Method for operating an electrohydraulic device
By using variable speed electric drive devices and multiple protection mechanisms in electronic hydraulic equipment, adjusting the working point of the hydraulic pump, solving the availability and reliability of the equipment under high pressure and high load conditions, achieving higher Equipment availability and lower risk of damage.
Patent Information
- Application Number
- CN202380042015.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2022-05-25
- Filing Date
- 2023-05-17
- Publication Date
- 2025-01-03
AI Technical Summary
When operating electronic hydraulic equipment, it is difficult for the prior art to effectively adjust the working point of the hydraulic pump, prevent the machine from stopping state and reduce the damage or wear of the pump, especially in the pressure-volume flow operation, there are limitations on the adjustment of rotation speed and discharge volume. This results in insufficient availability and reliability of the equipment.
By using an electric drive device with variable speed in the hydraulic pump, the speed and discharge volume of the hydraulic pump are adjusted according to the preset pressure and volume flow target value, ensuring that the working point is within the allowable range, and the current setting is determined through monitoring and calculation models The specific discharge volume value adopts a variety of protection mechanisms such as limiting the speed change rate and pressure change rate to avoid component damage and overload.
It improves the availability of hydraulic pumps, prevents the machine from being stopped, reduces the damage and wear of the pump, ensures the stable operation of the equipment under high pressure and high load conditions, and avoids thermal overload and mechanical damage of the electric motor and inverter.
Smart Images
Figure CN119256161A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a method for operating an electrohydraulic device. Background Art
[0002] The electrohydraulic device (so-called motor-pump unit) on which the invention is based has a hydraulic pump with a variable displacement volume per working cycle (so-called hydraulic positive displacement machine, for example an axial piston machine), which is driven at a variable speed by means of an electric drive (motor). The displacement volume can be adjusted continuously or in steps. When operating such an electrohydraulic device, the volume flow and / or the delivery pressure (that is to say the pressure difference between the inlet and the outlet) are usually adjusted by correspondingly adapting the rotational speed and the displacement volume of the hydraulic pump, that is to say such an electrohydraulic device has in principle two degrees of freedom in the regulation.
[0003] DE 102007007005 A1 shows an electrohydraulic control arrangement with an adjustable fluid pump and with a variable speed electric drive. A pressure detection device allows the fluid pressure to be detected. The main control circuit of the electrohydraulic control arrangement has a speed control mechanism of the electric drive as a control mechanism. With the help of the main control circuit, the fluid pressure can be adjusted and thus, for example, the force applied by the cylinder or a subordinate control variable such as position or speed can be adjusted. With the help of an additional control chain (Nebenstellkette), the discharge volume adjustment mechanism of the fluid pump is controlled according to the detected fluid pressure. A particularly simple design is provided, namely: the additional control chain includes a control device, in particular a two-point regulator, by which the discharge volume of the adjustable fluid pump can be adjusted between a predetermined minimum value and a maximum value according to predetermined switching conditions. Summary of the invention
[0004] According to the invention, a method for operating an electrohydraulic device as well as an electrohydraulic device, a computer program and a data carrier are proposed having the features of the independent claims. Advantageous embodiments are the subject matter of the dependent claims and the following description.
[0005] In an electro-hydraulic system, the present invention leads to an increase in the availability of the pump, prevents machine standstills and avoids or reduces damage to the pump or additional wear. In particular, in the so-called pressure-volume flow-operation (pQ) of the pump, the pressure is regulated by means of the speed as a control variable and the volume flow is obtained as a product of the speed and the discharge volume, and in this pressure-volume flow-operation it can be ensured that only operating points (that is to say pressure / speed combinations) in the permitted range are started. If an unpermitted operating point is started by a target value preset or configuration, this is prevented in the scope of the present invention by switching, in particular reducing the discharge volume. In the case of small discharge volumes, there is usually no operating point restriction. The permissible or impermissible operating points for each hydraulic pump are known in advance and are determined in particular in a data table. They can be stored and monitored accordingly in the memory of the actuated computing unit.
[0006] In a variable speed electronic hydraulic device, a hydraulic pump that can be adjusted between a first larger displacement volume value and a second smaller displacement volume value for each working cycle in the displacement volume is driven by means of a variable speed electric drive. In order to operate the variable speed electronic hydraulic device, a target value of the rotation speed of the variable speed electric drive is obtained and pre-set to the electric drive. This can be achieved according to a superior preset, such as pressure and / or volume flow regulation, wherein the target value of the rotation speed of the variable speed electric drive is obtained as a control variable of a superior pressure regulation unit, and as an input variable, a target value for the delivery pressure of the hydraulic pump or generally a pressure at a certain position of the system is supplied to the superior pressure regulation unit. Here, the displacement volume is set to a first larger displacement volume value or a second smaller displacement volume value in an appropriate manner, also by a superior preset, such as an operating strategy. For example, the torque load of the electric drive is reduced in the case of a small displacement volume value, because the load torque is obtained as the product of the delivery pressure and the displacement volume. For example, in the case of a small displacement volume, a high pressure can be maintained with a small torque. In this case, in particular, no thermal overload of the electric motor and the inverter of the electric drive will occur.
