Air Supply System

Abstract

To provide an air supply system that can reduce loads on a compressor.SOLUTION: An air supply system 10 comprises a compressor that can switch between load operation and non-load operation, and a desiccant agent that removes moisture from compressed air fed out to a connection passage by the compressor. Further, the system comprises an unload control valve 26B that is driven to switch the compressor to non-load operation and is not driven to switch the compressor to load operation, and a drain discharge valve 25 connected to a branched passage 16 of the connection passage, which makes the branched passage 16 to be sealed or communicated depending on whether a governor 26A is driven or not. Further, the system comprises an ECU 80 that can switch between driving and non-driving of the unload control valve 26B and switch between driving and non-driving of the governor 26A.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an air supply system for supplying compressed air to equipment. [Background technology]

[0002] In vehicles such as trucks, buses, and construction machines, pneumatic systems such as brakes and suspensions are controlled using compressed air sent from a compressor. This compressed air contains liquid impurities such as moisture contained in the atmosphere and oil that lubricates the inside of the compressor. If compressed air containing a lot of moisture or oil enters a pneumatic system, it can cause rust and swelling of rubber components, resulting in malfunction. For this reason, a compressed air dryer is provided downstream of the compressor to remove impurities such as moisture and oil from the compressed air.

[0003] The compressed air dryer performs a load operation (dehumidification operation) to remove oil and moisture, and an unload operation (regeneration operation) to remove the oil and moisture adsorbed on the desiccant and release the oil and moisture as drain. The air dryer also discharges the drain discharged from the air dryer to an oil separator to prevent the drain from being discharged onto the road surface. In the oil separator, the air containing oil and moisture is collided with a collision material to separate gas and liquid, recovering the oil and discharging clean air (for example, see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2013-234632 A Summary of the Invention [Problem to be solved by the invention]

[0005] Because purging and regeneration operations consume some amount of compressed air, even the purging and regeneration operations necessary to discharge clean air increase the operating load of the compressor. Therefore, an increase in the operating load of a compressor that generates compressed air using rotational force transmitted from a rotary drive source such as an engine increases the load on the rotary drive source, thereby increasing the consumption of energy such as fuel.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an air supply system capable of reducing the load on the compressor. [Means for solving the problem]

[0007] An air supply system that achieves the above-mentioned object includes a compressor capable of switching between a loaded operation in which compressed air is discharged and an empty operation in which the compressed air is not discharged, a desiccant that removes moisture from the compressed air discharged by the compressor, a connecting passage that connects the compressor and the desiccant to allow the compressed air to flow, a first solenoid valve that switches between the loaded operation and the empty operation of the compressor, the first solenoid valve switching the compressor to the empty operation when driven and switching the compressor to the loaded operation when not driven, a drain discharge valve connected to a branch passage of the connecting passage, the drain discharge valve sealing or opening the branch passage depending on whether a second solenoid valve is driven or not, and a control device that can switch between driving / not driving the first solenoid valve and switching between driving / not driving the second solenoid valve.

[0008] If the solenoid valve for running the compressor dry (unloading) and the solenoid valve for switching the drain discharge valve are the same, the air pressure in the connecting passage and in the desiccant will become atmospheric pressure when the compressor is running dry. Therefore, the compressor cannot draw air through the reed valve that closes when the piston descends during dry operation, and the cylinder becomes negative pressure, which increases the operating load. With this configuration, the first solenoid valve switches between loaded operation and dry operation of the compressor, and the second solenoid valve switches between sealing and communication of the drain discharge valve. Therefore, when the compressor is running dry, the drain discharge valve can be sealed. For example, if the drain discharge valve is sealed, the air pressure in the connecting passage and the air pressure in the desiccant can be maintained at a pressure higher than atmospheric pressure by the air pressure supplied by the compressor. Therefore, the pressure in the compressor cylinder is also maintained at a high pressure when the piston rises, and this maintained pressure suppresses the negative pressure generated in the cylinder when the piston descends. This makes it possible to reduce the load on the compressor.

[0009] In a preferred configuration, the control device controls the second solenoid valve to operate the drain valve to seal the branch passage during at least a portion of the period during which the first solenoid valve is driven.

[0010] According to this configuration, since the branch passage is sealed during at least a part of the period during which the compressor is running without draining, the air pressure in the connecting passage connected to the reed valve of the compressor and the air pressure in the desiccant are maintained high. In particular, even when the compressor switches from load operation to idle operation, a decrease in the air pressure in the connecting passage and the air pressure in the desiccant is suppressed by keeping the drain valve sealed.

[0011] In a preferred configuration, the connecting passage is provided with an upstream check valve between the compressor and the branch passage for allowing the supply of air from the compressor. According to this configuration, the air pressure in the connecting passage between the reed valve on the outlet side of the compressor and the upstream check valve can be maintained at the sealing pressure of the upstream check valve.

[0012] In a preferred configuration, there is provided a downstream check valve that allows the flow of air output from the desiccant to the opposite side to the compressor, and a regeneration control valve provided in the middle of a passage parallel to the downstream check valve, and the control device is capable of switching the regeneration control valve between open and closed, and opens the regeneration control valve for a predetermined period of time when the first solenoid valve is driven and the second solenoid valve operates the drain discharge valve to seal the branch passage.

[0013] With this configuration, when the branch passage is sealed by the drain discharge valve, the regeneration control valve is opened to supply compressed air downstream of the downstream check valve, thereby increasing the air pressure in the connecting passage and the air pressure in the desiccant.

[0014] In a preferred configuration, a pressure sensor for detecting an air pressure is provided in the connecting passage, and the control device determines the predetermined period during which the regeneration control valve is opened in accordance with the air pressure detected by the pressure sensor.

[0015] With this configuration, the opening / closing of the regeneration control valve can be controlled in accordance with the air pressure in the connecting passage and the air pressure in the desiccant, so that the air pressure in the connecting passage and the air pressure in the desiccant can be adjusted to a pressure higher than atmospheric pressure.

[0016] In a preferred configuration, the pressure sensor is located between the compressor and the upstream check valve. With this configuration, the air pressure in the connecting passage connected to the reed valve on the outlet side of the compressor is measured by a pressure sensor, and the opening / closing of the regeneration control valve can be adjusted based on this measured residual pressure.

