JPH0565779B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a refrigerant flow rate measuring device for measuring the flow rate of refrigerant flowing through a refrigeration cycle.

[Background of the invention]

As a refrigerant flow measuring device for refrigeration cycle
As shown in Section 3.2.2. "Refrigerant flowmeter method" of Annex 1 of JISB8615-1979, a turbine flowmeter is installed between the condenser and the expansion valve to directly measure the flow rate of high-pressure liquid refrigerant. What is being measured is known.

However, devices that directly measure the flow rate of refrigerant, such as turbine-type metering meters, are large and have moving parts, making them less reliable for long-term use or under conditions of use that are subject to vibrations. It had the disadvantage of being insufficient, and was used only in places where space was not an issue, such as test equipment, and where it was used infrequently and where the usage conditions were mild.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a refrigerant flow rate measuring device for a refrigeration cycle that is small in size, has a long device life, and can be used even under severe usage conditions.

[Summary of the invention]

The present invention is the Transactions of the Japan Society of Mechanical Engineers (Part 2), Volume 34.
As shown on page 92 of No. 257 (S43-1), we focused on the fact that the flow rate of fluid can be calculated based on the opening degree of a valve installed in the middle of a pipe and the fluid pressure difference upstream and downstream of that valve. means for detecting the opening degree of the expansion valve of the cycle; pressure detection means for detecting the refrigerant pressure on the upstream side of the expansion valve; pressure detection means for detecting the refrigerant pressure on the downstream side of the expansion valve; and both pressure detection means. A refrigerant flow measuring device is constructed by calculating the differential pressure from the output of the differential pressure, and calculating the refrigerant flow rate from the product of the square root of the differential pressure and the output of the expansion valve opening detection means, thereby achieving the above-mentioned purpose. The goal is to achieve the following.

The present invention will be specifically described below based on an embodiment shown in the drawings.

This embodiment is an application of the present invention to an air conditioner for automobiles disclosed in Japanese Patent Publication No. 56-16353.

The compressor 1 is rotationally driven by transmitting the rotational force of the engine 30 through the electromagnetic clutch 1a.

The high-temperature, high-pressure gas-liquid mixed refrigerant compressed by the compressor 1 is cooled by the condenser 2 and becomes a high-pressure liquid phase refrigerant.

After the refrigerant is separated into gas and liquid in the liquid tank 3, only the liquid refrigerant is taken out.

When this liquid medium passes through the valve part of the expansion valve 4, it is adiabatically expanded and becomes a low-pressure mist refrigerant that is easily vaporized.

The low-pressure mist refrigerant absorbs heat in the evaporator 2, vaporizes, and returns to the compressor 1.

A thermistor 10 attached to the refrigerant pipe on the inlet side of the evaporator 5 detects the temperature of the refrigerant on the evaporator inlet side.

A thermistor 10 attached to the refrigerant pipe on the outlet side of the evaporator 5 detects the temperature of the refrigerant on the outlet side of the evaporator.

When passing through the evaporator 5, the refrigerant exchanges heat with the surrounding air and is superheated. If the heat load on the air side is large, the degree of superheating is large, and if the heat load is small, the degree of superheating is small.

Therefore, if the flow rate of the refrigerant is controlled so that the degree of superheating of the refrigerant at the outlet of the evaporator reaches an optimal value determined by the properties of the refrigerant, the capacity of the heat exchanger, etc., it is possible to operate the refrigeration cycle efficiently according to the heat load. Become.

In this embodiment, as shown in Japanese Patent Publication No. 56-16353, the degree of superheat is calculated from the refrigerant temperatures T ₁ and T ₂ at the entrance and exit of the evaporator, and based on that, the ON--
The refrigerant flow rate is controlled by controlling the OFF duty (ratio of valve opening time to valve closing time).

As shown in Japanese Patent Publication No. 56-16353, the refrigerant temperatures T ₁ and T ₂ at the inlet and outlet of the evaporator and the degree of superheating SH of the refrigerant at the outlet of the evaporator
The correlation with is approximated by the following equation.

SH=(T ₂ − T ₁ )+ΔT ……(1) Here, ΔT is the correction value for the pressure loss occurring inside the evaporator. For example, if ΔT=3.25−3/40T ₁ ……(2) Experiments have confirmed that it is good.

