Patent Publication Number: US-2023151812-A1

Title: Hydraulic pump

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to foreign French Patent Application No. FR 2111834, filed on Nov. 8, 2021, the disclosure of which is incorporated by reference in its entirety. 
     FIELD OF THE INVENTION 
     The invention relates to a hydraulic pump intended to transform mechanical energy into hydraulic energy. A hydraulic fluid conveyed by the hydraulic pump can notably be used as source of energy in a hydraulic motor or, more simply, to convey fluid, for example used to transport heat to or to lubricate certain mechanical components. More specifically, certain members, such as electrical machines for example, need to be cooled in their operation. A hydraulic fluid can circulate in parts of an electrical machine to take heat therefrom and transport it to a heat exchanger, to be discharged there. 
     BACKGROUND 
     The main parameters to be taken into account in choosing a hydraulic pump to ensure the circulation of fluid are: the pressure and the flow rate. These two parameters are of course linked. Indeed, for a given pump, a curve can be defined linking these two parameters for a given rotation speed. The operating point on this curve is defined as a function of the hydraulic circuit and notably of its height differences and its head losses. 
     Gear volumetric pumps are widely used for the circulation of hydraulic fluid. They deliver a flow rate that varies little as a function of the pressure, unlike centrifugal pumps. Gear pumps are simpler and more robust than piston pumps. 
     In the family of gear pumps, it is possible to distinguish the external gear pumps in which two wheels with outer toothing revolve in a chamber and the internal gear pumps that have two interleaved rotors, one with internal toothing and the other with external toothing meshing in one another. The internal rotor has fewer teeth than the external rotor. This difference in the number of teeth makes it possible to create mobile cavities between the teeth, cavities which displace the fluid. The internal gear pumps are more compact than the external gear pumps. Indeed, in an external gear pump, the two toothed wheels are disposed side by side whereas, in an internal gear pump, the two toothed wheels are disposed one inside the other. In an internal gear pump, it is possible to provide a protuberance of the stator in crescent form locally separating the two rotors. A pump without this protuberance is often called trochoid pump or “gerotor”, the term “gerotor” being more specific in the literature. 
     In some particular uses, such as in aeronautics for example, the atmospheric pressure can be very low at high altitude and lead to difficulties in maintaining the circulation of the fluid. Indeed, a part of the circuit, notably present in a tank serving as buffer reservoir can be left at the surrounding pressure. In case of a flight at high altitude, the low pressure can result in the unpriming of the hydraulic pump. Other undesirable phenomena such as cavitation may also appear. 
     Moreover, the gear pumps operate well at low speed. However, in aeronautics, the turboprop engines operate within very high speed ranges, typically between 12000 and 30000 revolutions per minute. Currently, to drive a hydraulic pump by means of the shaft of a turboprop engine, it is necessary to provide a speed reducer. 
     SUMMARY OF THE INVENTION 
     The invention aims to mitigate all or part of the problems cited above by proposing a hydraulic pump that can be directly driven, without speed reducer, by a shaft that can revolve at high speed, typically up to 30000 revolutions per minute, and that can operate in an environment at very low pressure, typically when the atmospheric pressure corresponds to an altitude greater than 10000 m. 
     To this end, the subject of the invention is a hydraulic pump, comprising:
     a casing,   an impellor pump comprising a rotor that is rotationally mobile with respect to the casing about a first axis, the rotor comprising several blades in helix form,   a transition zone belonging to the casing, and having, on the side of the impellor pump, a ramp in helix form developing in the same direction as the helix form of the blades,   a trochoid pump comprising a rotor with external toothing secured to the rotor of the impellor pump, and a rotor with internal toothing that is rotationally mobile with respect to the casing about a second axis parallel to and offset from the first axis, the trochoid pump being fed by the impellor pump through the transition zone running along the ramp.   

     A helix pitch of the blades, defined along the first axis, advantageously increases towards an outlet of the impellor pump. 
     For each blade, an upper surface line is advantageously longer than a corresponding lower surface line, the lower surface and upper surface lines being both defined on a same cylindrical surface about the first axis. 
     The stator of the impellor pump can comprise a cavity in which the rotor of the impellor pump revolves, a section of the cavity, and a section of the rotor of the impellor pump, advantageously have a diameter that decreases towards the outlet of the impellor pump, the sections being defined at right angles to the first axis. 
