Ignition system with ignition coils connected to each other on the secondary side

Abstract

Ignition system for an internal combustion engine, comprising - a spark plug (7), - an ignition voltage generator for generating an ignition voltage for the spark plug (7), which includes - a first ignition coil (3a) with a primary winding (4a) and a secondary winding (5a) and - at least a second ignition coil (3b) with a primary winding (4b) and a secondary winding (5b), wherein the secondary winding (5a) of the first ignition coil and the secondary winding (5b) of the second coil are connected in parallel and are connected to each other without a diode in between, - a first switching device (9a) for selectively operating the first ignition coil in the charging state and the discharging state and - a second switching device (9a) for selectively operating the second ignition coil in the charging state and the discharging state, wherein the switching devices (9a, 9b) are switching transistors which are controlled by means of a soft-turn-on control and the respective switching transistor is switched on to put an ignition coil into the charging state, and wherein the ignition system is arranged such that - to ignite a spark, the first ignition coil (3a) and the at least second ignition coil (3b) are brought into the discharge state essentially simultaneously and - then the ignition coils (3a, 3b) are put into the discharge state in a time-shifted manner relative to each other.

Description

[0001] The invention relates to an ignition system with several ignition coils which are coupled to each other on the secondary side.

[0002] In a conventional ignition system with at least one ignition coil and typically one spark plug per cylinder of the internal combustion engine, the electrical energy supplied by the battery is stored in the ignition coil during the charged state. To switch to the discharged state, the current flow in the primary circuit of the ignition coil is typically interrupted by a switching device, creating a voltage on the secondary side so high that the air connection between the two electrodes of the spark plug becomes low-resistance, and a hot air spark is created at the spark gap between the two electrodes. The air spark ignites the fuel-air mixture located between the electrodes.

[0003] Current combustion processes primarily utilize ignition systems that generate an ignition spark using a single ignition coil (although multiple ignition coils may be incorporated into the ignition system). The ignition coil can produce a single spark per ignition event or multiple sparks. The generation of multiple sparks per ignition event is also referred to as Multi-Spark Ignition (MSI).

[0004] It is also known to couple two coils together on the secondary side and connect them to the same spark plug. By repeatedly charging and discharging the ignition coils during the ignition process, a long-lasting ignition spark can be generated using both ignition coils. Ignition using a long-lasting ignition spark is also known as continuous spark ignition.

[0005] The ignition coils are decoupled on the secondary side with two high-voltage blocking diodes, so that when one ignition coil discharges, the current flows into the spark plug and not into the other. At high engine pressures, especially with highly charged combustion processes, a sufficiently high ignition voltage (e.g., 35 to 50 kV) must be provided by the ignition coils for ignition. The availability of suitable high-voltage blocking diodes for such a high ignition voltage is problematic, since with increasing ignition voltage, the required diode length increases to ensure sufficient decoupling of the diode terminals during blocking operation.

[0006] Further ignition systems are known from patent documents DE 600 12 073 T2 and DE 100 21 170 A1.

[0007] The object of the invention is to provide an ignition system with at least two ignition coils coupled to one another on the secondary side and a corresponding ignition method, wherein the use of corresponding high-voltage blocking diodes can be dispensed with.

[0008] This object is achieved by the features of the independent patent claims. Advantageous embodiments are described in the dependent claims.

[0009] A first aspect of the invention relates to an ignition system for an internal combustion engine, comprising at least one spark plug and an ignition voltage generator for generating an ignition voltage for the spark plug. The ignition voltage generator comprises a first ignition coil with a primary winding and a secondary winding, and at least one second ignition coil with a primary winding and a secondary winding. The secondary winding of the first ignition coil and the secondary winding of the second coil are connected in parallel and interconnected without the use of a diode; in particular, the secondary windings are short-circuited. Furthermore, a first switching means for selectively operating the first ignition coil in the charged and discharged states, and a second switching means for selectively operating the second ignition coil in the charged and discharged states, are provided.This could, for example, be a switching device connected in series with the respective primary winding, which is closed to charge the coil and opened to discharge it. Alternatively, switching devices connected in parallel with the respective primary winding can also be provided: The control in the ignition system is such that the first ignition coil and the at least second ignition coil are shifted from the charged state to the discharged state essentially simultaneously, so that an ignition spark is ignited. The ignition coils are then shifted in time relative to one another and preferably alternately shifted to the discharged state. This makes it possible to maintain the ignition spark essentially continuously for a long combustion duration (for example, 2 to 12 ms), with the ignition spark essentially not interrupted. For this purpose, for example, after the ignition spark has been ignited, the ignition coils together can be shifted to the discharged state on the order of 4 to 30 times. In principle, any desired combustion duration can be achieved.

