CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Japanese Patent Application No. 2020-078887 filed on Apr. 28, 2020. The entire contents of this application are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to V-type OHV engines, and more specifically, to a V-type two-cylinder OHV engine for use in a mower or other equipment.

2. Description of the Related Art

As an example of conventional techniques of this kind, JP-A H5-1566 discloses a V-type engine equipped with a supercharger. The engine includes a pair of banks opposing each other in a left and right direction. The supercharger is provided by a mechanical supercharger disposed between the two banks and driven by an engine output shaft. The V-type engine has an intercooler installed between the two banks, the intercooler and the engine's main body provide a closed space between the two banks, and in this closed space there is provided a cover surrounding the mechanical supercharger. Also, the mechanical supercharger has a drive shaft to which a coupling is connected. A pulley is attached to the coupling's shaft portion. The pulley receives drive power transmitted via a belt from a crank pulley which is attached to a crank shaft so that the mechanical supercharger is rotationally driven.

The V-type engine disclosed in JP-A H5-1566 requires an intercooler installed between the two banks, and therefore it is impossible to miniaturize the V-type engine.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide V-type OHV engines that are each able to be miniaturized.

According to a preferred embodiment of the present invention, an OHV engine includes V-shaped banks, a crank shaft, a cam shaft connected with the crank shaft, a mechanical supercharger located between the V-shaped banks to be driven based on an output from the crank shaft, and a power transmission supported by the cam shaft and that connects the crank shaft and the mechanical supercharger with each other in order to transmit an output from the crank shaft to the mechanical supercharger.

According to a preferred embodiment of the present invention, since the engine is an OHV engine, the cam shaft which is located adjacent to the crank shaft rotatably supports the power transmission that connects the crank shaft and the mechanical supercharger with each other. In other words, the power transmission connects the crank shaft and the mechanical supercharger via the cam shaft. As described above, the cam shaft defines and functions not only conventionally as a member included in a valve driving mechanism but also as a member which supports the power transmission. Therefore, it is possible to decrease the number of parts and to miniaturize the OHV engine that includes the mechanical supercharger.

Preferably, the power transmission includes a gear mechanism. For a task of changing a given number of rotations of the crank shaft into a desired number of rotations and transmitting the output to the mechanical supercharger, a gear mechanism is more advantageous than a belt mechanism as the power transmission in that it is possible to decrease the space. In other words, if the space is the same, a gear mechanism is able to change the number of rotations of the crank shaft into a greater number of rotations than a belt mechanism and transmit the output to the mechanical supercharger. Therefore, by utilizing a gear mechanism as the power transmission, it becomes possible to perform supercharging more efficiently and to miniaturize the engine. The above structural arrangement is effective, in particular, when the number of rotations of the engine is relatively low (about 3,600 rpm, for example).

Further preferably, the gear mechanism has a gear ratio not greater than a predetermined value. When the gear ratio does not exceed a predetermined value, the number of rotations of the mechanical supercharger is controlled. This reduces an increase of the supercharging pressure from the mechanical supercharger, thus reducing a temperature increase of air which enters the engine and preventing undesired detonation in the cylinders. As a result, it becomes possible to further decrease the size of the engine without using an intercooler.

Further, preferably, the gear mechanism includes a first gear supported rotatably by the cam shaft and that is rotated based on an output from the crank shaft, a second gear on a rotation shaft of the mechanical supercharger, and an idle gear connecting the first gear and the second gear with each other. In this case, by placing the idle gear between the first gear and the second gear, it becomes possible to span a distance between the rotation shaft of the first gear and the rotation shaft of the second gear, thus making it possible to flexibly handle the distance between the crank shaft and the mechanical supercharger. Also, it is possible to easily change the number of rotations of the crank shaft to a greater number of rotations with the first gear, the second gear, and the idle gear.

Preferably, the V-shaped banks include two cylinders each offset with respect to a center of the crank shaft toward an anti-thrust side of the two cylinders, that is, in a direction of rotation of the crank shaft, and the mechanical supercharger is offset with respect to the center of the crank shaft in the same direction, i.e., on the anti-thrust side of the two cylinders. By offsetting each of the cylinders of the V-shaped banks on the anti-thrust side as described above, it becomes possible to decrease friction between the pistons and the respective cylinders of the engine, thus increasing torque. Further, by offsetting the mechanical supercharger in the same direction on the anti-thrust side of the two cylinders, it becomes possible to shorten the distance between the crank shaft and the mechanical supercharger, thus decreasing the size of the engine.

Further preferably, each of the V-shaped banks further includes a cylinder head, a spark plug in the cylinder head, and an oil cooling path adjacent to the spark plug in the cylinder head. In this case, engine oil flows in the oil cooling path making it possible to cool a region adjacent the spark plug of the cylinder head. This makes it possible to provide efficient cooling even when the temperature of the engine increases due to supercharging.

Preferred embodiments of the present invention are applicable to V-type two-cylinder OHV engines that are required to be small but yet have a high output.

According preferred embodiments of the present invention, V-type OHV engines are miniaturized.

The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings.

