Ignition system, internal combustion engine, and handheld power tool

Abstract

An ignition system (1) is disclosed configured to generate an ignition current. The ignition system (1) comprises a supply line (4), an ignition coil (5), a charge capacitor (C) connected to the supply line (4) and to the ignition coil (5), a generator (7) configured to generate an alternating current in the supply line (4), and a boost circuit (8) electrically connected to the supply line (4). The boost circuit (8) comprises a switch assembly (9) controllable to a second state in which current is drawn from the supply line (4) into the boost circuit (8). The ignition system (1) further comprises a thyristor (11) controllable to an open state to trigger generation of the ignition current. The ignition system (1) further comprises a control arrangement (21) configured to control the switch assembly (9) to the second state when the thyristor (11) is controlled to the open state. The present disclosure further relates to an internal combustion engine (2) and a handheld power tool (3).

Description

[0001] Ignition System, Internal Combustion Engine, and Handheld Power Tool

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to an ignition system configured to generate an ignition current to an ignition device of an internal combustion engine. The present disclosure further relates to an internal combustion engine comprising an ignition device and an ignition system, as well as a handheld power tool comprising an internal combustion engine.

[0004] BACKGROUND

[0005] A handheld power tool is a tool intended to be supported by one or two hands of a user during operation. Moreover, a handheld power tool comprises a tool which can be driven by a power source other than solely manual labour. The power source may for example comprise a combustion engine, an electric motor, a pneumatic motor, or the like.

[0006] Today, there are many kinds of power tools available on the market. Examples are chain saws, circular saws, trimmers, hedge trimmers, multi-tools, and the like. Power tools are for example used in industry, in construction, in gardens, for housework tasks, and around houses for purposes of cutting, shaping, sanding, grinding, routing, polishing, and the like.

[0007] As indicated above, some handheld power tools comprise a combustion engine configured to power the tool. In most cases, single-cylinder two-stroke petrol engines are used because of the mechanical simplicity, light weight, and high power-to-weight ratio as compared to other types of combustion engines. A two-stroke engine is a type of internal combustion engine which completes a power cycle with two strokes of the piston during only one crankshaft revolution. Compared to four-stroke engines, two-stroke engines have a greatly reduced number of moving parts, and consequently can be made more compact and significantly lighter.

[0008] Most small sized two-stroke engines comprise an ignition device, such as a spark plug, and an ignition system configured to generate an ignition current to the ignition device. The ignition system comprises components designed to generate and deliver an ignition current. In larger systems, such as in vehicles, the electricity from a battery of an electric system of the vehicle can be utilized as a source for generating the ignition current. In contrast, handheld power tools like chainsaws typically do not include a battery, due to constraints in space and weight. Therefore, the ignition system of a combustion engine of a handheld power tool normally comprises a generator configured to generate electricity upon rotation of a crankshaft of the combustion engine. Typically, the generator comprise a number of magnets and a winding arrangement arranged such that a relative movement is obtained between the magnets and the winding arrangement upon rotation of a crankshaft of the combustion engine. Such a generator may also be referred to as a magneto. The generator generates electrical pulses in a supply line upon rotation of the crankshaft.

[0009] The ignition system further normally comprises a charge capacitor and an ignition coil, wherein the electrical pulses from the generator are sent to the charge capacitor via the supply line. A charge capacitor is a type of component capable of accumulating and storing the electrical energy.

[0010] Some ignition systems comprise a boost circuit configured increase the voltage supplied from the generator to the charge capacitor. A boost circuit can increase the voltage by using a switch, such as a transistor, which is rapidly controlled between an open and a closed state during operation of the combustion engine. When the switch is controlled to the closed state, an electric current is drawn into the boost circuit. Conversely, when the switch is controlled to the open state, the collapse of a generated magnetic field induces a high voltage in the supply line, significantly exceeding the original voltage.

[0011] Once the charge in the capacitor reaches a sufficient level, it can be rapidly discharged through the ignition coil upon triggering of a spark timing device of the combustion engine. The ignition coil's role is to step up the voltage from the stored charge in the charge capacitor, transforming it into a high-voltage current suitable for generating a spark at the ignition device.

[0012] The efficiency of small two-stroke engines in handheld power tools, such as chainsaws, heavily relies on this ignition system. That is, problems, particularly during start-up and idling, can emerge if the spark generated is too weak. The strength of the charge delivered by the ignition coil is crucial as it directly influences the voltage, duration, and energy of the spark at the ignition device, affecting the overall performance of the engine.

[0013] During start-up, a weak spark might not effectively ignite the air / fuel mixture, resulting in hard starting or complete failure to start the engine. This issue becomes more pronounced in cold weather where the air / fuel ratio can be altered by the increased air density in cold conditions, necessitating a stronger spark for effective ignition. Moreover, during idling, similar issues can occur. The engine runs at lower rotational speeds, meaning the generator produces less electrical power. If the boost circuit or the ignition coil cannot sufficiently compensate for this reduced power input, the resulting spark may be too weak to maintain consistent combustion. This can lead to rough idling, where the engine runs unevenly or stalls intermittently.

[0014] Furthermore, a weak spark can lead to incomplete combustion of the air / fuel mixture, resulting in higher emissions of unburnt hydrocarbons, contributing to environmental pollution, and reducing engine efficiency. It can also cause carbon buildup on the ignition device and inside the cylinder of the engine, further increasing starting and idling problems.

