EP0106808B1 - Radial piston machine with a variable displacement - Google Patents

Description

This invention relates to a hydrostatic machine with radial pistons.

The word "hydrostatic machine" is used to design a machine which can be a motor or an operator, for example a motor or a pump in which a hydraulic fluid, generally oil, exchanges pressure energy with an element. mechanical.

In the word "hydrostatic machine" one must also design the hydraulic transmissions which include a motor and a pump.

Hydrostatic machines with radial pistons already exist which are generally of fixed displacement, since there are very few embodiments with variable displacement which in general are limited to obtaining only two displacements. This is due to the great technical difficulties encountered until today to achieve this variation in displacement, in addition to the higher cost compared to variable displacement machines of the axial type already present on the market.

The use of the variable displacement machine solved in particular many problems of oleostatic transmission, in particular is widely used today the combination of a variable displacement pump and a fixed displacement motor, since it results easier to intervene on the variability of the pump to obtain in the motor, with fixed displacement, a continuous variation of the number of revolutions and consequently the inverse continuous variation of the driving torque.

On the other hand, by having a variable displacement motor, obvious constructive advantages are obtained when it is supplied with a fixed mounted pump, for example a simple gear pump, coupled to a heat or electric motor. .

If, in addition, a variable displacement pump is also available, the functional characteristics of the hydraulic transmission greatly increase.

In this respect, as we have already said, we build radial and axial machines with variable displacement.

In machines with axial pistons the displacement varies by continuously varying the inclination of the axis of the cylinder-holder body relative to the engine axis, or by varying a control plate for the axial pistons, while in the radial piston machines the displacement is obtained by varying the eccentricity of the eccentric which determines the stroke of the radial pistons.

A known embodiment provides a movable eccentric back and forth, controlled by small hydraulic pistons inserted in the body of the shaft on which this eccentric is mounted.

It should be noted that in both cases a clean command is required to obtain the displacement change, this means that the machine is not caused to spontaneously equalize with the variations in the load.

In addition, this control mechanism is difficult to produce and a considerable effort is required if the displacement of the machine is to be varied during the operation of the machine under load.

To circumvent this obstacle have had some success the radial machines used as engines, in which one limits oneself to only two possible cubic capacities, which one can obtain through a pressure signal which with a set of valves, reduces the active surface , that is to say the piston thrust area, or, we join, in series or in parallel, displacement groups, in which slide pistons which act on the CAMES housed in the contour of the rolling case .

Among all the attempts that have been made in the past, to make these machines with variable displacement, in addition to the motors, in which the eccentric is displaceable radially with respect to the shaft, and to the motors in which one acts by reducing the active surface of the pistons themselves, of which we have already said, we can cite several very complicated mechanisms which can vary the stroke of the pistons through the use of two rotating eccentrics, mounted one inside the other and by rolling them between them with a suitable order.

SUMMARY OF THE INVENTION

The object of this invention is a hydrostatic machine with radial pistons having a shaft joined to an eccentric cam, with variable eccentricity, in the manner of obtaining a hydraulic machine with variable displacement which, among other things, can be automatically self-adjusted to adapt to varying load conditions.

This hydrostatic machine is configured in its general layout as a radial piston machine of the type generally used as a hydraulic motor with several radial pistons with shaft provided with eccentric cam and which comprises a carcass in which the cavities of the cylinders are drilled and a cam eccentric circular, the axis of symmetry which is parallel to the axis of rotation of the machine, linked to the shaft in the axial direction and which has an eccentricity with respect to the axis of the shaft and therefore of the machine.

The radially movable pistons inside these radial cavities are moved back and forth by this eccentric cam so that this eccentricity defines the displacement of the machine and transmits power by means of the fluid which circulates in which.

In the machine according to this invention, unlike the machines of the previous technique in which the eccentric cam was integral with the shaft, the eccentric cam is pivotally movable about the axis of a movable body interposed between the shaft and the eccentric cam, which is in turn pivoted around the same axis, which is parallel to the axis of the shaft and to the axis of symmetry of the cam, so that in a rotation of the eccentric cam around the axis of the body mo bile, the center of the cam passes from a position where it is located at a distance from the shaft in which the resulting eccentricity is the difference of the two eccentric distances, to another diametrically opposite position where the two eccentricities lie between them.

This point passed, the center of the cam approaches the axis of the shaft to the position of the minimum of the distance from which we had started.

As a result, the distance from the center of the cam to the shaft axis measures the effective eccentricity that this cam has in relation to the shaft.

Since in the machine of this invention this eccentricity does not have a fixed value, but variable, according to the loading conditions of the machine, as will be better explained, following the description and the claims, the word "eccentricity" will be used to indicate the instantaneous and variable distance between the axis of symmetry of the eccentric circular cam (this means the axis which passes through its center) and the axis of the shaft.

On the contrary, the word "disaxation" and its derivatives will be used to indicate the distance between the axis of the movable body (which is also the axis of rotation of the eccentric cam) and the axis of the shaft, and this distance is a characteristic which has a fixed value, this means that it is a constructive characteristic of the machine.

This movable body is also engaged with the shaft and the eccentric cam respectively with screw couplings, at least one of which is with reversible screws, these screws having cylindrical helix threads with different geometric characteristics (one of these screws can be simply axial grooves); as well as a relative rotation between the shaft and the eccentric cam corresponds to a displacement of the movable body along its axis.

