CA1141266A

CA1141266A - Fluid motor control circuit with fast-acting quick-drop valve

Info

Publication number: CA1141266A
Application number: CA000338957A
Authority: CA
Inventors: Robert G. Henderson; John A. Junck
Original assignee: Caterpillar Tractor Co
Current assignee: Caterpillar Inc
Priority date: 1978-11-01
Filing date: 1979-11-01
Publication date: 1983-02-15
Also published as: JPS5563003A; EP0010699A1; DE2966924D1; EP0010699B1

Abstract

FLUID MOTOR CONTROL CIRCUIT
WITH FAST-ACTING QUICK-DROP VALVE
Abstract of the Disclosure A control circuit for a fluid pressure-operated cylinder or the like has a quick-drop valve which enables faster gravity-assisted lowering of a load and which quickly shifts to a power-down mode of operation when dropping of the load by gravity ceases. Means sensing flow rate to the head end of the cylinder and sensing cavitation in the head end initiate the quick-drop operation at which the discharge path from the cylinder back to tank is totally blocked and all discharge from the rod end is recirculated to the head end.
When resistance to further lowering of the load occurs, the quick-drop valve responds by shifting to block communication between ends of the cylinder while establishing a rod end discharge path to tank to initiate a power-down mode of operation quickly and without lag or bounce.

Description

l~l31 Z66 FLUID ~OTOR CONTROL CIRCUIT
~1IT1~ FAS~'-ACTI1`~G QUICK-D~OP VALVE

Technical Field This invention relates to control systems for fluid pressure-operated motors, such as fluid cylinders, fluid actuators or the like, and more particularly to a quick-drop valve which enables fast gravity-assisted lowering of a load or member by directing fluid which discharges from one motor port back to the other motor port.
Back~round Art -Control systems for fluid cylinders or the lilce usually have a main control valve connected between the cylinder and a pump or other source Or pressurized fluid. In many systems the main control valve has a raise position at which pressurized fluid is supplied to the rod end of the cylinder and at which fluid is discharged from the head end in order to move a load against gravity or against some other resistance. In this raise mot~e of operation the rate~ of cylinder retraction is determined by the rate at which the pump forces fluid into the cylinder. This is not necessarily the case when the main control valve is shifted to the lower or power-down position at which the pressurized fluid is applied to the head end of the cylinder and at which fluid discharges from the rod end back to tank. During the power-down mode of operation gravity or other forces may becapable of causing a rate of cylinder extension exceeding that established by the rate of flow of pressurized fluid to the head end of the cylinder. ~evere negative pressures or cavitation may then cause a loss of precision in controlling the cylinder. The cylinder may not respond quickly to shifts of the control valve and other adverse erfects occur such as erratic cylinder notion and vibration and bounce or temporary reversals Or cylinder motion. Iilhile these effects can be avoidcd by restricting the rate at which fluid can discharge back to tank through the main control valve at the power-down position of the valve this may undesirably limit the rate Or lowering of the load.
qo enable rast lowering of a load a variety of quick-drop valves have heretoI`ore been designed for connection between the two flow passages to the ends of the cylinder at a location relatively close to the cylinder and in some cases as a built-in component of the cylinder itself.
Quick-drop valves provide a relatively short ~nd low resistance fluid interchange path between the two ends of the cylinder that remains closed during the raise mode Or operation but which is opened during gravity-assisted lowering Or the load so that f`luid which is discharging from one cylinder port is directed to the other port to supplement the incoming flow from the main control valve. Typically the quick-drop valve senses cavitation in the cylinder during the power-down mode of operation and opens automatically while such condition is present.
Prior quicl--drop valves of known forms are subject to certain operational disadvantages. rlany prior quick-drop valves operate in response to a discharge pressure dirferential across a restriction in the flow path which connects thc discharging end Or the cylinder with the tank through the main control valve~ Consequently the discharge flow path must remain at least partially open and part of the discharge flow must be returned to tank durin the quick-drop mode Or operation instead Or being recirculated to the head end to inhibit cavitation. Some other prior quick-drop valves respond to a flow restriction situated in the flow path to the pressurized end of the cylinder, but in these cases the discharging ~low path remains communicated with tanlc during the quick-drop mode of operation again preventing use of the entire discharge flow for the purpose of enabling fast lowering of a load without adverse effects.
The prior art has not provided a quick-drop valve which fully seals off the rod end flow passage from tank during the quiclc-drop modc of operation and which fully returns all discharge fluid to the head end cr the cylinder at that time.
Cons:idering an additional problem encountered with prior quick-drop valves, there are fluid cylinder usages in which it is desired to continue lowering the load by reverting to a power-down mode of operation after gravity ceases to be effective for this purpose. The fluid cylinders used to raise and lower a bu]ldozer blade relative to a tractor body are typical of such systems. Control systems for such cylinders often provide a quick-drop mode of operation to ~5 speed the dropping of the bulldozer blade towards the ground in prcparation for work operations. \~len the blade contacts the ground lt may be necessary to convert to a power-down mode of operation to drive the blade forcibly downward a short distance into the ground. An undesirable time lag tends to occur between the quick-drop operation and the subsequent power-down operation and in some cases an undesirable bounce effect or momentary reversed motion of the bulldozer blade or other driven mechanism may occur. This effect is found in prior quick-drop systems which shift automatically by sensing increased resistance to lowering of the load as well as in systems in which the operator must manually shift the main control valve from a float or quick-drop setting to a power-down setting.
Disclosure of the Invention In one aspect of the present invention, there is provided a fluid motor control circuit having a source of pressurized fluid; a fluid motor having first and second ports;
a control valve connected to said source and to said first and second ports through first and second fluid pathways respectively; a housing having a valve chamber with first, second, and third spaced apart valve ports having means for communication with said first motor port, said second motor port and said first fluid pathway respectively; a valve member in said valve chamber movable between a first position at which said first and third valve ports are intercommunicated while being blocked from said second valve port and a second position at which said first and second valve ports are intercommunicated while said third valve port is blocked from both thereof; resilient means for biasing said valve member to said first position; and comprising flow restriction means for developing a pressure differential between first and second spaced apart regions in said second fluid pathway in response to fluid flow therethrough, said first region being between said flow restriction means and said control valve and said second region being between said flow restriction means and said second motor port, and pilot means for moving said valve member to said second position in response to said pressure differential exceeding a predetermined value, said pilot means lZ66 including first fluid pressure pilot means Eor exerting a force which urges said valve member towards said second position and second fluid pressure pilot means for exerting a counterforce which urges said valve member towards said first position, said first pilot means including a first pilot chamber connected to said first region and having a first diameter, and said second pilot means including a second pilot chamber connected to said second region and having a second diameter which is larger than said first diameter.
Brief Description of the Drawings Figure 1 depicts a fluid motor control circuit including a quick-drop valve under conditions which establish the raise mode of operation at which the motor lifts a load against gravity, 6~