The output signals of the thermistors 10 and 11 are sent to the control circuit 1.
The signal is input to the differential amplifier 15a of No. 5.

The differential amplifier 15a outputs a voltage signal _VSH according to the difference between the outputs of both thermistors.

The degree of superheat setting circuit 15b sets the degree of superheat in a range of 5 to 10 degrees according to the operating state of the refrigeration cycle, and outputs a voltage output signal V _SHO according to the set degree of superheat.

The operating state of the refrigeration cycle includes the rapid acceleration/deceleration state of the compressor, the pressure drop in the evaporator, whether or not the cycle is started, the discharge gas temperature Td of the compressor, etc.

In an automobile air conditioner, the compressor is rotationally driven by the engine, so the rotation speed of the compressor is determined regardless of the magnitude of the heat load. If the rotational speed change is smooth, the change in the refrigerant flow rate due to the change in the compressor rotational speed will appear as a gradual change in the degree of superheat, and the expansion valve opening degree control based on proportional-integral calculation will follow this. On the other hand, a sudden change in the refrigerant flow rate due to a change in the rotational speed of the compressor when the engine suddenly accelerates or decelerates causes a sudden change in the degree of superheating. However, since a proportional-integral calculation is used to control the opening degree of the expansion valve, an integral term acts, and the change in the opening degree of the expansion valve cannot follow this sudden change in the degree of superheat. For this reason, when the engine suddenly accelerates or decelerates, insufficient cooling or excessive cooling may occur.

Therefore, during such a transient operating state, it is necessary to correct the expansion valve opening control signal based on the degree of superheating according to the degree of acceleration/deceleration.

Also, inside the evaporator, liquid refrigerant and gaseous refrigerant after vaporization coexist, and depending on where the boundary is, even if the temperature difference between the entrance and exit of the evaporator is the same, the actual degree of superheating will be simply the above temperature. It is necessary to correct for the degree of superheating based on the difference. This is generally called pressure loss and is explained in detail in Japanese Patent Publication No. 56-16353. This pressure drop correction value can be approximated as a linear function of the temperature T ₁ at the inlet of the evaporator, for example, the above equation (2)
It is indicated by.

Furthermore, immediately after the cycle is started, the refrigerant at the evaporator inlet and outlet has the same physical properties, so there is no temperature difference. In this state, the differential amplifier 15a which calculates the degree of superheat from the outputs of the thermistors 10 and 11 outputs an output with a degree of superheat of zero. When the degree of superheat is a small value such as zero, the expansion valve is controlled in the valve closing direction. Therefore, the expansion valve, which was closed before activation, attempts to maintain its closed state, resulting in a malfunction in which the valve does not open forever.
For this reason, as shown in Japanese Patent Publication No. 56-16353, it is necessary to forcibly open the expansion valve at a predetermined on/off time ratio at startup, and to provide an output that forcibly opens the valve at startup. .

Thus, the superheat degree setting circuit 15b outputs a superheat degree setting signal that takes into account the correction signal CN corresponding to the degree of acceleration/deceleration of the compressor, the pressure loss correction signal, and the forced valve opening signal SS at startup.

Furthermore, if the compressor discharge gas temperature becomes abnormally high, it is necessary to fully open the expansion valve to lower the discharge gas temperature, regardless of the expansion valve opening signal, to prevent compressor seizure and cycle breakdown. There is. For this reason, when such an abnormally high temperature occurs, the arithmetic circuit 15
A fully open signal is output from b.

A calculation circuit 15c calculates the deviation ΔV between the set superheat degree signal V _SHO set by the superheat degree setting circuit 15b and the superheat degree signal V _SH based on the deviation of the temperature at the entrance and exit of the evaporator 5.
Performs a proportional integral calculation and outputs the result as a voltage signal _VX .

The output circuit 15d generates an ON-OFF duty signal of the expansion valve based on the output voltage signal _VX of the arithmetic circuit 15c.
Outputs V _O and turns the expansion valve ON and OFF using the output V _O
The deute is controlled to control the refrigerant flow rate so that the actual superheat degree V _SH becomes the set superheat degree V _SHO .

