DE102013217307B4 - Damping of non-harmonic pressure pulsations of a hydraulic pump by varying the speed - Google Patents

Abstract

Method for controlling a variable-speed fluid pump (10) with a setpoint speed signal (ωSoll) for pumping a fluid, a hydraulic pressure (pIst, 201) of the fluid being detected as a function of a rotational angle position (φIst) of the fluid pump, the hydraulic pressure (pIst , 201) depending on the rotational angle position (φactual) is divided into delivery periods, each delivery period comprising a number of delivery segments, with one delivery segment being limited by two adjacent minima depending on the hydraulic pressure of the rotational angle position (φactual), with each of the conveyor segments, a mean hydraulic pressure (202) of the conveyor segment is determined, with a correction value for the first of the conveyor segments being determined from a difference in the mean hydraulic pressure between a first of the conveyor segments and an adjacent second of the conveyor segments, with a setpoint speed for the first of the conveyor segments with the correction value for the first of the Conveyor segments is corrected.

Description

The present invention relates to a method for controlling a variable-speed fluid pump with a target speed signal for pumping a fluid.

State of the art

In the hydraulic systems on which the invention is based, hydraulic fluid is pumped through a hydraulic line by a variable-speed hydraulic pump. Such hydraulic pumps consist of a pumping mechanism with a mostly fixed (or rarely also variable) displacement volume (or pumping volume) per working cycle (usually revolution), which is driven by an electric drive (electric motor, e.g. synchronous motor) with variable speed. The conveyor is a hydraulic displacement machine, e.g. gear pump, radial piston or axial piston pump. By varying the speed of the drive, a volume flow through and a hydraulic pressure in the hydraulic line (system pressure) can be controlled or regulated.

Positive displacement pumps do not deliver a constant volume flow, but a slightly fluctuating volume flow (so-called flow pulsation). This is essentially due to the so-called geometric delivery flow pulsation, which is due to the design and is caused by the alternating work of the individual displacers. In addition to this harmonic pulsation, there is also a non-harmonic or discontinuous pulsation pattern that is not represented by the volume change function and is caused by manufacturing tolerances or wear. For example, not all displacement volumes of the individual pistons of a piston pump or of the individual teeth of a gear pump are the same.

Typical duty cycles of such a system include pressure hold operation. This mode of operation is characterized by the fact that a high pressure must be regulated with a very low volume flow (only leakage) and that there is a low hydraulic capacity. If you look at the pump as an actuator/converter that converts the 'speed' control signal into a volume flow, the delivery characteristics of the pump (delivery volume over the angle of rotation) are clearly evident in pressure-maintaining operation. This is characterized by the fact that a direct component of the volume flow, which is proportional to the average pump speed and the nominal value of the delivery volume per revolution, is superimposed by an alternating component whose spectral composition is essentially determined by the geometry of the conveyor system (e.g. by the number of teeth in the case of an internal gear pump). of the gear and the ring gear) is given. This alternating component causes pressure pulsation during pressure maintenance operation, which can have a negative or harmful effect on the hydraulic system (units and lines), but also on the quality of a product manufactured by the hydraulic system or the operating noise.

Pressure pulsations can be reduced by varying the pump speed accordingly. This is basically in the DE 10 2008 061 828 A1 and the DE 10 2011 121 837 A1 described, to which reference is also made with regard to control engineering and mechanical details. Also the DE 10 2010 039 943 A1 and the DE 10 2009 023 278 A1 show methods for reducing pulsation by varying the speed.

It is desirable to dampen non-harmonic pressure pulsations as much as possible, i.e. in particular to reduce their amplitude.

Disclosure of Invention

According to the invention, a method for controlling a variable-speed fluid pump with a setpoint speed signal for pumping a fluid is proposed with the features of patent claim 1. Advantageous configurations are the subject of the dependent claims and the following description.

Advantages of the Invention

The invention provides a simple way of reducing non-harmonic pressure pulsations by correcting a setpoint speed for controlling the speed-variable hydraulic pump as a function of the angle of rotation. The invention is easy to implement and requires little computing power. It can also be easily retrofitted in existing pumps or their control units. Furthermore, easy-to-implement methods for determining the angle-of-rotation-dependent correction of the setpoint speed are presented, which can also be easily implemented in existing systems. The invention is suitable especially to reduce pressure pulsations caused by manufacturing tolerances or wear. The invention can preferably be combined with other methods which dampen a harmonic or geometry-related pressure pulsation. Such a method is used, for example, in DE 10 2013 216 342.8 "Damping of harmonic pressure pulsations of a hydraulic pump by means of speed variation". The present invention is particularly suitable as a supplement and alternative to the compensation of higher orders, since it resolves and compensates for individual tooth defects.

