Method for limiting rotational speed of engine of hand-held power tool, control device and hand-held power tool

Abstract

A method (100) of limiting a rotational speed of a crankshaft (3) of an engine (10) of a hand-held power tool (1). The engine (10) comprises an ignition device (7), an intake system (9), a throttle valve (11) located in the intake system (9), and an electric actuator device (13) configured to move the throttle valve (11) between an open position and a closed position. The method (100) comprises the steps of: delaying (110) the ignition timing of the ignition device (7) from an initial ignition timing to a delayed ignition timing when the rotational speed of the crankshaft (3) reaches above an upper threshold speed; and controlling (120) the electric actuator device (13) to move the throttle valve (11) towards the closed position. The present disclosure also relates to a control device (21) and a hand-held power tool (1).

Description

Technical Field

[0001] The present disclosure relates to a method for limiting the rotational speed of a crankshaft of an internal combustion engine of a handheld power tool. The present disclosure also relates to a control device configured to limit the rotational speed of a crankshaft of an internal combustion engine of a handheld power tool, and a handheld power tool including an internal combustion engine. Background Art

[0002] Internal combustion engines (such as four-stroke internal combustion engines and two-stroke internal combustion engines) are used in some handheld power tools to provide power for the tools of the handheld power tools. Typical examples of such handheld power tools are chain saws, power cutters, hedge trimmers, leaf blowers, multi-tools, etc.

[0003] An internal combustion engine for a handheld power tool generally includes a cylinder, a piston disposed in the cylinder, a crankshaft, and a connecting rod connecting the piston to the crankshaft so that the piston reciprocates in the cylinder as the crankshaft rotates.

[0004] The highest position of the piston in the cylinder is typically referred to as top dead center, TDC, and the lowest position of the piston in the cylinder is typically referred to as bottom dead center, BDC.

[0005] Furthermore, Otto-type two-stroke and four-stroke engines include an ignition device (such as a spark plug) configured to ignite the air / fuel mixture in the cylinder. The air / fuel mixture is typically ignited when the piston is in the region of top dead center (TDC), such as several crankshaft angles before or after TDC, depending on engine operating conditions. However, in most engines and under most operating conditions, the air / fuel mixture is ignited several crankshaft angles before TDC to optimize the engine's fuel efficiency and power output.

[0006] A two-stroke engine is a type of internal combustion engine that completes the power cycle via two piston strokes during just one crankshaft rotation. Compared to a four-stroke engine, a two-stroke engine has significantly fewer moving parts, allowing it to be more compact and significantly lighter. Consequently, two-stroke gasoline engines are often used in applications where mechanical simplicity, lightweight design, and a high power-to-weight ratio are key considerations.

[0007] Most small two-stroke engines are crankcase-scavenged, meaning they use the area beneath the piston as an air pump to build pressure in the crankcase during the piston's power stroke. Typically, a crankcase-scavenged two-stroke engine includes an intake port connected to the crankcase, where air or an air / fuel mixture is drawn into the crankcase as the piston moves toward top dead center. Traditionally, two-stroke engines have been equipped with a carburetor located at the intake port to supply the crankcase with an air / fuel mixture.

[0008] During the power stroke of a two-stroke engine, the increased pressure and temperature in the cylinder caused by the combustion of fuel are partially converted into mechanical work supplied to the engine crankshaft. At the same time, the pressure in the crankcase increases as the piston moves towards bottom dead center.

[0009] When the piston reaches a first position relative to the cylinder during its movement toward bottom dead center, an exhaust port arranged in the cylinder wall opens to allow exhaust gases to flow out of the cylinder. The piston continues to move toward bottom dead center, and when the piston reaches a second position below the first position, an intake port arranged in the cylinder wall opens. The intake port is fluidly connected to the crankcase via a scavenging passage. The overpressure in the crankcase forces the air / fuel mixture in the crankcase to flow into the cylinder through the intake port. Therefore, as can be understood from the above, in this type of engine, the exhaust port and the intake port in the cylinder open simultaneously during the engine's scavenging phase (i.e., when the piston is in the region of bottom dead center).

[0010] A four-stroke internal combustion engine completes four independent strokes within two crankshaft rotations. A stroke is the full travel of the piston along the cylinder in both directions. The strokes occur in the following order: intake stroke, compression stroke, expansion stroke, and exhaust stroke. A four-stroke internal combustion engine typically includes one or more inlet and outlet valves and one or more fuel supply devices. The one or more inlet and outlet valves are controlled by corresponding valve control devices, which typically include one or more camshafts rotatably connected to the engine crankshaft via a belt, chain, gears, or similar components.

[0011] During the operation of a conventional four-stroke internal combustion engine, the inlet valve control device controls the inlet valve of the cylinder to an open position during the intake stroke of the piston in the cylinder to allow air or a mixture of air and fuel to enter the cylinder. During the compression stroke, all valves should be closed to allow the air or a mixture of air and fuel to be compressed in the cylinder. When the engine is in the power generation position, the fuel in the cylinder is usually ignited, for example by a spark plug, near the end of the compression stroke. The combustion of the fuel in the cylinder significantly increases the pressure and temperature in the cylinder. The combustion of the fuel usually continues for a considerable part of the subsequent expansion stroke. The pressure and temperature increased in the cylinder by combustion are partially converted into mechanical work supplied to the crankshaft during the expansion stroke.

[0012] Obviously, all valves should remain closed during the expansion stroke to allow the increased pressure and temperature to be converted into mechanical work. The expansion stroke is also often referred to as the combustion stroke because the majority of combustion typically occurs during the expansion stroke. During the subsequent exhaust stroke, the exhaust valve control device controls the cylinder's exhaust valve to an open position to allow exhaust gases to be discharged from the cylinder into the engine's exhaust system.

[0013] The internal combustion engines of handheld power tools are typically optimized to operate at relatively high speeds. One reason is that higher speeds allow for a higher power output from the engine for a given engine displacement and weight.

[0014] The weight of the engine of the preferred handheld power tool is lighter, because the weight of the power tool can bring a burden to the user's hands, arms and back.In addition, lighter weight can allow the user to operate the handheld power tool in a safer manner.

[0015] In order to ensure the durability of the engine, the rotation speed of the crankshaft of the internal combustion engine must generally be limited. This limitation generally begins when the rotation speed of the crankshaft reaches an upper threshold speed.

[0016] The internal combustion engine of a handheld power tool is typically optimized for rapid acceleration. Furthermore, during a work session using the handheld power tool, the engine may operate at an operating speed close to an upper threshold speed. When the user removes the tool from the object being worked on, the drag torque faced by the engine is rapidly dissipated, and in such circumstances, the engine speed often rapidly increases above the upper threshold speed.

[0017] The combination of the facts that handheld power tool engines are typically optimized to operate at higher speeds, are optimized for rapid acceleration, and that drag torque can be dissipated quickly, means that the engine's upper threshold speed may be exceeded multiple times during a work session using the handheld power tool.

[0018] A common approach to limiting the crankshaft speed of a handheld power tool's engine is to control the engine's ignition mechanism to skip ignition of the air / fuel mixture in the cylinder when the crankshaft speed reaches an upper threshold speed. This solution is a simple and cost-effective way to limit the crankshaft's speed. However, it also comes with several problems and drawbacks. One issue is that it causes the engine to produce unnecessary fuel consumption and emissions. This is because the fuel added to the cylinder due to the skip fire event is not burned, resulting in a large amount of unburned fuel being supplied to the engine's exhaust system.

[0019] Such a large amount of unburned fuel increases the fuel consumption of the engine and has a negative impact on the environment and people and animals near the handheld power tool.In addition, a large amount of unburned fuel may also cause problems when using the exhaust after-treatment system (such as a catalytic converter) on the engine.

