Vane Pump Having Extended Undervane Suction Ports

Abstract

Improved high speed operation of vane pumps is obtained by the provision of undervane suction ports that are positioned to establish continuing fluid communication with the inner end of each rotor vane slot, angularly beyond the end of the main suction port. The undervane suction port advantageously extends in the direction of rotor rotation to a position just short of the point at which it would provide a short circuit connection between the pressure and suction zones.

Description

This invention relates to improvements in hydraulic pressure energy translating devices of the type having rotor and stator members, one of which mounts vanes that engage a cam surface carried by the other member. More particularly, the invention is directed to improvements in the "timing" of fluid communication between the respective fluid transfer pockets and the pump suction porting in a vane pump.

In the most common type of commercial vane pump, the vanes are mounted in slots in a rotor. As the rotor turns, the tips of the vanes engage and slide over a cam surface which is around the rotor. The sides of the rotor and the side edges of the vanes are in sliding, sealing engagement with cheek or port plates on opposite sides of the rotor.

The cam surface is contoured so that the spacing between it and the rotor periphery varies around the rotor. This so-called pumping space, bounded by the rotor surface, the cheek plates, and the cam surface, is generally regarded as comprising four zones: the pressure zone, the suction zone, a transfer zone (which lies between the suction zone and the pressure zone in the direction of rotation), and a sealing zone (which lies between the pressure zone and the suction zone in the direction of rotation). The variations in cam surface-rotor spacing in these zones cause vane movement and consequent changes in the volume of the intervane spaces or transfer pockets between the respective pairs of vanes.

A pocket increases in volume as it traverses the suction zone, and decreases in volume in the pressure zone. The volume increase at the suction zone occurs because the cam surface recedes from the rotor surface there. This permits the vanes to extend from their rotor slots. The recession of the cam surface from the rotor surface across the suction zone is called the suction ramp, the term "ramp" being used to designate an inclined surface, as opposed to an arc of fixed or constant diameter about the rotor axis. The volume of the intervane is decreased in the pressure zone, where the cam surface has a so-called pressure ramp, which approaches the rotor surface.

One or more main suction ports open through each cheek plate, and fluid flows through such main suction ports into the transfer pockets between the pairs of vanes as the vanes sequentially move past it. The front or leading vane of each pocket-defining pair seals and prevents pressure fluid in the pressure zone of the pump from "short circuiting" by escaping past it to the suction port. As the rotor turns, the pocket transfers the fluid in it across a transfer zone to the pressure port in the pressure zone. The trailing vane of the pocket pair closes or seals the pocket from the main suction port, before the leading vane of the pair has moved far enough to permit communication of the pressure zone with the pocket, in order to prevent internal pressure fluid loss by short circuiting.

For the most efficient pumping action to take place, it is essential that each transfer pocket fill completely with fluid as it traverses the suction zone. At low speed operation, fluid can readily flow into the transfer pockets as they sequentially pass the main suction port, and each pocket fills completely. However, as the speed of rotation increases beyond a certain speed (the value of which depends on the structural details of the particular pump), the time period during which the transfer pocket is open to (i.e., in fluid communication with) the suction zone becomes so brief that it is insufficient for the pocket to fill completely. Above that speed the pump will not deliver its full volumetric capacity, and cavitation, noise, and wear increase rapidly. Such partial and inadequate filling of the pockets is apparent on a graph showing pump out-put flow rate as a function of speed of rotation. Starting at zero, the curve is essentially a straight line, corresponding to a proportional increase in output flow rate with increasing speed. Eventually, however, the slope of the curve begins to decline; the flow continues to increase, but at a decreasing rate. The flow does not increase in direct relation to pumping speed. Whatever the precise speeds at which these phenomena occur, it is generally true that a vane pump will become increasingly inefficient above a certain speed of rotation, once pocket filling begins to be incomplete.