[0010] A long burning time typically improves ignition reliability and reduces the likelihood of misfiring.

[0011] By simultaneously completing the initial charging process of both coils and simultaneously discharging the ignition coils, both ignition coils essentially represent two symmetrical voltage sources when the spark is generated, providing the same voltage and summing their energy. This means that the full ignition voltage range (e.g., 40 kV) of an ignition coil is available for generating the spark, without the voltage supplied by one ignition coil being reduced by the load from the other ignition coil. This prevents the ignition coils from placing mutual strain on each other when the first spark is generated. This eliminates the need for high-voltage blocking diodes to decouple the ignition coil on the secondary side.

[0012] After the ignition spark has been generated, the ignition coils are staggered and preferably alternately placed into the discharge state so that the ignition spark can be maintained. When one ignition coil switches to the discharge state, it is loaded by the other coil, and the secondary voltage offered is significantly lower than when the ignition spark is ignited (e.g., 20 kV compared to 40 kV previously). However, this secondary voltage is fully sufficient to provide the necessary operating voltage (e.g., 1 kV - 2 kV) to maintain the ignition spark. Should the ignition spark fail, for example, due to a fuel droplet, the ignition spark will be re-ignited due to a subsequent ignition coil discharge during the staggered discharge of the coils.

[0013] Two or more ignition coils can be used to supply voltage to the spark plug, for example three or four ignition coils, whereby to ignite the ignition spark the three or four ignition coils are simultaneously put into the discharge state and then the three or four ignition coils are shifted in time relative to one another and in particular alternately put into the discharge state.

[0014] It is advantageous if the ignition voltage generator is controlled in such a way that one of the two ignition coils is in the charging state while the other is in the discharging state. Similarly, the other of the two ignition coils is in the charging state while one of the two ignition coils is in the discharging state. Thus, while one coil is charging, the other coil is discharging. When the coil is charging, new energy is supplied to one coil for a subsequent discharging process.

[0015] It is advantageous if the ignition system is configured such that, after the ignition spark is generated, one of the two ignition coils is only switched from the discharged state to the charged state after the other of the two ignition coils has already been switched to the discharged state. The discharged states of both coils thus overlap in time. This overlap prevents the ignition spark from being interrupted. The reason for this is that after one coil has ended its discharged state and switched to the charged state, the other coil is in the discharged state and can supply energy to the ignition spark, so that it generally does not interrupt.

[0016] According to the invention, switching transistors are used for the switching means (for example an IGBT - insulated gate bipolar transistor), wherein the respective switching transistor is switched on when an ignition coil is placed in the charged state. In this case, a soft-turn-on control is preferably provided. With a soft-turn-on control, the control voltage is switched more slowly when an ignition coil is switched to the charged state, so that the mutual induction voltage is reduced when an ignition coil is switched to the charged state. The drop in current across the spark gap caused by the mutual induction voltage is thereby reduced, so that the spark is not interrupted as far as possible. In this way, a drop in current across the spark gap when an ignition coil is switched to the charged state can be reduced even without the use of EFU diodes (EFU - turn-on spark suppression).Such EFU diodes are typically not designed for operation with high voltages (e.g. 20 kV) in reverse direction and could otherwise be destroyed during continuous operation.

[0017] A further aspect of the invention relates to an ignition method for an ignition system of an internal combustion engine. The ignition system comprises a spark plug and an ignition voltage generator as described above with at least two ignition coils. In the ignition method, to ignite an ignition spark, the first ignition coil and the second ignition coil are shifted from the charged state to the discharged state essentially simultaneously. The first ignition coil and the second ignition coil are then shifted in time relative to one another and, in particular, alternately shifted to the discharged state.

