EP3839256B1 - Method for operating a variable-speed adjustable pump - Google Patents

Description

The present invention relates to a method for operating a variable-speed variable-speed pump, in which a delivery mechanism that can be adjusted in terms of a displacement volume per working cycle is driven by means of a variable-speed drive, and an electrohydraulic system.

State of the art

Pumps on which the invention is based have a delivery system with variable displacement volume per working cycle (so-called hydraulic displacement machine, e.g. axial piston machine), which is driven by a drive with variable speed. When such pumps are operated, the volumetric flow and/or the delivery pressure (i.e. pressure difference between inlet and outlet) are usually regulated by appropriately adjusting the displacement volume of the delivery system and the speed, i.e. such pumps have two degrees of freedom in regulation.

From the EP 2 192 309 B1 a method is known, for example, in which such a pump is operated in that a pressure or a quantity of pressure medium is regulated by controlling the volume setting of the pump. A speed deviation of the drive is taken into account.

Disclosure of Invention

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

The invention deals with the operation of a variable-speed variable displacement pump, such as in particular an axial piston pump with e.g. two-point adjustment or proportional adjustment, in which a displacement mechanism that can be adjusted in a displacement volume per working cycle is driven by means of a variable-speed drive such as an electric motor. In such a variable displacement pump, a so-called swash plate, for example, can be provided to adjust the conveying mechanism.

When operating such a variable displacement pump, at least one variable, such as a pressure, is usually adjusted to a target value (the at least one variable ) regulated.

The at least one variable is preferably selected from a pressure and/or a volume flow of a medium such as oil, with which the variable displacement pump is operated (or which is used as the operating medium), a force that is generated directly or indirectly by the medium, and a position of an element moved directly or indirectly through the medium. In particular, force and position can relate not only to the variable displacement pump and drive system, but also to a higher level system in which the variable displacement pump and drive is used, e.g. an electro-hydraulic axle or an electro-hydraulic system in general.

The parameter determining the displacement volume per working cycle can be a swivel angle - e.g. in the case of the mentioned axial piston pump with swivel disk. In this example, an adjustment of the swivel angle causes a change in the stroke of the individual pistons in the delivery system of the pump and thus the displacement volume per working cycle by changing the angle of attack of the swivel disk.

It has been shown that, depending on the situation, operating the variable displacement pump with a specific, in particular small, displacement volume per working cycle is expedient and, in particular, energy-efficient. This is based on the fact that - at least with constant pressure - the required torque drops. If now during operation the need for a change or adjustment of the displacement volume per cycle - recognized and initiated - via the corresponding parameter such as the swivel angle, then a readjustment of the Speed is necessary in order - as is often desired - to keep the (superordinate) controlled at least one variable such as the pressure (as much as possible) constant.

However, it has now been found that such a change or adjustment of the displacement volume per working cycle has repercussions on the (superordinate) variable to be controlled or its actual value, so that a readjustment of this at least one variable is necessary or the corresponding controller has to intervene . As has been recognized, this is due to the fact that the speed dynamics of the drive are usually not good enough to quickly compensate for the adjustment of the displacement volume per working cycle, which can lead to a drop in pressure, for example.

In the context of the invention, it is now proposed that the speed setpoint (and preferably also a torque setpoint) when there is a change in the setpoint for the characteristic variable that determines the displacement volume per working cycle by way of a pilot control as a function of a dynamic or speed of an adjustment of the conveyor, in particular also working point dependent, is adjusted. This pre-control of the speed setpoint, which takes place in particular parallel to the change or adaptation of the displacement volume per working cycle, makes it possible to prevent a readjustment of the speed and thus also a possible drop in pressure. The (higher-level) controller does not have to intervene at all, rather the relevant at least one variable remains constant. This is particularly effective when a change or adaptation of the speed of the drive takes place or can take place faster than a change or adjustment of the displacement volume per working cycle.

The specification of the speed setpoint and/or the adjustment of the speed setpoint and/or the specification of the setpoint for the characteristic variable that determines the displacement volume per working cycle is preferably carried out using a model in which the speed of the adjustment of the conveying mechanism is taken into account, and particularly preferably using a model predictive control (with such a model). A model predictive control (MPC) enables a particularly simple and precise and therefore also efficient control, in particular because the non-linear behavior of the present electrohydraulic system with variable displacement pump and drive can be mapped particularly well.

Model predictive control is a control concept that is already being used in industry. A very high control quality is achieved by predicting the future system behavior in each sampling step, i.e. a specific time interval. In contrast to classic control concepts, input, output and state restrictions can be explicitly taken into account. The effect of changing the controller parameters on the system behavior is usually very intuitive. For the realization of the computationally intensive control concept for fast mechatronic systems, approaches such as move blocking to reduce the optimization parameters on the prediction horizon, or other approaches such as explicit model predictive control can be used.

