Abstract:
An ignition apparatus for an internal combustion engine has an arrangement comprising a power part and a control part which are accumulated in a one-chip in an IGBT monolithic silicon substrate. The control circuit part has current limiting function of prevent the flowing of any current which is above a predetermined value as well as function of detecting malfunction heat generation by which a primary electric current is blocked compulsorily. The secondary voltage of an ignition coil is generated repeatedly below a plug discharge voltage so as not to generate spark discharge in the sparking plug when the electric current compulsory blocking is carried out, and energy charged in the ignition coil is emitted or discharged. With this arrangement, the one-chip ignition apparatus with high reliability can be achieved.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to an ignition apparatus for an internal combustion engine and a one-chip semiconductor for this.  
           [0002]    There is an ignition apparatus for an internal combustion engine described in Japanese Patent Application Laid-Open No. Hei 8-335522 as one prior art, in which a power switching part, a current limiting circuit acting as a protection circuit and a thermal shut-off circuit which compulsorily intercepts or blocks current flowing at the time of abnormal heat generation are integrated all together on an IGBT monolithic silicon substrate. Moreover, a suppression method is devised by setting up a collector clamping voltage to be tens of voltages, as a method of not generating high voltage at the secondary side of an ignition coil, at the time when compulsion turn the current off by the voltage generation of as many as the turn ratio times. There is an ignition apparatus for an internal combustion engine described in Japanese Patent Application Laid-Open No. Sho 53-118781 as another prior art. In this ignition apparatus, a hybrid IC equipped with electronic parts on a ceramic substrate etc. is used. This ignition apparatus has its function for dully intercepting the primary electric current due to the Miller integration effect using a capacitor by detecting the malfunction of the ignition signal.  
           [0003]    The prior art as shown in Japanese Patent Application Laid-Open No. Hei 8-335522 has installed a current limit circuit and a thermal shut-off circuit in the igniter apparatus as security or protection function. However, when an element temperature becomes more than a set temperature, such a simple thermal shut-off circuit compulsorily makes the gate signal of the power transistor LOW, is generated high voltage by this operation at the ignition coil secondary side because it is the function to intercept the primary current which flows in the ignition coil quickly, and generates electrical discharge in the sparking plug. Therefore, there is a possibility to cause deleterious combustion like backfire, etc. according to the process of the engine. It is necessary not to generate a high voltage at the secondary side of the ignition coil to prevent this deleterious combustion at the compulsion turn the current off. A suppression method is devised by dropping the collector clamping voltage to tens of V as a simplest prevention method by the voltage generation of as many as the turn ratio times. However, it is usually undesirable to be necessary to operate by 24V+α of the battery series connection, and to adjust the collector clamping voltage to 30V or less as the ignition apparatus for cars. In case where the coil turn ratio of the ignition coil is 100 and the collector clamp voltage is 30V, for example, if the Vce voltage during the current limit is thought to be 7V, because the voltage of which value is turn ratio times of the collector voltage is generated at the secondary side of the ignition coil, the high voltage of 2.3 kV which is 100 times of 30V−7V=23V is generated. Spark discharge voltage generated at a spark plug differs depending upon the operating condition of the engine, and in case where pressure is high and air density thick, the spark discharge voltage is high, and conversely, in case where pressure is low and air density is thin, the discharge voltage is low. That is, because pressure goes up in the state to take a lot of air in the compression process of the engine, a high secondary voltage is demanded, and because negative pressure occurs in the state that air flow rate is small during the engine air suction process, spark discharge is generated at a low secondary voltage. High negative pressure is generated in case where the engine is operated at high speed and a throttle valve is closed rapidly when piston speed is high. This general value is Absolute Pressure 13-14 kPa (atmospheric pressure: 106.7 kPa). In case where the primary current is compulsorily blocked, since it is necessary for spark discharge not to be generated in any condition of the engine, so it is needed to suppress the secondary voltage to above such a value that spark discharge does not occur, even though the spark discharge can be easily generated by negative pressure. Especially, since when the engine shows negative pressure is in its suction process, igniting under such a condition causes the deleterious combustion of the engine such as backfire, etc. The one that the relation between negative pressure and spark discharge was found by the experiment is shown in FIG. 1. In this experiment, Sparking Plug F7LTCR made by BOSCH (GAP width: 1.2 mm) mounted in an aluminum chamber of which internal pressure is decreased by a outside negative pressure pump was used, and its pressure and the secondary voltage at which spark discharge generates at at that time were measured.  1   a,    1   b,    1   c  and  1   d  show discharge voltage waveforms at the time of the atmospheric pressure (106.7 kPa), 40 kPa, 20 kPa and 13 kPa, respectively. As is clear from the results of this experiment, the plug discharge voltage at the time of the absolute pressure of 13 kPa is 1.5 kV, so in order not to generate the spark discharge at the sparking plug it is needed to suppress the secondary voltage to under about 1 kV. Waveform  1   e  shows the fact that discharge does not occur at 1 kV even at the time of the absolute pressure 1.3 kV. This means that with the system in which said collector clump voltage is made to 330V, the plug discharge cannot be avoided.  
