Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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COMPRESSOR UNLOADER
Technical Field
The invention relates to air compressors and more particularly to an
unloader for an air compressor which is responsive to a compressor motor
5 reaching a predetermined minimum speed before leading the compressor.
Background Art
Air compressors are commonly used, for example, for operating
pneumatic tools, for inflating tires, etc. A common type of air compressor has
a motor connected to reciprocate a piston in a cylinder. The piston
10 reciprocates alternately between a suction stroke and a compression stroke.
One or more intake valves direct a flow of ambient air into the cylinder
during the suction stroke and one or more outlet valves direct pressurized air
from the cylinder to an air tank or through a hose to a tool, for example,
during the compression stroke. In some compressors, the electric motor is
strained when the motor is started while the compressor is subject to a load.
For example, where the compressor is connected to an air tank, a switch turns
the motor off when the tank pressure reaches a preset maximum pressure and
turns the motor on when the tank pressure drops to a preset minimum
pressure. The motor will be subjected to a high starting torque if it is started2 o against the load of the preset minimum tank pressure on the compressor.
Starting problems are especially of concern under low voltage conditions, as
might occur, for example, at a construction site where long extension cords
are often used to connect the compressor motor to the power source. For
compressors powered by an internal combustion engine, engine starting is
25 more difficult while the compressor is subject to a load. In addition, with
internal combustion engines, it is desirable to let the engine and compressor
run continuously during normal usage. During continuous operation, when
air is not being used and the tank pressure reaches maximum, it is desirable to
idle the engine and reduce the compressor torque to save fuel and reduce wear
3 o on the engine and compressor.
In order to reduce the starting and idling load demands on a
compressor motor, valves are often used to unload the compressor motor
when the motor is stopped. Various designs are known for unloader valves.
One type of unloader valve operates in response to the motor speed through a
3 5 mechanism activated by centri-fugal force. Electric timers also have been used
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to unload a compressor for a predetermined time while the motor comes up to
speed. In still another design, the motor output is coupled through a magnet
to a cam. The cam opens a valve to unload the compressor when the motor is
stopped. When the motor speed is sufficiently high, the rnagnet rotates the
cam to close an unloader valve.
Disclosure Of Invention
According to the invention, a compressor unloader is designed to
respond to the flow of cooling air from a fan driven by the compressor motor.
In one embodiment of the invention, the suction or inlet valve is held open
0 during both the intake and the compression strokes of the piston to unload the
compressor while the motor is stopped or operating at a low speed during
startup and idle. When the motor speed is sufficiently high, the flow of
cooling air from the -fan moves a vane and a connected mechanism which
allows the suction valve to close. Once the suction valve can close during the
compression stroke, the compressor will have a normal compressed air output.
In a second embodiment of the invention, a vent passage is connected
either to the compression chamber or to the outlet side of a valve head on the
compressor. When the compressor motor is stopped or idling, the passage is
open to vent high pressure. When the motor reaches a predetermined speed,
2 o cooling air from a fan driven by the motor moves a vane to close the vent
passage. When the vent passage is closed, the compressor and connected
drive motor become fully loaded.
It is an object of the invention to provide an improved low cost
unloader to facilitate starting and idling for an air compressor motor.
2 5 Other objects and advantages of the invention will be apparent from
the following detailed description and the accompanying drawings.
Brief Description Of The Drawings
Fig. l is a fragmentary cross sectional view showing a portion of an air
compressor incorporating an unloader according to one embodiment of the
3 o invention;
Fig. 2 is a fragmentary top view showing an unloader according to a
modified embodiment of the invention;
Fig. 3 is a fragmentary cross sectional view illustrating details of the
unloader of Fig. 2;
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Fig. 4 is an enlarged cross sectional view taken along line 4-4 of Fig.
2;
Fig. 5 is a fragmentary top view showing an unloader according to a
-further modified embodiment of the invention;
Fig. 6 is a fragmentary cross sectional view showing details of the
cylinder, the valve plate and the unloader of Fig. 5;
Fig. 7 is an enlarged *agmentary cross sectional view showing the
closed compressor inlet valve as taken along line 7-7 of Fig. S;
Fig. 8 is an enlarged -fragmentary view, similar to Fig. 7, but showing
0 the compressor inlet valve held open by the unloader; and
Fig. 9 is a fragmentary cross sectional view, similar to Fig. l, ~ut
showing a compressor incorporating a further modified embodiment of an
unloader according to the invention.
