U.S. patent number 3,807,447 [Application Number 05/335,431] was granted by the patent office on 1974-04-30 for fluid controlling apparatus.
This patent grant is currently assigned to Daikin Kogyo Co., Ltd.. Invention is credited to Kenji Masuda.
United States Patent |
3,807,447 |
Masuda |
April 30, 1974 |
FLUID CONTROLLING APPARATUS
Abstract
An apparatus for controlling the flow of fluid, comprising a
directional control valve unit for controlling the operating
direction and operating speed of a fluid motor, and a
pressure-compensating valve unit for controlling the flow of fluid
passing in said directional control valve such that it will be
proportional to the displacement of a valve spool of said
directional control valve unit.
Inventors: |
Masuda; Kenji (Takatsuki,
JA) |
Assignee: |
Daikin Kogyo Co., Ltd. (Osaka,
JA)
|
Family
ID: |
26356840 |
Appl.
No.: |
05/335,431 |
Filed: |
February 23, 1973 |
Foreign Application Priority Data
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|
|
|
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Feb 24, 1972 [JA] |
|
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47-19954 |
Feb 29, 1972 [JA] |
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47-21325 |
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Current U.S.
Class: |
137/596.13;
91/433; 137/596.1; 91/436; 91/446 |
Current CPC
Class: |
F15B
13/02 (20130101); F16H 61/4061 (20130101); F15B
13/0417 (20130101); Y10T 137/87233 (20150401); Y10T
137/87185 (20150401) |
Current International
Class: |
F15B
13/02 (20060101); F15B 13/04 (20060101); F15B
13/00 (20060101); F15b 013/02 () |
Field of
Search: |
;137/116.3,596.1,596.12,596.13 ;91/433,436,446 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Cohan; Alan
Assistant Examiner: Michalsky; Gerald A.
Attorney, Agent or Firm: Cushman, Darby & Cushman
Claims
What is claimed is:
1. A fluid controlling apparatus for controlling the operation of a
hydraulic actuator, comprising
a. a directional control valve unit (40) having a spool slide
cavity (42), and an inlet passage (50), actuator ports (a,b) and a
return passage (51) respectively arranged in crossing relation to
said spool slide cavity (42), and including a valve spool (55)
disposed in said spool slide cavity (42) for sliding movement
therein to provide variable dimension flow regulating portions and
to establish or sever communication between said inlet passage (50)
and the inlet port (a or b ) of the actuator or between the outlet
port (b or a) of the actuator and said return passage (51);
b. a pressure-compensating unit (10) having a plunger slide cavity
(13), and an inlet passage (21), a bypass passage (20), an outlet
passage (25), an outlet passage (22) and a tank passage (24)
respectively communicating directly with the inlet passage (50) and
the return passage (51) of said directional control valve unit
(40), all of which are arranged in crossing relation to said
plunger slide cavity (13), and including a pressure-compensating
plunger (30) disposed in said plunger slide cavity (13) to define a
reference pressure chamber (9) and a back pressure chamber (36) on
both sides thereof respectively and being slidable in said plunger
slide cavity (13) to control the flow of fluid between said inlet
passage (21) and said bypass passage (20), between said inlet
passage (21) and said outlet passage (22) or between said tank
passage (24) and said outlet passage (25), and further having
surfaces respectively for receiving the fluid pressure in said
reference pressure chamber (9) and the fluid pressure in said back
pressure chamber (36) applied thereto in squarely opposite
directions against each other, and a spring (35) disposed in said
back pressure chamber (36) to urge said plunger (30) to move up to
a position to sever communication between said inlet passage (21)
and said bypass passage (20); and
c. passage means for communicating said outlet passage (25)
directly with said motor port (a) or (b) while said
pressure-compensating plunger (30) is in the position to sever
communication between said inlet passage (21) and said outlet
passage (22).
2. A fluid controlling apparatus for controlling the operation of a
hydraulic actuator, according to claim 1, wherein said directional
control valve unit (40) is adapted to form therein the variable
flow regulating portion between the inlet passage (50) and the
inlet port (a or b) of the actuator, and there are provided a
passage (29) for establishing communication between the inlet
passage (50) and the reference pressure chamber (9) and a passage
(37) for establishing communication between the motor port (a) or
(b) and the back pressure chamber (36).
3. A fluid controlling apparatus according to claim 2, wherein a
back pressure valve (72) is provided between the outlet passage
(25) of the pressure-compensating unit (10) and a fluid storage
tank (80).
4. A fluid controlling apparatus according to claim 2, wherein
pilot ports (39, 39') are provided between the inlet passage (50)
of the directional control valve unit (40) and the actuator ports
(a, b) respectively and are communicated with the passage (37)
communicating with the back pressure chamber (36).
5. A fluid controlling apparatus according to claim 1, wherein said
directional control valve unit (40) is adapted to form therein the
flow regulating portion between the return passage (51) connected
with a fluid storage tank (80) and the outlet port (b or a) of the
actuator, and there are provided a passage (34) for communicating
the return passage (51) with the back pressure chamber (36) and a
passage (69) for communicating the actuator port (a) or (b) on the
outlet side with reference pressure chamber (9).
6. A fluid controlling apparatus according to claim 5, wherein the
inlet passage (50) communicating with a fluid pressure source is
communicated with the actuator port (a) and/or (b) while the spool
valve (55) is in its neutral position.
7. A fluid controlling apparatus according to claim 5, wherein
pilot valves (39, 39') are provided between a passage of the
directional control valve unit (40) connected with the fluid
storage tank (80) and the outlet ports (a) and (b) of the actuator
respectively and are adapted to be communicated with the passage
(69) communicating with the reference pressure chamber (9).
Description
Various fluid controlling apparatus have been proposed heretofore,
which control the operating direction and operating speed of an
actuator, e.g. a fluid motor, by varying the displacement of a
single valve spool wherein the operating direction and speed of the
actuator is controlled in proportion to the displacement of said
valve spool. Such prior art apparatus, however, have the
shortcoming of having a limiting range of application because they
might be highly satisfactory as one to achieve one function but do
not concurrently achieve other functions. For instance, the fluid
controlling apparatus disclosed in U.S. Pat. No. 3,488,953 and U.S.
Pat. No. 3,602,104 are excellent in that a loss of driving force
can be minimized by holding pump pressure as low as possible, both
when the actuator for operating a working machine is in operation
and when the same is not in operation. The apparatus of the latter
patent has, in addition to such advantage, the further advantage
that a plurality of actuators can be operated concurrently with a
single pressure source. However, the aforementioned apparatus have
the disadvantage that, while a satisfactory operation may be
obtained when the direction of the load exerted on the actuator is
opposite to the direction of operation of said actuator, in the
event when the direction of the load exerted on the actuator is the
same as the direction of operation of the actuator, and hence, the
load aids the operation of said actuator, the apparatus do not
perform the intended function. Even if the apparatus were arranged
so as to perform the intended function when the direction of the
load is the same as the operating direction of the actuator, an
abnormal pressure would occur in the circuit, causing breakage of
the entire circuit.