This has restricted the useful range of pump operation, and has reduced efficiency of pumps running at speeds beyond the range of "straight line" operation. Beyond the "limiting" speed, further speed increases do not produce comparable increases in output, and the pump becomes increasingly inefficient. Moreover, cavitation causes noise and increased metal erosion that leads to excessive wear. In such cases the pump is operating past the point of diminishing returns.

It has been a primary objective of this invention to improve the high speed operation of vane pumps, and to extend the range of speeds at which such pumps can operate efficiently.

In many vane pumps there is a second area, in addition to the respective intervane pocket, which must be filled with fluid as the pocket moves through the suction zone. This is the volume at the inner end of the rotor slot in which the vane slides. The vane is moving outwardly as it traverses the suction ramp, and the unoccupied volume of the vane slot is also increasing. In order to provide for filling of this volume, a so-called under-vane suction port is commonly provided in the cheek plate. This undervane port is spaced radially inwardly from the main suction port, and it communicates with the inner end of the vane slot as the latter sweeps by it.

In addition to undervane suction ports, the prior art has also provided supplementary means to connect the inner end of each vane slot to an intervane pocket, in the form of a bore extending angularly from the rotor periphery to the respective vane slot inner end. Such bores are shown in Pettibone U.S. Pat. No. 3,479,962, issued Nov. 25, 1969. However, inward flow in such rotor bores is restricted by centrifugal force, and such rotor bores would more likely provide an outward flow if an adequate source of fluid were to be provided at the inner end of the rotor slot. In the absence of an adequate source of fluid at the inner end of the vane slots, it would be expected that some of the available fluid would flow to the intervane pocket, tending to starve or cavitate the undervane spaces.

In the past, the angular dimension of the undervane suction port has been substantially the same as that of the main suction port. Communication between the main suction port and a given transfer pocket cuts off when the trailing vane of the pocket crosses the downstream edge of the main suction port. This occurs when the trailing vane is at its most extended position, at the outer end of the suction ramp where the vane is about to start its traverse of the major diameter portion or so-called pumping arc of the cam surface. Similarly, it has been the accepted practice in the industry to "time" the closing of the undervane port to occur (i.e., to cut off communication between the undervane port and the inner end of a vane slot which is passing it) very shortly after the vane has reached its most extended position.

It is mandatory that the main suction port close before the pocket it has been filling comes into communication with the pressure port. If the main suction port closed later with respect to that pocket, there would exist a short circuit path from the pressure port through the pocket, directly to the suction port. Hence, for a very practical reason the main suction port cannot be extended to provide a longer filling space.

This invention is predicated on the discovery that the undervane suction port--in contradistinction to the main suction port--does not need to be limited to the same angular dimension as the main suction port, and that in fact there is an advantage to be obtained, particularly in respect to better high speed operation of the pump, by extending the undervane suction port in the direction of rotor rotation, to a substantially greater angular extent than has previously been known. This extension delays the closing of the undervane suction port with respect to a given vane slot. More importantly, it provides longer communication between the under-vane port and a given pocket via the slot of the leading vane of the pocket. A longer filling time is thereby provided for fluid to flow into the pocket from the slot of the leading vane of that pocket.

The extended undervane suction port is preferably closed only just before it would provide a short circuit path for fluid from the pressure zone to escape through it toward the suction zone. Test data has confirmed that such elongation of the undervane ports will extend the linear part of the flow-speed curve, up to higher operating speeds than would otherwise be obtained.

Any substantial elongation or extension of the undervane port, beyond the traditional duration of the prior art, will afford an improvement. Preferably, however, the undervane suction port is extended almost to the position at which it would afford a bridge or path between the high pressure zone of the pump and the suction zone, and thereby short circuit the pump. Such short circuiting would be highly undesirable. Nonetheless, it has been found that closure of the undervane suction port only a few degrees ahead of the point of connection to the pressure zone is sufficient to maintain an adequate seal, while at the same time permitting the pump to be run on a lineal part of the flow versus speed curve, at speeds several hundred rpm greater than are possible with conventional undervane port timing.

