DE3930553A1 - Lifting mechanism hydraulic control system - has pressure-equalisers for flow to and from pressure accumulator - Google Patents

Abstract

The hydraulic control system for a lifting mechanism is particularly for an electric forklift truck, having a battery-driven pumping set supplying a control circuit with a selector valve. Energy is recovered by a storage circuit with hydraulic accumulator and connected by a valve to the selector valve on the return stroke. The system (10) is load-pressure-compensated, there being between the selector valve (14) and the pump (28) a first pressure-equaliser (21) at the measuring throttle (55) of the valve. A second pressure-equaliser (57) regulates the flow from the accumulator (62) via the selector valve to the lifting ram (13). The valve in the return pipe forms a third pressure-equaliser (58) for the fluid from the ram when lowering. A non-return valve (89) protecting the accumulator is released by the load pressure in the control piping (25). USE/ADVANTAGE - Simple and low cost hydraulic control system for forklift trucks.

Description

State of the art
The invention relates to a hydraulic control device for a linear actuator according to the preamble of the main claim.

It is such a hydraulic control device for one Lift drive of an electric stacker known from DE-OS 27 41 496, in which during the lowering process of the lift drive under Influence of an external load flowing back flow over a ma solenoid-operated directional control valve controlled in a storage circuit becomes. The energy gained when reloading the storage can be on can be used to actuate auxiliary drives. At this control device can be with the help of the memory circuit limited energy recovery can be carried out where in the control device with a relatively simple, electrical switchable constant pump works. A disadvantage of this tax However, the facility is that it does not compensate for load pressure wise enabled and therefore not in the so-called LS technology is led. It is also disadvantageous in this control device that the energy recovered in the hydraulic accumulator is not for the Lift actuator can be used. This control device is therefore sufficient no longer meet the high demands in terms of ease of use especially with an electric forklift.  

Furthermore, a hydraulic control device is known from EP 02 62 098 A1 device for several hydraulic consumers known in LS technology is executed. With this control device, each directional valve is assigned a pressure compensator, the one when lowering a linear actuator return pressure occurring due to an external load via a hy draulic cross connection under the pressure compensator in the closing direction supports, so that the pump current can be limited. With this Control is an energy limitation possible; recovery of energy, however, is not due to a lack of storage system possible.

Furthermore, from US-PS 47 07 988 a hydraulic control device device known for a linear actuator, which is an energy recovery possible with a press drive. To do this will be preferred Way uses a flywheel with a hydraulic unit is coupled, which in both flow directions both as Pump can work as a motor as well. This control device is building relatively complex and expensive and is especially for mobile use cases less suitable. Also occur in the conversion of hydrauli shear in mechanical and then in electrical energy relative high losses, so that the overall efficiency becomes insufficient.

Advantages of the invention

The hydraulic control device according to the invention for a Huban drove with the characterizing features of the main claim compared to the advantage that they egg in a control in LS technology ne energy recovery enabled. The tax institution is building relatively simple, inexpensive and allows a purely hydraulic Energy recovery. The control device is therefore suitable especially for use with electric forklifts, especially an increase Use of labor with difficult load spectra possible is. In addition, the relatively light design favors a mobile approach turn.  

The measures listed in the subclaims provide for partial training and improvements in the main claim specified control device possible. Egg is particularly advantageous ne control device according to claim 2, whereby at a substantially existing system in LS technology with the help of a additional module reali the control device according to the invention is sizable. It is also advantageous if a control device is formed according to claim 3, wherein two pressure compensator functions in can be summarized in a single pressure compensator. That way he is a simpler and more compact design, in which ins especially the expenditure on channels and connecting lines is lower can be held. Training is also particularly favorable according to claim 8, whereby with the help of the limit switch on and off switchable operation of the pump is possible and thus the frequency the battery charge can be reduced. The stake too a smaller battery. For a stable, low-vibration operation of the control device, it is favorable if according to claim 15, the pressure drop effective at two simultaneously the pressure compensators is set to different sizes. Further advantageous configurations result from the remaining claims chen, the description and the drawing.

drawing

Two embodiments of the invention are shown in the drawing represents and explained in more detail in the following description. It demonstrate

Fig. 1 shows a first embodiment of the hydraulic control device for a linear actuator in a simplified representation and Fig. 2 shows a second embodiment of the invention.

Description of the embodiments

Fig. 1 shows a hydraulic control device for a stroke drive of an electric forklift, the control device 10 having a directional control valve block 11 and an energy recovery module 12 flanged thereon.

The directional valve block 11 has a first directional valve 14 for controlling a single-acting lifting cylinder 13 and a second and third directional valve 15 and 16 for controlling two double-acting functions. All directional control valves 14 , 15 , 16 are connected in parallel to a running channel 17 which is connected to a P-connection 19 in a connecting plate 18 . For a load pressure compensated control, a first pressure compensator 21 is arranged in the connection plate 18 , which takes over a first pressure compensator function and is connected to a bypass line 22 which is led from the P connection 19 to a tank connection 22 . The first pressure compensator 21 is essentially designed as a 2-way throttle valve, which is loaded by the force of a spring 24 and the load pressure in a control line system 25 in the direction of a blocking position 26 , while it is opposed by the pressure in the inlet channel 17 Direction in an open position 27 is pressed.

