METHOD FOR OPERATING A COMPRESSED AIR SUPPLY DEVICE, AND COMPRESSED AIR SUPPLY DEVICE

Abstract

A compressed air supply device for an air suspension system of a motor vehicle comprising a motor-driven compressor, a dryer, a discharge path from the dryer to the outside, and an adjustment device for changing a flow cross section of the discharge path is provided in the discharge path.

Claims

1-9. (canceled)

10. A compressed air supply device for an air suspension system of a motor vehicle, the compressed air supply device comprising: a motor-driven compressor; a dryer, a discharge path from the dryer to an outside environment; and an adjustment devices for changing a flow cross section of the discharge path provided in the discharge path.

11. The compressed air supply device as claimed in claim 10, wherein the adjustment device is a choke.

12. The compressed air supply device as claimed in claim 10, further comprising a first discharge valve arranged in a first path portion of the discharge path between the choke and the dryer.

13. The compressed air supply device as claimed in claim 12, further comprising a second discharge valve arranged in a second path portion of the discharge path parallel to the first path portion.

14. The compressed air supply device as claimed in claim 10, wherein the adjustment device is a proportional valve.

15. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Further preferred embodiments of the invention are provided by the following description of exemplary embodiments on the basis of the figures.

[0027] In the drawings:

[0028] FIG. 1 shows a pneumatic circuit diagram of an air suspension system with a first exemplary compressed air supply device, and

[0029] FIG. 2 shows a pneumatic circuit diagram of an air suspension system with a second exemplary compressed air supply device.

DETAILED DESCRIPTION

[0030] FIG. 1 shows a pneumatic circuit diagram of an electronically controllable air suspension system 13 of a motor vehicle, which may work in the open or closed air supply mode. The air suspension system 13 comprises a compressed air supply unit 1 and an air spring device 11 which are connected together via a connecting line 12. The air spring device 11 comprises air springs (not shown), which are each assigned to a respective wheel of the motor vehicle, and the air spring valves which are shown. A pressure accumulator (not shown), which can be connected to the connecting line 12, may form part of the air suspension system 13. In this case, a changeover valve device (not shown) comprising at least four 2/2-way directional valves is then provided. The compressed air supply unit 1, the air spring device 11 and the pressure accumulator are connected to this changeover valve device. The air suspension system 13 also includes a control unit (ECU) (not shown) which actuates the valves of the air suspension system 13 and the compressor 2.

[0031] The compressed air supply unit 1 comprises a compressor 2 which is driven by a motor 3. Furthermore, the compressed air supply unit 1 comprises a dryer 4 and a choke check valve device 10. In order to convey compressed air into the air suspension system 13, an inlet path 9 is provided which leads to the input side of the compressor 2. Compressed air is discharged to the atmosphere from the air suspension system 13 via a discharge path 5. The discharge path 5 branches from a pressure path between the compressor 2 and the dryer 4, and leads to the outside into the environment of the compressed air supply unit 1.

[0032] In order to provide compressed air for the air suspension system 13, the compressor 2 draws air in from the atmosphere/environment via the inlet path 9, compresses this and supplies it to the air spring device 11 via the dryer 4. This is called the compression process.

[0033] During the compression process, the moisture contained in the air is adsorbed by the dryer 4. This is achieved using an adsorbent which is stored in the dryer 4. Above a certain quantity of moisture or water bound in the adsorbent, the dryer 4 must be regarded as saturated. It must therefore be regenerated. In other words, the moisture contained in the dryer 4 must be discharged. This is usually achieved by conducting compressed air through the dryer 4 in the counterflow direction (i.e. against the compression direction), which then escapes to the atmosphere/environment via the discharge path 5. Normally, for such a “flushing process”, compressed air is taken from the air spring device 11 or from the pressure accumulator. Then when the air spring valves are opened, the compressed air escapes into the environment from the air spring device 11 via the connecting line 12, choke check valve device 10, dryer 4 and discharge path 5. The compressed air flowing through the dryer 4 absorbs the moisture from the adsorbent and releases it to the environment. This flushing process however is not very efficient because of the high flow speed of the compressed air and the low temperature of the compressed air.

