U.S. patent application number 15/021164 was filed with the patent office on 2016-08-04 for variable displacement pump with electric control of displacement regulation and method of regulating pump displacement.
The applicant listed for this patent is VHIT S.P.A.. Invention is credited to Leonardo Cadeddu, Alessandro Fauda.
Application Number | 20160222963 15/021164 |
Document ID | / |
Family ID | 49683989 |
Filed Date | 2016-08-04 |
United States Patent
Application |
20160222963 |
Kind Code |
A1 |
Cadeddu; Leonardo ; et
al. |
August 4, 2016 |
VARIABLE DISPLACEMENT PUMP WITH ELECTRIC CONTROL OF DISPLACEMENT
REGULATION AND METHOD OF REGULATING PUMP DISPLACEMENT
Abstract
A rotary positive displacement pump for fluids, in particular,
for the lubrication of a motor vehicle engine (61), has a
displacement that can be regulated through the rotation of a stator
ring (42) having an eccentric cavity (43) in which the rotor (15)
of the pump (1) rotates. The stator ring (42) is housed within an
in eccentric cavity (13) of an external ring (12). A rotor actuator
(50), controlled by the electronic control unit of the motor
vehicle, causes a synchronous rotation by an equal amount in
opposite directions of both rings. A method of regulating the
displacement of the pump (1) and lubrication system for a motor
vehicle engine in which the pump is used are also provided.
Inventors: |
Cadeddu; Leonardo;
(Offanengo (CR), IT) ; Fauda; Alessandro;
(Offanengo (CR), IT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
VHIT S.P.A. |
Offanengo (CR) |
|
IT |
|
|
Family ID: |
49683989 |
Appl. No.: |
15/021164 |
Filed: |
September 9, 2014 |
PCT Filed: |
September 9, 2014 |
PCT NO: |
PCT/IB2014/064338 |
371 Date: |
March 10, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F01M 1/02 20130101; F04C
2/3441 20130101; F04C 2240/81 20130101; F01M 2001/0238 20130101;
F04C 14/223 20130101; F01C 21/106 20130101 |
International
Class: |
F04C 14/22 20060101
F04C014/22; F01M 1/02 20060101 F01M001/02; F04C 2/344 20060101
F04C002/344 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 11, 2013 |
IT |
TO2013A000735 |
Claims
1. A variable displacement rotary positive displacement pump for
fluids, comprising a rotor (15; 115) arranged to rotate within an
eccentric cavity (43; 143) of a stator ring (42; 142) in turn
arranged to be rotated within a predetermined angular interval, as
operating conditions of the pump (1; 101) vary and upon command of
a system (62, 63) detecting such conditions, in order to vary a
relative eccentricity between the eccentric cavity (43; 143) and
the rotor (15; 115) and hence the pump displacement, the pump (1;
101) further including an electromagnetic actuator (50), integrated
into or coupled with the pump, which is driven by said detecting
system (62, 63) and is arranged to generate a rotary motion and to
transmit it to said stator ring (42; 142) through a toothed wheel
(53; 153); the pump being characterised in that: said toothed wheel
(53; 153) is located at least in part in a stator cavity (11a, 11b;
111) located in a peripheral position relative to said stator ring
(42; 142); and in that a toothed sector (52; 152) is located at the
base of said peripheral stator cavity (11a, 11b; 111).
2. The pump as claimed in claim 1, wherein said toothed sector (52;
152) located at the base of said peripheral stator cavity (11a,
11b; 111) meshes with said toothed wheel (53; 153) driven by the
actuator (50) and develops according to a profile defined by an
involute of the teeth of the wheel (53; 153).
3. The pump as claimed in claim 2, wherein the stator ring (42) is
housed within an eccentric cavity (13) of an external ring (12),
and said actuator (50) is arranged to transmit the rotary motion to
both rings (12; 42) in such a way as to cause a synchronous
rotation thereof by an equal amount in opposite directions.
4. The pump as claimed in claim 3, wherein the eccentric cavities
(13, 43) have the same eccentricity and, in a minimum displacement
condition, are arranged so that their eccentricities are offset by
180.degree..