The P-connection 19 in the connection plate 18 is supplied by a constant pump 28 with pressure medium which can be driven by an electric motor 29 . The electric motor 29 is supplied with energy by a battery not shown, with the electric motor 29 being switched on and off by an electric circuit, not shown, with associated switches and electromechanical limit switches, as is known per se. The tank connection 22 in the connection plate 18 is relieved to a tank 31 .

The two directional control valves 15 and 16 for the double-acting func tions are identical to one another and each have a control slide 32 which , in addition to a spring-centered central position 33 , can assume two working positions 34 and 35 , respectively. In each of the directional control valves 15 , 16 , as is known per se in the LS technology, the load pressure in the directional control valve 15 or 16 is tapped and passed on via branch lines 36 and shuttle valves 37 to a manifold 38 , which is also part of the control line system 25 form. The control slide 32 of the second and third directional control valve 15 and 16 is each assigned an electromechanical limit switch 39 or 41 , which is actuated when the control slide is deflected from its neutral position. The directional control valves 15 and 16 in connection with the circuit board 18 are known per se and therefore represent inexpensive, commercially available components which are also connected to a common return channel 42 which leads to the tank connection 22 .

The first directional control valve 14 for single-acting function has a spool 43 which can be deflected from the drawn, spring-centered, new position 44 into a raised position 45 and into a lowering position 46 . The first directional valve 14 has an inlet connection 47 connected to the inlet channel 17 , a motor connection 48 connected to a lifting cylinder 13 acting in a multiple manner, a return connection 49 connected to the return channel 42 and an additional outlet connection 51 . Furthermore, it has a first Steueran circuit 52 , which is connected via a branch line 36 to the shuttle valve 37 in the control line system 25 , while a second control connection 53 leads to a pressure channel 54 . In the neutral position 44 , the inlet connection 47 secured by a check valve, the motor connection 48 and the outlet connection 51 are hydraulically blocked. At the same time in this neutral position 44, the two control connections 52 and 53 are connected to each other to the return connection 49 and thus relieved.

In the raised position 45 , the inlet connection 47 is connected to the motor connection 48 via a measuring throttle point 55 , which can be controlled in proportion to the deflection of the control slide 43 , and the load pressure downstream of the measuring throttle point 55 is guided into the first control connection 52 . At the same time, the second control connection 53 to the return connection 49 is relieved in the lifting position 45 and the drain connection 51 is blocked.

In the lowered position 46 , the motor connection 48 is now connected in a special way to the drain connection 51 , while the supply connection 47 is blocked. Furthermore, in this lower position 46, the load pressure upstream of the measuring throttle point 55 is tapped and fed into the second control connection 53 , while at the same time the first control connection 52 is connected to the return connection 49 . The control spool 43 of the proportionally working, first directional valve 14 is assigned a first limit switch 56 which is actuated when the control spool 43 is deflected from the neutral position 44 in the direction of the lifting position 45 .

In the energy recovery module 12 , which is flanged to the first way valve 14 , a second pressure compensator 57 and a third pressure compensator 58 are arranged. The second pressure compensator 57 assumes a second pressure compensator function and a control function within the control line system 25 , while the third pressure compensator ge 58 is assigned to a third pressure compensator function. A memory block 61 with a hydraulic accumulator 62 is connected to a memory connection 59 of the module 12 .

The second pressure compensator 57 is essentially designed as a 5-way three-position valve, of which two connections are used for working currents and three connections for control purposes. In particular, the second pressure compensator 57 has a memory connection 63 , which is connected via a memory channel 64 to the memory connection 59 , a working connection 65 , which has connection to the inlet channel 17 in the directional control valve block 11 , a return connection 66 connected to the return channel 42 , one with the manifold 38 connected first control connection 67 and a second control connection 68 which is connected to a load pressure line 69 which transmits the respective load pressure on the one hand to a pilot pressure relief valve 71 and on the other hand to the end face of the first pressure compensator 21 loaded by the spring 24 . The second pressure compensator 57 has a control member 72 which is loaded by a spring 73 in the direction of a zero position 74 . In this zero position 74 , the memory connection 63 is connected to the working connection 65 , the return connection 66 is blocked and the two control connections 67 and 68 are connected to one another. When deflecting the control member 72 against the force of the spring 73 , it can assume an intermediate position 75 , in which the connection between the storage connection 63 and the working connection 65 is throttled slightly, while the other connections remain. If the control member 72 is further deflected beyond the central position 75 , it can assume an end position 76 in which the throttled connection is throttled even more, the first control connection 67 is blocked and the second control connection 68 is connected to the return connection 66 . Of course, the second pressure compensator works as a continuously acting throttle valve, in which the positions shown in simplified form overlap one another. To deflect the control member 72 against the force of the spring 73 , a hydraulic pressure difference can be applied, as can occur at the measuring throttle point 55 in one of the directional control valves 14 to 16 . For this purpose, the control member 72 is struck on the side of the spring 73 by the respective pressure in the manifold 38 while it is acted upon in the opposite direction by the pressure in the inlet channel 17 at the end. Furthermore, the control member 72 is assigned an electromechanical limit switch 77 which can be actuated when the control member 72 is deflected from its zero position 74 .