[0017] In a preferred configuration, the control device includes a supply process in which, when the first solenoid valve is driven, the second solenoid valve operates the drain valve to seal the branch passage and close the regeneration control valve, a purge process in which the second solenoid valve operates the drain valve to open the branch passage and close the regeneration control valve, a regeneration process in which the second solenoid valve operates the drain valve to open the branch passage and open the regeneration control valve, and a pressurization process in which the second solenoid valve operates the drain valve to seal the branch passage and open the regeneration control valve.

[0018] According to this configuration, when the first solenoid valve is driven, the supply process, the purging process, the regeneration process, and the pressurization process can be performed at appropriate times. In a preferred configuration, the control device has an adjustment function for selecting and executing one of the supply process, the purging process, and the pressurizing process so that the air pressure in the connecting passage and the air pressure in the desiccant are maintained at a predetermined value.

[0019] With this configuration, the air pressure in the connecting passage and the air pressure in the desiccant can be maintained at a predetermined value higher than atmospheric pressure. In addition, by monitoring the pressure sensor value and performing feedback processing, the air pressure can be maintained at a predetermined value with higher accuracy.

[0020] In a preferred configuration, the control device sequentially executes the regeneration process and the pressurization process prior to the adjustment process. According to this configuration, the air pressure in the connecting passage and the air pressure in the desiccant, which have been reduced to atmospheric pressure during the regeneration process, can be raised to a pressure higher than atmospheric pressure. Effect of the Invention

[0021] According to the present invention, the load on the compressor can be reduced. [Brief description of the drawings]

[0022] [Figure 1]1 is a diagram showing a schematic configuration of an air supply system according to a first embodiment. [Diagram 2] 1A to 1F are diagrams showing operation modes of the air dryer of the same embodiment, where (a) is a diagram showing a first operation mode, (b) is a diagram showing a second operation mode, (c) is a diagram showing a third operation mode, (d) is a diagram showing a fourth operation mode, (e) is a diagram showing a fifth operation mode, and (f) is a diagram showing a sixth operation mode. [Diagram 3] 5 is a flowchart showing an example of a procedure for supplying compressed air in the embodiment. [Figure 4] 4 is a flowchart showing an example of a procedure of an air dryer and a regeneration process in the embodiment. [Diagram 5] 4 is a flowchart showing an example of a procedure for running the compressor without air in the embodiment. [Figure 6] 5 is a flowchart showing an example of a procedure for adjusting the pressure in a connection passage in the embodiment. [Figure 7] 10 is a flowchart showing an example of a procedure for adjusting the pressure of a connection passage in the second embodiment of the air supply system. [Figure 8] 10 is a flowchart showing an example of a procedure for adjusting the pressure of a connection passage in the air supply system according to the third embodiment. [Figure 9] 10 is a flowchart showing an example of a procedure for adjusting the pressure in a connection passage in the fourth embodiment of the air supply system. [Figure 10] 13 is a flowchart showing an example of a procedure for adjusting the pressure of a connection passage in the air supply system according to the fifth embodiment. [Figure 11] 5 is a flowchart showing an example of a procedure for performing an oil cut operation in the embodiment. [Figure 12] 13 is a flowchart showing an example of a procedure for performing a regeneration operation based on humidity in the air supply system according to the sixth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] (First embodiment) A first embodiment of an air supply system will be described with reference to Figures 1 to 6. The air supply system is mounted on automobiles such as trucks, buses, and construction machines.

[0024] <Configuration of Air Supply System 10> The configuration of an air supply system 10 will be described with reference to Fig. 1. The air supply system 10 includes a compressor 4, an air drying circuit 11, and an ECU 80 serving as a control device.

[0025] In the air supply system 10, a plurality of wires E61 to E66 are connected to an ECU 80. The ECU 80 includes a calculation unit, a volatile storage unit, and a non-volatile storage unit, and is configured to provide command values ​​to the air drying circuit 11 according to a program stored in the non-volatile storage unit.

[0026] The compressor 4 is switched, based on a command value from the ECU 80, between an operating state (load operation) in which the compressor 4 compresses and supplies air, and a non-operating state (idle operation) in which the compressor 4 does not compress air. The air drying circuit 11 is a so-called air dryer. The air drying circuit 11 is connected to the ECU 80 and dries the compressed air sent from the compressor 4 during load operation. The air drying circuit 11 sends the dried compressed air to the supply circuit 12.

[0027] The supply circuit 12 stores the compressed air sent from the air drying circuit 11 in an air tank (not shown) mounted on the vehicle, and supplies the air to each load (not shown). The air drying circuit 11 has a maintenance port P12. The maintenance port P12 is a port for supplying air to the air drying circuit 11 during maintenance.

[0028] <Configuration of the air drying circuit 11> The air drying circuit 11 includes a filter 17 in its interior 11A (see FIG. 2). In this embodiment, the filter 17 is provided in the middle of an air supply passage 18 that connects the compressor 4 and the supply circuit 12. The filter 17 corresponds to a desiccant. The air supply passage 18 functions as a connecting passage.

[0029] Filter 17 removes moisture from the air by passing it through a desiccant to dry it, and also removes oil from the air by the filtering section to purify it. The air that has passed through filter 17 is supplied to supply circuit 12 via downstream check valve 19, which serves as a check valve that allows air to flow only downstream from filter 17. In other words, when filter 17 is upstream and supply circuit 12 is downstream, downstream check valve 19 allows air to flow only from upstream to downstream. Since downstream check valve 19 has a predetermined valve opening pressure (sealing pressure), when compressed air flows, the upstream pressure is higher than the downstream pressure by the valve opening pressure.

[0030] Further, downstream of the filter 17, a bypass passage 20 serving as a detour around the downstream check valve 19 is provided in parallel to the downstream check valve 19. A regeneration control valve 21 is connected to the bypass passage 20.

[0031] The regeneration control valve 21 is an electromagnetic valve whose operation is switched by turning on and off (driven / non-driven) the power from the ECU 80 via the wiring E64. When the power is off, the regeneration control valve 21 closes to block the bypass passage, and when the power is on, it opens to communicate with the bypass circuit. The ECU 80 receives, for example, the value of the air pressure in the air tank and operates the regeneration control valve 21 when the air pressure value exceeds a predetermined range.