All the reasons may not be known for the improvement that flows from extension of the port length in accordance with the invention. The undervane slot volume is much smaller than the volume of the pocket between adjacent vanes, and it might therefore be thought that less difficulty would be encountered in filling it. It is theorized that cavitation in the under-vane slots has been severe and that an extended undervane fill period overcomes this effect. Also, some fluid in the under-vane slot can flow to the transfer pocket itself, to insure that the latter is also filled, and it may be assisted in doing so by the centrifugal force that tends to move it radially outwardly, up the vane groove and/or pressure balancing holes and into the transfer pocket. "Bubbles" arising from cavitation are believed to be most severe just behind the leading vane of a pocket, and these spaces can be filled by fluid from the leading vane slot flowing up from the slot through the vane grooves or balancing holes. This type of bubble filling may be more efficient than filling via the main suction port, since fluid flowing to a moving bubble from the vane in front of it requires less acceleration to reach that space than fluid from the main suction port which must catch up to the bubble from behind. The extended undervane ports enable this "two way" filling of a pocket (through the main port and the undervane port as well) to continue longer than previously, and this is believed to underlie the improvement in pump operation which the invention provides.

The invention can best be further described by detailed reference to the accompanying drawings, in which:

FIG. 1 is an axial section through one type of pump having undervane suction porting in accordance with a preferred embodiment of the invention, the pump being a balanced pump with piston actuated, double lip vanes, the section being taken through the suction ports;

FIG. 2 is a plan view of the front cheek plate, taken on the line 2--2 of FIG. 1;

FIG. 3 is a plan view of the opposite or rear cheek plate, taken on line 3--3 of FIG. 1;

FIG. 4 is a developed section through the undervane suction port, taken on line 4--4 of FIG. 2;

FIG. 5 is a fragmentary plan view of a portion of a rotor and cam ring of the pump shown in FIGS. 1-4, illustrating how the extended undervane suction port provides a longer filling period for the inner end of the vane slot;

FIG. 6 is a view similar to FIG. 5 but shows a pump having a conventionally timed undervane suction port in accordance with the prior art;

FIG. 7 is a diagrammatic illustration showing the effect of various types of suction zone filling on the maximum speed at which a pump can operate without cavitation; and

FIG. 8 is a diagrammatic view illustrating the preferred timing as embodied in a pump having single lip vanes.

The invention described and claimed herein is broadly applicable to vane pumps in which both the inner and the outer ends of the vanes are exposed to fluid at suction zone pressure as they traverse the suction zone of the pump, including pumps which have single lip vanes as well as those which have double lip vanes. The vanes may be actuated by hydraulically operated means, including pistons, or by springs. The invention is first described hereinafter in relation to a balanced pump having hydraulically operated vanes of the pressure balanced, two lip type, but it should be understood that this is by way of illustration and not limitation.

Referring to FIGS. 1-5, the pump there shown includes a housing or casing formed by a body casting 1 having a generally cylindrical internal chamber, and an end cap 2 having a recessed shoulder 3 which telescopes into one end of the body and is sealed thereto by an O-ring 4. The body and end cap are connected by bolts, not shown.

The end wall 5 of cap 2 has an opening through which the pump operating shaft 6 extends. In cap 2, shaft 6 is supported for rotation by a ball bearing 7 which is secured against axial movement in the opening. A seal 8 prevents the leakage of oil along shaft 6. The shaft extends into body 1 from end cap 2, and at its rear or inner end is carried for rotation by a needle roller bearing 9 mounted within a central bore in the body 1.