The arranged in the module 12 , the third Druckwaagefunk tion assigned pressure compensator 58 is essentially designed as a 3-way four-position valve. The third pressure compensator 58 has a storage connection 78 , to which the storage channel 64 is connected, so that both pressure compensators 57 , 58 are connected in parallel to the storage connection 59 . Furthermore, the third pressure compensator 58 has a return connection 79 to which the return channel 42 is connected. Furthermore, the pressure compensator 58 has a charging connection 81 which is connected via a charging channel 82 to the drain connection 51 of the first directional valve 14 . A longitudinal slide 83 of the third pressure compensator 58 is loaded by a spring 84 in the direction of a basic position 85 , in which it binds the charging port 81 to the return port 79 and blocks the storage port 78 . Upon deflection of the longitudinal slide 83 against the force of the spring 84 it can from its basic position 85 in a first, second and third Ar beitsstellung 86, 87 are brought or 88th With the deflection in working position 86 to 88 , one connection is increasingly opened and the other connection opened. It is in the first working position 86 of the charging port 81 unthrottled with the memory port 78 in connection, while the simultaneous connec tion to the return port 79 is already throttled. In the two-th working position 87 , the connection to the storage connection 78 is maintained unthrottled, while the return connection 79 is already blocked. Finally, in the third working position, the return connection 79 remains blocked, while the connection from the charging connection 81 to the return connection 78 is throttled again. Of course, the third pressure scale 58, shown only in simplified form, also works as a continuously acting throttle valve. The deflection of the steering slide 83 against the force of the spring 84 is possible by a pressure difference, as can occur at the measuring throttle point 55 of the first directional valve 14 in the lower position 46 . For this purpose the control slide 83 is acted on the loaded by the spring 84 side to additionally by the pressure in the charging passage 82 while it is acted upon on the opposite end side by the control pressure in the pressure channel 54th

In the energy recovery module 12 , an unlockable check valve 89 is also arranged, which is scarfed into the storage channel 64 . The check valve 89 is switched so that its output 91 is connected directly to the storage connection 59 , while its input 92 is connected in parallel to the storage connections 63 , 78 of the two pressure compensators 57 , 58 . To unlock the check valve 89 , the control connection of the control pressure in the manifold 38 can be applied. Furthermore, a second check valve 93 is connected in the memory channel 64 , which, however, secures the memory connection 63 of the second pressure compensator 57 .

To increase the stability of the control of the control device 10 , the pressure compensators 57 and 58 in the energy recovery module 12, on the one hand, and on the other hand, the first pressure compensator 21 in the connection plate 18 are set to different pressure drops. It can be particularly favorable if the two springs 73 and 84 in the module 12 are assigned a pressure drop of approximately 5 bar, while the Fe 24 of the first pressure compensator 18 generates a lower pressure drop of approximately 3 bar. As FIG. 1 also shows, the control element of the first pressure compensator 21 is loaded by the pressure in the inlet channel 17 in the direction of its open position 27 .

The mode of operation of the control device 10 is explained as follows, the basic control with the aid of LS technology being assumed to be known per se. The function will be explained using the control of the single-acting lifting cylinder 13 , which usually consists of two cylinders arranged in parallel in stackers. Only during lowering of the lifting cylinder 13 can vary depending on the size of the forces acting on the lifting cylinder 13 of the external load flowing back from the lifting cylinder 13 flow may be diverted into a memory circuit and thereby place an energy recovery. The load pressure-compensated control must be maintained both when lowering and when lifting the load. of decisive influence on the function of the control device 10 are the two circumstances as to whether the load on the lifting cylinder 13 is moved slowly or quickly and whether the hydraulic accumulator 62 is also full or empty. Therefore, these four functional states for lifting and then the corresponding four functional states for lowering are described below.

