GB2118688A - Fluid flow control systems - Google Patents

Abstract

A control system is provided for controlling fluid flow to a fluid- operated device, particularly hydraulic rams of chock-type supports of coal mining equipment. The control system comprises an electrically operable fluid flow control valve (3) operated by an electric motor (4) and a power supply (1). A d.c. motor (4) driven from the power supply (1) via a constant current circuit (5) is used, and the motor is powered in a stalled condition to hold the valve in one operational position. When the motor is switched off the valve returns to an opposite operational position. Alternatively d.c. motor (4) is driven from a local storage battery which is trickle charged from the power supply (1). The valve (3) latches in one operational position and the motor is used to drive the valve into and out of this position. In each case the valve (3) may be a ball valve. <IMAGE>

Description

SPECIFICATION Fluid flow control systems This invention relates to a control system for controlling fluid flow to a fluid-operated device.

In present day continuous mining at longwail coal faces it is common to use chock-type supports which support the roof and provide an overhead shield adjacent the face, such supports being advanced bodily together with an associated coal conveyer as the face is cut away.

These supports incorporate hydraulic rams which are usually controlled with main valves which in turn may be controlled with solenoid-operated pilot valves. In order to meet safety requirements, the operating solenoids bf the pilot valves and all associated electrical equipment, have to be "intrinsically safe" (IS), that is, in operation there should be no release of energy sufficient to give rise to any serious risk of explosion due to ignition of inflammable gases likely to be encountered in the coal mine environment (methane). It is customary therefore to operate the solenoids from a relatively low-power electrical supply, e.g. a d.c.

supply rated at say 1 2V 0.5a. However, for effective solenoid operation an appreciable current flow is required and a serious limitation is therefore imposed on the number of solenoids which can be operated simultaneously from the same power supply. Also a serious limitation is imposed in practical terms on the size of the valve orifice in so -far as larger orifices give rise to higher power requirements. Commonly therefore operating currents of the order of'say 1 25ma at 1 2V are used with valve orifices of the order of say 0.04" (0.1 cirri) diameter reduced by the presence of a push rod therethrough of say 0.035" (0.09cm) diameter giving at the worst an annular flow path of only 0.000259 ins.2 -(.0017cm2) in in area which can cause appreciable operational delays.

An object of the present invention is to provide a control system utilising an electrically operated valve which is capable of powerful, effective operation yet which requires only a relatively small operating current from an electrical supply therefor.

According to the invention therefore there is provided a control system for controlling fluid flow to a fluid-operated device, comprising an electrical power supply and an electrically operable fluid flow control valve arranged to be powered from said supply, characterised in that said valve is an electric motor-operated valve.

With this arrangement, effective operation can be obtained at relatively low power levels of said electrical supply.

It is visualised that the invention will find particular application in the context of valves for controlling flow of fluid (directly or via intermediate valves) to powerful hydraulic rams of coal mining equipment as described above, and indeed the invention may be especially suited to this application in so far as motor-operated valves can be readily made to conform to IS requirements. However, the invention is not intended to be restricted to this field of application and the control system may be used for any suitable purpose in any suitable context.

Most preferably, the electric motor is a d.c.

motor and this may be drivably connected to the valve via a suitable gearbox.

Any suitable mode of operation may be adopted for the motor. In one embodiment the valve is adapted to be held in one position by a sustained supply of power to the motor, such motor being capable of continuous actuation in a stalled position-without damage. This arrangement may be advantageous in so far as it may fail safe in the event of power failure. Particularly (although not necessarily) with this arrangement the motor may be operated at constant current conditions, and an appropriate constant current circuit may be provided in a housing of the motor operated valve.Alternatively, it is possible to use an arrangement in which a pulse of current of say 200 millisecs duration is used to drive the motor to an "on" position in which it latches and a further pulse of current (which may be of shorter duration) is used to drive the motor two an "off" position.

