Electro-hydraulic drive network and excavator comprising a hydraulic drive network

Abstract

The invention relates to an electro-hydraulic drive network (10) comprising a first hydraulic cylinder (12), a second hydraulic cylinder (14) and a third hydraulic cylinder (16), wherein each hydraulic cylinder (12, 14, 16) having a first chamber (42, 50, 52) and a second chamber (44), wherein the first chamber (42) of the first hydraulic cylinder (12) is fluidly connected to the second chamber (44) of the second hydraulic cylinder (14) forming a first volume (40), wherein the second chamber of the first hydraulic cylinder (12) forms a second volume (46), wherein the first chamber (50) of the second hydraulic cylinder (14) is fluidly connected to the first chamber (52) of the third hydraulic cylinder (16) forming a third volume (48), wherein the second chamber of the third hydraulic cylinder (16) forms a fourth volume (54), wherein the electro-hydraulic drive network (10) further comprises displacement units (18, 20, 22, 24).

Description

[0001] Electro-hydraulic drive network and excavator comprising a hydraulic drive network

[0002] The invention relates to the field of electro-hydraulic drive networks, especially for excavators.

[0003] State of the Art

[0004] An electro-hydraulic drive network integrates electrical and hydraulic components to facilitate various tasks, including control, actuation, and power transmission. Structurally, it consists of electrical components such as power supplies, control devices like switches, relays, PLCs, and hydraulic components like hydraulic fluid, pumps, actuators, and valves.

[0005] The electrical components, starting with a power supply, generate control signals through devices such as relays, timers, and PLCs based on input parameters. These parameters could include sensor readings or operator commands. On the hydraulic side, hydraulic fluid serves as the medium for energy transmission, with pumps generating flow and pressure, while actuators, such as cylinders and motors, convert hydraulic energy into mechanical motion. Usually, valves may regulate the flow rate of the fluid.

[0006] Control logic, ranging from simple on-off control to more sophisticated proportional control systems, governs the operation of the electro-hydraulic network. This logic processes input signals and generates output commands to control hydraulic components. Communication interfaces, such as serial protocols or Ethernet, may also be present for integration with higher-level control systems or remote monitoring.

[0007] In summary, an electro-hydraulic drive network combines electrical and hydraulic systems to deliver efficient, precise, and reliable control over mechanical processes, making it indispensable in numerous industrial and mobile applications. Valves play a crucial role in regulating the flow, within an electro-hydraulic drive network. However, they can also be a source of various problems that affect the performance, efficiency, and reliability of the system.

[0008] However, the use of valves in an electro-hydraulic drive network leads to inherent losses and therefore to low-energy efficiency.

[0009] The problem to be solved by the invention is to provide an electro-hydraulic drive network, which has a higher energy efficiency.

[0010] The task is solved by the objects of the independent claims.

[0011] Disclosure of the invention

[0012] According to a first aspect of the invention, the problem is solved by an electro- hydraulic drive network comprising a first hydraulic cylinder, a second hydraulic cylinder and a third hydraulic cylinder. Each hydraulic cylinder has a first chamber and a second chamber. The first chamber of the first hydraulic cylinder is fluidly connected to the second chamber of the second hydraulic cylinder, forming a first volume.

[0013] The second chamber of the first hydraulic cylinder forms a second volume. The first chamber of the second hydraulic cylinder is fluidly connected to the first chamber of the third hydraulic cylinder forming a third volume and the second chamber of the third hydraulic cylinder forms a fourth volume. The electro- hydraulic drive network further comprises displacement units for controlling the first, second, third and fourth volumes.

[0014] The term “fluidly connected” refers to a method or mechanism through which hydraulic fluids are used to convey pressure between different components or parts of a system. Fluidic connections are integral components in hydraulic systems, where hydraulic fluids serve as a means of transmitting power.

