V-type multi-cylinder internal combustion engine

A V-type multi-cylinder internal combustion engine in which ignition in a right bank and ignition in a left bank occur alternately and at equal intervals, and a suction manifold shaped symmetrically in respect of right and left is disposed between the right and left banks, said suction manifold comprising:

• a right first chamber to be connected to a right throttle body;
• a left first chamber to be connected to a left throttle body;
• right first suction passages directly communicating with respective suction ports of cylinders in said left bank;
• left first suction passages directly communicating with respective suction ports of cylinders in said right bank;
• a right second chamber positioned at a middle bottom part between said right and left banks, always communicating with said right first chamber through a right first communication passage;
• a left second chamber positioned at a middle bottom part between said right and left banks, always communicating with said left first chamber through a left first communication passage;
• right second suction passages connecting said right second chamber with respective base end portions of said right first suction passages, each formed in shape of a swirl surrounding said left and right second chambers in turn;
• left second suction passages connecting said left second chamber with respective base end portions of said left first suction passages, each formed in shape of a swirl surrounding said right and left second chambers in turn;
• right first opening-shutting valves disposed in said right first suction passages at upper stream side portions of said base end portions connected to said right second suction passages;
• left first opening-shutting valves disposed in said left first suction passages at upper stream side portions of said base end portions connected to said left second suction passages;
• and
• a second opening-shutting valve disposed in a second communication passage connecting said right and left first communication passages to each other,
• said first and second opening-shutting valves being able to be switched over in accordance with rotative speed of the engine so that when the rotative speed rises to a middle rotative speed region said first opening-shutting valves open and when the rotative speed further rises to a high rotative speed region said second opening-shutting valve shuts.

A V-type multi-cylinder internal combustion engine in which ignition in a right bank and ignition in a left bank occur alternately and at equal intervals, having variable valve timing switchover mechanisms provided at respective cylinders in right and left banks for switching over suction characteristics of the cylinders between a low-speed mode and a high-speed mode by changing working characteristics of suction valves of the cylinders, a suction passage switchover mechanism for switching over suction characteristic of a suction passage among a low-speed mode, a middle-speed mode and a high-speed mode, and a suction manifold shaped symmetrically in respect of right and left disposed between the right and left banks, said variable valve timing switchover mechanisms and said suction passage switchover mechanism being switched over in accordance with rotative speed of said engine, wherein said suction manifold comprising:

• a right first chamber to be connected to a right throttle body;
• a left first chamber to be connected to a left throttle body;
• right first suction passages directly communicating with respective suction ports of cylinders in said left bank;
• left first suction passages directly communicating with respective suction ports of cylinders in said right bank;
• a right second chamber positioned at a middle bottom part between said right and left banks, always communicating with said right first chamber through a right first communication passage;
• a left second chamber positioned at a middle bottom part between said right and left banks, always communicating with said left first chamber through a left first communication passage;
• right second suction passages connecting said right second chamber to respective base end portions of said right first suction passages, each formed in shape of a swirl surrounding said left and right second chambers in turn;
• left second suction passages connecting said left second chamber to respective base end portions of said right first suction passages, each formed in shape of a swirl surrounding said right and left second chambers in turn;
• right first opening-shutting valves disposed in said right first suction passages at upper stream side portions of said base end portions connected to said right second suction passages, for connecting said right first suction passages to said right first chamber to switch over the suction characteristic of the suction passage from the low-speed mode to the middlespeed mode;
• left first opening-shutting valves disposed in said first left suction passages at upper stream side portions of said base end portions connected to said second left suction passages, for connecting said left first suction passages to said left first chamber to switch over the suction characteristic of the suction passage from the low-speed mode to the middle-speed mode;
• a second opening-shutting valve disposed in a second communication passage connecting said right and left first communication passages to each other for intercepting communication between said right and left first communication passages to switch over the suction characteristic of the suction passage from the middle-speed mode to the high-speed mode,
• thereby, after switchover of the suction characteristic by said second opening-shutting valve, switchover of the suction characteristic from the low-speed mode to the high-speed mode by said variable valve timing switchover mechanisms is carried out.