Control apparatus and method for actuating an electrically driven compressor used in an air conditioning system of an automotive vehicle

A micro computer 6 reads a manual switch signal Sm from an operating section 15, and sets a target output W0 of an electrically driven compressor 11 based on the manual switch signal Sm. A temperature sensor 20 detects a temperature Ts of a designated component in the compressor control system. Micro computer 6 judges whether the detected temperature Ts is larger than a predetermined upper limit Ta, and generates an output command W equalized to the target output W0 when the temperature Ts is within a predetermined allowable range. On the other hand, when the detected temperature Ts is higher than the upper limit Ta, micro computer 6 sets a modified output W1 smaller than target output W0 by a predetermined correction value .DELTA.W (W1=W0-.DELTA.W>0), and adjusts the output command W to the modified output W1. Then, the compressor 11 is actuated based on thus obtained output command W.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention generally relates to a control apparatus and a method 
for actuating an electrically driven compressor used in an air 
conditioning system of an automotive vehicle, which is capable of promptly 
and adequately adjusting the output of the compressor in response to a 
detected increase of the inside or peripheral temperature of the control 
system, thereby stabilizing the operation of the compressor and assuring 
reliability of the air conditioning system. 
2. Prior Art 
A control system of an electric compressor is generally subjected to heat 
generation due to power consumption when it actuates the compressor. For 
example, an electrically driven compressor, when it has an output of 2 KW, 
will cause a heat generation of approximately 40 W which corresponds to 2% 
of the overall output. Various electronic components inside the control 
system are sensitive to heat; thus, it is essentially important to protect 
these electronic components for guaranteeing the performance of the 
control system. To this end, the control system is generally provided with 
a heat radiation device of normally an air-cooling type or a water-cooling 
type. Specifications of the heat radiation device needs to be designed 
based on the heat radiation conditions including ambient or peripheral 
temperatures and electric power consumption. 
Furthermore, in the event of unusual increase of temperature, some of 
electrically driven compressor can be automatically stopped to prevent any 
damage from occurring by such excessive heat generations. 
According to the above-described conventional systems, when the temperature 
of the control system is extraordinarily increased, the only effective 
countermeasure is to stop the electric compressor; otherwise, the control 
system of the electric compressor will be fatally damaged. 
However, in view of the driving safety, sudden stop or malfunction of an 
air conditioning system in an automotive vehicle is not desirable and 
recommendable. For example, sudden stop of the air conditioning system 
will make it impossible to keep a clean view through the front windshield 
glass since the glass will be clouded up with moisture. Furthermore, a 
drive or passenger may be surprised or frightened by the sudden stop of 
blow air. Needless to say, such sudden stop or malfunction will make 
passengers feel uncomfortable. 
Still further, it is essentially important to assure a long life of the 
control system of each electric compressor. In this respect, an 
electrolytic capacitor, which essentially determines the life of the 
electric compressor control system since its life is significantly short, 
needs to be kept safely so as not to suffer from increase of temperature. 
SUMMARY OF THE INVENTION 
In view of the above-described problems encountered in the prior art, the 
present invention has a principal object to provide a control apparatus 
and a method for actuating an electric compressor used in an air 
conditioning system, which is capable of promptly and adequately 
suppressing the output of the compressor in response to a detected 
increase of the inside or peripheral temperature of the control system, 
thereby stabilizing the operation of the compressor and assuring 
reliability of the air conditioning system for an automotive vehicle. 
To accomplish above and other related objects, a first aspect of the 
present invention provides a control apparatus for actuating an 
electrically driven compressor equipped in an automotive vehicle, 
comprising: a temperature sensor generating a signal representing a 
temperature of a component in the control apparatus; and control means 
connected to the temperature sensor for adjusting an output command 
supplied to the electrically driven compressor in accordance with the 
signal generated from the temperature sensor. 
According to features of the preferred embodiments, the temperature sensor 
detects a temperature of any one of a heat radiator such as a heat sink, a 
micro computer or like processing unit, a relay, a (switching) power unit, 
and an electrolytic capacitor substantially determining the life of the 
control system. 
In addition, it is possible to provide an alarm indicator generating an 
alarm Whenever the temperature detected by the temperature sensor goes out 
of a predetermined allowable range. 
