EP1948930B1 - Compressor arrangement having bypass means for avoiding freezing of the cooler unit - Google Patents

Description

The present invention relates to a compressor arrangement for generating compressed air by means of a motor-driven compressor unit, which is followed by at least one cooler unit for cooling the generated compressed air, which enters the cooler unit via at least one inlet, where it flows through a Kühlluftumströmte cooling structure of a plurality of parallel-connected cooling channels and the cooler unit via at least one outlet, wherein between the inlet and the outlet of the radiator unit bypass means for avoidance a freezing of the cooler unit are provided at low ambient temperatures.

The field of application of the present invention extends primarily to oil-free piston compressors, which are used for the production of compressed air, for example in commercial and rail vehicle construction. In such applications, the compressor assembly must operate over a temperature range of -50 ° C to + 50 ° C ambient temperature. Since the cooler design also provides a maximum cooling capacity at + 50 ° C, under specific environmental conditions - for example, 100% humidity, - 20 ° C ambient temperature and 50% duty cycle - icing of the cooling channels can be observed within the cooler unit of the compressor assembly. During the operation of the compressor unit, this icing may even progress over a period of several hours to the extent that sufficient air delivery is no longer possible and the compressor arrangement finally fails.

From the US 6,952,932 B2 shows a cooler unit for a compressor assembly, in which the above-described problem is solved in that not all of the heated by the upstream compressor unit compressed air passes through the cooling air flowed around cooling structure, but that a portion of the heated compressed air via a bypass line to the cooling structure over directly to the outlet is guided where it mixes with the cooled by the cooling structure of compressed air. For mixing, however, an inserted in the bypass line mixing valve is required, which is operated in accordance with an electronic control to mix depending on the ambient temperature hot compressed air with cooled compressed air.

A disadvantage of this known technical solution, however, is that the valve and control technology provided here causes a corresponding equipment expense. In case of failure or malfunction of valve or control electronics by, for example, interruption of the power supply for the control electronics or wear a seal in the valve could freeze the cooling unit unhindered until its destruction. Furthermore, this solution is primarily for protecting the units downstream of the cooler unit from icing.

From the US 5,669,363 is another technical solution for bypass means on a radiator unit forth, which, however, also requires a fairly complex valve control - here by means of a thermostatic valve. From the US Pat. No. 6,167,956 goes out another cooler unit for a compressor assembly.

It is therefore the object of the present invention to provide a compressor assembly whose at least one cooler unit is effectively protected against freezing by simply constructed bypass means.

The object is achieved on the basis of a compressor arrangement according to the preamble of claim 1 in conjunction with its characterizing features. The following dependent claims give advantageous developments of the invention.

The invention includes the technical teaching that is provided as a bypass means only a permanently open bypass pipe without any lying in the compressed air flow valves between the region of the inlet and the region of the outlet of the cooler unit. The internal cross section of the bypass tube is matched to the capacity of the compressor unit and to the pressure difference between the inlet and outlet so that the bypass tube causes a higher flow resistance than the cooling structure at normal ambient temperatures. Normal ambient temperatures are primarily temperatures above freezing. At temperatures below freezing and progressive freezing of the cooling structure, however, the compressed air increasingly flows over the bypass tube.

The advantage of the solution according to the invention lies in particular in the fact that compressed air generation can be maintained in the case of a freezing of the cooler unit with minimal loss of cooling and conveying power via this specially dimensioned bypass tube. Since the invention does not require any valves, this is feasible with very little technical effort. The solution according to the invention has an independent control activity based on the dimensioning of the bypass tube. In this case, the bypass pipe is designed such that the outlet temperature (measured after the radiator unit) is limited so that the function of downstream equipment - such as air dryer, control valves - is not affected.

Experiments have shown that, especially in oil-free piston compressors for rail vehicles, the optimum ratio of internal cross section of the bypass tube to delivery line at 10 bar operating pressure in the range between 0.8 to 1.2. This parameter applies to several cooler units of a compressor assembly only for the aftercooler. The unit of measure for the internal cross section of the bypass tube is mm ² . The unit of measure for the delivery rate is l / min.

Preferably, the bypass pipe according to the invention is to be dimensioned to achieve optimum function such that in the case of a frozen cooler unit, which no longer lets compressed air through, the pressure difference between the two ends of the bypass pipe increases to a maximum of 0.5 bar. Such a pressure drop is quite acceptable as a minimal loss of capacity. By the solution according to the invention can be achieved that at totally frozen cooler unit, the flow rate drops by not more than 5% and the outlet temperature rises after the cooler unit by not more than 20 ° C relative to the cooler without a bypass.

