The present invention also relates to a composite device formed by several devices of this kind, which are arranged in series and/or in parallel.

Background Art Even today, when dealing with the problem of realizing a device for the conversion of a rotary motion into a rectilinear reciprocating motion, and vice versa, and even in the context of advanced technologies, the conventional connecting rod-and-crank mechanism (of Fig. 1) is used, notwithstanding its numerous and well-known disadvantages (unbalance, lateral thrust on the piston, a, s. o.). Actually, a principle of the known art which would brilliantly solve the problems of this conventional mechanism, is that shown in Fig. 2. By comparing the conventional mechanism (Fig.

1) with that of Fig. 2, it may be noted that when the crank 01-03 of the conventional mechanism is split in two identical segments 02-03 and 01-02, and when opposite rotational movements are imparted to these segments, with one rotational movement being two times faster than the other, the point indicated by 03 moves along a rectilinear path. Further, it is known that this constraint in the movement of these two segments is obtainable through the use of a gearing (see Figs. 3,4,5, and 6).

As shown in Fig. 3, an example is given by a toothed wheel (or gearwheel) 6, having

an internal toothing with a pitch circle diameter PRC, which is stationary on a plane, and which engages a gearwheel (16) with external toothing and with a pitch circle diameter PRS = PRC/2. If the point 02 (see Fig. 4) is rotated around the point 01 by an angle b, the gearwheel (16) rotates by an opposite angle, equal to 2b, around the point 02. The point 03, which was the original tangential point between the pitch circles, will have shifted exactly along the axis X.

A further example is provided by the gearing shown in Fig. 5, wherein a gearwheel (6), which is supposed to be stationary on the plane and which has a pitch circle diameter PRC, imposes a rotational movement to the gearwheel (16),-of pitch circle diameter PRS-, through the intermediate gearwheel (13), the latter having a pitch circle diameter PR. A crank 03-02, indicated by the reference number (10), is integral with the gearwheel (16), and has a length D equal to the distance 02-01. If the ratio between the number of teeth of the gearwheel (16), and those of the gearwheel (6), is equal to 1: 2, then, by imposing a rotation to the centers OR and 02 (see Fig. 6), corresponding to a certain angle b around 01, the crank (10) will rotate around 02 by an angle 2b which is twice as large, and which has the opposite sign.

In this case too, the point 03 will move exactly along the line of the axis X.

Under the point of view of its practical applications, the system illustrated in Fig. 3 is more interesting. In fact, as compared to the kinematics shown in Fig. 5, it has the advantage of having : a) a gearing based on the mutual engagement between a gearwheel with internal toothing and a gearwheel with external toothing, so that the number of simultaneously engaging teeth is much higher, and greater loads can thereby be transmitted for the same size of the toothing; b) a lesser number of components making up the mechanism ; c) the possibility of handling also small strokes, by using gearwheels having nonetheless appreciable dimensions (this corresponds to the overwhelming majority of applications).

In what follows, the drawbacks of the classical crank mechanism will be briefly reminded.

Then, a somewhat detailed critical review of devices of the background art-known to the applicant-, will be given; these devices are based on the general principle of Figs. 3 and 4.

The principle of Figs. 5 and 6 is not directly relevant for the present invention. It generally leads to mechanisms which are more complex and which involve a greater number of gearwheels and components, and which for this reason cannot be advantageously applied.

The conventional crank thrust mechanism, which is usually employed in reciprocating machines, has a number of drawbacks and is subject to many restrictions (limitations). First of all, the lateral thrust exerted on the piston because of the inclination of the connecting rod, entails major organic losses (leaks), and an increased wear of the cylinder-piston interface. Therefore, there arises the need to ensure a good lubrication in order to avoid seizure. Particularly in two-stroke engines, it is required to mix to the fuel a conspicuous amount of oil (about 2%), which, when it is burned, increases the polluting emissions. The ordinary crank mechanism is also cumbersome in the direction of the cylinder axis. In fact, in order to limit the lateral thrust on the piston, the connecting rod length (1, Fig. 1) is never less than 3,5 times the radius (2D) of the crank. In the crank mechanism of Fig. 2, on the other hand, the length of the corresponding segment (which is an integral part of the"plunger 11"), may be reduced to values equal to the stroke (4D), plus a minimal length, in order to prevent the piston from hitting against the crank mechanism itself, in the BDC (bottom dead center). This disadvantage is particularly relevant for Diesel two-cycle large-stroke motors, typical of naval applications.

