JP2009228507A - Ignition device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ignition device capable of performing complicated and sophisticated combustion control by multiple ignition control, and outputting sufficient ignition energy while being sufficiently miniaturized. <P>SOLUTION: In the ignition device, an ignition coil CL with a primary coil L1 and a secondary coil L2 electromagnetically coupled with each other, and an ignition control circuit IGN for controlling a current flowing in the primary coil L1 are integrated with each other, and an ignition plug PG connected to the secondary coil can perform multiple ignition. The primary coil and the secondary coil are formed by providing each coil winding on a magnetic body forming a closed magnetic circuit, and arranged at a position exposed from a plug hole forming a communication passage with the ignition plug PG. The number of turns of the coil winding of the primary coil L1 is set to the value so as not to cause the magnetic saturation of the magnetic body even is the maximum current made to flow in a primary circuit including the primary coil. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an ignition device that can perform multiple ignition operations and can output necessary ignition energy while being sufficiently miniaturized.

In each cylinder of an internal combustion engine, a multiple ignition method is known in which an ignition operation for an air-fuel mixture is executed a plurality of times during one ignition cycle (for example, Patent Document 1).
Japanese Patent No. 3433941

  In the multiple ignition method, a plurality of ignition pulses are supplied from an ECU (Electronic Control Unit) during one ignition cycle, and the charging energy of the primary coil accumulated when each ignition pulse is turned on is released when the ignition pulse is turned off. Thus, ignition discharge of the spark plug is realized. Therefore, even if the air-fuel mixture in the internal combustion engine is not uniform, the combustion is reliably maintained, and it becomes possible to realize an improvement in fuel consumption by lean combustion or EGR control.

  However, an ignition device that employs a multiple ignition system is capable of outputting the necessary ignition energy, is capable of complex and advanced combustion control, and is sufficiently small in size. Absent. That is, in a general ignition device, since an ignition coil must be enlarged in order to accumulate sufficient ignition energy in a short time, there is a limit to downsizing. In the multiple ignition method, since the spark plug discharges a plurality of times at each ignition timing, the spark plug generates heat correspondingly, so that it is necessary to ensure sufficient heat dissipation performance. If it becomes, it will also become impossible to ensure the space which arrange | positions a thermal radiation member.

  The present invention has been made in view of the above-described problems, and is capable of complex and advanced combustion control by multiple ignition control, and outputs sufficient ignition energy while being sufficiently downsized. An object of the present invention is to provide an ignition device that can be used.

  In order to achieve the above object, the present invention integrates an ignition coil in which a primary coil and a secondary coil are electromagnetically coupled, and an ignition control circuit for controlling a current of the primary coil. An ignition device capable of igniting a plurality of connected ignition plugs, wherein the primary coil and the secondary coil are formed by providing each coil winding on a magnetic body forming a closed magnetic circuit, and Arranged at a position exposed from the plug hole forming the communication path, the coil winding of the primary coil is set to the number of coil turns that does not magnetically saturate the magnetic material even when the maximum current flows through the primary circuit including the primary coil. Has been.

  Since the present inventor has repeated various studies to arrive at the present invention, the principle content will be mainly described.

Assuming that the charging current I flows through the primary coil of the ignition coil, when the current I is increased from 0 [A] to I ₀ [A], the charging energy accumulated in the primary coil is 1/2 * L * I ₀ ² [J] (see charging curve A in FIG. 7). However, if the magnetic material of the primary coil is magnetically saturated before the charging current of the primary coil reaches the target value I ₀ , the subsequent current hardly contributes to the accumulation of charging energy.

A charging curve B in FIG. 7 (for the sake of convenience, the self-inductance L is set smaller than that in the charging curve A) shows a charging curve when magnetic saturation occurs in the middle of current increase. Although the charging current I increases rapidly, the current after magnetic saturation hardly contributes to energy storage. Therefore, even by interrupting the current in the primary coil at a timing reaches the target value I _0, it may be impossible to transfer a sufficient discharge energy to the secondary coil.

Therefore, although it is necessary to avoid magnetic saturation, as confirmed from the H-B curve (see FIG. 8) showing the relationship between the magnetic field H [AT] and the magnetic flux density B [Wb / m ² ], in general, a magnetic material is used. Even if the magnetic field H applied to is increased, the magnetic flux density B is always magnetically saturated at a certain level. Here, the magnetic field strength H is given by the product of the number of turns N of the coil wound around the magnetic material and the coil current I (H = N * I), and therefore corresponds to the maximum magnetic field strength H _MAX that does not cause magnetic saturation. If the product of the coil current I and the coil winding N is limited to N * I ≦ H _MAX , magnetic saturation is avoided.

In the present invention, based on the above consideration, the coil winding of the primary coil is set to the number of coil turns N that does not magnetically saturate the magnetic material even when the maximum current flows through the primary coil, and magnetic saturation can occur. Absent. Note that the maximum current of the present invention is typically defined by the DC power supply voltage (battery voltage) E supplied to the primary coil and the loss resistance r of the primary coil, and the maximum current = E / r. In the present invention, the number of turns N of the primary coil is simply set to be N = H _MAX * r / E. If such a configuration is adopted, even when an upper limit current (maximum current) I _MAX flows through the primary coil, I _MAX * N = H _MAX is established, and magnetic saturation does not occur.

