U.S. patent application number 14/652927 was filed with the patent office on 2015-11-12 for variable displacement vane pump and method of regulating the displacement thereof.
The applicant listed for this patent is VHIT S.P.A.. Invention is credited to Leonardo CADEDDU, Matteo CALDERONI.
Application Number | 20150322944 14/652927 |
Document ID | / |
Family ID | 47749969 |
Filed Date | 2015-11-12 |
United States Patent
Application |
20150322944 |
Kind Code |
A1 |
CALDERONI; Matteo ; et
al. |
November 12, 2015 |
VARIABLE DISPLACEMENT VANE PUMP AND METHOD OF REGULATING THE
DISPLACEMENT THEREOF
Abstract
A variable displacement rotary vane pump for fluids is provided
where displacement regulation is achieved thanks to the variation
of the relative eccentricity between a regulation ring (11) in
which a rotor (13) is arranged and the rotor itself. In a region of
engagement between the external surface (11A) of the regulation
ring (11) and the internal surface (40A) of a chamber (40) inside
which the regulation ring (11) moves, a plurality of rolling
elements (25), mounted in fixed position, is provided. The rolling
elements (25) are provided only over a portion of such a region of
engagement, including a zone (S) where a resultant of mechanical
and fluidic forces generated in the pump during the regulation
acts. A method of regulating the displacement of such a pump is
also disclosed.
Inventors: |
CALDERONI; Matteo;
(Offanengo (CR), IT) ; CADEDDU; Leonardo;
(Offanengo (CR), IT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
VHIT S.P.A. |
Offanengo (cr) |
|
IT |
|
|
Family ID: |
47749969 |
Appl. No.: |
14/652927 |
Filed: |
December 13, 2013 |
PCT Filed: |
December 13, 2013 |
PCT NO: |
PCT/IB2013/060918 |
371 Date: |
June 17, 2015 |
Current U.S.
Class: |
418/1 ;
418/22 |
Current CPC
Class: |
F04C 15/0088 20130101;
F01C 21/106 20130101; F04C 14/223 20130101; F04C 2240/50 20130101;
F04C 2/344 20130101 |
International
Class: |
F04C 14/22 20060101
F04C014/22; F04C 15/00 20060101 F04C015/00; F04C 2/344 20060101
F04C002/344 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 27, 2012 |
IT |
TO2012A001149 |
Claims
1. A variable displacement rotary vane pump for fluids, comprising:
a rotor (13) arranged to eccentrically rotate within a regulation
ring (11) with a relative eccentricity which varies depending on
operating conditions of the pump (1); means (17, 18) for moving the
regulation ring (11) in a chamber (40) formed in a pump body (10)
in order to vary said relative eccentricity, and hence the
displacement of the pump, as said operating conditions vary; and a
plurality of rolling elements (25) interposed between an external
surface (11A) of the regulation ring (11) and an internal surface
(40A) of the chamber (40); characterised in that: the rolling
elements (25) are mounted in a supporting cage (26) and are
provided only over a portion of a region of engagement between the
external surface (11A) of the regulation ring (11) and the internal
surface (40A) of the chamber (40), said portion including a zone
(S) where a resultant (SV1, SV2) of mechanical and fluidic forces
generated in the pump during the regulation acts; and the rolling
elements (25) and said supporting cage (26) are arranged, in said
portion of the region of engagement between said surfaces (11A,
40A), so as to move as an integral body along said surfaces (11A,
40A) during the movement of the regulation ring (11), the movement
of the rolling elements (25) and of the supporting cage (26) having
a smaller amplitude than a movement performed by the regulation
ring (11) in order to make the pump pass from a maximum
displacement to a minimum displacement.
2. The pump as claimed in claim 1, wherein the regulation movement
is a rotation of the regulation ring (11) and wherein: in said
portion of the region of engagement, the external surface (11A) of
the regulation ring (11) and the internal surface (40A) of the
chamber (40) form, together with the rolling elements (25), a
sector of a rolling bearing of which said surfaces form sectors of
an inner race and an outer race, respectively; and the rolling
elements (25) are arranged within a seat (28) formed in the surface
(11A) of the regulation ring (11) and having a greater extension
than the supporting cage (26) in which the rolling elements (25)
are mounted.
