WO2010045946A1

WO2010045946A1 - A servo valve

Info

Publication number: WO2010045946A1
Application number: PCT/DK2009/000222
Authority: WO
Inventors: Michael Birkelund
Original assignee: Danfoss A/S
Priority date: 2008-10-21
Filing date: 2009-10-21
Publication date: 2010-04-29

Abstract

A servo valve (100) comprising a valve seat (112) and a diaphragm (116) which may be moved between a closed state in which the servo valve is closed and an open state in which the servo valve is open whereby a fluid may flow between the diaphragm and the valve seat, wherein the diaphragm is stiffer and/or harder than the valve seat.

Description

A SERVO VALVE

FIELD OF THE INVENTION

The present invention relates to a servo valve. In particular the present invention relates to a servo valve with a valve seat and a diaphragm which under the influence of a pressure difference causes the servo valve to open or close.

BACKGROUND OF THE INVENTION

Generally servo valves exist in which a diaphragm is movable between an open and a closed position under the influence of a pressure difference between an inlet and an outlet and/or a control chamber. One advantage of such valves is that due to a relatively simple design, the pressure difference may be used to open and close the valve. The simple design causes the valve to have a relatively low weight and low power consumption compared to conventional valves.

In servo valves, it is normally desirable that the diaphragm is as resilient as possible so as to ensure that a passage defined between the diaphragm and the valve seat is sealingly closed, when the diaphragm abuts the valve seat. However, the stiffness of such resilient materials (e.g. rubber) is limited, whereby the ability of the diaphragm to slow down the velocity of its rim portion during closing of the valve is limited. This causes the closing of the valve to produce an undesirable noise.

It is an object of an embodiment of the present invention to provide a servo valve which is designed to reduce noise associated with opening and/or closing of the valve. Moreover, it is an object of an embodiment of the present invention to provide a servo valve which allows for an increased pressure difference between the inlet and the outlet before the servo valve opens, while it is open and while closing.

DESCRIPTION OF THE INVENTION

The present invention relates to a servo valve comprising:

- a housing defining:

- a control chamber, and

- a valve passage defining an inlet, and an outlet;

- a closure arrangement which is movable between an open and a closed state, in which the valve passage is open and closed, respectively, in response to a pressure difference between the pressure in control chamber and the inlet;

wherein the closure arrangement comprises a valve seat and a diaphragm which:

- abuts the valve seat when the closure arrangement is in its closed state, and

- does not abut the valve seat when the closure arrangement is in its open state whereby a flow passage is defined between the diaphragm and the valve seat whereby fluid may flow from the inlet to the outlet; and

wherein the diaphragm is made from a material which is stiffer and/or harder than the valve seat.

It has been found that during movement of the diaphragm from the open state to the closed state, the velocity of the inner rim portion of the diaphragm increases the closer the diaphragm is to contacting the valve seat. This is due to the pressure difference which causes the diaphragm to be sucked into engagement with the valve seat. Moreover, it has been found that the higher this velocity is, the more noise the valve will produce.

Contrary to conventional servo valves, the present invention is based on a principle in which the stiffness of the valve seat and the diaphragm is reversed. This provides the advantage that the valve seat may be sufficiently soft to ensure the seal between the diaphragm and the valve seat when the valve is closed. At the same time, the diaphragm may be designed to have the desired closing speed i.e. the speed of the inner rim portion of the diaphragm while the diaphragm is brought into contact with the valve seat. This may be used to reduce the noise associated with closing of the valve.

A further advantage of providing a stiffer diaphragm is that the operating pressure between the inlet and the outlet may be increased. A reason is that increased stiffness generally is associated with increased fatigue strength which allows the valve to be designed to cope with a larger operating pressure.

The valve seat may comprise rubber such as FKM, EPDM, HNBR, NBR, TFE/P, FVMQ, PVMQ, VMQ, LSR, TPE and/or plastic such as PTFE, REEK, PFA, TFM, PE, PVDF, ECTFE.

The diaphragm may comprise a metal material such as steel or hard plastic such as PTFE, REEK, PFA, TFM, PE, PVDF, ECTFE.