Figure 2 is a view of a portion of the apparatus Or ~igure 1 durin~ the power-down mode Or operation, Figure 3 is a view of a portion of the circuit Or ~igures 1 and 2 during the quick-drop mode of operation, 5I~igure 4 illustrates a modirication of a portion of the apparatus of ~igures 1 to 3, Figure 5 is a view of an alternate embodiment of the invention shown in the raise mode Or motor operation, Figure 6 is a view of a portion Or the alternate embodiment of Figure 5 shown in power-down mode of operation, and Figure 7 is a view Or the alternate embodiment Or ~igures 5 and 6 during the quic]c-dro~) mode Or operation.
Best ~'ode ror Carryin~ Out the nvention 15Referring initially to Figure 1 Or the drawing, a fluid circuit 11 includes a quick-drop valve meal1s 12 for controlling a fluid motor 13 that has first and second motor ports 14 and 17 respectively each of which may receive or discharge fluid depending on the direction Or motor motion.
~otor 13 in this example is a fluid cylinder 13a in which the first motor port is a rod end port 14a to which pressurized fluid is directed to cause cylinder retraction and consequent raising Or a load 16 and in which the second motor port is a head end port 17a to which the pressurized fluid may be directed to cause extension of the cylinder and lowering o~
the load.
'l'he load 16 in this particular example is a bulldozer blade 1~ coupled to the body of a tractor 19 through vertically pivotable push arms 21 to which the rod Or cylinder 13a is coupled. Thus by supplyin~ pressurized fluid to ro~ end port 14a while allowing fluid to discharge from hea(l end port 17a, the cylinder 13a may be caused to retract to raise the blade 18 against gravity. Lowerin of the blade 18 may be accomplished by directing pressurized fluid to head end port 17a while allowing fluid to discharge from rod end port 14a, but in this case two distinct modes of cylinder extension are possible.
If there is sizable resistance to lowerin~ of the load, such as when the blade 18 is in contact with ground 22, the rate of cylinder extension is primarily determined by the rate at whic}l pressurized fluid is directed into head end port 17a and the system is in the power-down mode of operation. Under other conditions, such as when the lower ed~e Or the blade 18 is above the ~round, cylinder extension may tend to outrun the incoming supply of pressurized fluid and the extension rate is then ~etermined by gravi-ty actin~
against mechanical friction and whatever degree of flow resistance may be present in the dischare path from rod end port 14a. It is often desirable to take advantage of the faster rate of cylinder extension obtainable by this gravity-induced or ouick-drop mode of operation but this is practical only to the extent that the previously described adverse effects which accompany excessive cavitation within the head end Or cylinder 13a can be prevented. The quick-drop valve means 12 of circult 11 inhibits such effects during the quick-drop mode Or operation to provide for extremely fast lo~rering of the load and further provides for an extremely quick automatic shirt into the power-down mode of operation --$--when resistance to lo~rering Or the load increases from contact Or blade 18 with the ground 22 or other causcs.
The circuit 11 may utili.e a fluid such as oil for example, stored in a tanlc 23, which is pressuri%ed and delivered to a fluid inlet 25 of a main control valve 26 by a pump 24. ~laln control valve 26 also has a ~rain outlet 27 for returning discharge fluid to tank 23. A relief valve

