GB2201234A - Ejector release unit and fluid flow dividing valve for the unit - Google Patents

Abstract

In an ejector release unit for a load suspended beneath an aircraft, hydraulic fluid at high pressure is arranged to be supplied from a source 3, Fig 1, to a pair of ejector pistons 9, 10 through a flow dividing valve 6 which controls the ratio of the two flows to the ejector pistons so that the ratio is maintained substantially constant throughout the stroke of the pistons, irrespective of the actual pressure of the fluid supplied to the pistons. For this purpose the flow dividing valve comprises a pair of adjustable metering orifices 19, 20, Fig 2, dividing the flow from the supply means 3 in a predetermined ratio, and control means which is sensitive to a difference in the pressures of the two fluid flows downstream of the metering orifices and is operative, preferably through a servo device, to equalise the two pressures. <IMAGE>

Description

1EDIQR > ELSSi UNLSD ELUID~ELi ING VALi FOR TH UNI: The invention relates to an ejector release unit for ejecting a bomb, rocket, or other similar weapon (hereinafter referred to as a load) from a modern strike or fighter aircraft, and to a fluid flow dividing valve suitable for use in the unit.

The load is- usually carried in a rack mounted on the underside ofthe aircraft so that it is held substantially horizontally in a forwardly facing position when the aircraft is flyin-g level, and it is usual to fit the- rack with an ejector release unit operative so that when the load is released it is also given a positive downward thrust to eject it clear of the aircraft airstream and its surrounding boundary layer. This greatly reduces the risk of the load colliding with either the aircraft or another simultaneously released load.

Usually the ejector release unit comprises a pair of ejector pistons which are held in a retracted position in engagement with the load at positions fore and aft of the centre of gravity of the load when it is held in the rack, and which are arranged --to -be highly pressurised simultaneously with the release of the load. In most existing units, the ejector pistons are arranged to be pressurised by separate similar pyrotechnic cartridges fired simultaneously, but without any real control of the acceleration and velocity of the pistons to compensate for aerodynamic load differences and centre of gravity displacements it is common for loads to separate from the ejector pistons with varying downward velocities fore and aft, and hence uncontrolled rotation.

Such units are now generally thought to be inadequate to meet future requirements.

Ideally the load should leave the ejector pistons either with substantially equal velocities fore and aft so that there is effectively no angular velocity, a condition which is sometimes referred to as pitch stiff", or with controlled different velocities to provide the load with a predetermined desired angular velocity.

Towards this end, an ejector release unit has been developed which makes use of a single pyrotechnic cartridge or other source of high pressure gas to drive a hydraulic piston accumulator having two equal active areas arranged to supply fluid under pressure separately to the two ejector pistons.

Control of the ejector piston velocities to compensate for expected aerodynamic and inertial forces during ejection, i.e. pitch control, is achieved by controlling the pressures of the fluid supplies to the ejector pistons in accordance with a predetermined setting. However, because th-is unit is pressure dependent, its pitch performance is very reliant on accurate location of the load centre of gravity. Also, the size and weight of the unit are a problem.

According to our invention there is provided an ejector release unit comprising a pair of load ejector pistons, means for providing fluid at high pressure for supply to the ejector pistons to acceierate the pistons quickly from their retracted rest position, and a flow dividing valve through which the fluid passes to the two ejector pistons and which includes means for controlling the ratio of the two flows to the pistons so that the ratio is maintained substantially constant throughout the stroke of the pistons.

By ensuring that the operating fluid is supplied to the ejector pistons in a substantially constant ratio, irrespective of pressure variations in the flows, the ratio of the ejector piston velocities will also be maintained substantially constant The fo-re and aft load velocities are therefore controlled in a de-sired manner, determined by the flow ratio set by the flow dividing valve, and the unit is much less sensitive to external load pressure variations and to the location of the load centre of gravity than the known units mentioned earlier.

