Abstract:
A failure detecting system of an exhaust purification apparatus includes, a catalyst unit including an electrically heated catalyst and intervened in an engine exhaust path, an air pump supplying a secondary air to the engine exhaust path, a first electric current sensor detecting electric current value for the electrically heated catalyst, and a second electric current sensor detecting electric current value for the air pump. The electrically heated catalyst and air pump are supplied with current upon a cold start of an engine. Presence of failures in the electrically heated catalyst and air pump is discerned on the basis of the electric current value each of the first and second electric current sensors, and the detection of the current value of the first electric current sensor starts prior to the detection of the current value of the second electric current sensor.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a failure detecting system of an exhaust purification apparatus, having a catalyst unit, inclusive of an electrically heated catalyst, that is inserted in an engine exhaust path and an air pump for supply of secondary air to the exhaust path in such a manner that current is supplied to a structure as the electrically heated catalyst and the air pump, upon cold start of the engine. 
     2. Description of the Related Art 
     Conventionally known as this kind of failure detecting system is an electric current sensor for detection of current value supplied to the electrically heated catalyst and an electric current sensor for detection of current value supplied to the air pump, wherein presence of failures in the electrically heated catalyst and air pump are discerned on the basis of electric current value detected by these electric current sensors (See Japan Patent Unexamined Publication No. Hei. 9-60554). 
     Immediately after the air pump is started, the electrical current increases temporarily under the influences of inertia mass and startup character of the air pump, and stabilization of the electric current takes a certain duration of time. Therefore, in the above-described conventional type, after the start of supply of current to the electrically heated catalyst and the air pump, a certain duration of time has been retained for a waiting time as required to stabilize the electric current for the pump, and then the detection of electric current value for the electrically heated catalyst and the detection of electric current value for the air pump are simultaneously started. 
     In order to secure durability of the electrically heated catalyst, supply of current to the electrically heated catalyst is stopped if the engine rotation frequency or vehicle speed exceeds a predetermined value even at the cold start. If a driver, however, attempts to start driving a car immediately after beginning of the startup, supply of current to the electrically heated catalyst is stopped because the engine rotation frequency or vehicle speed has exceeded the predetermined value before expiration of necessary duration of detection time after the start of detecting the electric currents for the electrically heated catalyst and the air pump, and thus discernment of failures of the electrically heated catalyst cannot be carried out. 
     Further, a conventionally known engine exhaust purification apparatus is provided with a catalyst unit which contains an electrically heated catalyst that is inserted in the engine exhaust path. The electrically heated catalyst is supplied with current upon cold start of the engine to facilitate exhaust purifying reaction in the catalyst unit for improvement in the exhaust emission at the cold start (Japanese Patent Unexamined Publication No. Hei. 9-21313). 
     Also known is the one provided with a failure detecting means in which, after detection of current value supplied to the electrically heated catalyst, an integrated power amount that has been applied to the electrically heated catalyst is calculated on the basis of the detected electric current value so as to be utilized as a parameter representing the generated heat amount of the electrically heated catalyst, and an electrically heated catalyst failure is discerned if the integrated power amount is not within a predetermined allowable range. 
     If the electrically heated catalyst is supplied with current when the engine temperature is substantially lower than the normal temperature, a heat shock which incurs bad influence in the durability thereof is liable to occur in the electrically heated catalyst. 
     SUMMARY OF THE INVENTION 
     In view of the above described problem, the object of the invention is to provide a failure detecting system of an exhaust purification apparatus wherein a frequency of disabled discernment of failure in the electrically heated catalyst is reducible so far as possible. 
     A failure detecting system of an exhaust purification apparatus includes, a catalyst unit including an electrically heated catalyst and intervened in an engine exhaust path, an air pump supplying a secondary air to the engine exhaust path, a first electric current sensor detecting electric current value for the electrically heated catalyst, and a second electric current sensor detecting electric current value for the air pump. The electrically heated catalyst and air pump are supplied with current upon a cold start of an engine. Presence of failures in the electrically heated catalyst and air pump is discerned on the basis of the electric current value each of the first and second electric current sensors, and the detection of the current value of the first electric current sensor starts prior to the detection of the current value of the second electric current sensor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing the engine control system with an exhaust purification apparatus having a failure detecting system according to the invention; 
     FIG. 2 is a circuit diagram showing the failure detecting system according to a first embodiment of the invention; 
     FIG. 3 is a flowchart showing a current supply control program for the electrically heated catalyst and the air pump according to the first embodiment of the invention; 
     FIG. 4 is a diagrammatic chart showing variation characters of the electric current IEHC for the electrically heated catalyst and the electric current IAP for the air pump; 
     FIG. 5 is a circuit diagram showing the failure detecting system according to a second embodiment of the invention; and 
     FIG. 6 is a flowchart showing a current supply control program for the electrically heated catalyst according to the second embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     With reference to FIG. 1, reference numeral  1  designates an engine for a vehicle, and in an intake air path  2  of the engine  1 , in order from the upstream side, there is provided an air cleaner  3 , a throttle valve  4 , and fuel injection valve  5 . With input of signals from a sensor  6  for detection of the throttle opening degree θ, a sensor  7  for detection of the intake air negative pressure PB, a sensor  8  for detection of the intake air temperature TA, a sensor  9  for detection of the engine revolution speed NE, a sensor  10  for detection of the engine cooling water temperature TW and a sensor  11  for detection of the vehicle velocity V into a controller  12  comprising of an onboard computer, the controller  12  controls the fuel injection amount from the fuel injection valve  5  according to the signals from the sensors. 
