Patent Publication Number: US-7908910-B2

Title: Combustion state detecting apparatus for internal combustion engine

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a combustion state detecting apparatus for an internal combustion engine, in particular, to a combustion state detecting apparatus for an internal combustion engine, which detects a change in the amount of ions generated at the time of combustion in the internal combustion engine to detect a combustion state in the internal combustion engine. 
     2. Description of the Related Art 
     Recently, environmental conservation and fuel exhaustion problems have been raised. Even for the automobile industry, a response to the above-mentioned problems is a big issue. 
     Although a large number of technologies for maximizing the efficiency of an internal combustion engine have been developed as countermeasures against the above-mentioned problems, it is necessary to know a combustion state to maximize the efficiency of the internal combustion engine. Therefore, there is a rapidly growing need for an apparatus capable of detecting the combustion state. 
     As a conventional apparatus capable of detecting the combustion state, for example, an apparatus described in JP 3753290 B (hereinafter, referred to as Patent Document 1) has been proposed. The apparatus described in Patent Document 1 detects ions generated according to the combustion in a combustion chamber in the form of current, and uses the detected ion current to determine the combustion state. 
     In order to detect the ion current, a high voltage is required to be applied to a detection probe provided in the combustion chamber. As means of generating the high voltage, a Zener diode and a capacitor are used. 
     As described in Patent Document 1, the Zener diode and the capacitor are connected to the low voltage side of a secondary winding of an ignition coil. However, since correspondingly large withstand voltage and capacity are required, the Zener diode and the capacitor become large in size as components. In addition, correspondingly high cost is required. Therefore, there is a problem in that the Zener diode and the capacitor prevent the size and cost of the apparatus from being reduced. 
     SUMMARY OF THE INVENTION 
     The present invention is devised in view of the above-mentioned problem, and has an object of providing a combustion state detecting apparatus for an internal combustion engine, which detects a combustion state with good accuracy at low cost and in compact size to enable an efficient operation of the internal combustion engine. 
     The present invention provides a combustion state detecting apparatus for an internal combustion engine, including: an ignition plug for generating a spark discharge for igniting an air-fuel mixture in a combustion chamber; an ignition coil for supplying a high voltage to cause the ignition plug to generate the spark discharge; ignition control means for feeding a driving signal for driving the ignition coil; ion current detection means for detecting an ion current generated in the combustion chamber; and combustion state detection means for detecting a combustion state in the ignition plug based on a detected value of the ion current, in which an electromotive force generated in a secondary winding of the ignition coil due to electromagnetic induction when a primary current is caused to flow through a primary winding of the ignition coil in response to the driving signal fed to the ignition coil is applied to the ignition plug to detect the ion current generated in the combustion chamber to detect the combustion state in the ignition plug based on the detected value of the ion current. 
     By providing the combustion state detecting apparatus for an internal combustion engine, including: the ignition plug for generating a spark discharge for igniting the air-fuel mixture in the combustion chamber; the ignition coil for supplying a high voltage to cause the ignition plug to generate the spark discharge; the ignition control means for feeding the driving signal for driving the ignition coil; the ion current detection means for detecting an ion current generated in the combustion chamber; and the combustion state detection means for detecting a combustion state in the ignition plug based on the detected value of the ion current, an electromotive force generated in the secondary winding of the ignition coil due to electromagnetic induction when a primary current is caused to flow through the primary winding of the ignition coil in response to the driving signal fed to the ignition coil being applied to the ignition plug to detect the ion current generated in the combustion chamber to detect the combustion state in the ignition plug based on the detected value of the ion current, the present invention enables the combustion state to be detected with good accuracy at low cost and in compact size and enables an efficient operation of the internal combustion engine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a configuration diagram of a combustion state detecting apparatus for an internal combustion engine according to a first embodiment of the present invention; 
         FIG. 2  is a circuit diagram of the combustion state detecting apparatus for the internal combustion engine according to the first embodiment of the present invention; 
         FIG. 3  is a timing chart of signals in the combustion state detecting apparatus for the internal combustion engine according to the first embodiment of the present invention; and 
         FIG. 4  is a block diagram illustrating an internal configuration of an engine control unit provided in the combustion state detecting apparatus for the internal combustion engine according to the first embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Hereinafter, a preferred embodiment of the present invention is described. 
