Air conditioner

An air conditioner which has a controller equipped with heat-producing electrical parts and in which the driving current of a compressor, etc., is controlled by the controller, includes a temperature sensor which is provided to or in the vicinity of at least one heat-sensitive electrical part (for example, a power transistor) of the electrical parts and adapted to detect the temperature of a heat-sensitive electrical part, and means for stepwise or linearly reducing the upper-limit value of the driving current of the compressor in accordance with the increase of the detected temperature when the temperature detected by the temperature sensor is higher than a predetermined value.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an air conditioner having controller 
equipped with electrical parts such as a power transistor, etc., the 
controller controlling a driving current of a compressor, etc. 
2. Description of Related Art 
A so-called inverter type air conditioner in which the rotational speed of 
a compressor is variable in accordance with an air-conditioning load so as 
to vary the power of the compressor, has been known, as disclosed in 
Japanese Post-examined Patent Application (KokoKu) No. Hei-2-5981. A 
controller used in this type of air conditioner is generally equipped with 
a power transistor as an electrical part for control. 
In some air conditioners of the above type, when cooling operation is 
carried out under an overload, in general the upper-limit value of the 
driving current of the compressor is suddenly reduced to a predetermined 
fixed value or less on the basis of the detected temperature of a detector 
for detecting the outside air temperature to protect the electrical parts 
such as the power transistor, etc., from heat. Further, in other air 
conditioners, a thermostat is mounted on a heat sink for cooling the power 
transistor, and the driving of the compressor is stopped when the 
thermostat detects a predetermined temperature. having the outside 
temperature detector, the control mode for the protection of the 
electrical parts is greatly varied between a situation where an outdoor 
unit having an outside air temperature detector is located under a sunny 
condition and a situation where it is located under an unsunny or shady 
condition. Particularly when the outdoor unit is located under the sunny 
condition, an indoor unit is often located in a room-having a sunny 
aspect. In this case, the cooling operation trends to be more frequently 
carried out as compared with such a situation that the indoor unit is 
located in a room with an unsunny aspect. Therefore, for example, in such 
a severely hot condition that the outside air temperature is very high, 
the reduction of the driving current of the compressor by the protection 
control and the stop control of the driving operation are more frequently 
performed. Therefore, it is very difficult to protect the power relay in 
accordance with the outside air temperature. 
Further, with respect to the air conditioners each using the thermostat, 
when the air-conditioning load is large, the stop control of the driving 
of the compressor trends to be more frequently performed by the protection 
control. This situation occurs in a case where the cooling operation is 
particularly required by a user. Therefore, the control of stopping the 
driving of the compressor greatly disturbs the user, who is prevented from 
enjoying a comfortable air-conditioning atmosphere, and it would be 
preferable to continue the driving of the compressor although the driving 
power of the compressor is a little lowered. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide an air conditioner which 
is enabled to be continuously operated even when the driving operation 
thereof is carried out under an overload. 
In order to attain the above object, according to the present invention, 
there is provided an air conditioner which has a controller equipped with 
heat-producing electrical parts and in which the driving current of a 
compressor, etc., is controlled by the controller, which includes a 
temperature sensor which is provided to or in the vicinity of at least one 
heat-sensitive electrical part of the electrical parts and adapted to 
detect the temperature of the heat-sensitive electrical part, and means 
for gradually reducing the upper-limit value of the driving current of the 
compressor when the temperature detected by the temperature sensor is 
higher than a predetermined value. 
In the air conditioner as described above, the controller is equipped with 
a power transistor, and a temperature sensor is provided to the transistor 
or in the vicinity of the transistor. When the temperature detected by the 
temperature sensor is higher than the predetermined value, the means 
reduces the upper-limit value of the driving current of the compressor. 
In the air conditioner as described above, the means reduces the 
upper-limit value of the driving current of the compressor stepwise or 
linearly in accordance with an increase of the temperature detected by the 
temperature sensor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
A preferred embodiment according to the present invention will be described 
hereunder with reference to the accompanying drawing. 
FIG. 1 is a diagram showing the outlook of the air conditioner 1, and the 
outline of FIG. 1 is different from the actual arrangement of the air 
conditioner because both the front face sides of the outdoor and indoor 
units of the air conditioner are illustrated as being faced to the same 
direction. 
The air conditioner 1 shown in FIG. 1 is mainly constructed of an indoor 
unit 2 and an outdoor unit 3, and both the units are connected to each 
other through an interunit pipe 4 and an interunit cable 5. 
