High flow hydraulic circuit for tractors

A hydraulic circuit is disclosed for a tractor in which a steering circuit and an implement circuit are utilized to provide a high flow capability to the implement valve stack. A series of priority valves are operable to divert hydraulic flow from the steering circuit to the implement circuit under conditions where the steering mechanism is not being operated and the implement circuit pump is operating at full capacity. The first priority valve diverts the hydraulic flow from the steering circuit to a second priority valve that is controlled by a pressure differential valve that senses the implement circuit pump working at full displacement, whereupon the second priority valve directs the diverted hydraulic flow into the implement circuit. The first priority valve retains hydraulic flow within the steering circuit whenever the steering mechanism is being operated. The second priority valve directs the diverted hydraulic flow back to the reservoir unless the implement circuit pump is operating at full capacity.

BACKGROUND OF THE INVENTION 
This invention relates generally to off-road motor vehicles, such as 
tractors, and more particularly, to a hydraulic circuit for providing a 
high flow to tractor control valves operatively coupled to an attached 
implement. 
Tractors are typically detachably connected to implements, such as 
harvesting machines or tillage implements, that are provided with 
hydraulically powered devices that are coupled in flow communication to 
the tractor hydraulic system through a hydraulic valve stack so that the 
implement is hydraulically powered through the tractor hydraulic system. 
In some instances, the hydraulic power required to operate the implement 
places a strain on the capabilities of the tractor hydraulic system. 
It would be desirable to provide a hydraulic circuit that would be operable 
to divert hydraulic flow from other hydraulic systems on the tractor, when 
those systems do not require hydraulic power, to supplement the capability 
of the tractor hydraulic system to meet the power demands of the implement 
hydraulics. 
SUMMARY OF THE INVENTION 
It is an object of this invention to overcome the aforementioned 
disadvantages of the prior art by providing a tractor hydraulic circuit to 
provide a means for diverting hydraulic flow under certain conditions to 
meet the power demand of the implement attached thereto. 
It is another object of this invention to provide a tractor hydraulic 
circuit that provides an increased hydraulic flow to the implement 
hydraulics when other tractor hydraulic systems do not require the 
hydraulic power. 
It is a feature of this invention that the tractor hydraulic circuit 
diverts the flow from the hydraulic steering mechanism to the implement 
circuit when the steering mechanism is not being operated. 
It is an advantage of this invention that a priority valve senses the 
demand for hydraulic fluid in the steering mechanism and diverts hydraulic 
fluid from the steering mechanism only when the steering mechanism is not 
being operated. 
It is another advantage of this invention that the tractor hydraulic 
circuit supplying hydraulic fluid to the implements also includes a 
priority valve that diverts the flow of diverted hydraulic fluid back to 
the reservoir if not needed by the implement. 
It is another feature of this invention that the tractor hydraulic circuit 
supplying diverted hydraulic fluid to the implement valves includes a 
pressure differential sensing valve that is operable to control the 
associated priority valve to direct diverted hydraulic fluid into the 
implement valve stack only when the implement power demand is greater than 
the capability of the implement hydraulic circuit without the diverted 
hydraulic flow. 
It is still another advantage of this invention that the pressure 
differential sensing valve monitors the pressure differential between the 
implement hydraulic circuit pump and the pressure at the implement valve 
stack, such that the diverted hydraulic flow from the steering mechanism 
is utilized in the implement circuit only when the pressure differential 
is less than the minimum setting for the implement circuit pump. 
It is yet another feature of this invention that the diverted hydraulic 
flow from the steering mechanism is utilized in the implement circuit only 
when the implement circuit pump is at full displacement. 
It is yet another object of this invention to provide a tractor hydraulic 
circuit for diverting hydraulic fluid from unused system under high flow 
demand conditions which is durable in construction, inexpensive of 
manufacture, carefree of maintenance, facile in assemblage, and simple and 
effective in use. 