A further limitation of the classical crank mechanism is that the law of motion of the piston is not perfectly sinusoidal, but includes higher-order harmonics, thereby giving rise to balancing difficulties. Said harmonics, including the first one, cannot

be simply balanced by the use of counterweights, but require use of counter-rotating shafts. The crank mechanism shown in Fig 2, presents only the first harmonic, which however may be balanced simply by counterweighing the movable parts.

Referring now to the non-classical crank mechanisms, which are based on the principle of Fig. 3, several techniques have been developed in order to put into practice this kinematics. However, in practice they have not been successful, because they propose technical solutions with profound inconsistencies, which are prejudicial for correct operation.

In the following, a brief review of these techniques is presented.

US Patent N. 2. 271, 766 of February. 3, 1942, of H. A. Huebotter (see Figs. 7 and 8 of the present application) For clarity, it is practical to define as"planetary gear"the component of axis 02 and comprising the (auxiliary crank) pin of axis 03, to which the piston or"plunger"11 (see Fig. 2) is directly connected, and to define further as"rotor"the component of axis 01, which contains one or more supports for the rotation of one or more planetary gears.

The mechanism proposed by H. A. Huebotter in 1942, see Fig. 7, whilst presenting a correct construction under the point of view of its kinematics, has a serious constructional drawback, which prevents its correct operation when a user U is connected thereto.

In fact, when analyzing this mechanism it can be noted that the bearings B1 and B2 are the supports of the planetary gear (S); the loads (forces) transmitted by the piston, are transferred to these supports through the planetary gear. These loads, due to the symmetry of the system-when no user is connected-, are equal on B1 and on B2, and therefore also the useful torque generated by them is the same. The system is in perfect equilibrium.

When a user U is connected to the system, thus applying a braking torque to the left- side rotor (9), the useful torque on the right side will instantly prevail over the

resulting torque on the left side. In this condition, the system-in order to reach a new equilibrium condition-reacts by transferring a couple, equal to the difference between the torque on the right and on the left side, to the only component connecting both rotors (9) to each other, that is, to the planetary gear S. This couple will substantially give rise to a transfer of forces tangential to the circular trajectories of the supports B 1 and B2, from the right to the left, and will act as a tilting moment on the constraints through which the planetary gear S is connected to the rotors (that is, on the bearings or bushings B 1 and B2).

This kind of load is proportional to the braking moment applied to the left side rotor by the user U, and it constitutes an anomalous load on the bushings or bearings ; therefore, under these conditions the system would almost immediately"collapse".

This reasoning may be applied both to a motor (e. g. an internal combustion engine), and to a machine which is driven by a motor, e. g. a reciprocating compressor; in fact, for a driven machine the user U simply becomes a motor, and the load analysis will remain valid if the signs of the forces are suitably changed.

Therefore, the planetary gear S is always subject to a tilting torque, although with an opposite sign. The same critical reasoning applies to the other system proposed by H. A. Huebotter, in the same patent, that is, to the embodiment with 4 pistons, which is obtained by connecting in series two of the above described mechanisms (see Fig.

8). In the latter embodiment, that part of the mechanism which is connected to the cylinders 3 and 4, is in the same condition as the system of Fig. 7, and therefore has the same drawback, while the planetary gear associated to the cylinders 1 and 2, is subject-in addition to the tilting moment which naturally arises in a twin cylinder engine-, to the transmission to the power take-off of the torque generated by the cylinders 3 and 4.

Patent DE 875110, filed on April, 30, 1953 by Harald Schultzc. Bochum (not schematically illustrated in the Figs. of the present application)

In 1953 the patent application DE 875,110 suggests to use a mechanism for a radial 4-cylinder motor, whose connecting rods are all connected to the same planetary gear assembly, and the latter is provided in this case with two crank pins shifted by 180° with respect to the axis of the planetary gear. Disregarding the fact that the planetary gear is subjected to the forces transmitted by four pistons instead of two, this solution is substantially identical to that proposed by H. A. Huebotter, and consequently the same reasoning applies.

US Patent 3, 626, 786 issued on December, 14, 1971, to Haruo Kinoshita et al. (see Fig. 9 of the present application for a schematical illustration of the operation) This US Patent N. 3,626,786 of 1970 proposes to use a crank mechanism of the kind shown in Fig. 9. This solution uses a pin (2) which is press-fitted inside and between two rotors (9a) and (9b), and a planetary gear assembly (consisting of the integrally formed pin 1 and gearwheel 16), which rotates thereon. According to this architecture, the crank pin (1) must have a sufficiently large diameter in order to entirely contain the pin 2 and its bearing 8, shifted by a distance equal to 1/4 of the stroke with respect to the center of the pin 1.