Best Mode For CarIYing Out The Invention
Referring now to Fig. 1 of the drawings, a fragmentary portion of an
air compressor 10 is shown incorporating an unloader 11 according to one
embodiment of the invention. The housing and support frame for the
compressor 10 have been omitted for better illustrating the invention. The air
compressor 10 generally includes an electric motor 12 or an internal
combustion engine (not shown) having an output shaft 13. Unless otherwise
specif1ed, the term "motor" as used herein shall mean either an electric motor
or an internal combustion engine. The output shaft 13 is connected to drive
an eccentric plate 14 having an eccentric shaft 15 which is offset -from the
axis of the output shaft 13. The eccentric shaft lS is connected through a
bearing 16 to a free end 17 of a connecting rod 18. The connecting rod 18
and a piston head 19 connected to an opposite end 20 of the connecting rod
18 form a wobble piston 21. As the motor drives the eccentric shaft 15 about
a circle, the piston head 19 reciprocates in a cylinder 22. At the same time,
the piston head 19 wobbles or rocks back and -forth because it is rigidly
30 connected to the connecting rod end 20. A piston seal 23 establishes a sliding
seal between the piston head 19 and the cylinder 22 as the piston reciprocates
and rocks.
An end 24 of the cylinder 22 is closed by a valve plate 25. The valve
plate 25 has one or more inlet or suction ports 26 and one or more outlet ports
35 27. A resilient reed 28 covers the inlet port 26 to form a suction valve 29 and
a resilient reed 30 covers the outlet port 27 to forrn an outlet valve 31. When
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the piston head l 9 is moved downwardly in the cylinder 22, ambient air is
drawn -from an inlet chamber 32 in a head 33, through the inlet port 26, past
the suction valve 29, and into the cylinder 22. When the piston head 19 is
moved upwardly in the cylinder 22, the suction valve 29 is closed and the air
5 in the cylinder 22 is compressed and forced through the outlet port 27, past
the outlet valve 31 and into an outlet chamber 34 in the head 33. As the air
flows through the outlet port 27, the valve reed 30 deflects as shown by the
dashed lines. When the air -flow from the cylinder 22 to the chamber 34
ceases, the resilient valve reed 30 returns to its original position closing the0 outlet port 27.
In order to prolong the operating life of the compressor 10 and to
prevent overheating during operation, a fan 35 is mounted on the motor sha-ft
13. During operation of the compressor 10, the fan 35 draws cooling air over
the motor 12 and blows the cooling air around the exposed exterior portions
of the cylinder 22 and the piston 21. A suitable housing (not shown) for the
compressor 10 and baffles within the housing (not shown) may be provided to
direct the cooling air *om the fan 35 to the locations needing cooling.
According to the invention, an improved unloader 11 is provided for
holding open the suction valve 29 while the motor 12 is stopped, just starting
20 or idling. A rocker arm 36 is mounted to rock within the inlet chamber 32. A
push rod 37 extends from one end 38 of the rocker arm 36 through the inlet
port 26 to the valve reed 28. A spring 39 tends to rock the arm 36 until the
push rod 37 contacts and holds the valve reeds 28 away from the inlet port 26,
as shown. Consequently, the suction valve 29 is held open and air is free to
25 flow through the inlet port 26 during both the intake and the compression
strokes of the piston 21. So long as the suction valve 29 is held open, the loadand the starting torque requirements for the motor 12 are at a minimum.
A second end 40 of the rocker arm 36 is connected through a rod 41 to
a vane 42. The vane 42 is mounted to pivot about an axis 43. The vane 42 is
30 mounted where it is subjected to air flow from the fan 35. When the motor
12 is started and the fan speed increases to a sufficient level, the air
discharged by the fan acts on the vane 42. The air flow causes the vane 42 to
pivot about the axis 43 in the direction of the arrow to pull on the rod 41.
