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

Abstract

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) includes an ignition device (7), an intake system (9), a throttle valve (11) in the intake system (9), and an electric actuator arrangement (13) configured to move the throttle valve (11) between an open position and a closed position. The method (100) includes a step (110) of retarding the ignition timing of the ignition device (7) from an initial ignition timing to a retarded ignition timing when the rotational speed of the crankshaft (3) exceeds an upper speed limit, and a step (120) of controlling the electric actuator arrangement (13) to move the throttle valve (11) toward the closed position. The present disclosure further relates to a control arrangement (21) and a handheld 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 hand-held power tool, and further to a control arrangement configured to limit the rotational speed of a crankshaft of an internal combustion engine of a hand-held power tool, and a hand-held power tool comprising an internal combustion engine. [Background technology]

[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 power the tools of the handheld power tools. Typical examples of such handheld power tools include chainsaws, power cutters, hedge trimmers, leaf blowers, multi-tools, etc.

[0003] An internal combustion engine for a handheld power tool typically 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 when the crankshaft rotates.

[0004] The uppermost position of the piston in the cylinder is usually referred to as top dead center (TDC), and the lowermost position of the piston in the cylinder is usually referred to as bottom dead center (BDC). Additionally, 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 crank angles before or after top dead center TDC, depending on the engine's operating conditions. However, for most engines and most operating conditions, the air / fuel mixture is ignited several crank angles before top dead center TDC to optimize fuel efficiency and engine power output.

[0005] A two-stroke engine is a type of internal combustion engine in which the piston completes two strokes during one revolution of the crankshaft. Compared to a four-stroke engine, a two-stroke engine has a significantly reduced number of moving parts, and as a result can be made more compact and significantly lighter. Therefore, two-stroke petrol engines are typically used in applications where mechanical simplicity, light weight, and a high power-to-weight ratio are primary concerns.

[0006] Most small two-stroke engines are crankcase-scavenged, meaning that they use the area under the piston as a charge pump to increase pressure in the crankcase during the piston's power stroke. Crankcase-scavenged two-stroke engines typically have an intake port connected to the crankcase, and air or an air / fuel mixture is drawn into the crankcase as the piston moves toward top dead center. Traditionally, two-stroke engines are provided with a carburetor located in the intake port to supply the air / fuel mixture to the crankcase.

[0007] During the power stroke of a two-stroke engine, the increased pressure and temperature in the cylinder resulting from the combustion of fuel is partially converted into mechanical work delivered to the engine's crankshaft. At the same time, pressure in the crankcase increases as a result of the piston's movement toward bottom dead center.

[0008] An exhaust port disposed in the cylinder wall is opened to allow exhaust gases to flow out of the cylinder when the piston reaches a first position relative to the cylinder during its movement toward bottom dead center. As the piston continues its movement toward bottom dead center and reaches a second position below the first position, an inlet port disposed in the cylinder wall is opened. The inlet port is fluidly connected to the crankcase via a scavenging channel. The air / fuel mixture in the crankcase is forced into the cylinder through the inlet port by overpressure in the crankcase. Thus, as can be seen from the above, in this type of engine, the exhaust port and the inlet port in the cylinder are opened simultaneously during the scavenging phase of the engine, i.e., when the piston is in the bottom dead center region.

[0009] A four-stroke internal combustion engine completes four separate strokes during two revolutions of the crankshaft. A stroke refers to the complete movement of a piston in either direction along a cylinder. Strokes are completed 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 delivery arrangements. The one or more inlet and outlet valves are controlled by respective valve control arrangements, typically including one or more camshafts rotatably connected to the engine's crankshaft via belts, chains, gears, etc.

[0010] During operation of a conventional four-stroke internal combustion engine, an inlet valve control arrangement controls a cylinder's inlet valve to an open position during the inlet stroke of the piston in the cylinder to allow air or an air-fuel mixture to enter the cylinder. During the compression stroke, all valves are closed to allow compression of the air or air-fuel mixture in the cylinder. When the engine is in a power-producing position, the fuel in the cylinder is ignited, for example, by a spark plug, usually toward 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 significant portion of the subsequent expansion stroke. The increased pressure and temperature in the cylinder resulting from the combustion are partially converted into mechanical work delivered to the crankshaft during the expansion stroke.

[0011] Of course, all valves remain closed during the expansion stroke to allow the conversion of the increased pressure and temperature into mechanical work. Since the majority of combustion usually occurs during the expansion stroke, the expansion stroke is also commonly referred to as the combustion stroke. On the subsequent exhaust stroke, the exhaust valve control arrangement controls the cylinder's exhaust valve to an open position to allow exhaust gases to exit the cylinder into the combustion engine's exhaust system.

[0012] Internal combustion engines in handheld power tools are typically optimized to operate at relatively high rotational speeds, in part because higher rotational speeds allow for higher engine power output, given the engine's displacement and weight.

[0013] Lightweight engines for handheld power tools are preferred because the weight of the power tool places strain on the user's hands, arms, and back. Furthermore, light weight allows the user to operate the handheld power tool more safely.

[0014] The rotational speed of the crankshaft of an internal combustion engine must usually be limited to ensure engine durability, and this limiting usually begins when the rotational speed of the crankshaft reaches an upper speed limit.

[0015] The internal combustion engine of a handheld power tool is typically optimized for rapid acceleration. Furthermore, during a work session with the handheld power tool, the engine may operate at a speed close to its upper limit. When the user removes the tool from the currently processed object, the resistive torque faced by the engine is rapidly removed, and the engine's rotational speed tends to rapidly increase above the upper limit.

[0016] The combination of these facts, namely that engines in handheld power tools are typically optimized for operation at high rotational speeds and for rapid acceleration, where resisting torque is quickly removed, means that the upper speed limit of the engine can be exceeded several times during a working session with the handheld power tool.

[0017] A common approach to limiting the rotational speed of a crankshaft in an engine of a handheld power tool is to control the engine's ignition device to skip an ignition event of an air / fuel mixture in a cylinder when the rotational speed of the crankshaft reaches an upper limit. This solution is a simple and cost-effective approach to limiting the rotational speed of the crankshaft. However, it also has several problems and drawbacks. One problem is that it can cause undesirable fuel consumption and engine emissions levels. This is because the lack of combustion of the fuel added to the cylinder resulting from the skipped ignition event causes a large amount of unburned fuel to be supplied to the engine's exhaust system.

[0018] Such large amounts of unburned fuel add to the engine's fuel consumption and have negative effects on the environment and on people and animals near the handheld power tool. Additionally, large amounts of unburned fuel can cause problems when the engine uses exhaust aftertreatment systems such as catalytic converters.

[0019] Another problem is that using the above solutions to limit crankshaft rotational speed can compromise engine durability. This is caused by the fact that restarting ignition of the air / fuel mixture after a skipped ignition event can result in an excessively large and violent combustion event. Such an excessively large and violent combustion can distort and damage one or more engine components, such as the engine's pistons, piston rings, connecting rods, crankshaft, and cylinders.

