JPH0684849B2 - Refrigerating cycle refrigerant flow rate control method and apparatus thereof - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a refrigerant flow rate control method and apparatus for a refrigeration cycle, and more particularly to setting a valve opening degree of an electric expansion valve and a deviation between a superheat degree and an actual superheat degree. The present invention relates to a device configured to control on the basis of an electric signal obtained by performing a proportional-plus-integral calculation.

[Background of the Invention]

Such a conventional refrigerant flow rate control method and device for a refrigeration cycle is proposed in Japanese Examined Patent Publication No. 56-16353.

However, if the valve opening of the expansion valve is controlled based on the result of the proportional-plus-integral calculation, even if the refrigeration cycle is in the liquid back state, the expansion valve is controlled with a large valve opening for a long time due to the existence of the integral term. , It was found that the compressor would be adversely affected.

[Object of the Invention]

In view of the above points, an object of the present invention is to provide a refrigerant flow rate control method and an apparatus therefor capable of escaping a refrigeration cycle from a liquid back state at an early stage.

[Outline of Invention]

The feature of the present invention is that in the so-called liquid back state in which the refrigerant returns to the compressor in a liquid state, the valve opening degree of the expansion valve is controlled only by the proportional calculation result of the deviation between the set superheat degree and the actual superheat degree. The point is that, in a low load condition where liquid backflow occurs, the effect of the integral term prevents the valve closing suppression effect, and the liquid backflow state can be eliminated early.

In order to embody the above method, another feature of the invention is to provide a judging means for judging whether or not the refrigeration cycle is in the liquid back state, and based on the output of the judging means, the integral calculation of the proportional-plus-integral calculating means is performed. The point is that a device for achieving the above object is configured by providing a means for invalidating the components.

Example of Invention

 An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a principle diagram of an embodiment of the present invention.

The superheat degree detecting means A detects the superheat degree of the refrigerant at the evaporator outlet of the refrigeration cycle.

The superheat degree deviation detecting means B obtains a deviation between the superheat degree set by the set superheat degree applying means C and the output from the superheat degree detecting means A. The operational amplification means D outputs an amplified signal proportional to the deviation. The integrating means E outputs a signal obtained by time-integrating the deviation. The addition means F adds the output from the operational amplification means D and the output from the integration means and outputs a control signal to the expansion valve drive circuit G. The expansion valve H controls the flow rate of the refrigerant so that the superheat degree at the outlet of the evaporator becomes the set superheat degree according to the control signal.

The judging means I detects whether or not the actual degree of superheat is lower than the set degree of superheat, and when it is low, judges that the liquid is in a back-up state and generates a signal. The set superheat degree at this time is the same as the set superheat degree used for the superheat degree deviation detecting means B or is a value lower than the set superheat degree by a predetermined value.

The integration stopping means J acts on the integrating means E while the determining means I outputs an output so that the output of the integrating means E is not input to the adding means F.

Thus, when the actual superheat degree becomes equal to or lower than the set superheat degree, the integral term contained in the expansion valve control signal is removed, and the expansion valve is quickly and stepwise controlled in the closing direction according to the proportional term.

As a result, the refrigeration cycle quickly recovers from the liquid back state.

In addition, as a determination means for determining whether or not the liquid is in the back state,
The state of the refrigerant may be directly detected without being limited to the above means.
For example, a heat ray flow meter is installed in the vicinity of the inner bottom wall of the pipe and in the center of the pipe, and if a predetermined difference occurs between the outputs of the two, it is determined that the liquid refrigerant is flowing through the inner bottom wall of the pipe. Alternatively, a sensor whose capacitance changes depending on the wetness of the refrigerant may be provided inside the tube to directly detect the wetness of the refrigerant.

In addition, it can be detected by the change of various physical quantities caused by the liquid back.

Hereinafter, one specific example of the present invention will be described in detail with reference to the drawings.

