GB2233712A - Rotary positive displacement hydraulic machines - Google Patents

Abstract

The machine housing defines two mutually intersecting parallel working chambers containing two meshing rotors (13 and 14). At least one of the bearing supports (19 and 20) on each of two opposite sides of the meshing rotors, is slidably inserted in the parallel chambers and is retained by an end cover (15, 16). A pressure balancing plate (27, 28) is urged into adequate sealing engagement with the meshing rotors by hydraulic fluid from the working space of the machine. A continuous seal (31) associated with the or each slidably inserted bearing support is provided at or adjacent to the end of the bearing support nearest to the meshing rotors so as, in use, to prevent high pressure hydraulic fluid entering between the bearing support and the housing. The seal may instead be located in a recess formed around the edge of the associated balancing plate. <IMAGE>

Description

ROTARY POSITIVE DISPLACEMENT HYDRAULIC MACHINES This invention relates to rotary positive displacement hydraulic machines, such as gear pumps and motors.

Known rotary positive displacement hydraulic machines, in the form of gear pumps and motors, are generally made according to one of two basic designs.

In the first of these, the machine, commonly referred to as a dowelled-type machine, comprises a housing having two mutually intersecting parallel working chambers, two meshing rotors mounted for rotation in respective chambers, two end covers closing opposite ends of the parallel chambers, and two pressure balancing plates interposed between the meshing rotors and respective end covers to minimise axial clearance losses between low and high pressure sides of the machine. In this first basic design, the rotors are journalled in bearings mounted in the end covers. At least one of the end covers must be non-integral with the housing, and dowels are used to position the or each non-integral end cover relative to the housing.This has the disadvantage of poor bearing alignment due to the difficulty in achieving close tolerance dowelling resulting in lower bearing capacities and reduced volumetric efficiencies.

In order to overcome the difficulties of bearing alignment, the second of the two basic designs, commonly referred to as a bush-type machine, utilises two bushes which support the bearings for the rotors and which are slidably inserted into the housing one on either side of the meshing rotors.

When, for example, these known machines are used as pumps, hydraulic fluid is drawn into the chambers through a low pressure inlet port and is delivered to a high pressure outlet port by rotating pockets between the rotors and the housing. The operating pressure on the delivery side of the pump is very high, often as high as 250 bar, and it follows that the pressure differential between the inlet or suction side of the pump and the delivery side of the pump is also very high. Clearly, therefore, it is most important that liquid clearance losses between low and high pressure sides of the pump are kept to a minimum in order to ensure good volumetric efficiency.

In the bush-type machine referred to above, axial clearance losses are minimised by connecting an area of each bush on its side remote from the meshing rotors to liquid pressures in the working space of the machine, and radial clearance losses are minimised, as in the dowelled-type machine, by using liquid pressure on the high pressure side of the machine to urge the rotors radially into metal-to-metal contact with the walls of respective chambers in the vicinity of the low pressure port.

The radial clearance losses thus remain small when the machine runs at or near maximum operating pressures, but because radial pressure is exerted not only on the rotors, but also on the bushes, the degree to which the rotors are displaced radially when run at maximum operating pressures is such that a significant radial clearance is present between the rotors and the machine housing when the machine is run at somewhat less than its maximum operating pressure.

When the machine is used as a pump these radial clearances give rise to a reduction in volumetric efficiency. Indeed, in practice it has been found that as the operating pressure of such a pump rises from zero to a maximum, the volumetric efficiency of the pump dips quite significantly before rising again as the operating pressure approaches a maximum.

The present invention seeks to mitigate this drawback, and accordingly the present invention provides a rotary positive displacement hydraulic machine comprising a housing defining two mutually intersecting parallel working chambers, each communicating with a low pressure port and a high pressure port provided in the housing, two meshing rotors mounted for rotation in the two chambers, respectively, a bearing support on each of two opposite sides of the meshing rotors, each bearing support being provided with bearings in which the two rotors are journalled for rotation, at least one of the bearing supports having been slidably inserted in the parallel chambers and being held in the two chambers by an end cover, a pressure balancing plate interposed between the meshing rotors and an adjacent bearing support, means communicating an area of that face of the pressure balancing plate which is remote from the meshing rotors with the working space of the machine so that, in use, the pressure balancing plate is urged into adequate sealing engagement with the meshing rotors without the generation of undue friction between the pressure balancing plate and the rotors, and means providing a continuous seal between the or each slidably inserted bearing support and the housing, said seal means being at or adjacent to the end of the bearing support nearest to the meshing rotors so as, in use, to substantially prevent high pressure hydraulic fluid entering between the or each slidably inserted bearing support and the housing.