3. The pump as claimed in claim 2, wherein the supporting cage (26)
is arranged to move in said seat, thereby moving the rolling
elements (25), against the action of an opposing resilient member
(30), which is arranged between one end of the cage (26) and one
end (29B) of the seat (28) and is capable of keeping or bringing
again the cage (26) in contact with an opposite end (29A) of the
seat (28) in the maximum displacement condition of the pump.
4. The pump as claimed in claim 3, wherein the rolling elements
(25) are mounted in the supporting cage (26) so as to give it a
labyrinth configuration arranged to maintain a fluidic support
bearing generated in said zone (S) as a reaction to the action of
the resultant (SV1, SV2) of said forces.
5. The pump as claimed in claim 4, wherein the rolling elements
(25) are rollers or needles, and wherein the supporting cage (26)
has an axial depth substantially corresponding to an axial depth of
the regulation ring (11) and the rollers or needles (25) have a
length shorter than the axial depth of the cage (26).
6. The pump as claimed in claim 1, wherein the rotation of the
regulation ring (11) is directly controlled by the pressure of the
pumped fluid.
7. The pump as claimed in claim 1, wherein the pump is a pump for
the lubrication circuit of a motor vehicle engine.
8. A method of regulating the displacement of a rotary variable
displacement pump for fluids, of a kind comprising a rotor (13)
arranged to eccentrically rotate within a regulation ring (11) with
a relative eccentricity that is variable depending on operating
conditions of the pump (1), the method comprising the steps of:
providing, between an external surface (11A) of the regulation ring
(11) and an internal surface (40A) of a chamber (40) housing the
ring (11), a plurality of rolling elements (25) mounted in a fixed
relative position; and making the regulation ring (11) move in the
chamber (40) in order to vary said relative eccentricity, and hence
the displacement of the pump, as said operating conditions vary;
and being characterised in that the step of providing rolling
elements (25) in the chamber (40) comprises the steps of: providing
the rolling elements (25) mounted in a supporting cage (26) only
over a portion of a region of engagement between the external
surface (11A) of the regulation ring (11) and the internal surface
(40A) of the chamber (40), said portion including a zone (S) where
a resultant (SV1, SV2) of mechanical and fluidic forces generated
in the pump during the regulation acts; and during the regulation,
making the rolling elements (25) and the supporting cage (26) move
as an integral body in said portion of the region of engagement
between said surfaces (11A, 40A), the movement of the rolling
elements (25) and the supporting cage (26) having a smaller
amplitude than a movement of the regulation ring (11) making the
pump pass from a maximum displacement to a minimum
displacement.
9. The method as claimed in claim 8, wherein the regulation
movement is a rotation of the regulation ring (11) and the step of
providing the rolling elements (25) and the supporting cage (26)
only over a portion of the region of engagement between said
surfaces (11A, 40A) comprises the step of configuring the rolling
elements (25) and the supporting cage (26), the external surface
(11A) of the regulation ring (11) and the internal surface (40A) of
the chamber (40) as a sector of a rolling bearing, of which said
surfaces form circular sectors of an inner race and an outer race,
respectively.
10. The method as claimed in claim 9, wherein the step of making
the rolling elements (25) and the supporting cage (26) move as an
integral body comprises moving the rolling elements (25) and the
supporting cage (26) in a seat (28) formed in the surface (11A) of
the regulation ring (11) and having a greater extension than an
overall extension of said rolling elements (25) and said supporting
cage (26).
11. The method as claimed in claim 8, wherein the step of making
the rolling elements (25) and the supporting cage (26) move as an
integral body comprises moving the rolling elements (25) and the
supporting cage (26) in a seat (28) formed in the surface (11A) of
the regulation ring (11) and having a greater extension than an
overall extension of said rolling elements (25) and said supporting
cage (26).
12. The pump as claimed in claim 2, wherein the rolling elements
(25) are mounted in the supporting cage (26) so as to give it a
labyrinth configuration arranged to maintain a fluidic support
bearing generated in said zone (S) as a reaction to the action of
the resultant (SV1, SV2) of said forces.
13. The pump as claimed in claim 12, wherein the rolling elements
(25) are rollers or needles, and wherein the supporting cage (26)
has an axial depth substantially corresponding to an axial depth of
the regulation ring (11) and the rollers or needles (25) have a
length shorter than the axial depth of the cage (26).