Note that the maximum magnetic field strength H _MAX in the present invention is a straight line obtained by a least-squares method between a horizontal line indicating the maximum magnetic flux density B _MAX in the H-B curve and an H-B curve up to B _MAX / SQR (2). It is defined by the contact point with the straight line obtained by approximation (see FIG. 8). SQR means route calculation.

On the premise of this point, the description of the present invention will be continued. For example, a self-inductance L _{01 of} a coil having a length T in which a coil winding N is wound around a round bar-shaped magnetic body (permeability μ) having a radius a. Is the Nagaoka count as C (C <1),
L ₀₁ = C * μ * π * a ² * N ² / T [H] = C * μ * S * N ² / T [H] (Expression 1) On the other hand, a self-inductance L ₀₂ of a coil in which a coil winding N is wound around a magnetic body (permeability μ) having a cross-sectional area S and an average magnetic path length T corresponding to the above-described coil,
L ₀₂ = μ * S * N ² / T [H] (Expression 2)

As is clear from the above relationship, when a linear open magnetic path is formed with a round bar magnetic body having a length T, the self-inductance L ₀₁ of (Equation 1) is obtained, whereas the same round bar magnetic body is Assuming that a closed magnetic circuit without a gap is formed by forming a loop, the self-inductance is given by (Equation 2), and naturally, L ₀₂ > L ₀₁ for the Nagaoka count C.

By the way, as initially confirmed, when the primary current of the ignition coil is increased from zero to the target current I ₀ ≦ H _MAX / N, the accumulated energy P by this charging operation is P = 1/2 * L * I ₀ ² [J] (Equation 3)

Since the target current I ₀ that does not cause magnetic saturation is inversely proportional to the number of coil turns N from the relationship of I ₀ = H / N, I ₀ ² is inversely proportional to the square of the number of coil turns N. On the other hand, as shown in (Equation 1) and (Equation 2), the self-inductance L is proportional to the square of the number of coil turns N in any coil type, so the accumulated energy P given by (Equation 3) is , Μ * S / T.

  Therefore, to increase the stored energy P of the primary coil, (a) increase the magnetic permeability μ of the magnetic material, (b) increase the cross-sectional area S of the magnetic material, or (c) decrease the coil length T, Either of these measures is required.

  Therefore, the present inventor has examined which of the measures (a) to (c) should be taken. However, if the length T of the magnetic material is shortened unnecessarily, the work efficiency at the time of manufacture deteriorates, and a predetermined amount of There is a possibility that the number of coil turns N cannot be maintained. Further, in the measure for increasing the magnetic permeability μ of the magnetic material, the manufacturing cost increases by the material cost.

However, very any measures, the self-inductance of the primary coil increases, unnecessarily increasing the self-inductance L, a result of the rise characteristics of the primary current is slow, the charging time to reach the target current I ₀ In addition to limiting the number of times of ignition in the prolonged and multiple ignition operations, there are problems such as increased power loss and promotion of heat generation. Incidentally, if the total resistance value for limiting the primary coil current of the primary circuit is r and the battery voltage is E, the amount of power W consumed by the resistance value r while increasing the primary current from zero to the target current I _0. [J] is W = ∫i ² * r * dt
= L * E ² / r ² [ln (E / (E−r * I ₀ )) − r * I ₀ / E−r ² * I ₀ ² / E ² ] (Formula 4) , Which is proportional to the self-inductance value L of the primary coil. And as shown in FIG. 6, if the self-inductance is the same, it is natural that the loss energy increases as the resistance value r increases. In the above equation, ln is a log symbol with the natural constant e as the base.

Therefore, the present inventor takes the above points into consideration and maintains the rise characteristic of the charging current of the primary coil in an appropriate condition (that is, the value of r / L is not lowered too much). We conclude that the strategy to increase S is most appropriate. In order to maintain the rising characteristic, if the value of the loss resistance r is increased corresponding to the value of L, the value of ln (E / (E−r * I ₀ ) increases remarkably, It is out of the question because the energy loss increases significantly.

According to further studies by the inventor, the charging time T from the current value 0 until reaching the target current I ₀ of 80% of the maximum current (I _MAX = E / r) is as follows: It came to the conclusion that it is preferable to set to 0 mS or less, more preferably 0.8 mS or less.

The case where the charging time T exceeds 1.0 mS is, in short, the case where the self-inductance is too large, and the energy (1/2 * L * I ₀ ² ) accumulated in the primary coil is large (Equation 4 ), The amount of heat generated in the primary coil is too high. Further, since the charging time is long, the number of multiple ignitions in one ignition cycle is limited, and there is a possibility that desired combustion control cannot be realized.

By the way, the charging time T required for the charging current I to increase from 0 to I ₀ is:
T = L / r * ln {E / (E−r * I ₀ )} (Expression 5) Therefore, substituting E / (E−r * I ₀ ) = 5 into (Equation 5) in accordance with the condition of I ₀ = 0.8 * E / r, L / r * ln (5) ≦ As a result, the self-inductance L [mH] should be limited to L ≦ 1.0 * r / ln (5). Usually, the loss resistance of the primary coil is around 1Ω, but when r = 1, for example, the self-inductance value of the primary coil should be set to about 0.622 mH or less. When the condition of T ≦ 0.8 mS is adopted, the self inductance value should be set to about 0.50 mH or less. According to such a configuration, the target current value I ₀ can be charged quickly, so that the ignition coil is not overheated and the number of multiple ignitions is not particularly limited.

