Multi-speed automatic transmissions for power tools are provided. A multi-speed automatic transmission includes an output shaft configured to be coupled to a chain sprocket to rotatably drive the chain sprocket, wherein the automatic transmission is configured to automatically shift between a plurality of gear ratios in response to a rotational speed of the output shaft reaching a preset rotational speed.

A chainsaw which has a low profile chain cover and a chain bar tightening clutch system. The chain bar tightening clutch system can have a bar tightening knob which drives a clutch which governs the amount of pressure applied to the chain bar by operating the bar tightening knob. The chainsaw can have a chain bar tensioning system which can have a tensioning drive member in an offset position from the tensioning post which positions the tensioning post to achieve a chain tension and compact chainsaw design. The chainsaw can also have an oil cap with a lock channel having a detent with produces a sound when moved from a disengaged to an engage position with an oil reservoir.

A chainsaw which has a low profile chain cover and a chain bar tightening clutch system. The chain bar tightening clutch system can have a bar tightening knob which drives a clutch which governs the amount of pressure applied to the chain bar by operating the bar tightening knob. The chainsaw can have a chain bar tensioning system which can have a tensioning drive member in an offset position from the tensioning post which positions the tensioning post to achieve a chain tension and compact chainsaw design. The chainsaw can also have an oil cap with a lock channel having a detent with produces a sound when moved from a disengaged to an engage position with an oil reservoir.

A power tool may include an engine, a tool driven for movement by the engine, a brake mechanism coupled to the tool, a charge forming device coupled to the engine and a transmission member operably coupled to the brake mechanism and a throttle valve of the charge forming device. The brake mechanism inhibits movement of the tool in an engaged position of the brake mechanism and permits movement of the tool in a disengaged position of the brake mechanism. The charge forming device is coupled to the engine to provide a combustible fuel and air mixture to the engine, and the throttle valve is movable between a first position and a second position. The transmission member is operably coupled to the brake mechanism and the throttle valve so that the throttle valve is moved away from the first position when the brake mechanism is moved to the engaged position.

An engine-driven working machine according to the present invention has a controller and a muffler. The controller is operated from starting of the engine in a rotational speed limitation mode in which the engine is prevented from rotating at a rotational speed that is higher than the predetermined limitation rotational speed. The controller forces to stop the engine, after a predetermined period has passed, during which the engine operates in the rotational speed limitation mode.

An engine-driven working machine according to the present invention has a controller and a muffler. The controller is operated from starting of the engine in a rotational speed limitation mode in which the engine is prevented from rotating at a rotational speed that is higher than the predetermined limitation rotational speed. The controller forces to stop the engine, after a predetermined period has passed, during which the engine operates in the rotational speed limitation mode.

An operator operates a throttle lever and by maximizing the extent of said operation, the drive state is initiated, and the crank shaft rotation rate R increases and reaches the maximal value (RC) thereof. Subsequently, the operator operates the dressing operation lever so as to be in a second state at elapsed time (t0) while keeping the extent of the throttle lever operation maximized. Because a microswitch is turned off, the crank shaft rotation rate (R) is controlled in a range of R1<R<R2. By placing the saw chain in contact with a grindstone fixed to the dressing operation lever simultaneously with said action, dressing work is performed. After the microswitch is turned off at elapsed time (t0), the output of an ignition coil is controlled cyclically by a control unit at a cycle (T1+T2) so as to be on (ignition) during period (T1) and off (flame off) during period (T2).

An operator operates a throttle lever and by maximizing the extent of said operation, the drive state is initiated, and the crank shaft rotation rate R increases and reaches the maximal value (RC) thereof. Subsequently, the operator operates the dressing operation lever so as to be in a second state at elapsed time (t0) while keeping the extent of the throttle lever operation maximized. Because a microswitch is turned off, the crank shaft rotation rate (R) is controlled in a range of R1<R<R2. By placing the saw chain in contact with a grindstone fixed to the dressing operation lever simultaneously with said action, dressing work is performed. After the microswitch is turned off at elapsed time (t0), the output of an ignition coil is controlled cyclically by a control unit at a cycle (T1+T2) so as to be on (ignition) during period (T1) and off (flame off) during period (T2).

A chain saw includes a chain, a guide plate for supporting and guiding the chain, a main body comprising a power output unit configured for driving the chain to cut a workpiece, and a locking device configured for fixing the guide plate and tensioning the chain. The locking device includes a device housing, an operating member configured to be operated by a user to rotate about a first axis, a first locking member configured for locking or releasing the guide plate, and a first clutch assembly comprising a first clutch and a second clutch. The first clutch assembly has a first state and a second state, the first clutch is operative to transmit a rotation of the operating member to the second clutch when the first clutch assembly is in the first state, the first clutch is operative to stop transmitting the rotation to the second clutch and the first clutch assembly is operative to produce a relative displacement relative to the second clutch when the first clutch assembly is in the second state.

A chain saw includes a chain, a guide plate for supporting and guiding the chain, a main body comprising a power output unit configured for driving the chain to cut a workpiece, and a locking device configured for fixing the guide plate and tensioning the chain. The locking device includes a device housing, an operating member configured to be operated by a user to rotate about a first axis, a first locking member configured for locking or releasing the guide plate, and a first clutch assembly comprising a first clutch and a second clutch. The first clutch assembly has a first state and a second state, the first clutch is operative to transmit a rotation of the operating member to the second clutch when the first clutch assembly is in the first state, the first clutch is operative to stop transmitting the rotation to the second clutch and the first clutch assembly is operative to produce a relative displacement relative to the second clutch when the first clutch assembly is in the second state.