CA1064368A - Hydraulic control valve for operating steering and braking means for crawler tractor - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A hydraulic control valve for operating steering and braking means for crawler tractor. The control valve comprises a housing and a pair of independently actuatable 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 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 the other main inlet port and the other of its associated pressure ports. Each valve spool when moved from neutral to 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

lQ~43tj8 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 ?
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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1()~43~8 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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... ~ . , , .. ~ . , , , ., " , ,,, ,, , ,. . . . , - -43~8 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.
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.~ ~ 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 , . , .; . ~ ~

~06~3~8 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 .i, .~. 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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~)643t;8 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, ~., 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.

1(~643~8 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 i ~
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 :-`~ tran5mission fluid. Valve 43 also comprises an axially movable ;~
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, , 10 -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 : L ~1 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.

` 1064368 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.
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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.

1()64368 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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Claims (8)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. In a hydraulic control valve: a housing, a pair of independently actuatable valve spools in said housing, each valve spool being biased into a neutral position and select-ively movable therefrom to other positions, a pair of main inlet ports and a main outlet port in said housing, a pair of pressure ports associated with each valve spool, and a pair of passages, each passage communicating with one main inlet port and one pressure port, each valve spool when in neutral enabling full communication through a passage between one main inlet port and one of its associated pressure ports but prevent-ing communication between the other main inlet port and the other of its associated pressure ports, each valve spool when moved from neutral to another position decreasing communication between said one main inlet port and said one of its associated pressure ports and enabling communication between said other main inlet port and said other of its associated pressure port.

2. A control valve according to claim 1 including first pressure regulating means for each valve spool and responsive to fluid pressure at said one of its associated pressure ports for controlling communication between one of said main inlet ports and said main outlet port.

3. A control valve according to claim 1 including second pressure regulating means for each valve spool and responsive to fluid pressure at said one of said pressure ports of the other valve spool for controlling communication between one of said main inlet ports and the other of its associated pressure ports.

4. A control valve according to claim 1 including check valves in said passages to prevent back flow from said one outlet port.

5. In a hydraulic control valve: a housing, a pair of independently actuatable valve spools in said housing, each valve spool being biased into a neutral position and select-ively movable therefrom to other positions, a pair of main inlet ports and a main outlet port in said housing, a pair of pressure ports associated with each valve spool, a pair of passages, each passage communicating with one main inlet port and one pressure port, each valve spool when in neutral enabling full communication through a passage between one main inlet port and one of its associated pressure ports but preventing communication between the other main inlet port and the other of its associated pressure ports, each valve spool when moved from neutral to another position decreasing communication between said one main inlet port and said one of its associated pressure ports and enabling communication between said other main inlet port and said other of its associated pressure port;
first pressure regulating means for each valve spool and responsive to fluid pressure at said one of its associated pressure ports for controlling communication between one of said main inlet ports and said main outlet port, second pressure regulating means for each valve spool and responsive to fluid pressure at said one of said pressure ports of the other valve spool for controlling communication between one of said main inlet ports and the other of its associated pres-sure ports; and check valves in said passages to prevent back flow from said one outlet port.

6. In a hydraulic control valve: a housing, first and second selectively operable valve spools in said housing, each spool movable between a neutral position and other positions, means for biasing said valve spools into said neutral position, a main fluid inlet port and a main fluid outlet port in said housing, first and second inlet ports for receiving fluid from said main inlet port, a flow divider for regulating the supply of fluid from said main inlet port to said first and second inlet ports; a first pair of pressure ports in said housing associated with said first valve spool, a second pair of pressure ports in said housing associated with said second valve spool; a first passage in said housing communicating between said first inlet port and one of said second pair of outlet ports, and a second passage in said housing communicat-ing between said second inlet port and one of said first pair of outlet ports, said valve spools operating so that, when both are in neutral position, said first inlet port is in communication through a first passage with one of said second pair of pressure ports while the other port of said second pair of pressure ports is maintained closed by said second valve spool and said second inlet port is in communication through a second passage with one of said first pair of pres-sure ports while the other port of said first pair of pressure ports is maintained closed by said first valve spool, and when either or both of said valve spools is moved from neutral, the pair of pressure ports associated with a particular valve spool assume a condition wherein one associated pressure port closes and the other associated pressure port opens.

7. A control valve according to claim 6, including a pair of spring biased pressure regulating members for each valve spool, one member on each valve spool controlling communication between one of the pair of pressure ports of that valve spool and said main fluid outlet port, the other member on each valve spool controlling communication between one of the first and second inlet ports and the other of the pair of pressure ports for the other valve spool, said one pressure regulating member tending to prevent communication unless fluid pressure exceeds a predetermined pressure, said other pressure regulating member operating to increase communi-cation to ensure that there is enough fluid pressure at said other pressure port as the fluid pressure at said one pressure port decreases.

8. A control valve according to claim 7 including check valves in said first and second passages to prevent back flow from the said one pressure port.