METHOD FOR STARTING IN A HYDROSTATIC DRIVE WITH BRAKE

Description

TECHNICAL AREA

[0001] The present invention relates to the field of a method for controlling a hydrostatic drive comprising a first hydraulic machine coupled to a drive and a second hydraulic machine coupled to an output, wherein the drive has a brake for blocking the output. STATE OF THE ART

[0002] In mobile machinery, drives are equipped with a braking device to hold the machine in a position without torque, preventing it from moving when stationary. Typical examples are cable winch drives. These drives can be either open or closed circuits with a hydraulic pump and a hydraulic motor, with the hydraulic pump typically being volumetrically controlled.

[0003] Under standard conditions, the hydraulic pump is driven by a motor, and the hydraulic motor is designed to transfer the hydraulic energy received from the first hydraulic pump in the form of mechanical energy to an external consumer (e.g., a motor shaft). The motor can be any internal combustion engine or electric motor, or any other element capable of providing rotation to the hydraulic pump.

[0004] In order to release the braking device without moving the wear part when starting up again, it is necessary for the drive machine to apply the exact load torque in advance.

[0005] For this purpose, an algorithm is typically used that applies a pre-determined, low flow rate to restart the system before the brake is released. This ensures that a moment equilibrium is maintained after the brake is released, thus stopping the winch. The pump flow rate, opposite to the load direction, is necessary to compensate for the leakage flow rates present in the hydraulic system. Information about the required moment is obtained from a rope force measuring device in the rope deflection device (permanent, even when the brake is applied).

[0006] The problem with the solution described above is that during the opening the drive torque does not adapt to the load conditions and the driver's expectations and sometimes undesirable behaviors occur on the part of the machine, so that balance is not created.

[0007] In particular, determining the required flow rate for smoothly opening the holding brake is very complex. Using hydromechanical position controllers on the pump, it is difficult to adjust the desired flow rate with the required accuracy. In particular, the pump's current displacement can only be determined indirectly through the control values ​​(electric current through the control magnets).

[0008] DE 102014109918 A1 basically describes the rope force control of a closed-circuit winch using a hydrostatic / through-pump pump and a control device. However, it makes no reference to the release of the holding brake and the associated load transfer by the drive.

[0009] US 2016 / 060082 A and US 3864915 A disclose methods for controlling a hydrostatic drive in which the output has a brake for blocking the output.

[0010] The object of the present invention is precisely to solve the problems described above and therefore to implement a method for controlling the hydrostatic drive that can automatically prevent undesirable behavior. SUMMARY

[0011] This application describes an example of a drive machine in which a hydrostatic motor is driven by a hydrostatic pump in a closed circuit. However, it will be clear to those skilled in the art that this invention can also be used in an open circuit.

[0012] This invention relates to a method for controlling a hydrostatic drive, wherein the hydrostatic drive has at least two hydraulic machines, of which a first hydraulic machine can be coupled to a drive machine and a second hydraulic machine can be coupled to an output, wherein the first hydraulic machine is fluidically connected to the second hydraulic machine, wherein the output comprises a brake for blocking the output, wherein the method comprises the following steps: a. Closing the brake so that rotation of the second hydraulic machine is blocked; b. Pressure control of the first hydraulic machine until the first hydraulic machine reaches a setpoint; c. After the first hydraulic machine has reached the setpoint, detecting the swivel angle of the first hydraulic machine; d. Controlling the first hydraulic machine so that the detected swivel angle is maintained or controlling the first hydraulic machine so that the volume flow dependent on the detected swivel angle is provided by the first hydraulic machine.

[0013] The core of this invention is that the required flow rate with the brake engaged is determined by adjusting the pump to the expected holding pressure and measuring the pump's swivel angle (and preferably its speed). The advantage is that the system automatically adapts to changing operating conditions and aging. SHORT DESCRIPTION OF THE CHARACTERS

[0014] The present invention is described with reference to the accompanying figures, wherein like reference numerals refer to like parts and / or similar parts and / or corresponding parts of the system. Regarding the figures: Figure 1 shows a schematic circuit diagram of a hydrostatic drive designed as a travel drive according to an embodiment of the present invention. DETAILED DESCRIPTION

[0015] The present invention will now be described with reference to specific embodiments as shown in the accompanying figures. Nevertheless, the present invention is not limited to the specific embodiments described in the following detailed description and shown in the figures; rather, the described embodiments merely illustrate some aspects of the present invention, the scope of which is defined by the claims.

