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.
The invention also concerns a method of regulating the displacement of such a pump.
Preferably, but not exclusively, the present invention is applied in a pump for the lubrication oil of a motor vehicle engine.
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.
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.
This kind of regulation is implemented in different ways. Thus, it is possible to recognise:
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:
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.
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.
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.
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.
According to the invention, this is achieved in that:
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.
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.
The invention also provides a method of regulating the displacement of a pump of the above kind, comprising the steps of:
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:
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.
Referring to
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
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.
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.
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
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.
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 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.
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.
This optimisation is obtained by means of the pump according to the invention, which will be now described with reference to
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.
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.
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.
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
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.
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.
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.
Number | Date | Country | Kind |
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TO2012A001149 | Dec 2012 | IT | national |
Filing Document | Filing Date | Country | Kind |
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PCT/IB2013/060918 | 12/13/2013 | WO | 00 |