Ignition system for an internal combustion engine

Abstract

An ignition system includes: a step-up transformer having a primary side and a secondary side; an electric energy source which is able to be connected to the primary side; a spark gap, which is designed to carry a current transferred to the secondary side by the step-up transformer. The step-up transformer has a bypass for transferring electric energy from the electric energy source to the secondary side. The bypass is designed to support a decaying electrical signal in the secondary coil of the high-voltage generator as of a predefined time, or as of a predefined intensity of the current being reached.

Claims

1. An ignition system, comprising: at least one high-voltage generator having one primary side and one secondary side; an electric energy source configured to be connected to the primary side; and a spark gap which is configured to carry a current transmitted by the high-voltage generator to the secondary side; wherein the high-voltage generator has a bypass for transferring electric energy to the secondary side, and wherein the bypass is configured to delay a decay of a decaying electrical signal in a secondary coil of the secondary side of the high-voltage generator one of (i) as of a predefined time, or (ii) as of a predefined intensity of the current being reached, wherein the bypass includes at least one capacitor as an energy store having a first terminal connected to a secondary side terminal of the high-voltage generator and a second terminal connected to electric ground; an inductor is provided in a switchable manner between the energy source and the energy store, wherein the inductor is a transformer having a primary side and a secondary side, a first terminal of the primary side of the inductor being connected to the energy source and a second terminal of the primary side of the inductor being connected via a switch to the electric ground, wherein a first terminal of the secondary side of the inductor is connected to the energy source and a second terminal of the secondary side of the inductor is connected via a first nonlinear two-terminal element to the at least one capacitor, at least one of a current measurement device, a voltage measurement device, and a power measurement device which is configured to measure the secondary side current or the voltage via the capacitor and provide the measured value to a control configured for controlling the switch, and wherein the power of the electrical variable inserted by the bypass into the spark gap is controlled via a control signal of the control running to the switch via at least one of a frequency or a pulse-no pulse ratio of the control signal.

2. The ignition system as recited in claim 1, wherein the at least one of a current measurement device, a voltage measurement device, and a power measurement device is configured to provide a signal to a switch in the bypass so that the switch is able to react to a critical current intensity in a loop on the secondary side.

3. The ignition system as recited in claim 2, wherein: the high-voltage generator is configured as a step-up transformer and has a primary coil on the primary side; the bypass is configured to generate a voltage which is one of (i) added to a voltage lying over the secondary coil or (ii) is fed in in parallel to the secondary coil; and an input capacitor is provided in parallel to the energy source.

4. The ignition system as recited in claim 1, wherein between the inductor and the energy store, the first nonlinear two-terminal element has a direction of flow in the direction of the capacitor, and a switchable connection is provided between a common terminal of the inductor and the first nonlinear two-terminal element on the one side and the electric ground on the other side.

5. The ignition system as recited in claim 4, wherein the switchable connection includes a switch in the form of a transistor.

6. The ignition system as recited in claim 2, wherein: the bypass has an inductor, the capacitor, a diode and a switch; a first terminal of the inductor is connected to the energy source and a second terminal of the inductor is connected to a first terminal of the diode; the switch is configured to selectively connect one of the second terminal or a third terminal of the inductor to the electric ground; a second terminal of the diode is connected to a first terminal of the capacitor; and a second terminal of the capacitor is connected to the electric ground, and a Zener diode of the capacitor is connected in parallel.

7. The ignition system as recited in claim 2, wherein at least one of: (i) the least one of the current measurement device, the voltage measurement device, and the power measurement device is a shunt resistor configured to provide a signal for controlling at least one switch in the bypass; and (ii) a second nonlinear two-terminal element parallel to the energy store protects the energy store from an overvoltage.

8. The ignition coil as recited in claim 1, wherein at least one of (i) the bypass includes a boost converter, and (ii) the high-voltage generator is bridged on the secondary side by a third nonlinear two-terminal element.

9. A method for generating an ignition spark for an internal combustion engine, comprising: generating an ignition spark using electric energy stored in an energy source, which electric energy is transferred via a step-up transformer to a spark gap, the step-up transformer having a primary side and a secondary side; maintaining the ignition spark using electric energy which is transferred from the energy source via a bypass to the secondary side, wherein the electric energy for maintaining the ignition spark is provided from the energy source as a controlled pulse sequence between 10 kHz and 100 kHz; and controlling a switch in the bypass responsive to a current intensity in the secondary side.

