Refrigerator Thermostat And Arrangement Thereof

Abstract

A temperature control device for use in a frozen-foods compartment of a refrigerator, or the like comprises a pair of temperature-sensitive elements one of which is adapted to be inserted into the material to be frozen. The two elements are connected in a logic circuit which in turn controls a switching device to thereby control the operation of the refrigeration unit to establish and then maintain a desired temperature in the compartment.

Parent Case Text

This is a continuation-in-part of an application, Ser. No. 679,356, filed on Oct. 31, 1967 now abandoned.

Description

The invention relates generally to temperature control devices, and particularly to a device for controlling the operation of a refrigerating unit for establishing suitable temperatures in a refrigerating chamber having freezing devices and adapted to contain frozen goods.

In freezer chests employing freezing devices the refrigerating unit can be switched from its normal refrigerating power, which maintains a temperature of at least -18.degree. C, in the refrigerating chamber, to maximum refrigerating power which is required for freezing with a so-called cold shock. Since the refrigerating temperatures should reach up to -35.degree. C, a considerably higher refrigerating power is required.

In the known arrangements the switching to the maximum refrigerating power is effected when goods such as frozen foods placed in the freezer chest are to be frozen by the intensive action of the cold shock. The freezing is completed when the goods have attained a prescribed freezing temperature in their interior. The time required for this freezing operation depends to a great extent upon the nature of the goods which are to be frozen. For example, the freezing of flat and thin pieces is much more rapid than that of thick pieces.

Heretofore the duration of such a cold shock process was determined by the operator largely by instinct. But there is a danger that the operator will switch too quickly from the maximum refrigerating power to the normal refrigerating power, so that the parts of the goods inside the freezer will not be subjected to cold-shock, and it will thus take much longer until the refrigerating chamber temperature of -18.degree. C is attained. This is harmful for the quality of the goods to be frozen. The maintaining of high refrigerating power for an excessive period has the disadvantage that an excessive demand is placed on the refrigerating unit, which in turn, results in greater wear and higher operating costs of the refrigerating unit.

Depending on the nature of the goods to be frozen, differing deviations from the nominal freezing temperature can be permitted during normal operation in the freezer chest or the refrigerating chamber. For example, a material which consists primarily of protein and fat requires a different accuracy in maintaining the nominal freezing temperature than a more sensitive material, such as vegetables. The presently known temperature control devices for refrigerating units do not provide the possibility for connecting and disconnecting the refrigerating unit for attaining the desired nominal temperature dependent on the sensitivity of the material to deviations in temperature. Only fixed temperature differences are provided after which the refrigerating unit is connected. For example, a deviation of plus or minus 1.degree. C is permitted, so that with a set refrigeration chamber temperature of -18.degree. C, the refrigerating unit is connected at -17.degree. C and disconnected at -19.degree. C. This difference of 2.degree. C is called the connection difference. Regardless of whether the material requires such a small connection difference, that same refrigerating power is always expended. It is therefore an object of the invention to provide a temperature control device which permits the accurate execution of a rapid freezing process, the so-called cold shock.

It is another object of the invention to provide a temperature control device which improves the economy of a refrigerating unit by providing the possibility of preselecting the connection difference and adapting it to the respective material to be frozen.

It is a further object of the invention to provide a temperature control device which does away with the need for mechanical switches in its operation.

The operation broadly resides in the provision of two temperature feelers, of which the feeler that switches the circuit breaker back to the lower power stage is mounted movably and can be introduced into the material to be frozen, while the other feeler, which connects and disconnects the circuit breaker, herein shown as a triac in the lower power stage, can be set to corresponding response values by an adjusting device. In order to eliminate mechanical switches in the temperature control device, which are susceptible to trouble, the switch-back of the circuit breaker and the switching in normal operation are controlled by a transistor ahead of which is arranged a trigger which is in turn connected to the feelers and which has a variable resistance in its feedback path.

One of the two temperature feelers determines the period during which the maximum power stage is in effect, while the other feeler effects in nominal operation the connection and disconnection of the refrigerating unit in dependence on the preset nominal value.

To the accomplishment of the above and to such further objects as may hereinafter appear, the present invention relates to a temperature control device for a refrigerating unit substantially as defined in the appended claims and as described in the following specification taken together with the accompanying drawings in which:

FIG. 1 is a circuit diagram of a temperature control device designed according to the invention; and

FIG. 2, is a schematic perspective view of a temperature feeler designed as a probe as employed in the temperature control device of the invention.

In the particular embodiment of the invention herein shown, the temperature control device of the invention, as shown in FIG. 1, includes a current source 1 at 220 volts a-c connected to the terminals 2 and 3 of a refrigerating unit 4. A switching device 5 is arranged in the circuit of refrigerating unit 4, and is herein shown as a gate-controlled thyristor or triac.

