The present invention concerns an air separator or deairing arrangement at a reservoir for a hydraulic system according to the introduction to claim 1.

It is well known that air or gas enclosed in the liquid or fluid (hydraulic oil) that circulates in hydraulic systems tends to create bubbles, which can damage the various consumers that are components of the hydraulic system. The occurrence of cavitation in pumps is particularly serious. The size of the bubbles increases as the vacuum increases relative to the surface tension of the liquid. The vacuum is generated principally in pumps as a result of the suction action of these. In order to avoid the said problem hydraulic systems, normally a hydraulic tank or oil reservoir, are equipped with some form of air separator Efficient air separation not only reduces the risk of damage as a result of the said cavitation but also reduces the power requirement of the hydraulic system, at the same time as the precision and accuracy of the hydraulic system improve.

The separation of air or gas is generally based on ensuring that the speed of flow through the reservoir of the systems is so low that air or gas bubbles have sufficient time to rise to the surface. This basis leads to a requirement for relatively large reservoirs. Since the space available for the reservoirs of hydraulic systems is in many cases limited, which is particularly the case for mobile hydraulic systems, the problem of air separation becomes more significant. In the case of mobile hydraulic systems, the combination of a limited volume of the oil reservoir and a high speed of flow is normally always desirable.

In order to achieve efficient air separation when a high speed of flow through a reservoir is required, the use of configurations with guide rails or similar is known, which guide rails or similar lead the liquid from a connector of a return line through a permeable wall with the ability to finely divide gas bubbles that arise in the liquid. The expression "permeable wall" is used below to denote a fine-mesh net, perforated sheet metal plate, plates with holes, or similar that allow the passage of liquid while at the same time the configuration forms a diffuser that brakes the speed of the fluid that arrives and reduces the turbulence that arises. The openings in the net or sheet metal plate have a magnitude (size) that has been selected and designed such that the gas bubbles are finely divided and released when they pass, and in this way they have time to dissipate.

Since the hydraulic oil in a closed system continuously passes the air separator, a final value is obtained that becomes evermore higher, i.e. a lower amount of gas bubbles arises in the hydraulic oil as the mesh of the net that is used is made finer, while the gas bubbles become finely divided according to the size of the net mesh. On the other hand, the fall in pressure through the configuration will increase, which is not desirable since it leads to other problems, such as the appearance of excess pressure, in particular during cold starts, in parts of the system that can result in damage. Prior art air separators at reservoirs for hydraulic systems have been bulky and inefficient. One significant problem has been that they function simply as air separators. The combined effect that the air separator is to function also as diffuser with the task of efficiently reducing the speed of the hydraulic fluid and the appearance of turbulence to such an extent that the gas bubbles have time to dissipate before the hydraulic fluid is recirculated in the hydraulic system has not been available.

The purpose of the present invention, therefore, is to achieve an efficient air separation arrangement for a reservoir at a hydraulic system that offers a combination of requiring a low volume and high speed of flow.

This purpose of the invention is solved through an air separation arrangement that demonstrates the distinctive features and characteristics that are specified in claim 1.

Further advantages of the invention are made clear by the non-independent claims.

As a consequence of the return oil being led in a configuration that includes two parts (one of which is taken up inside the other) that causes the hydraulic fluid to pass from the said return line 2 in a required manner in a central passage with falling flow from an inner surface of the configuration to a passage with rising flow at an outer surface of the same, while it passes one or several permeable walls at different levels and in this way in several steps in the vertical direction, the gas bubbles can be efficiently finely divided and are braked through the diffuser effect to such an extent that the gas bubbles have sufficient time to dissipate before the liquid once again is recirculated into the hydraulic system.

The invention will be described below in more detail with guidance from an embodiment that is shown in the attached drawings, of which:

Fig.1 shows a perspective view obliquely from above of a reservoir at a hydraulic system equipped with a deairing arrangement according to the invention,

Figure 2 shows a perspective view of the reservoir in Figure 1 at a larger scale and with parts that been removed such that the deairing arrangement according to the invention is more clearly seen,

Figure 3 shows a first side view of the reservoir with parts that been removed such that the deairing arrangement according to the invention is more clearly seen, and

Figure 4 shows a second side view of the reservoir with parts that been removed such that the deairing arrangement according to the invention is more clearly seen.