2~ is connected between the output of the pump 24 and tank 23 to establish a predetermined maximum fluid pressure and to return excess output fluid from the pump directly bac~; to the tank.
The main control valve 26 in this example is of the manually operated rorm and has four positions or settinrgs.
At the raise position of the main control valve depicted in 15 Figure 1, pressurized fluid is directed into a first or rod end flo~l path conduit 29 ~hile a second or head end flow path conduit 31 is communicated with tanlc 23 through drain outlet 27. The main control valve 26 may be shifted to a hold position at which both flow path conduits 29 and 31 are 2n closed at the main control valve, while inlet 25 is communicated with drain outlet 27, thereby immobilizing the cylinder 13a. At the third or lol1er position of the main control valve 26, head end flow path conduit 31 receives pressurized fluid from inlet 25 while the rod end flow path 25 conduit 29 is communicated with drain outlet 27. The ~ourth pOSitiOIl of the main control valve 26 is a float position at which flow path conduits 29 and 31 are intercommunicated with each other and with drain 27.
The quick-drop valve means 12 may have a housing 32 with a bore forming a cyllndrical valve chamber 33 in which a movable valve member or spool 34 is disposed. I~n annular groove 36 is formed in housing 32 and communicates with chamber 33 and with the first or rod end port 14a of cyllnder 13a through a first valve port 37 and a flow line 38. Another spaced-apart annular groove 40 opens into chamber 33 and is communicated with the second or head end port 17a of the cylinder 13a through a second valve port 41 and head end flow line 31. Still another annular groove 45 openin~ into chamber 33 is communicated with the rod end flow path conduit 29 at a third valve port 44. The head end flow path conduit 31 includes a flow restriction 117 situated between the main control valve 2(; and the connection to second valve port 41.
Spool 34 is shiftable in the axial direction from a normal position depicted in Figure 1, at which the spool abuts the left end of chamber 33 as viewed in the drawings, to an alternate or quick-drop pos:5,tion depicted in Flgure 3.
Referring again to Figure 1, the spool 34 has three axially spaced-apart annular lands l18, 49 and 51 of which lands IJ8 and llg jointly define a broad spool groove 52 wllile lands 49 and 51 jointly define a second spaced-apart broad spool groove 53. The lands 48, 49 and 51 are positioned on the spool to cause the first and third valve ports 37 and 44 to be communicated by spool ~roove 53 ancl to be isolated from the second valve port 41, by land 49, when the spool is at the normal position depicted in Figure 1. l~'hen the spool 3ll is shifted to the alternate or quick-drop position depicted in ~igure 3, spool groove 52 communlcates the first and second valve ports 37 and 41 while blocking and completely closing off the third valve port 44 from each of thc other valve ports.
Referring again to Figure 1 shifting Or the valve 5 spool 34 between the normal position and the quic~-drop position is controlled by first and second pilot means 54 and 56 respectivel~ situated at the left and right ends of spool 34 as viewed in Figure 1.
The first pilot means 54 in this example is formed by the left end of valve chamber 33, spool 34 including land 48 and a first pilot signal line 57 which communicates the first pilot chamber 55 at the left end of valve chamber bore 33 Wit}l a first region 5~ of tile head end flow path conduit 31 which is between main control valve 2G and flow restriction 47. The second pilot means 56 includes a second pilot chamber 59 t~hich is of greater diameter than the valve chamber 33 and which is within an enlar~;ed right end section 32 ' of housing 32. A pilot piston 61 is disposed in pilot chamber 59 and is movable in the axial direction between an 20 unactuated position at which the pilot piston abuts the ri~ht end of the pilot chamber 59 as depicted in Figure 1 and an actuated position depicted in Figure 2 at which the pilot piston abuts the left end of the pilot chamber 59. Biasing means in the form of a rcsilient compression spring 62 is 25 disposed in valve housing 32 between spool 34 and pilot piston 61 to bias the valvc spool towards the normal position while biasin~ the pilot piston 61 towards the unactuated position as depicted in ~igure 1. To exert a counter force on the pilot piston 61 under certain conditions to be described a seeond pilot signal line 63 eommunicates the outer or right end Or pilot ehamber 59 with a second reg:ion 6ll Or the head end flow path 31 that is on the opposite side Or restriction 47 from region 5~. ~ drain passa.ge ~6 communicates with the opposite end of the pilot chamber 59, at the region Or spring 62, to avoid aeeumulation of leakage fluid between the spool 34 and the pilot piston 61.
As will be diseussed in connection with ol~eration of the apparatus, second pilot ehamber 59 ineludin~ piston 61 have a larger diameter than the first pilot chamber 55 in order to prevent shifting of spool 34 to the quiek-drop position until the pressure in ehamber 55 exceeds that in ehamber 59 by a sizable amount indicative of cavitation in the head end of cylinder 13a. ~eferring no-.~ to Figure 4, this same effect may be reallzed with a second pilot chamber 59' which has the same diameter as quick-drop valve housing bore 33' if the first pilot ehamber 55' has a smaller diameter. In this modifieation, the piston 61 and drain 66 of the quiek-drop valve as depicted in ~igures 1 to 3 are 2~ eliminated and, as shown in Fi~ure 4, a relatively small piston 61' is situated in the first pilot chamber 55' and a drain ~6' is provided in the valve housing 32' between piston 61' and the valve spool 34', the apparatus otherwise being similar to that previously described.
Industrial ~licability of the First ~mbodiment _ . . .. . . .. .
