Abstract:
According to the present invention, by providing control whereby a rising slope or a descending slope of step-up current flowing to a step-up coil is detected, and corrections are made to step-up switching control, the step-up upper and lower limit current values of the step-up circuit can be controlled within intended current threshold values regardless of constant modifications or change in characteristics due to fluctuations of the battery power supply voltage or degradation of step-up circuit elements over time; heat emission by step-up circuit elements can be kept to a minimum; and the step-up recovery time can be adjusted to a constant value regardless of the slope of the step-up current.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an internal combustion engine controller. 
       BACKGROUND ART 
       [0002]    The present invention relates to an internal combustion engine controller that drives a load by using a high voltage, which is an increased battery power supply voltage, in an automobile, a motorcycle, a farm machine, a working machine, a vessel machine or the like using, for example, gasoline or light oil as fuel, and particularly relates to an internal combustion engine controller suitable for driving an in-cylinder direct-injection-type injector. The background techniques of the present technical field include, for example, Patent Literature listed below. 
       CITATION LIST 
     Patent Literature 
       [0003]    PTL 1: JP 2001-55948 A 
         [0004]    PTL 2: JP 09-285108 A 
         [0005]    PTL 3: JP 2009-22139 A 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0006]    The present invention provides an internal combustion engine controller that carries out corrections with respect to a step-up switching stop operation and a step-up switching start operation of a step-up controller in consideration of the overshoot and undershoot due to delays of a step-up control circuit when a battery voltage and the characteristics of electronic parts mounted on a step-up circuit are changed, thereby carrying out accurate control to obtain step-up upper/lower-limit current threshold values set in advance. 
       Solution to Problem 
       [0007]    In order to achieve the above-described object, an internal combustion engine controller according to the present invention includes: a step-up coil connected to a battery power source and configured to increase a voltage of the battery power source; a switch element connected to the step-up coil and configured to distribute or shut off a current to the step-up coil; a step-up capacitor configured to accumulate current energy of an inductance component from the step-up coil; and a step-up control circuit configured to control the step-up switching element by a value of a step-up current distributed to the step-up coil to charge the step-up capacitor with a high voltage generated at the step-up coil, wherein, the step-up control circuit measures a slope of the step-up current value and corrects on/off control of the switching element. 
       Advantageous Effects of Invention 
       [0008]    According to the present invention, regardless of fluctuations of a battery power supply voltage, changes in characteristics of step-up circuit elements caused by degradation over time, and constant modifications, the step-up current value of the step-up circuit can be controlled within set current threshold values, and heat generation of the step-up circuit elements can be suppressed to a minimum level. Moreover, regardless of the slope of the step-up current value, the step-up recovery time can be constantly adjusted. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0009]      FIG. 1  is a diagram showing step-up operation waveforms of a first embodiment of an internal combustion engine controller of the present invention. 
           [0010]      FIG. 2  is a diagram showing a circuit of the first embodiment of the internal combustion engine controller of the present invention. 
           [0011]      FIG. 3  is a diagram showing entire operation waveforms of the first embodiment of the internal combustion engine controller of the present invention. 
           [0012]      FIG. 4  is a diagram showing a circuit of a second embodiment of the internal combustion engine controller of the present invention. 
           [0013]      FIG. 5  is a diagram showing step-up operation waveforms of a third embodiment of the internal combustion engine controller of the present invention. 
           [0014]      FIGS. 6( a ) and 6( b )  are diagrams showing step-up operation waveforms for specifying new problems. 
           [0015]      FIG. 7  is a diagram showing a circuit for specifying the new problems. 
           [0016]      FIG. 8  is a diagram showing entire operation waveforms for specifying the new problems. 
           [0017]      FIG. 9  is a diagram showing a circuit of the first embodiment of the internal combustion engine controller of the present invention. 
           [0018]      FIG. 10  is a diagram showing step-up operation waveforms of a fourth embodiment of the internal combustion engine controller of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0019]    Hereinafter, preferred embodiments of the present invention will be described based on the accompanying drawings, and new problems will be also described. 
