Compressor and method of controlling compressor

Abstract

A compressor includes an electric motor, a compressor body that is actuated by the electric motor and has a compressor mechanism for discharging compressed air, and a control unit for controlling operation of the electric motor. The control unit stops operation of the electric motor when a discharged pressure from the compressor body reaches a predetermined stop pressure, causes the electric motor to operate when the discharged pressure reaches a predetermined return pressure lower than the stop pressure, and raises the return pressure when an ambient air temperature around the compressor body becomes equal to or lower than a predetermined temperature threshold value.

Description

CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application claims priority from Japanese application JP2025-057883, filed on Mar. 31, 2025, the content of which is hereby incorporated by reference into this application.BACKGROUND OF THE INVENTION1. Field of the Invention

[0002] The present invention relates to a compressor and a method of controlling a compressor.2. DESCRIPTION OF THE RELATED ART

[0003] Among conventional compressors are air compressors that have been well known in the art for producing compressed air for use as power sources for production lines and air sources for machine tools, presses, and air blowers. Another type of conventional compressors is a packaged air compressor including a compressor body and a motor for actuating the compressor body, with a control circuit and a control panel housed together in a package as a space saver.

[0004] There have also been other conventional compressors that include a temperature detector for detecting the temperature of compressed air discharged from a compressor body. Some of these conventional compressors incorporate a control system that performs a forced warming operation mode for preventing a compressor coolant from freezing if the temperature of the discharged compressed air becomes 5° C or lower, for example, and that stops the forced warming operation mode if the temperature of the discharged compressed air rises to 7° C to 8° C or higher, for example.

[0005] For example, Patent Document 1 discloses a configuration in which a controller is connected to a motor for actuating a compressor body and is adapted to be supplied with an input signal from a cold-climate setting switch on a control panel, and a sensor for detecting the temperature of the discharged compressed air is connected to the controller. Patent Document 1 also reveals a configuration in which, when the cold-climate setting switch is turned on, the temperature of the discharged compressed air that is detected by the sensor is input to the controller, and the controller energizes the motor to actuate the compressor body in the forced warming operation mode if the temperature of the discharged compressed air becomes 5 °C or lower, and stops the motor to stop the compressor body being actuated in the forced warming operation mode if the temperature of the discharged compressed air goes beyond 5 °C.

[0006] Patent Document 1: JP-2009-68368-ASUMMARY OF THE INVENTION

[0007] However, the forced warming operation mode that is enabled only for warming the compressor raises issues with electric power consumption. Moreover, since it is determined whether to perform the forced warming operation mode or not by detecting the temperature of the discharged compressed air, the forced warming operation mode is performed only if the temperature of the discharged compressed air becomes 5° C or lower, and the forced warming operation mode may be delayed despite a drop in the temperature of the discharged compressed air.

[0008] If the ambient temperature of the compressor is too low, then its liquid waste may possibly be frozen. When the liquid waste is frozen, it may cause damage to a tank and a drier that are main places where liquid waste occurs. The compressor and its peripheral devices need to be protected even in such circumstances.

[0009] It is an object of the present invention to provide a compressor that restrains liquid waste from being frozen at low temperatures and a method of controlling a compressor.

[0010] In accordance with an aspect of the present invention, there is provided a compressor including an electric motor, a compressor body that is actuated by the electric motor and has a compressor mechanism for discharging compressed air, and a control unit for controlling operation of the electric motor, in which the control unit stops operation of the electric motor when a discharged pressure from the compressor body reaches a predetermined stop pressure, causes the electric motor to operate when the discharged pressure reaches a predetermined return pressure lower than the stop pressure, and raises the return pressure when an ambient air temperature around the compressor body becomes equal to or lower than a predetermined temperature threshold value.

[0011] In accordance with another aspect of the present invention, there is provided a method of controlling a compressor including an electric motor and a compressor body that is actuated by the electric motor and has a compressor mechanism for discharging compressed air, the method including: stopping operation of the electric motor when a discharged pressure from the compressor body reaches a predetermined stop pressure, causing the electric motor to operate when the discharged pressure reaches a predetermined return pressure lower than the stop pressure, and raising the return pressure when an ambient air temperature around the compressor body becomes equal to or lower than a predetermined temperature threshold value.

[0012] According to the present invention, when the ambient air temperature is equal to or lower than the temperature threshold value, the return pressure is raised to quicken the resumption of the operation of the compressor, so that the liquid waste of the compressor can be prevented from freezing by the heat generated by the compressor during its operation.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 is a perspective view illustrating the appearance of a compressor according to a first embodiment of the present invention;

[0014] FIG. 2 is a perspective view illustrating the internal structural details of the compressor according to the first embodiment of the present invention;

[0015] FIG. 3 is a block diagram illustrating the conceptual configuration of the compressor according to the first embodiment of the present invention;

[0016] FIG. 4 is a block diagram illustrating the functions of a control board of the compressor according to the first embodiment of the present invention;

[0017] FIG. 5 is a flowchart of a control process carried out by the control board of the compressor according to the first embodiment of the present invention;

[0018] FIG. 6 is a flowchart of a control process carried out by a control board of a compressor according to a second embodiment of the present invention;

[0019] FIG. 7 is a flowchart of a control process carried out by a control board of a compressor according to a third embodiment of the present invention; and

[0020] FIG. 8 is a flowchart of part of the control process carried out by the control board of the compressor according to the third embodiment of the present invention.DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Compressors and methods of controlling compressors according to first through third embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Note that identical or corresponding parts are denoted by identical or corresponding reference characters throughout views, and their redundant description may be omitted hereinbelow.

[0022] According to each of the following first through third embodiments, as a compression type of a compressor body, there will be described by way of example a packaged scroll compressor including a fixed scroll and an orbiting scroll that are interleaved to define a compressor chamber therebetween for compressing air upon orbiting motion of the orbiting scroll around the center of the fixed scroll. However, the present invention is neither limited to packaged compressors nor to scroll compressors, but is also applicable to other compressors including reciprocating compressors, screw compressors, and turbo compressors. The working fluid to be compressed by the compressors is not limited to air, but may be other gases such as nitrogen, for example.First Embodiment

[0023] A compressor 100 and a method of controlling the compressor 100 according to the first embodiment will be described in detail below with reference to FIGS. 1 through 5.

[0024] First, the overall configuration of the compressor 100 will be described below with reference to FIGS. 1 through 3. FIG. 1 illustrates in perspective the appearance of the compressor 100 according to the first embodiment. FIG. 2 illustrates in perspective the internal structural details of the compressor 100 according to the first embodiment. FIG. 3 illustrates in block form the conceptual configuration of the compressor 100 according to the first embodiment.

[0025] As illustrated in FIGS. 1 and 2, the compressor 100 is a single-stage compressor including a compressor body 103 and an electric motor 104. The compressor 100 has a housing 120 including a front panel that constitutes a part of the housing 120 and is detachably fastened to the other part of the housing 120 by fasteners such as screws. In addition, the compressor 100 includes a control panel 117 mounted on a front side thereof and used for controlling the compressor 100 by a user.

[0026] As illustrated in FIG. 3, the compressor 100 includes the housing 120, a filter 102, the compressor body 103, the electric motor 104, a check valve 105, an aftercooler 106, a tank 107, a drier 108, a switch 110, a control board (control unit) 111 for controlling operation of the electric motor 104, a pressure sensor 112, a magnet switch 113, a compressor body temperature sensor 114, an ambient air temperature sensor 115, and a fan 116.

[0027] The housing 120 is a case that houses the components of the compressor 100. As illustrated in FIG. 2, the housing 120 has a machine compartment 121 and a control compartment 122 that are defined by panels in the housing 120. The machine compartment 121 houses the electric motor 104 and the compressor body 103 therein, and the control compartment 122 houses the control board 111 therein.

[0028] As illustrated in FIG. 3, air 101 that is introduced into the compressor 100 flows through the filter 102 and is supplied to the compressor body 103.

[0029] The compressor body 103 includes a compressor mechanism, not depicted, for compressing the supplied air and discharging the compressed air.

[0030] The electric motor 104 and the compressor body 103 are operatively coupled to each other by an endless belt trained around their pulleys. When the electric motor 104 is energized, power generated by the electric motor 104 is transmitted by the endless belt to the compressor body 103, actuating the compressor body 103 to compress the air supplied thereto. The compressed air is discharged from the compressor body 103 and flows through the check valve 105 and the aftercooler 106 to the tank 107 where it is temporarily stored. The air then flows from the tank 107 through the drier 108 and is supplied as compressed air 109 to a user’s external piece of equipment, not depicted.

[0031] In the compressor 100, the switch 110 of the control panel 117 is used to operate and stop the compressor 100 and operation of the components of the compressor 100 is controlled by the control board 111.

[0032] Moreover, depending on the pressure in the tank 107 that is sensed by the pressure sensor 112, the control board 111 issues a command to the magnet switch 113 to perform intermittent operation control on the compressor body 103.

[0033] In addition, in the compressor 100, the compressor body temperature sensor 114 measures the temperature of a side surface of the compressor body 103 as the temperature of a discharging area thereof, where the compressed air is discharged, and the ambient air temperature sensor 115 measures the temperature of air in the vicinity of an air intake port 118 as an ambient air temperature AT of the compressor 100.

[0034] Furthermore, the control board 111 performs a control process for issuing an alarm and abnormality signal if the ambient air temperature AT of the compressor 100, which is sensed by the ambient air temperature sensor 115, falls outside of a predetermined temperature range set for the compressor 100. The control board 111 also performs a control process for issuing an alarm and abnormality signal to prevent the compressor body 103 from suffering a failure in advance if the difference between the ambient air temperature AT and the temperature of the compressor body 103 sensed by the compressor body temperature sensor 114 exceeds a predetermined threshold value.

[0035] While the compressor 100 is in operation, the temperature sensed by the compressor body temperature sensor 114 is approximately 100° C because the compressed air discharged from the compressor body 103 is of a temperature of approximately 200° C. On the other hand, the temperature sensed by the ambient air temperature sensor 115 represents the temperature of an area where the compressor 100 operates, e.g., a room temperature ranging from 0° C to 40° C, because the ambient air temperature sensor 115 is provided near the air intake port 118.

[0036] The discharged air temperature sensed by the compressor body temperature sensor 114 is not limited to the temperature of the side surface of the compressor body 103. The compressor body temperature sensor 114 may measure the temperature of a component provided between the compressor body 103 and a position immediately before the aftercooler 106 or the temperature of the compressed air anywhere between the compressor body 103 and the aftercooler 106.

[0037] Similarly, the ambient air temperature AT sensed by the ambient air temperature sensor 115 is not limited to the temperature of the air near the air intake port 118. Instead, the ambient air temperature sensor 115 may directly measure the temperature of air outside the housing 120 in the vicinity of the air intake port 118 or the temperature of atmospheric air in the housing 120 at a position other than the air intake port 118. For example, the temperature of atmospheric air in the housing 120 may represent the temperature of air in the space within the housing 120 except the machine compartment 121 that is defined in the housing 120 and houses the electric motor 104 and the compressor body 103, e.g., the temperature of air in the control compartment 122. Stated otherwise, the ambient air temperature AT represents both the temperature of air in the space where the compressor 100 is present, i.e., the temperature of ambient air outside of the housing 120, and the temperature of air within the housing 120 except the machine compartment 121.

[0038] The ambient air temperature AT may not necessarily be measured by the ambient air temperature sensor 115 of the compressor 100. For example, a temperature sensor that is not a component of the compressor 100 may measure the temperature of air in the environment or space where the compressor 100 is installed, and the control board 111 of the compressor 100 may acquire the ambient air temperature AT from that temperature sensor.

[0039] The fan 116 delivers cooling air into the housing 120 to cool the compressor body 103, the drier 108, and other components of the compressor 100. The fan 116 thus functions as a cooling unit for cooling the components of the compressor 100.

[0040] FIG. 4 illustrates in functional block form the control board 111 of the compressor 100 according to the first embodiment.

[0041] As illustrated in FIG. 4, the control board 111 includes as its functional features a pressure controlling section 201, an ambient air temperature determining section 202, a pressure setting determining section 203, a pressure setting changing section 204, a fan operation determining section 205, and a storing section 206.

