DE102008034301B4 - Hydraulic system with an adjustable quick-release valve - Google Patents

Abstract

Hydraulic system, comprising:
a hydraulic actuator (1) comprising at least a first chamber (a) and a second chamber (b) each having a connection for connection to the hydraulic system,
at least one adjustable hydraulic pump (2), comprising at least one first port and a second port, wherein the first port with the first chamber (a) of the hydraulic actuator and the second port with the second chamber (b) of the hydraulic actuator (1) connected is,
characterized,
in that the first chamber (a) is connected to the second chamber (b) via at least one fast-flow valve (7) with a controllable flow cross-section, and in that the rapid-flow valve (7) acts on the pressure of the first chamber (a) in the direction of a closed position is.

Description

The invention relates to a hydraulic system with a hydraulic actuator and at least one adjustable hydraulic pump.

In known pump-controlled hydraulic systems of a shovel loader or the like, the flow rates and thus, for example, the lifting and lowering speed are determined by the pump (s) present in the system, as described for example in US Pat US 2007 166 168 A1 . DE 10 344 480 B3 . EP 1 571 352 A1 and DE 10 2007 025 742 A1 was disclosed. During a normal work operation of a machine, in the case of a bucket, a gravitational force always acts on the boom of the bucket loader, that is, in the hydraulic system, for example, a load pressure always acts on a bottom side of the boom cylinder. In this case, the lifting speed as well as the lowering speed is controlled by the flow rate on the bottom side of the cylinder. Generally, in the operation of a machine controlled by such a hydraulic system, the lowering speed should be 30% to 70% higher than the lifting speed to allow efficient operation of the machine. However, this requirement for the asymmetrical operation generates a nominal size problem in the pump-controlled hydraulic system. If the pump is designed according to the lowering speed, the resulting pump has a very large nominal size. With this pump, however, the maximum lifting speed can not be achieved when lifting at full load, because the available power of the engine is not sufficient. Consequently, during the load stroke, the swing angle of the pump would only be about 50% and thus the efficiency of the pump would not be in the optimum range.

This problem leads to the desire to develop a hydraulic system for controlling lifting cylinders or comparable hydraulic actuators, which allows a faster than the lifting speed lowering of the lifting cylinder or reduce the nominal size of the pump at the same lowering speed. This achieves better pump efficiency when lifting as well as lowering a lifting cylinder.

From the US 6,804,957 B2 is a hydraulic system known that allows a quick lowering function of a hydraulic cylinder. The system includes a bypass valve located between the bottom of the hydraulic cylinder and the pump and connected directly to the tank. The valve can be opened in the lowering operation of the cylinder and directs part of the volume flow directly into the tank. The derived oil volume is therefore missing in the system and an additional pump is required as a storage loading pump, which promotes the oil in the circulation or in the memory, whereby additional energy is needed. In order to enable energy-efficient and efficient work, however, a hydraulic system would be desirable that does not require an additional pump and in which the nominal size of the pump by the required operating speed against the load, for example when lifting a bucket or the pressing of garbage in refuse collection vehicles , is determined.

The aim of the present invention is therefore to achieve a higher speed in the load direction in a pump-controlled hydraulic working circle at the speed against the load direction predetermined nominal size of a hydraulic pump or vice versa to reduce the nominal size of the pump at the same lowering speed, without using an additional pump and thus to increase energy consumption in the system.

The object is achieved by the hydraulic system according to the invention according to claim 1 and the method according to claim 13.

In a first aspect, the invention relates to a hydraulic system having at least one hydraulic actuator, for example for lifting loads, comprising at least two chambers for moving the actuator in or against the load direction. The chambers each have a connection for connection to the hydraulic system. The hydraulic system comprises at least one adjustable hydraulic pump with at least two ports, one port being connected to a first chamber of the hydraulic actuator and the second port being connected to a second chamber of the hydraulic actuator. Furthermore, the hydraulic system has at least one fast-flow valve with a controllable flow cross-section, via which both chambers can be connected. In addition, the quick-flow valve is acted upon by the pressure of the first chamber in the direction of a closed position.