[0020] Another issue is that when using the aforementioned solution for limiting the crankshaft's rotational speed, engine durability may be compromised. This arises from the fact that excessively large and violent combustion events may occur when ignition of the air / fuel mixture is restored after a skipped-fire event. Such excessively large and violent combustion events may stress and potentially damage one or more engine components (such as the piston, piston rings, connecting rods, crankshaft, and engine cylinders).

[0021] Another way to limit the rotational speed of the crankshaft of the engine of a handheld power tool is to retard the ignition timing when the rotational speed of the crankshaft reaches an upper threshold speed. Compared to a solution that skips ignition events, such a solution can reduce the emission level of the engine because at least the combustion of the air / fuel mixture in the cylinder of the engine will be delayed, thereby reducing the unburned fuel discharged from the engine. However, such a solution for limiting the rotational speed is slower than a solution that skips ignition events. This is because the delayed combustion event of the air / fuel mixture in the cylinder increases the positive crankshaft torque of the engine's crankshaft. In addition, the delayed combustion event caused by the delay of the ignition timing causes a significant increase in exhaust temperature, which may damage engine components.

[0022] Yet another way to limit the speed of the engine's crankshaft is to control the engine's throttle valve to a closed position, thereby restricting airflow into the engine and, thereby, the speed of the engine's crankshaft. Compared to the solutions described above, this solution can reduce the engine's fuel consumption and emissions. Furthermore, this solution of limiting the crankshaft's speed can improve engine durability by avoiding the problems of high exhaust gas temperatures and excessively large and intense combustion events, as compared to solutions of the type described above.

[0023] However, in solutions utilizing throttle valve closure, the throttle valve must be controlled independently of user input to ensure engine durability. Therefore, the throttle valve position must be controlled by some automatic device (such as an electric actuator) that moves the throttle valve to the closed position when the crankshaft speed reaches an upper threshold speed.

[0024] Furthermore, in such solutions, the electric actuator must be able to quickly move the throttle valve to the closed position in order to quickly limit the crankshaft speed. Specifically, to quickly limit the crankshaft speed and ensure engine durability, the electric actuator must be able to move the throttle valve from the open position to the closed position within a few milliseconds. Furthermore, due to the air flow through the throttle valve when the crankshaft speed is within the upper threshold speed range, the valve faces a significant resistive torque during movement toward the closed position.

[0025] Therefore, in the solution of using the throttle valve to close, the electric actuator device must have a fast response and be strong enough to quickly move the throttle valve to the closed position, which requires a large and bulky electric actuator device. In the case where mechanical simplicity and the weight of the handheld power tool are the main considerations, such a large and bulky electric actuator device is generally not suitable for use on a handheld power tool. Summary of the Invention

[0026] It is an object of the present invention to overcome or at least partially alleviate at least some of the above problems and disadvantages.

[0027] According to a first aspect of the present invention, the object is achieved by a method for limiting the rotational speed of a crankshaft of an internal combustion engine of a handheld power tool. The internal combustion engine comprises a crankshaft, a cylinder, a piston arranged in the cylinder and connected to the crankshaft, an ignition device configured to ignite an air / fuel mixture in the cylinder, an intake system for directing air to the cylinder, a throttle valve arranged in the intake system, and an electric actuator device configured to move the throttle valve between an open position and a closed position. The throttle valve is configured to restrict the flow of air through the intake system when positioned in the closed position. The method comprises the following steps: when the rotational speed of the crankshaft reaches a speed above an upper threshold value:

[0028] - retarding the ignition timing of the ignition device from the initial ignition timing to the retarded ignition timing; and

[0029] - Controlling the electric actuator device to move the throttle valve towards the closed position.

[0030] In this manner, the method provides for rapidly limiting the rotational speed of the crankshaft while allowing the use of a small electrical actuator device to move the throttle valve toward a closed position.

[0031] That is, because this method includes a combination of retarding the ignition timing and controlling the electric actuator device to move the throttle valve toward the closed position, a smaller, less expensive, and lighter electric actuator device can be used to move the throttle valve toward the closed position, compared to a solution that uses closing the throttle valve as the sole means for limiting the rotational speed of the crankshaft. This is because the rotational speed of the crankshaft can be limited during the period required to move the throttle valve to the closed position, thereby allowing the use of a less rapid, powerful, and bulky electric actuator device.

[0032] Likewise, because this method includes a combination of retarding the ignition timing and controlling the electric actuator device to move the throttle valve toward the closed position, the period of time required for operation with the retarded ignition timing can be shortened compared to a solution that uses retarded ignition timing as the sole means for limiting the rotational speed of the crankshaft. Since the period of time required for operation with the retarded ignition timing can be shortened, prolonged periods of excessively high exhaust temperatures and the resulting damage to the engine can be avoided.

[0033] Thus, a robust and reliable method is provided which is able to quickly limit the rotational speed of the crankshaft while avoiding damage to components of the engine.

[0034] Furthermore, since the method includes the steps of controlling the electric actuator device and retarding the ignition timing, a method is provided that can quickly limit the rotational speed of the crankshaft without unnecessarily emitting unburned fuel. Furthermore, a method is provided that allows the use of an exhaust aftertreatment device (such as a catalytic converter) to treat engine exhaust gas.

[0035] Furthermore, since the method includes the step of controlling the electric actuator device to move the throttle valve toward the closed position, a method capable of reducing fuel consumption of the engine is provided.

[0036] Therefore, a method is provided that overcomes or at least alleviates at least some of the above problems and disadvantages.

[0037] Optionally, the step of retarding the ignition timing of the ignition device includes the following steps:

[0038] - When the rotation speed of the crankshaft is higher than an upper threshold speed, the ignition timing of the ignition device is kept controlled so that the ignition timing is the retarded ignition timing.

[0039] Thereby, can guarantee that the rotational speed of the crankshaft is limited during at least most of the time required for the throttle valve to be moved to the closed position.In other words, can guarantee that the rotational speed of the crankshaft is limited quickly, while allowing the use of small electric actuator device to move the throttle valve.

[0040] Optionally, the step of retarding the ignition timing of the ignition device includes the following steps:

[0041] - Controlling the ignition timing of the ignition device so that when the speed exceeds an upper threshold speed, the ignition timing is retarded as the speed increases.

[0042] Thereby, situation-based control is achieved which is able to limit the rotational speed of the crankshaft in a quick and effective manner under a wider range of operating conditions of the handheld power tool.

[0043] Optionally, the step of retarding the ignition timing of the ignition device includes the following steps:

[0044] - Controlling the ignition timing of the ignition device so that when the rotation speed exceeds an upper threshold speed, the ignition timing is advanced as the rotation speed decreases.

[0045] Thus, a situation-based control is achieved, which is able to limit the rotational speed of the crankshaft in a fast and effective manner under a wide range of operating conditions of the handheld power tool while avoiding the prolonged generation of hot exhaust gases. Thus, in this way, damage to engine components can be further avoided.

[0046] Optionally, the method comprises the following steps:

[0047] - When the rotational speed of the crankshaft drops below an upper threshold speed, the ignition timing is advanced to the initial ignition timing.

[0048] Thus, a situation-based control is achieved, which can limit the rotational speed of the crankshaft in a fast and effective manner while avoiding the long-term generation of hot exhaust gases. Therefore, in this way, damage to engine components can be further avoided.

[0049] Optionally, the method comprises the following steps:

[0050] - When the rotational speed of the crankshaft drops below an upper threshold speed, controlling the electric actuator device to move the throttle valve to an open position.

[0051] Thereby, a situation-based control is achieved, ie, the rotational speed of the crankshaft can be limited in a fast and effective manner while avoiding excessive limitation of the rotational speed of the crankshaft.

