JPH0350471A - Insufficient refrigerant detector device for cooling apparatus - Google Patents

Abstract

PURPOSE:To prevent an insufficient refrigerant signal from being erroneously issued even if a temperature difference signal is temporarily varied by providing means for averaging the temperature difference signal, and means for issuing the insufficient refrigerant signal when the averaged temperature difference signal is changed exceeding a predetermined value. CONSTITUTION:An operational amplifier 2A issues a temperature difference signal corresponding to a temperature difference between an inlet piping P1 and an outlet piping P2. An operational amplifier 2B issues a temperature a temperature difference signal corresponding to a temperature difference between an inlet piping P3 and the inlet piping P1. Smoothing circuits 3A, 3B as averaging means are connected to later stages of the respective operational amplifiers 2A, 2B. Respective smoothed signals are inputted into comparators 4A, 4B where they are compared with predetermined voltages Va, Vb. For example, even though a refrigerant flow is temporarily interrupted owing to activation of a frost prevention device and hence temperature difference voltage from the operational amplifier 2A is temporarily lowered or temperature difference signal voltage from the operational amplifier 2B is lowered, those voltage variations are absorbed by the smoothing circuits 3A, 3B, and hence outputs of the comparators 4A, 4B remain unchanged. Hereby, operator of a compressor is maintained without issuing any erroneous alarm.

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] When an air conditioner is operated with a lack of refrigerant, not only does the efficiency of the air conditioner deteriorate, but also problems such as the compressor overheating and malfunctioning 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
Japanese Patent No. 97969 discloses 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: Detection of refrigerant shortage using the above thermistor is... It is excellent in that it can quantitatively detect the amount of refrigerant shortage, but when the anti-frost device is activated or the engine speed suddenly decreases, the temperature difference signal mentioned above fluctuates temporarily, resulting in the problem of false detection of refrigerant shortage. was there.

The present invention has been made to solve such problems, and an object thereof is to provide a refrigerant shortage detection device that does not cause false detection when the frost prevention device is activated, and can set the refrigerant shortage detection level over a wide range. shall be.

[Means for Solving the Problems] To explain the structure of the present invention using a diagram, in a cooling device having a refrigerant circulation path connecting a compressor 51, an expansion valve 52, and an evaporator 53, the refrigerant shortage detection device according to claim 1 is provided. The first temperature detection stage IA detects the temperature on the inlet side of the evaporator 53, the second temperature detection means IB detects the temperature on the outlet side of the evaporator 53, and the first temperature detection means IA. A temperature difference calculation means 2A that calculates the difference between the temperature signals respectively obtained from the second temperature detection means 1B and generates a temperature difference signal, a thousand steps 3A that averages the temperature difference signals, and It is equipped with a stage 4A that issues a refrigerant shortage signal when the signal changes beyond a predetermined value.

Further, the refrigerant shortage detection device according to claim 2 further includes:
A third temperature detection means IC is provided for detecting the temperature on the inlet side of the expansion valve 52 or the temperature of the intake air of the evaporator 53, and the temperatures obtained from the third temperature detection means IC and the first temperature detection means 1A, respectively, are provided. A temperature difference calculation means 2B that calculates the difference between the signals and issues a temperature difference signal, a means 3B that averages the temperature difference signal, and generates a refrigerant shortage signal when the averaged temperature difference signal changes beyond a predetermined value. Means for emitting 4
It is equipped with B.

Furthermore, the refrigerant shortage detection device according to the third aspect of the present invention is provided with means for detecting the stoppage of the compressor and inhibiting the operation of the averaging means while the compressor is stopped.

Further, the refrigerant shortage detection device according to claim 4 further includes:
means for detecting the rotational speed of an engine that drives the compressor; and means for detecting the intake air temperature of the evaporator; and means for prohibiting the averaging means from operating.

[Function] According to the device according to claim 1, even if the temperature difference signal temporarily fluctuates greatly when the anti-frost device is activated or when the engine speed suddenly decreases, the signal averaged by the averaging means is equal to the above-mentioned signal. It is not affected by fluctuations and therefore no erroneous refrigerant shortage signal is issued.

