Integrated drive generator recirculation valve with feedback control

A fluid circulation system in accordance with the invention includes a first fluid utilizing device (12) requiring a minimum fluid flow having an input (14) for receiving the minimum flow and an output (16) for discharging fluid received from the input; a second fluid utilizing device (24) having an input (26) for receiving fluid and an output (31) for outputting fluid; and a valve (80) having a first input (32) for receiving the fluid flow flowing from the output of the second device, a first output (36) for supplying the minimum fluid flow to the first device, a second input (34) for receiving the fluid flow flowing from the output of the first device and a second output (38) for supplying the fluid flow to the second device wherein any deficiency in fluid flow below the first fluid flow flowing from the first input to the first output is supplied with additional fluid flow (102) from the second input to the first output with any remaining fluid flow (104) from the second input flowing from the second output.

TECHNICAL FIELD 
The present invention relates to fluid circulation systems and methods of 
operation thereof and a fluid control valve in which fluid flow is 
controlled by the valve from two fluid sources to provide a minimum fluid 
flow to a primary outlet which requires a minimum fluid flow giving 
preference to the flow from a primary source while routing excess flow 
from a secondary source to a secondary outlet. 
BACKGROUND ART 
The Assignee of the present invention manufactures electrical power 
generating systems for airframes which convert a variable speed shaft 
output from a propulsion engine into a constant speed output drive which 
drives a three phase alternator to produce 400 Hz. electrical power. These 
systems are known as integrated drive generators. Integrated drive 
generators require a minimum fluid flow of oil for proper operation. 
Operation of an integrated drive generator with a supply of oil below the 
minimum flow for a significant time interval can cause catastrophic 
failure or serious damage. 
FIG. 1 illustrates a prior art diagram showing the oil circulation circuit 
of an integrated drive generator of the type manufactured by the Assignee, 
such as used in the Assignee's model 75EGS01I integrated drive generator. 
The oil circulation system 10 includes an integrated drive generator 12 
having an oil input 14 and an oil output 16. The construction and 
operation of integrated drive generators are well known and described in 
numerous patents of the Assignee as is not part of the present invention. 
The output oil from output 16 of the integrated drive generator 12 flows 
to scavenge pump 18 through input 20. The oil flow 62 from output 22 of 
the scavenge pump 18 flows to a recirculation valve 23. Additionally, an 
aircraft mounted accessory drive 24 receives oil flowing from the 
recirculation valve 23 at an input 26. The aircraft mounted accessory 
drive 24 supplies shaft power to the integrated drive generator 12 in a 
well-known manner. A supply pump 28 is located within an oil reservoir 30 
of the aircraft mounted accessory drive for pumping oil flow 60 to the 
recirculation valve 23. 
The recirculation valve 23 is comprised of a first input 32 and a second 
input 34 which respectively receive oil pumped from the supply pump 28 and 
the scavenge pump 18. The recirculation valve 23 also has a first output 
36 through which the minimum critical supply of oil flows to the 
integrated drive generator 12. As stated above, the oil flow from the 
first output 36 must always be above a minimum oil flow rate in order to 
avoid serious damage or catastrophic failure of the integrated drive 
generator 12. The recirculation valve 23 also has a second output 38 which 
applies oil to the input 26 of the aircraft mounted accessory drive 24. 
Flow path 40 indicates the operation of the recirculation valve to 
recirculate oil under normal operation from the output 22 of the scavenge 
pump 18 through the second output 38 to the input 26 of the aircraft 
mounted accessory drive 24. In this circumstance, all of the oil outputted 
from the aircraft mounted accessory drive is pumped by the head produced 
by supply pump 28 through the input 32 of the recirculation valve 23 and 
to the first output 36 of the recirculation valve to the input 14 of the 
integrated drive generator 12 to satisfy the minimum oil flow requirement. 
As will be described in more detail below, assuming that the quantity of 
oil provided by the flow from the aircraft mounted accessory drive 24 
through the input 32 is interrupted, oil is shunted from the input 34 of 
the recirculation valve 23 under the head produced by scavenge pump 18 to 
the first output 36 of the recirculation valve 23 to the input 14 which, 
in all instances, is desirable and if not accomplished can cause undue 
wear or damage. The foregoing operational modes are described in more 
detail in FIGS. 2-4 which illustrate specific operational modes of the oil 
circulation system 10 of FIG. 1. 
