JPH01121657A - Temperature controller for cooling machine - Google Patents

Abstract

PURPOSE: To ensure a high temperature control accuracy by providing means for detecting actual quantity of liquid refrigerant stored in a liquid receiver, means for setting a target cooling temperature and a control means. CONSTITUTION: A liquid receiver 16 is provided with a level sensor 34 having a pair of electrodes 30, 32 for detecting the quantity of liquid refrigerant and delivering a level signal indicative of the quantity of liquid refrigerant to a controller 36. The level sensor 34 functions as means for detecting the quantity of liquid refrigerant. Conduction resistance of a reducing valve 18 is regulated such that the actual quantity of liquid refrigerant matches the quantity of liquid refrigerant in the receiver 16 determined based on a target temperature being set by a target temperature setter 44 according to a prestored relationship and the actual cooling temperature. Since the quantity of liquid refrigerant in the receiver 16 is regulated such that a cooling capacity for attaining a target temperature is generated at an evaporator 20, a target temperature is sustained in a room being cooled by the evaporator 20 with a sufficiently high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to a temperature control device for regulating the temperature of a cooler.

BACKGROUND ART One of the important functions necessary for cooling machines used in freezers, refrigerators, air conditioners, etc. is a temperature control function that maintains an arbitrarily set target temperature regardless of load fluctuations. The simplest temperature control device is one in which a thermostat controls the drive of a compressor for compressing a gaseous refrigerant. Normally, a chiller is designed to have a capacity that corresponds to the maximum load required of it, and the cooling capacity becomes excessive during normal use, so the thermostat-based temperature control device described above cannot provide sufficient temperature control accuracy. do not have.

In contrast, by changing the refrigerant flow resistance of a pressure reducing device that is placed between the condenser and evaporator and reduces the pressure of the refrigerant supplied to the evaporator, the target temperature can be achieved by matching the load and cooling capacity. There is temperature control that you try to maintain. For example, a pressure-controlled pressure reducing valve (pressure-controlled expansion valve) that provides flow resistance so that the internal pressure of the evaporator reaches a predetermined pressure, or a saturation temperature T that corresponds to the outlet pressure of the evaporator may be installed. The liquid temperature T, or the difference from the evaporator temperature (T, -'rt
) In other words, a temperature-controlled pressure reducing valve (temperature-controlled expansion valve) that provides flow resistance so that the superheat temperature remains constant, or in other words, the amount of liquid refrigerant in the evaporator remains constant. They may be set up. However, in the former pressure-controlled expansion valve, the amount of liquid (distribution of refrigerant) in the evaporator is not properly controlled, so when the load increases, the liquid refrigerant evaporates and the evaporator becomes full of heated steam. When the cooling capacity decreases and the load decreases, the inside of the evaporator becomes filled with liquid refrigerant, which may lead to an accident in which the compressor inhales liquid refrigerant. In addition, the latter temperature-controlled expansion valve is effective in lowering the temperature, but in raising the temperature, the set temperature must be maintained unless it is used in conjunction with compressor rotation speed control or hot gas bypass control. I couldn't. In this case, if the rotational speed of the compressor is constant, the suction amount is proportional to the refrigerant density, so the cooling capacity is determined by the evaporation temperature.

Problems to be Solved by the Invention For this reason, during pull-down with a large cooling load, the temperature is lowered at maximum capacity, and when the cooling temperature reaches the target temperature, the rotation speed of the compressor is gradually lowered or stopped by switching the number of poles. When the cooling temperature reaches the target temperature, part of the hot gas on the discharge side of the compressor is returned to the suction side via the bypass passage, and the amount is controlled to match the cooling amount in the evaporator with the cooling load. A device that maintains a target temperature by controlling the temperature is being considered. However, this device had the disadvantage of increasing its scale and not being able to perform fine temperature control.

In addition, it is conceivable to continuously adjust the rotational speed of the compressor using an inverter circuit, and also adjust the flow resistance of the refrigerant supplied to the evaporator using a temperature-controlled expansion valve. frequency is 30
Since the temperature does not drop below about Hz, there are cases where sufficient temperature control accuracy cannot be obtained due to excessive cooling capacity.

