U.S. patent application number 12/439981 was filed with the patent office on 2010-03-04 for oil-free air compressor system with inlet throttle.
This patent application is currently assigned to New York Air Brake Corporation. Invention is credited to Michael Hartl, William B. McCurdy.
Application Number | 20100054958 12/439981 |
Document ID | / |
Family ID | 39157960 |
Filed Date | 2010-03-04 |
United States Patent
Application |
20100054958 |
Kind Code |
A1 |
Hartl; Michael ; et
al. |
March 4, 2010 |
OIL-FREE AIR COMPRESSOR SYSTEM WITH INLET THROTTLE
Abstract
The present air compressor system includes at least one piston
stage connected to the air inlet of the compressor by an inlet
valve and connected to the compressed air outlet of the compressor
by an outlet valve; a motor driving the piston stage; and an
adjustable throttle connected between the air inlet and the inlet
valve. A controller controls the motor and the throttle to
substantially close the throttle to unload the piston stage when
necessary.
Inventors: |
Hartl; Michael;
(Unterhaching, DE) ; McCurdy; William B.; (Adams,
NY) |
Correspondence
Address: |
BARNES & THORNBURG LLP
750-17TH STREET NW, SUITE 900
WASHINGTON
DC
20006-4675
US
|
Assignee: |
New York Air Brake
Corporation
Watertown
NY
|
Family ID: |
39157960 |
Appl. No.: |
12/439981 |
Filed: |
August 30, 2007 |
PCT Filed: |
August 30, 2007 |
PCT NO: |
PCT/US07/77274 |
371 Date: |
October 20, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60824516 |
Sep 5, 2006 |
|
|
|
Current U.S.
Class: |
417/53 ;
417/295 |
Current CPC
Class: |
F04B 25/00 20130101;
F04B 49/06 20130101; F04B 53/1037 20130101; F04B 49/03
20130101 |
Class at
Publication: |
417/53 ;
417/295 |
International
Class: |
F04B 49/03 20060101
F04B049/03 |
Claims
1. An oil-free air compressor comprising: an air inlet and a
compressed air outlet; at least one piston stage connected to the
air inlet by an inlet valve and the compressed air outlet by an
outlet valve; a motor driving the piston stage; an adjustable
throttle connected between the air inlet and the inlet valve; and a
controller controlling the motor and the throttle; the controller
substantially closing the throttle to unload the piston stage.
2. The compressor according to claim 1, wherein the throttle is a
butterfly valve.
3. The compressor according to claim 1, wherein the compressor has
two piston stages; and the throttle is between the air inlet and
the inlet valve of the first piston stage.
4. The compressor according to claim 1, wherein the controller
substantially closes the throttle to unload the piston stage for a
pre-selected state of the compressor.
5. The compressor according to claim 4, wherein the pre-selected
state is the restart of the motor after a brief delay.
6. The compressor according to claim 1, wherein the compressor
includes a crankcase to which piston stage and the air inlet are
mounted; and the throttle is mounted in a conduit connecting the
crankcase to inlet valve.
7. The compressor according to claim 1, wherein the piston stage
includes two parallel connected pistons and each piston has an
adjustable throttle connected to the inlet valve.
8. An oil-free air compressor comprising: an air inlet connected to
a crankcase and a compressed air outlet; at least one piston stage
mounted to on the crankcase, having an inlet valve connected to the
crankshaft by conduit and having an outlet valve connected to the
compressed air outlet; and an adjustable throttle in the conduit
between the crankcase and the inlet valve.
9. The compressor according to claim 8, wherein the piston stage
includes two parallel connected pistons, and each piston has an
adjustable throttle mounted in the conduit connecting the inlet
valve and the crankcase.
10. A method of operating an oil-free air compressor which includes
an adjustable throttle between an air inlet of the compressor and
the inlet of a piston stage driven by a motor, the method
comprising: determining the state of the compressor; and
substantially closing the throttle to unload the piston stage for a
pre-selected state of the compressor.