With such a hydraulic system, it is possible to reciprocate pressure means between the chambers of the hydraulic actuator by means of the pump, thereby enabling actuation, for example lifting and lowering. Since the actuator can be installed in a variety of ways in a machine can, for example, it would also be conceivable to arrange the actuator horizontally, whereby an extension and retraction of the actuator is made possible by the hydraulic pump of the system described above. In the following, for the sake of simplicity, we will talk about lifting and lowering a load.

Since the quick-flow valve is arranged parallel to the pump and connects the two chambers of the actuator with each other, the fast-lowering valve is used as a by-pass circuit for the pump to increase the total volume flow and thus the operating speed. It is therefore possible to convey a portion of the pressure medium not by the pump, but by an existing pressure difference due to a load from the first chamber of the actuator directly into the second chamber of the actuator. Since in this case no longer the entire pressure medium has to be conveyed by the pump, but a part of the pressure medium is conveyed by bypassing the pump through the quick-flow valve, it is possible to achieve an overall larger volume flow of the pressure medium. Accordingly, the quick-flow valve can be used to achieve, for example, a higher lowering speed when lowering the actuator. The increase in the operating speed is generally possible when the actuator is actuated in the load direction.

An advantage of the above-described design of the system is that, unlike conventional systems, there are no additional lines between the quick-release valve and a tank of the hydraulic system. In addition, can be dispensed with a feed pump that promotes pressure fluid from the tank back into the lines.

Consequently, the energy consumption of the system can be reduced compared to other systems.

Preferably, the quick-flow valve is opened only when the pump is fully swung out. This already creates a pressure difference between the chambers of the actuator before the opening of the quick-release valve. Preferably, the flow cross-section of the quick-release valve is dimensioned so that the setting of a pressure drop over the quick-flow valve is achieved. It is thus possible to pass a part of the volume flow through the quick-flow valve.

The flow cross section of the quick-release valve is preferably freely adjustable in a value range from 0% to 100%. It is therefore possible to influence the volume of oil delivered by the quick-flow valve or the volume flow with the aid of the adjustment of the flow cross-section. The lowering speed or operating speed in the load direction of the actuator can thus be adapted individually to the wishes of a user.

With the system described above, different speeds of the actuator can be achieved, depending on whether and how far the fast-flow valve is opened. The pump thereby promotes the same maximum oil volume when lifting and during lowering of the actuator, regardless of whether the quick-lowering valve is open or not. It is therefore possible to operate the pump in both modes of the actuator, in the lifting as well as in the lowering operation close to their optimum efficiency.

Preferably, in the stroke operation of the actuator, the quick-flow valve is closed, whereby a by-pass circuit of the actuator or the pump is prevented. In the lifting operation, therefore, the entire pressure medium to be pumped is conveyed only with the help of the pump in one of the chambers.

The pump of the hydraulic system described above is preferably a dual-circuit pump and has a nominal size, which is designed according to the required speed against the load, that is, for example, the stroke speed of the actuator. As a result, the pump is smaller and cheaper than when dimensioning the pump according to the required speed in the load direction, ie the lowering speed, which is generally above the required lifting speed.

Also possible is the integration of a memory for pressure medium in the system described above. This allows the provision of pressurized pressure medium. The pressure medium is stored there when lowering from a load increasing the stored pressure energy.

In a further preferred embodiment, the hydraulic system according to the invention also has a flow compensating valve, via which the first or the second chamber of the actuator can be connected to a tank volume, preferably via a pressure limiting valve. The quantity compensation valve is designed such that an excess of pressure medium in one of the chambers of the actuator or in one of the lines which connect the chambers of the actuator to the pump during the Operation of the quick-lowering valve is prevented. This prevents pressure equalization between the two chambers of the actuator and thus ensures the function of the quick-release valve.