Note that a machine of the aforementioned type is illustrated in British patent GB-A-538,230 where two eccentric elements are connected through an axially movable cylindrical element, which has a screw or spiral connection (and also to the axial grooves) with each of these eccentric elements.

According to the invention it is fundamental that the axial displacement of this movable body is contrasted by elastic means respectively between the movable body and the eccentric cam, so that there will be a self-adjusting system by the balance between the torsional moment which causes a relative rotation between the cam and the shaft, and the elastic reaction of these elastic means.

Even if the self-adjusting system, which has been mentioned above, is highly preferable, in certain particular applications the machine can be made, in the medium of this invention, as an outside system.

In this case, the movement of the movable body to cause the variation in the displacement of the machine can happen through actuation from the outside, for example, through an oleodynamic control. DESCRIPTION OF IMAGES

• la première image, fig. 1, nous montre d'une façon schématique la machine de cette invention vue latéralement;
• la deuxième image, fig. 2, nous montre schématiquement la machine vue en face;
• la troisième image, fig. 3, est un diagramme qui nous montre la loi sinusoïdale de la variation de l'excentricité;
• la quatrième image, fig. 4, est un diagramme qui nous montre la relation d'équilibre entre la force qui correspond au moment dû à la pression qui fonctionne contre les pistons et la réaction du moyen élastique qui crée le moment antagoniste;
• la cinquième image, fig. 5, est une première forme de réalisation de machine à arbre fixé et carcasse roulante;
• la sixième image, fig. 6, est une seconde forme de réalisation de la machine à arbre roulant et carcasse fixée;
• la septième image, fig. 7, est la troisième forme de réalisation de la machine à arbre fixé et carcasse roulante.

The invention will now be described with reference to the accompanying drawings, including:

• the first image, fig. 1 shows schematically the machine of this invention seen from the side;
• the second image, fig. 2, shows schematically the machine seen in front;
• the third image, fig. 3, is a diagram which shows us the sinusoidal law of the variation of the eccentricity;
• the fourth image, fig. 4, is a diagram which shows us the equilibrium relation between the force which corresponds to the moment due to the pressure which functions against the pistons and the reaction of the elastic means which creates the antagonistic moment;
• the fifth image, fig. 5 is a first embodiment of a machine with a fixed shaft and a rolling carcass;
• the sixth image, fig. 6 is a second embodiment of the machine with a rolling shaft and a fixed carcass;
• the seventh image, fig. 7 is the third embodiment of the machine with fixed shaft and rolling carcass.

DETAILED DESCRIPTION OF THE INVENTION

As already said, the machine of the invention has an offset between the axis of the shaft and the axis of the movable body.

There is also a distance between the axis of symmetry of the eccentric cam and the axis of the movable body.

Although this last distance and this offset may be different from each other, and this is part of the scope of this invention, to facilitate description and as a preferred embodiment it is then assumed that this distance and this offset are of the same length.

In this way, if we refer to the second image, and if we call this length d, we will have that in the rotation of the eccentric cam 2 around the axis c of the movable body 3, the geometric center or axis B of the eccentric cam 2, will gain a variable distance or eccentricity E with respect to the axis A of the shaft 1, so that this eccentricity will pass from a minimum value to a maximum value 2d, and which after will return to a minimum value (in the example illustrated is zero) after a further 180 ° rotation of the cam.

Referring to images 1 and 2, the machine of the invention generally comprises: a shaft 1 with axis A, an eccentric disc 2 or cam with axis of symmetry B and a movable body 3 with axis of rotation C.

The movable body 3 is coupled to the shaft 1 and the cam 2 with screw coupling 4 and 5 respectively.

The screws 4 and 5, according to the invention, must be of different threads and at least one must be reversible. As a particular case, the thread 4 is represented as a coupling with axial slots, as well as the shaft 1 and the movable body 3 are coupled with axial sliding, without reciprocal rotation.

Furthermore, it should be understood that in the machine according to the invention the shaft 1 and the cam 2 are coupled so as not to move axially with respect to each other, by mechanical construction, but they can roll one compared to each other.

At least one elastic element pushes the mobile body 3 towards an axial direction.

In the first image, two compression springs 6 and 7 are shown which act between the movable body 3 and the shaft 1 and the cam 2 respectively, each in one direction.

The axis C of the movable body 3 is offset from the axis A of the shaft by a distance d.

The axis B of the cam 2 is disposed at the same distance d from the axis C of the movable body 3.

As already mentioned above, the equality between the distances AC and CB is only by way of example, the distances possibly being different without departing from the invention, all the rest remaining equal.

In a machine of this type the cam 2 is coupled on its periphery with radial pistons (not shown) which are arranged in a conventional manner in a cylinder block (not shown).

Also by conventional means, the fixed element of the machine can be the carcass, in this case the shaft-cam assembly rotates around the axis of the shaft, or else the carcass is the rotating element and the assembly camshaft is fixed.

It should also be remembered that, unlike the previous technique, in this invention, the shaft-cam assembly is not rigid, but the cam 2 can take different positions by varying its eccentricity while the shaft 1 can be actually fixed.

