Hydraulic system for pressure supply to hydraulic actuator

Abstract

To provide a compact and lightweight hydraulic system for pressure supply to a hydraulic actuator.SOLUTION: A hydraulic system for pressure supply of a hydraulic actuator, comprises a double-acting hydraulic cylinder 20 having a frist pressure chamber 21 and a second pressure chamber 22, which can be pressurized by a hydraulic pump 12, and a rapid traverse device 52, 66, 70 that hydraulically interconnects the two pressure chambers in a rapid traverse mode, causes hydraulic oil pushed out from one pressure chamber to flow into the other pressure chamber, and hydraulically separates the two pressure chambers in a normal traverse mode.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The invention relates to a hydraulic system according to the preamble of claim 1, as well as to a valve unit and a work machine, in particular a mobile crane, equipped with such a system. [Background technology]

[0002] A piston-cylinder unit has a cylinder housing and a piston movably mounted therein with a piston rod. In a double-acting piston-cylinder unit, pressure chambers are located on both sides of the piston, and pressurizing one or the other pressure chamber causes the piston rod to retract (contract) or extend. The pressure chamber through which the piston rod passes is called the annular chamber or annular space because of the annular piston surface, while the pressure chamber through which the piston rod does not pass is called the piston chamber or piston space. A double-acting piston-cylinder unit in which the piston has a piston rod on only one side is called a differential cylinder.

[0003] One application of such a piston-cylinder unit is the telescoping cylinder of a telescoping boom of a known mobile crane. Such a telescoping boom has an outer telescoping section and one or more inner telescoping sections movably mounted therein. For particularly large telescoping booms, a single telescoping cylinder in the form of a hydraulic differential cylinder is often used to extend and retract the telescoping sections, which in turn extends and retracts the inner telescoping sections. For this purpose, one part of the telescoping cylinder, typically a piston rod, is connected to the base of the outer telescoping section, while another part, typically a cylinder housing, extends and retracts relative to the outer telescoping section, applying pressure to each pressure chamber. Corresponding hydraulic lines typically run through the piston rods to the pressure chambers.

[0004] To operate the individual telescopic sections, the telescopic cylinders must be connected to them accordingly. For this purpose, a locking device (a so-called locking head) is usually provided on the telescopic cylinder, particularly on the piston rod end or collar of the housing. This locking device engages and pushes into each inner telescopic section via a number of spring-return drive pins, thereby extending the telescopic section together with the telescopic cylinder. Furthermore, the individual telescopic sections can be locked together in a predetermined ejection position by a locking bolt supported by a spring on the telescopic section. To unlock or withdraw the locking bolt, the locking device usually grasps the locking bolt and moves it to the unlocked position. For this purpose, the locking device generally has a spring-return yoke that can engage with the withdrawal form of the locking bolt rod that protrudes inside the telescopic section.

[0005] Both the drive pin and the yoke are preloaded into the locked position by a spring element and can be hydraulically retracted to the unlocked position against the force of a return spring. The hydraulic supply for this can be achieved via a pipe penetration integrated into the piston rod of the telescopic cylinder. This pipe penetration can comprise two penetration tubes that are movably mounted relative to one another, sealed to one another, and extend and retract together with the cylinder. When the telescopic cylinder extends, for example, the inner penetration tube also extends, thereby executing the extension and retraction movement of the cylinder. The outer penetration tube, with a larger diameter, can be fixedly connected to the piston rod. At the cylinder end of the telescopic cylinder, a supply line is led out and runs outside the cylinder back to the locking device. Summary of the Invention [Problem to be solved by the invention]

[0006] A known issue with this configuration is that when the bolted connection is released (i.e., in the unlocked position), pressure within the pipe penetration can, under certain circumstances, cause undesired extension or retraction of the telescopic cylinder, particularly when the boom is in a horizontal position, with low friction, and / or with light loads. To prevent this undesired movement, one of the pressure chambers (usually the ring side) can be preloaded to counter the pressure within the pipe penetration, preventing extension. This preload must be switchable, as otherwise the preload would result in unnecessarily large power losses during normal telescopic operation. The control block required for this adds cost and weight, installation space, and corresponding piping installation.

[0007] Furthermore, the retraction time required for this type of telescopic cylinder is a bottleneck, especially in the case of dead strokes. The goal is always to minimize the retraction time. The dead stroke of a telescopic cylinder can in principle occur both during retraction and extension, and is particularly noticeable in this case because no movement visible to the crane operator occurs (for example, the telescopic cylinder retracting within the boom to accommodate the next extension section). In this case, the difference between the piston and the annular surface makes a difference: extending a telescopic cylinder is significantly slower than retracting a telescopic cylinder because it takes longer to fill the larger piston space with the same oil flow rate.

[0008] To shorten the extension time, the telescopic cylinder piston speed can be increased. Higher speeds require a higher oil flow rate into the piston. This can be achieved by using a larger pump or, if possible, by increasing the drive speed. Both options have the disadvantages of increased cost and / or weight, as well as increased noise and fluid losses. Additionally, the piston surface size can be reduced, but at the same time, this leads to a loss of payload (useful load) unless a higher pressure can be achieved.

[0009] Another solution is to connect the ring side and the piston side with a rapid-moving circuit when the cylinder is extended, so that the oil flowing out of the ring side returns directly to the piston side for extension, increasing the flow rate of oil returning to the piston side and improving the speed during extension.The force of the cylinder during extension / retraction decreases according to the ratio of the piston area to the rod cross-sectional area, but this does not generally limit the extension / retraction process, but only in the high load range of the extension / retraction load.