In operatiorl, raising~ of the load 16 against gravity is initiated by shifting the main control valve 26 to the raise position depicted in Figure 1 at which pressurized fluid rrom pump 24 is transmitted to rod end conduit 29 and at which the head enà conduit 31 is opened to drain outlet 27~ ~pring 62 holds spool 3ll at the normal position since the first pilot chamber 55 is open to drain and only lightly pressurized if at all. In addition, a somewllat higher 5 pressure is present in the second pilot chamber 59 owing to the pressure differential created across restriction 47 by the discharging f'low. If the discharge flow is sufficiently hi~h this may shift pilot plston 61 but the practical effect is simply to increase the spring force which is holding spool 10 34 at the normal position depicted in Figure 1.
Accordin~ly, pressurlzed fluid frorn pump 24 is transrnitted to thc rod end port 14a of the cylinder 13a through main control valve 26, rod end conduit 29, valve ports 44 and 37 and flow line 3~3. The head end port 17a of 15 the cylinder is open to drain outlet 27 throu~,h head end flo~
conduit 31 including restriction Ij7 and the main control valve 26. Thus cylinder 13a retracts to raise the load 16.
,'~s the main control valve 2G is of the inrinLtely variable form, the operator may, wit}lin lirnits, control the rate Or 20 raising of the load by adJustirlg the main control valve to re~ulate fluid flo~ rate to the cylin(ler.
'l'o stop the retraction of the cylinder 13a, rnain control valve 26 may be shifted to the hold position at which both the rod end flow conduit 29 and the head erld flow conduit 25 31 are bloclced at the main control valve. The systern has not been depicte(l in the drawings in the hold position as all components other than the rnairl control valve 2(, remain in the positions depicted in ~igure 1. The load 16 is immobilized as fluid from rod end port 14a cannot flow bacl~ to drain owing to the closed condition of the main control valve and cannot flow into the head end of the cylinder owin~ to the position of land 49 which blocks first valve port 37 from second valve port 41. Similarly, fluid cannot flow into or out of the head end port 17a as the head end flow path conduit 31 is also bloclced at the main control valve 26.
rl'he first and second pilot means 54 and 56 are unable to shift spool 34 or pilot piston 61 at this time since there is no flow across restriction 47 to create a pressure differential ~ ich might activate the pilot means.
~dditionally, the pressure within the pilot signal lines 57 and 63 tends to be low at this t3me a;. the weight of the load 16 tends to create a high-pressure condition in the rod end of cylinder 13a and a relatively low-pressure condition in t'ne head end.
Lowering of the load 16 is initiated by shirting the main control valve 26 to the third or lower position as depicted in ~oth of Figures 2 and 3. rrhe quic~-drop valve means 12 may self-operate to either the power-down position depicted in Figure 2 or to the quick-drop position depicted in Figure 3 depending on the interrelationship between two factors. 'rhe first f'actor is the direction of the external forces actin~ on cylinder 13a. If external forces are such as to oppose lowerirlg of the load, the circuit 11 assumes the power-down position depicted in l~igure 2 without regar~ to the second factor. The second factor is the extent to w}lich the operator has opened the main control valve 26 into the lower setting or, in other words the rate at which pressurized fluid is 'ceing transmitted to the cylin~er through restriction 47 and ~einLr dischar~ed from the cylinder throu~h the main control valve. If external forces such as gravity are actinLr to extend the cylinder, then the action of the circuit 11 depends on the relationsllip of the magnitude Or the external force to the degree of openin~ of the maln control valve 2~).
This action can best be understood by first considerinL the operation of the circuit in the pot~er-down mode under conditions where there is external resistance to extension Or the cylinder 13a or where the main control valve 26 has been opened only to a limited extent insufficient to enable the quic~-drol) mode of operation.
Durin~ the po~rer-down mode Or operatiorl as depicted in ~ipure 2, spool 34 of the cuicl~-drop va]ve 12 remains in the normal or left~ard position IJhile the pilot piston Gl is shirted to the actuated or leftt~ard position by the second ~,ilot mcans 5~ as trill hereinarter be discussed in more detail.
At this normal positlon of spool 34, the first and thir~ valve ports 37 and 4IJ remain comrnunicated across spool ~roove 53 and remain b]ocked from the second valve port 41 by spool land 1i9 Pressurized fluid is therefore supplied to the head end ~lort 17a of cylinder 13a throu~h head end floh~ conduit 31, includin~> restriction 47. The rod end port 14a of the cylinder is communicated to drain outlet 27 through flo~r line 38, valve port 37, spool groove 53, valve port 44, rod end flo~r path conduit 2~ and the main control valve 2~. The resulting~ hi~h fluid pressure ~ithill the head end of the cylinder extends tlle cylinder to forcibly lot~ler the load aLainst the resistance to such movement.
Pilot ~iston ~1 shlfts to the actuated position at i6 this time since the relatively hi~h pressure within the head end of the cylinder 13a is transmitted to pilot chamber 59 by the second pilot signal line 63 where the pressure acts a~ainst the pilot piston 61 with a force greater t~an that of sprin~ 62. The flow of fluid through restriction 47 creates a pressure drop thereacross causing a some~hat hicher pressure to be present in the pilot chamber 55 of the first pilot means 54 than in the second pilot chamber 59 but owin~
