Air supply system, control method for air supply system, and control program for air supply system

Abstract

The air supply system (10) includes an air drying circuit (11) having a filter (17) for capturing moisture, the filter (17) being disposed between a compressor (4) that delivers compressed air and an air tank (30), and an ECU (80) that controls the air drying circuit, the ECU (80) controlling the air drying circuit to perform a dehumidifying operation in which compressed air delivered from the compressor (4) passes through the filter (17) in a forward direction and is supplied to the air tank (30), and a filter cleaning operation in which compressed, dried air passes through the filter (17) in a reverse direction and the fluid that has passed through the filter (17) is discharged from a drain outlet (27), the ECU (80) acquires operation information indicating the operating state of the compressor (4), and changes the frequency of the filter cleaning operation based on the acquired operation information of the compressor (4).

Description

[Technical Field]

[0001] The present disclosure relates to an air supply system, a control method for an air supply system, and a control program for an air supply system. [Background technology]

[0002] In vehicles such as trucks, buses, and construction machinery, pneumatic systems, including brake systems and suspension systems, 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 large amount of moisture and oil enters the pneumatic system, it can cause rust and swelling of rubber components, potentially resulting in malfunctions. For this reason, a compressed air dryer is installed downstream of the compressor to remove impurities such as moisture and oil from the compressed air.

[0003] A compressed air dryer is equipped with a filter containing a desiccant and various valves. The compressed air dryer performs a dehumidifying operation by passing compressed air through a filter to remove moisture and other substances from the compressed air. The compressed dry air generated by the dehumidifying operation is stored in an air tank. The cleaning function of the compressed air dryer decreases depending on the amount of compressed dry air passing through. For this reason, the compressed air dryer performs a regeneration operation by removing oil and moisture adsorbed on the desiccant from the desiccant and releasing the removed oil and moisture as drain (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-201323 Summary of the Invention [Problem to be solved by the invention]

[0005] Some compressed air dryers, like the regeneration operation described above, perform a discharge operation that consumes compressed air delivered from a compressor driven by a rotary drive source such as an engine or compressed dry air stored in a storage unit for purposes other than dehumidification. Such a discharge operation increases the load on the rotary drive source to some extent. Meanwhile, there has been a demand in recent years for improved fuel efficiency of vehicles. For this reason, there is a demand for improvements that maintain the dehumidifying function of compressed air dryers while reducing the consumption of compressed air or compressed dry air.

[0006] An object of the present disclosure is to maintain the dehumidifying function of the air drying circuit well while suppressing air consumption for purposes other than dehumidification by the air drying circuit. [Means for solving the problem]

[0007] An air supply system that solves the above problem includes an air drying circuit that is arranged between a compressor that outputs compressed air and a storage section that stores compressed, dry air, and that has a filter that captures moisture, and a control device that controls the air drying circuit, wherein the control device controls the air drying circuit to perform a dehumidification operation in which the compressed air output from the compressor passes forward through the filter and is supplied to the storage section, controls the air drying circuit to perform a filter cleaning operation in which the compressed, dry air passes backward through the filter and the fluid that has passed through the filter is discharged from an outlet, obtains operating information that indicates the operating state of the compressor, and changes the frequency of the filter cleaning operation based on the obtained operating information of the compressor.

[0008] A control method for an air supply system that solves the above problem is a control method for an air supply system that includes an air drying circuit that is arranged between a compressor that outputs compressed air and a storage section that stores compressed, dry air and has a filter that captures moisture, and a control device that controls the air drying circuit, wherein the control device performs the following steps: controlling the air drying circuit to perform a dehumidification operation in which the compressed air output from the compressor passes forward through the filter and is supplied to the storage section; controlling the air drying circuit to perform a filter cleaning operation in which the compressed, dry air passes backward through the filter and the fluid that has passed through the filter is discharged from an outlet; acquiring operation information that indicates the operating status of the compressor; and changing the frequency of the filter cleaning operation based on the acquired operation information of the compressor.

[0009] A control program for an air supply system that solves the above problem is a control program for an air supply system that includes an air drying circuit that is located between a compressor that outputs compressed air and a storage section that stores compressed, dry air and has a filter that captures moisture, and a control device that controls the air drying circuit, and that causes the control device to function as a dehumidification operation execution unit that controls the air drying circuit to perform a dehumidification operation in which the compressed air output from the compressor passes forward through the filter and is supplied to the storage section, a filter cleaning operation execution unit that controls the air drying circuit to perform a filter cleaning operation in which the compressed, dry air passes backward through the filter and the fluid that has passed through the filter is discharged from an outlet, an acquisition unit that acquires operating information that indicates the operating status of the compressor, and a change unit that changes the frequency of the filter cleaning operation based on the acquired operating information of the compressor.

[0010] When the compressor operates continuously or non-continuously for a long period of time within a certain period, the amount of air passing through the filter during that period also increases, inevitably resulting in more moisture being trapped by the filter. Furthermore, as the compressor operates for a longer period of time, the temperature of the compressed air increases, and the amount of moisture contained in the compressed air per unit volume also tends to increase. According to the above configuration, the control device changes the frequency of the filter cleaning operation based on the compressor operation information. That is, when the control device determines, based on the operating status of the compressor, that priority should be given to the supply of compressed dry air from the storage unit to devices other than the air drying circuit, the frequency of the filter cleaning operation can be reduced. Furthermore, when the control device determines, based on the operating status of the compressor, that filter cleaning is necessary, the frequency of the filter cleaning operation can be increased.

[0011] In the above air supply system, the control device may be configured to increase the frequency of the filter cleaning operation when it determines that the operating state of the compressor is a second operating state based on the operating information, compared to a first operating state, and the amount of air discharged from the compressor within a certain period in the second operating state may be greater than the amount of air discharged from the compressor within the certain period in the first operating state.

[0012] When the compressor is in the second operating state, it is estimated that the amount of air passing through the filter increases, resulting in a larger amount of moisture trapped by the filter. Furthermore, when the compressor is in the second operating state, the temperature of the compressed air discharged from the compressor increases, which tends to increase the amount of moisture contained in the compressed air. According to the above configuration, when the compressor is in the second operating state, the frequency of the discharge operation is increased, thereby enabling the moisture trapped in the filter to be discharged more frequently. This allows the filter's dehumidifying performance to be maintained at a good level.

[0013] In the above air supply system, the control device may be configured not to perform the filter cleaning operation when it determines that the operating state of the compressor is a third operating state, and the amount of air discharged from the compressor within a certain period in the third operating state may be greater than the amount of air discharged from the compressor within the certain period in the second operating state.

[0014] According to the above configuration, the filter cleaning operation is not performed when the compressor is in the third operating state. Therefore, in a situation where a large amount of compressed dry air is consumed by a device other than the air drying circuit, the operating mode is not switched to the filter cleaning operation, and the supply of compressed dry air to that device can be continued.

[0015] In the above air supply system, the air drying circuit may include a connecting passage connecting the compressor and the filter, a supply passage through which the compressed dry air that has passed through the filter passes, and a discharge valve connected to a branch passage branching off from the connecting passage and connecting the branch passage to a discharge port to perform a discharge operation to discharge the fluid that has passed through the filter, and the control device may control the air drying circuit to open the discharge valve to perform a purging operation, as the filter cleaning operation, in which the compressed dry air in the air drying circuit passes through the filter in the reverse direction, and the control device may be configured to change the frequency of the purging operation based on operating information of the compressor.

[0016] According to the above configuration, the frequency of the purge operation can be changed based on the operating state of the compressor. In the above air supply system, the control device may be configured to acquire the moisture content of the compressed dry air supplied to the storage section, and if the moisture content is equal to or greater than a threshold value, determine to perform the purging operation, and set the threshold value lower when the operating state of the compressor is the second operating state compared to when the operating state of the compressor is not the second operating state.

[0017] According to the above configuration, the moisture content threshold is changed based on the operating state of the compressor, so that purging can be easily performed even when the compressor outputs highly humid compressed air, the filter captures a large amount of moisture, and the compressed, dried air that passes through the filter is in a significantly low moisture state. This makes it possible to optimize the frequency of purging.

[0018] In the above air supply system, the control device may be configured to perform the filter cleaning operation less frequently than in the first operating state when it determines that the operating state of the compressor is a second operating state based on the operating information, and the amount of air discharged from the compressor in the second operating state may be greater than the amount of air discharged from the compressor in the first operating state.

