[0001] This invention relates to a control device for multiple hydraulic actuators, and
more particularly to a control device which is adapted to control multiple hydraulic
actuators by means of one variable pump, thereby to be suitably used for an industrial
vehicle.
[0002] It is an object of the present invention to provide a control device for multiple
hydraulic actuators which is capable of permitting a discharge pressure of a variable
pump to be rapidly increased effectively to prevent the amount of fluid discharged
from the variable pump from being decreased even when a specific one of the actuators
requires that fluid is fed thereto at a micro flow rate under a low pressure.
[0003] In accordance with the present invention, there is provided a control device for
multiple hydraulic actuators which comprises a plurality of actuators provided with
operating valves, respectively, a single variable pump for feeding hydraulic fluid
to the actuators, a variable orifice which is connected to a feed passage and each
of the actuators communicating with the feed passage and of which a degree of opening
is controlled depending on the amount of changing-over of each of the operating valves,
a pressure compensating valve arranged on a downstream side of each of the variable
orifices to keep a pressure difference between a load pressure and a pressure on the
downstream side of the variable orifice constant, and a control mechanism for causing
the load pressure and a discharge pressure of the variable pump to act as a pilot
pressure and the discharge pressure of the variable pump to be kept increased by a
predetermined level as compared with the load pressure.
[0004] The control device of the present invention generally constructed as described above
is characterised in that the operating valve of specific one of the actuators is connected
on a downstream side thereof to a feed side of each of the other actuators through
the converging passage and the converging passage is provided with a change-over valve
which is changed over to an open position when the operating valve of each of the
other actuators is changed over.
[0005] In the control device of the present invention constructed as described above, when
a load pressure of the specific actuator is increased, the pilot change-over valve
is changed over to permit a part of hydraulic fluid fed to an operation system of
the specific actuator to be fed to the other actuators, resulting in an excessive
increase in circuit pressure of the operation system being effectively prevented.
[0006] The present invention is now described by way of example with reference to the accompanying
drawings, in which like reference characters designate like or corresponding parts
throughout, wherein:-
FIGURE 1 is a circuit diagram showing a first embodiment of a control device for multiple
hydraulic actuators according to the present invention;
FIGURE 2 is a circuit diagram showing a second embodiment of a control device for
multiple hydraulic actuators according to the present invention; and
FIGURE 3 is a circuit diagram showing a conventional or prior art control device for
multiple hydraulic actuators.
[0007] A conventional control device will first be described with reference to Figure 3,
which is a circuit diagram showing a power shovel which has been conventionally known
in the art. A variable pump 1 is connected on a discharge side thereof to a high pressure
flow passage 2. The high pressure passage 2 is connected to an input port 5 of a first
operating valve 40 connected to a boom cylinder 37, an input port 5 of a second operating
valve 41 connected to a bucket cylinder 38, and an input port 5 of a third operating
valve 42 connected to a spin motor 39.
[0008] When the first, second and third operating valves 40, 41 and 42 are each at a neutral
position shown in Figure 3, the input ports 5 are kept closed. When the operating
valves 40, 41 and 42 are shifted or changed over to either lateral position, variable
orifices 6 are rendered open. The degree of opening of the variable orifices 6 is
determined depending on the amount of changing-over of the operating valves 40, 41
and 42, respectively.
[0009] On a downstream side of the variable orifices 6 relay ports 61 are provided respectively.
The relay ports 61 are arranged so as to communicate with pressure compensating valves
8, respectively. The pressure compensating valves 8 are arranged so as to communicate
on a downstream side thereof with feed ports 9 of the first, second and third operating
valves 40, 41 and 42, respectively. The feed ports 9 are adapted to be kept closed
when the operating valves 40, 41 and 42 are each at the neutral position and communicate
with either actuator port 10 or 11, when the operating valves 40, 41 and 42 are changed
over the their respective lateral positions. At this time, the remaining actuator
ports which do not communicate with the feed ports are kept communicating with tank
passages 62, respectively.
[0010] Also, the first to third operating valves 40, 41 and 42 are formed with load detecting
ports 13, respectively. the load detecting ports 13 are adapted to communicate with
the tank passages 62, respectively, when the first to third operating valves 40, 41
and 42 are each at the neutral position. When the first to third operating valves
40, 41 and 42 are each changed over to either lateral position, the load detecting
ports 13 are caused to communicate with the actuator ports positioned on a high pressure
side.
