ITTO20111188A1 - VARIABLE DISPLACEMENT PUMP AND ADJUSTMENT METHOD OF ITS DISPLACEMENT - Google Patents

Description

VARIABLE DISPLACEMENT PUMP AND ADJUSTMENT METHOD OF ITS

DISPLACEMENT

Technical sector

The present invention relates to variable displacement pumps, and more particularly it relates to a volumetric rotary pump in which the displacement variation is obtained by translating a stator ring inside which the pump rotor rotates eccentrically.

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 regulation systems can be identified, and one of these is based on the translation of an element (stator ring) which is arranged in a cavity of the pump body and surrounds the pump rotor with an eccentricity which depends on the position assumed by the ring itself due to the translation.

Examples of pumps of this type are described in US 2004247643, US 2008038117, WO2005068838A1 and EP 1600637.

In particular, WO2005068838A1 describes a displacement pump with a vane rotor, in which the stator ring is made to slide in response to the pressure difference in two chambers located on opposite sides of the stator ring and connected to the pump delivery, the one directly and the other through a control valve. The translation is guided by the same elements on which the translation control pressure acts.

This known pump presents a series of problems that concern, first of all, precisely the ring and concern in particular:

- feasibility: given the way in which the stator ring of the known pump is kept in position against the action of the internal pressures generated by the operation of the pump and is guided during translation, mechanical tolerances and particular surface conditions are required for ensure correct sliding without jamming and leaks;

- pressure stability: the pressure that regulates the displacement of the stator ring is that of the delivery, and this means that the system is remarkably sensitive to pressure fluctuations, typical of volumetric pumps, present at the pump outlet;

- wear: due to the pressures acting on the stator ring and the consequent possibility of jamming, severe wear is generated between the parts in contact with the ring and the pump body.

Pumps with a similar stator ring, which gives rise to the same problems, are described in US 2004247463 and US 2008038117.

An object of the present invention is to provide a pump with displacement adjustment by means of translation of the stator ring and a method for regulating the displacement of this pump which obviate the drawbacks of the known art.

Description of the Invention

According to the invention, this is achieved by the fact that the stator ring has guide means able to slide in a guide chamber formed in the pump body and communicating, preferably, with a pressure zone of the pump to receive fluid under pressure. , and the guide means, during the translation of the stator ring, are able to be pushed by the fluid under pressure in sealing contact with a surface of the guide chamber and, in an area of contact with this surface, have a curvature with a radius such as to guarantee a homogeneous distribution of contact pressures as the operating conditions of the pump and, therefore, the position of the stator ring vary.

Advantageously, the guide means comprise a pair of fins which extend substantially tangentially to the stator ring and in opposite directions from an external surface thereof, define a common thrust surface on which the pressurized fluid acts and a pair of areas of contact with the radius of curvature such as to guarantee the homogeneous distribution of the pressures upon contact, and have rounded free ends.

In this way, the possibility of jamming and consequent wear is drastically reduced. In addition, the need for sealing elements is eliminated.

The translation can be controlled mechanically, by the action of the pressures in a circuit of use of the pumped fluid, or electronically, by means of a motor controlled by an electronic control unit which detects the conditions of the fluid itself in a circuit of use.

The invention also implements a method of regulating the displacement of a rotary volumetric pump by means of the translation of a stator ring inside which the rotor of the pump rotates eccentrically. In this method, this translation is guided by means of guide means adapted to slide in contact with a surface of a guide chamber formed in the pump body by the action of pressurized fluid coming, preferably, from the pump delivery, and contact is made between the guide means and the surface of the guide chamber in an area of the surface of the guide means which has a curvature with a radius such as to ensure a homogeneous distribution of pressures as the operating conditions of the pump and, consequently, the position vary of the stator ring.

According to a further aspect of the invention, there is also provided a lubrication system for the engine of a motor vehicle in which the pump with adjustable displacement and the method of regulating the displacement presented above are used.