As a practical example of the case wherein a load is exerted on an
actuator in the same direction as the operating direction of the
actuator and aids the operation of said actuator, reference may be
made to a vehicle (working machine) in which the wheel driving
force is obtained from a fluid motor (actuator). In case of such
vehicle, the direction of the load and the operating direction of
the fluid motor are opposite to each other when the vehicle is
running on the normal flat surface, but when the vehicle is running
on a descending slope, the wheels rotate freely due to the
gravitational downward movement of the vehicle, so that the fluid
motor does not operate as motor but operates as pump. Thus, the
load is exerted on the actuator in the same direction as the
operating direction of the actuator and increasingly aids the
operation (running) of the vehicle. Such a condition also occurs
also in winches, elevators and other various fluid-driven apparatus
which utilize an actuator.
A primary object of the present invention is to provide a novel and
improved fluid controlling apparatus which obviates the
above-described disadvantage and which is so designed that, when a
load exerted on an actuator is acting in a direction to aid the
operation of said actuator, fluid passage between a pressure supply
line and the inlet side of the actuator is blocked and the fluid is
controlled between a return line and the outlet side of the
actuator. Further the return line and the inlet side of the
actuator are interconnected to form a short circuit therebetween,
whereby the pressure of the actuator appears only in said short
circuit and thus, the occurrence of an abnormal pressure which has
occurred in the prior art apparatus is avoided.
Another primary object of the invention is to provide a fluid
controlling apparatus which uniquely is capable of meeting any and
all demands including such demands for which a plurality of
different types of apparatus have been required in the past, and
which is capable of mass production.
Still another object of the invention is to provide a fluid control
apparatus which is capable of operating a plurality of actuators
with a single pressure source.
A further object of the invention is to provide a fluid control
apparatus which, when used for operating a plurality of actuators,
is capable of supplying the flow of fluid, preferentially to a
primary actuator, without being influenced by the states of loads
exerted on the other actuators.
An additional object of the invention is to provide a fluid control
apparatus which, when used for operating a plurality of actuators,
is capable of maintaining the pump pressure at a level equal to or
slightly higher than the largest one of the loads exerted on the
actuators, whereby the rotational force required for driving a
pressure generating source is reduced.
Another additional object of the invention is to provide a fluid
control apparatus in which a fluid inlet passage connected to a
fluid pressure source when a valve spool of a directional control
valve member is in its neutral position can be formed so as to
enable in a desired fluid controlling operation to be achieved, and
which can be provided in a compact form as a whole.
Other objects and advantages of the invention will become apparent
from the following description of the embodiments thereof shown in
the accompanying drawings.
FIG. 1 is a sectional view of a first embodiment of the fluid
control apparatus according to the present invention, in which a
flow regulating portion is provided on the meter-in side;
FIG. 2 is a sectional view of the fluid controlling apparatus of
FIG. 1, in which the spool is displaced to the left;
FIG. 3 is a fragmentary enlarged view of the plunger shown in FIG.
2;
FIG. 4 is a second embodiment of the fluid control apparatus
according to the invention, in which a flow regulating portion is
provided on the meter-in side;
FIG. 5 is a sectional view of a third embodiment of the fluid
control apparatus of the invention, in which a flow regulating
portion is provided on the meter-out side;
FIG. 6 is a sectional view of the apparatus of FIG. 5, in which the
spool is displaced to the left; and
FIG. 7 is a sectional view of a fourth embodiment of the fluid
control apparatus of the invention, in which a flow regulating
portion is provided on the meter-out side.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention will be described here-under with reference
to the drawings showing diagrammatically the most preferred
embodiments thereof. Since the constructions and modes of operation
of these embodiments are considerably different depending upon
whether a flow regulating portion provided on a directional control
valve is in a so-called meter-in circuit communicating a pump with
the inlet side of a fluid motor, or in a so-called meter-outer
circuit communicating the pump with the outlet side of the fluid
motor with a tank port, the case wherein the flow regulating
portion is provided in the meter-in circuit, will be described at
first.
I. the case wherein the flow regulating portion is in the meter-in
circuit:
The fluid controlling apparatus shown in FIG. 1 comprises two units
including a directional control valve unit generally indicated at
40 which operates an actuator 61 in a desired direction at a
desired speed, and a pressure-compensating unit generally indicated
at 10 which controls the pressure acting on the directional control
valve unit 40. While the pressure-compensating unit 10 and the
directional control valve unit 40 are shown as being provided
separately and coupled together, they may alternatively be provided
integrally as a monoblock, or another same directional control
valve unit or units may be mounted in turn on the directional
control valve unit 40 in stacked relation.
The directional control valve unit 40 will be described
hereunder:
This directional control valve unit 40 includes a main body 41
defining therein a spool slide cavity 42. The spool slide cavity 42
has seven annular grooves 43, 44, 45, 46, 47, 48 and 49 formed in
the wall thereof. Of these seven annular grooves, the four annular
grooves 44, 45, 46 and 47 are open in the outside of the main body
41 at four ports b, 50a, a and 51a respectively. The leftmost
annular groove 43 is communicated with the annular groove 47 by a
passage 52 and, therefore, is communicated with a return passage 51
through said annular groove 47. A closed circuit 60 is connected
between the motor ports a, b (hereinafter referred to simply as
ports a and b respectively) communicating with the annular grooves
46, 44 respectively, and a fluid motor 61 is provided in said
closed circuit 60. The fluid motor 60 is capable of operating a
load 63 (working machine) by its drive shaft 62 which is rotated in
one or the other direction by the fluid passing in the closed
circuit 60 in the right or left direction. The rightmost annular
groove 49 is connected with a tank 80 through a passage 79.
In the spool slide cavity 42 is slidably disposed a valve spool 55
having four lands 56, 57, 58 and 59. The flow of fluid is
controlled as described below by the sliding movement of the spool
55.
Thus, the leftmost land 56 serves to sever communication between
the annular grooves 43 and 44 when the valve spool 55 is in neutral
position (the position shown in FIG. 1), and to establish
communication between the annular grooves 43 and 44 when said spool
valve 55 is displaced to the left to the position shown in FIG. 2.
The second land 57 from the left closes off an inlet passage 50 and
pilot ports 39, 39' provided on both sides of said passage 50 when
the valve spool 55 is in its neutral position as shown in FIG. 1,
and opens the pilot port 39 and forms a variable inlet orifice
between the right end face of the land 57 and the annular groove
45, or a flow regulating portion 54 in a passage communicating the
inlet passage 50 with the port a, when said spool valve 55 is
displaced to the left as shown in FIG. 2. Conversely, when the
valve spool 55 is displaced to the right, the land 57 opens the
pilot port 39' and forms a flow regulating portion 54' in a passage
communicating the inlet passage 50 with the port b. The third land
58 from the left serves to establish or sever communication between
the annular grooves 46 and 47 by its left end face, according to
the position of the valve spool 55. Thus, it severs the
communication when the valve spool is in its neutral and leftward
position, and establishes the communication when the valve spool is
in its rightward position. The right end face of the land 58 and
the rightmost land 59 serve to open or close off a vent passage of
the pressure-compensating unit 10 to be described later, according
to the position of the valve spool 55.