[0015] SUMMARY

[0016] It is an object of the present invention to overcome, or at least alleviate, at least some of the above-mentioned problems and drawbacks. The object is achieved by the subject-matter of the appended independent claim(s).

[0017] According to a first aspect of the present disclosure, the object is achieved by an ignition system configured to generate an ignition current to an ignition device of an internal combustion engine, wherein the ignition system comprises a supply line, an ignition coil, a charge capacitor connected to the supply line and to the ignition coil, and a generator configured to generate an alternating current in the supply line to charge the charge capacitor, wherein the generator comprises a winding arrangement electrically connected to the supply line. The ignition system further comprises a boost circuit electrically connected to the supply line. The boost circuit comprises a switch assembly controllable between a first and a second state to cause an increase in the voltage in the supply line, wherein current is drawn from the supply line into the boost circuit when the switch assembly is controlled to the second state. The ignition system further comprises a thyristor controllable to an open state in which the thyristor allows a discharge of the charge capacitor through the ignition coil to generate the ignition current to the ignition device. The ignition system further comprises a control arrangement configured to control the switch assembly to the second state when the thyristor is controlled to the open state.

[0018] Since ignition system comprises the switch assembly and the control arrangement configured to control the switch assembly to the second state when the thyristor is controlled to the open state, an ignition system is provided capable of generating high discharge currents through the ignition coil in order to generate high ignition currents to the ignition device across various operational states of the combustion engine, including start-up and idling.

[0019] This is because, as realized by the inventors of the concept of the present disclosure, some limitations exist in prior art ignition systems of combustion engines. Specifically, if an electrical pulse is generated by the generator when the thyristor is in the open state, the thyristor will remain in the open state for the duration of the pulse. This not only wastes the energy of the electrical pulse but also risks damaging the thyristor and the generator. The reason for this behaviour of the thyristor is intrinsic to the design thereof because a thyristor is a type of electrical component that remains in the open state as long as there is sufficient current flowing through the thyristor.

[0020] Accordingly, since the control arrangement of the ignition system according to the present disclosure is configured to control the switch assembly to the second state when the thyristor is controlled to the open state, it can be ensured that any electrical pulses generated by the generator are drawn into the boost circuit, instead of through the thyristor, when the thyristor is controlled to the open state.

[0021] In this manner, the energy of the electrical pulse can be used for charging the charge capacitor, after the discharge of the charge capacitor through the ignition coil, by controlling the switch assembly to the first state. Thereby, more energy can be supplied to the charge capacitor, and consequently also to the ignition device via the ignition coil, upon rotation of a crankshaft of the combustion engine. In addition, damage to the generator and the thyristor can be prevented.

[0022] Accordingly, due to these features an ignition system is provided capable of generating high discharge currents through the ignition coil in order to generate high ignition currents to the ignition device across various operational states of the combustion engine, including start-up and idling, while preventing damage to the generator and the thyristor of the ignition system.

[0023] Thus, a high-energy spark at the ignition device can be ensured across various operational states of the combustion engine. A high-energy spark can ensure more complete combustion of the air / fuel mixture, which reduces emissions of unburnt hydrocarbons, lessening environmental pollution and enhancing engine efficiency. A high-energy spark can also ensure better fuel economy and smoother engine operation, while minimizing carbon deposits within the engine, which prolongs engine life and reduces maintenance needs. Accordingly, an ignition system is provided overcoming, or at least alleviating, at least some of the above-mentioned problems and drawbacks. As a result, the above-mentioned object is achieved.

[0024] The open state of the thyristor, as referred to herein, means a state in which the thyristor is “open” for the transfer of electricity. In other words, the open state of the thyristor, as referred to herein, corresponds to a conducting state. Similarly, the closed state of the thyristor, as referred to herein, means a state in which the thyristor is “closed” for the transfer of electricity. In other words, the closed state of the thyristor, as referred to herein, corresponds to a non-conducting state.

[0025] Optionally, the control arrangement is configured to maintain the switch assembly in the second state until the current through the thyristor reaches below a threshold level. Thereby, it can be further ensured that energy of electrical pulses generated by the generator can be used for charging the charge capacitor instead of being wasted through the thyristor. Moreover, damage to the thyristor and the generator can be further prevented.

[0026] Optionally, the control arrangement is configured to output a trigger signal to the thyristor and to the switch assembly to control the thyristor to the open state and to control the switch assembly to the second state. Thereby, a simultaneous control of the thyristor to the open state and the switch assembly to the second state can be ensured so as to ensure that energy of electrical pulses generated by the generator can be used for charging the charge capacitor, rather than being wasted through the thyristor when the thyristor is controlled to the open state. Moreover, damage to the thyristor and the generator can be further prevented.

[0027] Optionally, the switch assembly is configured to remain in the second state for the duration of the trigger signal. Thereby, it can be further ensured that energy of electrical pulses generated by the generator can be used for charging the charge capacitor instead of being wasted through the thyristor. Moreover, damage to the thyristor and the generator can be further prevented.

[0028] Optionally, the duration of the trigger signal is set to a time period that is equal to or greater than the time needed for discharging the charge capacitor through the ignition coil. Thereby, it can be further ensured that energy of electrical pulses generated by the generator can be used for charging the charge capacitor instead of being wasted through the thyristor when the thyristor is in the open state. This is because it can be ensured that the charge capacitor is fully discharged through the ignition coil before the switch assembly is controlled to the second state. Moreover, damage to the thyristor and the generator can be further prevented.

