Abstract: An internal combustion engine comprising three intake valves. The first intake valve and the second intake valve open at a crank angle near to the top dead center of the intake stroke. The third intake valve opens approximately at the center of the intake stroke. An air control valve is arranged in the second intake passage connected to the combustion chamber via the second intake valve. The air control valve is closed when the engine is operating under a partial load. A fuel injector is arranged in the third intake passage connected to the combustion chamber via the third intake valve. The injecting operation of the fuel injector is stopped during the intake stroke.

Abstract: An engine having an intake port which comprises a straight port and a helical-shaped port which are separated by a separating wall. A control valve is arranged in the inlet portion of the straight port and opens when the engine is operating under a heavy load. A projection is formed on the side wall of the separating wall, which defines the straight port and is located downstream of the control valve. A bypass passage connected to the helix terminating portion of the helical portion of the helical-shaped port is formed in the separating wall. The projection has an arc-shaped cross-sectional tip face which is directed towards the upstream of the intake port. The inlet opening of the bypass passage is formed on the tip face of the projection.

Abstract: An engine in which the cylinders are each provided with a first intake valve, a second intake valve and an intake passage common to the first and second intake valves. The intake passage is divided into a central passage and two side passages located on each side of the central passage by two side separating walls, which extend from the valve stem guides of the first and second intake valves toward the upstream of the intake passage. The downstream end portion of the central passage is divided into two branch passages. Each of the branch passages is in communication with the corresponding side passage via an opening formed in the corresponding side separating wall. A fuel injector is arranged in the central passage, and a control valve is arranged in the central passage upstream of the fuel injector and opens when the engine is operating under a heavy load.

Abstract: A piston for an internal combustion engine formed as an integrally cast article having a crown portion and a hollow cylindrical side wall portion, wherein the crown portion is formed with a transverse hollow space, radially outside portions of which are axially traversed by integrally formed ribs, the hollow space being adapted to be circulated by lubricant for the purpose of cooling the crown portion. To supply lubricant into and to drain lubricant from the hollow space, a transverse wall portion formed in the crown portion on the inner side of the hollow space is formed with a lubricant inlet opening and at least one lubricant outlet opening, preferably at portions located between the ribs.

Abstract: A fuel injection quantity is calculated on the basis of an engine speed and an engine load and is corrected by an output incremental value determined in accordance with acceleration and deceleration of an engine, at least. The position of an intake throttle valve is detected with regard to whether it is located within a small-opening region, an intermediate-opening region or a large-opening region. When the intake throttle valve is switched over from the small-opening region to the large-opening region, the output incremental value is increased to its maximum value. When the intake throttle valve is switched over from the small-opening region to the intermediate-opening region, the output incremental value is increased such as to gradually approach the maximum value. When the intake throttle valve is switched over from the large-opening region to the small-opening region, the output incremental value is decreased to almost zero.

Abstract: A helically-shaped intake port comprising a helical portion and an inlet passage portion which is tangentially connected to the helical portion and extends so as to be slightly curved. The intake valve is arranged at the outlet open end of the helical portion. The first side wall of the inlet passage portion, which is located near the axis of the intake valve, has on its upper portion an inclined wall portion which is arranged to be directed downwards. The width of the inclined wall portion of the inlet passage portion is gradually increased towards the helical portion. The second side wall of the inlet passage portion, which is located remote from the axis of the intake valve, is vertically arranged and smoothly connected to the peripheral side wall of the helical portion, which extends circumferentially about the axis of the intake valve.

Abstract: An engine comprising an intake port which has a separating wall projecting downwardly from the upper wall of the intake port. The separating wall defines a helical portion, an inlet passage portion tangentially connected to the helical portion, and a bypass passage interconnecting the inlet passage portion and the helical portion. The side wall of the helical portion has a slightly inclined portion located near the outlet portion of the bypass passage and expanding towards the separating wall so as to define a narrow passage portion between the inclined portion and the separating wall. A rotary valve is arranged in the bypass passage and is actuated by a vacuum-operated diaphragm apparatus. The rotary valve is opened when the amount of air fed into the cylinder of the engine is increased beyond a predetermined value.

