JPH11201560A - Supercritical refrigerating cycle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a decrease in a refrigerating capacity when a rotational speed of a compressor is decelerated. SOLUTION: When a rotational speed of a compressor 1 is decelerated so that a pressure of a low pressure side becomes a prescribed value or more, an opening of a pressure control valve 3 is reduced to enhance an output side refrigerant pressure of a radiator 2 to higher than a prescribed pressure decided by an optimum control line ηmax, and the opening of the valve 5 is reduced to increase a heating degree to larger than a prescribed value. Thus, since a specific enthalpy difference of an evaporator 6 can be increased, even when the rotational speed to the compressor 1 is decelerated, it can prevent a refrigerating capacity from being largely lowered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a supercritical refrigeration cycle in which the pressure on the discharge side (high pressure side) of a compressor exceeds a critical pressure of a refrigerant, and is effective for use in vehicles.

[0002]

2. Description of the Related Art Carbon dioxide (CO)_Two) As a refrigerant
Field refrigeration cycle (hereinafter, this supercritical refrigeration cycle is referred to as CO
_TwoCalled a cycle. ) Then, when increasing the refrigeration capacity
As described in JP-A-3-503206,
CO at radiator outlet side (high pressure side) _TwoNeed to increase pressure
There is.

However, if the pressure on the high pressure side is simply increased to increase the refrigeration capacity, the amount of increase in the compression work of the compressor is larger than the increase in the refrigeration capacity.
There is a problem that the coefficient of performance of _two cycles is deteriorated. Therefore, the applicant has already filed an application for a pressure control valve that controls the CO ₂ pressure at the radiator outlet side based on the CO ₂ temperature at the radiator outlet side so that the coefficient of performance is maximized (Japanese Patent Application No. Hei 10-26138). 9-231249).

[0004]

In a vehicle air conditioner, the compressor is driven by an engine for running the vehicle. Therefore, when the engine speed is low such as when the vehicle is stopped (during idling), the compressor is not operated. The number of revolutions also decreases. For this reason, when the CO ₂ cycle is applied to an air conditioner for a vehicle, when the engine speed is low, such as during idling, the speed of the compressor decreases and the CO ₂
In addition to the decrease in the mass flow rate of CO ₂ circulating in the cycle, the pressure control valve adjusts its opening so as to maximize the coefficient of performance, so that the refrigeration capacity becomes insufficient (FIG. 2). To the two-dot chain line).

[0005] Further, in the CO ₂ cycle, in addition to operating in a region (supercritical region) where the pressure is higher than that of a refrigeration cycle using chlorofluorocarbon as a refrigerant, the slope of the CO ₂ saturated air line is reduced. Since it is smaller than the slope of the saturated air line, when the mass flow rate decreases as the compressor rotation speed decreases and the pressure in the evaporator (low pressure side) increases, it becomes larger than the refrigeration cycle using Freon as a refrigerant. The refrigeration capacity decreases (FIG. 6).

SUMMARY OF THE INVENTION In view of the foregoing, it is an object of the present invention to prevent a decrease in the refrigerating capacity when the number of rotations of a compressor decreases.

[0007]

The present invention uses the following technical means to achieve the above object. Claim 1,
In the invention described in Item 3, when the refrigerant pressure on the suction side of the compressor (1) exceeds the second predetermined pressure, the opening degree of the pressure control valve (3) is reduced to reduce the refrigerant on the outlet side of the radiator (2). Pressure first
It is characterized in that the heating degree is higher than a predetermined value and the opening degree of the heating degree control valve (5) is reduced to make the heating degree larger than a predetermined value.

As a result, the specific enthalpy difference between the inlet side and the outlet side of the evaporator (6) can be increased.
Even when the refrigerant pressure on the suction side of the compressor (1) exceeds the second predetermined pressure and the number of revolutions of the compressor (1) decreases, it is possible to prevent the refrigerating capacity from greatly decreasing. Claim 2,
In the invention described in Item 3, when the rotation speed of the compressor (1) is equal to or lower than the predetermined rotation speed, the opening degree of the pressure control valve (3) is reduced to reduce the outlet-side refrigerant pressure of the radiator (2) from the predetermined pressure. In addition to increasing the heating degree, the opening degree of the heating degree control valve (5) is reduced to make the heating degree larger than a predetermined value.

