BALANCED-PRESSURE, VOLUMETRIC ENDOTHERMIC ENGINE

* § * § * § * Field of the Invention

The present invention concerns a volumetric, endothermic engine, in particular a piston engine. Background Art

As known, conventional internal-combustion engines use solutions which have been tried and tested for decades comprising a cylinder chamber, wherein a piston moves of alternate motion, whereto a series of valves and pipes for the injection and ejection of working fluids are connected. The alternate movement of the piston is transformed into continuous rotary movement through a connecting-rod/crank transmission.

The 4-phase work cycle, more suited to curb pollutants, has a useful thrust phase (gas expansion and combustion phase) and three energy-absorbing phases: the result is a pulsating output of the torque which may conventionally be improved, in its average value and evenness, only by using multiple cylinders operating simultaneously in different phases. Among the various aspects which penalise the efficiency of such an engine there are some connected with the input/output of the gases and with the fuel mixture detonation phase.

As a matter of fact, it is known that mixture detonation occurs in the proximity of the top dead centre of the piston stroke, when the desired mixture compression has been achieved. In correspondence of the detonation, a high pressure peak occurs. This occurs both in a typical Otto cycle and, even more so, in a diesel cycle. Therefore, the pressure follows the general trend illustrated in the phantom line curve of fig. IA (showing only the positive pressure part according to the phase angle of a piston) .

In the top dead centre position the connecting-rod/crank transmission is therefore in an unfavourable condition for transmitting motion, because the lever arm is nil (as can be de- tected at the left end of fig. IB) . Therefore, the achieved pressure peak cannot be used advantageously for producing a useful torque, but ends up simply imparting significant stress to

the transmission members, which forces to oversize such members compared to what would be necessary in the other phases of the work cycle, to the detriment of system costs and inertias.

Secondly, the volumetric efficiency is penalised by the discontinuity of the incoming and outgoing flows due to the inertia of the gaseous masses.

The object of the present invention is to provide an endo- thermic engine provided with pistons moving of alternate motion in respective cylinders, which allows to reduce detonation stresses and to improve the efficiency and continuity of the drive action. Summary of the Invention

The above object is achieved through an engine as described in its essential features in the attached main claim. Other inventive aspects of the engine are described in the dependent claims.

According to a first aspect of the invention, an endother- mic, piston engine is provided, of the type comprising one or more pistons alternately moving in respective cylinders, the one or more pistons being connected to an engine shaft through a transmission having a lever arm varying between a maximum value and a minimum value in correspondence at least of the top dead centre of the piston, in the cylinder occurring the combustion and expansion of a gaseous mixture, characterised in that said cylinder is in communication with a transfer device capable of transferring a peak pressure, in correspondence of said top dead centre, to the same cylinder, or to a cylinder of the same engine, in a subsequent phase wherein said crank lever arm has a higher value than the minimum one. According to a further aspect of the invention, an endo- thermic engine with parallel cylinders arranged in a circle is provided, said cylinders being rotatably mounted revolver-like about a common axis, and equipped with a single combustion area, a single inlet port and a single outlet port of the exhaust gases.

According to a preferred aspect of the invention, in the inlet and outlet area the chambers of subsequent cylinders are

temporarily put in communication with each other or with a same combustion area to preserve the continuity of the incoming and outgoing flows and to improve volumetric efficiency. Brief Description of the Drawings Further features and advantages of the engine according to the invention will in any case be more evident from the following detailed description of some preferred embodiments of the same, given by way of example and illustrated in the accompanying drawings, wherein: fig. IA is a diagram showing the pressure in a prior art cylinder (phantom line) and in a cylinder according to the invention (continuous line) with respect to the phase angle; fig. IB is a diagram showing the crank lever arm of a piston in correspondence of the work points of the diagram of fig. IA; fig. 1C is a diagram showing the product of the diagrams of figs. IA and IB for one piston; figs. 2A-2C are schematic section views, referring to three different operation phases, of a first embodiment of the inven- tion; fig. 3 is a schematic view of a second embodiment of the invention in an 8-cylinder engine; fig. 4 is a longitudinal-section view of an 8-cylinder engine according to a third embodiment of the invention; fig. 5 is a schematic view of a planar development of the arrangement of cylinders/pistons of the engine of fig. 4; fig. 6 is a longitudinal-section view of a circularly- arranged engine according to a fourth embodiment of the invention; fig. 7 is a transversal-section view taken along the line VII-VII of fig. 6; fig. 8 is a section view taken along the line VIII-VIII of fig. 7 with some members showing through; fig. 9 is a top-plan view of the distribution and exhaust system of a fifth embodiment of the invention; fig. 10 is a partial section view taken along the line E-E of fig. 9;