[0020] Another approach to limiting the rotational speed of a crankshaft of a handheld power tool engine is to retard the ignition timing when the rotational speed of the crankshaft reaches an upper limit. Such a solution can reduce the level of emissions from the engine compared to a solution in which an ignition event is skipped because there is at least a late combustion of the air / fuel mixture in the engine's cylinders, which reduces the emission of unburned fuel from the engine. However, such a solution for limiting the rotational speed is slower than a solution in which an ignition event is skipped. This is because the late combustion event of the air / fuel mixture in the cylinder also applies a positive crankshaft torque to the engine's crankshaft. Furthermore, the late combustion event resulting from the retarded ignition timing causes a significant increase in exhaust temperature, which can damage engine components.

[0021] Another approach to limiting the rotational speed of the engine's crankshaft is to control the engine's throttle valve to a closed position so as to restrict the airflow into the engine, thereby limiting the rotational speed of the engine's crankshaft. Such a solution can reduce fuel consumption and engine emissions compared to the above solutions. Furthermore, such a solution to limit the rotational speed of the crankshaft can improve engine durability because it avoids the problems of hot exhaust gases and excessively large, concentrated combustion events compared to the above types of solutions.

[0022] However, in solutions that utilize throttle valve closure, the throttle valve control must be independent of user input to ensure engine durability, and therefore the throttle valve position must be controlled by some type of automatic mechanism, such as an electric actuator, that can move the throttle valve to a closed position when the crankshaft rotational speed reaches an upper limit.

[0023] Furthermore, in such a solution, the electric actuator arrangement must be able to quickly move the throttle valve to a closed position so that the crankshaft rotational speed can be quickly limited. That is, the electric actuator arrangement must be able to move the throttle valve from an open position to a closed position within a few milliseconds so that the crankshaft rotational speed can be quickly limited to ensure engine durability. Furthermore, due to the air flow rate passing through the throttle valve when the crankshaft rotational speed is in the upper speed range, the valve faces a high resistance torque when moving toward the closed position.

[0024] Therefore, in solutions that utilize throttle valve closure, the electric actuator arrangement must have a fast response and be powerful enough to quickly move the throttle valve to a closed position, which requires a large and heavy electric actuator arrangement that is not typically suitable for use in handheld power tools where mechanical simplicity and weight of the handheld power tool are primary concerns. Summary of the Invention [Problem to be solved by the invention]

[0025] It is an object of the present invention to overcome or at least mitigate at least some of the problems and disadvantages mentioned above. [Means for solving the problem]

[0026] According to a first aspect of the present invention, this 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 comprising the crankshaft, a cylinder, a piston disposed 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 into the cylinder, a throttle valve disposed in the intake system, and an electric actuator arrangement configured to move the throttle valve between an open position and a closed position, the throttle valve configured to restrict the flow of air through the intake system when in the closed position. The method further comprises: when the rotational speed of the crankshaft exceeds an upper speed limit, an ignition timing retarding step of retarding the ignition timing of the ignition device from an initial ignition timing to a retarded ignition timing; and controlling the electrical actuator arrangement to move the throttle valve toward the closed position.

[0027] In this way, the method provides the conditions for obtaining rapid limiting of the rotational speed of the crankshaft while allowing the use of a compact electric actuator arrangement for moving the throttle valve towards the closed position.

[0028] That is, because the method involves a combination of retarding the ignition timing and controlling an electric actuator arrangement to move the throttle valve toward a closed position, a smaller, less expensive, and lighter electric actuator arrangement can be used to move the throttle valve toward a closed position compared to solutions in which the only means to limit the rotational speed of the crankshaft is to use the closing of the throttle valve. This is because it is possible to ensure that the rotational speed of the crankshaft is limited for the period of time required to move the throttle valve toward a closed position, thereby allowing for a less agile, stronger, and heavier electric actuator arrangement.

[0029] Similarly, because the method involves a combination of retarding the ignition timing and controlling an electrical actuator arrangement to move the throttle valve toward a closed position, the period required for retarded ignition timing operation can be reduced compared to solutions in which retarding the ignition timing is the only means for limiting the rotational speed of the crankshaft. Because the time required for retarded ignition timing operation can be reduced, long periods of excessively high exhaust gas temperatures, which can also damage the internal combustion engine, can be avoided.

[0030] Thus, a robust and reliable method is provided for quickly limiting the rotational speed of the crankshaft while avoiding damage to engine components. Furthermore, because the method includes controlling an electrical actuator arrangement and retarding ignition timing, a method is provided that can rapidly limit the rotational speed of the crankshaft without undesirably releasing unburned fuel. As a further result, a method is provided that enables the use of an exhaust aftertreatment arrangement, such as a catalytic converter, to treat exhaust gases from the engine.

[0031] Furthermore, because the method includes controlling the electrical actuator arrangement to move the throttle valve toward a closed position, a method is provided that can reduce engine fuel consumption.

[0032] Accordingly, there is provided a method which overcomes or at least mitigates at least some of the problems and disadvantages discussed above, thereby achieving the above objectives. Optionally, the ignition timing retarding step comprises: Maintaining control of the ignition timing of an ignition device to retard ignition timing when the rotational speed of the crankshaft exceeds the upper speed limit.

[0033] This ensures that the rotational speed of the crankshaft is limited for at least the majority of the time required to move the throttle valve to the closed position, i.e., the rotational speed of the crankshaft can be quickly limited while allowing the use of a compact electric actuator configuration for moving the throttle valve.

[0034] Optionally, the ignition timing retarding step comprises: and controlling the ignition timing of an ignition device so that the ignition timing is retarded as the rotational speed increases above the upper limit speed.

[0035] This provides situation-based control that can quickly and efficiently limit crankshaft rotational speed over a wider range of operating conditions of the handheld power tool. Optionally, the spark retard step comprises: and controlling the ignition timing of the ignition device so that the ignition timing is advanced as the rotational speed above the upper speed decreases.

[0036] This provides situation-based control that can quickly and efficiently limit crankshaft rotational speed over a wide range of operating conditions of the handheld power tool while avoiding the generation of hot exhaust gases over long periods of time, thus further avoiding damage to engine components.

[0037] Optionally, the method further comprises: The method includes a step of advancing the ignition timing to the initial ignition timing when the rotational speed of the crankshaft falls below the upper limit speed.

[0038] This provides a situation-based control that can quickly and efficiently limit the crankshaft rotational speed while avoiding the generation of hot exhaust gases over long periods of time, thus further avoiding damage to engine components.

[0039] Optionally, the method further comprises: Controlling the electrical actuator arrangement to move the throttle valve to the open position when the rotational speed of the crankshaft falls below the upper speed limit.

[0040] This provides situation-based control that can quickly and efficiently limit the rotational speed of the crankshaft while avoiding excessive limiting of the rotational speed of the crankshaft.

