Abstract:
It is an object to provide an electric heated catalyst failure diagnostic device that is compact, lightweight, inexpensive, and can accurately detect a disconnection of the heater and an abnormality in a circuit from the power supply to the heater with a simple configuration. When an ECU orders to apply the current to a heater drive circuit, a heater failure diagnostic device applies the current to the heater and the heater drive circuit. If energizing via a diode, the heater failure diagnostic device determines the circuit is abnormal. If not so, the circuit is normal. Meanwhile, when the ECU orders not to apply the current to the heater drive circuit, the heater failure diagnostic device turns on electricity to the heater and the heater drive circuit. If energizing via the diode, the heater failure diagnostic device determines the heater is not disconnected, and if not so, the heater is disconnected.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   The disclosure of Japanese Application No. 2004-167727 filed on Jun. 4, 2004 including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an electric heated catalyst failure diagnostic device that uses a high voltage to efficiently heat a catalyst in a vehicle, for example a equipped with a 42-V power supply system. 
   2. Description of the Related Art 
   A device is known where, in a vehicle such as an automobile, an electric heated catalyst is disposed in an exhaust system for the purpose of cleaning exhaust gas at the time the engine is started. Because a catalyst is heated by electricity before engine starting, the electrical heated catalyst activates the catalyst early. (e.g., see JP-A-7-42541). 
   In a vehicle equipped with such an electric heated catalyst, when a failure occurs in a heater of the electric heated catalyst, the catalyst is not heated sufficiently, the activation of the catalyst is delayed, and the capability to clean the exhaust gas deteriorates. Thus, it is necessary to quickly determine failure of the heater. 
   In order to counter this problem, as disclosed in JP-A-9-218233, it is conceivable to use a load disconnection detector that includes a measurement-use power supply separate from the power-use power supply of loads such as the heater. The detector switches the connection of the power supply with respect to the loads from the power-use power supply to the measurement-use power supply when detecting disconnection of the loads, supplies a current from the measurement-use power supply to the loads, and detects the disconnection of the loads with the current flowing through the loads or the voltages at both ends of the loads. 
   However, in the disconnection detector according to JP-A-9-218233, there are problems in that the detector becomes complicated, large, heavy, and expensive because a measurement-use power supply with good accuracy is needed. Also, in the disconnection detector according to JP-A-9-218233, there are the problems that only the disconnection of the heater can be detected, and the disconnection detector cannot diagnose abnormality in the circuit from the power supply to the heater. 
   SUMMARY OF THE INVENTION 
   The present invention was made in view of these circumstances, and it is an object thereof to provide an electric heated catalyst failure diagnostic device that is compact, lightweight, inexpensive, and can accurately detect disconnection of the heater, and a failure in the circuit from the power supply to the heater, with a simple configuration. 
   An electric heated catalyst failure diagnostic device pertaining to the present invention includes: an electric heated catalyst having a heater and being disposed in an engine exhaust system to which electricity is supplied by a power supply; heater energizing control means that controls the energizing of the heater; first heater failure detecting means that detects a failure in the circuit from the power supply to the heater of the electric heated catalyst at the time of a command to energize the heater of the electric heated catalyst from the heater energizing control means; and second heater failure detecting means that detect disconnection of the heater at the time of a command not to energize the heater from the heater energizing control means. 
   The electric heated catalyst failure diagnostic device of the invention is compact, lightweight, inexpensive, and can accurately detect disconnection of the heater and failure in the circuit from the power supply to the heater with a simple configuration. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a system block diagram showing a power supply system in an automobile; 
       FIG. 2  is an explanatory drawing of for a heater drive circuit and a circuit of a heater failure diagnostic device; and 
       FIG. 3  is an explanatory drawing of the operation and voltage of each element and each point in  FIG. 2 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   An embodiment of the invention will be described below with reference to the drawings.  FIGS. 1 to 3  pertain to the embodiment of the invention.  FIG. 1  is a system configuration diagram showing a power supply system for an automobile,  FIG. 2  is an explanatory drawing of a heater drive circuit and a circuit of a heater failure diagnostic device, and  FIG. 3  is an explanatory drawing of the operation and voltage of each element and each point in  FIG. 2 . 
