Automatic temperature and humidity regulation – Mixing fluid of dissimilar temperature – Mixing valve with temperature motive means
Reexamination Certificate
2000-06-09
2001-10-23
Wayner, William (Department: 2859)
Automatic temperature and humidity regulation
Mixing fluid of dissimilar temperature
Mixing valve with temperature motive means
C068S012030
Reexamination Certificate
active
06305610
ABSTRACT:
FIELD OF THE INVENTION
This invention is directed to fluid temperature controllers, and more particularly to fluid temperature controllers suited for regulating the temperature of the water used in a clothes washing machine.
BACKGROUND OF THE INVENTION
Continuing advances and changes in the types of fabrics, materials, and colors used in the apparel industry are putting increasing pressure on the garment and clothes cleaning industry. Brighter colors and more delicate fabrics require specialized care and tighter tolerances on every aspect of the cleaning cycle, including better regulation of water temperature. While businesses may be able to afford more sophisticated controls for their industrial washing machines to allow them to be better regulated, modern pressures on time and personal budgets diminish the desirability of new fashions that require professional cleaning only. Unfortunately, the current state of the art for water temperature control in consumer washing machines may not maintain the water temperature within tight enough tolerances for these new fabrics, materials, or colors.
In current washing machines the water temperature control regulates temperature of the water during the fill of the tub. This is done by having either the cold or the hot water valve on, and then modulating the other valve to maintain the aggregate temperature of the water in the tub within a certain range. The particular valve that is commanded to be continuously on (cold or hot) is selected via a user actuated water temperature control switch. If the user selects HOT on the temperature selector switch, for example, the controller may turn on the hot water valve continuously and modulate the cold water valve on and off to maintain the temperature at a pre-selected setpoint. If, on the other hand, a user selects WARM, the controller may turn on the cold water valve continuously and modulate the hot water valve to maintain the water temperature in the tub at a different pre-selected setpoint.
One problem with many conventional water temperature controllers which introduces an unacceptable tolerance error in the control set points may be better understood with reference to FIG.
5
. As may be seen from this conventional temperature controller, a single reference voltage Vcc is used for both temperature set points as monitored by comparators
13
and
15
. The actual temperature measurement is made by a thermistor
17
placed in the water flow. A pull-up resistor
19
biases the thermistor
17
to establish a voltage at node
11
used by comparator
13
to turn on a water solenoid driver circuit
21
. A shunt resistor
23
coupled across the thermistor
17
is used to develop the second temperature reading for the comparator
15
to turn on a water solenoid driver circuit
21
.
The particular water valve that is controlled by the solenoid driver circuitry
21
is determined by the position of selector switch
25
. The particular comparator
13
,
15
that is enabled for temperature sensing control is determined by comparators
27
,
29
based on the position of the hot water valve (via input
31
). When the hot water valve is turned on full time, comparator
15
modulates the cold water valve, and when the cold water valve is turned on full time, comparator
13
modulates the hot water valve. Unfortunately, this sensing of the hot water valve at input
31
and selection via comparators
27
and
29
increases the cost and complexity, and reduces the reliability of this circuit. Further, the requirement for the valve driver selector switch
25
and its associated driver circuitry
33
also adds to the cost and detracts from the reliability of the water temperature controller. In the highly competitive and cost conscience consumer appliance industry, the requirement for four comparators
13
,
15
,
27
, and
29
, a hot water valve sense input
31
, and a selector switch
25
(and its associated circuitry
33
) in the water temperature control circuit detrimentally impacts the marketability of appliances that incorporate such high cost circuitry.
There, therefore, exists a need in the art for a new and improved water temperature controller that has tighter tolerance on temperature variation, that is more cost effective, and that is less complex with a higher reliability than current designs.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the instant invention to provide a new and improved fluid temperature control circuit that overcomes the above described and other problems existing in the art. Specifically, it is an object of the instant invention to provide a new and improved temperature control circuit that provides temperature regulation within narrow tolerances. Further, it is an object of the invention to provide a temperature controller that is less complex and more cost effective with improved reliability over prior designs. Additionally, it is an object of the invention to provide a fluid temperature controller that is suitable for use in a washing machine environment to control the water temperature.
In view of these objects, it is a feature of the instant invention to provide a fluid temperature controller that modulates the hot and cold water valves to regulate the water temperature of the fill water in a washing machine. It is a further feature that the proper modulation of the hot and cold valves is accomplished without input sensing of either these valves, and without an output driver selection switch. It is also a feature of the instant invention that the water temperature for both the hot and cold valve modulation is accomplished with a single thermistor without the necessity of a shunt resistor. Another feature of the instant invention is the use of a window comparator having two thresholds, with hysteresis, to maintain the temperature at the desired level.
In view of these objects and features of the invention, a preferred embodiment of the instant invention provides a fluid temperature control circuit for a washing machine having a hot water valve and a cold water valve controllable to provide a flow of hot and cold water, respectively, into a washing chamber. A temperature selector switch having an output to energize the hot water valve, an output to energize the cold water valve, and an output to enable operation of the fluid temperature control circuit. The fluid temperature control circuit comprises a temperature sensing element positioned to sense a temperature of water flowing into the washing chamber and a window detector circuit in sensory communication with the temperature sensing element. The window detector circuit includes a first and a second output, the first output being active when the temperature of the water is below a first threshold, and the second output being active when the temperature of the water is above a second threshold. The control circuit also includes a pair of water valve driver circuits responsive to the first and the second outputs of the window detector circuit to energize the hot water valve and the cold water valve.
Preferably, the temperature sensing element is a thermistor. Further, the first output of the window detector circuit is inactive when the temperature of the water is above a third threshold. The first and the third thresholds define a temperature regulation band in which the water temperature is maintained when the second and third outputs of the temperature selector switch are energized. Additionally, the second output of the window detector circuit is inactive when the temperature of the water is below a fourth threshold. In this embodiment, the second and the fourth thresholds define a temperature regulation band in which the water temperature is maintained when the first and third outputs of the temperature selector switch are energized. The window detector circuit preferably comprises a first and a second comparator, each having an inverting and a non-inverting input and an output. The inverting input of the first comparator and the non-inverting input of the second comparator are coupled to a common
England, Jr. John M.
Martin Terrence (Terry)
Morris Jules Jay
Ranco Incorporated of Delaware
Wayner William
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