     In an exhaust path  13  of the engine  1  there is provided a catalyst unit including an electrically heated catalyst (hereinafter referred to as an EHC)  14  that functions as a heater that generates heat by supplying current, a starting catalyst  15  that is mainly in charge of exhaust purification immediately after start of the engine and a three-way catalyst  16 . Further, an air pump  17  is connected to a part of an exhaust path  13  on the upstream side of the catalyst unit so as to supply air from the intake air path  2  between the air cleaner  3  and the throttle valve  4  to the exhaust path  13  as secondary air by the air pump  17 . 
     Supply of current of the EHC  14  and the air pump  17  is controlled with a circuit shown in FIG.  2 . That is, a changeover switch  20  which has a normally-closed contact  20   a  for connection of an onboard battery  19  is provided on the output side of an alternator  18  driven by the engine  1  while the EHC  14  is connected to a normally-open contact  20   b  of the changeover switch  20 . The air pump  17  is connected to the normally-closed contact  20   a  of the changeover switch  20  via an on-off switch  21 . The controller  12  controls switching of the changeover switch  20  and the on-off switch  21  and, the EHC  14  and the air pump  17  is supplied with current when the on-off switch  21  is turned on with the normally-open contact  20   b  of the changeover switch  20  being closed. The controller  12  controls a regulator  22  which varies the output voltage of the alternator  18  in such a manner that the output voltage from the alternator  18  is set to be relatively low (ex. 14.5 V) when the normally-closed contact  20   a  of the changeover switch  20  is closed while the output voltage from the alternator  18  is set to be relatively high (ex. 30V) when the normally-open contact  20   b  of the changeover switch  20  is closed. 
     A connection circuit  14   a  between the changeover switch  20  and the EHC  14  and a connection circuit  17   a  between the open-close switch  21  and the air pump  17  are respectively provided with electric current sensors  23   1  and  23   2 , and after detection of the current value IEHC supplied to the EHC  14  (hereinafter referred to as heater current) by the electric current sensor  23   1 , and detection of the current value IAP supplied to the air pump  17  (hereinafter referred to as pump current) by the electric current sensor  23   2 . With input of the detection signals from the electric current sensors  23   1  and  23   2  into the controller  12 , voltage signal lines  14   b  and  17   b  which are branched from the connection circuits  14   a  and  17   a  are connected to the controller  12 , so that the controller  12  can detect the applied voltage VEHC to the EHC  14  (hereinafter referred to as heater voltage) and the applied voltage VAP to the air pump  17  (hereinafter referred to as pump voltage). 
     FIG. 3 shows a current supply control program for the EHC  14  and the air pump  17 , executed by the controller  12 . First, at step S 1 , whether or not an explosion has completed in the engine  1  is discerned. If the explosion has not completed yet, step S 2  is performed to close the normally-closed contact  20   a  of the changeover switch  20  and also to turn off the on-off switch  21 , without supplying current to the EHC  14  and the air pump. After the complete explosion, at step S 3 , the timing action of a first timer tml is started and then, at step S 4 , whether or not the timing result of the first timer tml, that is, the lapsed time after complete explosion, is within a setup time Ytm 1  (ex. 60 seconds) is discerned. If tm 1 ≦Ytm 1 , at step S 5 , whether or not water temperature TW is a predetermined value YTW (ex. 50° C.) of a criterion for cooling state or less is discerned. If TW≦YTW, at step S 6 , whether or not the engine revolution speed NE is a predetermined value YNE (ex. 2,500 rpm) or less is discerned. If NE≦YNE, at step S 7 , whether or not the vehicle velocity V is a predetermined value YV (ex. 40 km/h) or less is discerned. If V≦YV, step S 8  is performed to close the normally-open contact  20   b  of the changeover switch  20  and also to turn on the on-off switch  21 , to thereby supply current to the EHC  14  and the air pump  17 . 