Abstract: A piston assembly for an internal combustion engine is made up from a piston main body and a lubricant reservoir defining member. The piston main body has a cup-shaped structure including a crown portion and a hollow cylindrical wall portion joining thereto, two piston pin bosses being formed at opposite sides of the wall portion. The lubricant reservoir defining member is made from a shelf plate main body portion which provides a central lubricant reservoir and two openings on its opposite sides, and two major legs extending from the shelf plate main body portion and each formed with a hole surrounded by an annular portion. Each of the annular portions is engaged with an inner end portion of a corresponding one of the bosses and surrounds the piston pin hole thereof.

Abstract: A piston assembly for an internal combustion engine is made up from a piston main body and a lubricant reservoir defining member. The piston main body has a cup shaped structure including a crown portion and a hollow cylindrical wall portion joining thereto. The lubricant reservoir defining member includes a shelf plate main body portion formed with first and second depressions which define first and second lubricant reservoirs, and is securely mounted within the cup shaped piston structure with the shelf plate portion generally to and opposing the piston crown. The ratio of the surface area of the first lubricant reservoir to the surface area of the second lubricant reservoir is less than the ratio of the volume of the first lubricant reservoir to the volume of the second lubricant reservoir. Lubricant is supplied more towards the first lubricant reservoir and is drained more from the second reservoir.

Abstract: An engine comprising an intake port which has a separating wall projecting downwardly from the upper wall of the intake port. The separating wall defines a helical portion, an inlet passage portion tangentially connected to the helical portion, and a bypass passage interconnecting the inlet passage portion and the helical portion. The separating wall has an upstream end portion centrally located between the opposed side walls of the intake port. A rotary valve is arranged in the bypass passage and is actuated by a vacuum-operated diaphragm apparatus. The rotary valve is opened when the amount of air fed into the cylinder of the engine is increased beyond a predetermined value.

Abstract: An engine comprising an intake port which has a separating wall projecting downwardly from the upper wall of the intake port. The separating wall defines a helical portion, an inlet passage portion tangentially connected to the helical portion, and a bypass passage interconnecting the inlet passage portion and the helical portion. The upper wall of the bypass passage is higher than that of the inlet passage portion. A rotary valve is arranged in the bypass passage and is actuated by a vacuum-operated diaphragm apparatus. The rotary valve is opened when the amount of air fed into the cylinder of the engine is increased beyond a predetermined value.

Abstract: An engine comprising an intake port which has a separating wall projecting downwardly from the upper wall of the intake port. The separating wall defines a helical portion, an inlet passage portion tangentially connected to the helical portion, and a bypass passage interconnecting the inlet passage portion to the helical portion. A rotary valve is arranged in the bypass passage and actuated by a vacuum operated diaphragm apparatus. The rotary valve is opened when the amount of air fed into the cylinder of an engine is increased beyond a predetermined value.

Abstract: An engine comprising an intake port which has a separating wall projecting downwardly from the upper wall of the intake port. The separating wall defines a helical portion, an inlet passage portion tangentially connected to the helical portion, and a bypass passage interconnecting the inlet passage portion and the helical portion. The separating wall extends to near the side wall of the helical portion and defines a narrow passage portion therebetween. The width of the upper wall of the inlet passage portion is gradually reduced towards the narrow passage portion. A rotary valve is arranged in the bypass passage and is actuated by a vacuum-operated diaphragm apparatus. The rotary valve is opened when the amount of air fed into the cylinder of the engine is increased beyond a predetermined value.

