Variable displacement compressor

Details Variable displacement compressor Variable displacement compressor

2000-03-23

2003-02-11

Freay, Charles G. (Department: 3746)

Pumps

Condition responsive control of drive transmission or pump...

Adjustable cam or linkage

C417S222200

Reexamination Certificate

active

06517321

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to variable displacement compressors which can vary displacement by changing the crank chamber pressure.
FIG. 5
shows a swash plate type variable displacement compressor used in automobile air conditioners. A crank chamber
82
is formed between a front housing
80
and a cylinder block
81
. A drive shaft
83
,that is driven by the automobile engine is supported by the front housing
80
and the cylinder block
81
. A lug plate
84
that rotates integrally with the drive shaft
83
is arranged inside the crank chamber
82
. A swash plate
85
is connected to the lug plate
84
through a hinge mechanism
102
.
A plurality of cylinder bores
86
are formed in the cylinder block
81
. Each cylinder bore
86
is arranged at equal intervals about the axis of the drive shaft
83
. Pistons
87
are housed inside the cylinder bores
86
. When the drive shaft
83
is driven, the swash plate
85
rotates and each piston
87
connected to the swash plate
85
reciprocates inside the associated cylinder bore
86
between a top dead center position and a bottom dead center position. The swash plate
85
converts the rotation of the drive shaft
83
to a reciprocating motion of the piston
87
. The displacement is varied by the stroke of the piston
87
, which changes in response to the inclination angle of the swash plate
85
.
A valve plate
88
is located between the cylinder block
81
and a rear housing
89
. A suction chamber
90
and a discharge chamber
91
are located in the rear housing
89
. The reciprocating motion of each piston
87
causes refrigerant gas to be drawn into the cylinder bore
86
from the suction chamber
90
and discharges the refrigerant gas, which is compressed in the cylinder bore, into the discharge chamber
91
.
The inclination angle of the swash plate
85
and the stroke of the pistons
87
are determined by the pressure (crank pressure) inside the crank chamber
82
and the pressure inside the cylinder bore
86
. The displacement of the compressor is varied by changing the inclination angle of the swash plate
85
or, in other words, the stroke of the pistons
87
.
The pressure in the crank chamber
82
is varied in response to the difference between the flow rate of refrigerant gas flowing into the crank chamber
82
from the discharge chamber
91
and the flow rate of refrigerant gas flowing out from the crank chamber
82
to the suction chamber
90
. A pressurizing passage
92
connects the discharge chamber
91
and the crank chamber
82
by way of an electromagnetic control valve
93
. The electromagnetic control valve
93
controls the amount of refrigerant gas flowing into the crank chamber
82
through the pressurizing passage
92
. A bleed passage
94
connects the crank chamber
82
and the suction chamber
90
. Refrigerant gas inside the crank chamber
82
constantly flows into the suction chamber
90
through the bleed passage
94
.
The control valve
93
opens fully when de-excited. This maximizes the flow rate of refrigerant gas entering the crank chamber
82
through the pressurizing passage
92
. When the control valve
93
is excited, the control valve
93
closes in accordance with the level of an electrical current supplied to the control valve
93
. This restricts the flow rate of refrigerant gas flowing from the discharge chamber
91
to the crank chamber
82
.
A lip seal
95
is used to seal the space between the drive shaft
83
and the inner wall surface of the front housing
80
. The end of the drive shaft
83
extends to the outside of the housing. An electromagnetic clutch
96
is fixed to the end of the drive shaft
83
. The electromagnetic clutch selectively transfers the drive power of the engine E to the drive shaft
83
.
A thrust bearing
97
is located between the lug plate
84
and the front housing
80
. The end of the drive shaft
83
is supported in a bore
98
. A support spring
100
, which is a compression spring, is located between a retaining ring
99
that is located inside the bore
98
and the end of the drive shaft
83
. The support spring
100
applies axial force to the drive shaft
83
in a direction towards the front housing
80
(to the left in FIG.
1
). Further, the support spring
100
eliminates slack in the axial direct-ion of the drive shaft
83
.
The swash plate
85
is at its maximum inclination angle position when it makes contact with the lug plate
84
and is at its minimum inclination angle position when it contacts a stopper ring
101
that is fixed to the drive shaft
83
.
When the engine E is stopped, the control valve
93
fully opens and the refrigerant gas flows inside the crank chamber
82
through the pressurizing passage,
92
. There is a chance that the crank pressure at this time may temporarily increase to an excessively high value. If this occurs, the swash plate
85
(indicated by the broken lines in
FIG. 5
) presses against the stopper ring
101
with excessive force when it reaches the minimum inclination position. Further, the swash plate
85
pulls the lug plate
84
rearward (to the right in
FIG. 1
) through a hinge mechanism
102
. As a result, the drive shaft
83
will move axially rearward against the support spring
100
.
When the automobile accelerates, the displacement of the compressor is reduced to reduce the load of the compressor on the engine E. To accomplish this, the control valve
93
is fully opened and refrigerant gas in the discharge chamber
91
suddenly flows to the crank chamber
82
. Therefore, the crank pressure may temporarily increase to an excessively high level, which applies a rearward force to the drive shaft
83
.
If the crank pressure increases excessively in this manner, the drive shaft
83
will move rearward in the axial direction. This causes the pistons
87
to move to a position that is closer to the valve plate
88
. Consequently, there is a possibility that the head of each piston
87
may strike the valve plate
88
when reaching the top dead center position. This will produce striking noises or vibrations and will damage the pistons
87
and the valve plate
88
.
If the drive shaft
83
moves rearward, a movable clutch plate
96
a
of the electromagnetic clutch
96
will also move rearward. Because of this, the movable clutch plate
96
a
and a fixed clutch plate
96
c
make contact even if a magnetic coil
96
b
is demagnetized. As a result, friction occurs between the clutch plates
96
a,
96
c
leading to noise and heat generation.
Moreover, if the drive shaft
83
moves rearward, the axial position of the drive shaft
83
changes relative to the lip seal
95
, which is supported on the front housing
80
. Normally, the drive shaft
83
makes contact with the lip seal
95
at a predetermined axial position,. Foreign matter, such as sludge, is adhered to the outer surface of the drive shaft
83
at locations other than the predetermined axial position. Thus, if the axial position of the drive shaft
83
changes relative to the lip seal
95
, sludge gets caught between the lip seal
95
and the drive shaft
83
. This reduces the sealing performance of the lip seal
95
and causes gas leaks from the crank chamber
82
.
In order to solve this problem, increasing the compressive force of the support spring
100
such that the drive shaft
83
does not move rearward even if the crank pressure increases to an excessively high value has been considered. However, this increases the load applied to the thrust bearing
97
. Consequently, friction between the thrust bearing
97
and the front housing
80
increases, which shortens the life of the compressor, increases power loss, and decreases the compression efficiency.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a variable displacement compressor that restricts axial movement of the drive shaft and enables each compressor member to function properly.
To achieve the above object, the present invention provides a compressor including a housing, a crank chamber defined in the housing, a drive shaft arran

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