(. fig. 11 is a section view taken along line D-D of fig. 9; figs. 12A and 12B are partial section views of the valve system of fig. 9 developed on a plane; and fig. 13 is a section view taken along line B-B of fig. 11. The diagrams of figs. 1A-1C show very clearly how the pressure peak which develops in correspondence of the detonation at the top dead centre of a piston, according to the prior art (phantom line) cannot produce much work because the crank lever arm (fig. IB) is extremely short in this position. The Applicant has solved this drawback distributing the pressure curve differently - with the area subtended by the curve of fig. IA being substantially equal - in particular lowering the peak and bringing part of the useful pressure into the phase wherein the crank lever arm is longer and hence more favourable.

Fig. IA illustrates this principle, as a comparison between the continuous-line and the phantom-line curves. While the peak is reduced, pressure is distributed more towards the central part of the diagram, which corresponds to the maximum crank lever arm phase. The comparison makes evident the opportunity of achieving greater power (area subtended by the curves of fig. 1C) and a more centred torque distribution.

From a practical point of view, the displacement of the pressure distribution may be obtained in various ways, which are suggested here below illustrating different embodiments of the invention. First embodiment

According to this embodiment (figs. 2A-2C) , an elastic- member power accumulator absorbs the pressure peak when the pis- ton is in correspondence of the top dead centre. The accumulated energy is returned, in more favourable conditions, when the pressure decreases due to piston displacement.

Figs. 2A-2C show an example of a piston-cylinder assembly.

On the cylinder head a spark plug and a variable-volume expan- sion box 200 in communication with the combustion chamber are mounted. In particular expansion box 200 is in the shape of a cylindrical chamber wherein a small piston 201 slides in opposi-

tion to elastic means 202.

When piston P arrives at its top dead centre (TDC) and pressure increases beyond a preset threshold (for example in correspondence of detonation, fig. IB) , small piston 201 over- comes the thrust of elastic means 202 and rises back into expansion box 200. This volume increase of the combustion chamber reduces the pressure peak, which is hence being accumulated as mechanical energy in elastic means 202. As soon as the pressure in the combustion chamber drops again below the preset threshold (since the lowering of piston P increases the volume in which combustion occurs) , elastic means 202 return the energy pushing back small piston 201, thereby returning pressure also.

Since pressure return occurs in a post-TDC phase, it certainly works in a more efficient way, because it can act on a crank lever arm which in the meantime has become longer.

Pressure expansion box 200 acts as a sort of pressure flywheel, suited to accumulate energy when there is a pressure peak and to give it back when it is more efficient because the crank lever arm is more favourable. For the rest, the piston-cylinder system is identical to the prior-art one. Second embodiment

The operation principle is again that of the pressure flywheel . In this case (fig. 3), small piston 201 does not work in opposition to elastic means, but acts on an incompressible fluid which is in communication, through suitable pipes 205, with a pressure distributor 206.

The individual pipes 205 of a series of small pistons 201 of eight cylinders of the same engine are connected to distributor 206. Distributor 206 has a rotating body 207 whereon a connecting groove 208 is obtained. Distributor 206 is shaped so as to sequentially connect the pipes 205 belonging to adjacent cylinders. Thereby it is possible to distribute, through the re- spective small pistons communicating with the incompressible fluid, the pressure peak of one cylinder to an adjacent cylinder, where this pressure may act more advantageously.

The adjacent cylinders, since it is an 8-cylinder engine, are out of phase by 45°, which makes it convenient to transfer pressure. As a matter of fact, while a cylinder is at the TDC, the adjacent one is in expansion, farther by 45°, with a more advantageous crank lever arm for exploiting the pressure transfer.

This embodiment may of course be usefully applied in all engines where the piston/cylinder assemblies are mutually out of phase by an angle below 90°. Third embodiment

According to an advantageous aspect of the invention, a variant of the invention provides that the pressure transfer between one cylinder and the other occurs through a flow of the same combustion gases. In this case, in order to ensure continu- ity of operation, the cylinders are mounted in a circular pattern, as shown in the subsequent drawings.

Figs. 4-5 show an endothermic engine with 8 rotating cylinders. Such a "revolver-like" engine, in case it employs eight cylinders, allows to obtain excellent flow continuity, as will be better shown in the following. A larger number of cylinders, although theoretically acceptable, would be little advantageous from an industrial point of view.

For convenience, in the drawings reference is made to an engine with injector and without spark plug (diesel cycle) , but it is evident that with suitable changes within the reach of any engineer, the same principles are applicable to an engine of a different construction.

