VARIABLE DELIVERY ROTARY VANE PUMP

TECHNICAL FIELD

The present invention relates to a variable delivery rotary vane pump of the type comprising a pump body closed by a lid, a stator and a rotary unit which comprises, in turn, a rotor and a plurality of vanes.

BACKGROUND ART

In conventional applications, the contact between the head of the vanes and the stator, and thus the sealing between the various vane chambers of the pump, is ensured by the centrifugal force alone to which the vanes are subjected during rotation. As a consequence, at a low number of revolutions, when the centrifugal force is low, leakages of fluid occur between one vane chamber and those contiguous thereto, thus lowering the volumetric efficiency of the pump. On the contrary, at a high number of revolutions, the centrifugal force is high and therefore the contact between the head of the vanes and the stator occurs under a considerable force which implies an increase of wear of the head of the vanes and a decrease of mechanical efficiency of the pump due to the energy lost by contact friction.

Furthermore, again in the vane pumps of conventional type, the relative motion between vanes and rotor is essentially of translational type and occurs by sliding the vanes in specific radial grooves obtained on

the rotor, thus providing a prismatic type coupling . As known, such type of coupling is often subject to seizing especially when solid particles due, for example, to impurities present in the fluid processed by the pump, interpose between the relative sliding surfaces. If the relative sliding between vanes and rotor is not smooth, anomalous wear of the components and even seizing of the rotary pump itself may easily occur. DISCLOSURE OF THE INVENTION In order to avoid the aforesaid problems, in the pump object of the present invention, the relative translational motion between vanes and rotor is replaced by a rotary motion about a cylindrical hinge made on the external surface of the rotor itself. In this manner, the prismatic coupling between vane and rotor is replaced by a rotary type coupling which, due to its nature, is less affected by undesired effects, .such as seizing.

Again in the pump object of the present invention, the vanes, fed by the rotor, move maintaining the external surface of their head in contact with a cylindrical ring placed inside the rotor, like a tappet on a cam. Since the surface of the vane head is cylindrical and the surface of the cam is also cylindrical, consequently the heads of the vanes, during their motion, have as envelope surface two cylindrical surfaces, one of which is indeed the cylindrical ring

placed inside the rotor and the other constitutes the external surface of the stator. In this manner, the maximum working clearance between the head of the vanes and the stator depends only on the manufacturing tolerance of the components and not on the centrifugal force, the effect of which, being no longer necessary to ensure the sealing between the vane chambers, may be limited thus forming the vanes of light material, as such of plastic for example. The present invention thus implements a variable delivery rotary vane pump according to the features claimed in claim 1.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to the accompanying drawings which illustrate a non - limitative embodiment thereof, in which:

- figures Ia - Id diagrammatically show a variable delivery vane pump object of the present invention;

- figures 2a - 2c relate to a first element (not in scale) of the pump object of the present invention;

- figures 3a - 3c relate to a second element (not in scale) of the pump object of the present invention;

- figures 4a - 4b relate to a third element (not in scale) of the pump object of the present invention; - figure 5 relates to a fourth element (not in scale) of the pump object of the present invention; figure 6 relates to a fifth element (not in

scale) of the pump object of the present invention;

- figures 7a - 7d relate to a sixth element (not in scale) of the pump object of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION In the accompanying figures, numeral 10 indicates as a whole a rotary pump object of the present invention.

Such rotary pump 10 comprises (figures Ia - Id) a hollow pump body 11 (figures 7a - 7d) ; an adjustable stator 13 (figures 4a - 4b) ; a rotor 14 (figures 2a -

2c); a plurality of swinging vanes 16 (figures 3a - 3c); a rotor 14 (figure 5); a toothed adjustment rod 17

(figure 6); a helical spring 18; a cap 19; and a lid 12 which, fixed by means of four screws 20, closes the hollow pump body 11. • • '

The swinging vanes 16 are rotationally fed by the rotor 14 by means of cylindrical pins 21, according to methods which will be described below, and perform the desired pumping action on the fluid. As shown more in detail in figures 7a - 7d, the hollow pump body 11 is essentially a prismatic body which presents a cylindrical cavity lip, the flat surface Hq of which is crossed by a through hole Hc.

