U.S. patent number 3,797,140 [Application Number 05/286,025] was granted by the patent office on 1974-03-19 for fluid suspension system.
This patent grant is currently assigned to Caterpillar Tractor Co.. Invention is credited to Orcenith D. McWilliams, Roger A. Rice.
United States Patent |
3,797,140 |
McWilliams , et al. |
March 19, 1974 |
FLUID SUSPENSION SYSTEM
Abstract
A fluid suspension system for a sprung mass includes a fluid
motor having a cushioning end and an opposite end disposed in
elevational supporting relation between the sprung mass and an
unsprung mass. A resiliently biased fluid pressure system is in
constant communication with the cushioning end of the fluid motor
normally to resiliently support the sprung mass at substantially a
predetermined elevated cushioning position relative to the unsprung
mass. A lockout valve affords selective communication of the
opposite end of the fluid motor with the fluid pressure system to
equalize pressure in both ends of the motor and permit the sprung
mass temporarily to move to a lowr predetermined fixed
position.
Inventors: |
McWilliams; Orcenith D.
(Morris, IL), Rice; Roger A. (Joliet, IL) |
Assignee: |
Caterpillar Tractor Co.
(Peoria, IL)
|
Family
ID: |
23096723 |
Appl.
No.: |
05/286,025 |
Filed: |
September 5, 1972 |
Current U.S.
Class: |
37/414; 37/417;
91/461; 137/624.27; 172/307; 137/102; 137/625.68; 267/64.16;
267/126 |
Current CPC
Class: |
B62D
53/021 (20130101); Y10T 137/86702 (20150401); Y10T
137/2544 (20150401); Y10T 137/86485 (20150401) |
Current International
Class: |
B62D
53/00 (20060101); B62D 53/02 (20060101); B60d
001/00 () |
Field of
Search: |
;172/307,4,4.5
;37/124,126R,129 ;280/488,489,124,423 ;180/14R ;267/64,65D,124,126
;137/102,106,596.12,624.27,625.6,625.68 ;60/52HE ;91/461 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Pulfrey; Robert E.
Assistant Examiner: Eickholt; Eugene H.
Attorney, Agent or Firm: Walters; Ralph E.
Claims
What is claimed is:
1. A fluid suspension system in which a fluid motor having a
cushioning end and a normally vented opposite end is disposed in
elevational supporting relation between a sprung mass and an
unsprung mass, said fluid suspension system comprising;
resiliently biased fluid pressure means in constant communication
with said cushioning end of said fluid motor to resiliently support
said sprung mass at substantially a predetermined elevated
cushioning position relative to said unsprung mass when said
opposite end is vented; and
lockout valve means operative selectively to communicate said
opposite end of said fluid motor with said fluid pressure means and
simultaneously to block the venting thereof to equalize pressure in
said ends of the motor and minimize said resilient supprt whereby
the weight of the sprung mass is operative temporarily to move the
sprung mass to a lower predetermined fixed position.
2. The fluid suspension system of claim 1 including fluid flow
restricting means disposed between said fluid pressure means and
said opposite end of said fluid motor to control the lowering rate
of the sprung mass.
3. The fluid suspension system of claim 1 including a non-return
valve disposed between said fluid pressure means and said opposite
end of said fluid motor to prevent flow of fluid from said opposite
end toward said fluid pressure means temporarily to lock said
sprung mass in said predetermined fixed position.
4. The fluid suspension system of claim 1 including;
a reservoir; and
separate valve means having open and closed positions for
controlling communication between said opposite end and said
reservoir and operative to move to said open position communicating
said opposite end with said reservoir responsive to operation of
said lockout valve means to block communication of said opposite
end with said fluid pressure means and return said sprung mass to
said predetermined cushioning position.
5. A fluid suspension system in which a fluid motor having a
cushioning end and a normally vented opposite end is disposed in
elevational supporting relation between a sprung mass and an
unsprung mass, said fluid suspension system comprising;
resiliently biased fluid pressure means in constant communication
with said cushioning end of said fluid motor to resiliently support
said sprung mass at substantially a predetermined elevated
cushioning position relative to said unsprung mass when said
opposite end is vented;
lockout valve means operative selectively to communicate said
opposite end of said fluid motor with said fluid pressure means and
simultaneously to block the venting thereof to equalize pressure in
said ends of the motor whereby the weight of the sprung mass is
operative temporarily to move the sprung mass to a lower
predetermined fixed position;
a reservoir;
separate valve means having open and closed positions for
controlling communication between said opposite end and said
reservoir and operative to move to said open position communicating
said opposite end with said reservoir responsive to operation of
said lockout valve means to block communication of said opposite
end with said fluid pressure means and return said sprung mass to
said predetermined cushioning position;
a source of fluid pressure; and
leveling valve means, having a neutral position normally blocking
communication of said cushioning end of said fluid motor with said
source of fluid pressure and said reservoir and being responsive to
predetermined variations in the relative position of said sprung
mass to said unsprung mass to control communciation of said
cushioning end with said source of fluid pressure and said
reservoir to maintain said sprung mass substantially in said
predetermined cushioning position.