Meanwhile, stored energy in the state of reaching the target current I ₀ is proportional to the self-inductance L of the primary coil, based on the required stored energy P _MIN, the lower limit of the self-inductance L is determined. That is, L ≧ 2 * P _MIN / I ₀ ² is set.

Thus, in the present invention, preferably, 2 * P _MIN / I ₀ ² ≦ L ≦ 0.8 * r / ln (5), the magnetic body of the present invention has a closed magnetic circuit. Therefore, the necessary self-inductance can be realized by a small magnetic body having a moderately increased cross-sectional area S.

  Here, in the ignition coil having a structure in which the primary coil is accommodated in the plug hole, the cross-sectional area S is limited due to the shape of the plug hole. Therefore, the primary coil should be provided outside the plug hole. Therefore, in the present invention, the primary coil and the secondary coil are formed by providing each coil winding on a magnetic body that forms a closed magnetic circuit, and are disposed at positions that are exposed from a plug hole that forms a communication path with the spark plug. ing.

  If such a configuration is adopted, a magnetic body having a desired shape can be used without being limited by the shape of the plug hole. Moreover, since the magnetic body is a closed magnetic circuit, a predetermined self-inductance can be obtained without unnecessarily increasing the cross-sectional area S, as confirmed from the comparison between (Equation 1) and (Equation 2). Then, it is possible to incorporate a complicated and sophisticated ignition control circuit in the ignition device of the present invention by utilizing the space where the margin is generated. For example, as shown in the embodiment, even if a one-chip microcomputer is mounted on the head of the plug hole, normal operation can be maintained such that sufficient heat dissipation performance can be realized by effectively utilizing the remaining space.

  The ignition control circuit of the present invention preferably includes a computer circuit that receives an ignition pulse from an ECU (Electronic Control Unit) and controls ON / OFF of the primary coil. In the present invention, since the magnetic body is constituted by a closed magnetic path, the cross-sectional area can be suppressed and the exclusive space is small. Therefore, even if the computer circuit is mounted on the ignition device, a sufficient space for disposing the heat dissipation member Can be ensured, and the computer circuit can function normally.

  Here, it is preferable that the computer circuit receives the first and second ignition pulses from the ECU and executes the multiple ignition operation during one ignition cycle. In this case, it is effective that the first ignition pulse defines the first ON operation time of the primary coil during one ignition cycle. Further, it is effective that the second ignition pulse defines an allowable interval for the second and subsequent multiple ignition operations in one ignition cycle.

  Furthermore, if a primary current detection circuit for detecting the current of the primary coil is provided, the computer circuit can grasp the overheat state of the ignition coil based on the detection value of the primary current detection circuit. On the other hand, when a secondary current detection circuit for detecting the current of the secondary coil is provided, the computer circuit can determine the deterioration state of the spark plug based on the detection value of the secondary current detection circuit.

  When the primary current detection circuit for detecting the current of the primary coil and the secondary current detection circuit for detecting the current of the secondary coil are provided, the computer circuit detects each detected value of the primary current detection circuit and the secondary current detection circuit. Therefore, it is possible to control the multiple ignition operation by itself.

  As described above, according to the present invention, it is possible to realize an ignition device capable of performing complex and advanced combustion control by multiple ignition control and outputting sufficient ignition energy while being sufficiently downsized. it can.

  Hereinafter, an embodiment of the present invention will be described in detail. FIG. 2 is an ignition device capable of multiple ignition, and illustrates a circuit configuration of an ignition control circuit IGN integrated with an ignition coil CL that drives an ignition plug PG. In this ignition device, an ignition coil CL and an ignition control circuit IGN are integrated and arranged at the head of the plug hole. An ignition plug PG is disposed at the bottom of the plug hole, and a plug boot of the ignition device extends toward the ignition plug PG. The plug boot contains a conductor, and the output of the ignition coil is supplied to the spark plug via this conductor.

  As shown, the ignition control circuit IGN has an input terminal IN for receiving a control signal CTL for ignition operation from the ECU, an output terminal OUT for outputting a notification signal ERR indicating deterioration of the ignition plug PG to the ECU, and a battery voltage E. Power supply terminal BT, a first terminal 1ST connected to the primary coil L1, a second terminal 2ND connected to the secondary coil L2, and a ground terminal GND connected to the ground. The secondary coil L2 is connected to the spark plug PG via a diode D that blocks reverse current.

  Specifically, the ignition control circuit IGN ignites by an ignition coil CL composed of a primary coil L1 and a secondary coil L2, a transistor Q1 that controls ON / OFF of the current of the primary coil L1, and an induced voltage of the secondary coil L2. It is mainly composed of a spark plug PG to be discharged.

