Abstract:
An automobile air conditioner having a charging device for charging a power source capacitor preliminarily before driving a motor-driven compressor, which comprises a discharge circuit for discharging the electric charge in the capacitor through a power feeding device, and a controller for controlling the discharge by the discharge circuit. Further by comprising a cut-off detecting circuit for detecting when the battery is cut off, it is discharged automatically. Moreover, the voltage of the battery is converted, and supplied as a power source for the controller.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an automobile air conditioner having a motor-driven compressor driven by an electric power from a direct-current power source. 
     2. Description of the Related Art 
     FIG. 9 is a block diagram of a conventional automobile air conditioner having a motor-driven compressor driven by an electric power from a direct-current power source. To drive a motor-driven compressor  14 , an output unit  11  (generally known as inverter circuit) converts a direct-current supply voltage into an alternating-current driving voltage. A capacitor  7  is provided to suppress the ripple voltage of the direct-current power source. When a circuit breaker  3  is closed, this capacitor  7  of a large capacity is charged from a battery  1  by way of fuse  2 , circuit breaker  3 , diode  4  and resistor  5 . The diode  4  is intended to protect the circuit so that the current may not flow in case the battery  1  is connected in wrong polarity. 
     A controller  10  receives a command for operating the motor-driven compressor  14  from an air conditioner controller  12 , and confirms the charge voltage of the capacitor  7  detected by a voltage detector  8 . When the voltage of the capacitor  7  has reached a specified value, the controller  10  closes a relay  6 . Consequently, the output unit  11  provides with a driving voltage, and drives the motor-driven compressor  14 . A 12-volt power source of the controller  10  is supplied from the power source  13 . Although not shown, a switching power supply unit  9  converts the voltage of the battery  1 , and supplies the converted voltage to the output unit  11  and voltage detector  8 . 
     On the other hand, when receiving a stop command of the motor-driven compressor  14  from the air conditioner controller  12 , the controller  10  stops the output from the output unit  11 , and opens the relay  6 . 
     In the conventional configuration, when checking or repairing the air conditioner, first, the circuit breaker  3  is opened, and the capacitor  7  is allowed to discharge. After the electric charge is discharged sufficiently, checking or repairing can be started. In this case, the electric charge accumulated in the capacitor  7  is discharged as it is consumed by the switching power supply unit  9 . This discharging, however, takes a long time because the load is light. 
     To shorten the discharge time, with the circuit breaker  3  being opened, the controller  10  can discharge the capacitor  7  by driving the motor-driven compressor  14  by means of the output unit  11 . In this case, the discharge speed is faster, but the following problems are involved. 
     1. The motor-driven compressor  14  must be connected. 
     2. Complicated software for driving the motor-driven compressor  14  is needed. It is difficult to realize this method by a hardware circuit instead of using this software. 
     3. The power source  13  must be connected to the controller  10 . 
     Moreover, a method of using other discharge resistance is known, but this method requires a discharge resistor of a large current rating, and hence the equipment size is increased. 
     SUMMARY OF THE INVENTION 
     The present invention is devised in the light of such conventional problems. The automobile air conditioner of the invention comprises a direct-current power source, a power feeding device connected in series to the direct-current power source, a switching device connected in parallel to the power feeding device, a first capacitor charged through the power feeding device from the direct-current power source, an output unit for driving a motor-driven compressor for air conditioning by receiving electric power from the switching device, a discharge circuit for discharging the electric charge in the first capacitor through the power feeding device, and a controller for controlling the discharge circuit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of an automobile air conditioner in embodiment 1 of the invention. 
     FIG. 2 is a block diagram of an automobile air conditioner in embodiment 2 of the invention. 
     FIG. 3 is a block diagram of an automobile air conditioner in embodiment 3 of the invention. 
     FIG. 4 is a block diagram of an automobile air conditioner in embodiment 4 of the invention. 
     FIG. 5 is a characteristic diagram of a switching power supply unit in embodiment 4 of the invention. 
     FIG. 6 is a block diagram of a controller in embodiment 4 of the invention. 
     FIG. 7 is a block diagram of an automobile air conditioner in embodiment 5 of the invention. 
