current becomes high, a high secondary voltage is generated, and the spark plug is ignited.

This disclosure is intended to provide an ignition device that can further reduce the secondary voltage generated when performing a soft switching operation.

A first aspect of the present disclosure is an ignition device for igniting a spark plug connected to a secondary winding of an ignition coil,
An ignition switching element connected to the primary winding of the ignition coil;
A capacitor connected to the control terminal of the ignition switching element;
A pre-drive switching element connected in parallel to the capacitor;
A pull-up resistor connected between the control terminal and the capacitor, and a current source;
An ignition device comprising: an off constant current circuit that is electrically connected between the control terminal and the capacitor and discharges the electric charge stored in the capacitor with a constant current.

A second aspect of the present disclosure is an ignition device for igniting a spark plug connected to a secondary winding of an ignition coil,
An ignition switching element connected to the primary winding of the ignition coil;
A capacitor connected to the control terminal of the ignition switching element;
A pre-drive switching element connected in parallel to the capacitor;
An ignition device comprising: an ON constant current circuit that is electrically connected between the control terminal and the capacitor and charges the capacitor with a constant current.

The ignition device according to the first aspect includes the off-state constant current circuit.
Therefore, the secondary voltage generated when performing the soft-off operation can be further reduced, and the variation in the secondary voltage can be reduced. That is, since the off constant current circuit discharges the capacitor with a constant current, the voltage of the capacitor, that is, the voltage applied to the control terminal of the ignition switching element can be reduced linearly. Therefore, the time change rate of the primary current can be made constant and small as compared with the conventional case where the voltage applied to the control terminal is decreased exponentially using an RC circuit, and the secondary winding can be reduced. The generated secondary voltage can be reduced. Therefore, ignition of the spark plug when performing the soft-off operation can be more effectively and stably suppressed.
Further, the ignition device can make the rate of change with time of the control voltage constant and small when performing the soft-off operation. Therefore, even if the control voltage when turning on the ignition switching element is increased, the time change rate of the control voltage at the moment of starting the soft-off operation can be reduced. Therefore, the temporal change rate of the primary current at this time can be reduced, and the secondary voltage can be reduced. Therefore, it is possible to increase the control voltage applied at the time of turning on while suppressing ignition of the spark plug at the time of soft-off, and it is possible to operate the ignition switching element in the saturation region. Therefore, the loss of the ignition switching element can be reduced.

The ignition device according to the second aspect includes the on-state constant current circuit.
Therefore, the capacitor can be charged with a constant current when performing the soft-on operation. Therefore, the voltage of the capacitor, that is, the voltage applied to the control terminal of the ignition switching element can be increased in a linear function. Therefore, the time change rate of the primary current can be made constant and small as compared with the conventional case where the voltage applied to the control terminal is increased exponentially using an RC circuit, and the secondary winding is The generated secondary voltage can be reduced. Therefore, ignition of the spark plug when performing the soft-on operation can be more effectively and stably suppressed.
Further, the ignition device can make the rate of change of the control voltage with time constant when performing the soft-on operation. Therefore, even if the threshold voltage of the ignition switching element varies, the time change rate of the control voltage when the control voltage reaches the threshold voltage during the soft-on operation can be made constant. Therefore, it is possible to suppress variation in the temporal change rate of the primary current at this time, and it is possible to suppress generation of a high secondary voltage. For this reason, even if the threshold voltage of the ignition switching element varies, it is possible to more effectively suppress ignition of the spark plug during the soft-on operation.

As described above, according to this aspect, it is possible to provide an ignition device that can further reduce the secondary voltage generated when the soft switching operation is performed.

