Refrigeration – Automatic control – Of external fluid or means
Reexamination Certificate
2002-03-01
2003-09-23
Jiang, Chen Wen (Department: 3744)
Refrigeration
Automatic control
Of external fluid or means
C062S187000, C062S151000
Reexamination Certificate
active
06622503
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to temperature control systems for multi-compartment refrigerators, and more particularly to evaporator fan and damper control systems for regulating the temperature of the fresh food and freezer compartments of a refrigerator.
BACKGROUND OF THE INVENTION
In a typical multi-compartment refrigerator there are several methods for controlling the temperature of each of the compartments. It is common practice for the refrigeration system, i.e. the compressor, evaporator, fan, etc., to directly cool the freezer compartment. Air from the freezer compartment is directed to the fresh food compartment by means of an opening from the freezer to the fresh food compartment. Air is throttled in this opening by means of some type of air damper control. The damper has traditionally been a manually operated mechanism, which can be adjusted by the user to vary the freezer temperature. The fresh food temperature is generally controlled by a thermostat which senses the fresh food compartment temperature. The thermostat governs the operation of the compressor and evaporator fan. The resulting freezer temperature is a function of the fresh food compartment set point temperature and the position of the manual damper. It is generally known that this type of control system is not ideal for temperature stability of the freezer, especially when the outside temperature changes and the fresh food set point temperature is changed. The advantage of this system is that it is very inexpensive to produce.
A less traditional means of control used currently in only approximately 15% of standard refrigerators produced in the United States is to cycle the compressor using a thermostat that senses the freezer temperature. The air flow to the fresh food compartment is attenuated by a modulating air damper control. This control uses a refrigerant charged bellows that expands and contracts in response to the temperature of the fresh food compartment. The bellows movement is then used to drive a door, located in the air flow stream, to attenuate air flow to the fresh food compartment. The movement of the door is very predictable, thus allowing this device to be offered on a production basis. This type of control system allows for more accurate temperature control for both compartments than the method described above. Outside temperature variance and door openings are better compensated using this system.
The principal drawback for such a system is cost. Manufacturers positioning certain product as “high performance” are the users of this type of system. The second drawback for such a system is that the fresh food compartment is still slaved to the freezer compartment. The modulating damper can better compensate for changes in set point temperature of the freezer than a manually operated device, but some changes to the temperature of the fresh food compartment are apparent since the fan is only operating when the compressor is operating. The compressor operation is dependent on the thermostat, which is sensing freezer temperature only. Another advantage of the modulating damper is that no external power is required for it to perform. Refrigerator manufacturers are very concerned about power consumption, and are very competitive in reducing power consumption. They are also under tremendous pressure from the Department of Energy to make incremental power consumption reductions.
In response to these pressures and desires to reduce power consumption, manufacturers have sought to solve the problem of temperature variances due to the slaving of the air flow from the freezer to the fresh food compartment. Systems resulting from such endeavors, unlike the prior systems that operated based only on the temperature input from one of the freezer or the fresh food compartment, control the refrigeration components by sensing both the freezer temperature and the fresh food compartment temperature and by using a plurality of single and multi-throw switches to transfer control between the two thermostats. Unfortunately, the use of so many single and multi-throw switches to coordinate the control of the two thermostats, the evaporator fan, and the damper motor greatly increases the cost and complexity of such a system. The required wiring of these switches also increases the labor cost and reduces the overall reliability of such a system.
Such systems, such as that illustrated in
FIG. 3
, typically utilize a freezer thermostat
101
to control the compressor
103
, condenser fan
105
, and evaporator fan
107
to regulate the freezer temperature to the set point of the freezer thermostat. A multi-contact fresh food compartment thermostat
109
is then used to control a motorized damper
111
that regulates an opening between the freezer and the fresh food compartment. In addition to the damper, the motor
111
also operates a multi-control-surface cam used to control two multithrow switches
113
,
115
that connect and disconnect control of evaporator fan
107
between the two thermostats
101
,
109
and energize the motorized damper
111
to open or close.
The state of the switches illustrated in
FIG. 3
relates to both compartments being at or below their set point temperatures. If the fresh food compartment thermostat
109
calls for cool (connection between terminal A and B), the motorized damper
111
is energized to open the damper and rotate the cam. When the cam reaches its fully open position, both switches
113
and
115
transition. Switch
113
then allows the fresh food compartment thermostat
109
to control the evaporator fan
107
. This increases circulation between the compartments, thereby reducing the amount of time that it takes to achieve the desired temperature. The cam control surface that transitions the evaporator control switch
113
waits until the damper is fully open to allow the fresh food thermostat
109
to energize the fan
107
to reduce the power consumption of running the fan while the damper is in transition. In this state, however, the control of the evaporator fan via the freezer thermostat is disabled as its input through the multi-throw switch
113
is opened.
When the fresh food compartment reaches its desired temperature, the multi-contact fresh food compartment thermostat
109
switches to again close contacts A and C. The motorized damper
111
is energized to drive the damper closed. The control surface on the cam immediately transitions switch
113
to return control of the evaporator fan
107
to the freezer thermostat
101
. However, since the control cam does not transition the switch
115
until the damper is fully closed, a power failure that occurs while the damper is in the process of closing but is not yet fully closed can result in a condition where the damper cannot be opened and the evaporator fan
107
cannot be energized. This situation occurs when the power failure lasts long enough for the fresh food compartment to warm above its thermostat set point, thereby closing contact A and B of thermostat
109
. Since the switch
115
has not been transitioned by the cam to the state show in
FIG. 3
because the damper was not allowed to fully close, no power is provided to the motor
111
. As such, the switch
113
stays in the freezer control position illustrated in
FIG. 3
, which means that the call for cooling from the fresh food compartment cannot be accommodated, and the temperature in this compartment. will likely continue to rise. A service call is then required to reset the cam and the control switches to allow the system to work properly again.
One system that overcomes this failure condition is described in U.S. Pat. No. 5,490,395, entitled AIR BAFFLE FOR A REFRIGERATOR. In the system of this patent, the functionality of the single motorized damper control switch
115
illustrated in
FIG. 3
is divided among two single pole, single throw switches
117
,
118
as illustrated in the simplified FIG.
4
. Unfortunately, the addition of an additional switch also requires a more complex cam that includes an add
Bennett William B.
Reier James T.
Jiang Chen Wen
Leydig , Voit & Mayer, Ltd.
Ranco Inc. of Delaware
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