Electrostatic hydraulic actuation system

Abstract

The invention describes an electrostatic hydraulic actuation system and a method for driving a hydraulic actuator, such as a hydraulic cylinder, wherein the system comprises a leakage branch and an additional pump is preferably arranged in the leakage branch. The system also comprises: a source for providing hydraulic liquid; a high-pressure circuit, which guides the hydraulic liquid to a hydraulic actuator, such as a hydraulic cylinder, for example; a low-pressure circuit, which has several branches; a main pump for the hydraulic liquid, which is arranged in the high-pressure circuit and comprises a housing having a high-pressure section and a low-pressure section separated by a gap seal, wherein the high-pressure section comprises a first outlet and a second outlet for providing a flow of hydraulic liquid in the high-pressure circuit; and wherein the low-pressure section comprises a leakage outlet; an electric motor, which drives the main pump.

Description

[0001] The present invention relates to the field of hydraulics. More particularly, the present invention relates to an electrostatic motor pump unit with an extended operating range.

[0002] Electrostatic hydraulic actuator systems are frequently encountered in the art and represent the main type of drive devices used, for example, in molding machines and presses, where large forces per unit area have to be delivered.

[0003] The variable speed electro-hydrostatic motor pump unit results from a direct coupling of a variable speed electric motor to a hydrostatic pump, wherein the drive shafts of the two machines can also be connected via an elastically compensated coupling. The electric motor provides the mechanical drive power in the form of speed and torque. This mechanical power is converted by the hydrostatic pump into a hydraulic output power in the form of a volume flow and an operating pressure or pressure difference on the hydraulic operating ports of the pump.

[0004] The hydrostatic pump of the variable speed electric hydrostatic motor pump unit can also be operated in motor mode. Thus, the hydrostatic pump converts hydraulic power into mechanical power, which drives the shaft of the electric motor.

[0005] The conversion of electrical power into hydraulic power or energy and vice versa takes place between the electric motor and the hydrostatic pump.For the energy transmission in the hydraulic parts of the drive train, a liquid is used, usually hydraulic oil.

[0006] Variable speed electrostatic motor pump units, and in particular when used to operate self-contained axles or similar actuators, are usually integrated in a closed hydraulic circuit. The entire volume of hydraulic oil is enclosed in such a circuit, and the low-pressure section of the circuit is pre-pressurized at a pressure greater than atmospheric pressure. In self-contained axle systems, the entire system is hydraulically disconnected from atmospheric pressure, and the oil volume of the system is usually smaller than in conventional hydraulic actuation systems.

[0007] These constructional, structural and mechanical features influence the functionality of such systems, making the dynamics of such systems extremely dependent on these features. In fact, if large forces need to be applied per unit area, and / or if large volumes are required, the tendency is to observe the onset of instabilities in the system and an attendant drop in pressure, for example after sufficiently large speed values ​​as a critical point for the pressure at the rotary shaft seal. The pressure at the rotary shaft seal reflects the lower pressure in the low-pressure section of the main pump in the actuation system.

[0008] Large hydraulic accumulators are used in the art to provide at least partial compensating assistance in such events. However, large accumulators are at least detrimental to the structural stability of such systems.

[0009] The existing challenges encountered in the prior art are at least partially solved by an electrostatic hydraulic actuation system as described in the present invention.The scope of the present invention is defined by the appended claims.

[0010] Specifically, according to one embodiment of the present invention, an electrostatic hydraulic actuation system for driving a hydraulic actuator, such as a hydraulic cylinder, includes a leakage branch. The electrostatic hydraulic actuation system generally includes a motor or an electric generator that powers a hydraulic machine. The hydraulic machine provides displacement of a hydraulic fluid through a hydraulic circuit; the displacement of the hydraulic fluid in the circuit (wherein "circuit" may be used hereinafter and throughout the application as a synonym for hydraulic circuit) causes the movement of the actuator.

[0011] A hydraulic actuator within the meaning of the present invention is a device capable of displacement due to a displacement of a hydraulic fluid volume by a hydraulic machine connected thereto; typical examples of hydraulic actuators are hydraulic cylinders of many kinds, such as synchronous or differential cylinders, hydraulic rotary drives, self-contained axles, etc. The displaced hydraulic fluid volume results in a mechanical displacement of a movable component or part of the actuator.

[0012] The system further comprises: a source for providing hydraulic fluid; a high pressure circuit that guides the hydraulic fluid to a hydraulic actuator such as, for example, a hydraulic cylinder; a low pressure circuit having several branches; a main pump for the hydraulic fluid, the main pump being arranged in the high pressure circuit, comprising a housing having a high pressure section and a low pressure section separated by a gap seal, wherein the high pressure section comprises a first outlet and a second outlet for providing a flow of hydraulic fluid in the high pressure circuit; and wherein the low pressure section comprises a leakage outlet; an electric motor that drives the main pump. According to this embodiment, the electrostatic hydraulic actuation system further comprises a leakage branch that connects the hydraulic leakage outlet of the low pressure section of the housing of the main pump to the low pressure circuit, in which leakage branch an additional pump is preferably arranged.