     FIG. 8 is a block diagram of an automobile air conditioner in embodiment 6 of the invention. 
     FIG. 9 is a block diagram of an automobile air conditioner in a prior art. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, preferred embodiments of the invention are described below. 
     (Embodiment 1) 
     FIG. 1 is a block diagram of an automobile air conditioner in embodiment 1 of the invention. 
     In FIG. 1, when a circuit breaker  3  is closed, a capacitor  7  is charged by a battery  1  by way of fuse  2 , circuit breaker  3 , diode  4 , resistor  5 , and charge/discharge changeover relay  16 . At this time, the relay  16  is closed at the contact (b) side as shown in FIG.  1 . 
     When driving a motor-driven compressor  14 , a controller  10  receives a command for operating the motor-driven compressor  14  from an air conditioner controller  12 , and checks the charge voltage of the capacitor  7  detected by a voltage detector. When the voltage detected by the voltage detector  8  has reached a specified value, the controller  10  closes a relay  6 . Then, the motor-driven compressor  14  is driven by an output unit  11 . 
     To stop the motor-driven compressor  14 , the controller  10  receives a stop command of the motor-driven compressor  14  from the air conditioner controller  12 , and stops the output from the output unit  11 , and then opens the relay  6 . 
     When the relay  6  is opened, the electric charge in the capacitor  7  is discharged. Discharge operation is explained in the following. The air conditioner controller  12  first opens the circuit breaker  3 , and issues a discharge command to the controller  10 . Then, the controller  10  closes the charge/discharge changeover relay  16  to the contact (a) side. As a result, the electric charge in the capacitor  7  is discharged through the charge/discharge changeover relay  16  and resistor  5 . 
     In this embodiment, the resistance value of the resistor  5  is tens of ohms, the capacitance of the capacitor  7  is 1000 μF, and the discharge time is about 1 second. On the other hand, the discharge time by the switching power supply unit  9  is about tens of seconds. That is, the discharge time in this embodiment is about tens of times faster. 
     Thus, according to the embodiment, a resistor of large capacity is not needed separately for discharging, and the electric charge in the capacitor  7  can be discharged only by the software for operating the charge/discharge changeover relay  16 . Hence, the size of the apparatus can be reduced. Further, without requiring connection of motor-driven compressor or complicated software, the electric charge in the capacitor can be discharged promptly. 
     (Embodiment 2) 
     FIG. 2 is a block diagram of an automobile air conditioner in embodiment 2 of the invention. In FIG. 2, same components as in FIG. 1 are identified with same reference numerals, and detailed explanation is omitted. 
     In this embodiment, the charge/discharge changeover relay  16  in embodiment 1 is replaced by diodes  17 ,  18 , and a transistor  19 . 
     When a circuit breaker  3  is closed, a capacitor  7  is charged by a battery  1  by way of fuse  2 , circuit breaker  3 , diode  4 , resistor  5 , and diode  18 . At this time, the transistor  19  is turned off. 
     Discharge operation of the capacitor  7  is explained in the following. The air conditioner controller  12  first opens the circuit breaker  3 , and issues a discharge command to the controller  10 . Receiving the discharge command, the controller  10  turns on the transistor  19 . As a result, the electric charge in the capacitor  7  is discharged through the diode  17 , resistor  5 , and transistor  19 . At this time, the diode  18  prevents the current from flowing directly from the capacitor  7  to the transistor  19  to break it down. Hence, according to the embodiment, since the semiconductors are used instead of the relay  16  in embodiment 1, the apparatus is reduced in size, and the durability of the apparatus can be enhanced. 
     (Embodiment 3) 
     FIG. 3 is a block diagram of an automobile air conditioner in embodiment 3 of the invention. In FIG. 3, same components as in FIG. 2 are identified with same reference numerals, and detailed explanation is omitted. 
     In this embodiment, the resistor  5  in embodiment 2 is replaced by a constant current circuit  20 . 