  The primary coil L1 and the secondary coil L2 are configured by winding each coil winding around a magnetic body forming a closed magnetic circuit. The structure of the magnetic body may be a so-called outer iron type or an inner iron type. Moreover, you may arrange | position a permanent magnet etc. in a magnetic path.

In any case, the magnetic material is not magnetically saturated even when the maximum current E / r is passed through the primary coil L1. Specifically, when the reverse bias is not supplied, the number of turns N of the primary coil is N ≦ r * B _max / () with respect to the maximum value B _max [Wb / m ² ] of the magnetic flux density of the magnetic material. μ * E). In the previous equation, the battery voltage is E, the total value of the loss resistance of the primary circuit including the primary coil L1 is r, and the magnetic permeability of the magnetic material is μ. For simplicity, N = r * H _max / E.

On the other hand, when reverse bias ΔB [Wb / m ² ] by a magnet or the like is supplied in the direction opposite to the excitation by the primary coil, N * E / r ≦ (B _max + ΔB) / μ is set. . In this case, the magnetic permeability μ of the magnetic material is sufficient as much as the reverse bias ΔB is added.

  In any case, the primary coil L1 is connected between the collector terminal of the transistor Q1 and the battery and receives the battery voltage E. On the other hand, the secondary coil L2 forms a closed circuit with the diode D that prevents reverse discharge, the spark plug PG, and the secondary current detection circuit DT2. When the spark plug PG is discharged, a discharge current flows through the path of the diode D → secondary coil L2 → secondary current detection circuit DT2.

  The secondary current detection circuit DT2 includes a current detection resistor R6 connected between the secondary coil L2 and the ground, and a T-type low-pass filter Fi2 that receives the voltage across the current detection resistor R6. As illustrated, the low-pass filter Fi2 includes resistors R7 and R8 connected in series, and a capacitor C2 connected between the connection point of the resistors R7 and R8 and the ground. The voltage across the current detection resistor R6 is supplied to the one-chip microcomputer MC via the low-pass filter Fi2.

  The transistor Q1 is specifically composed of an IGBT (Insulated Gate Bipolar Transistor), and a primary current detection circuit DT1 is connected between the emitter terminal and the ground. The primary current detection circuit DT1 is provided to prevent the ignition coil CL from being overheated and realize an optimal multiple ignition operation. Therefore, it is not always necessary to detect the deterioration of the spark plug PG, and this can be omitted.

  However, in this embodiment, since the primary current detection circuit DT1 is provided to enable the multiple ignition suppression control (negative feedback control), the power consumption at the loss resistance of the ignition coil CL by the repetition of the multiple ignition. Corresponding to this, the resistance value of the loss resistance further increases, the charging characteristics of the primary coil L1 become slow, and troubles that promote further heat generation of the ignition coil CL are prevented.

  The primary current detection circuit DT1 includes a current detection resistor R1 connected between the primary coil L1 and the ground, a T-type low-pass filter Fi1 that receives a voltage across the current detection resistor R1, and non-inverting amplification by an OP amplifier. It is composed of a circuit.

  In order to suppress power loss in the current detection resistor R1, the resistance value of the current detection resistor R1 is desirably as low as possible, and is set to, for example, a resistance value of about 10 mΩ. Both ends of the current detection resistor R1 are connected to a low-pass filter Fi1 connected in a T-shape with two resistors R2 and R3 and a capacitor C1, and the output voltage of the low-pass filter Fi1 is the non-inverting input terminal ( +).

  On the other hand, an input resistor R4 is connected between the inverting input terminal (−) of the OP amplifier Q2 and the ground, and a feedback resistor R5 is connected between the inverting input terminal (−) and the output terminal. . Therefore, the OP amplifier Q2 functions as a non-inverting amplifier circuit having an amplification factor (1 + R5 / R4).

  A drive circuit DR is connected to the gate terminal of the transistor Q1, and the drive circuit DR turns on / off the transistor Q1 based on the control of the one-chip microcomputer MC. The one-chip microcomputer MC has a built-in AD converter, and the signal voltage e1 proportional to the primary current of the ignition coil CL and the signal voltage e2 proportional to the secondary current of the ignition coil CL are separated into separate AD converters. Have been supplied. The one-chip microcomputer MC has a built-in timer circuit CT that realizes a timekeeping operation, an input port that receives a control signal CTL from the ECU, and an output port that outputs a notification signal ERR to the ECU. The power supply voltage of the one-chip microcomputer MC and the OP amplifier Q2 is generated in the stabilized power supply circuit RG that steps down the battery voltage.

  The one-chip microcomputer MC performs ON / OFF control of the transistor Q1 based on a control signal CTL received from the ECU. As shown in FIG. 2B, in the ignition cycle in which the multiple ignition operation is to be executed, a control signal CTL composed of two ignition pulses SG1, SG2 is supplied from the ECU to the one-chip microcomputer MC. Here, the first ignition pulse SG1 is a control signal that defines the first ON operation time of the transistor Q1, and the second ignition pulse SG2 defines an allowable interval for the second and subsequent multiple ignition operations. Control signal.

