Quantcast

Air Compressor Control

Imported: 10 Mar '17 | Published: 27 Nov '08

Roger L. Sweet, David J. Pfefferl

USPTO - Utility Patents

Abstract

Controlling air compressors based on a temperature of air compressed by the air compressor. A temperature of air compressed by the air compressor is sensed. The sensed compressed air temperature is compared with a predetermined threshold temperature. The air compressor is deactivated when the sensed temperature exceeds the threshold temperature. The threshold temperature may be selected to inhibit carbon formation caused by oil thermal breakdown.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of pending U.S. patent application Ser. No. 11/010,851 entitled Air Compressor Control filed on Dec. 13, 2004, the entire disclosure of which is incorporated by reference as if fully rewritten herein.

FIELD OF THE INVENTION

The present disclosure relates generally to air compressor control in an internal combustion engine, and more particularly, to controlling activation and deactivation of an air compressor based on a temperature of compressed air.

BACKGROUND OF THE INVENTION

Modern trucks contain air compressors which are used to charge an air tank from which air-powered systems, such as service brakes, windshield wipers, air suspension, etc., can draw air. In a typical trucking application, an air compressor can run in a loaded or activated state a large percentage of the time. Systems have been developed to reduce the amount of time the air compressor is activated. For example, systems have been developed that activate the compressor when pressure in a reservoir drops below a first predetermined value, and deactivates the compressor when pressure in the reservoir reaches a second, higher predetermined value.

U.S. Pat. No. 6,036,449 to Nishar et al. discloses an air compressor control that monitors the pressure in the reservoir and the head metal temperature of the compressor. When the reservoir is of a pressure between the two set pressures and is in a loaded state, the air compressor will be unloaded after a set time interval that is based on a compressor head metal temperature to maintain threshold temperatures of the compressor head metal within a suitable range. Additionally, the compressor head is evaluated such that whenever the compressor head temperature exceeds a predetermined threshold temperature the air compressor is placed in an unloaded state until the compressor head temperature drops below the predetermined threshold temperature. The head metal temperature is controlled to prevent excessive heating of the head.

SUMMARY

The present application relates to controlling air compressors based on a temperature of air compressed by the air compressor. In one method of controlling an air compressor, a temperature of air compressed by the air compressor is sensed. The sensed compressed air temperature is compared with a predetermined threshold temperature. The air compressor is deactivated when the sensed temperature exceeds the threshold temperature. In one embodiment, the air compressor is deactivated when the sensed temperature exceeds the threshold temperature and a sensed reservoir pressure is above the threshold pressure. In one embodiment, the threshold temperature is selected to inhibit carbon formation caused by oil breakdown.

The temperature of the compressed air may be sensed at a variety of locations. For example, the temperature of the compressed air may be sensed in a compressor port, such as an exhaust port, or an unloader valve port. The temperature of the compressed air may be sensed in a compression chamber. In one embodiment, the temperature of the compressed air is sensed by a temperature sensor mounted in a compressor unloader valve that is in fluid communication with a compression chamber.

One air compressor that is adapted for control based on a temperature of the compressed air includes a housing, a head, a piston, and a temperature sensor. The head is mounted to the housing, such that the head and the housing define a compression chamber and a fluid passage in communication with the compression chamber. The piston is disposed in the compression chamber for compressing air in the compression chamber. The temperature sensor is positioned to measure a temperature of air compressed by the piston. In one embodiment, the temperature sensor is substantially isolated from the head and the housing.

One air compressor controller includes an input, a memory, a processor, and an output. The input receives compressor air temperature signals. The memory stores a compressor control algorithm. The processor applies the compressor control algorithm to the compressor air temperature signals. The processor provides an air compressor deactivation signal when the compressor air temperature signal exceeds the threshold temperature signal value. The output communicates the compressor deactivation signal to selectively deactivate a controlled air compressor. Alternatively, the controller can be comprised of discrete electronic components with no processor or memory. For example, the controller could comprise one temperature component integrated circuit could convert input signals to voltages and one voltage comparator component could control the output based on voltage thresholds.

One vehicle air supply system includes a reservoir, an air compressor, a temperature sensor, and a controller. The reservoir stores compressed air provided by the compressor. The temperature sensor is positioned to sense a temperature of the compressed air. The controller is linked to the compressor. The controller compares a sensed temperature of the air compressed by the air compressor with a predetermined threshold temperature and deactivates the air compressor when the sensed temperature exceeds the threshold temperature. In one embodiment, the controller activates the compressor when an air pressure in the reservoir is less than a predetermined threshold pressure and the sensed temperature exceeds the threshold temperature.

