US3669577A - Variable high speed gear pump - Google Patents

Abstract

A GEAR TYPE FLUID PUMP HAVING PUMPING GEARS PROVIDED WITH BOOSTING CHANNELS AND COOPERATING HEAD CHANNELS WHICH SUPPLY FLUID FROM THE PRESSURE OF THE PUMP VIA THE BOOSTING CHANNELS TO THE MATING POCKETS OF THE ASSOCIATED PUMPING GEAR TO THEREBY IMPROVE THE EFFICIENTY OF THE PUMP. THE OIL ADMITTED INTO AND CARRIED IN THE BOOSTING CHANNELS IS SLUNG RADIALLY OUTWARDLY THEREFROM BY CENTRIFUGAL FORCE INTO THE GEAR POCKETS OF THE MATING GEAR TO THEREBY REDUCE THE TENDENCY OF THE FLUID BEING PUMPED TO BE VAPORIZED IN THESE POCKETS AS THE GEARS DISENGAGE ON THE INLET SIDE OF THE PUMP, THUS REDUCING GASSIFICATION IN THE PUMP AND WEAR ON THE GEAR PUMPING TEETH.

Description

June 1972 s. G. SWANSON 3,669,577-

VARIABLE HIGH SPEED GEAR PUMP Filed Dec. 31. 1970 5 Sheets-Sheet} June 13, 1972 5. sw s 3,669,577

VARIABLE HIGH SPEED GEAR PUMP Filed Dec. 31. 1970 5 Sheets-Sheet 2 June 13, 1972 s. s. SWANSON 3,669,577

VARIABLE HIGH SPEED GEAR PUMP Filed Dec. 31, 1970 5 Sheets-Sheet 5 June 13, 1972 s. G. swANsoN I 77 I VARIABLE HIGH SPEED GEAR PUMP Filed Dec. 51, 1970 5 Sheets-Sheet 4 7////\ -IIHI June 13, 1972 s. G. SWANSON VARIABLE HIGH SPEED GEAR PUMP 5 Sheets-Sheet 5 Filed Dec. 31. 1970 United States Patent 3,669,577 VARIABLE HIGH SPEED GEAR PUMP Swan G. Swanson, Rte. 1, Rock, Mich. 49880 Filed Dec. 31, 1970, Ser. No. 103,263 Claims priority, applicatit/i li0 Sweden, Jan. 2, 1970,

Int. Cl. F01c 1/18, 21/16; F04c 15/04 US. Cl. 418-21 9 Claims ABSTRACT OF THE DISCLOSURE A gear type fluid pump having pumping gears provided with boosting channels and cooperating head channels which supply fluid from the pressure side of the pump via the boosting channels to the mating pockets of the associated pumping gear to thereby improve the efliciency of the pump. The oil admitted into and carried in the boosting channels is slung radially outwardly therefrom by centrifugal force into the gear pockets of the mating gear to thereby reduce the tendency of the fluid being pumped to be vaporized in these pockets as the gears disengage on the inlet side of the pump, thus reducing gassification in the pump and wear on the gear pumping teeth.

This invention relates to improvements in gear type pumps of the type used to deliver fluid under pressure to various types of fluid driven motors or the like.

In known types of gear pumps there is created, mainly at high speeds, vacuum pockets between the teeth as the gears disengage at the inlet side of the pump, and these vacuum pockets may greatly reduce the capacity of the pump and such pockets also can cause cavitation phenomena which may damage the pumping gears. Accordingly it is an object of this invention to eliminate the aforementioned disadvantages by providing a gear type pump with improved capacity over a greater speed range, preferably in a variable capacity type of pump wherein this object is obtained while retaining the capability of varying the volume of the pump within this range.

Another object of this invention is to provide a source of centrifugally pressurized fluid to prevent gas or vacuum pocket formation between the teeth of the pumping gears as they disengage, thereby aflording greater efliciency in a higher speed range than a gear pump in which vacuum alone is relied upon as the prime source to supply fluid to the demeshing teeth.