14. The pump as claimed in claim 2, wherein the rotation of the
regulation ring (11) is directly controlled by the pressure of the
pumped fluid.
15. The pump as claimed in claim 1, wherein the supporting cage
(26) is arranged to move in said seat, thereby moving the rolling
elements (25), against the action of an opposing resilient member
(30), which is arranged between one end of the cage (26) and one
end (29B) of the seat (28) and is capable of keeping or bringing
again the cage (26) in contact with an opposite end (29A) of the
seat (28) in the maximum displacement condition of the pump.
16. The pump as claimed in claim 15, wherein the rolling elements
(25) are mounted in the supporting cage (26) so as to give it a
labyrinth configuration arranged to maintain a fluidic support
bearing generated in said zone (S) as a reaction to the action of
the resultant (SV1, SV2) of said forces.
17. The pump as claimed in claim 16, wherein the rolling elements
(25) are rollers or needles, and wherein the supporting cage (26)
has an axial depth substantially corresponding to an axial depth of
the regulation ring (11) and the rollers or needles (25) have a
length shorter than the axial depth of the cage (26).
18. The pump as claimed in claim 15, wherein the rotation of the
regulation ring (11) is directly controlled by the pressure of the
pumped fluid.
19. The pump as claimed in claim 1, wherein the rolling elements
(25) are mounted in the supporting cage (26) so as to give it a
labyrinth configuration arranged to maintain a fluidic support
bearing generated in said zone (S) as a reaction to the action of
the resultant (SV1, SV2) of said forces.
20. The pump as claimed in claim 19, wherein the rolling elements
(25) are rollers or needles, and wherein the supporting cage (26)
has an axial depth substantially corresponding to an axial depth of
the regulation ring (11) and the rollers or needles (25) have a
length shorter than the axial depth of the cage (26).
Description
TECHNICAL FIELD
[0001] The present invention relates to variable displacement
rotary pumps, and more particularly it concerns a pump of a kind in
which displacement regulation is obtained thanks to the variation
of the relative eccentricity between a regulation ring and the pump
rotor, obtained by varying the relative position of the ring and
the rotor depending on the pump operating conditions.
[0002] The invention also concerns a method of regulating the
displacement of such a pump.
[0003] Preferably, but not exclusively, the present invention is
applied in a pump for the lubrication oil of a motor vehicle
engine.
PRIOR ART
[0004] It is known that, in pumps for making lubricating oil under
pressure circulate in motor vehicle engines, the capacity, and
hence the oil delivery rate, depends on the rotation speed of the
engine. Hence, the pumps are designed so as to provide a sufficient
delivery rate at low speeds, in order to ensure lubrication also
under such conditions. If the pump has fixed geometry, at high
rotation speed the delivery rate exceeds the necessary rate,
whereby high power absorption, with consequently higher fuel
consumption, and a greater stress of the components due to the high
pressures generated in the circuit occur.
[0005] In order to obviate this drawback, it is known to provide
the pumps with systems allowing a delivery rate regulation at the
different operating conditions of the vehicle, in particular
through a displacement regulation. Different solutions are known to
this aim, which are specific for the particular kind of pumping
elements (external or internal gears, vanes . . . ). However, some
general kinds of displacement regulation systems can be recognised
and, in case of rotary vane pumps, one system is based on the
variation of the relative position between an external regulation
ring, also known as "stator ring", inside which the rotor
eccentrically rotates, and the rotor itself. A variation of the
relative eccentricity of those components, and hence a variation of
the pump displacement, is thus obtained.
[0006] This kind of regulation is implemented in different ways.
Thus, it is possible to recognise: [0007] pumps where the rotor
causes rotation of the external ring to which the radially outer
ends of the vanes are hingedly connected ("pendulum" pumps); [0008]
pumps where the stator ring can be displaced transversally to the
axis of rotation of the rotor; [0009] pumps where the stator ring
oscillates about an axis external to the same ring; and [0010]
pumps where the stator ring is rotatable about an axis internal to
the same ring and parallel to the axis of rotation of the
rotor.
