Patent Publication Number: US-2016222963-A1

Title: Variable displacement pump with electric control of displacement regulation and method of regulating pump displacement

Description:
TECHNICAL FIELD 
     The present invention relates to variable displacement pumps, and more particularly it concerns a rotary positive displacement pump of the kind in which the displacement variation is obtained by means of the rotation of an eccentric ring (stator ring). 
     The invention also concerns a method of regulating the displacement of such a pump. 
     Preferably, but not exclusively, the present invention is employed in a pump for the lubrication oil of a motor vehicle engine. 
     PRIOR ART 
     It is known that, in pumps for making lubricating oil under pressure circulate in motor vehicle engines, the capacity, and hence the oil delivery rate, depends on the rotation speed of the engine. Hence, the pumps are designed so as to provide a sufficient delivery rate at low speeds, in order to ensure lubrication also under such conditions. If the pump has a fixed geometry, at high rotation speed the delivery rate exceeds the necessary rate, so that part of the delivered flow is to be discharged in order to limit the delivery rate and the pressure. Of course, the discharged oil volume has already been compressed, whereby high power absorption occurs, with a consequent higher fuel consumption and a greater stress of the components due to the high pressures constantly generated in the pump. 
     In order to obviate this drawback, it is known to equip the pumps with systems allowing a delivery rate regulation at the different operating conditions of the vehicle, in particular through displacement regulation. Different solutions are known to this aim, which are specific for the particular kind of pumping elements (external or internal gears, vanes . . . ). 
     A system often used in rotary pumps employs a stator ring with an internal cavity, eccentric relative to the external surface, inside which the rotor, in particular a vane rotor, rotates, the rotor being eccentric with respect to the cavity under operating conditions of the pump. By making the stator ring rotate by a given angle, the relative eccentricity between the rotor and the cavity, and hence the displacement, is made to vary between a maximum value and a minimum value, substantially tending to zero (stall operating condition). A suitably calibrated opposing resilient member allows the rotation when a predetermined delivery rate is attained and makes the pump substantially deliver such a predetermined delivery rate under steady state conditions. An example is disclosed in U.S. Pat. No. 2,685,842. 
     Pumps with a pair of stator rings are also known, where displacement is varied by rotating the rings relative to each other in opposite directions. An example is disclosed in U.S. Pat. No. 4,406,599. 
     The evolution of such pumps and the diffusion of electronics in motor vehicle engines have lead to displacement regulation systems controlled by the electronic control unit of the vehicle depending on the oil pressure, preferably detected downstream the filter, and possibly on other operating parameters of the engine. Generally, such systems are electro-hydraulic systems, where the control unit controls electrically operated valves that, in turn, control hydraulic actuators acting on the stator ring. For instance, US 2011/0209682 discloses a system in which a control module of the pump, being part of the electronic control unit, controls through an electrically operated valve the flow of pressurised oil towards either of two chambers, which apply the oil pressure to the stator ring. Application of the pressure of either chamber corresponds to two different pressure/delivery rate conditions of the pump. 
     Generally, the provision of the hydraulic actuators makes electro-hydraulic systems complex and expensive. Moreover, when the engine is off, it is impossible to modify the displacement presetting, since no control pressure is available. 
     It is an object of the present invention to provide a variable displacement pump, and a method of regulating the displacement of such a pump, which obviate the drawbacks of the prior art. 
     DESCRIPTION OF THE INVENTION 
     According to the invention, this is obtained in that the pump includes an electromagnetic rotary actuator, integrated into or coupled with the pump, which is driven by an electronic system detecting operating conditions of the pump and is arranged to transmit the rotary motion to the stator ring. 
     Advantageously, the stator ring is housed within an eccentric cavity of an external ring, and the rotary actuator is arranged to simultaneously transmit the rotary motion to both rings, in such a way as to cause a synchronous rotation thereof by an equal amount in opposite directions. 