Further, according to the apparatus according to the second aspect of the present invention, it is possible to prevent the erroneous transmission of the refrigerant shortage signal and to set the refrigerant shortage detection level within a wider range.

Further, according to the apparatus according to the third aspect, even when the compressor is stopped for a relatively long time when the outside temperature is low (approximately 20° C. or less), for example, no erroneous transmission of the refrigerant shortage signal occurs.

According to experiments conducted by the inventors, when the rotational speed of the engine driving the compressor is high or when the intake air temperature during evaporation is high, a refrigerant shortage signal can be issued even if the decrease in refrigerant amount is relatively small. be. However, claim 4
According to the described device, in such a case, the operation of the averaging means is prohibited, thereby preventing erroneous transmission of a refrigerant shortage signal.

[First Embodiment] FIG. 1 shows a first embodiment of the present invention, in which the cooling device includes a compressor 51, a condenser 54, a receiver 55, and an expansion valve 5.
2, and a refrigerant circulation path that circulates through the evaporator 53. And the inlet pipe P1 of the evaporator 53,
Thermistors 1A, IB, and IC are provided in the outlet pipe P2 and the inlet pipe P3 of the expansion valve 52, respectively.

Each thermistor 1A to 1C has a resistance of 6l, 62,
63 in series to the power supply, and these resistors 61 to 63 are connected in series to the power supply.
The voltage at the connection point with 63 is input to operational amplifiers 2A and 2B forming a differential amplifier circuit. The resistance values of the thermistors 1A to IC become smaller as the measured temperature increases, and the operational amplifier 2A outputs a temperature difference signal corresponding to the temperature difference between the inlet pipe P1 and the outlet pipe P2.

Also, from the operational amplifier 2B, the inlet pipe P3 and the inlet pipe P
A temperature difference signal corresponding to a temperature difference of 1 is output.

Smoothing circuits 3A and 3B as averaging means are connected to the latter stage of each of the operational amplifiers 2A and 2B, and each of these smoothing circuits 3A and 3B is constituted by resistors 31 and 33 and capacitors 32 and 34, respectively. . Each smoothed signal is input to comparators 4A and 4B, and constant voltages Va,
It is compared with Vb.

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. Also,
The temperature difference between the inlet pipe P3 and the inlet pipe P1 is determined by the amount of refrigerant being 20
% or less, it suddenly decreases. 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 the flip-flop 71
The set output of the flip-flop 71 is input to the NAND gate 72. This NA
The output of the timer 73 is also input to the ND gate 72,
The timer 73 is activated by the reset switch 74 or by turning on the power, and outputs an output that is at the ``J'' 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 the 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 the rl=J level.
The output of the NAND 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 "H" level. Therefore, the output of the NAND gate 75 becomes "L" level, the transistor 78 is non-conductive, and the alarm lamp 81
is off, and the relay coil 82 is in a non-energized state. Therefore, the electromagnetic clutch is energized and the compressor is operated.

In this state, the flow of refrigerant is temporarily stopped due to, for example, a frost prevention device operating, and the operational amplifier 2
Even if the voltage of the temperature difference signal of A temporarily drops, or even if 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, a false alarm will not be issued, and the operating state of the compressor will be maintained.

When the refrigerant amount decreases to below 50%, thermistor IA,
The temperature difference detected at 1B becomes large, and the temperature difference detected at op amp 2A
The voltage of the temperature difference signal output from
exceed. The comparator outputs a refrigerant shortage signal of r}{J level, and the output of the flip-flop 71 becomes r
H J level.

Since the above timer output is rH, level, NA
The outputs of the ND gates 72 and 75 are at "L" level, respectively.
It becomes "H" level. Thus, the transistor 78 becomes conductive, the warning lamp 8l lights up, and the electromagnetic clutch 511 is de-energized, so that the compressor 51 stops operating.

In this state, if it is absolutely necessary to operate the air conditioner due to extreme heat, etc., operating the reset switch 74 will cause
The timer 73 starts, and the timer 73 outputs “L” for a certain period of time.
level output is issued, and the NAND gates 72 and 75
The outputs of are at the rHJ level and the "L" level, respectively, and the compressor 51 is forced to operate.