6. The fluid suspension system of claim 5 wherein said unsprung
mass is a tractor and said sprung mass is a trailer, and said fluid
suspension system is a cushion hitch which couples said trailer to
said tractor for relative vertical movement therebetween, said
cushion hitch being tuned and damped to generate out-of-phase
vertical movement of said trailer relative to vertical movement of
said tractor to suppress bounce of said tractor and said trailer as
a unit.
7. The fluid suspension system of claim 6 including link means
pivotally coupling said trailer and said tractor for vertical
relative movement therebetween with said fluid motor connected
between said link means;
a valve spool movably disposed in said leveling valve means for
controlling said communication of said cushioning end of said fluid
motor with said source and said reservoir to maintain a preselected
elevational relationship between said trailer and said tractor;
detent/release means in said leveling valve means engaging said
valve spool in a neutral blocking position and requiring a selected
minimum break-out force for moving said valve spool; and
resilient lost motion linkage means for connecting said valve spool
to said link means to exert an increasing actuating force on said
valve spool in response to relative vertical movement of said
tractor and trailer so that limited relative movement of said
trailer from said preselected elevational relationship can occur
without exceeding said selected minimum break-out force required to
move said valve spool from said neutral blocking position.
8. The fluid suspension system of claim 5 further comprising;
pilot circuit means including a source of pilot fluid pressure;
actuation means responsive to pilot fluid pressure for actuating
said lockout valve means and said separate valve means; and
a pilot selector valve means interposed between said source of
pilot fluid pressure and said actuation means for selectively
conditioning said lockout valve means and said separate valve means
to establish said preselected elevational position of said trailer
and to condition said lockout valve means and said separate valve
means to permit said trailer to move to said predetermined fixed
position.
9. The fluid suspension means of claim 8 wherein said separate
valve means comprises a poppet type check valve and is coaxially
aligned with said lockout valve means;
actuating means on said lockout valve for moving said separate
valve means to said open position when said lockout valve is
conditioned to block communication between said opposite end of
said fluid motor and said fluid pressure means.
10. The fluid suspension means of claim 8 wherein said lockout
valve means includes pilot fluid pressure responsive actuating
means;
separate actuation means, responsive to said pilot fluid pressure
for actuating said separate valve means simultaneously with said
lockout valve means.
11. The fluid suspension system of claim 8 wherein said leveling
valve means includes a valve spool;
a resilient lost motion linkage connected to said spool and
responsive to movement of said sprung mass toward said
predetermined fixed position to move said valve spool to a position
communicating said source of fluid pressure with said cushioning
end of said fluid motor; and
fluid actuation means operatively associated with said valve spool
and selectively communicable by said lockout valve means with said
source of fluid pressure to act in opposition to said resilient
lost motion linkage and return said valve spool to said neutral
position.
12. In a hitch assembly coupling a tractor and a trailer through
link members for vertical relative movement with a hydropneumatic
support connected between the link members to improve the riding
qualities by suppressing bounce, an improved, low-cost hitch
control valve and linkage comprising:
a control valve mounted adjacent to said hitch assembly and
connected to a source of pressurized fluid;
a suspension cushioning means connected to said control valve and
connected across said link members of said hitch assembly allowing
relative vertical movement between said tractor and said trailer,
said suspension cushioning means having at least one pneumatic
accumulator commonly connected thereto;
a valve spool movable in said control valve to admit pressurized
fluid to said suspension cushioning means and vent fluid therefrom
to maintain a preselected relationship between said tractor and
said trailer;
a detent/release means in said valve engaging said valve spool and
having a neutral engaged position requiring a selected mininum
break-out force;
a lost motion linkage means connecting said valve spool and one of
said link members of said hitch assembly moving relative to said
control valve through which vertical movement of said hitch
assembly is transmitted to said valve spool and whereby limited
hitch movement relative to said preselected relationship of said
tractor and said trailer can occur without actuation of said
control valve and smooth fluid adjustment will be available once
said break-out force of said valve spool has been exceeded by
forces displacing it from said lost motion linkage means.
13. The improved control valve and linkage defined in claim 12
wherein the force generated by said lost motion linkage means is
proportional to its absorbed motion and the break-out force of the
valve spool is sufficient to cause said lost motion linkage means
to absorb some motion before it exceeds said break-out force.
14. The improved control valve and linkage defined in claim 13
wherein the lost motion linkage means includes a displaceable
spring member having a force generally linear relative to its
absorbed displacement.
15. The improved control valve and linkage defined in claim 13
wherein several pneumatic accumulators are connected to the
suspension cushioning means, each accumulator having a different
preload to increase the load range of the trailer over which said
cushioning means will effectively suppress bounce.
16. The improved control valve and linkage defined in claim 13
wherein the hitch assembly is a multi-pivoted unit connecting a
tractor portion with a trailer portion of an articulated
vehicle.
17. The improved control valve and linkage defined in claim 16
wherein the trailer portion is an earthmoving scraper.
