Device for recovering energy

Abstract

A device for recovering energy in working machines, with at least one power drive, which can be actuated to move a load mass back and forth, and with an energy storage system (16) which absorbs the energy released in the movement of the load mass in one direction and which makes it available for a subsequent movement in the other direction, is characterized in that there is an energy storage system in the form of an accumulator cylinder (16) which, mechanically coupled to the load mass, stores pneumatic pressure energy for movement in one direction, and, for movement in the other direction, acts as an auxiliary working cylinder which supports the power drive and which converts the stored pressure energy into driving force.

Description

The invention relates to a device for recovering energy in working machines, with at least one power drive, which can be actuated to move a load mass back and forth, and with an energy storage system, which absorbs the energy released in the movement of the load mass in one direction and which makes it available for a subsequent movement in the other direction.

Devices of this type for recovery of potential energy in working machines are prior art; see, for example, WO 93/11363 or EP 0 789 816 B1. As energy storage systems, such devices have pressure accumulators which store the released potential energy as pressure energy of a working gas. It is crucial for the efficiency of these devices that the lowest possible energy losses occur in operation. Said losses consist primarily of losses of thermal energy of the accumulator gas. Generally, a large part of the thermal energy which forms when the working gas is compressed is released via the outer walls of the hydraulic accumulator which is used in the prior art as an energy storage system, and the large-area contact region between the working gas and the exterior can lead to considerable heat losses for the relatively large surface of the accumulator housing (preferably of steel) under consideration.

In light of these problems, the object of the invention is to provide a device of the type under consideration which, in contrast, is characterized by a greatly improved energy balance with an especially simple and money-saving design.

According to the invention, this object is achieved by a device which has the features of claim 1 in its entirety.

Accordingly, an important particularity of the invention consists in that there is an energy storage system in the form of an accumulator cylinder which, mechanically coupled to the load mass, stores pneumatic pressure energy for movement in one direction, and for movement in the other direction acts as an auxiliary working cylinder which supports the power drive and which converts the stored pressure energy into driving force.

In one especially preferred embodiment, it is stipulated that the accumulator cylinder as the auxiliary working cylinder is coupled to a load mass which is to be raised and lowered and stores potential energy released in lowering processes in the form of pneumatic pressure energy.

The use of an energy storage system in the form of an accumulator cylinder as a replacement of conventional hydraulic accumulators improves the energy balance in more than one respect. On the one hand, the direct mechanical coupling of the accumulator cylinder to the load mass, as a result of which the stored pressure energy can be converted directly into lifting force so that the accumulator cylinder acts as an additional power drive, results in the elimination of the hydraulic system as required in the prior art between the hydraulic accumulator and power drive, so that the associated energy losses, which otherwise occur, are eliminated. Furthermore, an accumulator cylinder, when compared to a hydraulic accumulator, affords considerably more design options for reducing the direct heat loss of the working gas.

This direct heat loss can be reduced quite significantly when, for especially advantageous exemplary embodiments, the piston rod of the accumulator cylinder that exhibits a hollow, end-side open part forms the piston whose cavity in the position fully retracted into the cylinder contains essentially the entire volume of the working gas. In this construction of the piston, generation of heat takes place when the piston rod is lowered within the piston, that is, in a region which is isolated from the cylinder wall by the wall of the hollow piston. Since, moreover, the piston is dimensioned such that in its cavity it contains essentially the entire volume of the working gas; when the piston is fully retracted, in this operating state which corresponds to the strongest compression and, thus, to the greatest generation of heat, the piston wall extends over the entire length of the cylinder so that it is double walled in this state of greatest generation of heat. Heat loss is thus minimized.

On the other hand, in this construction, as a result of the specific overall length of the piston, in the fully extended position its wall with a corresponding flat portion is outside the cylinder wall. In this fully extended position, the working gas has cooled in response to the expansion. At the same time, for this piston position the wall surface which is exposed to the exterior, formed from a cylinder surface and the exposed jacket surface of the piston, has a maximum value. Accordingly, the thermal resistance of the total wall area is minimal so that a relatively large amount of thermal energy is absorbed from the ambient air and released to the cooled working gas. This results in an optimal energy balance.

Not only does the double wall arrangement which is present in certain sections contribute to optimization of the thermal energy balance, but also the working or operating medium enclosed in the double wall, for example, in the form of a working gas and/or in the form of hydraulic oil.

The accumulator cylinder can be formed in the shape of a cup on whose closed bottom there is a filler port for the working gas, such as N₂.

In especially advantageous exemplary embodiments, on the open end of the accumulator cylinder, opposite the bottom, a guide is formed which guides the outside of the piston at a distance from the inner wall of the cup, which distance forms an oil gap.

Preferably, on the open end of the piston, a second guide is formed which guides the end of the piston while maintaining the oil gap. In this way, the piston can be guided without problems.