         [0020]    Compared with a method of injecting fuel to a conventional indirect injection-type injector, in other words, to an air-intake passage or an air-intake port and forming a gas mixture of the fuel and air, an engine using an in-cylinder direct-injection-type injector is required to use the fuel pressurized to a high pressure and therefore requires high energy (voltage) in a valve-opening operation of the injector. Moreover, in order to improve the controllability of the injector and support high-speed drive, high energy is required to be supplied to the injector in a short period of time. Many conventional internal combustion engine controllers, which control injectors of internal combustion engines, employ a method in which the distribution current distributed to an injector is increased by using a step-up circuit, which increases the voltage of a battery power source.  FIG. 7  is a circuit diagram showing an internal combustion engine controller used for specifying the new problems. As shown in  FIG. 7 , the internal combustion engine controller is provided with a step-up circuit  100 . The step-up circuit  100  is disposed between a drive circuit ( 2 ), which drives a direct-injection injector ( 3 ), and a battery power source ( 1 ), increases the voltage thereof to a voltage higher than a battery power supply voltage Vbat in a short period of time, and supplies the step-up voltage  100 A to the drive circuit  2 . The step-up circuit  100  has a step-up coil  110 , which increases the voltage of the battery power source; a switch element  120 , which turns on/off the power distribution to the step-up coil  110 ; and a step-up capacitor  130 , which is inserted in parallel to the switch element  120  via a charge diode  140  for backflow prevention and accumulates the energy from the step-up coil  110 . A step-up control circuit  150 , which carries out on/off control of the switch element  120 , is connected to the switch element  120 . The step-up control circuit  150  has a step-up control unit  151 , which control s drive of the switch element  120 ; a voltage detection unit  152 , which detects the charge voltage of the step-up capacitor  130 ; and a current detection unit  153 , which detects a step-up current  110 A flowing through the switch element  120  and the step-up circuit  140  by a current detection resistor  160 . If the switch element  120  is turned on by control of the step-up control unit  151 , a current flows from the battery power source  1  to the step-up coil  110  through the switch element  120 , and energy is accumulated in the step-up coil  110 . If the switch element  120  is turned off, the current flowing to the step-up coil  110  is shut off, and the step-up capacitor  130  is charged with electric energy by an inductance component of the step-up coil  110 . 
         [0021]      FIG. 8( e )  used for specifying the new problems is an example of current waveforms of an injector current  3 A distributed to the direct-injection injector  3 . As shown in  FIG. 8( e ) , at the beginning of power distribution of the injector  3 , the injector current  3 A is increased to an upper-limit peak current  260  determined in advance by the step-up voltage  100 A in a short period of time (peak-current distribution period  263 ). The peak current value thereof is about 5 to 20 times larger than the peak current value of an injector current flowing in an injector of a conventional indirect injection method. 
         [0022]    After the peak-current distribution period  263  is finished, the energy supply source to the injector  3  makes a transition from the step-up voltage  100 A to the battery power source  1 , is controlled to first retention stop currents  261 - 1  to  261 - 2 , which are the currents about ½ to ⅓ of the peak current, and is then controlled to a second retention stop current  262 , which is the current about ⅔ to ½ of the first retention stop currents. In the period in which the peak current  260  and the first retention stop currents are distributed, the injector  3  opens a valve and injects fuel into a cylinder. 
         [0023]    The process of making the transition from the upper-limit peak current  260  to the first retention stop currents is determined by: magnetic-circuit characteristics and fuel-spray characteristics of the injector  3 , the fuel pressure of a common rail which supplies the fuel to the injector  3 , an injector-current distribution period corresponding to a fuel supply amount determined by the motive power required for the internal combustion engine, etc. This process includes, for example, a case in which the current is decayed in a short period of time, a case in which the current is gently decayed, or a case in which, as shown in  FIG. 8( e ) , the current is gently decayed in a peak-current slow-descending period  264 - 1  and the current is decayed in a short period of time in a peak-current rapid-descending period  264 - 2 . 
         [0024]    In the internal combustion engine controller, in order to quickly carry out valve-closing of the injector  3  when fuel injection is finished, a distribution-current descending period  266  (period of decaying from the second retention stop current  262 ) of the injector distribution current  3 A has to be shortened to shut off the injector current  3 A. Furthermore, also in the process  264 - 2  in which the peak current  260  is lowered to the first retention stop current  261 - 1  and in a process  265  in which the first retention stop current  261 - 2  is lowered to the second retention stop current  262 , the injector current  3 A has to be decayed in a short period of time in some cases. 
