Dryness Sensor

Abstract

A liquid holder located within a washing apparatus chamber collects a predetermined amount of liquid during a wash cycle. The collected liquid is evaporated during a dry cycle of the apparatus. A thermistor mounted to the liquid holder bottom rapidly changes resistance upon complete evaporation of the collected liquid. The change in resistance fires an SCR to generate a signal which terminates the dry cycle of the apparatus.

Description

BACKGROUND OF THE INVENTION

This invention relates to washing apparatus or more particularly to a dryness sensor having means for holding a preselected quantity of the washing liquid, the holding means being open to an enclosed space and arranged to indicate when a predetermined dryness condition is present.

In washing apparatuses having a chamber for containing liquid for cleaning a load placed within the chamber and means for subsequently drying the washed load, various systems have been devised for determining when the load has a predetermined dryness condition. Typically, both laundry and dishwasher appliances terminate the drying cycle in response to the lapse of a fixed time period long enough to dry any load which might be placed within the chamber. It is desirable to minimize the drying cycle by terminating the cycle when the load within the chamber is dry rather than requiring the lapse of the preset time period. Conventional humidity sensors and like devices are too expensive and/or fragile for this purpose.

In accordance with the present invention, a dryness sensor having a container opening to the wash chamber collects a predetermined amount of liquid during the wash cycle. A temperature-responsive device is located in thermal contact with the container so that a substantial change in temperature occurs at the time the last portion of the collected fluid is evaporated. In a preferred embodiment, the device is located within a dishwasher chamber in such a manner that liquid during a rinse cycle is allowed to collect within the container. The volume of collected fluid is preselected so that at the time all the liquid has evaporated the dishes within the dishwasher chamber are dry. A sensor determines when the collected liquid is fully evaporated, and in response thereto terminates the dry cycle of the dishwasher.

SUMMARY OF THE INVENTION

The invention comprehends the provision of a dryness sensor which collects and disperses a predetermined amount of liquid to a space for washing and drying a load the dryness condition of which is to be sensed.

One feature of the invention is the provision of an improved washing apparatus control in which the dryness condition of a load of dishes is monitored in order to terminate the dry cycle of the apparatus.

Another feature of this invention is the provision of a dryness sensor for a drying chamber, in which a predetermined amount of fluid is collected and vented to the chamber, and having temperature-responsive means sensing evaporation of the fluid in order to control the operation of the drying means.

BRIEF DESCRIPTION OF THE DRAWING

Further features and advantages of the invention will be apparent from the following description and from the drawing, in which:

FIG. 1 is a fragmentary front elevation of a washing and drying apparatus provided with a dryness sensor embodying the invention;

FIG. 2 is a partly schematic and partly block diagram of a circuit embodying the invention;

FIG. 3 is an exploded view of the dryness sensor used in the apparatus of FIGS. 1 and 2; and

FIG. 4 is a front elevation of the dryness-sensing sensor of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the illustrated embodiment of the invention, a dryness-sensing device 10 is shown in a system for controlling a dishwasher apparatus. Illustratively, the dishwasher apparatus includes a dishwasher tub 11 having a lower sump portion 12 in which is provided a recirculating pump 13 and a drain pump 14 concurrently operated by an electric motor 15. The pump 13 is arranged to pump dishwashing liquid, such as water W, upwardly through a shaft 16 to a spray arm 17 to spray upwardly through an enclosed dishwashing chamber 18 defined by the upper portion 19 of the tub 11.

The dishwashing liquid W, herein hot water, is delivered into the tub 11 through an inlet 22 connected to a conventional fluid control system for dishwashers. Conventional means for draining the water W from the tub connects with an inlet portion 23 opening to the bottom of the sump 14. After one or more cycles of wash and rinse operation, the water W is drained from the lower sump portion 12 and a heater 25 is energized to heat the atmosphere within chamber 18 and dry the dishes (not illustrated) suitably contained within the chamber.

In accordance with the present invention, dryness sensor device 10 is electrically connected in a circuit which determines when a predetermined dryness condition is present within chamber 18 in order to control deenergization of heater 25. As seen in FIGS. 3 and 4, device 10 comprises a mounting base 30 having upstanding fingers 31 which hold a disc 33 in a generally horizontal plane. Disc 33 is formed of a heat-conductive material, such as copper, etc. and has a circular plane bottom portion 35 surrounded by a ridge 36 to define a shallow container for holding a predetermined amount of water W therein. A temperature sensor, in the form of a thermistor 40, is mounted to the underside of the bottom portion 35 so as to be in thermal transfer association with the disc 33. Covering the thermistor 40 mounted on bottom portion 35 of disc 33 is a quantity of thermal insulating material 41. The quantity of material 41 is sufficient to substantially prevent heat transfer to the thermistor 40 from the space beneath disc 33.

Device 10 is mounted within chamber 18, FIG. 1, so that during a rinse cycle, a predetermined amount of water W which is forced through arms 17 will collect and be held in the shallow disc 33. The volume of water which disc 33 holds is selected so that substantially all the trapped water will have evaporated from the metal disc when the dishes within chamber 18 are dry. As the water captured within disc 33 evaporates, the temperature sensed by the thermistor 40 stays low inasmuch as insulating material 41 precludes heat transfer to thermistor 40 from the space beneath disc 33 and evaporation of water cools the disc 33. When substantially all the water has evaporated, the temperature of thermistor 40 rapidly rises, inasmuch as the disc 33 is no longer cooled by evaporation of water captured thereon. The rapid rise in temperature of the thermistor 40 causes a corresponding rapid change in resistance, which change in resistance is used in the circuit of FIG. 2 to terminate the drying cycle of the dishwasher.