[0013] Hydraulic leakage, as leakage in the meaning of the present invention means, is generally the loss of a hydraulic liquid, generally hydraulic oil, at a given pressure from a volume containing said liquid, such as, for example, a housing of a pump, and provided with a sealing system, such as a combination of sealing devices, gap seals, shaft seals and other similar sealing components; depending on the operation of the hydraulic system (speed, temperature, hydraulic liquid volume, etc.), leakage is generally allowed to occur in the volume in order to simplify the operation of the machine itself and, for example, to keep the system at a specific given or required pressure during one cycle or multiple cycles.

[0014] Small holes, orifices or grooves or any similar tracks may be provided in the pump's housing structure to allow hydraulic fluid to flow from a higher pressure section to a lower pressure section of the housing for lubrication, cleaning and cooling along a specific path.

[0015] Therefore, in every working hydraulic and electrohydraulic actuation system there is usually a moderate amount of leakage, such as the above-mentioned leakage, which is also considered as planned leakage. In contrast, leakage caused by wear or poor design of otherwise leak-proof parts is generally considered to be harmful to the normal operation of the hydraulic system, because the undesirable or large loss of fluid is associated with undesirable and therefore large pressure changes in the system, resulting in serious interruptions in functionality and overall poor performance.

[0016] Gap seals are generally designed as devices for sealing between static and dynamic components and are particularly associated with hydraulic systems such as, for example, hydraulic pumps. The shape and width of the gap are carefully designed to maximize the efficiency of the hydraulic system, particularly by maintaining an optimally low amount of fluid loss at the interface.

[0017] The leakage branch according to the invention originates from the hydraulic connection of the hydraulic circuit to the leakage outlet, which leakage branch is usually located at the interface between the main pump and the hydraulic circuit as a connection of the housing to the low-pressure section. According to the invention, the leakage branch is provided with an additional pump so that the additional pump operates as a supplement to the main pump.

[0018] The electrostatic hydraulic actuation system is essentially a hydraulic circuit provided with several parts, including branches as smaller components of one or more parts themselves. The hydraulic pump essentially causes the hydraulic fluid or liquid to flow or move, thereby converting mechanical energy into hydraulic energy. In the following, the hydraulic fluid will be mainly focused on, while gas or plasma will be left aside.

[0019] The main pump according to the invention determines the required hydraulic liquid flow in order to generate pressure in different parts or branch combinations of the circuit and in particular determines the distinction between two main parts of the actuation system, which are essentially a low-pressure circuit and a high-pressure circuit in a relative sense with respect to the operating pressure of the pump in the hydraulic system. The main pump provides said distinction by an internal partition with a low-pressure section and a high-pressure section, wherein said sections at different pressures are separated by a sealing system such as a combination of sealing means, gap seals, shaft seals and other similar sealing components.

[0020] The values ​​associated with the low and high pressure qualifiers depend on the quality and / or structural characteristics and / or operating dynamics of such sealing systems, gaps, shaft seals or rings. Depending on the structural characteristics of the sealing components, the pressure acting on these sealing components should not exceed predefined values.

[0021] In the meaning of the present invention, the source for providing hydraulic liquid is a pre-pressurized or pre-stressed container, or a hydraulic accumulator or even just an accumulator, in which a hydraulic liquid of a given density and viscosity (usually hydraulic oil or a viscous liquid) is stored at a certain given pressure. Large accumulators are usually the solution for closed hydraulic circuits maintained at a given low pressure to increase the operating range of the motor, since the hydraulic liquid is recirculated in each cycle. However, large accumulators are not an ideal or efficient solution for compact systems.

[0022] The size (i.e. volume) of the hydraulic accumulator depends largely on the dynamic / thermal use (adiabatic-isothermal) and the permissible pressure difference between the minimum and maximum filling of the hydraulic accumulator and the specific actuator working dynamics; specifically, for example when using a differential cylinder as an actuator, the size of the accumulator will be influenced by the size of the oscillating volume flow between the piston and rod side.

[0023] Therefore, a higher permissible pressure difference between the minimum working pressure and the maximum working pressure of the hydraulic accumulator allows the required storage volume of the accumulator to be reduced. However, the maximum working pressure and therefore the maximum pressure difference of the hydraulic accumulator is influenced by the maximum permissible pump case pressure, which in turn is due to the load limitations of the shaft seal or sealing system used. Therefore, as mentioned above, due to this limitation, the volume of the hydraulic accumulator, especially in a closed system such as a self-contained shaft according to the prior art, must be made correspondingly larger.

[0024] In the meaning of the invention, the main pump comprises a housing comprising a high-pressure section and a low-pressure section separated by a gap seal; the outlet for providing a flow of hydraulic liquid in the high-pressure circuit is arranged in the high-pressure section, while the leakage outlet as mentioned above is arranged in the low-pressure section. Using an additional pump arranged on a leakage branch connecting the leakage outlet to the low-pressure circuit, the pressure acting on the shaft sealing ring or alternative sealing component in the main pump housing is intentionally reduced relative to the prestressed low pressure of the main pump. The qualifiers low pressure and high pressure for parts of the hydraulic circuit according to the invention or sections of the main pump are intended to be relative, so that if the operating pressure of a section or circuit or the pressure a section or circuit has is lower than another section or another part of the circuit or another circuit, the section or circuit will be named as a low-pressure section or low-pressure circuit, and vice versa.

