Apparatus for producing different flow rates of a fluid

A fluid system (10, 10A, 10B) which supplies two work systems (26, 38) with respective different fluid flow rates, including a pressure-flow compensated pump (12), a first control valve (18) for delivering the fluid to one of the work systems, a second control valve (28) for receiving the fluid from the first control valve and delivering the fluid to the other of the work systems (38), a first device ([20,42,50] or [20,56,58] or [20,90,96]) coupled between the pump output and the first control valve, for providing one control signal causing the pump to produce one flow rate of fluid for activating the one work system (26), and a second device ([20,40,44,46,50] or [22,58,66,72,78] or [22,88,92,96,102]) for overriding the first device for providing another control signal causing the pump to produce another flow rate of fluid for actuating the other work system.

TECHNICAL FIELD 
This invention relates to fluid control systems and, more particularly, to 
apparatus for producing different flow rates of a fluid through the 
system. 
BACKGROUND ART 
Earthworking vehicles, such as track-type tractors, typically will have 
various implements for performing different functions. For example, the 
vehicle will have a dozer blade supported on a forward end of the vehicle 
main frame and a backhoe supported on a rearward end of the main frame. 
Usually, hydraulic fluid systems are employed to operate these implements 
under the control of the vehicle operator. 
The above implements normally have different fluid flow requirements for 
their operation. For example, a relatively small rate of fluid flow is 
needed for operating the dozer blade or some other implement at the 
forward end of the frame, whereas a relatively large rate of fluid flow is 
required to run the backhoe. Because of these dual flow requirements, a 
problem in prior hydraulic fluid systems is that they have employed 
relatively complex fluid systems, including complex controls for the 
systems, so that different flow rates of fluid could be provided to 
operate the implements as needed. 
DISCLOSURE OF THE INVENTION 
The present invention is directed to overcoming one or more of the problems 
as set forth above. 
In one aspect of the present invention, apparatus is provided for producing 
different flow rates of a fluid, comprising a pump having means for 
changing the flow rate of the fluid at the output of the pump, first means 
for providing a first control signal to the changing means, and second 
means, selectively movable for overriding the first providing means, for 
providing a second control signal to the changing means. The flow rate 
changing means is responsive to the first control signal and the second 
control signal to produce respective flow rates at the pump output.

BEST MODE FOR CARRYING OUT THE INVENTION 
FIG. 1 shows, as one embodiment, a fluid control system 10 for producing 
different flow rates of a hydraulic fluid as needed. A variable 
displacement pump 12 has a flow compensator assembly 14 which controls the 
displacement of the pump 12 to provide different flow rates of fluid at a 
pump output 16. The flow compensator assembly 14 responds to pressure 
signals for changing the pump displacement and hence the flow rate at the 
output 16. One type of suitable pump 12 is known as a pressure-flow 
compensated piston pump manufactured by the Cessna Corporation, 
Hutchinson, Kansas, under model No. 70523, which operates as a function of 
differential pressure in the compensation assembly 14. 
A control valve 18 receives the hydraulic fluid from a fluid conductor 20 
which is coupled at one end to the pump output 16. The control valve 18 
can be one of several types well-known in the art. For purposes of the 
present discussion, the control valve 18 is assumed to be an interrupted 
series type valve. Other types of valves will be mentioned below. The 
control valve 18 can direct the hydraulic fluid from the conductor 20 to a 
fluid connector 22 and a fluid conductor 24. In a centered position, the 
valve 18 will direct all the fluid from the conductor 20 to the conductor 
22. In a fully shifted position, the valve 18 will direct all the fluid in 
the conductor 20 to the conductor 24. In positions between the centered 
and fully shifted positions, the valve 18 will direct a portion of the 
fluid in the conductor 20 to the conductor 24, with the remaining portions 
being directed to the conductor 22. 
A work system shown generally at 26 is actuated by the fluid flowing in the 
conductor 24. 
A control valve 28, which can be one of several types well-known in the 
art, similar to valve 18, receives the hydraulic fluid from the conductor 
22. If the valve 28 is assumed to be an interrupted series type, then in a 
centered position, the valve 28 will direct all the fluid in the conductor 
22 to a fluid conductor 30 leading to a drain 34. In a fully shifted 
position, the valve 28 will direct all the fluid in conductor 22 to a 
conductor 36. In positions between the centered and fully shifted 
positions, the valve 28 will direct a portion of the fluid in the 
conductor 22 to the conductor 36, with the remaining fluid being directed 
to the conductor 34. A work system shown generally at 38 is actuated by 
the fluid flowing in the conductor 36. 
