HYDRAULIC DRIVE SYSTEM

Description

[0001] The invention relates to a hydraulic drive system, a method for adjusting a delivery volume in a hydraulic drive system and the use of the hydraulic drive system for controlling a hydraulic cylinder.

[0002] Hydraulic drive systems are used in many types of industrial applications. For example, hydraulic drive systems of this type can be found in metal forming systems such as presses and rolling mills, as well as in the construction of hydraulic power units in general.

[0003] From the publication DE 10 2010 020 690 A1, a drive system with two mechanically coupled hydraulic machines is known. These are driven by a primary drive. In the hydraulic drive system shown, two hydraulic machines are jointly driven at variable speeds by a motor via a drive shaft. The motor is designed as an electric motor. The said electric motor can be operated at a variable speed and direction of rotation. The two hydraulic machines of the said hydraulic drive system are each fluid-hydraulically connected via a hydraulic connection to a respective side of the hydraulic cylinder and thus to the corresponding hydraulic cylinder surface, as well as to a reservoir. The two hydraulic machines can be arranged on the drive shaft in such a way that one of the two hydraulic machines functions as a pump and the other hydraulic machine acts as a motor.For example, the first hydraulic machine can provide the functionality of a pump for clockwise rotation, while the second hydraulic machine acts as a motor. By changing the direction of rotation of the hydraulic machine so that it is driven counterclockwise, the first hydraulic machine assumes the functionality of a motor, and the second hydraulic machine acts as a pump. The problem with the solution described in DE 10 2010 020 690 A1 is that the displacement or displacement volume of the two mechanically coupled hydraulic machines must be precisely matched to the cylinder area ratio.

[0004] This leads to very limited usability, as neither the hydraulic machines with defined displacement or displacement, nor the cylinder rods or piston rod diameters can be varied arbitrarily. The cylinder area ratio is generally determined by the drive task and its framework conditions. Hydraulic machines are available with fixed displacement or displacement. If the displacement of the two hydraulic machines is not precisely matched to the cylinder area ratio, a total pressure increase occurs over the cylinder stroke. This pressure increase leads to a lower usable force of the cylinder, as the cylinder chamber pressure level cannot be arbitrarily high.Furthermore, the fixed connection of each hydraulic machine to each cylinder chamber means that when using a differential cylinder with an area ratio of 2:1, one hydraulic machine has twice the displacement of the other and must be designed accordingly. This impacts the space requirements and costs of the drive system shown.

[0005] Furthermore, EP 292 1700 A1 discloses a hydraulic drive system with a radial piston hydraulic machine with a control pin. The hydraulic machine is driven by a motor at variable speed. The hydraulic machine has at least three hydraulic connections, with the delivery volume of the hydraulic connections being determined by the control pin. The delivery volume is the volume of hydraulic fluid that flows through the cross-section of a component per revolution of the motor. A solution for differential cylinder adjustment is provided in this document via the aforementioned control pin of the hydraulic machine. The solution presented in EP 292 1700 A1 also presents the problem that the control pin must be precisely adapted to the cylinder area ratio. This results in the total pressure varying depending on the cylinder stroke.

[0006] DE 10 2011 056 894 A1 shows a drive with a differential cylinder whose inputs are connected to the outputs of a hydraulic differential transformer. An output of a pressure relief valve is connected to a hydraulic oil reservoir. An input of a feed pump is connected to the reservoir. The feed pump pumps the hydraulic oil to a low-pressure side, and the pressure relief valve allows hydraulic oil to flow into the reservoir when a specified maximum pressure on the low-pressure side is exceeded.

[0007] DE 10 2013 008047 A1 shows a linear actuator with a double pump and a differential cylinder, whose annular space or piston rod space is defined by an annular surface or piston rod surface of a piston and is connected to a first pump, and whose piston crown space is defined by a piston crown surface of the piston and is connected to a second pump. Both pumps are driven by a common variable-speed electric motor. The ratio of the annular area to the piston crown area is equal to the ratio of the displacement of the first pump to the displacement of the second pump.

[0008] JP 2002 039110 A describes operating a single-ended rod cylinder at the same speed on both an expansion side and a contraction side using a hybrid system that drives a pump with an electric motor, simplifying the circuit configuration. The cylinder is operated at the same speed on both the expansion side and the contraction side by supplying and discharging oil to and from both the head-side and rod-side oil chambers of the single-ended rod hydraulic cylinder at a flow rate corresponding to the cross-sectional area ratio of the two side oil chambers by both a first hydraulic pump and a second hydraulic pump driven by the electric motor.

[0009] EP 2 857 696 A1 discloses a closed hydraulic circuit system with hydraulic pumps that maintains a balanced flow rate by automatically controlling the flow rate even when a flow rate imbalance is caused by a pump capacity error during the extension / retraction of a hydraulic cylinder device. In this system, a first hydraulic pump is connected to the hydraulic cylinder device to form a closed hydraulic circuit; a second hydraulic pump is connected to a bottom side of the hydraulic cylinder device at one of the paired discharge ports and to a tank at the other of the ports; and a prime mover drives the first and second hydraulic pumps and recovers drive power from these pumps.A pump capacity control unit detects a moving direction of the hydraulic cylinder device and a pressure in a negative pressure side of the device, and controls a capacity of the second hydraulic pump so that the flow rate during extension / contraction of the hydraulic cylinder device is balanced between the first and second hydraulic pumps and the hydraulic cylinder device.