Means for Solving the Problems The inventor of the present invention has conducted various studies against the background of the above-mentioned circumstances, and has developed a receiver provided between the condenser and the evaporator to send liquid refrigerant to the evaporator. In the liquid container, there is a gas-liquid mixture of refrigerant between the liquid refrigerant in the bottom layer and the gas refrigerant in the top layer, and the gas-liquid interface is not clear, and the liquid refrigerant is supplied from the receiver to the evaporator. The cooling capacity increases by increasing the proportion of liquid refrigerant in the liquid receiver. Therefore, if the flow resistance in the pressure reducing device is controlled so that the amount of liquid refrigerant in the liquid receiver corresponds to the target temperature, the evaporator It has been discovered that the temperature can be suitably controlled by changing the proportion of liquid in the refrigerant supplied to the refrigerant. The present invention has been made based on the above findings.

That is, the gist of the present invention is to provide a condenser that condenses a vaporized refrigerant by releasing heat, an evaporator that absorbs heat by vaporizing a liquid refrigerant, and a depressurizer that reduces the pressure of the refrigerant sent from the condenser to the evaporator. J, z for a type of chiller equipped with a liquid refrigerant receiver disposed between the condenser and the depressurizer to receive the liquid refrigerant, and for controlling the cooling temperature of the chiller. A temperature control device comprising: (al) liquid refrigerant amount detection means for detecting the actual amount of liquid refrigerant stored in the liquid receiver; (bl) target temperature setting means for setting a target temperature for cooling; (C) determining the target amount of liquid refrigerant to be stored in the liquid receiver based on the target temperature and the actual cooling temperature from a predetermined relationship in order to obtain the target temperature; and control means for controlling the flow resistance of the pressure reducing device so that the actual amount of liquid refrigerant matches the target amount of liquid refrigerant.

Operation and Effect of the Invention By doing this, the amount of liquid refrigerant in the liquid receiver determined from the pre-stored relationship corresponding to the target temperature and the actual cooling temperature matches the actual amount of liquid refrigerant. Since the flow resistance in the pressure reducing device is adjusted, the amount of liquid refrigerant in the liquid receiver is adjusted so that the cooling capacity to obtain the target temperature is generated in the evaporator, and the room cooled by the evaporator is sufficiently cooled. The target temperature is maintained with high accuracy. Therefore, depending on the cooling load, the rotation speed of the compressor can be gradually lowered or stopped by switching the number of poles, or a part of the hot gas on the discharge side of the compressor can be recirculated to the suction side via a bypass passage. Since there is no need to control the amount, the equipment does not become large (and high temperature control accuracy can be obtained.In addition, the inverter circuit continuously adjusts the rotation speed of the compressor and Since there is no need to adjust the flow resistance of the refrigerant supplied to the evaporator using the temperature control expansion valve, there is no possibility of excessive cooling capacity due to the restriction of the control range in the inverter circuit, which also improves temperature control accuracy. will not be damaged.

EXAMPLE Hereinafter, an example of the present invention will be described in detail based on the drawings.

In FIG. 1, a compressor 10 is equipped with an AC motor (not shown), and compresses and discharges the refrigerant it sucks in.
The thus compressed refrigerant (hot gas) is sent under pressure to the condenser 12. The condenser 12 is a type of heat exchanger, and is constantly blown with cooling air by a continuously rotating fan 14 to cool and liquefy the compressed refrigerant. The refrigerant thus liquefied by the condenser 12 is separated into gas and liquid in the receiver 16, and the liquid refrigerant is supplied to the evaporator 20 through the pressure reducing valve 18.

As shown in FIG. 2, the liquid receiver 16 includes an airtight tank 22, a manual port 24 that communicates with the condenser 12 and opens at the top of the tank 22, and a certain height from the bottom of the tank 22. The raised cylindrical projection 26 and the evaporator 2
0 and an output port 28 that opens at the upper end of the cylindrical projection 26, and separates the gas refrigerant into the upper layer and the liquid refrigerant into the lower layer according to the density difference among the refrigerant flowing in from the input port 24, and separates the refrigerant into the upper layer and the liquid refrigerant into the lower layer. The liquid refrigerant is delivered beyond the cylindrical projection 26. This liquid receiver 16 is provided with a level sensor 34 including a pair of electrodes 30 32 for detecting the amount of liquid refrigerant, and a level signal indicating the amount of liquid refrigerant is supplied to the control device 36 . In this embodiment, this level sensor 34 functions as liquid refrigerant amount detection means.

In addition, in the liquid receiver 16, there is a region where the boundary between the liquid refrigerant and the gas refrigerant is in a gas-liquid mixed state with air bubbles mixed in, so it is unclear. The density increases and the proportion of liquid refrigerant increases.