to the differellce in the diameters of the two pilot chambers and to the force exerted by spring 62, the pressure difference is insufficient to shift spool 34 and pilot piston ~1 riglltwardly. Spool 34 therefore remains at the normal position depicted in ~igure 2 to establish the power-dol~n mode of operation. The relative diameters of the two pilot chambers 55 and 59 and the force characteristics of sprin~ ~2 are fixed to offset the effect of the pressure drop across restriction 47 at times when the flow rate through the restriction 47 has been limited by opening of the main control valve only to a li~ited extent.
If the main control valve 2~ is opened into the lower setting to a Creater extent thereby increasing the flow rate across restriction 47 and if gravity is acting to extend the cylinder 13a more rapidly than provided for by that flow rate, the circuit 11 shifts to the quick-(lrop mode Or operation depicted in i~`igure 3. ~ith spool 31l in the power-down position of ~'igure 2, a reversal of the pressure relationship between the ends of cylinder 13a occurs at the time that gravitational cylinder extension starts to overrun the fluid pressure-caused extension. Pressure at rod end port ll~lZ1~6 14a rises while the pressure at head end port 17a drops to a negative level at which vaeuum or cavitation conditions are ereated in the hcad end. The pressure in second pilot ehamber 59 is therefore redueed relative to the pressure in the first pilot ehamber 55. The pressure differential across flow restrietion 47 is then able to offset the effeet of the differenee of diameters Or pllot ehambers 55 and 5~.
Spool 34 and pilot piston Gl are then foreed ri~ht~rardly as viewed in the dra~in~ to the quiek-drop position of ~'igure I0 3.
At the quiek-clrop position the rod end port ll~a of the eylinc]er 13a is eon~unieate~ with the head end port 17a ~rithin the quiek-drop valve, speeifically throuh flo~
line ~c~, first valve port 37, spool ~roove 52, seeond valve port lll and head end flow conduit 31, At the full quick-drop position, land ~l9 completely bloeks the dischar~,e flow path f'rom the rod end port 14a baclc to drain outlet 27 throuL,h rod encl f]o~r eonduit 29 an(l the main eontrol valve 2~. ~s there is no dischar~,e patll back to drain, all discharge fluid from rod encl port 14a is re~eneratecl hack to the head end port 17a to enable very rast ~,ravitational eylirlcler extension ~rithout aclverse effeets from an ina(lequate supply Or rluid in the head end.
Thus there are basically two conditions which must 2'j be presellt for the systern to shift into the quick-drop mode of opcration. ~irst, the main cont;rol valve 2~ must be shlfted suff'iciently into the lower position to providc a flow rate throu~,h restriction 47 which l~roduces a pressure clifrercrltial ~etsecn pilol; charnbers 55 and 5n hi~h erlou~}l to :a~ 6 compress sprin~ 62. Second, the head end Or cylinder 13a must be voided of positive pressure.
The circuit 11 quickly and automatically reverts from the quick-drop mode of operation of ~i~ure 3 bacl. to the power-down Itlode of operation cr Fi~ure 2 when a substantial resistance to continued cylinder extension is encountered, for example, upon contact of the bulldozer blade 1~ Or Fiure 1 with ground sur~'ace 22. ~eferrin~ to ~i~,ures 2 and 3 in con,~unction, this quick automatic reversion to the power-do~ln mode occurs since slowin~ or stoppin~ Or the rate Or cylinder extension eliminates the void or neative pressure in the head end of cylinder 13a and thus eliminates at least one of the two conditions w!lich, as discussed above, are necessary to put tlle system in the ~uick-drop mode Or 1~ operation. ~!hen the head end of the cylinder is no longer voided, pressure rises in the second pi]ot chamber 59. The force exerted on spool 34 by the lar~,er pilot piston 61 and sprin~ G2 then exceeds t1le opposillg force on the spool exerted within first pllot chamber 5[, causin~ the valve spool and pilot piston to be moved to the left, as viewed in the drawin~, back to the po~rer-down position dcl)icted in ~i~ure 2. Cylinder extensiorl therl continues at a slower rate in the manner described abovc with reference to the power-down mode cr operation until such time as t1le operator s1lirts 25 the main control valve 2G back to the hold or raise posit~on or until SUC11 tine as the lir,it of c,ylill(ler extension is reached .
Althou~rh the system s1lirts automatically bet~een the po:ter-do~ mode and the quick-drop mode, the operator may optionally restrict ~he circuit to the power-down mode and lo~er the load slowly by limitin~; the extent to which the main control valve 26 is opened :tnto the lower position.
This restricts thc rate Or flow throu~,h restriction 47 to a value which is less than that needed to produce a pressure difference, between pilot chambers 55 and 59~ sufficient to compress sprin~, G2. I~lith spring 62 uncompressed, valve spool 31l is necessarily at the lcftward or powcr-down position Or ~i~urc 2. If the operator then opens the control valve 26 more completely, increasing the rlow rate through restriction ll7, the pressure differential between pilot chambers 55 and 59 increases to compress sprin~ 62 and the quic~-drop mode Or operation rnay result lr the hereinbefore-described necessary conditions are preserlt.
The system has been described above with reference to a usaF~c involvin~ a sin~,le cylindcr ]3a, but it should be appreciated that the invention is equally applicable to systems which may employ a plurality Or cylinders 13 or the like and it is preferable in such cases to provide a separate quick-drop valve 12 for each such cylinder. As a practical matter, it is rnore common to employ a pair of cylinders of this kind to manipulate a bulldozer blade l~.
',imilarly, it should be appreciated that thc invention may also be applied to the control of other fluid actuated ~5 devices provided they are of a type in which the amount of fluid disc}lar~ed from one port durin~ the quick-drop mode cr operation is less tharl the amount whlch can be admitted to the other port (which condition ~ould not be met in the systcm of l`i,~ure 1 if cylindcr 13a were Invcrted so that the lLi~'llZ~

