System for improving the energy efficiency in hydraulic systems, piston accumulator and pressure accumulator provided for such a system

A hydraulic system includes an actuator operating as a consumer of hydraulic energy and as a generator of hydraulic energy in different operating states, and includes a hydraulic accumulator (1). In an operating state of the actuator (49), the accumulator can be charged by the actuator for storing energy. In a different operating state, the accumulator can be discharged for delivering energy to the actuator (49). The hydraulic accumulator is an adjustable hydropneumatic piston accumulator having a plurality of pressure chambers (19, 21, 23, 25) adjoining effective surfaces (11, 13, 15, 17) of different sizes on the fluid side of the accumulator piston (5). An adjusting arrangement (51) connects a selected pressure chamber (19, 21, 23, 25) or a plurality of selected pressure chambers (19, 21, 23, 25) of the piston accumulator (1) to the actuator (49) as a function of the pressure level that prevails on the gas side of the piston accumulator (1) and on the actuator (49).

FIELD OF THE INVENTION

The invention relates to a system for improving the energy efficiency in hydraulic systems, having an actuator. In one operating state, the actuator functions as a consumer of hydraulic energy. In another operating state, the actuator functions as a generator of hydraulic energy. A hydraulic accumulator, when in one operating state of the actuator, can be charged by the actuator for the storage of energy. When in another operating state, the accumulator 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.

BACKGROUND OF THE INVENTION

Given the increasing scarcity of resources and the increased efforts to save energy associated therewith, systems of the above type are becoming increasingly important. Such systems are used in hydraulic devices and systems for example, in which actuators in the form of working cylinders are provided. The working cylinders generate movements against a load as consumers, or generate energy from load forces for storage in the hydraulic accumulator. 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. The 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 efficiency issue 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, energy cannot be acquired 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 valves, so that the energy contained in the differential pressure between the accumulator pressure and the system pressure is lost due to throttling losses.

SUMMARY OF THE INVENTION

In view of these problems, an object of the invention is to provide an improved system of the type under consideration, with a piston accumulator and a pressure accumulator, making a more favorable energy conversion possible.

This object is basically achieved according to the invention by a system having, as an essential feature of the invention, at least one hydraulic accumulator that offers a preferably discontinuous option for adjustment. 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. 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 selection 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 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 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. The 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 deciding how to charge or discharge the accumulator according to the load at the actuator and the load state at the accumulator. In so doing, the possibility exists 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 is step-shaped. Partial piston surfaces are on the fluid side of the accumulator piston that are adjacent to cylinder surfaces. 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 those 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 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. The pressure sensors 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.

The subject matter of the invention also includes a hydropneumatic piston accumulator for a system, as described above. In the accumulator housing, which guides the accumulator piston axial such that it is axially movable, a plurality of pressure chambers are formed. The pressure chambers are adjacent to effective surfaces having different sizes on the fluid side of the piston.

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.

An object of the invention is also basically achieved by a pressure accumulator, in particular designed in the manner of a hydropneumatic piston accumulator, having an accumulator housing, which has a top part and a bottom part at the ends thereof. In the accumulator housing, at least one accumulator piston is disposed such that it is longitudinally displaceable. The 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 housing 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.

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.

DETAILED DESCRIPTION OF THE INVENTION

The schematic, simplified illustration of a hydropneumatic piston accumulator1shown inFIG. 1has an accumulator piston5that is guided in an accumulator housing3such that the accumulator piston5is axially movable. The accumulator piston separates a gas side7on which a filling connector9is located, from pressure chambers on the fluid side in an accumulator housing3. The accumulator piston5is designed in the manner of a stepped piston in such a way that the accumulator piston, in cooperation with correspondingly stepped sections of the of the accumulator housing3, delimits fluid-side pressure chambers19,21,23and25. These chambers are adjacent to effective surfaces having different sizes on the fluid side of the accumulator piston5. InFIG. 1, these effective surfaces11,13,15and17are arranged in sequence from the smallest surface to the largest surface. The effective surfaces11,13and15are thereby each formed by annular surfaces that are concentric relative to the longitudinal axis. The annular surfaces enclose the innermost effective surface17in the form of a circular surface. Pressure chambers19,21or23respectively, which are adjacent to the effective surfaces11,13and15, are delimited by mating surfaces27or29or31respectively of the accumulator housing3, as well as by cylinder surfaces35of the cylinder housing3and cylinder surfaces37on the accumulator piston5. The pressure chamber25, which is adjacent to the effective surface17, is delimited by a mating surface33of the accumulator housing3, as well as by a cylinder surface39of the accumulator piston5.