In another aspect, the present invention describes a method of actuating a hydraulic actuator by means of a hydraulic system. In the method according to the invention, on the one hand, a volume flow is generated from a first chamber of the hydraulic actuator into a second chamber of the hydraulic actuator by a pump. In addition, the volume flow is increased to further increase the speed by opening a fast scavenge valve connecting the first to the second chamber. The method according to the invention has the advantage that it is no longer necessary to convey the entire volume flow required for lowering a load from the first chamber into the second chamber through the pump. Rather, a portion of the total volume flow is conveyed via the quick-flow valve directly from the first chamber into the second chamber. Accordingly, the pump can be made smaller.

According to an advantageous embodiment, the movement of the actuator in the load direction is divided into two areas. First, to increase the actuation speed, first the pump is swung out in the direction of its maximum delivery volume. After reaching the maximum delivery volume of the pump, to further increase the actuation speed of the hydraulic actuator, an adjustable quick-release valve is moved toward its open position, thus providing an increasingly open connection between the first chamber and the second chamber of the hydraulic actuator. The total volume flow from the first chamber into the second chamber is thus increased beyond the maximum delivery volume of the pump. This makes it possible to achieve an increased speed in the direction of the load compared to the actuation speed of the actuator against the load direction, that is to say, for example, when lifting a load.

In this case, the user preferably selects from two control ranges, wherein the controllable fast-flow control valve can be opened in at least one of the two control ranges. The user thus has the choice between the first control range, in which the conveying speed of the pump can be adjusted continuously, and a second control range, in that the fast-flow control valve can be actuated at the maximum delivery rate of the pump.

In this way, it is ensured that the pump already delivers maximum when opening the quick-release valve and thus has already set a pressure gradient between the two chambers of the actuator. In addition, a user thereby has the choice of having the actuator lowered only by means of the pump or additionally adding the quick-flow valve for a faster lowering of the actuator. A certain overlap area, in which the delivery volume of the pump increases at the same time and the fast-flow valve is already opened, is also conceivable.

With opposite movement of the actuator, the user can also adjust the speed of the pump continuously. The quick-lowering valve can not be opened during this movement.

Furthermore, the quick-lowering valve is automatically closed in the lowering operation, if the load pressure exceeds a certain limit. It can thus be prevented that e.g. A machine boom under load in the quick lowering mode represents a danger to the user or bystanders.

According to the invention, an overpressure in one of the two chambers of the actuator can be prevented by a quantity compensation valve integrated in the hydraulic system. This compensates for an excessive pressure medium flow generated by the hydraulic pump. The resulting difference quantity is discharged via the flow compensating valve into the tank.

• 1 eine schematische Darstellung des erfindungsgemäßen hydraulischen Systems nach einer bevorzugten Ausführungsform,
• 2 eine schematische Darstellung des erfindungsgemäßen hydraulischen Schnellsenkventils,
• 3 eine schematische Darstellung des erfindungsgemäßen hydraulischen Schnellsenkventils mit Schwimmstellungsventil
• 4 eine schematische Darstellung des erfindungsgemäßen hydraulischen Systems mit einem Mengenausgleichsventil und Abführen des Druckmittels über ein Druckbegrenzungsventil der Speiseeinrichtung, und
• 5 eine schematische Darstellung des erfindungsgemäßen hydraulischen Systems mit einem Mengenausgleichsventil und separatem Druckbegrenzungsventil.

A preferred embodiment of the hydrostatic system according to the invention is illustrated in the drawings and will be explained in more detail in the following description. Show it:

• 1 a schematic representation of the hydraulic system according to the invention according to a preferred embodiment,
• 2 a schematic representation of the hydraulic quick-release valve according to the invention,
• 3 a schematic representation of the hydraulic quick-release valve according to the invention with float valve
• 4 a schematic representation of the hydraulic system according to the invention with a flow compensating valve and discharge of the pressure medium via a pressure relief valve of the feed device, and
• 5 a schematic representation of the hydraulic system according to the invention with a flow compensating valve and separate pressure relief valve.

The inventive hydraulic system in 1 has an actuator 1 with two chambers a and b on. Furthermore, the actuator consists of a piston rod 1a and a piston 1b , The separation of the two chambers a, b takes place through the piston 1b , The second chamber b is on a piston rod side of the actuator 1 arranged and the first chamber a is on the bottom side of the piston 1b of the actuator 1 arranged. By introducing into pressure medium in the first chamber a, the actuator 1 thus be lifted. The introduction of pressure medium in the second chamber b allows a lowering operation of the actuator.