5. The pump as claimed in claim 3, wherein facing surfaces of the
external ring (12) and the stator ring (42) have formed thereon
respective toothed sectors (51, 52) with which a toothed wheel (53)
driven by the actuator (50) meshes and which develop according to a
profile defined by an involute of the teeth of the wheel (53), so
that, during the rotation of the rings (12, 42), a centre (O') of
the cavity of the stator ring moves along a rectilinear path.
6. The pump as claimed in claim 2, wherein the toothed wheel (53;
153) is arranged to cooperate with a member (34) opposing the
rotation of the stator ring (42; 142), which member consists of a
flat spiral spring secured at one end to a shaft (54) of the
toothed wheel and at the other end to an element (33) rigidly
connected to the pump body, the spring being associated with
setting means (33, 55) arranged to set a desired steady state value
for the displacement of the pump (1; 101), and wherein the flat
spiral spring (34) is made of a bimetallic material and has a
temperature-depending characteristic.
7. The pump as claimed in claim 2, wherein the actuator (50) is a
step-by-step micromotor or is a linearly moving actuator equipped
with an escapement ratchet gear arranged to convert the actuator
motion into a rotary motion.
8. The pump as claimed in claim 1, wherein the pump (1; 101) is a
pump for a lubrication circuit (60) of a motor vehicle engine
(61).
9. A method of regulating the displacement of a rotary positive
displacement pump (1; 101) of a kind comprising a rotor (15; 115)
arranged to rotate within an eccentric cavity (43; 143) of a stator
ring (42; 142), the method comprising the step of making the stator
ring (42; 142) rotate within a predetermined angular interval in
order to vary the eccentricity between the cavity (43; 143) and the
rotor (15; 115) as operating conditions of the pump (1; 101) vary,
and being characterised in that it further comprises the steps of:
providing an electromagnetic actuator (50) integrated into or
coupled with the pump and arranged to transmit a rotary motion to
the stator ring (42) through a toothed wheel (53; 153) located at
least in part in a stator cavity (11a, 11b; 111) located in a
peripheral position relative to said stator ring (42; 142);
supplying the actuator (50) with commands corresponding to a
desired rotation of the stator ring (42; 142).
10. The method as claimed in claim 9, further comprising the steps
of: providing an external ring (12) having an eccentric cavity (13)
within which the stator ring (42) is housed; and making the stator
ring (42) and the external ring (12) rotate by a same angle at the
same time and in opposite directions.
11. The method as claimed in claim 9 or 10, arranged for regulating
the displacement of a pump for the lubrication oil of a motor
vehicle engine.
12. A lubrication system for a motor vehicle engine (61),
comprising a pump (1; 101) as claimed in claim 1.
13. The pump as claimed in claim 1, wherein the stator ring (42) is
housed within an eccentric cavity (13) of an external ring (12),
and said actuator (50) is arranged to transmit the rotary motion to
both rings (12; 42) in such a way as to cause a synchronous
rotation thereof by an equal amount in opposite directions.
14. The pump as claimed in claim 13, wherein the eccentric cavities
(13, 43) have the same eccentricity and, in a minimum displacement
condition, are arranged so that their eccentricities are offset by
180.degree..
15. The pump as claimed in claim 14, wherein facing surfaces of the
external ring (12) and the stator ring (42) have formed thereon
respective toothed sectors (51, 52) with which a toothed wheel (53)
driven by the actuator (50) meshes and which develop according to a
profile defined by an involute of the teeth of the wheel (53), so
that, during the rotation of the rings (12, 42), a centre (O') of
the cavity of the stator ring moves along a rectilinear path.
16. The pump as claimed in claim 13, wherein facing surfaces of the
external ring (12) and the stator ring (42) have formed thereon
respective toothed sectors (51, 52) with which a toothed wheel (53)
driven by the actuator (50) meshes and which develop according to a
profile defined by an involute of the teeth of the wheel (53), so
that, during the rotation of the rings (12, 42), a centre (O') of
the cavity of the stator ring moves along a rectilinear path.
17. The pump as claimed in claim 13, wherein the toothed wheel (53;
153) is arranged to cooperate with a member (34) opposing the
rotation of the stator ring (42; 142), which member consists of a
flat spiral spring secured at one end to a shaft (54) of the
toothed wheel and at the other end to an element (33) rigidly
connected to the pump body, the spring being associated with
setting means (33, 55) arranged to set a desired steady state value
for the displacement of the pump (1; 101), and wherein the flat
spiral spring (34) is made of a bimetallic material and has a
temperature-depending characteristic.