[0052] According to a second aspect of the present invention, the object is achieved by a control device configured to limit the rotational speed of a crankshaft of an internal combustion engine of a handheld power tool, wherein the internal combustion engine comprises a crankshaft, a cylinder, a piston arranged in the cylinder and connected to the crankshaft, an ignition device configured to ignite an air / fuel mixture in the cylinder, an intake system for directing air to the cylinder, a throttle valve arranged in the intake system, and an electric actuator device configured to move the throttle valve between an open position and a closed position. The throttle valve is configured to restrict the flow of air through the intake system when positioned in the closed position. The control device is configured to, when the rotational speed of the crankshaft reaches a speed above an upper threshold value:

[0053] - retarding the ignition timing of the ignition device from the initial ignition timing to the retarded ignition timing; and

[0054] - Controlling the electric actuator device to move the throttle valve towards the closed position.

[0055] In this way, a control device is provided which has the conditions for achieving rapid limitation of the rotational speed of the crankshaft while allowing the use of a small electric actuator device for moving the throttle valve towards the closed position.

[0056] That is, because the control device is configured to retard the ignition timing and control the electric actuator device to move the throttle valve toward the closed position, a smaller, less expensive, and lighter electric actuator device can be used to move the throttle valve toward the closed position, compared to a solution that uses closing the throttle valve as the sole means for limiting the rotational speed of the crankshaft. This is because the rotational speed of the crankshaft can be limited during the period required to move the throttle valve to the closed position, thereby allowing the use of a less rapid, powerful, and bulky electric actuator device.

[0057] Likewise, because the control device is configured to control the electric actuator device to move the throttle valve toward the closed position, the period of time required for operation with retarded ignition timing can be shortened compared to a solution that uses retarded ignition timing as the sole means for limiting the rotational speed of the crankshaft. Since the period of time required for operation with retarded ignition timing can be shortened, prolonged periods of excessively high exhaust temperatures and the resulting damage to the engine can be avoided.

[0058] Thus, a control device is provided which is able to quickly limit the rotational speed of the crankshaft in a robust and reliable manner while avoiding damage to components of the engine.

[0059] Furthermore, since the control device is configured to retard the ignition timing and control the electric actuator device to move the throttle valve toward the closed position, a control device is provided that can quickly limit the rotational speed of the crankshaft without unnecessarily discharging unburned fuel. As a further result, a control device is provided that allows the use of an exhaust aftertreatment device (such as a catalytic converter) to treat engine exhaust gas.

[0060] Furthermore, since the control apparatus is configured to retard the ignition timing and control the electric actuator apparatus to move the throttle valve toward the closed position, there is provided a control apparatus capable of reducing fuel consumption of the engine.

[0061] Therefore, a control device is provided which overcomes or at least alleviates at least some of the above problems and disadvantages.

[0062] It will be understood that the various embodiments described for the method can be combined with the control device described herein. That is, the control device according to the second aspect of the invention can be configured to perform any of the method steps of the method according to the first aspect of the invention.

[0063] According to a third aspect of the present invention, the object is achieved by a handheld power tool, the handheld power tool comprising an internal combustion engine for powering a tool of the handheld power tool, wherein the internal combustion engine comprises a crankshaft, a cylinder, a piston arranged in the cylinder and connected to the crankshaft, an ignition device configured to ignite an air / fuel mixture in the cylinder, an intake system for directing air to the cylinder, a throttle valve arranged in the intake system, and an electric actuator device configured to move the throttle valve between an open position and a closed position. The throttle valve is configured to restrict the flow of air through the intake system when positioned in the closed position. The handheld power tool comprises a control device configured to, when a rotational speed of the crankshaft reaches a speed above an upper threshold value:

[0064] - retarding the ignition timing of the ignition device from the initial ignition timing to the retarded ignition timing; and

[0065] - Controlling the electric actuator device to move the throttle valve towards the closed position.

[0066] In this way, a handheld power tool is provided which has provisions for achieving rapid limitation of the rotational speed of the crankshaft while allowing the use of a small electric actuator device to move the throttle valve towards a closed position.

[0067] In other words, a handheld power tool is provided which can use a smaller, less expensive and more lightweight electric actuator device to move the throttle valve towards the closed position, while ensuring rapid limitation of the crankshaft rotational speed and avoiding excessively high exhaust gas temperatures for extended periods of time, compared to a solution that uses closing the throttle valve as the only means for limiting the rotational speed of the crankshaft.

[0068] Thus, a handheld power tool is provided that is capable of quickly limiting the rotational speed of the crankshaft in a robust and reliable manner while avoiding damage to components of the engine and avoiding unnecessary emissions of unburned fuel.

[0069] Furthermore, a handheld power tool is provided that allows the use of an exhaust aftertreatment device, such as a catalytic converter, to treat exhaust gases from the handheld power tool's engine.

[0070] Furthermore, since the control device of the handheld power tool is configured to retard the ignition timing and control the electric actuator device to move the throttle valve toward the closed position, a handheld power tool having conditions for reducing fuel consumption is provided.

[0071] Therefore, a handheld power tool is provided that overcomes or at least alleviates at least some of the above problems and disadvantages.

[0072] Optionally, the electric actuator device comprises an electric motor.Thereby, a simple and cost-effective electric actuator device is provided, which is capable of moving the throttle valve towards the closed position when the rotational speed of the crankshaft reaches above an upper threshold speed.

[0073] Optionally, the motor is a stepper motor. Thus, the need for a sensor to monitor the current position of the throttle valve is avoided.

[0074] Optionally, the electric actuator device includes a transmission, and wherein the motor includes an output shaft connected to the throttle valve via the transmission. This provides for the use of a small and lightweight motor that can generate the torque required to move the throttle valve to the closed position.

[0075] Optionally, the transmission provides a positive transmission ratio between the output shaft of the motor and the throttle valve, thereby allowing the use of a small and lightweight motor that can generate the torque required to move the throttle valve to the closed position.

[0076] Optionally, the transmission includes a planetary gear set. This allows for a simple, efficient, and compact transmission with a relatively high transmission ratio between the output shaft of the electric motor and the throttle valve. Furthermore, it allows for the planetary gear set to be arranged coaxially with respect to the output shaft of the electric motor and / or coaxially with respect to the shaft of the throttle valve, thereby achieving a compact electric actuator device.

[0077] Optionally, the internal combustion engine includes a crankcase at least partially surrounding a crankshaft, wherein the intake system includes an intake duct connected to the crankcase, and wherein the throttle valve is arranged in the intake duct, thereby effectively restricting air flow into the engine when the throttle valve is controlled toward a closed position.

[0078] Optionally, the internal combustion engine is a crankcase-scavenged two-stroke internal combustion engine, and wherein the air intake system is configured to at least partially direct air to the cylinders via the crankcase of the internal combustion engine. Thus, provision is made for a handheld power tool comprising a mechanically simple, lightweight engine having a high power-to-weight ratio.

[0079] Optionally, the internal combustion engine includes a main throttle valve disposed in the intake system, wherein the handheld power tool includes a first handle and a throttle actuator disposed at the first handle, and wherein the throttle actuator is operatively connected to the main throttle valve. Accordingly, when the rotational speed of the crankshaft reaches a speed above an upper threshold, the throttle valve can be moved toward a closed position in a manner independent of the position and control of the main throttle valve. In this manner, the rotational speed of the crankshaft can be limited in a more reliable manner.

[0080] Furthermore, a hand-held power tool is provided, wherein the power of the engine can be regulated in a simple, efficient and reliable manner, wherein the control of the position of the main throttle valve is independent of the function and operation of the electric actuator device.

