The present invention relates to the layout structure of catalytic converters for an engine and, more particularly, to the layout of catalytic converters applied to a transverse engine. A so-called transverse engine is known as a conventional engine which is arranged in an engine room such that the engine output shaft is almost vertical to the longitudinal direction of a vehicle. Of transverse engines of this type, a V-cylinder engine which has banks in the longitudinal direction of a vehicle, and is used for an FF automobile or a 4WD automobile is known to have two catalytic converters. One catalytic converter is arranged to face the forward direction of the vehicle so as to clean an exhaust gas expelled from the front engine bank. The other catalytic converter is arranged to face the backward direction of the vehicle so as to clean an exhaust gas expelled from the rear engine bank. For example, Japanese Utility Model Laid-Open No. 63-102922 discloses the detailed arrangement of such an engine.
On the other hand, for example, Japanese Utility Model Publication No. 3-46180 discloses an arrangement in which an air-cooling inter cooler for cooling air compressed by a supercharger is disposed above an engine having an exhaust supercharger (turbo charger).
Assume that a mechanical supercharger (supercharger) is to be arranged for a V-cylinder engine. In this case, when the mechanical supercharger is arranged in a space between the above-mentioned front and rear engine banks, a driving force of the mechanical supercharger can be easily obtained as part of an engine output. In addition, the overall structure can be reduced in size.
The following problems, however, are posed in the above-described structure in which one catalytic converter (to be referred to as a front catalytic converter hereinafter) is arranged near the front engine bank, of the V-cylinder engine, which is arranged to face the forward direction of the vehicle, so as to clear an exhaust gas from the front engine bank, and the other catalytic converter (to be referred to as a rear catalytic converter hereinafter) is arranged near the rear engine bank, which is arranged to face the backward direction of the vehicle, so as to clean an exhaust gas from the rear engine bank.
Cool air which is generated when the vehicle travels or a radiator fan is driven can be positively blown to only the front catalytic converter. However, the cool air is blocked by the engine itself including an engine block and hence cannot be sufficiently blown to the rear catalytic converter. For this reason, various problems are pointed out, e.g., an abnormal temperature rise of the rear catalytic converter, a deterioration in the catalyst due to the temperature rise, and accumulation of heat in portions behind the engine.
In addition, since the degree to which traveling air is blown to the front catalytic converter is inevitably larger than that to the rear catalytic converter, the temperature rise of the front catalytic converter differs from that of the rear catalytic converter, resulting in a difference between the cleaning effect of the front catalyst and that of the rear catalyst.
On the other hand, for example, in order to arrange a turbo charger or supercharger with respect to a transverse V-cylinder engine, an air-cooling inter cooler for cooling air compressed by each supercharger is disposed above the V-cylinder engine. In this case, intake air to the air-cooling inter cooler to be used for a cooling operation is introduced into the engine room from a portion in front of the engine, and the air is then caused to quickly escape outside the vehicle. Therefore, intake air cooled by the air-cooling inter cooler is not effectively used.