ITTO20121149A1 - ADJUSTABLE DISPLACEMENT PUMP PUMP AND METHOD FOR ADJUSTING THE PUMP DISPLACEMENT. - Google Patents

Description

VANE PUMP WITH ADJUSTABLE DISPLACEMENT AND METHOD FOR ADJUSTING THE DISPLACEMENT OF THIS PUMP

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Technical sector

The present invention relates to variable displacement rotary pumps, and more particularly it relates to a pump of the type in which the displacement adjustment is obtained thanks to the variation of the relative eccentricity between an adjustment ring and the rotor of the pump, obtained by varying the relative position of the ring and rotor according to the operating conditions of the pump.

The invention also relates to a method for adjusting the displacement of this pump.

Preferably, but not exclusively, the invention finds application in a pump for the lubricating oil of a motor vehicle engine.

Known technique

It is known that, in pumps for circulating lubricating oil under pressure in motor vehicle engines, the capacity, and therefore the flow rate of the oil at the outlet, depends on the rotational speed of the engine, and therefore the pumps are designed to provide a sufficient flow rate at low speeds, to guarantee lubrication even in these conditions. If the pump has a fixed geometry, at high rotation speed the flow rate is higher than necessary, so that there is a strong power absorption with consequent greater fuel consumption and greater stress on the components due to the high pressures generated in the circuit.

To obviate this drawback, it is known to equip the pumps with systems that allow the regulation of the flow rate at the different operating speeds of the vehicle, in particular through the regulation of the displacement. Various solutions are known for this purpose, specific for the particular type of pumping elements (external or internal gears, vanes ...). However, some general types of displacement adjustment systems can be identified and, for rotary vane pumps, one of these is based on the variation of the relative position between an external adjustment ring, also known as a "stator ring", inside which it rotates eccentrically the rotor, and the rotor itself. In this way a variation of the relative eccentricity between the two components is obtained and therefore a variation of the pump displacement.

This type of regulation is implemented in several ways. The following are recognized as follows: - pumps in which the rotor rotates the external ring in which the radially external extremity of the vanes is hinged ("pendulum" pumps);

- pumps in which the stator ring can slide transversely to the rotation axis of the rotor;

- pumps with stator ring pivoting around an axis external to it; And

- pumps in which the stator ring can rotate on an axis inside the ring itself and parallel to the rotation axis of the rotor.

In these types of pumps, while the stator ring is moving to vary the displacement, it is necessary to oppose its movement by means that generate antagonistic forces and which are normally made up of springs. These means of contrasting the movement of the stator ring generate problems of:

a) vibration / noise, when an unstable balance of forces and friction occurs during movement;

b) triggering of vibrations / pressure pulsations as a function of the rapid transients of variation of the rotation speed and / or of the adjustment of the pressure thresholds; c) pressure regulation hysteresis between the increase and decrease of the rotation speed;

d) wear due to excessive specific pressure in the support area of the stator ring.

To reduce these problems, in the case of a pump in which the displacement is adjusted by rotation of the stator ring, it has already been proposed to insert rolling elements between an external surface of the stator ring and an internal surface of a chamber in which the stator ring rotates. It is clear that transforming the sliding friction into rolling friction reduces the resistance to rotation of the stator ring, on which the hysteresis depends.

An example is described in US 5,863,189, in which the outer surface of the stator ring and the inner surface of the chamber form the inner and outer rings of an annular roller bearing, in which the rollers are kept equidistant by a suitable cage. annular. In this known solution, the cage with the rollers extends over the entire circumference of the aforesaid surfaces and can be operated exclusively by means of a lateral lever arm which makes its realization complicated.

The Applicant has also observed that an analysis of the mechanical and fluidic forces (in particular hydraulic) which are generated during the operation of the pump shows that, in the pumps of the type considered, the resultant of these forces acts in a limited area of the engagement region. between the outer surface of the stator ring and the inner surface of the chamber in which the stator ring rotates and, therefore, it is in this area that it is necessary to avoid the generation of unstable balances or balances that oppose the movement in an important way adjustment.

