FIELD OF THE INVENTION

The present invention relates to a gear pump, more specifically to an internal gear pump with tapered-edged crescent member for displacing fluids from the inlet port to the outlet port of the internal gear pump with higher level of cavitation resistance, better directional control for the flow of a fluid from the inlet port to the outlet port, and higher volumetric pump efficiency and longevity.

BACKGROUND OF THE INVENTION

A conventional internal gear pump consists of two moving elements, namely, an internal gear and an external gear. These two elements are in constant mesh at a specific meshing point and conventionally a crescent member is disposed diametrically opposite to the meshing point. The crescent member is normally integrated to the housing of the internal gear pump. The external gear is rotated by an active engagement, e.g., a shaft which in turn is rotated by a prime mover. This active engagement provides the drive to the external gear in order to rotate the internal gear. This rotation of the gears results in suction of fluid, via an inlet port of the internal gear pump into the region between the two gears. The rotation of the two gears allows fluid to be transmitted to an outlet port of the internal gear pump. The fluid is transferred by the gear sets through the gear pockets that are associated with each of them. For this arrangement the crescent member ensures smooth and controlled flow towards the outlet port. The region of gear meshing also ensures that the possibility of reverse flow of the fluid, i.e., from the outlet region to the inlet region, is negated.

One of the major problems affecting an internal gear pump is cavitation. Cavitation occurs when air collects in the pockets of the gear sets, thereby resulting in the loss of volumetric efficiency, that may eventually lead to the damage of the pump or reduction of its useful life.

In some cases, as disclosed in the internal gear pumps of US patent no. 5 242 286, US patent no. 6 095 782, and US patent no. 6 152 717, the internal gear pump may not comprise a crescent member between the external and internal gear.

However, in most of the conventional internal gear pumps, presently in use, a crescent-shaped or sickle-shaped or an arcuate member is present between the external and internal gear located diametrically opposite to the meshing region of the external and internal gear.

US patent no. 3 785 756 discloses a gear pump with a crescent member with a leading edge having a shape to simultaneously end the zero displacement interval for the teeth of both internal and external gear thereby preventing direct fluid communication between the inlet and outlet port of the pump.

US patent no. 3 586 465 discloses a gear pump with a sickle-shaped segment between the external and internal gear, the segment including a hollow space which open axially towards both sides and is in communication in the radial direction by at least one bore each with the sealing surface for the internally toothed gear, thereby helping to reduce the noise level and improving the sealing arrangement.

US patent no. 5 299 923 discloses a gear pump that provides a ring shaped housing intermediate part in which the shaft is supported with cut outs in peripheral direction, a web bridging the single cut out located approximately in that area of the pinion which is diametrically opposite the pressure socket that helps to reduce the noise level.

US patent no. 7 625 192 discloses an internal gear pump with a crescent that aims to solve the problem of crescent vibration due to pressure difference caused by the difference in the speed of rotation of internal and external gears by ensuring the start of separation of crescent and top of each tooth of the outer rotor, and start of separation of the crescent and top of each tooth of the inner rotor occur substantially simultaneously, and linking of the outer port occurs at the start of separation through proper design of the crescent member.

Internal gear oil pumps frequently use trochoid-shaped rotors. Using trochoid-shaped gear teeth has the advantages that the inner and outer rotors are in rolling contact, so gear impact noise is small, and cavitation does not easily occur.

In conventional crescent pumps, normal gears, in other words, gears with comparatively low teeth, are generally used, so pressure fluctuations are not much of a problem.

However, in recent years the requirements for greater efficiency and performance are increasing. In response to these requirements usually performance (flow rate) is improved by increasing the height of the teeth, and reducing the number of teeth. However, crescent pumps have the disadvantage that when height of the teeth is increased and the number of teeth is reduced, outlet vibrations and cavitation can more easily occur.

There is therefore, a need to overcome the problem of cavitation in an internal gear pump in order to increase the efficiency and longevity of the internal gear pump. The present invention aims to address the problem of cavitation in an internal gear pump by an optimal design of the crescent member used in the pump, not disclosed in the prior art.

SUMMARY OF THE INVENTION

In one embodiment, the present invention provides an internal gear pump for displacing fluid from an inlet port to an outlet port, the gear pump comprising an external gear, an internal gear operatively and eccentrically connected to the external gear, forming a meshing region with the external gear; and a crescent member located diametrically opposite to the meshing region and extending between the inlet port and the outlet port, the crescent member comprising a trailing edge adjacent to the outlet port, and a tapered leading edge region adjacent to the inlet port comprising an exterior leading edge profile and an interior leading edge profile, said exterior and interior leading edge profiles having a specific geometric relationship amongst them to optimize the volumetric efficiency of the pump and reduce the cavitation effect.

