U.S. patent number 3,910,731 [Application Number 05/411,224] was granted by the patent office on 1975-10-07 for screw rotor machine with multiple working spaces interconnected via communication channel in common end plate.
This patent grant is currently assigned to Svenska Rotor Maskiner Aktiebolag. Invention is credited to Walther Persson, Lauritz Benedictus Schibbye.
United States Patent |
3,910,731 |
Persson , et al. |
October 7, 1975 |
Screw rotor machine with multiple working spaces interconnected via
communication channel in common end plate
Abstract
Two stage screw compressor having two working spaces provided
side by side with parallel axes within a common barrel member and
extending in the same direction from a common plane surface of an
end plate member in which one rotor of each stage are
interconnected by a gear transmission including an input power
shaft.
Inventors: |
Persson; Walther (Johanneshov,
SW), Schibbye; Lauritz Benedictus (Saltsjo-Duvnas,
SW) |
Assignee: |
Svenska Rotor Maskiner
Aktiebolag (Nacka, SW)
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Family
ID: |
27259130 |
Appl.
No.: |
05/411,224 |
Filed: |
October 31, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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158176 |
Jun 30, 1971 |
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Foreign Application Priority Data
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Jul 9, 1970 [GB] |
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33405/70 |
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Current U.S.
Class: |
418/9; 418/201.1;
418/97 |
Current CPC
Class: |
F04C
18/16 (20130101); F04C 23/001 (20130101) |
Current International
Class: |
F04C
23/00 (20060101); F04C 18/16 (20060101); F01c
001/16 (); F01c 011/00 (); F04c 023/00 () |
Field of
Search: |
;418/9,10,97,197,199,201-203 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Vrablik; John J.
Attorney, Agent or Firm: Flynn & Frishauf
Parent Case Text
This application is a continuation of our copending application
Ser. No. 158,176, filed June 30, 1971, now abandoned.
Claims
We claim:
1. Screw rotor machine for an elastic working fluid comprising:
a casing enclosing at least two working spaces, each generally
comprising two intersecting bores with parallel axes and provided
with barrel walls, with low pressure and high pressure end walls
perpendicular to said axes, and with low pressure and high pressure
ports disposed in said walls;
a pair of intermeshing rotors respectively disposed in each working
space, each rotor provided with helical lands and intervening
grooves having a wrap angle of less than 360.degree., each pair of
intermeshing rotors comprising one rotor of male rotor type and one
rotor of female rotor type; and
a transmission chamber housing a power transmission, one rotor of
each stage being further interconnected by said power transmission
disposed in said separate transmission chamber;
the improvement wherein the casing comprises:
a common barrel member enclosing at least the major portions of the
working spaces in parallel side by side; and
an end plate member directly connected to said barrel member, said
end plate member having:
one common plane surface constituting an end wall of each of said
working spaces;
means for carrying bearings for all the rotors;
means for enclosing said transmission chamber; and
depressions in said common plane surface which form at least
portions of a communication channel between said working
spaces.
2. Machine as defined in claim 1, in which said end plate member is
provided with an internal communication channel connecting two
working spaces in series through the high pressure port of the low
pressure stage and through the low pressure port of the high
pressure stage, respectively.
3. Machine as defined in claim 2, in which means are provided for
liquid injection into at least one of said working spaces.
4. Machine as defined in claim 3, in which said transmission
chamber forms a part of said communication channel.
5. Machine as defined in claim 4, in which an axially slidable
valve is so provided in the barrel walls of the low pressure stage
that in fully open position said valve extends into said
transmission chamber.
6. Machine as defined in claim 3, in which said transmission is
provided to give the male rotor of the low pressure stage a higher
tip speed than that of the male rotor of the high pressure
stage.
7. Machine as defined in claim 6, in which the ratio between the
tip speeds of the male rotors of the low pressure stage and of the
high pressure stage, respectively, lies within the range 1.5:1 to
3:1.
8. Machine as defined in claim 7, in which the ratio between the
tip speeds of the male rotors of the low pressure stage and of the
high pressure stage, respectively, is about 2.2:1.
9. Machine as defined in claim 7, in which the tip speed of the
male rotor of the high pressure stage is defined by the formula
s = c .sup.. P.sub.2 /P.sub.1
where
s is the tip speed in m/s,
c is a constant within the range 1 to 1.5, preferably about 1.25,
and
P.sub.2 /P.sub.1 is the total pressure ratio of the machine.
10. Machine as defined in claim 1, in which the length of the
rotors are the same in the different working spaces.
11. Machine as defined in claim 10 acting as a compressor, in which
the male rotor in one working space has the diameter as that of the
male rotor in another working space.