The end cap 2 supports and is sealed around a front cheek plate 10, sometimes called a port plate, which has a smooth, flat inner surface 11 that bears against a side or radial face 13 of an annular cam ring or stator 14. On its opposite side surface 17, cam ring 14 bears against a smooth flat surface 18 of a rear cheek or port plate 19, and clamps the latter against an internal shoulder (not shown in FIG. 1) in body 1. The cam ring itself, as well as the housing and cam ring together, are sometimes referred to in the art as a stator. The cam ring 14 is clamped between the two cheek plates by four bolts, not shown, which pass through bolt holes in the cam ring that are aligned with holes in cheek plates 10 and 19.

A fluid intake passageway 22 extends radially into body 1 and communicates with a pair of annular channels 23, 24 which encircle the internal cavity within the body. These annular channels 23, 24 distribute fluid from the intake passageway 22 to the suction ports in the cheek plates, to be described.

The cam ring 14 is supported radially by an annular rib 26 formed in body 1 between the annular channels 23, 24. The cam ring encircles a rotor 28 which is connected to and driven by shaft 6 through splines 29. The spline joint permits proper running alignment of the rotor between the opposed flat surfaces 11 and 18 of the front and rear cheek plates 10 and 19 respectively. Both cheek plates have central openings through which shaft 6 passes. The rotor has a plurality of radial vane slots 31 (see FIG. 5) in each of which a vane 32 is mounted.

The cam ring 14 has an inward facing cam surface 34 that is contoured to provide a balanced or symmetrical pump construction in which suction ramps 34a establishing pairs of diametrically opposite low pressure, inlet or suction zones (one of which is designated at 37 in FIG. 5) and or pressure ramp 34b establishing high pressure, outlet or exhaust zones (one of which is designated at 38 in FIG. 5). Each vane engages the cam surface 34 of cam ring 14, and the side edges of the vanes slide over the smooth flat surfaces 11 and 18 of the front and back cheek plates on opposite sides of the rotor. The pairs of adjacent vanes divide the annular pumping space between the rotor, cam surface, and cheek plates into a series of transfer pockets or intervane spaces 40.

Intake passageway 22 communicates via the annular channel 23, 24 around cam ring 14 through passages cored in the cheek plates 10 and 19, to paired main suction ports spaced 180.degree. apart in surfaces 11 and 18 thereof. Two main suction ports 43 and 44 are formed in front cheek plate 10, as seen in FIG. 2, and are fed through channel 24. Two additional main suction ports 45 and 46 are formed in rear cheek plate 19 (see FIG. 3) and are fed through channel 23. These four main suction ports are aligned with the corresponding suction zones 37 in the pumping space between the rotor periphery 36 and the cam surface 34. Increased filling area for each suction zone may be provided by a bore 33 through the cam ring, for leading fluid from inlet 22 and the outer surface of the cam ring, directly into the suction zone. Such increased main suction area filling means are known in the art.

Each main suction port 43 and 44 of the front cheek plate 10 is connected by a branch passage 47, with an undervane suction port 50 in the cheek plate; similarly, each suction port 45 and 46 in rear cheek plate 19 is connected by a passage 48 in the rear cheek plate with an undervane suction port 51. The undervane suction ports 50 and 51 are radially positioned so that the inner ends 49 of the vane slots 31 will pass across them as the rotor turns. (In FIGS. 2 and 3 the inner ends 49 of the vane slots are superimposed in phantom on the cheek plates). The opening of each undervane port 50 and 51 in its cheek plate surface 11 and 18 is sausage shaped, as viewed in plan. Each port 50 and 51 is extended in the direction of rotor rotation (indicated by arrows), by a groove or channel at 58 (see FIG. 4), and a bleed slot in the form of a V groove 59 that projects beyond the end of groove 58. Together, the portions 58 and 59 define a port extension in the direction of rotor movement. A shallow drain slot designated at 60 extends radially in the faces 11 and 18 of the respective cheek plates 10 and 19, from the under-vane ports 50 and 51, to the central shaft openings therein. The purpose of this is to provide for draining fluid from the cavity around shaft 6.