           [0004]    Moreover, with the technology which prevents electrical discharge at the sparking plug by dully intercepting the primary electric current using the Miller integration effect with the capacitor and controlling a high voltage generated at the secondary side of the ignition coil, as shown in the above-mentioned Japanese Patent Application Laid-Open No. Sho 53-118781, to intercept the primary electric current dully to prevent the electrical discharge at the sparking plug, a capacitor with large capacity is needed. Therefore, making it on a silicon substrate is extremely disadvantageous in the size.  
         SUMMARY OF THE INVENTION  
         [0005]    In order to settle the problems of the above-mentioned prior techniques, in accordance with this invention, when the collector current of a power transistor is blocked compulsorily at the time of abnormal heat generation, the collector current is changed so that the secondary voltage becomes under the plug discharge voltage in order not to generate spark discharge due to the secondary voltage generated at the secondary side of the ignition coil, said secondary voltage is generated repeatedly by repeating this control, and energy is emitted which has been charged in the ignition coil. Experiment waveforms on the desk of the circuit which achieves the present invention is shown in FIG. 2. It is understood from the waveforms to be able to obstruct deleterious ignition by no generating the plug electrical discharge because the generated secondary voltage is discharged repeatedly by 800V peak. Through the control of the gate voltage like this and the control of the amount of change of the primary electric current, it is possible to intercept compulsorily the primary electric current while controlling the voltage generated at the secondary side of the ignition coil to become 1 kV or less.  
           [0006]    As means for generating repeating the secondary voltage below this plug discharge voltage, a digital control circuit which changes the collector electric current in a step way by using a pulse waveform is used. As a result, it is possible to form the control circuit easily on a silicon substrate without needing a capacitor with large capacity. Moreover, after compulsory interception is performed once, a latch circuit which does not carry out current flowing until the ignition control signal becomes LOW again is installed. As a result, abnormal current flowing operation is prevented by the control which does not provide the current flowing again, even if chip temperature becomes below a set value while generating the malfunction current flow. These control circuit components are integrated in the monolithic substrate of the power transistor.  
           [0007]    As mentioned above, flying sparks to the sparking plug can be obstructed by controlling the gate voltage of the power transistor to intercept the electric current in a step way so that the secondary voltage generated at the secondary side of the ignition coil is suppressed below the plug discharge voltage when the ignition apparatus generates abnormal heat and intercepts the primary current compulsorily. By integrating these control circuits and power part on the monolithic silicon substrate of the power transistor, it is possible to provide a one-chip ignition apparatus of multi-function with high stability and reliability of operation. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is waveforms by which the relation between negative pressure and spark discharge voltage is shown:  
         [0009]    [0009]FIG. 2 is experiment waveforms prepared on the desk of the present invention:  
         [0010]    [0010]FIG. 3 is an arrangement of a usual ignition apparatus:  
         [0011]    [0011]FIG. 4 is an example of a typical driving circuit:  
         [0012]    [0012]FIG. 5 is a block diagram which shows an embodiment of the present invention:  
         [0013]    [0013]FIG. 6 is one example of a current limiting circuit:  
         [0014]    [0014]FIG. 7 is an arrangement of an input stage &amp; protection network:  
         [0015]    [0015]FIG. 8 is one example of an over-heat detecting circuit and latch circuit:  
         [0016]    [0016]FIG. 9 is one example of a pulse generating circuit:  
         [0017]    [0017]FIG. 10 is one example of a counter circuit:  
         [0018]    [0018]FIG. 11 is one example of a step waveform generating circuit:  
         [0019]    [0019]FIG. 12 is a pulse waveform, a counter waveform and a step waveform: and  
         [0020]    [0020]FIG. 13 is operative sequence by which an embodiment of the present invention is shown.