10. The method as recited in claim 9, wherein the electric energy for maintaining the ignition spark is coupled in as electric voltage to the secondary side of the high-voltage generator.

11. The method as recited in claim 10, further comprising: outputting a signal to the switch in the bypass; and based on the signal, providing a remedial measure in response to a critical current intensity in the loop on the secondary side.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a diagram over time comparing ignition currents setting in according to the related art and the present invention.

(2) FIG. 2 shows a circuit diagram according to a first exemplary embodiment of an ignition system according to the present invention.

(3) FIG. 3 shows representations of current-time diagrams as well as associated switching sequences for the circuit shown in FIG. 2.

(4) FIG. 4 shows a circuit diagram according to a second exemplary embodiment of an ignition system according to the present invention.

(5) FIG. 5 shows a circuit diagram according to a third exemplary embodiment of an ignition system according to the present invention.

(6) FIG. 6 shows representations of current-time diagrams as well as associated switching sequences for the circuit shown in FIG. 4 and FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

(7) FIG. 1 shows a diagram over time of the ignition current, that is, of that current which, upon the sparkover of the spark gap, flows within the coil on the secondary side of the step-up transformer as the high-voltage generator. In this context, an area 103 is marked, within which the current is so high that the electrodes of the spark plug are able to be damaged by increased erosion. Area 104 marks those (low) current intensities within which a required stability of the electric arc for igniting ignitable mixture cannot be assured. As was described at the outset, thus a current 100, implemented by an ignition system of the related art, after a steep rise, runs into area 103, that endangers the electrodes, and thereafter drops off essentially linearly (in approximation to an exponential discharge function). By contrast, the energy conducted, according to the present invention, to the spark gap, divides into two energy portions, which are provided by a current, flowing through the step-up transformer, for generating an ignition spark and a current, flowing through the bypass, for maintaining an ignition spark. After the step-up transformer (that is dimensioned smaller compared to the related art) has generated an electric arc without the bypass, according to the present invention, the current would become steeply reduced (corresponding to the discharge of the small secondary inductor—with reference to conventional secondary inductors) (cf. illustration in FIG. 1, 101) and would already “vanish” briefly after its creation in area 104. Using the bypass according to the present invention, the current intensity on the secondary side or, to put it more accurately, in the spark gap, is able to be held (cf. illustration in FIG. 1, 102) over a substantially longer time period between the critical areas 103 and 104. After the bypass is switched off, the energy stored in the secondary coil discharges, same as in the related art, which leads to a spark current that is steeply dropping off. The result is an overall current which, however, dips into the unstable area 104 clearly later than current intensity 100 of the known ignition system.

