EP4621247A1

EP4621247A1 - Computer-implemented method for controlling an electro-hydraulic drive network

Info

Publication number: EP4621247A1
Application number: EP24164075.4A
Authority: EP
Inventors: Lasse Schmidt; Mikkel VAN BINSBERGEN-GALÁN
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2024-03-18
Filing date: 2024-03-18
Publication date: 2025-09-24
Also published as: WO2025196047A1

Abstract

The invention relates to a computer-implemented method for controlling an electro-hydraulic drive network, the network comprising n hydraulic cylinders (10, 12) each having two chambers (20, 22, 24, 28), n-1 chamber short-circuiting's between the cylinder's chambers, and n+1 displacement units (14, 16, 18),
the method comprises generating a signal for the displacement units (14, 16, 18), wherein the signals for the displacement units (14, 16, 18) are generated from a representation of an aimed rod velocity,
wherein the representation of the aimed rod velocity is determined using a piston speed reference and system level active damping functions for each of the n hydraulic cylinders (10, 12),
wherein the system level active damping functions describe the influence of the hydraulic cylinders (10, 12) on the oscillatory behavior of the mounting system.

Description

The invention relates to the field of designing control systems for electro-hydraulic drive networks, especially for excavators.

State of the Art

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.
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 regulate the direction, pressure, and flow rate of the fluid.
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.
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.
However, the use of valves in an electro-hydraulic drive network leads to inherent losses and therefore to low-energy efficiency.
An electro-hydraulic drive network without valves may comprise n hydraulic cylinders, wherein some chambers of the hydraulic cylinders are short-circuited with n-1 chamber short-circuiting's, and wherein the electro-hydraulic drive network contains n+1 displacement units.
Any displacement unit may be a fixed displacement unit.
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 pumps and hydraulic motors, both of which maintain a constant output flow rate under varying conditions.
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.
However, the displacement units must be controlled individually, but not independently. Because of the short-circuiting's the pressures of the volumes connected to the displacement units is divided to all the chambers of these hydraulic cylinders that are short-circuited.
This means that the coupling between the hydraulic cylinders must be considered when controlling the electro-hydraulic drive network. It is not possible to control individual cylinders without further ado.
In other words, if a displacement unit is activated to increase the pressure in a chamber that is short-circuited to another chamber, another displacement unit must be used to equalize the pressure in the second chamber and compensate for the actuation of the second hydraulic cylinder.
When mechanical systems move, such as an excavator comprising an electro-hydraulic drive network as described above, oscillations can occur due to various factors inherent in the system's design, operation, or external influences. Oscillations refer to repetitive, back-and-forth movements around a central equilibrium point or position. These oscillations can manifest in different forms, such as vibrations, fluctuations, or periodic motions, depending on the specific characteristics of the system and the nature of the forces acting upon it.
One common cause of oscillations in mechanical systems is dynamic instability, which arises when the system's natural frequencies coincide with external excitation frequencies. For example, when a machine operates near its resonance frequency, small disturbances or inputs can amplify and sustain oscillations, leading to undesirable vibrations or motion. This phenomenon is known as resonance and can result in increased wear and tear on system components, reduced accuracy, and compromised performance.
Additionally, oscillations can occur due to unbalanced forces, uneven loading, or misalignment within the system. Imbalances in mass distribution, stiffness, or damping properties can introduce periodic fluctuations in motion, causing the system to oscillate around its equilibrium position. These oscillations can lead to excessive wear, fatigue, and premature failure of mechanical components, compromising the system's reliability and safety.
Furthermore, external factors such as environmental conditions, operating conditions, or interactions with neighboring systems can also induce oscillations in mechanical systems. For instance, wind gusts, ground vibrations, or interactions with adjacent machinery can introduce disturbances that trigger oscillatory behavior. These external influences can exacerbate existing oscillations or introduce new oscillation modes, posing challenges for system stability, control, and performance.
Advanced control algorithms and feedback mechanisms play a crucial role in suppressing oscillations and maintaining system stability. Implementing closed-loop control systems that continuously monitor system parameters, such as pressure, flow rate, and position, enables real-time adjustment of hydraulic actuators to counteract oscillations and maintain desired performance levels. By actively regulating hydraulic parameters, control systems can effectively mitigate the impact of external disturbances and dynamic instabilities, ensuring smooth and precise operation of the hydraulic system.
However, when an electro-hydraulic drive network with several hydraulic cylinders and short-circuited chambers is used, known damping algorithms reach their limits. Due to the dependence of the pressures in the chambers of the hydraulic cylinders, the control of displacement units for an oscillation-free movement of the hydraulic cylinders is difficult.
Thus, the problem of the invention is to provide a method for controlling an electro-hydraulic drive network with multiple hydraulic cylinders having short-circuited chambers, which reduces oscillation within the system housing said electro-hydraulic drive network.
The problem is solved by the objects of the independent claims.

