Patent Publication Number: US-6705302-B2

Title: Ignition device for an internal combustion engine

Description:
FIELD OF THE INVENTION 
     The present invention relates to an ignition device for an internal combustion engine having multiple cylinders and direct gasoline injection, at least one ignition coil being provided for each cylinder, the primary side of the ignition coil being switched by an ignition switch controlled by a microprocessor and a spark plug being connected to the secondary side of the ignition coil. 
     BACKGROUND INFORMATION 
     In direct gasoline injection, gasoline is injected into the combustion chamber of a cylinder, where it is evaporated and ignited by the secondary high voltage of the ignition coil. If the secondary current is cut off too soon, uncombusted or partially combusted gas may escape. To guarantee reliable operation with low exhaust emissions, several ignition sparks, for example, can be produced by double coil ignition or pulse train ignition. In addition, the secondary current can be prolonged. 
     In principle, the duration of the secondary current can be prolonged by increasing the primary current in the ignition coil, because this increases the energy transferred to the secondary side. Such an energy increase, however, is counteracted by the coil saturation that occurs with an increase in the primary current and the increasing power losses in the ignition coil, preventing an effective increase in the secondary current and its duration. In addition, the ignition output stage and the ignition coil may be overloaded thermally by high switching currents. Therefore, this measure for prolonging the duration of the secondary current should be limited only to those operating states in which it is absolutely necessary, such as a cold start, to avoid unnecessary bum-up of the spark plugs. In all other operating states, it should be possible to switch back to the “natural” secondary current conditions. 
     SUMMARY Of THE INVENTION 
     The present invention provides an ignition device for an internal combustion engine with which the secondary current conduction time of the ignition coil can be prolonged controllably without increasing the primary current. 
     This is achieved according to the present invention by applying an external voltage to the ignition coil to prolong the secondary current conduction time. 
     The present invention is based on the recognition of the fact that the secondary current conduction time can be prolonged if an external voltage which supplies the power required for the prolonged secondary current is applied at the primary side or at the secondary side of the ignition coil. 
     Although it is possible in principle to supply an external voltage on the secondary side of the ignition coil, this is difficult because of the high voltage (30 kV) occurring on the secondary side, so that the external voltage can advantageously be applied to the primary side of the ignition coil. 
     There are essentially various options for implementation of the ignition device according to the present invention. 
     In a first advantageous variant of the present invention, the secondary current in the ignition coil is prolonged by controlled switching on and switching off of an auxiliary voltage source on the primary side. In this variant, the starter hardware known from practice can be used without conversion. In the future, a 14-volt voltage source operated via the ignition coil as well as a 42-volt voltage source will be available in motor vehicles, the latter then being available for use as an auxiliary voltage source to advantage. 
     In a second advantageous variant of the present invention, the secondary current in the ignition coil is prolonged with the help of the cut-off voltage of an auxiliary circuit having an auxiliary switch and an external inductor. The auxiliary transistor is switched off shortly before the end of the “natural” secondary current. This variant requires a second inductor and under certain circumstances also requires redesign of the ignition coil. 
     A third variant of the present invention makes use of the fact that prolonging the combustion time in direct gasoline injection is usually the goal in the case of single-spark coils, where an attached or external ignition switch and a rod coil can always be allocated to one cylinder of the engine. In this case, there are several inactive coil-ignition switch combinations for each active coil-ignition switch combination at any given moment, so that in the case of engines having an even number of cylinders, an inactive coil-ignition switch combination can be associated with each disconnecting coil-ignition switch combination. It is also conceivable to have an association such as that in the case of double coil ignition, where a parasitic spark is ignited in the exhaust. In the case of the ignition device according to the present invention, however, no ignition sparks should be produced by the passive coil-ignition switch combination. The passive coil-ignition switch combination should contribute only to prolonging combustion time. It is important that once the association of coil-ignition switch combinations has been made, it is reversible. In other words, when one coil-ignition switch combination generates an ignition spark, the associated coil-ignition switch combination serves only to prolong the combustion time and vice versa. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows the schematic diagram of an ignition device according to the present invention, in which the combustion current is prolonged by connecting a fixed voltage source to the primary side of the ignition coil. 
     FIG. 2 shows a first illustration of the time characteristics of secondary voltage U sek , primary voltage U prim  and secondary current I sek  in comparison with primary current I prim  for the ignition device illustrated in FIG. 1 in the case of various switching on and switching off times for the fixed voltage source. 
     FIG. 3 shows a second illustration of the time characteristics of secondary voltage U sek , primary voltage U prim  and secondary current I sek  in comparison with primary current I prim  for the ignition device illustrated in FIG. 1 in the case of various switching on and switching off times for the fixed voltage source. 
     FIG. 4 shows a third illustration of the time characteristics of secondary voltage U sek , primary voltage U prim  and secondary current I sek  in comparison with primary current I prim  for the ignition device illustrated in FIG. 1 in the case of various switching on and switching off times for the fixed voltage source. 
     FIG. 5 shows the schematic diagram of an ignition device according to the present invention with which the combustion current is prolonged using the cut-off voltage of an auxiliary circuit. 