[0081] Optionally, the throttle actuator is operatively connected to the main throttle valve via a mechanical connection. Thus, a simple, efficient and reliable connection is provided between the throttle actuator and the main throttle valve, which provides conditions for simple, efficient and reliable control of the power of the engine.

[0082] Furthermore, compared to a solution in which the main throttle valve is controlled by an electric actuator assembly, a more lightweight solution for controlling the power of the engine can be provided. Furthermore, compared to a solution in which the engine includes a throttle valve for controlling the power of the engine and for limiting the rotational speed of the engine crankshaft according to the features of the control device and method of the embodiments herein, a more lightweight solution for controlling the power of the engine can be provided.

[0083] Specifically, to be able to control engine power according to the aforementioned solution, the electric actuator assembly needs to be relatively tall and strong, which necessitates the use of a relatively large and heavy electric actuator assembly. Furthermore, such solutions typically require a position sensor to sense the position of the throttle actuator, and possibly also the position of the battery, to enable a position reading of the throttle actuator before and during engine start-up. Such components increase the weight and complexity of the handheld power tool.

[0084] Thus, since the internal combustion engine comprises a main throttle valve, and since the throttle actuator is operatively connected to the main throttle valve via a mechanical connection, a low-weight and uncomplicated solution may be provided for controlling the power of the engine.

[0085] Optionally, the internal combustion engine includes an exhaust system configured to direct exhaust gas from the cylinders to the surrounding environment, and the exhaust system includes a catalytic converter. This provides a more environmentally friendly handheld power tool that produces lower emissions of unburned hydrocarbons. Furthermore, because the control device is configured to limit the rotational speed of the crankshaft by retarding ignition timing and controlling the electric actuator device to move the throttle valve toward a closed position, the functionality and durability of the catalytic converter can be ensured.

[0086] Optionally, the handheld power tool is a chainsaw or a power cutter. Thus, a chainsaw or a power cutter having at least some of the above advantages is provided.

[0087] Other features of, and advantages with, the present invention will become apparent upon careful reading of the appended claims and the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0088] Aspects of the present invention, including specific features and advantages thereof, will be readily understood through the exemplary embodiments discussed in the following detailed description and the accompanying drawings, in which:

[0089] Figure 1 shows a first side view of a handheld power tool according to some embodiments of the present disclosure;

[0090] Figure 2 Schematically shows Figure 1 A cross section of an internal combustion engine of a hand-held power tool is shown;

[0091] Figure 3 Schematically shows Figure 2 a cross-section of an internal combustion engine shown in which a throttle valve has been moved from an open position to a closed position by an electric actuator device; and

[0092] Figure 4 A method of limiting the rotational speed of a crankshaft of an internal combustion engine of a handheld power tool is schematically illustrated. DETAILED DESCRIPTION

[0093] The various aspects of the present invention will now be described in more detail. Throughout the specification, like reference numerals refer to like elements. For the sake of brevity and / or clarity, well-known functions or configurations will not necessarily be described in detail.

[0094] Figure 1 A first side view of a handheld power tool 1 according to some embodiments of the present disclosure is shown. The handheld power tool 1 comprises a tool 30 and an internal combustion engine 10 configured to power the tool 30. According to the illustrated embodiment, the handheld power tool 1 is a chain saw comprising the tool 30 in the form of a cutting chain movably arranged around a guide bar 32. Figure 1 In FIG, the cutting chain and the guide rod 32 are schematically shown.

[0095] The internal combustion engine 10 is configured to rotate the cutting chain about the guide rod 32 during operation of the handheld power tool 1. According to further embodiments, the handheld power tool 1 referred to herein may be another type of handheld power tool 1 besides a chain saw, such as, for example, a power cutter, a circular saw, a trimmer, a hedge trimmer, a multi-tool, or the like. Obviously, according to such embodiments, the handheld power tool 1 may include other types of tools 30 besides a cutting chain, such as a circular saw blade, a trimmer head, a hedge trimmer cutting assembly, or the like. The handheld power tool 1 includes a fuel tank 13 configured to store fuel supplied to the internal combustion engine 10 during operation. The internal combustion engine 10 of the handheld power tool 20 may be configured to operate using gasoline (also known as petroleum), alcohol, a similar volatile fuel, or a combination thereof.

[0096] The handheld power tool 1 includes a first handle 33 and a second handle 34. The second handle 34 is separate from the first handle 33 and is arranged at a distance from the first handle 33. The handheld power tool 1 is configured to be supported via each of the first handle 33 and the second handle 34 during operation of the handheld power tool 1. In other words, the handheld power tool 1 is configured to be supported by both hands of the user during operation of the handheld power tool 1, that is, configured to be supported by one hand grasping the first handle 33 and the other hand grasping the second handle 34.

[0097] According to the illustrated embodiment, the first handle 33 is a rear handle located at the rear portion of the handheld power tool 1, and the second handle 34 is a so-called front handle. According to the illustrated embodiment, the second handle 34 is located closer to the tool 30 of the handheld power tool 1 than to the first handle 33. Furthermore, the second handle 34 is positioned between the tool 30 of the handheld power tool 1 and the first handle 33 of the handheld power tool 1. According to the illustrated embodiment, the second handle 34 is formed from an elongated, curved body, allowing the user to conveniently grip the second handle 34 from a variety of orientations. This allows the user to conveniently and safely operate the handheld power tool 1 in different orientations relative to the gravitational field.

[0098] The handheld power tool 1 comprises a throttle actuator 35 arranged at the first handle 33. The throttle actuator 35 may be used to control the power output of the internal combustion engine 10, as further explained herein.

[0099] Figure 2 Schematically shows Figure 1 The cross section of the internal combustion engine 10 of the handheld power tool 1 is shown. For the sake of brevity and clarity, the internal combustion engine 10 is also referred to as a "combustion engine" or simply as an "engine". Figure 1 and Figure 2 , unless otherwise indicated.

[0100] The combustion engine 10 includes a crankshaft 3, a cylinder 2, and a piston 5 arranged in the cylinder 2. The combustion engine 10 includes a connecting rod 22 that connects the piston 5 to the crankshaft 3 so that the piston 5 reciprocates between the bottom dead center and the top dead center in the cylinder 2 when the crankshaft 3 rotates. In other words, the piston 5 is connected to the crankshaft 3 via the connecting rod 22. Figure 2 In FIG, the piston 5 is shown positioned between top dead center and bottom dead center.

[0101] According to the illustrated embodiment, the internal combustion engine 10 of the handheld power tool 1 is a small crankcase-scavenged two-stroke internal combustion engine. According to another embodiment, the internal combustion engine 10 referred to herein may be a four-stroke internal combustion engine, such as a small four-stroke internal combustion engine. In this context, the term "small" may encompass an engine 10 having a displacement of less than 250 cubic centimeters.

[0102] The internal combustion engine 10 comprises a crankcase 6 which encloses a crankcase volume V. The crankcase 6 encloses a portion of the crankshaft 3 . In other words, at least a portion of the crankshaft 3 is arranged inside the crankcase volume V of the crankcase 6 .

[0103] The piston 5 includes a first face that forms a bounding surface of the combustion chamber 4 and a second face that forms a bounding surface of the crankcase volume V. Thus, the first face of the piston 5 faces the combustion chamber 4, and the second face of the piston 5 faces the crankcase 6 of the engine 10. As the piston 5 moves in a direction toward bottom dead center, the size of the crankcase volume V decreases. Thus, as the piston 5 moves toward bottom dead center, the pressure inside the crankcase volume V of the crankcase 6 can increase, as further described herein.

