WO2025016764A1

WO2025016764A1 - Ignition system

Info

Publication number: WO2025016764A1
Application number: PCT/EP2024/069150
Authority: WO
Inventors: Anders Johnsson; Daniel BÄCK; Bert Gustavsson; Jakob ÄNGEBY
Original assignee: SEM AB
Current assignee: SEM AB
Priority date: 2023-07-14
Filing date: 2024-07-08
Publication date: 2025-01-23
Anticipated expiration: 2026-01-14

Abstract

An ignition system (2) for controlling spark generation of a sparkplug (4) in a combustion engine, comprising an electronic circuit (6) comprising an ignition coil (8) including a primary winding (10), and a secondary winding (12) across which the sparkplug (4) is connectable, a voltage source (14) configured to supply energy to said primary winding (10), and a control unit (16) configured to control said spark generation including to initiate spark generation and thereby enter a spark initialization mode. Upon receipt of a breaktrough detection signal (20), the control unit (16) is configured to terminate the spark initialization mode and to enter a spark maintenance and control mode, to control and maintain the spark by controlling the current of the spark to follow a preset value, and to maintain the duration of the spark until a predetermined time period has lapsed. When the predetermined time period has lapsed, the control unit generated a spark termination control signal (22) to be applied to said electronic circuit (6) to terminate the spark and thereby enter a spark termination mode.

Description

Ignition system

Technical field

The present disclosure relates to an ignition system, and more particularly to an ignition system provided with means for reducing wear of a spark.

Background

Generally, the present disclosure will describe how to achieve a robust ignition using significantly less spark energy and less sparkplug electrode wear by controlling the spark characteristics accordingly.

Spark ignition is an energy- exchange phenomenon, where electrical (spark) energy is converted to thermal energy (increased temperature) around the electrode gap such that the auto-ignition temperature of the fuel is exceeded and initiates a self-sustained exothermic combustion process. The sparking process is described by three phases: Breakthrough, arc, and glow. The spark is initiated during the breakthrough phase when a conductive plasma is created between the sparkplug electrodes. It is characterized by a short timescale (tens of nanoseconds) and requires a high voltage (10 kV or more). The temperature of the plasma formed between the electrodes at the breakthrough reaches up to 60.000 K. The current during the breakthrough is high, in the range of 100 A. The voltage required for breakthrough is linearly dependent on the in-cylinder gas pressure and the gap between the sparkplug electrodes. There are also other factors that effects the voltage requirement, such as temperature and gas mixture.

After the breakthrough the arc-phase follows, which is characterized by a highly conductive thin medium of plasma and the temperature drops down to below 10.000 K. The electrode wear is expected to be high, due to the high electrode temperature which leads to evaporation of molten metal. The current during the arc phase is in the range 10- 20 A and mainly supplied by parasitic capacitances in the sparkplug and ignition coil extension. When the charge in the parasitic capacitances have discharged, the current decreases to a lower value, typically in the range of 10-200 mA and the spark discharge is characterized by a more diffuse glow discharge. The current supply during the glow phase is from the ignition system (primary and secondary coil windings). A strong enough current is required to sustain the plasma. In the presence of turbulence, the plasma channel is “stretched”, forming a bow-shaped trajectory. A higher current can sustain a longer plasma elongation than a weak, increasing the flame kernel area, which in turn is expected to enhance the capability to trigger a self- sustained combustion.

The spark generates a flame kernel. The laminar flame speed of the flame kernel is determined by the property of the air-fuel mixture between and around the sparkplug electrodes. When the diameter of the flame kernel has reached a few millimeters the ignition process has played out its role and the rest of the combustion process is determined by the fuel property and engine design.

The spark discharge phases transfer different fractions of their energy to the air-fuel mixture. The breakthrough phase is the most efficient, followed by the arc and glow phases, respectively.

If the property of the fuel mixture around the electrodes is favorable, which is normally the case at medium and high load conditions, then it can be expected that a very short spark (breakthrough plus arc) should be sufficient to ignite. During idling conditions and/or highly diluted fuel mixtures, however, the fuel mixture may be less homogenous, and the ignition process is expected to require a longer spark (glow) duration for the spark to hit a favorable fuel mixture.

The ability to ignite a fuel mixture depends on the spark characteristics, which in turn depends on the ignition system design that generates and controls the spark release.

Spark ignited internal combustion engines (SI-ICE) running on alternative and/or renewable fuels are an important complement to electrification in the effort to mitigate greenhouse gas emission and global warming, motivated by their ability to efficiently make use of renewable fuels with low cetane numbers. The availability of such fuels is expected to increase. However, introduction of new fuels for SLICE introduces new challenges on the ignition system to meet the requirements on performance and the total cost of ownership (TCO).