Cylinders Ci-C _n and the respective pistons Pi-P _n are mounted in parallel, according to a circular arrangement and rotatable integrally with a central shaft A.

In particular, as visible in fig. 6, cylinders C _x -C _n are fastened to a support cage G _x intended to be engaged with a grooved portion of central shaft A.

Each piston is equipped with a conventional connecting rod 100 acting on a crank 101 rotatably mounted at one end thereof on a support rotor 102 and at the other end thereof in the ec ^¬ centric hole of a bevel gear 103 cooperating with another common

bevel gear 104.

Of course, between the big end of rod 100 and crank gear 101 a sliding bushing is provided in a conventional manner.

The gear or common bevel wheel 104 is intended to transfer the motion to central engine shaft A.

In order to accomplish a 4-stroke operation cycle, the bevel gears 103 of the various connecting rods must perform two full rotations for each turn of rotor 102 integral with cage Gi; since the diameter of bevel gear 103 is limited by the 45° angu- lar space which is intended for each of the eight cylinders arranged on a circumference of 360°, the velocity thereof is by all means greater than desired. It is hence provided that common bevel wheel 104 rotates in the same direction as rotor 102 to compensate this excessive speed. For such purpose, common bevel wheel 104 is connected to the satellite gears of a planetary gear set, consisting of a central wheel 105, of an outer wheel 106 and of satellite gears 107.

The central shaft A is rotatably mounted on end bearings 2 and 3 mounted on a cylinder head M ₁ and on an engine base

M ₂ , respectively, which are generically part of an engine housing M, possibly provided with cooling flaps.

By this construction, shaft A together with cylinders C ₁ -C _n and with respective pistons Pi-P _n , are rotatable about the longi- tudinal engine axis with respect to engine housing M. A relative rotary movement may hence establish between the combustion chambers of the cylinders and cylinder head M ₁ .

Due to this type of constraint it is possible to transform the load on connecting rods 100, imparted by the combustion cy- cle which occurs between pistons P ₁ -P _n and the respective chambers C ₁ -C _n , into a "revolver-like" rotation of the entire assembly of pistons integral with shaft A about the longitudinal axis of the shaft.

In the illustrated embodiment there is provided a fuel in- jector 13 mounted on loading port Lc of cylinder head M ₁ , in correspondence of combustion chamber Br.

Since the cylinders/pistons rotate about the engine axis,

the cylinder head has a single pair of loading and discharge ports, Lc and Ls, respectively, and a single hole for the engagement of any spark plug or of an injector, with which the various pistons cooperate in succession. Advantageously, hence, in the "revolver-like" engine, according to the invention, it is not necessary to provide a pair of loading/discharge ports for each cylinder, but a single one is sufficient for all cylinders.

Fig. 5 shows the series of cylinders on the development of the primitive surface they run on during rotation. Cylinder displacement occurs leftwards in the drawing (as shown by arrow F) with respect to cylinder head M ₁ which is fixed.

The first piston on the right is at top dead centre and has just completed the ejection phase; when rotating, it moves left- wards in the drawing and intercepts loading port Lc, while descending and drawing fresh gases.

The third piston from the right is shown in the position of lower end stop, at the end of the intake phase; rotating, it moves leftwards in the picture and compresses the fresh gases - with the cylinder crown closed by the cylinder head - until it reaches top dead centre.

The fifth piston from the right is illustrated in the top dead centre at the end of the compression phase and is intercepting a fuel-injection compartment. Just beyond this point, detonation of the mixture occurs (possibly triggered by a spark plug if it is an Otto cycle) and the high-pressure expansion of the combustion gases starts. Rotating, the piston moves leftwards and descends, completing the combustion and the expansion of the gases. The seventh piston from the right is shown at the bottom dead centre, at the end of the expansion of the combustion gases, the cylinder crown having been hermetically closed by cylinder head Mi. By rotating further, the piston moves leftwards intercepting discharge port Ls: in this phase the exhaus- tion of the burnt gases hence occurs. When it arrives at the top dead centre, the piston crown is again closed by cylinder head M ₁ , as illustrated in the last position on the left which coin-

cides with the first position on the right.

As can be guessed, during the "revolver-like" movement of the cylinders, a relative sliding between the same and the lower surface of cylinder head M ₁ occurs. It is hence necessary to es- tablish a seal between these mutually slidable surfaces, as well as between piston and cylinder, where conventional elastic rings may also be provided.

The seal between these components is guaranteed by a system which will not be further described in detail here because it does not belong to the main teaching offered.