The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description with reference to the accompanying drawings.
FIG. 1 is a circuit diagram of an ignition device in a state where an ignition switching element is turned off in the first embodiment. FIG. 2 is a circuit diagram of the ignition device when the primary winding is energized in the first embodiment. FIG. 3 is a circuit diagram of the ignition device when performing an ignition operation in the first embodiment. FIG. 4 is a circuit diagram of the ignition device when performing the soft-off operation in the first embodiment. FIG. 5 is a time chart of the ignition device when the ignition operation is repeated in the first embodiment. FIG. 6 is a time chart of the ignition device when the ignition command is not input for a certain period in the first embodiment. FIG. 7 is a waveform diagram of the gate voltage, the primary current, and the secondary voltage when the soft-off operation is performed using the off-state constant current circuit in Embodiment 1, and the soft-off operation is performed using the RC circuit. This is a drawing of overlapping waveform diagrams. FIG. 8 is a cross-sectional view of the ignition device in the first embodiment. FIG. 9 is a circuit diagram of the ignition device in the second embodiment. FIG. 10 is a circuit diagram of the ignition device when performing the soft-on operation in the second embodiment. FIG. 11 is a circuit diagram of an ignition device when performing an ignition operation in the second embodiment. FIG. 12 is a circuit diagram of the ignition device when performing the soft-off operation in the second embodiment. FIG. 13 is a waveform diagram of the gate voltage, primary current, and secondary voltage when the soft-on operation is performed using the constant current circuit for turning on in Embodiment 2, and the soft-on operation is performed using the RC circuit. This is a drawing of overlapping waveform diagrams. FIG. 14 is a graph showing the variation in the gate voltage increase rate and the variation in the threshold voltage of the ignition switching element in the second embodiment. FIG. 15 is a circuit diagram of the ignition device in the third embodiment. FIG. 16 is a circuit diagram of an ignition device according to a comparative embodiment. FIG. 17 is a graph showing the variation in the rising speed of the gate voltage and the variation in the threshold voltage of the ignition switching element in the comparative example.

The ignition device may be a vehicle ignition device for igniting a spark plug of an automobile engine.

(Embodiment 1)
An embodiment according to the ignition device will be described with reference to FIGS. The ignition device 1 of this embodiment is used for igniting a spark plug 13 connected to the secondary winding 12 of the ignition coil 10. As shown in FIG. 1, the ignition device 1 includes an ignition switching element 2, a capacitor 3, a pre-drive switching element 5, a pull-up resistor 19, and an off constant current circuit 4 _OFF .

One end of the primary winding 11 of the ignition coil 10 is connected to the power source 18, and the other end is connected to the collector of the ignition switching element 2. The emitter of the ignition switching element 2 is connected to the ground.
The capacitor 3 is connected to the control terminal 21 of the ignition switching element 2, and one end is connected to the ground.
The predrive switching element 5 is connected to the capacitor 3 in parallel.
The pull-up resistor 19 is connected between the control terminal 21 and the capacitor 3 and between the current source 14. The current source 14 is a low voltage power source such as a lead storage battery.
The off constant current circuit 4 _OFF is electrically connected between the control terminal 21 and the capacitor 3. As shown in FIG. 4, the off constant current circuit 4 _OFF is configured to discharge the electric charge stored in the capacitor 3 with a constant current I _3D .

The ignition device 1 of this embodiment is a vehicle ignition device for igniting a spark plug 13 of an automobile engine.

Next, the operation of the ignition device 1 when the ignition plug 13 is ignited will be described. As shown in FIG. 1, the ignition device 1 first turns off the ignition switching element 2 when the power is turned on. At this time, the potential of the signal line 49 (that is, point B) of the _OFF constant current circuit 4 _OFF is set to L, and the potential of the control terminal 59 (that is, point A) of the predrive switching element 5 is set to H. . As a result, the pre-drive switching element 5 is turned on, and the current I ₁₉ flows from the current source 14 through the pull-up resistor 19 and the pre-drive switching element 5 to the ground. Therefore, no charge is stored in the capacitor 3 and the voltage of the capacitor 3 does not increase. Therefore, the voltage at the control terminal 21 does not reach the threshold voltage, and the ignition switching element 2 is turned off.

Thereafter, the ignition device 1 receives the Low signal of the ignition operation instruction signal sent from an engine control unit (not shown) or the like, and turns off the pre-drive switching element 5. Therefore, as shown in FIG. 2, the capacitor 3 is charged by the current I ₁₉ flowing through the pull-up resistor 19, the ignition switching element 2 is turned on, and the primary current i ₁ starts to flow through the primary winding 11. At this time, the voltage applied to the control terminal 21 gradually increases due to the charging characteristics of the pull-up resistor 19 and the capacitor 3. Therefore, the ignition switching element 2 is turned on slowly, and the primary current i ₁ gradually starts to flow through the primary winding 11. As a result, the primary current i ₁ is passed through the primary winding 11 while suppressing ignition of the spark plug 13.