   In  FIG. 1 , reference numerals  1  and  2  indicate batteries disposed in an automobile. In the present embodiment, the battery  1  is a nominal voltage 12-V battery (voltage at the time the automobile is driven: 14 V), and the battery  2  is a nominal voltage 36-V battery (12 V×3; voltage at the time the automobile is driven: 14 V×3=42 V). Hereinafter, the battery  1  will be referred to as “the low voltage battery,” and the battery  2  will be referred to as “the high voltage battery.” The voltage system of the low voltage battery  1  will be referred to as “the 14-V system,” and the voltage system of the high voltage battery  2  will be referred to as “the 42-V system.” 
   In the present embodiment, the high voltage battery  2  is charged by a motor generator  4  disposed in an engine  3 . A pulley  7  at the end portion of a rotary shaft is coupled to a crank pulley  5  of the engine  3  via a belt  6 . The motor generator  4  is rotated by the engine  3  to generate electricity. Also when the automobile is started after idling has stopped, the motor generator  4  drives the engine  3  to restart the engine  3 . The motor generator  4  is electrically connected to an inverter  8 . 
   A wire of the 42-V system with the high voltage battery  2  is connected to a terminal of the 42-V side of the inverter  8 , and loads requiring a large amount of electrical power are connected to this wire o. Examples of loads requiring a large amount of electrical power include a starter motor  9  that is used only when the engine  3  is initially started, a heater-heated electric heated catalyst  11  disposed in an exhaust pipe  10  of the engine  3 , and a power steering device  13  that generates steering assist power during operation of a steering wheel  12  by the driver. The starter motor  9  and the power steering device  13  are connected to the wire of the 42-V system via relay contacts (normally open contacts) of relays RY 1  and RY 2 , and the electric heated catalyst  11  is connected to the wire of the 42-V system via a heater drive circuit  20 . 
   In the present embodiment, the electric heated catalyst  11  is configured to include a catalyst  11   a , which cleans the exhaust gas of the engine  3 , and a heater  11   b , which includes a honeycomb path disposed directly upstream of the catalyst  11   a . The electric heated catalyst  11  energizes the heater  11   b  when the engine is cold to heat the exhaust gas passing through the heater  11   b  and improve the early activation of the catalyst  11   a . The heater  11   b  is an ordinary electric resistance heater, whereby costs can be reduced with a simple configuration. 
   A resistance value of the heater  11   b  is set to a rated value that is smaller than the rated value of the continuous energization from the high voltage power supply of the 42-V system. For a short time during an early energization stage, a heater drive circuit  20  supplies electricity more than the rated value to the heater  11   b , and catalyst  11   a  is heated quickly. Afterwards, the heater drive circuit  20  inhibits an energization current by means of a chopper control, and current consumption is reduced. Thus, battery voltage drop can be controlled and affects on in-vehicle devices can be avoided. 
   A later-described heater failure diagnostic device  30  is electrically connected between the heater  11   b  and the heater drive circuit  20 . 
   In the present embodiment, the power steering device  13  is configured to include an electrically-operated motor, which is coupled to the steering mechanism of the steering wheel  12 , and a drive circuit, which drive-controls the electrically-operated motor. The power steering device  13  generates assist power with the rotational torque of the electrically-operated motor. By supplying power from the 42-V system to the power steering device  13 , not only the consumed current can be reduced in comparison to the case using a conventional 14-V system power, but a greater assist power can be obtained while avoiding affects on other loads resulting from a battery voltage drop. 
   The electric heated catalyst  11  may be one where the catalyst is retained in the surface of a porous conductor and the catalyst retainer is used as an electric resistance heater. Also, the power steering device  13  may be one that uses hydraulic pressure generated by an electrically-operated pump to generate the assist power. 
   As the voltage system of the low voltage 14-V system, a DC-DC converter  14  that converts a 42-V voltage to a 14-V voltage is connected to the inverter  8 . The low voltage battery  1  is connected to the DC-DC converter  14 , and the heater failure diagnostic device  30  and low voltage loads (14-V loads) such as various kinds of lamps and audio not shown are connected to the DC-DC converter  14  via a relay contact (normally open contact) of a relay RY 3 . 