  Therefore, the first ignition pulse SG1 is supplied as it is from the one-chip microcomputer MC to the drive circuit DR, and the transistor Q1 is turned on. Here, if the pulse width of the first ignition pulse is T, the primary current i1 of the primary coil L1 starts from zero, and the cutoff current value = E / r * (1-exp (−r * T / L1), the spark plug PG is discharged by the high voltage induced in the secondary coil L2 when the primary current i1 is interrupted, where E is the battery voltage and r is The total loss resistance on the primary side of the ignition coil CL, L1 represents the inductance value of the primary coil, and exp represents an exponential function.

  As described above, the first ignition operation in each ignition cycle is completely realized based on the control of the ECU. Therefore, the ECU can realize the ignition operation of the air-fuel mixture at an optimal timing according to each operation state while grasping the operation state based on a large number of sensor signals.

When the primary current i1 is cut off (timing A), the current of the primary coil L1 at the timing A (primary peak current I _1P ) and the current of the secondary coil L2 (secondary peak current I _2P ) are , Respectively, based on the outputs of the primary current detection circuit DT1 and the secondary current detection circuit DT2. The primary peak current I _1P is a current threshold value TH1 that defines the cutoff timing of the primary current i1 in the second and subsequent ignition operations in the ignition cycle.

On the other hand, in this embodiment, the discharge characteristics of the secondary coil corresponding to the levels of the primary peak current I _1P and the secondary peak current I _2P are experimentally specified in advance, and the one-chip microcomputer MC has the primary peak For each current I _1P or secondary peak current I _2P , an inclination angle (= ΔI ₂ / Δt _S ) at the time of discharging the secondary current i 2 realized by a normal spark plug is stored. Accordingly, a normal discharge angle (= ΔI ₂ / Δt _S ) is specified in the discharge operation of the secondary current i2 to be realized from now on, corresponding to the specified primary peak current I _1P and secondary peak current I _2P. That's right.

Thereafter, the one-chip microcomputer MC continuously checks the elapsed time TM from the timing A, and detects the timing at which this reaches the elapsed reference time Δt _S. Then, at the timing when the elapsed time TM = the elapsed reference time Δt _S , the secondary current i2 is specified based on the output signal of the secondary current detection circuit DRT2, and the specified secondary current i2 is converted into a current determination value ( = I _2P -ΔI ₂ ). Then, when the secondary current i2 greatly exceeds the current determination value, in short, when the discharge characteristics are steep, it is determined that the spark plug is abnormal.

  FIG. 1 explains the principle of determining the deterioration of the spark plug described above, and shows a primary current characteristic (a), a secondary voltage characteristic (b), and a secondary current characteristic (c), respectively. ing. As shown in FIG. 1A, the energization period of the primary coil is about 0.7 mS, and the primary peak current is about 10A. 1 (b) and 1 (c) show operating characteristics when the plug-to-plug gap is changed to change the discharge start voltage of the spark plug. Specifically, the discharge start voltage is any one of 520 V, 800 V, and 2 kV, and the voltage change and current change of the secondary coil after the discharge start are illustrated.

As can be seen from FIG. 1C, the secondary peak current has the same value of about 80 mA even though the discharge start voltage (secondary peak voltage) is different such as 520 V, 800 V, and 2 kV. . On the other hand, since the transition characteristics of the secondary current are significantly different corresponding to the difference in the discharge start voltage, the deterioration of the spark plug can be detected based on the difference in the drop characteristics. That is, when the discharge characteristic is steeply deviated from the normal discharge inclination angle (= ΔI ₂ / Δt _S ), this is the case when the spark plug is deteriorated. Although omitted in FIG. 1, when the primary peak current is increased by extending the energization period of the primary coil, the secondary peak current increases correspondingly.

  Now, when the one-chip microcomputer MC is executing such a determination process, the second ignition pulse SG2 is eventually supplied from the ECU to the one-chip microcomputer MC. That is, the control signal CTL rises again at the timing B in FIG. Therefore, the one-chip microcomputer MC turns on the transistor Q1 again based on the second ignition pulse SG2. Then, the secondary current of the secondary coil L2 at this timing B is specified based on the output of the secondary current detection circuit DT2. The identified secondary current becomes a current threshold value TH2 that determines the start timing of the charging operation of the primary coil after the third time in the ignition cycle.

  As shown in FIG. 2C, after the timing B defined by the ECU, the second charging operation for the primary coil L1 is started. The transistor Q1 that has been turned on is controlled by the one-chip microcomputer MC so as to be turned off when the primary current i1 reaches the current threshold value TH1.

After that, the secondary current i2 increases from the negative current initial value _I2P toward zero, but at the timing when the secondary current i2 reaches the current threshold value TH2, the third ON operation of the transistor Q1 starts. Is done.

  The same applies to the following. When the primary current reaches the current threshold value TH1, the one-chip microcomputer MC controls the transistor Q1 from the ON state to the OFF state. After that, when the secondary current reaches the current threshold value TH2, the one-chip microcomputer. The MC controls the transistor Q1 from the OFF state to the ON state, thereby realizing a multiple ignition operation. If such multiple ignition operation is repeated, the second ignition pulse SG2 eventually returns from the ON state to the OFF state, and thereafter the ignition operation is prohibited.