With regard to the valve, this may take any suitable form although in one embodiment a ball valve is used having one or more valve balls and a push rod which acts on the or each ball and which is drivably connected to the electric motor via an eccentric movable between limit positions. In the case of a latching valve, the eccentric may be arranged to stop at or slightly over dead centre whereas in a non-latching valve it may stop before dead centre.

With the control system of the invention a number of said motor-operated valves can be operated from a common power supply which may be a conventional IS supply rated to provide say 1 2V at 0.5a d.c.from an a.c. source. In the case of latching valves-where current pulses are used, a larger number of valves can be operated efficiently from the same supply by integrating their operation over a period of time. Where a sustained current is used, it may not be possible to operate many valves from the same supply, but, in so far as the power requirements are relatively low, it may still be possible to operate several (say six or seven) valves simultaneously.The motoroperated valve may be operated directly from the power supply although alternatively it is possible to use a local battery for operation purposes, which battery may be charged (e.g. continuously trickle charged) from the power supply.

Further, with the control system of the invention it can be feasible to use valves having relatively large orifices in so far as the reduced power requirement arising from the use of a motor actuator can compensate for the increased power requirement arising from the larger orifice.

Where a storage battery is used, as mentioned above, this can provide a relatively large current as and when required to operate the motor yet the power supply need provide only a relatively small trickle current to maintain the battery in a charged state. For this reason, and in so far as the power conversion efficiency of the electric motor may be higher than that of a solenoid, it is possible to achieve powerful, effective valve operation without requiring the use of a high power electrical supply, and it is feasible to operate large orifice valves from a conventional low power IS supply.

In this case preferably the arrangement is such that the motor is driven by an impulse of battery power to one position (e.g. the "on" position) of the valve and a further impulse of battery power is required to return the valve to a further position (e.g. the "off" position), a detent or other latching arrangement being provided to hold the valve in the said one position pending application of the further power impulse. Such impulses could be conveniently initiated and controlled by an appropriate switching arrangement forming part of the control system and which may be of an electrical or electronic nature and may be remotely operable.With this arrangement, in order to give a fail safe facility in the event of failure of electrical supply to the switching arrangement, the battery is preferably adapted to drive the valve from the said one position to the said further position in the event that power is disconnected from the switching arrangement. To effect stopping of the motor at angular positions corresponding to the different positions of the valve, the motor may be arranged to drive a cam switch interposed between the motor and the battery. To limit overrunning, provision may be made for applying a short circuit across the motor when it is switched off.

The invention will now be described further by way of example only and with reference to the accompanying drawings in which: Fig. 1 is a circuit diagram of one form of a control system according to the invention; Fig. 2 is an elevation of a motor-operated valve of the system of Fig. 1, with parts broken away; Fig. 3 is a sectional elevation of the arrangement of Fig. 2; and Fig. 4 is a circuit diagram of an alternative control system.

The system of Fig. 1 is for use in conjunction with a conventional chock-type powered support as used in "continuous" coal mining which is now generally applied in the case of longwall coal faces. With this mining procedure multiple chocks are disposed side-by-side in a line parallel to the coal face and alongside a coal conveyor. Each chock has an overhead shielding structure which is supported on upright hydraulic rams so as to act as a roof prop and protective cover.In use, coal is cut from the face and removed on the conveyor and, as the coal face is cut away the chocks are advanced stepwise together with the conveyor, such advancement involving a number of procedures including for example: horizontal retraction and extension of overhead shield parts, vertical retraction and extension of the upright rams to allow movement of the chock away from and up to the roof, and bodily movement of the entire chock towards the coal face. Operations of the upright rams and also of auxiliary rams which effect the other movements of the chock, are effected by feed of hydraulic fluid to such rams via control valves and operation of these valves'is controlled hydraulically with control systems incorporating pilot valves.Unlike the conventional arrangement the embodiments described with reference to the accompanying drawings utilise control systems incorporating motor-driven pilot valves rather than solenoid-operated valves.

