Patent Publication Number: US-6666195-B2

Title: Method for producing a sequence of high-voltage ignition sparks and high-voltage ignition device

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method of generating a sequence of high-voltage ignition pulses and a high-voltage ignition device. 
     BACKGROUND INFORMATION 
     Various high-voltage ignition devices are known in the related art. In addition to inductive ignition, known systems also include capacitive ignition systems and a.c. ignition systems. Furthermore, there are known ignition systems in the related art in which a sequence of high-voltage ignition sparks is generated. This device, which is also known as double ignition, generates multiple ignition sparks during one combustion cycle in a cylinder in order to improve combustion. For this purpose, for example, there are known ignition systems having multiple ignition energy storage devices, e.g., ignition coils. The ignition spark sequence is controlled in time in the related art, this time control being implemented through software and/or hardware using a control unit. One disadvantage of the known multiple-spark systems is that there is a relatively long period of time between a charging and discharging operation of the ignition storage device. In addition, a greater material expenditure is necessary for ignition systems having multiple ignition energy storage devices. 
     SUMMARY OF THE INVENTION 
     Using the method of generating a sequence of high-voltage ignition pulses and using the high-voltage ignition device, it is possible in an advantageous manner to shorten the time between a discharging operation and a charging operation of an ignition energy storage device. This makes it possible to provide multiple high-voltage ignition sparks during one ignition cycle. However, it is also possible to reduce the capacitance of the ignition energy storage device due to the increase in the number of ignition sparks, i.e., for example, it is possible to use a smaller ignition coil in comparison with the related art. Essentially the shortening of the recharging time of the ignition energy storage device is achieved by recharging it before it is completely discharged. Thus, there remains a certain residual ignition energy in the ignition energy storage device, regardless of changes in such parameters as ignition voltage, operating voltage of the ignition spark, rotational speed of the internal combustion engine, ratio of the air-fuel mixture, battery voltage situation or the like, so that the recharging operation is shortened whereupon subsequent sparks may be generated at a much shorter interval after the first spark. 
     To prevent the ignition energy storage device from discharging completely by a simple method, in a refinement of the present invention, the ignition spark current is measured (while the ignition spark is burning) and when the ignition spark current drops below a specifiable value, the recharging operation of the ignition energy storage device is started. To prevent uncontrolled re-ignition on the ignition spark generating device which may be caused by current peaks in the ignition spark current, for example, in an especially preferred embodiment the recharging operation of the ignition energy storage device is started only when the ignition spark current has dropped below the specifiable value for a specified period of time. This also guarantees, however, a minimum spark duration, which will be necessary for ignition of the air-fuel mixture in the combustion chamber. Since restarting takes place only when the ignition spark current drops below the specifiable value, the short recharging time of the ignition spark storage device is also reached because residual ignition energy is available in the storage device. 
     If a measuring lead is provided from the ignition energy storage device to a control unit for an ionic current measurement, this measuring lead may be used to measure the ignition spark current. This also yields an inexpensive and robust implementation of control of the recharging operation by the control unit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a first embodiment of a high-voltage ignition device. 
     FIG. 2 shows the charging current of an ignition energy storage device of the high-voltage ignition device, the ignition spark current, and a control voltage, all plotted over time. 
     FIG. 3 shows a second embodiment of a high-voltage ignition device. 
     FIG. 4 shows the current and voltage curves over time of the high-voltage ignition device according to FIG.  3 . 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a high-voltage ignition device  1  including an ignition energy storage device  2 , a control unit  3  and a switching element  4 . High-voltage ignition device  1  supplies electric power to a spark gap  5  to generate a high-voltage ignition spark. Spark gap  5  is formed on an ignition spark generating device  6 , which may preferably be implemented as a spark plug. 