     Embodiment 1 
       FIG. 1  is a view illustrating an example of an overall configuration of a combustion state detecting apparatus for an internal combustion engine according to Embodiment 1 of the present invention. In  FIG. 1 , the combustion state detecting apparatus includes an ignition coil  1 , an ignition plug  2 , and an engine control unit (hereinafter, abbreviated as an ECU)  3 . The ignition coil  1  supplies a high voltage to the ignition plug  2 . The ignition plug  2  generates a spark discharge for igniting an air-fuel mixture in a combustion chamber with the high voltage supplied from the ignition coil  1 . The ECU  3  feeds a signal for driving the ignition coil  1  to control the internal combustion engine (hereinafter, also referred to as an engine).  FIG. 1  also illustrates a path  4  through which an energization signal is transmitted from the ECU  3  to the ignition coil  1 , and a path  5  through which an ion current flows from the ignition plug  2  to the ECU  3 . 
     In the configuration illustrated in  FIG. 1 , the ignition coil  1  is a device for generating the high voltage for causing the ignition plug  2  to generate the spark discharge for igniting the air-fuel mixture in the combustion chamber. In addition to the function of generating the high voltage, the ignition coil  1  includes a device for generating a voltage for detecting the ion current and a device for amplifying the detected ion current and outputting the amplified ion current (an amplifier circuit  24 ). 
     The ignition plug  2  is a device for generating the spark discharge for igniting the air-fuel mixture in the combustion chamber. In addition to the function of generating the spark discharge, the ignition plug  2  has a role of a detection probe for detecting the ion current (ion current detection means). 
     As illustrated in  FIG. 4 , the ECU  3  includes ignition control unit  40  for feeding the signal for driving the ignition coil  1  to be in charge of the control of the engine. In addition, the ECU  3  also includes combustion state detection unit  43  for processing the ion current signal indicating a change in the amount of ions generated at the time of combustion in the internal combustion engine to determine a combustion state in the ignition plug  2 . The ignition control unit  40  includes first energization unit  41  for feeding a first energization signal for igniting the air-fuel mixture in the combustion chamber and second energization unit  42  for feeding a second energization signal for detecting the ion current in the combustion chamber, as driving signals for the ignition coil  1 . 
       FIG. 2  is a view illustrating an example of an apparatus circuit in the combustion state detecting apparatus for the internal combustion engine according to the Embodiment 1 of the present invention.  FIG. 2  illustrates a primary wiring  21  in the ignition coil  1 , a secondary wiring  22  in the ignition coil  1 , a primary current  23  flowing through the primary wiring  21 , and the amplifier circuit  24 . Since the reference numerals  1  to  5  denote the same components as those of the configuration illustrated in  FIG. 1 , those components are denoted by the same reference numerals, and the description thereof is omitted here. Although a plurality of the ECUs  3  are illustrated in  FIG. 2 , these are illustrated for illustrating a flow of the signal in  FIG. 2  in an easily comprehensive and simple manner. It is apparent that the single ECU  3  is actually provided. 
     An operation of the combustion state detecting apparatus for the internal combustion engine according to the Embodiment 1 of the present invention is described referring to the circuit diagram of  FIG. 2 . 
     When the energization signal is fed from the ECU  3  to the ignition coil  1  through the path  4 , the primary current  23  flows through the primary winding  21  in the ignition coil  1 . In response to the flow of the primary current  23 , a secondary voltage due to electromagnetic induction is generated in the second winding  22  in the ignition coil  1 . 
     Next, the secondary voltage is applied to an electrode of the ignition plug  2 . At this time, if ions are generated by a discharge from the ignition plug  2  and there are the ions in the vicinity of the electrode of the ignition plug  2 , the ion current containing the ions is detected in the ignition plug  2 . The detected ion current signal is input to the amplifier circuit  24  through the secondary winding  22  to be amplified. The amplified ion current signal is transmitted to the ECU  3  through the path  5 . The ECU  3  determines a state of combustion in the combustion chamber based on the transmitted ion current signal. More specifically, the ECU  3  compares a value of the ion current signal and a predetermined threshold value for ion current detection (see a threshold value  301  for ion current detection illustrated in  FIG. 3 ) to detect the state of combustion. 
