Abstract: A control system for an internal combustion engine is provided which comprises a compression ratio control mechanism and a control unit for controlling the compression ratio control mechanism. The control unit including an acceleration parameter obtaining section for obtaining an acceleration parameter corresponding to a change of an engine speed, an acceleration determining section for determining whether the engine is in a slow or fast acceleration state on the basis of the acceleration parameter, and a control section for controlling at least one of a compression ratio change speed at which the engine compression ratio during engine acceleration is changed and a compression ratio change start time at which a change of the engine compression ratio during engine acceleration is started, on the basis of whether the engine is in a slow or fast acceleration state. A control method is also provided.

Abstract: In a rockable-cam equipped reciprocating internal combustion engine, a rockable cam is rotatably fitted on the outer periphery of an intake-valve drive shaft that is rotatable in synchronism with rotation of a crankshaft. The rockable cam oscillates within predetermined limits during rotation of the intake-valve drive shaft so as to directly push an intake-valve lifter. As viewed from an axial direction of the crankshaft, an axis of the intake-valve drive shaft is offset from a centerline of the intake-valve stem in a first direction that is normal to both the cylinder centerline and the crankshaft axis and directed from the cylinder centerline to the intake valve side. The crankshaft axis is also offset from the cylinder centerline in the first direction.

Abstract: In a variable compression ratio mechanism for an internal combustion engine employing an upper link, a lower link, and a control link, the lower link includes a crankpin bearing portion into which a crankpin is fitted, a first connecting-pin bearing portion into which a first connecting pin for the upper link is fitted, and a second connecting-pin bearing portion into which a second connecting pin for the control link is fitted. A central connecting portion is provided to connect an axial central portion of at least one of the first and second connecting-pin bearing portions to an axial central portion of the crankpin bearing portion. The central connecting portion has an axial length L1 shorter than each of an axial length L2 of the crankpin bearing portion, an axial length L3 of the first connecting-pin bearing portion, and an axial length L4 of the second connecting-pin bearing portion.

Abstract: A control system for an internal combustion engine is provided. The engine includes a compression ratio control mechanism and an ignition timing control system. The control system comprises an engine control for controlling the compression ratio control mechanism and the ignition timing control system so that when the engine is cold, the ignition timing is retarded largely from an MBT point and the compression ratio is set higher than that obtained when the engine is cold and operated at corresponding engine rpm and engine load. A method for controlling such an internal combustion engine is also provided.

Abstract: In an internal combustion engine of variable compression ratio type, a piston control mechanism is employed which comprises a lower link rotatably disposed on a crank pin of a crankshaft of the engine, an upper link having one end pivotally connected to the lower link and the other end pivotally connected to a piston of the engine, a control link having one end pivotally connected to the lower link; and a position changing mechanism which changes a supporting axis about which the other end of the control link turns. When the piston comes up to a top dead center, a compression load is applied to the control link in an axial direction of the control link in accordance with an upward inertial load of the piston.

Abstract: A paired counterweights of a crankshaft have projected inner surfaces which protrude toward each other defining a given space therebetween. A plurality of links are arranged to convert a reciprocating motion of a piston to a rotational motion of the crankshaft. One of the links is pivotally connected to other links through link connecting portions and swingably disposed on a crank pin of the crankshaft so that upon rotation of the crankshaft, a peripheral portion of the link passes through the given space. At least one of the link connecting portions is placed within an imaginary circle which would be described by a radially innermost part of the projected inner surfaces of the paired counterweights when the paired counterweights turn about an axis of the crank pin.

Abstract: A piston crank mechanism of an internal combustion engine includes an upper link connected to a piston, a lower link connected to both the upper link and a crankpin, and a control link through which the lower link is linked to an eccentric cam of a control shaft to restrict the degree of freedom of the lower link. By varying the angular position of the eccentric cam with respect to the control-shaft axis, the center of oscillating motion of the control link varies, thus varying a compression ratio. The center of gravity of the lower link, determined by an equivalent inertia weight obtained by adding weights of connecting pins and weights of the upper-link boss-shaped end and the control-link boss-shaped end connected to the lower link via the respective connecting pins to the lower-link self-weight, is situated closer to the center of the crankpin.

Abstract: A variable compression ratio mechanism for a reciprocating engine includes a connecting rod split into upper and lower connecting rod portions linked to each other through a first connecting pin. A rockable arm is oscillatingly linked at one end to the lower connecting rod portion through a second connecting pin. A control mechanism shifts the center of oscillating motion of the rockable arm to vary a compression ratio of the engine. A piston stroke is set to be greater than two times a crank radius of a crank, irrespective of variations in the compression ratio. A linkage is dimensioned and laid out, so that its crankpin load is less than a crankpin load produced by a linkage that the crankpin is located on a perpendicular line at a substantially midpoint of a line segment between and including the centers of the first and second connecting pins.