Chemistry: electrical current producing apparatus – product – and – Having magnetic field feature
Reexamination Certificate
1999-05-27
2001-09-04
Brouillette, Gabrielle (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Having magnetic field feature
C429S010000, C429S010000, C429S006000
Reexamination Certificate
active
06284397
ABSTRACT:
FIELD OF THE IMPROVED ROTARY PISTON BLOWER
The present improved rotary piston blower provides a rotary piston blower for supplying an oxidant stream to a fuel cell. In one embodiment, an improved rotary piston blower includes cantilevered shafts.
BACKGROUND OF THE IMPROVED ROTARY PISTON BLOWER
FIG. 1
was reproduced from a catalog published by Aerzener Maschinen Fabrik GmbH (“Aerzener”), a German manufacturer of rotary piston blowers.
FIG. 1
depicts a longitudinal sectional view of a prior art rotary piston blower
10
. Two pistons
15
and
20
are synchronized to rotate at the same speed by timing gears
25
and
30
which are mounted on the respective piston shafts
35
and
40
. Piston
15
is known as the driven piston because it is mounted on shaft
35
which extends from the housing for coupling to a motor (not shown). Piston
20
is known as a secondary piston because the rotation of piston
20
is governed by timing gears
25
and
30
.
FIG. 2
was also reproduced from a catalog published by Aerzener. As shown in
FIG. 2
, the rotating pistons are shaped so that pistons
15
and
20
are in close proximity with each other and the piston housing without touching either one.
The piston housing has a piston cylinder
45
which has an interior surface in the general shape of two intersecting bore holes. The piston housing comprises two side plates
50
and
55
which have substantially flat interior surfaces which face the ends of the piston.
Diagrams (a) through (d) in
FIG. 2
depict a cross sectional view of the inside of the piston housing looking in the direction of piston shafts
135
and
140
. Pistons
115
and
120
typically comprise a body with at least two lobes as shown in FIG.
2
. The contoured surfaces of lobed pistons
115
and
120
are shaped such that a contoured surface of rotating piston
115
is normally in close proximity with a contoured surface of rotating piston
120
. Timing gears (not shown in
FIG. 2
) prevent pistons
115
and
120
from touching by ensuring that piston shafts
135
and
140
and corresponding pistons
115
and
120
all rotate at the same speed.
FIG. 2
is a series of drawings which diagrammatically depict how a fluid is blown through a rotary piston blower by showing how the pistons cooperate with one another while rotating at the same speed to compress the fluid against the piston cylinder at different angles of rotation. The process fluid enters through an inlet port
160
in piston cylinder
145
while process fluid exits through an outlet port
165
which is typically opposite inlet port
160
. Pistons
115
and
120
are shaped so that the inlet fluid stream is substantially sealed from the outlet fluid stream. However, the inlet and outlet fluid streams are never completely sealed because there is a small gap between the two pistons and between the pistons and piston cylinder
145
, since these components are preferably not in contact with each other. An advantage of this arrangement is that because there is no contact between the moving internal components no lubricant is required and a rotary piston blower can be used to supply oil-free fluid streams.
With reference again to
FIG. 1
, the piston housing of conventional rotary piston blowers comprises at least three pieces, namely piston cylinder
45
, and side plates
50
and
55
. In some cases, particularly for larger blowers, for ease of assembly and maintenance, piston cylinder
45
and side plates
50
and
55
may each comprise more than one piece. To provide better sealing between the piston housing components, gaskets may be used. Any known fastening devices may be used to join piston cylinder
45
with side plates
50
and
55
, such as, for example, flanges with bolts and nuts or tapped holes.
Lubricated fixed bearings
70
mounted on side plate
50
support one end of shafts
35
and
40
between the piston housing and timing gears
25
and
30
. The opposite end of shaft
40
is supported by floating bearing
75
which is mounted on side plate
55
. A fourth shaft bearing assembly
80
, which may be, for example a cylindrical roller bearing, supports shaft
35
where it extends from the housing for connection to the motor coupling. Seals
85
are provided between shaft bearings
70
,
75
and
80
and side plates
50
and
55
to prevent lubricants from entering the piston housing while also preventing the fluid inside the piston housing from contaminating or blowing lubricants out of the bearings. An additional shaft seal
90
may also be provided where driven shaft
35
extends from the housing.
There are several disadvantages of the prior art rotary piston blowers which are inherent in the typical designs, one of which has been described above and illustrated in FIG.
1
. For example, one disadvantage is that the piston housing is typically made from at least three pieces, namely piston cylinder
45
and side plates
50
and
55
; all three of these components contribute to the proper alignment of the piston and shaft assemblies so each of these three pieces must be carefully fabricated to ensure proper alignment. In particular, side plates
50
and
55
both provide supports for bearings
70
,
75
and
80
so side plates
50
and
55
both need to be accurately machined and carefully assembled with piston cylinder
45
so that piston shafts
35
and
40
and pistons
15
and
20
are properly aligned within piston cylinder
45
. Misalignment of piston shafts
35
and
40
can result in unbalanced rotation and/or accelerated wear of the bearings and seals. Severe misalignment can also cause serious damage to pistons
15
and
20
and the housing if the pistons touch each other or the piston cylinder while rotating.
Another disadvantage of prior art rotary piston blowers is that since piston shafts
35
and
40
are supported on both sides of respective pistons
15
and
20
, there are four shaft bearings which each require a seal to isolate the interior of the piston housing from the lubricated shaft bearings and timing gears. Known rotary piston blower designs such as the one shown in
FIG. 1
must have shafts which extend from both sides of the pistons because the timing gears are located on one side of the pistons and the shaft extends from the other side of the pistons for coupling to a motor. Because rotary piston blowers are commonly used for process streams which are oil-free and sealed against contaminants, it would be beneficial to reduce the number of openings in the piston housing, and the number of seal and bearing arrangements adjacent the piston housing.
In the prior art, it is not known to use a rotary piston blower to supply an oxidant stream to a fuel cell. A rotary piston blower required for supplying an oxidant stream to a portable or low power fuel cell would generally (depending upon the power output of the fuel cell) be smaller than rotary piston blowers which are commonly available. For example, the rotary piston blowers commercially available from Aerzener have intake flow volumes between 30 cubic meters per hour (500 liters/minute) for their smallest capacity model, up to 15,000 cubic meters per hour for their largest capacity model. The flow rate required for a typical portable or low power fuel cell is in the range of approximately 6 cubic meters per hour (100 liters/minute) or less.
SUMMARY OF THE IMPROVED ROTARY PISTON BLOWER
An improved rotary piston blower has fewer components, fewer seals, and is easier to fabricate, compared to the prior art rotary piston blower shown in FIG.
1
. The improved rotary piston blower is also able to supply an oil-free oxidant stream to an electrochemical fuel cell.
In particular, the improved rotary piston blower comprises:
(a) an elongated drive shaft having a longitudinal axis;
(b) a driven piston mounted on a first end of the drive shaft;
(c) a secondary shaft having a longitudinal axis parallel to the longitudinal axis of the drive shaft;
(d) a secondary piston mounted on a first end of the secondary shaft;
(e) a first timing gear mounted on the drive shaft;
(f) a second timing g
Ballard Power Systems Inc.
Brouillette Gabrielle
McAndrews Held & Malloy Ltd.
Wills M.
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