Hydraulic system, especially for military vehicles

Abstract

1. Hydraulic system, in particular for military vehicles, with at least two functional units, one of which represents a supply unit (2) and the other a consumer unit (4), which, spatially separated from one another, are exposed to partly the same, but in particular to different ambient temperatures which, when a temperature limit value is exceeded, lead to the evaporation of a water-based, flame-resistant liquid according to its vapor pressure curve, by means of which the hydraulic system can be operated, wherein a pretensioning device (42;52) is present which, in order to prevent the evaporation of the liquid when the temperature limit value is exceeded, increases the operating pressure in the hydraulic system in accordance with the vapor pressure curve of the liquid, characterized in that the supply unit (2) has a pressure-resistant storage container (18) which, as a prestressing device, has an air inlet valve (52) with an opening pressure greater than 1 bar absolute, which allows the air to flow freely into the container (18) when the liquid is withdrawn in the direction of the consumer unit (4) and, when the liquid is returned to the container (18), only allows the air to flow out into the environment at a predeterminable pressure, the pressure value of which is selected in accordance with the vapor pressure curve, related to the temperature limit value. ; 2. Hydraulic system according to claim 1, characterized in that in a return line (38) coming from the consumer unit (4) the pretensioning device is connected, which comprises a pretensioned, preferably hermetically sealed check valve

Description

[0001] The invention relates to a hydraulic system, in particular for military vehicles, having the features in the preamble of claim 1.

[0002] As disclosed, for example, in EP 0 185 871 A1, military vehicles, such as battle tanks, infantry fighting vehicles, or personnel carriers, have hydraulic systems that define their essential functions via hydraulically actuated actuation systems, such as piston-cylinder units that adjust the firing position of weapon barrels, travel drives, opening and closing systems for armored doors, covers, and the like. If such vehicles are fired upon in combat situations, damage to a hydraulic system that uses a highly flammable fluid, such as hydraulic oil, as the operating medium, represents a significant risk. To counteract this, a water-based, flame-resistant fluid can be used as the operating medium instead of hydraulic oil.According to the vapor pressure curve of water-based fluids, and considering that in military vehicles, especially armored vehicles, the functional units of the hydraulic system are generally located in different compartments, exceeding the temperature limit in one or both compartments can cause the fluid to evaporate. The advantage of significantly reducing the fire hazard when using flame-resistant, water-based fluids is therefore offset by the disadvantage that evaporation leads to compressibility of the operating medium, thus negatively impacting the operating behavior of the hydraulic system.

[0003] DE 10 2009 035 810 A1 describes a hydraulic system, in particular for military vehicles, with at least two functional units, one of which is a supply unit and the other a consumer unit, which, spatially separated from one another, are exposed to partly the same, but in particular to different ambient temperatures which, when a temperature limit is exceeded, lead to the evaporation of a water-based, flame-resistant liquid in accordance with its vapor pressure curve, by means of which the hydraulic system can be operated, wherein a pretensioning device is provided which, in order to prevent the liquid from evaporating when the temperature limit is exceeded, increases the operating pressure in the hydraulic system in accordance with the vapor pressure curve of the liquid.

[0004] Another hydraulic system is described in DE 10 2015 003 014 A1.

[0005] In view of this problem, the invention has the object of providing a hydraulic system of the type mentioned at the outset which is characterized by particularly favorable operating behavior when operated with a water-based fluid that reduces the risk of fire.

[0006] According to the invention, this object is achieved by a hydraulic system which has the features of patent claim 1 in its entirety.

[0007] According to the characterizing part of claim 1, an essential feature of the invention is that the supply unit has a pressure-resistant storage container which, as a pre-tensioning device, has an air inlet valve with an opening pressure greater than 1 bar absolute, which allows the air to flow freely into the container when the liquid is withdrawn in the direction of the consumer unit and, when the liquid is returned to the container, allows the air to flow out into the environment only at a predeterminable pressure, the pressure value of which is selected according to the vapor pressure curve, related to the temperature limit value.

[0008] It is further provided that a pre-tensioning device is provided which, in order to prevent the liquid from evaporating when the temperature limit is exceeded, increases the operating pressure in the hydraulic system in accordance with the vapor pressure curve of the liquid.

[0009] The protection against evaporation achieved by the pre-stressing enables trouble-free operation with flame-resistant, water-based operating fluids, even in applications where temperatures of the functional units exceeding the limit value are to be expected, as is particularly the case with armored vehicles. A commercially available HFC fluid can advantageously be used as the flame-resistant hydraulic fluid. This fluid is biodegradable and meets the requirements of DIN EN ISO 12922 for flame-resistant fluids. The solution according to the invention is particularly suitable for armored military vehicles, whereby the term "vehicles" should also include aircraft, ships, submarines, and the like.

