GB2033053A - Normally closed valve assembly - Google Patents

Abstract

A modulating two stage valve and compensator assembly comprises a first stage poppet 23 movable between a normally closed state seating in a first stage orifice 25a and an open state, for controlling flow of fluid through a passage 25e-25g in a second stage poppet 25. The poppet 25 moves between an open state and a closed state seating in and closing a second stage orifice 35a when the first stage poppet 23 is in the normally closed state thereby to prevent any substantial flow of fluid through the first and second orifices. Electromagnetic means has applied thereto a predetermined value electrical signal for moving the first stage poppet 23 to an open position related to the value of the electrical signal. The resultant drop in pressure behind the second stage poppet 25 causes it to move to a position which is a function of that signal value. The end 12b of a fixed core of the electromagnet is recessed to receive an armature 20 attached to the poppet 23 and has a cross- section which tapers towards the poppet. <IMAGE>

Description

SPECIFICATION Background of the Invention A. Field of the Invention This invention relates to the field or proportional control valves.

B. Prior Art Proportional control valves are well known in which a valve assembly is used to modulate fluid flow in accordance with a selected value electrical signal. However, such proportional valves have left much to be desired in the efficient use of energy, particularly when the operating system is maintained over a period of time at a null. Some of these prior systems have required a continuous fluid flow to maintain the null position. In other prior systems, fluid would leak during null, since these systems were not able to achieve a substantially tight shutoff. When the systems were required to be in a null state for an extended period of time, a substantial amount of wasted power, or inefficiency in operation would thus result.

Accordingly, an object of the present invention is a normally closed modulating valve system which achieves a substantially shut tight shutoff during the normally closed state, thereby to conserve energy.

Summary of the Invention A normally closed two stage electrohydraulically operated valve assembly for modulating fluid flow in accordance with electrical signals of predetermined value. A first stage poppet means is movable between a first stage normally closed state in which it seats in and closes a first stage orifice and a first stage open state for controlling flow of fluid through a second of the stages. A second stage orifice forms an outlet for the valve assembly. Second stage poppet means is movable between (1) a second stage open state and (2) a second stage closed state seating in and closing the second stage orifice when the first stage poppet means is in the first stage normally closed state thereby to prevent any substantial flow of fluid through the first and second orifices.Electromagnetic means has applied thereto the electrical signals for moving the first stage poppet means to a predetermined open position which is related to the value of the electrical signal and in this manner, the second stage poppet means moves to a position which is also a function of the electrical signal value.

Brief Description of the Drawings Figure 1 is a perspective view of a normally closed two stage electrohydraulically operated valve and compensator assembly of the present invention; Figure 2 is an elevational sectional view of the assembly of Fig. 1 taken along lines 2-2 in the valve normally closed state; Figure 3 is an exploded view of the valve elements of the two stage valve assembly section of Figs. 1 and 2; and Figures 4A-C show a sectional view of a portion of the two stage valve assembly of Fig. 3 in a normally closed position, a valve partially open position, and a valve fully open position, respectively.

Detailed Description Referring to the drawings, modulating two stage valve and compensator assembly 10 is a normally closed electro-hydraulic device designed to provide modulation of fluid flow to an associated hydraulic motor in response to a variation in voltage applied to the valve's electromagnet 40. In a typical application assembly 10 may control the reel speed of a harvester combine (not shown). As described for example, in our copending application Serial No. 705,920 filed July 16, 1976 for Feathering Valve Assembly, control voltage may be sensed from a potentiometer 40a or it may be a function of combine ground speed, as sensed by a conventional tachometer.

Valve assembly 10 comprises in general a body 11 housing, on one side, a two stage valve assembly 1 Oa and, on the other side, a compensator mechanism 14 that is effective to provide a fixed pressure drop across the second stage orifice 35a.

The detailed construction of modulating two stage valve assembly 1 0a is shown in Figs.

1-3. Valve assembly 10a comprises a tubular sleeve assembly or housing 1 2 having threads 1 2a formed on the outer surface of a lower sleeve section 12d. Threads 1 2a engage upper internal threads 11 a of a valve body 11.

