Method for operating a regulating pump with variable rotational speed

Abstract

The invention relates to a method for operating a variable speed variable pump, in which a delivery mechanism (122) whose displacement per working cycle can be adjusted is driven by means of a variable speed drive (121), wherein within the scope of control, a speed target value (n) for the speed of the drive is predefined. soll ) and the target value of the characteristic parameter for determining the displacement of each working cycle (α soll ), adjust at least one parameter to the target value (p soll ), where the target value of the characteristic parameter (α) used to determine the displacement of each working cycle is changed. soll ), the speed target value (n soll ).

Description

Field of the Invention

[0001] The present invention relates to a method for operating a regulating pump with variable speed and an electrohydraulic system, in which a delivery mechanism adjustable in displacement in each working cycle is driven by a drive device with variable speed. Background Art

[0002] The pump on which the present invention is based has a delivery mechanism (so-called hydraulic piston machine, such as an axial piston machine) with variable displacement within each working cycle, and the delivery mechanism is driven by a drive device with variable speed. In the operation of such a pump, the volumetric flow and / or the delivery pressure (i.e., the pressure difference between the inlet and the outlet) are usually regulated by a corresponding matching of the displacement and the speed of the delivery mechanism, that is, such a pump has two degrees of freedom in regulation.

[0003] For example, from EP 2 192 309 B1, a method is known in which the pressure or the amount of pressure medium is regulated by controlling the volumetric setting of the pump, thereby operating such a pump. Here, the speed deviation of the drive device is taken into account. Summary of the Invention

[0004] According to the present invention, a method and an electrohydraulic system are proposed. Advantageous design solutions are the subject of the preferred embodiments and the following description.

[0005] The present invention relates to the operation of a regulating pump with variable speed, such as especially an axial piston pump with, for example, two-point regulation or proportional regulation, in which a delivery mechanism adjustable in displacement in each working cycle is driven by a drive device with variable speed, such as an electric motor. In order to regulate the delivery mechanism, a so-called swash plate can be provided in such a regulating pump, for example.

[0006] In the operation of such a regulating pump, usually within the range of regulation, at least one parameter, such as pressure, is regulated to the target value (of the at least one parameter) by pre-giving a target value for the speed of the drive device and a target value for a characteristic parameter for determining the displacement in each working cycle.

[0007] Preferably, the at least one parameter is selected from the following: the pressure and / or the volumetric flow of a medium, such as oil, in which the regulating pump operates (or serves as the working medium); the force directly or indirectly generated by the medium; and the position of an element directly or indirectly moved by the medium. In particular, the force and the position can relate not only to the system having the regulating pump and the drive device, but also to a superior system in which the regulating pump and the drive device are used together, such as an electrohydraulic shaft or generally an electrohydraulic system.

[0008] Characteristic parameters for determining the displacement volume per working cycle - such as in the case of the axial piston pump with a swash plate mentioned - can be the swivel angle. In this example, by changing the adjustment angle (Anstellwinkel) of the swash plate, the swivel angle is adjusted, thereby changing the stroke of each piston in the delivery mechanism of the pump and thus the displacement volume per working cycle.

[0009] It has been shown that, depending on the situation, the operation of a regulating pump with a specific, especially small, displacement volume per working cycle is expedient and especially energy-efficient. This is based on - at least at constant pressure - a reduction in the required torque. Now if, during operation, a need to change or match the displacement volume per working cycle is identified and caused - by means of a corresponding characteristic parameter such as the swivel angle, then the rotational speed needs to be readjusted (Nachregelung) in order to - as is generally desired - (as far as possible) constantly maintain at least one parameter to be regulated (at a higher level), such as pressure.

[0010] However, it has now been found that such a change or matching of the displacement volume per working cycle has a counter-effect on the parameter to be regulated (at a higher level) or its actual value, such that a readjustment of this at least one parameter or the corresponding regulator must intervene. As is recognized, this is based on the fact that the rotational speed dynamics of the drive device is usually not sufficient to compensate for the adjustment of the displacement volume per working cycle quickly enough, which can, for example, lead to a pressure drop (Druckeinbruch).