[0042] The pressure controlling section 201 processes sensor input signals from the pressure sensor 112, the compressor body temperature sensor 114, and the ambient air temperature sensor 115, and issues a command for selectively opening and closing the magnet switch 113 and a command for operating the fan 116.

[0043] The pressure controlling section 201 carries out an operation status flow of the compressor 100 illustrated in FIG. 5 on the basis of the ambient air temperature AT determined by the ambient air temperature determining section 202 and the pressure setting determined by the pressure setting determining section 203, that is, on the basis of the pressure setting changed by the pressure setting changing section 204 and the determination result of the operation of the fan 116 determined by the fan operation determining section 205.

[0044] Specifically, the pressure controlling section 201 of the control board 111 controls the operation of the electric motor 104 on the basis of either a normal operation mode, i.e., a first operation mode, or a low-pressure shifting mode, i.e., a second operation mode.

[0045] The normal operation mode is a mode of operation in which the electric motor 104 operates the compressor 100 until the pressure of the discharged compressed air, i.e., a discharged pressure P, reaches a preset stop pressure (hereinafter, a stop pressure in the normal operation mode will be denoted by “Pmax”), stops operating the compressor 100 when the discharged pressure P becomes equal to the stop pressure Pmax (P = Pmax), and thereafter resumes operating the compressor 100 when the discharged pressure P becomes equal to a return pressure (hereinafter, a return pressure in the normal operation mode will be denoted by “Pu”) (P = Pu).

[0046] The low-pressure shifting mode is similar to the normal operation mode in that the electric motor 104 stops operating the compressor 100 when the discharged pressure P becomes equal to a stop pressure (hereinafter, a stop pressure in the low-pressure shifting mode will be denoted by “P’max”) (P=P’max) and resumes operating the compressor 100 when the discharged pressure P becomes equal to a return pressure (hereinafter, a return pressure in the low-pressure shifting mode will be denoted by “P’u”) (P = P’u). The low-pressure shifting mode is different from the normal operation mode in that, when the low-pressure shifting mode is selected, the stop pressure P’max and the return pressure P’u are lowered from those in the normal operation mode by a shifting pressure Ps, i.e., 0.1Mpa, (P’max = Pmax - Ps, P’u = Pu - Ps). The low-pressure shifting mode is thus able to give a trouble-free energy saving option to the user who has been using the compressor 100 for unnecessarily high compressed air pressures.

[0047] The user can freely select the normal operation mode or the low-pressure shifting mode for operating the compressor 100 using the control panel 117. The mode of operation selected by the user is stored in the storing section 206 of the control board 111.

[0048] The storing section 206 stores beforehand values representing the stop pressure Pmax set in the normal operation mode (hereinafter referred to as a “normal stop pressure Pmax”) and the return pressure Pu set in the normal operation mode (hereinafter referred to as a “normal return pressure Pu”), and a value representing the shifting pressure Ps in the low-pressure shifting mode. The storing section 206 further stores beforehand a value representing a temperature threshold value T to be described later. The values of the normal stop pressure Pmax, the normal return pressure Pu, the shifting pressure Ps, and the temperature threshold value T can be set as desired by the user. Regarding the shifting pressure Ps, although the shifting pressure with regard to the stop pressure and the shifting pressure with regard to the return pressure are identical to each other, i.e., the shifting pressure is common to the stop pressure and the return pressure, as described later, they may be set to values different from each other.

[0049] A control sequence for the compressor 100 according to the present embodiment will be described below with reference to FIG. 5. FIG. 5 is a flowchart of a control process carried out by the control board 111 of the compressor 100 according to the first embodiment. In FIG. 5, though the steps are performed by the various functional features of the control board 111, they will be described below for the sake of brevity as being performed by the control board 111. The stop pressure P’max and the return pressure P’u in the low-pressure shifting mode will also be hereinafter referred to as a “low-pressure stop pressure P’max” and a “low-pressure return pressure P’u,” respectively.

[0050] As illustrated in FIG. 5, the control board 111 starts the control flow in step S301 to start operating the compressor 100 in step S302. Thereafter, the control board 111 determines whether the low-pressure shifting mode is effective or not in step S303. If the control board 111 determines that the low-pressure shifting mode is effective in step S303 (Yes), then the processing goes to step S305. If the control board 111 determines that the low-pressure shifting mode is not effective, then the processing goes to step S304, bringing the processing to an end.

[0051] If the control board 111 determines that the low-pressure shifting mode is effective in the determination of whether the low-pressure shifting mode is effective in step S303 (Yes), then the control board 111 enters the low-pressure shifting mode control.

[0052] In the low-pressure shifting mode control, the control board 111 sets the low-pressure stop pressure P’max to a value that is lowered from the normal stop pressure Pmax by the shifting pressure Ps, in step S305, and then sets the low-pressure return pressure P’u to a value that is lowered from the normal return pressure Pu by the shifting pressure Ps, in step S306.

[0053] Thereafter, the control board 111 performs a looping process in step S307 for liquid waste freezing prevention control using the low-pressure stop pressure P’max set in step S305 and the low-pressure return pressure P’u set in step S306. According to the present embodiment, the liquid waste freezing prevention control looping process described herein covers not only a process of completely preventing liquid waste from freezing, but also a process of minimizing liquid waste freezing, e.g., making liquid waste less likely to freeze or reducing the degree to which liquid waste freezes.

[0054] In the liquid waste freezing prevention control looping process, the control board 111 compares the ambient air temperature AT of the compressor 100 with the temperature threshold value T, e.g., 5°C, in step S308. If the ambient air temperature AT is equal to or lower than the temperature threshold value T in step S308 (Yes), then the control flow goes to step S309. If the ambient air temperature AT is higher than the temperature threshold value T in step S308 (No), then the control flow goes to step S312.

[0055] If the ambient air temperature AT is equal to or lower than 5° C of the temperature threshold value T, then the control board 111 sets an ambient air temperature drop flag F in step S309. Then, the control board 111 sets the low-pressure stop pressure P’max to be returned from the value that is changed to be lowered by the shifting pressure Ps, to the normal stop pressure Pmax in step S310, and then sets the low-pressure return pressure P’u to be returned from the value that is changed to be lowered by the shifting pressure Ps, to the normal return pressure Pu in step S311. Then, the control flow goes to step S312.

[0056] In step S312, the control board 111 determines whether the ambient air temperature drop flag F has been set or not. If it is determined that the ambient air temperature drop flag F has been set in step S312 (Yes), then the control board 111 performs the ambient air temperature determination in step S313. If it is determined that the ambient air temperature drop flag F has not been set in step S312 (No), then the control flow goes to step S317, bypassing the ambient air temperature determination in step S313.

[0057] In the ambient air temperature determination in step S313, the control board 111 compares the ambient air temperature AT with a deletion threshold value Td, e.g., 10° C, that has been preset in order to determine whether to delete the ambient air temperature drop flag F or not. The value of 10° C as the deletion threshold value Td represents a numerical value used by way of example to prevent chattering due to the setting changes for the low-pressure stop pressure P’max and the low-pressure return pressure P’u owing to the comparison between the ambient air temperature AT and the temperature threshold value T. The deletion threshold value Td may be other values as long as they are effective in preventing chattering.

[0058] If the ambient air temperature AT is equal to or higher than the deletion threshold value Td in step S313 (Yes), then the control board 111 deletes the ambient air temperature drop flag F in step S314. Then, the control board 111 sets the low-pressure stop pressure P’max to a value that is lowered from the normal stop pressure Pmax by the shifting pressure Ps, in step S315. Then, the control board 111 sets the low-pressure return pressure P’u to a value that is lowered from the normal return pressure Pu by the shifting pressure Ps, in step S316. Thereafter, the control flow goes to step S317.

[0059] If the ambient air temperature AT is lower than the deletion threshold value Td in step S313 (No), then the control flow goes to step S317, skipping steps S314, S315, and S136.

[0060] During the liquid waste freezing prevention control looping process in step S307, the user may terminate the low-pressure shifting mode. In step S317, during the liquid waste freezing prevention control looping process, the control board 111 confirms whether it has received a signal for terminating the low-pressure shifting mode from the user or not by determining whether the low-pressure shifting mode is ineffective or not.

[0061] If the control board 111 determines that the low-pressure shifting mode is ineffective in step S317 (Yes), then the control flow leaves the liquid waste freezing prevention control looping process in step S317 and goes to step S319. In step S319, the control board 111 sets the low-pressure stop pressure P’max to be returned from the value that is changed to be lowered by the shifting pressure Ps, to the normal stop pressure Pmax. Then, in step S320, the control board 111 sets the low-pressure return pressure P’u to be returned from the value that is changed to be lowered by the shifting pressure Ps, to the normal return pressure Pu. As the low-pressure shifting mode is terminated, the control flow goes to step S304 and comes to an end.

[0062] If the control board 111 determined that the low-pressure shifting mode is effective in step S317 (No), then the control flow goes to step S318 in which the liquid waste freezing prevention control looping process repeats the processing from step S307.

[0063] The control board 111 controls the operation of the electric motor 104 in the manner described above.

[0064] According to the present embodiment, when the ambient air temperature AT is lowered, i.e., when the ambient air temperature drop flag F is set, the low-pressure return pressure P’u is set so as to be returned from the value that is lowered by the shifting pressure Ps, to the normal return pressure Pu. Similarly, the low-pressure stop pressure P’max is returned from the value that is lowered by the shifting pressure Ps, to the normal stop pressure Pmax.

[0065] However, when the ambient air temperature AT is lowered, it is enough for the control board 111 to least raise the low-pressure return pressure P’u and the low-pressure stop pressure P’max, and the control board 111 may not necessarily need to return the low-pressure return pressure P’u and the low-pressure stop pressure P’max to the normal return pressure Pu and the normal stop pressure Pmax, respectively. Stated otherwise, when the ambient air temperature AT is lowered in the low-pressure shifting mode control, although it is desirable for the control board 111 to return the low-pressure return pressure P’u and the low-pressure stop pressure P’max to the normal return pressure Pu and the normal stop pressure Pmax, respectively, it may be enough for the control board 111 to raise the low-pressure return pressure P’u and the low-pressure stop pressure P’max closer to the normal return pressure Pu and the normal stop pressure Pmax, respectively. Furthermore, when the ambient air temperature AT is lowered, it is desirable for the control board 111 not to raise the low-pressure return pressure P’u and the low-pressure stop pressure P’max beyond the normal return pressure Pu and the normal stop pressure Pmax, respectively.

[0066] The first embodiment described above offers the following advantages:

[0067] In this embodiment, when the ambient air temperature AT is low, the low-pressure shifting mode to be performed for energy saving is canceled, and the low-pressure return pressure P’u and the low-pressure stop pressure P’max are set to values raised to the normal return pressure Pu and the normal stop pressure Pmax, respectively. This delays the timing to stop the operation of the compressor 100 and quickens the timing to resume operating the compressor 100, thereby preventing its liquid waste from freezing with the heat generated by the compressor 100 while in operation. Consequently, the first embodiment is effective to perform energy saving and liquid waste freezing prevention appropriately depending on the situation in which the compressor 100 operates.

[0068] Moreover, according to the control in the present embodiment, the low-pressure stop pressure P’max and the low-pressure return pressure P’u are changed to delay the timing to stop the compressor 100 or quicken the timing to resume operating the compressor 100, and the compressor 100 is not forcibly warmed up separately from its normal operation. It is therefore possible to minimize electric power consumption of the compressor 100 while keeping the compressor 100 warmed up, i.e., preventing the compressor 100 from freezing its liquid waste. The liquid waste of the compressor 100 is frozen when the ambient air temperature At is lowered. In a low-temperature environment, the temperature of the compressed air discharged from the compressor 100 is usually higher than the ambient air temperature AT. Since the control process performed by the control board 111 according to the present embodiment is carried out on the basis of the ambient air temperature AT, the compressor 100 can be warmed up earlier than it is carried out on the basis of the temperature of the compressed air discharged from the compressor 100, making it more effective to prevent the liquid waste of the compressor 100 from freezing.Second Embodiment

[0069] A compressor 100 and a method of controlling the compressor 100 according to the second embodiment of the present invention will be described in detail below.

[0070] The second embodiment is different from the first embodiment with respect to the manner in which the low-pressure stop pressure P’max and the low-pressure return pressure P’u are set.

[0071] FIG. 6 is a flowchart of a control process carried out by the control board 111 of the compressor 100 according to the second embodiment.