     FIG. 6 shows a first illustration of the time characteristics of secondary voltage U sek , primary voltage U prim  and secondary current I sek  for the ignition device illustrated in FIG. 5 in the case of different switching on and switching off times of the auxiliary circuit. 
     FIG. 7 shows a second illustration of the time characteristics of secondary voltage U sek , primary voltage U prim  and secondary current I sek  for the ignition device illustrated in FIG. 5 in the case of different switching on and switching off times of the auxiliary circuit. 
     FIG. 8 shows the schematic diagram of an ignition device according to the present invention, in which two ignition trigger systems are connected in series for reciprocal recharging. 
     FIG. 9 shows a schematic diagram of the collector-emitter voltages of the two ignition Darlingtons of the circuitry illustrated in FIG.  8 . 
     FIG. 10 shows the construction of a J-FET-like construction of a resistor with a narrowed cross section such as that used with the ignition device illustrated in FIG.  8 . 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows the principle of an ignition device according to the present invention for a cylinder of a internal combustion engine having direct gasoline injection or for an ignition coil  1 . Primary side  2  of ignition coil  1  is operated at 14 volts and is switched by an ignition switch  4  controlled via  20 . Ignition switch  4  is implemented here in the form of a bipolar ignition Darlington  4 , or as an alternative, an IGBT could also be used as the ignition switch. 
     The connection time and connection duration of ignition switch  4  are set by a microprocessor (not shown here). Secondary side  3  of ignition coil  1  is connected to ground over diode  6 , which suppresses the switch on ignition, and to a spark plug  5  over an interference-suppression resistor  7 . 
     To prolong the combustion current, a fixed voltage source, namely a 42-volt battery in this case, is connected for a defined period of time to primary side  2  of ignition coil  1 . To do so, the fixed voltage source is connected to primary side  2  of ignition coil  1  via a high-side switch in the form of a pnp-Darlington  8 . pnp-Darlington  8  is clamped with a Z50 Zener diode  9  to handle the load-dump voltage of more than 50 V occurring at the 42-volt fixed voltage source. As an alternative to the pnp-Darlington shown here, an n-MOSFET could also be used for connecting the fixed voltage source. 
     Decoupling diode  10  is connected between the high-side switch and primary side  2  of the ignition coil, or more precisely between the collectors of pnp-Darlington  8  and ignition Darlington  4 , so that the clamping of ignition Darlington  4  does not influence the process of activation of the high-side switch taking place independently thereof. Decoupling diode  10  here is a high-blocking Zener diode which exceeds the value of the clamping voltage of ignition Darlington  4 , namely 410 volts in the example shown here. 
     For accurate timing of the connection of the fixed voltage source at the end of the combustion current after charging ignition Darlington  4 , a npn-switching transistor  11  controlled via  21  is connected upstream from the base of pnp-Darlington  8 . For this purpose, the collector of the npn-switching transistor  11  is connected to the base of pnp-Darlington  8  across a 100 Ω resistor  12  and is connected to the fixed voltage source across a 2 kΩ resistor  13 . 
     With regard to the integratability of the circuit illustrated in FIG. 1, it should be pointed out that the decoupling diode  10  can be integrated into the ignition Darlington  4 . The pnp-Darlington  8  can be integrated into the control IC in bipolar CMOS-DMOS (BCD) technology. Since a dielectric strength of 80 V can be achieved in BCD technology, pnp-Darlington  8  is secured with the 50-volt Zener diode against load-dump voltages of 60 V occurring at the 42-volt fixed voltage source. Because of the reduced current requirements, the area of ignition Darlington  4  may be reduced significantly. However, a portion of the emitter area thus saved is used for decoupling diode  10 . 
     FIG. 2 shows the primary current I prim  measured on the supply side of primary coil  2  as illustrated in FIG. 1, and then the inverse current flowing from the 42-volt fixed voltage source over pnp-Darlington  8  through decoupling diode  10  and through primary coil  2  to the 14-volt voltage source. Furthermore, this also shows the three phases of secondary current I sek  (measured as shown in FIG.  1 ), primary voltage U prim  and secondary voltage U sec . The first phase is the natural combustion phase, in which the current drops from 60 mA to 0 after 1.3 ms. The combustion voltage occurring on the secondary side amounts to −548 V. In the second phase, pnp-Darlington  8  is switched on. The primary voltage here is 35 V, while the secondary voltage is −345 V. After switching off pnp-D arlington  8  in the third phase, the power transmitted to secondary side  3  of ignition coil  1  drops because of the inverted direction of current flow as a negative secondary current in spark plug  5 . The secondary voltage here is +550 V. The two following requirements are to be met for these three phases to occur: 
     1. pnp-Darlington  8  is not to be switched on too late because otherwise the secondary current drops to 0 and the ignition spark is extinguished. Then it is no longer possible to restart the ignition spark. 
     2. pnp-Darlington  8  is to be switched off before the secondary current drops to 0 in the second phase. If it is switched off later, as is the case in FIG. 3, the power stored on the primary side can no longer be transferred to secondary side  3  of ignition coil  1  because spark plug  5  is then no longer conducting. The current on the primary side then drops without an inverse spark current. 
     FIG. 3 illustrates the behavior of the circuit shown in FIG. 1 with an even longer on-time of pnp-Darlington  8 . In this case the charging current of pnp-Darlington  8  increases from 7 A originally to more than 12 A after the combustion current drops in the second phase of combustion. Secondary coil  3 , now open, no longer has a current limiting effect on pnp-Darlington  8 . This high power consumption in primary coil  2  is associated with extremely long switch on times of pnp-Darlington  8  and should be prevented. 
     The secondary current and voltage values shown in FIG. 2 permit a rough energy estimate in the three phases, assuming a linear decay of the secondary current and a constant combustion voltage over time. The following table summarizes the corresponding relationships. 
     