The requirements on ignition systems for SLICE are increasing. A smaller size is requested due to engine down-sizing and higher voltages are required to create sparks when in-cylinder pressures are increasing. At the same time, the TCO needs to be low enough to make SI-ICE fueled by renewable fuels a viable alternative in the competition with other zero emission solutions such as battery electric and fuel cell drivelines. Examples of renewable and alternative fuels are hydrogen, electro-methane, natural gas, biogas, methanol, ethanol, and ammonia. The ignition requirements when using such fuels vary significantly. When using hydrogen, for example, the voltage that the ignition system shall be able to provide the available spark voltage (ASV) is typically higher than when using other fuels of essentially two reasons. First, the flame propagation speed (heat release) is relatively fast and therefore the maximum braking torque (MBT) ignition timing is close to TDC where the pressure is high. Second, it is needed to inject as much H2 as possible since it has such low volumetric energy density.

This leads to higher breakthrough voltage (BTV) and a higher required ASV. However, the ignition energy required to ignite hydrogen is relatively small. Therefore, an ignition system that can provide a high ASV and low spark energy is required. Low spark energy is desired to minimize the sparkplug electrode wear, i.e., to keep the TCO as low as possible. The cost associated with sparkplug maintenance is a significant part of the TCO, and there are substantial savings to be made if the electrode wear is minimized. Also, a low as possible spark energy is desired when using hydrogen as fuel to keep the sparkplug electrode temperature as low as possible to avoid pre-ignition due to hot spots on the electrodes. When biogas or natural gas (CNG or LNG) or electro methane is used as fuel, then the requirements on the spark are different than those when using hydrogen. The spark energy needs to be higher, and the required spark duration may be longer. Clearly, if a fuel agnostic engine is considered, then the ignition system needs to provide different spark characteristics depending on the fuel used.

The requirements on the ignition system will vary even in the case when using one and the same fuel due to the wear of the sparkplug electrodes. As the electrodes erode, then the gap between them increases and the voltage required to create a spark increases as well. Hence, if the ignition system is not able to adapt to the actual breakthrough voltage as the electrodes erode and the gap increases, then the ignition system will have to be calibrated for the worst case, i.e., the high voltage needed when the sparkplug is close to the end-of- life. This leads to more powerful sparks than needed throughout the life span of the sparkplug, and an accelerated ageing and significantly shortened sparkplug lifetime, and an increase of the TCO as a result.

To meet the requirements, the system should be able to control the characteristics of the sparks and optimize the ignition depending on the fuel, the engine operating point and the condition (age) of the sparkplug. This is not possible when using a conventional inductive ignition system, because then the available spark voltage (ASV), the spark current, and the spark duration cannot be separately controlled. When using a conventional inductive ignition system, an increase in ASV inevitably leads to an increase in current and duration, i.e., an increased electrode wear.

When using a capacitive ignition system, a spark is controlled by an ignition control unit that discharges electrical charge stored in a capacitor over an ignition coil, which essentially is a transformer. The ignition coil transforms the electric pulse on the primary side to one electric pulse having a higher voltage on the secondary side, than on the primary side, which, in turn, generates a spark over sparkplug electrodes. A conventional capacitive ignition control unit starts transferring electrical charge to the ignition coil when a spark has been requested. The electrical charge transfer continues until the energy in the ignition control unit capacitor runs out or for a preset time. The preset time is long enough to ensure that enough energy to create a spark in the combustion chamber has been transferred to the coil. This required amount of energy increases with, for example, the cylinder pressure at the time of the spark and the size if the gap between the sparkplug electrodes.

In many cases, e.g. when the sparkplugs are new or when running the engine below maximum torque, the spark is formed long before the energy transferred is ended, causing unnecessary high spark currents and hence excessive sparkplug wear.

US2012/0247441 relates to an ignition system for extending igniter life. The system comprises a controller configured to energize the ignition coil during a first ignition sequence until a threshold current has been directed to the ignition coil, measure a rise time associated with reaching the threshold current, and calculate a desired ignition duration based on the rise time and a time margin.

W02020/050765 relates to an ignition system for controlling spark ignited combustion engines. The voltage over a coil winding on the primary side of the ignition coil is regulated to a sufficiently low voltage level during timed period of the ignition cycle, such that e.g. spark suppression after onset of ignition is obtained.

