Patent Publication Number: US-11384778-B2

Title: Electro-hydrostatic actuator system

Description:
The present invention relates to an electrohydrostatic actuator system and in particular an electrohydrostatic actuator system having two movable shafts. 
     Electrohydrostatic actuator systems are widely known in the prior art, wherein usually only one consumer is operated by an actuator. If several consumers are used in the system, then several actuators are required in the prior art. 
     Once several consumers are simultaneously operated with one or more parallel pump units, the volume flow takes the path of least resistance and the consumers, e.g., the shafts, move in an undefined manner, resulting in an uncontrollable system. 
     Furthermore, for using several actuators, a constant pressure system may be provided. This constant pressure system is fed either continuously or non-continuously through a pump line, wherein if peak powers are required, they are output via an accumulator system. However, such a system consumes much energy and manifests sluggish control, therefore requiring improved actuator systems. 
     Based on this prior art, it is thus an object of the present invention to at least partially overcome or improve upon the disadvantages of the prior art. 
     The object is achieved with a device according to claim  1 . Preferred embodiments and modifications are the subject matter of the subclaims. A method according to the invention for using the system according to the invention is specified in claims  15  and  16 . 
     The electrohydrostatic actuator system according to the invention comprises a volume-variable and/or rotational-speed-variable hydro machine, which is driven by an electric motor, for providing a volume flow of a hydraulic fluid, and a main shaft which is movable by the hydraulic fluid and which has at least one first chamber, wherein the first chamber, with at least one first main hydraulic line and a first main valve, is hydraulically connected to the hydro machine via a connection line. 
     The actuator system according to the invention further comprises a secondary shaft which is movable by the hydraulic fluid and which has at least one first chamber, wherein the first chamber, with at least one first secondary hydraulic line and a first secondary valve, is hydraulically connected to the hydro machine via a connection line. 
     Furthermore, according to the invention, a hydraulic accumulator is hydraulically connected to the first secondary hydraulic line in the area between the first chamber of the secondary shaft and the first secondary valve. 
     According to the invention, an electrohydrostatic actuator system is accordingly provided which has a volume-variable or rotational-speed variable hydro machine which is driven by an electric motor and has a main shaft and a secondary shaft, each having at least one chamber. The at least one chamber of the main and secondary shafts is in each case hydraulically connected to a main or secondary hydraulic line and via a main or secondary valve to the hydro machine. A hydraulic accumulator, which is hydraulically connected to the secondary hydraulic line, is arranged between the chamber of the secondary shaft and the secondary valve. 
     Electric motors are known in the prior art and serve to drive the hydro machine. 
     The hydro machine is volume-variable and/or rotational-speed-variable and can preferably provide two possible flow directions of the hydraulic fluid in the closed hydraulic circuit during operation. The hydro machine may further comprise either an electric motor with variable rotational speed and a fixed displacement pump, or an electric motor with constant rotational speed and a variable displacement pump, or an electric motor with variable rotational speed and a variable displacement pump. The selection of the hydro machine is in this case determined by factors such as system costs, reliability, permitted noise emission or efficiency. 
     The shafts of the actuator system according to the invention are movable, wherein the movement is preferably provided by hydraulic fluid entering or exiting the chambers and the pressure buildup or pressure reduction associated therewith. 
     For example, in one embodiment according to the invention, the main shaft may be a reshaping shaft and the secondary shaft may be a clamping shaft. In this case, a workpiece to be machined is clamped by the clamping shaft and (re)shaped by the reshaping shaft. However, according to further embodiments, the shafts may also have further functions. 
     According to a further embodiment of the actuator system according to the invention, the main shaft and/or the secondary shaft is preloaded mechanically and in particular with a spring system and/or a weight system. 
     In this case, it is particularly advantageous to use the shafts for the same process flow and not for different functions which are not correlated with one another. Namely, if the functions are connected to one another, the present invention is particularly advantageous since a process requiring two shafts can be controlled by means of a single hydro machine, as explained in more detail later. 
     The terms “main shaft” and “secondary shaft” are not to be understood as meaning that one of the shafts is more important than the other but rather serve only to distinguish the shafts; in particular, both shafts can also perform an identical function, such as the clamping of a workpiece. 
