EP0184484B1 - Rotary piston machine with a ring coupled to a crank - Google Patents

Abstract

A rotary piston machine with a chamber having a crank coaxial to a shaft, a rotary piston and a crown wheel for driving the piston. The crown wheel is coupled to the crank by a trunnion mounted in a bore of the crank. A fork joint is integral with the crown wheel. The bore axis is offset in the direction of rotation of the shaft with respect to the point of contact of the piston on the wall of the chamber. A spring bears on a shoe integral with the crown wheel and on the crank so that the line of force of the spring passes through the axis of the shaft and is prependicular to the straight line connecting the center of the piston and the center of the trunnion.

Description

The present invention relates to rotary piston machines, in particular to rotary piston compressors, comprising a cylindrical chamber, in which are arranged an eccentric or crank part of a shaft coaxial with said chamber, an annular rotary piston being able to roll in contact. of the wall of the chamber and a crown for driving the piston mounted with clearance inside thereof, the timing of the piston on its raceway being ensured by elastic means.

We know such machines and the problems posed by their realization and in particular the machining tolerances and the mounting of the parts to ensure the tightness of the piston on its raceway, when no take-up system has been provided. One observes in particular the detachment of the piston in the zone where the point of contact rolling between the piston and the bore of the chamber approaches the neutral point, that is to say the discharge orifice located upstream of the flap separating the compartment high pressure of the low pressure compartment. For high speeds of rotation and low working pressures, the centrifugal forces arising in the mobile crown-piston assembly are sufficient to oppose such detachment. This is no longer the case, at low speeds and high pressures, and several solutions have been devised to remedy this and to ensure that the piston is wedged on the bore of the chamber and delay its lifting.

Realizations, as described in French patents 2 468 770 and 2 470 267, require a mechanical adjustment of the piston on the very delicate stator, because it cannot allow backlash and requires very high assembly precision.

According to another proposal, French patent 2,280,808, only delaying the detachment of the piston by maintaining the angle formed between the line connecting the center of the chamber to the center of the piston with the line connecting the latter center to the center of the eccentric at an optimal value between 20 ° and 40 °.

According to another embodiment, French patent 1,256,125, the rotor is constituted by a cylindrical jacket freely mounted in the chamber around the shaft and kept in contact with the wall of said chamber by means of a rolling device with movable mounting, which consists in a lever wedged on the shaft and carrying at one end a roller and at the other end an arm ending in a roller, a spring being provided to separate the arm from the lever.

Such a solution, according to which the cylindrical jacket is free in the stator, is not free from drawbacks, since the jacket can reflect a shock at start-up in the shutter separating the compartments from the chamber. In addition, it requires a very precise calculation of the admissible rotation speeds of the rollers as a function of the maximum rotation speed of the piston, in order to guarantee the life of the compressor. According to another embodiment, French patent 2,275,664, the piston rolls freely on a ball bearing outside of a ring secured to the eccentric of the shaft. We are trying to remedy the detachment problem by using the toggle lever principle, by placing the center of the piston in the center of the eccentric or in the area between the center of the eccentric and the center of the rotary piston near the center. eccentric. Such a solution is difficult to carry out, since the slightest imbalance of rotating masses causes vibrations and oscillations harmful to the bearings of the compressor.

According to another embodiment, French patent 2,223,570, which constitutes the state of the art and recommends the mounting of the rotary piston on an eccentric drive ring secured to the eccentric of the shaft, the angle made by the straight line. connecting the axis of the shaft to the axis of the eccentric part with the straight line which connects the latter axis to the central axis of the eccentric crown is between 70 ° and 110 °, so that the piston rolls in applying to the inner wall of the housing and that, once a certain release pressure is reached, the piston moves away from the wall of the housing. Such a compressor does not perform mechanical setting of the piston in operation, but only drives the piston by means of the eccentric ring.

The present invention relates to a machine in which one realizes both a good drive of the piston and its setting on the bore of the chamber, while preventing its detachment in the high pressure zone, without this embodiment comprising the mounting mechanical with adjustment of the eccentric or mounting on ball bearings directly on the eccentric, necessarily requiring costly precision in terms of machining and assembly of the machine.