[0019] According to the above configuration, when the operating state of the compressor is the second operating state, the frequency of the discharge operation is reduced, thereby allowing a sufficient amount of compressed dry air to be stored in the storage section, and priority can be given to supplying compressed dry air to devices other than the air drying circuit.

[0020] In the above air supply system, the air drying circuit may include a connecting passage connecting the compressor and the filter, a supply passage through which the compressed dry air that has passed through the filter passes, and a discharge valve connected to a branch passage branching off from the connecting passage and connecting the branch passage to an outlet to perform a discharge operation to discharge the fluid that has passed through the filter, and the control device may control the air drying circuit to open the discharge valve and perform a regeneration operation to pass the compressed dry air in the storage section through the filter in the reverse direction as the filter cleaning operation, and the control device may be configured to change the frequency of the regeneration operation based on operating information of the compressor.

[0021] According to the above configuration, when the operating state of the compressor is the second operating state, the frequency of the regeneration operation is changed, so that, for example, priority can be given to the supply of compressed dry air to devices other than the air drying circuit.

[0022] An air supply system that solves the above problem includes an air drying circuit that is arranged between a compressor that outputs compressed air and a storage unit that stores compressed, dried air, and that has a filter that captures moisture, and a control device that controls the air drying circuit, wherein the control device controls the air drying circuit to perform a dehumidification operation in which the compressed air output from the compressor passes forward through the filter and is supplied to the storage unit, and controls the air drying circuit to perform an oil discharge operation in which the compressed air output from the compressor is discharged from an outlet without passing through the filter, and may be configured to acquire operating information that indicates the operating state of the compressor, and change the frequency of the oil discharge operation based on the acquired operating information of the compressor.

[0023] A control method for an air supply system that solves the above problem is a control method for an air supply system that includes an air drying circuit that is arranged between a compressor that sends out compressed air and a storage section that stores compressed, dried air and has a filter that captures moisture, and a control device that controls the air drying circuit, wherein the control device performs the following steps: controlling the air drying circuit to perform a dehumidification operation in which the compressed air sent out from the compressor passes forward through the filter and is supplied to the storage section; controlling the air drying circuit to perform an oil discharge operation in which the compressed air sent out from the compressor is discharged from an outlet without passing through the filter; acquiring operation information that indicates the operating state of the compressor; and changing the frequency of the oil discharge operation based on the acquired operation information of the compressor.

[0024] A control program for an air supply system that solves the above-mentioned problems is a control program for an air supply system that includes an air drying circuit that is arranged between a compressor that sends out compressed air and a storage unit that stores compressed, dried air and has a filter that captures moisture, and a control device that controls the air drying circuit, and that causes the control device to function as a dehumidification operation execution unit that controls the air drying circuit to perform a dehumidification operation in which the compressed air sent out from the compressor passes forward through the filter and is supplied to the storage unit, a discharge operation execution unit that controls the air drying circuit to perform an oil discharge operation in which the compressed air sent out from the compressor is discharged from an outlet without passing through the filter, an acquisition unit that acquires operation information that indicates the operating state of the compressor, and a change unit that changes the frequency of the oil discharge operation based on the acquired operation information of the compressor.

[0025] When the compressor operates continuously or non-continuously for a long period of time within a certain period, the amount of air passing through the filter during that period also increases, inevitably resulting in a large amount of oil being trapped in the filter. Furthermore, as the compressor operates for a long period of time, the temperature of the compressed air increases, and the amount of oil contained in the compressed air per unit volume tends to increase. According to the above configuration, the control device changes the frequency of the oil discharge operation based on the compressor operation information. That is, when the control device determines, based on the operating status of the compressor, that priority should be given to the supply of compressed dried air from the storage unit to devices other than the air drying circuit, the frequency of the oil discharge operation can be reduced. Furthermore, when the control device determines, based on the operating status of the compressor, that oil discharge operation is necessary, compressed air containing a large amount of oil can be discharged without passing through the filter, thereby reducing the load on the filter.

[0026] In the above air supply system, the control device may be configured to increase the frequency of the oil discharge operation when it determines, based on the operation information, that the operating state of the compressor is a second operating state compared to a first operating state, and the amount of air discharged from the compressor within a certain period in the second operating state may be greater than the amount of air discharged from the compressor within the certain period in the first operating state.

[0027] When the compressor is in the second operating state, it is estimated that the amount of air passing through the filter increases, resulting in a larger amount of oil trapped in the filter. Furthermore, when the compressor is in the second operating state, the temperature of the compressed air discharged from the compressor increases, which tends to increase the amount of oil contained in the compressed air. According to the above configuration, when the compressor is in the second operating state, the frequency of the discharge operation is increased, thereby enabling the oil trapped in the filter to be discharged more frequently. This allows the filter's performance to be maintained at a good level.

[0028] In the above air supply system, the control device may be configured not to perform the oil discharge operation when it determines that the operating state of the compressor is a third operating state, and the amount of air discharged from the compressor within a certain period in the third operating state may be greater than the amount of air discharged from the compressor within the certain period in the second operating state.

[0029] According to the above configuration, when the compressor is in the third operating state, the filter cleaning operation is not performed. Therefore, when a large amount of compressed dry air is consumed, the operating mode is not switched to the discharge operation, and the supply of compressed dry air can be continued.

[0030] In the above air supply system, the control device may be configured to acquire the operating time and non-operating time of the compressor as the operating state of the compressor, and to calculate the operating rate of the compressor based on the acquired operating time and non-operating time.

[0031] Since the operating time of the compressor affects the temperature of the compressed air, by determining the operating state of the compressor based on the operating time, it is possible to accurately determine the timing to perform operations other than the dehumidification operation. [Effects of the Invention]

[0032] According to the present disclosure, it is possible to effectively maintain the dehumidifying function of the air drying circuit while suppressing air consumption for purposes other than dehumidification by the air drying circuit. [Brief explanation of the drawings]

[0033] [Figure 1] 1 is a diagram showing a schematic configuration of an embodiment of an air supply system; [Figure 2] 2A to 2F are diagrams showing first to sixth operation modes of the air drying circuit of the embodiment of FIG. 1, respectively. [Figure 3] FIG. 2 is a schematic diagram of start threshold information in the embodiment of FIG. 1; [Figure 4] 2 is a flowchart showing an example of a procedure for supplying compressed air in the embodiment of FIG. 1. [Figure 5] 10 is a flowchart showing an example of a procedure for updating the start threshold in the embodiment of FIG. [Figure 6] 2 is a flowchart showing an example of the procedure of a purification step in the embodiment of FIG. 1. [Figure 7] 4 is a flowchart showing an example of a procedure for an oil cut operation in the embodiment of FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0034] An embodiment of an air supply system will be described with reference to Figures 1 to 7. The air supply system is mounted on a vehicle such as a truck, a bus, or a construction machine. The compressed, dry air generated by the air supply system is used in a pneumatic system such as a brake system or a suspension system.

[0035] <Air Supply System 10> The 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 (Electronic Control Unit) 80 as a control device.

[0036] The ECU 80 is connected to the air drying circuit 11 via multiple wirings E61 to E67. The ECU 80 includes a calculation unit, a communication interface unit, a volatile storage unit, and a nonvolatile storage unit. The calculation unit is a computer processor configured to control the air drying circuit 11 in accordance with an air supply program stored in the nonvolatile storage unit (storage medium). The calculation unit may implement at least a part of the processing it executes using a circuit such as an ASIC. The air supply program may be executed by one computer processor or by multiple computer processors. The ECU 80 also includes a storage unit 80A that stores information for determining the frequency of execution of each operation of the air drying circuit 11. The storage unit 80A is a nonvolatile storage unit or a volatile storage unit, and may be the same as or different from the storage unit in which the control program is stored.

[0037] The ECU 80 is connected to other ECUs (not shown) mounted on the vehicle, such as an engine ECU and a brake ECU, via an in-vehicle network such as a CAN (Controller Area Network). The ECU 80 acquires information indicating the vehicle state from these ECUs. The information indicating the vehicle state includes, for example, ignition switch off information, vehicle speed, engine operating information, etc.

[0038] The state of the compressor 4 is switched 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, based on a command from the ECU 80. The compressor 4 is operated by power transmitted from a rotary drive source such as an engine.