[0025] According to another embodiment of the present invention, the electrostatic hydraulic actuation system as described above further includes a first valve and a second valve that isolate the high-pressure circuit from the low-pressure circuit.

[0026] In the meaning of the invention, a valve or hydraulic valve constitutes a device for directing the flow of hydraulic liquid along a branch of a circuit in which the valve is arranged. The positioning of the valve specifies the separation between the low-pressure circuit and the high-pressure circuit and thus regulates the flow of hydraulic liquid in a manner adapted to the required working pressure in the system.

[0027] According to another embodiment of the invention, the first valve and the second valve in the electrostatic hydraulic actuation system are check valves or control valves.

[0028] In the meaning of the present invention, a check valve directs the flow of hydraulic liquid from one end to the other end, or vice versa, in order to prevent the hydraulic liquid flow from flowing back; in the meaning of the present invention, the first valve and the second valve may alternatively be control valves, so that when arranged in a system as described above, these valves control the flow of hydraulic liquid by, for example, changing the aperture of the flow channel and parameters related to the hydraulic liquid flow such as, for example, the flow rate and subsequently the pressure and temperature.

[0029] According to another embodiment of the invention, the electrostatic hydraulic actuation system further comprises a flushing branch which connects a flushing inlet of the low-pressure section of the housing of the main pump to the low-pressure circuit and has a hydraulic connection with the leakage branch.

[0030] In the sense of the invention, the flushing inlet is arranged in the low-pressure section of the housing of the main pump and is hydraulically connected to a leakage branch in which an additional pump is arranged, which brings the following advantages: the lower pressure at the sealing components in the low-pressure section of the housing of the main pump is reduced using the leakage flow through the low-pressure circuit and through the flushing branch connected to the flushing inlet.

[0031] As described above, reducing the lower pressure of the main pump enables the electrostatic hydraulic actuation system to operate at higher speeds than the size of the hydraulic accumulator would normally allow. This allows the system to be kept compact by reducing the size of the accumulator.

[0032] Furthermore, a higher adjustable low pressure determines a better clamping of the actuator by increasing the hydraulic elastic modulus of the actuator, which in turn improves the controllability of the actuator due to a higher natural frequency.

[0033] According to a further embodiment of the invention, an additional valve is arranged in the flushing branch of the electrostatic hydraulic actuation system.

[0034] By introducing a valve in the flushing branch, in addition to one of the valves that may be present according to other embodiments, several parameters of the hydraulic flow can be controlled at will, depending on the type of valve installed.

[0035] According to another embodiment of the invention, the electrostatic hydraulic actuation system further comprises a flushing branch, which connects the flushing inlet of the low-pressure section of the housing of the main pump to the high-pressure circuit, in which an additional valve is arranged, and the flushing branch has a hydraulic connection with the leakage branch. In this embodiment, the hydraulic connection between the high-pressure circuit and the leakage branch comprises an additional pressure control valve, preferably a pressure-controlled non-return check valve.

[0036] In the meaning of the present invention, another embodiment is provided, in which the flushing branch is arranged in the high pressure circuit, still connected to the low pressure section of the housing of the main pump. This embodiment enables greater flexibility in system design to better adapt to the structural constraints of the system architecture. By the same above-mentioned principles, the flushing branch provides the following benefits: reducing the lower pressure at the sealing components in the low pressure section of the housing of the main pump to achieve a higher operating speed of the actuation system.

[0037] According to a further embodiment of the invention, the additional valve arranged in the flushing branch of the electrostatic hydraulic actuation system is a one-way check valve.

[0038] By adding a one-way check valve, according to this further embodiment of the invention, hydraulic flow can be directed in a preferred direction to allow the system to operate under controlled conditions.

[0039] According to another embodiment of the invention, the additional valve arranged in the flushing branch of the electrostatic hydraulic actuation system is a prestressed (or non-return) valve.

[0040] In the meaning of the invention, the valve arranged in the flushing branch according to this embodiment is prestressed to open at a certain pressure load given by the upper pump pressure limit and possibly given for a given pressure range. This allows to control the operating conditions of the circuit and increase the operating efficiency in particular by isolating the pressure in the main pump housing of the actuation system from the low pressure in the system.

[0041] According to a further embodiment of the invention, the additional pump of the electrostatic actuation system has a delivery volume which is greater than the leakage volume of the main pump occurring in the low-pressure section of the housing of the main pump.

[0042] In the meaning of the invention, a delivery volume of the additional pump greater than the leakage volume increases the efficiency of the actuation system and allows a pressure reduction in the pump housing compared to the low pressure. The volume flow delivered via the additional pump and exceeding the external leakage of the system is controlled by the upper prestressing valve.

[0043] According to another embodiment of the invention, a further valve is arranged in hydraulic connection with the leakage branch before the additional pump and has a hydraulic connection with the low-pressure circuit of the electrostatic actuation system.

[0044] This further valve allows further control of pressure peaks and can provide a limitation of case pressure peaks or provide protection against failure of an additional pump arranged on a leakage branch by limiting the internal pressure of the main pump.