[0010] The object of the present invention is to avoid the drawbacks of the prior art and to provide an effective development thereon, in particular by means of a compact and lightweight device.

[0011] This object is achieved by a hydraulic system having the features of claim 1 and a valve unit according to claim 13. Advantageous embodiments of the invention emerge from the dependent claims and the following description. [Means for solving the problem]

[0012] Therefore, a hydraulic system is proposed for supplying pressure to the hydraulic actuators. The hydraulic actuators can be actuators of the aforementioned locking devices (e.g., at least one actuator for driving a retraction yoke and / or at least one actuator for unlocking a drive pin). However, the invention is not limited to this use. The actuators can be part of a hydraulic system. This hydraulic system has a double-acting hydraulic cylinder with first and second pressure chambers that can be pressurized by a hydraulic pump to move a piston of the hydraulic cylinder. The hydraulic cylinder can be a telescopic cylinder.

[0013] The hydraulic system further includes a rapid-travel device configured to hydraulically connect the two pressure chambers in a rapid-travel mode, allowing hydraulic fluid displaced from one pressure chamber to flow into the other pressure chamber, thereby increasing the rate of filling of the pressure chamber that increases in size during the retraction or extension of the hydraulic cylinder. The rapid-travel device is further configured to hydraulically isolate the two pressure chambers from each other in a normal-travel mode, such that hydraulic fluid displaced from one pressure chamber does not flow into the other pressure chamber (but rather flows out, for example, to a hydraulic tank).

[0014] In the present invention, the hydraulic system includes a valve unit with an integrated rapid-movement device. The valve unit has a first connection and a second connection, each of which is connected to one of the pressure chambers of the hydraulic cylinder. Note that the connection refers to a hydraulic connection. The valve unit further includes a third connection, which is pressurized by a hydraulic pump. Preferably, the third connection is selectively connectable to the hydraulic pump or a hydraulic tank via a control valve.

[0015] The valve unit includes a movably mounted shift piston that, in a normal-travel position, hydraulically isolates the first and second connection portions from each other, and, in a rapid-travel position, hydraulically connects the first and second connection portions to each other and isolates them from the third connection portion. In the rapid-travel position, hydraulic fluid forced out of one pressure chamber can flow into the other pressure chamber through the valve unit as described above.

[0016] In accordance with the present invention, the valve unit further includes a preloading means integrated therein, the preloading means including a switchable preloading element configured to separate the third connection portion from the second connection portion in a locked position, thereby locking a pressure chamber (e.g., an annular chamber of a telescopic cylinder) connected to the second connection portion from the outside. This locking prevents a pressure increase in the hydraulic cylinder from causing the hydraulic cylinder to retract or extend. This may be necessary, for example, when the telescopic cylinder has a pipe penetration, to prevent an undesired extension of the piston rod due to a pressure increase in the pipe penetration (see above). Preferably, in the locked position, the preloading element separates the third connection portion from the first and second connection portions.

[0017] In the normal travel position, the shift piston allows fluid communication between the second connection portion and the third connection portion, which may be separated from each other by the preload element in the locked position.

[0018] Combining the rapid travel and preload functions into a common valve unit allows for a more compact, cost-effective and lighter construction. Additionally, the valve unit can be configured as a valve cartridge and integrated directly into the hydraulic cylinder.

[0019] In a possible embodiment, the valve unit includes an actuating unit, which is capable of moving the shift piston between a normal movement position and a rapid movement position. The actuating unit can be mechanically, hydraulically, or electrically controlled, with the electrically controlled actuating unit being preferred. The actuating unit can be a solenoid valve. The valve piston of the solenoid valve can be arranged coaxially with the shift piston. The shift piston is preloaded to the normal movement position by a first preloading device, which can be a spring or a spring, and is movable to the rapid movement position by the actuating unit. Therefore, when the actuating unit is in an inactive state (e.g., when the aforementioned solenoid valve is not energized), the valve unit is in the normal movement mode.

[0020] In yet another embodiment, the preload element is configured as a sleeve that surrounds the shift piston and is mounted movably relative to the shift piston, which results in a particularly compact design of the valve unit. The sleeve is preferably arranged in the region of the third connection.

[0021] The valve unit may be provided with a mechanical stop that limits the axial movement of the preload element. Alternatively or additionally, a mechanical stop for the preload element may be arranged / formed on the shift piston.

[0022] In yet another embodiment, the shift piston has a flow passage extending in its direction of movement, i.e., in its axial direction. This flow passage can extend inside the shift piston, preferably coaxial therewith. This flow passage is led outward in the region of the sleeve (preload element) (perpendicular or at an acute angle to the axis of the shift piston) and communicates with an annular chamber formed between the shift piston and the sleeve, the opening of which is preferably located on the shift piston in the region of the first connection. The sleeve can be provided with a control surface (e.g., an end annular control surface) that limits the annular chamber, and the sleeve can be moved by applying pressure to this control surface through the flow passage. The flow passage can be provided with one or more restrictions.

[0023] Preferably, the opening of the flow passage is arranged near the first connection part of the shift piston, in particular so that the annular chamber is hydraulically connected to the first connection part regardless of the position of the shift piston. The flow passage may also lead to a chamber on the opposite side of the shift piston that is hydraulically connected to the actuation unit.

[0024] Additionally, the preload element is preloaded to the locked position by a second preload device, which can include or be a second spring supported by the preload element. By applying pressure to the first or third connection in the normal travel mode, the second preload device can be moved to an open position in which the second and third connection are hydraulically connected. As a result, when intentionally applying pressure to one of the pressure chambers to retract or extend the hydraulic cylinder, the preload is preferably "deactivated," eliminating the need to retract or extend against the preload force. In the event of insufficient pressure in the first or third connection, the pressure chamber connected to the second connection is shut off.