18. The improved control valve and linkage defined in claim 16
wherein the hitch assembly is constructed with link members
arranged to cause pitch to be suppressed along with bounce by the
cushioning means.
19. The improved control valve and linkage defined in claim 13
wherein the source of pressurized fluid is a pump driven by an
engine in the tractor and the control valve has a pressure
controlled valve operable to bleed pressure from the suspension
cushioning means when said engine is stopped.
20. The improved control valve and linkage defined in claim 13
wherein the detent/release means includes cammed surfaces on
opposite sides of its neutral engaged position whereby the
centering force on the valve spool is increased as the hitch
assembly approaches the preselected relationship between said
tractor and trailer.
21. The improved control valve and linkage defined in claim 13
wherein the control valve includes controllable piston means
operable to activate and deactivate the cushion means of the hitch
assembly.
22. The improved control valve and linkage defined in claim 13
wherein the cushioning means is a hydraulic cylinder.
Description
BACKGROUND OF THE INVENTION
Hydropneumatic suspension hitches for coupling a two wheel tractor
with a scraper unit or the like have met with increasing acceptance
because of the ability to control pitch and bounce in such vehicles
in both the loaded and unloaded condition. U.S. Pat. No. 3,311,389,
issued to Barton et al, and U.S. Pat. No. 3,449,845, issued to
Jessen et al, are illustrative of hydropneumatic suspension hitches
of this type. The theory and operation of such hydropneumatic
suspension hitches are best described in U.S. Pat. No. 3,311,389
which is hereby incorporated by reference for a complete
understanding of this invention.
Improved riding qualities are obtained in tractor-scraper
combinations with the hydropneumatic suspension systems described
in the above patents. However, the control valves of such systems
must be highly sophisticated and precision manufactured in order
for the hitches to operate properly under all field operating
conditions. For example, actuating a particular system for a
temporarily fixed lockout condition to permit lowering of the hitch
to a mechanical stop at a desired controlled rate requires precise
dual rate metering of flow at both ends of the fluid suspension
motor of the system. To accomplish this control it is necessary to
meter flow out of the lower or cushioning end of the fluid
suspension motor to allow the hitch to lower. Simultaneously,
pressure fluid from suspension system must be metered into the
upper end of the fluid suspension motor at a slower rate than fluid
is metered from the lower end of the suspension motor. This dual
rate metering is necessary to prevent pressure fluid in the upper
end of the suspension motor from driving the hitch downward to
mechanical stops which could result in excessive stresses in the
hitch structure.
Additionally, complex and costly pilot controlled leveling valves
with double-acting fluid damping capabilities have been employed by
the prior art to prevent operation of the leveling valve during
normal dynamic motion of the machine when traveling over rough
terrain. Such unnecessary repetitive energizing or "hunting" of the
leveling valve adversely affects the life of the system's
components and is also detrimental to the function of the
suspension system as a tuned and damped vibration absorber.
SUMMARY AND OBJECTS OF THE INVENTION
Accordingly, it is an object of this invention to provide an
improved fluid suspension system of greatly simplified construction
and which is capable of more efficient operation than presently
available suspension systems.
Another object of this invention is to provide a fluid suspension
system wherein simplified fluid metering is accomplished by a
single orifice to control lowering of the hitch to a temporarily
fixed lockout condition.
Another object of this invention is to provide a fluid suspension
system which utilizes a double acting fluid suspension motor
wherein the cushioning end is constantly pressurized in both of its
operating conditions.
Other objects and advantages of the present invention will become
more readily apparent upon reference to the accompanying drawings
and following description.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an elevation of a two wheel tractor and an earthmoving
scraper combination connected through a hydropneumatic suspension
hitch with the instant fluid suspension system incoporated
therein.
FIG. 2 is an enlarged broken-away elevation of the hydropneumatic
suspension hitch with parts of its hydraulic circuit schematically
illustrated.
FIG. 3 is a section through the low-cost control valve illustrated
in FIG. 1.
FIG. 4 is a graph illustrating the dead-band area where the control
valve remains in its neutral position even though minor up and down
relative movements between the tractor and trailer occur in the
hitch members.
FIG. 5 is an enlarged broken away section of the suspension hitch
with an alternate control valve oriented differently on the
A-frame; and
FIG. 6 is a section through the alternate low-cost control valve
shown in FIG. 5.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring more particularly to the drawings, a fluid suspension
system embodying the principles of the present invention is
generally indicated by the reference numeral 10 and is illustrated
in FIG. 1 thereof as operatively associated with an articulated
vehicle 11. The forward portion of the vehicle is depicted as a
two-wheel tractor generally indicated at 13 which is mounted on a
pair of rubber tired wheels 14. The rear portion of the vehicle is
illustrated as an earthmoving scraper generally indicated at 15 and
has a bowl 16 which is supported for oscillation about the axis of
rotation of a pair of rubber tired wheels 18.
The bowl 16 is a box-like forwardly opening material carrying
receptacle having a cutting edge 19 disposed transversely along the
lower leading edge thereof. An apron 20 is pivotally supported on
the bowl for closing and opening the forward end thereof to control
the entry and exit of dirt or other material over the cutting edge.