[0029] Optionally, the second state of the switch assembly constitutes a state in which the switch assembly electrically connects the supply line to a low potential point. Thereby, it can be ensured that current is efficiently drawn from the supply line into the boost circuit when the thyristor is controlled to the open state. As a result, it is further ensured that energy of electrical pulses generated by the generator can be used for charging the charge capacitor, rather than being wasted through the thyristor when the thyristor is controlled to the open state.

[0030] Optionally, the first state of the switch assembly constitutes a state in which the switch assembly electrically disconnects the supply line from a low potential point. Thereby, it can be ensured that a magnetic field, generated by the control of the switch assembly to the second state, collapses and induces a voltage in the supply line in order to charge the charge capacitor. In this manner, an efficient usage of the energy of electrical pulses can be ensured to charge the charge capacitor.

[0031] Optionally, the switch assembly comprises a transistor. Thereby, a rapid and efficient control of flow of electricity into and out of the boost circuit can be further ensured.

[0032] Optionally, the generator comprises a number of magnets and the winding arrangement arranged such that a relative movement is obtained between the magnets and the winding arrangement upon rotation of a crankshaft of the internal combustion engine. Thereby, an ignition system is provided comprising a simple and efficient generator, while it is ensured that electrical pulses generated thereof can be effectively utilized for generating ignition currents to the ignition device.

[0033] According to a second aspect of the present disclosure, the object is achieved by an internal combustion engine comprising an ignition device and an ignition system according to some embodiments of the present disclosure, wherein the ignition system is configured to generate an ignition current to the ignition device.

[0034] Since the combustion engine comprises an ignition system according to some embodiments, a combustion engine is provided in which the ignition system is capable of generating high ignition currents to the ignition device of the combustion engine across various operational states of the combustion engine, including start-up and idling, while preventing damage to the generator and the thyristor of the ignition system.

[0035] Accordingly, a high-energy spark at the ignition device can be ensured across various operational states of the combustion engine. A high-energy spark can ensure more complete combustion of the air / fuel mixture, which reduces emissions of unburnt hydrocarbons, lessening environmental pollution and enhancing engine efficiency. A high-energy spark can also ensure better fuel economy and smoother engine operation, while minimizing carbon deposits within the engine, which prolongs engine life and reduces maintenance needs.

[0036] Accordingly, an internal combustion engine is provided overcoming, or at least alleviating, at least some of the above-mentioned problems and drawbacks. As a result, the above- mentioned object is achieved.

[0037] Optionally, the ignition device is a spark plug. Thereby, a combustion engine is provided in which the ignition system is capable of generating high ignition currents to the spark plug across various operational states of the combustion engine, including start-up and idling, while preventing damage to the generator and the thyristor of the ignition system.

[0038] Optionally, the internal combustion engine is a single-cylinder two-stroke internal combustion engine. Thereby, a single-cylinder two-stroke internal combustion engine is provided having at least some of the above-mentioned advantages.

[0039] According to a third aspect of the present disclosure, the object is achieved by a handheld power tool comprising an internal combustion engine according to some embodiments of the present disclosure.

[0040] Since the handheld power tool comprises an internal combustion engine according to some embodiments, a handheld power tool is provided comprising a combustion engine having conditions for improved startability and idling operation characteristics. Moreover, a handheld power tool is provided comprising a combustion engine with conditions for a more complete combustion of the air / fuel mixture, which reduces emissions of unburnt hydrocarbons, lessening environmental pollution and enhancing engine efficiency. Moreover, a handheld power tool is provided comprising a combustion engine having conditions for better fuel economy and smoother engine operation, while minimizing carbon deposits within the engine, which prolongs engine life and reduces maintenance needs. Accordingly, a handheld power tool is provided overcoming, or at least alleviating, at least some of the above-mentioned problems and drawbacks. As a result, the above-mentioned object is achieved.

[0041] Optionally, the power handheld tool is configured as one selected from the group consisting of: a chainsaw, a power cutter, a trimmer, a hedge trimmer, a combi-trimmer, and a leaf / debris blower. Thereby, a power tool configured as one selected from the group above is provided having at least some of the above-mentioned advantages.

[0042] Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following detailed description.

[0043] BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Various aspects of the present disclosure, including its particular features and advantages, will be readily understood from the example embodiments discussed in the following detailed description and the accompanying drawings, in which:

[0045] Fig. 1 illustrates a first perspective view of a handheld power tool according to some embodiments of the present disclosure,

[0046] Fig. 2 illustrates a second perspective view of the handheld power tool illustrated in Fig. 1 in which an external cover has been removed, and

[0047] Fig. 3 schematically illustrates an ignition system of an internal combustion engine of the handheld power tool illustrated in Fig. 1 and Fig. 2.

[0048] DETAILED DESCRIPTION

[0049] Aspects of the present disclosure will now be described more fully. Like reference signs refer to like elements throughout. Well-known functions or constructions will not necessarily be described in detail for brevity and / or clarity.

[0050] Fig. 1 illustrates a first perspective view of a handheld power tool 3 according to some embodiments of the present disclosure. The handheld power tool 3 comprises a tool 18 and an internal combustion engine 2 configured to power the tool 18. In Fig. 1 , the internal combustion engine 2 is obscured by an external cover 47 of the handheld power tool 3. For reasons of brevity and clarity, in some places herein, the internal combustion engine 2 is referred to as “the combustion engine 2”, or simply “the engine 2”. In Fig. 1 , the tool 18 of the handheld power tool 3 is schematically indicated in dotted lines.