[0015] Fluidic connections can also be found in pneumatic systems, where compressed air is used instead of hydraulic fluid for conveying signals or commands. In such systems, pneumatic lines and components facilitate the transmission of pressure signals for control purposes.

[0016] The cylinders used in this invention are differential cylinders. The piston rod moves according to the fluid pressure within the cylinder’s chambers. Each cylinder having a first and a second chamber. One of these chambers is the chamber also containing the piston rod. The other chamber is the opposite chamber. This configuration enables the cylinder to operate at a much faster speed during pushing motions, although its maximum force output is akin to that of a plunger cylinder. Manufacturing a differential cylinder is similar to producing a standard cylinder, with the addition of a specialized control mechanism.

[0017] Which of the chambers, the piston-side chamber or the opposite chamber, is the first or the second chamber, defines how the displacement units must be controlled to move the pistons to the desired position. The control system for the electro-hydraulic drive network must be set accordingly.

[0018] Known control circuits typically include valves and a piping system that, when the piston extends, direct the hydraulic fluid from the rod side to the opposite side of the piston’s chambers instead of returning it to the pump reservoir.

[0019] According to the invention, the electro-hydraulic drive network contains two hydraulic short-circuiting’s. One short-circuiting is realized between the piston first chamber of the first hydraulic cylinder and the second chamber of the second hydraulic cylinder. This results in a single control volume.

[0020] The second short-circuiting is realized between the piston side chambers of the first chambers of the second hydraulic cylinder and the first chamber of the third hydraulic cylinder. This results in another shared single control volume. The short-circuit connections may be realized directly between the appropriate cylinder chambers or via a manifold or similar and enables unobstructed (near loss-free) fluid flow between the given control volumes entailing nearly identical pressures in the short-circuited cylinder chambers.

[0021] The electro-hydraulic drive network therefore has a total of four volumes that must be controlled with displacement units. By cleverly positioning the displacement units, the number of valves required for this electro-hydraulic drive network can be greatly reduced, possibly even to zero. As this electro-hydraulic drive network requires fewer or no valves for its function, the susceptibility to the aforementioned problems with valves is reduced or completely prevented. The invention thus solves its problem.

[0022] In an embodiment, a first displacement unit is connected to the third volume.

[0023] The third volume consists of the volume of the first chamber of the second hydraulic cylinder and the first chamber of the third hydraulic cylinder. Therefore, the first displacement unit may move the rods of the second hydraulic cylinder and third hydraulic cylinder directly. However, the second chamber of the second hydraulic cylinder is fluidically connected to the first chamber of the first hydraulic cylinder. Thus, actuating the second hydraulic cylinder will influence the first volume and therefore, actuate the first hydraulic cylinder unless countermeasures are initiated.

[0024] In an embodiment, the first displacement unit is connected to a flexible fluid volume.

[0025] Any of the hydraulic cylinders comprises one chamber, in which the piston rod is located. When all hydraulic cylinders are extended to their maximum, the rods volumes must be replaced within the electro-hydraulic drive network. Otherwise, a negative pressure would prevent the rod from extracting to their maximum.

[0026] Usually, this is compensated by connecting the electro-hydraulic network to a fluid reservoir, from which the fluid may be taken. Therefore, the electro-hydraulic drive network is connected to the flexible fluid volume via the first displacement unit.

[0027] The first displacement unit’s task is primarily to regulate the available fluid within the electro-hydraulic drive network. Although, the network's control system must consider, that increasing the volume of fluid in the network via the first displacement unit will not only affect the first volume in the first chambers of the second and third hydraulic cylinder but also indirectly all other volumes. In an embodiment, a second displacement unit is connected to the first volume and the second volume.

[0028] The second displacement unit is configured to displace fluid from the second volume in the second chamber of the first hydraulic cylinder to the first volume, consisting of the volumes of the first chamber of the first hydraulic cylinder and the second chamber of the second hydraulic cylinder.

[0029] Thus, the second displacement unit can directly influence the position of the rod of the first hydraulic cylinder. But it may also have an impact upon the pressure in the second hydraulic cylinder due to the short-circuiting forming the first volume.

