EP2597310B1 - Method for operating a variable-speed adjustable pump - Google Patents

Description

The present invention relates to a method for operating a variable speed variable displacement pump according to the preamble of claim 1, a computing unit for its implementation and a variable speed variable displacement pump with such a computing unit.

State of the art

The pumps on which the invention is based consist of a conveyor with variable displacement (per stroke or revolution), which is driven by a drive with variable speed. In the operation of such pumps, usually the volume flow and / or the delivery pressure (i.e., pressure difference between inlet and outlet) are controlled by appropriate adjustment of the conveyor's displacement and speed, i. Such pumps have two degrees of freedom in the control.

In the DE 10 2009 018 071 A1 is disclosed in this context, a method for controlling a pressure medium supply to operate with such a pump, a hydraulic actuator of a cyclically operating machine. Here, an optimal drive speed and a delivery volume for a required pressure and a required flow rate are determined. When using such a pump in a non-cyclical machine, there is the disadvantage that with larger changes in volume, the Aufregelverhalten is limited by the dynamics of the speed change. This may possibly lead to a collapse of the delivery pressure.

The object is to improve the operation of such pumps in non-cyclical machines.

Disclosure of the invention

According to the invention, a method for operating a variable-speed variable-displacement pump, a computing unit for its implementation, and a variable-speed variable displacement pump having such a computing unit with the features of the independent patent claims are proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

Advantages of the invention

The invention provides a way to significantly increase the dynamics of a speed change in variable-speed variable displacement pumps and thus counteract a delivery pressure drop with large changes in quantity. This allows the restriction-free use of such pumps even in non-cyclical machines. The invention uses to increase the target speed in the context of a feedforward control upon entry of at least one predetermined triggering condition. This is done, for example, by triggering a ramp function and / or by applying the setpoint speed with a precontrol value.

In the prior art, during operation of the pump for pressure control, the setpoint speed is usually determined as a function of the actual delivery volume. However, the speed is subject to a limited dynamics, so that they can not follow changes arbitrarily fast. It comes to the pressure drop. In the context of the invention, an optionally energy-optimal operating point in favor of better dynamics is now left by the precontrol, the pressure drops are at least reduced. The additional pilot signal for speed also leads to improved dynamics of the pump.

Preferably, the target speed is thereby increased so that there is a maximum possible speed gradient. When driving the setpoint speed is usually performed via a ramp function, so that the drive is applied to a continuous increase in speed. The gradient of the ramp is essentially determined by the difference between the output speed and the increased set speed, wherein a maximum gradient (usually constructive condition) must be taken into account. A specification of the target speed so that the maximum possible speed gradient results in the fastest possible speed increase to keep pressure drops as short as possible.

In addition, the invention reduces the time delay between the switching operation in the pump-driven machine (which leads to a change in quantity) and the start of the speed ramp.

If at least one trigger condition exists, the speed control is intervened and the setpoint speed is increased, so that a higher setpoint speed is specified for the drive than would result from the control alone.

In particular, a threshold value monitoring of the difference between nominal delivery pressure p _soll and actual delivery pressure p _is suitable as the triggering condition for the speed increase. If the difference exceeds a predefinable threshold value, this indicates an incipient pressure drop, which is to be counteracted.

As a trigger condition for the speed increase is also a threshold value monitoring of a temporal gradient of the (actual or target) delivery volume. If, for example, the (actual or target) delivery volume rises sharply in a short time, this can, as described, likewise lead to a pressure drop, which is to be counteracted.

In the triggering conditions are in a preferred embodiment essentially only in the arithmetic unit ("controller") known or derived variables, in particular target delivery pressure p _soll , actual delivery pressure p _is , target volume flow Q _soll , actual volume flow Q _is , target delivery volume V _soll , actual delivery volume V _is , times, manipulated variables of the conveyor, such as, for example, the swivel angle for axial piston pumps, the setpoint speed and the actual speed. The invention can therefore be implemented particularly advantageously also in existing systems, in particular by means of a software update.

