Vehicle steering and auxiliary function hydraulic circuit

A hydraulic circuit includes as its major constituents a pump supplying hydraulic fluid to a main steering valve and to an auxiliary function valve through a priority valve. The priority valve allows the main steering valve to preempt the auxiliary function valve on demand. A secondary valve is provided to allow an accumulator to discharge hydraulic fluid to the main steering valve should the hydraulic circuit experience a loss of pressure and flow. Electrical circuit means are provided to warn the operator that the hydraulic circuit has lost pressure and flow.

BACKGROUND OF THE INVENTION 
The present invention relates to the hydraulic circuit for providing fluid 
to a vehicle's steering and auxiliary functions and, more particularly, 
relates to such hydraulic circuits giving steering priority over auxiliary 
functions and having an accumulator for providing emergency steering 
capability. 
Industrial vehicles such as skidders, loaders and scrapers, or the like, 
are provided with hydraulically fed steering systems which make it 
possible for large vehicles to be maneuvered with relative ease during all 
operations. Such vehicles are also provided with hydraulically fed 
auxiliary function capabilities to operate such things as grapples, loader 
buckets and scraper blades. The auxiliary functions share hydraulic fluid 
with the steering system. Conventionally, hydraulic fluid is passed 
through a priority valve which branches fluid to both the steering system 
and the auxiliary functions giving priority to the steering system. That 
is, the fluid requirements of the steering system have preemption over the 
fluid requirements of the auxiliary function. Emergency steering 
capability is provided by an accumulator which is in fluid communication 
with a secondary valve which ports accumulator contained fluid to the 
steering system upon sensing the last of a substantial degree of fluid fed 
pressure to the steering system. 
Conventionally, the priority valve includes a valve spool acted upon by 
fluid pressure to overcome a spring and assume a first spool position. The 
first position allows the priority valve to port fluid to both the main 
steering valve of the steering system and to the auxiliary functions. When 
the fluid pressure drops below a predetermined amount occasioned by a 
fluctuation in hydraulic circuit pressure, the spring force on the valve 
spool shifts the valve spool to a second position porting all incoming 
fluid to the main steering valve. 
Large vehicles utilize steering systems which require relatively high fluid 
pressure on the order of 1500 to 2000 psi, in contrast, the fluid pressure 
requirements of auxiliary functions can be only a few hundred psi under 
certain conditions. As a result, when the vehicle is using an auxiliary 
function and is not being steered, the conventional priority valve, which 
is pressure sensitive, experiences high pressures necessary to overcome 
the spring force on the valve spool. The absence of the production of work 
in light of high spool valve pressures results in the production of 
excessive heat necessitating the inclusion of a heat exchanger in the 
hydraulic circuit. 
SUMMARY OF THE INVENTION 
It is an objective of the present invention to present a hydraulic circuit 
for providing hydraulic fluid to a vehicle steering system and auxiliary 
functions which does not generate excessive heat during any particular 
mode of operation and, thereby, eliminating the need for a heat exchanger 
in the hydraulic circuit. 
It is a further objective of the present invention to present a priority 
valve which is flow sensitive within the hydraulic circuit. 
It is a still further objective of the present invention to present a means 
of alerting a vehicle operator to the loss of primary hydraulic pressure 
and flow within the hydraulic circuit. Additional objectives and benefits 
of the present invention will be noted in the subsequent detailed 
description. 
The primary constituents of the hydraulic circuit are a pump, a priority 
valve, a secondary valve and a main steering valve. The pump supplies 
hydraulic fluid to a priority valve which is flow sensitive. In a normal 
mode, fluid passes through the priority valve and is delivered to the main 
steering valve and to non-priority auxiliary functions. Fluid is returned 
from the steering valve to the priority valve through a load sensing 
conduit. The secondary valve receives fluid from the pump to charge an 
accumulator. When the accumulator is charged, the secondary valve blocks 
flow from the accumulator to the main steering valve. An electrical 
circuit is provided for delivering a warning signal to the vehicle 
operator should flow in the priority valve and pressure in the secondary 
valve be reduced below a predetermined amount. 
The priority valve includes a valve spool biased in a first position by 
fluid pressure within the hydraulic circuit feeding fluid the main 
steering valve and auxiliary functions, overcoming a spring force and 
additive fluid pressure delivered from the steering system through a load 
sensing conduit. A switch is provided in the priority valve. The switch 
contains a pin encountered perpendicularly by the priority valve spool 
when the valve spool is in a second position resulting from steering 
preemption occasioned by a substantial fluctuation or decrease in the 
primary hydraulic pressure. The switch in the priority valve acts 
thereupon in conjunction with a switch in the secondary valve to permit an 
electric circuit to energize an operator warning device. The collective 
effect of the switches prevent the electric circuit from sending false 
alerts to the operator during minor fluctuations of hydraulic pressure.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, a hydraulic circuit, generally indicated as 11, 
includes as primary constituents a pump 13, a priority valve 15, a 
secondary valve 17, and a substantially conventional main steering valve 
19 more commonly employed to provide steering for off-road vehicles. In 
normal operation, the pump 13 provides hydraulic fluid to the priority 
valve 15 which is responsible for porting fluid to non-priority auxiliary 
functions and to priority functions, e.g., the main steering valve 19. The 
main steering valve 19 communicates with a crossover relief valve 21 and 
therethrough a right- and a left-hand steering cylinders 23 and 25, 
respectively, in a generally conventional manner. It is noted that it is 
within the contemplation of the invention that a plurality of priority 
functions, singularly represented herein by the main steering valve 19, 
may be associated with the hydraulic circuit 11. It is noted that the 
connotation of right and left are employed for ease of description and are 
referenced from a direct viewing of the drawings. 
