Method for determining a volume flow

Abstract

Method for determining a volume flow flowing through a valve, such as a proportional valve, wherein the volume flow is determined by means of an estimation method, using a disturbance observer and an orifice equation.

Description

[0001] Method for determining a volume flow rate

[0002] The invention relates to a method for determining a volume flow rate that flows through a valve, such as a proportional valve.

[0003] Flow meters and flow switches are particularly useful for measuring fluid volume flow in machines and systems, including those with fluid valves. For example, the patent holder offers an aluminum-framed flow meter in its catalog material (DE 18.331.3 / 03.17) under the series designation "EVS 3100," specifically designed for use in hydraulic and other fluid power systems. This transmitter operates on the turbine principle, measuring the rotational speed of an impeller rotating within the fluid flow and converting it into an evaluable analog signal to measure the actual volume flow of the fluid.

[0004] Furthermore, the patent holder offers so-called flow switches for determining volumetric flow rates in its brochures (DE 18.379.1 / 03.17) under the designation "HFS 2100," which are based on a position-independent float-type measuring principle. A fluid measuring medium deflects a spring-loaded float in the flow direction depending on the volumetric flow rate. A reed switch is located outside the device and thus outside the fluid flow circuit. When the magnet integrated in the float reaches a preset target position, the reed switch activates, thus enabling reliable limit value monitoring even with changes in viscosity. The flow switch therefore serves as a type of flow monitor for the fluid volumetric flow rate.

[0005] By determining the volume flow rate through a valve, such as a proportional valve, the function of the respective valve can be monitored, and thus also the hydraulic systems of a complete plant that are in operative connection with the respective valve, whose control and regulation part is partly determined by the valve.

[0006] Hydraulic valves are freely available on the market in a wide variety of designs. For example, the patent holder's catalog (DE 5.231.5 0_05.22) discloses a hydraulically piloted 4 / 3 proportional directional control valve equipped with onboard electronics and a position sensor. This valve combines directional control with speed control for the respective hydraulic actuator connected to the valve. Due to the complexity of such a valve, it is highly advantageous to be able to monitor its operation, for example, by measuring the volumetric flow rate of the fluid passing through the valve.

[0007] The volumetric flow sensors used in the prior art and mentioned at the outset are expensive to purchase and also require corresponding maintenance and monitoring, which in turn incurs costs. Furthermore, they occupy a relatively large amount of installation space when used on the valve. Based on this prior art, the invention aims to provide an alternative method for determining the volumetric flow rate of a valve that does not have the disadvantages described. A method with the features of claim 1 in its entirety achieves this objective.

[0008] The method according to the invention is characterized in that the volume flow rate is determined by means of an estimation method, using a disturbance observer and an orifice equation. Thus, the estimator itself requires only two input signals in the form of the estimated disturbance force and a measured stroke position of a valve piston of the valve.

[0009] A Luenberger observer is preferably used as the disturbance observer, and the associated idea is based on connecting the observer in parallel to the controlled system model. The difference between the measured value of the system and the "measured value" of the observer is then fed back to the model.

[0010] Insofar as the volumetric flow rate is calculated using the orifice equation, the corresponding function A(x) represents a non-linear function of the valve's opening area. Furthermore, the pressure difference Ap across the valve, which depends on the applied pressure, is incorporated into the orifice equation. This pressure difference Ap is determined by a sensor at the valve or, if no sensor is present, by a pressure estimate performed prior to the volumetric flow rate estimate.

[0011] In a preferred embodiment of the method according to the invention, the pressure estimation is based on the profile of the estimated disturbance forces of the disturbance observer, for which individual disturbance force profiles are recorded at known and constant or regulated pressures at the valve. In a further preferred embodiment of the method according to the invention, it is provided that when displaying the disturbance force F stoer The characteristic curves resulting from the pressure p, especially for larger valve strokes, are essentially linear, and the pressure Ap can be calculated from the slope a(%) and the offset / ?(%) of the force or characteristic curves.