     Both the main shaft and the secondary shaft have at least one first chamber into which hydraulic fluid can flow. The chambers are each hydraulically connected via a line and via a valve to a connection of the hydro machine. The hydro machine operated by the electric motor thus provides a hydraulic fluid flow into the respective first chambers of the main and secondary shafts, which causes a movement of the shafts to occur. 
     The arrangement of the hydraulic accumulator in the first secondary hydraulic line in the area between the first chamber of the secondary shaft and the first secondary valve is advantageous in this embodiment according to the invention. Through the arrangement of the hydraulic accumulator according to the invention, the hydraulic fluid in the hydraulic accumulator is also loaded by the loading of the hydraulic fluid of the secondary shaft so that the pressure of the hydraulic fluid in the first chamber of the secondary shaft corresponds to the pressure of the hydraulic fluid in the hydraulic accumulator. 
     It is thus possible, by closing the secondary valve, to maintain the pressure in the area of the first chamber of the secondary shaft and in the secondary hydraulic line by means of the hydraulic accumulator without requiring the hydro machine for pressure maintenance. 
     Accordingly, after the secondary shaft has been loaded, the hydro machine can be used for loading or for controlling the primary shaft. Thus, the primary shaft can be operated by means of the same hydro machine, wherein in particular both shafts can work in parallel by means of a single hydro machine. 
     The use of a single hydro machine for the parallel control of two shafts is advantageous since it leads both to savings in effort and savings in cost. Furthermore, a reduction of the required devices occurs, which in turn leads to a minimization of potential failures and/or damage. 
     In a further embodiment according to the invention, the hydraulic fluid is preloaded in the connection lines. The preloading may be provided, for example, by means of a further hydro machine, a pressure accumulator or the like. 
     In this case, the connection lines are the lines which hydraulically connect the main or secondary valve to the connections of the hydro machine. In this case, preloading the connection lines is advantageous since a certain pressure thus always prevails in the system; accordingly, hydraulic fluid does not have to be continuously loaded from a completely relieved state to the desired state, which in turn leads to substantial savings in energy. The pressure in the connection lines can be 10 bar, for example. The main reason for preloading is to ensure a minimum pressure in the two actuator chambers and thus to avoid cavitation even in the event of a great pressure drop, for example in the event of rapid pressure changes and movements. 
     Furthermore, in a further embodiment according to the invention, the first secondary hydraulic line can be hydraulically connected to a drain line and a safety valve and/or a 2-way valve, in particular a drain valve. 
     The pressure in the secondary hydraulic line, and accordingly the pressure of the first chamber of the secondary shaft and the pressure of the hydraulic accumulator, can be relieved by the drain line. 
     Such a drainage system can correspondingly also be used and arranged in the main hydraulic line. Accordingly, the drain lines of the main hydraulic line and of the secondary hydraulic line may also be the same. Within the meaning of the invention, it is also the case that the hydraulic fluid relieved in the drain line flows into a tank where it can be used for further purposes. In this case, the tank can be the same tank which serves for feeding hydraulic fluid into the system, whereby a closed system is provided. Furthermore, cleaning, venting and/or cooling devices can also be connected to the drain line so that, for example, the hydraulic fluid is vented before it is fed back into the system. 
     The connection line can also be arranged in such a way that it serves only for relieving the hydraulic accumulator, while the first chamber of the secondary shaft is relieved by means of a further line, for example by means of the connection line, which is also connected to the tank. It is thus possible to precisely control where the pressure is to be relieved. 
     It is also within the meaning of the invention that the hydro machine can be used for relieving the chambers of the main and/or secondary shaft. For example, the hydro machine may provide a hydraulic fluid flow from one of the chambers into the tank by displacement. 
     In a further embodiment according to the invention, the first chamber of the main shaft and the first chamber of the secondary shaft are hydraulically connected to the same connection line of the hydro machine. 
     The further connection line of the hydro machine can, for example, be hydraulically connected to the tank from which the hydraulic fluid for loading the actuator system is taken. 