     On the other hand, in a case of tm 1 &gt;Ytm 1 , TW&gt;YTW, NE&gt;YNE or V&gt;YV, the step S 2  is performed to stop supplying current to the EHC  14  and the air pump  17 . Thus, the EHC  14  and the air pump  17  are supplied with current under the conditions NE≦YNE and V≦YV for a certain duration of time at the cold start. 
     While the EHC and the air pump are supplied with current, at step S 9 , a second timer tm 2  starts timing action and then, at step S 10 , whether or not the timing result of the second timer tm 2 , that is, the lapsed time after start of supplying of current to the EHC  14  and the air pump  17 , is within a first setup time Ytm 2 A is discerned. If tm 2 ≧Ytm 2 A, at step S 11 , a third timer tm 3  starts timing action and then, at step S 12 , whether or not the timing result of the third timer tm 3  is a predetermined setup time Ytm 3  (ex. 10 seconds) or less is discerned. If Tm 3 ≦Ytm 3 , at step S 13 , the heater current IEHC and the heater voltage VEHC are sampled. At step S 14 , whether or not the timing result of the second timer tm 2  has reached a predetermined second setup time Ytm 2 B is discerned. If tm 2 ≧Ytm 2 B is realized, at step S 15 , a fourth timer tm 4  starts timing action and then, at step S 16 , whether or not the timing result of the fourth timer tm 4  is a predetermined setup time Ytm 4  (ex. 10seconds) or less is discerned. If Tm 4 ≦Ytm 4 , at step S 17 , the pump current IAP and the pump voltage VAP are sampled. 
     If at step S 12 , tm 3 &gt;Ytm 3  is discerned, at step S 18 , WEHC=∫VEHC·IEHCdt, an integrated heater power that has been applied on the EHC  14  during the sampling time Ytm 3  is calculated. Then, at step S 19 , whether or not WEHC is within the predetermined allowable range is discerned; if not, the EHC  14  is discerned as failure and, at step S 20 , a failure processing, such as illumination of a failure indicator lamp for the EHC  14 , is performed. If Tm 4 &gt;Ytm 4  is discerned at step S 16 , WAP =∫VAP·IAPdt, an integrated pump power that has been applied to the air pump during the sampling time Ytm 4 , is calculated at step S 21  and, at step S 22 , whether or not WAP is within the predetermined allowable range is discerned; if not, the air pump  17  is discerned as failure, at step S 23 , a failure processing, such as illumination of a failure indicator lamp for the air pump  17 , is performed. 
     If the EHC  14  and the air pump  17  are supplied with current, as shown in FIG. 4, under the influence of inertia mass and startup character of the air pump  17 , the pump current IAP increases immediately after supply of current so as to form a peak, and stabilization of the pump current IAP takes a certain duration of time. Since the start of the sampling of the pump current IAP before the stabilization of the IAP possibly causes erroneous detection, the above-described second setup time Ytm 2 B is set up so as to match the duration of time required for stabilization of the IAP, for example, 2 seconds. On the other hand, since the heater current IEHC stabilizes promptly, the above-described setup time Ytm 2 A is set up so as to be shorter than the second setup time Ytm 2 B, for example, 0.5 seconds. In this way, even if supply of current to the EHC  14  and the air pump  17  may be stopped by early establishment of the NE&gt;YNE and V&gt;YV state which is caused by the start of driving immediately after beginning of the startup, the frequency of current supply stop before Ytm 3  sampling time is lapsed, that is, the frequency of disabled discernment of failure in the EHC  14  is reducible so far as possible since the heater current IEHC sampling starting time has been advanced. 
     Although, in the first embodiment, the existence of the failure is discerned on the basis of the integrated electric powers WEHC and WAP which are applied during the sampling time, the existence of the failure may be discerned on the basis of the integrated value or mean value of the electric currents IEHC and IAP which are supplied during the sampling time if stability of the voltages VEHC and VAP can be assured. 
     As elucidated with the explanation above, since current value detection starting time of the electrically heated catalyst has been advance, the frequency of disabled discernment of failures in the electrically heated catalyst is reduced so far as possible. 
     Second Embodiment 
     A description will be given of a second embodiment which prevents the durability degradation of the electrically heated catalyst caused by a heat shock. The control system of the second embodiment is used with the system shown in FIG. 1 as well as the first embodiment. Thus, the portions identical to the first embodiment are referred to by common symbols. 
     Supply of current to the EHC  14  and the air pump  17  is controlled with a circuit shown in FIG.  5 . That is, a changeover switch  20  which has a normally-closed contact  20   a  for connection of an onboard battery  19  is provided on the output side of an alternator  18  drivenby the engine  1  while the EHC  14  is connected to a normally-open contact  20   b  of the changeover switch  20 . The air pump  17  is connected to the normally-closed contact  20   a  of the changeover switch  20  via an on-off switch  21 . The controller  12  controls switching of the changeover switch  20  and the on-off switch  21  and, the EHC  14  and the air pump  17  is supplied with current when the on-off switch  21  is turned on with the normally-open contact  20   b  of the changeover switch  20  being closed. The controller  12  controls a regulator  22  which varies the output voltage of the alternator  18  in such a manner that the output voltage from the alternator  18  is set to be relatively low (ex. 14.5 V) when the normally-closed contact  20   a  of the changeover switch  20  is closed while the output voltage from the alternator  18  is set to be relatively high (ex. 30 V) when the normally-open contact  20   b  of the changeover switch  20  is closed. 