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    The example of composing a usual ignition system is shown in FIG. 1. Reference numeral  1  shows an ECU,  2  shows an ignition apparatus,  3  shows an ignition coil, and  4  shows a sparking plug. The output stage of the ECU  1  is composed of a resistor  11 , a PNP transistor  9  and an NPN transistor  10 . An transistors  9  and  10  are turned on or off according to proper ignition timing calculated by CPU  8 , and the pulse of HIGH and LOW is output to the ignition apparatus  2 . The ignition apparatus  2  comprises a power transistor  5 , and a current detecting resistor  6 , a current controlling circuit  7  and an input resistor  12  mounted on a hybrid IC  13 . High voltage which corresponds to the coil winding number ratio between the primary and secondary windings of the ignition coil is generated at the secondary side of the ignition coil by generating a voltage on the collector of the power transistor  5  by beginning the conduction of the transistor with LOW→HIGH of the output signal of ECU  1  and intercepting or blocking its current flowing with HIGH→LOW, and it generates spark discharge between the electrodes of the sparking plug and burns the mixture. Additionally, a typical driving circuit is shown in FIG. 4. Reference numeral  4   a  shows PMOS and NMOS transistors tied to make up a complementary combination, and  4   b  is the one having composed of a pull-up resistor and an NPN transistor. Moreover,  4   c  is a method to flow an electric current with a PNP transistor Although, they are different from each other in their circuit systems, each circuit outputs an electric current and voltage necessary to drive the igniter to charge energy in the ignition coil at timing to generate spark discharge in the sparking plug at the optimum ignition time obtained by ECU.  
         [0022]    The block diagram of an ignition apparatus which is one embodiment of the present invention is shown in FIG. 5. Reference numeral  14  is an ignition coil,  15  is an ignition apparatus according to this inventions  16  is a main IGBT making up the main circuit for flowing and blocking the primary current through the primary coil of the ignition coil, and  17  is a sense IGBT making up a shunt circuit for detecting the current through the IGBT  16 . A resistor  18  is connected to the emitter  17  of the IGBT  17 , which acts as a current detecting element. It is also connected to a current limiting circuit  19 . The input stage of the ignition apparatus connected to an ECU  35  has a protection circuit  22 . A control circuit comprises a pulse generating circuit  23 , a counter circuit  24 , an over-heat sensing circuit  25 , a latch circuit  26 , an AND logic gate  27 , a step waveform generating circuit  28 , a buffer  29 , a MOS transistor  30  and a resistor  31 . The level of the ignition controlling signal from the circuit  22  is applied as an operative voltage to the circuits  23 ,  24 ,  25 ,  26  and  28 .  
         [0023]    One example of the current limiting circuit  19  is shown in FIG. 6. This circuit compares the voltage generated on the current detecting resistor  18  by a differential amplifier circuit  36  with Vref1 voltage  37  When the voltage of the current detecting resistor  18  becomes the Vref1 voltage  37  or more, the diffferential amplification circuit  36  outputs Hi output which turns on the transistor  38  and makes the voltage of the gate of the IGBT  16  descend, and thereby limits the current by making the IGBT no-saturation state. In this circuit, by decreasing the Vref1 voltage in a step way, the secondary voltage generated at the secondary side of the ignition coil is repeatedly blocked with the plug discharge voltage and whereby energy which has been charged in the ignition coil is emitted.  
         [0024]    An arrangement of the input stage &amp; protection circuit is shown in FIG. 7. A resistor  40  is a pull-down resistor which acts to secure the contact electric current of the input terminal is secured by pouring a certain electric current with a constant value into the circuit. In addition, by composing a network which consists of breakdown or Zener diodes  41  and  42 , and a resistor  43  and  44 , an amount that various surges assumed for the car are endured is secured.  
         [0025]    One example of the over-heat detecting circuit is shown in FIG. 8. This circuit uses the temperature coefficient of the forward voltage of a diode. The diode  48  receives a constant current from a constant current circuit  49  and generates a forward voltage, which is compared in a differential amplification circuit  45  with the Vref2 voltage. The forward voltage of the diode has the negative temperature coefficient of about 2 mV/° C. Therefore, malfunction or abnormal over-heating can be judged by comparing the forward voltage of the diode with the set voltage Vref2 in the differential amplification circuit. Moreover, a method of providing the same function can be devised by using the temperature characteristic of the operating voltage Vth of a MOS transistor. The latch circuit can operate the latch function with a D-type flip-flop  50  as shown in FIG. 8. FIG. 9 shows one example of the pulse generation circuit. This circuit is a free-run pulse generating circuit, in which the output of NAND gate  51  is input to an inverter  54  after it has been integrated by a resistor  52  and a capacitor  53 , and further feed-backed through an inverter  55  into the input of the NAND gate  51 . As a result, self-oscillation is carried out. A capacitor  56  differentiates the output of the inverter  55  and the resulting waveform is applied to the integration circuit comprising the resistor  52  and the capacitor  53 , so that a large amplitude integrated waveform can be provided. A timer circuit is possible with a 2 n  divisional circuit by using flip-flops like FIG. 10. The input of the first stage and the output of the final stage are ANDed, and, as a result, one pulse shape is output at a certain cycle by giving reset to the flip-flops.  
