TECHNICAL FIELD

This invention relates to fuel-burning engines of the type in which rotors, instead of reciprocating pistons, are driven by combustion of the fuel within a confined volume. Volume expansion of the combusted fuel produces forces which drive the rotation of the rotors and thus of a power shaft coupled to the rotors.

This disclosure relates generally to internal combustion engines and specifically to a dual-rotor, counter-rotating rotary engine.

BACKGROUND

Many variations of the internal combustion engine have been patented in the past. The primary operational engines have been of either the reciprocating piston variety or the rotary variety. Many improvements on the reciprocating piston engine have been made over the past century; but the primary problem of inefficiency has been only marginally improved over the past 10-15 years with fuel injection, double overhead cams, multiple valves per cylinder, variable valve timing, variable ignition timing, turbocharging etc. Nonetheless, the reciprocating piston engine remains very inefficient because of the following issues: 1) Very large surface area of the combustion chamber that rapidly cools the combustion gases; 2) Slow combustion gas pressure rise because the air-fuel charge can only be ignited in the head and not over the piston; 3) Reciprocal power must be converted to rotary power; 4) Inability to capture the last 50% of the expansion power of the combustion gases because the power stroke is the same length as the compression stroke; 5) High energy loss due to friction of the rings moving up and down four times on the cylinder wall for each power stroke (four cycle engine); and 6) The engine must also serve as a air compressor, which reduces the number of possible power strokes per revolution.

The first commercially successful rotary engine was patented in Germany by Felix Wankel and associates in the 1950's. Both Mazda and General Motors developed their version of the Wankel engine, Mazda to use in the automobile and General Motors to use in recreational vehicles such as snowmobiles and boats. Both of these companies have ceased production of the rotary engine because of numerous problems with seals, pollution, reliability and efficiency. Nonetheless, the potential for the rotary engine to be lightweight and efficient has prompted many more patents for versions of the rotary engine. The rotary engine may be the ideal engine to generate power for the new electric vehicles.

Some of the more successful and recent rotary engines include Wankel, Freedom, Liquid Piston and Split-Chamber rotary. Although the embodiments disclosed here are entirely unrelated to these rotary engines, it is worth reviewing them to see how they differ from the disclosed embodiments.

The Wankel engine has been the single most successful rotary engine, although none are presently in production. The Wankel was produced by Mazda for automobile use and by General Motors Corp. for use in recreational vehicles such as snowmobiles and boats. The Wankel engine consists of a triangular, eccentric rotor with slightly curved sides and an epitrochoid-shaped housing. The rotor surfaces each complete one Otto cycle per revolution, with each face having one intake, compression, power and exhaust stroke. Thus, the rotor produces three power strokes per revolution; but, because of the eccentric gear drive to the power shaft, one revolution of the rotor causes the power shaft to rotate three revolutions. Therefore, the power shaft has one power stroke per revolution. As will be seen below, embodiments disclosed here have nine power strokes per revolution.

The Wankel has apex seals that ride over the outer housing to seal the compression and combustion in each face of the rotor. Because of the friction on the housing, the seals need to be lubricated by a sprayed mist of oil. This oil burns in the combustion chambers causing an increase in hydrocarbon pollution. While the seals move over the ovoid housing, they are forced to expand and contract and this then causes the seals to lose their seat on the housing and float off the surface causing leakage of the gases and inefficiency. As will be seen below, embodiments disclosed here have virtual seals which do not need lubrication. The surface area of the combustion chamber in the embodiments disclosed below is smaller than the stator surface area in most rotary engines. The piston excursion of the embodiments disclosed below is less than in most rotary engines. The combustion chamber of the embodiments disclosed below is preferably coated with a material such as BAM to insulate heat loss.