Now, the pressure-compensating unit 10 will be described. This
pressure-compensating unit 10 includes a main body 12 defining
therein a plunger slide cavity 13. The plunger slide cavity 13 has
five annular grooves 14, 15, 16, 17 and 18 formed in the wall
thereof. The leftmost annular groove 14 is communicated with a port
g, formed in the main body 12, through a bypass passage 20. The
second annular groove 15 from the left is communicated with a port
P through an inlet passage 21. The third annular groove 16 from the
left is provided with an outlet passage 22 and a passage 23. The
outlet passage 22 is communicated with the inlet port 50a of the
directional control valve unit 40 and the passage 23 is
communicated with a port 27 through a check valve 26. The fourth
annular groove 17 from the left is communicated with the return
port 51a of the directional control valve unit 40 through a tank
passage 24. The fifth annular groove 18 is communicated with a port
T through an outlet passage 25.
In the plunger slide cavity 13 of the main body 12 is slidably
disposed a pressure-compensating plunger 30. The plunger 30 is held
in its leftward position by a spring 35 disposed in a back pressure
chamber 36 formed on the right side of said plunger 30, whereby the
inlet passage 21 and the bypass passage 20 are isolated from each
other. To the back pressure chamber 36 is connected one end of a
passage 37, and the other end of said passage 37 is branched into
three passages in the main body of the directional control valve
unit 40. One of the branch passage 38 is communicated with the
annular groove 48 and the other two branch passages form the
aforesaid pilot ports 39, 39' respectively which are open in the
spool slide cavity 42 on both sides of the annular groove 45. A
reference pressure chamber 9 formed on the left side of the plunger
30 is communicated with the outlet passage 22 through the passage
29 on the upstream side of the flow regulating portions 54, 54',
for receiving a reference pressure to operate the plunger 30. The
pressure-compensating plunger 30 has two lands 31, 32 at about mid
portion thereof. The width of the left hand land 31 is determined
in relation with the width of the annular groove 15 and the
displacement and diameter of the plunger 30. Namely, in FIG. 1, the
plunger 30 is urged to the left by the spring 35 and in this
position the land 31 severs communication between the passage 21
and the bypass passage 20, but establishes communication between
the inlet passage 21 and the outlet passage 22. When high pressure
fluid is introduced into the reference pressure chamber 9 and the
plunger 30 is displaced to the right, the inlet passage 21 is
communicated with the bypass passage 20 at first. The width of the
land 31 is made smaller than that of the annular groove 15 so that
the inlet passage 21 is communicated also with the outlet passage
22 in this case. This state is shown in FIG. 3 in an enlarged
scale. In general, when fluid is passed in a conduit provided with
an orifice, a pressure differential occurs between the fluid
pressure upstream of said orifice and the fluid pressure downstream
of the same when the opening area of said orifice is smaller than a
certain value. Based on this knowledge, in the present invention
the land 31 is formed so as to form between the left end face
thereof and the annular groove 15 an orifice to create a pressure
differential (hereinafter called divided flow controlling portion
(.alpha.)) during the period before said left end face reaches the
position 31a shown in FIG. 3. When the left end face of the land 31
is in the divided flow controlling position, the right end face
thereof is not in the pressure controlling position to be described
later. As the plunger 30 is displaced further to the right and when
the left end face of the land 31 is located rightwardly of the
position 31a, the divided flow control is released. As the plunger
30 is displaced further to the right and when the right end face
thereof is located in the position 31b shown in FIG. 3, an orifice
to create a pressure differential (hereinafter called first
pressure controlling portion (.beta.)) is formed between the right
end face of said land 31 and the annular groove 15 conversely to
the preceding case. In summation, the land 31 and the annular
groove 15 are arranged in the relation of Z<Y in FIG. 1 (with
the plunger 30 being in the leftmost end of its stroke), so that,
during the rightward stroke of the plunger 30, the divided flow
controlling state may be obtained at first upon displacement of
said plunger over a certain distance, then said divided flow
controlling state be released upon further displacement of the
plunger over a predetermined distance, and the first pressure
controlling state be obtained upon further displacement of the
plunger. The other land 32 is given the same consideration as that
given to the land 31. Namely, the land 32 is arranged so as to form
an orifice to create a pressure differential (hereinafter called
second pressure controlling portion (.gamma.)) between the right
end face thereof and the annular groove 17 when the plunger 30 is
displaced further to the right to a point to sever communication
between the inlet passage 21 and the outlet passage 22. That is to
say that the lands 31, 32 are formed in the relation of Z<Y<X
in FIG. 1.
The port P mentioned above is connected to a pressure supply line
71 which is provided therein with a fixed type fluid pump 70, and a
port T is connected to the tank 80 through a back pressure valve
72. A relief valve 73 is connected to the pressure supply line 71
on the outlet side of the fluid pump 70 and the secondary side of
said relief valve 73 is connected to the port 27 and the primary
side of the back pressure valve 72. Further, a divided flow line 74
connected at one end to the port g is connected to the primary side
of the back pressure valve 72, and an actuator is provided in said
divided flow line 74. In FIG. 1, this actuator is represented by a
pressure regulating valve 75 for the sake of convenience. Where it
is necessary to distinguish clearly the actuator 75 from the fluid
motor 61, the former will be referred to as second actuator and the
latter as first actuator.
The function and effect of this embodiment of the fluid controlling
apparatus according to the invention will be described hereinafter.
In the apparatus, the relation between a load exerted on the first
actuator 61 and a load exerted on the second actuator 75 brings
about substantial differences in function and effect. Therefore,
the case wherein the load exerted on the second actuator 75 is
larger than the sum of the load exerted on the first actuator 61
and the force of the spring 35 and the case wherein the former is
smaller than the latter, will be described in sequence.
a. The case wherein the load exerted on the second actuator 75 is
larger than the sum of the load exerted on the first actuator 61
and the force of the spring 35.
In the directional control valve unit 40, when the valve spool 55
is in its neutral position as shown in FIG. 1, the port a, the port
b, the inlet passage 50 communicating with the port P and the port
T are blocked respectively by the valve spool 55, whereby the fluid
motor 61 is positively held inoperative. However, the pressure
supply line 71 is communicated with the reference pressure chamber
9 on the left side of the plunger 30 through the port P, the inlet
passage 21, the outlet passage 22 and the passage 29, while the
back pressure chamber 36 is communicated with the tank 80 through
the passage 37, the branch passage 38, the annular grooves 48, 49
and the passage 79 and maintained at the atmospheric pressure.