12. Machine as defined in claim 1, in which the power shaft of the
transmission is coaxial with the axis of one male rotor and rigidly
connected thereto.
13. Machine as defined in claim 12, in which the male rotors carry
directly intermeshing gears of helical type having helix angles
providing a distribution of the thrust forces between the thrust
bearings for said male rotors.
Description
This invention relates to a screw rotor machine for an elastic
working fluid of the kind comprising a casing enclosing at least
tow working spaces, each generally comprising two intersecting
bores having parallel axes and provided with barrel walls, with
high pressure and low pressure end walls perpendicular to said axes
and with high pressure and low pressure ports disposed in said
walls, and a pair of intermeshing rotors respectively disposed in
each working space, each rotor being provided with helical lands
and intervening grooves and having a wrap angle of less than
360.degree. and each pair of intermeshing rotors including one male
rotor and one female rotor.
In such machines each male rotor has at least the major portion of
each land and groove disposed outside the pitch circle of the rotor
and the lands are formed with generally convex flanks while each
female rotor has the major portion of each land and groove disposed
inside the pitch circle of the rotor, and the lands are formed with
generally concave flanks.
While in the following part of the specification the invention is
described as applied to compressors it is obvious that it may also
be applied to expanders. Even though the invention primarily is
related to multistage compressors it can also be used for one stage
compressors comprising two or more separate units acting in
parallel.
Multistage compressors of the above general type have up to now
been built in two different ways.
One way is to use a plant comprising separate one stage compressor
units in series, which units are either completely independent from
each other or driven by a common prime mover through an
interconnecting transmission disposed in a separate transmission
casing. A plant of such a type is known for instance from U.S. Pat.
No. 3,407,996. In this patent is shown a compressor plant
comprising two separate compressors, each of which is a complete
unit including a casing providing barrel walls, high pressure and
low pressure end walls of a working space in which the two
intermeshing rotors are located. The two units are carried
separately and spaced from each other by a common transmission
casing, which casing per se does not in any way be in contact with
the gaseous working fluid.
The other way frequently used for two stage compressors has been to
design the compressor as a tandem plant in which at least the male
rotors of the two stages have been arranged coaxially, and
interconnected, and driven at the same speed of rotation from a
common prime mover. Such tandem compressors are known for instance
from U.S. Pat. Nos. 2,659,239, 3,093,300 and 3,265,292.
The tandem plant is much more compact than the plant having two
separate units especially with respect to bulk, weight and
manufacturing costs and also with regard to noise generation since
the outer surface thereof is much smaller than that of the two unit
plants which, moreover, must include noise emitting communication
conduits between the different units.
The tandem plant, however, has some disadvantages owing to the fact
that at least the two male rotors are coaxial and form a rigid
rotor unit. Those disadvantages are (a) a long distance between the
radial bearings of the rigid rotor unit resulting in a relatively
large radial deflection, (b) only one thrust bearing for the rotor
unit, resulting in a high loading thereof and in inaccurate axial
clearances in the low pressure stage, (c) complicated and expensive
manufacture of the rotor unit, (d) the same speed of rotation of
the rotor unit in both stages resulting in difficulties in
obtaining optimum tip speeds in both stages and a desirable volume
ratio between the two stages with optimum wrap angles, lead angles
and length to diameter ratio of each of the rotors. Furthermore,
the intermediate wall separating the working spaces must be very
accurately manufactured with parallel surfaces and the
communication channels in order to obtain counter-directed thrust
forces acting on the separate rotors to minimize the load of the
thrust bearing, must be long and thus produce considerable
losses.
The aim of the present invention is to produce a new type of screw
rotor machine avoiding the disadvantages of the known types of
machines mentioned above.
This new type of machine is a very compact machine having at least
two separate working spaces disposed in parallel side by side in a
casing comprising one common barrel member and at least one end
plate member provided with a common plane surface constituting an
end wall for each of the working spaces, and in which one rotor of
each stage are interconnected by a power transmission disposed in a
transmission chamber within said end plate member.
This new machine is especially advantageous when the two working
spaces communicate through a communication channel provided within
the end plate member thus eliminating all external piping and
resulting noise production.
Tests have shown that in a two stage compressor unit with oil
injection compressing air of atmospheric pressure with a total
pressure ratio of 8:1 to 12:1 the ratio between the tip speeds of
the male rotors in the low pressure stage and in the high pressure
stage, respectively, should lie within the range 1.5:1 to 3:1 and
preferably be about 2.2:1, which among others means that the noise
deriving from the outlet of the high speed low pressure stage is
effectively trapped by the low speed high pressure stage thus
allowing only the working fluid of relatively low speed from the
outlet of the second stage to pass into the oil separator with its
large noise emitting surface, whereby a considerable reduction of
the noise emission is achieved.