[0030] In an embodiment, a third displacement unit is connected to the third volume and to the first volume.

[0031] The third displacement unit is configured to influence the pressure within the first volume and the third volume, parts of which are the first chamber and the second chamber of the second hydraulic cylinder. Thus, the third displacement unit is suited to control the position of the rod of the second hydraulic cylinder.

[0032] But, since the first volume also consists of the first chamber of the first hydraulic cylinder and the third volume comprises the first chamber of the third hydraulic cylinder, the third displacement unit may or must be used to control the rods of all hydraulic cylinders.

[0033] In an embodiment, a fourth displacement unit is connected to the third volume and to the fourth volume.

[0034] The fourth displacement unit being connected to both chambers of the third hydraulic cylinder makes it suitable for controlling the position of the rod of the third hydraulic cylinder. However, the third volume also comprises the first chamber in the second cylinder. So, increasing the pressure within the third volume will result in not only moving the rod of the third hydraulic cylinder but also the rod of the second hydraulic cylinder. In an embodiment, the displacement units are fixed displacement units or variable displacement units.

[0035] The primary difference between fixed displacement units and variable displacement units lies in their methods of controlling hydraulic fluid flow and, consequently, output power.

[0036] Fixed displacement units operate by delivering a consistent volume of hydraulic fluid per revolution or stroke, regardless of the load or demand placed on them. This consistency in output flow rate ensures that the speed of the hydraulic cylinder or actuator it powers remains constant, assuming the load remains steady. Examples of fixed displacement units include fixed displacement hydraulic pumps and motors, both of which maintain a constant output flow rate under varying conditions.

[0037] On the other hand, variable displacement units offer the flexibility to adjust the volume of hydraulic fluid delivered per revolution or stroke. This adjustment can be achieved manually, hydraulically, or electronically, depending on the specific design and application requirements. By varying the displacement, variable displacement units can dynamically adjust the output flow rate and pressure of hydraulic fluid to match changing load or demand conditions. This adaptability enables more precise control over the speed and force of hydraulic actuators, leading to improved efficiency and performance across a range of applications. Variable displacement hydraulic pumps and motors are typical examples of such units.

[0038] While both fixed displacement units and variable displacement units are essential components of electro-hydraulic systems, their fundamental distinction lies in their ability to provide either a constant or adjustable flow of hydraulic fluid. This distinction directly influences the system's capacity to regulate speed, force, and overall efficiency.

[0039] In an embodiment, each of the displacement units is driven by an electric machine, wherein each of the electric machines is controlled by an electric drive. The control of a displacement unit by an electric machine, which includes an electric drive, involves several interconnected components and processes working together seamlessly.

[0040] At the heart of the system is the electric machine, typically an electric motor, which serves as the prime mover. The electric motor is powered by an electrical power source and is controlled by an electric drive system. The electric drive system consists of control electronics, such as inverters or motor drives, which regulate the electrical power supplied to the motor, allowing precise control over its speed, torque, and direction of rotation.

[0041] The electric drive system receives control signals from the higher-level control system, which could be a programmable logic controller (PLC), a computer, or another type of controller. These control signals are generated based on input parameters such as operator commands, sensor readings, or desired system behavior. Due to the short-circuiting’s within the electro-hydraulic drive network, the controlling system must consider all displacement units simultaneously.

[0042] When the electric motor rotates, it drives the displacement unit mechanically through a coupling or gearbox. The displacement unit generates hydraulic fluid flow and pressure, which are then directed to the chambers of the hydraulic cylinders.

[0043] The electric drive system modulates the speed and torque of the electric motor based on the system's requirements. For example, if the system needs to increase hydraulic flow or pressure, the electric drive system can increase the motor speed to drive the displacement unit faster. Conversely, if the system needs to reduce flow or pressure, the motor speed can be decreased accordingly.