The refrigerant compressed by the compressor 1 is sent to the condenser 2 as high-pressure and high-temperature gas. The refrigerant that has been cooled in the condenser 2 and turned into a high-pressure liquid is separated into a gas and a liquid in the liquid receiver 8,
Only the liquid is sent to the expansion valve 3. Expansion valve 3 for high-pressure liquid refrigerant
It becomes a mist-like low pressure refrigerant that is adiabatically expanded and easily vaporized.

When the low-pressure refrigerant passes through the evaporator 4, it removes heat from the surrounding gas to cool it, while the low-pressure refrigerant is completely vaporized and overheated to return to the compressor 1.

The expansion valve 3 is drive-controlled by an electric signal. The opening degree is controlled by the step motor 10.

The electric signal θ _s is obtained by performing proportional integral calculation of the deviation ΔSH between the superheat degree SH ₁ of the refrigerant at the outlet of the evaporator 4 and the set superheat degree SH _s based on the equation (1).

_{θ s = (SH 1 -SH s} ) + k 1 ∫ (SH 1 -SH s) dt ...... (1) ( where, k ₁ is a constant) electrical signals theta _s applied voltage pulses _{V s} of the step motor 10 Which in turn corresponds to the target opening of the expansion valve 3 controlled by the step motor 10.

If the electric signal θ _s has a positive value, the step motor 10 rotates in a direction in which the opening of the expansion valve 3 increases according to its magnitude. On the contrary, if the electric signal θ _s has a negative value, the step motor 10 rotates in the direction in which the opening of the expansion valve 3 decreases depending on the magnitude thereof.

The control circuit 7 calculates and outputs the drive signal pulse number V _s corresponding to the electric signal θ _s , and the step motor 10 rotates by a predetermined angle according to the pulse number V _s . This rotation is decelerated via the speed reduction mechanism and converted into linear motion by the rotation-linear motion conversion mechanism provided at the output end of the speed reduction mechanism. It is set based on the speed reduction ratio of the reduction mechanism or the stroke of the expansion valve 3 of the rotation angle per step of the step motor 10. By the way, the stroke of expansion valve 3 is 0.5m.
Since it is about m, it rotates about 7.5 degrees for one step.
Using a 48-pole step motor, the reduction ratio of the reduction mechanism is 1:30.
Then, the output shaft of the reduction mechanism can be rotated by 7.5 / 30 degrees in one step of the step motor. Therefore, if the rotation-linear motion conversion mechanism is set so that the expansion valve strokes 0.5 mm while the output shaft of the reduction mechanism makes one rotation, the expansion valve opening can be adjusted to 0.5 / 14 by one step of the step motor.
It can be opened and closed by 40 mm (about 0.35 micron).

If the drive signal pulse V _s for the step motor 10 can be generated at 200 pulses per second, the expansion valve can operate at about 7
Strokes from fully open to fully closed in seconds.

The control circuit 7 calculates the degree of superheat at the outlet of the evaporator 4 based on the output signals of the sensors 5 and 6 that detect the refrigerant temperature at the inlet and outlet of the evaporator 4.

The temperature and pressure of the refrigerant at the inlet of the evaporator 4 (expansion valve outlet) are T ₁ and P ₁ , respectively, the temperature and pressure of the refrigerant at the outlet of the evaporator 4 and T ₂ and P ₂ , respectively, and the pressure of the refrigerant at the evaporator outlet. If the saturation temperature for P ₂ is T ₃ , the superheat degree SH of the refrigerant at the outlet of the evaporator 4
₁ is represented by SH ₁ = T ₂ −T ₃ (2).

Here, if the equation (2) is transformed by using the refrigerant temperature T ₁ at the inlet of the evaporator 4, then SH ₁ = T ₂ −T ₁ + (T ₁ −T ₃ ) ... (3).

Assuming Δt = T ₁ −T ₃ here, the refrigerant temperature T ₁ at the inlet of the evaporator 4
Between Δt and Δt can be approximated by a linear function as shown by the broken line in FIG. 4, and the relationship is due to the difference ΔP (= P ₁ −P ₂ ) in the refrigerant pressure at the inlet and outlet of the evaporator 4. It is known to change as shown in FIG.