In FIG. 2, reference numeral 10 represents a refrigerant circuit of the air 
conditioner 1, reference numeral 11 represents a compressor for 
compressing the refrigerant, reference numeral 12 represents a muffler, 
reference numeral 13 represents a four-way valve for changing the 
direction of the refrigerant flow, reference numeral 14 represents an 
outdoor heat exchanger, reference numeral 15 represents an expansion 
device (pressure-reducing device) using capillary tubes, reference numeral 
16 represents a strainer for removing impurities from the refrigerant, 
reference numeral 17 represents a service valve, reference numeral 4A 
represents an interunit pipe, reference numeral 18 represents an auxiliary 
pipe, reference numeral 19 represents an indoor heat exchanger, reference 
numeral 20 represents an auxiliary pipe, reference numeral 4B represents 
an interunit pipe, reference 21 represents a service valve, reference 
numeral 22 represents a muffler, reference numeral 23 represents an 
accumulator, and reference numerals 24A to 24G represent refrigerant pipes 
for connecting the respective equipments as described above. 
In FIG. 2, an arrow indicated by a solid line represents the refrigerant 
flow in cooling operation (under defrosting operation) and an arrow 
indicated by a dotted line represents the refrigerant flow in heating 
operation. The cooling and heating operation of the air conditioner is 
substantially similar to that of the conventional air conditioner, and 
thus the detailed description thereof is omitted from the specification. 
FIG. 3 is an exploded view showing an outdoor unit of the air conditioner 
shown in FIG. 1. 
In FIG. 3, reference numeral 30 represents a panel comprising a top plate 
and a front plate which are integrally formed with each other, reference 
numeral 31 represents a panel comprising both side plates and a back plate 
which are integrally formed with each other, and reference numeral 32 
represents a bottom plate. The panel 30, the panel 31 and the bottom plate 
32 constitute an outer case 33. Reference numeral 34 represents a drain 
pipe, and reference numeral 35 represents a fan guard. 
Reference numeral 36 represents a propeller fan, reference numeral 37 
represents a fan motor for driving the fan 36, reference numeral 38 
represents a motor stand for supporting the motor 37, reference numeral 39 
represents an outside air temperature detector (sensor) for detecting the 
outside air temperature, reference numeral 40 represents an outdoor heat 
exchanger detector (sensor) for detecting the temperature of the outdoor 
heat exchanger, reference numeral 41 represents a vibration preventing 
rubber member for suppressing the vibration of the compressor, reference 
numeral 42 represents a cover for covering a terminal stand and wires, 
reference numeral 43 represents a valve cover, reference numeral 44 
represents a partition plate for partitioning a heat exchanger chamber and 
a mechanical chamber from each other, reference numeral 45 represents a 
reactor mounted to the partition plate 44, reference numeral 13A 
represents an electromagnetic coil for driving a needle of the four-way 
valve 13, reference numeral 46 represents a detector for detecting the 
temperature of the refrigerant, reference numeral 47 represents an 
electrical equipment box, reference numeral 48 represents a cover for the 
electrical equipment box, reference numeral 49 represents a control board, 
reference numeral 50 represents electrolytic capacitors, reference numeral 
51 represents a terminal board, reference numeral 52 represents a fuse, 
reference numerals 53 and 54 represent integrated circuits (Ics), 
reference numeral 55 represents a capacitor, reference numeral 56 
represents an HIC (hybrid IC) having a power transistor and a driving 
circuit for driving the power transistor, reference numeral 57 represents 
a cooler to which the HIC is secured, and reference numerals 58 and 59 
represent lead wires for connecting electrical parts to one another. 
FIG. 4 shows an electrical circuit diagram 1A of the air conditioner, and 
it mainly comprises an electrical circuit 2A at the indoor unit side and 
an electrical circuit 3A at the outdoor unit side. 
Reference numeral 61 represents a plug for supplying power to the 
controller of the indoor unit, reference numeral 62 represents a switch 
for the power source, reference numeral 63 represents a power relay, and 
reference numeral 64 represents a power relay board. A power relay 65 and 
a fuse 66 are provided on the power relay board 64. Reference numeral 67 
represents a power source board, reference numeral 68 represents a power 
source for the motor, reference numeral 69 represents a serial power 
source, reference numeral 70 represents a power source for a control 
circuit, reference numeral 71 represents a driving circuit, reference 
numeral 72 represents a fuse, reference numeral 73 represents a fan motor, 
reference numeral 74 represents a control board, reference numeral 75 
represents a serial circuit, reference numeral 76 represents a driving 
circuit, reference numeral 77 represents a microcomputer (which is 
abbreviated as "micron"), reference numeral 78 represents a service LED 
(light emitting diode) used for service, reference numeral 79 represents a 
driving change-over switch, reference numeral 80 represents an up-and-down 
flap motor for driving an up-and-down flap (an air blow direction changing 
plate which is located to extend in a lateral direction and adapted to 
change the direction of the air flow (upward and downward directions)), 
and reference numeral 81 represents a display board which has a display 
LED 82 and a reception circuit 83 for receiving a signal from a wireless 
remote controller. Reference numeral 84 represents a room temperature 
sensor for detecting the temperature of the room air, reference numeral 85 
represents a heat exchange temperature sensor for detecting the 
temperature of the indoor heat exchanger, reference numeral 86 represents 
a 3-pin terminal board at the indoor unit side, and reference numerals 
5A,5B,and 5C represent interunit cables. 