Switching device 5 permits refrigerating unit 4 to switch between a maximum power state and a power state for normal operation, in which refrigerating unit 4 can also be connected and disconnected in dependence on the temperature in the refrigerating chamber. The control of the triac is effected by a control transistor 6, ahead of which is arranged a trigger circuit, which in turn is connected to the temperature sensors or feelers 21 and 22. The trigger circuit consists of the two transistors 7, 8 and the resistors 9 to 14 connected in a conventional manner as shown in FIG. 1. Temperature feelers 21 and 22 are advantageously in the form of temperature-dependent NTC or PTC resistors. The resistance values of feelers 21 and 22 vary as a function of temperature. At least temperature feeler 21 is designed as a probe, by inserting the NTC or PTC resistor into a metal tube. This probe is adapted to be introduced into the material to be frozen.

A fixed resistor 19 and a variable resistor 20 connected in series define a feedback path for the trigger circuit. In addition, a power supply unit 16 is provided which consists of the conventional rectifiers, filters and stabilizers for providing the electronic control with voltages from a supply voltage 17 and a supply transformer 18. The output of power supply 16 is a stabilized d.c. voltage which has, as is conventional, a residual hum. A voltage of 3 volts is applied from power supply 16 to the collector electrode of the control transistor 6, and the rest of the electronic control circuit is provided with a voltage of 22 volts. The temperature feeler 22 is series-connected with a fixed resistor 23, and the feeler 21 is connected parallel thereto and is selectively coupled to one of three fixed resistors 24, 25, and 26, with which it can be connected by the operation of a selector switch 27 to form a voltage divider circuit. The parallel-connected feelers 21 and 22, which are connected as an "OR" circuit, are provided with rectifier diodes 30 and 31 for decoupling. In addition, capacitors 32 and 33 are connected in parallel to ground to form along with resistor 11 an a-c filter. The capacitors 32 and 33 serve to suppress high frequency noise. In an apparatus having poor suppression of radio noise (e.g., vacuum cleaners or drilling machines, etc.) there can occur switching sparks which can release the trigger consisting of the transistors 7, 8. This is avoided by the capacitors 32 and 33.

The method of operation of the electronic temperature control device of FIG. 1 is as follows:

In order to freeze a material placed in a freezer chest or the like, with a high refrigerating power by a so-called cold-shock, refrigerating unit 4 is initially switched by setting switching device 5 to its maximum power state to supply maximum refrigerating power to unit 4. This switching can be effected by control elements (not shown) or by hand. Switching back of switching device 5 to its normal state is effected when the material in unit 4 has fully attained the freezing temperature required for cold shock. The firing (initial setting) of switching device or thyristor 5 occurs through the gate electrode of that device by means of transistor 6, which is supplied with a separate supply voltage. The signal at the base of transistor 6 and indirectly the opening or cut-off times of switching device 5 is controlled by the trigger consisting of the transistors 7 and 8. This trigger oscillates according to the setting of variable resistor 20 and selector switch 27. This freezing temperature is sensed by the variable-resistance feeler 22 designed as a probe, which is movably mounted and introduced into the material. When the resistance of feeler 22 reaches a predetermined value, a determination is made that the material has attained the required temperature in its interior. When the interior of the material has reached the freezing temperature, the resistance value of feeler 22 reaches a level at which switching device 5 is switched by control transistor 6 to its normal power state for normal operation at a reduced refrigeration power. In this normal power stage temperature feeler 21 then takes over the control of refrigerating unit 4 by connecting refrigerating unit 4 over the trigger and control transistor 6 with switching device 5. Temperature feelers or sensors 21 and 22 supply a voltage proportional to the temperature which voltage is decoupled through diodes 30 and 31. That voltage is supplied through resistor 11 to the input of the trigger. The diodes 31 and 32 are provided to carry out an "OR" function. The following conditions may exist:

"OR" function: Sensor 22 Sensor 21 1 1 Everything is switched off

1 0 The trigger and thus 0 1 switching device 5 0 0 is switched on

It can be seen that in case of a temperature difference between the sensors (condition 0/1 ) cooling will continue between the sensors 21 and 22 until such time as the sensors reach the same preselected temperature (1/1 ). That temperature is preselected by the setting of selector switch 27. The condition 0/0 will be avoided by resistor 23. At a sufficiently low temperature the same voltage is present at the sensors 21 and 22 and thus at the common connection of the diodes 30 and 31 at the resistor 11. Thereby a cut-off effect occurs after the "OR" function, and the cooling will be interrupted through the trigger.