In accordance with the present invention, the improvement in pump capacity is obtained by taking advantage of the centrifugal force created by the rotation of the pumping gears, to sling the fluid present in booster channels provided in the pumping gears, which channels are previously supplied with fluid from the pumps pressure head channels, into the gear pockets of the mating gear as the gears disengage on the inlet side of the pump. The variation of the volumetric pumping capacity may be achieved through structure which changes the degree of pumping gear interengagement, so arranged that on each of the two pump shafts is mounted one of two pumping gears. One gear is fast on its shaft and coacts with a movable jawclutch or gear fitting claw coupling and a stationary abutment member provided with head channels. The other gear is movable on its shaft and coacts with an axially stationary claw coupling and a movable abutment member on the same shaft. These axially movable parts are coupled to a control piston mounted in the pump housing which with the help of a control device of combined manual and hydraulic type is movable to change the pumping capacity of the pump by changing the extent of axially overlapped engagement between the pumping gears. The boosting slots or channels are ice preferably formed one in each tooth of each pumping gear, each slot having an inlet Opening in one of the annular side faces of the gear at one axial end of the gear. Each slot terminates in an outlet in the outermost face of the gear tooth disposed radially outwardly of its inlet. The slots cooperate with sealing members so as to be effectively sealed closed as the teeth pass from the inlet to the outlet chamber in carrying out their main pumping function. As the teeth come into mesh upon their return travel from the outlet to the inlet chamber, the slots are closed at their side inlets by an associated pumping gear abutment member, and the outlet of each slot registers with the mating pocket of the opposed pumping gear. At the full mesh position, the mesh of the flanking teeth of the opposed gear with the interposed tooth effectively seals the slot outlet from the outlet (high pressure) chamber of the pump, but the outlet remains open to the mating pocket between these flanking teeth to supply them with a pocket of fluid as the teeth begin to demesh.

Other objects as well as features and advantages of the invention will become apparent and are explained in more detail in the following description taken in conjunction with the accompanying drawings and in which:

FIG. 1 is a longitudinal vertical sectional view of the pump mechanism as taken on line 1--1 of FIG. 2, and illustrates the pump in minimum volume position.

FIG. 2 is a longitudinal horizontal sectional view taken as indicated on the line 2-2 of FIG. 1, the control mechanism being shown in positions E and F, see FIG. 9.

FIG. 3 is a view similar to FIG. 1, but showing the pump mechanism in maximum volume position as taken on line 3-3 of FIG. 4.

FIG. 4 is a view similar to FIG. 2, but showing the pump mechanism in maximum volume position as in FIG. 3, the control mechanism being in positions A and B, see FIG. 9.

FIG. 5 is a transverse vertical sectional view through the inlet and outlet chambers, showing the arrangement between the driving pumping gear and the associated intercepting partitions or locks dividing the compartments, the view being taken on the line 55 of FIGS. 1 and 2.

FIG. 6 is a view similar to FIG. 5, but taken in the reverse direction on the line 6--6 of FIGS. 3 and 4, show ing the arrangement between the driven pumping gear and the associated intercepting partition or locks dividing the inlet and outlet compartments.

FIG. 7 is a fragmentary horizontal sectional view taken on the lines 2-2 of FIG. 1 and 44 of FIG. 3, showing the control mechanism in positions C and F.

FIG. 8 is a view similar to FIG. 7, but illustrating a solid spacer sleeve substituted for the spring shown in FIG. 7, with the control mechanism shown in positions C and D.

FIG. 9 is a vertical end view showing 'various settings of the control levers, the view being taken on the line 9-9' of FIG. 10.

FIG. 10 is a side elevational view of the pump as a whole.

FIG. 11 is also a side elevational view but with the housing and end plates cut open.

The improved pump mechanism, as herein shown, may be conveniently attached to, and driven by, any suitable motor, and hydraulic as well as mechanical controls may be linked to any other control means required to control the pump output.

Referring now in detail to that embodiment of the in- 'vention illustrated by way of example in the drawings,

10 indicates as a whole the main housing of the mechanism which is cylindrical and open at both ends. In one end of housing 10, hereinafter referred to as the forward 3 part of the housing, is a cylindrical bore 11 (FIGS. 2, 4 and 11) terminating at a bulkhead 12, and in the opposite end of housing 10, hereinafter referred to as the aft part of the housing, is another cylindrical bore 13 terminating at a bulkhead 14 which coacts with housing and bulkhead 12 to provide a central chamber 15 within housing 10. Housing 10 is also provided at one side of its axis with an inlet passage 16 and at the opposite side is an outlet passage 17, both of which communicate with chamber 15 (FIGS. 2, 4, 5 and 6).