According to the invention, the rotary piston machine, in particular rotary piston compressor, comprising a cylindrical chamber, in which are arranged an eccentric or crank part of a shaft coaxial with said chamber, an annular rotary piston being able to roll in contact with the wall of the chamber and a coaxial ring for driving the piston in contact with the internal wall of the piston over its entire circumference and mounted inside the latter, so as to be able to slide relative to the piston, the setting of the piston on its raceway being provided by elastic compensation means bearing on the crank or the shaft and on the bore of the crown, the machine further comprising a flap dividing the free space around the piston into two compartments to variable volume is the crown being driven in rotation by means of a journal, the axis of the journal extending in the longitudinal direction of the machine and being located in an eccentric position p ar relative to the crown, characterized in that the pin is mounted in a yoke making the coupling of the crown and the crank.

We can imagine means of coupling various, preferably the coupling member is a pin mounted in a yoke.

According to a preferred embodiment, the journal is mounted in a bore of the crank and in a yoke secured to the crown. One can also conceive of a reverse solution, a clevis secured to the crank and a bore made in the crown.

The timing of the piston on its raceway can be ensured by elastic means of compensation with various progressive adjustment.

According to a first variant, a spring is mounted transversely upstream of the point of contact of the piston and of the wall of the chamber with respect to the direction of rotation, bearing on the crown and on the crank, so that the straight line d he action of the spring passes through the axis of the shaft and is perpendicular to the right connecting the center of the piston and the center of the journal. Preferably, the spring is housed between a centering stud fixed to the crown and a cylindrical housing with counterbore made in the crank, the bottom of the housing being parallel to the right connecting the centers of the piston and the crank.

As a variant, the elastic wedging means consist of at least one wedge with a conical slope urged by a spring working in compression along a line of action transverse to the axis of the shaft. According to a preferred embodiment, one of the longitudinal faces of the crank has two concave longitudinal flats inclined relative to the axis of the shaft and forming with the bore of the crown a housing, two wedges being housed at the ends of said housing, each having an inner face with a slope of angle corresponding to that of the inclined flat, a spring being disposed between the shims. The part of the crown on which the wedges bear has a flat, while the outer face of each wedge which bears has a rounded profile.

• la figure 1 montre une vue en coupe longitudinale selon B-B de la figure 2 du compresseur,
• la figure 2 une vue en coupe transversale selon A-A de la figure 1,
• la figure 3 une vue en coupe transversale d'une variante de réalisation,
• la figure 4 un graphique montrant la variation de la force de réaction Re au point glissant de contact E en fonction de l'angle de la manivelle w que forme la droite 0₁E et l'axe central 01 G (J=2,5mmeta_i=36°)
• la figure 5 un graphique montrant la variation de l'angle en fonction du jeu J
• la figure 6 un graphique montrant la variation du rendement de compression en fonction de l'angle de calage
• la figure 7 un graphique montrant la variation de la force de réaction Re maximale au point de contact glissant E en fonction du jeu J (repère 46 de la courbe figure 4),
• la figure 8 un graphique montrant la variation de la force de réaction Re minimale en fonction du jeu J (repère 47 de la courbe figure 4),
• la figure 9 le diagramme de forces pour un angle de manivelle 0<w<w₁, lorsque la force de réaction Re est positive,
• la figure 10 le diagramme de forces pour un angle de manivelle w₁, lorsque Re est nul (repère 45 de la figure 4),
• la figure 11 le diagramme de forces pour un angle de manivelle w₂, lorsque Re est négatif et à son minimum (repère 47 de la figure 4), avec positionnement du ressort destiné à compenser Re,
• la figure 12 une vue en coupe du ressort et de son logement selon C-C de la figure 11,
• la figure 13 une vue en coupe transversale schématique montrant l'utilisation de cales de compensation à pente transversale d'une autre variante de compresseur,
• la figure 14 une vue fragmentaire selon D- D de la figure 13 d'un détail de montage de cales
• la figure 15 une vue en coupe transversale montrant une autre disposition de cale à pente axiale, et
• la figure 16 une vue fragmentaire en coupe axiale selon E- de la figure 15.

