Method for operating a compressed air supply system and a compressed air supply system

Abstract

Method for operating a compressed air supply device (1) for an air suspension system (13) of a motor vehicle, wherein the compressed air supply device (1) comprises a motor-driven compressor (2) and a dryer (4), wherein a drain path (5) leads from the dryer (4) to the outside, wherein a regeneration process is carried out for the regeneration of the dryer (4) with a quantity of compressed air that is contained exclusively in the dryer (4), characterized in that an actuating device (6) is provided for changing a flow cross-section of the drain path (5), wherein for the regeneration process the flow cross-section of the drain path (5) is set by means of the actuating device (6) to a value which depends on a time duration predetermined for the regeneration process or on a pressure prevailing in the dryer (4).

Description

[0001] The invention relates to a method for operating a compressed air supply device according to the preamble of claim 1 and a compressed air supply device according to the preamble of claim 7.

[0002] Compressed air supply systems for electronically controlled air suspension systems essentially comprise a compressor driven by a motor, a dryer unit, and several switching valves. For the operation of the air suspension system, the compressor draws air from the atmosphere, compresses it, and supplies it to the components of the air suspension system.

[0003] The ambient air drawn in contains water or moisture, which can lead to individual components, such as the switching valves, freezing. To prevent this, the dew point of the intake air is lowered by means of a dryer. This means the air is dried or dehumidified by a desiccant / adsorbent, such as silica gel. The intake air thus releases its moisture to the desiccant and is then passed on to the air springs or a pressure accumulator.

[0004] The dryer's function is to dry the air drawn into the air suspension system. At a certain point, the dryer is considered saturated because the adsorbent has already absorbed a large amount of moisture and can therefore only partially perform its drying function. For this reason, the dryer must be regenerated regularly to ensure reliable drying.

[0005] The dryer is regenerated through desorption. This means that the moisture contained in the adsorbent is absorbed by the flowing air and released into the environment. Dry compressed air from the air suspension system is used for this purpose. For example, during a lowering process, the compressed air from the air springs flows through the dryer to regenerate it. The compressed air from the air springs flows counter-currently through the dryer and is released to the environment via a drain valve. Since the lowering process is usually intended to be rapid, the drain valve has a large cross-section. However, a large flow cross-section also results in rapid venting of the dryer. For efficient regeneration, a slow flow through the dryer is advantageous.

[0006] Higher air temperatures also allow moisture to be drawn more effectively from the adsorbent. Therefore, heated air is advantageous for efficient regeneration. However, the system air in the air suspension system usually corresponds to the ambient temperature present at components such as air springs or pressure accumulators. This results in poor regeneration efficiency.

[0007] Therefore, the prior art patent DE 10 2010 036 742 A1 proposes utilizing the waste heat from the compressor or motor. In the air supply system described therein, the heat is generated primarily as compression heat or in the form of waste heat from the electric drive motor. This type of heat is used to support dryer regeneration by establishing a direct heat coupling between the dryer or desiccant and the heat sources in the air supply system. The desiccant, heated in this way, releases its water content more effectively into the air flowing through it. This increases the efficiency of dryer regeneration. Consequently, less regeneration air is required for systems with closed air supply systems, and the dryer in open air supply systems is regenerated more effectively.

[0008] A drying device used in a compressed air system is known from US 8,557,030 B2. The drying device includes a desiccant for filtering and drying compressed air that flows into the device during a charging cycle. The desiccant reduces the moisture content of the compressed air during the charging cycle. The desiccant is contained in a cylindrical cartridge located within a housing. The housing is closed by a lid that has an inlet and an outlet for the compressed air. The housing defines a cleaning volume containing dried compressed air. To regenerate the desiccant, it is flushed exclusively with dry compressed air from this cleaning volume. The dry compressed air flows from the cleaning volume through the desiccant and out through the outlet, which is equipped with a check valve.

[0009] In open air supply systems, the necessary amount of regeneration air is usually only available when the air suspension system is unloaded from full to empty. However, these are exceptions, as load changes between two people with luggage and empty loads occur more frequently during operation, resulting in small amounts of regeneration air and correspondingly poor performance. In a closed air supply system, the described air release options are inherently unavailable. After the initial system fill, only a portion of the system air can be used for regeneration; otherwise, the system will not fill. This portion should be as small as possible to minimize compressor run times for filling.In these cases, air control is usually achieved by the minimum number of actuators present, such as air spring valve, pressure accumulator valve, switching valve in closed systems, or drain valve.

[0010] As a result, there is always a risk of water or moisture penetrating the system. This occurs particularly when leaks in the air suspension system mean that the system air is only partially available for dryer regeneration, because the compressor has to constantly fill the system with air.

[0011] The object of the invention is to improve the regeneration of the dryer of a compressed air supply system.

