Electro-hydraulic compact drive for rotational movements

Abstract

The invention relates to an electro-hydraulic compact drive for underwater use and for driving an output element - for example, a propeller (40), a wheel, or a cable winch. For this purpose, the compact unit comprises as components a hydraulic motor (31), which has an output shaft (37), a hydraulic pump (30), by means of which the hydraulic motor can be supplied with a hydraulic fluid via a working line (32), and an electric motor (50), by means of which the hydraulic pump can be driven. The aim of the invention is to design such an electro-hydraulic drive so as to be particularly suitable for underwater use. This is achieved by an electro-hydraulic compact drive in which the components are located in a closed container (12) filled with a hydraulic fluid, and the container has an opening for coupling the output shaft of the hydraulic motor to the output element.According to the invention, the electro-hydraulic compact drive thus forms a closed unit which contains the complete Electric motor / hydraulic pump / hydraulic motor arrangement. The compact drive combines the advantages of the high power density of hydraulics with a decentralized electric Direct drive. A high degree of reliability, safety, and energy efficiency are achieved. The handling of the drive is simplified, thus also simplifying the control of underwater vehicles and machines.

Description

Electro-Hydraulic Compact Drive for Rotational Movements Description The invention relates to an electro-hydraulic compact drive which is used particularly, but not only, for underwater use and for rotarily driving an output element, e.g., a propeller, a wheel, or a cable winch. For this purpose, the compact unit comprises as components a hydraulic motor, which has an output shaft, a hydraulic pump, which can supply a hydraulic fluid to the hydraulic motor via a working line, and an electric motor, which can drive the hydraulic pump. For many underwater activities in connection with the extraction of fossil energy, such as oil and gas, with the mining of natural resources, with the natural sciences, with robotics using remote operated vehicles (ROV's) or automated underwater vehicles (AUV's), with infrastructure measures, or with renewable energies, special machines and equipment with underwater systems that can drive and control in this difficult environment are required. Many underwater devices must be equipped with a controllable drive system or several controllable drive systems, which are also called thrusters. In most cases, these thrusters have a propeller as output element. Especially, underwater robots, such as ROV's or AUV's, require a thruster or several thrusters, e.g., eight thrusters, in order to make possible the necessary movability of the robot in all six degrees of freedom. The output element does not necessarily have to be a propeller. Rather, the output element can also be a wheel that stands on the ocean floor or that drives a chain, as is the case, for example, in an underwater mining vehicle. Moreover, the compact drive can also drive a cable winch that serves to position ships or underwater devices. Mooring, anchoring, compensating for the motion of the sea, or tensioning a chain underwater are mentioned as examples. Devices specifically provided for operating underwater must function safely and reliably. The popular solution is to use hydraulic motors, which can be supplied by a common hydraulic pump with a hydraulic fluid via electrically controlled underwater valves, for driving output elements. Such a device is known from GB 2 181 040 A. If 1 the pump fails, the underwater robot or the underwater device can no longer be moved and must be brought up for repair immediately. In order to be able to compensate for the movements and currents of the water, an underwater drive moreover needs a dynamic control system. At the same time, the drive is to work with minimal energy consumption at all times. These two requirements for high dynamics and for energy efficiency can be realised only with difficulty with the systems outlined above. Moreover, the requirements for functional safety increase in order to be able to work safely even under complex application conditions. By way of example for functional safety, a safely reduced speed when approaching an object is mentioned here. An electro-hydraulic drive that is provided for underwater use and in which a hydraulic pump driven by an electric motor and a hydraulic motor are interconnected in a closed hydraulic circuit is known from DE 29 24 364 A1. The hydraulic motor drives a propeller, which constitutes the output element. A total of three electro-hydraulic drives of the aforementioned type, which serve to move the device underwater or to move parts of the device relative to a device frame, are arranged on a scraper. The aim of the invention is to design an electro-hydraulic drive that is provided for underwater use and that comprises as components a hydraulic motor, which has an output shaft, a hydraulic pump, which can supply a hydraulic fluid to the hydraulic motor via a working line, and an electric motor, which can drive the hydraulic pump, such that the electro-hydraulic drive is particularly suitable for underwater use. This aim is achieved by an electro-hydraulic compact