[0041] According to a second aspect of the present invention, this object is achieved by a control arrangement configured to limit the rotational speed of a crankshaft of an internal combustion engine of a hand-held power tool, the internal combustion engine comprising: the 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 into the cylinder; a throttle valve arranged in the intake system; and an electric actuator arrangement configured to move the throttle valve between an open position and a closed position, the throttle valve being configured to restrict the flow of air through the intake system when in the closed position. The control arrangement is configured to: retarding the ignition timing of the ignition device from an initial ignition timing to a retarded ignition timing; and controlling the electric actuator arrangement to move the throttle valve toward the closed position.

[0042] In this way, a control arrangement is provided which provides for rapid limiting of the crankshaft rotational speed whilst allowing the use of a compact electric actuator arrangement for moving the throttle valve towards the closed position.

[0043] That is, because the control arrangement is configured to retard the ignition timing and control the electric actuator arrangement to move the throttle valve toward the closed position, a smaller, less expensive, and lighter electric actuator arrangement can be used to move the throttle valve toward the closed position compared to a solution in which the only means to limit the rotational speed of the crankshaft is to use the closing of the throttle valve. This is because it can be ensured that the rotational speed of the crankshaft is limited for the period of time required to move the throttle valve toward the closed position, thereby allowing the use of a less rapid, stronger, and heavier electric actuator arrangement.

[0044] Similarly, because the control arrangement is configured to control the electric actuator arrangement to move the throttle valve toward the closed position, the duration required for retarded ignition operation can be reduced compared to solutions in which retarded ignition timing is the only means for limiting the rotational speed of the crankshaft. Because the duration required for retarded ignition operation can be reduced, long periods of excessively high exhaust gas temperatures, which can also prevent damage to the internal combustion engine, can be avoided.

[0045] Thus, a robust and reliable control arrangement is provided that can quickly limit the rotational speed of the crankshaft while avoiding damage to engine components. Furthermore, the control arrangement is configured to retard the ignition timing and control the electrical actuator arrangement to move the throttle valve toward a closed position, thereby providing a control arrangement that can quickly limit the rotational speed of the crankshaft without undesirably releasing unburned fuel.As a further result, a control arrangement is provided that enables the use of an exhaust aftertreatment arrangement, such as a catalytic converter, to treat exhaust gases from the engine.

[0046] Furthermore, the control arrangement is configured to retard the ignition timing and control the electric actuator arrangement to move the throttle valve toward a closed position, thereby providing a control arrangement that can reduce engine fuel consumption.

[0047] There is therefore provided a control arrangement which overcomes or at least mitigates at least some of the problems and disadvantages discussed above, thereby achieving the above objectives. It will be understood that the various embodiments described for the method are all combinable with the control arrangements described herein, i.e. the control arrangement according to the second aspect of the invention may be configured to perform any one of the method steps of the method according to the first aspect of the invention.

[0048] According to a third aspect of the present invention, this object is achieved by a hand-held power tool comprising an internal combustion engine for powering the tool, the internal combustion engine comprising the crankshaft, a cylinder, a piston disposed 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 into the cylinder, a throttle valve disposed in the intake system, and an electric actuator arrangement 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 in the closed position. The hand-held power tool is configured to: retarding the ignition timing of the ignition device from an initial ignition timing to a retarded ignition timing; and controlling the electric actuator arrangement to move the throttle valve toward the closed position.

[0049] In this way, a handheld power tool is provided which has provisions for 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.

[0050] In other words, a handheld power tool is provided that can use a smaller, lower cost, and lighter electric actuator configuration to move the throttle valve toward a closed position, compared to solutions where the use of throttle valve closure is the only means for limiting the crankshaft rotational speed while ensuring rapid limitation of the crankshaft rotational speed and avoiding long periods of excessive exhaust temperatures.

[0051] Thus, a robust and reliable handheld power tool is provided that can quickly limit the rotational speed of the crankshaft while avoiding damage to engine components and avoiding the unnecessary release of unburned fuel.

[0052] Additionally, a handheld power tool is provided that allows for the use of an exhaust after-treatment arrangement, such as a catalytic converter, to treat exhaust gases from the engine of the handheld power tool. Furthermore, the control configuration of the handheld power tool is configured to control the electric actuator configuration to retard the ignition timing and move the throttle valve toward a closed position, thereby providing a handheld power tool with conditions for reducing fuel consumption.

[0053] There is therefore provided a handheld power tool that overcomes or at least mitigates at least some of the problems and disadvantages discussed above. Optionally, the electric actuator arrangement comprises an electric motor, thereby providing the conditions for a simple and cost-effective electric actuator arrangement capable of moving the throttle valve towards a closed position when the rotational speed of the crankshaft exceeds an upper speed limit.

[0054] Optionally, the electric motor is a stepper motor, thereby avoiding the need for a sensor to monitor the current position of the throttle valve. Optionally, the electric actuator arrangement comprises a transmission, and the electric motor comprises an output shaft connected to the throttle valve via the transmission, thereby enabling the torque required to move the throttle valve to a closed position to be generated while providing the conditions for using a small and lightweight electric motor.

[0055] Optionally, the transmission provides a positive gear ratio between the output shaft of the electric motor and the throttle valve, thereby enabling the torque required to move the throttle valve to a closed position to be generated while providing the means for using a small, lightweight electric motor.

[0056] Optionally, the transmission comprises a planetary gear set, which provides the conditions for a simple, efficient and compact transmission with a relatively high gear ratio between the output shaft of the electric motor and the throttle valve, and further provides the conditions for arranging the planetary gear set coaxially to the output shaft of the electric motor and / or to the shaft of the throttle valve, thereby resulting in a compact electric actuator arrangement.

[0057] Optionally, the internal combustion engine comprises a crankcase at least partially surrounding the crankshaft, the intake system comprises an intake duct connected to the crankcase, and the throttle valve is disposed in the intake duct, thereby providing conditions for efficiently restricting airflow into the engine when the throttle valve is controlled towards a closed position.

[0058] Optionally, the internal combustion engine is a crankcase-scavenged two-stroke internal combustion engine, and the intake system is configured to direct air into the cylinders at least in part through a crankcase of the internal combustion engine, thereby providing conditions for a handheld power tool with an engine that is mechanically simple, lightweight, and has a high power-to-weight ratio.

[0059] Optionally, the internal combustion engine includes a main throttle valve disposed in the intake system, and the handheld power tool includes a first handle and a throttle actuator disposed on the first handle, the throttle actuator operatively connected to the main throttle valve, whereby, when the rotational speed of the crankshaft exceeds an upper speed limit, the throttle valve can move toward a closed position independently of the position and control of the main throttle valve, thereby more reliably limiting the rotational speed of the crankshaft.

