Patent Description:
In vehicles such as trucks, buses, construction machines, and the like, compressed air fed from a compressor is used to control an air pressure system such as brakes, a suspension, and the like. The compressed air contains liquid impurities such as moisture, which is suspended in the atmosphere, and oil for lubricating the interior of the compressor. The entrance of compressed air containing a large amount moisture and oil into an air pressure system will cause rust and swelling of rubber members and result in operational failure. Thus, a compressed-air drying device that removes impurities such as moisture and oil from the compressed air is arranged downstream to the compressor. Such an air supply system is known from <CIT>.

The compressed-air drying device performs a loading operation (dehumidification operation) that removes oil and moisture and an unloading operation (regeneration operation) that extracts the oil and moisture adsorbed with a desiccant and drains the oil and moisture. An air dryer discharges the drainage to an oil separator to prevent the drainage from being discharged onto the road. In the oil separator, the air containing oil and moisture is struck against impingement members to separate gas and liquid in order to collect the oil and the purified air is discharged (refer to Patent Document <NUM>). Furthermore, <CIT> and <CIT> disclose an air supply system according to the preamble of claim <NUM>.

A purging operation and a regeneration operation consume a certain amount of compressed air. Thus, even though the purging action and the regeneration operation are necessary for discharging purified air, the operation load on the compressor will increase. The increase in the operation load on the compressor that generates compressed air with rotational force transmitted from a rotary drive source such as an engine will increase the load on the rotary drive source and increase the consumption amount of energy such as fuel.

It is an object of the present disclosure to provide an air supply system that reduces the load on a compressor.

To continuously supply purified air from an air dryer of which purging function declines in accordance with the amount of compressed air supply, a regeneration operation and a purging operation are necessary to reverse the flow of compressed air and restore the purging function of the air dryer. For example, the purging operation is performed whenever an unloading operation is performed and the regeneration operation is performed in accordance with the number of times unloading is performed and the elapsed time. Such a purging operation and a regeneration operation consume compressed air and increase the engine load to a certain extent. Vehicles have been required to improve fuel efficiency. Thus, there is room for improvement in maintaining the functionality of the air dryer while reducing consumption of the compressed air by optimizing executing conditions instead of automatically performing a purging operation and a regeneration operation.

It is an object of the present disclosure to provide an air supply system that reduces the amount of consumption of compressed air.

In order to achieve said object, an air supply system according to claim <NUM> is provided. According to one aspect disclosed herein, an air supply system includes a compressor including a load operation mode, in which the compressor feeds compressed air, and an idling operation mode, in which the compressor does not feed compressed air; a desiccant configured to remove moisture from the compressed air fed by the compressor; a connection passage that connects the compressor and the desiccant, where the connection passage permits the compressed air to flow; a first electromagnetic valve configured to selectively switch the compressor between the load operation mode and the idling operation mode, where the compressor is configured to be switched to the idling operation mode when the first electromagnetic valve is activated, and the compressor is configured to be switched to the load operation mode when the first electromagnetic valve is deactivated; a drain discharge valve that is connected to a branch passage branched from the connection passage, where the drain discharge valve is configured to open the branch passage when a second electromagnetic valve is activated, and the drain discharge valve is configured to close the branch passage when the second electromagnetic valve is deactivated; and a controller configured to switch activation and deactivation of the first electromagnetic valve and activation and deactivation of the second electromagnetic valve.

An air supply system according to a first embodiment will now be described with reference to <FIG>. The air supply system is installed in automobiles such as trucks, buses, and construction machines.

The configuration of an air supply system <NUM> will now be described with reference to <FIG>. The air supply system <NUM> includes a compressor <NUM>, an air drying circuit <NUM>, and an ECU <NUM> that serves as a controller. The controller or its elements may be circuitry including: <NUM>) one or more processors that operate according to a computer program (software); <NUM>) one or more dedicated hardware circuits (such as application-specific integrated circuits: ASIC) that execute at least part of various processes, or <NUM>) a combination thereof. The processor includes a CPU and memories such as RAM and ROM. The memories store program codes or commands configured to have the CPU execute processes. The memories, or computer-readable media, include any type of media that are accessible by general-purpose computers or dedicated computers.

The ECU <NUM> of the air supply system <NUM> is connected to multiple wires E61 to E66. The ECU <NUM> includes a processor, a volatile storage, and a nonvolatile storage. The ECU <NUM> is configured to feed an instruction value to the air drying circuit <NUM> in accordance with a program stored in the nonvolatile storage.

The compressor <NUM> is selectively switched, based on the instruction value sent by the ECU <NUM>, between an operation state (load operation mode) in which air is compressed and supplied and a non-operation state (idling operation mode) in which air compression is not performed. That is, the compressor <NUM> includes the load operation mode in which the compressor <NUM> feeds compressed air and the idling operation mode in which the compressor <NUM> does not feed compressed air.

The air drying circuit <NUM> includes, for example, an air dryer. The air drying circuit <NUM> is connected to the ECU <NUM> and dries compressed air fed from the compressor <NUM> during a load operation. The air drying circuit <NUM> sends dried compressed air to a supply circuit <NUM>.

The supply circuit <NUM> stores the compressed air, which is fed from the air drying circuit <NUM>, in an air tank (not shown) installed in a vehicle and supplies the compressed air to a load (not shown).

The air drying circuit <NUM> includes a maintenance port P12. The maintenance port P12 supplies air to the air drying circuit <NUM> during maintenance.

The air drying circuit <NUM> includes a filter <NUM> in an inner portion 11A (refer to <FIG>). In the first embodiment, the filter <NUM> is arranged in an air supply passage <NUM> that is connected to the compressor <NUM> and the supply circuit <NUM>. The filter <NUM> corresponds to a desiccant. The air supply passage <NUM> corresponds to a connection passage.

The filter <NUM> allows air to pass through the desiccant to dry the air by removing moisture from the air and purify the air at a filtration portion by removing oil from the air. The air that has passed through the filter <NUM> is supplied to the supply circuit <NUM> via a downstream check valve <NUM> that permits only a flow of air from the filter <NUM> to the downstream side. That is, the downstream check valve <NUM> permits only the flow of air from the upstream side where the filter <NUM> is located to the downstream side where the supply circuit <NUM> is located. The downstream check valve <NUM> has a predetermined valve opening pressure (sealing pressure). Thus, when compressed air flows, the upstream pressure is higher than the downstream pressure by the valve opening pressure.

At the downstream side of the filter <NUM>, a bypass passage <NUM> that bypasses the downstream check valve <NUM> is arranged in parallel with the downstream check valve <NUM>. The bypass passage <NUM> includes a regeneration control valve <NUM>. That is, the regeneration control valve <NUM> is arranged in the passage that is connected in parallel to the passage in which the downstream check valve <NUM> is arranged.