Referring now to FIG. 2, the priority valve 15 includes a valve body 27 
defining a valve bore 29. A threaded first plug 31 is threadably mounted 
in the right-hand end of valve bore 29. A rod 33 is fixably mounted by any 
conventional means centrally to the plug 31 and extends into valve bore 
29. A second threaded plug 35 is threadably mounted to the left-hand end 
of valve bore 29. The plug 35 includes a formed tubular extension 37 
centrally located extending through the plug 35 and into valve bore 29. 
The tubular extension 37 defines a passageway 39. Fixably mounted by any 
conventional means such as by press fitting within the right-hand end of 
passageway 39 is a plug 41. Plug 41 defines a longitudinal passageway 43. 
Within the tubular extension 37 is a poppet 47 biased into a seat member 
45 by a compression spring 49. A drain plug 51 is fixably mounted by any 
conventional means within the left-hand portion of the tubular extension 
37 of plug 35. A cylindrical member 52 is seated within passageway 39 of 
plug 35 between left-hand end of drain plug 51 and the right-hand end of 
spring 49. The member 52 contains an axial orifice 54. 
The valve body 27 also defines a plurality of ports intersecting to the 
valve bore 29 which will be subsequently described generally from the 
right-hand side to the left-hand side. An inlet port 53 receives fluid 
from pump 13 through conduit 55. A check valve 57 interrupts conduit 55 to 
prevent conduit back flow. Generally located opposite to inlet port 53 is 
a priority function outlet port 59 (hereinafter called steering outlet 
port 59) which is in communication with the main steering valve 19 through 
conduit 61. Non-priority functions are supplied fluid from the priority 
valve 15 through a non-priority function outlet port 63 by conduit 65 
which communicates in a conventional manner with a non-priority function 
valve (not shown). A priority load sensing port 67 is in communication 
with the main steering valve 19 through a load sensing conduit 69. Biased 
by inlet fluid pressure to the left-hand side within bore 29 against an 
annular step 68 in bore 29 is a valve spool 71. A compression spring 73 
having a relatively low spring rate is abutting to a valve spool 71 on the 
left-hand side. The valve spool 71 is slidably mounted in bore 29. The 
compression spring 73 is abutting to the plug 35 at the other end, and is 
located around the tubular extension 37. Port 67 is located leftwardly of 
the valve spool's 71 leftward-most position. The valve spool 71 occupies 
either a first position which is against step 68 just opposite tubular 
extension 37 or (as shown in FIG. 2) a second position abutting to the 
left-hand end of rod 33 (as shown in phantom in FIG. 2). The relief valve 
51 provides a means of relieving fluid pressure to the left-hand side of 
valve spool 71. 
It is noted that the valve bore 29 includes a circumferential step 160 
located just rightwardly of non-priority outlet port 63. It has been found 
that the inclusion of step 160 promotes flow through the priority valve to 
the non-priority outlet port 63. Step 160 alters the velocity profile of 
fluid as it passes initially over the region of step 160. 
An electrical switch 77 is fixably mounted in an additional port 79 in the 
priority valve 15. The electrical switch 77 includes an insulator 81 which 
in the preferred embodiment is an elastomer having a pin 83 fixably 
mounted by any conventional means such as by press fitting therein and 
extending centrally through the insulator 81. In the preferred embodiment, 
the insulator 81 is pressed mounted in the port 79 such that pin 83 
extends into valve bore 29 slightly leftward of the leftwardmost extension 
of pin 33. A plug 85 has a screw 87 extending therethrough, wherein screw 
87 is insulated by insulation material 89 within the plug 85. The plug 85 
is fixably mounted within port 79 such that one end of screw 87 is in 
contact with an opposite end of pin 83. 
The pin 83 of switch 77 is set at a right angle to the valve spool 71 such 
that perpendicular contact of the valve spool 71 to pin 83 closes switch 
77. The right angle alignment of pin 83 to valve spool 71 causes the pin 
83 to experience slight angular deflection upon contact by valve spool 71. 
By so aligning pin 83 to valve spool 71 contact can be maintained between 
pin 83 and screw 87 when the valve spool 71 is in the second position. 