[0045] According to a further embodiment of the invention, the electrostatic actuation system further comprises a filter unit which is hydraulically connected to the leakage branch for filtering the hydraulic liquid volume delivered by the additional pump.

[0046] The filter unit filters the hydraulic fluid volume provided by the additional pump to remove oil contamination such as wear particles and to increase the reliability of system operation.

[0047] According to a further embodiment of the invention, the electrostatic hydraulic actuation system further comprises a cooling unit which is hydraulically connected to the leakage branch in order to cool or heat the volume of hydraulic liquid delivered by the additional pump.

[0048] In the meaning of the present invention, a cooling unit can be added to the actuation system in order to ensure the maintenance of the hydraulic liquid. In particular, a cooling unit according to one embodiment of the present invention provides heating or cooling capabilities specifically aimed at adjusting the temperature of the hydraulic liquid volume provided by the additional pump. The heat losses generated by the actuation system are removed near their origin and this ensures that the actuator remains thermally stable.

[0049] According to a further embodiment of the invention, the additional valve arranged in the flushing branch of the electrostatic hydraulic actuation system is a pressure reducing valve.

[0050] In the meaning of the invention, the pressure relief valve serves, if necessary, to regulate the case pressure of the main pump in the actuation system to a constant low value, independently of resulting external leakage and independently of the low pressure level.

[0051] According to another embodiment of the present invention, the electric motor in the electrostatic hydraulic actuation system has a variable speed, such as a servomotor, and the main pump has a constant volume, such as a static one, or the electric motor has a constant speed, such as a constant motor, and the main pump is a variable displacement pump, or the electric motor has a variable speed, such as a servomotor, and the main pump is a variable displacement pump.

[0052] In the meaning of the invention, an electric motor or electric engine drives a hydrostatic pump to determine the conversion of electric power into hydraulic power in order to drive different types of actuators, in particular hydraulic actuators, such as for example cylinders.

[0053] In particular, variable speed electric motors, variable speed drives or adjustable speed drives are advantageous when it is necessary to control hydraulic flow to increase energy conservation and operating efficiency of the actuation system. Variable displacement pumps typically convert mechanical energy into hydraulic energy, but there are many pumps whose working function can be reversed in order to convert hydraulic energy into mechanical energy. According to embodiments of the present invention, several types of variable displacement pumps exist and can be used; however, their common principle is that the displacement or amount of liquid pumped per revolution of the pump shaft can be controllably changed while the pump is running.

[0054] Another object of the invention is to provide a method for extending the operating range of an electrostatic hydraulic actuation system, in particular using any one of the embodiments of the actuation system described so far or a combination of these embodiments.

[0055] Within the meaning of the invention, the method for increasing the operating range of the electrostatic hydraulic actuation system according to the described embodiment provides that the additional pump controls the pressure in the low-pressure section of the housing of the main pump.

[0056] The additional pump arranged on the leakage branch of the actuation system according to the invention acts on sealing components in the housing of the main pump to reduce the lower operating pressure and thus allows the actuation system to be operated at a higher speed.

[0057] Within the meaning of the invention, the method for increasing the operating range of the electrostatic actuation system according to the described embodiment provides that the pressure difference between the pressure in the low-pressure circuit and the pressure in the low-pressure section of the housing of the main pump does not drop below a predefined value.

[0058] Within the meaning of the present invention, a method for increasing the operating range of an electrostatic hydraulic actuation system according to the described embodiment provides that a predefined value of the pressure difference between the pressure in the low-pressure circuit and the pressure in the low-pressure section of the housing of the main pump is in the range of 0.2 bar to 20 bar, and preferably in the range of 0.5 bar to 10 bar, and more preferably in the range of 1 bar to 5 bar.

[0059] The ability to maintain the pressure difference between the pressure in the low-pressure circuit and the pressure in the low-pressure section of the housing of the main pump within a given value range and to check that said pressure difference does not drop below a predefined value ensures that the system remains in efficient working conditions and can adapt to the requirements of its components and the application, thereby saving energy and maintaining performance.

[0060] Within the meaning of the present invention, a method for increasing the operating range of an electrostatic hydraulic actuation system according to the described embodiment is provided: the pressure generated in the low-pressure section of the housing of the main pump is limited by the difference between the flow of the additional pump and the leakage flow originating from the gap seal separating the high-pressure section of the housing of the main pump from the low-pressure section, and the hydraulic resistance in the flushing branch.

[0061] In this embodiment of the invention, the leakage flow generated by the additional pump in the leakage branch works together with the flushing branch of the previous embodiment. In this case, the final effect can be better adapted to different applications and structural requirements according to the given architecture of the existing system or the specific actuator driven.

[0062] The use of an electrostatic hydraulic actuation system according to the embodiments presented above for driving a self-sufficient or self-contained axle is also included within the scope of the invention.

[0063] The use of an electrostatic hydraulic actuation system for driving actuators, such as twin-rod or synchronous cylinders, pivot drives, hydraulic rotary drives and / or differential cylinders, is also included within the scope of the invention.

[0064] Additional aspects of the present invention are provided in the following detailed description of features of possible embodiments of the present invention in the form of exemplary embodiments and simulations. It is worth noting that any modifications or additions that can be directly derived by a person skilled in the art are included in these examples. In particular, it should be noted that such examples or preferred embodiments are not intended or formulated to limit the scope of protection of the present application.