It will be appreciated that the shape of the diaphragm and the valve seat are different making it difficult to determine and compare the stiffness and/or hardness of said elements. Accordingly, the stiffness and/or hardness of two elements may in some embodiments be determined by comparing two identically shaped elements, a first made from the same material as the diaphragm, and a second made from the same material as the valve seat. Such elements could be rod shaped elements or sheets of the two materials. In one embodiment, the stiffness is quantified in terms of the module of elasticity, whereby the module of elasticity of the diaphragm in some embodiments is larger than the module of elasticity of the valve seat.

In one embodiment, the module of elasticity of the diaphragm is at least 10 times larger than the module of elasticity of the valve seat, such as 50 times larger, such as 100 times larger, such as 200 times larger, such as 500 times larger, such as 1000 times larger.

In one embodiment, the module of elasticity of the valve seat is below 100 N/mm², such as below 50 N/mm², such as below 20 N/mm².

In one embodiment, the module of elasticity of the diaphragm is above 100 N/mm², such as above 200 N/mm², such as above 500 N/mm², such as above 1000 N/mm².

In one embodiment, the diaphragm is harder than the valve seat. The hardness of the valve seat and the diaphragm may be determined by means of any known methods for determining surface hardness such as ball-indentation hardness, Brinell-hardness or Shore-D-hardness.

In one embodiment, the diaphragm has a larger surface hardness relative to the valve seat, such as a surface hardness which is 20 percent larger, such as a surface hardness which is 50 percent larger, such as a surface hardness which is 100 percent larger, such as 500 percent larger, such as 1000 percent larger.

In one embodiment, the diaphragm has a ball-indentation hardness above 10 N/mm², such as above 50 N/mm², such as above 100 N/mm². Moreover, the ball-indentation hardness of the valve seat may be below 10 N/mm², such as below 5 N/mm². In one embodiment, a tubular section is defined inside by housing. The tubular section may define an inner surface which defines a conduit that is fluidly connected to the inlet and/or the outlet of the housing.

The tubular section and the housing may form a monolithic element (i.e. defining one element without seams between the housing and the tubular section). Alternatively, the tubular section may be a separate element which during assembly is inserted into the housing and fastened/mounted thereto.

The tubular section may extend in a direction transverse to an initial or final flow direction of the inlet or the outlet, respectively. By initial flow direction is meant the direction the fluid generally flows upon entering the servo valve through its inlet. Similarly, the final flow direction shall be understood as the direction the fluid generally flows upon exiting the servo valve through its exit.

In one embodiment, the outer surface of the tubular section defines a receiving zone which is adapted to receive the valve seat. The receiving zone may define a shape adapted to be engaged by the valve seat. In one embodiment, the receiving zone defines a recess into which a corresponding protrusion of the valve seat may be inserted so as to fasten the valve seat to the tubular section. The recess may extend along the outer circumference of tubular section. Alternatively, the recess extends in a longitudinal direction of the tubular section.

It will be appreciated that the valve seat may be attached to the tubular section in any other manner. As an example the valve seat may be detachably attached to the receiving zone e.g. by means of a threaded outer surface of the tubular section and a corresponding threaded inner surface of the valve seat. In order to provide an inner threaded surface of the valve seat, the valve seat may comprise an inner attachment member such as a metal ring with a threaded inner surface. In another embodiment, the valve seat is fastened to the tubular section by means of an interference fit or by means of an adhesive or by means of a locking ring or by means of a snap-lock connection.

In one embodiment, the valve seat is retained in relation to the tubular section by means of a support plate. Such a plate may comprise two abutment zones, a first adapted to abut the valve seat and a second adapted to abut another surface of the servo valve such.

The support plate may be adapted to retain the valve seat radially and/or axially relative to the tubular section. In one embodiment, the support plate is a circular disc defining a centre hole adapted to abut a corresponding circular outer surface of the valve seat so as to retain the valve seat radially.

Moreover, the circular disc may be concave such that the cavity extends from the outer rim portion of the disc and into the centre hole. In the latter embodiment, the disc may be arranged to retain the valve seat both radially and axially relative to the tubular section.

In one embodiment, the support plate defines a plurality of passages through which the fluid flows when the closure arrangement is in its open state. The passages makes is possible to arrange the support plate such that it extends across the flow channel while at the same time allowing the fluid to flow through the flow channel.