Furthermore, a second aspect of the present invention provides a control 
apparatus for actuating an electrically driven compressor equipped in an 
automotive vehicle, characterized by manual switch means, command 
generating means, drive means, temperature sensing means, and adjusting 
means. 
According to the second aspect compressor control apparatus, the manual 
switch means allows a use to adjust an output of the compressor and 
generates a request signal representing a quantity of user's manual 
adjustment. The command generating means receives the request signal and 
generates an output command supplied to the compressor in accordance with 
the quantity of manual adjustment. 
The drive means actuates the compressor based on the output command. The 
temperature sensing means generates a temperature signal representing a 
temperature of a component in the control apparatus. And the adjusting 
means receives the temperature signal from the temperature sensing means 
and generates a modified output command, when the temperature detected by 
the temperature sensing means exceeds a predetermined upper-limit value. 
In this case, the modified output command is smaller than the output 
command but larger than 0. 
Still further, a third aspect of the present invention provides a control 
apparatus for actuating an electrically driven compressor equipped in an 
automotive vehicle, characterized by manual switch means, target output 
means, temperature sensing means, modified output means, command 
generating means, and drive means. 
According to the third aspect compressor control apparatus, the manual 
switch means allows a use to adjust an output of the compressor and 
generates a request signal representing a quantity of user's manual 
adjustment. The target output means receives the request signal from the 
manual switch means and obtains a target output of the compressor. In this 
case, the target output is proportional to the quantity of user's manual 
adjustment. 
The temperature sensing means generates a temperature signal representing a 
temperature of a component in the control apparatus. The modified output 
means receives the temperature signal from the temperature sensing means, 
and obtains a modified output when the temperature detected by the 
temperature sensing means exceeds a predetermined upper limit. The 
modified output is set smaller than the target output obtained by the 
target output means but larger than 0. 
The command generating means generates an output command supplied to the 
compressor in such a manner that the output command is equalized to the 
target output when the temperature detected by the temperature sensing 
means is within a predetermined allowable range while the output command 
is equalized to the modified output when the temperature detected by the 
temperature sensing means exceeds the upper limit. And, the drive means 
actuates the compressor based on the output command generated from the 
command generating means. 
Yet further, a fourth aspect of the present invention provides a control 
apparatus for actuating an electrically driven compressor equipped in an 
automotive vehicle, characterized by manual switch means, target output 
means, temperature sensing means, modified output means, emergency means, 
command generating means, and drive means. 
According to the fourth aspect compressor control apparatus, the manual 
switch means allows a use to adjust an output of the compressor and 
generates a request signal representing a quantity of user's manual 
adjustment. The target output means receives the request signal from the 
manual switch means and obtains a target output of the compressor, which 
is proportional to the quantity of user's manual adjustment. 
The temperature sensing means generates a temperature signal representing a 
temperature of a component in the control apparatus. The modified output 
means receives the temperature signal from the temperature sensing means, 
and obtains a modified output when the temperature detected by the 
temperature sensing means exceeds a predetermined upper limit. 
The modified output is set smaller than the target output obtained by the 
target output means but larger than 0. 
The emergency means receives the temperature signal from the temperature 
sensing means, and forcibly stops the compressor when the temperature 
detected by the temperature sensing means exceeds a predetermined critical 
value higher than the upper limit. 
The command generating means generates an output command supplied to the 
compressor in such a manner that the output command is equalized to the 
target output when the temperature detected by the temperature sensing 
means is within a predetermined allowable range while the output command 
is equalized to the modified output when the temperature detected by the 
temperature sensing means is higher than the upper limit but lower than 
the critical value. 
And, the drive means actuates the compressor based on the output command 
generated from the command generating means. 
Moreover, the present invention provides the method for actuating the 
electrically driven compressor of an air conditioning system installed in 
an automotive vehicle. 
More specifically, a fifth aspect of the present invention provides a 
control method for actuating an electrically driven compressor equipped in 
an automotive vehicle, comprising the following first to sixth steps. 
A first step is to read a request signal representing a quantity of user's 
manual adjustment. A second step is to set a target output of the 
compressor based on the request signal. A third step is to detect a 
temperature of a component in the control apparatus. A fourth step is to 
judge whether the temperature is larger than a predetermined upper limit. 
