Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a hydraulic control
valve for operating steering clutches and brakes for a crawler
; tractor or the like.
This application is a division of application Ser
No. 266,754 filed November 29, 1976. -
- Descr~ptlon of the Prior Art ~ -
- In some prior art crawler tractors the hydraulic
control system for the steering clutches and the track brakes
includes a pair of manually operated steering clutch levers
which actuate the valves for the steering clutches which trans~
mit motive power from the tractor transmission to the tracks.
A pair of brake pedals are used to selectively actuate a pair
of brake cylinders which, in turn, control a pair of brakes for
the tracks. Straight line vehicle movement is accomplished by
i~ engaging both clutches so as to drive both tracks in the same -~
direction at the same speed. Steering is accomplished by
operating one steering clutch lever so as to disengage its
"
associated steering clutch and thereby slow down or stop its
a~sociated track while continuing to drive the other. Braking
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is accomplished during straight line vehicle movement by using
both brake pedals and, during steering, by using the brake
pedal for that track whose clutch i9 disengaged.
In such prior art tractors the steering clutches and
the brake actuators are sometimes embodied in separate control
systems which are supplied from separate hydraulic pumps. Aside
~;
from increased costs of such systems resulting from redundancy
of components, such prior art systems often lack various auto-
matic control functions which, if provided, would simplify and
provide for safer tractor operation. The following pages dis-
close various types of prior art steeri~g and braking controlsystem~ for vehicles: United States of America patents:
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3,437,184, issued April 8, 1969; 3,358,786, issued December 19,
1967, 3,386,523, issued June 4, 1968, 3,351,149, issued
November 7, 1967, and 2,375,959, issued May 15, 1975
SUMMARY OF_THE INVENTION
A crawler tractor has an engine-driven fluid power
shifted transmission for supplying motive power to left and
right crawler tracks through spring-applied fluid-released
left and right steering clutches and also has spring-applied
fluid-released brake actuators for the track brakes. A hyd-
raulic control system for steering and braking the tractor
includes a combined steering and braking valve having a pair
of lever operated valve spools, a shuttle valve, and a supple-
mental brake control valve operated by a single brake pedal.
The combined steering and braking valve, which includes a flow
divider, directs fluid from a pump to the brake actuators to
maintain the brakes released when the valve spools are in
neutral. When a lever operated valve spool is moved from
neutral to some other position, the combined steering and
braking valve directs fluid to disengage a clutch and causes
the brake for the associated track to be applied. The com-
bined steering and braking valve operates to regulate fluid
pressure in the system and also operates to ensure that suffi-
cient fluid pressure is available for clutch operation regard-
less of brake actuator demands. The shuttle valve is connected
to the brake actuators and is responsive to the supplemental
brake valve to apply either or both brakes when the supplemental ;
brake valve is actuated either by the brake pedal or in res-
ponse to a drop of fluid pressure in the power shift trans-
mission. If both levers are in neutral and transmission fluid
pressure drops below a predetermined value, as during reverse ~
shifting to change direction of tractor travel, the supple- - -
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mental valve effects automatic spring application of both
brakes,
A control system having combined steering and brak-
ing valve in accordance with the invention require fewer
duplicate components than prior art systems, is easier to
operate and more reliable in operation, The system provides
for a single brake pedal,usable for steering and braking,
The system employs fail-safe spring-applied brakes, requires
- only one pump for supplying the steering clutches and brake
actuators, and enables automatic braking when the steering
levers are in neutral and transmission fluid pressure drops,
as during tractor direction reversal, The system employs an
improved yet relatively uncomplicated pedal operated supple-
mental brake valve to enable selective as well as automatic
braking, Other objects and advantages will hereinafter
~ appear,
,~ According to a broad aspect of the present invention,
'~,, there is provided a hydxaulic control valve for operating
, steering and braking means for crawler tractor, The control
, 20 valve comprises a housing and a pair of independently actuat-
~,
able valve spools in the housing, each spool being biased into
a neutral position and selectively movable therefrom to other
positions, A pair of main inlet ports and a main outlet port
are provided in the housing, A pair of pressure ports are
~, associated with each valve spool, A pair of passages each
ij~ communicate with one main inlet port and one pressure port,
Each valve spool, when in neutral, enables full communication
through a passage between one main inlet port and one of its
associated pressure ports but prevent communication between
,` 30 the other main inlet port and the other of its associated
pressure ports. Each valve spool when moved from neutral to
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another position decreases communication between the one main
inlet port and the said one of its associated pressure ports
and enables communication between the other main inlet port
and the said other of its associated pressure port.
DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic diagram of a control system
in accordance with the invention,
Figure 2 is a top elevation view of a combined
- steering-brake valve shown in Fig. 1: -
Fiyure 3 is a side elevation view of the valve of
- Fig. 2,
Figure 4 is a cross section view of the valve taken
on line 4-4 of Fig. 3:
Figure 5 is a cross section view of the valve taken
on line 5-5 of Fig. 4,
Figure 6 is a cross section view of the valve taken
on line 6-6 of Fig. 4,
Figure 7 is a cross section view of the valve taken
on line 7-7 of Fig. 4, and
Figure 8 is a schematic diagram of the steering-brake
valve.
DESCRIPTION_OF A PREFERRED EMBODIMENT
Referring to Figure 1, a crawler tractor has left and
right crawler tracks 1 and 2, re~p~ctively, on opposite lateral
qides thereof, an engine 3 for driving a transmission 4 to
~upply motive power to the tracks through conventional spring-
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applied fluid-released .left and right steering clutches S and 6,
and conventional spring-applied fluid-released left and right
brakes 7 and 8, respecti~ely, which are actuated by left and
right brake actuators 9 and 10, respectively. The tractor also
comprises manually operable left and right steering clutch and
brake control levers 31 and 32 and a single brake pedal 33.
: Transmission 4 is a power shift transmission for
driving the tractor and has an output shaft 11 which extends
. into a housing 12 to drive a main shaft 13 through bevel
: 10 gears 14. Main shaft 13 is connectable through the clutches
. 5, 6 when the latter are engaged to drive the left and right
final drive shafts 15 and 16, respectively, to which track
drive sprockets 17 and 18, respectively, are affixed.
.~: Each brake 7, 8 comprises a brake drum 20 for the
final drive shaft 15, 16 and a brake band 21 engageable with
the brake drum. Each brake actuator 9, 10 comprises a housing
22 having a piston 23 therein for moving a piston rod 24 :
: attached thereto which extends from the housing. Each housing
22 is rigidly secured to the tractor frame by means not shown.
,~.
.~ ~ Each piston rod 24 i8 connected by a linkage 26 to an associated
brake band 21. Each brake actuator 9, 10 comprises biasing
spring means in the form of a pair of balanced compression
spring5 27 and 28 within its housing 22 for biasing the piston
23 in one direction to a position toward one end of the housing
wherein brake band 21 fully engages its brake drum 20 and the
brake 7, 8 is applied. Each housing 22 further comprises a
, fluid inlet port 30 for admitting fluid between the piston 23
. and the said one end of the housing to effect piston movement .
`~ in the opposite direction to release the brake 7, 8. The
actuators 9 and 10 are mechanically connected to the brakes
7 and 8, respectively, and are spring biased to effect engagement
of the brakes when the fluid pressure in the actuators 9 and
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10, respectively, drops below a predetermined value.
The control system for steering and braking includes a
Qingle engine~driven pump 40 for supplying fluid to operate
the steering clutches 5, 6 and the brake actuators 9, 10; a
combined steering and braking valve 41 responsive to actuation
of the levers 31, 32 to supply fluid to release the steering
clutches 5, 6 and to release the brakes 7, 8; a shuttle valve
42 responsive to operation of the steering clutches 5, 6 to
cause the brake actuators 9, 10 to effect brake application,
and a supplemental brake control valve 43 operated by a pedal
33 and al~o responsive to transmission fluid pressure.
