JPH0769043A - Air conditioner for vehicle - Google Patents

Abstract

PURPOSE:To restrain an undesired change in engine speed to the minimum by reducing the number of ON and OFF times of a compressor at a low outside air temperature. CONSTITUTION:An air conditioner for a vehicle has a variable displacement compressor 101 driven by an engine, an evaporator 102 to cool air by evaporating a refrigerant forcibly sent by this variable displacement compressor 101 and a control means 103 to carry out evaporator freezing preventive control to stop forcibly the compressor 101 when a temperature of the evaporator 102 becomes less than a prescribed temperature when an outside air temperature is less than the prescribed temperature, and has a vehicle speed sensor 104 to detect travel speed of the vehicle and a prohibiting means 105 to prohibit the evaporator freezing preventive control by, the control means 103 even if the outside air temperature is lower than the prescribed temperature when detected vehicle travel speed is less than prescribed speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle air conditioner having an evaporator freeze prevention function.

[0002]

2. Description of the Related Art In a vehicle air-conditioning system in which a variable capacity compressor driven by an engine pumps a refrigerant under pressure, and an evaporator cools the air by evaporating the refrigerant, the outside air temperature is usually detected. Equipped with an air temperature sensor and an evaporator outlet temperature sensor that detects the air temperature at the outlet of the evaporator.If the outside air temperature is below the specified temperature, the compressor will be forcibly stopped (OFF when the air temperature at the evaporator outlet falls below the specified temperature). In this way, the evaporator is prevented from freezing (for example, a new model vehicle manual (Y32-1) issued by Nissan Motor Co., Ltd., June 1991). When the compressor is stopped by such compressor freeze prevention control, the air temperature at the evaporator outlet gradually rises, and when the temperature exceeds a predetermined temperature, the compressor operates (turns on) again. Therefore, when the outside air temperature is low, the compressor is intermittently operated, for example, as shown in FIG.

By the way, the engine control device of the vehicle is
The auxiliary air flow rate to the engine is adjusted by an AC (auxiliary air introduction) valve or the like to appropriately control the idle speed, and when the compressor is operated intermittently as described above, On
It is also necessary to intermittently change the engine idle speed as indicated by the solid line in FIG. But,
In a variable displacement compressor, the load during operation of the compressor (torque required for the engine) changes depending on the outside air temperature, so it is extremely difficult to adjust the auxiliary air flow rate to maintain an appropriate engine speed.

FIG. 7 shows the load of the variable displacement compressor with respect to the outside air temperature. As is clear from this figure,
The load on the compressor increases as the outside air temperature increases. Now, in FIG. 7 (a), when the outside air temperature is T1, the AAC valve is adjusted so that the engine speed becomes appropriate when the compressor is turned on and off and when the compressor is turned off (hereinafter referred to as on / off switching). Assuming that the auxiliary air flow rate is set according to the above, when the outside air temperature is lower than T1, the set auxiliary air flow rate becomes excessive as the outside air temperature becomes lower as indicated by the diagonal line, and when the outside air temperature is higher than T1, the outside air temperature becomes The higher the price, the less. When the auxiliary air flow rate becomes excessively large, the engine speed undesirably increases, and when it is insufficient, it undesirably decreases.

In addition to the AAC valve, FIG.
The case where a rotation speed correction mechanism called ICD (first idle control device) is also used is shown.
Now, for example, when the outside air temperature is T1, the engine speed at the time of the compressor on / off conversion is set to an appropriate value A
While setting the auxiliary air flow rate by the AC valve, set the auxiliary air flow rate by both the AAC valve and the FICD so that the engine speed at the time of switching the compressor on / off becomes an appropriate value when the outside air temperature is T2, Further, if the FICD is turned off when the outside air temperature is lower than T3 and turned on when the outside air temperature is T3 or higher, the excess or deficiency of the auxiliary air amount becomes as shown by the diagonal lines in the figure.

[0006]

As described above, the evaporator freezing prevention control is performed at low ambient temperatures, and the compressor is frequently turned on and off. However, as shown in FIG.
Looking at (b), it can be seen that the auxiliary air flow rate at the time of turning on and off is excessive in both low ambient temperatures when the compressor is turned on and off frequently.
Therefore, when the compressor is turned on,
As indicated by the one-dot chain line in (b), the engine speed may rise undesirably, while the engine speed may drop undesirably when the compressor is on and off. Especially when the engine speed is low, such as during idle speed, it is easy to feel a rise or drop in the engine speed.
This will make passengers uncomfortable.

