1. Field of the Invention
The present invention relates to an inlet passage structure of a V-type internal combustion engine having an inlet chamber at the downstream of a throttle body.
2. Description of Background Art
As an internal combustion engine, there has heretofore been an engine that attempts to improve engine output and engine response by disposing a tank-type inlet chamber in an inlet passage between a throttle body and an inlet pipe; relieving the pressure variation (pulsation) of inlet air in the inlet passage with the inlet chamber; and improving an inlet efficiency. (Refer to JP-A No. H8-338253, for example.)
Meanwhile, in the apparatus disclosed in JP-A No. H8-338253, when a pair of front and rear banks are disposed in the shape of V, two connecting rods of the front and rear banks are connected to a common crankshaft in the manner of being offset from each other in the axial direction of the crankshaft and hence the cylinders of the front and rear banks are offset from each other in the axial direction of the crankshaft. Consequently, when a throttle body common to the front and rear banks is disposed, since the lengths of inlet passages extending from the throttle body to combustion chambers of the front and rear banks are different from each other, difference in inlet air volume occurs between the combustion chambers and a required performance is hardly outputted because of the unbalance of output between the cylinders.
JP-A No. 2005-207254, for example, discloses another internal combustion engine having a variable valve mechanism wherein the phase/lift of a camshaft is variable. In such a variable valve mechanism, one inlet valve and one exhaust valve are driven by one camshaft.
JP-A No. 2005-36681, for example, discloses a V-type internal combustion engine having a pair of front and rear banks disposed in the shape of V, there is an internal combustion engine of a cylinder injection type to inject a fuel directly from an injector as a fuel injection device into a combustion chamber. In such an internal combustion engine, a bank angle between a front bank and a rear bank is set at a narrow angle of 45 to 50 degrees and the inlet ports of the front and rear banks are disposed inside the V bank.
Meanwhile, in the case of the internal combustion engine described in JP-A No. 2005-207254, since the numbers of the inlet and exhaust valves are one each, the inlet and exhaust efficiency cannot be increased so much and output is also restricted.
As a means for overcoming the problems, it may be possible to dispose camshafts for inlet and exhaust individually and drive two valves for inlet and exhaust with one of the camshafts, namely four valves in total as described in JP-A No. 2005-36681. In this case however, the width of a cylinder head in the anteroposterior direction increases, the space inside the V bank reduces, injectors cannot be disposed inside the V bank, and thus the injectors have to be disposed at the center portions of the cylinders as shown in JP-A No. 2005-36681. For that reason, the direction of fuel injection, the ignition plug attaching location, and the like are restricted. JP-A No. 2005-36681 discloses that fuel is injected directly from an injector as a fuel injection device into a combustion chamber. In such an internal combustion engine, a nip angle (a bank angle) between a front bank and a rear bank is set at a narrow angle of 45 to 50 degrees and the inlet ports of the front and rear banks are disposed inside the V bank.
Meanwhile, in the case of a cylinder injection type internal combustion engine, it is desirable to dispose an injector on an inlet port side in the manner of laying down the injector away from the cylinder axis of a bank in order to improve ignitability or the like.
By a previous configuration however, the bank angle is too narrow to dispose the injector inside the V bank that is on the inlet port side and it is impossible to carry out operations such as the attachment or the detachment of the injector. Consequently, there has been no other way than to dispose the injector in the manner of standing up along the cylinder axis and thus it has been impossible to dispose the injector at the most appropriate place.