[0010] WO 2020 / 105560 A1 discloses a hydraulic system comprising: a cylinder that moves a movable body in a vertical direction by utilizing the expansion and contraction of a rod; a first bidirectional pump connected to a head-side chamber in the cylinder through a first supply / discharge line; a second bidirectional pump connected to a rod-side chamber in the cylinder through a second supply / discharge line and coupled to the first bidirectional pump so as to be capable of transmitting torque; a relay line connecting the first bidirectional pump and the second bidirectional pump so that hydraulic fluid discharged from either the first bidirectional pump or the second bidirectional pump is directed to the other pump; and a servo motor that drives either the first bidirectional pump or the second bidirectional pump.At least one of the first bidirectional pump and the second bidirectional pump is a variable capacity pump capable of varying the flow rate per revolution at will.

[0011] Variable displacement pumps are also known in the prior art. In hydraulic drive systems, a hydraulic cylinder is operated by at least two hydraulic machines, with at least one hydraulic machine being a variable displacement pump. In a variable displacement pump, the adjustment of the cam ring and thus the vanes of the variable displacement pump are moved via a hydraulic cylinder. This cylinder must be pressurized and supplied with hydraulic fluid, which necessitates a proportional valve to control the cylinder. This results in significant structural and design complexity. Furthermore, a control system for this cylinder is required, which leads to increased energy consumption, as a constant pressure system is required to supply this proportional valve.Therefore, a variable displacement pump is inefficient and complicated in terms of its design and supply, and is prone to maintenance due to the additional components, reducing reliability and cost-intensive in terms of purchase, maintenance and repair.

[0012] When operating a hydraulic cylinder, the total pressure in the hydraulic system must remain constant to ensure maximum usable power. If the hydraulic cylinder is driven by a hydraulic drive system with only one motor, the flow rate applied to both sides of the hydraulic cylinder must be precisely matched to the ratio of the two sides of the hydraulic cylinder. For example, if a differential cylinder with an area ratio of 2:1 is driven by a hydraulic drive system, the ratio of the displacement at the hydraulic connections of the two sides of the hydraulic cylinder must also be 2:1.

[0013] The resulting problem for the hydraulic drive systems known in the prior art is that the displacement of the hydraulic connections of the hydraulic machine(s) connected to the hydraulic cylinder sides must be adapted to the hydraulic cylinder. In the prior art, this is achieved by selecting the two hydraulic machines or the control pin. The hydraulic machines here have a fixed displacement. The displacement provided by the control pin is also fixed. If the hydraulic drive system is connected to a hydraulic cylinder that does not have the volume ratio for which the hydraulic drive system is designed, at least one of the hydraulic machines or the control pin must be replaced.This involves considerable labor and expense, as at least one of the two hydraulic machines must be replaced, and a third hydraulic machine with a different displacement than the one being replaced must be installed in its place. Alternatively, the control pin must be removed and replaced with a control pin with a different displacement than the previously used control pin. This entire process is not only time-consuming and costly, but also error-prone, which can lead to downtime and rework.

[0014] A technical problem underlying the invention can thus consist in at least partially eliminating the disadvantages identified in the prior art and providing a hydraulic drive system in which the displacement of the hydraulic machine(s) can be adapted to a hydraulic cylinder. According to the invention, this problem is solved according to a first aspect by a hydraulic drive system having the features of independent patent claim 1. Advantageous developments of the hydraulic drive system emerge from the subclaims relating to the hydraulic drive system.

[0015] According to the invention, the hydraulic drive system comprises a first hydraulic machine and a second hydraulic machine. The first hydraulic machine and the second hydraulic machine are mechanically connected to one another. For example, the first hydraulic machine and the second hydraulic machine can be mechanically connected to one another via a drive shaft.

[0016] Furthermore, the first hydraulic machine and the second hydraulic machine are jointly operated by a variable-speed drive. The variable-speed drive can be a variable-speed or variable-direction electric motor. Essentially, variable-speed drives consist of an electric motor, a hydraulic pump, and a frequency converter whose software continuously adjusts the motor speed to the optimal operating point depending on the load. For example, an electrically driven fixed-displacement pump delivers a demand-oriented flow rate to regulate pressure, speed, power, position, or force depending on the task.

[0017] Furthermore, it is provided that the first hydraulic machine and the second hydraulic machine are hydraulically connected to at least one first hydraulic cylinder. According to the invention, the hydraulic cylinder has a first hydraulic cylinder surface and a second hydraulic cylinder surface. The hydraulic cylinder is preferably designed as a differential cylinder. Alternatively, the hydraulic cylinder can be designed as a double-action cylinder. The first hydraulic cylinder surface and the second hydraulic cylinder surface of the hydraulic cylinder can each be designed as the annular side or as the piston side of the hydraulic cylinder.