     The rotor of the impellor pump can comprise a shaft extending along the first axis, the blades extending primarily radially about the shaft of the impellor pump, a diameter of the shaft of the impellor pump, defined at right angles to the first axis, increases advantageously towards the outlet of the impellor pump. 
     Each of the blades advantageously has a leading edge approaching the outlet of the impellor pump when its distance to the first axis increases. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood and other advantages will become apparent on reading the detailed description of an embodiment given as an example, the description being illustrated by the attached drawing in which: 
         FIG.  1    represents, in longitudinal cross-section, an example of a hydraulic pump according to the invention; 
         FIG.  2    represents, in transverse cross-section, a trochoid pump belonging to the pump of  FIG.  1   ; 
         FIG.  3    represents, in a longitudinal view, the rotor of an impellor pump belonging to the pump of  FIG.  1   ; 
         FIG.  4    represents an asymmetrical form that the blades of the impellor pump can take; 
         FIG.  5    represents, in perspective, a transition piece belonging to the pump of  FIG.  1   . 
     
    
    
     In the interests of clarity, the same elements will bear the same references in the different figures. 
     DETAILED DESCRIPTION 
     The example described relates to a hydraulic pump  10  intended to be implemented in the aeronautical field and primarily to circulate a hydraulic fluid, in particular oil used to cool an electrical machine driven by the shaft of a turboprop engine. The hydraulic pump  10  is driven directly, that is to say without speed reducer, by the shaft of the turboprop engine. In other words, the hydraulic pump  10  is intended to operate within a very high speed range, that can typically reach a speed of the order of 30000 revolutions per minute. 
     The invention is not limited to the aeronautical field and can be implemented in any other field. The main benefit of the invention remains the possibility of achieving very high rotation speeds and of allowing operation in an environment where the intake pressure of the pump can drop well below the conventional atmospheric pressure at ground level. 
       FIG.  1    represents an example of a hydraulic pump  10  according to the invention. The hydraulic pump  10  is driven by a motor shaft  12  that revolves with respect to a casing  14  about an axis  16 .  FIG.  1    is a cross-sectional view in a plane containing the axis  16 . A twin rolling bearing  18  guides the rotation of the motor shaft  12  with respect to the casing  14  about an axis  16 . The hydraulic pump  10  comprises two pumps mounted in series: an impellor pump  20  and a trochoid pump  22 . The impellor pump  20  feeds the trochoid pump  22 . The impellor pump  20  and the trochoid pump  22  are driven by the same motor shaft  12 . In  FIG.  1   , there are an intake duct  24  produced in the casing  14  and forming the intake of the impellor pump  20  and a discharge duct  26 , also produced in the casing  14  and forming the outlet of the trochoid pump  22 . A transition piece  28  forms both the outlet of the impellor pump  20  and the inlet of the trochoid pump  22 . In practice, the casing  14  can be produced in several mechanical parts, two in the example represented: a first flange  14   a  and a second flange  14   b . The transition piece  28  is nested in the flange  14   a . It is also possible to nest the transition piece  28  in the flange  14   b . The two flanges  14   a  and  14   b  and the transition piece  28  are all three secured to one another. Any other type of securing of the flanges  14   a ,  14   b  and of the transition piece  28  in position is possible in the context of the invention. To facilitate the manufacture or the assembly of the flanges  14   a ,  14   b  and of the transition piece  28 , it is possible to provide for the functions of these parts to be fulfilled in more or fewer mechanical parts. Hereinbelow, the two flanges  14   a ,  14   b  and the transition piece  28 , which jointly form the casing  14 , will not be distinguished. The function fulfilled by the transition piece  28  will be called transition zone  28  of the casing  14 . 
       FIG.  2    represents the trochoid pump  22  in cross-section in a plane at right angles to the axis  16 . The trochoid pump  22  comprises a rotor with external toothing  30  driven in rotation by the shaft  12  about the axis  16 . The rotor with external toothing  30  is secured to the shaft  12 . In practice, the rotor with external toothing  30  and the shaft  12  can be produced in one and the same mechanical part. The trochoid pump  22  also comprises a rotor with internal toothing  32  that can revolve freely in the casing  14  about an axis  34  that is offset from the axle  12  and parallel thereto. The casing  14  comprises a cylindrical cavity  36  of axis  34  forming the stator of the trochoid pump  22 . 