[0007] If the displacement volume now has a first, larger displacement volume value, a monitoring is performed within the scope of the invention, in which actual values for the delivery pressure of the hydraulic pump and the actual values for the rotational speed of the hydraulic pump (or the actual value for the rotational speed of the electric drive, since these are usually transformed 1:1 or at least have a known transformation ratio) are detected. It is determined whether a permissible operating point results from the actual values for the delivery pressure and the actual values for the rotational speed of the hydraulic pump, and if a permissible operating point does not result, the displacement volume is set to a second, smaller displacement volume value.
[0008] Preferably, it can be determined by monitoring the current torque, ie by acquiring an actual value of the torque of the variable-speed electric drive, whether a setting of a second, smaller displacement volume value is or has been carried out, since the torque thereby changes, in particular decreases.
[0009] As an alternative or in addition, the currently set displacement volume value can be determined with the aid of a calculation model or a model-based observer, into which existing measured variables such as rotational speed, torque or drive current, delivery pressure are input. This displacement volume value can also be used to determine whether a setting of a second, smaller displacement volume value is being or has already been made.
[0010] Furthermore, the currently set displacement volume value can advantageously be taken into account as a control path characteristic in the pressure control. In particular, depending on the actual controller outputting the manipulated variable, a function for path adaptation is provided, which changes the manipulated variable (e.g., a rotational speed target value) depending on the currently set displacement volume value. This, for example, eliminates the need to adapt controller parameters (e.g., coefficients such as proportional control, reset time, etc.) and allows the desired dynamics of the control to be maintained.
[0011] According to a preferred embodiment of the present invention, when the target value of the speed of the variable speed electric drive changes, the rate of change of the target value is limited to the maximum speed change rate. In particular, in normal operation, the change in the target value of the speed is obtained by the upper preset, but also because the discharge volume changes to a smaller second discharge volume value, that is, when the discharge volume decreases, the speed must be increased to maintain the volume flow or pressure. The change in the speed target value is carried out at a predetermined angular acceleration. This allows additional component protection, in particular pump protection. The speed change rate is in particular a rotational acceleration and can be expressed in [angle / time 2 ] to give the speed change rate. If the acceleration / deceleration of the pump rotation is limited, mechanical damage to internal components can be avoided. High accelerations on the system side can lead to local underpressures in the hydraulic fluid, since the hydraulic fluid cannot dynamically follow the movement of the pump rotor. This can lead to cavitation. The limit values for acceleration and deceleration can be listed in the data sheet of the pump.
[0012] According to a preferred embodiment of the present invention, the rate of change of the target value of the pressure is limited to the maximum pressure change rate and / or the target value itself is limited to the maximum pressure value (e.g. the rated pressure of the pump) in the pressure regulating unit. This represents two other advantageous component protection mechanisms to protect the pump from overload or damage. If the target pressure change rate has been limited (i.e. on the input side), this also automatically leads to a time deceleration at the output end, that is, in particular a deceleration of the speed change rate, and therefore also has the above-mentioned advantages. In particular, the pressure change rate can be given as [pressure / time]. Because it is possible to exceed the maximum pressure value for a short time according to the structural form and the design scheme, the limitation of the target value of the pressure to the maximum pressure value preferably includes waiting for the allowed overload time before limiting the target value of the pressure, that is, before adjusting.
[0013] According to a preferred embodiment of the present invention, when the actual value of the delivery pressure corresponds at most to the minimum pressure value, the target value of the speed of the variable speed electric drive is limited to the minimum speed. Usually, for energy and dynamic reasons, the hydraulic pump should be operated with the maximum possible discharge volume, that is, the current discharge volume should have a larger first discharge volume value. However, this means a large hydraulic torque, so that here, under high pressure (exceeding a threshold value of, for example, 5 bar or 50 bar), a particularly small or even negative speed (for example <200 rpm) is only allowed for a short time (for example, a few seconds) (it goes without saying that the corresponding values depend on the specific pump and should be understood purely as an example). As another component protection mechanism, the minimum pressure value and the minimum speed can then be monitored to prevent cavitation of the pump. If the speed cannot be further reduced due to the limitation, the discharge volume is reduced (and the speed is increased accordingly) to maintain the volume flow. The limitation can be implemented immediately or with a time delay, that is, if necessary, it can be allowed to be below the minimum speed for a short time. However, if it is shown in the second case that the allowed time is exceeded, especially in the case of taking into account the swing time, a switch to a small discharge volume is made. Taking the oscillation time into account means that the permissible time is not exceeded until the discharge volume has reached the small discharge volume value (and can then no longer be exceeded because of the presence of non-critical operating points).
