CRANE WITH CLOSED HYDRAULIC CIRCUIT

Description

[0001] The present invention relates to a crane, in particular a mobile crane, with a closed hydraulic circuit in which a hydraulic pump is hydraulically connected to at least one hydraulic motor via an inlet and an outlet, and bypasses between the inlet and outlet bypass the hydraulic motor. The present invention further relates to a corresponding control device and a corresponding crane control program for controlling the closed hydraulic circuit.

[0002] In mobile cranes, a basic distinction is made between two types of hydraulic circuits, by means of which the power generated by a drive pump is transmitted to the crane functions to be driven, such as hydraulic cylinders, winches or the slewing gear of the superstructure.

[0003] In smaller cranes, the slewing gear is often driven by an open hydraulic circuit. This allows for separate control of the oil supply and drain. This enables a variety of control options that permit different functions within a slewing gear. For example, a fixed-displacement pump can be used, whose flow is controlled exclusively by a valve. This allows for a variety of starting and braking scenarios to be implemented. An important function is the so-called "freewheel," which allows the crane superstructure to be rotated from a standstill using external forces without actively using the slewing gear. For example, the crane superstructure can be pulled over a load to be lifted using the hoist. Here, the slewing gear drive is switched to a virtually force-free state, which also offers the possibility of implementing a low-force run-out of the slewing gear from a rotating movement.In this way, an experienced crane operator can bring the slewing gear up to the desired speed and then, by removing the control signal fed in via a joystick, cause the crane to coast to the desired operating point. Precise positioning can then be achieved by operating a brake pedal or even by accelerating again if it is foreseeable that the crane will come to a standstill before reaching the desired operating point. The freewheel is also useful when the crane is performing a tandem lift with another crane. In this case, a load is lifted by two or more cranes. These cranes must therefore work synchronously during working movements. In the slewing gear, the freewheel offers the option of one crane actively taking over control of the slewing movement while the other crane(s) follow passively in freewheel mode.

[0004] A closed hydraulic circuit is primarily used in larger cranes to drive the slewing gear. Here, the slewing motion is usually controlled by an adjustable pump, which controls the speed of one or more hydraulic motors depending on the flow rate. In this system, a freewheel circuit is easiest to implement by using a digitally switchable bypass valve to create a direct short circuit between the inlet and outlet sides of the hydraulic motor(s). This allows the crane to rotate freely, but smooth restarting during movement is not possible, nor is sensitive braking possible.

[0005] For controlling the superstructure slewing drive, the prior art provides solutions with a closed hydraulic circuit in the documents DE 27 01 297 C2, DE 33 46 800 A1, DE 42 31 637 C2, DE 44 05 472 A1, DE 199 20 867 A1, EP 1 175 318 B1, and US Pat. No. 5,448,148 A, and solutions with an open hydraulic circuit in the documents DE 10 2006 040 459 B4 and EP 2 791 427 B2. CN 203699748 proposes a crane with a hydraulic circuit according to the preamble of patent claim 1. WO 91 / 05966 shows a hydraulic circuit for limiting the torque of a hydraulic motor connected to a hydraulic pump in a closed circuit, which operates as a hydraulic pump during braking. JPH05248537 shows a closed hydraulic circuit with a hydraulic motor and a hydraulic pump connected to it.

[0006] The object of the present invention is to create a closed crane hydraulic circuit that enables sensitive braking and restarting of hydraulic motors. This object is achieved by the subject matter of the independent patent claims 1, 5, and 6. The subclaims define preferred embodiments of the present invention.

[0007] According to the invention, a crane, in particular a mobile crane, is provided with a closed hydraulic circuit in which a hydraulic pump is hydraulically connected to at least one hydraulic motor via an inlet and an outlet, and the inlet is hydraulically connected to the outlet via two bypasses connected in parallel and bypassing the at least one hydraulic motor, and the bypasses each comprise a proportional valve and a check valve for the variable control of the fluid flow for the opposite directions of rotation of the at least one hydraulic motor, wherein the respective proportional valve is open when the at least one hydraulic motor is freewheeling and can be closed proportionally to brake the at least one hydraulic motor.

[0008] In other words, the bypasses that short-circuit the inlet and outlet each have a proportionally switching valve that continuously opens or closes the respective bypass depending on a control signal, so that the fluid flow passing through the bypasses can also be continuously varied. This enables very sensitive movements, accelerations, and decelerations of the crane functions driven by the respective hydraulic circuit. This is particularly desirable for the crane's slewing gear, which rotates the crane superstructure and boom, which are mounted on the crane undercarriage or chassis, around a vertical axis.