     The constant current circuit  20  is, as shown in FIG. 3, composed of a transistor  201 , resistors  202 ,  203 , and a Zener diode  204 . The constant current circuit  20  continues to charge the capacitor  7  at a constant current until its voltage becomes about Vc 1  (Vc 1 =Vs−2Vd−Vz, where Vs is output voltage of battery  1 , Vd is forward voltage of diodes  4 ,  18 , and Vz is Zener voltage of Zener diode  204 ). Then the capacitor  7  is charged up to about Vc 2  (Vc 2 =Vs−2Vd−Vbe, where Vbe is base-emitter voltage of transistor  201 , Vbe&lt;Vz). 
     Same as in embodiment 2, when the relay  6  is open, receiving the discharge command from the air conditioner controller  12 , the controller  10  turns on the transistor  19 , and the electric charge in the capacitor  7  is discharged. That is, when the transistor  19  is turned on, the electric charge in the capacitor  7  is discharged through the diode  17 , constant current circuit  20 , and transistor  19 . At this time, the constant current circuit  20  discharges the electric charge at a constant current until the voltage of the capacitor  7  becomes about Vd 1  (Vd 1 =Vd+Vz, the forward voltage of diode  17  is also Vd). Then the capacitor  7  is further discharged until the voltage becomes about Vd 2  (Vd 2 =Vd+Vbe). Herein, Vd is about 0.7 V. In the embodiment, Vz is about 3 V. 
     For example, supposing the voltage of battery  1  to be 200 V, the capacitance of capacitor  7  to be 1000 μF, and the constant current to be 0.2 A, both the charge time and discharge time is 1 second (200 V×1000 μF/0.2 A). The discharge time by the switching power supply unit  9  is about tens of seconds conventionally. That is, the discharge speed is about tens of times faster in this embodiment. 
     According to the embodiment, the value of discharge current can be set arbitrarily. As compared with embodiment 1 or 2, the maximum current can be smaller, and a circuit element of a small rated current value can be used, so that the apparatus is further reduced in size. 
     (Embodiment 4) 
     FIG. 4 is a block diagram of an automobile air conditioner in embodiment 4 of the invention. In FIG. 4, same components as in FIG. 3 are identified with same reference numerals, and detailed explanation is omitted. 
     In this embodiment, instead of the power source  13  of the controller  10  in embodiment 3, it is designed to feed a supply voltage of 12 V from the switching power supply unit  9  to the controller  10 . 
     In the embodiment, the transistor  19  remains in ON state until the supply voltage of the controller  10  declines and the controller  10  fails to operate. When the supply voltage of the controller  10  declines and the controller  10  fails to operate, the transistor  19  is turned off, and discharge of the capacitor  7  stops. Thereafter, the electric charge in the capacitor  7  is discharged by the switching power supply unit  9  as the load. 
     This embodiment does not require external power source  13  as used in embodiments 1 to 3. That is, when discharging the electric charge in the capacitor  7 , it is not necessary to connect the 12 V power source  13 , and the work for discharge is simple and easy. When starting checking, discharge is possible by disconnecting immediately. 
     FIG. 5 is a diagram showing characteristics of supply voltage supplied from the switching power supply unit  9  to the controller  10  in this embodiment. In FIG. 5, the input voltage on the axis of abscissas is the input voltage to the switching power supply unit  9 , which is equal to the voltage of the capacitor  7 . When the input voltage is higher than VL, the switching power supply unit  9  delivers a voltage at rated supply voltage V 0  of the controller  10 . In this embodiment, V 0  is 5 V. When the input voltage becomes lower than VL, as shown in FIG. 5, the output voltage also declines. The controller  10  operates at the rated voltage VO (5 V), but substantially operates until the voltage becomes lower than 3 V. That is, from the time of the voltage of the capacitor  7  becoming lower than VL until the output voltage becomes 3 V, the electric charge in the capacitor  7  is discharged through the constant current circuit  20 . When the supply voltage becomes lower than 3 V, and the controller  10  stops, the transistor  19  is turned off. As a result, the constant current circuit  20  stops, and the voltage of the capacitor  7  at this time is lower than VL. When this voltage VL is set at a low voltage not to cause trouble in checking and repairing at the time of designing of the switching power supply unit  9 , same as in the foregoing embodiments, checking or repairing can be started in a short time. 
