Hydrostatic drive system and method for producing hydrostatic drive system

Abstract

The present disclosure relates to a hydrostatic drive system having at least one hydraulic cylinder with a cylinder surface wherein the cylinder surface of the at least one hydraulic cylinder, which is hydraulically connected to a metering pump, is dimensioned; and / or a method for producing a hydrostatic drive system having at least one hydraulic cylinder with a cylinder surface. The hydrostatic drive system comprises: a metering pump (3) for delivering a volumetric flow rate, the metering pump (3) being designed to provide at least two and at most three delivery states for delivering the volumetric flow rate; a switching device (5) having a switching valve (4) and a switching element (6), a switching pressure being provided by means of the switching valve (4) in order to switch the switching element (6), and wherein the switching element (6) is designed to switch the metering pump (3) to one of the delivery states on the basis of the switching pressure and to provide a volumetric flow to the hydraulic cylinder (2).

Description

[0001] The present disclosure relates to a hydrostatic drive system having at least one hydraulic cylinder with a cylinder surface, wherein the cylinder surface of the at least one hydraulic cylinder, which is in hydraulic connection with a metering pump, is designed to be of the same size; and / or a method for manufacturing a hydrostatic drive system having at least one hydraulic cylinder with a cylinder surface. Additionally or alternatively, an application system comprising a hydrostatic drive system according to the present disclosure is provided.

[0002] Hydraulic drive systems are known in the prior art. Generally, a combination of a 2Q fixed displacement pump and a reversing valve, a combination of a 2Q variable displacement pump and a reversing valve, or a 4Q variable displacement pump can be provided as a corresponding drive system. The above drive system can be arranged in a hydraulically driven supercharger for compressing a fluid (including a gas or a liquid).

[0003] The drive system combining a 2Q metering pump and a reversing valve can be distinguished by high dynamics and low cost factors. However, in the case of providing the required volume flow, this drive system has disadvantages because it can only provide the maximum volume flow (±Q) in the direction to be actuated for the booster. max ). In addition, flow throttling losses may occur in the reversing valve and idling losses may occur in the drive system. In addition, energy recovery cannot be achieved. In addition, the drive system with a 2Q metering pump and a reversing valve has the following disadvantages: the constant volume flow is switched to the A side or the B side of the supercharger by the reversing valve (switching valve), which may cause collisions and / or vibrations in the corresponding system. As a result, such a system has a large noise emission and a limited service life.

[0004] The disadvantages of collision and / or vibration caused by the drive system of the combination of 2Q fixed pump and reversing valve can be reduced by the drive system of the combination of 2Q variable pump and reversing valve. With the help of such a drive system, the volume flow can be adapted by a proportional regulating device. When the motor speed is constant, the delivery volume of the 2Q variable pump can be arbitrarily selected (including from 0 to V max Thus, the volume flow can be adapted and a volume flow slope (0 to Q max ). Any arbitrary volume flow can be approached. The reversing valve used in this solution of the drive system can be used to switch the variable volume flow to the A side or the B side of the supercharger. The design of the drive system with a 2Q variable pump disadvantageously requires more expensive components, such as a variable pump and a corresponding reversing valve (switching valve). In addition, there are typical disadvantages of hydraulic drive systems, such as throttling losses in the control system and a large tank volume to be maintained for the required large amount of hydraulic fluid. In addition, energy recovery cannot be achieved.

[0005] The drive system with a 4Q variable pump differs from the design with a 2Q variable pump in the following ways on the pump side: pressure can be built up on the A and B sides of the 4Q variable pump and can approach a pressure between -Q max With +Q max Any arbitrary volume flow between . Thus, a hydrostatic transmission with a correspondingly smaller tank volume can be constructed without having to provide an additional directional control valve. Since the pumping control is performed with a corresponding proportional valve, such a design is complex (including the necessary pumping adaptation), cost-intensive and has losses due to the proportional valve.

[0006] Against the background of the prior art, the object of the present disclosure is to provide a hydrostatic drive system and / or a method for producing a hydrostatic drive system, both of which are suitable for enriching the prior art.

[0007] This object is achieved by the features of the independent claims. The contents of the parallel claims and the dependent claims are all optional improvements of the present disclosure.

[0008] Therefore, the purpose is achieved by a hydrostatic drive system, which has at least one hydraulic cylinder with a cylinder surface. It is proposed that the cylinder surface of the at least one hydraulic cylinder that is in hydraulic connection with the metering pump (of the hydrostatic drive system) is designed to be of the same size. The hydrostatic drive system includes a metering pump for conveying a volume flow. The metering pump is designed to provide at least two and at most three conveying states to convey the volume flow. In addition, the hydrostatic drive system includes a switching device with a switching valve and a switching element, wherein a switching pressure is provided by the switching valve to switch the switching element. The switching element is designed to switch the metering pump to a conveying state in the conveying state based on the switching pressure and provide a volume flow to the hydraulic cylinder. Therefore, in particular, the corresponding metering pump volume flow can be provided to the hydraulic cylinder. In particular, the volume flow is provided to the hydraulic cylinder by the connection end of the metering pump. The switching element can be designed to control the metering pump in such a way that the metering pump provides a conveying state. In particular, the switching element can switch the corresponding switching piston on the metering pump to provide the conveying state.

[0009] In the sense of the present disclosure, a hydrostatic drive system is a hydraulic drive system designed to use a fluid under pressure to generate motion and driving force. The fluid may include gases and liquids. The hydrostatic drive system is designed as a closed system, in which the fluid is held in a closed circuit. Alternatively, a semi-open system may be provided, in which the circuit may be supplied with fluid by a fluid source.

