Note: Descriptions are shown in the official language in which they were submitted.
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INCHING VA~,VE OF THE HYDRAIJLIC BALANCE TYPE
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¦ BACKGROUND OF THE INVENTION
I! This invention relates to an inching valve of the
hydraulic balance type used in hydraulic circuits o~ the
- " construction machinery.
The Japanese Utility Model Publication No. 52-52127 -
' discloses an inching valve utilized in a hydraulic circuit for
~, supplying hydraulic fluid to a clutch of a variable speed gear.
, The inching valve includes a valve box having a bore hole and
10an inlet and an outlet ports formed therein, a spool slidably
mounted within the bore hole, the spool having a spring chamber
and a hydraulic pressure receiving chamber formed therein, and
a valve stem slidably mounted within the spool, one end of the
. valve stem being mechanïcally connected to an inching pedal.
A spring is accommodated within the spring chamber
Il and a load piston is slidably mounted within the hydraulic ;
¦I pressure receiving chamber. Since the hydraulic pressure
t exerted on the load piston is absorbed by a collar mounted
Il within the bore hole by contacting thereof with a plate slidably
20 1l mounted on the valve stem, this valve stem is not hydraulically ,~
balanced and therefor~ a sharp response and a precise inching
control are difficult to obtain.
To improve this problem, a hydraulically balanced -
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inching valve has been proposed by providing a bypass passage
to introduce the hydraulic fluid in the outlet port into a
second hydraulic pressure receiving chamber formed between the
outer periphery of the valve stem and the wall of the bore hole.
In order to make the valve hydraulically balanced, both the
hydraulic pressure receiving chambers must have the-same
pressure receiving area. The precise equivalency in the pres-
sure receiving area is, however, difficult to obtain due to
manufacturing problems.
Further, since the hydraulic fluid in the outlet port
is introduced into the first hydraulic pressure receiving
chamber through a narrow restriction while it is introduced
into the second hydraulic pressure receiving chamber through a
relatively large bypass passage, a time-lag`may exist in
response time between the two chambers which may sometimes
cause a chattering problem.
It is therefore an object of an aspect of the
present invention to provide an inching valve of the hydraulic
balance type which can overcome the above noted problems.
An object of an aspect of the present invention is to
provide an inching valve of the hydraulic balance type which is
simple in construction and provides a precise inching control.
In accordance with an aspect of the present inven-
tion, there is provided an inching valve of the hydraulic
balance type comprising: a valve box having a bore hole form-
ed therein, said valve box also having a first, second, third
and fourth ports formed therein, the first and the fourth
ports being drain ports;
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! a spool slidably mounted within said bore hole, said spool
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having a spring chamber formed at one end thereof and a hydrau-
lic pressure receiving chamber formed at the other end thereof,
said hydraulic fluid receiving chamber being communicated with
said third port through a restriction; a valve stem slidably
mounted within said spool, said valve stem having a step formed
thereon at an intermediate portion thereof, one end of said valve
stem being connectible to a manual operating means of said
inching valve and the other end being provided with nut means
screw-threaded thereon; load piston means slidably mounted on :
said valve stem within said hydraulic pressure receiving
chamber, said load piston means being in touch with said nut
; means when hydraulic pressure is introduced into said hydraulic
pressure receiving chamber; and spring means accommodated within
said spring chamber, one end of said spring means being in touch :.
with the step formed on said valve stem thereby normally urging
said spool and said valve to separate from each other wherein
the spring force applied against said valve stem in an axial
,j direction is balanced with the hydraulic pressure applied on ~ ~`
j said valve stem through said load piston in the opposite axial :
20 7~ direction.
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. ~ The above and other objects, features and advantages
! of the present invention will be readily apparent from the
'i following description taken in conjunction with the accompanying ~
~¦ drawing. . .
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' BRIEF DESCRIPTION OF THE DRAWING
!. - The attached drawing is a cross-sectional view of
an inching valve according to the present invention.
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DETAILED DESCRIPTION OF THE INVENTION
The present invention will now be described in detail
with reference to the accompanying drawing.
. Reference numeral 2 denotes a valve box having a
longitudinal bore hole 4 formed therein. The valve box 2 also
has four ports 5, 6, 7 and 8 formed therein. The ports 5 and 8
' are connected to a reservoir. The port 6 is an inlet port which
is connected, for example, to a modulate valve (not shown) while
the poTt 7 is an outlet port connected, for example, to a clutch ~ -
of a variable speed gear (not shown). Slidably mounted within ~ ;
the bore hole 4 is a spool 10 having a reduced diameter portion
12 at an intermediate part thereof.