[0012] It is also preferred that, for estimating the volume flow rate, a further polynomial of the opening area y(%) is required, which is calculated from measured volume flow characteristics relating to the respective valve.

[0013] Having said that, the pressure Ap and the volume flow rate Ap can preferably be calculated or estimated using the following formulas.

[0014]

[0015] The application of the method has proven particularly advantageous for a proportional valve, especially in the form of a 4 / 3-way slide valve, which uses a valve piston arranged longitudinally in a valve housing to control two service ports A, B as well as a pressure supply port P and at least one tank or return port T.

[0016] Preferably, an actuator, particularly a magnetic actuator, is used on each side of the valve piston to actively control the position of the valve piston. At least one return spring is provided, each serving to return the valve piston to its initial position as soon as the actuators are de-energized. Based on the input signal at the respective magnetic actuator, it generates a control pressure that hydraulically moves the main piston or valve piston against a compression spring acting as a return spring. This opens cross-sectional areas or surfaces that determine the volume flow through the valve, depending on the pressure differential. Thus, the proportional valve enables control of the magnitude and direction of a fluid volume flow with high repeatability.Depending on which of the two magnetic actuators is energized, the pilot, in the form of the valve piston, opens the connection to the service ports A and B. This means that either service port A or B is connected to the pressure supply port P for fluid supply, or the other service port B or A delivers fluid to a storage tank via the tank or return port T. The respective control pressure for the valve piston is determined by the set magnetic current at the actuators.

[0017] By applying control pressure from the magnetic actuators to one of the two end faces of the valve or main piston, the resulting force counteracts the spring force of the return spring and moves the valve or main piston until a force equilibrium is reached and the desired connections PABT or PBAT, mentioned previously, are released. Upon subsequent pressure release of the valve, the return or centering spring returns the valve or main piston to a central zero or starting position.

[0018] In addition, improved control of the fluid flow is achieved by determining the position of the valve piston with the integrated displacement measuring system, for example using a Hall sensor, and the actuators can be controlled intelligently via a microcontroller, which is preferably arranged in a space-saving manner on the outside of the valve housing. The inventive method is described in more detail below using an application in a 4 / 3-way slide valve as an example. The following are shown in a schematic and not-to-scale representation:

[0019] Figure 1 shows a model of the essential components of the 4 / 3-way slide valve as a proportional valve; and Figure 2 shows diagrammatic representations of the estimated disturbance force at different pressures, plotted over the travel path of the magnetically actuated valve piston or valve slide in both deflection directions.

[0020] The volumetric flow rate estimator used here is tasked with estimating the volumetric flow rate passing through a valve. This estimation is based on a disturbance observer and incorporates the orifice equation.

[0021] A proportional valve, such as a 4 / 3-way slide valve, as shown in the model in Figure 1, is to be used. The proportional valve shown in Figure 1, which is known as such, has a valve housing 10 in which a valve piston 12 is longitudinally guided for actuating two service ports A, B, a pressure supply port P, and two tank or return ports T, which are provided in the valve housing 10 in the usual manner. One possible direction of travel of the valve piston 12 is designated x in Figure 1, whereby the valve piston 12 can, of course, also assume the opposite travel position. An actuator in the form of a magnetic actuator 14, 16 is arranged on each side of the valve piston 12 to actively control the position of the valve piston 12, which, according to the illustration in Figure 1, is in an unactuated center position.The two magnetic actuators 14, 16 are identical in construction and each has a coil 18 and an associated magnetic armature 20. One free rear end of the armature is supported by an armature spring 22, while the other free front end is operatively connected to a rod-like actuating element 24, the free end of which can come into contact with the valve piston 12. Furthermore, two return springs 26 in the form of compression springs are provided. One free end of each return spring is supported by an annular spring plate 28, which is oriented end-to-end with the outer surface of the valve housing 10 and is penetrated by the actuating element 24. The other end of each return spring 26 is supported by the outer wall of a magnetic housing 30 containing the magnetic armature 20.