[0010] In the sense of the present disclosure, a metering pump is a hydraulic pump that can be used in a hydraulic drive system to provide a constant volume flow of a fluid without being affected by changes in system pressure or load. A metering pump can provide a predetermined amount of hydraulic fluid per revolution, and does not change its delivery volume per revolution. This is particularly advantageous in such hydraulic systems, in which a uniform supply of liquid is required to constantly and accurately control machine motion or other working processes. A metering pump can be designed as a piston pump or a vane pump. The metering pump is actuated by an electric machine, such as an asynchronous machine. A metering pump has an A side and a B side, through which a fluid hydraulic connection can be provided between a metering pump and an actuator (such as a hydraulic cylinder). In particular, the surface of each chamber of the hydraulic cylinder can be connected to the A side or the B side of the metering pump in a fluid hydraulic manner via a fluid pipeline. A metering pump can also provide at least two and at most three delivery states, including providing a maximum volume flow or an idle volume flow on the A side or the B side of the metering pump, wherein a hydraulic fluid is not provided at one of the two sides (connection ends) of the hydraulic cylinder.

[0011] In the sense of the present disclosure, the switching pressure is a specific pressure provided by the switching valve to activate and / or switch the switching element of the metering pump. In particular, the switching pressure is the pressure difference between the two switching pistons of the switching element, and this pressure difference is sufficient to switch the metering pump at the corresponding operating point from one delivery state to another delivery state.

[0012] It can be provided that the switching piston of the switching element is designed as a single-acting hydraulic cylinder. The switching pistons are arranged opposite each other in the metering pump. These switching pistons are designed to displace the stroke ring of the metering pump and thus provide a speed change from Q to Q at the applied speed of the electric machine. max+ To Q max- The volume flow rate Q is 0 (and vice versa). In the case of a pressure difference value of zero, the spring in the switching element moves the stroke ring closer to the center to produce the third delivery state. Therefore, the pressure difference between the two switching pistons of the switching element is decisive for the conversion of the pump delivery state. Other technical designs can also be provided to control the regulating element of the metering pump to provide the maximum volume flow Q max+ , Q max- Here, the use of a stroke ring for a metering pump in the above-described embodiment should not be interpreted as restrictive.

[0013] The above-described hydrostatic drive system offers a series of advantages. In particular, good energy efficiency is achieved, since the metering pump is directly connected to the hydraulic cylinder without any flow friction elements (e.g. via a reversing valve) that may be located in between. In addition, a fast and energy-saving change of direction can be achieved by switching the displacement volume of the metering pump from positive to negative (or vice versa). Therefore, it is not necessary to change the rotational reversal of the electric machine in order to change the direction of movement of the actuator or hydraulic cylinder. The rotating parts of the electric machine (regardless of the type of construction) generally have an inertia that is several times greater than that of the rotating parts of the hydraulic pump.

[0014] Furthermore, the hydrostatic drive system according to the present disclosure is more energy-efficient, since the drive system itself does not have to consume energy to brake and reaccelerate the drive shaft. Furthermore, the hydrostatic drive system according to the present disclosure is faster, since the inertia of the moving parts is lower, whereby a higher switching frequency can be achieved with the same existing power. This is particularly true with respect to variable speed fixed displacement pump drives. Compared to conventional valve switching, the switching achieved by the change in displacement volume is more continuous, which can achieve a reduction in pressure shocks and can have a positive effect on the service life of the entire hydrostatic drive system. Compared to conventional variable displacement pumps, the hydrostatic drive system according to the present disclosure does not require permanent control pressure preparation, which can increase the overall energy efficiency of the drive system. Furthermore, compared to drive systems known from the prior art, noise emissions are reduced, which is beneficial to occupational safety.

[0015] Embodiments and developments of the disclosure are apparent from the dependent claims and from the description with reference to the figures.

[0016] It can be provided that the hydrostatic drive system is designed to transfer pressure from the hydrostatic drive system to a further system in mechanical connection by means of a hydraulic cylinder. Via the mechanical connection, the force and / or movement and / or work of the hydraulic cylinder can be transferred to the further system and have an effect on the further system. The further system can be designed as a test system.

[0017] Mechanical connection can be achieved by directly connecting the piston rod of the hydraulic cylinder to another mechanical component or device of the system to transfer mechanical work. The piston rod of the hydraulic cylinder can be connected to a lever arm, crankshaft or other device, for example, to generate torque or motion (vibration).

[0018] Furthermore, a rack can be fastened to the hydraulic cylinder, and a pinion or gear can also be used to convert the linear motion of the hydraulic cylinder into a rotary motion (or vice versa). Furthermore, a rope or wire rope can be connected to the piston of the hydraulic cylinder in order to transmit the force or motion to another system (mechanical system). Furthermore, various joints, couplings and connecting elements can be used in order to connect the piston rod of the hydraulic cylinder to other mechanical parts of another system.

[0019] As a result, very large forces can be generated and precisely controlled and transmitted. In addition, hydraulic systems have a high working efficiency, especially when transmitting forces over long distances or lifting heavy loads. Hydraulic systems are generally very robust and durable, which makes them excellent for applications in harsh environments. In addition, fast and precise manipulation is possible, which enables fast movement reversal with high precision and repeatability.

[0020] It can be provided that the hydraulic cylinder has a connection to a second hydraulic cylinder (process cylinder) in order to provide the second delivery medium with a pre-settable pressure by means of the second hydraulic cylinder. The connection between the hydraulic cylinder and the second hydraulic cylinder can comprise a mechanical connection or a fluid hydraulic connection. By means of the two hydraulic cylinders, it is possible to transfer the pressure of the hydraulic cylinder to another pressure on the other hydraulic cylinder. Advantageously, a higher pressure or volume flow can be provided by the second hydraulic cylinder, for example for downstream applications.

[0021] It can be provided that the hydraulic cylinders are designed to provide a synchronous situation and that cylinder surfaces designed to be of equal size are positively coupled mechanically or hydraulically.

[0022] Synchronous conditions in the sense of the present disclosure with regard to hydraulic cylinders mean that the piston surfaces on both sides of the hydraulic cylinder (or cylinders) have the same size and / or the same effective surface and that they are coupled to one another mechanically or hydraulically.

