|
(11) | EP 0 790 389 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
|
|
|
|
|||||||||||||||||||
| (54) | A rotary positive displacement fluid machine |
| (57) A fluid machine includes: a casing (1) with internal cavity (2), and axis (3), about
which the cavity (2) is symmetrical and two sections (4, 4a), respectively for the
infeed into and discharge from the cavity (2) of the fluid; a pair of vanes (5, 6),
positioned in the cavity (2) in such a way that they divide it into a corresponding
pair of separate chambers (7, 8) designed to alternately receive and discharge the
fluid. The vanes (5, 6) are mounted in the casing (1): in such a way that they can
turn about the axis (3), and independently, so that one (5, 6) moves relative to the
other (6, 5) to cause a corresponding variation in the volumes of the chambers (7,
8) between them. The machine (20) includes drive means (21, 12a, 12b, 14a, 14b) designed
to cause the vanes (5, 6) to turn at a cyclically variable speed, and being timed
differently for each of the vanes (5, 6) so as to cause variations in the volumes
of the chambers (7, 8) suited to the changes in state of the fluid. |
[0001] The present invention relates to a rotary positive displacement fluid machine for general use as a motor, pump, compressor or suction pump. As is widely known, fluid machines are machines in which mechanical energy is mainly processed by means of forces applied to a compressible fluid (gas or vapour) or incompressible fluid (liquid).
[0002] Positive displacement machines represent a category within this general technical sector. In positive displacement machines, the fluid acts statically upon the mobile walls of vessels with variable volumes which the fluid alternately fills and from which it is then emptied.
[0003] The present invention relates to a rotary positive displacement fluid machine of the type which includes: (a) a casing with internal cavity, an axis about which the cavity is symmetrical and two sections, respectively for the infeed and discharge of the fluid in the cavity and (b) at least one pair of vanes, mounted inside the cavity in such a way as to divide it into a corresponding pair of separate chambers, designed to alternately receive and discharge the fluid. The configurations of several such machines are generally known, in particular pumps and compressors, in which the variability of the volumes of the said chambers is obtained by the eccentric installation, in the cavity, of a rotor with radial vanes. More particularly, the rotor is fitted so that it is tangent to a generatrix of the casing and the vanes are contained in radial slots in the rotor.
[0004] When the rotor turns, the vanes protrude from the slots due to centrifugal force and, making contact with the internal surface of the casing, together with the rotor and casing itself they delimit the chambers which hold the fluid.
[0005] The relative sliding of the vanes along the slots and scraping of the ends of the vanes against the surface of the casing involve a high level of wear and source of noise which are amongst the disadvantages of such machines.
[0006] Other disadvantages are caused by the fact the compression ratio is adjusted by varying the eccentricity of rotor mounting. This, on one hand, means that the configuration of the adjustment system is complex (where present) and, on the other hand, the existence of precise configuration limitations (maximum eccentricity value possible) upon which the performance of the machine depends.
[0007] The aim of the present invention is to provide a machine of the afore-mentioned type, in which the said disadvantages are overcome.
[0008] According to the present invention, this aim is achieved with a machine:
- in which the vanes are mounted in the casing, in such a way that they can turn about the axis of symmetry of the cavity and independently, so that they move relative to one another in such a way as to correspondingly vary the volumes of the chambers between the vanes; and including:
- drive means designed to cause the vanes to turn about an axis, having a speed which varies cyclically and being timed separately for each vane, so as to determine the variations in the volumes of the chambers suitable for the changes in state required of the fluid between the infeed and discharge sections.
[0009] The technical specifications of the machine, in accordance with the afore-mentioned aims, are described in the claims herein and their advantages are clearly described in the following description, with reference to the accompanying drawings, which show a preferred embodiment of the present invention, and in which:
- figure 1 is a schematic cross-section of the casing on the machine disclosed, with the vanes in a first typical operating position;
figure 2 is a view similar to that in figure 1, in which the vanes are shown in a second typical operating position;
figure 3 is a cross-section of figure 1, along the line III - III and in particular illustrates the vane drive means envisaged;
figure 4 is a plan view showing several details of the drive means in figure 3, with some parts cut away to better illustrate others;
figure 5 shows a detail of a machine vane;
figures 6 and 7 are cross-sections illustrating a first embodiment of a machine according to the invention disclosed, used as a pump for an incompressible fluid and represented with the vanes in the typical positions corresponding to those in figures 1 and 2;
figures 8 and 9 are cross-sections illustrating a second embodiment of a machine according to the invention disclosed, used as a compressor or suction pump for a compressible fluid.