Thereafter, as shown in FIG. 3, when the point A is set to H, the pre-drive switching element 5 is turned on and the capacitor 3 is rapidly discharged. Therefore, the ignition switching element 2 is suddenly turned off, and the primary current i ₁ is suddenly cut off. Along with this, a high secondary voltage V ₂ is generated in the secondary winding 12, a spark discharge S is generated in the spark plug 13, and the air-fuel mixture in the cylinder is ignited.

In addition, as shown in FIG. 2, when an abnormality occurs after the primary current i ₁ flows and the H signal at point A that turns on the pre-drive switching element 5 is not input for a certain period of time, a soft-off operation is performed. Do. That is, the ignition switching element 2 is turned off while suppressing ignition of the spark plug 13. When the soft-off operation is performed, the point B is set to H while the point A is set to L as shown in FIG. In this way, the off constant current circuit 4 _OFF is turned on, and a constant current set by the circuit constant flows. For this reason, the electric charge stored in the capacitor 3 is discharged with a constant current I _3D , and the voltage of the capacitor 3 decreases with a constant slope. Therefore, the voltage applied to the control terminal 21 gradually decreases with a constant slope, and the primary current i ₁ gradually decreases with a constant rate of change. Therefore, the secondary voltage V ₂ is suppressed compared to the case where the primary current i ₁ is changed exponentially as in the conventional case, and the ignition of the spark plug 13 can be suppressed.

Next, the timing chart of the ignition device 1 will be described with reference to FIGS. 5 and 6. FIG. 5 is a timing diagram of the ignition device 1 when the ignition of the engine is repeated, and FIG. 6 is a timing diagram when a soft-off operation is performed when an abnormality occurs. A point A in FIGS. 5 and 6 is the control terminal 59 of the pre-drive switching element 5. A signal for controlling energization and interruption of the primary winding 11 when the ignition operation is performed is input to the point A. Point B is a signal line 49 connected to the control terminal of the _OFF constant current circuit 4 _OFF . Further, point C is the control terminal 21 of the ignition switching element 2, and point D is the collector 29 of the ignition switching element 2.

As shown in FIG. 5, when the engine is ignited, the primary coil 11 is first energized. That is, the point B is set to L, and the point A is switched from H to L at time t1. In this way, the pre-drive switching element 5 is turned off, the current I ₁₉ gradually flows from the current source 14 through the pull-up resistor 19, and the capacitor 3 is slowly charged with the RC time constant. Therefore, the voltage of the capacitor 3 gradually increases, the ignition switching element 2 is gradually turned on, and the primary current i ₁ flows through the primary winding 11.

Thereafter, when the point A is switched to H at time t2, the pre-drive switching element 5 is turned on, and the charge stored in the capacitor 3 is rapidly discharged. Therefore, the ignition switching element 2 is turned off, and the primary current i ₁ is rapidly cut off. Therefore, a high primary voltage V ₁ is generated in the primary winding 11. Along with this, a high secondary voltage V ₂ is also generated in the secondary winding 12, a spark discharge S is generated in the spark plug 13, and the air-fuel mixture in the engine is ignited.

Further, as shown in FIG. 6, when an abnormality occurs after the point A is set to L at time t <b> 3 and a command for igniting the spark plug 13 is not input for a certain period of time, a soft-off operation is performed. That is, at time t4, the point B is set to H while the point A of the ignition signal is set to L, that is, the predrive switching element 5 is turned off. By doing so, the off constant current circuit 4 _OFF is turned on, and the electric charge stored in the capacitor 3 is discharged with a constant current. Therefore, the voltage at the point C gradually decreases at a constant rate of change, and the primary current i ₁ gradually decreases. Therefore, the primary voltage V ₁ and the secondary voltage V ₂ are suppressed, and the ignition switching element 2 can be turned off while suppressing ignition of the spark plug 13.

FIG. 7 shows waveforms of the gate voltage V _g , the primary current i ₁ , and the secondary voltage V ₂ when the ignition switching element 2 is soft-off using the _OFF constant current circuit 4 _OFF . In addition, in the same figure, the waveforms when the ignition switching element 2 is soft-off using the RC circuit (see FIG. 16) as in the prior art are shown superimposed.