It is relevant to notice that, thanks to the phase shift existing in an 8-cylinder engine (45° between adjacent cylinders) , it is possible to arrange the ports and the combustion chamber so as to obtain two advantageous effects. Firstly, an excellent gas flow evenness can be achieved.

As a matter of fact, the only fixed loading port Lc and the only fixed discharge port Ls are configured so that they flare out internally with openings Lc ¹ and Ls ¹ which encompass an arc of a circle of about 45°. The openings Lc' and Ls' are prefera- bly flared, widening towards the inside of the engine, as exem- plifyingly outlined in fig. 5.

Thereby the incoming and outgoing gas flows are even and continuous because, in correspondence of one of the ports, when two pistons involved in the action are at the opposite dead cen- tres, and hence do not operate, a third piston is at the peak of action. On average there is hence greater flow continuity and evenness, because a continuous compensation occurs in the action of the pistons for air intake and for the output of the burnt gases and this, together with the opportunity of having large- sized ports, dramatically improves volumetric efficiency.

In substance, a continuous flow of fresh gases and exhaust gases from the respective ports is determined, which does hence not require the presence of valves and which maximises volumetric efficiency (since there is no pulsation of fluids) . Secondly, and consistently with the main teaching provided here, a pressure transfer in correspondence of the injection and ignition position (chamber Br) of the fuel mix can be obtained.

Thanks to this operation condition, it is feasible to continuously inject fuel from injector 13, to the benefit of adjustment simplification, but especially part of the pressure may be transferred from one cylinder to that in a more advanced phase, dampening the pressure peak upon detonation and transferring pressure to a piston wherein it is best employed for generating work.

As a matter of fact, by suitably adjusting the angular extension of injection chamber Br, it is possible to determine an operation condition (visible for the two central cylinders in fig. 5) wherein two adjacent cylinders are in partial communication with each other. This allows to propagate not only the pressure, but also the combustion from one cylinder to the o- ther, even without the need to provide an ignition system, such as a spark plug. Fourth Embodiment

According to the embodiment of figs. 6-8, the 8-cylinder engine is still arranged and mounted similarly to what is shown in fig. 4, but the cylinders are fixed. Compared to the third embodiment, this fourth embodiment has eight cylinders arranged in a circle but fixed, hence each is provided with its own loading/discharge ports and possibly with a respective spark plug.

The connecting-rod/crank system of each piston drives in rotation a shaft Al through a transmission similar to that of fig. 4. Due to similar synchronisation problems of the rotation speeds, shaft Al is connected to a distribution shaft A2 through a planetary gear set. In particular, the end of shaft Al is connected to satellite elements E' of a planetary gear set E. The central gear E' ' ' of gear set E is connected to the end of distribution shaft A, while the outer wheel E' ' of gear set E is engaged with a control member which determines the position thereof. Preferably, the control member of outer wheel E'' has the shape of a worm screw V (better depicted in fig. 8) through which it is possible to act from the outside to vary the transmission ratio of gear set E.

Distribution shaft A2 projects beyond the engine cylinder

head and carries at the end thereof, integral in rotation, a distribution device comprising distribution channels and a radial-cam control D.

The distribution channels obtained on the distribution de- vice are configured so as to put the various cylinders alternately in communication with the common loading and discharge ports Lc and Ls (fig. 7) for fresh and burnt gases, respectively.

Cam device D, as better visible in fig. 12, is configured so as to act radially on a series of radial intercepting mechanisms Dl-Dn.

Intercepting mechanisms Dl-Dn are designed to maintain normally closed an equal number of communication channels between adjacent combustion chambers. In fig. 7 combustion chambers Hl- Hn show through underneath holes 4A engaging with spark plugs 4. The communication channels are in the shape of a single circular channel 7 intercepting all combustion chambers Hl-Hn. Between one combustion chamber and the other, communication channel 7 is kept normally closed by intercepting devices Dl-Dn. Cam device D, integral in its rotation with distribution shaft Al, acts on the individual devices Dl-Dn momentarily opening communication channel 7 and hence allowing pressure and gas transfer between one combustion chamber and the adjacent one.

The configuration of the distribution system is such that communication between two combustion chambers is allowed at a time synchronised with the theoretical pressure peak in a combustion chamber, resulting from the detonation of the fuel mixture, according to the principles set forth above.

Fig. 8 shows the eight crank-mounting assemblies, arranged in a circle, which support with suitable bearings the crankshafts and the respective big ends Bp of the rod.

