JP7630357B2 - Cooling Storage - Google Patents

Description

This technology relates to refrigerated storage.

Conventionally, it is known to use a variable speed inverter compressor as a compressor constituting a refrigeration circuit, and one example is disclosed in Patent Document 1. The compressor described in Patent Document 1 is used in a cooling storage cabinet, and the upper limit of the rotation speed of the electric motor built into the compressor is controlled based on the temperature inside the cabinet or the room temperature. More specifically, when the temperature inside the cabinet or the room temperature is low and the operating margin of the compressor is high, the upper limit of the rotation speed of the electric motor is controlled to be high, so that the cooling capacity can be maximized. On the other hand, when the temperature inside the cabinet or the room temperature is high and the operating margin of the compressor is low, the upper limit of the rotation speed is controlled to be low, so that the current flowing through the electric motor, etc. can be suppressed while fully utilizing the cooling capacity.

Patent No. 4827416

In general, inverter compressors are designed to prevent components from being overloaded and becoming unreliable (e.g., shortening the lifespan of components and generating abnormal noise). The allowable upper limit of the refrigerant pressure is set small when the motor speed is low, and if the allowable upper limit is exceeded, the motor may automatically stop to avoid overload and protect the components. Automatic motor stoppage is particularly likely when the motor is operating at a low allowable upper limit of the refrigerant pressure, i.e., at the lower limit of the variable speed range. If the motor automatically stops, the compressor may stop unexpectedly and not operate stably.

The technology described in this specification was developed based on the above-mentioned circumstances, and aims to operate the compressor stably.

In order to solve the above problem, the cooling storage related to this technology includes a storage body capable of accommodating stored items, a cooling device for cooling the inside of the storage body, the cooling device having a compressor equipped with a variable speed electric motor for compressing refrigerant gas, and a condenser for condensing the refrigerant gas from the compressor, a temperature sensor capable of detecting the condensation temperature in the condenser, and a control unit for controlling the electric motor, and when the temperature detected by the temperature sensor is equal to or higher than a threshold temperature, the control unit determines whether the speed of the electric motor is at the lower limit value within the variable speed range, and when the speed of the electric motor is at the lower limit value, increases the speed of the electric motor.

In the condenser, the refrigerant gas from the compressor is condensed when its temperature drops to the condensation temperature by cooling. Since the condensation temperature is correlated with the refrigerant pressure, it is possible to indirectly detect whether the refrigerant pressure used by the compressor exceeds the allowable upper limit by detecting the condensation temperature with a temperature sensor. Therefore, if the temperature detected by the temperature sensor is equal to or higher than the threshold temperature, the control unit determines whether the motor speed is at the lower limit within the speed variable range, since there is a possibility that the refrigerant pressure in the compressor exceeds the allowable upper limit (overload state). As a result, if the motor speed is at the lower limit, the control unit increases the motor speed. When the motor speed increases, the allowable upper limit of the refrigerant pressure used by the compressor increases, and the compressor is no longer overloaded. This prevents the motor from automatically stopping unexpectedly, allowing the compressor to operate stably.

The control unit may also increase the speed of the motor for a predetermined set time when the speed of the motor is at the lower limit. In this way, the motor speed is reliably kept not at the lower limit for the set time, and the motor is reliably prevented from automatically stopping.

The speed of the motor may be changed in stages, and the control unit may increase the speed of the motor to the next higher speed when the speed of the motor is at the lower limit. In this way, the speed of the motor can be easily and reliably increased, and the motor can be reliably prevented from automatically stopping.

The control unit further includes an internal temperature sensor for detecting the temperature inside the storage body,
When the temperature inside the cabinet detected by the temperature sensor is equal to or higher than a predetermined set temperature, the speed of the motor may be determined based on a temperature gradient indicating the change in the temperature inside the cabinet per unit time, and when the temperature detected by the temperature sensor is equal to or higher than the threshold temperature, it may be determined whether the determined speed is equal to the lower limit. In this way, the speed of the motor is determined based on the temperature gradient of the temperature inside the cabinet, making it easier to adjust the temperature inside the cabinet to the set temperature. In addition, since the motor is not driven at a higher speed than necessary, unnecessary power consumption is avoided. Furthermore, by determining whether the speed of the motor determined in this way is equal to or higher than the lower limit, it is possible to prevent the motor from automatically stopping using the above-mentioned technology.