US2017/0030319 relates to an ignition apparatus for internal combustion engine configured such that an energy input line from an energy inputting circuit to a main ignition circuit can be opened, halting the inputting of energy from the energy inputting circuit to the primary winding.

US2019/0301423 relates to a method that includes receiving a collection of electric current amplitude in a primary winding of an engine ignition system having the primary winding and a spark plug.

US2002/0043255 relates to an apparatus and method for controlling ignition of an internal combustion engine

A general object of the present invention is to achieve an ignition system capable of controlling the characteristics of the spark and optimize the ignition depending on the fuel, the engine operating point and the condition (age) of the sparkplug, irrespectively if a capacitive or an inductive ignition system is applied.

A more specific object is to provide the desired degrees of freedom of spark control, giving robust ignition while keeping the electrode wear to a minimum.

Summary

The above-mentioned objects are achieved by the present invention according to the independent claims.

Preferred embodiments are set forth in the dependent claims.

The present invention relates to an ignition system, e.g. a capacitive or an inductive ignition system, and how to control the spark such that a spark is achieved, while keeping the sparkplug wear at a minimum. According to the invention, an ignition control unit is provided, configured to detect that the spark has been formed, and after detection stops transferring electrical charge to the ignition coil. In this way the spark current is minimized after the spark has been formed. If the spark current is required to be above a certain value to ensure a robust combustion a minimum time of energy transfer from the ignition control unit to the ignition coil can be used.

By the ignition system and method defined in the appended claims, a system and a method are achieved that provide enough voltage but not more and minimizes the current while providing a predetermined spark duration, the spark energy can be significantly reduced, typically to be in the range of 2-5 mJ and the electrode erosion decreased accordingly.

Spark breakthrough may be detected by detecting the change in current and/or voltage on the primary and/or secondary sides of the ignition coil when current suddenly begins to rush through the spark gap of the sparkplug.

The present invention of detecting the breakthrough and allowing this detection to feedback control, the regulation (termination) of the spark solves the aforementioned problems and significantly extends the life of the sparkplugs and thus reduces the operating costs of the end users. By detecting when the breakthrough occurs and terminating the spark a controllable time after the breakthrough detection, the spark will obtain a controllable burning time.

By applying the ignition system according to the present invention wear of the sparkplug electrodes is considerably reduced by detecting the spark breakthrough and immediately switch over from a spark initialization mode to a spark maintenance and control mode. During the spark maintenance and control mode, i.e. when a spark breakthrough has been detected, the current through the plasma is controlled to a target value until terminated after a set time interval. The system has now entered the spark termination mode. Hereby a spark is always released and excess current is eliminated, saving sparkplug wear. The desired spark current and duration are set by the control unit. Brief description of the drawings

Figure 1 schematically illustrates a capacitive ignition system according to prior art. Figure 2 schematically illustrates an inductive ignition system according to prior art. Figure 3 is a block diagram schematically illustrating the ignition system according to the present invention.

Figure 4 is a schematic illustration of an embodiment of the present invention.

Figure 5 is a schematic illustration of another embodiment of the present invention.

Figure 6 is a schematic illustration of a further embodiment of the present invention. Figure 7 shows graphs illustrating aspects of embodiments of the present invention. Figure 8 is a schematic illustration of another embodiment of the present invention. Figure 9 is a flow diagram illustrating the method according to the present invention. Figures lOa-lOj, and 1 la-11g, show curves of voltages/currents of the primary and secondary windings of the electronic circuit of respectively a capacitive ignition system and an inductive ignition system.

Detailed description

The energy to be released in an ignition system in the form of a spark needs to be stored and controlled. There are two main approaches - a capacitive energy storage and an inductive energy storage. A capacitive system in its simplest form is illustrated in figure 1, and an inductive system in figure 2.

In a capacitive system, see figure 1, the energy from the energy source B to be supplied to the sparkplug SP is stored in a capacitor C. When the switch SW1 is closed, the voltage is transformed from the primary winding LI to the secondary winding L2 and a spark is generated. The discharge of the capacitor may be controlled, enabling control of the spark characteristics such as current and duration (energy) by an electronic circuit and control unit CU.

In a “basic” inductive system, see figure 2, the energy to be supplied to the sparkplug is stored in a magnetic field in the coil. When the switch SW2 is closed, current flows through the primary winding generating a magnetic field. When the switch is opened the current is stopped and a high electric voltage is transformed to the secondary coil L2 generating a spark. The spark continues until the energy stored in the magnetic field has been emptied. The only degree of freedom in this “basic” inductive system is the time by which current is drawn through the primary, denoted dwell time.

