Apparatus for controlling automobile air-conditioner

An apparatus for controlling the operation of an automobile air-conditioner of the type including a variable displacement compressor capable of controlling the discharge rate of a refrigerant in response to an externally supplied compressor displacement signal, wherein a total signal is calculated based on at least a vehicle compartment temperature, an outside air temperature, a solar radiation quantity, and a setting signal from a temperature setter, and when a rapid cooling is designated by the total signal, the displacement of the compressor is fixed at a maximum level for a predetermined period of time so as to preclude an undesired drop of the cooling power which would otherwise occur from the middle to the final stage of the rapid cooling operation.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an apparatus for controlling an automobile 
air-conditioner having an externally controllable variable displacement 
compressor. 
2. Description of the Related Art 
In automobile air-conditioner controllers, when the temperature in a 
vehicle passenger compartment is high and hence a rapid cooling is needed, 
various control functions are abandoned to perform a rapid cool-down 
operation for a predetermined period of time. Japanese Patent Publication 
No. 1-56922 discloses a displacement control apparatus for controlling the 
displacement of a variable displacement compressor based on the detected 
evaporator temperature and the target evaporator temperature. In this 
apparatus, when a rapid cool-down of the vehicle compartment temperature 
is desired, the target evaporator temperature is shifted from a normal 
target evaporator temperature setting value (first target evaporator 
temperature setting value) to a second target evaporator temperature 
setting value which is lower than the first evaporator target temperature 
setting value. Subsequently, when a predetermined condition is satisfied, 
a third target evaporator temperature setting value which varies 
progressively from the second toward the first target evaporator 
temperature setting value is set. 
With this arrangement, when a rapid cool-down of the vehicle compartment 
temperature is needed after a long parking in the sun, for instance, the 
evaporator target temperature setting value is lowered from the first 
evaporator target temperature setting value to the second evaporator 
target temperature setting value to promote or accelerate the cooling 
effect. Thereafter, when a predetermined condition is reached (for 
example, after an elapse of a preset time period), the third evaporator 
target temperature setting value is set. The third evaporator target 
temperature setting value changes to progressively approach the first 
evaporator target temperature setting value whereby the vehicle 
compartment temperature can be regulated to the desired temperature 
smoothly. 
In addition, there have recently been developed variable displacement 
compressors of the externally controllable type. One example of such 
compressors is disclosed in Japanese Laid-open Patent Publication No. 
2-31918. The disclosed variable displacement compressor is of the swash 
plate type (also known as the wobble plate type) having a swash plate 
pivotally mounted on a drive shaft within a crank chamber and pivotally 
movable about a hinge ball mounted on the drive shaft. The swash plate is 
pivotally connected with a plurality of pistons movable back-and-fourth 
within corresponding cylinder bores in response to oscillation of the 
swash plate. A pressure control valve disposed in confrontation to the 
crank chamber operates to reduce the quantity of a working fluid flowing 
from the crank chamber back to an intake side depending on the magnitude 
of an electric current (I.sub.SOL) supplied to the pressure control valve. 
As the current intensity or strength (I.sub.SOL) is increased, the 
pressure in the crank chamber rises to reduce the angle of oscillation of 
the swash plate and thereby to lower the displacement of the compressor. 
On the contrary, with a reduction of the current strength, the pressure in 
the crank chamber goes down, so that the angle of oscillation of the swash 
plate is enlarged to increase the displacement of the compressor. The 
current strength (I.sub.SOL) serving as a compressor displacement control 
signal is determined by the target post-evaporator temperature T'.sub.E 
and the post-evaporator temperature T.sub.E such that .vertline.T.sub.E 
-T'.sub.E .vertline.&lt;1 is satisfied. 
In the case of the automobile air-conditioner having such a variable 
displacement compressor, when a need for the rapid cool-down operation 
arises, the target post-evaporator temperature T'.sub.E is lowered to 
-10.degree. C., for example, and subsequently the thus lowered target 
post-evaporator temperature is maintained for a predetermined time period. 