[0011] The above-described pressure compensating valves 8 are adapted to introduce a pressure
on an upstream side of the pressure compensating valves 8 to one of the pilot chambers
8a of the respective valve 8 and a pressure on a side of the load detecting ports
13 to the other pilot chamber 8b of the respective valve 8. Such introduction of the
pressure is selected by a plurality of shuttle valves 14 so that a maximum load pressure
in each of circuit systems is introduced into each of the other pilot chambers 8b.
[0012] Thus, the pressure compensating valves 8 carry out controlling in a manner to permit
a pressure on the downstream side of the variable orifices 6 to be kept increased
by a predetermined level as compared with the maximum load pressure.
[0013] The maximum load pressure selected by the shuttle valves 14 is introduced to one
pilot chamber 63a of a control valve 63 for controlling the variable pump 1. The other
pilot chamber 63b of the control valve 63 is fed with a pressure in the high pressure
flow passage 2 or a discharge pressure of the variable pump 1. Thus, the control valve
63 is caused to operate depending on a relative difference between the discharge pressure
of the variable pump 1 and the maximum load pressure. Such operation of the control
valve 63 causes a control cylinder 64 to operate so that the discharge pressure of
the variable pump 1 may be kept constantly increased by a predetermined level as compared
with the maximum load pressure.
[0014] In Figure 3, reference numeral 65 designates a main relief valve, which functions
to set a maximum pressure of the circuit system of each of the boom cylinder 37, bucket
cylinder 38 and spin motor 39.
[0015] Co-operation between the amount of discharge of the variable pump 1 and the amount
of control of the pressure compensating valves 8 permits fluid to be fed to the actuators
in an amount proportional to the amount of changing-over of the first to third operating
valves 40, 41 and 42.
[0016] The conventional control system constructed as described above is of the load-sensing
type, wherein the variable pump 1 discharges a pressure slightly higher than the maximum
load pressure and the pressure compensating valves 8 of the circuit system control
the variable orifices 6 of the first to third operating valves 40, 41 and 42 depending
on the maximum load pressure. This causes a pressure difference between both sides
of each of the variable orifices 6 to be kept constant, thereby to permit fluid to
be fed to the actuators in an amount proportional to the amount of changing-over of
the operating valves.
[0017] Such circuit construction results in the maximum discharge pressure of the variable
pump 1 being controlled to a set pressure of the main relief valve 65.
[0018] Thus, in the conventional control device constructed as described above, the maximum
load pressure established in any of the multiple hydraulic actuators causes the discharge
pressure of the variable pump 1 to be controlled, thereby to increase energy loss
in the following cases.
[0019] For example, when the conventional control circuit is used for a power shovel and
an inertia body is used as a load as in spin motion, a load pressure is rapidly increased
for accelerating the inertia body at a moment of changing-over of the operating valves,
resulting in a pressure in the circuit being increased to a set pressure of the main
relief valve 65.
[0020] The circuit pressure thus increased, as described above, constitutes a control signal
for each of the first to third operating valves 40, 41 and 42 and variable pump 1.
Therefore, if a large amount of hydraulic fluid is flowed under a low pressure in
a circuit system other than a spin circuit system, the variable pump 1 is obliged
to discharge hydraulic fluid at an increased flow rate under a high pressure. Thus,
it is required to feed hydraulic fluid at a large flow rate under a high pressure
to the circuit system which requires that hydraulic fluid is fed thereto at a large
flow rate under a high pressure for the sake of the spin circuit system which requires
to feed hydraulic fluid at a micro flow rate and under a high pressure, so that energy
loss is extensively increased.
[0021] In particular, when the discharge pressure of the variable pump 1 is increased during
controlling which is carried out so as to keep an output of the variable pump 1 constant,
a discharge capability of the variable pump is decreased along a pump output control
curve. This causes restriction of a flow rate of hydraulic fluid fed to the circuit
system which requires that hydraulic fluid is fed at a large flow rate under a low
pressure. For example, when a power shovel is pivotally moved for the purpose of charging
a truck with a material in the power shovel, a swinging-up speed of a boom is caused
to be decreased during pivotal movement of the power shovel. Unfortunately, this leads
to striking of a bucket of the shovel against the truck before the bucket is lifted
to a desired height.
[0022] The present invention has been made in view of the foregoing disadvantage of the
prior art.