[0016] Further modifications and variations of the present invention will be apparent to those skilled in the art. This description thus encompasses all modifications and / or variations of the present invention, the scope of which is defined by the claims.

[0017] According to Figure 1A hydrostatic drive has a hydraulic pump 4, which is fluidly connected in a closed hydraulic circuit via working lines 5 and 6 to a hydraulic motor 8 for supplying pressure to the motor. The hydraulic pump 4 is coupled to a drive motor 2 via a drive shaft to transmit torque. In this example, the coupling is geared, so that the speeds of the drive motor 2 and the hydraulic pump 4 are different. However, the gearing is not required.

[0018] The hydraulic pump 4 is designed as an axial piston pump with a swashplate design and can be operated in both directions of rotation and in both pump and motor mode. It typically has an adjustable displacement and preferably an adjustment device 10 designed as a double-acting hydraulic cylinder.

[0019] The adjustment device 10 is controlled by a control unit 100. In this exemplary embodiment, the hydraulic pump 4 can be both pressure- and volume-controlled by means of the control unit 100. In this example, the hydraulic motor is not adjustable. It will be clear to those skilled in the art that the present invention can also function with an adjustable hydraulic motor.

[0020] The hydraulic motor is connected to an output 14. The output 14 has a brake 15 for blocking the output 14. When the brake 15 is closed, rotation of the hydraulic motor 8 is blocked. The brake 15 is provided with an actuator 17 configured to actuate the brake 15 (for opening and closing).

[0021] The hydrostatic drive of the present invention is a hydrostatic drive of a mobile work machine, wherein the output is preferably a cable winch drive that can lift, lower, or pull loads 16 using a cable winch. However, this invention can also be applied to other work machines that require low volume flows, preferably to work machines whose hydraulic pumps are volume-controlled, such as a sweeper or milling machine.

[0022] The hydraulic pump 4 can preferably be controlled by means of an electronic swivel angle control, wherein the swivel angle control is carried out on the basis of the swivel angle sensor 41 on the first hydraulic machine 4 in order to improve the positioning accuracy.

[0023] The hydraulic pump 4 can preferably be controlled by means of an electronic pressure control 100, wherein the pressure control is carried out on the basis of pressure sensor signals 101, 103 in the working lines of the first hydraulic machine in order to improve the control accuracy

[0024] The following sections describe a method for controlling the hydrostatic drive according to one embodiment of the present invention. This method makes it possible to achieve a balance of the load 16 when the brake 15 is released.

[0025] In a first step, the brake 15 is closed by the actuator 17, thus blocking the rotational movement of the hydraulic motor. Before the brake 15 was closed, the pump was volume-controlled, so that a certain volume flow was supplied to the hydraulic motor 8.

[0026] After receiving this information, the controller 100 will begin regulating the pressure of the hydraulic pump 4 until a certain pressure is reached by the pump. The reason for this is that in this situation, rotation of the hydraulic motor 8 is blocked, and due to the leakage, if the hydraulic pump were at a standstill, the pressure in the working lines 5 and 6 would drop. For this reason, it is necessary to actuate the hydraulic pump 4 to compensate for these losses. Therefore, the controller 100 will receive information about the target pressure required after the brake 15 is released to maintain load balance.

[0027] This information is obtained either by a pressure sensor 101 located downstream of the hydraulic pump 4 or by the force sensor 102, which detects a load. Once the information is received from the force sensor 102, this information is converted into a target pressure in the controller 100.

[0028] For this reason, the hydraulic pump 4 is pressure-controlled until the specified pressure is reached. After the hydraulic pump 4 has reached the setpoint, the swivel angle of the hydraulic pump 4 is detected by the swivel angle sensor 41.

