US20140037473A1

US20140037473A1 - Pumping assembly for feeding oil under pressure to a user

Info

Publication number: US20140037473A1
Application number: US13/981,678
Authority: US
Inventors: Davide Gambetti; Roberto Zambardi; Bruno Bertagna
Original assignee: TRW Automotive Italia SRL
Current assignee: ZF Automotive Italia SRL
Priority date: 2011-01-25
Filing date: 2012-01-25
Publication date: 2014-02-06
Also published as: IT1403528B1; WO2012101588A2; WO2012101588A8; EP2668371A2; WO2012101588A3; CN103443401A; ITBO20110025A1

Abstract

A pumping assembly for feeding oil under pressure to a user is defined by a gear pump, which is actuated by an electric motor, and has a pair of gears, which are coupled to each other within a pump body, and are each provided with a respective plurality of teeth facing radially to a respective lateral surface of the pump body and axially to two recesses formed on two side elements of the pump body itself; the radial distance of the teeth from the respective lateral surface increasing in the direction of rotation of the gears around their own rotation axes.

Description

TECHNICAL FIELD

The present invention relates to a pumping assembly for feeding oil under pressure to a user.
In particular, the present invention relates to a pumping assembly of the type comprising a gear pump and an electric motor for actuating the gear pump itself.

BACKGROUND ART

Generally, the gear pump comprises a pair of gears coupled to each other, each of which comprises a gear wheel with external teeth formed at an intermediate portion of a support shaft assembled so as to rotate around a rotation axis parallel to the rotation axis of the other gear wheel.
The two gears are mounted in a pump body comprising a sleeve, which extends around the gear wheels, has a length substantially equal to the length of the gear wheels, and is closed axially by two side elements, which are mounted in contact with the end faces of the sleeve perpendicular to the rotation axes of the gears, are engaged in a rotary manner by said support shafts, and define, together with the sleeve itself, a containing chamber of the gear wheels.
The containing chamber is limited internally by a pair of substantially cylindrical lateral surfaces, each of which extends around a respective gear wheel, is substantially coaxial with a respective rotation axis, and presents a concavity facing the other lateral surface.
The torque delivered by the electric motor for actuating the gear pump depends on the outlet pressure of the oil from the gear pump, on the forces of mechanical friction generated between the gears, and on the forces of viscous friction generated in the oil advanced by the gears themselves.
The forces of viscous friction are transmitted between layers of oil adjacent to each other and are proportional, for fluids such as oil, to the viscosity and to the shear rate of the oil in a direction perpendicular to said lateral surfaces.
The shear rate and, therefore, the viscous friction forces present the maximum values in correspondence of the clearance present between the gears, that is to say the mobile elements of the gear pump, and the pump body, namely the fixed element of the gear pump itself.
In this regard it should be specified that the oil viscosity increases with a decrease of the operating temperature of the pumping assembly and that the shear rate is relatively high since the gear wheels are substantially fluid-tight radially with the relative lateral surfaces and axially with the side elements so as to fluid-tight separate an oil inlet in the containing chamber from an outlet of the oil under pressure from the containing chamber itself.
Since, for relatively low operating temperatures, the viscosity of the oil and, therefore, the frictional force of a viscous type are relatively high, the known pumping assemblies of the type described above have several drawbacks, mainly due to the fact that the electric motor must be dimensioned to deliver a relatively high drive torque and is therefore relatively complex and expensive.

DISCLOSURE OF INVENTION

The purpose of the present invention is to provide a pumping assembly for feeding oil under pressure to a user that is free from the drawbacks described above and which is of simple and inexpensive implementation.
According to the present invention a pumping assembly is provided for feeding oil under pressure to a user as claimed in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to the attached drawings, which illustrate a non limitative example of an embodiment, in which:

FIG. 1 is a schematic perspective view of a preferred embodiment of the pumping assembly of the present invention;

FIGS. 2 and 3 are two schematic perspective views of a detail of the pumping assembly of FIG. 1; and