To control the compensator assembly 14 and, hence, vary the fluid flow rate 
at the pump output 16 by changing the pump displacement, the fluid within 
the conductor 20 is transferred to the control valve 18 through a 
two-position control valve 40. In one position of the control valve 40, a 
flow restrictor 42 is placed within the conductor 20 so that there is a 
pressure drop across this restrictor from the upstream or input end to the 
downstream or output end. In the other position of the control valve 40, a 
flow passage 44 of less restriction than the flow restrictor 42 is placed 
within the conductor 20. In the example given, the passage 44 provides no 
restriction so that there is no pressure drop through this passage. A 
mechanism shown generally at 46 is manually operable to move selectively 
the valve 40 to either position for placing either the flow restrictor 42 
or the flow pressure 44 in the conductor 20. As ilustrated, the control 
valve 40 is biased by a spring 48 to a normal position in which the flow 
restrictor 42 is within the conductor 20. 
A signal line 50 is coupled at one end 52 to the conductor 20 between the 
control valve 40 and the control valve 18, and at the other end 54 to the 
flow compensator assembly 14. The signal line 50 responds to the fluid 
flowing through the conductor 20 to the control valve 18 by generating or 
providing pressure control signals to the flow compensator assembly 14 
having a value depending on the pressure of the fluid flowing past the end 
52. 
When the control valve 40 is in the position shown in FIG. 1, and the pump 
12 is in operation, the hydraulic flow from the pump output 16 will flow 
through the conductor 20 and the flow restrictor 42 and past the signal 
line 50 to the control valve 18. Due to the pressure drop provided by the 
flow restrictor 42, the fluid flowing past the end 52 will produce a 
signal in the line 50 which will create a pressure differential within the 
flow compensator assembly 14 to provide a pump displacement to maintain 
one rate of fluid flow. If the pump 12 is to provide a different flow rate 
at the output 16, then the control valve 40 will be manually shifted to 
decouple the flow restrictor 42 from the conductor 20 and replace or 
override it with the relatively unrestricted flow passage 44. 
Consequently, there will be less or no pressure drop across the passage 44 
than across the restrictor 42 so that the fluid flowing to the control 
valve 18 past the end 52 will be at a higher pressure thane when the flow 
restrictor 42 is within the conductor 20. Therefore, this higher pressure 
fluid flow will result in another pressure signal in the line 50 thus 
eliminating the differential pressure in the flow compensator assembly 14 
to change the displacement of the pump 12 to produce a different flow rate 
at the pump output 16. Thus, depending on the position of control valve 
40, different flow rates of fluid will be provided by the pump 12. 
As one example of a particular use for the fluid control system 10, the 
work system 26 constitutes a hydraulically operated dozer blade on a 
track-type tractor earthworking vehicle, while the work system 38 
constitutes a hydraulically operated backhoe on the same vehicle. The 
control valves 18 and 28 can be controlled manually by the vehicle 
operator or actuated automatically in any well-known manner to control the 
direction of the hydraulic fluid through these valves. The work system 26 
requires a lesser flow rate of the hydraulic fluid for its operation, 
whereas the work system 38 requires a greater flow rate of the hydraulic 
fluid for its operation. 
If, for example, the work system 26 is to be actuated, the control valve 40 
will be in the position shown in FIG. 1 and the control valve 18 moved to 
a position to direct all of the fluid within the conductor 20 to the 
conductor 24. With the pump 12 in operation, the flow compensator assembly 
14 will respond to the one pressure control signal in the signal line 50 
to provide the lesser flow rate at the pump output 16 in the manner 
already described. 
Should it be desired to operate the work system 38, without operating the 
work system 26, the control valve 40 will be shifted to override the flow 
restrictor 42 and place the flow passage 44 in the conductor 20. Also, the 
control valve 18 will be shifted to its centered position to communicate 
all the fluid in the conductor 20 with the conductor 22. The control valve 
28 also will be shifted to communicate the conductor 22 with the conductor 
36 so that the work system 38 will be actuated by the hydraulic fluid 
pumped by the pump 12. In this shifted position of the control valve 40, 
as already described the compensator assembly 14 will respond to the new 
control signal in line 50 to vary the displacement of the pump 12 so that 
a greater flow rate will be provided at the pump output 16. 
FIG. 2 illustrates a fluid control system 10A for providing different flow 
rates of hydraulic fluid, which is an alternative embodiment to the fluid 
control system 10 shown in FIG. 1. In FIG. 2, like reference numerals are 
used to indicate like elements shown in FIG. 1. As illustrated, the system 
10A includes the variable displacement pump 12 which pumps the hydraulic 
fluid through the conductor 20 to the control valve 18 and the control 
valve 28 for actuating the work system 26 or 38 in the manner described in 
connection with FIG. 1. 