The regeneration control valve <NUM> includes an electromagnetic valve that switches operations in accordance with the activation and deactivation (driving/non-driving) of power from the ECU <NUM> via the wire E64. The regeneration control valve <NUM> is closed when the power goes off to close the bypass passage <NUM> and is opened when the power goes on to open the bypass passage <NUM>. The ECU <NUM> receives, for example, the value of the air pressure inside the air tank and operates the regeneration control valve <NUM> if the air pressure value exceeds a predetermined range.

The bypass passage <NUM> includes an orifice <NUM> between the regeneration control valve <NUM> and the filter <NUM>. When the regeneration control valve <NUM> is energized, the compressed air flowing toward the supply circuit <NUM> is fed to the filter <NUM> via the bypass passage <NUM> as the orifice <NUM> regulates the flow rate. The flow of air fed to the filter <NUM> is reversed from the upstream side of the filter <NUM> toward the downstream side so as to pass through the filter <NUM>. Such a process regenerates the filter <NUM> and is referred to as a regeneration process on a dryer. Since the compressed air fed to the filter <NUM> is dried and purified air from the air supply passage <NUM> that has passed through the filter <NUM> and is supplied to the supply circuit <NUM>, the moisture and oil trapped in the filter <NUM> is removed from the filter <NUM>. Thus, the ECU <NUM> opens the regeneration control valve <NUM> for a predetermined period. The predetermined period is set based on logic, experiments, or experience to a period that allows for regeneration of the filter <NUM>.

A branch passage <NUM> between the compressor <NUM> and the filter <NUM> is connected to a drain discharge valve <NUM>. That is, the branch passage <NUM> branches from the air supply passage <NUM>. A drain discharge port <NUM> is arranged at the end of the branch passage <NUM>.

The drainage containing moisture and oil removed from the filter <NUM> is fed together with compressed air to the drain discharge valve <NUM>. The drain discharge valve <NUM> is a pneumatically driven valve that is driven by air pressure. The drain discharge valve <NUM> is arranged between the filter <NUM> and the drain discharge port <NUM> in the branch passage <NUM> branching from the air supply passage <NUM>. The drain discharge valve <NUM> is a two-port two-position valve that changes positions between a closed position and an open position. The drain discharge valve <NUM> in the open position sends drainage to the drain discharge port <NUM>. The drainage discharged from the drain discharge port <NUM> may be collected by an oil separator (not shown).

The drain discharge valve <NUM> is controlled by a governor 26A. The governor 26A is an electromagnetic valve that is actuated by the activation and deactivation (driving/non-driving) of power from the ECU <NUM> via the wire E63. The governor 26A, when activated, inputs an air pressure signal to the drain discharge valve <NUM> to open the drain discharge valve <NUM>. The governor 26A, when deactivated, closes the drain discharge valve <NUM> by setting the drain discharge valve <NUM> to the atmospheric pressure instead of inputting an air pressure signal to the drain discharge valve <NUM>. The governor 26A corresponds to a second electromagnetic valve.

The drain discharge valve <NUM> is maintained in the closed position when receiving no air pressure signal from the governor 26A. The drain discharge valve <NUM> is in the open position when receiving an air pressure signal from the governor 26A. If the pressure of an input port of the drain discharge valve <NUM> at the side closer to the compressor <NUM> is high and exceeds an upper limit value, the drain discharge valve <NUM> is forcibly switched to the open position.

An upstream check valve <NUM> is arranged between the compressor <NUM> and the filter <NUM> and between the compressor <NUM> and the branch passage <NUM>. When the side toward the compressor <NUM> is referred to as the upstream side and the side toward the filter <NUM> is referred to as the downstream side, the upstream check valve <NUM> permits only the flow of air from the upstream side toward the downstream side. The upstream check valve <NUM> has a predetermined valve opening pressure (sealing pressure). Thus, when compressed air flows, the upstream pressure is higher than the downstream pressure by an amount corresponding to the valve opening pressure. A reed valve located at the upstream side of the upstream check valve <NUM> is arranged in the outlet of the compressor <NUM>. The branch passage <NUM> and the filter <NUM> are arranged at the downstream side of the upstream check valve <NUM>.

The compressor <NUM> is controlled by an unloading control valve 26B. The unloading control valve 26B is an electromagnetic valve that is actuated by the activation and deactivation (driving/non-driving) of power from the ECU <NUM> via the wire E62. The unloading control valve 26B, when deactivated, shifts to an open position to open the passage extending to the compressor <NUM> to the atmosphere. The unloading control valve 26B, when activated, shifts to a supply position and sends an air pressure signal of compressed air to the compressor <NUM>. The unloading control valve 26B and the governor 26A are separately controlled. The unloading control valve 26B corresponds to a first electromagnetic valve.

The compressor <NUM>, when receiving an air pressure signal from the unloading control valve 26B, is in a non-operation state (idling operation). For example, if the pressure of the supply circuit <NUM> reaches the upper limit pressure, there is no need to supply dry and compressed air. The pressure of the supply circuit <NUM>, which is measured by a pressure sensor (not shown), is input to the ECU <NUM>. The unloading control valve 26B shifts to a supply position when activated (activated) by the ECU <NUM> based on the measurement result of the pressure sensor. This supplies an air pressure signal from the unloading control valve 26B to the compressor <NUM>.

A pressure sensor <NUM> is arranged between the compressor <NUM> and the upstream check valve <NUM>. The pressure sensor <NUM> measures the air pressure of the air supply passage <NUM> where the pressure sensor <NUM> is connected and sends the measurement result to the ECU <NUM> via the wire E61.

A humidity sensor <NUM> and a temperature sensor <NUM> are arranged between the downstream check valve <NUM> and the supply circuit <NUM>. The humidity sensor <NUM> measures the humidity of the compressed air, and the temperature sensor <NUM> measures the temperature of the compressed air at the downstream side of the filter <NUM>. The humidity sensor <NUM> and the temperature sensor <NUM> output the measurement results to the ECU <NUM> via the wires E65, E66. The ECU <NUM> calculates a dew point based on the input humidity and temperature of the compressed air. The humidity sensor <NUM>, the temperature sensor <NUM>, and the ECU <NUM> may form a humidity measurement unit. For example, when the humidity of compressed air output by the compressor <NUM> is substantially <NUM>%, the amount of moisture removed by the filter <NUM> can be calculated based on the difference from the humidity measured as <NUM>% and the amount of saturated steam at the temperature.

As shown in <FIG>, the air drying circuit <NUM> has six operation modes, namely, a first operation mode to a sixth operation mode.

As shown in <FIG>, the first operation mode is for performing a normal loading operation for a supply process. The first operation mode closes the regeneration control valve <NUM>, the governor 26A, and the unloading control valve 26B. That is, the regeneration control valve <NUM>, the governor 26A, and the unloading control valve 26B are each closed. In this case, none of the regeneration control valve <NUM>, the governor 26A, and the unloading control valve 26B is supplied with power. Further, the governor 26A and the unloading control valve 26B open ports of the compressor <NUM> and the drain discharge valve <NUM>, which are connected to the downstream sides of the governor 26A and the unloading control valve 26B, to the atmosphere. In the first operation mode, when compressed air is being supplied from the compressor <NUM>, the desiccant removes moisture and oil from the compressed air supplied to the supply circuit <NUM>. That is, the compressor <NUM> is on.

