JPH0399931A - Refrigerant deficiency detecting device for cooling device - Google Patents

Abstract

PURPOSE:To surely detect refrigerant deficiency by detecting the inlet temperature and the outlet temperature of an evaporator respectively, averaging the difference signal between the inlet temperature multiplied by the preset number and the outlet temperature, and comparing the averaged temperature difference signal with the preset value. CONSTITUTION:In a cooling device having a refrigerant circulating path circulating a compressor 51, a condenser 54, a receiver 55, an expansion valve, and an evaporator 53, the first and second thermistors 1A and 1B detecting the inlet temperature and the outlet temperature of the evaporator 53 respectively are provided. The temperature signal obtained by the first thermistor 1A is multiplied by the preset number in an operation amplifier 5A serving as an amplifying means, then it is fed to an operation amplifier 2A serving as a temperature difference calculating means to calculate the difference with the temperature signal detected by the second thermistor 1B. The temperature difference signal is averaged by a smoothing circuit 3A serving as an averaging means, and a refrigerant deficiency signal is generated from a comparator 4A when the averaged temperature difference signal exceeds the preset value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a refrigerant shortage detection device for detecting refrigerant shortage in a cooling device.

[Prior Art] If a cooling device is operated in a state where there is a shortage of refrigerant, not only will the efficiency of cooling become poor, but also problems such as overheating of the compressor and breakdown will occur.

Conventionally, a pressure switch is installed in the refrigerant circulation path to stop the compressor below a certain pressure, but this method requires consideration of pressure fluctuations due to outside temperature, so it is difficult to It can only be detected when the refrigerant is almost completely exhausted.

In order to solve this problem, for example, Nippondenso Publication Technical Report 50-
020 (November 15, 1986), JP-A-61-1
97969 and Japanese Utility Model Application Publication No. 62-43268 disclose a system in which a pair of thermistors is provided in a refrigerant circulation path, and a shortage of refrigerant is detected from a difference signal between temperature signals of these thermistors.

[Problems to be Solved by the Invention] The refrigerant shortage detection using the above-mentioned thermistor is excellent in that it can constantly detect the amount of refrigerant shortage, but when the frost prevention device is activated or the engine speed suddenly decreases, - Since the temperature difference signal fluctuates over time, there is a problem of false detection of refrigerant shortage.

In order to solve this problem, the inventors proposed a refrigerant shortage detection device that first provided an averaging means (Japanese Patent Application No. 63-3).
No. 15381). This device effectively solved the above problem, but in cooling systems that perform evaporator pressure control (EPR), the drop in temperature on the evaporator inlet side is relatively small even when there is a refrigerant shortage. , there were cases where detection could not be performed effectively.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a refrigerant shortage detection device that can reliably detect refrigerant shortage even in a cooling device that controls the pressure of an evaporator.

[Means for Solving the Problems] To explain the present invention in detail, in a cooling device having a refrigerant circulation path connecting a compressor 51, an expansion valve 52, and an evaporator 53, a refrigerant shortage detection device is installed on the inlet side of the evaporator 53. a first temperature detection means IA for detecting temperature; a second temperature detection means IB for detecting the outlet side temperature of the evaporator 53; and a first temperature detection means I
Amplifying means 5A for multiplying the temperature signal obtained from A by a predetermined value;
The amplified temperature signal and the second temperature detection means IB
A temperature difference calculation means 2A calculates the difference between the temperature signals obtained from the above and generates a temperature difference signal, and a means 3A averages the temperature difference signal. It also includes means 4A for issuing a refrigerant shortage signal at certain times.

[Function] According to the device configured as described above, even if the temperature difference signal temporarily fluctuates greatly when the anti-frost device is activated or the engine speed suddenly decreases, the signal averaged by the averaging means 3A will compensate for the fluctuation. is unaffected and therefore no erroneous refrigerant shortage signal is issued.

Since the amplification means 5A amplifies the evaporator inlet side temperature obtained from the first temperature detection means IA by a predetermined time, the amount of change in temperature is also amplified by a predetermined time, and the temperature difference signal changes. Changes in the temperature on the evaporator inlet side can be largely reflected in the evaporator inlet temperature. Therefore, even in an EPR-controlled cooling device in which the inlet side temperature decreases relatively little when there is a refrigerant shortage, it is possible to effectively detect a refrigerant shortage.

[Embodiment] The figure shows an embodiment of the present invention, and the cooling device has a refrigerant circulation path that circulates through a compressor 51, a condenser 54, a receiver 55, an expansion valve 52, and an evaporator 53. Thermistors IA, IB, and IC are provided in the inlet pipe P1 of the evaporator 53, the outlet pipe P2 thereof, and the inlet pipe P3 of the expansion valve 52, respectively. Each thermistor I
A to IC are connected to a power supply through resistors 61, 62, and 63 in series, respectively.

