Control valve for variable displacement compressor

Details Control valve for variable displacement compressor Control valve for variable displacement compressor

2000-07-18

2002-09-03

Freay, Charles G. (Department: 3746)

Pumps

Condition responsive control of drive transmission or pump...

Adjustable cam or linkage

C251S062000

Reexamination Certificate

active

06443707

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a control valve for variable displacement compressors that are used in vehicle air conditioners.
A typical variable displacement compressor includes a control passage for connecting a discharge pressure zone with a crank chamber. The pressure in the crank chamber is adjusted to change the inclination of a cam plate. Accordingly, the displacement is controlled.
Japanese Unexamined Patent Publication No. 4-119271 discloses a typical control valve for variable displacement compressors. As shown in
FIG. 7
, this control valve has a valve chamber
101
in a distal portion of a valve housing
102
. The valve chamber
101
is connected to a discharge pressure zone by the upstream portion of a control passage
103
. The valve chamber
101
is also connected to a crank chamber by a valve hole
104
, a port
105
and the downstream portion of the control passage
103
. The valve hole
104
is formed axially in the housing
102
and the port
105
is perpendicular to the valve hole
104
. A valve body
106
is housed in the valve chamber
101
to open and close the valve hole
104
.
A pressure sensing chamber
107
is formed adjacent to the valve chamber
101
and is connected to a suction pressure zone. A bellows
108
is housed in the pressure sensing chamber
107
to detect the pressure of the suction pressure zone. The pressure sensing chamber
107
is separated from the valve chamber
101
by a dividing wall
102
a
. A guide hole
109
is formed in the dividing wall
102
a
to be continuous with the valve hole
104
. The chambers
101
and
107
are therefore connected to each other. A rod
110
is slidably fitted in the guide hole
109
to couple the bellows
108
with the valve body
106
. The bellows
108
is deformed in accordance with the suction pressure of the refrigerant gas. The deformation of the bellows
108
is transmitted to the valve body
106
by the rod
110
.
A solenoid portion
111
is attached to a proximal portion of the valve housing
102
and is coupled to the valve body
106
by the bellows
108
. The solenoid portion
111
is excited and de-excited for changing the attraction force between a fixed iron core
112
and a movable iron core
113
. Accordingly, the load acting on the valve body
106
is changed. Therefore, the opening size of the control passage
103
is determined by the equilibrium of forces, such as the force of the solenoid portion
111
and the force of the bellows
108
.
The pressure in the port
105
is relatively high and the pressure in the pressure sensing chamber
107
is relatively low. The rod
110
and the guide hole
109
are machined with meticulous care for allowing the rod
110
to slide in the hole
109
and for preventing leakage of gas between the port
105
and the pressure sensing chamber
107
. However, small machining errors are inevitable, and the space between the surface of the rod
110
and the surface of the guide hole
109
is different between a location near the port
105
and a location near the pressure sensing chamber
107
. Particularly, when the space near the port
105
is smaller than the space near the pressure sensing chamber
107
, the pressure difference between the port
105
and the pressure sensing chamber
107
generates a lateral force acting on the rod
110
. The lateral force presses the rod
110
against the surface of the guide hole
109
, which increases the sliding resistance between the rod
110
and the guide hole
109
(this phenomena will hereafter be referred to as fluid fixation).
A recent trend is to reduce the size of the solenoid portion
111
to reduce the size of the compressor. In a valve having a small solenoid portion
111
, the bellows
108
is relatively small and the valve body
106
is moved by the equilibrium of the difference between small forces, that is, the force of the solenoid portion
111
and the force of the bellows
108
. Therefore, the control valve is easily affected by an increase of the sliding resistance between the rod
110
and the guide hole
109
due to the fluid fixation. As a result, even a small sliding resistance, which would be negligible if the bellows
108
were large, causes hysteresis. Therefore, the controllability of the displacement significantly deteriorates.
SUMMARY OF THE INVENTION
The present invention was made in view of drawbacks in the above described prior art. Accordingly, it is an objective of the present invention to provide a control valve for a variable displacement compressor that reduces sliding resistance between a rod and a guide hole.
To achieve the foregoing objective, the present invention provides a control valve for a variable displacement compressor. The control valve includes a valve body. The valve body opens and closes a control passage, which connects a control pressure chamber with a suction pressure zone or with a discharge pressure zone, to adjust the opening size of the control passage for varying the displacement of the compressor. The valve body is opened and closed by a drive member. A dividing wall separates a portion that accommodates the valve body from a portion that accommodates the drive member. A guide hole is formed in the dividing wall to communicate the valve body accommodating portion with the drive member accommodating portion. A sliding rod is located in the guide hole to operably couple the valve body to the drive member. The control valve is characterized by means for preventing fluid fixation. The fluid fixation preventing means is located on at least one of the outer surface of the rod and on the inner surface of the guide hole.
The invention of the above structure has the means for preventing fluid fixation between the rod and the guide hole, which decreases the hysteresis of the control valve and prevents deterioration of the displacement controlling performance of the control valve.
In the above structure, the means may include a tapered surface formed on at least one of the outer surface of the rod and the inner surface of the guide hole such that the space between the outer surface of the rod and the inner surface of the guide hole widens toward one of the valve body accommodating portion and the drive member accommodating portion that has a higher pressure.
If the axis of the rod is displaced from the axis of the guide hole for some reason, the rod receives a lateral force, the direction of which is opposite to the displacement direction. The misalignment of the axes is automatically corrected.
In the above structures, the tapered surface may be one of a plurality of tapered surfaces formed along the axial direction of the rod.
In this structure, the cross-sectional area of the space between the outer surface of the rod and the inner surface of the guide hole changes in the axial direction in a completed fashion and functions like a labyrinth seal. This effectively prevents pressure leakage and refrigerant gas leakage between the high pressure location and the low pressure location.
In the above structure, the outer surface of the rod may be tapered such that the diameter of the rod decreases toward one of the valve body accommodating portion and the drive member accommodating portion that has higher pressure. This eliminates the necessity for tapering the inner wall of the guide hole, which is formed in the dividing wall and has a small cross-section, by inserting a tool into the guide hole.
In the above structures, the means may include a circumferential annular groove formed in at least one of the outer surface of the rod and the inner surface of the guide hole.
The annular groove circumferentially equalizes the pressure in the space between the outer surface of the rod and the inner surface of the guide hole. Accordingly, fluid fixation does not occur between the rod and the guide hole.
If the annular groove is formed in the outer surface of the rod, the groove is easily formed.
In the above structure, the drive member may include a pressure sensing mechanism having a pressure sensing chamber and a pressure sensing member

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