Method for operating a variable-speed pump

Abstract

The invention relates to a method for operating a variable speed pump (120) in which a conveying unit (122) adjustable in a displacement volume per working cycle is driven by means of a variable speed drive (121), comprising determining a load torque on the variable speed pump (120) as a function of an operating condition, and specifying a setpoint (VPu,Set) for a characteristic parameter determining the displacement volume per working cycle such that a drive torque of the variable speed drive (121) corresponds at most to a peak drive torque (Man,max) of the drive (121) or a continuous drive torque (Man,0) of the drive (121).

Description

[0001] The present invention relates to a method for operating a variable speed pump in which a pumping mechanism adjustable in a displacement volume per working cycle is driven by means of a variable speed drive, as well as to an electrohydraulic system. State of the art

[0002] The pumps underlying the invention have a pumping mechanism with a variable displacement volume per working cycle (a so-called hydraulic displacement machine, e.g., an axial piston machine), which is driven by a variable-speed drive. During operation of such pumps, the volume flow and / or the discharge pressure (i.e., the pressure difference between the inlet and outlet) are typically controlled by adjusting the pumping mechanism's displacement volume and the speed accordingly; i.e., such pumps have two degrees of freedom in control.

[0003] For example, EP 2 192 309 B1 discloses a method in which such a pump is operated by regulating a pressure or pressure medium quantity by controlling the pump's volume setting. A speed deviation of the drive is taken into account.

[0004] US 2021 / 025414 A1 shows a hydraulic pressure medium supply arrangement with a hydraulic machine for supplying pressure medium to at least one hydraulic consumer, with a hydraulic control block for controlling the at least one consumer, and with a first and second control module, wherein the control block can be controlled via the first control module via at least one control signal, wherein a data interface is provided between the control modules, and wherein the first control module transmits a target output pressure for the hydraulic machine and / or a target delivery volume for the hydraulic machine to the second control module as an input variable(s) via the data interface, wherein the second control module controls an adjustment mechanism of the hydraulic machine with a valve control signal based on the target output pressure and / or the target delivery volume.and wherein at least one hydraulic parameter and / or another control signal is transmitted to the second control module for the data interface, which parameter specifies and / or limits a dynamic of the adjustment mechanism of the hydraulic machine.

[0005] US 2021 / 025138 A1 shows a hydraulic pressure medium supply arrangement having an adjustable axial piston machine, wherein an actuating cylinder is controlled via a pilot valve. The pilot valve is actuated by a control device. The control device has an actual pressure and / or an actual swivel angle of the adjustable axial piston machine as input variables. One or more of the aforementioned input variables are compared with a suitable setpoint, and a control value or a control value is output. The control of the aforementioned input variables is part of a first control loop. A subordinate second control loop has an input variable based on the control variable(s), which serves as the setpoint. Another input variable of the second control loop is an actual displacement adjustment speed of the axial piston machine. A control value for the pilot valve is then provided as the output variable for the second control loop. Disclosure of the invention

[0006] According to the invention, a method and an electrohydraulic system with the features of the independent patent claims are proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

[0007] The invention relates to the operation of a variable-speed variable displacement pump, such as an axial piston pump with, for example, proportional adjustment, in which a pumping mechanism whose displacement can be adjusted per working cycle is driven by a variable-speed drive, such as an electric motor. A so-called swash plate, for example, can be provided in such a variable-speed pump to adjust the pumping mechanism. On the basis of the load torque (in particular load pressure or differential pressure) on the pump and load parameters of the drive motor (e.g. peak and continuous drive torque, max. overload time (= duration of the max. torque)), a targeted setpoint for the displacement volume is generated to limit the drive torque. The invention thus creates a decoupling of the drive torque from the load pressure of the driven pumping mechanism by adjusting the displacement volume, with the aim of achieving optimum motor utilization.

[0008] The current or drive torque of electric drives is usually thermally limited and dependent on the duration of the load. However, hydrostatic motor-pump units often have to provide high load pressures over a relatively long period of time. A suitable adjustment of the displacement volume decouples pressure and drive torque. The invention prevents overloading of the drive. Within the scope of the invention, the displacement volume is specified so that it can always be provided by the electric drive. The invention is particularly applicable to pumps equipped with an adjustment device for the targeted influence of their displacement volume based on control-related specifications. In particular, two operating states, static and dynamic, with different displacement volume specifications can be distinguished.