[0010] If the hydraulic system according to the invention is intended for applications in which only the consumer unit, for example in the engine compartment of the vehicle in question, is potentially exposed to a temperature exceeding the limit value, while the supply unit, for example in the crew compartment of the vehicle in question, is not at risk of being exposed to a temperature leading to evaporation of the fluid, then the preloading device can be connected in a return line coming from the consumer unit. The preloading device has a preloaded, preferably hermetically sealed check valve that closes in the direction of the consumer unit and opens in the opposite direction. If the check valve is set to an opening pressure above the vapor point of the vapor pressure curve, the system remains at the preload pressure provided by the supply unit when the return is blocked.

[0011] If the hydraulic system is intended for applications in which both the supply unit, for example in the crew compartment of the vehicle, and the consumer unit, such as in the engine compartment of the vehicle, may be exposed to a temperature above the evaporation temperature, the supply unit has a pressure-resistant storage tank which, as a pre-tensioning device, has an air inlet valve with an opening pressure greater than 1 bar absolute, which allows the air to flow freely into the tank when the fluid is withdrawn towards the consumer unit and, when the fluid is returned to the tank, only allows the air to flow out into the environment at a pre-determined pressure, the pressure value of which is selected according to the vapor pressure curve, related to the temperature limit value.By selecting the opening pressure of the air inlet valve in the outflow direction, the supply unit can build up a preload pressure that is above the vapor point for the maximum ambient temperature occurring in one or the other room.

[0012] For applications where temperatures above the vapor point are expected in the supply unit and consumer unit spaces, such as the crew compartment and engine compartment, a preloaded, preferably hermetically sealed, check valve is provided in a return line from the consumer unit, in addition to the preload of the pressure-resistant storage container. This check valve closes toward the consumer unit and opens in the opposite direction. The opening pressure of this valve is set to the value of the vapor pressure curve corresponding to the maximum occurring temperature.

[0013] The check valve inserted into the return line can be arranged outside the storage tank, preferably in a receiving bore of the supply unit, which has the storage tank as a component.

[0014] In advantageous embodiments, a pressure accumulator unit is arranged between the supply and consumer units. When the system is shut down, the preload pressure preventing the liquid in the closed system from evaporating is therefore available from the pressure accumulator unit.

[0015] The supply unit is designed in such a way that the pressure built up in a supply line for the consumer unit by means of the supply unit is so high that evaporation of the liquid is prevented.

[0016] For this purpose, the supply unit has the following components: - a pressure supply pump, - a line filter, - optionally a preloaded check valve, - optional air inlet valve, - a safety valve and / or a pressure relief valve to protect the pressure supply pump.

[0017] The consumer unit may have at least one hydraulically actuated working cylinder.

[0018] At least one hydraulic accumulator can be provided for the storage unit, which can be a bladder accumulator, piston accumulator or an accumulator of another design.

[0019] The supply unit and / or the storage unit can be located in a crew compartment of the armored vehicle, while the consumer unit can be located in its engine compartment.

[0020] The invention is explained in detail below with reference to the drawings. They show: Fig. 1 shows in symbolic representation the hydraulic circuit of a first embodiment of the hydraulic system according to the invention; Fig. 2 and Fig. 3 shows in symbolic representation the hydraulic circuit of a second or third embodiment of the system according to the invention; Fig. 4 in symbolic representation the separately shown supply unit of the embodiment of Fig. 3; and Fig. 5 the vapor pressure curve for HFC fluid.

[0021] The embodiments of the hydraulic system according to the invention shown in the figures each have a supply unit 2, a consumer unit 4, a storage unit 6, and a control block 8. The consumer unit 4 is located in a chamber 10 that is spatially separated from a chamber 12 containing the supply unit 2, the storage unit 6, and the control block 8. The chambers 10 and 12, which in the present example are the engine compartment and the crew compartment of a military vehicle, respectively, can have different ambient temperatures during operation due to the spatial separation. In the examples shown in the figures, the consumer unit 4 has hydraulically actuated working cylinders 14 that are connected to the control block 8 via a common working line 16, in which HFC fluid flows in the forward or return direction to actuate the cylinders.When the hydraulic system is used in military vehicles, ambient temperatures of up to 80°C can occur in the crew compartment 12, which houses the supply unit 2, the storage unit 6, and the control block 8, while maximum temperatures of up to 160°C can occur in the engine compartment 10. Therefore, in both compartments 10 and 12, the vaporization point temperature of 60°C can be exceeded when using HFC fluid.