   The inverter  8 , the heater drive circuit  20 , and the relays RY 1  to RY 3  are controlled by an electronic control unit (ECU)  50 . The ECU  50  is configured to include a microcomputer and peripheral circuits such as constant voltage circuits and input/output circuits. The ECU  50  conducts control of the engine  3 , idle stop control that executes automatic stopping and restarting of the engine  3 , control of the energizing of the electric heated catalyst  11  via the heater drive circuit  20 , steering assist control via the power steering device  13 , control of the motor generator  4  via the inverter  8 , and mainly management of the charge and discharge state of the high voltage battery  2 . Namely, the ECU  50  is configured to include a function as a heater energizing control means. 
   In  FIG. 1 , the ECU  50  is shown as a single unit including plural control functions, but these control functions may be dispersed among plural units that are interconnected via a communication line. 
   The power of the 14-V system is supplied to the constant voltage circuit of the ECU  50 , and the ECU  50  operates at a predetermined stable constant voltage. Signals from an ignition switch  15 , a start switch  16  and other various kinds of switches not shown, a signal from the heater failure diagnostic device  30 , signals from various kinds of sensors not shown, and a monitor voltage of the high voltage battery  2  are inputted to an input side of the ECU  50 . 
   The inverter  8 , the heater drive circuit  20 , the heater failure diagnostic device  30 , the relays RY 1  to RY 3 , and various kinds of actuators that operate on 14 V and are disposed in the engine  3  are connected to the output side of the ECU  50 . Moreover, an alarm device  17  for issuing an alarm to the driver using light or sound when the heater failure diagnostic device  30  has detected a failure in the heater  11   b , or when the heater failure diagnostic device  30  has detected a failure such as a voltage drop while monitoring the voltage of the 42-V system, is connected to the output side of the ECU  50 . 
   Next, the details of a circuit configuration of the heater  11   b , the heater drive circuit  20 , the heater failure diagnostic device  30  and the ECU  50  will be described with reference to  FIG. 2 . 
   The heater drive circuit  20  comprises a relay Rly, an NPN transistor Tr 1 , a resistor R 1 , and a fuse Fu. The high voltage battery  2  is connected to one terminal of a make contact of the relay Rly and one coil terminal of the relay Rly via the fuse Fu. 
   A signal from the ECU  50  is outputted to a base of the NPN transistor Tr 1  via the resistor R 1 , and a collector of the NPN transistor Tr 1  is connected to the other coil terminal of the relay Rly. 
   The other terminal of the make contact of the relay Rly is connected to the heater  11   b  and to a cathode of a diode Dy of the heater failure diagnostic device  30 . 
   The heater failure diagnostic device  30  comprises the diode Dy, an NPN transistor Tr 2 , resistors R 2 , R 3  and R 4 , inverter circuits In 1  and In 2 , AND circuits Icand 1  and Icand 2 , and an OR circuit Icor. 
   The cathode of the diode Dy is connected to the other terminal of the make contact of the relay Rly of the heater drive circuit  20  and to the heater  11   b . An anode of the diode Dy is connected to the low voltage battery  1  via the resistor R 2  and to a base of the NPN transistor Tr 2  via the resistor R 3 . The value of the resistor R 2  is far larger than that of the heater  11   b  (e.g., if the resistance value of the heater  11   b  is 1 Ω, then the value of the resistor R 2  is 10 kΩ). 
   The low voltage battery  1  is connected, via the resistor R 4 , to a collector of the NPN transistor Tr 2 , to one input of the AND circuit Icand 1 , and to the input of the inverter circuit In 2 . 
   The inputted signal from the ECU  50  to the heater failure diagnostic device  30  consists of the other input of the AND circuit Icand 1  and to the input of the inverter circuit In 1 . 
   The outputs of the inverter circuits In 1  and In 2  are inputted to the inputs of the AND circuit Icand 2 . The output of the AND circuit Icand 2  is outputted to one input of the OR circuit Icor. The output of the AND circuit Icand 1  is outputted to the other input of the OR circuit Icor. The output of the OR circuit Icor is outputted to the ECU  50 . 
   Operation of the circuit configuration of the heater  11   b , the heater drive circuit  20 , the heater failure diagnostic device  30 , and the ECU  50  is described on the basis of  FIG. 3 . 