     The rotor with external toothing  30  comprises six teeth and the rotor with internal toothing  32  comprises seven teeth in the example represented. The rotor with external toothing  30  drives the rotor with internal toothing  32  in rotation. More generally, the rotor with external toothing  30  comprises fewer teeth than the rotor with internal toothing  32 . The difference in number of teeth creates a space between teeth which sucks the fluid into a zone  38  where the teeth separate and discharges it into a zone  40  where the teeth meet again in the rotation of the two rotors  30  and  32 . In  FIG.  2   , the suction and discharge zones are represented respectively on the right and on the left of the figure. In practice, the suction zone  38  corresponds to an aperture  42  produced in the transition zone  28  and the discharge zone  40  corresponds to an aperture  44  produced in the casing  14  and communicating with the discharge duct  26 . 
       FIG.  3    represents a rotor  46  of the impellor pump  20 . The rotor  46  is secured to the shaft  12 . The rotor  46  and the rotor with external toothing  30  of the trochoid pump  22  are therefore driven in rotation with respect to the casing  14  about the axis  16  by the same shaft  12 . The rotor  46  of the impellor pump  20  can be directly produced with the shaft  12  or produced in a separate mechanical part, as represented in  FIGS.  1  and  3   . The rotor  46  is immobilized with respect to the shaft  12 , for example by means of a key  48 . Separate production of the shaft  12  and of the rotor  46  makes it possible to avoid producing a shaft  12  that is too complex. 
     The rotor  46  revolves in a cavity  50  forming the stator of the impellor pump  20 . The cavity  50  has a form of revolution about the axis  16 . In the example represented, the cavity  50  is produced in the transition piece  28 . It is recalled that the transition piece  28  and the flanges  14   a ,  14   b  are secured to one another. 
     The rotor  46  comprises several blades in helix form. In the example represented, the rotor  46  comprises four blades  52 ,  54 ,  56  and  58 . Another number of blades can be envisaged. The number of blades depends notably on the desired helix pitch. This pitch can be fixed and identical for all the blades. Alternatively, it is advantageous to vary the helix pitch of each blade between the inlet and the outlet of the impellor pump  20 . A smaller pitch at the inlet makes it possible to avoid abrupt pressure variations in the fluid between the intake duct  24  and the blades. Indeed, to allow the hydraulic pump  10  to operate with a low fluid pressure at the intake duct  24 , it is advantageous to limit the variation in fluid pressure at the inlet of the impellor pump  20 , notably to avoid the risk of cavitation. The helix pitch can then increase towards the outlet of the impellor pump  20  in order to increase the fluid pressure gradually before reaching the trochoid pump  22 . In  FIG.  3   , the variation in pitch can be visualized by dimensions extending parallel to the axis  16 . A first dimension c1 separates the blades  52  and  54  closest to the intake duct  24  and a second dimension c2, greater than the dimension c1, separates the blades  54  and  56  closest to the aperture  42  produced in the transition piece  28 . 
       FIG.  4    represents an example of profile of the blades  52 ,  54 ,  56  and  58 . This profile is a cross-section of a blade through a cylindrical surface  60  of axis  16  represented flat. The profile extends between a leading edge  62  situated closest to the intake duct  24  and a trailing edge  64  situated closest to the transition piece  28 . The profile is asymmetrical. More specifically, an upper surface line  66  is longer than a corresponding lower surface line  68 . The terms lower surface and upper surface are defined by analogy to those used for an aeroplane wing. The lower surface corresponds to the face of the blade where the pressure of the fluid is highest and the upper surface corresponds to the face of the blade where the pressure of the fluid is lowest. Among the asymmetrical profiles, it is possible to choose a profile defined by the “National Advisory Committee for Aeronautics” known by its acronym NACA. The implementation of such an asymmetrical profile makes it possible to increase the rotation speed of the impellor pump  20  by limiting the risks of cavitation to obtain the desired increase in pressure and flow rate. Other profiles are of course possible. 