In the embodiments of the invention, a lifting and lowering of a load is assumed. In general, however, it is so that the hydraulic actuator can be actuated against a load direction, which corresponds to the lifting, or can be operated in the load direction, which is the case when lowering. This can be the case, for example, in a waste compactor, where work is performed against the load direction when compacting the refuse. It is assumed that for actuation against the load direction pressure medium of the first chamber a is supplied.

It should be noted that instead of the illustrated actuator 1 also another hydraulic actuator 1 can be used. So it is conceivable, for example, a hydraulic actuator 1 with a continuous piston rod 1a to use on both sides of the piston 1b of the actuator 1 to obtain the same large pressure surfaces for the application of a pressure medium.

Furthermore, the inventive hydraulic system in 1 a pump 2 on top of that by a motor 3 , preferably a diesel engine, is driven. The pump 2 is designed to be adjustable in terms of their stroke volume and preferably a hydraulic axial piston machine in swash plate construction, which is pivotable from a neutral position in two directions. The stroke volume is adjusted by adjusting an inclination of the swash plate. In the example shown, the pump is 2 a two-circuit pump.

The dual-circuit pump has two individual pumps 2a . 2 B on. The first single pump 2a is via a storage line 15 with a hydraulic accumulator 4 connected. With its second connection is the first single pump 2a with a first control pressure line 16 connected to the first single pump 2a connects to the first chamber a. The second single pump 2 B also has two connections. A first connection is via a connecting line, which is in the first control pressure line 16 terminates connected to the first chamber a. The second connection he second single pump 2 B is on the other hand via a second control pressure line 17 connected to the second chamber b.

The first control pressure line 16 and the second actuating pressure line 17 are over a first connection line 18 connected with each other. In the first connection line 18 is a quick-release valve 7 arranged so that, depending on the setting of the quick-release valve 7 a throttled connection between the first control pressure line 16 and the second actuating pressure line 17 is made.

Furthermore, it is parallel to the connecting line 18 a second connection line 19 formed, which is the first control pressure line 16 with the second control pressure line 17 combines. In the connection line 19 are two oppositely arranged check valves V1 and V2 intended. Between these two check valves V1 , V2, each in the direction of the first control pressure line 16 to or the second control pressure line 17 to open, opens a supply pressure line 20 in the second connection line 19 out.

That of the second connection line 19 opposite end of the feed pressure line 20 is with a feed pump 6 connected. The feed pump 6 sucks from a tank volume 5 Pressure medium via a suction line 21 at. The feed pressure line 20 is via a pressure relief valve 11 connectable to the tank volume.

The feed pump 6 is also one via a drive shaft with the pump 2 connected engine 3 driven. The valves V1 and V2 are non-return valves that provide a flow only in the conveying direction of the pump 6 allow and thus enable the tracking of pressure medium occurring pressure medium leakage.

As already stated above, the first control pressure line 16 with the connecting lines 18 and 19 connected. The second control pressure line B is connected to the other ends of the connecting lines 18 and 19 connected. This is the hydraulic actuator 1 and the quick-release valve disposed in the first connection line 7 connected in parallel.

The following is the operation of the hydraulic system with the quick-lowering valve 7 be explained in more detail.

When lifting the actuator 1 promotes the pump 2 Pressure medium in the first control pressure line 16 , The quick-lowering valve 7 is closed in lifting operation. Thus, there is no promotion of the pressure medium in the direction of the second chamber b. The pressure medium enters the first chamber a of the actuator 1 , At the same time, the second chamber b becomes the pump 2 promoted. The result is a lifting or extending the piston 1b of the actuator 1 ,

In addition, with the help of the feed pump 6 Pressure medium can be provided from the tank to compensate pressure medium leakage.