[0065] The accompanying schematic drawings and diagrams incorporated herein form a part of the specification and illustrate several aspects of the present invention; together with the description, the drawings and diagrams help explain certain principles of the present invention.

[0066] Figure 1a : Sectional view of a pump with external leakage oil connection showing the pressure conditions inside the housing.

[0067] Figure 1b : Example of speed-dependent pressure limitation - case pressure derating characteristics of a rotating shaft seal.

[0068] Figure 2 : An electrostatic hydraulic actuation system for driving a hydraulic actuator, such as a hydraulic cylinder, comprising a leakage branch in which an additional pump is arranged.

[0069] Figure 3 :For driving Figure 2 An electrostatic hydraulic actuation system of a hydraulic actuator such as a hydraulic cylinder, the electrostatic hydraulic actuation system further comprising a flushing branch connecting a flushing inlet of a low-pressure section of a main pump to the low-pressure circuit and having a hydraulic connection with a leakage branch.

[0070] Figure 4 :For driving Figure 2An electrostatic hydraulic actuation system of a hydraulic actuator such as a hydraulic cylinder, the electrostatic hydraulic actuation system further comprising a flushing branch connecting a flushing inlet of a low-pressure section of a main pump to a high-pressure circuit and having a hydraulic connection with a leakage branch.

[0071] Figure 5 :For driving Figure 2 An electrostatic hydraulic actuation system for a hydraulic actuator such as a hydraulic cylinder, the electrostatic hydraulic actuation system also includes a flushing branch, which connects the flushing inlet of the low-pressure section of the main pump to the low-pressure circuit and has a hydraulic connection with the leakage branch, and the electrostatic hydraulic actuation system also includes an additional valve before the additional pump.

[0072] Figure 6 :For driving Figure 2 An electrostatic hydraulic actuation system for a hydraulic actuator such as a hydraulic cylinder, the electrostatic hydraulic actuation system also comprising a Figure 4 The flushing branch also includes a filtration unit.

[0073] Figure 7 :For driving Figure 2 An electrostatic hydraulic actuation system for a hydraulic actuator such as a hydraulic cylinder, the electrostatic hydraulic actuation system also comprising a Figure 5 The flushing branch also includes a cooling unit.

[0074] Figure 8 :For driving Figure 2 An electrostatic hydraulic actuation system for a hydraulic actuator such as a hydraulic cylinder, the electrostatic hydraulic actuation system also comprising a Figure 6 A flushing branch, wherein the valve on the flushing branch is a pressure reducing valve.

[0075] Fig. 9 : Schematic diagram showing the volume flows in a pump with external leakage oil connection (QLext - external leakage oil, QLint - internal leakage oil).

[0076] Fig.10 :Used according to Figure 7 A simulation loop is arranged and the system performance is tested as described in Example 1.

[0077] Fig.11 :according to Fig.10 Results of simulations of the circuit in for a lower pressure in the accumulator and in the housing of the main pump at a hydraulic liquid flow of 7 l / min from the additional pump and high actuator forces. The pressure reduction is approximately 2.8 bar.

[0078] Fig.12 :according to Fig.10Results of simulations of the circuit in for a lower pressure in the accumulator and in the housing of the main pump at a hydraulic liquid flow of 7 l / min from the additional pump and low actuator forces. The pressure reduction is approximately 2.7 bar.

[0079] Figure 1a A cross-sectional view of the internal structure of a pump with an external leakage oil connection is shown, which shows the pressure conditions within the housing. The pump includes a first outlet 300; a second outlet 350, which is connected to the Figures 2 to 8 The electrostatic hydraulic actuation system or hydraulic circuit shown is hydraulically connected to and defines a high pressure circuit such as in 100; a clearance seal / seal 320 on which an additional pump can act to regulate the low pressure in the low pressure section of the main pump housing; a shaft seal 310 which limits the permissible pump housing pressure; and an external leakage outlet 340 which is hydraulically connected to the leakage branch. In the low pressure section 330 of the pump housing, a pressure value is equal to the pressure of the hydraulic fluid leakage. The pump includes a drive shaft 360 for connection to an electric motor.

[0080] Figure 1b A derating graph of an electrostatic hydraulic actuation system is shown, wherein the pressure in the housing of the main pump is plotted for the speed at which the system is operated. Specifically, as discussed above, the housing pressure at speeds above 1800 r / min decreases with increasing speed. In fact, this means that the operation of the electrostatic hydraulic actuation system is limited by process dynamics at the maximum permissible pressure of the low-pressure section of the housing of the main pump in the system. However, the shaft seal of the pump has a pressure limitation, which allows a maximum pressure of 10 bar in the low-pressure section of the main pump, for example in the case of a rotating shaft seal, when the system is running at a higher speed, the maximum pressure is reduced to 4 bar at 4500 RPM, for example, wherein the higher speed refers to a speed starting from 1800 RPM. Therefore, in systems existing in the prior art, when the motor pump unit is operated at up to 4500 RPM, the pressure in the low-pressure section of the main pump is limited to a maximum of 4 bar, for example, and the rotating shaft seal is pressurized at said 4 bar.