A fluid connection41,43,45or47respectively is provided for each pressure chamber19,21,23,25. As the effective surfaces11,13,15and17are disposed on the accumulator piston5, the associated mating surfaces27,29,31or33respectively are disposed on the accumulator housing3in steps that are axially spaced apart from one another.

FIG. 2shows the piston accumulator1in conjunction with system components allocated thereto. An actuator49is operatively connected to an adjustment arrangement51. As already noted, the actuator49may be a component of a lifting and lowering arrangement for example, or of a hydraulic hybrid systems for rotary drives. A control logic53is allocated to the adjustment arrangement51. The control logic actuates a valve assembly57of the adjustment arrangement51by a control and regulating unit55. As is explained in greater detail based onFIGS. 3 to 5, the valve assembly57has switching valves, which create selected fluid connections between the actuator49and the fluid ports41,43,45,47of the piston accumulator1, to selectively activate the pressure chambers19,21,23and25for charging or discharging processes. To this end, the control logic53processes signals, which are provided by sensor devices and which represent the operating conditions of the actuator49and piston accumulator1. Of these sensor devices, only one pressure sensor59on the filling connector9of the piston accumulator1is shown inFIG. 2.

FIG. 3shows the system according to the invention in conjunction with a lifting and lowering arrangement. The actuator has a working cylinder58for lifting and lowering a load61. A pressure sensor63, which detects the load pressure, and a path sensor65, which detects the lifting and lowering speed, are provided on the working cylinder58to generate the signals that are to be processed by the control logic53. A hydraulic pump67, safeguarded on the output side by a pressure relief valve69, is connected to a main line71of the adjustment arrangement51that controls the system pressure. This pump has a connecting line73,75,77and80for the connection between the main line71and each of the fluid ports41,43,45and47of the piston accumulator1. A valve group, designated by the symbols v1, v2, etc., is located in each of the connecting lines, which valve group can be actuated by the control logic53. Each valve group comprises two fast-switching 2/2-way valves79and81. In the case of the valve group v1to v4, the valves are designated with the indices1to4. The associated connecting line can be connected to or blocked on the associated fluid ports of the piston accumulator1by the directional valves81. The respective connecting line73,75,77,80can be connected to the tank83by the directional valves79. In addition, each pressure chamber19,21,23,25is safeguarded by a pressure relief valve, which is not shown in greater detail.

In the case of a lifting process, the main line71can be connected to the working cylinder58, which is safeguarded by a pressure relief valve86, by a valve designed as a proportional throttle valve87for the control of the lifting speed, as well as by a fluid filter85. The lifting movement is made with the aid of the energy stored in the piston accumulator by a discharge process from a selected pressure chamber19,21,23,25or from a plurality of selected pressure chambers, which have the appropriate pressure level for the lifting movement of the load61. In the case of the lowering movement, the potential energy of the load61is stored as hydraulic energy in the piston accumulator1. A charging process occurs by an application-dependent proportional throttle valve84that adjusts the lowering speed, and by a selected connecting line73,75,77,80or by a plurality of selected connecting lines, to a respective fluid port41,43,45,47. One or a plurality of the directional valves81is or are opened respectively. Directional valves79in connecting lines that are not selected establish the connection to the tank83. Through this connection, non-selected pressure chambers19,21,23,25of the piston accumulator1are unpressurized during the discharging processes, and can be refilled from the tank83during recharging processes. A directional valve88located on the main line71permits depressuring or emptying of the system as needed.

