Gear cutting – milling – or planing – Milling – Process
Reexamination Certificate
2000-09-06
2002-12-03
Wellington, A. L. (Department: 3722)
Gear cutting, milling, or planing
Milling
Process
C409S143000, C409S165000, C409S200000, C082S001110, C451S050000, C029S888040, C029S898048
Reexamination Certificate
active
06488454
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, in general, to a method for machining a piston for a variable displacement swash plate type compressor, the pistons being fitted over the peripheral portion of a swash plate and reciprocated in the bores of a cylinder by the rotation of the swash plate owing to the rotation of a drive shaft. In particular, the present invention relates to a method for machining a pair of shoe pocket for a piston in a variable displacement swash plate type compressor, which is capable of cutting the shoe pocket, conforming to a single imaginary sphere, respectively on the opposed walls of a slot in the piston of the compressor.
2. Description of the Prior Art
A compressor constituting one of the main elements of an air-conditioning apparatus for automobiles is an apparatus that selectively receives power from an engine by the intermittence action of an electromagnetic clutch, converts refrigerant gas supplied from an evaporator to a state of high temperature and high pressure by means of a compressing process, and discharges the refrigerant gas to the condenser.
A swash plate type compressor is operated in such a way that a swash plate mounted around a drive shaft while being inclined and shaped in the form of a disk is rotated together with the drive shaft and a plurality of pistons fitted over the peripheral portion thereof are linearly reciprocated in the bores of a cylinder by the rotation of the swash plate. In the process of the reciprocating movement of the pistons, refrigerant gas is sucked into the compressor, compressed in the cylinder bore, and discharged to a condenser.
FIG. 1
is a sectional view showing a typical variable displacement swash plate type compressor that can variably compress refrigerant gas.
As illustrated in
FIG. 1
, the variable displacement swash plate type compressor comprises front and rear housings
1
and
2
, a cylinder block
3
having a plurality of circumferentially arranged bores
3
a
and being positioned between the front and rear housings
1
and
2
, a drive shaft
4
rotatably mounted across the interiors of the front housing
1
and the cylinder block
3
, a circular lug plate
5
fixed around the drive shaft
4
and rotated together with the drive shaft
4
, a swash plate
6
mounted around the drive shaft
4
and connected to one side of the lug plate
5
by means of hinge structures
5
a
and
6
a
, a plurality of pistons
8
fitted over the peripheral portion of the swash plate
6
via a pair of shoes
7
and respectively reciprocated in the bores
3
a
of the cylinder
3
by the rotation of the peripheral portion of the swash plate
6
owing to the rotation of the drive shaft
4
, and a suction reed valve
10
and a discharge reed valve
11
selectively opening and closing the inlet
9
a
and outlet
9
b
of a valve plate
9
by pressure variation in the cylinder bore
3
a
. The variable displacement swash plate type compressor further comprises a control valve
12
for controlling the stroke of pistons
8
by regulating the pressure of the crank chamber
1
a
of the front housing
1
, and the suction chamber
2
a
and discharge chamber
2
b
of the rear housing
2
.
The variable displacement swash plate type compressor constructed as described above compresses refrigerant gas supplied from an evaporator and discharges it to a condenser.
When the drive shaft
4
is rotated by means of the power of an engine, the lug plate
5
fixedly fitted around the drive shaft
4
is rotated together with the swash plate
6
and the pistons
8
fitted over the peripheral portion of the swash plate
6
are reciprocated at a distance proportional to the inclination angle of the swash plate
6
. In the process of the reciprocation of the pistons
8
, refrigerant gas supplied from an evaporator is sucked from the suction chamber
2
a
through the inlet
9
a
into the bores
3
a
while each piston
8
is moved rearward (in a right direction in FIG.
1
), and the refrigerant gas sucked into the bores
3
a
is compressed by the compressing action of the piston
8
and discharged to the discharge chamber
2
b
through the outlet
9
b
at a high pressure and, thereafter, discharged to a condenser(not shown) while the piston
58
reaches the bottom dead point and moves forward.
In the above refrigerant gas compressing process, the swash plate
6
performs a rotating movement, whereas the piston
8
fitted over the peripheral portion of the swash plate
6
and reciprocated by the rotation of the swash plate
6
performs a repeated linear movement back and forth.
Referring to
FIGS. 1 and 2
, the shoes
7
are semispherical bodies, each of the shoes
7
having a plane and a semispherical surface. The shoes
7
are respectively situated in shoe pocket
83
and
84
that are respectively formed on both opposed walls
81
and
82
of the slot
80
of the piston
8
. Therefore, the shoes
7
are situated between the piston
8
and the swash plate
6
and are respectively slid on the shoe pocket
83
and
84
by the variation of the inclination angle of the swash plate
6
while the swash plate
6
is rotated, so that the variation of the inclination angle of the swash plate
6
is accommodated by the sliding of the shoes
7
and, consequently, the wobbling force of the peripheral portion of the swash plate
6
can be transmitted to the piston without hindrance.
Meanwhile, the shoe pocket
83
and
84
on which the shoes
7
are situated and which are formed on the opposed walls
81
and
82
of the slot
80
of the piston
8
should have curved surfaces corresponding to the semispherical surfaces of the shoes
7
. In order to allow the shoes
7
to perform a sliding rotation, the curvature centers of the shoe pocket
83
and
84
should coincide with each other and the curvature centers of the shoe pockets
83
and
84
should coincide respectively with the curvature centers of the shoes
7
. This means that the two shoe pockets
83
and
84
preferably conform to a single imaginary sphere I.
The present invention is concerned with a method for precisely machining two shoe pockets
83
and
84
on both opposed walls
81
and
82
of the slot
80
of the piston
8
so that the shoe pockets
83
and
84
conform to the imaginary sphere I.
The knotty point in precisely machining the shoe pockets
83
and
84
is that the two shoe pockets
83
and
84
should conform to the single imaginary sphere I having a spherical center at the center of the slot of the piston
8
, but a cutter
100
having a spherical cutter blade cannot be inserted into the slot so as to machine the shoe pockets
83
and
84
because the space between the opposed walls
81
and
82
of the slot of the piston
8
is narrow in comparison with the diameter of the imaginary sphere I.
In order to overcome the problem, U.S. Pat. No. 6,053,081 issued on Apr. 25, 2000 discloses a method for machining a pair of shoe pockets in a compressor piston.
As illustrated in
FIG. 2
, the US patent discloses a method for machining a pair of shoe pockets
83
and
84
, which conforms to the imaginary sphere I, on the opposed walls
81
and
82
of the slot
80
of a compressor piston
8
, wherein the slot
80
is narrower than the diameter of the imaginary sphere I. In the method for machining a pair of shoe pockets
83
and
84
, there is provided an asymmetrical cutter blade
101
that is, at its widest point, narrower than the slot as measured in the direction of the longitudinal axis L
1
of the piston
8
, wherein the cutter blade
101
generates a sphere if rotated about a cutter axis. One of the cutter blade
101
and the piston
8
is moved with respect to the other such that the cutter blade
101
enters the slot without contacting either of the opposed walls
81
and
82
, wherein the cutter blade
101
has a center point that coincides with the center of the generated sphere, and wherein the generated sphere is the same size as the imaginary sphere I. The piston
8
is rotated about a machining axis L
2
to simultaneously machin
Ahn Hew Nam
Yoon Young-seop
Cadugan Erica E
Halla Climate Control Corp.
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