A suitable linkage system 21 under control of a hydraulic jack, a
portion of which is shown at 22, is provided for elevational
adjustment of the apron between open and closed positions.
A draft frame 23 includes a pair of laterally spaced draft arms 24
pivotally connected to opposite sides of the bowl 16, and a
forwardly extending centrally disposed arched goose-neck 25
articulately connected to the tractor 13 by means of a
hydropneumatic suspension hitch 26. A pair of bowl lift jacks, one
of which is shown at 27, are pivotally supported on the draft frame
for elevationally adjustable support of the forward end of the
bowl.
The hydropneumatic suspension hitch 26 is more clearly illustrated
in FIG. 2 and includes an A-frame 28 centrally mounted on a main
frame 29 of the tractor 13 in substantially upright aligned
relation with the longitudinal axis of the tractor. The A-frame is
pivotally secured on the frame with pins 30 through lugs 31 and 32
which allow the A-frame to swing about a generally horizontal pivot
axis through the pins. A stop 28a is provided on the A-frame to
limit downward movement of the hitch. A suspension bracket 33 is
connected to the A-frame by a pair of vertically spaced generally
horizontally disposed links 34 and 35. The bracket 33 includes a
stop 33a for engagement with the stop 28a. The links have their
respective forward ends pivotally connected to the A-frame 28 by
pins 36 and 37 respectively and their rearward ends are pivotally
connected to the suspension bracket by a pair of pins 38 and 39,
respectively.
Suspension bracket 33 includes a pair of upper and lower rearwardly
extending mounting ears 40 and 41 for a pivotal connection with the
forward end of the gooseneck 25 by a pair of vertically disposed
pivot pins 42 and 43 forming an articulation joint about which the
vehicle is steered.
Since the suspension bracket 33 can move vertically with respect to
the tractor 13 and the A-frame 28 due to the pivotal connection
therebetween through links 34 and 35, a cushioning jack or double
acting fluid suspension motor 44 is diagonally coupled between the
pivots 37 and 38. Cushioning jack 44 is of the normal
piston-cylinder type defining therein a head end or cushioning
chamber 44a and a rod or opposite end chamber 44b and forms a part
of the fluid suspension system 10. The head end chamber of the
cushioning jack is in constant fluid communication with a pair of
pneumatic accumulators 45 and 46 by way of a line 47 during all
modes of operation.
The provision of different gas pressure preloads in the
accumulators 45 and 46 provides the proper cushioning conditions
for either a loaded or empty scraper condition. Since the load in
the scraper 15 will vary and hence the vertical position of the
suspension bracket 33 will vary accordingly, it is desirable to
permit the admission to or venting of fluid from the fluid
suspension system to maintain a preselected vertical relationship
between the tractor 13 and the scraper.
Control of the fluid suspension system 10 is accomplished by a
control circuit indicated generally at 48. The control circuit
includes a pump 50 adapted to draw fluid from a reservoir 51 for
supply through a line 52 to a manual selector valve 53 and a
simplified relatively low cost control valve 54. The manual
selector valve has two positions for alternately and selectively
establishing a cushion ride condition or a lockout condition of the
suspension system by controlling communication of pilot pressure
through a line 55 to the control valve 54.
The internal components of the selector valve 53 are identical with
the selector valve illustrated in U.S. Pat. No. 3,511,276 and needs
no further amplification other than to indicate that it connects
line 55 either to pump pressure or drain as dictated by the
position of a control lever 53a.
Valve 54 communicates with the cushioning chamber 44a of the jack
44 and the accumulators 45 and 46 by way of a line 56 and the line
47. The valve also communicates by way of a line 57 with the
opposite end chamber 44b of the jack.
Referring more particularly to FIG. 3, the valve 54 includes a body
60 having a safety valve section 61, a leveling valve section 62, a
lockout valve section 63, and a vent valve section 64.
The safety valve 61 includes a spool 66 disposed for reciprocation
in a bore 67 to control communication between a cushioning port 68
and a passage 69 which communicates with a tank return port 70 by
way of a passage 72, a restrictor valve 73, an orifice 74 and a
return chamber 75. One end of bore 67 communicates with a pump
inlet port 77 so that an end 78 of the spool 66 is exposed to the
pressure in the pump line 52 in opposition to the bias of a spring
80. A drilled passage 81 in spool 66 provides communication between
the cushioning port 68 and the passage 69 when the spool 66 is in
the position shown. The chamber of spring 80 is vented to the
passage 69 and hence to the reservoir by way of a slot 82 in the
spool 66.
The leveling valve section 62 includes a leveling spool 83 disposed
for reciprocation in a bore 84 defined by the housing 60. The spool
83 includes a pair of grooves 85 and 86 which in cooperation with a
plurality of metering slots 88, 89 and 90 selectively control fluid
communication between the pump inlet port 77, the cushioning port
68, the passage 69 and an annulus 92 communicating with the check
valve 73.