[0023] Referring now to Figure 1, a first embodiment of a control device for multiple hydraulic
actuators according to the present invention is illustrated. In the illustrated embodiment,
the relay port 61 of the third operating valve 42 and the pressure compensating valve
8 communicating with the relay port 61 are connected through a converging passage
44 to a side of an inlet port 68 of a change-over valve 67. An outlet port 69 of the
change-over valve 67 is connected through a load check valve 72 to a side of a bottom
of the boom cylinder 37.
[0024] When the change-over valve 67 thus arranged is at a normal position shown in Figure
1, it interrupts communication between the inlet port 68 and the outlet port 69. Also,
the change-over valve 67 is changed over to its upper open position (as shown in Figure
1) when a pilot pressure acts on a pilot chamber 70 of the change-over valve 67, thereby
to cause both ports 68 and 69 to communicate with an orifice 71. Thus, when the boom
cylinder 37 is extended, the change-over valve 67 is changed over to the open position.
[0025] The remaining part of the illustrated embodiment is constructed in substantially
the same manner as the prior art described above.
[0026] When the first operating valve 40 is changed over to its left-side position as viewed
in Figure 1 in order to extend the boom cylinder 37, a pilot pressure acting on the
first operating valve 40 then acts on the pilot chamber 70 of the change-over valve
67, leading to changing-over of the change-over valve 67 to the open position. This
results in a part of hydraulic fluid fed to a circuit system of a spin motor 39 being
fed to the bottom side of the boom cylinder 37 through the change-over valve 67.
[0027] Thus, a part of hydraulic fluid fed to the circuit system of the spin motor is fed
to the boom cylinder 37. This effectively prevents a rapid increase in load pressure
of the circuit system of the spin motor 39, even when the spin motor 39 is rapidly
accelerated or a load pressure on the side of the spin motor 39 is increased. Thus,
the illustrated embodiment effectively eliminates a problem that an excessive increase
in pressure of the spin motor 39 causes the amount of hydraulic fluid to the boom
cylinder 37 to be insufficient.
[0028] Referring now to Figure 2, a second embodiment of a control device for multiple hydraulic
actuators according to the present invention is illustrated, which is so constructed
that a downstream side of a pressure compensating valve 8 and a feed port 9 of a third
operating valve 42 are connected to an inlet port 68 of a change-over valve 67 through
a converging passage 44. The remaining part of the second embodiment is constructed
in substantially the same manner as the first embodiment described above.
[0029] The control device for the multiple hydraulic actuators according to the present
invention permits, when a load pressure of one of the actuators is increased, a part
of hydraulic fluid fed to the one actuator to be fed to the other actuators. This
effectively prevents the one actuator which is required to be fed with hydraulic fluid
in a micro-amount under a high pressure from decreasing a discharge quantity of the
variable pump, thereby to minimize energy loss.
[0030] While preferred embodiments of the invention have been described with a certain degree
of particularity with reference to the drawings, obvious modifications and variations
are possible in light of the above teachings. It is therefore to be understood that
within the scope of the appended claims, the invention may be practised otherwise
than as specifically described.
1. A control device for multiple hydraulic actuators comprising a plurality of actuators
provided with operating valves (40,41,42) respectively, a single variable pump (1)
for feeding hydraulic fluid to the actuators, each of which has a variable orifice
(6) which is connected to a feed passage and each of the actuators communicating with
the feed passage and the degree of opening of the variable orifice being controlled
dependent on the amount of changing-over of each of the operating valves, a pressure
compensating valve (8) arranged on a downstream side of each of the variable orifices
to keep a pressure difference between a load pressure and a pressure on the downstream
side of the variable orifice constant, and a control mechanism for causing the load
pressure and a discharge pressure of the variable pump to act as a pilot pressure
and the discharge pressure of the variable pump to be kept increased by a predetermined
level as compared with the load pressure, characterised in that the operating valve
of one of the actuators is connected on a downstream side thereof to a feed side of
each of the other actuators through a converging passage (44), and the converging
passage is provided with a change-over valve (67) which is changed over to an open
position when the operating valve of each of the other actuators is changed over.
2. A control device for multiple hydraulic actuators as defined in claim 1, characterised
in that the converging passage is connected at one end thereof between the operating
valve for controlling the one actuator and the pressure compensating valve connected
thereto.
3. A control device for multiple hydraulic actuators as defined in claim 1, characterised
in that the converging passage is connected at one end thereof to a downstream side
of the pressure compensating valve connected to the operating valve for controlling
the one actuator.