Patent Application
20070068467
The present invention relates generally to internal combustion engines, and more particularly, to a radial compression-ignition engine for aircraft.
Internal combustion engines, and more specifically, reciprocating internal combustion engines are well known in the art. A conventional internal combustion engine typically includes a crankshaft, a crankcase disposed about the crankshaft, one or more cylinders exposed to the crankcase, a piston adapted to reciprocate within each cylinder, and a connecting rod drivingly coupling each piston to the crankshaft. The crankcase may be fixed to the frame of a vehicle such that the reciprocation of the pistons causes the crankshaft to rotate about an axis. Alternatively, the crankshaft may be fixed to the frame of a vehicle such that the reciprocation of the pistons causes the crankcase and cylinders to rotate about the crankshaft. Both of these configurations were commonly used to power aircraft in the early days of aviation. In particular, engines having the latter configuration with several cylinders radially disposed about the crankshaft were often referred to as “Gnome”-type engines.
Reciprocating internal combustion engines may be further classified as being spark-ignited (SI) or compression-ignited (CI). SI engines control the start of combustion by appropriately timing a spark plug that ignites an air-fuel mixture in the cylinder. The spark plug is often timed such that the start of combustion occurs when the piston reaches the top of the cylinder. To this end, the compression ratio of the engine must be kept relatively low in order to avoid engine “knock,” or the premature ignition of the air-fuel mixture. Traditional gasoline engines are typically of the SI type.
CI engines, on the other hand, control the start of combustion by compressing air within the cylinder and directly injecting fuel into the compressed air. Typically diesel fuel is injected into the compressed air, which is why traditional diesel engines are of the CI type. The increased pressure raises the temperature in the cylinder and eventually causes the air-fuel mixture to self-ignite. Such an arrangement requires CI engines to achieve higher compression ratios, and therefore, higher thermal efficiencies than comparable SI engines. In other words, traditional diesel engines are capable of more horsepower (BTUs) per volume of fuel when compared to their traditional gasoline counterparts. With the ever-increasing costs of gasoline, this aspect of a traditional diesel engine is particularly appealing to manufacturers and consumers of airplanes and other vehicles that consume large quantities of fuel.
Although several early attempts were made to develop a suitable CI or diesel engine for propeller-driven aircraft, there are many challenges associated with using these engines to power such aircraft. For example, combustion of the highly compressed air-fuel mixture in the cylinders can cause the pistons to generate significant shock “pulses” throughout the engine. These pulses can cause the engine to vibrate and thus lead to unsafe operating conditions. To reduce vibrations, CI engines are typically designed with heavier cylinders and crankcases to dampen the effect of the pulses. The additional weight, however, limits the aircraft's speed and altitude ability and thus has heretobefore discouraged the use of CI engines in airplanes and other aircraft.
Maintenance difficulties are another challenge often associated with CI engines. For example, CI engines typically have a two-piece construction including a heavy cylinder head, a head gasket, and heat bolts coupling the cylinder head with the cylinder body. The cylinder head, head gasket, and head bolts are known to be common sources of failure because they are continuously exposed to the tremendous pressures associated with the cylinders.
In summary, the increased weight and maintenance challenges associated with CI engines has discouraged their use in the aircraft industry. Those in the industry abandoned attempts to capitalize on the advantages of CI engines and have instead relied upon SI engines due of their lighter weight. This is particularly true in the light to medium aircraft market. Moreover, over the past several decades there has been a significant trend towards using “jet-propelled” aircraft. Jet-propelled aircraft are typically powered by a gas turbine instead of the Si and CI reciprocating engines discussed above. Gas turbine engines generally experience much higher combustion temperatures than reciprocating engines and are adapted to deliver more power when compared to a reciprocating engine of the same weight.
Although jet engines have helped address some of the drawbacks associated with reciprocating engines, the solutions have come at an enormous cost to aircraft owners. For example, gas turbines often require complex designs and expensive materials because of the high combustion temperatures. Gas turbines can also be more costly to fuel than comparable reciprocating engines.
Therefore, there is a need for an improved compression-ignition engine that addresses the design challenges discussed above in order to provide an effective alternative to Si engines and an inexpensive alternative to gas turbine engines.