The feedforward control may, for example, include a proportional element with a matching proportional gain K _P into which, for example, the difference between the desired delivery pressure p _soll and the actual delivery pressure p _is received. A suitable proportional gain K _P can be determined as a function of the system.

The invention develops particular advantages in the field of injection molding machines, presses, woodworking machines, test benches, etc., since here a pressure drop is particularly disadvantageous. The use or the use of the invention in these areas is therefore particularly useful.

An arithmetic unit according to the invention, e.g. a control unit of a variable-speed variable, is, in particular programmatically, adapted to perform a method according to the invention. The arithmetic unit is for example an integrated electronics (for example ASIC) on the pump or in the converter or an external controller.

Also, the implementation of the invention in the form of software is advantageous because this allows very low cost, especially if an executing processing unit is still used for other tasks and therefore already exists. Suitable data carriers for providing the computer program are, in particular, floppy disks, hard disks, flash memories, EEPROMs, CD-ROMs, DVDs and the like. It is also possible to download a program via computer networks (Internet, intranet, etc.).

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

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or in isolation, without departing from the scope of the present invention.

The invention is illustrated schematically by means of exemplary embodiments in the drawing and will be described in detail below with reference to the drawing.

figure description

FIG. 1

schematically shows a preferred embodiment of a variable-speed variable displacement pump according to the invention.

FIG. 2

shows a control scheme according to a preferred embodiment of the invention.

In FIG. 1 a preferred embodiment of a variable speed variable displacement pump according to the invention is shown schematically and designated 10 in total. The variable displacement pump 10 has an adjustable conveyor 20 (which can feed in two directions in the present example), a variable speed drive 30, and a computer 40 for operating the pump.

The conveyor 20 is formed as an axial piston pump with an adjustable swivel angle α for a swash plate or inclined axis, in which the swivel angle α for setting a delivery volume V per stroke or rotation can be specified. For this purpose, a control signal from the arithmetic unit 40 is given to the axial piston pump 20 and an actual pivot angle is returned. The control signal may, for example, be a desired value for a so-called pilot valve on the pump.

The drive is designed here as a so-called standard motor, which has an asynchronous motor 31 and a frequency converter 32. In principle, synchronous servomotors can also be used. The rotational speed n of the asynchronous motor 31 is variable. For this purpose, a desired rotational speed is predetermined by the arithmetic unit 40 to the drive 30. The actual speed can be determined by an angle encoder or by calculation, as for example. In the DE 10 2009 055 978 A1 is disclosed.

For the control of the pump 10, the arithmetic unit 40, which is supplied to a target delivery pressure p and a target volume flow Q is used. Within the scope of the invention, the arithmetic unit determines the two manipulated variables available, rotational speed n and a control signal for the swivel angle α of the control pump. A preferred way of determination will be described below with reference to FIG. 2 1, which schematically illustrates a control according to a preferred embodiment of the invention, which may be implemented in the arithmetic unit 40.

The lower part of the control scheme shows a common pump control. The pump control generates setpoints for the speed n _soll and a control signal β _to (it is not in this case usually by an angle set point, but rather a control signal for a pilot valve) based on the desired operating point p _should, Q _should. For this purpose, a pump controller incl. Logic member 201 is provided, which is based on the desired operating point p _soll , Q _{soll determines} the setpoints. In particular, computing methods are known for this, which enable energy-saving operation. The target rotational speed n _set, for example, is then. Forwarded to the drive 30, the drive controller 32, the speed of the electric motor 31 to the target speed n _soll adjusts. On the basis of the actuating signal β _soll , a pivot angle is set at the conveyor. Such a regulation is, for example, from the DE 10 2009 018 071 A1 which is why it is not necessary to go deeper into this at this point.

In the context of the invention, this basic pump control is extended by a functionality for adjusting the target speed in order to increase the dynamics of the pump and to prevent pressure drops. This pilot control is at the top of the FIG. 2 shown. If a certain triggering condition occurs, the setpoint speed is increased.