This in turn rotates the rocker arm 36 to lift the rod 37 away from the valve
35 reed 28, allowing the suction valve 29 to close. Thus, the suction valve 29 is
held open by the rod 37 both when the motor 12 is stopped and during startup
for the motor 12. When the motor reaches a desired rninimum speed, air flow
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from the fan 35 causes the rod 37 to be drawn away from the valve reed 28
and the suction valve 29 becomes operational to load the compressor motor
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Figs. 2-4 are fragmentary views showing a modified embodiment of a
5 compressor unloader 48 according to the invention. A valve plate 49 is
mounted to close a cylinder 50 in which a piston 51 reciprocates. The valve
plate 49 defines a plurality of inlet or suction ports 52 and a plurality of outlet
ports 53. The inlet ports 52 are closed by resilient valve reeds 54 and the
outlet ports 53 are closed by resilient valve reeds 55. A resilient flat spring
lO 56 is secured to the valve plate 49. The spring 56 has at least one finger 57(two shown) which extends through at least one of the inlet ports 52 and
contacts the adjacent reed 54. The spring 56 is stronger than the resilient reed54 and, consequently, the fingers 57 can deflect the adjacent reeds 54 away
-from the valve plate 49, as shown in Fig. 4. So long as the fingers 57 hold
one or more of the inlet valve reeds 54 away from the valve plate 49, the
compressor will be unloaded and minimum torque is required to start the
compressor motor.
A rigid wire 58 is secured by suitable mounts 59 to rotate about an axis
60. The wire 58 has an S-shaped end 61 which extends between a tab 62 on
20 the spring 56 and the valve plate 49. The wire 58 is generally U-shaped and
has a side 63 which is spaced *om an edge 64 of the valve plate 49 and is
generally parallel to the axis 60. A vane 65 is secured to the wire side 63. If
the cylinder 50 is generally vertically oriented, the vane 65 will fall through
gravity to the position shown in dashed lines in Fig. 3. A finger 66 extending
25 from the vane 65 will contact the cylinder 50 to limit travel of the vane 65.When the vane is in this position, the end 61 of the wire 58 will be in the
position shown in Fig. 4 and the spring fingers 57 will hold at least one valve
reed 54 open to unload the compressor. When the compressor motor is
started and reaches a predetermined speed, air flow from a fan driven by the
30 motor (such as the motor 12 and fan 35 of Fig. 1) will deflect the vane 65 tothe position shown in solid in Fig. 3. This vane deflection rotates the wire 58
about the axis 60 and the wire end 61 lifts the spring tab 62 and fingers 57 to
allow the previously open suction valve reeds 54 to close. Thus, the
compressor begins to operate and the motor is loaded after the motor is
35 started.
Figs. 5-8 are fragmentary views showing a -further modified
embodiment of a compressor unloader 70 according to the invention. As with
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the previous embodiments, a piston 71 is reciprocated in a cylinder 72. The
cylinder 72 's closed by a valve plate 73 having a plurality of inlet ports 74
and a plurality of outlet ports 75. Resilient valve reeds 76 normally close the
inlet ports 74 and resilient valve reeds 77 normally close the outlet ports 75.
The unloader 70 includes a rigid wire 78 attached to rotate in mounts
79 about an axis 80. The wire 78 has an end 81 which is bent to extend into
one of the inlet ports 74. The wire 78 has a second end 82 which is spaced
from an edge 83 of the valve plate 73 and extends substantially parallel to the
axis 80. A vane 84 is attached to the wire end 82. The vane 84 is located to
be moved in response to a predetermined flow of air -from a -fan driven by the
compressor motor (such as the fan 35 driven by the motor 12 in Fig. 1).
When the motor is off, gravity moves the vane 84 to the position shown in
dashed lines in Fig. 6. While the vane 84 is in this position, the bent wire end81 pushes an adjacent inlet valve reed 76 open, as shown in Fig. 8, to unload
the compressor motor. While any of the inlet valve reeds 76 is held open, air
will flow through the inlet port 74 on both suction and compression strokes of
the piston 71. Consequently, the motor is subjected to only a minimum
torque during startup. When the motor reaches a sufficient speed during
startup, the air flow moves the vane 84 to the position shown in solid in Fig. 62 o and the wire end 81 is moved away from the adjacent inlet valve reed 76, asshown in Fig. 7. At this speed and at higher motor speeds, the inlet valve
reeds 76 are all allowed to close during the compression stroke of the piston
71 and the compressor will operate.