Further advantages and benefits will become apparent to those skilled in the art after considering the following description and appended claims in conjunction with the accompanying drawings.

DETAILED DESCRIPTION

The present invention is directed to controlling activation and deactivation of an air compressor 10 based on a temperature of compressed air. The present invention can be implemented in a wide variety of different vehicle air supply systems. FIG. 1 illustrates an example of one such vehicle air supply system 12.

The illustrated air supply system 12 includes an air compressor 10, a reservoir 16, a governor 18, and an air dryer 20. The air compressor 10 includes a housing 11, a head 13, and a piston 15. The head 13 is mounted to the housing 11 such that the head and the housing define a compression chamber 17. The piston 15 reciprocates in the compression chamber 17 to compress air in the compression chamber in a known manner. The compressor 10 may be driven by a vehicle crank shaft (not shown). The compressor 10 receives air from an air source 22, such as an engine air intake. The compressor 10 compresses the air and provides the compressed air to the reservoir 16. In the air system illustrated by FIG. 1, the governor 18 places the compressor 10 in an activated or loaded state when the pressure in the reservoir 16 falls below a predetermined minimum pressure and places the compressor in a deactivated or unloaded state when the pressure in the reservoir reaches a predetermined maximum pressure. In the example illustrated by FIG. 1, the governor 18 places the compressor 10 in an unloaded state by providing an air signal to a compressor unloader 24. The compressor unloader may take a variety of different forms. For example, the unloader 24 may be a mechanism that holds an inlet valve 25 open, or may be a separate valve assembly 54 (shown in FIGS. 6 and 7).

FIG. 2 illustrates a method of controlling the air compressor 10 based on a temperature of air compressed by the air compressor. A temperature TA of air compressed by the air compressor is sensed 30. The sensed compressed air temperature TA is compared 32 with a predetermined threshold temperature TH. If the sensed air temperature TA is greater than the predetermined threshold temperature TH, the compressor is deactivated 34 or unloaded. If the sensed air temperature TA is less than the predetermined threshold temperature TH, the compressor is allowed to be activated 36 or loaded.

In the exemplary embodiment, the compressor 10 is lubricated by oil. For example, the compressor 10 may be lubricated by oil of the engine that drives the compressor. When the engine oil gets too hot, the oil may break down and carbon will form. Carbon formation may damage the compressor and/or clog lines 37 in the air supply system, such as a line between the compressor 10 and the reservoir 16. In one embodiment, the predetermined threshold temperature TH is set to prevent the formation of carbon. In one example, the predetermined threshold temperature or the compressed air may be set in the range of 325 to 400 degrees Fahrenheit measured in the compressor outlet passage. For example, the predetermined threshold temperature TH could be set at 375 degrees Fahrenheit measured in the compressor outlet passage 46.

In one embodiment, the compressor is maintained in the deactivated state until the sensed air temperature falls below a predetermined lower boundary temperature TL. The difference between the threshold temperature TH and the lower boundary temperature TL prevents the compressor from being rapidly cycled between the activated and deactivated states. In one embodiment, the compressor is allowed to be activated as soon as the sensed compressed air temperature TA falls below the upper control temperature TH.

FIG. 3 illustrates a compressor control circuit 40 that controls a compressor 10 in an air supply system 12 based on a temperature of compressed air. The illustrated control circuit 40 includes a controller 42, a temperature sensor 44, and a control valve 47. The temperature sensor 44 is positioned to sense a temperature of the compressed air. The temperature sensor 44 can be positioned at a variety of positions to sense the temperature of compressed air provided by the compressor. In the embodiment illustrated by FIG. 3, the temperature sensor 44 is positioned in the compressor outlet passage 46 to measure the temperature of the compressed air in the outlet port port. Additional examples of locations for the temperature sensor include in the compression chamber 17, in an exhaust port 50, in a line 37 that couples the compressor 10 to the reservoir 16, and in an unloader valve 54 (FIG. 6).

