Starting method for internal combustion engine and starting device for the same

A starting method for an internal combustion engine comprising the steps of:

• rotating a crankshaft with an electric motor during an engine startup;
• opening an engine valve which is opened and closed by a valve train cam by a decompression mechanism, wherein said valve train cam is provided on a camshaft that is rotated synchronously with a rotation of the crankshaft, wherein the decompression mechanism includes a decompression cam provided on the camshaft in such a manner that the decompression cam is capable of rotating in the rotational range of the camshaft between a first stop position of the camshaft in a reverse rotational direction and a second stop position of the camshaft in a normal rotational direction and has a cam profile to bring the engine valve into an opened state at the first stop position and into a closed state at the second stop position;
• rotating the crankshaft in the reverse rotational direction with the electric motor to rotate the decompression cam in the reverse direction to place the decompression cam in the first stop position at startup;
• rotating the crankshaft in the normal rotational direction with the electric motor to rotate the decompression cam in the normal direction;
• and
• opening the engine valve with the decompression cam at a plurality of compression strokes during a period until the decompression cam reaches the second stop position.

A starting device for an internal combustion engine, wherein the starting device includes an electric motor for rotating a crankshaft during an engine startup, an engine valve with a valve train cam, a control device for controlling rotation of the crankshaft with the electric motor, and a decompression mechanism for opening the engine valve to be opened and closed by the valve train cam provided on a camshaft that is rotated synchronously with rotation of the crankshaft, said decompression mechanism comprising:

• a reverse rotation stopper defining a first stop position;
• a normal rotation stopper defining a second stop position;
• a decompression cam rotatably mounted on the camshaft so as to be capable of rotating in a rotational range of the camshaft between the first stop position in a reverse rotational direction of the camshaft and the second stop position in a normal rotational direction of the camshaft;
• a decompression cam profile for opening the engine valve at the first stop position and closing the same at the second stop position;
• a torque transmission device transmitting reverse rotation torque from the camshaft to the decompression cam, said torque transmission device including
• a constrained state in which relative rotation between the camshaft and the decompression cam is constrained during a reverse rotation of the crankshaft, and
• an unconstrained state in which a drag torque is transmitted in the normal direction from the camshaft to the decompression cam by permitting a relative rotation between the camshaft and the decompression cam during a normal rotation of the crankshaft;
• and
• a rotation control device alternately preventing and permitting dragging of the decompression cam between the first stop position and the second stop position in the normal rotational direction.