To lower a load with energy recovery, the load pressure on the cylinder58is transmitted to the control logic53during operation by the pressure sensor63, and likewise, the gas pressure on the accumulator1is detected by the pressure sensor59. Using this information, the feedback control can decide how the available potential energy of the cylinder58can be optimally fed back into the accumulator1. In the case of low loads, a large effective surface may be selected to charge the accumulator to a high pressure level. If there is a high load61on the cylinder58, the accumulator1is charged with a small effective surface. The lowering speed of the load is adjusted by the proportional throttle valve84.

The load compensation effected by the system may be done discontinuously by selecting and/or switching the suitable effective surfaces. With a sufficiently large number of pressure levels made available in the accumulator1, the load can be lowered smoothly. In so doing, the throttle valve84can smooth out the discontinuity with a pressure compensator. To lift a load61in the case of a charged piston accumulator1, either with or without the aid of the pump67, the appropriate effective surface, or the appropriate effective surfaces, is or are selected according to the load61to the cylinder58as a function of the gas pressure in the accumulator1. To smoothly initiate the movement of the load61, a smaller pressure level is preferably initially selected. The speed for raising the load61is adjusted by the proportional throttle valve87. The pressure differential is kept as small as possible by the suitable selection of the effective surfaces of the accumulator1, so that a low-loss conversion of the storage energy is possible during the lifting work.

The embodiment inFIG. 4differs from the example inFIG. 3only in that a pressure compensator89or90respectively is provided on each of the proportional throttle valves84and87, to generate a constant pressure differential on the associated proportional throttle valve84,87. Jumps to the pressure difference at the respective proportional throttle valve84,87may be compensated for by switching the effective surfaces of the accumulator1.

Instead of the proportional throttle valves84,87, these jumps may also be controlled by pulse-width modulation in the case that fast-switching directional valves79and81are used. A desired average volume flow can then be adjusted as a function of the impulse modulation or of the pulse duty factor.

FIG. 5shows the system according to the invention in use in a hydraulic hybrid system for rotary drives. A motor pump unit91is provided as an actuator. The pump shaft92of motor pump unit91is coupled on one side with a drive source, for example, an internal combustion engine93, and on the other side with a rotary driven device94. This device may be a working hydraulics, a traction drive or the like, i.e. it may be a device that, in one operating state, functions as a consumer of hydraulic energy and in other operating states, for example during braking of the traction drive, may generate a corresponding torque on the pump shaft92as a generator of hydraulic energy. The pressure side of the motor pump unit91is connected to a main line71of the adjustment arrangement51that controls the system pressure by a non-return valve95. This adjustment arrangement has a connecting line73,75,77,80for each connection between the main line71and the fluid ports41,43,45and47of the piston accumulator1. A valve group, designated by the symbols v1, v2etc., which can be actuated by the control logic53, is located in each of the connecting lines. Each valve group comprises two fast-switching 2/2-way valves79and81, and in the case of the valve group v1to v4, are designated with the indices1to4. The respective associated connecting line73,75,77,80can be connected to or blocked on the associated fluid port41,43,45or47, respectively, of the piston accumulator1by the directional valves81.1to81.4. The respective connecting line can be connected to the tank83by the directional valves79.1to79.4.