Indeed ( ^2nd image) the axis of symmetry B of the cam 2 can move along the circle F, having as its center the axis C of the moving body 3.

In the positions 2a, 2b and 2c of the cam 2 indicated in dashed lines, the relative positions of the axis of symmetry B, are Ba, Bb and Bc. We observe that the position Bc is on the axis of the tree 1, since we assume the equidistance between the distances AC and CB.

In correspondence of these positions, the eccentricity of the cam 2 takes the values Ea = 2d, Eb the zero.

In the example illustrated in the first image (fig. 1), a rotation of the cam 2 relative to the shaft 1 causes an axial displacement of the movable body 3, by effect of the screw coupling 5.

Opposed to this movement is the elastic force of one of the springs 6 or 7 depending on the direction of movement.

• E = 2d sin 2 puisque 0 est variable entre 0 et 2π ainsi que l'excentricité est nulle par 0 = 0 et elle est maxime par 0 = 2π.

However, by matching the axial rest position of the movable body 3, pushed by these elastic means 6 or 7, to the position in which the eccentric cam 2 is arranged with its axis of symmetry B coincident with the axis of rotation A of l 'shaft 1 and therefore of the machine, this cam 2 has zero eccentricity, being centered relative to the machine. Now applying a torsional moment to the cam 2, holding the shaft 1 stationary, we obtain a rotation of the cam 2 with eccentricity E which increases with respect to the axis A of the shaft 1, with a consequent variation of the displacement of the machine, and an axial displacement of the movable body 3 with stress on the elastic means 6 to 7 until reaching a position of equilibrium between the torsional moment and the reaction of these elastic means 6 or 7. The moment of torsion which causes the cam to roll derives from the force explained by the pressure in the pistons multiplied by .the eccentricity E gained by the cam which serves as a crank arm. (This condition does not occur naturally at zero eccentricity). The eccentricity E, that means the length of this crank arm, is a sinusoidal function of the angle of rotation 0 of the eccentric cam 2 around the axis C or moving body 3. Indicated with d the value of the distance from the axis C of the movable body 3 from the axis A of the shaft 1 and from the axis B of the eccentric cam 2, the resulting eccentricity E is easily expressed as a function of the angle of rotation of 2 the cam about the axis C of the movable body and with reference to the construction of the 3 ^rd image, we have this relationship:

• E = 2d sin 2 since 0 is variable between 0 and 2π so that the eccentricity is zero by 0 = 0 and it is maximized by 0 = 2π.

The value of the torsional moment also has a sinusoidal shape, and consequently the axial thrust of the mobile body 3 will also have a sinusoidal shape due to the torsional moment.

Against by the reaction of the elastic means 6, 7 has (on the contrary) a linear law since the axial displacement of the movable body 3 is proportional to the angular rotation of the cam.

It happens that, the constructive characteristics of the device fixed, by each pressure acting on the pistons, there is always a well-defined equilibrium position between the torsional moment and the reaction of the elastic means.

On the other hand, this torsional moment is none other than the motor moment which manifests itself in the machine as a consequence of the value of the pressure in the cylinders, the motor moment it takes to overcome the resistant moment.

There is therefore a direct and simple relationship between the angular displacement of the eccentric cam 2 and the resistive moment (load) applied to the machine, as will be determined by self-regulating means intrinsically and continuously, a variation of the eccentricity E of the cam 2 relative to the axis A of the shaft 1, with consequent variation in the displacement of the machine, which eccentricity E therefore stabilizes in the position at which there is the balance between the torque and the reaction of elastic means.

It is simple to convince yourself of this fact, noting that the crank arm increases as a result of the increase in pressure and this until 0 = π and when; after π, the pressure has reached relatively high values, this pressure more than compensates for the decrease in the crank arm, as well as the torque still believes by subsequently compressing along the axis, these elastic means 6 or 7.

An analytical study which describes the behavior of the device shows that the pressure increases with the increase of the angle 0 and tends to infinity when one approximates to 2 π (this last condition naturally is only theoretical). By values 0 close to 2π the crank arm, this means the eccentricity, returns to 0 (zero), as well as the moment resulting from these two opposing tendencies, surprisingly tends to a maximum value that cannot be superimposed.

Another surprising result which derives from the analytical study is that the device is insensitive to values of the pressure lower than a well determined minimum pressure corresponding to the equilibrium between torsional moment and reaction of the elastic means when 0 tends to 0.

The curves p ,, _P2 ; ... p _n illustrated in the 4 ^th image (fig. 4), show on the ordinate the sinusoidal shape of the axial thrust values H, caused by a torsional moment produced by the action of various pressures in the cylinders.

Each curve represents a constant pressure at the variation of the angle 0 (on the abscissa) and therefore of the eccentricity. A variation of the pressure will thus obtain a family of curves each of which is at constant pressure and these curves are arranged with increasing pressure upwards.

The line m shown in the 4 ^th picture (Fig. 4) which starts from the origin, represents the characteristic, for example linear, elastic imployé means that provides a Z reaction (ordinate).

This line has an inclination which depends on the rigidity of the elastic means adopted. The points Q of intersection between this line and the curves of the axial thrust H due to the moment of torsion are thus shown.

These intersection points Q represent the point of equilibrium between the pressure on the cam 2 (torsional moment) and the reaction of the elastic means depending on the rotation 0 of the cam 2.