[0029] The hydraulic pump is then controlled so that the detected swivel angle is maintained or so that the volume flow dependent on the detected swivel angle is provided by the hydraulic pump 4. In particular, if the speed of the hydraulic pump 4 remains constant, only the swivel angle can be directly controlled. However, if the speed changes, the new speed must be taken into account, since the volume flow depends on the speed. For this reason, the hydraulic pump 4 or the external drive (as in Figure 1 shown) a speed sensor 21 is arranged, which is configured to supply information about the speed of the hydraulic pump 4 to the controller 100.

[0030] After this step, the hydrostatic drive is ready for the re-opening of brake 15. Therefore, if the driver wishes to re-open brake 15, the controller 100 will authorize this action. This solution prevents any unwanted movement when releasing brake 15, as the system-related leakage flow rate has been compensated for by this process. This leakage flow rate depends on numerous system conditions and component aging, and the described solution eliminates this effect.

[0031] In a further embodiment of the present invention, when the speed of the hydraulic pump 4 changes, the volume flow of the hydraulic pump 4 is adjusted accordingly, taking the change in the leakage volume flow into account in the adjustment. The reason for this is that higher speeds result in higher leakage volume flows.

[0032] In a further embodiment of the present invention, the method described above is used to determine a characteristic curve that can be used in the future to represent information about the target swivel angle or the target volume flow as a function of a target pressure. Thanks to this characteristic curve, it will no longer be necessary to perform the method described above every time, since the information about the target swivel angle or the target volume flow can be determined from the characteristic curve. The only information required is the target pressure, which can be determined using a pressure sensor or a force sensor (as explained in the course of the description).

[0033] To determine this characteristic curve, the procedure described above is repeated for different target pressures, and the value for the target swivel angle or the target flow rate is stored for each pressure. A function is then calculated from these stored values. For this reason, the target pressures are distributed as evenly as possible across the actuator's working pressure range.

[0034] This function is then saved and can also be used for various purposes. In another embodiment, this function is used to control the hydraulic pump 4 when the brake 15 is open, so that the position of the load 16 can be maintained.

[0035] Since leakage depends on various conditions that can change over time, the function can be updated regularly. Therefore, the procedure can be repeated at intervals for one or more target pressures, and the function can be corrected using the information obtained about the target swivel angle.

[0036] It may be provided that the traction device (the cable winch), as in Figure 1 As shown, it is guided over a deflection pulley, wherein the force sensor 102 can comprise a force measuring pin on which the deflection pulley is rotatably mounted. Corresponding force measuring pins are available on the market in many designs, allowing precise force measurement to be achieved in a simple and cost-effective manner.

[0037] It is politely pointed out that even if the hydraulic motor 8 of Figure 1As described above as a motor with a constant displacement volume, this invention can also be applied with a hydraulic motor 8 with an adjustable displacement volume. In this case, the swivel angle of the hydraulic pump 4 is increased, preferably at low speeds of the cable winch. When the swivel angle of the hydraulic pump has reached its maximum position and the speed is to be further increased, the swivel angle (of the displacement volume) of the hydraulic motor is reduced.

[0038] Furthermore, a control element is provided (not in Figure 1shown), which is also connected to the controller 100. The operating element is designed, for example, as an operating lever that can be pivoted in two opposite directions starting from a neutral position. In the spring-loaded neutral position, the cable winch does not move. When the operating lever is pivoted forward, as viewed by the operator, the load 16 is lowered, with the lowering speed being approximately proportional to the lever deflection. When the operating lever is pivoted backward, the load 16 is raised, with the lifting speed being approximately proportional to the lever deflection. The position of the operating element is preferably transmitted to the controller 100 in the form of an electrical or digital signal.

[0039] It can be provided that, while the deflection of the control element falls below a predetermined limit, a maximum first displacement volume is set on the at least one first hydraulic machine 4, wherein, moreover, a first displacement volume is set that is reduced compared to the maximum first displacement volume. This allows the cable winch to be moved particularly quickly when the control element is deflected to a large extent. The specified limit value can be selected differently depending on the direction of the deflection of the control element, i.e., depending on the desired direction of movement of the load 16.

