A motorcycle has a crankcase containing a crank shaft and a balancer shaft, and a cylinder and a cylinder head positioned above the crankcase, and an exhaust pipe extends from the cylinder head. The balancer shaft is positioned in front of the crank shaft, and the crankcase has a balancer shaft housing supporting the balancer shaft thereinside, and has a recessed part depressed rearward in a front end center part of the balancer shaft housing. The balancer shaft has balancer shaft weights apart from each other in one side and in the other side in an axis direction.

A motorcycle has a crankcase containing a crank shaft and a balancer shaft, and a cylinder and a cylinder head positioned above the crankcase, and an exhaust pipe extends from the cylinder head. The balancer shaft is positioned in front of the crank shaft, and the crankcase has a balancer shaft housing supporting the balancer shaft thereinside, and has a recessed part depressed rearward in a front end center part of the balancer shaft housing. The balancer shaft has balancer shaft weights apart from each other in one side and in the other side in an axis direction.

A two-wheeled vehicle includes a frame having a front frame portion, a mid-frame portion, and a rear frame portion. The mid-frame portion is coupled to the rear frame portion and the front frame portion. The vehicle further includes a plurality of ground-engaging members for supporting the frame. The engine includes an air deflector to assist in cooling a rear cylinder of a V-twin engine. An accessory windshield is also shown which may be coupled to the handlebars and front forks of the vehicle. Also, a rear accessory attachment is shown mountable to the rear fender.

A two-wheeled vehicle includes a frame having a front frame portion, a mid-frame portion, and a rear frame portion. The mid-frame portion is coupled to the rear frame portion and the front frame portion. The vehicle further includes a plurality of ground-engaging members for supporting the frame. The engine includes an air deflector to assist in cooling a rear cylinder of a V-twin engine. An accessory windshield is also shown which may be coupled to the handlebars and front forks of the vehicle. Also, a rear accessory attachment is shown mountable to the rear fender.

A straddled vehicle, including a vehicle frame structure, a drive unit including a drive motor that receives electric power and outputs driving power, a driving wheel that receives the driving power, and an electric power generation unit. The electric power generation unit includes an electric power generation engine configured to output engine power, and an electric power generator that is fixed to the electric power generation engine and is electrically connected to an electric power transfer medium having flexibility. The electric power generator is configured to convert the engine power into the electric power, and supply the electric power to the drive motor via the electric power transfer medium. The straddled vehicle is series-hybridized by the drive unit and the electric power generation unit. The electric power generation engine is swingably supported, independently of the drive unit, by the vehicle frame structure, such that the engine power is not mechanically supplied to the driving wheel.

A straddle-type vehicle comprises a supercharging device which compresses intake-air, an air-intake chamber which is disposed downstream of the supercharging device, a pressure rising suppressing valve which is actuated by a pressure and connected to an inner space of the air-intake chamber, the pressure rising suppressing valve being configured to open the inner space of the air-intake chamber to a relief passage, in a case where a difference between a preset pressure in a pilot space and a pressure in the air-intake chamber reaches a predetermined value or more, a control valve which is electrically actuated and is capable of performing switching of a space to be in communication with the pilot space, between a high-pressure space and a low-pressure space; and a valve controller which provides to the control valve an operation command for controlling the control valve.

A straddle-type vehicle comprises a supercharging device which compresses intake-air, an air-intake chamber which is disposed downstream of the supercharging device, a pressure rising suppressing valve which is actuated by a pressure and connected to an inner space of the air-intake chamber, the pressure rising suppressing valve being configured to open the inner space of the air-intake chamber to a relief passage, in a case where a difference between a preset pressure in a pilot space and a pressure in the air-intake chamber reaches a predetermined value or more, a control valve which is electrically actuated and is capable of performing switching of a space to be in communication with the pilot space, between a high-pressure space and a low-pressure space; and a valve controller which provides to the control valve an operation command for controlling the control valve.

An intake air mass estimation unit is provided that sets predetermined degrees of crank angle to an angle that can divide an intake stroke into a plurality of sections, measures at every the predetermined degrees of crank angle the pressure downstream of the throttle valve and the time taken for the predetermined degrees of crank angle rotation, estimates the intake air mass flowing from the upstream to downstream of the throttle valve at every the predetermined degrees of crank angle, using the pressure downstream of the throttle valve and the time taken for the predetermined degrees of crank angle rotation measured at every the predetermined degrees of crank angle, and integrates the intake air mass at every the predetermined degrees of crank angle for 720 degrees of crank angle rotation, thereby estimating the intake air mass needed for one combustion.

An intake air mass estimation unit is provided that sets predetermined degrees of crank angle to an angle that can divide an intake stroke into a plurality of sections, measures at every the predetermined degrees of crank angle the pressure downstream of the throttle valve and the time taken for the predetermined degrees of crank angle rotation, estimates the intake air mass flowing from the upstream to downstream of the throttle valve at every the predetermined degrees of crank angle, using the pressure downstream of the throttle valve and the time taken for the predetermined degrees of crank angle rotation measured at every the predetermined degrees of crank angle, and integrates the intake air mass at every the predetermined degrees of crank angle for 720 degrees of crank angle rotation, thereby estimating the intake air mass needed for one combustion.

An intake cam is positioned between first and second shaft supports that support an intake camshaft. An exhaust cam is positioned between third and fourth shaft supports that support an exhaust camshaft. An ignition plug unit extends between the intake camshaft and the exhaust camshaft and inward of the intake cam and the exhaust cam with a cylinder axis defining a reference position. A cylinder head includes a joint plane that is joined to a cylinder body. In a case where a virtual plane is defined by the joint plane and is perpendicular or substantially perpendicular to the cylinder axis, a distance between a portion, closest to the virtual plane, of the intake camshaft and the virtual plane is less than a distance between a portion, farthest from the virtual plane, of the intake port and the virtual plane.