Variable displacement rotary pump for fluids including means for opposing the displacement regulation and method of regulating the displacement of the pump

Abstract

 A variable displacement pump (1) for fluids is provided where displacement regulation is achieved thanks to the variation of the relative eccentricity between a regulation ring (11) in which the rotor (13) is located and the rotor itself. Means (19) opposing the movement of the regulation ring (11) are provided between the regulation ring (11) and a pump body (10), which means have a first end (22) articulated onto the body (10) of the pump (1) so that the means themselves can perform an oscillatory movement about such a first end (22), and a second end (25) arranged, during the oscillatory movement, to move along a track (26) formed on the surface of the ring (11) and consisting of an arc of a curve such that a tangent to the curve in each position of the second end (25) is perpendicular to a longitudinal axis of symmetry (S) of the opposing means (19). The disclosure also concerns a method of regulating the displacement of such a pump.

Description

Technical field

[0001] The present invention relates to variable displacement rotary pumps, and more particularly it concerns a pump with optimised means for opposing the displacement regulation.

[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 the engine and/or the drive system of a motor vehicle.

Prior art

[0004] It is known that, in pumps for making lubricating oil under pressure circulate in engines and drive systems in motor vehicles, 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 higher lubricant heating occur. This heating causes a decrease of the lubricating power and a stress of the components, as well as the need, in some cases, to use heat exchangers (radiators).

[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.

[0006] Variable displacement pumps require a resistance to displacement variation, which resistance determines the starting value of the regulation of the displacement and hence of the pressure/delivery rate of the fluid being pumped. Such resistance is generally provided by a resilient member, typically consisting of one or more suitably calibrated mechanical springs. Moreover, as the rotation speed increases, the pump needs to modify its configuration in order to keep the pressure/delivery rate at the regulation value and, to this end, the regulating mechanism opposed by the resilient member is to be displaced. Yet, the resilient member has an own rigidity and consequently, when the regulating mechanism is moved, the opposing force exerted by the resilient member increases, thereby modifying the value of the pressure/delivery rate with respect to the starting regulation value.

[0007] Solutions have been proposed for optimising the behaviour of the opposing member, so as to avoid undesired increase of the pump delivery pressure during displacement regulation. For instance, US 8,186,969 and US 2012/03013342 disclose variable displacement rotary pumps in which the rotor eccentrically rotates inside a cavity of a regulation stator ring, which can be made to oscillate in order to vary the relative eccentricity of the cavity and the rotor, and hence the displacement. In the first document, the oscillation of the stator ring is opposed by a pair of coaxial springs which intervene at different values of the delivery pressure. In the second document, the oscillation of the stator ring is opposed by a pair of springs operating in opposite directions. The solutions proposed by both documents are rather complex and do not effectively ensure maintenance of the desired pressure.

Description of the invention

[0008] It is an object of the present invention to provide a rotary positive displacement pump with variable displacement of the above kind, which obviates the drawbacks of the prior art.

[0009] According to the invention, this is achieved in that the opposing means have:

• a first end articulated onto the pump body so that the opposing means can perform an oscillatory movement about the first end during the movement of the ring; and
• a second end arranged, during said oscillatory movement, to move along a track formed on the surface of the ring and having a profile consisting of an arc of a curve such that a tangent to the curve at each position of the second end is perpendicular to a longitudinal axis of symmetry of the opposing means, passing through the first and second end.

[0010] Preferably, the track profile is an arc of a circumference the centre of which lies on said longitudinal axis of symmetry.

[0011] The invention also provides a method of regulating the displacement of a pump of the above kind, in which the movement of the regulation ring is opposed by opposing means arranged between the regulation ring and a pump body, and the step of opposing the movement of the ring comprises the steps of:

• articulating a first end of the opposing means onto the pump body, so that the opposing means can perform an oscillatory movement about the first end during the movement of the regulation ring; and
• during said oscillatory movement, making a second end of the opposing means move along a track formed on a surface of the ring and consisting of an arc of a curve such that a tangent to the curve at each position of the second end is perpendicular to a longitudinal axis of symmetry of the opposing means, passing through the first end.

Brief description of the figures

[0012] The above and other features of the present 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:

• Fig. 1 is a plan view of a pump according to the invention, without the closure cover and in the maximum displacement condition;
• Fig. 2 is a view similar to Fig. 1 and shows the pump in a displacement condition intermediate between the maximum and the minimum displacement;
• Fig. 3 is a view similar to Figs. 1 and 2 and shows the pump in the minimum displacement condition;
• Fig. 4 is an enlarged view of part of Fig. 2; and
• Fig. 5 shows an example of qualitative behaviour of the resistant torque versus the stator rotation for the pump shown in Figs. 1 to 4.

Description of a preferred embodiment

[0013] By way of example only, in the Figures there is shown a rotary vane pump of a kind comprising a rotor rotating inside an eccentric cavity of a regulation ring or stator ring (hereinafter referred to as "stator" for the sake of brevity), which may be displaced, as the operating conditions of the pump vary, in order to vary the relative eccentricity between the cavity and the rotor, and hence the pump displacement. In particular, always by way of example only, there is shown a pump where the displacement variation is achieved through the rotation of the stator, within a predetermined angular range, about an internal 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.