[0025] In a further possible embodiment, the valve unit comprises a check valve arranged between the first connection and the second connection, the check valve being configured to allow hydraulic fluid to flow from the second connection to the first connection and to prevent hydraulic fluid from flowing from the first connection to the second connection in the fast-moving position of the shift piston. If the valve unit is configured as a valve cartridge, the check valve can be integrated into the cartridge or arranged between the cartridge and a cartridge housing that accommodates the cartridge. The check valve allows hydraulic fluid to flow in only one direction from one pressure chamber to the other pressure chamber in the fast-moving mode (e.g., during extension of a hydraulic cylinder, when a larger piston chamber is filled compared to the annular chamber).

[0026] The check valve preferably has a valve body that annularly surrounds the shift piston and is movably mounted relative to the shift piston, resulting in a particularly compact design. The valve body has an end face that is provided with at least one chamfered control surface, and the check valve opens when pressure is applied from the second connection.

[0027] In yet another possible embodiment, the hydraulic system can be provided with a control valve for contracting and extending the hydraulic cylinder. Depending on the switching position of the control valve, a first pressure chamber or a second pressure chamber of the hydraulic cylinder is filled with hydraulic fluid. The control valve has a first inlet connected to the hydraulic pump, a second inlet preferably connected to a hydraulic tank, and a first outlet connected to the first pressure chamber of the hydraulic cylinder and a second outlet connected to the second pressure chamber of the hydraulic cylinder. Preferably, depending on the switching position, each outlet, and therefore the pressure chamber, is connected to the hydraulic pump or the hydraulic tank.

[0028] In particular, one of the outlets of the control valve is connected to the third connection of the valve unit, for example, through which a pressure chamber connected to the second connection is filled with hydraulic fluid in normal movement mode (and preferably vice versa, hydraulic fluid flows from the pressure chamber through the third connection to the hydraulic tank). Alternatively or additionally, one of the outlets of the control valve can be connected to the first connection of the valve unit.

[0029] Preferably, the valve unit comprises a fourth connection part that is permanently hydraulically connectable to the first connection part (regardless of the switching position of the shift piston), one outlet of the control valve being connected to the third connection part and the other outlet of the control valve being connected to the fourth connection part, and via the fourth connection part the working fluid can flow into a pressure chamber connected to the first connection part and vice versa (in this case the pressure chamber may be, for example, a piston chamber of a hydraulic cylinder).

[0030] The control valve can be controlled by one, preferably two, pre-control valves. The control valve can be configured as a main valve.

[0031] It is conceivable to provide a hydraulic system with a pressure balancer that maintains a constant pressure difference between one of the two outlets of the control valve and the hydraulic pump, thereby maintaining a constant flow of working fluid through the control valve.

[0032] In yet another possible embodiment, the hydraulic system comprises an electrically controllable control unit for switching the actuating unit for moving the shift piston between a rapid movement mode and a normal movement mode. The actuating unit can be configured as described above. The control unit is preferably configured to detect the load of the hydraulic cylinder based on at least one pressure measurement value in the hydraulic system and to compare this load with at least one stored characteristic value (reference value). For pressure measurement, the hydraulic system can be provided with at least one pressure sensor. Preferably, the pressure in the pressure chamber is detected by two pressure sensors, from which the current load is determined. The at least one characteristic value can be a threshold value stored in a set of characteristic values ​​and / or a payload table. Alternatively, it is conceivable that the characteristic value can be calculated by the control unit.

[0033] The maximum payload that can be operated using the hydraulic cylinder may be smaller in the rapid travel mode than in the normal travel mode. In order to prevent the maximum load from being exceeded when switching to the rapid travel mode, in a preferred variant the control unit is further configured to detect the load that will result from the switch before switching from the rapid travel mode to the normal travel mode or vice versa, compare this load with at least one stored characteristic value, and determine whether the switch is possible based on the comparison.

[0034] In the case of a mobile crane equipped with a telescopic cylinder, the crane operator must make this decision by referring to a payload table, but looking at the payload table significantly distracts the operator from operating the crane. Therefore, it is desirable for the control unit to automatically switch between rapid travel and normal travel. The control unit pre-calculates the operating pressures on the piston and ring sides before and after switching between rapid travel and normal travel modes to determine whether switching is actually possible and then decides whether to switch accordingly. This reduces the burden on the crane operator, allowing them to concentrate on handling the load and achieving the fastest extension time in each situation.

[0035] In yet another possible embodiment, the hydraulic system comprises a descending brake valve arranged between the valve unit and one of the pressure chambers. In the case of a telescopic cylinder, the descending brake valve is arranged in particular between the piston chamber and the valve unit (in particular the first connection of the valve unit). In a first switching position, the descending brake valve prevents the return flow of hydraulic fluid from the pressure chamber (e.g., preventing the hydraulic cylinder from retracting), but preferably also allows the flow of hydraulic fluid into said pressure chamber (e.g., allowing the hydraulic cylinder to extend), in particular by means of an integrated non-return valve. The descending brake valve has a second switching position in which the return flow of hydraulic fluid from the pressure chamber is allowed (e.g., for controlled retraction of the hydraulic cylinder under an external load). For this purpose, the descending brake valve can be provided with a throttle that reduces the flow rate through it in the second switching position.