The main difference between a capacitive and inductive system is how the energy is stored prior to the release of the spark. As indicated by their names - the energy is stored as charge in a capacitance or a magnetic field in a coil, respectively. Due to the designs, the systems have different generic degrees of control freedom. The only degree of freedom when using a basic inductive ignition system is the dwell time, i.e., the time by which a current is drawn from the voltage source (battery) through the primary winding, hereby transforming electrical to magnetic energy in the form of a magnetic field in the coil. When using a basic inductive approach, a demand for a high available spark voltage (ASV) therefore inevitably implies a long spark duration and current. This leads to an excessive electrode erosion.

The ignition system and the method of the ignition system according to the present invention will now be described in detail with references to the appended figures. Throughout the figures the same, or similar, items have the same reference signs. Moreover, the items and the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

In figure 3 is schematically illustrated an ignition system 2 for controlling spark generation of a sparkplug 4 in a combustion engine.

The ignition system 2 comprises an electronic circuit 6 comprising an ignition coil 8 including a primary winding 10, and a secondary winding 12 across which the sparkplug 4 is connectable. The ignition system further comprises a voltage source 14 configured to supply energy to the primary winding 10 being high enough to generate a spark breakthrough, and a control unit 16 configured to control the spark generation by applying control signals to the electronic circuit 6 including to initiate spark generation and thereby enter a spark initialization mode. The ignition system 2 further comprises a spark breakthrough detection unit 18 configured to detect spark breakthrough of a sparkplug 4. The detection unit 18 is configured to generate a spark breakthrough detection signal 20 when spark breakthrough is detected.

The control unit 16 is configured to receive the detection signal 20, and, upon receipt of the detection signal 20, to terminate the spark initialization mode and to enter a spark maintenance and control mode. Being in the spark maintenance and control mode, the control unit is configured to control and maintain the spark by controlling the current of the spark to follow a preset value, and to maintain the duration of the spark until a predetermined time period has lapsed. When the predetermined time period has lapsed, the control unit is configured to generate a spark termination control signal 22 to be applied to said electronic circuit 6 to terminate the spark and thereby enter a spark termination mode.

According to an embodiment, the termination of spark is performed by the electronic circuit 6 by reducing energy supply to the primary winding 10 of the ignition coil 8 a predetermined time period after the timing of the breakthrough detection. The termination of the spark may be performed by reducing the energy supply by completely terminating the energy supply, which in particular is applicable when the ignition system is a capacitive discharge ignition system which will be further described below.

The predetermined time period is preferably within an interval being equal to or larger than zero and less than an adjustable maximum value Tmax.

According to a further embodiment, the spark breakthrough detection unit 18 is configured to detect spark breakthrough by measuring voltage and/or current of the primary and/or secondary winding, and by detecting a signal related to the measured voltage and/or current caused by, and being characteristic of, breakthrough that correlates in time with the timing of the breakthrough, i.e. the timing of the start of the spark initialization mode which is a known point of time.

Detection of spark breakthrough by analysing a measured voltage and/or current of a primary and/or secondary winding may be performed in many different ways using a plurality of different techniques. Spark breakthrough causes characteristics of the signal related to the measured voltage/current signal that may be identified using for example matched filters, by identifying characteristic oscillations of the signal, by identifying steplike changes of the signal, by identifying specified derivates of the signal, and many other. In one exemplary variation, a matched filter may be obtained by correlating a known signal, or template, representing spark breakthrough with an unknown signal being the measured voltage/ current to detect the presence of the template in the unknown signal. Using a matched filter is the optimal linear filter for maximizing the signal-to-noise ratio (SNR) in the presence of additive stochastic noise.

Other examples of detecting spark breakthrough will be discussed below.

According to further embodiments, the preset spark current and duration are set by the control unit, wherein the current is controlled in a closed loop to set values typically in the range of 50-200 mA, and the duration in the range of 40-3000 ps, resulting in spark energies in the range of 2-350 mJ.

The preset spark current and the duration depend on combustion engine operating conditions and sparkplug conditions.

Thus, the desired set-points for current and duration depend on the engine operating and sparkplug conditions. The sparkplug condition is diagnosed using an estimate of the breakthrough voltage which is communicated to the control unit over the CAN-bus together with other diagnostics such as confirmation that a spark has been released and spark pre-termination (blow-out). The diagnostics enable a closed loop control of the ignition in the control unit that optimizes the ignition performance and decreases the TCO. In addition, the diagnostics may also include so-called ion-sense based combustion diagnostics for pre-ignition and misfire and knock detection, as well as combustion phase estimation. The combustion diagnostics can be used for closed loop optimization of the combustion process and hereby compensate for, e.g., the varying fuel property that is common in bio- and natural gas applications.