[0060] Furthermore, a handheld power tool is provided in which engine power can be adjusted simply, efficiently and reliably, and in which control of the position of the main throttle valve is independent of the function and operation of the electric actuator arrangement.

[0061] Optionally, the throttle actuator is operatively connected to the main throttle valve via a mechanical connection, thereby providing a simple, efficient and reliable connection between the throttle actuator and the main throttle valve, providing the conditions for simple, efficient and reliable control of engine power.

[0062] Additionally, a lighter weight solution for controlling engine power can be provided compared to solutions in which the main throttle valve is controlled by an electric actuator assembly. Additionally, the control arrangements and method features of embodiments herein can provide a lighter weight solution for controlling engine power compared to solutions in which the engine includes a single throttle valve that is used to control engine power and limit the rotational speed of the engine crankshaft.

[0063] That is, to be able to control the engine power according to the above solutions, the electric actuator assembly needs to be relatively fast and powerful, which requires a relatively large and heavy electric actuator assembly. Furthermore, such solutions typically require a position sensor to detect the position of the throttle actuator and may also require a battery to be able to obtain a reading of the throttle actuator position before and during engine start-up. Such components add weight and complexity to the handheld power tool.

[0064] Therefore, since the internal combustion engine is equipped with a main throttle valve and the throttle actuator is operably connected to the main throttle valve via a mechanical connection, it is possible to provide a lightweight and uncomplicated solution for controlling the power of the engine.

[0065] Optionally, the internal combustion engine includes an exhaust system configured to direct exhaust gases from the cylinders to the ambient, the exhaust system including a catalytic converter, thereby providing a more environmentally friendly handheld power tool capable of reducing unburned hydrocarbon emissions. The control arrangement is also configured to retard ignition timing and limit crankshaft rotational speed by controlling the electric actuator arrangement to move the throttle valve toward a closed position, thereby ensuring the function and durability of the catalytic converter.

[0066] Optionally, the handheld power tool is a chainsaw or a power cutter, thereby providing a chainsaw or a power cutter having at least some of the advantages described above.

[0067] Further features and advantages of the present invention will become apparent from a review of the appended claims and the following detailed description. The various aspects of the present invention, including its particular features and advantages, will be readily understood from the illustrative embodiments discussed in the following detailed description and the accompanying drawings. [Brief explanation of the drawings]

[0068] [Figure 1] 1 is a first side view of a handheld power tool according to some embodiments of the present disclosure. [Figure 2] 2 is a schematic cross-sectional view of the internal combustion engine of the hand-held power tool shown in FIG. 1; [Figure 3] 3 is a schematic diagram of a cross section of the internal combustion engine shown in FIG. 2 with the throttle valve moved from an open position to a closed position by an electric actuator arrangement. [Figure 4] Schematic diagram of a method for limiting the rotational speed of the crankshaft of an internal combustion engine of a hand-held power tool. DETAILED DESCRIPTION OF THE INVENTION

[0069] Aspects of the present invention will now be more fully described. Like numbers refer to like elements throughout. Well-known functions or constructions are not necessarily described in detail for the sake of brevity and / or clarity.

[0070] 1 shows a first side view of a handheld power tool 1 according to some embodiments of the present disclosure. The handheld power tool 1 includes a tool 30 and an internal combustion engine 10 configured to power the tool 30. According to the embodiment shown, the handheld power tool 1 is a chainsaw including the tool 30 in the form of a cutting chain movably disposed around a guide bar 32. The cutting chain and guide bar 32 are shown schematically in FIG. 1.

[0071] The internal combustion engine 10 is configured to rotate a cutting chain around the guide bar 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 other than a chainsaw, such as, for example, a power cutter, a circular saw, a trimmer, a hedge trimmer, or a multi-tool. Obviously, according to such embodiments, the handheld power tool 1 may include another type of tool 30 other than a cutting chain, such as, for example, a circular saw blade, a trimmer head, or a hedge trimmer cutting assembly. The handheld power tool 1 includes a fuel tank 13 configured to store fuel that is supplied to the internal combustion engine 10 during operation. The internal combustion engine 10 of the handheld power tool 20 may be configured to run on gasoline, also known as petrol, alcohol, similar volatile fuels, or a combination thereof.

[0072] The handheld power tool 1 includes a first handle 33 and a second handle 34. The second handle 34 is separate from and spaced apart 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 a user during operation of the handheld power tool 1, i.e., by one hand gripping the first handle 33 and the other hand gripping the second handle 34.

[0073] According to the embodiment shown, the first handle 33 is a rear handle located at the rear of the hand-held power tool 1, and the second handle 34 is a so-called front handle. According to the embodiment shown, the second handle 34 is located closer to the tool 30 of the hand-held power tool 1 than the first handle 33. Also, the second handle 34 is located between the tool 30 of the hand-held power tool 1 and the first handle 33 of the hand-held power tool 1. According to the embodiment shown, the second handle 34 is formed by an elongated, curved body that allows the user to conveniently hold the second handle 34 from various directions. This allows the user to conveniently and safely operate the hand-held power tool 1 at different orientations relative to the gravitational field.

[0074] The handheld power tool 1 includes a throttle actuator 35 disposed on the first handle 33. The throttle actuator 35 can be used to control the power output of the internal combustion engine 10, as described further herein.

[0075] Figure 2 shows a schematic cross-section of the internal combustion engine 10 of the handheld power tool 1 shown in Figure 1. For reasons of brevity and clarity, the internal combustion engine 10 is also referred to as a "combustion engine" or simply an "engine." In the following, unless otherwise indicated, reference will be made simultaneously to Figures 1 and 2.

[0076] The combustion engine 10 comprises a crankshaft 3, a cylinder 2, and a piston 5 disposed in the cylinder 2. The combustion engine 10 comprises a connecting rod 22 connecting the piston 5 to the crankshaft 3 such that the piston 5 reciprocates between bottom dead center and top dead center in the cylinder 2 as the crankshaft 3 rotates. In other words, the piston 5 is connected to the crankshaft 3 via the connecting rod 22. In Figure 2, the piston 5 is shown positioned between top dead center and bottom dead center.

[0077] According to the embodiment shown, the internal combustion engine 10 of the handheld power tool 1 is a compact, crankcase-scavenged, two-stroke internal combustion engine. According to further embodiments, the internal combustion engine 10 referred to herein may be a four-stroke internal combustion engine, such as a compact four-stroke internal combustion engine. The term "compact" in this context may encompass the engine 10 having an engine displacement of less than 250 cubic centimeters.

[0078] 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 within the crankcase volume V of the crankcase 6.

[0079] Piston 5 includes a first surface that bounds combustion chamber 4 and a second surface that bounds crankcase volume V. Thus, the first surface of piston 5 faces combustion chamber 4, and the second surface of piston 5 faces crankcase 6 of engine 10. The size of crankcase volume V decreases as piston 5 moves toward bottom dead center. In this manner, the pressure within crankcase volume V of crankcase 6 may increase as piston 5 moves toward bottom dead center, as described further herein.

