Field of the Invention
The present invention typically relates to a four-cycle multi-cylinder engine preferable for motorcycles or similar vehicles.
Description of the Related Art
To improve controllability and stability of motorcycles, disposing a shaft center of a crankshaft at an appropriate position with respect to a position of a front wheel is required. In the case where a cylinder is inclined forward with respect to the position of the crankshaft, a cylinder head projects forward. Therefore, when an appropriate clearance is attempted to be secured between a radiator, an exhaust pipe, and a similar member; and the front wheel, there is no choice but to dispose the shaft center of the crankshaft rearward. This makes it difficult to configure the shaft center of the crankshaft at the appropriate position with respect to the position of the front wheel, consequently making it difficult to improve the controllability and stability.
For example, Patent Document 1 discloses an example of an engine that includes an upper crankcase integrated with a cylinder and the cylinder is appropriately inclined forward.
As conventional measures, there has been provided a method that turns an entire engine rearward around a drive shaft (an output shaft) to shift a cylinder head rearward. This aims to secure an appropriate clearance between a radiator and a similar member; and a front wheel without shaft center of a crankshaft being disposed rearward.
Patent Document 1: Japanese Laid-open Patent Publication No. 2010-174776
However, with the conventional engine, turning the entire engine rearward heightens vertical positions of the crankshaft, the cylinder head, and a similar member, rather inhibiting the controllability and stability. Additionally, spaces for an air cleaner box and a fuel tank disposed above the engine are restricted, causing a problem such as a difficulty in securing capacities for these spaces.
Further, an extension of a wheel base is applicable as another method for the measures; however, this causes a problem such as an increase in vehicle weight and an increase in minimum rotation radius.
USPTO Backgrounds
USPTO Backgrounds