     The invention also implements a method of regulating the displacement of a rotary positive displacement pump by means of the rotation of an eccentric stator ring inside which the rotor rotates, the method comprising the steps of:
         providing an electromagnetic rotary actuator integrated into or coupled with the pump;   supplying the actuator with rotation commands corresponding to a desired rotation of the stator ring.       

     Preferably, the method further comprises the steps of:
         providing an external ring having an eccentric cavity within which the stator ring is housed; and   making both rings rotate by a same angle at the same time and in opposite directions.       

     According to a further aspect of the invention, a lubrication system for a motor vehicle engine is also provided, in which the adjustable displacement pump and the method of regulating the displacement set forth above are employed. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Further features and advantages of the invention will become apparent from the following description of preferred embodiments, given by way of non limiting examples with reference to the accompanying drawings, in which: 
         FIG. 1  is a plan view of a first embodiment of the pump according to the invention, from which the cover and the regulation actuator have been removed, in the minimum displacement position; 
         FIG. 2  is a view similar to  FIG. 1 , in the maximum displacement position; 
         FIG. 3  is a plan view similar to  FIG. 2 , showing the delivery rate regulation mechanism integrated in the cover; 
         FIG. 4  is a cross-sectional view of the pump taken according to a plane passing through line Y-Y in  FIG. 3 ; 
         FIGS. 5 and 6  are views similar to  FIGS. 1 and 2 , relating to a second embodiment of the pump according to the invention; and 
         FIG. 7  is a principle block diagram of the displacement regulating circuit. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to  FIGS. 1 to 4 , a pump  1  according to the invention, more particularly a vane pump, includes a body  10  having a cavity  11  with substantially circular cross-section in which a first movable ring  12  (external ring) is located. The ring in turn has an axial cavity  13 , also with substantially circular cross-section, eccentrically arranged relative to cavity  11 . A second movable ring  42  (stator ring) is located in cavity  13 , which ring in turn has an axial cavity  43 , also with substantially circular cross-section, eccentrically arranged relative to cavity  13  and having a centre O′. Rings  12  and  42  are arranged to rotate in mutually opposite directions by a certain angle in order to vary the pump displacement, as it will be disclosed below. Advantageously, cavities  13 ,  43  have the same eccentricities. In the example illustrated, cavity  11  is blind and is closed at one end by a cover  14  ( FIG. 4 ), also closing the corresponding ends of cavities  13 ,  43 . 
     Cavity  43  in turn houses a rotor  15 , rigidly connected to a driving shaft  15   a  making it rotate about a centre O, for instance in clockwise direction, as shown by arrow F. Cavity  43  thus forms the pumping chamber. In a minimum displacement position (shown in  FIG. 1 ), rotor  15  and cavity  43  are coaxial or substantially coaxial, whereas, in a maximum displacement position (shown in  FIG. 2 ), centres O and O′ are located on the same axis X-X and are mutually spaced apart, and rotor  15  is substantially tangent to side surface  43   a  of cavity  43 . In the present description, the term “coaxial or substantially coaxial” is used to denote a minimum distance, tending to 0, between centres O and O′. 
     Advantageously, eccentric rings  12  and  42  are mounted in such a manner that, in the minimum displacement position, external ring  12  is oriented so that its minimum radial thickness is located at the top in the Figure and internal ring  42  is oriented so that its minimum radial thickness is located at the bottom in the Figure. Otherwise stated, the eccentricities of the respective cavities  13 ,  43  are offset by 180°. Preferably, cavities  13 ,  43  have the same eccentricity relative to the external surface of the respective ring. 
     Rotor  15  has a set of vanes  16 , radially slidable in respective radial slots. At an outer end, vanes  16  are at a minimum distance from side surface  43   a  of cavity  43 , whereas at their inner end they rest on guiding or centring rings  17 , mounted at the axial ends of rotor  15  and arranged to maintain the minimum distance between vanes  16  and surface  43   a  under any condition of eccentricity. Also centring rings  17  will be coaxial or substantially coaxial with rotor  15  in the minimum displacement position. 