Disclosure of the invention

According to a first aspect of the invention, the problem is solved by a computer-implemented method for controlling an electro-hydraulic drive network. The network comprises n hydraulic cylinders each having two chambers, n-1 chamber short-circuiting's between the cylinder's chambers, and n+1 displacement units, wherein n is equal to or greater than two.
Each hydraulic cylinder comprises a piston rod, which is moved by a pressure difference between the chambers of the corresponding hydraulic cylinder.
The method comprises generating a signal for the displacement units for increasing, decreasing or maintaining the pressure within the chambers of the hydraulic cylinders, wherein the signals for the displacement units are generated from a representation of an aimed rod velocity and a decoupling matrix D. The representation of the aimed rod velocity is determined using a piston speed reference and system level active damping functions for each of the n hydraulic cylinders, wherein the system level active damping functions describe the influence of the hydraulic cylinders on the corresponding hydraulic cylinder.
The short-circuited chambers are always chambers of different hydraulic cylinders. For example, a first hydraulic cylinder having a first chamber and a second chamber and a second hydraulic cylinder having a first chamber and a second chamber may be fluidly connected by a short-circuiting between the second chamber of the first hydraulic cylinder and the first chamber of the second hydraulic cylinder.
The decoupling matrix D maps the desired piston speed of each hydraulic cylinder of the electro-hydraulic drive network to the required signal input into the displacement units for increasing, decreasing or maintaining the current pressure within the connected volume. Using the decoupling matrix D is essential since the hydraulic cylinders are fluidically coupled by the short-circuiting, but they should be individually controllable.
The oscillation behavior of hydraulic systems is more complex the more hydraulic components are used in the system. Other aspects, such as the size and use of the system, also influence the oscillation behavior. The aim of this invention is to dampen the oscillation behavior caused by the work of the hydraulic cylinders.
For this purpose, the oscillation behavior of the electro-hydraulic drive network is broken down into individual components, which can be expressed by the system level active damping functions.
Decoupling these components enables the control system to counteract the oscillation behavior and dampen oscillations by effectively controlling the individual hydraulic cylinders via the displacement units. The invention thus solves its problem.
In an embodiment, the short-circuited chambers form a single common volume, wherein the not-short-circuited chambers form individual volumes, wherein the pressure within each volume is monitored by a pressure sensor.
As the volumes of the chambers are partially connected to each other via the short circuits, it is sufficient to control and record the pressures in the volumes. Ordinary but suitable pressure sensors can be used for recording the pressures within the volumes.
In an embodiment, the load pressure of each hydraulic cylinder is determined from the monitored pressures of the volumes.
Load pressure refers to the pressure exerted by the hydraulic system on the load being acted upon by hydraulic actuators. This pressure level is directly related to the force required to move or manipulate the load and is influenced by factors such as the size of the load, the resistance encountered, and the hydraulic system's operating conditions. Load pressure is typically measured at the point where the hydraulic actuator interfaces with the load, such as at the cylinder piston or hydraulic motor output shaft. In applications such as lifting, pushing, or pulling heavy loads, the hydraulic system must generate sufficient load pressure to overcome resistance and perform the desired work effectively.
The pressure sensors can only measure the pressure within each volume. Thus, the load pressures cannot be measured directly. Therefore, the measured pressures must be converted to the load pressures.
In an embodiment, the system level active damping functions are based on high pass filtering with a filter frequency associated with one of the hydraulic cylinders' natural frequency, respectively.
Systems can oscillate at several frequencies, which can amplify each other. The damping can be effectively increased by filtering the relevant frequencies.
In an embodiment, the system level active damping functions are functionalities for each hydraulic cylinder, wherein each functionality comprises the ratio of the Laplace frequency and the gain to the sum of the Laplace frequency and the filter frequency of the respective filter each corresponding to one of the hydraulic cylinders.
In the context of the transfer function of a system, the gain is often defined as the ratio of the amplitude of the output signal to the amplitude of the input signal. It therefore represents the factor by which the signal is amplified or attenuated by the system. A gain greater than 1 means an amplification of the signal, while a gain less than 1 represents an attenuation of the signal.
In an embodiment, additionally a sum pressure of the electro-hydraulic drive network is used for generating signals for the displacement units.
The sum pressure is the pressure acting upon the whole electro-hydraulic drive network. It may be derived from adding up all load pressures.
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 chambers of the companion cylinder is fluidly connected to a first chamber of the corresponding hydraulic cylinder and wherein the second chamber of the companion cylinder is fluidly connected to a second chamber of the corresponding hydraulic cylinder, wherein the companion cylinder and the corresponding hydraulic cylinder are treated as one hydraulic cylinder by applying rules for parallel connections for hydraulic cylinders.
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.
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.
By distributing the load among multiple cylinders, each cylinder experiences a reduced load, minimizing wear and extending the service life of the components.
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 an 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.
In another aspect, the invention relates to an excavator comprising an electro-hydraulic drive network, wherein the electro-hydraulic drive network is operated with a method as described above.
In another aspect, the invention relates to a computer program comprising program code, for executing a method as described above when the computer program is executed on a computer.
In another aspect, the invention relates to a computer-readable medium containing program code of a computer program to execute a method as described above when the computer program is executed on a computer.
In another aspect, the invention relates to a system for controlling an electro-hydraulic drive network, wherein the system is configured to execute a method as described above.
In summary, a computer-implemented method for controlling an electro-hydraulic drive network, an excavator using said method, a computer program, a computer-readable medium containing program code and a system for running said method are presented.
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.

