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 the crankshaft of an internal combustion engine of a hand-held power tool. The invention further relates to a control configuration configured to limit the rotational speed of the crankshaft of an internal combustion engine of a hand-held power tool, and to a hand-held power tool comprising 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 hand-held power tools to power the tools. Typical examples of such hand-held power tools are chain saws, power cutters, hedge trimmers, leaf blowers, multi-tools, and the like.

[0003] An internal combustion engine for a hand-held power tool typically comprises a cylinder, a piston disposed in the cylinder, a crankshaft, and a connecting rod connecting the piston to the crankshaft such that the piston reciprocates in the cylinder upon rotation of the crankshaft.

[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). Furthermore, Otto-type two-stroke and four-stroke engines comprise an ignition device, such as a spark plug, configured to ignite an 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), at some crank angle before or after top dead center (TDC), depending on the operating conditions of the engine. However, for most engines and most operating conditions, the air / fuel mixture is ignited at some crank angle before top dead center (TDC) in order to optimize fuel efficiency and the power output of the engine.

[0005] A two-stroke engine is a type of internal combustion engine in which the power cycle is completed by the piston making two strokes while the crankshaft rotates once. Compared to a four-stroke engine, a two-stroke engine has a significantly reduced number of moving parts, which can result in a more compact and significantly lighter design. Therefore, two-stroke petrol engines are typically used in applications where mechanical simplicity, light weight, and a high power-to-weight ratio are the primary concerns.

[0006] The smallest two-stroke engines are crankcase scavenging engines, which means these engines use the area below the piston as a charge pump to increase the pressure in the crankcase during the piston's power stroke. Typically, crankcase scavenging two-stroke engines have an intake port connected to the crankcase, and as the piston moves towards top dead center, air or an air / fuel mixture is drawn into the crankcase. Traditionally, two-stroke engines have been provided with a carburetor located at the intake port to supply the air / fuel mixture to the crankcase.

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

[0008] The exhaust port located in the cylinder wall opens 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, the inlet port located in the cylinder wall opens. 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 the overpressure in the crankcase. Thus, as can be understood from the above, in this type of engine, the exhaust port and 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 distinct strokes in the time it takes to complete two rotations of the crankshaft. A stroke refers to the complete movement of the piston in any direction along the cylinder. The strokes are completed in the following order: intake stroke, compression stroke, expansion stroke, and exhaust stroke. A four-stroke internal combustion engine typically comprises one or more inlet and outlet valves, and one or more fuel supply configurations. The one or more inlet and outlet valves are controlled by their respective valve control configurations, which typically include 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, the inlet valve control configuration controls the cylinder's inlet valve to the open position during the piston's inlet stroke, allowing air or a mixture of air and fuel 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 the power generation position, the fuel in the cylinder is ignited, for example, by a spark plug, usually towards the end of the compression stroke. The combustion of fuel in the cylinder significantly increases the pressure and temperature in the cylinder. The combustion of fuel usually continues for a considerable portion of the subsequent expansion stroke. The increased pressure and temperature in the cylinder resulting from combustion are partially converted into mechanical work supplied to the crankshaft during the expansion stroke.

[0011] Naturally, all valves remain closed during the expansion stroke to allow the increased pressure and temperature to be converted into mechanical work. Since most of the combustion usually occurs during the expansion stroke, the expansion stroke is also commonly referred to as the combustion stroke. In the subsequent exhaust stroke, the exhaust valve control configuration controls the cylinder's exhaust valve to the open position, allowing the exhaust gases to be discharged from the cylinder into the combustion engine's exhaust system.

[0012] The internal combustion engines in handheld power tools are typically optimized to operate at relatively high rotational speeds. One reason for this is that higher rotational speeds, given the engine's displacement and weight, allow for greater engine power output.

[0013] Because the weight of power tools puts a strain on the user's hands, arms, and back, it is preferable that the engine of a handheld power tool be lightweight. Furthermore, being lightweight allows the user to operate the handheld power tool more safely.

[0014] The rotational speed of the crankshaft in an internal combustion engine typically needs to be limited to ensure the engine's durability. This limitation usually begins when the crankshaft rotational speed reaches its upper limit.

[0015] The internal combustion engines in handheld power tools are typically optimized for rapid acceleration. Furthermore, during a work session using a handheld power tool, the engine can operate at speeds close to its upper limit. When the user removes the tool from the object being processed, the resistive torque facing the engine is rapidly removed, and in this case, the engine's rotational speed tends to increase rapidly above its upper limit.

[0016] The combination of these facts—namely, that the engines of handheld power tools are typically optimized for operation at high rotational speeds, optimized for rapid acceleration, with resistance torque quickly eliminated, allowing the engine's upper speed limit to be exceeded several times during a work session with a handheld power tool—means that the engine's upper speed limit can be exceeded several times during a work session.

[0017] A common technique for limiting the crankshaft rotation speed of a handheld power tool engine is to control the engine's ignition device so that it skips the ignition event of the air / fuel mixture in the cylinder when the crankshaft rotation speed reaches its upper limit. This solution is a simple and cost-effective method for limiting the crankshaft rotation speed. However, it also comes with several problems and drawbacks. One problem is that it causes unwanted fuel consumption and exhaust levels from the engine. This is because the lack of combustion of the fuel added to the cylinder resulting from skipping the 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 impacts on the environment, as well as on people and animals near handheld power tools. Furthermore, large amounts of unburned fuel can cause problems when using exhaust aftertreatment systems such as catalytic converters in engines.

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

[0020] Another method for limiting the crankshaft rotation speed of a handheld power tool engine is to retard the ignition timing when the crankshaft rotation speed reaches its upper limit. Such a solution can reduce the level of emissions from the engine compared to a solution where the 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 rotation speed is slower than a solution where the ignition event is skipped. This is because the late combustion event of the air / fuel mixture in the cylinders also adds positive crankshaft torque to the engine's crankshaft. Furthermore, the late combustion event resulting from retarding the ignition timing causes a significant increase in exhaust temperature, which can damage engine components.