The output voltage of the thermistor IA is directly input to the operational amplifier 2B that constitutes the differential amplifier circuit, and is also input to the operational amplifier 5A that constitutes the non-inverting amplifier circuit, where it is amplified by a predetermined factor to constitute the differential amplifier circuit. It is input to operational amplifier 2A. The outputs of the other thermistors IB and IC are input to the operational amplifiers 2A and 2B, respectively. The amplification factor of the amplification circuit is determined by the ratio of resistors 91.92, and is approximately 2 to 3 times.

An operational amplifier 2A constituting an inverting circuit is connected to the rear stage of the operational amplifier 2A, and its output is input to a smoothing circuit 3A serving as averaging means at the next stage. The smoothing circuit 3A is made up of a resistor 31 and a capacitor 32, and a smoothing circuit 3B having the same structure and made up of a resistor 33 and a capacitor 34 is also provided downstream of the operational amplifier 2B. Each smoothed signal is input to comparators 4A and 4B and compared with constant voltages Va and vb, respectively.

Here, the temperature difference between the inlet pipe P1 and the outlet pipe P2 is
It increases as the amount of refrigerant decreases, and when the amount of refrigerant is normal, it increases.
It reaches its maximum when it decreases to about 0 to 30%. Therefore, the constant voltage Va is set to a value such that the temperature difference signal exceeds this when the amount of refrigerant becomes 50% or less. Further, the temperature difference between the inlet pipe P3 and the inlet pipe P1 becomes suddenly smaller when the amount of refrigerant becomes about 20% or less. Therefore, the constant voltage vb is set to a value such that the temperature difference signal falls below this when the amount of refrigerant becomes equal to or less than the above ratio.

The output of the comparator 4A is input to the set terminal of the flip-flop 71, and the set output of the flip-flop 70 is input to the NAND gate 72. This NAN
The output of a timer 73 is also input to the D gate 72, and the timer 73 is activated by the reset switch 74 or when the power is turned on, and produces an output that remains at the "L" level for a certain period of time.

The output of the NAND gate 72 is input to the next stage NAND gate 75 and also to the reset terminal of the set priority flip-flop 76. The output of the comparator 4B is input to the set terminal of this flip-flop 76. The output of the flip-flop 76 is input to the reset terminal of the next-stage flip-flop 77, and the output of the flip-flop 77 is input to the NAND gate 75.

The NAND gate 75 is connected to the base of a transistor 78, and an alarm lamp 81 and a relay coil 82 are connected to the transistor 78 and are turned on or energized, respectively. A normally closed contact 82a operated by the relay coil 82 is interposed in the power supply line to the electromagnetic clutch 511 of the compressor 51.

The operation of the refrigerant shortage detection device having the above configuration will be explained below.

When there is a sufficient amount of refrigerant, the voltage of the temperature difference signal output from the operational amplifier 2A is low, and the output of the comparator 4A and the output of the flip-flop 71 are at "L" level, N
The output of the AND gate 72 is rH, level.

At this time, the voltage of the temperature difference signal output from the operational amplifier 2B is high, the output of the comparator 4B is at the "L" level, and the output of the flip-flop 77 is at the rH level. Therefore, the output of the NAND gate 75 is at the "J" level, the transistor 78 is non-conductive, and the alarm lamp 81 is turned off.
is off, and the relay coil 82 is in a non-energized state. Therefore, the electromagnetic clutch 511 is excited and the compressor 51 is operated.

In this state, the flow of the refrigerant is temporarily stopped due to the operation of the anti-frost device, for example, and the operational amplifier 2
Even if the voltage of the temperature difference signal of A temporarily drops, or the voltage of the temperature difference signal of the operational amplifier 2B temporarily drops, these voltage fluctuations are absorbed by the smoothing circuits 3A, 3B, and the comparators 4A, The output state of 4B remains unchanged. As a result, the operating state of the compressor can be maintained without false alarms being issued.

When the amount of refrigerant decreases to below 50%, the temperature on the evaporator outlet side rises and the output voltage of thermistor IB increases, and at this time, the temperature on the evaporator inlet side decreases to some extent even under EPR control. The output voltage of thermistor IA becomes smaller.

This output voltage is amplified by the operational amplifier 5A, and the decrease in the output voltage is multiplied and input to the operational amplifier 2A. Therefore, the temperature difference signal calculated by the operational amplifier 2A has a negative value with a sufficiently large absolute value, and the signal voltage obtained by inverting this value exceeds the constant voltage Va.