[0072] According to the second embodiment, as illustrated in FIG. 6, the processing after the control board 111 has set the ambient air temperature drop flag F in step S309 is different from that according to the first embodiment. Steps S301 through S309 and steps S312 through S320 illustrated in FIG. 6 according to the second embodiment are the same as those illustrated in FIG. 5 according to the first embodiment, and will be omitted from detailed description.

[0073] After having set an ambient air temperature drop flag F in step S309, the control board 111 determines whether the difference between the low-pressure stop pressure P’max and the normal return pressure Pu is smaller than a predetermined differential threshold value, e.g., 0.1 Mpa, or not in step S401. If the difference is equal to or larger than 0.1 Mpa, then the control board 111 sets the low-pressure return pressure P’u to be returned from the value that is lowered by the shifting pressure Ps, to the normal return pressure Pu in step S402. If the difference is smaller than 0.1 Mpa, then the control board 111 sets the low-pressure return pressure P’u to the value obtained by subtracting 0.1 Mpa from the low-pressure stop pressure P’max, in step S403.

[0074] After step S402 or step S403 is carried out, the control flow goes to step S312. The processing from step S312 is the same as that according to the first embodiment.

[0075] According to the second embodiment, when the ambient air temperature AT is lowered, only the low-pressure return pressure P’u is changed, and the low-pressure stop pressure P’max is not changed. This makes it possible to prevent the liquid waste from freezing while stabilizing the pressure supplied from the compressor 100 to the user’s external piece of equipment. In other words, when the ambient air temperature AT is lowered, the liquid waste is prevented from freezing by changing or setting at least the low-pressure return pressure P’u so as to be larger than the present setting.

[0076] According to the second embodiment, moreover, the differential threshold value may be established in consideration of the components of the compressor 100 and another apparatus that affects the compressor 100, e.g., the user’s external piece of equipment to be supplied with the compressed air from the compressor 100. For example, the differential threshold value may be set to such a value, i.e., 0.1 Mpa, that does not make the load on the compressor 100 large when the magnet switch 113 for intermittently operating the compressor 100 is frequently turned on and off.

[0077] The second embodiment described above offers the same advantages as the first embodiment.Third Embodiment

[0078] A compressor 100 and a method of controlling the compressor 100 according to the third embodiment will be described in detail below.

[0079] FIGS. 7 and 8 are flowcharts of a control process carried out by the control board 111 of the compressor 100 according to the third embodiment.

[0080] According to the third embodiment, as illustrated in FIGS. 7 and 8, the liquid waste freezing prevention control looping process is different from that according to the first embodiment. Steps S301 through S304 and steps S317 through S320 illustrated in FIG. 7 according to the third embodiment are the same as those according to the first embodiment, and will be omitted from detailed description.

[0081] According to the third embodiment, a first temperature threshold value T1, a second temperature threshold value T2, and a third temperature threshold value T3 are established as temperature threshold values. The first temperature threshold value T1, the second temperature threshold value T2, and the third temperature threshold value T3 are progressively smaller in the order named (T1> T2> T3). The second temperature threshold value T2 corresponds to a “first determination threshold value” referred to in the claims, whereas the third temperature threshold value T3 corresponds to a “second determination threshold value” referred to in the claims.

[0082] As illustrated in FIG. 7, when the liquid waste freezing prevention control looping process is carried out in step S307, the control substrate 111 compares the ambient air temperature AT with the first temperature threshold value T1, e.g., 10° C, to perform the ambient air temperature determination in step S501. If the ambient air temperature AT is higher than the first temperature threshold value T1 in step S501 (No), then the control flow goes to step S512. The processing branching from step S512 will be described later.

[0083] If the ambient air temperature AT is equal to or lower than the first temperature threshold value T1 in step S501 (Yes), then the control board 111 sets a first ambient air temperature drop flag F1 in step S502, which is followed by step S503.

[0084] In step S503, the control substrate 111 compares the ambient air temperature AT with the second temperature threshold value T2, e.g., 7° C, to perform the ambient air temperature determination. If the ambient air temperature AT is higher than the second temperature threshold value T2 in step S503 (No), then the control board 111 turns off the fan 116 in step S504. Then, the control flow goes to step S512.

[0085] If the ambient air temperature AT is equal to or lower than the second temperature threshold value T2 in step S503 (Yes), then the control board 111 sets a second ambient air temperature drop flag F2 in step S505, which is followed by step S506.

[0086] In step S506, the control substrate 111 compares the ambient air temperature AT with the third temperature threshold value T2, e.g., 5°C, to perform the ambient air temperature determination. If the ambient air temperature AT is higher than the third temperature threshold value T3 in step S506 (No), then the control board 111 sets the low-pressure stop pressure P’max to a value obtained by subtracting one half of the shifting pressure Ps from the normal stop pressure Pmax (P’max = Pmax - (Ps / 2)), in step S507. Then, the control board 111 sets the low-pressure return pressure P’u to a value obtained by subtracting one half of the shifting pressure Ps from the normal return pressure Pu (P’u = Pu - (Ps / 2)), in step S508. After step S508, the control flow goes to step S512.

[0087] If the ambient air temperature AT is equal to or lower than the third temperature threshold value T3 in step S506 (Yes), then the control board 111 sets a third ambient air temperature drop flag F3 in step S509. Then, the control board 111 sets the low-pressure stop pressure P’max to the normal stop pressure Pmax in step S510. Then, the control board 111 sets the low-pressure return pressure P’u to the normal return pressure Pu in step S511. After step S511, the control flow goes to step S512.

[0088] In step S512, the control board 111 determines whether the first ambient air temperature drop flag F1 has been set or not. If it is determined that the first ambient air temperature drop flag F1 has been set in step S512 (Yes), then the control board 111 determines whether the second ambient air temperature drop flag F2 has been set or not in step S513 (see FIG. 8). If it is determined that the first ambient air temperature drop flag F1 has not been set in step S512 (No), then the control flow goes to step S317 for determining whether the low-pressure shifting mode is ineffective or not.

[0089] As illustrated in FIG. 8, if it is determined that the second ambient air temperature drop flag F2 has been set in step S513 (Yes), then the control board 111 determines whether the third ambient air temperature drop flag F3 has been set or not in step S517. If it is determined that the second ambient air temperature drop flag F2 has not been set in step S513 (No), then the control board 111 compares the ambient air temperature AT with a first flag deletion threshold value Td1, e.g., 13° C, to perform the ambient air temperature determination in step S514. The first flag deletion threshold value Td1 is a threshold value for deleting the first ambient air temperature drop flag F1, and is set to a value larger than the first temperature threshold value T1 (Td1 > T1).

[0090] If it is determined that the ambient air temperature AT is equal to or higher than the first flag deletion threshold value Td1 in step S514 (Yes), then the control board 111 deletes the first ambient air temperature drop flag F1 in step S515 and operates the fan in step S516. If the ambient air temperature AT is lower than the first flag deletion threshold value Td1, then the control flow jumps to step S317 (see FIG. 7), bypassing steps S515 and S516.

[0091] If it is determined that the third ambient air temperature drop flag F3 has been set in step S517 (Yes), then the control flow goes to step S522. If it is determined that the third ambient air temperature drop flag F3 has not been set in step S517 (No), then the control flow goes to step S518.

[0092] In step S518, the control board 111 compares the ambient air temperature AT with a second flag deletion threshold value Td2, e.g., 10° C, to perform the ambient air temperature determination. The second flag deletion threshold value Td2 is a threshold value for deleting the second ambient air temperature drop flag F2, and is set to a value larger than the second temperature threshold value T2 (Td2 > T2).

[0093] If it is determined that the ambient air temperature AT is equal to or higher than the second flag deletion threshold value Td2 in step S518 (Yes), then the control board 111 deletes the second ambient air temperature drop flag F2 in step S519. Then, the control board 111 sets the low-pressure stop pressure P’max to a value obtained by subtracting the shifting pressure Ps from the normal stop pressure Pmax, in step S520. Then, the control board 111 sets the low-pressure return pressure P’u to a value obtained by subtracting the shifting pressure Ps from the normal return pressure Pu, in step S521. If it is determined that the ambient air temperature AT is lower than the second flag deletion threshold value Td2 in step S518 (No), then the control flow jumps to step S317 (see FIG. 7), bypassing steps S519, S520, and S521.

[0094] In step S522, the control board 111 compares the ambient air temperature AT with a third flag deletion threshold value Td3, e.g., 8° C, to perform the ambient air temperature determination. The third flag deletion threshold value Td3 is a threshold value for deleting the third ambient air temperature drop flag F3, and is set to a value larger than the third temperature threshold value T3 (Td3> T3).

[0095] If it is determined that the ambient air temperature AT is equal to or higher than the third flag deletion threshold value Td3 in step S522 (Yes), then the control board 111 deletes the third ambient air temperature drop flag F3 in step S523. Then, the control board 111 sets the low-pressure stop pressure P’max to a value obtained by subtracting one half of the shifting pressure Ps from the normal stop pressure Pmax (P’max = Pmax - (Ps / 2)), in step S524. Then, the control board 111 sets the low-pressure return pressure P’u to a value obtained by subtracting one half of the shifting pressure Ps from the normal return pressure Pu (P’u = Pu - (Ps / 2)), in step S525. If it is determined that the ambient air temperature AT is lower than the third flag deletion threshold value Td3 in step S522 (No), then the control flow jumps to step S317 (see FIG. 7), bypassing steps S523, S524, and S525.

[0096] The processing from step S317 is the same as that according to the first embodiment.

[0097] According to the third embodiment, a drop in the ambient air temperature AT is determined stepwise in different stages based on the three temperature threshold values T1, T2, and T3, and the fan 116 is turned off and the setting of the stop pressure and the setting of the return pressure are changed by shifting amounts depending on the respective stages. A drop in the temperature in the compressor body 103 and hence the housing 210 is restrained when the fan 116 is turned off, and therefore, this is effective in preventing the liquid waste from freezing.

[0098] More specifically, when the ambient air temperature AT is equal to or lower than the second temperature threshold value T2 and higher than the third temperature threshold value T3, the low-pressure stop pressure and the low-pressure return pressure are set to respective values that are lowered by one half of the shifting pressure Ps, i.e., shifting amount of Ps / 2, from the normal stop pressure and the normal return pressure from values that are lowered by the shifting pressure Ps. When the ambient air temperature AT is equal to or lower than the third temperature threshold value T3, the low-pressure stop pressure and the low-pressure return pressure are set to be returned to the normal stop pressure and the normal return pressure from values that are lowered by the shifting pressure Ps, i.e., shifting amount of Ps. A value representing one half of the shifting pressure Ps corresponds to the “first shifting amount” referred to in the claims and a value representing the shifting pressure Ps corresponds to the “second shifting amount” referred to in the claims.

[0099] According to the third embodiment, the liquid waste is prevented from freezing by performing a process for imposing stepwise pressure limitations depending on the ambient air temperature AT. According to the third embodiment, therefore, the liquid waste is prevented from freezing while achieving a higher energy saving capability in the low-pressure shifting mode.

[0100] The third embodiment described above offers the same advantages as the first embodiment.

[0101] The present invention also covers various modifications to be described below. According to the present invention, it is possible to combine configurational and functional details of the modifications and configurational and functional details of the embodiments, combine configurational and functional details of different ones of the embodiments, and combine configurational and functional details of different ones of the modifications. According to the present invention, it is also possible to add other configurational and functional details to some of the configurational and functional details of the embodiments, delete some of the configurational and functional details of the embodiments, and replace some of the configurational and functional details of the embodiments with other configurational and functional details.First Modification

[0102] In the case where the compressor 100 includes a plurality of compressor bodies 103, it is possible to perform the control to set a stop pressure and a return pressure for each of the compressors body 103 when the ambient air temperature AT drops. This makes it possible to prevent the liquid waste from freezing while achieving an energy saving capability in the low-pressure shifting mode.<Second Modification>

[0103] According to each of the above modifications, the liquid waste freezing prevention control is performed while in the low-pressure shifting mode. However, the present invention is not limited to such a feature. Stated otherwise, the liquid waste freezing prevention control is not necessarily applicable to only the compressor 100 whose control board 111 is configured to be capable of executing the low-pressure shifting mode.

