EP4177471A1 - Hydraulic pump - Google Patents

Abstract

The invention relates to a hydraulic pump comprising:- a casing (14),- a vane pump (20) comprising a rotor movable in rotation relative to the casing (14) around a first axis (16), the rotor (46 ) comprising several propeller-shaped vanes, - a transition zone (28) belonging to the casing (14) and having, on the side of the vane pump (20), a propeller-shaped ramp developing in the same meaning that the helical shape of the vanes, - a trochoid pump (22) comprising a rotor with external teeth fixed to the rotor of the vane pump (20), and a rotor with internal teeth movable in rotation relative to the casing (14) around a second axis parallel and offset from the first axis (16), the trochoid pump (22) being fed by the vane pump (20) through the transition zone (28) along the ramp.

Description

The invention relates to a hydraulic pump for converting mechanical energy into hydraulic energy. A hydraulic fluid conveyed by the hydraulic pump can in particular be used as a source of energy in a hydraulic motor or more simply to convey fluid, for example used to transport heat or to lubricate certain mechanical components. More precisely, certain components, such as electrical machines, for example, need to be cooled during their operation. A hydraulic fluid can circulate in parts of an electrical machine to take heat there and transport it to an exchanger to be evacuated there.

The main parameters to take into account when choosing a hydraulic pump to ensure fluid circulation are: pressure and flow rate. These two parameters are of course linked. Indeed, for a given pump, it is possible to define a curve linking these two parameters for a given speed of rotation. The operating point on this curve is defined according to the hydraulic circuit and in particular its differences in height and its pressure drops.

Positive displacement gear pumps are widely used for hydraulic fluid circulation. They deliver a flow that varies little depending on the pressure, unlike centrifugal pumps. Gear pumps are simpler and more robust than piston pumps.

Within the family of gear pumps, it is possible to distinguish between external gear pumps where two wheels with external teeth rotate in a chamber and internal gear pumps with two interlocking rotors, one with internal teeth and the other with external teeth meshing with each other. The inner rotor has fewer teeth than the outer rotor. This difference in the number of teeth makes it possible to create mobile cavities between the teeth, cavities which move the fluid. Internal gear pumps are more compact than external gear pumps. Indeed, in an external gear pump, the two toothed wheels are arranged side by side whereas in an internal gear pump, the two toothed wheels are arranged one inside the other. In an internal gear pump, it is possible to provide a protrusion of the crescent-shaped stator locally separating the two rotors. A pump without this protuberance is often called a trochoid pump or "gerotor", the name "gerotor" being more specific to Anglo-Saxon literature.

In certain particular uses, such as for example in aeronautics, the atmospheric pressure can be very low at high altitude and lead to difficulties in maintaining the circulation of the fluid. Indeed, part of the circuit, in particular present in a tank serving as a buffer tank, can be left at the surrounding pressure. When flying at high altitude, the low pressure may cause the hydraulic pump to lose prime. Other undesirable phenomena such as cavitation may also appear.

Also, gear pumps work well at low speeds. However, in aeronautics, turboprops operate in very high speed ranges, typically between 12,000 and 30,000 revolutions per minute. To date, to drive a hydraulic pump by means of the shaft of a turboprop, it is necessary to provide a speed reducer.

The invention aims to overcome all or part of the problems mentioned above by proposing a hydraulic pump which can be directly driven, without a speed reducer, by a shaft which can rotate at high speed, typically up to 30,000 revolutions per minute and which can operate in a environment with very low pressure typically when the atmospheric pressure corresponds to an altitude higher than 10000 m.

• un carter,
• une pompe à aube comprenant un rotor mobile en rotation par rapport au carter autour d'un premier axe, le rotor comprenant plusieurs aubes en forme d'hélice,
• une zone de transition appartenant au carter, et possédant, du côté de la pompe à aube, une rampe en forme d'hélice se développant dans le même sens que la forme en hélice des aubes,
• une pompe trochoïde comprenant un rotor à denture externe solidaire du rotor de la pompe à aube, et un rotor à denture interne mobile en rotation par rapport au carter autour d'un second axe parallèle et décalé du premier axe, la pompe trochoïde étant alimentée par la pompe à aube au travers de la zone de transition en longeant la rampe.

To this end, the subject of the invention is a hydraulic pump, comprising:

• a crankcase,
• a vane pump comprising a rotor movable in rotation relative to the casing around a first axis, the rotor comprising several vanes in the form of a propeller,
• a transition zone belonging to the casing, and having, on the side of the vane pump, a helix-shaped ramp developing in the same direction as the helix shape of the blades,
• a trochoid pump comprising a rotor with external teeth integral with the rotor of the vane pump, and a rotor with internal teeth that can rotate relative to the housing around a second axis parallel and offset from the first axis, the trochoid pump being powered by the vane pump through the transition zone along the ramp.

