Patent Publication Number: US-9410526-B2

Title: Ignition device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority based on 35 USC 119 from prior Japanese Patent Application No. 2015-002226 filed on Jan. 8, 2015, entitled “IGNITION DEVICE”, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND 
     This disclosure relates to an ignition device provided with an ignition coil for an internal combustion engine. 
     As a conventional ignition device, there has been known an ignition device disclosed in Japanese Patent Application Publication No. 2001-217131 (Patent Document 1), for example. As illustrated in  FIG. 6 , the ignition device provided with an ignition coil described in Patent Document 1 includes igniter control circuit  11 , igniter switch Q 1 , transformer Ta, battery E, and diode D 5 , and adopts a fly-back control method. 
     Igniter control circuit  11  inputs an ignition signal and turns igniter switch Q 1  on and off by using the ignition signal. Energy is stored in transformer Ta while igniter switch Q 1  is on, and the energy stored in transformer Ta is supplied to plug  16  when igniter switch Q 1  is turned off, and plug  16  is thus ignited. 
     SUMMARY 
     An embodiment of an ignition device comprises an ignition coil including a first winding, a second winding, and a third winding electromagnetically coupled to one another, a first switch electronically connected to a first end of the first winding, a battery electronically connected to a second end of the first winding, a booster with a first end electronically connected to the battery and a second end electronically connected to a first end of the third winding, a second switch electronically connected to a second end of the third winding, and a drive device electrically connected to the first and the second switches, that turns the first and the second switch on and off, wherein the drive device feeds a secondary current to the second winding by changing the first switch from an on-state to an off-state, and supplies an output from the booster to the third winding by changing the second switch from an off-state to an on-state. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram illustrating a circuit configuration of an ignition device according to Example 1. 
         FIG. 2  is an operation waveform diagram regarding constituents of the ignition device according to Example 1. 
         FIG. 3  is a diagram illustrating a circuit configuration of an ignition device according to a modified example. 
         FIG. 4  is an operation waveform diagram regarding constituents of the ignition device according to the modified example. 
         FIG. 5  is a diagram illustrating a circuit configuration of an ignition device according to another modified example. 
         FIG. 6  is a diagram illustrating a circuit configuration of a conventional ignition device. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments are described below in detail with reference to the drawings.  FIG. 1  is a diagram illustrating a circuit configuration of an ignition device according to Example 1. Note that constituents in  FIG. 1 , which are the same as those in the conventional ignition device illustrated in  FIG. 6  are denoted by the same reference numerals used in the description of the background. 
     In the conventional ignition device illustrated in  FIG. 6 , electric power is supplied only from the battery. On the other hand, in the following example, electric power is supplied from an auxiliary boost converter to energy superposition winding. In addition, the ignition device of the example controls a constant current by detecting a plug current and feeding the detected plug current back to the auxiliary boost converter. 
     The ignition device of Example 1 includes igniter control circuit  11 , igniter switch Q 1 , transformer T, battery E, diodes D 1  to D 5 , Da, and Db, inverter  12 , DC/DC converter  13 , delay circuit  13   a , buffer circuit  14 , constant current control PWM circuit  15 , MOSFET Q 2 , resistors R 1  and R 2 , and shunt resistor Rs. 
     Engine control unit (ECU)  10  outputs an ignition signal to igniter control circuit  11 . Igniter control circuit  11  receives the ignition signal from ECU  10 , and turns igniter switch Q 1  on and off via resistor R 1  by using the ignition signal. Igniter switch Q 1  corresponds to a first switch and includes an N-type MOSFET. 
     Transformer T corresponds to an ignition coil and includes igniter winding P 1  (corresponding to a first winding), secondary winding S (corresponding to a second winding) in a reverse phase to igniter winding P 1 , and energy superposition winding P 2  (corresponding to a third winding), which are electromagnetically coupled to one another. 
     One end of igniter winding P 1  is connected to a drain of igniter switch Q 1 . Meanwhile, a positive electrode of battery E is connected to another end of igniter winding P 1  while a negative electrode of battery E is grounded. Diode Da is connected between the drain and a source of igniter switch Q 1 . Diode Da may be a parasitic diode in igniter switch Q 1 . 
     Inverter  12  inverts the ignition signal from igniter control circuit  11  and outputs the inverted ignition signal to buffer circuit  14 . Delay circuit  13   a  delays the inverted ignition signal from inverter  12  by a predetermined time period and then outputs the signal to DC/DC converter  13 . 
     DC/DC converter  13  corresponds to a booster, which boosts a voltage of battery E by using the inverted ignition signal from inverter  12 , and supplies the boosted voltage to anodes of four diodes D 1  to D 4  that are connected in parallel. 
     Four diodes D 1  to D 4  are provided corresponding to four cylinders of an internal combustion engine. In  FIG. 1 , one end of energy superposition winding P 2  is connected to a cathode of diode D 1 . Meanwhile, a drain of MOSFET Q 2  is connected to another end of energy superposition winding P 2  while a source of MOSFET Q 2  is grounded. Diode Db is connected between the drain and the source of MOSFET Q 2 . Diode Db may be a parasitic diode in MOSFET Q 2 . 