This means that due to a certain torsional moment the cam rolls at a certain angle, gaining a certain eccentricity E.

We see that on the left the axial thrust H due to the torsional moment (which has a sinusoidal shape) increases more quickly from the reaction Z of the elastic means (which has a linear shape), while to the right of the point of equilibrium the opposite; this means that the axial thrust H due to the torsional moment increases less rapidly and once past π, decreases with respect to the linear characteristic of the elastic means.

The machine which adjusts itself according to this invention has subsequent notable advantages which derive from its intrinsic properties.

Firstly, the fact that the turning moment has a maximum, makes it possible to establish exactly the maximum stress values at which all the mechanical members are stressed and it is certain that these values will never be exceeded.

Only the pressure can reach high values, but it is very simple to take precautions against overpressures and with great confidence, by introducing a clean valve of maximum pressure in the supply circuit.

In addition, since the pressure presents a functional minimum characteristic of the machine, an appropriate choice of this minimum puts cavitation phenomena on the tree (this means suction of small air balls at low suction pressures in the case of operation as a pump, or irregular operation when the pressure is lowered in correspondence with the number of revolutions too high in the case of operation as a motor).

On the contrary to the tender of the pressure at its well defined lower limit, to the tender at Zero of the eccentricity of the cam, this means in correspondence of the high velocities of rotation, the flow also tends to an asyntotic maximum, the value of which is never exceeded and therefore ensures the presence of fluid in the circuit at any rotation speed once this maximum flow has been properly dimensioned. This is contrary to what happens in all traditional hydrostatic machines, axial and radial with variable displacement, in which the increase in the rotation velocity requires an increasing flow linearly however requests for flow higher than the maximum flows of project can easily be check.

This was achieved by significantly limiting the minimum angle of regulation and therefore the gain in torque that could be obtained was relatively small.

Furthermore, in the machine of this invention, since for a large level of displacement control, the operating pressures are relatively low, ie not much higher than the minimum asyntotic pressure and at the same time the same flow rates of this interval vary very little, we have that all the hydraulic losses which depend on the pressure (between filaments) of the flow (pressure drop) remain practically unchanged and independent of the number of turns. The total output of the machine therefore only depends on the mechanical friction of resistance to rotation which naturally increases with the increase in the number of revolutions and constitutes the only reason which limits the economic use of this machine at high rotational velocities.

The movable body 3, as already said, is characterized in that it has two screw threads with different geometric characteristics on two different parts of its surface.

Several embodiments make it possible to produce a mobile body which satisfies this condition.

It may consist of a cylindrical element which has two cylindrical ends on the surface of which these threads are executed with screws engaging with the shaft and with the cam, as shown in the first image. (Fig. 1).

Another embodiment consists in making the movable body in the form of a sleeve with a thread on the outside and the other inside the hole of the sleeve as illustrated with 8 in the 5th image (fig. 5).

Another embodiment provides a body generically in the form of a cylindrical mushroom in which an external thread is executed on the external surface of the cylinder which constitutes the cap of the mushroom and another thread on the cylindrical tail of this mushroom. This embodiment is illustrated with the 9 in the 5th image and with 10 in the 7 "" "'image.

Many forms of execution are obtained by the combination of those mentioned.

Naturally, each of these embodiments corresponds to the conjugate form of the couplings in the shaft or in the eccentric cam to guarantee the correct functioning of the screw coupling.

Even the firm execution of the screw thread can vary widely, since we only ask that the screws executed on the surfaces of the movable body be geometrically different in such a way that a translation of the movable body along its axis always gives as a result an angular displacement of the eccentric cam relative to the shaft. In particular by paying attention to the fact that it is necessary that at least one of the screws is reversible, one can execute the other screw in the most favorable form, for example as a screw with infinite pitch, this means a screw degenerated into simple longitudinal grooves. This is of great advantage since it makes it possible to limit the reversibility to the screw of minor diameter with a consequent reduction in the pitch, that is to say the space necessary for the axial displacement of the mobile body.

We relate to the technique of construction of the screws, the choice of the best value for the pitch and for the angle of envelopment of the screw, and the shape of the thread section.

The embodiment of the elastic means is as wide as possible, since it is requested that these elastic means oppose the movement of this movable body being engaged between the latter and the shaft or the cam.

However, it is possible to provide a single elastic means interposed indifferently between the movable body and the shaft, in this case the device is limited in its operation to a rotation of the cam of an entire turn in one direction (0 <0 <2 π ).

If two elastic means are provided which act respectively between the movable body and the shaft, between the movable body and the cam, the device is activated by a rotation of the cam for a whole revolution in the two opposite directions (- 2π <0 <2π). It is therefore possible to use an entire revolution of both parts relative to the rest position 0 = 0.

These elastic means can be cylindrical springs, springs with valuts, springs with cut or undercut, which are expediently requested from suitable appendages applied to the movable body and the same springs can be housed inside or inside. outside of the shaft or cam.

A particularly interesting embodiment plans to replace the springs, which are too heavy and bulky, with a servo-amplifier amplifier of the characteristic of a small calibrated spring, leads to control, depending on the deformation of the spring, the value of the pressure oil which acts on a piston which contrasts the axial movement of the moving body and therefore the rotation of the eccentric cam.