Description of the invention

An object of the present invention is to provide a variable displacement rotary volumetric pump of the aforesaid type which obviates the drawbacks of the known art.

According to the invention this is achieved due to the fact that:

- the rolling elements are arranged only in a part of a region of engagement between the outer surface of the adjusting ring and the inner surface of a chamber in which the ring moves, this part comprising an area in which a resultant of mechanical and fluidic forces generated in the pump during adjustment and in which, due to the effect of said resultant, a fluidic support bearing is created; And

- the rolling elements are arranged, in said part of the region of engagement between said surfaces, in such a way as to be able to move as a single body along said surfaces during the adjustment movement, the movement of the rolling elements having an amplitude smaller than that of a movement performed by the adjustment ring to make the pump pass from a condition of maximum displacement to a condition of minimum displacement.

Preferably, the adjusting movement is a rotation, the part of the region of engagement between the surfaces is configured as a rolling bearing sector of which said surfaces respectively form sectors of the inner ring and of the outer ring, and the rolling elements they are arranged in a seat formed in the external surface of the adjustment ring.

According to another preferred feature of the invention, the rolling elements are rollers or needles mounted in a support and guide cage adapted to move in said seat against the action of an elastic contrast movement arranged between an end of the cage and one end of the seat and preloaded so as to keep the guide in contact with an opposite end of the seat in a condition of maximum displacement or rest of the pump.

The invention also provides a method for regulating the displacement of a pump of the aforesaid type, in which the operations of:

- arranging a plurality of rolling elements in a part of a region of engagement between an external surface of the adjustment ring and an internal surface of a chamber in which the ring moves for adjustment, this part comprising an area in which it acts a resultant of mechanical and fluidic forces generated in the pump during adjustment and in which, due to the effect of said resultant, a fluidic support bearing is created;

- causing the rolling elements to move as a single body in this part of the region of engagement between said surfaces during the adjustment movement, the movement of the rolling elements having an amplitude smaller than that of an adjustment movement which causes the pump to pass from a state of maximum displacement to one of minimum displacement.

Brief description of the figures

These and other characteristics of the present invention will become clear from the following description of a preferred embodiment made by way of non-limiting example with reference to the attached drawings, in which:

- fig. 1 shows, in a view without the closing cover and in the condition of maximum displacement, a vane pump in which the invention can be applied;

- fig. 2 is a view similar to fig.1 and shows the same pump in the condition of minimum displacement;

- fig. 3 represents the intensity and direction of the main forces involved during operation of the pump of figures 1 and 2, of their partial resultants and of the overall resultant in the condition of maximum pump displacement, at the start of pressure regulation;

- fig. 4 is a view similar to fig. 3 and represents the intensity and direction of the forces involved and their resultants, partial and overall, in the condition of minimum displacement, at the end of the pressure regulation;

figures 5 and 6 show a pump according to the invention, respectively in the conditions of maximum and minimum displacement;

- fig. 7 is an enlarged isometric view of the roller-holder cage of figures 5 and 6; and - fig. 8 is an exploded isometric view of the pump according to the invention.

Description of preferred embodiments

In the figures we consider, purely by way of example, a pump in which the displacement variation is obtained thanks to the rotation of the regulating stator ring (hereinafter referred to as "stator" for short) around an axis parallel to the rotation of the rotor and in which the rotation of the stator is controlled directly by the pressure of the pumped fluid.

With reference to Figures 1, 2 and 8, a pump 1 of the aforesaid type comprises a body 10 which has a suitably shaped cavity 40 in which the stator 11 is mounted, free to rotate along an arc of circumference, in the example illustrated in clockwise direction as indicated by arrow A. The rotation axis of the stator 11 is indicated by B. The stator 11 has a chamber 12 in which the vane rotor 13 is housed, keyed on a shaft 14 offset from the center C chamber 12. The rotor 13 can also rotate clockwise. 41, 42 indicate the outlets of the intake and delivery ducts, when the rotor 13 rotates clockwise.