[0104] For example, the liquid waste freezing prevention control may be performed while in the normal operation mode. In this case, when the ambient air temperature AT is equal to or higher than a predetermined threshold value, at least the return pressure is set to a higher pressure level, i.e., raised to a higher pressure level, to prevent the liquid waste from freezing. As with each of the above embodiments, in addition to increasing the return pressure, the stop pressure may also be set to a higher pressure level, i.e., raised to a higher pressure level, to make it more effective to prevent the liquid waste from freezing.Third Modification

[0105] According to the second embodiment described above, when the ambient air temperature AT is lowered, only the return pressure is changed, and the stop pressure is not changed. However, when the ambient air temperature AT is lowered, only the stop pressure may be changed, and the return pressure may not be changed. At least either the return pressure or the stop pressure may be raised when the ambient air temperature AT is lowered, and therefore, this is effective in preventing the liquid waste from freezing.Fourth Modification

[0106] According to the third embodiment, the fan 116 is turned off in a state where the first ambient air temperature drop flag F1 is set and the second ambient air temperature drop flag F2 is not set. Providing the compressor 100 includes a cooling unit other than the fan 116, however, the cooling unit may be de-energized instead of turning off the fan 116 or in addition to turning off the fan 116. The cooling unit has a function to cool the components of the compressor 100 including the housing 120 or the interior of the housing 120. For example, if the compressor 100 has a cooling jacket for cooling the compressor body 103 and / or a cooler having a Peltier device as the cooling unit, then the cooling unit may be turned off.Other Modifications

[0107] The embodiments described above are illustrated by way of example only for an easier understanding of the present invention, and should not be construed as limiting the scope of invention. Various other components or elements may be added to the embodiments, and some of the components or elements of the embodiments may be deleted or replaced with other components or elements without departing from the scope of the invention.

[0108] The various functional sections described above in the embodiments may be hardware-implemented by circuits, and the circuits may be dedicated circuits for performing certain functions or general-purpose circuits such as processors.

[0109] At least a portion of the processing according to each of the above embodiments may be implemented by a general-purpose computer as a basic piece of hardware. Programs for performing the processing may be stored in a storage medium readable by the computer. The programs are stored in the storage medium as files that can be installed in or executed by the computer. The storage medium may be in the form of a magnetic disk, an optical disk such as a CD-ROM, a CD-R, or a DVD, a magneto-optical disk (MO), or a semiconductor memory. The storage medium may be any one of these memories as long as it can store programs and it can be read by the computer. Alternatively, the programs for performing the above processing may be stored in a computer as a server connected to a network such as the Internet and downloaded via the network to a computer as a client.

[0110] The configurational and functional details and advantages of the embodiments of the present invention will be summarized as follows:

[0111] (1) The compressor 100 includes the electric motor 104, the compressor body 103 that is actuated by the electric motor 104 and has the compressor mechanism for discharging compressed air, and the control board 111 for controlling operation of the electric motor 104. The control board 111 stops the operation of the electric motor 104 when a discharged pressure P from the compressor body 103 reaches a predetermined stop pressure, causes the electric motor 104 to operate when the discharged pressure P reaches a predetermined return pressure lower than the stop pressure, and raises the return pressure when an ambient air temperature AT around the compressor body 103 becomes equal to or lower than a predetermined temperature threshold value.

[0112] With the compressor 100, when the ambient air temperature AT is equal to or lower than the temperature threshold value, the control board 111 increases the return pressure but does no change the stop pressure.

[0113] The method of controlling the compressor 100 includes stopping the operation of the electric motor 104 when the discharged pressure P from the compressor body 103 reaches the predetermined stop pressure, causing the electric motor 104 to operate when the discharged pressure P reaches the predetermined return pressure lower than the stop pressure, and raising the return pressure when the ambient air temperature AT around the compressor body 103 becomes equal to or lower than the predetermined temperature threshold value.

[0114] Moreover, the method of controlling the compressor 100 includes raising the return pressure but not changing the stop pressure when the ambient air temperature AT is equal to or lower than the temperature threshold value.

[0115] With this configuration, when the ambient air temperature AT is lowered, the timing to resume operating the compressor 100 is quickened by increasing the return pressure. This warms up the compressor 100, preventing its liquid waste from freezing.

[0116] Furthermore, since the compressor 100 is not forcibly warmed up separately from its normal operation, it is possible to minimize electric power consumption of the compressor 100 while preventing the compressor 100 from freezing its liquid waste. In addition, as the compressor 100 is controlled on the basis of the ambient air temperature AT, the compressor 100 can be warmed up earlier than it is controlled on the basis of the temperature of the compressed air discharged from the compressor 100, making it more effective to prevent the liquid waste of the compressor 100 from freezing.

[0117] (2) Furthermore, with the compressor 100, the control board 111 is configured to be capable of executing the low-pressure shifting mode for shifting the stop pressure and the return pressure toward lower pressures by predetermined pressures, raises the stop pressure and the return pressure when the ambient air temperature AT around the compressor body 103 becomes equal to or lower than the predetermined temperature threshold value, and raises the stop pressure and the return pressure to return to respective values that are values before they are shifted, when the ambient air temperature AT becomes equal to or lower than the temperature threshold value while the electric motor 104 is being controlled in the low-pressure shifting mode.

[0118] Moreover, the method of controlling the compressor 100 includes carrying out the low-pressure shifting mode for shifting the stop pressure and the return pressure toward lower pressures by predetermined pressures, raising the stop pressure and the return pressure when the ambient air temperature AT around the compressor body 103 becomes equal to or lower than the predetermined temperature threshold value, and raising the stop pressure and the return pressure to return to respective values that are values before they are shifted, when the ambient air temperature AT around the compressor 103 becomes equal to or lower than the temperature threshold value while the electric motor 104 is being controlled in the low-pressure shifting mode.

[0119] With this configuration, when the ambient air temperature AT is low, the low-pressure shifting mode control carried out for energy saving is canceled, and the low-pressure stop pressure P’max and the low-pressure return pressure P’u are set to values raised respectively to the normal stop pressure Pmax and the normal return pressure Pu. The capabilities of energy saving and liquid waste freezing prevention are thus appropriately performed depending on the situation.

[0120] (3) Furthermore, with the compressor 100, the temperature threshold values include the second temperature threshold value T2 and the third temperature threshold value T3, and the control board 111 raises the low-pressure return pressure P’u by the value represented by one half of the shifting pressure Ps as the first shifting amount when the ambient air temperature AT is equal to or lower than the second temperature threshold value T2 and higher than the third temperature threshold value T3, and raises the low-pressure return pressure P’u by the value represented by the shifting pressure Ps as the second shifting amount larger than the first shifting amount when the ambient air temperature AT is equal to or lower than the third temperature threshold value T3.

[0121] According to the method of controlling the compressor 100, furthermore, the temperature threshold values include the second temperature threshold value T2 and the third temperature threshold value T3, and the method raises the low-pressure return pressure P’u by the value represented by one half of the shifting pressure Ps as the first shifting amount when the ambient air temperature AT is equal to or lower than the second temperature threshold value T2 and higher than the third temperature threshold value T3, and raises the low-pressure return pressure P’u by the value represented by the shifting pressure Ps as the second shifting amount larger than the first shifting amount when the ambient air temperature AT is equal to or lower than the third temperature threshold value T3.

[0122] With this configuration, the liquid waste is prevented from freezing by performing a process for imposing stepwise pressure limitations depending on the ambient air temperature AT. Therefore, the liquid waste is prevented from freezing while achieving a higher energy saving capability in the low-pressure shifting mode.

[0123] (4) Moreover, the compressor 100 includes the fan 116 for cooling the components of the compressor 100, and the control board 111 turns off the fan 116 when the ambient air temperature AT becomes equal to or lower than the temperature threshold value T.

[0124] The method of controlling the compressor 100 turns off the fan 116 when the ambient air temperature AT becomes equal to or lower than the temperature threshold value T.

[0125] With these configurations, when the ambient air temperature AT drops, the fan 116 is turned off to prevent the liquid waste from freezing.

[0126] While the embodiments of the present invention have been described above, the embodiments are only illustrative of some of possible applications of the present invention and should not be interpreted as limiting the scope of the invention to the specific configurations of the embodiments.DESCRIPTION OF REFERENCE CHARACTERS

[0127] 100: compressor

[0128] 103: compressor body

[0129] 104: electric motor

[0130] 111: control board (control unit)

[0131] 116: fan (cooling unit)

Examples

first embodiment

[0023]A compressor 100 and a method of controlling the compressor 100 according to the first embodiment will be described in detail below with reference to FIGS. 1 through 5.

[0024]First, the overall configuration of the compressor 100 will be described below with reference to FIGS. 1 through 3. FIG. 1 illustrates in perspective the appearance of the compressor 100 according to the first embodiment. FIG. 2 illustrates in perspective the internal structural details of the compressor 100 according to the first embodiment. FIG. 3 illustrates in block form the conceptual configuration of the compressor 100 according to the first embodiment.

[0025]As illustrated in FIGS. 1 and 2, the compressor 100 is a single-stage compressor including a compressor body 103 and an electric motor 104. The compressor 100 has a housing 120 including a front panel that constitutes a part of the housing 120 and is detachably fastened to the other part of the housing 120 by fasteners such as screws. In addition...

second embodiment

[0069]A compressor 100 and a method of controlling the compressor 100 according to the second embodiment of the present invention will be described in detail below.

[0070]The second embodiment is different from the first embodiment with respect to the manner in which the low-pressure stop pressure P’max and the low-pressure return pressure P’u are set.

[0071]FIG. 6 is a flowchart of a control process carried out by the control board 111 of the compressor 100 according to the second embodiment.

[0072]According to the second embodiment, as illustrated in FIG. 6, the processing after the control board 111 has set the ambient air temperature drop flag F in step S309 is different from that according to the first embodiment. Steps S301 through S309 and steps S312 through S320 illustrated in FIG. 6 according to the second embodiment are the same as those illustrated in FIG. 5 according to the first embodiment, and will be omitted from detailed description.

[0073]After having set an ambient air...

third embodiment

[0078]A compressor 100 and a method of controlling the compressor 100 according to the third embodiment will be described in detail below.

[0079]FIGS. 7 and 8 are flowcharts of a control process carried out by the control board 111 of the compressor 100 according to the third embodiment.

[0080]According to the third embodiment, as illustrated in FIGS. 7 and 8, the liquid waste freezing prevention control looping process is different from that according to the first embodiment. Steps S301 through S304 and steps S317 through S320 illustrated in FIG. 7 according to the third embodiment are the same as those according to the first embodiment, and will be omitted from detailed description.

[0081]According to the third embodiment, a first temperature threshold value T1, a second temperature threshold value T2, and a third temperature threshold value T3 are established as temperature threshold values. The first temperature threshold value T1, the second temperature threshold value T2, and the...

CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application claims priority from Japanese application JP2025-057883, filed on Mar. 31, 2025, the content of which is hereby incorporated by reference into this application.BACKGROUND OF THE INVENTION1. Field of the Invention

[0002] The present invention relates to a compressor and a method of controlling a compressor.2. DESCRIPTION OF THE RELATED ART

[0003] Among conventional compressors are air compressors that have been well known in the art for producing compressed air for use as power sources for production lines and air sources for machine tools, presses, and air blowers. Another type of conventional compressors is a packaged air compressor including a compressor body and a motor for actuating the compressor body, with a control circuit and a control panel housed together in a package as a space saver.

[0004] There have also been other conventional compressors that include a temperature detector for detecting the temperature of compressed air discharged from a compressor body. Some of these conventional compressors incorporate a control system that performs a forced warming operation mode for preventing a compressor coolant from freezing if the temperature of the discharged compressed air becomes 5° C or lower, for example, and that stops the forced warming operation mode if the temperature of the discharged compressed air rises to 7° C to 8° C or higher, for example.

[0005] For example, Patent Document 1 discloses a configuration in which a controller is connected to a motor for actuating a compressor body and is adapted to be supplied with an input signal from a cold-climate setting switch on a control panel, and a sensor for detecting the temperature of the discharged compressed air is connected to the controller. Patent Document 1 also reveals a configuration in which, when the cold-climate setting switch is turned on, the temperature of the discharged compressed air that is detected by the sensor is input to the controller, and the controller energizes the motor to actuate the compressor body in the forced warming operation mode if the temperature of the discharged compressed air becomes 5 °C or lower, and stops the motor to stop the compressor body being actuated in the forced warming operation mode if the temperature of the discharged compressed air goes beyond 5 °C.