[0011] Within the scope of the present invention, it is now proposed that when changing the target value of the characteristic parameter for determining the displacement volume per working cycle, the rotational speed target value (and preferably also the torque target value) is matched by pre-control according to the dynamics or speed of the adjustment of the delivery mechanism, especially also according to the operating point. By means of this pre-control of the rotational speed target value, which is especially carried out in parallel with the change or matching of the displacement volume per working cycle, readjustment of the rotational speed can be prevented and thus also possible pressure disturbances. Therefore, the regulator (at a higher level) does not have to intervene at all, but the at least one parameter involved remains constant. This is particularly effective if the change or matching of the rotational speed of the drive device takes place faster or can take place faster than the change or matching of the displacement volume per working cycle.

[0012] The rotational speed target value is preferably pre-given and / or the rotational speed target value is matched and / or the target value of the characteristic parameter for determining the displacement per working cycle is pre-given in the case of using the model and particularly preferably in the case of using the regulation predicted by the model (with such a model), and the adjustment speed of the conveying mechanism is taken into account in the model. The regulation predicted by the model (English: “Model Predictive Control”, MPC) enables a particularly simple, precise and thus also effective regulation, especially because the nonlinear characteristics of the electrohydraulic system with an adjustable pump and a drive device existing here can be mapped particularly well thereby.

[0013] Model predictive control is a regulation scheme that has already been applied in industry. By predicting the future system characteristics in each sampling step, i.e., in a specific time interval, a very high regulation quality is achieved. Contrary to traditional regulation schemes, the input, output and state limitations can be explicitly considered. The influence of changing the regulator parameters on the system characteristics is usually very intuitive. In order to implement a regulation scheme with high computational cost for fast electromechanical systems, schemes such as Move-Blocking for reducing the optimization parameters at the prediction level or other schemes such as explicit model predictive control can be used.

[0014] In the mentioned model, the adjustment speed of the conveying mechanism is preferably taken into account in the case of using at least one of the following parameters: the maximum possible displacement per working cycle, the minimum possible displacement per working cycle, the pressure of the medium used to operate the adjustable pump, the actual value of the rotational speed of the drive device, the viscosity of the medium, and the mechanical and / or electrical parameters of the adjustment system of the adjustable pump. The maximum possible displacement and the minimum possible displacement per working cycle can also be considered as a quotient.

[0015] These parameters usually affect the adjustment speed of the conveying mechanism to different degrees, that is, how fast or slow the adjustment is after the manipulation. The conversion of the displacement change per working cycle is achieved faster or slower according to the current speed of the adjustment of the conveying mechanism (also called the swing angular velocity in the case of an axial piston pump with a swash plate), which also has an impact on the equalization of the rotational speed of the drive device. When adjusting the displacement per working cycle slowly, i.e., in the case of low dynamics or speed, for example, less pre-control or less rising pre-control for the rotational speed is required than when the speed is high.

[0016] In the mentioned model, the adjustment speed of the conveying mechanism is preferably considered as the actual value for modeling the characteristic parameter for determining the displacement per working cycle. In particular, a rotational speed correction value (for example, an additive rotational speed value) for matching the rotational speed target value can be determined from this modeled actual value.

[0017] Preferably, when changing the target value of the characteristic parameter for determining the displacement per working cycle, the target speed value is further matched according to at least one optimization criterion, which is especially selected from the following: the noise generated by the regulating pump, the efficiency of the regulating pump, and the load of the drive device. Thereby, especially when the pump is operating at part load, the operation can be further optimized.

[0018] According to whether the process of swinging out or swinging in of the regulating pump (or the swash plate) should be started now, for example, the target trajectories for the speed and the necessary change torque are suitably determined according to the swinging direction (i.e., in the direction of higher or lower displacement), system parameters, other component parameters, and / or the current state of the (electrohydraulic) system. At the same time, the changing hydraulic torque is directly pre-controlled, especially, for example, according to the current pressure and the model of the change in the delivery volume of the pump.

