Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
O~Z7
Thls in~.rent~on relates to a control ~ralve ror hydrau-
licnll~ controlli~ the liftin~; operations Or a worl~ing
~achine such as ~ rotary, plow, etc., connected to ~n
~grlcultural power machine such ca tractor.
Do~cription Or the Prior ~rt:
Ge~erall~, ror hydraulic control Or worklng mach~es~
~p
l~Z~827
there has be~n employed a ~pool unit ~dapted to switch
the h~draulic oil passage to and from the ascending posi- b~
tion of the ~orkin~ machine where hydraulic oil i8 supplied
~rom a pump into d cylinder which oper~te~ to force up F
the workin~ machine, the descending position of the working
machine where hydraulic oil in the cyllnder i~ discharged
out into a tank, and the neutral position where the cylin-
der i3 shut off from both of said pump and tank. According
to such system, however, i~ the spool cleara~ce i8 large,
hydraulic oil in the cylinder would leak out ~rom the spool
section at the neutral position of the working machine,
cau~ing ~radual drop of the working ~achino. In the ~o- -
called draft control ~ystem, in order to maintain the wor~-
ing machine traction within the optimal range throughout
the plowing operation, control i9 made to feed back ~n~
escess tillin~ resi~tanc~ to the control vHlvo so that
~hen the tilling r~8i8ta~ce of the working machin~ i~ too
high, the working machine i~ ra~sed up to decrease the
tillin~ re~stance, ~nd when the tilling resista~ce i8 too
low, the ~orkin6 ma~hl~e i8 lowered down to increa~e the
tillin~ resistance, but in such dra~t control eyatem, ~all
aod rise of ths working machine are r~peeted due to oil
loak ~uch as ~aid abov~, resultinK in unstable depth o~ ~,
plo~ing. ~180 ~ if the ~pool clearance i~ les~e~ed in the
des~ning ror preventing such oil leak, the ~trok~ move~ent
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Or the spool would become sluggi~h and also the spool might
ba sti~fene~ due to te~peratur~ vari~tion or other causes.
~,.
This lnvention was proposed ror ov~rcomin~ these
derects Or the oonventlonal control valv~ 8y8tem~ ~ and lt
relates to an improved mechani~m o~ the chec~ valve di~po~ed
between the change-over valvc and c~l~ndqr and the other
a~sociated eleme~ts roquired for the operation of said
valve. ~he ob~ect o~ this invention, therofore, i8 to
reali~e a check valv~ which i~ simple in construction a~d
sure and reliablo ln operation, ~o as to provide a control
valve 8y8tem for ~orkin~ machine which moe~c the essential ..
requiro~ent~ ~or auch typo o~ valve syHto~ that i~, eRsi-
noss a~d 8nr~ne88 O~ operation, mechanical reliQbility and
sA~ety.
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~ igures 1, 2 and 3 are sectional Vi0~8 showing the
di~erent ~odes o~ operatio~ of a control v~lve for working
machine according to thi~ in~ention.
Th~ control ~alvo tor ~orkln~ ~achin~ Rccordin~ to L
this i~cntion i3 ~OW described in detail concerning itB
eonstruction a~d operation by wa~ o~ au ombodiment thereor
i
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0827
as illustrated in the ~ccomp~n~ing drawin~.
Rererr~ng generally to Fi~s. 1 to 3, numeral 1 indi- _
c:ates a control ~alve casin~, 2 a spool type change-over .:
~al~e, 3 relief val~e, 4 a compensator, and 5 a check valve.
h, i8 a cylinder adapted to act ~8 an actuator, said cylin-
der being connected to a cylinder port C in the casing 1
and op~rated by hydraulic oil ~upplied fro~ a pump P.
