Randy,
So what we have in the TCH is a standard IC engine that we all are used to, modified through valve timing to create an expansion ratio that is higher than the compression ratio. Got it!
According to wikipedia, the hallmark of the Atkinson cycle is not necessarily that all four strokes occur in one rev of the crankshaft, but that the expansion ratio must be higher than the compression ratio:
"The
Atkinson cycle may also refer to a
four stroke piston engine in which the intake valve is held open longer than normal to allow a reverse flow of intake air into the intake manifold. This reduces the effective compression ratio and, when combined with an increased stroke and/or reduced combustion chamber volume, allows the expansion ratio to exceed the compression ratio while retaining a normal compression pressure. This is desirable for improved fuel economy because the compression ratio in a spark ignition engine is limited by the octane rating of the fuel used. A high expansion ratio delivers a longer power stroke, allowing more expansion of the combustion gases and reducing the amount of heat wasted in the exhaust. This makes for a more efficient engine."