The control system shown in Fig. 1 comprises a common electric power supply 1, a common switching control 2 and a plurality of valves 3 (only two of which are shown) each with a respective drive motor 4 and regulating circuit 5, which components are described in more detail hereinafter.

As shown in Figs. 2 and 3, each pilot valve 3, which may have an aperture of say 0.04" (0.1 cm) and may be arranged to operate with hydraulic fluid at a pressure of say 100 to 400 bar, is a three-port ball valve. The valve 3 comprises a cylindrical valve body 6 which is screwed into a solid housing 6a and has an axially extending bore 7 therethrough and three sets of passages 8.

9, 10 extending radially between the bore 7 and annular spaces which communicated with three ducts 8a, 9a, 1 Oa extending radially through the housing 6a at axially spaced positions. Within the bore 7 there is adjustably mounted an encapsulated valve assembly 11 comprising a tubular body 12 with central valve seats 13, 14 at opposite ends thereof, two balls 1 5, 1 6 movable respectively into sealing engagement with the two valve seats 13, 14 and a push rod 1 7 extending axially between the balls 15, 16. The valve assembly 11-is located within the bore 7 such that the two outermost sets of passages 8, 1 0 communicate respectively with the bore 7 beyond the two valve seats 13, 14 and the central set of passages 9 communicate with the bore 7 between such seats 13, 14. Above the valve assembly 11 a further push rod 1 8 is axially slidably mounted within a bore 21. The upper end 1 9 of this rod 18 projects beyond the top 20 of the valve body 6. The lower end 22 of the rod is of reduced diameter and projects through the top valve seat 13 for engagement with the pertaining top ball 1 5.

On the top end 20 of the valve body 6 there is mounted a motor compartment 23. This compartment has therein the pertaining regulating circuitry 5 and electric motor 4 described above.

Also, the compartment contains an eccentric 24 and a gear train 25. The eccentric 24 is fixed to a sleeve 26 which is fixed in turn to an axle 27 which is rotatably mounted between brackets 28 secured to the top of the valve housing 6a such that the periphery of the eccentric 24 engages the top end 1 9 of the push rod 18. If desired, a return spring (not shown) may be coupled to the axle 27 to urge same in one direction of rotation. The axle 27 is drivably connected via the gear train 25 to the motor 4 and a fixed stop 50 is provided for engagement with a transverse pin 51 mounted on one end of the axle 27 for limiting the rotation of the axle in each direction.

The compartment 23 is sealed and a screw socket 52 is provided to permit connection of an external cable to the internal circuitry 5 and motor 4.

The compartment further contains a manual override device comprising a leaf spring 53 which is fixed at one end and at its opposite end fits freely beneath a push rod 54 which is vertically slidable within a bore formed in the compartment structure. The push rod 54 is connected at its upper end to a button 55 which is covered by a flexible rubber boot 56. The leaf spring 53 passes over the eccentric 24 and can be moved downwardly against the resilience of the spring, by pushing the button 55 through the boot 56, to bear against and effect rotation of the eccentric 24.

The bottom set of passages 10 of the valve is connected to a source of pressurised fluid and the upper and central sets of passages 8, 9 are connected respectively to a drain outlet and to a main valve (not shown) to be hydraulically controlled by the pilot valve 3. The valve 3 may be mounted near to the pertaining main valve and the motor 4 and regulating circuitry 5 may be connected remotely to the control 2 and power supply 1 via IS leads, such remote control and supply being alongside the chock or an adjacent chock or at any other suitable position. The control 2 and/or the power supply 1 may be common to all pilot valves of a single chock or of multiple chocks as desired. In particular the control 2 may be connected to or may form part of a central electronic control system.