Generally speaking, the control system operates in
such a manner that actuation of either lever 31, 32 effects
flu$d release of its associated steering clutch 5, 6 and
application of the appropriate br~ke 7, 8. Operation of the
single brake pedal 33 will also effect spring application of
the brake 7, 8 for that track 1, 2 whose clutch 5, 6 is
relea~ed. If both levers 31, 32 are in neutral and transmission
fluid presisure drops below a predetermined value, as during
rever~e shifting to change direction of tractor travel, both
~`; brakes 7, 8 are automatically spring-applied. Functions for
both situations occur without 1089 of fluid pressure necessary
for control of the steering clutches 5, 6 because of a pressure
; regulating sequance in valve 41. If both levers 31, 32 are in
. 25 neutral with both steering clutches 5, 6 engaged, operation
of the single brake pedal 33 will then effect spring application
of both brakes 7, 8 such as may be desirable during down hill
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.~. coast.
Valve 41, which is understood to have a flow divider
46 therein, has a fluid inlet port 50 connected to pump 40
by a fluid line 51, an outlet port G connected to a reservoir
112 by a line 124, and al80 has clutch supply ports C and D
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which are connected by fluid lines 55 and 56, respectively,
to the clutches 5 and 6, respectively. Valve 41 also has ports
F and E for supplying the fluid ports 30 of the brake actuators
9 and 10, respectively, through lines 89 and 90, respectively.
The lines 89 and 90 are connected by lines 83 and 84, respectively,
to the ports 81 and 82, respectively, of shuttle valve 42.
Yalve 41 is provided with a housing 200 and with left and right
valve spools 211 and 217, slideable in bores 201 and 202,
respectively, which are connected for actuation by the
levers 31 and 32, respectively. The spools 211 and 217 are
normally biased in neutral position wherein they prevent fluid
flow from pump 40 to the steering clutches 5 and 6 to maintain
the clutches spring-engaged but permit flow to the brake
actuators 9 and 10 to maintain the brakes 7 and 8 releaAed.
The spopls are axially movable therefrom by the levers 31 and
32 to effect fluid flow from pump 40 to release the clutches
5 and 6, respectively, and to prevent fluid flow to the
actuators 9 and 10 to apply the brakes 7 and 8, respectively.
To ensure engagement of clutche~ 5 and 6 when valve spools
211 and 217 are in neutral poqition, bleed-down restrictor
orifices 124 and 125 are provided to allow pressure fluid in
lines 55 and 56 to escape to reservoir 112A. Valve 41 is
hereinafter described in detail.
In addition to steering clutch and brake control,
the valve 41 also provides pressure regulation sequence and
pressure control valving. Referring to Figs. 1, 4, and 8,
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val~e 41 comprises a housing 200. Fluid from the flow divider
46 entering port A passes into a chamber 210 that is as~ociated
``~ with spool 211. In the neutral po~ition of the valve spool 211,
an opening 212 is availabla for the flu~d to enter from
chamber 210 into anothex chambex 213, then through a passage
214 and a check valve 215 to a chamber 216 associated with the
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other valve spool 217. Fluid in chamber 216 is available at
port E with pressuxe to apply against the spring 27 in the
right hand brake cylinder 10 to release the right hand spring
applied brake 8 (shown in Fig. 1). Fluid pressure is regulated
by a sleeve 218 surrounding spool 217 and slideable within the
spool bore 202 in the valve housing 200. A spring 219 reacting
axially against a washer 220 on spool 217 forces sleeve 218
upward tending to close an annular passage 221 between chamber
. 216 and chamber 222. The combination of spring 219 force
and the cross sectional area at the upper end of sleeve 218
tending to close passage 221 establishes the fluid pressure
. O applied at port E to release the right hand brake 7. The
reaction force axially applied downwardly on spool 217 by
: spring 213 is amply resisted by a spring 223 located at the
;~ 15 upper end of spool 217 and biasing the spool upward against
~- a stop 224. The fluid in chamber 222 is returned to tank
. through port G.
Similarly, fluid from the flow divider 46 entering
port B progresses in li~e manner with relation to like components
to provide pressure at port F for releasing the left hand brake 8.
~n order to release (disengage) the normally spring-
applied steering clutcheQ S, 6, either or both valve spools :
, 211 and 217 are manually moved downwardly (in Figs. 1, 2, 3, 4
' S, and 8) against the force o~ spring 223 of spool 217 and spring
, 25 223a of spool 211.