FIG. 2 illustrates a normal mode of operation of the recirculation valve 23 
when all of the minimum oil flow requirement of the integrated drive 
generator 12 is satisfied from oil flowing from the aircraft mounted 
accessory drive 24 through the first input 32 to the first output 36. The 
recirculation valve 23 has a valve stem 50 which moves within valve body 
52 between a first position and a second position with the second position 
being illustrated in FIG. 2. The valve body is biased by a spring 54 to 
the first position as illustrated in FIG. 3. The pressure of the pumped 
oil produced by the supply pump 28 is applied to a first face 56 of the 
valve stem and the pressure of the oil pumped by the scavenge pump 18 is 
applied to a second face 58 and a third face 58'. As is apparent, the 
relative surface areas of the third face 58' and the second face 58 are 
such that they apply no net force to the valve stem 50. The valve stem 
position is unaffected by pressure produced from the scavenge pump 18 and 
is determined by the bias spring 54 and the pressure produced by the 
supply pump 28. The oil flow paths 60 and 62, respectively illustrate the 
flow of oil between the first input 32 and the first output 36 and the 
second input 34 and the second output 38. 
The recirculation valve 23 has a first port 62' in fluid communication with 
the first input 32 for receiving oil from the first input 32. Oil flows 
through the first port 62 into a first chamber 64 and out through a second 
port 66 in fluid communication with the first output 36. Oil flows from 
the second input 34 through a first port 68 in fluid communication with a 
second chamber 70 out through a second port 72 in fluid communication with 
the second output 38. 
FIG. 3 illustrates the second mode of operation in which the minimum oil 
flow to the input 14 of the integrated drive generator 12 is satisfied 
totally from oil flowing from the output 22 of the scavenge pump 18 
through the second input 34 out through port 100 to the first output 36 to 
the input 14 of the integrated drive generator 12. In this particular mode 
of operation, the force exerted by the spring 54 biases the valve stem 50 
to the first position in which the face 56 of the valve stem is seated 
against the first port 62 to block the flow of oil 60 from the input 32 to 
the output 36. In this particular mode of operation, the pressure of the 
oil flow 60 outputted from the supply pump 28 drops sufficiently below the 
pressure required to overcome the force exerted on the valve stem 50 by 
the bias spring 54. 
The first mode of operation, as illustrated in FIG. 2, is the ideal mode of 
operation in which the required minimum oil supply is from the aircraft 
mounted accessory drive 24 where it is cooled, filtered and routed to the 
inlet 14 of the integrated drive generator 12 through the first output 36 
of the recirculation valve 23. FIG. 3 illustrates the alternative 
methodology for supplying the minimum flow to the inlet 14 of the 
integrated drive generator 12 in the absence of an oil supply from the 
aircraft mounted accessory drive 24 which is made up by the oil flow 62 
outputted by the scavenge pump 18 pumping oil from the integrated drive 
generator 12. The modes of operation depicted in FIGS. 2 and 3 do not pose 
a problem of operation. 