As shown in FIG. 2, the front cheek plate 10 includes two diametrically opposed pressure ports 52, 52. The pressure ports are centered substantially 90.degree. from the main suction ports 43 and 44, and they open to the pressure zones 38 between the rotor and the cam surface. The pressure ports 52, 52 are connected through internal passageways (partly shown at 54 in FIG. 1) in cheek plate 10 and end cap 2, to a fluid outlet or delivery coupling 56. In use, coupling 56 connected to an external hydraulic circuit not shown.

The cam ring may be aligned with respect to the two cheek plates by dowel pins (not shown in the drawings) projecting from its faces 13 and 17. The dowel pins are registrable in holes 62, 63 in the respective cheek plate surfaces 11 and 18, as is known in the art.

In the embodiment of FIGS. 1-5, each vane 32 has grooved outer and side edges, as designated at 67 (see FIGS. 1 and 5). The grooves 67 reflect the pressure acting on the outer end of the vane into the inner end 49 of the vane slot. Two lips are defined on the outer end of each vane, on opposite sides of grooves 67. The leading lip is designated at 64 and the trailing lip at 65. Only the front or leading lip 64 of a vane will engage the cam surface 34 in the pressure zone 38 by reason of the inward ramp on the cam surface there, while only the rear or trailing lip 65 will engage the cam surface in the suction zone 37, by reason of the outward direction of the suction ramp (see FIG. 5).

It should be pointed out that only leading lip 64 contacts the cam surface while traversing the major diameter or pumping arc 34c through the so-called transfer zone, due to a slight inward slope or ramp on this portion of the cam. This is described in U.S. Pat. No. 3,481,276 to which reference is hereby made. This slight inward ramp provides a small gap between the trailing vane lip 65 and the cam, and therefore a flow path from groove 67 to the trailing transfer pocket. This makes it possible for small flows to pass from the undervane suction ports through the passageway which leads from the inner ends 49 of the vane slots up through the grooves 67 and over the trailing lip 65 into a transfer pocket 40 as the pocket traverses the major diameter or transfer zone.

To provide an actuating force on the vanes to urge them outwardly against the cam surface, it is known to use either springs or hydraulic force. The pump illustrated uses the latter, but this is not part of the invention and is not critical. A radial bore or cylinder 69 is formed in rotor 28 (FIG. 1), extending inwardly from the inner end 49 of each vane slot 31. The bores 69 are interconnected at their inner ends through an annular chamber 71. Fluid can flow into pressure chamber 71 only through the radial bores 69. A generally cylindrical hollow piston valve element 72 slides in each radial bore 69, and includes an axial bore 73. The outer end of each piston 72 is conically tapered, and forms a valve with the inwardly facing end surface 68 of the vane. The operation of such pistons is described in the above mentioned U.S. Pat. No. 3,481,276 and in U.S. Pat. No. 3,223,044, to which reference is hereby made. Apart from the piston, vane surface 68 is exposed to the pressure of fluid in slot end 49 which together with the piston urges the vane outwardly.

Fluid from the channels 23, 24 enters the transfer pockets 40 and the inner ends 49 of the vane slots as they sequentially traverse the suction zone 37. This fluid is at low pressure, as designated by the letter S in FIG. 5. Fluid enters these spaces through the main suction ports 43-46, and through the associated undervane ports 50 and 51 as the vanes move outward of the suction ramp to expand the volume of the pocket.

FIG. 5 shows two adjacent transfer pockets 40a and 40b. The pocket 40a is bounded by a trailing vane 32a and a leading vane 32b, and is traversing the suction zone, while the preceding pocket 40b is bounded by a leading vane 32c and the vane 32b which trails it and is approaching the pressure zone. The inner ends 49 of the slots of vanes 32a, 32b are in communication with the undervane suction ports, one of which is visible at 50. The slot of vane 32c is out of communication with the undervane ports and is almost in communication with the pressure zone.