Reference numeral 87 represents a control board, reference numeral 88 
represents a noise filter, reference numeral 89 represents a serial 
circuit, reference numeral 90 represents a noise filter, reference numeral 
91 represents a fuse, reference numeral 92 represents a fuse, reference 
numeral 93 represents a noise filter, reference numeral 94 represents a 
switching power source, and reference numeral 95 represents a 
microcomputer. Reference numeral 96 represents a diode, and reference 
numeral 56A represents a power transistor which is provided in the HIC. 
The power transistor is connected to a drive circuit (not shown) for 
driving the transistor. Reference numeral 97 represents a temperature 
sensing element (temperature sensor) which is provided to the power 
transistor to detect the temperature of the power transistor. The 
temperature sensing element (temperature sensor) 97 is formed of a 
thermistor and serves to output a signal representing the detected 
temperature to the microcomputer 95. Reference numeral 37A represents a 
capacitor for the fan motor. 
The driving current of the compressor can be controlled by adjusting the 
driving frequency of the compressor under control of the control board. 
Accordingly, not only the driving power of the compressor can be varied, 
but also the driving current of the compressor can be varied under control 
of the control board (controller). 
The operation of the air conditioner thus constructed will be next 
described. 
During the operation of the air conditioner, the microcomputer receives 
signals from various sensors, and controls the driving frequency of the 
compressor to control the driving (rotational speed) of the compressor. 
When a large cooling load is required in cooling operation, for example, 
when many persons gather in a room which is to be air-conditioned or when 
a low temperature value is set, the driving of the compressor is carried 
out at a driving level which is relatively near to the maximum level. In 
such a case, the temperature of the HIC is liable to rises up to a 
relatively high temperature. In normal practical use, the temperature of 
the HIC is required to be set to 70.degree. C. or less. However, when the 
outside air temperature is extremely high or when the outdoor unit is 
located under a sunny condition, the temperature and the pressure in the 
refrigerant circuit are increased, and the temperature of the HIC is also 
increased. In this case, a protection circuit is actuated to stop the 
driving of the air conditioner. When the driving of the air conditioner is 
stopped by the protection circuit in the above situation, some users may 
feel uncomfortable due to the loss of air conditioning. Accordingly, 
according to the present invention, the driving of the air conditioner is 
controlled to be carried out as continuously as possible even if the 
driving power (cooling power) thereof is lowered. 
Specifically, the driving of the compressor under such a situation is 
carried out as follows. It is assumed that the upper limit value of the 
driving current of the compressor is normally set to 15A. In this case, if 
the temperature detected by the temperature sensor is equal to a 
predetermined value (for example, :80.degree. C.), the driving frequency 
is controlled so that the upper limit value of the driving current of the 
compressor is reduced by 0.5A and thus it is set to 14.5A, for example. 
Therefore, the maximum value (upper limit value) of the cooling power is 
reduced. Nonetheless, the cooling operation continues, and the cooling 
operation avoids being suddenly stopped. Furthermore, when the detected 
temperature rises to 81.degree. C., the upper limit value is further 
reduced by 0.5A, and thus the driving current is set to 14.0A, for 
example. Likewise, when the temperature successively rises up to 
82.degree. C., 83.degree. C., 84.degree. C., 85.degree. C., 86.degree. C., 
87.degree. C., 88.degree. C., or 89.degree. C., the upper limit value of 
the cooling operation is further successively reduced by every 0.5A and 
set to 13.5A, 13.0A, 12.5A, 12.0A,11.5A, 11.0A, 10.5A, 10.0A respectively. 
When the detected temperature further rises up to 100.degree. C., the 
driving of the air conditioner is finally stopped to prevent the power 
transistor from being damaged (see FIG. 5). In this embodiment, the 
predetermined value is set in the range of 80.degree. C. to 89.degree. C., 
and it is varied every one degree. However, the value may be set in a 
broader range, and be varied by smaller or larger increments. In addition, 
in the above embodiment, the driving current of the compressor is varied 
by every 0.5A, however, it may be varied by every smaller or larger value. 