[0040] While the present invention has been described with reference to the embodiments described above, it will be apparent to those skilled in the art that it is possible to make various modifications, variations and improvements to the present invention in light of the above teachings and within the scope of the appended claims without departing from the scope of the invention.

[0041] For this reason, although this application describes an example of a prime mover in which a hydrostatic motor is driven in a closed circuit by a hydrostatic pump, this invention can also be used in an open circuit.

[0042] Accordingly, the invention is not to be limited by the specific illustrative embodiments, but only by the scope of the appended claims.

Claims

1. Method for controlling a hydrostatic drive, wherein the hydrostatic drive has at least two hydraulic machines (4, 8), of which a first hydraulic machine (4) can be coupled to a drive machine (2) and a second hydraulic machine (8) can be coupled to an output (14), wherein the first hydraulic machine (4) is fluidly connected to the second hydraulic machine, wherein the output (14) comprises a brake (15) for blocking the output (14), wherein the method comprises the following steps: a. closing the brake (15), with the result that a rotational movement of the second hydraulic machine (8) is blocked; b. regulating the pressure of the first hydraulic machine (4) until the first hydraulic machine (4) reaches a setpoint value; c. after the first hydraulic machine (4) has reached the setpoint value, detecting the swash angle (41) of the first hydraulic machine (4); d. regulating the first hydraulic machine (4), with the result that the detected swash angle is maintained, or regulating the first hydraulic machine (4), with the result that the volume flow dependent on the detected swash angle is provided by the first hydraulic machine (4).

2. Method according to Claim 1, wherein the setpoint value for regulating the pressure of the pump is dependent on a load information item of the output (14).

3. Method according to Claim 1 or 2, wherein the setpoint value for regulating the pressure of the pump is a detected pressure before the closure of the brake (15), wherein the pressure is preferably detected downstream of the first hydraulic machine (4).

4. Method according to one of Claims 1 to 3, wherein, after step d., the brake (15) is opened again.

5. Method according to one of Claims 1 to 4, wherein the first hydraulic machine (4) is in a closed circuit with the second hydraulic machine (8).

6. Method according to one of Claims 1 to 5, wherein the steps a. to c. are repeated for different setpoint values for regulating the pressure of the pump, wherein a function is determined with the consideration of the detected values of the swash angle, which function represents a function for the setpoint swash angle of the first hydraulic machine (4) or for the setpoint volume flow rate of the first hydraulic machine (4) which is dependent on the swivel angle, as a function of a value for controlling the pressure of the first hydraulic machine (4).

7. Method according to Claim 6, wherein the function is stored, and wherein the function is adapted at time intervals by means of the implementation of steps a. to c. in the case of at least one setpoint value for regulating the pressure of the pump.

8. Method according to Claim 6 or 7, wherein, in the method, the function is used to control the first hydraulic machine (4) with the brake (15) open.

9. Method according to one of Claims 1 to 8, wherein the hydrostatic drive is a hydrostatic drive of a mobile working machine.

10. Method according to Claim 9, wherein the unit (14) is a cable winch drive.

11. Method according to one of Claims 1 to 10, wherein, in step d., when the speed of the first hydraulic machine (4) changes, the volume flow of the first hydraulic machine (4) is adapted accordingly, wherein the change of the leakage volume flow is taken into account in the adaptation.

12. Method according to one of Claims 1 to 11, wherein, in step d., the first hydraulic machine (4) is controlled by means of an electronic swash angle regulation (100), wherein the swash angle regulation is carried out on the first hydraulic machine (4) based on the swash angle sensor (41), in order to improve the positioning accuracy.

13. Method according to one of Claims 1 to 12, wherein, in step b., the first hydraulic machine (4) is controlled by means of an electronic pressure regulation (100), wherein the pressure regulation is carried out based on pressure sensor signals (101, 103) in the working lines of the first hydraulic machine, in order to improve the actuation accuracy.