[0009] The dependence on the operating state is expediently taken into account by considering the dependence on a temporal change in the load torque on the variable-speed pump. This is a simple way to characterize the operating state.

[0010] According to the invention, a first manipulated variable is determined from the load torque and the peak drive torque of the drive in accordance with a first filter function with a time delay, in particular a PDT1 function, and a second manipulated variable is determined from the load torque and the continuous drive torque of the drive in accordance with a second filter function with a time delay, in particular a PDT1 function, wherein the setpoint for the parameter determining the displacement volume per working cycle is specified based on the smaller of the first and second manipulated variables. This allows an operating state or load gradient dependency to be implemented with a predefinable time profile, in particular such that a timely change from the peak drive torque to the continuous drive torque takes place quasi-automatically before the engine is damaged.For this purpose, the first filter function preferably has a smaller time delay than the second filter function, preferably zero.

[0011] Preferably, in a dynamic operating condition, the setpoint for the parameter determining the displacement volume per working cycle is specified such that the drive torque of the variable-speed drive is greater than the continuous drive torque and corresponds at most to the peak drive torque of the drive. In this way, the displacement volume is controlled or regulated in such a way that dynamic operating conditions are realized by utilizing the corner power or peak power of the electric drive.

[0012] In particular, in the dynamic operating state, the setpoint for the parameter determining the displacement volume per working cycle is specified such that the drive torque of the variable-speed drive corresponds to the peak drive torque of the drive for a maximum permissible overload period. This allows peak power to be accessed for as long as possible. It can also be provided to adjust the overload period using a determined (in particular, measured (e.g., using a temperature sensor) or estimated) thermal drive load. This can prevent thermal damage to the drive.

[0013] According to a further advantageous embodiment, in a static operating state, the setpoint for the parameter determining the displacement volume per working cycle is specified such that the drive torque of the variable-speed drive corresponds at most to the continuous drive torque of the drive. This ensures long-term or continuous operation; steady-state operating states are realized by utilizing the rated power of the electric drive.

[0014] A computing unit according to the invention, e.g. a control and / or regulating unit for a variable speed pump with variable speed drive, is configured, in particular in terms of programming, to carry out a method according to the invention.

[0015] The invention further relates to an electro-hydraulic drive system such as an electro-hydraulic axle comprising a variable speed pump with a variable speed drive and a computing unit according to the invention.

[0016] Implementing a method according to the invention in the form of a computer program or computer program product with program code for performing all method steps is also advantageous, as this entails particularly low costs, especially if an executing control unit is also used for additional tasks and is therefore already present. Suitable data storage devices for providing the computer program include, in particular, magnetic, optical, and electrical storage devices, such as hard disks, flash memories, EEPROMs, DVDs, and others. Downloading a program via computer networks (Internet, intranet, etc.) is also possible.

[0017] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0018] It is understood that the features mentioned above and those to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the present invention.

[0019] The invention is illustrated schematically in the drawing using exemplary embodiments and is described in detail below with reference to the drawing. Character description

[0020] Figure 1 shows a circuit diagram of a hydraulic system comprising a drive motor and a control system with a device for adjusting the speed and a conveyor system with a device for adjusting the delivery volume. Figure 2shows a signal flow diagram of a control scheme according to a preferred embodiment of the invention. Figure 3 shows exemplary curves of operating variables pressure, drive torque and delivery volume when applying a control scheme according to a preferred embodiment of the invention. Detailed description of the drawing

[0021] In Figure 1 An electrohydraulic system 100, such as may form the basis of the invention, is shown schematically. The electrohydraulic system 100 has an actuator designed as a hydraulic cylinder 110 with a piston 111 movable along an x-axis, which is actuated by a variable-speed pump 120. A hydraulic circuit 130 with, for example, oil as the medium or operating medium is arranged between the variable-speed pump 120 and the hydraulic cylinder 110.

