GB2386670A

GB2386670A - Proportional valve and method for detecting the position of the valve throttle body

Info

Publication number: GB2386670A
Application number: GB0301234A
Authority: GB
Inventors: Christian Ellwein
Original assignee: Buerkert Werke GmbH and Co KG
Current assignee: Buerkert Werke GmbH and Co KG
Priority date: 2002-01-21
Filing date: 2003-01-20
Publication date: 2003-09-24
Anticipated expiration: 2023-01-20
Also published as: DE10202108A1; FR2835050A1; GB2386670B; GB0301234D0

Abstract

A proportional valve comprising a throttle body (2) biassed towards a closed position by means of a return spring (4), characterised in that the return spring (4) is associated with a force detector (6) which measures a force developed by the return spring (4), the measured force of which being used to derive a value representative of the current position of the throttle body (2). The force detector (6) may be integrated in an adjustment screw (5) for setting the spring tension and further, may be attached to the end of the adjustment screw (5) facing the return spring (4) or alternatively incorporated in a transverse bore extending at right angles to the longitudinal axis of the adjustment screw. The force detector (6) may be a piezoelectric element or may be realised in the nature of a resistor bridge.

Description

Proportional Valve and Method of Detecting the Position of a Throttle Body

in a Valve The present invention generally relates to proportional valves and to a method of 5 detecting the current position of the throttle body (armature, flap, rocker, cone or the like [1]) which throttles the volume flow to be controlled. In particular, the present invention relates to a method of detecting the position of the armature in continuous or proportional valves having a solenoid drive.

DESCRIPTION OF PRIOR ART

10 Proportional valves are distinguished in that they can not only be operated in two distinct states (opened or closed), but in that the crosssection of flow can be continuously adjusted. This is obtained, for example, in that by specific influence on the lines of magnetic flux and the frictional behaviour in the valve, the armature in a lifting armature valve assumes a position which is almost equivalent to the current 15 through the solenoid. Proportional valve technology known from prior art is disclosed

in [2], [3] and [4], for example. The most wide-spread principle of these proportional valves is to have a continuously controllable force (developed by a solenoid, for instance) acting on the movable throttle body which, in turn, is urged against a spring.

A force balance between spring and solenoid forces results in a specific position of 20 the throttle body. The force developed by the solenoid is usually altered in that its supply voltage is pulse width modulated by variation of the duty cycle.

There are not only spring and solenoid forces acting on the throttle body, but also frictional forces, flow-induced forces and the like. These additional forces are of stochastic nature and can not be predicted in real applications. For that reason there 25 exists a considerable interest of being able to measure and control such position.

There are known various methods of detecting such position: [3] proposes the use of a Linear Variable Differential Transformer (LVDT), according to the differential

- 2 transformer principle, as a displacement transducer. [5] basically deals with an inductive measuring system for detecting and controlling the position, with illustration 2.4 in this reference suggesting a principle similar to the one known from the LVDT mentioned above. For commutating valves, which are switched over 5 between two distinct positions only, there are known methods of detecting the position which analyse the profile of the current through the solenoid. Reference is made to Patent Documents DE 198 34 405 A1 and DE 198 50 687 A1, for example.

DE 199 60 796 A1 describes a control system for inlet and outlet valves in an internal combustion engine which is based on a PWM control for the valve and a detection of 10 the core position. However, there is no explanation in terns of realizing such detection. In this respect, this disclosure only relates to a control unit of higher order

for the purpose of a slow touch-down of the core, and does not relate to the detection of the position itself. In Patent Document DE 199 13 050 A1 there is described a method in which a plunger body is moved in relation to at least one plunger coil, the IS plunger body being connected to the moving throttle body. The voltage induced by the motion is used for detecting the position and/or the speed of the throttle body in the valve. In DE 199 09 109 A1 there is described a method of detecting the position, in which the magnetic dispersion field is detected which is altered by the motion of

the armature.

20 SUMMARY OF THE INVENTION

It is the object of the present invention to provide a novel method of detecting the current position of the throttle body in a proportional or continuous valve. The idea of this novel measuring principle is to measure the force generated by the return spring in the valve, this force being counteracted by the solenoid. The force developed by a 25 straight cylindrical coil spring, as it is preferably used in solenoid valves, has a linear relation with the deformation of the spring and is given by the expression F=-c*x (1)

- 3 In this expression c is the so-called spring rate and x is the spring deformation. In the case of a proportional valve with electromagnetic drive, the cross-section of flow of the valve is set by the variable solenoid force. Acting on the movable throttle body in the valve are, among others, the spring force which in most constructional 5 principles closes the valve, and the solenoid force which opens the valve against the spring force. There are other forces such as frictional forces or flow-induced forces which also act on the throttle body and have influence on the position thereof. These additional interfering forces are unwanted, but they can not be completely eliminated.

They are the reason for the fact that the relation between electrical current and, hence, 10 the solenoid force on the one hand and the resultant position of the throttle body on the other hand is not a steady one, but rather can have discontinuity points. A further effect of these interfering forces could be that inclination and offset of the current/position characteristics (or the (local) linearisations thereof are displaced and influenced. Thus, it is desirable to detect the actual position of the throttle body and 15 to closed-loop control it, if required.

The novel method of detecting the position of the throttle body relates to an indirect detection of the position by way of measuring the spring force. The spring is arranged in a valve between the movable throttle body and a fixed support point which is connected with the valve housing. The position for the force detector which 20 is proposed for detecting the spring force is the fixed support point of the spring or another place suitably connected therewith.