In further embodiments the ignition system according to the invention is applicable both in a capacitive discharge ignition system, and in an inductive discharge ignition system. In the following various exemplary variations will be discussed applicable to a capacitive discharge ignition system, and also to an inductive discharge ignition system. Thus, breakthrough detection may be performed in a number of ways, for example, breakthrough detection may be performed by:

-Identifying high frequency oscillations of the current(s) through the primary winding and/or the secondary winding that is/are correlated with the breakthrough.

-Identifying high frequency oscillations in the voltage over the primary winding that is correlated with the breakthrough.

-Measuring the voltage over the secondary winding and detect a step correlated with the breakthrough.

-Measuring the current(s) through the primary winding and/or the secondary winding and comparing it with predefined limit(s). The limit is set at a level which is never reached unless current starts to flow in the spark gap. The currents increase faster after breakthrough.

Below is a list of further examples of how the change of current/voltage related to spark breakthrough may be detected:

-Determining the derivative(s) of measured current(s) through primary winding and/or secondary winding and compare to derivative threshold(s). When current begins to flow in the spark gap, the derivative of the current increases which then will be detected.

-Determining the derivative of measured voltages over secondary winding and compare to derivative threshold. When the current starts flowing in the spark gap, the secondary voltage drops momentarily from often tens of kV to about 1 kV, which then will be detected.

-When spark breakthrough occurs, there is a high-frequency pulse that may be detected with an inductive or capacitive “sensor”, the energy content of the pulse can be used to determine whether it is overshoot or PD.

All limit values and threshold values applied during detection may be dynamic over time regardless of the detection method.

In figures lOa-lOj, and 1 la-11g, are shown curves of voltages/currents of the primary and secondary windings of the electronic circuit of respectively a capacitive ignition system and an inductive ignition system in order to illustrate the parts of the curves used to identify the starting and ending points of the different modes, i.e. the spark initialization mode, the spark maintenance and control mode, and the spark termination mode.

In these figures one or many of primary voltage (Prim Volt), primary current (PrimCurr), secondary voltage (SecVolt), and secondary current (SecCurr) are shown in graphs were voltage or current are indicated on the Y-axes, and time in seconds on the X-axes.

Figure 10a shows primary and secondary voltages/currents, and figure 10b shows the same curves in a larger scale.

Figure 10c shows the primary current, and figure lOd shows the same curve in a larger scale, where the encircled part in figure 10c clearly is possible to detect as the derivative of the curve changes which is shown by the lines in figure lOd.

This indicates that the spark breakthrough can be detected from measurements of the primary current. There are many algorithms that can detect the break-through from measurements of the primary current. A matched filter can be used, or a frequency-based approach using a band pass filter centered around the characteristic frequency of the primary current during the breakthough, or a time-frequency approach such as wavelets could be used. There are multiple ways to detect spark breakthrough from measurements of the primary current that enables detection of the signal related to said measured current caused by, and being characteristic of, breakthrough that correlates in time with said breakthrough.

Figure lOe shows the primary voltage, and figure lOf shows the same curve in a larger scale, where the encircled part in figure lOe clearly is possible to detect due to the characteristic oscillation part of the curve.

This indicates that the break-through can be detected from said characteristic oscillation present in measurements of the primary voltage. There are multiple ways to detect spark breakthrough from measurements of the primary voltage that enables detection of the signal related to said measured voltage caused by, and being characteristic of, breakthrough that correlates in time with said breakthrough. Figure 10g shows the secondary current, and figure lOh shows the same curve in a larger scale, where the encircled part clearly is possible to detect due to the oscillation part of the curve.

This indicates that the breakthrough can be detected from said characteristic oscillation present in measurements of the secondary current, or from other characteristics related to the breakthough such as the change in derivate or the like, or by using a time-frequency approach.

Figure lOi shows the secondary voltage, and figure lOj shows the same curve in a larger scale, where the encircled part clearly is possible to detect due to a step-like part of the curve.

This indicates that the break-through can be detected from measurements of the secondary voltage. There are many ways such a detection can be performed.

Figure I la shows primary and secondary voltages, and secondary current, of an inductive ignition system.

Figure 1 lb shows the primary current, and figure 11c shows the same curve in a larger scale. The primary current in an inductive ignition system is not well suited to detect the breakthrough because the conducting path through the primary is broken by the switch that is open during spark initialization.