       
         
           
               
               
               
               
             
               
                   
                   
               
               
                   
                   
                   
                 Inverse 
               
               
                   
                 1 st  phase of 
                 2 nd  phase of 
                 combustion 
               
               
                   
                 combustion 
                 combustion 
                 phase 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 U prim (V) 
                 30 
                 35 
                 5 
               
               
                 U sec [[U sek]](V)   
                 −550 
                 −350 
                 +550 
               
               
                 I sec[[I   sek ]] max (mA) 
                 60 
                 60 
                 60 
               
               
                 t sec [[t sek ]](ms) 
                 1.25 
                 1.25 
                 1.20 
               
               
                 E sec [[E sek ]](mWs) 
                 20.6 
                 13.1 
                 19.8 
               
               
                 Total 
                 20.6 
                 32.9 
               
               
                   
               
            
           
         
       
     
     Charging of primary coil  2  with ignition Darlington  4  without taking into account the losses in ignition Darlington  4  is associated with an energy consumption of 
     
       
         ½ ×L× 1 2 =0.5×2.4×10 −3 ×10×10=120 mWs. 
       
     
     The estimated losses in switching on ignition Darlington  4  amount to: 
     
       
         8 V×10 A×3×10 −3 /4=60 mWs. Yielding as the total 180 mWs. 
       
     
     Recharging with pnp-Darlington  8  without taking into account the charging effect of the 42-volt fixed voltage source into the 14-volt voltage source is associated with a power consumption of 
     
       
         (42−14)×7×1.25×10 −3 =245 mWs. 
       
     
     On the basis of this rough energy estimate, the ratio E sec /E prim  without recharging can be compared with that for the case of recharging: 
     without recharging: 20.6 mWs÷180 mWs=0.114 
     with recharging: 32.9 mWs÷245 mWs=0.134 
     This comparison illustrates that spark combustion takes place with a comparable energy efficiency in recharging from the 42-volt source as with the standard spark operation without recharging. 
     For the circuit illustrated in FIG. 1, the secondary currents at different charging currents are compared with the natural combustion conditions. 
     
       
         
           
               
               
               
            
               
                   
                   
               
               
                   
                 I(4) 
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 1 st   
                 2 nd   
                 Inverse 
                   
               
               
                   
                 combustion 
                 combustion 
                 combustion 
               
               
                   
                 phase 
                 phase 
                 phase 
               
            
           
           
               
               
               
            
               
                   
                 I(8) 
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Maximum 
                 Maximum 
                 Maximum 
                   
                   
               
               
                   
                 combustion 
                 combustion 
                 combustion 
                   
                 Pro- 
               
               
                   
                 current 
                 current 
                 current 
                 Total 
                 longing 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 3 A 
                 0.8 
                 ms 
                 1.1 
                 ms 
                 0.95 
                 ms 
                 2.85 
                 ms 
                 3.56 
               
               
                 6 A 
                 30 
                 mA 
                 45 
                 mA 
                 −40 
                 mA 
               
               
                 5 A 
                 1.0 
                 ms 
                 1.0 
                 ms 
                 1.0 
                 ms 
                 3.0 
                 ms 
                 3.00 
               
               
                 6 A 
                 45 
                 mA 
                 50 
                 mA 
                 −60 
                 mA 
               
               
                 7.5 A 
                 1.3 
                 ms 
                 1.0 
                 ms 
                 1.0 
                 ms 
                 3.3 
                 ms 
                 2.54 
               
               
                 6 A 
                 75 
                 mA 
                 45 
                 mA 
                 −40 
                 mA 
               
               
                 10 A 
                 1.2 
                 ms 
                 1.0 
                 ms 
                 0.8 
                 ms 
                 3.0 
                 ms 
                 2.50 
               
               
                 (satur- 
               
               
                 ation) 
               
               
                 6 A 
                 60 
                 mA 
                 50 
                 mA 
                 −40 
                 mA 
               
               
                 10 A 
                 1.3 
                 ms 
                 1.0 
                 ms 
                 1.0 
                 ms 
                 3.3 
                 ms 
                 2.54 
               
               
                 (active) 
               
               
                 6 A 
                 60 
                 mA 
                 50 
                 mA 
                 −50 
                 mA 
               
               
                   
               
            
           
         
       
     
