DE102011119299A1 - Method for operating a variable-speed variable-displacement pump - Google Patents

Abstract

The invention relates to a method for operating a variable-speed variable displacement pump, in which an adjustable conveyor is driven by a variable-speed drive, wherein an actual volume flow to a desired volume flow (Qsoll) and / or an actual discharge pressure (pist) to a target Pumping pressure (psoll) is controlled by a desired delivery volume of the conveyor set and a target speed (nsetpoint) of the drive is specified, the target speed (nsetpoint) is increased upon entry of at least one predetermined triggering condition in the context of a pilot control.

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 delivery volume of the conveyor and the speed, d. H. 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 can u. U. 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 suitable 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. B. swivel angle for axial piston pumps, target speed and 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, for. B. 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, integrated electronics (eg 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 the provision of the computer program are in particular floppy disks, hard disks, flash memories, EEPROMs, CD-ROMs, DVDs and the like. a. m. 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

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

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

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

The conveyor 20 is designed as an axial piston pump with 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 to the axial piston pump 20 predetermined and an actual swivel 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 is an asynchronous motor 31 and a frequency converter 32 having. In principle, synchronous servomotors can also be used. The speed n of the asynchronous motor 31 is variable. For this purpose, a target speed of the arithmetic unit 40 to the drive 30 specified. 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 regulation of the pump 10 serves the arithmetic unit 40 in which a target delivery pressure p and a target volume flow Q are supplied. 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 2 explains, in the roughly schematically a scheme according to a preferred Embodiment of the invention is shown, which in the arithmetic unit 40 can be implemented.

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 regulator incl. Logic element 201 provided, which _{is intended} on the basis of the desired operating point P, Q, _is to determine the setpoint values. In particular, computing methods are known for this, which enable energy-saving operation. The setpoint speed n _soll is then, for example, the drive 30 transmitted, whose drive controller 32 the speed of the electric motor 31 to the target speed n _{should be} regulated. 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 2 shown. If a certain triggering condition occurs, the setpoint speed is increased.

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

Alternatively or additionally, the speed increase may also include applying the speed setpoint n _soll to a pre-control value n ₊ . To determine the precontrol value n ₊ , the logic element 203 For example, include a proportional element with matching proportional gain K _P , for example, in which a difference between a setpoint and an actual value is received (eg. Target delivery pressure p _soll , actual delivery pressure p _is , target volume flow Q _soll , actual volume 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 is a logic gate 203 provided, which also determines the pre-tax value n ₊ and outputs. 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 , target speed n _soll and actual speed.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102009018071 A1 [0003, 0027]
• DE 102009055978 A1 [0025]

Claims (14)

Method for operating a variable-speed variable displacement pump ( 10 ), in which an adjustable conveyor ( 20 ) of a variable speed drive ( 30 ) Is driven, wherein an actual flow rate _(Q) (to a desired volume flow Q _setp) and / or an actual delivery pressure _{(p) to} a target delivery pressure (p) is regulated by a desired pump discharging the conveyor ( 20 ) and a desired speed (n _soll ) of the drive ( 30 ) is predetermined, wherein the target speed (n _soll ) is increased upon entry of at least one predetermined triggering condition in the context of a pilot control. Method according to Claim 1, in which, to increase the setpoint rotational speed, an upward ramp ( 202 ) (For the setpoint speed n _soll) is started. The method of claim 1 or 2, wherein the target speed (n _soll ) is applied to the increase with a pilot control value (n ₊ ) additive. The method of claim 3, wherein the pilot control value (n ₊ ) is determined from at least one setpoint value and / or at least one actual value of delivery pressure, flow rate, delivery volume or speed. The method of claim 3 or 4, wherein the pilot control value (n ₊ ) is determined from at least one difference between a setpoint and an actual value of delivery pressure, flow rate, displacement or speed. The method of claim 3, 4 or 5, wherein the pilot control value (n ₊ ) is determined from a rate of change of at least one setpoint or actual value of delivery pressure, flow rate, displacement or speed. Method according to one of claims 3 to 6, wherein the precontrol value (n ₊ ) is determined so that a maximum possible speed gradient results. Method according to one of claims 3 to 7, wherein the precontrol value (n ₊ ) is determined using a proportional gain proportional element K _P. Method according to one of the preceding claims, wherein at least one desired value and / or at least one actual value of delivery pressure, volume flow, delivery volume or rotational speed is received in the triggering condition. Method according to one of the preceding claims, wherein the tripping condition exceeding a predetermined threshold value by a difference between a nominal value and an actual value of delivery pressure, volume flow, delivery volume or speed and / or exceeding a predetermined threshold by a rate of change of a setpoint or actual value of delivery pressure, Volume flow, displacement or speed is monitored. Method according to one of the preceding claims, wherein as conveyor ( 20 ) a swash plate or inclined axis pump with adjustable swivel angle or a radial piston or vane pump with Hubringverstellung is used and the delivery volume of the conveyor ( 20 ) is set according to the control signal of a pressure or flow control. A method according to claim 11, wherein the actual and / or desired value of the delivery volume are replaced by the actual or desired value of the swivel angle. Arithmetic unit which is adapted to carry out a method according to one of the preceding claims. Variable speed variable displacement pump with an adjustable conveyor ( 20 ), a variable-speed drive ( 30 ) and a computing unit ( 40 ) according to claim 13.

Images