         [0026]    [0026]FIG. 11 is one example of the step waveform generating circuit, and it uses an application form of integration operation using an OP amplifier  57 , and an input resistor  58  and a capacitor  59 . The signal output from the counter circuit is input to the inverting terminal of the OP amplifier  57  through the resistor  58 . The electric current of I=signal Voltage/Resistance flows virtually because non-inverting terminal of the OP amplifier  57  is the GND level, and the voltage change shown by the expression of V=(1×T)/C in proportion to this occurs in the output of the OP amplifier  57 . As a result, it is possible to change the voltage in a step way at each applied pulse. The relation between the pulse generating counter waveform and the step waveform is shown in FIG. 12.  
         [0027]    The operation of each circuit is explained by operation waveforms of FIG. 13. sequence {circle over (1)} in FIG. 14, the gate control voltage  3   b  is impressed to the main IGBT by the ignition control signal  3   a  output from the ECU  35 , and the primary electric current  3   f  flows. The secondary voltage  3   g  is generated at the secondary side of the ignition coil due to a rapid change in magnetic flux at the time when this electric current is intercepted or blocked. When the ignition controlling signal is in Hi, the pulse generating circuit acts as a free-run oscillation circuit which always generates the pulse. This reference pulse is input to the counter circuit  24 , and, then, divided. As a result, one pulse will be output for a predetermined period of time as shown in FIG. 12. in sequence {circle over (2)} in FIG. 13, the ignition controlling signal  3   a  becomes Hi, the gate control voltage  3   b  is turned on, and the primary electric current  3   f  flows. When the primary electric current becomes a set value, the current limiting circuit operates, and the gate controlling voltage is made to descend. As a result, the main IGBT is made in no-saturated condition, and the primary electric current  3   g  is maintained as the value is. In Sequence {circle over (5)} in FIG. 14, when in the case of the ignition controlling signal being in Hi as it is, the primary electric current  3   g  keeps being flowed at the current limiting value of its value, the heat generation of the IGBT element grows. When the operating temperature of the over-heat detecting circuit  25  is exceeded, a signal is output from the over-heat detecting circuit  25 . The latch circuit  26  outputs the Hi output in response to the output of the over-heat detecting circuit  25 . When the signal is output once, this latch circuit  26  keeps outputting Hi as long as the ignition control signal  3   a  does not become LOW even if the output signal of the over-heat detecting circuit  25  becomes OFF. The logical product is taken by the AND logical circuit  27  as for the latch output  3   e  and the counter output  3   c,  and the resultant output is input to the step waveform generating circuit  28 . Said step-like waveform drives the gate of the transistor  30  through the buffer  29  so that the gate voltage of the main IGBT is decreased in a step way. In Sequence {circle over (4)} in FIG. 13, the primary electric current  3   f  decreases in a step way while being kept the main IGBT  16  active by decreasing the gate control voltage  3   b  step-wise. Therefore, the changed portion of the gate control voltage  3   b  is set so that the generated secondary voltage may become 1 kV or less. The secondary voltage V2 generated by the change in this primary electric current becomes the value defined by V2=a×L1×(di/dt), in which L1 is the primary inductance of the ignition coil, a is the turn ratio and di/dt is the change portion of the primary electric current. Such control of the gate voltage for controlling the amount of change of the primary current enables to control the voltage generated at the secondary side of the ignition coil to 1 kV or less. By repeating this control the primary electric current gradually decreases, finally becomes zero and the compulsory blocking is completed. Thereafter, the primary current continues the zero condition until the ignition control signal becomes LOW.  
         [0028]    In accordance with this invention, by compulsorily blocking the primary current in case where abnormal heat generation occurs, it is possible to avoid damage of elements, and by decreasing the current in a step way so as not to generate spark discharge at the ignition plug when the primary current is compulsorily blocked. it is possible to block the current safely, and further by integrating this circuit on a monolithic substrate for the power transistor, it is possible to provide a one-chip igniter with high reliability.