[0012] The problem underlying the invention is solved by the features of the method claim and the dependent apparatus claim. Preferred embodiments are described in the respective dependent claims.

[0013] According to the invention, a method for operating a compressed air supply device for an air suspension system of a motor vehicle is provided, wherein the compressed air supply device comprises a motor-driven compressor and a dryer, wherein a drain path leads from the dryer to the outside, wherein a regeneration process is carried out for the regeneration of the dryer, which is carried out with a quantity of compressed air that is contained exclusively in the dryer, wherein an actuating device is provided for changing a flow cross-section of the drain path, wherein for the regeneration process the flow cross-section of the drain path is set by means of the actuating device to a value which depends on a time duration predetermined for the regeneration process or on a pressure prevailing in the dryer.

[0014] If a certain amount of compressed air is present in the dryer, it is used to regenerate the dryer. Some of the moisture present in the dryer is absorbed by the compressed air and released into the environment when the drain is open. This regeneration process has the advantage that the dryer is regenerated directly with the compressed air it contains. Consequently, this regeneration process already results in a partial regeneration of the dryer.

[0015] The compressed air supply unit can be connected to an air suspension system. On the device side, the switching valves of the air suspension system remain closed during the regeneration process, ensuring that the regeneration process is carried out exclusively with compressed air contained in the dryer and that no compressed air from the air suspension system flows through the dryer during this regeneration process.

[0016] Dryer regeneration is particularly efficient at high air temperatures. Therefore, the regeneration process is preferably carried out after a compressor compression cycle. It is advantageous to utilize the heated compressed air after compression. During air compression, the temperature of the compressed air rises. During the compression process, this compressed air is passed through the dryer, where the moisture it contains is adsorbed. The compressed air collected in the dryer after compression still has a temperature higher than the ambient temperature. Therefore, as long as the compressed air in the dryer has not yet cooled down after compression, it is advantageously used to regenerate the dryer. It is therefore highly beneficial if the regeneration process immediately follows the compression cycle.The regeneration process preferably takes place immediately after the compressor's compression cycle. Particularly preferably, this compression cycle preheats the compressed air used for regeneration to a temperature within a range of 60 to 100°C. The higher the temperature of the compressed air in the dryer, the better it absorbs and releases the moisture bound in the dryer when discharged through the discharge path.

[0017] According to the invention, the flow cross-section is specifically adjusted to a value determined based on the duration of the regeneration process or the pressure within the dryer. If only a certain amount of time is available for the regeneration process, the flow cross-section of the drain path is set to a specific value, ensuring that a defined quantity of compressed air flows out and the dryer is regenerated optimally. Alternatively, the pressure within the dryer can be determined using a pressure sensor, allowing a defined quantity of compressed air to escape by adjusting the flow cross-section of the drain path. Preferably, the flow cross-section of the drain path is set such that the compressed air escapes from the dryer at a pressure of 10 to 20 bar / min.

[0018] Preferably, the flow cross-section of the drain path is variably adjusted by the control device during the regeneration process. If required, the flow cross-section of the drain path can also be adjusted over the duration of the regeneration process. For example, at the beginning of the regeneration process, the flow cross-section of the drain path can be set as small as possible, and as soon as the pressure in the dryer drops, the flow cross-section of the drain path can be opened so that the remaining compressed air can quickly escape. The time- or pressure-dependent, and also time-dependent, adjustment of the flow cross-section of the drain path is preferably achieved by a proportional valve as the control device, which sets the value for the flow cross-section of the drain path.

[0019] Another aspect of the invention is the provision of a compressed air supply device for an air suspension system of a motor vehicle, comprising a motor-driven compressor and a dryer, wherein a drain path leads from the dryer to the outside, wherein an actuating device for changing the flow cross-section of the drain path is provided in the drain path, wherein a proportional valve is used as the actuating device for changing the flow cross-section of the drain path. For the regeneration of the dryer, an actuating device for changing the flow cross-section of the drain path is advantageously provided so that the regeneration process proceeds optimally. Due to the change in the flow cross-section, in particular the constriction, the amount of compressed air in the dryer takes longer to escape than at the nominal dimension of the drain path.This causes the compressed air to absorb more moisture from the dryer and release it into the environment, thus reducing the dryer's saturation level. Therefore, the actuating device for changing the flow cross-section of the drain path is preferably designed as a throttle. The proportional valve allows the drain path to be used for both the regeneration process and the regular rinsing process, as the proportional valve can continuously adjust the flow cross-section from closed to fully open.

[0020] The air suspension system is electronically controlled by a control unit, which is used to control the actuator, the release valves and the compressor.

[0021] The compressed air supply unit is used in an air suspension system for a motor vehicle.

[0022] Further preferred embodiments of the invention will become apparent from the following description of exemplary embodiments with reference to the figures.