The tests referred to above have also shown that the male rotor tip
speed of the high pressure stage should be extremely low for
obtaining maximum efficiency and be of the order 7-15 m/s depending
on the pressure ratio. According to the tests the optimum tip speed
of the male rotor of the second stage will follow the formula
s = c .sup.. P.sub.2 /P.sub.1
where
s is the tip speed in m/s,
c is a constant within the range 1 to 1.5, preferably about 1.25,
and
P.sub.2 /P.sub.1 is the total pressure ratio of the compressor.
Furthermore the new type of machine opens up possibilities to
simplify the design of the machine in many respects which reduces
the costs for manufacture and maintenance.
Thus the transmission chamber can in a machine with oil injection
form a part of the commmunication channel, whereby the gears of the
transmission can be lubricated by the oil accompanying the working
fluid, resulting in elimination of special means for this
lubrification and reduction of the necessary channel area and
consequently reduction of bulk, weight and cost.
The rotors of the two stages may further be of the same length so
that both the end plate members of the casing may be provided with
plane surfaces constituting the end walls of the working spaces. In
combination with the fact that all rotors may have the same outer
diameters additional advantages can be obtained. Thus the bores of
the working spaces in the two stages will be exactly the same with
the same centre distances, the rotors and also the bearings in the
two stages will be exactly the same which not only simplifies
production but also reduces the maintenance costs as the number of
spare parts will be drastically reduced.
Moreover the fact that the working spaces are enclosed in a common
barrel member results in a less bulky and lighter machine having a
more rigid casing with smaller free surfaces which further reduces
the noise emission.
Summing up it can be said that the machine, apart from the very
high efficiency that can be obtained, will be less bulky with a
reduction of the maximum volume by about 30 percent and at the same
time the weight is considerably reduced compared with a
corresponding tandem unit which up to now has been the most compact
two stage machine for the same purpose.
These and other features of the invention will be clearly shown in
the following detailed description of compressors comprising
different embodiments of the invention shown in the accompanying
drawings, in which:
FIG. 1 shows a vertical longitudinal section through one form of
compressor according to the invention taken along the line 1--1 in
FIG. 2;
FIG. 2 is a section taken along the line 2--2 in FIG. 1;
FIG. 3 is a section taken along the line 3--3 in FIG. 1;
FIG. 4 is a section taken along the line 4--4 in FIG. 1;
FIG. 5 shows a vertical section through another form of compressor
according to the invention taken along the line 5--5 in FIG. 6;
and
FIG. 6 is a section taken along the line 6--6 in FIG. 5.
The compressor shown in FIGS. 1 to 4 comprises a casing composed of
a common barrel member 10 and of an end plate member 12 in which
casing a low pressure working space 14 and a high pressure working
space 16 are provided side by side within the common housing member
10. Each of said working spaces is generally composed of two
intersecting bores with parallel axes. The working spaces 14, 16
project in the same direction from a common plane surface 18 of the
end plate member 12 which surface constitutes the high pressure end
wall of the low pressure working space 14 and the low pressure end
wall of the high pressure working space 16. An inflow channel 20 is
provided in the barrel member 10 communicating with the low
pressure working space 14 through a low pressure port 22 thereof. A
communication channel 24 is provided in the end plate member 12
communicating with the low pressure working space 14 through a high
pressure port 26 thereof and with the high pressure working space
16 through a low pressure port 28 thereof. An outflow channel 30 is
provided in the barrel member 10 communicating with the high
pressure working space 16 through a high pressure port 32
thereof.
In each of the low pressure and high pressure working spaces 14, 16
a pair of intermeshing rotors 34, 36 and 38, 40, respectively, are
mounted for rotation around parallel axes. One rotor 34, 38 of each
pair is of male rotor type and provided with four helical lands 42,
44 with intervening grooves 46, 48 which have a wrap angle of about
300.degree.. The lands 42, 44 have flanks the major portions of
which are convex and located outside the pitch circle 50, 52 of the
rotor and have a radial extent outside the pitch circle of about 19
percent of the outer diameter of the rotor 34, 38. The other rotor
36, 40 of each pair is of female rotor type and provided with six
helical lands 54, 56 with intervening grooves 58, 60 which have a
wrap angle of about 200.degree.. The grooves 58, 60 have flanks the
major portions of which are concave and located inside the pitch
circle 62, 64 of the rotor. The profiles of the rotors are of the
type shown for instance in U.S. Pat. No. 3,423,017 but also other
types of rotor profiles can be used.