[0018] According to the present invention, the first hydraulic machine or the second hydraulic machine has an adjustable displacement. According to the invention, the first hydraulic machine and the second hydraulic machine are designed as fixed-displacement pumps.

[0019] For the purposes of the present invention, adjustment refers to a manual mechanical stroke adjustment. The displacement volume per pump revolution can be determined by means of the manual mechanical stroke adjustment. Particularly in piston pumps and vane pumps, the stroke of the pistons or vanes can be manually adjusted using this adjustment. This stroke adjustment leads to a change in the displacement volume per revolution. Furthermore, the displacement volume is mechanically adjustable.

[0020] The selected stroke setting can be locked using a mechanical locking device. If the stroke is adjusted using an adjusting spindle, the locking can be achieved using a lock nut.

[0021] The delivery volume at the hydraulic connection of the first hydraulic cylinder surface and the delivery volume at the hydraulic connection of the second hydraulic cylinder surface can thus be adapted to the volume ratio of the first hydraulic cylinder surface and the second hydraulic cylinder surface.

[0022] Advantageously, the displacement volume can be ideally adjusted to the cylinder area ratio. A total pressure increase over the cylinder stroke and thus a reduction in effective power can be avoided. Another advantage is that the displacement volume only needs to be mechanically adjusted once according to a first adjustment parameter. No permanent adjustment is required. In particular, the present invention provides a reliable and energy-efficient hydraulic drive system by preventing the system pressure increase, especially in differential cylinders.

[0023] In an advantageous embodiment, a ratio of the delivery volumes of the first hydraulic machine and the second hydraulic machine can be mechanically adjusted to an area ratio of the first hydraulic cylinder area and the second hydraulic cylinder area.

[0024] The ratio of the displacement of the first hydraulic machine to the displacement of the second hydraulic machine should correspond to the area ratio of the two hydraulic cylinder surfaces. The volume flow Q in the hydraulic drive system is provided by the variable speed of the first and second hydraulic machines, and the displacement is adjusted via the adjustment parameter.

[0025] In a further advantageous embodiment, a delivery volume (volume V = dQ / dt) of the hydraulic drive system is controlled by a specific adjustment parameter. In the sense of the invention, the delivery volume corresponds to the volume of hydraulic fluid that is moved per unit of time in the hydraulic drive system. The adjustment parameter can be determined, for example, using a method according to the further aspect of the present invention. In particular, the specific adjustment parameter (specific) results with reference to the connected cylinder. This is determined and set for the cylinder used. The specific adjustment parameter results from the area ratio of the cylinder surfaces of the cylinder.

[0026] In a further advantageous embodiment, the first hydraulic cylinder surface and the second hydraulic cylinder surface are different. Differential cylinders are generally used, which are designed with only one piston rod. This can, for example, lead to a shorter overall length, a greater achievable force on the piston side, and a simplified sealing structure on the hydraulic cylinder. It is known that approximately 80% of hydraulic cylinders used in practice are designed as differential cylinders.

[0027] In a further advantageous embodiment, the first hydraulic machine and / or the second hydraulic machine is / are selected from a group of pumps comprising at least one positive displacement pump. The hydraulic machine can be configured, for example, as an axial piston pump, radial piston pump, vane pump, gear pump, spindle pump, and the like. Furthermore, it is provided that the manually adjustable pump is configured as a positive displacement pump, in particular an axial piston pump, radial piston pump, or vane pump.

[0028] The axial piston pump is used in hydraulics to convert mechanical energy into hydraulic energy. The axial piston pump allows the flow rate to be adjusted.

[0029] In contrast to axial piston pumps, the working pistons of radial piston pumps are arranged radially and perpendicular to the drive shaft. Radial piston pumps are characterized by their high efficiency.

[0030] The vane pump is a positive displacement pump with a hollow cylinder in which another cylinder rotates. The displacement is mechanically adjustable and / or adjustable.

[0031] According to the invention, the second hydraulic machine is connected to the second hydraulic cylinder surface of the hydraulic cylinder. Preferably, the second hydraulic machine is connected to the second hydraulic cylinder surface of the hydraulic cylinder via a first connection. This configuration advantageously allows the volume flow to be reduced, while the volume of the first hydraulic machine of the hydraulic drive system can be made smaller. In this regard, the design of the first hydraulic machine is correspondingly smaller and thus more cost-effective, less maintenance-intensive, and / or less susceptible to errors and malfunctions.

[0032] In a further advantageous embodiment, the first hydraulic machine is connected to the first hydraulic cylinder surface of the hydraulic cylinder. Preferably, the first hydraulic machine is connected to the first hydraulic cylinder surface of the hydraulic cylinder via a first connection. In this embodiment, the volume of the first hydraulic machine is smaller. Furthermore, the first hydraulic machine has two connections, each of which can be supplied with the entire working pressure.

[0033] According to the invention, the first hydraulic machine is connected to a reservoir of the hydraulic drive system. Preferably, the first hydraulic machine is connected to a reservoir of the hydraulic drive system via a second connection.