Abstract: An engine comprising an intake port which has a separating wall projecting downwardly from the upper wall of the intake port. The separating wall defines a helical portion, an inlet passage portion tangentially connected to the helical portion, and a bypass passage interconnecting the inlet passage portion and the helical portion. The intake port has a bottom wall having a transverse width which is approximately equal to the diameter of the valve head of the intake valve. The opposed peripheral edges of the bottom wall are located on the extensions of the tanget lines of the outer periphery of the valve head of the intake valve. A rotary valve is arranged in the bypass passage and is actuated by a vacuum-operated diaphragm apparatus. The rotary valve is opened when the amount of air fed into the cylinder of the engine is increased beyond a predetermined value.

Abstract: An engine comprising an intake port which has a separating wall projecting downwardly from the upper wall of the intake port. The separating wall defines a helical portion, an inlet passage portion tangentially connected to the helical portion, and a bypass passage interconnecting the inlet passage portion and the helical portion. A rotary valve is arranged in the inlet portion of the bypass passage so that the axis of the rotary valve is substantially parallel to the axis of the stem of the intake valve. The rotary valve is actuated by a vacuum-operated diaphragm apparatus and is opened when the amount of air fed into the cylinder of the engine is increased beyond a predetermined value.

Abstract: An engine comprising an intake port which has a separating wall projecting downward from the upper wall of the intake port. The separating wall defines a helical portion, an inlet passage portion tangentially connected to the helical portion, and a bypass passage interconnecting the inlet passage portion to the helical portion. A rotary valve is arranged in the bypass passage and actuated by a vacuum operated diaphragm apparatus. The rotary valve is opened when the amount of air fed into the cylinder of an engine is increased beyond a predetermined value. The separating wall has a height which is equal to approximately half the height of the intake port in the vicinity of the rotary valve.

Abstract: An engine comprising an intake port which has a separating wall projecting downwardly from the upper wall of the intake port. The separating wall defines a helical portion, an inlet passage portion tangentially connected to the helical portion, and a bypass passage interconnecting the inlet passage portion to the helical portion. A rotary valve is arranged in the bypass passage and actuated by a vacuum operated diaphragm apparatus. The rotary valve is opened when the amount of air fed into the cylinder of an engine is increased beyond a predetermined value. A downwardly projecting rib is formed on the bottom face of the separating wall. The rib extends toward the helical portion from the rotary valve.

Abstract: An internal combustion engine has a cylinder head formed with a wedge shaped cylinder head recess which has on its one side closer to a spark plug a steeply inclined roof surface of about 38.degree. to 40.degree. inclination and on its other side a gently inclined roof surface of about 5.degree. to 20.degree. inclination formed with an intake valve opening, and a piston formed with a piston recess which generally mates with the cylinder head recess and which has on its one side closer to the spark plug an inclined side surface of about 45.degree. inclination. The planar surface portion of the piston crown and the planar surface portion of the cylinder head on opposite sides of the recessed portions mutually define a relatively large squish area on the side of the gently inclined roof surface and a relatively small squish area on the side of the steeply inclined roof surface. A helical port is connected to the intake valve opening so as to generate a swirl flow of air-fuel mixture in the combustion chamber.

Abstract: An engine comprising an intake port which has a separating wall projecting downward from the upper wall of the intake port. The separating wall defines a helical portion, an inlet passage portion tangentially connected to the helical portion, and a bypass passage interconnecting the inlet passage portion to the helical portion. A rotary valve is arranged in the bypass passage and actuated by a vacuum operated diaphragm apparatus. The rotary valve is opened when the amount of air fed into the cylinder of an engine is increased beyond a predetermined value. A conical shaped groove is formed on the bottom wall of the intake port. The lower end of the rotary valve is located in the groove.

Abstract: A helically-shaped intake port comprising a helical portion formed around an intake valve, and a substantially straight inlet passage portion tangentially connected to the helical portion. A bypass passage is branched off from the inlet passage portion and connected to the helical portion. A slide valve is arranged in the bypass passage and controlled by a stepper motor so that the opening area of the slide valve changes in proportion to the amount of air to be fed into the cylinder of the engine.