11. The compressor according to claim 10, wherein the pre-selected
state is the restart of the motor after a brief delay.
Description
BACKGROUND AND SUMMARY OF THE INVENTION
[0001] The present disclosure relates generally to air compressors
and more specifically to an oil-free air compressor having an inlet
throttle.
[0002] An air compressor, for example, two-stage air compressors
include a first low pressure compression stage connected through an
inter-cooling stage to a high pressure compression stage whose
output is provided through an after cooling stage to an air
reservoir. Examples are shown by U.S. Pat. Nos. 6,776,587 and
6,973,868.
[0003] It is well-known in the multistage air compressors to have
unloading valves at the output of the inter-cooling stage as
illustrated by U.S. Pat. No. 6,287,085 and at the output of the
after cooling stage as illustrated in U.S. Pat. No. 4,819,123. The
unloading valve connects the pressurized air in the system to
atmosphere or vents the pressure to unload the compression stage.
Unloading is required for starting torque which exceeds 100 ft-lbs
for example. Depending on the type of drive, for example,
pneumatic, hydraulic, electric or chain, the torque at which the
unlading takes place will vary. The unloading reduces the load on
the drive and reduces power consumption.
[0004] Screw compressors have been unloaded by providing a throttle
or butterfly valve at the air inlet to the compressor. The
butterfly valve is normally open during operation of the
compressor. To unload the compressor, the butterfly valve is
closed. Thus no air is being provided to be compressed and
therefore the compressor is unloaded. Screw compressor also
includes an air oil filter at its output to remove the lubricating
oil inherent in the system.
[0005] Piston air compressors which include lubrication of the
pistons have not used an adjustable throttle valve at the input.
This is because the vacuum created in the compression cylinder when
the throttle valve is closed will suck or draw the oil past the
piston sealing rings. This area around the sealing rings is the
only inlet to the compression cylinder during the intake or sucking
cycle. This action creates undesirable and excessive oil
consumption.
[0006] An oil-free air compressor according to the present
disclosure includes an air inlet and a compressed air outlet; and
at least one piston stage connected to the air inlet by an inlet
valve and the compressed air outlet by an outlet valve. A motor
drives the piston stage; and an adjustable throttle is connected
between the air inlet and the inlet valve. A controller controls
the motor and the throttle to close the throttle to unload the
piston stage when necessary.
[0007] The compressor includes crankcase to which piston stage and
the air inlet are mounted; and the throttle is mounted in a conduit
connecting the crankcase to inlet valve. The throttle may be a
butterfly valve. The compressor may have two piston stages; and the
throttle is between the air inlet and the inlet valve of the first
piston stage. The controller substantially closes the throttle to
unload the piston stage for a pre-selected state of the
compressor.
[0008] A method of operating the oil-free air compressor includes
determining the state of the compressor; and substantially closing
the throttle to unload the piston stage for a pre-selected state of
the compressor. The pre-selected state is the restart of the motor
after a brief delay.
[0009] Other objects, advantages and novel features of the present
invention will become apparent from the following detailed
description of the invention when considered in conjunction with
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a perspective view of a compressor system
according to the prior.
[0011] FIG. 2 is a schematic of an oil-free compressor system
according to the present disclosure.
[0012] FIG. 3 is perspective view of an inlet throttle according to
the present disclosure.
[0013] FIG. 4 is another perspective view of an inlet throttle
according to the present disclosure
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0014] An oil-free or dry-running piston compressor is illustrated
in the FIGS. 1 and 3 as a two-stage compressor unit 10. A drive
unit 12 is mounted to a crankshaft 13A (shown in FIG. 2) in
crankcase 13 and may be, for example, an electric motor. The
crankshaft 13 includes at least one piston cylinder 14 per stage.
The first stage of compression includes piston cylinders 14b and
14c, for example receiving air from air inlet 11 through filter 15
and conduit 21. The second high-pressure stage is performed by
piston cylinder 14a. The compressor unit 10 includes a cooling
system 16 having an output 17 of the compressed air. A compressed
air outlet 17 is generally connected via a check valve 19 to a
reservoir (not shown).