One end of spool 83 projects into a chamber 95 formed at one end of
the bore 84 with the other end of the spool projecting outwardly of
body 60 for connection through appropriate linkage with the
suspension hitch 26, as will hereinafter be described. The bore 84
further includes an annulus 96 which communicates by way of passage
69 with the bore 67 of the safety vent valve 61, an annulus 97
which communicates with the bore 67, and cushioning port 68 by way
of a passage 98 and also communicates by way of a passage 99 with a
bore 100 in the lock-out valve section 63. An annulus 102
communicates by way of a passage 103 with the bore 67 and pump
inlet port 77 and also communicates through a high pressure relief
valve 104 and an orifice 105 with the tank return chamber 75. The
annulus 102 further communicates through a passage 107 with the
bore 100 at a point axially spaced from the passage 99. The bore
100 also communicates by way of a passage 110 with the chamber 95
which further communicates through a passage 111, an orifice 112
and a passage 113 to the reservoir 51.
A mechanical detent generally indicated by the reference numeral
116 has a spring biased ball 117 cooperating with a groove 118 to
establish a neutral centered position for spool 83. A second groove
120 in the spool cooperates with the ball to releasably lock the
spool in a raise position communicating the pump inlet port 77 with
the cushioning port 68. A pair of contiguous cam surfaces 121 and
122 on the right hand side of groove 118 cooperate with ball 117
when the spool 83 is moving toward or returning from a lower
position to provide essentially a snap action of the valve spool.
The cam surfaces are conical with the outer cam 122 remote from the
groove being less oblique to the longitudinal axis of spool 83 than
the inner cam 121 which is contiguous to the groove, in order to
increase the valve spool centering forces as the spool approaches
its centered neutral position. The detent area around the spool is
vented to the tank 114 by way of a passage 123 and the passage
113.
The lockout valve section 63 provides a spool 124 movably disposed
in the bore 100 and includes a pair of grooves 125 and 126. The
groove 125 selectively controls communication between the passages
107 and 110, depending upon the positioning of the spool. The
groove 126 controls communication between the passage 99 and a
passage 127 which communicates between the bore 100 and the vent
valve section 64. The passage 127 includes an orifice 128 to
control the rate of fluid flow to the vent valve as will later be
more fully explained.
A pilot actuating chamber 129 formed at one end of spool 124
communicates with the line 55 which may be selectively pressurized
or vented by the selector valve 53 to control the position of the
spool 124. The spool further includes an actuating extension 130
extending axially toward the vent valve section 64.
The vent valve section 64 includes a poppet type check valve 132
disposed for reciprocation in a bore 133 and is biased by a spring
134 into sealing engagement with a conical seat 136. The conical
seat defines the juncture between a passage 137 communicating
between the tank return chamber 75 and an annulus 139 provided in
the bore 133. The annulus 139 is in open communication with a
lockout port 140 and communicates via a passage 142 and a check
valve 143 with the passage 127 and through the orifice 128 with the
bore 100 of the lockout valve 63. The check valve 143 is spring
biased to a closed position, as shown in FIG. 3, to normally block
flow from the annulus 139 toward bore 100 and yet permit relatively
free flow from the orifice 128 toward the annulus 139.
A central passage 147 formed in one end of the check valve 132 is
normally closed by a spring biased poppet 148 to permit
equalization of pressure between the lockout port 140 and the
chamber of the spring 134 behind the check valve 132 by way of an
orifice 150 and a passage 151. The poppet includes an actuating
stem 153 which extends outwardly of the check valve 132 in
engagable coaxially aligned relation to the actuating extension 130
of the spool 124.
As is best shown in FIG. 2, the outwardly extending end of the
leveling spool 83 is pivotally connected by a link 155 to the free
end of a leaf spring 156 which has its other end secured to a
bracket 157 by a plurality of bolts 158. The bracket 157 is rigidly
secured to the link 35 so that as the bracket 33 moves vertically
by pivotal movement of the links the spring exerts an actuating
force on the spool 83 depending on the direction of hitch movement.
This resilient linkage in cooperation with mechanical detent 116
permits limited hitch movement without actuation of the leveling
spool 83 to minimize the frequency at which the leveling circuit is
energized. As a result, pressure loading of the pump and other
circuit components due to dynamic bouncing of the hitch during
travel operations of the vehicle is minimized.
SECOND FORM
An alternate embodiment of the present invention is illustrated in
FIGS. 5 and 6 wherein a modified form of control valve indicated
generally at 160 is supported for pivotal connection through a link
161 to the free end of a generally horizontally disposed leaf
spring 162. The opposite end of the leaf spring is secured to a
bracket 164 integrally formed with the lower link 35. With this
arrangement vertical movement of the bracket 33 by pivotal swinging
of the links 34 and 35 imparts an actuating force through the
spring 162 to the leveling valve spool 83 of the control valve 160
which is fixedly mounted with respect to the A-frame 28.
The fluid connection of control valve 160 to the cushioning jack
44, accumulators 45 and 46, pump 50, and selector valve 53 is
substantially the same as in the previously described
embodiment.