[0044] Additionally, the electric drive system may incorporate feedback mechanisms to monitor and adjust the motor's performance in real-time. This feedback could come from sensors measuring parameters such as motor speed, current, temperature, or hydraulic system pressure. The control system uses this feedback information to dynamically adjust the motor's operation to maintain desired performance levels and respond to changing operating conditions. Overall, the control of a displacement unit by an electric machine in an electro- hydraulic drive network involves sophisticated coordination between electrical and hydraulic components, with the electric drive system playing a central role in regulating the motor's operation to meet the system's hydraulic power requirements accurately and efficiently.

[0045] In an embodiment, one or more of the hydraulic cylinders have at least one companion cylinder, wherein the companion cylinder comprises a first chamber and a second chamber, wherein the first chamber of the companion cylinder is fluidly connected to the first chamber of the corresponding hydraulic cylinder and wherein the second chamber of the companion cylinder is fluidly connected to the second chamber of the corresponding hydraulic cylinder.

[0046] Replacing a single hydraulic cylinder with a parallel connection of two or more hydraulic cylinders involves connecting multiple cylinders in parallel to achieve a combined output force or motion. This configuration offers several advantages in terms of increased force output, enhanced stability, and improved load distribution.

[0047] In a parallel connection setup, each hydraulic cylinder operates independently but simultaneously. Hydraulic fluid is supplied to all cylinders through a common manifold or hydraulic circuit, ensuring equal pressure distribution among the cylinders. As a result, the combined force output of the cylinders is equal to that of a single cylinder.

[0048] By distributing the load among multiple cylinders, each cylinder experiences a reduced load, minimizing wear and extending the service life of the components.

[0049] Parallel connection of hydraulic cylinders also enhances system stability and control. With multiple cylinders operating in unison, any imbalances or uneven loading are mitigated as the cylinders work together to maintain equilibrium. This results in smoother operation and reduced risk of mechanical stress or failure, particularly in applications with heavy or asymmetric loads. Furthermore, the parallel connection offers flexibility in system design and customization. Engineers can tailor the configuration by adjusting the number, size, and placement of cylinders to suit specific application requirements, such as desired force output, stroke length, or speed.

[0050] Additionally, redundancy is built into the system, providing a level of fault tolerance. In the event of a failure or malfunction in one cylinder, the remaining cylinders can continue to operate, ensuring uninterrupted performance and productivity.

[0051] In another aspect, the invention relates to an excavator comprising a hydraulic drive network as described above for operating a boom, a stick, and a bucket.

[0052] An excavator is a heavy construction machine used for digging, lifting, and moving large quantities of materials. In modern excavators, the movement of the boom, stick (also known as the arm), and bucket is typically controlled via hydraulic components.

[0053] The electro-hydraulic drive network in an excavator comprises three hydraulic cylinders and multiple displacement units, wherein the chambers of the hydraulic cylinders are short-circuited as described above. The displacement units are configured to generate hydraulic pressure, which is transmitted through hydraulic lines to the hydraulic cylinders and actuators located at different points on the excavator's structure.

[0054] The boom, stick, and bucket of the excavator are each connected to one of the hydraulic cylinders, which extend and retract to control their movement. The boom is the large arm that extends from the excavator's chassis and supports the stick and bucket assembly. The stick, or arm, is attached to the boom and can be extended or retracted to reach different distances. The bucket is attached to the end of the stick and is used for digging, lifting, and loading materials.

[0055] Control signals for the movement of the boom, stick, and bucket are generated by the operator through control inputs, such as joysticks or pedals, located in the excavator's cab. These control inputs are processed by the excavator's electronic control system, which translates them into hydraulic commands for the displacement units.

[0056] For example, when the operator moves a joystick to extend the boom, the control system sends a signal to the displacement units to increase hydraulic pressure in the corresponding hydraulic cylinder, causing it to extend and raise the boom. Similarly, movement of the stick and bucket is controlled by adjusting the hydraulic flow to the respective cylinders. However, due to the short-circuiting, the control of one displacement unit must consider the control of the remaining displacement units as well.