An object of the present invention is to provide an air conditioning system for a vehicle in which the number of times the compressor is turned on and off is reduced under a low outside air temperature to suppress undesired fluctuations in the engine speed to a minimum.

[0008]

The invention will be described with reference to FIG. 1 which is a diagram corresponding to claims. In the present invention, a variable displacement compressor 101 driven by an engine and a refrigerant pumped by the variable displacement compressor 101 are evaporated. A vehicle having an evaporator 102 that cools air, and control means 103 that performs evaporator freeze prevention control that forcibly stops the compressor 101 when the temperature of the outside air is lower than a predetermined temperature when the temperature of the outside air is lower than the predetermined temperature. It is applied to air conditioners for automobiles. Then, the vehicle speed sensor 104 for detecting the traveling speed of the vehicle, and when the detected vehicle traveling speed is less than the predetermined speed, the evaporator freeze prevention control by the control means 103 is prohibited even if the outside air temperature is less than the predetermined temperature. The prohibition means 105 is provided to solve the above problems. In particular, the invention of claim 2 is the compressor 10 by the freeze prevention control of the evaporator.
When the vehicle traveling speed changes from a predetermined speed or more to a predetermined speed or less while 1 is stopped, the prohibition means 105 prohibits the evaporator freeze prevention control until the temperature related to the evaporator 102 becomes equal to or higher than the predetermined temperature. The prohibition canceling means for canceling is further provided.

[0009]

When the vehicle traveling speed detected by the vehicle speed sensor 104 is lower than the predetermined speed, the prohibiting means 105 prohibits the evaporator freeze prevention control by the control means 103 even if the outside air temperature is lower than the predetermined temperature. According to this
For example, the compressor 101 is not frequently turned on and off when the fluctuation of the engine speed is easily felt, such as at the time of idle rotation, and undesired fluctuations of the engine speed (up and down) occur at the time of switching the compressor on and off. Inclusion) is suppressed to a minimum. Here, when the vehicle speed is lower than the predetermined speed, the flow velocity of the low-temperature outside air guided to the evaporator 102 is low, so that the evaporator 102 is unlikely to freeze. Therefore, the evaporator may freeze even if the above-mentioned evaporator freeze prevention control is not performed. Is low. In particular, according to the invention of claim 2, when the vehicle speed changes from a predetermined speed or higher to a speed lower than the predetermined speed while the compressor is stopped by the evaporator freezing prevention control, the evaporator freezes until the temperature of the evaporator becomes higher than or equal to the predetermined temperature. The prohibition of prevention control is released. That is, the compressor is turned off until the temperature related to the evaporator becomes equal to or higher than the predetermined temperature, the compressor is turned on when the temperature becomes equal to or higher than the predetermined temperature, and thereafter, the compressor is kept in the on state regardless of the temperature related to the evaporator.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described with reference to FIGS. FIG. 2 is a block diagram of a vehicle air conditioner according to the present invention. The air-conditioning control circuit indicated by reference numeral 1 includes an outside air temperature T
An outside air temperature sensor 2 for detecting amb, an evaporator outlet temperature sensor 3 for detecting an air temperature Tint near the outlet of an evaporator (not shown), an air conditioner switch 4 for instructing the operation of the variable capacity compressor 14, and an operation of a blower fan. The fan switch 5 for instructing the vehicle speed and the vehicle speed sensor 6 for detecting the traveling speed V of the vehicle are connected. The air conditioning control circuit 1 forms a compressor on / off signal as described later according to an input signal from each sensor or switch, and inputs the compressor on / off signal to the engine control circuit indicated by reference numeral 11.

A relay coil 13a of a compressor relay 13 is connected to the engine control circuit 11 via a refrigerant pressure switch 12, and a relay switch 13b is connected to an electromagnetic clutch 14a of a variable capacity compressor 14. When the relay switch 13b is turned on, the electromagnetic clutch 14a is excited, the power of the engine (not shown) is transmitted to the compressor 14, and the compressor 14 operates (turns on). When the relay switch 13b is turned off, the electromagnetic clutch 14a is demagnetized, the engine and the compressor 14 are cut off, and the compressor 14 is stopped (turned off). The refrigerant pumped by the compressor 14 returns to the compressor 14 through a condenser, a liquid tank, an expansion valve and an evaporator 15 which are not shown. At this time, the evaporator 15 cools the air from the blower fan (not shown) by evaporating the refrigerant.

The detection output of the vehicle speed sensor 6 described above is also input to the engine control circuit 11, and the engine control circuit 11 controls the engine speed based on the input signal. The refrigerant pressure switch 12 is switched from ON to OFF when the refrigerant pressure in the refrigeration cycle exceeds a predetermined value. When the switch 12 is turned OFF, the electromagnetic clutch 14a is turned OFF and the compressor 14 is stopped.