As known to the technician, the rotation of the stator 11 around the axis B causes a variation of the relative eccentricity between the stator 11 and the rotor 13, and therefore a variation of the displacement, between a condition of eccentricity and maximum displacement (represented in Fig . 1), which is assumed also in conditions of rest of the pump and in which the rotor 13 is substantially tangent to the surface 12A of the chamber 12, and a condition of minimum displacement (represented in fig. 2), in which the rotor 13 is coaxial or substantially coaxial to chamber 12. This arrangement is entirely conventional and does not require a more detailed description.

In the example illustrated, for the control of its rotation, the stator 11 has a pair of radial appendages 17, 18 which penetrate into respective chambers 15, 16 formed by recesses of the cavity 40 and slide sealingly on the base of the chambers 15, 16. One of the two chambers, for example chamber 15, is permanently connected to the delivery side of the pump or to the devices for using the pumped fluid (in particular, in the preferred application, with a point of the motor lubrication circuit located downstream of the oil filter), through a first adjustment duct, not shown in these figures. The other chamber can in turn be put in communication with the delivery side or with the devices for using the pumped fluid by means of a valve operated by the vehicle's electronic control unit and a second regulation duct (not shown). In this way, the appendix 17 is exposed, or both appendages 17, 18, are exposed to the pressure conditions of the pumped fluid.

An end wall of one of the chambers, for example the chamber 15, can be shaped so as to form a support 19 for the appendix 17 in the position of maximum displacement.

The chamber 16 houses an organ 20 to contrast the rotation of the stator 11, which in the illustrated example consists of two opposed mushroom elements 21, 22, connected for example telescopically and stressed in the opposite direction by a spring 23, inserted between the heads 21A, 22A of the two elements. The spring 23 is preloaded so as to oppose the rotation of the stator 11 - and therefore keep it in the position of fig. 1 as long as the pressure applied to the appendix 17 (or the overall pressure applied to the appendices 17, 18) is lower than a predetermined threshold, and to subsequently maintain the pump displacement at the value corresponding to the pressure threshold. This condition is reached when a balance is established between the torques generated by the pressure acting on the appendages 17, 18 and the antagonist torque generated by the spring 23.

The two heads 21A, 22A, for example substantially semi-cylindrical, engage in cavities of complementary shape 21B, 22B provided respectively on the surface of the appendix 18 opposite to that on which the regulation pressure acts and on a wall of the chamber 16. It forms thus a pair of articulated joints which allow the ends of the spring 23 to be kept parallel to each other during the rotation of the stator 11, ensuring good lateral stability of the spring itself.

The circumferential width and the radial dimension of the chambers 15, 16 will be defined by the operating characteristics required of the pump. In particular, as regards the circumferential width, a rotation of the stator 11 of the order of about 20 ° is typical for the preferred application and has been illustrated in the drawings. As for the radial dimension, it can be constant for the whole circumferential width, so that the appendages 17, 18 have a constant thrust area and therefore generate a torque, proportional to the actuation pressure, constant for the whole arc of rotation. Alternatively, the radial dimension of one or both chambers can vary along the circumferential width and the appendages 17, 18 are made with a variable thrust area, so as to generate a variable torque along the arc of rotation of the stator 11 This solution allows to take into account the fact that the resisting torques encountered during the adjustment of the displacement can be variable, for example because the resistance opposed by the contrast spring 20 and / or the rotation frictions vary.