Further, the temperature sensor is a condenser temperature sensor provided in a condensation tube of the condenser,
The control unit may determine whether the speed of the motor is at the lower limit value when the temperature of the condenser temperature sensor is equal to or higher than a first threshold temperature. In this way, the condensation temperature of the condenser can be easily detected by the condenser temperature sensor.

The condenser may be an air-cooled heat exchanger, the temperature sensor may be an external temperature sensor that detects the external temperature around the storage body, and the control unit may determine whether the speed of the motor is at the lower limit value when the temperature of the external temperature sensor is equal to or higher than a second threshold temperature. When the condenser is an air-cooled heat exchanger, it is generally known that the condensation temperature of the refrigerant during stable operation is correlated with the outside air temperature. Therefore, by using an external temperature sensor, the condensation temperature of the condenser can be easily and indirectly detected.

This technology allows the compressor to operate stably.

FIG. 1 is a front view of a freezer according to a first embodiment; A diagram showing the internal structure of the freezer as seen from the right side Freezer top view Block diagram showing the electrical configuration related to the control of the electric motor Flowchart for motor control Flowchart for controlling an electric motor according to the second embodiment

<Embodiment 1>
A four-door freezer 10 (an example of a cooling storage) according to a first embodiment will be described with reference to Figs. 1 to 5. As shown in Figs. 1 and 2, the freezer 10 includes a storage body 12, a door 14, a machine room 16, and a cooling device 18. As shown in Fig. 2, the storage body 12 is an insulated box body that opens to the front, and is configured by foam-filling an insulating material between an outer box 30 and an inner box 32. The door 14 is attached by a hinge member so that an opening 12A of the storage body 12 can be opened and closed. The doors 14 are provided in two pairs, one above the other, in a double-door style, with two doors on each side.

As shown in FIG. 2, most of the interior of the storage body 12 is a storage chamber 34, which has multiple shelves 38 on which food and other stored items are placed. A cooler chamber 36 is provided at the top of the storage body 12, and the cooler chamber 36 houses a cooler (evaporator) 28 and a circulating fan (internal fan) 44. The storage chamber 34 and the cooler chamber 36 are separated by a cooling duct 40.

As shown in FIG. 2, the cooling duct 40 has an inclined portion 42 that inclines downward toward the rear. The inclined portion 42 has an intake port 42A and an exhaust port 42B. A circulation fan 44 is provided above the intake port 42A in the cooler chamber 36. Furthermore, an internal temperature sensor 46 (specifically, a temperature thermistor) is provided above the circulation fan 44. The cooler 28 is disposed behind the circulation fan 44 and the internal temperature sensor 46. The inclined portion 42 of the cooling duct 40 separates the storage chamber 34 from the cooler chamber 36, and receives defrost water generated when frost adhering to the cooler 28 melts. An exhaust pipe 48 is connected to the rear end of the inclined portion 42, and the defrost water is exhausted to the outside of the storage body 12 through the exhaust pipe 48 extending downward.

As shown in Figures 2 and 3, the machine room 16 is located above the storage body 12 with an open top. The machine room 16 houses the machinery (compressor 22, condenser 26, etc.) that constitutes the cooling device 18, an electrical equipment box 50, an operation box 52, etc. An opening is provided in part of the front of the machine room 16 as shown in Figure 1, and the display screen 54 and operation unit 56 provided on the front of the operation box 52 are exposed to the outside through the opening. Various information is displayed on the display screen 54. The operation unit 56 is a button that the user operates to change various settings of the freezer 10.

The cooling device 18 is a device that cools the inside (storage chamber 34) of the storage body 12. As shown in FIG. 2, the cooling device 18 includes a compressor 22, a condenser fan 24, a condenser 26, and a cooler 28. The compressor 22, the condenser 26, and the cooler 28 are connected by piping 21, and a refrigerant is circulated to form a known refrigeration cycle. Note that an expansion valve (capillary tube) is interposed between the condenser 26 and the cooler 28.