In yet another embodiment of the present invention the angle a formed between the leading edge and the diameter of the outer boundary (OD) passing through the starting point of the taper on said outer boundary is smaller than angle p formed between the leading edge and the diameter of the inner boundary (ID) passing through the starting point of the taper on said inner boundary.

In a preferred embodiment of the present invention said angle P is 1.875 times the angle a in the leading edge region of the tapered crescent member.

In a still another embodiment of the present invention the geometric design of the tapered crescent member produce a venturi effect to the flow of fluid that helps to reduce, if not eliminate, cavitation effect.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Fig. 1 shows a cross sectional view of the gear pump according to the present invention.

Fig. 2a shows a cross sectional view of the gear pump depicting the specific design of the crescent member according to the present invention.

Fig. 2b shows the occurrence of the venturi effect created by the crescent member according to the present invention.

Figs. 3a and 3b show working mechanism of a prior art crescent member with uniform curvature of crescent ID and OD.

Figs. 3c and 3d show working mechanism of a crescent member with leading edge profiles according to the present invention.

Fig. 4 provides a graph showing the efficiency-curve of a conventional internal gear pump and efficiency-curve of an internal gear pump according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention is now described with reference to the drawings.

Fig. 1 shows an internal gear pump having an inlet port (1) for allowing fluid to enter the internal gear pump and an outlet port (2) to discharge the fluid out of the internal gear pump in a pump housing (6). The internal gear pump has two moving elements, namely, an externally toothed external gear (4) and an internally toothed internal gear (5). The external gear (4) is coupled to a shaft (8) via one or more key-ways (9). The shaft (8) is in turn coupled to and driven by a prime mover as required for the specific application. The external gear (4) meshes with the internal gear (5) eccentrically at a meshing region (12) consisting of a meshing point (7). A crescent member (3) is located diametrically opposite to the meshing region (12) and extends between the inlet port (1) and the outlet port (2). The crescent member (3), separating the internal gear (5) and external gear (4), forms an integral part of housing (6) of the internal gear pump.

The crescent member (3) comprises an inner boundary, i.e., concave side (20) adjacent to the gear teeth of the external gear (4) and an outer boundary, i.e., convex side (22) adjacent to the gear teeth of the internal gear (5). The inner boundary (20) has a center at 0 while the outer boundary (22) has a center at O'. The crescent member (3) also comprises a tapered trailing edge (11) adjacent to the outlet port (2) and a tapered leading edge region (13) adjacent to the inlet port (1). The tapered leading edge region (13) further comprises a leading edge (10) extending between the end points (10a, 10b) forming the end of the tapered leading edge region (13), an exterior leading edge profile (14a) close to the gear teeth of the internal gear (5), and an interior leading edge profile (14b) close to the gear teeth of the external gear (4). The exterior leading edge profile (14a) and the interior leading edge profile (14b) forms the tapered profile of the crescent member (3) near the inlet port (1). The leading edge profiles (14a, 14b) preferably forms a taper of angle 20°.

Fig. 2a shows the crescent region (17) near the inlet port (1). The exterior leading edge profile (14a) extends from a starting point (28) of the taper of the exterior leading edge profile on the outer boundary or convex side (22) of the crescent member (3) to the end-point (10a) of the leading edge (10) such that a line joining the starting point (28) on the outer boundary (22) of the crescent member (3) to the center (O') of the outer boundary (22) of the crescent member (3) forms an angle a with the leading edge (10). Similarly, the interior leading edge profile (14b) extends from a starting point (30) of the taper of the interior leading edge profile on the inner boundary or concave side (20) of the crescent member (3) to the end-point (10b) of the leading edge (10) such that a line joining the starting point (30) on the inner boundary (20) of the crescent member (3) to the. center (O) of the inner boundary (20) of the crescent member (3) forms an angle p with the leading edge (10), wherein angle a is less than angle p\ and more preferably, angle P: angle a = 1.875. Also, the starting point (28) of the taper of the exterior leading edge profile is away from starting point (30) of the interior leading edge profile in relation to end points (10a and 10b) of the leading edge which are on the same plane.