In lowering mode of the actuator 1 promotes the pump 2 Pressure medium from the first chamber a of the actuator 1 and into the second chamber b. Because of the piston rod 1a the volume flows from / to the first chamber a and into / from the second chamber b are different. The resulting difference volume is increasing the potential energy in the hydraulic accumulator 4 promoted. The result is a lowering or retraction of the actuator 1 , Since there is between the removal of pressure fluid from the hydraulic accumulator 4 and returning to a volume difference, as can be seen from the example set forth below, is one way of charging the hydraulic accumulator 4 intended. This could be done, for example, by the feed pump 6 then done via a check valve with the hydraulic accumulator 4 would be connected.

To increase the lowering speed, the quick-lowering valve is 7 intended. The quick-lowering valve 7 creates a throttled connection between the first control pressure line 16 and the second actuating pressure line 17 , In addition to the volume flow, which is due to the pump pivot angle from the first chamber a in the second chamber b is promoted, can thus at least partially open fast-flow valve 7 Pressure medium from the first chamber a, bypassing the hydraulic pump 2 flow into the second chamber b. The total volume flow from the first chamber a into the second chamber b thus increases, as a result of which the lowering speed is likewise increased.

The quick-lowering valve is, for example, an adjustable 2/2-way valve with proportional control between two end positions. In this case, a control signal proportional to a control signal is generated, the fast-lowering valve 7 against a quick-lowering valve 7 acted upon in its closed position acting on return spring.

Preferably, a control of the quick-release valve 7 designed such that the opening of the quick-lowering valve 7 by a user only at maximum flow rate of the pump 2 is possible. Thus, a user can control the delivery volume of the pump 2 infinitely variable up to the maximum delivery volume. In addition, the user can use the quick-lowering valve 7 at maximum delivery of pressure medium by the pump 2 open and close as needed. Accordingly, an acceleration of the lowering process is achieved because in addition to the pump 2 Pressure fluid from the chamber a through the quick-flow valve 7 is encouraged.

Because even before opening the quick-lowering valve 7 the pump 2 its maximum delivery performance, creates a pressure gradient between the first chamber a and second chamber b of the actuator 1 , This pressure gradient allows correct operation of the quick-release valve 7 , Due to the pressure difference in the chambers a and b prevails in the control pressure lines 16 and 17 and therefore also in the line 18 also a pressure gradient. When opening the quick-lowering valve 7 Accordingly flows a volume flow Q from the first control pressure line 16 in the second control pressure line 12 , This volume flow Q is higher, the greater the pressure gradient between the lines 16 and 17 is. Therefore, a small valve cross-section of the quick-release valve is preferred 7 to choose a significant pressure drop and thus a high volume flow Q above the quick-release valve 7 allows.

The quick-lowering valve 7 is equipped with a variable flow cross-section. A user can thus control the opening of the valve between 0 and 100% and thus the lowering speed of the actuator 1 influence. The control of the quick-lowering valve 7 is preferably carried out electromagnetically. moreover can also other control options for the quick-release valve 7 be provided, as exemplified in 2 is shown.

For safety reasons, a limitation of the lowering speed can be provided, which is the opening of the quick-lowering valve 7 prevented at a certain load pressure or an already opened quick-lowering valve 7 brings back to its starting position, in which the first connecting line 18 is interrupted. In this case, for example, an integrated pressure sensor, the load pressure, ie the pressure in the first chamber a of the actuator 1 measure and pass this to a control unit of the hydraulic system. If the load pressure exceeds a previously set limit, the quick-release valve closes automatically 7 , This limit value preferably corresponds to 1.2 times the pressure level of the actuator operation without load.

2 shows a preferred wiring of the quick-release valve 7 located in the first connection line 18 located. It is in the illustrated embodiment, a 2/2-proportional valve. In the starting position, by a return spring 7b is set, is the connection between the control pressure lines 16 and 17 blocked. When controlling the quick-lowering valve 7 through the control valve 8th is a restricted flow through the quick-lowering valve 7 allows. In this case, pressure medium passes from the first control pressure line 16 to the second actuating pressure line 17 , An integrated non-return valve function allows the flow to be reversed even when the quick-release valve is open 7 blocked. The illustrated pressure line 7a allows the above-mentioned safety function on hydrostatic way. As the load pressure increases, it increases in addition to the spring force of the return spring 7b acting hydraulic force in the closing direction. Thus, the opening force required for opening also increases, and at constant opening force, the quick-lowering valve becomes 7 automatically placed in a closed position.