[0021] Another method for limiting the rotational speed of the engine's crankshaft is to control the engine's throttle valve to the closed position so as to limit the rotational speed of the engine's crankshaft by restricting the airflow to the engine. Compared to the above solution, such a solution can reduce fuel consumption and emissions from the engine. Furthermore, compared to the above type of solution, such a solution that limits the rotational speed of the crankshaft can improve engine durability because it avoids the problems of high-temperature exhaust gases and excessively large and concentrated combustion events.

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

[0023] Furthermore, in such solutions, the electric actuator configuration must be able to quickly move the throttle valve to the closed position so that the crankshaft rotation speed can be rapidly limited. That is, the electric actuator configuration must be able to move the throttle valve from the open position to the closed position within a few milliseconds so that the crankshaft rotation speed can be rapidly limited to ensure the durability of the engine. In addition, due to the airflow through the throttle valve when the crankshaft rotation speed is in the upper speed range, the valve faces a high resistance torque in its movement toward the closed position.

[0024] Therefore, in solutions that utilize the closure of the throttle valve, the electric actuator configuration must be powerful enough to have a quick response and to move the throttle valve to the closed position rapidly, which requires a large and heavy electric actuator configuration. Such large and heavy electric actuator configurations are generally unsuitable for use in handheld power tools, where the mechanical simplicity and weight of the handheld power tool are the primary concerns. [Prior art documents] [Patent Documents]

[0025] [Patent Document 1] U.S. Patent Application Publication No. 2015 / 0184595 [Overview of the Initiative]

Problems to be Solved by the Invention

[0026] An object of the present invention is to overcome or at least mitigate at least some of the above problems and drawbacks.

Means for Solving the Problems

[0027] According to a first aspect of the present invention, this object is achieved by a method of limiting the rotational speed of a crankshaft of an internal combustion engine of a hand-held power tool. The internal combustion engine includes 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 guiding air into the cylinder, a throttle valve disposed in the intake system, and an electric actuator configuration 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 method includes, when the rotational speed of the crankshaft exceeds an upper limit speed, a step of retardation of ignition timing of the ignition device from an initial ignition timing to a retarded ignition timing, and a step of controlling the electric actuator configuration to move the throttle valve toward the closed position.

[0028] In this way, the method provides conditions for obtaining a rapid limitation of the rotational speed of the crankshaft while enabling the use of a small electric actuator configuration for moving the throttle valve toward the closed position.

[0029] In other words, since this method involves a combination of retarding the ignition timing and controlling the electric actuator configuration to move the throttle valve toward the closed position, it is possible to use a smaller, lower-cost, and lighter electric actuator configuration to move the throttle valve toward the closed position, compared to a solution where the use of throttle valve closure is the sole means of limiting the rotational speed of the crankshaft. This is because it can be ensured that the rotational speed of the crankshaft is limited for the period required to move the throttle valve toward the closed position, thus allowing for a less rapid, stronger, and heavier electric actuator configuration.

[0030] Similarly, because this method involves a combination of retarding the ignition timing and controlling an electric actuator configuration to move the throttle valve toward the closed position, it can shorten the period required for operation at retarded ignition timing compared to solutions where retarding the ignition timing is the sole means of limiting the crankshaft rotation speed. By shortening the time required for operation at retarded ignition timing, it is possible to avoid prolonged periods of excessively high exhaust temperatures, thereby also avoiding damage to the internal combustion engine.

[0031] Therefore, a robust and reliable method is provided that allows for the rapid limiting of the crankshaft's rotational speed while avoiding damage to engine components. Furthermore, the method comprises the steps of controlling the electric actuator configuration and retarding the ignition timing, thereby providing a method for rapidly limiting the rotational speed of the crankshaft without causing the unwanted release of unburned fuel. As a further consequence, a method is provided that enables the use of exhaust aftertreatment configurations such as catalytic converters to process exhaust gases from the engine.

[0032] Furthermore, the method includes a step of controlling an electric actuator configuration to move the throttle valve toward the closed position, thereby providing a method that can reduce engine fuel consumption.

[0033] Therefore, a method is provided to overcome, or at least mitigate, at least some of the aforementioned problems and drawbacks. As a result, the above objectives are achieved. The ignition timing retardation process may be performed at the discretion of the user. The process includes maintaining control of the ignition timing of the ignition device to a retarded ignition timing when the rotational speed of the crankshaft exceeds the upper limit speed.

[0034] This ensures that the crankshaft rotation speed is limited for at least the majority of the time required to move the throttle valve to the closed position. In other words, the crankshaft rotation speed can be quickly limited while allowing the use of a small electric actuator configuration to move the throttle valve.

[0035] The ignition timing retardation process may be performed at the discretion of the user. The process includes controlling the ignition timing of the ignition device such that the ignition timing is retarded as the rotational speed increases beyond the upper limit speed.

[0036] This provides situation-based control that allows for rapid and efficient limiting of the crankshaft rotation speed under a wider range of operating conditions for handheld power tools. The ignition timing retardation process is optional. The process includes controlling the ignition timing of the ignition device such that the ignition timing advances as the rotational speed, which exceeds the upper limit speed, decreases.

[0037] This provides a situation-based control system that allows for rapid and efficient limiting of the crankshaft rotation speed under a wide range of operating conditions for handheld power tools, while avoiding the generation of high-temperature exhaust gases over extended periods. Thus, damage to engine components is further avoided.

[0038] At your discretion, this method is The system 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.

[0039] This results in situation-based control that can quickly and efficiently limit the crankshaft rotation speed while avoiding the generation of high-temperature exhaust gases over a long period of time. Thus, damage to engine components is further avoided.

[0040] At your discretion, this method is The method includes a step of controlling the electric actuator configuration to move the throttle valve to the open position when the rotational speed of the crankshaft falls below the upper limit speed.

[0041] This results in situation-based control that allows for rapid and efficient limiting of the crankshaft's rotational speed while avoiding excessive restriction of the crankshaft's rotational speed.