Therefore, when the fluid pump 70 is driven from a prime mover (not
shown) under such condition, the fluid discharged from said fluid
pump 70 flows into the reference pressure chamber 9 on the left
side of the plunger 30 through the pressure supply line and starts
to act on the left end face of said plunger 30. At the point when
the reference pressure acting on the left end face of the plunger
30 has become larger than the biasing force of the spring 35, the
plunger 30 starts to move to the right, opening the divided flow
controlling portion (.alpha.) at first and then closing the first
pressure controlling portion (.beta.). Thus, the entire fluid being
discharged from the fluid pump 70 is bypassed to the tank 80
through the divided flow controlling portion (.alpha.) and the
divided flow line 74, with a pressure which is the sum of the set
pressures of the pressure regulating valve 75 and the back pressure
valve 72. As such, this embodiment has the capacity of bypassing
the fluid discharged from the pump while the valve spool 55 is in
its neutral position.
When the valve spool 55 is displaced to the left to the position
shown in FIG. 2 thereafter, communication between the annular
grooves 48 and 49 is severed by the rightmost land 59 at first, and
successively thereafter the pilot port 39 is opened by the valve
spool 55 and then the flow regulating portion 54 is opened in a
desired degree. As a result, the pressure in the reference pressure
chamber 9, by which the plunger 30 is held in its rightward
position, becomes temporarily the same as the pressure in the back
pressure chamber 36, allowing said plunger 30 to make a return
movement to the left under the biasing force of the spring 35.
Concurrently, the fluid in the pressure supply line 71 flows to the
fluid motor 61 via the port a and returns to the tank 80 via a
return line constituted by the port b, the annular grooves 44, 43,
the passage 52, the tank passage 24, the second pressure
controlling portion (.gamma.), the outlet passage 25, the port T
and the back pressure valve 72. Thus, the fluid motor 61 starts
rotating at a speed corresponding to the flow of fluid passing at
the flow regulating portion 54 formed on the inlet side of said
motor and concurrently a pressure differential is created by the
resistance to flow of said flow regulating portion 54, by which
pressure differential a circuit is formed to lead the pressure on
the upstream side of the flow regulating portion 54 or in the
pressure supply line to the reference pressure chamber 9 on the
left side of the plunger 30 through the passage 29, and a circuit
is formed to lead the pressure on the downstream side of said flow
regulating portion 54 to the back pressure chamber 36 through the
pilot port 39 and the passage 37. The plunger 30 again starts to
move to the right against the biasing force of the spring 35, due
to the pressure differential between both sides thereof, and is
held stationary in the position where the pressures acting on both
ends of said plunger 30 are balanced as a result of the force of
spring 35 increasing.
The discharge pressure of the pump in this case is the sum of the
pressure in the second actuator 75 and the set pressure of the back
pressure valve 72. The pressure differential between both sides of
the flow regulating portion 54 becomes larger as the opening at the
first pressure controlling portion (.beta.) is larger, with the
result that the fluid passes in the fluid motor 61 at a rate higher
than actually required. However, the plunger moves to the right
under the effect of said pressure differential, diverging the fluid
in excess of that required for operating the fluid motor 61 from
the flow in the inlet passage 21 through the divided flow
controlling portion (.alpha.) and reducing the fluid pressure in
the outlet passage 22 to thereby maintain the pressure of fluid at
the portion from said first pressure controlling portion (.beta.)
to the flow regulating portion 54 at a value which is the sum of
the pressure created by the load 63, that is, the load pressure,
the pressure created by the resistance to flow at the flow
regulating portion 54 and the resistance to flow at the back
pressure valve 72. Thus, it will be understood that, in the event
that the supply of fluid to the fluid motor 61 is larger than
necessary, the pressure differential between both sides of the flow
regulating portion 54 becomes large, displacing the plunger 30
further to the right according to the interrelation between said
pressure differential and the biasing force of the spring 35,
whereby the pressure reducing effect at the first pressure
controlling portion (.beta.) is increased. Conversely, in the event
when the supply of fluid to the fluid motor 61 is smaller than
necessary, the pressure differential between both sides of the flow
regulating portion 54 becomes small, so that the plunger 30
displaces to the left according to the interrelation between said
pressure differential and the biasing force of spring 35, whereby
the opening at the first pressure controlling portion (.beta.)
becomes large and the supply of fluid to the fluid motor 61
increases. Thus, the supply of fluid to the fluid motor 61 is
maintained constant. In other words, the pressure differential
between both sides of the flow regulating portion 54 is maintained
constant by the spring 35. Consequently, the flow of fluid at the
flow regulating portion 54 is maintained always constant with
respect to a certain preset opening of said flow regulating portion
54, whereby the operating speed of the fluid motor 61 is maintained
constant.
By changing the operation of the flow regulating portion 54
thereafter, upon operating the valve spool 55, a flow of fluid
corresponding to the changed opening is obtained. Namely, the
displacement of the valve spool 55 and the flow of fluid can be
controlled in proportional relation.
The operating speed of the fluid motor 61 is thereafter maintained
constant in the following manner, with the opening of the flow
regulating portion 54 being constant, even when the load 63 exerted
to the fluid motor 61 has, for instance, increased.
Thus, when the load 63 has increased, the pressure between the
first pressure controlling portion (.beta.) and the fluid motor 61
increases, with the result that the pressure differential between
both sides of said first pressure controlling portion (.beta.)
becomes small and a larger portion of the fluid discharged from the
fluid pump 70 is diverged to the divided flow controlling portion
(.alpha.) where the resistance to flow is relatively small, so that
the supply of fluid to the fluid motor 61 decreases and the
pressure differential between both sides of the flow controlling
portion 54 becomes small. As a result, the plunger 30 displaces to
the left according to the interrelation between said pressure
differential and the biasing force of spring 35, making large the
opening at the first pressure controlling portion (.beta.) and
increasing the supply of fluid to the fluid motor 61. In other
words, the predetermined pressure differential set by the spring 35
is restored between both sides of the flow regulating portion 54,
with which the operating speed of the fluid motor 61 is maintained
constant.
On the contrary, when the load 63 exerted on the fluid motor 61 has
decreased, the operating speed of said fluid motor 61 is controlled
to be constant in the following manner:
Thus, with the load 63 decreasing, the supply of fluid to the fluid
motor 61 increases, with the result that the pressure differential
between both sides of the flow regulating portion 54 becomes large.
The plunger 30 displaces to the right according to the
interrelation between said pressure differential and the biasing
force of spring 35 to decrease the opening of the first pressure
controlling portion (.beta.). Thus, an excess pressure is removed
at the first pressure controlling portion (.beta.) and the supply
of fluid to the fluid motor 61 is decreased concurrently, whereby
the pressure differential between both sides of the flow regulating
portion 54 is maintained constant irrespective of the varying
load.
Accordingly, the operating speed of the fluid motor 61 is
maintained always constant corresponding to the set value of the
flow regulating portion 54, irrespective of pressure variation in
the fluid circuit.