[0036] In yet another embodiment, the hydraulic cylinder comprises a piston and a piston rod with a pipe penetration, the latter being configured similarly to the prior art described above. The pressure supply of at least one hydraulic actuator is via the pipe penetration (e.g. a locking device for a telescopic cylinder). The piston rod preferably leads out from one side of the cylinder housing of the hydraulic cylinder (differential cylinder), which preferably has an annular chamber connected to the second connection of the valve unit and a piston chamber preferably connected to the first connection of the valve unit.

[0037] In the locked position, preload means integrated in the valve unit prevent backflow from the annular chamber via the valve unit, in particular upon actuation of an actuator supplied via a pipe penetration, to prevent an unwanted extension of the piston rod (reduction in the size of the annular chamber) due to a pressure buildup in the pipe penetration. When one of the pressure chambers is intentionally pressurized by a hydraulic pump for retraction or extension, the preload means preferably opens automatically.

[0038] In yet another possible embodiment, the hydraulic cylinder is a telescopic cylinder, and the hydraulic system comprises a locking device connected to the telescopic cylinder for reversibly locking the telescopic cylinder to the telescopic section and / or for reversibly locking the two telescopic sections of the telescopic boom, at least one hydraulic actuator of the locking device being pressure-supplyable by the hydraulic system.

[0039] In yet another possible embodiment, the components of the quick-moving device and the preloading means are arranged in a common housing of the valve unit, which allows for a compact design. Alternatively or additionally, the valve unit can be configured as a valve cartridge and arranged in the cylinder housing of the hydraulic cylinder.

[0040] In yet another embodiment, the control piston has at least one control notch to prevent or at least mitigate the shock of pressure release when the shift piston switches between the normal and rapid-movement positions (delayed pressure reduction). The control notch can be configured as an axially cut groove or a radially inclined surface (chamfer) (a combination of several such grooves is also conceivable). The at least one control notch is formed in a part of the control piston that forms the end of the valve housing or sleeve that accommodates the control piston, and the control piston contacts a part that forms a sealing state in the rapid-movement position. The at least one control notch mitigate the sudden increase in the flow cross-sectional area when transitioning to the normal-movement position, thereby preventing a sudden pressure drop.

[0041] In yet another possible embodiment, the hydraulic pump is configured as a variable displacement pump, which may be equipped with an electric proportional controller to implement a load sensing system.

[0042] The present invention further relates to a valve unit having an integrated rapid-movement device and an integrated preload means, which is incorporated into the hydraulic system according to the invention. The valve unit according to the invention includes all the features of the device described in relation to the hydraulic system, has the same properties, or provides the same effects. Therefore, a redundant description will be omitted. In particular, the valve unit according to the invention can be configured according to any of the embodiments described above in this regard.

[0043] The invention further relates to a work machine, in particular a mobile crane, equipped with a hydraulic system according to the invention, which preferably controls actuators for performing work functions of the work machine.

[0044] In one possible embodiment, the work machine is configured as a mobile crane with a telescopic boom, the telescopic boom comprising an outer telescopic section, at least one inner telescopic section movably arranged therein, hydraulic telescopic cylinders for retracting and extending the at least one inner telescopic section, and locking devices connected to the telescopic cylinders for reversibly locking the telescopic cylinders to the inner telescopic section and / or for locking the two telescopic sections relative to each other, at least one actuator of the locking device being pressure-supplied by the hydraulic system according to the invention. The actuators may be at least one actuator for driving a retraction yoke and / or at least one actuator for driving a drive pin.

[0045] Further features, details and advantages of the invention will become apparent from the following description of the embodiments with reference to the drawings. [Brief explanation of the drawings]

[0046] [Figure 1] FIG. 1 is a schematic diagram of a hydraulic system according to one embodiment of the present invention. [Figure 2] FIG. 2 is a vertical cross-sectional view of an embodiment of a valve unit according to the present invention in a switching position. [Figure 3]3A to 3C are longitudinal cross-sectional views of an embodiment of a valve unit according to the invention in different switching positions. [Figure 4] 4A to 4C are longitudinal cross-sectional views of an embodiment of a valve unit according to the present invention in different switching positions. [Figure 5] 5A to 5C are longitudinal cross-sectional views of an embodiment of a valve unit according to the present invention in different switching positions. DETAILED DESCRIPTION OF THE INVENTION

[0047] 1 shows an embodiment of a hydraulic system according to the present invention. In this embodiment, the hydraulic system 10 includes a double-acting hydraulic cylinder 20 configured as a telescoping cylinder for a telescoping boom having a locking device outside the cylinder housing 27. However, the following description and the operating method of the hydraulic system according to the present invention are not limited to this application.

[0048] The locking device is intended to achieve the purpose described above and includes a spring-return drive pin that can be operated (retracted) by a first hydraulic actuator 1, and a spring-return retraction yoke that can be operated by a second hydraulic actuator 2. Hydraulic pressure is supplied to and controlled by a hydraulic pump 12 and valves 3 and 4 of a hydraulic system 10. Valve 3 is connected to valve 4 via a supply line 5, and valve 4 is connected to either the hydraulic pump 12 or a hydraulic tank 11 depending on the switching position.

[0049] The hydraulic cylinder 20 has a piston 24 and a piston rod 23 extending from one side of a cylinder housing 27, forming a differential cylinder. The piston rod 23 is provided with hydraulic pipe penetrations 25, 26 connected to a supply line 5 to supply hydraulic pressure to the actuators 1, 2. The pipe penetrations have two penetration tubes 25, 26 which are movably arranged relative to each other, sealed to each other, and extendable together with the hydraulic cylinder 20. The inner penetration tube 26 is connected to the cylinder housing 27 and configured to extend together with the cylinder housing 27, and the outer penetration tube 25 is fixedly connected to the piston rod 23.