A fifth step is to obtain an output command in such a manner that the 
output command is equalized to the target output when the temperature is 
within a predetermined allowable range while the output command is reduced 
to a modified value larger than 0 when the temperature exceeds the upper 
limit. And, a sixth step is to actuate the compressor based on the output 
command. 
Furthermore, a sixth aspect of the present invention provides a control 
method for actuating an electrically driven compressor equipped in an 
automotive vehicle, characterized by the following first to eighth steps. 
A first step is to read a request signal representing a quantity of user's 
manual adjustment. A second step is to set a target output of the 
compressor based on the request signal. In this case, the target output is 
proportional to the quantity of user's manual adjustment. 
A third step is to detect a temperature of a component in the control 
apparatus. A fourth step is to judge whether the temperature is larger 
than a predetermined upper limit. A fifth step is to generate an output 
command equalized to the target output, when the temperature is within a 
predetermined allowable range. 
A sixth step is to set a modified output by reducing the target output by a 
predetermined correction value. The modified output is smaller than the 
target output but larger than 0. A seventh step is to generate an output 
command equalized to the modified output, when the temperature exceeds the 
upper limit. And, an eighth step is to actuate the compressor based on the 
output command. 
Still further, a seventh aspect of the present invention provides a control 
method for actuating an electrically driven compressor equipped in an 
automotive vehicle, characterized by the following first to tenth steps. 
A first step is to read a request signal representing a quantity of user's 
manual adjustment. A second step is to set a target output of the 
compressor based on the request signal, so that the target output is 
proportional to the quantity of user's manual adjustment. A third step is 
to detect a temperature of a component in the control apparatus. 
A fourth step is to judge whether the temperature is larger than a 
predetermined critical value. A fifth step is to stop the compressor when 
the temperature exceeds the critical value, regardless of the quantity of 
user's manual adjustment. 
A sixth step is to judge whether the temperature is larger than a 
predetermined upper limit. In this case, the upper limit is lower than the 
critical value. A seventh step is to generate an output command equalized 
to the target output when the temperature is within a predetermined 
allowable range. An eight step is to set a modified output by reducing the 
target output by a predetermined correction value. The modified output is 
smaller than the target output but larger than 0. A ninth step is to 
generate an output command equalized to the modified output when the 
temperature is higher than the upper limit but lower than the critical 
value. And, a tenth step is to actuate the compressor based on the output 
command. 
According to features of the preferred embodiment, it is desirable to 
provide the following steps. 
an eleventh step is to judge whether the temperature is larger than a 
Predetermined reference value. The reference value is set lower than the 
upper limit. And, a twelfth step is to restore the output command to the 
target output when the temperature falls below the reference value. 
Thus, according to the present invention, it becomes possible to promptly 
and adequately suppress the output of the compressor in response to a 
detected increase of the inside or peripheral temperature of the control 
system, thereby stabilizing the operation of the compressor and assuring 
reliability of the air conditioning system for an automotive vehicle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Preferred embodiments of the present invention will be explained in greater 
detail hereinafter, with reference to the accompanying drawings. Identical 
parts are denoted by identical reference numerals throughout the views. 
FIG. 3 shows a circuit arrangement of the control system of an electrically 
driven compressor in accordance with the present invention. 
A control unit 1, connected to a battery 16, receives DC (direct-current) 
power from battery 16. The control unit 1 comprises a drive power output 
section 4, a micro computer 6, a relay 7, a switching power unit 8, an 
electrolytic capacitor 9, and a temperature sensor 20. The drive power 
output section 4 converts the supplied DC power into AC 
(alternating-current) form and supplies thus converted AC power to an 
electrically driven compressor 11 connected to control unit 1. 
The switching power unit 8 converts the voltage of battery 16 into a 
voltage required in the drive power output section 4. The electrolytic 
capacitor 9, connected in parallel to switching power unit 8, absorbs 
current and voltage ripples when the drive power output section 4 converts 
the voltage of battery 16 into AC form. The relay 7 opens or closes the 
power supplying circuit connecting battery 16 and drive power output 
section 4. 
The micro computer 6 controls the power conversion performed in the drive 
power output section 4 in response to the quantity of a user's manual 
adjustment entered through an operating section 15. The operating section 
15, connected to the control unit 1 via a signal line such as harness, is 
usually disposed on the instrument panel in a passenger compartment of an 
automotive vehicle. 