;l A vehicle turn to the right is accomplished by pulling : ::
on the xlght hand steering l~ver 32 to shift valve sp~ol 217
away from stop 224 against the force of spring 223. Fluid
pressure æupplied by the flow divider 46 at port B from the
hydraulic pump 40 passes through chamber 210a, to chamber 225,
out port D to the right hand steering clutch 6 thereby releasing
it.
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Supplemental pressure regulation i8 provided by a
sleeve 226 on spool 217 backed up by spring 227 tending to
close annular passage 212a in much the same manner that sleeves
218 and 218a tend to close annular passages 221 and 221a when
spools 217 and 211 are in their neutral positions. This
arrangement provides pressure seguencing to assure that pressure
- is always available to release the steering clutch 6 regardless
of the subse~uent variable re~uirements for brake control.
5pecifically, pressure in lines 89, 90 may be depleted without
similar depletion of fluid pre6sure that is available from
pump 40 for control of steering clutches 5 and 6. The
O importance of this is evident during several operational
maneuvers of the tractor, such as when manually applying one
or both brakes 7 and 8 when accompanied by the release of one or
both steering clutches 5 and 6.
Fluid pressure from the flow divider 46 supplied to
port A, to chamber 210, through annular passage 212, chamber
213, passage 214, through check valve 215 and into chamber
216 is reduced a~ a result of spool 217 movement downward.
This movement causes spring 219 to reduce the force on sleeve
. .
218 thereby permitting fluid from chamber 216 to flow through
annular passage 221 and chamber 222 through outlet port G
to th~ tank 112 at progressively lower pressure in proportion
to the spool travel. This action cauQes pressure in the right
,` 25 hand brake cylinder 10 to dacay and allows the spring 27 in
thi5 cylinder 10 to apply the right hand brake 8.
; A vehicle turn to the left is accomplished by pulling
; on the left hand steering lever 31 thereby moving valve spool
- 211 away from the stop 224a with the result that, in a like
' 30 manner with relation to like components, pressure delivered
.
from port C will release the left hand steering clutch S and
pressure reduction at port F will automatically allow the
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spring to apply the left hand brake 7.
Check valves 215 and 215a are required to prevent
pressure feedback (pressure 108s) from the brake cylinders 9
and 10 when the spools 211 and 217 are starting to apply
pressure to disengage the steering clutches 5 and 6.
- The pedal actuated supplemental brake control valve
43 serves to enable selective application of either or both
~ brakes ~ and 8 in response to depression of single pedal 33
: and also serves to automatically apply the brakes 7 and 8
when the tractor transmission 4 is operating in neutral and
.~ fluid pressure in the transmission drops below some predetermined
value. Valve 43 comprises a housing 100 having an axial bore ~.
101 therein in which a valve spool 102 is slideably mounted.
Spool 102 is biased toward the right (referring to Fig. 1) by
15 a compression spring 103 in chamber 99 which acts in combination
with transmission fluid pilot pressure supplied to a port 104
~A' through a supply line 105 from tractor transmission 4. Rightward
,:~ movement of spool 102 operates to close an annular fluid passage
~, 106 in valve 43 communicating between chambers 107 and 108 in
. ~ J valve 43. Chamber 107 has a port 109 by means of which it
communicates through a ~luid line 95 with port 58 in shuttle
` valve 42. Chamber 108 has a port 110 by means of which it
communicates through a flu~d line 111 to reservoir 112. Valve
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43 comprises another pas~age 113 having a port 114 by means
of which fluid leakage from line 105 that passes spool 102
may be returned through a line 115 to a reservoir 116 for the
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`~ tran5mission fluid. Valve 43 also comprises an axially movable
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rod 120 which is connected by a linkage 121 to brake pedal 33
and has its innermost end in abutting engagement with the end
of valve spool 102. Valve spool 102 i5 provided wi h a groove
123 which i8 in registry with the pa~sage 113 in valve 43.