FIG. 4 illustrates an operational mode of transition between the fully open 
position of FIG. 2 in which all oil of the minimum oil flow to the input 
14 of the integrated drive generator 12 from the first output 36 of the 
recirculation valve 23 is satisfied by oil pumped from the aircraft 
mounted accessory drive 24 through the input 32 and the closed position of 
FIG. 3, in which all oil of the minimum flow pumped to the input 14 of the 
integrated drive generator 12 from the first output 36 of the 
recirculation valve 23 is satisfied by oil pumped from the scavenge pump 
22 through the input 34. In the transition mode, the position of the valve 
stem 50 between the first position as illustrated in FIG. 3 and the second 
position as illustrated in FIG. 2, respectively, is controlled solely by 
the pressure of the oil flow 60 at the first input 32 and is insensitive 
to the output pressure of the oil flow 62 from the scavenge pump 18. When 
the recirculation valve 23 is operating in the fully open position as 
illustrated in FIG. 2, and the pressure of the oil flow 60 drops below 
that required to exert sufficient force on the face 56 of the valve stem 
50 to overcome the force exerted by the spring 54 at the fully open 
position, the valve stem moves to the left as illustrated in FIG. 4. This 
creates an additional drop in the oil pressure at the inlet 14 of the 
integrated drive generator 12 because the flow path through the valve 23 
from the inlet 34 and the inlet 32 through the outlet 38 to the reservoir 
30 of the aircraft mounted accessory drive experiences substantially less 
flow resistance to the reservoir 30 than the flow resistance to enter the 
integrated drive generator 12 through outlet 36. This produces a distinct 
drop in the net flow to the integrated drive generator 12 through the 
input 14 through the first output 36 thereby partially starving the 
integrated drive generator of the requisite oil supply below the required 
minimum flow rate. The valve stem 50 dwells in the intermediate position 
until either the force from the oil flow 60 applied to the face 56 drops 
below the force exerted by the spring 54 at the valve closed position of 
FIG. 3 or, where the flow to the reservoir 30, a combination of flow from 
the scavenge pump 18 and the flow from the aircraft mounted accessory 
drive 24 is large enough to generate a back pressure to the supply 28 
sufficient to raise the pressure applied to the face 56 to compress the 
spring 54 to restore it to the fully open position as illustrated in FIG. 
2. It takes a relatively small change (increase or decrease) in the oil 
flow 60 through the inlet 32 to move the valve stem 50 into the transition 
range, but a substantially larger change in flow 60 to achieve transition 
to either the fully closed position or the fully open position. 
In actual practice, operation of an integrated drive generator can occur 
below a rated pressure, such as 100 psi minimum, but above a pressure 
which is indicative of an oil interruption mode of operation. This mode of 
operation corresponds to that illustrated in FIG. 4 in which the overall 
flow and pressure of oil to the input 14 is representative of a starvation 
condition below the minimum required flow rate. It is necessary to avoid 
damage to integrated drive generators to prevent the operational mode of 
the transitional nature, as illustrated in FIG. 4, because of a 
significant possibility of increased wear or failure resultant from 
starvation of the integrated drive generator parts from the condition 
below the minimum oil pressure flow, such as the minimum 100 psi pressure, 
required on some integrated drive generators manufactured by the Assignee 
of the present invention. 
DISCLOSURE OF INVENTION 
The present invention is a fluid circulation system, a method of 
circulating fluid to a first fluid utilizing device requiring a minimum 
fluid flow and to a second fluid utilizing device using a valve and a 
fluid control valve in which the flow of fluid to the first fluid 
utilizing device is always supplied at least at the minimum fluid level 
necessary to sustain operation without damage or failure. With the 
invention, when the minimum fluid flow is not available from the preferred 
source of fluid, a secondary source of fluid is used to provide additional 
fluid flow to bring the fluid flow level up to at least the minimum fluid 
flow with any remaining fluid flow flowing to a second fluid utilizing 
device. A preferred application of the present invention is for oil 
circulation systems with a preferred oil circulation system being 
electrical power generating systems containing an integrated drive 
generator and an aircraft mounted accessory drive such as the type 
manufactured by the Assignee of the present invention. However, it should 
be understood that the invention is not limited thereto. 
Because the surface areas of the opposed faces of the first element are 
equal, no pressure differential exists between the first and second 
chambers which eliminates the transitional mode of FIG. 4 of the prior 
art. This insures that all of the primary fluid supply to the fluid 
utilizing device having the minimum flow requirement is used and is not 
shunted to the second fluid utilizing device. 