The support plate may be made of a metal material such as stainless steel or brass. In one embodiment the support plate is made from a plastic material such as PPS or PVDF.

In one embodiment, the servo valve is a servo valve with assisted lift (also called forced servo valves) in which means for forcing the diaphragm way from abutment with the valve seat is provided. Such means may be a spring. One advantage of providing such a spring is that when the pressure difference between the inlet and the outlet is small, the spring will force the diaphragm away from abutment with the valve seat and thus keep the valve open despite the low pressure difference.

DESCRIPTION OF THE FIGURES

The present invention will now be described in further detail with reference to the figures in which:

Fig. 1 discloses a sectional view of the servo valve in its closed state,

Fig. 2 discloses a close up of the zone marked "E" in Fig. 1 ,

Fig. 3 discloses a close up of the zone marked "B" in Fig. 4,

Fig. 4 discloses a sectional view of the servo valve in its open state,

Figs. 5 and 6 disclose the servo pilot nozzle arrangement according to the present invention, and

Figs. 7 and 8 disclose the valve seat according to the present invention.

Fig. 1 discloses the servo valve 100 comprising a housing 102, which defines a control chamber 104, a closure arrangement 106 and a valve passage

108,110,115 which is defined by an inlet 108 and an outlet 110 and the below described flow passage 115. In Figs. 1 and 2 the servo valve 100 is disclosed in a closed state, whereas the servo valve 100 is disclosed in its open state in Figs. 3 and 4.

The housing 102 comprises an upper part 101 and a lower part 105. The latter defines the inlet 108 and the outlet 110. The upper part 101 is fastened to the lower part 105 by means of a threaded connection and a sealing member 103, e.g. an o-ring, is provided in an area of overlap between the upper part 101 and the lower part 105. The closure arrangement 106 comprises a ring-shaped valve seat 112 (visible in Figs. 2 and 3) which is secured to a tubular section 113 of the housing 102. The tubular section 113 defines a conduit 111 with an inner surface 109 and which is fluidly connected to the outlet 110. The closure arrangement 106 further comprises a servo pilot nozzle 114 and a diaphragm 116 which are secured to each other and which are moveable between an open state - disclosed in Fig. 3 - and a closed state - disclosed in Fig. 2. In the closed state (Fig. 2), the diaphragm 116 contacts the valve seat 112, whereby no flow passage 115 is defined between the valve seat 112 and the diaphragm 116. In the open state (Fig. 3), the diaphragm 116 and the valve seat 112 are spaced apart, whereby a flow passage 115 is defined between the valve seat 112 and the diaphragm 116. When the closure arrangement 106 is in its open state, a fluid may flow from the inlet 108 through passages 136, further through the flow passage 115 and finally out through the outlet 110, as indicated by arrow 118. It will be appreciated that a small part of the fluid will flow from the inlet 108, through a throttling bore 119, further through the control chamber 104, the pilot channel 120, and into the outlet 110.

The control chamber 104 is fluidly connected to the inlet 108 by means of the throttling bore 119.

The servo pilot nozzle 114 defines an upper surface 122 which is adapted to be engaged by a closure member 124. In the embodiment of the figures, the closure member 124 is movable by means of an electromagnet (not shown) between a proximal and a distal direction, relative to the closure arrangement 106. It will be appreciated that in other embodiments the closure member 124 may be moved by means of hydraulics and/or pneumatics and/or manually.

When the closure member 124 is positioned in the distal position (i.e. in its upper position in Figs. 1-4), the closure member 124 does not abut the upper surface 122 of the servo pilot nozzle 114. In this situation, the control chamber 104 is fluidly connected to the outlet 110 via the servo pilot nozzle 114, which causes the closure arrangement 106 to move upwards until the servo valve is completely opened.