[0014] The computing unit according to the invention, for example a control unit of an electrohydraulic system, is provided, in particular in terms of programming, for carrying out the method according to the invention.
[0015] It is also advantageous to implement the method according to the invention in the form of a computer program or computer program product with a program code for executing all method steps, since this results in particularly low costs, in particular if the executing control device is also used for other tasks and is therefore already present. Suitable data carriers for providing the computer program are in particular magnetic, optical and electrical memories, such as hard disks, flash memories, EEPROMs, DVDs, etc. In addition, the program can also be downloaded via a computer network (such as the Internet, intranet, etc.).
[0016] Further advantages and embodiments of the invention are apparent from the description and the drawings.
[0017] It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the respectively specified combination but also in other combinations or alone, without departing from the scope of the present invention.
[0018] The invention is schematically illustrated by means of exemplary embodiments in the drawings and is described in detail below with reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Figure 1 A preferred embodiment of the variable speed electrohydraulic device according to the invention is shown schematically. DETAILED DESCRIPTION
[0020] exist Figure 1 A preferred embodiment of a variable speed electrohydraulic device according to the invention is schematically shown in FIG. 1 and is generally designated by 10. The electrohydraulic device 10 has an adjustable hydraulic pump 20, which in the present exemplary embodiment can deliver in two directions, a variable speed electric drive 30 and a computing unit 40 for operating the electrohydraulic device.
[0021] The hydraulic pump 20 is designed as an axial piston pump, which has a pivot angle α for the swash plate or the swash shaft that can be adjusted between two positions. As a result, the displacement volume can be adjusted between a first, larger displacement volume value and a second, smaller displacement volume value. For this purpose, a control signal from the calculation unit 40 to the axial piston pump 20 can be used. The control signal can be, for example, a control value for a so-called pilot valve 21 on the pump.
[0022] The electric drive is constructed as a so-called standard motor with a synchronous servomotor 31 and a frequency converter 32. In principle, an asynchronous motor can also be used. The speed n of the asynchronous motor 31 is variable. For this purpose, the target speed is pre-set to the electric drive 30 by the calculation unit 40. The actual speed can be determined by an angle sensor. However, control can also be achieved without feedback.
[0023] The calculation unit 40 is used to adjust the pump 10, the target delivery pressure p S and / or target volume flow Q S The calculation unit 40 can be designed as a so-called electric drive regulator and thus determine the speed n as a control variable within the scope of the invention. The calculation unit can also be separate from the drive regulator and serve as its superior and communicate with it via an interface (speed target value, speed actual value, etc.). The actual delivery pressure is determined in a suitable manner by means of a sensor. Pressure regulation can thus be achieved.
[0024] For example, the displacement volume can be switched during operation according to the operating strategy. For example, by monitoring the current, the calculation unit 40 can determine, for example, whether the electric drive is in full-load operation or partial-load operation, so as to determine the electric drive torque provided by the electric drive 30 and compare it with the maximum possible electric drive torque for the current rotational speed, or by monitoring the rotational speed. In particular, a threshold comparison can be provided, wherein an electric drive torque less than a threshold value (for example 75%) or a rotational speed less than a threshold value is identified as partial load. The rotational speed threshold value is predefined in a suitable manner depending on the intended use.
[0025] In full-load operation, a control signal is output for a swivel angle of the pump 20, which results in a larger first displacement volume value. In partial-load operation, a control signal is output for a swivel angle of the pump 20, which results in a lower second displacement volume. In particular, the dependence of the lower second displacement volume on the rotational speed can be derived from a characteristic diagram or the like in a calculation unit.
[0026] The setting of the discharge volume can be realized in a suitable manner by actuating a pilot valve or control valve 21. A switching valve (or proportional valve) can be used for this purpose.