Brief Description of the Figures

Other characteristics and advantages of the invention will appear clearly from the following description of preferred embodiments, given by way of non-limiting example with reference to the attached drawings, in which:

- fig. 1 is an axial section of a pump according to the invention;

fig. 2 is a front view of the pump, without the front cover, showing the stator ring in the position of maximum displacement;

- figures 3 and 4 are enlarged views of the details A and B of fig.2;

- fig. 5 and 6 are cross-sectional views of the pump, with the stator ring in the position of maximum displacement and respectively of minimum displacement;

Figures 7 and 8 are enlarged views of details of the guide fins of the stator ring; And

- Figures 9 - 11 are diagrams of a lubrication circuit of a motor vehicle engine which uses the pump according to the invention, in different operating conditions.

Description of Preferred Forms of Realization

With reference to Figures 1 - 6, the reference numeral 1 generally indicates a rotary volumetric pump with adjustable displacement, in particular a pump for the lubricating oil of a motor vehicle engine, of a type comprising a body 2 in which A chamber 3 is formed which gives seat to a stator ring 4, which has an internal cavity 40 in which the rotor 5 rotates eccentrically and can be made to translate transversely to its axis to adjust the displacement of the pump. The rotor 5 is for example a vane rotor, the vanes 6 of which slide radially in radial slots 7, and is driven by a shaft (not shown), suitably shaped, inserted in a cavity 10 of complementary shape. A centering ring 11 is inserted on each of the two axially opposite ends of the rotor 5 to keep the vanes in contact with the inner surface of the ring 4 at low temperature and / or low speed.

The cavity 3 is closed by a front cover 41 and a rear cover 42. In the rear cover 42 are formed the channels 8, 9 for the suction of oil from the sump and for delivery of oil to the oil filter, as well as © lubrication channels, not visible in the drawing.

The suction channel 8 communicates, through a chamber 45 in the rear cover 42, with the suction chambers 43, 44 formed respectively in the lower part of the chamber 3 and the internal cavity 40 of the stator ring (ring) 4. The two chambers 43, 44 also communicate through a chamber 46 formed in the front cover 41. This supply on the two sides of the rotor of the pump 1, which can be called â € œdouble supplyâ €, allows the pump to work in a non-cavitation regime up to high speeds of rotation.

From the suction room 44 the oil is transferred in a conventional way to a delivery room 47 formed in the cavity 40 and in turn communicating with the delivery channel 9.

The environment 43 allows, preferably, to collect any oil leaks inside the pump 1, coming from the delivery environment 47, in general, or from environments under pressure, as described further on.

The environment 43, if positioned lower than the channel 8, also prevents the pump from emptying when priming from standstill after a prolonged stop.

In the illustrated embodiment, the translation of the ring 4, which by way of example is assumed to be horizontal, is controlled by the oil pressure in the lubrication circuit of the engine, as will be described below.

The translation of the ring 4 is caused by a pair of substantially cylindrical thrust heads 13, 14, which act on two diametrically opposite areas of the ring 4. Advantageously, the contact surfaces of the heads 13, 14 and of the ring 4 are flat surfaces, as illustrated in FIG. 3 for the head 14. The flat contact surface does not require special machining. A projection 12 in the wall of the chamber 3 acts as the maximum displacement limit switch, and is adapted to maintain in this condition a certain clearance between the ring 4 and the rotor 5, as can be seen better in fig. 4. The position taken by the ring 4 in the condition of maximum pump displacement is also the reference position for assembling the ring in the seat 3.

The heads 13, 14 are mounted in the body 2 so as to slide in respective chambers 15, 16, closed by plugs 17, 18, which receive pressurized oil from the lubrication circuit of the engine directly (chamber 16) or respectively through a valve. regulation 19 (chamber 15), also controlled by the oil pressure in the regulation circuit.

The first thrust head 13 is also stressed by a spring 20 which is preloaded so that the head 13 keeps the ring 4 in a position of maximum displacement of the pump (Figures 2, 5) in conditions of low pressure of the oil, especially when starting the engine. The flat surface of the head 13 and of the ring 4 in the contact area allows a homogeneous distribution of the force generated by the spring 20 on the ring 4.

The second head 14 is operated to move the ring 4 from the position of maximum displacement towards that of minimum displacement when the oil pressure in the chamber 16 exceeds the preload of the spring 20, and is pushed back by the ring 4 when this it returns to the position of maximum displacement as the oil pressure in chamber 16 decreases. Thanks to a spacer 21, which can also be made in one piece with the head 14, this always remains in contact with the ring 4 and does not adheres to cap 18.