By conventional means such as screws 18 shown in FIG. 9, the aft cylindrical bore 13 is securely enclosed by an end plate 19 in which bearing elements 20 and 21 are mounted. As illustrated in FIGS. 1, 3 and 11 the cylindrical bore 11 in the forward end of housing 10 is similarly enclosed by an end plate 22 in which a seal 23 and a bearing element 24 are mounted. Plate 22 is secured to housing 10 by screws in a manner similar to end plate 19, but plate 22 is square in outline to provide outwardly projecting corners provided with mounting holes 25 (FIG. 9). In the cylindrical bore 11, securely mounted to the base of bulkhead 12, is a disk 26 (FIGS. 1-4 andll) in which bearing elements 27 and 28 (FIGS. 1 and 3) are mounted and conventionally held in place by a retainer 29. Disk 26, at its upper side and paralleling the housing axis, is provided with a hollow cylindrical abutment 30 (FIGS. 1, 3 and 11). Abutment 30 has a concave recess 31 formed in its outer periphery on the lower side thereof (FIGS.

1 and '6), the axis of recess 31 also being parallel with that of housing 10. Abutment 30 projects through a bore 32 (FIG. 6) in bulkhead 12,. and its aft annular surface is cut away on each side to form booster head channels 33 and 34 (FIGS. 6 and 11) which coact to form a central partition made up of intercepting locks 35 and 36 which are disposed within chamber 15.

In the cylindrical bore 13 is a longitudinally (axially of housing 10) movable piston 37 (FIGS. 2, 4, 7, 8 and 11) in which bearing elements 46 and 47 are mounted (FIGS. 1 and 3). Piston 37, at the lower side of its axis and parallel with said axis, is provided with a hollow cylindrical element 38 (FIGS. 3 and 11). Abutment 38 is provided with a concave recess 39 (FIG. 5) in its outer periphery and on its upper side which extends axially parallel with piston 37. Abutment 38 is thus identical to abutment 30 except for being arranged below the housing axis in an end-for-end position, as best seen in FIG. 11. Abutment 38 projects through a bore 40 (FIG. 5) in bulkhead 14, and at its forward end has booster head channels 41 and 42 which coact to define a central median partition made up of intercepting locks 43 and 44, which are disposed within chamber 15. A retainer disk 45 (FIGS. 3, 4 and 11) conventionally mounted by screws (not shown) to piston 37 secures bearing elements 46 and 47 as well as piston seal 48 and shaft seals 49 and 50.

The recess 39 in abutment 38 coacts to complete the periphery of a bore 40a (FIG. 5) which is axially overlapped with bore 40 in bulkhead 14. Bore 40a receives a jawclutch 51 (FIGS. 1-4 and 11) provided on its forward end with extra deep axially projecting jaws 51a arranged in a circular row. The aft end of jawclutch 51 is provided with an axially bored sleeve or shaft 51b which is conventionally secured for thrust as well as radial loading by bearing element 46 in piston 37. Shaft 51b extends afterward beyond bearing element 46 to provide support for other means explained hereinafter.

As best seen in FIGS. 3 and 11, the forward end surface of each of the jaws 51a is disposed flush with the forward annular surface of abutment 38, and jaws 51a are complemental in contour to the teeth 52 of a pumping gear 52 (FIG. 5). Jaws 51a are thus closely fitted to teeth 52' to seal off passage of fluid between jaws 51a and teeth 52' but are longitudinally (axially) slidable relative to teeth 52'. Pumping gear 52 and jawclutch 51 have the same outside diameters and are journalled together in constant mesh in bore 40a.

Pumping gear 52 is mostly disposed within chamber 15 with its forward annular surface slidably abutting the aft end surface of the median partition on the aft end of abutment 30 (defined by diametrically opposite intercepting locks 35 and 36 (FIG. 6) Gear 52 on its aft end is provided with an alignment shaft 52a which projects through the axial bore of shaft 51b and is laterally supported by bearing element 20 in end plate 19 to prevent lateral, but not'longitudinal (axial), movement of jawclutch 51. Shaft 52a, being axially offset from the axis of piston 37, prevents piston 37 from rotating in its cylinder 13. Pumping gear 52 also has a main shaft 52b projecting axially from its forward end through the hollow of abutment 30 which is journalled in bearing element 27 in disk 26 where it is conventionally supported for thrust as well as radial loading. Main shaft 52b extends through seal 23and terminates in a splined portion 520 outside base plate 22.

As best seen in FIG. 6, recess 31in the outer periphery of abutment 30 coacts to complete the periphery of an overlapping bore 32a in bulkhead 12, and bore 32a receives a jawclutch 53 (FIGS. 1, 3 and 11) provided on its aft end with extra deep axially projecting jaws 53a, similar to jaws 51a. Jawclutch 53 has projecting from its forward end an axially bored sleeve or shaft 5312 which is conventionally secured for thrust as well as radial loading by bearing element 28 in disk 26.

