Abstract: An engine is provided with a mechanical supercharger which is disposed in an intake passage of the engine and is driven by the output power of the engine. The supercharger is connected to and disconnected from the output power of the engine by a clutch. The engine has intake and exhaust valves which are opened and closed with an overlap time. A valve timing changing mechanism changes the overlap time in order to change the amount of air communicated between the intake and exhaust ports.

Abstract: A supercharged engine has a geometric compression ratio of more than 8.5, and engine specifications are set to establish a relation, Y.gtoreq.-1.75X+10, in which an intake port closing timing Y is expressed by a crank angle after the piston reaches BDC and an overlapping angle X is expressed by a crank angle for an overlapping time period during which the intake valve and exhaust valve are both open.

Abstract: An intake system with a simple and compact structure for an internal combustion engine having a plurality of cylinders each cylinder having an intake port, the opening timing of the intake ports being determined so that that of each cylinder overlaps with that of another in which the intake stroke takes place subsequently to that in the former, the intake system comprising intake passges each being connected to the intake port of one of the cylinders, a juction portion connected to the respective intake passages, a resonance intake passage connected to the junction portion at one end thereof, in which the intake pressure resonance effect is to be produced and control valves provided in the respective intake passages, the opening timing of the respective control valves being determined so as to be retarded relative to that of said respective intake ports under at least a low speed and heavy load engine operating condition.

Abstract: An intake system for a multiple-cylinder engine has a main intake passage open to the atmosphere at its upstream end, a plurality of discrete intake passages which communicate the respective cylinders with the main intake passage by way of intake ports, and a circular passage which is communicated with the cylinders. The circular passage is adapted to propagate pressure waves generated by the intake strokes without reflecting the pressure waves, and is provided with a valve which opens the circular passage to permit propagation of the pressure waves in a predetermined high engine speed range. The length of the circular passage is selected so that the pressure waves resonate in the predetermined high engine speed range.

Abstract: An engine intake system including an intake passage opening to the combustion chamber through an intake port having an intake valve. A control valve is provided in the intake valve for cyclically opening the intake passage. Upstream the control valve, the intake passage is provided with a tank which functions to reverse the negative pressure propagated from the control valve into a positive pressure which is then transmitted to the combustion chamber to increase the intake charge. A timing control mechanism is provided for retarding the opening timing of the control valve in a low speed, high load engine operation.