[0019] In addition to pre-controlling the speed, it is preferably specified that when changing the target value of the characteristic parameter for determining the displacement per working cycle, the target torque value for the drive device is also matched by pre-control according to the dynamics or speed of the adjustment of the delivery mechanism, especially also according to the operating point. Here, especially the product of the modeled actual value of the characteristic parameter for determining the displacement per working cycle and the actual pressure can be considered, that is, especially the modeled value of the hydraulic torque is pre-controlled. The above points also apply to torque pre-control. When the torque controller is subordinate to the speed controller during the operation of the electric drive device, the pre-control of the torque value is especially advantageous.

[0020] The computing unit according to the invention, for example, the control and / or regulation unit for a speed-variable regulating pump with a speed-variable drive device, is especially programmed to perform the method according to the invention.

[0021] Furthermore, the subject matter of the present invention also relates to an electrohydraulic drive system, such as an electrohydraulic shaft, which includes a speed-variable regulating pump with a speed-variable drive device, and a computing unit according to the invention.

[0022] It is also advantageous to implement the method according to the invention in the form of a computer program or a computer program product having program code for performing all method steps, because this incurs particularly low costs, especially when the implemented controller is also used for other tasks and thus already exists anyway. Suitable data carriers for providing the computer program are especially magnetic memories, optical memories, and electrical memories, such as hard disks, flash memories, EEPROMs, DVDs, etc. The program can also be downloaded via a computer network (Internet, intranet, etc.). Description of the Drawings

[0023] Other advantages and design solutions of the present invention can be derived from the description and the drawings.

[0024] It is understood that the features mentioned above and those yet to be explained hereinafter can be used not only in the combinations specifically described, but also in other combinations or individually, without departing from the scope of the present invention.

[0025] The present invention is schematically illustrated by way of examples in the drawings and will be described in detail hereinafter with reference to the drawings.

[0026] Figure 1 Schematically shown is an electro-hydraulic system that can operate according to the present invention.

[0027] Figure 2 Schematically shown is the flow of a method according to the present invention in a preferred embodiment as a control loop.

[0028] Figure 3 Schematically shown is the flow of a method according to the present invention in another preferred embodiment as a control loop. Detailed Description of the Preferred Embodiment

[0029] In Figure 1 schematically shown is an electro-hydraulic system 100, as the present invention can be based on such an electro-hydraulic system. The electro-hydraulic system 100 has an actuator configured as a hydraulic cylinder 110, which has a piston 111 movable along the x-axis, and the actuator is actuated by a speed-variable regulating pump 120. A hydraulic circuit 130 with, for example, oil as the medium or working medium is arranged between the speed-variable regulating pump 120 and the hydraulic cylinder 110.

[0030] The speed-variable regulating pump 120 has a speed-variable drive device configured as an electric motor 121 and a delivery mechanism 122 and is in particular configured as an axial piston pump in the form of a swash plate structure. By adjusting the angle of the swash plate, i.e., the so-called swash angle, the displacement of the delivery mechanism can be changed in each working cycle.

[0031] The control and / or regulation unit 140 is technically programmed to execute a preferred embodiment of the method according to the present invention and to pre-give a speed target value n soll and a swash angle target value α soll as target values of characteristic parameters for determining the displacement in each working cycle. For regulating the regulating parameters, actual values n ist and α ist are respectively provided with feedback. This can be accomplished, for example, using conventional sensors.

[0032] In Figure 2shows a control loop according to a preferred embodiment of the present invention or according to the method of the present invention, which can be implemented in a control and / or regulation unit in a program technology. Here, exemplarily in the (superposed) control loop, the pressure p in the hydraulic circuit 130 ist (as shown, for example, in Figure 1 ) is regulated to the target value p soll .