These and other objects, features and advantages are accomplished according 
to the instant invention by providing a hydraulic circuit for a tractor in 
which a steering circuit and an implement circuit are utilized. A series 
of priority valves are operable to divert hydraulic flow from the steering 
circuit to the implement circuit under conditions where the steering 
mechanism is not being operated and the implement circuit pump is 
operating at full capacity. The first priority valve diverts the hydraulic 
flow from the steering circuit to a second priority valve that is 
controlled by a pressure differential valve that senses the implement 
circuit pump working at full displacement, whereupon the second priority 
valve directs the diverted hydraulic flow into the implement circuit. The 
first priority valve retains hydraulic flow within the steering circuit 
whenever the steering mechanism is being operated. The second priority 
valve directs the diverted hydraulic flow back to the reservoir unless the 
implement circuit pump is operating at full capacity.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings and, particularly, to FIG. 1, a 
representative view of an agricultural tractor incorporating the 
principles of the instant invention can best be seen. Left and right 
references are used as a matter of convenience and are determined by 
standing at the rear of the tractor and facing the forward end in the 
normal direction of travel. The tractor chassis 10 is supported above the 
ground in a conventional manner by front wheels 11, which on large 
tractors are typically drivingly powered, and rearward drive wheels 19 
rotatably mounted in a customary transversely spaced orientation. 
The chassis supports a conventional engine 12 serving to provide 
operational power for the tractor T and an operator's cab 15 positioned in 
an elevated location. The operator's cab 15 includes a steering wheel 16, 
positioned forwardly of the conventional operator's seat 17, to operate 
the steering of the tractor T through manipulation of the hydraulic 
cylinder 18 controlling the articulation of the tractor chassis 10 in a 
known conventional manner. The operator's cab 15 is also provided with 
conventional operative controls, such as the transmission control lever 
21, to permit the operative control of the tractor T. 
The tractor T is provided with a transmission 20 supported on the chassis 
10 to receive rotational power from the engine 12 and transfer rotational 
power to the front and rear wheels 11, 19 at selected speeds of operation. 
The transmission control lever 21, which is mounted in the operator's cab 
15 within normal reach of the operator's seat 17, effects a shifting of 
the available speeds of operation through a conventional push/pull cable 
(not shown). 
A master clutch 25 is mounted on the transmission 20 and is operatively 
associated therewith to control the application of operative power from 
the engine 12 to the transmission 20 in a conventional manner. The master 
clutch 25 is hydraulically controlled through the operation of the control 
valve 26, which is also mounted on the transmission 20 in a manner 
described in greater detail below and is operated in a conventional manner 
by the clutch pedal 27 located in the operator's cab 15. 
Referring now to the schematic diagrams of FIGS. 2, 2A and 2B, the details 
of the tractor hydraulic system 30 can best be seen. The tractor hydraulic 
circuit 30 includes an implement circuit 40 and a steering circuit 50, 
both of which draw hydraulic fluid from a reservoir 35. The tractor 
hydraulic circuit 30 further includes a cooling mechanism 32 and a filter 
34 arranged in series to cool and filter the hydraulic fluid passing 
therethrough before being re-circulated into the hydraulic circuit 30. 
The implement circuit 40 includes a variable displacement, pressure and 
flow compensated, piston pump 41 that is operable to supply hydraulic 
fluid under pressure from the steering circuit return line 59, and 
ultimately from the reservoir 35, through intake line 36 to a conventional 
implement remote valve stack 45 via line 43. As will be recognized by one 
skilled in the art, the hydraulic devices (not shown) on the implement 
(not shown) are connected to the tractor hydraulic system 30 through the 
respective remote valves in the conventional valve stack 45. 
The variable displacement piston pump 41 provides hydraulic fluid as 
demanded by the devices (not shown) coupled in flow communication with the 
valve stack 45. One skilled in the art will further recognize that the 
implement devices (not shown) may require more power from the pump 41 that 
the pump 41 can supply. Hydraulic fluid utilized through the implement 
valve stack 45 is returned to the reservoir 35 via return line 49 through 
the filter 34. Hydraulic fluid not used in the valve stack 45 is returned 
to the reservoir 35 via the return line 47. 