The dishwasher is controlled by a suitable dishwasher control 43 having conventional circuitry for controlling energization of motor 15, heater 25, and associated devices for operation of the dishwasher, such as a fill solenoid 45 and other conventional devices (not illustrated). The energization and deenergization of the electrically operated motor 15, dryer heater 25, and fill solenoid 45 is partly under control of a timer motor 50 which is connected across a source of power connected between lines 52 and 53 through a switch 54. When switch 54 is closed, timer motor 50 is energized in order to move cams which control the electrical actuation of the various devices associated with the different cycles of operation of the dishwasher, as is conventional.

In accordance with the present invention, the dishwasher control 43 is also controlled by dryness-sensing device 10. Thermistor 40, having a negative coefficient of temperature response, is connected to a resistor 60 in a series voltage divider connected between power supply lines 52 and 53. Switch 54 is shunted by a gatable conduction device such as a silicon-controlled rectifier (SCR) 62 having its anode connected to line 52 and its cathode connected to the junction between switch 54 and timer motor 50. The control or gate electrode of SCR 62 is coupled through a voltage breakdown device, as neon lamp 64, and a capacitor 66 to potential line 53. The junction between neon lamp 64 and capacitor 66 is electrically connected via a line 68 to the junction between thermistor 40 and resistor 60.

In operation, thermistor 40 initially has a high voltage drop thereacross, due to the low temperature of metal disc 33 maintained by the evaporation of the water from the shallow container. This produces a low voltage drop across resistor 60, charging capacitor 66 to a small voltage insufficient to fire the neon lamp 64. When substantially all of the water has evaporated from the metal container, however, the temperature sensed by thermistor 40 suddenly rises rapidly, causing the resistance of thermistor 40 to rapidly lower to a value such that the voltage drop across resistor 60 exceeds the firing point for neon 64. This causes neon 64 to fire and forward bias SCR 62, providing a current path to timer motor 50.

Switch 54 is open during the dry cycle, causing timer motor 50 to be stopped at a position in which its cams are actuating heater 25 but are not actuating the other devices. When the dishes are dry, as indicated by the firing of SCR 62, timer motor 50 is again energized to cause the timer to advance through the next interval which deenergizes heater 25 and causes termination of the drying cycle.

While the dryness sensor circuit has been described in connection with a conventional dishwasher control, it is to be understood that the dryness sensor is adaptable for use with any control system in which the dryness condition of the atmosphere is to be sensed. The device is especially adaptable for use with various washer-dryer appliances in which the sensor is mounted so that washing liquid is supplied to the container 33 automatically each time a wash operation is effected so that the subsequent drying cycle can be monitored as discussed above.

Claims

We claim:

1. In an apparatus having means for drying articles within an enclosed drying space, a sensor for determining the dryness condition within said enclosed drying space, comprising:

means for containing a predetermined amount of liquid;

means mounting said containing means within said enclosed space and open to the atmosphere therein so that the contained liquid evaporates during the time necessary to reach a preselected dryness condition within said enclosed space; and

means associated with said containing means for producing a signal when a predetermined amount of the contained liquid has evaporated.

2. The sensor of claim 1 wherein said associated means includes temperature-responsive means located in thermal transfer association with said containing means, and means responsive to a predetermined temperature sensed by said temperature-responsive means for generating said signal.

3. The sensor of claim 2 wherein said temperature-responsive means comprises a thermistor having a resistance proportional to temperature, and said generating means includes a potential source and means connecting said potential source to said thermistor for generating said signal in accordance with a predetermined voltage drop across said thermistor.

4. The sensor of claim 3 wherein said generating means further includes a gatable conduction device, a neon lamp requiring a predetermined voltage thereacross for passing a current therethrough, and means connecting said voltage breakdown means between said gatable device and said thermistor for causing said gatable device to generate said signal.

5. The sensor of claim 1 in a system having a chamber defining said enclosed space, said chamber containing fluid therein, said drying means including means for evaporating fluid in said chamber, and control means responsive to said signal for terminating the operation of said evaporating means.

6. The sensor of claim 5 in a system including means for dispersing said fluid through a load contained in said chamber, said mounting means locating said containing means so that dispersement of said fluid causes said containing means to capture said predetermined amount of fluid.

7. The sensor of claim 6 wherein said containing means includes means forming a depression for capturing fluid therein, said depression being opened to said chamber.

8. The sensor of claim 7 wherein said depression means comprises a disc having a lip surrounding its edge to form a shallow depression therein, said depression containing said predetermined amount of fluid.

9. The sensor of claim 8 wherein said disc is formed from a heat-conductive substance, and said generating means comprises temperature-responsive means located in heat transfer relation with said disc means on one side and in heat-insulating relationship with said space on another side, whereby a predetermined temperature indicates that a predetermined amount of fluid captured by said disc has been evaporated in said chamber.

10. The sensor of claim 9 wherein said control means includes a potential source and means connecting said temperature-responsive means to said potential source for producing a predetermined voltage thereacross when said predetermined dryness condition has occurred, and circuit means responsive to said predetermined voltage drop for generating said signal to terminate the operation of said evaporating means.

11. The sensor of claim 6 for a dishwasher in which said evaporating means is actuated during a drying cycle for dishes located in said chamber, said control means terminating said dry operation in response to the dishes within said chamber being dry.

12. The sensor of claim 1 wherein said predetermined amount of liquid is that which completely evaporates during said time.