Patent Application
20140318115
The invention relates to a system for improving the energy efficiency in hydraulic systems, having an actuator which, in one operating state, functions as a consumer of hydraulic energy and in another operating state, functions as a generator of hydraulic energy, and having a hydraulic accumulator which, when in one operating state of the actuator, can be charged by the same for the storage of energy, and when in another operating state, can be discharged for the delivery of energy to the actuator. In addition, the invention relates to a hydropneumatic piston accumulator for use with such a system and a pressure accumulator.
Given the increasing scarcity of resources and the increased efforts to save energy associated therewith, systems of the above type are becoming increasingly important. Thus such systems are used in hydraulic devices and systems for example, in which actuators in the form of working cylinders are provided, which generate movements against a load as consumers, or which generate energy from load forces for storage in the hydraulic accumulator. Thus for example in lifting and lowering applications, the potential energy of a lifted load can be converted into hydraulic energy, which may be stored and recycled. Hydraulic hybrid systems for rotary drives are a further field of application. In this case, the actuator has a motor pump unit between a drive motor and a working hydraulics or hydrostatic drive, which motor pump unit functions as a consumer or as a generator of hydraulic energy for storage and recycling in the hydraulic accumulator in corresponding operating states.
Regardless of the application, the efficiency of the energy conversion in the known systems leaves something to be desired. One reason for this is the dependence of the charging and discharging processes of the hydraulic accumulator on the respective system pressure. More specifically, the hydraulic accumulator can still only be charged when the system pressure is greater than the gas pressure found in the accumulator on the gas side. When the system pressure cannot be built up in the respective operating situation of the actuator, it is not possible to acquire energy in the accumulator. The discharge process of the accumulator is subject to the restriction that energy can only be fed back from the accumulator when the accumulator pressure is still greater than the current system pressure. In addition, there is the problem that in the case of an accumulator pressure that is greater than the currently needed system pressure, the pressure levels of the accumulator and the system must be balanced by means of valves, so that the energy contained in the differential pressure between the accumulator pressure and the system pressure is lost due to throttling losses.
In view of these problems, the object of the invention is to provide a system of the type under consideration, a piston accumulator and a pressure accumulator, which make a more favorable energy conversion possible.
This object is achieved according to the invention by a system that has the features of claim 1 in its entirety. Advantageous embodiments of the system are apparent from the dependent claims 2 to 11.
Accordingly, an essential feature of the invention is that at least one hydraulic accumulator is provided, which offers a preferably discontinuous option for adjustment, in that the accumulator provides a plurality of pressure chambers, which are adjacent to effective surfaces on the fluid side of the accumulator piston having different sizes, wherein an adjustment assembly is provided, which connects a selected pressure chamber or a plurality of selected pressure chambers of the piston accumulator to the actuator as a function of the respective pressure level prevailing on the gas side of the piston accumulator. This results in the possibility of recycling energy independent of the pre-charge pressure on the gas side of the accumulator, and independent of the respective load pressure, because the respectively desired pressure level on the accumulator can be used for charging and discharging by selecting an effective surface of suitable size. An optimum energy conversion is thereby possible for all operating conditions.
The use of a “multi-step accumulator” of this kind also opens up the possibility of influencing the load time by means of selecting the effective surfaces. Selecting a small surface at a constant volume flow results in a short charge time for the accumulator, while selecting a larger surface at a constant volume flow results in a longer charge time. A finer or coarser pressure gradation can be achieved by forming a larger or smaller number of pressure chambers of different effective piston surfaces. More than one accumulator with different pressure chambers may also be provided in order to achieve an especially high degree of resolution.
In an especially advantageous manner, the adjustment arrangement may be associated with a control logic, which process the signals from sensor devices for the control of the valves associated with the adjustment arrangement, which signals represent the pressure level on the gas side of the piston accumulator and the respective operating state of the actuator. In so doing, the logic controls the energy transformation, in that it is decided how to charge or discharge the accumulator according to the load at the actuator and the load state at the accumulator. In so doing, there is the possibility that the user may influence the logic with his own requirements, and thereby influence the operating characteristics of the system.