[0050] The hydraulic cylinder 20 has a piston-side pressure chamber or piston chamber 21 (first pressure chamber) and a piston-rod-side pressure chamber or annular chamber 22 (second pressure chamber). To retract or contract the hydraulic cylinder 20, pressure is applied to the annular chamber 22 by the hydraulic pump 12. To extend the hydraulic cylinder 20, pressure is applied to the piston chamber 21 by the hydraulic pump 12. Pressurization to each of the pressure chambers 21, 22 is performed through the control valve 14, which in this example is a main valve that operates via two pre-control valves 15.

[0051] The inlet of the control valve 14 is connected to the hydraulic pump 12 and the hydraulic tank 11, and the outlet of the control valve 14 is connected to the piston chamber 21 via one supply line 6 and to the annular chamber 22 via another supply line 7. The piston rod 23 may be provided with connections that connect the supply lines 6, 7 to the pressure chambers 21, 22, respectively, via internal spaces or flow paths (see Figure 1).

[0052] The hydraulic pump 12 may be provided with an electric proportional controller to implement a load detection system to which the control valve 14 belongs. The hydraulic system 10 may be provided with a pressure balancer to maintain a constant pressure difference between the inlet and outlet sides of the control valve 14 and thereby maintain a constant amount of oil flowing through the control valve 14. In FIG. 1, a pressure limiter valve (relief valve) 42 is an optional component of the pressure balancer.

[0053] Pressure limiter valves 45, 46 may be provided to limit the load sense pressure (see Figure 1). Optionally, two pressure limiter valves 43, 44 connected to the supply lines 6, 7 limit the pressure in the hydraulic cylinder 20. A pressure limiter valve 41 may be connected in parallel to the valve 3.

[0054] One or more pressure sensors or pressure transducers may be provided in the hydraulic system 10. For example, a pressure sensor 32 provided in the pressure balancer and a pressure sensor 31 connected to the pump outlet allow the difference between the pressure readings of the pressure sensors 31, 32 to be used as a control variable and used to control the hydraulic pump 12 accordingly.

[0055] Preferably, a pressure sensor 33, 34 is connected to one of the pressure chambers 21, 22 or to one of the supply lines 6, 7 leading to each pressure chamber 21, 22, so that the current load on the hydraulic cylinder 20 can be determined, for example, based on the acquired pressure (see below).

[0056] The hydraulic system 10 preferably includes a down-brake valve 16 to allow controlled retraction or stopping of the hydraulic cylinder 20, even under load. This is especially important for telescopic cylinders. In the switching position shown in FIG. 1, the check valve in the down-brake valve 16 prevents backflow of oil from the piston chamber 21 while allowing the piston chamber 21 to fill for extension. In the second switching position, the integrated throttle allows both braking and controlled retraction (backward movement) of the hydraulic cylinder 20. To prevent overpressure when the down-brake valve 16 is closed, for example due to heating of the hydraulic oil by solar radiation, a pressure limiter valve 47 can be connected in parallel with the down-brake valve 16.

[0057] The aforementioned components (load sensing system, pressure limiter valves, pressure balancers, down brake valves, pressure sensors, etc.) are optional and may be provided in any combination in hydraulic system 10.

[0058] In accordance with the present invention, a hydraulic system includes a valve unit 50 that combines rapid travel and preload functions in one unit, as described below with reference to the preferred embodiment shown in Figures 2 to 5. The main components of the valve unit 50 are also shown schematically as valve components in Figure 1.

[0059] On the one hand, the valve unit 50 is equipped with a quick-displacement device (components 52, 66, 70 shown in FIG. 1) that, when activated, allows the two pressure chambers 21, 22 to be interconnected. Thus, when the hydraulic cylinder 20 extends, the hydraulic oil flowing out of the annular chamber 22 returns directly to the piston chamber 21, significantly increasing the oil flow rate to the piston side and improving the extension or forward speed. In the embodiment of FIG. 1, the valve unit 50 is arranged after the down-stroke brake valve 16 leading from the hydraulic cylinder 20, which only performs the safety function (blocking the piston chamber 21).

[0060] The preloading means (item 54 shown in Figure 1) is provided to prevent unwanted extension of the telescopic cylinder 20 when the actuators 1, 2 are activated (i.e. when the boltings are unlocked). In this case, the operating pressure (operating force) of the boltings in the pipe penetrations 25, 26 can lead to a situation where the telescopic cylinder 20 is unnecessarily extended, because the inner penetration tube 26 is pushed out by the hydraulic pressure in the two penetration tubes 25, 26, which in turn extends the telescopic cylinder 20. In this case, hydraulic oil is pushed out of the annular chamber 22. This is prevented by the preloading element 54 of the preloading means.

[0061] The valve unit 50 has a first connection 61 connected to the piston chamber 21. In Figure 1, the first connection 61 is connected to the supply line 6 in front of the down brake valve 16. The valve unit 50 has a second connection 62 connected to the annular chamber 22 and a third connection 63 connected to the outlet of the control valve 14.

[0062] In the embodiment of Fig. 1, the first connection 61 communicates with another connection of the control valve 14 and thus with the piston chamber 21 via the down-stroke brake valve 16. In the longitudinal section of the valve unit 50 shown in Figs. 2 to 5, an additional fourth connection 64 is provided which is connected to the control valve 14, and the first connection 61 is connected to the piston chamber 21. However, the first connection 61 and the fourth connection 64 are hydraulically interconnected in each switching position, so that the functional state is the same as in Fig. 1.