When the capacitor 3 is discharged with a constant current using the _OFF constant current circuit 4 _OFF , the voltage of the capacitor 3 decreases in a linear function. Therefore, as shown in FIG. 7, in the case of using the _OFF constant current circuit 4 _OFF , after starting soft-off at time t4, the voltage of the capacitor 3, that is, the gate voltage V _g of the ignition switching element 2 is a linear function. Decline. Accordingly, the primary current i ₁ also decreases linearly. For this reason, the temporal change rate di ₁ / dt of the primary current i ₁ is constant and can be set to a relatively small value, so that the generated secondary voltage V ₂ is also relatively low. Therefore, the spark plug 13 rarely sparks and the generated energy is small even if sparks are generated, so that it is possible to suppress ignition of the air-fuel mixture.

In contrast, in the case of using an RC circuit as in the prior art, after starting to soft-off at time t4, the gate voltage V _g of the ignition switching element 2 decreases exponentially. Therefore, the primary current i ₁ also decreases exponentially. Therefore, the temporal change rate di ₁ / dt of the primary current i ₁ is relatively large, and a high secondary voltage V ₂ is likely to be generated. Therefore, the secondary voltage V ₂ may cause a spark discharge S in the spark plug 13 and ignite the air-fuel mixture.

Next, a description will be given of a circuit configuration of the constant current circuit 4 _OFF for off. As shown in FIG. 1, the off constant current circuit 4 _OFF includes a switching transistor 40 and a constant current transistor 41. The switching transistor 40 is provided for switching between energization and non-energization of current. The constant current transistor 41 is provided to keep the current I ₄₀ (see FIG. 4) flowing through the switching transistor 40 at a constant value.

In this embodiment, an Nch type MOSFET is used as the switching transistor 40, and an NPN type bipolar transistor is used as the constant current transistor 41. The source 401 of the switching transistor 40 is connected to the base 413 of the constant current transistor 41 and is connected to the ground via the second resistor 43 for current setting. The drain 402 of the switching transistor 40 is connected to the capacitor 3. The emitter 411 of the constant current transistor 41 is connected to the ground through the first resistor 42. The collector 412 of the constant current transistor 41 is connected to the gate 403 of the switching transistor 40.

As shown in FIG. 4, when the potential of the gate 403 is set to H, the switching transistor 40 is turned on and a current I ₄₀ flows. The current I ₄₀ is the sum of the discharge current I _3D of the capacitor 3 and the current I ₁₉ flowing from the power source 14 via the pull-up resistor 19. The current I ₄₀ is divided at a connection point 414 into I ₄₃ flowing through the second resistor 43 and a base current I _41b of the constant current transistor 41. The base current I _41b has a correlation with the collector current I _41c of the constant current transistor 41 and the coefficient 1 / h _fe . The sum of the base current I _41b and the collector current I _41c is a current I ₄₂ flowing through the first resistor 42.

The voltage drop from the connection point 414 to the ground is the same on the first resistor 42 side and the second resistor 43 side. That is, the product of the second resistor 43 and the current I ₄₃ flowing therethrough, the sum of the product of the first resistor 42 and the current I ₄₂ flowing therethrough, and the base-emitter voltage V _be of the constant current transistor 41 become equivalent. As described above, the voltage of the base 413 is determined, and the current I ₄₃ and the base current I _41b flowing through the second resistor 43 are determined. Therefore, the sum of these currents I ₄₃ and I _41b (current I ₄₀ ) is constant. The current I ₄₀ is the sum of the current I ₁₉ flowing through the pull-up resistor 19 and the discharge current I _3D of the capacitor 3, and the current I ₁₉ is constant. Therefore, the discharge current I _3D is constant.

Further, since the current I ₄₀ can be arbitrarily set according to the resistance values of the first resistor 42 and the second resistor 43 as described above, even when a high voltage is applied to the control terminal 21 of the ignition switching element 2, The value of the current I ₄₀ can be easily set so that the time change rate di ₁ / dt of the current i ₁ is constant and small. Therefore, even when a high voltage is applied to the control terminal 21 and the ignition switching element 2 is in the saturation region, the soft-off operation can be reliably performed from this state. Therefore, when performing a normal ignition operation, the ignition switching element 2 can be operated in the saturation region. That is, when the ignition switching element 2 is turned on and the primary current i ₁ flows through the primary winding 11 (see FIG. 2), the ignition switching element 2 can be in the saturation region, and the ignition switching element by the primary current i ₁ 2 loss can be suppressed.

