Earth working – Automatic power control
Reexamination Certificate
2002-09-19
2004-01-13
Novosad, Christopher J. (Department: 3671)
Earth working
Automatic power control
C037S348000, C037S382000, C414S699000, C701S050000
Reexamination Certificate
active
06675904
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for controlling an amount of fluid for heavy construction equipment, which can constantly supply an amount of hydraulic fluid to an actuator and prevent fluid from being fed back from the actuator in occasions that a load pressure on the actuator mounted in heavy construction equipment such as excavators and a pressure of a hydraulic pump vary.
2. Description of Prior Art
FIG. 1
is a view for showing a hydraulic circuit of a conventional apparatus for controlling an amount of fluid for heavy construction equipment.
As shown in
FIG. 1
, the conventional apparatus for controlling an amount of fluid for heavy construction equipment includes a hydraulic pump P connected to an engine, an actuator
300
connected to the hydraulic pump P and driven upon supplying hydraulic fluid, a control valve
100
mounted to a parallel hydraulic path
103
between the hydraulic pump P and the actuator
300
and for controlling starts, stops, and direction switchings of the actuator
300
, and fluid amount control valves
400
,
400
A, and
400
B mounted in paths between ports
101
and
102
on outlets of the control valve
100
and the actuator
300
and for restricting an amount of fluid supplied to the actuator
300
and controlling a driving speed thereof.
A reference number
105
not described in the drawing denotes a central bypass path, and
106
a relief valve for draining hydraulic fluid into a hydraulic oil tank T when a load over a pressure set in the hydraulic circuit is developed.
Accordingly, as a pilot signal pressure Pi based on a manipulation of a joy stick not shown is applied to the right end of the control valve
100
to switch an inner spool to the left direction on the drawing of
FIG. 1
, hydraulic fluid discharged from the hydraulic pump P is supplied to a large chamber
302
of the actuator by way of the parallel path
103
and the position-switched control valve
100
, and, at the same time, hydraulic fluid fed back from a small chamber
301
of the actuator
300
is drained to the hydraulic oil tank T via a check valve
405
B, causing the actuator
300
to drive.
At this time, in case of restricting the amount of fluid in order to control a driving speed of the actuator
300
according to a work condition, the fluid amount control valve
400
A can control the amount of fluid flowing in the large chamber
302
based on a pressure difference with a spring valve
404
A set according to a pressure difference of inlet and outlet paths
402
A and
403
A of a spool
402
due to the extent of the opening of a throttle valve
401
A.
However, the fluid amount control apparatus as stated above requires separate blocks to install the hydraulic amount control valve
400
in the hydraulic paths between the ports
101
and
102
at the outlets of the control valve
100
and the actuator
300
, causing problems increasing the costs due to the increase of the number of parts, interfering among parts on a layout when designing, and making its use impossible in a place of narrow space.
Further, as mentioned above, the fluid amount control valve
400
does not have a check function for the case that a load pressure on the side of the actuator is higher than a discharge pressure on the side of the hydraulic pump P, causing a problem separately installing the check valve
104
in the parallel path
103
at the side of the inlet of the control valve
100
.
FIG. 2
is a view for showing a hydraulic circuit for a conventional apparatus for controlling an amount of fluid.
As shown in
FIG. 2
, the fluid amount control apparatus has a hydraulic pump P, actuators A, B, and C connected to the hydraulic pump and driven upon hydraulic fluid supplies, and direction switching valves D, E, and F installed in hydraulic paths between the hydraulic pump P and the actuators A, B, and C and for controlling the flow directions of the hydraulic fluids supplied to the actuators A, B, and C.
At this time, the direction switching valve E includes a pump path
500
connected to the actuator B, load paths
503
and
504
having load ports
501
and
502
communicated with the actuator B, a transfer path
505
branched from the pump path
500
and connected to the load paths
503
and
504
, a control valve
511
mounted in a central bypass path
510
and for controlling hydraulic fluid supplied to the actuator B, a seat valve
512
mounted to be opened and shut between the pump path
500
and the control valve
511
, and a pilot spool valve
513
mounted between the seat valve
512
and the control valve
511
, enabling to restrict an amount of hydraulic fluid supplied to variable throttle valves
515
and
516
of the control valve
511
through the pump path
500
and the transfer path
505
from the hydraulic pump P and to control an amount of hydraulic fluid flowing in the load paths
503
and
504
of the actuator B.
At this time, the transfer path
505
has a path
506
communicated with the pump path
500
, a pair of paths
507
and
508
positioned on both sides of the path
506
, and an annular path
509
connecting the pair of paths
507
and
508
and the path
506
.
Accordingly, as a pilot signal pressure due to an manipulation of a driver is applied to a control valve
514
of the direction switching valve D, hydraulic fluid discharged from the hydraulic pump P is supplied to the actuator A via the position-switched control valve
514
to drive the actuator A, thereby proportionally controlling the amount of the hydraulic fluid supplied to the actuator B via the control valve
511
switched owing to the application of the pilot signal pressure.
However, since the pilot spool valve
513
maintains an initial open state all the time, in case that load pressures occurring on the load paths
503
and
504
of the actuator B are higher than a pressure of the hydraulic fluid discharged from the hydraulic pump P, a feedback flow occurs through the seat valve
512
and then a set working pressure is not supplied to the actuator B to make impossible its controls, causing a problem bringing out a safety incident.
In taking it into account, a feedback prevention check valve is installed in a seat valve not shown, but it has a loose response to the feedback, causing a problem deteriorating the reliability of equipment and raising the manufacture cost due to the increase the number of parts.
Further, an amount of hydraulic fluid supplied to the actuator B according to a load pressure of the actuator B and a discharge pressure from the hydraulic pump P varies, leading to a problem developing a safety incident.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an apparatus for controlling an amount of fluid for heavy construction equipment, which can prevent layout interferences when designing and be used in a narrow space due to a compact structure that a fluid amount control valve controlling a driving speed of an actuator is installed inside a control valve controlling a flow direction of hydraulic fluid supplied to the actuator.
It is another object of the present invention to provide an apparatus for controlling an amount of fluid for heavy construction equipment, which can enhance the durability of parts by reducing hunting and shock phenomena due to variations of a load pressure of an actuator and a pressure of a hydraulic pump.
It is yet another object of the present invention to provide an apparatus for controlling an amount of fluid for heavy construction equipment, which can enhance a response property by carrying out a function of a check valve when a load pressure of a work device is higher than a discharge pressure of a hydraulic pump.
In order to achieve the above objects, an apparatus for controlling an amount of fluid for heavy construction equipment according to a preferred embodiment of the present invention, in an apparatus for controlling an amount of fluid for heavy construction equipment having a hydraulic pump, an actuator connected to the hydraulic pump and driven
Ladas and Parry
Novosad Christopher J.
Volvo Construction Equipment + Holding Sweden AB
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