ead end eoupled to the load 16).
Sce nd _m _ di ent for Car_yinF~ Out _the _nvention It should also be appreciated that variations of the eireuit 11 are readily possible. ~igures 5 to 7 depiet another embodiment of the circuit llb havin~, a modified form of pilot mealls for controllin~, shifting Or the quielc-drop valve hetween the power-down position and the quiek-drop position.
Referring initially to Figure 5 in partieular, 1~ the pressuri~,ed fluid source or purnp 24b together with tank 23b, relief valve 28b and main eontrol valve 2Gb may all be similar to tlle eorrespondin~ components of the previously descrihed embodi.ment. Similarly, the cylinder 13b including head end and rod end ports 17b and 14b respectively and the load l~b may if desired be similar to the correspondin~;
mechanisms hereinbefore described with reference to the first embodiment, As in the previous ease, a head end flow path eonduit 31b containin~ a flow rcstriction 47l) is eonnected between rain control valve 2~h ~nd the head end port 17b of the eylinder and with the secon(l valve port 41b of quiek--drop va]ve housing 32b. A rod end flow path conduit 29b is a~ain connected between the main control valve 2Gb and third valve port 1l4b Or quick-drop va]ve housin~, 32b while thc flrst valve port 37b a~ain connects to cyllnder rcd end port ~5 14b throu~,h ~ flow line 3~b.
The quick--drop valvc housin~ 32b has a cylindrical valvc c'na~ber 33b with three axially spaced-apart grooves 40b, 3Ob and 45b at which valve ports 41b, 37b and 44b respective]y are locatcd. Valve spool 31!b is disposed in ;6 bore 33b for axial movernent betwecn a normal position, depicted in Fi~ures 5 and f~, at which the spool abuts the left end Or charnber 33b as vi.ewed in the drawin~ and a quick~drop position depicted in l-igure 7 at which the spool abuts the opposite end of the charnber. Spool 3Jlb is formed with four lands 71, 72, 73 and 74 which define three axially spaced-apa.rt spool ~.rooves 76, 77 and 7~.. The lands and ~rooves are located on the spool to cause ~roove 78 to communicate valve ports 37b and 44b when the spool is at the normal ~osition dep~cted in Fi~ures 5 and f; whilc land 73 bloc'r~s both such valve ports from the other valve port 41b.
~t the ~uic~-drop position depictcd in Fi~ure 7, the intermediate spool ~roove 77 communlcates valve ports 37b and 41b while land 73 blocks both such ports from valve port 411b.
At cither position Or the valve spool 3llb, a second pilot si~nal line f)3b containing a contro] orifice 75 communi.cates spool ~roove 7~ with a re~riorl ~4b Or hea~ end flow conduit 31b located betwecll flow restriction 47b ar-ld 2~ head end motor ~ort 17b. rt. first pilot si~nal linc 57b con~unicates the f:irst pilot chamber 55b dcrined by the left end Or valve chamber 33b with a re~ion 5~b of head end rlo~!
passare conduit 31b which is betweerl restriction 47b and the main control va].ve 25b.
~hc orposlte cnd of chamber 33b constitutes a secor.d pi]ot chamber 59b an(l is conrnunicated !ith spool ~roove 7~ by a pas~a~c 79 wit;hin the spool. A corrllressi.on sprin~; ~2b i.s situated within pilot chamber 59b to bias slool 31lb to.!ards t~le nornal E~osition depicte(l :i.n Fi~ure 5.