     The cavity  50  forming the stator of the impellor pump  20  is of revolution about the axis  16 . Between the blades  52 ,  54 ,  56 ,  58  and the cavity  50 , a functional play is provided to allow the rotation of the blades. This functional play is as small as possible to limit the leaks and improve the efficiency of the impellor pump  20 . The functional play is notably a function of the manufacturing tolerances of the various mechanical parts and of the possible thermal expansions during operation. It is possible to produce a cylindrical cavity  50  over the entire length of the cavity  50  defined along the axis  26  and swept by the blades. Alternatively and advantageously, the section of the cavity  50 , defined at right angles to the axis  16 , has a diameter D that decreases towards the aperture  42  forming the outlet of the impellor pump  20 . The decrease in the diameter D is advantageously continual in order to limit the head losses. The radial dimensions of the blades  52 ,  54 ,  56 ,  58  follow this decrease. It is considered that, for any section, the nominal diameters of the blades and of the cavity  50  are equal plus or minus the functional plays. This change in the diameter D makes it possible to reduce the section of passage of the fluid from upstream to downstream of the impellor pump  20 . This reduction of passage section makes it possible to increase the speed of the fluid and therefore its pressure in its passage through the impellor pump  20 . This makes it possible to improve the efficiency of the impellor pump  20 . 
     Alternatively or in addition to the form of the cavity  50 , it is also possible to act on the internal diameter of the blades. More specifically, the rotor  46  of the impellor pump  20  comprises a shaft  70  secured to the shaft  12 . As has been seen previously, the shaft  70  and the shaft  12  can be produced in a single mechanical part or in two separate mechanical parts. The shaft  70  is of revolution about the axis  16 . The blades  52 ,  54 ,  56  and  58  extend radially from the shaft  70 , about the axis  16 . The shaft  70  and the blades  52 ,  54 ,  56 ,  58  form the rotor  46  of the impellor pump  20 . The external diameter d of the shaft  70 , defined at right angles to the axis  16 , can be constant over the entire zone where the blades  52 ,  54 ,  56  and  58  are installed. Alternatively, the external diameter d of the shaft  70  can increase towards the outlet of the impellor pump  20 . This change in the diameter d of the shaft  70  contributes to the reduction of section of passage of the fluid towards the outlet of the impellor pump  20 . Advantageously, the external diameter d increases continually towards the outlet of the impellor pump  20  in order to limit the head losses. 
     In the impellor pump  20 , the fluid is in direct contact on the one hand with the shaft  70  and on the other hand with the cavity  50 . 
     The fact of increasing the diameter d of the shaft  70  and/or of reducing the diameter D of the cavity  50  towards the outlet of the impellor pump  20  makes it possible to better adapt to the definition of the trochoid pump  22  and more specifically to the position of the aperture  42  of the transition piece  28  forming both the outlet of the impellor pump  20  and the suction zone  38  of the trochoid pump  22 . 
     The leading edge  62  of the blades  52 ,  54 ,  56  and  58  of the impellor pump  20  can extend at right angles to the axis  16 . Alternatively, it is possible to incline the leading edge with respect to a direction at right angles to the axis  16 . More specifically, the leading edge  62  approaches the outlet of the impellor pump  20  when its distance to the axis  16  increases. Inclination can be constant and the leading edge  62  can form a line segment as represented in  FIG.  3   . The inclination of the line segment is represented by an angle α. It is also possible to incline the leading edge  62  in a changing manner when its distance to the axis  16  increases. This inclination makes it possible to improve the penetration of the fluid into the impellor pump  20  to limit the risk of cavitation and its potentially destructive effects. 
       FIG.  5    represents, in perspective, the transition piece  28 . The aperture  42  forming the outlet of the impellor pump  20  and the suction zone  38  of the trochoid pump  22  are distinguished. The transition piece  28  comprises a ramp  72  that makes it possible to guide the fluid at the outlet of the impellor pump  20  before reaching the aperture  42 . In other words, the ramp  72  is situated between the impellor pump  20  and the trochoid pump  22  on the side of the impellor pump  20 . The fluid runs along the ramp  72  to reach the aperture  42 . The ramp  72  is advantageously in helix form developing in the same direction as the helix form of the blades  52 ,  54 ,  56  and  58  in order to limit the head losses between the two pumps  20  and  22 .