     Here, although not illustrated, one end of winding corresponding to energy superposition winding P 2  is also connected to a cathode of each of diodes D 2  to D 4 . In the meantime, a drain of a MOSFET corresponding to MOSFET Q 2  is connected to another end of the winding while a source of such a MOSFET is grounded. 
     MOSFET Q 2  (corresponding to a second switch) is formed from an N-type MOSFET. MOSFET Q 2  is turned on and off by the inverted ignition signal from inverter  12  inputted to a gate of MOSFET Q 2  via buffer circuit  14 . 
     Meanwhile, DC/DC converter  13  operates to continue supply of electric energy to energy superposition winding P 2  in response to an internal signal to be described later during a period when MOSFET Q 2  is in an on-state. In this regard, DC/DC converter  13  starts supply of the electric energy after a lapse of a predetermined time period from a point when MOSFET Q 2  is changed from an off-state to the on-state. 
     Igniter control circuit  11  and inverter  12  correspond to a drive device. The drive device feeds a secondary current to secondary winding S by changing igniter switch Q 1  from an on-state to an off-state, and supplies an output from DC/DC converter  13  to energy superposition winding P 2  by changing MOSFET Q 2  from the off-state to the on-state, thereby extending a time period for supplying the secondary current. 
     One end of plug  16  is connected to one end of secondary winding S of transformer T, and an anode of diode D 5  is connected to another end of secondary winding S. A cathode of diode D 5  is connected to one end of shunt resistor Rs and to an input terminal of constant current control PWM circuit  15 . Another end of shunt resistor Rs is connected to another end of plug  16  and to the ground. A plug current signal from shunt resistor Rs is outputted to ECU  10 . 
     Constant current control PWM circuit  15  outputs to DC/DC converter  13  the internal signal for controlling the secondary current at a constant value by detecting the secondary current flowing on secondary winding S of the ignition coil while using shunt resistor Rs, and comparing a detected value with an internal reference value. 
     Here, constant current control PWM circuit  15  illustrated in  FIG. 1  is provided outside DC/DC converter  13 . Instead, constant current control PWM circuit  15  may be provided inside DC/DC converter  13 , for example. 
     Next, an operation of the ignition device of the example thus configured is described in detail with reference to an operation waveform diagram illustrated in  FIG. 2  regarding the constituents of the ignition device. 
     Note that in  FIG. 2 , a line indicated with IGNITION SIGNAL represents a signal sent from ECU  10 , a line Q 1  represents an output from igniter switch Q 1 , a line Q 2  represents an output from MOSFET Q 2 , a line DC/DC CONVERTER represents an output from DC/DC converter  13 , and a line S represents energy of secondary winding S of transformer T. 
     First, during a period from time t 0  to time t 1 , igniter control circuit  11  applies an H-level ignition signal to a gate of igniter switch Q 1 . Hence, igniter switch Q 1  is on during the period from time t 0  to time t 1 . 
     Then, a current is fed from battery E to the ground via igniter winding P 1  and igniter switch Q 1 , and the energy is stored in igniter winding P 1 . At this time, electric potential on a winding finish side of igniter winding P 1  is higher than electric potential on a winding start side thereof. Accordingly, electric potential on a winding finish side of secondary winding S is higher than electric potential on a winding start side thereof as well. For this reason, diode D 5  on the secondary winding side is turned off and no secondary current flows thereon. 
     Next, at time t 1 , igniter control circuit  11  applies an L-level ignition signal to the gate of igniter switch Q 1 . Hence, igniter switch Q 1  is turned off. Here, the electric potential on the winding start side is higher than the electric potential on the winding finish side in each of igniter winding P 1  and secondary winding S. Accordingly, the secondary current flows from the winding start side of secondary winding S via diode D 5  and shunt resistor Rs and the energy is supplied to plug  16 . The energy of secondary winding S is supplied to plug  16  and therefore gradually reduced over period T 1  from time t 1  to time t 3 . 
     Meanwhile, at time t 1 , the L-level ignition signal from igniter control circuit  11  is inverted to the H level by inverter  12 . Thus, the H-level ignition signal is supplied to the gate of MOSFET Q 2  via buffer circuit  14 . As a consequence, MOSFET Q 2  is on during a period from time t 1  to time t 4 . 
     Next, delay circuit  13   a  delays the H-level ignition signal inverted by inverter  12  for a predetermined time period starting from time t 1 . At time t 2  (at time in the middle of time t 1  and time t 3 ) after the delay for the predetermined time period, DC/DC converter  13  is activated for a period from time t 2  to time t 4 . DC/DC converter  13  boosts the voltage of battery E and supplies the boosted voltage to the anodes of four diodes D 1  to D 4  that are connected in parallel. 