First functional state: lifting, slow, memory filled. For this purpose, the first directional valve 14 is deflected out of its drawn neutral position 44 in the direction of its lifting position 45 , the control slide 43 only executing a partial stroke in accordance with the slow lifting. Here, the first limit switch 56 turns on the electric motor 29 , so that the volume flow delivered by the constant pump 28 flows through the inlet channel 17 , the connections 47 , 48 in the most directional valve 14 and the measuring throttle 55 effective therein to a lifting cylinder 13 which acts in a fold. In this case, a control pressure gradient is built up via the measuring throttle 55 , which acts on both the first pressure balance 21 , the second pressure balance 57 and the unlockable check valve 89 . In particular, the pressure upstream from the measuring throttle point 55 acts via the inlet channel 17 and the pressure connections (not described in more detail) on the non-spring-loaded end faces of the first pressure compensator 21 and the second pressure compensator 57 . At the same time, the load pressure is tapped downstream of the measuring throttle point 55 in the first directional valve 14 and is controlled via the first control connection 52 , the branch line 36 , the shuttle valves 37 , the manifold 38 on the spring side of the second pressure compensator 57 and at the same time into the control connection of the unlockable check valve 89 . Furthermore, with the second pressure compensator initially in the zero position 74 , this load pressure can reach the load pressure line 69 and act on the first pressure compensator 21 . This load pressure also opens the unlockable check valve 89 and when the hydraulic accumulator 62 is filled, a volume flow from this reservoir 62 now flows via the check valve 89 , the storage channel 64 , the second check valve 93 , the still open pressure compensator 57 into the inlet channel 17 and further via the first Directional control valve 14 for single-acting Hubzy cylinder 13 . When the hydraulic accumulator 62 is full, the control member 72 moves beyond its intermediate position 75 in the direction of its end position 72 . The volume flow flowing from the hydraulic accumulator 62 to the stroke cylinder 13 is throttled to an increasing extent. As before, the effective via the measuring throttle point 55 Druckge falls on the spool 72 of the second pressure compensator 57 , so that a load pressure compensated control is achieved. When the control member 72 moves into its end position 76 , the end switch 77 is actuated, which switches off the electric motor 29 and, as a rule, deactivates the pump 28 . At the same time, the first control connection 67 is blocked in this end position 76 and the second control connection 68 to the return connection 66 is relieved, so that the first pressure compensator 21 can now function as a changeover valve and, in the event of pump operation, the volume flow coming from the pump 28 via the bypass line 23 to the tank 31 can flow out. The third pressure compensator 58 is not in operation here, so that its longitudinal slide 83 assumes the basic position 85 in which the storage connection 78 is shut off.

Second functional state: lifting, fast, memory filled. If, for fast lifting of the lifting cylinder 13, the control slide 43 on the first directional valve 14 is moved beyond its position with slow lifting into an end position during lifting 45 , then the measuring throttle point 55 is opened to a greater or maximum extent in accordance with the "fast lifting" function. The volume flow made available in the hydraulic accumulator 62 is no longer sufficient, as a result of which the control element 72 of the second pressure compensator 57 again moves continuously in the direction of its zero position 74 when the pressure drop decreases. As a result, the volume flow from the hydraulic accumulator 62 can flow unthrottled in the directional directional control valve 14 and to the lifting cylinder 13 , while on the other hand the load pressure prevailing in the collecting line 38 is guided into the load pressure line 69 via the second pressure compensator 57 and applied to the first pressure compensator 21 . During the described return movement of the control member 72 , the limit switch 77 switches the electric motor 29 on again, as a result of which the constant pump 28 additionally promotes a volume flow into the inlet channel 17 . The volume flows from the hydraulic accumulator 62 and from the constant pump 28 are thus jointly available for controlling the lifting cylinder 13 , so that rapid lifting is ensured. The first pressure compensator 21 and the second pressure compensator 57 are simultaneously acted upon by the control pressure drop prevailing over the measuring throttle point 55 . For stable operation, it is now provided that the second pressure balance 57 is set to a somewhat higher pressure drop than the first pressure balance 21 . It is therefore also possible to return a portion of the volume flow of the constant pump 28 from the first pressure compensator 21 to the tank 31 during the transition to the "fast lifting" function. In this functional state, the third pressure compensator 58 is also out of operation.

Functional status: lifting, slow, memory empty. Here too, when the lifting cylinder 13 is slowly raised, the control slide 43 in the first directional valve 14 is only partially deflected in the direction of the lifting position 45 . The electric motor switched on by the limit switch 56 causes the constant pump 28 to promote its volume flow via the directional control valve 14 to the stroke cylinder 13 . The occurring defects in this case at the Meßdrosselstelle 55 observed rule pressure gradient as described previously at the first pressure compensator 21 effectively. This is possible because when the memory 62 is empty, the control member 72 of the second pressure compensator 57 assumes its intermediate position 75 under the influence of the effective control pressure gradient, in which the load pressure is still controlled in the load pressure line 69 and to the first pressure compensator 21 . In the intermediate position 75 , the second pressure compensator 57 creates a throttled connection between the working connection 65 and the storage connection 63 , but the second check valve 93 prevents the volume flow from reaching the storage circuit via the storage channel 64 . With slow lifting, a load pressure-compensated control of the lifting cylinder 13 takes place , the first pressure compensator 21 returning the non-required partial flow of the constant pump 28 to the tank 31 .

Functional status: lifting, fast, memory empty. In these states, the spool 43 of the first directional control valve 14 is deflected even further in its lever position 45 in comparison with slow lifting, so that a larger volume flow is controlled in a load pressure compensating manner to the lifting cylinder 13 . The first pressure compensator 21 will throttle or control the discharge via the bypass line 23 to a large extent, so that the entire volume flow of the constant pump 28 flows to the consumer 13 . As with slow lifting with empty memory 62 , the control member 72 of the second pressure compensator 57 will assume its intermediate position 75 , so that the first pressure compensator 21 can work unhindered. The third pressure compensator 58 is also inoperative here.