[0027] According to a preferred embodiment of the invention, different protection mechanisms are now used to protect the electronic hydraulic system or its components from damage. For this purpose, (especially) when the displacement volume has a first, larger displacement volume value, the actual value of the delivery pressure of the hydraulic pump and the actual value of the rotational speed n of the asynchronous motor 31 (as the rotational speed of the hydraulic pump) are acquired, and it is determined from this whether a permissible operating point exists. If there is no permissible operating point (especially because the rotational speed is too low and / or the pressure is too high), the displacement volume is set to a second, smaller displacement volume value. In order to maintain the pressure p S Or volume flow Q S , the speed is increased accordingly and the impermissible operating point is left. As explained above, there is usually no operating point limitation in the case of small discharge volumes.
[0028] Additional beneficial protection mechanisms include:
[0029] - limiting the rate of change of the target value of the speed of the variable speed electric drive (30) to a maximum rate of change of the speed,
[0030] - limiting the rate of change of the target value of the delivery pressure of the hydraulic pump (20) to a maximum pressure change rate,
[0031] - limiting the target value for the delivery pressure of the hydraulic pump (20) to a maximum pressure value, if necessary after a permissible overload time has expired,
[0032] - limiting the target value of the speed of the variable speed electric drive (30) to the minimum speed, if necessary after a permissible overload time has expired, when the actual value of the delivery pressure corresponds at most to a minimum pressure value.
[0033] In electrohydraulic systems, the invention leads to an increase in the availability of the pump, prevents machine standstills and avoids or reduces damage to the pump or excessive wear.
Claims
1. A method for operating a variable speed electrohydraulic device (10), in which a hydraulic pump (20) whose displacement volume can be adjusted between a first, larger displacement volume value and a second, smaller displacement volume value for each working cycle is driven by means of a variable speed electric drive (30), the method comprising: When the discharge volume has a larger first discharge volume value, obtaining a target value of the rotation speed of the variable speed electric drive device (30), Acquiring an actual value of the delivery pressure of the hydraulic pump (20), Obtaining the actual value of the rotation speed of the hydraulic pump (20), determining whether an allowable operating point is obtained from the actual value of the delivery pressure and the actual value of the rotational speed of the hydraulic pump (20), and If an admissible operating point is not obtained from the actual value of the delivery pressure and the actual value of the rotational speed of the hydraulic pump (20), a second smaller displacement volume value is set.
2. The method according to claim 1, further comprising: An actual value of the torque of the variable speed electric drive device (30) is acquired, and whether to set a smaller second displacement volume value is determined based on the acquired actual value of the torque.
3. The method according to claim 1 or 2, further comprising: The rate of change of a target value of the rotational speed of the variable-speed electric drive (30) is limited to a maximum rotational speed change rate.
4. A method according to any one of the preceding claims, wherein: A target value of the speed of the variable speed electric drive device (30) is acquired as a regulating variable of a superior pressure regulating unit, and a target value of the delivery pressure of the hydraulic pump (20) is supplied to the superior pressure regulating unit as an input variable.
5. The method according to claim 4, further comprising: A rate of change of a target value of a delivery pressure of the hydraulic pump (20) is limited to a maximum pressure change rate.
6. The method according to claim 4 or 5, further comprising: A target value for the delivery pressure of the hydraulic pump (20) is limited to a maximum pressure value.
7. The method according to claim 6, wherein: The definition of the target value of the delivery pressure of the hydraulic pump (20) to the maximum pressure value includes waiting for an allowable overload time before defining the target value of the delivery pressure.
8. The method according to any one of claims 4 to 7, further comprising: The currently set discharge volume value is used as the path characteristic of the pressure control for changing the manipulated variable.
9. The method according to any one of the preceding claims, further comprising: The currently set discharge volume value is determined with the aid of a calculation model.
10. The method according to any one of the preceding claims, further comprising: If the actual value of the delivery pressure corresponds at most to a minimum pressure value, the target value of the rotational speed of the variable-speed electric drive (30) is limited to a minimum rotational speed.
11. The method according to claim 10, wherein: Limiting the target value of the rotational speed of the variable speed electric drive device (30) to a minimum rotational speed includes waiting for a permissible overload time before limiting the target value of the rotational speed of the variable speed electric drive device (30).
12. A computing unit (40) comprising a processor, the processor being configured in such a way that it carries out the method according to any of the preceding claims.
13. An electrohydraulic device (10) comprising a hydraulic pump (20) whose displacement volume can be adjusted for each working cycle between a first, larger displacement volume value and a second, smaller displacement volume value, a variable speed electric drive (30) and a computing unit (40) according to claim 12.
14. A computer program comprising commands which, when executed, cause a computing unit of an electrohydraulic device (10) as claimed in claim 12 to cause the computing unit to carry out a method as claimed in claims 1 to 9.
15. A computer-readable data carrier having stored thereon a computer program according to claim 14.