     As a result, the following conclusions can be reached: 
     1. Combustion times can be prolonged by a factor of at least 2.5 for all charging currents of ignition Darlington I( 4 ). 
     2. With standard ignition, an increase in charging current I( 4 ) from 3 A to 10 A prolongs combustion time only from 0.8 ms to 1.3 ms. 
     3. The ignition system having ignition coil  1  and ignition Darlington  4  can be operated with so little power that although reliable ignition is guaranteed, the “natural” secondary current lasts only a short time. Following the spark head, the secondary current is supplied from the “left branch,” i.e., the 42 V fixed voltage source. This means a definite reduction in power loss for both ignition coil  1  and ignition Darlington  4 , thus yielding a cost advantage and a gain in terms of reliability. 
     4. Prolonging the combustion current is not associated with an increase in the maximum combustion current, so spark plug burn-up is not increased. 
     5. By choosing a suitable engine characteristics map, combustion time can be set either short or long as needed, e.g., from 1.2 ms to 3.3 ms with all the intermediate stages. These conditions can thus be optimized for the driving situation at any given time. 
     6. The time pnp-Darlington  8  is switched on is to be selected so that switching still takes place at the end of the natural combustion time. If it is switched on too late, the spark current is extinguished and recharging via pnp-Darlington  8  proves to be of no benefit. Thus, reliable overlapping of the switching on time of pnp-Darlington  8  with the natural combustion time must be ensured. The same thing is also valid for the switching off time of the pnp-Darlington  8 . The inverse current can flow only if it is switched off while still in the second combustion phase. 
     In the case of the ignition device according to the present invention as illustrated in FIG. 5, primary side  2  of ignition coil  1  is operated at 14 volts and is switched via an ignition switch  4  controlled via  20 . Here again, ignition switch  4  is implemented in the form of an ignition Darlington  4 . The switching-on time and duration of ignition switch  4  are determined by a microprocessor (not shown here). Secondary side  3  of ignition coil  1  is connected to ground over diode  6  and to a spark plug  5  over an interference-suppression resistor  7 . 
     In the case of the circuit illustrated in FIG. 5, the combustion current is prolonged with the help of the cut-off voltage of an auxiliary Darlington  15  connected on primary side  2  of ignition coil  1 . Auxiliary Darlington  15  is controlled with an external inductor  16  via  23 . The collectors of ignition Darlington  4  and auxiliary Darlington  15  are isolated with a high-blocking Zener diode  10  which exceeds the value of the clamping voltage of ignition Darlington  4 , namely 410 volts in this case, so that the clamping operation of ignition Darlington  4  does not have any effect on the operation of switching on auxiliary Darlington  15  which takes place independently. On the other hand, however, the clamping voltage of auxiliary Darlington  15  can be transferred to the collector of ignition Darlington  4 . When ignition Darlington  4  is switched on, Zener diode  10  functions as a decoupling diode, and the charging current is distributed to the two inductors connected in parallel, namely primary coil  2  and external inductor  16 . 
     The total inductance is 1.5 mH, with 2.4 mH for primary coil  2  and 4 mH for external inductor  16 . The rate of rise of the collector current of ignition Darlington  4  increases with dI/dt˜U/L. Activation of auxiliary Darlington  15  is timed so that its switch off phase occurs in the period of time when the combustion current produced by ignition Darlington  4  is flowing or immediately thereafter. Auxiliary Darlington  15  is then clamped with the transformed combustion voltage which is 30 V in the case of this ignition coil  1 . The secondary current conduction time can thus be prolonged maximally by the clamping time of auxiliary Darlington  15 , which in the case of a 6 A charging current, 4 mH external inductor  16  and a 30 V clamping voltage amounts to 0.8 ms. In the case of a charging current of 10 A but the same conditions otherwise, this yields a clamping time of 1.3 ms, which can be utilized as additional combustion time. 