Although the foregoing description has been made with reference to
the case wherein the operating direction of the actuator 61 and the
direction of load exerted thereon are opposite to each other, it
will be understood from the following description that the
operating speed of the fluid motor is controlled to be constant
also in the case when said both direction are the same:
Thus, in such case the fluid motor 61 operates as a pump, sucking
the fluid on the inlet side and discharging the same to the outlet
side or into the return line unrestrictedly. As a result, the
pressure of fluid on the inlet side of the fluid motor 61 falls
rapidly and the pressure in the back pressure chamber 36 also falls
rapidly, so that the pressure differential between both sides of
the flow regulating portion 54 increases, causing the plunger 30 to
move further to the right to close off the first pressure
controlling portion (.beta.) at first. With the first pressure
controlling portion (.beta.) being thus closed off, the pressure of
fluid in the passage from said first pressure controlling portion
to the fluid motor 61 tends to become negative. However, since the
return fluid discharged from the fluid motor 61 and the fluid
discharged from the pump and returning to the tank 80 through the
divided flow controlling portion (.gamma.) undergo the resistance
created by the back pressure valve 72, a portion of these return
fluid flows to the inlet side of the fluid motor 61 with the
pressure set in the back pressure valve 72 while forcibly opening a
check valve 26, and enables said fluid motor to continue its
rotation. Thus, the return line is communicated with the inlet side
of the fluid motor 61 by a passage 23 and the check valve 26. In
this case, the pressure on the upstream side of the flow regulating
portion 54 is equal to the pressure value set in the back pressure
valve 72 and the pressure on the downstream side of the same is
lower than said pressure value just by a value corresponding to the
resistance to flow created at the flow regulating portion 54. The
plunger 30 continues its rightward movement by this pressure
differential. When the opening of the second pressure controlling
portion (.gamma.) is decreased to smaller than necessary by the
displacement of the plunger 30, the pressure on the outlet side of
the fluid motor 61 becomes extremely high, decreasing the rate of
rotation of said fluid motor 61. Consequently, the rate of suction
by the fluid motor 61 decreases and the resistance to flow at the
flow regulating portion 54 becomes small, so that the pressure
differential between both sides of said flow regulating portion
becomes small. The plunger 30 moves to the left, expanding the
opening of the second pressure regulating portion (.gamma.).
Conversely, when the opening of the second pressure regulating
portion (.gamma.) is excessively large, the pressure on the outlet
side of the fluid motor 61 falls, increasing the rate of rotation
of said fluid motor. Therefore, the pressure on the inlet side of
the fluid motor 61 tends to be negative and the resistance to flow
at the flow regulating portion 54 increases. Consequently, the
pressure differential between both sides of the flow regulating
portion 54 becomes large, causing the plunger 30 to move to the
right to decrease the opening of the second pressure controlling
portion (.gamma.). Thus, the plunger 30 is held immovably in a
position where the sum of the pressure on the downstream side of
the flow regulating portion 54 and the biasing force of the spring
35 is balanced with the pressure on the upstream side of said flow
regulating portion 54 or the set pressure of the back pressure
valve 72 owing to the pressure controlling function of the second
pressure controlling portion (.gamma.) of said plunger. Thus, it
will be understood that the pressure differential between both
sides of the flow regulating portion 54 is maintained constant by
the spring 35, even when the fluid motor 61 is running by
itself.
The most important feature of the apparatus of this invention is
that exertion of an excessively large pressure on the outlet side
of the fluid motor 61 can be avoided in such state, as may be
understood from the following description: when the fluid motor 61
starts running by itself as described above, the plunger 30 moves
to the right to a position closing off the first pressure
controlling portion (.beta.) but leaving the divided flow
controlling portion (.alpha.) fully opened. Therefore, the
discharge pressure of the fluid pump 70 is equal to the sum of the
set pressures of the pressure regulating valve 75 and back pressure
valve 72. However, the outlet passage 22 and tank passage 25 are
communicated with each other through the check valve 26 and the
pump discharge pressure is not supplied to the fluid motor 61 as
the first pressure controlling portion (.beta.) is closed off, so
that the pressure occurring in the short circuit is only that
created by the self-running fluid motor 61.
For rotating the fluid motor 61 in the opposite direction, this can
be achieved by displacing the valve spool 55 rightward from its
neutral position. By the displacement, the flow regulating portion
54 and the pilot port 39 on the right side of the annular groove 45
are kept closed off, and the pilot port 39' and the flow regulating
portion 54' on the left side of said annular groove are opened by
the valve spool 55. In this case, a bent unload passage leading
from the back pressure chamber 36 to the tank is closed off by the
land 58 and a circuit symmetrical with that described above is
formed, and the flow of fluid can be controlled during the reverse
rotation of the fluid motor 61 by the same flow controlling
function as described above.
Summarizing the embodiment described hereinbefore, the directional
control valve unit is of a four-way, all ports block,
neutral-unloading, and flow regulating portion on meter-in type and
the pressure-compensating valve unit is of a type having a first
pressure controlling portion (.beta.) and a second pressure
controlling portion (.gamma.) for fluid control. The main relief
valve 73 operates only when the fluid motor 61 stops its rotation
under excessive load.
The pressure differential between both sides of the flow regulating
portion 54 is maintained constant corresponding to the biasing
force of the spring 35 in either case. Therefore, by operating the
valve spool 55, it is possible to start, accelerate, decelerate and
stop the fluid motor 61, as well as to proportion the displacement
of the valve spool 55 with the speed of the fluid motor 61
indpendently of fluctuation of the circuit pressure. It is further
possible to achieve a proportional control without the occurrence
of excessively large pressure even when the load direction and
motor operating direction are the same.
Although the present invention has been described in detail
hereinbefore with reference to FIGS. 1, 2 and 3, the embodiment of
the apparatus described above is adapted for use in the case
wherein the load exerted on the other hydraulic means (second
actuator) connected to the divided flow line is larger than the sum
of the load exerted on the first actuator 61 and the biasing force
of the spring 35, and the divided flow controlling portion
(.alpha.) serves merely to bypass or divide excess fluid. It should
be noted, however, that the divided flow controlling portion
(.alpha.) has a pressure compensating function per se which has not
been described. It should also be understood that the divided flow
controlling portion (.alpha.) is not necessary when the other
hydraulic means is not connected to the divided flow line, and the
same function and effect may be achieved by arranging the
apparatus, for example, such that the divided flow controlling
portion (.alpha.) is held closed by blocking the port g either by
extending the width i of the land 31 in the leftward direction or
by means of a plug, and the relief valve 73 is connected to the
outlet side of the fluid pump 70 for discharging the bypass and
divided flow therethrough. Thus, a completely different apparatus
can be submitted simply by plugging the port g.
However, with the other hydraulic means connected to the divided
flow line, the load exerted on said means changes frequently from
time to time during the operation of an actuator of said means, as
is well known, and it is not always the case that the changing load
is larger than the sum of the load exerted on the actuator 61 and
the biasing force of the spring 35.