Pl and P2 are pump ports provided on the casing 1 in connec-
tion to the pump P, and Tl and T2 are tank ports also pro-
~ided o~ the casing 1 in connection to a tank. Hydraulic
oil from the pump port Pl passes throu6h a pa~sage 6 to
reach the relier valv~ 3, while hydraulic oil fro~ the pump
port P2 passe~ through a pQssage 30 to enter a ch~mber 10
~hile simult~neousl~ reachin~ the right end ~ace of the
compensator 4.
~h~ compensator 4 is lo~ded with a spring 4a on the
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left side of it~ plunger and al80 provided with a by-pass
orifice 7 near the ri~ht end face thereo~. It is designed
to move under the conditio~ where the sum Or h~draulic
pressure in the left side cbamber 31 ~nd elastic force of
the spring 4a is bal~nced with the pump discharge pressure
on the side o~ the pas~age 30, 80 as to guide the pump
discharge pressure i~ the pas-age 30 into the t~nk port
Tl through the orifice 7, passage 8 ~nd chamber 9.
:
Ch~ber 31 i8 communicated with chamber 32 by a passage
_ 4 _
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1, .
25, said ch~ber 32 rOrming th~ orificcs 28 and 29 between
it and both ends o~ the la~ld ~ort$on 15 of the check ~ralve L
2.
5aid orifice 28 i8 designed to co~nect or disconnect
th~ chamber 32 and a passage 27, which i8 connected to a
tank provided outside OI the casing 1, i~ accordance with
~o~rement of tho ¢h~ck valve 2.
Chamber 12 i8 ~onnected into a chamber 17 through a
passage 16 and rurther i~to the cylinder port C with movement
Or the check valve 5. It i9 al80 connected into the chamber
10 through an ori~ice 11 or into a chamber 14 through an ~,
orifice 13 in accordancc ~ith movement Or tho change-over
~alve 2. ~n oririce 18 18 provided for co~unicating the
ch~mber 10 with a ~hamber 19 which i~ connected into a
ch~ber 21 through ~ passagQ 20. ~here i8 al~o provided an
orifice 23 adapt~d for connocting or shutting ofr a passage
~2 oonnected into the tan~ pro~ided outside of the c~sing
1. 24 is a hydraullc oil passage provided in the check
valve 2. . ¦
26 is a pilot valve of which movement i8 controlled
b~ the pressure in the chamber 21 and pressi~6 force o~ the
oppofiing sprin6 26a and which i8 adapted to connect the
l~rt-side chamber 33 ~erYing a8 pilot ¢h~mber for the chec~ L
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~al~e 5 into the tan~ port ~2 through a passa~e 34 or into
the ch~mber 17 through the pas~a~es 34 a~d 35.
O82'7
No~ the operation Or khe control valve of thi~ in-
~ntion i8 described concerning the ~ituation where the
change-ovor valve 2 i~ at lt~ n~utral position as sho~n :
i~ Fig. l. Since th~ ori~lc~ 28 o~ the change-over valve
2 18 open und~r this condition, th~ hydreulic oil in the
chamber 31 on the 16~t side of the compensator 4 i8 in
~luid communication with the tank through the passage 25,
chamb~r 32 and passage 27, reducing pressure in the chamber
31 to ~ero. ~hererore, hydrauli¢ oll ~rom the pump port
~ compre~ses the ~pring 4a to move the compensator 4 to
the lo~t and rurth~r pa~ses throu~h the orlfico 7, passage
8 ~nd chambor 9 to tlo~ out ~rom the tank port ~1- Thus,
the dischfirgo pressure of the pump P in this situation i8
Or a ~alue surficient to counterv~il the forco of the
spring 4B- Under this condition, tho ori~ico 18 o~ tho
cha~ber 19 i9 closod while the ori~ico 23 i8 open, 80
that the chamber 19 i~ communicated with tho tan~ through
the passage 22 to make pressurs in the chamber 19 ~ero.
~ccordingly, thc pilot ~alve 26 i~ pr~ssed by the spri~
26a to the positiou ~ho~ i~ tho drauing, koeping the
pa~sages ~4 and 35 in communioation with each otber~
Thus, as pre3sure i~ the c~linder ~ is led into the chamber
33, the check valve 5 i8 pros~ed a~ain~t the valve seat
as shown b~ sald cylinder pressure and pre~sing force Or
the spring 5a to shut orf co~municatlon between the passa~e 1 .