[0022] The variable-speed pump 120 has a variable-speed drive embodied as an electric motor 121 and a pumping mechanism 122. It is designed, for example, as an axial piston pump with a swashplate design. By adjusting the angle of the swashplate, the so-called swash angle, the displacement volume of the pumping mechanism can be changed per working cycle.

[0023] A control and / or regulation unit 140 is programmed to carry out a preferred embodiment of a method according to the invention. In the example shown, it has several modules 141, 142, 143, here a control module 141, a speed control module 142, and a displacement volume control module 143. However, it should be clarified that the individual modules do not have to be installed in a single unit and do not have to be implemented in the program. In particular, a displacement volume control module 143 is often designed, for example, as an analog swivel angle controller.

[0024] A speed setpoint n soll and an actual speed value n ist are supplied to the speed control module 142, from which a setpoint M An for a drive torque is determined according to conventional control methods, e.g., using P and / or I and / or D transfer functions. The speed setpoint can originate, e.g., as a controlled specification from a user or as a control value from a higher-level pressure / force / position / speed controller for the hydraulic circuit or the output machine (e.g., cylinder or hydraulic motor).

[0025] The displacement volume control module 143 is supplied with a displacement volume setpoint V PU,soll and a displacement volume actual value V PU,ist, from which a control variable for the conveyor is determined according to conventional methods.

[0026] Two pressure sensors are provided to measure the pressure p 1 , p 2 in front of and behind the conveyor.

[0027] The pressure values ​​p 1 , p 2 and the (setpoint or actual) value M An (in electric machines, the time constant is significantly shorter than in hydraulics, so that in this case, the setpoint and actual values ​​can always be considered equal) for the drive torque are supplied to the control module 141, from which the setpoint for the displacement volume is determined. The drive torque can preferably be used here to account for a non-negligible friction component of the total torque (present in addition to the external load). As shown below, it is taken into account in particular in the form of an additional load pressure.

[0028] Hydrostatic pumps provide a flow rate that is essentially proportional to the product of the speed and the pump size, which is characterized by the displacement. The flow rate varies depending on the direction of rotation, from one working port to the other. If different pressures p 1 , p 2 prevail at the working ports, a drive motor must provide a corresponding torque. The required torque is proportional to the product of the pressure difference and the pump size, which is characterized by the displacement.

[0029] By adjusting the pump's displacement volume and adopting a suitable operating strategy, the application range of the motor-pump unit can be significantly expanded compared to a system with a fixed pump, as a high flow rate can be provided at low load pressures, while the drive motor is not overloaded at high load pressures. The present invention takes into account both the limitation of the continuous torque M 0 as well as peak torque M max and allows the temporary use of the maximum power of the drive motor / converter.

[0030] A pressure difference at the pump drive requires / generates a proportional moment ML,P on the pump shaft according to: M L , p = V Pu , Ist 2 ⋅ π ⋅ p 1 − p 2

[0031] One speed approximately generates (minus leakage volume flows) a volume flow according to: Q Pu = V Pu , Ist ⋅ n

[0032] Overall, the torque balance on the drive of the motor-pump unit is: J MoPu ⋅ φ ¨ = M an − M L , p − M R , ges where J MoPu is the moment of inertia of the unit, ϕ̈ the angular acceleration and MR, please the total friction torque on the engine.

[0033] When limiting the engine torque Man to a limit M in the , maximum must therefore be considered as a minimum requirement: M L , p ≤ M an , max to maintain control over the drive speed and prevent it from dropping unintentionally.

[0034] This condition can be met by a suitable adjustment of the displacement volume as follows: V Pu , Soll , Spitze V Pu , max ≤ 2 ⋅ π V Pu , max ⋅ M an , max p 1 − p 2 + p ^ R , ges , s c h ä tz

[0035] This already takes into account that devices for adjusting the displacement volume of a pump (such as a swivel angle adjustment) often expect a setpoint signal that is based on the maximum displacement volume V PU, maxand the actual displacement volume is also given as a relational quantity. The real (total) friction on the engine can be calculated as an estimated additional pressure difference p̂ R,ges,est. which is derived from the drive torque and the displacement.