In the model mentioned, the speed of the adjustment of the conveyor system is preferably taken into account using at least one of the following parameters: a maximum possible displacement volume per working cycle, a minimum possible displacement volume per working cycle, a pressure of a medium with which the variable displacement pump is operated, an actual value of the Speed of the drive, a viscosity of the medium, and mechanical and/or electrical parameters of an adjustment system of the variable displacement pump. The maximum and the minimum possible displacement volume per working cycle can also be taken into account as a quotient.

These parameters affect, typically to varying degrees, the speed of displacement of the conveyor, i.e. how fast or slow the displacement will be after activation. Depending on the current speed of the adjustment of the conveyor - in the case of an axial piston pump with a swash plate also referred to as the slewing angle speed - a change in the displacement volume per working cycle will be implemented faster or slower, which also has an influence on the adjustment of the speed of the drive. With slow adjustment of the displacement volume per working cycle - ie low dynamics or speed - for example a lower or less increasing pre-control of the speed is necessary than at high speed.

In the model mentioned, the speed of the adjustment of the conveying system is preferably taken into account as a modeled actual value for the characteristic variable that determines the displacement volume per working cycle. In particular, a speed correction value can be derived from this modeled actual value (e.g. an additive speed value) to adjust the speed setpoint.

When there is a change in the setpoint for the characteristic variable that determines the displacement volume per working cycle, the speed setpoint is preferably further adjusted as a function of at least one optimization criterion, which is selected in particular from: a noise generated by the variable displacement pump, an efficiency of the variable displacement pump, and a utilization of the drive. This allows the operation to be further optimized, especially when the pump is operated at partial load.

Depending on whether, e.g ) system determines a target trajectory for the speed and the necessary torque change. At the same time, the changing hydraulic torque, e.g. depending on the current pressure and a model of the change in the delivery volume of the pump, is then directly pre-controlled.

In addition to the pre-control of the speed, it is preferably provided that a torque setpoint for the drive, when there is a change in the setpoint for the characteristic variable that determines the displacement volume per working cycle, by means of a pre-control as a function of the dynamics or speed of an adjustment of the conveying mechanism, in particular also as a function of the operating point, is adjusted. In particular, a product of the modeled actual value for the parameter determining the displacement volume per working cycle and the actual pressure can flow in here, i.e. in particular a modeled value for a hydraulic moment is pre-controlled. The points presented above then also apply to the torque pre-control. The pilot control of a torque value is particularly advantageous if, during the operation of an electric drive, a torque controller is subordinate to the speed controller.

A computing unit according to the invention, for example a control and/or regulating unit for a variable-speed variable-speed pump with a variable-speed drive, is set up, in particular in terms of programming, to carry out a method according to the invention.

The subject of the invention is also an electrohydraulic drive system such as an electrohydraulic axle comprising a variable-speed variable displacement pump with a variable-speed drive and a computing unit according to the invention.

The implementation of a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is advantageous because this causes particularly low costs, especially if an executing control unit is also used for other tasks and is therefore available anyway. Suitable data carriers for providing the computer program are, in particular, magnetic, optical and electrical memories, such as hard drives, flash memories, EEPROMs, DVDs, etc. It is also possible to download a program via computer networks (Internet, intranet, etc.).

Further advantages and refinements of the invention result from the description and the attached drawing.

It goes without saying that the features mentioned above and those still 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.

The invention is shown schematically in the drawing using an exemplary embodiment and is described in detail below with reference to the drawing.

Figur 1

zeigt schematisch ein elektrohydraulisches System, das erfindungsgemäß betrieben werden kann.

Figur 2

zeigt schematisch einen Ablauf eines erfindungsgemäßen Verfahrens einer bevorzugten Ausführungsform als Regelkreis.

Figur 3

zeigt schematisch einen Ablauf eines erfindungsgemäßen Verfahrens einer weiteren bevorzugten Ausführungsform als Regelkreis.

character description

figure 1

shows schematically an electro-hydraulic system that can be operated according to the invention.

figure 2

shows schematically a sequence of a method according to the invention of a preferred embodiment as a control loop.

figure 3

shows schematically a sequence of a method according to the invention of a further preferred embodiment as a control loop.

Detailed description of the drawing

In figure 1 is an electrohydraulic system 100, as it may be the basis of the invention, shown schematically. The electrohydraulic system 100 has an actuator designed as a hydraulic cylinder 110 with a piston 111 that can move along an x-axis and is actuated by a variable-speed variable-speed pump 120 . A hydraulic circuit 130 with, for example, oil as the medium or operating medium is arranged between the variable-speed variable displacement pump 120 and the hydraulic cylinder 110 .