Preferably the flow dividing valve comprises a pair of metering orifices, preferably adjustable in area, for dividing the flow from the supply means in a predetermined ratio, and control means which is sensitive to a difference in the pressure of the two fluid flows downstream of the metering orifices and is operative to equalise the two pressures. In this way the pressure drop across each metering orifice will be maintained substantially the same as that across the other, with the result that the ratio of fluid flow through the two orifices will be maintained substantially constant and in proportion to the ratio of their areas.

Preferably the control means comprises a pair of regulating orifices through which the two fluid flows are arranged to pass, and a regulating spool which controls the areas of the regulating orifices and is movable in response to a pressure difference between the flows upstream of the regulating orifices to increase the area of the regulating orifice of the flow at the higher pressure and to decrease correspondingly the area of the other regulating orifice, the spool being biased to adopt a neutral position in which the areas are equal when the flow pressures are equal.

In one arrangement the opposite ends of the spool are fitted with equal area pistons, each of which is located in a control chamber in communication with the flow pressure upstream of the corresponding regulating orifice. In this case any pr-essure difference between the two flows acts directly on the spool. However, with the size and weight criteria which are likely to be set for future ejector release units, the possible area of the spool end pistons will be limited and it is possible that relatively small pressure differences will be insufficient to overcome the flow forces which may be generated during operation. These can largely be avoided by making the flow paths through the valve substantially symmetrical, but will nevertheless be present if the loading on the ejector pistons is unequal.

Preferably therefore, the flow dividing valve of the ejector release unit in accordance with the invention is provided with a servo device for assisting the movement of the regulating spool in response to a pressure difference between the flows upstream of the regulating orifices.

In this case the control means preferably includes means communicating the flow pressures upstream of the regulating orifices as inputs to the -servo device, which is operative to provide outputs having a pressure difference which is amplified in proportion to the difference between the input pressures, and the opposite ends of the spool are fitted with equal area pistons located in control chambers which are connected to receive the servo outputs.

Such an arrangement provides a valve which is highly responsive, even at the high pressures and flow rates existing during the short operating time of the ejector release unit (for some loads the total ejection time may be in the region of 40 to 60 milliseconds only), and possesses excellent static accuracy. Also, the very fast and accurate response of the valve will tend to minimise undesirable dynamic effects as well.

Such a valve may well have use in other applications, and according to a further aspect of the invention therefore, there is provided a fluid flow dividing valve comprising means for dividing an input flow in two in a preseter,mined ratio, and servo assisted control means which is sensitive to a difference in the pressures of the two fluid flows downstream of the dividing means and is operative to equalize the said pressures whereby the flow ratio of the two output flows is maintained substantially constant.

Further preferred features of the invention will become apparent from the following description which is of particular examples of the ejector release unit and flow dividing valve in accordance with the invention and is with reference to the accompanying drawings, in which: Figure 1 is a diagram illustrating the principle of an ejector release unit in accordance with the invention; Figure 2 is a diagrammatic-section through one example of a flow dividing valve which may be used in the ejector release unit of Figure 1; and Figure 3 is a schemmatic flow diagram of an alternative form of flow dividing valve which may be used in the ejector release unit.

.Xs The ejector release unit illustrated in Figure 1 comprises acompressed gas source 1 connected by a normally closed solenoid valve 2 to one end of a hydraulic piston accumulator 3 and also to the cylinder of a load release piston 4. The output from the piston accumulator 3 is connected by a line 5 to a flow dividing valve 6 having two outputs connected by lines 7 and 8 to the cylinders of a pair of load ejector pistons 9 and 10 respectively. These pistons 9 and 10 are biased towards a retracted rest position by retractor springs 11 and 12 respectively, -and are held -in this position with their leading ends in contact with the load substantially equidistant fore and aft of the load ce-ntre of gravity when a load 13 is being carried. The load is held by claws or hooks (not shown) which are arranged to be released by operation of the load release piston 4.In flight the release piston 4 is operated in response to closure of the actuating valve 2, and at the same time the piston accumulator 3 is operated to drive hydraulic fluid through the dividing valve 6 to the ejector pistons 9 and 10 so that these pistons are driven very rapidly to eject the released load from the rack. The fluid pressure supply means 1 and 3 (which may be replaced by a conventional bladder accumulator), the load release piston and the ejector piston assemblies may be of conventional construction and will not therefore be described in further detail.