Figure l id shows the secondary current, and figure l ie shows the same curve in a larger scale, where a current increase is possible to detect.

This indicates that the breakthrough can be detected from measurements of the secondary current. There are multiple ways to perform such a detection.

Figure 1 If shows the secondary voltage, and figure 11g shows the same curve in a larger scale, where a sharp decrease of the voltage is possible to detect.

This indicates that the break-through can be detected from measurements of the secondary voltage. There are multiple ways to perform such a detection, of which some, but not all, approaches were mentioned above. In one exemplary variation, the ignition system 2 being a capacitive discharge ignition system, and the spark breakthrough detection unit 18 is configured to detect spark breakthrough by identifying high frequency oscillations in the current through the primary and/or secondary windings 10, 12 that are correlated with the breakthrough.

In another variation, the ignition system 2 being a capacitive discharge ignition system, and the breakthrough detection unit 18 is configured to detect spark breakthrough by identifying high frequency oscillations in the voltage over the primary winding 10 that are correlated with the breakthrough.

In still another variation, the ignition system 2 being a capacitive discharge ignition system spark, and the spark breakthrough detection unit 18 is configured to detect spark breakthrough by measuring the voltage over the secondary winding 12, and wherein a breakthrough is detected if the measured voltage displays a predefined step-like change correlated with the breakthrough. An exemplary variant of this embodiment is illustrated in figure 6, and the voltage UI2 is measured and used to calculate the secondary current 12.

In yet another embodiment, the ignition system 2 being a capacitive discharge ignition system spark, and the spark breakthrough detection unit 18 is configured to detect spark breakthrough by measuring the current through the primary and/or secondary winding 10, 12 and comparing the measured current with a predefined limit, and wherein the predefined limit is defined to reflect that the current increases faster after breakthrough.

Two exemplary variants of breakthrough detection are illustrated in figures 4 and 5.

The functionality of the variant illustrated in figure 4 will now be described.

The spark initialization mode is started by closing switch SW1 and measuring the voltage UI1 over the resistor Rl. The current II through the first winding LI and the resistor R1 is determined by calculating II = UI1 / Rl and comparing II to a current limit II by the breakthrough detection unit 18. This comparison is performed until II > Iliimit. When II is greater than the Iliimit, spark breakthrough is detected, the system enters the spark control and maintenance mode, and a timer is configured to start running for a predetermined time period. The predetermined time period is within an interval being equal to or larger than zero and less than an adjustable maximum value Tmax. When the predetermined time period has lapsed the spark is terminated by opening switch SW1, and the system now enters the spark termination mode.

The functionality of the variant illustrated in figure 5 is similar to that of the variant illustrated in figure 4. The only difference is that the diode DI has been replaced by a second switch SW2. At start of the spark initialization mode, when switch SW1 is closed, switch SW2 remains open, and at termination of the spark control and maintenance mode, when switch SW1 is opened, switch SW2 is closed.

Figure 7 shows graphs of an exemplary variant of breakthrough detection according to an embodiment of the present invention in order to clearly illustrate the benefits of the present invention. In the figure, subscript “0” refers to a conventional capacitive ignition system, and subscript “1” refers to a capacitive ignition system according to an embodiment of the present invention.

In figure 7 the Y-axis represents the current I through the primary winding, and the X-axis represents time t. U1 is the voltage applied to the primary winding during the time period from 0 until tUl, and U0 is the voltage applied to the primary winding during the time period from 0 until tUO in a conventional system. IOCO is the current through the primary winding in a conventional system, i.e. an open circuit current, which is calibrated in the control unit of the system to be used as a reference value of the current through the primary winding. 10 is the current through the primary winding in a conventional system, and II is the current in the primary winding of a system in an embodiment of the present invention. S designates spark formation. I1LIM is a limit value for the current through the primary winding. When the spark initialization mode starts, the voltage U1 is supplied to the primary winding, and the current II through the primary winding increases. A spark S is formed, and the current II is compared to I1LIM. When II > I1LIM the voltage supply to the primary winding is terminated, and the current II through the primary winding decreases. As clearly illustrated in figure 7, in a conventional system, the voltage U0 is supplied during a longer time period, resulting in higher energy consumption, and higher wear of the sparkplug, in comparison to the ignition system according to the present invention.

In yet another embodiment, the ignition system 2 being an inductive discharge ignition system. Spark breakthrough detection unit 18 is configured to detect spark breakthrough e.g. by measuring the current through the secondary winding 12 and comparing the measured current with predetermined current characteristics defining spark breakthrough.