(8) FIG. 2 shows a circuit using which current flows 101, 102, shown in FIG. 1, are implemented. What is shown is an ignition system 1 which includes a step-up transformer 2 as the high-voltage generator, whose primary side 3 is able to be supplied with electric energy from an electric energy source 5 via a first switch 30. Secondary side 4 of step-up transformer 2 is supplied with electric energy via an inductive coupling of primary coil 8 and secondary coil 9 and has a diode 23, known from the related art, for closing spark suppression, this diode being able also alternatively to be replaced by diode 21. In a loop with secondary coil 9 and diode 23, a spark gap 6 relative to frame 14 is provided, via which ignition current i.sub.2 is supposed to ignite the combustible gas mixture. According to the present invention, a bypass 7 (bordered by a dash-dotted line) is provided between electric energy source 5 and secondary side 4 of step-up transformer 2. For this purpose, an inductor 15 is connected via a switch 22 and a diode 16 to a capacitor 10, whose one end is connected to secondary coil 9 and whose other end is connected to electric ground 14. In this instance, the inductor is used as an energy store, in order to maintain a current flow. Diode 16 is oriented conductive in the direction of capacitor 10. Consequently, the design of bypass 7 is comparable to a boost converter, for example. Between capacitor 10 and secondary coil 9 a shunt 19 is provided as a current measuring device or a voltage measuring device, whose measuring signal is supplied to switch 22 and switch 27. In this way, switches 22, 27 are designed to react to a specified range of current intensity i.sub.2 through secondary coil 9. The terminal of switch 22 facing diode 16 is able to be connected via a further switch 27 to electric ground 14. To protect capacitor 10, a Zener diode 21 is connected in inoperative direction parallel to capacitor 10. Furthermore, switching signals 28, 29 are indicated, by the use of which switches 22, 27 are able to be controlled. While switching signal 28 represents a switching in and a “remaining closed” for an entire ignition cycle, switching signal 29 sketches a contemporaneous alternating signal between “closed” and “open”. During a closed switch 22, inductor 15 is supplied with a current via electric energy source 5, which, during closed switches 22, 27, flows directly into electric ground 14. During an open switch 27, the current is conducted via diode 16 and terminal 35 to capacitor 10. The voltage setting in in capacitor 10 in response to the current is added to the voltage dropping off over secondary coil 9 of step-up transformer 2, whereby the electric arc at spark gap 6 is supported. In this context, however, capacitor 10 discharges, so that by closing switch 27, energy is able to be brought into the magnetic field of inductor 15, in order to charge this energy again onto capacitor 10, in response to a renewed opening of switch 27. In a recognizable way, the control of switch 30 that is provided on primary side 3 is clearly held to be shorter than is the case for switches 22 and 27. These processes will be discussed in greater detail in connection with FIG. 3. Since switch 22 for the processes according to the present invention does not assume any decisive function, but only switches the circuit on and off, it is only optional, and may therefore also be omitted.

(9) FIG. 3, in Diagram a), shows a short and steep rise in primary coil current i.sub.zs, which sets in at that particular time at which switch 30 (see Diagram 3c) is in conductive state (“ON”). When switch 30 is switched off, primary coil current i.sub.zs also drops off to 0 A. Diagram b) shows the curves of secondary coil current i.sub.2, as they come about for a use of System 1 shown in FIG. 2 with (301) and without (300) the bypass. As soon as primary coil current i.sub.zs comes down to 0 based on the opening of switch 30, and as a result the magnetic energy stored in the step-up transformer discharges in the form of an electric arc over spark gap 6, a secondary coil current i.sub.2 sets in which, without bypass (300) drops off rapidly towards 0. In contrast to this, because of a closed switch 22 (see Diagram d)) and a pulse-shaped control (see Diagram e)), switching signal 29) of switch 27 an essentially constant secondary coil current i.sub.2 (301) is driven over spark gap 6. Secondary current i.sub.2 depending on the sparking voltage at spark gap 6, and at this point a constant sparking voltage is assumed, for the sake of simplicity. Only after the interruption of bypass 7 by the opening of switch 22 and the opening of switch 27 does secondary coil current i.sub.2 now also drop off towards 0. From Diagram b) it is recognizable that the side falling off in each case is delayed by a time duration t.sub.HSS.sub._.sub.a. The entire time duration during which the bypass is used is characterized as t.sub.HSS and the time during which energy is input on the primary side into step-up transformer 2 is characterized by t.sub.i. The starting time of t.sub.HSS as compared to t.sub.i may be variably selected.