  The normal time when the ignition coil is not in an overheated state has been described based on FIGS. However, when the ignition coil is overheated, the one-chip microcomputer MC reduces the current threshold value TH1 from the above-described cutoff current value = E / r * (1−exp (−r * T / L1). Thus, the ON operation time after the second time is shortened.

Whether or not the ignition coil CL is in an overheated state depends on the first ON operation time T of the transistor Q1 and the first cutoff current value = E / r * (1-exp (−r * T / L1)). Although it can be determined from the ratio, more accurately, it can be determined by the energization time T of the primary coil L1 until the predetermined target value I ₀ is reached. When the first ignition pulse SG1 is turned on, the signal voltage e1 from the primary current detection circuit DT1 is monitored to determine whether the ignition coil CL is overheated.

  The principle of the present embodiment has been described above. Next, specific operation contents of the one-chip microcomputer MC will be described with reference to FIG. FIG. 3 is a flowchart showing the steady operation contents of the one-chip microcomputer during operation of the internal combustion engine.

  First, the one-chip microcomputer MC accesses the built-in input port and determines whether or not the ECU is outputting the control signal CTL (ST1). When the rising edge of the control signal CTL is detected (ST2 is Yes), it is determined whether the determination flag FG is 0 or 1 (ST3). Here, the determination flag FG indicates whether the ignition operation by the first ignition pulse SG1 (FG = 1) or the ignition operation by the second ignition pulse SG2 (FG = 2), or the ignition control operation is still started. It is a flag for distinguishing whether or not (FG = 0).

  Therefore, if the determination flag FG is 0, it can be determined that it is now the rising timing of the first ignition pulse SG1, so that the transistor Q1 is driven ON and the determination flag FG is set to 1 (ST4). . On the other hand, when the determination flag FG is 1, since it can be determined that the current timing is the rising timing (= timing B) of the second ignition pulse SG2, the transistor Q1 is driven ON to set the determination flag FG to 2. (ST5). Further, based on the signal voltage e2 from the secondary current detection circuit DT2 at this moment, the subsequent threshold TH2 (see FIG. 2D) of the secondary current is determined (ST6). At timing B, since it is already known whether or not the ignition coil CL is in an overheated state (see ST18), for example, a corrected current threshold TH2 is adopted in the overheated state. If the value of the determination flag FG is 2, such as 2, it is an error state and nothing is done.

  By the way, if the determination in step ST2 is No, it is next determined whether or not the falling edge of the control signal CTL is detected (ST7), and if the falling edge of the control signal CTL is detected. Then, it is determined whether the determination flag FG is 1 or 2 (ST8). Here, when the determination flag FG = 1, since it is considered that this is the falling timing (= timing A) of the first ignition pulse SG1, the transistor Q1 is driven OFF (ST9). Further, the timer circuit CT built in the one-chip microcomputer MC is started to measure the elapsed time TM from the timing A (ST9).

Then, based on the signal voltage e1 from the primary current detection circuit DT1, I grasp the primary peak current _{I 1P} (ST10), based on a signal voltage e2 from the secondary current detection circuit DT2, the secondary peak current _{I 2P} (ST11). Then, in correspondence with the grasped primary peak current I _1P and secondary peak current I _2P , the normal discharge inclination angle (= ΔI ₂ / Δt _S ) in the discharge operation of the secondary coil L 2 started from now is specified. To do. Specifically, in this embodiment, the current determination value I _2P −ΔI ₂ and the elapsed reference time Δt _S are determined corresponding to the primary peak current I _1P .

Further, the primary peak current I _1P is set as the current threshold TH1 of the subsequent primary current i1 (ST10). However, in this timing A, since whether the ignition coil CL is overheating have already been grasped (see ST18), if it is overheated, the value dropped corrected primary peak current I _1P current threshold TH1 Adopted.

  On the other hand, if it is determined in step ST8 that the determination flag FG = 2, it is considered that this is the falling timing of the second ignition pulse SG2, so that the transistor Q1 at that time is turned on / off. Regardless of the state, the transistor Q1 is forcibly turned off to end the process of the current ignition cycle (ST12).

When any of the processes described above is completed, it is determined whether or not the elapsed time TM measured by the timer circuit CT exceeds zero in order to determine whether or not the ignition plug PG can be determined to be abnormal (ST13). ). As described above, since the operation of the timer circuit CT is started by the process of step ST9 executed at the timing A, the elapsed time TM> 0 after the timing A. On the other hand, the elapsed time TM = 0 until the timing A is reached, and when the elapsed reference time Δt _S is exceeded, the elapsed time TM = 0 is processed (see ST15).

Therefore, if it is determined in step ST13 that the elapsed result TM = 0, the process related to overheating determination and suppression control (ST18) is executed, and then the process returns to step ST1. On the other hand, when it is determined that the elapsed time TM> 0, it is determined whether or not the elapsed time TM has reached a predetermined elapsed reference time Δt _S (ST14). If elapsed time TM ≠ elapsed reference time Δt _S , the process returns to step ST1.