The power is taken from the shaft of one of the two rotors (9a in Fig. 9), as for the cases analyzed above.

The pin 2 must support the planetary gear, it must coordinate the movements of both rotors, and it must transmit the loads from one rotor to the other, while maintaining at the same time the parallelism with regard to the motor principal axis 01 (a necessary condition for the correct operation of the crank pin bearing, and planetary gear bearing).

This condition is satisfied only if the torsional angle, which manifests itself during operation between the two rotors, is extremely small. This angle is essentially due to the flexional and torsional deformation of the pin 2; therefore, it is required to choose an appropriate size for the latter pin, even if this influences the sizing of the crank pin (1) and of the rotors (9a and 9b), when said pin reaches certain diameter values;

thereby, due to weight and size increases, this system is no more advantageous (competitive) with respect to a mechanism based on the ordinary crank mechanism.

Note that (see Fig. 9), in order to allow the passage of the planetary gear pin 2, with diameter d, it is necessary to use for the crank pin 1, a diameter value P equal to: P = 2C/4 +dB + 2s = C/2 + dB + 2s, where C is the piston stroke, dB the diameter of the bearing of the pin of planetary gear assembly, and s is the thickness of the crank pin 1 which delimits (covers) the bushing. Obviously, if d becomes very large, the diameter P becomes excessively large.

US Patent N. 3, 791, 227 of February. 12, 1974 to Myron E. Cherry (not illustrated in the drawings of the present application) Although this patent is concerned with the solution of balancing problems, it suggests a mechanism similar to that proposed by H. A. Huebotter in 1942 (Fig. 7) and for this reason the same critical arguments apply.

DE 44 31 726 Al. of September, 6. 1994 (Hans Gerhards) (for a schematical view see Fig. 10 of the present application) The mechanism suggested by H. Gerhards (Fig. 10), notwithstanding the fact that it is provided with a synchronization shaft, does not solve the problem of the tilting moment acting on the planetary gear, because it does not ensure a perfect alignment of the two supports B1 and B2 during operation. The reason for this misalignment is that a couple of meshing gears must have a play (clearance) in order to function properly.

The ideal motion transmission law of two meshing gearwheels, in the absence of a play, is: #1 = #'#2 where #1 and #2 are the reference angles defining the angular position of the couple of gearwheels, and £ is the transmission ratio. The presence of a play (clearance) introduces a deviation of the actual angular positions of the gearwheels with respect

to the ideal ones given by the preceding formula; this deviation being proportional to the play between the gearwheels.

When asking why the existence of a play between the gearwheels is the cause of improper functioning of the device of DE 44 31 726 Al, two main reasons may be found: - the fact that the intermediate rotor (9b, Fig. 10) between two consecutive cylinders is integrally formed and not formed by two independent sub-units, each having a peripheral gearwheel used to transmit the motion to the transmission shaft; - the fact that power is taken from the last rotor (9c) and not from the synchronization shaft.

The first point may be clarified (Fig. 10) by analyzing the proposed schematic assembly, and considering that during motor operation the piston PI must be in the passive phase (absorption of mechanical energy from the transmission shaft) when the cylinder P2 is in the active phase (mechanical energy transfer to the synchronization shaft). In the following, Mpl denotes the motor torque (or moment) produced by the cylinder P1, and Mp2the motor torque (moment) produced by the cylinder P2; then, according to the preceding assumption we may take Mpl < 0, Mp2 > 0, and Mpl + Mp2 > 0 because the overall motor moment must be positive.

In this situation, the moment transmitted by the gearwheel (15a) to the gearwheel (14a) will be : Mpl/2 < 0 therefore, the gearwheel (14a) will drag ("push") the gearwheel (15a), and if the rotation directions are those indicated in the cross-section A-A', the couple of gearwheels will recover (eliminate) all the play (clearance) to the right of the engaging tooth (X) of the gearwheel (14a).

Analogously, the moment or torque transmitted by the gearwheel (15b) to the gearwheel 14b will be: (MPi +Mp2)/2>0

therefore, the gearwheel (14b) will be dragged ("pushed") by the gearwheel (15b): the couple of gearwheels will thus recover all the play (clearance) to the left of the engaging tooth (Y) of the gearwheel (14b) (cross-section B-B').

