EP0107824A1

EP0107824A1 - Internal gear pump

Info

Publication number: EP0107824A1
Application number: EP19830110014
Authority: EP
Inventors: Mamoru c/o Itami Works of Sumitomo Sugimoto
Original assignee: Sumitomo Electric Industries Ltd
Current assignee: Sumitomo Electric Industries Ltd
Priority date: 1982-10-29
Filing date: 1983-10-06
Publication date: 1984-05-09
Also published as: JPS5982594A; ES8407559A1; ES526851A0

Abstract

An improved internal gear pump having a casing formed with a suction port and a discharge port, an outer rotor and an inner rotor of a paratrochoidal profile. The suction port formed in one end of the casing is formed with an extension protruding in the direction of rotation of the rotors.

Description

The present invention relates to an internal gear pump and, more specifically, to a special tooth profile gear pump employing an inner rotor which has a paratrochoidal profile.
The term "paratrochoidal" herein used is an adjective representing an envelop of a set of circles of a fixed diameter having their centers on a trochoid or a roulette.
In known internal gear pumps of the aforementioned type, a pump casing 1 is formed in at least one end thereof with a generally arcuate suction port 2.and a discharge port 3 which is almost similar in shape to the suction port 2 but disposed generally opposedly thereto, as shown in Fig. 1. Both of the suction port 2 and the discharge port 3 are defined by an inner arcuate side edge 4 of a smaller radius r, an outer arcuate side edge 5 of a larger radius R which is eccentric to but warped on the same side as the inner side edge 4, and two linear end edges 6 and 7 each connecting the corresponding ends of the inner and outer side edges.
Although such conventional internal gear pumps might be almost free from shortcomings so long as the discharge side is concerned, their suction side is not without outstanding problems. More specifically, as an inner rotor 8 rotates in the direction of the arrow in driving engagement with an outer rotor 9, a space 10 shown in Fig. 2, defined by the inner rotor 8 and outer rotor 9, comes close'to its closed state shown in Fig. 3, in which it is shut off from the suction port 2 as well as from the discharge port 3. In this course, the cross- sectional area S₂ of the space 10 formed, in end view, between the profile of the inner rotor and that of the outer rotor increases gradually, while the area S₁ of the portion of the space 10 enclosed by the profiles of the inner and outer rotors and the edge 6 of the suction port decreases rather sharply. That is, the opening of the suction port 2 to the space 10 permitting the inflow of the fluid thereinto decreases sharply. As a result, heavy cavitation occurs with resultant loud noise and abnormal abrasion of the rotors, if the pump is operated at a high speed.
To prevent such cavitation, various solutions have heretofore been proposed such as the provision of the suction port 2 in not one but both of the end plates of the casing 1, reduction in the rotor speed and increase in the number of teeth of the rotors to reduce the cross- sectional area S of the space 10 in its closed state shown in Fig. 3. With such solutions, however, it is not only impossible for a pump of a given size to have an increased delivery, but the foregoing problems are not completely solved.
The present invention has for its object to provide an internal gear pump which obviates the aforementioned problems.
According to the present invention, the suction port is provided with an extension to enlarge its opening to the space defined by the inner and outer rotors so that before the closure thereof no sharp decrease occurs in the inflow of the fluid. The extension protrudes in the direction of rotation of the rotors from the leading end edge of the suction port.. Further, the extension is formed in such a size and shape that it has no adverse effect on the closure of the space.
As fully described herein before, the internal gear pump according to the present invention has a-suction port which is extended in .the rotational direction of the rotors so that its opening, permitting the inflow of the fluid into the space defined by the inner and outer rotors, will be kept relatively wide until the space is shut off.
Thus, according to the present invention, cavitation can be effectively minimized even if the rotor speed is high.
Further, this also makes it possible to decrease the number of teeth of the rotors to increase the volume of the space defined thereby. Therefore, it will be understood that the present invention realizes a remarkable improvement in the efficiency of internal gear pumps.
Other objects and advantages of the present invention will become apparent from the following description taken with reference to the accompanying drawings, in which:

Fig: 1 is a schematic end view of an internal gear pump of the prior art, showing the configuration of its suction and discharge ports;
Fig. 2 and 3 are schematic cross-sections of the pump of Fig. 1, showing how the area defined by its inner and outer rotors changes;
Fig. 4 is a schematic cross-section corresponding to Fig. 3 of one preferred embodiment of the internal gear pump according to the present invention; and
Fig. 5 is a similar view thereof corresponding to Fig. 2.

Referring to Figs. 4 and 5, the internal gear pump of the present invention has a generally cylindrical casing 1 which has two end plates, one of them being formed with a suction port 2' having an extension'11 which will be described below and with a discharge port 3 having a known configuration. In the casing are rotatably mounted an inner rotor 8 having a paratrochoidal profile and coupled to a drive shaft (not shown) and an outer rotor 9 which is eccentric to and driven by the inner rotor 8.
According to the present invention, the extension 11 of the suction port 2' protrudes, in the end plate, in the rotational direction of the rotors from the leading end edge 6 of the suction port 2 of the aforementioned known configuration. In other words, it has a partially embayed end edge 6' as shown in Fig. 4. In terms of the cross-section of the pump taken when the space 10 defined by the inner rotor 8 and outer rotor 9 is just shut off from the suction port ₂' (See Fig. 4), the exten- tion 11 may be formed to extend up to a border determined by the profile segment 8' of the inner rotor facing the delivery space 10 and a circle C inscribing to its paratrochoidal profile. In practice, the edge of the extension 11 may be straight lines or curves partially almost in parallel with the profile segment 8' and partially with the inscribed circle C. Preferably, the extension 11 is configured and sized so as to be closed by the end surface of the inner rotor 8 immediately before the space 10 reaches its maximum volume.
In the suction port 2' having the extension 11 according to the present invention, the opening to the space 10 before its closure is enlarged, as shown in Fig. 5. Namely, the opening S'₁ is significantly larger than the opening S₁ provided by the conventional suction port (See Fig. 2). Therefore, the fluid is sucked into the space 10 much more smoothly.
The extension 11 may have such a size and shape that its edge comes somewhat inside the space 10 in the closed state thereof shown in Fig. 4. However, as described previously, the extension 11 preferably has such a size and shape that it is closed by the end surface of the inner rotor 8 immediately before the space 10 reaches its maximum volume, in order to ensure that the fluid sucked therein is smoothly delivered to the discharge side substantially without leakage.

Claims

1... An internal gear pump comprising:

a generally cylindrical casing having two ends, at least one end thereof being formed with a generally arcuate suction port and a discharge port similar in shape but disposed generally opposedly to said suction port;

said suction port and said discharge port being defined 'by an arcuate inner side edge, an arcuate outer side edge which is eccentric to but warped on the same side as said inner side edge, and end edges connecting the corresponding ends of said inner and outer side edges,

an outer rotor having an internal gear-like profile and rotatably mounted in said casing; and

an inner rotor having a paratrochoidal profile and rotatably mounted in said outer rotor eccentrically thereto and in driving engagement therewith;

said suction port being formed at a leading edge thereof with an extension protruding in the direction of rotation of said rotors up to a border defined substantially by that segment of said paratrochoidal profile of said inner rotor facing a space defined by said inner rotor and said outer rotor and by a circle inscribing to said paratrochoidal profile in the cross-section of the pump taken when said space is shut off from both of said suction and discharge ports.

2. The.internal gear pump according to claim 1, wherein said extension is configured and sized so that it is fully closed by the end surface of said inner rotor when the volume of said space reaches the maximum thereof.