[0036] An alternative form for equation 5a can be given if the relative quantity α is introduced for the relative displacement volume. This results in the requirement: α Soll , Spitze ≤ 2 ⋅ π V Pu , max ⋅ M an , max p 1 − p 2 + p ^ R , ges , s c h ä tz which, depending on the respective load pressure, carries out the pump adjustment in such a way that the peak torque of the engine is not exceeded by the output torque.

[0037] In an analogous manner, a setpoint for the (relative) displacement volume can be derived, which ensures compliance with the (lower) continuous torque M an,0 of the drive motor ensures: α Soll , Dauer ≤ 2 ⋅ π V Pu , max ⋅ M an , 0 p 1 − p 2 + p ^ R , ges , s c h ä tz

[0038] There M in the, 0 ≤ Man, max.If the torque limitation rules formulated in Eqs. 5b and 6 were applied directly, the displacement volume would always be reduced to such an extent that the continuous torque is not exceeded. This would prevent the use of the drive motor's corner power.

[0039] To (short-term) utilize the maximum power of the drive, the setpoints for the swivel angle resulting from Eqs. 5b and 6 are advantageously filtered in order to influence them temporally in such a way that the motor utilization is suitably optimized.

[0040] This advantageously results in the rule for specifying a pump displacement volume for torque limitation in general form: α Soll , Dauer ≤ 2 ⋅ π V Pu ,max ⋅ MIN f K redM 0 ⋅ M an , 0 p 1 − p 2 + p ^ R , ges , s c h ä tz ω g K redMmax ⋅ M an , max p 1 − p 2 + p ^ R , ges , s c h ä tz ω

[0041] This includes the K redM* designated correction values, that on a real drive system the torque limit values ​​may deviate from the nominal values.

[0042] A filter or a filter function can be technically advantageous g ( M an,max , Δ p , ω ) should be designed to compensate for any dynamic delay in the adjustment device, ensuring instantaneous maximum torque limitation and thus guaranteeing functionality even during dynamic load changes. A PDT1 transfer function can be advantageously used as a filter function.

[0043] Furthermore, a filter or a filter function f ( M on,0 , Δp, ω) can be designed in such a way that, as the load increases, the reduction of the displacement volume is delayed for a defined period of time, in order to optimally utilize the drive's peak power. However, as the load decreases, the displacement volume is adjusted back as quickly as possible in order to achieve a high volume flow for load reduction. A PDT1 transfer function can be advantageously used as a filter function.

[0044] In order to maintain an application-specific flow rate, a change in the displacement volume is advantageously taken into account when specifying the speed n target. The product of speed and displacement volume is proportional to the requested or required flow rate.

[0045] The signal flow diagram of a preferred implementation of such a filter concept is shown in Figure 2 shown and labeled with 200 in total.

[0046] On the input side (left), the difference between the pressure values ​​p 1 and p 2 is first calculated and fed to an amount calculation 201. Likewise, the amount 202 of the estimated additional pressure difference p̂ = p̂ R,ges,est. added to form the total relevant differential pressure Δp. This is calculated in a division element 203 or 204 with the maximum drive torque M an,max or the continuous drive torque M an,0 and then calculated in an element 205, 206 with the aforementioned correction values ​​and the maximum volume to obtain the relational volume control values.

[0047] These are fed to a filter function 207, 208, which represents a PDT transfer behavior, in particular according to the following equation. The corresponding transfer functions are: g : G s = T N , Spitze ⋅ s + 1 T P , Spitze ⋅ s + 1 f : G s = T N , Dauer ⋅ s + 1 T P , Dauer ⋅ s + 1

[0048] The resulting output values ​​or manipulated variables α S,peak and α S,duration are fed to a minimum value element 209, which selects the respective smaller displacement volume as the actual manipulated variable α setpoint.

