Two-Stroke Engine Control

Abstract

A two-stroke combustion engine comprising a user-operated throttle control, an adjustable valve arranged to control one or more air intakes of the combustion engine, and a control unit arranged to control a state of the adjustable valve, wherein the combustion engine is arranged to operate in a first idle mode at an idle engine speed below a clutch engagement engine speed when the user-operated throttle control is not engaged, wherein the combustion engine is arranged to operate in a second idle mode at a target engine speed above the clutch engagement engine speed when the user-operated throttle control is engaged and when the engine is not subject to an external load, the control unit being arranged to control the state of the adjustable valve to maintain engine speed at the target engine speed when the engine operates in the second idle mode.

1 . A two-stroke combustion engine for use with a tool associated with an inertia, comprising a user-operated throttle control, an adjustable valve arranged to control one or more air intakes of the combustion engine, and a control unit arranged to control a state of the adjustable valve,
 wherein the combustion engine is arranged to operate in a first idle mode at an idle engine speed below a clutch engagement engine speed when the user-operated throttle control is not engaged,   wherein the combustion engine is arranged to operate in a second idle mode at a target engine speed above the clutch engagement engine speed when the user-operated throttle control is engaged and when the engine is not subject to an external load, and wherein   the control unit is arranged to control the state of the adjustable valve to maintain engine speed at the target engine speed when the engine operates in the second idle mode.   
     
     
         2 . The two-stroke combustion engine according to  claim 1 , wherein the control unit is arranged to determine an unwanted operating zone comprising a range of adjustable valve states in dependence of an engine speed value, and to control the state of the adjustable valve to be outside of the unwanted operating zone. 
     
     
         3 . The two-stroke combustion engine according to  claim 2 , wherein the control unit is arranged to determine the unwanted operating zone based on engine torque resulting from a combination of engine speed value and engine throttle angle, wherein the unwanted operating zone corresponds to sub-optimal engine scavenging operation. 
     
     
         4 . The two-stroke combustion engine according to  claim 2 , comprising one or more throttle state sensors and an engine speed sensor, wherein the control unit s arranged to determine a current operating point of the engine in relation to the unwanted operating zone based on one or more throttle state input signals from the one or more throttle state sensors, and on an engine speed signal from the engine speed sensor. 
     
     
         5 . The two-stroke combustion engine according to  claim 2 , wherein the control unit is arranged to control the state of the adjustable valve by increasing an opening of the adjustable valve by a first amount if the engine speed is below the target engine speed, and by decreasing an opening of the adjustable valve by a second amount if the engine speed is above the target engine speed, wherein the first and second amounts are determined to control the state of the adjustable valve to be outside of the unwanted operating zone. 
     
     
         6 . The two-stroke combustion engine according to  claim 5 , wherein a magnitude of the first amount and/or a magnitude of the second amount is determined in dependence of a rate of change in engine speed,
 wherein the control unit is arranged to determine the unwanted operating zone in dependence of a temperature value of the combustion engine, or   wherein the control unit is arranged to determine the unwanted operating zone in dependence of a user profile associated with the combustion engine.   
     
     
         7 . (canceled) 
     
     
         8 . (canceled) 
     
     
         9 . The two-stroke combustion engine according to any previous  claim 1 , wherein the target engine speed is a function of the state of the adjustable valve, or
 wherein the target engine speed is a function of a type of cut-off disc mounted.   
     
     
         10 . (canceled) 
     
     
         11 . The two-stroke combustion engine according to  claim 1 , wherein the control unit is arranged to control the state of the adjustable valve in dependence of a state of the user-operated throttle control. 
     
     
         12 . The two-stroke combustion engine according to  claim 1 , wherein the user-operated throttle control and the control unit are arranged to control the same adjustable valve, or
 wherein the user-operated throttle control is arranged to control a throttle valve arranged separate from the adjustable valve.   
     
     
         13 . (canceled) 
     
     
         14 . The two-stroke combustion engine according to  claim 1 , wherein the adjustable valve is arranged to control a pure air intake and an air/fuel intake of the engine. 
     
     
         15 . The two-stroke combustion engine according to  claim 1 , wherein the control unit is arranged to determine the unwanted operating zone comprising the range of adjustable valve states in dependence of a sensor input signal related to an operating condition of the two-stroke combustion engine. 
     
     
         16 . The two-stroke combustion engine according to  claim 15 , wherein the sensor input signal is any of an engine misfire sensor, a microphone, a vibration sensor, and an ignition timing sensor. 
     
     
         17 . The two-stroke combustion engine according to  claim 1 , wherein the control unit is arranged to regularly update the unwanted operating zone. 
     
     
         18 . The two-stroke combustion engine according to  claim 1 , wherein the control unit is arranged to control the state of the adjustable valve to limit engine speed to speeds below a configured maximum engine speed. 
     
     
         19 . The two-stroke combustion engine according to  claim 1 , wherein the state of the adjustable valve is a binary state comprising an open state and a closed state, or
 wherein the state of the adjustable valve comprises a continuous range of configurable air flow levels between a fully closed state and a fully open state, or   wherein the adjustable valve is an electrically controllable valve arranged to be controlled by a control signal received from the control unit.   
     
     
         20 . (canceled) 
     
     
         21 . (canceled) 
     
     
         22 . The two-stroke combustion engine according to  claim 1 , wherein the combustion engine is arranged to operate in the second idle mode when the engine is not subject to an external load below an idle load threshold, wherein the idle load threshold is configured below 50% of a maximum engine load. 
     
     
         23 . The two-stroke combustion engine according to  claim 1 , wherein the target engine speed lies between a configured maximum engine speed and a speed of the combustion engine associated with maximum engine torque. 
     
     
         24 . The two-stroke combustion engine according to  claim 1 , wherein the control unit is arranged to control the state of the adjustable valve by temporarily decreasing the opening of the adjustable valve by a third amount when the combustion engine accelerates past the clutch engagement engine speed, thereby allowing a clutch operation of the two-stroke combustion engine to complete at a temporarily reduced engine torque. 
     
     
         25 . The two-stroke combustion engine according to  claim 12 , wherein the adjustable valve comprises a valve portion arranged to be controlled by the user-operated throttle control via throttle linkage, the adjustable valve comprising a throttle linkage tensioning device configured to release tension in the throttle linkage in response to a control signal from the control unit whereby the control unit is arranged to control the state of the adjustable valve by controlling the throttle linkage tensioning device. 
     
     
         26 . (canceled) 
     
     
         27 . The two-stroke combustion engine according to  claim 25 , wherein the throttle linkage tensioning device is arranged to maintain tension in the throttle linkage when in a default state, and to release tension in the throttle linkage in response to the control signal from the control unit, or
 wherein the throttle linkage is a throttle cable or a throttle control rod, or   wherein the throttle linkage tensioning device is a pull action solenoid device or a push action solenoid device.   
     
     
         28 - 53 . (canceled)