The hydraulic oil tank or reservoir 1 shown in Figure 1 has a return line connection 2 and an inlet line connection 3 for connection with a hydraulic system that is not shown in more detail, such as a mobile hydraulic system that is a component of a vehicle that supports the said reservoir.

The reservoir 1 has an air-release opening 4 equipped with a filter on an upper surface of a part at a high location in order to allow changes of volume of oil in the tank. The reservoir 1 is equipped internally with an air separator or deairing arrangement generally denoted by 5, which will be described in more detail below.

As is made most clear by Figure 2, the reservoir 1 is divided into two compartments that include a principal compartment 6 that is located in principle in an upper part of the reservoir and an air separation compartment 7 that is located in a lower part of the reservoir. As the drawing makes clear, a lower part of the principal compartment 6 of the reservoir is located at the side of the air separation compartment 7. The connector for the return line 2 opens out into an inlet that is located high on the air separation compartment 7, while the inlet line connector 3 opens out into in an outlet that is located low on the principal compartment 6. The air-release opening 4 opens out into in an upper part of the principal compartment 6, which also serves as an expansion compartment at this part. The oil level of the reservoir during normal operation is suggested in Figures 3 and 4 with the dashed line 8, whereby 9 in Figure 1 denotes a sighting glass.

As is made clear by Figure 2, the air separation arrangement 5, which is located in the lower part of the reservoir 1 in the air separation compartment 7, comprises a separator element 10 with a configuration that includes two parts 10A, 10B, one of which is taken up into the other.

Such an internal/external configuration is constituted in the present design given as an example by a deairing housing 10A located inside the principal compartment 6 of the reservoir 1 , at one side of this, and a return line 10B taken up into the housing for the reception of the return flow Q2 from the said hydraulic system at an upper end of the return line. The deairing housing 10A and the return line 10B are so oriented that they extend together along an essentially vertical main axis suggested by a dashed centre line C-C.

With reference also to Figures 3 and 4, the deairing housing 10A demonstrates an essentially rectangular cross-section shape that is limited in the sideways direction by a vertical riser plate 1 1 that extends between two opposite side walls 12, 13 that are defined by two opposing sheet metal walls 14, 15 (see Figure 1 ) that are joined at the ends and that form the external limiting walls of the lower part of the reservoir 1 .

The riser plate 1 1 that is arranged at the lower part of the reservoir 1 forms an intermediate wall that extends from a bottom plate 16 to which it is united with welded joins, and onwards upwards in order to be terminated at its upper edge a certain distance below a sheet metal part 17 folded at a right-angle that, together with an end plate 18, resting on and joined to the said folded sheet metal part, forms a principal part of the upper surface of the air separation compartment 7.

The return line 10B demonstrates a cross-section shape that is principally circularly cylindrical and is taken up into the deairing housing 10A in such a manner that a flow-through passage for the liquid, which will below be denoted the "passage with rising flow" 21 , is limited between the vertical riser plate 1 1 , parts of the two sheet metal walls 14, 15, and the outer surface of the return line 10B. The return line 10B limits an internal passage for the liquid, which will below be denoted the "passage with falling flow" 20. The said passages with rising and falling flows 20, 21 are denoted for the sake of simplicity with flow arrows in Figure 2 and depict the direction of flow of the liquid passing through downwards or upwards, respectively.

The return line 10B extends from the bottom plate 16 of the reservoir and onwards up through a central opening at a removable flange 22, that is connected by screwed or bolted joints 23 in a manner that allows it to be removed at the end plate 18, in order to be terminated its upper end by a blind flange 25. The upper end of the connecting return line 10B is connected by means of a screwed or bolted joint 26 to the said blind flange 25 in a manner that allows it to be removed. The return line 10B and the removable flange 22 are united through a surrounding welded join that extends in a manner that seals for both gas and liquid around the complete circumference of a contact area between the cavity walls of the central opening of the removable flange 22 and the outer surface of the return line 10B.