[0006] Patent Document 1: JP-2009-68368-ASUMMARY OF THE INVENTION

[0007] However, the forced warming operation mode that is enabled only for warming the compressor raises issues with electric power consumption. Moreover, since it is determined whether to perform the forced warming operation mode or not by detecting the temperature of the discharged compressed air, the forced warming operation mode is performed only if the temperature of the discharged compressed air becomes 5° C or lower, and the forced warming operation mode may be delayed despite a drop in the temperature of the discharged compressed air.

[0008] If the ambient temperature of the compressor is too low, then its liquid waste may possibly be frozen. When the liquid waste is frozen, it may cause damage to a tank and a drier that are main places where liquid waste occurs. The compressor and its peripheral devices need to be protected even in such circumstances.

[0009] It is an object of the present invention to provide a compressor that restrains liquid waste from being frozen at low temperatures and a method of controlling a compressor.

[0010] In accordance with an aspect of the present invention, there is provided a compressor including an electric motor, a compressor body that is actuated by the electric motor and has a compressor mechanism for discharging compressed air, and a control unit for controlling operation of the electric motor, in which the control unit stops operation of the electric motor when a discharged pressure from the compressor body reaches a predetermined stop pressure, causes the electric motor to operate when the discharged pressure reaches a predetermined return pressure lower than the stop pressure, and raises the return pressure when an ambient air temperature around the compressor body becomes equal to or lower than a predetermined temperature threshold value.

[0011] In accordance with another aspect of the present invention, there is provided a method of controlling a compressor including an electric motor and a compressor body that is actuated by the electric motor and has a compressor mechanism for discharging compressed air, the method including: stopping operation of the electric motor when a discharged pressure from the compressor body reaches a predetermined stop pressure, causing the electric motor to operate when the discharged pressure reaches a predetermined return pressure lower than the stop pressure, and raising the return pressure when an ambient air temperature around the compressor body becomes equal to or lower than a predetermined temperature threshold value.

[0012] According to the present invention, when the ambient air temperature is equal to or lower than the temperature threshold value, the return pressure is raised to quicken the resumption of the operation of the compressor, so that the liquid waste of the compressor can be prevented from freezing by the heat generated by the compressor during its operation.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 is a perspective view illustrating the appearance of a compressor according to a first embodiment of the present invention;

[0014] FIG. 2 is a perspective view illustrating the internal structural details of the compressor according to the first embodiment of the present invention;

[0015] FIG. 3 is a block diagram illustrating the conceptual configuration of the compressor according to the first embodiment of the present invention;

[0016] FIG. 4 is a block diagram illustrating the functions of a control board of the compressor according to the first embodiment of the present invention;

[0017] FIG. 5 is a flowchart of a control process carried out by the control board of the compressor according to the first embodiment of the present invention;

[0018] FIG. 6 is a flowchart of a control process carried out by a control board of a compressor according to a second embodiment of the present invention;

[0019] FIG. 7 is a flowchart of a control process carried out by a control board of a compressor according to a third embodiment of the present invention; and

[0020] FIG. 8 is a flowchart of part of the control process carried out by the control board of the compressor according to the third embodiment of the present invention.DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Compressors and methods of controlling compressors according to first through third embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Note that identical or corresponding parts are denoted by identical or corresponding reference characters throughout views, and their redundant description may be omitted hereinbelow.

[0022] According to each of the following first through third embodiments, as a compression type of a compressor body, there will be described by way of example a packaged scroll compressor including a fixed scroll and an orbiting scroll that are interleaved to define a compressor chamber therebetween for compressing air upon orbiting motion of the orbiting scroll around the center of the fixed scroll. However, the present invention is neither limited to packaged compressors nor to scroll compressors, but is also applicable to other compressors including reciprocating compressors, screw compressors, and turbo compressors. The working fluid to be compressed by the compressors is not limited to air, but may be other gases such as nitrogen, for example.First Embodiment

[0023] A compressor 100 and a method of controlling the compressor 100 according to the first embodiment will be described in detail below with reference to FIGS. 1 through 5.

[0024] First, the overall configuration of the compressor 100 will be described below with reference to FIGS. 1 through 3. FIG. 1 illustrates in perspective the appearance of the compressor 100 according to the first embodiment. FIG. 2 illustrates in perspective the internal structural details of the compressor 100 according to the first embodiment. FIG. 3 illustrates in block form the conceptual configuration of the compressor 100 according to the first embodiment.

[0025] As illustrated in FIGS. 1 and 2, the compressor 100 is a single-stage compressor including a compressor body 103 and an electric motor 104. The compressor 100 has a housing 120 including a front panel that constitutes a part of the housing 120 and is detachably fastened to the other part of the housing 120 by fasteners such as screws. In addition, the compressor 100 includes a control panel 117 mounted on a front side thereof and used for controlling the compressor 100 by a user.

[0026] As illustrated in FIG. 3, the compressor 100 includes the housing 120, a filter 102, the compressor body 103, the electric motor 104, a check valve 105, an aftercooler 106, a tank 107, a drier 108, a switch 110, a control board (control unit) 111 for controlling operation of the electric motor 104, a pressure sensor 112, a magnet switch 113, a compressor body temperature sensor 114, an ambient air temperature sensor 115, and a fan 116.

[0027] The housing 120 is a case that houses the components of the compressor 100. As illustrated in FIG. 2, the housing 120 has a machine compartment 121 and a control compartment 122 that are defined by panels in the housing 120. The machine compartment 121 houses the electric motor 104 and the compressor body 103 therein, and the control compartment 122 houses the control board 111 therein.

[0028] As illustrated in FIG. 3, air 101 that is introduced into the compressor 100 flows through the filter 102 and is supplied to the compressor body 103.

[0029] The compressor body 103 includes a compressor mechanism, not depicted, for compressing the supplied air and discharging the compressed air.

[0030] The electric motor 104 and the compressor body 103 are operatively coupled to each other by an endless belt trained around their pulleys. When the electric motor 104 is energized, power generated by the electric motor 104 is transmitted by the endless belt to the compressor body 103, actuating the compressor body 103 to compress the air supplied thereto. The compressed air is discharged from the compressor body 103 and flows through the check valve 105 and the aftercooler 106 to the tank 107 where it is temporarily stored. The air then flows from the tank 107 through the drier 108 and is supplied as compressed air 109 to a user’s external piece of equipment, not depicted.

[0031] In the compressor 100, the switch 110 of the control panel 117 is used to operate and stop the compressor 100 and operation of the components of the compressor 100 is controlled by the control board 111.

[0032] Moreover, depending on the pressure in the tank 107 that is sensed by the pressure sensor 112, the control board 111 issues a command to the magnet switch 113 to perform intermittent operation control on the compressor body 103.

[0033] In addition, in the compressor 100, the compressor body temperature sensor 114 measures the temperature of a side surface of the compressor body 103 as the temperature of a discharging area thereof, where the compressed air is discharged, and the ambient air temperature sensor 115 measures the temperature of air in the vicinity of an air intake port 118 as an ambient air temperature AT of the compressor 100.

[0034] Furthermore, the control board 111 performs a control process for issuing an alarm and abnormality signal if the ambient air temperature AT of the compressor 100, which is sensed by the ambient air temperature sensor 115, falls outside of a predetermined temperature range set for the compressor 100. The control board 111 also performs a control process for issuing an alarm and abnormality signal to prevent the compressor body 103 from suffering a failure in advance if the difference between the ambient air temperature AT and the temperature of the compressor body 103 sensed by the compressor body temperature sensor 114 exceeds a predetermined threshold value.

[0035] While the compressor 100 is in operation, the temperature sensed by the compressor body temperature sensor 114 is approximately 100° C because the compressed air discharged from the compressor body 103 is of a temperature of approximately 200° C. On the other hand, the temperature sensed by the ambient air temperature sensor 115 represents the temperature of an area where the compressor 100 operates, e.g., a room temperature ranging from 0° C to 40° C, because the ambient air temperature sensor 115 is provided near the air intake port 118.

[0036] The discharged air temperature sensed by the compressor body temperature sensor 114 is not limited to the temperature of the side surface of the compressor body 103. The compressor body temperature sensor 114 may measure the temperature of a component provided between the compressor body 103 and a position immediately before the aftercooler 106 or the temperature of the compressed air anywhere between the compressor body 103 and the aftercooler 106.

[0037] Similarly, the ambient air temperature AT sensed by the ambient air temperature sensor 115 is not limited to the temperature of the air near the air intake port 118. Instead, the ambient air temperature sensor 115 may directly measure the temperature of air outside the housing 120 in the vicinity of the air intake port 118 or the temperature of atmospheric air in the housing 120 at a position other than the air intake port 118. For example, the temperature of atmospheric air in the housing 120 may represent the temperature of air in the space within the housing 120 except the machine compartment 121 that is defined in the housing 120 and houses the electric motor 104 and the compressor body 103, e.g., the temperature of air in the control compartment 122. Stated otherwise, the ambient air temperature AT represents both the temperature of air in the space where the compressor 100 is present, i.e., the temperature of ambient air outside of the housing 120, and the temperature of air within the housing 120 except the machine compartment 121.

[0038] The ambient air temperature AT may not necessarily be measured by the ambient air temperature sensor 115 of the compressor 100. For example, a temperature sensor that is not a component of the compressor 100 may measure the temperature of air in the environment or space where the compressor 100 is installed, and the control board 111 of the compressor 100 may acquire the ambient air temperature AT from that temperature sensor.

[0039] The fan 116 delivers cooling air into the housing 120 to cool the compressor body 103, the drier 108, and other components of the compressor 100. The fan 116 thus functions as a cooling unit for cooling the components of the compressor 100.

[0040] FIG. 4 illustrates in functional block form the control board 111 of the compressor 100 according to the first embodiment.

[0041] As illustrated in FIG. 4, the control board 111 includes as its functional features a pressure controlling section 201, an ambient air temperature determining section 202, a pressure setting determining section 203, a pressure setting changing section 204, a fan operation determining section 205, and a storing section 206.

[0042] The pressure controlling section 201 processes sensor input signals from the pressure sensor 112, the compressor body temperature sensor 114, and the ambient air temperature sensor 115, and issues a command for selectively opening and closing the magnet switch 113 and a command for operating the fan 116.

[0043] The pressure controlling section 201 carries out an operation status flow of the compressor 100 illustrated in FIG. 5 on the basis of the ambient air temperature AT determined by the ambient air temperature determining section 202 and the pressure setting determined by the pressure setting determining section 203, that is, on the basis of the pressure setting changed by the pressure setting changing section 204 and the determination result of the operation of the fan 116 determined by the fan operation determining section 205.

[0044] Specifically, the pressure controlling section 201 of the control board 111 controls the operation of the electric motor 104 on the basis of either a normal operation mode, i.e., a first operation mode, or a low-pressure shifting mode, i.e., a second operation mode.

[0045] The normal operation mode is a mode of operation in which the electric motor 104 operates the compressor 100 until the pressure of the discharged compressed air, i.e., a discharged pressure P, reaches a preset stop pressure (hereinafter, a stop pressure in the normal operation mode will be denoted by “Pmax”), stops operating the compressor 100 when the discharged pressure P becomes equal to the stop pressure Pmax (P = Pmax), and thereafter resumes operating the compressor 100 when the discharged pressure P becomes equal to a return pressure (hereinafter, a return pressure in the normal operation mode will be denoted by “Pu”) (P = Pu).

[0046] The low-pressure shifting mode is similar to the normal operation mode in that the electric motor 104 stops operating the compressor 100 when the discharged pressure P becomes equal to a stop pressure (hereinafter, a stop pressure in the low-pressure shifting mode will be denoted by “P’max”) (P=P’max) and resumes operating the compressor 100 when the discharged pressure P becomes equal to a return pressure (hereinafter, a return pressure in the low-pressure shifting mode will be denoted by “P’u”) (P = P’u). The low-pressure shifting mode is different from the normal operation mode in that, when the low-pressure shifting mode is selected, the stop pressure P’max and the return pressure P’u are lowered from those in the normal operation mode by a shifting pressure Ps, i.e., 0.1Mpa, (P’max = Pmax - Ps, P’u = Pu - Ps). The low-pressure shifting mode is thus able to give a trouble-free energy saving option to the user who has been using the compressor 100 for unnecessarily high compressed air pressures.

