"Desmodromic endothermic rotary engine with external combustion chamber at variable volume "

This invention arises from a research aim to solve a motorist problems in the new aeronautic applications, because of the more growing inclination, either in civil field or military, towards the unmanned aircrafts manufacturing with high performances of endurance, high speed and ceiling altitude, better handiness.

For this kind of application it is required to have engines of smaller size compared with the ones already available in the market that endure a self technologic limit of propulsive, motoring nature.

The reciprocating engines, often known as piston engines, to obtain high ration power/weight require a supercharger and the cubic capacity splitting in order to limit the average speed of piston and consequently the allowable rpm.

The gas turbines, applied to turboprop or turbofan, also suffer of a limited speed and altitude field as they have an high thermodynamic efficiency only at high speed and high altitude with steady rotation speed. A technical limit that males the gas turbines performances little flexible, much costly and sophisticated to manufacture and with skilled maintenance requirements that can be done only in pledged structures.

The desmodromic rotary engine subject of this invention, of which a prototype had been designed and produced to be used for test, similarly to the Wankel rotary engines, realizes one power stroke at every shaft round, but differently from Wankel type, it has a construction shape fundamentally different as it can be developed in length independently from the cross section and with the same cubic capacity allows a rpm increase. The introduction of this new technologic system eases the engine manufacturing, substantially reduces the manufacturing cost and the maintenance requirements supporting the production even in a small range. The desmodromic rotary engine has a piston with a round section that rolls, without brushing, inside a cylinder itself round and of larger diameter. That it is possible using an eccentric located on the seats placed on the top of the cylinder (ref. 2 - Fig. 1 / Fig 3 / Fig. 5). This systems allows a proper engine operation and consequently the engine can be produced using traditional machines tool. With such configuration it is possible to obtain thousandth tolerances regard to diameters, even on piston and cylinder high lengths; a solution very difficult to achieve with Wankel engines where the cylinder trochoid profile with cylinder pseudo triangular does not allow a tight tolerance on great engine length develop and consequently the manufacturing, surely more complicated, can be realized only using machines tool high sophisticated.

Here are explained the technologic convenience of the desmodromic rotary engine which has high benefits if particularly utilized in the modern aviation applications.

1) Remarkable increase of engine life due to the absence of brush between piston and cylinder (rolling friction instead of kinetic friction), a solution that considerably reduces the wear of the pieces giving advantage to their life.

2) High allowable limit rotation speed due to lack of kinetic friction. The local superheating in the contact zone is notably lower due to the greater surface of thermic exchange because the heat is distributed onto the total surface of piston and cylinder.

3) Excellent gastight in the contact zone achieved with the application of a compression preloading carried out during the assembling which is realized through a slight interference between the eccentric that support the piston and the piston (ref. 5 - Fig. 1 / Fig. 5). The compression preloading slightly increase the braking couple because it is generated only by the rolling friction and not by the kinetic friction.

4) The resulting pertinent motion between piston and slippers (Ref. 12 - Fig.

1 / Fig. 8) allows to reduce the contact angles with the advantage of a greater eccentricity of the engine, and consequently the piston minimum diameter can be roughly reduced up to 50% of the cylinder diameter thus increasing the air sucked at every round, boosting in such way the cubic capacity with the same cylinder diameter (Ref. 4 - Fig. 1 / Fig. 2 / Fig. 3 / Fig. 4 - Fig. 5 / Fig. 8).

The other essential components inside the engine are the transverse mobile prisms to which ends are hinged the piston contact slippers whose axes converge toward the centre of cylinder for any position of sliding eyelets in respect to circumference. The mobile segments carry out the function of formation of inlet, compression, expansion and exhaust chambers allowing, during the rotation, the right phases sequence (Fig. 6 / Fig. 8).

The convenience to design the position of the two transverse mobile prisms qith any reciprocal angle, compatibly with the thickness encumbrances and the mechanisms, is a factor of fundamental importance because in function to the requested performances of the application shall be possible choice if bring out the engine efficiency or the specific power. In such way the compression and expansion cycles are not coerced between the equal volumes as happens with rotating engine type Wankel and with reciprocating engines (Otto cycle or diesel) but such cycles can be also considerably different (Fig. 7).

From the simulations carried out on the engine coupled with a supercharger operating at high altitude (8.000 - 18.000 meters) it has been verified that with an expansion volume double than the compressed volume it is possible to obtain a thermodynamic efficiency of approximately 50%), a value higher also that one of the more modern aeronautic turbines.