   First, when the ECU  50  issues an energize command with respect to the heater drive circuit  20  in order to energize the heater  11   b , in a case where the circuit from the high voltage battery  2  to the heater  11   b  is normal, as shown in the first line of  FIG. 3 , the voltage at a point A in  FIG. 2  becomes a high level (H), the NPN transistor Tr 1  is turned ON, the coil of the relay Rly is energized, and the switch of the relay Rly is switched ON. Thus, 42 V is applied to the heater  11   b  and the heater  11   b  generates heat. 
   Then, the diode Dy becomes non-energized, the transistor Tr 2  is turned ON, and the voltage of the collector of the transistor Tr 2  (i.e., the voltage at a point B) becomes a low level (L). 
   In this manner, the output (voltage at a point C) becomes a low level (L) because the voltage (L) at the point. B and the voltage (H) at the point A are inputted to the AND circuit Icand 1 . 
   Also, the voltage (H) at the point A is inputted to the inverter circuit In 1 , and the output from the inverter circuit In 1  (the voltage at a point D) becomes a low level (L). Moreover, the voltage (L) at the point B is inputted to the inverter circuit In 2 , and the output from the inverter circuit In 2  (the voltage at a point E) becomes a high level (H). 
   The outputs from the inverter circuits In 1  and In 2  are inputted to the inputs of the AND circuit Icand 2 , and the output of the AND circuit Icand 2  (the voltage at a point F) becomes a low level (L). 
   Then, the voltage (L) at the point C and the voltage (L) at the point F are inputted to the OR circuit Icor, and the signal (the voltage at a point G) of the low level (L) from the OR circuit Icor is outputted. As a result, it is determined that the circuit from the high voltage battery  2  to the heater  11   b  is normal. 
   Next, when the ECU  50  issues an energize command with respect to the heater drive circuit  20  in order to energize the heater  11   b , in a case where there is a failure in the circuit from the high voltage battery  2  to the heater  11   b , as shown in the second line of  FIG. 3 , the voltage at the point A in  FIG. 2  becomes a high level (H), and the NPN transistor Tr 1  is turned ON, but the operation of the relay Rly becomes unknown. Thus, a voltage is not applied to the heater  11   b.    
   Then, the diode Dy becomes energized, and the current supplied from the low voltage battery  1  is supplied from the diode Dy to the heater  11   b . Thus, the transistor Tr 2  is switched OFF, and the voltage of the collector of the transistor Tr 2  (i.e., the voltage at the point B) becomes a high level (H). 
   In this manner, the output (the voltage at the point C) becomes a high level (H) because the voltage (H) at the point B and the voltage (H) at the point A are inputted to the AND circuit Icand 1 . 
   Also, the voltage (H) at the point A is inputted to the inverter circuit In 1 , and the output from the inverter circuit In 1  (the voltage at the point D) becomes a low level (L) Moreover, the voltage (H) at the point B is inputted to the inverter circuit In 2 , and the output from the inverter circuit In 2  (the voltage at the point E) becomes a low level (L). 
   The outputs from the inverter circuits In 1  and In 2  are inputted to the inputs of the AND circuit Icand 2 , and the output of the AND circuit Icand 2  (the voltage at the point F) becomes a low level (L). 
   Then, the voltage (H) at the point C and the voltage (L) at the point F are inputted to the OR circuit Icor, and the signal (the voltage at a point G) of the high level (H) is outputted from the OR circuit Icor. As a result, it is determined that there is a failure in the circuit from the high voltage battery  2  to the heater  11   b.    
   In this manner, the heater drive circuit  20  and the heater failure diagnostic device  30  include a function as a first heater abnormality detecting means. 
   Next, when the ECU  50  issues a non-energize command with respect to the heater drive circuit  20  in order not to energize the heater  11   b , in a case where the heater  11   b  is not disconnected and is normal, as shown in the third line of  FIG. 3 , the voltage at the point A in  FIG. 2  becomes a low level (L), the NPN transistor Tr 1  is turned OFF, the coil of the relay Rly becomes not energized, and the switch of the relay Rly is switched OFF. Thus, a voltage is not applied to the heater  11   b.    
