JPH0135263B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the operation of a variable capacity compressor in a vehicle cooling system.

Generally, in a vehicle cooling system, when the cabin temperature is high and the cooling load on the compressor is greater than the cooling capacity, such as at the beginning of operation, the compressor is operated with increased capacity, causing the cabin temperature to drop. When the cooling load becomes smaller than the cooling capacity, the compressor is operated at reduced capacity. Conventionally, when the cooling load becomes smaller, the pressure of the refrigerant drawn into the compressor is reduced. Focusing on the decrease in air pressure, a pressure detection device detects the suction pressure, and when this pressure falls below a set value, the compressor capacity is reduced, and when the cooling load becomes small, the compressor There is a system that uses a temperature sensor to detect the temperature of the refrigerant gas being sucked into the engine, and when this temperature falls below a set value, the capacity of the compressor is reduced. .

However, the two conventional control methods mentioned above,
In either case, when the discharge pressure of the compressor fluctuates due to changes in the outside temperature, the suction pressure and temperature also fluctuate, but it may not be possible to change the capacity accordingly, resulting in the defect of causing wet vapor compression. It was hot. Regarding this point, as shown in Figures 1 and 2, the horizontal axis represents enthalpy i and the vertical axis represents absolute pressure p, and the saturated liquid line changes depending on the type of refrigerant.
L ₁ , saturated vapor line L ₂ , isothermal line T, isobaric line, isoenthalpy line or isentropic line K (not shown)
The explanation will be based on the refrigeration cycle (A→B→C→D) displayed on the Mollier (pi) diagram.

Generally, in a refrigeration cycle, gas in the suction state A determined by the suction pressure and temperature is sucked into a compressor and compressed to a high temperature and high pressure state B, and the refrigerant in this state radiates heat in the condenser. It liquefies and becomes state C and accumulates in the liquid receiver. This liquid is throttled and expanded by an expansion valve to become a low-pressure, low-temperature gas-liquid mixture state D, and is vaporized by taking heat from the surrounding medium to be cooled in an evaporator, becoming state A and being sucked into the compressor again. The change AB in the gas compressed by the compressor is adiabatic and almost coincides with the isentropic line K, and the throttle expansion CD in the expansion valve is an isenthalpic change. A′-- Inhaling refrigerant gas in a wet vapor state
The compression of B′ is called wet compression, the change in A″-B″ or A-B when the gas is sucked and compressed in a dry saturated or superheated state is dry compression, and A″-A is called superheat. Although A-B wet compression has good compression efficiency, it is liquid compression in which liquid is sucked into the compressor, and there is a risk of valve cracking.
Cp/Cv (Cp: heat capacity at constant pressure, Cv: heat capacity at constant volume)
If the temperature is 1.18 or less, heating the intake gas will theoretically increase the refrigerating capacity, so it is desirable to superheat the Freon refrigerant by about 5 degrees Celsius.

On the other hand, if the throttling amount of the expansion valve reaches its limit and the compression operation is performed in the state A-B, then when the discharge pressure remains the same and the cooling load decreases, as shown in Figure 2.
As shown in A ₁ - B ₁ , the suction and discharge pressures are the same, the suction and discharge temperatures decrease, and the degree of superheating decreases. However, among the conventional control methods, when the temperature control method, that is, the isothermal line Tc in Fig. 2 is used as the set temperature, A
Since the detected temperature reaches the set value and the capacity of the compressor is reduced before the point reaches point _A1 , it is possible to prevent the degree of superheating from falling below 0°C, and there is no problem. In the pressure control method, which reduces the capacity when the set pressure Pc is reached,
There is a defect in that even if A becomes _A1 and further exceeds the saturated vapor line _L2 , it cannot be detected. Also, if the outside temperature rises and the discharge pressure increases, and the cooling load remains the same, the suction/discharge pressure and temperature will rise as shown in Figure 2 A ₂ - B ₂ , and the degree of superheat will decrease slightly. ,
In this case, the suction pressure or temperature does not reach the set value, so the capacity of the compressor is not reduced, and the degree of superheat is sufficiently ensured, so there is no problem. However, when the outside temperature rises, the discharge pressure increases, and the cooling load decreases, as shown in Figure 2 A3 _{- B3} , the suction and discharge pressures rise and the suction and discharge temperatures drop slightly. The degree of superheating becomes very small, but
In both conventional control methods, the suction pressure or temperature does not fall to the set value, so the compressor capacity is not reduced, and therefore the cooling load is further reduced.
There was a defect that when A ₃ exceeded the saturated vapor line L ₂ , wet vapor compression occurred.