In particular, together with an oil charge located in the oil gap, a high pressure sealing system can be formed which works reliably in long-term operation even in applications with high pressures, for example, of more than 100 bar.

In order to accommodate the oil that is displaced when the piston is extended and with the resulting reduction of the length of the oil gap and to make it available again upon retraction, a hydraulic accumulator can be connected to the oil gap; said accumulator compensates for changes of the volume of the oil gap when the piston moves.

In especially advantageous exemplary embodiments, the accumulator cylinder is used as an auxiliary working cylinder which is mechanically shunted to a hydraulic working cylinder which can be actuated by the hydraulic system and which is used as a power drive. This enables an especially simple construction, especially for hoists, crane booms, and the like, where hydraulic cylinders are provided as a power drive which acts directly on the load mass.

While in the prior art recovered energy is available in the form of hydraulic pressure energy from a hydraulic accumulator, so that the recovered energy can be used only for hydraulic power drives such as working cylinders or hydraulic motors, the invention can be used in conjunction with any power drives which need not be able to be hydraulically actuated, for example, in spindle drives, cable pulls, or the like, which are activated by an electric motor and which are provided for the lifting of loads.

The invention is detailed below using the exemplary embodiments shown in the drawings.

FIG. 1 shows a schematically simplified representation of a crane boom, provided with one exemplary embodiment of the device according to the invention for recovering potential energy;

FIG. 2 shows a symbolic representation which shows an accumulator cylinder in mechanical shunting to a working cylinder in explanation of the operating principle of the invention;

FIG. 3 shows a schematically simplified longitudinal section of an accumulator cylinder of a first exemplary embodiment of the device according to the invention;

FIG. 4 shows a longitudinal section of a second exemplary embodiment corresponding to FIG. 3, and

FIGS. 5 and 6 show corresponding sections of a third and a fourth exemplary embodiment of the device.

The invention is explained below using exemplary embodiments in which a crane boom 2 forms a load mass 4 (FIG. 2). The boom 2 can be raised by means of a power drive in the form of a hydraulic working cylinder 6; more specifically, it can be pivoted around a coupling point 8. The working cylinder 6 is a hydraulic cylinder which can be actuated by a hydraulic system 10, which is symbolically represented only in FIG. 2, of which only a control valve arrangement is numbered 12 and a hydraulic pump is designated as 14; see FIG. 2. The hydraulic system 10 can be, in particular, of a design that is conventional for working machines, so that it need not be detailed here.

An accumulator cylinder 16 is mechanically shunted to the working cylinder 6 which forms the power drive; i.e., the piston rod 18 of the accumulator cylinder 16, like the piston rod 20 of the working cylinder 6, acts directly on the load mass 4 (boom 2).

FIG. 3, in a separate representation, shows details of the accumulator cylinder 16. As is apparent, it has the shape of a cup 22 with a closed bottom 24, on the latter there being a filler port, which is not shown in the figure, for a working gas, in this example N₂. In the illustrated example, the end of the piston rod 18 forms the piston 26 in the form of a hollow body with an inner cavity 30 which is open on the piston end 28 and which in the fully retracted position of the piston 26, when the piston end 28 is on the bottom 24 of the cup 22, contains the entire volume of working gas. FIG. 3 shows the piston 26 more or less in the middle position in which the gas volume is composed of the inner space of the cup 22 free of the piston 26 and the cavity 30 of the piston 26.

The piston 26 is guided on the inner wall of the cup 22 of the accumulator cylinder 16 such that there is an oil gap 32 on the outside of the piston 26. For this purpose, there is a guide 36 for the piston 26 on the open end 34 of the cup 22. On the open piston end 28, there is a second guide 38. Both guides 36, 38 ensure preservation of the oil gap 32 during piston movements, and they are additionally each provided with a seal arrangement 40 so that together with oil filling of the oil gap 32 not only piston lubrication, but also a high pressure sealing system are formed. In order to compensate for the volume of the oil gap 32, which varies during piston movements, a hydraulic accumulator 42 is connected to the oil gap 32 and accommodates the oil displaced when the piston 26 is extended and releases it again when the piston 26 is retracted.

As mentioned, in FIG. 3 the piston 26 is in a middle position at which the load mass 4 is partially lowered. If the load mass 4 is completely lowered, the piston 26 moves in the direction of the bottom 24 of the cup 22 so that the piston end 28 in the end position of the lowering motion approaches the bottom 24. When the piston 26 is retracted, the working gas is compressed to a volume which corresponds to the volume of the cavity 30 of the piston 26 in the fully retracted position. In this way, the potential energy of the load mass 4 that is released during lowering is converted into pressure energy in the accumulator cylinder 16. The fully retracted position of the piston 26 corresponds to the state of strongest compression and thus to the maximum heating of the working gas. At the same time, in the invention in this operating state, the heated working gas is enclosed double walled, because the piston wall 44 in this position extends over the entire length of the cup 22 along the cup wall 46. In addition, the medium which has collected in the oil gap 32 and which extends essentially over the entire length of the cup 22 forms an additional insulating layer between the cup wall 46 and piston wall 44.