[0042] According to a second aspect of the present invention, this objective is achieved by a control configuration configured to limit the rotational speed of the crankshaft of an internal combustion engine of a handheld power tool, wherein the internal combustion engine comprises the crankshaft, a cylinder, a piston located 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 located in the intake system, and an electric actuator configuration configured to move the throttle valve between an open position and a closed position. The throttle valve is configured to limit the airflow through the intake system when it is in the closed position. The control configuration is configured to take action when the rotational speed of the crankshaft exceeds an upper limit speed. The ignition timing of the ignition device is retarded from the initial ignition timing to the retarded ignition timing, The system is configured to control the electric actuator configuration so as to move the throttle valve toward the closed position.

[0043] In this way, the control configuration is provided to have the conditions for obtaining a rapid limit on the rotational speed of the crankshaft, while allowing the use of a small electric actuator configuration to move the throttle valve toward the closed position.

[0044] In other words, the control configuration is configured to retard the ignition timing and control the electric actuator configuration in order to move the throttle valve toward the closed position. Compared to a solution where the use of throttle valve closure is the sole means of limiting the rotational speed of the crankshaft, it is possible to use a smaller, lower-cost, and lighter electric actuator configuration to move the throttle valve toward the closed position. This is because it can be ensured that the rotational speed of the crankshaft is limited for the period required to move the throttle valve toward the closed position, thus allowing the use of a less rapid, stronger, and heavier electric actuator configuration.

[0045] Similarly, the control configuration is configured to control the electric actuator configuration to move the throttle valve toward the closed position, thus reducing the time required for operation at retarded ignition timing compared to a solution where retarding the ignition timing is the only means of limiting the crankshaft rotation speed. Reducing the time required for operation at retarded ignition timing avoids prolonged periods of excessively high exhaust temperatures, thereby also avoiding damage to the internal combustion engine.

[0046] Therefore, a robust and reliable control configuration is provided that can quickly limit the rotational speed of the crankshaft while avoiding damage to engine components. Furthermore, the control configuration is configured to retard the ignition timing and control the electric actuator configuration in order to move the throttle valve toward the closed position, thereby providing a control configuration that can quickly limit the rotational speed of the crankshaft without causing the unwanted release of unburned fuel. As a further result, a control configuration is provided that allows the use of exhaust aftertreatment configurations such as catalytic converters to process exhaust gases from the engine.

[0047] Furthermore, the control configuration is configured to retard the ignition timing and control the electric actuator configuration in order to move the throttle valve toward the closed position, thereby providing a control configuration that can reduce the engine's fuel consumption.

[0048] Therefore, a control configuration is provided that overcomes, or at least mitigates, at least some of the problems and drawbacks described above. As a result, the above objectives are achieved. It is understood that the various embodiments described in the method are all combinatable with the control configurations described herein. That is, a control configuration according to a second aspect of the present invention may be configured to perform any one of the method steps of the method according to a first aspect of the present invention.

[0049] According to a third aspect of the present invention, this objective is achieved by a handheld power tool comprising an internal combustion engine for supplying power to the tool of the handheld power tool, the internal combustion engine comprising: a crankshaft; a cylinder; a piston located 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 located in the intake system; and an electric actuator configuration 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 it is in the closed position. The handheld power tool is configured such that when the rotational speed of the crankshaft exceeds an upper limit speed, The ignition timing of the ignition device is retarded from the initial ignition timing to the retarded ignition timing, The system is configured to control the electric actuator configuration so as to move the throttle valve toward the closed position.

[0050] In this way, a handheld power tool is provided that has the conditions for rapid limiting of the crankshaft rotation speed, while allowing the use of a small electric actuator device to move the throttle valve toward the closed position.

[0051] In other words, while the use of throttle valve closure is the only means of limiting the crankshaft rotational speed, a handheld power tool is provided that can use a smaller, lower-cost, and lighter electric actuator configuration to move the throttle valve toward the closed position, compared to a solution that ensures rapid limitation of the crankshaft rotational speed and avoids prolonged periods of excessive exhaust temperature.

[0052] Therefore, 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 the unnecessary release of unburned fuel.

[0053] Furthermore, a handheld power tool is provided that allows the use of exhaust aftertreatment configurations such as catalytic converters to process 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 the closed position, thus providing a handheld power tool that has conditions for reducing fuel consumption.

[0054] Therefore, a handheld power tool is provided that overcomes, or at least mitigates, at least some of the problems and drawbacks described above. As a result, the above objectives are achieved. Optionally, the electric actuator configuration includes an electric motor. This provides conditions for a simple and cost-effective electric actuator configuration that can move the throttle valve toward the closed position when the rotational speed of the crankshaft exceeds an upper limit speed.

[0055] Optionally, the electric motor is a stepping motor. This avoids the need for a sensor to monitor the current position of the throttle valve. Optionally, the electric actuator configuration includes a transmission, and the electric motor includes an output shaft connected to the throttle valve via the transmission. This allows for the generation of the torque necessary to move the throttle valve to the closed position and provides conditions for the use of a small and lightweight electric motor.

[0056] Optionally, the transmission provides a positive gear ratio between the output shaft of the electric motor and the throttle valve. This allows for the generation of the torque necessary to move the throttle valve to the closed position and provides conditions for the use of a small and lightweight electric motor.

[0057] Optionally, the transmission includes a planetary gear set. This provides 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. Furthermore, conditions are provided for arranging the planetary gear set coaxially with respect to the output shaft of the electric motor and / or coaxially with respect to the shaft of the throttle valve, thereby resulting in a compact electric actuator configuration.

[0058] Optionally, the internal combustion engine comprises a crankcase that at least partially encloses the crankshaft, and the intake system comprises an intake duct connected to the crankcase, with the throttle valve positioned in the intake duct. This provides conditions for efficiently restricting the airflow into the engine when the throttle valve is controlled toward the closed position.

[0059] Optionally, the internal combustion engine is a crankcase scavenging two-stroke internal combustion engine, and the intake system is configured to guide air to the cylinder at least partially through the crankcase of the internal combustion engine. This provides conditions for a handheld power tool having an engine that is mechanically simple, lightweight, and has a high power-to-weight ratio.

[0060] Optionally, the internal combustion engine comprises a main throttle valve located in the intake system, and the handheld power tool comprises a first handle and a throttle actuator located on the first handle, the throttle actuator being operably connected to the main throttle valve. Thereafter, when the rotational speed of the crankshaft exceeds an upper limit, the throttle valve can move toward a closed position independently of the position and control of the main throttle valve. In this way, the rotational speed of the crankshaft can be more reliably limited.