[0022] In all embodiments, the supply unit 2 comprises a motor-pump unit 20 which draws from a reservoir 18 containing an HFC fluid and, via a line filter 22, provides a supply pressure at a pressure port P that prevents evaporation at the maximum temperatures encountered. The pressure port P is connected via a supply line 24 to the storage unit 6, which is connected to the control block 8 by its outlet side 26. The storage unit 6 is constructed in a conventional manner and comprises a pressure accumulator 28, the oil side of which is connected to the supply line 24 via a check valve 30 and to the outlet side 26 via a check valve 32, with the check valves 30, 32 each opening in the forward flow direction.Via a pressure relief valve 34 forming an overpressure protection device and a manually operable drain valve 36 enabling emptying, the pressure accumulator 28 is also connected to a return line 38 which leads to the tank connection T of the supply unit 2 and thus, via a tank line 40 located in the supply unit 2, into the storage container 18. The output side 26 of the accumulator unit 6 is connected via a supply line 44 to a switching valve 46 located in the control block 8, to which the return line 38 is also connected. The switching valve 46 is designed as a 3 / 2-way valve which is electromagnetically controllable in order to connect the supply line 44 or the return line 38 to the cylinders 14 via the working line 16 for the actuation of the working cylinders 14.

[0023] The embodiment of Fig. 1 is intended for applications in which ambient temperatures in compartment 10, as the engine compartment of the vehicle in question, can prevail that are above the vapor point temperature of 60 °C of the HFC fluid, while in compartment 12, as the crew compartment 12, an ambient temperature of 60 °C is not exceeded. In this case, the pre-tensioning device is formed by a valve 42 inserted into the return line 38, which is a hermetically sealed check valve that closes in the direction of the working cylinders 14. Against opening in the return direction, i.e. from the consumer unit 4 to the tank connection T, the valve 42 is pre-tensioned in such a way that it only opens at a pressure that is above the pressure at which evaporation occurs at the maximum temperature.As a result, even when the switching valve 46 is switched to the return flow, the pressure applied by the supply unit 2 remains as a preload pressure in the system part belonging to the chamber 10. The embodiment of is completed. Fig. 1 through a ventilation line 48, which leads from the storage container 18 via a ventilation connection B of the supply unit 2 and via a ventilation filter 50 to the environment. In Fig. 1 shows two optional arrangements for the valve 42. The valve 42 can be inserted outside the supply unit 2 into the return line 38 or can be associated with the supply unit 2, wherein it can be inserted into the bore of the T-connector of the tank line 40.

[0024] The second embodiment, as shown in Fig. 2, is intended for applications in which the same ambient temperature prevails in both compartments 10 and 12 during operation, which ambient temperature is above the limit value for HFC fluid and can, for example, be up to 80 °C, the highest ambient temperature occurring in the crew compartment 12. In this case, the fluid storage container 18 is formed by a closed, pressure-resistant container to which an air inlet valve 52 is connected as a pre-tensioning device. At an opening pressure which is below 1 bar absolute and, for example, 0.5 bar, this air inlet valve allows air to flow freely into the closed storage container 18 via the ventilation filter 50 and the ventilation line 48 when fluid is withdrawn from it in order to flow via the supply line 24 to the storage unit 6 and to the consumer unit 4.However, during the liquid return via the return line 38 and the tank line 40, the inlet valve 52 closes until a selected pressure is reached in the reservoir 18, preventing evaporation. The entire system in chambers 10 and 12 is thus pre-pressurized with the same pressure.

[0025] The Fig. Figure 3 shows a third embodiment which is designed for applications in which temperatures above 60 °C can occur in both compartments 10 and 12, but the temperature in the engine compartment 10 exceeds the temperature in the crew compartment 12. In this case, it is not necessary to heat the entire system, as in Fig. 2, to be designed for the maximum temperature of the compartment 10. In other words, this means that the pressure-resistant storage container 18, with regard to its pressure resistance in terms of wall thickness and weight, does not have to be designed for a container pressure that corresponds to the pressure value for the maximum possible temperature in the compartment 10, but can be designed for the container pressure that corresponds to the lower temperature occurring in the crew compartment 12. For this purpose, in accordance with Fig. 2, the closed reservoir 18 is provided with the air inlet valve 52, which is set to an outlet opening pressure that is adapted to the maximum temperature in the crew compartment 12. However, in order to provide a correspondingly higher preload pressure for the system part located in the engine compartment 10 with a higher ambient temperature, in the embodiment of Fig. 3, corresponding to the embodiment of Fig. 1, the pre-tensioned check valve 42 is arranged in the return line 38, which is set for a correspondingly higher opening pressure in the return direction, so that, as in the example of Fig. 1, the pressure provided by the supply unit 2 remains as preload pressure, even if the switching valve 46 is switched to return. As in the example of Fig. 1, the valve 42 can be integrated into the supply unit 2 or installed externally in the return line 38.