[0104] Furthermore, because the second face of the piston 5 forms a delimiting surface of the crankcase volume V of the crankcase 6, the size of the crankcase volume V is smallest when the piston 5 is at the bottom dead center, and the size of the crankcase volume V is largest when the piston 5 is at the top dead center. Therefore, the piston 5 of the engine 10 according to the embodiments herein functions as a scavenging pump member, i.e., a pump member for replacing combustion gas inside the combustion chamber 4 of the engine 10, as further described herein.

[0105] Engine 10 includes an intake system 9 configured to direct air to cylinder 2 during operation of engine 10. According to the illustrated embodiment, intake system 9 includes an intake duct 9' connected to crankcase 6. Furthermore, intake system 9 includes an air filter unit 19 connected to intake duct 9'. Thus, according to the illustrated embodiment, intake system 9 is configured to direct air to cylinder 2 via crankcase 6 of internal combustion engine 10. Cylinder 2 of engine 10 includes an intake port 42. When the piston is in the region of top dead center, intake port 42 fluidically connects crankcase 6 to intake duct 9'.

[0106] The engine 10 comprises a main throttle valve 31 arranged in an intake duct 9 ′ of the intake system 9 . Figure 1 The throttle actuator 35 of the handheld power tool 1 is shown to be operatively connected to the main throttle valve 31. In more detail, according to these embodiments, the throttle actuator 35 is connected via Figure 2A mechanical connection 37 schematically indicated in FIG is operatively connected to the main throttle valve 31. Thereby, the amount of air drawn into the cylinders 2 of the engine 10, and therefore the power produced by the engine 10, can be adjusted in a simple and reliable manner via the throttle actuator 35, as further explained herein.

[0107] According to the illustrated embodiment, an intake port 42 is provided in the wall of the cylinder 2, and as the piston 5 moves in the direction toward bottom dead center, the pressure in the crankcase volume V of the crankcase 6 increases because the intake port 42 is closed by the covering surface of the piston 5. However, according to other embodiments, the intake duct 9' may be directly connected to the crankcase 6, and the engine 10 may not have the intake port 42 provided in the wall of the cylinder 2. According to such an embodiment, as well as other embodiments herein, the engine 10 may include one or more one-way valves (such as reed valves) arranged to prevent gas from flowing from the crankcase volume V of the crankcase 6 to the intake duct 9' when the piston 5 moves toward bottom dead center.

[0108] like Figure 2 As can be seen in FIG, engine 10 includes an intake port 45 provided in the wall of cylinder 2. Furthermore, engine 10 includes a scavenging channel 24 fluidly connecting the crankcase volume V of crankcase 6 with intake port 45. According to the illustrated embodiment, intake port 45 is open when piston 5 is in the region of bottom dead center. More specifically, according to the illustrated embodiment, intake port 45 is closed by the covering surface of piston 5 when the covering surface of piston 5 is above the upper edge of intake port 45. When the covering surface of piston 5 moves toward bottom dead center and reaches a position where the covering surface of piston 5 is below the upper edge of intake port 45, intake port 45 becomes open, i.e., uncovered. As used herein, the term "upper edge" means that the upper edge of intake port 45 is the uppermost edge if the engine is oriented relative to the local gravitational field such that the direction from top dead center toward bottom dead center coincides with the local gravity vector. Obviously, engine 10 may be configured to operate in other orientations relative to the local gravitational field.

[0109] As understood from the above, when the air intake port 45 is opened, gas (such as air or air / fuel mixture) can be introduced into the scavenging passage 24 and the air intake port 45 ( Figure 2 ) is delivered from the crankcase volume V of the crankcase 6 to the combustion chamber 4. The engine 10 may include more than one air intake port 45 and more than one scavenging air passage 24.

[0110] The engine 10 includes an exhaust system 41 configured to direct exhaust gases from the cylinders 2 to the surrounding environment. According to the illustrated embodiment, the exhaust system 41 includes a catalytic converter 43. Figure 2 , the engine 10 includes an exhaust port 38 disposed in the wall of the cylinder 2. The exhaust port 38 is fluidly connected to the exhaust system 41 of the engine 10. The intake port 45 and the exhaust port 38 are configured such that the upper edge of the exhaust port 38 is located above the upper edge of the intake port 45.

[0111] The feature that the upper edge of the exhaust port 38 is located above the upper edge of the air intake port 45 indicates that when the engine 10 is oriented relative to the local gravity field so that the direction from the top dead center toward the bottom dead center coincides with the local gravity vector, the uppermost edge of the exhaust port 38 is located above the uppermost edge of the air intake port 45 as viewed relative to the local gravity vector.

[0112] Therefore, due to these features, when the piston 5 moves from the bottom dead center toward the top dead center, the intake port 45 is completely closed before the exhaust port 38. When each of the intake port 45 and the exhaust port 38 is completely closed, the gas trapped inside the combustion chamber 4 is compressed by the movement of the piston 5 toward the top dead center.

[0113] The engine 10 also includes a fuel supply system. For reasons of brevity and clarity, Figure 2 The fuel supply system is not indicated in FIG. The fuel supply system may include one or more carburetors arranged in the intake system 9 of the engine 10 (such as arranged in the intake duct 9 ′ of the intake system 9 ). Alternatively or in addition, the engine 10 may include one or more of the following: a fuel injector configured to inject fuel into the crankcase volume V of the crankcase 6 , a fuel injector configured to inject fuel into the combustion chamber 4 , a fuel injector configured to inject fuel into the scavenging passage 24 , and the like.

[0114] Therefore, when each of the intake port 45 and the exhaust port 38 is fully closed and the piston 5 moves in a direction toward the top dead center, the fuel added or delivered to the combustion chamber 4 from such a fuel supply system may be compressed together with the air trapped in the combustion chamber 4 .

[0115] The engine 10 also includes an ignition device 7. The ignition device 7 is configured to ignite the air / fuel mixture in the cylinder 2. According to the illustrated embodiment, the ignition device 7 is a spark plug, i.e., an ignition device configured to ignite the air / fuel mixture by generating a spark inside the combustion chamber 4 when supplied with a high voltage. According to other embodiments, the engine 10 may include other types of ignition devices besides a spark plug.

[0116] According to the illustrated embodiment, the engine 10 includes an ignition system 17 configured to control an ignition device 7 to ignite an air / fuel mixture in the combustion chamber 4 based on a rotational position of a crankshaft 3 of the engine 10. According to the illustrated embodiment, the engine 10 includes a sensor device 26, 26' configured to sense a current rotational position of the crankshaft 3, wherein the ignition system 17 is operatively connected to the sensor device 26, 26' and configured to control the ignition device 7 to ignite the air / fuel mixture in the combustion chamber 4 based on the sensed current rotational position of the crankshaft 3.

[0117] During normal operation of the engine 10, when the piston 5 is at a certain crankshaft angle relative to the top dead center during its movement toward the top dead center, the ignition device 7 is controlled to ignite the air / fuel mixture in the combustion chamber 4. During the remaining movement of the piston 5 toward the top dead center, combustion of the air / fuel mixture develops, and the increased pressure and temperature in the combustion chamber 4 due to the combustion forces the piston 5 to move in the direction toward the bottom dead center. This force acting on the piston 5 can be converted into mechanical work supplied to the crankshaft 3 of the engine 10.

[0118] Due to the arrangement of the exhaust port 38 and the intake port 45, when the piston 5 moves in the direction d2 toward the bottom dead center, the exhaust port 38 opens earlier than the intake port 45. As a result, exhaust gas can be discharged from the combustion chamber 4 to the exhaust system 42 before fresh air is delivered into the combustion chamber 4 via the scavenging passage 24 and the intake port 45 by the pumping action achieved by the movement of the piston 5 toward the bottom dead center.