Thus, the same effect as the first aspect of the present invention can be obtained. In addition, the code | symbol in the parenthesis of each said means shows the correspondence with the concrete means of embodiment mentioned later.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment)
The CO ₂ cycle according to the present invention is applied to a vehicle refrigeration cycle, and FIG. 1 is a schematic diagram of a CO ₂ cycle according to the present embodiment. Reference numeral 1 denotes a compressor that obtains driving force from a vehicle driving engine to compress CO ₂ , and 2 denotes a compressor 1
A radiator (gas cooler) for cooling the refrigerant discharged from the radiator. Note that the temperature inside the radiator 2 exceeds the critical temperature of the refrigerant (CO ₂ ) in each state (normal operation state), as described later.

Reference numeral 3 denotes the CO ₂ temperature at the outlet side of the radiator 2 and the CO ₂ temperature.
₂ is an electric pressure control valve whose opening is controlled so that the temperature has a relationship shown by an optimum control line ηmax (see FIG. 2). Gas liquid 2
This is a receiver that flows out only the liquid-phase refrigerant out of the CO _{2 in} the phase state and stores excess CO ₂ during the CO ₂ cycle.

The optimum control line ηmax is defined as the temperature at the outlet of the radiator 2 at which the coefficient of performance of the CO ₂ cycle (supercritical refrigeration cycle) becomes maximum with respect to the temperature of the refrigerant at the outlet of the radiator 2 (CO ₂ ). The refrigerant (CO ₂ ) pressure is drawn on a Mollier diagram. Reference numeral 5 further decompresses the liquid phase CO ₂ flowing out of the receiver 4 and sets the degree of heating of the CO ₂ on the inlet side of the compressor 1 (the outlet side of the evaporator 6 described later) to a predetermined value (0 in this embodiment). (° C.) is an electric heating degree control valve whose opening is controlled, and 6 is an evaporator for evaporating the liquid-phase refrigerant flowing out of the heating degree control valve 5.

Reference numeral 7 denotes a first temperature sensor (first temperature detecting means) for detecting the CO ₂ temperature on the outlet side of the radiator 2, and 8 denotes an inlet side of the compressor 1 (an outlet side of the evaporator 6). CO
A second temperature sensor for detecting a _second temperature (second temperature detection means)
It is. Reference numeral 9 denotes a first pressure sensor (first pressure detecting means) for detecting the CO ₂ pressure on the outlet side of the radiator 2, and reference numeral 10 denotes the CO ₂ pressure on the inlet side of the compressor 1 (the outlet side of the evaporator 6). This is a second pressure sensor (second pressure detecting means) for detecting. The electronic control unit (ECU) 11
The control valves 3 and 5 are controlled in accordance with a preset program on the basis of the signals (10) to (10).

Next, the operation and features of the CO ₂ cycle according to this embodiment will be described. 1. As when the pressure constant each run at the outlet side of the evaporator 6 (the suction side of the compressor 1) is a predetermined pressure range, the electronic control device 11, CO ₂ cycle is the constant respective operating state, CO ₂ The cycle is controlled to operate as shown by the solid line in FIG. Here, the predetermined pressure range is set so that the pressure on the suction side of the compressor 1 is substantially equal to the predetermined pressure (second predetermined pressure) even when the operation of the CO ₂ cycle is stable. This is because the variation in the center is considered.

That is, the CO ₂ that has been compressed (AB) by the compressor 1 and has become high temperature and high pressure is cooled by the radiator 2 (BC). At this time, the pressure on the high pressure side (the CO ₂ pressure on the outlet side of the radiator 2) is controlled so as to change along the optimum control line ηmax by adjusting the opening of the pressure control valve 3. Then, the pressure control valve 3 and the heating degree control valve 5
Is decompressed (CD) by gas and becomes a gas-liquid two-phase state
Of the _two , the liquid phase CO ₂ evaporates in the evaporator 6 to cool the air. At this time, the heating degree is calculated from the detection values of the second temperature sensor 8 and the second pressure sensor 10, and the heating degree becomes 0
The degree of opening of the heating degree control valve 5 is controlled so that the temperature becomes ° C.