Next, the procedure of compressor control by the air conditioning control circuit 1 will be described with reference to the flow chart of FIG. This program is called periodically in air conditioning control. First, in step S1, it is determined whether the air conditioner switch 4 is on or off.
In step 2, the compressor off signal is output to the engine control circuit 11. If the air conditioner switch 4 is on, the process proceeds to step S3, and it is determined whether the fan switch 5 is on or off. If the fan switch 5 is off, the process proceeds to step S2, and if it is on, the process proceeds to step S4. In step S4, based on the illustrated characteristics, the outside air temperature sensor 2
It is determined which of the states A, B, and C the outside air temperature Tamb detected in step A is. Note that T11 to T14 in step S4 are constants set in advance for the outside air temperature.

Next, in step S5, if the result of the above determination is that the state is C, that is, if the outside air is at or above the predetermined temperature T13 or T14, then the operation proceeds to step S6, and a compressor ON signal is output. If it is determined in step S7 that the state is not state B, that is, state A,
In step S2, the compressor off signal is output. Further, when it is determined in step S7 that the state is state B, the process proceeds to step S8, and according to the vehicle speed V detected by the vehicle speed sensor 6, "high speed" or "low speed" is determined from the illustrated characteristics.
That is, it is determined whether the vehicle speed V is equal to or higher than the predetermined speed V1 or V2. When it is determined in step S9 that the speed is "low speed", the process proceeds to step S6 and the compressor 14
Output an ON signal.

On the other hand, when it is determined that the speed is "high speed" in step S9, the above-described evaporator freeze prevention control is performed. That is, first, in step S10, it is determined whether the compressor 14 should be turned on or off based on the evaporator outlet temperature Tint detected by the evaporator outlet temperature sensor 3. When it is determined in step S11 that the result is "ON", that is, when the evaporator outlet temperature Tint is equal to or higher than the predetermined temperature T21 or T22, the process proceeds to step S6 and the compressor ON signal is output. On the other hand, if it is determined to be “OFF”, that is, if the evaporator outlet temperature Tint is determined to be less than the predetermined temperature T21 or T22, step S
Proceed to step 2 to output the compressor off signal.

When the compressor on signal is output from the compressor control circuit 1, the engine control circuit 11
Turns on the relay 13 to operate the compressor 14, and when the compressor off signal is output, the relay 1
3 is turned off and the compressor 14 is stopped.

According to the procedure of FIG. 3 described above, when both the air conditioner switch 4 and the fan switch 5 are on and the outside air temperature Tamb is within the predetermined temperature range (state B),
If the vehicle speed V detected by the vehicle speed sensor 6 is equal to or higher than a predetermined speed, the evaporator freeze prevention control is performed. That is, the compressor 14 is turned on when the air temperature Tint at the evaporator outlet is equal to or higher than a predetermined temperature, and the compressor 14 is turned off when Tint is lower than the predetermined temperature.
Therefore, as shown in FIG. 6A, the compressor 14 is repeatedly turned on and off, which prevents the evaporator 15 from freezing.

On the other hand, even if both the air conditioner switch 4 and the fan switch 5 are on and the outside air temperature Tamb is within the predetermined temperature range (state B), the evaporator freeze prevention control is prohibited when the vehicle speed V is less than the predetermined speed. The compressor 14 is kept in the ON state. Therefore, the compressor 14 is not frequently turned on / off when the fluctuation of the engine speed is easily felt, for example, at the time of idle rotation, and the undesired fluctuation of the engine speed generated at the time of switching the compressor on / off is minimized. It can be reduced to the limit. When the vehicle speed V is lower than the predetermined speed, the flow velocity of the low temperature outside air guided to the evaporator 15 is low, and therefore the evaporator 15 is unlikely to freeze even if the evaporator freeze prevention control is not performed.

In the configuration of the above embodiment, the air conditioning control circuit 1 and the engine control circuit 11 respectively constitute the control means 103 and the prohibition means 105.

4 and 5 show another embodiment. In the above embodiment, the example in which the evaporator freeze prevention control is always prohibited when the vehicle speed V is lower than the predetermined speed has been shown. However, in this embodiment, the vehicle speed is stopped when the compressor 14 is stopped by the evaporator freeze prevention control. When V changes from above a predetermined speed to below a predetermined speed, the prohibition of the evaporator freeze prevention control is released until the air temperature Tint at the evaporator outlet falls below the predetermined temperature.