[0119] According to the embodiment herein, the engine 10 includes a throttle valve 11 arranged in the intake system 9. The throttle valve 11 is separate from the main throttle valve 31 and may also be referred to as an auxiliary or additional throttle valve 11. According to the illustrated embodiment, the throttle valve 11 is arranged in the intake duct 9' of the intake system 9. In addition, the engine 10 includes an electric actuator device 13, which is configured to move the throttle valve 11 between an open position and a closed position.

[0120] exist Figure 2 , the throttle valve 11 is shown in an open position. The open position of the throttle valve 11 constitutes a position in which the throttle valve 11 provides no or only slight restriction to air flowing through the intake system 9. The closed position of the throttle valve 11 constitutes a position in which the throttle valve 11 restricts air flow through the intake system 9. As used herein, restricting air flow means partially blocking air flow through the intake system 9.

[0121] Figure 3 Schematically shows Figure 2 The cross section of the internal combustion engine 10 is shown, wherein the throttle valve 11 has been moved from the Figure 2The open position shown is moved to the closed position. Figures 1 to 3 , unless otherwise indicated.

[0122] like Figure 2 and Figure 3 As can be seen in the figure, according to the embodiment shown, the throttle valve 11 is of the butterfly valve type. According to other embodiments, the throttle valve 11 may include other types of valves. According to the embodiment shown, the throttle valve 11 is pivotally arranged around a pivot axis Pa. Figure 2 As can be seen, according to these embodiments, the open position of the throttle valve 11 constitutes a position in which the throttle valve 11 is positioned such that the throttle valve 11 is substantially parallel to the direction of air flow through the intake duct 9' of the intake system 9. Thus, when the throttle valve 11 is positioned in the open position, the throttle valve 11 provides no or only a slight restriction to the air flowing through the intake system 9. Therefore, according to the illustrated embodiments, the "open position" of the throttle valve 11 referred to herein may also be referred to as the "fully open position."

[0123] In addition, if Figure 3 As shown in , according to these embodiments, the closed position of the throttle valve 11 constitutes a position in which the throttle valve 11 is positioned such that the throttle valve 11 is transverse to the direction of the air flow through the intake duct 9 ' of the intake system 9. Thus, the throttle valve 11 restricts (ie partially blocks) the air flow through the intake duct 9 ' of the intake system 9 when positioned in the closed position. Figure 3 As can be seen in FIG, the throttle valve 11 does not completely block the air flow through the intake duct 9 ′ of the intake system 9 when positioned in the closed position. Therefore, according to the illustrated embodiment, the “closed position” of the throttle valve 11 referred to herein may also be referred to as an “at least partially closed position”.

[0124] According to the illustrated embodiment, the electric actuator device 13 includes a motor 23. The motor 23 may be a stepper motor. This eliminates the need for a sensor to monitor the position of the throttle valve. Furthermore, according to the illustrated embodiment, the electric actuator device 13 includes a transmission 25, and the motor 23 includes an output shaft 27 connected to the throttle valve 11 via the transmission 25. According to the illustrated embodiment, the transmission 25 provides a positive gear ratio between the output shaft 27 of the motor 23 and the throttle valve 11. This allows the use of a small motor 23 to move the throttle valve 11 while being able to generate the torque required to move the throttle valve 11 under various operating conditions of the engine 10.

[0125] More specifically, according to the illustrated embodiment, the transmission 25 includes a planetary gear set. The planetary gear set is coaxially arranged with respect to the output shaft 27 of the motor 23 and with respect to the shaft of the throttle valve 11. This allows for a compact electric actuator device 13. Furthermore, by utilizing the planetary gear set between the output shaft 27 of the motor 23 and the throttle valve 11, a simple, efficient, and compact transmission with a high gear ratio between the output shaft 27 of the motor 23 and the throttle valve 11 is provided.

[0126] The engine 10 comprises a control device 21 operatively connected to the electric actuator device 13 and to the ignition device 7 of the engine 10. According to the illustrated embodiment, the control device 21 is operatively connected to the ignition device 7 by being operatively connected to the ignition system 17.

[0127] exist Figure 2 , each of the throttle valve 11 and the main throttle valve 31 is shown in a respective open position. Figure 2 The illustrated engine 10 is shown operating at full throttle (ie, full power).

[0128] According to the embodiment herein, the control device 21 is configured to retard the ignition timing of the ignition device 7 from the initial ignition timing to the retarded ignition timing when the rotational speed of the crankshaft 3 reaches a speed higher than the upper threshold value, and is configured to control the electric actuator device 13 to move the throttle valve 11 toward the closed position.

[0129] Closing the throttle valve 11, i.e., moving the throttle valve 11 from the open position to the closed position, is associated with a specific closing time period. The closing time period of the throttle valve 11, i.e., the time period required to move the throttle valve 11 from the open position to the closed position, may be, for example, a few tenths of a second. For example only, the closing time period of the throttle valve 11 may be in the range of 0.04 to 0.35 seconds or 0.07 to 0.2 seconds.

[0130] However, since the control device 21 is configured to delay the ignition timing of the ignition device 7 from the initial ignition timing to the delayed ignition timing when the rotational speed of the crankshaft 3 reaches a speed higher than the upper limit threshold speed, and is configured to control the electric actuator device 13 to move the throttle valve 11 toward the closed position, the rotational speed of the crankshaft 3 can be quickly limited while allowing the use of a small electric actuator device 13 to move the throttle valve 11 toward the closed position.

[0131] When the ignition timing is retarded, the exhaust gas temperature (i.e., the temperature of the exhaust gas flowing from the combustion chamber 4 to the exhaust system 41 via the exhaust port 38) increases. This can be partially explained by the fact that when combustion is retarded in the combustion chamber 4, the proportion of the energy of the combustion of the air / fuel mixture in the combustion chamber 4 that is converted into mechanical work supplied to the crankshaft 3 of the engine 10 is reduced.

[0132] However, because the control device 21 is configured to control the electric actuator device 13 to move the throttle valve 11 toward the closed position when the rotational speed of the crankshaft 3 reaches a speed higher than the upper threshold speed, the time period required for operation with retarded ignition timing can be shortened compared to a solution in which retarded ignition timing is the sole means of limiting the rotational speed of the engine's crankshaft. Since the time period required for operation with retarded ignition timing can be shortened, prolonged periods of excessively high exhaust temperatures can be avoided. Consequently, damage to the engine 10 can be avoided.

[0133] The control device 21 may be configured to use the current rotational speed of the crankshaft 3 as an input to control the electric actuator device 13 to move the throttle valve 11 between the open position and the closed position. According to some embodiments, the control device 21 may be configured to control the electric actuator device 13 to move the throttle valve 11 toward the closed position when the rotational speed of the crankshaft 3 reaches above an upper threshold speed, and may be configured to control the electric actuator device 13 to move the throttle valve 11 toward the open position when the rotational speed of the crankshaft 3 drops below the upper threshold speed.

[0134] According to some embodiments, the control device 21 may include a proportional-integral-derivative controller (also known as a PID controller or a three-term controller), which uses the current speed of the crankshaft 3, the desired speed of the crankshaft 3, the current position of the throttle valve 11, and the desired position of the throttle valve 11 as input.

[0135] For example only, the upper threshold speed referred to herein may be in the range of 7,000 to 15,000 rpm, or may be in the range of 12,000 to 14,000 rpm.

[0136] The control device 21 may be configured to retard the ignition timing of the ignition device 7 such that, when the rotational speed exceeds an upper threshold speed, the ignition timing is retarded as the rotational speed increases. That is, the control device 21 may be configured to control the ignition timing of the ignition device 7 such that the amount of retardation of the ignition timing at least substantially follows the extent to which the current rotational speed of the crankshaft 3 exceeds the upper threshold speed. Control may be performed such that the amount of retardation at least substantially linearly follows the extent to which the current rotational speed of the crankshaft 3 exceeds the upper threshold speed. The control device 21 may be configured to control the ignition timing of the ignition device 7 using map data and the current rotational speed of the crankshaft 3 as inputs.