Since the teeth (X) and (Y) are aligned to each other and rigidly connected to the synchronization shaft, this difference in play recovery between the gearwheels (14a)/(15a) on one hand, and (14b)/ (15b) on the other hand, will result in a different angular position of the rotor (9a), integral with the gearwheel (15a) (angle 6 + y, cross-section A-A') with respect to the rotor (9b), integral with the gearwheel (15b) (angle 0, cross-section B-B'). This angular difference will induce a misalignment of the planetary gear supports Bl and B2, which, in spite of its smallness, of the order of some tenths of a millimeter, will prevent the proper operation of the bearings, which at most can endure misalignments of some thousandths of a millimeter, as is well known.

An analogous problem manifests itself due to the presence of the power take-off on one end-side-rotor. In fact, considering the rotor (9c) from which the power is drawn, the moment transmitted to and by the transmission shaft (assembly (15c)/ (14c) in Fig. 10) is: M15c/14c = Mt - MP2/2 where Mjsc/i4c is the couple mutually transmitted by the gearwheels (15c)/ (14c), and Mt is the total motor moment of all cylinders. For the fellow rotor (assembly (15b)/ (14b) in Fig. 10) this moment is equal to : M15b/14b= (MPI +MP2)/2 where Mjsb/i4b is the couple transmitted mutually by the gearwheels (15b)/ (14b).

Due to the intrinsic properties of operation of reciprocating engines or machines, these moments are necessarily different, and when the signs are different, a different and opposite recovery of the play between the gearwheels (14b)/ (15b) and the gearwheels (15c)/(14c) occurs; thus the same drawback of the preceding case will be encountered.

Disclosure of Invention The present invention solves the problems of the background art, in the case of stationary gearwheels with internal toothing (Figs. 3 and 4), by means of the features defined in the independent claims.

By providing a lateral driving shaft (output shaft) comprising two gearwheels, each meshing with a corresponding gearwheel associated to a rotor of an elementary (that is basic) device, and by avoiding to draw the power only from one of the two rotors as in the background art, it is possible to obtain a system which is perfectly balanced and symmetric with regard to applied loads.

It is also essential that the pitch circle diameters of both gearwheels of the lateral driving shaft be identical to each other.

While the first independent claim seeks protection for a basic device including two rotors'and a single planetary gear, the other independent claim is concerned with an assembly of elementary-or basic-devices arranged in series, and/or in parallel, which are all synchronized by a single driving shaft, and which are provided with one or more crank pins for each planetary gear.

The dependent claims relate to particular variants and configurations of the elementary device, and of the assembly formed by such elementary devices respectively.

In the case of an assembly of basic or elementary devices, it is required that two rotors facing each other and associated with distinct elementary devices, and further located on the same side of the driving shaft, are not rigidly connected to each other, but are disengaged or free with respect to each other, with regard to a rotation around their common geometric axis 01. This requirement may be met simply by arranging side by side, separate elementary devices, in a straightforward and intuitive manner, or by providing a means (e. g. a pin) for the axial alignment between said two rotors which face each other. In the latter case it will be possible to omit the contiguous

rotor supports (e. g. bushings), provided at the ends of two rotors which are located near to each other and which are associated with different elementary devices.

The fact that there is no constraint between the rotations of two contiguous rotors associated with distinct elementary devices arranged in a line, is of fundamental importance for solving the problem of the background art (Patent DE 44 31 726) with regard to the misalignment between the supports B 1 and B2 of the planetary gear, which is the cause of anomalous stress on the bushings.

Brief description of drawings The objects and advantages of the present invention will more clearly result from a more detailed description of some of its embodiments and variants, which are intended only for illustrative and non-binding purposes, and as shown in the annexed drawings, wherein: Fig. 1 is a schematic drawing of the classical crank mechanism; Fig. 2 is a schematic drawing of the general principle of operation of the device according to the present invention, corresponding to the known principle of Cardano ; Fig. 3 is a view of an assembly formed by a gearwheel with internal toothing, a planetary gear which is integral with a crank, and the crank itself, in the position corresponding to the top dead center (TDC) of the movable member (not shown) performing a reciprocating rectilinear motion; Fig. 4 is a view illustrating the assembly of Fig. 3, but in a different position than that of Fig. 3;