Next, the three-dimensional structure of the ignition device 1 will be described with reference to FIG. As shown in the figure, in this embodiment, the off constant current circuit 4 _OFF and the predrive switching element 5 are formed on one semiconductor chip 8. Further, the ignition device 1 includes a control unit 7 for the on-off control of the off constant-current circuit 4 _OFF, and the pre-drive switching element 5. The control unit 7, the semiconductor chip 8, and the ignition switching element 2 are sealed by a sealing member 80 and are made into one part.

The control unit 7, the semiconductor chip 8, and the ignition switching element 2 are placed on a heat sink 81. Further, a terminal 82 for electrical connection with an external device protrudes from the sealing member 80.

Next, the effect of this form is demonstrated. As shown in FIG. 1, the ignition device 1 of this embodiment includes an off constant current circuit 4 _OFF . The off constant current circuit 4 _OFF is configured to discharge the capacitor 3 connected to the control terminal 21 with a constant current.
Therefore, the secondary voltage V ₂ generated when performing the soft-off operation can be further reduced. That is, since the off constant current circuit 4 _OFF discharges the capacitor 3 with a constant current, the voltage V _g applied to the control terminal 21 of the ignition switching element 2 as shown in FIG. It can be reduced by a linear function. Therefore, the time change rate di ₁ / dt of the primary current i ₁ can be made constant and small as compared with the conventional case where the voltage applied to the control terminal is exponentially reduced using an RC circuit. The secondary voltage V ₂ generated in the secondary winding 12 can be reduced. Therefore, ignition of the spark plug 13 when performing the soft-off operation can be more effectively suppressed.

As described above, according to this embodiment, it is possible to provide an ignition device that can further reduce the secondary voltage generated when the soft switching operation is performed.

In this embodiment, as shown in FIG. 1, the IGBT is used as the ignition switching element 2, but the present invention is not limited to this, and a MOSFET or a bipolar transistor can also be used.

Further, in this embodiment, as shown in FIG. 8, the semiconductor chip 8 on which the off constant current circuit 4 _OFF and the predrive switching element 5 are formed, the control unit 7 and the ignition switching element 2 are sealed. However, the present invention is not limited to this. That is, you may make what is called a discrete product which separated these components. Further, the off-state constant current circuit 4 _OFF is not limited to that disclosed in this embodiment, and other known circuit configurations or dedicated ICs may be used.

In the following embodiments, the same reference numerals used in the drawings among the reference numerals used in the drawings represent the same constituent elements as those in the first embodiment unless otherwise specified.

(Embodiment 2)
In this embodiment, the circuit of the ignition device 1 is changed. As shown in FIG. 9, the ignition device 1 of the present embodiment includes an ignition switching element 2 connected to a primary winding 11 of an ignition coil 10, a capacitor 3, a predrive switching element 5, and an on-state constant current circuit 4. _{With ON} .

As shown in FIG. 10, the ON constant current circuit 4 _ON is connected between the control terminal 21 and the capacitor 3 and is configured to charge the capacitor 3 with a constant current I _3C . The on-state constant current circuit 4 _ON includes a switching transistor 40 and a constant-current transistor 41 in the same manner as the off-state constant current circuit 4 _OFF . The source of the switching transistor 40 is connected to the current source 14 via the fourth resistor 45. The emitter of the constant current transistor 41 is connected to the current source 14 via the third resistor 44.

The capacitor 3 is charged by a constant current I _3C flowing through the switching transistor 40. This current I _3C is the sum of I ₄₅ flowing through the fourth resistor 45 at the connection point 415 and the base current I _41b of the constant current transistor 41. The base current I _41b is correlated with the collector current I _41c of the constant current transistor 41 and the coefficient 1 / h _fe, and the sum of the base current I _41b and the collector current I _41c flows through the third resistor 44. The current I ₄₄ is obtained. The product of the fourth resistor 45 and the current I ₄₅ flowing therethrough, the product of the third resistor 44 and the current I ₄₄ flowing therethrough, and the sum of the base-emitter voltage V _be of the constant current transistor 41 are made equivalent. The voltage of the base 413 is determined, and the current I ₄₅ flowing through the fourth resistor ₄₅ and the base current I _41b are determined. Therefore, the sum (current I _3C ) of these currents I ₄₅ and I _41b is constant.