18. The pump as claimed in claim 13, wherein the actuator (50) is a
step-by-step micromotor or is a linearly moving actuator equipped
with an escapement ratchet gear arranged to convert the actuator
motion into a rotary motion.
19. The pump as claimed in claim 1, wherein the toothed wheel (53;
153) is arranged to cooperate with a member (34) opposing the
rotation of the stator ring (42; 142), which member consists of a
flat spiral spring secured at one end to a shaft (54) of the
toothed wheel and at the other end to an element (33) rigidly
connected to the pump body, the spring being associated with
setting means (33, 55) arranged to set a desired steady state value
for the displacement of the pump (1; 101), and wherein the flat
spiral spring (34) is made of a bimetallic material and has a
temperature-depending characteristic.
20. The pump as claimed in claim 1, wherein the actuator (50) is a
step-by-step micromotor or is a linearly moving actuator equipped
with an escapement ratchet gear arranged to convert the actuator
motion into a rotary motion.
Description
TECHNICAL FIELD
[0001] The present invention relates to variable displacement
pumps, and more particularly it concerns a rotary positive
displacement pump of the kind in which the displacement variation
is obtained by means of the rotation of an eccentric ring (stator
ring).
[0002] The invention also concerns a method of regulating the
displacement of such a pump.
[0003] Preferably, but not exclusively, the present invention is
employed 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 a fixed geometry, at high
rotation speed the delivery rate exceeds the necessary rate, so
that part of the delivered flow is to be discharged in order to
limit the delivery rate and the pressure. Of course, the discharged
oil volume has already been compressed, whereby high power
absorption occurs, with a consequent higher fuel consumption and a
greater stress of the components due to the high pressures
constantly generated in the pump.
[0005] In order to obviate this drawback, it is known to equip the
pumps with systems allowing a delivery rate regulation at the
different operating conditions of the vehicle, in particular
through displacement regulation. Different solutions are known to
this aim, which are specific for the particular kind of pumping
elements (external or internal gears, vanes . . . ).
[0006] A system often used in rotary pumps employs a stator ring
with an internal cavity, eccentric relative to the external
surface, inside which the rotor, in particular a vane rotor,
rotates, the rotor being eccentric with respect to the cavity under
operating conditions of the pump. By making the stator ring rotate
by a given angle, the relative eccentricity between the rotor and
the cavity, and hence the displacement, is made to vary between a
maximum value and a minimum value, substantially tending to zero
(stall operating condition). A suitably calibrated opposing
resilient member allows the rotation when a predetermined delivery
rate is attained and makes the pump substantially deliver such a
predetermined delivery rate under steady state conditions. An
example is disclosed in U.S. Pat. No. 2,685,842.
[0007] Pumps with a pair of stator rings are also known, where
displacement is varied by rotating the rings relative to each other
in opposite directions. An example is disclosed in U.S. Pat. No.
4,406,599.
[0008] The evolution of such pumps and the diffusion of electronics
in motor vehicle engines have lead to displacement regulation
systems controlled by the electronic control unit of the vehicle
depending on the oil pressure, preferably detected downstream the
filter, and possibly on other operating parameters of the engine.
Generally, such systems are electro-hydraulic systems, where the
control unit controls electrically operated valves that, in turn,
control hydraulic actuators acting on the stator ring. For
instance, US 2011/0209682 discloses a system in which a control
module of the pump, being part of the electronic control unit,
controls through an electrically operated valve the flow of
pressurised oil towards either of two chambers, which apply the oil
pressure to the stator ring. Application of the pressure of either
chamber corresponds to two different pressure/delivery rate
conditions of the pump.
[0009] Generally, the provision of the hydraulic actuators makes
electro-hydraulic systems complex and expensive. Moreover, when the
engine is off, it is impossible to modify the displacement
presetting, since no control pressure is available.
[0010] It is an object of the present invention to provide a
variable displacement pump, and a method of regulating the
displacement of such a pump, which obviate the drawbacks of the
prior art.