[0015] A cooling system 16 for the two-stage compressor includes an
inter-cooling stage 20 and an after cooling stage 22. The
inter-cooling stage 20 has an inlet connected by pipe 24 from the
outlet of first stage piston cylinder 14b to the inter-cooling
stage 20. The outlet of inter-cooling stage 20 is connected via
pipe 26 to the inlet of the second stage piston cylinder 14a. The
output of the second stage piston cylinder 14a is connected via
pipe 28 to an inlet of the after cooling stage 22.
[0016] The piston cylinders 14a, 14b and 14c each include an inlet
valve 30 and outlet valve 32 connected to compression chamber 34.
For illustrative purposes the valves 30 and 32 are shown as simple
check valves in FIG. 2. The valves 30 and 32 may be pneumatically
or electrically controlled by controller 52 or may be pneumatically
controlled by pilot signals from various pipe and passages in the
compressor system. The first stage 14b, c is shown at the end of
its input or suction cycle and second stage 14a is shown at the end
of its compression cycle.
[0017] There is a feedback passage 36 between the chambers 34 and
the connection to the air inlet valve 30 of pistons stages 14a and
14b, c.
[0018] An adjustable throttle 40 is connected between the air inlet
11 and the inlet valve 30 of the first stage 14b, c. As shown in
FIG. 2, the throttle 40 is in conduit 21 between the filter and the
inlet valve 30 or specifically between the crankcase 13 and the
inlet valve 30 in FIGS. 3 and 4. The throttle 40 may be a butterfly
valve as shown in FIGS. 2 and 4. The throttle 14 is pivotally
mounted in the modified conduit 21' as is actuator 42. A control
port 44 is connected to, not shown, the controller 52. The actuator
may be pneumatic or electric. The conduit 21' is mounted to the
crankcase 13 at flange 21 A and to the first piston stage 14b, c at
flange 21B. Both of the pistons would include the throttle at its
input.
[0019] The throttle 40 is controlled by the controller 52 which
also controls the motor 12. The controller 52 controls the on/off
cycling of the motor 12 based on sensed conditions through sensor
input 54. There may be one or more inputs connected to the
controller 52 to different sensors throughout the system. As
well-known in prior art, these may be pressure sensors to different
ports of the system, it may be temperature sensors or other sensors
used in the control of compressors.
[0020] When the controller 40 is cycling the motor 12, the pressure
build-up in the system acts as a load on the compressor and back
onto motor 12. If the system is charged, the restarting of the
motor is against the pressure in the piston's cylinders 34, as well
as the various pipes and passages. It is well-known in the prior
art, the pressurized system is unloaded to allow easy restarting of
the motor 12. This is generally after a brief period of shut-down
when the system has maintained the pressure. In the present
compressor system when unloading is required, the controller 52
substantially closes the normally open throttle 40 to prevent the
introduction of air from inlet 11 into chamber 34. The downward
motion or the sucking or inlet cycle of 14b will not introduce any
air into chamber 34. Thus there will be no additional air
compressed by the compression cycle of 14b in chamber 34. This
effectively unloads the first stage.
[0021] Although the maximum unloading occurs when the throttle 40
is totally closed, a small crack or leak allowing some input from
air inlet 11 prevents overheating in the piston chamber 34. This
does not adversely affect the efficiency of the unloading.
[0022] Since the compressor 10 is an oil-free compressor, there is
no oil to be sucked into chamber 34 when the throttle 40 is
substantially closed and a partial vacuum is created. Thus the
compressor passages stay clean and there is no air/oil separator
needed at the output 17 of the system.
[0023] Although the present invention has been described and
illustrated in detail, it is to be clearly understood that the same
is by way of illustration and example only, and is not to be taken
by way of limitation. The present adjustable throttle may be used
on an oil-free piston compressor with a single compression stage.
The scope of the present invention is to be limited only by the
terms of the appended claims.
* * * * *