HYDRAULIC DEVICE FOR DEGATING AND DRAINING OF HYDRAULIC OIL

Description

[0001] The invention relates to a hydraulic device for degassing and dewatering a hydraulic oil with a pressure source from which the hydraulic oil to be degassed flows via a throttle point.

[0002] Air contained in hydraulic oil poses a problem in hydraulic systems for a variety of reasons. The higher the proportion of free or undissolved air, the greater the inherently undesirable compressibility of the hydraulic oil. If the hydraulic oil drawn in by the pump contains air bubbles, this can lead to poor efficiency and high noise levels. The more free air there is in hydraulic oil, the faster the hydraulic oil ages. In general, the attempt is made to use a generously dimensioned reservoir with a correspondingly long residence time for the hydraulic oil to allow the air bubbles that occur in a hydraulic system to rise from the hydraulic oil in the reservoir and outgas. Depending on the size of the air bubbles, this process can be relatively slow.

[0003] It has also been proposed to accelerate and improve the degassing of hydraulic oil through the use of ultrasound or by creating a vacuum. Degassing using ultrasound or a vacuum requires additional equipment, which incurs costs, increases susceptibility to failure, and potentially consumes energy. Furthermore, these methods can cause additional oil pollution.

[0004] A system for degassing hydraulic oil is already known from CN 203023182 U. Hydraulic oil drawn and discharged from a tank by a pump flows back to the tank via a nozzle arrangement. After flowing through the nozzle arrangement, air contained in the hydraulic oil can be separated by cavitation and removed through what the document calls a degassing device.

[0005] CN 1087375 discloses a hydraulic system in which an oil tank is divided into two compartments by a partition wall extending to a certain height. A first hydraulic pump draws hydraulic oil from the bottom of one compartment of the oil tank. A second pump conveys hydraulic oil from the bottom of the second compartment via a throttle element. Air bubbles form downstream of the throttle element, rise in the oil contained in the second compartment, and are then sucked away. The oil level in the second compartment is determined by the height of the partition wall.

[0006] JP 2013-2031 discloses a device for removing air bubbles from hydraulic oil. The hydraulic oil is forced from a high-pressure chamber through several throttles into a low-pressure chamber, causing cavitation. Several low-pressure inlets for hydraulic oil also open into the low-pressure chamber.

[0007] In addition to the air contained in a hydraulic system's hydraulic oil, water also has various undesirable effects. Water accelerates the aging of hydraulic oil through oxidation, impairs its lubricating properties, impairs the filterability of the oil through hydrolytic decomposition and corrosion products, and promotes surface corrosion. Therefore, efforts are made to keep the water content in hydraulic oil as low as possible.

[0008] There are various known approaches to reducing water in hydraulic oils. A distinction must be made between the reduction of dissolved water and the reduction of free water. Free water can be present either in the form of an emulsion or as a collected water deposit, for example, at the bottom of the tank. Free water can be removed from hydraulic oil by drainage, centrifuges, or absorbent filters. Drainage takes advantage of the fact that free water settles at the bottom of a tank containing hydraulic oil and can be drained from there. When using a centrifuge, free water is separated from the hydraulic oil due to applied centrifugal forces. A filter matrix coated with a super-absorbent polymer is used as the absorbent filter.

[0009] Vacuum dehydration is a well-known method for reducing the dissolved water content in hydraulic oil. This process involves subjecting the hydraulic oil to a vacuum for drying. The resulting concentration gradient between the hydraulic oil and the evacuated space causes the water to evaporate from the hydraulic oil. This process can also heat the hydraulic oil. Due to the low pressure, water boils at temperatures that do not yet damage the oil or its additives. This further accelerates the reduction of the water content in the oil.

[0010] If oil containing free water is pumped into the vacuum dehydration system, the water evaporates directly. Since the reduction of dissolved water in the hydraulic oil allows free water to be dissolved again, vacuum dehydration is ultimately also capable of reducing free water in a system, even if it is not pumped directly into the system but is located elsewhere in the hydraulic system. By reducing the dissolved water, the hydraulic oil can dissolve free water again, so that vacuum dehydration ultimately also removes free water from the hydraulic oil.

[0011] The invention is based on the object of creating a hydraulic device which enables a highly effective, cost-effective and rapid degassing of a hydraulic oil and, without great effort, also a reduction of the water content of the hydraulic oil with a high water separation rate.