Each pocket 40 is increasing its volumetric size or capacity while either of its adjacent vanes is traversing the suction ramp. The volume increase continues until the trailing vane 32b reaches the top of the suction ramp. This approximately coincides with the cut-off of direct communication between the main suction port and the pocket ahead of that vane. Fluid can flow directly into that pocket through the main suction port until its trailing vane has passed the port. This direct path will be closed when the leading edge of the trailing vane of that pocket has passed the downstream edge 76 of the main port. (Further extension of the main suction port would provide a short circuit path for fluid from the pressure zone through the pocket directly to the suction zone, and would therefore be disastrous to operation.) The leading lip of the trailing vane of that pocket will thereafter seal the pocket from the suction port. Thus, in FIG. 5, the vane 32b will cut off communication between port 43 and pocket 40b when its leading edge 64 crosses the downstream edge 76 of the port. This occurs when the lip is just coming off the end of the suction ramp. As previously described, the trailing lip 65 will not seal against the cam surface as the vane traverses the major diameter of cam, since the cam has a slight inward ramp in this transfer zone. This sustains a small degree of fluid communication between the groove 67 in the vane crossing the transfer zone and the pocket behind it.

Fluid can flow into the inner end 49 of the slot containing vane 32b through the undervane ports 50, 51 while they are in communication with it, that is, until the slot end passes beyond the trailing or downstream edge 78 of the undervane port.

In prior art pumps, as shown in FIG. 6, the trailing edge 79 of the undervane port has conventionally been positioned or "timed" so that communication to the vane slot inner end is cut off when the vane comes off of the suction ramp of the cam surface. This has apparently been due to a belief that filling of the vane slot end should be complete at this point, since no further outward vane movement will occur beyond the suction ramp, and that there is no further increase in the space to be filled.

We have discovered that the situation is in fact considerably more complex than that, and that there are definite although subtle advantages in extending the downstream edge of the undervane suction port, to permit filling through the vane slot inner end to continue through that port past the time or rotor position at which slot cut-off has previously occurred.

We believe that in previous designs without this invention, when the pump is operated at a speed where cavitation or incomplete filling is first detected, voids or gas bubbles appear in the vane groove 67, as well as slot 49, and just behind the leading vane of the pocket. At a lower speed, these voids or bubbles are filled or collapsed by filling from the main suction port. However, as speed increases these bubbles become increasingly difficult to fill from the main port, and they remain in and behind a vane as it moves completely across the sealing zone and into the pressure port. This produces serious pump damage and limits the useful rating.

In accordance with the invention, as shown in FIGS. 3-5, the undervane suction ports 50 and 51 are extended by the groove 58 and bleed slot 59 in the direction of rotor rotation, past the conventional position shown in FIG. 6, toward but short of the point (indicated at 77 in FIG. 5 in phantom) at which they would act as a short circuit path for pressure fluid from the pressure zone designated by P.

The extension permits a longer undervane fill time continuing while the vane completely traverses the transfer zone. It is believed that, in addition to better filling of the vane slot inner end, fluid is "slung" outwardly by centrifugal force, from the slot inner end via groove 67 and into the pocket behind it through the gap between the trailing vane lip 65 and the cam surface, to insure filling of the pocket. We also believe that undervane cavitation may have been more serious than was previously realized, and that the prolonged filling time permits filling of bubbles caused by undervane cavitation, as well as in the pocket itself.

Since, as described, the voids or bubbles tend to appear within a vane and vane slot, and also follow a vane across the sealing zone at cavitating speeds, even though the main suction port has not yet been closed, it can be seen how this construction can alleviate the problem. The extended undervane suction ports can continue to supply fluid to the critical areas long after the leading portion of a pocket has passed the main suction port.

It can also be seen that pumps without this improvement would not have a continued source of fluid to supply the areas that need it as a vane sweeps across the major cam diameter.

