A method for starting an internal combustion engine of a snowmobile is disclosed. The method comprises actuating a start switch of the snowmobile; in response to the start switch being actuated, sensing a temperature; in response to the sensed temperature being above a predetermined temperature, starting the engine using a motor-generator; and in response to the sensed temperature being below the predetermined temperature, starting the engine using a recoil starter.

A control device for a hybrid vehicle that includes an internal combustion engine, a motor, and a clutch provided between the internal combustion engine and the motor includes a first start control unit that starts the internal combustion engine without causing the motor to perform cranking, and a second start control unit that starts the internal combustion engine by causing the motor to perform cranking. After the first start control unit performs start control of the internal combustion engine, the second start control unit starts the internal combustion engine when a crank shall of the internal combustion engine stops for a predetermined time or longer or the crank shaft rotates in an opposite direction to the direction of the cranking.

An engine synchronization method may include: detecting teeth numbers of crank teeth installed on a crankshaft based on a pulse signal generated from a crankshaft position sensor; calculating a tooth period between a falling edge and a next falling edge of the pulse signal generated from the crankshaft position sensor and detecting a missing tooth based on the calculated tooth period; determining whether the detected missing tooth is an actual missing tooth based on a tooth number detected at the time of detecting the missing tooth; and performing synchronization control of an engine when it is determined that the detected missing tooth is the actual missing tooth.

A method actively dampens a start-up resonance of a torsional damper when starting an internal combustion engine. The torsional damper (4) is fixed between an internal combustion engine (1) and a secondary side (5) of a torsional elasticity, and the internal combustion engine (1) is started using a starter generator (3) arranged on a side of the internal combustion engine (1) counter to the torsional elasticity. A counter excitation is applied to a torque generated by the starter generator (3) when the internal combustion engine (1) is started, which counter excitation is modulated on the basis of a parameter of the internal combustion engine (1) which changes when the internal combustion engine (1) is being started.

A control device prevents damage due to backward rotation of a rotary engine and prevents misjudgment of backward rotation of the rotary engine. The control device for a rotary engine includes a motor mechanically connected to the shaft of the rotary engine, a controller (a motor ECU) that performs energization control of the motor to start the rotary engine by driving the motor, and a sensor (such as a motor rotation sensor). When starting the rotary engine, the controller stops energization to the motor based on an electric signal from the sensor when the shaft of the rotary engine rotates backward a predetermined angle or more, and then the shaft of the rotary engine continues to rotate backward for a predetermined time.

A decompression shaft (56) of a decompression device (50) includes an engagement pin (53) that is guided by a guide groove (51a) formed in a decompression weight (51), a decompression cam (54) that is provided on one cam surface of an intake valve cam (25c) and an exhaust valve cam (25b) so as to advance and retreat, and a connection portion (55) that connects the engagement pin (53) and the decompression cam (54). The decompression weight (51) is formed with a rotation restricting groove (51e) that restricts rotation of the decompression shaft (56) when a force acts in a direction in which the decompression cam (54) moves on the decompression shaft (56) from an advanced position to a retracted position when an engine (E) is stopped and that is continuous with the guide groove (51a).

A method actively dampens a start-up resonance of a torsional damper when starting an internal combustion engine. The torsional damper (4) is fixed between an internal combustion engine (1) and a secondary side (5) of a torsional elasticity, and the internal combustion engine (1) is started using a starter generator (3) arranged on a side of the internal combustion engine (1) counter to the torsional elasticity. A counter excitation is applied to a torque generated by the starter generator (3) when the internal combustion engine (1) is started, which counter excitation is modulated on the basis of a parameter of the internal combustion engine (1) which changes when the internal combustion engine (1) is being started.

A method for updating a crank position tooth number in a crank position sensor signal obtained from a crankshaft position sensor of an engine of a vehicle includes: calculating, in platform software of an engine control unit (ECU), a pulse width of a crank position sensor signal, determining, in the platform software of the ECU, a forward rotation and a reverse rotation of an engine, and updating, in the platform software of the ECU, the crank position tooth number.

An engine start control device includes an pass determination section that performs a pass determination process of determining, based on a rotation state of the engine output shaft, whether a piston in a cylinder of the engine can pass over a compression top dead center for a rotation drop period in response to an occurrence of the start request. The engine start control device also includes a start control section that when it is determined that the piston cannot pass over the compression top dead center, starts driving of the motor in a low reaction force period to start the engine, the low reaction force period being a period in which a reaction force applied to the piston by a cylinder internal pressure in the cylinder is a predetermined value or less.

A decompression shaft (56) of a decompression device (50) includes an engagement pin (53) that is guided by a guide groove (51a) formed in a decompression weight (51), a decompression cam (54) that is provided on one cam surface of an intake valve cam (25c) and an exhaust valve cam (25b) so as to advance and retreat, and a connection portion (55) that connects the engagement pin (53) and the decompression cam (54). The decompression weight (51) is formed with a rotation restricting groove (51e) that restricts rotation of the decompression shaft (56) when a force acts in a direction in which the decompression cam (54) moves on the decompression shaft (56) from an advanced position to a retracted position when an engine (E) is stopped and that is continuous with the guide groove (51a).