The internal design of the control valve 160, as is best disclosed
in FIG. 6, has been modified as compared with the design of the
control valve 54 disclosed in FIG. 3. As best shown in FIG. 6, pump
line 52 communicates with the pump inlet 77 which in turn
communicates with one end of the bore 67 so that the safety spool
66 is responsive to pump pressure in the pump inlet. The drilled
passages 81 and the slots 82 in safety spool 66 serve to vent the
accumulators when the system is inactive.
The inlet port 77 also communicates through a relatively low
pressure restrictor valve 166 which is disposed in series with a
second low pressure restrictor valve 168 when the leveling spool 83
is in the neutral position as illustrated. The series arrangement
of the restrictor valves maintains the pilot pressure required in
the inlet 77 for actuation of the safety valve 66 and pilot
positioning of the leveling valve 83 by pressurization of chamber
95. This series arrangement of two restrictor valves permits a
second pilot or control pressure somewhat lower than that required
in inlet port 77 to be provided by the restrictor valve 168 for
supply through a passage 169 and a line 170 for use external of the
control valve 160. The valve 166 also prevents the reverse flow
from line 47 to passage 172, pressurizing the end of stem 66. This
could happen when the engine is shut down, as pressure in the
chamber 95 decreases, allowing the spool 83 to shift upward,
connecting accumulator to pump, thus pressurizing passage 77. Under
these conditions, the spool 66 will not return to the vent position
shown and the accumulators will not be vented.
The pump inlet port 77 also communicates through a passage 172, a
relief valve 173, a passage 174, and the restrictor valve 168 to
the tank return chamber 75 from where it is returned to the
reservoir by way of a tank return port 70.
The leveling valve section 62, including the spool 83, is
substantially identical to that previously described with respect
to FIG. 3. The mechanical detent mechanism 116 is associated with
spool 83 for controlling positioning of the spool in response to
vertical movement of the bracket 33 and a resultant spool actuating
force transmitted throug the leaf spring 162.
A lockout valve spool 176 is reciprocably disposed in a bore 177
and is spring biased to the position shown to communicate pump
inlet port 77 to the chamber 95 by way of a passage 179 and a line
180. The chamber 95 communicates via an orifice 112 and a passage
111 to the spring chamber of restrictor valve 168 which
communicates with tank return chamber 75. The cushioning pressure
from the accumulators 45 and 46 and the cushioning chamber 44a of
the cushioning jack 44 is communicated by way of the line 47, a
passage 181, a passage 182, the lockout spool 176, a passage 183, a
non-return check valve 185, a passage 186, a line 187, a passage
189 and the line 57 to the rod end of the cushioning jack. The
passage 186 and hence the accumulator or cushioning pressure is
also communicated by way of a passage 190, the lock-out spool 176,
a passage 192 and a line 193 to the spring chamber 194 of a vent
valve 196. The vent valve 196 is a poppet-type valve, somewhat
similar to the vent valve 132 of FIG. 3, which is spring biased for
closing engagement with a conical seat 197 to block communication
between the rod end chamber 44b of the cushioning jack by way of
line 57 and the tank return chamber 75. A vent valve actuating
piston 198, including an actuating extension 199, is disposed in
coaxial alignment with the vent valve 196 for axially urging the
vent valve to an open position under the influence of pilot
pressure in an actuating chamber 200. The actuating chamber is in
communication with the pilot line 55 from selector valve 53 by way
of line 201.
When the system is conditioned for cushion ride, the chamber 194 is
vented to tank by way of line 193, passage 192, lockout spool 176,
a passage 202, a line 203, a passage 204, an annulus 205, passage
211, return chamber 75 and return port 70.
The line 55 also communicates by way of a passage 206 with an
actuating chamber 207 operatively associated with the lockout valve
spool 176 for selectively moving the spool to a cushioning
position.
The passage 186 also communicates by way of a passage 208 with a
high-pressure relief valve 209 to prevent damage from an
overpressure condition due to initiation of a lockout condition.
When the cushioning jack 44 is allowed to collapse due to a lockout
signal, there is an increase in system volume as the piston-rod
assembly retracts. If the gas volume of the accumulators 45-46 is
insufficient to handle this additional volume, the pressure will
become excessive, causing the valve 209 to vent.
OPERATION
While the operation of the present invention is believed clearly
apparent from the foregoing description, further amplification will
subsequently be made in the following brief summary of such
operation. With the vehicle parked and the engine not running,
pressure is not available in the circuit and the safety spool 66 is
urged by the spring 80 to the position shown in FIG. 3. This vents
the accumulators 45 and 46 and the head end of cushioning jack 44
by way of the passage 81, passages 69 and 72 and the check valve 73
to the tank return chamber 75 from where it is communicated to the
tank by way of return port 70. In the absence of pressure in the
accumulators and the cushioning jack, bracket 35 is permitted to
lower until the stop 35a engages the stop 26a on the hitch A-frame
28. Downward movement of the bracket 35 through pivotal action of
the links 34 and 35 imparts a force through the leaf spring 156 to
move the spool 83 of the leveling valve to the right as viewed in
FIG. 3 to a position communicating pump inlet port 77 with the
cushioning port 68 by way of passage 103, slots 89 and passage 98.