According to the present invention, the temperature sensor is provided to 
(mounted on or built in) the power transistor or in the vicinity of the 
power transistor, and the upper limit value of the driving current of the 
compressor is reduced (particularly, gradually) when the temperature of 
the power transistor is higher than a predetermined value. Preferably, the 
upper limit value of the driving current of the compressor is reduced in 
accordance with the increase of the temperature detected by the detector. 
Therefore, although the driving power of the compressor is lowered, 
excessive heating of the power transistor and other electrical parts in 
the vicinity of the power transistor can be prevented by the reduction of 
the driving power, so that stopping of the driving operation of the 
compressor due to the protection control can be reduced as much as 
possible. Therefore, unlike the conventional air conditioner in which the 
compressor is suddenly stopped, the present compressor is prevented from 
being suddenly stopped, and thus the present invention can provide a 
relatively comfortable air-conditioning atmosphere to the user. 
Further, the upper limit value of the driving current of the compressor is 
gradually reduced in accordance with the temperature of the temperature 
sensor. Accordingly, when the temperature detected by the temperature 
sensor is relatively low, the reduction level of the upper limit value of 
the driving current is set to a small level. On the other hand, when the 
temperature detected by the temperature sensor is relatively high, the 
reduction level of the upper limit value of the driving current is set to 
a large level. That is, the upper limit value of the driving current of 
the compressor can be controlled so that the driving operation of the air 
conditioner is carried out as continuously as possible without being 
ceased. Therefore, the user hardly feels uncomfortable because the driving 
operation of the air conditioner is carried out continuously although the 
driving power is somewhat reduced (the cooling effect is less, as compared 
with a case where the air conditioning operation is completely ceased due 
to the stop of the driving operation. 
FIG. 6 is a graph showing a different control characteristic of the 
above-described controller. The difference between the control 
characteristics of FIGS. 5 and 6 resides in that the control operation of 
FIG. 6 is carried out linearly, whereas the control operation of FIG. 5 is 
performed stepwise. When the slope of the current value, where the 
temperature of the power transistor is equal to 80.degree. to 90.degree. 
C., is equal to -0.5A/.degree.C., by reducing the driving current of the 
compressor linearly (in place of stepwise), the driving power of the 
compressor can be reduced more smoothly when it is driven at the maximum 
power. Thus, the situation is avoided where the comfortable air 
conditioning level is suddenly lowered due to rapid reduction in cooling 
power. 
In the above-described embodiment, the power transistor is provided with 
the temperature sensor. The temperature sensor may be provided to another 
electrical part which is sensitive to heat (for example, the semiconductor 
parts, the ICs 53, 54, the electrolytic transistor 50, etc. on the board 
49) to reduce the upper limit value of the driving current of the 
compressor. 
Further, the temperature sensor may be disposed in the vicinity of the 
power transistor, or in a cooler to indirectly detect the temperature of 
the power transistor. In this case, the correlation between the 
temperature of the cooler and the temperature of the power transistor must 
be examined in advance to preset a predetermined value of the cooler. 
In addition, a power transistor in which a temperature sensor is beforehand 
built may be manufactured and used. 
According to the present invention, a temperature sensor is provided to or 
in the vicinity of a heat-sensitive electrical part such as a power 
transistor or the like, and when the temperature detected by the 
temperature sensor is high, the upper limit value of the driving current 
of the compressor is reduced. Therefore, although the driving power of the 
air conditioner is lowered, the heating of the electrical parts such as 
the power transistor, etc., can be reduced due to the reduction of the 
driving power, so that sudden stopping of the driving operation of the air 
conditioner by the protection control is avoided as much as possible. 
Accordingly, as compared with the conventional air conditioner in which 
the driving of the compressor is relatively often stopped by the 
protection control, the present invention can provide an air condition 
which make users less uncomfortable. 
Further, the present invention can provide an air conditioner which can 
prevent the heat-sensitive electrical parts such as the power transistor, 
etc., from being damaged and make users less uncomfortable as compared 
with the conventional air conditioner in which the driving of the 
compressor is relatively often stopped by the protection control. 
Particularly, according to the present invention, the upper limit value of 
the driving current of the compressor is reduced in accordance with the 
temperature detected by the temperature sensor. Therefore, when the 
temperature detected by the temperature sensor is relatively low, the 
reduction level of the upper limit value of the driving current is set to 
a smaller value. On the other hand, when the temperature detected by the 
temperature sensor is relatively high, the reduction level of the upper 
limit value of the driving current is set to a larger value. That is, the 
upper limit value of the driving current of the compressor is gradually 
controlled so that the driving of the compressor is carried out as 
continuously as possible without being ceased. Therefore, there is 
provided an air conditioner which prevents reduction in cooling power from 
occurring suddenly and thus makes users uncomfortable as little as 
possible.