In this instance, if the vehicle compartment temperature is relatively 
high at the initial stage of the cool-down operation, the post-evaporator 
temperature T.sub.E is also high and the current strength (I.sub.SOL) is 
low on the contrary, so that the compressor is operated at a maximum 
displacement level. However, from the middle to the final stage of the 
rapid cool-down operation, the vehicle compartment temperature gradually 
goes down in response to which the current strength (I.sub.SOL) is 
increased progressively to lower the displacement of the compressor and to 
thereby reduce the air quantity. As a consequence, a cooling power 
supplied to the vehicle passenger compartment goes down and the desired 
rapid cool-down of the vehicle passenger compartment cannot be 
accomplished. 
SUMMARY OF THE INVENTION 
With the foregoing difficulties in view, it is an object of the present 
invention to provide an apparatus for controlling an automobile 
air-conditioner which is capable of maintaining the displacement of a 
compressor at a maximum level without being influenced by the 
post-evaporator temperature, thereby keeping the necessary cooling power 
to preclude the deterioration of the cool-down state. 
According to the present invention, there is provided an apparatus for 
controlling the operation of an air-conditioner for a motor vehicle, 
comprising: a variable displacement compressor constituting a part of a 
refrigeration cycle of the air-conditioner for controlling the discharge 
rate of a refrigerant in response to an externally supplied compressor 
displacement signal; a thermal load calculation means for calculating a 
total signal based on at least a vehicle compartment temperature, an 
outside air temperature, a solar radiation quantity, and a setting signal 
from a temperature setter; a cool-down judgment means for judging from the 
total signal calculated by the thermal load calculation means whether or 
not a rapid cooling is necessary; a cool-down control means for performing 
a rapid cool-down control when the cool-down judgment means judges it 
necessary to perform the rapid cooling; and a displacement fixing means 
for fixing a value of the compressor displacement signal for maintaining a 
maximum displacement level of the compressor during a predetermined period 
of time starting from when the rapid cool-down control by the cool-down 
control means to be performed. 
With this construction, while the rapid cooling is performed under the 
control of the cool-down control means, the displacement of the variable 
displacement compressor is fixed at a maximum level to prevent the cooling 
power from dropping in the middle to the final stage of the cool-down 
control operation. Thus, the desired effect of the rapid cooling can be 
maintained without suffering deterioration. 
The above and other objects, features and advantages of the present 
invention will become manifest to those versed in the art upon making 
reference to the detailed description and the accompanying sheets of 
drawings in which a preferred structural embodiment incorporating the 
principles of the present invention is shown by way of illustrative 
example.

DETAILED DESCRIPTION 
The present invention will be described hereinbelow in greater detail with 
reference to a certain preferred embodiment shown in the accompanying 
drawings. 
As shown in FIG. 1, an apparatus embodying the invention for controlling 
the operation of an automobile air-conditioner includes a thermal load 
calculation means 100 for calculating a total signal based on at least a 
vehicle compartment temperature, an outside air temperature, a solar 
radiation quantity, and a setting signal from a temperature setter. The 
total signal calculated by the thermal load calculation means 100 is then 
judged by a cool-down judgment means 110 to determine whether or not it is 
equivalent to a value requiring a rapid cooling. When the cool-down 
judgment means 110 judges it necessary to perform the rapid cooling, a 
cool-down control means 120 performs a rapid cool-down control. While the 
cool-down control is performed under the control of the cool-down control 
means 120, a displacement fixing means 130 issues a control signal to a 
displacement adjustment device 37 incorporated in a variable displacement 
compressor 18 for fixing the displacement of the compressor 18 at a 
maximum level. Thus, the maximum compressor displacement is maintained 
throughout the cool-down control operation. 
FIG. 2 diagrammatically shows an automobile air-conditioner incorporating 
the control apparatus of this invention. The air-conditioner includes an 
air-flow duct 1 having an intake air changeover device 2 disposed at an 
upstream end there. The intake air changeover device 2 includes a selector 
door 5 disposed at the junction between a recirculating air inlet 3 and an 
outside air inlet 4 disposed at the upstream end of the air-flow duct 1 in 
bifurcated fashion. The selector door 5 is actuated by an actuator 6 to 
select the recirculated air or the outside air to be introduced into the 
air-flow duct 1. 
A blower 7 is disposed in the air-flow duct 1 adjacent to the air inlets 3 
and 4 for forcing the air to flow downstream through the air-flow duct 1. 