         [0025]    However, since the injector current  3 A is flowing to a drive coil of the injector  3 , high energy caused by the inductance of the coil is accumulated. In order to lower the injector current  3 A, this accumulated energy has to be eliminated from the injector  3 . Examples of the method of realizing the elimination of the accumulated energy from the injector drive coil in the distribution-current descending period  266 , which is a short period of time, include a method of converting power-distribution energy to thermal energy by utilizing zener diode effects in a drive element of the drive circuit  2  forming the injector current  3 A and a method of carrying out regeneration to the step-up capacitor  130 , which is for drive energy of the injector drive coil, via a current regenerative diode  5  disposed between the drive circuit  2  and the step-up circuit  100 . 
         [0026]    The above-described method of conversion to thermal energy can simplify the drive circuit  2  but is not suitable for a drive circuit which distributes a large current since the power-distribution energy of the injector  3  is converted to thermal energy. 
         [0027]    On the other hand, the above-described method of regeneration to the step-up capacitor  130  is capable of relatively suppressing heat generation of the drive circuit  2  even when a large current flows to the injector  3  and is therefore particularly widely used in engines in which the distribution current to the injector  3  is large such as an engine using a direct-injection injector using light oil (sometimes also referred to as “common-rail engine”) and an engine using a direct-injection injector using gasoline as fuel. 
         [0028]    A controller that uses a step-up circuit that regenerates the accumulated energy of an injector drive coil to a step-up capacitor is shown, for example, in PTL 1. Herein, operation of the step-up circuit will be described by using  FIGS. 7 and 8  again. 
         [0029]    The drive circuit  2  distributes the injector current  3 A to the injector  3  by using the step-up voltage  100 A of the step-up circuit  100 . As a result, as shown in  FIG. 8( a ) , when a fact that the step-up voltage  100 A is reduced to a voltage  201  or lower serving as a sign of a step-up start is detected by the voltage detection unit  152 , the step-up control unit  151  starts a step-up operation (in  FIG. 8( a ) , reference sign  200  represents 0 [V]). The step-up control unit  151  changes a step-up control signal  151 B, which is for distributing power to the switch element  120 , from LOW to HIGH. As a result, the switch element  120  is turned on, a current  160 A flows from the battery power source  1  to a current detection resistor  160 , the current  110 A flows to the step-up coil  110 , and energy is accumulated in the step-up coil  110 . Herein, the current  160 A and the current  110 A have the same current value. The step-up coil current  110 A flowing through the step-up coil  110  is converted to a voltage as the step-up current  160 A by the current detection resistor  160  and is detected by the current detection unit  153 . The waveforms of the step-up switching current  160 A detected by the current detection unit  153  are as shown in  FIG. 8( b ) . As shown in  FIG. 8( b ) , when the step-up switching current  160 A exceeds a switching stop current  210 - 1  set in advance, the step-up control unit  151  changes the step-up control signal  151 B, which controls opening/closing of the switch element  120 , from HIGH to LOW and shuts off the step-up switching current  160 A. As a result of this shut-off, the current flowing to the step-up coil  110  can no longer flow to a ground  4  through the switch element  120 , and the energy accumulated by the inductance component of the step-up coil  110  generates a high voltage. If the voltage of the step-up coil  110  becomes higher than the voltage obtained by adding the step-up voltage  100 A accumulated in the step-up capacitor  130  and a forward voltage of the charge diode  140 , the energy accumulated in the step-up coil  110  makes a transition to the step-up capacitor  130  as a charge current  140 A through the charge diode  140 . The charge current  140 A starts from the level of the current which has been flowing to the step-up coil  110  immediately before the switch element  120  is shut off, in other words, from the level of the switching stop current  210 - 1  and is rapidly reduced. 