[0032] An orifice 22 is provided between the regeneration control valve 21 and the filter 17 in the bypass flow passage 20. When the regeneration control valve 21 is energized, the compressed air on the supply circuit 12 side is sent to the filter 17 through the bypass flow passage 20 with the flow rate regulated by the orifice 22. The air sent to the filter 17 flows backward through the filter 17 from the downstream side to the upstream side of the filter 17. This process is a process for regenerating the filter 17, and is called a dryer regeneration process. The compressed air sent to the filter 17 at this time is dried and purified air that has passed through the filter 17 from the air supply passage 18 and been supplied to the supply circuit 12, so that the moisture and oil captured by the filter 17 are removed from the filter 17. Therefore, the regeneration control valve 21 is opened for a predetermined period by the ECU 80. The predetermined period is set based on logic, experiment, or experience as a period during which the filter 17 can be regenerated.

[0033] Between the compressor 4 and the filter 17, a branch passage 16 connected to a drain discharge valve 25 is provided. At the end of the branch passage 16, a drain discharge port 27 is provided. The drain containing the water and oil removed from the filter 17 is sent to the drain discharge valve 25 together with compressed air. The drain discharge valve 25 is an air-pressure-driven valve that is driven by air pressure, and is provided between the filter 17 and a drain discharge port 27 in the branch passage 16 of the air supply passage 18. The drain discharge valve 25 is a two-port two-position valve that changes its position between a closed position and an open position. When in the open position, the drain discharge valve 25 sends the drain to the drain discharge port 27. The drain discharged from the drain discharge port 27 may be collected by an oil separator (not shown).

[0034] The drain discharge valve 25 is controlled by a governor 26A. The governor 26A is an electromagnetic valve, and is operated by turning on and off (driving / non-driving) the power from the ECU 80 via a wire E63. When the power is turned on, the governor 26A inputs an air pressure signal to the drain discharge valve 25 to open the drain discharge valve 25. When the power is turned off, the governor 26A does not input an air pressure signal to the drain discharge valve 25, but sets the pressure to atmospheric pressure, to close the drain discharge valve 25. The governor 26A functions as a second electromagnetic valve.

[0035] The drain discharge valve 25 is maintained in the closed position when no air pressure signal is input from the governor 26A, and is opened when an air pressure signal is input from the governor 26A. When the input port on the compressor 4 side of the drain discharge valve 25 becomes high pressure beyond the upper limit, the drain discharge valve 25 is forcibly switched to the open position.

[0036] An upstream check valve 15 is provided between the compressor 4 and the filter 17, and also between the compressor 4 and the branch passage 16. When the compressor 4 side is the upstream and the filter 17 side is the downstream, the upstream check valve 15 only allows air to flow from upstream to downstream. Since the upstream check valve 15 has a predetermined valve opening pressure (sealing pressure), when compressed air flows, the upstream pressure is higher than the downstream pressure by the valve opening pressure. A reed valve at the outlet of the compressor 4 is provided upstream of the upstream check valve 15, and the branch passage 16 and the filter 17 are provided downstream of the upstream check valve 15.

[0037] <Compressor 4> The compressor 4 is controlled by the unloading control valve 26B. The unloading control valve 26B is a solenoid valve, and operates in response to the power being turned on and off (driven / non-driven) from the ECU 80 via a wire E62. When the power is turned off, the unloading control valve 26B is in the open position, and opens the flow path between the unloading control valve 26B and the compressor 4 to the atmosphere. When the power is turned on, the unloading control valve 26B is in the supply position, and sends an air pressure signal consisting of compressed air to the compressor 4. The unloading control valve 26B functions as a first solenoid valve.

[0038] The compressor 4 is put into a non-operating state (idle operation) when an air pressure signal is input from the unloading control valve 26B. For example, when the pressure in the supply circuit 12 reaches the upper limit pressure, it is not necessary to supply dry compressed air. The pressure in the supply circuit 12 is measured by a pressure sensor (not shown) and input to the ECU 80. The unloading control valve 26B is set to the supply position when the power is turned on (driven) by the ECU 80 based on the measurement result of the pressure sensor. As a result, an air pressure signal is supplied from the unloading control valve 26B to the compressor 4.

[0039] <Sensor> A pressure sensor 50 is provided between the compressor 4 and the upstream check valve 15. The pressure sensor 50 measures the air pressure in the connected air supply passage 18, and transmits the measurement result to the ECU 80 via a wire E61.

[0040] A humidity sensor 51 and a temperature sensor 52 are provided between the downstream check valve 19 and the supply circuit 12. The humidity sensor 51 and the temperature sensor 52 measure the humidity and the temperature of the compressed air downstream of the filter 17, respectively, and output the measurement results to the ECU 80 via wires E65 and E66. The ECU 80 calculates the dew point based on the humidity and temperature of the input compressed air. For example, if the humidity of the compressed air output by the compressor 4 is approximately 100%, the amount of moisture removed by the filter 17 can be calculated based on the difference between 100% and the measured humidity and the amount of saturated water vapor at the temperature.

[0041] <Operation of the air drying circuit 11> As shown in FIG. 2, the air drying circuit 11 has six operation modes, namely, a first operation mode to a sixth operation mode.

[0042] As shown in FIG. 2(a), the first operation mode is a mode in which normal loading operation is performed for supply processing, and the regeneration control valve 21, the governor 26A, and the unloading control valve 26B are each closed on the upstream side (the supply circuit 12 side) (indicated as "CLOSE" in the figure). At this time, power is not supplied to the regeneration control valve 21, the governor 26A, and the unloading control valve 26B. In addition, the governor 26A and the unloading control valve 26B open the port of the compressor 4 and the port of the drain discharge valve 25 connected downstream thereof to the atmosphere, respectively. In the first operation mode, when compressed air is supplied from the compressor 4 (indicated as "ON" in the figure), moisture and oil are removed by a desiccant, and the compressed air is supplied to the supply circuit 12.

[0043] As shown in FIG. 2(b), the second operation mode is a mode in which the compressor is stopped (with purging) for purging, in which the regeneration control valve 21 is closed and the governor 26A and the unloading control valve 26B are opened (indicated as "OPEN" in the figure). At this time, the governor 26A and the unloading control valve 26B are each supplied with power, and the port of the compressor 4 and the port of the drain discharge valve 25 connected downstream of them are each connected to the upstream side (the supply circuit 12 side). In the second operation mode, when the compressor 4 is not in operation (indicated as "OFF" in the figure), the compressed air in the desiccant of the filter 17 and the air supply passage 18 is discharged together with moisture, oil, etc. from the drain discharge port 27, and the air pressure in the filter 17 and the air supply passage 18 is made atmospheric pressure.