     A suction chamber  18 , communicating with a suction duct  20 , and a delivery chamber  19 , communicating with a delivery duct  21 , are defined at the bottom of body  10  between rotor  15  and surface  43   a . Such chambers are substantially symmetrical with respect to a plane passing through axis X-X and have phasings that are ideal for the maximum volumetric efficiency, as it is clearly apparent for the skilled in the art. It is to be appreciated that, should the rotor rotate in counterclockwise direction, the functions of such chambers, and hence of the respective ducts, would be mutually exchanged 
     In order to control the rotation of rings  12 ,  42 , toothed sectors  51 ,  52  are formed on their facing surfaces and are preferably positioned at the base of suitable stator cavities  11   a ,  11   b  formed in rings  12 ,  42 . A toothed wheel  53  having a shaft  54  rigidly connected to an actuator  50  ( FIG. 4 ) driving it into rotation is interposed between toothed sectors  51 ,  52  located in said stator cavities  11   a ,  11   b . Thus, rings  12 ,  42  rotate in opposite directions and are synchronous with each other. 
     Preferably, actuator  50  is an electromagnetic actuator. It may be a rotary actuator, e.g. a step-by-step micromotor integrated into pump  1  or coupled therewith (e.g. interfaced through the partition wall separating the inside from the outside of the engine sump), or a linearly moving actuator coupled with a suitable escapement ratchet gear in order to convert the actuator motion into a rotary motion. 
     Actuator  50  is controlled by the electronic control unit of the vehicle, which manages the displacement variation in closed loop (e.g. with feedback), by increasing or reducing the displacement depending on the requirements of the thermal engine and the accessories thereof. The variation is independent of the pressures upstream and downstream the oil filter. 
     Shaft  54  is guided within a support  40  formed in cover  14  or in body  10 . Toothed sectors  51 ,  52 , while rotating, develop according to a profile defined by the involute of the teeth of wheel  53 , which, on the contrary, rotates about its stationary axis. If the eccentricities are the same, the relative rotation of the rings causes a translation of centre O′ of pumping chamber  43  along axis X-X. This makes the geometry of pumping chamber  43  perfectly symmetric in all displacement conditions, and makes the ratio between the rotation of toothed wheel  53  and the displacement variation because of the translation of axis of chamber  43  constant. 
     In the illustrated embodiment, wheel  53  cooperates with a member  34  opposing the rotation of rings  12 ,  42 , in particular a flat spiral spring, preloaded so as to prevent the rotation of the rings as long as the torque applied by actuator  50  is lower than a predetermined threshold. Spiral spring  34  is located in a casing  33  that, in the illustrated exemplary embodiment, is fastened to cover  14 . The inner end portion of spring  34  is so shaped as to be coupled with the end portion of shaft  54  of wheel  53 , whereas the outer end portion is locked to the internal wall of casing  33 . The latter may be rotated, for instance by using a dynamometric key, in order to adjust the preloading of spring  34 . A ring nut  55  allows blocking casing  33  in the desired calibration position, independently of the constructional tolerances of the whole mechanism. A sealing gasket  56  is moreover provided between casing  33  and cover  14  in order to isolate the internal chamber of the same casing from the outside. A drain puts such a chamber in communication with suction chamber  18 , for the aims that will be disclosed below. 
     It is to be appreciated that, during the regulation rotation, spiral spring  34 , thanks to the negligible variation of the twisting torque and to the transmission ratio of the gear mechanism, will undergo negligible variations of its torque opposing the hydraulic torque. In the preferred embodiment in which actuator  50  is a step-by-step motor, spring  34  may contribute to make the magnetic resistance torque between subsequent steps sufficient to maintain the position of rings  12 ,  42  when the motor in not excited (energy saving). Moreover, due to a diametrically opposite effect, spring  34  could contribute to maintaining a maximum displacement upon the occurrence of an electric failure. 