drive, in which the components are located in a closed container filled with a hydraulic fluid and in which the container has an opening for coupling the output shaft of the hydraulic motor to the output element. According to the invention, the electro-hydraulic compact drive thus forms a closed unit which contains the complete electric motor / hydraulic pump / hydraulic motor arrangement. The compact drive combines the advantages of the high power density of hydraulics with a decentralized electric direct drive. A high degree of reliability and safety are achieved. The handling of the drive is simplified. The electric motor, which is coupled to the hydrostatic transmission formed by the hydraulic pump and the hydraulic motor, can be a small, lightweight, and compact electric motor running at high rotational speeds. Advantageously, the electric motor can be driven at variable rotational speed. 2 In order to achieve particularly high dynamics of the drive, the stroke volume of the hydraulic pump can, advantageously, be adjusted. Preferably, the stroke volume of the hydraulic motor can also be adjusted, since the dynamics and energy efficiency of the electro-hydraulic drive can be further increased thereby. It is expedient when an electrical control for supplying power to the electric motor is arranged in the container. Advantageously, the electrical control is equipped with a computing power and programmed with algorithms for operating the components or is suitable for being programmed with algorithms for operating the components. It is advantageous if the hydraulic motor can also be operated as a hydraulic pump, the hydraulic pump can also be operated as a hydraulic motor, and the electric motor, driven by the hydraulic pump working as a hydraulic motor, can also be operated as a generator. Then, driven by a propeller or a wheel, electrical energy can be recovered and stored in a battery for later use. For this purpose, algorithms for recovering and storing energy are integrated into the electrical control. The compact drive can contain an electronic control module with an installed functionality for dynamically controlling the position of a vehicle equipped with the drive. The control module can be an integral module of the electronic vehicle control system. Preferably, sensors - particularly sensors such as sensors for the pressure in the hydraulic circuit, for the rotational speed, for the position, for the speed, for the acceleration, for the temperature, and for the condition, e.g., for the degree of contamination of the hydraulic fluid, and for the water depth - particularly, micro-electro-mechanical sensors (MEMS) - are integrated into the electro-hydraulic compact drive. By monitoring the temperature, it can be avoided that the drive fails when it is operated in an environment with extreme temperatures, such as can prevail above the surface of the water. The stroke volume of the hydraulic units can be detected by means of sensors. For particularly good controllability, the rotational speed of the components can likewise be detected by means of sensors. An algorithm can be implemented, by means of which the output moment of the hydraulic motor is limited, in order to prevent damage to the output element - particularly, a propeller. An algorithm can also be implemented, by means of which the pressure in the hydraulic circuit is increased, in order to free the propeller from an object that has been caught in it. 3 Control functions for automatically compensating for external interferences, such as water currents or opposite forces when activating an actuator, can be integrated. For example, the accelerations at the drives are measured by means of sensors. The propellers are then driven in such a way that the forces along the orientation axis of the propeller are reduced as much as possible by producing opposite forces of the same magnitude. Algorithms for condition monitoring, such as an operating hours counter and monitoring of the torque and vibration, can likewise be integrated. Algorithms for maximising the dynamics and efficiency can be integrated. An electro-hydraulic compact drive according to the invention advantageously has at least one communication interface for exchanging data with or without a cable. Safety functions can be integrated as closed control circuits into the electronic control. The following safety functions are, in particular, conceivable: a) Safe torque off (STO): When the electrical control receives an emergency stop command via the communication interface, the electric motor, and thus also the hydraulic pump and the hydraulic motor, are turned off (de-energized). The propeller will stop after an uncontrolled period of time and an uncontrolled travel. b) Safe stop 1 and 2 (SS1 and SS2): When the electrical control receives a certain command (e.g., “SS1” or “SS2” messages) via the communication interface, the electric motor, and thus also the hydraulic pump and the hydraulic motor, are controlled such that the propeller is stopped after a controlled maximum period of time and a controlled maximum travel. c) Safe maximum speed / safe limited speed (SMS / SLS): The electrical control adjusts the rotational speed of the propeller with appropriate sensors (e.g., rotational speed sensors) such that the rotational speed does not exceed