[0061] Furthermore, the engine output can be adjusted simply, efficiently, and reliably, and a handheld power tool is provided that controls the position of the main throttle valve independently of the function and operation of the electric actuator configuration.

[0062] Optionally, the throttle actuator is operably connected to the main throttle valve via a mechanical connection. This provides a simple, efficient, and reliable connection between the throttle actuator and the main throttle valve, thus providing conditions for simple, efficient, and reliable control of the engine's power.

[0063] Furthermore, compared to a solution in which the main throttle valve is controlled by an electric actuator assembly, a lighter solution for controlling engine power can be provided. Moreover, according to the features of the control configurations and methods of the embodiments herein, a lighter solution for controlling engine power can be provided compared to a solution in which the engine has one throttle valve used to control engine power and limit the rotational speed of the engine's crankshaft.

[0064] In other words, in order to control engine power according to the solutions described above, 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 allow readings of the throttle actuator position before and during engine startup. Such components add weight and complexity to the handheld power tool.

[0065] Therefore, since the internal combustion engine has a main throttle valve and the throttle actuator is operably connected to the main throttle valve via a mechanical connection, a lightweight and uncomplicated solution for controlling the engine's power can be provided.

[0066] Optionally, the internal combustion engine may be equipped with an exhaust system configured to guide exhaust gases from the cylinder to the surroundings, and the exhaust system may be equipped with a catalytic converter. This provides a more environmentally friendly handheld power tool that can reduce the emission of unburned hydrocarbons. Furthermore, the control configuration is configured to limit the rotational speed of the crankshaft by retarding the ignition timing and controlling the electric actuator configuration to move the throttle valve toward the closed position, thereby ensuring the function and durability of the catalytic converter.

[0067] The handheld power tool is optionally a chainsaw or a power cutter. This provides a chainsaw or power cutter that has at least some of the advantages mentioned above.

[0068] Further features and advantages of the present invention will become apparent by considering the appended claims and the detailed description below. Various aspects of the present invention, including their specific features and advantages, will be readily apparent from the exemplary embodiments discussed in the following detailed description and accompanying drawings. [Brief explanation of the drawing]

[0069] [Figure 1] A first side view of a handheld power tool according to some embodiments of the present disclosure. [Figure 2] Schematic diagram of the cross-section of the internal combustion engine of the handheld power tool shown in Figure 1. [Figure 3] A schematic cross-section of an internal combustion engine shown in Figure 2, where the throttle valve moves from the open position to the closed position by an electric actuator. [Figure 4] A schematic diagram illustrating a method for limiting the rotational speed of the crankshaft of an internal combustion engine in a handheld power tool. [Modes for carrying out the invention]

[0070] The embodiments of the present invention are described more fully hereafter. Throughout, similar numbers refer to similar elements. Well-known functions or configurations are not necessarily described in detail for the sake of brevity and / or clarity.

[0071] Figure 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 comprises a tool 30 and an internal combustion engine 10 configured to power the tool 30. According to the embodiments shown, the handheld power tool 1 is a chainsaw comprising a tool 30 in the form of a cutting chain that is movably arranged around a guide bar 32. Figure 1 schematically shows the cutting chain and the guide bar 32.

[0072] The internal combustion engine 10 is configured to rotate the cutting chain around the guide bar 32 during the 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 a power cutter, circular saw, trimmer, hedge trimmer, or multi-tool. Obviously, according to such embodiments, the handheld power tool 1 may comprise another type of tool 30 other than the cutting chain, such as a circular saw blade, trimmer head, or hedge trimmer cutting assembly. The handheld power tool 1 comprises a fuel tank 13 configured to store fuel supplied to the internal combustion engine 10 during its operation. The internal combustion engine 10 of the handheld power tool 20 may be configured to operate on gasoline, alcohol, similar volatile fuels, also known as petrol, or a combination thereof.

[0073] The handheld power tool 1 comprises a first handle 33 and a second handle 34. The second handle 34 is separate from the first handle 33 and is positioned at a distance from the first handle 33. The handheld power tool 1 is configured to be supported by the first handle 33 and the second handle 34, respectively, during operation. In other words, the handheld power tool 1 is configured to be supported by both hands of the user during operation, that is, supported by one hand gripping the first handle 33 and the other hand gripping the second handle 34.

[0074] According to the shown embodiment, the first handle 33 is a rear handle located at the rear of the handheld power tool 1, and the second handle 34 is a so-called front handle. According to the shown embodiment, the second handle 34 is located closer to the tool 30 of the handheld power tool 1 than the first handle 33. The second handle 34 is also located between the tool 30 of the handheld power tool 1 and the first handle 33 of the handheld power tool 1. According to the shown embodiment, the second handle 34 is formed by an elongated, curved body that allows the user to conveniently grip the second handle 34 from various directions. This allows the user to conveniently and safely operate the handheld power tool 1 in different orientations relative to the gravitational field.

[0075] The handheld power tool 1 includes a throttle actuator 35 located on a first handle 33. The throttle actuator 35 can be used to control the power output of an internal combustion engine 10, as further described herein.

[0076] Figure 2 schematically shows a cross-section of the internal combustion engine 10 of the handheld power tool 1 shown in Figure 1. For simplicity and clarity, the internal combustion engine 10 is also referred to as the "combustion engine" or simply the "engine." Hereafter, unless otherwise indicated, Figures 1 and 2 will be referred to together.

[0077] The combustion engine 10 comprises a crankshaft 3, a cylinder 2, and a piston 5 positioned 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 bottom dead center and top dead center within 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. In Figure 2, the piston 5 is shown positioned between top dead center and bottom dead center.

[0078] According to the embodiments shown, the internal combustion engine 10 of the handheld power tool 1 is a small crankcase scavenging 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 small four-stroke internal combustion engine. In this context, the term “small” may encompass the engine 10 having an engine displacement of less than 250 cubic centimeters.

[0079] The internal combustion engine 10 includes a crankcase 6 that surrounds a crankcase volume V. The crankcase 6 surrounds a portion of the crankshaft 3. In other words, at least a portion of the crankshaft 3 is located within the crankcase volume V of the crankcase 6.

