JPS6239346B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air conditioner using a variable capacity compressor, and relates to an improvement of a controller that controls the amount of throttle of a throttle device.

A refrigeration cycle of an air conditioner using a variable capacity compressor is configured as shown in FIG. 2, for example. 1 is a compressor, 2 is a condenser, 3 is a throttle device, and 4 is an evaporator. The throttling device is one that can control the throttling amount by an electric signal, and a motor or a valve drive unit composed of a combination of a heater and a bimetal is used. The temperature detected by the first temperature sensor 5A
The difference between T ₁ and the temperature T ₂ detected by the second temperature sensor 5B provided at the outlet of the evaporator 4 SH' = (T ₂
-T ₁ ) is controlled by the control device 5 to control the aperture amount of the aperture device 3 so that the amount of the aperture is approximately constant. Further, the capacity of the compressor 1 is determined by the capacity control device 6, which determines the capacity, according to the output of an air conditioning state detector (for example, a room temperature sensor) 6A. Variable capacity compressors 1 include, for example, twin type, two-speed electric compression stage, cylinder bypass type, and continuously variable speed electric compressors. As the control device 5, for example, a circuit as shown in FIG. 3 is used. That is, the temperature difference SH' detected by the thermistors 5A and 5B as the first and second temperature sensors is amplified by the operational amplifier 5C, and this voltage V _T
A voltage equal to is applied to the throttling device, for example a thermoelectric expansion valve.

Such a control device has the following drawbacks. The refrigerant circulation amount is different when the compressor 1 is operating at a large capacity and when it is operating at a small capacity, and naturally the amount is larger in the former. Change amount ΔSH′ _H of temperature difference SH′ with respect to unit valve opening ΔO of expansion valve 3 when refrigerant circulation amount θc is large
is smaller than the amount of change ΔSH′ _L when the circulation amount θc is small. That is, the process gain GP of the refrigerant process consisting of the expansion valve 3 and the evaporator 4 is
SH'/ΔO depends on the circulation amount θc, and when θc is large, the gain G _P becomes small. Therefore, if the gain G _C of the control device 5 is kept constant by the ratio of the resistor 50 and the resistor 5E, as in the conventional example, there will be a difference in control performance depending on the circulation amount θ _C , and the optimal You can't always expect a response. In other words, in a control system that forms a closed loop like this, when the process gain G _P fluctuates, the system does not oscillate the gain G _C for the highest process gain G _PMAX , and the response is stable. Therefore, when the process gain G _P is low, the response deteriorates, the response speeds are close, and the residual deviation becomes large.

Further, depending on the inlet pressure P _I of the evaporator 4, the inlet/outlet pressure difference ΔP of the evaporator 4 changes, and the temperature difference ΔT changes accordingly. If ΔP is constant, ΔT is also constant, so the temperature difference SH' and the superheat degree SH of the refrigeration cycle are SH = SH' + ΔT. By keeping the temperature difference SH' at an appropriate value, the superheat degree SH can be reduced. It can be kept at the optimum value. In the variable capacity compressor 1, there is a change in the refrigeration cycle, and this appears as a change in pressure P _I. If pressure P _I
As the pressure difference ΔP increases, the pressure difference ΔP also increases, and therefore ΔT also changes. Therefore, in order to keep the degree of superheat SH constant, the predetermined temperature difference SH′ _R must be changed depending on the state of the refrigeration cycle, and control must be performed so that the predetermined temperature difference SH′ _R and the temperature difference SH match. However, since this cannot be done with the conventional control device shown in FIG. 3, the superheat degree SH cannot actually be maintained at the degree of superheat that makes the refrigeration cycle optimal for all conditions of the refrigeration cycle.

The present invention aims to eliminate the drawbacks of the above-mentioned conventional examples and provide an air conditioner that can always operate in an optimal refrigeration cycle state. The present invention will be described in detail below with reference to the drawings.