When both contxol .levers.31 and.32 are in neutral position,
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both brakes 7 and 8 will be applied if either ~1) the single
foot brake pedal 33 is depressed, or (2) the transmission 4
is shifted to neutral thereby reducing the pilot pressure
in line 105. In either event pressure fluid in chamber 107
escapes at a lower pressure through passage 106 to chamber
108 and to reservoir 112. Chamber 107 communicates with port
58 in shuttle valve 42. Fluid pressure from transmission
hydraulic circuit line 105 acts on piston or spool 102 to urge
poppet valve passage 106 closed. Spring 103 serves to achieve
a proper balance between the transmission pilot pressure acting
on spool 102 and the brake control pressure in line 95 so that
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when transmission pilot pressure in transmission 4 and line -
105 drops below a predetermined value, such as during a change
in vehicle direction during shift, the poppet valve passage
106 is permitted to open and release the pressure in line
95 to r~servoir 112 and in brake actustors 9 and 10, thus
allowing the brake spxings 27 and 28 to apply brakes 7 and 8.
Shuttle valve 42 comprises a housing 70 having a bore
71 therein in which a shuttle valve spool 72 is slideably
mounted and normally maintained in centered position by
compres8ion type centering springs 73 and 74 located in pilot
pressure chambers 75 and 76 in the bore and disposed between
the spool ends and the ends of the housing. Valve spool 72 i8
provided with a pair of spaced apart grooves 77 and 78 which are
., .
aligned or register with fluid flow passages 79 and 80,
respectively, when the spool is centered. The passages 79 and
80, each of which communicates with fluid inlet port 58, also
communicate with the fluid ports 81 and 82, respectively, which
are co~nected by fluid lines 83 and 84, respectively, to the
j 30 ports 30 o~ the brake actuators 9 and 10. The pilot pressure
- chamber9 75 and 76 of shuttle valve 42 are connected by passages
~`~ 91 and 92, respectively, to the lines 83 and 84, respectiv~ly.
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When shuttle valve 42 is in neutral position, fluid from lines
83 and 84 is combined and directed through passages 79 and
80, respectively, to port 58. Chamber 107 in valve 43
communicates with a "Y" passage 79, 80 in shuttle valve 42
S shown in Fig. 1. Lines 83 and 84 are branches of lines 89 and
90, respectively, leading from ports F and E, respectively,
of valve 41 to the left hand and right hand brake cylinders
9 and 10, respectively, and communicate with the passages 79
and 80, respec~ively. Branch passages 91 and 92 from lines
83 and 84 are directed to the pilot chambers 75 and 76, ;
respectively, of valve 42 and act on spool 72 so that it will
; ~ move to the right or left in response to a difference in pressure
in lines 83 and 84. This action is such as to isolate the one ~
of these passages 91 or 92 with the highest pressure from the -
- 15 other passages 91 or 92 and from action resulting from the
operation o~ supplemental brake control valve 43.
.
Valve 43 acting in conjunction with shuttle valve 42
then provides for supplemental control of the automatic operation
of the brakes 7 and 8 in response to operation of the left and
right ~teering levers 31 and 32 and also provides for automatic
braking in neutral. The degree by which automatic braking i8
coordinated with steering control depends on the designed force
and rate of springs 219 and 219a in valve 41.
Manual application of the brakes 7 and 8 is
accomplished by depressing the single brake pedal 33 thereby
moving valve spool 102 of valve 43 to the left in the drawing
against spring 103. This allows fluid to pass throu~h line 95
into chamber 107, through passage 106 at modulatingly controlled
` pressure, to chamber 108 and then to sump 112. ~luid in line
... .
95 normally communicates with both brake actuator cylinders 9
and 10 by means of the dual passage~ 79 and 80 in shuttle
valve 42.
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If both control levers.31 and.32 are moved from
neutral simultaneously, fluid pressure in both lines 83 and 84
acts on opposite ends of the shuttle valve spool 72. Equalization
springs 73 and 74 at both ends of spool 72, along with the equal
pilot fluid pressure in the chambers 75 and 76, retain the
spool in a neutral position. This allows fluid in both brake
actuators 9 and 10 to escape to sump 112 and results in
application of both braXes 7 and 8.
If only one control lever 31 or 32 is moved from
neutral, then the fluid pressure being used to release the one
brake acts on one end of the shuttle valve spool 72 to shift
~: ~ it in a direction to block one of the passages 79 or 80 so
that fluid from only one brake actuator 9 or 10 is allowed
to escape to sump 112 to effect brake application.
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