Intake system for four-cycle engine powering an outboard motor

Abstract

An engine includes an improved induction system which reduces the girth of the engine, simplifies assembly, and improves better power output balance between the cylinders of the engine. The illustrated engine is a multi-cylinder engine and is designed to power an outboard motor; hence, the cylinders of the engine are arranged above one another. Thus, the engine comprises at least first and second combustion chambers. The induction system selectively communicates with the combustion chambers to supply a fuel/air charge thereto. The induction system includes a first intake passage leading to the first combustion chamber and having a first fuel injector communicating therewith, and a second intake passage leading to the second combustion chamber and having a second fuel injector communicating therewith. The second intake passage descends from the second fuel injector toward the second combustion chamber by a greater degree than the first intake passage descends from the first fuel injector toward the first combustion chamber. Additionally, a length of the second intake passage from the second fuel injector to second combustion chamber is greater than a length of the first intake passage from the first fuel injector to the first combustion chamber. Both of these factors enhance the combustion efficiency of the lower cylinder to balance better the power outputs between the cylinders. Each fuel injector also is mounted to a throttle body which regulates air flow through the corresponding intake passage. In one mode, the fuel injector is mounted between the throttle device and the engine so as to reduce the girth of the engine. This arrangement also simplifies engine assembly.