A piston compound internal combustion engine is disclosed with an expander piston deactivation feature. A piston internal combustion engine is compounded with a secondary expander piston, where the expander piston extracts energy from the exhaust gases being expelled from the primary power pistons. The secondary expander piston can be deactivated and immobilized, or its stroke can be reduced, under low load conditions in order to reduce parasitic losses and over-expansion. Two mechanizations are disclosed for the secondary expander piston's coupling with the power pistons and crankshaft. Control strategies for activation and deactivation of the secondary expander piston are also disclosed. In addition, six-cylinder engine configurations are defined by replicating groups of two power pistons and one expander piston.

A split-cycle engine includes a compression cylinder having a first volume for a first working fluid and a second volume for a second working fluid, the first volume and second volume being separated by the compression piston, an expansion cylinder having a first volume for the first working fluid and a second volume for the second working fluid, the first volume and second volume being separated by the expansion piston, and a fluid coupling between the second volume of the compression cylinder and the second volume of the expansion cylinder, wherein the two second volumes and the fluid coupling provide a closed volume for the second working fluid, wherein the fluid coupling includes a regenerator arranged such that the two second volumes are thermally decoupled.

A split-cycle engine includes a compression cylinder having a first volume for a first working fluid and a second volume for a second working fluid, the first volume and second volume being separated by the compression piston, an expansion cylinder having a first volume for the first working fluid and a second volume for the second working fluid, the first volume and second volume being separated by the expansion piston, and a fluid coupling between the second volume of the compression cylinder and the second volume of the expansion cylinder, wherein the two second volumes and the fluid coupling provide a closed volume for the second working fluid, wherein the fluid coupling includes a regenerator arranged such that the two second volumes are thermally decoupled.

An internal combustion engine includes a first low-pressure cylinder housing a first low-pressure piston, and a first high-pressure cylinder housing a first high-pressure piston, the first high-pressure cylinder being arranged in upstream fluid communication with the first low-pressure cylinder for providing exhaust gas into the first low-pressure cylinder. The internal combustion engine further includes a second low-pressure cylinder housing a second low-pressure piston, the second low-pressure cylinder being arranged in upstream fluid communication with the first high-pressure cylinder for providing compressed gas into the first high-pressure cylinder, and a second high-pressure cylinder housing a second high-pressure piston, the second high-pressure cylinder being arranged in downstream fluid communication with the first low-pressure cylinder for receiving compressed gas from the first low-pressure cylinder, and further arranged in upstream fluid communication with the second low-pressure cylinder for providing exhaust gas into the second low-pressure cylinder.

An internal combustion engine includes a first low-pressure cylinder housing a first low-pressure piston, and a first high-pressure cylinder housing a first high-pressure piston, the first high-pressure cylinder being arranged in upstream fluid communication with the first low-pressure cylinder for providing exhaust gas into the first low-pressure cylinder. The internal combustion engine further includes a second low-pressure cylinder housing a second low-pressure piston, the second low-pressure cylinder being arranged in upstream fluid communication with the first high-pressure cylinder for providing compressed gas into the first high-pressure cylinder, and a second high-pressure cylinder housing a second high-pressure piston, the second high-pressure cylinder being arranged in downstream fluid communication with the first low-pressure cylinder for receiving compressed gas from the first low-pressure cylinder, and further arranged in upstream fluid communication with the second low-pressure cylinder for providing exhaust gas into the second low-pressure cylinder.

An internal combustion engine includes a first low-pressure cylinder housing a first low-pressure piston, and a first high-pressure cylinder housing a first high-pressure piston, the first high-pressure cylinder being arranged in upstream fluid communication with the first low-pressure cylinder for providing exhaust gas into the first low-pressure cylinder. The internal combustion engine further includes a second low-pressure cylinder housing a second low-pressure piston, the second low-pressure cylinder being arranged in upstream fluid communication with the first high-pressure cylinder for providing compressed gas into the first high-pressure cylinder, and a second high-pressure cylinder housing a second high-pressure piston, the second high-pressure cylinder being arranged in downstream fluid communication with the first low-pressure cylinder for receiving compressed gas from the first low-pressure cylinder, and further arranged in upstream fluid communication with the second low-pressure cylinder for providing exhaust gas into the second low-pressure cylinder.

An internal combustion engine includes a first low-pressure cylinder housing a first low-pressure piston, and a first high-pressure cylinder housing a first high-pressure piston, the first high-pressure cylinder being arranged in upstream fluid communication with the first low-pressure cylinder for providing exhaust gas into the first low-pressure cylinder. The internal combustion engine further includes a second low-pressure cylinder housing a second low-pressure piston, the second low-pressure cylinder being arranged in upstream fluid communication with the first high-pressure cylinder for providing compressed gas into the first high-pressure cylinder, and a second high-pressure cylinder housing a second high-pressure piston, the second high-pressure cylinder being arranged in downstream fluid communication with the first low-pressure cylinder for receiving compressed gas from the first low-pressure cylinder, and further arranged in upstream fluid communication with the second low-pressure cylinder for providing exhaust gas into the second low-pressure cylinder.

This invention relates to internal combustion engines and more particularly to internal combustion engines and methods of operating the engines with a new fuel saving cycle. Various embodiments use a passage between adjacent cylinders to enable a mode in which fuel combusted in one cylinder supplies pressure to the other that has not been supplied with fuel, thus enabling driving of both cylinders with less fuel.

This invention relates to internal combustion engines and more particularly to internal combustion engines and methods of operating the engines with a new fuel saving cycle. Various embodiments use a passage between adjacent cylinders to enable a mode in which fuel combusted in one cylinder supplies pressure to the other that has not been supplied with fuel, thus enabling driving of both cylinders with less fuel.