The design of a single-cylinder Otto-cycle test engine is described in which the timing of both intake- and exhaust valves, as well as the volume of the compression space can be independently varied within wide limits during operation.
The proposed engine is of all-welded construction and uses stock engine components where practical to minimize production cost. Valve opening and closing is by positive cam action (desmodromic) with a differential gearset providing the phase shift between these functions.
The upper portion of the engine, comprising the cylinder head and block, is connected to the crankcase through a hinge parallel with the crankshaft axis and a pre-loaded hydraulic actuator. This arrangement allows variations of the minimum distance between the top of the piston and the cylinder head without affecting the valve timing significantly.
An oscillating counterweight, in line with, and 180 deg. out-of-phase with the piston, eliminates vibration due to first and second order inertia forces, thus allowing the 0.72 liter displacement engine to be run at high speeds without requiring a heavy test bed foundation.
A simplified form of the valve mechanism, offering a reduced range of adjustment, as well as the “hinged-block” construction which enables VCR, are readily incorporated in production-type engines.