In accordance with the present invention, the valve 23 of the prior art as 
illustrated in FIGS. 2-4 is modified to split the valve stem therein into 
first and second elements which respectively move within first and second 
chambers between first and second positions to control the flow of fluid 
inputted from the first and second inputs such that the first output 
always receives at least the minimum flow rate. This is accomplished by 
using the flow from the preferred source in its entirety with the 
additional flow to meet minimum flow requirements at the first output 
coming from the second input with any remaining fluid flow from the second 
input flowing to a second output. The valve body of the present invention 
contains the same ports and inputs as the prior art of FIGS. 1-4 and 
differs from the prior art in using feedback of the pressure of the fluid 
from the second input in conjunction with the pressure of the first input 
to determine the position of the first element within the first chamber 
between the first and second positions, which respectively represent an 
open and closed condition, to control the quantity of the additional fluid 
flow from the second input to the first output dependent upon the relative 
position of the first element between the first and second positions in 
the first chamber. The intermediate position of the first element within 
the first chamber controls the degree of blocking of the port connecting 
the first input to the first output. Furthermore, the degree of flow 
through the second input and a first port in a second chamber in fluid 
communication with the second input to a second port in fluid 
communication with the second output supplies fluid to the second output 
with the second port being in fluid communication with the second chamber 
when the second element is in the first position. The second port of the 
second chamber is open when the second element is in the second position 
and supplies the excess fluid flow when the second element is in between 
the first and second positions. A third port in the second chamber in 
fluid communication with the first output supplies the additional fluid 
flow representing the deficiency in the fluid flow from the first input to 
the first output from fluid flowing in the second input. As the first 
element moves from the first position to the second position, the quantity 
of fluid flowing from the first input to the first output proportionally 
increases. As the second element moves from the first position to the 
second position, the quantity of additional fluid flowing from the second 
input to the first output decreases in proportion to the increase of the 
remaining fluid flow which is diverted from the first output to the second 
output. Preferably, the first and second chambers are coaxial.

BEST MODE FOR CARRYING OUT THE INVENTION 
The preferred embodiment of the present invention is in an electrical power 
generating system as illustrated in FIG. 1 as described above but it 
should be understood that the present invention is not limited to the 
control of oil flow and has other applications where a critical minimum 
flow must be provided at all times to one fluid utilizing device with the 
minimum flow rate being satisfied by additional oil diverted from flow to 
a second fluid utilizing device, which does not have a minimum flow 
requirement, to the first fluid utilizing device to avoid damage or 
failure consequent from sustained flow rates to the first fluid utilizing 
device below the minimum fluid flow. 
FIGS. 5-7 respectively illustrate sectional views of an oil recirculation 
valve 70 in accordance with the invention which correspond respectively 
operationally to the prior art sectional views of FIGS. 2-4. FIG. 5 
illustrates the normal operation mode in which fluid flow to the first 
output 36, which has the critical minimum flow, is satisfied solely from 
oil flow 60 to the first input 32. FIG. 6 illustrates the oil flow to the 
first output 36 which is satisfied solely from oil flow 62 to the second 
input 34 with the first input 32 being totally blocked. FIG. 7 illustrates 
the transitional mode in which the required minimum flow to the first 
output 36 is satisfied partially from the fluid flow 60 to the first input 
32 and partially from additional flow 102 from the fluid flow 62 through 
the second input 34 with the remaining fluid flow 104 to the second input 
flowing to the second output 38. 
Structurally, the valve 80 is similar to the prior art valve 23 of FIGS. 
2-4 with the exception that the valve stem of the prior art has been split 
into a first movable element 82 and a second movable element 84 which 
respectively move between first and second positions in the valve body 52 
and stops 88 and 92 have been provided to limit travel of the first 
movable element 82. The stop 88 is removable for assembly purposes. The 
first element 82 is movable within the first chamber 64 between a first 
position at which a first opposed surface 86 contacts the first stop 88 
which defines the first position in the first chamber and a second 
position at which a second opposed face 90 contacts the second stop 92 at 
the second position. The stops 88 and 92 are defined by annular ridges 
which have a diameter slightly smaller than the outside diameter of the 
wall 94 which defines the first chamber 64 in the valve body 52. The 
second movable element 84 is biased to the first position in chamber 70 by 
spring 54 and opposes a force applied by pressure in the second oil flow 
62 through the second input 34 as applied to face 96. The input port 68 
and output ports 72 and 100 of the recirculation valve 80 are unchanged 
from the prior art of FIGS. 2-4. 