According to another arrangement, a housing is disposed between the bore of the crown and the crank having a slope on the side of the crank which is inclined transversely to the right connecting the center of the piston and the center of the journal, the action of the shim housed in this housing and urged by a spring acting on a transverse straight line with respect to the shaft. In this case, the wedge has a sloping longitudinal face corresponding to the slope of its housing on the side of the crank. Other features of the machine according to the invention will appear in the light of the description of different embodiments presented by way of examples and illustrated by the drawings,

• FIG. 1 shows a view in longitudinal section along BB of FIG. 2 of the compressor,
• FIG. 2 a cross-sectional view along AA of FIG. 1,
• FIG. 3 is a cross-sectional view of an alternative embodiment,
• FIG. 4 a graph showing the variation of the reaction force Re at the sliding point of contact E as a function of the angle of the crank w formed by the line 0 ₁ E and the central axis 01 G (J = 2.5 mmeta _i = 36 °)
• FIG. 5 a graph showing the variation of the angle as a function of the clearance J
• FIG. 6 a graph showing the variation of the compression efficiency as a function of the setting angle
• FIG. 7 is a graph showing the variation of the maximum reaction force Re at the sliding contact point E as a function of the clearance J (reference 46 of the curve in FIG. 4),
• FIG. 8 a graph showing the variation of the minimum reaction force Re as a function of the clearance J (reference 47 of the curve in FIG. 4),
• FIG. 9 the force diagram for a crank angle 0 <w <w ₁ , when the reaction force Re is positive,
• FIG. 10 the force diagram for a crank angle w ₁ , when Re is zero (reference 45 of FIG. 4),
• FIG. 11 the force diagram for a crank angle w ₂ , when Re is negative and at its minimum (reference 47 of FIG. 4), with positioning of the spring intended to compensate for Re,
• FIG. 12 is a sectional view of the spring and of its housing according to CC of FIG. 11,
• FIG. 13 a schematic cross-sectional view showing the use of compensation wedges with transverse slope of another variant of compressor,
• Figure 14 a fragmentary view along D- D of Figure 13 of a block mounting detail
• FIG. 15 is a cross-sectional view showing another arrangement of the shim with an axial slope, and
• FIG. 16 is a fragmentary view in axial section along E- of FIG. 15.

The compressor of a refrigeration machine according to the invention shown in FIGS. 1 and 2 comprises a central body of compressor 2 provided with two external flanges before 11 and rear 12, crossed by a motor shaft 4 of axis 0 ₁ , Body 2 contains a coaxial cylindrical chamber of the shaft 4, the internal wall 10 of which constitutes the raceway of the piston.

Inside the cylindrical chamber, the shaft 4 is made integral with an eccentric or crank 3. In addition, a rotary piston 5 of axis 0 ₂ of diameter smaller than that of the chamber is placed inside of the latter, so as to be able to roll in contact with the wall of the chamber, while a movable drive ring 6 is mounted inside the piston 5, so as to be able to slide relative to the piston according to the sliding surface 7.

The crown 6 is provided with a yoke 8, 9 and the end of the crank 3 with a bore 24, so as to be able to couple the crown 6 and the crank 3 by means of a pin pin 0 _{3 which} can freely rotate in bore 24.

The virtual piston drive rod 5 is represented by the right connecting the center of the crown and of the piston 0 ₂ to the center of the journal 0 ₃ .

The body of the compressor 2 contains under the cylinder head 34 provided with cylinder head gasket 37 of the organs usual, such as suction and discharge conduits, the latter provided with two valves 17, HP outlets 41, 42, as well as a separation flap 15 rocking around its axis 16 and provided with sealing segments 54. The shutter 16 separates the interior of the cylinder in the HP chamber 13 and the BP chamber 14, the point of contact of the end of the shutter and of the piston 5 being effected by means of the bearing surface 29 of the shutter cut in bevel, in the central axis of the cylinder at point G.