The optimum extension of the undervane port is to a point short-- preferably just by a few degrees, typically about 2.degree.-5.degree. -- of the position at which fluid could flow from the pressure zone to the vane slot inner end and through the latter to the undervane suction port. If the undervane port extended beyond the "short circuit" point illustrated in FIG. 5 by dash-dot line 77, fluid would blow from the pressure zone past the leading edge of vane 32c through vane groove 67, the inner end slot, to the undervane port. Terminating the extension of the undervane port somewhat prior to the short circuit point is necessary to provide an effective seal at the rotor side surface. The approximate 2.degree.-5.degree. spacing mentioned above has been found entirely adequate for this purpose.

The provision of the extended undervane ports demonstrably improves pump operation at high speed. This is illustrated in FIG. 7, which compares maximum speeds of operation without cavitation for four pumps which differ in the means of filling in the suction zone. A pump having standard suction porting (as illustrated in FIG. 6) fills without cavitating up to a maximum speed of about 2,300 rpm. The provision of an increased main suction filling area (as shown at 33) raises the maximum fill speed by about 100 rpm, to about 2,400 rpm. Inclusion of extended undervane ports, in accordance with the invention, in the standard pump (without use of an increased main suction filling area), provides a maximum filling speed of about 2,550 rpm. Use of both extended undervane ports and the bores 33 raises the limit to about 2,650 rpm. Only then does the pump begin to depart from linear operation. This thus indicates the reduction in cavitation and the improvement in filling that the invention provides.

FIG. 8 shows diagrammatically a single lip vane pump having extended undervane porting. Here the slot inner end 79 of the trailing vane of a pocket 83 remains in communication with the undervane port 80 as single lip vane 90 traverses the transfer zone. The undervane port communication continues to a point just short of the position (indicated at 84 in phantom) at which pressure fluid from the pressure port 85 acting behind the leading vane 86 of the pocket, could flow into it through the pressure balancing port 87 of the vane.

In the pump illustrated in FIGS. 1-5 the benefits of the invention are not obtained if the direction of rotor movement is reversed. (If rotation were reversed, the extension of the undervane ports would project under the so-called minor diameter portion 84 of the cam surface and would not provide the benefits described at the major diameter.)

However, it is pointed out that the invention can be utilized in two-lip vane type reversible pumps, provided the pump has a slight outward ramp on the minor diameter such as is described in the copending application of Adams, Swain and Wilcox, titled "Vane Pump with Ramp on Minor Diameter," Ser. No. 246,774, filed Apr. 24, 1972, to which reference is hereby made.

Without such a ramp on the minor diameter, and with extended undervane ports extending across the minor diameter, the vanes may short circuit pressure fluid over the trailing vane lip, into the vane slot in the rotor, and on out to the suction port through the undervane port extensions. This can happen if the leading vane lip contacts an imperfect cam surface as described in the above copending application. Such a combination can cause "vane blow down," resulting in noisy and rough operation. The proper ramp on the minor cam diameter can prevent this problem.

To impart reversibility to the undervane porting, in a pump having a ramp on the minor or minimum diameter as referred to above, the port is formed so that an extension (which may be similar to that at 58 and 59) projects in both directions from the center of the port, rather than only in one direction as shown in FIG. 2. The extension in the direction of rotor movement will function as described above. The extension in the opposite direction will extend under the minor diameter; it will help provide filling at the start of the suction ramp, and the outward ramp on the minor diameter will prevent pressure from blowing over the tip of the vanes and there will be no short circuiting or harmful effect.

It should be noted that the bleed slots shown at 59 in the drawings are not essential to the invention, and they can be omitted in the extension of the undervane port. When used, they determine the effective length of the undervane port.