In WO-2020/050765 is disclosed an inductive discharge system.

This know solution provides control of the primary voltage regulation that makes it possible to end the spark a certain controllable time after “spark onset”, i.e. when breaking the current through the primary winding, e.g. by opening a switch. This leads to the voltage across the sparkplug increases, and when the voltage across the sparkplug electrodes is high enough, there is a breakthrough - a spark. The electrical voltage required to make a breakthrough varies from cycle to cycle and depends on the composition of the fuel mixture that happens to be between the electrodes of the spark at the time. The varying breakthrough voltage means that the time from “spark onset” to breakthrough varies. The time can vary as much as several tens of ps, perhaps up to 100 ps, typically in the range [15-100] ps.

In some applications, as discussed in the background section of the present application, it is important to produce a short spark with controllable burning time. In a hydrogen- powered spark-ignited internal combustion engine, for example, very short sparks are required with a known burning time in some operating points and longer in other operating points.

In the solution disclosed in WO-2020/050765, it is not possible to control the burning time of the spark, because it is not known when the spark actually occurred. Instead, it is assumed that the breakthrough voltage is the maximum that the system can deliver, and thus that the time from “spark onset” to breakthrough is the maximum, e.g. 100 ps. If a burning time of e.g. 40 ps is required, the spark is terminated after 140 ps from “spark onset”. This procedure actually produces sparks whose burning time can vary between [40, 120] ps. The “extra” and unwanted burning time of up to 80 ps that occurs in this known device leads to unnecessary wear of the sparkplug electrodes, which need to be replaced considerably earlier than would be necessary if the spark’s burning time could be better controlled.

In figure 8 is shown a variant of an inductive ignition system of a variation of the present invention. The illustrated variant is similar to the system disclosed in WO-2020/050765, but a break through detection unit 18 is included (which here is part of the control unit 16) that is configured to determine the current 12 through the secondary winding, by measuring the voltage over resistor Rl. The determined current 12 is compared to a predetermined current limit, and the control strategy of the system is changed immediately after detection, i.e. when 12 is greater than a predetermined current limit. The time for changing the control strategy is then adapted to the current need for breakthrough voltage for an ongoing spark (e.g. cylinder pressure, sparkplug condition, lambda, temp, etc.).

The present invention also relates to a method in an ignition system for controlling spark generation of a sparkplug 4 in a combustion engine.

The ignition system has been described in detail above and it is herein referred to that description. The method will now be described with references to the flow diagram shown in figure 9.

Thus, the ignition system 2 comprises an electronic circuit 6 comprising an ignition coil 8 including a primary winding 10, and a secondary winding 12 across which the sparkplug 4 is connectable; a voltage source configured to supply energy to the primary winding 10 being high enough to generate a spark breakthrough, and a control unit 16 configured to control the spark generation including to initiate spark generation.

As shown in the flow diagram of figure 9, the method comprises:

- entering a spark initialization mode when a spark is initiated;

- detecting spark breakthrough of a sparkplug 4, by a spark breakthrough detection unit 18 included in said ignition system 2;

- generating a spark breakthrough detection signal 20, by said breakthrough detection unit 18, when spark breakthrough is detected, and applying said detection signal 20 to said control unit 16; - terminating the spark initialization mode and entering a spark maintenance and control mode;

- controlling and maintaining the spark by controlling the current of the spark to follow a preset value, and by maintaining the duration of the spark until a predetermined time period has lapsed, and, when said predetermined time period has lapsed,

- generating a spark termination control signal 22 to be applied to said electronic circuit 6 to terminate the spark, and

- entering a spark termination mode.

In the following, some embodiments of the method are listed. These have the same technical features and advantages as for the corresponding features of the ignition system described above. Consequently, these technical features and advantages are not repeated or explained anew in order to avoid unnecessary repetition.

In one embodiment, the method comprises terminating the spark by the electronic circuit 6 by reducing energy supply to the primary winding 10 of the ignition coil 8 a predetermined time period after the timing of the breakthrough detection.

Preferably, the predetermined time period is within an interval being equal to or larger than zero and less than an adjustable maximum value Tmax.

In a further embodiment, the method comprises detecting spark breakthrough by measuring voltage and/or current of the primary and/or secondary winding, and by detecting a signal related to said measured voltage and/or current caused by, and being characteristic of, breakthrough that correlates in time with said breakthrough.

The method in the ignition system is applicable both in a capacitive discharge ignition system and an inductive discharge system as disclosed in detail above in connection with the detailed description of the ignition system, and it is herein referred to that description.