[0080] The piston 5 has a first surface that forms the interface with the combustion chamber 4 and a second surface that forms the interface with the crankcase volume V. Thus, the first surface of the piston 5 faces the combustion chamber 4, and the second surface of the piston 5 faces the crankcase 6 of the engine 10. The size of the crankcase volume V decreases as the piston 5 moves toward bottom dead center. In this way, the pressure in the crankcase volume V of the crankcase 6 may increase as the piston 5 moves toward bottom dead center, as will be further described herein.

[0081] Furthermore, since the second surface of the piston 5 forms the interface of the crankcase volume V of the crankcase 6, the size of the crankcase volume V is minimum when the piston 5 is at bottom dead center and maximum when the piston 5 is at top dead center. Thus, the piston 5 of the engine 10 according to the embodiment herein acts like a scavenging pump member, i.e., a pump member for replacing combustion gases in the combustion chamber 4 of the engine 10, as further described herein.

[0082] The engine 10 includes an intake system 9 configured to guide air into the cylinder 2 during the operation of the engine 10. According to the shown embodiment, the intake system 9 includes an intake duct 9' connected to the crankcase 6. Furthermore, the intake system 9 includes an air filter unit 19 connected to the intake duct 9'. Thus, according to the shown embodiment, the intake system 9 is configured to guide air into the cylinder 2 via the crankcase 6 of the internal combustion engine 10. The cylinder 2 of the engine 10 includes an intake port 42. The intake port 42 fluidly connects the crankcase 6 to the intake duct 9' when the piston is in the top dead center region.

[0083] The engine 10 includes a main throttle valve 31 located in the intake duct 9' of the intake system 9. The throttle actuator 35 of the handheld power tool 1 shown in Figure 1 is operably connected to the main throttle valve 31. More specifically, according to these embodiments, the throttle actuator 35 is operably connected to the main throttle valve 31 via a mechanical connection 37 schematically shown in Figure 2. In this way, the amount of air drawn into the cylinder 2 of the engine 10, and therefore the power generated by the engine 10, can also be easily and reliably controlled via the throttle actuator 35, as will be further described herein.

[0084] According to the embodiments shown, an intake port 42 is provided in the wall of the cylinder 2, and as the piston 5 moves toward bottom dead center, a pressure increase is obtained in the crankcase volume V of the crankcase 6 due to the closure of the intake port 42 by the mantle surface of the piston 5. However, according to further embodiments, an intake duct 9' may be directly connected to the crankcase 6, and the engine 10 may lack the intake port 42 provided in the wall of the cylinder 2. According to such embodiments, as with other embodiments herein, the engine 10 may include one or more unidirectional valves, such as reed valves, which are arranged to obstruct the flow of gas from the crankcase volume V of the crankcase 6 to the intake duct 9' as the piston 5 moves toward bottom dead center.

[0085] As shown in Figure 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 to the inlet port 45. According to the shown embodiment, the inlet port 45 is open when the piston 5 is in the bottom dead center region. More specifically, according to the shown 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 open, 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. As used herein, the term “upper edge” means that the edge of the inlet port 45 is the uppermost edge when the engine is oriented to a local gravity field such that the direction from top dead center to bottom dead center coincides with the local gravity vector. Obviously, the engine 10 may be configured to operate in other orientations toward a local gravity field.

[0086] As can be understood from the above, when the inlet port 45 is opened, transport of gas such as air or an air / fuel mixture is obtained from the crankcase volume V of the crankcase 6 to the combustion chamber 4 through the scavenging channel 24 and the intake port 45 shown in Figure 2. The engine 10 may have two or more inlet ports 45 and two or more scavenging channels 24.

[0087] The engine 10 includes an exhaust system 41 configured to guide 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 seen in Figure 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.

[0088] The characteristic that the upper edge of the exhaust port 38 is above the upper edge of the inlet port 45 means that when the engine 10 is oriented with respect to the local gravity field such that the direction from top dead center to bottom dead center coincides with the local gravity vector, the uppermost edge of the exhaust port 38 is positioned above the uppermost edge of the intake port 45 as seen with respect to the local gravity vector.

[0089] Therefore, these features ensure that the inlet port 45 is completely closed before the exhaust port 38 as the piston 5 moves from bottom dead center to top dead center. Once both the inlet port 45 and the exhaust port 38 are completely closed, the gas trapped in the combustion chamber 4 is compressed by the movement of the piston 5 toward top dead center.

[0090] Engine 10 further comprises a fuel supply system. The fuel supply system is not shown in Figure 2 for reasons of brevity and clarity. The fuel supply system may comprise one or more carburetors located in the intake system 9 of engine 10, such as in the intake duct 9' of the intake system 9. Alternatively, or in addition thereto, engine 10 may comprise one or more of the following: fuel injectors configured to inject fuel into the crankcase volume V of the crankcase 6, fuel injectors configured to inject fuel into the combustion chamber 4, and fuel injectors configured to inject fuel into the scavenging channel 24.

[0091] Therefore, the fuel added to or transported to the combustion chamber 4 from such a fuel supply system can be compressed together with the air trapped in the combustion chamber 4 when each of the inlet port 45 and exhaust port 38 is completely closed and the piston 5 moves toward top dead center.

[0092] 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 shown 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 in the combustion chamber 4 when a high voltage is supplied. According to a further embodiment, the engine 10 may comprise another type of ignition device other than a spark plug.

[0093] According to the shown embodiment, the engine 10 includes an ignition system 17 configured to control an ignition device 7 to ignite the air / fuel mixture in the combustion chamber 4 based on the rotational position of the crankshaft 3 of the engine 10. According to the shown embodiment, the engine 10 includes sensor configurations 26, 26' configured to sense the current rotational position of the crankshaft 3, and the ignition system 17 is operably connected to the sensor configurations 26, 26' and configured to control an 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.

[0094] During normal operation of the engine 10, the ignition device 7 is controlled to ignite the air / fuel mixture in the combustion chamber 4 when the piston 5 is a few crank angles from top dead center as it moves toward top dead center. During the remaining motion of the piston 5 toward top dead center, combustion of the air / fuel mixture progresses, and the increase in pressure and temperature in the combustion chamber 4 resulting from the combustion pushes the piston 5 toward 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.

