PROPORTIONAL VALVE

Abstract

A proportional valve is provided having a pilot control valve that can be controlled by means of a control signal and having a booster valve that can be actuated by means of the pilot control valve. The proportional valve has a compressed-air connection for connecting a compressed-air supply, a working connection, and an air-removal connection. The booster valve has three valve elements, which are arranged one after the other and can each be moved in an axial direction against a spring force.

Claims

1. A proportional valve (1) with a pilot valve (2) that can be activated by a control signal and a booster valve (3) that can be actuated by means of the pilot valve (2), wherein the proportional valve (1) has a compressed-air port (6) for connection of a compressed-air supply, a working port (5) and a vent port (4), wherein the booster valve (3) has three valve elements (8, 9, 10) connected in series and respectively movable in an axial direction against a spring force, namely a first valve element (8) actuated by the pilot valve (2), a second valve element (9), which is actuated by the first valve element (2), and a third valve element (10), which is actuated by the second valve element (9), wherein, in a basic position of the proportional valve (1), the first, the second and the third valve elements (8, 9, 10) are spaced apart from one another in pairs and, within the booster valve (3), a first sealing seat (26) acting between the first valve element (8) and the second valve element (9) and a second sealing seat (27) acting between the third valve element (10) and the housing (16) are formed and disposed in such a way that during variation of the control signal that activates the pilot valve (2) and of the resulting cascade-like positioning of the axial positions of the first, second and third valve elements (8, 9, 10), various switched states can be set for venting of and air admission to the working port (5) and for holding a pressure present at the working port (5), wherein further a position sensor (31) is provided to detect the axial position of the first valve element (8) and a control unit (36) of the proportional valve (1) is set up in such a way that the measured signal of the position sensor (31) is evaluated for calculation of the control signal for the pilot valve (2), needed in order to achieve a desired switched state of the booster valve (3).

2. The proportional valve of claim 1, wherein the position sensor (31) is set up for contactless measurement of the axial position of the first valve element.

3. The proportional valve of claim 2, wherein the position sensor (31) is based on an optical, capacitive or magnetic measurement principle.

4. The proportional valve of claim 3, wherein the position sensor (31) is a magnetic-field angle sensor.

5. The proportional valve of claim 4, wherein the position sensor (31) is an AMR, TMR or GMR sensor.

6. The proportional valve of claim 1, wherein the control unit (36) of the proportional valve (1) is set up in such a way that the control signal for the pilot valve (2), needed in order to achieve a desired switched state of the booster valve (3), is calculated by utilizing exclusively the measured signal of the position sensor (31).

7. The proportional valve of claim 1, wherein the first valve element (8) is formed by a diaphragm disk (11) with a diaphragm-disk shank (12) that extends in axial direction and is provided with an axial bore (13), wherein the second valve element (9) is formed by a valve tappet (18), which is spring-preloaded in a direction pointed toward the diaphragm disk (11) and is provided on an end face pointing toward the diaphragm-disk shank (12) with a first sealing seat for the free end of the diaphragm-disk shaft (12), which can be brought into contact therewith, and wherein the third valve element (10) is formed by a base element (19), which is spring-preloaded against a second sealing seat in a direction pointing toward the valve tappet (18) and can be lifted from the second sealing seat by axial displacement of the valve tappet (18) that has been brought into contact on the base element (19).

8. The proportional valve of claim 7, wherein the position sensor (31) interacts with a magnetic element (30) integrated in the diaphragm disk (11).

9. The proportional valve of claim 1, wherein a surface (25, 28) forming the first and/or second sealing seat and/or interacting therewith for fine regulation of the fluid flow is made of a polymer material.