Figures 1 and 2 also indicate the various forces acting on the components of the pump 1 during operation and the reactions caused by these forces. Note that in figures 1 and 2 it is only intended to give a representation of the areas in which the various forces act and of the directions and directions of these, while their intensity is not taken into consideration. In particular:

- FP1, FP2 are the thrust forces applied to the appendages 17, 18 by the fluid introduced into the chambers 15, 16; it is assumed that the pressurized fluid is introduced into the chamber 16 during the adjustment and for this reason the force FP2 is present only in fig.2;

- FM is the force of contrasting rotation of the stator 11 applied by the contrasting member 20;

- FACT is the friction force between the heads 21A, 22A of the two elements 21, 22 that make up the member 20 and the respective seats 21B, 22B;

- FHYD is the force applied by the fluid present in the pumping chamber 12 on the rotor 13 and on the stator 11;

- FCÃ is the contrast force of FHYDeserted by the body 10;

- RVÃ is the hydraulic reaction to the resultant of the forces mentioned above;

- RHÃ is the friction between the stator 11 and the internal surface 40A of the chamber 40 during the rotation of the stator 11;

Figures 3 and 4 have plotted the representative vectors of the forces FP1-FC described above and their resultants, partial and overall, in the two extreme operating conditions represented in figures 1 and 2. In figures 3, 4, the origin of the axes coincides with the center of rotation B of the stator 11. As can be immediately seen by superimposing the diagram on the right of figures 3 and 4 respectively on fig. 1 and 2, the resulting SV1 and SV2 respectively of the aforesaid forces have an orientation such as to act in correspondence with a zone S of the surfaces in engagement with the stator 11 and the cavity 40. In this zone, by reaction, the pressurized fluid present in the chamber 12 creates a hydraulic support bearing. The reaction provided by this bearing is the force RV mentioned above, having the same intensity and opposite direction to the resultants above.

To optimize the operation of the pump, it is important to minimize the irregularities and jamming during the movement of the stator 11 and the consequent vibrations, noise and hydraulic pulsations in the S zone in which the resulting SV1, SV2 act, while the remaining part of the engagement region between the surfaces 11A, 40A it has a much less influence and does not require any particular interventions.

This optimization is obtained with the pump according to the invention, which will now be described with reference to figures 5 - 8. The elements already described with reference to figures 1 and 2 are indicated with the same reference numbers.

According to the invention, between the external surface 11A of the stator 11 and the internal surface 40A of the cavity 40, along a section comprising the zone S where the hydraulic support bearing is formed and where the resultant SV1, SV2 of the various forces acts, A plurality of rolling elements 25 are arranged, in the illustrated example rollers or needles (hereinafter generically referred to as "rollers"). In correspondence with this portion a rolling bearing sector is thus formed, of which the outer surface 11A of the stator 11 constitutes the corresponding inner ring sector while the inner surface 40A of the cavity 40 constitutes the corresponding outer ring sector. The rollers 25 are mounted, for example by snap action, in respective seats 27 of a support cage 26, preferably made of plastic material, which in a conventional way acts as a guide and spacer for the rollers 25.

The cage 26 with the rollers 25 is housed in a recess 28 of the external surface 11A of the stator 11, which extends axially for the entire axial depth of the stator 11 and of the chamber 40. The recess 28, the cage 26 and the rollers 25 have dimensions radial such that the contact between the surfaces 11A and 40A is ensured by the rollers 25. Typical diameters for the rollers, in the preferred application, are of the order of a few millimeters, for example 2 - 4 mm. The cage 26 also extends axially for the entire depth of the stator 11, while the rollers 25 will have an axial dimension (length) slightly less than that of the cage 26. This gives the cage 26 - rollers 25 assembly a labyrinth configuration, which allows the maintenance of the hydraulic support bearing.

The cage 26 has an angular amplitude lower than the angular amplitude of the recess 28, so as to be able to move in it during the rotation performed by the stator 11 for adjusting the displacement, and the angular amplitude of the movement performed by the cage 26 is less than angular amplitude of the rotation of the stator 11 to pass from the position of maximum displacement to that of minimum displacement. Taking into account that only the surface 11A is movable and of the difference in radius between the movable surface 11A and the fixed one 40A, the described solution, with seat 28 for the cage 26 obtained in the movable part, allows the rollers 25 to complete the same path on the two surfaces and then to rotate without crawling.