[0009] According to the present invention, each bypass has a check valve designed to automatically block the bypass for the fluid flow in at least one flow direction. Such a check valve, provided in addition to the proportional valve, can, for example, be configured to block the bypass for the fluid flow as soon as the fluid flow would flow through the bypass in an undesired opposite direction.

[0010] The hydraulic circuit according to the invention has two bypasses connected in parallel, which hydraulically connect the inlet and outlet. One bypass is provided for variably controlling the fluid flow for each of the two directions of rotation of the at least one hydraulic motor. Each bypass has at least one proportional valve and at least one check valve, by means of which the fluid flows provided for the two directions of rotation can be continuously varied or blocked.

[0011] In other words, a bypass is responsible for exactly one direction of rotation of the hydraulic motor(s), whereby flow through the bypasses in the opposite direction can be prevented by the check valve.

[0012] Preferably, the proportional valves are electrically operated proportional valves. However, a control valve or servo valve for variable control of the fluid flow through the respective bypass would also be conceivable.

[0013] According to the present invention, automatically shut-off check valves are used to shut off the respective bypass. This automatically prevents hydraulic fluid from flowing through the bypass in an unwanted opposite direction. In the two parallel bypasses, these check valves are switched in opposite directions, so that each of the two bypasses is automatically flowed during exactly one direction of rotation of the hydraulic motor.

[0014] Furthermore, it is possible for the hydraulic pump's flow rate to be variably adjustable, in particular by means of an electrically proportional controller (EP controller). In this way, a suitable control system can be used to achieve interaction between the proportional valve(s) and the hydraulic pump, enabling extremely sensitive movements, accelerations, and decelerations of the crane functions driven by the hydraulic circuit, especially a slewing gear. In particular, this also enables re-acceleration from a freewheeling state of the hydraulic circuit.

[0015] Furthermore, it is conceivable that the displacement volume of at least one hydraulic motor is variably adjustable, in particular controllable, so that a smooth "driving behavior" of the crane functions driven via the hydraulic circuit is enabled by means of a suitable control.

[0016] According to a further preferred embodiment of the present invention, the crane further comprises a control device that is in contact with the hydraulic pump and the proportional valves via at least one interface, which is designed to coordinately control the hydraulic pump and the proportional valves during crane operation. In other words, the control device controls the hydraulic pump, the proportional valves, and possibly even a hydraulic motor in such a way that a "smooth driving behavior" of the crane functions driven by the closed hydraulic circuit is enabled.

[0017] A further aspect of the present invention relates to such a control device for controlling a closed hydraulic circuit of a crane, in particular a mobile crane. Although such a control device can be part of the crane according to the invention and described above, it can also be viewed as an independent invention. The control device is connected to the variably adjustable hydraulic pump and the continuously adjustable proportional valves via respective interfaces and is designed to coordinately control the hydraulic pump and the proportional valves during crane operation, so that the respective proportional valve is open during freewheeling of the at least one hydraulic motor and is closed proportionally to brake the at least one hydraulic motor, thus enabling sensitive movements, accelerations, and decelerations of crane functions, in particular of the crane slewing gear.

[0018] A further aspect of the present invention relates to a corresponding crane control program for controlling a closed hydraulic circuit of a crane, in particular a mobile crane, in one of the embodiments described above. Such a crane control program can, for example, be a software-based closed-loop or closed-loop control system that runs on the control device described above and enables coordinated control of the hydraulic pump and the proportional valves.

[0019] If at least one of the hydraulic motors is variably adjustable or controllable in its displacement volume, the control device or the crane control program is also designed to control or control this at least one hydraulic motor in a coordinated manner in interaction with the hydraulic pump and the proportional valves.

[0020] A preferred embodiment of the present invention is described in more detail below with reference to the accompanying figure. The invention may include all features described herein individually or in any meaningful combination.

[0021] The Figure 1 shows a hydraulic circuit diagram of a closed crane hydraulic circuit 1, in which two hydraulic motors 3, 9 can be supported on the controllable hydraulic pump 2 via both their common inlet 4 and their common outlet 5. It should be noted here that when the direction of rotation of the motors 3, 9 is reversed, the inlet 4 takes over the function of the outlet, while the outlet 5 takes over the function of the inlet 4.