Since ΔP can be experimentally obtained if the evaporator is specified, the relationship between ΔT and T ₁ in each evaporator can be approximated by one linear function according to the experimentally obtained ΔP.

For example, if the evaporator has ΔP of 0.3 Kg / cm ² , it can be represented by a linear function of Δt = 3.25−3 / 40T _{1 as} shown by the solid line in FIG.

Therefore, equation (3) is Then, the superheat degree at the outlet of the evaporator 4 can be obtained as a function of the temperature at the inlet and outlet of the evaporator 4 by the equation (4).

The control circuit 7 internally calculates the superheat degree SH ₁ at the outlet of the evaporator 4 according to the equation (4), obtains the deviation between the calculated value and the set superheat degree SH _s, and follows the equation (1). The drive signal θ _s of the step motor 10 as the opening signal of is calculated.

The control circuit 7 further determines the second set superheat degree SH ₁ lower than the set superheat degree SH _s and SH ₁ obtained by the calculation based on the equation (4).
When SH ₁ <SH ₁ , the addition of the integral term is stopped in the process of calculating the electric signal θ _s based on the previous equation (1),
Until the actual degree of superheat calculated by the equation (4) becomes higher than the set degree of superheat SH _s , the electric signal θ _s is calculated only by the proportional term of the equation (1).

In this example, the set superheat degree SH _s was set to 5 ° C and SH ₁ was set to 2 ° C.

In this embodiment, when the degree of superheat at the outlet of the evaporator 4 becomes 2 ° C. or less, addition of the integral term is stopped, so that a negative electric signal θ _s proportional to the deviation of about 3 ° C. is generated, and the integral term up to that point. Even if is a value that biases the proportional term in the positive direction, the influence is removed, and the expansion valve 3 is rapidly operated in the closing direction in a step-like manner. This operation is performed when the superheat SH _{1 at the} outlet of the evaporator 4 is 5 ° C.
It is maintained until it recovers. Once the superheat is 2 ° C or less and once the control is started using only the proportional term, the control is maintained until the superheat reaches 5 ° C. This is because the system has hysteresis and hunting of control signals is performed. In order to prevent the step motor from oscillating due to signal hunting by avoiding the situation where the signal becomes a signal including an integral term or a signal having only a proportional term at the boundary of 2 ° C. Is.

This embodiment will be described more specifically.

The control circuit 7 is composed of a temperature control element group S such as an air-mix door, a mode door or a hot water cock, a blower motor B, or a microcomputer M ₁ for controlling the operation of the compressor ₁ which is not shown.

Microcomputer M ₁ various control flow, calculating the flow or ROM for various program instructions, and out ALU, RAM that stores the information ALU uses the information signal and a control signal to perform it on the basis of the instructions of the ROM Counter COUN and clock pulse generator CL for making the cycle of I / O port IO and instruction from ROM, timing of operation, etc.
Composed of OCK etc.

FIG. 3 shows the control flow chart of this microcomputer.

An analog voltage V ₁ corresponding to the inlet refrigerant temperature T ₁ of the evaporator 4,
The analog voltage V _d corresponding to the outlet refrigerant temperature T ₂ is the analog voltage V _R from the inside air temperature sensor, the analog voltage V _a from the outside air temperature sensor, the analog voltage V _Z from the solar radiation sensor, and the A / D converter AD. Is converted into a digital signal.

When the air conditioner is driven, the microcomputer M _{1 first} sets all control signals to initial values in step 101 according to the control flow of FIG.

The A / D converted digital signal corresponding to each analog signal is sent to the multiplexer M _p together with the digital signal D _s corresponding to the set temperature signal set on the operation panel and the digital signal M _s corresponding to the selected mode. Therefore, in step 102, the values are sequentially read into the microcomputer M _1, and the values are temporarily stored in the RAM.