For pilot control is with the quick-lowering valve 7 a control valve 8th through the pressure line 8a connected. It is via the pressure line 8a a pressure surface of the quick-release valve 7 with a hydrostatic control force against the force of the return spring 7b applied. A realization of different flow rates due to different switching positions of the quick-release valve 7 is possible by adjusting the hydraulic control force.

The control valve 8th is preferably a 3/2 solenoid proportional solenoid valve. With the help of an additional spring 8c is set a starting position of the valve. In the initial position, which forms a first end position of the valve, the control valve 8th to 2 therefore with the tank 5 connected. In this switching position thus no pressure fluid from the control valve 8th through the pipe 8a to the quick-lowering valve 7 promoted and the pressure surface of the quick-release valve 7 is relieved. With a control of the control valve 8th with the help of the associated electromagnet 8d becomes the pressure line 8a depending on the height of the control signal increasingly with a pressure medium source 8b connected. With an adjustment of the control valve 8th in the direction of this second end position can therefore pressure medium from the pressure medium source 8b to the pressure line 8a be promoted, creating a targeted control of the quick-release valve 7 in the opening direction. Due to the variable adjustability of the valve, the height of the pressure surface of the quick-release valve 7 adjusted pressure.

The promotion of pressure medium from the source 8b can be realized for example by a feed pump. As it is at the control valve 8th is a proportional valve can, with the help of the control by the electromagnet 8d different switching positions and thus also different flow rates through the control valve 8th will be realized.

3 shows an embodiment of the quick-release valve according to the invention 7 combined with an additional float valve 9 , Here is the float valve 9 in the second connection line 19 arranged. In the illustrated float valve 9 it is 2/2-way valve. In the starting position is the float valve 9 blocked. This initial position of the valve is controlled by the spring 9a certainly. In addition, a second pressure line 9b present, which is the float valve 9 with the first connection line 18 on the side facing the first chamber a side of the quick-release valve 7 combines. The spring force of the spring 9a and the force of pressurization on the float valve 9 by the pressure in the pipe 9b add up. The electromagnetic control of the float valve 9 is thus overridden hydraulically at elevated load pressure. The float valve 9 For safety reasons, therefore, it moves into its closed position when the load pressure rises above a value which can be determined by the magnitude of the electromagnetic force.

The electromagnetic force is generated by an electromagnet 9c as a counterforce to the spring 9a and for pressurizing through the conduit 9b generated. When exposed to the electromagnetic force and a non-critical low load pressure is an opening of the float valve 9 causes. Through the open switching position of the float valve 9 becomes while opening the quick-release valve 7 realized a floating position of the hydraulic system. Here is the first connection line 18 of the hydraulic system on the side facing the second chamber b with respect to the quick-lowering valve 7 with the tank 5 through a throttle circuit 10 connected. The flow of pressure medium to the tank 5 is therefore limited. The throttle circuit 10 is carried out with a check valve thus possibly pressure medium from the tank 5 can be sucked, so that, for example, cavitation is prevented in the hydraulic system.

4 shows an inventive embodiment of the hydraulic system according to 1 with a quantity compensating valve 23 , This is over a first connection line 22a with the actuating pressure line 16 and thus with the first chamber a of the actuator 1 connected. Via a second connecting line 22b is the quantity balance valve 23 with the actuating pressure line 17 and thus with the second chamber b of the actuator 1 connected. The quantity compensation valve 23 is also connected to the feed system and thus via the pressure relief valve 11 with the tank 5 connected.

In the quantity compensation valve according to the invention 23 it is preferably a 3/3-way valve, which is controlled by occurring pressure forces or pressure differences. Depending on the occurring pressure conditions on the piston and the bottom side of the actuator 1 becomes either the first chamber a or the second chamber b with the tank 5 connected via the pressure relief valve. At pressure equilibrium is the quantity compensation valve 23 in its initial position.