The micro computer 6 further receives a detection signal from the 
temperature sensor 20 to adjust the power conversion performed in the 
drive power output section 4 in response to the detected sensor 
temperature. 
Thus, the micro computer 6 drives a motor of compressor 11 in accordance 
with not only the user's request (i.e. quantity of user's manual 
adjustment) but also the detected sensor temperature. In the driving 
operation of compressor 11, electric power is chiefly consumed in the 
drive power output section 4. 
FIG. 1 shows a schematic arrangement of the control system for an 
electrically driven compressor in accordance with a first embodiment of 
the present invention. The control unit 1 comprises a printed circuit 
board 3 on which micro computer 6, relay 7 and switching power unit 8 are 
mounted. The micro computer 6 is connected to the temperature sensor 20 
(through a conductive path on the printed circuit board 3). The 
temperature sensor 20 is disposed inside the housing 2 of control unit 1. 
The drive power output section 4 is located under the printed circuit board 
3 and brought into direct contact with a heat sink 5 at the bottom 
thereof. The heat sink 5, serving as a water-cooling type radiator, 
receives cooling water forcibly circulated by a pump 12 through a hose 10. 
A water cooling unit 13, disposed in series and upstream of pump 12, is 
connected to pump 12 through hose 10, in order to cool down the circulated 
hot water before it is sucked up by pump 12. A unit disposed upstream of 
water cooling unit 13 is a heat generator 14 serving as a heat generating 
source other than control unit 1. 
Housing 2 and heat sink 5 are integrally united as a single package 
accommodating the control unit 1. 
The operating section 15 has a knob slidable in a right and left direction. 
Users can manipulate this knob to adjust the output of compressor 11. 
Harness outgoing to compressor 11 or entering from battery 16 or operating 
section respectively passes through the wall of housing 2 and connected to 
the printed circuit board 3, although not shown in the drawings. 
FIGS. 2A through 2D show the correlations among various factors, such as 
temperature, output, power consumption, and cooling ability, in the 
electric compressor control system. 
As illustrated in FIG. 2A, the electric power consumption increases with 
increasing output. As illustrated in FIG. 2B, the heat generation inside 
the control unit 1, i.e. inner temperature, is increased in proportion to 
the increase of the electric power consumption. As illustrated in FIG. 2C, 
the inner temperature increases with increasing outer temperature 
(temperature outside the control unit 1). Furthermore, as illustrated in 
FIG. 2D, the inner temperature is reduced with increasing cooling ability. 
It is now assumed that pump 12 is out of order, and the water circulation 
amount is so reduced that the cooling ability is lowered from "D" to "E". 
In this case, the inner temperature will exceed the predetermined upper 
limit if the compressor 11 is driven at the output J. The inner 
temperature is detected by temperature sensor 20 and sent to micro 
computer 6. In response to the detection of such an excessive increase of 
inner temperature, micro computer 6 adjusts the power conversion performed 
by the drive power output section 4 so as to reduce the output of 
compressor 11 to the level of output K where the inner temperature is 
equal to the predetermined upper limit. 
According to the correlation shown in FIG. 2C, an upper limit of an outer 
temperature corresponding to the upper limit of the inner temperature can 
be identified in a one-to-one manner when the output of the compressor 11 
is known. For example, when the outer temperature is "C", the 
corresponding inner temperature will exceeds the upper limit when the 
compressor 11 is driven at the output H, but will be identical with the 
upper limit when the compressor 11 is driven at the output I. Thus, 
measuring an outer temperature makes it possible to indirectly detect the 
corresponding inner temperature. 
Furthermore, according to the correlation shown in FIG. 2B, when the 
electric power consumption is increased from "B" to "A", the inner 
temperature will exceed the upper limit if the compressor 11 is driven at 
the output F. Hence, the output of compressor 11 needs to be reduced to 
the level of output G where the inner temperature is identical with the 
upper limit. 
Next, an operation of the present invention will be explained with 
reference to FIG. 4 which shows a control routine performed by the control 
system for actuating the compressor in accordance with the present 
invention. 
First, in step S1, micro computer 6 reads a manual switch signal Sm from 
the operating section 15, since the manual switch signal Sm represents a 
user's request entered through manipulation of the slidable knob provided 
on the operating section 15. 