Functional state: lowering, slow, memory empty. In this work sequence of the lifting cylinder 13 , a hydraulic energy recovery can be carried out by using the volume flow flowing out under the action of an external load on the lifting cylinder 13 for charging the empty hydraulic accumulator 62 . During slow lowering of the control slide 43 is deflected from its neutral position 44 in the lowering direction position 46, the spool 43 carries out only a portion of its total stroke. In the lower position, the end switch 56 is not actuated, so that the motor-pump unit 28 , 29 is not switched on. When slowly lowering, the volume flow flows from the lifting cylinder 13 via the motor connection 48 to the outlet connection 51 and further via the charging channel 82 to the third pressure compensator 58 . In the first directional valve 14 , the load pressure is tapped upstream of the measuring throttle point 55 and via the second control circuit 53 and the pressure channel 54 to the effective end face of the longitudinal slide 83 of the third pressure compensator 58 . Opposed to this load pressure in the pressure channel 54 acts on the longitudinal slide 83, the force of the spring 84 and the pressure in the charging channel 82 , which corresponds to the pressure downstream of the measuring throttle point 55 . In the third pressure compensator 58 and the unlockable check valve 89 , the longitudinal slide 83 will assume its third working position 88 under the influence of this control pressure drop, in which it throttles the connection from the charging connection 81 to the storage connection 78 , but blocks the connection to the return connection 79 . The flowing from the Hubzy cylinder 13 volume flow can therefore slowly escape through the first directional valve 14 and the third pressure compensator 58 into the empty hydraulic accumulator 62 and charge it. The third pressure compensator 58 ensures a load pressure-compensated mode of operation of the slow lowering process. The build up in the storage channel 64 de pressure can also build up via the second check valve 93 and the second pressure compensator 57 in the inlet channel 17 , where, however, a third check valve 94 in the connecting plate 18 prevents further pressure reduction in the direction of the P connection 19 . The pressure thus prevailing in the inlet channel 17 also acts on the non-spring-loaded end face of the control member 72 and adjusts it against the force of the spring 73 into its end position 76 . In this end position 76 , the load pressure line 69 to the return channel 42 is relieved, so that the first pressure compensator 21 assumes its blocking position 26 . The spring-loaded end face on the control member 72 of the second pressure balance 57 is relieved in the end position 76 to the tank. Since the second and third directional control valves 15 and 16 are in their middle positions 33 , the volume flow escaping from the lifting cylinder 13 can only escape into the hydraulic accumulator 62 , a load-pressure-compensated lowering process being controllable. The constant pump 28 is not actuated here. The control connection of the unlockable check valve 89 is also relieved and the valve 89 is flowed through by the volume flow only in the flow direction, that is from the input 92 to the outlet 91 .

Functional state: lowering, fast, memory empty. This mode of operation is achieved by the control slide 43 of the first directional valve 14 being deflected even further into its lowering position 46 and the measuring throttle point 55 opening up a larger opening cross section. The regulating pressure points that build up via the measuring throttle point 55 are still on the longitudinal slide 83 third pressure compensator 58 effective and now ensures that the longitudinal slide 83 is adjusted in the direction of its second working position 87 during rapid lowering. The connection from the charging port 81 to the storage port 78 is fully controlled while the return channel 42 is still closed. Thus, even with rapid lowering, a load pressure-compensated control takes place, with energy recovery being possible by charging the empty hydraulic accumulator 62 . The recovered energy in the memory 62 can then be used if necessary when one of the directional valves 14 to 16 is actuated.

Status function: lower, slow, memory filled. In this Ar beitsweise the spool 43 of the first directional valve in Rich direction lowering position 46 is deflected, the measuring throttle point 55 is relatively little opened only by a partial stroke. As is when lowering an empty memory the at Meßdrosselstelle 55 ge to passing control pressure differential across the longitudinal slide 83 of the third Druckwaa 58 effectively, the longitudinal slider 83 to its first working position 86 is adjusted here too. The connection from the charging connection 81 to the storage connection 78 is still open here, but via which no volume flow can flow when the hydraulic accumulator 62 is loaded. Rather, the pressure medium flow flowing out of the lifting cylinder 13 must flow in the first working position 86 via the throttled connection from the charging connection 81 to the return connection 79 before the volume flow can escape into the tank 31 . Thus, even when the hydraulic accumulator 62 is filled, a slow lowering in load pressure-compensated ar takes place, the second pressure compensator 57 as in the function "lowering with an empty accumulator" assuming its end position 76 unchanged, so that the first pressure compensator 21 is relieved and therefore out of function is. The constant pump 28 is not in operation when slowly lowering with ge filled memory 62 .

Functional state: lowering, fast, memory filled. In this Ar beitsweise the spool 43 of the first directional valve is fully deflected into its lower position 46 , the throttle restriction 55 is fully opened. When the control pressure drop occurs here at the measuring throttle point 55 , the spring 84 adjusts the longitudinal slide 83 in the third pressure compensator 58 to its basic position 85 , as a result of which the volume flow flowing back from the lifting cylinder 13 via the first directional valve 14 flows almost unhindered via the third pressure compensator 58 into the return duct 42 can flow off. At the same time, the connection to the storage connection 78 is interrupted in the third pressure balance 58 , so that no pressure can build up in the storage channel 64 and thus via the second pressure balance 57 in the inlet channel 17 , as a result of which the control element 72 in the second pressure balance 57 has its spring-centered zero Position 74 . The first pressure compensator 21 thus remains ineffective and the constant pump 28 is switched off.