[0039] The air drying circuit 11 is a so-called air dryer. The air drying circuit 11 is connected to the ECU 80 and removes moisture and other substances contained in the compressed air sent from the compressor 4 during load operation. The air drying circuit 11 supplies the dried compressed air (hereinafter referred to as compressed dry air) to the supply circuit 12. The compressed dry air supplied to the supply circuit 12 is stored in the air tank 30.

[0040] The compressed dry air stored in the air tank 30 is supplied to an air pressure system such as a brake system mounted on the vehicle. For example, when the brakes are applied frequently, such as when the vehicle is traveling downhill or in an urban area, a large amount of the compressed dry air stored in the air tank 30 is consumed. Conversely, when the brakes are applied infrequently, a small amount of the compressed dry air stored in the air tank 30 is consumed.

[0041] The air drying circuit 11 has a maintenance port P12. The maintenance port P12 is a port through which air is supplied to the air drying circuit 11 during maintenance.

[0042] The air drying circuit 11 includes a filter 17 inside the case 11A (see FIG. 2A ). The filter 17 is provided midway through the air supply passage 18 that connects the compressor 4 and the supply circuit 12. The filter 17 contains a desiccant. In addition to the desiccant, the filter 17 also includes an oil capture section that captures oil. The oil capture section may be a foam such as urethane foam, a metal material with many air holes, a glass fiber filter, or any other material that can capture oil while allowing air to pass through.

[0043] Filter 17 dries the compressed air by passing the compressed air sent out from compressor 4 through a desiccant to remove moisture contained in the compressed air. The oil trapping section traps oil contained in the compressed air to purify the compressed air. The compressed air that has passed through filter 17 is supplied to supply circuit 12 via downstream check valve 19. When the filter 17 side is upstream and the supply circuit 12 side is downstream, downstream check valve 19 only allows air to flow from upstream to downstream. Note that downstream check valve 19 has a predetermined valve opening pressure (sealing pressure), so when compressed air flows, the upstream pressure is higher than the downstream pressure by the valve opening pressure.

[0044] Further, downstream of the filter 17, a bypass flow path 20 is provided in parallel to the downstream check valve 19 as a detour path that bypasses the downstream check valve 19. A regeneration control valve 21 is provided in the bypass flow path 20.

[0045] The regeneration control valve 21 is a solenoid valve controlled by the ECU 80. The ECU 80 switches the operation of the regeneration control valve 21 by controlling the on / off (drive / non-drive) of the power supply to the regeneration control valve 21 via a wire E64. When the power is off, the regeneration control valve 21 closes to block the bypass flow path 20, and when the power is on, the regeneration control valve 21 opens to communicate with the bypass flow path 20. The ECU 80 receives, for example, the value of the air pressure in the air tank 30 and operates the regeneration control valve 21 when the air pressure value exceeds a predetermined range.

[0046] An orifice 22 is provided in the bypass flow path 20 between the regeneration control valve 21 and the filter 17. When the regeneration control valve 21 is energized, compressed dry air from the supply circuit 12 is sent to the filter 17 via the bypass flow path 20 with the flow rate regulated by the orifice 22. The compressed dry air sent to the filter 17 flows backward through the filter 17 from downstream to upstream and passes through the filter 17. This process is an operation to regenerate the filter 17 and is called a regeneration operation of the air drying circuit 11. At this time, the compressed dry air sent to the filter 17 is dry and purified air that has passed through the filter 17 and other components from the air supply passage 18 and been supplied to the supply circuit 12. Therefore, moisture and oil trapped in the filter 17 can be removed from the filter 17. In normal control, the ECU 80 opens the regeneration control valve 21 when the pressure in the air tank 30 reaches an upper limit (cutout pressure). On the other hand, when the pressure in the air tank 30 reaches a lower limit value (cut-in pressure), the regeneration control valve 21 that has been opened is closed.

[0047] A branch passage 16 branches off from the section between the compressor 4 and the filter 17. A drain discharge valve 25 is provided in the branch passage 16, and a drain discharge port 27 is connected to the end of the branch passage 16.

[0048] Drain, which is a fluid containing 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-operated valve that is driven by air pressure and is provided in the branch passage 16 between the filter 17 and a drain discharge port 27. 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 the drain discharge valve 25 is in the open position, the drain is sent to the drain discharge port 27. The drain discharged from the drain discharge port 27 may be collected by an oil separator (not shown). The drain corresponds to the fluid that has passed through the filter 17 in the reverse direction.

[0049] The drain discharge valve 25 is controlled by a governor 26A. The governor 26A is a solenoid valve controlled by the ECU 80. The ECU 80 switches the operation of the governor 26A by controlling the on / off (drive / non-drive) of the power supply to the governor 26A via a wiring E63. When the power supply to the governor 26A is turned on, the governor 26A switches to an input position that inputs an air pressure signal to the drain discharge valve 25, thereby opening the drain discharge valve 25. When the power supply to the governor 26A is turned off, the governor 26A switches to an open position that does not input an air pressure signal to the drain discharge valve 25, thereby opening a port of the drain discharge valve 25 to atmospheric pressure, thereby closing the drain discharge valve 25.

[0050] When no air pressure signal is input from the governor 26A, the drain discharge valve 25 is maintained in a closed position that blocks the branch passage 16, and when an air pressure signal is input from the governor 26A, the drain discharge valve 25 switches to an open position that communicates with the branch passage 16. Furthermore, when the pressure of the input port of the drain discharge valve 25 that is connected to the compressor 4 exceeds an upper limit value, the drain discharge valve 25 is forcibly switched to the open position.

[0051] 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 side and the filter 17 side is the downstream side, the upstream check valve 15 only allows air to flow from upstream to downstream. Because 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. The branch passage 16 and the filter 17 are provided downstream of the upstream check valve 15.

[0052] The compressor 4 is controlled by an unloading control valve 26B. The unloading control valve 26B is a solenoid valve controlled by the ECU 80. The ECU 80 switches the operation of the unloading control valve 26B by controlling the on / off (drive / non-drive) of the power supply to the unloading control valve 26B via a wiring E62. When the power supply to the unloading control valve 26B is turned off, the unloading control valve 26B switches to an open position, opening the flow path between the unloading control valve 26B and the compressor 4 to the atmosphere. When the power supply to the unloading control valve 26B is turned on, the unloading control valve 26B switches to a supply position, sending an air pressure signal consisting of compressed air to the compressor 4.

[0053] When an air pressure signal is input from the unloading control valve 26B, the state of the compressor 4 switches to a non-operating state (idle operation). For example, when the pressure in the air tank 30 reaches the cutout pressure, the supply of compressed dry air is no longer necessary. When the pressure on the supply circuit 12 side reaches the cutout pressure and the ECU 80 turns on the power of the unloading control valve 26B (drives the unloading control valve 26B), the unloading control valve 26B switches to the supply position. As a result, an air pressure signal is supplied from the unloading control valve 26B to the compressor 4, and the state of the compressor 4 switches to a non-operating state.

[0054] A pressure sensor 50 is provided between the compressor 4 and the upstream check valve 15. The pressure sensor 50 is connected to the air supply passage 18, measures the air pressure in the air supply passage 18, and transmits the measurement result to the ECU 80 via a wire E61.

[0055] 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 may detect either absolute humidity or relative humidity. The humidity sensor 51 and the temperature sensor 52 measure the humidity and 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 determines the wetness state of the compressed dry air based on the humidity and temperature input from the humidity sensor 51 and the temperature sensor 52.

[0056] Furthermore, a pressure sensor 53 is provided between the downstream check valve 19 and the supply circuit 12. The pressure sensor 53 is provided to be able to detect the air pressure in the air tank 30 and outputs the detected pressure value to the ECU 80 via a wire E67. The pressure between the downstream check valve 19 and the supply circuit 12 is the same as the pressure in the air tank 30, and the detection result of the pressure sensor 53 can be used as the pressure in the air tank 30. The pressure sensor 53 may be provided in the supply circuit 12 or in the air tank 30.

[0057] <Operation of the air drying circuit 11> As shown in FIGS. 2A to 2F, the air drying circuit 11 has a plurality of operation modes including at least a first operation mode to a sixth operation mode.

[0058] (First operating mode) As shown in FIG. 2A, the first operating mode is a mode in which normal dehumidification operation (load operation) is performed. In the first operating mode, the regeneration control valve 21 and the unloading control valve 26B are closed (indicated as "CLOSE" in the figure), and the governor 26A is set to an open position in which no air pressure signal is input to the compressor 4 (indicated as "CLOSE" in the figure). At this time, no power is 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 ports of the compressor 4 and the drain discharge valve 25, which are connected downstream of them, to the atmosphere. In the first operating mode, when compressed air is supplied from the compressor 4 (indicated as "ON" in the figure), moisture and the like are removed by the filter 17, and the compressed air is supplied to the supply circuit 12.