         [0030]    If it is detected that the step-up voltage  100 A increased by the above-described operation is less than a voltage  202  of a predetermined step-up stop level, the step-up control unit  151  detects by the current detection unit  153  that the level of the current flowing to the charge diode  140  has become a switching start current  210 - 2  and changes the step-up control signal  151 B from LOW to HIGH in order to cause the switch element  120  to distribute power. This operation is repeated until the step-up voltage becomes the voltage  202  of the predetermined step-up stop level (step-up recovery time  203 ). 
         [0031]    On the other hand, when shut-off or short-time decaying of the injector current  3 A is started by the drive circuit  2 , a regeneration current from the injector  3  flows to the step-up capacitor  130  through the current regenerative diode  5  during the distribution-current descending period  266 , the peak-current rapid-descending period  264 - 2 , and the first retention-stop-current descending period  265 . As a result, as well as the step-up operation by the step-up coil  110 , the energy accumulated by the inductance component of the injector  3  makes a transition to the step-up capacitor  130 , and the step-up voltage  100 A is increased. 
         [0032]    As described above, compared with a step-up circuit that carries out control by the time determined in advance without detecting the step-up switching current  160 A (for example, see PTL 2), the step-up circuit  100  that detects the step-up switching current and the current  160 A flowing to the charge diode and carries cut control so that the current  160 A does not become equal to or higher than the switching stop current  210 - 1  and equal to or lower than the switching start current  210 - 2  is capable of suppressing the step-up switching current  160 A to a low level. Therefore, the step-up circuit  100  is capable of suppressing heat generation of the switch element  120 , the step-up coil  110 , and the charge diode  140  to a minimum level. 
         [0033]    However, in the above description, as shown in  FIGS. 6( a ) and 6( b ) , in the method of detecting the switching stop current  210 - 1  serving as a target and the switching start current  210 - 2  serving as a target and controlling HIGH and LOW of the step-up control signal  151 B, switching-off delay time  213 - 1  and switching-on delay time  213 - 2  are generated from detection of a current threshold value by the current detection unit  153  until on/off control of the switch element  120 . In this process, the actual switching-stop-current control value with respect to the switching stop current  210 - 1  serving as the target generates an overshoot current value  211 - 1 ; and, with respect to the switching start current  210 - 2  serving as the target, the actual switching-start-current control value generates an undershoot current value  211 - 2 . 
         [0034]    With respect to the switching-off delay time  213 - 1  and the switching-on delay time  213 - 2 , a slope  214 - 1  of the current value which charges energy to the step-up coil  110  and a slop  214 - 2  of the current value which charges energy from the step-up diode  140  to the step-up capacitor  130  are changed by the inductance values and resistance values of the battery voltage  1  and the step-up coil  110  shown in  FIG. 7 , the capacitance value of the step-up capacitor  130 , and the resistance value of the step-up diode  140 . 
         [0035]    Therefore, even if the switching-off delay time  213 - 1  and the switching-on delay time  213 - 2  are known, the currents cannot be corrected by the step-up control unit  151  so as to be the switching stop current  210 -i serving as the target and the switching start current  210 - 2  serving as the target. 
         [0036]    Therefore, there are demands for an internal combustion engine controller that carries out corrections with respect to a step-up switching stop operation and a step-up switching start operation of a step-up controller in consideration of the overshoot and undershoot due to delays of a step-up control circuit when a battery voltage and the characteristics of electronic parts mounted on a step-up circuit are changed, thereby carrying out accurate control to obtain step-up upper/lower-limit current threshold values set in advance. 
         [0037]    Hereinafter, the present embodiment will be more specifically described. 
       First Embodiment 
       [0038]      FIG. 1  shows typical operation waveforms of a first embodiment of an internal combustion engine controller of the present invention,  FIG. 2  shows an exemplary configuration thereof, and  FIG. 3  shows waveforms of an entire step-up operation thereof. 