A further embodiment provides for the use of the elastic qualities of a compressed gas, for example by placing in fluid communication a hydraulic accumulator with a variable volume cavity defined by a piston which moves in a cylinder, the piston and the cylinder being respectively joined to the movable body and to the shaft or to the movable body and to the cam.

In addition, the hydraulic accumulator, which has very contained dimensions, can be installed outside the machine and can find a favorable position very close to it.

Easily, the combination of elastic springs, servomechanism and hydraulic accumulator makes it possible to obtain the elastic characteristic most indicated in the various fields of use.

In the machine according to this invention the eccentric cam is pivotally movable relative to the shaft to which it is coupled with its own means which allow it to rotate but prevent it from axial movements.

The simplest embodiment of this connection provides for a cylindrical sliding accomplishment with clean lateral shoulders to prevent axial displacements.

This cylindrical seat is executed on the, or in the head of the shaft and has an axis which coincides with the axis of the movable body and a corresponding housing in the cam to the axis which coincides with the axis of eccentricity of drug.

Because of the very good lubrication conditions, being the whole device immersed in the fluid, which also serves as a lubricant, it is possible a perfect rotation.

However, the large load on the eccentric cam and the slowness of the rotation can be such as to drive out all the oil from the two surfaces until contact thus obstructing the regular functioning of the device.

Provision is therefore made to make the cam bearing on the shaft in the form of a hydrostatic bearing supplied by the fluid even at the supply pressure.

Some success can be achieved by supporting the eccentric cam with a continuous ring of small rollers. It is good to prefer embodiments in which the axial forces of the elastic means are internal to the mobile body - eccentric cam system, to avoid axial forces which stress the cam relative to the shaft.

However in certain embodiments it is not possible to balance these axial forces, and the orders which hold the eccentric cam in place are notably stressed.

In this case, by performing the cam-shaft completion as a conical hydrostatic support, one can proportion the taper so that the axial component of the thrust on the cam, due to the pistons, partially or completely balances these axial forces.

In radial piston machines, in addition to automatic non-return valves, three types of distributor for the actuating fluid of the cylinders are used, in particular the axial type distributor with cylindrical rotation, the plain rolling axial type distributor, and the pentagonal distributor mounted on the peripheral surface of the eccentric cam.

In the machine, according to this invention, the application of automatic non-return valves and of the pentagonal rolling distributor presents no particular problem.

For the application of axial cylindrical and plain rolling distributors, it must be remembered that the eccentric cam rolls at a certain angle relative to the shaft, therefore the position of upper dead center (PMS) moves from the same amount.

It therefore serves that the P.M.S. from the distributor followed the P.M.S. of the eccentric cam.

Considering, moreover, that the distributor rotates in axis with the drive shaft, while the cam rotates in axis with the movable body, provision must be made for the connection between distributor cam and eccentric cam to occur commonly despite this misalignment, for example using a coupling with pad and radial button, to allow the radial displacement of the pad, while the button turns, and in this way drag the distributor, as well as the PMS of the eccentric cam is always radially aligned with the P.M.S. from the distributor.

As can be seen in the diagram of the ₄ ^th picture (Fig. 4) which shows the shape of the characteristic curves at constant pressure according to the angle 0 of the eccentric cam positioning, the curves are located one beside on the other to the small values of the angle 0, since they all arise from the same origin and open to fan to the large values of the angle 0. This indicates that at small eccentricities, the value of the pressure in the point of equilibrium varies little.

Indeed, the linear characteristic of the elastic means meets these curves in the rapidly increasing line.

It may happen that the value of the angle of equilibrium is no longer determined by a well-determined pressure but depends significantly on the constructive and functional parameters of the machine such as friction, variations in oil viscosity and ecc work tolerances.

At high rotation velocities, however, the engine rotation speed is uncertain.

It may therefore be appropriate to modify the elastic characteristic of the elastic means intervening in some way on them in order to move to the right the points of intersection of the elastic characteristic with the curves representing the axial thrust H due to the turning moment.

We thus obtain equilibrium points corresponding to more differentiated pressures, with consequent more stable operation of the machine at high rotational velocities.

One possible means for modifying the elastic characteristic of the elastic means is to use a pressure control fluid to increase or decrease the force, for example using a piston employed by these elastic means and which moves in a cylinder. . This control fluid can come from an own hydraulic power plant, or can be taken from the supply line and therefore have the same variable supply pressure depending on the operating conditions.

A particularly effective solution is to control the pressure of this control fluid through a throttle subject to the axial movement of the movable body, thus obtaining an exact correspondence between the position of the movable body which is a function of the supply pressure and the value of the pressure of the control fluid leaving the choke.

In certain applications it is useful to have a machine whose displacement is variable with control to carry out a prefixed program of machine operation.

In this case, the elastic means are dimensioned in such a way as to have a reduced residual response by an assigned quantity, as well as these elastic means have the function of reducing, to the desired extent, the positioning force necessary for move the moving body on command, regardless of the load conditions.

It therefore follows that the servomechanism to which the mobile body is attached will have reduced power supplies and require a small power for its actuation.