As shown in <FIG>, the second operation mode is for performing a compressor stop operation (process with purging) for a purging process. The second operation mode closes the regeneration control valve <NUM> and opens the governor 26A and the unloading control valve 26B. That is, the regeneration control valve <NUM> is closed. The governor 26A and the unloading control valve 26B are opened. In this case, the governor 26A and the unloading control valve 26B are supplied with power and connect the port of the compressor <NUM> and the port of the drain discharge valve <NUM>, which are connected at the downstream sides of the governor 26A and the unloading control valve 26B, to the upstream sides (supply circuit <NUM>). In the second operation mode, when the compressor <NUM> is in a non-operation state, the compressed air in the desiccant of the filter <NUM> and the air supply passage <NUM> is discharged from the drain discharge port <NUM> together with moisture, oil, and the like, and the air pressure of the desiccant of the filter <NUM> and the air supply passage <NUM> is equal to the atmospheric pressure. That is, the compressor <NUM> is off.

As shown in <FIG>, the third operation mode is for performing a regeneration operation for a regeneration process. The third operation mode opens the regeneration control valve <NUM>, the governor 26A, and the unloading control valve 26B. In this case, the regeneration control valve <NUM> is supplied with power. In the third operation mode, the compressor <NUM> is in a non-operation state and the compressed air in the supply circuit <NUM> flows back in the filter <NUM> (through desiccant) and is discharged from the drain discharge port <NUM> to remove moisture from the desiccant of the filter <NUM>.

As shown in <FIG>, the fourth operation mode is for performing an oil cut operation. The fourth operation mode closes the regeneration control valve <NUM> and the unloading control valve 26B and opens the governor 26A for a fixed period and then closes the governor 26A. In the fourth operation mode, the compressor <NUM> is in an operation state and the compressed air supplied from the compressor <NUM> is discharged from the drain discharge port <NUM> for a fixed period so that, for example, the compressed air containing a relatively large amount of oil immediately after switching from a non-operation state to an operation state is discharged from the drain discharge port <NUM>. This retards deterioration of the filter <NUM>. The oil cut operation may be performed if oil from the operating compressor <NUM> increases such as when the engine rotation speed rises or the load on the engine increases.

As shown in <FIG>, the fifth operation mode is for performing a compressor stop operation (non-purging process). The fifth operation mode closes the regeneration control valve <NUM> and the governor 26A and opens the unloading control valve 26B. In the fifth operation mode, the compressor <NUM> is in a non-operation state and compressed air remaining in the air supply passage <NUM> and the desiccant of the filter <NUM> is not discharged from the drain discharge port <NUM> to maintain the air pressure.

As shown in <FIG>, the sixth operation mode is for performing an assist operation for a pressurization process. The sixth operation mode opens the regeneration control valve <NUM> and the unloading control valve 26B and closes the governor 26A. In the sixth operation mode, the compressor <NUM> is in a non-operation state and the compressed air of the supply circuit <NUM> is supplied (flows back) to the air supply passage <NUM> and the desiccant of the filter <NUM> so that the pressure becomes higher than the atmospheric pressure. This maintains the back pressure (air pressure) of the upstream check valve <NUM> at a pressure higher than the atmospheric pressure.

A compressor assist operation will now be described with reference to <FIG>.

When a piston descends during an idling operation, the compressor <NUM> generates negative pressure inside a cylinder as the volume increases. The negative pressure increases the operation load. Compressor assist reduces the increase in the operation load caused by negative pressure. Specifically, when the piston of the compressor <NUM> descends during an idling operation, compressor assist maintains the desiccant of the filter <NUM> and the air supply passage <NUM> at a higher pressure than the atmospheric pressure. This closes the reed valve in the outlet of the compressor <NUM> and maintains the pressure generated in the cylinder when the piston ascends to a certain extent to limit the generation of negative pressure inside the cylinder. Thus, the operation load on the compressor <NUM> is reduced during an idling operation. Specifically, during the idling operation of the compressor <NUM>, the drain discharge valve <NUM> is closed so that compressed air supplied from the compressor <NUM> maintains the desiccant of the filter <NUM> and the air supply passage <NUM> at a higher pressure than the atmospheric pressure.

When starting the supply of compressed air, the air supply system <NUM> performs an air supply step that supplies compressed air, which is output from the compressor <NUM>, to the supply circuit <NUM> (step S10 in <FIG>). In the air supply step, the air drying circuit <NUM>, which is in the first operation mode, removes moisture and oil from the compressed air, which is supplied from the compressor <NUM>, and outputs the compressed air to the supply circuit <NUM>. The air supply step ends if the air pressure of the supply circuit <NUM>, such as the air pressure inside the air tank, exceeds an upper limit value.

When the air supply operation ends in the air supply step (step S10 in <FIG>), the air supply system <NUM> shifts the compressor <NUM> to a non-operation state and performs a dryer regeneration step (step S11 in <FIG>). In the dryer regeneration step, a dryer regeneration process that regenerates the filter <NUM> is performed.

As shown in <FIG>, in the dryer regeneration process, the ECU <NUM> performs a humidity measurement step (step S20 in <FIG>). In the humidity measurement step, the humidity of the compressed air is measured based on the humidity measured by the humidity sensor <NUM> and the temperature measured by the temperature sensor <NUM>.

Then, the ECU <NUM> determines whether the filter <NUM> needs to be purged (step S21 in <FIG>). The ECU <NUM> determines that purging is necessary if the humidity of the compressed air is greater than or equal to a first humidity threshold value. The ECU <NUM> determines that purging is unnecessary if the humidity of the compressed air is less than the first humidity threshold value. The necessity of purging may be determined based on the amount of gas flowing through the filter and the amount of oil in the filter.

When determining that purging is necessary (YES in step S21 in <FIG>), the ECU <NUM> shifts the air drying circuit <NUM> to the second operation mode to perform a compressor stop operation (process with purging) (step S22 in <FIG>) and then determines whether a regeneration process on the filter <NUM> is necessary (step S24 in <FIG>). The ECU <NUM> determines that a regeneration process is necessary if the humidity of the compressed air is greater than or equal to a second humidity threshold value. The ECU <NUM> determines that a regeneration process is unnecessary if the humidity of the compressed air is less than the second humidity threshold value.

When determining that a regeneration process is necessary (YES in step S24 in <FIG>), the ECU <NUM> shifts the air drying circuit <NUM> to the third operation mode and performs a regeneration operation (step S25 in <FIG>). When the regeneration process ends, the ECU <NUM> ends the dryer regeneration step (step S11 in <FIG>) and proceeds to the next step.

When determining that a regeneration process is unnecessary (NO in step S24 in <FIG>), the ECU <NUM> ends the dryer regeneration step (step S11 in <FIG>) and proceeds to the next step.