Cooling of the large combustion surface area in the stator is a problem with many rotary engines. Since the heat is generated during the power stroke and not during the intake and exhaust strokes, the housing is unevenly heated and the cooling must be significant enough to cool the hottest parts of the housing. In doing so, the cooler parts of the housing are also cooled further and this extracts more heat from the combustion event and decreases efficiency. The embodiments disclosed below have a small combustion chamber and a small piston excursion after combustion and the combustion chamber is preferably coated with a material such as BAM. These will reduce the heat loss and increase efficiency. Because the combustion heating is distributed evenly over the perimeter of the rotors, there will be minimal differential heating and cooling.

After these problems with the Wankel engine became well known, a number of new arts attempted to solve these problems. Among these are the Freedom Motors (formerly General Motors Corporation U.S. Pat. No. 2,988,008) and the Split-chamber rotary engine (U.S. Pat. No. 8,056,527). When production of the GMC version of the Wankel was discontinued, GMC sold their entire engine development to Freedom Motors. Freedom Motors has since done the following things to improve the function of the GMC Wankel: 1) Patented intake and porting improvements that they say increase power by 50%, 2) Developed a method to insulate the rotor bearing from the rotor, 3) Patented a new tip seal and a rotor housing coating, 4) Developed tuned intake and exhaust systems, 5) Patented a lubrication system that eliminates oil mixing and spraying oil into the intake air. This company has also demonstrated its lightweight and high power-to-weight engines in vehicles from motor scooters and automobiles to their Skycar (a flying car) and an aerial vehicle for rescuing people from burning high-rise buildings. The embodiments disclosed below will also have a high power-to-weight ratio.

The Split-Chamber rotary engine demonstrates a new method to separate the Otto cycle function of air compression from combustion and expansion and, in so doing, increases the efficiency of the rotary engine. The engine consists of a circular rotor in a housing with combustion chambers formed peripherally around the rotor. The rotor is subdivided into combustion chambers by rotor vanes. Installed peripherally to the rotor housing are compression modules that are attached to the housing. In the compression modules the air is compressed by reciprocating pistons that are driven by combustion gas that is transferred through valves from the combustion chambers. This does separate the compression function from the power function of the engine. The embodiments disclosed below also separate the compression and power functions of the engine, but in a totally different fashion.

One rotary engine type stands out as unique, namely, the Liquid Piston engine (U.S. Pat. No. 8,365,698). While the engine, at first glance, appears similar to the Wankel engine, the inventor explains that it has an entirely new high efficiency hybrid cycle that combines the best of the Otto, Diesel, Rankine and Atkinson cycles. The rotor is essentially oval and the housing is essentially triangular and in the central core of each triangular housing are small, recessed combustion cavities. When the rotor moves past the combustion area, the volume remains essentially constant for about 20 degrees of rotation. This allows the fuel to be injected and ignited and allows the pressure and temperature to rise before the rotor is driven. This increases the efficiency of the engine. The rotor runs in the triangular housing path and connects to the power shaft in a similar manner to the Wankel. The engine has demonstrated use with spark ignited and compression ignited fuels. The engine also has the ability to hyper-expand the power stroke. The inventor claims a theoretical efficiency of 75%, which is far greater than any existing piston or rotary engine.

Similar to the embodiments disclosed below, the Liquid Piston engine has the following advantages: 1) Simplicity and light weight, 2) High power-to-weight ratio, 3) Ability to hyper-expand the combustion gases to capture all of the expansion energy and 4) Efficient, quiet and vibration-free operation. In addition to these advantages, embodiments disclosed below have the following advantages: 1) Separation of air compression from power stroke to allow rapid repetition of power and exhaust strokes, 2) Ability to ignite fuel from two sides, 3) Ability to use spark-controlled compression ignition and 4) Nine power strokes per revolution.