[0010] In accordance with the accompanying drawings, and in particular figures 1 and 2, the numeral 20 is used to indicate as a whole a fluid machine which basically consists of a cylindrical casing 1, closed by two covers 25, 26, and having an internal cavity 2, which is symmetrical about a horizontal axis 3 and communicates with the external environment through two sections 4, 4a (see figures 6, 7, 8, 9) of the casing 1, respectively for the infeed and discharge of the fluid in the cavity 2.
[0011] A pair of vanes 5, 6 is mounted inside the casing 1. The vanes are rigidly fixed to the ends of two coaxial shafts 10, 11, attached to one another in such a way that they can turn and aligned on the axis 3 of the cavity 2 (see figures 3 and 5).
[0012] The vanes 5, 6 protrude crosswise to the axis 3 towards the internal surface la of the casing 1 and their free ends 5a, 6a make contact with the internal surface la of the casing 1, against which they form a seal against the fluid. The vanes 5, 6, together and with the casing 1, divide the cavity 2 into a pair of opposite, complementary chambers 7, 8 which are not inter-communicating.
[0013] Figure 3 in particular shows that the vanes 5, 6 are mounted in the casing 1 in such a way that they can turn about an axis 3 and are independent of one another, so that they move relative to one another about the axis of rotation 3. This allows (see figures 1 and 2) variations in the volumes of the chambers 7,8 located between the vanes 5, 6 according to the specific operating requirements of the machine 20, as is more clearly indicated in the following description.
[0014] The vanes 5, 6 are driven by specific means which include (see figures 3 and 4) two pairs Ea and Eb of identical elliptic gears 12a, 12b, 14a, 14b, reciprocally meshing in pairs.
[0015] Two first gears 12a, 14a of each pair Ea, Eb are fitted on a shared drive shaft 21, which is keyed to the gears 12a, 12b at one of the two focal points of the primitive ellipse of the said gears 12a, 14a.
[0016] The second two gears 12b, 14b of each pair Ea, Eb are rigidly keyed to the shafts 10, 11 which transmit the rotation to the vanes 5, 6. Again (see figure 4) the gears 12b, 14b are keyed to the shafts 10, 11 at one of the focal points of the primitive ellipse.
[0017] Figure 3 in particular shows that the two pairs Ea, Eb of elliptic gears 12a, 12b, 14a, 14b are fitted so that the respective first gears 12a, 12b (driving gears) are keyed to the drive shaft 21 in such a way that they are offset by 180°.
[0018] The drive means 12a, 12b, 14a, 14b described above cause the vanes 5, 6 to turn about the axis 3 of the cavity 2, having a speed which varies cyclically and being timed separately for each vane 5, 6.
[0019] In other words, the vanes 5, 6 move with a speed which varies cyclically and which is identical for both vanes 5, 6 but offset so that during a full turn of the vanes 5, 6 the said vanes 5, 6 periodically move towards and away from one another in a circle inside the casing 1 (see figures 1 to 9).
[0020] These relative movements of the vanes 5, 6 are necessary to determine the variations in the volumes of the chambers 7, 8 suitable for the changes in state which the fluid must assume between the initial and final states which correspond to the existing (or desired) thermodynamic conditions in the infeed and discharge sections 4, 4a of the machine 20.
[0022] The vanes 5 and 6 (see figures 1 and 2), rigidly fixed to the two respective hubs 27, 28 which are integral with the shafts 10, 11 (see figure 3) turn inside the cylindrical casing 1 about the same axis 3, creating a seal: on the hubs 27, 28 against the surface of the casing 1 and against the two covers 25 and 26 (see figure 3) which close the casing 1.
[0023] As indicated, this configuration allows the creation of two chambers 7, 8 delimited by: the internal surface la of the casing 1, the two covers 25, 26, the two hubs 27, 28 and the two vanes 5, 6. For the machine 20 to function, a variation in the volumes of the two chambers 7, 8 must be obtained (as one increases, the other is reduced), and, as a result, the fluid is acted upon mechanically. This is obtained by making the vanes 5, 6 turn at relative speeds, meaning that they must turn at different speeds. However, given that, for obvious geometric reasons, the vanes 5, 6 must both simultaneously complete a full 360° turn, to avoid impact with one another, they must turn at variable speeds.
[0024] In this way, although they complete a full turn in the same amount of time, they simultaneously cover different angles within the said round angle. As a result, while the average rotation speed of the vanes 5, 6 is constant, the instantaneous speeds are variable in time.
[0025] Figure 1 shows two points labelled H and K (dead centres) at which the two vanes 5, 6 have the same rotation speed. However, at the said points H, K (considering, for example, a clockwise turn of the vanes 5, 6) vane 6 is decelerating whilst vane 5 is accelerating. Once it has passed point H, vane 6 continues to slow until it reaches the minimum speed at X (see figure 2), then begins to accelerate towards point K. In contrast, vane 5, having passed point K, continues to accelerate until it reaches the maximum speed at Y, then begins to slow after passing that point and as it approaches point H. When vane 5 reaches point H, vane 6 reaches point K and while both again turn at the same instantaneous speed, a half-cycle is completed. In short, the two vanes 5, 6 follow one another, moving towards and away from each other twice per turn; always turning at the same speed when at points H and K and, when one reaches the minimum speed at X the other reaches the maximum speed at Y.