To generate the signals, which are to be processed by the control logic53, a pressure sensor59that detects a pressure level on the gas side is provided on the filling connector9of the piston accumulator1. A pressure sensor63detects the system pressure and is provided on the main line71. A speed sensor96is provided on the drive motor93. Based on these signals, the control logic53decides which of the connecting lines73,75,77or80or which combination of these lines will create the connection between the main line71and the respectively associated fluid port41,43,45,47on the piston accumulator1. In so doing, a selection is made as to which of the pressure chambers19,21,23,25, 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 line71) and of the accumulator1. In the case of the discharging process, the recovered energy is returned to the suction side of the motor pump unit91from the main line71, which is safeguarded by a pressure relief valve86, by a switching valve97. In the case of charging processes, the switching valve97is closed and a connecting line, or a plurality of the connecting lines73,75,77,80, is/are activated by the directional valves81.1to81.4. Each of the associated directional valves79.1to79.4are closed. On the other hand, in the case of each of the non-activated connecting lines73,75,77,80, the directional valves79.1to79.4establish the connection to the tank83, so that the connected, non-selected pressure chambers19,21,23or25of the accumulator1are without pressure during discharging processes, and can be refilled from the tank83during charging processes. In the case of changing system conditions, the respectively selected combination of the effective surfaces11,13,15,17may be changed during the charging processes or discharging processes. An inverse shuttle valve99is provided to remove the excess quantity of fluid in the circuit that is discharged from the accumulator1during the discharging processes from the now depressurized downstream side of the motor pump unit91to the tank83. In the case of charging processes, the upstream side of the motor pump unit91may also be connected to the tank83for refilling processes by this shuttle valve.

The schematic, simplified illustration of an alternative embodiment of the hydropneumatic piston accumulator101shown inFIG. 6has an accumulator piston105guided in a tubular accumulator housing103such that the piston can be axially displaced. The accumulator piston105separates a gas side107from fluid-side pressure chambers11,121,123,125in the accumulator housing103. On the gas side107, a filling connector109in the form of an excentrically disposed bore is located. The accumulator piston105is movably disposed between a sleeve-shaped extension185of the gas-side top part149and a fluid-side bottom part151. The top part149and the bottom part151are supported, and to this extent, fixed on projections153by snap rings155on grooves157on the inner circumference of the accumulator housing103. The bottom part151and the accumulator piston105are designed such that they are step-shaped and having wall parts159,161, wherein the wall parts159,161overlap and two of the pressure chambers119,121are axially held by two notional planes163,163in the longitudinal direction shown inFIG. 6. Both the accumulator piston105and also the bottom part151have inner pistons171,173that are held by pins167in recesses169. The inner pistons171,173likewise have wall parts175,177, which overlap one another and overlap with the wall parts159,161of the accumulator piston105and bottom part151.

Radial seals179are provided between the accumulator housing103and the top part149, the accumulator piston105, and the bottom part151, respectively. Additional radial seals181are disposed between the accumulator piston105and the bottom part151, as well as the inner pistons171,173. The pressure chambers119,121,123,125are adjacent to effective surfaces having different sizes on the fluid side of the accumulator piston105the inner piston171thereof, respectively. InFIG. 6, these effective surfaces111,113,115,117are arranged from the largest surface to the smallest surface. In so doing, the effective surfaces111,113,115are each formed by annular surfaces. These annular surfaces are concentrically disposed relative to the longitudinal axis183, which annular surfaces enclose the innermost effective surface117in the form of a circular surface. Pressure chambers119,121,123, which are adjacent to the effective surfaces111,113,115, are delimited by mating surfaces127,129,131of the bottom part151or of the inner piston173thereof, as well as by a cylinder surface135of the cylinder housing103and cylinder surfaces137on the accumulator piston105, the bottom part151and the inner piston171,173.

The pressure chamber125, which is adjacent to the effective surface117, is delimited by a mating surface133of the inner piston177on the bottom part side, as well as by a cylinder surface137of the inner piston177on the accumulator piston side. A fluid port141,143,145,147, in each case in the form of a bore in the bottom part151, is provided for each pressure chamber119,121,123,125. Adjacent to the top part149, a tubular sleeve185is used as a stop for the accumulator piston105in the accumulator housing103. The sleeve185contacts the accumulator housing103on the outside. In addition, a displacement measuring device187is provided such that the distance A, from the top part149to the accumulator piston105, may be determined at any time. Moreover, a wire191is attached to an eyelet189on the accumulator piston105, which may be extended from a sensor device193. Moreover, a pressure measuring device, not shown in greater detail, may be integrated within the sleeve185.