SUMMARY

In general terms, a rotary engine comprises two counterrotating rotors of which one is directly coupled to and, therefore, rotates in the same direction as the power shaft (i.e., clockwise viewed from above); and the other (which rotates in the opposite direction or counter-clockwise) is coupled to the power shaft through a reversing gear arrangement. Both rotors are driven by hyper-expansion of combustion gases in a repeating combustion cycle. Each rotor has a generally circular working surface lying in a plane perpendicular to the common axis of rotation (i.e., the axis of symmetry of the power shaft). The two working surfaces face each other and are separated by a gap, preferably a two-millimeter gap, although other distances are possible in alternative embodiments provided the two working surfaces do not touch each other. They are preferably coated with BAM, which is an alloy that is heat resistant, insulating and has a very low coefficient of friction. The topology of each rotor surface (i.e., the shape, height and depth of the surface in a particular location or region of the rotor) creates chambers within the rotor. Within such chambers air and fuel are introduced, mixed, ignited, allowed to hyper-expand (and thus drive the rotors) and exhausted. The power shaft (as driven by the rotors) may be connected to a conventional clutch, torque converter, gearbox, differential, alternator or similar power transfer system.

The rotary engine consists of dual, counter-rotating rotors with compression cylinders and combustion chambers arrayed around the outer, inner margins of the rotor discs. In the large version of the art, air enters the engine through the power shaft after compression by a supercharger. When a supercharger is employed, it feeds air through membrane oxygen concentrators to raise the oxygen concentration and lower the nitrogen concentration of the ambient air, thus, increasing the efficiency of fuel combustion and decreasing the energy wasted heating inert nitrogen and then sending this energy out the exhaust. The air entering the power shaft is monitored for oxygen concentration, temperature and pressure. The airflow into the power shaft is controlled by an iris valve controlled by the engine control module. In an alternative embodiment (the “small” version discussed below), air enters both ends of the power shaft at atmospheric pressure.

Once air enters the power shaft, it is spun to the rpm of the engine and flows down the power shaft to the air intake ports in the primary rotor. When the engine is running, it spins the air down the air intake tubes to the compression cylinders. In so doing, it creates negative pressure in the air intake tubes and this then continues to pull air in from the power shaft. Once in the power shaft, the air intake tube and the compression chamber, the air is further compressed by centrifugal force and then by ram compression before it is driven into the hemi combustion chambers which then merge into the full combustion chambers. Air enters the combustion chamber while spinning in a vortex. The fuel is then injected into the center of the vortex and this immediately results in a thinner outer and a denser inner concentration of fuel and air mixture. This mixture is then ignited by two spark plugs (one in each rotor). The ignition of the outer layer of mixture causes a rapid rise in temperature and pressure that then causes the inner, denser mixture to instantaneously ignite by compression ignition resulting in a very rapid pressure rise that drives the pistons before they have a chance to move away from the expanding gases. This results in increased efficiency.

The pistons on the opposing rotors are driven apart in opposite directions. The combustion chambers and the compression cylinders are preferably coated with BAM (boron, aluminum, magnesium alloy) to decrease energy loss. The combustion gases are allowed to expand to approximately two times the width of the combustion chamber to use all of the expanding combustion gas pressure. Once the gas expansion is complete, the gases are expelled through exhaust ports by a combination of centrifugal force, Venturi effect and compressed air. The reversed power of the secondary rotor is reversed by a gearbox to turn the power shaft in the same direction as the primary rotor.

The air in the compression cylinders and the combustion gas in the combustion chambers are contained in their respective places by a virtual seal around the periphery of the rotors. This seal is composed of tongues and grooves with two millimeter (preferably) spacing between them. In order to escape to the external air pressure along the outer perimeter of the rotors, the gases must make a number of turns, preferably eight 90-degree turns. The passage of gas through the grooves may be slowed by concave reflectors at the end of each straight passage and by turbulence blocks that line the passages and create mini vortices in the passages. The gases cannot escape centrally because the primary rotor and the bearing on the secondary rotor are pressed on the power shaft and there is no gap to move through. They can move in the direction of the moving rotors and pistons but will be obstructed by the following facts: 1) The rotors are moving at a very high speed, i.e., 2,000 rpm, away from the escaping gas; 2) The gap between the rotors is very small (preferably two millimeters) and the escape time is one-half the time of a piston engine because there are two pistons being driven by the same charge; 3) The gas escapes in a straight line (Newton's First Law) and the rotor moves in a circular path causing the escaping gas to hit the outer wall of the rotor and then be reflected back into the combustion chamber; 4) The outer margin of the combustion chamber is very short, in the preferred embodiment only 4 inches, compared to a comparable piston engine ring seal of 12 inches (a four inch bore and a four inch stroke require a 12 inch seal); and 5) The combustion gas is escaping into the compression cylinder which has a pressure in the preferred embodiment of about 10 atmospheres, therefore slowing the escaping gas.