[0057] The electro-hydraulic drive network allows for precise control over the movement of the excavator's boom, stick, and bucket, enabling the operator to perform a wide range of tasks with accuracy and efficiency. Whether digging trenches, loading trucks, or excavating foundations, the excavator's electro-hydraulic system ensures smooth and responsive operation, making it an indispensable tool in construction, mining, and other heavy-duty industries.

[0058] An excavator comprising an electro-hydraulic drive network like described above does not use any or at least fewer valves, thus, reducing the disadvantages described at the beginning.

[0059] In yet another aspect, the invention relates to a method for operating the pistons of an electro-hydraulic drive network as described above, wherein each cylinder comprises a piston, wherein the pistons are moved by hydraulic pressure within the chambers of the cylinders, wherein the pressure is generated by the displacement units.

[0060] In summary, an electro-hydraulic drive network, an excavator incorporating said electro-hydraulic drive network and a method for operating an electro-hydraulic drive network are presented.

[0061] The described embodiments and further developments can be combined with each other as desired. Further possible embodiments, further developments and implementations of the invention also include combinations of features of the invention described above or below with respect to the embodiments that are not explicitly mentioned.

[0062] Brief description of the drawings

[0063] The accompanying drawings are intended to provide a further understanding of embodiments of the invention. They illustrate embodiments and, in connection with the description, serve to explain principles and concepts of the invention.

[0064] Other embodiments and many of the advantages mentioned will be apparent with reference to the drawings. The elements shown in the drawings are not necessarily shown to scale with respect to each other.

[0065] The figures show:

[0066] Fig. 1 a schematic view of the electro-hydraulic drive network according to an embodiment of the invention.

[0067] In the figures of the drawings, identical reference signs denote identical or functionally identical elements, parts, or components, unless otherwise indicated.

[0068] Fig. 1 shows an electro-hydraulic drive network 10. The electro-hydraulic drive network 10 comprises a first hydraulic cylinder 12, a second hydraulic cylinder 14 and a third hydraulic cylinder 16. It further comprises a first displacement unit 18, a second displacement unit 20, a third displacement unit 22 and a fourth displacement unit 24.

[0069] Each hydraulic cylinder 12, 14 and 16 comprises two chambers separated by a piston head 26, 28 and 30. The piston heads 26, 28 and 30 are moved by a pressure difference within the chambers of the hydraulic cylinders 12, 14 and 16. Furthermore, the piston heads 26, 28, 30 are connected to piston rods 32, 34 and 36, which are connected to a working system, e.g., a boom, a stick, and a bucket of an excavator (not shown). In Fig. 1 , the first chamber of each hydraulic cylinder is the left chamber, while the right chamber is always the second chamber containing the rods. However, in other embodiments, the first chamber of a hydraulic cylinder may house the rod and the second chamber is opposite to said first chamber.

[0070] The chambers of the hydraulic cylinders are short-circuited to form common volumes. A first volume 40 is formed by the first chamber 42 of the first hydraulic circuit 12 and the second chamber 44 of the second hydraulic cylinder 14. Of course, the volume within the lines between the chambers is technically part of the first volume 40, but it is neglected due to its size and for simplicity.

[0071] The second volume 46 is formed only by the second chamber of the first hydraulic cylinder 12.

[0072] The third volume 48 is formed by the first chamber 50 of the second hydraulic cylinder 14 and the first chamber 52 of the third hydraulic cylinder 16. The remaining second chamber of the third hydraulic cylinder 16 forms the fourth volume 54.

[0073] The first displacement unit 18 is connected to the third volume 48 and, thus, to the first chamber 50 of the second hydraulic cylinder 14 and the first chamber 52 of the third hydraulic cylinder 16. On the other side, the first displacement unit 18 is connected to the flexible fluid volume 38 to equalize the fluid volume within the electro-hydraulic drive network 10.