Next, in step S2, micro computer 6 makes a judgement as to whether the 
switch knob is in an OFF position. If the judgement is "YES" in step S2, 
this control routine is ceased at this moment. On the other hand, if the 
user sets the switch knob somewhere other than the OFF position (i.e. "NO" 
in step S2), the control routine proceeds to step S3 wherein a target 
output W0 of compressor 11 is determined based on the manipulation volume 
of the knob slidable on the operating section 15. The target output W0 is 
proportional to the user's request. 
Next, in step S4, micro computer 6 reads a sensor temperature Ts detected 
by temperature sensor 20. Then, lit is judged in step S5 whether the 
sensor temperature Ts is larger than a predetermined critical temperature 
Tb. When the sensor temperature Ts exceeds the critical temperature Tb, 
the control routine proceeds to step S6 to set the output command W to 0 
(W=0) and send this command to the compressor thereby forcibly stopping 
the compressor 11. The critical temperature Tb is a fairly high 
temperature that possibly causes the fatal damage unavoidable without 
shutdown of the electric compressor control system. 
When the sensor temperature Ts is not larger than the critical temperature 
Tb, the control routine proceeds to step S7 to further make a judgement as 
to whether the sensor temperature Ts is larger than a predetermined 
upper-limit temperature Ta. 
When the sensor temperature Ts is not larger than the upper-limit 
temperature Ta, the control routine proceeds to step S8 to set the output 
command W to the target output W0 obtained in step S3 (W=W0) and send this 
command to the compressor 11, thereby driving the compressor 11 in direct 
proportion to the user's request. In other words, the temperature Ta forms 
the reference or criterion point for judging whether the compressor 11 
should be driven as requested by the user. 
After completing step S8, the control routine returns to step S1 to repeat 
the above-described processing. 
On the other hand, when the sensor temperature Ts is larger than the 
upper-limit temperature Ta ("YES" in step S7), micro computer 6 proceeds 
to step S9 to set a modified output W1 which is smaller than the target 
output W0 by .DELTA.W, i.e. W1=W0-.DELTA.W (&gt;0). Subsequently, in step 
S10, micro computer 6 sets the output command W to the modified output W1 
(W=W1) and sends this command to the compressor 11, thereby driving the 
compressor 11 at a slightly smaller output compared with the user's 
request. 
In other words, the sensor temperature Ts is higher than the allowable 
upper-limit temperature Ta but less than the critical temperature Ta in 
this case; therefore, the micro computer 6 basically continues to drive 
compressor 11 although the output command W is set lower than the user's 
request. 
After completing step S10, the control routine returns to step S4 to repeat 
the processing of step S4 and below. 
FIG. 5 is a time chart showing a change of compressor output in relation to 
a detected temperature in accordance with the present invention. 
As shown in FIG. 5, the output command W of the compressor 11 is reduced 
from W0 to W1 when the sensor temperature Ts exceeds the allowable 
upper-limit temperature Ta. The micro computer 6 maintains the output 
command W at a constant value W1 for a while unless the sensor temperature 
Ts exceeds the critical temperature Tb (Steps S4, S5, S7, S9 and S10 of 
FIG. 4). In the event the sensor temperature Ts accidentally reaches the 
critical temperature Tb as shown by an alternate long and two dashes line 
in FIG. 5, micro computer 6 immediately changes the output command W to 0 
so as to forcibly stop the compressor 11 (Steps S5 and S6 of FIG. 4). 
On the other hand, when the increase of sensor temperature Ts is relatively 
moderate as shown by a solid line in FIG. 5, micro computer 6 continues to 
drive compressor 11 at the reduced output W1 until the sensor temperature 
Ts falls below the allowable upper-limit temperature Ta. Once the sensor 
temperature Ta falls within the allowable range, micro compressor 6 
restores the output command W to the target output W0 so as to drive the 
compressor 11 in accordance with the user's request, i.e. in direct 
proportion to the manipulation volume of the knob slidable on the 
operating section 15 (Steps S1-S5, S7 and S8 of FIG. 4). 