[0051] According to the illustrated embodiments, the handheld power tool 3 is a chainsaw comprising a tool 18 in the form of a cutting chain movably arranged around a guide bar.

[0052] However, according to further embodiments, the handheld power tool 3, as referred to herein, may be another type of handheld power tool, such as a power cutter, a trimmer, a hedge trimmer, a combi-trimmer, and a leaf / debris blower. Obviously, according to such embodiments, the handheld power tool 3 may comprise another type of tool than a cutting bar and a cutting chain, such as for example a saw blade, a trimmer head, a hedge trimmer cutting assembly, a fan assembly, or the like.

[0053] A combi-trimmer refers to a type of multifunctional gardening tool that combines several functions into one device, making it versatile for various tasks. A combi-trimmer typically has a base unit with a motor and interchangeable attachments that can be swapped out depending on the task to be performed, such as trimming grass, cutting brush, or pruning hedges.

[0054] The feature that the power tool 3 is “handheld” means that the power tool 3 is configured to be supported by one or two hands of a user during operation thereof. According to the illustrated embodiments, the handheld power tool 3 comprises a first handle hi and a second handle h2. The second handle h2 is separate from the first handle hi and is arranged at a distance from the first handle hi . The handheld power tool 3 is configured to be supported via each of the first and second handles hi , h2 during operation of the handheld power tool 3. In other words, the handheld power tool 3 is configured to be supported by two hands of a user during operation of the handheld power tool 3, i.e., is configured to be supported by one hand grabbing the first handle hi and the other hand grabbing the second handle h2.

[0055] According to further embodiments, the handheld power tool 3 may comprise one handle only.

[0056] According to the illustrated embodiments, the first handle hi is a rear handle arranged at a rear portion of the handheld power tool 3 and the second handle h2 is a so-called front handle. The second handle h2 is formed by an elongated curved-shaped body allowing a user to grip the second handle h2 from various directions in a convenient manner which allows a user to operate the handheld power tool 3 at different orientations relative to the gravitational field in a convenient and safe manner.

[0057] According to the illustrated embodiments, the second handle h2 is attached to a tool body of the handheld power tool 3 at a region of a tool portion of the handheld power tool 3. The tool portion of the handheld power tool 3 is a portion of the handheld power tool 3 to which the tool 18 is connected. In other words, according to the illustrated embodiments, the second handle h2 of the handheld power tool 3 is arranged closer to the tool 18 of the handheld power tool 3 than the first handle hi . Moreover, the second handle h2 is arranged at a position between the tool 18 of the handheld power tool 3 and the first handle hi of the handheld power tool 3.

[0058] The handheld power tool 3 comprises a throttle actuator 35 arranged at the first handle hi . The throttle actuator 35 can be used to control a power output of the combustion engine 2. The handheld power tool 3 further comprises a safety actuator 36 arranged at the first handle hi . The safety actuator 36 is operably connected to a mechanism configured to prevent actuation of the throttle actuator 35 when the safety actuator 36 is not pressed and configured to allow actuation of the throttle actuator 35 when the safety actuator 36 is pressed. According to the illustrated embodiments, the safety actuator 36 is arranged to be pressed by the palm of a hand of a user whereas the throttle actuator 35 is arranged to be actuated, i.e., pressed, by one or more fingers of the hand of a user.

[0059] Fig. 2 illustrates a second perspective view of the handheld power tool 3 illustrated in Fig. 1 in which the external cover 47 has been removed. In Fig. 2, the components of the combustion engine 2 can be more clearly seen, such as a cylinder 20 of the combustion engine 2. Below, simultaneous reference is made to Fig. 1 and Fig. 2, if not indicated otherwise.

[0060] According to the illustrated embodiments, the combustion engine 2 is a small sized singlecylinder two-stroke internal combustion engine, i.e., a small sized two-stroke internal combustion engine comprising one cylinder 20 only. According to further embodiments, the combustion engine 2 as referred to herein may be a small sized single-cylinder four-stroke internal combustion engine. The term “small sized” in this context may encompass that the combustion engine has an engine displacement of less than 250 cubic centimetres.

[0061] The combustion engine 2 comprises a piston configured to reciprocate within the cylinder 20. The piston is not seen or indicated in Fig. 2. The combustion engine 2 comprises an air filter unit 49. The air filter unit 49 is configured to filtrate air flowing from the surroundings into an air supply system of the combustion engine 2. The combustion engine 2 further comprises a fuel supply system 50 configured to supply fuel from a fuel tank 33 of the handheld power tool 3 into the cylinder 20 during operation of the combustion engine 2. In Fig. 2, the fuel supply system 50 is schematically indicated. According to the illustrated embodiments, the fuel supply system 50 is a fuel injection system comprising a number of fuel injectors. The fuel supply system 50 may comprise one or more of a fuel injector configured to inject fuel into a crankcase volume of the combustion engine 2, a fuel injector configured to inject fuel into the air inlet system of the combustion engine 2, a fuel injector configured to inject fuel into an air inlet duct of the air inlet system of the combustion engine 2, a fuel injector configured to inject fuel into a scavenging conduit of the combustion engine 2, and a fuel injector configured to inject fuel directly into the cylinder 20 of the combustion engine 2. According to further embodiments, the combustion engine 2 may comprise another type of fuel supply system, such as a carburettor.