The usual equipment of a compressor comprises a lubricant reservoir 38 with its level control plug 39. The motor shaft 4 rests in bearings 43, 44, it is provided with rotary seals 31 and a bubbling spoon 32 and a balancing weight 33. Centering feet 35 equip the rear and front flanges of the stator. Spider legs 40 serve to lubricate the plain bearing of the movable crown and of the piston. The lateral sealing of the piston 5 is ensured by circular segments 36.

The wedging means used to take up the initial mounting clearance and the wear clearance consist, according to FIGS. 2 and 3, of a compensating spring 30 working in compression, whose axis of action 23 (FIG. 11) is perpendicular to the right connecting the center of the crown 0 ₂ and the center of the pin 0 ₃ . One of the ends of the spring 30 bears on a centering shoe 52, integral with the crown 6 and the other in a centering counterbore 53 present on the motor shaft 4.

The compressor of FIG. 3 represents an alternative embodiment in which the piston 5 is mounted on a needle bearing 22 and the compensation device comprises a pair of wedges with conical slopes 55 urged by a locking spring 57 with an axis 61, the outer surface 60 of the wedge 55 of rounded shape bearing on a contact shoe 59 secured to the crown (see FIG. 14).

When the setting of the piston 5 on the wall 10 of the chamber is ensured at the point of contact E by elastic compensation means, such as shims and springs (see FIG. 9), a line O ₁ can be drawn connecting the center 0 ₁ from the tree to point E. It is with respect to this straight line that we define the wedging angle α _{1 '} between the line 0 ₁ E and the line 0 ₁ 0 ₃ connecting the center 0 ₁ of l tree in the center of the trunnion. The angle α ₁ is therefore the angle by which the axis of the journal 0 ₃ is offset, relative to the straight line 0 ₁ E in the direction of rotation of the shaft.

The value of this angle must be carefully chosen. Indeed, the angle α ₁ is mathematically linked to the value of the clearance J between the piston and the wall of the chamber. This clearance J is calculated and measured when, the effects produced by elastic compensation means being canceled, the axis of the piston 0 ₂ is located in alignment with the axes 0 ₁ and 0 ₃ of the shaft and the journal, on the line of alignment of these axes. This play can be observed, when the crank is pivoted around the axis 0 ₃ to bring the center of the piston 0 ₂ to the right O ₁ O ₃ .

The graph in FIG. 5 represents a curve 48 giving the variation of the clearance J in 10 ^-1 mm as a function of the angle a, in radians. We see that the variation is almost linear for values of J greater than 1 mm. The values of J and a, are mathematically linked and can be calculated for given dimensions of the chamber, the crank arm and other construction parameters.

FIG. 4 represents, for a clearance of 2.5 mm corresponding to an angle α ₁ of approximately 36 °, a variation of the reaction force Re expressed in decanewton at the sliding contact point E of the piston on the wall of the chamber as a function of the crank angle w in radians, i.e. the instantaneous angular position of the straight line 0 ₁ E.

This curve shows an equilibrium point 45 for a crank angle value w, to which the force diagram of FIG. 10 corresponds, where the reaction force Re at the contact point E is zero. The curve has a maximum at 46 corresponding to a value of the crank angle w located between 0 ° and w, for which the reaction force Re at the contact point E is maximum.

By exceeding the angle w ₁ , the direction of application of the force Re is reversed and the piston tends to detach from the raceway. This negative reaction force Re has a minimum at 47, the effect of which must be combated by the use of elastic compensation means, such as springs or a combination of shims and springs (see the force diagram, FIG. 11).

FIG. 6 presents a curve 49 of variations in the compression efficiency in percent as a function of the setting angle a, in radians. As a result, the ascending part of the curve corresponds to the low values of a, which should theoretically be the choice. However, the reaction force Re, the variations of which as a function of the crank angle w are shown in FIG. 4, can reach prohibitive values incompatible with the tolerable forces that can be imposed on the materials due to their resistance. to break and wear quickly. For values of α ₁ , equal to or less than 20 °, the reaction on the motor shaft is too strong and as a result of the increase in mechanical forces the efficiency decreases. The smaller a _i , the greater the forces exerted on the piston and the journal which generate energy losses by transformation into friction heat.