[0011] In such kinds of pumps, while the stator ring is being moved
in order to vary the displacement, it is necessary to oppose its
movement through means creating antagonist forces and generally
consisting of springs. Such means opposing the movement of the
stator ring generate problems of: [0012] a) vibrations/noise, when
an unstable equilibrium of the forces and the frictions occurs
during the movement; [0013] b) generation of vibrations/pressure
pulsations depending on the fast transients of variation of the
rotation speed and/or of the regulation of the pressure thresholds;
[0014] c) hysteresis of the pressure regulation between the
increase and the decrease of the rotation speed; [0015] d) wear due
to an excessive specific pressure in the area where the stator ring
is supported.
[0016] In order to alleviate such problems, in case of a pump where
displacement regulation is performed through a rotation of the
stator ring, it has already been proposed to interpose rolling
elements between an external surface of the stator ring and an
internal surface of a chamber where the stator ring rotates.
Clearly, by converting the sliding friction into rolling friction,
the resistance to the stator ring rotation, on which hysteresis
depends, is reduced.
[0017] An example is disclosed in U.S. Pat. No. 5,863,189, in which
the external surface of the stator ring and the internal surface of
the chamber form the inner and outer races of an annular roller
bearing, in which the rollers are kept at the same mutual distance
by a suitable annular cage. In this known solution, the cage with
the rollers extends over the whole circumference of said surfaces
and can be actuated only by means of a side lever arm which makes
its construction complex.
[0018] Moreover, the Applicant has realised that an analysis of the
mechanical and fluidic (in particular, hydraulic) forces which are
generated during the pump operation shows that, in the pumps of the
kind considered here, the resultant of such forces acts in a
limited zone of the region of engagement between the external
surface of the stator ring and the internal surface of the chamber
in which the stator ring rotates and, therefore, it is in such a
zone that is necessary to prevent generation of instable
equilibriums or of equilibriums opposing the regulation movement in
important manner.
DESCRIPTION OF THE INVENTION
[0019] It is an object of the present invention to provide a rotary
positive displacement pump with variable displacement of the kind
disclosed above, which obviates the drawbacks of the prior art.
[0020] According to the invention, this is achieved in that: [0021]
the rolling elements are provided only over a portion of a region
of engagement between the external surface of the regulation ring
and the internal surface of a chamber in which the ring moves, said
portion including a zone where a resultant of mechanical and
fluidic forces generated in the pump during the regulation acts and
where a fluidic support bearing is generated due to the effect of
such a resultant; and [0022] the rolling elements are arranged, in
said portion of the region of engagement between said surfaces, so
as to be movable as an integral body along said surfaces during the
regulation movement, the movement of the rolling elements having a
smaller amplitude than a movement performed by the regulation ring
in order to make the pump pass from a maximum displacement
condition to a minimum displacement condition.
[0023] Preferably, the regulation movement is a rotation, the
portion of the region of engagement between the surfaces is
configured as a sector of a rolling bearing of which said surfaces
form sectors of the inner race and the outer race, respectively,
and the rolling elements are arranged within a seat formed in the
external surface of the regulation ring.
[0024] According to another preferred feature of the invention, the
rolling elements are rollers or needles mounted in a supporting and
guiding cage arranged to move in said seat against the action of an
opposing resilient member, which is arranged between one end of the
cage and one end of the seat and is preloaded so as to keep the
cage in contact with the opposite end of the seat in a maximum
displacement or rest condition of the pump.
[0025] The invention also provides a method of regulating the
displacement of a pump of the above kind, comprising the steps of:
[0026] providing a plurality of rolling elements over a portion of
a region of engagement between an external surface of the
regulation ring and an internal surface of a chamber in which the
ring moves for the regulation, such a portion including a zone
where a resultant of mechanical and fluidic forces generated in the
pump during the regulation acts and where a fluidic support bearing
is generated due to the effect of such a resultant; and [0027]
during the regulation movement, making the rolling elements move as
an integral body in said portion of the region of engagement
between said surfaces, the movement of the rolling elements having
a smaller amplitude than a regulation movement making the pump pass
from a maximum displacement condition to a minimum displacement
condition.
BRIEF DESCRIPTION OF THE FIGURES
[0028] The above and other features and advantages of the invention
will become apparent from the following description of a preferred
embodiment, made by way of non limiting example with reference to
the accompanying drawings, in which:
[0029] FIG. 1 is a view showing a vane pump in which the invention
can be applied, without the closure cover and in the maximum
displacement condition;
[0030] FIG. 2 is a view similar to FIG. 1 and shows the same pump
in the minimum displacement condition;
[0031] FIG. 3 shows the magnitudes and the directions of the main
forces intervening during the operation of the pump shown in FIGS.