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 1B will only appear for a short time and may not be detected by the converter 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.
Plan it out. 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. As a result, the output of the NAND gate 75 becomes rH, the alarm lamp 81 lights up, and the operation of the compressor 51 is stopped.

In this case, short-term operation of the compressor 52 by 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 the thermistor 1B is installed at the inlet fin of the evaporator 53.
The installation position of the intermediate fin may be placed closer to the outlet side than the inlet fin. In particular, the temperature of the intermediate fin rises rapidly when the temperature of the refrigerant drops below a certain value, and the installation position of the intermediate fin 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 1B 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.

[Second Embodiment] By the way, when the 7-burner strike prevention is performed, for example, when the outside temperature drops to about 20°C or lower, the compressor will stop frequently and for a relatively long time, and the averaging circuit in the above embodiment will not work. , it may become impossible to absorb the drop in the temperature difference signal voltage of the operational amplifier.

That is, when the compressor 51 stops and the refrigerant flow is interrupted, the temperature difference detected by the thermistors LA and IB becomes smaller, and the temperature difference signal voltage of the operational amplifier 2A decreases.

If this continues for a relatively long time, the smoothing circuit voltage will gradually decrease,
When the compressor 51 is restarted, unless the refrigerant level falls significantly below 50% and approaches 20 to 30%, the smoothing circuit heavy pressure will not rise and no alarm will be issued.

Further, when the temperature difference signal voltage of the operational amplifier drops due to the compressor stopping, and the smoothing circuit voltage follows this and drops, a problem arises in that an alarm is issued even though there is sufficient refrigerant.

Therefore, in this embodiment, as shown in FIG. 2, an averaging prohibition circuit 9 is provided between each operational amplifier and the comparator.

The above-mentioned averaging prohibition circuit 9 has rH,
Compressor stop detection circuit 9■, which emits a level output and outputs an "L" level output when stopped, and a comparator 9
2. Transistors 931, 932, 941, 942, 9
5, etc., and the l transistors 931 to 934 are
They are connected in parallel in opposite directions and their bases are grounded via the transistor 95 to form switch circuits 93 and 94, respectively, and these switch circuits 93 and 94 are connected to the comparators 2A and 2B and the smoothing circuit 3.
It is connected between A and 3B.

Further, a resistor 96 and a capacitor 97 are connected in series between the output terminal of the stop detection circuit 9l and the ground.
This contact d portion is input connected to the “10” terminal of the comparator 92. A constant voltage Vc generated by resistance voltage division is input to the "1" terminal of the comparator 92.

In this configuration, when the combustor 51 is operating, the output of the stop detection circuit 9 is at the r }{ j level, and the voltage at the "10" terminal of the comparator 92 is "1".
Since the voltage at the terminal becomes higher than Vc, the transistor 95 becomes conductive, and as a result, the transistors 931932, 941, 942 that control the Swiss-Sochi circuits 93, 94 also become conductive, and the temperature difference signal voltage of each operational amplifier 2A, 2B is applied to the smoothing circuits 3A and 3B.

When the compressor 51 stops, the output of the stop detection circuit 9l becomes "L" level, and the "+" of the comparator 92
” terminal voltage becomes lower than the “1” terminal voltage Vc. Therefore, the transistor 95 becomes non-conductive, and accordingly, the transistors constituting each switch circuit 9 also become non-conductive, and the temperature difference signal voltage at this time is changed to the smoothing circuit 3A, 3
B is not applied to the smoothing circuits 3A and 3B, and the voltages of the smoothing circuits 3A and 3B are maintained at the values immediately before the compressor was stopped.

By providing the capacitor 97, it takes a certain amount of time for the "+" terminal voltage of the comparator 92 to exceed the "1" terminal voltage Vc when the compressor 51 is started. Therefore, the temperature difference signal voltage is not applied to the smoothing circuits 3A and 3B when the refrigerant flow is unstable at startup.

If the flow of refrigerant at the time of starting the compressor 5l is sufficiently stable, the capacitor 97 and the comparator 92 can be omitted, and the transistor can be directly activated by the output of the stop detection circuit #I91.