A flow restrictor 56 is permanently fixed within the conductor 20 to 
provide a pressure drop thereacross relative to the fluid flow rate from 
the pump output 16. A signal line 58 is coupled at one end 60 to the 
conductor 20 and at the other end 62 to the flow compensator assembly 14. 
A check valve 64 is positioned within the signal line 58 for reasons which 
will be described below. 
Another openable and closeable signal line 66 is coupled at one end 68 to 
the conductor 20 between the pump output 16 and the flow restrictor 56 and 
at another end 70 to the signal line 58 between the flow compensator 
assembly 14 and the check valve 64. A two-position control valve 72 is 
selectively moveable to one position shown in FIG. 2 in which the signal 
line 66 is closed, i.e., the end 68 is not in communication with the end 
70, and is selectively movable to another position to open the line 66 
through a signal passage 74 in which the end 68 is in communication with 
the end 70. A spring 76 biases the control valve 72 to the one or normal 
position shown in FIG. 2. 
The control valve 72 is responsive to a pressurized signal in a signal line 
78 to be moved from the normal position shown in FIG. 2 to the other 
position in which the signal line 66 is opened. The signal line 78 is 
coupled at one end 80 to the conductor 22 between the control valve 18 and 
the control valve 28, and at the other end 82 to the control valve 72. The 
signal line 78 has a parallel path in which one branch has a check valve 
84 and another branch has a restrictor 86. 
If it is assumed the valve 28 has been shifted to actuate the work system 
38, as the hydraulic fluid flows through the conductor 22 past the end 80, 
a pressure signal will be provided in and carried along the signal line 78 
via a one way path through the check valve 84 and via a restricted two-way 
path through the restrictor 86 to the valve 72. This signal will be high 
enough due to the load of the system 38 to cause the valve 72 to change 
positions to open the signal line 66 with the signal passage 74. This 
communication between ends 68 and 70 of line 66 interrupts the originally 
established differential pressure acting on flow compensator assembly 14. 
In the event there is a short temporary drop in the fluid pressure through 
the conductor 22, for whatever reason, the check valve 84 will close, 
forcing the pressure signal at the end 82 of the line 78 to bleed slowly 
back through the restrictor 86. This will prevent the control valve 72 
from quickly returning to the position shown in FIG. 2. This in turn will 
provide time for the fluid pressure in the conductor 22 to return to 
normal so that the control valve 72 may be maintained in its position for 
opening the signal line 66. If the valve 28 is centered, i.e., directing 
all the fluid in the conductor 22 to the drain 34, there will not be any 
such system load so that any pressure signal in the line 78 will not be 
high enough or of sufficient magnitude to cause the valve 72 to change 
positions to open the signal line 66. Hence, the valve 72 is only shifted 
when the work system 38 is being actuated. 
In the operation of the system 10A, assume that the pump 12 is pumping the 
hydraulic fluid from its output 16 and the control valve 18 is in a 
position communicating at least some fluid in the conductor 20 with the 
conductor 24. Also assume that the work system 38 is not being actuated so 
that any fluid flow in the conductor 22 at this time is being dumped to 
the drain 34 by the valve 28. As the fluid flows through the restrictor 56 
and past the end 60, a pressure control signal is generated or provided in 
the line 58 and carried through the check valve 64 to the flow compensator 
assembly 14. Consequently, the pump 12 will be displaced to provide one 
flow rate of fluid. Since at this time the work system 38 is not being 
operated, no pressurized control signal of sufficient magnitude will be 
provided in the line 78 to move the control valve 72 to the position for 
opening the signal line 66. Thus, at this time the flow compensator 14 
will be responsive to the pressure control signal in the line 58 and not 
to any pressure control signal in the line 66 thereby providing the lesser 
flow rate of fluid at the output 16. 
If the greater flow rate of fluid is required at the pump output 16, the 
pressurized control signal of sufficient magnitude is provided in the 
signal line 78 by transferring the hydraulic fluid from the conductor 20 
to the conductor 22 and shifting the valve 28 off center. This pressurized 
signal in the line 78 will thereby move the control valve 72 to its 
position in which the signal line 66 is opened with the signal passage 74. 
