Variable displacement type compressor

Details Variable displacement type compressor Variable displacement type compressor

2000-03-31

2001-09-04

Walberg, Teresa (Department: 3742)

Pumps

Condition responsive control of drive transmission or pump...

Adjustable cam or linkage

C092S012200

Reexamination Certificate

active

06283722

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a variable displacement type compressor that has a coupling mechanism for coupling a cam plate, which drives pistons, to a drive shaft and changes the reciprocation stroke of the pistons by altering the inclination angle of the cam plate by controlling the pressure in a crank chamber.
FIG. 15
shows one type of a variable displacement type compressor for use in a vehicle air-conditioning system. Accommodated in a housing
101
of the compressor are a crank chamber
102
, a suction chamber
108
, a discharge chamber
109
and a plurality of cylinder bores
107
(only one shown). A piston
110
is retained in each cylinder bore
107
. A drive shaft
103
and a lug plate
104
, which are fixed to each other, are located in the crank chamber
102
. To seal the crank chamber
102
, the housing
101
is provided with a lip seal
114
around the front end of the drive shaft
103
. The front end of the drive shaft
103
is coupled to the engine (external drive source) of the vehicle directly or indirectly. A spring
112
for urging the drive shaft
103
in a forward direction is located at the rear end of the drive shaft
103
. The spring
112
positions the drive shaft
103
and the lug plate
104
in the crank chamber
102
in the axial direction while absorbing the tolerances of the drive shaft
103
and various components associated with the drive shaft
103
.
Provided around the drive shaft
103
is a swash plate
105
, or cam plate. The swash plate
105
, which is coupled to the individual pistons
110
via shoes
113
, converts the rotational motion of the drive shaft
103
to reciprocal motion of each piston
110
. This swash plate
105
is coupled to the lug plate (rotary support)
104
via a coupling mechanism
115
. The coupling mechanism
115
has guide pins
116
protruding from the front face of the swash plate
105
and support arms
117
protruding from the rear face of the lug plate
104
. The head of each guide pin
116
is inserted into a cylindrical guide hole
117
a
formed in the associated support arm
117
. This coupling mechanism
115
allows the swash plate
105
to rotate with the drive shaft
103
and to tilt as the swash plate
105
moves along the drive shaft
103
(in the axial direction).
The stroke of the pistons
110
, or the discharge displacement, is determined by the inclination angle of the swash plate
105
, which is mainly determined by the difference between the pressure of the crank chamber
102
(crank pressure Pc) and the pressure in the cylinder bores
107
via the associated piston
110
. This difference is controlled by a displacement control valve
120
. Generally speaking, as the crank pressure Pc rises, the swash plate
105
disinclines, or slides on the drive shaft
103
away from the lug plate
104
, making the inclination angle of the swash plate
105
smaller. A restriction ring
106
is fixed on the drive shaft
103
so that, when the swash plate
105
contacts the restriction ring
106
, further disinclination of the swash plate
105
is restricted, thereby defining the minimum inclination angle of the swash plate
105
. In the compressor in
FIG. 15
, the control mechanism for the crank pressure Pc comprises a restriction-equipped bleed passage
118
, which connects the crank chamber
102
to the suction chamber
108
, an supply passage
119
, which connects the discharge chamber
109
to the crank chamber
102
, and the displacement control valve
120
located midway in the supply passage
119
. The opening of this displacement control valve
120
can be adjusted by external energization. As the opening of this control valve
120
is adjusted externally, the amount of high-pressure refrigerant gas supplied into the crank chamber
102
from the discharge chamber
109
via the supply passage
119
is adjusted. The crank pressure Pc is determined by the relationship between the flow rate of gas supplied to the crank chamber
102
and the flow rate of gas that is released from the crank chamber
102
via the bleed passage
118
.
In the air-conditioning system of a vehicle, the capacity of the compressor is minimized to reduce the engine load as much as possible when rapidly accelerating the vehicle. When the air-conditioning system is switched off or the engine is stopped, the discharge capacity of the compressor is often minimized in advance to prevent the next activation of the compressor from applying an excess load to the engine. As far as the compressor in
FIG. 15
is concerned, the capacity of the compressor is minimized by supplying high-pressure refrigerant gas into the crank chamber
102
from the discharge chamber
109
with the displacement control valve fully opened by an external signal. To minimize the capacity of the compressor when rapidly accelerating the vehicle, particularly, it is necessary to quickly minimize the discharge capacity. Thus, high-pressure refrigerant gas is often rapidly led into the crank chamber
102
.
When high-pressure gas in the discharge chamber
109
is led into the crank chamber
102
to swiftly increase the crank pressure Pc, however, various problems may arise depending on the amount of the pressure rise. Anything serious may not occur until the sudden rise of the crank pressure Pc minimizes the inclination angle of the swash plate
105
. If the difference between the crank pressure and the cylinder-bore inner pressure is too large even after the inclination angle of the swash plate
105
is minimized, the excess pressure difference causes the pistons
110
to move rearward (in the direction away from the lug plate). This applies a rearward force to the swash plate
105
. At this time, the inclination angle of the swash plate
105
is minimized and the swash plate
105
abuts against the restriction ring
106
. When the rearward force acts on the swash plate
105
, therefore, the swash plate
105
urges the drive shaft
103
against the force of the spring
112
via the restriction ring
106
. Further, the swash plate
105
is coupled to the lug plate
104
by the engagement of each guide pin
116
and the associated guide hole
117
a
of the coupling mechanism
115
. If the swash plate
105
is rapidly disinclined, the swash plate
105
pulls the lug plate
104
and the drive shaft
103
rearward against the force of the spring
112
. In other words, when the crank pressure becomes too large, a strong rearward force acts on the entire inner mechanism of the compressor which includes the pistons, the swash plate, the coupling mechanism, the lug plate and the drive shaft, causing those components to move rearward beyond the design limit for such movement(i.e., the axial position corresponding to the minimum inclination angle of the swash plate
105
). This brings about the following problems.
Problem 1: When the drive shaft
103
moves rearward beyond the design limit, the position of contact between the lip seal
114
and the drive shaft
103
changes from a predetermined position called the contact line. Foreign matter such as sludge adheres to the outer surface of the drive shaft
103
at locations other than the contact line. If the drive shaft
103
moves axially, therefore, foreign matter may come between the outer surface of the drive shaft
103
and the lip seal
114
, which will break the seal produced by the lip seal
114
.
Problem 2: In some compressors of vehicles, an electromagnetic clutch is located in the power transmitting path between the engine and the drive shaft
103
. The typical electromagnetic clutch has a drive clutch plate on the engine side and a driven clutch plate (armature), which rotates with the drive shaft
103
and can be shifted axially by the force of a spring. The clutch is engaged by electromagnetically engaging the armature and the drive clutch plate when the electric power is cut off, a predetermined gap should exist between the armature and the drive clutch plate. When the engine is stopped, in the air-conditioning system, the electromagnetic clutch is deactivated and the displacement co

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