In this embodiment, the expansion valve 4 is composed of an ON-OFF solenoid valve shown in Japanese Patent Publication No. 56-16353, and the electromagnetic drive unit 4
a and a valve part 4b operated by the valve part 4b. Its operation is as shown in Japanese Patent Publication No. 56-16353.

Next, measurement of the refrigerant flow rate will be explained.

In the field of refrigeration cycles, Hitachi Review (VOL.53.No.
5, 1971, p. 447, it is well known that the flow rate of the refrigerant passing through the expansion valve is given by the following equation.

Q=CA√( _1-0 ) ₁ (Kg/s)...(3) Here, C: Refrigerant flow coefficient ₍ constant) A: Opening area of expansion valve ( ^m2 ) _P1 : Inlet of expansion valve Pressure (Kg/ ^m2 ) _P0 : Expansion valve outlet pressure (Kg/ ^m2 ) r: Refrigerant density at the expansion valve inlet (Kg/ ^m2 ) Therefore, in the present invention, these quantities are detected directly or indirectly. A means for converting the refrigerant into an electrical signal is provided, and a calculation means for calculating the flow rate Q from the electrical signals indicating these various quantities is provided in the control circuit of the refrigeration cycle, so that the refrigeration cycle itself has a function of measuring the refrigerant flow rate.

A specific example will be explained in detail below based on FIG.

The expansion valve opening area calculation circuit 18a can be constructed from a well-known function generation circuit.

The opening area of the expansion valve is given by the following formula in the case of an ON-OFF valve.

A ₁ = A ₀ × T _d ...(4) However, A ₀ : Opening area when fully opened (m ³ ) T _d : Ratio of opening time in one opening/closing cycle of the valve (%) A ₀ is measured in advance. It is a fixed value.

T _d is uniquely determined as a value corresponding to the output voltage V _X of the arithmetic circuit 15c.

Therefore, equation (4) can be transformed as follows.

A _{1 =} A ₀ ×K ₁・V _X = (A ₀・K ₁ )× _V It is configured to generate a signal voltage V _a that is the voltage V _X multiplied by (A ₀ · K ₁ ).

The inlet pressure detection means of the expansion valve is the liquid tank 3.
Temperature sensor 1 such as a key mister installed in the gas phase of
2, and a temperature-pressure conversion circuit 18b.

The temperature-pressure conversion circuit 18b includes a well-known function generation circuit.

Considering that liquid refrigerant and gas refrigerant coexist in the liquid tank 3, it can be said that the gas refrigerant temperature trg in the gas phase part in the liquid tank 3 is equal to the saturation temperature _ts2 .

It is well known that the saturation characteristics of a refrigerant (Freon R12) are shown as the solid line A in FIG. 3, and once the type of refrigerant is specified, the saturation pressure relative to its saturation temperature can be determined from this characteristic diagram.

Therefore, if the characteristics of the function generating circuit of the temperature-pressure conversion circuit 18b are made to match the saturation characteristics of this refrigerant, the temperature will be adjusted according to the output voltage of the thermistor 12 corresponding to the saturation temperature of the gas phase refrigerant in the liquid tank 3. - A voltage signal V _pvi corresponding to the saturation pressure of the gas phase refrigerant in the liquid tank 3 can be output from the pressure conversion circuit 18b.

Here, the pressure loss ΔP _rv in the pipe between the liquid tank 3 and the expansion valve 4 is generally negligible.

However, if the piping is routed for a long time, it is necessary to measure or calculate the pressure loss therein in advance and correct the characteristics of the function generating circuit based on it.

The outlet pressure detection means of the expansion valve includes a thermistor 10 for detecting the refrigerant temperature at the inlet of the evaporator 5, and a temperature-pressure conversion circuit 18c.

The temperature-pressure conversion circuit 18c also includes a well-known function generation circuit.

As is well known, the gas-liquid mixture is in a saturated state from the outlet of the expansion valve 4 to the inlet of the evaporator 5. Therefore, similarly to the detection of the expansion valve inlet pressure P _V1 , by setting the characteristics of the function generation circuit to correspond to the refrigerant saturation characteristics shown in Figure 3, it is possible to detect the thermistor corresponding to the evaporator inlet saturation temperature of the refrigerant. According to the output voltage of 10, the temperature-pressure conversion circuit 18c can output a voltage signal V _PVO corresponding to the saturation pressure P _VO of the refrigerant at the inlet of the evaporator 5 .