Current I _3C, as described above, it is possible to arbitrarily set by the third resistor 44 resistance value of the fourth resistor 45, even when applying a high voltage to the control terminal 21, the time rate of change of the primary current i ₁ di ₁ / The value of the current I _3C can be easily set so that dt is constant and small. Accordingly, when the primary current i ₁ starts to flow, a high voltage can be gradually applied to the control terminal 21, and the ignition switching element 2 can be brought into a saturation region. Therefore, the loss of the ignition switching element 2 due to the primary current i ₁ can be suppressed.

Further, the ignition device 1 of the present embodiment includes an OFF constant current circuit 4 _OFF as in the first embodiment. The off constant current circuit 4 _OFF is connected between the control terminal 21 and the capacitor 3 and is configured to discharge the electric charge stored in the capacitor 3 with a constant current I _3D .

Next, the operation of the ignition device 1 when the ignition plug 13 is ignited will be described. As shown in FIG. 10, the ignition device 1 first performs a soft-on operation. That is, by turning on the ignition switching element 2 slowly at a constant current, the primary current i ₁ flows through the primary winding 11 while suppressing ignition of the spark plug 13 at the start of energization. At this time, both point A and point B are set to L as shown in FIG. In this way, the _ON constant current circuit 4 _ON is turned ON and the soft-off constant current circuit 4 _OFF is turned _OFF , so that the capacitor 3 is charged with a constant current I _3C . Therefore, the voltage of the capacitor 3, that is, the voltage of the control terminal 21 increases in a linear function. Therefore, the time change rate di ₁ / dt of the primary current i ₁ can be made constant and small, and the secondary voltage V ₂ can be reduced. Therefore, it is possible to flow the primary current i ₁ while suppressing ignition of the spark plug 13.

Thereafter, as shown in FIG. 11, the point A is switched from L to H while the point B is kept at L. As a result, the pre-drive switching element 5 is turned on, and the electric charge stored in the capacitor 3 is rapidly discharged through the pre-drive switching element 5. Therefore, it is suddenly cut off the primary current i _1, the secondary winding high 12 secondary voltage V ₂ is generated. Accordingly, a spark discharge S is generated in the spark plug 13.

If the signal for igniting the spark plug 13 is not input for a certain time from the state shown in FIG. 10, the point B is switched to H while the point A is kept low as shown in FIG. In this way, the on-state constant current circuit 4 _ON is turned off and the flowing current I _3C is stopped, and the off-state constant current circuit 4 _OFF is turned on, so that a constant current I _3D flows. Therefore, the capacitor 3 is discharged with a constant current I _3D , and the voltage of the capacitor 3, that is, the voltage of the control terminal 21 is reduced in a linear function. Therefore, the time change rate di ₁ / dt of the primary current i ₁ can be made constant and small, and the secondary voltage V ₂ can be reduced. Therefore, the ignition switching element 2 can be turned off while suppressing ignition of the spark plug 13.

Next, FIG. 13 shows waveforms of the gate voltage V _g , the primary current i ₁ , and the secondary voltage V ₂ when the ignition switching element 2 is soft-on using the _ON constant current circuit 4 _ON . In addition, in the same figure, the waveforms when the ignition switching element 2 is soft-on using the RC circuit (see FIG. 16) as in the prior art are shown superimposed.

As shown in FIG. 13, when the gate voltage V _g rises and exceeds the threshold voltage V _th , the ignition switching element 2 is turned on and the primary current i ₁ starts to flow. Further, as described above, when the ON constant current circuit 4 _ON is used, the capacitor 3 is charged with a constant current, so that the voltage of the capacitor 3 rises in a linear function. Therefore, in the case of using a constant current circuit 4 _ON for one, after starting to soft on at time t1, the voltage of the capacitor 3, i.e., the gate voltage V _g of the ignition switching element 2 rises a linear function manner. Therefore, the primary current i ₁ can be increased linearly. Therefore, the time change rate di ₁ / dt of the primary current i ₁ can be made constant and small, and the generated secondary voltage V ₂ can be made relatively small. Therefore, it is possible to suppress the occurrence of the spark discharge S in the spark plug 13.

In contrast, in the case of using an RC circuit as in the prior art, after starting to soft on at time t1, the gate voltage V _g of the ignition switching element 2 increases exponentially. Therefore, the primary current i ₁ also increases exponentially. Therefore, the temporal change rate di ₁ / dt of the primary current i ₁ is relatively large, and a high secondary voltage V ₂ is generated. Therefore, the secondary voltage V _2, the spark discharge S may occur in the spark plug 13.