Since there is complete expansion of the combustion gases to atmospheric pressure, there is no expansion outside of the engine and, thus, minimal exhaust sound. There should be no need for a muffler on this engine. Also, since the blowby gases (i.e., incompletely combusted fuel) are thrown by centrifugal force into the “ring of fire” around the outer margin of the rotors, there is no need for a catalytic converter.

To calculate the amount of combustion gas that can escape to atmospheric pressure with each power stroke, while possible, would require very complex derivative functions since the pressure in the combustion chamber rises very rapidly and then decreases continually and the potential escape time is very limited at each power level. The total potential escape time at 2,000 rpm (cruise) with a twenty-two inch circumference at the combustion chamber and a four-inch length of the virtual seal would be 0.033 second. Referring briefly toFIG. 3D, since the escaping gas would have to navigate through passage125, past a concave reflector123, around four turbulence blocks124and past other reflectors and turbulence blocks throughout the passage and start and stop eight times to make all the turns created by the tongues121and grooves122in the virtual seal120, it is unlikely that any significant amount of gas could escape before the pistons move and consume all the expansion pressure of the gas. Also, the gas has only a (preferably) two-millimeter gap (the nominal “height” of passage125measured between the primary rotor101and the secondary rotor102) to move through, severely limiting the amount of gas that can flow in this limited time.

The engine does not run in oil (no surface tension) and has no friction parts other than the bearings and gears which are all sealed and run in synthetic lubricant. There are no rings or rotor seals rubbing on the block or casing. There are no mechanical internal parts such as wrist pins, rods, cam shafts, valves etc. The fuel and exhaust gases move through ports that open through the virtual seal. Because the rotors are inherently balanced in counter-rotation and because there are nine power strokes per revolution, the engine will be very stable and smooth running.

When the exhaust has been expelled, the combustion chambers again divide into hemi combustion chambers. The hemi combustion chambers that advance toward each other form the next series of combustion chambers and the process begins again. This allows for multiple power strokes per revolution. Because the compression range is quite large, any hydrocarbon fuel can be used if the compression and combustion chamber temperature are allowed to reach the proper level for ignition and combustion.

The power produced by the engine may be determined by the size of the rotors and combustion chambers, the number of combustion chambers per rotor, the number of rotors that are connected in series and whether the engine utilizes the ability to have a supercharger and oxygen concentrator. Therefore, the engine should have a wide range of applications from automobiles to small equipment like blowers and chainsaws. Because of the simplicity of the engine, it should be less expensive to build and maintain than any present piston or rotary engine. Because of the following aspects, the engine should be extremely efficient: 1) Rotary, no conversion of reciprocal to rotary power, a 18% energy saving; 2) No piston rings moving up and down a cylinder wall four times for each power stroke, a 20% energy saving; 3) No friction parts, unknown saving; 4) The engine does not run in oil, unknown saving; 5) The engine has oxygen concentration of O2to N2of 1:1 instead of 1:4 with ambient air, energy saving of at least 25% because much less energy is expended heating inert nitrogen and then throwing the hot gas out the exhaust; 6) More complete combustion with higher oxygen concentration; 7) Three power strokes per revolution for each of three combustion chambers resulting in nine power strokes per revolution; 8) New spark-controlled compression ignition causing very rapid pressure and temperature rise and increased efficiency because the pistons have no chance to move away before the combustion gases have a chance to push them; 9) 100% hyper-expansion of the power stroke to capture the residual expansion energy that a piston engine throws out the exhaust; 10) Supercharged for maximum compression and efficiency (large engine only); and 11) Intake and compression strokes operate continually outside of combustion chamber allowing for rapid repetition of power and exhaust strokes.