[0014] Referring to Figs. 1 to 4, 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 rotatable about an axis A over a given arc of circumference. In the illustrated example, stator 11 is assumed to rotate in counterclockwise direction, as indicated by arrow F. Stator 11 has a substantially circular chamber 12 where vane rotor 13, keyed on a shaft 14 arranged off-axis relative to centre B of chamber 12, is housed. In the illustrated example, also rotor 13 rotates in counterclockwise direction.

[0015] As known to the skilled in the art, rotation of stator 11 about axis A 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 or displacement (shown in Fig. 1), which is taken also under 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. 3), 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.

[0016] 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 the outer ends of 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, preferably, to the units utilising the pumped fluid (for instance, to a point of the engine lubrication circuit located downstream the oil filter), through a first regulation duct 30. 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 31. In this manner, appendage 17 is, or both appendages 17, 18 are, exposed to the pressure conditions of the pumped fluid acting onto rear surfaces (with reference to the direction of rotation of the stator) 17a, 18a of the appendages.

[0017] 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° 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 torque, proportional to the actuation pressure, which is constant 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 one of appendages 17, 18, or both, may be formed with a variable thrust area, so as to generate a torque varying over the arc of rotation of stator 11. Such a solution allows taking into account that the resistant torques encountered during displacement regulation may be variable, for instance because the resistance opposed by a member 19 opposing the rotation of stator 11, which member will be described later on, and/or the rotational frictions vary.

[0018] Chamber 16 houses member 19 opposing the rotation of stator 11, which member is arranged between front surface 18b of appendage 18 and body 10. Opposing member 19 comprises for instance a helical spring 20, 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 equilibrium is established between the torques generated by the pressure acting on appendages 17, 18 and the antagonist torque generated by opposing member 19.

[0019] Opposing member 19 has a first end articulated onto body 10 so that the opposing member 19 can perform an oscillatory movement about its first end during the movement of ring 11, whereas the opposite end is arranged to move on surface 18b of appendage 18 during such an oscillatory movement.

[0020] More particularly, as better shown in Fig. 4, on the side of the first end, spring 20 is wound on a first tappet 21 to which a first roller 22 is fixedly connected. The roller engages a complementary recess 22a in body 10 thereby forming an articulation for said first end such as to allow said oscillatory motion. On the opposite side, spring 20 is received in a spring-guiding sleeve 23, which is closed by a bottom 23a associated with a second tappet 24 bearing a member, for instance a second roller 25, arranged to move, in particular to roll, over a track 26 formed on surface 18b of appendage 18.

[0021] As it is apparent for the skilled in the art, sleeve 23 prevents spring 20 from becoming deformed during displacement regulation.

[0022] In turn, the provision of roller 25 ensures a reduced friction between opposing member 19 and track 26 during the oscillation of the opposing member and the consequent displacement of the second end thereof along track 26.

[0023] In the embodiment shown in the drawings, track 26 is an arc of a circumference with radius R, the centre of which always lies on axis of symmetry S of spring 20, i.e. on the line joining the centres of rollers 22 and 25. In general, track 26 will be an arc of a curve such that, at each position of opposing member 19, axis S of spring 20 always is perpendicular to the tangent to the curve in the contact point of roller 25 and lies on the axis passing through the centres of rollers 22 and 25. In this manner, opposing member 19 is self-aligning, so as to prevent spring 20 from becoming deformed during displacement regulation.

[0024] As it will be readily understood by the skilled in the art, the specific shape of the curve of track 26 will depend on the configuration of opposing member 19, in particular on the relative position of the articulation point and the moving end.

[0025] With the arrangement illustrated, the resistant force applied by opposing member 19 and arm B thereof (the distance between axis S and centre A of rotation of ring 11) change as the position of ring 11 changes. In the maximum displacement condition, roller 25 is at one end of track 26 (the bottom end in the drawing), opposing member 19 has a maximum length Lmax and hence exerts a minimum force, and arm B also has a maximum value Bmax. When ring 11 rotates, opposing member 19 rotates about the axis of the articulation consisting of the first roller 22 and recess 22a, and the second roller 25 moves along track 26 towards the top end thereof. Length L and arm B decrease because of the roller displacement, and they attain respective intermediate values Lmed, Bmed upon a rotation by about 10° (Fig. 2), and respective minimum values Lmin (to which a maximum force corresponds), Bmin at the end of the rotation by about 20°, in the minimum displacement position (Fig. 3). In case of track 26 such as considered here, the resistant torque has the qualitative behaviour shown in Fig. 5: after an initial increase (until a rotation by about 5°), the torque constantly decreases. The variation of the spring load due to the rigidity of the same spring is thus compensated.