The duct 1 also includes an evaporator 8 disposed downstream of the blower 
6 and a heater core 9 disposed downstream of the evaporator 8 for 
circulating engine cooling water to heat air flowing around the heater 
core 9. 
An air-mix door 10 is disposed in front of the heater core 9. The opening 
of the air-mix door 10 is regulated by an actuator 11 to changed 
proportions of air flowing through the heater core 9 and air bypassing the 
heater core 9. The air-flow duct 1 has at its downstream end a defrost 
outlet 12, a vent outlet 13 and a heat outlet 14 opening to a vehicle 
passenger compartment in a branched fashion. A mode door 15a is disposed 
at the junction between the vent outlet 13 and the heat outlet 14, while 
another mode door 15b is disposed at the junction between the heat outlet 
14 and the defrost outlet 12. The mode doors 15a, 15b are actuated by a 
pair of actuators 16 and 17, respectively, to change over the discharge 
mode of the air-conditioner. 
The evaporator 8 is connected in fluid circuit with a compressor 18, a 
condenser 19, a reservoir 20 and an expansion valve 21 so as to jointly 
constitute a refrigeration system to perform a refrigeration cycle of the 
air-conditioner. 
The compressor 18 is a swash plate type variable displacement compressor, 
as shown in FIG. 3 and includes a drive shaft 24 coupled to an engine 22 
(FIG. 2) of the motor vehicle via an electromagnetic clutch 23 (FIG. 2). 
The drive shaft 24 is rotatably received in a body 25 of the compressor 18 
and pivotally support thereon a swash plate 26 with a hinge ball 27 
disposed therebetween. The swash plate 26 thus pivoted on the drive shaft 
24 is pivotally movable or oscillates about the hinge ball 27 within a 
crank chamber 28 defined in the compressor body 25. The swash plate 26 is 
pivotally connected with a plurality of pistons 29 (only one being shown) 
for reciprocating the latter within a corresponding one of plural cylinder 
bores 30 in response to the oscillation of the swash plate 26. The stroke 
of the pistons 29 is proportional to the angle of oscillation of the swash 
plate 26. The compressor 18 further includes a pressure control valve 31 
disposed in confrontation to the crank chamber 28. The pressure control 
valve 31 includes a valve element 33 movable to adjust the degree of flow 
communication between the crank chamber 28 and an intake chamber 32 
communicating the intake side, a pressure-responsive member 34 responsive 
to the pressure in the intake chamber 32 to move the valve element 33, and 
a solenoid 36 for driving the valve clement 33 in response to the 
amplitude of an electric current I.sub.SOL (hereinafter referred to as 
"current strength") supplied to an electromagnetic coil 35 of the solenoid 
36. By controlling the current strength I.sub.SOL from the outside of the 
compressor 18, the amount of return of a blowby gas from the crank chamber 
28 to the intake side. The pressure control valve 31 constitutes a main 
part of the displacement adjustment device 37 for varying the displacement 
of the compressor 18. When the current strength I.sub.SOL flowing through 
the electromagnetic coil 35 increases to enhance the magnetic force or 
intensity of the solenoid 36, the valve element 33 is subjected to a force 
tending to reduce the degree of flow communication between the crank 
chamber 28 and the intake chamber 32 and thereby to reduce the amount of 
the blowby gas returning from the crank chamber 28 to the intake chamber 
32. With this reduced return of the blowby gas, the pressure in the crack 
chamber 28 and hence the pressure acting on the rear end of the respective 
pistons 29 is increased, so that the swash plate 26 pivots in a direction 
to reduce the angle of oscillation of its pivotal movement about the hinge 
ball 27. As a result, the stroke of the pistons 29 and hence the 
displacement of the compressor 18 is reduced. 
In the illustrated embodiment, the displacement adjustment device 37 is 
constructed to adjust the amount of return of the blowby gas to the intake 
side by means of the pressure control valve. The displacement adjustment 
device 37 may be constructed either to change the number of effective 
cylinders of the compressor 18, or to vary the pulley ratio of a belt 
transmission mechanism connecting between the engine 22 and the compressor 
18. In the case of a sliding vane rotary compressor, the number of 
effective vanes can be changed. In sum, any measure may be taken as long 
as it is effective to vary the displacement of the compressor. 