[0018] The above statements regarding the ignition system according to the first aspect of the invention also apply correspondingly to the ignition method according to the second aspect of the invention. Advantageous embodiments of the method according to the invention correspond to the described advantageous embodiments of the ignition system according to the invention.

[0019] The invention is described below with reference to an exemplary embodiment with the aid of the accompanying drawings. In these drawings: Fig. 1 a circuit diagram for an embodiment of the ignition system according to the invention; Fig. 2 exemplary time courses for the switching signals 31a, 31b; and Fig. 3 exemplary measured time courses for the switching signals 31a, 31b and the spark current.

[0020] In Fig. Figure 1 shows an exemplary embodiment of an ignition system according to the invention for an internal combustion engine, for example, of a motor vehicle. The ignition system comprises two ignition output stages 9a, 9b in the form of two switching devices 9a, 9b, which operate two ignition coils 3a, 3b, which are coupled on the high-voltage side to a spark plug 7. The ignition system is powered by a battery 1, for example, a 12V battery. The positive pole of the battery 1 is connected via an ignition switch 2 to a first ignition coil 3a and a second ignition coil 3b. The ignition coils 3a, 3b each comprise a primary winding 4a, 4b and a secondary winding 5a, 5b. The ignition coils 3a, 3b serve to generate a high ignition voltage for a spark plug and are connected directly to a spark plug 7 or to several spark plugs via an ignition distributor 6. Each ignition coil 3a, 3b comprises four terminals: Terminal 15, Terminal 1, Terminal 4a, Terminal 4b. The positive terminal of battery 1 can be connected as shown in Fig. 1 - be connected to terminal 15. To control the spark plug with a negative voltage, the positive pole of the battery is connected to terminal 15 of the ignition coils 3a, 3b and the spark plug 7 to terminal 4b of the ignition coils 3a, 3b. To control the spark plug 7 with a positive voltage, for example, the positive pole of the battery can instead be connected to terminal 1 of the ignition coils or the spark plug 7 to terminal 4a of the ignition coils 3a, 3b. In the following, it is assumed that the spark plug 7 is controlled with a negative voltage; however, the concept described below can also be applied in an analogous manner for a positive control of the spark plug.

[0021] Furthermore, a first switching means 9a is provided for selectively operating the ignition coil 3a in the charged or discharged state. A second switching means 9b is provided correspondingly for selectively operating the ignition coil 3a in the charged or discharged state. The switching means 9a, 9b are each connected in series with the respective primary winding 3a, 3b, wherein the corresponding switching means 9a, 9b is closed to charge the respective coil 3a, 3b and opened to discharge the coil. The switching means 9a, 9b typically each comprise an IGBT. The switching means 9a, 9b can be integrated, for example, in a control unit 8 or in the ignition coil 7. To control the switching means 9a, 9b, they are each controlled by a switching signal 31a, 31b. The switching signals 31a, 31b are generated by a driver circuit 30a, 30b, which can be integrated, for example, in the control unit 8.Preferably, a soft-turn-on control is used to generate the switching signals 31a, 31b. An example driver circuit with a soft-turn-on function is the ELMOS E910.89 driver module.

[0022] In Fig. 2 shows an exemplary time profile 32a for the switching signal 31a and an exemplary time profile 32b for the switching signal 31b. Fig. The curves 32a, 32b shown in Figure 2 illustrate the generation of an ignition spark across the spark gap of the spark plug 7. The switching signals 31a, 31b are shown in a simplified manner with infinitely steep switching edges; however, a soft turn-on control is preferably used to switch on a switching device. A high voltage value (high level) corresponds to a closed switching device 9a, 9b, so that the respective ignition coil 3a, 3b is in the charged state. A low voltage value (low level) corresponds to an open switching device 9a, 9b, so that the respective ignition coil 3a, 3b is in the discharged state. Alternatively, an exactly inverse switching logic can also be used.