When the closure member 124 is positioned in the proximal position (i.e. in its downwards position in Fig. 1-4), the closure arrangement 106 is forced into contact with the valve seat 112, and is prevented from moving between the open and closed state. In order to bias the closure member 124 in the proximal direction a spring 125 is provided

A support plate 126 is provided for retaining the valve seat 112 in relation to the housing 102. The support plate 126 is arranged to abut an upper surface 128 of the valve seat 112 so as to force a lower surface 130 of the valve seat 112 into contact with a receiving zone 132 of the housing 102. The receiving zone 132 is defined on an outer surface 134 of the tubular section 113. The outer rim 135 portion of the support plate 126 is received in the upper part 101 of the housing 102. The support plate 126 may be fastened to the upper part 101 by means of an interference fit or by means of a locking member such as a locking ring or by being screwed into the upper part or by any other suitable fastening method. When the support plate 126 is screwed into the upper part 101 , the outer rim 135 of the support plate 126 may define a threaded surface adapted to engage a corresponding inner threaded surface of the upper part 101.

A plurality of passages 136 are provided for allowing a fluid to flow from the inlet 108 to the outlet 110, when the closure arrangement 106 is positioned in the open state.

Figs. 5 and 6 discloses a sectional view and an isometric view of the closure arrangement 106. As previously described the closure arrangement 106 comprises servo pilot nozzle 114 and a diaphragm 116. A diaphragm washer 138 is provided for retaining the diaphragm 116 in relation to the servo pilot nozzle 114. Moreover any force applied to the diaphragm 116 by the fluid is transferred to the diaphragm washer 138 due to the large abutment surface between the diaphragm 116 and the diaphragm washer 138. Figs. 7 and 8 discloses a sectional and an isometric view of the valve seat 112. As described previously, the valve seat 112 defines an upper surface 128 for abutment with the support plate 126 and a lower surface 130 for abutment with the receiving zone 132 of the housing 102.

Claims

1. A servo valve (100) comprising:

- a housing (102) defining:

- a control chamber (104), and

- a valve passage (108,110,115) defining an inlet (108), and an outlet

(110);

- a closure arrangement (106) which when the servo valve (100) is in operation mode is movable between an open and a closed state, in which the valve passage (108,110,115) is open and closed, respectively, in response to a pressure difference between the pressure in control chamber (104) and the inlet (108);

wherein the closure arrangement (106) comprises a valve seat (112) and a diaphragm (116) which:

- abuts the valve seat (112) when the closure arrangement (106) is in its closed state, and

- does not abut the valve seat (112) when the closure arrangement (106) is in its open state whereby a flow passage is defined between the diaphragm (116) and the valve seat (112) whereby fluid may flow from the inlet to the outlet

2. A servo valve according to claim 1 , wherein the module of elasticity of the diaphragm (116) is larger than the module of elasticity of the valve seat (112).

3. A servo valve according to any of the preceding claims, wherein the module of elasticity of the diaphragm (116) is at least 10 times larger than the module of elasticity of the valve seat (112).

4. A servo valve according to any of the preceding claims, wherein the module of elasticity of the diaphragm (116) is above 100 N/mm².

5. A servo valve according to any of the preceding claims, wherein the diaphragm (116) is harder than the valve seat (114).

6. A servo valve according to any of the preceding claims, wherein the diaphragm (116) has a larger surface hardness relative to the valve seat (114).

7. A servo valve according to any of the preceding claims, wherein the diaphragm (116) has a ball-indentation hardness above 10 N/mm².

8. A servo valve according to any of the preceding claims, wherein the diaphragm (116) is made from PTFE or modified PTFE and wherein the valve seat (114) is made from rubber.

9. A servo valve according to any of the preceding claims, wherein the housing (102) defines tubular section (113) the inner surface (109) of which defines a conduit (111) that is fluidly connected to the outlet (110), and the outer surface (134) of which defines a receiving zone (132) which is adapted to receive the valve seat 112.

10. A servo valve according to claim 9, wherein the valve seat 112 is attached to the receiving zone (132).

11. A servo valve according to any of claims 9 or 10, wherein the valve seat 112 is detachably attached to the receiving zone (132).

12. A servo valve according to any of claims 9-11 , further comprising a support plate (126) which is arranged to retain the valve seat (112) in the receiving zone (132).

13. A servo valve according to claim 12, wherein the support plate (126) is adapted to retain the valve seat (112) radially and/or axially relative to the tubular section (113).

14. A servo valve according to any of claims 9-13, wherein the support plate (126) defines a plurality of passages (132) through which the fluid flows when the closure arrangement (106) is in its open state.