     Thus an additional inductor  16 , a high-blocking decoupling diode  10  and an auxiliary Darlington  15 , which consumes only a reduced clamping voltage of 50 V, for example are needed for implementation of the circuit illustrated in FIG.  5 . To prevent loss of power charged in external inductor  16  when charging primary coil  2 , it is also advantageous for external inductor  16  to be wound onto the primary side of ignition coil  1 . In this case, ignition coil  1  would have two primary windings connected in parallel with a common positive terminal and two separate terminals for the collectors of ignition Darlington  4  and auxiliary Darlington  15 . Recharging external inductor  16  via auxiliary Darlington  15  in the combustion phase of ignition Darlington  4  would then take place directly from external inductor  16  to secondary side  3  of ignition coil  1 . Decoupling diode  10  between ignition Darlington  4  and auxiliary Darlington  15  could then be optionally omitted because energy would be transferred directly from external inductor  16  to secondary side  3  of the ignition coil. 
     FIG. 6 shows the current and voltage relationships without the second charging circuit with auxiliary Darlington  15  and external inductor  16  and, on secondary side  3 , the spark head with a voltage of 13 kV and then the combustion voltage of −300 V, building up to approximately −1.6 kV toward the end of the combustion process. After ignition, the ionic current drops after 1.2 ms from 100 mA to zero. During the combustion phase, transformed combustion voltage having values between 30 V and 40 V is applied to the collector of ignition Darlington  4 , returning to the battery voltage at the end of the combustion process. 
     FIG. 7 shows the relationships for the same process with auxiliary Darlington  15  switched on. The secondary current phase is prolonged from 1.2 ms (FIG. 6) to 1.8 ms. The on-time of auxiliary Darlington  15  was selected so that its switch-off time approximately coincides with the end of the “natural” combustion time. The combustion process is thus prolonged by 0.6 ms, which corresponds to the clamping phase of auxiliary Darlington  15 . The combustion voltage transformed on the primary side acts as the voltage limit for auxiliary Darlington  15 . In addition, the charging current of auxiliary Darlington  15  on the primary side has also been plotted. It begins suddenly at approximately 4 A because external inductor  16  was also charged in charging ignition Darlington  4  due to its being connected in parallel to primary coil  2 . External inductor  16  thus still contains residual energy which is further charged to 6 A, depending on the on-time of auxiliary Darlington  15 . 
     In the variant of an ignition device according to the present invention as explained in conjunction with FIGS. 5 through 7, decoupling diode  10  can be integrated into the ignition Darlington circuit, but auxiliary Darlington  15  is not integratable. 
     FIG. 8 shows one possibility for alternating connection of two coil-ignition Darlington combinations for mutual recharging of power during the combustion phase of the other coil-ignition Darlington combination. All the circuit components of this circuit can be integrated monolithically into the respective Darlington output stages. 
     FIG. 8 shows two ignition switch systems  30  and  50  having ignition coils  31  and  51 , ignition Darlingtons  34  and  54  and spark plugs  35  and  55  connected in a symmetrical arrangement. Drivers  25  and  26  of ignition Darlingtons  34  and  54  are controlled by a computer (not shown here). In addition, a path may be opened between two primary circuits  32  and  52  of ignition coils  31  and  51  by two oppositely switched npn-Darlingtons  36  and  56 , each with its high-blocking collectors being connectable to the collectors (the substrate sides) of ignition Darlingtons  34  and  54 , and thus also being integratable. npn-Darlingtons  36  and  56  are each controlled by a voltage-dependent resistor  37  and  57  in the base-collector segment of driver  38  or  58 . In order for Darlingtons  36  and  56  not to be controlled incorrectly due to interference voltage, they have base-emitter resistors. These resistors have the effect that they can be controlled only above a base current threshold which depends on the base-emitter resistance (biasing current). For the biasing current, npn-Darlingtons  36  and  56  have an emitter-base resistor  39  and  59  only in the output stage. In addition, there is an inverse diode  40  and  60  parallel to the collector-emitter segment. The current for recharging in the combustion phase flows over inverse diode  40  of npn-Darlington  36  and npn-Darlington  56 , which has been switched on, or vice versa. A three-stage npn-Darlington may also be used to increase the base current sensitivity. Again in this case, the driver does not have a base-emitter resistor. 