When determining that purging is unnecessary (NO in step S21 in <FIG>), the ECU <NUM> shifts the air drying circuit <NUM> to the fifth operation mode and performs a compressor stop operation (non-purging process) (step S23 in <FIG>). By performing the compressor stop operation (non-purging process), the desiccant of the filter <NUM> and the air supply passage <NUM> are not exposed to the atmosphere after the compressor <NUM> is stopped. Thus, the back pressure of the upstream check valve <NUM> remains higher than the atmospheric pressure and allows compressor assist to be performed. Thus, the dryer regeneration step (step S11 in <FIG>) ends and the next step is performed.

Subsequently, as shown in <FIG>, the air supply system <NUM> performs an air non-supply step (step S12 in <FIG>). In the air non-supply step, the ECU <NUM> performs an air non-supply process so that the back pressure of the upstream check valve <NUM> remains high during a compressor stop operation.

Specifically, as shown in <FIG>, in the air non-supply process, the ECU <NUM> determines whether the air pressure in the desiccant of the filter <NUM> and the air supply passage <NUM> is high (step S30 in <FIG>). The ECU <NUM> compares a measurement value of the pressure sensor <NUM> with a high pressure threshold value. The ECU <NUM> determines that the air pressure is high if the measurement value is greater than or equal to the high pressure threshold value. The ECU <NUM> determines that the air pressure is low if the measurement value is less than the high pressure.

When determining that the air pressure in the desiccant of the filter <NUM> and the air supply passage <NUM> is high (YES in step S30 in <FIG>), the ECU <NUM> shifts the air drying circuit <NUM> to the fifth operation mode and performs a compressor stop operation (non-purging process) (step S32 in <FIG>). When determining that the air pressure in the desiccant of the filter <NUM> and the air supply passage <NUM> is low (NO in step S30 in <FIG>), the ECU <NUM> performs an assist operation (step S31 in <FIG>). In the assist operation, the air drying circuit <NUM> is shifted to the sixth operation mode and the air pressure in the desiccant of the filter <NUM> and the air supply passage <NUM> is raised. Then, the air drying circuit <NUM> is shifted to the fifth operation mode to perform a compressor stop operation (non-purging process) (step S32 in <FIG>). Thus, the back pressure of the upstream check valve <NUM> remains higher than the atmospheric pressure. This allows compressor assist to be performed.

Subsequently, the ECU <NUM> performs a pressure adjustment step (step S33 in <FIG>). In the pressure adjustment step, the ECU <NUM> performs a pressure adjustment process.

As shown in <FIG>, in the pressure adjustment process, the ECU <NUM> determines whether the air pressure in the desiccant of the filter <NUM> and the air supply passage <NUM> is low (step S40 in <FIG>). The ECU <NUM> determines that the air pressure is low if a measurement value of the pressure sensor <NUM> is less than or equal to a low pressure threshold value. The ECU <NUM> determines that the air pressure is not low if the measurement value of the pressure sensor <NUM> is greater than the low pressure threshold value. In the first embodiment, the upstream check valve <NUM> is arranged at the downstream side of the pressure sensor <NUM> where the value of the pressure sensor <NUM> is stable. This reduces the number of times assist operations and purging operations are performed.

When determining that the air pressure is low (YES in step S40 in <FIG>), the ECU <NUM> shifts the air drying circuit <NUM> to the sixth operation mode and performs an assist operation (step S41 in <FIG>). Then, the ECU <NUM> shifts the air drying circuit <NUM> to the fifth operation mode and performs a compressor stop operation (non-purging process) (step S42 in <FIG>). When determining that the air pressure is not low (NO in step S40 in <FIG>), the ECU <NUM> shifts the air drying circuit <NUM> to the fifth operation mode and performs a compressor stop operation (non-purging process) (step S42 in <FIG>).

The ECU <NUM> also determines whether the air pressure is high (step S43 in <FIG>). The ECU <NUM> determines that the air pressure is high if a measurement value of the pressure sensor <NUM> is greater than or equal to a high pressure threshold value. The ECU <NUM> determines that the air pressure is not high if the measurement value of the pressure sensor <NUM> is less than the low pressure threshold value.

When determining that the air pressure is high (YES in step S43 in <FIG>), the ECU <NUM> shifts the air drying circuit <NUM> to the second operation mode and performs a compressor stop operation (process with purging) (step S44 in <FIG>). Then, the ECU <NUM> shifts the air drying circuit <NUM> to the fifth operation mode and performs a compressor stop operation (non-purging process) (step S45 in <FIG>). When determining that the air pressure is not high (NO in step S43 in <FIG>), the ECU <NUM> shifts the air drying circuit <NUM> to the fifth operation mode and performs a compressor stop operation (non-purging process) (step S45 in <FIG>). This keeps the back pressure of the upstream check valve <NUM> higher than the atmospheric pressure and allows compressor assist to be performed. That is, the height of air pressure has a relationship expressed by "atmospheric pressure < low pressure threshold value < high pressure threshold value. " Next, the ECU <NUM> performs an air pressure determination process (step S46 in <FIG>). In the air pressure determination process, air pressure is determined to be appropriate if a measurement value of the pressure sensor <NUM> is less than the high pressure threshold value and greater than or equal to the low pressure threshold value. The air pressure is determined to be inappropriate if the measurement value is greater than or equal to the high pressure threshold value or less than the low pressure threshold value.

As shown in <FIG>, when the pressure adjustment process ends, the pressure adjustment step ends and the next step is performed.

Subsequently, it is determined whether to end the air non-supply process (step S34 in <FIG>). The ECU <NUM> determines to end the air non-supply process if the compressor <NUM> needs to perform a load operation. The ECU <NUM> determines not to end the air non-supply process if the compressor <NUM> does not need to perform the load operation.

More specifically, when determining not to end the air non-supply process (NO in step S34 in <FIG>), the ECU <NUM> continues to perform the pressure adjustment (step S33 in <FIG>). When determining to end the air non-supply process(YES in step S34 in <FIG>), the ECU <NUM> ends the air non-supply step (step S13 in <FIG>) and proceeds to the next step.

Then, as shown in <FIG>, it is determined whether to end air supply (step S13 in <FIG>). The ECU <NUM> determines to end the air supply based on the stopping of a vehicle engine or the like. The ECU <NUM> determines not to end the air supply based on continuous rotation of the vehicle engine or the like.

When determining not to end the air supply (NO in step S13 in <FIG>), the ECU <NUM> returns to step S10 and performs the processes from the air supply step (step S10 in <FIG>). When determining to end the air supply (YES in step S13 in <FIG>), the ECU <NUM> stops the air supply.

As described above, the first embodiment has the following advantages.

The air supply system according to a second embodiment will now be described with reference to <FIG>. The second embodiment differs from the first embodiment in that the air supply passage <NUM> does not include the upstream check valve <NUM>. That is, the second embodiment does not include the upstream check valve <NUM> of the first embodiment shown in <FIG>.