Microcomputer M ₁ is step 1 based on ROM command
The values stored in the RAM in 02 are fetched from the RAM and the arithmetic unit ALU
The temperature control signal is calculated (step 103), the blower motor control signal is calculated (step 104), and the mode is determined (105). The results of these calculations and judgments are temporarily stored in RAM.

Next, the micro computer M ₁ calculates the superheat degree SH ₁ of the evaporator outlet, the proportional term θ ₀ of the electric signal, the integral term θ ₁ and the sum θ _{s of} both terms in step 106 based on the command of the ROM, and each value is calculated.
Store in RAM.

Next, the microcomputer M ₁ determines in step 107 whether the evaporator superheat degree SH ₁ is larger or smaller than the set superheat degree SH _s , and when YES (when it is larger), θ _s calculated in step 106 is used as it is. It is stored in RAM as a control signal at 108a.

When NO (when small), step 108b is used to superheat the evaporator outlet
Determine whether SH ₁ is greater than or less than the set superheat degree SH _s . When NO (small), the proportional term θ ₀ calculated in step 106 is stored in RAM as θ _s , and when YES (large), the previous expansion valve opening control is performed only by the proportional term θ _0. It is determined whether or not If the result of the determination is YES, it is determined that the hysteresis operation is currently in progress and at step 108c θ
Replace _s with the proportional term θ ₀ again and store it in RAM.
In this case, it is determined that the engine is in normal operation, and the proportional-plus-integral term θ _s calculated in step 106 is stored as it is in the RAM as θ _s .

The hysteresis operation ends when SH ₁ becomes greater than SH _s .

Thus θ _s stored in RAM at step 108a or 108c
Based on the above, the expansion valve is controlled in step 109.

In step 109, θ _s determined in step 108a or 108c
To the step motor drive circuit 12, and the drive circuit 12 outputs θ
_The number of voltage pulses V _s corresponding to _s is supplied to the step motor 10 to rotate the step motor 10.

Since the cycle demands the maximum refrigerant flow rate at the time of starting the refrigeration cycle, the voltage pulse V _s becomes 1440 pulses, and the expansion valve is fully opened about 7 seconds after the start.

In addition, in order to open and close the valve reliably, an extra pulse of 50 pulses can be added to the above-mentioned pulse so that the valve is surely pressed to the fully open position. This can be done similarly when fully closed.

Next, in step 110, the temperature control signal calculated in step 103 is fetched from the RAM, and the control circuit 1 is output via the input / output port IO.
Output to 3. The control circuit 13 controls the temperature control element group S based on the control signal.

Further, in step 111, the blower motor control signal calculated in step 103 is fetched from the RAM and output to the control circuit 14 via the input / output port IO. The control circuit 14 controls the rotation speed of the blower motor B based on the control signal.

In step 112, the mode determined in step 105 is fetched from the RAM and output to the mode control circuit 15 via the input / output port IO. The mode control circuit 15 switches the mode control element E based on the mode signal to switch the outlet of the air conditioner and the temperature control mode.

In step 113, the set temperature, the room temperature, etc. read in step 102 and stored in the RAM are taken out and displayed on the temperature display portion F of the display device 16. Similarly, the display device can be provided with a display unit for displaying operation modes and the like.

At step 114, ON / OFF control of the compressor is performed based on the temperature control signal calculated at step 103.

In this step, a condition determined by another interrupt routine (not shown), for example, when the evaporator is about to be connected (when the degree of superheat reaches a low value of 1 degree or 0 degree or less over a predetermined time), The compressor is turned on when the refrigerant leaks (when the degree of superheat becomes abnormally high), when the outside temperature falls below 15 ° C, or when the device enters the energy-saving operation mode. Switch from OFF to OFF and control. The control signal is given to a control circuit composed of a relay or the like, and is performed by controlling energization to a magnet clutch (not shown).