[0062] Moreover, the combustion engine 2 comprises an ignition device 13, configured to ignite an air / fuel mixture inside the cylinder 20 of the combustion engine 2. According to the illustrated embodiments, the ignition device 13 is a spark plug configured to ignite the air / fuel mixture inside the cylinder 20 by generating a spark inside the cylinder 20. The combustion engine 2 further comprises an ignition cap 23’ connected to an end portion of the ignition device 13 as well as an ignition cable 23 attached to the ignition cap 23’. As is further explained herein, the ignition cable 23 is connected to an ignition system 1 of the combustion engine 2 of the handheld power tool 3. As is explained in more detail below, the ignition system 1 is configured to generate an ignition current to the ignition device 13 via the ignition cable 23.

[0063] Fig. 3 schematically illustrates the ignition system 1 of the internal combustion engine 2 of the handheld power tool 3 illustrated in Fig. 1 and Fig. 2. In Fig. 3, the ignition device 13 and the ignition cable 23 of the combustion engine 2 are schematically illustrated. Below, simultaneous reference is made to Fig. 1 - Fig. 3, if not indicated otherwise.

[0064] The ignition system 1 comprises a supply line 4, an ignition coil 5, and a charge capacitor C connected to the supply line 4 and to the ignition coil 5. The ignition system 1 further comprises a generator 7 configured to generate an alternating / varying current in the supply line 4 to charge the charge capacitor C.

[0065] The ignition system 1 according to the embodiments illustrated in Fig. 3, as well as the handheld power tool 3 illustrated in Fig. 1 and Fig. 2, lacks a battery for supplying electric current to the supply line 4. Instead, in these embodiments, the generator 7 is the only means for generating an alternating current supplied to the supply line 4. According to the illustrated embodiments, the generator 7 comprises a number of magnets ml , m2 and a winding arrangement 16 arranged such that a relative movement is obtained between the magnets ml , m2 and the winding arrangement 16 upon rotation of a crankshaft of the internal combustion engine 2. In more detail, according to the illustrated embodiments, the generator 7 comprises two magnets ml , m2 arranged on a flywheel 32 of the combustion engine 2. The flywheel 32 is connected to the crankshaft of the combustion engine 2 and is configured to rotate with the crankshaft. According to further embodiments, the generator 7 may comprise another number of magnets ml , m2. Moreover, the magnets ml , m2 of the generator 7 may be arranged on another part of the combustion engine 2 being configured to rotate with the crankshaft of the combustion engine 2.

[0066] The magnetic fields of the magnets ml , m2 induces a current in the winding arrangement 16 upon rotation of the flywheel 32. As seen in Fig. 3, the winding arrangement 16 of the generator 7 is electrically connected to the supply line 4. In this manner, the generator 7 generates an alternating / varying current in the supply line 4 upon rotation of the crankshaft of the combustion engine 2. According to further embodiments, the generator 7 may be configured differently from what is depicted in Fig. 3. As understood from the above described, the charge capacitor C is electrically connected to the winding arrangement 16 of the generator 7 via the supply line 4. In other words, the supply line 4 extends between, and electrically connects, the winding arrangement 16 of the generator 7 and the charge capacitor C.

[0067] The ignition system 1 further comprises a boost circuit 8. The boost circuit 8 is electrically connected to the supply line 4 at a connection point P indicated in Fig. 3. According to the illustrated embodiments, the supply line 4 comprises a first diode d1 located between the winding arrangement 16 of the generator 7 and the connection point P and a second diode d2 located between the connection point P and the charge capacitor C. The first diode d1 is configured to allow transfer of current in a direction from the winding arrangement 16 of the generator 7 to the connection point P and is configured to block transfer of current in a direction from the connection point P to the winding arrangement 16 of the generator 7. Similarly, the second diode d2 is configured to allow transfer of current in a direction from the connection point P to the charge capacitor C and is configured to block transfer of current in a direction from the charge capacitor C to the connection point P.

[0068] The boost circuit 8 comprises a switch assembly 9. The switch assembly 9 is controllable between a first and a second state to cause an increase in the voltage in the supply line 4. In more detail, the second state of the switch assembly 9 constitutes a state in which the switch assembly 9 electrically connects the supply line 4 to a low potential point g1 via a resistor r1 . The first state of the switch assembly 9 constitutes a state in which the switch assembly 9 electrically disconnects the supply line 4 from the low potential point g1 . In this manner, current is drawn from the supply line 4 into the boost circuit 8 when the switch assembly 9 is controlled to the second state. When the switch assembly 9 is controlled to the first state, a magnetic field, generated by the inflow of current into the boost circuit 8 during the second state of the switch assembly 9, collapses and induces a voltage at the connection point P, wherein the induced voltage is higher than the original voltage at the connection point P.

[0069] According to the illustrated embodiments, the low potential point g1 is a ground point p1 , wherein the ground point g1 is electrically connected to a ground point g2 to which a return line 14 of the winding arrangement 16 of the generator 7 is connected. In other words, according to the illustrated embodiments, the low potential point g1 is electrically connected to the return line 14 of the winding arrangement 16 of the generator 7 via the ground point g2. The ground point g2 may also be referred to as a generator ground point or generator grounding point. According to further embodiments, the low potential point g1 , as referred to herein, may be another type of point of the ignition system 1 having a low electric potential. For example, the low potential point g1 , as referred to herein, may be a point or portion of the return line 14 of the generator 7.