[0059] (Second operating mode) As shown in FIG. 2B , the second operating mode is a mode in which a purge operation is performed in which compressed, dried air in the air drying circuit 11 is passed through the filter 17 to purify the filter 17. In the second operating mode, the regeneration control valve 21 is closed, the unloading control valve 26B is set to the supply position (indicated as "OPEN" in the figure), and the governor 26A is set to the input position (indicated as "OPEN" in the figure). At this time, power is supplied to the governor 26A and the unloading control valve 26B, and the ports of the compressor 4 and the drain discharge valve 25 connected downstream thereof are connected upstream (to the supply circuit 12 side). As a result, the compressor 4 is switched to a non-operating state (indicated as "OFF" in the figure), and the drain discharge valve 25 is opened. As a result, the compressed dry air between downstream check valve 19 and filter 17 flows through filter 17 in the opposite direction (backflow) to the air flow in the first operation mode (dehumidification mode), and moisture and other matter captured by filter 17 is discharged as drain from drain outlet 27. In addition, the air pressure in filter 17 and air supply passage 18 is released to atmospheric pressure.

[0060] (Third operating mode) As shown in FIG. 2C , the third operating mode is a mode in which a regeneration operation is performed to regenerate the filter 17. In the third operating mode, the regeneration control valve 21 is opened, the governor 26A is set to the input position, and the unloading control valve 26B is set to the supply position (each of which is labeled "OPEN" in the figure). At this time, power is supplied to the governor 26A, the unloading control valve 26B, and the regeneration control valve 21. In the third operating mode, the compressor 4 is deactivated, and compressed dry air stored in the supply circuit 12 or the air tank 30 is caused to flow back through the filter 17 and discharged from the drain outlet 27. This removes moisture and other contaminants trapped in the filter 17. While both the second and third operating modes are modes in which the filter 17 is purified, the third operating mode differs from the second operating mode in that at least the regeneration control valve 21 is opened. As a result, in the third operating mode, the compressed dry air in the air tank 30 can be passed through the filter 17 via the supply circuit 12 and the bypass flow path 20. Therefore, the filter 17 is more effectively purified than in the second operating mode. Also in the third operating mode, the air pressure in the filter 17 and the air supply passage 18 is released to atmospheric pressure.

[0061] (4th operating mode) As shown in FIG. 2D , the fourth operating mode is a mode in which oil-cut operation is performed. In this mode, while the compressor 4 is operating, oil-rich air sent from the compressor 4 is discharged from the drain outlet 27 without passing through the filter 17. When the compressor 4 is not operating, oil may accumulate in the compression chamber of the compressor 4. If the compressor 4 is switched to an operating state with oil accumulated in the compression chamber, the amount of oil contained in the compressed air sent from the compression chamber increases. If oil adheres to the desiccant, the dehumidifying performance of the desiccant decreases. Therefore, an oil-cut operation is performed to discharge the compressed air with excess oil. In the fourth operating mode, the regeneration control valve 21 is closed, the unload control valve 26B is set to the open position (indicated as “CLOSE” in the figure), and the governor 26A is set to the open position (indicated as “CLOSE” in the figure) after being driven for a certain period of time. As a result, even if compressed air containing a relatively large amount of oil is sent out from compressor 4, the compressed air can be discharged from drain outlet 27 without passing through filter 17. This makes it possible to prevent a decrease in the dehumidifying performance of filter 17 immediately after compressor 4 is switched from a non-operating state to an operating state. When the engine speed increases in an operating state or when the engine is under high load, causing an increase in the amount of oil from compressor 4, an oil cut operation can also be performed.

[0062] (5th operation mode) As shown in FIG. 2E, the fifth operating mode is a mode in which the compressor is stopped without purging. In the fifth operating mode, the regeneration control valve 21 is closed, the governor 26A is set to the open position (indicated as "CLOSE" in the figure), and the unload control valve 26B is set to the supply position (indicated as "OPEN" in the figure). In the fifth operating mode, when the compressor 4 is not operating, the compressed air or compressed dry air remaining in the air supply passage 18 or the desiccant in the filter 17 is not discharged from the drain outlet 27, thereby maintaining the air pressure.

[0063] (6th operating mode) As shown in FIG. 2F, the sixth operating mode is a mode in which an assist operation is performed for pressurization. In the sixth operating mode, the regeneration control valve 21 is opened, the unload control valve 26B is set to the supply position (indicated as "OPEN" in the figure), and the governor 26A is set to the open position (indicated as "CLOSE" in the figure). In the sixth operating mode, when the compressor 4 is not operating, compressed air from the supply circuit 12 is supplied (backflowed) into the desiccant in the air supply passage 18 and the filter 17, thereby increasing the pressure in the air supply passage 18 and the filter 17 above atmospheric pressure and maintaining the back pressure (air pressure) of the upstream check valve 15 at a pressure higher than atmospheric pressure.

[0064] <Setting the execution conditions for the operation mode> Next, the conditions for performing the purge operation (second operation mode), the regeneration operation (third operation mode), and the oil-cut operation (fourth operation mode) will be described with reference to Figures 3 and 4. While the purge operation and the oil-cut operation maintain good dehumidification performance of the filter 17, they consume compressed dry air in the air drying circuit 11 or compressed air delivered from the compressor 4, thereby increasing the operating load on the compressor 4. Because the compressor 4 generates compressed air using rotational force transmitted from a rotary drive source such as an engine, an increase in the operating load on the compressor 4 increases the load on the rotary drive source and further leads to an increase in the consumption of energy, such as fuel, for the vehicle.

[0065] On the other hand, the regeneration operation, like the purging operation and the oil-cutting operation, is performed for the purpose of maintaining good purification performance of the filter 17, but differs from the purging operation and the oil-cutting operation in that it consumes compressed dry air in the air tank 30. The consumption of compressed dry air not only increases the operating load on the compressor 4, but may also lead to a shortage of compressed dry air in the air tank 30. In other words, if the regeneration operation is performed under driving conditions in which a large amount of compressed dry air in the air tank 30 is consumed, such as driving conditions in which the brakes are applied frequently, the amount of compressed dry air consumed in the air tank 30 will increase because compressed dry air is consumed by the regeneration operation in addition to the compressed dry air consumed by pneumatic systems such as the brake system.

[0066] Therefore, the consumption amount of compressed air or compressed dry air is optimized by optimizing the execution frequency of the regeneration operation, purge operation, and oil cut operation through the setting of execution conditions for these operations.

[0067] First, the conditions for performing the purge operation will be described. The purge operation is preferably performed when the amount of moisture captured and held by the filter 17 increases. When the amount of moisture captured by the filter 17 increases and exceeds the moisture capturing capacity of the filter 17, the humidity of the compressed dry air that has passed through the filter 17 inevitably becomes highly humid. Therefore, whether or not to perform the purge operation is determined based on a comparison between an index indicating the humidity of the compressed dry air and a threshold value. In this embodiment, the amount of moisture contained in the compressed dry air supplied to the air tank 30 within a certain period (hereinafter referred to as moisture content) is used as the index indicating the humidity of the compressed dry air. The moisture content of the compressed dry air can be estimated, for example, from the amount of air delivered (discharge amount) from the compressor 4, the humidity detected by the humidity sensor 51 during regeneration operation, etc.

[0068] On the other hand, it is not possible to infer from the humidity state of the compressed dry air after passing through the filter 17 whether the amount of moisture captured by the filter 17 is gradually increasing or rapidly increasing. The rate at which the amount of moisture captured by the filter 17 increases depends on the amount and humidity of the compressed air delivered from the compressor 4. The amount of compressed air increases as the operating rate of the compressor 4 increases. Furthermore, as the temperature of the compressed air increases, the amount of saturated water vapor (saturated water vapor pressure) in the compressed air increases, and the amount of water vapor contained in the compressed air tends to increase. The temperature of the compressed air increases due to the compression of the air by the compressor 4, and therefore increases as the operating rate of the compressor 4 increases. Therefore, in this embodiment, the threshold moisture content for starting the purge operation is set according to the operating rate R of the compressor 4, thereby optimizing the frequency of the purge operation.