[0026] It should be noticed that, having divided the round angle into two angles R and S (see figure 1), while the slow vane passes through the circular sector relative to angle R, the fast vane covers the sector relative to angle S.
[0027] Once per turn, both chambers 7, 8 reach their maximum volume Cmax and minimum volume Cmin, corresponding to the representation of the said chambers 7 and 8 in figure 1.
[0028] The work per turn obtained by this mechanical movement, that is to say, the fluid displacement, is equal to the variation in the volumes of the two chambers = 2xCmax - Cmin. The Cmax/Cmin ratio defines the difference in pressure between the two chambers 7, 8. If one of the vanes 5, 6 is seen as if on a system of co-ordinates, it is evident that, on one side, the second vane 6 or 5 moves away, and on the other, the remaining vane simultaneously moves towards it along a circular arc subtended by a centre angle equal to S - R, then the motion is inverted as soon as the vanes arrive at the points marking the end of stroke (points H and K). If the said circular arc is developed along a straight line, the result is an alternating motion whose stroke is equal to the length of the said arc, as for a double action piston.
[0029] This variable-speed rotary motion can be obtained mechanically in various ways. A preferred embodiment, indicated by way of example only and without limiting the application of the present invention, can be obtained with four identical elliptic gears 12a, 12b, 14a, 14b arranged in two pairs Ea, Eb (see figure 4) turning about a focal point F of the primitive ellipse. With such a configuration, the centre-to-centre I between the two pairs of gears 12a, 12b or 14a, 14b is constant, and the two gears 12a, 12b or 14a, 14b complete the same number of turns, although the gear ratio is variable within the 360° arc.
[0030] The pair of gears 12a, 12b which drives vane 5 is labelled Ea (see figure 3), and the pair of gears 14a, 14b which drives vane 6 is labelled Eb, and in both pairs Ea, Eb, the driving gear 12a, 14a turns at a constant speed and the driven gear 12b, 14b turns at a variable speed.
[0031] In figure 3, vane 6 is represented in the position corresponding to point X in figure 2, where the rotation speed is at its minimum. It may be noticed that the pair of elliptic gears Eb is at the point where the turns of shaft 21 have been reduced to the minimum; whilst, at the same time, vane 5 is in the position Y of maximum rotation speed: it may be noticed that its pair of elliptic gears Ea is at the point where the turns of shaft 21 have been increased to the maximum.
[0032] Since the two driving gears 12a, 14a are offset by 180°, the major axis/minor axis ratio of the primitive ellipse of the said gears 12a, 14a is correlated with the value of angles R and S (see figure 1), and so also with the Cmax-Cmin value, that is to say, the displacement of the machine 20. If this ratio is increased, the value of angle R is reduced, and as a result Cmax-Cmin is increased. Therefore, the displacement is increased with the same number of turns. At the same time, Cmax/Cmin, i.e.: the difference in pressure between the two chambers 7, 8, increases. Obviously, if any actual work (in terms of displacement and pressure) is to be obtained, the two chambers 7, 8 must be able to come into contact with the environment outside the cylindrical casing 1 through the infeed and discharge sections 4, 4a which, in figures 6, 7, 8 and 9 are shown as corresponding holes.
[0033] According to the shape and position of the said infeed and discharge sections 4, 4a and the shape given to the vanes 5, 6, the machine 20 may operate both as a driving machine or a machine in itself, becoming either a pump or a compressor/suction pump, depending whether or not the fluid is compressible.
[0034] To obtain a pump (see figures 6, 7) the two holes 4, 4a, one for infeed and the other for discharge of the liquid pumped, must be precisely positioned close to the two dead centres H and K of the vanes (see figure 6).
[0035] Given that at these points the vanes 5 and 6 turn at the same instantaneous speed, their relative speed is zeroed and, therefore, there is no difference in the volumes of the two chambers 7, 8, as is necessary for the changes in an incompressible fluid such as a liquid. At this point, both vanes 5, 6 must be positioned exactly in front of the two holes 4, 4a and close them completely so as to avoid a direct connection between suction and delivery, which would prevent the pumping action.