[0023] They show: Fig. 1 a pneumatic circuit diagram of an air suspension system with a first exemplary compressed air supply device, and Fig. 2 a pneumatic circuit diagram of an air suspension system with a second exemplary compressed air supply device.

[0024] The Fig. Figure 1 shows a pneumatic circuit diagram of an electronically controlled air suspension system 13 of a motor vehicle, which can operate in open or closed air supply mode. The air suspension system 13 comprises a compressed air supply unit 1 and an air spring assembly 11, which are connected via a connecting line 12. The air spring assembly 11 includes air springs (not shown), each assigned to a wheel of the motor vehicle, and the air spring valves shown. The air suspension system 13 may include a pressure accumulator (not shown) which can be connected to the connecting line 12. In this case, a changeover valve assembly (not shown) consisting of at least four 2 / 2-way valves is provided. The compressed air supply unit 1, the air spring assembly 11, and the pressure accumulator are connected to this changeover valve assembly.Also belonging to the air suspension system 13, but not shown, is a control unit (ECU) which controls the valves of the air suspension system 13 and compressor 2.

[0025] Compressed air supply unit 1 comprises a compressor 2, which is driven by a motor 3. Compressed air supply unit 1 also includes a dryer 4 and a throttle check valve 10. To supply compressed air to the air suspension system 13, an inlet path 9 is provided, which leads to the inlet side of the compressor 2. Compressed air from the air suspension system 13 is discharged into the atmosphere via a discharge path 5. Discharge path 5 branches off from a pressure path between the compressor 2 and the dryer 4 and leads to the outside environment of the compressed air supply unit 1.

[0026] To provide compressed air for the air suspension system 13, compressor 2 draws in air from the atmosphere / ambient via inlet path 9, compresses it, and feeds it to the air suspension device 11 via dryer 4. This is referred to as the compression process.

[0027] During the compression process, the moisture contained in the air is adsorbed by dryer 4. This is achieved by an adsorbent stored within dryer 4. Once a certain amount of moisture or water has been bound to the adsorbent, dryer 4 is considered saturated. Therefore, it must be regenerated. This means that the moisture contained in dryer 4 must be removed. This is generally done by passing compressed air through dryer 4 in a counterflow direction (i.e., against the direction of compression) and allowing it to escape into the atmosphere / environment via drain path 5. Normally, compressed air for this "purge" is taken from the air spring assembly 11 or the pressure accumulator. With the air spring valves open, the compressed air then escapes from the air spring assembly 11 via connecting line 12, throttle check valve assembly 10, dryer 4, and drain path 5 into the environment.The compressed air flowing through dryer 4 absorbs the moisture from the adsorbent and releases it into the environment. However, this rinsing process is not very efficient due to the high flow rate of the compressed air and the low compressed air temperature.

[0028] To ensure better regeneration of the dryer 4 and to support the normal rinsing process, a regeneration process is carried out, for example, using only compressed air contained within the dryer 4. When a certain amount of compressed air is present in the dryer 4, it is advantageously used to absorb moisture and release it from the dryer 4 to the atmosphere via drain path 5. During this process, the air spring valves of the air spring assembly 11 are closed, while drain path 5 is open. Thus, only the amount of compressed air contained in the dryer 4 escapes, carrying away the moisture absorbed during the compression process back to the environment.If a pressure accumulator with a changeover valve assembly is present in air suspension system 13, the valves of the changeover valve assembly, especially the pressure accumulator valve, are kept closed so that when the drain path 5 is open, only the compressed air from the dryer 4 escapes. This ensures that no compressed air escapes from air suspension system 13 that is still needed for control processes for adjusting the vehicle's height.

[0029] This regeneration process using only compressed air from dryer 4 reduces the dryer saturation level, independent of any subsequent flushing processes. This exemplary regeneration process supplements the usual flushing process with compressed air from the air suspension system 13, thereby improving the overall regeneration of dryer 4. This exemplary regeneration process can be performed if dryer 4 is suspected of being overloaded with moisture. This is detected either by a malfunction in the normal flushing process or monitored by software.

[0030] The regeneration process described above is supported by the use of heated compressed air. A quantity of heated compressed air is present in dryer 4 following a compression cycle. During compression, the air heats up, and this heated compressed air is then passed through dryer 4. The compressed air then distributes itself into the pressure chambers (air springs or pressure accumulators), where it mixes with the cold air already present in the chambers and cools down. However, a certain amount of compressed air remains in dryer 4, which has a higher temperature than both the ambient temperature and the compressed air in the pressure chambers. For example, a regeneration process is carried out immediately after filling the system, partially regenerating dryer 4 with the heated compressed air already present within it.