The said passages with falling and rising flows, 20 and 21 respectively, are connected in a manner that allows liquid to flow through a part at the lower end of the return line 10B that is terminated flush against the bottom plate 16. The said lower part of the return line 10B is designed as a vertically oriented permeable ring-shaped wall 28 and it permits liquid to pass in a radial or in a direction that is transverse to the direction of flow out from the passage with falling flow 20 of the return line and onwards out to the passage with rising flow 21 . It should be understood that the return line 10B forms a removable unit that can be removed and can be simply lifted up out of the air separation compartment 7 of the reservoir, for, for example, inspection, exchange or cleaning.

As has been described above, in the internal/external configuration according to the invention that has passages with falling and rising flows 20 and 21 , respectively, hydraulic fluid is caused to flow from the said connection at the return line 2 in a required manner into the passage with falling flow at the configuration 10A that is formed by the return line, whereby the return flow Q2 that is led into an upper end of the passage with falling flow 20 is caused to move downwards, as is illustrated by the flow arrows drawn with dashed lines, in order to be transferred from an inner surface of the configuration at a lower end of the passage with falling flow to the passage with rising flow 21 in an outer surface of the latter, limited between the said first 10A and second 10B configurations, i.e. in a compartment that is limited between the return line 10B and the deairing housing 10A, whereby the flow moving upwards passes one or several horizontal permeable intermediate walls 30: 1 , 30:2- 30n located at different levels in the vertical direction. As has been mentioned above, the passage with rising flow 21 is terminated at its upper end by the horizontal end plate 18 and communicates the said passage in an upper end with the principal compartment 6 of the reservoir 1 through a first partial outlet 31 of a flow outlet, which partial outlet, limited between the upper edge of the vertical riser plate 1 1 and the lower surface of the folded sheet metal part 17 and the end plate 18, undergoes a transition into a flow collection compartment 32. The first partial outlet 31 has its extent in a vertical plane and forms a passage from the passage with rising flow 21 to the said flow collection compartment 32.

The said flow collection compartment 32 is limited by a vertical permeable side wall 33 that is plane parallel with the vertical riser plate 1 1 and located at a distance outside of this with respect to the passage with rising flow 21 , and by a horizontal permeable bottom wall 34 that is designed as an extension of one of the said horizontal permeable intermediate walls 30:2 that form the bottom of the flow collection compartment 32.

The vertical permeable side wall 33 and the sheet metal part 17 that has been folded at an angle, which supports the end plate 18, limit between them a second partial outlet 36, with the nature of a gap, of the said flow outlet. This second partial outlet 36 that extends in a horizontal plane permits not only the finely divided gas bubbles 37 in the liquid that have collected in the flow collection compartment 32, but also the finely divided gas bubbles 37 that have collected under the horizontal end plate 18, to move freely towards the second partial outlet 36 with the nature of a gap in order to freely continue to rise upwards in the principal compartment 6 towards the expansion compartment to be ventilated through the air-release opening 4. The second partial outlet 36 has its extent in a horizontal plane and forms a passage that permits gas bubbles to rise from the said flow collection compartment 32 and onwards up into the expansion compartment of the reservoir 1 .

The deairing process for the finely divided gas bubbles 37 described above is illustrated in Figure 4.

As is shown in Figure 2, during operation of the hydraulic system a fluid volume denoted by Q2 is withdrawn by suction through the inlet line connection 3 that is at the lower part of the principal compartment 6, located in an outlet. The flow collection compartment 32 is in connection with the said inlet line 3 through the vertical permeable intermediate wall 33 and the horizontal permeable intermediate wall 34, which means that the essentially deaired volume of liquid that has been withdrawn by suction from the flow collection compartment 32 is compelled to pass through the said permeable intermediate walls 33, 34 that limit the flow collection compartment against the principal compartment 6 before the volume of liquid reaches the outlet of the inlet line 3. The permeable flow side wall 33 and bottom wall 34 form a shielding barrier between the first partial outlet 31 of the flow outlet and the inlet line 3 arranged at a lower part of the principal compartment 6 of the reservoir. In this way, any remaining gas bubbles in the liquid are finely divided and caused to be released by their motion upwards along the vertical permeable intermediate wall 33, and onwards upwards towards the upper flow outlet 36 with the nature of a gap in order to subsequently rise freely, as is illustrated in Figure 4 with reference number 37, up towards the expansion compartment.

The invention is not limited to what has been described above and shown in the drawings: it can be changed and modified in several different ways within the scope of the innovative concept defined by the attached patent claims.