In proportional valves such fixed support point of the spring is configured as a screw in most cases, by means of which the biasing of the spring can be altered. This so-called adjustment screw serves for compensating dimensional imperfections of the 25 spring which are caused by variations in length of the spring, its wire diameter as well as its material properties. Due to the constructional conception of a proportional valve, the force detector can be integrated in the adjustment screw. Realising the screw with an integrated sensor can be done in various ways: the force detector can be configured as a round load cell which is concentrically arranged on the end of the

- 4 screw facing the spring. In this arrangement, the spring will apply a force to the deformation element of the force detector. The position of the force detector is determined by the position of the adjustment screw. In an alternative approach the adjustment screw may also be provided with a transverse bore extending S perpendicularly to the longitudinal axis of the screw. This bore can also receive an appropriate force detector.

Due to the proportional relation between the force exerted by the spring and the deformation of the spring, the measuring of the force will also produce a suitable travel signal of the throttle body, because the spring is deformed by the throttle body.

10 Thus, all interfering variables which have influence on the position of the throttle body (for instance frictional forces or pressure variations of the medium) are detected and can be compensated in a closed loop control. In case only the electrical current flowing through the solenoid is used as the controlled magnitude, the influence o these interfering variables will remain uncompensated.

IS Since the back-pressure of the medium in the valve will also have an effect on the output signal of the force detector, the valve together with the sensor has to be calibrated, so that the closed loop control is not affected by this magnitude.

The prior art methods have the disadvantage that they considerably increase the

size of the valve. This is unwanted because the field of application of the valve is

20 noticeably limited thereby. The method described in DE 199 O9 109 Al focuses on regulating the speed of the armature in commutating valves. In this method, the resolution of the travel signal depends on the position of the armature: with the distance to the pole surface being small, the resolution is at its maximum. With this technology it is also not possible to perform measuring across the entire travel of the 25 armature. For both reasons, such approach is not suitable for a closed loop position control in a proportional valve.

- 5 BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a proportional valve having a force detector integrated in the adjustment screw, the solenoid not being illustrated; Figure 2 shows the adjustment screw with a force detector which is concentrically 5 arranged on the end of the screw facing the spring; and Figure 3 shows the adjustment screw with a force detector in a transverse bore.

The proportional valve shown in Fig. 1 has a valve housing 1 with fluid ports and a valve seat; a medium flows through it. The valve seat can be continuously closed or opened by the seal connected with a throttle body 2. A return spring 4 urges they 10 throttle body 2 including the seal against the valve seat and, hence, exerts a force for closing the valve. The throttle body 2 is lifted off the valve seat, in a manner so as to compress the return spring 4, by the magnetic force generated by a solenoid (not shown) surrounding it. As the return spring is subject to specific tolerances with respect to material and manufacture, its tension and, hence, the operating point of the 15 proportional valve can be adjusted by an adjustment screw 5. A force detector 6 is arranged between the adjustment screw 5 and the return spring 4.

Fig. 2 shows the adjustment screw with a concentrically mounted force detector 6.

The latter has a cup-like or cylindrical shape. Joining these components is performed by means of a suitable method such as gluing, welding, pressing or any other known 20 technology.

Fig. 3 shows the force detector 6 being integrated in a transverse bore of the adjustment screw. Here, the adjustment screw has the function of a deformation element which transmits the spring force, acting on it, to the active surface of the force detector (e.g. a diaphragm including a resistor bridge).

- 6 CITED REFERENCES

The above cited references are set out in the following: [1] Gevatter, Hans-Jurgen: Automatisierungstechnik 3; Berlin: Publishing House Springer; 2000 5 [2] Gevatter, Hans-Jurgen: Automatisierungstechnik 2; Berlin: Publishing House Springer; 2000 [3] Skinner, S.C.: Grundlagen der Proportionalventil-Technik; Internal Company Document of Vickers Systeme GmbH, Bad Homburg v.d.H.; 1987 [4] Kabisch, G.; Berg, H.; Beck, K.: Stetigventile in der Pneumatik und irn 10 General Purpose-Bereich; Industriearmaturen; Vol. 4; Number 3; 1996; pp. 232-239 [5] Scholz, D.: Proportionalhydraulik; Berlin: Publishing House Springer; 1997.

Claims

- 7 Claims

1. A method of detecting the current position of a throttle body in a valve, the throttle body being biased by a return spring, the force developed by the return spring 5 is measured and a value representative of the position of the throttle body is derived from the measured force.

2. The method according to Claim 1, characterized in that the force developed by the return spring is measured by means of a force detector which is integrated in an adjustment screw for setting the spring tension.

10

3. The method according to Claim 2, characterized in that the force detector is attached to the end of the adjustment screw facing the return spring.

4. The method according to Claim 2, characterized in that the force detector is incorporated in a transverse bore extending at right angles to the longitudinal axis of the adjustment screw.

15

5. The method according to any of the Claims I to 4, characterized in that the force developed by the return spring is measured by means of a force detector which for measuring the applied force makes use of the piezoelectric or piezoresistive effect.

6. The method according to any of the Claims 1 to 4, characterized in that the force developed by the return spring is measured by means of a force detector which 20 is realised in the nature of a resistor bridge which can be influenced according to the force applied to it.

7. A proportional valve comprising a throttle body biased towards a closed position by means of a return spring, characterized in that the return spring is associated with a force detector which measures a force developed by the return 25 spring, the measured force of which being representative of the current position of the throttle body.

8. The proportional valve according to Claim 7, characterized in that the force detector is arranged between the throttle body and an adjustment screw.

9. The proportional valve according to Claim 8, characterized in that a connecting cable extends through the adjustment screw to the force detector.