[0023] To generate the high ignition voltage for the spark plug 7, the control unit 8 switches the switching means 9a, 9b on for a certain closing time starting at time t1 by switching the switching signals 31a, 31b to a high voltage value, so that the switching means 9a, 9b are closed. When the switching means 9a, 9b are closed, the ignition coils 3a, 3b are in a charging state in which the ignition coils are charged with energy. During the closing time, the primary circuit of the primary windings 4a, 4b is closed, and the magnitude of the primary current in the primary winding 4a, 4b increases against the mutual induction voltage to a certain current value, whereby a magnetic field is built up in the ignition coils 3a, 3b. By building up the magnetic field, energy is stored in the magnetic field, the magnitude of which depends on the achieved magnitude of the primary current and the inductance of the primary winding 4a, 4b.

[0024] At time t2, control unit 8 simultaneously opens switching means 9a, 9b by switching switching signals 31a, 31b to a low voltage value, so that switching means 9a, 9b interrupt the two primary circuits of ignition coils 3a, 3b and thus the current flow in the primary circuits. The magnetic field collapses, so that a high voltage is induced in the secondary windings 5a, 5b of each of the ignition coils. At time t2, ignition coils 3a, 3b are thus simultaneously switched from the charged state to the discharged state.

[0025] The maximum possible voltage on the secondary side (i.e., the so-called ignition voltage supply) depends on the transformation ratio of the individual coils and the magnitude of the magnetic field, and thus typically depends on the primary current achieved when the primary circuit opens. For an air spark breakdown between the center electrode and the ground electrode in spark plug 7, the ignition voltage supply must be at least as large as the so-called ignition voltage requirement (i.e., the voltage necessary for breakdown). The ignition voltage requirement depends on the cylinder pressure at the time of ignition. If the ignition voltage supply is sufficient, an ignition spark occurs shortly after time t2.

[0026] By simultaneously completing the first charging process of both coils 3a, 3b, a symmetrical control of the spark plug 7 is enabled, thereby achieving essentially the same ignition voltage as with a single ignition coil. This prevents the two coils 3a, 3b from negatively influencing each other in such a way that the ignition voltage supply drops significantly below the ignition voltage supply with only one ignition coil.

[0027] Depending on the selected duration of the discharge state, the energy stored in the respective ignition coil 3a, 3b can be partially or essentially completely retrieved.

[0028] Thereafter, the ignition coil 3a and the ignition coil 3b are charged and discharged at different times and are alternately put into the discharge state.

[0029] To this end, switching means 9a is first closed at time t3 by switching signal 31a. While coil 3a is now returned to the charging state, coil 3b remains in the discharging state.

[0030] At time t4, the ignition coil 3a is switched back to the discharge state by opening the switching means 9a, so that energy stored during the charge state is fed into the ignition spark, preventing it from breaking off. Should the ignition spark be temporarily lost, the ignition spark is re-ignited.

[0031] Preferably, only after the first ignition coil 9a has already been set to the discharge state, the second ignition coil 9b is set to the charge state at time t5 by closing the switching means 9b. The discharge states of both coils 3a, 3b thus overlap in time. Fig. The temporal overlap Ü shown in Figure 2 can prevent the ignition spark from breaking off.

[0032] At time t6, the ignition coil 3b is switched back to the discharge state by opening the switching means 9b, so that energy stored during the charge state is fed into the ignition spark. Only after the second ignition coil 9b has already been switched to the discharge state is the first ignition coil 9a switched back to the charge state at time t7 by closing the switching means 9a (see overlap Ü).

[0033] Subsequently, the ignition coils 3a, 3b are alternately switched to the discharge state for a specific number of times in a similar manner, with the respective ignition coil 3a, 3b being charged for a certain period of time before switching to the discharge state. By supplying additional energy during the individual discharge states, the ignition spark can be maintained continuously for a long combustion duration BD, for example, for a combustion duration BD of 4 ms or more. During a discharge state, the energy stored in the respective ignition coil can be partially or essentially completely utilized, depending on the duration of the discharge state.

[0034] In Fig. 3 shows an exemplary measured time profile 33a for the switching signal 31a and an exemplary measured time profile 33b for the switching signal 31b. Furthermore, the time profile 34 of the spark current through the spark plug is shown, wherein Fig. 3 the zero value of the current coincides with the low level of the switching signal 31b. Fig. The temporal current drops shown in Figure 3 when closing a switching device 9a, 9b could be reduced by a soft turn-on control (when measuring Fig. 3 no soft-turn-on control was used). As can be seen from Fig. 3, the spark current is essentially greater than zero during the illustrated burning time BD, so that an ignition spark is essentially continuously present during the burning time BD.