The regulating valve 19 can be made to slide parallel to the direction of movement of the ring 4, to manage the regulating pressures, thanks to a pair of thrust surfaces 19a, 19b on which the oil pressure acts. A spring 24 tends to keep the valve 19 in the position necessary for the ring 4 to remain in the position of maximum displacement. The valve 19 can be integrated in the body 2 of the pump, in a seat 22 closed by a plug 23, as seen in figures 5, 6, or in the motor base, according to the particular motor. The pump body 2 will in any case have the seat 22, regardless of the actual presence of the valve, so that the same pump body can always be used.

The connections of the chambers 15, 16 and of the regulating valve 19 to the lubrication circuit will be described later.

The ring 4 is shaped in such a way as to present a guide element, advantageously constituted by a pair of fins 25, formed for example in the upper part of the ring 4, which extend substantially tangentially to the ring in opposite directions, and are seat in a guide chamber 26 formed in the body 2 and communicating with the delivery channel 9. During the translation of the ring 4, the fins 5 slide in contact with the walls of the chamber 26, and contact is ensured by the pressure of the oil drawn from the delivery channel 9 and acting on the upper face 27 of the fins 25, which defines a common thrust surface. The communication between the delivery duct 9 and the chamber 26 is obtained by means of a duct (not visible in the drawing) made by means of an appropriate machining of the rear cover 41 and / or of the body 2.

The shape of the contact area 28 between each fin 25 and the body 2 is such as to counterbalance the pressure forces that are generated inside the pump during the working phase and to maintain contact with the body 2 in a limited area in any working condition. In this way there is no need for sealing elements. In particular, as indicated in fig. 7, the fins 25 are in contact with the body 2 according to a curved surface having a curvature with a relatively large radius R designed to: - keep the contact pressure within acceptable limits (cylinder-plane contact) without any upsetting of the material in the underlying area;

- guaranteeing a homogeneous distribution of contact pressures as the operating conditions vary, despite the fact that, as the pressure applied to the fins 25 increases, they bend with consequent displacement of the contact points.

Furthermore, the free ends of the fins 25 have a rounded shape, designed to avoid that, due to the forces generated by the moving vanes or internal overpressures (which could bring the vanes into contact with the upper face of the chamber 26, fig. 8) , ring 4 is blocked in the event of imbalance due to an overpressure peak inside the pump.

With reference to figures 9 - 11, the lubrication circuit 100 of a motor vehicle engine 30 using pump 1 is illustrated. 31 and 32 indicate the oil sump and the oil filter, connected in the usual way to the suction and delivery channels 8, 9 (fig. 1), through ducts also indicated with references 8 and 9, and with 33 indicates the outlet duct of the filter 32, which carries the oil to the engine 30 In these figures, an embodiment is shown in which the regulating valve 19 is external to the pump body 2.

This embodiment allows to see more clearly the connections of the valve 19 with the lubrication circuit 100 and with the rest of the pump 1.

A branch 9a of the delivery 9 carries the oil into the chamber 26 to push the fins 25 into contact with the base of the chamber 26. As stated above, this branch is actually a conduit formed inside the pump body. A first branch 33a of the duct 33 constitutes a first regulating duct which carries the oil under pressure to the chamber 16. A second and a third branch 33b, 33c of the same duct carry the oil to a first and a second inlet 49a, 49b of the valve 19. The oil supplied to the first inlet 49a preferably acts on the first thrust surface 19a to control the possible displacement of the valve 19, while the oil supplied to the second inlet 49b can be transferred to a second regulating duct 35, which communicates with the chamber 15, or to the drain 37. The second branch 33b also leads to a distribution valve 36, p. ex. an electromagnetic valve. According to the position of this valve, the oil coming out of the filter 32 can be brought, through a duct 34, to a third inlet 49c of the valve 19, where the oil acts on a second thrust surface 19b, or the oil present in the valve 19 at the inlet 49c it can be returned to the oil sump 31 (duct 38).

According to other embodiments, the oil supplied to the first inlet 49a and to the third inlet 49c can act in an inverted manner, for example so that the first inlet 49a and the third inlet 49c act on the second thrust surface 19b and on the first thrust surface 19a, respectively.

Thanks to the presence of the distribution valve 36, and by suitably dimensioning the thrust surfaces 19a and 19b, it is possible to obtain two or more different intervention points for the regulation valve 19.