     Only by adjusting the main or secondary valve is it thus possible to set the chamber in which a hydraulic fluid flow is provided by the hydro machine. For this purpose, it is advantageous and a further embodiment according to the invention that the first main valve and/or the first secondary valve are controlled valves. In particular, it is advantageous if both valves are controllable since improved and more accurate actuator control is thus made possible and the process sequences can thus be controlled more easily. The secondary valve can also be a continuous valve in further embodiments according to the invention so that a local constant pressure system is produced by the hydraulic accumulator and the valve. 
     Controlling can occur in any way known in the prior art, such as by means of electrically controlled valves. 
     In a further embodiment according to the invention, the main shaft has at least one second chamber, wherein the second chamber, with at least one second main hydraulic line and a second main valve, is hydraulically connected to the hydro machine via a connection line. 
     In a further embodiment of the actuator system according to the invention, the secondary shaft also has at least one second chamber, wherein the second chamber, with at least one second secondary hydraulic line and a second secondary valve, is hydraulically connected to the hydro machine via a connection line. 
     In the embodiments in which the shafts have at least two chambers, the main shaft and the secondary shaft may be selected from a group including, for example, differential cylinders, common-mode cylinders, telescoping cylinders, and similar cylinders. The choice of shaft type is dependent on the function the shafts must perform; for example, the main shaft may be a differential cylinder if the shaft is used in a press. The main shaft and the secondary shaft do not necessarily have to be designed as the same type of cylinder. 
     If both the main shaft and the secondary shaft each have a second chamber, then, in a further embodiment according to the invention, the second chamber of the main shaft and the second chamber of the secondary shaft are hydraulically connected to the same connection line of the hydro machine, wherein the connection line is different from the connection line to which the first chamber of the main and secondary shafts is hydraulically connected. 
     It is advantageous if the respective second chambers of the shafts are connected to the same line since fewer lines are thus used and the system can be operated in a simplified manner. 
     In a further embodiment according to the invention, the second main valve and/or the second secondary valve are controlled valves. 
     As already is the case with the first main valve and the first secondary valve, the controllability of the second main and/or secondary valves offers improved control of the entire system, whereby the efficiency of the system can be improved and can thus be operated in a more energy-saving and cost-saving manner. 
     In a further embodiment of the actuator system according to the invention, at least one of the controlled valves can be released by means of a control valve. 
     In a further embodiment of the actuator system according to the invention, at least one of the control valves is hydraulically connected to at least one of the connection lines of the hydro machine by means of non-return valves. 
     This means that the circuits of the control valves for the main and/or secondary valves are hydraulically connected to the connection lines of the hydro machine. Thus, hydraulic fluid which is in the system also flows through the circuits of the control valves, as a result of which no additional loading and in particular no additional independent control circuit is required. 
     A method for operating the electrohydrostatic actuator system according to the invention according to one of the described embodiments is also claimed. In such a method according to the invention, the main shaft and the secondary shaft are operated in parallel or sequentially by the same hydro machine. 
     This is an advantageous method compared to the methods known from the prior art since in particular the parallel operation of the shafts by means of a single hydro machine brings about several already mentioned advantages. 
     The parallel operation of the shafts generally consists of several steps. First, the secondary shaft is loaded by means of the hydro machine, wherein the hydraulic accumulator or the hydraulic fluid in the hydraulic accumulator is also loaded by the loading of the first chamber of the secondary shaft. 
     At a sufficient pressure in the first chamber of the secondary shaft, the connection to the hydro machine is interrupted by means of the secondary valve. Since the loaded hydraulic accumulator is connected to the chamber of the secondary shaft, the secondary shaft remains loaded. Accordingly, the hydro machine is used to provide a hydraulic fluid flow into the primary shaft. After the process, the shafts are relieved. 
     Not least, the use of an actuator system according to the invention by means of one of the methods described above is also claimed. In this case, the system can be used for reshaping molded parts, for deep-drawing molded parts, or by other similar methods in which an electrohydrostatic actuator system is required. 
     The invention is explained below on the basis of various exemplary embodiments, wherein it is pointed out that these examples encompass modifications or additions as they immediately arise for the person skilled in the art. 
    