In the exemplary embodiment, the temperature sensor 44 is positioned, such that the temperature sensor is substantially isolated from structures with significant mass, such as the head 13 and the housing 11. Substantially isolating the temperature sensor 44 from the head 13 and the housing 11 provides a more accurate measure of the temperature of the compressed air. If the temperature sensor is thermally coupled to the head 13 or the housing 11, the temperature sensor 44 will sense the temperature of the head or the housing, rather than the temperature of the compressed air. The temperature of the compressed air cannot accurately be correlated from the temperature of the head 13 or the housing 11. The head 13 and the housing 11 have a large thermal mass that heats up or cools down over a substantial period of time. As a result, there is a significant lag in changes in the head or housing temperature due to the changes in the compressed air temperature. In addition, the head and the housing are typically cooled by the engine cooling system. The engine cooling system typically operates to control the temperature of the engine, regardless of the temperature of the compressed air. As a result, head or housing temperature controlled by the engine cooling system is independent of the temperature of the compressed air. As such, an accurate estimate of the compressed air temperature cannot be obtained by measuring the temperature of the head 13 or the housing 11. The temperature sensor 44 senses a temperature of the compressed air and provides a signal that is indicative of the sensed temperature to the controller 42.

Referring to FIG. 3, the illustrated control valve 47 includes an inlet 54 that is coupled to the reservoir 16 and an outlet that is coupled to the unloader 24. The controller 42 controls the control valve 47 to selectively communicate an air signal from the reservoir 16 to the unloader selectively deactivate the compressor 10. For example, the controller may open the control valve to provide the air signal to the unloader when the sensed temperature exceeds the predetermined threshold temperature TH to place the compressor in an unloaded state. The controller may close the control valve when the sensed temperature is below the predetermined threshold temperature to allow the compressor to be placed in a loaded state. In one embodiment, the control valve is a solenoid controlled valve.

In the illustrated embodiment, the path from the reservoir 16, through the control valve 47, to the unloader 24 is parallel to the path from the reservoir 16, through the governor 18, to the unloader. As a result, the control valve 46 may operate to bypass the governor 18 and deactivate the compressor 10 when the sensed compressed air temperature exceeds the predetermined threshold temperature under the control of the controller 42.

In one embodiment, the air compressor 10 is activated when an air pressure PR in the reservoir 16 is less than a predetermined minimum pressure PL and the sensed temperature TA exceeds the threshold temperature TH. In the example illustrated by FIG. 3, a pressure sensor 60 senses the pressure in the reservoir 16. The pressure sensor 60 provides a signal to the controller 42. In this embodiment, the controller 42 deactivates the compressor 10 when the compressed air temperature is above the predetermined threshold temperature and the reservoir pressure is above the predetermined minimum pressure. In this embodiment, the controller 42 does not deactivate the compressor 10 when the compressed air temperature TA is above the predetermined threshold temperature TH and the reservoir pressure PR is below the predetermined minimum pressure. This keeps the pressure in the reservoir from falling below the predetermined minimum pressure PL. The predetermined minimum pressure set by the controller 42 may be different than the predetermined minimum pressure set by the governor 18.

FIG. 4 illustrates a method of controlling an air compressor based on a compressed air temperature and a reservoir pressure. In the method illustrated by FIG. 4, upper and lower compressor control temperatures TH, TL and upper and lower reservoir pressures PH, PL are set 70. For example, the compressor control temperatures and pressures may be read from memory. In the exemplary embodiment, the upper compressor control temperature TH is selected to prevent the formation of carbon and the lower control temperature TL corresponds to an acceptable compressed air temperature. For example, the upper and lower control temperatures TH, TL may be 375 degrees Fahrenheit and 325 degrees Fahrenheit respectively, measured at an outlet 46 of the air compressor 10. The upper compressor control pressure PH may correspond to a safe upper operating pressure of the reservoir and the lower control pressure temperature PL may be selected to ensure that there is enough air in the reservoir to operate the air powered systems. In one embodiment, the state (activated or deactivated) is initially determined or set. The compressor 10 may initially be set 72 to the activated state. After the initial temperature and pressure control values are set, a compressor control loop 74 repeats each time a predetermined time delay elapses. In the compressor control loop, the temperature of air compressed by the air compressor is sensed 76. The pressure of compressed air in the reservoir is sensed 78. The sensed temperature is compared 80 to the upper control temperature TH and the sensed pressure is compared 82, 83 to the lower control pressure PL. The air compressor is activated 84, 85 when the sensed pressure is less than the lower control pressure PL regardless of the sensed temperature. The air compressor is deactivated 86 when the sensed temperature exceeds the upper control temperature TH and the sensed pressure is above the lower control pressure PL. If the temperature TA is less than the upper control temperature TH and the pressure PR is greater than the lower control pressure PL, the pressure PR is compared 87 to the upper control pressure PH. If the pressure PR is greater than the upper control pressure PH, the compressor 10 is deactivated 88. If the pressure PR is less than the upper control pressure PH, the compressor is maintained in its current state (activated or deactivated). The control loop is repeated to control the activation and deactivation of the compressor. In one embodiment, the method illustrated by FIG. 4 is performed by a governor and an electronic controller. In another embodiment, the method illustrated by FIG. 4 is performed by a controller that processes both pressure and temperature signals. In this embodiment, the governor may be eliminated.