[0012] The object is achieved in a hydraulic device comprising a pressure source, an air source, a flow channel, a throttle point designed as a nozzle, wherein liquid to be degassed flows from the pressure source via the throttle point, in that the amount of liquid flowing via the throttle point and the flow cross section of the throttle point are coordinated with one another in such a way that a cavitation or supercavitation zone is formed downstream of the throttle point, and in that an air path is provided, one end of which is connected to the air source and the other end of which is located downstream of the throttle point directly in or on the (super)cavitation zone, so that any type of air such as ambient air or, for example, compressed air, hot air, cold air or dry air from outside can be introduced into the hydraulic oil via the air path.The nozzle is arranged so that its outlet coincides with the central axis of the flow channel formed, for example, by a pipe.

[0013] The applicant's previously filed German patent application 10 2015 216 174.9 applies to a hydraulic device that uses cavitation, particularly supercavitation, to separate air from hydraulic oil. Supercavitation occurs when the oil flow rate through a throttle point, such as a nozzle, and the flow cross-section of the throttle point are coordinated in such a way that an oil jet is generated in a flow channel downstream of the nozzle, surrounded by a continuous area of ​​liquid vapor and air. Supercavitation then occurs downstream of the throttle point. Supercavitation is typically referred to when a body moving very rapidly through a fluid is completely surrounded by vapor.

[0014] In a direction perpendicular to the direction of relative motion between solid and liquid, one then has a central solid, on the outside of which is a gas-filled region, and then the liquid. The device according to the invention has an inverse arrangement. The liquid jet, and thus the liquid, is located in the center. The liquid jet is surrounded by a gas-filled region, which is delimited by the solid forming the flow channel. When the liquid condenses in the vapor region, relatively large air bubbles are formed. These can be easily separated, leading to rapid degassing of the oil.

[0015] Air separation through cavitation or supercavitation surprisingly also has an effect on dewatering hydraulic oil, as air can absorb water depending on its temperature, and thus the air bubbles released by (super)cavitation also contain water. When the air bubbles separate at the oil surface and the air is removed, both air and water are removed from the oil. The temperature increase associated with (super)cavitation of the fluid flow leaving the throttle point has a positive effect because air can absorb more water as the temperature increases.

[0016] The oil jet runs along the pipe's central axis from the nozzle exit to its collapse.

[0017] By appropriately selecting pressure drop and flow rate, supercavitation creates a coherent liquid vapor / air region of a defined size between the nozzle and the jet collapse. Upon condensation, this region converts the air content into relatively large air bubbles. When these air bubbles separate from the oil surface in the tank, this leads not only to a reduction in the air content but also to a reduction in the water content in the oil.

[0018] In order to further increase the rate of water separation from the oil, an air path is now available with which any type of air from outside, such as ambient air or compressed air or hot air or cold air or dry air, can be introduced into the hydraulic oil.

[0019] According to the invention, the air is supplied via the air path, one end of which is connected to the air source, and the other end of which is located downstream of the throttle point, directly in or near the (super)cavitation zone. This results in the formation of numerous very small air bubbles from the supplied air, each with a large bubble surface area over the sum of all the air bubbles. As the size of the bubble surface increases, the amount of water diffusing from the oil into the air bubbles formed by the externally supplied air increases, and thus the water separation rate.

[0020] If the throttle point is followed by a flow channel, for example, formed by a pipe, with a flow cross-section significantly larger than the flow cross-section of the throttle point, the additional air is preferentially introduced into the flow channel. For this purpose, the flow channel can have one opening in its wall or several openings evenly distributed around the circumference, preferably at the same height, to which the air path is connected.

[0021] Preferably, the flow channel runs straight from the nozzle and, during use, in the direction of gravity, i.e., vertically. This avoids asymmetry in the forces acting on the flowing medium relative to the axis of the flow channel. However, degassing and dewatering are also generally possible with a horizontal flow channel or with an arrangement between vertical and horizontal.

[0022] Preferably, a container for holding degassed liquid is provided, with the flow channel advantageously extending from the throttle point straight down to below the level of the liquid in the container. The flow between the throttle point and the container inlet is thus guided without deflection, so that the stability of the liquid jet is not compromised by the upstream effect of an asymmetric pressure distribution across the cross-section of the flow channel. The air bubbles enter the container directly and can be easily separated there due to their large volume and the associated increased buoyancy, which leads to rapid degassing and dewatering of the oil.