    
     
       Shown are: 
         FIG. 1 : a schematic general representation of a system according to the invention; 
         FIG. 2 : a schematic representation of an exemplary embodiment of the system according to the invention according to  FIG. 1 ; 
         FIG. 3 : a schematic representation of an exemplary embodiment of the system according to the invention according to  FIG. 2 ; 
         FIG. 4 : a schematic representation of a further exemplary embodiment of the system according to the invention according to  FIG. 1 ; 
         FIG. 5 : a schematic representation of a further exemplary embodiment, wherein the secondary shaft is preloaded; 
         FIG. 6 : a schematic representation of a further exemplary embodiment of the system according to the invention according to  FIG. 5 ; 
     
    
    
       FIG. 1  shows a general arrangement of an exemplary embodiment of the actuator system  1  according to the invention with two movable shafts. 
     The exemplary embodiment of the actuator system  1  according to the invention has a volume-variable and/or rotational-speed-variable hydro machine  11 , which is driven by an electric motor  10 , for providing a volume flow of a hydraulic fluid. 
     The system  1  further comprises a main shaft  20  which is designed as a differential cylinder with a first chamber  22  and a second chamber  24 , wherein the first chamber  22  is hydraulically connected by a first main hydraulic line  52  and by a first connection line  12 , and the second chamber  24  is connected by a second main hydraulic line  54  and by a second connection line  14 , to a connection of the hydro machine  11  in each case. 
     A first and a second main valve  23  and  25  are arranged between the hydro machine and the first and second chambers  22 ,  24  of the main shaft  20 , respectively. These main valves are shown in  FIG. 1  as a controlled 2/2-way valve with a flow and a shut position. 
     Furthermore, as can be seen in  FIG. 1 , the exemplary embodiment of the actuator system  1  according to the invention comprises a secondary shaft  30  which also has a first chamber  32  and a second chamber  34 , wherein the first chamber  32  is hydraulically connected by a first secondary hydraulic line  62  and by the first connection line  12 , and the second chamber  34  is connected by a second secondary hydraulic line  64  and by the second connection line  14 , to a connection of the hydro machine  11  in each case. 
     In the present exemplary embodiment according to the invention, a valve assembly  90  and a hydraulic accumulator  40  are hydraulically connected to the secondary shaft  30 . Some embodiments of how the valve assembly  90  is designed are illustrated in the next figures. 
     In general, the arrangement should be such that it is possible to operate both the main shaft  20  and the secondary shaft  30  sequentially and/or in parallel by means of a single hydro machine  11 . It is, for example, important that, by means of the valve assembly  90 , a hydraulic fluid flow from the first and/or second chambers  32 ,  34  of the secondary shaft  30  toward or from the hydro machine  11  can be shut off as desired so that the hydro machine  11  acts mainly on the main shaft  20 . The valve assembly  90  should further be designed to allow the first and/or second chambers  32 ,  34  of the secondary shaft  30  to be relieved. 
     Furthermore, the system  1  has a source  80  and a preloading source  82 , which serve to preload the connection lines  12  and  14  of the hydro machine  11 . The hydro machine  11  is furthermore hydraulically connected to a tank  84  from which the hydro machine  11  extracts hydraulic fluid and feeds it into the system. 
     In this exemplary embodiment according to the invention, when one of the two first chambers  22  or  32  of the primary or secondary shaft  20 ,  30  is relieved, the hydraulic fluid flows into the preloading source  82  or the tank  84 . This can be done, for example, by means of the hydro machine  11  and/or, as shown in  FIG. 1 , by an additional line  98   a  which is connected to the tank  84  or the preloading source  82  by a releasable valve  92 , in this case a releasable non-return valve. 
     A further line  98   b  with a further releasable valve  94  serves both for hydraulically connecting the source  80  and the preloading source  82  to the hydro machine  11  and for relieving the second chamber  24 ,  34  of the main and/or secondary shaft  20 ,  30 . 
     Alternatively or additionally, a drain line  42  may be hydraulically connected to the tank  84  and to a releasable valve  43  at the connection of the hydraulic accumulator. According to further exemplary embodiments according to the invention, the hydraulic accumulator  40  may be relieved by means of the additional line  42  and the releasable valve  43 . 
       FIG. 2  shows an exemplary embodiment of the system according to the invention from  FIG. 1 . The general structure of the system  1  is unchanged. 
     The arrangement of the valves on the secondary shaft  30  is different. In particular, as can be seen in  FIG. 2 , the secondary shaft  30  is shown as a differential cylinder, wherein the arrangement of a synchronous cylinder is also conceivable. The secondary shaft  30  has a first chamber  32  and a hydraulic accumulator  40 , which is connected to the first chamber  32  by the first secondary hydraulic line  62 , and a second chamber  34 . 
     The valve assembly  90  comprises a secondary valve  33 , wherein the first chamber  32  and the second chamber  34  of the secondary shaft are hydraulically connected by the common secondary valve  33  to the hydro machine by the first secondary hydraulic line  62  or the second secondary hydraulic line  64 . 