[0081] In a self-contained axle system, a lower pressure in the low pressure section of the main pump (such as, for example, the 4 bar mentioned above) requires a larger low pressure hydraulic accumulator than a system where the pressure in the low pressure section of the main pump is higher (e.g., 10 bar). Due to the need for a larger low pressure hydraulic accumulator due to the lower pressure in the low pressure section of the main pump, such a system is less compact.

[0082] Furthermore, the actuator clamping of the self-contained shaft is less due to the lower pressure in the low pressure section of the main pump. Therefore, the elastic modulus of the shaft is smaller, resulting in a smaller natural frequency and, therefore, a much lower effective control of the shaft.

[0083] Figure 2 An electrostatic hydraulic actuation system or hydraulic circuit 100 according to one embodiment of the present invention is shown. In the figure, the actuation system 100 is shown connected to a hydraulic actuator, such as a hydraulic cylinder 101. The actuation system or hydraulic circuit 100 includes a source or accumulator 102, an electric motor 112 driving a main pump 107. The main pump 107, which includes an outlet 108 and an outlet 109 for providing a hydraulic flow of hydraulic liquid in a high-pressure circuit 103, is provided with a leakage outlet 110 hydraulically connected to a low-pressure circuit 104 through a leakage branch 113. An additional pump 114 is arranged on the leakage branch 113 to facilitate the leakage flow through the low-pressure circuit 104. A first valve 105 and a second valve 106 are arranged in the low-pressure circuit 104 to provide parameter control of the hydraulic flow in the actuation system or hydraulic circuit 100.

[0084] Figure 3 An electrostatic hydraulic actuation system or hydraulic circuit 100 is shown according to another embodiment of the present invention.

[0085] In the figure, an actuation system 100 is shown connected to a hydraulic actuator, such as a hydraulic cylinder 101. The actuation system or hydraulic circuit 100 comprises a source or accumulator 102, an electric motor 112 driving a main pump 107. The main pump 107, which comprises an outlet 108 and an outlet 109 for providing a hydraulic flow of hydraulic liquid in a high pressure circuit 103, is provided with a leakage outlet 110 hydraulically connected to a low pressure circuit 104 via a leakage branch 113. An additional pump 114 is arranged on the leakage branch 113 in order to facilitate the leakage flow through the low pressure circuit 104. A first valve 105 and a second valve 106 are arranged in the low pressure circuit 104 to provide parameter control of the hydraulic flow in the actuation system or hydraulic circuit 100. In Figure 3 In FIG. 1 , an additional branch or flushing circuit 200 is shown, which comprises a flushing branch 115 connecting a flushing inlet 111 arranged in the low pressure section of the main pump 107 to the low pressure circuit 104. A valve 116 is arranged on the flushing branch in order to exert a parameter control of the hydraulic flow in the entire circuit.

[0086] Figure 4An electrostatic hydraulic actuation system or hydraulic circuit 100 according to another embodiment of the present invention is shown. In this figure, the actuation system 100 is shown connected to a hydraulic actuator, such as a hydraulic cylinder 101. The actuation system or hydraulic circuit 100 includes a source or accumulator 102, an electric motor 112 driving a main pump 107. The main pump 107, which includes an outlet 108 and an outlet 109 for providing a hydraulic flow of hydraulic liquid in a high-pressure circuit 103, is provided with a leakage outlet 110 hydraulically connected to a low-pressure circuit 104 via a leakage branch 113. An additional pump 114 is arranged on the leakage branch 113 to facilitate the leakage flow through the low-pressure circuit 104. A first valve 105 and a second valve 106 are arranged in the low-pressure circuit 104 to provide parameter control of the hydraulic flow in the actuation system or hydraulic circuit 100. In Figure 4 , an additional branch or flushing circuit is shown, which includes a flushing branch 215, which connects the flushing inlet 111 arranged in the low-pressure section of the main pump 107 to the high-pressure circuit 103 through control branches 217 and 218. A valve 216 is arranged on the flushing branch in order to exert parameter control on the hydraulic flow in the entire circuit. The control branches 217 and 218 include a first valve 219 and a second valve 220 and are arranged to establish and maintain a safe hydraulic connection between the flushing branch 215 and the high-pressure circuit 103.

[0087] Figure 5 An electrostatic hydraulic actuation system or hydraulic circuit 100 according to yet another embodiment of the present invention is shown. The electrostatic hydraulic actuation system or hydraulic circuit includes Figure 3 In addition to the arrangement first shown in Figure 3 In addition to the implementation plan, Figure 5 The embodiment of also comprises an additional valve 117 which is arranged upstream of the additional pump 114 and has a hydraulic connection to the low-pressure circuit 104 .

[0088] Figure 6 An electrostatic hydraulic actuation system or hydraulic circuit 100 according to yet another embodiment of the present invention is shown. The electrostatic hydraulic actuation system or hydraulic circuit includes Figure 5 In addition to the arrangement first shown in Figure 5 In addition to the implementation plan, Figure 6 The embodiment of the invention further comprises a filter unit 118 which is hydraulically connected to the leakage branch 113 in order to filter the hydraulic liquid volume delivered by the additional pump 114 .