[0044] As shown in Fig. 2(c), the third operation mode is a mode in which a regeneration operation for regeneration processing is performed, and the regeneration control valve 21, the governor 26A, and the unload control valve 26B are each opened. At this time, power is also supplied to the regeneration control valve 21. In the third operation mode, the compressor 4 is put into a non-operating state, and the compressed air in the supply circuit 12 is caused to flow back through the filter 17 (in the desiccant) and discharged from the drain outlet 27, thereby removing moisture from the desiccant in the filter 17.

[0045] As shown in Fig. 2(d), the fourth operation mode is a mode in which an oil cut operation is performed, in which the regeneration control valve 21 and the unload control valve 26B are closed, and the governor 26A is opened for a certain period of time and then closed. In the fourth operation mode, when the compressor 4 is in an operating state, the compressed air supplied by the compressor 4 is discharged from the drain outlet 27 for a certain period of time, for example, immediately after switching from a non-operating state to an operating state, and compressed air containing a relatively large amount of oil is discharged from the drain outlet 27, thereby reducing deterioration of the filter 17. When the engine speed increases in an operating state or when the engine is under high load, the oil cut operation can also be performed.

[0046] 2(e), the fifth operation mode is a mode in which the compressor is stopped (without purging), in which the regeneration control valve 21 and the governor 26A are closed, and the unload control valve 26B is opened. In the fifth operation mode, when the compressor 4 is not in operation, the compressed air remaining in the air supply passage 18 and the desiccant of the filter 17 is not discharged from the drain outlet 27, thereby maintaining the air pressure.

[0047] 2(f), the sixth operation mode is a mode in which an assist operation is performed for pressurization, in which the regeneration control valve 21 and the unload control valve 26B are opened, and the governor 26A is closed. In the sixth operation mode, when the compressor 4 is not in operation, compressed air in the supply circuit 12 is supplied (backflowed) into the air supply passage 18 and the desiccant in the filter 17 to raise the pressure higher than atmospheric pressure, thereby maintaining the back pressure (air pressure) of the upstream check valve 15 at a pressure higher than atmospheric pressure.

[0048] <Compressor assist operation> The compressor assist operation will be described with reference to FIGS. When the piston of the compressor 4 descends during idling operation, negative pressure is generated in the cylinder in response to the expansion of the volume, and this negative pressure increases the operating load. Therefore, the compressor assist is used to reduce the increase in operating load caused by the negative pressure. Specifically, when the piston of the compressor 4 descends during idling operation, the compressor assist closes the reed valve at the outlet of the compressor 4 by maintaining the pressure in the desiccant of the filter 17 and in the air supply passage 18 at a pressure higher than atmospheric pressure, and the pressure generated when the piston ascends is maintained in the cylinder to some extent, thereby suppressing the generation of negative pressure in the cylinder. This reduces the operating load of the compressor 4 during idling operation. Specifically, when the compressor 4 is idling, the drain discharge valve 25 is closed, and the compressed air supplied by the compressor 4 is used to maintain the air pressure in the desiccant of the filter 17 and in the air supply passage 18 at a pressure higher than atmospheric pressure.

[0049] When the air supply system 10 starts supplying compressed air, it performs an air supply process in which the compressed air output from the compressor 4 is supplied to the supply circuit 12 (step S10 in FIG. 3). In the air supply process, the air drying circuit 11 is in the first operation mode, and removes moisture and oil from the compressed air supplied from the compressor 4 and outputs the air to the supply circuit 12. The air supply process ends when the air pressure in the supply circuit 12, for example, the air pressure in an air tank, exceeds an upper limit value.

[0050] When the air supply operation is completed in the air supply step (step S10 in FIG. 3), the air supply system 10 puts the compressor 4 in a non-operating state and performs a dryer regeneration step (step S11 in FIG. 3). In the dryer regeneration step, a dryer regeneration process for regenerating the filter 17 is performed.

[0051] 4, in the dryer regeneration process, the ECU 80 performs a humidity measurement step (step S20 in FIG. 4). In the humidity measurement step, the humidity of the compressed air is measured based on the humidity measured by the humidity sensor 51 and the temperature measured by the temperature sensor 52.

[0052] Next, the ECU 80 determines whether or not "purging" of the filter 17 is necessary (step S21 in FIG. 4). The ECU 80 determines that "purging" is necessary when the humidity of the compressed air is equal to or higher than the first humidity threshold, and determines that "purging" is not necessary when the humidity of the compressed air is less than the first humidity threshold. In addition, the necessity of "purging" can also be determined based on the "amount of air passing through the filter" and the "amount of oil in the filter".

[0053] Then, when it is determined that "purging" is necessary (YES in step S21 in FIG. 4), the ECU 80 sets the air drying circuit 11 to the second operation mode, performs a compressor stop operation (with purging) (step S22 in FIG. 4), and then determines whether or not "regeneration processing" of the filter 17 is necessary (step S24 in FIG. 4). The ECU 80 determines that "regeneration processing" is necessary when the humidity of the compressed air is equal to or higher than the second humidity threshold, and determines that "regeneration processing" is not necessary when the humidity of the compressed air is less than the second humidity threshold.

[0054] When it is determined that the "regeneration process" is necessary (YES in step S24 in FIG. 4), the ECU 80 sets the air drying circuit 11 to the third operation mode and performs the regeneration process (step S25 in FIG. 4). Then, when the regeneration process is completed, the ECU 80 ends the dryer regeneration process (step S11 in FIG. 3) and proceeds to the next step.

[0055] On the other hand, when it is determined that the "regeneration process" is not necessary (NO in step S24 in FIG. 4), the ECU 80 ends the dryer regeneration process (step S11 in FIG. 3) and advances the process to the next step.

[0056] On the other hand, when it is determined that "purging" is not necessary (NO in step S21 in FIG. 4), the ECU 80 sets the air drying circuit 11 to the fifth operation mode and performs a compressor stop operation (without purging) (step S23 in FIG. 4). By performing the compressor stop operation (without purging), the desiccant in the filter 17 and the air supply passage 18 are not opened to the atmosphere after the compressor 4 is stopped, so that the back pressure of the upstream check valve 15 can be maintained higher than atmospheric pressure. This makes it possible to perform compressor assist. This also ends the dryer regeneration process (step S11 in FIG. 3), and the process proceeds to the next step.

[0057] 3, the air supply system 10 performs an air non-supply step (step S12 in FIG. 3). In the air non-supply step, the ECU 80 performs an air non-supply process so that the back pressure of the upstream check valve 15 is maintained high during the compressor stop operation.