Here, the pressure loss ΔP _V-0 in the pipe from the expansion valve 4 to the evaporator 5 is even smaller than the pressure loss ΔP _rv from the liquid tank 3 to the expansion valve, and can be almost ignored. This means that the expansion valve 4 is generally placed inside a unit case that houses the evaporator 5.
This is because they are in the same atmosphere and the length of the piping between them is extremely short. Therefore, the refrigerant saturation pressure at the evaporator 5 inlet can be regarded as the refrigerant saturation pressure at the expansion valve 4 outlet.

However, in order to detect the pressure in this part more precisely, this does not prevent measuring the pressure loss in this part and correcting the characteristics of the function generating circuit of the temperature-pressure conversion circuit 18c.

The output signal of the thermistor 12 is further input to a temperature-density conversion circuit 18d.

The temperature-density conversion circuit 18d can also be constructed from a well-known function generation circuit.

The refrigerant at the inlet of the expansion valve 4 is a liquid, and its density has a correlation with the saturation temperature of the refrigerant at that portion as shown in FIG.

As mentioned above, if the pressure loss can be ignored, the saturation temperature of the refrigerant at the expansion valve inlet valve is the same as that of the liquid tank 3.
It can be considered that the temperature of the refrigerant in the gas phase is the same as that of the gas phase within.

Therefore, if the characteristics of the function generating circuit constituting the temperature-density conversion circuit 18d are made to match the characteristics shown in FIG. expansion valve 4
A voltage signal output V _r corresponding to the inlet density γ ₁ can be obtained.

The refrigerant flow rate calculation circuit 18e can be configured with a well-known microcomputer or A/D converter.

Expansion valve opening area calculation circuit 18, temperature-pressure conversion circuits 18b, 18c, and temperature-density conversion circuit 18
The respective outputs V _a , V _pvi , V _pvp and V _r from the refrigerant flow rate calculation circuit 18e are converted into digital values by the A/D converter in the refrigerant flow rate calculation circuit 18e, and then sent to the microcomputer.
Stored in RAM.

The calculation flow for executing equation (3) is programmed in the ROM of the microcomputer.
The various values stored in the RAM are read out at predetermined intervals, and the refrigerant flow rate is calculated according to the calculation flow.

The calculation result is D/A converted and the refrigerant flow rate signal V _G
is output as

In this embodiment, this refrigerant flow rate signal V _G is used as one element of pressure loss value calculation in order to improve the accuracy of the pressure loss correction signal used for setting the degree of superheat.

Since the pressure loss value changes quadratically according to the refrigerant flow rate, if the pressure loss value is corrected according to the refrigerant flow rate signal V _G , it can be calculated using the formula disclosed in Japanese Patent Publication No. 56-16353. The pressure loss value can be determined with much higher accuracy.

This refrigerant flow rate signal can be further utilized for the following value calculations and determinations.

(1) Detection of refrigerant leaks The flow rate G _c of the refrigerant discharged from the compressor is given by the time equation where the rotation speed of the compressor is N, the volumetric efficiency of the compressor is η _V , and the specific volume of the compressor is V. It will be done.

G _e = K _c・N・η _V /V ...(6) (However, K _c is a constant) By the way, the volumetric efficiency of the compressor η _V is determined by the rotation speed N of the compressor and the pressure inlet and outlet of the expansion valve P _vi , P It is known that it is given as a function of _vp .

Furthermore, the specific volume v of the compressor is the pressure P _ve at the outlet of the expansion valve
It is known that it is given as a function of .

Therefore, the flow rate of refrigerant discharged from the compressor G _e
is the rotation speed N of the compressor, the pressure P _vi at the expansion valve inlet and outlet,
P is given as a function of _vp .

The thus obtained refrigerant flow rate G _e passing through the compressor is compared with the refrigerant flow rate Q passing through the expansion valve, and when the preset relationship between the two breaks down, for example, Q
When it becomes G _e, it is determined that the refrigerant is leaking.