With this arrangement, the radial forces applied by the hydraulic fluid on the high pressure side of the machine act over a smaller axial distance than in the known bushing-type machine with the result that radial displacement of the rotors from nil to maximum operating pressures is less, and the radial clearance between the rotors and the housing at less than maximum operating pressure is therefore smaller than it would be at a similar operating pressure in an equivalent known bushing-type machine. Indeed, it has been found that it is possible to make a machine according to the present invention, which will run as a pump at very high, substantially constant volumetric efficiency regardless of operating pressure.

Also, a machine according to the present invention has the added advantages that the housing experiences less stress as there is less load on the housing, and that there is also less strain on bolts which are advantageously used to clamp the end cover(s) to the housing, with the result that the number of bolts used can be reduced giving more flexibility of design.

Advantageously, the machine has two pressure balancing plates interposed between the meshing rotors and respective bearing supports, and means communicating an area of that face of each pressure balancing plate which is remote from the meshing rotors with the working space of the machine.

Preferably, each bearing support has been slidably inserted in a respective end of the parallel chambers, and is held in the two chambers by a respective cover.

Preferably, the or each slidably inserted bearing support is of unitary construction.

Preferably, the or each slidably inserted bearing support is integral with an end cover.

The invention will now be more particularly described, by way of example, with reference to the accompanying drawings, wherein: Figure 1 is a longitudinal section to one embodiment of a rotary positive displacement hydraulic machine according to the present invention, Figure 2 is a view on the left hand end of the machine shown in Figure 1, and Figure 3 is a sectional view taken along the line III-III of Figure 1, with the end cover and integral bearing support removed.

Referring now to the drawings, the rotary positive displacement hydraulic machine shown therein is in the form of a gear pump. The pump comprises a housing 10, typically formed of extruded aluminium, which defines two mutually intersecting parallel working chambers 11 and 12 formed by an appropriately shaped through bore in the housing 10, two meshing pump rotors in the form of steel gears 13 and 14 which are mounted for rotation in the chambers 11 and 12, respectively, and two end covers 15 and 16 typically formed of die cast aluminium, closing opposite ends of the parallel chambers 11 and 12.

The housing 10 has a low pressure or inlet port 17 and a high pressure or outlet port 18, each of which communicates with both chambers 11 and 12.

Each end cover 15, 16 has an integral one piece bearing support 19, 20, respectively. The bearing supports 19 and 20 are received in opposite ends, respectively, of the parallel chambers 11 and 12, and each supports two sleeve bearings 21 and 22.

The gear 14 is integral with a drive shaft 23 which is supported in the sleeve bearings 21 in the two bearing supports 19 and 20, and which passes through an aperture 24 in the end cover 15 so that it can be connected to a power source. The gear 13 is integral with a driven shaft 25 which is supported in the sleeve bearings 22 in the two bearing supports 19 and 20 and which is contained entirely within the pump.

The end covers 15 and 16 are clamped to opposite ends of the housing 10 by bolts 26 which extend through the two end covers and through the walls of the housing 10, and a seal 9 is provided between each end cover 15, 16 and a respective end wall of the housing 10.

The pump also includes two pressure balancing plates 27 and 28 interposed between the side faces of the two meshing gears 13 and 14 and respective bearing supports 19 and 20, with a small degree of axial freedom.

The pressure balancing plates 27 and 28 are typically of leaded bronze, and the face F of each plate 27, 28 remote from the meshing gears is provided with contiguous rubber and plastic seals 29 and 30, respectively, mounted in a groove in the plate, although the seals 29 and 30 could be mounted in a groove in the end face of the adjacent bearing support. Each plate 27, 28 is of figure of eight shape and each seal 29, 30 is roughly in the shape of a figure three, but at each end has a tail which extends radially outwards to the outer edge of a respective plate 27, 28. Other seal configurations could be utilised including those which provide for bi-directional operation of the pump.As best shown in Figure 3, the seals divide the face F of each plate into two areas, one of which is a high pressure area H and is in communication with the port 18 and the other of which is a low pressure area L and is in communication with the port 17.

The high and low pressure areas are designed to coincide with the high and low pressure sides of the pump so that when the pump is in operation liquid pressures acting upon the two areas L and H of the face F act in opposition to the pressure applied to the opposite face of each plate 27, 28 by the liquid being carried through the pump by the gears, and ensure that the plates 27, 28 are urged into adequate sealing engagement with the side faces of the gears without the generation of undue friction between the plates and the side faces.