The important component of the ejector release unit is the flow dividing valve 6, which is designed to ensure that fluid is supplied to the ejector pistons 9 and 10 in a substantially constant predetermined ratio determined in accordance with the expected aerodynamic and inertial parameters affecting the load during its release and ejection. If the ratio of the fluid flows to the ejector pistons is kept constant, the ratio of the resulting piston velocities'will also be constant throughout their stroke and the load will be ejected in the desired controlled manner.

As will be appreciated, in order to operate effectively, the valve 6 must have a very fast and accurate response to any pressure changes in the fluid flows to the ejector pistons which would change the flow ratio.

A basic example of a flow dividing valve 6 suitable for use in the ejector release unit is shown in Figure 2. The valve has a single inlet port 14 opening centrally into a transverse passage 15 housing an adjuster spool 16 having a pair of control edges 17,18 co-operating with two outlet openings from the passage 15 to form two metering orifices 19 and 20 respectively. The adjuster spool 16 is movable axially in the passage 15 to vary the areas of the metering orifices 19 and 20, movement of the spool in one direction increasing the area of one of the orifices while correspondingly decreasing the area of the other, and vice versa.Consequently the area ratio of the metering orifice-s 19 and 20 necessary to achieve a desired output flow ratio from the valve is set by suitable adjustment of the spool 16, for which purpose an adjuster rod projects from one end of the spool through the wall of the valve. This may be adjusted manually when the load is fitted to the rack prior to flight, but the opportunity exists for pilot or computer controlled in-flight adjustment through a suitable electrohydraulic or electromechanical adjuster rod drive mechanism.

In an alternative arrangement, which may be preferred for units required to operate with very high flow rates and/or where weight is to be kept to a minimum, the metering orifices may be formed by a pair of fixed area apertures each operating in parallel with a small adjustable area aperture for controlling the effective total area of each metering orifice and hence their area ratio. The adjustable area apertures may be controlled by a spool in a similar manner to that described above, but in this case the dimensions of the spool needed will be much smaller.

The metering orifices 19 and 20 lead into a pair of passages 22,23 which in turn open into a pair of regulating chambers 2tri,25 defined by a regulating spool 26 - which is axially slidable within a further passage 27 within the valve body.

The regulating chamber 24 is located between one end portion 28 of the spool and a central portion defining a control edge 29 co-operating with an opening in the wall of the passage -27 to define a regulating outlet orifice 30 leading to an outlet port 31 of the valve. Similarly, the regulating chamber 25 is located between the opposite end portion 32 of the spool and a central portion of the spool forming a control edge 33 which co-operates with a further opening in the wall of the passage 27 to define a regulating outlet orifice 34 leading to a second outlet port 35 of the valve. One end 36 of the passage 27 is blind and the other end is closed by an axially adjustable stop 37. Between each end 36,37 of the passage and the corresponding end portion 28,32 of the spool is a chamber 38,39 containing a centering spring 40,41.These springs serve to centre the spool between the ends 36,37 of the passage when the pressures in the chambers 38 and 39 are equal, each chamber being in communication with its corresponding regulating chamber 24,25 via a throttled passage 42,43 respectively through 'the spool 26 itself, and the end stop 37 is adjusted so that under these conditions the areas of the regulating orifices 30 and 34 are equal.

The valve 6 operates as follows. Assuming the areas cf the metering orifices 19 and 20 are set to be equal, then the flows of fluid through the metering orifices and the regulating or-ifices 30,34 to the outlet ports 31,35 will also be equal provided the pressures in the passages 22 and 23 are equal. However, if for example an external force on the actuator piston served by the outlet port 31 causes the pressure in the flow to that pi piston to increase, the pressure in the passage 22 will also increase causing the rate of flow through the metering orifice 19 to decrease.