[0034] In order to ensure a better regeneration of the dryer 4 or to support the normal flushing process, according to the example, a regeneration process is performed which takes place exclusively with compressed air present in the dryer 4. If a certain quantity of compressed air is present in the dryer 4, this is advantageously used for capturing moisture and releasing this to the atmosphere from the dryer 4 via the discharge path 5. For this process, the air spring valves of the air spring device 11 are closed, while the discharge path 5 is open. Thus only the quantity of compressed air contained in the dryer 4 escapes and releases back to the environment the moisture absorbed in the dryer 4 during the compression process. If a pressure accumulator with a changeover valve device is present in the air suspension system 13, the valves of the changeover valve device, above all the pressure accumulator valve, remain closed so that when the discharge path 5 is open, only the compressed air escapes from the dryer 4. This ensures that no compressed air quantity, which would still be required for control processes for adjusting the height of the motor vehicle, escapes from the air suspension system 13.

[0035] This regeneration process using exclusively compressed air from the dryer 4 already lowers the level of dryer saturation irrespective of any temporally subsequent flushing processes. This exemplary regeneration process constitutes a supplement to the usual flushing process with compressed air from the air suspension system 13, whereby the regeneration of the dryer 4 as a whole is improved. The exemplary regeneration process may be performed when it is found that the dryer 4 is overloaded with moisture. This is either established by a fault in the normal flushing process or monitored by software.

[0036] The exemplary regeneration process is supported in that this is performed with heated compressed air. Such a quantity of heated compressed air is present in the dryer 4 following a compression process. During compression, the air is heated and the now heated compressed air is conducted through the dryer 4. Then the compressed air is distributed into the pressure chambers (air springs or pressure accumulators), whereby this compressed air mixes with the cold air already present in the pressure chambers and is thereby cooled. However, a certain quantity of compressed air remains in the dryer 4, and has a higher temperature value than the ambient temperature and than the compressed air in the pressure chambers. For example, directly after system filling, a regeneration process is carried out which ensures partial regeneration of the dryer 4 using the heated compressed air present in the dryer 4.

[0037] The exemplary regeneration process is supported further by controlling the discharge speed in the discharge path 5. For example, for this an adjustment device 6 is provided in the discharge path 5, by means of which a flow cross section of the discharge path 5 is variable. By changing the flow cross section of the discharge path 5 from wide open to almost closed, the discharge speed of the compressed air from the dryer 4 can be set. The temporally slower the quantity of compressed air can escape from the dryer 4, the more moisture is extracted. If the pressure prevailing in the dryer is dissipated slowly, the concentration of the moisture present in the desiccant and the compressed air present in the dryer 4 can be balanced as efficiently as possible. This progress of the exemplary regeneration process is controlled either by measurement of the pressure prevailing in the dryer 4 or by temporal control.

[0038] For example, therefore, with respect to the device, a compressed air supply device 1 is proposed which provides an adjustment device 6 in the discharge path 5. Preferably, the adjustment device 6 is configured as a choke or as a proportional valve. A choke or a proportional valve allows constriction of the flow cross section of the discharge path 5 so that the quantity of compressed air present in the dryer 4 flows out for as long as possible. In the configuration of the discharge path 5 of the compressed air supply device 1 according to FIG. 1, a proportional valve is suitable as an adjustment device 6 because this allows complete opening of the flow cross section of the discharge path 5, so that a large quantity of compressed air can escape from the air spring device 11 as quickly as possible for a height adjustment process. On the other hand, for a particularly efficient regeneration process, the flow cross section of the discharge path 5 can be set as narrow as possible, so that the compressed air present in the dryer 4 absorbs and extracts as much moisture as possible.

[0039] Alternatively, another configuration of the discharge path 5 is proposed in the compressed air supply device 1 of FIG. 2. Two path portions 5a and 5b, which run parallel to one another, are provided in the discharge path 5. A first discharge valve 7 and an adjustment device 6 are provided in the first path portion 5a. Only a second discharge valve 8 is provided in the second path portion 5b.

[0040] For the exemplary regeneration process, the first path portion 5a is used for regeneration with compressed air present in the dryer 4. In other words, the first discharge valve 7 is opened while the second discharge valve 8 remains closed. Thus the quantity of compressed air escapes from the dryer 4 to the environment only through the first path portion 5a. For this, the compressed air must pass through an adjustment device 6, which in FIG. 2 is configured as a choke. The discharge path 5 with path portion 5a thus serves for a lengthy discharge of compressed air, so that the dryer 4 is optimally regenerated.

[0041] For a height change process of the air suspension system 11 or for a regular flushing process of the dryer 4, the second path portion 5b of the discharge path 5 is then used. In other words, the first discharge valve 7 remains closed while the second discharge valve 8 is open. Since no adjustment device constricting the flow cross section is provided in the second path portion 5b, the compressed air can escape to the environment via this path as quickly as possible.