The recess 28 is delimited by two steps or shoulders 29A, 29B. Against one of these shoulders, for example the shoulder 29A, an end of the cage 26 rests in the rest condition (maximum displacement) of the pump illustrated in fig. 5. Between the other end of the cage 26 and the other shoulder 29B there is instead disposed an elastic element 30 to contrast the movement of the cage, p. ex. a leaf spring suitably preloaded, which holds the cage 25 in contact with the shoulder 29A in the condition of maximum displacement.

In Figures 5 and 6 it is possible to clearly see the behavior of the cage 26 with the rollers 25 during the adjustment of the displacement. To facilitate understanding, the segments X, Y, Z have indicated three reference points belonging respectively to the body 10, the stator 11 and the cage 26. The three points are chosen so that their positions coincide in the maximum condition displacement (fig. 5). At the end of the rotation that brings the stator 11 to the position of minimum displacement (fig. 6), the point X obviously remained fixed while the point Z moved clockwise, describing an arc which, in the example illustrated, is ̈ about 20 °. Point Y also rotated clockwise, however for a shorter arc than that performed by point Z. Due to the smaller rotation of the cage 26 with respect to the stator 11, at the end of the rotation the cage 26 is no longer in contact with shoulder 29A and spring 30 it is more compressed.

It is clear that the invention overcomes the drawbacks indicated above for the known art. In fact, the presence of rolling elements 25 between the two engaging surfaces 11A, 40A per se reduces friction with respect to the case in which the stator 11 is supported only by the hydraulic bearing. Furthermore, the configuration of the area of engagement between the surfaces as a bearing sector (or open bearing) which extends into the area where the resultant of the mechanical and hydraulic forces generated during adjustment acts avoids the jamming due to these forces. Finally, the arrangement of the rolling elements 25 in such a way that they can move in a seat 28 obtained in the stator 11, following a shorter path than that completed by the stator itself, avoids the sliding of the rolling elements 25 and therefore reduces the resistance to the adjustment movement.

It is evident that what has been described is given by way of non-limiting example and that variations and modifications are possible without departing from the scope of the invention.

For example, even if a pump has been illustrated in detail in which the adjustment of the displacement occurs by means of a rotation of the stator around an axis inside the stator itself, controlled directly by the pressure of the pumped fluid, the invention can also be applied to pumps in which the rotation of the stator is obtained in another way (e.g. it is obtained by means of a gear which engages with a toothed sector of the external surface of the stator, as in US 5.863.189) or with pumps with a movement of adjustment of the displacement different from the rotation of the stator illustrated here (pendulum pumps, pumps with pivoting stator, pumps with translation of the stator ring, etc.). Obviously, if the adjustment movement performed by the stator is a translation, the cage 26 will be of the linear type.

Claims (10)