[0069] As shown in FIG. 3, the ECU 80 stores the start threshold information 100 in the storage unit 80A. The start threshold information 100 includes a range 101 of the operating rate R of the compressor 4, a rank 102, a cut-out pressure 103, a moisture content threshold 104, and a temperature threshold 105 that are respectively associated with each of the ranges 101 of the operating rate R. The rank 102 indicates the state mode of the air drying circuit 11 and is set according to the range of the operating rate R of the compressor 4. Note that the start threshold information 100 associates each range with a threshold, but the start threshold information 100 only needs to be information capable of determining the start threshold from the operating rate R of the compressor 4, and its format is not limited. For example, the start threshold information 100 may be a map in which axes corresponding to the operating rate R, the cut-out pressure, the moisture content threshold, and the temperature threshold are respectively associated, and the start threshold of each operation is set.

[0070] In the start threshold information 100, the moisture content threshold Mth of the contained moisture content, which is the criterion for starting the purge operation, is set lower as the operating rate R of the compressor 4 is higher. Thereby, when the operating rate R of the compressor 4 is high, the purge operation is likely to be executed, so that the execution frequency of the purge operation can be increased under certain conditions. However, when the operating rate R of the compressor is greater than or equal to a predetermined value, the purge operation is prohibited, and a prohibited value is set for the moisture content threshold Mth. More specifically, when the operating rate R is "less than 10%", the moisture content threshold Mth1 is set as the threshold of the contained moisture content, and when the operating rate R is "10% or more and less than 30%", the moisture content threshold Mth2 (<Mth1) is set. Further, when the operating rate R is "30% or more and less than 50%", the moisture content threshold Mth3 (<threshold Mth2) is set. That is, when the operating rate R is "less than 50%", the high-value moisture content threshold Mth1 (High), the medium-value moisture content threshold Mth2 (Middle), and the low-value moisture content threshold Mth3 (Low) are set in ascending order of the operating rate R. Also, when the operating rate R is "50% or more", the purge operation is prohibited.

[0071] On the other hand, when the availability rate R is equal to or greater than a predetermined value (e.g., 50%), it is estimated that the vehicle is in a driving situation in which a large amount of compressed dry air is consumed. During the transition of the operation mode, compressed dry air cannot be supplied from the air drying circuit 11 to the air tank 30. Therefore, if the operation mode of the air drying circuit 11 is switched from the dehumidification operation (first operation mode) to the purging operation (second operation mode) under such circumstances, the amount of compressed dry air stored in the air tank 30 may become insufficient. For this reason, when the availability rate R is equal to or greater than a predetermined value, priority is given to the supply of compressed dry air to the pneumatic system, and the purging operation is not performed.

[0072] Next, the conditions for performing the oil cut operation will be described. Immediately after the air drying circuit 11 is switched from a non-operating state to an operating state, the compressed air discharged from the compressor 4 may contain a large amount of oil. This oil may pass through the flow path (charge line) between the compressor 4 and the filter 17 in the air supply passage 18 and adhere to the filter 17. If the oil remains on the filter 17, the moisture capture capacity of the desiccant decreases, causing the desiccant to deteriorate relatively quickly. For this reason, to reduce the load on the filter 17, the oil cut operation is preferably performed immediately after the air drying circuit 11 is switched from a non-operating state to an operating state. Because the compressed air contains a large amount of oil when its temperature is high, the need for the oil cut operation is determined based on a comparison between the temperature detected by the temperature sensor 52 and its threshold value. Furthermore, because the amount of oil increases as the operating rate of the compressor 4 increases, the frequency of the oil cut operation is optimized by setting the temperature threshold value of the compressed dry air according to the operating rate R of the compressor 4.

[0073] As shown in FIG. 3, in the start threshold information 100, the temperature threshold Tth is set lower as the operation rate R of the compressor 4 is higher. However, when the operation rate R of the compressor is greater than or equal to a predetermined value, the oil cut operation is prohibited, and a prohibited value is set for the temperature threshold Tth. Specifically, when the operation rate R is "less than 10%", the temperature threshold Tth1 is set. When the operation rate R is "10% or more and less than 30%", the temperature threshold Tth2 (<Tth1) is set. Further, when the operation rate R is "30% or more and less than 50%", the temperature threshold Tth3 (<threshold Tth2) is set. That is, when the operation rate R is "less than 50%", the temperature thresholds Tth1 (High), which is a high value, Tth2 (Middle), which is a medium value, and Tth3 (Low), which is a low value, are set in ascending order of the operation rate R. Also, when the operation rate R is "50% or more", the oil cut operation is prohibited.

[0074] The reason for lowering the temperature threshold Tth as the operation rate R increases will be explained. First, as the operation rate R of the compressor 4 increases, the amount of air delivered from the compressor 4 increases. Therefore, the amount of air passing through the filter 17 also increases, and it is estimated that the amount of oil captured by the filter 17 tends to increase accordingly. Second, the increase in the temperature of the compressed air is a factor that increases the amount of oil contained in the compressed air. Therefore, by changing the temperature threshold Tth for starting the oil cut operation according to the operation rate R and optimizing the execution frequency of the oil cut operation, the load on the filter 17 is reduced. When the operation rate R of the compressor 4 is high, the execution frequency of the oil cut operation is increased to reduce the amount of oil held in the filter 17. On the other hand, when the execution frequency of the operation of the compressor 4 is low, the execution frequency of the oil cut operation is decreased to reduce the amount of compressed air consumed by the oil cut operation. The reason for prohibiting the oil cut operation when the operation rate R is greater than or equal to a predetermined value is the same as in the case of the purge operation.

[0075] Next, the threshold value for starting the regeneration operation will be described. The regeneration operation is performed on the premise that the pressure inside the air tank 30 is equal to or greater than the cutout pressure Po, which is the threshold value. The regeneration operation is started when the pressure inside the air tank 30 is equal to or greater than the cutout pressure Po and when the amount of moisture inside the air tank 30 is equal to or greater than the threshold value. Therefore, the cutout pressure Po is changed according to the operating rate R of the compressor 4 to optimize the frequency at which the regeneration operation is performed.

[0076] As shown in Fig. 3, in the start threshold information 100, the cutout pressure Po is set higher as the availability R of the compressor 4 is higher. In detail, when the availability R is "less than 50%, a relatively low cutout pressure Po1 (Low) is set, and when the availability R is "50% or more", a relatively high cutout pressure Po2 (High) is set (Po2>Po1). Note that in the start threshold information 100 shown in Fig. 3, the cutout pressure is set in two stages, but it may also be set in three or more stages.

[0077] The reason why the cutout pressure Po is increased as the availability rate R increases will be explained. When the availability rate R is low, for example, when it is "less than 50%,," it is estimated that the consumption of compressed dry air by a pneumatic system such as a brake system is relatively low. In such a situation, the cutout pressure Po is set to a relatively low value, and the frequency of the regeneration operation is relatively high, thereby increasing the frequency of cleaning the filter 17. On the other hand, when the availability rate R is high, for example, when it is "50% or higher," it is estimated that the consumption of compressed dry air by a pneumatic system such as a brake system is relatively high. In such a situation, the cutout pressure is set to a relatively high value, and the frequency of the regeneration operation is relatively low, giving priority to the supply of compressed dry air to the pneumatic system.

[0078] (Control of air drying circuit 11) Next, a procedure for the ECU 80 to control the air drying circuit 11 will be described with reference to FIGS.

[0079] 4, the ECU 80 performs an air supply process in which compressed air output from the compressor 4 is supplied to the supply circuit 12 (step S1). The air supply process is started under a predetermined condition, for example, when the engine is started. Alternatively, the air supply process may be started when the pressure in the air tank 30 reaches a predetermined pressure, such as a cut-in pressure, which is a lower limit value. During the air supply process, the air drying circuit 11 is in the first operation mode.

[0080] When the air supply process is started, the ECU 80 determines whether or not to stop the supply of air (step S2). More specifically, the ECU 80 acquires the pressure in the air tank 30 detected by the pressure sensor 53 and determines whether or not the pressure has reached the cutout pressure. If the ECU 80 determines that the pressure in the air tank 30 has not reached the cutout pressure (step S2: NO), the process returns to the air supply process (step S1).

[0081] When the ECU 80 determines that the pressure in the air tank 30 has reached the cutout pressure (step S2: YES), it terminates the air supply process, puts the compressor 4 into a non-operating state, and executes a purification process that performs regeneration operations, etc. (step S3).