[0063] FIG. 2 shows the valve unit 50 in an inactive state, ie, the hydraulic cylinder 20 is not controlled by the hydraulic pump 12 and no pressure is applied to either of the pressure chambers 21, 22.

[0064] The valve unit 50 has a valve housing 68 with the aforementioned connections 61-64. A control piston (shift piston) 52 is axially movably mounted in the valve housing 68. The control piston 52 is disposed in a sleeve 69 inserted into a recess in the valve housing 68 and has openings corresponding to the connections 61-64. For simplicity's sake, only the valve housing 68 will be referred to below, but this may also refer to the sleeve 69. The control piston 52 is preloaded to its left position (see FIG. 2) by a first spring 53 (first preload device). In this case, the control edge 51 of the control piston 52 (see FIG. 3) interacts with a corresponding step in the valve housing 68 / 69 to close the connection between the first connection 61 and the second and third connections 62, 63.

[0065] The valve unit 50 further comprises a preload element 54, which in the illustrated embodiment is configured as a sleeve 54 movably mounted relative to the control piston 52 and annularly surrounding the control piston. The preload element 54 is preloaded by a second spring 55 (second preload device) into a right-hand position (see FIG. 2), in which a valve face 75 of the sleeve 54 interacts with a valve seat 76 (see FIG. 3) formed in the valve housing 68 / 69, thereby blocking the connection between the second connection part 62 and the third connection part 63. The preload element 54 is arranged in a chamber formed in particular in the area of ​​the third connection part 63. FIG. 2 shows the control piston 52 and the preload element 54 in their basic positions (control piston 52: normal movement position, preload element 54: locked position).

[0066] Furthermore, the valve unit 50 can be provided with a check valve 66 having a valve body that annularly surrounds the control piston 52 and a spring that preloads the valve body into a locked position (see FIG. 2). In the locked position, the valve body blocks the connection between the first connection 61 and the second connection 62. The valve body has a chamfered control surface facing the control piston 52, which is configured such that when pressure is applied from the side of the second connection 62 (if the pressure is greater than the pressure at the first connection 61), the check valve 66 opens (see FIG. 4), thereby interconnecting the first connection 61 and the second connection 62.

[0067] 2 to 5, a sleeve 69 mounted on the valve housing 68 has an end in the region of the first connection 61, in which the control piston 52 is supported at the end via the first spring 53, while the check valve 66 is arranged in a chamber 84 formed between the end of the sleeve 69 connectable to the fourth connection 64 (see FIG. 2) and the valve housing 68, surrounding the end. The end is configured to terminate a predetermined distance before the fourth connection 64 formed on the end face of the valve housing 68, so that a hydraulic connection is always maintained between the first connection 61 and the fourth connection 64. However, other embodiments are also possible.

[0068] The control piston 52 can have a drilling 56 or a channel 56 extending axially, in particular concentrically with its longitudinal axis, from its end face facing the first spring 53 to at least the region of the preload element 54. The channel 56 is connected via a radial drilling 57 to an annular chamber 58 (see FIG. 3) formed between the control piston 52 and the sleeve-shaped preload element 54. On its left side (away from the first spring 53), the annular chamber 58 is delimited by the annular control surface of the preload element 54, so that pressurization of the annular chamber 58 via the channels 56, 57 moves the preload element 54 to its left-hand open position (see FIG. 3) against the preload force of the second spring 55. As a result, the connection between the second connection part 62 and the third connection part 63 is opened (see FIG. 3).

[0069] The preload element 54 has an outwardly chamfered control surface 74 in the region of the third connection 63, which control surface is configured so that the preload element 54 moves to the left, open position under the action of pressure via the third connection 63. The preload element 54 therefore moves to the open position both when the third connection 63 is pressurized and when the first connection 61 (via the flow passage 56) is pressurized. The preload means of the valve unit 50 are therefore released whenever one of the pressure chambers 21, 22 is pressurized due to an active retraction or extension of the hydraulic cylinder 20 via the hydraulic pump 12.

[0070] However, the preload element 54 is configured to be held in the locked position (see FIGS. 2 and 4) when pressurized only via the second connection 62. As a result, unwanted extension of the hydraulic cylinder 20 due to a pressure buildup in the annular chamber 22 is prevented, while the preload means is "deactivated" during normal contraction and extension of the hydraulic cylinder 20.

[0071] The valve unit 50 further comprises an actuating unit 70 which, when actuated, pushes the control piston 52 into the quick-travel position (see FIG. 4), thereby interconnecting the first connection 61 and the second connection 62, i.e., the two pressure chambers 21, 22. The actuating unit 70 can be a solenoid valve which, when energized, actuates a valve piston 72 mounted axially relative to the control piston 52 and presses the valve piston against a valve seat (see FIG. 4), whereby a pressure increase via a passage 56 in the pressure chamber closed by the valve piston 72 and hydraulically connected to the third connection 63 moves the control piston 52 into the quick-travel position.

[0072] The flow passage 56 preferably extends to the other end of the control piston 52 on the solenoid valve side, where it leads, preferably via a throttle, into a space connected to the aforementioned chamber 73 which can be closed by the valve piston 72. A throttle may also be provided in the connection between the chamber 73 and the third connection 63. The throttle allows a pressure increase and decrease in the space between the chamber 73 and the control piston 52. Furthermore, the throttle limits the switching speed.