[0095] Due to the arrangement of the exhaust port 38 and the inlet port 45, when the piston 5 moves in the direction d2 toward bottom dead center, the exhaust port 38 opens earlier than the inlet port 45. In this way, the exhaust gas can be discharged from the combustion chamber 4 to the exhaust system 42 before fresh air is transported to the combustion chamber 4 through the scavenging channel 24 and the inlet port 45 by the pumping action resulting from the movement of the piston 5 toward bottom dead center.

[0096] According to embodiments of this specification, the engine 10 includes a throttle valve 11 located in the intake system 9. The throttle valve 11 is separate from the main throttle valve 31 and may also be called an auxiliary or additional throttle valve 11. According to the embodiments shown, the throttle valve 11 is located in the intake duct 9' of the intake system 9. Furthermore, the engine 10 includes an electric actuator configuration 13 configured to move the throttle valve 11 between an open position and a closed position.

[0097] In Figure 2, the throttle valve 11 is shown in the open position. The open position of the throttle valve 11 constitutes a position in which the throttle valve 11 does not restrict the airflow through the intake system 9 at all, or only slightly restricts it. The closed position of the throttle valve 11 constitutes a position in which the throttle valve 11 restricts the airflow through the intake system 9. When used herein, the expression restricting the airflow means a partial blockage of the airflow through the intake system 9.

[0098] Figure 3 schematically shows a cross-section of the internal combustion engine 10 shown in Figure 2, where the throttle valve 11 moves from the open position shown in Figure 2 to the closed position by the electric actuator configuration 13. Hereafter, unless otherwise indicated, Figures 1 to 3 will be referred to simultaneously.

[0099] As can be seen in Figures 2 and 3, according to the embodiments shown, 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 embodiments shown, the throttle valve 11 is pivotally positioned around a pivot axis Pa. As can be seen in Figure 2, 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 it is substantially parallel to the direction of airflow through the intake duct 9' of the intake system 9. In this way, the throttle valve 11 does not restrict the airflow through the intake system 9 at all, or only slightly, when the throttle valve 11 is in the open position. Therefore, in the embodiments shown, the “open position” of the throttle valve 11 is also referred to as the “fully open position” as used herein.

[0100] Furthermore, as shown in Figure 3, 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 it is perpendicular to the direction of airflow through the intake duct 9' of the intake system 9. In this way, when the throttle valve 11 is in the closed position, it restricts, or partially blocks, the airflow through the intake duct 9' of the intake system 9. As shown in Figure 3, when the throttle valve 11 is in the closed position, it does not completely block the airflow through the intake duct 9' of the intake system 9. Therefore, according to the embodiments shown, the “closed position” of the throttle valve 11 as referred to herein may also be called the “at least partially closed position”.

[0101] According to the shown embodiment, the electric actuator configuration 13 comprises an electric motor 23. The electric motor 23 may be a stepping motor. In this way, the need for a sensor to monitor the position of the throttle valve is avoided. Furthermore, according to the shown embodiment, the electric actuator configuration 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. According to the shown embodiment, 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, the throttle valve 11 can be moved using a small electric motor 23, and the torque required to move the throttle valve 11 can be generated under various operating conditions of the engine 10.

[0102] More specifically, according to the embodiment shown, the transmission 25 includes a planetary gear set. The planetary gear set is arranged coaxially with respect to the output shaft 27 of the electric motor 23 and also coaxially with respect to the shaft of the throttle valve 11. In this way, a compact electric actuator configuration 13 is obtained. Furthermore, by utilizing the planetary gear set between the output shaft 27 of the electric motor 23 and the throttle valve 11, conditions are provided 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.

[0103] The engine 10 comprises an electric actuator configuration 13 and a control configuration 21 operably connected to the ignition device 7 of the engine 10. According to the shown embodiment, the control configuration 21 is operably connected to the ignition device 7 by being operably connected to the ignition system 17.

[0104] In Figure 2, the throttle valve 11 and the main throttle valve 31 are indicated by their respective open positions. Therefore, the engine 10 shown in Figure 2 is shown operating in a full throttle state, i.e., a full power state.

[0105] According to embodiments of this specification, the control configuration 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 the upper limit speed, and is configured to control the electric actuator configuration 13 to move the throttle valve 11 toward the closed position.

[0106] Closing the throttle valve 11, that is, moving the throttle valve 11 from the open position to the closed position, is accompanied by a predetermined closing time. The closing time of the throttle valve 11, that is, the time 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. As a simple example, 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.

[0107] However, the control configuration 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 configuration 13 to move the throttle valve 11 toward the closed position when the rotational speed of the crankshaft 3 exceeds the upper speed limit, thereby providing a rapid limit on the rotational speed of the crankshaft 3 while allowing the use of a small electric actuator configuration 13 to move the throttle valve 11 toward the closed position.

[0108] Retarding the ignition timing increases the exhaust temperature, which is the temperature of the exhaust gas 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 combustion energy of the air / fuel mixture in the combustion chamber 4 is converted into mechanical work supplied to the crankshaft 3 of the engine 10 during the delayed combustion in the combustion chamber 4.

[0109] However, since the control configuration 21 is configured to control the electric actuator configuration 13 to move the throttle valve 11 toward the closed position when the rotational speed of the crankshaft 3 exceeds the upper limit speed, the period required for operation at retarded ignition timing can be shortened compared to a solution in which retarding the ignition timing is the only means of limiting the rotational speed of the engine's crankshaft. Because the time required for operation at retarded ignition timing is shortened, a longer period of excessive exhaust temperature is avoided. In this way, damage to the engine 10 is avoided.

[0110] The control configuration 21 may be configured to use the current rotational speed of the crankshaft 3 as input to control the electric actuator configuration 13 to move the throttle valve 11 between the open and closed positions. According to some embodiments, the control configuration 21 may be configured to control the electric actuator configuration 13 to move the throttle valve 11 toward the closed position when the rotational speed of the crankshaft 3 exceeds an upper limit speed, and to control the electric actuator configuration 13 to move the throttle valve 11 toward the open position when the rotational speed of the crankshaft 3 falls below the upper limit speed.