A helix pitch of the blades, defined along the first axis, advantageously increases in the direction of an outlet of the vane pump.

For each blade, an extrados line is advantageously longer than a corresponding intrados line, the intrados and extrados lines both being defined on the same cylindrical surface around the first axis.

The stator of the vane pump may comprise a cavity in which the rotor of the vane pump rotates, a section of the cavity, and a section of the rotor of the vane pump, advantageously have a diameter decreasing in the direction of the outlet of the vane pump. the vane pump, the sections being defined perpendicular to the first axis.

The vane pump rotor may include a shaft extending along the first axis, the vanes extending primarily radially around the vane pump shaft, a diameter of the vane pump shaft, defined perpendicular to the first axis, advantageously increases in the direction of the outlet of the vane pump.

Each of the vanes advantageously has a leading edge approaching the outlet of the vane pump when its distance from the first axis increases.

• la figure 1 représente en coupe longitudinale un exemple de pompe hydraulique conforme à l'invention ;
• la figure 2 représente en coupe transversale une pompe trochoïde appartenant à la pompe de la figure 1 ;
• la figure 3 représente en vue longitudinale le rotor d'une pompe à aubes appartenant à la pompe de la figure 1 ;
• la figure 4 représente une forme asymétrique que peut prendre des aubes de la pompe à aube ;
• la figure 5 représente en perspective une pièce de transition appartenant à la pompe de la figure 1 ;
• Par souci de clarté, les mêmes éléments porteront les mêmes repères dans les différentes figures.

The invention will be better understood and other advantages will appear on reading the detailed description of an embodiment given by way of example, description illustrated by the attached drawing in which:

• there figure 1 shows in longitudinal section an example of a hydraulic pump according to the invention;
• there figure 2 shows in cross section a trochoid pump belonging to the pump of the figure 1 ;
• there picture 3 shows in longitudinal view the rotor of a vane pump belonging to the pump of the figure 1 ;
• there figure 4 represents an asymmetrical shape that the vanes of the vane pump can take;
• there figure 5 shows in perspective a transition piece belonging to the pump of the figure 1 ;
• For the sake of clarity, the same elements will bear the same references in the different figures.

The example described relates to a hydraulic pump 10 intended to be implemented in the aeronautical field and mainly to circulate a hydraulic fluid, in particular oil for cooling an electric machine driven by the shaft of a turboprop . The hydraulic pump 10 is driven directly, that is to say without a speed reducer, by the shaft of the turboprop. In other words, the hydraulic pump 10 is intended to operate in a very high speed range, typically being able to reach a speed of the order of 30,000 revolutions per minute.

The invention is not limited to the aeronautical field and can be implemented in any other field. The main interest of the invention remains the possibility of reaching very high speeds of rotation and of allowing operation in an environment where the inlet pressure of the pump can drop well below the conventional atmospheric pressure at the level of the floor.

There figure 1 represents an example of a hydraulic pump 10 according to the invention. The hydraulic pump 10 is driven by a motor shaft 12 rotating relative to a casing 14 around an axis 16. The figure 1 is a sectional view in a plane containing the pin 16. A bearing with two bearings 18 guides the rotation of the motor shaft 12 with respect to the housing 14 about a pin 16. The hydraulic pump 10 comprises two pumps mounted in series: a vane pump 20 and a trochoid pump 22. The vane pump 20 allows the boosting of the trochoid pump 22. The vane pump 20 and the trochoid pump 22 are driven by the same motor shaft 12. On the figure 1 , there is an inlet duct 24 made in the casing 14 and forming the inlet of the vane pump 20 and a discharge duct 26, also made in the casing 14 and forming the outlet of the trochoid pump 22. transition 28 forms both the vane pump outlet 20 and the inlet of the trochoid pump 22. In practice, the casing 14 can be made of several mechanical parts, two in the example shown: a first flange 14a and a second flange 14b. The transition piece 28 is nested in the flange 14a. It is also possible to nest the transition piece 28 in the flange 14b. The two flanges 14a and 14b as well as the transition piece 28 are all three integral with each other. Any other type of holding in position of the flanges 14a, 14b and of the transition piece 28 is possible within the scope of the invention. To facilitate the manufacture where the assembly of the flanges 14a, 14b and of the transition piece 28, it is possible to provide for fulfilling the functions of these parts in a larger number or a smaller number of mechanical parts. Thereafter, the two flanges 14a, 14b and the transition piece 28 which together form the casing 14 will not be distinguished. The function fulfilled by the transition piece 28 will be called the transition zone 28 of the casing 14.