[0023] In the sense of the present disclosure, a synchronous situation with respect to a hydraulic cylinder also means that when a volume flow is supplied to the cylinder chamber of a hydraulic cylinder in the synchronous situation, the same volume flow is drawn from the other cylinder chamber of the hydraulic cylinder in the synchronous situation. A synchronous situation can be produced by a synchronous cylinder or a combination of a plurality of hydraulic cylinders which do not necessarily form a synchronous situation themselves (e.g. a differential cylinder) but which nevertheless form a synchronous situation as a whole.

[0024] The hydraulic cylinders can be designed such that the piston surface on one side and the piston surface on the other side are of the same size and have the same working surface. Furthermore, a mechanical or hydraulic forced coupling can be provided, wherein the piston surfaces are coupled to one another by a mechanical connection (e.g. by means of a common shaft or a rigid connection) or by a hydraulic connection (e.g. by using lines and valves) in order to ensure that they move in parallel and / or simultaneously. In particular, it can be provided that a hydraulic or mechanical forced coupling is provided between two hydraulic cylinders and thus their surfaces are coupled.

[0025] It can be mentioned that the two states of the metering pump include: the maximum positive volume flow Q max+ and the maximum negative volume flow Q max-The third delivery state includes a stationary state of the metering pump, in which the hydrostatic drive system imposes an idle volume flow Q0 for the hydraulic cylinder. In the sense of the present disclosure, the third delivery state and the idle volume flow Q0 are generated by the metering pump and include that no volume flow is provided in an imposed manner at the hydraulic cylinder.

[0026] The metering pump may have two connections, which are each connected to a fluid line A, B. Via a respective one of the two connections, a maximum positive volume flow Q can be provided. max+ or maximum negative volume flow Q max- The maximum volume flow to be achieved is provided by means of a metering pump. In the sense of the present disclosure, a metering pump has a direction of rotation. The output of the volume flow achieved via the A side or the B side (pipeline) of the metering pump is implemented by switching the delivery state. Correspondingly, the connected actuator, in particular the hydraulic cylinder, can be controlled.

[0027] In addition, the metering pump can switch states by means of a switching element, which state includes a third delivery state with an idling volume flow Q0. In the third delivery state, the maximum volume flow (positive or negative) for operating the hydraulic cylinder is not provided on both the A side and the B side of the metering pump. The third delivery state includes a slightly adjusted intermediate position of the metering pump, in which a defined volume flow (idling volume flow Q0) can be provided at the A line or the B line of the metering pump. The third delivery state in the adjusted intermediate position is advantageous so as to be able to switch from a delivery state with an idling volume flow Q0 to one of the states with a maximum volume flow.

[0028] It can be proposed that the switching element includes a return spring, and if no switching pressure is applied, the return spring brings the switching element to a third delivery state corresponding to the idle volume flow at the metering pump. The remaining volume flow of the metering pump can be derived by means of a switching device, such as a switching valve, so that the hydrostatic drive system generates an idle volume flow Q0 to the hydraulic cylinder. The switching element is designed to switch the metering pump to a state in which the maximum volume flow is provided by means of the connection end A or the connection end B of the metering pump. To this end, the switching element can be correspondingly made to respond / control the switching element by means of the switching pressure, and the metering pump is switched. When no switching pressure is applied to the switching element, the switching element remains in the zero position (the middle position of the adjustment), and the idle volume flow Q0 is provided by means of the A side or the B side of the metering pump.

[0029] It can be proposed that the switching device is connected to the hydraulic cylinder via a fluid pipeline, or that the hydraulic cylinder and the switching device are designed as a whole. The switching device can be designed as a unit comprising a metering pump with a switching element and a switching valve. In addition, the switching device can include another unit. The switching device can be in fluid hydraulic connection with the hydraulic cylinder via a fluid pipeline. In this design, the switching device and the hydraulic cylinder are designed as two components, which are arranged in different positions and separated from each other. Alternatively, it can be proposed that the hydraulic cylinder is formed as a unit and arranged on the switching device. A compact structural mode is thus achieved. In addition, additional fluid hydraulic components for establishing a connection can be saved.

[0030] It can be provided that a maximum positive volume flow Q can be provided by means of the switching pressure max+ With the maximum negative volume flow Q max- The transition between the maximum positive volume flow and the maximum negative volume flow can be performed continuously. In addition, the transition to the third delivery state can be performed continuously. Due to the continuous transition, the volume flow in the hydrostatic drive system can be changed smoothly and evenly between different states or values ​​without sudden changes or shocks. Here, the volume flow can gradually and continuously transition from one value (preferably the maximum value or zero value of the volume flow) to another value without experiencing sudden fluctuations or interruptions. As a result, gentle control and precise movements can be produced, especially in situations involving changes in the direction or speed of the movement. In addition, noise emissions in the hydrostatic drive system are reduced.

[0031] It can be provided that the switching valve is designed as a 4 / 2-way switching valve. The 4 / 2-way switching valve can be designed as a hydraulic or pneumatic switching valve, which is used to control the flow of liquids or gases in different directions. The 4 / 2-way switching valve has 4 connection ends and 2 switching positions. In addition, the 4 / 2-way switching valve can be switched hydraulically, pneumatically, mechanically or electromagnetically. By using a 4 / 2-way switching valve, two delivery states of a metering pump can be realized, which include a maximum positive delivery volume flow Q max+ and maximum negative delivery volume flow Q max- .

[0032] It can be provided that the switching valve is designed as a 4 / 3-way switching valve. A 4 / 3-way switching valve is a special type of hydraulic or pneumatic switching valve, which is used to control the flow of liquids or gases in different directions. A 4 / 3-way switching valve has 4 connection ends and 3 switching positions. Furthermore, a 4 / 3-way switching valve can be switched hydraulically, pneumatically, mechanically or electromagnetically. By using a 4 / 3-way switching valve, three delivery states of a metering pump can be realized.