Fig. 5 is a view of an assembly formed by a gearwheel with external toothing, an intermediate gearwheel, a planetary gear integral with a crank, and the crank itself, in a position corresponding to the TDC of the piston; Fig. 6 is a view of the assembly shown in Fig. 5, but in a position different from the TDC; Fig. 7 is a very schematic representation of a first device of the background art, including only one planetary gear ; Fig. 8 is a very schematic representation of a second device of the background art, including two planetary gears; Fig. 9 is a very schematic representation of a third known device, which uses a technique different from the technique used by the devices of Figs. 7 and 8 ; Fig. 10 is a very schematic drawing of a mechanism of the background art, using a synchronization shaft for various series-connected devices, wherein this synchronization shaft is not a driving shaft; Fig. 11 is a front (or end) view, of a first embodiment of the device according to the present invention; Fig. 12 is a cross sectional view along a plane A-A of the device shown in Fig. 11 ; Fig. 13 is a sectional view along a plane B-B of Fig. 11 ;

Fig. 14 is the equivalent of the cross section A-A shown in Fig. 12, in the case of a first variant of the first embodiment; Fig. 15 is the equivalent of the cross section A-A shown in Fig. 12, in the case of a second variant of the first embodiment ; Fig. 16 is the equivalent of the cross section A-A shown in Fig. 12, in the case of a third variant of the first embodiment; Fig. 17 is a front (or end) view, of a second embodiment of the device of the present invention, wherein the planetary gear has two crank pins; Fig. 18 is a cross section along the line A-A of the device shown in Fig. 17; Fig. 19 is a cross section along the line B-B (Fig. 18) of the device of the second embodiment shown in Figs. 17 and 18; Fig. 20 is a side view of a planetary gear with two crank pins; Fig. 21 is a cross section along the line A-A of Fig. 20; Fig. 22 is the equivalent of the cross section A-A of Fig. 12, for a fourth,- geometrically asymmetric variant-, of the device according to the first embodiment; Fig. 23 is the equivalent of the cross section A-A of Fig. 12, for a fifth variant of the first embodiment, wherein said variant is also geometrically asymmetric;

Fig. 24 is a front (or end) view of an assembly according to the present invention, which is obtained by arranging in parallel two devices like that shown in Fig. 16 ; Fig. 25 is the cross sectional view along the plane B-B in Fig. 24; Fig. 26 is a front view of a second assembly. according to the present invention, which is obtained by connecting along a line (i. e. in series) two devices like that of Fig. 16; Fig. 27 is the cross sectional view along A-A in Fig. 26; Fig. 28 is the cross sectional view along B-B in Fig. 26 ; Fig. 29 is a cross sectional view of a third assembly according to the invention, which is obtained by arranging in parallel two assemblies like that shown in Fig. 28.

Best Modes of Carrying out the Invention Some preferred embodiments and variants of the invention will be described below.

The reference numerals which refer to the device (100) of the first embodiment, and corresponding ones relating to analogous components of the device (200) of the second embodiment, differ by 100 units form each other. For instance, in the first embodiment the rotor is indicated by 109, whilst in the second embodiment it is indicated by 209.

The principal features of the present invention, allowing to solve the problems of the background art and which are present in all embodiments, will be described first in a general way.

Then, all different embodiments and their variants will be described in turn, in a detailed manner. The present invention solves the above mentioned problems, by means of a basic or elementary device (100 ; 200) for converting a rotational motion

into a rectilinear reciprocating motion and vice versa, exclusively based on the principle of Fig. 3. This device is characterized by the fact that it provides for a symmetric load distribution, and for this reason it can be defined as a"symmetric device", although it is not indispensable that the device be symmetric in the geometrical sense (see for instance Figs. 22 and 23 in which the planetary gear 117'is geometrically asymmetric with respect to the crank pin 101). Therefore, in the present context the expression'symmetric device'means an elementary device, from which it is possible to construct an assembly of devices arranged in series and/or in parallel, as shown in Fig. 24 to 29.

An elementary-or basic-device comprises: only one planetary gear (117; 117' ; 217) ; two rotors (109,109 ; 209,209) located at sides of the crank pin (s) (101 ; 201a ; 201b) ; a driving shaft (107; 207); two stationary gearwheels with internal toothing (106,106; 206,206) located at the sides of the crank pin (s).

Said two rotors, and said two gearwheels, must not necessarily be disposed symmetrically at both sides of the crank pins, in accordance with the above principle that only a load symmetry is required, as will be specified below. Therefore, all figures must be intended only as exemplifying the invention.