In the testing simulator the mobile prisms (Ref. 4 - Fig. 1 ), in order ti simplify, are made with the support located externally while in the future large production the mobile prims will be realized partially on the seats (Ref. 13 - Fig. 1 / Fig. 2) and partially on the external supports (Ref. 14 - Fig. 1 / Fig. 2 / Fig. 3 /Fig. 4) in such way we reduce the lateral dimension of the engine. The geometry of the guide keyways and the particular configuration of the contact sliders are designed to assure a better gas tightness between the mobile segments, the sliders and the piston in any position of the round angle. The gas tightness is practically obtained on two portions of the slider cylindrical surfaces, one developed on piston circumference and the other one on the semicircle diameter alike to mobile segments thickness. In order to make more precise the mobile segments motion in confront of rotating piston, it has been chosen a desmodronic mechanism external to the cylinder that grants a suitable tolerance between segments, sliders and piston, keeping steady kinetic friction of the sliders on piston independently from the engine rpm.

In the Wankel engines, instead, the gas tightness is obtained through a segment that slides on a rounded track which indeed is the tightness line. In the reciprocating engine the friction between piston and cylinder increases with square οίφπι making un limit to the sliding maximum speed beyond which there is the risk of engine seizing.

With the desmodromic rotary engine we have solved the engine seizing at high speeds, moving the stress of rocking nature outside the cylinder using an eccentric located externally and in parallel to the one inside the cylinder; with a base inside the desmodronic track bounds to the mobile prisms (Ref. 15 - Fig. 2 / Fig. 4). Between the two desmodronic tracks are interject two bearings in order that the stress produce a rolling friction on the external rollers that can be easily oversized. Consequently the is a low energy dissipation even at high rpm (Ref. 6 - Fig. 2 / Fig. 4).

The "desmodromic" term (from the Greek desmos δεσμός: bond, and dromos δρόμος ΐτΆθ ί) has been used to define the precise kinematic with track bond controlled in both the sliding directions. The profile of the desmodromic tracks is made with circular section with thickness equal to the diameter of the rollers located at foot of external eccentric, and with radius equal to the one of the piston. This profile is necessary in order to have an excursion of the distance from slider to slider during the rotation, from a maximum equal to the piston diameter to a minimum in function of the design eccentricity. The right operation of the desmodromic kinematism requires that the tracks concavities being opposite similarly to the mobile prisms which are to them bound. The desmodromic tracks are also themselves bound to the cylinder by two supports with bushings that facilitate the sliding of the tracks themselves (Ref. 16 - Fig. 2 / Fig. 3 / Fig. 4). To allow the four mixed phases: ignition, exhaust-expansion, compression- exhaust, intake-compression (Fig.4) it has been necessary the introduction of four slots made longitudinally to the cylinder e located near the transversal mobile prisms in order to limit the formation of air volumes that will create, by blow-by, the power dispersion and will limit the cubic capacity maximization. The slots are located in couple, a manner to have every prism between them, corresponding to compression valve, to exhaust valve, to intake and exhaust ducts respectively, as shown in the engine layout (Fig. 5, ref. 7 - 8 - 9 - 10).

The intake and exhaust slots do not require valves controlled by a distribution system, however in case the engine is not coupled with a supercharger it will be possible to put inside the intake duct a check valve, lamellar type, suitable to avoid the partial back air volume already sucked before the piston transit in front of slot. In Fig. 3, Fig. 4 and also in layout of Fig.5 it can be noted that there it has been provided on the other slots two rotating valve along the total engine length (Ref. 7 - Ref. 8).

The function of the rotating valves is to provide the compression and the expansion in respect to the combustion chamber located outside the cylinder. The choice of this type of valve has been directed by the fact that they allow a very high rpm, they have not wear and their geometry allows the possibility of developing in length with the advantage of a more easy configuration that simplify the engine construction. Furthermore with the addition of two equal gearings located on the pertaining axis, this type of valve are more synchronizing between them. The gearings are designed to engage between themselves with the same valve axle spacing (Ref. 17 - Fig. 1 / Fig. 3 / Fig.4).

The combustion chamber located outside the cylinder, along with the synchronized valves, allow a combustion at steady volume, very closed to the ideal thermodynamic cycles. In this manner there is a very high temperatures increase at combustion end, both in the Otto cycle or in the diesel cycle, thus obtaining a clear efficiencies improvement. The combustion is enhanced because the fuel ignition or the fuel injection takes place at compression valve closure, after the piston transit on the compression valve related slot, as it happens in a steady volume till the expansion valve reopening and after the piston transit on the expansion valve related slot.