[0033] It can be proposed that the switching valve can be switched by the pressure provided by the metering pump and / or the fluid source. The fluid source can be designed as an external fluid source or a compensation container. By using the hydrostatic pressure for activating the switching valve, it is possible to flexibly control the hydrostatic drive system. By changing the pressure in the hydraulic control line to the switching valve, the switching valve can be converted and the path to the switching element can be opened or closed thereby, so as to determine / switch the delivery state of the metering pump. This method of controlling pressure can be easily integrated into the hydrostatic drive system according to the present disclosure, because it is based on the existing pressure already present in the hydrostatic drive system. This requires fewer additional components or requires additional high-cost control, which increases the cost efficiency of the hydrostatic drive system. Therefore, using the existing pressure to switch the switching valve can be designed cost-effectively. In addition, the pressure from the metering pump or the fluid source can usually be provided stably and reliably. This can help the switching valve to work reliably and meet the required functions. In addition, the use of the existing pressure can improve the energy efficiency of the hydrostatic drive system, because no additional energy is required to actuate the switching valve.

[0034] Alternatively, it can be provided that the switching valve is designed so that it can be switched electromagnetically by a control signal. For this purpose, a computing unit can be used, which can be provided for controlling the switching valve.

[0035] It can be proposed that the switching pressure switched by the switching valve is provided by a compensation container. By using a compensation container, the switching pressure can be obtained from a separate pressure source independently of the metering pump. As a result, the flexibility of the configuration of the hydrostatic drive system can be increased, and at the same time the adaptability of the pressure can be achieved as required. In addition, since the use of multiple pressure sources (including metering pumps and compensation containers) can increase the reliability of the hydrostatic drive system, a redundancy concept is generated. In the event of failure of one pressure source, another pressure source can be used as a backup.

[0036] It can be proposed that the switching pressure provided by the switching valve is provided by the metering pump. The highest pressure of the lines A, B and T of the metering pump is provided as the switching pressure by the check valve and the switching valve, which transmits the switching pressure to the switching element of the metering pump. Therefore, the delivery volume flow can be switched. This method for switching the metering pump can be easily integrated into a hydrostatic drive system because it is based on the existing pressure already present in the drive system. Using the existing pressure to switch the metering pump can be cost-effective because no additional pressure source or expensive control is required, such as is the case in a proportionally controlled variable displacement pump.

[0037] Alternatively, the switching pressure provided by the switching valve can be provided by an external pump. By using an external pump (e.g. a gear pump), the switching pressure can be obtained independently of the metering pump. As a result, the flexibility of the configuration of the hydrostatic drive system can be increased, and at the same time the pressure can be changed as needed. In addition, since the use of multiple pressure sources (including metering pumps and external pumps) can improve the reliability of the hydrostatic drive system, redundancy is generated. In the event of failure of one pressure source, another pressure source can be used as a safeguard.

[0038] It can be proposed that the metering pump is designed as a 4Q metering pump and includes a piston pump and / or a vane pump. By using a 4-quadrant pump structure (4Q), the described hydraulic pump can work under restorative load conditions and can also utilize a suitable electrical system to recover / recover energy. In addition, in a reversing valve system, the return of the hydraulic fluid must be controlled to avoid an uncontrollable state. This is not necessary in a 4Q metering pump, which improves efficiency. In addition, the 4Q metering pump is more efficient, which can reduce the demand for hydraulic fluid and therefore reduce the impact on ecology.

[0039] It can be provided that the metering pump can be operated at a constant speed or at a variable speed of the electric machine, preferably an asynchronous machine.

[0040] Asynchronous machines can be started independently without the use of external auxiliary devices such as starters or external rotating field sources. This simplifies commissioning and operation. In addition, asynchronous machines are robust against load fluctuations and torque shocks. Asynchronous machines can adapt to changing loads without losing synchronism.

[0041] Furthermore, asynchronous machines are cost-effective to purchase and operate.

[0042] It can be provided that the hydrostatic drive system comprises at least one safety valve. By means of the safety valve, the actuator, preferably the hydraulic cylinder, can be disconnected from the connection end of the metering pump. Thus, the piston of the hydraulic cylinder can be locked to ensure process safety. Alternatively, the safety valve can be used to short-circuit the pipelines A, B of the metering pump to compensate for the pressure difference between the pipelines and thus protect the components of the hydrostatic drive system in the event of a fault. These two ways of using the safety valve and a combination of the two can be used in the hydrostatic drive system according to the present disclosure.

[0043] It can be proposed that the hydrostatic drive system comprises at least one pressure limiting valve. The pressure limiting valve can be used as a pressure protection device at the connection ends A, B of the metering pump. As a result, the pressure at the connection ends of the metering pump cannot exceed the pressure predetermined by the pressure limiting valve. Thus, the component is protected.

[0044] It can be provided that the hydrostatic drive system comprises at least one non-return valve. The non-return valve can be designed as a suction valve in order to provide a suction function of the metering pump and to avoid cavitation of the metering pump. The non-return valve can be connected to a connection piece leading to the compensation container on one side and to a connection end of the metering pump on the other side. By drawing fluid from the compensation container by means of the non-return valve, cavitation of the metering pump can be avoided.

[0045] As mentioned above, it can be proposed that the hydrostatic drive system comprises at least one compensation container. Fluid can be supplied to the hydrostatic drive system via the compensation container. The compensation container can be designed as an open or closed reservoir. An oil compression volume can be provided via the compensation container. The compensation container also serves as a liquid reservoir for the hydrostatic drive system and, together with the non-return valve, ensures that a minimum suction pressure at the metering pump is maintained at all operating points to prevent cavitation at the metering pump.