[0137] The initial ignition timing referred to herein is the current ignition timing used when the rotational speed of the crankshaft 3 reaches the upper threshold speed. For example only, the initial ignition timing may be within a range of 6 to 15 crankshaft angles before top dead center of the piston 5. This initial ignition timing indicates that the ignition device 7 is controlled to ignite the air / fuel mixture in the combustion chamber 4 of the cylinder 2 when the piston is located 6 to 15 crankshaft angles before top dead center during its movement toward top dead center.

[0138] As used herein, retarded ignition timing is ignition timing that is retarded (i.e., delayed) relative to the initial ignition timing. As mentioned, control of the ignition timing can be performed such that the amount of retardation follows, at least substantially linearly, the degree to which the current rotational speed of the crankshaft 3 exceeds an upper threshold speed. Control of the ignition timing can be performed such that the amount of retardation of the ignition timing increases as the rotational speed increases above the upper threshold speed, until a maximum retardation of the ignition timing is reached. By way of example only, the maximum retardation of the ignition timing can be in the range of 15 to 35 crankshaft degrees relative to the initial ignition timing, or can be in the range of 20 to 30 crankshaft degrees.

[0139] As understood from the above, under some operating conditions of the engine 10 , the ignition timing of the ignition device 7 can be retarded to ignite the air / fuel mixture in the combustion chamber 4 of the cylinder 2 several crankshaft angles after top dead center.

[0140] As implied above, the control device 21 can be configured to control the ignition timing of the ignition device 7 so that, when the rotational speed exceeds an upper threshold speed, the ignition timing is advanced as the rotational speed decreases. Given a specific difference in the rotational speed of the crankshaft 3 above the upper threshold speed, the amount by which the ignition timing advances as the rotational speed decreases above the upper threshold speed can correspond to the amount of retardation of the ignition timing. Furthermore, as will be understood from the above, the control device 21 can be configured to advance the ignition timing to the initial ignition timing when the rotational speed of the crankshaft 3 drops below the upper threshold speed.

[0141] Figure 4 A method 100 of limiting the crankshaft speed of an internal combustion engine of a handheld power tool is schematically shown. The internal combustion engine may be based on Figure 2 and Figure 3 The internal combustion engine 10 of the embodiment shown, and the handheld power tool can be according to Figure 1 The handheld power tool 1 of the embodiment shown. Therefore, the following will also refer to Figures 1 to 4 , unless otherwise indicated.

[0142] Method 100 is a method of limiting the rotational speed of a crankshaft 3 of an internal combustion engine 10 of a handheld power tool 1. The internal combustion engine 10 includes the crankshaft 3, cylinders 2, pistons 5 disposed in the cylinders 2 and connected to the crankshaft 3, an ignition device 7 configured to ignite an air / fuel mixture in the cylinders 2, an intake system 9 for directing air to the cylinders 2, a throttle valve 11 disposed in the intake system 9, and an electric actuator device 13 configured to move the throttle valve 11 between an open position and a closed position. The throttle valve 11 is configured to restrict air flow through the intake system 9 when positioned in the closed position. The method 100 includes the following steps: when the rotational speed of the crankshaft 3 reaches a speed above an upper threshold value:

[0143] - a retarding step 110 of retarding the ignition timing of the ignition device 7 from the initial ignition timing to a retarded ignition timing; and

[0144] - Control step 120 , controlling the electric actuator device 13 to move the throttle valve 11 towards the closed position.

[0145] When the rotation speed of the crankshaft 3 reaches a speed higher than the upper threshold, the retarding step 110 of retarding the ignition timing of the ignition device 7 and the control step 120 of controlling the electric actuator device 13 to move the throttle valve 11 toward the closed position may be simultaneously performed.

[0146] like Figure 4 As indicated in FIG. 1 , the delay step 110 of delaying the ignition timing of the ignition device 7 may include the following steps:

[0147] - Maintaining step 111 , when the rotation speed of the crankshaft 3 is higher than the upper threshold speed, maintaining the control of the ignition timing of the ignition device 7 so that the ignition timing is the retarded ignition timing.

[0148] In addition, if Figure 4 As indicated in FIG. 1 , the delay step 110 of delaying the ignition timing of the ignition device 7 may include the following steps:

[0149] - Control step 113, controlling the ignition timing of the ignition device 7 so that when the rotation speed exceeds the upper threshold speed, the ignition timing is retarded as the rotation speed increases.

[0150] In addition, if Figure 4 As indicated in FIG. 1 , the delay step 110 of delaying the ignition timing of the ignition device 7 may include the following steps:

[0151] - Control step 115, controlling the ignition timing of the ignition device 7 so that when the rotation speed exceeds the upper threshold speed, the ignition timing is advanced as the rotation speed decreases.

[0152] In addition, if Figure 4 As indicated in , method 100 may include the following steps:

[0153] - Advance step 117 , when the rotation speed of the crankshaft 3 drops below the upper threshold speed, the ignition timing is advanced to the initial ignition timing.

[0154] Moreover, if Figure 4 As indicated in , method 100 may include the following steps:

[0155] - Control step 121 , when the rotational speed of the crankshaft 3 drops below an upper threshold speed, controlling the electric actuator device 13 to move the throttle valve 11 to the open position.

[0156] It will be understood that the various embodiments described for method 100 can be combined with the control device 21 described herein. That is, the control device 21 can be configured to perform any of the method steps 110, 111, 113, 115, 117, 120 and 121 of method 100.

[0157] Those skilled in the art will appreciate that the method 100 for limiting the rotational speed of the crankshaft 3 of the internal combustion engine 10 of the handheld power tool 1 can be implemented by programming instructions. These programming instructions typically consist of a computer program that, when executed in the control device 21, ensures that the control device 21 performs the desired control, such as the method steps 110, 111, 113, 115, 117, 120, and 121 described herein. The computer program is typically part of a computer program product that includes a suitable digital storage medium on which the computer program is stored. According to such embodiments, the computer-readable medium includes a computer program that contains instructions that, when executed by a computer, cause the computer to perform the method 100 according to some embodiments.

[0158] The control device 21 may include a computing unit that may take the form of substantially any suitable type of processor circuit or microcomputer, such as a digital signal processing circuit (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 can interpret and execute instructions. The expression "computing unit" as used herein may refer to a processing circuit system that includes a plurality of processing circuits, such as, for example, any, some, or all of the processing circuits mentioned above.

[0159] The control device 21 may also include a storage unit, wherein the computing unit may be connected to the storage unit, and the storage unit may provide the computing unit with, for example, stored program code and / or stored data that may be required for the computing unit to perform calculations. The computing unit may also be adapted to store partial or final results of the calculations in the storage unit. The storage unit may include a physical device for temporarily or permanently storing data or programs (i.e., instruction sequences). According to some embodiments, the storage unit may include an integrated circuit comprising silicon-based transistors.

[0160] The control device 21 is connected to components of the internal combustion engine 10 and / or components of the handheld power tool 1 for receiving and / or transmitting input signals and output signals. These input signals and output signals may include waveforms, pulses, or other properties, which the input signal receiving device may detect as information and convert into signals that can be processed by the control device 21. These signals may then be supplied to the computing unit. One or more output signal transmitting devices may be arranged to convert the calculation results from the computing unit into output signals for transmission to other parts of the control system of the handheld power tool 1 and / or the components to which the signals are directed. Each of the connections to the corresponding components of the internal combustion engine 10 for receiving and transmitting input signals and output signals may take the form of one or more of a cable or a wireless connection.

