Assembly and method for safe starting of an internal combustion engine

A power tool comprising:

• a working assembly configured to perform a cutting operation;
• a clutch for driving the working assembly;
• and
• an internal combustion engine for driving the working assembly with the clutch, the internal combustion engine comprising:
• a combustion chamber into which a mixture of fuel and air is supplied;
• a spark plug disposed proximate to the combustion chamber to ignite the mixture by generating a spark, ignition of the mixture driving a piston operably coupled to a crank portion of the engine;
• a fuel supply system including a fuel valve and a throttle valve, the fuel valve being configured to control fuel provision into the mixture and the throttle valve being adjustable to control the provision of air into the mixture;
• a throttle position sensor configured to detect a throttle position of the throttle valve within a full range of operation of the throttle valve;
• a speed sensor configured to determine engine speed;
• and
• a controller configured to control the operation of the fuel valve and the spark plug, the controller being configured to receive an indication of the engine speed from the speed sensor and to determine whether the engine speed exceeds a threshold value, and, if so, initiate a speed limitation operation maintaining the engine speed below a predetermined speed,
• wherein said controller is further configured to detect that the throttle valve is moved a predetermined angular value from an initial position of the throttle valve, either in an opening or closing direction of the throttle valve thereby indicating an intentional movement of a throttle of the power tool, and in response to detecting that the throttle valve is moved the predetermined angular value, the controller is further configured to discontinue the speed limitation operation.

A method of controlling an internal combustion engine of a power tool, the internal combustion engine including a throttle valve, the method comprising:

• determining an initial position of the throttle valve within a full range of operation of the throttle valve at start-up of the engine;
• determining whether the engine should be started in a start-up mode or a normal mode, wherein starting the engine in the start-up mode comprises initiating a speed limitation operation at the start-up of the engine, the speed limitation operation maintaining an engine speed below a predetermined level and, wherein starting the engine in the normal mode comprises no initiation of the speed limitation operation at the start-up of the engine;
• starting the engine in the start-up mode unless the throttle valve is moved a predetermined amount within the full range of operation of the throttle valve, either in an opening or closing direction of the throttle valve, from an initial position of the throttle valve thereby indicating an intentional movement of a throttle of the power tool;
• and
• maintaining the speed limitation operation of the start-up mode until the throttle valve is moved the predetermined amount.

An engine control arrangement for an internal combustion engine, comprising:

• a throttle position sensor configured to determine an angular position of a throttle valve of the engine and produce throttle position data, the throttle position sensor being an analog magnetic flux sensor;
• and
• a controller configured to operate in one of a normal mode and a start-up mode dependent upon the throttle position data,
• wherein the normal mode includes controlling a fuel supply dependent upon the throttle position data,
• wherein the start-up mode includes initiating a speed limitation mode that maintains the engine speed below a predetermined speed, and
• wherein the controller is further configured to detect that the throttle valve is moved a first predetermined angular value by more than an angular threshold, either in an opening or closing direction of the throttle valve thereby indicating an intentional movement of a throttle of the power tool, and in response to detecting that the throttle valve is moved the first predetermined angular valve by more than the angular threshold, the controller is further configured to begin operating in the normal mode.