In one embodiment of the method illustrated by FIG. 4, once the compressor is deactivated, activation is delayed to prevent rapid cycling between the activated and deactivated states. For example, if the compressor is deactivated due to a sensed elevated compressed air temperature, activation of the compressor may be delayed until the sensed pressure reaches the lower control pressure PL, even though the sensed compressed air temperature may have fallen below the lower control temperature TL.

FIG. 5 is a schematic illustration of a controller 42 that can be used to control the compressor based on a temperature of air compressed by the compressor. For example, the controller could be used to perform the methods illustrated by FIGS. 2 and 4. The controller 42 illustrated in the example of FIG. 5 includes an input 90, memory 92, a processor 94, and an output 96. The input 90 receives compressor air temperature signals 98 and/or reservoir pressure signals 100. The memory 92 stores a compressor control algorithm and predetermined values, such as upper and lower control temperature values and/or upper and lower. Examples of compressor control algorithms are illustrated by FIGS. 2 and 4. The processor 94 applies the compressor control algorithm to the compressor air temperature signals and/or the reservoir pressure signals to produce output signals 102. In the embodiment illustrated by FIG. 6, the output signals 102 are provided from the controller output 96 to the control valve 46 (FIG. 3). Examples of output signals 102 include an air compressor activation signal that causes the compressor to be activated and an air compressor deactivation signal that causes the compressor to be deactivated.

FIG. 5A illustrates another example of a controller 42. The controller 42 includes an input 103 from a thermocouple or other temperature measuring device, a temperature to voltage converter component 105, an input 104 from a pressure transducer or other pressure measuring device and a pressure to voltage converter component 106. The input 103 receives compressor air temperature signals 98. The input 104 receives reservoir pressure signals 100. The temperature to voltage converter component 105 converts compressor air temperature signals to voltage signals 109. The pressure to voltage converter component 106 converts reservoir pressure signals to voltage signals 110. The voltage comparator 107 provides a deactivation signal 111 when voltage signals provided to the voltage comparator by the voltage converters are outside threshold limits.

Referring to FIGS. 6 and 7, in one embodiment the temperature of air compressed by the air compressor 10 is sensed by a temperature sensor 44 mounted in an unloader valve assembly 54 that is in fluid communication with the compression chamber 17. The illustrated unloader valve assembly 54 includes a stationary member 112, a moveable member 114, and a biasing member 116, such as a spring. The biasing member 116 biases the moveable member 114 away from the stationary member and into engagement with a valve seat 118. When the moveable member 114 is in engagement with the valve seat 118, an unloader passage 120 through head 13 is closed and the compressor 10 is in an activated state. An air control signal is selectively communicated to a control port 120 of the unloader valve assembly 54 by the governor and/or the control valve 46. When the air control signal is applied to the unloader valve assembly, the moveable member 114 is forced out of engagement with the valve seat by the air control signal against the force applied by biasing member. When the moveable member 114 is not in engagement with the valve seat 118, the unloader passage 120 is open and the compressor 10 is in a deactivated state.

In the example of FIG. 7, the moveable member 114 includes an opening 122 to a cavity 124. The stationary member 112 extends into the cavity 124. Air is compressed and forced into the cavity 124 and around the fixed member 112. In the example of FIG. 7, the temperature sensor 44 is mounted to the stationary member in the cavity 124. For example, a bore 126 may be provided through the stationary member and the temperature sensor 44 is passed through the bore 126 and positioned at an end 128 of the stationary member. Positioning the temperature sensor 44 in the unloader valve assembly positions the temperature sensor in close proximity to the compression chamber 17 and substantially isolates the temperature sensor from large heat sinking components, such as the housing and the head. This close proximity to the compression chamber and substantial isolation from the head and housing provides an accurate measure of the temperature of the air in the compression chamber. In addition, changes in temperature in the compression chamber are quickly sensed by the temperature sensor 44, due to the close proximity to the compression chamber and isolation from the housing 11 and head 13.