It should be noted that, according to the needs of the users of the pump, the adjustment pressures (ducts 33a - 33c) could be taken from the delivery duct 9, instead of from the outlet duct 33 of the filter. The solution illustrated is however the one that guarantees the greatest stability in the regulation pressure, since, as known, due to the nature of the volumetric pumps, the delivery pressure has peaks which are dampened by the filter 32. It is instead preferable to take it directly from the the pressure which acts on the fins 25, to constantly guarantee contact between these and the pump body 2, even if other embodiments are possible.

It should also be noted that, in the event that the valve 19 is arranged in the pump body 2, the ducts 33a, 33b, 34, 35 will be formed, at least in part, in the body 2 by means of an appropriate machining, in a similar way to what said for the duct which connects the delivery 9 with the chamber 26.

The operation of pump 1 is as follows.

When the engine is started, there is low oil pressure on the delivery side and the pump is in the position of maximum displacement (fig. 9). In this condition, the preload of the spring 24 pushes the valve 19 completely to the left, so that the oil can pass from the inlet 49b to the duct 35 and from there to the chamber 15. In contrast to the reaction given by the pressure sent in this chamber, the first regulation duct 33a takes pressure downstream of the filter 32 sending it into the chamber 16. For a balance of forces in the direction of action of the thrust heads 13, 14, the ring 4 is in contact with the mechanical stop 12 (figures 2, 3).

During the operation of the pump 1, the pressure at the outlet 33 of the filter 32 (and therefore at the inlet 49a of the valve 19) increases and, once a certain threshold is exceeded, it overcomes the preload of the spring 24, causing the valve 19 to move to the right. The displacement of the valve 19 progressively closes the inlet 49b and puts the chamber 15 in communication with the outlet 37. In this way the pressure in the chamber 15 is reduced and the pressure present in the chamber 16 is able to overcome the preload of the spring 21 and to move ring 4 in proportion to the pressure drop in chamber 15. The displacement of ring 4 obviously ends when the minimum displacement position is reached (fig. 10).

When the pressure in the duct 33 decreases, it is possible to return to the maximum displacement configuration thanks to the movement of the adjustment valve 19 to the left by the action of the spring 24. With this movement, the connection between the inlet 49b and the duct is restored 35, and the pressure always present in the chamber 16 is no longer able to overcome the combined action of the pressure in the chamber 15 (which is gradually restored) and of the spring 21.

If it is desired to make the valve 19 intervene at a pressure level other than the high pressure one described above, the electromagnetic valve 36 will be activated so as to bring the pressure present at the outlet 33 of the filter 32 also to the inlet 49c of the valve 19 (fig. 11). The thrust is now exerted on both thrust surfaces 19a, 19b and therefore the preload of the spring 20 can be overcome by a pressure lower than the previous one. It is clear to the technician that the valve 36 allows to obtain even more actuation levels of the regulating valve 19 other than the high pressure one.

Thanks to the particular shape of the ring 4, the invention effectively solves the problems indicated above of the known art.

In fact, the mechanical and / or geometric tolerances and the surface conditions suitable to guarantee the correct sliding of the ring 4 affect only the small contact area between the ring 4 and the body 2 (i.e. between the fins 25 and the guide 26) , while all the rest of the surface of the fins can remain rough. There is also no need for special machining of the areas of the ring surface in contact with the thrust heads 13, 14. This allows for a reduction in manufacturing costs.

Furthermore, the large radius R in the zone 28 allows to reduce the contact pressure and, as the pressure acting on the ring 4 varies during operation, to move this point while keeping the pressure distribution in contact constant in shape. This avoids the jamming and wear of the parts in relative motion which are always possible in the known art. The rounded shape of the ends of the fins 25 also helps to avoid jamming during the normal sliding of the ring 4 or during any imbalance of the same due to overpressure peaks inside the pump.

On the other hand, the constant contact between the fins 25 and the body 2 eliminates the need for sealing elements to avoid excessive oil leaks, thus contributing to the simplicity of construction and therefore to the limitation of manufacturing costs. The absence of sealing elements also favors a more rapid response of the system to the displacement change signal.