The pressure increase in the passage 22 is communicated via the duct 42 with the chamber 38, thus changing the force balance on the spool 26 which accordingly moves from left to right as shown in Figure 2 such that the area of the regulating orifice 30 increases and that of the regulating orifice 34 decreases. This reduces the restriction to the fluid flow through the regulating chamber 214 and increases the restriction to the flow through the regulating chamber 25, with the effect that the pressure in the passage 22 starts to decreases and that in the passage 23 starts to increase. The spool 26 continues to move until the pressures in these passages are equalised at a level slightly higher than before, at which time the rates of flow through the outlet ports 31 and 35 are again equal but at a lower absolute value than before.

As will be appreciated, whenever the pressure in either of the passages 22 and 23 increases or decrease relative to the other the valve will operate to equalise the pressures at a level which is slightly higher or lower than before, thus maintaining the output flow rates substantially equal to each other but not necessarily at the same absolute value. Unlike a pressure compensated flow control valve the divider valve 6 does not control the absolute value of the flow, only the flow ratio. The absolute value is determined by the load. In an unregulated system the ejector piston with the least external load would extend at a higher velocity. By controlling the relative velocities of the ejector piston, the valve ensures effective load sharing between them.

As will be appreciated from the drawing, the flow paths through the valve 6 are sub-stantially symmetrical. This helps to reduce the sources of error due to steady state hydraulic flow forces and dynamic flow forces, but will not eliminate them all, particularly when the external loading on the ejector pistons is unequal, such as due to an off-set centre of gravity. To cope bett-er with this and provide the valve with a much greater response capability, the pressures in the regulating chambers 24 and 25 are preferably communicated with the end chambers 38 and 39 respectively through a servo device instead of- directly through the spool ducts 42 and 43 as in the example of Figure 2.

An example ofwsuch a servo assisted flow divider valve is shown diagrammatically in Figure 3. The valve has essentially the same construction as that shown in Figure 2 apart from the absence of the regulator spool ducts 42 and 43, and the addition of a regulator servo 44 and an optional by-pass relief valve 45 which may be provided for preventing ejector piston cavitation (premature separation from the load) in extreme circumstances as will be described further below. The parts of the flow divider valve corresponding to those described with reference to Figure 2 are given the same reference numerals and will not be described further.

The servo device 44 is arranged to receive a supply 46 of fluid under pressure, for example from the piston accumulator 3, when the- actuator valve 2 is operated. This fl-ow 46 is divided into two throttled flows 47 and 48 leading into spool chambers 49,50 respectively defined by a servo spool 51 which is axially slidable in a passage 52.

The spool chambers 49,50 have outlet orifices 53,54 respectively controlled by control edges on the spool 51, and the outlet flows from the orifices 53,54 lead to a common spring loaded reservoir chamber 55. At opposite ends of the spool 51 the passage 52 has chambers 56 and 57 respectively com.m.unlcating through throttled lines 58,59 with the flow passages 22,23 respectively of the divider valve 6. The chambers 56 and 57 also contain centering springs 60,61 which act to centre the spool 51 in the passage 52 so that the control orifices 53 and 54 are of equal area when the pressures in the divider valve passages 22,23, and hence in the servo chambers 56,57 are equal.

Finally, the throttled flow passages 47 and 48 of the servo device also communicate through throttled lines 62,63 with the divider valve chambers 38,39.

In operation, when the pressures in the divider valve passages 22,23 and the servo chambers 56,57 are equal, the servo spool 51 is centred so that there is equal flow through the control orifices 53 and 54 and the pressures in the passages 47,48 upstream thereof are also equal. There is therefore no flow through the lines 62 and 63, and the regulator spool 26 also remains centred. If, for example, there is now a pressure increase in the divider valve passage 22 relative to the passage 23, this pressure difference is communicated to the servo chambers 56 and 57 so that the spool 51 moves to the right to decrease the area of the control orifice 53 and correspondingly increase the area of the control orifice 54. The pressures in the flow passages 47 and 48 upstream thereof are accordingly increased and decreased respectively.This resulting pressure difference is communicated via the lines 62 and 63 te the divider valve chambers 38 and 39, whereupon the regulator spool 26 moves in the manner described earlier to reduce the pressure in the passage 22 and re-establish a pressure balance between the two passages 22 and 23.