     Rings  12  and  42 , as well as centring rings  17 , rotor  15  and wheel  53 , are preferably formed by moulding and/or metal powder sintering, with possible finishing operations on some limited areas, according to the dictates of the art. More particularly, axial thicknesses will undergo finishing. Body  10  and cover  14  can be formed by moulding either an aluminium alloy or a thermoplastic and/or thermosetting resin. Advantageously, spring  34  may be made of a bimetallic material, so that its characteristic may change depending on the operation temperature. 
     A second embodiment of the pump according to the invention, denoted  101 , is shown in  FIGS. 5 and 6 . Elements that are functionally identical to those already disclosed with reference to  FIGS. 1 to 4  are preferably denoted by the same reference numerals, increased by 100. Pump  101  differs from pump  1  in that external ring  12  is lacking and therefore actuator  150  acts through wheel  153  onto stator ring  142  alone, which is formed internally of body  110  with substantially circular cross-section. 
     In accordance with such an embodiment, as shown in  FIGS. 5 and 6 , stator ring  142  preferably comprises a stator cavity  111  in which both toothed sector  152  and toothed wheel  153  are arranged. 
     More particularly, toothed sector  152  is located at the base of stator cavity  111  and the toothed wheel is preferably wholly included between toothed sector  152  and body  110  with substantially circular cross-section. 
     Thanks to such a structure, in accordance with the second embodiment, the arrangement of toothed sector  152  and toothed wheel  153  allows minimising the size of pump  101 . 
     Moreover, rotor  115  rotates in counterclockwise direction (arrow F′). With such an arrangement, the translation of centre O′ of chamber  143  takes place along a non-rectilinear trajectory. Apart from those aspects, the structure is identical to that of pump  1  ad it is not necessary to describe it again. 
       FIG. 7  shows a principle block diagram of the regulation of the displacement of pumps  1 ,  101 . Dashed line denotes the mechanical drive of the pump by actuator  50  and hence corresponds to toothed wheels  53 ,  153  of the previous Figures. Dotted and dashed line  60  denotes the lubrication circuit which conveys oil from pump  1  to the engine and the various accessories, denoted in the whole  61 . Reference numeral  62  denotes the electronic control unit of the vehicle, which receives signals from detectors denoted in the whole  63  and controls actuator  50 , possibly through a digital-to-analogue converter, not shown. Solid lines denote the paths of the electric signals incoming into/outgoing from control unit  62 , and dotted lines denote the detection of the operating parameters of engine  61 , pump  1 , lubrication circuit  60  and possibly actuator  50  by detectors  63 . The parameters on which regulation of the delivery rate of the pump for lubrication of a motor vehicle engine may depend are well known to the skilled in the art and are not of interest for the invention. A more detailed description can be found in US 2011/0209682. 
     The operation of the pump described is as follows. 
     Considering first pump  1 , under rest conditions, the pump is in the maximum displacement condition shown in  FIG. 2 . As said, centre of rotation O of rotor  15  is offset relative to centre O′ of cavity  43  of eccentric ring  42  and rotor  15  is located close to wall  43   a  of the cavity. When pump  1  is started, the clockwise rotation of rotor  15  will give rise to an oil flow through chamber  19  and the associated delivery duct  21  and, at the same time, an equal volume of oil will be sucked from chamber  18  and the associated suction duct  20 . As the rotation speed and the flow rate increase, the lubrication system of the engine, by opposing an increasing resistance to the flow, will make pressure increase. 