The operation principle of this embodiment is similar to that of a conventional engine with a circular arrangement, wherein, however, the advantageous opportunity is provided of putting in mutual communication adjacent combustion chambers Hl- Hn. Thereby it is possible to transfer pressure and gas between one cylinder and the other, achieving the advantageous effect

set out also in the previous embodiment. Fifth Embodiment

This embodiment provides again an 8-cylinder engine with a piston and transmission arrangement fully identical to that of the fourth embodiment (as can be inferred from observing the right part of fig. 11) .

Fig. 9 shows the distribution system which, according to this embodiment, provides twenty-four longitudinal-lift valves. In particular, each cylinder traditionally has two valves, one (Vc) on the loading port and one (Vs) on the discharge port; the loading and discharge ports of the individual cylinders are then put in communication with common circular manifolds, one on top of the other, referred to as Mfc and Mfs, respectively. According to the invention, between two adjacent cylinders a third in- tercepting valve (Vi) is provided, intended to open/close a short communication channel 7 ¹ between the two adjacent cylinders .

Figs. 12A and 12B show two sections according to a curved line passing through five example valves. In fig. 12A it can be seen that intercepting valve Vi has risen into its seat and keeps closed communication channel 7' between the two adjacent cylinders. In fig. 12B instead valve Vi is in a descended position and opens channel T .

From fig. 11 a possible solution for the distribution sys- tern can be appreciated which operates the twenty-four engine valves, whereof fig. 10 shows a section out of phase by 15°. In particular, in the section of fig. 10 the controls of a discharge valve and of an opposite intercepting valve Vi can be noticed, while in the section of fig. 11 the control of a loading valve can be detected.

All valves are guided in a traditional way and are controlled by control rods receiving their rising/descending movement by respective cam-shaped discs Kl, K2 e K3, integral in rotation with distribution shaft A2, through the engagement with pairs of rollers 401 and 402, 403 and 404, 405 and 406, respectively.

Discs Kl, K2 and K3, or better circular flanges, have a

suitably-shaped surface for imparting to the pairs of rollers engaged therewith the motion law to be imparted to the respective valves Vs, Vi and Vc.

According to this embodiment, a planetary transmission as- sembly Ep is provided between distribution shaft δ2 and cam- bearing assembly K. In particular, in planetary transmission Ep, the outer wheel is integral with cam-bearing assembly K, the spider is integral with distribution shaft A2 and the centre wheel is integral with an output shaft A3 through which it is easy to adjust the phase difference of the Ep assembly.

Fig. 13 shows cylinder head Ml from the inside, showing the crown of the combustion chambers. For each cylinder, hole 4a for the ignition plug and the two seats of loading valves Vc and discharge valves Vs can be identified. The seats of intercepting valves Vi and, with a discontinuous line, communication channels 7' between the adjacent combustion chambers are further visible. The operation of this engine is fully identical to that of the fourth embodiment .

As can be guessed from the above description, the engine according to the invention achieves a series of significant advantages .

Firstly, the peak pressure transfer from the TDC phase to a phase wherein the crank lever arm of the transmission crank mechanism is more favourable improves energy efficiency and re- duces mechanical resistance requirements. This principle may be used in an equivalent way both transferring the pressure of a cylinder to a pressure accumulator - which gives it back in a later phase - and to another cylinder which is already in a phase with a more favourable crank lever arm. Where the pressure transfer is achieved through direct communication of the combustion gases between adjacent cylinders, arranged according to a circular pattern, the advantageous result of having the combustion propagate in a smooth and continuous manner is also achieved. This condition, together with the previous one, allows to use also alternative fuels, which would not be employed in modern engines where the detonation phase is tied to very critical times and conditions.

Again, in the embodiments with revolver-like rotating pistons, the presence of a single loading and discharge port allows dramatic simplification of fuel injection and ignition systems, but especially produces a continuity of action which further promotes the use of little-refined, alternative fuels.

The provision of a common injection/combustion chamber, capable of connecting, at least at a very short time interval, two adjacent cylinders, further simplifies the ignition of the mixture. Using Diesel fuel, for example, the need to compress air at high rates to reach the ignition temperature disappears; moreover, the partial use of organic fuels is made easier, as provided in compliance with recent directives.

However, it is understood that the invention is not limited to the particular embodiments illustrated above, which represent only non-limiting examples of the scope of the invention, but that a number of variants are possible, all within the reach of a person skilled in the field, without departing from the scope of the invention.

In particular, the provision of eight cylinders in order to be able to favourably transfer combustion gases is unbinding, but represents only an example indication which is also reasonably effective. Certainly, nevertheless, the number of cylinders for obtaining such result must be above four, for a phase difference greater than 45° to exist which makes pressure transfer advantageous .