JP5899823B2 - Ignition device for internal combustion engine - Google Patents

Description

  The present invention relates to an ignition device for an internal combustion engine, which includes an ignition coil and a means for controlling an energization state of a primary coil of the ignition coil.

  In general, a discharge in which a center electrode of a spark plug is a negative electrode, a ground electrode is a positive electrode, and a spark is extended toward the ground electrode starting from the center electrode side is called a negative discharge. On the other hand, a discharge in which a center electrode is used as a positive electrode and a spark is extended toward a negative ground electrode is called a positive discharge. Therefore, electrode wear caused by cations colliding (sputtering) with the electrodes during discharge occurs at the central electrode as the negative electrode during negative discharge, and occurs at the ground electrode as the negative electrode during positive discharge. However, since the ground electrode is closer to the combustion center than the center electrode and is at a high temperature, the degree of wear is large. For this reason, an ignition device that performs minus discharge with little wear is generally popular (see Patent Document 1).

JP 2007-120374 A

  On the other hand, the present inventors examined a method of performing positive discharge at the beginning of discharge and switching to negative discharge during the positive discharge. According to this method, since the positive discharge period in which electrode consumption is large can be shortened, positive discharge can be performed while electrode consumption is suppressed. In order to realize this method, the present inventors examined the ignition device shown in FIG.

  That is, the primary coil L1A for positive discharge and the primary coil L1B for negative discharge are separately provided for the same core member 21x. Further, semiconductor switches SWA and SWB for controlling energization are provided for each of the primary coils L1A and L1B. Then, the ECU 10x controls both switches SWA and SWB so that the semiconductor switch SWB is cut off and switched to minus discharge while the semiconductor switch SWA is cut off and the plus discharge is being performed. In the example of FIG. 4, the core member 21x for concentrating the magnetic flux generated by the primary coil L1A and the core member 21x for concentrating the magnetic flux by the primary coil L1B are shared to reduce the size of the ignition coil 20x. .

  FIG. 5 is a time chart for explaining the operation of the apparatus shown in FIG. 4. In the period from t1 to t5, the primary coil L1B is energized to store negative discharge magnetic energy in the coil L1B ((b) (d )reference). Further, the primary coil L1A is energized during the period from t2 to t3, and magnetic energy for plus discharge is stored in the coil L1A (see (a) and (c)). Then, energization to the primary coil L1A is cut off at time t3 to start plus discharge, and thereafter, energization to the primary coil L1B is cut off at time t5 to start minus discharge. As a result, positive discharge is performed during the Ta period from t3 to t5, and negative discharge is performed during the Tb period from t5 to t6. That is, the positive discharge is switched to the negative discharge at time t5.

  However, in the examination apparatus of FIG. 4, the direction of the magnetic flux in the core member 21x generated by the primary current I1 (-) for negative discharge and the magnetic flux in the core member 21x generated by the primary current I1 (+) for positive discharge. The direction is opposite. Therefore, in the period from t2 to t3 in which both the primary coils L1A and L1B are energized, the mutual magnetic fluxes cancel each other, so that the power loss is large. Moreover, since it is necessary to provide the primary coil L1A for positive discharge and the primary coil L1B for negative discharge, respectively, the size of the ignition coil is increased.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an ignition device for an internal combustion engine that enables positive discharge while suppressing electrode consumption while suppressing increase in size of the ignition coil. Is to provide.

  Hereinafter, means for solving the above-described problems and the operation and effects thereof will be described.

In the first invention, an ignition coil having a primary coil and a secondary coil, and the absolute value of the secondary voltage generated in the secondary coil are boosted by discharging the stored electric power to the primary coil. A capacitive discharge circuit for performing capacitive discharge, an induction discharge circuit for boosting an absolute value of a secondary voltage generated in the secondary coil by inducing energization to the primary coil and inductively discharging with the spark plug; Control means for controlling the energization state of the primary coil so as to perform a positive discharge with the center electrode of the spark plug as a positive electrode and switch to a negative discharge with the center electrode as a negative electrode in the middle of the positive discharge; And the control means performs the positive discharge by the capacitive discharge and performs the negative discharge by the induction discharge. And controlling the operation of the preliminary the inductive discharge circuit.