FIG. 4 is a schematic cross section, with parts removed and parts enlarged for clarity, of the detail of FIGS. 2 and 3.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to FIG. 1, with 1 is indicated as a whole, a pumping unit, which is adapted to draw oil from a containing tank (not shown) at atmospheric pressure and to feed oil under pressure to a user (not shown), for example, a user of the automotive sector, and comprises a gear pump 2, in this case a pump with external gears, substantially immersed in said containing tank (not shown) and an electric motor 3 for actuating the pump 2 itself.
As shown in FIGS. 2, 3, and 4, the pump 2 is provided with a pair of gears 4 coupled to each other, each of which comprises a support shaft 5 presenting a longitudinal axis 6 parallel to axis 6 of the other gear 4, and an externally toothed gear wheel 7, which is formed at an intermediate portion of the shaft 5, and has a plurality of teeth 8 equally spaced about axis 6.
The gear wheels 4 are mounted in a pump body 9 comprising a sleeve 10, which extends around the gear wheels 7, presenting a length, measured parallel to axes 6, substantially equal to the length of gear wheel 7, also measured parallel to the axes 6, and is limited internally by a shaped lateral wall 11.
The wall 11 defines two lateral surfaces 12, each of which has, in this case, a substantially cylindrical shape with concavity facing the other surface 12, extends around a respective gear wheel 7, and presents a longitudinal axis 13, which is parallel to the relative axis 6, is distinguished from relative axis 6, and is arranged at a distance from the axis 13 of the other surface 12 less than the sum of the radii of curvature of the two surfaces 12.
As a result of the eccentricity between each axis 6 and the relative axis 13, each surface 12 is wound in a spiral around the relative gear wheel 7 from one of its ends 14 substantially tangent to the gear wheel 7 itself so that the radial distance Dr between the surface 12 and the relative teeth 8 increases progressively in the direction of rotation of the relative gear 4.
Obviously, according to a variant not shown, each surface 12 is wound around teeth 8 of the respective gear wheel 7 according to a profile different from that described and illustrated in FIG. 4, and presents, for example, downstream of the end 14, a constant radial distance Dr from teeth 8 themselves.
The sleeve 10 is closed axially by two substantially flat closing plates 15, which are mounted on opposite sides of the sleeve 10 perpendicularly to axes 6, are engaged in a rotary manner by the shafts 5, each being limited axially by a respective flat lateral surface 16 facing the sleeve 10, and are locked against the end faces of the sleeve 10 to define, together with the sleeve 10 itself, a containing chamber 17 of the gear wheels 7.
Since the gear wheels 7 are substantially fluid-tight coupled with the ends 14 of the surfaces 12 and with the surfaces 16 of plates 15, the chamber 17 comprises an area 18 of low pressure hydraulically connected with said containing tank (not shown) of the oil through a suction conduit 19 formed radially through the sleeve 10, and an area 20 of high pressure, which is separated in a substantially fluid-tight manner from the area 18, and is hydraulically connected with said user (not shown) by a delivery conduit 21 formed in part through the sleeve 10 and in part through one of the plates 15 parallel to axes 6.
Each plate 15 has an elongated cavity 22, which opens towards the outside in correspondence with the relative surface 16, presents a substantially ω shape, and comprises two sections connected to each other, each of which presents a substantially circular shape, is facing axially to the teeth 8 of a relative gear wheel 7, extends around relative axis 6 substantially at the area 20 of high pressure, and is limited by a bottom wall 24 arranged at a substantially constant axial distance Da from the teeth 8 of the relative gear wheel 7.
According to some variations not shown:
the wall 24 of each sections 23 may present a profile and an axial distance from the teeth 8 of the relative gear wheel 7 different from those described and illustrated in FIGS. 2 and 3; and
the cavity 22 of each plate 15 is eliminated and replaced with two cavities separated from each other and each facing the teeth 8 of the relative gear wheel 7.
The presence of a free radial space between the teeth 8 of each gear wheel 7 and the relative surface 12 and of a free axial space between the teeth 8 of each gear wheel 7 and the two cavities 22 allow to reduce the shear rates present between the gear wheels 7, i.e. the mobile elements of the pump 2, and the sleeve 10 and the plates 15, i.e. the fixed elements of the pump 2 itself.
The reduction of shear rates results in the reduction of the frictional forces of a viscous type, which are, consequently, relatively small even at relatively low operating temperatures, i.e. at operating temperatures to which the oil viscosity is relatively high.
The operation of the pump 2 requires, therefore, a relatively low driving torque even at relatively low operating temperatures and allows the use of relatively simple and inexpensive electric motors 3.
According to a variant not shown, the external gear pump 2 is eliminated and replaced with an internal gear pump comprising a pump body, inside which are housed an internally toothed crown wheel and an externally toothed gear wheel, which presents an outer diameter smaller than the inner diameter of the crown wheel, is mounted inside of the crown wheel, and is coupled with the crown wheel itself.
The internal gear pump further comprises at least one filling body, which is mounted inside the pump body between the crown wheel and the gear wheel, and is limited by two lateral surfaces, which are radially facing the teeth of the crown wheel and, respectively, to the teeth of the gear wheel, and present respective ends substantially tangent to the crown wheel and, respectively, to the gear wheel.
The two lateral surfaces are wrapped helically from their ends around the crown wheel and, respectively, to the gear wheel so that the radial distance Dr between the lateral surfaces and the relative teeth increases in the direction of rotation of the crown wheel and, respectively, of the gear wheel.
Obviously, the pump body of the internal gear pump can be closed axially by two closing plates similar to the plates 15.