     In the exemplary embodiment according to the invention of  FIG. 2 , the first secondary valve  33  is a 4/2-way valve  33  having a flow position and a shut position so that both the first secondary hydraulic line  62  and the second secondary hydraulic lines  64  are either open at the same time or shut off simultaneously. In the first case, the hydro machine  11  can operate directly in the two chambers  32 ,  34  of the secondary shaft  30  and in the hydraulic accumulator  40 . For example, the hydro machine  11  may provide a hydraulic fluid flow into the first chamber  32  of the secondary shaft  30  and into the hydraulic accumulator  40  so that the secondary shaft  30  is loaded as hydraulic fluid is withdrawn from the second chamber  34 . 
     In the second case, that is to say when the secondary valve  33  is brought into the shut position, the hydraulic connection of the secondary shaft  30  to the hydro machine  11  is interrupted by the valve  33 , wherein the secondary shaft  30  remains in a loaded state by the hydraulic accumulator  40 . The hydro machine  11  can accordingly act in this case in the primary shaft  20  while the secondary shaft remains in a loaded state. 
     If relieving the first and/or second chambers of the secondary shaft  30  is intended, the secondary valve  33  can be adjusted to flow and the valves  92  and/or  94  are released so that hydraulic fluid can flow into the preloading source  82 . 
     As in the exemplary embodiment of  FIG. 1 , the hydraulic accumulator  40  can be directly relieved into the tank  84  by means of a valve  43  and a drain line  42 . 
       FIG. 3  shows a similar exemplary embodiment according to the invention of the actuator system as  FIG. 2 , wherein the valve assembly  90  comprises, instead of a single secondary valve, a first secondary valve  33  arranged in the first secondary hydraulic line  62  and a second secondary valve  35  arranged in the second secondary hydraulic line  64 . 
     In this exemplary embodiment according to the invention, both the first and second secondary valves  33 ,  35  are controlled 2/2-way valves, each having a flow and a shut position. Thus, the loading and relieving of the first and/or second chambers  32 ,  34  of the secondary shaft can be controlled individually. 
       FIG. 4  shows an exemplary alternative embodiment of the system  1  according to the invention in accordance with one of the previous figures. 
     In this exemplary embodiment according to the invention of the actuator system  1 , the valve assembly  90  comprises a 4/3-way valve  33  which has a flow, cross-flow and shut position and which is arranged in both the first secondary hydraulic line  62  and the second secondary hydraulic line  64 , and a 2/2-way valve  35  which has a flow and shut position and which is arranged in a line connecting the hydraulic accumulator  40  and the secondary shaft  30  to the connection line  12 . 
     In particular, a drain line  94  is connected to the 4/3-way valve  33  so that, in the respective flow positions, either the first chamber  32  or the second chamber  34  of the secondary shaft  30  is connected to the drain line  94 . Furthermore, the drain line  94  is hydraulically connected to the tank  84  so that when the hydraulic fluid from one of the two chambers  32 ,  34  is relieved, it can flow directly into the tank  84 . 
     The second secondary valve  35  blocks the connection of the secondary shaft  30  and the hydraulic accumulator  40  to the connection line  12  and accordingly to the rest of the system  1 . 
     The hydraulic accumulator  40  can be relieved, for example, by means of the second secondary valve  35 , through the line  12 ,  98   a  and by releasing the valve  92  or, as shown in the previous figures, through an alternative line  42 . 
     As shown in  FIG. 5 , according to a further exemplary embodiment, the secondary shaft  30  may also be a preloaded cylinder instead of a differential cylinder. 
     The cylinder can be preloaded by means of a spring or also by means of a weight system, wherein the cylinder has at least one venting device in its preloaded chamber  34  so that the air can escape during the pressing process. 
     In this exemplary embodiment according to the invention, the valve assembly  90  comprises a 2-way valve  33  with a flow and a shut position; in this case, the first chamber  32  of the secondary shaft  30  is hydraulically connected to the connection line  12  and to the hydro machine  11  through the first hydraulic line  62  and the secondary valve  33 , respectively. 
     Furthermore, the pressure accumulator  40  is also hydraulically connected both to the secondary hydraulic line  62  and to the secondary valve  33 . For example, in order to relieve the first chamber  32  and the hydraulic accumulator  40 , the secondary valve  33  and the controlled valve  92  may be released so that the relieved hydraulic fluid flows into the preloading source  82 . Alternatively, in this exemplary embodiment according to the invention, the hydraulic accumulator  40  may also be hydraulically connected by a drain line  42  to a drain valve  43  in the tank  84 . In this embodiment, however, it is only possible to relieve the first chamber  32  at the same time as the hydraulic accumulator  40 . 
     In the exemplary embodiment according to the invention shown in  FIG. 6  by contrast, the first chamber  32  of the secondary shaft  30  and the hydraulic accumulator  40  can each be relieved individually or together by means of the selected valve assembly  90 . 
     In this case, the valve assembly  90  comprises a 3-way valve connected to the secondary hydraulic line, with a flow, a cross-flow and a shut position. Furthermore, the valve assembly comprises a second secondary valve  35  which, as in the previous example, is designed as a 2-way valve and connects the connection line  12  to the secondary shaft  30  and/or the hydraulic accumulator  40 . 
     When the second secondary valve  35  is shut and the first secondary valve  33  is switched to the cross-flow position, a connection between the first chamber of the secondary shaft and the tank  84  is established by means of a line  94 . In this case as well, the hydraulic accumulator  40  can be hydraulically connected to the tank  84  by a drain line  42  having a drain valve  43 ; thus, by shutting the first secondary valve  33  and opening the drain valve  43 , just the relieving of the hydraulic accumulator  40  can be achieved. 
     
