Motors: expansible chamber type – Working member position feedback to motive fluid control – Electrical input and feedback signal means
Reexamination Certificate
2002-11-07
2004-08-10
Lazo, Thomas E. (Department: 3745)
Motors: expansible chamber type
Working member position feedback to motive fluid control
Electrical input and feedback signal means
C091S380000
Reexamination Certificate
active
06772671
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to an electrohydraulic motor for use in hydraulic shovels, asphalt finishers, machine tools, and cranes. More particularly, the invention relates to an electrohydraulic motor enabled to relieve superfluous operation oil during stoppage of a driving operation without using excessive energy.
As shown in
FIG. 7
, in a hydraulic drive system
700
using a conventional electrohydraulic motor, operation oil stored in a tank
710
is caused by a pump
720
to flow through a main oil passage, and then reaches a spool valve
741
provided in the electrohydraulic motor
740
. The operation oil having reached the spool valve
741
is caused by movement of the spool valve
741
to flow through one of two communicating oil passages
742
a
and
742
b
. Then, the operation oil is supplied to a cylinder block (not shown) of a hydraulic actuator
743
. The operation oil supplied to the cylinder block provides a pressure to a piston (not shown). In response to a sliding operation of the piston, an output shaft
743
of the hydraulic actuator
743
is rotated. When the output shaft
743
is rotated, the operation oil having provided the pressure to the piston receives a pressure from the cylinder block. Subsequently, the operation oil having received the pressure from the cylinder block flows through the other communicating oil passage
742
a
or
742
b
. Finally, such operation oil reaches the spool valve
741
. This operation oil having reached the spool valve
741
is returned to the tank
710
through a return oil passage
750
.
The rotation direction of the output shaft
743
a
is determined according to which of the two communicating passage
742
a
and
742
b
the operation oil having reached the spool valve
741
is supplied to, that is, which direction the spool valve
741
moves. The spool valve
741
and a drive shaft
744
a
of a pulse motor
744
are connected to each other so that each of the spool valve
741
and the drive shaft
744
a
is rotatable. Further, a rotation shaft
745
is connected to the drive shaft
744
a
. A first threaded shaft
746
is screw-connected to the rotation shaft
745
. The first threaded shaft
745
engages a second threaded shaft
747
in such a way as to be perpendicular thereto. Thus, the spool valve
741
is moved by rotation of the pulse motor
744
according to the difference in the number of revolutions between the drive shaft
744
a
and the output shaft
743
a.
Incidentally, the hydraulic actuator
743
is provided with a revolution speed changing member
748
that comprises a receptive capacity changing member
748
a
for changing the operation oil receiving capacity of the hydraulic actuator
743
, a cylinder
748
b
connected to the receptive capacity changing member
748
a
, a higher-pressure oil selection valve
748
c
for drawing operation oil from one of the communicating oil passages
742
a
and
742
b
, which has a pressure higher than that of the other communicating oil passage, and a switch valve
748
d
for switching the connection between the cylinder
748
b
and the higher-pressure oil selection valve
748
c.
To prevent the pumped operation oil from returning to the pump
720
, a check valve
749
is provided in the main oil passage
730
that connects the pump
720
to the spool valve
730
. Further, when the internal pressure of the main oil passage
730
becomes abnormally high, the operation oil contained in the main oil passage
730
is discharged into the tank
710
through a relief valve
760
.
Furthermore, as illustrated in
FIGS. 8 and 9
, the conventional electrohydraulic motor has a cup-like first casing
50
, and a second casing
52
fastened and fixed to the first casing
50
with bolts
52
. A main oil passage
50
a
, a return oil passage
50
b
, and two communicating oil passages
50
c
and
50
d
are formed in the first casing
50
.
The output shaft is rotatably supported in the first casing
50
and the second casing
52
by bearings
55
and
54
, respectively. A first helical gear
56
is rotatably connected to the spool valve
59
through the bearings
54
and
55
. The first helical gear
56
and a second helical gear
57
, which is fixed to the output shaft, engage each other so that axes of the gears
56
and
57
are perpendicular to each other.
Annular grooves are formed in an outer peripheral portion of the spool valve
59
in such a manner as to extend in the circumferential direction thereof. When the spool valve
59
moves in the direction of a rotation shaft
58
of a pulse motor
60
, the annular grooves are connected to a drain oil passage, the main oil passage
50
a
, the return oil passage
50
b
, and the communicating oil passages
50
c
and
50
d
. Further, when gears formed on the shaft
58
move, the main oil passage
50
a
and the return oil passage
50
b
are connected to the communicating oil passages
50
c
and
50
d.
The drive shaft
58
is connected to a drive shaft
61
of the pulse motor
60
, and screw-connected to the second helical gear
57
. Thus, the second helical gear
57
can be moved in the direction of the drive shaft
61
by rotation of the drive shaft
61
of the pulse motor
60
(see JP-A-2000-213502).
However, in the case of the hydraulic drive system
700
using the conventional electrohydraulic motor, when the spool valve is in a neutral position, the operation oil supplied by the pump stagnates in the main oil passage. When the operation oil stagnates in the main oil passage, the internal pressure of the main oil passage increases. When the internal pressure thereof becomes high, the pump supplies the operation oil into the main oil passage by utilizing a pressure that is higher than the internal pressure of the main oil passage. Incidentally, the pressure for operating the relief valve is set at a very high value. Thus, the internal pressure of the main oil passage reaches the set pressure of the relief valve. Consequently, the conventional electrohydraulic motor has encountered a problem in that very high energy is consumed only for relieving (hereunder referred to as “bleeding off”) the operation oil, which is supplied by the pump, from the relief valve.
Moreover, in the case of the conventional electrohydraulic motor, when the output shaft of the hydraulic actuator is rotated by an external force, the hydraulic actuator operates as a pump. When the hydraulic actuator operates as a pump, the operation oil is sent from one of the two communicating oil passages to the other communicating oil passage. At that time, in the case that the spool valve and the hydraulic actuator constitute a closed circuit, and that the hydraulic actuator operates as a pump, the pumped amount of operation oil is not replenished to the communicating oil passage from which the operation oil is pumped out. Consequently, a cavity is produced (hereunder, such production of a cavity will be referred to as “cavitation”) in the communicating oil passage, from which the operation oil is pumped out, especially, in the conventional electrohydraulic motor adapted to perform mechanical feedback. Thus, the conventional electrohydraulic motor has encountered drawbacks caused in the hydraulic actuator owing to the cavitation, for example, a problem that the hydraulic actuator becomes uncontrollable.
Furthermore, in the conventional electrohydraulic motor, the return oil passage and the drain oil passage are not separated from each other. The drain oil passage is connected to the return oil passage. Consequently, pressure oil from the drain oil passage flows into the return oil passage that is in a high pressure condition. Thus, the conventional electrohydraulic pump has a problem that an oil seal provided at an output-shaft-side portion of the hydraulic actuator is ruptured.
SUMMARY OF THE INVENTION
Accordingly, an object of the invention is to provide an electrohydraulic motor enabled to discharge superfluous oil without consuming very high energy. Another object of the invention is to provide an electrohydraulic motor enabled to p
Asano Youji
Shimizu Nobuaki
Akin Gump Strauss Hauer & Feld L.L.P.
Lazo Thomas E.
TS Corporation
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