Claims

1. In a vane type hydraulic pressure energy translating device including a stator, a rotor rotatable with respect to said stator, said stator presenting a cam surface including a suction ramp, a pressure ramp spaced from said suction ramp, and a pumping arc between said suction ramp and said pressure ramp in the direction of rotor rotation from said suction ramp, said rotor having vane slots with vanes mounted in the respective slots, said vanes having inner ends within the vane slots and outer ends which are held in sliding engagement against the said cam surface, a space between each pair of adjacent vanes comprising a transfer pocket, said cam surface in cooperation with the rotor and a pair of cheek plates defining a pumping space, a main suction port and a pressure port in said cheek plates, and an undervane suction port communicating with the main suction port for admitting fluid to the respective vane slots below the inner ends of the vanes therein,

the improvement wherein,

said undervane suction port extends substantially beyond said suction ramp in the direction of rotor rotation to an angular position at which a vane whose slot is in communication with said undervane suction port is part way across said pumping arc, thereby providing a continuing supply of fluid from the undervane suction port to the inner ends of the respective vanes while they are traveling on said pumping arc, said undervane suction port terminating short of a position at which pressure fluid could short

2. The improvement of claim 1, wherein the undervane suction port terminates about 2 to 4 degrees short of the position at which such short

3. The improvement of claim 1, wherein said main suction port terminates at

6. The improvement of claim 1, wherein the undervane port includes a bleed

7. The improvement of claim 1, further wherein passageways are provided in either the rotor or the vanes for establishing a fluid flow path from the undervane suction port into a transfer pocket while the leading vane of said pocket is on said pumping arc and said undervane suction port is in

8. The improvement of claim 7 wherein said passageways include grooves in the vanes connecting the inner ends of the vanes with the outer ends

9. The improvement of claim 1 further wherein said vanes are double lip vanes having a leading lip and a trailing lip, said pumping arc has an inward slope so that the trailing lip of each vane is spaced from the pumping arc as the vane moves over said arc with the leading lip in engagement therewith,

and passageways comprising edge grooves in each vane provide fluid communication from the inner end of the vane in the vane slot to the outer end of the vane, the spacing of the trailing lip from the pumping arc thereby permitting flow across the trailing lip of the vane to the

10. In a vane type hydraulic pressure energy translating device including a stator, a rotor rotatable with respect to said stator, one of said stator or said rotor presenting a cam surface including a suction ramp, a pressure ramp spaced from said suction ramp, and a pumping arc between said suction ramp and said pressure ramp in the direction of rotor rotation from said suction ramp, the other of said stator and said rotor having vane slots with vanes mounted in the respective slots, said vanes having inner ends within the vane slots and outer ends which are held in sliding engagement against the said cam surface, a space between each pair of adjacent vanes comprising a fluid pocket, said cam surface in cooperation with the rotor and a pair of cheek plates defining a pumping space, a main suction port and a pressure port in said cheek plates, said main suction port communicating with each fluid pocket sequentially to admit fluid thereinto and an undervane suction port communicating with the main suction port for admitting fluid to the respective vane slots below the inner ends of the vanes therein,

the improvement wherein,

said undervane suction port extends substantially beyond said suction ramp in the direction of rotor rotation to an angular position at which a vane whose slot is in communication with said undervane suction port is a substantial distance across said pumping arc, thereby providing continuing suction port communication to the inner ends of the respective vanes while they are traveling on said pumping arc, said undervane suction port terminating short of a position at which pressure fluid could short

11. In a method of operating a vane pump wherein vanes move sequentially from a suction ramp across a pumping arc to a pressure ramp and fluid is admitted to a transfer pocket between vanes through a main suction port in a suction zone, the pocket then moves past the main suction port, and fluid in the pocket is expelled from the pocket to a pressure zone, and further wherein an inwardly facing surface of each vane is connected to fluid at suction zone pressure while said surface is passing through the suction zone, the improved method of operation comprising,

timing the cutoff of said connection of the said inwardly facing surface of each vane to fluid at suction zone pressure to occur when that vane has traveled past the suction ramp and is on the span of said pumping arc and just before said surface would come into communication with the pressure zone of the pump.