According to a further measure improving the invention, it is provided that the bypass tube has screw connections at both ends, with which a releasable fastening the bypass tube can be made on the radiator unit. By this measure, it is possible to produce cooler units without bypass tube as a further product variant. It is also conceivable that the bypass tube is totally integrated in the cooler unit, for example by soldering or welding. For the bypass tube itself is a tube made of steel or a light metal, which can be used on a normalized semi-finished, for example, a tube with the basic dimensions of 10 x 1.5 mm. When selecting and dimensioning the bypass pipe, care must also be taken to ensure that it withstands the required test pressure.

Furthermore, it is possible that the bypass pipe is provided with cooling fins or cooling fins or is designed in the manner of a finned tube in order to improve the cooling effect, if necessary. The bypass tube can be designed as a casting-produced hollow body, or contain such. In addition to steel and non-metallic materials for production are conceivable, provided that they are sufficiently temperature resistant and pressure resistant. Thus, it is also conceivable that the bypass pipe is designed as a hose line, or includes such.

According to another measure improving the invention, it is provided that the bypass tube is arranged relative to the cooler unit in such a way that it lies in the flow of the cooling air flowing through the cooler unit. This ensures that the bypass tube exerts a minimum cooling effect on the compressed air flowing through it. The bypass tube can be arranged either vertically or horizontally relative to the radiator unit and run straight. If the self-cooling effect of the bypass pipe is not sufficient for a straight course, the bypass pipe can alternatively be designed in the manner of a pipe coil or the like.

Furthermore, it is conceivable to add a drain valve or a safety valve in the wall of the bypass pipe, if that makes sense. A drain valve would be located at the lowest point of the bypass tube.

The solution according to the invention is suitable for use in both single-stage and multi-stage compressor units. In the case of a single-stage compressor unit, the cooler unit is provided as an aftercooler, which can then be equipped with at least one bypass pipe according to the invention. In the case of a multi-stage compressor unit usually each individual compressor stage is provided with a downstream cooler unit in the form of an intermediate or aftercooler, wherein each cooling unit is associated with at least one bypass tube.

Regardless of the specific embodiment of the compressor unit, however, the at least one associated bypass pipe is preferably designed such that even with a totally frozen cooler unit, the entire capacity of the upstream compressor unit via the at least one associated bypass pipe is conductive.

Fig.1

eine perspektivische Außenansicht einer Kompressoranordnung, und

Fig.2

eine schematische Darstellung von Bypassmitteln an der Kühlereinheit der Kompressoranordnung nach Fig.1.

Further, measures improving the invention will be described in more detail below together with the description of a preferred embodiment of the invention with reference to FIGS. It shows:

Fig.1

an external perspective view of a compressor assembly, and

Fig.2

a schematic representation of bypass means on the radiator unit of the compressor assembly according to Fig.1 ,

According to Fig.1 a compressor assembly consists of a driven by an electric motor 1 multi-stage compressor unit 2 for generating compressed air. For this purpose, 3 air is sucked from the environment via a filter unit. Each compressor stage of the compressor unit 2 is assigned its own cooler unit 4a and 4b, which serve for cooling the compressed air generated in the respective upstream compressor stage. In that regard, the first compressor stage downstream cooler unit 4a as intercooler and a second compressor stage of the compressor unit 2 downstream cooler unit 4b is to be referred to as aftercooler. Each radiator unit 4a and 4b has an inlet 5 for incoming heated compressed air. From here, the heated compressed air passes for cooling via a cooling air-circulated cooling structure 6, which - in a conventional manner - from a plurality of parallel-connected cooling channels of smaller diameter flows to leave the cooler unit 4a or 4b via an outlet 7 again. The cooling air for flowing around the cooling structure 6 is generated via a motor or shaft-driven fan wheel 8 arranged between the cooler units 4 a and 4 b and the compressor unit 2.

According to Fig.2 For example, the cooler unit 4a shown here by way of example between the inlet 5 and the outlet 7 has a bypass tube 9 for avoiding freezing of the cooler unit 4a at low ambient temperatures.

The continuous, permanently open bypass pipe 9 is characterized by an internal cross-section, which is matched to the capacity of the compressor unit 2 and the pressure difference between inlet 5 and outlet 7 such that the bypass pipe 9 causes a higher flow resistance than the cooling structure 6 at normal ambient temperatures, whereas with progressive freezing of the cooling structure 6 as a result of crystal attachment to the wall and inner disks, the compressed air increasingly flows via the bypass pipe 9. It has been shown that the bypass pipe 9 does not freeze itself under these conditions, since it is heated up quickly by the compressed air itself and its flow friction in the bypass pipe 9.