[0034] According to the invention, the second hydraulic machine is hydraulically connected to the first hydraulic cylinder surface. Preferably, the second hydraulic machine is hydraulically connected to the first hydraulic cylinder surface via a second connection.

[0035] The reservoir is designed to supply additional hydraulic fluid to the hydraulic drive system as needed. A suction valve can be provided between the first hydraulic machine and the reservoir. Since the invention provides for connecting the second hydraulic machine to the first hydraulic cylinder side and the second hydraulic cylinder side, the second hydraulic machine conveys the hydraulic fluid between the two hydraulic cylinder sides, depending on the direction of rotation, from the first hydraulic cylinder side to the second hydraulic cylinder side or from the second hydraulic cylinder side to the first hydraulic cylinder side.

[0036] In this case, the first hydraulic machine can be designed to balance only the volume ratio of the first hydraulic cylinder side and the second hydraulic cylinder side. The required displacement of the first hydraulic machine is thus lower compared to a design in which the second hydraulic machine is not connected to the first hydraulic cylinder side. The first hydraulic machine can thus be smaller, which reduces the space required for installation and assembly, and thus the associated technical complexity and costs.

[0037] In an example not covered by the present invention, the second hydraulic machine is hydraulically connected to a reservoir of the hydraulic drive system. In this example, not according to the invention, the second hydraulic machine is hydraulically connected to a reservoir of the hydraulic drive system via a second connection.

[0038] In this example, not according to the invention, the second connection of the second hydraulic machine is preferably always connected to the reservoir. Thus, in this example, not according to the invention, a hydraulic machine comprising a pressure connection can be provided. This allows the internal structure of the hydraulic machine to be simplified. In contrast to the simplified second hydraulic machine, in this example, not according to the invention, the first hydraulic machine must provide the entire volume flow requirement of the first cylinder chamber and must therefore be significantly larger.

[0039] According to the invention, the reservoir is under an overpressure. According to the invention, the reservoir is designed as a prestressed reservoir.

[0040] The overpressure can preferably be in a range of 2-25 bar, particularly preferably in a range of 2-10 bar. This allows for increased suction of the first hydraulic machine and the second hydraulic machine. Furthermore, this design advantageously allows the hydraulic medium (e.g., hydraulic fluid) to be separated from the atmosphere, thus counteracting aging of the hydraulic medium.

[0041] In a further preferred embodiment, the preloaded reservoir 6 is pressurized within a fluctuation range of preferably 22 bar, more preferably 14 bar. Advantageously, the hydraulic pumps can be operated within this fluctuation range without reducing their seal performance and / or quality. Furthermore, the hydraulic pumps can be operated within a range in which the load limits of the pump housing are maintained to prevent damage.

[0042] In a further advantageous embodiment, the first hydraulic machine and the second hydraulic machine have at least one high-pressure connection.

[0043] In a further advantageous embodiment, the first hydraulic machine or the second hydraulic machine has at least one high-pressure connection.

[0044] For example, a hydraulic connection of the first hydraulic machine and a hydraulic connection of the second hydraulic machine, which is connected either to the first hydraulic cylinder surface or to the second hydraulic cylinder surface, can be designed as a high-pressure connection. In a further advantageous embodiment of the hydraulic drive system, the first hydraulic machine and / or the second hydraulic machine have a low-pressure connection. A hydraulic connection of the first hydraulic machine and a hydraulic connection of the second hydraulic machine, which is connected to the reservoir, can be designed as a low-pressure connection. A high-pressure line can be connected via the high-pressure connection. For example, a high-pressure line for connection to the hydraulic cylinder can be connected to the high-pressure connection. The low-pressure connection can be permanently connected to a tank line and provide a hydraulic connection to the reservoir.

[0045] In a further advantageous embodiment of the hydraulic drive system, the first hydraulic machine and / or the second hydraulic machine have a high-pressure and low-pressure accumulator. The first hydraulic machine is connected to the second hydraulic cylinder side of the hydraulic cylinder, and the second hydraulic machine is connected to the first hydraulic cylinder surface of the hydraulic cylinder. In a further advantageous embodiment of the hydraulic drive system, the first hydraulic machine and / or the second hydraulic machine have a high-pressure and low-pressure accumulator. The first hydraulic machine is connected to the first hydraulic cylinder surface of the hydraulic cylinder, and the second hydraulic machine is connected to the second hydraulic cylinder surface of the hydraulic cylinder.

[0046] According to a further aspect, the present invention relates to a method for adjusting a delivery volume of a hydraulic drive system having the features of independent patent claim 9. Advantageous developments of the method result from the subclaims to the method.

[0047] In an advantageous embodiment of the method, this comprises the further step: Testing the corresponding first hydraulic machine or second hydraulic machine having an adjustable displacement on a test bench and / or by means of a test run to determine whether the adjusted displacement corresponds to the area ratio of the hydraulic cylinder.

[0048] Advantageously, by testing the hydraulic machine, the adjusted delivery volume can be checked to see whether it meets the requirements of the hydraulic drive system.