The variable-speed variable-speed pump 120 has a variable-speed drive designed as an electric motor 121 and a delivery system 122 and is designed in particular as an axial piston pump with a swashplate design. By adjusting the angle of the swashplate, i.e. the so-called slewing angle, the displacement volume of the conveyor system can be changed for each working cycle.

A control and/or regulating unit 140 is programmed to carry out a preferred embodiment of a method according _to the invention and specifies a speed setpoint n setpoint and a swivel angle setpoint α _setpoint as a setpoint for the parameter determining the displacement volume per working cycle. Feedback of the actual values n actual and α _{actual is provided} for controlling the manipulated variables. This can be accomplished using conventional sensors, for example.

In figure 2 a control circuit according to a preferred embodiment of the invention or a method according to the invention is shown, as it can be implemented in terms of programming in a control and/or regulating unit. In this case, for example, in a (superimposed) control circuit, a pressure p _{actual in a hydraulic circuit 130, as is} shown, for example, in figure 1 is shown _, regulated to a setpoint p setpoint.

For this purpose _, a speed setpoint n' set or n set (the difference between these set values will _be discussed later) for a speed of drive 121 and a set value α _set for a swivel angle than the determines or presets the characteristic that determines the displacement volume per working cycle. These setpoint values for the rotational speed and swivel angle are then converted accordingly in the drive 121 or in the conveyor 122. Drive 121 and swivel angle adjustment of the conveying system 122 usually react to the setpoint specifications in accordance with a PT1 behavior with corresponding time constants T1 or T2. Actual values obtained in this way, an actual speed value n _ist and an actual swivel angle value α _ist , then result in a volume flow Q and then in hydraulic circuit 130, taking into account the compression factor and volume of the medium that is compressed, the corresponding actual value p _ist for the pressure of the medium in hydraulic circuit 130 This also has a corresponding influence on the speed of the drive via a hydraulic torque M _hyd to be overcome.

If the swivel angle or generally the displacement volume per working cycle of the conveying system is to _be changed, e.g of the conveyor and adjusted by means of a pre-control, so that the (adapted) speed setpoint n target _is obtained, which is then used further. This takes place in particular within the framework of a model-predictive control 160 with a corresponding model (often also referred to as "digital twin") for the variable displacement pump.

In particular, various parameters are also taken into account. At the speed 165, for example, a ratio or quotient of the maximum possible to the minimum possible swivel angle (or a corresponding quotient of the displacer volumes) can be included in the determination of the adjusted speed setpoint, which in turn can depend on a current swivel angle, which here - through the model - as an estimated or calculated value α* _is taken into account.

The type of adjustment or the adjustment system for the swivel angle can also have an effect on the speed. For example, an electronic swivel angle adjustment can be provided, in which a magnetic force is generated by means of electricity, which counteracts a (mechanical) spring force in an adjustment cylinder.

In this way, the rotational speed is adjusted at the same time as the swivel angle and there is no change in the pressure in the hydraulic circuit 130, so that no intervention by the (superordinate) controller 150 is necessary. At this point it should be noted that, instead of the pressure, the position x of the element or piston 111 according to FIG figure 1 can be used.

In figure 3 a control circuit according to a further preferred embodiment of the invention or a method according to the invention is shown, as it can be implemented in terms of programming in a control and/or regulation unit. A pressure p _actual in a hydraulic circuit 130, as is shown, for example, in FIG figure 1 is shown _, regulated to a setpoint p setpoint.

For this purpose _, a speed setpoint n setpoint for a speed of the drive 121 is determined or specified as a manipulated variable by a controller which is also designed here as a PI controller 150 . A speed error e _{n is} calculated from the speed setpoint n setpoint _, taking into account a correction or pre-control term Δn* (this will be discussed later) by subtracting the actual speed value n actual and fed to a speed controller 151 (here also designed as a PI controller), which outputs a setpoint torque M setpoint and acts on the drive 121, which _is again modeled with a PT1 behavior. This then results in an electric drive torque M _A of the pump 120.

Likewise, a swivel angle α is specified as the parameter determining the displacement volume per working cycle for the conveyor 122, whose swivel angle adjustment is again modeled with a PT1 behavior, from which the swivel angle (or a corresponding volume variable) α* results.

An effective torque M _eff of the pump 120, which acts on the speed, results from the drive torque MA, taking into account _a hydraulic torque M _hyd to be overcome. The hydraulic moment M _{hyd results} as above as the product of the volume variable α* and the actual pressure, which can be weighted or amplified via a P element if necessary.

The product of the speed n _actual and the volume variable α* results in a volume flow Q, which can optionally be weighted or amplified via a P element, and then in the hydraulic circuit 130 taking into account the compression factor and volume of the medium that is compressed , the corresponding actual pressure pist.