     The delivery pressure or the pressure downstream the oil filter are detected by the suitable detectors  63  and communicated to control unit  62 , which will make actuator  50  rotate. The actuator will in turn generate a rotation torque that, through wheel  53  and once the calibration value of counteracting spring  34  has been attained, will make rings  12 ,  42  rotate by the same angle in opposite directions. If, as it has been assumed, the eccentricities of cavities  13 ,  43  relative to the external surfaces of the respective rings are the same, the rotation of ring  42  will cause a rectilinear translation of centre O′ towards the right, proportional to the amount of the rotation, thereby proportionally reducing the eccentricity between rotor  15  and cavity  43 , and consequently the pump displacement, and stabilising the pressure at the calibration value. As parameters such as the speed, the fluidity/temperature of the fluid, the engine “permeability” (intended as the amount of oil used by the engine) and so on, detected by detectors  63 , change, such a pressure will be maintained and controlled through the variation of the eccentricity and hence of the displacement. 
     When, as a function of the different operating parameters of the engine, it is desired to operate at a lower pressure value, with a consequent reduction in the absorbed power, control unit  62  will generate a suitable command for actuator  50 , so as to further reduce the displacement. 
     The rotation of the rings may continue until the position shown in  FIG. 1  is attained, where centres O and O′ coincide and vanes  16  and centring rings  17  rotate with the rotor without changes in their radial relative position. Consequently, the displacement is null and the pump is in stall condition. It is to be pointed out that this position may be taken when a hydraulic lock of the delivery pressure is approaching. In the constructional practice, a minimum displacement is preferably maintained by protecting the pump with a maximum pressure valve. 
     The operation of pump  101  is wholly similar, with the changes due to the provision of stator ring  42  alone. 
     An important parameter in managing the delivery rate/pressure of an oil pump for thermal engines is temperature, the increase of which makes oil become more fluid and the engine permeability increase. Consequently, the pump displacement should proportionally increase. This may be favoured if the opposing load of the counteracting spring increases. In order to obtain this, flat spiral spring  34  may be made of a bimetallic material such that temperature causes an increase in the rigidity and hence in the counteracting torque. In order to obtain the change in the rigidity, the small oil flow rate for the lubrication of shaft  54  of wheel  53  may be exploited: the oil, after having licked casing  33  of spring  34  and having transmitted its temperature to the same spring, freely discharges towards the suction chamber through the drain provided in chamber  57 . 
     The invention actually attains the desired aims. 
     Use of an electromagnetic actuator, directly controlled by the electronic control unit of the vehicle, allows eliminating the hydraulic actuators of the prior art and the necessary connections to the lubrication circuit, and makes the system less cumbersome, simpler and more reliable as well as less expensive. Moreover, elimination of the hydraulic actuators enables modifying the displacement presetting even when the thermal engine is off, since no control pressure is required. This is advantageous in particular for vehicles provided with the “stop and go” function, because it allows for instance increasing the displacement between the stop of the thermal engine and its start in order to start again the engine with a good lubrication. 
     Moreover in both embodiments, given the respective rotation direction of the rotor, in case of an electric failure causing deactivation of actuator  50  the hydraulic torque of the pump causes the rotation of the stator ring, or of the stator ring and the external ring, towards the maximum displacement condition. As said, this action can be favoured by spring  34 . In case of other failures, the minimum displacement is ensured and the electronic control, by detecting low lubrication pressures, will bring control unit  62  to the vehicle “recovery” function, 
     It is clear that the above description has been given only by way of non-limiting example and that changes and modifications are possible without departing from the scope of the invention. 
     For instance, even if in the illustrated embodiment shaft  15   a  of rotor  15  is guided by body  10  whereas spiral spring  34  and the calibration means consisting of casing  33  and ring nut  55  are housed within cover  14 , the arrangement could be reversed, or also the spring and the calibration means could be housed within body  10 . 
     Moreover, spring  34  could not be a bimetallic spring and, at least in the embodiments where actuator  50  is a step-by-step motor, the spring could be dispensed with, the only magnetic resistance torque between subsequent steps maintaining the position of rings  12 ,  42  when the motor is not excited. 
     Lastly, even if the invention has been disclosed in detail with reference to a pump for the lubrication oil of a motor vehicle engine, it may be applied to any positive displacement pump for conveying a fluid from a first to a second working environment, in which a delivery rate reduction as the pump speed increases is convenient.