The temperature sensor 44 can be positioned at a variety of other positions to sense the temperature of compressed air provided by the compressor. The temperature sensor 44 may be positioned in the outlet port 46, in the exhaust port, in the compression chamber 17, or in lines 37 that couple the compressor 10 to the reservoir 16, and in an unloader valve 54. In the exemplary embodiment, the temperature sensor is substantially isolated from large heat sinking components, such as the head and the housing. Isolating the temperature sensor 44 from large heat sinking components significantly shortens the time required for changes in the temperature of the compressed air to be sensed by the temperature sensor.

While the invention has been described with reference to specific embodiments, it will be apparent to those skilled in the art that may alternatives, modifications, and variations may be made. Accordingly, the present invention is intended to embrace all such alternatives, modifications, and variations that may fall within the spirit and scope of the appended claims.

Claims

1. A method of controlling an air compressor, comprising:
a) sensing a pressure of compressed air in a reservoir;
b) comparing the sensed pressure of the compressed air in the reservoir with a predetermined threshold pressure;
c) activating the air compressor when the compressed air in the reservoir is less than the threshold pressure;
d) sensing a temperature of air compressed by the air compressor;
e) comparing the sensed temperature of the air compressed by the air compressor with a predetermined threshold temperature; and
f) deactivating the air compressor when the sensed temperature exceeds the threshold temperature and the sensed pressure is above the threshold pressure.
a) sensing a pressure of compressed air in a reservoir;
b) comparing the sensed pressure of the compressed air in the reservoir with a predetermined threshold pressure;
c) activating the air compressor when the compressed air in the reservoir is less than the threshold pressure;
d) sensing a temperature of air compressed by the air compressor;
e) comparing the sensed temperature of the air compressed by the air compressor with a predetermined threshold temperature; and
f) deactivating the air compressor when the sensed temperature exceeds the threshold temperature and the sensed pressure is above the threshold pressure.
2. The method of claim 1 wherein the temperature of the air compressed by the air compressor is sensed in a compressor outlet port.
3. The method of claim 1 wherein the temperature of the air compressed by the air compressor is sensed at a compression chamber.
4. A method for controlling an air compressor, comprising the steps of:
a) receiving a signal indicative of the temperature of air compressed by the air compressor;
b) comparing the temperature to a predetermined threshold temperature value;
c) receiving a signal indicative of the pressure of compressed air in a reservoir;
d) comparing the pressure with a first predetermined threshold pressure value and a second predetermined threshold pressure value; and
e) providing a control signal to deactivate the air compressor in response to the temperature exceeding the predetermined threshold temperature value and the pressure being between the first predetermined threshold pressure value and the second predetermined threshold pressure value.
a) receiving a signal indicative of the temperature of air compressed by the air compressor;
b) comparing the temperature to a predetermined threshold temperature value;
c) receiving a signal indicative of the pressure of compressed air in a reservoir;
d) comparing the pressure with a first predetermined threshold pressure value and a second predetermined threshold pressure value; and
e) providing a control signal to deactivate the air compressor in response to the temperature exceeding the predetermined threshold temperature value and the pressure being between the first predetermined threshold pressure value and the second predetermined threshold pressure value.
5. The method of claim 4 further comprising providing a control signal to activate the air compressor when the pressure is below the first threshold pressure value.
6. The method of claim 4 wherein the temperature is indicative of the temperature of air in a compressor outlet port.
7. The method of claim 4 wherein the temperature is indicative of the temperature of air in a compression chamber.
8. The method of claim 4 wherein the temperature is sensed by a temperature sensor mounted in a compressor unloader valve that is in fluid communication with a compression chamber.
9. The method of claim 4 wherein the threshold temperature value is representative of temperature at a compressor outlet port in a range from about 325 degrees Fahrenheit to about 400 degrees Fahrenheit.
10. The method of claim 4 wherein the threshold temperature value is selected to inhibit carbon formation in the air compressor caused by oil breakdown.
11. A controller for an air compressor comprising:
a) a first input for receiving a temperature signal, the temperature signal indicative of the temperature of air at an outlet of the air compressor;
b) a second input for receiving a pressure signal, the pressure signal indicative of pressure of air in a reservoir;
c) means for comparing the temperature with a predetermined threshold temperature value and the pressure with a first predetermined threshold pressure value and a second predetermined threshold pressure value; and
d) an output for providing an air compressor control signal, wherein the air compressor control signal deactivates the compressor when the temperature exceeds the predetermined threshold temperature value and the pressure is between the first predetermined threshold pressure value and the second predetermined threshold pressure value.