The combustion chamber, located outside, easily allows the possibility to provide systems controlling the volume variation during engine running and it can be designed with a suitable geometry referred to the fuel type, allowing in such way the temperature control (Ref. 1 1 - Fig. 2 / Fig. 4 / Fig. 5). The combustion chamber at volume variable is of essential substance for the engine utilization in aeronautical applications since at very high altitude it allows to keep steady the combustion conditions even at very low pressures and at the temperatures of sucked air. To grant the right movement and the related phase of the two valves, it has been adopted a chain drive located between a toothed wheel secured on the driving shaft and a toothed wheel keyed on the axis of one of the rotating valves (Ref. 18 - Fig. 1 / Fig. 3 /Fig. 4). To improve the piston balance there is the adoption of two masses located outside of their related seats, both keyed on the driving shaft (Ref. 19 - Fig. 1 / Fig. 2 /Fig. 4). The possible balance of the two cross mobile prisms, which depends form the vibration level of the engine, is demanded to a system with two equal masses (Ref. 20 - Fig. 8) located in parallel with the prisms and moved to opposite direction regard the prisms themselves motion by means of two racks (Ref. 21 - Fig. 8), respectively keyed on mass and prism with one or more idle toothed wheels (Ref. 22 - Fig. 8), interjected between themselves and bound to prisms seats (Ref. 14 - Fig. 1 / Fig. 2 / Fig. 3 / Fig. 4). With type of kinematic system on the oscillatory motion of prisms the engine vibrations, generated by inertial forces, are totally and very well eliminated. The oscillations absence is another reason that suggest the use of this engine in aeronautical field, especially on aircrafts with sensitive flight instruments, surely susceptible to vibrations. The engine designed in such way, for the way the phases act and for the specific possibility to modify the compression ratio through the compression chamber volume variation, is especially suitable to be couple with a supercharger, while in the traditional reciprocating engine the adoption of a supercharger requires to reduce the compression ratio in order to avoid the gasoline detonation and for the diesel engine the adoption of supercharger will generate an excessive compression. The supercharger impossibility to reach the continuous rate generates a high lowering of thermodynamic efficiencies at low rpm, in addition the pressure drop for the excessive turbulence that is generated around the valves provoke the outbreak of sonic events inside the intake duct.

The desmodromic rotary engine subject of this invention has not restrictions on coupling with supercharger because, changing the compression ratio according to rpm and the pressure and temperature conditions inside the supercharger, we get a good regularity in thermodynamic efficiencies.

The exhaust duct without interject valves grants low pressure losses and consequently a better supercharger efficiency. The particular way of the phases succession allow the total filling of the cubic capacity because during the exhaust- expansion phase (Fig. 6) the supercharger has a higher time for increasing the pressure till the reaching of maximum limit, about the double compared to a traditional reciprocating engine of same cubic capacity, working at the same rpm. These motorist expedients and the optimal ratio Power/Weight originate a factor of fundamental importance for the applications of the desmodromic rotary engine subject of this invention in aeronautical field.

From calculations made during the design stage e from data obtained during test carried out on engine prototype we have observed ration 4 KW/KG and we can reach 15 KW/KG in models supercharged and with high rpm. These results are not matched even by the most sophisticated reciprocating engines that can reach a ratio of 1,5 2 KW/KG.

In the turbine engine the ratio power/ weight is between 3 and 5 KW KG (including weight of reducers and propeller included). In the turbofan engines the ratio power/weight is between 10 and 16 KW/KG (fan included) and it is in function of bypass ratio, in other words the ratio air fan/air developed inside the reactor. It is necessary to point out that the speed of the flow exiting the turbofan that is suitable for the applications in subsonic field require bypass ration between 2 and 4 (10 - 12 KW/KG). at lower ration we are in transonic applications with bypass 0,5-1 and ration power/weight between 12 and 16 KW/KG. These data confirm that the desmodromic rotary engine subject of this invention is suitable, in optimal way, with good propulsive efficiencies, to be keyed on directly (in other words without a reducer) on prop fan that are similar to fan not intubated but of smaller diameter compared to traditional propellers, allowing to reach cruise speed of 600-800 KM/HOUR, with power between 10 and 1000 KW. It is possible to finish saying that the desmodromic rotary engine subject of this invention, designed to solve the problems ratio power/weight, developed in length with a reduced cross dimension, is for some aeronautical applications surely competitive versus turbojet, a frontier that cannot be overtaken by the tradition reciprocating engines.