The aft end surfaces of jaws 53a are disposed flush with the aft annular surface of abutment 30 (FIGS. 1 and 3), and jaws 53a are complemental to the teeth 54 of a pumping gear 54 and are closely fitted therewith to seal off passage of fluid between jaws 53a and teeth 54' while allowing longitudinal sliding engagement of gear 54 in jawclutch 53. Pumping gear 54 and jawclutch 53, like gear 52 and jawclutch 51, have the same outside diameters and are journalled together in constant mesh in bore 32a.

On its aft end pumping gear 54 is provided with an axially bored shaft 54a (FIG. 3) which is conventionally secured for thrust as well as radial loading by bearing element 47 in piston 37. Like shaft 51b, and for the same reason as set forth hereinafter, shaft 54a is also extended beyond its bearing element.

Pumping gear '54, being partly disposed within chamber 15, is mounted with its aft annular surface slidably abutting the adjacent median partition surface of abutment 38, i.e. intercepting locks 43 and 44 and the contiguous hub portion 38'. 1

An alignment shaft 55 (FIG. 1) is arranged in the axial bores of shafts 53b and 54a, its forward end being laterally supported by bearing element 24 and its aft end by bearing element 21. Shaft 55 coacts with alignment shaft 52b to prevent piston 37 from rotating in its cylinder 13.

Thus it will now be understood that bulkhead 12 together with abutment 30 and jawclutch 53 make up the axially stationary front wall of pump chamber 15, and that bulkhead 14 together with abutment 38 and jawclutch 51 provide chamber 15 with a rear wall, parts 38 and 51 of this rear wall being axially movable into chamber 15.

In accordance with one feature of the present invention, as best shown in FIGS. 1-5, the forward end of each tooth 52 of pumping gear 52 is provided with a radially arranged booster channel 52d. Channels 52d are normally open at their forward ends to head channels 33 and 34, but are at these ends closed as they register with and sweep across intercepting lock 35. Each booster channel 52d is also open at its radially outer end through a major part of the outer peripheral face of the associated tooth 52, and hence channels 52d are also normally open via their outer ends to chamber 15. However, the outer end of each channel 52d is closed as they journal through a concave recess 39a (FIGS. 5 and 11) in the upper inner periphery of chamber 15.

Thus, jaws 51a, intercepting lock 35 and recess 39a coact to form a look through which only fluid deposited in the booster channels 52d and in between the teeth 52' of pumping gear 52 may pass from inlet compartment 15a to outlet compartment 15b.

As can be seen in this arrangement, the fluid deposited between gear teeth 52' is only trapped between lock 35 and jaws 51a for as short an angular movement of the pump as may be practical to allow maximum uninterrupted longitudinal movement for the volume controlling piston 37.

In a similar manner booster channels 54b (FIGS. 6 and 11) are provided in the aft end of pumping gear 54 which are identical to booster channels 52d in pumping gear 52, and their cooperation with intercepting lock 44 and recess 31a (FIGS. 5, 6 and 11) is similar to the coaction of channels 52d at intercepting lock 35, except that this action occurs in the lower part of chamber 15 and the structure is in an end-for-end position.

Because of the pecularity of the sectional cut illustrated in FIG. 6, only part of the booster channels 54b are shown, but as illustrated in FIGS. 3 and 4 the pumping gears 52 and 54 are in mesh, and at such time the operation of the booster channels is as follows.

As the pumping gears rotate in direction indicated by the arrows in FIGS. and 6, booster channels 52d and 54b draw fluid axially from the high pressure (outlet side) head channels 34 and 42, and in response to rotation of gears 52 and 54 a centrifugal (radially outward) circulation is imparted to the fluid present in the booster channels. This circulation is blocked and then reversed as channels 520? and 54b enter the dedendum portion of the opposing gear in response to the progressive meshing of teeth 52 and 54', and then axial escape is cut off upon intercepting locks 36 and 43, whereupon the fluid in channels 52d and 54b becomes trapped and stagnant as the channels reach high point at said locks. At this point a centrifugal pressure, depending on pump speed, is built up in the booster channels 52d and 54b and as they proceed to where they come into registry with head channels 33 or 41 respectively, the fluid is centrifugally impelled into the dedendum portion of the opposing gear. Hence the intertooth vacuum condition caused by demeshing of the gear pumping teeth 52' and 54 is relieved by this source of pressure fluid, which in turn greatly reduces vaporization of the liquid being pumped, with a consequent improvement in the efficiency of the pump.