[0089] Figure 7 An electrostatic hydraulic actuation system or hydraulic circuit 100 according to yet another embodiment of the present invention is shown. The electrostatic hydraulic actuation system or hydraulic circuit includes Figure 6 In addition to the arrangement first shown in Figure 6 In addition to the implementation plan, Figure 7 The embodiment also comprises a cooling unit 119 which has a hydraulic connection with the leakage branch to cool or heat the volume of hydraulic liquid delivered by the additional pump 114; this ensures thermal stability of the system by providing temperature regulation of the hydraulic liquid flow.

[0090] Figure 8 An electrostatic hydraulic actuation system or hydraulic circuit 100 according to yet another embodiment of the present invention is shown. The electrostatic hydraulic actuation system or hydraulic circuit includes Figure 7 The arrangement first shown in FIG. Figure 7 An alternative embodiment of the implementation scheme, Figure 8 The embodiment of 1 shows a pressure reducing valve 120 arranged in the flushing branch 115. The pressure reducing valve 120 is used to regulate the case pressure of the main pump in the actuation system to a constant low value, independently of the resulting external leakage and independently of the low pressure level / value.

[0091] Fig. 9 A schematic diagram is used to illustrate the hydraulic liquid volume flow in a pump with an external leakage oil connection. In the schematic diagram, V theo Indicates the theoretical displacement in a variable displacement pump; pressure value p 108 and P 109 is associated with the high pressure outlet of the main pump, thereby defining a high pressure circuit and being connected thereto, the third pressure value p Le Indicates the pressure at the leakage outlet of the main pump. The hydraulic leakage flow from the leakage outlet is indicated as Q L , and divide it into Q Lext or external leakage of hydraulic fluid and Q Lint Or internal leakage of hydraulic fluid. The solid arrow indicates the flow direction of the hydraulic fluid.

[0092] Fig.10 Shown is a test for Figure 7 A simulation circuit for the robustness of the preferred embodiment of the invention is described. Example 1 reports the simulation conditions and the results obtained in two different setups.

[0093] Fig.11 consists of a graphical representation showing the Fig.10 The simulation circuit in Figure 7 The described embodiment, results of simulations for lower pressures in the accumulator and in the housing of the main pump at a hydraulic liquid flow of 7 l / min from the additional pump and high actuator forces. The pressure reduction is approximately 2.8 bar.

[0094] Fig.12 consists of a graphical representation showing the Fig.10 The simulation circuit in Figure 7The described embodiment, results of simulations for lower pressures in the accumulator and in the housing of the main pump at a hydraulic liquid flow of 7 l / min from the additional pump and low actuator forces. The pressure reduction is approximately 2.7 bar.

[0095] Example 1 - Simulation

[0096] According to Figure 7 The calculation of the system performance of the described embodiment shows the robustness of the solution to load variations and different leakages obtained. Fig.10 , Fig.11 , Fig.12 Shown in.

[0097] The simulations were performed using the software Simulation X and the following boundary conditions:

[0098] - Pump size is 19cm 3 The variable speed of the electro-hydraulic actuation system rotates at a sinusoidal 2Hz + / - 4500rpm;

[0099] - External leakage modelled according to Moog measurements (approximately 2.5 l / min at 350 bar);

[0100] - Variable speed of the electro-hydraulic actuation system through all 4 quadrants;

[0101] -Synchronous cylinder dimensions: piston diameter 110mm, rod diameter 50mm;

[0102] - Cylinder stroke: 50mm;

[0103] - Preload in the system: approximately 8 bar;

[0104] - Hydraulic storage volume: 0.5l;

[0105] - Cooling / filtration pump constant at 7 l / min;

[0106] - Opening pressure check valve: 1 bar.

[0107] Simulation No. 1: Sine wave 1 Hz + / - 90 kN load on cylinder => pressure on HP (high pressure) side adjusted to approximately 130 bar

[0108] Simulation No. 2: Sine wave 1 Hz + / - 0.09 kN load on cylinder => pressure on HP side adjusted to approximately 10 bar

[0109] Both simulations provided nearly identical results with respect to the resulting low pressure and reduced case pressure.

[0110] Components List

[0111] 100 actuation system or hydraulic circuit 119 cooling unit

[0112] 101 Hydraulic actuator, such as a hydraulic cylinder 120 Pressure reducing valve

