Patent Publication Number: US-10323657-B2

Title: System for improving the energy efficiency in hydraulic systems

Description:
FIELD OF THE INVENTION 
     The invention relates to a system for improving the energy efficiency in hydraulic systems. At least one working cylinder operates as a consumer of hydraulic energy in one operating state and as a generator of hydraulic energy in another operating state. A hydraulic accumulator can be charged by the working cylinder for storing energy in one operating state of the working cylinder, and can be discharged for delivering energy to the working cylinder in another operating state. 
     BACKGROUND OF THE INVENTION 
     Given the increasing scarcity of resources and the increased efforts to save energy associated therewith, systems of the type described above are becoming increasingly important. For this reason, such systems are frequently used in hydraulic equipment and systems, in which actuators in the form of working cylinders are provided. In the case of raising and lowering applications, the potential energy of a load that has been lifted can thereby be converted into hydraulic energy by the working cylinder, which energy can be stored and fed back. Such a system can also be used for load compensation. 
     In the relevant systems of this kind from the prior art, the efficiency of the energy conversion leaves something to be desired. One reason for this problem is the dependency of the charging and discharging processes of the hydraulic accumulator on the respective system pressure. More specifically, the hydraulic accumulator can only be charged when the system pressure is greater than the gas pressure present in the accumulator on the gas side. If the system pressure cannot be established in the respective operating situation of the working cylinder, it will not be possible to acquire energy in the accumulator. The discharging process of the accumulator is thus subject to limitation if energy from the accumulator can only be fed back when the accumulator pressure is greater than the current system pressure. An additional problem is that, in the case of an accumulator pressure that is greater than the current, needed system pressure at the working cylinder, the pressure level of the accumulator and the system needs to be balanced by valves. The energy, which is latent in the differential pressure between the accumulator pressure and the system pressure, is then lost as a result of throttling losses. 
     DE 100 06 013 A1 discloses a device for saving energy in hydraulically actuated work equipment through the use of a piston accumulator. In the known solution, a fluid control has a control device, by which the piston accumulator can be connected to, or disconnected from, a fluid circuit of the work equipment. The control device has a monitoring device for such switching operations, which monitoring device at least detects system conditions of the work equipment and/or of the piston accumulator. The device for saving energy then is only used when an actuation of the work equipment appears to be necessary during normal operation. Special operations with the machine, in which the work machine is completely unloaded or very heavily loaded, are not hindered. A favorable energy conversion is thereby achieved with the known solution. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide an improved system of the type under consideration that allows an even more favorable energy conversion. 
     This object is basically achieved according to the invention by a system, which has at least one hydraulic accumulator providing an adjustment option. The accumulator provides a plurality of pressure chambers, which are adjacent to active surfaces of different sizes on the fluid side of the accumulator piston. An adjustment assembly is provided, which adjustment assembly connects a selected pressure chamber or a plurality of selected pressure chambers of the piston accumulator to the working cylinder, depending on the respective prevailing pressure level on the gas side of the piston accumulator and at the working cylinder. This arrangement provides the possibility of recycling energy regardless of the pre-charge pressure on the gas side of the accumulator and independently of the respective load pressure, because the respective desired pressure level at the accumulator can be used for charging or discharging by selecting an active surface of the appropriate size. An optimal energy conversion is thereby possible for all operating states. 
     In addition, the use of such a “multi-step accumulator” allows influencing the loading time by selecting the effective surfaces. If a small surface is selected at a constant volume flow for example, this situation will result in a short loading time of the accumulator. If a large surface is selected at a constant volume flow, this situation will result in a longer loading time. A finer or coarser pressure gradation can be obtained by forming a larger or smaller number of pressure chambers of different effective piston surfaces. More than one accumulator having different pressure chambers could also be provided to achieve particularly high degrees of resolution. 
     In an especially advantageous manner, a control logic unit may be associated with the adjustment assembly, which logic unit processes the signals from sensor devices for the control of the valves associated with the adjustment assembly. The sensor devices display or provide a signal representative the pressure level on the gas side of the piston accumulator and the respective operating state of the working cylinder. The logic unit thereby controls the energy transformation by deciding how the accumulator should be charged or discharged based on the load condition at the working cylinder and the load condition at the accumulator. In so doing, the user can influence the logic unit by entering his own presets, and thereby, determine the load characteristic of the system. 
     With regard to the construction of the piston accumulator, advantageously the accumulator piston is configured as a step piston for the formation of active surfaces of different sizes. The piston has partial piston surfaces that are adjacent to cylinder surfaces on the fluid side thereof. The accumulator housing has corresponding mating surfaces that are adjacent to cylinder surfaces. The mating surfaces together with partial piston surfaces associated therewith each delimit separate pressure chambers. 
     Active surfaces on the accumulator piston and mating surfaces on the accumulator housing are preferably disposed at an axial spacing to one another. The active surfaces and mating surfaces may be provided in the form of annular surfaces or circular surfaces, which are disposed concentrically to the longitudinal axis. 
