GB2336876A

GB2336876A - Noise reducing helical gear pump

Info

Publication number: GB2336876A
Application number: GB9809158A
Authority: GB
Inventors: Roderick Howell Spurry
Original assignee: Sauer Sundstrand Ltd
Current assignee: Sauer Danfoss Swindon Ltd
Priority date: 1998-04-29
Filing date: 1998-04-29
Publication date: 1999-11-03
Anticipated expiration: 2018-04-29
Also published as: GB2336876B; GB9809158D0

Abstract

A gear pump 1 for pumping fluid from an inlet line 13 to an outlet line 25 has intermeshing helical gear wheels 3,5 mounted on parallel shafts 7,9. The high pressure outlet side of the pump is divided into two distinct sections 17,19 by a separation fin or key 11, preferably tapered and counter sunk into the pump housing. Each outlet section 17,19 is connected to a separate exhaust passage 21,23 which merge at a point downstream, preferably within the body of the pump housing. A phased difference between high pressure pulses between the outlet sections 17,19 provides a clarification of the fluid pulse generated by the intermeshing gear teeth, and a noise reduction in pump operation.

Description

2336876 TITLE Noise Reducing Helical Gear Pump

DESCRIPTION Inventive Field:

The invention relates to a gear pump arrangement, whereby pulsating pressures in the pumped fluid are reduced, with reduction of the attendant noise in use.

Background Art:

Gear pumps are very commonly used in the pumping of fluids, and there is great interest in making improvements to their basic functioning. one of the problems with gear pumps relates to the generation of pulsating pressure in the fluid being pumped.

The intermeshing of rotating gears causes the formation of fluid-filled cavities between adjacent pairs of gear teeth and a pump housing as the gear wheels rotate. As the gear wheels rotate, the cavities and their contents are carried around the circumference of the gear wheels through to the other side of the pump. Since it is not possible for fluid to pass between the gear wheels after the point of intermeshing, the transfer fluid is in one direction only.

Because the fluid is moved in discrete packets, the rotation of the gear wheels causes pulsations in the output pressure of the gear pump. The pulsations produce noise as well as vibrations which eventually degrade machinery.

One method of reducing vibration has been investigated by the applicants in GB 9621136.2. In this Application two pairs of spur gears are mounted alongside one another on common shafts in a single pump in such a way that the pulsations caused by the release of fluid by the two sets of gears occur at mutually different times. This has a smoothina effect on the final 1Dressure output. Although 1 significant noise reduction is attainable using the double gear set approach, such pumps are inherently expensive and difficult to produce.

Another method, well known in the f ield, to address the problem is to use helical gears. This technology is predominantly used to reduce the noise level as compared with conventional spur gear pumps. Inherently, there is an element. of phase shift across the helical gears so that each high pressure peak at the pump outlet is spread over the angular extent of the helical tooth form from one end of the gear set to the other. Helical gear sets, however, have as yet not been able to achieve noise reduction levels approaching that of the double gear set assembly.

It has now been appreciated by the Applicants that separation of the fluid flow at the outlet side of a helical gear pump improves the clarity of the pulsations within the fluid, permitting an improvement in the overall noise reduction characteristic of the conventional helical gear pump.

The Invention The invention provides an apparatus comprising a helical gear pump for pumping fluid from an inlet to an outlet, wherein two intermeshing helical gear wheels are mounted on parallel shafts in a pump housing; the high pressure side of the helical gears is divided into two sections by a separation fin mounted between the pump housing and the meshing gear wheels at a position intermediate the ends of the gear wheels; each of the outlet sections is connected to an exhaust passage and the fluid flowing through the exhaust passages is blended at some point further downstream.

The separation fin is preferably tapered and counter sunk into the body of the pump.

The outlet sections may be of unequal size, however, it is preferable to have outlet sections of approximately the same size, by mounting the separation fin approximately midway between the opposite end faces of the gear wheels.

For practical purposes, the point at which the fluid from the exhaust passages merges is preferably embodied within the body of the pump.