[0022] As an example, when viewed from the perspective of Figure 1, if the left magnetic actuator 14 is actuated, the coil winding of the coil 18 is energized and the associated left magnetic armature 20 moves from its initial position shown in Figure 1 to a right actuating position. In this position, the left actuating part 24 is carried along, moving the valve piston 12 from its initial position shown in Figure 1 to the right in the direction of arrow x. During this movement, the left armature spring 22 relaxes and the left return spring 26 is compressed. Since the valve piston 12 moves to the right, the right spring plate 28 is also carried along accordingly, compressing the right return spring 26. Because the right actuating part 24 maintains an axial gap to the valve piston 12, the right magnetic actuator 16 remains in its initial position shown.When the valve piston is deflected to the right, the pressure supply port P is connected to the service port B, and the service port A is fluid-carrying to the left tank or return port T. This results in the connection assignment PBAT.

[0023] Conversely, with the right magnetic actuator 16 energized and the magnetic actuator 14 unenergized, the situation is reversed, and the valve piston 12 moves in the opposite direction to the arrow marked x, resulting in a fluid occupancy PABT. Based on this model of the valve shown in Figure 1, the function of the volume flow estimator can be explained in more detail. The estimator requires two input signals: the estimated disturbance force and the measured stroke position of the valve piston 12.

[0024] The valve shown in Figure 1, a model of a mechanical circuit, is essentially a spring-mass resonant circuit with viscous damping. The 4 / 3-way valve has two solenoid actuators 14 and 16, which actuate the valve piston 12. As already explained, there are two stroke directions, each controlled by one of the two solenoid actuators 14 and 16. Depending on the direction of travel, the valve piston 12 moves against an associated proportional spring 26, which is supported on the valve housing 10 by a spring plate 28.

[0025] The relevant differential equation for the system is then as follows:

[0026] Fmag = mẍ + dẋ + cx + ΔF.

[0027] The force AF is also referred to here as the disturbance force Fstoer. The disturbance force thus includes all unmodeled forces as well as forces that are difficult to model. Since the damping parameter d is also difficult to determine, it is included in the disturbance force AF, so that the following holds:

[0028] Fmag = mẍ + cx + ΔF.

[0029] This equation requires an assumption for AF. Simulations have shown that the simple model of a constant perturbation force ΔḞ = 0

[0030] Especially with jumps in the reference, insufficient results are achieved. Therefore, the disturbance force model is used with

[0031] ΔḞ = 0

[0032] chosen. This allows a disturbance observer to be implemented as a Luenberger observer with the state vector [x, x, AF, AF], in the form

[0033] ż= Az + Bu + l(y -c T z)

[0034] with the entrance

[0035] x

[0036] u = F mag - F FO tanh(ẋ / v₀)

[0037] design. The term

[0038] F FO tanh(ẋ / v₀)

[0039]

[0040] The estimated disturbance force AF is used to calculate a continuous force profile of the spring system near the neutral position (x=0). This force profile is used to calculate or estimate the volume flow rate, with reference to Figure 2, which illustrates the estimated disturbance force at different pressures. The estimated disturbance force is plotted in Newtons against the travel distance x in μm. Viewed from the starting position 0 [μm] in Figure 2, the force profile for 0 bar is shown at the top, with the force profiles for 30, 50, 70, and 100 bar shown on the branch below. On the opposite side from the starting position 0 [μm], the disturbance force profile for 0 bar is shown at the bottom left, and the disturbance force profile for 100 bar is shown at the top. The respective lines are continuous around the starting point 0 [μm], with jump values ​​forming continuous values.

[0041] The volume flow rate is calculated using the aperture equation.