       
         
           
               
             
               
                   
               
               
                 List of reference signs 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                  1 
                 Actuator system 
               
               
                   
                 10 
                 Electric motor 
               
               
                   
                 11 
                 Hydro machine 
               
               
                   
                 12 
                 First connection line 
               
               
                   
                 14 
                 Second connection line 
               
               
                   
                 20 
                 Main shaft 
               
               
                   
                 22 
                 First chamber of the main shaft 
               
               
                   
                 23 
                 First main valve 
               
               
                   
                 24 
                 Second chamber of the main shaft 
               
               
                   
                 25 
                 Second main valve 
               
               
                   
                 30 
                 Secondary shaft 
               
               
                   
                 32 
                 First chamber of the secondary shaft 
               
               
                   
                 33 
                 First secondary valve 
               
               
                   
                 34 
                 Second chamber of the secondary shaft 
               
               
                   
                 35 
                 Second secondary valve 
               
               
                   
                 40  
                 Hydraulic accumulator 
               
               
                   
                 42 
                 Drain line 
               
               
                   
                 43 
                 2-way drain valve 
               
               
                   
                 52 
                 First main hydraulic line 
               
               
                   
                 54  
                 Second main hydraulic line 
               
               
                   
                 62 
                 First secondary hydraulic line 
               
               
                   
                 64  
                 Second secondary hydraulic line 
               
               
                   
                 80 
                 Source 
               
               
                   
                 82  
                 Preloading source 
               
               
                   
                 84  
                 Tank 
               
               
                   
                 90 
                 Valve assembly 
               
               
                   
                 94  
                 Drain line 
               
               
                   
                 98a, 98b 
                 Drain lines