In minimum volume setting as illustrated in FIGS. 1 and 2, all fluid passages are closed between inlet compartment 15a and outlet compartment 15b. In such setting, the pumping gears 52 and 54 are out of mesh. For this reason this pump is provided with a synchronizing unit comprising spur gears 56 and 57. Gear 56 is conventionally secured on shaft sleeve 51b for rotation therewith and is driven through jawclutch 51 which in turn is in constant mesh with gear 52. Gear 57, which is in constant mesh with gear 56, is conventionally secured on shaft sleeve 54a for rotation therewith, sleeve 54 directly driving gear 54 which is in constant mesh with jawclutch 53. Gears 56 and 57, in addition to maintaining synchronization of pumping gears 52 and 54, also reduce wearing of the pumping gears.

The mechanism described previously herein comprises the elements capable of achieving the prime objects of this invention, but, as some means by which the volume of this type of variable volume gear pump may be controlled is also a practical necessity, the following is a description of one kind of such control means.

Forwardly, at the upper side of cylindrical bore 11 (FIGS. 1 and 3), housing is provided with a breather passage 58 which is open to atmospheric pressure, and aft, on the same side, the cylindrical bore 13 is provided with a pressure control passage 59.

Mounted in the rear end plate 19, as illustrated in FIGS. 2, 4, 7 and 8, are mechanical control shafts 60 and 61 having securely press-fitted thereon flanges 62 and 63 respectively. Shafts 60 and 61 are held in axial position by retainer rings 64 and 65, secured to plate 19,

but may be rotationally oscillated by control levers 66 and 67 respectively fixed to the outwardly protruding ends of shafts 60 and 61.

Piston 37 in the rear end thereof is provided with a pair of cylindrical hollows 6'8 and 69 to provide clearance for the heads of the control shafts 60 and 61 respectively. Retainer disk 45 is provided with internally threaded bores 70 and 71 which respectively are in axial alignment with blind bores 68 and 69 in a right hand threaded worm wheel 72, and in bore 71, which is left hand threaded, is a left hand threaded worm Wheel 73. Worm wheels 72 and 73 are conventionally keyed to oscillate with their respective shafts 60* and 61, but are arranged to axially float on shafts 60 and 61 with retainer disk 45.

For applications where delayed action is favorable when increasing the pumping volume, a spring 74 '(FIG. 7) is arranged between the floating worm wheel 72 and the forward head of increase control shaft 60. Alternatively, for positive increase, a spacer sleeve 75 is substituted for spring 74 as shown in FIG. '8. In the minimum volume setting illustrated in FIG. 2 the increase control lever 66 is set on the position indicated by letter E in FIG. 9 or minimum output, but this is not blocking the pump from increasing volume. However, because volume decrease lever 67 is set on F, worm wheel 73 abuts and is blocked by the forward sleeve extension 63' of flange 63, thereby preventing the pump from increasing volume through the hydraulic system.

FIGS. 3 and 4 show the pump in maximum output position. The increase lever 66 is now set on A (FIG. 9) and decrease lever 67 is set on B. This moves piston 37 to its extreme rearward position shown in FIGS. 3 and 4. When spring 74 is provided, and at such setting, the pump may be urged to reduce output as by increasing the pressure in compartment 59b via suitable hydraulic connections such as a line (not shown) connected between the output line and port 59, thereby forcing disk 45 forward and thus compressing spring 74. Spring 74 then urges disk 45 (and piston 37) rearward to return the pump to maximum output when pressure in compartment 5% is reduced.

With the embodiment using spring 74 and with the controls at a setting as illustrated in FIG. 7, i.e., with the increase lever 66 on C and the decrease lever 67 on B, the pump may be controlled entirely by a hydraulic system due to spacing between worm wheel 73 and extension 63'. However, at a control setting as shown in FIGS. 8 and 9, with the embodiment having a spacer sleeve 75 substituted for spring 74, the pump is held in a positive medium output position.

From the foregoing description it will now be apparent that the present invention may be applied to various types of gear pumps, fixed or variable volume, by providing in the pumping gear teeth fluid supply booster channels or slots 52d and 54b which have side access or communication via channels 34 and 42 with the high pressure output chamber 15b. Due to the radial outlets of such booster slots, the fluid carried therein in the pumping teeth of one pumping gear thus can serve as a supply of fluid to the dedendum portion between the associated teeth of the other pumping gear. The booster slots thus function to put the fluid, which is in the immediate state of being sucked into the dedendum portion of the pumping gears, under centrifugal pressure to facilitate, or boost, the intake of said fluid. This in turn reduces or eliminates vaporization of the liquid which otherwise tends to occur as the meshed pumping teeth begin to demesh or separate just after they have passed their full meshed condition and are entering chamber 15a.