Brief description of the drawings

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.
Other embodiments and many of the advantages mentioned will be apparent with reference to the drawing. The elements shown in the drawing are not necessarily shown to scale with respect to each other.
The figure shows:

Fig. 1: a schematic overview of an electro-hydraulic drive network and its control system.

In the figure of the drawing, identical reference signs denote identical or functionally identical elements, parts, or components, unless otherwise indicated.
Fig. 1 shows a schematic overview of an electro-hydraulic drive network and its control system. The electro-hydraulic drive network comprises two hydraulic cylinders 10, 12, and three displacement units 14, 16, 18. The hydraulic cylinders each comprise a first chamber 20, 22 and a second chamber 24, 26. The hydraulic cylinders 10, 12 are short-circuited, wherein the short-circuiting is realized by a fluidic connection between the first chamber 20 of the first hydraulic cylinder 10 and the second chamber 26 of the second hydraulic cylinder 12.
The second chamber 24 of the first hydraulic cylinder 10 forms a first volume. The first chamber 20 of the first hydraulic cylinder 10 and the second chamber 26 of the second hydraulic cylinder 12 form a common second volume 28. The first chamber 22 of the second hydraulic cylinder 12 forms a third volume.
The volumes each are connected to a displacement unit 14, 16, 18 and a pressure sensor 30, 32, 34. The positions of the pistons of each hydraulic cylinder 10, 12 is monitored by position sensors 36, 38 respectively. Furthermore, displacement unit 18 is connected to a flexible fluid volume 40 for equalizing the fluid volume within the electro-hydraulic drive network.
The electro-hydraulic drive network is controlled by a control system 42 on which a control software 44 is executed. The control software 44 comprises several modules 46, 48, 50, 52.
The position data measured by the position sensors 36, 38 are sent to a first module 42, which represents a motion controller. The module also uses piston speed references coming from another software or some external operator input 54. The first module 46 uses the input 54 and the position data to provide a general motion control for the positions.
The pressure data received from the pressure sensors 30, 32, 34 is input to the second module 48. The second module 48 uses the pressure data to derive a load pressure for every hydraulic cylinder 10, 12 in the electro-hydraulic drive network. The load pressures are then transmitted to the third module 50.
The third module 50 also receives the output of the first module 46 and the position data measured by the position sensors 36, 38. The third module 50 generates piston speed references, which will be used as target values for controlling the displacement units 14, 16, 18.
The system level active damping functions are included in generating the piston speed references. For each hydraulic cylinder 10, 12 the system level active damping functions are used to generate damped pressures from the load pressures and the functionalities of the system level active damping functions. Then the position data and the generated damped pressures are used to derive the piston speed references.
In the fourth module 52, the decoupling matrix D is used to derive electric motor shaft speed references for the electric motors 56, 58, 60, which are coupled to the displacement units 14, 16, 18 to control them. Thus, the signal for the electric motors 56, 58, 60 lead to a damped actuation of the hydraulic cylinders.