FIGS. 7 and 8 show the curves 50 and 51 showing the variations of the forces Re expressed in decanewton as a function of the value of the clearance J in 10 ^-1 mm, corresponding respectively to the maximum reaction force at the contact point E ( point 46 of the curve according to FIG. 4) and at the maximum negative reaction force (point 47 of the same curve). We see that the positive reaction force Re decreases when the clearance J increases. This force tends to infinity for zero play, which would direct the manufacturer towards the greatest possible play. The force Re for an angle w ₂ (Figure 4) becoming increasingly negative according to Figure 8, we would tend to choose, on the contrary, a value of J as low as possible.

We notice that the difference between Re positive and Re negative decreases with the play and reaches a plateau for a play of about 10 mm. The choice of J determines the value of the angle α ₁ , since the angle α ₁ varies almost linearly as a function of the clearance J for values of J greater than 1 mm (see FIG. 5).

In practice, to determine the clearance J or the angle α ₁ , a range of angles α ₁ is chosen in FIG. 5 corresponding to the desired efficiency. For reasons of resistance of the materials mentioned above, we will choose α ₁ greater than 20 °, or better, greater than 30 °. To know the positive and negative reactive forces to which the materials will be subjected, we will draw force diagrams, according to Figure 4 for each of the chosen values of the angle α ₁ . We will take into account, on the one hand, the maximum value of the positive reactive force Re to which the materials may be exposed and, on the other hand, the maximum value of the negative force Re, because the larger it is, the more important must be the elastic means of compensation to be used with a limit threshold which represents the extreme possibilities of compensation by the use of springs because of their mechanical resistance. Thus, we will choose the curve where the positive Re value and the negative Re value are acceptable for the reasons mentioned.

In Figures 9, 10 and 11 are shown the force diagrams for different crank angles w exerted in a compressor, where the setting angle α ₁ is 32 ° 64 'and the play of 5 mm.

These diagrams correspond, respectively, as regards FIG. 9, to any crank angle w between 0 ° and w, (FIG. 4), that is to say where the force Re is positive, as regards the figure 10, at an equilibrium angle w, (point 45, figure 4) just before the detachment of the piston from its raceway and, with regard to figure 11, at an angle between w ₁ and w ₂ ( point 47, figure 4) in the separation zone where the negative Re force is maximum.

• Rc représente le cercle décrit par le rayon du cylindre Rc ayant pour centre O₁,
• Rp le cercle décrit par le rayon du piston Rp ayant pour centre O₂,
• Rf le cercle décrit par le centre du tourillon 0₃,
• Rcp le cercle décrit par le centre du piston O2, et
• R la portion du cercle décrit par le centre du piston O2 pivotant autour du centre du tourillon 0₃.

According to these figures,

• Rc represents the circle described by the radius of the cylinder Rc having for center O ₁ ,
• Rp the circle described by the radius of the piston Rp having O _{2 as} its center,
• Rf the circle described by the center of the pin 0 ₃ ,
• Rcp the circle described by the center of the piston O2, and
• R the portion of the circle described by the center of the piston O2 pivoting around the center of the journal 0 ₃ .

In the case of Figure 9, the piston is in equilibrium for a crank angle w between 0 ° and w ₁ (Figure 4). It is subjected to a torque resulting from the positive force FPc which represents the pressure force prevailing in the HP chamber and passing through the center of the piston 0 ₂ . The letter a indicates the arm of the lever which makes it possible to calculate the torque acting on the axis O ₃ of the journal and which keeps the piston applied on its raceway for a rotation of the crankshaft corresponding to an angle of 0 ° to w ₁ in radians.

FIG. 10 represents the piston in equilibrium for an angle w equal to w _{1, that} is to say just before the detachment of the piston.