1 and 2, of their partial resultants and of the overall resultant
in the maximum displacement condition of the pump, at the start of
the displacement regulation;
[0032] FIG. 4 is a view similar to FIG. 1 and shows the magnitudes
and the directions of the forces, of their partial resultants and
of the overall resultant in the minimum displacement condition, at
the end of the displacement regulation;
[0033] FIGS. 5 and 6 show a pump according to the invention, in
maximum and minimum displacement conditions, respectively;
[0034] FIG. 7 is an enlarged isometric view of the roller-carrying
cage shown in FIGS. 5 and 6; and
[0035] FIG. 8 is an exploded isometric view of the pump according
to the invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0036] By way of example only, in the Figures there is considered a
pump where the displacement variation is achieved through the
rotation of the regulation stator ring (hereinafter referred to as
"stator" for the sake of brevity) about an axis parallel to the
axis of rotation of the rotor and where the rotation of the stator
is directly controlled by the pressure of the pumped fluid.
[0037] Referring to FIGS. 1, 2 and 8, a pump 1 of the above kind
comprises a body 10 having a suitably shaped cavity 40 in which
stator 11 is mounted so as to be freely rotatable along an arc of
circumference, in the illustrated example in clockwise direction,
as indicated by arrow A. Reference character B denotes the axis of
rotation of stator 11. Stator 11 has a chamber 12 where vane rotor
13 is housed. The rotor is keyed on a shaft 14 arranged off-axis
relative to centre C of chamber 12. Also rotor 13 is rotatable in
clockwise direction. Reference numerals 41 and 42 denote the ends
of the suction and delivery ducts, when rotor 13 rotates in
clockwise direction.
[0038] As known to the skilled in the art, rotation of stator 11
about axis B causes a variation of the relative eccentricity
between stator 11 and rotor 13, and hence a variation of the
displacement, between a condition of maximum eccentricity and
displacement (shown in FIG. 1), which is taken also in rest
conditions of the pump and in which rotor 13 is substantially
tangent to surface 12A of chamber 12, and a condition of minimum
displacement (shown in FIG. 2), in which rotor 13 is coaxial or
substantially coaxial with chamber 12. Such an arrangement is
wholly conventional and a more detailed description is not
required.
[0039] In the example illustrated, for the control of its rotation,
stator 11 has a pair of radial appendages 17, 18, which project
into respective chambers 15, 16 formed by recesses of cavity 40,
and which slide in fluid-tight manner on the bases of chambers 15,
16. One of the chambers, for instance chamber 15, is permanently
connected to the delivery side of the pump or to the units
utilising the pumped fluid (in particular, in the preferred
application, to a point of the engine lubrication circuit located
downstream the oil filter), through a first regulation duct, not
shown in these Figures. The other chamber can in turn be put in
communication with the delivery side or with the units utilising
the pumped fluid through a valve operated by the electronic control
unit of the vehicle and a second regulation duct (not shown). In
this manner, appendage 17 is, or both appendages 17, 18 are,
exposed to the pressure conditions of the pumped fluid.
[0040] An end wall of one of the chambers, e.g. chamber 15, may be
shaped so as to form an abutment 19 for appendage 17 in the maximum
displacement condition.
[0041] Chamber 16 houses a member 20 opposing the rotation of
stator 11. That member, in the example illustrated, comprises two
opposite mushroom-shaped elements 21, 22, connected for instance in
telescopic manner and biased in opposite directions by a spring 23
arranged between heads 21A, 21B of both elements. Spring 23 is
preloaded so as to oppose the rotation of stator 11, and hence to
keep it in the position shown in FIG. 1, as long as the pressure
applied to appendage 17 (or the overall pressure applied to
appendages 17, 18) is lower than a predetermined threshold, and to
subsequently keep the pump displacement at the value corresponding
to the pressure threshold. Such a condition is attained when an
equilibrium is established between the torques generated by the
pressure acting on appendages 17, 18 and the antagonist torque
generated by spring 23.