The advantage of using such a servo device 44 is that the pressures in the passages 47 and 48 can be arranged to vary between the input pressure Ps and about 0.2 Ps so as to generate very - high regulator spool driving forces for relatively small pressure variations in the divider valve passages 22 and 23. This greatly increases the sensitivity and response of the divider valve 6, and the use of the servo device also offers the opportunity for advantageous trade-offs in producing the optimum practical design for any given situation. A disadvantage is the existence of a continuous leakage flow through the control orifices 53 and 54 during operation.This flow is accommodated by the reservoir 55, but is not a major problem since the operating time (i.e. the ejection time) is very short, and the volume of fluid involved is therefore very small.

The by-pass relief valve 45 is provided as a purely precautionary measure in order to counter premature separation of the load from one or other of the actuators as a result of transient flow conditions which the operation of the flow divider valve is unable to control. For example, if telescopic actuator pistons are used such a transient can arise half way through the ejection stroke when the pistons switch to their smaller driving area. The valve 45 simply comprises a pressure regulating valve which is connected to each of the divider valve outlet passages 31 and 35 via lines 64 and 65 containing non-return valves 66 and 67 respectively. If load separation from one of the actuators is about to occur, the pressure in the fluid supply to that actuator would fall below a predetermined value at which the non-return valves 66,67 are designed to open, and the relief valve 45 is then operative to supply additional fluid from the source 3 at a reduced pressure to the actuator in order to maintain it in contact with the load at a relatively low pressure until the transient causing the tendency to separate has passed and the flow divider valve 6 regains control of the actuators.

It is to be understood, however, that although the flow divider valve of Figure 3 has been - described with the presence of the by-pass relief valve 45, it is hoped that the design of the servo assisted divider valve can be optimized such that ejection can be fully controlled, even through transients and under the worst possible loading conditions, such that the relief valve 45 will not be needed.

It should thus be appreciated from the foregoing that the present invention provides an ejector release unit which can provide: - 1. Accurate control over the angular velocity of the load being ejected; 2. Insensitivity to external loads and to the location of the load centre of gravity; 3. Effective load sharing. between the actuators during ejection; 4. Active compensation for transients such as caused by telescopic actuators switching to their smaller driving area during mid stroke; and 5. The potential for in-flight adjustment of the flow ratios to be supplied to the actuators by electrohydraulic or electromechanical means tied into the aircraft avionics.

Claims (1)

1. An ejector release unit comprising a pair of load ejector pistons, means for providing fluid at high pressure for supply to the ejector pistons to accelerate the pistons quickly from a retracted rest position, and a flow dividing valve through which the fluid passes to the two ejector pistons and which includes means for controlling the ratio of the two flows to the pistons so that the ratio is maintained substantially constant throughout the stroke of the pistons.

2. A unit according to claim 1; in which the valve comprises a pair of metering orifices for dividing the flow from the supply means in a predetermined ratio, and control means which is sensitive to a difference in the pressure of the two fluid flows downstream of the metering orifices and is operative to equalise the two pressures.

3. A unit according to claim 2, in which the control means comprises a pair of regulating orifices through which the two fluid flows are arranged to pass, and a regulating spool which controls the area of the regulating orifices and is movable in response to a pressure difference between the flows upstream of the regulating orifices to increase the area of the regulating orifice of the flow at the higher pressure and to decrease correspondingly the area of the other regulating orifice, the spool being biased to adopt a neutral position in which the areas are equal when the flow pressures are equal.