The rotors 34, 36 of the low pressure stage are mounted in combined
radial and thrust bearings 66, 68 in the end plate member 12 and in
radial bearings 70, 72 in the opposite end of the barrel member 10.
The rotors 38, 40 of the high pressure stage are mounted in radial
bearings 74, 76 in the end plate member 12 and in combined radial
and thrust bearings 78, 80 in the opposite end of the barrel member
10. The low pressure male rotor 34 is outside the bearing 66
provided with a gear 82. The high pressure male rotor 38 is outside
the bearing 74 provided with a gear 84 intermeshing with the gear
82 and mounted on a stub shaft 86 of the rotor 38 extending outside
the end plate member 12 and adapted for connection with a prime
mover, not shown. The gears 82, 84 are of helical type having lead
angles such that some of the thrust forces of the high pressure
male rotor 38 is transferred to the low pressure male rotor 34 thus
attaining a reduction of the thrust forces of both the male rotors
34, 38.
In the barrel member 10 there are further provided chambers 88, 90
communicating with a pressure oil source not shown and injection
holes 92, 94 forming communications between the chambers 88, 90 and
the working spaces 14 and 16, respectively.
The barrel member 10 and the end plate member 12 are further
provided with channels 96, 98, 100 (FIGS. 3 and 4) for supply of
sealing oil around the shafts of the rotors 34, 36, 38, 40 at the
high pressure end of the low pressure stage and at both ends of the
high pressure stage.
The transmission 82, 84 is designed so that the tip speed of the
male rotor 34 of the low pressure stage is higher than that of the
male rotor 38 of the high pressure stage, and so that volume ratio
between the swept volumes of the low pressure stage and of the high
pressure stage, respectively, is about 2.5:1.
The compressor acts in the same manner as known compressors.
However, owing to the short communication channel 24 and the
minimum of change of direction of flow therein the losses are
minimized and the efficiency is improved. The fact that the two
male rotors 34, 38 are connected by means of gears instead of being
rigidly interconnected means that the two rotors can be driven at
different speeds so that the volumetric ratio and/or the volumetric
capacity can be easily varied and also that an optimum peripheral
speed can be used in each stage, which further improves the
efficiency. Owing to the fact that the speed of the working fluid
in the high pressure port 32 of the high pressure stage is
relatively low the noise produced thereby is much lower than that
of the working fluid passing out from a compressor of tandem type.
The relatively high speed of the working fluid passing out through
the high pressure port 26 of the low pressure stage does not
produce any noise as the communication with the outlet channel 30
is effectively blocked by the high pressure stage and the overflow
channel 24 is completely enclosed within the end plate member 12.
Furthermore the noise emission from the compressor is considerably
decreased as the surface of the casing and the maximum longitudinal
extent thereof is drastically reduced in relation to a two stage
tandem compressor. Owing to the very compact design of the
compressor plant the bulk and the weight is decreased which in
combination with the rather simple manufacture of the components of
the plant results in a considerable reduction of the cost which
considerably improves the capability of competing with other types
of compressors.
The compressor shown in FIGS. 5 and 6 differs from the compressor
shown in FIGS. 1 to 4 in the following way. The casing is composed
of a barrel member 102 and two end plate members 104, 106, one 104
of which provides the communication channel 24 and a transmission
chamber 108 communicating with the communication channel 24
enclosing a gear transmission comprising one gear 110 mounted on
the low pressure male rotor 34, one gear 112 mounted on a separate
input shaft 114, and one gear 116 mounted on the high pressure male
rotor 38, the input gear 112 being in mesh with the gears 110 and
116 of the rotors 34, 38. Furthermore all rotors 34, 36, 38, 40
have the same lengths and the same diameters. Moreover a slidable
valve member 118, of a type shown for instance in U.S. Pat. No.
3,314,597 is provided in the barrel wall of the low pressure
working space 14 for variation of the volumetric capacity of the
machine. The slidable valve member 118 is so disposed in the
machine that it extends into the transmission chamber 108, when
being in the position for minimum capacity.
While the shown compressors have been shown with oil injection it
is obvious that this type of compressor may also be used with water
injection. In such a case the compressor must be slightly changed
by introduction of shaft seals and possibly also by introduction of
synchronizing gears and by changing of the power transmission gear
ratio. In a compressor of this type with water injection the amount
of water injected into the low pressure stage may be so limited
that all the unevaporated water will form a mist allowing
practically the same rotor tip speed as that of a dry running
compressor, whereas the amount of water injected to the high
pressure stage may flood this stage resulting in a practically
isothermic compression.
* * * * *