DESCRIPTION OF THE INVENTION
[0011] According to the invention, this is obtained in that the
pump includes an electromagnetic rotary actuator, integrated into
or coupled with the pump, which is driven by an electronic system
detecting operating conditions of the pump and is arranged to
transmit the rotary motion to the stator ring.
[0012] Advantageously, the stator ring is housed within an
eccentric cavity of an external ring, and the rotary actuator is
arranged to simultaneously transmit the rotary motion to both
rings, in such a way as to cause a synchronous rotation thereof by
an equal amount in opposite directions.
[0013] The invention also implements a method of regulating the
displacement of a rotary positive displacement pump by means of the
rotation of an eccentric stator ring inside which the rotor
rotates, the method comprising the steps of: [0014] providing an
electromagnetic rotary actuator integrated into or coupled with the
pump; [0015] supplying the actuator with rotation commands
corresponding to a desired rotation of the stator ring.
[0016] Preferably, the method further comprises the steps of:
[0017] providing an external ring having an eccentric cavity within
which the stator ring is housed; and [0018] making both rings
rotate by a same angle at the same time and in opposite
directions.
[0019] According to a further aspect of the invention, a
lubrication system for a motor vehicle engine is also provided, in
which the adjustable displacement pump and the method of regulating
the displacement set forth above are employed.
BRIEF DESCRIPTION OF THE FIGURES
[0020] Further features and advantages of the invention will become
apparent from the following description of preferred embodiments,
given by way of non limiting examples with reference to the
accompanying drawings, in which:
[0021] FIG. 1 is a plan view of a first embodiment of the pump
according to the invention, from which the cover and the regulation
actuator have been removed, in the minimum displacement
position;
[0022] FIG. 2 is a view similar to FIG. 1, in the maximum
displacement position;
[0023] FIG. 3 is a plan view similar to FIG. 2, showing the
delivery rate regulation mechanism integrated in the cover;
[0024] FIG. 4 is a cross-sectional view of the pump taken according
to a plane passing through line Y-Y in FIG. 3;
[0025] FIGS. 5 and 6 are views similar to FIGS. 1 and 2, relating
to a second embodiment of the pump according to the invention;
and
[0026] FIG. 7 is a principle block diagram of the displacement
regulating circuit.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0027] Referring to FIGS. 1 to 4, a pump 1 according to the
invention, more particularly a vane pump, includes a body 10 having
a cavity 11 with substantially circular cross-section in which a
first movable ring 12 (external ring) is located. The ring in turn
has an axial cavity 13, also with substantially circular
cross-section, eccentrically arranged relative to cavity 11. A
second movable ring 42 (stator ring) is located in cavity 13, which
ring in turn has an axial cavity 43, also with substantially
circular cross-section, eccentrically arranged relative to cavity
13 and having a centre O'. Rings 12 and 42 are arranged to rotate
in mutually opposite directions by a certain angle in order to vary
the pump displacement, as it will be disclosed below.
Advantageously, cavities 13, 43 have the same eccentricities. In
the example illustrated, cavity 11 is blind and is closed at one
end by a cover 14 (FIG. 4), also closing the corresponding ends of
cavities 13, 43.
[0028] Cavity 43 in turn houses a rotor 15, rigidly connected to a
driving shaft 15a making it rotate about a centre O, for instance
in clockwise direction, as shown by arrow F. Cavity 43 thus forms
the pumping chamber. In a minimum displacement position (shown in
FIG. 1), rotor 15 and cavity 43 are coaxial or substantially
coaxial, whereas, in a maximum displacement position (shown in FIG.
2), centres O and O' are located on the same axis X-X and are
mutually spaced apart, and rotor 15 is substantially tangent to
side surface 43a of cavity 43. In the present description, the term
"coaxial or substantially coaxial" is used to denote a minimum
distance, tending to 0, between centres O and O'.
[0029] Advantageously, eccentric rings 12 and 42 are mounted in
such a manner that, in the minimum displacement position, external
ring 12 is oriented so that its minimum radial thickness is located
at the top in the Figure and internal ring 42 is oriented so that
its minimum radial thickness is located at the bottom in the
Figure. Otherwise stated, the eccentricities of the respective
cavities 13, 43 are offset by 180.degree.. Preferably, cavities 13,
43 have the same eccentricity relative to the external surface of
the respective ring.