[0111] According to some embodiments, the control configuration 21 may include a proportional-integral-derivative controller, also known as a PID controller or ternary controller, which uses the current rotational speed of the crankshaft 3, a desired rotational speed of the crankshaft 3, the current position of the throttle valve 11, and a desired position of the throttle valve 11 as inputs.

[0112] For example, the upper speed limits referenced herein may be in the range of 7,000 to 15,000 revolutions per minute, or in the range of 12,000 to 14,000 revolutions per minute.

[0113] The control configuration 21 may be configured to retard the ignition timing of the ignition device 7 so that the ignition timing is retarded as the rotational speed increases above the upper limit speed. That is, the control configuration 21 may be configured to control the ignition timing of the ignition device 7 such that the magnitude of the retardation follows at least approximately as the current rotational speed of the crankshaft 3 exceeds the upper limit speed. Such control may be performed such that the magnitude of the retardation follows at least approximately linearly as the current rotational speed of the crankshaft 3 exceeds the upper limit speed. The control configuration 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.

[0114] As used herein, initial ignition timing is the current ignition timing used when the rotational speed of the crankshaft 3 reaches its upper limit. For example, the initial ignition timing may be within 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.

[0115] As used herein, retarded ignition timing is ignition timing that is retarded, i.e., delayed, relative to the initial ignition timing. As described above, the control of the ignition timing may be carried out such that the magnitude of retardation follows at least substantially linearly to the extent that the current rotational speed of the crankshaft 3 exceeds the upper limit speed. The control of the ignition timing may be carried out such that the magnitude of retardation of the ignition timing increases as the rotational speed increases above the upper limit speed, up to the maximum retardation of the ignition timing. For example, the maximum retardation of the ignition timing may be in the range of 15 to 35 crank angles from the initial ignition timing, or in the range of 20 to 30 crank angles.

[0116] As can be understood 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 a few crank angles after top dead center.

[0117] As described above, the control configuration 21 may be configured to control the ignition timing of the ignition device 7 such that the ignition timing advances as the rotational speed decreases above the upper limit speed. If there is a predetermined difference in the rotational speed of the crankshaft 3 above the upper limit speed, the advance of the ignition timing accompanying the decrease in rotational speed above the upper limit speed may correspond to the magnitude of retardation of the ignition timing. Furthermore, as can be understood from the above, the control configuration 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 limit speed.

[0118] Figure 4 schematically illustrates a method 100 for limiting the rotational speed of the crankshaft of an internal combustion engine in a handheld 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 handheld power tool may be the handheld power tool 1 according to the embodiment shown in Figure 1. Therefore, unless otherwise indicated, Figures 1 to 4 will be referred to together below.

[0119] Method 100 is a method for limiting the rotational speed of the crankshaft 3 of an internal combustion engine 10 of a handheld power tool 1. The internal combustion engine 10 comprises a crankshaft 3, a cylinder 2, a piston 5 located 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 the cylinder 2, a throttle valve 11 located in the intake system 9, and an electric actuator configuration 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 airflow through the intake system 9 when it is in the closed position. Method 100 is a method for limiting the rotational speed of the crankshaft 3 when the rotational speed exceeds the upper limit speed. A process 110 to retard the ignition timing of the ignition device 7 from the initial ignition timing to the retarded ignition timing, The process includes a step 120 of controlling an electric actuator configuration 13 to move the throttle valve 11 toward the closed position.

[0120] The steps 110 to retard the ignition timing of the ignition device 7 and 120 to control the electric actuator configuration 13 to move the throttle valve 11 toward the closed position may be performed simultaneously when the rotational speed of the crankshaft 3 exceeds the upper limit speed.

[0121] As shown in Figure 4, the step 110 for retarding the ignition timing of the ignition device 7 is, The procedure may include step 111 of maintaining control of the ignition timing of the ignition device 7 to a retarded ignition timing when the rotational speed of the crankshaft 3 exceeds the upper limit speed.

[0122] Furthermore, as shown in Figure 4, the step 110 for retarding the ignition timing of the ignition device 7 is, The process may include a step 113 to control the ignition timing of the ignition device 7 such that the ignition timing is retarded as the rotational speed increases beyond the upper limit.

[0123] Furthermore, as shown in Figure 4, the step 110 for retarding the ignition timing of the ignition device 7 is, The process may include a step 115 to control the ignition timing of the ignition device 7 such that the ignition timing advances as the rotational speed, which exceeds the upper limit speed, decreases.

[0124] Furthermore, as shown in Figure 4, Method 100 is, The system may include a step 117 to advance the ignition timing to the initial ignition timing when the rotational speed of the crankshaft 3 falls below the upper limit speed.

[0125] Furthermore, as shown in Figure 4, Method 100 is, The system may include a step 121 to control the electric actuator configuration 13 so as to move the throttle valve 11 to the open position when the rotational speed of the crankshaft 3 falls below the upper limit speed.

[0126] It will be understood that all of the various embodiments described for Method 100 are combinatorially compatible with the control configuration 21 described herein. That is, the control configuration 21 may be configured to perform any one of the method steps 110, 111, 113, 115, 117, 120, and 121 of Method 100.

[0127] Those skilled in the art will understand that a method 100 for limiting the rotational speed of the crankshaft 3 of the internal combustion engine 10 of a handheld power tool 1 can be implemented by programmed instructions. These programmed instructions typically consist of a computer program, which, when executed in a control configuration 21, ensures that the control configuration 21 performs desired controls such as method steps 110, 111, 113, 115, 117, 120, and 121 described herein. The computer program is usually part of a computer program product that includes a suitable digital storage medium in which the computer program is stored. According to such embodiments, the computer-readable medium comprises a computer program that, when the program is executed by a computer, includes instructions that cause the computer to perform a method 100 according to some embodiment.

[0128] The control configuration 21 may include virtually any suitable type of processor circuit or microcomputer, such as a computing unit which may take the form of 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. As used herein, the term “computing unit” may refer to a processing circuit comprising, for example, one, some, or all of the processing circuits described above.