On the other hand, as shown in FIG. 9, the switching transistor 40p for the _ON constant current circuit 4 _{ON and} the switching transistor 40n for the _OFF constant current circuit 4 _OFF are connected to each other in series. The control terminals (that is, the gates 403) of these two switching

transistors

40p and 40n are connected to a common signal line 49. The two

switching transistors

40p and 40n are complementary transistors, as shown in FIGS. 10 and 12, in which one is turned on and the other is turned off.

Next, the effect of this form is demonstrated. As shown in FIG. 10, the ignition device 1 of the present embodiment includes an _ON constant current circuit 4 _ON .
Therefore, it is possible to perform a soft-on operation, that is, an operation that starts flowing the primary current i ₁ while suppressing ignition of the spark plug 13. That is, in this embodiment, since the ON constant current circuit 4 _ON is provided, the capacitor 3 can be charged with a constant current I _3C . Therefore, the voltage applied to the capacitor 3, that is, the voltage applied to the control terminal 21 of the ignition switching element 2 can be increased in a linear function. Therefore, the time change rate di ₁ / dt of the primary current i ₁ can be made constant and small as compared with the conventional case where the voltage applied to the control terminal is increased exponentially using an RC circuit. The secondary voltage V ₂ generated in the secondary winding 12 can be reduced. Therefore, it is possible to suppress ignition of the spark plug when performing the soft-on operation.

Further, when the ON constant current circuit 4 _ON is used as in this embodiment, even when the threshold voltage V _th of the ignition switching element 2 varies due to manufacturing variations, the variation in the secondary voltage V ₂ can be reduced. Can do. That is, as shown in FIG. 17, the threshold voltage V _th of the ignition switching element 2 varies. When performing the soft-ON operation using the RC circuit, the manufacturing variation of the resistance R and the capacitor C included in the RC circuit, variation RC time constant, the rising speed of the gate voltage V _g varies. The curve L3 is when the rising speed is the fastest, and the curve L4 is when the slowing speed is the slowest. Therefore, for example, the threshold voltage V _th is low and if the rising speed of the gate voltage V _g is high (i.e., the curve L3), the switching element 2 is turned on ignition at a relatively earlier time T11. Further, since the gate voltage V _g rises exponentially, the time change rate dV _g / dt of the gate voltage Vg at time T11 is high, and the time change rate di ₁ / dt of the primary current i ₁ is also high. Therefore, a particularly high secondary voltage V ₂ is likely to be generated. Further, when the threshold voltage V _th is high and the rising speed of the gate voltage V _g is slow (that is, in the case of the curve L4), the ignition switching element 2 is turned on at a relatively late time T12. At this time, since the time change rate dV _g / dt of the gate voltage V _g is low, the secondary voltage V ₂ is relatively low.
As described above, when the soft-on operation is performed using the RC circuit, if the threshold voltage V _th and the RC time constant vary and the time when the ignition switching element 2 is turned on varies between T11 and T12, The voltage V ₂ tends to vary greatly. Therefore, it is necessary to design the circuit in consideration of the case where the highest secondary voltage V ₂ is generated, and the circuit design tends to be difficult.

On the other hand, when the ON constant current circuit 4 _ON is used as in this embodiment, the variation in the secondary voltage V ₂ can be reduced even if the threshold voltage V _th of the ignition switching element 2 varies. it can. That is, as shown in FIG. 14, when the _ON constant current circuit 4 _ON is used, the rising speed of the gate voltage V _g varies due to manufacturing variations of the capacitor 3. The straight line L1 is when the rising speed is the fastest, and the straight line L2 is when the rising speed is the slowest. Therefore, the threshold voltage V _th is low, if the rising speed of the gate voltage V _g is high (i.e., when the straight line L1), the switching element 2 is turned on ignition at a relatively earlier time t11. Further, the threshold voltage V _th is high, if the rising speed of the gate voltage V _g is low (i.e., when the straight line L2), the switching element 2 is turned on ignition at a relatively slow time t12. In this embodiment, in order to charge the capacitor 3 at a constant current, the gate voltage V _g increases a linear function manner. Therefore, even if the threshold value of the ignition switching element 2 varies between V _th 1 and V _th 2, the time change rate dV _g / dt of the gate voltage V _{g at} the threshold value does not vary. Therefore, the temporal change rate di ₁ / dt of the primary current i ₁ does not vary, and variations in the primary voltage V ₁ generated according to the current change can be suppressed. Therefore, variations in the secondary voltage V ₂ can be suppressed, and the circuit design of the ignition device 1 can be easily performed.