  According to the above-described invention, the positive discharge is performed by the capacitive discharge and the negative discharge is performed by the induction discharge. Therefore, as illustrated in the symbols I1 (+) and I1 (−) in FIG. The direction in which the current I1 (+) flows through the primary coil and the direction in which the primary current I1 (−) for negative discharge flows through the primary coil can be made the same. As a result, the directions of the magnetic flux due to I1 (+) and the magnetic flux due to I1 (−) are the same. Therefore, it is possible to avoid a power loss due to mutual cancellation of the magnetic fluxes, and consequently to suppress an increase in the size of the ignition coil.

  In addition, the negative discharge primary coil and the positive discharge primary coil can be used in common because the flow directions of the two currents I1 (+) and I1 (−) can be made the same as described above. That is, it is unnecessary to provide the positive discharge primary coil L1A and the negative discharge primary coil L1B as in the examination apparatus of FIG. 4, so that the size of the ignition coil can be suppressed.

  As described above, according to the present invention, it is possible to switch to negative discharge during the positive discharge and shorten the positive discharge period in which electrode consumption is large while suppressing the increase in size of the ignition coil.

  By the way, the absolute value of the secondary voltage necessary for starting the discharge is higher than the absolute value of the secondary voltage necessary for maintaining the discharge. In general, capacitive discharge has a shorter secondary voltage generation period than induction discharge, but the absolute value of the secondary voltage can be increased compared to induction discharge. In the above-mentioned invention in view of these, the positive discharge for starting discharge is performed by capacitive discharge, and the negative discharge for maintaining discharge is performed by induction discharge. Therefore, the secondary voltage required for starting and maintaining the discharge can be generated with high efficiency. Can be generated.

In the second invention, the control means starts energization of the primary coil by the induction discharge circuit, and thereafter energizes the primary coil by the capacitive discharge circuit, and then the induction discharge. The circuit is controlled so as to cut off the energization of the primary coil by the circuit.

  According to the above invention, since the energization of the primary coil by the induction discharge circuit is started before the capacity discharge is started by starting the energization of the primary coil by the capacity discharge circuit, the induction discharge is started after the start of the capacity discharge. Compared with the case where energization by the circuit is started, it is possible to secure a sufficiently long period for storing the magnetic energy for minus discharge in the primary coil.

In a third aspect of the invention, the ignition coil has a core member that concentrates magnetic flux generated by energization of the primary coil, and the capacitive discharge circuit starts from energization start to the primary coil by the induction discharge circuit. The core member is selected so that the magnetic flux generated in the core member does not reach the saturation amount immediately before the start of energization of the primary coil.

  Here, the amount of magnetic flux (saturated magnetic flux) that can be concentrated by the core member is determined according to the material, shape, and size of the core member. For this reason, if a material having a low saturation magnetic flux density or a small core member is adopted in the above invention, the following problems are concerned. That is, if the magnetic flux in the core member saturates during the period from when the primary current I1 (−) for negative discharge starts to flow until the primary current I1 (+) for positive discharge starts to flow, then I1 (+ ) Flows through the primary coil, the amount of magnetic flux in the core member does not increase. Then, there is a concern that the plus discharge cannot be performed.

  In response to this concern, in the above invention, the core member is selected so that the magnetic flux generated in the core member does not reach the saturation amount from the start of energization of I1 (−) to immediately before the start of energization of I1 (+). Therefore, the above concerns can be resolved.

The circuit diagram which shows the ignition device concerning one Embodiment of this invention. The figure explaining the difference between positive discharge and negative discharge. The time chart which shows the action | operation of the ignition device of FIG. The circuit diagram which shows the apparatus which is the ignition device which the present inventors examined, and becomes a comparison object with this invention. The time chart which shows the action | operation of the ignition device of FIG.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the drawings.