[0022] In addition to the parallel-connected hydraulic motors 3, 9, circuit 1 has two parallel-connected, counter-rotating bypasses 6a, 6b that bypass both motors 3, 9. While the bypass 6a can only be flowed through counterclockwise due to the check valve 8a, the bypass 6b can only be flowed through clockwise due to the check valve 8b. Thus, each of the bypasses 6a, 6b is responsible for exactly one direction of rotation of the crane slewing gear (not shown) and is flowed through by the hydraulic fluid as soon as the proportional valve 7a, 7b assigned to it is opened. As shown in the Figure 1As can be seen, the proportional valves 7a, 7b are held in their closed basic position by a spring and can be opened continuously by means of an unspecified actuator. However, the valves can also be constructed inversely, i.e., opened without current and then closed proportionally. Depending on the degree of opening of the respective proportional valve 7a, 7b, a portion of the hydraulic fluid flows through the respective bypass 6a, 6b, which is consequently not available to drive the motors 3, 9.

[0023] In the following, various operating states of the Figure 1 The hydraulic circuit shown is described in more detail.

[0024] When hydraulic circuit 1 is open and the joystick is deflected, the proportional valve 7a (or 7b) assigned to the direction of rotation opens. Hydraulic pump 2, an axial piston pump, increases the volume flow of the hydraulic fluid by pivoting outward, and the slewing gear starts operating as in conventional closed circuits. No flow passes through proportional valve 7a (or 7b), as the higher pressure in inlet 4 closes check valve 8a.

[0025] During freewheeling, the proportional valve 7a remains open, whereupon the hydraulic pump 2 pivots inward, thus reducing the delivered volume flow of hydraulic fluid. The load side of the hydraulic motors 3, 9 changes, creating a free circulation similar to the freewheeling in previously closed circuits. During counter-steering, the proportional valve 7a (or 7b) is closed using a ramp function, which increases the pressure in the outlet 5. This ramp function can be controlled or regulated. After reaching the rest position, the proportional valve 7b (or 7a) of the opposing bypass 6b (or 6a) is opened, and the hydraulic pump 2 drives in the other direction. The crane moves in the opposite direction.

[0026] The brake pedal (not shown) is coupled to the two valves 7a, 7b, whereby a rotation direction detection system determines which of the valves 7a, 7b is to be actuated. The corresponding proportional valve 7a, 7b is closed proportionally, and the pump is swung in, which reduces the supplied volume flow of hydraulic fluid. The brake pressure increases and the slewing gear slows down. To start moving again, both the proportional valve 7a, 7b is opened, and the hydraulic pump 2 is swung out (volume flow increases). As soon as the driving load pressure is higher than the pressure in the respective outlet 5, the check valve 8a, 8b closes.

Claims

1. Crane having a closed hydraulic circuit (1), in which a hydraulic pump (2) is hydraulically connected to at least one hydraulic motor (3, 9) via an inlet (4) and an outlet (5), and the inlet (4) is hydraulically connected to the outlet (5) via two bypasses (6A, 6B) connected in parallel that bypass the at least one hydraulic motor (3, 9), characterised in that the bypasses (6A, 6B) each comprise a proportional valve (7A, 7B) and a check valve (8A, 8B) for variable control of the fluid flow for the opposing rotational directions of the at least one hydraulic motor (3, 9), wherein the respective proportional valve (7A, 7B) is opened in the freewheel of the at least one hydraulic motor (3, 9), and can be closed proportionally for braking the at least one hydraulic motor (3, 9).

2. Crane according to claim 1, wherein the flowrate of the hydraulic pump (2) can be variably adjusted.

3. Crane according to one of claims 1 and 2, wherein the displacement of at least one hydraulic motor (3, 9) can be variably adjusted.

4. Crane according to one of claims 1 to 3, also having a control device that is in contact with the hydraulic pump (2) and the proportional valve (7A, 7B) via at least one interface, said control device being designed for coordinated control of the hydraulic pump (2) and the proportional valve (7A, 7B) while operating the crane.

5. Control device for controlling a closed hydraulic circuit (1) of a crane according to one of claims 1 to 3, wherein the control device is in contact with the hydraulic pump (2) and the proportional valve (7A, 7B) via at least one interface and is designed for coordinated control of the hydraulic pump (2) and the proportional valve (7A, 7B) while operating the crane, so that the respective proportional valve (7A, 7B) is opened in the freewheel of the at least one hydraulic motor (3, 9), and can be closed proportionally for braking the at least one hydraulic motor (3, 9).

6. Crane control program for controlling a closed hydraulic circuit (1) of a crane, in particular mobile crane, according to one of claims 1 to 4, when it runs on a control device according to claim 5.