     Voltage-dependent resistors  37  and  57  are each implemented in a J-FET like construction having a narrowed cross section. Their design is explained in greater detail below in conjunction with FIG. 10 (J-FET). At a low voltage, they have a value of approximately 5 kΩ, which increases with the voltage. At approximately 100 V, resistors  37  and  57  disconnect one another completely. Short-circuit transistors  41  and  61 , connected directly to ground, are provided on the emitter of drivers  38  and  58  of npn-Darlingtons  36  and  56 . The base drivers of short-circuit transistors  41  and  61  are connected across 500 Ω resistors  42  and  62 . The common connection of the two base terminals is connected to drivers  25  and  26  of ignition Darlingtons  34  and  54  over diodes  43  and  63 , so that their base terminals are always high when one (or both) ignition Darlington drivers  25  and  26  is/are at high potential. 
     FIG. 9 shows schematically the collector-emitter voltages of both ignition Darlingtons  34  and  54 . After switching on ignition Darlington  34 , collector-emitter voltage U CEon  increases until it enters the short clamping phase of ignition Darlington  34 . This is followed by the phase of combustion voltage transformed at the primary side, lasting approximately 1 ms. Power supply voltage U Batt  of 14 V is applied during the pause. During the on-time of ignition Darlington  34 , ignition Darlington  54  also receives current with a time offset. Shortly before the end of the “natural” combustion voltage, ignition Darlington  54  clamps with the combustion voltage of ignition coil  31 . 
     The circuit arrangement illustrated in FIG. 8 functions in all switch states. The trigger conditions, offset in time relative to one another, do not lead to malfunctioning or misfiring on the wrong side of the ignition coil. Furthermore, the two sides of the ignition components are interchangeable, i.e., when ignition Darlington  34  generates an ignition spark, ignition Darlington  54 t ensures recharging of the combustion phase and vice versa. Otherwise, the connection of monolithically integrated ignition switch systems  30  and  50  is similar to that of the ignition output stages known in practice. In addition, the emitters of npn-Darlingtons  36  and  56  and control lines  25  and  26 , which are isolated over diodes  43  and  63 , are connected by plug connections. 
     The following states are to be discussed: 
     1. Both ignition Darlingtons  34  and  54  are turned off. 
     2. Only ignition Darlington  34  is turned on, while ignition Darlington  54  is still turned off. 
     3. Both ignition Darlingtons  34  and  54  are turned on at the same time. 
     4. Ignition Darlington  34 , which was turned off first, clamps and generates an ignition spark, while ignition Darlington  54  is still turned on. 
     5. The transformed combustion voltage is applied to the collector of ignition Darlington  34  while ignition Darlington  54  is still turned on. 
     6. Ignition Darlington  54  is turned off and clamps the transformed combustion voltage, while ignition Darlington  34  is currentless. The combustion process is prolonged by the clamping time of ignition Darlington  54 . 
     7. Clamping of ignition Darlington  54  and the combustion process is terminated. 
     Re 1: 
     The collectors of ignition Darlingtons  34  and  54  are at 14 V, and both short-circuit transistors  41  and  61  are deactivated. The path between npn-Darlingtons  36  and  56  is currentless. 
     Re 2: 
     The collector of ignition Darlington  34  is at saturation voltage or becomes active. In any case, there is a voltage gradient between the collector of ignition Darlington  54 , to which 14 V is applied, and the collector of ignition Darlington  34 , to which 2 V to 8 V is applied. However, this voltage gradient does not result in activation of npn-Darlington  56 , because short-circuit transistor  61 , which is turned on, prevents activation of npn-Darlington  56 . Primary side  32  of ignition coil  31  is thus charged, but no cross-current is allowed to flow from primary side  52  of ignition coil  51 . 
