GB2180330A - Refrigerating appliance with an improved defrosting device - Google Patents

Abstract

A refrigerating appliance has an electric-resistance defrosting device which is activated at the end of a time period preset by means of a timing member 17. The timing member 17 is stopped when the electric resistance 6 is activated and is started again when the resistance 6 is de-activated by a thermostatic sensor 7 which is able to detect the temperature of the evaporator 3. The result is that the time intervals between two successive defrosting cycles are kept constant, while the duration of each defrosting cycle is made variable. The refrigerating appliance also has a compressor 2 which, due to the switching arrangement thereof, is de-activated on the resistance being activated and vice-versa. A fan 5 in normal operation blows air over the evaporator 3 but prior to a defrosting operation the fan is de-activated. <IMAGE>

Description

SPECIFICATION Refrigerating appliance with an improved defrosting device The present invention relates to a refrigerating appliance of the type comprising an electric compressor, an evaporator, an electric resistance for defrosting the evaporator, a timing member capable of activating the electric resistance at the end of a preset time period by de-activating the compressor, and a thermostatic sensor which is able to detect the temperature of the evaporator so as to de-activate the said resistance when the evaporator reaches a preset temperature.

During the defrosting cycle of a refrigerating appliance, it is important, on the one hand, to free the evaporator completely of accumulated ice and, on the other hand, to prevent an increase in the temperature of the products being stored.

The defrosting cycle of a refrigerator is distinguished by three main stages: a first stage where the electric resistance is activated and the refrigerating cycle is de-activated, a second stage where the electric resistance is deactivated and a third stage where the refrigerating cycle is activated again.

The control parameter used for determining the first and the third stage is usually time.

According to the known art, a timer is used for this purpose, deactivating the compressor and activating the defrosting resistance at preset intervals.

The second stage of the defrosting cycle, however, is controlled, in accordance with the temperature of the evaporator, by means of thermostatic sensors which de-activate the electric defrosting resistance. The timer remains energized during operation of the defrosting resistance.

Since the control parameters for these stages (time and temperature) are not uniform with respect to each other, the result is that the defrosting cycle of a refrigerating appliance is necessarily subject to variations in respect of the abovementioned requirement.

In fact, to ensure complete defrosting of the evaporator, it is necessary to provide for a time interval between the first and the third stage which is greater than the normal time period during which the resistance is activated.

If, on the other hand, the compressor is activated again as soon as the defrosting resistance is deactivated, it cannot be ensured that the evaporator will be completely free of ice.

The problem underlying the present invention is to provide a refrigerating appliance which is structurally and operationally designed such that it is able to overcome the drawbacks mentioned above in connection with the known art cited.

This problem is solved by means of a refrigerating appliance of the abovementioned type, which is characterized in that it comprises means for stopping the said timer when the said resistance is active and for starting it again when the said resistance is deactivated by the said sensor.

The characteristic features and advantages of the present invention will emerge more clearly from the detailed description of a preferred embodiment thereof, illustrated, by way of a non-limiting example, with reference to the attached drawing, in which the sole Figure shows, in schematic form, an electric circuit for supplying power to and defrosting a refrigerating appliance according to the present invention.

In the attached drawing, 1 denotes, in its entirety, an electric circuit diagram of a refrigerating appliance according to the present invention.

The diagram 1 shows a power supply line L with branches L1, L2, between which a mains potential difference, for example 220 volts, is established.

In the diagram 1, 2 denotes an electric compressor conventionally connected, by means of a fluid-conveying line, to an evaporator 3 with a condenser (not shown).

An electric fan 5 is provided so as to circulate forced air over the surface of the evaporator 3.

An electric resistance 6 is also provided in the vicinity of the evaporator 3 so as to cause, in the manner explained below, defrosting at preset time intervals.

A sensor 7 is located on the evaporator 3 and is designed to detect the temperature of the latter. The sensor 7 is connected to an actuator 8 of a first switch 9.

The switch 9 has a movable contact element 10 which is connected to the branch L2 of the line L and can be switched between a first and a second contact terminal indicated by 11 and 12, respectiveiy.

The terminal 11 is connected to the movable element 13 of a second switch 14 which is also provided with a first and a second contact terminal indicated by 15 and 16, respectively.

A timing member 17, which is of the electromechanical type, is connected to the line L in series with the resistance 6; the timing member 1 7 and the resistance 6 are connected to each other at the terminal 15 of the second switch 14.

The terminal 16 of this switch 14 is, in turn, connected to the terminal 12 of the first switch 9 and, together with the latter, to a terminal 20 supplying power to the compressor 2.

A second terminal 21 supplying power to the compressor 2 is connected tb the branch L1 of the line L.

The movable element 22 of a switch 23 is also connected to the terminals 16 and 12 and is capable of interrupting the power supply to the fan 5 in the manner explained below.