Although FIG. 5 shows the reduction amount .DELTA.W as a constant value, it 
is desirable to increase the reduction amount .DELTA.W in accordance with 
the difference between sensor temperature Ts and allowable upper-limit Ta, 
i.e. .DELTA.W=k1.multidot.(Ts-Ta), as shown by a solid line in FIG. 6. 
Using such setting, it becomes possible to eliminate sudden changes of the 
compressor output as well as to suppress the overshoot of the sensor 
temperature Ts. 
Furthermore, it is also desirable to increase the reduction amount .DELTA.W 
in accordance with the time deviation of the difference between sensor 
temperature Ts and allowable upper-limit Ta in addition to the difference 
itself, i.e. 
.DELTA.W=k1.multidot.(Ts-Ta)+k2.multidot..DELTA.(Ts-Ta)/.DELTA.t, as shown 
by an alternate long and dash line in FIG. 6. Using such setting, it 
becomes possible to further quicken the convergence of sensor temperature 
Ts. 
Next, a modified operation of the present invention will be explained with 
reference to FIG. 7 which shows another control routine performable by the 
control system for actuating the compressor in accordance with the present 
invention. 
The control routine shown in FIG. 7 is different from that of FIG. 4 in 
that some hysteresis is provided in the setting of allowable range. 
More specifically, in step S11, micro computer 6 reads manual switch signal 
Sm from the operating section 15, the manual switch signal Sm representing 
the user's request entered through manipulation of the slidable knob 
provided on the operating section 15. 
Next, in step S12, micro computer 6 makes a judgement as to whether the 
switch knob is in the OFF position. If the judgement is "YES" in step S12, 
this control routine is ceased at this moment. On the other hand, if the 
user sets the switch knob somewhere other than the OFF position (i.e. "NO" 
in step S12), the control routine proceeds to step S13 wherein target 
output W0 of compressor 11 is determined based on the manipulation volume 
of the knob slidable on the operating section 15. The target output W0 is 
proportional to the user's request. 
Next, in step S14, micro computer 6 reads sensor temperature Ts detected by 
temperature sensor 20. Then, it is judged in step S15 whether the sensor 
temperature Ts is larger than predetermined critical temperature Tb. When 
the sensor temperature Ts exceeds the critical temperature Tb, the control 
routine proceeds to step S16 to set the output command W to 0 (W=0) and 
send this command to the compressor 11, thereby forcibly stopping the 
compressor 11. The critical temperature Tb is a fairly high temperature 
that possibly causes the fatal damage unavoidable without shutdown of the 
electric compressor control system. 
When the sensor temperature Ts is not larger than the critical temperature 
Tb, the control routine proceeds to step S17 to check whether or not a 
flag F is 1 (i.e. F=1?). This flag F is used to indicate the fact that, 
when F is 1, compressor 11 undergoes the output reduction control in 
accordance with the present invention. When the flag F is "0", i.e. "NO" 
in step S17, the control routine proceeds to step S18. On the contrary, 
when the flag F is "1", i.e. "YES" in step S17, the control routine 
proceeds to step S19. 
In step S18, micro computer 6 makes a judgement as to whether the sensor 
temperature Ts is larger than predetermined upper-limit temperature Ta. 
When the sensor temperature Ts is not larger than the upper-limit 
temperature Ta, the control routine proceeds to step S20 to set the output 
command W to the target output W0 obtained in step S13 (W=W0) and send 
this command to the compressor 11, thereby driving the compressor 11 in 
direct proportion to the user's request. 
After completing step S20, flag F is set to 0 (i.e. F=0), and the control 
routine returns to step S11 to repeat the above-described processing. 
On the other hand, when the sensor temperature Ts is larger than the 
upper-limit temperature Ta ("YES" in step S18), micro computer 6 proceeds 
to step S22 to set a modified output W1 which is smaller than the target 
output W0 by .DELTA.W, i.e. W1=W0-.DELTA.W (&gt;0). Subsequently, in step 
S23, micro computer 6 sets the output command W to the modified output W1 
(W=W1) and sends this command to the compressor 11, thereby driving the 
compressor 11 at a slightly smaller output compared with the user's 
request. 
In other words, the sensor temperature Ts is higher than the allowable 
upper-limit temperature Ta but less than the critical temperature Ta in 
this case; therefore, the micro computer 6 basically continues to drive 
compressor 11 although the output command W is set lower than the user's 
request. 