The present invention provides a compression-ignition internal combustion engine for aircraft or the like. The engine generally comprises a stationary crankshaft, a crankcase positioned about the crankshaft, and a plurality of cylinders radially extending through a plurality of ports in the crankcase. Each cylinder includes a piston adapted to reciprocate therein and a connecting rod drivingly coupling the piston to the crankshaft. Because the engine is a Gnome-type engine, the crankcase and cylinders are adapted to rotate about the stationary crankshaft. The crankcase and cylinders also have a unitary construction in order to reduce the overall weight of the engine and eliminate the need for head gaskets and other sources of engine failure. Accordingly, the engine may be used to power propeller-driven aircraft by attaching a plurality of propeller blades to the rotating crankcase.
An engine according to the invention further includes a valve assembly and fuel assembly associated with the cylinders. The valve assembly includes an exhaust valve associated with each cylinder, a valve tappet associated with each exhaust valve, and a valve housing coupled to the crankcase for aligning the valve tappets with a first cam mounted on the crankshaft. The valve tappets are adapted to cooperate with the first cam in order to operate the exhaust valves in a timed manner as the crankcase rotates about the crankshaft. In one aspect of the invention, the first cam only has one lobe for cooperating with the valve tappets such that the exhaust valves operate once per revolution of the crankcase about the crankshaft.
Similarly, the fuel assembly includes a fuel injector associated with each cylinder, a plurality of fuel pumps corresponding to the plurality of cylinders, and a fuel assembly housing coupled to the crankcase for aligning the fuel pumps with a second cam mounted on the crankshaft. The fuel pumps are adapted to cooperate with the second cam to provide pressurized fuel to the fuel injectors in a timed manner as the crankcase rotates about the crankshaft. Like the first cam, the second cam has only one lobe for cooperating with the fuel pumps such that the fuel injectors operate once per revolution of the crankcase about the crankshaft.
In one embodiment, a starter motor and an air blower are mounted to the crankshaft. The starter motor is selectively coupleable to the crankcase and adapted to rotate the crankcase when coupled thereto. Meanwhile, the air blower is coupled to the crankcase by a drive belt such that the air blower is powered by the rotation of the crankcase. The air blower is adapted to deliver pressurized air through a hollow portion of the crankshaft and into the crankcase. From there, the pressurized air is delivered to the plurality of cylinders by an air manifold.
The invention also provides a propeller synchronizer for selectively adjusting the pitch of the propellers. The propeller synchronizer is generally positioned within the spinner of the engine, and generally comprises a motor secured to the crankcase, a pinion gear rotatably coupled to the motor, a main synchronizer gear operable to rotate relative to the crankcase and coupled to each propeller, and a drive shaft coupling the pinion gear to the main gear such that operation of the motor causes rotation of the propellers so as to change their pitch.
These and other objects, advantages and features of the invention will become more readily apparent to those of ordinary skill in the art upon review of the following detailed description.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the principles of the invention.
With reference to
The crankcase 14 is of a unitary construction and may be formed from a one-piece round seamless steel tube. The one-piece construction increases structural integrity and reduces crack initiation and other failure sites. The tube is preferably balanced (i.e., symmetric) in order to prevent or reduce engine vibration during the rotation of the crankcase 14. As shown in
With reference to
A top end, or “head” 40, of each cylinder 16 is provided with one or more bores 42 that are each adapted to receive an exhaust valve 44. The exhaust valves 44 may be passed from the interior of the crankcase 14, through the ports 18, and into the cylinders 16 before being received in the bores 42. As shown in
With reference to
Referring back to
After installing the exhaust valves 44 and fuel injectors 80, a piston 104 may be inserted into the interior of each cylinder 16. Each piston 104 is provided with seal rings 106 to form a combustion chamber 108 within the cylinder 16 by sealing off a portion of the interior of each cylinder 16 from the interior of the crankcase 14. Because the pistons 104 are adapted to reciprocate within cylinders 16, the volume of the combustion chamber 108 constantly changes during operation. As shown in
With reference to
The crankshaft 12 is preferably formed from a single piece of material, such as steel, that has been machined into the appropriate shape. As shown in
Once the main bearing 134 has been installed onto the crankshaft 12, a forward thrust plate 176 (
The forward thrust plate 176 further includes a plurality of ports (not shown) similar to the plurality of ports 186 in main synchronizer gear 222 shown in
Thus, in use, an operator activates the starter motor 164 to thereby drive the starter ring gear 194 and rotate the crankcase 14 about the crankshaft 12. As the crankcase 14 rotates, the pistons 104 reciprocate within the cylinders 16 and compress air in the combustion chambers 108 as they approach the cylinder heads 40. The nozzle 82 of the fuel injectors 80 sprays fuel into the combustion chambers 108 when the pistons 104 approach or reach the outer most position of their reciprocal movement. Eventually, the compressed air-fuel mixture reaches a kindle temperature sufficient to ignite the injected fuel such that the engine 10 begins operating independent of the starter motor 164.