In the second embodiment, a compressor assist operation is performed so that the ECU <NUM> performs the pressure adjustment step (step S33 in <FIG>) of the first embodiment shown in <FIG>. In the pressure adjustment step, the ECU <NUM> performs a pressure adjustment process.

As shown in <FIG>, in the pressure adjustment process, the ECU <NUM> determines whether the air pressure in the desiccant of the filter <NUM> and the air supply passage <NUM> is low (step S50 in <FIG>). In the second embodiment, the pressure sensor <NUM> is arranged between the compressor <NUM> and the filter <NUM>, and there is no upstream check valve. Thus, the value of the pressure sensor <NUM> may be somewhat unstable as compared with the configuration of the first embodiment. However, the pressure adjustment process will be performed in a preferred manner by relatively increasing the number of times assist operations and purging operations are performed.

When determining that the air pressure is low (YES in step S50 in <FIG>), the ECU <NUM> performs an assist operation (step S51 in <FIG>). When determining that the air pressure is not low (NO in step S50 in <FIG>) or when the assist operation in step S51 ends, the ECU <NUM> performs a compressor stop operation (non-purging process) (step S52 in <FIG>).

Subsequently, the ECU <NUM> determines whether the air pressure is high (step S53 in <FIG>).

When determining that the air pressure is high (YES in step S53 in <FIG>), the ECU <NUM> performs a compressor stop operation (process with purging) (step S54 in <FIG>). When determining that the air pressure is not high (NO in step S53 in <FIG>) or when the purging operation in step S54 ends, the ECU <NUM> performs a compressor stop operation (non-purging process) (step S55 in <FIG>). This keeps the air pressure in the desiccant of the filter <NUM> and the air supply passage <NUM>, arranged at the upstream side of the downstream check valve <NUM>, higher than the atmospheric pressure and allows compressor assist to be performed. The ECU <NUM> also performs an air pressure determination process (step S56 in <FIG>). In the air pressure determination process, the ECU <NUM> determines that the air pressure is appropriate if a measurement value is less than a high pressure threshold value and greater than or equal to a low pressure threshold value. The ECU <NUM> determines that the air pressure is inappropriate in other cases.

As described above, the second embodiment has the following advantage in addition to the advantages (<NUM>), (<NUM>), (<NUM>), (<NUM>), and (<NUM>) to (<NUM>) of the first embodiment. (<NUM>) Although the upstream check valve <NUM> is not included, during an idling operation of the compressor <NUM>, the drain discharge valve <NUM> is kept closed so that the air pressure in the desiccant of the filter <NUM> and the air supply passage <NUM> remains somewhat higher than the atmospheric pressure. This reduces the load on the compressor <NUM>.

The air supply system according to a third embodiment will now be described with reference to <FIG>. The third embodiment differs from the first embodiment in that the air supply passage <NUM> does not include the pressure sensor <NUM>. That is, the third embodiment does not include the pressure sensor <NUM> of the first embodiment shown in <FIG>.

In the third embodiment, a compressor assist operation is performed so that the ECU <NUM> performs the pressure adjustment step (step S33 in <FIG>) of the first embodiment shown in <FIG>. In the pressure adjustment step, the ECU <NUM> performs a pressure adjustment process.

As shown in <FIG>, in the pressure adjustment process, the ECU <NUM> determines whether to perform assistance (step S60 in <FIG>). The third embodiment includes the upstream check valve <NUM>. Thus, the ECU <NUM> determines that assistance is unnecessary if, subsequent to a compressor stop, a compressor stop operation (non-purging process) is performed or the preceding operation is an assist operation. The ECU <NUM> determines that assistance is necessary if the preceding operation is a compressor stop operation (process with purging) or a regeneration operation.

When determining that assistance is necessary (YES in step S60 in <FIG>), the ECU <NUM> performs an assist operation (step S61 in <FIG>). When determining that assistance is unnecessary (NO in step S60 in <FIG>) or when the assist operation in step S61 ends, the ECU <NUM> determines whether to end the assist operation (step S62 in <FIG>). If a condition for the compressor <NUM> to perform a load operation is satisfied, the ECU <NUM> determines to end the assistance.

When determining not to end the assistance (NO in step S62 in <FIG>), the ECU <NUM> returns to step S60 and continues the operation determined in accordance with the necessity of the assist operation. When determining to end the assistance (YES in step S62 in <FIG>), the ECU <NUM> performs a compressor stop operation (non-purging process) (step S63 in <FIG>). Then, the ECU <NUM> returns to the pressure adjustment step and proceeds to the step following the pressure adjustment step.

As described above, the third embodiment has the following advantage in addition to advantages (<NUM>) to (<NUM>) and (<NUM>) to (<NUM>) of the first embodiment. (<NUM>) Although the pressure sensor <NUM> is not included, during an idling operation of the compressor <NUM>, the drain discharge valve <NUM> is kept closed so that the air pressure in the desiccant of the filter <NUM> and the air supply passage <NUM> is kept somewhat higher than the atmospheric pressure by the sealing pressure of the upstream check valve <NUM>. This reduces the load on the compressor <NUM>.

The air supply system according to a fourth embodiment will now be described with reference to <FIG>. The fourth embodiment differs from the first embodiment in that the air supply passage <NUM> does not include the pressure sensor <NUM> or the upstream check valve <NUM>. That is, the fourth embodiment includes neither the pressure sensor <NUM> nor the upstream check valve <NUM> of the first embodiment shown in <FIG>.

In the fourth embodiment, a compressor assist operation is performed so that the ECU <NUM> performs the pressure adjustment step (step S33 in <FIG>) of the first embodiment shown in <FIG>. In the pressure adjustment step, the ECU <NUM> performs a pressure adjustment process. The fourth embodiment does not include an upstream check valve. Thus, air pressure may be somewhat unstable as compared with the first embodiment. Further, a pressure sensor is arranged, and feedback control cannot be performed based on air pressure. Thus, control for a pressure adjustment process is performed based on a predetermined condition.

As shown in <FIG>, in the pressure adjustment process, the ECU <NUM> determines whether to perform assistance (step S70 in <FIG>). The fourth embodiment includes neither the pressure sensor <NUM> nor the upstream check valve <NUM>. Thus, the ECU <NUM> determines that assistance is unnecessary if, subsequent to a compressor stop, a compressor stop operation (non-purging process) is performed or the preceding operation is an assist operation. The ECU <NUM> determines that assistance is necessary if a compressor stop operation (process with purging) has been performed or a regeneration operation has been performed.

When determining that assistance is necessary (YES in step S70 in <FIG>), the ECU <NUM> performs an assist operation (step S71 in <FIG>). When determining that assistance is unnecessary (NO in step S70 in <FIG>) or when the assist operation in step S71 ends, the ECU <NUM> determines whether to end the assist operation (step S72 in <FIG>). If a condition for the compressor <NUM> to perform a load operation is satisfied, the ECU <NUM> determines to end the assistance.