The spool 10 has a spring chamber 14 formed at oneend thereof and a hydraulic pressure receiving chamber 16 formed
at the other end thereof. A cylindrical wall 18 of the hydrau- -
lic pressure receiving chamber 16 has formed therein a restriction
` 20 communicating the port 7 with the hydraulic pressure receiv-
ing chamber 16. A plurality of small holes 22 are also formed
', in the cylindrical wall 18.
Slidably inserted within the spool 10 is a valve stem24 having a laTge diameter section 26 and a small diameter
i section 28. A stepped portion 30 is formed between the large
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diameter section 24 and the small diameter section 26. A
compression spring 32 is disposed within the spring chamber 14
with one end being in touch with the stepped portion 30 of the
valve stem 24. Thus, the spring 32 normally urges the spool 10
and the valve stem 24 to separate from each other. Disposed
within the hydraulic pressure receiving chamber 16 is a load
piston 34 with its inner surface being in sliding contact
with the small diameter section 28 of the valve stem 24 and
its outer surface being in sliding contact with the inner : :
surface of the cyllndrical wall 18. :
Right-hand end 35 of the load piston 34 is brought in
contact with a washer 36 mounted around the small diameter
section 28 of the valve stem 24 when hydraulic fluid is
introduced into the hydraulic pressure receiving chamber 16.
A nut 38 is screw-threaded on the valve stem 24 at right-hand
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end thereof. A plug 40 having a collar 42 integrally formed
therewith is threadably engaged with the valve box 2 at right-
hand end thereof to close the bore hole 4. The collar 42 :; .
i functions as a stopper for the spool 10.
. A block 44 is fastened by a plurality of bolts 46 to
the left-hand end of the valve box 2 to close the bore hole 4. .
Pivotally connected at 48 to the valve stem 24 is a
. link 50 which in turn is pivotable about a pin 52. A rod 54 :
, is provided for interconnecting the link 50 and an inching pedal ~-
,l 56. The inching pedal 56 is pivotable about a pin 58 and is
- 1, normally urged clockwise by a spring 60. 1 .
¦¦ Th~ link 50 is urged couter-clockwise abcut the pin : .
¦j 52 by a spring 62, thereby normally pushing the valve stem 24
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toward right in the drawing.
i In operation, when the inching pedal 56 is not
depressed~ the inching valve remains as it is shown in the
drawing. The inlet port 6 is communicated with the outlet
port 7 through the reduced diameter portion 12 of the spool 10
thus hydraulic pressure remains same in the both ports. In the
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state shown, the spool 10 is urged toward right by the spring 32
but is also urged leftward by the hydraulic pressure introduced
into the hydraulic pressure receiving chamber 16 through the
restriction 20 from the outlet port 7 and therefore the spool 10 ;
is hydraulically balanced. Similarly, the valve stem 24 is
urged toward left ln the drawing by thè spring 32 but is also
urged toward right by the hydraulic fluid pressure in the
hydraulic pressure receiving chamber 16 because the rightward
movement of the load piston 34 is transmitted to the valve
- stem 24 ~hrough the washer 36 and the nut 38. Thus the valve
stem 24 is also hydraulically balanced.
When the inching pedal 56 is depressed the valve
stem 24 is pulled toward left through the rod 54 and the link 50,
thus the spring force of the spring 32 is weakened. To compensate
this the spool 10 is moved toward left thereby blocking the com-
munication between the port 6 and the port 7. Therefore the
hydraulic pressure in the port 7 is lowered and the hydraulic
, pressure in the chamber 16 is also lowered. As a consequence,
" the spool lO is moved rightward by the force of the spring 32,
I allowing communication between the port 6 and the port 7. By
i' repeating these steps the hydraulic pressure in the port 7 is
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set lower than that of the port 6. In short, the hydraulic
pressure in the port 7 is reduced in proportion to the amount
'I of depression of the inching pedal 56.
;, When the inching pedal 56 is depressed to its stroke
end, the spool 10 is moved leftward to a position where the
port 7 is communicated with the drain port 8 through the
plurality of small holes 22.
As mentioned hereinabove, since the spring force is
balanced by the hydraulic pressure introduced into the single
hydraulic pressure receiving chamber 16, the inching valve of -;~: :
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~ the present invention can provide a good response to the de-
. pression of the inching pedal 56 and hardly produce the so-called
chat~ering problem.
Since various changes and modifications of the present
invention will occur to and can be made readily by those skilled
in the art without departing from the concept and the spirit of ~ .
the invention, the present invention is not to be taken as ~:.
iimited except by the scope of the appended claims. ~ ~
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