On the contrary, if the elapsed time TM has reached the elapsed reference time Δt _S , the operation of the timer circuit CT is stopped and the elapsed time TM is initialized to zero (ST15). Then, the secondary current i2 at that timing is specified based on the output of the secondary current detection circuit DT2, and the secondary current i2 is compared with a predetermined current determination value (= I _2P −ΔI ₂ ). (ST16). Note that the current determination value I _2P −ΔI ₂ is a value selected in the process of step ST1 as with the elapsed reference time Δt _S. Specifically, the elapsed reference time Δt _S and the current determination value I _2P −ΔI ₂ extracted from the memory of the one-chip microcomputer MC using the primary peak current I _1P detected at the timing A as a search key.

  And when the difference between the secondary current i2 and the current determination value exceeds the allowable range, it is determined that the spark plug is deteriorated. Further, when such an abnormality determination occurs continuously, An abnormal signal ERR to that effect is output to the ECU (ST17). Note that the result of abnormality determination is not immediately transmitted to the ECU, and the history of past abnormality determination is taken into consideration in order to prevent erroneous determination.

  FIG. 4 is a flowchart showing overheat determination and suppression control, and illustrates the specific contents of step ST18 of FIG.

First, it is determined whether or not the value of the determination flag FG is 1 (ST20). If the determination flag FG = 1, the primary current i1 of the primary coil L1 is acquired (ST21). Then, the primary current i1 obtained is compared with a reference current _{I S} (ST22), the primary current i1 is when I reach the level of the reference current _{I S,} to obtain the current time _{T S} of the primary coil L1 (ST23). Note that this timer operation uses another timer circuit CT ′ built in the one-chip microcomputer. At this timing, the overheat variable OVR indicating the overheat state is cleared to zero (ST23). If the energization time T _S exceeds the energization threshold T _TH , it is determined that the heating state is set, the overheating variable OVR is set to 1, and the process ends (ST25).

However, and if the determination flag FG ≠ 1, in the case of the primary current i1 ≠ reference current _{I S} is then determined flag FG is determined whether 2 or not (ST26). This is because it is determined whether or not this timing is when the second ignition pulse SG2 is ON, and when the multiple ignition operation is performed by the one-chip microcomputer MC. When the determination flag FG = 2, it is determined whether or not the primary current i1 has reached the current threshold value TH1 based on the signal voltage e1 from the primary current detection circuit DT1 (ST27), and the current threshold value TH1 is reached. If it has reached, the transistor Q1 is driven OFF (ST28).

  On the contrary, when the primary current i1 has not reached the current threshold value TH1, it is determined whether or not the secondary current i2 has reached the current threshold value TH2 (ST29). Q1 is turned ON (ST30). The multiple ignition operation by the control unique to the one-chip microcomputer MC is realized by the processing of steps ST26 to ST30.

  As described above, in the present embodiment, for each ignition cycle, the abnormality of the ignition plug is determined based on the discharge characteristic of the secondary current, and deterioration of the ignition plug can be detected at an early stage. In addition, it is determined whether or not the ignition coil is overheated in each ignition cycle, and during overheating, the number of multiple discharges and the charging time of the primary coil are suppressed, so that deterioration of the spark plug can be suppressed.

  Hereinafter, in order to explain the importance of such suppression control, the relationship between the heat generation of the ignition coil CL and the signal voltage e1 will be described just in case.

Assume that the transistor Q1 is turned ON at the moment t = 0, and the charging current i to the primary coil L1 increases from zero. During such a coil charging operation, since the spark plug PG is not discharged, the secondary current of the secondary coil L2 can be ignored, and the following circuit equation is established with the battery voltage as E. E = L1 * di / dt + r * i (formula A)
In (Expression A), r is the sum of the loss resistance of the primary coil L1, the detection resistance R1, etc., but since R1≈0, it is considered that r is almost the loss resistance of the primary coil. Good. And when solving (Formula A), the charging current i of the primary coil L1 is
i = E / r * (1-exp (−r * t / L1) (Formula B)

  As is clear from (Formula B), the rising of the charging current i is closely related to the inductance value of the primary coil L1 and the loss resistance r. Here, the inductance of the primary coil L1 has a negative temperature coefficient, whereas the loss resistance≈r of the primary coil L1 has a positive temperature coefficient. Therefore, when the ignition coil CL is overheated by repeating multiple ignition, the value of r / L increases, but the saturation current E / r of the primary coil L1 greatly decreases. As shown in FIG. The rising characteristic of the charging current i becomes slow.

Here, the energization time T required for the charging current i to increase from 0 to a specific target current I ₀ is T = L / r * Ln (E / (E−r * I ₀ )) (formula Therefore, as the ignition coil CL generates heat, the energization time T until the target current I ₀ is reached increases (FIG. 5). Note that Ln is a log symbol with the natural constant e as the base.

Further, when calculating the power consumption P [J] = ∫ [i ² * r] dt in the loss resistance r from t = 0 to t = T,
_{^{P = E 2 * L / r}} 2 * Ln (E / (E-r * I 0)) - become E * L * I 0 / r -L * I 0 2/2 ··· ( wherein D).

In (Formula D), the first term increases corresponding to the increase of the loss resistance r, the second term decreases corresponding to the increase of the loss resistance r, and the third term is a fixed value. Therefore, the power consumption P [J] increases as the loss resistance r shown on the horizontal axis increases as shown in FIG. Therefore, when the loss resistance r of the primary coil L1 increases due to the heat generation of the ignition coil CL, the heat generation of the primary coil L1 is accelerated by the increased power consumption P [J]. If the current threshold value TH1 (= target current I ₀ ) is fixed, an overheated positive feedback loop is formed.