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0827
16 and chamber 17, thus substantially inhibiting n~tural
~all o~ tha ~laton W i~ the cylinder A.
When th~ change-over valve 2 i~ moved in the direc-
tion o~ arrow R from the po~ltion Or Fi~. 1 to the po~ition i
of Fig. 2, that i8, when tha change-over valve 2 is set
at its ascending po~ition, the orifice 28 i8 closed while
the ori~ice 29 i8 opened, and the chamber 10 i~ communi~
cated with the chamber 12 through the ori~ice 11, 80 thBt
the h~draulic oil in the chumber 10 flow~ through the
orifice 11, chamber 12, pas~age 24, orifice 29, chamber
32 and pa~a~e 25 to enter th~ chamber 31, whereby the
pre~sure in ~aid chamber 31 i~ equalized with that in
the ch~mber 30 and the comp~ator 4 i~ moved to the right
b~ the force of the spring 4a to clo~e the oriflce 7 Or
the co~pensator 4, c~u~inK ~n increase Or the pump dis-
charge pressure. When thi~ pump di~char6e pressure becomes ~'~
great~r than the sum Or c~linder pressure ~nd pressing
rorce Or the spring 5a, the check valve 5 i8 moved to the
ls~t to create a situation shown in the drawing, 80 that
h~draulic oil in the passage 16 flows tow~rd the cylinder
port C through the passage 17 to push up the piston W.
~or better understa~di~g of this pressure rel~tion, it
is herob~ e~plained by givinS actual numerical value~. _
Let it be as~umed thst the rOrc~-up pres~ure Or the cyli~-
der A i8 100 kg/cm2 and the pressing rorce Or the spring
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0~327
5a, a~ reduced to thfl h~draullc pro~sure basi~ 1 kg/
e~2. Under this condition, whe~ the hydraulic pressure
in tha pansage 16 esceods 101 kg/cm2, the checX valve 5
.~8 ope~ed ~d ~ovoe to the left. ~l~o assu~lng that the
pressing force of the spring 4a on the compensator 4 i8
4 kg/cm a~ calculated in terms of hydraulic pressure,
the hydraul~c pr~ssur~ i~ the chamber 30 i8 held at 105
kg/cm2 at highest when the hydraulic pressure in the pa-
88age 16 i8 101 k~/cm2~ ~nd when thls highest oil pressure
i8 exceeded, the superflous oil i8 bled o~f into the tan~
port ~1 throu6h t~e ori~ice 7. ~hun, under this condition,
di~charge pres~ure of the pu~p P i~ always maintained at
105 ~g/cm2. As ea~ understood from the above explana- tion, the di~erential pressure acros~ the orifice 11
(that i~, pressure difrerencc between the ch~mbers 10 a~d
12) is always ~ai~tained constant (4 kg/cm2 in the prese~t ~_
case) regardles~ o~ the c~linder push-up pressure or pump
oil discharge. I~ this relation is reviewed from the
aspect of control, the ~act i8 noted that the oil rate
through the orifice 11 i8 constantly controlled to an
a~ount proportio~al to the opening area o~ the orifice 11,
~o that control o* small ~low rate i8 facilitated by a
suitable selection of the ~ize and shape of the oritice 11.
It is also made easy to minimize the shoc~ at the time o~ `."
start or stop of the lifting opération. ~ -
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li;~O827
When the ~troke of the chnn6e-ovor vslve 2 in the
direction Or arrow R i8 ~urth~r ~xpanded ~n~ the openin~ _
area Or thc oririce 11 i8 sufriciently enl~rsed, the dir-
ferential pressure across the orifice 11 is eliminated
aud the hydraulic pressures ~pplied to the left and ri~ht
~ides of the compensator 4 are equalized. A~ a result,
the compensator 4 i9 ~orc~d to the right by the spring 4a
to perfectl~ clo~ th~ oriric~ 7, 80 that th~ disch~rge
oil from the pump P ~ 8 now allowed to rlow entirel~ into
lo the cylinder ~ to ~orce up the piston W at full ~peed.