~t~ ;6 Thus pilot chamber 55b in ccn~unction with sl)ool land 71 and pilot siGnal line 57b constitute a first pilot mcans 54b for exertinr a force tend.in~ tG ur~re the spool 34b away from the nGrrr.al posi.tion depicted in l~ ure 5.
The opposite pilot chamber 59b in con~unction with land 7IJ, pilot signal line 63b, spool ~roove 7~ and spool passa~e 79 constitute a second pilot means 5fb in ~hich fluid pressure forces aidcd by thc force of sprin~ ~2b act to ur~e the valve spool towards the normal position depicted in l~iure 5.
Pressure-responsive valve means Do arc provided ror equalizinfr the fluid pressures in thc two pilot cham.bers 55b and 59b duri.n~ the power-down mode of operation and for producin~ an abrupt chan~e of pilot pressllres w'lell conditions dictate a shi.ft betwcen the power-dotln position of valve spool 3llb and the quicl~-drop position of the spool the pressure-resporlsive va.lve means bein~ a piloted check valve 81 Or the pilot-to-close form in this example. rhe check valve ~1 has an inlet 82 in one end communicated with first pilot si~nal li.ne 57b and has an outlet 811 in onc side communicated t~lith groove 7~ of the quick-drop valve spool

3~b. Check valve ~1 further has an internal spool. 8~ which may recract from inlet R2 to communicatc p:ilot si~nal line 57b with outlet 8ll in response to fluid pressure at the inlet except when a hiher pilot pressure is present in a pilot chamber ~7 hehind the spool. A pilot port ~8 at the other end of the check valve 31 comrnunicates pil.ot chamber 87 with the flow line 38bwhich connects first valve port IJlb with the rod end port llJb of cylindcr 13b.