FIG. 5 illustrates the normal mode of operation in which oil flow 60 from 
the aircraft mounted accessory drive 24 enters the first input 32, flows 
through the first port 62 into the first chamber 64 and out through the 
second port 66 to the first output 36. In this mode of operation, the 
pressure in the oil flow 60 exceeds the pressure in the feedback oil flow 
62 which causes the first element 82 to assume the second position as 
illustrated in FIG. 5. The relative greater pressure of the flow 60 in 
comparison to the flow 62 is applied to the equal surface areas of the 
opposed faces 86 and 90 which causes the first element 82 to assume the 
second position as illustrated in FIG. 5. The hysteresis of the 
transitional mode of FIG. 4 is eliminated. Furthermore, the feedback 
pressure in the second flow 62 applied to the face 96 of the second 
element 84 is greater than the force applied by the spring 54 which forces 
the second element to assume the second position as illustrated in FIG. 5. 
FIG. 6 illustrates the recirculation valve 80 in the mode of operation in 
which the oil flow to the first output 36 is totally supplied from the 
second input 62. In this position, the first element 82 is in the first 
position in which the first input 32 is blocked off from the oil flow 60. 
The oil flow 62 from the integrated drive generator 12 flows through the 
second input 34 through the second port 68 into the second chamber 70, 
through a third port 100, to the first output 36 and then to the 
integrated drive generator. The second element 84 is positioned in the 
first position in the second chamber 70 which blocks off the second port 
72 (illustrated in FIG. 5) to totally divert the fluid flow 62 from the 
second output 38, as illustrated in FIG. 5, to the first output 36. In 
this mode, the pressure of the first flow 60 is less than the second flow 
62 which causes the first element 82 to assume the first position and the 
force generated by the flow 62 as applied to the face 96 is less than the 
force generated by the spring 54 causing the second element to assume the 
first position. 
FIG. 7 illustrates the transitional mode of operation of the recirculation 
valve 80 of the present invention which solves the problems of the prior 
art as illustrated in FIG. 4. At all times the minimum required flow rate 
of oil to the first output 36 is maintained even when the flow rate of the 
oil flow 60 from the aircraft mounted accessory drive 23 is insufficient 
to satisfy the minimum flow requirement of the integrated drive generator 
12 to maintain trouble free and non-damaging operation. In this mode of 
operation, the oil flow 62 from the integrated drive generator is split 
into two flows 102 and 104 which respectively are the additional flow 
required to supplement the deficiency of flow provided by the first oil 
flow 60 to provide the minimum flow rate through the output 36 and the 
remaining oil flow which flows to the aircraft mounted accessory drive 24 
which exceeds the oil flow which is required to be diverted to the first 
output to satisfy the minimum flow rate requirement therein. 
As is seen from this mode of operation, the first fluid utilizing device at 
all times receives the minimum flow requirement which, in the preferred 
application, is oil, to prevent potential damage or destruction of the 
first fluid utilizing device. As a result, the feedback pressure of the 
second oil flow 62 is used to control the position of the first element 82 
between the first position and the second position such that the 
additional oil flow 102 required to supplement the deficiency of oil flow 
below the minimum flow requirement provided by the first oil flow 60 is 
always provided from the second oil flow with the remaining oil flow 104 
always being diverted to the aircraft accessory mounted drive 24. The 
position of the first element 86 between the first and second positions 
proportions the relative quantity of the additional flow 102 and the 
remaining flow 104 to satisfy the minimum flow requirement which makes up 
the oil flow 62 to always provide sufficient oil to the first output 36 
which prevents damage to the integrated drive generator 12 of the prior 
art as described above in conjunction with FIGS. 1-4. 
While the invention has been described in terms of a preferred embodiment 
in which a minimum oil flow is provided to a first device having a 
critical flow requirement, it should be understood that the invention has 
utility in other applications involving fluid flow where a minimum flow 
requirement to a first device is required and when a deficiency in fluid 
flow from a second fluid utilizing device is insufficient and fluid may be 
diverted to flow back from the first fluid utilizing device to provide 
additional fluid flow to supplement the deficiency in the minimum flow 
requirement provided by flow from the second fluid utilizing device. The 
valve of the present invention has applications wherever primary and 
secondary fluid sources and outlets are provided and preference for the 
primary outlet is required (i.e. flow back is not required). It should be 
understood that numerous modifications may be made to the invention 
without departing from the spirit and scope of the invention. It is 
intended that all such modifications fall within the scope of the appended 
claims.