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Description  |
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FIELD OF THE INVENTION
This invention relates to sliding vane pumps.
BACKGROUND OF THE INVENTION
Sliding vane pumps are well known. Such pumps typically have a plurality of
vanes slidably retained in radial slots of a rotor. The rotor has an axis
about which it is rotated and which is eccentric to the axis of a cylinder
in which the rotor is positioned. This creates a crescent shaped space
between the rotor and the cylinder. When the rotor is rotated, the outer
ends of the vanes follow the wall of the cylinder so that on one side of
the rotor the pockets defined between the vanes increase in volume and on
the other side of the rotor the pockets decrease in volume. An intake port
of the pump is provided to the cylinder on the increasing side of the
rotor, and an exhaust port is provided in the cylinder on the decreasing
side. Thus, as the rotor is rotated, a gas or vapor is drawn into the
intake and expelled through the exhaust.
In some applications of such a pump, for example as a vapor recovery pump
for use in pumping liquid gasoline into the tank of an automobile at a
gasoline station, the pump is required to operate pumping a vapor at
sub-zero temperatures without seizing due to ice and frost accumulation
inside the pump. To permit that, relatively large clearances are
desirable. Such clearances are also desirable to reduce the failure rate
due to inhaling debris.
However, a disadvantage of greater internal clearances is a reduction in
the vacuum level capability of the pump. For example, in a gasoline vapor
recovery system, it is known to sense the electric motor current which
increases with increasing vacuum, and shut the system down when the
current reaches a level that would indicate a blocked pipe. However, it is
possible for the clearances inside the pump to be so great that such a
high vacuum level cannot be reached, even if a pipe is blocked, so that
the sensor does not perform its intended function.
SUMMARY OF THE INVENTION
The invention provides an improvement in a sliding vane pump of the type
having a housing, a rotor received in a cylinder defined in the housing,
the rotor having an axis which is eccentric to the cylinder, vanes
slidable in slots in the rotor so as to follow the cylinder when the rotor
is rotated about its axis, and a rotary drive shaft for rotating the rotor
about its axis. The improvement is that a diaphragm plate is secured to
the housing adjacent to and generally parallel with an end of the rotor,
the plate being resilient so as to deflect axially closer to the rotor as
a vacuum drawn by the pump increases and to retract axially away from the
rotor as the vacuum subsides. Thus, during normal operation, the vacuum
drawn by the pump is not sufficient to significantly reduce the axial
clearance between the rotor and the plate. However, when a high vacuum is
drawn, the plate flexes toward the end face of the rotor to reduce the
axial spacing. This reduces leakage around the ends of the vanes and past
the end of the rotor, which would otherwise limit the level of the vacuum
the pump is capable of. Thus, a higher vacuum is attainable, while still
maintaining a relatively high clearance at start up of the pump and during
normal operation.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an exploded side plan view of a pump incorporating the invention;
FIG. 2 is a front plan view of a diaphragm plate for use in the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 illustrates a side plan exploded view of a sliding vane air pump 10
incorporating the invention. Sliding vane air pumps are well known and the
invention is not limited to any particular one of them. For example, the
invention could be practiced with the sliding vane air pump described in
abandoned, commonly owned U.S. patent application Ser. No. 08/188,761, the
disclosure of which is hereby incorporated by reference.
The pump 10 has a housing 12 which includes the housing of electric motor
14, adapter 16, cylinder 18, and head 20. As is conventional in sliding
vane air pumps, a rotor 22, and vanes 24, which slide in radial slots 25
of the rotor 22, are also provided. Non-conventionally, however, a
resilient flexible diaphragm plate 26 is provided, as will be described in
further detail below.
The motor 14 of the preferred embodiment is an electric motor of any
suitable type. The motor 14 has a rotary power drive shaft 30 extending
from it, which mounts rotor 22 by key 32 on shaft 30 in conventional
fashion so as to rotate the rotor 22 about its axis 35.
As is well known in sliding vane air pumps, the cylinder 18 defines with
its inner surface a cylinder 34, and the axis 35 of the drive shaft 30 and
rotor 22 is eccentric with respect to the axis 37 of the cylinder 34, so
as to define a crescent shaped space between the outer surface of the
rotor 22 and the cylinder 34. As the rotor 22 is rotated, the vanes 24
slide in the slots 25 of the rotor so as to follow the surface of the
cylinder 34, so that when the vanes are extending out of the slots, the
volumes of the pockets between those vanes are expanding, and when the
vanes are retracting back into the slots, the volumes of the pockets
between the vanes is contracting. When the volume of a pocket is
expanding, the pressure in that pocket is declining, and when a pocket is
contracting in volume, its pressure is increasing. Thus, an intake port is
provided in the head 20 opening into the crescent shaped chamber defined
between the rotor 22 and cylinder 34 at a position in which the pocket
volume is expanding, and an outlet port is formed in the head 20 opening
into the crescent shaped chamber at a position in which the volume of the
pockets is contracting.