  FIG. 1 is a schematic circuit diagram showing an ignition system of an internal combustion engine to which the ignition device according to the present embodiment is applied. A microcomputer (control means) provided in an electronic control unit (ECU 10) Operating state information representing the operating state of the engine such as an accelerator operation amount is acquired, and an optimal ignition timing is calculated based on the operating state information. Then, in accordance with the ignition timing, a positive discharge ignition signal IGt (+) and a negative discharge ignition signal IGt (−) are generated and output to semiconductor switches SW (+) and SW (−) described later.

  Here, positive discharge and negative discharge will be described with reference to FIG. FIG. 2A shows the center electrode 41 and the ground electrode 42 of the spark plug 40. As shown in the figure, the center electrode 41 has a needle-like protrusion as compared with the flat surface of the ground electrode 42. For this reason, electric field concentration occurs at the protruding portion, so that the discharge generated between the electrodes 41 and 42 extends to the ground electrode 42 starting from the protruding portion of the center electrode 41.

  However, the direction of the secondary current I2 differs between the positive discharge shown in FIG. 2B and the negative discharge shown in FIG. That is, at the time of positive discharge, the center electrode 41 functions as a positive electrode and the ground electrode 42 functions as a negative electrode, and the secondary current I2 flows from the center electrode 41 side to the ground side. On the other hand, during positive discharge, the center electrode 41 functions as a negative pole and the ground electrode 42 functions as a positive pole, and a secondary current I2 flows from the ground side to the center electrode 41 side.

  Returning to the description of FIG. 1, the ignition coil 20 provided for each cylinder of the internal combustion engine includes a core member 21, a primary coil L1, a secondary coil L2, and the like that form a magnetic circuit. More specifically, the coils L1 and L2 are wound around the outer peripheral surface of the core member 21 via an insulating sheet (not shown).

  The core member 21 functions to concentrate the magnetic flux generated by the primary current I1 flowing through the primary coil L1, but the amount of magnetic flux (saturated magnetic flux) that can be concentrated by the core member 21 is as follows. It is determined according to the material, shape and size of the core member 21. Therefore, in order to increase the saturation magnetic flux amount and generate the desired secondary voltage V2 while reducing the size of the ignition coil 20, a material having a high saturation magnetic flux density may be adopted, but the cost increases.

  On the other hand, if a material having a low saturation magnetic flux density is adopted, it occurs in the core member 21 during a period from when the primary current I1 (−) for negative discharge starts to flow until the primary current I1 (+) for positive discharge starts to flow. Magnetic flux reaches saturation. Then, even if I1 (+) is then passed through the primary coil L1, there is a concern that the amount of magnetic flux in the core member 21 will not increase, and positive discharge cannot be performed.

  Therefore, in the present embodiment, the core having the minimum saturation magnetic flux density so that the magnetic flux generated in the core member 21 does not reach the saturation amount from the start of energization of I1 (−) to immediately before the start of energization of I1 (+). Since the member 21 is selected, the above-mentioned concern can be solved while suppressing an increase in cost.

  The power supplied to the primary coil L1 can be obtained from two systems of a capacitive discharge circuit and an induction discharge circuit described below.

  The capacity discharging circuit is composed of the semiconductor switch SW (+), the DC-DC converter 50 (boosting means), the capacitor 51 (power storage means), and the diode 52 described above. The output voltage of the battery 30 is boosted by the DC-DC converter 50, and the boosted power is stored in the capacitor 51 during the period when the semiconductor switch SW (+) is turned off. When the semiconductor switch SW (+) is turned on, the high voltage power stored in the capacitor 51 is discharged to the primary coil L1, and due to this discharge, the absolute value of the secondary voltage V2 at the secondary coil L2. Is increased, and a capacitive discharge is generated at the spark plug 40. This capacitive discharge is applied to the implementation of the positive discharge described above.