4. A unit according to claim 3, in which the opposite ends of the spool are fitted with equal area pistons, each piston being located in a control chamber which is in communication with the flow pressure upstream of the corresponding regulating orifice.

5. A unit according to claim 3, in which the movement of the regul-ating spool in response to a pressure difference between the flows upstream of the regulating orifices is servo-assisted.

6. A unit according to claim 5, in which the control means includes means communicating the flow pressures upstream of the regulating orifices as inputs to a servo device which is operative to provide outputs having a pressure difference which is amplified in proportion to the difference between the input pressures, and the opposite ends of the spool are fitted with equal area pistons located in control chambers which are connected to receive the servo outputs.

7. A unit according to claim 6, in which the servo device comprises means for providing separate flows of fluid at equal pressure through a pair of control orifices when the servo input pressures are equal, and a spool which is movable in response to a difference in the input pressures to decrease the area of one of the control orifices and correspondingly increase the area of the other whereby the flow pressures upstream thereof are increased and decreased respectively, the servo outputs communicating with the flows upstream of the control orifices.

8. A unit according to claim 7, in which the servo device includes a spring loaded reservoir for collecting the fluid which passes through the control orifices.

9. ffi unit according to any one of claims 2 to 8, in which the areas of the metering orifices are adjustable to vary the ratio thereof and hence adjust the ratio of the fluid flows to the ejector pistons.

1C. A unit according to claim 9, in which the areas of the metering orifices are adjusted by movement of a member having control edges co-operating with the orifices so that movement of the member in one direction causes the control edges to increase the area of one orifice and correspondingly decrease the area of the other, and vice v er sa.

11. A unit according to any one of the preceding claims, comprising means for sensing when the actual pressure of either flow to the ejector pistons falls below a predetermined minimum value and for supplying additional fluid to the said flow or flows downstream of the flow ratio control means of the flow dividing valve.

12. A unit according to claim 1, substantially as described with reference to Figure 1 and either Figure 2 or Figure 3 of the accompanying drawings.

13. A fluid flow dividing valve comprising means for dividing an input flow in two in a predetermined ratio, and servo assisted control means which is sensitive to a difference in the pressures of the two fluid flows downstream of the dividing means and is operative to equalise the said pressures whereby the flow ratio of the two output flows is maintained substantially constant.

14. A v-alve according to claim 13, in which the dividing means comprises pair of metering orifices provided with means for adjusting the areas thereof in order to vary the ratio of the areas and hence vary the flow ratio of the output flows.

15. A valve according to claim 14, in which the adjusting means comprises a member which has control edges cooperating with the metering orifices and which is movable so that movement of the member in one direction causes the control edges to increase the area of one orifice and correspondingly decrease the area of the other and vice v er sa.

16. A valve according to any one of claims 13 to 15, in which the control means comprises a pair of regulating orifices through which the divided fluid flows are arranged to pass, and a regulating spool which controls the area of the regulating orifices and is movable by the servo device in response to a pressure difference between the flows upstream of the regulating orifices to increase the area of the regulating orifice of the flow at the higher pressure and to decrease correspondingly the area of the other regulating orifice, the spool being biased to adopt a neutral position in which the areas are equal when the flow pressures are equal.

17. A valve according to claim 16, in which the servo device has inputs communicating with the flow pressures upstream of the regulating orifices, and is operative to provide outputs having a pressure difference which is amplified in proportion to the difference between the input pressures, and the opposite ends of the spool are fitted with equal area pistons located in control chambers which are arranged to receive the servo outputs.

18. A valve according to claim 17, in which the servo device comprises means for providing separate flows of fluid at equal pressure through a pair of control orifices when the servo input pressures are equal, and a spool which is movable in response to a difference in the input pressures to decrease the area of one of the control orifices and correspondingly increase the area of the other whereby the flow pressures upstream thereof are increased and decreased respectively, the servo outputs communicating with the flow passages upstream of the control orifices.

19. A valve acco-rding to claim 13, substantially as described with reference to Figure 3 of the accompanying drawings.