When determining not to end the assistance (NO in step S72 in <FIG>), the ECU <NUM> returns to step S70 and performs the operation determined in accordance with the necessity of the assist operation. When determining to end the assistance (YES in step S72 in <FIG>), the ECU <NUM> performs a compressor stop operation (non-purging process) (step S73 in <FIG>). Then, the ECU <NUM> returns to the pressure adjustment step and proceeds to the step following the pressure adjustment step.

As described above, the fourth embodiment has the following advantage in addition to advantages (<NUM>), (<NUM>), (<NUM>), and (<NUM>) to (<NUM>) of the first embodiment. (<NUM>) Neither the pressure sensor <NUM> nor the upstream check valve <NUM> is included. Nevertheless, during an idling operation of the compressor <NUM>, the drain discharge valve <NUM> is kept closed so that the air pressure in the air supply passage <NUM> and the desiccant of the filter <NUM> remains somewhat higher than the atmospheric pressure. This reduces the load on the compressor <NUM>.

The air supply system according to a fifth embodiment will now be described with reference to <FIG> and <FIG>. The fifth embodiment differs from the first embodiment in that an oil cut process is performed during a normal load operation. In the following example, an oil cut process is performed when a load operation starts.

As shown in <FIG>, the air supply system <NUM> starts supplying air and performs an oil cut process in an oil cut step (step S83 in <FIG>).

As shown in <FIG>, in the oil cut process, the ECU <NUM> determines whether to perform oil cut (step S90 in <FIG>). When determining that oil cut is necessary (YES in step S90 in <FIG>), the ECU <NUM> shifts the air drying circuit <NUM> to the fourth operation mode (refer to <FIG>) and performs an oil cut operation (step S91 in <FIG>). When determining that oil cut is unnecessary (NO in step S90 in <FIG>) or when an oil cut operation of step S91 ends, the ECU <NUM> ends the oil cut step (step S83 in <FIG>).

Subsequently, the air supply system <NUM> performs the same steps as when starting supplying air in the first embodiment. Specifically, the air supply system <NUM> sequentially performs an air supply step that supplies compressed air, which is output from the compressor <NUM>, to the supply circuit <NUM> (step S80 in <FIG>), a dryer regeneration step (step S81 in <FIG>), and an air non-supply step (step S82 in <FIG>).

Then, the ECU <NUM> determines whether to end the air supply (step S84 in <FIG>).

When determining not to end the air supply (NO in step S84 in <FIG>), the ECU <NUM> returns to step S83 and continues the air supply step. When determining to end the air supply (YES in step S84 in <FIG>), the ECU <NUM> ends the air supply.

As described above, the fifth embodiment has the following advantage in addition to advantages (<NUM>) to (<NUM>) of the first embodiment to the fourth embodiment described above. (<NUM>) Compressed air containing a relatively large amount of oil is discharged from the drain discharge port <NUM>, and deterioration of the filter <NUM> resulting from oil and moisture is retarded. Discharging may be performed immediately after the compressor <NUM> is switched from a non-operation state to an operation state.

The air supply system according to a sixth embodiment will now be described with reference to <FIG>. The sixth embodiment differs from the first embodiment in that a forced regeneration process is performed during a load operation of the compressor <NUM>. In the sixth embodiment, during a load operation of the compressor <NUM>, the humidity of compressed air is measured and a forced regeneration process is performed based on the measured humidity.

As shown in <FIG>, when air supply starts, the ECU <NUM> performs an air supply operation that supplies compressed air, which is output from the compressor <NUM>, to the supply circuit <NUM> (step S100 in <FIG>). Then, the ECU <NUM> performs a humidity measurement step that measures the humidity of the compressed air supplied to the supply circuit <NUM> (step S101 in <FIG>).

The ECU <NUM> determines whether a regeneration process is necessary (step S102 in <FIG>).

When determining that a regeneration process is necessary (YES in step S102 in <FIG>), the ECU <NUM> shifts the air drying circuit <NUM> to the third operation mode (refer to <FIG>) and forcibly performs a regeneration operation (step S103 in <FIG>). When determining that a regeneration process is unnecessary (NO in step S102 in <FIG>), the ECU <NUM> determines whether to end the air supply while maintaining the load operation (first operation mode) of the compressor <NUM> (step S104 in Fig. <FIG>).

When determining not to end the air supply (NO in step S104 in <FIG>), the ECU <NUM> returns to step S100 of <FIG> and continues the air supply step. When determining to end the air supply step (YES in step S104 in <FIG>), the ECU <NUM> ends the air supply.

As described above, the sixth embodiment has the following advantage in addition to advantages (<NUM>) to (<NUM>) of the first embodiment described above. (<NUM>) A regeneration process can be performed during air supply to retard deterioration of the filter <NUM>.

The air supply system according to a seventh embodiment will now be described with reference to <FIG>. The seventh embodiment differs from the first embodiment in that an operation for optimizing usage of compressed air is performed instead of the compressor assist operation.

An operation for optimizing the usage of compressed air will now be described with reference to <FIG>.

A regeneration operation and a purging operation, which restore dehumidification performance of the filter <NUM>, consume a certain amount of compressed air. Thus, the supply of consumed compressed air increases the operation load on the compressor <NUM>. Specifically, an increase in the operation load on the compressor <NUM> that generates compressed air with the rotational force transmitted from a rotary drive source such as an engine will increase the load on the rotary drive source and increase the consumed amount of energy such as fuel. Conditions for performing a regeneration operation and a purging operation are set to optimize the number of times the regeneration operation and the purging operation are performed so that the usage of compressed air is optimized to reduce the load on the compressor <NUM>.

Further, when neither a regeneration operation nor a purging operation is performed during an idling operation of the compressor <NUM>, the drain discharge valve <NUM> is closed so that compressed air supplied from the compressor <NUM> keeps the air pressure in the desiccant of the filter <NUM> and the air supply passage <NUM> higher than the atmospheric pressure. This provides an effect corresponding to compressor assist that reduces the operation load on the compressor <NUM> during the idling operation.

As shown in <FIG>, when starting the supply of compressed air, the air supply system <NUM> performs the air supply step that supplies compressed air, which is output from the compressor <NUM>, to the supply circuit <NUM> (step S110 in <FIG>). In the air supply step, the air drying circuit <NUM>, which is in the first operation mode, removes moisture and oil from the compressed air, which is supplied from the compressor <NUM>, and outputs the compressed air to the supply circuit <NUM>. The air supply step ends if the air pressure of the supply circuit <NUM>, such as the air pressure inside the air tank, exceeds an upper limit value.

When the air supply operation ends in the air supply step (step S110 in <FIG>), the air supply system <NUM> shifts the compressor <NUM> to a non-operation state and performs a dryer regeneration step (step S111 in <FIG>). In the dryer regeneration step, a dryer regeneration process that regenerates the filter <NUM> is performed.