     In terms of controlling the pressure chambers of the piston accumulator, advantageously the adjustment assembly has selector valves, by which the respective pressure chambers of the piston accumulator, which are selected for charging or discharging, can be connected to the working cylinder, and the remaining pressure chambers can be connected to the tank. Controlled by the control logic unit, a selected pressure chamber or a combination of selected pressure chambers can be connected to the working cylinder for charging or discharging. Non-selected pressure chambers can be emptied without pressure to the tank during the discharging of the active pressure chamber, and refilled from the tank during the charging of the active pressure chambers. 
     In terms of the supply of signals to the control logic unit, advantageously the associated sensor device has at least pressure sensors, which provide signals to the control logic unit. Those signals indicate the filling pressure on the gas side of the piston accumulator and the system pressure at the working cylinder. In addition, a position sensor is preferably provided at the working cylinder, which signals the piston position and/or piston speed of the working cylinder. 
     In especially advantageous embodiments, the adjustment assembly comprises a main line that is connected to the pressure side of a hydraulic pump, as well as connecting lines that run therefrom to the fluid ports of the piston accumulator. These connecting lines can each be selectively blocked, released or connected to the tank by the switching valves. 
     Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the drawings, discloses preferred embodiments of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring to the drawings that form a part of this disclosure: 
         FIG. 1  is a highly schematic, side view in section of an exemplary embodiment of a hydropneumatic piston accumulator in a multi-stage design for use in the system according to the invention; 
         FIG. 2  is a schematic diagram that shows the piston accumulator from  FIG. 1  in conjunction with associated system components of the system according to an exemplary embodiment of the invention; 
         FIG. 3  is a hydraulic diagram of the piston accumulator of  FIG. 1  in conjunction with a system for a raising and lowering application according to a first exemplary embodiment of the invention; and 
         FIG. 4  is a hydraulic circuit diagram of the piston accumulator of  FIG. 1  in conjunction with a system for a raising and lowering application according to a second exemplary embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The hydropneumatic piston accumulator  1 , which is shown in a schematic, simplified depiction in  FIG. 1 , has an accumulator piston  5  that is axially movably guided in an accumulator housing  3 . The accumulator piston  5  separates a gas side  7 , on which a filling port  9  is located, from fluid-side pressure chambers in the accumulator housing  3 . The accumulator piston  5  is configured in the manner of a step piston such that, in combination with corresponding stepped portions of the accumulator housing  3 , the accumulator piston delimits fluid-side pressure chambers  19 ,  21 ,  23  and  25 , which are adjacent to active surfaces  11 ,  13 ,  15  and  17  of different sizes on the fluid side of the accumulator piston  5 . In  FIG. 1 , these active surfaces  11 ,  13 ,  15  and  17  are arranged in order from the largest surface to the smallest surface. Here, the active surfaces  11 ,  13  and  15  are each formed by annular surfaces disposed concentrically relative to the longitudinal axis, which surfaces surround the inner-most active surface  17  in the form of a circular surface. Pressure chambers  19 ,  21  or  23 , respectively, which are adjacent to the active surfaces  11 ,  13  and  15 , are delimited by mating surfaces  27  or  29  or  31 , respectively, of the accumulator housing  3 , as well as by cylinder surfaces  35  of the cylinder housing  3  and cylinder surfaces  37  on the accumulator piston  5 . 
     The pressure chamber  25  adjacent to the active surfaces  17  is delimited by a mating surface  33  of the accumulator housing  3 , as well as by a cylinder surface  39  of the accumulator piston  5 . 
     A fluid port  41 ,  43 ,  45  or  47 , respectively, is provided for each pressure chamber  19 ,  21 ,  23 ,  25 . Just as the active surfaces  11 ,  13 ,  15  and  17  are disposed on the accumulator piston  5 , the associated mating surfaces  27 ,  29 ,  31  or  33 , respectively, are disposed on the accumulator housing  3  in steps that are axially spaced relative to one another. 
       FIG. 2  shows the piston accumulator  1  in conjunction with associated system components. An actuator  49  is operatively connected to an adjustment assembly  51 . As already noted, a working cylinder  58  ( FIG. 3 ) may be provided as an actuator  49 , which cylinder may be a component in a raising and lowering assembly, for example. A control logic unit  53  is associated with the adjustment assembly  51 , which logic unit actuates a valve arrangement  57  of the adjustment assembly  51  by a control and regulation unit  55 . As will be explained in greater detail on the basis of  FIGS. 3 and 4 , the valve arrangement  57  has selector valves, which produce selected fluid connections between the actuator  49  and the fluid ports  41 ,  43 ,  45 ,  47  of the piston accumulator  1  to selectively activate the pressure chambers  19 ,  21 ,  23  and  25  for charging and discharging processes. To this end, the control logic unit  53  processes signals, which are provided by sensor devices and which represent the operating states of actuator  49  and piston accumulator  1 . Only one of the sensor devices, a pressure sensor  59  at the filling port  9  of the piston accumulator  1 , is shown in  FIG. 2 . 