Thus, it becomes necessary to arrange the apparatus such that the
same function and effect as stated above may be obtained even if
the load exerted on the second actuator happens to be smaller than
the sum of the load exerted on the actuator 61 and the biasing
force of the spring 35 (including the case wherein no load is
exerted on the second actuator).
b. Now, the operation of the apparatus in the event when the load
on the second actuator is smaller than the sum of the load on the
actuator 61 and the biasing force of the spring 35 will be
described in detail hereinafter with reference to FIGS. 1 and
3:
In the event when the load on the other hydraulic means, that is,
the load created by the resistance of the second actuator 75 is
larger than the sum of the load 63 on the actuator 61 and the
biasing force of the spring 35, during normal operation of the
actuator, the fluid discharged from the fluid pump 70 tends to flow
toward the actuator 61 from the pressure supply line, and the
plunger 30 is displaced corresponding to the load 63 on the
actuator so as to control the flow of said fluid at the first
pressure controlling portion (.beta.) (pressure reducing function).
When the load on the other hydraulic means, i.e. the load on the
second actuator 75, becomes smaller than the sum of the load 63 on
the first actuator and the biasing force of the spring 35
(including the case wherein no load is exerted on the second
actuator) under such condition, the fluid discharged from the fluid
pump 70 is conversely bypassed into the port g through the divided
flow controlling portion (.alpha.). In order to avoid this, the
plunger 30 moves to the left to control the flow bypassing into the
divided flow line.
Thus, the plunger 30 displaces to the left to a position in which
the left end face of the land 31 is located in the position
indicated by the phantom line 31a illustrated in FIG. 3, whereby
the divided flow controlling portion (.alpha.) comes into effect,
with the first pressure controlling portion (.beta.) being
ineffective.
With the divided flow controlling portion (.alpha.) being in
effect, the pump discharge pressure takes a value which is the sum
of the pressure created by the load 63, the flow regulating portion
54 and the back pressure valve 72 respectively, and the pressure of
the fluid in the passage from the divided flow controlling portion
(.alpha.) to the pressure regulating valve 75 is maintained at a
value which is the sum of the set pressures of said pressure
regulating valve 75 and back pressure valve 72.
Thereafter, when the load 63 comes to have a changing tendency, the
flow of fluid is controlled by the changing opening of the divided
flow controlling portion only, with the first pressure controlling
portion (.beta.) being held open, in a manner to maintain the
pressure differential between both sides of the flow regulating
portion 54 constant, contrary to the controlling function of said
first pressure controlling portion (.beta.) mentioned above. Since
the excess flow of fluid discharged from the pump can be bypassed
into the divided flow line and this bypass flow can be utilized for
driving the other hydraulic means, during both the normal operation
and self running of the actuator 61, effective use of the driving
force of the pump 70 becomes possible.
Further, since the fluid can be supplied to the actuator 61 at a
constant rate proportional to the displacement of the valve spool
55, in spite of a fluctuation of load exerted on the other
hydraulic means, it is possible to supply fluid preferentially to
the first actuator 61 to ensure satisfactory operation thereof,
without being influenced by the operating condition of the other
hydraulic means. The apparatus of the invention has the following
advantageous feature when the load on the pressure regulating valve
75, during normal operation of the actuator is smaller than the sum
of the load 63 and the biasing force of the spring 35.
In the conventional valve apparatus the pump discharge pressure is
influenced by the relief valve 73 but in the present invention it
is influenced by the load 63 on the actuator 61, and therefore, the
output of the pump can be smaller than in the conventional
apparatus an amount corresponding to the difference between the
load on the relief valve and the load on the actuator. Thus, the
outpt loss of the pump can be minimized.
The output loss of the pump can be minimized also because the fluid
discharged from the pump is bypassed in its entirety into the
divided flow line during the self-running operation of the
actuator.
It will be obvious that, when the pressure regulating valve 75 is
not provided and the divided flow line 74 is arranged to open
directly into the tank, a functional effect equivalent to that
obtainable when the load on the pressure regulating valve 75 is
smaller than the sum of the load 63 on the actuator 61 and the
biasing force of the spring 35, can be achieved and further
self-running control is possible.
In the present invention, as described above, the pressure
compensation is achieved by the effect of the first pressure
controlling portion (.beta.) when the resistance of the pressure
regulating valve 75 is larger than the sum of the load 63 and the
biasing force of the spring 35 during normal operation, and by the
effect of the divided flow controlling portion (.alpha.) when the
former is smaller than the latter. Since the pressure compensation
is effected independently of the sizes of the two loads, pressure
compensation can be achieved satisfactorily regardless of the
fluctuation of the load exerted on the second actuator provided in
the divided flow line (the line leading to the port g). This is
true whether the load on said second actuator becomes larger or
smaller than the sum of the load 63 during normal operation of the
first actuator and the biasing force of the spring 35.
Hereinbefore, an embodiment of the invention has been described in
detail with reference to FIGS. 1, 2 and 3, and now other
embodiments will be described briefly.
The embodiment shown in FIG. 4 differs from that of FIG. 1 in
respect of the path of fluid when the fluid motor 61 is in
self-running operation. It differs from the latter also in that it
is superior in respect to the stability of operation when the load
63 on the fluid motor 61 is larger than a predetermined value, and
in the bent unload type. These differences will be described in
detail hereunder:
First of all, the difference in respect of the flow path of fluid
during self-running operation of the fluid motor will be described.
In this embodiment, the positions of the annular grooves 17, 18 in
the pressure-compensating unit 10 are swapped as shown in FIG. 4,
whereby, while in the embodiment of FIG. 1 the fluid passing at the
second pressure controlling portion (.gamma.) flows from the tank
pressure 24 into the plunger slide chamber 13 to form a so-called
converging flow, in the embodiment of FIG. 4 the fluid passing at
the same controlling portion (.gamma.) flows from the plunger slide
chamber 13 into the outlet passage 25 to form a so-called expanding
flow. Further, in this embodiment the width L of the annular groove
18 and the width of the land 32 are selected in the relation of l
< L and Z, Y, W, X in the relation of Z< Y.ltoreq. W< X.
With such an arrangement, when the fluid motor 61 starts
self-running and the first pressure controlling portion (.beta.) is
closed off by the plunger 30 which is displaced to the right by
virtue of the pressure differential beween both sides of the flow
regulating portion 54, a flow direction controlling portion
(.delta.) is opened fully, either concurrently or immediately
thereafter, owing to the relation of Y.ltoreq. W mentioned above,
whereby the tank passage 24 and outlet passage 22 are communicated
directly with each other. The pressure set by the back pressure
valve 72, during this period, is led into the upstream side of the
flow regulating portion 54 through the check valve which is
forcibly opened by said pressure, and maintains the pressure in
said portion at a superatmospheric pressure.