the maximum value provided by the communication interface. If this value is exceeded, the electric motor is turned off. In addition to the maximum rotational speed, the control can adjust a temporary reduced speed, in order to allow a certain 4 delicate movement, for example. This function makes possible driving up close to an object, for example. d) Safe direction (SDI): When the electrical control receives a command via the communication interface to safely drive in a certain rotational direction, this rotational movement of the propeller is monitored by means of a sensor. If the wrong rotational direction is indicated, the electric motor is turned off - in order to drive out of a dangerous area, for example. e) Safe maximum torque (SMT): The torque of the propeller is adjusted by an appropriate sensor or by appropriate sensors (e.g., a pressure sensor and a stroke volume sensor). If the torque exceeds the maximum value specified, the electric motor is turned off. f) Safe holding system in alignment with the propeller axis: The external forces acting on the drive are measured by means of an acceleration sensor, and the electric motor is controlled such that an opposite force is produced in order to thereby hold the position. If the acceleration nonetheless exceeds the specified value, another safety function is activated, such as “safe direction” or “safe torque off”. By arranging several, variously oriented compact drives on an underwater robot (e.g., AUV or ROV), and by combining these functions, the position of the robot can be controlled, and held in several directions. g) Safe communication (SCO): The transmission of safety-relevant data, such as commands or parameters, via the communication interface is monitored by means of appropriate error detection methods. If an error is detected, the electrical control initiates a safety function, e.g., “safe torque off”. The electro-hydraulic compact drive can have at least one interface, via which the hydraulic fluid can be refilled or changed underwater. Advantageously, electrical or mechanical interfaces of an electro-hydraulic compact drive according to the invention can be disconnected underwater. This allows a diver or a robot (remotely operated vehicle or autonomous underwater vehicle) to replace a compact drive. 5 Expediently, the electro-hydraulic compact drive has a filter or several hydraulic filters, with or without status sensors, in order to prevent too high a contamination of the hydraulic fluid with water or particles, for example. The status sensors can indicate whether the hydraulic fluid needs to be changed. For use at greater depths, the container of an electro-hydraulic compact drive has a movable compensation piston, which limits the internal space of the container with a first surface and is subjected to ambient pressure on a second surface, which is as large as and opposite the first surface. If an additional force in the direction of the internal space of the container is also exerted on the compensation piston by, for example, a spring, the pressure inside the container is always somewhat greater than outside the container, so that no water can enter. By monitoring the position of the compensation piston, leakage of the hydraulic fluid outwards can be detected. On a device to be moved, a set of at least two electro-hydraulic compact drives according to the invention can be arranged, wherein the movement of the device is realised by operating the electro-hydraulic compact units in a coordinated fashion, with or without a higher-level control. If a vehicle is equipped with several electro-hydraulic compact drives according to the invention, i.e., a set of electro-hydraulic compact drives according to the invention, it is possible by means of an intelligent algorithm or control circuit to compensate as much as possible for the failure of one compact unit by operating the other compact units. An exemplary embodiment of an electro-hydraulic compact drive according to the invention, a set of eight electro-hydraulic compact drives according to the invention, and various output options are illustrated in the drawings. The invention is now explained in more detail with reference to the figures of these drawings. The drawings show: Figure 1 - the exemplary embodiment as a drive of a propeller, Figure 2 - a set of eight electro-hydraulic compact drives according to the invention, Figure 3a-3d - various output options, and Figure 4 - the exemplary embodiment as a drive of a cable winch. 6 From the electro-hydraulic compact drive 10 according to figure 1, only one electrical cable 11 leads to the ocean surface or another higher-level electrical control located underwater. The electro-hydraulic compact drive has a container 12 with an internal space 1, which is closed off from the environment and filled with a hydraulic fluid as working medium. The container is pressure-compensated with respect to the ambient pressure prevailing underwater by means of a compensation device 25. To this end, a lid 17 is mounted using a flange 16 on a flat rim 15 surrounding an opening 14 in the container wall, and a membrane 18 is tightly clamped between the flat rim 15 and the lid 17. In the lid 17 are located holes 19, so that the space between the membrane and the lid is part of the environment and filled with seawater. The