1. Field of the Invention
This invention relates to an intake system for an engine, and more particularly to an intake system for an engine which is arranged to supercharge the engine by kinetic effect of intake air.
2. Description of the Prior Art
There has been known an intake system an engine which is arranged to supercharge the engine by kinetic effect of intake air such a inertia effect of intake air, thereby increasing the air charging efficiency and the engine output torque.
That is, in the supercharging of the engine by the inertia effect of intake air, a negative pressure wave generated in the intake port at the beginning of the intake stroke in each of the cylinders in response to opening of the intake valve in a predetermined engine speed range (tuning engine speed range) propagates upstream at a sonic speed through the discrete intake passage connected to the intake port and is reflected at a volume chamber as a positive pressure wave. The positive pressure wave propagates downstream at a sonic speed through the same path and reaches the intake port of the same cylinder immediately before closure of the intake valve at the end of the intake stroke to force air into the cylinder.
As the volume chamber which reflects the pressure wave, a surge tank is generally used. However, in the case of the surge tank, the effective length of the passage which joins the discrete intake passage and the intake passage upstream of the surge tank through the surge tank differs from cylinder to cylinder and accordingly, distribution of intake air and the inertia effect of intake air varies from cylinder to cylinder.
In the intake system disclosed in Japanese Unexamined Utility Model Publication No. 60(1985)-88062, discrete intake passages communicating with respective cylinders of an engine extend from the cylinders on one side of the engine and merge into an integrated chamber having an inner space which is like a truncated cone in shape. The upstream ends of the discrete intake passages are connected to the larger end face of the integrated chamber and the downstream end of a common intake passage is connected to the smaller end face of the same. The openings at which the discrete intake passages communicate with the integrated chamber are symmetrically disposed about the central axis of the larger end face of the integrated chamber. With this arrangement, the distances between the downstream end of the common intake passage and the upstream ends of the discrete intake passages are substantially equal to each other, whereby the intake air distribution is uniformed. Further, the upstream ends of the discrete intake passages are disposed close to each other, each discrete intake passage functions as a volume chamber in the inertia effect supercharging of the cylinders communicated with the other discrete intake passages, whereby the integrated chamber can be small in volume.
In the case of an in-line engine, when the integrated chamber is disposed on one side of the engine body at the middle between the front and rear ends of the engine body, the discrete intake passages can be substantially equal to each other in length and radius of curvature. However when the integrated chamber is disposed on one side of the engine body, the width of the engine body increases.
However, when the integrated chamber is disposed above one end of the engine body and the discrete intake passages are simply connected to the integrated chamber, the discrete intake passages for the cylinders far from the end of the engine body must be longer than the discrete intake passages for the cylinders near the end, and at the same time, the discrete intake passages for the cylinders near end of the engine body must be curved more sharply than those far from the end, which leads to non-uniform air distribution and non-uniform inertia effect of intake air.