JPS5827126B2 - car cooler control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a car cooler control device that controls the interior temperature of a car by on/off control of a refrigerant compressor.

This type of car cooler control device is equipped with a temperature detection element such as a thermistor on the cold air outlet side of the refrigerant evaporator, and when the air temperature on the outlet side of the evaporator drops to a predetermined value, the refrigerant compressor is stopped. When the temperature of the air on the outlet side rises and reaches a predetermined value that is sufficiently higher than the predetermined value, the refrigerant compressor is driven again to control the temperature inside the car, and a temperature detection element is also installed inside the car to control the temperature inside the car. There are also devices that allow similar control.

However, in either device, when the temperature outside the vehicle is high in midsummer, the temperature inside the vehicle is difficult to drop, so control is essentially performed based on the air temperature on the outlet side of the evaporator.

Here, if the air temperature on the outlet side is set low to turn off the refrigerant compressor, the operating rate of the refrigerant compressor will also increase, and if this continues for a long time, the surface temperature of the evaporator will be below 0°C, so Frost begins to form.

This frost formation not only obstructs heat exchange in the evaporator and prevents the temperature of the air on the outlet side from decreasing, but also destabilizes the amount of air blown out and disrupts the output of the temperature detection element installed on the outlet side of the evaporator. In order to stabilize the temperature inside the car, the temperature control becomes unstable.

Therefore, in order to ensure reliable on/off control of the refrigerant compressor, it is necessary to set the outlet air temperature slightly higher when the refrigerant compressor is turned off. The drawback was that the capacity could not be fully utilized and the cooling effect would be poor.

The present invention aims to eliminate such drawbacks, and aims to provide a car cooler control device that has a frost-preventing function on the evaporator and can fully demonstrate its cooling capacity.

In addition to a circuit that stops the refrigerant compressor when the air temperature on the outlet side of the evaporator drops to a predetermined value, the present invention also provides a circuit that stops the refrigerant compressor when the air temperature on the outlet side of the evaporator is below a temperature slightly higher than the predetermined value for a predetermined period of time. This is a car cooler control device that is equipped with a circuit that stops the refrigerant compressor, and can also be combined with a circuit that controls the refrigerant compressor on and off depending on the temperature of the air inside the car.

The present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a first embodiment of the present invention up to an electromagnetic clutch that drives a refrigerant compressor.

Th1 is a thermistor as a temperature detection element installed on the blowout side of the evaporator (not shown) (may be between the fins of the evaporator), and OPl is the detection output of thermistor Th1, and the blowout side air temperature is set to T1 (for example, 3 Similarly, the comparator amplifier OP2 outputs a low level when the temperature drops below T1 (℃), and the output goes to a low level when the air temperature on the outlet side drops to a temperature T2 (for example, 0℃), which should be the lower limit value lower than T1. The comparison amplifier OF2 is connected to the comparison amplifier OP1 through a delay circuit consisting of a resistor R7 and a capacitor C.
A comparator amplifier whose output becomes low level after a predetermined time 11 (for example, 10 minutes) determined by the discharge time constant of the delay circuit after the output of P1 becomes low level; Only when both outputs of OP3 are at a high level, transistor Q is made conductive to operate relay RL, thereby energizing electromagnetic clutch MC for driving the refrigerant compressor.

R5 and R6 are respectively comparator amplifiers OP1. This is a resistor for providing hysteresis characteristics to OP2.

Note that the output of the comparison amplifier OP2 is determined when the air temperature on the outlet side is T.
When the refrigerant compressor is stopped and the temperature rises to a predetermined value T3, it reverses and becomes a high level. It is set so that, in some cases, a sufficient amount of time can be obtained to remove this by continuing air blowing without refrigerant supply, and this can be arbitrarily adjusted by the value of the resistor R6.

Dl is a diode for resetting the operation of the delay circuit made up of resistor R7 and capacitor C, and when the air temperature on the outlet side falls below T1 and the output of comparator amplifier OP1 becomes low level, capacitor C starts discharging. If the air temperature on the outlet side becomes higher than T1 within the predetermined time 11 thereafter, the capacitor C is instantly charged through the diode D1 to stop the delay operation.