     In a preferred embodiment, ignition energy storage device  2  is designed as an inductor, i.e., as ignition coil  7  having a primary winding  8  and a secondary winding  9 . Ignition spark generating device  6  is connected to secondary winding  9 , an interference-suppression resistor  10  and a spark suppression diode  11  are also situated in this circuit, the anode being connected to spark gap  5  and the cathode being connected to secondary winding  9 . Furthermore, bum-off resistor  12  of ignition spark generating device  6  and resistor  13  of ignition energy storage device  2  are also shown in this circuit. At one of its ends, secondary winding  9  is connected to spark gap  5 , and at the other end of the winding it is connected to control unit  3 . 
     At one of its ends, primary winding  8  is connected to a power supply voltage U B  which is, for example, the battery voltage of an onboard battery of a motor vehicle. The other end of primary winding  8  may be connected to ground via switching element  4 . The power supply circuit for primary winding  8  is opened or closed, depending on how switching element  4  is triggered by control unit  3  via a control output  4 ′. When switching element  4  is closed, ignition energy storage device  2  is charged. After successful charging of ignition energy storage device  2 , the stored ignition energy is dissipated through spark gap  5  by opening switching element  4 , thereby discharging ignition energy storage device  2 . 
     Control unit  3  has a voltage measuring input  14  which is connected to a voltage tap  15  which is situated between primary coil  8  and switching element  4  in the circuit on the primary side to measure bracket voltage of ignition energy storage device  2 . Furthermore, control unit  3  has a current measurement input  16  which is connected to a current tap  17  of switching element  4 . Primary current I P  is measured via this current measurement input  16 , at least during the charging operation of ignition energy storage device  2 . In addition, control unit  3  includes a determination device  19  which determines the charge state of energy storage device  2  at least during the generation of ignition sparks. To do so, in a preferred embodiment, the determination device has a current measurement input  20  which is connected to one end of secondary winding  9  to enable spark current I F  to be measured during generation of the ignition spark. To allow this to be implemented easily and simply, one terminal of a measuring shunt  21 , also known simply as a shunt, is connected to the connecting line between current measuring input  20  and secondary winding  9 , the other terminal of measuring shunt  21  being connected to ground  18 . Finally, control unit  3  has a control input  22  to which a control voltage U E  may be applied, this voltage being output by a switching device. 
     The functioning of high-voltage ignition device  1  is explained below on the basis of FIGS. 1 and 2 a  through  2   c . When control input  22  is activated, control voltage U E  is applied during a period of time t 0  through t E  (FIG. 2 c ). Then control unit  3  triggers switching element  4  so that the power supply circuit for primary winding  8  is closed and primary current I P  increases after time t 0 . Current I P  changes as a function of the charge state of ignition energy storage device  2 . On reaching a specifiable value I P,ZÜND  at time t 1  switching element  4  is opened again via control unit  3  so that the subsequent discharging operation of ignition energy storage device  2  causes spark current I F  to increase at time t 1  (FIG. 2 b ) whereupon the ignition spark bums at spark gap  5 . Spark current I F  drops due to the progressive discharge of ignition energy storage device  2 . On reaching a specifiable trigger value I TR  of spark current I F  which is detected by determination device  19 , switching element  4  is closed again by control unit  3  and a recharging operation of ignition energy storage device  2  is started at time t 2 . The charging operation is implemented again until reaching value I P,ZÜND  which was determined for the primary current at time t 3 , whereupon switching element  4  is opened again by control unit  3  so that a subsequent ignition spark is ignited by the discharge operation at spark gap  5  at time t 3  and burns until ignition spark current I F  has dropped back to trigger value I TR  at time t 4 , whereupon switching element  4  is closed again and another charging operation of the ignition energy storage device is carried out until the value of primary current I P  has again reached value I P,ZÜND  at time t 5 . By opening switching element  4  again, a discharging operation of ignition storage device  2  takes place again which in turn generates an ignition spark at time t 5  at spark gap  5 . However, triggering voltage U E  at time t E  is no longer applied to control output  22  so that control unit  3  does not close switching element  4  again and the ignition spark burns out completely. It is thus readily apparent that depending on triggering time t 0  through t E  at time t 1  an initial spark may be generated, in period of time t 2  through t 4  at least one or more subsequent sparks may be generated, and at time t 5  a concluding ignition spark, which may burn out, is generated. 