[0033] For this purpose, as a regulating parameter, the speed target value n' for driving the device 121 is determined or pre-given by a regulator configured here as a PI regulator 150 soll or n soll (the difference between these target values will be explained later), and the target value α for the swing angle as a characteristic parameter for determining the displacement of each working cycle soll . The target values for speed and swing angle are then correspondingly converted in the drive device 121 or the conveying mechanism 122. The swing angle regulation of the drive device 121 and the conveying mechanism 122 usually responds to the target preset value according to the PT1 characteristic with the corresponding time constant T1 or T2. The actual values obtained here, that is, the speed actual value n ist and the swing angle actual value α ist , then result in the volume flow Q, and subsequently, in the hydraulic circuit 130, considering the compression coefficient and volume of the compressed medium, the corresponding actual value p of the pressure of the medium in the hydraulic circuit 130 is obtained ist . This affects the speed of the drive device correspondingly through the hydraulic torque M to be overcome hyd .

[0034] If now, for example, for efficiency reasons, the swing angle or generally the displacement should be changed within each working cycle of the conveying mechanism, then simultaneously or in parallel, according to the current speed 165 of the regulation of the conveying mechanism and through pre-control, the speed target value n' first determined or pre-given by the regulator 150 is matched soll , so as to obtain the (matched) speed target value n soll , and then this speed target value is continued to be used. This is especially carried out in the scope of model predictive control 160 using a corresponding model for regulating the pump (usually also called "Digital Twin").

[0035] Here, different parameters are especially also considered. For the speed 165, for example, the ratio or quotient of the maximum possible swing angle to the minimum possible swing angle (or the corresponding quotient of the displacement) can be considered for determining the matched speed target value, which in turn can depend on the current swing angle, and this is considered here (through the model) as an estimated value or a calculated value α*ist.

[0036] Likewise, the type of adjustment for the swing angle or the adjustment system affects the speed. Thus, for example, an electronic swing angle adjustment can be provided, in which a magnetic force is generated by means of an electric current, and this magnetic force acts counter to the (mechanical) spring force in the adjustment cylinder.

[0037] In this way, the rotational speed is simultaneously matched to the swing angle, and no pressure change takes place in the hydraulic circuit 130, so that no intervention in the (superordinate) regulator 150 is required. It should be noted here that, as the (superordinate) regulated variable, instead of the pressure, for example, the position x of the element or piston 111 according to Figure 1 can also be used.

[0038] In Figure 3 a control loop according to a further preferred embodiment of the invention or according to the method of the invention is shown, as it can be implemented technically in a control and / or regulation unit. Here, the pressure p in the hydraulic circuit 130 ist (as shown, for example, in Figure 1 ) is regulated to the target value p soll .

[0039] For this purpose, as the adjustment variable, a rotational speed target value n for driving the drive device 121 is determined or pre-given by a regulator, which is also configured here as a PI regulator 150 soll . Taking into account a correction term or a pre-control term Δn* (which will be explained later), the rotational speed error e is calculated by subtracting the actual rotational speed value n ist from the rotational speed target value n soll , and the rotational speed error is fed to a rotational speed regulator 151 (also implemented here as a PI regulator), which outputs a target torque M n and has an impact on the drive device 121, which is again modeled with a PT1 characteristic. Then, an electric driving torque M soll of the pump 120 is generated therefrom. A

[0040] Likewise, a swing angle α is pre-given for the conveying mechanism 122 as a characteristic variable for determining the displacement per working cycle, and the swing angle adjustment of the conveying mechanism is again modeled with a PT1 characteristic, from which the swing angle (or the corresponding volume variable) α* results.

[0041] Taking into account the hydraulic torque M hyd to be overcome, the effective torque M A of the pump 120 is derived from the driving torque M eff , and this effective torque acts on the rotational speed. Here, the hydraulic torque M hydAs described above, it is obtained as the product of the volume parameter α* and the actual pressure, and this product can be weighted or amplified by the P element if necessary.

[0042] From the rotational speed n ist and the volume parameter α*, the following volume flow Q is obtained. The volume flow can be weighted or amplified by the P element if necessary, and then the corresponding actual pressure p is obtained in the hydraulic circuit 130 taking into account the compressibility of the compressed medium and the volume. ist .