[0080] Furthermore, since the second surface of the piston 5 forms a boundary surface of the crankcase volume V of the crankcase 6, the magnitude of the crankcase volume V is minimum when the piston 5 is at bottom dead center, and the magnitude of the crankcase volume V is maximum when the piston 5 is at top dead center. Thus, the piston 5 of the engine 10 according to embodiments herein acts like a scavenging pump member, i.e., a pump member for displacing combustion gases in the combustion chamber 4 of the engine 10, as further described herein.

[0081] The engine 10 comprises an intake system 9 configured to direct air into the cylinder 2 during operation of the engine 10. According to the embodiment shown, the intake system 9 comprises an intake duct 9' connected to the crankcase 6. Furthermore, the intake system 9 comprises an air filter unit 19 connected to the intake duct 9'. Thus, according to the embodiment shown, the intake system 9 is configured to direct air into the cylinder 2 via the crankcase 6 of the internal combustion engine 10. The cylinder 2 of the engine 10 comprises an intake port 42. The intake port 42 fluidly connects the crankcase 6 to the intake duct 9' when the piston is in the region of top dead center.

[0082] The engine 10 includes a main throttle valve 31 arranged in an intake duct 9' of the intake system 9. A throttle actuator 35 of the handheld power tool 1 shown in FIG. 1 is operably connected to the main throttle valve 31. More particularly, according to these embodiments, the throttle actuator 35 is operably connected to the main throttle valve 31 via a mechanical connection 37 shown schematically in FIG. 2. In this way, the amount of air drawn into the cylinders 2 of the engine 10, and therefore also the power generated by the engine 10, can be simply and reliably adjusted via the throttle actuator 35, as will be further described herein.

[0083] According to the embodiment shown, an intake port 42 is provided in the wall of the cylinder 2, and as the piston 5 moves in a direction towards bottom dead centre, a pressure increase is obtained in the crankcase volume V of the crankcase 6 due to closure of the intake port 42 by the mantle surface of the piston 5. However, according to further embodiments, the intake duct 9' may be connected directly to the crankcase 6, and the engine 10 may lack an intake port 42 provided in the wall of the cylinder 2. According to such an embodiment, as with other embodiments herein, the engine 10 may comprise one or more one-way valves, such as reed valves, arranged to prevent the flow of gases from the crankcase volume V of the crankcase 6 to the intake duct 9' as the piston 5 moves towards bottom dead centre.

[0084] As can be seen in FIG. 2 , the engine 10 includes an inlet port 45 provided in the wall of the cylinder 2. Furthermore, the engine 10 includes a scavenging channel 24 that fluidly connects the crankcase volume V of the crankcase 6 with the inlet port 45. According to the illustrated embodiment, the inlet port 45 is open when the piston 5 is in the bottom dead center region. More specifically, according to the illustrated embodiment, the inlet port 45 is closed by the mantle surface of the piston 5 when the mantle surface of the piston 5 is above the upper edge of the inlet port 45, and the inlet port 45 is opened, i.e., uncovered, when the mantle surface of the piston 5 moves toward the bottom dead center and reaches a position where the mantle surface of the piston 5 is below the upper edge of the inlet port 45. The term "upper edge" as used herein means that the edge of the inlet port 45 is the uppermost edge when the engine is oriented with respect to the local gravitational field such that the direction from the top dead center to the bottom dead center coincides with the local gravitational vector. Obviously, the engine 10 may be configured to operate in other orientations with respect to the local gravitational field.

[0085] As can be seen from the above, when the inlet port 45 is open, transport of gases such as air or an air / fuel mixture is obtained from the crankcase volume V of the crankcase 6 through the scavenging channels 24 and the intake ports 45 shown in Figure 2 to the combustion chamber 4. The engine 10 may be equipped with two or more inlet ports 45 and two or more scavenging channels 24.

[0086] The engine 10 includes an exhaust system 41 configured to direct exhaust gases from the cylinder 2 to the surroundings. According to the embodiment shown, the exhaust system 41 includes a catalytic converter 43. Furthermore, as can be seen in FIG. 2 , the engine 10 includes an exhaust port 38 provided in the wall of the cylinder 2. The exhaust port 38 is fluidly connected to the exhaust system 41 of the engine 10. The inlet port 45 and the exhaust port 38 are configured such that the upper edge of the exhaust port 38 is above the upper edge of the inlet port 45.

[0087] The feature of the upper edge of the exhaust port 38 being above the upper edge of the inlet port 45 means that when the engine 10 is oriented relative to the local gravitational field so that the direction from top dead center to bottom dead center coincides with the local gravitational vector, the uppermost edge of the exhaust port 38 will be located above the uppermost edge of the intake port 45 as seen relative to the local gravitational vector.

[0088] Therefore, due to these features, the inlet port 45 is fully closed before the exhaust port 38 as the piston 5 moves from bottom dead center toward top dead center. Once the inlet port 45 and the exhaust port 38 are each fully closed, gas trapped within the combustion chamber 4 is compressed by the movement of the piston 5 toward top dead center.

[0089] The engine 10 further includes a fuel supply system, which is not shown in FIG. 2 for reasons of brevity and clarity. The fuel supply system may include one or more carburetors arranged in the intake system 9 of the engine 10, such as in an intake duct 9′ of the intake system 9. Alternatively, or in addition, the engine 10 may include one or more of 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 channel 24, and the like.

[0090] Therefore, fuel added or transported to the combustion chamber 4 from such a fuel supply system can be compressed along with air trapped within the combustion chamber 4 when each of the inlet port 45 and exhaust port 38 is fully closed and the piston 5 moves in a direction toward top dead center.

[0091] The engine 10 further comprises an ignition device 7. The ignition device 7 is configured to ignite the air / fuel mixture in the cylinder 2. According to the embodiment shown, the ignition device 7 is a spark plug, i.e. an ignition device configured to ignite the air / fuel mixture by generating a spark in the combustion chamber 4 when a high voltage is supplied to it. According to further embodiments, the engine 10 may comprise another type of ignition device other than a spark plug.

[0092] According to the embodiment shown, engine 10 includes an ignition system 17 configured to control an ignition device 7 to ignite an air / fuel mixture in a combustion chamber 4 based on the rotational position of a crankshaft 3 of engine 10. According to the embodiment shown, engine 10 includes a sensor arrangement 26, 26′ configured to sense a current rotational position of crankshaft 3, and ignition system 17 operably connected to sensor arrangement 26, 26′ and configured to control ignition device 7 to ignite the air / fuel mixture in combustion chamber 4 based on the sensed current rotational position of crankshaft 3.