[0036] In figure 7, the arrows indicate the direction of flow of the liquid for one clockwise turn of the vanes 5, 6. Chamber 7, whose volume is increasing, is the suction chamber, and chamber 8, whose volume is reduced, is the pressing chamber. If the vanes 5, 6 are suitably shaped, it is possible to further reduce the minimum volumes of the chambers 7, 8 (Cmin) (figure 6) which represents the clearance volume. Even if the geometric shape of the vanes 5, 6 created for this purpose also reduces the Cmax, the Cmax-Cmin value (and so also the displacement) remains unchanged. In contrast, the Cmax/Cmin ratio (which has a directly proportional effect on the head at start-up when the pump contains no liquid) increases considerably, so that the pump has a strong self-priming action.
[0037] By fitting the vanes symmetrically about the vertical axis passing through points X-Y (see figure 7), it is possible to obtain a machine which is perfectly symmetrical, completely reversible, and in which the delivery and suction action can be inverted by simply inverting the direction of rotation of the vanes 5, 6.
[0038] To obtain a compressor/suction pump (see figures 8 and 9), the circumference of the fluid infeed section 4 (suction) must be large enough to remain open for the entire expansion of the suction chamber (see figure 9). This allows the entry of the largest possible quantity of fluid (maximising the displacement, with the same number of turns) and, if used as a suction pump, allows the maximum expansion to be obtained, which is transformed into a vacuum.
[0039] In contrast, the circumference of the discharge section 4a (delivery) must be smaller, so that it opens only when the pressing chamber 8 is reduced to the point at which it has generated the desired internal pressure. Therefore, the smaller the discharge section 4a, the greater the output pressure.
[0040] In figure 9, the arrows indicate the direction of flow of the fluid for a clockwise turn. Chamber 7 (suction) is completing its expansion and chamber 8 (pressing) is completing its compression. In this case the vanes 5, 6 must be shaped so that they have circular sectors, so that they also create a seal along the circumference of the casing 1 long enough to maintain the discharge section 4a (delivery hole) closed for the time necessary to obtain the desired pressure (see figure 9). Moreover, the vanes 5, 6 must be shaped so as to reduce the value of the clearance volume to a minimum Cmin (see figure 8) and, finally, must allow the fluid infeed section 4 to open as soon as the volume of chamber 7 (suction) begins to increase, so as to fully exploit the expansion and, therefore, maximise the displacement (if used as a compressor) and vacuum (if used as a suction pump).
[0041] Again, as for the pump, the reduction of Cmin (and, as a result, of Cmax) leaves the Cmax-Cmin value (displacement) unchanged, but considerably increases the Cmax/Cmin ratio which has a directly proportional effect on the head during suction, or on the vacuum which the compressor/suction pump can produce.
1. A fluid machine including: a casing (1) with an internal cavity (2), an axis about
which the cavity (2) is symmetrical and two sections (4, 4a) respectively for the
infeed into and discharge from the cavity (2) of the fluid; at least one pair of vanes
(5, 6), these being mounted inside the cavity (2) in such a way as to divide it into
a corresponding pair of separate chambers (7, 8) designed to alternately receive and
discharge the fluid, characterised in that the vanes (5, 6) are fitted on the casing
(1) in such a way that they can turn independently about the axis (3), so that one
(5, 6) moves relative to the other (6, 5), causing a corresponding variation in the
volumes of the chambers (7, 8) between them, and also characterised in that it includes
drive means (21, 12a, 12b, 14a, 14b), these being designed to cause the vanes (5,
6) to turn, said means having a cyclically variable speed and being timed differently
for each of the vanes (5, 6) so as to cause changes in the volumes of the chambers
(7, 8) suited to the changes in the fluid between the infeed and discharge sections
(4, 4a).
2. The machine as described in claim 1, characterised in that it includes coaxial shafts
(10, 11) which are attached to one another in such a way that they can turn, and to
which the said vanes (5, 6) are rigidly fixed.
3. The machine as described in claim 1, characterised in that the said drive means are
designed to cause each vane (5, 6) to move with one maximum rotation speed and one
minimum rotation speed per turn.
4. The machine as described in claim 2, characterised in that the speeds of the vanes
(5, 6) are offset by 180°, this being intended to create a condition such that when
one of the vanes (5, 6) reaches the maximum rotation speed, the other (6, 5) reaches
the minimum rotation speed, and vice versa.
5. The machine as described in claim 1, characterised in that the said drive means include
two pairs of elliptic gears (12a, 12b, 14a, 14b), each of the two gears in the pairs
engaging with one another, and being attached to a drive shaft (21) and the vanes
(5, 6) respectively.
6. The machine as described in claim 5, characterised in that the said pairs of elliptic
gears (12a, 12b, 14a, 14b) are fitted so that they mesh in such a way that the two
driving gears (12a, 14a) are offset by 180°.
7. The machine as described in claim 1, characterised in that the vanes (5, 6) are positioned
symmetrically about an axis of symmetry (X-Y) of the casing (1).