Referring to the 5th image (fig. 5) an embodiment of the machine according to this invention has been described which functions as a motor with a rolling carcass and fixed shaft. Inside a rolling carcass 11, coaxial with the axis A of the shaft 12 and therefore of the machine, are defined cavities 13 of the cylinders in which flow in and out of the pistons 14 movable radially. These pistons 14 which receive the thrust in the cylinders by a hydraulic fluid under pressure, transmit their reciprocating movement to the eccentric circular cam 15 through suitable pads with hydrostatic support.

This eccentric cam 15 is movably coupled to the shaft 12 being rotatably supported for example through rolling bearings 16 by a cylindrical head 17, preferably conical, projecting from the shaft 12, with axis C eccentric relative to axis A of tree 12.

The eccentric cam 15 has a cylindrical recess 18, preferably conical, complementary to the head 17 of the shaft 12, with its axis coinciding with the axis C of offset. On cam 15 is secured, through bolts 19, an enlarged head 20 of a reversible screw 21 having its axis coincide with the axis C of offset of the recess 18 and therefore of the cam 15, which screw is disposed at the inside this recess 18, the other end 23 of this screw 21 being rotatably supported in a seat 22 executed in the shaft 12. The reversible screw 21 is engaged in the hole 24 of a cylindrical sleeve 8 which constitutes the body mobile, this sleeve 8 having on its outer surface rectilinear slots 25 or helix with very long pitch.

The slots 25 of the sleeve 8 are engaged in the corresponding slots 26 of an axial hole in the shaft 12, the axis of this hole being coincident with the axis C of the screw and therefore eccentric with respect to the axis A of the shaft 12, so that this hole results in an axis with the eccentric head 17 of the shaft 12.

The hole in the shaft 12 opens at the other end into a recess 27 with an enlarged diameter in which slides, with fluid holding, a piston disc 28 which is secured, through an appendage 29, to the sleeve 8.

This piston disc 29 is also crossed in the center, from the other end 23 of the screw 25 which in this case is executed with a smooth tail.

The recess 27 having a widened diameter in the shaft 12, results however closed to being held by the piston disc 28 and by the engagement between the head 17 of the shaft 12, and the corresponding recess 18 in the eccentric cam 15 among the linings inserted in correspondence with the bearings 16 for supporting the disc 15. In this recess 27 with an enlarged diameter is another housed a compression spring 30 which acts between this piston disc 28 and the shaft 12. Under the action of the thrust transmitted by the pistons 14, the eccentric cam 15 rotates by a certain angle and the sleeve 8 is returned by the screw 21 secured to the eccentric 15, so as to be guided to slide in the annular gap between the screw 21 and the head 17 of the shaft, driving the disc of the piston 28 which, in addition to pressing the spring 30, also reduces the volume of the widened recess 27.

This enlarged recess 27 is placed in fluid communication, preferably with a hydraulic accumulator (not shown) from which the elastic compression of the gas it contains is used.

The pressure increase in the accumulator as a function of the reduction in volume of this recess 27 causes the accumulator to operate in parallel with the spring 30.

The cylinder chamber located on the other side of the piston disc 28, when it moves in the enlarged recess 27, can be used to modify the characteristic of the spring by sending oil into this chamber at controlled pressure.

An annular distributor 31 is arranged around the shaft 12. Since the disc 15 moves angularly relative to the shaft 12, the distributor also must perform the same angular rotation around the shaft 12.

In this respect the eccentric cam 15 has a button 32 tilting laterally, which engages in a radial slot 33 executed in the distributor 31, as it carries it in rotation despite the eccentricity between the eccentric cam 15 and the axis A of the tree 12.

Referring to the 6th image (fig. 6), an embodiment of the machine according to this invention is described which functions either as a pump or as a motor with a fixed carcass 34 and with the rotating shaft 35. Inside the carcass 34 are defined recesses 36 of the cylinders in which the pistons 37 radially movable slide back and forth.

The pistons 37 receive the thrust in the cylinders of a hydraulic fluid under pressure and transmit it through suitable hydrostatic pads to the eccentric cam 38 by rotating it.

The eccentric cam 38 is pivotally engaged on the shaft 35, being rotatably supported for example through a mechanical sliding coupling, on a cylindrical or slightly conical head 39, projecting from the shaft 35 and with axis C eccentric relative to axis A of the shaft 35.

The disc 38 has a complementary recess 40, cylindrical or slightly conical, with an axis coinciding with the axis of misalignment and a central protuberance 41 inside this recess 40 in which a threaded hole 42 with reversible screw is made having the same axis C of offset.

In this threaded hole 42 there is engaged a screw 43 which constitutes the movable body 9, this screw 43 has, integral with itself at the other end, an appendage 44 with disc or mushroom shape which has on its peripheral edge straight threads 45 or with long pitch propeller.

The shaft 35 inside has an axial cylindrical recess 46, the axis of this recess being coincident with the axis C of the screw 43, and therefore off-center with respect to the axis A of the shaft 35.

The inner surface of the recess 46 has slots 47 in which the slots 45 of this appendage 44 in the form of a mushroom are engaged. This recess 46 opens into the cylindrical projecting head 39. The mushroom disc 44 in turn is integral with a peripheral mantle 48 thus defining a recess 51 of the cylinder in which a counter-cylinder 49 is engaged slidingly and with fluid resistance 49 housed in the recess 40 of the eccentric cam 38.