[0035] In the example in Fig. 3, a single discharge state and a single charge state after ignition of the spark last approximately 0.5 ms (the first discharge state of the ignition coil 3a after ignition lasts approximately 1 ms). The burning time BD is approximately 4.2 ms.

[0036] The ignition system according to the invention fundamentally enables a virtually unlimited spark duration with a high ignition voltage available at the ignition point, without the need for high-voltage diodes to decouple the ignition coils. This increases ignition reliability, particularly during cold starts. Furthermore, residual gas tolerance is improved across the entire engine map. The coils connected in parallel can provide virtually any desired energy.

Claims

[1] Ignition system for an internal combustion engine, comprising - a spark plug (7), - an ignition voltage generator for generating an ignition voltage for the spark plug (7), which comprises - a first ignition coil (3a) with a primary winding (4a) and a secondary winding (5a) and - at least a second ignition coil (3b) having a primary winding (4b) and a secondary winding (5b), wherein the secondary winding (5a) of the first ignition coil and the secondary winding (5b) of the second coil are connected in parallel and are connected to each other without a diode in between, - a first switching means (9a) for selectively operating the first ignition coil in the charging state and the discharging state and - a second switching means (9a) for selectively operating the second ignition coil in the charging state and the discharging state, wherein the switching means (9a, 9b) are switching transistors which are controlled by means of a soft-turn-on control and the respective switching transistor is switched on to put an ignition coil into the charging state, and wherein the ignition system is designed such that - to ignite an ignition spark, the first ignition coil (3a) and the at least second ignition coil (3b) are set into the discharge state essentially simultaneously, and - the ignition coils (3a, 3b) are then shifted in time relative to one another into the discharge state. [2] Ignition system according to claim 1, wherein the ignition system is arranged such that after the substantially simultaneous setting of both ignition coils (3a, 3b) into the discharge state, the ignition coils (3a, 3b) are alternately set into the discharge state. [3] Ignition system according to one of the preceding claims, wherein the ignition system is arranged in such a way that after the substantially simultaneous setting of both ignition coils (3a, 3b) into the discharge state, one of the two ignition coils (3a, 3b) is only set from the discharge state to the charge state after the other of the two ignition coils has already been set into the discharge state. [4] Ignition system according to one of the preceding claims, wherein the ignition system is arranged in such a way that after the substantially simultaneous setting of both ignition coils (3a, 3b) into the discharge state - one of the two ignition coils is in the charging state while the other ignition coil is in the discharging state, and - the other of the two ignition coils is in the charging state, while one of the two ignition coils is in the discharging state. [5] Ignition system according to one of the preceding claims, wherein the high voltage generator provides an ignition voltage supply of 35 kV or more. [6] Ignition system according to one of the preceding claims, wherein a substantially continuous ignition spark with a combustion duration (BD) of 2 to 12 ms is generated. [7] Ignition method for an ignition system of an internal combustion engine, the ignition system comprising - a spark plug (7), - an ignition voltage generator for generating an ignition voltage for the spark plug (7), which comprises - a first ignition coil (3a) with a primary winding (4a) and a secondary winding (4b) and - a second ignition coil (3b) having a primary winding (4b) and a secondary winding (4b), wherein the secondary winding of the first ignition coil and the secondary winding of the second coil are connected in parallel and are connected to each other without a diode therebetween, - a first switching means (9a) for selectively operating the first ignition coil in the charging state and the discharging state and - a second switching means (9b) for selectively operating the second ignition coil in the charging state and the discharging state, wherein the switching means (9a, 9b) are switching transistors which are controlled by means of a soft-turn-on control and the respective switching transistor is switched on to put an ignition coil into the charging state, and wherein the ignition method provides that - to ignite an ignition spark, the first ignition coil and the second ignition coil are placed into the discharge state essentially simultaneously, and - then the first ignition coil and the second ignition coil are put into the discharge state at a time delay.

Images