[0049] In a further advantageous embodiment of the method, the delivery volume is adjusted by setting an adjustment element with the determined first adjustment parameter. Preferably, the adjustment element is secured by a locking element.

[0050] Advantageously, the displacement of one of the hydraulic machines can be efficiently adjusted and thus changed via the adjusting element. Furthermore, with the present invention, the displacement only needs to be changed / adjusted once via the adjusting element and can be fixed at this setting by using a counter element.

[0051] According to a preferred embodiment, the adjusting element is designed as at least one threaded spindle, one threaded bolt, or one threaded screw. The adjusting element can be designed as a corresponding lock nut.

[0052] According to a further aspect, the present invention relates to a hydraulic drive system for controlling a hydraulic cylinder with a constant total pressure in the hydraulic drive system.

[0053] Within the scope of the present invention, as defined by the appended claims, the above embodiments and further developments can be combined with one another where appropriate. In particular, the features of the method claims can be implemented as structural features in the hydraulic drive system. In addition, it can be provided to make the method more concrete by structural features. Within the scope of the present invention, as defined by the appended claims, possible embodiments, further developments and implementations of the invention also include combinations of features of the invention described previously or below with regard to the exemplary embodiments that are not explicitly mentioned. In particular, a person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the present invention, provided that these lie within the scope of the present invention, as defined by the appended claims.

[0054] The invention is explained below using various embodiments, whereby it is pointed out that these examples also include modifications or additions that would immediately become apparent to a person skilled in the art, provided that they are within the scope of the present invention as defined by the appended claims.

[0055] Furthermore, these preferred embodiments do not represent a limitation of the invention in that modifications and additions are within the scope of the present invention as defined by the appended claims.

[0056] In the figures of the drawing, identical, functionally identical and acting elements, features and components are provided with the same reference symbols, unless otherwise stated.

[0057] Showing: Fig. 1 shows a first embodiment of the hydraulic drive system according to the present invention; Fig. 2 shows an example of a hydraulic drive system not covered by the present invention, Fig. 3 and a flowchart of an embodiment of a method according to the present invention.

[0058] Fig. 1shows a hydraulic drive system 1. The hydraulic drive system 1 comprises a first hydraulic machine 2 and a second hydraulic machine 3. The first hydraulic machine 2 and the second hydraulic machine 3 are driven jointly via a shaft by a variable-speed drive 4. According to the invention, the first hydraulic machine 2 and the second hydraulic machine are mechanically connected to one another. The mechanical connection can be made via a shaft. The first hydraulic machine 2 and the second hydraulic machine 3 are designed as fixed displacement pumps. The first hydraulic machine 2 is hydraulically connected to a reservoir 6. A suction valve (not shown) can be interposed between the first hydraulic machine 2 and the reservoir 6. A reservoir 6 (compensation tank) is understood to be a container which holds the hydraulic oil or the hydraulic medium of the hydraulic drive system 1. In the hydraulic fluid orThe hydraulic medium can be a special mineral oil. Reservoir 6 is intended to store the hydraulic fluid, but otherwise keeps it pressureless. The reservoir is to be understood as a tank without excess pressure. This means that reservoir 6 can be filled and emptied safely. Reservoir 6 is designed as a closed container that is connected to the surrounding air via vent valves. This connection is necessary to allow pressure equalization. Otherwise, returning hydraulic fluid or the hydraulic medium would create excess pressure and escaping hydraulic fluid would create negative pressure. The closed system ensures that no cavitation occurs and thus the quality of the hydraulic medium (e.g. oil) is maintained and / or that it does not age and / or ages less quickly. This reduces premature replacement and / or maintenance intervals.

[0059] In a further preferred embodiment, the reservoir 6 can be designed to be under an overpressure. In particular, the reservoir 6 can be designed as a prestressed reservoir.

[0060] Preferably, an overpressure in a range of 2-25 bar can be provided, particularly preferably in a range of 2-10 bar. A reservoir with overpressure enables increased suction by the first hydraulic machine and the second hydraulic machine. Furthermore, this design can separate the hydraulic medium from the atmosphere, thus counteracting aging of the hydraulic medium.

[0061] In a further preferred embodiment, the preloaded reservoir 6 is pressurized within a fluctuation range of preferably 22 bar, more preferably 14 bar. Advantageously, the hydraulic pumps can be operated within this fluctuation range without reducing their seal performance and / or quality. Furthermore, the hydraulic pumps can be operated within a range in which the load limits of the pump housing are maintained to prevent damage.

[0062] The first hydraulic machine 2 and the second hydraulic machine 3 are hydraulically connected to a first surface 5a of a hydraulic cylinder 5, corresponding to the first hydraulic cylinder surface. The second hydraulic machine 3 is hydraulically connected to the second surface 5b of the hydraulic cylinder 5, corresponding to the second hydraulic cylinder surface.

