Variable displacement balanced vane pump

A variable displacement balanced vane pump includes an alternate flow passage for fluid being compressed in an intervane chamber whereby the excess portion of the fluid is by-passed from the pump discharge zone to the pump inlet zone without appreciably increasing the pressure of the excess fluid portion to minimize the required pump input energy.

FIELD OF THE INVENTION 
This invention relates to fluid pumps and particularly to variable 
displacement balanced vane pumps. More particularly, this invention 
relates to pumps of the type described having an alternate fluid flow 
passage from the pump discharge zone to the pump inlet zone which 
minimizes the pump input energy. 
DESCRIPTION OF THE PRIOR ART 
High pressure vane pumps for aircraft applications and the like must be 
designed with size and weight requirements in mind. This is accomplished 
by providing a "balanced rotor" arrangement. That is to say, bearing loads 
are eliminated by an even number of lobes (usually two) on a cam ring so 
that any diametral line through the axis of the pump bisects the pump into 
two "mirror image" halves. This balances the radial forces on the pump 
rotor journal bearings, with the sum of such forces thereupon being zero. 
Most variable displacement vane pumps known in the art utilize a single 
lobe cam ring design. Usually a circular transfer cylinder which provides 
zero fluid flow when concentric with the pump rotor and maximum fluid flow 
when displaced to its position of maximum eccentricity is employed. Under 
these conditions, massive bearings are required to sustain the rotor 
reaction forces under high discharge pressure conditions as are likely to 
occur. 
Heretofore, efforts to develop a variable displacement balanced vane pump 
have featured a deformable cam ring. The cam ring is made flexible by 
using a laminated construction, and is distorted from a perfectly circular 
form to an elliptical form, with the amount of distortion governing the 
pump's displacement. An arrangement of this type has obvious disadvantages 
which have not been satisfactorily solved. 
A variable fluid timing arrangement has been used wherein the reaction 
forces on the cam ring require an excessively large actuator and the 
internal leakage is necessarily high as port plates must be free to move 
relative to the cam ring, hence necessitating a discrete clearance between 
the port plates and the cam ring. 
Other designs for variable displacement balanced vane pumps have been 
attempted but none have been satisfactory so as to provide a variable 
displacement balanced vane pump which is in common use. 
SUMMARY OF THE INVENTION 
This invention contemplates a variable displacement balanced vane pump 
including a rotor which rotates in a cam ring and a plurality of radially 
extending vanes. Check valves are built into the rotor between the vanes 
to permit fluid flow radially inward to an annular discharge port formed 
in port plates. In one embodiment of the invention, an alternate flow 
passage for fluid compressed in an inter-vane chamber is provided by holes 
extending through the cam ring which open to by-pass ports carried by a 
rotatable control ring in close diametrical fit with the outside diameter 
of the cam ring. In another embodiment of the invention the holes extend 
through the port plates. Rotation of the control ring in one or the 
opposite directions opens or closes the holes to increase or decrease 
fluid flow, as the case may be, through the check valves to the discharge 
port. Means are provided for preventing fluid leakage through the holes 
past the vane tips and for preventing rapid wear of said tips.