(10) FIG. 4, as opposed to FIG. 2, shows an alternative specific embodiment of a circuit of an ignition system 1 according to the present invention. At the input to the circuit, thus in other words, at the terminal to electric energy source 5, a fuse 26 is provided. In addition, for the stabilization of the input voltage, a capacitor 17 is provided in parallel to the input of the circuit or rather, in parallel to electric energy source 5. Furthermore, inductor 15 has been replaced by a transformer having a primary side 15_1 and a secondary side 15_2, primary side 15_1 having a primary coil and secondary side 15_2 having a secondary coil. The first terminals of the transformer are each connected to electric energy source 5 or rather, fuse 26. In this context, a second terminal of primary side 15_1 is connected via switch 27 to electric ground 14. The second terminal of secondary side 15_2 of transformer 15 is now connected without a switch, directly to diode 16. Based on the transmission ratio, a switching process by switch 27 in the branch of primary side 15_1 acts also on secondary side 15_2. Since, however, current and voltage according to the transformation ratio are higher or lower on the one side than on the other side of transformer 15, more favorable dimensioning for switch 27 may be found for switching processes. For example, smaller switching voltages may be implemented, whereby the possibilities of dimensioning switch 27 are simpler and more cost-effective. Switch 27 is controlled via a control 24, which is connected to switch 27 via a driver 25. As shown in FIG. 2, a shunt 19 is provided in order to measure secondary current i.sub.2 or the voltage over capacitor 10, and to provide this or these to control 24 of switch 27. Moreover, control 24 obtains a control signal s.sub.HSS. Via this, on the one side, the input of energy via the bypass into the secondary side may be switched on and off. In this context, the power of the electrical variable inserted by the bypass or rather into the spark gap, may be controlled, particularly via the frequency and/or the pulse-no pulse ratio, via a suitable control signal. A nonlinear two-terminal element, symbolized below as a high-voltage diode 33, may optionally be connected in parallel to the secondary side coil of the boost converter. This high-voltage diode 33 bridges high-voltage generator 2 on the secondary side, whereby the energy supplied by bypass 7 in the form of a boost converter (bordered by a dash-dotted line) is carried directly to spark gap 6, without being carried by secondary coil 9 of high-voltage generator 2. Consequently, no losses are created via secondary coil 9 and the efficiency goes up. The remaining elements of the drawing shown in FIG. 4 correspond to those shown in FIG. 2 and which have already been discussed above.

(11) FIG. 5 shows an alternative specific embodiment of the circuit introduced in FIG. 4. In it, a high-voltage diode 33 having a direction of flow towards the spark gap between energy store 10 of bypass 7 in the form of a boost converter (bordered by a dash-dotted line) and spark gap 6. Hereby high-voltage diode 33 bridges high-voltage generator 2 on the secondary side, whereby the energy supplied by bypass 7 is carried directly to spark gap 6, without being carried by secondary coil 9 of high-voltage generator 2. Consequently, no losses are created via secondary coil 9 and the efficiency goes up.

(12) FIG. 6 shows a diagram over time for a) ignition coil current i.sub.zs, b) bypass current i.sub.HSS, c) output side voltage over spark gap 6, d) secondary coil current i2 for the ignition system shown in FIG. 4 without (501) and with (502) the use of the bypass according to the present invention, e) switching signal 31 of switch 30 and f) switching signal 32 of switch 27 for the pulse signal in bypass 7. On the diagrams shown in connection with FIG. 3, we refer to the above discussion, for the sake of brevity.

(13) Diagram b) illustrates, in addition, the current input of bypass 7 according to the present invention, which comes about by a pulse-shaped control of switch 27. In practice, pulse rates in the range of several times ten kHz have proven themselves as pulse rates, in order, on the one hand, to implement appropriate voltages and, on the other hand, acceptable efficiencies. For example, we may name whole-number multiples of 10000 Hz in the range between 10 and 100 kHz as possible range borders. In this context, for the regulation of the power output to the spark gap, one might recommend an, in particular, stepless regulation of the pulse-no pulse ratio of signal 29 and 32 for generating an appropriate output signal. In addition it is also possible, by using an additional DC-DC converter, to increase the voltage supplied by the electric energy source, before it is processed further in the bypass according to the present invention. It should be noted that specific designs depend on many circuit-inherent and external boundary conditions. It does not confront the concerned person skilled in the art with unreasonable problems for himself to undertake the suitable dimensioning, based on the boundary conditions he should observe for his own purposes.

(14) The disclosure of the present invention is supplemented by the following subject matters:

(15) 1. An ignition system (1) including at least one high-voltage generator (2) each having one primary side (3) and one secondary side (4), an electric energy source (5), that is able to be connected to the primary side (3), and a spark gap (6), which is designed to carry a current transmitted by the high-voltage generator (2) to the secondary side (4), wherein the high-voltage generator (2) has a bypass (7) for transferring electric energy to the secondary side (4).

(16) 2. The ignition system as recited in subject matter 1, wherein the high-voltage generator (2) is designed as a step-up transformer and has a primary coil (8) on the primary side and a secondary coil (9) on the secondary side, the bypass (7) is designed to generate a voltage which is added to a voltage lying over the secondary coil (9) or is fed in in parallel to the secondary coil, and in particular an input capacitor (17) is provided in parallel to the energy source (5).