[0129] The control configuration 21 may further comprise a memory unit, and a computing unit may be connected to the memory unit, which may provide the computing unit with stored program code and / or stored data that may be necessary, for example, to enable the computing unit to perform calculations. The computing unit may also be configured to store partial or final results of calculations in the memory unit. The memory unit may include physical devices used 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.

[0130] The control configuration 21 is connected to the components of the internal combustion engine 10 and / or the 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 can be detected as information by an input signal receiving device and converted into signals that can be processed by the control configuration 21. These signals may then be supplied to a calculation unit. One or more output signal transmitting devices may be configured to convert the calculation results from the calculation 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 to which the signals are intended. Each of the connections to each component of the internal combustion engine 10 for sending and receiving input and output signals may take one or more forms from cables or wireless connections.

[0131] In the embodiment shown, the handheld power tool 1 includes a control configuration 21, but alternatively, it may be implemented entirely or partially in two or more control configurations or two or more control units.

[0132] The computer program product may be provided, for example, in the form of a data carrier that carries computer program code to perform at least some of the method steps 110, 111, 113, 115, 117, 120, and 121 according to some embodiment, when loaded into one or more computing units of the control configuration 21. The data carrier may be, for example, a CD-ROM disk, or any other suitable medium such as a ROM (read-only memory), PROM (programmable read-only memory), EPROM (erasable PROM), flash memory, EEPROM (electrically erasable PROM), hard disk, memory stick, optical storage device, magnetic storage device, or a disk or tape capable of holding non-temporarily machine-readable data. The computer program product may also be provided as computer program code on a server, which may be downloaded to the control configuration 21.

[0133] The above describes various exemplary embodiments, and it will be understood that the present invention is defined solely by the appended independent claims. Those skilled in the art will understand that exemplary embodiments may be modified without departing from the scope of the present invention as defined by the appended independent claims, and different features of exemplary embodiments may be combined to create embodiments other than those described herein.

[0134] As used herein, the terms “comprising” or “comprises” are open-ended and include one or more described features, elements, processes, components, or functions, but do not exclude the presence or addition of one or more other features, elements, processes, components, functions, or groups thereof.

Claims

1. A method (100) for limiting the rotational speed of the crankshaft (3) of the internal combustion engine (10) of a handheld power tool (1), The internal combustion engine (10) is The crankshaft (3) and, Cylinder (2) and A piston (5) is positioned 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 guiding air to the cylinder (2), The throttle valve (11) located in the intake system (9), The system includes an electric actuator configuration (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 it is in the closed position. The method (100) is performed when the rotational speed of the crankshaft (3) exceeds the upper limit speed. The ignition timing of the ignition device (7) is retarded from the initial ignition timing to the retarded ignition timing, and the ignition timing retardation step (110) is performed. A method comprising the step (120) of controlling the electric actuator configuration (13) to move the throttle valve (11) toward the closed position.

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

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

4. The ignition timing retardation step (110) is, The method (100) according to claim 1 or 2, comprising the step (115) of controlling the ignition timing of the ignition device (7) such that the ignition timing advances as the rotational speed, which exceeds the upper limit speed, decreases.

5. The method according to claim 1 or 2 (100), 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 limit speed.

6. The method according to claim 1 or 2 (100), further comprising the step (121) of controlling the electric actuator configuration (13) to move the throttle valve (11) to the open position when the rotational speed of the crankshaft (3) falls below the upper limit speed.

7. A control configuration (21) configured to limit the rotational speed of the crankshaft (3) of the internal combustion engine (10) of a handheld power tool (1), wherein the internal combustion engine (10) is The crankshaft (3) and, Cylinder (2) and A piston (5) is positioned 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 guiding air to the cylinder (2), The throttle valve (11) located in the intake system (9), The system includes an electric actuator configuration (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 it is in the closed position. The control configuration (21) is configured such that when the rotational speed of the crankshaft (3) exceeds the upper limit speed, The ignition timing of the ignition device (7) is retarded from the initial ignition timing to the retarded ignition timing, A control configuration (21) is configured to control the electric actuator configuration (13) so as to move the throttle valve (11) toward the closed position.

8. A handheld power tool (1), comprising an internal combustion engine (10) for supplying power to the tool (30) of the handheld power tool (1), The internal combustion engine (10) is Crankshaft (3) and Cylinder (2) and A piston (5) is positioned 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 guiding air to the cylinder (2), The throttle valve (11) located in the intake system (9), The system includes an electric actuator configuration (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 it is in the closed position. The handheld power tool (1) is configured such that when the rotational speed of the crankshaft (3) exceeds the upper limit speed, The ignition timing of the ignition device (7) is retarded from the initial ignition timing to the retarded ignition timing, A handheld power tool (1) is provided with a control configuration (21) configured to control the electric actuator configuration (13) so as to move the throttle valve (11) toward the closed position.

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

10. The handheld power tool (1) according to claim 9, wherein the electric motor (23) is a stepping motor.

11. The handheld power tool (1) according to claim 9 or 10, wherein the electric actuator configuration (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. The handheld 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. The handheld power tool (1) according to claim 11, wherein the transmission (25) comprises a planetary gear set.

14. The handheld power tool (1) according to claim 8, wherein the internal combustion engine (10) comprises a crankcase (6) that at least partially surrounds the crankshaft (3), the intake system (9) comprises an intake duct (9') connected to the crankcase (6), and the throttle valve (11) is located in the intake duct (9').

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

16. The handheld power tool (1) according to any one of claims 8 to 10, 14, wherein the internal combustion engine (10) comprises a main throttle valve (31) located in the intake system (9), and the handheld power tool (1) comprises a first handle (33) and a throttle actuator (35) located on the first handle (33), the throttle actuator (35) being operably connected to the main throttle valve (31).

17. The handheld power tool (1) according to claim 16, wherein the throttle actuator (35) is operably 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 10, 14, wherein the internal combustion engine (10) comprises an exhaust system (41) configured to guide exhaust gas from the cylinder (2) to the surroundings, and the exhaust system (41) comprises a catalytic converter (43).

19. A handheld power tool (1) according to any one of claims 8 to 10, 14, which is a chainsaw or a power cutter.

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