With the proposed control device 10 , a load pressure-compensated control of a plurality of consumers is thus possible, with the aid of the storage circuit 61 , 62 simple, inexpensive and purely hydraulic energy recovery is possible. For this purpose, the control device 10 only requires three pressure balance functions, in each case one pressure balance function being assigned to one pressure balance. The control device 10 has the advantage that a largely known, existing directional valve block can be used, to which an additional energy recovery module 12 is attached. In connection with a simple-build, switchable constant pump 28 , the control device 10 can also meet difficult working conditions when used in an electric forklift, so that relatively small batteries can be used to drive the electric motor 29 .

Fig. 2 shows a second control device 100 , which differs from the first control device 10 of FIG. 1 mainly in that the first pressure compensator function and the second pressure compensator function are realized in a common main pressure compensator 101 and the third pressure compensator 58 together with the main pressure balance 101 is arranged in the connection plate 102 . For the rest, the same components and parts in the second control device 100 as in Fig. 1 are also provided with the same reference numerals.

The main pressure compensator 101 is essentially designed as a 4-way three-position valve, whereby it has an inlet connection 102 and an outlet connection 103 for realizing the first pressure compensator function, via which the bypass line 23 leads from the P connection 19 to the tank connection 22 in a comparable manner is. To implement the second pressure compensator function, the main pressure compensator also has a storage connection 104 and a working connection 105 . The memory port 104 of the main pressure compensator 101 is connected in a manner comparable to that of the second pressure compensator according to FIG. 1 via the second check valve 93 and the storage channel 64 parallel to the third pressure compensator 58 to the unlockable check valve 89 and further to the storage connection 59 . In the connection plate 106 are thus formed in addition to the two pressure compensators 101 and 58 , the unlockable check valve 89 and the memory port 59 . Furthermore, the first, single-acting directional control valve 14 for controlling the lifting cylinder 13 is closed at the connection plate 106 . The working port 105 of the main pressure compensator 101 is connected within the connecting plate 106 downstream of the third check valve 94 to the inlet channel 17 . A spool 107 of the main pressure compensator 101 assumes a zero position 108 under the action of the force of the spring 24 , in which it interrupts the bypass line 23 and the connection from the storage port 104 to the working port 105 is fully open. The control spool 107 is acted upon in the same way as the control member of the first pressure compensator 21 according to FIG. 1 by the associated control pressure gradient of the directional control valve 14 against the force of the spring 24 and is therefore displaceable from its zero position 108 into at least one intermediate position 109 which it can be deflected further into an end position 111 . In the intermediate position 109 , the connection via the bypass line 23 is opened in a throttled manner, while the connec tion from the memory connection 104 to the working connection 105 is still fully open. Finally, in the end position 111 , the connection via the bypass line 23 is fully open, while the other connection to the working connection 105 is throttled. The control slide 107 can actuate an assigned limit switch 112 . By Zusammenfas the first pressure balance function and the second pressure compensator radio solution tion in the main pressure regulator 101 can be omitted, which was acquired in Fig. 1 of the second pressure regulator 57 control function within the Steuerlei processing system, and the control line system 25 thereby simplified. The individual branch lines 36 of the control line system 25 are connected directly to the load pressure line 69 via the shuttle valves 37 , so that a comparable collecting line is not required. In addition, the shuttle valve 37 of the directional valve 16 adjoining an end plate 113 in the end plate 113 is connected to the return channel 42 , as is known per se in LS technology.

The principle of operation of the second control device 100 is the same as that of the first control device 10 according to FIG. 1, but the main pressure compensator 101 takes over the functions of the previous first and second pressure compensators. It is therefore only discussed as far as their function is necessary to understand the second control device 100 .

In the functional state "lifting, slow, memory filled", the first directional control valve 14 is actuated in a comparable manner, the control pressure difference effective on the main pressure compensator, the control slide of which moves 107 against the force of the spring 24 into its end position 111 . As a result, a volume flow can flow from the hydraulic accumulator 62 via the unlocked check valve 89 and the main pressure compensator 101 and the directional control valve 14 to the lifting cylinder 13 , a load pressure-compensated control being maintained. The constant pump 28 can be switched off via the limit switches 112 or 56 . However, as long as the constant pump 28 is still in operation, its volume flow flows back to the tank practically unthrottled via the bypass line 23 opened in the end position 111 . The third pressure compensator 58 remains inoperative when lifting.

In the functional state "lifting, fast, memory filled" is caused by the further deflection of the control slide on the first directional valve 14 that the control slide 107 of the main pressure compensator 101 assumes its zero position 108 , so that the volume flow coming from the hydraulic accumulator 62 continues to the lifting cylinder 13 can flow. At the same time switches in the zero position 108 of the spool 107 on the En switch 112, the electric motor 29 , so that the constant pump 28 also promotes pressure medium. Since the bypass line 23 is closed in the zero position 108 , the pressure medium flow from the constant flow pump past the main pressure compensator 101 into the inlet channel 17 , merges with the volume flow coming from the accumulator 62 and enables the supply of the lifting cylinder 13 .