[0030] Rotor 15 has a set of vanes 16, radially slidable in
respective radial slots. At an outer end, vanes 16 are at a minimum
distance from side surface 43a of cavity 43, whereas at their inner
end they rest on guiding or centring rings 17, mounted at the axial
ends of rotor 15 and arranged to maintain the minimum distance
between vanes 16 and surface 43a under any condition of
eccentricity. Also centring rings 17 will be coaxial or
substantially coaxial with rotor 15 in the minimum displacement
position.
[0031] A suction chamber 18, communicating with a suction duct 20,
and a delivery chamber 19, communicating with a delivery duct 21,
are defined at the bottom of body 10 between rotor 15 and surface
43a. Such chambers are substantially symmetrical with respect to a
plane passing through axis X-X and have phasings that are ideal for
the maximum volumetric efficiency, as it is clearly apparent for
the skilled in the art. It is to be appreciated that, should the
rotor rotate in counterclockwise direction, the functions of such
chambers, and hence of the respective ducts, would be mutually
exchanged
[0032] In order to control the rotation of rings 12, 42, toothed
sectors 51, 52 are formed on their facing surfaces and are
preferably positioned at the base of suitable stator cavities 11a,
11b formed in rings 12, 42. A toothed wheel 53 having a shaft 54
rigidly connected to an actuator 50 (FIG. 4) driving it into
rotation is interposed between toothed sectors 51, 52 located in
said stator cavities 11a, 11b. Thus, rings 12, 42 rotate in
opposite directions and are synchronous with each other.
[0033] Preferably, actuator 50 is an electromagnetic actuator. It
may be a rotary actuator, e.g. a step-by-step micromotor integrated
into pump 1 or coupled therewith (e.g. interfaced through the
partition wall separating the inside from the outside of the engine
sump), or a linearly moving actuator coupled with a suitable
escapement ratchet gear in order to convert the actuator motion
into a rotary motion.
[0034] Actuator 50 is controlled by the electronic control unit of
the vehicle, which manages the displacement variation in closed
loop (e.g. with feedback), by increasing or reducing the
displacement depending on the requirements of the thermal engine
and the accessories thereof. The variation is independent of the
pressures upstream and downstream the oil filter.
[0035] Shaft 54 is guided within a support 40 formed in cover 14 or
in body 10. Toothed sectors 51, 52, while rotating, develop
according to a profile defined by the involute of the teeth of
wheel 53, which, on the contrary, rotates about its stationary
axis. If the eccentricities are the same, the relative rotation of
the rings causes a translation of centre O' of pumping chamber 43
along axis X-X. This makes the geometry of pumping chamber 43
perfectly symmetric in all displacement conditions, and makes the
ratio between the rotation of toothed wheel 53 and the displacement
variation because of the translation of axis of chamber 43
constant.
[0036] In the illustrated embodiment, wheel 53 cooperates with a
member 34 opposing the rotation of rings 12, 42, in particular a
flat spiral spring, preloaded so as to prevent the rotation of the
rings as long as the torque applied by actuator 50 is lower than a
predetermined threshold. Spiral spring 34 is located in a casing 33
that, in the illustrated exemplary embodiment, is fastened to cover
14. The inner end portion of spring 34 is so shaped as to be
coupled with the end portion of shaft 54 of wheel 53, whereas the
outer end portion is locked to the internal wall of casing 33. The
latter may be rotated, for instance by using a dynamometric key, in
order to adjust the preloading of spring 34. A ring nut 55 allows
blocking casing 33 in the desired calibration position,
independently of the constructional tolerances of the whole
mechanism. A sealing gasket 56 is moreover provided between casing
33 and cover 14 in order to isolate the internal chamber of the
same casing from the outside. A drain puts such a chamber in
communication with suction chamber 18, for the aims that will be
disclosed below.
[0037] It is to be appreciated that, during the regulation
rotation, spiral spring 34, thanks to the negligible variation of
the twisting torque and to the transmission ratio of the gear
mechanism, will undergo negligible variations of its torque
opposing the hydraulic torque. In the preferred embodiment in which
actuator 50 is a step-by-step motor, spring 34 may contribute to
make the magnetic resistance torque between subsequent steps
sufficient to maintain the position of rings 12, 42 when the motor
in not excited (energy saving). Moreover, due to a diametrically
opposite effect, spring 34 could contribute to maintaining a
maximum displacement upon the occurrence of an electric
failure.