There figure 2 represents the trochoid pump 22 in section in a plane perpendicular to the axis 16. The trochoid pump 22 comprises a rotor with external teeth 30 driven in rotation by the shaft 12 around the axis 16. The rotor with external teeth 30 is secured to the shaft 12. In practice, the rotor with external teeth 30 and the shaft 12 can be made in the same mechanical part. The trochoid pump 22 also comprises a rotor with internal teeth 32 which can rotate freely in the casing 14 about an axis 34 offset from the axis 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 teeth 30 comprises six teeth and the rotor with internal teeth 32 comprises seven teeth in the example represented. The rotor with external teeth 30 rotates the rotor with internal teeth 32. More generally, the rotor with external teeth 30 comprises fewer teeth than the rotor with internal teeth 32. The difference in the number of teeth creates an interdental space which sucks the fluid into a zone 38 where the teeth separate and discharges it into a zone 40 where the teeth meet during the rotation of the two rotors 30 and 32. On the picture 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 opening 42 made in the transition zone 28 and the discharge zone 40 corresponds to an opening 44 made in the housing 14 and communicating with the discharge duct 26.

There picture 3 represents a rotor 46 of the vane pump 20. The rotor 46 is integral with the shaft 12. The rotor 46 and the externally toothed rotor 30 of the trochoid pump 22 are therefore driven in rotation relative to the housing 14 around the shaft 16 by the same shaft 12. The rotor 46 of the vane pump 20 can be made directly with the shaft 12 or made in a separate mechanical part, as shown in the figures. figure 1 And 3 . The rotor 46 is immobilized with respect to the shaft 12 for example by means of a key 48. The separate production of the shaft 12 and the rotor 46 makes it possible to avoid making a shaft 12 that is too complex.

The rotor 46 rotates in a cavity 50 forming the stator of the vane pump 20. The cavity 50 has a shape of revolution around the axis 16. In the example shown, the cavity 50 is made in the transition piece 28 It is recalled that the transition piece 28 and the flanges 14a, 14b are integral with each other.

Rotor 46 includes several propeller-shaped blades. 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 in particular on the desired pitch of the propeller. This pitch can be fixed and identical for all the blades. Alternatively, it is advantageous to vary the propeller pitch of each vane between the inlet and the outlet of the vane pump 20. A smaller pitch at the inlet makes it possible to avoid sudden variations in fluid pressure between the conduit 24 inlet and vanes. Indeed, to allow the hydraulic pump 10 to operate with low fluid pressure at the inlet duct 24, it is advantageous to limit the fluid pressure variation at the inlet of the vane pump 20 , in particular to avoid the risk of cavitation. The pitch of the propeller can then increase towards the outlet of the vane pump 20 in order to increase the fluid pressure gradually before reaching the trochoid pump 22. picture 3 , the variation in pitch can be visualized by dimensions extending parallel to the axis 16. A first dimension c1 separates the vanes 52 and 54 as close as possible to the inlet duct 24 and a second dimension c2, greater than the dimension c1, separates the blades 54 and 56 closer to the opening 42 made in the transition piece 28.

There figure 4 represents an example of the profile of the blades 52, 54, 56 and 58. This profile is a section of a blade by a cylindrical surface 60 of axis 16 represented flat. The profile extends between a leading edge 62 located closest to the inlet duct 24 and a trailing edge 64 located closest to the transition piece 28. The profile is asymmetrical. More specifically, an extrados line 66 is longer than a corresponding intrados line 68. The designations of intrados and extrados are defined by similarity to those used for an airplane wing. The lower surface corresponds to the face of the blade where the fluid pressure is the highest and the upper surface corresponds to the face of the blade where the fluid pressure is the 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 speed of rotation of the pump blade 20 by limiting the risks of cavitation to obtain the increase in pressure and the desired flow rate. Other profiles are of course possible.

The cavity 50 forming the stator of the vane pump 20 is of revolution around the axis 16. Between the vanes 52, 54, 56, 58 and the cavity 50, a functional clearance is provided to allow rotation of the vanes. This functional clearance is as low as possible to limit leaks and improve the efficiency of the vane pump 20. The functional clearance is in particular 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 perpendicular to the axis 16, has a diameter D decreasing in the direction of the opening 42 forming the outlet of the vane pump 20. The decrease in diameter D is advantageously continuous in order to to limit load 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 to the functional clearances. This evolution of the diameter D makes it possible to reduce the passage section of the fluid from upstream to downstream of the vane pump 20. This reduction in passage section makes it possible to increase the speed of the fluid and therefore its pressure during its transit in the vane pump 20. This makes it possible to improve the efficiency of the vane pump 20.