Since the pump is not running and pressure is not available, the
hitch will remain in the lowered position.
Under these conditions, the selector valve 53 is disposed in a
lockout position as may be more clearly understood with reference
to the description in U.S. Pat. No. 3,511,276 mentioned above so
that line 55 is vented to the reservoir and line 52 is blocked from
communication with the line 55. Under these conditions, the lockout
spool 124 assumes the position shown so that vent valve 132 is
urged by its spring 134 to the closed position.
When the tractor engine is started, the pump 50 supplies pressure
to the line 52 and even though leveling spool 83 is at that point
in a position which would raise the hitch, the pump pressure is
immediately communicated by way of passage 107, groove 125 of the
lockout spool and passage 110 to the chamber 95. The restriction of
orifice 112 provides sufficient pressure in that chamber to
overcome the bias of the leaf spring 156 and return spool 83 to the
neutral position illustrated to vent the pump to the reservoir by
way of slots 88, annulus 92 and check valve 73. This establishes a
lockout condition wherein the bracket 33 remains in the lowered
position until such time as the operator actuates the selector
valve 53 to a cushion ride position by manipulation of lever
53a.
Movement of the valve 53 to the cushion ride position communicates
pump line 52 with the pilot line 55 to pressurize the lockout valve
actuating chamber 129 to urge spool 124 to the right as viewed in
FIG. 3. Such movement of the lockout spool blocks communication of
the pump pressure to the chamber 95 so that pressure in that
chamber is bled to the reservoir at a controlled rate through the
passage 111, orifice 112, and passage 113 to permit leaf spring 156
to return the leveling valve to a raise position wherein detent
ball 117 engages detent groove 120 in the spool. Movement of
lockout spool to the right also engages actuating extension 130
with stem 153 of the poppet valve 148 to open that valve and vent
the pressure from the chamber of spring 134. Continued movement of
the spool 124 causes the extension 130 to engage the front face of
the check valve 132 to urge it to an open position communicating
the rod end of the cushioning jack with the reservoir by way of
port 140, passage 137, return chamber 75 and return port 70.
Communication of the accumulator pressure from line 47 to the rod
end of the jack is also blocked as the spool 124 blocks
communication between the passage 99 and the passage 127.
Under these conditions and with the leveling spool 83 in a raise
detented position as previously described, the pump pressure from
line 52 is communicated to the head end of the cushioning jack 44
and the accumulators 45 and 46 to pressurize the cushioning system.
That pressure acting on the full area of the piston is effective to
raise the bracket 33 and the forward end of the scraper 15 toward a
centered or "level" position within its total range of movement
wherein the spring force and the weight of the scraper is balanced.
As the bracket 33 raises, the pivotal movement of line 35 relaxes
the actuating force inleaf spring 156.
The above described action is best explained with reference to FIG.
4 wherein leveling spool displacement relative to hitch
displacement is plotted in solid line for movement of the hitch
away from a centered or level position toward either extreme of
movement with the action of the system as the hitch is returned
toward a level position being plotted in dashed lines. For example,
with the vehicle engine running and the system in a hitch lowering
lockout condition, the leveling stem is disposed at point A in FIG.
4. Since the chamber 95 is pressurized, the leveling spool is
displaced to a neutral condition in opposition to the force of
spring 156 as depicted at point B. When the selector valve 53 is
shifted to a cushion ride position, the leveling spool is returned
to a fully actuated position, point A on the graph, so that the
hitch will begin to rise as last described. As this point, the
spring is deflected and is exerting approximately 75 pounds of
force to hold the leveling spool in a raise position for
communicating pump pressure to the cushioning circuit. As the hitch
reaches approximately point C on the curve, the force of the spring
is zero; however, since the spool 83 is held in a raise position by
detent 116, the hitch continues to rise. As the hitch reaches a
level condition, point D, the force exerted by the spring is
approximately 20 pounds and acting in a direction to urge spool 83
toward a neutral position. Since approximately 30 pounds is
required to disengage detent ball 117 from the groove 120, the
hitch continues to rise to point E at which point the spring force
reaches 30 pounds and returns the spool 83 to the neutral
position.
The over-leveled condition resulting from the detented raise
position of the leveling spool 83 increases the leak-down time or
load required to depress the hitch sufficiently to actuate the
leveling spool to a raise position. This minimizes cycling of the
system and reduces wear and stress on the pump and other hydraulic
components.
As load is added to the scraper bowl or the hitch settles due to
internal fluid leakage after an extended period of machine
operation, the engagement of the ball 117 with the neutral groove
118 is effective to resist movement of the leveling valve until the
force in spring 156 reaches approximately 30 pounds. This condition
is achieved at point F in the downward direction at which point the
spool 83 snaps to a full open position represented at point G. This
communicates the pump inlet port 77 by way of passage 103, slots 89
and passage 98 with the cushioning port 68. Such admission of fluid
to the cushioning jack and accumulators raises or returns the hitch
to the over-leveled condition as previously described and as
indicated by point H in FIG. 4.