[0026] The storage unit 6, which is connected with its outlet side 26 to the flow line 44, provides a preload pressure even during downtimes of the motor-pump unit 20, which prevents the evaporation of the fluid when a correspondingly high ambient temperature occurs. Fig. Figure 4 shows details of the design of the supply unit 2 for embodiments in which the closed reservoir 18 has a volume of more than 1 liter, which is usually the case. Then, at the preload pressures under consideration here, the reservoir 18 must be designed as a pressure device in accordance with the Pressure Equipment Directive 2014 / 68 / EU and therefore have a safety valve. As shown in Fig. 4, a pressure relief valve 54 is connected to the ventilation line 48. As Fig. As further shown in Figure 4, a further pressure relief valve 56 is connected between the pressure side 58 of the motor-pump unit 20 and the line filter 22, which is protected on the inlet side against backflow by a check valve 60. A bypass valve 62 is provided to bypass the line filter 22.

[0027] The Fig.Figure 5 shows a simplified, unspecified representation of the vapor pressure curve for a specific HFC fluid used as a hydraulic medium. As can be seen, the vaporization temperature value in the absence of pre-pressure is 60 °C. It is understood that the vaporization temperature value may be different for other HFC fluids used, for example, it may even exceed 60 °C.

Claims

[1] Hydraulic system, in particular for military vehicles, with at least two functional units, one of which represents a supply unit (2) and the other a consumer unit (4), which, spatially separated from one another, are exposed to partly the same, but in particular to different ambient temperatures which, when a temperature limit is exceeded, lead to the evaporation of a water-based, flame-resistant liquid according to its vapour pressure curve, by means of which the hydraulic system can be operated, wherein a pretensioning device (42; 52) is provided which, in order to prevent the liquid from evaporating when the temperature limit is exceeded, increases the operating pressure in the hydraulic system according to the vapour pressure curve of the liquid, characterized bythat the supply unit (2) has a pressure-resistant storage container (18) which, as a pretensioning device (42; 52), has an air inlet valve (52) with an opening pressure greater than 1 bar absolute, which allows the air to flow freely into the container (18) when the liquid is withdrawn in the direction of the consumer unit (4) and, when the liquid is returned to the storage container (18), only allows the air to flow out into the environment at a predeterminable pressure, the pressure value of which is selected in accordance with the vapor pressure curve, related to the temperature limit value. [2] Hydraulic system according to claim 1, characterized by in that the prestressing device (42; 52) is connected in a return line (38) coming from the consumer unit (4), which prestressing device has a prestressed, preferably hermetically sealed check valve (42) which closes in the direction of the consumer unit (4) and opens in the opposite direction. [3] Hydraulic system according to claim 2, characterized by that the check valve (42) inserted into the return line (38) is arranged outside the storage container (18), preferably inserted in a receiving bore (T) of the supply unit (2), which has the storage container (18) as a component. [4] Hydraulic system according to one of the preceding claims, characterized by that a pressure storage unit (6) is arranged between the supply unit (2) and the consumer unit (4). [5] Hydraulic system according to one of the preceding claims, characterized by that the pressure built up during operation in a supply line (24) for the consumer unit (4) by means of the supply unit (2) is so high that evaporation of the liquid is prevented. [6] Hydraulic system according to one of the preceding claims, characterized by that the supply unit (2) has the following components: - a pressure supply pump (20), - a line filter (22), - optionally a preloaded check valve (42), - optionally an air inlet valve (52), - a safety valve and / or a pressure relief valve (56) to protect the pressure supply pump (20). [7] Hydraulic system according to one of the preceding claims, characterized by that the consumer unit (4) has at least one hydraulically actuated working cylinder (14). [8] Hydraulic system according to one of the preceding claims, characterized by that the pressure accumulator unit (6) has at least one hydraulic accumulator (28). [9] Hydraulic system according to one of the preceding claims, characterized by that the supply unit (2) and / or the pressure storage unit (6) are accommodated in a crew compartment (12) of the military-used vehicle and the consumer unit (4) in its engine compartment (10).

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