The method can be adapted to the displacer with just a few parameters. It requires no calibration or manual optimization. By evaluating the angle of rotation, the method can be represented with little computing effort and can therefore also be used on inexpensive control units.

The non-harmonic pulsation is assumed to be periodic with a pumping period which is determined by the design of the pump and consists of a number of pumping segments. For example, in the case of an internal gear pump, each occurring pair of internal gear tooth and ring gear tooth forms a delivery segment; in the case of an axial piston pump, each piston forms a delivery segment. The individual conveying segments can be delimited from one another in the pressure profile by minima.

A measure of the pressure pulsation is defined for each conveyor segment and calculated from the ongoing measurement of the actual pressure and actual speed. This can be done particularly easily if the signals are processed synchronously with the angle of rotation. These deviations are compensated for by correcting the setpoint speed specific to the conveyor segment with a correction value K(i), preferably multiplicatively or additively. Within the scope of the invention, a suitable correction value K(i) is determined for each conveyor segment.

The correction values can be calculated solely from the pressure profile. This has the advantage that e.g. the hydraulic capacity of the system does not have to be known. In a preferred embodiment, the correction values K(i) are determined only on the basis of the sign and the relative magnitude of the pressure pulsation. The process automatically learns and compensates for the manufacturing and wear-related tolerances of the displacer, which can be observed particularly clearly in pressure-maintaining operation. In addition, the adapted correction values can be used for diagnostic purposes.

• Jede Zahnpaarung aus Zahnrad/Hohlrad weist auf Grund von u.a. Fertigungstoleranz eine für die Zahnpaarung i = 1, ..., N_ZP signifikante Abweichung von einer idealen Volumenänderungsfunktion auf.

The considerations on which the invention is based will now be explained using the example of an internal gear pump with a gear wheel with 12 teeth and a ring gear with 18 teeth:

• Due to, among other things, manufacturing tolerances, each pair of teeth consisting of gear wheel/ring gear has a deviation from an ideal volume change function that is significant for the pair of teeth i=1, . . . , N _ZP .

The tooth pairing is a periodic function with a period of: $$T_{tOl}=2\frac{N_{Z,H}}{N_{Z,Z}}=2\frac{18}{12}=3\text{turns}$$

This results in a number of pairs of teeth N _ZP = 36, i.e. a delivery period with 36 delivery segments.

In 2 an exemplary pressure curve is shown over the rotation angle φ of the pump. The gear wheel with 12 teeth causes a geometric delivery flow pulsation or pressure pulsation with a 30° period, which is clearly reflected in the _actual pressure pact.

The different conveying behavior due to tolerances can be observed in the mean value of the pressure p ₃₀ , viewed over a toothed segment (30° angle of rotation). The mean value filtering removes all signal components that correspond to the tooth frequency (30°) and integer multiples of it (volume function).

N_Z,Z Zahl der Zähnen des Zahnrads
V_h Hubvolumen der PumpeWith an ideal displacer, the volume V _ZS is conveyed into the system per toothed segment on average over one segment. $$V_{ZS}=\frac{V_H}{N_{Z,Z}}$$

N _Z,Z Number of gear teeth
V _h displacement of the pump

e_V(i) relative Abweichung vom nominellen FördervolumenDue to the tolerance, the actually delivered volume V _ZP (i) deviates from this. i =1, ..., N _ZP is the running index over the tooth pairs. $$V_{ZP}\left(i\right)=V_{ZS}\cdot e_V\left(I\right)$$

e _V (i) relative deviation from the nominal delivery volume

If e _V (i) is greater than 1, this leads to an increasing mean value of the pressure. If e _V (i) is less than 1, this leads to a falling mean value of the pressure funding segment is.