As shown in FIG. 2, the actuators 6, 11, 16 and 17, a motor 7a of the 
blower 7, the electromagnetic clutch 23 of the compressor 18, and the 
displacement adjustment device 37 are controlled based on output signals 
delivered through corresponding ones of drive circuits 40a-40f from a 
microcomputer 41. 
The microcomputer 41 is of the construction known per se and includes a 
central processing unit (CPU), a read only memory (ROM), a random access 
memory (RAM), an input/output port (I/0), etc, (neither shown). To the 
microcomputer 41, an output signal from a vehicle compartment temperature 
sensor 42 indicative of the vehicle compartment temperature T.sub.R, an 
output signal from an outside air temperature sensor 43 indicative of the 
outside air temperature T.sub.A, an output signal from a solar radiation 
quantity sensor 44 indicative of the solar radiation quantity T.sub.S, and 
an output signal from a duct sensor 45 disposed immediately downstream of 
the evaporator 8 for detecting the cooling intensity T.sub.E in terms of 
the temperature of air moving past the evaporator are inputted after they 
are digitized by an A/D converter 47 in the order selected by a 
multiplexer (MPX) 46. 
The microcomputer 41 is also supplied with output signals delivered from an 
instrument panel 48. The instrument panel 48 has an AUTO switch 49 for 
setting all the components of the air-conditioner to an automatically 
controlled condition, an OFF switch 50 to reset the automatically 
controlled condition, an A/C switch 51 for manually operating the 
compressor 18, a REC switch 52 for selecting the intake air between the 
recirculated air and the outside air, a DEF switch 53 for setting the 
discharge mode to the defrost mode, a temperature setter 54 for setting 
the temperature of the vehicle compartment, a speed setter 55 for setting 
the rotational speed of the blower 7, and a mode setter 56 for setting the 
discharge mode other than the defrost mode. The temperature setter 54 is 
composed of up-and-down switches 54a, 54b and a digital temperature 
indicator or display 54c. By properly actuating the up-and-down switches 
54a, 54b, the setting temperature indicated on the digital temperature 
display 54c can be charged within a predetermined range. The speed setter 
55 is composed of a FAN switch 55a for shifting the rotational level of 
the blower 7, and a digital level indicator or display 55b for indicating 
the current rotational level. By successively actuating the FAN switch 
55a, the rotational level of the blower 7 can be changed between the STOP 
(level 0), LOW (level 1), MED (level 2), HI (level 3) and MAX HI (level 4) 
levels. The character "MANUAL" is lighted above the rotational level 
display 55b. The mode setter 56 is composed of a MODE switch 56a for 
changing over the discharge modes successively between vent, bi-level and 
heat modes, and a pictorial indicator or display 56b for indicating the 
current discharge mode by a picture or illustration. By the actuation of 
the MODE switch 56a, a selected one of two air-flows indicated by the 
arrows 57a, 57b is lighted on the pictorial display 56b. The character 
"MANUAL" is lighted above the display 56b. The lighted display or the 
displays 54c, 55b, 56b are controlled by the microcomputer 41 via a 
display circuit 58. 
FIG. 4 is a flowchart showing a control routine achieved by the 
microcomputer 41 for controlling the operation of the air-conditioner. The 
controlling operation will be described hereinbelow in greater detail with 
reference to the flowchart. 
A step 200 regularly starts the control routine of the microcomputer 41 for 
controlling the compressor 18 from a main control routine which controls 
all the devices for controlling the air-conditioner and in the next 
following step 210, output signals from the respective sensors 42 through 
45 are inputted in the microcomputer 41. Then the control advances to a 
step 220 to input various output signal delivered from the instrument 
panel 48. 
Thereafter, a step 230 calculates a total signal T in accordance with the 
following expression (1) by using the vehicle compartment temperature 
T.sub.R, the outside air temperature T.sub.A, the solar radiation quantity 
T.sub.S, the setting temperature T.sub.D, and the evaporator cooling 
intensity T.sub.E that are inputted in the preceding steps 210 and 220. 