[0073] The valve unit 50 compactly integrates the rapid movement function and preload function of the hydraulic cylinder, and is capable of operating in the following modes:

[0074] In the non-operated state (see Figures 2 and 3), the control piston 52 is in a normal movement position. In this normal movement mode, the hydraulic cylinder 20 contracts and extends normally, and hydraulic oil is forced out of each pressure chamber 21, 22 and flows into the hydraulic tank 14 via the control valve 14. In this case, the preload element 54 can be put into a locked position (see Figure 2) or an open position (see Figure 3) depending on the pressure applied.

[0075] By actuation of the actuation unit 70, the control piston 52 is pushed into the rapid-travel position (see FIG. 4), and the control edge of the control piston 52 disconnects the second connection part 62 and the third connection part 63, and when the first connection part 61 is pressurized, the first connection part 61 and the second connection part 62 are interconnected for the rapid-travel mode.

[0076] When switching to the rapid travel mode, the working pressure (working force) increases, given the same load, depending on the ratio of the piston surface to the rod surface of the hydraulic cylinder 20. When switching back to the normal travel mode, this pressure must be reduced again. To prevent this from causing a pressure release shock in the telescopic cylinder that would load the mobile crane's support structure, at least one control notch 80 can be formed in the control piston 52 (see FIG. 3). The control notch 80 can be configured as an axially cut groove or a radially cut chamfer (bevel), and is located in particular in the area of ​​the control edge that closes the connection between the second and third connection parts 62 and 63 in the rapid travel position. The number of control notches 80 can be determined by the required total opening cross-sectional area. The at least one control notch 80 ensures a gradual pressure drop when the control piston 52 returns to the normal travel position, preventing a pressure release shock that would interfere and load.

[0077] 5 shows the control piston 52 during switching back to the normal movement position, in which case an opening 82 connecting the second connection part 62 and the third connection part 63 is formed in the area of ​​the control notch 80.

[0078] In the case of a telescopic cylinder, the telescopic load during rapid travel is smaller than that during normal travel. Depending on the current load, telescopic boom angle, and telescopic length, switching to rapid travel mode may or may not be possible and effective. The crane operator must make this decision by referring to a load table, which significantly detracts from crane operation. Therefore, it is preferable that the switching between rapid travel mode and normal travel mode be performed automatically by the control unit of the hydraulic system 10 (not shown).

[0079] In a preferred embodiment, the current load is determined by pressure measurements by the two pressure sensors 33, 34. The maximum permissible load is known from a load table stored in a memory unit. By pre-calculating the working pressures in the piston chamber 21 and the annular chamber 22 before and after switching from rapid travel to normal travel or vice versa, the control unit can determine whether a switch is actually possible and decide accordingly whether to switch or not. The crane operator can avoid having to worry about this decision and can concentrate on handling the load and always achieve the desired extension and retraction times in each situation.

[0080] The valve unit 50 can be preferably configured as a valve cartridge. This eliminates external piping and allows for direct oil flow without piping losses. Furthermore, the valve cartridge can be placed directly inside the hydraulic cylinder 20, thereby saving space. [Explanation of symbols]

[0081] 1 First Actuator 2 Second Actuator 3,4 valves 5-7 Supply Line 10 Hydraulic System 11 Hydraulic tank 12 Hydraulic pump 14 Control valve 15 Pre-control valve 16 Downward brake valve 20 Hydraulic cylinder 21 First Pressure Chamber 22 Second Pressure Chamber 23 Piston rod 24 pistons 25 Outer penetration pipe 26 Inner penetration pipe 27 Cylinder housing 31-34 Pressure sensors 41 Pressure Limiter Valve 42 Pressure balancer 43-47 Pressure Limiter Valve 50 valve unit 51 Control Edge 52 Shift piston 53 First preload device 54 Preload Elements 55 Second preload device 56 Flow path 57 Radial Drilled Holes 58 Annular Chamber 61 First connection part 62 Second connection part 63 Third connection part 64 4th connection part 66 Check valve 68 Valve housing 69 Sleeve 70 Operating Unit 72 Valve piston 73 Chamber 74 Control Surface 75 valve surface 76 Valve seat 80 Control Notch 82 Opening 84 Chamber

Claims

1. A hydraulic system (10) for supplying pressure to hydraulic actuators (1, 2) comprises a double-acting hydraulic cylinder (20) having a first pressure chamber (21) and a second pressure chamber (22) that can be pressurized by a hydraulic pump (12), and a rapid movement device that hydraulically connects the first and second pressure chambers (21, 22) in a rapid movement mode to allow hydraulic oil pushed out from one pressure chamber (22) to flow into the other pressure chamber (21), and hydraulically separates the two pressure chambers (21, 22) from each other in a normal movement mode; The rapid movement device is integrated into a valve unit (50) of the hydraulic system (10), the valve unit being connected to the first and second pressure chambers (21, 22) via first and second connection parts (61, 62) and having a third connection part (63) that can be pressurized by the hydraulic pump (12), the valve unit (50) having a movably mounted shift piston (52), the shift piston (52) hydraulically separating the first connection part (61) and the second connection part (62) from each other in a normal movement position. and in a quick-travel position, hydraulically connects the first connection part (61) and the second connection part (62) to one another and separates them from the third connection part (63), and the valve unit (50) is further integrated with a preloading means having a switchable preloading element (54), which is configured to separate the third connection part (63) from the second connection part (62) in a locked position, thereby externally locking the pressure chamber (22) connected to the second connection part (62). A hydraulic system (10) characterized in that:

2. 2. The hydraulic system (10) of claim 1, The valve unit (50) preferably comprises an electrically controllable actuation unit (70), in particular a solenoid valve, by means of which the shift piston (52) is movable between a normal movement position and a rapid movement position, the shift piston (52) being preloaded to the normal movement position by a first preload device (53) and movable to the rapid movement position by the actuation unit (70). Hydraulic system (10).