The planetary gear 117 or 217, which may be monolithic, or may consist of a rigid group of several integral parts, always includes the following essential components: - one or more crank pins (101 ; 201a, 201b), with axis 03, which are all arranged in the intermediate part of the planetary gear, and are connectable to the respective piston (not shown) (note that the case of more than one crank pin corresponds to the second embodiment) ; - two gearwheels with external toothing, 116,116, or 216,216, all having a geometric axis 02 (see also Fig. 3), and being respectively arranged on the right and on the left of said intermediate part ; each of said gearwheels having a pitch circle

diameter equal to half (2D) the stroke (4D) of a piston or generally of a movable reciprocating member (not shown) ; - one or more supports, for allowing the support and the rotation of the planetary gear 117 or 217 around its own axis 02 (see also Fig. 3). Said supports, which are indicated in the figures by the numbers 102, may be realized in the form of seats for a rolling-contact bearing, or seats for rolling tracks for rolling bodies, or seats for parts of friction bearings (bushings), depending on the design. A further necessary condition for the operation of the devices 100 or 200, i. e. of the first or second embodiment, is that the axes 02 and 03 must be mutually parallel and spaced apart by a distance equal to 1/4of the stroke. Since the stroke is equal to 4D, the distance 02-03 must be equal to D (see e. g. Fig. 12).

The rotors, 109,109, or 209,209, forming a monolithic body, or alternatively, a rigid group of several parts (according to the embodiments), are arranged individually on the left and on the right of the planetary gear 117 or 217 respectively.

Each rotor 109 (first embodiment of the device), or 209 (second embodiment of the device), must necessarily include the following essential elements: - one or more supports of axis 02 (see also Fig. 3), which are complementary to those of the planetary gear, for the support and the rotation of the latter. In the case of Fig. 16, these planetary gear 117 supports are replaced by a cylindrical seat, used for introducing (press-fitting) therein a pin 102', which is fixed between the two rotors 109,109 and which is designed to accomplish the same function ; - one or more supports 103, 118, 203,218 of axis 01 (see also Fig. 3), which serve for allowing the support and rotation of each rotor 109,209 with respect to the device base 112,212; - a gearwheel 115 or 215, of axis O1, having an external toothing, and which meshes with a respective gearwheel 114,214 of the synchronization shaft 107 or 207.

The axes O1 and 02 must be parallel, and must be spaced apart by l/4 of the stroke of the movable member, which performs a rectilinear reciprocating motion and which is

connected to the crank pin. Moreover, the axis 01 of the right rotor must coincide with the axis O1 of the left rotor, and the same holds for the axis 02 of the planetary gear.

The driving shaft, 107 or 207, which is either monolithically formed-or alternatively - realized by a rigid group of several integral parts, consists of the following essential components: - two gearwheels, having the same pitch circle diameter, which are indicated by 114, 114 and 214,214 respectively, and wherein each of them meshes with a gearwheel of a respective rotor; - a cylindrical stem, or shaft proper 102 or 207, having an axis parallel to 01, and on which there are keyed said gearwheels (114,114; 214,214); this shaft rigidly connects the gearwheels to each other.

According to the present invention, the driving shaft 107 or 207 serves for the purpose of synchronizing the movements of the two rotors, and it constitutes the only means from which-or to which-, it is possible to draw-or transmit-power.

The stationary gearwheels with internal toothing, having the axis 01, which are indicated by 106 or 206 (see also the component 6 in Fig. 3), are integral with the device base 112 or 212, and mesh with the corresponding gearwheel of the planetary gear 117,217 ; a necessary condition for enabling device operation is that their pitch circle diameter be equal to the stroke 4D.

In the following, the various figures from Fig. 11 onwards will be individually described.

In Figs. 11 to 13, there is shown the first embodiment of the invention. This embodiment comprises the planetary gear 117, formed by the crank pin 101, two gearwheels 116,116 and two supports 102,102. Moreover, this embodiment includes the two rotors 109,109, each of which includes the"complement"of the planetary gear support 102,102, said complement being formed for instance by the other half of a ball bearing or simply by a bushing in contact with the rolling surface 102 of the

planetary gear. Each rotor 109, 109 comprises also the supports 103 and 118, for their support inside the device base 112, and the gearwheel 115 which meshes with the respective gearwheel 114, which is keyed on the driving (or power) shaft 107 proper.

The driving shaft, 107, intended as an assembly of parts, includes instead the shaft or stem proper, 107, and the couple of gearwheels 114, each of which meshes with the respective gearwheel 115 of the corresponding rotor 109 (see Fig. 13).

The device also includes the two stationary gearwheels with internal toothing, 106, which are integrally formed on the device base 112, or else mounted thereon, and which engage with the corresponding gearwheels with external toothing, 116,116 of the planetary gear 117.

The"user"U (Fig. 13), which draws the power from the shaft 107 (acting also as a synchronization shaft of the rotors), is obviously replaced by a motor in the case of a compressor or other machine of this category, that is a machine transforming a rotational motion into a reciprocating motion.