The functionality is realized in the present example, that an up ramp function 202 is triggered within the pump controller 201, so that the target speed is continuously increased. The ramp-up function 202 continuously increases the desired speed until a predeterminable threshold is reached and / or the ramp-up function is terminated.

Alternatively or additionally, the speed increase may also include applying the speed setpoint n _soll to a pre-control value n ₊ . In order to determine the pre-control value n ₊ , the logic element 203 may, for example, also contain a proportional element with appropriate proportional gain K _P , into which, for example, a difference between a nominal value and an actual value is received (for example, target delivery pressure p _soll , actual delivery pressure p _ist , Soll Volumetric flow Q _soll , actual volumetric flow Q _is , target swivel angle α _soll , actual swivel angle α _is ).

In the present case, the trigger condition is monitored as to whether, for example, the difference between the setpoint pressure p _soll and the actual pressure p _ist exceeds a predetermined threshold value. The threshold can be selected in absolute or percentage terms. For monitoring, a logic element 203 is provided, which at the same time also determines and outputs the precontrol value n ₊ . The determination can be carried out, for example, on the basis of a characteristic map which can depend on at least one of the following variables: target delivery pressure p _soll , actual delivery pressure p _ist , target volume flow Q _soll , actual volume flow Q _ist , target pivot angle α _soll , Actual swivel angle α _is setpoint speed n _soll and actual speed.

Claims (13)

1. Method for operating a variable-speed adjustable pump (10), in which a variable delivery mechanism (20) is driven by an adjustable-speed drive (30), an actual volume flow (Q_ist) being controlled to a target volume flow (Q_soll) and/or an actual delivery pressure (p_ist) being controlled to a target delivery pressure (p_soll) by a target delivery volume of the delivery mechanism (20) being adjusted and a target speed (n_soll) of the drive (30) being predefined,
   characterized in that
   the target speed (n_soll) is additionally increased within the scope of pilot control upon the entry of at least one predetermined triggering condition, wherein the exceeding of a predefined threshold value by a difference in a target value and an actual value from delivery pressure, volume flow, delivery volume or speed and/or the exceeding of a predefined threshold value by a rate of change of a target value or actual value from delivery pressure, volume flow, delivery volume or speed is monitored as the triggering condition.
2. Method according to Claim 1, wherein in order to increase the target speed, an upward ramp (202) for the target speed (n_soll) is started.
3. Method according to Claim 1 or 2, wherein the target speed (n_soll) has a pilot value (n₊) applied additively for the increase.
4. Method according to Claim 3, wherein the pilot value (n₊) is determined from at least one target value and/or at least one actual value from delivery pressure, volume flow, delivery volume or speed.
5. Method according to Claim 3 or 4, wherein the pilot value (n₊) is determined from at least one difference between a target value and an actual value from delivery pressure, volume flow, delivery volume or speed.
6. Method according to Claim 3, 4 or 5, wherein the pilot value (n₊) is determined from a rate of change of at least one target value or actual value from delivery pressure, volume flow, delivery volume or speed.
7. Method according to one of Claims 3 to 6, wherein the pilot value (n₊) is determined in such a way that the result is a maximum possible speed gradient.
8. Method according to one of Claims 3 to 7, wherein the pilot value (n₊) is determined by using a proportional element with a proportional gain K_P.
9. Method according to one of the preceding claims, wherein at least one target value and/or at least one actual value from delivery pressure, volume flow, delivery volume or speed is included in the triggering condition.
10. Method according to one of the preceding claims, wherein the delivery mechanism (20) used is a swash-plate pump or inclined-axis pump with adjustable pivot angle or a radial piston or vane pump with stroke-ring adjustment, and the delivery volume of the delivery mechanism (20) is set in accordance with the actuating signal from a pressure or delivery flow controller.
11. Method according to Claim 10, wherein the actual and/or target value of the delivery volume is replaced by the actual or target value of the pivot angle.
12. Computer unit which is configured to carry out a method according to one of the preceding claims.
13. Variable-speed adjustable pump with an adjustable delivery mechanism (20), a variable-speed drive (30) and a computer unit (40) according to Claim 12.

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