With the status function “lifting, slow, storage empty”, the constant pump 28 promotes a volume flow which is controlled to the lifting cylinder 13 via the inlet channel 17 and the actuated first directional valve 14 . The control pressure drop caused by the measuring throttle point 55 ver sets the spool 107 in the main pressure compensator 101 in an intermediate position 109 , the bypass line 23 being partially throttled. The effective main pressure regulator 101, thereby controlling the unused portion of the conveyed from the constant pump 28 Volu menstroms back into the tank 31st The second check valve 93 in the storage channel 64 prevents pressure medium from flowing to the hydraulic accumulator 62 , although the unlockable check valve 89 is unlocked by the effective load pressure in its control connection.

With the status function "lifting, fast, memory empty", the adjustment of the control slide in the first directional valve 14 causes the main pressure compensator 101 to assume its zero position 108 . Thus, the bypass line 23 is blocked and the pressure medium delivered by the constant pump 28 is controlled via the inlet channel 17 and the first directional valve 14 to the lifting cylinder 13 , a load pressure-compensated working method being possible.

In the functional state "lowering, slow, memory empty", energy recovery is possible as in the first control device 10 , the volume flow flowing back from the lifting cylinder 13 via the first directional valve being used in a corresponding manner via the third pressure compensator 48 to charge the hydraulic accumulator 62 . As usual, the directional control valves 15 and 16 are in their middle positions, the pressure-loaded inlet channel 17 being shut off. In this process, the spool 107 is relieved in the main pressure compensator 101 on its end facing the spring 24 via the control line system 25 to the tank, while on the other side it is loaded by the pressure in the inlet channel 17 and is thus pressed into its end position 111 . The constant pump 28 is not in operation.

In the functional state "lowering, fast, memory empty", the third pressure compensator 58 again occupies its second position 87 in a comparable manner, so that the pressure medium flow flowing back can charge the memory 62 . The control slide 107 of the pressure compensator 101 is unchanged in its end position 111 . The constant pump 28 is in turn switched off.

In the functional state "lowering, slow, memory filled", the third pressure compensator 58 takes its first working position 86 in a comparable manner, so that the position of the lifting cylinder 13 via the directional control valve 14 in the lowering must flow out to the tank 31 in a throttled manner. Here, too, the control slide 107 is un changed in its end position 111 , since the pressure prevailing in the storage channel 64 can act via the second check valve 93 and the main pressure compensator 101 in the inlet channel 17 and acts upstream from the third check valve 94 on the control slide 107 while whose opposite end is relieved of pressure via the control line system 25 .

In the functional state "lowering, fast, memory filled" is finally enough by further deflection of the first directional valve 14 that the longitudinal slide 83 of the third pressure compensator 58 assumes its basic position 85 , whereby the volume flow flowing out of the lifting cylinder 13 via the first directional valve 14 and can flow unrestricted to the tank 31 via the third pressure compensator 58 . Since the storage connection 78 is blocked in this position, no pressure builds up in the storage channel 64 either, and the main pressure compensator 101 is displaced into its zero position 108 by the spring 24 . The control connection of the unlockable check valve 89 is also relieved, so that the check valve 89 securely seals the filled hydraulic valve 62 . The motor pump unit 28 , 29 is switched off.

With the second control device 100 , the same functions can be achieved as with the first control device 10 , with load pressure-compensated control of all functions being possible and energy recovery during the lowering process of the lifting cylinder being feasible. The recovered energy can also be easily used to lift the lifting cylinder. The second control device 100 builds considerably more compact by using only two pressure compensators 101 , 58 in conjunction with a reduced effort for the control line system and is therefore particularly suitable for mobile applications.

Of course, there are changes to the embodiments shown gene possible without departing from the spirit of the invention. That's how it is Energy recovery of the facility in LS technology not on the For the sake of simplicity, the system has a vertical arrangement Lift cylinder limited, but can be used for other controls such as B. presses, etc., where the movements of a Drive in the same direction and in the opposite direction to the load. Can too the drive instead of a longitudinal movement, for example a rota execution movement. The terms lifting and lowering are therefore chosen only for the sake of easier presentation and have none restrictive meaning.

Claims (14)