  The induction discharge circuit is configured by the semiconductor switch SW (−) and the diode 53 described above, and controls energization and interruption of the primary coil L <b> 1 supplied from the battery 30. That is, when the semiconductor switch SW (−) is turned on to start energization of the primary coil L1, magnetic energy for negative discharge is stored in the primary coil L1. Thereafter, when the semiconductor switch SW (−) is turned off to cut off the energization, the absolute value of the secondary voltage V2 generated in the secondary coil L2 is increased, and induction discharge is generated in the spark plug 40. This induction discharge is applied to the implementation of the negative discharge described above.

  The arrows I1 (+) and I1 (−) in FIG. 1 indicate the direction in which the primary current I1 (+) for positive discharge by the capacitive discharge circuit flows through the primary coil L1 and the primary for negative discharge by the induction discharge circuit. The direction in which the current I1 (−) flows through the primary coil is shown. The directions in which the primary currents I1 (+) and I1 (−) flow through the primary coil L1 are the same, and the reversal of this direction is limited by the diodes 52 and 53.

  The ECU 10 controls the semiconductor switches SW (+) and SW (−) to start discharge at the spark plug 40 by capacitive discharge (plus discharge), and inductive discharge (minus discharge) during the plus discharge. The discharge state at the spark plug 40 is controlled so as to switch to.

  FIG. 3 is a time chart when a positive discharge ignition signal IGt (+) and a negative discharge ignition signal IGt (−) are output in order to carry out such control of the discharge state.

  First, at time t1 when the ignition signal IGt (−) is switched from off to on, the semiconductor switch SW (−) is turned on, and the primary current I1 (−) for negative discharge flows from the battery 30 to the primary coil L1. Start (see FIGS. 3A and 3C). That is, accumulation of magnetic energy for induction discharge (minus discharge) is started at time t1.

  Next, at time t2 when the ignition signal IGt (+) switches from off to on, the semiconductor switch SW (+) is turned on. As a result, the power energy stored in the capacitor 51 is discharged, and the primary current I1 (+) for positive discharge starts to flow through the primary coil L1 (see FIGS. 3B and 3D). As a result, the secondary voltage V2 changes so that the potential of the center electrode 41 is rapidly higher than the potential of the ground electrode 42 (see FIG. 3F). As a result, discharge (plus discharge) occurs in the direction in which the secondary current I2 flows from the center electrode 41 to the ground electrode. That is, capacity discharge (plus discharge) is started at time t2.

  The primary current I1 (actual primary current I1) that actually flows through the primary coil L1 is a value obtained by adding I1 (+) to I1 (−) as shown in FIG. The actual primary current I1 has a peak value at time t3 with the start of capacitive discharge (plus discharge). At time t4 after the predetermined time, the ignition signal IGt (−) is switched from on to off, the semiconductor switch SW (−) is turned off, and the energization of the negative discharge primary current I1 (−) is interrupted. Is done.

  As a result, the magnetic energy stored in the primary coil L1 is released, and the secondary voltage V2 changes so that the potential of the center electrode 41 becomes lower than the potential of the ground electrode 42 (FIG. 3 (f)). reference). As a result, a discharge (minus discharge) occurs in the direction in which the secondary current I2 flows from the ground electrode 42 to the center electrode 41.

  At time t4 when the primary current I1 (−) is cut off, the ignition signal IGt (+) is switched from on to off and the semiconductor switch SW (+) is turned off. The capacity discharge (plus discharge) ends at the same time as the start. That is, at time t4, the discharge is switched to induction discharge (minus discharge) while the capacity discharge (plus discharge) is continued.

  Thereafter, the discharge voltage V2 between the electrodes 41 and 42 becomes zero (precisely, the battery voltage (12V)) at time t5. In short, a positive discharge is performed in the period indicated by the symbol Ta, and is switched to a negative discharge in the middle of the positive discharge (at time t4), and a negative discharge is performed in the period indicated by the symbol Tb.

  According to the embodiment described in detail above, the following effects can be obtained.

  (1) Since positive discharge is performed at the initial stage of discharge and is switched to negative discharge in the middle of the positive discharge, the period of positive discharge with a lot of electrode consumption can be shortened. Therefore, positive discharge can be performed while suppressing electrode consumption.