The working mechanism of the tapered edged crescent member (3) according to the present invention will now be discussed in detail. Near the inlet port (1) the fluid velocity starts increasing from zero to the nearest velocity of the gear tooth. Hence, to compensate the turbulence in this region, a larger cross-sectional area of the inlet port (1) is designed, and preferably, the inlet port (1) is larger than the outlet port (2). The leading edge profiles (14a, 14b) on the crescent member (3) create a taper or wedge formation which is similar to a convergent venturi tube in which the fluid is filled up. Fig. 2(b) shows regions of occurrence of the venturi effect (18) which are formed around the inlet port (1) of the internal gear pump on both sides of the leading edge profiles (14a, 14b). The venturi tubes on both sides of the leading edge profiles (14a, 14b) have dissimilar volumes and are swiped by the gears at different peripheral velocities. The tapered profile of the crescent member (3) work as a venturi, whereby the fluid is forced into the pockets of the gear sets (15,16) when traveling beyond the tapered leading edge profiles (14a, 14b) of the crescent member (3). This occurs due to the reduction in cross-sectional area as the gear tooth moves over the tapered leading edge profiles (14a, 14b) of the crescent member (3) in the clockwise direction towards the outlet port (2). Fluid pressure at the end of venturi increases as the fluid pocket is swiped along the converged cross-sectional area. This gives rise to a pressure difference between the gear pockets (15, 16) at the start and end of the venturi mechanism. This differential pressure contributes to the positive suction of fluid into the gear pockets (15, 16), thereby reducing the likelihood of cavitation occurring in the pump. By virtue of the tapered leading edge region (13), fluid through the inlet port is guided into each of the adjacent pockets with increased pressure aided by the venturi effect that is formed as a result of the tapered profile. This pressurized flow of fluid into the gear pockets leads to minimal or no accumulation of air in the pocket.

The tapered leading edge region (13) design and its relation to internal and external crescent boundaries (20,22) and their respective centers (O, O') is arrived at by various iterative methods and simulation experimentation. The invented geometric shape of the tapered leading leading edge region (13) and relation with crescent gear centers (O, 0') has been optimized to achieve highest efficiency with minimum noise effect, which leads to no or minimum cavitation. The angles a and P formed by the exterior and interior leading edge profiles (14a, 14b) of the crescent member (3) with respect to centers 0' and 0 of the OD (outer diameter) and ID (inner diameter) of the crescent member (3) remain constant and their ratio also remains constant irrespective of rotation of gear sets (4, 5) and the gear locations, corresponding to their respective centers. A further proof of this concept is analyzed and proved with rotation of the gear pair (4, 5) with respect to their number of teeth. This results in generating a non-contacting region 18 near the inlet port (1). This geometry enables easy fluid flow into the pockets between the gear pair (4, 5).

The combination of the leading edge (10) and tapered leading edge profiles (14a, 14b) allows the pump to maintain the level of volumetric efficiency high enough as desired for the particular application. The tapered edges are devised such that they reduce cutting action on ID and OD of the crescent surface by the gear tip of external and internal gears respectively. Minimizing the cutting-in action ensures the continual better efficiency during long time operational working of the pump. This also results in reduction of metal particle accumulation which is detrimental to life of pump. This is further explained below with reference to Figs. 3a - 3d of the drawings.

If the relation P = 1.875 a is not adopted in the crescent geometry, then crescent geometry has continuous curvature on its ID and OD without leading edge profiles as shown in Fig. 3a. When pump is nonning, high pressure oil in gear tooth pockets tends to push the external gear towards ED of crescent member as shown in Fig. 3b. External gear tooth touches the crescent ID resulting in metal to metal to contact between crescent ID and external gear. Consequently, cutting-in action take place.

If the geometry relation p = 1.875 a is adopted in crescent design, thereby generating a deliberate chamfer, an entry clearance will provide gap between external gear and crescent ID leading edge as shown in Fig. 3c with the direction of build up pressure shown by parallel arrows. Though high pressure oil in gear tooth pockets push the external gear towards ID of the crescent leading edge, the clearance is still maintained between external gear and crescent ID as shown in Fig. 3d due to such geometry relation.

This clearance avoids external gear tooth touching the leading edge of crescent ID and due to this cutting-in action is minimized. Minimizing the cutting-in action improves the pump efficiency and durability. Also when pump is running, the locus of external gear tooth tip and ID of the crescent leading edge forms venturi shape. Due to the venturi action during pump running, the pressure increases at the end of the chamfer. As a result of this, the differential pressure is created between pump suction side and oil carriage side at localized zone. This improves the pump performance. Geometry relation |3 = 1.875 a holds good for all sizes of the pumps if the diameter of ID and OD are changed parametrically.