If the swivel angle α or, in general, the displacement volume per working cycle of the conveying mechanism is to be changed, for example for reasons of efficiency, then at the same time or parallel to this, the speed setpoint n setpoint initially determined or specified by the controller 150 _is changed adjusted by means of a pre-control with the correction or pre-control term Δn*. The pre-control term Δn* is determined in particular within the framework of a model-predictive control 160 with a corresponding model (often also referred to as "DigitalTwin") for the variable displacement pump (whose swivel angle reaction to the swivel angle specification α is modeled within block 160 with a PT1 behavior). In the present example, the resulting modeled actual swivel angle is fed via a P element for weighting or amplification and applied to the speed setpoint n set as an additive speed value _Δn *. At the same time, the modeled actual swivel angle (or the volume) is multiplied by the actual pressure via a P-element and applied _to the torque setpoint M set as an additive torque value M* _hyd .

With the described scheme, certain influences can be taken into account in the case of an adjustment or variation of a transmission ratio (ie the swivel angle) in the hydraulic circuit. A change in the gain of the open loop can be countered by adjusting the gain k _p in the pressure controller 150, a change in the volume flow Q of the medium by adjusting the speed of the pump (via Δn*), and a change in the hydraulic torque by an adjustment of the target torque (via M* _hyd ) for the drive. This can be taken into account accordingly in the model mentioned or in the model-predictive control. Compared to example from figure 2 the hydraulic torque is also pre-controlled here in particular.

Claims (12)

1. Method for operating a variable-speed adjustable pump (120), in which a delivery mechanism (122) that can be adjusted in a displacement volume per working cycle is driven by means of a variable-speed drive (121), wherein, within the context of control, at least one variable is controlled to a setpoint (p_soll) by specifying a speed setpoint (n_soll) for a speed of the drive and a setpoint (α_soll) for a characteristic variable determining the displacement volume per working cycle,
   wherein, in the event of a change in the setpoint (α_soll) for the characteristic variable determining the displacement volume per working cycle, the speed setpoint (n_soll) is adapted by means of feedforward control, depending on a current speed (1065) of an adjustment of the delivery mechanism (122).
2. Method according to Claim 1, wherein the specification of the speed setpoint (n_soll) and/or the adaptation of the speed setpoint (n_soll) and/or the specification of the setpoint (α_soll) for the characteristic variable determining the displacement volume per working cycle is carried out by using a model in which the speed of the adjustment of the delivery mechanism (122) is taken into account.
3. Method according to Claim 2, wherein the specification of the speed setpoint (n_soll) and/or the adaptation of the speed setpoint (n_soll) and/or the specification of the setpoint (α_soll) for the characteristic variable determining the displacement volume per working cycle is carried out by using model-predictive control (160).
4. Method according to Claim 2 or 3, wherein, in the model, the speed (165) of the adjustment of the delivery mechanism (122) is taken into account by using at least one of the following parameters: a maximum possible displacement volume per working cycle, a minimum possible displacement volume per working cycle, a pressure of a medium with which the adjustable pump is operated, a current value of the speed (n_ist) of the drive, a viscosity of the medium, and mechanical and/or electrical parameters of an adjustment system of the adjustable pump (120) .
5. Method according to one of the preceding claims, wherein, within the context of the control, at least one variable regulated to the setpoint (p_soll) is selected from: a pressure and/or a volume flow of a medium with which the adjustable pump is operated, a force which is generated directly or indirectly by the medium, and a position (x) of an element (111) which is moved directly or indirectly by the medium.
6. Method according to one of the preceding claims, wherein, in the event of a change in the setpoint (α_soll) for the characteristic variable determining the displacement volume per working cycle, the speed setpoint (n_soll) is further adapted on the basis of at least one optimization criterion, which is in particular selected from: a noise generated by the adjustable pump (120), an efficiency of the adjustable pump (120), and a load factor of the drive (121).
7. Method according to one of the preceding claims, wherein, in the event of a change in the setpoint (α_soll) for the characteristic variable determining the displacement volume per working cycle, a torque setpoint (M_soll) for the drive (121) is adapted by means of feedforward control, depending on a speed (165) of an adjustment of the delivery mechanism (122).
8. Method according to one of the preceding claims, in which an axial piston pump is used as the adjustable pump (120), in particular with two-point adjustment or proportional adjustment.
9. Computing unit (140) which is set up to carry out a method according to one of the preceding claims in a variable-speed adjustable pump (120).
10. Electrohydraulic system (100) comprising a variable-speed adjustable pump (120) with a variable-speed drive (121) and a computing unit (140) according to Claim 9.
11. Computer program which causes a computing unit (140) to carry out a method according to one of Claims 1 to 8 in a variable-speed adjustable pump (120) when it is executed on the computing unit (140).
12. Machine-readable storage medium having a computer program according to Claim 11 stored thereon.

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