Thus, the compressed air generation is maintained with minimal loss of cooling and delivery.

The bypass pipe 9 is designed here as a horizontal straight pipeline, which lies in the flow of cooling air flowing through the cooler unit 4 a, in order to also cool the bypass pipe 9. In addition, in the wall of the bypass tube 9 in this embodiment, a safety valve 10 is inserted, which opens from a defined pressure value to prevent bursting of the bypass tube 9. Furthermore, the bypass tube 9 in the interior can also have surface and cross-sectional changes to achieve a nozzle function, if flow dynamic sense.

LIST OF REFERENCE NUMBERS

1

electric motor

2

compressor unit

3

filter unit

4

cooler unit

5

inlet

6

cooling structure

7

outlet

8th

fan

9

bypass pipe

10

Drainage and / or safety valve

Claims (12)

1. Compressor arrangement for generating compressed air by means of a motor-driven compressor unit (2), downstream of which is positioned at least one cooler unit (4a, 4b) for cooling the generated compressed air, which compressed air enters into the cooler unit (4a, 4b) via at least one inlet (5), flows through a cooling structure (6) around which cooling air flows and which is composed of a plurality of parallel cooling ducts, and leaves the cooler unit (4a, 4b) via at least one outlet (7), with bypass means being provided between the inlet (5) and the outlet (7) of the cooler unit (4a, 4b) in order to prevent freezing of the cooler unit (4a, 4b) at low ambient temperatures,
   characterised in that a continuous and permanently open bypass pipe (9) is provided as a bypass means between the region of the inlet (5) and the region of the outlet (7), the inner cross section of which is matched to the delivery capacity of the compressor unit (2) and to the pressure difference between the inlet (5) and the outlet (7) in such a way that the bypass pipe (9) generates a higher flow resistance than the cooling structure (6) at normal ambient temperatures, whereas with progressive freezing of the cooling structure (6), the compressed air flows to an increasing extent via the bypass pipe (9), the ratio between the inner cross-section [mm²] of the bypass pipe (9) and the output [l/min] at an operating pressure of 10 bar being in the range between 0.8 and 1.2, and in that the bypass pipe (9) is further arranged relative to cooler unit (4a, 4b) in such a way that it lies in the flow of the cooling air passing through cooler unit (4a, 4b).
2. Compressor arrangement according to claim 1,
   characterised in that the pressure difference between the inlet and the outlet of the bypass pipe (9) into / out of the cooler unit (4a; 4b) is a maximum of 0.5 bar.
3. Compressor arrangement according to claim 1,
   characterised in that the bypass pipe (9) has screw connections at both ends, by means of which screw connections a detachable fastening to the cooling unit (4a, 4b) takes place.
4. Compressor arrangement according to any of the preceding claims,
   characterised in that the bypass pipe (9) is embodied either as a vertically or horizontally aligned straight pipe line or in the manner of a hose pipe.
5. Compressor arrangement according to any of the preceding claims,
   characterised in that a dewatering and/or safety valve (10) is inserted into the wall of the bypass pipe (9).
6. Compressor arrangement according to claim 1,
   characterised in that the compressor unit (2) is of single-stage construction with a cooler unit positioned downstream as a post-cooler, which is assigned at least one bypass pipe (9).
7. Compressor arrangement according to claim 1,
   characterised in that the compressor unit (2) is of multi-stage construction with a cooler unit (4a and 4b) positioned downstream of each compressor stage as an intermediate cooler and post-cooler, with each cooler unit (4a and 4b) being assigned at least one bypass pipe (9).
8. Compressor arrangement according to any of the preceding claims,
   characterised in that, in the event of the cooler unit (4a, 4b) being completely frozen up, the entire output of the compressor unit (2) positioned upstream can be conducted via the associated bypass pipe (9), and in that after the freezing has been eliminated, the initial state before the freezing is automatically re-established.
9. Compressor arrangement according to claim 1,
   characterised in that the bypass pipe (9) is integrated into the cooler unit (4a and 4b).
10. Compressor arrangement according to claim 1,
    characterised in that the bypass pipe (9) is provided with cooling ribs or cooling fins or is embodied in the manner of a finned pipe.
11. Compressor arrangement according to claim 1,
    characterised in that the bypass pipe (9) is embodied as or comprises a hollow body mass-produced by casting.
12. Compressor arrangement according to claim 1,
    characterised in that the bypass pipe (9) is embodied as or contains a hose line.

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