[0058] 5, in the air non-supply process, the ECU 80 determines whether the air pressure in the desiccant of the filter 17 or in the air supply passage 18 is high (step S30 in FIG. 5). The ECU 80 compares the measurement value of the pressure sensor 50 with a high-pressure threshold, and determines that the air pressure is high if the measurement value is equal to or higher than the high-pressure threshold, and determines that the air pressure is low if the measurement value is lower than the high-pressure threshold.

[0059] When it is determined that the air pressure in the desiccant of the filter 17 or in the air supply passage 18 is high (YES in step S30 in FIG. 5), the ECU 80 sets the air drying circuit 11 to the fifth operation mode and performs a compressor stop operation (without purging) (step S32 in FIG. 5). On the other hand, when it is determined that the air pressure in the desiccant of the filter 17 or in the air supply passage 18 is low (NO in step S30 in FIG. 5), the ECU 80 performs an assist operation (step S31 in FIG. 5). In the assist operation, the air drying circuit 11 is set to the sixth operation mode, and the air pressure in the desiccant of the filter 17 or in the air supply passage 18 is increased. Then, the air drying circuit 11 is set to the fifth operation mode and performs a compressor stop operation (without purging) (step S32 in FIG. 5). Therefore, the back pressure of the upstream check valve 15 is maintained higher than the atmospheric pressure, and compressor assist becomes possible.

[0060] Next, the ECU 80 performs a pressure adjustment process (step S33 in FIG. 5). In the pressure adjustment process, the ECU 80 performs a pressure adjustment process. As shown in Fig. 6, in the pressure adjustment process, the ECU 80 determines whether the air pressure in the desiccant of the filter 17 or in the air supply passage 18 is low (step S40 in Fig. 6). The ECU 80 determines that the air pressure is low if the measurement value of the pressure sensor 50 is equal to or lower than the low pressure threshold, and determines that the air pressure is not low if the measurement value of the pressure sensor 50 is greater than the low pressure threshold. In this embodiment, the upstream check valve 15 is provided downstream of the pressure sensor 50, so that the value of the pressure sensor 50 is stable, and the number of assist operations and purge operations can be reduced.

[0061] When it is determined that the air pressure is low (YES in step S40 in FIG. 6), the ECU 80 sets the air drying circuit 11 to the sixth operation mode and performs an assist operation (step S41 in FIG. 6), and then sets the air drying circuit 11 to the fifth operation mode and performs a compressor stop operation (without purging) (step S42 in FIG. 6).On the other hand, when it is determined that the air pressure is not low (NO in step S40 in FIG. 6), the ECU 80 sets the air drying circuit 11 to the fifth operation mode and performs a compressor stop operation (without purging) (step S42 in FIG. 6).

[0062] Furthermore, the ECU 80 determines whether the air pressure is high or not (step S43 in FIG. 6). The ECU 80 determines that the air pressure is high if the measurement value of the pressure sensor 50 is equal to or higher than the high pressure threshold, and determines that the air pressure is not high if the measurement value of the pressure sensor 50 is lower than the low pressure threshold.

[0063] When the air pressure is determined to be high (YES in step S43 in FIG. 6), the ECU 80 sets the air drying circuit 11 to the second operation mode and performs the compressor stop operation (with purging) (step S44 in FIG. 6), and sets the air drying circuit 11 to the fifth operation mode and performs the compressor stop operation (without purging) (step S45 in FIG. 6). On the other hand, when the air pressure is determined to be not high (NO in step S43 in FIG. 6), the ECU 80 sets the air drying circuit 11 to the fifth operation mode and performs the compressor stop operation (without purging) (step S45 in FIG. 6). As a result, the back pressure of the upstream check valve 15 is maintained higher than the atmospheric pressure, and the compressor assist becomes possible. That is, the height of the air pressure has a relationship of "atmospheric pressure<low pressure threshold<high ​​pressure threshold". Next, the ECU 80 performs an air pressure determination process (step S46 in FIG. 6). In the air pressure determination process, if the measurement value of the pressure sensor 50 is less than the high pressure threshold and greater than or equal to the low pressure threshold, the air pressure is determined to be “appropriate,” and if the measurement value is greater than or equal to the high pressure threshold or less than the constant pressure threshold, the air pressure is determined to be “inappropriate.”

[0064] Then, as shown in FIG. 5, when the pressure adjustment process is completed, the pressure adjustment step (step S33 in FIG. 5) ends, and the process proceeds to the next step. Next, it is determined whether or not to end the air non-supply process (step S34 in FIG. 5). When the compressor 4 needs to be operated under load, the ECU 80 determines to end the air non-supply process, whereas when the compressor 4 does not need to be operated under load, the ECU 80 determines not to end the air non-supply process.

[0065] That is, when it is determined not to end the air non-supply process (NO in step S34 in FIG. 5), the ECU 80 continues to perform the pressure adjustment process (step S33 in FIG. 5). On the other hand, when it is determined to end the air non-supply process (YES in step S34 in FIG. 5), the air non-supply process (step S13 in FIG. 3) is ended, and the process proceeds to the next step.

[0066] Then, as shown in Fig. 3, it is determined whether or not to end the air supply (step S13 in Fig. 3). For example, it is determined that the air supply is to be ended based on the engine of the vehicle being stopped, and it is determined that the air supply is not to be ended based on the engine of the vehicle continuing to rotate, etc.

[0067] When it is determined not to end the air supply (NO in step S13 in FIG. 3), the ECU 80 returns the process to step S10 and executes the air supply step (step S10 in FIG. 3) and subsequent processes. On the other hand, when it is determined to end the air supply (YES in step S13 in FIG. 3), the air supply is stopped.

[0068] As described above, according to this embodiment, the following effects can be obtained. (1) The unload control valve 26B switches the compressor 4 between loaded operation and empty operation, and the governor 26A switches the drain discharge valve 25 between closed and open. Therefore, when the compressor 4 is in empty operation, the drain discharge valve 25 can be kept closed. For example, if the drain discharge valve 25 is kept closed, the air pressure in the air supply passage 18 and the air pressure in the desiccant of the filter 17 can be maintained at a pressure somewhat higher than atmospheric pressure by the air pressure supplied by the compressor 4. Therefore, the pressure in the cylinder of the compressor 4 is also maintained at a high pressure by the rise of the piston, and this maintained pressure suppresses the negative pressure generated in the cylinder when the piston descends. This reduces the load on the compressor 4.