[0082] When the purification process (step S3) is completed, the ECU 80 performs an air non-supply process (step S4). In the air non-supply process, when the compressor 4 is not operating, the air pressure is adjusted so that the back pressure of the upstream check valve 15 is maintained high. For example, in the air non-supply process, the air pressure is adjusted by executing at least one of the second operation mode, the fifth operation mode, and the sixth operation mode one or more times. When the air pressure adjustment is completed, the ECU 80 determines whether or not to terminate the air supply based on the vehicle state (step S5). The termination of the air supply is determined based on the vehicle state, for example, whether the vehicle engine is stopped.

[0083] If it is determined not to terminate the air supply (step S5: NO), the ECU 80 returns to step S1 and executes the air supply step (step S1) and subsequent processes. On the other hand, if it is determined to terminate the air supply (step S5: YES), the ECU 80 stops the air supply.

[0084] The ECU 80 defines one cycle as the period from the end of one regeneration operation to the start of the next regeneration operation. At the start of one cycle, the ECU 80 determines the rank, which is the status mode of the air drying circuit 11, based on the operating rate R of the compressor 4, and sets various start thresholds, such as the cutout pressure, moisture content threshold, and temperature threshold, according to this rank.

[0085] Setting of the start threshold will be described with reference to Fig. 5. The ECU 80 determines whether or not to update the start threshold (step S100). For example, the ECU 80 determines whether or not a new cycle has started. When the ECU 80 determines that a new cycle has not started and that updating the start threshold is not necessary (step S100: NO), the ECU 80 ends the processing. Note that the start threshold may be updated at other timings. For example, the start threshold may be updated at intervals shorter than the average time of one cycle, at the end of one cycle, or between the start and end of one cycle.

[0086] When determining that the start threshold should be updated (step S100: YES), the ECU 80 acquires the compressor operation status (operation information) (step S101). In this embodiment, the compressor operation status is the operation time (load time) and non-operation time (unload time) of the compressor 4 during one cycle. The ECU 80 defines the dehumidification operation (first operation mode) as the load operation, and the purge operation (second operation mode), the regeneration operation (third operation mode), the oil cut operation (fourth operation mode), the compressor stop operation without purging (fifth operation mode), and the compressor assist operation (sixth operation mode) as the unload operation. The ECU 80 then stores the time during which the load operation is performed as the load time T1 and the time during which the unload operation is performed as the unload time T2 in the storage unit 80A of the ECU 80, and updates them at predetermined intervals.

[0087] Next, the ECU 80 calculates the availability of the compressor 4 based on the operating state of the compressor 4 (step S102). The availability is calculated as the ratio of the load time T1 to the sum of the load time T1 and the unload time T2, as shown in the following formula (1).

[0088] Availability R = (load time T1) / (load time T1 + unload time T2)…(1) Next, the ECU 80 determines the rank of the air drying circuit 11 based on the operation rate of the compressor 4 using the start threshold information 100 (step S103). For example, if the operation rate of the compressor 4 is "less than 10%, "1" is set as the rank.

[0089] After setting the rank, ECU 80 uses start threshold information 100 to set start thresholds for the cutout pressure, moisture content threshold, and temperature threshold corresponding to the rank (step S104). If the rank is "1," "cutout pressure Po1" is set as the cutout pressure, "moisture content threshold Mth1" is set as the moisture content threshold, and "temperature threshold Tth1" is set as the temperature threshold. These start thresholds are held until the next cycle and are updated when the next cycle starts.

[0090] (Purification process) The purification process (step S3) will be described in detail with reference to Fig. 6. As described above, the purification process is started when the pressure in the air tank 30 reaches or exceeds the cutout pressure. This cutout pressure is updated based on the operating rate of the compressor 4. In other words, even if the operating rate of the compressor 4 is high, if the pressure in the air tank 30 reaches the cutout pressure, which is set to be relatively high, it is determined that sufficient compressed dry air is stored in the air tank 30, and the purification process is started.

[0091] The ECU 80 determines whether a regeneration operation of the filter 17 is necessary (step S30). The conditions for determining whether a regeneration operation is necessary are not particularly limited. For example, the ECU 80 may estimate the moisture content of the compressed dry air on the supply circuit 12 side using at least one of the humidity and temperature on the supply circuit 12 side, and determine that regeneration is necessary if the moisture content tends to be high. For example, the ECU 80 may estimate the moisture content of the compressed dry air in the air tank 30 (hereinafter, tank moisture content) using humidity detected by the humidity sensor 51, and determine that regeneration is necessary if the moisture content is equal to or greater than a threshold value. The tank moisture content is updated at predetermined intervals, such as every cycle. For example, the tank moisture content Mtk can be calculated using the temperature Tmp detected by the temperature sensor 52, the saturated water vapor pressure at the temperature Tmp, the humidity Hmd detected by the humidity sensor 51, and the capacity of the air tank 30.

[0092] For example, if the ECU 80 determines that the water content Mtk in the tank is equal to or greater than a threshold and that a regeneration operation is necessary (step S30: YES), it switches the air drying circuit 11 to the third operation mode and performs the regeneration operation (step S31). The regeneration operation ends when a termination condition is met, such as when the pressure in the air tank 30 reaches the cut-in pressure or a certain period of time has passed. When the regeneration operation ends, the purification process (step S3) ends, and the process proceeds to the next step.

[0093] On the other hand, when the ECU 80 determines in step S30 that regeneration of the filter 17 is not necessary (step S30: NO), it determines whether the moisture content of the compressed dry air is equal to or greater than the moisture content threshold value Mth (step S32). Note that the moisture content threshold value Mth used at this time has been updated based on the operating state of the compressor 4.

[0094] When the ECU 80 determines that the moisture content is equal to or greater than the moisture content threshold Mth (step S32: YES), it switches the air drying circuit 11 to the second operating mode and performs the purge operation (step S33). When the operating rate of the compressor 4 is low, the moisture content threshold Mth is set relatively high, so that the frequency of the purge operation is reduced when the pressure in the air tank 30 reaches the cutout pressure. When the operating rate of the compressor 4 is high, the moisture content threshold Mth is set low, so that the frequency of the purge operation is increased when the pressure in the air tank 30 reaches the cutout pressure. Note that when the operating rate R of the compressor 4 is equal to or greater than a predetermined value, the moisture content threshold Mth set for prohibition is used, so that the purge operation is not performed.

[0095] On the other hand, when the ECU 80 determines that the moisture content is less than the moisture content threshold value Mth (step S32: NO), it switches the air drying circuit 11 to the fifth operation mode and performs the compressor stop operation (step S34).

[0096] (Oil cut operation control) Next, the control by the ECU 80 to cause the air drying circuit 11 to perform the oil cut operation will be described with reference to Fig. 7. The oil cut operation is performed as a process separate from the purification step (step S3).

[0097] As a premise, the ECU 80 stores in the storage unit 80A or the like the time elapsed since the previous oil cut operation was completed. The ECU 80 also stores in the storage unit 80A or the like the number of times the oil cut operation has been performed, and updates that number during one cycle or within another fixed period of time. The number of times the operation has been performed may be reset at a predetermined timing, such as when the fixed period has elapsed, when the vehicle ignition switch is turned off, or when maintenance is performed.

[0098] The ECU 80 acquires the time elapsed since the previous oil cut operation was completed from the memory unit 80A, etc., and compares the elapsed time with a preset fixed time to determine whether the fixed time has elapsed since the previous oil cut operation (step S110). If it determines that the fixed time has not elapsed since the previous oil cut operation (step S110: NO), the process ends.

[0099] When the ECU 80 determines that a certain time has elapsed since the previous oil cut operation (step S110: YES), it determines whether the number of times the oil cut operation has been performed is equal to or less than a predetermined number of times that can be performed (step S111). When the ECU 80 determines that the number of times the oil cut operation has been performed exceeds the number of times that can be performed (step S111: NO), it ends the processing. On the other hand, when the ECU 80 determines that the number of times the oil cut operation has been performed is equal to or less than the number of times that can be performed (step S111: YES), it acquires the temperature detected by the temperature sensor 52 (step S112).