In the state of maximum heating, the accumulator cylinder 26 is thus at the same time in the state of best heat insulation. On the other hand, in the fully extended position of the piston 26, that is, a state in which as a result of expansion the working gas is in the most heavily cooled state, the piston 26 with almost the entire length of its piston wall 44 is outside the cup 22; i.e., during the “supercooled” operating state, the accumulator cylinder 16 exhibits the highest value of the wall surface which is exposed to the exterior, specifically, the essentially entire surface of the cup wall 46 and the piston wall 44, so that a relatively large amount of heat can be absorbed from the ambient air. Therefore, the energy balance is good overall due to the low heat release for the “superheated” state and the high heat absorption for the “supercooled” state of the working gas in the invention.

FIG. 4 shows one exemplary embodiment which is simplified compared to FIG. 3 to the extent that there is no hydraulic accumulator at the oil gap 32. Instead, the oil gap 32 does not contain a complete oil charge, but is divided into an oil side 62 which contains an oil charge and a gas side 64 which is filled with nitrogen by a floating, that is, axially movable seal 60. In the movements of the piston 26, the oil gap thus forms a type of miniaturized hydraulic accumulator.

FIG. 5 shows a further modified example, in which, with the hydraulic accumulator 42 connected to the oil gap 32, the accumulator's gas side is connected to the interior of the piston 26 via a charging line 66 so that the filling pressure of the accumulator 42 is automatically held at the pressure level of the working cylinder 16. There can be pressure limitation and/or check valves in the charging line 66, which is not shown, in order to dictate the filling pressure of the hydraulic accumulator 42 or guide it in one direction, if so desired. In a modification of this solution, it can also be advantageous to connect the line 66 to the bottom 24 of the accumulator cylinder 16 and not in the region of the upper, head-side cover of the piston rod 18 so that there is a direct fluid-carrying connection between the interior of the working cylinder 16 and the accumulator 42, specifically, on the side of the accumulator 42 which is opposite the outlet site of the line which leads to the space 32.

FIG. 6 shows another version in which the interior of the accumulator cylinder 6 is connected to a supply source 70 for working gas via a supply line 68. Moreover, to further improve heat insulation, the inner cavity 30 of the piston 26 is completely filled with a large-pore foam material 72 which can partially also accommodate the working gas.

It should be noted that in the highly schematically simplified representations of FIGS. 3 to 6, which illustrate only the operating principle, design details have been omitted, for example, a divided configuration of the open end 34 of the cup 22 which enables installation of the piston 26 or connections for delivery of the media into the oil gap 32.

Claims

1. A device for recovering energy in working machines, with at least one power drive (6), which can be actuated to move a load mass (4) back and forth, and with an energy storage system (16), which absorbs the energy released in the movement of the load mass (4) in one direction and which makes it available for a subsequent movement in the other direction, characterized in that there is an energy storage system in the form of an accumulator cylinder (16) which, mechanically coupled to the load mass (4), stores pneumatic pressure energy for movement in one direction, and, for movement in the other direction, acts as an auxiliary working cylinder which supports the power drive (6) and which converts the stored pressure energy into driving force.

2. The device according to claim 1, characterized in that the accumulator cylinder (16) as the auxiliary working cylinder is coupled to a load mass (4) which can be raised and lowered and stores potential energy released in lowering processes in the form of pneumatic pressure energy.

3. The device according to claim 1 or 2, characterized in that the piston rod (18) of the accumulator cylinder (16) with a hollow, end-side open part forms the piston (26) whose cavity (30) in the position fully retracted into the cylinder (16) contains essentially the entire volume of the working gas.

4. The device according to claim 1 characterized in that the accumulator cylinder (16) has the shape of a cup (22) on whose closed bottom (24) there is a filler port for the working gas, such as N2.

5. The device according to claim 3, characterized in that on the open end (34) of the accumulator cylinder (16) a guide (36) is formed which guides the outside of the piston (26) at a distance from the inner wall (46) of the cup (22), which distance forms an oil gap (32).

6. The device according to claim 1, characterized in that on the open end (28) of the piston (26) a second guide (38) is formed which guides the end (28) of the piston (26) while maintaining the oil gap (32).

7. The device according to claim 1, characterized in that the two guides (36, 38), together with an oil charge located in the oil gap (32), form a high pressure sealing system.

8. The device according to claim 1, characterized in that a hydraulic accumulator (42) is connected to the oil gap (32) and compensates for changes of the volume of the oil charge in the oil gap (32) when the piston (26) moves.

9. The device according to claim 1, characterized in that the accumulator cylinder (16), as an auxiliary working cylinder, is mechanically shunted to a hydraulic working cylinder (6) which can be actuated by a hydraulic system (10) and which is used as a power drive.