Sleeve assembly 1 2 comprises the lower sleeve section 12d, a middle sleeve section 12c, and an upper sleeve section 12b. Sections 1 2b and 1 2d are made of very high magnetically permeable material which is defined as ferromagnetic. On the other hand, section 1 2c is made of very low magnetically permeable material, such as for example, stainless steel and is described, for example, in U.S. patent nos. 3,737,141; 3,903,919 and 3,977,649. As shown, sections 12b-d are rigidly secured together, as for example, by welding.

It will be noted from Figs. 2 and 4A-C that the lower (pole piece) extremity of section 1 2b is tapered inwardly and downwardly at approximately 20 with respect to the vertical inner wall of chamber 1 6 where it joins section 12c. Stated differently, the taper decreases in a direction towards armature 20 in a normally closed position.A purpose of the taper is to permit the armature 20 to have a relatively long stroke, as compared to the stroke that would be possible with nonmagnetic section 1 2c extending horizontally level with the face of pole piece 1 7. Another and important purpose of the tapering of section 1 2b is to provide a substantially linear relationship between an applied modulating voltage and the position of poppet 23.

In the situation where section 1 2c extends level with the pole piece face, for the desired long stroke, upper face 20c of armature 20 would be too distant from pole piece 1 7 to be attracted thereto, since the air gap is large.

With the tapered magnetic section (tapered section of very high mangetically permeable material) energized, however, there is sufficient electromagnetic force to begin upward travel of armature 20. As the armature moves upward, the axial force on it is somewhat diluted by the increasing attractive radial force of the tapered section. However, the design of the pole piece 1 7 and tapered magnetic section is such that sufficient force is provided to bring armature 20 up to its maximum uppermost travel position (shown in Fig. 4C). This provides a substantially long armature stroke with a substantially linear relationship between the value of the electrical signal and the position of armature 20 and, thus, poppet 23.

It will be understood that under normal conditions, if the nonmagnetic section 1 2c were level with face 17, then armature 20 would have the tendency to move from its lowermost to its uppermost position in a single movement rather than making the desired change in position as a substantially linear response to an electrical signal. The reason for this is that electromagnetic force increases with respect to the inverse of the square of the distance, while spring force is substantially linear with respect to distance. Accordingly, if the electromagnetic force were raised sufficiently to attract the armature and to overcome the spring force, once the armature began moving, the increase in electromagnetic force with respect to spring force would have the tendency to cause the armature to immediately reach its uppermost position.

Sections 1 2b-d together provide an internal cylindrical chamber 1 6 for housing tubular armature 20 and a tubular stop 22. Armature 20 has a cylindrical central chamber 20a and a reduced inner diameter section 20b. Stop 22 has a cylindrical central chamber 22a coaxial with chamber 20a. Armature 20 is slideably received within chamber 16, with the upper portion thereof being within section 1 2c and the lower portion thereof being within section 12d. A tetrafluroethylene (Teflon) sleeve 24 surrounds armature 20 to reduce friction. Stop 22 nests in chamber 1 6 with a lower flange 22b of stop 22 engaging a lip formed in chamber 1 6.

Located axially within chambers 20a and 22a is a poppet 23. Poppet 23 may be formed in one piece having a lower portion 23a and intermediate or guide portion 23b and an upper portion 23c. Lower portion 23a terminates in a valve plug 23d. Guide 23b has side walls which contact and slide within chamber 20a and are dimensioned to assure proper alignment of plug 23d into and out of an orifice 25a formed in the top face 25b of second stage poppet 25. A lower shoulder 239 of guide 23 is engaged by reduced section 20b when armature 20 moves upwardly. Section 20b has a larger inner diameter than the outer diameter of poppet portion 23a to avoid contact therebetween.

A spring 30 is disposed between and engages the upper wall or pole piece 1 7 of chamber 1 6 and the upper shoulder of guide 23b. The compressive effect or bias of spring 30 on poppet 23 will later be descrbed. It will be understood that in the normally closed position shown in Figs. 2 and 4A, armature 20 is free to move between shoulder 23g and stop 22.

It will also be understood that the upper end 23f of poppet 23 does not engage wall of pole piece 1 7 in the full open position as shown in Fig. 4C; on the other hand, the upper end 25b of second stage poppet 25 does engage the lower face of stop 22. The reason for this is to avoid peening of the poppet seat in orifice 25a as a result of continual impacting by poppet plug 23d. Located in a reduced section of the bore in valve body 11 is a pressed-in bushing 26 forming a guide for second stage poppet 25. Poppet 25 is equipped with an O-ring 25c, which is received between the poppet and bushing 26 to prevent flow from chamber 32 to port 62.