An annular seal 31 is provided between each bearing support 19, 20 and the housing 10 in close proximity to a respective plate 27, 28. The seals 31 are located in continuous peripheral grooves in the bearing supports. Each groove is positioned as close as is practically possible to that end face of its respective bearing support nearest to the meshing gears 13 and 14 and the seals 31 prevent hydraulic fluid passing beyond them between the bearing supports 19, 20 and the housing 10. This confines the radial pressure which is applied between the high and low pressure sides of the pump to the axial separation between the two seals 31 with the result that the radial displacement of the gears 13 and 14, which takes place as the pump operating pressure increases from nil to a maximum, is significantly less than it would have been if the seals 31 had been omitted.

At maximum operating pressure the gear teeth make contact with a respective chamber wall in the vicinity of the low pressure or inlet port 17, and indeed the teeth do in fact mill a shallow crescent shaped groove in the chamber wall in the vicinity of the inlet port when the pump is initially run-in. Thus if the pump is run at below maximum operating pressure, as is often the case, a gap will be present between the gear teeth and the chamber wall. By confining the radial pressures to the axial separation between the seals 31, this gap will be less than it would have been if the seals had been omitted, and consequently the volumetric efficiency of the pump is increased.

The limited radial displacement of the gears 13 and 14 also means that the housing 10 will experience less stress as the load on the housing will be less so increasing the fatigue life of the housing, and because the hydraulic fluid is confined between the seals 31, it cannot enter between the end covers and the ends of the housing 10 with the result that the strain on the bolts 26 is less than in hitherto known pumps designed to operate at equivalent pressures. The number of bolts used can, therefore, be reduced, and this gives more flexibility of design.

The space between each bearing support 19, 20 and the housing 10 and between respective seals 9 and 31 may be communicated with the low pressure port 17 by a passage (not shown) in order to drain away any liquid leaking past the seal 31.

The embodiment described above is given by way of example only and various modifications will be apparent to persons skilled in the art without departing from the scope of the invention. For example, the pump could be operated as a motor. The seal 31, instead of being between the outer peripheral surface of the bearing support and the housing, could be supported in a recess formed around the edge of that face of a pressure balancing plate proximate the bearing support. In that case, the seal 31 will be at that end face of the bearing support proximate the meshing gears, and still provide a continuous seal between the bearing support and the housing. The bearing supports could be separate from the end covers. One of the end covers and its respective bearing support could be integral with the housing. In that case it will not be necessary to provide a seal between that bearing support and the housing. Each bearing support could be formed in two parts each provided with a suitable bearing. It may be possible to omit one of the pressure balancing plates.

Also, any number of meshing rotors may be provided.

Claims (8)

1. A rotary positive displacement hydraulic machine comprising a housing defining two mutually intersecting parallel working chambers, each communicating with a low pressure port and a high pressure port provided in the housing, two meshing rotors mounted for rotation in the two chambers, respectively, a bearing support on each of two opposite sides of the meshing rotors, each bearing support being provided with bearings in which the two rotors are journalled for rotation, at least one of the bearing supports having been slidably inserted in the parallel chambers and being held in the two chambers by an end cover, a pressure balancing plate interposed between the meshing rotors and an adjacent bearing support, means communicating an area of that face of the pressure balancing plate which is remote from the meshing rotors with the working space of the machine so that, in use, the pressure balancing plate is urged into adequate sealing engagement with the meshing rotors without the generation of undue friction between the pressure balancing plates and the rotors, and means providing a continuous seal between the or each slidably inserted bearing support and the housing, said seal means being at or adjacent to the end of the bearing support nearest to the meshing rotors so as, in use, to substantially prevent high pressure hydraulic fluid entering between the or each slidably inserted bearing support and the housing.

2. A rotary positive displacement hydraulic machine as claimed in Claim 1, comprising two pressure balancing plates interposed between the meshing rotors and respective bearings supports, and means communicating an area of that face of each pressure balancing plate which is remote from the meshing rotors with the working space of the machine.

3. A rotary positive displacement hydraulic machine as claimed in Claim 1 or Claim 2, wherein both bearing supports have been slidably inserted in opposite ends, respectively, of the parallel chambers, and are held in the two chambers by respective end covers.

4. A rotary positive displacement hydraulic machine as claimed in Claim 3, wherein the two end covers are clamped to opposite ends of the housing by bolts which extend through the two end covers and through the housing.

5. A rotary positive displacement hydraulic machine as claimed in any one of the preceding claims, wherein the or each slidably inserted bearing support is of unitary construction.

6. A rotary positive displacement hydraulic machine as claimed in any one of the preceding claims, wherein the or each slidably inserted bearing support is integral with a respective end cover.

7. A rotary positive displacement hydraulic machine as claimed in any one of the preceding claims, wherein the or each seal means is located in a groove in the outer peripheral surface of the bearing support.

8. A rotary positive displacement hydraulic machine substantially as hereinbefore described with reference to the accompanying drawings.