[0016] The constant operation refers to a state in which the engine speed is higher than, for example, the idling speed, and the vehicle is running (for example, at a speed of 30 km / h or more). 2. When each operation is not fixed When the engine speed (the number of revolutions of the compressor 1) decreases without decreasing the heat load in the evaporator 6, the pressure and the heating degree in the evaporator 6 (low pressure side) increase. In order to maintain the heating degree at 0 ° C., the degree of opening of the heating degree control valve 5 is increased to increase the mass flow rate of CO ₂ flowing through the evaporator 6.

On the other hand, as the pressure on the low pressure side rises, the compressor 1
The temperature of CO ₂ sucked into the compressor 1 rises, so that the temperature of CO ₂ on the discharge side (high pressure side) of the compressor 1 rises. For this reason, the pressure control valve 3 raises the pressure on the high pressure side along the optimum control line ηmax according to the rise in the CO ₂ temperature on the high pressure side (the exit side of the radiator 2) (two-dot chain line in FIG. 2). However, in this state, the refrigerating capacity (the specific enthalpy difference between the inlet side and the outlet side of the evaporator 6) becomes small.

Therefore, in the present embodiment, when the pressure on the outlet side of the evaporator 6 rises beyond a predetermined pressure range,
The electronic control unit 11 considers that the engine speed is equal to or lower than a predetermined speed (idling speed) and further reduces the opening of the pressure control valve 3 to reduce the outlet side CO ₂ pressure of the radiator ₂ to an optimal control line. ηmax (first predetermined pressure), and the degree of heating is made greater than 0 ° C. by reducing the degree of opening of the heating degree control valve 5 (the dashed line in FIG. 2).

As a result, the specific enthalpy difference between the inlet side and the outlet side of the evaporator 6 can be increased, so that the refrigerating capacity is greatly reduced even when the rotational speed of the compressor 1 is reduced. Can be prevented. By the way, the refrigerating capacity is
Strictly speaking, it is indicated by the product of the specific enthalpy difference in the evaporator 6 and the mass flow rate of CO ₂ flowing through the evaporator 6.
In the CO ₂ cycle, since the operating pressure is high and the CO ₂ density is high, the refrigerating capacity may be considered to change in conjunction with the increase or decrease in the specific enthalpy difference.

When the engine speed is equal to or lower than the idling speed, CO ₂ indicated by the optimum control line ηmax
Since the pressure at the outlet of the radiator 2 is increased beyond the CO ₂ pressure corresponding to the temperature, the compression work of the compressor 1 is increased and the coefficient of performance is deteriorated, but the degree of heating is also increased.
Deterioration of the coefficient of performance can be minimized (Fig. 3
reference). Therefore, it is possible to prevent the refrigerating capacity from being significantly reduced even when the rotational speed of the compressor 1 is reduced, while suppressing the deterioration of the coefficient of performance.

(Second Embodiment) In this embodiment, as shown in FIG. 4, a third temperature sensor 12 for detecting the CO ₂ temperature at the inlet side of the evaporator 6 is used instead of the second pressure sensor 10. is there. That is, in the gas-liquid two-phase state, the liquid phase CO ₂ is
Since the temperature and the pressure are constantly changed and the CO ₂ pressure is uniquely determined from the CO ₂ temperature, the pressure at the outlet side of the evaporator 6 (in the evaporator 6) is indirectly detected. In the present embodiment, the heating degree is calculated from the temperature difference between the second temperature sensor 8 and the third temperature sensor 12.