     To prevent uncontrolled charging or discharging of the ignition energy storage device between two ignition sparks, e.g., in period of time t 2  to t 3 , switching element  4  is closed for a charging operation of ignition storage device  2  only when ignition spark current I F  has dropped below trigger value I TR  for a certain period of time, e.g., 20 μs to 80 μs, so that current peaks are more or less filtered out and are not taken into account in triggering switching element  4 . Trigger value I TR  is lower than maximum current I F,max  and may amount to 0.3 to 0.7 times maximum spark current I F,max , for example. This trigger value I TR  is thus variable, preferably as a function of at least one operating parameter of the engine. For example, the rotational speed and/or the engine load may be used for this purpose. In particular, a characteristics map field is available containing several characteristic curves so that trigger value I TR  may be selected as a function of these operating characteristic curves of the engine. By changing trigger value I TR , the duration of a single spark changes, and thus the number of sparks for a spark sequence may be changed. 
     FIG. 1 also shows that both control unit  3  and measuring shunt  21  as well as switching element  4 , which is designed as a power switch in particular, may be manufactured inexpensively as unit  3 ′ on a semiconductor substrate, so that only four terminals  23  through  26  need lead out of a housing accommodating this substrate. Of course control unit  3 , measuring shunt  21  and switching element  4  may also be designed as separate components, which, however, may also be situated in a single housing having terminals  22  through  26 . 
     FIG. 3 illustrates a second embodiment of a high-voltage ignition device  1  in which determination device  19  is implemented in a switch unit  27  upstream from control unit  3 , including a switch device  28  whose output end is connected to control input  22  of control unit  3  and which supplies control voltage U E  for control unit  3 . Control voltage U E  is provided in pulse form according to FIG. 4 a , namely as a function of spark current I F . If this spark current I F  reaches trigger value I TR  (FIG. 4 c ) a control voltage pulse U E  is again applied to control input  22  so that control unit  3  closes switching element  4  until primary current I P  has reached ignition value I P,ZÜ ND (FIG. 4 b ) whereupon switching element  4  is opened again so that by discharging spark energy storage device  2  a spark may again be supplied at spark gap  5 . It is an advantage of this method of supplying control voltage U E  that only three terminals  23 ,  24  and  25  lead out of housing which holds unit  3 ′ having control unit  3  and switching element  4 . 
     In this embodiment of high-voltage ignition device  1  according to FIG. 3, current measuring input  20  is tapped between a Zener diode  29  and measuring shunt  21 , Zener diode  29  being connected in the forward direction for spark current I F . The connecting line between secondary winding  9  and Zener diode  29  is continued up to an ionic current measuring device  30  with which the ionic circuit in the combustion chamber may be measured during ignition spark pauses to permit an evaluation of the knock characteristics of the engine, for example. Otherwise the same parts or those having the same effect as in FIGS. 1 and 2 are provided with the same reference notation in FIGS. 3 and 4. To this extent, reference is made to the description of these figures. 
     High-voltage ignition device  1  thus implements a way of multiple charging and discharging of ignition energy storage device  2 , whereby, in order to reduce the pause times between two ignition sparks, the charging time is greatly shortened with respect to known systems for recharging ignition energy storage device  2  because residual energy always remains in ignition energy storage device  2 . Thus it is possible to use inexpensive ignition energy storage devices, in particular coils having a primary energy of &lt;100 mJ. By changing trigger value I TR  for the spark current and changing shutdown current I P,ZÜND , it is also possible to achieve an adaptation to the respective power supply voltage level in particular the charge state of the onboard battery. Furthermore, the duration of a spark sequence or the number of sparks during a spark sequence, may be varied. 
     The adjustment of the discharge time of the ignition energy storage device may also be adapted to the conditions in the secondary circuit of ignition energy storage device  2  and ignition spark generating device  6  so that tolerances in resistors  12 ,  10  and  13  in the secondary circuit may be compensated.