As shown in <FIG>, in the dryer regeneration process, the ECU <NUM> performs a humidity measurement step (step S120 in <FIG>). In the humidity measurement step, the ECU <NUM> measures the humidity of compressed air based on the humidity measured by the humidity sensor <NUM> and the temperature measured by the temperature sensor <NUM>. The humidity sensor <NUM> corresponds to a humidity measurement unit.

Subsequently, the ECU <NUM> determines whether the humidity is moderate or greater (step S121 in <FIG>). The ECU <NUM> determines that the humidity of the compressed air is moderate or greater if the humidity is greater than or equal to a low humidity threshold value. The ECU <NUM> determines that the humidity of the compressed air is not moderate or greater if the humidity is less than the low humidity threshold value.

When determining that the humidity is moderate or greater (YES in step S121 in <FIG>), the ECU <NUM> shifts the air drying circuit <NUM> to the second operation mode, performs a compressor stop operation (process with purging) (step S122 in <FIG>) and then determines whether the humidity is high or greater (step S124 in <FIG>). The ECU <NUM> determines that the humidity of the compressed air is high or greater if the humidity is greater than or equal to a high humidity threshold value. The ECU <NUM> determines that the humidity of the compressed air is high or greater if the humidity is less than the high humidity threshold value.

When determining that the humidity is high or greater (YES in step S124 in <FIG>), the ECU <NUM> shifts the air drying circuit <NUM> to the third operation mode and performs a regeneration operation (step S125 in <FIG>). When the regeneration process ends, the ECU <NUM> ends the dryer regeneration step (step S111 in <FIG>) and proceeds to the next step.

When determining that the humidity is less than high (NO in step S124 in <FIG>), the ECU <NUM> ends the dryer regeneration step (step S111 in <FIG>) and proceeds to the next step.

When determining that the humidity is less than moderate (NO in step S121 in <FIG>), the ECU <NUM> shifts the air drying circuit <NUM> to the fifth operation mode and performs a compressor stop operation (non-purging process) (step S123 in <FIG>). By performing the compressor stop operation (non-purging process), the desiccant of the filter <NUM> and the air supply passage <NUM> are not exposed to the atmosphere after the compressor <NUM> is stopped. Thus, a compressor assist effect can be obtained. This ends the dryer regeneration step (step S111 in <FIG>), and the next step is performed.

Thus, during an idling operation of the compressor <NUM>, if the humidity of compressed air supplied from the compressor <NUM> is high and the amount of moisture absorbed in the desiccant is high, the oil and moisture are discharged together with air from the air supply passage <NUM> and the desiccant of the filter <NUM>, which are connected to the drain discharge valve, to maintain the cleanliness of air (steps S122, S25). In this case, if the humidity is high or greater, a regeneration operation is performed using the compressed air, of which the flow is reversed, from the supply circuit <NUM> (step S125). If the humidity is moderate or greater, a purging operation is performed using the residual compressed air in the air drying circuit <NUM> (step S122). Air is not discharged from the air supply passage <NUM> or the desiccant of the filter <NUM> as long as the humidity of the compressed air supplied from the compressor <NUM> is low, the amount of moisture absorbed in the desiccant is low, and the amount of oil discharged together with the compressed air from the compressor <NUM> is low. This reduces consumption of the compressed air (step S123).

Subsequently, as shown in <FIG>, the air supply system <NUM> performs an air non-supply step (step S112 in <FIG>). In the air non-supply step, the ECU <NUM> performs an air non-supply process so that the back pressure of the upstream check valve <NUM> remains high during a compressor stop operation.

Specifically, as shown in <FIG>, in the air non-supply process, the ECU <NUM> performs a non-supply operation (step S130 in <FIG>). In the non-supply operation, the ECU <NUM> performs a pressure adjustment step based on the measurement value of the pressure sensor <NUM> (<FIG>). In the pressure adjustment step, the ECU <NUM> performs a pressure adjustment process. For example, in the pressure adjustment process, the air pressure in the desiccant of the filter <NUM> and the air supply passage <NUM> may be adjusted.

As shown in <FIG>, in the pressure adjustment process, the ECU <NUM> determines whether the air pressure in the desiccant of the filter <NUM> and the air supply passage <NUM> is low (step S140 in <FIG>). The ECU <NUM> determines that the air pressure is low if the measurement value of the pressure sensor <NUM> is less than or equal to a low pressure threshold value. The ECU <NUM> determines that the air pressure is not low if the measurement value of the pressure sensor <NUM> is greater than the low pressure threshold value. In the seventh embodiment, the upstream check valve <NUM> is arranged at the downstream side of the pressure sensor <NUM> where the value of the pressure sensor <NUM> is stable. This reduces the number of times assist operations and purging operations are performed.

When determining that the air pressure is low (YES in step S140 in <FIG>), the ECU <NUM> shifts the air drying circuit <NUM> to the sixth operation mode and performs an assist operation (step S141 in <FIG>), and then the ECU <NUM> shifts the air drying circuit <NUM> to the fifth operation mode and performs a compressor stop operation (non-purging process) (step S142 in <FIG>). When determining that air pressure is not low (NO in step S140 in <FIG>), the ECU <NUM> shifts the air drying circuit <NUM> to the fifth operation mode and performs a compressor stop operation (non-purging process) (step S142 in <FIG>).

The ECU <NUM> also determines whether the air pressure is high (step S143 in <FIG>). The ECU <NUM> determines that the air pressure is high if a measurement value of the pressure sensor <NUM> is greater than or equal to a high pressure threshold value. The ECU <NUM> determines that the air pressure is not high if the measurement value of the pressure sensor <NUM> is less than the low pressure threshold value.

When determining that the air pressure is high (YES in step S143 in <FIG>), the ECU <NUM> shifts the air drying circuit <NUM> to the second operation mode and performs a compressor stop operation (process with purging) (step S144 in <FIG>). Then, the ECU <NUM> shifts the air drying circuit <NUM> to the fifth operation mode and performs a compressor stop operation (non-purging process) (step S145 in <FIG>). When determining that the air pressure is not high (NO in step S143 in <FIG>), the ECU <NUM> shifts the air drying circuit <NUM> to the fifth operation mode and performs a compressor stop operation (non-purging process) (step S145 in <FIG>). This keeps the back pressure of the upstream check valve <NUM> higher than the atmospheric pressure and allows compressor assist to be performed. That is, the height of air pressure has a relationship expressed by "atmospheric pressure < low pressure threshold value < high pressure threshold value. " Next, the ECU <NUM> performs an air pressure determination process (step S146 in <FIG>). In the air pressure determination process, air pressure is determined to be appropriate if the measurement value of the pressure sensor <NUM> is less than the high pressure threshold value and greater than or equal to the low pressure threshold value. The air pressure is determined to be inappropriate if the measurement value is greater than or equal to the high pressure threshold value or less than the low pressure threshold value.

As shown in <FIG>, when the pressure adjustment process ends, the non-supply operation (step S130 in Fig. <FIG>) ends and the next step is performed.