As described above, the expansion valve 3 of the embodiment is controlled on the basis of the signal θ _s obtained by performing the proportional integral calculation of the deviation between the two while the actual superheat degree is larger than the first set superheat degree, and further, the actual When the superheat degree is lower than the first set superheat degree and lower than the second set superheat degree, control is performed based on a signal θ ₀ obtained by proportionally calculating a deviation between the actual superheat degree and the first set superheat degree. As a result, the valve closing control of the expansion valve will not be delayed due to the influence of the integral term in the operating state where the heat load is small, and the occurrence of the liquid return phenomenon to the compressor can be prevented.

In the present embodiment, whether or not the cycle is in the liquid back state is determined indirectly by determining whether or not the degree of superheat at the evaporator outlet has become equal to or lower than a predetermined value. Attach a sensor to detect the liquid state, detect the liquid back state,
This output may be used to determine whether or not θ _s should be a proportional term only.

Further, in the present embodiment, two set superheat degrees are set to perform the hysteresis control, but the set superheat degree is set to (for example, 2
1), and when the actual superheat becomes higher than that, the operation is switched to the proportional term only and the timer is activated at the same time, and the actual superheat becomes higher than the set superheat for a predetermined time. Also, the operation may not be returned to the proportional integral term.

Further, in the present embodiment, the step motor is used as the drive means of the expansion valve, but it can be similarly applied to a proportional solenoid type electromagnetic valve, an electrically controlled expansion valve using a heater and bimetal, and the like.

Furthermore, in this embodiment, the temperature of the refrigerant at the evaporator inlet / outlet is detected, and the superheat degree at the evaporator outlet is calculated from the value,
A pressure sensor may be provided at the evaporator outlet, and the superheat degree at the evaporator outlet may be calculated from the output of this refrigerant pressure sensor and the output of the refrigerant temperature sensor provided at the evaporator outlet.

〔The invention's effect〕

As described above, according to the present invention, the integral term is not added to the target opening calculation of the expansion valve in the operating state where the refrigeration cycle is in the liquid back state. The valve closing control will be performed promptly and the accident of damaging the compressor due to the liquid back can be prevented.

[Brief description of drawings]

FIG. 1 is a drawing for explaining the principle of the present invention, FIG. 2 is a control circuit diagram of an automobile air conditioner to which the present invention is applied, FIG. 3 is a control flow chart of the control circuit, and FIG. It is a characteristic view used for describing an example. 1 ... compressor, 2 ... condenser, 3 ... (electronically controlled) expansion valve, 4 ... evaporator, 5,6 ... temperature sensor, M ₁ ... microcomputer, 10 ... step motor.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kozo Sayo 2520 Takaba, Katsuta-shi, Ibaraki Pref., Sawa Plant, Hitachi, Ltd. Inside the Mechanical Research Laboratory (72) Inventor Masahiko Fujita 502 Jinritsucho, Tsuchiura City, Ibaraki Prefecture Inside the Mechanical Research Laboratory, Hiritsu Seisakusho Co., Ltd. (56) Reference JP-A-58-24770 (JP, A)

Claims (2)

[Claims] 1. A deviation between the set superheat degree and the actual superheat degree is proportionally integrated so that the superheat degree at the outlet of the evaporator is detected so that the superheat degree becomes the predetermined set superheat degree. In the one in which the valve opening of the expansion valve provided at the evaporator inlet is electrically controlled based on the signal to adjust the refrigerant flow rate, the refrigerant is returned to the compressor in a liquid state in the liquid back operation state. A refrigerant flow rate control method characterized in that the valve opening degree of the expansion valve is controlled only by the proportional portion of the deviation of the superheat degree. 2. A superheat detection means for detecting the superheat at the evaporator outlet, and a proportional integral calculation of a deviation between a predetermined set superheat and the superheat detected by the superheat detection means. Comprising arithmetic means and control means for electrically controlling the valve opening of an expansion valve provided at the inlet of the evaporator according to the output signal of the arithmetic means to adjust the refrigerant flow rate, wherein the refrigerant is in a liquid state. And a means for judging whether or not the liquid back-operation state is returned to the compressor, and a means for invalidating the component based on the integral calculation in the output of the calculating means in response to the output of the judging means. Characteristic refrigerant flow control device.