In the embodiments shown in Figs. 2-8, the vanes 65 and 84 move
25 through the action of gravity to open one or more of the inlet valves when the
motor is stopped. In tested compressors, gravity has been found sufficient to
move the vane and unload the compressor with the cylinders arranged from a
vertical orientation to tilted up to about 45. If the cylinder is tipped too far
from the vertical, a spring may be needed to move the vane to assure positive
3 o action of the unloader.
Fig. 9 is a fragmentary cross sectional view of a modified embodiment
of an air compressor 90 according to the invention. The compressor 90
includes an electric motor 91 having an output shaft 92 which rotates both a
cooling air fan 93 and an eccentric plate 94. An end 95 of a wobble piston 96
3 5 is connected to an eccentric pin 97 on the eccentric plate 94. As the motor 9 L
rotates the eccentric plate 94, the piston 96 is caused to reciprocate in a
cylinder 98. A valve plate 99 and a head 100 are secured to a top 101 of the
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cylinder 98. An inlet chamber 102 in the head 100 is connected through a
port 103 in the valve plate 99 and an intake check valve 104 to a compression
chamber 105. The compression chamber 105 is connected through an outlet
port 106 in the valve plate 99 and an outlet checlk valve 107 to an outlet
5 chamber 108. A tube or hose 109 receives compressed air from the chamber
108.
According to the invention, the compressor 90 is unloaded during
starting either by venting the outlet chamber 108 (as shown) or by venting the
compression chamber 105 (not shown) through a normally open small vent
o hole 110. A vane 111 is mounted to pivot on a bracket 112 which is
illustrated as being secured to the head 100. The vane 111 is influenced by
air flow -from the fan 93. Either through gravity or through the action of a
spring (not shown), the vane will be in the position illustrated by the solid
lines in Fig. 9 when the motor 91 is stopped or operating at a low startup or
15 idle speed. When the motor speed reaches a predetermined level, the flow of
cooling air ~rom the fan 93 will be su-fficient to pivot the vane 111 to the
position 113 shown in dashed lines. A stopper 114 is secured to the vane at a
location to plug the vent hole 110 when the vane 111 pivots to the position
113. Consequently, when the compressor motor reaches a predetermined
2 o minimum speed, the vent hole 1 10 will be plugged and the compressor 90 will supply compressed air to the tube 109. At lower motor speeds, the
compressed air will be vented to atmosphere through the open hole 110.
It should be noted that the flow of cooling air required to close the vent
hole 110 is determined by various factors. If, for example, the vent hole is
2 5 0.05 inch (1.27 mm) in diameter and the maximum output pressure from the
compressor is 100 psi (0.0703 Kg/mm~), a maximum force of 0.2 pounds
(0.00089 Kg) is required to stop the vent hole 110. This force is significantly
reduced by the leverage exerted by the vane 111 due to the difference in
distances between the pivotal connection of the vane 111 to the bracket 112
3 o and the stopper 114 and between the pivotal connection of the vane 111 to the
bracket 112 and an end 115 of the vane 111 on which the cooling air flow
acts. The required air flow for stopping the vent hole 110 may be further
reduced by increasing the area of the vane 111 impinged by the air flow.
Thus, the motor speed at which the vent hole 110 will be closed will be set by
3 5 adjusting various design factors for the vane 111.
The compressors shown and described above are of a type sometimes
called oilless compressors because the wobble piston does not require an oil
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sump -for continuous lubrication. It will be appreciated that the compressor
unloader of the invention will be equally applicable to a compressor having a
purely reciprocating piston of the type which is hinged to a connecting rod by
a wrist pin. ~he invention is also applicable to other known compressor
5 designs, such as rotating piston compressors. V~rious modifications and
changes may be made to the above described preferred embodiments of the
invention without departing from the spirit and the scope of the following
claims.
