Abstract: A helically-shaped intake port comprising a helical portion formed around an intake valve, and a substantially straight inlet passage portion tangentially connected to the helical portion. A bypass passage is branched off from the inlet passage portion and connected to the helical portion. A rotary valve is arranged in the bypass passage and has an arm connected to a vacuum operated diaphragm apparatus. The rotary valve has a stop which is engageable with the arm. The arm is normally in engagement with the stop due to the spring force of a coil spring for retaining the rotary valve precisely at the maximum open position.

Abstract: A helically-shaped intake port comprising a helical portion formed around an intake valve, and a substantially straight inlet passage portion tangentially connected to the helical portion. A bypass passage is branched off from the inlet passage portion and connected to the helical portion. A rotary valve is arranged in the bypass passage and actuated by a vacuum operated diaphragm apparatus. The rotary valve is opened when the amount of air fed into the cylinder of an engine is increased beyond a predetermined value. The diaphragm apparatus comprises a diaphragm and a control rod interconnecting the diaphragm to the rotary valve. A first stop and a second stop, which are engageable with the housing of the diaphragm apparatus, are fixed onto the control rod for retaining the rotary valve at the full open position and at the completely closed position, respectively.

Abstract: A helically-shaped intake port comprising a helical portion formed around an intake valve and a substantially straight inlet passage portion tangentially connected to the helical portion. A bypass passage is branched off from the inlet passage portion and connected to the helical portion. A flow control valve is arranged in the bypass passage and actuated by a bellows. The flow control valve is opened when the amount of air fed into the cylinder of an engine is increased beyond a predetermined value.

Abstract: A helically-shaped intake port comprising a helical portion formed around an intake valve, and a substantially straight inlet passage portion tangentially connected to the helical portion. A bypass passage is branched off from the inlet passage portion and connected to the helical portion. A rotary valve is arranged in the bypass passage and actuated by a vacuum operated diaphragm apparatus. The rotary valve is opened when the amount of air fed into the cylinder of an engine is increased beyond a predetermined value.

Abstract: A helically-shaped intake port comprising a helical portion formed around an intake valve and a substantially straight inlet passage portion tangentially connected to the helical portion. A bypass passage is branched off from the inlet passage portion and connected to the helical portion. A rotary valve is arranged in the bypass passage and actuated by a vacuum operated diaphragm apparatus. The rotary valve is opened when the amount of air fed into the cylinder of an engine is increased beyond a predetermined value. A cooling water passage is arranged beneath and near the bypass passage.

Abstract: A helically-shaped intake port comprising a helical portion formed around an intake valve and a substantially straight inlet passage portion tangentially connected to the helical portion. A bypass passage is branched off from the inlet passage portion and connected to the helical portion. A rotary valve is arranged in the bypass passage and actuated by a vacuum operated diaphragm apparatus. The rotary valve is opened when the amount of air fed into the cylinder of an engine is increased beyond a predetermined value. The rotary valve comprises a valve holder, a valve shaft rotatably supported by the valve holder, and a valve body formed in one piece on the valve body and extending across the bypass passage. The valve shaft and the valve body are made of a polymer such as a rubber or synthetic resin.

Abstract: A helically-shaped intake port comprising a helical portion formed around an intake valve, and a substantially straight inlet passage portion tangentially connected to the helical portion. A bypass passage is branched off from the inlet passage portion and connected to the helical portion. A rotary valve is arranged in the bypass passage and actuated by a vacuum operated diaphragm apparatus. The vacuum chamber of the diaphragm apparatus is selectively connected to the atmosphere or the suction pump driven by the diesel engine for opening the rotary valve when the level of load of the diesel engine is increased beyond a predetermined level.

Abstract: A helically-shaped intake port comprising a helical portion formed around intake valve, and a substantially straight inlet passage portion tangentially connected to the helical portion. A bypass passage is branched off from the inlet passage portion and connected to the helical portion. A rotary valve is arranged in the bypass passage and actuated by a vacuum operated diaphragm apparatus. The vacuum chamber of the diaphragm apparatus is connected to the interior of the intake manifold via a vacuum port and a check valve cooperating with the vacuum port. The check valve opens the vacuum port when the level of vacuum in the intake manifold becomes greater than that of vacuum in the vacuum chamber. In addition, the vacuum chamber is connected to the atmosphere via an atmosphere port and an air valve cooperating with the atmosphere port. The air valve opens the atmosphere port when the level of vacuum in the venturi portion of the carburetor becomes greater than a predetermined level for opening the rotary valve.