After completing step S23, flag F is set to 1 (i.e. F=1) to indicate that 
compressor 11 undergoes the output reduction control in accordance with 
the present invention. Then, the control routine returns to step S14 to 
repeat the processing of step S14 and below. 
FIG. 8 is a time chart showing a change of compressor output in relation to 
a detected temperature in accordance with the present invention. 
As shown in FIG. 8, the output command W of the compressor 11 is reduced 
from W0 to W1 when the sensor temperature Ts exceeds the allowable 
upper-limit temperature Ta. The micro computer 6 maintains the output 
command W at the reduced value W1 for a while unless the sensor 
temperature Ts exceeds the critical temperature Tb. In the event the 
sensor temperature Ts accidentally reaches the critical temperature Tb, 
micro computer 6 immediately changes the output command W to 0 so as to 
forcibly stop the compressor 11 (Steps S15 and S16 of FIG. 7). 
On the other hand, when the increase of sensor temperature Ts is relatively 
moderate, micro computer 6 continues to drive compressor 11 at the reduced 
output W1 until the sensor temperature Ts falls below the temperature Tc. 
The temperature Tc is set lower than Ta by .DELTA.T. It means that the 
compressor 11 is continuously driven at the reduced 20 output W1 even the 
sensor temperature Ts falls below the upper-limit temperature Ta unless it 
reaches the temperature Tc (Steps S14, S15, S17, S19, S22, S23 and S24 of 
FIG. 7) 
Namely, the difference .DELTA.T (=Ta-Tc) is a hysteresis set for avoiding 
the hunting phenomenon in the convergence of sensor temperature Ts. 
Once the sensor temperature Ts falls below the temperature Tc, micro 
computer 6 restores the output command W to the target output W0 so as to 
drive the compressor 11 in accordance with the user's request, i.e. in 
direct proportion to the manipulation volume of the knob slidable on the 
operating section 15 (Steps S19 and S20 of FIG. 7). Then, the flag F is 
reset to 0, i.e. F=0 (Step S21 of FIG. 7), thereby indicating that the 
output reduction control of compressor 11 in accordance with the present 
invention is terminated. 
In this manner, the present invention makes it possible to prevent the 
control unit from being damaged or malfunctioning, and also to prevent an 
electrically driven compressor from being suddenly stopped except 
emergency conditions which require the shutdown of the compressor. 
Other Embodiments 
FIGS. 9A through 9C show schematic arrangements of a control system for an 
electrically driven compressor in accordance with a second embodiment of 
the present invention. According to the second embodiment of the present 
invention, the temperature sensor 20 is attached on the heat sink 5 to 
directly detect the temperature of heat sink 5. 
In an embodiment shown in FIG. 9A, heat sink 5 is cooled down by an 
air-cooling unit 17 with an axial-flow fan. In an embodiment shown in FIG. 
9B, heat sink 5 is cooled by water in the same manner as the first 
embodiment- According to an embodiment shown in FIG. 9C, heat sink 5 is 
cooled down by a heat sink package 18, where electric compressor control 
unit 1 is directly mounted on the heat sink package 18 by means of screws 
19. The heat sink package 18 is a water-cooling type which mounts the heat 
generator 14 together with control unit 1. 
If the axial-flow fan equipped air-cooling unit 17 or the water cooling 
unit 13 is out of order, or the connection between the control unit 1 and 
the heat sink package 18 is not sufficiently tight (for example, due to 
looseness of screws 19), the cooling ability will be fairly lowered 
accompanied by an increase of temperature of heat sink 5 which may exceeds 
the allowable upper-limit (Ta). Receiving the temperature of heat sink 5 
from temperature sensor 20, micro computer 6 adjusts the power conversion 
in the drive power output section 4, i.e. reduces the output command W 
from W0 to W1 when the sensor temperature Ts exceeds the upper-limit 
temperature Ta until the sensor temperature Ts falls below within the 
allowable range. 
If the temperature of heat sink 5 exceeds the critical temperature (Tb), 
micro computer 6 immediately stops the compressor 11 (i.e. W=0) regardless 
of the knob position of operating section 15. 
FIG. 10 shows an arrangement of a control system for an electrically driven 
compressor in accordance with a third embodiment of the present invention. 