In this way, when the outside temperature fluctuates, the discharge pressure of the compressor changes, and the suction pressure and temperature are created and fluctuated, resulting in a change in the degree of superheat, but in conventional methods, the suction pressure or temperature is set. Since the capacity will not decrease unless the value is reached, it will not be detected even if the degree of superheat is outside the allowable range, which will induce wet vapor compression.
There are defects such as valve damage or extra power consumption.

The purpose of the present invention is to detect the suction pressure and temperature, and when the actual state point determined by these is out of the permissible range preset on the Mollier diagram, by switching the capacity of the compressor, Variable capacity compression in vehicle cooling systems that can maintain the appropriate degree of superheating even when the outside temperature fluctuates, prevent wet vapor compression, reduce power loss, and prevent compressor damage. The purpose of this invention is to provide a method for controlling the operation of a machine.

Hereinafter, one embodiment of a vehicle cooling system used in the control method of the present invention will be described with reference to FIG.
In the figure, 1 is an engine, and 2 is a variable capacity compressor driven by this engine. Between the discharge flange 3 and the suction flange 4, there are a condenser 5, a liquid receiver 6, an expansion A valve 7 and an evaporator 8 are connected in sequence. As the variable capacity compressor 2, in this embodiment, a swash plate type compressor whose capacity can be switched between 100% and 50% is used, but a compressor whose capacity can be switched in three or more stages or steplessly is used. Good too. Reference numeral 9 denotes a temperature detection device disposed in a conduit 10 connecting the evaporator 8 and the suction flange 4, and is adapted to detect the temperature of the refrigerant sucked into the compressor 2. Reference numeral 11 denotes a pressure detection device similarly disposed in the pipe line 10, and is adapted to detect suction pressure.

12 is the pressure detection device 9 and the temperature detection device 1
1 is a control device consisting of a microcomputer, etc. connected to 1, and its memory circuit (not shown) stores the parallelogram-shaped allowable region E of the inhalation state point A shown in FIG. A comparison and determination circuit (not shown) of the control device 12 compares and determines whether or not the state point A determined by the suction pressure and temperature is within the permissible range E, and if the state point A is outside the permissible range E, A switching command signal is output from an operating circuit (not shown) of the control device 12 to the capacity switching mechanism 13 of the compressor 2.

Now, to explain the settings of the permissible region E stored in the control device 12, in this embodiment, as shown in _FIG . The line _H2 is constant regardless of the suction pressure (for example, if _H1 is 5℃,
_H2 is set to 15℃), that is, the distance from the saturated steam line _L2 is set to be constant. When the actual state point A moves to the left in FIG. 4 and deviates from the minimum allowable superheat degree line _H1 , the control device 1
2 outputs a compressor capacity down command signal, and conversely, when state point A moves to the right in FIG. 4 and deviates from the maximum allowable superheat degree line _H2 ,
The capacitance up signal is output from the
Also, the maximum allowable pressure line P ₁ on both the upper and lower sides of the allowable area E
and the minimum allowable pressure line P ₂ are constant regardless of the suction temperature (for example, P ₁ is 4Kg/cm ² and P ₂ is 1Kg/cm 2 ).
cm ² ), and even if the detected intake temperature is within the allowable range E, due to fluctuations in the outside temperature, the state point A moves upward (downward) in Fig. 4 and reaches the maximum (minimum).
When it deviates from the allowable pressure line P ₁ (P ₂ ), the control device 1
2 outputs a compressor capacity up (down) signal.

Next, a method for controlling the operation of the vehicle cooling system configured as described above will be explained.

The compressor is running at 100% when the temperature inside the vehicle is high.
If the air conditioner is operated, the cooling capacity and the cooling load on the compressor are almost the same, and the expansion valve 7 can adjust the suction pressure and temperature to an appropriate state, the actual state point A determined by the suction pressure and temperature is acceptable. Since it is within region E, the capacity of the compressor is not switched.

After that, as the cabin temperature decreases, the cooling load decreases, and the cooling capacity increases, both the suction pressure and temperature decrease. The drop is promoted, the degree of superheating becomes small, and the state point A deviates from the degree of superheating line H ₁ in the tolerance region E. Then, a capacity down signal is output from the control device 12, and the capacity of the compressor is switched from 100% to 50%. As a result, the suction temperature begins to rise, and state point A returns to the allowable region E.
be returned within.

Furthermore, when the compressor is operating at 50%, the cooling capacity is smaller than the cooling load, and both the suction pressure and temperature rise and the flow rate is insufficient even if the expansion valve 7 is fully opened. As a result, the controller ₁₂ outputs a capacity up signal and the compressor is switched to 100% operation, so the suction pressure and temperature start to fall, and the state point A is again within the tolerance range E. will be returned to.