It should be noted, that the axes of the crank pin 101 (O3), the planetary gear 117 (02), and the rotors 109 (01), are parallel and spaced a distance D from one another, and moreover, that the distance 2D is the pitch circle radius of the gearwheels 106, 106, and the pitch circle diameter of the gearwheels 116,116.

In this device, the planetary gear 117 rotates around the axis 02, due to the engagement of the gearwheels 116,116 with their fellow gearwheels 106,106; at the same time, the axis 02 rotates around the axis 01. According to the well-known principle shown in Fig. 3, it is clear, that when a rotation is imparted to the two rotors 109,109 around the axis 01, the planetary gear 117 will rotate by twice that angle and in the opposite sense around its own axis 02, and therefore, that the crank pin 101 will move along a rectilinear path.

The two gearwheels 114, which are integral with the driving shaft 107, ensure- during the motion-the synchronism between the rotors themselves, by meshing with the respective fellow wheels 115,115 integral with the rotors 109,109.

It is fundamental that the driving shaft 107 must be the only element of the device of the present invention, from which or to which it is possible to draw/transmit power ; actually, only in this way it is possible to ensure a perfect symmetry of loads distribution between the right rotor and the left rotor, thereby eliminating all the drawbacks of the known systems, at least for applications involving only one planetary gear. The system is perfectly equilibrated and no stress is transferred from one rotor the other rotor, through the planetary gear 117.

Figs. 14 to 16 show some variants of the device shown in Figs. 11,12,13. Even in these cases, there is a prefect symmetry in the loads applied to the system.

For simplicity, only a cross-section corresponding to cross-section of Fig. 12, is illustrated for each variant.

Fig. 14 shows a configuration according to which the couples of gearwheels 106 and 116 are located"internally"with respect to the supports 102,102 of the planetary gear 117.

Fig. 15 shows a configuration according to which the supports 102 of the planetary gear, are formed by parts (bushings) inserted therein; it can be noted that the rotors 109,109 are provided with cylindrical portions introduced in complementary cavities of the planetary gear, in which said bushings, integral with the planetary gear 117, have been introduced.

Fig. 16 shows a third variant of the first embodiment of the device, in which the planetary gear 117 is connected by means of bushings or bearings 108, to a pin 102' ; the latter is press-fitted inside the two rotors 109. This pin 102', due to a perfect distribution of loads during the operation of the device of the present invention, may have acceptable diameters, unlike the above mentioned mechanism of Kinoshita et al., which, moreover, differs from the present one, in that it has only one gearwheel

16 of the planetary gear, and only one stationary gearwheel with internal toothing 6, and is not at all equilibrated in respect of the forces involved, as already mentioned in the critical review of the background art.

The second embodiment of the device, shown in Figs. 17 to 19, includes a planetary gear 217 provided with two crank pins 201a, 201b; it should be noted that only for illustrative purposes we have chosen the variant shown in Fig. 16 of the first embodiment. The crank pins 201a, 201b are phase-shifted of 180° to each other and with respect to the axis 02 of the planetary gear, and they have their axes (respectively 03a and 03b) parallel and spaced apart by a distance D from 02. It should be noted, that only in the particular position of the device 200 which is shown in the drawing, will the axis 03b coincide with the axis of the rotors 209,209.

In a device of this kind (Fig. 19), the crank pin 201a will reciprocate along a vertical rectilinear axis"Y", whereas the crank pin 201b will reciprocate along a rectilinear axis"X", perpendicular to the former.

As may be noted from the cross-section B-B of Fig. 19, the driving shaft 207 is arranged at 45° with respect to both the axes"X"and"Y", in order to not hinder the motions of the pistons (not shown) connected to the crank pins 201a, 201b.

At this point, it is necessary to observe the following: - the phase shift (of 180°), of the crank pins, with respect to the axis 02 of the planetary gear 217, is not restricted to this value, and it may assume also different values; - on the same planetary gear it will be possible to provide even more than two crank pins, which are phase-shifted by arbitrary angles.

Obviously, it will be possible to use a planetary gear with more than one crank pin, even in the case of the other two variants of the first embodiment (Figs. 11 to 15), as in the case of any other embodiment based on the same inventive concept.

This will give rise to innumerable variants for the second embodiment (which includes more than one crank pin), based on the same inventive concept.