In cas~ the discharge pressure of the pump P should
become high2r than the settin~ pressure of the relief valvc
3 due to exces~ load of the piston W, or in case the piston
W should ~ail to mov~ due to ~n external forco in the
course Or ascent o~ th9 pi9ton W, the relie~ valve 3 i8
open~d to let oil in the passa~ 6 flow out into the tank
port Tl, 80 that the discharge pre~sure sf thc pump P
never exceeds said setting pressure. Al~o, in case the
pump P should become inoperative or unable to produce re-
quired prcssure due to engine shutdown or other causes
during the elevating operation, the check valve 5 i8
immediately closed to shut off the hydraulic oil passQge
~rom the cylinder port C to inhibit fall o~ the piston W.
~hu~ in ~uch case, the orifice 18 of the chamber 19 i8
clo~ed while the ori~ice 23 i~ opened to produce a condition I .
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82~7
~lmilar to th~t ot the neutral po~itlon ~hown in Plg.
1, ~o that the pre~sure in the ch~ber 21 becomos zero L
and the pilot valvo 26 i8 prsssed by the spring 26a to
the ri~ht end Or the stroke, and hencc the pressure in
the chamber 33 on the left side of the check valve 5 i~
maintai~ed equal to the c~linder pressure because Or
communication through the passages 34 and 35. Thus, when
the pump side pres~ure in the passaga 16 drops~ the check
~alve 5 i8 naturally moved to the ri~ht to ~hut Orr the
oil pa~sage.
Now the operation Or the valve ~tem when the change- _
over valve 2 i8 at it8 descending po8it~0n i8 described.
~is. 3 sho~ the geometry o~ the s~stem when the ch~nge-
over ~al~e 3 was moved from the position Or ~ig. 1 in the
direction of arrow R' to the de~cendin~ position. Under
thi~ condition, the orifice 28 i8 openod while the orifice -
29 i8 closed, 80 that the cha~ber 32 i8 connected into
the t~nk through the pas~a~e 27 to reduce to zero the
pre~ure i~ the chamber 31 o~ the l¢rt side of the co~-
pen~ator. ~ccord~n~ly, the influent hydraullc oil from
the pump port P2 compresses the spring 4a to move tho
compen3ator 4 to the left and further paRses through the
orifice 7, pa~sage 8 and chamber 9 to rlow out ~rom the L
tank port Tl. There~ore, t~e discharge pressure of the
pump P in this situatio~ i8 regulsted to n pre~sure
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82~
,,
surflcient ror aountervailing the force of the sprlng
4~ as in th~ case of the neutral position ~hown in Fig.
1, ~nd ir e~pre~sed by a numoric~l ~alue in the ~me way :.
as discussed be~ore, the pu~p diRcharge pressure i9 held
at 4 to 5 kg/cm2. Also, unde~ this condition1 the orifice
18 iR opened whilo the oririce 23 i8 clo~ed, and the cham-
b~r 19 maintai~s the pump discharge pressure, 30 that a
part of hydraulic oil i8 ~nt ~nto the chamber 21 through
the passage 20 and th~ pilot valve 26 i8 mo~d to the left
lo end o~ the ~troke aBainst the ~prin~ 26a, with the re~ult
that the passage 35 i8 shut ofr while the passage 34 i8 ~,
communicated with the tunk port T2. Accordi~gly, the check ---
valve 5 i8 moved to th~ lcft by the holding pre~sure of
the c~linder A to open the pa88a~0. Since chamber 12 is
in communication with ch~mber 14 throu~h orifice 13,
hydraulic oil in the cylinder A flows through the check ~'valve 5, pas~age 16, chamber 12 and orifice 13 to entsr
the chember 14 whence it further pa88e8 through the passage
8 to ~low into the tank port Tl, causing descent Or the
pi8ton W. In this ca8e~ if the opening area Or the orifice
13 $3 small, a pre~sure is produced in the chamber 12 and
RÇt~ a braking ~orce to allow ~low descent o~ the piston
W, and ir said ope~ing area is enlarKed, tbe piston W
ma~ be dropped at ~ull speed.