[0038] Rings 12 and 42, as well as centring rings 17, rotor 15 and
wheel 53, are preferably formed by moulding and/or metal powder
sintering, with possible finishing operations on some limited
areas, according to the dictates of the art. More particularly,
axial thicknesses will undergo finishing. Body 10 and cover 14 can
be formed by moulding either an aluminium alloy or a thermoplastic
and/or thermosetting resin. Advantageously, spring 34 may be made
of a bimetallic material, so that its characteristic may change
depending on the operation temperature.
[0039] A second embodiment of the pump according to the invention,
denoted 101, is shown in FIGS. 5 and 6. Elements that are
functionally identical to those already disclosed with reference to
FIGS. 1 to 4 are preferably denoted by the same reference numerals,
increased by 100. Pump 101 differs from pump 1 in that external
ring 12 is lacking and therefore actuator 150 acts through wheel
153 onto stator ring 142 alone, which is formed internally of body
110 with substantially circular cross-section.
[0040] In accordance with such an embodiment, as shown in FIGS. 5
and 6, stator ring 142 preferably comprises a stator cavity 111 in
which both toothed sector 152 and toothed wheel 153 are
arranged.
[0041] More particularly, toothed sector 152 is located at the base
of stator cavity 111 and the toothed wheel is preferably wholly
included between toothed sector 152 and body 110 with substantially
circular cross-section.
[0042] Thanks to such a structure, in accordance with the second
embodiment, the arrangement of toothed sector 152 and toothed wheel
153 allows minimising the size of pump 101.
[0043] Moreover, rotor 115 rotates in counterclockwise direction
(arrow F'). With such an arrangement, the translation of centre O'
of chamber 143 takes place along a non-rectilinear trajectory.
Apart from those aspects, the structure is identical to that of
pump 1 ad it is not necessary to describe it again.
[0044] FIG. 7 shows a principle block diagram of the regulation of
the displacement of pumps 1, 101. Dashed line denotes the
mechanical drive of the pump by actuator 50 and hence corresponds
to toothed wheels 53, 153 of the previous Figures. Dotted and
dashed line 60 denotes the lubrication circuit which conveys oil
from pump 1 to the engine and the various accessories, denoted in
the whole 61. Reference numeral 62 denotes the electronic control
unit of the vehicle, which receives signals from detectors denoted
in the whole 63 and controls actuator 50, possibly through a
digital-to-analogue converter, not shown. Solid lines denote the
paths of the electric signals incoming into/outgoing from control
unit 62, and dotted lines denote the detection of the operating
parameters of engine 61, pump 1, lubrication circuit 60 and
possibly actuator 50 by detectors 63. The parameters on which
regulation of the delivery rate of the pump for lubrication of a
motor vehicle engine may depend are well known to the skilled in
the art and are not of interest for the invention. A more detailed
description can be found in US 2011/0209682.
[0045] The operation of the pump described is as follows.
[0046] Considering first pump 1, under rest conditions, the pump is
in the maximum displacement condition shown in FIG. 2. As said,
centre of rotation O of rotor 15 is offset relative to centre O' of
cavity 43 of eccentric ring 42 and rotor 15 is located close to
wall 43a of the cavity. When pump 1 is started, the clockwise
rotation of rotor 15 will give rise to an oil flow through chamber
19 and the associated delivery duct 21 and, at the same time, an
equal volume of oil will be sucked from chamber 18 and the
associated suction duct 20. As the rotation speed and the flow rate
increase, the lubrication system of the engine, by opposing an
increasing resistance to the flow, will make pressure increase.