     Re 3: 
     Likewise, opening of the path between primary sides  32  and  52  of two ignition coils  31  and  51  is also prevented when ignition Darlingtons  34  and  54  are triggered simultaneously. 
     Re 4: 
     In the clamping phase of ignition Darlington  34 , npn-Darlington  36  is prevented from being switched through base-collector resistor  37  which is not conducting at a high voltage. In addition, in the case of possible leakage of base-collector resistor  37  at high temperatures, rev activated short-circuit transistor  41  prevents npn-Darlington  36  from being turned on. npn-Darlington  36  and ignition Darlington  34  diffuse on the same substrate and have the same blocking properties. Thus, npn-Darlington  36  remains blocked when ignition Darlington  34  is clamped. Destruction of short-circuit transistor  41  is prevented because the clamping voltage of ignition Darlington  34  does not penetrate through to the power base of npn-Darlington  36 . Ignition occurs in the coil branch whose ignition Darlington is the first to be turned off. Thus, the ignition sequence is not defined by the process of switching on of the ignition stages but instead by their switching-off process. 
     Re 5: 
     In the phase when primary side  32  of ignition coil  31  is at the potential of the transformed combustion voltage with ignition Darlington  54  turned on, npn-Darlington  56  remains currentless because short-circuit transistor  61  is activated by the driver of ignition Darlington  54 . 
     Re 6: 
     Both ignition Darlingtons  34  and  54  are turned off, so both short-circuit transistors  41  and  61  are currentless. npn-Darlington  56  is controlled over base-collector resistor  57 , so the current flows from primary side  52  of ignition coil  51  into primary side  32  of ignition coil  31  over npn-Darlington  56 , which has been activated, and inverse diode  40  of npn-Darlington  36 . The clamping voltage of ignition Darlington  54  is elevated in comparison with the transformed combustion voltage of ignition coil  31  until the voltage drop at base-collector resistor  57  is so high that npn-Darlington  56  is switched through. The increase in voltage between two primary sides  32  and  52  of ignition coils  31  and  51  occurs first due to the voltage drop across inverse diode  40 , which is typically 1.5 V at 10 A. Secondly, npn-Darlington  56  is operated actively until it receives enough base current over base-collector resistor  57  to be able to take over the flowing primary current. To reduce this voltage drop, several J-FET resistors may be connected in parallel, but also a sufficient emitter area of npn-Darlington  56  to increase the Darlington gain may be ensured. The clamping voltage of ignition Darlington  54  is at such a low level, preferably below 40 V, that no ignition spark occurs on secondary side  53  of ignition coil  51 . The same conditions are to be met here as in the case of a bias current disconnect. If the same pairing of coil-ignition Darlington combinations is selected here as in the case of double-coil ignition, any spark that may occur will ignite into the exhaust flowing out and will not destroy the engine. 
     Re 7: 
     After the end of the combustion phase, both primary sides  32  and  52  go back to 14 V, and the cross-current path from npn-Darlington  56  to npn-Darlington  36  becomes currentless again. 
     FIG. 10 illustrates the construction of a J-FET resistor  70  having a constricted cross section such as that used as a base-collector resistor  37  or  57  in the circuit arrangement illustrated in FIG.  8 . J-FET resistor  70  is shown here in the form of a hole in a π-diffusion  71  in a high-resistance n 31 -starter substrate  72  of 60 Ωcm, for example. To improve the ohmic terminal resistance, n + -diffusion  73  is applied to the contact hole. An n +  terminal diffusion  74  approximately 160 μm thick is provided on the back of the substrate. The shape of space charge zone  75  is shown with dotted lines. It expands laterally in the hole in π-diffusion  71  with an increase in voltage between p +  terminal  76  of π-diffusion  71  and the back of the substrate until the current channel is interrupted completely. The expansion of space charge zone  75  as a function of the voltage and specific resistance of the substrate material can be described with the following formula: 
     