The movable elements 13 and 22 of the second switch 14 and of the switch 23 are actuated in a manner per se conventional, for example via cam means, by the timing member 17.

The actuator 8 constitutes, together with the sensor 7, a system for controlling the temperature of the evaporator 3. This system has two activation thresholds, an upper threshold which, purely by way of example, is given as 7"C and a lower threshold with, again by way of example, is given as -25"C.

When these thresholds are reached, a signal is emitted by the sensor 7 and the actuator 8 switches the movable element 10 of the switch 9 from the first terminal to the second terminal 11, 12 or vice versa, as will be explained below.

During normal operation of the refrigerating appliance where, for example, the temperature of the evaporator 3 is between +7"C and -25"C, the movable element 10 of the first switch 9 forms a closed circuit with the contact terminal 12, thereby supplying power to the compressor 2.

The movable element 13 of the second switch 14 forms a closed circuit with the ter minal 16 and the switch 23 supplies power to the fan 5.

The timing member 17 has a considerable internal resistance which is greater than that of the resistance 6. Therefore, the effect of the resistance 6 on the current flowing inside the timing member 17 is negligeable and this current flow is sufficiently low not to cause the resistance to heat up appreciably.

At a preset time, the timing hmember 17 operates the switch 23, cutting off the power supply to the fan 5.

The evaporator 3, which no longer has forced air blowing over it, undergoes a drop in temperature which is detected by the sensor 7.

When the lower threshold 11 is reached, the signal sent by the sensor 7 activates the actuator 8 which switches the movable element 10 of the first switch 9 to the contact terminal 11.

The compressor 2 remains active since it is supplied with power via the second switch 14, the movable element 13 of which forms a closed circuit with the contact terminal 16.

After a preset time interval foilowing deactivation of the fan 5, the timing member 17 operates the movable element 13 of the second switch 14, causing it to switch from the terminal 16 to the terminal 15.

The timing member 17 is stopped since it is short-circuited to the branch L2 of the line L and at the same time the defrosting resistance 6 is activated.

The resistance 6 causes heating of the eva porator 3, the temperature of which is always monitored by the sensor 7.

When the temperature of the evaporator 3 exceeds the upper threshold level programmed for the actuator 8, the movable element 10 of the first switch 9 is again moved from the contact terminal 11 to the contact terminal 12.

The power supply of the resistance 6 is thus interrupted, while the power supply of the compressor 2 and of the timing member 17 is restored.

The timing member 17, once it has been reactivated, switches again the movable ele ment 13 of the second switch 14 so as to form a closed circuit with the contact terminal 16 and, after a preset time interval following re-activation of the compressor 2, operates the switch 23 so as to activate the fan 5 again.

A first advantage of the refrigerating appli ance according to the present invention is that it keeps the operating time interval of the compressor 2 unchanged, independently of the duration of the defrosting cycle. Another advantage of the invention is that it ensures that, at the end of each defrosting cycle, the evaporator 3 is completely free of ice and is ready for immediate re-activation of the com pressor 2.

Another important advantage of the refrigerating appliance according to the present invention is that it cools the products arranged in the immediate vicinity of the evaporator to a temperature lower than the operating temperature before each defrosting cycle, causing operation of the fan to be interrupted before the compressor is de-activated. Moreover, by starting up the fan a preset time interval after the compressor is re-activated, the evaporator is able to reach the operating temperature ra pidly and air heated by the defrosting cycle which has just been completed is prevented from circulating inside the refrigerating appliance.

It will of course be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope of the invention.

Claims (4)

1. Refrigerating appliance comprising an electric compressor, an evaporator, an electric resistance for defrosting the evaporator, a tim ing member capable of activating the said re sistance at the end of a preset time period by de-activating the compressor, and a thermostatic sensor which is able to detect the tem perature of the evaporator so as to de-activate the said resistance when the evaporator reaches a preset temperature, characterized in that it comprises means for stopping the said timer when the said resistance is active and for starting it again when the said resistance is de-activated by the said sensor.

2. Appliance according to Claim 1, characterized in that the said timer and the said resistance are connected in series between the branches of a power supply line and in that the said means comprise a first and a second switch, the first switch having a movable contact element supplied with power by the same branch of the said line to which the said timer is connected and alternately forming a closed circuit with the power supply termi nal of the said compressor or with the movable element of the second switch and the second switch having a movable element alternately forming a closed circuit with the said power supply terminal of the compressor or with the said resistance, the first switch being controlled by the thermostatic sensor and the second switch being controlled by the said timing member.

3. Appliance according to Claim 1, characterized in that it comprises an electric fan which is associated with the said evaporator and the power supply of which is controlled by a switch operated by the said timing member so as to be stopped at a preset time interval before the said electric compressor is stopped and restarted a preset time interval after the said electric compressor is started.

4. A refrigerating appliance substantially as hereinbefore described with reference to the accompanying drawing.