10. The proportional valve of claim 1, wherein the pilot valve is a 3/2-way valve.

11. The proportional valve of claim 1, wherein the booster valve is a 3/3-way valve.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0030] An exemplary embodiment of an inventive valve will be explained in more detail hereinafter on the basis of the drawing, wherein

[0031] FIG. 1 shows a schematic view of a proportional valve and its components, and

[0032] FIGS. 2-4 show three different diagrams of different characteristics of a valve to illustrate the complex relationships between various valve parameters.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] FIG. 1 shows an exemplary embodiment of an inventive proportional valve 1, which has a pneumatic, piezoelectric pilot valve 2 as preliminary stage and a booster valve 3 as power stage.

[0034] Valve 1 further has a vent port 4, a working port 5 for connection of a pneumatic fitting (not illustrated) to be actuated with valve 1 and a port 6 for a compressed-air supply with a predetermined air pressure of 8 bar, for example. Furthermore, a pressure regulator 7 is provided, with which a pressure of 1.2 bar, for example, which is lower than the pressure prevailing for the compressed-air supply at port 6, can be drawn therefrom as input pressure for pilot valve 2 provided for actuation of booster valve 3.

[0035] Valve 1 further has three valve elements 8, 9, 10 connected in series and respectively movable in an axial direction according to double arrow R.

[0036] In this connection, first valve element 8 (topmost in FIG. 1) comprises a diaphragm disk 11 and a diaphragm-disk shank 12 with an axial bore 13.

[0037] Diaphragm disk 11 is in operative connection (via a mechanical coupling in the present case) with a first diaphragm 14, wherein a control pressure chamber 15 is formed above first diaphragm 14 and diaphragm-disk 11. The air pressure prevailing in control pressure chamber 15 is generated via pilot valve 2.

[0038] Furthermore, first valve element 8 (formed by diaphragm disk 11 plus diaphragm-disk shank 12) is spring-preloaded in (axial) direction relative to control pressure chamber 15. For this purpose, in total three spring elements (springs) 17 braced on housing 16 of valve 1 are provided in the present exemplary embodiment. Only one of those (left of center axis M) lies in the section plan in FIG. 1, while the other two spring elements 17 (of which only one is visible in FIG. 1) lie in front of or behind the section plane. These three spring elements 17 are respectively disposed equidistant (i.e. with the same radial spacing) from center axis M, and in the plane passing perpendicularly through center axis M are offset, in pairs, by the same angle of 120 relative to one another (i.e. around center axis M), so that, relative to the axial center axis M, completely symmetric preloading of first valve element 8 in the direction of control pressure chamber 14 is achieved.

[0039] Second valve element 9 in the present case is formed by a valve tappet 18 and third valve element 10 by a base element 19. In this connection, valve tappet 18 is preloaded in the direction of first valve element 8 (=diaphragm disk 11 and diaphragm-disk shank 12) by means of a spring 20, which is braced on base element 19, while base element 19 in turn is preloaded by means of a spring 21, which is braced on housing 16.

[0040] In the basic position of valve 1 illustrated in FIG. 1, all three axially movable valve elements 8, 9, 10 of booster valve 3 are preloaded in the same direction, but are spaced apart from one another in pairs.

[0041] Diaphragm-disk shank 12 is coupled with a second diaphragm 22, which circumferentially surrounds diaphragm-disk shank 12 sealingly and separates (continuously vented) vent chamber 23, which is disposed between first diaphragm 14 and second diaphragm 22 and which leads to vent port 4, from a working pressure chamber 24 leading to working port 5. This second diaphragm 22 may serve simultaneously as radial bearing of diaphragm shank 12. By virtue of the spacing present between the free end of diaphragm-disk shank 12 and valve tappet 18 in the basic position of valve 1, working pressure chamber 24 (and thus also a pneumatic fitting connected to working port 5) is vented in the valve position illustrated in FIG. 1.

[0042] At its top face pointing toward diaphragm-disk shank 12, valve tappet 18 has a polymer material, which serves sealing face 25 and on which a lower edge 26 of diaphragm-disk shank 12 can come into contact to form a first sealing seat. Depending on the hardness of the polymer, this compliant sealing face permits particularly precise proportional fine regulation during positioning of the valve in the vicinity of the contact area.