[0049] An advantageous parameterization of the filter parameters is as follows: Derivative time: T N , Spitze = T Stell Delay time: T P , Spitze = 0 Derivative time: T N , Dauer = T Maxmoment ⋅ 1 − 1 e ⋅ SGN ∝ ˙ S , Dauer , stat Delay time: T P , Dauer = T Maxmoment ⋅ 1 − 1 e

[0050] This corresponds to T-shirt the parameter of a simplified model of the pump adjustment dynamics. T maximum torque is the time the drive is expected to be able to deliver its peak torque. This is considered a key operating parameter of the proposed adjustment strategy and must be less than the actual time after which the drive reaches thermal overload. Furthermore, e is Euler's number.

[0051] To further improve the process, the friction torque estimate can be adapted to the current operating conditions using a suitable estimation device. One possible device would be an integral controller for the static engine torque or other estimation devices commonly used in control engineering, such as observers.

[0052] To further improve the method, using the measured or estimated thermal drive load via adaptation of the correction factor K redM0 The effective limit value for the continuous torque can be adjusted to the existing operating conditions. Similarly, the permissible overload time T max moment, which is used in the signal filter, must be adapted to the existing operating conditions.

[0053] An exemplary course of operating variables when using a preferred embodiment of the invention is shown in Figure 3 shown.

[0054] In the upper diagram, the pressure difference 301 at the conveyor and a drive torque 302 at the electric drive are plotted against time t in exemplary units, also in exemplary units. In particular, starting from a time 0 to a time approximately 0.85, the pressure difference and thus the load are increased from 0 to approximately 100%.

[0055] The lower diagram plots the displacement volume in percent against time t for different control variables. These include α set, duration, stat 303, α set, peak, dyn 304, α set, duration, dyn 305, α set, peak, stat 306. Furthermore, the actual swivel angle α actual 307 resulting from an exemplary control dynamic is plotted.

[0056] The two conditions for limiting to the maximum torque or the continuous torque result in the two static swivel angle setpoints α setpoint, duration, stat 303 and α setpoint, peak, stat 306 for the increasing pressure difference shown. After filtering through the corresponding signal filters 207 and 208, the setpoints α setpoint, duration, dyn 305 and α setpoint, peak, dyn 304 valid for the swivel angle control are available. The minimum value element 209 supplies the control device 143 with the smaller value of α setpoint, duration, dyn 305 and α setpoint, peak, dyn 304 at the respective time as the valid setpoint for the swivel angle. In a typical embodiment of the control device 143 for the swivel angle as a proportional controller, there is a time delay of the swivel angle actual value compared to the setpoint value, which is shown as an example by the actual value curve α Ist 307.

[0057] With an advantageous parameterization of the filter times, the filter 207 for the peak torque limitation compensates the actuating dynamics of the control device 143 in such a way that the actual value α Ist 307 exactly follows the static setpoint value α Soll,Pitze,stat 306, so that the peak torque is not exceeded despite the limited actuating dynamics of the swivel angle controller.

[0058] Furthermore, the filter 208 for the continuous torque limitation is designed with a direction-dependent signal component, so that when the load torque increases, the effective setpoint α Soll,Dauer,dyn 305 lags behind the filter input α Soll,Dauer,stat 303 in order to be able to utilize the desired time-limited maximum load of the electric drive machine, while when the load torque decreases, the effective setpoint α Soll,Dauer,dyn 305 leads the filter input α Soll,Dauer,stat 303. With advantageous parameterization of the filter times, as shown above, the filter 208 for the continuous torque limitation compensates the actuating dynamics of the control device 143 in such a way that the actual value α Ist 307 exactly follows the static setpoint α Soll,Dauer,stat 303, so that when the load decreases, the full performance of the motor-pump unit is available without time delay and while adhering to the torque limitation, despite the limited actuating dynamics of the swivel angle controller.