Furthermore, the cylindrical cavity Hp is adapted to accommodate the adjustable stator 13 so that, except for clearances, the rotation axis X of the adjustable stator 13 (figures 4a - 4b) coincides with the axis φ

of the hollow pump body 11.

The through hole lie is adapted to accommodate a cylindrical body 14d of the rotor 14 (see below) so that, except for clearances, a rotation axis ω of the rotor 14 (figures 2a - 2c) coincides with an axis σ of the hollow pump body 11.

The fixed distance between the two axes φ and σ is indicated by ^« e*" and serves to vary the working eccentricity "e" of the rotary pump 10. Again on the flat surface Hq, there are obtained two through slots which represent a delivery cavity Hf and a suction cavity He of the rotary pump 10, respectively; i.e. they are the two cavities through which the rotary pump 10 takes in and discharges the working fluid, respectively. ^'

A blank hole Hd is adapted to accommodate the toothed adjustment rod 17 (figures Ia, Ib, 6) and is closed by the cap 19 driven into the blank hole Hd itself. A groove Hg puts the delivery cavity Hf into communication with a pit Hh which, in turn, by means of a slot Hi carries the pressurized fluid into the blank hole Hd on the side of a surface Ht.

On the opposite side of the pit Hh, a groove Hb puts a blank hole Hd into communication with the suction cavity He. In such manner, the pressure difference of the fluid may act on two surfaces 17d and

17e of the toothed adjustment rod 17. Some threaded through holes 11m are adapted to accommodate the screws 20 which fix the lid 12 so as to mate with a surface Hn and thus close the rotary pump 10. As shown more in detail in figures 4a - 4b, the adjustable stator 13 is essentially a plate, the external cylindrical surface 13c of which is interrupted by a toothed profile 13a adapted to couple with a toothed segment 17c of the toothed adjustment rod 17, while it presents a cylindrical through hole 13b inside, not in axis with the external surface.

Hereinafter, X indicates the axis of the external cylindrical surface 13c, while Y indicates the axis of an internal cylindrical surface 13d. The fixed distance between the two axes X and Y is equal, except for manufacturing tolerances, to the distance between the axes φ and σ of the hollow pump body 11 and therefore will also be indicated by "e*". When the rotary pump 10 is assembled, a flat surface 13e works in contact with the flat surface Hq of the hollow pump body 11, while the external cylindrical surface 13c works in contact with the cylindrical cavity Hp of the hole of the hollow pump body 11 so that the axis X coincides, except for clearances, with the axis φ of the hollow pump body 11.

As shown more in detail in figures 3a - 3c, the swinging vanes 16, in a non - binding number, consist of

a shank 16b and a ^' cylindrical head lβa cut by a surface

16g, also cylindrical, having axis δ. The cylindrical surface lβg divides the cylindrical surface 16c into two parts, named 16c' and 16c''. A cylindrical hole 16e materializes the axis δ and engages a cylindrical pin 21

(figures Ia - Id, 2) allowing the swinging vanes 16 to rotate freely about said axis δ.

In this manner, the cylindrical surface lβg forms with a surface 14e of the rotor 14 (figures Ia - Id) a narrow gap which limits the leakages of fluid, as a cylindrical surface Iβd, also having the same axis δ, forms with the surface 14m of the rotor 14 a narrow gap which also limits the leakages of fluid.