       
           D (μm)=( p  (Ωcm)× U ( V )×0.27) 1/2   
       
     
     The switch off voltage is reached when the width of the space charge zone corresponds to half the channel diameter. The channel resistance without applied voltage can be estimated by assuming only a vertical current characteristic. In the following table, the channel diameter has been determined from different channel resistances without applied voltage. For a channel length of 60 μm and p=60 Ωcm, this yields: 
     
       
         
           
               
               
               
             
               
                   
               
               
                 Channel diameter 
                 Channel resistance without 
                 Disconnect voltage 
               
               
                 d (μm) 
                 voltage 
                 V off  (V) 
               
               
                   
               
             
            
               
                 50 μm 
                 18.34 kΩ 
                 38.5 V 
               
               
                 60 μm 
                 12.73 kΩ 
                 55.5 V 
               
               
                 70 μm 
                  9.35 kΩ 
                 75.6 V 
               
               
                 80 μm 
                  7.16 kΩ 
                 98.7 V 
               
               
                   
               
            
           
         
       
     
     The true channel resistance is lower because a current propagation effect is expected under π-diffusion  71 . The true channel resistance is therefore approximately 60% to 70% below the value of the calculated vertical channel resistance. 
     The lowest possible J-FET resistance as base-collector resistance  37  or  57  is desirable for activating npn-Darlingtons  36  and  56  in the circuit arrangement illustrated in FIG.  8 . This can be achieved by providing an elongated, strip-shaped hole instead of a round hole in π diffusion  71 . The disconnect voltage is determined by the width of the hole, while the reduction factor of the J-FET resistance with respect to the values given in the preceding table is determined by the ratio of the strip length to the strip width. In this way, it is possible to implement resistance values that are lower than those given in the table by a factor of 10.