The refrigeration cycle changes due to various reasons,
The largest variable factor is compressor capacity. Therefore, when the compressor capacity changes, the predetermined temperature difference SH' _R and control gain G _C as control parameters may be changed accordingly.

FIG. 1 shows an embodiment of the control device of the present invention when a two-speed electric compressor is used as the variable capacity compressor. In Fig. 1, 5D1 and 5D2 are resistors that determine the control gain _GC , and _GC is R _5E /R _5D1 , respectively.
It becomes R _5E /R _5D2 . However, R _5D1 , R _5D2 , and R _5E are the resistance values of the resistors 5D1, 5D2, and 5E, respectively. Resistance 5F1, 5F2, set temperature difference SH' _R1 ,
SH' _R2 , and the control amount operates so that the sum of the resistance value R _TB of thermistor 5B and the resistance value R TA of the thermistor 5A becomes equal to the resistance value R _TA of the thermistor 5A. 5G is a relay as a parameter changing means, which is controlled by the capacity control device 6, and is turned on when a high capacity is output to the compressor 1. During low capacity operation, relay 5G is off, set temperature difference SH' _R is SH' _R1 , and control gain G _C is G _C1 . During low capacity operation, the evaporator inlet pressure P ₁ is low, P _1L , the pressure difference ΔP is also small, and the temperature difference Δ
T also becomes smaller and becomes ΔT _L. Therefore,
Select the resistance values of resistors 5F1 and 5F2 so that SH' _R1 >SH' _R2 . Also, the process gain G _PL during low capacity operation is higher than that during high capacity operation G _PL > _G
Since it is _PH , control gain G _C1 = R _5E / R ₅ 〓 ₁ < G _C2
=R _5E /R ₅ 〓 Select the relationship of ₁ . In this way, the temperature difference SH' will be controlled to SH' _RH during high capacity operation and SH' _RL during low capacity operation, and the superheat degree SH will change due to the difference in ΔT due to the difference in the pressure difference ΔP. This allows the refrigeration cycle to operate optimally at all times. Furthermore, the loop gain _GH of the control system during high capacity operation, etc. can be made approximately equal to the gain _GL during low capacity operation, and an optimal response can always be obtained.

In the above explanation, a two-speed electric compressor was used as the variable capacity compressor 1, but it may be of other types, for example, in the case of a continuously variable compressor, setting SH' _R and control gain may be changed. may be changed continuously according to the output of the capacity control device 6, and such a speed change does not depart from the gist of the present application.

In addition, in the above explanation, P control (proportional control) was explained as a control device, but in addition to this, Pi
The present invention can be similarly applied to (proportional integral control), PD (proportional differential control), and PiD (proportional integral differential control) control, and furthermore, in order to optimize the response,
The differential time TD and integral time Ti are also controlled by the control gain G.
It may be controlled at the same time when adjusting _C.

As described above, according to the present invention, the refrigeration cycle can always be kept in the optimal condition, so
It also maintains a higher EER value than conventional air conditioners and has an excellent energy saving effect.

[Brief explanation of the drawing]

FIG. 1 is a control circuit diagram showing an embodiment of the air conditioner of the present invention, FIG. 2 is a refrigeration cycle diagram of the same air conditioner, and FIG. 3 is a conventional control circuit diagram. 1... variable capacity compressor, 2... condenser, 3...
Throttle device, 4... Evaporator, 5... Control device, 6...
...Capacity control device, 5G...Relay as parameter changing means.

Claims (1)

[Claims] 1. A refrigeration cycle consisting of a variable capacity compressor, an evaporator, a condenser, a throttle device, etc., a capacity control device that controls the capacity of the compressor according to the air conditioning condition, and a a temperature sensor provided therein, and a control device that controls the amount of throttle of the throttle device so that the temperature difference detected by each of the temperature sensors is equal to the set temperature difference, and the control device is configured to An air conditioner comprising parameter changing means for changing the set temperature difference according to a capacitance signal.