Note that for crank pins whose size is relatively small in comparison with the distance D,-as very often occurs-, the planetary gear may assume the configuration shown in Figs. 20 and 21, in which a planetary gear 217'is shown, only for illustrative and non-binding purposes, having two 180° phase-shifted crank pins, wherein said planetary gear is directly derived from the configuration of the planetary gear of Fig. 12 having only one crank pin. An element 204, in the form of a connecting bracket, has been interposed between these two crank pins 201a'and 201b', in order to ensure the continuity and rigidity of the planetary gear 217'.

In the above described figures the rotors were always identical in size and shape.

However, they could also differ from each other with respect to their shape and dimensions.

Even for the planetary gear it will be possible to adopt a geometrically asymmetric configuration, provided that the symmetry of the loads applied to the rotors is ensured at the same time, according to the principle of the present invention which is clearly stated in the claims.

Figs. 22 and 23 are cross-sectional examples of such innumerable configurations of devices with only one crank pin, which could be called'asymmetric devices'in view of the architecture of their various components (the same concept is obviously applicable to devices with more than one crank pin).

Each of them is in accord with the general principles of the invention: - the planetary gear 117'is supported by two rotors (109a, 109b ; or 109a'and 109b'); - the planetary gear (117') has two gearwheels (116), each having the same pitch circle diameter, and which are disposed at the sides of the intermediate zone where said at least one crank pin (101) is provided; - the device meshes with a driving shaft (107 ; 207) ; - the gearwheels (114,114; 214,214) of the driving shaft have the same pitch circle diameter;

- the power take-off for the"user"U, or alternatively the connection to a motor, is always on the driving shaft (107,207) side, and is never connected to one rotor.

Each of these'elementary'or'basic'devices 100,200, may be combined with other- not necessarily identical-devices (see for instance the various variants described above), in such a way as to give rise to an assembly of devices which are mounted in parallel.

For example, Figs. 24 and 25 illustrate an assembly obtained by the integration of two elementary devices of the type shown in Fig. 16, which have been arranged with their axes 01 parallel to each other, but not coincident. As may be observed, there is only one driving shaft 107. It meshes, through the gearwheels 114, with four gearwheels 115 which are arranged two by two on opposite sides of the driving shaft 107. Each couple of gearwheels 115,115 is associated with an elementary device 100.

In Figs. 26,27 and 28, it is suggested to use an assembly formed by two elementary devices 100, which is obtained by aligning, along their axis 01, two elementary-and in this example identical-devices, of the kind shown in Fig. 16. From the cross section B-B (Fig. 28) it can be seen that the driving shaft 107, with its three gearwheels 114,114', 114, meshes with the four gearwheels 115 of the four rotors 109, thereby coordinating the latter, and transmitting or drawing power to/from each of them. Therefore, also in the case of an assembly or"composite device", like that shown in Figs. 26,27,28, the general requirement of the invention is fulfilled, that is, the loads are equilibrated between two respective rotors making up the same elementary device. Note also, that according to a further aspect of the present invention, notwithstanding the fact that in the intermediate part of the"composite device", the adjacent rotors 109 of each elementary device corresponding to a device of Fig. 16, have been deprived of their respective end supports 103 of Fig. 16, said rotors have not been made integral with respect to each other. A pin 104, introduced between said rotors, has the task of maintaining the axial alignment between the two

pieces 109,109, allowing nonetheless relative rotations around the axis 01. This measure is necessary for the correct operation of the composite device, since if the adjacent rotors of two contiguous elementary devices were made integral to each other, relative microrotations would occur continuously between the rotors of the same (i. e. of each) elementary device, and this would cause a failure of the planetary gear supports.

Naturally, by applying the same criteria as set forth above with regard to the assembly of Figs. 27,28, it will be possible to align even more than two elementary devices-each with a single planetary gear-, so as to obtain reciprocating machines with three or more cylinder rows. The latter may, in turn, be connected in parallel according to the scheme of Fig. 25 ; an example of this is shown in Fig. 29. The single elementary devices of a complex machine, like that shown in Fig. 29, could also differ from each other.

However, it should be noted that such a complex machine, or an in-line engine, must not necessarily have the configuration shown in Fig. 28 ; in fact, several elementary devices (like that shown in Fig. 16), could simply be put side by side and synchronized by means of a single driving shaft 107.

In other words, it is essential that the two rotors 109 (or 209), facing each other and making part of two distinct and axially aligned elementary devices 100 (or 200), are neither rigidly connected to each other, nor form a monolithic piece.

In any case, the driving shaft 107 (or 207) must always be the only member from which to draw or transmit the power, and having the task of synchronizing the various rotors.