Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Reexamination Certificate
2000-07-18
2002-08-27
Lopez, F. Daniel (Department: 2837)
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
C074S416000, C091S362000
Reexamination Certificate
active
06439101
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an electro-hydraulic servomotor used for hydraulic shovels, cranes, asphalt finishers and machine tools (those machines will be referred to simply as external machines).
In this type of the electro-hydraulic servomotor, as shown in
FIGS. 13 and 14
, an output shaft
2
is rotatably supported on a casing
1
by bearings
3
and
4
. A valve plate
9
is fastened to the inner wall of the casing
1
, and a cylinder block
7
is fastened to the circumferential portion of the output shaft
2
. A plurality of pressure chambers
7
a
is formed in the cylinder block
7
. Pistons
8
are disposed within those pressure chambers
7
a
, and the pistons
8
are reciprocally moved in their axial direction by a hydraulic pressure of an operation oil introduced into the pistons
8
.
A slanted plate, which is slanted at a given angle with respect to the valve plate
9
, is fastened to a portion of the inner wall of the casing
1
which is closer to the top end of the output shaft
2
. The top ends of the pistons
8
slidably push the slanted plate
6
, and the cylinder block
7
slides to the valve plate
9
, whereby the output shaft
2
and the cylinder block
7
are rotated together.
A spool valve
11
, which moves in the axial direction, is provided in the casing
1
. A screw member
12
and a gear
13
are fastened to the top end and the base end of the spool valve
11
, respectively. A pulse motor
14
is mounted on the casing
1
. A motor shaft
15
of he pulse motor
14
is rotatably supported on the casing
1
. A rotational force of the motor shaft
15
is transmitted to the spool valve
11
via gears
16
and
13
. A rotational force of the output shaft
2
is transmitted to the spool valve
11
via screw members
10
and
12
. When the spool valve
11
is turned, an oil discharging passage
1
, an oil supplying passage
1
b
, and communicating passages
1
d
and
1
d
communicate with one another. In the electro-hydraulic servomotor, the output shaft
2
, the spool valve
11
and the pulse motor
14
are disposed on the same axial line.
Since in the thus constructed electro-hydraulic servomotor, the output shaft
2
, spool valve
11
and the pulse motor
14
are disposed on the same axial line, the entire length of it is long. For this reason, it is difficult to neatly assemble the electro-hydraulic servomotor into another machine. A speed ratio of the screw members
10
and
12
is 1:1. Because of this, to increase the spindle speed of the output shaft
2
, it is necessary to increase a capacity of the pulse motor
14
and to drive the pulse motor
14
at high speed. The spool valve
11
rotates together with the screw member
12
. Therefore, a sliding surface of the casing
1
, which is in contact with the spool valve
11
, will be worn because of presence of its friction resistance.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an electro-hydraulic servomotor which is small in size.
Another object of the present invention is to provide an electro-hydraulic servomotor which enables the capacity of it to be reduced, and is free from wearing of the spool valve and the casing.
Another object of the invention is to provide a small electro-hydraulic servomotor which reliably controls a spool position of the spool in the axial line direction independently of temperature of the operation oil.
As a preferred embodiment of the present invention, an electro-hydraulic servomotor is provided, which includes: an electric motor which rotates a drive shaft in response to an inputted signal; a hydraulic motor which rotates an output shaft using hydraulic pressure of operation oil; a first geared shaft rotatable along with the output shaft; a second geared shaft threadingly engaged with the drive shaft and meshed with the first geared shaft; a spool axially movable along with the second geared shaft depending on a rotational difference between the drive shaft and the first geared shaft to control supply and discharge of the operation oil to and from the hydraulic motor. According to the servomotor can be made small in size.
In the electro-hydraulic servomotor, the spool may be constructed as a single integral member, maybe divided into first and second discrete spool members. The first and second spool members are preferably urged toward one another.
The electro-hydraulic servomotor may further include: a displacement sensor which detects an axial position of the spool.
The electro-hydraulic servomotor may further include: a rotary sensor which detects number of rotation of the first geared shaft.
The present disclosure relates to the subject matter contained in Japanese patent application Nos. Hei. 11-13633 (filed on Jan. 21, 1999), Hei. 11-291477 (filed on Oct. 13, 1999), Hei. 11-291478 (filed on Oct. 13, 1999) and Hei. 11-348927 (filed on Dec. 8, 1999), which are expressly incorporated herein by reference in their entireties.
REFERENCES:
patent: 3310284 (1967-03-01), Inaba et al.
patent: 3530764 (1970-09-01), Tomita
patent: 4793561 (1988-12-01), Burda
patent: 5560387 (1996-10-01), Devier et al.
Asano Youji
Kodama Haruo
Shimizu Nobuaki
Akin Gump Strauss Hauer & Feld L.L.P.
Lazo Thomas E.
Lopez F. Daniel
Teijin Seiki Co. Ltd.
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