Abstract: A control device for a compression ratio variable internal combustion engine is provided with a compression ratio variable mechanism for changing an engine compression ratio in accordance with a rotational position of a control shaft, and a detection unit that detects an actual compression ratio. In a predetermined engine operating condition such as immediately after an engine start, reference position learning operation for the detection unit is carried out with the control shaft mechanically locked up at a predetermined reference position. During operation of the engine, even when the actual compression ratio is lost or a difference between the actual compression ratio and a target compression ratio becomes greater than an assumed deviation, due to some abnormalities, the reference position learning operation is immediately carried out, thereby enabling a quick return to a state where normal compression ratio control can be carried out.

Abstract: A target compression ratio ?(t+Tact) after a prescribed time Tact has expired from a current point of time is calculated from an intake air volume drawn into a cylinder after expiration of the prescribed time Tact from the current point of time. A control command to an electric motor that drives a variable compression ratio mechanism is calculated so as to bring an actual compression ratio ?r(t+Tact) after the prescribed time Tact into accordance with the target compression ratio ?(t+Tact) after the prescribed time Tact. This enables the actual compression ratio to follow the target compression ratio accurately.

Abstract: A control device for a compression ratio variable internal combustion engine is provided with a compression ratio variable mechanism for changing an engine compression ratio in accordance with a rotational position of a control shaft, and a detection unit that detects an actual compression ratio. In a predetermined engine operating condition such as immediately after an engine start, reference position learning operation for the detection unit is carried out with the control shaft mechanically locked up at a predetermined reference position. During operation of the engine, even when the actual compression ratio is lost or a difference between the actual compression ratio and a target compression ratio becomes greater than an assumed deviation, due to some abnormalities, the reference position learning operation is immediately carried out, thereby enabling a quick return to a state where normal compression ratio control can be carried out.

Abstract: A wave motion gearing speed reducer (20) is disposed between a driving motor (15) and a control shaft (11) of a variable compression ratio mechanism. There are provided a input shaft rotation sensing sensor (31) to sense the rotational position of an input shaft (16) of the speed reducer (20), and an output shaft rotation sensing sensor (32) to sense the rotational position of an output shaft (12) of the speed reducer (20). When a discrepancy quantity (??) between sensed quantities of both sensors is greater than or equal to a predetermined value, a judgment is made that a ratcheting of slippage of an engaging position between internal teeth (22) and external teeth (25) is generated.

Abstract: An internal combustion engine (1) that has a variable-compression-ratio mechanism (2) has variable valve mechanisms (7, 8) for an intake valve (4) and an exhaust valve (5), respectively. If a malfunction in the variable-compression-ratio mechanism (2), which controls a mechanical compression ratio via an electric motor (31), is detected from the amplitude of variations in an actual compression ratio, then if the fuel supply to the engine is cut, a throttle valve (14) is opened wider than would be the case if the variable-compression-ratio mechanism (2) were not malfunctioning, thereby reducing in-cylinder negative pressure during the intake stroke. Also, the timing with which the intake valve is closed is advanced and the timing with which the exhaust valve is opened is retarded, increasing the in-cylinder positive pressure during the compression and power strokes. This prevents the variable-compression-ratio mechanism (2) from increasing the compression ratio when control is lost.

Abstract: A target compression ratio ?(t+Tact) after a prescribed time Tact has expired from a current point of time is calculated from an intake air volume drawn into a cylinder after expiration of the prescribed time Tact from the current point of time. A control command to an electric motor that drives a variable compression ratio mechanism is calculated so as to bring an actual compression ratio ?r(t+Tact) after the prescribed time Tact into accordance with the target compression ratio ?(t+Tact) after the prescribed time Tact. This enables the actual compression ratio to follow the target compression ratio accurately.

Abstract: An internal combustion engine (1) that has a variable-compression-ratio mechanism (2) has variable valve mechanisms (7, 8) for an intake valve (4) and an exhaust valve (5), respectively. If a malfunction in the variable-compression-ratio mechanism (2), which controls a mechanical compression ratio via an electric motor (31), is detected from the amplitude of variations in an actual compression ratio, then if the fuel supply to the engine is cut, a throttle valve (14) is opened wider than would be the case if the variable-compression-ratio mechanism (2) were not malfunctioning, thereby reducing in-cylinder negative pressure during the intake stroke. Also, the timing with which the intake valve is closed is advanced and the timing with which the exhaust valve is opened is retarded, increasing the in-cylinder positive pressure during the compression and power strokes. This prevents the variable-compression-ratio mechanism (2) from increasing the compression ratio when control is lost.

Abstract: A wave motion gearing speed reducer (20) is disposed between a driving motor (15) and a control shaft (11) of a variable compression ratio mechanism. There are provided a input shaft rotation sensing sensor (31) to sense the rotational position of an input shaft (16) of the speed reducer (20), and an output shaft rotation sensing sensor (32) to sense the rotational position of an output shaft (12) of the speed reducer (20). When a discrepancy quantity (??) between sensed quantities of both sensors is greater than or equal to a predetermined value, a judgment is made that a ratcheting of slippage of an engaging position between internal teeth (22) and external teeth (25) is generated.