(2) Calculation of cooling power The cooling power Y of the refrigeration cycle is given by the following formula.

Y=Q(i ₁ − i ₂ ) where i ₁ : Enthalpy at the evaporator input part i ₂ : Enthalpy at the evaporator outlet part However, the enthalpy i ₁ at the evaporator input part is given as a function of the temperature T ₂ at the evaporator outlet. Since the enthalpy i ₂ at the evaporator outlet is given as a function of the expansion valve inlet pressure P _vi , the cooling power Y can be calculated from these values.

The calculated cooling force Y can be used to directly or indirectly perform various controls on the air side, such as the opening degree of the air mix door, the rotational speed control of the blower, mode switching, etc.

According to this embodiment described above, the pressure at the inlet and outlet of the expansion valve is converted from the temperature at the inlet of the evaporator and the temperature at the gas phase of the liquid tank, which have a correlation with these, so an expensive pressure sensor is used. This eliminates the need for an inexpensive flow rate measuring device.

Furthermore, since the thermistor for detecting the refrigerant temperature at the outlet of the expansion valve is also used as the thermistor attached to the inlet of the evaporator for measuring the degree of superheat, the number of thermistors can be further reduced.

Next, modified examples and applied examples of the present invention will be explained.

(1) Although the first embodiment describes a refrigeration cycle using an electric expansion valve, the present invention can also be applied to a refrigeration cycle using a conventionally known mechanical expansion valve. In this case, in order to detect the opening degree of the expansion valve, a well-known electromagnetic stroke sensor can be used, and the opening degree can be calculated from the output signal S _X of the stroke sensor. Further, even when the expansion valve is a proportional solenoid valve type expansion valve, the opening degree can be calculated from the control signal _VX of the expansion valve. In particular, if the well-known poppet valve shown in FIG. 2 is used as the valve body, its opening area A can be determined by the following equation.

A=π・x・sinθ(d _s −x・sinθ・cosθ) However, x: Valve stroke (m) d _s : Orifice diameter (m) θ: Valve top angle (degrees) And the valve stroke x is the stroke Since it is given by the sensor output S _x or the expansion valve control signal V _x , it can be calculated electrically if another fixed value is set.

(2) In this example, the refrigerant density γ _i at the inlet of the expansion valve was given as one element for calculating the refrigerant flow rate Q, but the operating conditions of the refrigeration cycle do not change much, and the range of fluctuation of the gas phase refrigerant temperature in the liquid tank is comparatively small. If the objective is narrow, the density γ _i may be treated as a constant value, that is, as a predetermined constant. In this case, the flow rate is ultimately determined by the pressure at the inlet and outlet of the expansion valve and the opening degree of the expansion valve.

(3) In this example, the evaporator inlet refrigerant temperature and the refrigerant temperature in the gas phase in the liquid tank were used to detect the pressure at the expansion valve inlet and outlet. The latter may be detected anywhere as long as the refrigerant temperature is between the condenser outlet and the expansion valve inlet. As mentioned above, it is best to detect in the gas phase of the liquid tank, where the temperature is closest to the saturation temperature of the refrigerant.

Alternatively, if cost increase is not an issue, semiconductor pressure sensors may be disposed in the refrigerant flow path of each section to directly detect the pressure at the expansion valve inlet and outlet.
At this time, the pressure detection means does not require a temperature-pressure conversion means, and the output from the sensor is converted to the calculation circuit 18.
You can input directly to e.

(4) In this embodiment, a temperature-pressure conversion circuit is provided before the arithmetic circuit composed of a microcomputer, but a temperature-pressure conversion map is programmed in the ROM of the microcomputer, and The output may be input directly to the microcomputer.

(5) In this example, the refrigerant flow rate measuring device and the expansion valve opening degree control device were configured as independent circuits, but the calculation formula for the expansion valve opening degree was programmed into the microcomputer that constitutes the refrigerant flow rate calculation circuit, and the It is also possible to calculate the valve opening degree and the refrigerant flow rate using the same microcomputer.