In terms of the design of the piston accumulator, the assembly may be advantageously made in such a way that, for the formation of effective surfaces having different sizes, the accumulator piston is designed as a stepped piston or step-shaped, and has partial piston surfaces on the fluid side thereof that are adjacent to cylinder surfaces, wherein the accumulator housing has corresponding mating surfaces that are adjacent to cylinder surfaces, which mating surfaces, together with the partial piston surfaces associated therewith, each delimit separate pressure chambers.
Effective surfaces on the accumulator piston and mating surfaces on the accumulator housing are preferably disposed in steps or levels that are disposed such that they are spaced axially apart from one another.
At least one of the pressure chambers can be disposed while also maintaining the axial offset in the interior of the piston. In this respect, a guiding spike for the cylinder is formed, protruding from the cylinder housing. The piston is therefore guided both from outside and from within. The installation height of the piston accumulator is thus shortened and the guidance of the piston substantially improved.
Effective surfaces and mating surfaces may be provided in the form of annular surfaces or circular surfaces, which are concentrically disposed relative to the longitudinal axis.
In terms of the control of the pressure chambers of the piston accumulator, the assembly may be advantageously made in such a way that the adjustment arrangement has switching valves, by means of which valves respective pressure chambers of the piston accumulator, which are selected for charging or discharging, can be connected to the actuator, and the remaining pressure chambers can be connected to the tank. Thus a selected pressure chamber or a combination of selected pressure chambers for charging or discharging can be connected to the actuator by means of the control logic, while pressure chambers that are not selected can be emptied into the tank without pressure during the discharge, and can be refilled from the tank again during the charging of active pressure chambers.
In terms of the provision of signals of the control logic, the arrangement can be advantageously made such that the assigned sensor device has at least pressure sensors, which provide signals to the control logic, which represent the filling pressure on the gas side of the piston accumulator and the system pressure at the actuator. In addition, the sensor device may have a displacement measuring device, with which the stroke of the accumulator piston may preferably be detected.
Pursuant to claim 11, the subject matter of the invention also includes a hydropneumatic piston accumulator for a system according to one of the claims 1 to 10, wherein, in the accumulator housing, which guides the accumulator piston axial such that it is axially movable, a plurality of pressure chambers are formed, which are adjacent to effective surfaces having different sizes on the fluid side of the piston.
Further embodiments of the hydropneumatic piston accumulator are defined in the dependent claims 12 to 21.
For the formation of effective surfaces having different sizes, the accumulator piston may be designed as a stepped piston or step-shaped, and have partial piston surfaces on the fluid side thereof that are adjacent to cylinder surfaces. The accumulator housing may have corresponding mating surfaces that are adjacent to cylinder surfaces, which mating surfaces, together with the partial piston surfaces associated therewith, each delimit separate pressure chambers.
The effective surfaces on the accumulator piston and the mating surfaces on the accumulator housing may be disposed in steps or levels that are disposed such that they are spaced axially apart from one another.
At least one, preferably at least two; of the pressure chambers may be disposed in the interior of the accumulator piston while maintaining the axial spacing.
The effective surfaces and the mating surfaces may be provided in the form of annular surfaces or circular surfaces, which are concentrically disposed relative to the longitudinal axis.
A step-shaped bottom part may be provided, wherein the accumulator piston and the bottom part have overlapping wall parts.
All pressure chambers may be separated from one another in a media-tight manner within the accumulator housing.
The pressure chamber disposed in the longitudinal axis of the accumulator housing may be encompassed by a step-shaped part of the accumulator piston, in particular the inner piston thereof. The step-shaped part of the accumulator piston may delimit a further pressure chamber on the outer circumference with a cylinder surface and additional parts of the accumulator piston.
A middle extension of the bottom part, in particular an inner piston, which is designed as a displacement piston, may retract during a relative movement of the accumulator piston and bottom part towards one another in the step-shaped part of the accumulator piston, in particular in the inner piston thereof.
The object is also achieved by a pressure accumulator having the features of claim 22. Advantageous embodiments of the pressure accumulator embodiments of the system are apparent from the dependent claims 23 and 24.