Under the action of the thrust transmitted by the pistons 37, the eccentric cam 38 rotates by a certain angle, while the shaft 35 is retained by the load applied and the screw 43 is returned to the hole 40 of the eccentric 38, driving the mushroom disc 44 and reducing the volume of the cylinder recess 51 and compressing a spring 50 disposed inside this recess 51.

This cylinder recess 51 is arranged in fluid communication with a hydraulic accumulator (not shown) from which the elastic properties of the gas are used and which, however, operates in parallel with the spring.

The embodiment presented provides for a rotating planar distributor 52 and yet the planar distributor 52 must be rotated in synchro- nie with the eccentric cam 38, while this cam 38 rotates with the shaft 35. But during the rotation of the shaft, this cam performs small angular displacements relative to the shaft.

In this respect, the eccentric cam 38 has a cylindrical projection 53 in axis with the screw 43, this projection 53 being housed in a cylindrical sleeve 54 suitably supported in the carcass 34 and in axis with the axis A of the shaft 35.

The housing hole of the projection of the sleeve 54 has, on the contrary, its axis displaced by the same offset as the axis C of the screw 43, as are the angular displacements of the eccentric cam 38 during rotation. In the end part of the cylindrical projection 53 is executed a radial slot 55 in which a sliding prismatic shoe 53 is engaged, executed in the end part of a small shaft 57.

This small shaft in turn drives the disc to distribute the rotating plane 52.

Referring to the 7 ^th picture (fig. 7) discloses an embodiment of the machine according to this invention, as Working motor fixed shaft and rotating casing mounted within a wheel of a vehicle. Inside a rotating carcass 58 coaxial with the axis A of the shaft 59, and therefore of the machine, are defined recesses 60 of cylinders in which the pistons 61 radially movable slide back and forth.

These mobile pistons which receive the thrust in the cylinders of a hydraulic fluid under pressure, transmit their reciprocating movement to the eccentric circular cam 62 through a pentagonal shoe 63 which also serves as a distributor, supplied through the channel 64.

This eccentric cam 62 is pivotally engaged with the shaft 59, being rotatably supported, for example with a mechanical sliding coupling by means of a counter-shaft 65 integral with the disc and which rotates a hole 66 executed in the shaft 59 having the axis C eccentric with respect to the axis A of the shaft. This countershaft 65 is integral with a part of the disc 62 and on the other hand with a reversible screw 67, the axis C of the screw coincides with the axis of the countershaft, being offset from the axis of symmetry of the eccentric disc. The reversible screw 67 is engaged in a threaded hole 68 executed in the central tail 69 of a cap 70 in the form of a mushroom which constitutes the movable body 10.

This cap 70 has on the peripheral edge threads 71 straight or with long pitch propeller, which engage in axial sliding in a cylindrical recess 72 executed in an enlarged part 73 of the shaft, the axis of this recess 72 being coincide with the axis C of the screw, therefore off-axis with respect to the axis A of the shaft.

The front surface of this recess of the shaft has threads 74 in which the threads 71 of the cap 70 in the form of a mushroom are engaged. The peripheral mantle 74 of the cap delimits a recess 76 of the cylinder in which a counter-cylinder 77 is engaged in sliding and fluid-holding 77 and in turn mounted on a seat 78 executed on the counter-shaft 65 in axis with the screw 67 .

Under the action of the thrust transmitted by the pistons 61, the eccentric cam 62 rotates by a certain angle while the shaft 59 is fixed, and the screw, bending into the hole in the tail, recalls the cap in the form of fungus by reducing the volume of the cylinder recess.

This cylinder recess is full of oil which in this way is pressurized and slows down the rotation of the screw.

The increase in oil pressure is transmitted through a hole 79 made in the tail, also in the recess of the hole 68 screw threaded and therefore acts on a small piston 80 which slides with fluid holding in a hole axial 81 executed centrally with the screw 67 and which passes inside the counter-shaft 65 and the eccentric cam 62. The small piston 80 is contrasted by a calibrated and calibrated spring 82 housed inside the axial hole 81. Under the action of the oil pressure, the small piston 80 compresses the spring 28 so that the pressure which prevails in the cylinder recess is essentially a linear function of the deformation of the spring.

The small piston 80 has inside a recess at the bottom of which is provided a discharge hole 83 which has a conical seat.

This conical seat, by effect of the reaction of the calibrated spring on the small piston, is held normally closed by a small cone head 84, supported at one end of a bar 85, the other end of which controls a valve of high pressure 86 normally closed, outside placed in communication with a source of oil under pressure.

However, as we have already said, the recall of the screw corresponds to an increase in the pressure in the cylinder recess and therefore a displacement of the small piston in the direction of compressing the calibrated spring 82.

Consequently the conical seat 83 moves away from the small head 84 and part of the oil can escape to the other side of the small piston 80 in the axial hole 81 suitably collegated to the discharge by means of a pipe. 87.

The cap 70 can thus be attracted by the screw until when the pressure inside the cylindrical recess balances the action of the spring on the small piston, followed by closing of the conical seat. In contrast, a reduction in the action of the screw on the cap corresponds to an instantaneous drop in pressure in the cylinder recess and the spring acting against the small piston, by means of the bar, opens the valve 86 of high pressure, allowing the oil to enter the cylinder recess, until the spring action is rebalanced. The device constituted by the small piston, by the bar and by the high pressure valve, functions in the manner of a servomechanism amplifying the elastic characteristic of the calibrated spring.

