Patent ID: 8689745

Claim:
A split-cycle air-hybrid engine comprising: a crankshaft rotatable about a crankshaft axis; a compression piston slidably received within a compression cylinder and operatively connected to the crankshaft such that the compression piston reciprocates through an intake stroke and a compression stroke during a single rotation of the crankshaft; an expansion piston slidably received within an expansion cylinder and operatively connected to the crankshaft such that the expansion piston reciprocates through an expansion stroke and an exhaust stroke during a single rotation of the crankshaft; a crossover passage interconnecting the compression and expansion cylinders, the crossover passage including a crossover compression (XovrC) valve and a crossover expansion (XovrE) valve defining a pressure chamber therebetween; an air reservoir is connected to the crossover passage to store compressed air from the compression cylinder and to deliver compressed air to the expansion cylinder; an air reservoir valve is operable to selectively control air flow into and out of the air reservoir; and a controller controls operation of the air reservoir valve; the engine being operable in an Air Expander and Firing (AEF) mode, wherein, through operation of the air reservoir valve control in the AEF mode: a flow rate of compressed air from the air reservoir to the expansion cylinder decreases as a pressure in the air reservoir decreases, thereby decreasing the mass of charge air entering the expansion cylinder; and the pressure in the air reservoir is maintained greater than or equal to approximately 5 bar absolute to allow a necessary mass of charge air for combustion to enter the expansion cylinder.