At the in 4 illustrated quantity compensation valve 23 it is a 3/3-way valve. In the starting position is the flow compensating valve 23 locked and the connecting lines 22a and 22b from each other and from the tank 5 separated. Two pressure measuring lines 25a . 25b are with the signal pressure lines 16 and 17 connected, whereby in the case of overpressure in one of the two control pressure lines 16 . 17 the valve 23 is activated. This is done in such a way that by an overpressure in the control pressure line 17 the control pressure line 16 with the tank 5 via the pressure relief valve 11 is connected.

At an overpressure in the control pressure line 16 on the other hand, the control pressure line 17 with the tank 5 via the pressure relief valve 11 connected. As a result, by operating the quantity compensating valve 23 optional oil volume from the control pressure line 16 or from the control pressure line 17 to the tank 5 be dissipated.

dabei entspricht A_st der Fläche der Stangenseite des Aktuators 1 und A_bo der Fläche der Bodenseite des Aktuators 1.The quantity compensation valve 23 is preferably activated when the ratio of the current fast lowering speed to the maximum speed of the actuator 1 (in operation without fast-flow valve) exceeds a factor K. The factor K is calculated as follows: $$K=\frac{-1}{2\left(A\_st/A\_bO-1\right)}.$$

where A_st corresponds to the area of the rod side of the actuator 1 and A_bo the area of the bottom side of the actuator 1 ,

The operation of the quantity compensation valve 23 is explained below.

Is the ratio of the quick lowering speed to the maximum speed of the actuator 1 less than the previously defined factor K, less oil volume is delivered from the rod side and thus from the first chamber a to the second chamber b than is needed in the second chamber b. This means that the pumped volume of the quick-release valve 7 and the pump 2 is insufficient to meet the needs of the rod side (chamber b) of the actuator 1 cover up. Therefore, in this case, additional volume of oil to the chamber b using the feed pump 6 promoted. The quantity compensation valve 23 will not be activated in this case.

Is the ratio of the quick lowering speed to the maximum speed of the actuator 1 more than the previously defined factor K, more oil volume is delivered from the rod side and thus from the first chamber a to the second chamber b than is needed in the second chamber b. This means that an excess of oil volume in the control pressure line 17 is encouraged. In this case, the quantity compensation valve 23 through the pipe 25b activated, whereby an excess of oil volume is prevented by oil volume from the control pressure line 16 via the pressure relief valve 11 of the feed system directly to the tank 5 flows.

Accordingly, with the quantity compensation valve according to the invention 23 prevents the pressures on the bottom side and on the rod side of the actuator 1 during operation of the quick-release valve 7 adjust and the operation of the quick-release valve 7 influence negatively.

For setting a response limit for a pressure difference between the rod and bottom side and for returning the flow compensating valve 23 in its initial position centering springs may be provided, which are not shown in the drawing.

For the sake of clarity, a numerical example for k = 1.21 is shown below, which corresponds to a typical ratio of the piston areas on the rod side and bottom side.

Case A: Lowering speed 1.2 times faster than quick-lowering valve

Q of cylinder (chamber a) 204 l / min Q by pumps 2a, 2b 85 and 85l / min Q through quick-release valve 34 l / min Q_total (quick-lowering valve + pump 2b) 119 l / min Q requires from chamber b 120 l / min → 1 l / min is missing and is from feed pump 6 delivered

Case B: Lowering speed 1.25 times faster than without quick-lowering valve

Q cylinder (chamber a) 212 l / min Q by pumps 2a, 2b 85 and 85l / min Q through quick-release valve 42 l / min Q_total (quick-lowering valve + pump 2b) 127 l / min Q requires from chamber b 125 l / min → Excess is forwarded through purge valve 23 via the pressure relief valve to the tank

The 5 shows a starting from the embodiment of 4 modified embodiment. Unlike the 4 Here is a separate pressure relief valve 11 ' provided, which the quantity compensation valve 23 connects to the tank. The function is essentially the same as the one already 4 function described. However, it is advantageous in the embodiment according to 5 that over the separate pressure relief valve 11 ' a flush valve in a conventional hydrostatic drive equivalent function is achieved. This embodiment is therefore preferred. It also allows the pressure relief valve 11 ' to adapt to the quantity compensation function with regard to the quantities flowing through and the set pressure, without having to compromise with regard to other functions of the pressure limiting valve, such as a pressure limitation of the permissible feed pressure. A commonly existing pressure relief valve for limiting the feed pressure of a feed system is in the 5 not explicitly shown. However, it is usually present as well. In rare exceptional cases could also be a direct connection of the quantity compensation valve 23 be provided with the tank volume.