[0100] The ECU 80 determines whether the acquired temperature is equal to or greater than the temperature threshold value Tth (step S113). The temperature threshold value Tth used here is set according to the operation rate of the compressor 4. When the ECU 80 determines that the acquired temperature is equal to or greater than the temperature threshold value Tth (step S113: YES), the ECU 80 switches the air drying circuit 11 to the fourth operation mode and performs the oil cut operation (step S114). When the operation rate of the compressor 4 is low, the temperature threshold value Tth is set high, so the oil cut operation is performed less frequently. When the operation rate of the compressor 4 is high, the temperature threshold value Tth is set low, so the oil cut operation is performed more frequently. Note that when the operation rate R of the compressor 4 is equal to or greater than a predetermined value, the temperature threshold value Tth set for prohibition is used, so the oil cut operation is not performed.

[0101] On the other hand, if the ECU 80 determines that the acquired temperature is lower than the temperature threshold value Tth (step S113: NO), the ECU 80 ends the process. As described above, according to the above embodiment, the following effects can be obtained.

[0102] (1) The ECU 80 of the air drying circuit 11 acquires operation information indicating the operating state of the compressor 4, and changes the frequency of the purge operation, oil cut operation, and regeneration operation based on the acquired operation information of the compressor 4. In other words, if the ECU 80 determines, based on the operating state of the compressor, that priority should be given to the supply of compressed dry air to the pneumatic system mounted on the vehicle, it can reduce the frequency of the operations. Furthermore, if the ECU 80 determines that cleaning of the filter 17 is necessary under conditions in which the supply of compressed dry air to the pneumatic system is secured, it can increase the frequency of the operations to clean the filter 17.

[0103] (2) When the pressure in the air tank 30 reaches the cutout pressure, that is, when the air tank 30 is sufficiently filled with compressed dry air and the operating rate of the compressor 4 is high, the frequency of the purging operation is increased. Also, when the operating rate of the compressor 4 is low, the frequency of the purging operation is decreased. In other words, when the operating rate of the compressor 4 is high, the amount of air passing through the filter 17 within a certain period increases, and the temperature of the compressed air discharged from the compressor 4 increases, the frequency of cleaning the filter 17 can be increased. Also, when the operating rate of the compressor 4 is low, the amount of air passing through the filter 17 decreases, and the temperature of the compressed air discharged from the compressor 4 decreases, the amount of compressed dry air consumed can be reduced.

[0104] (3) Whether or not to perform the purge operation is determined based on whether the moisture content of the compressed dry air is equal to or greater than the moisture threshold value Mth. Furthermore, if it is determined that the operating rate of the compressor 4 is low, the moisture threshold value Mth is set high, and if it is determined that the operating rate of the compressor 4 is high, the moisture threshold value Mth is set low. Therefore, the purge operation can be performed taking into consideration not only the moisture state of the compressed dry air after passing through the filter 17, but also the moisture state of the compressed air before passing through the filter 17. In other words, even if highly humid compressed air is discharged from the compressor 4 and the filter 17 captures a large amount of moisture, causing the compressed dry air that has passed through the filter 17 to be significantly less humid, the purge operation is likely to be performed. This makes it possible to optimize the frequency of the purge operation.

[0105] (4) In the start threshold information 100, prohibition values ​​are set for the threshold for the purge operation and the threshold for the oil cut operation, which correspond to the case where the operating rate of the compressor 4 is higher than a predetermined value. Therefore, when the pneumatic system consumes a large amount of compressed dry air, the operation mode is not switched, and the supply of compressed dry air from the air drying circuit 11 to the air tank 30 can be stably and continuously performed.

[0106] (5) When the operating rate of the compressor 4 is high, the cutout pressure is set high. By setting the cutout pressure high in this way, the filter cleaning operation, including the purging operation and the regeneration operation, can be performed after a sufficient amount of compressed dry air has accumulated in the air tank 30. This allows the supply of compressed dry air to the air pressure system installed in the vehicle to be given priority.

[0107] (6) Whether or not to perform the oil cut operation is determined based on whether the temperature of the compressed dry air is equal to or higher than the temperature threshold value Tth. Furthermore, if it is determined that the operating rate of the compressor 4 is low, the temperature threshold value Tth is set high, and if it is determined that the operating rate of the compressor 4 is high, the temperature threshold value Tth is set low. Therefore, it is possible to reduce the frequency of the oil cut operation when the operating rate of the compressor 4 is low, resulting in a low temperature of the compressed dry air, and to increase the frequency of the oil cut operation when the operating rate of the compressor 4 is high, resulting in a high temperature of the compressed dry air.

[0108] (7) The operating rate based on the load time and unload time was used as the operating information for the compressor 4. Because the load time and unload time affect the temperature of the compressed air generated by the compressor 4, determining the operating state of the compressor 4 based on these factors makes it possible to accurately determine the timing for performing purge operation, oil cut operation, and regeneration operation.

[0109] The above embodiment can be modified as follows: This embodiment and the following modifications can be combined with each other within the scope of technical compatibility. In the above embodiment, the condition for starting the purging operation is that the moisture content of the compressed dry air supplied to the air tank 30 is equal to or greater than the moisture content threshold, assuming that the pressure in the air tank 30 is equal to or greater than the cutout pressure. However, any indicator indicating the moisture content of the compressed dry air or the moisture state in the air tank 30 may be used instead of the moisture content. The indicator may be, for example, the moisture content per unit volume of the compressed dry air, the humidity detected by the humidity sensor 51 during the dehumidification operation, or the moisture content in the air tank 30. Furthermore, whether or not to perform the purging operation may be determined based only on the moisture content of the compressed dry air or the moisture state in the air tank 30, regardless of whether the pressure in the air tank 30 is equal to or greater than the cutout pressure.

[0110] In the above embodiment, the condition for starting the regeneration operation is that the amount of moisture in the air tank 30 is equal to or greater than a threshold value, assuming that the pressure in the air tank 30 is equal to or greater than the cutout pressure. However, any index indicating the amount of moisture in the compressed dry air or the wet state of the air tank 30 may be used instead of the amount of moisture in the air tank 30. The index may be, for example, the amount of moisture contained in the compressed dry air per unit volume, the humidity detected by the humidity sensor 51 during the dehumidification operation, or the amount of moisture contained in the compressed dry air supplied to the air tank 30.

[0111] In the above embodiment, the conditions for starting the oil cut operation are that the elapsed time since the previous oil cut operation is equal to or greater than a certain time, that the number of times the operation has been performed is equal to or less than the maximum number of times possible, and that the temperature of the compressed dry air is equal to or less than the temperature threshold. However, one or two of these conditions may be satisfied. Furthermore, the conditions for starting the oil cut operation may also include that the pressure in the air tank 30 is equal to or greater than the cutout pressure. In this case, the oil cut operation will not be performed unless a sufficient amount of compressed dry air is stored in the air tank 30. Therefore, by suppressing consumption of compressed air delivered from the compressor 4, the supply of compressed dry air to the pneumatic system can be prioritized.

[0112] In the above embodiment, when the operating rate of the compressor 4 is low (e.g., less than 10%), the temperature threshold is set high to reduce the frequency of the oil cutoff operation, and when the operating rate of the compressor 4 is high (e.g., 30% or more but less than 50%), the temperature threshold is set low to increase the frequency of the oil cutoff operation. Furthermore, for operations other than the purge operation and oil cutoff operation, in which the moisture content threshold is set high to reduce the frequency of the purge operation when the operating rate of the compressor 4 is low (e.g., less than 10%) and the moisture content threshold is set low to increase the frequency of the purge operation when the operating rate of the compressor 4 is high (e.g., 30% or more but less than 50%), the frequency of the operation may also be increased when the operating rate of the compressor 4 is low and decreased when the operating rate is high. For example, even in the case of a regeneration operation, if a predetermined condition, such as reducing the consumption of compressed dry air in the air tank 30, is met, the frequency of the regeneration operation may be decreased when the operating rate of the compressor 4 is low and increased when the operating rate is high. Alternatively, even if the operation is other than the purge operation, oil cut operation, or regeneration operation, as long as it is an operation that discharges air from the drain outlet 27 other than a dehumidification operation, the frequency of the operation may be reduced when the operating rate of the compressor 4 is low, and may be increased when the operating rate is high.

[0113] In the above embodiment, when the operating rate of the compressor 4 is equal to or higher than a predetermined value, a prohibition value is set as the threshold value, and the purge operation and the oil cut operation are prohibited. Alternatively, the threshold value may be set for all operating rates of the compressor 4 (0% to 100%). Even in this case, the threshold value may be lowered as the operating rate of the compressor 4 increases. Alternatively, for example, when the operating rate of the compressor 4 is less than a predetermined value, such as 50%, the threshold value may be lowered as the operating rate of the compressor 4 increases, and when the operating rate of the compressor 4 is equal to or higher than the predetermined value, the threshold value may be higher as the operating rate of the compressor 4 increases.