[0042] Heads 21A, 21B, for instance substantially shaped as half
cylinders, engage recesses 22A, 22B of complementary shape formed
in the opposite surface of appendage 18 with respect to the surface
acted upon by the regulating pressure and in a wall of chamber 16,
respectively. Thus, a pair of articulated joints is formed allowing
keeping the ends of spring 23 mutually parallel during the rotation
of stator 11, thereby ensuring a good lateral stability of the
spring itself.
[0043] The circumferential extension and the radial size of
chambers 15, 16 will be determined depending on the operation
characteristics required of the pump. In particular, as far as the
circumferential extension is concerned, a rotation of stator 11 of
the order of about 20.degree. is typical for the preferred
application and has been shown in the drawings. As to the radial
size, it may be constant over the whole circumferential extension,
so that appendages 17, 18 have a constant thrust area and hence
generate a constant torque, proportional to the actuation pressure,
over the whole arc of rotation. In the alternative, the radial size
of one chamber or both chambers may change along the
circumferential extension, and appendages 17, 18 have a variable
thrust area, so as to generate a variable torque over the arc of
rotation of stator 11. Such a solution allows taking into account
the fact that the resistant torques encountered during displacement
regulation may be variable, for instance because the resistance
opposed by opposing spring 20 and/or the rotational frictions
vary.
[0044] FIGS. 1 and 2 also show the different forces acting on the
components of pump 1 during operation and the reactions caused by
such forces. It is to be appreciated that FIGS. 1 and 2 only are
intended to give a representation of the zones where the different
forces act and of the directions of the forces, whereas their
magnitudes are not considered. More particularly: [0045] F.sub.P1,
F.sub.P2 are the thrust forces applied to appendages 17, 18 by the
fluid introduced into chambers 15, 16; it is assumed that the fluid
under pressure is introduced into chamber 16 during regulation,
that is why force F.sub.P2 is shown only in FIG. 2; [0046] F.sub.M
is the force opposing the rotation of stator 11 applied by opposing
member 20; [0047] F.sub.ATT is the frictional force between heads
21A, 22A of elements 21, 22 forming member 20 and the respective
seats 21B, 22B; [0048] F.sub.HYD is the force applied on rotor 13
and stator 11 by the fluid present in pumping chamber 12; [0049]
F.sub.C is the force opposing F.sub.HYD exerted by body 10; [0050]
R.sub.V is the hydraulic reaction to the resultant of the forces
mentioned above; [0051] R.sub.H is the friction between stator 11
and the internal surface 40A of chamber 40 during the rotation of
stator 11.
[0052] FIGS. 3 and 4 show the vectors representing forces
F.sub.P1-F.sub.C mentioned above and their partial and overall
resultants in the extreme operating conditions shown in FIGS. 1 and
2. In FIGS. 3 and 4, the origin of the axes coincides with centre
of rotation B of stator 11. As it clearly appears from a
superposition of the diagrams on the right side of FIGS. 3 and 4
onto FIGS. 1 and 2, respectively, resultants SV1 and SV2,
respectively, of the above forces have such orientations that they
act in correspondence of a zone S of the mutually engaging surfaces
in stator 11 and cavity 40. In this zone, by reaction, the fluid
under pressure present in chamber 12 creates a hydraulic support
bearing. The reaction provided by such a bearing is force R.sub.V
mentioned above, which has the same magnitude as and opposite
direction to the above resultants.
[0053] In order to optimise the pump operation, it is necessary to
minimise irregularities and jamming during the movement of stator
11 and the resultant vibrations, noise and hydraulic pulsations in
zone S where resultants SV1, SV2 act. The remaining portion of the
region of engagement between surfaces 11A, 40A has a far lower
influence and does not require particular interventions.
[0054] This optimisation is obtained by means of the pump according
to the invention, which will be now described with reference to
FIGS. 5-8. Elements already disclosed with reference to FIGS. 1 and
2 are denoted by the same reference numerals.
[0055] According to the invention, a plurality of rolling elements
25, in the illustrated example rollers or needles (herein below
generally referred to as "rollers"), are arranged between external
surface 11A of stator 11 and internal surface 40A of cavity 40,
over a portion including zone S where the hydraulic support bearing
is created and where resultants SV1, SV2 of the various forces act.
In correspondence of such a portion a sector of a rolling bearing
is thus formed, of which external surface 11A of stator 11 forms
the corresponding sector of the inner race whereas internal surface
40A of cavity 40 forms the corresponding sector of the outer race.