EQU T=K.sub.R (T.sub.R -25)+K.sub.A (T.sub.A -25)+K.sub.S .multidot.T.sub.S 
+K.sub.E .multidot.T.sub.E 
EQU -K.sub.d (T.sub.D -25)+C (1) 
where K.sub.R, K.sub.A, K.sub.S, K.sub.E and K.sub.D are gain constants and 
C is a calculation constant. 
Then, the control advances to a step 240 in which a judgement is made to 
determine whether the stop level (level 0) of the blower 7 is selected by 
the FAN switch 55a. Subsequently, a step 250 judges whether the OFF switch 
50 is turned on to stop the compressor 18. If the judgment of these steps 
240 and 250 indicates that the stop level (level 0) is selected and the 
compressor OFF switch is actuated, then the operation of the compressor 18 
is stopped on a step 260 and the control returns from a step 270 to the 
main control routine. On the contrary, if the judgment in the steps 240 
and 250 indicates that the blower 7 and the compressor 18 are operating, 
then the control advances to a step 280. 
The step 280 compares the total signal T with a first predetermined value 
T.sub.1 (usually T.sub.1 =11). If T.gtoreq.T.sub.1, then the control goes 
on to a step 290. If T&lt;T.sub.1, the control advances to a step 300. 
The step 290 starts a rapid cooling (cool-down) and sets the flag to "1". 
In the cool-down control, the target post-evaporator temperature T'.sub.E 
is set to -10.degree. C. and this condition continues for 10 minutes after 
the post-evaporator temperature T.sub.E goes down below 3.degree. C. 
The step 300 judges whether or not the cool down flag is a "1" or not. If 
yes, the control goes on to the step 290 to continue the cool-down 
control. If no, this means that the cool down flag is "0". Then the 
control advances to a step 390 and subsequently the normal control of the 
compressor is performed through steps 420 and 440. 
A step 310 judges whether the total signal T is greater than a second 
predetermined temperature T.sub.2 (normally, T.sub.2 =2). Based on the 
result of this comparison, a decision is made as to whether or not the 
cool-down is to be reset in view of the thermal load condition. If 
T&gt;T.sub.2 in the step 310, the control proceeds to a step 320 which in 
turn judges whether the cool down control continues 10 minutes after the 
post-evaporator temperature T.sub.E becomes equal to or greater than 
3.degree. C. If no (10 minutes has not elapsed), the control advances to a 
step 330. On the contrary, if yes (10 minutes has elapsed), then the 
control goes on to a step 350. 
The step 330 sets the displacement control signal (I.sub.SOL) to O to 
thereby fix the displacement of the compressor 18 at a maximum 
displacement level for 10 minutes and then the control returns to the main 
control routine on a step 340. 
The cool-down control is performed such that the post-evaporator 
temperature T.sub.E approaches the target post-evaporator temperature 
T'.sub.E. As a consequence, if the cool-down control depends solely on the 
control of the variable displacement compressor 18 by the displacement 
control signal (I.sub.SOL), it occurs likely that the displacement of the 
compressor 18 is changed (lowered) with a change of the post-evaporator 
temperature T.sub.E. According to this invention, however, since the 
cool-down control is fixed for a predetermined period of time, the 
variable displacement compressor 18 operates at a maximum displacement 
level during the cool-down operation. 
If T.ltoreq.T.sub.2 in the step 310, the control goes on to a step 350 in 
which the cool-down control is reset. After the cool down flag is set to 
"0", the control advances to a step 360 which in turn sets the transition 
control flag to "1". Subsequently, the control proceeds to a step 370. 
The step 370 judges whether or not the transition control flag has changed 
from "0" to "1". If yes, this means that the transition control to shift 
the cool-down control to the normal control is to be started. Then, the 
control advances to a step 380 in which the T'.sub.EO value used for the 
calculation of the target post-evaporator temperature T'.sub.E is set to 
-13.degree. C. This process ensures that the displacement of the 
compressor 18 is set to the maximum level. If the judgment by the step 370 
indicates that the transition control flag has not changed and hence the 
transition control still continues, the control jumps over the step 380 
and goes on to a step 400. 
The step 400 judges whether or not the post-evaporator temperature T.sub.E 
is more than 3.degree. C. or not. If yes, this means that the transition 
control is not needed. Consequently, the transition control is terminated. 
