Methods and systems are provided for estimating an actual compression ratio of an engine cylinder based on the electric current applied to an actuator of the associated variable compression ratio mechanism. The compression ratio is estimated as a function of both a value and a location, relative to cylinder piston position, of a peak holding current applied by an electric motor on the actuator to maintain the actuator at a commanded compression ratio setting. In this way, the vehicle control system may more accurately infer the current actual compression ratio of each cylinder.

The invention relates to a method for diagnosing and/or controlling a reciprocating engine having a variable compression ratio, wherein the method comprises the working steps: determining (S30) a first value (U.sub.1,1, U.sub.1,2; .sub.1) of a rotational irregularity parameter of a crankshaft (1) of the reciprocating engine; and determining (S60) a value of a compression ratio parameter for the reciprocating engine based on said first rotational irregularity parameter value.

In a combustion chamber of a piston combustion engine there is a displaceable piston that can be moved progressively up or down between an upper and a lower turning position. The displacement takes place via an electrically controlled step motor which is connected to the piston via a hydraulic link, including a hydraulic lock. The lock is deactivated during the displacement a certain number of steps up or down ordered by a motor control system, and when the displacement is ended, the lock is activated by said engine control system and the moving piston is locked in a certain position ordered by the motor control system.

A check valve for a connecting rod for a variable compression internal combustion engine with at least one hydraulic chamber arranged in the connecting rod and connectable with a supply connection or a tank through the check valve, the check valve including a valve housing; and a valve closure element that is axially movable in the valve housing along a longitudinal valve axis, wherein the valve closure element is applicable to a valve seat and arranged in the valve housing secured against separation from the valve housing, wherein a pin shaped separation prevention element is provided which secures the valve closure element in the valve housing and limits a stroke of the valve closure element.

A check valve for a connecting rod for a variable compression internal combustion engine with at least one hydraulic chamber arranged in the connecting rod and connectable with a supply connection or a tank through the check valve, the check valve including a valve housing; and a valve closure element that is axially movable in the valve housing along a longitudinal valve axis, wherein the valve closure element is applicable to a valve seat and arranged in the valve housing secured against separation from the valve housing, wherein a pin shaped separation prevention element is provided which secures the valve closure element in the valve housing and limits a stroke of the valve closure element.

Methods and systems are provided for indicating degradation of a VCR mechanism that mechanically alters a cylinder compression ratio. Degradation is detected based on an elevated knock incidence and increased spark retard usage. If the VCR mechanism is stuck, knock and pre-ignition that could be induced by continued operation in a higher than intended compression ratio is mitigated by limiting the engine load.

Methods and systems are provided for indicating degradation of a VCR mechanism that mechanically alters a cylinder compression ratio. Degradation is detected based on an elevated knock incidence and increased spark retard usage. If the VCR mechanism is stuck, knock and pre-ignition that could be induced by continued operation in a higher than intended compression ratio is mitigated by limiting the engine load.

The variable compression ratio mechanism 1, 1 comprises: a connecting rod 20 provided with a crank receiving opening 23; an eccentric member 30, 30 provided with a piston pin receiving opening 36 and attached to the connecting rod to be able to turn so as to change a length between a center axial line of the piston pin receiving opening and a center axial line of the crank receiving opening; a swing member 40, 50, 40 attached to the connecting rod to be able to swing and able to engage with the eccentric member; and an actuating member 60, 60 swinging the swing member from an initial position toward a stop position. The swing member engages with the eccentric member to turn the eccentric member when swinging from the initial position toward the stop position, and returns from the stop position to the initial position when disengaged form the eccentric member.

The variable compression ratio mechanism 1, 1 comprises: a connecting rod 20 provided with a crank receiving opening 23; an eccentric member 30, 30 provided with a piston pin receiving opening 36 and attached to the connecting rod to be able to turn so as to change a length between a center axial line of the piston pin receiving opening and a center axial line of the crank receiving opening; a swing member 40, 50, 40 attached to the connecting rod to be able to swing and able to engage with the eccentric member; and an actuating member 60, 60 swinging the swing member from an initial position toward a stop position. The swing member engages with the eccentric member to turn the eccentric member when swinging from the initial position toward the stop position, and returns from the stop position to the initial position when disengaged form the eccentric member.

Provided is an actuator for a link mechanism for an internal combustion engine, which is capable of improving a degree of freedom in layout while reducing the number of components. The actuator for a link mechanism for an internal combustion engine according to the present invention includes a rolling bearing provided between a wave generator of a wave gear speed reducer and a housing or a motor housing. An inner ring of the rolling bearing is fixed to the wave generator. A restricting portion configured to restrict movement of an outer ring of the rolling bearing to both sides in an axial direction with respect to the housing or the motor housing is provided.