As appare~t ~rom the foregoin6 e~planation, the control
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8:~7
valve system for working machines according to this invention
i9 SO constructed that when the change-over valve is at the
neutral position (Fig. 1), the check valve is closed, and
when the change-over valve is at its ascending position
(Fig. 2), the check valve is opened in correspondence to the
elevation exceeding a specified value of pump pressure,
and when the change-over valve is at its descending position
(Fig. 3), the pilot chamber of the check valve is connected
to the tank to thereby open the check valve, and since all
of these operations are performed in association with the
change-over valve moving operation, easiness and reliability
of operation are maintained. Further, provision of the pilot
valve 26 allows integration of said operations in close
relation to the change-over valve operation to realize further
simplification of operation. Moreover, in case the pump
discharge pressure should drop suddenly for some reason or
other, the pilot valve 26 i~ immediately moved to introduce
the cylinder holding pressure into the pilot chamber of the
check valve to securely close the check valve so that the
cylinder holding pressure and capacity are maintained just
as they are, thus precluding any likelihood of inadvertent
drop of the piston while appreciably improving reliability
and safety of the valve system.
Both the feeding and discharging of oil into
and from the cylinder A are carried out through t~e check
valve 5. Accordingly, when the pump P is deactuated with the
change-over valve 2 in a "neutral" position or during a lifting
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li~O82~
operation or a lowering operation, the check valve 5 is closed
immediately to stop the downward movement of the piston,W,
i.e. the working machine. No matter how the change-over valve
2 is operated after the pump P has been deactuated to close
the check valve S, the passage extending from the cylinder A
to the check valve 5 is ~ept closed thereby, qo that the piston
W is never moved downwardly in error.
The control valve according to the present
invention with respect to different operational conditions
with different pressure oil charging conditions will be
described.
When the contro~ valve is in a lifting condition
as shown in Fig. 2, the check valve 5 is opened with a high
pressure from the pump in an on load state to allow the
passage extending to the cylinder port C to be opened. When
the control valve is in a lowering condition as shown in Fig. 3,
the check valve 5 is opened with a low pressure from the pump
in a no-load state. When an output pressure from t~e pump P
becomes z~ro with the control valve in a lifting condition,
the check valve 5 is directly closed. When an output pressure
from the pump P becomes zero with the control valve in a lowering
condition, the pump pressure to the pilot valve 26 becomes zero.
As a result, the pilot valve 26 is moved back to the right in
the drawing immediately to allow the pressure oil in the
cylinder A to flow into the pilot chamber 33. Consequently,
the check valve 5 i8 closed.
8~7
After the check valve 5 has been closed as
mentioned above, the pilot valve 26 cannot be operated even
if t:he change-over valve 2 is moved to the right or left.
Thi~; may be clearly understood in a case where a no-load
pressure from the pump P is zero with the change-over valve in
a "neutral" position is imagined. Therefore, when the pump P
is deactuated, the check valve is kept closed and the piston
W is held stationary.
Therefore, in an emergency in which the pump
is ~topped or output pressure from the pump is rapidly
decreased, a cylinder retaining pressure and the volume of
the cylinder can thus be maintained as they are. In fact,
a control valve according to the present invention is free
from the drawbacks encountered in a conventional control
valve of this kind, in which erroneous operation of a change-
over valve causes an unexpected downward movement of a piston
which results in accidental falling of the working machine.
In other words, a control valve according to the present
invention permits a working machine to be retained safely
at all times.
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