FIG. 4 is obtained by adding step S21 to the process of FIG. 3, and the parts not shown are the same as those in FIG.
In FIG. 4, when the above step S9 is denied,
That is, when the vehicle speed V is "low speed", step S21
It is determined whether or not the compressor off signal is being output. If step S21 is negative, the routine proceeds to step S6, where a compressor ON signal is output, and if affirmative, step S21 is executed.
Go to 10.

According to the above procedure, if the compressor 14 is on when the vehicle speed V changes from "high speed" to "low speed", step S21 is denied.
Similar to the previous embodiment, as shown by the solid line in FIG. 5A, the compressor 14 keeps the ON state thereafter. On the other hand, if the compressor 14 is off when the vehicle speed V changes from “high speed” to “low speed”, step S21 is affirmative, and therefore, as shown by the solid line in FIG. The compressor 14 continues to be turned off (the prohibition of the evaporator freeze prevention control is released) until the air temperature Tint of the predetermined temperature is equal to or higher than the predetermined temperature, and is turned on when the air temperature Tint is equal to or higher than the predetermined temperature (as indicated by a dashed line in the previous embodiment). The compressor 14 is turned on immediately when the speed becomes low). That is, the fact that the compressor 14 is turned off when the vehicle speed V changes from "high speed" to "low speed" means that the evaporator 15 is in a state where it is likely to freeze, so that state is released. The compressor 14 is turned on after waiting for the operation. This can reliably prevent the evaporator 15 from freezing.

In the above description, the example in which the air temperature at the outlet of the evaporator is used as the temperature related to the evaporator has been shown, but instead of this, for example, the temperature of the evaporator may be directly detected and the detection result may be used as the temperature related to the evaporator. .

[0024]

According to the present invention, when the vehicle traveling speed is lower than the predetermined speed, the evaporator freeze prevention control is prohibited even if the outside air temperature is lower than the predetermined temperature.
For example, the compressor is not frequently turned on and off when the fluctuation of the engine speed is easily felt, such as at the time of idle rotation, and undesired fluctuations of the engine speed that occur at the time of switching the compressor on and off (up and down). Included)
Can be minimized. In particular, according to the invention of claim 2, when the vehicle speed changes from a predetermined speed or more to less than the predetermined speed while the compressor is stopped by the evaporator freeze prevention control, the evaporator is kept until the temperature of the evaporator becomes the predetermined temperature or more. Since the prohibition of the antifreezing control is released, in addition to the above effects, the freezing of the evaporator can be surely prevented.

[Brief description of drawings]

FIG. 1 is a complaint correspondence diagram.

FIG. 2 is a block diagram showing a configuration of a vehicle air conditioner according to an embodiment of the present invention.

FIG. 3 is a flowchart showing a procedure of compressor control.

FIG. 4 is a flowchart showing a procedure of compressor control in another embodiment.

FIG. 5 is a diagram illustrating a compressor on / off state according to another embodiment.

FIG. 6 is a diagram for explaining fluctuations in engine speed with respect to compressor on / off.

FIG. 7 is a diagram illustrating a conventional problem.

[Explanation of symbols]

 1 Air Conditioning Control Circuit 2 Outside Air Temperature Sensor 3 Evaporator Outlet Temperature Sensor 4 Air Conditioner Switch 5 Fan Switch 6 Vehicle Speed Sensor 11 Engine Control Circuit 13 Compressor Relay 14 Compressor 15 Evaporator 101 Compressor 102 Evaporator 103 Control Means 104 Vehicle Speed Sensor 105 Prohibition Means

Claims (2)

[Claims] 1. A variable capacity compressor driven by an engine, an evaporator for evaporating a refrigerant pressure-fed by the variable capacity compressor to cool air, and an evaporator when the outside air temperature is lower than a predetermined temperature. In a vehicle air conditioner having a control means for performing evaporator freeze prevention control for forcibly stopping the compressor when the temperature becomes lower than a predetermined temperature, a vehicle speed sensor for detecting a traveling speed of the vehicle, and the detected vehicle traveling speed is A vehicle air conditioner comprising: a prohibiting unit that prohibits the evaporator freeze prevention control by the control unit even when the outside air temperature is lower than a predetermined temperature when the speed is lower than the predetermined speed. 2. When the vehicle traveling speed changes from the predetermined speed or more to a predetermined speed or less while the compressor is stopped by the evaporator freeze prevention control,
The vehicle air conditioner according to claim 1, further comprising a prohibition canceling unit that cancels prohibition of the evaporator freeze prevention control by the prohibiting unit until a temperature related to the evaporator reaches or exceeds a predetermined temperature.