The compressor 22 is an inverter compressor equipped with a variable speed motor 23. The compressor 22 uses the motor 23 as a power source to draw in and compress the refrigerant gas, and discharges the high-temperature, high-pressure refrigerant gas. The motor 23 is a motor, and may be, for example, an AC induction motor or a DC brushless motor. When the rotation speed V23 of the motor 23 increases, the amount of refrigerant gas drawn in and discharged by the compressor 22 increases, and the amount of refrigerant circulating in the refrigeration cycle increases, thereby improving the cooling capacity of the cooling device 18. On the other hand, when the rotation speed V23 of the motor 23 decreases, the amount of refrigerant circulating in the refrigeration cycle decreases, and the cooling capacity of the cooling device 18 decreases. In addition, the smaller the rotation speed V23 of the motor 23, the smaller the power consumption of the motor 23, etc., and energy saving can be achieved. In this embodiment, the rotation speed of the electric motor 23 is variable in seven stages (specifically, 30 rps (rounds per second), 35 rps, 40 rps, 47 rps, 55 rps, 65 rps, and 76 rps).

The condenser 26 cools and liquefies the refrigerant gas compressed by the compressor 22 using air blown by the condenser fan 24. As shown in Figures 2 and 3, the condenser 26 includes a condenser tube 26A, a number of fins, and a condenser box 26B that houses them. The condenser tube 26A extends in the left-right direction and is folded back multiple times. The condenser tube 26A passes through the fins in the condenser box 26B, penetrates the side of the condenser box 26B, and is folded back in a U-shape.

As shown in Figures 2 and 3, the condenser fan 24 is installed behind the condenser box 26B. When the condenser fan 24 is activated, outside air passes through the condenser box 26B from front to back, cooling the condenser tube 26A. The refrigerant in the condenser tube 26A is a high-temperature gas near the inlet on the compressor 22 side, and as it travels along the condenser tube 26A, it is cooled and its temperature drops. When the temperature of the refrigerant gas drops to a saturation temperature (condensation temperature) according to the pressure, it begins to condense into liquid. The liquefaction rate of the refrigerant gas increases as it travels along the condenser tube 26A, and it is condensed into refrigerant liquid near the outlet on the cooler 28 side (liquefaction rate 100%).

As shown in Figures 2 and 3, a condenser temperature sensor 25 (specifically, a temperature thermistor) is attached to the condensing tube 26A of the condenser 26 in a manner that it is housed in a thermistor holder. The condenser temperature sensor 25 is attached to the central pipe including the central portion between the inlet and outlet of the condensing tube 26A. At least a portion of the refrigerant in the condensing tube 26A in the central pipe is condensed and liquefied, and its temperature matches the condensation temperature. Therefore, the condenser temperature sensor 25 detects the condensation temperature of the refrigerant. In addition, since the condensation temperature of the refrigerant changes depending on the refrigerant pressure, it can be said that the condenser temperature sensor 25 can indirectly detect the refrigerant pressure.

As shown in FIG. 3, an air filter 26C is attached to the front opening of the condenser box 26B. The air filter 26C prevents foreign matter such as dust from entering the condenser box 26B and adhering to the fins, etc. The condenser temperature sensor 25 also serves as a clogging temperature sensor that detects clogging of the air filter 26C. When the air filter 26C becomes clogged, the condenser tube 26A becomes less air-cooled, causing the temperature of the condenser temperature sensor 25 to rise higher than normal. This temperature rise can also be used to detect clogging abnormalities.

The cooler 28 reduces the pressure of the refrigerant liquid from the condenser 26 using an expansion valve (capillary tube) and then vaporizes it, thereby cooling the air passing through the cooler 28 with the heat of vaporization. The refrigerant gas from the cooler 28 is returned to the compressor 22. The air inside the storage chamber 34 is drawn into the cooler chamber 36 from the intake port 42A by the circulation fan 44, as shown by the white arrows in FIG. 2. The drawn air is cooled by the cooler 28 and blown out into the storage chamber 34 from the exhaust port 42B. This cools the items stored in the storage chamber 34. In addition, the air drawn in by the circulation fan 44 hits the internal temperature sensor 46, thereby detecting the temperature inside the storage chamber 34 (internal temperature).