It will also be understood, as best seen in FIGS. 1 and 3, that suitable venting is provided to permit the axial volume varying movement of gear 54 and its associated abutment follower 38, as well as to accommodate corresponding axial movement of jaw clutch 51. Such venting includes axial passgaes in gear 54 and in jaw clutch 53 and the space between the races of bearing28 communicating with the relief chamber at the forward end of housing 10 and hence relief port 58, and similar axial passages in gear 52, abutment member 30 and bearing 27 also leading to the relief chamber and port 58.

I claim:

1. In a gear type fluid pump having a pair of intermeshable pumping gears, the improvement comprising boosting channels in the pumping teeth of said gears, each of said boosting channels having communication via an inlet in the side of its associated tooth with fluid in the high pressure side of the pump when the tooth is transversing the same, each said boosting channel also having an outlet in the apex of the associated tooth disposed radially outwardly of said inlet, whereby in response to rotation of the pumping gears fluid is admitted to each boosting channel via said inlet thereof from the high pressure side of the pump and centrifugal force is developed to sling such fluid admitted into such boosting channel radially outwardly into the associated gear pocket of the mating gear as the gears disengage in their travel toward the inlet side of the pump.

2. A gear type fluid pump as set forth in claim 1, wherein said boosting channels are provided one in each pumping gear tooth, each said channel comprising a radial slot opening in one axial end face of the gear and terminating at an outlet in the outer periphery of the tooth.

3. A gear type fluid pump as set forth in claim 2 wherein each said channel has a length axially of the gear less than that of the gear tooth.

4. A gear type fluid pump as set forth in claim 3 wherein each said channel has a width circumferentially of the gear less than that of the associated tooth.

5. A gear type fluid pump as set forth in claim 4 wherein each said channel has a radial depth which decreases from a maximum at said opening of the boosting channel.

6. A gear type fluid pump as set forth in claim 5 wherein each said channel has a curved root surface conforming to the contour of a milling cutter.

7. A gear type fluid pump as set forth in claim 1, wherein the pumping volume is variable, further including first and'second shafts each carrying one of said pumping gears and a coacting gear-fitting claw coupling and an abutment member provided with a head channel to communicate said booster channels with an outlet chamber of the high pressure side of the pump, one of said gears being fast on said first shaft, and the other of said gears and its associated abutment member being axially movable on said second shaft, said claw coupling associated with said one gear also being axially movable with said other gear, and control means manipulative for changing the volumetric output of the pump by causing axial movement of said other gear, its associated abutment member and the abutment member associated with said one gear to thereby change the extent of axially overlapping engagement between said pumping gears.

8. A gear type fluid pump as set forth in claim 7, wherein said boosting channels are provided one in each pumping gear tooth, each said channel comprising a radial slot opening in one axial end face of the gear and terminating at an outlet in the radially outermost face of the tooth, each said slot having a length axially of the gear less than that of the gear tooth, a width circumferentially of the gear less than that of said face of the tooth and a radial depth which decreases from a maximum at said opening of the boosting channel.

9. A gear type fluid pump as set forth in claim 8, wherein said control means includes a movable piston coupled to said axially movable gear, abutment member and claw coupling, and wherein said pump has a housing with fluid chambers on each side of said movable piston adapted for connection to means for producing pressure differences to thereby move said piston, said control means further including two control shafts rotatably mounted in said piston and adjacent housing end and extending parallel with said first and second shafts, each of said control shafts having an axially movable coupling means keyed thereon operable in response to rotation of the associated control shaft to move said piston, and means on said control shafts for limiting axial movement of said coupling means whereby the volumetric pumping capacity of the pump is controlled by setting of the control shafts to either positively mechanically position the piston or to allow movement of the piston in respons to said pressure differences.

References Cited UNITED STATES PATENTS 1,659,771 2/1928 Fox 418- 1,742,215 1/1930 Pigott 418-21 2,236,980 4/1941 Ungar 418-190 3,431,862 3/1969 Bottoms 418-206 3,588,295 6/1971 Burk 418-21 CARLTON R. CROYLE, Primary Examiner I. J. VRABLIK, Assistant Examiner US. 01, X.R. 418-180, 206

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