FIG. 11 represents a force diagram for an angle w comprised between w ₁ and w ₂ , that is to say in the separation zone. After crossing the angle w ₁ , the force Re becomes negative and reaches its maximum for an angle w ₂ . This force is exerted via the lever arm b and forms a torque tending to detach the piston from its point of contact E with the cylinder. To avoid detachment of the piston, the effect of the negative force Re is compensated for by the action of one or more springs 30 (Figures 11 and 12), whose torque FR ^x O ₁ O ₃ cos a ₃ is equal to the torque Re x b.

The bearing face 62 of the spring 30 on the crown is parallel to the straight line 25 connecting the centers of the piston 0 ₂ and of the pin O ₃ and its line of action 23 passing through the center 0 ₁ of the shaft is perpendicular to the right 25.

The calculation of the spring force must take into account several factors, such as the working pressure in the HP chamber and the dimensions of the chamber and the piston.

The spring 30 is disposed upstream of the contact point E with respect to the direction of the piston bearing (FIG. 2), its axis 67 passes through the axis O ₁ of the shaft and is perpendicular to the straight line 25. It is housed between a centering stud 65 fixed to the crown and a cylindrical housing with counterbore 64 formed in the crank and the bottom 66 of which is parallel to the straight line 25 (FIG. 12).

The device using one or more springs to keep the piston applied on its raceway and to compensate for the negative force Re represents a first solution for setting the piston. Other compensation and setting means consist in using wedges with conical slopes urged by one or more springs and allow a progressive setting of setting.

According to the embodiment shown in Figures 13 and 14, between the crank 3 and the crown 6 is formed a concave housing formed by two inclined longitudinal flats 58 to accommodate a pair of wedges 55 with conical slopes 58 of opposite direction. To this end, the crank block has two slopes at the location of the housing, the angle of orientation of each corresponding to the slope of the wedge which is housed there. The conical slopes of the housing and of the shims are inclined at an angle a ₄ with respect to the axis O ₁ of the shaft 4. At the two transverse ends of the housing are housed the shims 55. The faces of the shims opposite the faces with a slope d 'angle a ₄ and bearing on a flat 62 or shoe that has the crown 6 at this location are convex and rounded, so that the wedges are supported on their shoes according to a generatrix designated by K. The plane of symmetry 63 longitudinal of shims passes through the center 0 ₁ . The two wedges 55 are biased in opposite directions by a spring 57 working under compression, the centering axis 61 of which is housed at the two ends in the wedges. The thrust of the wedges 55 exerted against the shoe 62 of the crown is per pendulum to the right connecting the axis of the piston 0 ₂ and the axis of the pin 0 ₃ .

Another embodiment of shims is shown in Figures 15 and 16. Instead of being oriented at an angle a ₄ relative to the axis 0 ₁ of the shaft 4, the slope 71 of the shim 70 is inclined transversely by with respect to the axis 0 ₁ and in particular of an angle a5 relative to the straight line connecting the center 0 ₃ of the journal and the center O2 of the piston. To this end, the housing provided for the shim is between the longitudinal flat 71 of the crank 3 and the flat 72 that has the bore of the crown 6. The shim 70, one longitudinal face of which has a slope of angle a5 , is pierced on a lateral face of the two blind housings 73 to accommodate the ends of the two springs 74 working under compression, the opposite ends of which are retained by centering studs 75 placed on a flat part of the crown 6.

The action of wedges is exerted along a transverse straight line with respect to the axis of the shaft 4 and has the effect of pushing the crown 6 of the crank in the direction perpendicular to said straight line.

The presented application of the machine according to the invention in the field of compressors in no way excludes other applications according to the principle explained, such as in the fields of internal combustion engines, vacuum pumps, energy recovery or pneumatic or hydraulic brakes.

