Displacement control valve for variable displacement compressor

Details Displacement control valve for variable displacement compressor Displacement control valve for variable displacement compressor

2000-01-28

2001-07-10

Walberg, Teresa (Department: 3742)

Pumps

Condition responsive control of drive transmission or pump...

Adjustable cam or linkage

Reexamination Certificate

active

06257836

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a displacement control valves for a variable displacement compressors used in a vehicle air conditioners.
A typical variable displacement compressor includes a crank chamber to accommodate a cam plate. The crank chamber is connected to a suction pressure zone by a control passage. The crank chamber pressure is adjusted for changing the inclination of the cam plate, which varies the compressor displacement. The crank chamber is connected to a discharge pressure zone by a supply passage. The supply passage supplies highly pressurized refrigerant gas to the crank chamber. Also, blowby gas is supplied to the crank chamber. A displacement control valve is located in the control passage. The position of the control valve, or its opening size, is changed to regulate the amount of refrigerant gas supplied from the crank chamber to the suction pressure zone, which alters the crank chamber pressure.
Japanese Unexamined Patent Publication No. 6-26454 discloses such a displacement control valve for compressors. The valve of the publication is illustrated in
FIGS. 8 and 9
. The valve includes a valve chamber
101
, which is connected to a crank chamber of a compressor by a valve hole
102
and an upstream portion of a control passage. The valve chamber
101
is also connected to a suction pressure zone by a downstream portion of the control passage. A valve body
103
is housed in the valve chamber
101
to regulate the opening size of the valve hole
102
. A bellows
104
is accommodated in the valve chamber
101
. The bellows
104
is coupled to the valve body
103
.
When the pressure in the valve chamber
101
is higher than a target value (target pressure), the bellows
104
contracts and moves the valve body
103
in a direction to open the valve hole
102
. Accordingly, the amount of refrigerant gas flowing from the crank chamber to the suction pressure zone is increased, which lowers the crank chamber pressure. As a result, the compressor displacement is increased. When the pressure in the valve chamber
101
is lower than the target pressure, the bellows
104
expands and moves the valve
103
in a direction to close the valve hole
102
. This decreases the amount of refrigerant gas flowing from the crank chamber to the suction pressure zone, which increases the crank chamber pressure. As a result, the compressor displacement is decreased. As described below, the target pressure is changed by altering the level of current supplied to a coil
108
.
A plunger chamber
105
is defined in the control valve. A fixed core
106
is located in the plunger chamber
105
. A plunger
107
is accommodated in the plunger chamber
105
and is located between the fixed core
106
and the valve chamber
101
. The plunger
107
is coupled to the valve body
103
. The coil
108
is located about the plunger chamber
105
and is located radially outward of both the fixed core
106
and the plunger
107
.
When a current is sent to the coil
108
, the plunger
107
is attracted to the fixed core
106
. The attraction opposes, or reduces, the force that moves the valve body
103
in the direction to open the valve hole
102
. The attraction thus raises the target pressure. The target pressure is increased when the current to the coil
108
is increased and the attractive force between the fixed core
106
and the plunger
107
is increased. The target pressure is maximized when the current to the coil
108
is maximized. The target pressure is decreased when the current to the coil
108
is decreased and the attractive force between the fixed core
106
and the plunger
107
is decreased. The target pressure is minimized when the current to the coil
108
is stopped.
The compression load of the compressor is great when the compressor is operating at a large displacement. If the engine speed is increased when the compressor is operating at a large displacement, the moving parts of the compressor will receive a great load. The compressor is connected to an external refrigerant circuit, which includes a condenser. If the condenser is not sufficiently cooled while the compressor is operating at a large displacement, the discharge pressure will be abnormally high. As a result, the compression load will be excessive, which increases the load on the moving parts.
In order to reduce the excessive load on the compressor, a clutch, which is located between the engine and the compressor, may be disengaged to stop the compressor. However, it is preferred that the vehicle air conditioner continue running to maintain a minimum cooling performance for the comfort of the passengers. Therefore, when the load on the compressor is excessive, the current to the coil
108
is maximized to maximize the target pressure. As a result, the compressor operates at the minimum displacement and the load on the compressor is reduced. Further, the air conditioner continues operating at a minimum performance level.
However, when the current to the coil
108
is stopped, the target pressure is minimized. In other words, when the target pressure is maximized, the current to the coil
108
must continue. Thus, if current cannot be sent to the coil
108
because of, for example, a broken wire, the target pressure is fixed to the minimum value. As a result, excessive loads on the compressor cannot be reduced. Also, even if the compressor is not operating under an excessive load, the displacement is unnecessarily increased if current cannot be sent to the coil
108
, which abnormally increases the load on the compressor.
SUMMARY OF THE INVENTION
Accordingly, it is an objective of the present invention to provide a displacement control valve that prevents a variable displacement compressor from bearing excessive loads when current cannot be sent to the coil due to, for example, a broken coil wire.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a displacement control valve for a variable displacement type compressor is provided. The compressor has a suction chamber, a crank chamber, and a control passage connecting the suction chamber to the crank chamber. The valve changes the displacement of the compressor by opening and closing the control passage. The valve includes a valve chamber, a valve body, a pressure sensing member and a solenoid. The valve chamber forms part of the control passage. The valve body is located in the valve chamber for opening and closing the control passage. The pressure sensing member is connected to the valve body and positions the valve body according to the pressure in the suction chamber. The solenoid applies force to the valve body through a rod. The force applied to the valve body by the solenoid depends on the level of current supplied to the solenoid such that an increase in the level of current supplied to the solenoid results in an increase in the force applied to the valve body by the solenoid in a direction to open the control passage.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.


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