[0093] During normal operation of engine 10, ignition device 7 is controlled to ignite the air / fuel mixture in combustion chamber 4 a few crank angles from top dead center as piston 5 moves toward top dead center. During the remaining movement of piston 5 toward top dead center, combustion of the air / fuel mixture progresses, and the increase in pressure and temperature in combustion chamber 4 resulting from the combustion in combustion chamber 4 pushes piston 5 toward bottom dead center. This force acting on piston 5 may be converted into mechanical work delivered to crankshaft 3 of engine 10.

[0094] The arrangement of the exhaust port 38 and the inlet port 45 causes the exhaust port 38 to open earlier than the inlet port 45 as the piston 5 moves in the direction d2 towards bottom dead center. In this way, exhaust gases can be expelled from the combustion chamber 4 to the exhaust system 42 before fresh air is transported into the combustion chamber 4 via the scavenging channel 24 and the inlet port 45 by the pumping action resulting from the movement of the piston 5 towards bottom dead center.

[0095] According to an embodiment herein, the engine 10 includes a throttle valve 11 disposed 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 embodiment shown, the throttle valve 11 is disposed in an intake duct 9' of the intake system 9. Furthermore, the engine 10 includes an electric actuator arrangement 13 configured to move the throttle valve 11 between an open position and a closed position.

[0096] 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 a slight restriction to the 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 the flow of air through the intake system 9. The expression restricting the flow of air, as used herein, means a partial blockage of the air flowing through the intake system 9.

[0097] Figure 3 shows a schematic cross section of the internal combustion engine 10 shown in Figure 2, with the throttle valve 11 moved from the open position shown in Figure 2 to the closed position by an electric actuator arrangement 13. In the following, unless otherwise indicated, Figures 1 to 3 will be referred to simultaneously.

[0098] As can be seen in FIGS. 2 and 3 , according to the illustrated embodiment, the throttle valve 11 is a type of butterfly valve. According to further embodiments, the throttle valve 11 may comprise another type of valve. According to the illustrated embodiment, the throttle valve 11 is pivotally arranged about a pivot axis Pa. As can be seen in FIG. 2 , according to these embodiments, the open position of the throttle valve 11 constitutes a position in which the throttle valve 11 is arranged 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. In this way, the throttle valve 11 provides no or only slight restriction to the air flowing through the intake system 9 when the throttle valve 11 is arranged in the open position. Therefore, in the illustrated embodiment, the “open position” of the throttle valve 11 is also referred to as the “fully open position” when referred to herein.

[0099] Furthermore, as can be seen in FIG. 3 , according to these embodiments, the closed position of the throttle valve 11 constitutes a position in which the throttle valve 11 is disposed so that the throttle valve 11 is transverse to the direction of airflow through the intake duct 9′ of the intake system 9. In this manner, the throttle valve 11 restricts, i.e., partially blocks, the flow of air through the intake duct 9′ of the intake system 9 when disposed in the closed position. As can be seen in FIG. 3 , the throttle valve 11 does not completely block the flow of air through the intake duct 9′ of the intake system 9 when disposed in the closed position. Therefore, according to the illustrated embodiments, the “closed position” of the throttle valve 11 referred to herein may also be referred to as an “at least partially closed position.”

[0100] According to the embodiment shown, the electric actuator arrangement 13 includes an electric motor 23. The electric motor 23 may be a stepper motor. In this way, the need for a sensor to monitor the position of the throttle valve is avoided. Furthermore, according to the embodiment shown, the electric actuator arrangement 13 includes a transmission 25, and the electric motor 23 includes an output shaft 27 that is connected to the throttle valve 11 via the transmission 25. According to the embodiment shown, the transmission 25 provides a positive gear ratio between the output shaft 27 of the electric motor 23 and the throttle valve 11. In this way, a small electric motor 23 can be used to move the throttle valve 11 and generate the torque required to move the throttle valve 11 under various operating conditions of the engine 10.

[0101] More specifically, according to the embodiment shown, the transmission 25 comprises a planetary gear set which is arranged coaxially with respect to the output shaft 27 of the electric motor 23 and also with respect to the shaft of the throttle valve 11. In this way, a compact electric actuator arrangement 13 is obtained. Furthermore, the use of a planetary gear set between the output shaft 27 of the electric motor 23 and the throttle valve 11 provides the conditions for a simple, efficient and compact transmission with a high gear ratio between the output shaft 27 of the electric motor 23 and the throttle valve 11.

[0102] The engine 10 comprises a control arrangement 21 operably connected to the electric actuator arrangement 13 and to the ignition device 7 of the engine 10. According to the embodiment shown, the control arrangement 21 is operably connected to the ignition device 7 by being operably connected to the ignition system 17.

[0103] In Figure 2, the throttle valve 11 and the main throttle valve 31 are each shown in their respective open positions, and therefore the engine 10 shown in Figure 2 is shown as operating at full throttle, i.e., full power.

[0104] According to an embodiment of the present specification, the control arrangement 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 exceeds an upper speed limit, and is configured to control the electric actuator arrangement 13 to move the throttle valve 11 towards a closed position.

[0105] Closing of the throttle valve 11, i.e., moving the throttle valve 11 from an open position to a closed position, involves a predetermined closing time. The closing time of the throttle valve 11, i.e., the time required to move the throttle valve 11 from an open position to a closed position, may be, for example, a few tenths of a second. By way of example only, the closing time of the throttle valve 11 may be in the range of 0.04 to 0.35 seconds, or 0.07 to 0.2 seconds.

[0106] However, since the control arrangement 21 is configured to retard the ignition timing of the ignition device 7 from the initial ignition timing to the retarded ignition timing, and is configured to control the electric actuator arrangement 13 to move the throttle valve 11 toward the closed position when the rotational speed of the crankshaft 3 exceeds the upper speed limit, it is possible to provide a rapid limit on the rotational speed of the crankshaft 3 while enabling the use of a small electric actuator arrangement 13 for moving the throttle valve 11 toward the closed position.

[0107] Retarding the ignition timing increases the exhaust temperature, which is the temperature of the exhaust gases flowing from the combustion chamber 4 through the exhaust port 38 to the exhaust system 41. This is partly explained by the fact that a lower proportion of the energy of combustion of the air / fuel mixture in the combustion chamber 4 is converted into mechanical work delivered to the crankshaft 3 of the engine 10 during late combustion in the combustion chamber 4.

[0108] However, because the control arrangement 21 is configured to control the electric actuator arrangement 13 to move the throttle valve 11 toward the closed position when the rotational speed of the crankshaft 3 exceeds the upper speed limit, the period required for operation with retarded ignition timing can be reduced compared to a solution in which retarded ignition timing is the only means for limiting the rotational speed of the engine crankshaft. Because the time required for operation with retarded ignition timing is reduced, long periods of excessive exhaust gas temperatures are avoided, thereby avoiding damage to the engine 10.