Δp_ZP(i) ist die Änderung des segmentweise gemittelten Ist-Drucks im Vergleich zum vorherigen Segment und wird berechnet, indem der winkelsynchron erfasste Ist-Druck über ein Zahnsegment gemittelt und anschließend differenziert wird: $${\overline{p}}_{ZP}\left(i\right)=\frac{1}{N\varphi }\cdot {\displaystyle \sum _{k=1}^{N\varphi }p\left(\varphi \left(k\right)\right)}\text{mittlerer Druck}\ddot{\text{u}}\text{ber ein F}\ddot{\text{o}}\text{rdersegment}$$

N_ϕ : Anzahl der Drehwinkelstellungen pro Fördersegment, an denen der Ist-Druck p(φ(k)) erfasst wurde $$\Delta p_{ZP}\left(i\right)=\frac{{\overline{p}}_{ZP}\left(i\right)-{\overline{p}}_{ZP}\left(i-1\right)}{{\mathrm{\Phi }}_{ZS}}\cdot {\overline{\omega }}_{ZS}\left(i\right)$$

Φ_ZS: Winkel eines Zahnsegments (=Fördersegment), hier 30°
ω̅_ZS(i): mittlere Drehzahl über das ZahnsegmentThe change in pressure in segments is linked to the pumped volume as follows: $$\Delta p_{ZP}\left(i\right)=\frac{1}{C_H}\cdot V_{ZS}\cdot e\left(I\right)$$

Δp _ZP (i) is the change in the segmentally averaged actual pressure compared to the previous segment and is calculated by averaging the angle-synchronously recorded actual pressure over a toothed segment and then differentiating: $${\overline{p}}_{ZP}\left(i\right)=\frac{1}{N\varphi }\cdot {\displaystyle \sum _{k=1}^{N\varphi }p\left(\varphi \left(k\right)\right)}\text{medium pressure}\ddot{\text{and}}\text{About an F}\ddot{\text{O}}\text{wheel segment}$$

N _ϕ : number of angular positions per conveyor segment at which the actual pressure p(φ(k)) was recorded $$\Delta p_{ZP}\left(i\right)=\frac{{\overline{p}}_{ZP}\left(i\right)-{\overline{p}}_{ZP}\left(i-1\right)}{{\mathrm{\Phi }}_{ZS}}\cdot {\overline{\omega }}_{ZS}\left(i\right)$$

Φ _ZS : Angle of a toothed segment (=conveyor segment), here 30°
ω̅ _ZS (i): average speed over the toothed segment

If (6) is inserted into (4) and solved for e _V (i), one has a variable for evaluating the tolerance-related deviation of the conveyed volume.

This design-related deviation can be compensated by correcting the volume flow in the toothed segment i by adjusting the speed ω _ZS (i).

über eine Periode der Zahnpaarungen minimiert wird. $$\left|E\left(i\right)\right|=\left|e_V\left(i\right)=\frac{1}{N_{ZP}}\cdot {\displaystyle \sum _{k=1}^{N_{ZP}}{e}_V}\left(k\right)\right|$$

A possible quality criterion for reducing the tolerance-related pulsation is that the amount of deviation of the e _V (i) from the mean value $\frac{1}{N_{ZP}}\cdot {\displaystyle \sum _{k=1}^{NZP}{e}_V}\left(k\right)$

is minimized over a period of tooth pairing. $$\left|E\left(i\right)\right|=\left|e_V\left(i\right)=\frac{1}{N_{ZP}}\cdot {\displaystyle \sum _{k=1}^{N_{ZP}}{e}_V}\left(k\right)\right|$$

Criterion (7) is minimized via a multiplicative correction K(i) of setpoint speed ω(t). K(i) is adapted for each pair of teeth and is constant over a toothed segment. The absolute value of e _V (i) is not required for the adaptation of K(i). It is already sufficient to know the sign and the relative magnitude of the e _V (i). The hydraulic capacity C _h does not have to be known explicitly. The quality criterion can thus also be formed from Δp _ZP (i) according to (8). $$\left|E\left(i\right)\right|=\left|\Delta p_{ZP}\left(i\right)-\frac{1}{N_{ZP}}\cdot {\displaystyle \sum _{k=1}^{N_{ZP}}\Delta p_{ZP}}\left(k\right)\right|$$

δ: Inkrement zur Adaption des Korrekturwerts
ε: Schwellwert, bis zu dem eine Adaption erfolgen sollBased on the relative size, it can be decided in which tooth segment the largest deviation is present. A staggered or prioritized adaptation of the K(i) can thus take place. Depending on the sign, the K(i) can be adapted as follows: $$K\left(i\right)=\{\begin{array}{l}K\left(i\right)+\delta ,\text{f}\ddot{\text{and}}\text{right}E\left(i\right)\mathrm{,0,}\left|E\left(i\right)\right|>e\hfill \\ K\left(i\right),\text{f}\ddot{\text{and}}\text{right}\left|E\left(i\right)\right|<e\hfill \\ K\left(i\right)-\delta ,\text{f}\ddot{\text{and}}\text{right}E\left(i\right)>\mathrm{0,}\left|E\left(i\right)\right|>e\hfill \end{array}$$