As load is removed from the scraper the higher pressure which was
required to support the load causes the hitch to rise until the
force in spring 156 reaches approximately 30 pounds at point J of
FIG. 4. This overcomes the detent and moves spool 83 to the left,
as viewed in FIG, 3, to a full open or lower position at point K of
FIG. 4. This communicates the cushioning end of the jack 44 and the
accumulators 45 and 46 to the reservoir by way of the cushioning
port 68, passage 98, slots 90, passages 69 and 72, check valve 73,
return chamber 75 and return port 70. This is effective to vent
fluid from the cushioning system so that the hitch will lower as
indicated by broken line L. The spring force is approximately 0 at
point M. As the hitch continues to lower to point N the spool is
urged toward a neutral condition by the spring 156. At this point
the ball engages the ramps 122 and 121 to snap the spool 83 back to
a neutral condition just prior to a leveled condition so that the
hitch will remain slightly above level at point 0 of FIG. 4, for
the same reason as previously described with respect to point
H.
The distance between points F and J of FIG. 4 represents the hitch
displacement or "deadband" which can occur without shifting the
leveling valve spool 83. This "deadband" absorbs most of the normal
dynamic motion of the hitch to minimize actuation of the leveling
spool.
When leveling spool 83 is in a neutral condition, the fluid
displaced by pump 50 must open restrictor valve 73 to return to the
reservoir. This maintains sufficient pressure in the system to
overcome the spring 156 and return the leveling spool to a neutral
condition when spool 124 is moved to the lockout position for
communicating the pump pressure to the chamber 95.
Movement of spool 124 to the lockout position also communicates the
accumulators with the rod end of the cushioning jack 44 as
previously described to equalize the pressure in the opposite ends
of the jack. Although the differential area of the piston provides
an unbalanced upward force, the weight of the scraper 15 and the
bracket 33 is sufficient to move the piston downwardly until the
stop 33a engages the stop 28a. Since the head or cushioning end of
the jack is in constant communication with the accumulators,
control of the hitch lowering is accomplished solely by the fixed
orifice 128.
OPERATION OF SECOND FORM
The alternate embodiment disclosed in FIGS. 5 and 6 functions in a
manner very similar to that previously described for FIGS. 2 and 3.
However, a brief summary of the operation of that embodiment will
be provided to clarify the function of the modified valve of FIG.
6.
With the engine running and the selector valve 53 in a cushion ride
position, pilot pressure is available by way of lines 55 and 201 to
the actuating chambers 200 and 207 of the vent valve actuating
piston 198 and the lockout spool 176. The lockout valve is shifted
upwardly as viewed in FIG. 6 to block communication between pump
inlet 77 and chamber 95 by way of line 180. This is also effective
to block communication between the suspension system and the rod
end of cushioning jack 44 by way of line 47, passage 181, lockout
spool 176, passage 83, check valve 185, passage 186, line 187,
passage 189 and the line 57. Spring chamber 194 communicates by way
of the line 193, the passage 192, the lockout spool 176, the
passage 202, the line 203, the passage 204, the annulus 205, and
the passage 211 to the return chamber 75 from where it is directed
to the reservoir by way of the return port 70. This allows upward
movement of the actuating piston 198 to urge the vent valve 196 to
an open position by contact of the actuating extension 199 with the
face of the check valve. This vents the rod end of the cushioning
jack 44 to the reservoir by way of return chamber 75 and return
port 70.
Pressure in chamber 95 is metered at a controlled rate to the
reservoir by way of an orifice 112 and passage 111 to permit the
force of spring 162 to return spool 83 to a raised position, as
viewed in FIG. 6. This communicates the pump 50 with the cushioning
jack chamber 44a and accumulators 45 and 46 by way of restrictor
valve 166, leveling spool 83, passage 181 and line 47 to raise the
latch toward the over-leveled condition as disclosed in FIG. 4.
The mechanical deadband and over-leveled condition previously
described with respect to FIG. 4 also applies to the alternate
embodiment of FIGS. 5 and 6 since the detent 116 cooperates with
the spool 83 in exactly the same manner to provide those described
conditions.
In view of the foregoing, it is readily apparent that the structure
of the present invention provides an improved fluid suspension
system and simplified leveling valve to achieve a greatly improved
and simplified control for the descent rate of the hitch from a
cushion ride to a lockout condition. It further provides direct
mechanical actuation of the leveling spool in conjunction with
individual spools for each of the other hitch functions and/or
modes of operation to permit the use of a greatly simplified valve
construction with improved control of the hitch position. It
further provides a mechanical spring directly connected to the
leveling spool in combination with a mechanical detent to eliminate
the need for expensive complicated pilot systems and hydraulic
damping devices to provide the deadband desired to avoid excessive
energizing of the fluid suspension circuit. This combination also
permits the use of an extremely simplified valve to materially
reduce costs and yet achieve superior performance of the fluid
suspension system.
While the invention has been described and shown with particular
reference to the preferred embodiments, it will be apparent that
variations might be possible that would fall within the scope of
the present invention which is not intended to be limited except as
defined in the following claims.
* * * * *