Claims (11)

1. A rotary piston machine, more especially a rotary piston compressor, comprising a cylindrical chamber (13, 14) in which is disposed an excen- tric part or crank (3) of a shaft (4) having axis 0₁ coaxial with said chamber, an annular rotary piston (5) able to roll in contact with the wall (10) of the chamber and a crown wheel (6) for driving the piston (5) in contact with the inner wall of the piston on its whole circumference and mounted there inside, so as to be able to slide with respect to the piston, engagement of the piston on its rolling path being provided by resilient compensation means (30, 55 and 57, 70 and 74) bearing on the crank or shaft and on the bore of the crown wheel (6), the machine further comprising a flap (15) dividing the free space about the piston in to two variable volume compartments (13, 14), the crown wheel (6) being rotated by means of a trunnion (1), the axis 0₃ of the trunnion being aligned in longitudinal direction of the machine and in excentred position with respect to the crown wheel, characterized in that the trunnion is mounted in a fork joint (8, 9), so as to be able to couple the crown wheel (6) and the crank (3).

2. Machine according to claim 1, characterized in that the trunnion (1) is mounted in a bore (24) with axis 0₃ of the crank (3) and in a fork joint (8, 9) integral with the crown wheel (6).

3. Machine according to claim 1 or 2, characterized in that, the angle 111 being the angle by which the axis 0₃ of the trunnion (1) is offset with respect to the point of contact E, when the piston (5) is wedged against the wall (10) of the chamber, the value of α₁ being mathematically related to the value of the play J appearing between the piston and the wall and measured when, in the absence of the effects produced by the resilient compensation means, the axis of the piston 0₂ is located in the alignment of the axes 0₁ of the shaft and 0₃ of the trunnion, α₁ is chosen as a function of the working pressure, of the speed of rotation, of the dimensions of the piston and of the chamber greater than 20°, to which corresponds a play J of about 1 mm, to avoid to subject the materials to a too important mechanical stress.

4. Machine according to one of claims 1 to 3, characterized in that the resilient wedging means are formed by at least one spring (30) mounted transversely upstream of the point of contact E with respect to the direction of rotation of the piston, bearing on the one hand on the crank (3) and on the other on the crown wheel (6), so that the straight line of action of the spring passes through the axis 0₁ of the shaft and is perpendicular to the straight line (25) connecting the center O2 of the piston with the center 0₃ of the trunnion.

5. Machine according to claim 4, characterized in that the face (62) of the spring bearing on the crown wheel is parallel to the straight line (25) connecting the center 0₂ of the piston with the center 0₃ of the trunnion.

6. Machine according to claim 4, characterized in that the spring (30) is housed between a centering stud (65) fixed to the crown wheel and a cylindrical housing with spot facing (64) formed in the crank, whose bottom (66) is parallel to the straight line (25) connecting O2 with 0₃,

7. Machine according to one of the claims 1 to 6, characterized in that the resilient wedging means are formed by at least one wedge with conical slope urged by a spring working under compression along a straight line of action transversal with respect to the axis 0₁ of the shaft (4), the wedge being housed in the housing between the crank and the crown wheel, one wall of which has a conical slope.

8. Machine according to claim 7, characterized in that one of the longitudinal faces of the crank has two longitudinal concave flat portions (58) sloping at an angle a4 with respect to the axis 0₁ of the shaft and forming a housing with the bore of the crown wheel (6), two wedges (55) being housed at the two transverse ends of said housing, each one having an inner face sloping at an angle a4 corresponding to that of the sloping flat portion (58), a spring (57) working under compression being disposed between the wedges (55).

9. Machine according to claim 7 or 8, characterized in that the part of the crown wheel on which the wedges bear has a flat portion (62) forming a shoe, whereas the outer face of each wedge bearing on said shoe has a rounded portion.

10. Machine according to claim 7, characterized in that between the bore of the crown and the crank is disposed a housing for a wedge (70) with longitudinal sloping face, the slope (71 ) of the housing on the crank side being sloped transversely by an angle a₅ with respect to the straight line connecting the center O2 of the piston with the center 0₃ of the trunnion, the action of the wedge (70) urged by at least one spring (74) being exerted along a straight line transversal with respect to the shaft (4).

11. Machine according to claim 10, characterized in that a lateral face of the wedge (70) is pierced with at least one blind housing (73) in which is accommodated one end of the spring (74), the other end of the spring bearing on a centering stud (75) integral with a flat portion (72) of the crown wheel (6).

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