In Fig. 4 curve A represents the efficiency of an internal gear pump incorporating the present invention of the tapered crescent member (3) with tapered leading edge region (13) of the present invention and curve B represents the efficiency of an internal gear pump with the non-tapered conventional crescent member. It is observed that the efficiency for the internal gear pump incorporating the tapered crescent member (3) with tapered leading edge region (13) according to the present invention is relatively higher throughout the whole cycle of operation when compared to the efficiency recorded for the internal gear pump without the use of tapered crescent member. Further, the volumetric efficiency reaches near 100% with the crescent member of the invention much earlier at lower RPM and remains constant with increase in the rotor speed.

Therefore, the present invention provides a design for crescent member of an internal gear pump which when incorporated in an internal gear pump reduces the likelihood of cavitation occurring in the pump, delivers highest efficiency with minimum noise effect, maintains high level of volumetric efficiency in the pump, and also reduces metal particle accumulation in the pump by minimizing the cutting-in action.

INDUSTRIAL APPLICABILITY

The internal gear pump of the present invention may work as a part of a low pressure network, supplying fluid to the components of the transmission system of an internal combustion engine. The internal gear pump of the present invention can be used for supplying of lube oil to the components of an internal combustion engine and for pumping resins and polymers, alcohols and solvents, asphalt, bitumen, and tar, polyurethane foam (isocyanate and polyols), food products such as corn syrup, chocolate, and peanut butter, paint, ink, pigments, and soaps and surfactants.

While the invention has been described as having a preferred design, the present invention can be modified within the spirit and scope of the disclosure. The present application is intended to cover any variations, adaptations and uses of the invention using the general principles disclosed in the application without departing from the scope of the invention as claimed.

We Claim:

1. An internal gear pump for pumping fluid comprising :

an inlet port (1);

an outlet port (2);

an externally toothed external gear (4);

an internally toothed internal gear (5) operatively and eccentrically connected to the external gear with a meshing region (12) with the external gear;

a crescent member (3) located diametrically opposite to the meshing region and extending between the inlet port and the outlet port, and

a housing (6);

wherein said crescent member comprises :

a trailing edge (11) adjacent to the outlet port; and

a tapered leading edge region (13) adjacent to the inlet port comprising :

a leading edge (10);

an exterior leading edge profile (14a); and

an interior leading edge profile (14b),

wherein angle a formed between the leading edge and the diameter of the outer boundary passing through a first starting point (28) of the taper on said outer boundary is smaller than angle |3 formed between the leading edge and the diameter of the inner boundary passing through a second starting point (30) of the taper on said inner boundary.

2. The internal gear pump as claimed in claim 1, wherein the exterior and interior leading edge profiles make a taper of angle 20° approximately.

3. The internal gear pump as claimed in claim 1, wherein the crescent member further comprises an outer boundary (22) adjacent to the internal gear and an inner boundary (20) adjacent to the external gear on the convex and concave sides respectively of the crescent member.

4. The internal gear pump as claimed in claim 1, wherein angle |3 is 1.875 times the angle a in the leading edge region of the tapered crescent member.

5. The internal gear pump as claimed in claim 4, wherein the relation between angle a and P is valid for all sizes of pumps when the diameters of inner boundary and outer boundary of the crescent member are changed parametrically.

6. The internal gear pump as claimed in any of the preceding claims, wherein the tapered leading edge region by virtue of its geometric shape creates a venturi effect directing the fluid from the inlet port into the gear pockets formed by the teeth of the external and internal gear located adjacent to the exterior and interior leading edge profiles.

7. The internal gear pump as claimed in any of the preceding claims, wherein the conical venturi tube formed between the exterior leading edge profile and the gear pockets of the internal gear located adjacent to the exterior leading edge profile and the conical venturi tube formed between the interior leading edge profile and the respective gear pockets of the external gear located adjacent to the interior leading edge profile have dissimilar volumes.

8. The internal gear pump as claimed in claim 7, wherein there is a pressure difference between the the start and end of the conical venturi shape causing a positive suction of fluid into the gear pockets located adjacent to the conical venturi shape.

9. The internal gear pump as claimed in any of the preceding claims, wherein the inlet port is larger than the outlet port.

10. The internal gear pump as claimed in any of the preceding claims, wherein the trailing edge of the crescent member is also tapered.

11. The internal gear pump as claimed in any of the preceding claims, wherein the external gear is driven by a driving mechanism (8).

12. The internal gear pump as claimed in any of the preceding claims, wherein the crescent member forms an integral part of the housing.

13. The internal gear pump as claimed in any one of the preceding claims, wherein said gear pump is adapted for supplying fluids with pressure for any hydraulic/fluid applications.