[0026] In accordance with other embodiments, by varying the position of the articulation consisting of the first roller 22 and recess 22a and/or the shape of track 26, the curve shown in Fig. 5 may have a behaviour other than that shown, as it will be readily understood by the skilled in the art. For instance, the resistant torque may have a constant behaviour or a behaviour inverted with respect to that shown.

[0027] Essentially, the invention allows managing at the design phase the behaviour of the antagonist torque through different degrees of freedom while keeping the conventional resilient member opposing the displacement variation (a mechanical spring, in particular a compression spring).

[0028] 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.

[0029] For instance, even if there has been disclosed 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 indirectly controlled by said pressure, or to pumps where the displacement regulation movement is different from the rotation of the stator illustrated herein ("pendulum" pumps, pumps with a rocking or oscillating stator, and so on). Moreover, even if a vane pump has been illustrated, the invention can be applied also to pumps with a rotor of different kind, e.g. a gear rotor (for instance G-rotor or split G-rotor).

Claims

1. A variable displacement rotary pump for fluids, comprising:

- a rotor (13) arranged to eccentrically rotate within a chamber (12) defined by a regulation ring (11), with a relative eccentricity that is variable depending on operating conditions of the pump (1);

- moving means (17, 18) arranged to make the regulation ring (11) move within a cavity (40) formed in a pump body (10) in order to vary said relative eccentricity, and hence the displacement of the pump (1), as the operating conditions vary; and

- opposing means (19) arranged to oppose the movement of the regulation ring (11) and having a given longitudinal axis of symmetry;

characterised in that the opposing means (19) have:

- a first end (22) articulated onto the body (10) of the pump (1) so that the opposing means (19) can perform an oscillatory movement about the first end (22) during the movement of the ring (11); and

- a second end (25) arranged, during said oscillatory movement, to move along a track (26) formed on the surface of the ring (11) and consisting of an arc of a curve such that a tangent to the curve in each position of the second end (25) is perpendicular to the longitudinal axis of symmetry (S) of the opposing means (19), said axis of symmetry passing through said first and second ends (22, 25).

2. The pump as claimed in claim 1, wherein said arc of a curve is an arc of a circumference the centre of which lies on said axis (S).

3. The pump as claimed in claim 1 or 2, wherein the opposing means (19) include a spring (20) that, on the side of the first end of the opposing means (19), is associated with a first tappet (21) to which a member (22) arranged to form, with the body (10) of the pump (1), an articulation for said first end is fixedly connected, and that, on the opposite side, is received in a sleeve (23), which is configured so as to prevent deformations of the spring (20) during the oscillation of the opposing means (19) and to which a member (25) arranged to run along said track (26) is fixedly connected.

4. The pump as claimed in claim 3, wherein the member (25) fixedly connected to the sleeve (23) includes a roller arranged to roll over said track (26).

5. The pump as claimed in any one of the preceding claims, wherein said opposing means (19) have a resistant torque depending on a position of an articulation point of said first end (22) onto the body (10) of the pump and/or on the shape of the track (26).

6. The pump as claimed in any one of the preceding claims, wherein the regulation movement is a rotation or an oscillation of the regulation ring (11) directly controlled by the pressure of the fluid being pumped.

7. The pump as claimed in any one of the preceding claims, wherein the regulation ring (11) is configured as a multistage piston for displacement regulation arranged to rotate or oscillate about an axis, where at least a first stage is permanently exposed to the pressure of the fluid being pumped, and at least a second stage is exposed to the pressure of the fluid being pumped upon an external command, jointly with the first stage.

8. The pump as claimed in any one of the preceding claims, wherein the pump (1) is a pump for a lubrication circuit of an engine and/or a drive system of a motor vehicle.

9. A method of regulating the displacement of a variable displacement rotary pump for fluids comprising a rotor (13) arranged to eccentrically rotate within a regulation ring (11) with an eccentricity that is variable depending on operating conditions of the pump, the method comprising the steps of:

- moving the regulation ring (11) in order to vary said relative eccentricity, and hence the displacement of the pump, as said operating conditions vary;

- opposing the movement of the regulation ring (11) with opposing means (19) arranged between the regulation ring (11) and a pump body (10);

and being characterised in that the step of opposing the movement of the regulation ring (11) comprises the steps of:

- articulating a first end (22) of the opposing means (19) onto the body (10) of the pump (1), so that said opposing means can perform an oscillatory movement about said first end (22) during the movement of the regulation ring (11); and

- during said oscillatory movement, making a second end (25) of the opposing means (19) move along a track (26) formed on a surface of the ring (11) and consisting of an arc of a curve such that a tangent to the curve in each position of the second end is perpendicular to a longitudinal axis of symmetry (S) of the opposing means (19), said axis of symmetry passing through the first and second ends (22, 25).

10. The method as claimed in claim 9, wherein said step of making the second end (25) of the opposing means (19) move makes said second end (25) move along a track (26) consisting of an arc of a circumference the centre of which lies on said axis (S).

11. The method as claimed in claim 9 or 10, wherein said step of making the second end (25) of the opposing means (19) move along the track (26) includes a rolling movement.

Drawing