A control board equipped with a microcomputer is housed inside the electrical box 50. An operation board is housed inside the operation box 52, and an external temperature sensor 64 (specifically a temperature thermistor) that detects the external temperature around the storage body 12 is mounted on the operation board. The external temperature sensor 64 may be provided in a location other than the operation board, but by mounting it on the operation board, it is not necessary to lay a signal line cable connecting the external temperature sensor 64 and the operation board. Note that the temperature detected by the external temperature sensor 64 may be higher than the actual external temperature around the storage body 12 due to heat generation by the board, etc., but there is no problem as long as this is taken into consideration when using it.

The freezer 10 is provided with a control unit 20 that electrically controls various devices. The control unit 20 is composed of a control board in the electrical equipment box 50 and an operation board in the operation box 52. The control board in the electrical equipment box 50 and the operation board in the operation box 52 are communicatively connected. The control unit 20 controls the compressor 22, the condenser fan 24, the circulation fan 44, the defrost heater, etc., to perform cooling operation and defrosting operation to melt frost that has adhered to the cooler 28.

As shown in FIG. 4, the control unit 20 is electrically connected to the condenser temperature sensor 25, the internal temperature sensor 46, the external temperature sensor 64, the memory unit 68, and the inverter circuit 70. The memory unit 68 is a memory and may be built into the control unit 20. The memory unit 68 stores the set temperature Ts, which is the target freezing temperature, and a table of the time change of the set temperature Ts. The inverter circuit 70 is housed in the electrical equipment box 50 and is connected to the electric motor 23 of the compressor 22.

During cooling operation, the control unit 20 controls the rotation speed V23 of the electric motor 23 through the inverter circuit 70 based on the condenser temperature T25 detected by the condenser temperature sensor 25 and the inside temperature T46 detected by the inside temperature sensor 46. More specifically, the control unit 20 supplies a frequency command signal to the inverter circuit 70, and the inverter circuit 70 supplies a variable frequency AC signal to the electric motor 23 based on this frequency command signal. The electric motor 23 is driven to rotate at a speed according to the frequency of the AC signal from the inverter circuit 70. The control of the electric motor 23 by the control unit 20 will be described below with reference to the flowchart of FIG. 5.

When the cooling operation is started by the user's operation, the control unit 20 operates the condenser fan 24 and the circulation fan 44. As shown in FIG. 5, the control unit 20 also reads the internal temperature T46 detected by the internal temperature sensor 46 and compares it with the set temperature Ts in the memory unit 68 (S11). The set temperature Ts is the target freezing temperature, and is initially set to a predetermined temperature, but can be changed as appropriate by the user operating the operation unit 56. If the internal temperature T46 is lower than the set temperature Ts (NO in S11), the temperature is lower than the target freezing temperature, so the inverter circuit 70 is stopped, the rotation speed V23 of the motor 23 is set to 0 rps, and the compressor 22 is stopped (S12). On the other hand, if the internal temperature T46 is equal to or higher than the set temperature Ts (YES in S11), the temperature has not yet dropped to the target freezing temperature, so the motor 23 is driven at the predetermined rotation speed V23 through the inverter circuit 70 to operate the compressor 22 (S13).

Here, in step S13, the rotation speed V23 of the motor 23 is determined to be an optimal value within the variable speed range (30 to 76 rps in this embodiment) based on the change (temperature gradient) of the inside temperature T46. More specifically, the smaller the temperature gradient of the inside temperature T46 is than the temperature gradient (target temperature gradient) derived from the table of the time change of the set temperature Ts in the memory unit 68, the higher the rotation speed V23 is determined. For example, when a large amount of stored items is stored and the load inside the cabinet is large, the temperature gradient of the inside temperature T46 tends to be smaller than the target temperature gradient. In that case, the motor 23 is rotated at a high speed to increase the cooling capacity of the cooling device 18. On the other hand, when the temperature gradient of the inside temperature T46 is larger than the target temperature gradient, the rotation speed V23 of the motor 23 is rotated at a low speed to reduce the cooling capacity of the cooling device 18. In this way, the inside temperature T46 can be easily tracked to the time change of the set temperature Ts. In addition, the motor 23 does not need to rotate at a higher speed than necessary, which means less wasted power consumption.