Inclustr_al_~pplicabilit~ f the Second_r.m odiment In operation, setting of the main control valve 26b at the rai,se position as depicted in Figure 5 causes pressuri7,ed fluid from inlet 25b to be transmitted to rod end port 14b of the eylinder throu~h rod end flow conduit 29b, third valve port 44b, spool ~,roove 7~, first valve port 37b and flo~ line 3~b. Simultaneously, fluid being disehar~ed from the cylinder head end port 17b is drained to tank throu~h flow conduit 31b and the main control valve.
~s a result, cylinder 13b retracts to raise load lGb against gravity. 'I'he quick-drop valve spool 3~lh is held in the normal or leftward position at this time in part by the force Or sprin~ ~2b and in part because thc direction of flow through restriction 47b ereates a pressure differelltial at whieh a hi~her fluid pressure is transmitted to pilot ehamber 5~b than is transmitted to the opposite pilot pressure chamber 55b. l'iloted check valve ~1 remains closed at this time and does not affect the net pilot pressure force on valve spool 34b since the high fluid pressure beirlf, transmitted to the 2~ rod end of c,ylinder 13b is also transmitted to the pilot chamber ~,7 of the clleck valve.
If the ma:ln contro] valve 2~h is then shifte(l to the lo~ler settin~ as depicted in r~igures ~ and 7, the circuit llh shifts either to the po~!er-clol~n rrode of operation illustrated in ~ ure G or to the ~uick-drop mode of or-)eratlon depicte(l in r~igure 7 der,endirlr on the dircction Or the external load ~`orces on cylinder 13b ~nd also clepending on the degree to which the operator ha.s openecd the rnain control valve. If the external forces actillrg on the cylinder 13b resist eylinder extension, then the eireuit llb remains in thc power-down mode, reFardless of the extent er openin o~ the main eontrol valve. If external forees on the eylinder ].3b are ne~ative that is load fc)rces are tendin~
to extend the eylinder because Or gravity or other causes, then the circuit shifts to the ~uick-drop rnode of operation depicted in ~ir-rure 7 if the two conditions previously cleseribed with respcct to the first embodiment are present.
Specifica.lly, the main control valve 2~b must be opened to a ln sufficient extent to provide a flow rate through restri.ction 47b that creates a pressure difference between pilot chambers 55b and 59b hir~h enour~h to compress sprinr~ ~2b. ~oidinr~ or negative pressure must a.lso be present in the head end Or the cylinder 13b so that checlc valve 81 is held closecl by a pressure in pilot chamber ~1 hir-~her than that at inlet 82.
In the absence Or one or both of the above-described conditions, the quiek-drop valve spool ~4b remains in the norrnal position at which pressurized fluid i.s transmitted to the head end port 17b of the eylinder and dlsehar~e fluid 2~ from the rod elld port lllb is transmitted to drain throu~h flow line 3~b, valve port 37b, spool r~roove 7~ valve port 44b, rod end flow eonduit 29b and the main eontrol valve 2~)b.
If the flow rate throurh restrietion 47b is kept below a partieular value the pressure differential between pilot chambers 55b and 59b is not hir.~h enour~h to compress sprinr;
~)2b since such differential is a function of fl.ow rate throurrh the restrictlorl. Further, check valve ~1 opens to eliminate any pressure differential between the two pilot chambers 55b arld ~b as lonr~ as the pressure at the rod end port 14b of the cylinder is less than that in the first pilot signal line 57b which is the case until such time as a ne~ative pressure appears at the hea(l end port 17b.
~lith the main control valve 2f;b at the lower 5 settin~ the system shifts into the ~luick-drop mode depicted in Fi~ure 7, as opposed to the power-down mode depicted in Fi~ure (;, if both of the previously described necessary conditions are ?resent. In particular, external load forces must be causin~ cylinder 13b extension to overrun the 10 supply of fluid being transmitted to the cylinder through the main control valve so that hi~;h pressure at the rod end port lllb accompanicd by voidin~; in the head end of the cylinder closes pilot valve ~1 and isolatcs the first and second pilot chambers 55b and 59b from each other. In 15 addition, the main control valve 2f)b must have been opened into lower to a degree which r rovidcs a flow rate throu~h restriction 117b sufficient to cause the fluid pressure actin~;
on spool 34b within pilot chamber 55b to exceed the opposin~.
fluid pressure actin~ within pilot chamber 55b by arl amount 20 sufficient to compress the sprin~ ~i2b and move the spool to the Fi~ure 7 position.
~ t thc quiclc-drop position of l i~ure 7, spool land 73 completcly bloclcs the discharge path from the rod en(3 port 14b of the cylinder baclc to drain while divertin~; all dischar~e 25 flol~l from the rod end port to the hcad end port 17b of thc cylinder therel y enablin~ extrenlely fast cylinder extension without loss of control or other adverse effects.
Thc circuit llb automatically reverts to the power-cdown n!ocie of operation when rcsist-ancc to cylinder cxtcnsion increases or if thc operator reduces the flow rate througll restriction l17b by adjustment of the mai.n control va]ve 2fb since either occurrence removes one of the t~o conditions required for the tluick-drop mode. T~esistancc to cylin~er extensi.on causes a pressurt? drop at the rod end port 1llb accompanied by a pressure rise at head end port 17b ~hic}~
allolJs pi10t valve ~1 to open and c(lual.ize the ~`1ukl l~ressures in pi.lot c'-ambers 55b and 59b. ~pring f,2 then restores spool 34 to the power-down position. ~estoration of si~ool 31l to the power-do~n position also occurs if the flo~J ra.te throu~h rei-triction ll7b is reduced sufficient1y by manipu11tion of the mai.n control. valve 2fb since the fluid preisure ~ifferentia1 bet.t-~erl pilot chambers 55b an(l 5ab, correspt n~in to the pressure.drop across the res;tliction thell ~t~comes insufficient to mai.ntai.n the sprin~62~ in a state of compression.
~pri.n~ 62b thtll shi fts spool 3llb bacl~ to the po~!er-(loJn position (3epicted in ~ rure 6. In either instance cy1in(1er extension thcn conti.nues at a s10~Jer rate i.n the po~Jer-dolJn rmode unti.l terminatetl by operati.on of the rain control valve 2Cb or by bottomin out of the cylinder at tlle maximum limit of extensi.on.
Other aspects objects and advantaFes of this invention can be obtained from a study of the dra~in~s, the disclosurt-~ and the appended clai.ms.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a fluid motor control circuit having a source of pressurized fluid;
a fluid motor having first and second ports;
a control valve connected to said source and to said first and second ports through first and second fluid pathways respectively;
a housing having a valve chamber with first, second, and third spaced apart valve ports having means for communication with said first motor port, said second motor port and said first fluid pathway respectively;
a valve member in said valve chamber movable between a first position at which said first and third valve ports are intercommunicated while being blocked from said second valve port and a second position at which said first and second valve ports are intercommunicated while said third valve port is blocked from both thereof; and resilient means for biasing said valve member to said first position; the improvement comprising.
flow restriction means for developing a pressure differential between first and second spaced apart regions in said second fluid pathway in response to fluid flow therethrough, said first region being between said flow restriction means and said control valve and said second region being between said flow restriction means and said second motor port, and pilot means for moving said valve member to said second position in response to said pressure differential exceeding a predetermined value, said pilot means including first fluid pressure pilot means for exerting a force which urges said valve member towards said second position and second fluid pressure pilot means for exerting a counterforce which urges said valve member towards said first position, said first pilot means including a first pilot chamber connected to said first region and having a first diameter, and said second pilot means including a second pilot chamber connected to said second region and having a second diameter which is larger than said first diameter.

2. The fluid motor control circuit as set forth in claim 1 wherein said valve chamber is cylindrical and said valve member is a spool movable axially therein, said first and second pilot chambers of different diameter being at opposite ends of said valve chamber.

3. The fluid motor control circuit as set forth in claim 1 further including a movable pilot piston in one of said pilot chambers, said pilot piston being exposed to fluid pressure therein and being positioned to exert force against said valve member.

4. The fluid motor control circuit as set forth in claim 1 further including a pilot piston of said second diameter, said pilot piston being positioned therein to urge said valve member towards said first position thereof in response to said fluid pressure from said second region.

5. The fluid motor control circuit as set forth in claim 4 wherein said resilient means includes a compressible spring located between said pilot piston and said valve member.

6. The fluid motor control circuit as set forth in claim 1 further including a pilot piston of said first diameter, said pilot piston being disposed in said first pilot chamber and being positioned therein to urge said valve member towards said second position thereof in response to said fluid pressure from said first region.

7. The fluid motor circuit as set forth in claim 6 wherein said resilient means includes a compressible spring in said second pilot chamber and being positioned therein to urge said valve member towards said first position thereof.