Description with reference to the Drawings

Figure 1 is a graph showing the pulsating outlet pressure of a conventional spur gear pump with a single set of interme-shing gears; Figure 2 is a graph showing the pulsating outlet pressure of a conventional helical gear pump; Figure 3 is a graph showing the outlet pressure of a pump according to the invention; Figure 4 is a perspective view of a pump housing of a pump of the invention, with the end plates and helical gears removed to permit sight of the flow separating fin; Figure 5 is a side view of the housing of Figure 4, including the gears; and Figure 6 is a cross section taken along the line A-A of Figure 5, without the gears in place.

Referring to Figure 1, it will be seen that the outlet pressure of a conventional spur gear pump pulsates, with each pressure peak occurring as fluid is expressed from the fluid-filled cavities between pairs of gear teeth and the housing, by meshing of the gear teeth. In a conventional helical form gear pump the meshing of the gear teeth occurs over an angular extent dictated by the helix angle (typically about 70) and the length of the helical gears. A typical outlet pressure pulse form would be as shown in Figure 2. By increasing the helix angle or extending the length of the helical gears the length of the high pressure plateau can be increased, but leakage tends to occur and pumping efficiency falls if that plateau is extended too near to the low pressure pulse caused by the contact between the outer tip of the helical tooth and the housing wall immediately before delivery of a new fluid-filled cavity to the outlet side of the pump.

According to the invention, the angular extent of the meshing of the gear teeth can be increased to one tooth pitch, as measured from one side of the helical gear forms to the other. The resulting pressure outlet waveform is as shown in Figure 3, in which the arrows A and B indicate delivery of the outlet fluid to one or other of the outlet sections as directed by the separation fin.

Figures 4 to 6 show a pump of the invention.

Referring to Figures 4 to 6, gear pump 1 has intermeshing helical gear wheels 3 and 5. The gear wheels 3 and 5 are mounted on parallel shafts 7 and 9 respectively. There is a phase difference of one tooth pitch across each of the helical gears 3 and 5 from one end face to the other.

A separation f in 11 is inserted into the gear housing of the gear pump 1 on the outlet side of the intermeshing helical gear wheels 3 and 5. The fin is preferably tapered and slightly counter sunk into the gear housing of the pump 1 so as not to interfere with the gear pack 3 and 5.

Figure 6 illustrates the paths within the pump 1 for fluid flow.

The pump is supplied with fluid from an inlet port 13 and an inlet passage 15. The fluid is then transferred in conventional manner to the high pressure outlet side of the pump by the intermeshing helical gear wheels 3 and 5 At the high pressure outlet side, a high pressure pulse effectively traverses the width of the meshing gears from one end X to the other end Y.

The separation fin 11 effectively divides the outlet of the gear wheels 3 and 5 into two distinct sections 17 and 19. This separation of the flow is advantageous in that it clarifies the fluid pulse.

Each outlet section 17 and 19 is connected to a separate exhaust passage 21 and 23. The two flows are taken through the two separate exhaust passages 21 and 23, located either side of the separating fin 11, and are blended at some point further downstream. In the preferred embodiment the point where the two flows merge is located within the body of the gear pump 1 and the f luid emerges f rom the pump 1 through the outlet port 25.

There is sufficient isolation between the outlet sections on opposite sides of the separation fin 11 to ensure that the high pressure pulse is delivered first through the exhaust passage 21 to the outlet port 25 and then through the exhaust passage 23 to the outlet port 25. Naturally there is a phase difference between the averaged fluid flow from the two outlet sections 17 and 19.

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Claims

CLAIMS An apparatus comprising: a helical gear pump for pumping fluid from an inlet to an outlet, wherein two intermeshing helical gear wheels are mounted on parallel shafts in a pump housing; the high pressure side of the helical gears is divided into two sections by a separation fin mounted between the pump housing and the meshing gear wheels at a position intermediate the ends of the gear wheels; each of the outlet sections is connected to an exhaust passage; and the fluid flowing through the exhaust passages is merged at some point further downstream.

1 1

2. An apparatus according to claim 1, wherein the separation f in is tapered and is counter sunk into the body of the pump.

3. An apparatus according to claim 1 or claim 2, wherein, by mounting the separation fin approximately midway between the opposite end faces of the gear wheels, the-outlet sections are of approximately equal size.

4. An apparatus according to any preceding claim, wherein the exhaust passages merge within the body of the PUMP.

5. An apparatus substantially as described herein with reference to the drawings.