Thus, the fluid discharged from the self-running fluid motor 61
cycles in the circuit formed by the port b, the annular grooves 44,
43, the passages 52, 24, the second pressure controlling portion
(.gamma.), the flow direction controlling portion (.delta.), the
passage 22 and the flow regulating portion 54, and maintained at
its pressure by the back pressure valve 72. Thus, in the embodiment
of FIG. 4 the fluid sucked by the fluid motor 61 during the
self-running operation of said motor is supplied by the recycled
return fluid through the flow direction controlling portion
(.delta.), which in the embodiment of FIG. 1, is supplied through
the check valve 26 in its entirety, and therefore, the check valve
26 can be reduced in size.
The embodiment of FIG. 4 is distinguishable over that of FIG. 1
also in that safety of the circuit can be secured more
positively.
Namely, in this embodiment a pilot relief valve 67 is provided in
the line 66 upon branching said line 66 in a direction from the
back pressure chamber 36 towards the tank 80 and a restriction 65
is provided in the passage 37, while in the directional control
valve unit 40 the rightmost annular groove 49 and the passage 52
are communicated with each other through a passage 64. Such
arrangement enables one to enhance the safety of circuit in the
event when the load 63 on the fluid motor 61 has increased above a
predetermined value. Thus, when the load 63 on the fluid motor 61
has increased above the predetermined value and the pressure in the
back pressure chamber 36 has risen above the set pressure of the
pilot relief valve 67 during the period in which the fluid motor 61
is operating the load 63 in the normal condition and the load on
the second actuator is larger than the sum of the load on the first
actuator and the biasing force of spring 35, said pilot relief
valve 67 is opened to discharge the fluid. At the same time, a
pressure differential is produced between both sides of the
restriction 65 due to the resistance to flow of said restriction
and the plunger 30 is displaced to the right, with the result that
the pressure downstream of the first pressure controlling portion
(.beta.) is limited to a predetermined value set by said pilot
relief valve 67, by the pressure reducing effect of said first
pressure controlling portion (.beta.). It is to be noted that under
such condition, the rate of rotation of the fluid motor 61 is not
constant and is lower than the set value or the motor stops
running.
Further, the divided flow controlling portion (.alpha.) or flow
direction controlling portion (.delta.) of the plunger 30
respectively plays the role of relief valve, in the size relation
of the load 63 on the first actuator 61, the load on the second
actuator 75 and the set pressure of the pilot relief valve 67.
The apparatus of the invention wherein a flow regulating portion is
provided in a meter-in circuit (case I)) have been described
hereinbefore with reference to FIGS. 1, 2, 3, 4 but, as another
embodiment, the inlet side of the fluid motor 61 may be
communicated directly with the tank 80 through a check valve to
form a hydraulic circuit during self-running of the actuator.
The directional control valve unit 40 in each of the embodiments
described above is of a type having four ports or two flow
regulating portions 54, 54'. This is to meet the requirement that
the operating direction of the actuator 61 is changed between two
directions and the flow rate and pressure of fluid are controlled
during the operation of the actuator in each direction. However, in
the event when the flow rate and pressure of fluid are required to
be controlled in the operation of the actuator only in one
direction, such control can be achieved easily with only one flow
regulating portion. Thus, the apparatus of the invention may be
provided in various forms, without deviating from the scope of the
invention set forth in the appended claims, by optionally combining
the above-described embodiments with respect to the symbols of
directional control valve, such as the numbers of direction and
position.
In each of the embodiments described above, the flow resistance in
each passage is ignored but it should be understood that each
passage has a cross sectional area large enough not to impair
smooth operation of the apparatus. Descriptions of the detailed
portions which are well known in the art are also omitted.
(II) The foregoing description has been made with respect to the
embodiments of case (I) of the invention in which the flow
regulating portions 54, 54' are provided in the meter-in circuit
communicating the pump 70 with the inlet side of the fluid motor
61. Now, embodiments of the invention in which the flow regulating
portions 54, 54' are provided in the meter-out circuit
communicating the outlet side of the fluid motor 61 with the tank
80, will be described with reference to FIGS. 5, 6 and 7.
A distinct difference between the apparatus shown in FIGS. 5, 6, 7
and those shown in FIGS. 1, 2, 3, 4 is that, while in the latter it
is impossible to obtain a special spool function such as a tank
port block and the back pressure valve 72 is required, in the
former it is possible to obtain a special spool function and the
back pressure valve 72 is not required so that the apparatus can be
provided in a compact form as a whole.
1. First of all, how the special spool function is obtained will be
described with reference to FIG. 5. The embodiment of FIG. 5
differs from that of FIG. 1 in that the valve spool 55 is so
constructed as to form the flow regulating portion 54 between the
right end face of the land 56 and the annular groove 43 when said
spool is displaced leftward to the position shown in FIG. 6 and to
form the flow regulating portion 54' between the left end face of
the land 58 and the annular groove 47 when said valve spool is
displaced conversely rightward. Thus, the flow regulating portions
54, 54' are located in the meter-out circuit communicating the
outlet side of the fluid motor 61 with the tank 80 regardless of
which direction the valve spool is displaced. Further, as the
consequence of changing the locations of the flow regulating
portions 54, 54', the pilot port 39 is open between the annular
grooves 43 and 44, and the pilot port 39' between the annular
grooves 46 and 47, and said pilot ports 39, 39' are communicated
with the reference pressure chamber 9 through passages 77, 69 and
an opening 68 respectively.
With the flow regulating portions 54, 54' provided in the meter-out
circuit as described above, a special spool function can be
obtained in which the inlet passage connected to the port P can be
communicated with the ports a and/or b when the valve spool 55 is
in its neutral position.
If, in the apparatus of FIG. 1 having the flow regulating portion
54, 54' provided in the meter-in circuit, an arrangement is made to
establish communication between the inlet passage 50 and the ports
a and/or b in the neutral position of the valve spool, for
obtaining a tank port block type spool function, and when the valve
spool 55 is displaced to the left thereafter so as to establish
communication between the inlet passage 50 and the port a and
between the port b and the port T, control of fluid in proportion
to the displacement of the valve spool from said position would
only be possible and a flow rate of fluid below a predetermined
flow rate corresponding to the initial opening cannot be obtained,
as the port a has already opened when the valve spool was in
neutral, passing a predetermined quantity of fluid therethrough. In
the event that the flow rate is low, therefore, it would be
impossible to operate the actuator 61 in proportion to the
displacement of the valve spool 55, and thus the apparatus cannot
be used for other than special applications. Thus, with the flow
regulating portions 54, 54' provided in the meter-in circuit as in
the apparatus shown in FIG. 1, general proportional control cannot
be achieved when the inlet passage 50 communicating with the port P
is communicated with the port a and/or b in the neutral position of
the valve spool 55.
As contrasted, with the flow regulating portions 54, 54' provided
in the meter-out circuit as in the apparatus of FIG. 5, the inlet
passage 50 communicating with the port P may be in communication
with the port a or b in the neutral position of the valve spool
55.
