A variable valve mechanism includes a variable arm including a first arm and a second arm. The second arm is pivotally supported so as to be swingable by a support shaft. A position of the support shaft is a position where, during a base circle phase, in side view, a second segment connecting an axis of a roller to an axis of the support shaft is longer than a first segment connecting the axis of the roller to an axis of a camshaft, and an angle of the second segment formed with respect to a third segment connecting the axis of the roller to a swing axis of a roller arm is 60 to 120 toward the camshaft. The second arm extends from the support shaft such that a distal end portion of the second arm protrudes in between a cam and the roller.

An internal combustion engine is provided with a DOHC-type valve train in a cylinder head. The valve train includes an intake side camshaft with an intake side driven gear, and an exhaust side camshaft with an exhaust side driven gear. The cylinder head supports therein a spindle with an idle gear with an idle chain sprocket fixed thereto. The idle gear is in meshing engagement with both the intake and exhaust side driven gears. Rotary power of a crankshaft is transmitted via a cam chain to the idle gear to rotate both the intake and exhaust side camshafts. These camshafts are supported by bearings of a bearing wall and a camshaft holder. These bearings and camshaft holder are located, for compact arrangement, at a position axially coinciding or overlapping with the idle chain sprocket.

An engine variable valve train includes a cam changeover mechanism for axially shifting a cylindrical cam carrier fitted on and around a camshaft for changing over cam lobes on the cam carrier to cause one of the cam lobes to selectively act on an engine valve for engine operation. The cam changeover mechanism includes changeover pins adapted to be advanced and retracted for engagement with or disengagement from a lead groove formed around the cam carrier, and with a changeover driving shaft constituting a linear motion cam mechanism for causing the changeover pins to selectively advance to engage with the lead groove. The cam carrier, while rotating with the cam shaft, is axially shifted by the action of the lead groove having the changeover pins selectively engaged therewith, so that the cam lobes are changed over and one of the cam lobe is made to act on the engine valve.

A valve device for an internal combustion engine (1) includes a camshaft (16), a cam (17), a control shaft (15), an input arm (14), a first rocker arm (13a), a second rocker arm (13b), a first valve (603a), a second valve (603b), and a slider (18). The input arm (14) is configured such that a cam torque of the cam (17) is transmitted thereto. The slider (18) is configured to allow the input arm (14) to be supported by the control shaft (15). The slider (18) is configured to support the first rocker arm (13a) in a power transmittable manner such that the cam torque transmitted to the input arm (14) is transmitted to the first rocker arm (13a). The slider (18) includes a torsion portion (23) configured to connect the first rocker arm (13a) with the second rocker arm (13b) such that the cam torque transmitted to the first rocker arm (13a) is transmitted to the second rocker arm (13b) via the torsion portion (23).

An abnormality diagnosis system of an internal combustion engine that is installed on a vehicle and includes an actuator includes an electronic control unit. The electronic control unit receives vehicle outside information concerning a period of time for which the vehicle speed is less than a predetermined value, and determines whether the period for which the vehicle speed is less than the predetermined value is expected to be equal to or longer than a length of time required for an abnormality diagnosis of an abnormality diagnosis target device. The electronic control unit activates the actuator and starts the abnormality diagnosis as the vehicle speed becomes lower than the predetermined value, when it determines that the period for which the vehicle speed is lower than the predetermined value is expected to be equal to or longer than the time required for the abnormality diagnosis of the target device.

An internal combustion engine includes: a head cover covering a cylinder head; and a variable valve actuation mechanism. The variable valve actuation mechanism includes: a cam placed inside the head cover and rotating with a camshaft extending in a rotation axis direction; and an intermediate arm placed inside the head cover and sandwiched between the cam and a rocker arm. A pair of side through-holes, which are provided for a support rod supporting the intermediate arm to pass through, are formed in side portions of the head cover so as to face each other along the rotation axis direction.

A valve mechanism for an engine includes a camshaft, a rocker arm, a synchronization cam that rotates in synchronism with a valve driving cam, and a switch assembly that switches the driving state of an intake valve or an exhaust valve when a cam follower is pressed by the synchronization cam. The synchronization cam presses the cam follower at a time when the intake valve or the exhaust valve is closed. The switch assembly includes a switch unit that switches the driving state when a switch moves, a driver that drives the switch via a transmission, and a positioner including a spring-biased presser that engages with a concave portion of the transmission. The concave portion includes a first concave portion with which the presser engages in a first driving state, and a second concave portion with which the presser engages in a second driving state.

A variable valve timing system includes an exhaust swing arm swung in accordance with rotation of a camshaft, an intake swing arm similarly swung in accordance with the rotation of the camshaft, and a swing shaft swingably supporting the exhaust swing arm and the intake swing arm. In an engine including a plurality of the variable valve timing systems, the adjacent swing shafts are coupled to each other. The engine includes a link mechanism connected to one of the swing shafts, and an actuator for moving the link mechanism. The actuator controls turning angles of all the swing shafts via the link mechanism.

A continuously variable valve lift system includes a driving swing arm, a camshaft, a valve structure, a middle shaft, an adjusting member and an adjusting swing arm. The driving swing arm, the adjusting member and the adjusting swing arm are sleeved on the middle shaft and are respectively capable of swinging around the middle shaft. The first connecting part, the second connecting part and the third connecting part are arranged sequentially along a circumferential direction of the middle shaft. The second connecting part is located between the first connecting part and the third connecting part, and two sides of the second connecting part abut against the first connecting part and the third connecting part, respectively. The second connecting part abuts against the third connecting part to form a spiral surface therebetween. The adjusting member is further capable of sliding along an axial direction of the middle shaft.

In a variable valve mechanism of an internal combustion engine, when a slider is displaced relative to an input member and an output member in an axial direction, the output member turns relative to the input member in a swing direction, whereby a lift of a valve is increased or reduced. The variable valve mechanism is brought into a lift retaining state when the slider is placed in an idle running range located on a reducing direction side with respect to a boundary position. The lift retaining state is a state where when the slider is displaced in the axial direction, the input member and the output member are displaced together with the slider in the axial direction, so that the relative displacement of the slider and the relative turning of the output member do not occur and the lift of the valve is retained.