internal space 13 is thus sealed off against the environment by means of the membrane 18. The membrane is subjected to the pressure in the internal space on its first surface facing the internal space and to the pressure prevailing in the environment on its second surface, which faces the lid 17 and is as large as the first surface, and tries to always take a position and shape in which the sum of all forces acting on it is zero. So that the pressure in the internal space 13 is slightly greater than the ambient pressure, the membrane 18 is subjected to the internal pressure in addition to the ambient pressure by a spring 20 that is tensioned between a dimensionally stable, central membrane disc 21 and the lid 17. Taking into account the size of the pressure-loaded surfaces of the membrane, the force of the spring 20 is selected such that the pressure in the internal space is, for example, between 50 kPa to 200 kPa (between 0.5 bar to 2 bar) higher than the ambient pressure. On the membrane disc 21 is mounted a rod 22, which is guided in the lid 17, can be provided with a solid measure, and can be part of a sensor that detects the position of the centre of the membrane 18. According to the exemplary embodiment, the rod 22 protrudes beyond the membrane disc 21 into the internal space 13 of the container 12 and is provided with a solid measure there. A position sensor 56 detects the position of the rod 22, and thus of the membrane 18, and sends a corresponding signal to the electrical control unit 51. Then, contact of the solid measure and of the position sensor 56 with seawater is avoided, and reliability is increased. All mechanical, electric, and hydraulic components required or advantageous for controlling the electro-hydraulic compact drive 10, except for the source of the electrical power and of higher-level electrical control signals, are accommodated in the internal space 13 of the container 12. 7 The internal space 13 of the container 12 contains a hydraulic pump 30 and a hydraulic motor 31, which are connected to each other via two working lines 32 and 33 and are arranged together in a closed hydraulic circuit. The stroke volume of both the hydraulic pump 30 and the hydraulic motor 31 can be adjusted. In particular, the stroke volume of the hydraulic motor can be adjusted between a maximum value and zero, or close to zero. The hydraulic pump 30 is always driven in the same direction, and its stroke volume can be adjusted between a maximum positive value and a maximum negative value. Accordingly, the working line 32 is the high-pressure line and the working line 33 is the low-pressure line, or vice versa, depending upon in which direction the hydraulic pump is adjusted from a neutral or zero position. By adjusting the hydraulic pump to above zero while maintaining the rotational direction of the electric motor and of the hydraulic pump, the rotational direction of the hydraulic motor can thus be reversed. The pressure prevailing in the working line 32 is detected by a pressure sensor 34. Accordingly, the pressure prevailing in the working line 33 can also detected by a pressure sensor. In the working line 33 is located a throttle 35, parallel to which is connected a device 36 for separating the water contained in the hydraulic fluid, which is usually oil. As a result of the throttle 35, a portion of the hydraulic fluid flowing back from the hydraulic motor 31 to the hydraulic pump 30 flows through the separating unit 36, so that a portion of the oil flowing back is always cleaned. The device 36 can also be combined with a filter, in order to clean the hydraulic fluid of solid particles. The hydraulic motor 31 has an output shaft 37, which can be coupled in a rotationally fixed manner with a propeller 40 located outside the container 12 and forming the output element of the electro-hydraulic drive. A central drive shaft 41 of the propeller is tightly guided through a wall of the container 12 and connected inside to the output shaft 37 of the hydraulic motor 31. The rotational speed of the output shaft of the hydraulic motor and of the drive shaft of the propeller is detected by a rotational speed sensor 42 arranged inside the container. The hydraulic pump 30 is driven by an electric motor 50, the rotational speed of which can be controlled and which is connected for this purpose to an electrical control unit 51, which is also accommodated in the internal space 13 and connected via the cable 11 conducted out of the container 12 in a sealed fashion to an electrical energy source on the ocean surface, and possibly also to a higher-level electrical control arranged 8 underwater. The rotational speed of the electric motor 50 and of the hydraulic pump 30 is detected by a rotational speed sensor 52 and processed by the control unit 51. With the exception of the already mentioned sensors, a temperature sensor 53 for detecting the temperature of the hydraulic fluid in the container and an acceleration sensor 54 for detecting the accelerations of the compact drive are also provided. The electric motor 50 can also be operated as a generator, the hydraulic pump 30 can also be operated as a hydraulic motor, and the hydraulic motor 31 can also be operated as a hydraulic pump, which hydraulic motor, driven by the propeller as a pump, provides hydraulic fluid to the pump 