Load responsive pump controls of a fluid system

Apparatus of a fluid system of a work vehicle for controlling the fluid delivered to work elements of the vehicle in response to the load exerted on the fluid system by the work elements.

BACKGROUND OF THE INVENTION 
In the operation of a fluid system serving a plurality of parallel work 
elements, the work elements sometimes demand large volumes of fluid from 
their associated hydraulic fluid pump. Occasionally there arise situations 
where the work elements demand fluid at a rate greater than the capacity 
of the pump. In such situations, one or more of the work elements will be 
demanding more fluid than is available while another work element may be 
requiring fluid at a very high pressure in order to continue to function 
under its existing load. Since the fluid passing to the work elements is 
free to travel the path of least resistance, the above-mentioned work 
elements demanding additional fluid will be supplied the required fluid at 
the expense of denying the increased pressure demanded by said other work 
element. 
This problem associated with a plurality of work elements connected in 
parallel can be avoided by providing a pump having a capacity greater than 
the total demand capacity that could ever be required by the work 
elements. However, to so construct the work vehicle would produce a waste 
of materials, time, and labor for constructing, maintaining, and handling 
the resultant large pump. Further, the undesirably large pump would add 
considerable extra weight to the vehicle and would require extra fuel to 
operate which would further represent a waste of energy. 
It is therefore desirable to provide fluid system apparatus which will 
control the system in a manner such that when the work elements approach a 
total fluid demand exceeding the capacity of the associated fluid pump, 
the actual demands of the work elements will be automatically overridden 
in response to a load pressure signal and fluid delivery to the individual 
work elements will be automatically, controllably maintained at reduced 
rates relative to their individual actual demand. 
This invention therefore resides in controlling the fluid delivered to 
individual parallel work elements in response to a load pressure signal 
and the total fluid demand of the work elements relative to the maximum 
capacity or the pumps.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIGS. 1-3, a fluid system, preferably a hydraulic system 10 of 
a work vehicle 12, has a power source 14, for example an engine, connected 
to a pilot pump 16 and a plurality of variable displacement hydraulic 
fluid pumps 18,20 for delivering hydraulic fluid. The hydraulic system 10 
has one or more hydraulic circuits 22,24 served by the pilot pump 16 and 
the power source 14. 
Each hydraulic circuit 22,24 has a respective variable displacement pump 
18,20, and an associated pump control assembly 26,28 serving different 
work elements 30,32. 
Each hydraulic circuit 22,24 has its respective work elements 30,32 
connected to the discharge of its respective pump 18,20. Each of the work 
elements 30,32 has a control valve assembly 38,40. 
Each of the control valve assemblies 38,40 has a pressure compensated flow 
rate control element 42,42' and a directional flow control element 44,44'. 
The control valve assemblies 38,40 are positioned in the fluid stream 
passing from the respective pumps 18,20 to the respective work elements 
30,32. Elements of each control valve assembly 38,40 are movable between 
first and second positions for selectively substantially opening and 
closing valve outlets. Each control valve assembly 38,40 is opened and 
closed in response to respective pilot pressure signals delivered through 
respective lines 46,47 and 48,49 from a respective work element pilot 
control valve 50,52. The work element pilot control valves 50,52 and 
control valves 38,40 and their functions are well known in the art. 
A first means 54,54' is provided for sensing the discharge pressure of each 
pump 18,20 and delivering a respective pressure signal in response 
thereto. A second means 56,56' is associated with each work element 30,32 
for sensing the respective load pressure and delivering a load pressure 
signal. The load pressure signals are passed through lines 60,60'. 
Each circuit 22,24 has a control means, such as supply margin valves 
62,62', which is connected by lines 64,66,67 to the pilot pump 16 for 
controllably altering the magnitude of the pilot pressure signal from the 
pilot pump 16 and delivering resultant pressure signals "X","X'" for 
controlling the respective pumps 18,20. The pilot pressure signals are 
altered in response to respective preselected biasing forces and load 
pressure signals as opposed by the respective discharge pressure signals. 
The supply margin valves 62,62' are connected to the discharge of their 
pumps 18,20 via lines 76,77 and 78,79 and to their respective load 
pressure signal via lines 60,60'. The supply margin valves 62,62' each 
have a biasing means such as springs 82,82' for providing the preselected 
biasing force. 
Each of the variable displacement pumps 18,20 have a movable swash plate 
84,84' for controlling the fluid discharge rate of the respective pump 
18,20. Each of the respective pump control assemblies 26,28 have a servo 
valve 86, 86' for receiving a pressure signal and moving their swash plate 
84,84' in response to the received signal. Variable displacement pumps 
having associated servo valves are well known in the art. 
In the above-described system, the signal "X", "X'" are delivered to their 
servo valves 86,86' for controlling the discharge of the respective pumps 
18,20 in response thereto. 
A third means 88 is provided in the hydraulic system 10 for altering the 
magnitude of a pilot pump signal and delivering a resultant signal "Y" for 
controlling the pumps 18,20. The third means 88 alters the pilot pressure 
signal passing thereto via line 66,67,89 in response to a preselected 
biasing force that is opposed by a pressure signal that is responsive to 
the power output being required of the power source 14. The pump discharge 
pressures, which are a function of power output of the power source 14, 
are delivered to the third means 88 via lines 76,54 and 78,54' for 
opposing the biasing force. 
The third means 88 senses the power output of the power source 14, alters a 
pilot signal in response to a biasing force opposing the discharge 
pressures of the pumps, and delivers a resultant signal "Y" from the third 
means 88 via lines 98,100 to the respective pump control assemblies 26,28 
of the respective pumps 18,20. The third means 88 can be, for example, a 
summing valve as is known in the art, or other means for measuring drain 
of the power output and delivering a signal in response thereto. 
In the preferred embodiment shown, each circuit 22, 24 has a fourth means 
102,102' for sensing the associated signals "X", "Y", and "X'", "Y", and 
delivering the largest of each sensed signal pairs as resultant signals 
"Z", "Z'" for controlling the respective pump 18,20. As shown, the fourth 
means 102,102' can each be a pair of check valves 106,108 and 106', 108'. 
The signals "X" or "Y", or "Z" and "X'", or "Y" or "Z'" are delivered to 
their respective servo valves 86,86' for biasing the associated swash 
plates 84,84' and controlling the fluid discharge rate of the pumps 18,20. 
Other aspects, objects, and advantages of this invention can be obtained 
from a study of the drawings, the disclosure, and the appended claims.