The third embodiment is substantially identical with the first embodiment 
except that the temperature sensor 20 is directly attached on micro 
computer 6. The allowable upper-limit temperature of micro computers is 
approximately 80.degree. C. (i.e. Ta=80.degree. C.). 
When the cooling ability is lowered, the temperature of micro computer 6 
possibly exceeds 80.degree. C. If the sensor temperature Ts exceeds 
80.degree. C., micro computer 6 adjusts the power conversion in the drive 
power output section 4, i.e. reduces the output command W from W0 to W1 
until the sensor temperature Ts falls below within the allowable range 
less than 80.degree. C. 
FIG. 11 shows an arrangement of a control system for an electrically driven 
compressor in accordance with a fourth embodiment of the present 
invention. The fourth embodiment is substantially identical with the first 
embodiment except that the temperature sensor 20 is directly attached on 
relay 7. The allowable upper-limit of relays is approximately 80.degree. 
C. (i.e. Ta=80.degree. C.). 
For example, if the heat generation in relay 7 is largely increased due to 
excessive current, the temperature of relay 7 will exceed 80.degree. C. 
Upon sensor 20 detecting this excessive increase of temperature, micro 
computer 6 adjusts the power conversion in the drive power output section 
4, i.e. reduces the output command W from W0 to W1 until the sensor 
temperature Ts falls below within the allowable range less than 80.degree. 
C. 
FIG. 12 shows an arrangement of a control system for an electrically driven 
compressor in accordance with a fifth embodiment of the present invention. 
The fifth embodiment is substantially identical with the first embodiment 
except that the temperature sensor 20 is directly attached on switching 
power unit 8. The allowable upper-limit of switching power units is 
approximately 80.degree. C. (i.e. Ta=80.degree. C.). 
When the heat generation in the switching power unit 8 is largely increased 
due to, for example, an excessive increase of switching loss, the 
temperature of switching unit 8 possibly exceeds 80.degree. C. Upon sensor 
20 detecting this excessive increase of temperature, micro computer 6 
adjusts the power conversion in the drive power output section 4, i.e. 
reduces the output command W from W0 to W1 until the sensor temperature Ts 
falls below within the allowable range less than 80.degree. C. 
FIG. 13 shows an arrangement of a control system for an electrically driven 
compressor in accordance with a sixth embodiment of the present invention. 
The sixth embodiment is substantially identical with the first embodiment 
except that the temperature sensor 20 is directly attached on electrolytic 
capacitor 9. The allowable upper-limit of electrolytic capacitors is 
approximately 80.degree. C. (i.e. Ta=80.degree. C.). 
When the cooling ability is lowered due to, for example, disorder of pump 
12, the temperature of electrolytic capacitor 9 possibly exceeds 
80.degree. C. Upon sensor 20 detecting this excessive increase of 
temperature, micro computer 6 adjusts the power conversion in the drive 
power output section 4, i.e. reduces the output command W from W0 to W1 
until the sensor temperature Ts falls below within the allowable range 
less than 80.degree. C. 
In general, the life of electrolytic capacitors is doubled by reducing the 
temperature by an amount of 10.degree. C. Hence, the electrolytic 
capacitor 9, when it has a life of 5,000 hours at 85.degree. C., can 
extend its life to 10,000 hours by setting the allowable upper-limit 
temperature (Ta) at 75.degree. C. in this embodiment. 
FIG. 14 is an arrangement of a control system for an electrically driven 
compressor in accordance with a seventh embodiment of the present 
invention. The seventh embodiment is substantially identical with the 
first embodiment except that an alarm indicator 21 is provided on the 
operating section 15. According to the seventh embodiment, micro computer 
6 sends an alarm signal to operating section 15 as soon as the sensor 
temperature Ts exceeds the upper-limit temperature (Ta). Upon receiving 
the alarm signal, the alarm indicator 21 is turned on to inform passengers 
in a compartment room of an automotive vehicle of the output reduction 
operation of the compressor. 
This invention may be embodied in several forms without departing from the 
spirit of essential characteristics thereof, the present embodiments as 
described are therefore intended to be only illustrative and not 
restrictive, since the scope of the invention is defined by the appended 
claims rather than by the description preceding them, and all changes that 
fall within metes and bounds of the claims, or equivalents of such metes 
and bounds, are therefore intended to be embraced by the claims.