30 working as a hydraulic motor. The pump 30 working as a hydraulic motor can in turn drive the electric motor 50 as a generator. In this way, electrical energy can be recovered from a rotational movement of the propeller and stored in a battery, for example. The compact drive also contains an electronic control module 55, which module is a component of a control with which a vehicle is controlled that comprises the compact drive and which module has an installed functionality for dynamically controlling the position of the vehicle. Compared to the exemplary embodiment shown, variations of an electro-hydraulic system according to the invention are also possible. The container has two interfaces 56, which serve to refill or change hydraulic fluid underwater. The electrical control comprises, in the simplest form, a direct current motor, an electrical control device with appropriate analogue and digital input and output interfaces, and a suitable power supply. The electrical control comprises, in an advanced form, a three-phase alternating current motor with an appropriate drive and frequency converter, an electrical control device with appropriate analogue and digital input and output interfaces, and a suitable power supply and network interfaces - both LAN, bus systems and fibre optic cables or wireless LAN. In addition to the voltage supply, the electrical cable also comprises the electrical signals for the control communication, such as desired values, current values, and error messages. 9 A condition monitoring of the electro-hydraulic system can be implemented in the electrical control, in which all sensor signals are analysed with appropriate algorithms implemented in the form of software. In case of a fault, the control can autonomously bring the compact drive into a safe non-operating state and inform the higher-level control. To this end, preventative and reactive maintenance measures can be communicated to the higher-level control. Figure 2 shows a set of eight electro-hydraulic compact drives 10 according to the invention, each of which is designed in the same way as the electro-hydraulic compact drive of figure 1, and all of which are located on the same underwater vehicle. The electrical controls 51 of the compact drives are connected to a central master control 60, which controls the individual compact drives in accordance with the movement pattern specified for the vehicle. Two of the compact drives are responsible for opposite movements of the vehicle along an x-axis. Two other compact drives are responsible for opposite movements of the vehicle along a y-axis. Another compact drive is responsible for a movement of the vehicle in the direction of a z-axis, wherein it is assumed that a movement in the one direction of the z-axis takes place as a result of gravity. Of the three other compact drives, one is responsible for rotations about the x-axis, one for rotations about the y-axis, and one for rotations about the z-axis. In the case of a failure of one or more of the electro-hydraulic compact drives 10 shown in figure 2, the failure is compensated for as much as possible by an intelligent algorithm or control circuit, so that essential motion sequences are still performed in cases of emergency. Of the four output options shown in figure 3, the one according to figure 3a corresponds to the one shown in figures 1 and 2. A propeller 40 is driven directly by a hydraulic motor via a central drive shaft 41. Figure 3b shows a propeller 40, the central drive shaft 41 of which is indeed arranged in parallel to the output shaft 37 of a hydraulic motor, but at a distance from the shaft 37. The output shaft of the hydraulic motor and the drive shaft of the propeller are coupled with each other via a traction drive. 10 According to the embodiment according to figure 3c, an individual wheel 61 can also be driven directly by the hydraulic motor of an electro-hydraulic compact drive according to the invention. According to figure 3d, the wheel can be part of a crawler track. Figure 4 shows a cable winch 62, which is driven directly by the hydraulic motor 31 via a central drive shaft 41. Typical control algorithms for controlling a cable winch are then implemented in the electrical control unit, in order to control the position of a ship or an underwater machine, for example, or to move an actuator or lower or raise a load. Cable winches are used on ships for many applications. It is advantageous, in many applications, to implement algorithms for compensating for the motion of the sea (heave compensation system). Overall, an electro-hydraulic compact drive according to the invention with low total operating costs is thus created, which compact drive has high energy efficiency, high reliability, and a high degree of safety, is easy to maintain, and offers high performance. As a result of the compact construction, a reduction in the weight of the entire drive system, compared to a modular construction, is achieved. A compact drive according to the invention is therefore particularly suitable for use in new vehicles and machines for deep sea, such as underwater robots, ROV's and AUV's, or underwater machines for raw material extraction, for example, which are thus technically and economically more feasible. List of reference symbols 10 compact drive 11 electrical cable 