Air conditioner control system for vehicles

A control system for an air conditioner for a vehicle effects the switching between a heat mode and a heat/defrost mode on the basis of the ambient temperature and the amount of solar radiation present.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an air conditioner control system for a vehicle. 
2. Description of the Prior Art 
Conventional vehicle air conditioners generally operate in a vent mode, a 
bi-level mode, a heat mode, a heat/defrost mode or a defrost mode. In some 
vehicle air conditioners, the operational modes automatically change 
according to the conditions inside or outside the vehicle. 
In the air conditioner disclosed in Japanese Unexamined Patent Publication 
No. 62(1987)-299422 (where the engine coolant is employed as the heat 
source), the air blow rate is gradually increased (taking into account 
that the temperature of the coolant is still low) to the rate at which air 
is blown during the automatic control, and at the same time, the 
operational mode of the air conditioner is successively switched between 
the defrost mode, the defrost/heat mode and the heat mode as the coolant 
temperature increases, thereby improving the defrosting effect and the leg 
warming effect of the air condition. 
In the case of an air conditioner in which the operational mode is switched 
as the coolant temperature increases, it is preferable for the operational 
mode to be set to the heat/defrost mode when it is severely cold and the 
windowpane is apt to frost up. However, when there is insolation, even if 
the ambient temperature is extremely low the driver's head will get hot 
due to the hot air being discharged from the defroster vents. That is, 
because the altitude of the sun is low in winter, especially in northern 
countries, sunshine will impinge directly upon the driver's head through 
the windshield and heat it together with the hot air being discharged from 
the defroster vents. 
SUMMARY OF THE INVENTION 
In view of the foregoing observations and description, the primary object 
of the present invention is to provide an air conditioner control system 
for a vehicle which can prevent the windowpane from frosting over when it 
is severely cold and at the same time can prevent the driver's head from 
getting hot when it is severely cold and there is insolation. 
The air conditioner control system in accordance with the present invention 
is characterized in that switching between the heat mode and the 
heat/defrost mode is a function of the ambient temperature and the amount 
of solar radiation.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In FIGS. 1 and 2, an air conditioner 1 provided with a control unit 2 in 
accordance with an embodiment of the present invention has a duct 3 in 
which the following are provided: an intake door 4 through which the type 
of air selected by the driver (air from the passenger room or air from the 
ambience) is taken in, a blower 5 which blows the air taken in through the 
intake door 4 into the passenger room 10, an air mixing door 7 which 
controls how much of the total amount of air will branch off into a heater 
core 8, which total amount of air has passed through an evaporator 6 and 
has exchanged heat with the air to be blown into the passenger room 10, 
and three mode switching doors 9A to 9C. The heater core 8 heats the air 
passing therethrough with heat from the coolant of an engine E which 
circulates through the heater core 8. 
The mode switching door 9A is a vent door which causes the hot air to blow 
into the passenger room 10 through the central grill and left and right 
side grills by way of a vent duct 31 while the heater is operating. The 
mode switching door 9B is a defroster door which causes the hot air to 
blow against the windshield W through a defroster duct 32. The mode 
switching door 9c is a heat door which causes the hot air to blow toward 
the legs of the passenger through a heater duct 33. When the vent mode is 
selected, only the vent door 9A is open, and when the bi-level mode is 
selected, the vent door 9A and the heat door 9C are both open. When the 
heat mode is selected, only the heat door 9c is open. When the 
heat/defrost mode is selected, the heat door 9C and the defroster door 9B 
are both open. When the defrost mode is selected, only the defroster door 
9B is open. 
A cooler 14 comprises a compressor 11, a condenser 12, a receiver 13 and 
the evaporator 6. The compressor 11 is driven by the output shaft of the 
engine E by way of a pulley 15 and a magnet clutch 16. 
The intake door 4 is driven by a first motor actuator 17, the air mixing 
door 7 is driven by a second motor actuator 18, and the mode switching 
doors 9A to 9C are driven by a third motor actuator 19. Reference numeral 
20 denotes a blower motor which is driven by a power transistor 21. 
Outputs from a room temperature sensor 22 which detects the temperature in 
the passenger room, a solar radiation sensor 23 which detects the amount 
of solar radiation, a duct sensor 24 which detects the air temperature at 
the outlet of the evaporator 6, an ambient temperature sensor 25 which 
detects the temperature of the ambient air, a coolant temperature sensor 
26, a room temperature setter 27 for setting the temperature in the 
passenger room, a potentiometer 28 which detects the opening of the air 
mixing door 7, and a thermostat 29 are input into the control unit 2. The 
control unit 2 controls the driving voltage of the blower motor 20, the 
timing for the operation of the compressor 11 (which is controlled by way 
of the magnet clutch 16), and how far the air mixing door 7 is opened on 
the basis of those outputs and a program stored in a built-in ROM so that 
the temperature in the passenger room converges on the temperature set by 
the room temperature setter 27. 
FIG. 3 is a flow chart for illustrating the main flow of the control 
routine which the control unit 2 performs. 