[0069] (2) Because the branch passage 16 is sealed during at least a portion of the period during which the compressor 4 is running without air, the air pressure in the air supply passage 18 to which the reed valve of the compressor 4 is connected and the air pressure in the desiccant of the filter 17 are maintained high. In particular, even when the compressor 4 switches from load operation to idle operation, a decrease in the air pressure in the air supply passage 18 and in the desiccant of the filter 17 is suppressed by keeping the drain discharge valve 25 sealed.

[0070] (3) In the air supply passage 18 , the air pressure between the reed valve on the outlet side of the compressor 4 and the upstream check valve 15 can be maintained at the sealing pressure of the upstream check valve 15 .

[0071] (4) When the branch passage 16 is sealed by the drain discharge valve 25, the regeneration control valve 21 is opened, supplying compressed air downstream of the downstream check valve 19, thereby increasing the air pressure in the air supply passage 18 and in the desiccant of the filter 17.

[0072] (5) By referring to the measurement results of the pressure sensor 50 and controlling the opening / closing of the regeneration control valve 21 according to the air pressure in the air supply passage 18 and in the desiccant of the filter 17, the air pressure in the air supply passage 18 and in the desiccant of the filter 17 can be adjusted to a pressure higher than atmospheric pressure.

[0073] (6) The air pressure in the air supply passage 18 connected to the reed valve on the outlet side of the compressor 4 and in the desiccant of the filter 17 is measured by the pressure sensor 50, and the opening / closing of the regeneration control valve 21 can be adjusted based on this measured residual pressure.

[0074] (7) When the unloading control valve 26B is driven (during unloading), the purge process, the regeneration process, and the pressurization process can be performed at appropriate times. (8) The air pressure in the air supply passage 18 and in the desiccant of the filter 17 can be maintained at a predetermined value higher than atmospheric pressure. In addition, by monitoring the value of the pressure sensor 50 and performing feedback processing, the air pressure can be maintained at a predetermined value with higher accuracy.

[0075] (9) The air pressure in the air supply passage 18 and in the desiccant of the filter 17, which has been lowered to atmospheric pressure during the regeneration process, can be made higher than atmospheric pressure. Second embodiment A second embodiment of the air supply system will be described with reference to Fig. 7. This embodiment differs from the first embodiment in that the upstream check valve 15 is not provided in the air supply passage 18. In other words, this embodiment has a configuration in which the upstream check valve 15 in Fig. 1 of the first embodiment is not provided.

[0076] In this embodiment, as a result of the compressor assist operation being performed, the ECU 80 performs the pressure adjustment step (step S33 in FIG. 5) as shown in FIG. 5 of the first embodiment. In the pressure adjustment step, the ECU 80 performs pressure adjustment processing.

[0077] As shown in Fig. 7, in the pressure adjustment process, the ECU 80 determines whether the air pressure in the desiccant of the filter 17 or the air pressure in the air supply passage 18 is low (step S50 in Fig. 7). In this embodiment, a pressure sensor 50 is provided between the compressor 4 and the filter 17, but an upstream check valve is not provided. Therefore, the value of the pressure sensor 50 may be somewhat unstable compared to the configuration of the first embodiment, but the pressure adjustment process can be preferably performed by relatively increasing the number of assist operations and purge operations.

[0078] When it is determined that the air pressure is low (YES in step S50 in FIG. 7), the ECU 80 performs an assist operation (step S51 in FIG. 7). On the other hand, when it is determined that the air pressure is not low (NO in step S50 in FIG. 7) or when the assist operation in step S51 is completed, the ECU 80 performs a compressor stop operation (without purging) (step S52 in FIG. 7).

[0079] Next, the ECU 80 determines whether the air pressure is high or not (step S53 in FIG. 7). When the air pressure is determined to be high (YES in step S53 in FIG. 7), the ECU 80 performs a compressor stop operation (with purging) (step S54 in FIG. 7). On the other hand, when the air pressure is determined to be not high (NO in step S53 in FIG. 7) or when the purging operation in step S54 is completed, the ECU 80 performs a compressor stop operation (without purging) (step S55 in FIG. 7). This maintains the air pressure in the desiccant of the filter 17 and in the air supply passage 18, which are located upstream of the downstream check valve 19, higher than the atmospheric pressure, enabling compressor assist. In addition, the ECU 80 performs an air pressure determination process (step S56 in FIG. 7) in which the air pressure is determined to be "appropriate" if it is less than the high pressure threshold and equal to or greater than the low pressure threshold, and is determined to be "inappropriate" otherwise.

[0080] As described above, according to this embodiment, in addition to the advantages (1), (2), (4), (5), and (7) to (9) described in the first embodiment, the following advantages can be obtained. (10) Even if the upstream check valve 15 is not provided, when the compressor 4 is running dry, the air pressure in the desiccant of the filter 17 and the air pressure in the air supply passage 18 are maintained at a pressure somewhat higher than atmospheric pressure by closing the drain discharge valve 25. This reduces the load on the compressor 4.

[0081] (Third embodiment) A third embodiment of the air supply system will be described with reference to Fig. 8. This embodiment differs from the first embodiment in that the pressure sensor 50 is not provided in the air supply passage 18. In other words, this embodiment has a configuration in which the pressure sensor 50 is not provided in Fig. 1 of the first embodiment.

[0082] In this embodiment, as a result of the compressor assist operation being performed, the ECU 80 performs the pressure adjustment step (step S33 in FIG. 5) as shown in FIG. 5 of the first embodiment. In the pressure adjustment step, the ECU 80 performs pressure adjustment processing.

[0083] As shown in Fig. 8, in the pressure adjustment process, the ECU 80 determines whether or not to assist (step S60 in Fig. 8). In this embodiment, since the upstream check valve 15 is provided, the ECU 80 determines that assist is not required if the compressor is stopped (without purging) immediately after the compressor is stopped or if the immediately preceding operation is an assist operation. The ECU 80 also determines that assist is required if the immediately preceding operation is a compressor stop operation (with purging) or a regeneration operation.

[0084] When it is determined that assist is necessary (YES in step S60 in FIG. 8), the ECU 80 performs the assist operation (step S61 in FIG. 8). On the other hand, when it is determined that assist is not necessary (NO in step S60 in FIG. 8) or when the assist operation in step S61 ends, the ECU 80 determines whether or not to end the assist operation (step S62 in FIG. 8). For example, when a condition for operating the compressor 4 under load is established, it is determined that the assist operation is to end.