When the rotary pump 10 is assembled, except for clearances, the surface part 16c'' works in contact with an internal cylindrical surface 13d of the cylindrical through hole 13b of the adjustable stator 13 (figures 4a - 4b) , while the surface part 16c ' works in contact with the external cylindrical surface 15a of a central ring 15 (figure 5) so that the axis Z of the rotor 14 coincides, again except for clearances, with the axis Y of the cylindrical through hole 13b of the adjustable stator 13. As shown more in detail in figure 5, a central ring 15 is a ring one cavity 15b of which allows the drive shaft (not shown in the accompanying figures) to pass through the rotary pump 10.

Furthermore, the external cylindrical surface 15a

indeed constitutes the profile of the cam which determines the lift rule of the tappets represented by the swinging vanes 16 fed in motion by the rotor 14 by means of the cylindrical pins 21. As shown more in detail in figure 6, the toothed adjustable rod 17 is essentially a cylindrical element in the central part of which there is obtained a toothed segment 17c adapted to mesh with the toothed profile 13a of the adjustable stator 13. Such adjustable toothed rod 17 is inserted in the mentioned blank hole Hd of the hollow pump body 11 resting on two cylindrical surfaces Hr and Hs.

The surface 17a always works in contact with the contrast spring 18, while the surface 17d remains in contact with the surface lit of the blank hole Hd only until the forces exerted by the pressure difference between the surfaces 17d and 17e and the adjustable stator 13, by means of the toothed segment 17c, can overcome the preload of the contrast spring 18. As shown more in detail in figures 2a - 2c, the rotor 14 essentially comprises the cylindrical body 14d and some appendixes 14b of equal number to that of the swinging vanes 16.

Furthermore, the cylindrical body 14d presents a through hole 14g adapted to accommodate and transmit the torque of the drive shaft (not shown on the accompanying drawings ) .

Each appendix 14b presents a cylindrical hole 14i and a small column 14f. The cylindrical hole 14i accommodates therein the cylindrical joint pin 21 of the swinging vanes 16 so that, except for clearances, the rotation axis δ of the swinging vane 16 coincides with the axis π of the cylindrical hole 14i; the surface 14e of the small column 14f is a cylindrical surface of axis π and serves to form with the cylindrical surface lβg of the swinging vane 16 a narrow gap which limits the leakages of fluid.

The surface 14m of the small column 14f is also a cylindrical surface of axis Il and serves to form with the cylindrical surface lβd of the swinging vane 16 a narrow gap which also limits the leakages of fluid. When the rotary pump 10 is assembled, a surface 14c comes into contact with the flat surface Hq of the cylindrical cavity Hp of the hollow pump body 11, while the cylindrical body 14d is inserted in the through hole Hc of the hollow pump body 11 so that, except for clearances, the rotation axis ω of the rotor 14 coincides with the rotation axis σ of the hollow pump body 11 (figures Ia - Id) .

The operation of the rotary pump 10 object of the present invention will be described below with reference to the accompanying figures .

The rotor 14 is put into rotation by the drive shaft by means of the surfaces of the through hole 14g.

The rotor 14, in turn, feeds the swinging vanes 16 by means of the cylindrical pins 21.

In the rotary motion, except for clearances, the cylindrical head 16a of the swinging vanes 16 remains in contact, on the side where the surface 16c' lies, with the external cylindrical surface 15a of the central ring 15a and, on the side where the surface 16c '' lies, with the internal cylindrical surface 13d of the adjustable stator 13. The surface 14e of the rotor 14 forms with the cylindrical surface lβg of the swinging vane 16 a narrow gap which limits the leakages of fluid, as the surface 14m of the rotor 14 forms with the cylindrical surface 16d of the swinging vane 16 a narrow gap which also limits the leakages of fluid. In this manner, the internal cylindrical surface 13d of the adjustable stator 13, the rotor 14 and the swinging vanes 16 delimit a number of vane chambers equal to the number of vanes . During the rotary motion of the rotor 14, the distance between the rotation axes ω of the rotor 14 and Y of the adjustable stator 13 defines the working eccentricity "e" of the rotary pump 10 and determines the volume variation of the vane chambers according to well known rules.