         [0039]    As shown in  FIG. 2 , the internal combustion engine controller of the first embodiment has a step-up circuit ( 100 ), to which power is supplied by a battery power source ( 1 ) and a power-source ground ( 4 ) thereof, and a drive circuit ( 2 ), which drives an injector ( 3 ) by using a step-up voltage ( 100 A) increased to a high voltage by the step-up circuit ( 100 ). The internal combustion engine controller is equipped with a current regenerative diode ( 5 ) for regenerating a regeneration current of the injector ( 3 ) to the step-up circuit ( 100 ). The internal combustion engine controller is also equipped with input circuits of an engine rotation sensor and various sensors including that for the fuel pressure of a common rail, which supplies fuel to the injector. The internal combustion engine controller is further equipped with an arithmetic device which computes the power distribution timing of the injector ( 3 ) in accordance with input signals thereof, an ignition-coil drive circuit, a throttle drive circuit, and other drive circuits. The internal combustion engine controller may also include a circuit for communication with other controllers, a control circuit supporting various diagnoses and fail-safe, a power-source circuit, which supplies power thereto, etc. 
         [0040]    The step-up circuit ( 100 ) has a step-up coil ( 110 ) having an inductance component for increasing the voltage of the battery power source ( 1 ) and includes: a step-up switch element ( 120 - 2 ), which distributes/shuts off the current distributed to the step-up coil; a switching-side diode ( 120 - 1 ), which protects the step-up switch element from minus surges; a step-up-current detection resistor ( 160 ), which converts a step-up current ( 160 A) flowing to the step-up coil to a voltage; a charge diode ( 140 ), which is provided with a path for charging a step-up capacitor ( 130 ) with a high voltage generated by the energy accumulated in the step-up coil when the step-up switch element is shut off and prevents hack-flow from the step-up capacitor ( 130 ) to the battery power source ( 1 ); and a step-up control circuit ( 120 ). The step-up control circuit includes a step-up control unit ( 151 ), a voltage detection unit ( 152 ), a current detection unit ( 153 ), and a step-up-control correction table ( 154 ), which corrects the switching time of the step-up control unit ( 151 ) based on the voltage value of the current detection unit ( 153 ). 
         [0041]    The drive circuit ( 2 ) distributes an injector current ( 3 A) to the injector ( 3 ) by using a step-up voltage ( 100 A). As a result, as shown in  FIG. 3 , when reduction of the step-up voltage ( 100 A) to a step-up start voltage ( 201 ) or lower is detected by the voltage detection unit ( 152 ), the step-up control unit ( 151 ) starts a slope detecting operation of the step-up current ( 160 A). When the slope detecting operation of the step-up current ( 160 A) is started, the step-up control unit ( 151 ) changes a step-up control signal (l 51 B), which is for causing the step-up switch element ( 120 - 2 ) to distribute power, from LOW to HIGH. Herein, at the point of time when HIGH of the step-up control signal ( 151 B) undergoes elapse of a step-up-current rising time ( 310 - 2 ), the current detection unit ( 153 ) measures a step-up rising current value ( 310 - 1 ). Then, in order to shut off the step-up switch element ( 120 - 2 ), the step-up control unit ( 151 ) changes the step-up control signal ( 151 B) from HIGH to LOW. Herein, when LOW of the step-up control signal ( 151 B) undergoes elapse of a step-up-current descending time ( 311 - 2 ), the current detection unit ( 153 ) measures a step-up descending current value ( 311 - 1 ). 
         [0042]    Based on the step-up-current rising time ( 310 - 2 ), the step-up rising current value ( 310 - 1 ), the step-up-current descending time ( 311 - 2 ), and the step-up descending current value ( 311 - 1 ), the step-up-control correction table ( 154 ) determines first switching HIGH time ( 329 ), switching HIGH time ( 330 ), and switching LOW time ( 331 ) of the step-up control unit ( 151 ) in order to carry out control by a switching stop current ( 210 - 1 ) and a switching start current ( 210 - 2 ) satisfying step-up recovery time. 
         [0043]    When the first switching HIGH time ( 330 ), the switching HIGH time ( 330 ), and the switching LOW time ( 331 ) of the step-up control signal ( 151 B) are determined, a step-up operation is started. The step-up control unit ( 151 ) changes the step-up control signal ( 151 B), which is for causing the step-up switch element ( 120 - 2 ) to distribute power, from LOW to HIGH for first switching HIGH time ( 329 ) As a result, a current flows from the battery power source ( 1 ) to the step-up coil ( 110 ), and energy is accumulated in the step-up coil ( 110 ). 