Rollers 25 are fitted, for instance snap fitted, in respective
seats 27 in a supporting cage 26, preferably made of plastic
material, which in conventional manner acts as a guide and a spacer
for rollers 25.
[0056] Cage 26 with rollers 25 is housed in a recess of external
surface 11A of stator 11, which recess axially extends over the
whole axial depth of stator 11 and chamber 40. Recess 28, cage 26
and rollers 25 have such a radial size that the contact between
surfaces 11A and 40A is ensured by rollers 25. Typical diameters
for the rollers, in the preferred application, are of the order of
a few millimetres, for instance 2-4 mm. Also cage 26 axially
extends over the whole depth of stator 11, whereas rollers 25 have
an axial size (length) slightly shorter than that of cage 26. This
gives a labyrinth configuration to the assembly of cage 26 and
rollers 25, which configuration allows maintaining the hydraulic
support bearing.
[0057] Cage 26 has an angular extension smaller than the angular
extension of recess 28, so that it can move within the recess
during the rotation performed by stator 11 for the displacement
regulation, and the angular extension of the displacement of cage
26 is smaller than the angular extension of the rotation performed
by stator 11 for passing from the maximum displacement position to
the minimum displacement position. Considering that only surface
11A moves and taking into account the difference in the radiuses of
moving surface 11A and stationary surface 40A, the solution
described, in which seat 28 for cage 26 is formed in the moving
part, allows rollers 25 to displace over a same distance on both
surfaces, and hence to rotate without sliding.
[0058] Recess 28 is defined by two steps or abutments 29A, 29B. One
end of cage 26 abuts against one of such abutments, for instance
abutment 29A, in the rest condition (maximum displacement) of the
pump, shown in FIG. 5. A resilient member 30 opposing the cage
movement, e.g. a suitably preloaded leaf spring, is instead
arranged between cage 26 and the other abutment 29B and it keeps
cage 26 in contact with abutment 29A in the maximum displacement
condition.
[0059] FIGS. 5 and 6 clearly show the behaviour of cage 26 with
rollers 25 during displacement regulation. In order to make
understanding easier, three reference points belonging to body 10,
stator 11 and cage 26, respectively, have been shown by segments X,
Y and Z. The three points are chosen so that their positions
coincide in the maximum displacement condition (FIG. 5). At the end
of the rotation bringing stator 11 to the minimum displacement
position (FIG. 6), point X of course has remained stationary,
whereas point Z has displaced in clockwise direction and has
described an arc that, in the example illustrated, is of about
20.degree.. Also point Y has performed a rotation in clockwise
direction, yet over an arc shorter than that described by point Z.
Due to the shorter rotation of cage 26 with respect to stator 11,
cage 26 is no longer in contact with abutment 29A at the end of the
rotation and spring 30 is more compressed.
[0060] It is clear that the invention obviates the drawbacks
mentioned above of the prior art. Actually, the provision of
rolling elements 25 between engagement surfaces 11A, 40A reduces
per se the friction with respect to the case when stator 11 is
supported by the only hydraulic bearing. Moreover, configuring the
region of engagement between the surfaces as a sector of a bearing
(or an open bearing), extending in the zone where the resultant of
the mechanical and hydraulic forces generated during the regulation
acts, avoids the jamming due to such forces. Lastly, arranging
rolling elements 25 so that they can move within a seat 28 formed
in stator 11 over a distance shorter than that over which the
stator itself has moved prevents rolling elements 25 from sliding
and hence reduces the resistance to the regulation movement.
[0061] It is clear that the above description is given only by way
of non-limiting example and that changes and modifications are
possible without departing from the scope of the invention.
[0062] For instance, even if there has been shown in detail a pump
where displacement regulation is performed through a rotation of
the stator about an axis internal to the stator itself and said
rotation is directly controlled by the pressure of the pumped
fluid, the invention can be applied also to pumps where the
rotation of the stator is achieved in different manner (for
instance, through a gear engaging a toothed sector of the external
surface of the stator, like in U.S. Pat. No. 5,863,189) or to pumps
where the regulation movement is different from the rotation of the
stator disclosed here ("pendulum" pumps, pumps with oscillating
stator, pumps with a translation of the stator ring, and so on). Of
course, if the regulation movement performed by the stator is a
translation, cage 26 will be a linear cage.
* * * * *