[0114] In the above embodiment, when the operating rate of the compressor 4 is equal to or higher than a predetermined value, a prohibition value is set as the threshold value, and the purge operation and the oil cut operation are prohibited. In addition to this, when the operating rate of the compressor 4 is equal to or higher than a predetermined value, only the purge operation may be prohibited, or only the oil cut operation may be prohibited. Furthermore, when the operating rate of the compressor 4 is equal to or higher than a predetermined value, both the purge operation and the regeneration operation, both the oil cut operation and the regeneration operation, or all of the purge operation, the oil cut operation, and the regeneration operation may be prohibited.

[0115] In the above embodiment, conditions for the regeneration operation, the purge operation, and the oil cut operation are set, and each operation is performed according to these conditions. However, each operation may be performed according to one or two of these conditions. If at least one of the three operation modes is performed according to the conditions of the above embodiment, it is possible to maintain the dehumidification performance of the air drying circuit 11 while suppressing air consumption other than the dehumidification operation. For example, the purge operation may be performed under different conditions. Or the purge operation may be omitted from the operation modes of the air drying circuit 11. Or the oil cut operation may be performed under different conditions. Or the oil cut operation may be omitted from the operation modes of the air drying circuit 11. Or the regeneration operation may be performed under different conditions. Or the regeneration operation may be omitted from the operation modes of the air drying circuit 11.

[0116] In the above embodiment, the filter 17 includes an oil trapping portion, but the oil trapping portion may be omitted from the filter 17. The air drying circuit is not limited to the configuration described above. The air drying circuit may have any configuration as long as it can perform dehumidification and regeneration. Therefore, the second operation mode and the fourth to sixth operation modes are not essential operations for the air drying circuit.

[0117] In the above embodiment, the air supply system 10 has been described as being mounted on a vehicle such as a truck, a bus, or construction equipment. In other embodiments, the air supply system 10 may be mounted on other moving bodies such as a passenger car or a railroad vehicle.

[0118] The ECU 80 is not limited to a system that performs all of its processing using software. For example, the ECU 80 may include a dedicated hardware circuit (e.g., an application-specific integrated circuit (ASIC)) that performs hardware processing for at least some of the processing it performs. That is, the ECU 80 may be configured as a circuit including: 1) one or more processors that operate according to a computer program (software); 2) one or more dedicated hardware circuits that perform at least some of the various processes; or 3) a combination thereof. The processor includes a CPU and memory such as RAM and ROM, and the memory stores program code or instructions configured to cause the CPU to perform processing. The memory, i.e., computer-readable medium, includes any available medium that can be accessed by a general-purpose or special-purpose computer. [Explanation of symbols]

[0119] 4...Compressor, 10...Air supply system, 11...Air drying circuit, 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 as discharge outlet, 30...Air tank as storage unit, 50...Pressure sensor, 51...Humidity sensor, 52...Temperature sensor, 53...Pressure sensor, 80...ECU, 80A...Memory unit, E61 to E67...Wiring.

Claims

1. an air drying circuit disposed between a compressor for delivering compressed air and a reservoir for storing compressed dry air, the air drying circuit having a filter for capturing moisture; a control device for controlling the air drying circuit, The control device controlling the air drying circuit to perform a dehumidifying operation in which the compressed air delivered from the compressor is passed forward through the filter and supplied to the storage section; controlling the air drying circuit to perform a filter cleaning operation by passing the compressed dry air through the filter in a reverse direction and discharging the fluid that has passed through the filter through an outlet; acquiring operating time and non-operating time of the compressor as operation information indicating the operating state of the compressor; calculating an operating rate of the compressor based on the acquired operating time and non-operating time; The filter cleaning operation is started by setting a threshold value of the moisture content according to an operating rate of the compressor, thereby changing the frequency of the filter cleaning operation. The moisture content is either the moisture content contained in the compressed dry air supplied to the storage section or the moisture content in the storage section. Air supply system.

2. The control device When it is determined that the operating state of the compressor is a second operating state based on the operating rate, the frequency of the filter cleaning operation is increased compared to a first operating state, and the amount of air discharged from the compressor within a certain period in the second operating state is greater than the amount of air discharged from the compressor within the certain period in the first operating state.

10. The air supply system of claim 1.

3. The control device the filter cleaning operation is not performed when it is determined that the operating state of the compressor is in a third operating state, and the amount of air discharged from the compressor within a certain period in the third operating state is greater than the amount of air discharged from the compressor within the certain period in the second operating state.

3. The air supply system of claim 2.

4. The air drying circuit comprises: a connecting passage connecting the compressor and the filter; a supply passage through which the compressed dry air that has passed through the filter passes; a discharge valve connected to a branch passage branching from the connection passage, the discharge valve communicating with the branch passage and discharging the fluid that has passed through the filter by connecting the branch passage to the discharge port, the control device controls the air drying circuit to perform, as the filter cleaning operation, a purge operation by opening the discharge valve and passing the compressed dry air in the air drying circuit through the filter in the reverse direction; The control device is configured to change the frequency of the purge operation based on an operating rate of the compressor.

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

5. The control device acquiring a moisture content of the compressed dry air supplied to the storage section; If the moisture content is equal to or greater than the threshold value, it is determined that the purging operation should be performed; When the operating state of the compressor is the second operating state, the threshold value is set lower than when the operating state of the compressor is not the second operating state.

5. The air supply system of claim 4.

6. The control device When it is determined that the operating state of the compressor is a second operating state based on the operating rate, the frequency of the filter cleaning operation is reduced compared to a first operating state, and an amount of air discharged from the compressor in the second operating state is greater than an amount of air discharged from the compressor in the first operating state.

10. The air supply system of claim 1.

7. The air drying circuit comprises: a connecting passage connecting the compressor and the filter; a supply passage through which the compressed dry air that has passed through the filter passes; a discharge valve connected to a branch passage branching from the connection passage, the discharge valve communicating with the branch passage and discharging the fluid that has passed through the filter by connecting the branch passage to the discharge port, the control device controls the air drying circuit to perform a regeneration operation as the filter cleaning operation by opening the discharge valve and passing the compressed dry air in the storage portion through the filter in the reverse direction; The control device is configured to change the frequency of the regeneration operation based on the operating rate of the compressor.

7. The air supply system of claim 6.

8. A method for controlling an air supply system including an air drying circuit, the air drying circuit having a filter for capturing moisture, and a controller for controlling the air drying circuit, the method comprising: The control device controlling the air drying circuit to perform a dehumidifying operation in which the compressed air delivered from the compressor is passed forward through the filter and supplied to the storage section; controlling the air drying circuit to perform a filter cleaning operation by passing the compressed dry air through the filter in a reverse direction and discharging the filtered fluid through an outlet; acquiring operation time and non-operation time of the compressor as operation information indicating the operation state of the compressor; calculating an operating rate of the compressor based on the acquired operating time and non-operating time; a step of changing the frequency of the filter cleaning operation by setting a water content threshold for starting the filter cleaning operation in accordance with an operating rate of the compressor; The moisture content is either the moisture content contained in the compressed dry air supplied to the storage unit or the moisture content in the storage unit. A method for controlling an air supply system.

9. A control program for an air supply system including an air drying circuit, the air drying circuit having a filter for capturing moisture, and a control device for controlling the air drying circuit, the control program comprising: The control device a dehumidification operation execution unit that controls the air drying circuit to execute a dehumidification operation of passing the compressed air sent out from the compressor through the filter in a forward direction and supplying the compressed air to the storage unit; a filter cleaning operation execution unit that controls the air drying circuit to execute a filter cleaning operation in which the compressed dry air is passed through the filter in a reverse direction to discharge the fluid that has passed through the filter from an outlet; an acquisition unit that acquires an operating time and a non-operating time of the compressor as operation information indicating the operating state of the compressor; calculating an operating rate of the compressor based on the acquired operating time and non-operating time; a change unit that changes the execution frequency of the filter cleaning operation by setting a threshold value of the moisture content for starting the filter cleaning operation in accordance with the operating rate of the compressor; The moisture content is either the moisture content contained in the compressed dry air supplied to the storage unit or the moisture content in the storage unit. Air supply system control program.

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