〔Effect of the invention〕

As explained above, according to the present invention, the opening degree of the expansion valve is detected and converted into an electric signal, the pressure before and after the expansion valve is detected and converted into an electric signal, and a predetermined calculation is performed from these three electric signals. Since the refrigerant flow rate is calculated based on the formula, the refrigerant flow rate measurement device can be configured as part of the refrigeration cycle control device, and the refrigerant flow rate measurement function can be added not only to the test device but also to the product itself. As a result, the refrigerant flow rate can be used to calculate the opening of the expansion valve or as a control signal for other cycles, and it is possible to control the refrigerant flow rate with extremely high precision, and to obtain a multifunctional refrigeration cycle.

[Brief explanation of the drawing]

Fig. 1 is a system configuration diagram that is an embodiment of the present invention, Fig. 2 is a structural diagram of the main part of the valve body of the expansion valve, Fig. 3 is a saturation characteristic diagram of the refrigerant, and Fig. 4 is the saturation of the refrigerant at the valve inlet. FIG. 3 is a diagram showing the relationship between temperature and density. 1... Compressor, 1a... Electromagnetic clutch, 2...
Condenser, 3...Liquid reservoir, 4...Electric expansion valve, 4
a... Actuator, 4b... Valve body, 5... Evaporator, 10, 11, 12... Temperature sensor, 15...
...Control circuit, 15a...Differential amplifier circuit, 15b...
...Control target setting circuit, 15c...Control calculation circuit,
15d...Output circuit, 18...Flow rate calculation circuit, 1
8a...Opening area calculation circuit, 18b...Temperature-pressure conversion circuit, 18d...Temperature-density conversion circuit, 1
8e...Flow rate calculation circuit.

Claims (1)

[Scope of Claims] 1. In a device for measuring the refrigerant flow rate of a refrigeration cycle having an expansion valve that adiabatically expands the refrigerant, a high-pressure side pressure detection means for detecting the upstream pressure of the expansion valve, and a downstream pressure of the expansion valve. A pressure difference between both pressures is determined from the outputs of a low-pressure side pressure detection means for detecting the opening degree of the expansion valve, an expansion valve opening degree detection means for detecting the opening degree of the expansion valve, and the outputs of the both pressure detection means, and the square root of the pressure difference and the expansion valve A refrigerant flow rate measuring device for a refrigeration cycle, comprising calculation means for calculating the flow rate of refrigerant passing through the expansion valve from the product of the output of the opening degree detection means. 2. In the invention set forth in claim 1, a refrigerant density detection means for detecting the density of the refrigerant at the inlet of the expansion valve is provided, and the calculated refrigerant flow rate is increased or decreased in accordance with an increase or decrease in the output of the detection means. A refrigerant flow rate measuring device for a refrigeration cycle, characterized in that it performs correction. 3. In any of the inventions set forth in Claims 1 and 2, the high and low pressure detection means each include an upstream temperature detection means for detecting a refrigerant temperature on the upstream side of the expansion valve; downstream temperature detection means for detecting a refrigerant temperature downstream of the expansion valve;
A refrigerant flow measuring device for a refrigeration cycle, comprising a temperature-pressure conversion means for determining both high pressure and low pressure side pressures based on outputs from both temperature detection means. 4. In the invention according to any one of claims 1 to 3, the expansion valve opening detection means includes a stroke detection means for detecting a stroke of the expansion valve and an output of the stroke detection means. 1. A refrigerant flow rate measuring device for a refrigeration cycle, comprising a stroke valve opening conversion means for determining a valve opening. 5. In an apparatus for measuring the refrigerant flow rate of a refrigeration cycle having an expansion valve that adiabatically expands the refrigerant, a calculation means for calculating a target opening degree of the expansion valve according to the operating state of the refrigeration cycle, based on the output of the calculation means. an electromagnetic drive means for displacing the expansion valve, a high-pressure side pressure detection means for detecting the pressure on the upstream side of the expansion valve, a low-pressure side pressure detection means for detecting the pressure on the downstream side of the expansion valve, and outputs of both the pressure detection means. Refrigerant flow rate calculation means for calculating the flow rate of refrigerant passing through the expansion valve from the product of the square root of the pressure difference and the output of the target opening degree calculation means for the expansion valve. Cycle refrigerant flow measuring device.