Thus, the flow rate of fluid to the fluid motor 61 can be
controlled in proportion to the displacement of the valve spool 55,
even if communication between the inlet passage 50 and the port a
or b is previously established in the neutral position of the valve
spool 55, since the flow regulating portions 54, 54' are provided
in the meter-out circuit.
In the apparatus shown, for instance, in FIG. 5, similar to that
shown in FIG. 1, the spool function of the valve spool in the
neutral position is of the all port block type wherein all ports
are blocked. However, the apparatus shown in FIG. 7 is of the
so-called tank port block type wherein the inlet passage 50 is
communicated with the ports a and b and the port T is blocked when
the valve spool is in its neutral position.
In the apparatus of such spool function type, the inlet and outlet
sides of the fluid motor 61 are communicated with each other
through the annular groove 45 in the neutral position of the valve
spool, so that said fluid motor 61 can be driven easily by an
external force such as a external mechanical force.
Reference is made, as other practical example of establishing
communication between the inlet passage 50 in communication with
the port P and the ports a and b, to the case of achieving an
inching operation of the fluid motor 61 by providing notches on
both sides of the land 57 in FIG. 6.
2. Now, the manner in which the entire appartus can be provided in
a compact form due to the absence of the back pressure valve 72
will be described.
The omission of the back pressure valve 72 in the apparatus of FIG.
1 renders the apparatus completely unserviceable during
self-running operation of the fluid motor 61. Thus, in the
self-running state of the fluid motor 61, the return line
communicating the outlet side of said fluid motor 61 with the tank
80 and the pump line communicating the outlet passage 22 with the
inlet side of said fluid motor 61 are communicated directly with
each other, and the fluid motor is acting not as motor but as pump.
Therefore, the fluid pressure in the pump line is zero and the
pressure differential between both sides of each of the flow
regulating portions 54, 54' is also zero. The fluid pressure acting
on the opposite ends of the pressure compensating plunger 30 is
also zero, so that said plunger 30 is returned to its leftward
position under the biasing force of the spring 35. In other words,
the apparatus loses its fluid controlling function completely
during the self-running operation of the fluid motor 61.
If the back pressure valve 72 is eliminated from the apparatus
having the flow regulating portions 54, 54' provided in the
meter-in circuit, like that shown in FIG. 1, the apparatus will not
perform its intended function in the self-running state of the
fluid motor 61 as stated above, and hence, will be usable only with
specific working machines.
In order for such apparatus to be usable with any and all working
machines, therefore, it is necessary to provide the back pressure
valve 72 in cooperation with the short circuit as shown in FIG. 1,
to forcibly pressurize the pressure line and thereby to develop a
pressure differential between both sides of each of the flow
regulating portions 54, 54', necessary to operate the plunger
30.
However, the back pressure valve 72 is unnecessary where the flow
regulating portions 54, 54' are provided in the meter-out circuit
as in the apparatus shown in FIGS. 5, 6 and 7.
In this case, since the flow regulating portions 54, 54' are
provided between the fluid motor 61 and the tank 80, the fluid
pressurized by the fluid motor 61 passes at the flow regulating
portions 54, 54' even when said fluid motor is self-running and
acting as pump, and a pressure differential occurs without fail
between both sides of each of said flow regulating portions 54, 54'
in such state of the fluid motor 61. This is why the back pressure
valve 72 is not required.
The elimination of the back pressure valve 72 apparently enables
the apparatus of FIG. 5 to be provided in a much more compact from
than the apparatus shown in FIG. 1.
This is because, in the apparatus shown in FIG. 1, the back
pressure valve 72 needs to be essentially the same size as the
directional control valve unit 40 and pressure-compensating unit
10, since the fluid discharged from the pump 70 passes therethrough
in its entirety.
The apparatus shown in FIG. 5, because of the absence of the back
pressure valve 72, can be provided, as a whole, in a size two
thirds of that of FIG. 1, or in a very compact form.
3. Although the most distinct differences between the apparatus of
FIG. 5 and that of FIG. 1 have been described above, both apparatus
are different also in respect of the bent unload type in
neutral.
More specifically, in the apparatus of FIG. 5 the inlet passage 50
and the reference pressure chamber 9 are communicated with each
other through the annular groove 45, a passage 53, the annular
groove 49 and passages 77, 69. With such arrangement, the pump is
unloaded in the neutral state of apparatus, as in the apparatus of
FIG. 1.
4. The other portions are identical with those of the apparatus
shown in FIG. 1 and will not be described herein.
Hereinbefore, the embodiments of the invention have been described
with reference to the drawings upon categorizing them, for the sake
of convenience in description, into the case (I) wherein the flow
regulating portions 54, 54' are provided in the meter-in circuit
and the case (II) wherein the same are provided in the meter-out
circuit. In short, the apparatus of the invention have the
following meritorious features:
A. With the apparatus of the invention, the operating speed of a
working machine is in proportional relation with the displacement
of the valve spool in said apparatus, no matter how the load
exerted on said working machine changes, because the pressure of
fluid in the directional control valve unit 40 is compensated such
that the pressure differential between both sides of each of the
flow regulating portions 54, 54' be maintained constant, by the
pressure-compensating unit 10 having the divided flow controlling
portion (.alpha.), the first pressure controlling portion (.beta.)
and the second pressure controlling portion (.delta.). Further, in
the apparatus of the invention the occurrence of an abnormal
pressure in the hydraulic circuit, in the self-running state of the
fluid motor 61, can be completely avoided especially because the
second pressure controlling portion (.delta.) is provided and the
return line and pressure line are in communication with each other
when the first pressure controlling portion (.beta.) is closed
off.
B. The discharge of the pump can be effectively utilized because,
the second actuator 75 when provided in the bypass line 74 can be
operated by a flow in excess of that necessary for operating the
first actuator 61. Furthermore, the flow rate necessary for
operating the first actuator 61 may always be maintained at a
desired value for reason that the divided flow rate through the
divided flow regulating portion (.alpha.) may be reduced to an
extent by narrowing the open area thereof when the divided flow
rate led through the divided flow regulating portion (.alpha.) to
the second actuator 75 tends to increase owing to that the load
exerted on the second actuator is smaller than that on the first
actuator, and that the flow rate led into the first actuator 61
through the first pressure controlling portion (.beta.) may be
reduced to a extent by narrowing the open area thereof when the
flow rate led into the first actuator through the first pressure
controlling portion tends to increase owing to that the load
exerted on the first actuator is maller. Namely, the fluid may be
led preferentially to the first actuator 61 so as to enable the
operating speed of the first actuator 61 to be maintained at a
desired constant value predetermind by the displacement of the
spool 55. It is also to be noted that the driving force necessary
for driving the pump 70 can be reduced because the pump pressure is
maintained at a level equal to or slightly higher than the largest
one of the loads exerted on the actuators connected to the circuit
and is not maintained constant by a relief pressure as is in the
conventional apparatus.
* * * * *