[0074] The second displacement unit 20 is connected to the first volume 40 and, thus, to the first chamber 42 of the first hydraulic cylinder 12 and the second chamber 44 of the second hydraulic cylinder 14 on one hand. On the other hand, the second displacement unit 20 is connected to the second chamber of the first hydraulic cylinder 12, which forms the second volume 46.

[0075] The third displacement unit 22 is connected to the first volume 40 and the second volume 48, and thus all corresponding chambers of all the three hydraulic cylinders 12, 14 and 16. The fourth displacement unit 24 is connected to the second chamber of the third hydraulic cylinder 16, which is the fourth volume. On the other side, the fourth displacement unit 24 is connected to the third volume 48 and the corresponding chambers of the second and third hydraulic cylinders 14 and 16 respectively.

Claims

Claims1 . Electro-hydraulic drive network (10) comprising a first hydraulic cylinder (12), a second hydraulic cylinder (14) and a third hydraulic cylinder (16), wherein each hydraulic cylinder (12, 14, 16) having a first chamber (42, 50, 52) and a second chamber (44, 46, 54), wherein the first chamber (42) of the first hydraulic cylinder (12) is fluidly connected to the second chamber (44) of the second hydraulic cylinder (14) forming a first volume (40), wherein the second chamber of the first hydraulic cylinder (12) forms a second volume (46), wherein the first chamber (50) of the second hydraulic cylinder (14) is fluidly connected to the first chamber (52) of the third hydraulic cylinder (16) forming a third volume (48), wherein the second chamber of the third hydraulic cylinder (16) forms a fourth volume (54), wherein the electro-hydraulic drive network (10) further comprises displacement units (18, 20, 22, 24) for controlling the first, second, third and fourth volumes (40, 46, 48, 54).

2. Electro-hydraulic drive network (10) according to claim 1 , wherein a first displacement unit (18) is connected to the third volume (48).

3. Electro-hydraulic drive network (10) according to claim 2, wherein the first displacement unit (18) is connected to a flexible fluid volume (38).

4. Electro-hydraulic drive network (10) according to one of the previous claims, wherein a second displacement unit (20) is connected to the first volume (40) and the second volume (46).

5. Electro-hydraulic drive network (10) according to one of the previous claims, wherein a third displacement unit (22) is connected to the third volume (48) and to the first volume (40).

6. Electro-hydraulic drive network (10) according to one of the previous claims, wherein a fourth displacement unit (24) is connected to third volume (48) and to the fourth volume (54).

7. Electro-hydraulic drive network (10) according to one of the previous claims, wherein the displacement units (18, 20, 22, 24) are fixed displacement units or variable displacement units.

8. Electro-hydraulic drive network (10) according to one of the previous claims, wherein each of the displacement units (18, 20, 22, 24) is driven by an electric machine, wherein each of the electric machines is controlled by an electric drive.

9. Electro-hydraulic drive network (10) according to one of the previous claims, wherein one or more of the hydraulic cylinders (12, 14, 16) have at least one companion cylinder, wherein the companion cylinder comprises a first chamber and a second chamber, wherein the first chambers of the companion cylinder is fluidly connected to the first chamber of the corresponding hydraulic cylinder (12, 14, 16) and wherein the second chamber of the companion cylinder is fluidly connected to the second chamber of the corresponding hydraulic cylinder (12, 14, 16).

10. Excavator comprising a hydraulic drive network (10) according to one of the previous claims for operating a boom, a stick and a bucket.11 . Method for operating the pistons of an electro-hydraulic drive network (10) according to one of the claims 1 to 9, wherein each hydraulic cylinder (12, 14, 16) comprises a piston, wherein pistons are moved by hydraulic pressure within the chambers (42, 44, 50, 52) of the hydraulic cylinders (12, 14, 16), wherein the pressure is generated by the displacement units (18, 20, 22, 24).

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