[0023] The core of this advantageous development is that there is a straight pipe section behind the throttling point so that the cavitation or supercavitation zone can develop. However, deflections can also be present afterward. It is advantageous that the flow path from the collapse of the vapor region to the tank is as short as possible, so that the air bubbles have as little time as possible to dissolve again.

[0024] If necessary, a separate high-pressure circuit with a hydrostatic displacement pump is provided, which draws hydraulic fluid from the reservoir, which flows back to the reservoir via the nozzle. This ensures reliable degassing and drainage at every operating point of a hydraulic system to which the separate high-pressure circuit for degassing is assigned. However, it is also conceivable that a pump is used as the pressure source, supplying one or more hydraulic consumers with pressure fluid, with a portion of the oil pumped by the pump flowing through the nozzle as a bypass.

[0025] As already mentioned, the air supplied from outside can be drawn from the ambient air due to the negative pressure in the cavitation zone. The air path is then open to the ambient air at one end. By connecting to an appropriate air supply system, compressed air, hot air, cold air, or dry air can also be supplied. An air filter can prevent contaminants from being introduced into the oil.

[0026] To improve the separation of air bubbles and to set a constant air content in hydraulic systems, the air can be supplied from the outside in a pulsed operation, so that the cavitation or supercavitation is used to alternately degas with little separation of water or to create very small air bubbles from additionally sucked in air or actively supplied air to degas and separate water to a large extent.

[0027] The advantages achieved with the invention are that effective and efficient degassing and dewatering occur, that these can be implemented cost-effectively and robustly, and that, in principle, only passive components are required. Several embodiments of a hydraulic device according to the invention for degassing and dewatering hydraulic oil are illustrated in the drawings. The invention will now be explained in more detail with reference to these drawings.

[0028] It shows Figure 1 shows an example, which does not fall under the definition of the claims, within a hydraulic system, wherein the hydraulic oil flowing through a separation unit for degassing and dewatering is pumped by an auxiliary pump, Figure 2 shows an example, which does not fall under the definition of the claims, within a hydraulic system with removal of the hydraulic oil to be degassed and dewatered on the pressure side of a main pump, Figure 3 shows a first embodiment within a hydraulic system, wherein the hydraulic oil flowing through a separation unit for degassing and dewatering is pumped by an auxiliary pump, as in the example according to Figure 1 is pumped by an auxiliary pump and additional air is supplied to the separation unit from outside, Figure 4 shows a second embodiment within a hydraulic system similar to that of Figure 3, but with a switching valve for the pulsed supply of additional air, and Figure 5 the separation unit of the devices from the Figures 3 and 4 with details.

[0029] The hydraulic system according to Figure 1 comprises a hydraulic working circuit 10 and a hydraulic auxiliary circuit 11, which represents the degassing and dewatering device. The working circuit 10 includes a hydrostatic main pump 12 of the displacement type, which is adjustable in its displacement and driven by a motor 13, which is, for example, an internal combustion engine or an electric motor. The displacement pump 12 supplies one or more hydraulic consumers with hydraulic oil, if necessary via one or more hydraulic valves. The displacement pump 12 draws the hydraulic oil flowing to the hydraulic consumers from a tank 15, into which the hydraulic oil flowing from the hydraulic consumers flows back.

[0030] The hydraulic consumers and the hydraulic valves are in Figure 1 shown in a highly simplified manner and generally provided with the reference number 16.

[0031] The hydraulic auxiliary circuit 11 is a separate high-pressure circuit and serves to degas and drain the hydraulic oil contained in the tank 15. The auxiliary circuit, and thus the device for degassing and draining the hydraulic oil, comprises an auxiliary pump 20 of a positive displacement design, which is also adjustable in its displacement and which is also driven by the motor 13 via a through-drive of the main pump 12. The auxiliary pump 20 draws hydraulic fluid from the tank 15 and feeds it back to the tank 15 via a hydraulic line 21. The hydraulic line 21 leads to a throttle point designed as a nozzle 25, through which the hydraulic oil pumped by the auxiliary pump 20 flows to the tank 15.

[0032] The hydraulic fluid flows from the nozzle 25 into the tank via a pipe 26, which is directly connected to the nozzle 25 or into which the nozzle is built, runs straight and whose open end farthest from the nozzle is always below the liquid level inside the tank 15, even if the liquid level changes during operation. A flow channel is created through the pipe 26. The nozzle 25 forms a separation unit 27 with the pipe 26. The nozzle is arranged relative to the pipe 26 such that the outlet of the nozzle is in the pipe's central axis and the hydraulic oil jet runs along the pipe's central axis until it collapses. In this case, the pipe is arranged such that the axis of the pipe and also the hydraulic oil jet run in the direction of the gravitational force.