     FIG. 6 is a block diagram of the controller  10  in this embodiment. The controller  10  comprises a microcomputer  15  for starting the control software, and a capacitor  26  connected to the 5 V power source terminal of the microcomputer  15 . The capacitance of the capacitor  26  is set at a value enough to hold the supply voltage of the microcomputer  15  at 5 V for more than the time required to discharge the capacitor  7  sufficiently. Since the microcomputer  15  substantially operates at about 3 V, the voltage may be lowered to 3 V. (The standstill of the microcomputer  15  means the standstill of the controller  10 .). Therefore, until the capacitor  7  is discharged sufficiently, the controller  10  and discharge circuit function, and the capacitor  7  is discharged completely in a short time (in 1 second by applying an example of embodiment 3). Hence, checking or repairing can be started in a short time. 
     (Embodiment 5) 
     FIG. 7 is a block diagram of an automobile air conditioner in embodiment 5 of the invention. In FIG. 7, same components as in FIG. 4 are identified with same reference numerals, and detailed explanation is omitted. 
     In this embodiment, a cut-off detecting circuit for detecting that the connection of the battery  1  is cut off is added to the configuration in embodiment 4. The cut-off detecting circuit is composed of a resistor  21 , a resistor  22 , and a diode  23 . A potential voltage by the resistor  21  and resistor  22  is fed into the controller  10 . The diode  23  is a protective diode provided for the same purpose as the diode  4 . 
     In the embodiment, the electric charge in the capacitor  7  is discharged regardless of the signal from the air conditioner controller  12 . When the connection of the battery  1  is cut off, for example, due to opening of the circuit breaker  3 , melting of fuse  2 , or disconnection of connector, the potential voltage by the resistor  21  and resistor  22  becomes about 0 V. The controller  10  judges this about 0 V as a discharge signal, and turns on the transistor  19  for discharging. As a result, the electric charge in the capacitor  7  is discharged by way of the diode  17 , constant current circuit  20 , and transistor  19 . 
     According to the embodiment, the controller  10  controls the discharge circuit according to the signal from the cut-off detecting circuit, and hence discharge can be started without receiving signal from the air conditioner controller  12  (in other word, without receiving a cutoff signal of direct-current power source from outside). Therefore, at the time of checking or repairing, by cutting off the battery  1  by detaching the connector or the like, the capacitor  7  can be discharged easily. If the fuse is blown, meanwhile, discharge can be done without requiring any particular work. 
     (Embodiment 6) 
     FIG. 8 is a block diagram of an automobile air conditioner in embodiment 6 of the invention. In FIG. 8, same components as in FIG. 7 are identified with same reference numerals, and detailed explanation is omitted. 
     In this embodiment, the cut-off detecting circuit of embodiment 5 in FIG. 7 is designed to drive the transistor  19  directly. 
     While the battery  1  is not cut off, a transistor  24  is turned on by the potential voltage by the resistor  21  and resistor  22 , and the collector voltage of the transistor  24  becomes about 0 V. Therefore, the base voltage of the transistor  19  is about 0 V, and the transistor  19  is in OFF state. 
     When the electric charge in the capacitor  7  is discharged, it is discharged regardless of the signal from the air conditioner controller  12 . When the connection of the battery  1  is cut off, for example, due to opening of the circuit breaker  3 , melting of fuse  2 , or disconnection of connector, the potential voltage by the resistor  21  and resistor  22  becomes about 0 V, and the base voltage of the transistor  24  also becomes about 0 V, so that the transistor  24  is turned off. When the voltage of the capacitor  7  is applied to the base terminal of the transistor  19  through the diode  17  and resistor  25 , the transistor  19  is turned on. As a result, the electric charge in the capacitor  7  is discharged by way of the diode  17 , constant current circuit  20 , and transistor  19 . 
     According to the embodiment, since the discharge circuit is directly controlled by the cut-off detecting circuit, the controller  10  does not require software for discharging, and discharge can be started by the hardware circuit only. Therefore, the software of the controller  10  is lighter in load, and regardless of the situation of the controller  10 , for example, if the supply voltage is lowered and the controller  10  fails to function, discharge can be started. 
     In the foregoing embodiments, the resistor  5  or constant current circuit  20  is used as the power feeding device, but the same effects are obtained by using other means.