The invention is not limited to the illustrated embodiment. Rather, advantageous combinations of the individual features are possible with each other.

Claims (16)

A hydraulic system, comprising: a hydraulic actuator (1), comprising at least a first chamber (a) and a second chamber (b), each with a connection for connection to the hydraulic system, at least one adjustable hydraulic pump (2), comprising at least one first port and a second port, wherein the first port with the first chamber (a) of the hydraulic actuator and the second port with the second chamber (b) of the hydraulic actuator (1) is connected, characterized in that the first chamber (a) with the second chamber (b) via at least one quick-lowering valve (7) is connected to a controllable flow cross-section, and that the quick-lowering valve (7) with the pressure of the first chamber (a) is acted upon in the direction of a closed position. Hydraulic system after Claim 1 , characterized in that the flow cross-section of the controllable quick-lowering valve (7) by means of a control signal between 0 and 100% is adjustable. Hydraulic system according to one of the preceding claims, characterized in that the controllable quick-flow valve (7) is closed against a load when the hydraulic actuator (1) is actuated. Hydraulic system according to one of the preceding claims, characterized in that a nominal size of the pump (2) is dimensioned after a required stroke speed. Hydraulic system according to one of the preceding claims, characterized in that the hydraulic pump (2) is a dual-circuit pump. Hydraulic system according to one of the preceding claims, characterized in that a reservoir (4) for hydraulic fluid is connected to at least one pump (2,6). Hydraulic system according to one of the preceding claims, characterized in that the quick-lowering valve (7) by means of an electro-proportional pilot valve (8) is actuated. Hydraulic system according to one of the preceding claims, characterized in that a float position valve (9) is provided, via which the first and the second chamber (a, b) of the actuator (1) with a tank volume (5) are connectable. Hydraulic system after Claim 8 , characterized in that the float position valve (9) is connected to a between the fast-flow valve (7) and the second chamber (b) formed line section. Hydraulic system after Claim 8 or 9 , characterized in that the float position valve (9) is acted upon in the direction of a closed rest position with the pressure prevailing in the first chamber (a). Hydraulic system after Claim 1 to 10 , characterized in that a quantity compensating valve (23) is provided, via which the first or the second chamber (a, b) of the actuator (1) with a tank volume (5) preferably via a pressure relief valve (11, 11 ') are connectable. Hydraulic system after Claim 11 , characterized in that the quantity compensating valve (23) is designed such that an excess of hydraulic fluid during operation of the quick-lowering valve (7) preferably via a pressure relief valve (11, 11 ') to the tank volume (5) to direct. Method for actuating a hydraulic actuator (1) with the following method steps: generating a volume flow from a first chamber (a) of the hydraulic actuator (1) into a second chamber (b) of the actuator (1) and increasing the volume flow by opening one the first chamber (a) with the second chamber (b) connecting quick-lowering valve (7), characterized in that the fast-lowering valve (7) is acted upon by the pressure of the first chamber (a) in the direction of a closed position. Method according to Claim 13 , characterized in that to increase the operating speed, first the pump (2) is adjusted to maximum delivery volume and then to further increase the operating speed, the adjustable quick-lowering valve (7) in the direction of its open position. Method according to Claim 13 or 14 , characterized in that the controllable quick-flow valve (7) is closed when a prevailing in the first chamber (a) load pressure exceeds a limit. Method according to Claim 13 to 15 , characterized in that an excess of the quick-flow valve (7) conveyed hydraulic fluid by means of a purge valve (23) to a tank volume (5) preferably via a pressure relief valve (11, 11 ') is promoted.

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