The power supply 1 may be of the kind conventionally used with solenoid-operated pilot valves and thus for example may be of 5V to 12.5V 0.5a rating constructed to meet IS requirements. As indicated in Fig. 1, the regulating circuitry 5 comprises a constant current circuit based on an integrated circuit 29 (e.g. i.c. type 3347) with an external resistor 30 (say 6.7 Q) which sets the value of the current (e.g. 1 Oma).

The motor 4 is a d.c. motor which may be capable of operation over a wide voltage range (say 3V to 30V) with a stalled torque which is dependent on the current and independent of the applied voltage within the operating range.

The arrangement may be such that the valve 3 is held in the "on" position when the motor 4 is powered. That is, the motor 4 drives the eccentric 24 (against any return spring) via the gearbox 25 to one limit position at which the push rod 1 8 is moved down to the lowermost position of its travel and the eccentric 24 is short of its dead centre position, such that the top seat 1 3 is closed and the bottom seat 14 is open thereby to permit flow of hydraulic fluid in through passage 10 and out through passage 9, and the motor 4 stalls in this position. Having regard to the nature of the motor 4 and the affect of the constant current circuit it is possible to hold the motor 4 in the stalled position for any required period of time without damage to the motor or any overheating or other problem likely to constitute a safety risk.

When power is disconnected from the motor 4 the push rod 1 8 rises to its uppermost position and the eccentric rotates back through slightly less than 1 800 to its other limit position at which the bottom seat 14 is sealed and the top seat 13 is open thereby permitting flow of fluid from the passage 9 to the passage 8. The push rod 18 is lifted by the fluid pressure, and rotation of the eccentric 24 is facilitated by the action of the return spring, where fitted, (especially in low pressure applications) and also by the low friction contact between the eccentric 24 and the tip 1 9 of the push rod 1 8.

It is feasible to operate number of valves 3 simultaneously from the same power supply 1 having regard to the relatively low power requirements of the motors 4, and such operation can be achieved effectively and at an acceptable speed. The actual power requirement of the motors and the speed of operation will depend upon various parameters such as the operating characteristics of the motor, the valve aperture size, the ratio of the gears and (in the case of motor speed only) the magnitude of the supply voltage.With a valve of 0.04" (o. 1 cm) orifice diameter, a miniature d.c. motor type Portescap 22 Cl 1-205 with gearbox B24 of ratio 20:1 or 32:1, a hydraulic pressure of 400 bar, and a force multiplication at the operating point due to the action of the eccentric of 1.75:1 it is possible to achieve a satisfactory valve opening and sealing force (of say 7.27 Ibs = 3,3 kg) with a current of 10 ma, and it is possible to achieve an acceptable operational speed (of the order of 0.3 secs depending on the gearbox ratio) at a supply voltage of 1 0V. With regard to the force multiplication achieved with the eccentric, the eccentric gives a sinusoidal force distribution preferably with maximum thrust positions coinciding with the limit positions of the push rod 18.

With the arrangements so far described, due to the low power requirements and constant current operating conditions, the use of remote electronic switching controls is particularly facilitated.

Moreover, due to the constant current conditions, its possible to determine the number of valves operating at any time by monitoring overall current flow.

Valves of 0.04 (0.1 cm) orifice diameter are conventionally used as pilot valves but may be disadvantageous having regard to the close manufacturing tolerances and the limitations imposed on flow rate. Larger orifice valves are also known but their use can raise problems with conventional solenoid-based systems due to the relatively high power requirement. The control system described above advantageously renders feasible the use of larger valves in so far as the increased power requirement arising from a larger valve orifice is compensated by the reduced power requirement of the motor actuator for the valve.

Thus, for example, it is possible to use an orifice diameter as large as say 0.125" (0.32 cm) with an operating current of say 580ma although this might necessitate the use (alternatively to the above described arrangement) of a storage battery alongside the motor, such battery being continuously trickle-charged from the IS supply and being switched in and out of circuit across the motor by logic pulses generated remotely and applied to electronic switching circuitry adjacent and connected to the battery and the motor. With this trickle charge arrangement it may be possible to power up to several hundred valves from the same power supply. It may even be possible to use valves of orifice diameter large enough for controlling fluid flow directly to a ram in some circumstances.