The adapter 16 is provided so as to interface the motor 14 to the cylinder
18 and head 20. The adapter 16 is mounted to the motor 14, for example,
with two screws (not shown) which extend through holes 44 in diaphragm 26
and corresponding holes in the adapter 16. This connection serves to
secure these parts together in assembly while the rotor 22, vanes 24,
cylinder 18 and head 20 are being assembled to the unit. Screws 36 (five
total, only three are shown) extend through the head 20, cylinder 18,
diaphragm 26 and adapter 16 and are threaded into the housing of the motor
14, to secure these parts together.
To avoid problems such as freezing up of the rotor at sub-zero temperatures
or failures due to inhaling debris, it is desirable to provide relatively
large clearances between the axially facing ends of the rotor 22 and the
adapter 16 at one end, and the head 20 at the other end. However, large
clearances at the ends of the rotor can detract from pump performance as
they allow leakage past the edges of the rotor and past the end edges of
the vanes 24. During most conditions of operation, the rotor 22 can be
rotated fast enough to make up for leakage losses occasioned by the
relatively large clearances, and thereby create a high enough vacuum to
satisfy requirements. However, occasionally in the operation of the pump,
it may be desirable to significantly increase the vacuum beyond that
attainable with the particular motor 14 and fixed clearances at the ends
of the rotor 22.
For example, if the pump is being operated as a vacuum pump and the intake
to the pump becomes clogged, in a tight pump with low leakage losses, the
vacuum will go up dramatically, resulting in a higher current to the
motor. Some systems sense the current to the motor and when it goes up
dramatically, due to a higher vacuum being drawn, appropriate action is
taken, for example shutting down the system. However, where large
clearances are provided in the pump, even if the intake line becomes
clogged, the vacuum may not increase that much, since the flow inside the
pump can just flow around the side edges of the vanes and the ends of the
rotor to go from one vane chamber to another.
The invention solves this problem, while still providing the desirable
large clearances at the ends of the rotor, by providing a diaphragm plate
26 adjacent to one or both ends of the rotor 22. As shown in FIG. 1, the
diaphragm plate 26 is adjacent to the shaft end of the rotor 22. Referring
to FIG. 2, the diaphragm plate 26 has the same outline as the cylinder 18,
head 20 and adapter 16 and is secured by the previously mentioned screws
extending through holes 44 and by the bolts 36, which extend through holes
40 in the plate 26. A shaft hole 42 is also provided in the plate 26
through which drive shaft 30 extends.
The plate 26 is made of a resilient flexible sheet material, for example,
0.012 inch thick stainless steel. With its outer periphery clamped between
the cylinder 18 and the adapter 16, the inner area of the plate 26 is able
to flex toward the shaft end face 46 of the rotor 22. The plate 26 moves
closer to the shaft end face 46 of the rotor 22 as the vacuum drawn by the
pump increases. In turn, as the plate 26 moves closer to the end of the
rotor, thereby decreasing the effective clearance at the shaft end of the
rotor, the vacuum which the pump is capable of drawing increases. The
level of the vacuum at which the plate 26 starts to flex toward the rotor
22 and how much it flexes with increasing vacuum is determined by the
stiffness of the material from which the plate 26 is made, as well as by
mounting considerations, so essentially the plate can be designed to flex
more or less as desired, depending upon the application. When the vacuum
subsides, since the plate 26 is resilient, it returns to its normally
planar state in which the clearance between the shaft end face of the
rotor 22 is maximized, to prevent freezing up and clogging of the pump 10.
A diaphragm plate 26 could also be provided at the head end of the rotor
22, as shown by the plate 26 shown in phantom in FIG. 1, which would work
in essentially the same manner as the plate 26 provided at the shaft end
of the rotor. If provided at the head end, holes would have to be provided
in the plate 26 through which the inlet ports and outlet ports could pass.
It is desirable to place these holes adjacent to the external periphery of
the plate 26 so as to minimize leakage which may occur directly between
the intake and outlet on the head side of the plate 26 when the plate was
bowed toward the head end 48 of the rotor 22.
Preferred embodiments of the invention have been described in considerable
detail. Many modifications and variations to those preferred embodiments
will be apparent to those skilled in the art which will still incorporate
the invention. For example, the external shape of the plate 26 could be
any shape, so long as it provided for axial flexing of the plate 26.
Therefore, the invention should not be limited to the preferred
embodiments described, which should be defined by the claims which follow.
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