Therefore, as described above, it sets a predetermined reference current I _S, grasp the energization time T _S to reach the reference current I _S, is energized time T _S of the first-time ignition pulses in each ignition cycle Whether or not the ignition coil CL is in an overheated state is determined based on whether or not the energization threshold value _TTH is exceeded. The energization time T _S is in the overheated state exceeding the current threshold value T _TH, reduces the number and pulse width of the ignition pulse of second or later in the multiple ignition operation. Note that, when the overheat state is eliminated by such a suppression operation, the multiple ignition operation as initially set is resumed.

As described above, in the present embodiment, when the ignition coil CL generates heat abnormally, the multiple ignition operation is suppressed, so that further heat generation can be prevented, and wasteful power consumption and the ignition plug PG can be prevented. Deterioration can be suppressed. Incidentally, (Equation B) and as is seen from equation (D), the loss resistance r ignition coil CL is overheated increases, energization time T up to the target current I ₀ is increased (see FIG. 5) Since the power consumption also increases (see FIG. 6), if this state continues, the ignition coil CL may burn out.

The operation contents of the one-chip microcomputer MC have been described in detail above, but the specific description contents do not particularly limit the present invention. For example, the plug deterioration determination described above, has been waiting to reach the course reference time Delta] t _s by checking the elapsed time TM at all times, instead of this, by checking the secondary current i2 always this current determination value I Of course, it may wait until _2p− ΔI ₂ is reached.

Similarly, in the overheat determination, constantly checks the energization time T _S of the primary coil L1, which waits for reaching the current threshold value T _TH, it may be determined overheated based on the primary current i1 of the timing.

  As described above, in this embodiment, complicated and advanced combustion control is executed by a one-chip microcomputer provided separately from the ECU. However, the ignition coil of the present invention is formed by providing a coil winding on a magnetic material forming a closed magnetic circuit, and the coil winding of the primary coil is magnetic even when a maximum current is passed through the primary circuit including the primary coil. Since it is set to the number of coil turns that does not magnetically saturate the body, the ignition coil occupies the minimum necessary space. Therefore, it is possible to secure an arrangement space capable of realizing a complex and advanced control operation without causing the one-chip microcomputer to malfunction.

It is a characteristic view for demonstrating the principle of deterioration determination of an ignition plug. It is a circuit diagram which shows the ignition device which concerns on embodiment. It is a flowchart which shows operation | movement of the one-chip microcomputer of FIG. It is a flowchart which shows a part of FIG. 3 in detail. It is a time chart which shows the change of the primary current of an ignition coil. 6 is a diagram showing that power loss increases due to heat generated by an ignition coil. It is a time chart which shows the change of the primary current of an ignition coil. It illustrates a BH characteristic curve.

Explanation of symbols

L1 Primary coil L2 Secondary coil CL Ignition coil PG Ignition plug IGN Ignition control circuit

Claims (9)

An ignition coil in which a primary coil and a secondary coil are electromagnetically coupled and an ignition control circuit for controlling the current of the primary coil are integrated, and an ignition plug that can ignite multiple spark plugs connected to the secondary coil A device,
The primary coil and the secondary coil are formed by providing each coil winding on a magnetic body that forms a closed magnetic circuit, and are arranged at positions exposed from a plug hole that forms a communication path with the spark plug,
The ignition device for an internal combustion engine, wherein the coil winding of the primary coil is set to a number of coil turns that does not magnetically saturate the magnetic body even when a maximum current flows through a primary circuit including the primary coil.   2. The ignition device according to claim 1, wherein the ignition control circuit includes a computer circuit that receives an ignition pulse from an ECU (Electronic Control Unit) and controls ON / OFF of the primary coil.   3. The ignition device according to claim 2, wherein the computer circuit receives the first and second ignition pulses from the ECU and performs a multiple ignition operation during one ignition cycle.   The ignition device according to claim 3, wherein the first ignition pulse defines a first ON operation time of the primary coil during one ignition cycle.   5. The ignition device according to claim 3, wherein the second ignition pulse defines an allowable interval for the second and subsequent multiple ignition operations in one ignition cycle. A primary current detection circuit for detecting a current of the primary coil;
The ignition device according to any one of claims 1 to 5, wherein the computer circuit grasps an overheated state of the ignition coil based on a detection value of the primary current detection circuit. A secondary current detection circuit for detecting a current of the secondary coil;
The ignition device according to any one of claims 1 to 6, wherein the computer circuit determines a deterioration state of the spark plug based on a detection value of the secondary current detection circuit. A primary current detection circuit for detecting a current of the primary coil;
A secondary current detection circuit for detecting a current of the secondary coil, and
The ignition device according to any one of claims 1 to 5, wherein the computer circuit controls a multiple ignition operation by itself based on detection values of the primary current detection circuit and the secondary current detection circuit.   The self-inductance of the primary coil is set such that an elapsed time from when the current of the primary coil starts from zero current to 80% of the upper limit value is 1.0 mS or less. The ignition device according to any one of 8.

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