  (2) Since the positive discharge is performed by capacitive discharge and the negative discharge is performed by induction discharge, the direction of the primary current I1 (+) for positive discharge flowing through the primary coil L1 and the primary current I1 (− for negative discharge) ) Can flow in the primary coil L1 in the same direction. As a result, it is possible to avoid a power loss due to the magnetic flux due to I1 (+) and the magnetic flux due to I1 (−) canceling each other, and consequently the increase in size of the ignition coil 20 can be suppressed.

  (3) As described above, the direction in which both the currents I1 (+) and I1 (−) flow can be made the same, so that the primary coil for negative discharge and the primary coil for positive discharge can be shared. The enlargement of the ignition coil 20 can be suppressed.

  (4) From the start of energization of I1 (−) to immediately before the start of energization of I1 (+), the core member 21 having the minimum saturation magnetic flux density is set so that the magnetic flux generated in the core member 21 does not reach the saturation amount. Since it has selected, the said concern can be eliminated, suppressing the high cost.

  (5) By the way, the absolute value of the secondary voltage V2 required for dielectric breakdown (discharge start) at both electrodes 41 and 42 is higher than the absolute value of the secondary voltage V2 required for maintaining discharge after dielectric breakdown. In general, the capacitive discharge has a shorter generation period of the secondary voltage V2 than the induction discharge, but the absolute value of the secondary voltage V2 can be increased compared to the induction discharge. In view of these, in the present embodiment, the positive discharge for starting discharge is performed by capacitive discharge, and the negative discharge for maintaining discharge is performed by induction discharge. Therefore, the secondary voltage V2 required for starting and maintaining the discharge is increased. Can be generated efficiently.

(Other embodiments)
In the above embodiment, the semiconductor switch SW (+) for plus discharge and the semiconductor switch SW (−) for minus discharge are simultaneously turned off at time t4. On the other hand, the semiconductor switch SW (+) for minus discharge may be turned off after the semiconductor switch SW (−) for minus discharge is turned off to start the induction discharge, or the semiconductor switch SW (+) for plus discharge may be turned off. SW (+) may be turned off before turning off. In any case, SW (+) may be turned off after time t3 when the discharge from the capacitor 51 reaches a peak.

  DESCRIPTION OF SYMBOLS 10 ... ECU (control means), 20 ... Ignition coil, 21 ... Core member, 40 ... Spark plug, 41 ... Center electrode, L2 ... Secondary coil, L1 ... Primary coil, 50 ... DC-DC converter (capacitance discharge circuit) ), 51... Capacitor (capacitance discharge circuit), 52... Diode (capacitance discharge circuit), SW (+)... Semiconductor switch (capacitance discharge circuit), 53. ... Semiconductor switch (inductive discharge circuit).

Claims (1)

An ignition coil having a primary coil and a secondary coil;
A capacity discharging circuit for boosting the absolute value of the secondary voltage generated in the secondary coil by discharging the stored power to the primary coil and performing capacity discharge with a spark plug;
An induction discharge circuit that boosts the absolute value of the secondary voltage generated in the secondary coil and induces an inductive discharge with the spark plug by cutting off the energization of the primary coil;
Control means for controlling the energization state of the primary coil so as to perform a positive discharge with the center electrode of the spark plug as a positive electrode and switch to a negative discharge with the center electrode as a negative electrode in the middle of the positive discharge;
With
The ignition coil has a core member that concentrates magnetic flux generated by energization of the primary coil,
The control means starts energizing the primary coil by the circuit for inductive discharge so that the positive discharge is performed by the capacity discharge and the minus discharge is performed by the induction discharge, and then the capacity discharge is performed. Conducting the energization of the primary coil by a circuit, and then controlling the energization of the primary coil by the induction discharge circuit to be performed,
The core member so that the magnetic flux generated in the core member does not reach a saturation amount from the start of energization to the primary coil by the induction discharge circuit to immediately before the start of energization to the primary coil by the capacitive discharge circuit. An ignition device for an internal combustion engine, characterized in that is selected .

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