As can be seen in the 7 ^th picture (fig. 7) the axial hole 81 also serves as a discharge channel of the oil supplied to the cylinders and a small hole 88 made at the bottom of the axial hole makes it possible to drain the oil drawing which fills the carcass during operation. The carcass has at its periphery a circular flange 89 provided with holes 90 to allow mounting to the tire of a vehicle wheel.

The shaft has at its exterior a thread 91 so that it can be supported in a keeper 92 for mounting to the suspensions of a vehicle, by means of bolts which pass through the holes 93. Flexible conduits, joined to the mouths 94 allow to supply and discharge the oil.

The machine according to this invention finds its use in all fields in which pumps or hydraulic motors are used which can operate either as a pump or as a motor.

However, provision can be made for designs which are particularly studied for use only as pumps or only as motors.

In the case of use as a pump and by operating the machine with 8 between n and 2 π, one obtains a self-reduction of the displacement and therefore of the flow when increasing the pressure with a great advantage in use to operate hydraulic presses, or to charge hydraulic energy accumulators.

In the case of use as an engine, an advantageous embodiment provides a machine with the fixed shaft and rotating carcass, and by equipping this cylinder block with a strip or a tire, a compact driving wheel is obtained which self-adjusts for a vehicle. In a vehicle, the four wheels can thus be easily driven.

The differential effect in turns is exerted automatically since the reaction of the elastic means determines the position of the moving body and therefore the balance between engine moment and moment resist, this means the cubic capacity, while at the difference between the number of turns of the inner and outer wheels provides for the automatic distribution of volumetric capacities.

In addition, the hydraulic braking of the vehicle can also be obtained, since these machines behave like pumps whenever the external moment exceeds the moment of the machine, in the case where the energy of the pumped fluid can be immagined in an accumulator hydraulic with gas or dissipated through a properly cooled dissipative valve.

Claims (13)

1. Radial piston hydrostatic machine with a shaft (1), whose geometric axle is the rotational axle of the rotating portion of the machine, a cylinder block with the same axle of that shaft, having cylinder cavities inside, a circular discus or cam with a symmetrical geometric axle (8) parallel to the axle of the shaft and having a distance so that an eccentricity (d) of the discus is settled in relation to that axle of the shaft, the shaft and the discus are connected together in relation to a relative axiale displacement; radially movable pistons go and versus inside those cylinders driven by that discus or cam, so that this eccentricity determines the displacement of the machine, a hydraulic fluid for power transmission, a movable body (3) rotationally engaged with screws (4, 5) - on one side (4) with that shaft and on the other side (5) with that eccentric cam - the rotation axle (c) of that movable body being parallel to the axle of the shaft and to the symmetric axle of the discus and offset with a fixed distance (d) related to each of those axles; at least one of the coupling screws must be reversible, the other can be a simple axial ruling; support means for rotational engagement of that shaft and discus or cam to allow the rotation of the movable body, characterized by comprising: the elastic means (6, 7) connected on one side with that movable body and on the other side with that shaft or with that discus or cam, suitable to resist at the displacement of that movable body, so that the application on that cam of a torque causes a rotation of that movable body with regard to the shaft, and consequently excites the reaction force of that elastic means against the helicoidal displacement of that movable body until the balance between that torque and that reaction force of the elastic means, in relation to a well defined angular position of the cam.

2. Machine according to claim 1 in which that elastic means is a spring.

3. Machine according to claim 1 in which that elastic means is a control system (80-86) that amplifies the work of a little spring (82) used to drive - following the deformation of the spring - the oil pressure value on a piston (80) that resists the axiale movement of the movable body and consequently the rotation of the discus.

4. Machine according to claim 1 in which that elastic means is the gas contained in a hydraulic accumulator.

5. Machine according to claim 1 in which that elastic means comprises a combination of a spring with or without a control system and a gas contained in a hydraulic accumulator.

6. Machine according to any of the claims from 2 to 5, in which a control fluid under pressure is used with that elastic means to modify its elastic answer.

7. Machine according to claim 6, in which the control fluid is the power fluid of that machine.

8. Machine according to claims 6 or 7, in which a throttle valve, driven by the axial displacement of that movable body, controls the pressure of that fluid in function of the movement of that movable body.

9. Hydrostatic machine according to each preceeding claim, that also comprises a rotating valve plate to feed and exhaust the hydraulic fluid, characterized in that this valve plate (31, 52) - coaxial with the shaft - is connected to that ex- centric cam so that the upper dead point of that cam is always radially in line with the dead point of that valve plate.

10. Machine according to claim 1 characterized in that the machine is a pump.

11. Machine according to claim 1 characterized in that the machine is a motor.

12. Device compound of a machine according to claim 10 and a machine according to claim 11, in which the pump and the motor are linked together with pipeline in such a way to constitute a hydraulic transmission.

13. Device compound of a machine according to claim 10 and a machine according to claim 11 in which the pump and the motor are mechanically linked togehter in such a way to constitute a hydrostatic torque convertor or a variable speed hydrostatic drive.

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