It is evident that what has been described is given only 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 in the illustrated embodiment the movement of the ring 5 is mechanically controlled by the pressures in the lubrication circuit, an electronic control is also possible, through a small electric motor (brushless, synchronous three-phase or step-by-step ), directly connected to the ring 4 through a linkage, a mechanical joint or other connection suitable for converting the rotation movement of the motor into a translation movement. The engine will be electronically controlled by the electronic control unit of the vehicle, guaranteeing greater precision and greater promptness of intervention. The advantage of this solution is linked to the possibility of having a continuous displacement change in any conditions of use, at any speed, temperature and infinite pressure levels.

Finally, even if the invention has been described in detail with reference to a pump for the lubricating oil of a motor vehicle engine, it can be applied in any volumetric pump for the transport of fluid from a first to a second environment. of work, in which it is convenient to reduce the flow rate as the pump speed increases.

Claims (11)

Claims 1. Volumetric rotary pump for fluids, comprising a rotor (5) adapted to rotate eccentrically in a chamber (40) defined in a stator ring (4) arranged in a seat (3) formed in a body (2) of the pump and connected to means (13, 14, 15, 19) for translating said ring with respect to the rotor (5) as the operating conditions of the pump (1) vary to vary its displacement, in which the stator ring (4) has means of guide (25) adapted to slide in a guide chamber (26) formed in the pump body (2) and communicating with a pressure zone of the pump (1) or with members (100) for using a pumped fluid to receive fluid thereof under pressure, characterized by the fact that the driving means (25). during the translation of the stator ring (4), they are able to be pushed by the fluid under pressure into sealing contact with a surface of the guide chamber (26) and, in an area (28) in contact with this surface, they have a curvature with a radius of curvature (R) such as to ensure a homogeneous distribution of pressures upon contact as the operating conditions of the pump (1) and, consequently, the position of the stator ring (4) vary. 2. Pump according to rev. 1, wherein the guide means (25) comprise a pair of fins (35) which extend substantially tangentially to the stator ring (4) in opposite directions from an outer surface of the stator ring (4), and define a surface common thrust (27) on which the pressurized fluid acts and a pair of contact areas (28) which each have said curvature with a radius of curvature (R) such as to ensure the homogeneous distribution of pressures upon contact. 3. Pump according to claim 2, in which the fins (25) have a rounded free end. 4. Pump according to any one of claims 1 to 3, in which the translation of the stator ring (4) is controlled by a first and a second thrust head (13, 14) which act on diametrically opposite areas of the ring and are able to slide respectively in a first and second thrust chamber (15, 16), distinct from the guide chamber (26) and communicating with the pressure zone of the pump (1) or, preferably, with the members (100) of utilization of a fluid pumped through a regulating valve (19) or respectively directly. 5. Pump according to claim 4, wherein the regulating valve (19) is incorporated in the pump (1). 6. Pump according to claim 4 or 5, in which the thrust heads (13, 14) are adapted to separate a suction environment (43) of the pump from a high pressure environment in which the guide means (25 ). Pump according to any one of claims 1 to 3, wherein the translation of the stator ring (4) is controlled by an electric motor. Pump according to any one of the preceding claims, wherein the pump (1) is a pump for a lubrication circuit (100) of a motor vehicle engine. 9. Method for regulating the displacement of a volumetric rotary pump (1), comprising the operations of: - translating, with respect to a rotor (5) of the pump (1), a stator ring (4) inside which the rotor (5) rotates eccentrically; - guiding the translation of the stator ring (4) by means of guide means (25) able to slide in a guide chamber (26) formed in a body (2) of the pump and communicating with a pressure zone of the pump (1 ) or with members (100) for using a pumped fluid; characterized by the fact that it also includes the operations of: - causing the pumped fluid to act on the guide means (25) to keep them in sealing contact with a surface of the guide chamber (26) during the translation of the stator ring (4); And - making contact between the guiding means (25) and the surface of the guiding chamber (26) in correspondence with a surface area of the guiding means (25) which has a curvature with a radius of curvature (R) such as to guarantee a homogeneous distribution of pressures as the operating conditions of the pump (1) and, consequently, the position of the stator ring (4) vary. 10. Method according to rev. 9, for adjusting the displacement of a lubricating oil pump for a motor vehicle engine (30). Motor vehicle engine (30) lubrication system, comprising a pump (1) according to any one of claims 1 to 8.