12 container 13 internal space of 12 14 opening 15 flat rim of 12 16 flange 17 lid 18 membrane 19 holes in 17 20 spring 11 21 membrane disc 22 rod with solid measure 25 pressure compensation device 30 hydraulic pump 31 hydraulic motor 32 working line 33 working line 34 pressure sensor 35 throttle 36 separating device 37 output shaft of 31 40 propeller 41 drive shaft 42 rotational speed sensor 50 electric motor 51 electrical control unit 52 rotational speed sensor 53 temperature sensor 54 acceleration sensor 55 electronic control module 56 position sensor 60 electrical control 61 wheel 62 cable winch 12 Claims 1. Electro-hydraulic compact drive (10) for underwater use and for driving an output element (40, 61, 62), with a hydraulic motor (31) as a component, which has an output shaft (37), with a hydraulic pump (30) as a component, which can supply a hydraulic fluid to the hydraulic motor (31) via a working line (32), and with an electric motor (50) as a component, which can drive the hydraulic pump (30), characterised in that the components (30, 31, 50) are located in a closed container (12) filled with a hydraulic fluid and that the container (12) has an opening for coupling the output shaft (37) of the hydraulic motor (31) to the output element (40, 61, 62). 2. Electro-hydraulic compact drive according to claim 1 or 2, wherein the rotational speed of the electric motor (50) can be controlled. 3. Electro-hydraulic compact drive according to claim 3, wherein an electrical control (51) for supplying power to the electric motor (50) is arranged in the container (12). 4. Electro-hydraulic compact drive according to claim 4, wherein the electrical control (51) is equipped with a computing power and programmed with algorithms for operating the components (30, 31, 50) or is suitable for being programmed with algorithms for operating the components. 5. Electro-hydraulic compact drive according to claim 3 or 4, wherein the hydraulic motor (31) can also be operated as a hydraulic pump, the hydraulic pump (30) can also be operated as a hydraulic motor, and the electric motor (50), driven by the hydraulic pump working as a hydraulic motor, can also be operated as a generator, and wherein algorithms for recovering and storing energy are integrated into the electrical control (51). 6. Electro-hydraulic compact drive according to one of the preceding claims, wherein the stroke volume of the hydraulic pump (30) can be adjusted. 7. Electro-hydraulic compact drive according to one of the preceding claims, wherein the stroke volume of the hydraulic motor (31) can be adjusted. 13 8. Electro-hydraulic compact drive according to one of the preceding claims, wherein sensors (34, 42, 53, 54) - particularly, sensors for the pressure, rotational speed and position, speed and acceleration, and temperature and water depth - particularly, micro-electro-mechanical sensors (MEMS) - are integrated. 9. Electro-hydraulic compact drive according to one of the preceding claims, wherein control functions for automatically compensating for external interferences, such as water currents or opposite forces when activating an actuator, are integrated. 10. Electro-hydraulic compact drive according to one of the preceding claims, wherein it has at least one communication interface for exchanging data with or without a cable. 11. Electro-hydraulic compact drive according to one of the preceding claims, wherein safety functions are integrated as closed control circuits. 12. Electro-hydraulic compact drive according to one of the preceding claims, wherein algorithms for condition monitoring are integrated. 13. Electro-hydraulic compact drive according to one of the preceding claims, wherein algorithms for controlling a cable winch are integrated. 14. Electro-hydraulic compact drive according to one of the preceding claims, wherein it has at least one interface (56), via which hydraulic fluid can be refilled or changed underwater. 15. Electro-hydraulic compact drive according to one of the preceding claims, wherein its electrical or mechanical interfaces can be disconnected underwater. 16. Electro-hydraulic compact drive according to one of the preceding claims, wherein it has a hydraulic filter and / or a device (36) for separating contaminations by water or dirt particles from the hydraulic fluid, with or without status sensors. 14 17. Electro-hydraulic compact drive according to one of the preceding claims, wherein the container (12) has a movable compensation piston (18), which limits the internal space (13) of the container (12) with a first surface and is subjected to ambient pressure on a second surface, which is as large as and opposite the first surface. 18. Set of at least two electro-hydraulic compact drives according to one of the preceding claims, wherein the electro-hydraulic compact units (10) are arranged on a device to be moved and wherein the movement of the device is realised by operating the electro-hydraulic compact units (10) in a coordinated fashion, with or without a higher- level control (60). 19. Set of at least two electro-hydraulic compact drives according to claim 18, wherein an intelligent algorithm or control circuit compensates as much as possible for the failure of one compact unit (10) by operating the other compact units (10) (fault- tolerant control system). 15 1 / 4 2 / 4