[0043] When thereforeby appropriate increase of the pressure prevailing in control pressure chamber 15 by means of pilot valve 2, which in turn can be activated by an (electric) control voltagefirst valve element 8 is pushed so far that lower edge 26 of diaphragm-disk shank 12 comes sealingly into contact on top face 25 of valve tappet 18, the communication through axial bore 13 of diaphragm-disk shank 12 that existed between vent chamber 23 and working pressure chamber 24 is blocked, whereby the previous venting of working pressure chamber 24 is canceled.

[0044] A second sealing seat is formed in the illustrated exemplary embodiment of a proportional valve 1 by a sealing edge 27, which is integral with the housing and in FIG. 1 is pointing downward, and against which base element 19 functioning as third valve element 10 is preloaded by means of spring 21, wherein here a sealing face 28 of a polymer material, interacting with sealing edge 27 to form the second sealing seat, is provided in turn on the base-element side. A pressure supply chamber 29 in communication with port 6 for the pressure supply is situated underneath the second sealing seat, and is therefore separated fluidically from working pressure chamber 24 precisely when base element 19 bears sealingly with its top face on sealing edge 27, as is the case in the illustrated basic position.

[0045] Thus, only whenby suitable actuation of first valve element 8 by means of pilot valve 2first valve element 8 has been pushed so far that first valve element 8 bears on second valve element 9 and second valve element 9 bears on third valve element 10, does a further increase of the control pressure in control pressure chamber 15 cause third valve element 10 (=base element 19) to be lifted from the second sealing seat, whereby working pressure chamber 24 is placed fluidically in communication with pressure supply 6, i.e. the pressure at working outlet 5 is raised. During actuation of third valve element 10, it is otherwise of advantage that a hard stop is formed between valve tappet 18 and base element 19.

[0046] Last but not least, the particularly good regulation behavior of the valve is also achieved on the basis of the spacings provided in the basic state between the first, second and third valve elements 8, 9, 10, since hereby the various fluidic states of valve 1 can be differentiated particularly well and simply activated. In the basic state, working port 5 of the valve is vented. When first valve element 8 has then been pushed so far that it bears sealingly on the area of contact with second valve element 9, thus forming a sealing seat 26 therewith, the state for holding a pressure present at working outlet 5 is attained, since in this position third valve element 10 separates working pressure chamber 24 from pressure supply chamber 29 by contact with the second sealing seat. Only when second valve element 9 has been brought by further displacement into contact with third valve element 10 and third valve element 10 has been lifted against its spring preload from second sealing seat 27 is the valve state for admission of air to working port 5 at the pressure supplied from pressure supply 6 attained.

[0047] Regulation of the described valve 1despite the cascade-like configurationproves otherwise to be particularly simple. For this purpose, it is possible to provide a magnetic element 30 on first valve element 8 (e.g. in the region of the diaphragm-disk rim), so that, by using a suitable magnetic position sensor 31, especially in the form of an AMR, GMR or TMR sensor, the axial position of first valve element 8 can be determined energy-efficiently and precisely. From this position it is possible to deduce the instantaneous valve state directly, without having to determine other measurable parameters for the purpose. By using a suitably precise position sensor, it is also then possible in particular to achieve fine regulation of valve 1 in the immediate vicinity of those positions at which the changeover between the various switched states of the valve takes place.

[0048] By virtue of the purely mechanical coupling of the three valve elements 8, 9 and 10 and because of the fixed travels, predetermined by the location of the sealing seats, between the various valve positions, it is therefore possible to achieve regulation of valve 1 by utilizing (exclusively) the (axial) position of first valve element 8 determined by means of position sensor 31, as will be further explained hereinafter on the basis of various characteristics of valve 1.

[0049] In the present case, pneumatic pilot valve 2 is configured as a proportional 3/2-way valve, while booster valve 3 is a 3/3-way valve.