[0070] The ignition system 1 further comprises a thyristor 11 . The thyristor 11 is controllable to an open state in which the thyristor 11 allows a discharge of the charge capacitor C through the ignition coil 5 to generate the ignition current to the ignition device 13. In more detail, according to the illustrated embodiments, the ignition coil 5 comprises a primary winding w1 connected to the charge capacitor C and to the thyristor 11 and a secondary winding w2 connected to the ignition device 13 via the ignition cable 23.

[0071] According to the illustrated embodiments, the thyristor 11 allows a discharge of the charge capacitor C through primary winding w1 of the ignition coil 5 when the thyristor 11 is controlled to the open state. The open state of the thyristor 11 constitute a conducting state in which the thyristor 11 conducts electricity. When the thyristor 11 is controlled to the open state, electricity can flow in a circuit c1 from a first side of the charge capacitor C through the thyristor 11 and the primary winding w1 of the ignition coil 5 to a second side of the charge capacitor C. In this manner, a control of the thyristor 11 to the open state allows a discharge of the charge capacitor C through the ignition coil 5. According to the illustrated embodiments, the circuit c1 is grounded at a grounding point g3. The primary winding w1 has fewer turns of thicker wire, while the secondary winding w2 has many more turns of thinner wire. This design is what allows the ignition coil 5 to increase the voltage from a relatively low voltage provided by the charge capacitor C in the primary winding w1 to a high voltage in the secondary winding w2, to be able to create a spark at the ignition device 13.

[0072] As seen in Fig. 3, the ignition system 1 comprises a control arrangement 21 . According to embodiments herein, the control arrangement 21 configured to control the switch assembly 9 to the second state when the thyristor 11 is controlled to the open state.

[0073] In this manner, it can be ensured that any electrical pulses generated by the generator 7 are drawn into the boost circuit 8, instead of through the thyristor 11 , when the thyristor 11 is controlled to the open state. Thereby, an ignition system 1 is provided capable of generating high discharge currents through the ignition coil 5 in order to generate high ignition currents to the ignition device 13 across various operational states of the combustion engine 2, including start-up and idling.

[0074] This is because, as realized by the inventors of the concept of the present disclosure, some limitations exist in prior art ignition systems of combustion engines. Specifically, if an electrical pulse is generated by the generator 7 when the thyristor 11 is in the open state, the thyristor 11 will remain in the open state for the duration of the electrical pulse. This not only wastes the energy of the electrical pulse but also risks damaging the thyristor 11 and the generator 7. The reason for this behaviour of the thyristor 11 is intrinsic to the design thereof because a thyristor 11 is a type of electrical component that remains in the open state as long as there is sufficient current flowing through the thyristor 11 .

[0075] Accordingly, since the control arrangement 11 of the ignition system 1 according to the present disclosure is configured to control the switch assembly 9 to the second state when the thyristor 11 is controlled to the open state, it can be ensured that any electrical pulses generated by the generator 7 are drawn into the boost circuit 8, instead of through the thyristor 11 , when the thyristor 11 is controlled to the open state.

[0076] In this manner, the energy of an electrical pulse can be used for charging the charge capacitor C, after the discharge of the charge capacitor C through the ignition coil 5, by controlling the switch assembly 9 to the first state. Thereby, more energy can be supplied to the charge capacitor C, and consequently also to the ignition device 13 via the ignition coil 5, upon rotation of a crankshaft of the combustion engine 3. In addition, damage to the generator 7 and the thyristor 11 can be prevented. Accordingly, due to these features an ignition system 1 is provided capable of generating high discharge currents through the ignition coil 5 in order to generate high ignition currents to the ignition device 13 across various operational states of the combustion engine 3, including start-up and idling, while preventing damage to the generator 7 and the thyristor 11 of the ignition system 1 .

[0077] According to the embodiments illustrated in Fig. 3, the control arrangement 21 is configured to output a trigger signal S to the thyristor 11 and to the switch assembly 9. The timing at which the trigger signal S is outputted by the control arrangement 21 may be set by an ignition timing device of the ignition system 1 . Such an ignition timing device may be comprised in the control arrangement 21 as referred to herein.

[0078] Moreover, according to the embodiments illustrated in Fig. 3, the thyristor 11 is configured to assume the open state when the trigger signal S is sent to the thyristor 11 by the control arrangement 21 . Furthermore, in these embodiments, the switch assembly 9 is configured to assume the second state when the trigger signal S is sent to the switch assembly 9 by the control arrangement 21 .

[0079] However, according to further embodiments, the control arrangement 21 as referred to herein may be configured differently. For example, the control arrangement 21 , as referred to herein, may not be responsible for controlling the thyristor 11 to the open state. Instead, the control arrangement 21 may be configured to control the switch assembly 9 to the second state when the thyristor 11 is controlled to the open state, wherein the thyristor 11 is controlled to the open state by another type of unit or device of the ignition system 1 . According to such embodiments, the control arrangement 21 may be configured to input a signal from such another type of unit or device of the ignition system 1 when the unit or device controls the thyristor 11 to the open state, and wherein the control arrangement 21 is configured to control the switch assembly 9 to the second state in response to the input of such a signal.

[0080] According to the illustrated embodiments, the switch assembly 9 is configured to remain in the second state for the duration of the trigger signal S. Moreover, the duration of the trigger signal S is set to a time period that is equal to or greater than the time needed for discharging the charge capacitor C through the ignition coil 5. In this manner, the control arrangement 21 is configured to maintain the switch assembly 9 in the second state until the current through the thyristor 11 reaches below a threshold level. Thereby, it can be further ensured that energy of electrical pulses generated by the generator 7 can be used for charging the charge capacitor C instead of being wasted through the thyristor 11 . Moreover, damage to the thyristor 11 and the generator 7 can be further prevented.