The thyristor 5 functions in three possible states in a known manner; the energy control takes place through its gate electrode:

a. Switched off: The trigger blocks the transistor 6; no necessary positive control voltage is applied to the control electrode of the thyristor 5.

b. Fully switched on: The trigger oscillates and supplies a number (N) or half-waves to the control electrode so that the thyristor fully connects through.

c. Half switched off: The trigger supplies only (N/2) half-wave to the control electrode of the thyristor and thereby supplies electrical energy to refrigerating unit 4 only half of the time as in b). By switching to the various fixed resistors 24, 25 or 26 by means of the selector switch 27, a certain temperature range can be selected over which the temperature feeler 21 operates to control the operation of circuit breaker 5. By means of the variable resistor 20 provided in the feedback path across transistors 7 and 8, it is also possible to select the deviation from the nominal value over which temperature feeler 21 is effective to connect and disconnect circuit breaker 5. In dependence on the material to be frozen, it is then possible to determine what deviations from the nominal value of the refrigerating temperature are permitted in the refrigerating chamber. By means of variable resistor 20 it is possible, for example, to provide that the connection and disconnection of refrigerating unit 4 should be effected after a deviation of plus or minus 1.degree. C from the required refrigerating chamber temperature of -18.degree. C, for example. But it can also be provided that refrigerating unit 4 should only be connected or disconnected at much greater temperature differences, for example, at deviations of 7-1/2.degree. C from the nominal value. The connection difference can be adjusted between 2.degree. and 15.degree. C.

The switching of refrigerating unit 4 over circuit breaker 5, which is in turn switched by control transistor 6, is effected when the predetermined temperature has been sensed by temperature feelers 21 and 22 in such a way that the respective voltage variation is transmitted over diode 30 or 31 and resistor 11 to transistor 7. This transistor is cut off, so that transistor 8, connected in series with transistor 7 via the resistor 14, is turned on and the switching transistor 6 is in turn, cut off. As a result, circuit breaker 5 is cut off on one side so that refrigerating unit 4 is switched to the lower power stage, in the manner described above. Depending on the temperature, which is measured by feelers 21 and 22 respectively, the circuit breaker 5 is opened for both half-cycles or only for one half-cycle so that refrigerating unit 4 works at full or partial load.

FIG. 2 illustrates a possible configuration of temperature feeler 22 which as noted above is designed as a movable probe, for insertion into the material to be frozen. As shown, feeler 22 is secured in a metal tube 35 over a ring bush 34 of thermally conductive material, which may be, for example, a suitable metal. The two leads 36, 37 extending from temperature feeler 22 leave tube 35 through a plug 38. two leads are also represented in the circuit diagram of FIG. 1.

To make sure that the temperature can be sensed without delay, the generally stationary temperature feeler 21 is preferably also surrounded by a metallic body, for example, a metal plate which is in contact with the interior of the refrigerator.

Thus, while only a single embodiment of the present invention has been herein specifically described it will be apparent that modifications may be made therein without departing from the spirit and the scope of the invention.

Claims

I claim:

1. A temperature control system for establishing and maintaining a predetermined temperature in a refrigeration chamber in which frozen material is adapted to be stored, said control system comprising switch means capable of operating in first, second and third different states of conduction for controlling the operation of the refrigeration chamber, control circuit means for controlling the operation of said switch means, first and second temperature sensitive resistor sensors arranged in the chamber, one of said sensors being movable in the chamber for insertion in the frozen material stored therein, logic means coupled to said resistor sensors and to the input of said control circuit means, said logic means being effective in response to the temperatures sensed by said first and second sensors to provide a control signal to the input of said control circuit means, the latter in turn being effective to establish said switch means into one of said first, second and third states of conduction.

2. The temperature control system of claim 1, in which said control circuit means comprises an output switching device, a trigger having an input coupled to said sensors and an output coupled to the control terminal of said switching device, and variable resistance means coupled between said input and output for controlling the response of said trigger to variations in said first and second temperature sensors.

3. The temperature control system of claim 2, in which said first and second temperature-sensitive resistors are coupled in an OR-circuit, said OR-circuit being coupled to the input of said control circuit means.

4. The temperature control system of claim 3, further comprising means for selectively inserting resistance elements having different values of resistance in circuit arrangement with one of said first and second temperature sensors.

5. The temperature control system of claim 1, in which the movable one of said first and second temperature sensors is housed in a tube of heat-conducting material.

6. The temperature control system of claim 1, in which said first and second temperature-sensitive resistors are coupled in an OR-circuit, said OR-circuit being coupled to the input of said control circuit means.

7. The temperature control system of claim 6, further comprising means for selectively inserting resistance elements having different values of resistance in circuit arrangement with one of said first and second temperature sensors.