         [0044]    After the first switching HIGH time ( 329 ) elapses, the step-up control signal ( 151 B) changes the step-up control signal ( 151 B) from HIGH to LOW for the switching LOW time ( 331 ) Herein, the current flowing to the step-up coil ( 110 ) can no longer flow to the power-source ground through the step-up switch element ( 120 - 2 ), and the energy accumulated by the inductance component of the step-up coil ( 110 ) generates a high voltage. If the voltage becomes higher than the voltage obtained by adding the step-up voltage ( 100 A) accumulated in the step-up capacitor ( 130 ) and a forward voltage of the charge diode ( 140 ), the energy accumulated in the step-up coil ( 110 ) makes a transition to the step-up capacitor ( 130 ) as a charge current ( 110 A) through the charge diode ( 140 ). In this process, the charge current ( 110 A) starts from the switching stop current ( 210 - 1 ), which has been flowing to the coil immediately before the step-up switch element ( 120 - 2 ) is shut off, and is rapidly reduced along with the energy transition to the step-up capacitor ( 130 ). After the switching LOW time ( 331 ) elapses, the step-up control signal ( 151 B) changes the step-up control signal ( 151 B) from LOW to HIGH for the switching HIGH time ( 330 ). As a result, the current flows from the battery power source ( 1 ) to the step-up coil ( 110 ), and energy is accumulated in the step-up coil ( 110 ). 
         [0045]    When the voltage detection unit  152 , which detects the step-up voltage ( 100 A), detects that the step-up voltage ( 100 A) increased by the above-described operation is less than the step-up stop voltage ( 202 ), the step-up control unit ( 151 ) normally waits for a step-up-coil current charge time ( 302 ) in a step-up switching cycle ( 300 ), which is a charge period determined in advance, and then changes a step-up control signal ( 124 B) from LOW to HIGH in order to distribute power to the step-up switch element ( 120 - 2 ). This operation is repeated until the step-up voltage becomes the predetermined step-up stop voltage ( 202 ). 
         [0046]    When the configuration as described above is employed, based on the slope ( 214 - 1 ) of the current value charging the step-up coil ( 110 ) with energy and the slope ( 214 - 2 ) of the current value charging the step-up capacitor ( 130 ) with energy from the step-up diode ( 140 ), which are changed by the inductance values and resistance values of the battery voltage ( 1 ) and the step-up coil ( 110 ) shown in  FIG. 2 , the capacitance value of the step-up capacitor ( 130 ), and the, resistance value of the step-up diode ( 140 ), the switching-on time ( 330 ) and the switching-off time ( 331 ) are corrected with respect to the switching-off delay time ( 213 - 1 ) and the switching-on delay time ( 213 - 2 ) as shown in  FIGS. 6( a ) and 6( b ) . As a result, step-up control by a target step-up-current upper-limit value and a target step-up-current lower-limit value can be realized. 
         [0047]    The over-time degradation of the entire step-up circuit and overshoot/undershoot cannot be controlled by changes in step-up switching control by the battery power supply voltage ( 1 ) according to PTL 3, which is a conventional example. On the other hand, in the step-up recovery time ( 203 ) according to the first embodiment of the present invention, generation of the large switching delay time ( 213 - 1 ) ( 213 - 2 ) in the step-up control circuit can be prevented. Therefore, without changing a basic circuit configuration, control can be carried out within the current threshold values for which the switching stop current ( 210 - 1 ) and the switching start current ( 210 - 2 ) of the step-up circuit are set. 
       Second Embodiment 
       [0048]      FIG. 4  shows a configuration of a second embodiment of the internal combustion engine controller of the present invention. 
         [0049]    The basic operations and configurations for detecting the slope of the step-up current are the same as those in the first embodiment, and this is an example that is adapted to the target step-up-current upper-limit value and the target step-up-current lower-limit value by using the step-up-control correction table ( 154 ). 
         [0050]    Based on the step-up-current rising time ( 310 - 2 ), the step-up rising current value ( 310 - 1 ), the step-up-current descending time ( 311 - 2 ), and the step-up descending current value ( 311 - 1 ), the step-up-control correction table ( 154 ) determines the switching stop current ( 210 - 1 ) and the switching start current ( 210 - 2 ) satisfying the step-up recovery time. In this process, correction values for which circuit operation delays of the step-up control unit have been taken into consideration according to the step-up current slopes ( 214 - 1 ) ( 214 - 2 ) obtained by slope detection are set for the switching stop current ( 210 - 1 ) and the switching start current ( 210 - 2 ) of the step-up-control correction table ( 154 ). 