Alternatively or in addition to the shape of the cavity 50, it is also possible to act on the inside diameter of the blades. More specifically, the rotor 46 of the vane pump 20 comprises a shaft 70 integral with the shaft 12. As seen above, the shaft 70 and the shaft 12 can be made in a single mechanical part or two separate mechanical parts. The shaft 70 is of revolution around the axis 16. From the shaft 70 extend radially, around the axis 16, the vanes 52, 54, 56 and 58. The shaft 70 and the vanes 52, 54, 56, 58 form the rotor 46 of the vane pump 20. The outer diameter d of the shaft 70, defined perpendicular to the axis 16, can be constant over the entire area where the vanes 52, 54, 56 and 58 are implanted. Alternatively, the outer diameter d of the shaft 70 can increase in the direction of the outlet of the vane pump 20. This change in the diameter d of the shaft 70 contributes to the reduction in the fluid passage section in the direction of the outlet. of the vane pump 20. Advantageously the outside diameter d increases continuously in the direction of the outlet of the vane pump 20 in order to limit pressure drops.

In the vane 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.

Increasing the diameter d of the shaft 70 and/or reducing the diameter D of the cavity 50 in the direction of the outlet of the vane pump 20 makes it possible to better adapt to the definition of the trochoid pump 22 and more precisely at the position of the opening 42 of the transition piece 28 forming both the outlet of the vane 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 vane pump 20 can extend perpendicular to the axis 16. Alternatively, it is possible to incline the leading edge with respect to a direction perpendicular to axis 16. Specifically, leading edge 62 approaches the outlet of vane pump 20 as its distance from axis 16 increases. This inclination can be constant and the leading edge 62 can form a straight segment as shown in the picture 3 . The inclination of the line segment is represented by an angle a. It is also possible to tilt the leading edge 62 progressively when its distance from the axis 16 increases. This inclination makes it possible to improve the penetration of the fluid into the vane pump 20 to limit the risk of cavitation and its potentially destructive effects.

There figure 5 shows in perspective the transition piece 28. We can distinguish the opening 42 forming the outlet of the vane pump 20 and the suction zone 38 of the trochoid pump 22. The transition piece 28 comprises a ramp 72 making it possible to guide the fluid leaving the vane pump 20 before reaching the opening 42. In other words the ramp 72 is located between the vane pump 20 and the trochoid pump 22 on the side of the vane pump 20. The fluid runs along the ramp 72 until reaching the opening 42. The ramp 72 is advantageously in the shape of a helix developing in the same direction as the helix shape of the blades 52, 54, 56 and 58 in order to limit the pressure losses between the two pumps 20 and 22.

Claims (8)

Hydraulic pump, including: - a casing (14), - a vane pump (20) comprising a rotor (46) rotatable relative to the housing (14) around a first axis (16), the rotor (46) comprising several vanes (52, 54, 56, 58 ) propeller-shaped, - a transition zone (28) belonging to the casing (14) and having, on the side of the vane pump (20), a ramp (72) in the form of a helix developing in the same direction as the helix shape of the blades (52, 54, 56, 58), - a trochoid pump (22) comprising a rotor with external teeth (30) secured to the rotor (46) of the vane pump (20), and a rotor with internal teeth (32) rotatable relative to the housing (14) around a second axis (34) parallel and offset from the first axis (16), the trochoid pump (22) being supplied by the vane pump (20) through the transition zone (28) along the ramp ( 72). A hydraulic pump according to claim 1, wherein a helical pitch of the vanes (52, 54, 56, 58) being defined along the first axis (16) is increasing towards an outlet (42) of the dawn (20). Hydraulic pump according to one of the preceding claims, in which for each blade (52, 54, 56, 58), an extrados line (66) is longer than a corresponding intrados line (68), the lines intrados and extrados both being defined on the same cylindrical surface (60) around the first axis (16). Hydraulic pump according to one of the preceding claims, in which the stator of the vane pump (20) comprises a cavity (50) in which the rotor (46) of the vane pump (20) rotates, a section of the cavity , and a section of the rotor (46) of the vane pump (20), have a diameter (D) decreasing in the direction of the outlet (42) of the vane pump (20), the sections being defined perpendicular to the first axis (16). Hydraulic pump according to Claim 4, in which the diameter (D) decreases continuously. Hydraulic pump according to one of the preceding claims, in which the rotor (46) of the vane pump (20) comprises a shaft (70) extending along the first axis (16), the vanes (52, 54, 56 , 58) extending mainly radially around the shaft (70) of the vane pump (20), a diameter (d) of the shaft (70) of the vane pump (20), defined perpendicular to the first axis (16), believes in the direction of the outlet (42) of the vane pump (20). Hydraulic pump according to claim 6, in which the diameter (d) of the shaft (70) increases continuously. Hydraulic pump according to one of the preceding claims, in which each of the vanes (52, 54, 56, 58) has a leading edge (62) approaching the outlet (42) of the vane pump (20) when its distance from the first axis (16) increases.

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