With the signal line 66 opened, as the fluid from the pump output 16 flows 
past the end 68, a pressure control signal will be generated or provided 
in the line 66 that is coupled back to the flow compensator assembly 14 
through the connection of the end 70 with the line 58. The fluid flowing 
in the conductor 20, as it passes the end 68, does not experience a 
pressure drop as it would when passing through the flow restrictor 56 
towards the end 60 of the signal line 58. Consequently, the pressure 
signal in the signal line 66 is at a different value than the signal 
generated in the line 58 by the flow past the end 60. In fact, the 
pressure control signal in the line 66 is at a higher value than the 
signal generated at the end 60 so that the check valve 64 will be closed. 
Consequently, the control signal in the line 66 overrides the pressure 
signal generated at the end 60 so that the flow compensator assembly 14 
will respond only to the absence of a differential pressure. Therefore, 
the displacement of the pump 12 will be changed so that a greater flow 
rate is provided at the pump output 16. The check valve 64 also prevents 
the higher pressure signal in the line 66 from backing up through the line 
58 to the downstream side of the flow restrictor 56. 
While the above operation of the fluid control system 10A has been given, 
specific examples of its use will now be described for yet a better 
understanding of the invention. If only the work system 26 requiring a 
relatively smaller flow rate is to be activated, the control valve 18 can 
be moved to communicate all the fluid in the conductor 20 with the 
conductor 24. The pressure control signal will then be provided in the 
signal line 58 through the check valve 64 to control the flow compensator 
assembly 14 and, thereby, cause a relatively small flow rate at the pump 
output 16. If only the work system 38 requiring a relatively large flow 
rate is to be activated, the control valve 18 is shifted to communicate 
all the fluid in the conductor 20 with the conductor 22, while the control 
valve 28 is shifted to communicate the conductor 22 with the conductor 36. 
As a result, the displacement of the pump 12 will be automatically changed 
to provide a greater flow rate at the pump output 16. This is 
accomplished, as already noted, by coupling the greater pressure signal in 
the signal line 66 to the flow compensator assembly 14 after shifting the 
control valve 72 with the control signal generated in the line 78. If both 
work systems 26 and 38 are to be activated simultaneously, the greater 
flow rate will be provided by the pump 12 due to the control signal 
generated in the line 78. 
It may be appreciated that while different pressure control signals are 
provided in the control lines 58 and 66, substantially the same control 
signal may be provided in the control lines 58 and 78. However, whereas 
the signal in the line 58 controls the compensator 14, the signal in the 
line 78 controls the control valve 72. 
FIG. 3 illustrates a fluid flow control system 10B which is an alternative 
embodiment to the respective embodiments shown in FIGS. 1 and 2. In FIG. 
3, like reference numerals are used to indicate like elements shown in 
FIGS. 1 and 2. Again, the pump 12 may be used to deliver different flow 
rates of hydraulic fluid through the conductor 20 to actuate the work 
systems 26 and 38 through the control valves 18 and 28 in a similar manner 
to that already described. 
A selectively movable, two-position control valve 88 has one position in 
which a flow restrictor 90 is placed in the conductor 20 and another 
position in which a flow passage 92 of less or no restriction than the 
restrictor 90 is placed in the conductor 20. A spring 94 biases the valve 
88 into the normal position shown in which the flow restrictor 90 is in 
the conductor 20. 
A control signal line 96 is coupled at one end 98 to the conductor 20 
between the control valve 88 and the control valve 18, and at the other 
end 100 to the flow compensator assembly 14. As will be described, 
different pressure control signals are generated or provided in the signal 
line 96 to control the compensator assembly 14 for providing different 
flow rates of the fluid from the pump output 16. Another control signal 
line 102 is coupled at one end 104 to the conductor 22 between the control 
valve 18 and the control valve 28 and at the other end 106 to the control 
valve 88 to move the latter to its position in which the flow passage 92 
overrides or replaces the flow restrictor 90. The signal line 102 includes 
a parallel signal path having a check valve 108 and a restrictor 110 which 
have the same function as the check valve 84 and the restrictor 86 of FIG. 
2. 
In the position of the control valve 88 shown in FIG. 3, with the pump 12 
in operation, there will be a pressure down as the fluid flows through the 
restrictor 90. The fluid flowing past the end 98, which fluid has dropped 
in pressure, will thereby result in a pressure control signal of one value 
in the line 96 to cause the flow compensator to cause a change in the 
displacement of the pump and provide one flow rate from the pump output 
16. 