In step S1, the control unit 2 (CPU) is reset or initialized. In step S2, 
it is determined whether the CPU has failed and, then in step S3, it is 
determined whether the CPU has been in a check mode. When the answers to 
the questions in steps S2 and S3 are both NO, the outputs of the aforesaid 
sensors 22 to 26, the room temperature setter 27 and the potentiometer 28 
are read and are stored at once in a predetermined area of the RAM. Then a 
room temperature control signal (which will be referred to as "total 
signal", hereinbelow) T is calculated on the basis of the following 
formula (step S4): 
EQU T=(t.sub.r -25)+.alpha.(t.sub.a -25)+.beta.(t.sub.d -12)-.gamma.(T.sub.D 
-25) 
wherein t.sub.r, t.sub.a, t.sub.d and T.sub.D respectively represent the 
temperature in the passenger room as detected by the room temperature 
sensor 22, the ambient temperature as detected by the ambient temperature 
sensor 25, the air temperature at the outlet of the evaporator 6 as 
detected by the duct sensor 24 and the set room temperature (the 
temperature in the passenger room as set by the room temperature setter 
27), and .alpha., .beta. and .gamma. are constants. That is, the total 
signal T is related to the difference between the set room temperature 
T.sub.D and the actual temperature in the passenger room corrected by the 
air temperature at the outlet of the evaporator 6 and the ambient 
temperature. In other words, the total signal T is related to the heat 
load for converging the actual temperature in the passenger room on the 
set room temperature T.sub.D. 
Then the control unit 2 controls how far the air mixing door 7 is opened, 
and the air blow rate (steps S5 and S6). Further, the control unit 2 
controls the temperature at which the compressor 11 is to be driven (step 
S7). Then the control unit 2 selectively opens and closes the mode 
switching doors 9A to 9C according to the selected mode and opens or 
closes the intake door 4 in order to take in air from the passenger room 
or air from the ambience (steps S8 and S9). Then the control unit 2 
returns to step S3. When the answer to the question in step S3 is YES, the 
control unit 2 locates the fault in step S10. 
In step S8, switching between the heat mode and the heat/defrost mode is 
effected on the basis of a function in which the amount of solar radiation 
S depends on the ambient temperature t.sub.a. An example of such a 
function is shown in FIG. 4. In FIG. 4, the single line (which will be 
referred to as "the mode switching line", hereinbelow) is represented by 
the formula So=A.multidot.t.sub.a +B wherein A and B are constants. The 
mode switching line intersects the t.sub.a -axis at a predetermined value 
t.sub.ao. When the point associated with the actual ambient temperature 
and the actual amount of the solar radiation falls in the region below the 
mode switching line, the control unit 2 switches the mode to the 
heat/defrost mode, that is, the control unit 2 opens both the heat door 9C 
and the defroster door 9B. When it falls in the region above the mode 
switching line, the control unit 2 switches the mode to the heat mode; 
that is, the control unit 2 opens only the heat door 9C. 
FIG. 5 is a flow chart for illustrating the operation of the control unit 2 
when it controls the operational mode of the air conditioner 1. In step 
S11, the control unit 2 determines whether the air conditioner 1 is in the 
heat mode. When it is determined in step S11 that the air conditioner 1 is 
not in the heat mode, the control unit 2 causes the air conditioner 1 to 
remain in the current mode (step S13). Otherwise, the control unit 2 
detects the ambient temperature t.sub.a in step S12, and determines 
whether the ambient temperature t.sub.a is higher than the predetermined 
value t.sub.ao in step S14. When it is determined in step S14 that the 
ambient temperature t.sub.a is not higher than the predetermined value 
t.sub.ao, the control unit 2 detects how much solar radiation S is present 
in step S15. Then in step S15, the control unit 2 calculates the 
S-coordinate So of the point on the mode switching line which has a 
t.sub.a -coordinate equal to the ambient temperature t.sub.a detected in 
step S12. Then the control unit 2 determines in step S17 whether the 
amount of solar radiation S is larger than the amount indicated by the 
S-coordinate So. When it is determined that the former is larger than the 
latter, the control unit 2 causes the air conditioner 1 to remain in the 
heat mode. Otherwise, the control unit 2 causes the air conditioner 1 to 
switch the mode to the heat/defrost mode (steps S18 and S19). When it is 
determined in step S14 that the ambient temperature t.sub.a is higher than 
the predetermined value t.sub.ao, the control unit 2 directly proceeds to 
step S18 and causes the air conditioner 1 to remain in the heat mode. 
Though, in this embodiment, the switching between the heat mode and the 
heat/defrost mode is effected on the basis of a primary correlation 
between the ambient temperature t.sub.a and the amount of solar radiation 
S, it also may be effected on the basis of a secondary or higher 
correlation between the ambient temperature t.sub.a and the amount of 
solar radiation S. 
Further, though the switching between the heat mode and the heat-defrost 
mode is effected on the basis of a single mode switching line in the 
embodiment described above, the switching between the heat and the 
heat-defrost mode may be effected on the basis of a plurality of mode 
switching lines so that the heat/defrost mode is switched in a plurality 
of stages. For example, as shown in FIG. 6, three switching lines 
S.sub.01, S.sub.02 and S.sub.03 may be set, and three heat/defrost regions 
I, II and III may be set so that the amount of air discharged from the 
defroster vents is minimum in region I and maximum in region III.