The present invention is not limited to the above-described preferred embodiments.

Various alternatives, and modifications may be used. Therefore, the above embodiments should not be taken as limiting the scope of the invention, which is defined by the appending claims.

Claims

1. An ignition system (2) for controlling spark generation of a sparkplug (4) in a combustion engine, the ignition system (2) comprises:

- an electronic circuit (6) comprising an ignition coil (8) including a primary winding (10), and a secondary winding (12) across which the sparkplug (4) is connectable,

- a voltage source (14) configured to supply energy to said primary winding (10) being high enough to generate a spark breakthrough, and

- a control unit (16) configured to control said spark generation including to initiate spark generation and thereby enter a spark initialization mode, c h a r a c t e r i z e d i n that said ignition system (2) further comprises a spark breakthrough detection unit (18) configured to detect spark breakthrough of a sparkplug (4), and to generate a spark breakthrough detection signal (20) when spark breakthrough is detected, wherein said control unit (16) is configured to receive said detection signal (20), and, upon receipt of said detection signal (20), to terminate the spark initialization mode and to enter a spark maintenance and control mode, wherein in said mode, said control unit is configured to control and maintain the spark by controlling the current of the spark to follow a preset value, and to maintain the duration of the spark until a predetermined time period has lapsed, and when said predetermined time period has lapsed, the control unit is configured to generate a spark termination control signal (22) to be applied to said electronic circuit (6) to terminate the spark and thereby enter a spark termination mode.

2. The ignition system (2) according to claim 1, wherein termination of said spark initialization mode is performed by said electronic circuit (6) by reducing energy supply to said primary winding (10) of said ignition coil (8).

3. The ignition system (2) according to claim 1 or 2, wherein said predetermined time period is within an interval being equal to or larger than zero and less than an adjustable maximum value Tmax.

4. The ignition system (2) according to any of claims 1-3, wherein said spark breakthrough detection unit (18) is configured to detect spark breakthrough by measuring voltage and/or current of the primary and/or secondary winding, and by detecting a signal related to said measured voltage and/or current caused by, and being characteristic of, breakthrough that correlates in time with said breakthrough.

5. The ignition system (2) according to any of claims 1-4, wherein the preset spark current and duration are set by the control unit, wherein the current is controlled in a closed loop to set values in the range of 50-200 mA, and the duration in the range of 40- 3000 ps, resulting in spark energies in the range of 2-350 mJ.

6. The ignition system (2) according to any of claims 1-5, wherein said preset spark current and said duration depend on combustion engine operating conditions and sparkplug conditions.

7. The ignition system (2) according to any of claims 1-6, being a capacitive discharge ignition system.

8. The ignition system (2) according to any of claims 1-6, being an inductive discharge ignition system.

9. A method in an ignition system for controlling spark generation of a sparkplug (4) in a combustion engine, the ignition system (2) comprises:

- a voltage source configured to supply energy to said primary winding (10) being high enough to generate a spark breakthrough, and

- a control unit (16) configured to control said spark generation including to initiate spark generation, c h a r a c t e r i z e d i n that the method comprises:

- entering a spark initialization mode when a spark is initiated;

- detecting spark breakthrough of a sparkplug (4), by a spark breakthrough detection unit (18) included in said ignition system (2);

- generating a spark breakthrough detection signal (20), by said breakthrough detection unit (18), when spark breakthrough is detected, and applying said detection signal (20) to said control unit (16); - terminating the spark initialization mode and entering a spark maintenance and control mode;

- generating a spark termination control signal (22) to be applied to said electronic circuit (6) to terminate the spark, and

- entering a spark termination mode.

10. The method according to claim 9, comprising terminating said spark by applying a current through the primary winding (10) that counteracts the magnetic field of said ignition coil (8) a predetermined time period after the timing of said breakthrough detection.

11. The method according to claim 9 or 10, comprising detecting spark breakthrough by measuring voltage and/or current of the primary and/or secondary winding, and by detecting a signal related to said measured voltage and/or current caused by, and being characteristic of, breakthrough that correlates in time with said breakthrough.

12. The method according to any of claims 9-11, wherein the preset spark current and duration are set by the control unit, and wherein the method comprises controlling the current in a closed loop to set values in the range of 50-200 mA, and the duration in the range of 40-3000 ps, resulting in spark energies in the range of 2-350 mJ.

13. The method according to any of claims 9-12, wherein said preset spark current and said duration depend on combustion engine operating conditions and sparkplug conditions.