Then, the transition control flag is changed from "1" to "0" in a step 410 
and subsequently the normal cooling control is performed in a step 420. 
A step 430 calculates the target post-evaporator temperature T'.sub.E 
according to the following expression (2). 
EQU T'.sub.E =3-T'.sub.EO .multidot.e.sup.-t/T (2) 
where T is a time constant. 
The step 430 controls the target post-evaporator temperature T'.sub.E in 
such a manner that T'.sub.E gradually approaches 3.degree. C. as the time 
goes on. Subsequently, the control advances to a step 460. 
The step 460 changes the displacement of the compressor 18 based on the 
target post-evaporator temperature T'.sub.E determined by the step 420 or 
430 and the post-evaporator temperature T.sub.E in such a manner that 
.vertline.T.sub.E -T'.sub.E .vertline.&lt;1 is reached. This change in 
displacement is carried out by changing the displacement control signal 
(I.sub.SOL) which is determined by calculation according to the following 
expressions (3) and (4). 
EQU .DELTA.T.sub.E =T.sub.E -T'.sub.E (3) 
EQU I.sub.SOL =K.sub.1 .multidot..DELTA.T.sub.E +K.sub.2 
.multidot..intg..DELTA.T.sub.E dt (4) 
where .DELTA.T.sub.E is a deviation between the actual post-evaporator 
temperature T.sub.E and the target post-evaporator temperature T'.sub.E, 
and K.sub.1 and K.sub.2 are calculation constants. 
The I.sub.SOL value thus calculated is used to perform the 
proportional-plus-integral control (PI control) of the displacement 
adjustment device 37 by means of which the displacement of the compressor 
18 is controlled so as to maintain the deviation .DELTA.T below 1.degree. 
C. 
Thereafter, the control advances to a step 470 and thence to the main 
control routine. 
If the step 300 judges that the normal control of the compressor 18 is 
selected, the control goes on to a step 390. The step 390 judges whether 
or not the transition control flag is a "1" or not. If yes, this means 
that the transition control is now going on. Then the control advances to 
the step 400 in which the above-mentioned transition control is performed. 
If no (transition control flag is "0"), the control goes on to the step 
420 which fixes the target post-evaporator temperature to 3.degree. C. 
Thereafter, a step 440 is provided to prevent the evaporator from freezing 
and hence makes a judgment so as to determine whether the post-evaporator 
temperature T.sub.E is higher then 0.5.degree. C. If no (T.sub.E 
&lt;0.5.degree. C.), this means that freezing of the evaporator may take 
place. Then the control advances to a step 450 which in turn stops the 
operation of the compressor 18. If the evaporator temperature T.sub.E is 
higher than 3.degree. C. in the step 440, the control goes on to the step 
460. 
The step 460, as described above, changes the displacement of the 
compressor 18 based on the target post-evaporator temperature T'.sub.E 
determined by the step 420 or 430 and the post-evaporator temperature 
T.sub.E in such a manner that .multidot..vertline.T.sub.E -T'.sub.E 
.vertline.&lt;1 is reached. Thereafter, the control returns from the step 470 
to the main control routine. 
The T'.sub.EO value used in the step 380 for the calculation of the target 
post-evaporator temperature T'.sub.E may be replaced by a value determined 
by using the following expression (5). 
EQU T'.sub.EO =T.sub.E -23 (5) 
The T'.sub.EO value obtained by the expression (5) is variable with the 
actual post-evaporator temperature T.sub.E, so that the maximum 
displacement of the compressor 18 can be obtained more reliably than by 
using the fixed T'.sub.EO value. 
As described above, according to this invention, when the cool-down control 
is performed, the displacement of the compressor can be maintained at a 
maximum level without being influenced by the post-evaporator temperature 
T.sub.E. Thus, the necessary cooling power or intensity is maintained, 
thereby ensuring that the air-conditioner operates efficiently without 
causing deterioration in cooling effect resulting from the cool-down 
control. 
Obviously, various minor changes and modifications of the present invention 
are possible in the light of the above teaching. It is therefore to be 
understood that within the scope of the appended claims the invention may 
be practiced otherwise than as specifically described.