[0046] It can be mentioned that the hydrostatic drive system can be used in a self-contained configuration or in a semi-open configuration. In the sense of the present disclosure, a self-contained configuration refers to a closed hydrostatic drive system in which a preload is present. Therefore, no additional components (fluid source, reservoir) are required to build up the pressure, but the hydraulic components used should be designed for the pressure in the hydrostatic drive system, which may lead to increased expenditure and costs.

[0047] The semi-open configuration includes the use of a fluid source and / or a reservoir, by means of which the hydrostatic drive system can be supplied with fluid. No elaborate design of components is required, and very good cooling and filtering are possible.

[0048] The above can be summarized in other words and in conjunction with the possible more specific design solutions of the present disclosure described below, wherein the following description cannot be interpreted as limiting the present disclosure. It is proposed here to use a metering pump and switch it with a zero delivery volume. This allows the combination of the advantages of a drive system combining a 2Q metering pump with a reversing valve and a drive system with a 4Q variable pump, while minimizing the disadvantages of the solutions known in the prior art. The basis can be a 4Q metering pump, whose delivery volume V max+ 、V max- The selection can be made by means of a switching valve. Since pressure can be applied to both connection ends of the pump, on the one hand, the switching valve of the hydrostatic drive system can be omitted in the 2Q constant displacement pump, and on the other hand, the use of an expensive and high-cost variable displacement pump can be avoided. In addition, it is proposed that the constant displacement pump is implemented with a compact interface so that the control module can be directly integrated with the required hydraulic functions, such as the suction function and the pressure accumulator, in a very compact manner, and thus the fluid volume in the system can be kept as small as possible. Due to this principle, shocks and vibrations are significantly reduced, because there is a flow control valve in the pump that is connected to the delivery volume Vmax+ To V max- By using the transport volume position V max+ To V max- By switching the switching valve to its center position (idling), the volume flow to the actuator connection of the hydrostatic drive unit can be shut off.

[0049] The 4Q metering pump can be switched to zero delivery volume so that the Q max+ To Q max- and volume flow of Q0. The speed of the metering pump is constant or preferably variable by means of an asynchronous machine. The asynchronous machine can optionally obtain quasi-static speed adaptation by means of a frequency converter. A 4Q pump compact interface can be provided for direct flange connection of a control module or a synchronous cylinder. With the help of a specific design solution, a simple, advantageous and impact-free hydrostatic drive system can be provided.

[0050] In addition, an application system is provided, which includes a hydrostatic drive system according to the present disclosure for providing a pressurized medium. The application system may include a pressure intensifier and be used as a test system for the following applications: dynamic test applications for water jet cutting, metering applications using a metering pump, applications using a high density pump, applications using hot isostatic pressing (HIP) and cold isostatic pressing (CIP), applications for hydroforming (water and oil), applications with high pressure requirements, applications for gas intensifiers and / or autotighteners.

[0051] The rapid change of the direction of movement achieved by means of the hydrostatic drive system according to the present disclosure can reduce process pressure losses in the application of the intensifier. As a result, a better conveying quality can be achieved in applications such as water jet cutting. The continuous process pressure also has a positive impact on the life expectancy of the entire hydrostatic drive system.

[0052] Hydrostatic drive systems are particularly suitable for testing applications with high-frequency reciprocating piston movements (e.g. in pressure intensifiers). Speed-variable dual-displacement pumps that can be switched to zero delivery volume are particularly suitable for oscillating applications such as piston pumps and pressure intensifier applications. These applications require rapid reversal of the cylinder piston movement as well as quasi-static speed regulation.

[0053] The above description regarding the hydrostatic drive system also applies similarly to the application system, and vice versa.

[0054] In addition, a method for producing a hydrostatic drive system is provided, which has at least one hydraulic cylinder with a cylinder surface, wherein the cylinder surface of the at least one hydraulic cylinder, which is hydraulically connected to a metering pump, is designed to be of the same size. The method includes providing a metering pump for conveying a volume flow, wherein the metering pump is designed to provide at least two and at most three delivery states for conveying the volume flow. The method also includes providing a switching device with a switching valve and a switching element, wherein a switching pressure is provided by the switching valve to switch the switching element. In addition, the method includes designing the switching element so that the metering pump is switched to one of the delivery states based on the switching pressure and the volume flow is provided to the hydraulic cylinder.

[0055] The description above with reference to the hydrostatic drive system and the application system also applies analogously to the method, and vice versa.

[0056] The above-mentioned designs and improvements can be combined with each other arbitrarily when it makes sense. Other feasible designs, improvements and implementations of the present disclosure also include combinations of features previously or subsequently described with reference to the embodiments of the present disclosure that are not explicitly mentioned. Here, those skilled in the art can also add individual aspects as improvements or supplementary contents to the corresponding basic forms of the present disclosure.

[0057] Reference below Figures 1 to 4 Describe alternative implementations.

[0058] Figure 1 schematically illustrates a hydrostatic drive system according to the present disclosure;

[0059] Figure 2 Schematically illustrates another design of a hydrostatic drive system according to the present disclosure;

[0060] Figure 3 Schematically illustrates another design of a hydrostatic drive system according to the present disclosure; and

[0061] Figure 4 Another design of a hydrostatic drive system according to the present disclosure is schematically shown.

[0062] The accompanying drawings should provide a further understanding of the embodiments of the present disclosure. They show the embodiments and are used to explain the principles and concepts of the present disclosure in conjunction with the description. Other embodiments and many of the advantages mentioned can be obtained by referring to the accompanying drawings. The elements in the figures are not necessarily shown in proportion to each other.

[0063] In the figures, elements, features and components which are identical, have the same function and act in the same way are respectively provided with the same reference symbols unless otherwise specified.