The engine 10 shown in the figures operates on a two-stoke cycle. Thus, after the air-fuel mixture in the cylinder 16 is ignited, the resulting explosion causes the piston 104 to move downward and begin its power stroke. The downward motion of the piston 104 causes the cylinders 16 and crankcase 14 to rotate about the stationary crankshaft 12. As the piston 104 approaches its bottom most position in the cylinder 16, it moves below the air intake ports 110 so that high-pressured air can be delivered into the cylinder 16. More specifically, the air blower 160 forces pressurized air through the hollow portion 172 of the crankshaft 12 and into the interior of the crankcase 14. The air blower 160 is preferably a “Roots” type supercharger capable of supplying high pressure air to cylinders 16 during, for example, low altitude idling as well as high altitude, full power operation. From hollow portion 172, the pressurized air travels through the ports 186 in the main synchronizer gear 222 and through the ports in the front thrust plate 176 and into the spinner 188, eventually reaching the air delivery pipes 114 before being supplied to the air chambers 112.
Just prior to the air intake ports 110 becoming exposed to the combustion chamber 108, the respective valve tappet 62 contacts a lobe 76 (
The second cam 96 on the crankshaft 12 controls the operation of the fuel injectors 80 at the end of the compression stroke. In other words, as the piston 104 nears the top most position of its compression stroke, the fuel pump plunger contacts a lobe 98 (
Such an engine design provides several advantages that help address the challenges associated with conventional CI engines. By operating on a two-stroke cycle, the engine 10 is provided with a simplified construction that helps reduce its overall weight. For example, the engine 10 does not require intake valves and other components traditionally associated with four-stroke engines. Additionally, the two-stroke cycle ensures that the engine 10 fires each cylinder 16 once per revolution of the crankcase 14, instead of once per every other revolution as with four-stroke engines. The result is a power-to-weight ratio that makes it feasible to use the engine 10 to power the propellers 20 of an aircraft.
The propeller synchronizer 190 will now be described in further detail. As shown in
Still referring to
As shown in the figures, the propellers 20 each include a blade portion 230 extending from the crankcase 14 and a base portion 232 extending into the interior of the crankcase 14. A drive gear 234 is operatively connected to each base portion 232 and drivingly coupled to the main synchronizer gear 222. Whenever the drive gears 234 are rotated, the propellers 20 are rotated as well. Thus, when the motor 204 is activated, the pinion gear 212 rotates the drive shafts 216 and main synchronizer gear 222 to simultaneously turn the drive gears 234 and thereby adjust the pitch of the propellers 20. In order to facilitate the rotation or turning of the propellers 20, outer support bearings 236 are provided between the blade portion 230 of each propeller and the outer wall 34 of the crankcase 14. Likewise, inner support bearings 238 are provided between the drive gear 234 associated with each propeller 20 and the inner wall 28 of the crankcase 14.
The propeller synchronizer 190 advantageously allows the aircraft engine to operate at a constant angular velocity, i.e. revolutions per minute (rpm), at different altitudes and regardless of the aircraft airspeed. For example, the propeller synchronizer 190 may be used to automatically adjust the pitch of the propellers in order to accommodate the “thinner” air at higher altitudes. The propeller synchronizer 190 may also function as a safety feature that allows a pilot to “feather” the propellers to reduce drag during in-flight engine failure and to maintain better control of the aircraft to perform an emergency landing. Because the pitch may be adjusted in both a clockwise and counterclockwise direction, the pitch of the propellers may be advantageously reversed to help the aircraft stop on short runways.
While the invention has been illustrated by the description of one or more embodiments thereof, and while the embodiments have been described in considerable detail, they are not intended to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope or spirit of Applicant's general inventive concept.