[0081] According to the embodiments illustrated in Fig. 3, the switch assembly 9 comprises a transistor 15 and a boost control arrangement 17. Moreover, the boost circuit 8 comprises a voltage comparator 19. The voltage comparator 19 is configured to control the transistor 15 between an open state and a closed state based on a reference voltage Vr and a supply voltage at an input 19’ thereof, wherein the input 19’ of the voltage comparator 19 is connected to the boost control arrangement 17. The boost control arrangement 17 is configured to set the supply voltage at the input 19’ of the voltage comparator 19 based on a current voltage at the connection point P and based on the trigger signal S being sent from the control arrangement 21 .

[0082] That is, according to the embodiments illustrated in Fig. 3, the boost control arrangement 17 is configured to set the supply voltage at the input 19’ of the voltage comparator 19 to a voltage which causes a control of the transistor 15 to the closed state by the voltage comparator 19 upon receipt of the trigger signal S. The closed state of the transistor 15 corresponds to a conducting state, i.e., a state at which current can be drawn into the boost circuit 8 via the transistor 15. Correspondingly, the open state of the transistor 15 corresponds to a non-conducting state, i.e., a state at which current cannot be drawn into the boost circuit 8 via the transistor 15.

[0083] As understood from the above described, according to the illustrated embodiments, the switch assembly 9 is in the second state when the transistor 15 of the switch assembly 9 is in the closed state. Electrical pulses from the generator 7 can be drawn into the boost circuit 8 to the low potential point p1 via the transistor 15 and the resistor r1 when the switch assembly 9 is in the second state, i.e., when the transistor 15 is in the closed state. Correspondingly, electrical pulses from the generator 7 are blocked from being drawn into the boost circuit 8 by the transistor 15 of the switch assembly 9 when the switch assembly 9 is in the second state, i.e., when the transistor 15 is in the closed state.

[0084] The boost control arrangement 17 as referred to herein may comprise a number of components for performing the above mentioned function. Such a number of components may for example comprise one or more switches, one or more transistors, one or more resistors, one or more processing units, or the like. Likewise, the boost circuit 8 is shown in simplified form in Fig. 3 and may comprise a number of further components for performing the above mentioned function. Such a number of components may for example comprise one or more switches, one or more transistors, one or more resistors, one or more processing units, or the like.

[0085] As understood from the above described, the concept according to some embodiments of the present disclosure may be implemented as a method of controlling an ignition system 1 of an internal combustion engine 2, wherein the ignition system 1 configured to generate an ignition current to an ignition device 13 of the internal combustion engine 2, wherein the ignition system 1 comprises a supply line 4, an ignition coil 5, a charge capacitor C connected to the supply line 4 and to the ignition coil 5, a generator 7 configured to generate an alternating current in the supply line 4 to charge the charge capacitor C, a boost circuit 8 electrically connected to the supply line 4, wherein the boost circuit 8 comprises a switch assembly 9 controllable between a first and a second state to cause an increase in the voltage in the supply line 4, wherein current is drawn from the supply line 4 into the boost circuit 8 when the switch assembly 9 is controlled to the second state, a thyristor 11 controllable to an open state in which the thyristor 11 allows a discharge of the charge capacitor C through the ignition coil 5 to generate the ignition current to the ignition device 13, and wherein the method comprises the step of:

[0086] - controlling the switch assembly 9 to the second state when the thyristor 11 is controlled to the open state.

[0087] According to such embodiments, the method may comprise the step of:

[0088] - maintaining the switch assembly 9 in the second state until the current through the thyristor 11 reaches below a threshold level.

[0089] Moreover, according to such embodiments, the method may comprise the step of:

[0090] - outputting a trigger signal S to the thyristor 11 and to the switch assembly 9 to control the thyristor 11 to the open state and to control the switch assembly 9 to the second state.

[0091] It will be appreciated that the various embodiments described for the method are all combinable with the control arrangement 21 as described herein. That is, the control arrangement 21 may be configured to perform any one of the method steps of the method described above. One skilled in the art will appreciate that the method of controlling an ignition system 1 of an internal combustion engine 2 may be implemented by programmed instructions. These programmed instructions are typically constituted by a computer program, which, when it is executed in the control arrangement 21 , ensures that the control arrangement 21 carries out the desired control, such as the method steps described above. The computer program is usually part of a computer program product which comprises a suitable digital storage medium on which the computer program is stored.

[0092] The control arrangement 21 may comprise a calculation unit which may take the form of substantially any suitable type of processor circuit or microcomputer, e.g., a circuit for digital signal processing (digital signal processor, DSP), a Central Processing Unit (CPU), a processing unit, a processing circuit, a processor, an Application Specific Integrated Circuit (ASIC), a microprocessor, or other processing logic that may interpret and execute instructions. The herein utilised expression “calculation unit” may represent a processing circuitry comprising a plurality of processing circuits, such as, e.g., any, some or all of the ones mentioned above.