     A method for detecting the ion current is described referring to a timing chart of  FIG. 3 .  FIG. 3  illustrates a driving signal (ignition signal)  50  fed from the ECU  3  to the ignition coil  1 , a primary current  23  flowing through the primary winding  21 , which is illustrated in  FIG. 2 , a secondary voltage  52  to be applied to the ignition plug  2 , and an ion current  53 . 
     In the example illustrated in  FIG. 3 , for the purpose of igniting the air-fuel mixture in the combustion chamber at timing  31  at a predetermined crank angle (hereinafter, timing at a predetermined crank angle is referred to as crank angle timing), the first energization of the ignition coil  1  is started by the first energization unit  41  of the ECU  3  (the first energization signal). The secondary voltage  52  suddenly increases at the crank angle timing  31  as illustrated in  FIG. 3 . Therefore, the ion current can be detected after the timing  31 . However, the combustion does not generally occur in the combustion chamber yet at the timing  31 , and therefore, the ions are not generated. Specifically, a value of the ion current  53  is zero at this timing  31 , as illustrated in  FIG. 3 . 
     From the crank angle timing  31  to crank angle timing  32 , the secondary voltage gradually drops as illustrated in  FIG. 3 . 
     When the first energization of the ignition coil  1  (the first energization signal) is intercepted by the first energization unit  41  of the ECU  3  at the preset crank angle timing  32 , the large secondary voltage is generated on the negative side to generate the spark discharge at the electrode of the ignition plug  2 . Here, it should be noted that this first spark discharge mainly serves to ignite the fuel in the combustion chamber. During the spark discharge, the voltage on the negative side is applied to the electrode of the ignition plug  2 . Therefore, the ion current cannot be detected. 
     Note that the first energization unit  41  determines this first energization time period (time period for feeding the energization signal)  37 , that is, a time period from the crank angle timing  31  to the crank angle timing  32  for each operating condition. 
     Next, at crank angle timing  33 , the second energization of the ignition coil  1  is started by the second energization unit  42  of the ECU  3  (a second energization signal) for the purpose of detecting the ion current in the combustion chamber for this time. As a result, the secondary voltage due to the electromagnetic induction is applied to the ignition plug  2 . Therefore, the ion current  53  generated in a time period  38  from the crank angle timing  33  to the crank angle timing  34  can be detected. 
     The timing of starting the second energization (specifically, the crank angle timing  33 ) is set for each operating condition to be almost equal to a minimum value of the spark discharge time period, which allows combustibility to be ensured. 
     However, if an interval between the interception of the first energization (specifically, the crank angle timing  32 ) and the start of the second energization (specifically, the crank angle timing  33 ) becomes too short, the secondary voltage due to the electromagnetic induction becomes small in some cases. In such a case, the voltage high enough to detect the ion current cannot be supplied. Therefore, a lower limit threshold value is set for the interval, and the interval is set to a value larger than the lower limit threshold value. As described above, preferably, the second energization unit  42  starts feeding the second energization signal after the predetermined time period set for each operating condition from the end of the feeding of the first energization signal by the first energization unit  41 . 
     Alternatively, under an operating condition in which a required discharge time period is short, the first energization time period is set shorter. As a result, even if the interval between the interception of the first energization (crank angle timing  32 ) and the start of the second energization (crank angle timing  33 ) is short, the secondary voltage due to the electromagnetic induction can be prevented from being reduced. Therefore, the detectability of the ion current can be maintained. 
     In order to improve the detection accuracy of the ion current, it is necessary to apply the sufficiently high secondary voltage to the ignition plug  2 . In Embodiment 1, the secondary voltage of about 100V is supposed to be necessary for ensuring detection accuracy. 
     Since the secondary voltage gradually drops after the crank angle timing  33  as illustrated in  FIG. 3 , the secondary energization unit  42  of the ECU  3  intercepts the second energization (the second energization signal) at crank angle timing  35  before the secondary voltage fully drops. Then, if necessary, the third energization is carried out at crank angle timing  302 . Note that, this third energization in this case is also the energization of the ignition coil  1  (the second energization signal) by the second energization unit  42  of the ECU  3  for the purpose of detecting the ion current in the combustion chamber, similar to the case of the second energization. As described above, the energization of the ignition coil  1  for the purpose of detecting the ion current in the combustion chamber is performed at least once, and the number of times of energization (number of times of feeding the energization signal) is appropriately determined as needed. 