[0047] The user can freely select the normal operation mode or the low-pressure shifting mode for operating the compressor 100 using the control panel 117. The mode of operation selected by the user is stored in the storing section 206 of the control board 111.

[0048] The storing section 206 stores beforehand values representing the stop pressure Pmax set in the normal operation mode (hereinafter referred to as a “normal stop pressure Pmax”) and the return pressure Pu set in the normal operation mode (hereinafter referred to as a “normal return pressure Pu”), and a value representing the shifting pressure Ps in the low-pressure shifting mode. The storing section 206 further stores beforehand a value representing a temperature threshold value T to be described later. The values of the normal stop pressure Pmax, the normal return pressure Pu, the shifting pressure Ps, and the temperature threshold value T can be set as desired by the user. Regarding the shifting pressure Ps, although the shifting pressure with regard to the stop pressure and the shifting pressure with regard to the return pressure are identical to each other, i.e., the shifting pressure is common to the stop pressure and the return pressure, as described later, they may be set to values different from each other.

[0049] A control sequence for the compressor 100 according to the present embodiment will be described below with reference to FIG. 5. FIG. 5 is a flowchart of a control process carried out by the control board 111 of the compressor 100 according to the first embodiment. In FIG. 5, though the steps are performed by the various functional features of the control board 111, they will be described below for the sake of brevity as being performed by the control board 111. The stop pressure P’max and the return pressure P’u in the low-pressure shifting mode will also be hereinafter referred to as a “low-pressure stop pressure P’max” and a “low-pressure return pressure P’u,” respectively.

[0050] As illustrated in FIG. 5, the control board 111 starts the control flow in step S301 to start operating the compressor 100 in step S302. Thereafter, the control board 111 determines whether the low-pressure shifting mode is effective or not in step S303. If the control board 111 determines that the low-pressure shifting mode is effective in step S303 (Yes), then the processing goes to step S305. If the control board 111 determines that the low-pressure shifting mode is not effective, then the processing goes to step S304, bringing the processing to an end.

[0051] If the control board 111 determines that the low-pressure shifting mode is effective in the determination of whether the low-pressure shifting mode is effective in step S303 (Yes), then the control board 111 enters the low-pressure shifting mode control.

[0052] In the low-pressure shifting mode control, the control board 111 sets the low-pressure stop pressure P’max to a value that is lowered from the normal stop pressure Pmax by the shifting pressure Ps, in step S305, and then sets the low-pressure return pressure P’u to a value that is lowered from the normal return pressure Pu by the shifting pressure Ps, in step S306.

[0053] Thereafter, the control board 111 performs a looping process in step S307 for liquid waste freezing prevention control using the low-pressure stop pressure P’max set in step S305 and the low-pressure return pressure P’u set in step S306. According to the present embodiment, the liquid waste freezing prevention control looping process described herein covers not only a process of completely preventing liquid waste from freezing, but also a process of minimizing liquid waste freezing, e.g., making liquid waste less likely to freeze or reducing the degree to which liquid waste freezes.

[0054] In the liquid waste freezing prevention control looping process, the control board 111 compares the ambient air temperature AT of the compressor 100 with the temperature threshold value T, e.g., 5°C, in step S308. If the ambient air temperature AT is equal to or lower than the temperature threshold value T in step S308 (Yes), then the control flow goes to step S309. If the ambient air temperature AT is higher than the temperature threshold value T in step S308 (No), then the control flow goes to step S312.

[0055] If the ambient air temperature AT is equal to or lower than 5° C of the temperature threshold value T, then the control board 111 sets an ambient air temperature drop flag F in step S309. Then, the control board 111 sets the low-pressure stop pressure P’max to be returned from the value that is changed to be lowered by the shifting pressure Ps, to the normal stop pressure Pmax in step S310, and then sets the low-pressure return pressure P’u to be returned from the value that is changed to be lowered by the shifting pressure Ps, to the normal return pressure Pu in step S311. Then, the control flow goes to step S312.

[0056] In step S312, the control board 111 determines whether the ambient air temperature drop flag F has been set or not. If it is determined that the ambient air temperature drop flag F has been set in step S312 (Yes), then the control board 111 performs the ambient air temperature determination in step S313. If it is determined that the ambient air temperature drop flag F has not been set in step S312 (No), then the control flow goes to step S317, bypassing the ambient air temperature determination in step S313.

[0057] In the ambient air temperature determination in step S313, the control board 111 compares the ambient air temperature AT with a deletion threshold value Td, e.g., 10° C, that has been preset in order to determine whether to delete the ambient air temperature drop flag F or not. The value of 10° C as the deletion threshold value Td represents a numerical value used by way of example to prevent chattering due to the setting changes for the low-pressure stop pressure P’max and the low-pressure return pressure P’u owing to the comparison between the ambient air temperature AT and the temperature threshold value T. The deletion threshold value Td may be other values as long as they are effective in preventing chattering.

[0058] If the ambient air temperature AT is equal to or higher than the deletion threshold value Td in step S313 (Yes), then the control board 111 deletes the ambient air temperature drop flag F in step S314. Then, the control board 111 sets the low-pressure stop pressure P’max to a value that is lowered from the normal stop pressure Pmax by the shifting pressure Ps, in step S315. Then, the control board 111 sets the low-pressure return pressure P’u to a value that is lowered from the normal return pressure Pu by the shifting pressure Ps, in step S316. Thereafter, the control flow goes to step S317.

[0059] If the ambient air temperature AT is lower than the deletion threshold value Td in step S313 (No), then the control flow goes to step S317, skipping steps S314, S315, and S136.

[0060] During the liquid waste freezing prevention control looping process in step S307, the user may terminate the low-pressure shifting mode. In step S317, during the liquid waste freezing prevention control looping process, the control board 111 confirms whether it has received a signal for terminating the low-pressure shifting mode from the user or not by determining whether the low-pressure shifting mode is ineffective or not.

[0061] If the control board 111 determines that the low-pressure shifting mode is ineffective in step S317 (Yes), then the control flow leaves the liquid waste freezing prevention control looping process in step S317 and goes to step S319. In step S319, the control board 111 sets the low-pressure stop pressure P’max to be returned from the value that is changed to be lowered by the shifting pressure Ps, to the normal stop pressure Pmax. Then, in step S320, the control board 111 sets the low-pressure return pressure P’u to be returned from the value that is changed to be lowered by the shifting pressure Ps, to the normal return pressure Pu. As the low-pressure shifting mode is terminated, the control flow goes to step S304 and comes to an end.

[0062] If the control board 111 determined that the low-pressure shifting mode is effective in step S317 (No), then the control flow goes to step S318 in which the liquid waste freezing prevention control looping process repeats the processing from step S307.

[0063] The control board 111 controls the operation of the electric motor 104 in the manner described above.

[0064] According to the present embodiment, when the ambient air temperature AT is lowered, i.e., when the ambient air temperature drop flag F is set, the low-pressure return pressure P’u is set so as to be returned from the value that is lowered by the shifting pressure Ps, to the normal return pressure Pu. Similarly, the low-pressure stop pressure P’max is returned from the value that is lowered by the shifting pressure Ps, to the normal stop pressure Pmax.

[0065] However, when the ambient air temperature AT is lowered, it is enough for the control board 111 to least raise the low-pressure return pressure P’u and the low-pressure stop pressure P’max, and the control board 111 may not necessarily need to return the low-pressure return pressure P’u and the low-pressure stop pressure P’max to the normal return pressure Pu and the normal stop pressure Pmax, respectively. Stated otherwise, when the ambient air temperature AT is lowered in the low-pressure shifting mode control, although it is desirable for the control board 111 to return the low-pressure return pressure P’u and the low-pressure stop pressure P’max to the normal return pressure Pu and the normal stop pressure Pmax, respectively, it may be enough for the control board 111 to raise the low-pressure return pressure P’u and the low-pressure stop pressure P’max closer to the normal return pressure Pu and the normal stop pressure Pmax, respectively. Furthermore, when the ambient air temperature AT is lowered, it is desirable for the control board 111 not to raise the low-pressure return pressure P’u and the low-pressure stop pressure P’max beyond the normal return pressure Pu and the normal stop pressure Pmax, respectively.

[0066] The first embodiment described above offers the following advantages:

[0067] In this embodiment, when the ambient air temperature AT is low, the low-pressure shifting mode to be performed for energy saving is canceled, and the low-pressure return pressure P’u and the low-pressure stop pressure P’max are set to values raised to the normal return pressure Pu and the normal stop pressure Pmax, respectively. This delays the timing to stop the operation of the compressor 100 and quickens the timing to resume operating the compressor 100, thereby preventing its liquid waste from freezing with the heat generated by the compressor 100 while in operation. Consequently, the first embodiment is effective to perform energy saving and liquid waste freezing prevention appropriately depending on the situation in which the compressor 100 operates.

[0068] Moreover, according to the control in the present embodiment, the low-pressure stop pressure P’max and the low-pressure return pressure P’u are changed to delay the timing to stop the compressor 100 or quicken the timing to resume operating the compressor 100, and the compressor 100 is not forcibly warmed up separately from its normal operation. It is therefore possible to minimize electric power consumption of the compressor 100 while keeping the compressor 100 warmed up, i.e., preventing the compressor 100 from freezing its liquid waste. The liquid waste of the compressor 100 is frozen when the ambient air temperature At is lowered. In a low-temperature environment, the temperature of the compressed air discharged from the compressor 100 is usually higher than the ambient air temperature AT. Since the control process performed by the control board 111 according to the present embodiment is carried out on the basis of the ambient air temperature AT, the compressor 100 can be warmed up earlier than it is carried out on the basis of the temperature of the compressed air discharged from the compressor 100, making it more effective to prevent the liquid waste of the compressor 100 from freezing.Second Embodiment

[0069] A compressor 100 and a method of controlling the compressor 100 according to the second embodiment of the present invention will be described in detail below.

[0070] The second embodiment is different from the first embodiment with respect to the manner in which the low-pressure stop pressure P’max and the low-pressure return pressure P’u are set.

[0071] FIG. 6 is a flowchart of a control process carried out by the control board 111 of the compressor 100 according to the second embodiment.

[0072] According to the second embodiment, as illustrated in FIG. 6, the processing after the control board 111 has set the ambient air temperature drop flag F in step S309 is different from that according to the first embodiment. Steps S301 through S309 and steps S312 through S320 illustrated in FIG. 6 according to the second embodiment are the same as those illustrated in FIG. 5 according to the first embodiment, and will be omitted from detailed description.

[0073] After having set an ambient air temperature drop flag F in step S309, the control board 111 determines whether the difference between the low-pressure stop pressure P’max and the normal return pressure Pu is smaller than a predetermined differential threshold value, e.g., 0.1 Mpa, or not in step S401. If the difference is equal to or larger than 0.1 Mpa, then the control board 111 sets the low-pressure return pressure P’u to be returned from the value that is lowered by the shifting pressure Ps, to the normal return pressure Pu in step S402. If the difference is smaller than 0.1 Mpa, then the control board 111 sets the low-pressure return pressure P’u to the value obtained by subtracting 0.1 Mpa from the low-pressure stop pressure P’max, in step S403.

[0074] After step S402 or step S403 is carried out, the control flow goes to step S312. The processing from step S312 is the same as that according to the first embodiment.

[0075] According to the second embodiment, when the ambient air temperature AT is lowered, only the low-pressure return pressure P’u is changed, and the low-pressure stop pressure P’max is not changed. This makes it possible to prevent the liquid waste from freezing while stabilizing the pressure supplied from the compressor 100 to the user’s external piece of equipment. In other words, when the ambient air temperature AT is lowered, the liquid waste is prevented from freezing by changing or setting at least the low-pressure return pressure P’u so as to be larger than the present setting.

[0076] According to the second embodiment, moreover, the differential threshold value may be established in consideration of the components of the compressor 100 and another apparatus that affects the compressor 100, e.g., the user’s external piece of equipment to be supplied with the compressed air from the compressor 100. For example, the differential threshold value may be set to such a value, i.e., 0.1 Mpa, that does not make the load on the compressor 100 large when the magnet switch 113 for intermittently operating the compressor 100 is frequently turned on and off.