Subsequently, it is determined whether to end the air non-supply process (step S131 in <FIG>). The ECU <NUM> determines to end the air non-supply process if the compressor <NUM> needs to perform a load operation. The ECU <NUM> determines not to end the air non-supply process if the compressor <NUM> does not need to perform the load operation.

More specifically, when determining not to end the air non-supply process (NO in step S131 in <FIG>), the ECU <NUM> continues to perform the non-supply operation (S130 in <FIG>). When determining to end the air non-supply process (YES in step S131 in <FIG>), the ECU <NUM> ends the air non-supply step (step S113 in <FIG>) and proceeds to the next step.

Then, as shown in <FIG>, it is determined whether to end air supply (step S113 in <FIG>). The ECU <NUM> determines to end the air supply based on engine stop of the vehicle or the like. The ECU <NUM> determines not to end the air supply based on continuous engine rotation of the vehicle or the like.

When determining not to end the air supply (NO in step S113 in <FIG>), the ECU <NUM> returns to step S110 and performs the processes from the air supply step (step S110 in <FIG>). When determining to end the air supply (YES in step S113 in <FIG>), the ECU <NUM> stops the air supply.

As described above, the seventh embodiment has the following advantages. (<NUM>) If the same electromagnetic valve is used for an idling operation (unloading) of the compressor <NUM> and for switching the drain discharge valve <NUM>, the air in the supply passage and the desiccant is exposed to the atmosphere during the idling operation of the compressor <NUM>. Thus, some of the compressed air that is supplied from the compressor <NUM> would be discharged without being used. This would consume the compressed air. With the above structure, the unloading control valve 26B switches the compressor <NUM> between a load operation and an idling operation, and the governor 26A switches the drain discharge valve <NUM> between a closed state and a connection state in accordance with the humidity measured by the humidity measurement unit. Thus, during an idling operation of the compressor <NUM>, the drain discharge valve <NUM> can be kept closed. For example, when air is dry, the drain discharge valve <NUM> can be kept closed so that the air pressure provided by the compressor <NUM> keeps the air pressure in the air supply passage <NUM> and the air pressure of the desiccant of the filter <NUM> of a dryer higher than the atmospheric pressure. This reduces the consumption amount of compressed air.

(<NUM>) During an idling operation of the compressor <NUM>, if the humidity of compressed air supplied is high, the amount of moisture absorbed in the desiccant of the filter <NUM> is high. Thus, oil and moisture will be discharged together with air from the air supply passage <NUM> and the desiccant of the filter <NUM>, which are connected to the drain discharge valve <NUM>, to maintain the cleanliness of air. If the humidity of the compressed air supplied is low, the amount of moisture absorbed in the desiccant of the filter <NUM> is low, Thus the air pressure in the air supply passage <NUM> and the desiccant of the filter <NUM> will be maintained. This reduces consumption of the compressed air.

(<NUM>) By opening the regeneration control valve <NUM>, the flow of dry and compressed air from, for example, an air tank, is reversed. This allows the dry air, of which the flow has been reversed, to perform a regeneration process on the desiccant of the filter <NUM>.

(<NUM>) The regeneration control valve can be controlled to be open for a predetermined period so that a regeneration process can be performed during the predetermined period.

(<NUM>) A pressure adjustment process maintains a high air pressure in the air supply passage <NUM> and the desiccant of the filter <NUM> even after a regeneration process is performed. For example, compressor assist can be performed.

The above embodiments may be modified as follows.

The above embodiments may be combined as long as the combined modifications are not in technical contradiction. For example, the first to the fourth embodiments may be each combined with at least one of the fifth embodiment and the sixth embodiment. At least one of the fifth embodiment and the sixth embodiment may be combined with the seventh embodiment.

The first embodiment is an example of a case in which the pressure sensor <NUM> is arranged at the upstream side of the upstream check valve <NUM>. Instead, the pressure sensor may be arranged at the downstream side of the upstream check valve. This allows for direct detection of the air pressure in the branch passage.

In the above embodiments, the filter <NUM> includes the desiccant and the filtration portion. Instead, the filter <NUM> may include one of the desiccant and the filtration portion.

The above embodiments include the filter <NUM>. In addition, an oil mist separator may be arranged at the upstream side of the filter <NUM>.

The oil mist separator includes a filter that separates gas from liquid when compressed air strikes the filter, which captures the oil contained in the compressed air, which is fed from the compressor <NUM>. The filter may be formed by compression-molding of a metal material. Alternatively, the filter may be a porous material such as a sponge. The oil mist separator improves the cleanliness of compressed air.

After shifting the air drying circuit <NUM> to the third operation mode and performing a regeneration process, the ECU <NUM> may shift the air drying circuit <NUM> to the sixth operation mode by deactivating the governor 26A to close the drain discharge valve <NUM> without shifting the air drying circuit <NUM> to the fifth operation mode or the second operation mode to allow for compressor assistance. This promptly maintains a high air pressure in the connection passage and the desiccant even after a regeneration process is performed. Thus, compressor assistance can be performed.

In the above embodiments, the humidity sensor <NUM>, the temperature sensor <NUM>, and the ECU <NUM> form the humidity measurement unit. Instead, the humidity measurement unit may be formed by a device that includes a sensor as long as humidity is measured. Calculations do not have to be performed by the ECU.

Claim 1:
An air supply system (<NUM>), comprising:
a compressor (<NUM>) including a load operation mode, in which the compressor (<NUM>) feeds compressed air, and an idling operation mode, in which the compressor (<NUM>) does not feed compressed air;
a desiccant (<NUM>) configured to remove moisture from the compressed air fed by the compressor (<NUM>);
a connection passage (<NUM>) that connects the compressor (<NUM>) and the desiccant (<NUM>), wherein the connection passage (<NUM>) permits the compressed air to flow;
a first electromagnetic valve (26B) configured to selectively switch the compressor (<NUM>) between the load operation mode and the idling operation mode, wherein the compressor (<NUM>) is configured to be switched to the idling operation mode when the first electromagnetic valve (26B) is activated, and the compressor (<NUM>) is configured to be switched to the load operation mode when the first electromagnetic valve (26B) is deactivated;
a drain discharge valve (<NUM>) that is connected to a branch passage (<NUM>) branched from the connection passage (<NUM>), wherein the drain discharge valve (<NUM>) is configured to open the branch passage (<NUM>) when a second electromagnetic valve (26A) is activated, and the drain discharge valve (<NUM>) is configured to close the branch passage (<NUM>) when the second electromagnetic valve (26A) is deactivated; and
a controller (<NUM>) configured to switch activation and deactivation of the first electromagnetic valve (26B) and activation and deactivation of the second electromagnetic valve (26A),
characterized in that
the air supply system (<NUM>) further comprises:
a downstream check valve (<NUM>) that permits air to flow from the desiccant (<NUM>) toward a side opposite the compressor (<NUM>); and
a regeneration control valve (<NUM>) arranged in a passage that is connected in parallel to a passage in which the downstream check valve (<NUM>) is arranged, wherein
the controller (<NUM>) is configured to open and close the regeneration control valve (<NUM>).