[0093] The control arrangement 21 may further comprise a memory unit, wherein the calculation unit may be connected to the memory unit, which may provide the calculation unit with, for example, stored program code and / or stored data which the calculation unit may need to enable it to do calculations. The calculation unit may also be adapted to store partial or final results of calculations in the memory unit. The memory unit may comprise a physical device utilised to store data or programs, i.e., sequences of instructions, on a temporary or permanent basis. According to some embodiments, the memory unit may comprise integrated circuits comprising silicon-based transistors. The memory unit may comprise e.g., a memory card, a flash memory, a USB memory, a hard disc, or another similar volatile or non-volatile storage unit for storing data such as e.g., ROM (Read-Only Memory), PROM (Programmable Read-Only Memory), EPROM (Erasable PROM), EEPROM (Electrically Erasable PROM), etc. in different embodiments.

[0094] The control arrangement 21 may be connected to components of the combustion engine 2 and / or the handheld power tool 3 for receiving and / or sending input and output signals. These input and output signals may comprise waveforms, pulses, or other attributes which the input signal receiving devices can detect as information and which can be converted to signals processable by the control arrangement 21 . These signals may then be supplied to the calculation unit. One or more output signal sending devices may be arranged to convert calculation results from the calculation unit to output signals for conveying to other parts of the control system of the combustion engine 2 and / or the handheld power tool 3 and / or the component or components for which the signals are intended. Each of the connections to the respective components of the combustion engine 2 and / or the handheld power tool 3 for receiving and sending input and output signals may take the form of a cable.

[0095] In the embodiments illustrated, the ignition system 1 comprises a control arrangement 21 but might alternatively be implemented wholly or partly in two or more control arrangements or two or more control units.

[0096] The computer program product may be provided for instance in the form of a data carrier carrying computer program code for performing at least some of the method steps according to some embodiments when being loaded into one or more calculation units of the control arrangement 21 . The data carrier may hold machine readable data in a non-transitory manner. The computer program product may furthermore be provided as computer program code.

[0097] It is to be understood that the foregoing is illustrative of various example embodiments and that the invention is defined only by the appended independent claims. A person skilled in the art will realize that the example embodiments may be modified, and that different features of the example embodiments may be combined to create embodiments other than those described herein, without departing from the scope of the present invention, as defined by the appended independent claims.

[0098] As used herein, the term "comprising" or "comprises" is open-ended, and includes one or more stated features, elements, steps, components, or functions but does not preclude the presence or addition of one or more other features, elements, steps, components, functions, or groups thereof.

Claims

CLAIMS1. An ignition system (1) configured to generate an ignition current to an ignition device (13) of an internal combustion engine (2), wherein the ignition system (1) comprises:- a supply line (4),- an ignition coil (5),- a charge capacitor (C) connected to the supply line (4) and to the ignition coil (5),- a generator (7) configured to generate an alternating current in the supply line (4) to charge the charge capacitor (C), wherein the generator (7) comprises a winding arrangement (16) electrically connected to the supply line (4),- a boost circuit (8) electrically connected to the supply line (4), wherein the boost circuit (8) comprises a switch assembly (9) controllable between a first and a second state to cause an increase in the voltage in the supply line (4), wherein current is drawn from the supply line (4) into the boost circuit (8) when the switch assembly (9) is controlled to the second state,- a thyristor (11 ) controllable to an open state in which the thyristor (11 ) allows a discharge of the charge capacitor (C) through the ignition coil (5) to generate the ignition current to the ignition device (13), and- a control arrangement (21 ) configured to control the switch assembly (9) to the second state when the thyristor (11) is controlled to the open state.

2. The ignition system (1) according to claim 1 , wherein the control arrangement (21) is configured to maintain the switch assembly (9) in the second state until the current through the thyristor (11) reaches below a threshold level.

3. The ignition system (1) according to claim 1 or 2, wherein the control arrangement (21) is configured to output a trigger signal (S) to the thyristor (11) and to the switch assembly (9) to control the thyristor (11) to the open state and to control the switch assembly (9) to the second state.

4. The ignition system (1) according to claim 3, wherein the switch assembly (9) is configured to remain in the second state for the duration of the trigger signal (S).

5. The ignition system (1) according to claim 4, wherein the duration of the trigger signal (S) is set to a time period that is equal to or greater than the time needed for discharging the charge capacitor (C) through the ignition coil (5).

6. The ignition system (1) according to any one of the preceding claims, wherein the second state of the switch assembly (9) constitutes a state in which the switch assembly (9) electrically connects the supply line (4) to a low potential point (g1 ).

7. The ignition system (1) according to any one of the preceding claims, wherein the first state of the switch assembly (9) constitutes a state in which the switch assembly (9) electrically disconnects the supply line (4) from a low potential point (g1).

8. The ignition system (1) according to any one of the preceding claims, wherein the switch assembly (9) comprises a transistor (15).

9. The ignition system (1) according to any one of the preceding claims, wherein the generator (7) comprises a number of magnets (ml , m2) and the winding arrangement (16) arranged such that a relative movement is obtained between the magnets (ml , m2) and the winding arrangement (16) upon rotation of a crankshaft of the internal combustion engine (2).

10. An internal combustion engine (2) comprising an ignition device (13) and an ignition system (1) according to any one of the preceding claims, wherein the ignition system (1) is configured to generate an ignition current to the ignition device (13).

11. The internal combustion engine (2) according to claim 10, wherein the ignition device (13) is a spark plug.

12. The internal combustion engine (2) according to claim 10 or 11 , wherein the internal combustion engine (2) is a single-cylinder two-stroke internal combustion engine.

13. A handheld power tool (3) comprising an internal combustion engine (2) according to any one of the claims 10 - 12.

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