An axial passage 25e connects the orifice 25a, which in a typical example may measure about 0.041 inch, to a transverse passage 259 located just above the tapered plug end 25f. Passages 25e and 25g form an L-shaped path for the flow of fluid through second stage poppet 25.

The minor diameter 35 of the bore in valve body 11, which is in fluid communication with chamber 36, passage 64 and port 62, forms at its upper end an orifice 5a for second stage poppet 25. Chamber 36, sealed at its lower end by a plug 68, is in fluid communication by way of cross passage 54 with the lower section of compensator chamber 14d.

Chamber 32, sealed by a plug 32a, is also in fluid communication via orifice 38 and passages 54a and 54 with compensator chamber 14d.

Outlet port 62 communicates via cross passage 64, line 56, and orifice 56a with the upper end of compensator 14. A downward extension of line 56 communicates via line 60 with a load sensing port 58. A spring loaded ball 66 located at the junction of lines 56 and 66 acts as a one way valve to prevent backflow from port 58. Port 58 is adapted to be coupled to a load sensing pump (not shown).

For a source of magnetic flux, there is provided a hollow elongated cylindrically shaped electromagnet 40, which receives in a central opening sleeve assembly 1 2. A cupshaped cover 42 encloses and protects electromagnet 40, extends down to valve body 11, and encloses an upper portion thereof.

Cover 42 has a central opening for receiving therein an upper threaded portion 1 2e of sleeve section 12b. Cover 42 is secured in place by a nut 43 which threadedly engages the threads of portion 12e. Cover 42 as well as armature 20, poppet 23 and body 11 are formed of high magnetically permeable material (ferromagnetic). The circuit of magnetic flux lines produced by electromagnet 40 when energized may be traced as follows. The flux lines flow down through sleeve section 1 2b and then from pole piece surface 1 7 through air gap 45 to armature 20 and poppet 23. The flow continues from armature 20 and poppet 23 to sleeve section 12d, body 11 and cover 42, with the circuit being completed to section 1 2.

As illustrated in Figs. 2 and 4A, valve 10 is in a normally closed state. Spring 30 is providing a bias of about 2 pounds to maintain poppet 23 seated in orifice 25a and thereby also maintain second stage poppet 25 seated in orifice 35a. Pressure is applied through inlet 50, passage 52, compensator chamber 14d, and passage 54 to chamber 36, and thence to orifice 35a, closed by plug 25f of second stage poppet 25. Pressure is also simultaneously applied via passage 54a and orifice 38 to chamber 32. It will be understood that in the closed state of valve 10, there is no pressure in port 62, and therefore, no pressure applied to the upper end of compensator spool 14b, via passages 64, 56 and orifice 56a. Spool 1 4b will therefore be positioned by inlet pressure acting against spool biasing spring 1 4a only.Compensator 14 is described in detail for example, in our copending application Serial No. 842,264.

Consider now the situation when a voltage is applied to the electromagnet 40, for example, an intermediate voltage, as determined, for example, by the setting of controlling potentiometer 40a. Upon initial energization of electromagnet 40, the magnetic flux lines are effective to produce an attractive force between pole piece 1 7 and the upper annular surface 20c of armature 20 sufficient to begin moving armature 20, and thus poppet 23, to an intermediate position, as shown for example in Fig. 4B. As poppet plug 23d is partially withdrawn from orifice 25a, fluid is permitted to flow through this orifice, through axial passage 25e, transverse passage 25g and thus to port 62.The resultant drop in pressure across orifice 38 now reduces the pressure in chamber 32 below that in chamber 36, thus causing second stage poppet 25 to move upward until it reaches a point of equilibrium somewhere between fully closed and fully open. When this position is reached, pressures in chambers 32 and 36 are substantially equal. Pressure in port 62 is now communicated to the upper end of compensator spool 14b, via passages 64 and 56, and orifice 56a, where it is effective to augment the bias of spring 1 4a acting on spool 1 4b and thus pressure-compensate flow from inlet 50. At the same time, this pressure from port 62 is also applied to load sensing port 58 via line 56, one way valve 66 and line 60.