[0064] Figure 1 A schematic diagram of a hydrostatic drive system 1 according to one embodiment is shown. The hydrostatic drive system 1 has a hydraulic cylinder 2 and a metering pump 3. The hydraulic cylinder 2 has a cylinder surface. The cylinder surface of the hydraulic cylinder 2, which is hydraulically connected to the metering pump 3, is designed to be of the same size. Therefore, a synchronous movement can be implemented. The hydraulic cylinder 2 is in fluid-conducting connection with the connection ends A, B of the metering pump 3. The corresponding pipelines at the connection ends A, B of the metering pump 3 can also be regarded as / referred to as pipelines A, B respectively.

[0065] The metering pump 3 is designed to convey a fluid of a certain volume flow rate. The fluid may include a hydraulic fluid or a gaseous fluid. The metering pump 3 may be driven by an electric machine 10 at a constant speed or a variable speed. The electric machine 10 may be designed as an asynchronous motor. The electric machine 10 may, for example, be connected to the metering pump 3 via an axis and drive the metering pump accordingly. Other designs of the electric machine 10 may be used according to the application. The metering pump 3 may be designed as a 4Q metering pump. The metering pump 3 may also include a piston pump or a vane pump.

[0066] The metering pump 3 is designed to provide at least two delivery states for delivering a volume flow. In addition, the metering pump 3 is designed to provide at most three delivery states for delivering a volume flow. The two delivery states of the metering pump 3 for delivering a volume flow include a maximum positive volume flow Q max+ and the maximum negative volume flow Q max- . Maximum positive volume flow Q max+ and the maximum negative volume flow Q max- The hydraulic cylinder 2 is supplied via the connections A, B and the lines A, B of the metering pump 3. In the third delivery state of the metering pump 3, an idle volume flow Q0 for the hydraulic cylinder 2 can be forced to be achieved by the hydrostatic drive system 1.

[0067] Furthermore, a switching device 5 is provided. The switching device 5 has a switching valve 4 and a switching element 6. Figure 1 In the embodiment of the invention, a metering pump 3 belonging to a switching device 5 is shown. The switching valve 4 has a fluid connection to the switching element 6. In particular, the switching valve 4 has a fluid connection to the switching piston of the switching element 6. In addition, the switching valve 4 has a fluid connection P to at least one non-return valve 12 and a line or connection T of the metering pump 3. In addition, the switching device 5 can have a non-return valve 8, a pressure limiting valve 9, a safety valve 11 and / or a further non-return valve 12. Figure 1 The schematic illustration of the switching device 5 in the figure should not be interpreted as limiting the design of the switching device 5. The switching pressure is provided by the switching valve 4 to switch the switching element 6. The switching valve 4 can be designed as a 4 / 2-way switching valve or a 4 / 3-way switching valve.

[0068] The switching valve 4 can be actuated hydraulically, mechanically, pneumatically or electromagnetically. The above-mentioned actuation should not be restrictive here. Rather, it is known to those skilled in the art that the switching valve can have other switching designs. For this purpose, the pressure provided by the hydrostatic drive system 1 and the metering pump 3 can be used, and the switching valve 4 can be switched by the pressure provided, especially the fluid pressure. Alternatively or supplementally, a fluid source can be provided, by which the fluid pressure is provided to switch the switching valve 4. According to Figure 1 , the switching valve 4 is configured as a switching valve with an electromagnetic control for switching the switching valve 4. The switching valve 4 can receive control signals from a control device (such as a computer, SPS, etc.) or a sensor, and switch to a corresponding switching position based on these control signals. Corresponding to the switching position of the switching valve 4, the switching element 6 responds hydraulically and switches the metering pump 3 to provide the corresponding maximum (positive or negative) volume flow or switches it to the third delivery state of the metering pump.

[0069] The switching element 6 is designed to switch the metering pump 3 to one of the delivery states based on the switching pressure and thus provide the corresponding volume flow of the metering pump 3 to the hydraulic cylinder 2 via the connection terminals A, B. The switching element 6 is formed integrally with the metering pump 3 and switches the metering pump 3 to one of the delivery states. The switching element 6 switches the metering pump 3 in such a way that a maximum positive volume flow Q is provided at one of the connection terminals A, B of the metering pump 3. max+ , or provide a maximum negative volume flow Q at one of the connection ends A and B of the metering pump 3 max- For example, a maximum positive volume flow Q can be provided at connection A of the metering pump 3 by means of a correspondingly provided switching pressure. max+ The corresponding return volume flow is received via connection B. When the switching pressure is switched, a maximum negative volume flow Q can be provided at connection B of the metering pump 3. max- , and the corresponding return volume flow is received via the connection A. The metering pump 3 is switched by correspondingly switching the switching pressure, thereby changing the flow direction of the volume flow when the volume flow is maximum.

[0070] The maximum positive volume flow Q is provided by means of the switching pressure provided by the switching valve 4 max+ With the maximum negative volume flow Q max- The transition between the maximum positive volume flow rate Q max+ With the maximum negative volume flow Q max- The transition between Q and max+ To Q max- continuous transition.

[0071] Furthermore, the switching element 6 has a return spring. The return spring forms a mechanical switch of the switching element 6, which can force the metering pump 3 to reach the third delivery state. This means that if no switching pressure is provided to the switching element 6 by means of the switching valve 4, the return spring in particular mechanically places the switching element 6 in the zero position (adjusted intermediate position) in order to force the third delivery state of the metering pump 3. In the third delivery state, the idle volume flow for the hydraulic cylinder 2 is forced to be achieved at the connection ends A, B of the metering pump 3.

[0072] It is proposed that the switching pressure switched by the switching valve 4 is provided by the compensation container 7 and / or by the metering pump 3 itself. The switching pressure to be switched is provided by the non-return valve 12. In addition and / or alternatively, an external pump (not shown) can be provided. The external pump can be connected to the switching valve 4 in a fluid-conducting manner via the P line and provide the switching pressure to be switched.