The pressure accumulator, in particular designed in the manner of a hydropneumatic piston accumulator, has an accumulator housing, which has a top part and a bottom part at the ends thereof, and in which at least one accumulator piston is disposed such that it is longitudinally displaceable, which piston separates a first media side, in particular a gas side, from a second media side, in particular a fluid side. At least one of the two media sides has pressure chambers that are separated from one another, disposed concentrically relative to a longitudinal axis of the accumulator housing. The respective pressure chambers, which are delimited by the accumulator piston and/or by the bottom part, undergo a change in volume, provided that the bottom part retracts into the pressure chambers of the accumulator piston and the accumulator piston retracts into the pressure chambers of the bottom part in a relative movement of the accumulator piston and bottom part towards one another, starting from a maximum position in which at least one of the pressure chambers is maximally filled with a medium, in the direction of a minimum position in which the at least one pressure chamber is comparatively less filled. According to the invention, all pressure chambers are separated from one another in a media-tight manner within the accumulator housing.
The pressure chamber disposed in the longitudinal axis of the accumulator housing may be encompassed by a step-shaped part of the accumulator piston, in particular the inner piston thereof. The step-shaped part of the accumulator piston may delimit a further pressure chamber on the outer circumference with a cylinder surface and additional parts of the accumulator piston.
A middle extension of the bottom part, in particular an inner piston, which is designed as a displacement piston, may retract during a relative movement of the accumulator piston and bottom part towards one another in the step-shaped part of the accumulator piston, in particular in the inner piston thereof.
The invention is explained in detail below based on the embodiments illustrated in the drawings. Shown are:
The schematic, simplified illustration of a hydropneumatic piston accumulator 1 shown in
A fluid connection 41, 43, 45 or 47 respectively is provided for each pressure chamber 19, 21, 23, 25. As the effective 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 apart from one another.
In the case of a lifting process, the main line 71 can be connected to the working cylinder 58, which is safeguarded by a pressure relief valve 86, by means of a valve, which is designed as a proportional throttle valve 87 for the control of the lifting speed, as well as by means of a fluid filter 85. The lifting movement is made with the aid of the energy stored in the piston accumulator by means of a discharge process from a 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 the lowering movement, the potential energy of the load 61 is stored as hydraulic energy in the piston accumulator 1, in that a charging process occurs by means of an application-dependent proportional throttle valve 84 that adjusts the lowering speed, and a selected connecting line 73, 75, 77, 80 or by means of a plurality of selected connecting lines, to a respective fluid port 41, 43, 45, 47, wherein one or a plurality of the directional valves 81 is or are opened respectively, and directional valves 79 in connecting lines that are not selected establish the connection to the tank 83. Through this connection, non-selected pressure chambers 19, 21, 23, 25 of the piston accumulator 1 are unpressurized during the discharging processes, and can be refilled from the tank 83 during recharging processes. A directional valve 88 located on the main line 71 makes it possible to depressurize or empty the system as needed.
In order to lower a load with energy recovery, the load pressure on the cylinder 58 is transmitted to the control logic 53 during operation by means of the pressure sensor 63, and likewise, the gas pressure on the accumulator 1 is detected by means of the pressure sensor 59. Using this information, the feedback control can decide 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 may be 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 small effective surface. The lowering speed of the load is adjusted by means of the proportional throttle valve 84.
The load compensation effected by the system may be done discontinuously by selecting and/or switching the suitable effective surfaces, wherein, with a sufficiently large number of pressure levels made available in the accumulator 1, it is possible to achieve a resolution that allows the load to be lowered smoothly. In so doing, the throttle valve 84 can smooth out the discontinuity with a pressure compensator. In order to lift a load 61 in the case of a charged piston accumulator 1, either with or without the aid of the pump 67, the appropriate effective surface, or the appropriate effective surfaces, is or are selected according to the load 61 to the cylinder 58 as a function of the gas pressure in the accumulator 1. In order to smoothly initiate the movement of the load 61, a smaller pressure level is preferably initially selected. The speed for raising the load 61 is adjusted by means of the proportional throttle valve 87, wherein the pressure differential is kept as small as possible by means of the suitable selection of the effective surfaces of the accumulator 1, so that a low-loss conversion of the storage energy is possible during the lifting work.