[0085] If it is determined that the assist should not be ended (NO in step S62 in FIG. 8), the ECU 80 returns the process to step S60 and continues the operation according to the determination of whether the assist operation is necessary. On the other hand, if it is determined that the assist should be ended (YES in step S62 in FIG. 8), the ECU 80 performs a compressor stop operation (without purging) (step S63 in FIG. 8). Then, the ECU 80 returns to the pressure adjustment process and proceeds to the next step of the pressure adjustment process.

[0086] As described above, according to this embodiment, in addition to the advantages (1) to (4) and (6) to (9) described in the first embodiment, the following advantages can be obtained. (11) Even if the pressure sensor 50 is not provided, when the compressor 4 is running dry, the drain discharge valve 25 is closed to maintain the air pressure in the air supply passage 18 and the desiccant in the filter 17 at a pressure somewhat higher than atmospheric pressure by the sealing pressure of the upstream check valve 15. This reduces the load on the compressor 4.

[0087] (Fourth embodiment) A fourth embodiment of the air supply system will be described with reference to Fig. 9. This embodiment differs from the first embodiment in that the pressure sensor 50 and the upstream check valve 15 are not provided in the air supply passage 18. In other words, this embodiment has a configuration in which the pressure sensor 50 and the upstream check valve 15 in Fig. 1 of the first embodiment are not provided.

[0088] In this embodiment, as a result of the compressor assist operation being performed, the ECU 80 performs a pressure adjustment process (step S33 in FIG. 5) as shown in FIG. 5 of the first embodiment. In the pressure adjustment process, the ECU 80 performs pressure adjustment processing. In this embodiment, since an upstream check valve is not provided, the air pressure may be somewhat unstable compared to the configuration of the first embodiment. In addition, since a pressure sensor is provided, feedback control based on the air pressure cannot be performed. Therefore, control for the pressure adjustment process is performed based on predetermined conditions.

[0089] As shown in Fig. 9, in the pressure adjustment process, the ECU 80 determines whether or not to assist (step S70 in Fig. 9). In this embodiment, since the pressure sensor 50 and the upstream check valve 15 are not provided, the ECU 80 determines that assist is not required if the compressor stop operation (without purging) continues after the compressor is stopped, or if the operation immediately before is an assist operation. Also, the ECU 80 determines that assist is required if the compressor stop operation (with purging) is performed or a regeneration operation is performed.

[0090] When it is determined that assist is necessary (YES in step S70 in FIG. 9), the ECU 80 performs the assist operation (step S71 in FIG. 9). On the other hand, when it is determined that assist is not necessary (NO in step S70 in FIG. 9) or when the assist operation in step S71 ends, the ECU 80 determines whether or not to end the assist operation (step S72 in FIG. 9). For example, when the condition for operating the compressor 4 under load is satisfied, it is determined that the assist is to end.

[0091] If it is determined that the assist should not be ended (NO in step S72 in FIG. 9), the ECU 80 returns the process to step S70 and performs an operation according to the determination of whether the assist operation is necessary. On the other hand, if it is determined that the assist should be ended (YES in step S72 in FIG. 9), the ECU 80 performs a compressor stop operation (without purging) (step S73 in FIG. 9). Then, the ECU 80 returns to the pressure adjustment process and proceeds to the next step of the pressure adjustment process.

[0092] As described above, according to this embodiment, in addition to the advantages (1), (2), (4), and (7) to (9) described in the first embodiment, the following advantages can be obtained. (12) Even if the pressure sensor 50 and the upstream check valve 15 are not provided, when the compressor 4 is running dry, the air pressure in the air supply passage 18 and in the desiccant of the filter 17 is maintained at a pressure somewhat higher than atmospheric pressure by keeping the drain discharge valve 25 closed. This reduces the load on the compressor 4.

[0093] Fifth embodiment A fifth embodiment of the air supply system will be described with reference to Fig. 10 and Fig. 11. This embodiment differs from the first embodiment in that an oil cut process is performed during normal load operation. Here, an example in which the oil cut process is performed when load operation starts will be described.

[0094] As shown in FIG. 10, when the air supply system 10 starts to supply air, first, an oil cut process is performed in an oil cut process (step S83 in FIG. 10). As shown in Fig. 11, in the oil cut processing, the ECU 80 judges whether or not to perform oil cut (step S90 in Fig. 11). If it is judged that oil cut is necessary (YES in step S90 in Fig. 11), the ECU 80 sets the air drying circuit 11 to the fourth operation mode (see Fig. 2(d)) and performs the oil cut operation (step S91 in Fig. 11). On the other hand, if it is judged that oil cut is not necessary (NO in step S90 in Fig. 11) or if the oil cut operation in step S91 is completed, the ECU 80 ends the oil cut process (step S83 in Fig. 10).

[0095] Next, the same steps as those performed when the air supply is started in the first embodiment are performed. That is, the air supply system 10 sequentially performs an air supply step (step S80 in FIG. 10) of supplying compressed air output from the compressor 4 to the supply circuit 12, a dryer regeneration step (step S81 in FIG. 10), and an air non-supply step (step S82 in FIG. 10).

[0096] Then, the ECU 80 determines whether or not to end the air supply (step S84 in FIG. 10). When it is determined not to end the air supply (NO in step S84 in FIG. 10), the ECU 80 returns the process to step S83 and continues the air supply process. On the other hand, when it is determined to end the air supply process (YES in step S84 in FIG. 10), the air supply is stopped.

[0097] As described above, according to this embodiment, in addition to the effects (1) to (12) described in the first to fourth embodiments, the following effect can be obtained. (13) Compressed air containing a relatively large amount of oil is discharged from the drain outlet 27, which reduces deterioration of the filter 17. For example, this may be performed immediately after the compressor 4 is switched from a non-operating state to an operating state.

[0098] Sixth embodiment A sixth embodiment of the air supply system will be described with reference to Fig. 12. This embodiment differs from the first embodiment in that forced regeneration processing is performed while the compressor 4 is operating under load. In this embodiment, when the compressor 4 is operating under load, the humidity of the compressed air is measured, and forced regeneration processing is performed based on the measured humidity.

[0099] 12, when air supply is started, the ECU 80 performs an air supply operation to supply compressed air output from the compressor 4 to the supply circuit 12 (step S100 in FIG. 12). In addition, the ECU 80 performs a humidity measurement step to measure the humidity of the compressed air to be supplied to the supply circuit 12 (step S101 in FIG. 12).