[0063] When the variable-speed drive 4 drives the first hydraulic machine 2 and the second hydraulic machine 3, depending on the direction of rotation of the variable-speed drive 4, the first hydraulic machine 2 pumps hydraulic fluid from the reservoir 6 into the first hydraulic cylinder side 5a of the hydraulic cylinder, and the second hydraulic machine 3 pumps hydraulic fluid from the second hydraulic cylinder side 5b of the hydraulic cylinder 5 into the first hydraulic cylinder side 5a of the hydraulic cylinder 5. The piston of the hydraulic cylinder 5 is extended. If the drive 4 drives the first hydraulic machine 2 and the second hydraulic machine 3 in the other direction, the first hydraulic machine 2 pumps hydraulic fluid from the first hydraulic cylinder side 5a of the hydraulic cylinder 5 into the reservoir 6, and the second hydraulic machine 3 pumps hydraulic fluid from the first hydraulic cylinder side 5a of the hydraulic cylinder into the second hydraulic cylinder side 5b of the hydraulic cylinder 5.The piston of hydraulic cylinder 5 is retracted.

[0064] The displacement in the hydraulic drive system 1 can be controlled via the speed of the variable-speed drive 4. In this arrangement, the first hydraulic machine 2 only needs to balance the volume ratio of the first hydraulic cylinder side 5a and the second hydraulic cylinder side 5b. The displacement of the first hydraulic machine 2 can thus be smaller than in other arrangements. The first hydraulic machine 2 can thus be designed to be smaller.

[0065] The delivery volume of at least one hydraulic machine 2, 3 per pump revolution is intended to be adjusted or mechanically set and fixed. For this purpose, the fixed delivery volume of the first hydraulic machine 2 and / or the second hydraulic machine 3 is changed. For example, in the case of a radial piston pump (RKP), the delivery volume can be adjusted via the eccentricity of the stroke ring. This leads to an adjustment of the stroke of the pistons or vanes and thus to a change in the delivery volume per pump revolution. The eccentricity of the stroke ring can be adjusted using a correspondingly provided spindle, and the delivery volume per pump revolution can be adjusted and fixed. The stroke setting can be locked using a mechanical fixation. If the stroke is adjusted using an adjusting spindle, the locking can be done using a lock nut.Advantageously, the inventive design and the use of exclusively fixed displacement pumps (e.g. external gear pumps, internal gear pumps, screw pumps) or adjustable fixed displacement pumps (e.g. axial piston pumps, radial piston pumps, vane pumps) for the first hydraulic machine 2 and the second hydraulic machine 3 are substantially easier to implement and more reliable in operation than compared to variable displacement pumps, whose delivery volume can be continuously adjusted during operation. Variable displacement pumps in and of themselves have the disadvantage that a considerable additional expenditure is required for the control system. With variable displacement pumps, the adjustment is implemented via so-called control pistons, which are pressurized with a corresponding pressure or hydraulic fluid, which requires an additional proportional valve to regulate the pressure in the control piston. In addition, a displacement measuring system is provided for detecting the position.Furthermore, a control system is required to supply the proportional valve. This represents a considerable additional effort. The present invention is simpler to implement in this regard and more reliable due to the smaller number of components that need to be supplied.

[0066] Another advantage is that the control of the hydraulic drive system is more efficient and simple, since the displacement only needs to be set or adjusted once. The displacement of the second hydraulic machine 3 can be adjusted to the hydraulic cylinder area ratio by adjusting the extrinsicity of the cam ring. The delivered volume flow in the hydraulic drive system 1 is controlled by the speed of the first and second hydraulic machines 2, 3.

[0067] Preferably, at least one of the hydraulic machines 2, 3 is designed as an axial piston pump, radial piston pump, or vane pump and has a manual mechanical stroke adjustment of the displacement volume. The other hydraulic machine 2, 3 can be designed as a fixed-displacement pump or as an adjustable fixed-displacement pump.

[0068] At the Fig. 1 In the embodiment shown, the volume of the first hydraulic machine 2 can be smaller than in the exemplary embodiment shown in Fig. 2 used first hydraulic machine 2. This allows the first hydraulic machine 2 to Fig. 1 be designed accordingly smaller and is reflected in a more cost-effective use. Fig. 1 The second hydraulic machine shown has two connections, both of which can be pressurized to full working pressure.

[0069] In Fig. 1The second hydraulic machine 3 has the adjustment 7. The adjustment 7 is designed to adjust an adjustable delivery volume for the first hydraulic machine 2 and / or the second hydraulic machine 3. In particular, the delivery volume can be adjusted mechanically via the adjustment 7. In the Fig. 1 and 2the second hydraulic machine 3 has the adjustment 7. This is only an exemplary and not a restrictive representation. If necessary, the first hydraulic machine 2 can also have the adjustment 7. The stroke of the pistons or vanes can be manually adjusted via the adjustment 7, for example in piston pumps and vane pumps, by adjusting the adjustment 7. This stroke adjustment leads to a change in the delivery volume per revolution. The adjustment 7 can be changed with regard to the adjustment according to the determined first adjustment parameter by screwing it in or out. The adjustment 7 can be locked by means of a mechanical fixing device. This mechanical fixing device can be designed as a lock nut screwed onto the adjustment 7.