         [0051]    When the switching stop current ( 210 - 1 ) and the switching start current ( 210 - 2 ) are determined, a step-up operation is started. The step-up control unit ( 151 ) changes the step-up control signal ( 151 B) which is for causing the step-up switch element ( 120 - 2 ) to distribute power, from LO to HIGH. As a result, a current flows from the battery power source ( 1 ) to the step-up coil ( 110 ), and energy is accumulated in the step-up coil ( 110 ). 
         [0052]    If the step-up current ( 160 A) exceeds the switching stop current ( 210 - 1 ), the step-up control signal ( 151 B) changes the step-up control signal ( 151 B) from HIGH to LOW. Herein, the current flowing to the step-up coil ( 110 ) can no longer flow to the power-source ground through the step-up switch element ( 120 - 2 ), and the energy accumulated by the inductance component of the step-up coil ( 110 ) generates a high voltage. Then, if the voltage becomes higher than the voltage obtained by adding the step-up voltage ( 100 A) accumulated in the step-up capacitor ( 130 ) and a forward voltage of the charge diode ( 140 ), the energy accumulated in the step-up coil ( 110 ) makes a transition to the step-up capacitor ( 130 ) as a charge current ( 110 A) through the charge diode ( 140 ). In this process, the charge current ( 110 A) starts from the switching stop current ( 210 - 1 ), which has been flowing to the coil immediately before the step-up switch element ( 120 - 2 ) is shut off, and is rapidly reduced along with the energy transition to the step-up capacitor ( 130 ). If the step-up current ( 160 A) becomes lower than the switching start current ( 210 - 2 ), the step-up control signal ( 151 B) changes the step-up control signal ( 151 B) from LOW to HIGH. 
         [0053]    When the configuration as described above is employed, based on the slope ( 214 - 1 ) of the current value charging the step-up coil ( 110 ) with energy and the slope ( 214 - 2 ) of the current value charging the step-up capacitor ( 130 ) with energy from the step-up diode ( 140 ), the switching stop current ( 210 - 1 ) serving as the target and the switching start current ( 210 - 2 ) serving as the target are corrected with respect to the switching-off delay time ( 213 - 1 ) and the switching-on delay time ( 213 - 2 ), which are changed by the inductance values and resistance values of the battery voltage ( 1 ) and the step-up coil ( 110 ) shown in  FIG. 5 , the capacitance value of the step-up capacitor ( 130 ), and the resistance value of the step-up diode ( 140 ). As a result, optimum step-up control corresponding to the step-up recovery time ( 203 ) can be realized. 
         [0054]    Note that as other modification examples, it is possible to carry out, by using the step-up-control correction table ( 154 ), step-up control in which the switching stop current ( 210 - 1 ) serving as the target and the switching-off time ( 331 ) are corrected, and step-up control in which the switching-on time ( 330 ) and the switching start current ( 210 - 2 ) serving as the target are corrected. 
       Third Embodiment 
       [0055]      FIG. 5  shows a typical operation example of a third embodiment of the internal combustion engine controller of the present invention. 
         [0056]    The basic operations and configurations are the same as those of the first and second embodiments. However, according to the present embodiment, a current-rising-slope threshold value ( 340 - 1 ) and a current-descending-slope threshold value ( 340 - 2 ) are provided in the step-up slope detection of the first embodiment and, if the current slope is beyond the two slope threshold values, a malfunction of the step-up circuit is diagnosed. 
         [0057]    The malfunctions of the step-up circuit referred to herein indicate the malfunctions that largely affect the current slope of the step-up current ( 110 A), such as variations in the battery voltage ( 1 ) beyond specified values, opening or short-circuit failure of the step-up coil ( 110 ), and failure of the step-up capacitor. When the control as described above is carried out, the malfunctions generated in the battery voltage ( 1 ) and the step-up circuit ( 100 ) can be detected by the step-up control circuit ( 120 ). 