[0077] The second embodiment described above offers the same advantages as the first embodiment.Third Embodiment

[0078] A compressor 100 and a method of controlling the compressor 100 according to the third embodiment will be described in detail below.

[0079] FIGS. 7 and 8 are flowcharts of a control process carried out by the control board 111 of the compressor 100 according to the third embodiment.

[0080] According to the third embodiment, as illustrated in FIGS. 7 and 8, the liquid waste freezing prevention control looping process is different from that according to the first embodiment. Steps S301 through S304 and steps S317 through S320 illustrated in FIG. 7 according to the third embodiment are the same as those according to the first embodiment, and will be omitted from detailed description.

[0081] According to the third embodiment, a first temperature threshold value T1, a second temperature threshold value T2, and a third temperature threshold value T3 are established as temperature threshold values. The first temperature threshold value T1, the second temperature threshold value T2, and the third temperature threshold value T3 are progressively smaller in the order named (T1> T2> T3). The second temperature threshold value T2 corresponds to a “first determination threshold value” referred to in the claims, whereas the third temperature threshold value T3 corresponds to a “second determination threshold value” referred to in the claims.

[0082] As illustrated in FIG. 7, when the liquid waste freezing prevention control looping process is carried out in step S307, the control substrate 111 compares the ambient air temperature AT with the first temperature threshold value T1, e.g., 10° C, to perform the ambient air temperature determination in step S501. If the ambient air temperature AT is higher than the first temperature threshold value T1 in step S501 (No), then the control flow goes to step S512. The processing branching from step S512 will be described later.

[0083] If the ambient air temperature AT is equal to or lower than the first temperature threshold value T1 in step S501 (Yes), then the control board 111 sets a first ambient air temperature drop flag F1 in step S502, which is followed by step S503.

[0084] In step S503, the control substrate 111 compares the ambient air temperature AT with the second temperature threshold value T2, e.g., 7° C, to perform the ambient air temperature determination. If the ambient air temperature AT is higher than the second temperature threshold value T2 in step S503 (No), then the control board 111 turns off the fan 116 in step S504. Then, the control flow goes to step S512.

[0085] If the ambient air temperature AT is equal to or lower than the second temperature threshold value T2 in step S503 (Yes), then the control board 111 sets a second ambient air temperature drop flag F2 in step S505, which is followed by step S506.

[0086] In step S506, the control substrate 111 compares the ambient air temperature AT with the third temperature threshold value T2, e.g., 5°C, to perform the ambient air temperature determination. If the ambient air temperature AT is higher than the third temperature threshold value T3 in step S506 (No), then the control board 111 sets the low-pressure stop pressure P’max to a value obtained by subtracting one half of the shifting pressure Ps from the normal stop pressure Pmax (P’max = Pmax - (Ps / 2)), in step S507. Then, the control board 111 sets the low-pressure return pressure P’u to a value obtained by subtracting one half of the shifting pressure Ps from the normal return pressure Pu (P’u = Pu - (Ps / 2)), in step S508. After step S508, the control flow goes to step S512.

[0087] If the ambient air temperature AT is equal to or lower than the third temperature threshold value T3 in step S506 (Yes), then the control board 111 sets a third ambient air temperature drop flag F3 in step S509. Then, the control board 111 sets the low-pressure stop pressure P’max to the normal stop pressure Pmax in step S510. Then, the control board 111 sets the low-pressure return pressure P’u to the normal return pressure Pu in step S511. After step S511, the control flow goes to step S512.

[0088] In step S512, the control board 111 determines whether the first ambient air temperature drop flag F1 has been set or not. If it is determined that the first ambient air temperature drop flag F1 has been set in step S512 (Yes), then the control board 111 determines whether the second ambient air temperature drop flag F2 has been set or not in step S513 (see FIG. 8). If it is determined that the first ambient air temperature drop flag F1 has not been set in step S512 (No), then the control flow goes to step S317 for determining whether the low-pressure shifting mode is ineffective or not.

[0089] As illustrated in FIG. 8, if it is determined that the second ambient air temperature drop flag F2 has been set in step S513 (Yes), then the control board 111 determines whether the third ambient air temperature drop flag F3 has been set or not in step S517. If it is determined that the second ambient air temperature drop flag F2 has not been set in step S513 (No), then the control board 111 compares the ambient air temperature AT with a first flag deletion threshold value Td1, e.g., 13° C, to perform the ambient air temperature determination in step S514. The first flag deletion threshold value Td1 is a threshold value for deleting the first ambient air temperature drop flag F1, and is set to a value larger than the first temperature threshold value T1 (Td1 > T1).

[0090] If it is determined that the ambient air temperature AT is equal to or higher than the first flag deletion threshold value Td1 in step S514 (Yes), then the control board 111 deletes the first ambient air temperature drop flag F1 in step S515 and operates the fan in step S516. If the ambient air temperature AT is lower than the first flag deletion threshold value Td1, then the control flow jumps to step S317 (see FIG. 7), bypassing steps S515 and S516.

[0091] If it is determined that the third ambient air temperature drop flag F3 has been set in step S517 (Yes), then the control flow goes to step S522. If it is determined that the third ambient air temperature drop flag F3 has not been set in step S517 (No), then the control flow goes to step S518.

[0092] In step S518, the control board 111 compares the ambient air temperature AT with a second flag deletion threshold value Td2, e.g., 10° C, to perform the ambient air temperature determination. The second flag deletion threshold value Td2 is a threshold value for deleting the second ambient air temperature drop flag F2, and is set to a value larger than the second temperature threshold value T2 (Td2 > T2).

[0093] If it is determined that the ambient air temperature AT is equal to or higher than the second flag deletion threshold value Td2 in step S518 (Yes), then the control board 111 deletes the second ambient air temperature drop flag F2 in step S519. Then, the control board 111 sets the low-pressure stop pressure P’max to a value obtained by subtracting the shifting pressure Ps from the normal stop pressure Pmax, in step S520. Then, the control board 111 sets the low-pressure return pressure P’u to a value obtained by subtracting the shifting pressure Ps from the normal return pressure Pu, in step S521. If it is determined that the ambient air temperature AT is lower than the second flag deletion threshold value Td2 in step S518 (No), then the control flow jumps to step S317 (see FIG. 7), bypassing steps S519, S520, and S521.

[0094] In step S522, the control board 111 compares the ambient air temperature AT with a third flag deletion threshold value Td3, e.g., 8° C, to perform the ambient air temperature determination. The third flag deletion threshold value Td3 is a threshold value for deleting the third ambient air temperature drop flag F3, and is set to a value larger than the third temperature threshold value T3 (Td3> T3).

[0095] If it is determined that the ambient air temperature AT is equal to or higher than the third flag deletion threshold value Td3 in step S522 (Yes), then the control board 111 deletes the third ambient air temperature drop flag F3 in step S523. Then, the control board 111 sets the low-pressure stop pressure P’max to a value obtained by subtracting one half of the shifting pressure Ps from the normal stop pressure Pmax (P’max = Pmax - (Ps / 2)), in step S524. Then, the control board 111 sets the low-pressure return pressure P’u to a value obtained by subtracting one half of the shifting pressure Ps from the normal return pressure Pu (P’u = Pu - (Ps / 2)), in step S525. If it is determined that the ambient air temperature AT is lower than the third flag deletion threshold value Td3 in step S522 (No), then the control flow jumps to step S317 (see FIG. 7), bypassing steps S523, S524, and S525.

[0096] The processing from step S317 is the same as that according to the first embodiment.

[0097] According to the third embodiment, a drop in the ambient air temperature AT is determined stepwise in different stages based on the three temperature threshold values T1, T2, and T3, and the fan 116 is turned off and the setting of the stop pressure and the setting of the return pressure are changed by shifting amounts depending on the respective stages. A drop in the temperature in the compressor body 103 and hence the housing 210 is restrained when the fan 116 is turned off, and therefore, this is effective in preventing the liquid waste from freezing.

[0098] More specifically, when the ambient air temperature AT is equal to or lower than the second temperature threshold value T2 and higher than the third temperature threshold value T3, the low-pressure stop pressure and the low-pressure return pressure are set to respective values that are lowered by one half of the shifting pressure Ps, i.e., shifting amount of Ps / 2, from the normal stop pressure and the normal return pressure from values that are lowered by the shifting pressure Ps. When the ambient air temperature AT is equal to or lower than the third temperature threshold value T3, the low-pressure stop pressure and the low-pressure return pressure are set to be returned to the normal stop pressure and the normal return pressure from values that are lowered by the shifting pressure Ps, i.e., shifting amount of Ps. A value representing one half of the shifting pressure Ps corresponds to the “first shifting amount” referred to in the claims and a value representing the shifting pressure Ps corresponds to the “second shifting amount” referred to in the claims.

[0099] According to the third embodiment, the liquid waste is prevented from freezing by performing a process for imposing stepwise pressure limitations depending on the ambient air temperature AT. According to the third embodiment, therefore, the liquid waste is prevented from freezing while achieving a higher energy saving capability in the low-pressure shifting mode.

[0100] The third embodiment described above offers the same advantages as the first embodiment.

[0101] The present invention also covers various modifications to be described below. According to the present invention, it is possible to combine configurational and functional details of the modifications and configurational and functional details of the embodiments, combine configurational and functional details of different ones of the embodiments, and combine configurational and functional details of different ones of the modifications. According to the present invention, it is also possible to add other configurational and functional details to some of the configurational and functional details of the embodiments, delete some of the configurational and functional details of the embodiments, and replace some of the configurational and functional details of the embodiments with other configurational and functional details.First Modification

[0102] In the case where the compressor 100 includes a plurality of compressor bodies 103, it is possible to perform the control to set a stop pressure and a return pressure for each of the compressors body 103 when the ambient air temperature AT drops. This makes it possible to prevent the liquid waste from freezing while achieving an energy saving capability in the low-pressure shifting mode.<Second Modification>

[0103] According to each of the above modifications, the liquid waste freezing prevention control is performed while in the low-pressure shifting mode. However, the present invention is not limited to such a feature. Stated otherwise, the liquid waste freezing prevention control is not necessarily applicable to only the compressor 100 whose control board 111 is configured to be capable of executing the low-pressure shifting mode.

[0104] For example, the liquid waste freezing prevention control may be performed while in the normal operation mode. In this case, when the ambient air temperature AT is equal to or higher than a predetermined threshold value, at least the return pressure is set to a higher pressure level, i.e., raised to a higher pressure level, to prevent the liquid waste from freezing. As with each of the above embodiments, in addition to increasing the return pressure, the stop pressure may also be set to a higher pressure level, i.e., raised to a higher pressure level, to make it more effective to prevent the liquid waste from freezing.Third Modification

[0105] According to the second embodiment described above, when the ambient air temperature AT is lowered, only the return pressure is changed, and the stop pressure is not changed. However, when the ambient air temperature AT is lowered, only the stop pressure may be changed, and the return pressure may not be changed. At least either the return pressure or the stop pressure may be raised when the ambient air temperature AT is lowered, and therefore, this is effective in preventing the liquid waste from freezing.Fourth Modification

[0106] According to the third embodiment, the fan 116 is turned off in a state where the first ambient air temperature drop flag F1 is set and the second ambient air temperature drop flag F2 is not set. Providing the compressor 100 includes a cooling unit other than the fan 116, however, the cooling unit may be de-energized instead of turning off the fan 116 or in addition to turning off the fan 116. The cooling unit has a function to cool the components of the compressor 100 including the housing 120 or the interior of the housing 120. For example, if the compressor 100 has a cooling jacket for cooling the compressor body 103 and / or a cooler having a Peltier device as the cooling unit, then the cooling unit may be turned off.Other Modifications

[0107] The embodiments described above are illustrated by way of example only for an easier understanding of the present invention, and should not be construed as limiting the scope of invention. Various other components or elements may be added to the embodiments, and some of the components or elements of the embodiments may be deleted or replaced with other components or elements without departing from the scope of the invention.

[0108] The various functional sections described above in the embodiments may be hardware-implemented by circuits, and the circuits may be dedicated circuits for performing certain functions or general-purpose circuits such as processors.