Fig. 4 shows an alternative embodiment which involves the use of a trickle-charged storage battery.

The control system shown in Fig. 4, like the system of Fig. 1, comprises a common electric power supply 1, a common switching control 2, at least one valve 3 with a drive motor 4 and connected circuit 5.

The components 1 to 4 may be as described above in relation to the system of Fig. 1 and in particular the valve and motor may be as shown in Figs. 2 and 3 and as described in relation thereto with the exceptions that a return spring need not be provided for the axle 27, and the valve 3 may be of larger orifice as discussed hereinafter.

Unlike the system of Fig. 1, the circuit 5 of the system of Fig. 4 is a battery-operating circuit 5 comprising a battery 40 which is connected to the motor via contacts of a microswitch 41 which is operated by a cam 42 driven by the motor. The battery 40 is also connected to the power supply 1 via a charging resistor 43. Between the microswitch 41 and the battery 40 there is interposed a transistor switching circuit 44-which has an input 45 thereto which is connected to the control 2.

The arrangement is such that the battery 40 is continuously trickle-charged from the power supply 1 at a very low current level (say 1 ma).

When a positive control signal is first applied by the control to input 45, (with the microswitch 41 in the "off" position as shown in the drawing), transistor T1 of the circuit 44 is switched on and the motor 4 is powered by the battery 40 causing the eccentric 24 to rotate (through 1800) via the gearbox 25 to one limit position at which the push rod 18 is moved down to its lowermost position of its travel and the eccentric 24 is at its dead centre position such that the top seat 1 3 is closed and the bottom seat 14 is open thereby to permit flow of hydraulic fluid in through passage 10 and out through passage 9.At the same time, the cam 42 is rotated to a position at which it operates the microswitch 41 to disconnect the transistor T1 from the motor and instead to connect the collector of transistor T2 thereto. If the signal is still applied to input 45, transistor T2 is turned off via transistor T3 (which is held on by the signal) and the motor thereby remains disconnected from the battery. If the signal is removed from input 45, T3 is turned off, T2 is turned on and the motor rotates through a further 1 800 to the "off" position shown in the drawing.During this further rotation, the push rod 1 8 rises to its uppermost position (due to the action of the pressure fluid in passage 10) and the eccentric rotates through 1 800 to its other limit position at which the bottom seat 14 is sealed and the top seat 1 3 is open thereby permitting flow of fluid from the passage 9 to the passage 8. It will be seen therefore that the valve returns to the "off" position either when the signal is removed intentionally from input 45 due to a control operation, or when the signal is removed due to failure of the power for the control 2. The system therefore fails safe.

The battery-operating circuit may also include an arrangement of two transistors T4, T5 connected across the motor 4. When the motor 4 is running T5 holds T4 off because the base of T4 is biased positive by the battery supply. When the motor is switched off with the microswitch 41, the back e.m.f. generated by the motor appears across T4, but the base of T5 is isolated by diode 46 and T5 therefore turns off and T4 turns on forming a low resistance shunt path across the motor which applies a powerful braking torque.

With the arrangement described above the signal current (applied to input 45) is of the order of a few milliamps. Also, the charging current continuously drawn by the battery 40 is of the order of a few milliamps. Accordingiy, the power consumption can be kept to a very low level and it is possible to operate many valves from the same low power IS supply. On the other hand, however, large operating currents can be drawn when required from the battery and powerful effective valve operation can therefore be achieved. In particular, it is feasible to operate a relatively large orifice valve. For example, a valve of 0.1" (.25 cm) orifice can be operated using a battery with an onload terminal voltage of 7V and a three-ohm limiting resistor, in the case of a miniature d.c.

motor type Portescap 22 Ci 1-205 with gearbox 824 of ratio 20:1 or 32:1, a force multiplication at the operating point due to the action of the eccentric of say 1.75:1 and an operating speed of say 0.266 secs or 0.166 secs depending on the gearbox ratio. Moreover, figures of this order can be achieved even using a relatively slim push rod 1 8 (or even with an arrangement omitting the push rod).

