|A cutaway sketch of the RIDE engine in combustion mode. Note the offset of the crankshaft from central rotational axis.|
A Virginia inventor is devising a rotary engine with an integral flywheel effect to serve as a single-unit hybrid power plant. Gary Greenwell’s new RIDE (Rotational Inertial Dampening Engine) modifies the design of the Gnome rotary aircraft engine design of the WW I era to enable the rotating engine block to function as a freely-spinning flywheel, thereby offering an integrated flywheel-based hybrid power capability.
Greenwell (who has 30+ years in the engine side of the auto industry) estimates that the RIDE engine, through its combination of combustion power and kinetic energy storage, could support automotive fuel economies in the range of 100 to 120 mpg without the additional cost of electric motors and batteries.
|A cutaway drawing of the Gnome rotary engine. The inlet valve was in the piston.|
The Gnome. The Gnome radial engine—developed almost a century ago—seems counter-intuitive. It features a crankshaft mounted on the airplane, with the rotary engine block and cylinder heads—to which the propeller was attached—rotating around the crankshaft. In other words, the propeller and engine block rotated as a unitary segment.
A number of early aviation engines were designed in this manner. With the crankcase and cylinders revolving in one circle, and the pistons in another, offset circle, there were no reciprocating parts and no need for a heavy counterbalance. The momentum of the crankcase and cylinders smoothed out the power pulses, thereby eliminating the need for a heavy flywheel. These rotary engines had the best power-to-weight ratio of any configuration at the time.
They also had a number of downsides, notably their total-loss oil systems. Centrifugal force threw the lubricating oil out after the first trip through the engine. The aircraft’s range was thus limited by the amount of oil it could carry as well as fuel. A gyroscopic effect created by the spinning mass also made maneuvering the airplane difficult—not a good feature in a fighter aircraft.
RIDE as a rotary engine. Greenwell made a number of significant changes to the rotary design, including inverting the relationship between the cylinder heads and the pistons. Rather than have the cylinder heads rotate as part of the radial engine block, Greenwell has the pistons affixed to the exterior ring, with the cylinder heads attached to the crankshaft.
There are no connecting rods as in the Gnome, and no valves in either the piston or the cylinder head. Instead, the rotation of the cylinder ring uncovers inlet and exhaust ports.
Moving the cylinder heads close to the fixed center where the ports would be located allowed the elimination of valve train components. The inversion also addressed the issue of centrifugal forces that cause the lubricating oil to migrate into the cylinders (as in the Gnome).
Reversing the position causes the oil to migrate away from the combustion chambers, thereby reducing the need for fine-tuning the piston rings for oil control, according to Greenwell.
Avoiding the total oil loss system entirely, RIDE will use a lubrication system more similar to the dry sump systems used on aircraft engines. Pressurized oil would be supplied to the center of the engine, to be centrifugally distributed to the outer perimeter, where small return pumps would force it back to the center.
Although it can be applied as a spark ignition system, RIDE is ideally a compression ignition system.
The key invention, though, is the Powerswitch: the moveable crank journal that allows the engine to convert to flywheel mode, along with its management software.
RIDE as flywheel. While the rotary combustion engine capability of RIDE might be mildly interesting, it is its ability to convert to flywheel mode for energy recovery that is the unique aspect of this approach.
|RIDE switching to flywheel mode. Note the movement of the crankshaft from being offset in combustion mode to aligned on the central rotational axis in flywheel mode.|
RIDE makes the crankshaft a separate part from the engine support bearings. This change is critical to the revised radial design, as it allows the crankshaft to move to be positioned exactly as the rotational axis of the moving engine block—which, in turn, changes the running engine to a freely-spinning flywheel.
The pistons go from relative reciprocation to stationery in their cylinders when the engine is in flywheel mode. The switching mechanism—Powerswitch—is one of the key inventions for which Greenwell filed a patent in 2004.
The flywheel can store power for short periods of time, as well as recover energy from regenerative braking. (AFS Trinity was earlier exploring the viability of a flywheel-based hybrid drivetrain before opting for a more conventional battery/ultracapacitor approach it has under development with Ricardo. Earlier post.)
The RIDE engine will constantly transfer from fuel power to stored energy, while the vehicle speed remains constant, with the CVT (continuous variable transmission) adding power to the vehicle power train in the exact amounts necessary to compensate for all losses regardless of their origin.
This engine design recovers the vast majority of braking losses by converting linear inertia (vehicle) into rotational inertia (engine) in an exchange that involves no additional components than a currently produced vehicle.
This energy storage capability, Greenwell argues, will eliminate the vast majority of idling losses (100% losses). Utilizing the appropriate variable transmission and computer controls, regenerative braking can recover most of deceleration forces.
(Dynamometer figures, Greenwell notes, demonstrate that a reciprocating engine running at 2,000 rpm uses half the fuel consumed, to merely maintain that speed with no force applied to the drive wheels: “the penalty of reciprocation,” as he calls it.)
This is a large part of the function of hybrid designs—to replace combustion when it is least fuel-efficient (idling, stop-and-go driving, etc.) with a different, more efficient source of power and to recoup the kinetic energy from braking or deceleration—but hybrids require the addition of the additional power and energy storage systems (e.g., electric motor and battery pack).
The basic concept can be best understood in this example. You are stopping from 40 mph, and the linear inertia of the vehicle is converted to rotational inertia in the engine-flywheel, to be reapplied for acceleration when it is required.
If the system was capable of 90% efficiency re-acceleration would get your vehicle to 36 mph from the recovered energy. During the whole period of time this is occuring there would be no fuel consumed.
The flywheel storage would provide the power to accelerate, and after 36 mph you would need to run the engine (consume fuel) to restore flywheel inertia. The flywheel would never stop spinning while the vehicle was in operation, the fuel burning run mode [also] serves the purpose of restoring the flywheel’s inertia when it is depleted.—Gary Greenwell
RIDE, according to Greenwell, is capable of storing 4 times the force in regeneration that it can produce by combustion.
Applications. As initially envisioned, the RIDE engine is purely a combustion engine. However, its design optionally includes auxiliary energy storage in other forms, such as compressed air or electrical. It could also function as the motor/pump in a hydraulic drive system.
RIDE is a subsidiary of EDGE Office Solutions.