When the rotation speed V23 of the electric motor 23 is variably controlled in this manner, if the rotation speed V23 reaches the lower limit in the variable speed range (specifically, 30 rps in stage 1), the electric motor 23 may automatically stop, causing the compressor 22 to stop unexpectedly. As mentioned above, this is because when the rotation speed V23 is at the lower limit, it is likely to exceed the allowable upper limit of the refrigerant pressure used, as stipulated by the specifications, and if this allowable upper limit is exceeded, the electric motor 23 automatically stops to ensure reliability.

As shown in FIG. 5, in step S15 following step S13, the control unit 20 determines whether the refrigerant pressure of the compressor 22 exceeds the allowable upper limit by checking whether the temperature T25 of the condenser temperature sensor 25 is equal to or higher than a predetermined first threshold temperature Tth1 (e.g., 40°C). Since the refrigerant pressure is correlated with the refrigerant temperature (condensation temperature), if the temperature T25 (first threshold temperature Tth1) of the condenser temperature sensor 25 at which the motor 23 automatically stops is determined by a prior test, it can be said that the refrigerant pressure of the compressor 22 exceeds the allowable upper limit at that time. In this embodiment, the first threshold temperature Tth1 is set to 40°C because the motor 23 was definitely stopped when the temperature T25 of the condenser temperature sensor 25 exceeded 40°C in a prior test.

If the temperature T25 of the condenser temperature sensor 25 is equal to or higher than the first threshold temperature Tth1 (YES in S15), the control unit 20 judges whether the rotation speed V23 of the motor 23 is at the lower limit (30 rps, stage 1) (S17). The control unit 20 judges whether the rotation speed V23 is at the lower limit based on the value of the frequency command signal supplied to the inverter circuit 70. If the rotation speed V23 is at the lower limit (YES in S17), the rotation speed V23 is increased to the next higher stage 2 (35 rps) for a predetermined set time (e.g., 90 seconds) (S19). When the rotation speed V23 increases, the allowable upper limit of the refrigerant pressure used in the compressor 22 increases, so that a state in which the allowable upper limit is exceeded (overload state) can be avoided. As a result, the motor 23 does not automatically stop, and the compressor 22 continues to operate stably.

In addition, in step S19, the rotation speed V23 is increased to stage 2 (35 rps) for the set time (90 seconds). This ensures that the rotation speed V23 is not at the lower limit value for the set time, and reliably prevents the electric motor 23 from automatically stopping.

If the temperature T25 of the condenser temperature sensor 25 is less than the first threshold temperature Tth1 (NO in S15), if the rotation speed V23 of the electric motor 23 is not the lower limit value (30 rps) (NO in S17), after step S19 ends, and after step S12 ends, the control unit 20 returns to step S11 again and repeats the above-mentioned control until the cooling operation ends.

<Embodiment 2>
The control of the electric motor 23 by the control unit 20 according to the second embodiment will be described with reference to the flowchart of Fig. 6. The second embodiment differs from the first embodiment in that whether or not the refrigerant pressure used by the compressor 22 exceeds the allowable upper limit is determined based on the temperature T64 of the external temperature sensor 64. In the second embodiment, the same configuration, control, and effects as those of the first embodiment will not be described again.

In the condenser 26, which is an air-cooled heat exchanger, it is generally known that the condensation temperature of the refrigerant during stable operation is correlated with the outside air temperature. In this embodiment, the following relationship is established: temperature T25 of the condenser temperature sensor 25 = temperature T64 of the external temperature sensor 64 + 5°C (constant temperature). Therefore, instead of the condenser temperature sensor 25 in the first embodiment, in the second embodiment, the external temperature sensor T64 is used to indirectly detect the condensation temperature of the condenser 26. More specifically, as shown in FIG. 6, it is determined whether the temperature T64 of the external temperature sensor 64 is equal to or higher than a second threshold temperature Tth2 (e.g., 35°C) (S115).