[0100] Then, the ECU 80 determines whether or not the "regeneration process" is necessary (step S102 in FIG. 12). When it is determined that the "regeneration process" is necessary (YES in step S102 in FIG. 12), the ECU 80 sets the air drying circuit 11 to the third operation mode (see FIG. 2(c)) and forcibly performs the regeneration operation (step S103 in FIG. 12). On the other hand, when it is determined that the "regeneration process" is not necessary (NO in step S102 in FIG. 12), the ECU 80 determines whether or not to end the air supply while maintaining the load operation (first operation mode) of the compressor 4 (step S104 in FIG. 12).

[0101] When it is determined not to end the air supply (NO in step S104 in FIG. 12), the ECU 80 returns the process to step S100 in FIG. 12 and continues the air supply process. On the other hand, when it is determined to end the air supply process (YES in step S104 in FIG. 12), the air supply is stopped.

[0102] As described above, according to this embodiment, in addition to the effects (1) to (13) described in the first embodiment, the following effect can be obtained. (14) Since the regeneration process can be performed even while air is being supplied, deterioration of the filter 17 can be suppressed.

[0103] (Other embodiments) Each of the above-described embodiments can also be implemented in the following forms. The above-described embodiments may be combined to the extent that no contradiction occurs. For example, each of the first to fourth embodiments may be combined with at least one of the fifth and sixth embodiments.

[0104] In the first embodiment, the pressure sensor 50 is provided upstream of the upstream check valve 15. However, the present invention is not limited to this, and the pressure sensor may be provided downstream of the upstream check valve. This makes it possible to directly detect the air pressure in the branch passage.

[0105] In each of the above embodiments, the filter 17 includes a desiccant and a filtering portion, but may include only one of them. In each of the above embodiments, the case where the filter 17 is provided has been illustrated. However, the present invention is not limited to this, and an oil mist separator may be provided upstream of the filter 17.

[0106] The oil mist separator is equipped with a filter that separates gas and liquid by collision with the compressed air, and captures the oil contained in the compressed air sent from the compressor 4. The filter may be made of a compressed metal material or a porous material such as sponge. The installation of this oil mist separator can further improve the cleanliness of the compressed air.

[0107] In each of the above embodiments, the air supply system 10 has been described as being mounted on automobiles such as trucks, buses, construction machines, etc. In other embodiments, the air supply system may be mounted on other vehicles such as passenger cars, railroad cars, etc. [Explanation of symbols]

[0108] 4...compressor, 10...air supply system, 11...air drying circuit, 11A...interior, 12...supply circuit, 15...upstream check valve, 16...branch passage, 17...filter, 18...air supply passage, 19...downstream check valve, 20...bypass flow path, 21...regeneration control valve, 22...orifice, 25...drain discharge valve, 26A...governor, 26B...unload control valve, 27...drain discharge port, 50...pressure sensor, 51...humidity sensor, 52...temperature sensor, 80...ECU, E61~E66...wiring, P12...maintenance port.

Claims

1. A compressor capable of switching between a load operation in which compressed air is discharged and an empty operation in which the compressed air is not discharged; a desiccant for removing moisture from the compressed air delivered by the compressor; a connecting passage that connects the compressor and the desiccant so that the compressed air can flow therethrough; a drain valve connected to a branch passage of the connection passage, the drain valve sealing or connecting the branch passage; an upstream check valve provided in the connecting passage between the compressor and the branch passage, the upstream check valve allowing air to be supplied from the compressor; a pressure sensor provided in the connecting passage between the compressor and the upstream check valve for detecting an air pressure; a control device that operates the compressor and the drain discharge valve in response to the air pressure detected by the pressure sensor; When the control device determines that the air pressure detected by the pressure sensor is higher than a high pressure threshold for determining whether the air pressure is high or not, the control device stops the compressor and opens the drain discharge valve to communicate with the branch passage to discharge the compressed air, thereby performing a purged compressor stop operation, and then closes the drain discharge valve to seal the branch passage to perform a non-purged compressor stop operation that does not discharge the compressed air. Air supply system.

2. When the control device determines that the air pressure detected by the pressure sensor is lower than the high pressure threshold, the control device performs the compressor stop operation without purging, When it is determined that the air pressure detected by the pressure sensor is lower than a low pressure threshold for determining whether the air pressure is low or not, a compressor assist operation is performed to increase the air pressure in the desiccant and in the connecting passage, and then the non-purge compressor stop operation is performed; When it is determined that the air pressure detected by the pressure sensor is higher than the low pressure threshold, the non-purge compressor stop operation is performed.

2. The air supply system of claim 1.

3. a first solenoid valve for switching the compressor between the loaded operation and the empty operation, the first solenoid valve being driven to switch the compressor to the empty operation and being not driven to switch the compressor to the loaded operation; a second solenoid valve that closes or opens the branch passage by using the drain valve depending on whether the second solenoid valve is driven or not; a downstream check valve that permits the flow of air from the desiccant to an output opposite the compressor; a regeneration control valve provided in a passage parallel to the downstream check valve; the control device is capable of switching between driving / non-driving the first solenoid valve, switching between driving / non-driving the second solenoid valve, and switching between opening / closing the regeneration control valve, When the first solenoid valve is driven and the second solenoid valve operates the drain valve to seal the branch passage, the regeneration control valve is opened for a predetermined period of time.

3. An air supply system according to claim 1 or 2.

4. When the control device determines that the air pressure detected by the pressure sensor is lower than the high pressure threshold value, the control device performs a compressor assist operation in which the second solenoid valve operates the drain discharge valve to seal the branch passage and opens the regeneration control valve, and then performs the no-purge compressor stop operation in which the regeneration control valve and the second solenoid valve are each closed and the first solenoid valve is opened.

4. An air supply system according to claim 3.

5. The control device performs a pressure adjustment process to adjust the air pressure detected by the pressure sensor after the non-purge compressor stop operation to a pressure equal to or higher than a low pressure threshold and lower than the high pressure threshold, which is used to determine whether the air pressure detected by the pressure sensor is low or not.

5. An air supply system according to claim 4.

6. When the control device determines in the pressure adjustment process that the air pressure detected by the pressure sensor is lower than the low pressure threshold, the control device performs the compressor assist operation and then performs the no-purge compressor stop operation.

6. An air supply system according to claim 5.

7. When the control device determines that the air pressure detected by the pressure sensor is higher than the high pressure threshold after the non-purge compressor stop operation, the control device performs the non-purge compressor stop operation by closing the regeneration control valve and opening the first solenoid valve and the second solenoid valve, and then performs the non-purge compressor stop operation.

7. An air supply system according to claim 6.

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