Pumps – Condition responsive control of drive transmission or pump... – Adjustable cam or linkage
Reexamination Certificate
2001-04-26
2003-04-08
Freay, Charles G. (Department: 3746)
Pumps
Condition responsive control of drive transmission or pump...
Adjustable cam or linkage
C417S269000, C092S071000
Reexamination Certificate
active
06544004
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a swash plate type compressor having a single-headed piston for use in, for example, a vehicle air conditioner.
In a variable displacement swash plate type compressor shown in
FIG. 9
, in general, a compressor housing is formed such that a front housing
102
and a rear housing
103
are arranged to sandwich a cylinder block
101
. A crank chamber
104
is formed between the front housing
102
and the cylinder block
101
. A drive shaft
105
across the crank chamber
104
is rotatably supported by the housing. A first end of the drive shaft
105
penetrates through a through hole
106
of the front housing
102
, whereas a second end of the drive shaft
105
is in the crank chamber
104
. A shaft seal
107
is arranged to seal a gap between the drive shaft
105
and the front housing
102
, thereby preventing refrigerant in the crank chamber
104
from leaking out. A plurality of cylinder bores
108
are formed in the cylinder block
101
to surround the drive shaft
105
. A piston
109
is disposed in each of the cylinder bores
108
and reciprocates there. A suction chamber
110
and a discharge chamber
111
are formed in the rear housing
103
.
A swash plate
113
is mounted on the drive shaft
105
through a hinge mechanism
112
and rotates together with the drive shaft
105
. The swash plate
113
is capable of sliding in the axial direction of the drive shaft
105
and of inclining with respect to the drive shaft
105
. Each piston
109
is engaged with an outer peripheral portion of the swash plate
113
through a pair of shoes
114
so that the rotational movement of the drive shaft
105
is converted to the reciprocating movement of the piston
109
. Refrigerant in the suction chamber
110
is drawn into the cylinder bore
108
and compressed there by the reciprocating piston
109
. When pressure in the crank chamber
104
is adjusted, an inclination angle of the swash plate
113
changes. Therefore, the piston stroke changes. Accordingly, the discharge capacity of the compressor becomes variable. For example, the inclination angle of the swash plate
113
, the angle between a plane perpendicular to the drive shaft
105
and the swash plate
113
, decreases when the pressure in the crank chamber
104
increases. Reduction of the piston stroke decreases the discharge capacity of the compressor.
During operation of the compressor, compressive reaction force of each piston
109
acts on the drive shaft
105
through the swash plate
113
. On the other hand, pressure difference between the pressure Pc in the crank chamber
104
and the atmospheric pressure P
0
, which is multiplied by a cross-sectional area of the drive shaft
105
substantially at which the shaft seal
107
is provided, acts on the drive shaft
105
. Both the reaction force and the pressure difference intend to push the drive shaft
105
frontwards. The thrust load based on the reaction force and the pressure difference is supported by the front housing
102
through a thrust bearing
116
arranged between a rotor
115
or lug plate and the front housing
102
.
In recent years, a compressor has been proposed for use in a refrigerant circuit which employs a refrigerant gas such as carbon dioxide, instead of chloro-fluoro carbon. Such a circuit, after compression of the gas, cools down the gas in a super critical range that exceeds a critical temperature of the gas. For example, according to Japanese Patent Application Publication No. 11-223179 discloses a variable displacement type of compressor employing carbon dioxide as refrigerant. In this compressor, refrigerant in a discharge pressure region supplied into the crank chamber
104
is controlled by an electric displacement control valve
117
as shown conventionally in FIG.
9
. The amount of refrigerant passing through the refrigerant circuit is adjusted based on the external data such as a heat load.
When the circuit employs chloro-fluoro carbon as refrigerant, the pressure Pc in the crank chamber is relatively small, less than or equal to 9.8×10
5
Pa. However, when the refrigerant such as carbon dioxide is employed, the pressure Pc in the crank chamber rises greatly. For example, employment of carbon dioxide raises the pressure Pc higher than the pressure in employment of chloro-fluoro carbon by about several tens to a hundred ×10
4
Pa. As a result, the thrust load supported by the thrust bearing
116
increases greatly, and sealing function of the shaft seal
107
against the high pressure is required.
When the thrust load acting on the drive shaft
105
in the same direction as the compressive reaction force becomes higher, mechanical loss increases as well as the power consumption to drive the drive shaft
105
. The power consumption is typically apparent when the power of the drive source such as an engine is transmitted to the drive shaft
105
without using a clutch, for instance, in a clutchless variable displacement type of swash plate compressor. That is, when the compressor is driven in a minimum capacity state or off-drive state, the power consumption, which should be minimum, increases.
Further, when the shaft seal
107
is arranged in the crank chamber region, the lubrication of the shaft seal
107
is not satisfactorily performed because refrigerant in the crank chamber has not only high pressure but high temperature.
SUMMARY OF THE INVENTION
Accordingly, it is a first object of the present invention to provide a swash plate type compressor in which required power to drive the compressor is reduced by reducing a thrust load in the same direction as compressive reaction force acting on a drive shaft.
To achieve the above first object, a swash plate type compressor of the present invention has a housing including a suction chamber, a discharge chamber and a crank chamber, a drive shaft rotatably supported by the housing, the drive shaft having a first end protruding from the housing and a second end disposed in the crank chamber, a cylinder bore defined between the crank chamber and the first end of the drive shaft, a single-headed piston disposed in the cylinder bore to be reciprocated, and a cam plate rotatably mounted on the drive shaft in the crank chamber, the cam plate being operatively engaged with the piston, whereby rotational movement of the drive shaft is converted to reciprocating movement of the piston through the cam plate.
In the present invention, when refrigerant is compressed during operation of the compressor, the compressive reaction force of the piston acts on the drive shaft through the cam plate thereby pushing the drive shaft toward its second end. On the other hand, pressure in the crank chamber acts on the second end portion of the drive shaft against atmospheric pressure acting on the first end of the drive shaft so that pressure difference between them pushes the drive shaft in the opposite direction to the reaction force. Therefore, according to the present invention the power to drive the drive shaft of the compressor is reduced by reduction of thrust force acting on the drive shaft.
It is a second object of the present invention to provide a swash plate type compressor in which a shaft seal arranged to seal a gap between a drive shaft and a housing is improved.
To achieve the above second object according to the present invention, the suction chamber is in the housing defined adjacent to the first end of the drive shaft. The drive shaft is arranged in the housing such that the first end of the drive shaft penetrates the suction chamber and protrudes from the housing. A shaft seal is arranged between the suction chamber and the first end of the drive shaft, thereby sealing the suction chamber.
The foregoing shaft seal arrangement of the present invention simply requires resistance against pressure difference between atmospheric pressure and suction pressure which is lowest in the compressor. Accordingly, durability of the shaft seal is sufficiently extended, and sealing function thereof is improved. This is apparently effective
Fujii Toshiro
Koide Tatsuya
Yokomachi Naoya
Freay Charles G.
Gray Michael K.
Kabushiki Kaisha Toyoda Jidoshokki Seisakusho
Morgan & Finnegan , LLP
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