On the other hand, due to fluctuations in outside temperature, the suction temperature is maintained within the permissible range E, but the suction pressure becomes abnormally high (low) and the state point A changes to the maximum (minimum) permissible pressure line P ₁ (P ₂ ), a capacity up (down) signal is output from the control device 12, and the state point A is returned to within the allowable range E.

In this embodiment of the present invention, the allowable range E of the state point A determined on the Mollier diagram is stored by the control device 12, and the actual state point A determined by the suction pressure and temperature is Since the capacity of the compressor is changed to return it to the permissible range when it deviates from the permissible range E, it is possible to detect an abnormality in the degree of superheat, eliminate wet vapor compression, and operate the compressor properly. be.

Note that the present invention can also be embodied in the following embodiments.

(1) As shown in FIG. 5, the minimum (maximum) permissible superheat degree line H ₁ (H ₂ ) of the permissible region E should be set almost parallel to the isentropic line K.

(2) In the above embodiment, both the upper and lower limits of the allowable region E were defined by the suction pressure, but instead of this pressure, the maximum allowable temperature line T ₁ and the minimum allowable temperature line T ₂ were defined as shown in FIG. to use.

(3) Area E from H ₁ , P ₂ , T ₂ at 50% operation
If it comes off, it means that the compressor is over capacity and you should stop operating the compressor.

(4) It is also possible to set the _H3 line for excessive superheating, and if it crosses this line to the right in Figure 4, it will be determined that there is a refrigerant shortage and an abnormal signal will be issued.

As described in detail above, the present invention can maintain the degree of superheat at an appropriate level even when the outside temperature fluctuates, preventing wet compression, reducing power loss, and preventing damage to the discharge valve due to liquid compression. There is an effect that can be done.

[Brief explanation of drawings]

Fig. 1 is a Mollier diagram for explaining the general characteristics of a refrigeration cycle, Fig. 2 is a Mollier diagram for explaining the conventional operation control method of a variable capacity compressor, and Fig. 3 is a Mollier diagram for explaining the control method of the present invention. FIG. 4 is a Mollier diagram for explaining the operation control method of the present invention, and FIGS. 5 and 6 are schematic circuit diagrams showing one embodiment of a vehicle cooling system used in the method. FIG. 7 is a Mollier diagram showing another example. Variable capacity compressor...2, temperature detection device...9, pressure detection device...11, control device...12, capacity switching mechanism...13, allowable area...E, state point...A, maximum (minimum) allowable superheat degree line...H ₂ (H ₁ ), maximum (minimum) allowable pressure line...P ₁ (P ₂ ), maximum (minimum) allowable temperature line...T ₁
( _T2 ).

Claims (1)

[Scope of Claims] 1. In a vehicle cooling system that performs cooling by exchanging heat through condensation and evaporation of refrigerant circulating in a refrigeration cycle using a variable capacity compressor, the pressure of the refrigerant drawn into the compressor and the The temperature is detected by a pressure detection device and a temperature detection device, and the actual suction state point on the Mollier diagram determined by these suction pressures and temperatures is stored in advance by the control device and a predetermined degree of superheat is maintained. The control device compares and determines whether or not the compressor is within a set allowable range, and when the compressor falls outside the allowable range, outputs a capacity switching command from the control unit to switch the capacity of the compressor;
A method for controlling operation of a variable capacity compressor, characterized in that the suction state point is returned to within an allowable range. 2. The vehicle air conditioner according to claim 1, wherein the permissible region of the Mollier diagram stored by the control device is set by constant maximum and minimum permissible superheat degree lines regardless of the suction pressure. A method for controlling the operation of a variable capacity compressor in an apparatus. 3. The vehicle air conditioner according to claim 1, wherein the maximum and minimum permissible superheat degree lines of the permissible region of the Mollier diagram stored by the control device are set substantially parallel to the isentropic line. A method for controlling the operation of a variable capacity compressor in an apparatus. 4. The vehicle according to claim 1, wherein the upper and lower limits of the allowable region of the Mollier diagram stored by the control device are set by the maximum and minimum allowable pressure lines, regardless of the suction temperature. A method for controlling the operation of a variable capacity compressor in a cooling system. 5. The vehicle according to claim 1, wherein the upper and lower limits of the allowable range of the Mollier diagram stored by the control device are set by the maximum and minimum allowable temperature lines, regardless of the suction pressure. A method for controlling the operation of a variable capacity compressor in a cooling system. 6 Claim 1 provides that, when the compressor deviates from the minimum permissible superheat line, minimum permissible pressure line, or minimum permissible temperature line while operating at a small capacity, a command to stop operation of the compressor is issued. 6. A method for controlling the operation of a variable capacity compressor in a vehicle cooling system according to any one of items 5 to 6.