a) a first input for receiving a temperature signal, the temperature signal indicative of the temperature of air at an outlet of the air compressor;
b) a second input for receiving a pressure signal, the pressure signal indicative of pressure of air in a reservoir;
c) means for comparing the temperature with a predetermined threshold temperature value and the pressure with a first predetermined threshold pressure value and a second predetermined threshold pressure value; and
d) an output for providing an air compressor control signal, wherein the air compressor control signal deactivates the compressor when the temperature exceeds the predetermined threshold temperature value and the pressure is between the first predetermined threshold pressure value and the second predetermined threshold pressure value.
12. A controller for an air compressor as in claim 11 wherein the control signal activates the compressor when the pressure is below the first predetermined threshold pressure value.
13. A controller for an air compressor comprising:
a) a first input for receiving a signal indicative of the temperature of air compressed by the air compressor;
b) a second input for receiving a signal indicative of pressure of air in a reservoir;
c) means for deactivating the air compressor in response to the temperature exceeding a predetermined threshold temperature value and the pressure being between a first predetermined threshold pressure value and a second predetermined threshold pressure value.
a) a first input for receiving a signal indicative of the temperature of air compressed by the air compressor;
b) a second input for receiving a signal indicative of pressure of air in a reservoir;
c) means for deactivating the air compressor in response to the temperature exceeding a predetermined threshold temperature value and the pressure being between a first predetermined threshold pressure value and a second predetermined threshold pressure value.
14. A control apparatus for an air compressor, comprising:
a) means for receiving a signal indicative of the temperature of air compressed by the air compressor;
b) means for comparing the temperature of the air compressed by the air compressor with a predetermined threshold temperature value;
c) means for receiving a signal indicative of the pressure of compressed air in a reservoir;
d) means for comparing the pressure of the compressed air in the reservoir with a first predetermined threshold pressure value and a second predetermined threshold pressure value; and
e) means for providing a control signal to unload the air compressor when the temperature exceeds the predetermined threshold temperature value and the pressure is between the first predetermined threshold pressure value and the second predetermined threshold pressure value.
a) means for receiving a signal indicative of the temperature of air compressed by the air compressor;
b) means for comparing the temperature of the air compressed by the air compressor with a predetermined threshold temperature value;
c) means for receiving a signal indicative of the pressure of compressed air in a reservoir;
d) means for comparing the pressure of the compressed air in the reservoir with a first predetermined threshold pressure value and a second predetermined threshold pressure value; and
e) means for providing a control signal to unload the air compressor when the temperature exceeds the predetermined threshold temperature value and the pressure is between the first predetermined threshold pressure value and the second predetermined threshold pressure value.
15. A control apparatus for an air compressor as in claim 14 further comprising means for receiving a signal indicative of the loaded state of the air compressor.
16. A control apparatus for an air compressor as in claim 15 further comprising providing a control signal to load the air compressor when the pressure is below the first predetermined threshold pressure value.
17. The control apparatus of claim 14 wherein the temperature is sensed by a temperature sensor mounted in a compressor unloader valve that is in fluid communication with a compression chamber.
18. The control apparatus of claim 14 wherein the threshold temperature value is representative of temperature at a compressor outlet port in a range from about 325 degrees Fahrenheit to about 400 degrees Fahrenheit.
19. The control apparatus of claim 14 wherein the threshold temperature value is selected to inhibit carbon formation in the air compressor caused by oil breakdown.
20. A method of controlling an air compressor comprising:
a) receiving a signal at a controller indicative of the loaded state of the air compressor;
b) receiving a signal at the controller indicative of a temperature of air compressed by the air compressor;
c) receiving a signal at the controller indicative of a pressure in an associated reservoir; and
d) providing a control signal from the controller to deactivate the air compressor in response to the compressor being in the loaded state, the temperature exceeding a predetermined threshold temperature value, and the pressure being between a first predetermined threshold pressure value and a second predetermined threshold pressure value.
a) receiving a signal at a controller indicative of the loaded state of the air compressor;
b) receiving a signal at the controller indicative of a temperature of air compressed by the air compressor;
c) receiving a signal at the controller indicative of a pressure in an associated reservoir; and
d) providing a control signal from the controller to deactivate the air compressor in response to the compressor being in the loaded state, the temperature exceeding a predetermined threshold temperature value, and the pressure being between a first predetermined threshold pressure value and a second predetermined threshold pressure value.