     Here, if the ignition operation with the short spark discharge period is repeated, a value of the primary current  23  gradually increases as illustrated in  FIG. 3 . The ignition coil  1  includes a primary current restricting function for restricting an upper limit of the primary current  23  to protect the ignition coil  1  in some cases. When the primary current restricting function is provided, the value of the primary current  23  ultimately becomes constant at the limit value set for the primary current restricting function. When the value of the primary current  23  becomes constant, the secondary voltage due to the electromagnetic induction is not generated. Therefore, the ion current  53  can no longer be detected. Accordingly, the energization time period and the discharge time period of the ignition coil  1  are appropriately set to prevent the primary current  23  from being increased up to the limit value. Alternatively, the primary current restricting function is removed. Further alternatively, the primary current limit value is set as high as possible within the range where the ignition coil  1  can be protected. In Embodiment 1, about 14V is supposed as the primary current limit value. As described above, it is desired that the ignition coil  1  does not limit the primary current flowing through the primary winding  21 . 
     The secondary voltage generated in the secondary winding  22  of the ignition coil  1  due to the electromagnetic induction when the primary current  23  is caused to flow through the primary winding  21  of the ignition coil  1  in response to the signal fed to the ignition coil  1  from the secondary energization unit  42  of the ECU  3  is applied to the ignition plug  2  in the above-mentioned manner. As a result, the amount of change in the ion current  53  is detected in the ignition plug  2 . The detected ion current  53  is amplified by the amplifier circuit  24 , and is then transmitted to the combustion state detection unit  43  of the ECU  3 . The combustion state detection unit  43  of the ECU  3  determines the state of combustion in the combustion chamber based on a value of the ion current  53 . More specifically, the combustion state detection unit  43  compares the value of the ion current  53  and the threshold value  301  for ion current detection with each other to detect the state of combustion. 
     As described above, in Embodiment 1, the combustion state detecting apparatus for the internal combustion engine includes: the ignition plug  2  for generating the spark discharge for igniting the air-fuel mixture in the combustion chamber and for detecting the ion current generated in the combustion chamber; the ignition coil  1  for supplying the high voltage for causing the ignition plug  2  to generate the spark discharge; and the ECU  3  for feeding the driving signal for driving the ignition coil  1  and for detecting the combustion state in the ignition plug  2  based on the detected value of the ion current. In the combustion state detecting apparatus, the electromotive force (secondary voltage) generated in the secondary winding  22  of the ignition coil  1  due to the electromagnetic induction when the primary current is caused to flow through the primary winding  21  of the ignition coil  1  in response to the signal fed to the ignition coil  1  is applied to the ignition plug  2  to detect the ion current generated in the combustion chamber to detect the combustion state in the ignition plug  2  based on the detected value of the ion current. Thus, the number of components in the apparatus for detecting the ion current can be reduced as compared with that in the conventional apparatuses. The apparatus can be configured to have compact size at low cost and detect the combustion state at good accuracy. As a result, the internal combustion engine can be efficiently operated to enable the maximization of efficiency of the internal combustion engine, which in turn provides the effects in that the apparatus can be used to cope with the fuel exhaustion problem and environmental conservation. 
     Moreover, the ignition control unit  40  provided in the ECU  3  includes: the first energization unit  41  for feeding the first energization signal for igniting the air-fuel mixture in the combustion chamber to the ignition coil  1 ; and the second energization unit  42  for feeding the second energization signal for detecting the ion current in the combustion chamber to the ignition coil  1 . Since the second energization unit  42  feeds the second energization signal for detecting the ion current at least once, the ion current can be easily detected for an arbitrary number of times, thereby improving the detection accuracy. 
     The combustion state detecting apparatus according to the present invention is mounted in an automobile, a two-wheel vehicle, an outboard engine, and other special machines, which use the internal combustion engine, to enable the efficient operation of the internal combustion engine, and is used for coping with the fuel exhaustion problem and environmental conservation.