     As a consequence, concerning diode D 1 , the current is fed from DC/DC converter  13  to MOSFET Q 2  via diode D 1  and energy superposition winding P 2 . As with the case of diode D 1 , concerning each of diodes D 2  to D 4 , the current is fed from DC/DC  13  to the corresponding MOSFET via diode D 2 , D 3 , or D 4  and a constituent component corresponding to energy superposition winding P 2 . 
     At this time, electric potential on a winding start side is higher than electric potential on a winding finish side in each of energy superposition winding P 2  and secondary winding S. Accordingly, the secondary current flows from the winding start side of secondary winding S via diode D 5  and shunt resistor Rs and the energy is supplied to plug  16 . Thus, the energy of energy superposition winding P 2  is superposed on secondary winding S over a period T 2  from time t 2  to time t 4 . 
     In other words, by feeding the current from auxiliary DC/DC converter  13  to energy superposition winding P 2 , the energy from energy superposition winding P 2  is supplied from secondary winding S to plug  16  at the timing (the period from time t 1  to time t 3 ) when fly-back energy of secondary winding S is reduced. Thus, a time period to supply the secondary current is extended and ignition time of plug  16  is extended accordingly. 
     As described above, according to the ignition device of Example 1, igniter control circuit  11  and inverter  12  which serve as the drive device feed the secondary current to secondary winding S by changing igniter switch Q 1  from the on-state to the off-state, and supply the output from DC/DC converter  13  to energy superposition winding P 2  by changing MOSFET Q 2  from the off-state to the on-state, thereby extending the time period to supply the secondary current. It is therefore possible to extend the ignition time of plug  16  and thus to improve combustion efficiency of fuel. 
     Meanwhile, since the energy is supplied to plug  16  via energy superposition winding P 2 , the configurations of igniter winding P 1  and secondary winding S can be designed regardless of the energy to be superposed on secondary winding S. Accordingly, it is possible to improve the combustion efficiency of the fuel while suppressing an increase in size of transformer T or reduction in efficiency of the ignition device. 
     In the meantime, DC/DC converter  13  continues to supply the electric energy to energy superposition winding P 2  during the period when MOSFET Q 2  is in the on-state, in such away that the secondary current is controlled at the constant value. Accordingly, a fluctuation of electrical stress to be applied to constituent components of DC/DC converter  13  is reduced and reliability of the ignition device is thereby improved. 
     Meanwhile, MOSFET Q 2  is turned on earlier by a predetermined time period than the activation of DC/DC converter  13  and in the state where a relatively low voltage is applied thereto. Accordingly, electrical stress is reduced when turning MOSFET Q 2  on. 
     In the meantime, DC/DC converter  13  repeats start and stop in response to the ignition signal. This configuration suppresses heat generation from the constituent components of DC/DC converter  13  and thus improves the reliability of the ignition device. 
     As illustrated in  FIG. 3 , delay circuit  13   a  may be omitted and DC/DC converter  13  may be activated at the same time as turning MOSFET Q 2  on. Meanwhile, as illustrated in  FIG. 4 , DC/DC converter  13  may be activated by an activation signal different from the ignition signal, and may continue a boosting operation regardless of the state of MOSFET Q 2 . In the latter case, the output from DC/DC converter  13  is supplied to energy superposition winding P 2  at the timing when the fly-back energy of secondary winding S is reduced. In this case, electrical stress to be applied to transformer T and a secondary side circuit is reduced and the reliability of the ignition device is improved. 
     Meanwhile, as illustrated in  FIG. 5 , engine control unit (ECU)  10  may be configured to output the ignition signal to igniter control circuit  11  and to output a plug current change signal to constant current PWM circuit  15 . In this case, constant current control PWM circuit  15  outputs the internal signal for increasing or decreasing the secondary current to DC/DC converter  13  while adjusting the internal reference value in accordance with the plug current change signal. The increase in secondary current can prevent an accidental fire. 
     Transformer Ta of the technique disclosed in Patent Document 1 is configured to generate a high voltage on a secondary side and therefore has a high winding number ratio as the transformer. Accordingly, the energy stored in transformer Ta is significantly consumed by voltage conversion. For this reason, transformer Ta can supply the current to plug  16  only for a short time, and the ignition time of plug  16  is therefore limited. As a consequence, combustion efficiency of fuel is reduced and there is a concern of deterioration of exhaust gas due to incomplete combustion of part of the fuel. 
     According to the embodiment, the drive device feeds the secondary current to the secondary winding by changing the first switch from the on-state to the off-state, and supplies the output from the booster to the third winding by changing the second switch from the off-state to the on-state. Thus, it is possible to extend the ignition time of the plug, and thus to improve the combustion efficiency of the fuel. 
     As described above, the embodiment can provide the ignition device, which is capable of improving the combustion efficiency of the fuel by extending the ignition time of the plug. 
     The invention includes other embodiments in addition to the above-described embodiments without departing from the spirit of the invention. The embodiments are to be considered in all respects as illustrative, and not restrictive. The scope of the invention is indicated by the appended claims rather than by the foregoing description. Hence, all configurations including the meaning and range within equivalent arrangements of the claims are intended to be embraced in the invention.