Claims

1. Pumping assembly for feeding oil under pressure to a user, the pumping assembly comprising a gear pump, and an electric motor for actuating the gear pump; the gear pump comprising, in turn, two toothed members, which are coupled to each other, are assembled so as to rotate around respective rotation axes parallel to each other, and present respective teeth; and a pump body defining a containing chamber, which houses in its inside the two toothed members, presents, for each toothed member, a respective first lateral surface extending around, and at a given radial distance (Dr) from, the teeth of the respective toothed member, and is, furthermore, axially limited by two side elements parallel to each other and perpendicular to said rotation axes; the radial distance (Dr) increasing in the direction of rotation of the toothed members around respective rotation axes, and each side element being limited by a second lateral surface perpendicular to said rotation axes and facing the toothed members; wherein each side element presents, for each toothed member, a respective recess, which is formed on the relative second lateral surface, is facing the teeth of the respective toothed member, and is limited by a bottom wall arranged at a given axial distance from the teeth of the respective toothed member.

2. Pumping assembly according to claim 1, wherein the axial distance is constant in the direction of rotation of the toothed members around respective rotation axes.

3. Pumping assembly according to claim 1, wherein the axial distance increases in the direction of rotation of the toothed members around respective rotation axes.

4. Pumping assembly according to claim 1, wherein the two recesses are connected to each other, so as to define a cavity.

5. Pumping assembly according to claim 1, wherein the two recesses are separated from each other.

6. Pumping assembly according to claim 1, wherein each said first lateral surface presents a coupling end coupled in fluid-tight manner to the teeth of the relative toothed member and wherein each said second lateral surface is coupled in fluid-tight manner with the teeth (8) of the toothed members.

7. Pumping assembly according to claim 6, wherein the pump body presents an oil inlet to the containing chamber and an outlet of the oil under pressure from the containing chamber itself; the radial distance being substantially null in correspondence to each said coupling end and each said second lateral surface being arranged substantially in contact with the teeth of the toothed members so as to separate in a fluid-tight manner said inlet and said outlet from each other.

8. Pumping assembly according to claim 7, wherein each recess extends around the respective rotation axis downstream of said inlet the direction of rotation of the respective toothed member.

9. Pumping assembly according to claim 1, wherein each said first lateral surface presents a cylindrical shape, and is wound in a spiral around the respective toothed member.

10. Pumping assembly according to claim 9, wherein each said first lateral surface presents a longitudinal axis parallel to, and distinct from, said rotation axis of the relative toothed member.

11. Pumping assembly according to claim 9, wherein the pump body presents an oil inlet to the containing chamber and an outlet of the oil under pressure out of the containing chamber itself; each said first lateral surface presenting a coupling end substantially tangent to the teeth of the respective toothed member so as to separate in a fluid-tight manner said inlet and said outlet from each other.

12. Pumping assembly according to claim 1, wherein each toothed member is an externally toothed gear wheel, each said first lateral surface presenting a substantially cylindrical shape, a given radius of curvature, and a longitudinal axis arranged at a distance from the longitudinal axis of the other said first lateral surface less than the sum of the radii of curvature of the two said first lateral surfaces.