(17) 3. The ignition system as recited in one of the preceding subject matters, wherein the bypass (7) includes an energy store (10), such as a capacitor, whose first terminal is connected to a secondary side terminal of the high-voltage generator (2), and its second terminal is connected to electric ground (14), wherein particularly an inductor (15) being provided between the energy source (5) and the energy store (10), preferably in a switchable manner.

(18) 4. An ignition system as recited in one of the preceding subject matters, wherein between the inductor (15) and the energy store (10) a first nonlinear two-terminal element (16) is provided, for instance, in the form of a first diode, which has a direction of flow in the direction of the capacitor (10), and in particular a switchable connection is provided between a common terminal between the inductor (15) and the first nonlinear two-terminal element (16) on the one side and the electric ground (14) on the other side.

(19) 5. The ignition system as recited in one of the preceding subject matters, wherein means for current measurement (19) and/or voltage measurement and/or power measurement, especially a shunt resistor for measuring the ignition current or the voltage over the energy store (10) are provided, which are designed to give a signal for controlling at least one switch (22, 27) in the bypass (7) and/or a second nonlinear two-terminal element (21), particularly in the form of a second diode, parallel to the energy store (10), protects same from an overvoltage.

(20) 6. The ignition system as recited in one of the preceding subject matters 3 through 5, the inductor (15) being developed as a transformer having a primary side (15_1) and a secondary side (15_2); a first terminal of the primary side (15_1) being connected to the energy source (5) and a second terminal of the primary side (15_1) being connected via a switch (27) to the electric ground (14); and a first terminal of the secondary side (15_2) being connected to the energy source (5) and a second terminal of the secondary side (15_2) being connected to the first nonlinear two-terminal element (16).

(21) 7. The ignition system as recited in one of the preceding subject matters, wherein the bypass (7) includes a boost converter and/or the high-voltage generator (2) is bridged on the secondary side by a third nonlinear two-terminal element (33), especially in the form of a third diode.

(22) 8. A method for generating an ignition spark for an internal combustion engine, including the steps: generating an ignition spark using electric energy taken from an energy source (5), which is given via an high-voltage generator (2), particularly a step-up transformer, having a primary side (3) and a secondary side (4) to a spark gap (6), characterized by the maintaining of the ignition spark using electric energy which is transferred from the energy source (5) via a bypass (7) to the secondary side (4).

(23) 9. The method as recited in subject matter 8, wherein the electric energy for maintaining the ignition spark is coupled in as electric voltage in series or in parallel to the secondary side (4) of the high-voltage generator (2), and/or the electric energy for maintaining the ignition spark is provided from the energy source (5) via a controlled pulse sequence, particularly in the kiloHertz range, preferably between 10 kHz and 100 kHz.

(24) 10. The method as recited in subject matter 8 or 9, wherein the electric energy for maintaining the ignition spark reaches the spark gap (6) via a boost converter in the bypass (7).

(25) It is a central idea of the present invention advantageously to split up, according to the present invention, two functions which have unified the step-up transformers of known ignition systems, in order to make possible suitable dimensioning of the high-voltage generator and efficient utilization of the electric energy. For this purpose, a high-voltage generator is provided in order to generate an ignition spark according to the related art. A bypass is designed to maintain the existing electric arc over the spark gap. To do this, a bypass takes energy from, for instance, the same energy source as the primary side of the high-voltage generator and uses it to support the decaying edge of the transformer voltage, and thus to delay its dropping off below the sparking voltage. One skilled in the art will recognize, in this instance, preferred specific embodiments of the bypass, according to the present invention, as switching structures working in the manner of a boost converter. In this context, the input of the boost converter is connected in parallel to the electric energy source, while the output of the boost converter is situated in series or in parallel to the secondary coil of the high-voltage generator. The concept of an “energy source” should be broadly interpreted within the scope of the present invention, and may include additional energy-converting devices, such as DC-DC converters. Moreover, it is obvious to one skilled in the art that the inventive idea is not limited to a representational energy source.

(26) Even though the aspects according to the present invention and the advantageous specific embodiments have been described in detail with the aid of the exemplary embodiments explained in connection with the attached drawing figures, modifications and combinations of features of the exemplary embodiments are possible for one skilled in the art, without his having to leave the range of the present invention, whose range of protection is specified by the attached claims.