Specifically, during an entire revolution of the rotor 14 the volume of each vane chamber will vary from

a minimum value to a maximum value.

In fact, when during the rotation of the rotor 14 the volume of the vane chambers increases, then the vane chambers are facing the suction cavity lie of the hollow pump body 11 and, therefore, the rotary pump 10 takes the fluid in; on the other hand, when the volume decreases, then the vane chambers are facing the delivery cavity Hf of the hollow pump body 11 and thus the rotary pump 10 sends the fluid towards a user device (not shown) .

The suction cavity lie is always apart from the delivery cavity Hf for two segments of arc needed to prevent the fluid from going back from the delivery cavity Hf into the suction cavity He due to the difference -of pressure between the two environments, thus short - circuiting the rotary pump 10.

The surface 17d of the toothed adjustment rod 17 remains in contact with the surface Ht of the cylindrical hole Hd of the hollow pump body 11 until the forces exerted by the pressure difference between the surfaces 17d and 17e and by the adjustable stator 13, by means of the toothed sector 17c, can overcome the preload of the contrast spring 18, then the toothed adjustment rod 17 slides along the blank hole Hd making the adjustable stator 13 rotate about the axis X.

The rotation of the adjustable stator 13 varies the position of the axis Y of the cylindrical through hole

13b with respect to the rotation axis ω of the rotor 14, so that the working eccentricity "e" of the rotary pump 10 and thus, retroactively, the fluid flow output from the delivery cavity Hf are reduced. When the rotary pump 10 runs at minimum number of revolutions, the working eccentricity "e" is maximum. As the revolution rate increases, the flow rate delivered by the rotary pump 10 and, consequently, the pressure of the fluid, increase according to well known rules. The pressure increase of the fluid determines a reduction of the working eccentricity *e" of the pump and, consequently, a decrease of the delivered flow. In this manner, it is avoided to waste pumping action on a part of the fluid which, otherwise, should be somehow bypassed as occurs in conventional pumps which do not vary the delivery. With this operating method, considerably higher efficiencies of the rotary pump 10 than those of the known rotary pumps are obtained.

The advantages of the present variable delivery rotary vane pump are :

- high efficiency at low numbers of revolutions, in virtue of the fact that the sealing of the pumping vane chambers is no longer assigned to the centrifugal force as in the known constructions; - reduction of the wear problem of the vane heads in contact with the stator;

- reduced radial volume of the vanes in virtue of

which the pump may be mounted in axis with the drive shaft;

- ease of construction of the device which allows the stator movement; - optimization of the contact between the profile of each vane and the corresponding seat for the entire field of variation of the eccentricity; and

- simplicity of shape and thus of construction of the profiles provided with relative sliding motion.

LIST OF REFERENCE NUMBERS:

10 - rotary pump

11 - hollow pump body lib - groove lie - through hole

Hd - blank hole

He - suction cavity

Hf - delivery cavity

Hg - groove Hh - pit

Hi - slot

Hm - threaded through holes

Hn - surface

Hp - cylindrical cavity Hq - flat surface

Hr - surface

Hs - surface

lit - surface

12 - lid

13 - adjustable stator 13a -. toothed profile 13b - cylindrical through hole

13c - external cylindrical surface 13d - internal cylindrical surface 13e - flat surface

14 - rotor 14b - appendixes

14c - surface

14d - cylindrical body

14e - surface

14f - small column 14g - through hole

14i - cylindrical hole

14m - surface

15 - central ring

15a - external cylindrical surface 15b - cavity

16 - swinging vanes 16a - cylindrical head 16b - shank

16c - cylindrical surface 16c' - surface part 16c'' - surface part 16d - cylindrical surface

lβe - cylindrical hole 16g - cylindrical surface

17 - toothed adjustment rod 17c - toothed segment 17d - surface 17e - surface

18 - spring

19 - cap

20 - screw 21 - cylindrical pin