[0073] The hydrostatic drive system 1 has at least one safety valve 11. In the illustrated embodiment, the safety valve 11 is introduced into the fluid line A leading from the connection end A of the metering pump 3 to the hydraulic cylinder 2. By means of the safety valve 11, at least one of the hydraulic cylinders 2 can be separated from the hydrostatic drive system 1 to ensure process safety by blocking the fluid line A of the hydraulic cylinder 2 (or the line B when it is introduced into the line B) to prevent the piston movement of the hydraulic cylinder 2. In addition, the metering pump 3 can be short-circuited by means of the safety valve 11 in order to ensure pressure balance through the lines A and B. This serves as component protection. These two ways of using the safety valve 11 and a combination of the two can be used in the hydrostatic drive system 1 according to the present disclosure. In addition, the hydrostatic drive system 1 has at least one pressure limiting valve 9. In Figure 1 In the illustrated embodiment, a corresponding pressure-limiting valve 9 is provided for each connection end A, B of the metering pump 3. The pressure-limiting valve 9 is introduced from the pipeline A in a manner connected to the pipeline T. Another pressure-limiting valve 9 is introduced from the pipeline B in a manner connected to the pipeline T. In addition, the hydrostatic drive system 1 has at least one check valve 8 in each pipeline of the connection ends A, B of the metering pump 3. The check valve 8 is introduced from the pipeline A in a manner connected to the pipeline T in the cut-off direction. Another check valve 8 is introduced from the pipeline T in a manner connected to the pipeline B in the passing direction. The suction function of the metering pump 3 can be provided by means of the check valve 8 so as to minimize cavitation. In addition, a compensation container 7 is provided. The oil compression volume is provided by means of the compensation container 7.

[0074] Furthermore, the metering pump 3 has a further connection to a node T of the pipeline T. At the node T, a preload pressure provided by the compensation container 7 is applied. Figure 1In the embodiment of the metering pump 3, the housing and the pipeline to the node T are connected internally. This results in a closed system, whereby no external fluid supply is required. The switching valve 4 can be provided with a preload pressure by means of the non-return valve 12. Figure 1 The three non-return valves 12 shown in FIG. 1 have connections to the lines A, B, T, respectively, and a common connection to the switching valve 4 via the line P. Furthermore, the pressure of the connections A, B of the metering pump 3 is applied to the switching valve 4 .

[0075] In one embodiment, the switching device 5 is connected to the hydraulic cylinder 2 via a fluid line. The switching device 5 can be designed as a separate module, which is positioned independently of the hydraulic cylinder 2 and the application system. Alternatively, the hydraulic cylinder 2 can be designed as a unit together with the switching device 5. In this embodiment, the hydraulic cylinder 2 is flange-connected to a module including the switching device 5, the metering pump 3 and possibly the electric machine 10, and is therefore designed in one piece.

[0076] It is proposed that the hydraulic cylinders 2 are designed to provide a synchronous situation. For this purpose, the hydraulic cylinders 2 have cylinder surfaces designed to be of the same size. Figure 1 In the embodiment shown, the hydraulic cylinder 2 has two cylinder surfaces of identical size, which are mechanically connected to one another via a piston rod.

[0077] The hydraulic drive system 1 can be used to provide a pressurized medium. The hydrostatic drive system 1 is designed to transfer the pressure from the hydrostatic drive system 1 to another system in mechanical connection, such as a pressure intensifier, by means of a hydraulic cylinder 2. It can also be provided that the hydraulic cylinder 2 has a connection to a second hydraulic cylinder in order to provide a second conveying medium with a predeterminable pressure by means of the second hydraulic cylinder.

[0078] Figure 2 Another design of the hydrostatic drive system 1 according to the present disclosure is schematically shown. Figure 2 The design of the hydrostatic drive system 1 is similar to Figure 1 The same as the implementation shown in . Figure 1 , Figure 2 The hydrostatic drive system 1 shown in FIG. 1 has a first hydraulic cylinder and a second hydraulic cylinder 2 which are positively coupled hydraulically. For example, a maximum positive volume flow Q is delivered via a connection A via a metering pump 3. max+In this way, the upper hydraulic cylinder 2 is extended, and the fluid on the piston side is conveyed into the lower hydraulic cylinder 2 and causes the retraction movement of the lower hydraulic cylinder 2. A hydraulic forced connection is thus produced. The cylinder surfaces are designed to be of the same size, so that a synchronization situation occurs. This design can be advantageous, for example, in the application of boosters and in the application of high-density pumps with limited structural space (such as concrete pumps). Then there may be applications with limited structural space, in which, for example, the length of the synchronous cylinder is unacceptable. Additional uses can be realized in application systems where the process limits the structural space and requires a certain flexibility.

[0079] Figure 3 Another design of the hydrostatic drive system 1 according to the present disclosure is schematically shown. Figure 3 The design of the hydrostatic drive system 1 is similar to Figure 1 and Figure 2 The same implementation as shown in . Figure 3 The hydraulic cylinder 2 is based on Figure 1 and Figure 2 The hydraulic cylinder of the embodiment of is distinguished in that it has cylinder surfaces which are designed to be of equal size, which are positively coupled mechanically and in which synchronization occurs. Figure 3 The hydraulic cylinder 2 shown in FIG. 1 is characterized in that it has only one retractable piston rod, although it satisfies the synchronous conditions. This allows a compact design of the hydraulic cylinder 2 . This design can be advantageous, for example, in test applications with long strokes in a limited installation space, such as fatigue test benches for aircraft wings.

[0080] Figure 4 Another design of the hydrostatic drive system 1 according to the present disclosure is schematically shown. Figures 1 to 3 In addition to the components of the embodiment, according to Figure 4 The hydrostatic drive system 1 also has an external fluid source 14 and a reservoir 13. Figure 4 In the embodiment of , the preload pressure is provided at the node T by an external fluid source 14 (e.g., a pump). The constant pressure of the fluid can be provided by the external fluid source 14. In addition, a reservoir 13 is provided. The reservoir 13 is designed as an open reservoir. The reservoir 13 is in fluid connection with the housing of the metering pump 3 by means of a fluid line passing through the node L. Therefore, the preload pressure can be provided at the node T by the external fluid source 14. The preload pressure can be connected to the pipeline P by an additional check valve 12, and can therefore be switched by the switching valve 4 and the switching element 6 of the metering pump 3.