Moreover, the motor and battery-operating circuitry can be readily made to meet IS requirements. In this respect it will be noted that the charging resistor 43 and input resistors 47, 48 are interposed between external electrical connections and the charging circuit and the transistor switching circuit, and these resistors can be of high value to ensure adequate power isolation. if a very high power valve is to be operated, a more powerful battery without a limiting resistor may be used and in this case the battery and motor may be housed in a flameproof enclosure with IS charging and control inputs.

It is of course to be understood that the invention is not intended to be restricted to the details of the above embodiments which are described by way of example only. Thus, for example, with the embodiment of Fig. 4, although the valve is described as being a pilot valve, the valve may be of sufficiently large orifice to be used as a main control valve directly connectable to a ram. Also, the transistor circuits may be replaced by suitable i.c. gates so that operating currents can be reduced to a few microamps.

Further, in so far as the power take-off is low over a relatively long period (e.g. two years), it may be appropriate to use a battery as the sole power source (i.e. without any trickle-charging circuit).

Also, if desired, a manual override may be provided on the eccentric to move same from top dead centre to bottom dead centre.

Claims (17)

1. A control system, for controlling fluid flow to a fluid-operated device, comprising an electrical power supply and an electrically operable fluid flow control valve arranged to be powered from said supply, characterised in that said valve is an electric motor-operated valve.

2. A control system according to claim 1, characterised in that said electric motor is a d.c.

motor.

3. A control system according to claim 2, characterised in that said motor is arranged to be operated at constant current conditions.

4. A control system according to claim 3, characterised in that a constant current circuit is provided in a housing of the motor-operated valve.

5. A control system according to any one of claims 1 to 4, characterised in that said motor is drivably connected to the valve via a gearbox.

6. A control system according to any one of claims 1 to 5, characterised in that said valve is adapted to be held in position by a sustained supply of power to the motor with said motor in a stalled condition.

7. A control system according to any one of claims 1 to 5, characterised in that a pulse of current is used to drive the motor to an on position in which it latches and a further pulse of current is used to drive the motor to an off position.

8. A control system according to any one of claims 1 to 7, characterised in that said valve comprises a ball valve having one or more valve balls and a push rod which acts on the or each ball and which is drivably connected to the electric motor via an eccentric movable between limit positions.

9. A control system according to claim 8, when dependent on claim 7, characterised in that the eccentric is arranged to stop at or slightly over dead centre for latching purposes.

1 0. A control system according to any one of claims 1 to 9, characterised in that the motoroperated valve is arranged to be operated directly from said power supply.

11. A control system according to any one of claims 1 to 9, characterised in that the motoroperated valve is arranged to be operated from a storage battery which is adapted to be charged by said power supply.

12. A control system according to claim 11, when dependent on claim 7, characterised in that said current pulses are initiated and controlled by a switching arrangement forming part of the said control system.

13. A control system according to claim 12, characterised in that said battery is arranged to drive the valve from the said one position to the said further position in the event that power from the said power supply is disconnected from said switching arrangement.

14. A control system according to claim 12 or 13, characterised in that said motor is arranged to drive a cam switch interposed between the motor and the battery for use in stopping the motor at required angular drive positions thereof.

1 5. A control system according to any one of claims 12 to 14, characterised in that provision is made for applying a short circuit across the motor when it is switched off.

1 6. A control system substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

17. Mining equipment operated by hydraulic rams, characterised in that flow of hydraulic fluid to said rams is controlled with a control system according to any one of claims 1 to 16.

1 8. Coal mining equipment according to claim 1 7, which comprises mine roof supports, said rams being incorporated in said supports.