       FIG. 3  shows the system according to the invention in conjunction with a raising and lowering assembly, wherein the actuator has a working cylinder  58  for raising and lowering a load  61 . A pressure sensor  63  that detects the load pressure, and a position sensor  65  that detects a raising and lowering speed are provided on the working cylinder  58 , to generate the signals that are to be processed by the control logic unit  53 . A hydraulic pump  67 , which is secured on the output side by a pressure relief valve  69 , is connected to a main line  71  of the adjustment assembly  51 , which guides the system pressure. This assembly has connecting lines  73 ,  75 ,  77  and  80 , respectively, for the connection between the main line  71  and the fluid ports  41 ,  43 ,  45  and  47  of the piston accumulator  1 . A valve group, which is actuated by the control logic unit  53  actuated, and symbolically designated as v 1 , v 2 , etc., is located in each of the connecting lines. Each valve group is formed by two fast switching 2/2-way-valves  79  and  81 , which are identified with indices  1  to  4  for the valve groups v 1  to v 4 . Each of the connecting lines can be connected to, or blocked from, the associated fluid port of the piston accumulator  1  by the directional valves  81 . The respective connecting line  73 ,  75 ,  77 ,  80  can be connected to the tank  83  by the directional valve  79 . 
     For a lifting process, the main line  71  can be connected to the working cylinder  58  by a valve, which is designed as a proportional choke valve  87  for the control of the lifting speed. The flow is started through the fluid filter  85  when the working cylinder  58  is lowered. In addition, a pressure relief valve  86  is used to secure the relevant hydraulic circuit. The lifting movement is achieved with the aid of the energy stored in the piston accumulator by a discharge process from the selected pressure chamber  19 ,  21 ,  23 ,  25 , or from a plurality of selected pressure chambers, which have the appropriate pressure level for the lifting movement of the load  61 . In the case of lowering movements, the potential energy of the load  61  is stored as hydraulic energy in the piston accumulator  1 . A charging process then occurs by a proportional choke valve  84  that adjusts the lowering speed and a selected connecting line  73 ,  75 ,  77 ,  80 , or by a plurality of selected connecting lines to a corresponding fluid port  41 ,  43 ,  45 ,  47 . One or more of the directional valves  81  is or are opened, respectively, and directional valves  79  of non-selected connecting lines establish the connection to the tank  83 . Through this connection, non-selected pressure chambers  19 ,  21 ,  23 ,  25  of the piston accumulator  1  are depressurized during discharge processes, and can be refilled from the tank  83  during charging processes. A directional valve  88  located on the main line  71  permits depressurizing or emptying of the system as needed. 
     During operation, in order to lower a load with energy-recovery, the load pressure at the cylinder  58  is transmitted to the control logic unit  53  by the pressure sensor  63 . The gas pressure in the accumulator  1  is likewise transmitted, which is determined by the pressure sensor  59 . By this information, a decision can be made by the control system, as to how the available potential energy of the cylinder  58  can be optimally fed back into the accumulator  1 . In the case of low loads, a large effective surface is selected, in order to charge the accumulator to a high pressure level. If there is a high load  61  on the cylinder  58 , the accumulator  1  is charged with a smaller effective surface. The lowering speed of the load is adjusted by the proportional choke valve  84 . 
     The load compensation effected by the system may be done discontinuously by selecting and/or switching the suitable effective surfaces. If a sufficiently large number of pressure levels are provided in the accumulator  1 , a resolution can be achieved that allows a load to be smoothly lowered. To lift a load  61 , with or without the help of the pump  67 , when the piston accumulator  1  is loaded, the appropriate effective surface or effective surfaces are selected according to the load  61  on the cylinder  58  depending on the gas pressure in the accumulator  1 . To smoothly start up the movement of the load  61 , a lower pressure level is preferably initially selected. The speed of raising the load  61  is adjusted by the proportional choke valve  87 . The pressure differential is kept as small as possible by appropriately selecting the effective surfaces of the accumulator  1 , so that a low-loss conversion of the stored energy into lifting force is made possible. 
     The embodiment in  FIG. 4  only differs from the example in  FIG. 3  in that a pressure maintenance valve  89  or  90 , respectively, is provided at each of the proportional choke valves  84  and  87 , to create a constant pressure differential at the associated proportional choke valve  84 ,  87 . Jumps in the pressure differential at the respective proportional choke valve  84 ,  87  can be compensated for by switching the effective surfaces of the accumulator  1 . 
     If fast-switching directional valves  79  and  81  are used instead of the proportional choke valves  84 ,  87 , these directional valves may also be controlled by pulse-width modulation, whereby a desired average flow rate can be adjusted to, depending on the impulse modulation. 
     While various embodiments have been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the claims.