[0043] If now, for example, for reasons of efficiency, the swing angle α or generally the displacement should be changed within each working cycle of the conveying mechanism, then simultaneously or in parallel, the rotational speed target value n first determined or pre-given by the regulator 150 is matched by a correction term or pre-control term Δn*. soll The pre-control term Δn* is determined, in particular, in the context of model predictive control 160 using a corresponding model (usually also referred to as a "digital twin") for regulating the pump, the response of whose swing angle to the swing angle preset value α within block 160 is modeled with a PT1 characteristic. In this example, the modeled actual swing angle obtained thereby is led through the P element for weighting or amplification and is added as a rotational speed value Δn* to the rotational speed target value n. soll At the same time, the modeled actual swing angle (or volume) is multiplied by the actual pressure and led through the P element, and as an added torque value M* hyd is added to the torque target value M. soll .

[0044] By the described mode, the effects determined in the hydraulic circuit can be taken into account when matching or varying the transmission ratio (i.e., the swing angle). A change in the gain of the open-loop control circuit can be countered by matching the gain kp in the pressure regulator 150, a change in the volume flow Q of the medium can be countered by matching the rotational speed of the pump (by Δn*), and a change in the hydraulic torque can be countered by matching the target torque for the drive device (by M* hyd ). This can be taken into account accordingly in the mentioned model or in model predictive control. Compared with the Figure 2 example, the hydraulic torque is thus pre-controlled especially additionally here.

Claims

1. A method for operating a variable speed variable pump (120), in which a delivery mechanism (122) whose displacement per working cycle can be adjusted is driven by means of a variable speed drive (121), wherein: Within the scope of control, by predefining a speed target value (n soll ) and the target value (α soll ), adjust at least one parameter to the target value (p soll ), wherein, within the range of the regulation, the target value (p soll ) is selected from the following: the pressure and / or volume flow of the medium for operating the regulating pump, the force generated directly or indirectly by the medium, and the position (x) of the element (111) moved directly or indirectly by the medium, Among them, when changing the target value (α) of the characteristic parameter used to determine the displacement of each working cycle soll ), the rotational speed target value (n soll ).

2. The method according to claim 1, wherein When using a model, the speed target value (n soll ) and / or matching speed target value (n soll ) and / or predetermine a target value (α) of a characteristic variable for determining the displacement of each working cycle soll ), in which the speed of adjustment of the conveying mechanism (122) is taken into account.

3. The method according to claim 2, wherein: In the case of a control (160) using model prediction, a speed target value (n soll ) and / or matching speed target value (n soll ) and / or predetermine a target value (α) of a characteristic variable for determining the displacement of each working cycle soll ).

4. The method according to claim 2 or 3, wherein: In the model, the speed (165) of the control of the conveying device (122) is taken into account using at least one of the following parameters: the maximum possible displacement per working cycle, the minimum possible displacement per working cycle, the pressure of the medium for operating the regulating pump, the actual value of the speed of the drive (n ist ), the viscosity of the medium and the mechanical and / or electrical parameters of the regulating system of the regulating pump (120).

5. The method according to any one of claims 1 to 3, wherein: When changing the target value (α) of the characteristic parameter used to determine the displacement of each working cycle soll ), the speed target value (n soll ), the optimization criterion being selected from the following: the noise generated by the regulating pump (120), the efficiency of the regulating pump (120), and the load of the drive device (121).

6. The method according to any one of claims 1 to 3, wherein: When changing the target value (α) of the characteristic parameter used to determine the displacement of each working cycle soll ), a torque target value (M) for the drive device (121) is matched by pre-controlling a speed (165) adjusted according to the conveying mechanism (122). soll ).

7. The method according to claim 1, wherein an axial piston pump is used as a variable displacement pump (120) with two-point regulation or proportional regulation.

8. A computing unit (140) configured to carry out the method according to any one of the preceding claims.

9. An electrohydraulic system (100) comprising a variable speed variable displacement pump (120) having a variable speed drive (121) and a calculation unit (140) according to claim 8.

10. A computer program product which, when executed on a computer unit (140), causes the computer unit (140) to carry out the method according to any one of claims 1 to 7.

11. A machine-readable storage medium having a computer program stored thereon, which, when executed on a computer unit (140), causes the computer unit (140) to carry out the method according to any one of claims 1 to 7.

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