δ: Increment for adapting the correction value
ε: Threshold up to which an adaptation should take place

In other words, K(i) and thus the segment speed and the volume flow are increased if the pressure difference caused by the current pair of teeth is smaller than the mean value of the pressure differences caused by all pairs of teeth, and decreased if the pressure difference caused by the current pair of teeth is greater than is the mean of the pressure differences caused by all pairs of teeth. This adaptation takes place as long as the difference is above the threshold value.

K=0 is a suitable starting point. Thus, the pressure pulsations can be reduced iteratively during operation by only detecting the actual pressure as a function of the rotational angle position and, as described, evaluating it.

ε is an adjustable parameter that is selected in particular for the specific application. For example, 0.25 bar can be used as an initial value. Preferably δ << 1 is chosen, e.g. 0.1. Alternatively or additionally, δ can also depend on |E(i)| be adapted. Is |E(i)| large, δ becomes large to enable rapid learning. Is |E(i)| small, δ becomes small to ensure stable and robust behavior.

According to a preferred embodiment, the actual pressure p _actual (i) and the actual angle of rotation φ _actual (t) are recorded synchronously (eg with a sampling time of 1 ms). The pressure recorded synchronously can then be linearly interpolated on an angular grid with a certain resolution (eg of 2° rotation angle). The choice of resolution influences the possible speed range, for example a resolution of 2° allows the function to be used up to a speed of 300 rpm.

An angle-synchronously recorded actual pressure p _actual (k*Δφ) with Δφ=2° is then available.

For the recursive calculation of the correction values, the angle-synchronous actual pressure is stored in a ring buffer over a period of the tooth pairing. With an exemplary period of 1080° and an exemplary resolution of 2°, only 540 values have to be stored. Such a recursive calculation requires a particularly low computational effort.

A computing unit according to the invention, e.g. a control unit of a hydraulic pump, is set up, in particular in terms of programming, to carry out a method according to the invention.

The implementation of the invention in the form of software is also advantageous, since this enables particularly low costs, in particular if an executing processing unit is also used for other tasks and is therefore available in any case. Suitable data carriers for providing the computer program are, in particular, floppy disks, hard drives, flash memories, EEPROMs, CD-ROMs, 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.

character list

• 1 shows a hydraulic system with a variable speed pump, which can form the basis of the invention.
• 2 shows an example of a pressure curve over the rotation angle φ of an internal gear pump.
• 3 shows a similar pressure curve as 2 together with a quality function resulting therefrom and instructions for the adaptation of correction values K(i).
• 4 shows a preferred embodiment of the invention schematically in a flowchart.

Detailed description of the drawing

In 1 A hydraulic system 1 with a variable-speed pump 10, which can form the basis of the invention, is shown as a block diagram. The variable-speed pump 10 has an electric motor, designed here as a synchronous motor 11 , for driving a conveyor system, designed here as an internal gear pump 12 . The synchronous motor 11 is controlled by a control unit 20 set up in terms of programming for carrying out the invention with a setpoint speed signal ω _setpoint . The synchronous motor 11 is equipped with a rotary encoder 13 which detects a current rotary angle position φ _actual (t) and transmits it to the control device 20 . The control unit is set up to calculate an instantaneous actual speed ω _actual from the instantaneous rotational angle position φ _actual (t) by differentiation and to use it for controlling the rotational speed.

A fluid is pumped from the internal gear pump 12 into a line 30 and to a hydraulic unit 40 . An actual pressure p _actual (t) prevails in the line, which is detected by a pressure sensor 31 and transmitted to the control device 20 .

In 2 an exemplary profile 101 of the actual pressure p _{actual is} shown over the angle of rotation φ. In the present example, the rotating internal gear has 12 teeth, the stationary ring gear has 18 teeth. As explained above, this results in a period of the tooth pairing of three revolutions of the internal gear. The angle of rotation φ extends over a funding period of 3x360°.

Furthermore, a pressure averaged over a toothed segment of 30° is denoted by 102, which essentially originates from the non-harmonic pressure pulsation.

In 3 Corresponding curves of the actual pressure p _ist and of the actual pressure averaged over a toothed segment of 30° are shown in the upper diagram and denoted by 201 and 202, respectively, with the angle of rotation φ changing over two periods of the tooth pairing, each marked with a double arrow, ie funding periods.