[0042]

[0043] The pressure Ap is calculated, where the function A(x) is a non-linear function of the valve's opening area. The pressure Ap depends on the applied fluid pressure at the valve and is, in principle, unknown. The valve shown in Figure 1 has no pressure sensors that could measure the pressure Ap, so this pressure must also be estimated.

[0044] The pressure estimation must therefore be performed before the actual volumetric flow rate estimation. This pressure estimation is based on the profile of the estimated disturbance forces observed by the disturbance variable. For this purpose, the disturbance force profiles are recorded at known and constant (controlled) pressures, as shown in Figure 2.

[0045] If the disturbance force is represented as a function of pressure at constant strokes, it can be seen that the characteristic curves are almost linear, especially for larger strokes, so that the following applies:

[0046] Fstoer (x, Δp) = αₙ · Δp + βₙ

[0047] [α₁, α₂...αₙ] = α(x)

[0048] [β₁, β₂...βₙ] = β(x)

[0049] The function α(x) represents the slope and β(x) the offset of the force or characteristic curves. These two functions can be used to estimate the pressure Ap.

[0050] Another polynomial of the opening area γ(x) is needed to calculate the volume flow rate. It is calculated from the measured volume flow curves as follows.

[0051] Qmess(x, Ap)

[0052] y (*) = - —

[0053]

[0054] The polynomials described here are approximated to the available measurements using the commercially available software "Matlab". Subsequently, all polynomials are determined, and the model of the volume flow estimator is complete. With the equations

[0055]

[0056] The pressure Δp̂ and the formula

[0057]

[0058] The volume flow rate Q̂ is determined or estimated.

Claims

Patent claims 1. Method for determining a volume flow rate passing through a valve, such as a proportional valve, characterized in that the volume flow rate is determined by means of an estimation method, using a disturbance observer and an aperture equation.

2. Method according to claim 1, characterized in that a Luenberger observer is used as the disturbance observer.

3. Method according to claim 1 or 2, characterized in that the volume flow rate is calculated using the orifice equation, in which the pressure difference Ap at the valve is included, and that the determination of the pressure difference Ap is carried out by means of a sensor at the valve or, in the absence of a sensor, by a pressure estimate, which is carried out before the volume flow rate calculation.

4. Method according to one of the preceding claims, characterized in that the pressure estimation is based on the course of the estimated disturbance forces of the disturbance observer, for which individual disturbance force profiles are recorded at known and constant or controlled pressures.

5. Method according to one of the preceding claims, characterized in that in a representation of the disturbing force F stoer The characteristic curves resulting from the pressure p, especially for larger valve strokes, are essentially linear, and the pressure Δp̂ can be calculated from the slope α(x) and the offset β(x) of the force or characteristic curves.

6. Method according to one of the preceding claims, characterized in that a further polynomial of the opening area y(x) is required to estimate the volume flow rate, which is calculated from measured volume flow characteristic curves relating to the respective valve.

7. Method according to one of the preceding claims, characterized in that the pressure Δp̂ and the volume flow rate Q̂ are calculated or estimated according to the following formulas.

8. Method according to one of the preceding claims, characterized in that a 4 / 3-way slide valve is used as the proportional valve, which uses a valve piston (12) arranged longitudinally movable in a valve housing (10) for controlling two service ports A, B as well as a pressure supply port P and at least one tank or return port T.

9. Method according to one of the preceding claims, characterized in that an actuator, in particular a magnetic actuator (14, 16), is used on each side of the valve piston (12) to actively control the position of the valve piston (12), and that at least one return spring (26) is provided, which serves to bring the valve piston (12) into its initial position as soon as the actuators (14, 16) are de-energized.

10. Method according to one of the preceding claims, characterized in that the position (x) of the valve piston (12) is determined with an integrated displacement measuring system, and that the actuators (14, 16) are controlled via a microcontroller, which is preferably arranged on the outside of the valve housing (10).

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