[0109] The control arrangement 21 may be configured to control the electric actuator arrangement 13 to move the throttle valve 11 between an open position and a closed position using the current rotational speed of the crankshaft 3 as an input. According to some embodiments, the control arrangement 21 may be configured to control the electric actuator arrangement 13 to move the throttle valve 11 towards the closed position when the rotational speed of the crankshaft 3 exceeds an upper speed limit, and may be configured to control the electric actuator arrangement 13 to move the throttle valve 11 towards the open position when the rotational speed of the crankshaft 3 falls below the upper speed limit.

[0110] According to some embodiments, the control arrangement 21 may include a proportional-integral-derivative controller, also known as a PID controller or three-term controller, that uses the current rotational speed of the crankshaft 3, the desired rotational speed of the crankshaft 3, the current position of the throttle valve 11, and the desired position of the throttle valve 11 as inputs.

[0111] By way of example only, upper speed limits referred to herein may be in the range of 7,000 to 15,000 revolutions per minute, or may be in the range of 12,000 to 14,000 revolutions per minute.

[0112] The control arrangement 21 may be configured to retard the ignition timing of the ignition device 7 such that the ignition timing is retarded as the rotational speed increases above the upper speed limit. That is, the control arrangement 21 may be configured to control the ignition timing of the ignition device 7 such that the magnitude of the retard follows at least approximately the extent to which the current rotational speed of the crankshaft 3 exceeds the upper speed limit. Such control may be performed such that the magnitude of the retard follows at least approximately linearly the extent to which the current rotational speed of the crankshaft 3 exceeds the upper speed limit. The control arrangement 21 may be configured to control the ignition timing of the ignition device 7 using the map data and the current rotational speed of the crankshaft 3 as inputs.

[0113] As referred to herein, the initial ignition timing is the current ignition timing used when the rotational speed of the crankshaft 3 reaches an upper speed limit. By way of example only, the initial ignition timing may be in the range of 6 to 15 crank angles before top dead center of the piston 5. Such initial ignition timing means 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 6 to 15 crank angles before top dead center as it moves toward top dead center.

[0114] As referred to herein, a retarded ignition timing is an ignition timing that is retarded or delayed relative to the initial ignition timing. As described above, the ignition timing may be controlled such that the magnitude of the retard follows at least approximately linearly the extent to which the current rotational speed of the crankshaft 3 exceeds the upper speed limit. The ignition timing may be controlled such that the magnitude of the ignition timing retard increases as the rotational speed increases above the upper speed limit, up to a maximum ignition timing retard. By way of example only, the maximum ignition timing retard may be within a range of 15 to 35 crank angles from the initial ignition timing, or may be within a range of 20 to 30 crank angles.

[0115] As will be appreciated from the above, under some operating conditions of the engine 10, the ignition timing of the ignition device 7 may be retarded to an ignition timing at which the air / fuel mixture in the combustion chamber 4 of the cylinder 2 ignites several crank angles after top dead center.

[0116] As mentioned above, the control arrangement 21 may be configured to control the ignition timing of the ignition device 7 such that the ignition timing is advanced as the rotational speed decreases above the upper speed. For a predetermined difference in the rotational speed of the crankshaft 3 above the upper speed, the advance of the ignition timing as the rotational speed decreases above the upper speed may correspond to an amount of retardation of the ignition timing. Furthermore, as will be appreciated from the above, the control arrangement 21 may be configured to advance the ignition timing to the initial ignition timing when the rotational speed of the crankshaft 3 falls below the upper speed.

[0117] Figure 4 schematically illustrates a method 100 for limiting the rotational speed of a crankshaft of an internal combustion engine of a hand-held power tool. The internal combustion engine may be the internal combustion engine 10 according to the embodiment shown in Figures 2 and 3, and the hand-held power tool may be the hand-held power tool 1 according to the embodiment shown in Figure 1. Therefore, hereinafter, unless otherwise indicated, reference will be made simultaneously to Figures 1 to 4.

[0118] The method 100 is a method 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 includes a crankshaft 3, a cylinder 2, a piston 5 disposed in the cylinder 2 and connected to the crankshaft 3, an ignition device 7 configured to ignite an air / fuel mixture in the cylinder 2, an intake system 9 for directing air into the cylinder 2, a throttle valve 11 disposed in the intake system 9, and an electric actuator arrangement 13 configured to move the throttle valve 11 between an open position and a closed position. The throttle valve 11 is configured to restrict the flow of air through the intake system 9 when in the closed position. The method 100 includes a step of: a step 110 of retarding the ignition timing of the ignition device 7 from the initial ignition timing to the retarded ignition timing; and a step 120 of controlling the electric actuator arrangement 13 to move the throttle valve 11 towards a closed position.

[0119] Step 110 of retarding the ignition timing of the ignition device 7 and step 120 of controlling the electric actuator arrangement 13 to move the throttle valve 11 toward the closed position may be performed simultaneously when the rotational speed of the crankshaft 3 exceeds an upper speed limit.

[0120] As shown in FIG. 4, the step 110 of retarding the ignition timing of the ignition device 7 includes: The control may include a step 111 of maintaining control of the ignition timing of the ignition device 7 to a retarded ignition timing when the rotation speed of the crankshaft 3 exceeds an upper speed limit.

[0121] Further, as shown in FIG. 4, the step 110 of retarding the ignition timing of the ignition device 7 includes: The method may include a step 113 of controlling the ignition timing of the ignition device 7 so that the ignition timing is retarded as the rotation speed increases above the upper speed limit.

[0122] Further, as shown in FIG. 4, the step 110 of retarding the ignition timing of the ignition device 7 includes: The method may include a step 115 of controlling the ignition timing of the ignition device 7 so that the ignition timing is advanced as the rotation speed above the upper speed decreases.

[0123] Further, as shown in FIG. 4, the method 100 includes: The method may include step 117 of advancing the ignition timing to the initial ignition timing when the rotation speed of the crankshaft 3 falls below the upper limit speed.

[0124] Further, as shown in FIG. 4, the method 100 includes: The method may include a step 121 of controlling the electric actuator arrangement 13 to move the throttle valve 11 to an open position when the rotational speed of the crankshaft 3 falls below an upper speed limit.

[0125] It will be understood that the various embodiments described for method 100 can all be combined with the control arrangement 21 described herein. That is, control arrangement 21 may be configured to perform any one of method steps 110, 111, 113, 115, 117, 120, and 121 of method 100.

[0126] 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 programmed instructions. These programmed instructions are typically comprised of a computer program that, when executed in the control arrangement 21, ensures that the control arrangement 21 performs the desired control, such as 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 an embodiment, a computer-readable medium comprises a computer program including instructions that, when executed by a computer, cause the computer to perform the method 100 according to some embodiments.

[0127] The control arrangement 21 may include a computing unit which may take the form of substantially any suitable type of processor circuit or microcomputer, for example, 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 capable of interpreting and executing instructions. The expression "computing unit" as used herein may refer to a processing circuit comprising multiple processing circuits, such as, for example, any, some, or all of those mentioned above.