[0031] The regeneration process is further supported by controlling the discharge rate in the discharge path 5. For this purpose, an actuator 6 is provided in the discharge path 5, which allows the flow cross-section of the discharge path 5 to be varied. By changing the flow cross-section of the discharge path 5 from wide open to almost closed, the discharge rate of the compressed air from dryer 4 can be adjusted. The slower the rate at which compressed air can escape from dryer 4, the more moisture is removed. Therefore, if the pressure in dryer 4 is reduced slowly, the concentration of the moisture present in the desiccant and the compressed air in dryer 4 can be equalized as efficiently as possible. This process of the regeneration procedure is controlled either by measuring the pressure in dryer 4 or by timing the actuator.

[0032] As an example, a compressed air supply device 1 is proposed, which includes an actuating device 6 in the drain path 5. Preferably, the actuating device 6 is designed as a throttle or a proportional valve. A throttle or a proportional valve makes it possible to narrow the flow cross-section of the drain path 5 so that the amount of compressed air in the dryer 4 flows out for as long as possible. In the design of the drain path 5 of the compressed air supply device 1 according to Fig. 1. A proportional valve is suitable as an actuating device 6 because it makes it possible to fully open the flow cross-section of the drain path 5, allowing a large quantity of compressed air to escape as quickly as possible from the air spring device 11 for a height control process. On the other hand, for a particularly efficient regeneration process, the flow cross-section of the drain path 5 can be set as narrow as possible so that the compressed air present in the dryer 4 absorbs and carries away as much moisture as possible.

[0033] Alternatively, in the compressed air supply unit 1 of the Fig. 2. An alternative configuration of the drain path 5 is proposed. Drain path 5 comprises two parallel path sections, 5a and 5b. The first path section, 5a, contains a first drain valve 7 and an actuating device 6. The second path section, 5b, contains only a second drain valve 8.

[0034] For the exemplary regeneration process using compressed air present in dryer 4, the first path section 5a is used. This means that the first drain valve 7 is opened, while the second drain valve 8 remains closed. Thus, the compressed air from dryer 4 escapes into the environment only through the first path section 5a. The compressed air must be controlled by the actuating device 6, which is located in the Fig. 2 is designed as a throttle. Drain path 5 with path section 5a therefore serves for a long-lasting release of compressed air, so that dryer 4 is regenerated in the best possible way.

[0035] For a height adjustment operation of the air suspension system 11 or for a regular purging operation of the dryer 4, the second path section 5b of the drain path 5 is used. This means that the first drain valve 7 remains closed, while the second drain valve 8 is open. Since no actuating device restricting the flow cross-section is provided in the second path section 5b, the compressed air can escape into the environment as quickly as possible via this path. Reference symbol list 1 Compressed air supply unit 2 compressor 3 Engine 4 dryers 5 Drainage path 5a first path section 5b second path section 6 Actuator 7 first drain valve 8 second drain valve 9 Entrance Path 10 Throttle check valve device 11 Air suspension system 12 Connecting line 13 Air suspension system

Claims

[1] Method for operating a compressed air supply device (1) for an air suspension system (13) of a motor vehicle, wherein the compressed air supply device (1) comprises a motor-driven compressor (2) and a dryer (4), wherein a drain path (5) leads from the dryer (4) to the outside, wherein a regeneration process is carried out to regenerate the dryer (4) using a quantity of compressed air that is contained exclusively in the dryer (4), characterized by , that an actuating device (6) is provided for changing a flow cross-section of the drain path (5), wherein for the regeneration process the flow cross-section of the drain path (5) is set by means of the actuating device (6) to a value which depends on a time duration predetermined for the regeneration process or on a pressure prevailing in the dryer (4). [2] Method according to claim 1, characterized by, that the regeneration process takes place, in particular immediately, after a compression process of the compressor (2). [3] Method according to claim 2, characterized by , that the compression process preheats the compressed air quantity for the regeneration process to a temperature value within a temperature range between 60 and 100° C. [4] Method according to any one of claims 1 to 3, characterized by , that the value for the flow cross-section of the drain path (5) is set such that the compressed air volume escapes from the dryer (4) at 10 to 20 bar / min. [5] Method according to any one of claims 1 to 4, characterized by , that the value for the flow cross-section of the drain path (5) is variably adjusted by means of the actuating device (6) during the regeneration process. [6] Method of one of claims 1 to 5, characterized by, that the value for the flow cross-section of the drain path (5) is set by means of a proportional valve as an actuating device (6). [7] Compressed air supply device (1) for an air suspension system (13) of a motor vehicle, comprising a motor-driven compressor (2) and a dryer (4), wherein a drain path (5) leads from the dryer (4) to the outside, characterized by , that in the drain path (5) an actuating device (6) is provided for changing a flow cross-section of the drain path (5), wherein the actuating device (6) for changing a flow cross-section of the drain path (5) is a proportional valve. [8] Compressed air supply device (1) according to claim 7, which is configured to carry out a method according to any one of claims 1 to 6.

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