DESCRIPTION OF THE INVENTION 
With reference to FIGS. 1 and 2, the variable displacement balanced vane 
pump herein disclosed includes a rotor 2 which is arranged for rotation in 
a cam ring 4 having two diametrically opposed lobes 6 and 8. A plurality 
of slots 3 are equidistantly disposed around rotor 2. Each slot 3 has 
disposed therein a vane 10 including a plurality of integral vane numbers, 
shown for illustration purposes as two in number and carrying the 
designation 10A and 10B. 
Port plates 12 and 14 (FIG. 2) have formed therein diametrically opposed 
inlet ports 16 and 18 and an annular outlet or discharge port 20 as shown 
in FIG. 1. As will be understood by those skilled in the art, vanes 10 and 
port plates 12 and 14 are held firmly against cam ring 2 by the pump 
discharge pressure acting on associated spring biasing means (not shown). 
A plurality of check valves such as that designated by the numer 22 (FIG. 
1), and which may be conventional ball type check valves, are built in 
rotor 2 between adjacent vanes 10 and permit flow radially inward to 
annular discharge port 20. 
Cam ring 4 carries a plurality of radially extending through holes 24, 
which are in communication with an intervane chamber 26. A control ring 28 
is in close diametrical fit with the outer circumference 13 of cam ring 4 
and includes diametrically opposed by-pass ports 30, one of which is shown 
in FIGS. 1 and 2. 
Flow of fluid is normally in through inlet ports 16 and 18 and out via 
check valves 22 through discharge port 20. An alternate flow passage for 
fluid being compressed in intervane chamber 26 is via holes 24 and by-pass 
ports 30 as shown by the arrows in FIG. 2. Holes 24 are partially or fully 
blocked for controlling flow of fluid therethrough to by-pass ports 30 by 
the counterclockwise or clockwise rotation of control ring 28. 
Thus, if control ring 28 is rotated counterclockwise (FIG. 1), all of the 
holes 24 may be blocked and flow to check valves 22 and therethrough to 
discharge port 20 i.e., from the pump inlet zone to the pump discharge 
zone, will be at a maximum. If control ring 28 is rotated clockwise, holes 
24 are progressively opened to create the aforenoted alternate fluid flow 
passage. The creation of the alternate fluid flow passage, reduces 
discharge fluid flow as will now be understood. 
In this connection it is noted that control ring 28 is rotated by a 
conventional type servo device 32 coupled by suitable mechanical means 34 
to a node 36 integral with control ring 28. 
Although only one side of the pump arrangement has been illustrated and 
described, the diametrically opposite side is identical to preserve the 
aforenoted balanced conditions. It will be understood that discharge port 
20 is arranged to supply discharge pressure to the underside of vanes 10 
as is necessary to maintain the vanes in contact with cam ring 4. 
Another embodiment of the invention for providing the aforenoted alternate 
fluid flow passage is illustrated in FIG. 6. Thus, with port plates 12 and 
14, cam ring 4 and control ring 28 arranged as shown, the port plates 
carry holes 25 having axially extending portions 25A in communication with 
intervane space 26 (FIG. 1) and radially extending portions 25B. Control 
ring 28 carries a plurality of by-pass ports shown as two in number and 
designated as 30A and 30B. Rotation of control ring 28 as aforenoted 
brings the radially extending portions of holes 25 into or out of 
communication with by-pass ports 30A, 30B to increase or decrease 
discharge fluid flow through valves 22 as heretofore described. Fluid flow 
is as shown by the arrows. The diametrical opposite side of the pump 
arrangement may be identical to preserve the desired balanced conditions 
as aforenoted. The arrangement of FIG. 6 is advantageous in that more than 
one by-pass port is provided in the same control ring area as will now be 
understood. 
As best shown in FIG. 3, vanes 10 including integral vane members 10A and 
10B extend to the inner circumference 11 of the cam ring 4 as heretofore 
noted with reference to FIG. 1. It will be seen that the circumferential 
distance (A) between the vane/cam ring contact lines of vane members 10A, 
10B is greater than the diameter (B) of holes 24. This insures that a line 
of contact, forming a seal, is at all times interposed between discharge 
and inlet pressure zones and prevents internal pump leakage. Thus, 
integral vane members 10A and 10B insure that there will always be a vane 
surface contacting the cam ring and therefore providing a seal from high 
and low pressures as are likely to occur. In this connection it is noted 
that although two integral vane members 10A and 10B have been shown and 
described for illustration purposes, the number of such members required 
will depend on the size of holes 24. 
With particular reference to the embodiment of the invention shown in FIGS. 
4 and 5, it will be understood that for pump vanes 10 to function properly 
at the pressures involved, a film of fluid must be maintained at the vane 
tip to prevent metal to metal contact with the vane tip and inner 
circumference 11 of cam ring 4 which is likely to result in vane wear. It 
has been found that the arrangement of axial holes 24 in cam ring 4 (FIGS. 
1 and 2) contributes to the destruction of this film and causes rapid wear 
of the vane tips. 
In order to accommodate this situation, port plates 12 and 14 are modified 
to carry axial holes 34 which are in communication with radial slots 37 
carried by cam ring 4, which are in turn in communication with by-pass 
port 30, in the zone in which the fluid is being compressed, whereby the 
required fluid film is maintained. A pair of axial holes 34 is best shown 
in FIG. 5 with the ends of said holes being shown in FIG. 4. Fluid flow is 
as shown by the arrows. In this modified form, vane members 10A, 10B are 
not required and a single vane per rotor slot 3 will suffice for the 
purposes of the invention if the thickness of the vane is greater than the 
diameter of hole 34 as illustrated in FIG. 4. 
It will now be seen from the aforenoted description of the invention with 
reference to FIGS. 1-6 that a variable displacement balanced vane pump has 
been provided which includes an alternate flow passage for fluid being 
compressed in an intervane chamber, whereby the excess portion of the 
fluid is by-passed from the pump discharge zone to the pump inlet zone 
without appreciably increasing the pressure of the excess fluid portion 
and thereby minimizing the required pump input energy. An arrangement is 
described wherein each vane 10 is arranged as an integral plurality of 
vane members to insure a seal from fluid flow at high and low pressures 
through holes 24, and another arrangement is described wherein wear of the 
vane tips that would otherwise occur is alleviated.