[0113] 102 source or accumulator 200 flushing circuit

[0114] 103 high pressure circuit 215 flushing branch

[0115] 104 low pressure circuit 216 valve

[0116] 105 first valve 217 control branch

[0117] 106 Second valve 218 controls branch

[0118] 107 main pump 219 first valve

[0119] 108 first outlet 220 second valve

[0120] 109 Second Exit 300 First Exit

[0121] 110 Leakage outlet 310 Shaft seal

[0122] 111 Flush inlet 320 Gap seal / seal

[0123] 112 Electric motor 330 Low pressure section of pump housing

[0124] 113 leakage branch 340 leakage outlet

[0125] 114 Additional pump 350 Second outlet

[0126] 115 flush branch 360 to the drive shaft of the electric motor

[0127] 116 Valve 510 Low pressure value in low pressure circuit

[0128] 117 Additional valve 520 Lower low pressure value in pump housing

[0129] 118 Filter Units

[0130] 530 Low pressure value in low pressure circuit

[0131] 540 Lower low pressure value in pump housing

Claims

1. An electrostatic hydraulic actuation system (100) for driving a hydraulic actuator, the electrostatic hydraulic actuation system comprising: a source (102) for providing hydraulic fluid; a high pressure circuit (103) for directing the hydraulic fluid to a hydraulic actuator; A low-pressure circuit (104), wherein the low-pressure circuit has a plurality of branches; a main pump (107) for hydraulic liquid, the main pump being arranged in the high-pressure circuit (103) and comprising a housing having a high-pressure section and a low-pressure section separated by a sealing gap, wherein the high-pressure section comprises a first outlet (108) and a second outlet (109) for providing a flow of hydraulic liquid in the high-pressure circuit (103); and wherein the low-pressure section comprises a leakage outlet (110); an electric motor (112) driving the main pump (107), and Characterized in that the electrostatic hydraulic actuation system further comprises: a leakage branch (113) connecting the leakage outlet (110) of the low-pressure section of the housing of the main pump (107) to the low-pressure circuit (104), an additional pump (114) being arranged in the leakage branch, a flushing branch (115) which connects a flushing inlet (111) of the low-pressure section of the housing of the main pump (107) to the low-pressure circuit (104) and has a hydraulic connection with the leakage branch (113), wherein a non-return valve (116, 216) is arranged in the flushing branch, and The electrostatic hydraulic actuation system further comprises a flushing branch (215), which connects the flushing inlet (111) of the low-pressure section of the housing of the main pump (107) to the high-pressure circuit (103), an additional valve (216) being arranged in the flushing branch, the flushing branch having a hydraulic connection (217, 218) with the leakage branch (113), and wherein the hydraulic connection between the high-pressure circuit (103) and the leakage branch comprises an additional pressure control valve (219, 220).

2. The electrostatic hydraulic actuation system according to claim 1, characterized in that: The electrostatic hydraulic actuation system further includes a first valve (105) and a second valve (106), the first valve and the second valve isolating the high-pressure circuit (103) from the low-pressure circuit (104).

3. The electrostatic hydraulic actuation system according to claim 2, characterized in that: The first valve (105) and the second valve (106) are check valves or control valves.

4. The electrostatic hydraulic actuation system according to any one of claims 1 to 3, characterized in that: The additional pump (114) has a delivery volume that is greater than a leakage volume of the main pump (107) occurring in the low-pressure section of the housing of the main pump.

5. The electrostatic hydraulic actuation system according to any one of claims 1 to 3, characterized in that: A further valve (117) is arranged in hydraulic connection with the leakage branch (113) upstream of the additional pump (114) and has a hydraulic connection with the low-pressure circuit (104).

6. The electrostatic hydraulic actuation system according to any one of claims 1 to 3, characterized in that: The electrostatic hydraulic actuation system further comprises a filter unit (118) which is hydraulically connected to the leakage branch (113) for filtering the volume of hydraulic fluid delivered by the additional pump (114).

7. The electrostatic hydraulic actuation system according to any one of claims 1 to 3, characterized in that: The electrostatic hydraulic actuation system further comprises a cooling unit (119) which is hydraulically connected to the leakage branch (113) for cooling or heating the volume of hydraulic fluid delivered by the additional pump (114).

8. The electrostatic hydraulic actuation system according to any one of claims 1 to 3, characterized in that: The electric motor (112) has a variable speed and the main pump (107) has a constant volume, or the electric motor has a constant speed and the main pump (107) is a variable displacement pump, or the electric motor (112) has a variable speed and the main pump is a variable displacement pump.

9. A method for increasing the operating range of an electrostatic hydraulic actuation system according to one of claims 1 to 8, characterized in that The additional pump (114) controls the pressure in the low pressure section of the housing of the main pump (107).

10. A method for increasing the operating range of an electrostatic hydraulic actuation system according to claim 1, characterized in that: The pressure difference between the pressure in the low-pressure circuit (104) and the pressure in the low-pressure section of the housing of the main pump (107) does not drop below a predefined value.

11. A method for increasing the operating range of an electrostatic hydraulic actuation system according to claim 8, characterized in that: The predefined value of the pressure difference between the pressure in the low-pressure circuit and the pressure in the low-pressure section of the housing of the main pump (107) is in the range of 0.2 bar to 20 bar.

12. A method for increasing the operating range of an electrostatic hydraulic actuation system according to any one of claims 8 to 9, characterized in that: The pressure generated in the low-pressure section of the housing of the main pump (107) is defined by the difference between the flow of the additional pump and the leakage flow originating from the sealing gap separating the high-pressure section from the low-pressure section of the housing of the main pump (107) and the hydraulic resistance in the flushing branch (115, 215).

13. Use of an electrostatic hydraulic actuation system according to claims 1 to 8 for driving a self-sufficient or autonomous axle.

14. Use for driving an actuator in an electrostatic hydraulic actuation system according to claims 1 to 8, the actuator being a twin-rod or synchronous cylinder, a pivot drive, a hydraulic rotary drive and / or a differential cylinder.

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