Therefore, when level a in FIG. 2 is detected by the level sensor 34, almost no liquid refrigerant is sent to the evaporator 20, but liquid refrigerant is sent to the evaporator 20 as it passes through level b and approaches level C. The percentage of

The pressure reducing valve 18 is for applying flow resistance to the refrigerant compressed to a relatively high pressure to reduce the pressure thereof, and is configured similarly to a well-known electromagnetic on-off valve.

That is, the pressure reducing valve 18 is turned on and off according to commands from the control bag RFI 36, and a flow resistance corresponding to the duty ratio is applied to the liquid refrigerant, and the flow rate of the liquid refrigerant is controlled. When the pressure is reduced by the pressure reducing valve 18, the liquid refrigerant vaporizes in the evaporator 20 and takes away the heat of vaporization. The evaporator 20 is a type of heat exchanger provided in the freezer compartment 38, and uses the heat of vaporization of the liquid refrigerant to cause the fan 40 to
The air sent into the freezer compartment 38 is cooled. This cooling temperature T is detected by a temperature sensor 42 provided within the freezer compartment, and a temperature signal indicating the temperature is also supplied to the control device 36.

The control device 36 that functions as a control means in this embodiment is a microcomputer equipped with a CPU, ROM, and RAM (not shown), and processes the level signal according to a program stored in the ROM in advance. In order to obtain the target temperature T0 in the freezer compartment 38, which is set by the zero temperature setting device 44, which functions as a target temperature setting means,
The opening degree of the pressure reducing valve l8, that is, the flow resistance is controlled.

The operation of this embodiment will be explained below.

For example, assume that when the temperature inside the freezer compartment 38 is 25° C., the target temperature setter 44 is operated to set the target temperature T0 of -10° C., and the compressor IO and the fan 14.40 are started to operate. The control device 36 determines the target liquid refrigerant i H in the liquid receiver 16 based on the target temperature T0 and the actual internal temperature T in the freezer compartment 38 from the relationship shown in the following equation (1) stored in the ROM in advance. ”.In addition, (in Equation 11, Δt is the sampling time, ΔT is the decreasing temperature at the sampling time Δt (if it decreases, it is a positive value), and k
1 and 2 are constants, and HL and Hu are the lower and upper limits of the amount of liquid in the liquid receiver 16.

H” = に+ (, T To) kzΔT/Δt
・ ・ ・(1) However, Ht: 5H"≦Hu Since the difference between the target temperature T0 and the actual temperature T is large at startup, the first term in the above equation +1) becomes large, and (1)
The target liquid refrigerant amount H1 determined by the formula increases. In this case, since the difference between the target amount H'' of liquid refrigerant in the liquid receiver 16 and the actual amount H of refrigerant is large, the duty ratio of the pressure reducing valve 18 is controlled to quickly bring them into agreement. The flow resistance is increased.As a result, the liquid level of the liquid refrigerant in the liquid receiver 16 is raised to the upper limit value Hu, so that a large amount of liquid refrigerant is exclusively supplied from the liquid receiver 16 to the evaporator 20 through the pressure reducing valve 18. As a result, the inside of the freezer compartment 38 is rapidly cooled at maximum capacity.

Next, if the actual temperature T in the freezer compartment 38 approaches the target temperature T0 and drops to, for example, about -8°C, the difference between the target liquid refrigerant amount H8 and the actual refrigerant IH becomes relatively small. , the first term of equation (1) is relatively reduced, and the target liquid refrigerant IJH" is determined to be smaller than before. Therefore, the flow resistance of the pressure reducing valve 18 is made smaller than before. As a result, the actual liquid amount H in the liquid receiver 16 is made to match the target liquid refrigerant amount H'', and the actual liquid amount H in the liquid receiver 16 becomes smaller than the upper limit Hu (H< Hu).
. As a result, liquid refrigerant with a high gas mixture rate is supplied to the evaporator 20, and the cooling capacity of the evaporator 20 is reduced. The temperature inside is maintained.

Here, the second term of the +11 equation is a damping term, which becomes larger as the cooling load is lighter and the temperature drop is faster, and the target liquid refrigerant amount H8 in the liquid receiver 16 quickly decreases. On the other hand, the heavier the cooling load and the slower the temperature drop, the smaller the attenuation term becomes, so the target liquid refrigerant amount H'' decreases after the actual temperature T in the freezer compartment 38 sufficiently approaches the target temperature T0. Therefore, temperature can be stably maintained within a small control error range while suppressing overshoot.

