Concept: Oscillating Piston Engine (Another Toroidal Engine)
8 May 2006
|A cutaway view of the toroidal engine showing the pistons. Click to enlarge.|
Rotoblock, a startup company, is developing a new toroidal internal combustion engine: the Oscillating Piston Engine (OPE). The company has also signed a letter of intent with Apollo Energy Systems, a manufacturer of lead cobalt batteries and akaline fuel cell systems (earlier post), to develop a hybrid electric drivetrain with integrated OPE engine.
The OPE is one of a number of toroidal internal combustion engines currently under development, including the MYT engine (earlier post), the VGT RoundEngine, the Rotary Opposed Piston Engine (ROPE), and the Trochilic engine. Multiple designs for toroidal engines extend further back in time to the Tschudi engine (1968) and earlier.
A toroidal engine is one in which the power pistons rotate in a perfectly circular chamber with the drive shaft at the geometric center. (A torus is the doughnut-shaped surface of revolution generated by revolving a circle about an axis coplanar with the circle.)
One of the theoretical benefits of the design is a dramatic increase in power-to-weight ratio compared to a conventional reciprocating piston engine. The Rotoblock engine fires 16 times on one revolution of the crankshaft, compared to a V-8’s four times per crankshaft revolution, for example.
The original patent for the OPE was issued in 1993, with four follow-ons for specific applications, including the use of the OPE as the genset for a series hybrid (awarded 1994).
Rotoblock acquired the original OPE prototype engine and rights from the inventor (Dr. Monti Farrell). The company in now on its second-generation implementation of the technology.
|A schematic of the Rotoblock design. Click to enlarge.|
The current Oscillating Piston Engine design incorporates four pairs of pistons, each alternately attached, via two opposed oscillating adjacent thrust disks, to two coaxial driveshafts extending from one face of the cylinder block.
The thrust disks use coaxial shafts and a dual scotch yoke mechanism to couple the motion of the oscillating pistons to a single crankshaft.
|A sketch of the engine.|
The round cylinder block containing the pistons, connecting discs and coaxial output shafts continuously rotates in a counter-clockwise direction, with a 90° rotation for every complete revolution of the rotating crankshaft. This action is accomplished by a four-to-one ratio gear reduction mechanism that couples these two components together.
Rotation of the cylinder block causes a pair of inlet and exhaust ports, as well as two diametrically positioned spark plugs, to regularly appear in the intervening spaces formed between the faces of the oscillating pistons as they move back and forth through 22.5 degrees of axial rotation within the confines of the toroidal cylinder housing. The movement of the pistons form combustion chambers of variable volume in the toroidal cylinder.
Rotoblock had intended to show its 1st-generation OPE during the New York International Auto Show las month, but the display case that contains the prototype OPE was damaged in shipping.
The company is putting its 2nd-generation design through testing in its Santa Rosa, California, facility.
(A hat-tip to Robert Cummings!)
Rotoblock engine startup video
US Patent #5,222,463: Oscillating piston engine
US Patent #5,323,737: Electrical charging system for an electric powered vehicle
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