[0109] At least a portion of the processing according to each of the above embodiments may be implemented by a general-purpose computer as a basic piece of hardware. Programs for performing the processing may be stored in a storage medium readable by the computer. The programs are stored in the storage medium as files that can be installed in or executed by the computer. The storage medium may be in the form of a magnetic disk, an optical disk such as a CD-ROM, a CD-R, or a DVD, a magneto-optical disk (MO), or a semiconductor memory. The storage medium may be any one of these memories as long as it can store programs and it can be read by the computer. Alternatively, the programs for performing the above processing may be stored in a computer as a server connected to a network such as the Internet and downloaded via the network to a computer as a client.

[0110] The configurational and functional details and advantages of the embodiments of the present invention will be summarized as follows:

[0111] (1) The compressor 100 includes the electric motor 104, the compressor body 103 that is actuated by the electric motor 104 and has the compressor mechanism for discharging compressed air, and the control board 111 for controlling operation of the electric motor 104. The control board 111 stops the operation of the electric motor 104 when a discharged pressure P from the compressor body 103 reaches a predetermined stop pressure, causes the electric motor 104 to operate when the discharged pressure P reaches a predetermined return pressure lower than the stop pressure, and raises the return pressure when an ambient air temperature AT around the compressor body 103 becomes equal to or lower than a predetermined temperature threshold value.

[0112] With the compressor 100, when the ambient air temperature AT is equal to or lower than the temperature threshold value, the control board 111 increases the return pressure but does no change the stop pressure.

[0113] The method of controlling the compressor 100 includes stopping the operation of the electric motor 104 when the discharged pressure P from the compressor body 103 reaches the predetermined stop pressure, causing the electric motor 104 to operate when the discharged pressure P reaches the predetermined return pressure lower than the stop pressure, and raising the return pressure when the ambient air temperature AT around the compressor body 103 becomes equal to or lower than the predetermined temperature threshold value.

[0114] Moreover, the method of controlling the compressor 100 includes raising the return pressure but not changing the stop pressure when the ambient air temperature AT is equal to or lower than the temperature threshold value.

[0115] With this configuration, when the ambient air temperature AT is lowered, the timing to resume operating the compressor 100 is quickened by increasing the return pressure. This warms up the compressor 100, preventing its liquid waste from freezing.

[0116] Furthermore, since the compressor 100 is not forcibly warmed up separately from its normal operation, it is possible to minimize electric power consumption of the compressor 100 while preventing the compressor 100 from freezing its liquid waste. In addition, as the compressor 100 is controlled on the basis of the ambient air temperature AT, the compressor 100 can be warmed up earlier than it is controlled on the basis of the temperature of the compressed air discharged from the compressor 100, making it more effective to prevent the liquid waste of the compressor 100 from freezing.

[0117] (2) Furthermore, with the compressor 100, the control board 111 is configured to be capable of executing the low-pressure shifting mode for shifting the stop pressure and the return pressure toward lower pressures by predetermined pressures, raises the stop pressure and the return pressure when the ambient air temperature AT around the compressor body 103 becomes equal to or lower than the predetermined temperature threshold value, and raises the stop pressure and the return pressure to return to respective values that are values before they are shifted, when the ambient air temperature AT becomes equal to or lower than the temperature threshold value while the electric motor 104 is being controlled in the low-pressure shifting mode.

[0118] Moreover, the method of controlling the compressor 100 includes carrying out the low-pressure shifting mode for shifting the stop pressure and the return pressure toward lower pressures by predetermined pressures, raising the stop pressure and the return pressure when the ambient air temperature AT around the compressor body 103 becomes equal to or lower than the predetermined temperature threshold value, and raising the stop pressure and the return pressure to return to respective values that are values before they are shifted, when the ambient air temperature AT around the compressor 103 becomes equal to or lower than the temperature threshold value while the electric motor 104 is being controlled in the low-pressure shifting mode.

[0119] With this configuration, when the ambient air temperature AT is low, the low-pressure shifting mode control carried out for energy saving is canceled, and the low-pressure stop pressure P’max and the low-pressure return pressure P’u are set to values raised respectively to the normal stop pressure Pmax and the normal return pressure Pu. The capabilities of energy saving and liquid waste freezing prevention are thus appropriately performed depending on the situation.

[0120] (3) Furthermore, with the compressor 100, the temperature threshold values include the second temperature threshold value T2 and the third temperature threshold value T3, and the control board 111 raises the low-pressure return pressure P’u by the value represented by one half of the shifting pressure Ps as the first shifting amount when the ambient air temperature AT is equal to or lower than the second temperature threshold value T2 and higher than the third temperature threshold value T3, and raises the low-pressure return pressure P’u by the value represented by the shifting pressure Ps as the second shifting amount larger than the first shifting amount when the ambient air temperature AT is equal to or lower than the third temperature threshold value T3.

[0121] According to the method of controlling the compressor 100, furthermore, the temperature threshold values include the second temperature threshold value T2 and the third temperature threshold value T3, and the method raises the low-pressure return pressure P’u by the value represented by one half of the shifting pressure Ps as the first shifting amount when the ambient air temperature AT is equal to or lower than the second temperature threshold value T2 and higher than the third temperature threshold value T3, and raises the low-pressure return pressure P’u by the value represented by the shifting pressure Ps as the second shifting amount larger than the first shifting amount when the ambient air temperature AT is equal to or lower than the third temperature threshold value T3.

[0122] With this configuration, the liquid waste is prevented from freezing by performing a process for imposing stepwise pressure limitations depending on the ambient air temperature AT. Therefore, the liquid waste is prevented from freezing while achieving a higher energy saving capability in the low-pressure shifting mode.

[0123] (4) Moreover, the compressor 100 includes the fan 116 for cooling the components of the compressor 100, and the control board 111 turns off the fan 116 when the ambient air temperature AT becomes equal to or lower than the temperature threshold value T.

[0124] The method of controlling the compressor 100 turns off the fan 116 when the ambient air temperature AT becomes equal to or lower than the temperature threshold value T.

[0125] With these configurations, when the ambient air temperature AT drops, the fan 116 is turned off to prevent the liquid waste from freezing.

[0126] While the embodiments of the present invention have been described above, the embodiments are only illustrative of some of possible applications of the present invention and should not be interpreted as limiting the scope of the invention to the specific configurations of the embodiments.DESCRIPTION OF REFERENCE CHARACTERS

[0127] 100: compressor

[0128] 103: compressor body

[0129] 104: electric motor

[0130] 111: control board (control unit)

[0131] 116: fan (cooling unit)

Examples

first embodiment

[0023]A compressor 100 and a method of controlling the compressor 100 according to the first embodiment will be described in detail below with reference to FIGS. 1 through 5.

[0024]First, the overall configuration of the compressor 100 will be described below with reference to FIGS. 1 through 3. FIG. 1 illustrates in perspective the appearance of the compressor 100 according to the first embodiment. FIG. 2 illustrates in perspective the internal structural details of the compressor 100 according to the first embodiment. FIG. 3 illustrates in block form the conceptual configuration of the compressor 100 according to the first embodiment.

[0025]As illustrated in FIGS. 1 and 2, the compressor 100 is a single-stage compressor including a compressor body 103 and an electric motor 104. The compressor 100 has a housing 120 including a front panel that constitutes a part of the housing 120 and is detachably fastened to the other part of the housing 120 by fasteners such as screws. In addition...

second embodiment

[0069]A compressor 100 and a method of controlling the compressor 100 according to the second embodiment of the present invention will be described in detail below.

[0070]The second embodiment is different from the first embodiment with respect to the manner in which the low-pressure stop pressure P’max and the low-pressure return pressure P’u are set.

[0071]FIG. 6 is a flowchart of a control process carried out by the control board 111 of the compressor 100 according to the second embodiment.

[0072]According to the second embodiment, as illustrated in FIG. 6, the processing after the control board 111 has set the ambient air temperature drop flag F in step S309 is different from that according to the first embodiment. Steps S301 through S309 and steps S312 through S320 illustrated in FIG. 6 according to the second embodiment are the same as those illustrated in FIG. 5 according to the first embodiment, and will be omitted from detailed description.

[0073]After having set an ambient air...

third embodiment

[0078]A compressor 100 and a method of controlling the compressor 100 according to the third embodiment will be described in detail below.

[0079]FIGS. 7 and 8 are flowcharts of a control process carried out by the control board 111 of the compressor 100 according to the third embodiment.

[0080]According to the third embodiment, as illustrated in FIGS. 7 and 8, the liquid waste freezing prevention control looping process is different from that according to the first embodiment. Steps S301 through S304 and steps S317 through S320 illustrated in FIG. 7 according to the third embodiment are the same as those according to the first embodiment, and will be omitted from detailed description.

[0081]According to the third embodiment, a first temperature threshold value T1, a second temperature threshold value T2, and a third temperature threshold value T3 are established as temperature threshold values. The first temperature threshold value T1, the second temperature threshold value T2, and the...

Claims

1. A compressor comprising:an electric motor;a compressor body that is actuated by the electric motor and has a compressor mechanism for discharging compressed air; anda control unit for controlling operation of the electric motor, whereinthe control unitstops operation of the electric motor when a discharged pressure from the compressor body reaches a predetermined stop pressure,causes the electric motor to operate when the discharged pressure reaches a predetermined return pressure lower than the stop pressure, andraises the return pressure when an ambient air temperature around the compressor body becomes equal to or lower than a predetermined temperature threshold value.

2. The compressor according to claim 1, whereinthe control unitis configured to be capable of executing a low-pressure shifting mode for shifting the stop pressure and the return pressure toward lower pressures by predetermined pressures,raises the stop pressure and the return pressure when the ambient air temperature around the compressor body becomes equal to or lower than the temperature threshold value, andraises the stop pressure and the return pressure to return to respective values that are values before they are shifted, when the ambient air temperature becomes equal to or lower than the temperature threshold value while the electric motor is being controlled in the low-pressure shifting mode.

3. The compressor according to claim 2, whereinthe temperature threshold value includes a first determination threshold value and a second determination threshold value smaller than the first determination threshold value, andthe control unitraises the return pressure by a first shifting amount when the ambient air temperature is equal to or lower than the first determination threshold value and higher than the second determination threshold value, andraises the return pressure by a second shifting amount larger than the first shifting amount when the ambient air temperature is equal to or lower than the second determination threshold value.

4. The compressor according to claim 1, whereinthe control unit raises the return pressure but does not change the stop pressure when the ambient air temperature is equal to or lower than the temperature threshold value.

5. The compressor according to claim 1, further comprising:a cooling unit for cooling a component of the compressor, whereinthe control unit turns off the cooling unit when the ambient air temperature is equal to or lower than the temperature threshold value.

6. A method of controlling a compressor including an electric motor and a compressor body that is actuated by the electric motor and has a compressor mechanism for discharging compressed air, the method comprising:stopping operation of the electric motor when a discharged pressure from the compressor body reaches a predetermined stop pressure;causing the electric motor to operate when the discharged pressure reaches a predetermined return pressure lower than the stop pressure; andraising the return pressure when an ambient air temperature around the compressor body becomes equal to or lower than a predetermined temperature threshold value.

7. The method of controlling a compressor, according to claim 6, the method further comprising:executing a low-pressure shifting mode for shifting the stop pressure and the return pressure toward lower pressures by predetermined pressures;raising the stop pressure and the return pressure when the ambient air temperature around the compressor body becomes equal to or lower than the predetermined temperature threshold value; andraising the stop pressure and the return pressure to return to respective values that are values before they are shifted, when the ambient air temperature becomes equal to or lower than the temperature threshold value while the electric motor is being controlled in the low-pressure shifting mode.

8. The method of controlling a compressor, according to claim 7, whereinthe temperature threshold value includes a first determination threshold value and a second determination threshold value smaller than the first determination threshold value, andthe method includesraising the return pressure by a first shifting amount when the ambient air temperature is equal to or lower than the first determination threshold value and higher than the second determination threshold value, andraising the return pressure by a second shifting amount larger than the first shifting amount when the ambient air temperature is equal to or lower than the second determination threshold value.

9. The method of controlling a compressor, according to claim 6, the method further comprising:raising the return pressure and keeping the stop pressure unchanged when the ambient air temperature is equal to or lower than the temperature threshold value.

10. The method of controlling a compressor, according to claim 6, whereinthe compressor includes a cooling unit for cooling a component thereof, andthe method further includes turning off the cooling unit when the ambient air temperature is equal to or lower than the temperature threshold value.

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