[0070] Fig. 2shows a hydraulic drive system 1 according to an example not covered by the present invention. The exemplary drive system 1 according to the Fig. 2comprises a first hydraulic machine 2 and a second hydraulic machine 3. The first hydraulic machine 2 and the second hydraulic machine 3 are jointly driven, for example as shown, via a shaft by a variable-speed drive 4. The first hydraulic machine 2 is hydraulically connected to a first hydraulic cylinder side 5a of a hydraulic cylinder 5. The second hydraulic machine 3 is hydraulically connected to a second hydraulic cylinder side 5b of a hydraulic cylinder 5. The first hydraulic machine 2 and the second hydraulic machine 3 are each connected to a reservoir 6. A suction valve can be provided between the first hydraulic machine 2 and the reservoir 6 and between the second hydraulic machine 3 and the reservoir 6. In a further embodiment, the first hydraulic machine 2 and the second hydraulic machine 3 are jointly connected to the reservoir 6 via a suction valve.

[0071] If the variable-speed drive 4 drives the first hydraulic machine 2 and the second hydraulic machine 3, then, depending on the direction of rotation of the variable-speed drive 4, the first hydraulic machine 2 pumps hydraulic fluid from the reservoir 6 into the first hydraulic cylinder side 5a of the hydraulic cylinder 5, and the second hydraulic machine 3 pumps hydraulic fluid from the second hydraulic cylinder side 5b of the hydraulic cylinder 5 into the reservoir 6. The piston is moved to an end position, for example, the piston of the hydraulic cylinder 5 is extended. If the drive 4 drives the first hydraulic machine 2 and the second hydraulic machine 3 in the direction other than that described above, the first hydraulic machine 2 pumps hydraulic fluid from the first hydraulic cylinder side 5a of the hydraulic cylinder 5 into the reservoir 6, and the second hydraulic machine 3 pumps hydraulic fluid from the second hydraulic cylinder side 5b of the hydraulic cylinder 5 into the reservoir 6.The piston of the hydraulic cylinder 5 is retracted. The displacement (volume) in the hydraulic drive system 1 is also controlled by the adjustment parameter in this example, which is not covered by the present invention.

[0072] The connection of the first hydraulic machine 2 and the second hydraulic machine 3, as shown in the Figures 1 and 2 When using a differential cylinder with an exemplary area ratio of 2:1, this results in the first hydraulic machine 2 and the second hydraulic machine 3 having the same displacement volume. Thus, compared to the prior art mentioned above, at least one hydraulic machine can be made smaller, resulting in a smaller space requirement and lower economic costs. The delivered volume flow can be influenced by changing the speed of the primary drive, thus changing the travel speed of the hydraulic cylinder 5.

[0073] Furthermore, it can be provided that the second hydraulic machine 3 is designed as a 4-quadrant stage. The 4-quadrant stage can be operated in a 4-quadrant mode with positive torque and positive direction of rotation, with positive torque and negative direction of rotation, with negative torque and positive direction of rotation, and with negative torque and negative direction of rotation.

[0074] In the Fig. 2 In the example shown, not covered by the present invention, the volume of the first hydraulic machine 2 is larger compared to the first hydraulic machine of the Fig. 1 .

[0075] The second hydraulic machine 3 has two connections, only one of which is subjected to full working pressure.

[0076] In the Fig. 2In the structure shown, the second connection of the second hydraulic machine 3 is preferably always in fluid communication with the reservoir 6. The second hydraulic machine 3 can thus be provided with only one pressure connection. This makes the internal structure of the second hydraulic machine 3 simpler. The first hydraulic machine 2, however, now provides the complete volume flow requirement of the first cylinder chamber and is therefore larger compared to the embodiment of the Fig. 1 .

[0077] The reservoir 6 is designed as a prestressed reservoir under an overpressure.

[0078] Preferably, an overpressure in a range of 2-25 bar is provided, particularly preferably in a range of 2-25 bar. This enables improved suction of the first hydraulic machine 2 and second hydraulic machine 3 on the one hand, and on the other hand, such a corresponding design enables the hydraulic medium to be separated from the atmosphere, thus counteracting the aging of the hydraulic medium.

[0079] Fig. 3 shows a flow chart of a method 10 for adjusting a delivery volume in a hydraulic drive system 1. The hydraulic drive system 1 has a first hydraulic machine 2 and a second hydraulic machine 3. The Fig. 3The method shown can comprise the following method steps S1-S3. In a first step S1, an area ratio between a first hydraulic cylinder area 5a and a second hydraulic cylinder area 5b of a hydraulic cylinder 5 of the hydraulic drive system 1 is determined. In a further step S2, a target delivery volume of the first hydraulic machine or the second hydraulic machine of the hydraulic drive system 1 is determined. In a further step S3, a first adjustment parameter of the first hydraulic machine 2 or the second hydraulic machine 3 is determined. Using the determined first adjustment parameter, the delivery volume of the first hydraulic machine 2 or the second hydraulic machine 3 of the hydraulic drive system 1 is adjusted. In a further embodiment, it can be provided that further adjustment parameters are determined in order to adjust the delivery volume.In particular, it is provided that the delivery volume of the hydraulic drive system 1 is adjusted by adjusting the delivery volume of the first hydraulic machine 2 and the second hydraulic machine 3.