Claims

Computer-implemented method for controlling an electro-hydraulic drive network, the network comprising n hydraulic cylinders (10, 12) each having two chambers (20, 22, 24, 28), n-1 chamber short-circuiting's between the cylinder's chambers, and n+1 displacement units (14, 16, 18), wherein n is equal to or greater than two,
wherein each hydraulic cylinder (10, 12) comprises a piston rod, which is moved by a pressure difference between the chambers (20, 22, 24, 26) of the corresponding hydraulic cylinder (10, 12),

the method comprises generating a signal for the displacement units (14, 16, 18) for increasing, decreasing or maintaining the pressure within the chambers (20, 22, 24, 26) of the hydraulic cylinders (10, 12), wherein the signals for the displacement units (14, 16, 18) are generated from a representation of an aimed rod velocity and a decoupling matrix D,

wherein the representation of the aimed rod velocity is determined using a piston speed reference and system level active damping functions for each of the n hydraulic cylinders (10, 12),

wherein each system level active damping function describes the influence of the hydraulic cylinders (10, 12) on the corresponding hydraulic cylinder (10, 12).
Computer-implemented method according to claim 1, wherein the short-circuited chambers (20, 26) form a single common volume (28), wherein the not-short-circuited chambers (22, 24) form individual volumes, wherein the pressure within each volume is monitored by a pressure sensor (30, 32, 34).
Computer-implemented method according to claim 2, wherein the load pressure of each hydraulic cylinder (10, 12) is determined from the monitored pressures of the volumes.
Computer-implemented method according to claim 3, wherein the system level active damping functions are based on high pass filtering with a filter frequency associated with one of the hydraulic cylinders (10, 12), respectively.
Computer-implemented method according to claim 5, wherein the system level active damping functions are functionalities for each hydraulic cylinder (10, 12), wherein each functionality comprises the ratio of the Laplace frequency and the gain to the sum of the Laplace frequency and the filter frequency of the respective filter each corresponding to one of the hydraulic cylinders (10, 12).
Computer-implemented method according to one of the previous claims,
wherein additionally a sum pressure of the electro-hydraulic drive network is used for generating signals for the displacement units (14, 16, 18).
Computer-implemented method according to one of the previous claims, wherein one or more of the hydraulic cylinders (10, 12) 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 a first chamber (20, 22) of the corresponding hydraulic cylinder (10, 12) and wherein the second chamber of the companion cylinder is fluidly connected to a second chamber (24, 26) of the corresponding hydraulic cylinder (10, 12),
wherein the companion cylinder and the corresponding hydraulic cylinder (10, 12) are treated as one hydraulic cylinder by applying rules for parallel connections for hydraulic cylinders.
Excavator comprising an electro-hydraulic drive network, wherein the electro-hydraulic drive network is operated with a method according to one of the previous claims.
Computer program comprising program code, for executing a method according to one of the claims 1 to 7 when the computer program is executed on a computer.
Computer-readable medium containing program code of a computer program to execute a method according to one of the claims 1 to 7 when the computer program is executed on a computer.
System for controlling an electro-hydraulic drive network, wherein the system is configured to execute a method according to one of the claims 1 to 7.