The curve of a quality function E(i) resulting from the averaged pressure curve 202 is shown in a lower diagram and denoted by 301 . Furthermore, arrows are drawn in the lower diagram, which indicate changes in the correction values K(i) for the rotational speed resulting from the respective value of the quality function in accordance with equation (9).

If E(i) is negative, this means that the pressure change Δp _ZP (i) caused by the current pair of teeth is smaller than the mean value of the pressure changes caused by all pairs of teeth and therefore the correction value K(i) must be increased. This is indicated by an arrow pointing upwards.

Conversely, if E(i) is positive, this means that the pressure change Δp _ZP (i) caused by the current pair of teeth is greater than the mean value of the pressure changes caused by all pairs of teeth and the correction value K(i) must be reduced. This is represented by an arrow pointing down.

Furthermore, it can be seen that the pressure pulsation in the second run could be reduced from φ = 3240° - φ = 4319° through the adaptation in the first pass of φ = 2160° - 3239°. The non-harmonic pressure pulsation can be damped further and further by repeatedly adapting the correction values K(i).

In 4 a preferred embodiment of the invention is shown schematically in a flowchart. In a step 301, it is first determined whether a pressure maintenance mode DHB is present. If this is the case, in a step 302 the pressure change Δp _ZP (i) is determined for the tooth segments passing through. From this, the evaluation variable E(i) is continuously determined.

In a step 303 it is then checked whether the evaluation function E(i) is greater than a threshold value ε. If this is the case, the associated correction value K(i) is reduced in a step 304 by an increment δ.

Otherwise, in a step 305 it is checked whether the evaluation function E(i)<−ε. If this is the case, in a step 306 the correction value K(i) is increased by the increment δ.

Otherwise, in a step 307, the correction value K(i) is retained.

Claims (12)

Method for controlling a variable-speed fluid pump (10) with a setpoint speed signal (ω _setpoint ) for pumping a fluid, wherein a hydraulic pressure (p _actual , 201) of the fluid is detected as a function of a rotational angle position (φ _actual ) of the fluid pump, the Hydraulic pressure (p _Ist , 201) depending on the rotational angle position (φ _Ist ) is divided into delivery periods, each delivery period comprising a number of delivery segments, one delivery segment being limited by two adjacent minima depending on the hydraulic pressure of the rotational angle position (φ _Ist ). is determined for each of the conveyor segments, an average hydraulic pressure (202) of the conveyor segment, a correction value for the first of the conveyor segments being determined from a difference in the average hydraulic pressure between a first of the conveyor segments and an adjacent second of the conveyor segments, with a setpoint Speed for the first of the conveyor segments with the correction value is corrected for the first of the conveyor segments. procedure after claim 1 , wherein the correction value for the first of the conveyor segments is determined such that the difference in the mean hydraulic pressure between the first of the conveyor segments and the adjacent second of the conveyor segments is approximated to a mean value of all differences in a conveyor period. procedure after claim 1 or 2 , wherein the correction value for the first of the conveyor segments is reduced if the difference in the mean hydraulic pressure between the first of the conveyor segments and the adjacent second of the conveyor segments exceeds an upper threshold value. Method according to one of the preceding claims, wherein the correction value for the first of the conveyor segments is increased if the difference in the mean hydraulic pressure between the first of the conveyor segments and the adjacent second of the conveyor segments falls below a lower threshold value. procedure after claim 4 in reference to claim 3 , where the upper threshold and the lower threshold have the same absolute value and different signs. procedure after claim 3 , 4 or 5 , wherein the correction value for the first of the conveyor segments is reduced or increased by a predetermined increment. procedure after claim 3 , 4 or 5 , wherein the correction value for the first of the conveyor segments is reduced or increased by a variable increment, the value of the variable increment being determined as a function of the magnitude of the difference. A method according to any one of the preceding claims, performed iteratively during operation of the pump. Method according to one of the preceding claims, in which the hydraulic pressure (p _actual ) of the fluid is detected as a function of the rotational angle position (φ _actual ) of the fluid pump (10) in a pressure-maintaining mode. Arithmetic unit (20) which is set up to carry out a method according to one of the preceding claims. Computer program that causes a computing unit to carry out a method according to one of Claims 1 until 9 perform when it is on the computing unit, especially after claim 10 , is performed. Machine-readable storage medium with a computer program stored on it claim 11 .

Images