[Third Embodiment] FIG. 3 shows a third embodiment of the present invention, in which an engine rotation speed detection circuit 98 and an evaporator intake air temperature detection circuit are added to the averaging prohibition time 289 in the second embodiment. Nine more have been added.

In other words, according to experiments conducted by the inventors, when the engine rotates at high speed (e.g. 4500 rpm or more) or when the evaporator intake air temperature becomes extremely high (e.g. 60°C or more), the amount of refrigerant decreases slightly. If only this happens, the temperature difference detected by thermistors IA and IB will suddenly increase, or the temperature difference detected by thermistors IA and IC will suddenly decrease, and there is a risk that a refrigerant shortage signal will be erroneously transmitted.

However, in this embodiment, when the engine speed is high,
Alternatively, when the evaporator intake air temperature is high, an "L" level output is generated from the engine speed detection circuit 98 or evaporator intake air temperature detection circuit 99, respectively, the transistor 95 becomes non-conductive, and the temperature difference signal voltage is prohibited from being input to each smoothing circuit 3A, 3B, and erroneous transmission of a refrigerant shortage signal is prevented.

Also, when the outside temperature rises, the thermistors IA and IB mentioned above
The temperature difference detected by the thermistors 1A and 1C tends to increase, and the temperature difference detected by the thermistors 1A and 1C tends to decrease.

Therefore, in FIG. 3, the resistors that generate the reference voltages Va and Vb of the comparators 4A and 4B are thermistors 35 and 36 installed in the outside atmosphere, respectively, and the thermistor 3
5 uses a positive characteristic whose resistance increases as the temperature rises, and the thermistor 36 uses a negative characteristic whose resistance decreases as the temperature rises. As a result, when the outside temperature rises, the reference voltage Va. Vb
rise or fall, respectively, thereby preventing erroneous transmission of a refrigerant shortage signal.

[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. Moreover, the setting range of the detection level is also wide.

[Brief explanation of drawings]

1 to 3 are overall circuit diagrams of devices showing first to third embodiments of the present invention, respectively. 1A, IB. IC... Thermistor 2A, 2B... Operational amplifier (temperature difference calculation means) 3A,
3B... Smoothing circuit (averaging means) 35, 36... Thermistor 4A, 4B... Comparator (refrigerant shortage signal transmitting means) 51... Compressor 52... Expansion valve 53... Evaporator 81. ... Alarm lamp 82 ... Relay coil 9 ... Averaging prohibition circuit (means for prohibiting the operation of the averaging means) 91 ... Compressor stop detection circuit 92 ... Comparators 93, 94 ... Switch circuit 98...Engine speed detection circuit

Claims (4)

[Claims] (1) 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. temperature detection means; temperature difference calculation means for calculating a difference between temperature signals respectively obtained from the first temperature detection means and the second temperature detection means to generate a temperature difference signal; and averaging the temperature difference signals. 1. A refrigerant shortage detection device for a cooling system, comprising: means for generating a refrigerant shortage signal when an averaged temperature difference signal changes beyond a predetermined value. (2) The refrigerant shortage detection device according to claim 1, further comprising a third temperature detection means for detecting the temperature on the inlet side of the expansion valve or the temperature of the intake air of the evaporator.
temperature difference calculation means for calculating the difference between temperature signals respectively obtained from the temperature detection means and the first temperature detection means and generating a temperature difference signal; and means for averaging the temperature difference signals;
A refrigerant shortage detection device for an air conditioner, comprising: means for issuing a refrigerant shortage signal when an averaged temperature difference signal changes beyond a predetermined value. (3) The refrigerant shortage detection device according to claim 1 or 2, further comprising means for detecting stoppage of the compressor and prohibiting operation of the averaging means while the compressor is stopped. Refrigerant shortage detection device. (4) The refrigerant shortage detection device according to any one of claims 1 to 2, further comprising means for detecting the rotational speed of an engine that drives the compressor, means for detecting an intake air temperature of the evaporator, and a means for detecting the rotational speed of the engine that drives the compressor. A refrigerant shortage detection device for an air conditioner, comprising means for inhibiting operation of the averaging means when the number of revolutions exceeds a predetermined number of revolutions or the temperature of the intake air exceeds a predetermined temperature.