Claims

1. Method for operating a variable-speed variable displacement pump (120), in which a conveying mechanism (122), which is adjustable in a displacement volume per working cycle, is driven by means of a variable-speed drive (121), which has a peak drive torque (MAn.max) and a continuous drive torque (MAn,0), comprising: determining a load torque (Δp) at the variable-speed variable displacement pump (120), depending on an operating state, specifying a setpoint (VPu,Soll) for a characteristic variable determining the displacement volume per working cycle to an adjustment device (143) of the conveying mechanism such that a drive torque of the variable-speed drive (121) corresponds either to more than the continuous drive torque (Man,0) and to not more than the peak drive torque (Man,max) of the drive (121), or to not more than the continuous drive torque (Man,0) of the drive (121), wherein a first actuating variable (αS,Spitze) is determined from the load torque (Δp) and the peak drive torque (MAn,max) of the drive (121) according to a first filter function (207) with a time delay (TP,Spitze) and a second actuating variable (αS,Dauer) is determined from the load torque (Δp) and the continuous drive torque (MAn,0) of the drive (121) according to a second filter function (208) with a time delay (TP,Dauer), wherein the setpoint (VPu,Soll) for the characteristic variable determining the displacement volume per working cycle is specified by means of the smaller of the first and second actuating variable.

2. Method according to Claim 1, wherein the dependency on the operating state is taken into consideration by a dependency on a time change of the load torque (Δp) at the variable-speed variable displacement pump (120).

3. Method according to Claim 1 or 2, wherein the first filter function (207) has a shorter time delay (TP,Spitze) than the second filter function (208), preferably zero.

4. Method according to any one of the preceding claims, wherein the first filter function (207) and / or the second filter function (208) are / is a PDT1 transmission function having a lead time (TN,Spitze, TN,Dauer) and a delay time (TP,Spitze, TP,Dauer), wherein the lead time (TN,Spitze, TN,Dauer) is specified in particular depending on an actuating dynamics of the adjustment device (143) of the conveying mechanism.

5. Method according to any one of the preceding claims, wherein, in a dynamic operating state, the setpoint (VPu,Soll) for the characteristic variable determining the displacement volume per working cycle is specified in such a way that the drive torque of the variable-speed drive (121) corresponds to more than the continuous drive torque (MAn,0) of the drive (121) and to not more than the peak drive torque of the drive (121).

6. Method according to Claim 5, wherein, in the dynamic operating state, the setpoint (VPu,Soll) for the characteristic variable determining the displacement volume per working cycle is specified in such a way that the drive torque of the variable-speed drive (121) corresponds at most for a reliable overload time to more than the continuous drive torque (MAn,0) of the drive (121) and to not more than the peak drive torque of the drive (121).

7. Method according to Claim 6, wherein the overload time is adapted using a determined thermal drive capacity, and preferably with reference back to Claim 3, wherein the time delay (TP,Dauer) of the second filter function (208) is specified depending on the overload time.

8. Method according to any one of the preceding claims, wherein, in a static operating state, the setpoint (VPu,Soll) is specified for the characteristic variable determining the displacement volume per working cycle in such a way that the drive torque of the variable-speed drive (121) corresponds to not more than the continuous drive torque of the drive (121).

9. Method according to any one of the preceding claims, wherein the determination of the load torque at the variable-speed variable displacement pump (120) comprises determining a pressure difference (Δp) between an inlet and an outlet of the conveying mechanism (122).

10. Method according to any one of the preceding claims, wherein the determination of the load torque at the variable-speed variable displacement pump (120) comprises determining a friction as an additional pressure difference (p̈).

11. Method according to any one of the preceding claims, wherein the peak drive torque (Man,max) of the drive (121) and / or the continuous drive torque (Man,0) of the drive (121) are / is taken into consideration as a product with a correction factor (KredMmax, KredM0).

12. Method according to Claim 11, wherein the correction factor (KredMmax, KredM0) is adapted using a determined thermal drive capacity.

13. Method according to any one of the preceding claims, additionally comprising: specifying a setpoint (nSoll) for the speed of the variable-speed drive (121) depending on the setpoint (VPu,Soll) or an actual value (VPu,Sst) for the characteristic variable determining the displacement volume per working cycle.

14. Processing unit (140) which is designed to carry out a method according to any of the preceding claims.

15. Electrohydraulic system (100) comprising a variable-speed variable displacement pump (120) with a variable-speed drive (121) and a processing unit (140) according to Claim 14.

16. Computer program that causes the processing unit (140) of the electrohydraulic system (100) according to Claim 15 to carry out a method according to any one of Claims 1 to 13 when said computer program is executed on the processing unit (140).

17. Machine-readable storage medium with a computer program according to Claim 16 stored thereon.

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