Patent Publication Number: US-7215528-B2

Title: Turn-on coil driver for eliminating secondary diode in coil-per-plug ignition coils

Description:
BACKGROUND 
     1. Field of the Invention 
     The present invention generally relates to controlling an ignition coil. More specifically, the invention relates to a turn-on circuit for controlling an ignition coil. 
     2. Description of Related Art 
     In the area of ignition coils a high voltage zener diode is used in the standard design of a secondary circuit for a coil-per-plug (CPP) automotive ignition coil. The high voltage zener diode attenuates a voltage created in the secondary coil at the instant the coil is first turned on, also known as turn-on voltage or feed forward voltage. The high voltage zener diode precludes the feed forward voltage from causing early ignition. 
     The high voltage zener diode is a high cost component due to the high voltage value of the diode and its specialized purpose. The cost of the high voltage zener diode is a significant factor in the cost of the coil driver circuit and would represent a significant savings if eliminated. However, the high voltage zener diode in the prior art designs performs an essential function in reducing the feed forward voltage. Reducing the feed forward voltage prevents an over advanced spark which may cause early ignition and minimizes degradation of the spark gap. An over advanced spark could cause engine roughness, higher emissions, and increased fuel consumption. 
     In addition, removal of the high voltage zener diode may become vital for ODBII compliance, which mandates misfire detection. Ionization misfire detection with the ignition system is not possible if the high voltage zener diode is used because high voltage zener diode will block the ionization signal needed for misfire detection. 
     In view of the above, it is apparent that there exists a need for an improved circuit for controlling an ignition coil. 
     SUMMARY 
     In satisfying the above need, as well as overcoming the enumerated drawbacks and other limitations of the related art, an embodiment of the present invention provides a turn-on coil driver circuit that attenuates the feed forward voltage by slowing the initial turn-on of the coil driver. In addition, the diode provides a path for quickly discharging the capacitor. 
     The turn-on circuit includes a control signal input node, a capacitor, a resistor, a diode, and a coil driver. The control signal input node receives a coil control signal from an ignition control system. The capacitor begins charging after the control signal is received by the turn-on circuit. As the capacitor charges it gradually increases the voltage provided to the coil driver. The rate of the increase in voltage is controlled by the selection of the resistor and capacitor. The slowing of the initial turn-on of the coil driver has the effect of attenuating the feed forward voltage. The attenuating of the feed forward voltage minimizes degradation of the spark gap while alleviating the need for the high voltage zener diode. 
     Additionally, the turn-on circuit provides a diode to ensure quick discharge of the capacitor. Quick discharge of the capacitor is necessary so that the field of the coil is collapsed rapidly and the maximum secondary voltage is available to break down the spark plug gap when the coil is next fired. 
     Further, the present invention will permit the use of the smaller spark plug gap. The smaller spark plug gap and elimination of the high voltage zener diode would improve the signal strength and signal-to-noise ratio of an ionization misfire detection system. 
     Further objects, features and advantages of this invention will become readily apparent to persons skilled in the art after a review of the following description, with reference to the drawings and claims that are appended to and form a part of this specification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic view of the turn-on coil driver circuit for controlling an ignition coil according to the present invention. 
         FIG. 2  is a voltage plot of the coil driver output node for the turn-on circuit according to the present invention. 
         FIG. 3  is a diagrammatic view showing another embodiment of a turn-on coil driver circuit for controlling an ignition coil according to the present invention; 
         FIG. 4  is a diagrammatic view showing another embodiment of a turn-on coil driver circuit for controlling an ignition coil according to the present invention; and 
         FIG. 5  a diagrammatic view showing yet another embodiment of a turn-on coil driver circuit for controlling an ignition coil according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to  FIGS. 1 and 2 , a turn-on coil driver circuit embodying the principles of the present invention is illustrated therein and designated at  10 . The turn-on coil driver circuit  10  includes a control signal input node  12  a capacitor  16  a resistor  24 , a zener diode  22 , and a coil driver circuit  18 . Coil driver circuit  10  is configured to energize an ignition coil  30 . 
     Control signal input node  12  receives a control signal from a coil control module (not shown) to initiate activation of coil driver circuit  18  thereby energizing the coil  30 . Zener diode  22  is connected between control signal input node  12  and coil driver output node  14 . Zener diode  22  is oriented such that the cathode of zener diode  22  is connected to the control signal input node  12  and the anode of zener diode  22  is connected to coil driver output node  14 . 
     Capacitor  16  is connected on a first side to the coil driver output node  14  and a second side of capacitor  16  is in communication with an electrical ground  28  through zener diode  26 . Zener diode  26  is oriented such that the cathode of zener diode  26  is connected to capacitor  16  and anode of zener diode  26  is connected to electrical ground  28 . Further, resistor  24  is connected between the cathode of zener diode  26  and coil driver output node  14 . 
     As the control signal is received by control signal input node  12  capacitor  16  the voltage at coil driver output node  14  jumps to a level just below where the coil driver  18  begins to turn on, as shown in  FIG. 2 , during time period  32 . The effective resistance provided by zener diode  22  in cooperation with resistor  24  will allow capacitor  16  to charge gradually over the charging time period  34 . As the voltage increases coil driver  18  begins to fire coil  30  to initiate ignition. 
     Conversely, it is also important that the coil field collapse quickly after coil  30  has been fired. Therefore, capacitor  16  is allowed to discharge quickly via the path to electrical ground  28  created through zener diode  22  and resistor  20 . Resistor  20  is connected between cathode of zener diode  22  and electrical ground  28 . The value of resistor  20  is chosen so the discharge time period  36  of capacitor  16  is small in comparison to the charging time period  34 . Utilizing the capacitor  16  in this manner allows low voltage zener diodes to be used for zener diode  22  and zener diode  26  thereby eliminating the need for a high voltage zener diode. 