As increasing voltage is applied to the electromagnet 40 by the potentiometer or tachometer, the poppet 23 is attracted further upward until a sufficient value of signal is applied to cause poppet 23 to reach its upper limit, as shown in Fig. 4C. Second stage poppet 25 moves upward also in response until pressure equilibrium between chambers 32 and 36 is again established; in practice the distance between plug 23d and orifice 25b is substantially maintained. In this manner, for all open positions of poppet 23, poppet 25 follows with a substantially small separation between plug 23d and orifice 25b.

In this way, the second stage acts as a follower amplifier with the moving seat 25a following pilot poppet 23.

As previously described, there is a substantially linear relationship between the applied electrical signal value and the position of first stage poppet 23. As a result, there is a similar substantially linear relationship between that signal and the position of second stage poppet 25 which produces between input and output a modulation of fluid flow directly responsive to the change in applied electrical signal value. Removal of voltage from electromagnet 40, either by turning of switch 40b to the off position or by a fault condition, causes collapse of the magnetic field surrounding armature 20, permitting bias spring 30 to reassert its force to lower poppet 23 and close orifice 25a, which in turn drives second stage poppet 25 to its closed position, effectively cutting off all flow to output port 62.

An important advantage of valve assembly 10a is its ability to provide a normally closed assembly with a fine degree of (pilot) modulation of flow using only a single solenoid. This is made possible by a combination of features: First the construction of the sleeve assembly 1 2 in which the armature 20 slides. By interposing a nonmagnetically permeable section 1 2c between two highly permeable sections 1 2b and 1 2d and by tapering the joining surfaces of 1 2b to 12c, a long armature stroke, responsive to variations in voltage applied is provided.This taken in conjunction with the two stage sequence afforded by two poppets assemblies 23 and 25 operating in tandem, and with the second stage poppet also embodying the orifice 25a plugged by the first stage poppet assembly 23, provides not only a relatively simple means of modulating fluid flow in fine gradations, but also gives a positive, tight and instant shutoff of flow when the solenoid is deenergized (either by control switch action or by a failsafe feature in the control system) and the valve assembly 1 0a returns to its normally closed position.

This substantially tight shutoff during the normally closed state is effective to prevent any substantial flow of fluid through valve assembly 1 0a and thus prevent any substantial waste of fluid energy. In this manner, valve assembly 1 0a is very efficient of energy by achieving a substantially zero fluid flow in the normally closed state. Also contributing to this modulation capability is the action of the compensator assembly 14, which uses output port 62 pressure to establish the position of a spool 14b, which in turn regulates the flow from inlet port 50.

Claims (7)

1. A normally closed electrohydraulically actuated valve assembly for modulating fluid flow in accordance with predetermined value electrical signals comprising a pilot orifice a pilot poppet movable between a normally closed state seating in and closing the pilot orifice and an open state for controlling flow of fluid through the pilot orifice.

an armature for engaging the pilot poppet, and electromagnetic means for slidably receiving the armature and having a tapered magnetic section thereby to provide substantially long stroke for the armature and the pilot poppet, the electromagnetic means having applied thereto the predetermined value electrical signal for moving the armature which engages and moves the pilot poppet to a predetermined open position related to the value of the electrical signal.

2. The assembly of claim 1 including an additional stage having an additional orifice and poppet, the pilot orifice being formed on an upper surface of the additional poppet whereby the additional poppet follows the pilot poppet throughout the open state to provide a substantially small separation between pilot poppet and additional poppet.

3. The assembly of claim 2 in which the electromagnetic means has a housing and the tapered magnetic section is of very high magnetically permeable material within a wall of the housing with a decreasing taper toward the armature in the normally closed state to provide an increasing attractive electromagnetic radial force as the armature moves the poppet towards an increasingly open position.

4. The assembly of claim 3 in which there is provided a tetrafluoroethylene sleeve on the outer surface of said armature means thereby to reduce friction between said armature means and said housing means.

5. The assembly of claim 4 in which there is provided means for sensing the pressure of said fluid flow through said second orifice thereby to provide a load sensing response.

6. The assembly of claim 5 in which the pilot poppet includes a guide section and in which the armature includes a reduced inner section which engages the guide section when the armature within the housing.

7. A normally closed electrohydraulically actuated valve assembly substantially as herein before described with reference to the accompanying drawings.