The steering circuit 50 includes a fixed displacement gear pump 51 that is 
operable to supply hydraulic fluid under pressure from the reservoir 35 
through intake line 38 to a first priority valve 55 via line 53. The first 
priority valve 55, through a conventional operation of a steering valve 
56, is operable to sense a demand for hydraulic fluid from the steering 
cylinders 18 actuated by a turning of the steering wheel 16 to effect a 
steering of the tractor T. When the steering valve 56 detects a demand 
from the hydraulic cylinders 18, the priority valve 55 is shifted so that 
hydraulic fluid is directed into the steering valve 56 for operation of 
the steering cylinders 18 in a conventional manner. Hydraulic fluid is 
then return to the reservoir 35 through the cooler 32 and the filter 34 
via the return line 59. 
If no demand from the steering cylinders 18 is sensed, the first priority 
valve 55 diverts hydraulic fluid through the bypass line 57 to a second 
priority valve 60, which is controlled by a pressure differential sensing 
valve 65 that senses the pressure differential between the implement 
circuit pump 41 at point A and the pressure at the implement valve stack 
45. If pressure differential sensing valve 65 detects a pressure 
differential that is less than the minimum setting for the implement 
circuit pump 41, which indicates that the variable displacement implement 
circuit pump 41 is working at full capacity, the second priority valve 60 
is shifted to divert the hydraulic flow through bypass line 57 into the 
crossover line 58 which passes through check valve 62 and adds additional 
hydraulic fluid under pressure to the implement valve stack 45. The check 
valve 62 insures that hydraulic fluid will not back flow from the 
implement circuit 40 into the steering circuit 50. 
If the variable displacement piston pump 41 in the implement circuit 40 is 
operating at less than full capacity, and, therefore, can handle the power 
demand from the implement valve stack 45, the pressure differential 
sensing valve 65 keeps the second priority valve 60 directing hydraulic 
fluid coming through bypass line 57 into the return line 59 and, 
subsequently, into the reservoir 35 through the check valve 39, unless 
drawn into the implement circuit 40 through intake line 36 by the 
implement circuit pump 41. As a result, the hydraulic fluid diverted from 
the steering circuit 50 is used on an intermittent basis and only when 
required to meet the demand at the implement valve stack 45, and also only 
when the steering cylinders 18 do not require the flow from the gear pump 
51. 
One skilled in the art will readily realize that the pressure differential 
sensing valve 65 can be set to be operable through pressure differential 
from different points in the implement circuit and to be operable to shift 
the second priority valve 60 at some point less than full capacity of the 
piston pump 41. For example, the pressure differential sensing valve 65 
could be set to shift the second priority valve 60 to direct flow into the 
implement circuit 40 when the piston pump 41 achieves 80% of its 
displacement capacity, instead of at 100% capacity. Furthermore, the first 
priority valve 55 will preferably be set to give priority to the steering 
cylinders 18 of all the hydraulic flow required thereby, with all 
remaining flow, if any, being diverted to the second priority valve 60. 
Accordingly, the tractor hydraulic system 30 will be operable to provide a 
high hydraulic flow to the implement valve stack as necessary without 
requiring an oversized, and more expensive, piston pump 41 having a 
capacity that is only necessary on an intermittent basis. One skilled in 
the art will realize that, from a practical matter, the demand for high 
flow from the implement valve stack 45, which normally corresponds with 
substantial implement activity, does not normally occur at the same time 
as substantial steering maneuvers requiring operation of the steering 
cylinders and the full utilization of the gear pump 51 flow. Such steering 
activity typically occurs at the headlands of a field when the implement, 
whether a harvester, tillage device or other configuration, is inactive. 
It will be understood that changes in the details, materials, steps, and 
arrangements of parts which have been described and illustrated to explain 
the nature of the invention will occur to and may be made by those skilled 
in the art upon a reading of this disclosure within the principles and 
scope of the invention. The foregoing description illustrates the 
preferred embodiment of the invention; however, concepts, as based upon 
the description may be employed in other embodiments without departing 
from the scope of the invention. Accordingly, the following claims are 
intended to protect the invention broadly as well as in the specific form 
shown.