   Then, the diode Dy becomes energized, and the current supplied from the low voltage battery  1  is supplied from the diode Dy to the heater  11   b . Thus, the transistor Tr 2  is turned OFF, and the voltage of the collector of the transistor Tr 2  (i.e., the voltage at the point B) becomes a high level (H). 
   In this manner, the output (the voltage at the point C) becomes a low level (L) because the voltage (H) at the point B and the voltage (L) at the point A are inputted to the AND circuit Icand 1 . 
   Also, the voltage (L) at the point A is inputted to the inverter circuit In 1 , and the output from the inverter circuit In 1  (the voltage at the point D) becomes a high level (H). Moreover, the voltage (H) at the point B is inputted to the inverter circuit In 2 , and the output from the inverter circuit In 2  (the voltage at the point E) becomes a low level (L). 
   The outputs from the inverter circuits In 1  and In 2  are inputted to the inputs of the AND circuit Icand 2 , and the output of the AND circuit Icand 2  (the voltage at the point F) becomes a low level (L). 
   Then, the voltage (L) at the point C and the voltage (L) at the point F are inputted to the OR circuit Icor, and the signal (the voltage at the point G) of the low level (L) is outputted from the OR circuit Icor. As a result, it is determined that the heater  11   b  is not disconnected and is normal. 
   Next, when the ECU  50  issues a non-energize command with respect to the heater drive circuit  20  in order not to energize the heater  11   b , in a case where the heater  11   b  is disconnected, as shown in the fourth line of  FIG. 3 , the voltage at the point A in  FIG. 2  becomes a low level (L), the NPN transistor Tr 1  is turned OFF, the coil of the relay Rly becomes not energized, and the switch of the relay Rly is switched OFF. Thus, a voltage is not applied to the heater  11   b.    
   Then, the current supplied from the low voltage battery  1  cannot energize the heater  11   b  because of the disconnection of the heater  11   b . Thus, the diode Dy becomes not energized, the transistor Tr 2  is turned ON, and the voltage of the collector of the transistor Tr 2  (i.e., the voltage at the point B) becomes a low level (L). 
   In this manner, the output of the AND circuit Icand 1  (the voltage at the point C) becomes a low level (L) because the voltage (L) at the point B and the voltage (L) at the point A are inputted to the AND circuit Icand 1 . 
   Also, the voltage (L) at the point A is inputted to the inverter circuit In 1 , and the output from the inverter circuit In 1  (the voltage at the point D) becomes a high level (H). Moreover, the voltage (L) at the point B is inputted to the inverter circuit In 2 , and the output from the inverter circuit In 2  (the voltage at the point E) becomes a high level (H). 
   The outputs from the inverter circuits In 1  and In 2  are inputted to the inputs of the AND circuit Icand 2 , and the output of the AND circuit Icand 2  (the voltage at the point F) becomes a high level (H). 
   Then, the voltage (L) at the point C and the voltage (H) at the point F are inputted to the OR circuit Icor, and the signal (the voltage at the point G) of the high level (H) is outputted from the OR circuit Icor. As a result, it is determined that the heater  11   b  is disconnected. 
   In this manner, the heater drive circuit  20  and the heater failure diagnostic device  30  include a function as a second heater abnormality detecting means. 
   In this manner, according to the embodiment of the present invention, abnormality of the circuit from the high voltage battery  2  to the heater  11   b  and disconnection of the heater  11   b  can be inexpensively detected with a circuit configuration that is compact, lightweight, and simple, without having to dispose a complicated circuit such as a reference power supply. 
   In the present embodiment, the engine  3  equipped with the motor generator  4  was described as an example, but the invention may also be configured to include an alternator rather than a motor generator, so that the rectifier current of the alternator is supplied to the high voltage battery  2 , to the electric heated catalyst  11  and the power steering device  13  of the 42-V system, and also supplied to the low voltage battery  1  of the 14-V system and various loads via the DC-DC converter  14 . 
   Also, the various kinds of circuit elements described in the heater failure diagnostic device  30  are not limited to those in the present embodiment and may be of other circuit configurations. 
   Moreover, the heater failure diagnostic device  30  may be integrally configured with the heater drive circuit  20  or integrally configured with the ECU  50 .