Further, because the elastomer insulator 81 receives the resulting loads 
from spool 71 on pin 83, the integrity of switch 77 is substantially 
prolonged. 
Referring now to FIG. 3, the main steering valve 19 is of generally 
conventional design and includes a directional control valve 90 in 
communication with the priority valve 15 through conduit 61. A check valve 
101 interrupts conduit 61 to require single directional fluid in conduit 
61. A conduit 103 communicates the directional control valve 90 to sump. 
Downstream of check valve 101 is a conduit 105 communicating conduit 61 to 
conduit 103. A check valve 107 interrupting conduit 105 limiting the fluid 
flow direction from conduit 103 to conduit 61. The directional control 
valve 90 is further in communication with the load sensing conduit 69. The 
main steering valve 19 communicates with the load sensing conduit 69. The 
main steering valve 19 also communicates with the cross-over relief valve 
21 through conduits 109 and 111 and the gerotor set 100 in a generally 
conventional manner, further communicating with the right- and left-hand 
steering cylinders 23 and 25, respectively, through conduits 113 to 116, 
respectively, in a conventional manner. The operation of the main steering 
valve 19, cross-over relief valve 21, and steering cylinders 23 and 25 is 
thought to be well understood by those skilled in the art. 
Referring now to FIG. 4, the secondary valve 17 includes a valve body 119 
defining a valve bore 121 having a spool 123 slidably contained therein. A 
plurality of ports are contained in the secondary valve 17 which 
communicate with valve bore 121, namely, an inlet port 125, a 
charge-discharge port 127, outlet port 129, and sump port 131. The 
secondary valve 17 also contains a switch 133 activated by a pin 135 
slidably mounted in an axial bore 137. The secondary valve 17 is more 
particularly described in U.S. Pat. No. 4,326,558 issued to Douglas M. 
Gage on Apr. 27, 1982 and filed Nov. 24, 1980, herein incorporated by 
reference. Conduit 139 communicates inlet port 125 to conduit 61 upstream 
of check valve 101. A conventional accumulator 143 is in communication 
with the charge-discharge port 125 through a conduit 145. A conduit 147 
communicates the outlet port 129 to conduit 61 downstream of check valve 
101. 
A warning circuit, generally indicated as 149, is provided, and includes a 
relay 150 and audible warning device 151. The warning circuit 149 receives 
a positive potential through line 153. An intersecting line 157 to line 
153 delivers electrical potential to the relay 150 such that current flow 
through the relay 150 to line 157 causes the relay 150 to close. When the 
relay 150 is closed, current is permitted to flow between lines 153 and 
159 actuating alarm 151. Line 157 communicates with switch 133 associated 
with the secondary valve 17 and permits current to flow therethrough when 
switch 133 is closed by valve spool 123. Line 159 communicates with switch 
77 associated with the priority valve 15 and permits current to flow 
therethrough when switch 77 is closed. As a result, the operator is saved 
from the activation of the warning device 151 due to momentary fluctuation 
in hydraulic circuit pressure since it is necessary for the secondary 
valve switch 131 to be closed prior to alarm 151 activation. 
There are three modes of operation for the hydraulic circuit 11. The first 
mode of operation is occasioned when the carrying vehicle is being steered 
and simultaneously operating an auxiliary function (as shown in the 
FIGS.). Under such operating conditions, the secondary valve stands with 
the charge-discharge port blocked by spool 123 prohibiting discharge of 
the accumulator and the switch 133 "OFF". The priority valve 15 stands 
with the spool 71 in the furthermost left-hand position allowing fluid 
received in inlet port 53 through conduit 55 from pump 13 to be directed 
to both the steering outlet port 59 and the non-priority function port 63. 
The second mode of operation is occasioned when the vehicle is not being 
steered and an auxiliary function(s) may or may not be in operation. Under 
such operating conditions, the secondary valve remains in the previously 
described state. However, there is no fluid pressure in the load sensing 
conduit 69 resulting in a reduced counter load on the priority valve spool 
71 resulting in a highly significant reduction in heat generation in this 
operating mode as compared to the heat generated by a conventional 
priority valve used in similar circumstances. Under this condition, switch 
75 is open and the emergency steering is not activated. 
In the emergency mode resulting from the loss of hydraulic pressure, the 
absence of fluid flow through the priority valve 15 permits the spring 73 
to cause the spool 71 to displace to the right coming into contact with 
pin 83 grounding switch 75 "ON". Further, spool 123 of the secondary valve 
17 is displaced as a result of the loss of fluid pressure allowing the 
accumulator 143 to discharge. The displacement of spool 123, further, 
grounding switch 133 "ON". When switch 133 is grounded, current is allowed 
to flow from line 153 to line 157 actuating relay 150; the contemporaneous 
grounding of switch 75 allows current to flow from line 155 to line 159 
through relay 150 to activate the warning device 151. The discharge of the 
accumulator is directed to the main steering valve through the conduit 147 
.