[0047] The delivery pressure or the pressure downstream the oil
filter are detected by the suitable detectors 63 and communicated
to control unit 62, which will make actuator 50 rotate. The
actuator will in turn generate a rotation torque that, through
wheel 53 and once the calibration value of counteracting spring 34
has been attained, will make rings 12, 42 rotate by the same angle
in opposite directions. If, as it has been assumed, the
eccentricities of cavities 13, 43 relative to the external surfaces
of the respective rings are the same, the rotation of ring 42 will
cause a rectilinear translation of centre O' towards the right,
proportional to the amount of the rotation, thereby proportionally
reducing the eccentricity between rotor 15 and cavity 43, and
consequently the pump displacement, and stabilising the pressure at
the calibration value. As parameters such as the speed, the
fluidity/temperature of the fluid, the engine "permeability"
(intended as the amount of oil used by the engine) and so on,
detected by detectors 63, change, such a pressure will be
maintained and controlled through the variation of the eccentricity
and hence of the displacement.
[0048] When, as a function of the different operating parameters of
the engine, it is desired to operate at a lower pressure value,
with a consequent reduction in the absorbed power, control unit 62
will generate a suitable command for actuator 50, so as to further
reduce the displacement.
[0049] The rotation of the rings may continue until the position
shown in FIG. 1 is attained, where centres O and O' coincide and
vanes 16 and centring rings 17 rotate with the rotor without
changes in their radial relative position. Consequently, the
displacement is null and the pump is in stall condition. It is to
be pointed out that this position may be taken when a hydraulic
lock of the delivery pressure is approaching. In the constructional
practice, a minimum displacement is preferably maintained by
protecting the pump with a maximum pressure valve.
[0050] The operation of pump 101 is wholly similar, with the
changes due to the provision of stator ring 42 alone.
[0051] An important parameter in managing the delivery
rate/pressure of an oil pump for thermal engines is temperature,
the increase of which makes oil become more fluid and the engine
permeability increase. Consequently, the pump displacement should
proportionally increase. This may be favoured if the opposing load
of the counteracting spring increases. In order to obtain this,
flat spiral spring 34 may be made of a bimetallic material such
that temperature causes an increase in the rigidity and hence in
the counteracting torque. In order to obtain the change in the
rigidity, the small oil flow rate for the lubrication of shaft 54
of wheel 53 may be exploited: the oil, after having licked casing
33 of spring 34 and having transmitted its temperature to the same
spring, freely discharges towards the suction chamber through the
drain provided in chamber 57.
[0052] The invention actually attains the desired aims.
[0053] Use of an electromagnetic actuator, directly controlled by
the electronic control unit of the vehicle, allows eliminating the
hydraulic actuators of the prior art and the necessary connections
to the lubrication circuit, and makes the system less cumbersome,
simpler and more reliable as well as less expensive. Moreover,
elimination of the hydraulic actuators enables modifying the
displacement presetting even when the thermal engine is off, since
no control pressure is required. This is advantageous in particular
for vehicles provided with the "stop and go" function, because it
allows for instance increasing the displacement between the stop of
the thermal engine and its start in order to start again the engine
with a good lubrication.
[0054] Moreover in both embodiments, given the respective rotation
direction of the rotor, in case of an electric failure causing
deactivation of actuator 50 the hydraulic torque of the pump causes
the rotation of the stator ring, or of the stator ring and the
external ring, towards the maximum displacement condition. As said,
this action can be favoured by spring 34. In case of other
failures, the minimum displacement is ensured and the electronic
control, by detecting low lubrication pressures, will bring control
unit 62 to the vehicle "recovery" function,
[0055] It is clear that the above description has been given only
by way of non-limiting example and that changes and modifications
are possible without departing from the scope of the invention.
[0056] For instance, even if in the illustrated embodiment shaft
15a of rotor 15 is guided by body 10 whereas spiral spring 34 and
the calibration means consisting of casing 33 and ring nut 55 are
housed within cover 14, the arrangement could be reversed, or also
the spring and the calibration means could be housed within body
10.
[0057] Moreover, spring 34 could not be a bimetallic spring and, at
least in the embodiments where actuator 50 is a step-by-step motor,
the spring could be dispensed with, the only magnetic resistance
torque between subsequent steps maintaining the position of rings
12, 42 when the motor is not excited.
[0058] Lastly, even if the invention has been disclosed in detail
with reference to a pump for the lubrication oil of a motor vehicle
engine, it may be applied to any positive displacement pump for
conveying a fluid from a first to a second working environment, in
which a delivery rate reduction as the pump speed increases is
convenient.
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