The CO 2 at the outlet of the heating degree control valve 5
State of the CO ₂ from the _second state to the saturated vapor line, since known as CO ₂ temperature is constant, the third temperature sensor 12
Can also be arranged in the evaporator 6. (Third Embodiment) In this embodiment, as shown in FIG. 5, the engine speed (the speed of the crank pulley in this embodiment) is detected by a speed sensor 13 and the engine speed is determined to be lower than a predetermined speed. In this case, the pressure control valve 3 and the heating degree control valve 5 are controlled in the same manner as in the first embodiment, assuming that the operation is undefined.

Incidentally, the pressure fluctuation at the outlet side of the evaporator 6 is as follows.
The compressor 1 (engine) is interlocked with the rotation speed fluctuation. However, since the pressure fluctuation fluctuates with a time lag with respect to the rotation speed fluctuation, in the above-described embodiment, the refrigerating capacity temporarily decreases (2 in FIG. 2). After that, the degree of heating and the high-pressure side pressure increase (the state shown by the one-dot chain line in FIG. 2). On the other hand, in the present embodiment, the number of revolutions of the engine (compressor 1) is directly detected to control the pressure control valve 3 and the heating degree control valve 5, so that the refrigerating capacity is prevented from being reduced. it can.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a CO ₂ cycle according to a first embodiment of the present invention.

FIG. 2 is a Mollier diagram of CO ₂ .

FIG. 3 shows the relationship between the refrigeration capacity Q and the coefficient of performance COP of the CO ₂ cycle and the pressure according to the first embodiment.

FIG. 4 is a schematic diagram of a CO ₂ cycle according to a second embodiment of the present invention.

FIG. 5 is a schematic diagram of a CO ₂ cycle according to a third embodiment of the present invention.

FIG. 6A is a Mollier diagram of Freon, and FIG.
Is a Mollier diagram of CO ₂ .

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Compressor, 2 ... Radiator, 3 ... Pressure control valve, 4 ... Receiver, 5 ... Heating degree control valve 6 ... Evaporator.

Claims (3)

[Claims] A compressor (1) for compressing a refrigerant; a radiator (2) for cooling the refrigerant discharged from the compressor (1) and having an internal pressure temperature exceeding a critical pressure of the refrigerant; A pressure control valve (3) whose opening is controlled such that the outlet-side refrigerant pressure of the radiator (2) becomes a first predetermined pressure determined based on the outlet-side refrigerant temperature of the radiator (2).
And a heating degree control valve (the opening degree of which is controlled such that the refrigerant flowing out of the pressure control valve (3) is reduced in pressure and the degree of heating of the refrigerant on the inlet side of the compressor (1) is a predetermined value. 5)
And an evaporator (6) for evaporating the refrigerant depressurized by the heating degree control valve (5), and when the refrigerant pressure on the suction side of the compressor (1) exceeds a second predetermined pressure. Reducing the opening of the pressure control valve (3) to make the outlet side refrigerant pressure of the radiator (2) higher than the first predetermined pressure and reducing the opening of the heating degree control valve (5). A supercritical refrigeration cycle, wherein the heating degree is made larger than the predetermined value. 2. A compressor (1) for compressing a refrigerant, and a radiator (2) for cooling the refrigerant discharged from the compressor (1) and having an internal pressure exceeding a critical pressure of the refrigerant.
A pressure control valve (3) whose opening is controlled such that the outlet-side refrigerant pressure of the radiator (2) becomes a predetermined pressure determined based on the outlet-side refrigerant temperature of the radiator (2). And a pressure control valve for controlling the degree of opening such that the refrigerant flowing out of the pressure control valve (3) is reduced in pressure and the degree of heating of the refrigerant on the inlet side of the compressor (1) becomes a predetermined value. (5)
And an evaporator (6) for evaporating the refrigerant depressurized by the heating degree control valve (5). When the rotation speed of the compressor (1) is equal to or lower than a predetermined rotation speed, the pressure control valve (3) The opening degree of the radiator (2) is reduced to be higher than the predetermined pressure by reducing the opening degree, and the opening degree of the heating degree control valve (5) is reduced to reduce the heating degree. A supercritical refrigeration cycle characterized by being larger than a predetermined value. 3. The supercritical refrigeration cycle for a vehicle according to claim 1, wherein said compressor (1) is driven by a vehicle driving engine.