1. Hydraulic control device for a linear actuator, or the same, in particular for an electric stacker, with a motor-pump unit that can be driven by a battery and whose pressure medium flow can be fed to a control circuit with at least one valve, with which the lifting and lowering movements of the hydraulic lifting drive are controllable and with a storage circuit for energy recovery serving with a hydraulic accumulator which can be connected to the return of the directional control valve via a valve when the lifting drive is lowered, characterized in that the control device ( 10 ; 100 ) is designed as a load pressure-compensated control, for which purpose between the directional valve ( 14 ) and the pump ( 28 ) a first, a measuring throttle point ( 55 ) of the directional control valve ( 14 ) associated pressure balance ( 21 ; 101 ) is switched that a second pressure compensator function ( 57 ; 101 ) is provided to move the hydraulic accumulator ( 62 ) via the directional valve ( 14 ) to the stroke drive ( 13 ) to control the pressure medium flow independently of the load and that the valve switched into the return is designed in such a way that it performs a third pressure compensator function ( 58 ) for the pressure medium flow flowing away from the stroke drive ( 13 ) when lowering and that a hydraulic accumulator ( 62 ) starts to secure Check valve ( 89 ) from the load pressure in the control line system ( 25 ) can be unlocked. 2. Hydraulic control device according to claim 1, characterized in that each of the three pressure compensator functions is assigned a separate pressure compensator ( 21 , 57 , 58 ), of which the second and third pressure compensators ( 57 , 58 ) are arranged in a common housing ( 12 ) , which is separated in particular from the first pressure compensator ( 21 ). 3. Hydraulic control device according to claim 1, characterized in that the first and second pressure compensator function are combined together in a pressure compensator ( 101 ), which is arranged in particular with the pressure compensator ( 58 ) for the third pressure compensator function in a housing ( 106 ). 4. Hydraulic control device according to one of claims 1 to 3, characterized in that the unlockable check valve ( 89 ), which is connected with its outlet ( 91 ) to the hydraulic accumulator ( 62 ), with its inlet ( 92 ) parallel to the pressure compensators ( 57 , 58 ) for the second and third pressure compensator function. 5. Hydraulic control device according to one or more of claims 1 to 4, characterized in that the third Druckwaa ge ( 58 ) is essentially designed as a 3-way 4-position valve, the longitudinal slide ( 83 ) of which on the Meßdrosselstel le ( 55 ) effective pressure difference against the force of a spring ( 84 ) can be applied. 6. Hydraulic control device according to claim 5, characterized in that the longitudinal slide ( 83 ) in a spring-centered basic position ( 85 ) a with the directional valve ( 14 ) connected to the charging port ( 81 ) to a return port ( 79 ) relieves and a memory port ( 78 ) shuts off, with increasing deflection from the basic position ( 85 ) the connection to the return connection ( 79 ) is throttled and that to the storage connection ( 78 ) opens, whereby in a third working position ( 88 ) with blocked return connection ( 79 ) also the connection to the storage connection ( 78 ) is throttled. 7. Hydraulic control device according to one or more of claims 1 to 6, characterized in that the Meßdrosselstel le ( 55 ) containing directional valve ( 14 ) in addition to an inlet connection ( 47 ), a return connection ( 49 ), a motor connection ( 48 ) and a first control connection ( 52 ) for tapping the load pressure when lifting downstream of the measuring throttle point ( 55 ) has an additional outlet connection ( 51 ) which is connected to the pressure compensator ( 58 ) of the third pressure compensator function and that a second control connection ( 53 ) is provided is tapped via the load pressure upstream of the measuring throttle point ( 55 ) in the lowering position and used to control the pressure compensator ( 58 ) against the force of the spring ( 84 ). 8. Hydraulic control device according to one or more of claims 1 to 7, characterized in that the motor-pump unit Gat has a constant pump ( 28 ) which is driven by a batterieeange driven electric motor ( 29 ) and that for switching the electric motor ( 29 ) at least the directional control valve ( 14 ) and the pressure compensator ( 57 ) performing the second pressure compensator function are each assigned an electrical limit switch ( 56 , 57 ). 9. Hydraulic control device according to one of claims 1, 2 and 4 to 8, characterized in that the first pressure compensator ( 21 ) is designed as a 2/2 throttle valve lying in a bypass line ( 23 ) and the second pressure compensator ( 57 ) essentially is designed as a 5/3 valve which, in addition to two working connections ( 63 , 65 ), has three control connections ( 66 , 67 , 68 ). 10. Hydraulic control device according to claim 9, characterized in that the second pressure compensator ( 57 ) controls the connection from the pump ( 28 ) to the hydraulic accumulator ( 62 ) and the first pressure compensator ( 21 ) optionally with the tapped in the directional control valve ( 14 ) Load pressure or with the return pressure. 11. Hydraulic control device according to one or more of claims 3 to 8, characterized in that the first and two te pressure compensator function, common pressure compensator ( 101 ) has at least four working connections ( 102 , 103 , 104 , 105 ) with de NEN it is connected in a bypass line ( 23 ) and in a connection between a storage channel ( 64 ) and one of the pump ( 28 ) to the Wegeven valve ( 14 ) leading inlet line ( 17 ). 12. Hydraulic control device according to claim 11, characterized in that the pressure compensator ( 101 ) at least one spring-centered zero position ( 108 ), in which the bypass line ( 23 ) is blocked and the other connection ( 64 , 17 ) is open, an intermediate position ( 109 ) in which the bypass line ( 23 ) is throttled and the other connection is open and has an end position ( 111 ) in which the bypass line ( 23 ) is open and the other connection ( 64 , 17 ) is throttled. 13. Hydraulic control device according to one or more of claims 1 to 12, characterized in that in the from Hydrospei cher ( 62 ) to the pressure compensator ( 57 ; 101 ) for the second Druckwaagenfunk tion leading storage line ( 64 ) between the Druckwaa ge ( 57 ; 101 ) and the unlockable check valve ( 89 ) is a two-way check valve ( 93 ), which only opens to the pressure compensator ( 57 ; 101 ). 14. Hydraulic control device according to one or more of the preceding claims, characterized in that the pressure drop set on the first pressure compensator ( 21 ; 101 ) is different, in particular lower, in relation to the pressure drop the pressure compensator taking over the third pressure compensator function ( 58 ).