Further, as shown in FIG. 10, the ignition device 1 of the present embodiment includes both an on-state constant current circuit 4 _ON and an off-state constant current circuit 4 _OFF . Therefore, both the soft-on operation and the soft-off operation can be performed.

Further, as shown in FIG. 10, the on-state constant current circuit 4 _ON and the off-state constant current circuit 4 _{OFF of} this embodiment are switching transistors 40 (40p, 40n) for switching between energization and non-energization of the current I. Each is provided. The control terminals (that is, the gates 403) of these two switching transistors 40 are connected to a common signal line 49. The two switching transistors 40 are of a complementary type in which one is on and the other is off.
Therefore, in the case where a current is passed only to the _ON constant current circuit 4 _ON out of the two constant

current circuits

4 _ON and 4 _OFF while the signal line 49 is single (see FIG. 10), the OFF constant current circuit 4 _OFF It is possible to switch between the case where the current flows only in the case (see FIG. 12). Therefore, the circuit configuration of the ignition device 1 can be simplified.
In addition, the same configuration and operational effects as those of the first embodiment are provided.

(Embodiment 3)
In this embodiment, the circuit configuration of the ignition device 1 is changed. As shown in FIG. 15, the ignition device 1 of the present embodiment includes an ignition switching element 2 connected to the primary winding 11 of the ignition coil 10, a capacitor 3, a predrive switching element 5, and an ON constant current circuit 4. _{With ON} . In this embodiment, the off constant current circuit 4 _OFF is not provided.

In this embodiment, when the soft-on operation is performed, the pre-drive switching element 5 is turned off and the switching transistor 40 is turned on. Thereby, the capacitor 3 is charged with a constant current I using the _ON constant current circuit 4 _ON, and the voltage of the capacitor 3, that is, the voltage applied to the control terminal 21 of the ignition switching element 2 is increased with a constant slope. Thereby, the time change rate of the primary current i ₁ is made constant and small. Thereby, ignition of the spark plug 13 is suppressed.

Further, when the ignition plug 13 is ignited, the pre-drive switching element 5 is turned on. Thereby, the electric charge stored in the capacitor 3 is rapidly discharged, and the ignition switching element 2 is turned off at high speed. As a result, the primary current i ₁ is quickly cut off, a high secondary voltage V ₂ is generated, and the spark plug 13 is ignited.
In addition, the same configuration and operational effects as those of the first embodiment are provided.

Although the present disclosure has been described based on the embodiments, it is understood that the present disclosure is not limited to the embodiments and structures. The present disclosure includes various modifications and modifications within the equivalent range. In addition, various combinations and forms, as well as other combinations and forms including only one element, more or less, are within the scope and spirit of the present disclosure.

Claims

An ignition device (1) for igniting a spark plug (13) connected to a secondary winding (12) of an ignition coil (10),
An ignition switching element (2) connected to the primary winding (11) of the ignition coil;
A capacitor (3) connected to the control terminal (21) of the ignition switching element;
A pre-drive switching element (5) connected in parallel to the capacitor;
A pull-up resistor (19) connected between the control terminal and the capacitor and between a current source (14);
An ignition device comprising: an off constant current circuit (4 OFF ) that is electrically connected between the control terminal and the capacitor and discharges the electric charge stored in the capacitor with a constant current.
An ignition device for igniting a spark plug (13) connected to a secondary winding (12) of an ignition coil (10),
An ignition switching element (2) connected to the primary winding (11) of the ignition coil;
A capacitor (3) connected to the control terminal (21) of the ignition switching element;
A pre-drive switching element (5) connected in parallel to the capacitor;
An ignition device comprising: an ON constant current circuit (4 ON ) electrically connected between the control terminal and the capacitor and charging the capacitor with a constant current.
The ignition device according to claim 2, further comprising an off constant current circuit that is electrically connected between the control terminal and the capacitor and discharges the electric charge stored in the capacitor with a constant current.
The on-state constant current circuit and the off-state constant current circuit each include a switching transistor (40) for switching between energization and de-energization, and the control terminals of these two switching transistors are common. 4. The ignition device according to claim 3, wherein the two switching transistors are of a complementary type in which when one is turned on, the other is turned off.