[0081] exist Figure 4 It shows Figure 1 The hydrostatic drive system 1 of the hydraulic cylinder 2 is not excluded from the use of Figure 2 and Figure 3 Hydraulic cylinder 2. Instead, hydraulic cylinder 2 (such as Figure 2 and Figure 3 can also be Figure 4 The hydrostatic drive system 1 is used to operate.

[0082] Hydrostatic drive system 1 Figures 1 to 4 The embodiment shown in can be made using the method according to the present disclosure. In addition, the hydrostatic drive system 1 Figures 1 to 4 The embodiments shown in the embodiment can be used in the application system according to the present disclosure.

[0083] List of Reference Numerals

[0084] 1 Hydrostatic drive system

[0085] 2 Hydraulic cylinders

[0086] 3 Dosing pump

[0087] 4 Switching valve

[0088] 5 Switching devices

[0089] 6 Switching elements

[0090] 7 Compensation vessel

[0091] 8 Check valve

[0092] 9 Pressure limiting valve

[0093] 10 Electric machines

[0094] 11 Safety valve

[0095] 12 Additional check valve

[0096] 13 Storage

[0097] 14 External fluid source

Claims

1. A hydrostatic drive system (1), comprising at least one hydraulic cylinder (2) with a cylinder surface, wherein the cylinder surface of the at least one hydraulic cylinder (2) which is hydraulically connected to a metering pump (3) is designed to have the same dimensions, the hydrostatic drive system comprising: - the metering pump (3) for delivering a volume flow, wherein the metering pump (3) is designed to provide at least two and at most three delivery states for delivering the volume flow; - a switching device (5), the switching device having a switching valve (4) and a switching element (6), wherein a switching pressure is provided by the switching valve (4) to switch the switching element (6), and The switching element (6) is designed to switch the metering pump (3) to one of the delivery states based on the switching pressure and to provide a volume flow to the hydraulic cylinder (2).

2. The hydrostatic drive system (1) according to the preceding claim, wherein the hydrostatic drive system (1) is designed for transmitting pressure from the hydrostatic drive system (1) to another system in mechanical connection by means of the hydraulic cylinder (2).

3. The hydrostatic drive system (1) according to claim 1, wherein the hydraulic cylinder (2) has a connection to a second hydraulic cylinder in order to provide a second delivery medium with a predeterminable pressure by means of the second hydraulic cylinder.

4. The hydrostatic drive system (1) according to at least one of the preceding claims, wherein the hydraulic cylinders (2) are designed to provide a synchronous situation and wherein the cylinder surfaces designed to be of equal size are positively coupled mechanically or hydraulically.

5. The hydrostatic drive system (1) according to at least one of the preceding claims, wherein the two states of the metering pump (3) include: Maximum positive volume flow Q max+ and the maximum negative volume flow Q max- , and the third delivery state forces an idle volume flow Q0 for the hydraulic cylinder (2).

6. The hydrostatic drive system (1) according to the preceding claim, wherein the switching element (6) comprises a return spring and, if no switching pressure is applied, the return spring brings the switching element (6) into the zero position in order to enforce the idling volume flow Q0.

7. The hydrostatic drive system (1) according to at least one of the preceding claims, wherein the switching device (5) is connected to the hydraulic cylinder (2) via a fluid line, or the hydraulic cylinder (2) and the switching device (5) are designed as a whole.

8. The hydrostatic drive system (1) according to claim 1, wherein the maximum positive volume flow Q can be provided by means of the switching pressure max+ With the maximum negative volume flow Q max- transition between.

9. The hydrostatic drive system (1) according to one of the preceding claims, wherein the switching valve (4) is designed as a 4 / 2-way switching valve or a 4 / 3-way switching valve.

10. The hydrostatic drive system (1) according to one of the preceding claims, wherein the switching valve (4) can be switched by the pressure provided by the metering pump (3) and / or the fluid source or can be switched electromagnetically by means of a control signal.

11. The hydrostatic drive system (1) according to claim 1, wherein the switching pressure switched by the switching valve (4) is provided by a compensation container (7) and / or by the metering pump (3) and / or an external pump. 12 . The hydrostatic drive system ( 1 ) according to claim 1 , wherein the metering pump ( 3 ) is designed as a 4Q metering pump and comprises a piston pump or a vane pump.

13. The hydrostatic drive system (1) according to claim 1, wherein the fixed displacement pump (3) can be operated at a constant or variable speed of the electric machine (10), preferably an asynchronous machine.

14. The hydrostatic drive system (1) according to one of the preceding claims, wherein the hydrostatic drive system (1) comprises at least one safety valve (11).

15. The hydrostatic drive system (1) according to one of the preceding claims, wherein the hydrostatic drive system (1) comprises at least one pressure-limiting valve (9) and / or at least one non-return valve (8).

16. Application system comprising a hydrostatic drive system (1) according to one of the preceding claims for providing a pressurized medium.

17. A method for producing a hydrostatic drive system (1), the hydrostatic drive system having at least one hydraulic cylinder (2) with a cylinder surface, wherein the cylinder surface of the at least one hydraulic cylinder (2) which is hydraulically connected to a metering pump (3) is designed to be of the same size, wherein the method comprises: -supply: - the metering pump (3) for delivering a volume flow, wherein the metering pump (3) is designed to provide at least two and at most three delivery states for delivering the volume flow; - a switching device (5), comprising a switching valve (4) and a switching element (6), wherein a switching pressure is provided by the switching valve (4) to switch the switching element (6); as well as The switching element (6) is designed in such a way that, based on the switching pressure, the metering pump (3) is switched into one of the delivery states and provides a volume flow to the hydraulic cylinder (2).

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