[0080] Furthermore, the method may include a further step. This further step includes testing the first hydraulic machine 2 or the second hydraulic machine 3 on a test bench. Furthermore, testing the first hydraulic machine 2 or the second hydraulic machine 3 by means of a test run may be provided. This testing can determine whether the adjusted displacement corresponds to the area ratio of the hydraulic cylinder.

[0081] Furthermore, it can be provided that the delivery volume is adjusted by setting an adjusting element, preferably a threaded spindle, threaded bolt, or threaded screw, with the determined first adjustment parameter. Preferably, the adjusting element is fixed via a lock element, preferably a lock nut. List of reference symbols

[0082] 1 hydraulic drive system 2 first hydraulic machine 3 second hydraulic machine 4 variable-speed drive 5 hydraulic cylinder 5 a first hydraulic cylinder surface 5 b second hydraulic cylinder surface 6 reservoir 7 adjustment S1-S3 process steps

Claims

1. Hydraulic drive system (1) comprising a first hydraulic machine (2) and a second hydraulic machine (3) which are mechanically interconnected; wherein the first hydraulic machine (2) and the second hydraulic machine (3) are jointly operated by a variable-speed drive (4); wherein the first hydraulic machine (2) and the second hydraulic machine (3) are hydraulically connected to at least one first hydraulic cylinder (5) comprising a first hydraulic cylinder surface (5a) and a second hydraulic cylinder surface (5b); wherein the first hydraulic machine (2) or the second hydraulic machine (3) has an adjustable delivery volume and wherein the first hydraulic machine (2) and the second hydraulic machine (3) are in the form of constant pumps; wherein the first hydraulic machine (2) is connected to a reservoir (6) of the hydraulic drive system (1); and wherein the second hydraulic machine (3) is hydraulically connected to the first hydraulic cylinder surface (5a) and the second hydraulic cylinder surface (5b) ; characterized in that the reservoir (6) is in the form of a preloaded reservoir (6).

2. Hydraulic drive system (1) according to claim 1, wherein a ratio of the delivery volumes of the first hydraulic machine (2) and the second hydraulic machine (3) is mechanically adjustable to an area ratio of the first hydraulic cylinder surface (5a) and the second hydraulic cylinder surface (5b).

3. Hydraulic drive system (1) according to any of the preceding claims, wherein a delivery volume of the hydraulic drive system (1) is controlled by a specific adjustment parameter.

4. Hydraulic drive system (1) according to any of the preceding claims, wherein the first hydraulic cylinder surface (5a) and the second hydraulic cylinder surface (5b) are different.

5. Hydraulic drive system (1) according to any of the preceding claims, wherein the first hydraulic machine (2) and / or the second hydraulic machine (3) are / is selected from a group of pumps comprising at least one positive displacement pump, in particular an axial piston pump, radial piston pump or vane pump, gear pump, spindle pump and the like.

6. Hydraulic drive system (1) according to any of the preceding claims, wherein the first hydraulic machine (2) is connected to the first hydraulic cylinder surface (5a) of the hydraulic cylinder (5).

7. Hydraulic drive system (1) according to claim 1, wherein the preloaded reservoir (6) has a pressure in a fluctuation range preferably of 22 bar, more preferably of 14 bar.

8. Hydraulic drive system (1) according to any of claims 1 to 7, wherein the first hydraulic machine (2) and / or the second hydraulic machine (3) have / has at least one high-pressure connection.

9. Method (10) for adjusting a delivery volume in a hydraulic drive system (1) comprising a first hydraulic machine (2) and a second hydraulic machine (3) according to any of claims 1 to 8, the method comprising the following steps: - determining (S1) an area ratio between a first hydraulic cylinder surface (5a) and a second hydraulic cylinder surface (5b) of a hydraulic cylinder (5) of the hydraulic drive system (1); - determining (S2) a target delivery volume of the corresponding first hydraulic machine or second hydraulic machine (3) having an adjustable delivery volume; - determining (S3) a first adjustment parameter of the corresponding first hydraulic machine (2) or second hydraulic machine (3); and - adjusting the delivery volume of the corresponding first hydraulic machine (2) or second hydraulic machine (3) of the hydraulic drive system (1) using the determined first adjustment parameter.

10. Method according to the immediately preceding method claim, wherein the method comprises the following further step: - testing (S4) the corresponding first hydraulic machine (2) or second hydraulic machine (3) on a test bench and / or by means of a test run to determine whether the adjusted delivery volume corresponds to the area ratio of the hydraulic cylinder (5).

11. Method according to any of the preceding method claims, wherein the delivery volume is adjusted by setting an adjustment element using the determined first adjustment parameter, and wherein the adjustment element is preferably fixed via a counter element.

12. Method according to the immediately preceding method claim, wherein the adjusting element comprises at least one threaded spindle, as a threaded bolt or as a threaded screw.

13. Hydraulic drive system (1) according to any of claims 1 to 8, for controlling a hydraulic cylinder (5) at a constant total pressure in the hydraulic drive system (1) .