<Other embodiments>
The present technology is not limited to the embodiments described above and illustrated in the drawings, and for example, the following embodiments are also included in the technical scope of the present technology.

(1) The variable speed range, the number of variable stages, and the speed of each stage of the rotation speed V23 of the electric motor 23 can be changed as appropriate according to the required specifications. In addition, the rotation speed V23 may be configured to be continuously variable.

(2) The condenser temperature sensor 25 may be installed in a location other than the central pipe of the condenser tube 26A as long as it is located in a position where the condensation temperature can be detected. In addition, a temperature sensor other than the condenser temperature sensor 25 or the external temperature sensor 64 may be used as long as it is capable of detecting the condensation temperature of the condenser 26.

(3) In the control shown in Figures 5 and 6, when the rotation speed V23 of the electric motor 23 is the lower limit value in the variable speed range, the rotation speed V23 is increased to avoid a state in which the allowable upper limit value of the refrigerant pressure used in the compressor 22 is exceeded (overload state), but such control can also be applied to cases other than the lower limit value. For example, when the allowable upper limit value of the refrigerant pressure used is specified for each rotation speed V23 of the electric motor 23, control may be performed to increase the rotation speed V23 as long as the rotation speed V23 is not the upper limit value.

(4) This technology can also be applied to cooling storage units other than freezers 10 (e.g., refrigerators), and even to appliances equipped with cooling devices 18 other than cooling storage units (e.g., ice makers).

10: Freezer (cooling storage), 12: Storage body, 18: Cooling device, 20: Control unit, 22: Compressor, 23: Motor, 25: Condenser temperature sensor, 26: Condenser, 26A: Condenser tube, 46: Internal temperature sensor, 64: External temperature sensor, Tth1: First threshold temperature, Tth2: Second threshold temperature, Ts: Set temperature

Claims (6)

A storage body capable of accommodating stored items;
A cooling device for cooling the inside of the storage body, the cooling device having a compressor equipped with a variable speed motor for compressing a refrigerant gas, and a condenser for condensing the refrigerant gas from the compressor;
a temperature sensor capable of detecting a condensation temperature in the condenser;
A control unit that controls the electric motor,
The control unit is
When the temperature detected by the temperature sensor is equal to or higher than a threshold temperature, it is determined whether or not the speed of the electric motor is at a lower limit value within a speed variable range;
The cooling store increases the speed of the motor if the speed of the motor is at the lower limit. The cooling storage facility according to claim 1, wherein the control unit increases the speed of the motor for a predetermined set time when the speed of the motor is at the lower limit value. The speed of the motor is changed in steps;
3. The cooling storage facility according to claim 1, wherein the control unit increases the speed of the electric motor to a next higher speed when the speed of the electric motor is at the lower limit value. An internal temperature sensor is provided to detect the internal temperature of the storage body,
The control unit is
When the inside temperature detected by the inside temperature sensor is equal to or higher than a set temperature, a speed of the electric motor is determined based on a temperature gradient indicating a change in the inside temperature per unit time;
4. The cooling storage facility according to claim 1, further comprising: a step of determining whether the determined speed is equal to or greater than the lower limit value if the detected temperature of the temperature sensor is equal to or greater than the threshold temperature thereafter. the temperature sensor is a condenser temperature sensor provided in a condensation tube of the condenser,
The cooling storage facility according to claim 1 , wherein the control unit determines whether the speed of the motor is at the lower limit value when the temperature of the condenser temperature sensor is equal to or higher than a first threshold temperature. The condenser is an air-cooled heat exchanger,
The temperature sensor is an external temperature sensor that detects an external temperature around the storage body,
The external temperature sensor is capable of indirectly detecting a condensation temperature of the refrigerant during stable operation of the condenser,
The cooling storage facility according to claim 1 , wherein the control unit determines whether the speed of the motor is at the lower limit value when the temperature of the external temperature sensor is equal to or higher than a second threshold temperature.

Images