The embodiment in
Instead of the proportional throttle valves 84, 87, these jumps may also be controlled by pulse-width modulation in the case that fast-switching directional valves 79 and 81 are used, whereby a desired average volume flow can be adjusted as a function of the impulse modulation or of the pulse duty factor.
In order to generate the signals, which are to be processed by the control logic 53, a pressure sensor 59 that detects a pressure level on the gas side is provided on the filling connector 9 of the piston accumulator 1, a pressure sensor 63 that detects the system pressure is provided on the main line 71, and a speed sensor 96 is provided on the drive motor 93. Based on these signals, the control logic 53 decides which of the connecting lines 73, 75, 77 or 80 or which combination of these lines will create the connection between the main line 71 and the respectively associated fluid port 41, 43, 45, 47 on the piston accumulator 1. In so doing, a selection is made as to which of the pressure chambers 19, 21, 23, 25, or which combination of these pressure chambers, is best suited for a charging process or discharging process at the respective prevailing pressure level of the system pressure (main line 71) and of the accumulator 1. In the case of the discharging process, the recovered energy is returned to the suction side of the motor pump unit 91 from the main line 71, which is safeguarded by a pressure relief valve 86, by means of a switching valve 97. In the case of charging processes, the switching valve 97 is closed and a connecting line, or a plurality of the connecting lines 73, 75, 77, 80, is/are activated by means of the directional valves 81.1 to 81.4, wherein each of the associated directional valves 79.1 to 79.4 are closed. On the other hand, in the case of each of the non-activated connecting lines 73, 75, 77, 80, the directional valves 79.1 to 79.4 establish the connection to the tank 83, so that the connected, non-selected pressure chambers 19, 21, 23 or 25 of the accumulator 1 are without pressure during discharging processes, and can be refilled from the tank 83 during charging processes. In the case of changing system conditions, the respectively selected combination of the effective surfaces 11, 13, 15, 17 may be changed during the charging processes or discharging processes. An inverse shuttle valve 99 is provided in order to remove the excess quantity of fluid in the circuit that is discharged from the accumulator 1 during the discharging processes from the now depressurized downstream side of the motor pump unit 91 to the tank 83. In the case of charging processes, the upstream side of the motor pump unit 91 may also be connected to the tank 83 for refilling processes by means of this shuttle valve.
The schematic, simplified illustration of an alternative embodiment of the hydropneumatic piston accumulator 101 shown in
Radial seals 179 are provided between the accumulator housing 103 and the top part 149, the accumulator piston 105, and the bottom part 151, respectively. Additional radial seals 181 are disposed between the accumulator piston 105 and the bottom part 151, as well as the inner pistons 171, 173. The pressure chambers 119, 121, 123, 125 are adjacent to effective surfaces having different sizes on the fluid side of the accumulator piston 105 the inner piston 171 thereof, respectively. In
The pressure chamber 125, which is adjacent to the effective surface 117, is delimited by a mating surface 133 of the inner piston 173 on the bottom part side, as well as by a cylinder surface 137 of the inner piston 171 on the accumulator piston side. A fluid port 141, 143, 145, 147, in each case in the form of a bore in the bottom part 151, is provided for each pressure chamber 119, 121, 123, 125. Adjacent to the top part 149, a tubular sleeve 185 is used as a stop for the accumulator piston 105 in the accumulator housing 103. The sleeve 185 contacts the accumulator housing 103 on the outside. In addition, a displacement measuring device 187 is provided in order that the distance A, from the top part 149 to the accumulator piston 105, may be determined at any time. Moreover, a wire 191 is attached to an eyelet 189 on the accumulator piston 105, which may be extended from a sensor device 193. Moreover, a pressure measuring device, not shown in greater detail, may be integrated within the sleeve 185.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2011 120 228.9 | Mar 2011 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2012/004974 | 12/3/2012 | WO | 00 | 5/23/2014 |