3. A hydraulic system (10) according to claim 1 or 2, The preload element (54) is configured as a sleeve that surrounds the shift piston (52) and is movably mounted relative to the shift piston (52), the sleeve (54) being preferably located in the region of the third connection part (63). Hydraulic system (10).

4. A hydraulic system (10) according to any one of claims 1 to 3, The shift piston (52) has a flow passage (56) extending along its direction of movement, which is led radially outward in the region of the sleeve (54) and communicates with an annular chamber (58) formed between the shift piston (52) and the sleeve (54), preferably with an opening of the flow passage (56) located in the region of the first connection part (61) in the shift piston (52), and the annular chamber (58) is hydraulically connected to the first connection part (61) regardless of the position of the shift piston (52). Hydraulic system (10).

5. A hydraulic system (10) according to any one of claims 1 to 4, The preload element (54) is preloaded to a lock position by a second preload device (55), and is movable to an open position in which the second connection portion (62) and the third connection portion (63) are hydraulically connected by applying pressure to the first connection portion (61) or the third connection portion (63) in a normal movement mode. Hydraulic system (10).

6. A hydraulic system (10) according to any one of claims 1 to 5, The valve unit (50) includes a check valve (66) arranged between the first connecting portion and the second connecting portion, and the check valve (66) is configured to allow hydraulic oil to flow from the second connecting portion (62) to the first connecting portion (61) and to prevent hydraulic oil from flowing from the first connecting portion (61) to the second connecting portion (62) when the shift piston (52) is in a rapid movement position, and the check valve (66) preferably has a valve body that annularly surrounds the shift piston (52) and is movably attached to the shift piston (52). Hydraulic system (10).

7. A hydraulic system (10) according to any one of claims 1 to 6, The hydraulic cylinder (20) comprises a control valve (14) for contraction and extension, the control valve having a first inlet connected to the hydraulic pump (12), a second inlet preferably connected to a hydraulic tank (11), and two outlets connected to the pressure chambers (21, 22) of the hydraulic cylinder (20), in particular one of the outlets being connected to a first connection (61) of the valve unit (50) and / or one of the outlets being connected to a third connection (63) of the valve unit (50). Hydraulic system (10).

8. A hydraulic system (10) according to any one of claims 1 to 7, The device further comprises a control unit capable of controlling the switching of an actuation unit (70) for moving the shift piston (52) between a rapid transfer mode and a normal transfer mode, the control unit being configured in particular to detect a load on the hydraulic cylinder (20) based on at least one pressure measurement value in the hydraulic system (10) and compare it with at least one stored characteristic value, and preferably, the control unit further detects a load that will result from the switching before switching from the rapid transfer mode to the normal transfer mode or vice versa, compares it with at least one stored characteristic value, and decides whether the switching can be performed based on the comparison. Hydraulic system (10).

9. A hydraulic system (10) according to any one of claims 1 to 8, A descending brake valve (16) is arranged between the valve unit (50) and one of the pressure chambers (21), which in a first switching position prevents the reverse flow of hydraulic fluid from the pressure chamber (21) and preferably allows the flow of hydraulic fluid into the pressure chamber (21), in particular by means of an integrated check valve, and which in a second switching position allows the reverse flow of hydraulic fluid from the pressure chamber (21). Hydraulic system (10).

10. A hydraulic system (10) according to any one of claims 1 to 9, The hydraulic cylinder (20) includes a piston (24) and a piston rod (23) having pipe penetration parts (25, 26), pressure is supplied to the hydraulic actuators (1, 2) via the pipe penetration parts (25, 26), the piston rod (23) preferably leads out from one side of a cylinder housing (27) of the hydraulic cylinder (20), an annular chamber (22) formed on the piston rod (23) side is connected to the second connection part (62), and a piston chamber (21) formed on the opposite side of the piston (24) is connected to the first connection part (61) of the valve unit (50). Hydraulic system (10).

11. A hydraulic system (10) according to any one of claims 1 to 10, The hydraulic cylinder (20) is a telescopic cylinder, and the hydraulic system (10) comprises a locking device connected to the telescopic cylinder for reversibly locking the telescopic cylinder to a telescopic section and / or for reversibly locking two telescopic sections of a telescopic boom, and at least one hydraulic actuator (1, 2) of the locking device can be supplied with pressure by the hydraulic system (10). Hydraulic system (10).

12. A hydraulic system (10) according to any one of claims 1 to 11, The components of the quick-moving device and the preloading means are arranged in a common housing (68) of the valve unit (50), and / or the valve unit (50) is configured as a valve cartridge and is arranged in a cylinder housing (27) of the hydraulic cylinder (20). Hydraulic system (10).

13. 13. A valve unit (50) having an integral quick-moving device and an integral preload means in a hydraulic system (10) according to any one of claims 1 to 12.

14. A working machine, in particular a mobile crane, equipped with a hydraulic system (10) according to any one of claims 1 to 13.

15. 15. A work machine according to claim 14, The mobile crane has a telescopic boom, the telescopic boom comprising an outer telescopic section, at least one inner telescopic section movably arranged therein, a hydraulic telescopic cylinder for contracting and extending the at least one inner telescopic section, and a locking device connected to the telescopic cylinder for reversibly locking the telescopic cylinder to the inner telescopic section and / or for locking the two telescopic sections to each other, and at least one actuator (1, 2) of the locking device can be supplied with pressure by the hydraulic system (10). Work machinery.

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