The comparator 4A outputs a refrigerant shortage signal of "H" level, and the output of the flip-flop 71 becomes rHj level. The above timer output is rH.

Therefore, the outputs of the NAND gates 72 and 75 become "L" level, rH level, and rH level, respectively. In this way, the transistor 78 becomes conductive, the alarm lamp 81 lights up, and the electromagnetic clutch 511 is de-energized and the operation of the compressor 51 is stopped. When the reset switch 74 is operated,
The timer 73 starts, and the timer 73 starts “shu” for a certain period of time.
The level output is issued and the NAND gate 72.75
The output of each is rH.

level becomes "L" level, and the compressor 51 is forcibly operated.

The timer 73 is also activated when the power is turned on to prevent the compressor 51 from being stopped due to erroneous detection of refrigerant reduction in an unstable state when the compressor starts operating.

If the refrigerant leaks heavily and its amount decreases rapidly, the increase in the temperature difference between the thermistors IA and IB will only appear for a short time and may not be detected by the comparator 4A system. Therefore, in such cases, the amount of refrigerant is approximately 20%
When the temperature difference between the thermistor IA and the IC becomes smaller, the temperature difference signal voltage of the operational amplifier 2B becomes constant voltage vb.
below. As a result, a refrigerant shortage signal of "H" level is output from the comparator, and the flip-flop 76 is set and the flip-flop 77 is reset. Therefore, the output of the NAND gate 75 is r)(J
level, the alarm lamp 81 lights up, and the operation of the compressor 51 is stopped.

In this case, short-term operation of the compressor 51 using the reset switch 74 is not possible because there is a high possibility of failure.

In the above embodiment, the thermistor IA is installed at the inlet fin of the evaporator 53, and thermistor IB is installed at the inlet fin of the evaporator 53.
The installation position of the intermediate fin may be closer to the outlet side than the inlet fin. In particular, the temperature of the intermediate fin rises rapidly when the amount of refrigerant drops below a certain value, and the installation position is closer to the outlet side. As the temperature increases, even a slight decrease in the amount of refrigerant causes a rise in temperature. Therefore, by adjusting the attachment position of the thermistor IB to the intermediate fin, it is possible to know the level of decrease in the amount of refrigerant with a good S/N ratio.

Furthermore, the same effect can be obtained by installing the thermistor IC in the intake air path to the evaporator 53.

Although a smoothing circuit is used as the averaging means in the above embodiment, it goes without saying that other circuit configurations may be used.

In the above embodiment, if a circuit is provided to detect the engine speed or the evaporator intake air temperature, and the temperature detection is temporarily stopped when the engine speed is high or the evaporator intake air temperature is high, errors in such cases can be avoided. Detection can be avoided.

[Effects of the Invention] As described above, the refrigerant shortage detection device of the present invention can reliably detect a decrease in the amount of refrigerant without malfunctioning due to the operation of the frost prevention device or the sudden decrease in engine rotation. In particular, refrigerant shortage can be detected satisfactorily in an EPRIII # cooling system in which the temperature drop on the evaporator inlet side is relatively small when there is refrigerant shortage.

Furthermore, the detection level can be set within a wide range.

[Brief explanation of drawings]

The figure is an overall circuit diagram of an apparatus showing an embodiment of the present invention. IA, IB, IC...Thermistor 2A, 2B.
...Operational amplifier (temperature difference calculation means) 3A, 3B.
...Smoothing cycle I ¥1 (averaging means) 4A, 4B...
... Comparator (refrigerant shortage signal transmission means) 5A ... Operational amplifier (amplification means) 51 ...
... Compressor 52 ... Expansion valve 53 ... Evaporator 81 ... Alarm lamp 82 ... Relay coil

Claims (1)

[Claims] In a cooling device having a refrigerant circulation path connecting a compressor, an expansion valve, and an evaporator, a first temperature detection means detects the temperature on the inlet side of the evaporator, and a second temperature detection means detects the temperature on the outlet side of the evaporator. and an amplifying means for multiplying the temperature signal obtained by the first temperature detecting means by a predetermined value, and calculating a difference between the amplified temperature signal and the temperature signal obtained from the second temperature detecting means to generate a temperature difference signal. refrigerant shortage in a cooling system, comprising temperature difference calculation means for emitting a temperature difference signal, means for averaging the temperature difference signal, and means for emitting a refrigerant shortage signal when the averaged temperature difference signal changes beyond a predetermined value. Detection device.