[0050] Pilot valve 2 itself has a pressure inlet 33, which in the present case is fed with compressed air made available by pressure regulator 7. Furthermore, a pilot-valve vent port 32 (optionally in communication with vent port 4 of valve 1) is provided, as is a pilot-valve working outlet 34, which is fluidically in communication with control pressure chamber 15 of valve 1.

[0051] By means of a piezo-bending transducer 35, which can be electrically actuated and hereby swiveled in the region of its free end as indicated by double arrow B, pilot-valve working outlet 34 may now be optionally vented (i.e. placed fluidically in communication with pilot-valve vent port 32) or placed partly or completely in communication with the pressure prevailing at pressure inlet 33 of pilot valve 2. Thus pilot valve 2, by regulating the pressure prevailing in control pressure chamber 15, can be used with particularly high regulation quality and low energy consumption for actuation of first valve element 8 of valve 1.

[0052] Furthermore, a control unit 36 is provided, to which the measured signal of position sensor 31 is delivered via a signal line 37. Control unit 36, which controls pilot valve 2 (and therefore proportional valve 1 together), is set up to calculate the control voltage for pilot valve 2, needed to achieve a desired switched state of booster valve 3, and correspondingly to activate pilot valve 2 via control line 38, in which case the measured signal of the position sensor (as preferably the single measured parameter concerning the valve state) is evaluated during this calculation. In the process, therefore, firstly the instantaneous valve state is determined from the measured value representative of the position of first valve element 8 (by comparison with verification or calibration data saved appropriately in control unit 36) and then the control voltage for pilot valve 2 is regulated such that first valve element 8depending on desired valve stateholds its axial position or changes it to change the valve state.

[0053] FIG. 2 shows the flow characteristic of booster valve 3 at working port 5 as a function of its stroke (i.e. as a function of the axial position of the first valve element that can be determined by means of the position sensor). What are shown are two exemplary curves for various pressures p2 at the working port for a pressure of p1=8 bar at the pressure supply. In the process, the three valve positions are occupied in succession, i.e. the working port is vented (=negative flow), the pressure is held (=low flow) and air is admitted to the working port (=positive flow) in succession. The transition between the individual ranges is almost independent of the pressure at the working port. At worst, a (minimal) pressure dependence exists due to the pressure-dependent compression of the valve seats made of a polymer material, so that here only a marginal influence on the range transitions exists. In contrast to a power stage with slide design typically used in proportional valves, the valve geometry used in the present case permits greatly improved leak-tightness of the valve by forming two sealing seats, so that, in the holding range, the pressure at the working port can also be held for a long time.

[0054] FIG. 3 now shows the stroke characteristic of the booster valve of a proportional valve as a function of the control voltage present at the pilot valve (respectively in normalized units) for two different working pressures p2=1 bar and p2=7 bar, where p1=8 bar represents the pressure supplied by pressure supply 6. This diagram reveals distinct hysteresis in the activation signal on the one hand and a strong dependence on the working pressure on the other hand.

[0055] The pressure dependence is due to the specific valve geometry, which causes the force counter to the direction of actuation of the valve to increase with the working pressure. At high working pressure, therefore, a correspondingly higher control pressure is necessary in order to actuate the booster valve than is the case at a lower working pressure. The hysteresis of the characteristic is caused by the piezoelectric and fluidic hysteresis of the pilot valve.

[0056] FIG. 4 shows the overall characteristic of the flow through the booster valve as a function of the activating voltage, once again for two different pressures p2=1 bar and p2=7 bar at the working port for a pressure of p1=8 bar at the pressure supply. Because of the hysteresis of the control voltage, the individual valve positions can no longer be attributed to an unambiguous activation range in the control signal. Clearly, this is further impaired by the pressure dependence.

[0057] The characteristics from FIGS. 3 and 4 therefore show that pressure-dependent regulation of such a proportional valve would be extremely problematic. In contrast, the characteristic from FIG. 2 illustrates that particularly simple valve regulation is permitted by utilization of the measured signal of the position sensor that characterizes the valve stroke.