[0161] In the illustrated embodiment, the handheld power tool 1 includes a control device 21 , but alternatively, it may be fully or partially implemented with two or more control devices or two or more control units.

[0162] The computer program product may be provided, for example, in the form of a data carrier carrying computer program code that, when loaded into one or more computing units of control device 21, is used to perform at least some of method steps 110, 111, 113, 115, 117, 120, and 121 according to some embodiments. The data carrier may be, for example, a CD ROM, a ROM (Read Only Memory), a PROM (Programmable Read Only Memory), an EPROM (Erasable Programm ...

[0163] It should be understood that the foregoing is a description of various exemplary embodiments and that the present invention is limited only by the appended independent claims. Those skilled in the art will recognize that modifications may be made to the exemplary embodiments and that different features of the exemplary embodiments may be combined to produce embodiments other than those described herein without departing from the scope of the present invention as defined by the appended independent claims.

[0164] 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 existence or addition of one or more other features, elements, steps, components, functions or combinations thereof.

Claims

1. A method (100) for limiting the rotational speed of a crankshaft (3) of an internal combustion engine (10) of a handheld power tool (1), The internal combustion engine (10) comprises: - the crankshaft (3); - Cylinders (2); - a piston (5) arranged in the cylinder (2) and connected to the crankshaft (3); - an ignition device (7) configured to ignite the air / fuel mixture in the cylinder (2); - an air intake system (9) for directing air to the cylinders (2); - a throttle valve (11), arranged in the intake system (9); as well as - an electric actuator device (13) configured to move the throttle valve (11) between an open position and a closed position; wherein the throttle valve (11) is configured to restrict air flow through the intake system (9) when positioned in the closed position; And wherein the method (100) comprises the following steps: when the rotation speed of the crankshaft (3) reaches a speed higher than an upper threshold speed: - retarding (110) the ignition timing of the ignition device (7) from the initial ignition timing to a retarded ignition timing; and - controlling (120) the electric actuator device (13) to move the throttle valve (11) towards the closed position.

2. The method (100) according to claim 1, wherein The step of delaying (110) the ignition timing of the ignition device (7) comprises the following steps: - When the rotation speed of the crankshaft (3) is higher than the upper threshold speed, the ignition timing of the ignition device (7) is maintained (111) controlled so that the ignition timing is a retarded ignition timing.

3. The method (100) according to claim 1 or 2, wherein: The step of delaying (110) the ignition timing of the ignition device (7) comprises the following steps: - controlling (113) the ignition timing of the ignition device (7) so that when the rotation speed exceeds the upper threshold speed, the ignition timing is retarded as the rotation speed increases.

4. The method (100) according to any one of the preceding claims, wherein The step of delaying (110) the ignition timing of the ignition device (7) comprises the following steps: - controlling (115) the ignition timing of the ignition device (7) so that when the rotation speed exceeds the upper threshold speed, the ignition timing is advanced as the rotation speed decreases.

5. The method (100) according to any one of the preceding claims, wherein The method (100) comprises the following steps: - When the rotation speed of the crankshaft (3) drops below the upper threshold speed, the ignition timing is advanced (117) to the initial ignition timing.

6. The method (100) according to any one of the preceding claims, wherein The method (100) comprises the following steps: - When the rotational speed of the crankshaft (3) drops below the upper threshold speed, controlling (121) the electric actuator device (13) to move the throttle valve (11) to the open position.

7. A control device (21) configured to limit the rotational speed of a crankshaft (3) of an internal combustion engine (10) of a handheld power tool (1), wherein: The internal combustion engine (10) comprises: - the crankshaft (3); - Cylinders (2); - a piston (5) arranged in the cylinder (2) and connected to the crankshaft (3); - an ignition device (7) configured to ignite the air / fuel mixture in the cylinder (2); - an air intake system (9) for directing air to the cylinders (2); - a throttle valve (11), arranged in the intake system (9); and - an electric actuator device (13) configured to move the throttle valve (11) between an open position and a closed position; wherein the throttle valve (11) is configured to restrict air flow through the intake system (9) when positioned in the closed position; And wherein the control device (21) is configured to, when the rotational speed of the crankshaft (3) reaches a speed higher than an upper threshold speed: - retarding the ignition timing of the ignition device (7) from the initial ignition timing to the retarded ignition timing; and - Controlling the electric actuator device (13) to move the throttle valve (11) towards the closed position.

8. A handheld power tool (1) comprising an internal combustion engine (10) for powering a tool (30) of the handheld power tool (1), in, The internal combustion engine (10) comprises: - Crankshaft (3); - Cylinders (2); - a piston (5) arranged in the cylinder (2) and connected to the crankshaft (3); - an ignition device (7) configured to ignite the air / fuel mixture in the cylinder (2); - an air intake system (9) for directing air to the cylinders (2); - a throttle valve (11), arranged in the intake system (9); and - an electric actuator device (13) configured to move the throttle valve (11) between an open position and a closed position; wherein the throttle valve (11) is configured to restrict air flow through the intake system (9) when positioned in the closed position; And wherein the handheld power tool (1) comprises a control device (21), the control device being configured to: when the rotational speed of the crankshaft (3) reaches a speed higher than an upper threshold speed; - retarding the ignition timing of the ignition device (7) from the initial ignition timing to the retarded ignition timing; and - Controlling the electric actuator device (13) to move the throttle valve (11) towards the closed position.

9. The handheld power tool (1) according to claim 8, wherein: The electric actuator device (13) comprises an electric motor (23).

10. The handheld power tool (1) according to claim 9, wherein: The motor (23) is a stepper motor.

11. The handheld power tool (1) according to claim 9 or 10, wherein: The electric actuator device (13) comprises a transmission (25), and wherein the electric motor (23) comprises an output shaft (27) which is connected to the throttle valve (11) via the transmission (25).

12. The handheld power tool (1) according to claim 11, wherein: The transmission (25) provides a positive transmission ratio between the output shaft (27) of the electric motor (23) and the throttle valve (11).

13. The handheld power tool (1) according to claim 11 or 12, wherein: The transmission (25) includes a planetary gear set.

14. The handheld power tool (1) according to any one of claims 8 to 13, wherein: The internal combustion engine (10) comprises a crankcase (6) at least partially surrounding the crankshaft (3), and wherein the intake system (9) comprises an intake duct (9') connected to the crankcase (6), and wherein the throttle valve (11) is arranged in the intake duct (9').

15. The handheld power tool (1) according to any one of claims 8 to 14, wherein: The internal combustion engine (10) is a crankcase-scavenged two-stroke internal combustion engine, and wherein the intake system (9) is configured to guide air to the cylinder (2) at least partially via a crankcase (6) of the internal combustion engine (10).

16. The handheld power tool (1) according to any one of claims 8 to 15, wherein: The internal combustion engine (10) comprises a main throttle valve (31) arranged in the intake system (9), wherein the handheld power tool (1) comprises a first handle (33) and a throttle actuator (35) arranged at the first handle (33), and wherein the throttle actuator (35) is operatively connected to the main throttle valve (31).

17. The handheld power tool (1) according to claim 16, wherein: The throttle actuator (35) is operatively connected to the main throttle valve (31) via a mechanical connection (37).

18. The handheld power tool (1) according to any one of claims 8 to 17, wherein: The internal combustion engine (10) comprises an exhaust system (41) configured to direct exhaust gas from the cylinders (2) to the surrounding environment, and wherein the exhaust system (41) comprises a catalytic converter (43).

19. The handheld power tool (1) according to any one of claims 8 to 18, wherein: The handheld power tool (1) is a chain saw or a power cutter.

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