[0033] The hydraulic system according to Figure 2 includes as the one according to Figure 1a hydraulic working circuit 10 and a hydraulic secondary circuit 11, which represents the degassing and dewatering device. The working circuit 10 includes a hydrostatic main pump 12 of the displacement type, which is adjustable in its displacement and driven by a motor 13, which can be, for example, an internal combustion engine or an electric motor. The displacement pump 12 supplies one or more hydraulic consumers with hydraulic oil, if necessary via one or more hydraulic valves. The displacement pump 12 draws the hydraulic oil supplied to the hydraulic consumers from a tank 15, into which the hydraulic oil flowing from the hydraulic consumers flows back.

[0034] The hydraulic consumers and the hydraulic valves are as in Figure 1 shown in a highly simplified manner and generally provided with the reference number 16.

[0035] From the example to Figure 1The example differs according to Figure 2 only in that the hydraulic secondary circuit 11, which serves to degas and drain the hydraulic oil located in the tank 15, is now part of the working circuit insofar as the hydraulic oil flowing to the separation unit 27 is oil that is pumped by the main pump 12 and branched off at the pressure connection of the main pump 12. Degas and drain can therefore always be carried out when the pressure at the pressure connection of the pump is sufficiently high while supplying one or more hydraulic consumers. Alternatively, the degas and drain can be operated intermittently when no hydraulic consumer is to be supplied by the main pump 12. From the pressure connection of the pump 12, hydraulic oil flows via a hydraulic line 21 to the separation unit 27, which is the same as in the example according to Figure 1 and returns to tank 15 via the separation unit.

[0036] For an illustration of the processes in the separation unit 27, reference is made to Figure 5. By appropriately selecting the pressure loss across the nozzle 25 and the volume flow rate, a liquid jet is generated downstream of the nozzle 25 in the pipe 26 by supercavitation. This jet is surrounded over a certain distance by a continuous area of ​​liquid vapor, in this case oil vapor with a small proportion of water vapor, and air. Due to the condensation of evaporated liquid, this area is followed by an area of ​​foam, which also surrounds the central liquid jet. Eventually, all of the oil vapor has condensed, and one has a liquid containing large gas bubbles, which mainly contain air, but also water vapor, since air can absorb water depending on the temperature. Figure 5The various areas within pipe 26 are indicated. Depending on the parameters used, the area of ​​liquid vapor and air can extend over the entire length of the pipe. The large air bubbles, and thus also the water they contain, enter the area above the liquid level in tank 15 and exit through an opening in the tank. An air filter can be located in the opening to prevent ambient dirt from entering the tank. This separates air and water from the hydraulic oil.

[0037] In order to increase the rate of water separation, the Figures 3 and 4 The hydraulic devices shown in the drawing for degassing and dewatering hydraulic oil are intended to introduce ambient air from outside into the hydraulic oil in addition to the air released from the hydraulic oil. Apart from this, the hydraulic systems are designed according to the Figures 3 and 4 designed in the same way as the hydraulic system according to Figure 1 and have a hydraulic working circuit 10 with the main pump 12, the tank 15 and the hydraulic equipment 16 and a hydraulic secondary circuit 11 with the auxiliary pump 20, the hydraulic line 21 and the separation unit 27.

[0038] According to the Figures 3 and 4 The pipe 26 of the separation unit 27 in the cavitation zone downstream of the nozzle 25 has an opening with an air connection 30, which serves as an air path leading directly into the environment. Due to the negative pressure occurring in the cavitation zone during operation of the separation unit 27, additional air flows from the environment into the cavitation zone via the air path, ultimately resulting in numerous very small air bubbles and thus, in total, in a large air bubble surface. This large air bubble surface results in a high water separation rate.

[0039] It is possible to arrange two or more air connections 30 on the pipe 26 at the same height in a rotationally symmetrical manner, as shown in Figure 5 where there are two air connections located diametrically opposite each other on pipe 26. Overall, therefore, the situation is symmetrical.