When the hydraulic fluid is flowing through the conductor 22 and the valve 
28 is shifted to activate the system 38, a control signal of sufficient 
magnitude will be provided in the signal line 102 to cause the control 
valve 88 to shift automatically to its position in which the flow passage 
92 is within the conductor 20. Consequently, at this time, there will be 
no or a lesser pressure drop in the fluid flowing through the conductor 20 
so that a different control signal is provided in the line 96 than when 
the flow restrictor 90 is effective. The flow compensator assembly 14 will 
thereby respond to this different pressure control signal in the line 96 
by changing the pump displacement to provide a different flow rate at the 
pump output 16. Without the shifting of the valve 28 off center to actuate 
the system 38, any control signal in the line 102 will not be of 
sufficient magnitude to cause the valve 88 to shift from the position 
shown. 
The fluid control system 10B can be used in a similar manner as 10A to 
activate the work system 26 or the work system 38 or both simultaneously. 
If only the work system 26 requiring a lesser flow rate is to be 
activated, the control valve 18 can be shifted to communicate all the 
fluid in the conductor 20 with the conductor 24 and prevent communication 
between the conductor 20 and the conductor 22. Accordingly, the control 
valve 88 will be in its normal position shown with the flow restrictor 90 
in the conductor 20 and a pressure control signal of one value being 
generated in the line 96. Therefore, the displacement of the pump 12 will 
result in a relatively small flow rate of the fluid at the pump output 16 
for transfer to the conductor 20 and the control valve 18 to the conductor 
24. If only the work system 38 requiring a greater flow rate is to be 
activated, the control valve 18 is shifted to communicate the conductor 20 
with the conductor 22 and the control valve 28 shifted to communicate the 
conductor 22 with the conductor 36. With fluid flow through the conductor 
22, the valve 88 will be moved to place the flow passage 92 in the 
conductor 20 and, thereby, a pressure control signal of another value will 
be provided in the signal line 96. Consequently, the displacement of the 
pump 12 will be changed to provide a greater flow rate at the pump output 
96 to meet the requirements of the work system 38. If both systems 26 and 
38 are to be actuated simultaneously, the greater flow rate will be 
provided by the pump 12 due to the control signal generated in the line 
102. 
Industrial Applicability 
The control valves 18 and 28 have been shown to be in an interrupted series 
relationship. However, it will be appreciated by those skilled in the art 
that these valves 18 and 28 can be in a parallel flow relationship in 
which the same flow from pump 12 is conducted simultaneously to the inputs 
of the valves. In this parallel relationship, the valve 40 in FIG. 1 can 
be manually shifted as already discussed to provide the different flow 
rates for actuating the systems 26 and 38, and the valves 72 and 88 in 
FIGS. 2 and 3, respectively cam be automatically shifted in the manner 
described for actuating the work systems 26 and 38. It also will be 
appreciated that the present invention is applicable to systems in which 
the valves 18 and 28 are in a series relationship in which all the flow 
from the valve 18 is directed to the work system 26 and then from the work 
system 26 to the input of the valve 28. Again, in this series 
relationship, the valve 40 can be manually shifted and the valves 72 and 
88 automatically shifted to actuate the work systems 26 and 38 as 
described above. 
As one example, the work system 26 constitutes a hydraulically operated 
dozer blade on a track-type tractor earthworking vehicle, while the work 
system 38 constitutes a hydraulically operated backhoe on the same 
vehicle. The control valve 18, while shown generally, would comprise a 
valve package of three, normally centered valves which are in a parallel 
flow relationship with one another so that the fluid flow in the conductor 
20 is received simultaneously by each of these three valves. Each of the 
three valves may be shifted off center to independently control one 
operation of the dozer blade. For example, one valve of the package can be 
shifted to direct fluid from the conductor 20 to the work system 26 to 
control the raising and lowering of the dozer blade, the second valve of 
the package can be shifted to direct fluid from the conductor 20 to the 
system 26 to tilt the blade forward and backward, and the third valve can 
be shifted to direct fluid from the conductor 20 to the system 26 to angle 
the blade. 
The control valve 28, while also shown generally also can comprise a valve 
package of three, normally centered valves which are in a parallel flow 
relationship so that fluid in the conductor 22 is received simultaneously 
by each of these three valves. Each of the three valves of this package 
can be shifted off center to independently control one operation of the 
backhoe. For example, the first valve of the package can be shifted to 
direct fluid from the conductor 22 to the work system 38 to raise and 
lower a boom connected to the backhoe, the second valve can be shifted to 
direct fluid from the conductor 22 to the system 38 to swing the backhoe, 
and the third valve can be shifted to direct fluid from the conductor 22 
to the system 38 to cause the backhoe to dig. 
Other aspects, objects and advantages of this invention can be obtained 
from a study of the drawings, the disclosure and the appended claims.