Also, for example, when the target temperature T0 is revised upward, the temperature T in the freezer compartment 38 may be lower than the target temperature T for some reason.
When the temperature is lower than 0 and the temperature is decreasing, the actual liquid amount H in the liquid receiver 16 reaches the lower limit value H (H=H).
11) Therefore, the gas refrigerant is exclusively supplied to the evaporator 20, and the cooling capacity becomes the lowest, and the temperature of the evaporator 20 starts to rise, and the temperature T in the freezer compartment 38 rises to reach the target temperature T0. .

Here, the pressure reducing valve 18 of this embodiment is turned on and off by the control device 36, and the on time is fixed at 0.3 seconds, and the off time is variable.

The off time is the actual liquid refrigerant fiH in the liquid receiver 16.
When the amount of liquid refrigerant exceeds the target liquid refrigerant amount H'', it ends and moves on to the next on-time, after which on-off is repeated.For this reason, the temperature of the evaporator 20 immediately after startup is high and the amount of evaporation is low. In a state where the temperature is high, the off time is extremely short, and as the temperature of the evaporator 20 becomes lower, the off time gradually becomes longer, to about 3 seconds at around -10°C. The temperature inside the freezer compartment 38 is determined in synchronization with time or cycle period (quantum on time during off time).

As described above, according to this embodiment, the pressure is reduced so that the target amount of liquid refrigerant in the liquid receiver 16, which is determined according to the target temperature from the pre-stored relationship, matches the actual amount of liquid refrigerant. Valve 1
Since the flow resistance in the liquid refrigerant 8 is adjusted, the amount of liquid refrigerant in the receiver 16 has a cooling capacity sufficient to obtain the target temperature.
The temperature within the freezer compartment 38, which is cooled by the evaporator 20, is maintained at a target temperature with sufficiently high accuracy. Therefore, depending on the cooling load, the rotation speed of the compressor 10 can be gradually lowered or stopped by switching the number of poles, or a part of the hot gas on the discharge side of the compressor 10 can be returned to the suction side via the bypass passage. Since it is not necessary to control the temperature while controlling the amount, the device does not become large and complicated, and high temperature control accuracy can be obtained. In addition, there is no need to continuously adjust the rotation speed of the compressor using the inverter circuit, and there is no need to adjust the flow resistance of the refrigerant supplied to the evaporator using the temperature control expansion valve. Since the cooling capacity does not become excessive, temperature control accuracy is not impaired in this respect as well.

Further, according to this embodiment, since the compressor 10 is operated continuously, noise and vibration associated with turning on and off the compressor IO are eliminated, and there are advantages that power consumption is reduced. - Although one embodiment of the present invention has been described above based on the drawings, the present invention can also be applied to other aspects.

For example, in the above-described embodiment, an electromagnetic on-off valve that is driven on and off is used as the pressure reducing valve 18, but a linear solenoid electromagnetic valve that is controlled to an opening degree that corresponds to a driving voltage may also be used.

In addition, in the above-mentioned embodiment, when making the actual liquid refrigerant IH match the target liquid refrigerant amount H1 determined by equation (1), the proportional operation amount proportional to their deviation (H"-H) is In addition, a differential vibration amount proportional to the differential value of the deviation (H"-H) or an integral operation amount proportional to the integral value of the deviation (H"-H) may be added as necessary.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating the configuration of an embodiment of the present invention. FIG. 2 is a diagram showing the configuration of the liquid receiver shown in FIG. 1. 12: Condenser 16: Receiver 18: Pressure reducing valve (pressure reducing device) 20: Evaporator 34 Ni-level sensor (refrigerant amount detection means) 36: Control device (control means)

Claims (1)

[Scope of Claims] A condenser that condenses a vaporized refrigerant by heat radiation, an evaporator that absorbs heat by vaporizing a liquid refrigerant, a pressure reducing device that reduces the pressure of the refrigerant sent from the condenser to the evaporator, and the like. A temperature control device for controlling the cooling temperature of the cooler in a type of cooler including a liquid receiver disposed between a condenser and a pressure reducing device to receive liquid refrigerant, the temperature control device comprising: Liquid refrigerant amount detection means for detecting the actual amount of liquid refrigerant stored in the liquid container; Target temperature setting means for setting a target cooling temperature; and Based on a predetermined relationship to obtain the target temperature. A target amount of liquid refrigerant to be stored in the liquid receiver is determined based on the target temperature and the actual cooling temperature, so that the actual amount of liquid refrigerant stored in the liquid receiver matches the target amount of liquid refrigerant. A temperature control device for a cooler, comprising: a control means for controlling the flow resistance of the pressure reducing device.