Further, D2 is a diode which makes the output of the comparison amplifier OP2 low level with the low level output of the comparison amplifier OP3,
When a predetermined time t1 has elapsed since the air temperature on the outlet side became lower than T1, the output of the comparator amplifier OP2 is at a high level.
In other words, even if the air temperature on the outlet side is higher than T2, the output of the comparison amplifier OP2 is set to a low level via the diode D2,
The temperature at which the refrigerant compressor is re-driven is determined by the outlet air temperature being T.
As in the case where the temperature drops to 2, the setting is set to T3 so that sufficient time necessary for defrosting can be obtained.

Next, a second graph showing the hourly characteristics of the air temperature on the outlet side of the evaporator is shown.
The circuit operation will be explained with reference to the figures.

In the region a in FIG. 2, the air temperature on the outlet side has not decreased to the set temperature T1, and in this state, the comparator amplifier OP1. Both outputs of OP2 are at a high level, and energization of electromagnetic clutch MC is maintained.

The area in the middle of FIG. 2 is a case where the heat load on the evaporator is relatively small and the outlet air temperature drops to the set temperature T2. The voltage divided by R3 is compared with the voltage divided by resistor R4 and thermistor Th, and when the air temperature on the blowing side decreases to T2, the inverting terminal voltage and the non-inverting terminal voltage become equal and are output. When this becomes a low level, the power to the electromagnetic clutch MC is cut off and the refrigerant compressor is stopped.

Thereafter, when the air temperature on the outlet side begins to rise and reaches T3, the output of the comparator amplifier OP2 becomes high level again, and the electromagnetic clutch MC becomes energized.

Note that the periodic temperature changes shown in the area S occur when the cooling time is short and there is not much frost on the evaporator, and in such conditions the outlet air temperature changes from T1 to T
The time it takes for the temperature to drop to T2 and rise again to T2 is sufficiently shorter than the predetermined time t1.

However, with such control alone, it is difficult to completely prevent frost from forming on the evaporator when the evaporator continues to operate for a long time with a large heat load, and frost gradually begins to accumulate.

When frost begins to accumulate, the heat exchange efficiency of the evaporator deteriorates and the air temperature on the outlet side decreases to T2, as shown in area C in Figure 2.
It becomes difficult for the temperature to drop to T2, and the state continues to be slightly higher than T2.

Comparison amplifier OP1 compares the voltage divided by resistors R1, R2 and resistor R3 with the voltage divided by resistor R4 and thermistor Th1, and when the air temperature on the blowing side decreases to T1, the voltage at the inverting terminal changes. becomes equal to the voltage at the non-inverting terminal, and the output becomes low level.

- Comparison amplifier OP3 compares the voltage divided by resistors R1, R2 and resistor R3 with the terminal voltage of capacitor C, and at the same time the output of comparator amplifier OP1 becomes low level, capacitor C starts discharging. Therefore, when the non-inverting terminal voltage drops exponentially and becomes equal to the inverting terminal voltage, that is, after a predetermined time t1, the output becomes a low level.

As a result, the power to the electromagnetic clutch MC is cut off and the refrigerant compressor is stopped. However, as mentioned above, at this time, the output of the comparator amplifier OP2 is also reduced to a low level due to the diode D2, so the refrigerant compressor changes the temperature of the air on the outlet side. The stoppage continues until the temperature rises to T3, and during this time the frost on the evaporator surface is removed.

Note that a predetermined time t has elapsed since the air temperature on the outlet side decreased to T1.
If it becomes higher than T1 again within 1, as described above, the capacitor C is charged by the diode D1 and returns to the state before the start of discharging, and the comparator amplifier OP1
When the output returns to a high level and the air temperature on the blowing side falls to T1 again, the operation starts.

As can be understood from the above, the present invention not only controls the temperature inside the vehicle by detecting the air temperature of the evaporator or its outlet side and controlling the refrigerant compressor on and off, but also prevents the accumulation of frost on the evaporator. By detecting that frost is beginning to occur based on a stagnation phenomenon in the outlet air temperature and stopping the refrigerant compressor for a sufficient period of time necessary for defrosting, frost formation can be kept to a minimum.

This makes it possible to control the interior temperature of the vehicle with the set temperature T2 lower than before, making it possible to fully utilize the capacity of the refrigerant compressor, and providing sufficient cooling effect even in the middle of summer, ensuring a comfortable interior at all times. Can be used for cooling.

FIG. 3 is a circuit diagram of another embodiment of the present invention.

This embodiment uses a thermistor T installed on the outlet side of the evaporator.
In addition to h1, there is a thermistor T as a temperature detection element inside the car.
h2 is arranged so that the temperature inside the vehicle can be controlled by its output.