[0040] To improve the separation of air bubbles and to maintain a constant air content, pulsed operation is advantageous, as is the case with Figure 4 The device shown is intended for degassing and draining hydraulic oil and in which phases with the supply of additional air alternate with phases without the supply of additional air. Figure 4A 2 / 2-way switching valve 31 is inserted into the air connection 30, which blocks the supply of additional air in a first switching position and allows it in a second switching position. The switching positions of the switching valve 31, and thus the pulsation, change in such a way that the large bubbles created during degassing coalesce with the small bubbles supplied from outside, thus separating large quantities of air and water from the oil surface.

[0041] Atmospheric pressure typically prevails in tank 15. Therefore, in all of the exemplary embodiments shown, the pressure difference across the nozzle 25 can be adjusted, for example, by pressure-regulating the auxiliary pump 20 supplying the separation unit or the main pump 12 in intermittent operation. The volume flow is then determined by the selected opening cross-section of the nozzle 25. A large volume flow leads to faster degassing and dewatering, but also to increased heat input. A small volume flow can reduce the heat input. The coordination between degassing / dewatering speed and heat input depends on the respective system. Pressure control of the auxiliary pump is particularly advantageous when the speed of the motor 13 varies greatly.

[0042] However, the auxiliary pump can also be a fixed-displacement pump. Its flow rate, selected depending on the requirements of the respective system, and the opening cross-section of the nozzle 25 are then coordinated so that the desired pressure is achieved upstream of the nozzle 25. Such a design is particularly advantageous when the speed of the motor 13 does not vary greatly.

[0043] The hydraulic oil flowing via the nozzle 25 to the tank 15 is preferably taken from the working circuit when the pressure there is constant or predominantly so high that supercavitation is caused at the nozzle 25.

[0044] Furthermore, it is possible to measure the oxygen and / or air content in the hydraulic fluid and to operate the degassing and dewatering system in controlled or intermittent mode if specified limits are exceeded. Sensors can also be provided to detect the oxygen and / or air content. Suitable locations for this are in the high-pressure area of ​​the pumps, in the low-pressure area of ​​the working circuit, or at various positions in the tank. List of reference symbols

[0045] 10 hydraulic working circuit 11 hydraulic secondary circuit 12 main pump 13 motor 15 tank 16 hydraulic equipment 20 auxiliary pump 21 hydraulic line 25 nozzle 26 pipe 27 separation unit 30 air connection 31 switching valve

Claims

1. Hydraulic device for degassing and dewatering a hydraulic oil, comprising: a pressure source (20), an air source, a flow channel (26), a nozzle-shaped throttle point (25); wherein the outlet of the nozzle coincides with the centre axis of the flow channel, wherein hydraulic oil to be degassed flows from the pressure source (20) via the throttle point (25), wherein the quantity of liquid flowing via the throttle point (25) and the throughflow cross section of the throttle point (25) are coordinated with each other such that a cavitation or supercavitation zone is formed downstream of the throttle point (25), wherein the device comprises an air path (30), one end of which is connected to the air source, and the other end of which is situated downstream of the throttle point (25) directly in or at the cavitation or supercavitation zone, with the result that air can be introduced into the hydraulic oil from the outside via the air path (30).

2. Hydraulic device according to Patent Claim 1, wherein a flow channel (26) with a substantially larger throughflow cross section compared to the throughflow cross section of the throttle point (25) adjoins the throttle point (25), and wherein the air can be introduced into the flow channel (26).

3. Hydraulic device according to Patent Claim 2, wherein the flow channel (26) runs straight from the throttle point (25) and, in use, has an axis that runs in the direction of the gravitational force.

4. Hydraulic device according to Patent Claim 2 or 3, wherein the flow channel (26) has, in its wall, an opening, to which the air path (30) is connected.

5. Hydraulic device according to Patent Claim 2, 3 or 4, wherein it comprises a container (15) for receiving hydraulic oil, and wherein the flow channel (26) ends within the hydraulic oil contained in the container (15).

6. Hydraulic device according to Patent Claim 5, wherein air bubbles, which arise when steam condenses and pass into the container (15), are separated in the container (15).

7. Hydraulic device according to Patent Claim 5 or 6, wherein it comprises a hydrostatic positive displacement pump (20) which draws hydraulic oil from the container (15), which flows back via the throttle point (25) to the container (15).

8. Hydraulic device according to one of Patent Claims 1 to 7, wherein the air path (30) is open at one end to the environment.

9. Hydraulic device according to one of Patent Claims 1 to 7, wherein the air path (30) is connected at one end to an air supply device.

10. Hydraulic device according to one of Patent Claims 1 to 9, wherein a valve (31) is inserted into the air path (30), by way of which the air supply can be shut off.