Claims 1. Variable displacement rotary vane pump for fluids, comprising: - a rotor (13) adapted to rotate eccentrically in an adjustment ring (11) with a relative eccentricity that varies according to the operating conditions of the pump (1); 5 - means (17, 18) for making the adjustment ring (11) move in a chamber (40) formed in a pump body (10) to vary this relative eccentricity, and therefore the displacement of the pump (1), as these operating conditions vary; And - a plurality of rolling elements (25) inserted between an external surface (11A) of the adjustment ring (11) and an internal surface (40A) of the chamber (40); 10 characterized by the fact that: - the rolling elements (25) are arranged only in a part of an engagement region between the outer surface (11A) of the adjustment ring (11) and the inner surface (40A) of the chamber (40), this part comprising a zone (S) in which a resultant (SV1; SV2) of mechanical and fluidic forces generated in the pump 15 acts during the adjustment; And - the rolling elements (25) are arranged, in said part of the region of engagement between said surfaces (11A, 40A), in such a way as to be able to move as a single body along said surfaces (11A, 40A) during the movement of the ring adjustment (11), the movement of the rolling elements (25) having an amplitude smaller than that of a movement 20 performed by the adjustment ring (11) to make the pump pass from a maximum displacement to a minimum displacement. 2. Pump according to rev. 1, in which the adjustment movement is a rotation of the adjustment ring (11) and in which: - in said part of the engagement region, the outer surface (11A) of the adjustment ring 25 (11) and the inner surface (40A) of the chamber (40) form, together with the rolling elements (25), a bearing sector rolling element of which said surfaces constitute sectors of an inner ring and respectively of an outer ring; and - the rolling elements (25) are arranged in a seat (28) formed in the surface (11A) of the adjustment ring (11) and having an extension greater than an extension of a support and guide cage 30 (26) in which the rolling elements (25) are mounted. 3. Pump according to claim 2, in which the support and guide cage (26) is able to move in said seat (28), moving the rolling elements (25), against the action of an elastic contrast element (30) arranged between a 'end of the cage (26) and one end (29B) of the seat (28) and adapted to maintain or bring the cage (26) in contact with an opposite end (29A) of the seat (28) in the condition of maximum displacement of the pump. 4. Pump according to rev. 2 or 3, in which the rolling elements (25) are mounted in the support and guide cage (26) so as to give it a 5 labyrinth configuration suitable for maintaining a fluidic support bearing generated in said area (S) as a reaction to the action of the resultant (SV1, SV2) of said forces. 5. Pump according to claim 4, in which the rolling elements (25) are rollers or needles, and in which the support and guide cage (26) has an axial depth substantially corresponding to an axial depth of the adjusting ring ( 11) and the rollers or needles (25) 10 have a length shorter than the axial depth of the cage (26). Pump according to any one of claims 2 to 5, in which the rotation of the regulating ring (11) is controlled directly by the pressure of the pumped fluid. Pump according to any one of the preceding claims, wherein the pump is 15 a pump for the lubrication circuit of a motor vehicle engine. 8. Method of regulating the displacement of a variable displacement rotary pump for fluids, comprising a rotor (13) adapted to rotate eccentrically in an adjustment ring (11) with a variable eccentricity according to the operating conditions of the pump, the method including the operations of: 20 - arrange, between an external surface (11A) of the adjustment ring (11) and an internal surface of a chamber (40) which gives seat to the ring (11), a plurality of rolling elements (25) mounted in position relative fixed; And - causing the adjustment ring (11) to move in the chamber (40) to vary this relative eccentricity, and therefore the displacement of the pump, as said operating conditions vary; 25 characterized by the fact that the operation of arranging rolling elements (25) in the chamber (40) includes the operations of: - arranging the rolling elements (25) only in a part of an engagement region between the external surface (11A) of the adjustment ring (11) and the internal surface (40A) of the chamber (40), this part comprising a zone (S) in which a resultant 30 (SV1; SV2) of mechanical and fluidic forces generated in the pump during regulation acts; And - during the adjustment, making the rolling elements (25) move as a single body in this part of the region of engagement between said surfaces (11A, 40A), the movement of the rolling elements (25) having an amplitude smaller than that of a movement of the 'regulation ring (11) which makes the pump pass from a maximum displacement to a minimum displacement. 9. Method according to rev. 8, in which the adjustment movement is a rotation of the adjustment ring (11) and the operation of arranging the rolling elements (25) only in 5 a part of said engagement region between said surfaces (11A, 40A) comprises the operation of configuring the rolling elements (25), the outer surface (11A) of the adjustment ring (11) and the inner surface (40A) of the chamber (40) as a sector of a rolling bearing of which these surfaces they respectively form circular sectors of an inner ring and an outer ring. 10 10. Method according to rev. 8 or 9, in which the operation of making the rolling elements (25) move as a single body involves making the rolling elements (25) move in a seat (28) formed in the outer surface (11A) of the adjustment ring (11) and having a greater extension than an overall extension of these elements.