OF2 is the temperature T4 where the temperature inside the vehicle is set by the driver.
It is a comparison amplifier whose output becomes low level when the voltage drops to
This temperature T4 can be set arbitrarily by variable resistor VR (for example, 18~
28°C).

That is, the comparison amplifier OP4 compares the voltage divided by the resistor R1□ and the resistor R13 forming the bridge circuit with the voltage divided by the resistor R1□, the variable resistor VR, and the thermistor Th2, When the temperature inside the vehicle drops to T4 and the inverting terminal voltage and non-inverting terminal voltage become equal, the output becomes a low level and the electromagnetic clutch MC
Cut off the power to.

Such control based on the vehicle interior temperature is performed when the heat load on the evaporator is relatively small, and the operating rate of the refrigerant compressor does not increase, so there is almost no frost on the evaporator.

The control based on the air temperature on the outlet side is the same as in the embodiment described above, and temperature control is performed so that frost does not form on the evaporator.

As is clear from this, in this embodiment, frost formation prevention control is performed based on the air temperature on the outlet side of the evaporator, and vehicle interior temperature control is performed using the vehicle interior temperature, so as in the previous embodiment, frost formation on the evaporator is prevented. Of course, it is possible to comfortably cool the inside of the car at any set temperature.

FIG. 4 is a circuit diagram of an embodiment that enables frost prevention control and more comfortable vehicle interior temperature control than the embodiment of FIG.

This embodiment is the same as the circuit shown in Fig. 1 except for the peripheral circuit of the comparator amplifier OP2, but the reference voltage to the non-inverting input terminal of the comparator amplifier OP2 is connected to a variable resistor R for setting the temperature inside the vehicle.
By making the set value T2 of the air temperature of the evaporator or its outlet side variable within a certain range, the temperature set by the variable resistor VR1 can be controlled by turning on and off the refrigerant compressor. It is possible to control the interior temperature of the vehicle.

Further, a switch SW is linked to the variable resistor VR1, so that when the maximum cooling is set by the variable resistor vR1, the resistor R18 connected in series to the feedback resistor R6 of the comparator amplifier OP2 is short-circuited.

In this way, the positive feedback of the comparator amplifier OP2 is connected to the resistor R
6° R18, the time from when the refrigerant compressor is stopped by the comparator amplifier OP2 to when it is driven again can be shortened compared to the circuit shown in Fig. 1, thereby reducing the temperature inside the vehicle. Comfortable cooling can be achieved because the changes can be minimized.

On the other hand, when the strongest cooling is set using the variable resistor VR1, frost formation is likely to occur, but the feedback resistance of the comparator amplifier OP2 is reduced due to the short circuit caused by the switch SW.
As in the embodiment shown in the figure, by lengthening the time until the refrigerant compressor is driven again, control can be performed to reliably prevent frost formation.

Of course, a non-contact switch may be used instead of the switch SW.

[Brief explanation of the drawing]

Fig. 1 is a control circuit diagram of the first embodiment of the present invention, Fig. 2 is a characteristic diagram showing temporal changes in the air temperature on the outlet side of the evaporator and the temperature inside the vehicle due to this control circuit, Figs. The figures are control circuit diagrams of second and third embodiments of the present invention, respectively. In the figure, Th1. Th2 is a thermistor, OPl, OF2゜O20, OF2 are comparative amplifiers, RL is a relay, MC is an electromagnetic clutch, and A1 is an AND gate.

Claims (1)

[Scope of Claims] 1. In a car cooler control device that controls the temperature inside a car by on/off control of a refrigerant compressor, the air temperature of an evaporator or its outlet side is detected, and the detected temperature has decreased to a first value. A car cooler control device comprising: a circuit that stops the refrigerant compressor when the refrigerant compressor reaches a second value that is higher than the first value, and a circuit that stops the refrigerant compressor when a predetermined time elapses at or below a second value higher than the first value. 2. In a car cooler control device that controls the temperature inside a car by on/off control of a refrigerant compressor, the air temperature of the evaporator or its outlet side is detected, and when the detected temperature drops to a first value, the refrigerant compressor is turned on. a circuit for stopping the refrigerant compressor when a predetermined period of time has elapsed at or below a second value higher than the first value; and a circuit for detecting the temperature inside the car and when the temperature inside the car has decreased to a predetermined value. A car cooler control device comprising a circuit for stopping the refrigerant compressor.