     Now referring to  FIG. 3 , another embodiment of a turn-on coil driver circuit according to the present invention is illustrated therein and designated at  40 . The turn-on coil driver circuit  40  includes a control signal input node  42 , a capacitor  46 , a resistor  54 , a diode  52 , and a coil driver  48 . 
     The control signal input node  42  receives a control signal from a coil control module (not shown) to initiate activation of the coil driver circuit  48  thereby firing coil  60 . Resistor  54  is connected between the control signal input node  42  and the coil driver output node  44 . 
     Capacitor  46  is connected on a first side to the coil driver output node  44  and the second side is in communication with an electrical ground  58  through diodes  56  and  57 . Diodes  56  and  57  are oriented such that the anode of diode  56  is connected to the capacitor  46 , the cathode of diode  56  is connected to the anode of diode  57 , and the cathode of diode  57  is connected to electrical ground  58 . Further, resistor  54  is connected between the control signal input node  42  and the coil driver output node  44 . 
     As the control signal is received by the control signal input node  42  the voltage at the coil driver output node  44  jumps to a level just below where the coil driver  48  begins to turn on. The resistance provided by resistor  54  will allow the capacitor  46  to charge gradually over the charging time period. As the voltage increases the coil driver  48  fires coil  60  to initiate ignition. 
     Capacitor  46  is allowed to discharge quickly via the path to electrical ground  58  created through diode  52 , resistor  50 , diode  56 , and diode  57 . Diode  52  is connected between the control signal input node  42  and the coil driver output node  44 . Diode  52  is oriented such that the cathode of diode  52  is connected to the control signal input node  42  and the anode of diode  52  is connected to the coil driver output node  44 . Resistor  50  is connected between the cathode of diode  52  and the anode of diode  56 . The value of resistor  50  is chosen so the discharge time period of capacitor  46  is small in comparison to the charging time period. 
     Now referring to  FIG. 4 , yet another embodiment of a turn-on coil driver circuit according to the present invention is illustrated therein and designated at  70 . As its primary components, the turn-on coil driver circuit  70  includes a control signal input node  72  a capacitor  76  a resistor  84 , a diode  82 , in the coil driver  48 . 
     The control signal input node  72  receives a control signal from a coil control module (not shown) to initiate activation of the coil driver circuit  78  thereby firing the coil  90 . Resistor  84  is connected between the control signal input node  72  and the coil driver output node  74 . 
     Capacitor  76  is connected on a first side to the coil driver output node  74  and the second side is in communication with an electrical ground  88  through diodes  86  and  87 . Diodes  86  and  87  are oriented such that the anode of diode  86  is connected to the capacitor  76 , the cathode of diode  86  is connected to the anode of diode  87 , and the cathode of diode  87  is connected to electrical ground  88 . Further, resistor  83  is connected between the anode of diode  86  and the coil driver output node  74 . 
     As the control signal is received by the control signal input node  74  capacitor  76  the voltage at the coil driver output node  74  jumps to a level just below where the coil driver  78  begins to turn on. The resistance provided by resistor  84  in cooperation with resistor  83  will allow the capacitor  76  to charge gradually over the charging time period. As the voltage increases the coil driver  78  fires coil  90  to initiate ignition. 
     Capacitor  76  is allowed to discharge quickly via the path to electrical ground  88  created through diode  82  and resistor  80 . Resistor  80  is connected between the cathode of diode  82  and electrical ground  88 . Diode  82  is connected between the control signal input node  72  and the coil driver output node  74 . Diode  82  is oriented such that the cathode of diode  82  is connected to the control signal input node  72  and the anode of diode  82  is connected to the coil driver output node  74 . The value of resistor  80  is chosen so the discharge time period of capacitor  76  is small in comparison to the charging time period. 
     Now referring to  FIG. 5 , another embodiment of a turn-on coil driver circuit according to the present invention is illustrated therein and designated at  100 . As its primary components, the turn-on coil driver circuit  100  includes a control signal input node  102  a capacitor  106  a resistor  114 , a diode  112 , in the coil driver  108 . 
     The control signal input node  102  receives a control signal from a coil control module (not shown) to initiate activation of the coil driver circuit  108  thereby firing the coil  120 . Resistor  114  is connected between the control signal input node  102  and the coil driver output node  104 . Diode  112  is connected between the control signal input node  102  and the coil driver output node  104 . Diode  112  is oriented such that the cathode of diode  112  is connected to the control signal input node  102  and the anode of diode  112  is connected to the coil driver output node  104 . 
     Capacitor  106  is connected on a first side to the coil driver output node  104  and the second side is in communication with an electrical ground  118 . As the control signal is received by the control signal input node  102  the resistance provided by resistor  112  will allow the capacitor  106  to charge gradually over the charging time period. As the voltage increases the coil driver  108  fires coil  120  to initiate ignition. 
     Capacitor  106  is allowed to discharge quickly via the path to electrical ground  118  created through diode  112  and resistor  110 . Diode  112  is connected between the control signal input node  102  and the coil driver output node  104 . Diode  112  is oriented such that the cathode of diode  112  is connected to the control signal input node  102  and the anode of diode  112  is connected to the coil driver output node  104 . Resistor  110  is connected between the cathode of diode  112  and electrical ground  118 . The value of resistor  110  is chosen so the discharge time period of capacitor  106  is small in comparison to the charging time period. 
     As a person skilled in the art will readily appreciate, the above description is meant as an illustration of implementation of the principles this invention. This description is not intended to limit the scope or application of this invention in that the invention is susceptible to modification, variation and change, without departing from spirit of this invention, as defined in the following claims.