[0128] The control arrangement 21 may further comprise a memory unit, to which the computation unit may be connected, and which may provide the computation unit with, for example, stored program code and / or stored data that the computation unit may need to perform a computation. The computation unit may also be configured to store partial or final results of the computation in the memory unit. The memory unit may include a physical device utilized to temporarily or permanently store data or programs, i.e., sequences of instructions. According to some embodiments, the memory unit may comprise an integrated circuit comprising silicon-based transistors.

[0129] The control arrangement 21 is connected to components of the internal combustion engine 10 and / or components of the handheld power tool 1 to send and receive input and output signals. These input and output signals may include waveforms, pulses, or other attributes that the input signal receiving device can detect as information and convert into signals processable by the control arrangement 21. These signals may then be provided to the computing unit. One or more output signal transmitting devices may be configured to convert the computation 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 to one or more components for which the signals are intended. Each of the connections to the respective components of the internal combustion engine 10 to send and receive input and output signals may take the form of one or more of cables or wireless connections.

[0130] In the embodiment shown, the handheld power tool 1 comprises a control arrangement 21, but may alternatively be implemented wholly or partly in two or more control arrangements or two or more control units.

[0131] The computer program product may, for example, be provided in the form of a data carrier which, when loaded into one or more computing units of the control arrangement 21, carries computer program code for performing at least some of the method steps 110, 111, 113, 115, 117, 120, and 121 according to some embodiments. The data carrier may, for example, be a CD ROM disk or any other suitable medium such as a ROM (Read Only Memory), a PROM (Programmable Read Only Memory), an EPROM (Erasable PROM), a flash memory, an EEPROM (Electrically Erasable PROM), a hard disk, a memory stick, an optical storage device, a magnetic storage device, or a disk or tape capable of non-temporarily holding machine-readable data. The computer program product may also be provided as computer program code on a server and downloaded to the control arrangement 21.

[0132] The above describes various exemplary embodiments, and it is understood that the present invention is defined solely by the appended independent claims. Those skilled in the art will appreciate that the exemplary embodiments may be modified and different features of the exemplary embodiments may be combined to create embodiments other than those described herein, without departing from the scope of the invention as defined by the appended independent claims.

[0133] As used herein, the terms "comprising" or "comprises" are open-ended and include one or more stated features, elements, steps, components, or functions, but do not exclude the presence or addition of one or more other features, elements, steps, components, functions, or groups 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), comprising: The internal combustion engine (10) The crankshaft (3), A cylinder (2), a piston (5) disposed 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 intake system (9) for directing air into said cylinder (2); a throttle valve (11) arranged in the intake system (9); an electric actuator arrangement (13) configured to move the throttle valve (11) between an open position and a closed position; the throttle valve (11) is configured to restrict the flow of air through the intake system (9) when in the closed position; The method (100) includes, when the rotational speed of the crankshaft (3) exceeds an upper speed limit, an ignition timing retarding step (110) of retarding the ignition timing of the ignition device (7) from an initial ignition timing to a retarded ignition timing; and controlling (120) the electric actuator arrangement (13) to move the throttle valve (11) towards the closed position.

2. The ignition timing retard step (110) 2. The method (100) of claim 1, comprising the step (111) of maintaining control (112) of the ignition timing of an ignition device (7) to a retarded ignition timing when the rotational speed of the crankshaft (3) exceeds the upper speed limit.

3. The ignition timing retard step (110) 3. The method (100) of claim 1 or 2, comprising the step (113) of controlling the ignition timing of an ignition device (7) such that the ignition timing is retarded as the rotational speed above the upper speed increases.

4. The ignition timing retard step (110) 4. The method (100) of claim 1, further comprising the step of controlling (115) the ignition timing of the ignition device (7) such that the ignition timing is advanced as the rotational speed above the upper speed decreases.

5. 5. The method (100) of claim 1, further comprising the step (117) of advancing the ignition timing to the initial ignition timing when the rotational speed of the crankshaft (3) falls below the upper speed limit.

6. 6. The method (100) of claim 1, comprising the step (121) of controlling the electric actuator arrangement (13) to move the throttle valve (11) to the open position when the rotational speed of the crankshaft (3) falls below the upper speed limit.

7. A control arrangement (21) configured to limit the rotational speed of a crankshaft (3) of an internal combustion engine (10) of a hand-held power tool (1), said internal combustion engine (10) comprising: The crankshaft (3), A cylinder (2), a piston (5) disposed 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 intake system (9) for directing air into said cylinder (2); a throttle valve (11) arranged in the intake system (9); an electric actuator arrangement (13) configured to move the throttle valve (11) between an open position and a closed position; the throttle valve (11) is configured to restrict the flow of air through the intake system (9) when in the closed position; The control arrangement (21) is configured to: retarding the ignition timing of the ignition device (7) from an initial ignition timing to a retarded ignition timing; and controlling the electric actuator arrangement (13) to move the throttle valve (11) towards the closed position.

8. A hand-held power tool (1) comprising an internal combustion engine (10) for powering a tool (30) of the hand-held power tool (1); The internal combustion engine (10) The crankshaft (3), A cylinder (2), a piston (5) disposed 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 intake system (9) for directing air into said cylinder (2); a throttle valve (11) arranged in the intake system (9); an electric actuator arrangement (13) configured to move the throttle valve (11) between an open position and a closed position; the throttle valve (11) is configured to restrict the flow of air through the intake system (9) when in the closed position; When the rotation speed of the crankshaft (3) exceeds an upper limit speed, the handheld power tool (1) retarding the ignition timing of the ignition device (7) from an initial ignition timing to a retarded ignition timing; and a control arrangement (21) configured to control the electric actuator arrangement (13) to move the throttle valve (11) toward the closed position.

9. 9. The hand-held power tool (1) according to claim 8, wherein the electric actuator arrangement (13) comprises an electric motor (23).

10. 10. The hand-held power tool (1) according to claim 9, wherein the electric motor (23) is a stepper motor.

11. 11. A hand-held power tool (1) according to claim 9 or 10, wherein the electric actuator arrangement (13) comprises a transmission (25), and the electric motor (23) comprises an output shaft (27) connected to the throttle valve (11) via the transmission (25).

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

13. 13. A hand-held power tool (1) according to claim 11 or 12, wherein the transmission (25) comprises 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), the intake system (9) comprises an intake duct (9') connected to the crankcase (6), and 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 the intake system (9) is configured to direct air into the cylinder (2) at least in part via a crankcase (6) of the internal combustion engine (10).

16. A hand-held 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), and the hand-held power tool (1) comprises a first handle (33) and a throttle actuator (35) arranged on the first handle (33), the throttle actuator (35) being operably connected to the main throttle valve (31).

17. 17. A 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. A hand-held 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 gases from the cylinder (2) to the surroundings, the exhaust system (41) comprising a catalytic converter (43).

19. A hand-held power tool (1) according to any one of claims 8 to 18, which is a chainsaw or a power cutter.

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