       Fourth Embodiment 
       [0058]      FIG. 9  shows a typical operation example of a fourth embodiment of the internal combustion engine controller of the present invention. 
         [0059]    The basic operations and configurations are the same as those of the first embodiment. However, according to the present embodiment, instead of the step-up-current detection resistor ( 160 ), which is shown in  FIG. 2  of the first embodiment and converts the step-up current ( 160 A) to a voltage, a switching-on-current detection resistor ( 170 ), which converts a switching-on current ( 170 A) to a voltage, is provided in a downstream of the step-up switch element ( 120 - 2 ). 
         [0060]    The step-up control unit ( 151 ) changes the step-up control signal ( 151 B), which is for causing the step-up switch element ( 120 - 2 ) to distribute power, from LOW to HIGH. Herein, at the point of time when HIGH of the step-up control signal ( 151 B) undergoes elapse of switching-on-current rising time ( 410 - 2 ), the current detection unit ( 153 ) measures a switching-on rising current value ( 410 - 1 ). Then, in order to shut off the step-up switch element ( 120 - 2 ), the step-up control unit ( 151 ) changes the step-up control signal ( 151 B) from HIGH to LOW. Based on the current slope obtained by the switching-on-current rising time ( 410 - 2 ) and the switching-on rising current value ( 410 - 1 ), the step-up-control correction table ( 154 ) determines first switching HIGH time ( 429 ) switching HIGH time ( 430 ), and switching LOW time ( 431 ) of the step-up control unit ( 151 ) in order to carry out control by the switching stop current ( 210 - 1 ) serving as the target and the switching start current ( 210 - 2 ) serving as the target satisfying step-up recovery time. 
         [0061]    According to the present embodiment, compared with the first and second embodiments, an ESD protective element of the current detection unit ( 153 ) can be eliminated by using the switching-on-current detection resistor provided in the downstream of the step-up switch element. Moreover, since the switching LOW time ( 431 ) is corrected by the current slope obtained by the switching-on-current rising time ( 410 - 2 ) and the switching-on rising current value ( 410 - 1 ), correction waveforms and correction control can be simplified. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1  battery power source 
           2  injector drive circuit 
           3  injector 
           3 A injector current 
           4  power-source ground 
           5  current regenerative diode 
           100  step-up circuit 
           100 A step-up voltage 
           110  step-up coil 
           110 A step-up coil current 
           120  step-up switching FET 
           120 - 1  switching-side diode 
           120 - 2  step-up switch element 
           140  charge diode 
           140 A charge current 
           130  step-up capacitor 
           150  step-up control circuit 
           151  step-up control unit 
           151 B step-up control signal 
           152  voltage detection unit 
           153  current detection unit 
           154  step-up-control correction table 
           160  step-up-current detection resistor 
           160 A step-up current 
           170  switching-on-current detection resistor 
           170 A switching-on current 
           200  power-source ground voltage 
           201  step-up start voltage 
           202  step-up stop voltage 
           203  step-up return period 
           210 - 1  switching stop current 
           210 - 2  switching start current 
           211 - 1  overshoot current 
           211 - 2  undershoot current 
           213 - 1  switching-off delay time 
           213 - 2  switching-on delay time 
           214 - 1  step-up-current rising slope 
           214 - 2  step-up-current descending slope 
           220  switching ON signal 
           221  switching OFF signal 
           260  peak-current stop current 
           261 - 1  retention  1  rise stop current 
           261 - 2  retention  1  descend stop current 
           262  retention  2  stop current 
           263  peak-current distribution period 
           264 - 1  peak-current slow-descending period 
           264 - 2  peak-current rapid-descending period 
           265  retention  1  current descending period 
           266  distribution-current descending period 
           310 - 1  step-up rising current value 
           310 - 2  step-up-current rising time 
           311 - 1  step-up descending current value 
           311 - 2  step-up-current descending time 
           329  first switching HIGH time 
           330  switching HIGH time 
           331  switching LOW time 
           410 - 1  switching-on rising current value 
           410 - 2  switching-on current rising time 
           429  first switching HIGH time 
           430  switching HIGH time 
           431  switching LOW time