GB2318155A

GB2318155A - Reducing noise in gear pumps

Info

Publication number: GB2318155A
Application number: GB9621136A
Authority: GB
Inventors: Graham David Linney; Clive Wilfred Rushen
Original assignee: Sauer Sundstrand Ltd
Current assignee: Sauer Danfoss Swindon Ltd
Priority date: 1996-10-10
Filing date: 1996-10-10
Publication date: 1998-04-15
Anticipated expiration: 2016-10-10
Also published as: GB2318155B; GB9621136D0

Abstract

Two gear pumps for pumping fluid from an inlet line (13, Fig. 2) to outlet lines (14,15) include gears 1,3 mounted on separate shafts 5, 6 which are substantially axially aligned, the teeth of the gears being out of alignment with one another, preferably by about half a tooth pitch. The gears 2, 4 of the two pumps are connected by a drive 12 arranged such that the gear teeth are always out of alignment. The apparatus will minimize the effect of pulsating pressure in the working fluid arising from the intermeshing of the rotating gears.

Description

TITLE Reducing Noise in Gear Pumps DESCRIPTION Inventive Field: The invention relates to an arrangement of gear pumps, whereby pulsating pressures in the pumped fluid are minimised.

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 main problems with gear pumps relates to the generation of pulsating pressure in the fluid being pumped.

The intermeshing of the rotating gears causes the formation of fluid filled cavities as the individual gear teeth rotate out of contact with one another. As the gearwheels rotate, the cavities and their contents are carried around the circumference of the gearwheels to the other side of the pump. Since it is not possible for fluid to pass between the gearwheels at their point of intermeshing, the transfer of fluid is in one direction only.

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

One way of reducing vibrations is to mount two pairs of gears alongside one another on common shafts in a single pump in such a way that the pulsations caused by the release of fluid in the two sets of gears occur at mutually different times.

Mounting two pairs of gears alongside one another on common shafts can be problematic. The shafts may be each mounted between three sets of bearings; one on the outside of each gearwheel and one between the gearwheels. This causes serious alignment problems and one bearing almost inevitably ends up under excessive stress. An alternative way of mounting is to provide two sets of bearing members, one on the outside of each gearwheel, and only a pressure plate between the gearwheels. The pressure plate includes no bearing so provides no support. In this case, each of the two gearwheels is effectively supported by both of the two bearing members, one of the bearing members being positioned adjacent to the gearwheel and one at a distance dictated by the total width of the central pressure plate and the other gearwheel. The central shaft thus acts as a cantilever providing support for each pair from its opposite bearing member. This causes excessive stresses in the central portion of the shaft.

GB 2274489 shows a gear pump in which two sets of gearwheels are mounted such that there are no bearings on an outer side of one of the gearwheels. This reduces the length of the cantilever and reduces stresses. However, the pump still suffers from the problem that one of the gearwheel sets is unsupported by bearings on one side.

It has now been appreciated by the Applicants that it might be possible to reduce pulsations significantly without having to mount two pairs of gears within a single pump and on a common shaft.

The Invention The invention provides apparatus comprising two gear pumps each for pumping fluid from an inlet line to an outlet line; wherein: the two gear pumps have a common inlet line and/or a common outlet line; the two gear pumps are mounted on separate shafts; and the shafts of the two gear pumps are subsantially axially aligned but the gear teeth of the two pumps are out of alignment with one another.

Preferably the gear teeth of the pumps are approximately half a tooth pitch out of alignment with one another.

The inlet lines to the two pumps may be common. By this it is meant that the fluid to the pumps comes from a common source through common piping or from separate sources but with a balancing connection adjacent the inlet area of the two gears. Pulsations on the inlet side of gear pumps have been found to be very important in addition to those on the outlet side, and providing a common inlet provides significant benefits even if the outlet lines are separate.

A common outlet line is provided in addition, or as an alternative, to the common inlet line. By common it is meant that the outlet lines join preferably immediately adjacent the output of the gears, but at least before either of the flows reaches a piece of equipment.

Preferably a first gear of one of the pumps is driven, and is connected to a first gear of the second pump by a drive arranged such that the gear teeth of the pumps are always out of alignment.

Description with reference to the drawings Figure 1 is a cross section through a double gear pump arrangement according to the invention; and Figure 2 is a partly cut away side view of a double gear pump arrangement according to the invention.

Referring to Figure 1, the arrangement consists of a first gear pump having intermeshing gearwheels 1 and 2 and a second gear pump having intermeshing gearwheels 3 and 4.

The gearwheels 1 and 3 are mounted on two adjacent but separate shafts 5 and 6 respectively. The shaft 5 is mounted within two sets of bearings 7 and 8, one on each side of the gearwheel 1. The shaft 6 is also mounted within two sets of bearings 9 and 10, one on each side of the gearwheel 3.

The gearwheels 2 and 4 are also mounted on separate shafts in a corresponding manner.

The gearwheel 2 is driven by an input drive 11. A central drive 12 connects the gearwheels 2 and 4 in such a way that they are always half a tooth pitch out of alignment, and acts such that driving the gearhweel 2 results in gearwheel 4 also being driven. In Figure 2, the misalignment of the two gear sets can be seen.

Referring to Figure 2, the two gear pumps have a common inlet 13, but separate outlets 14 and 15. The common inlet has greatly reduced pulsations because of the alignment of the two pumps. Thus, the overall pulsations in the pump arrangement are maintained at an acceptable level.

Claims

1. An apparatus comprising: two gear pumps, each for pumping fluid from an inlet line to an outlet line, wherein: the two gear pumps have a common inlet line and/or a common outlet line; the two gear pumps are mounted on separate shafts and the shafts of the two gear pumps are substantially axially aligned but the gear teeth of the two pumps are out of alignment with one another.

2. An apparatus according to claim 1 wherein the gear teeth of the pumps are substantially half a tooth pitch out of alignment with one another.

3. An apparatus according to any previous claim wherein the inlet lines to the two gear pumps are common.

4. An apparatus according to claim 3 wherein the inlets of the two gear pumps receive fluid from a common source through common piping.

5. An apparatus according to claim 3 wherein the inlets of the two pumps receive fluid from different sources through separate pipes which have a balancing connection adjacent to the inlet area of the two gear pumps.

6. An apparatus according to claim 1, substantially as described herein with reference to the drawing.

6. An apparatus according to any preceding claim wherein the outlet lines of the two gear pumps are common.

7. An apparatus according to any previous claim wherein a first gear of one of the pumps is driven and is connected to a first gear of the second pump by a drive arrangement such that the gear teeth of the gear pumps are always out of alignment.

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

Amendments to the claims have been filed as follows CLAIMS 1. An apparatus comprising: two gear pumps, each for pumping fluid from an inlet line to an outlet line, wherein: the two gear pumps have separate inlets which receive fluid from different sources through separate pipes which have a balancing connection adjacent to the inlet areas of the two pumps and/or a common outlet line; the two gear pumps are mounted on separate shafts and the shafts of the two gear pumps are substantially axially aligned but the gear teeth of the two pumps are out of alignment with one another.

3. An apparatus according to claim 1 or claim 2 wherein the outlet lines of the two gear pumps are common.

4. An apparatus according to claim 1 or claim 2 wherein the outlet lines of the two gear pumps are separate.

5. An apparatus according to any previous claim wherein a first gear of one of the pumps is driven and is connected to a first gear of the second pump by a drive arrangement such that the gear teeth of the gear pumps are always out of alignment.