     A connection circuit  14   a  between a changeover switch  20  and an EHC  14  is provided with an electric current sensor  23  and, after detection of the current value IEHC of the EHC  14  by the electric current sensor  23  and with input of the detection signal from the electric current sensors  23  into the controller  12 , voltage signal line  14   b  which is branched from the connection circuit  14   a  is connected to the controller  12  so that the controller  12  can detect the applied voltage VEHC at the EHC  14 . 
     The current supply control of the EHC  14  and the air pump  17  is carried out according to a program shown in FIG. 3 with utilization of the following setup temperatures. The first setup temperature YTW 1  is set up on the upper limit temperature of the temperature range where the EHC  14  requires to be heated (ex. 50° C.), as a determined value regarding the engine temperature, that is, water temperature TW. The second setup temperature YTW 2  is set up on the temperature where degradation of durability caused by a heat shock on the EHC  14  is liable to occur (ex. 5° C.). The third setup temperature YTW 3  is set up on the temperature where supply of current to the EHC  14  is disabled for reason of durability (ex. −7° C.). 
     To describe this in details, first, at step S 101 , whether or not an explosion has completed in the engine  1  is discerned. If the explosion has not completed yet, step S 102  is performed to close the normally-closed contact  20   a  of the changeover switch  20  and also to turn off the on-off switch  21 , without supplying current to the EHC  14  and the air pump  17 . After the complete explosion, at step S 103 , whether or not the engine revolution speed NE is the predetermined value YNE (ex. 2,500 rpm) or less is discerned. If NE≦YNE, at step S 104 , whether or not the water temperature TW is the first setup temperature YTW 1  or lower is discerned. Then, if TW≦YTW 1 , at step S 105 , whether or not the water temperature TW is the second setup temperature YTW 2  or lower is discerned. If TW≦YTW 2 , at step S 106 , whether or not the water temperature TW is the third setup temperature YTW 3  or lower is discerned. 
     If YTW 2 &lt;TW≦YTW 1 , step S 107  is performed after the step S 105  so as to start the timing action of the timer and then, at step S 108 , whether or not the timing result of the timer tm is within a first setup time Ytml (ex. 60 seconds) is discerned. If tm≦Ytm 1 , at step S 109 , the output voltage of an alternator  18  is increased and, at step S 110 , the normally-open contact  20   b  of the changeover switch  20  is closed and also the on-off switch  21  is turned on, to thereby supply current to the EHC  14  and the air pump  17 . 
     If YTW 3 &lt;TW≦YTW 2 , step S 111  is performed after the step S 106  so as to start the timing action of the timer and then, at step S 112 , whether or not the timing result of the timer tm is within a second setup time Ytm 2  (ex. 5 seconds) which is setup to be shorter than the Ytml is discerned. If tm≦Ytm 2 , at step S 113 , the output voltage of the alternator  18  is decreased, and then, step S 110  is performed to thereby supply current to the EHC  14  and the air pump  17 . 
     If the discernment at step S 103  is NE&gt;YNE, or if the discernment at step S 104  is TW&gt;YTW 1 , or the discernment at step S 106  is TW≦YTW 3 , step S 102  is performed while, if the discernment at step S 108  is tm&gt;Ytm 1 , or if the discernment at step S 102  is tm&gt;Yte 2 , step S 2  is performed after a failure processing to be described below to stop supplying current to the EHC  14  and the air pump  17 . Therefore, the EHC  14  and the air pump  17  are supplied with current for the duration of Ytml if YTW 2 &lt;TW≦YTW 1  and for the duration of Ytm 2  if YTW 3 &lt; TW≦YTW 2  at the cold start of the engine  1 . 
     Since the current supplying time is shorter and the heater voltage VEHC is smaller at low temperatures where YTW 3 &lt;TW ≦YTW 2  than at normal temperatures where YTW 2 &lt;TW≦YTW 1 , the applied power amount to the EHC  14  is reduced and thus the durability degradation that results from the heat shock on the EHC  14 , which is liable to occur at low temperatures can be prevented. 
     While being supplied with current, at step S 114 , the heater current IEHC and the heater voltage VEHC are sampled and, if tm&gt;Ytm 1  was discerned at step S 108 , at step S 115 , WEHC =∫IEHC·VEHCdt, an integrated heater power that has been applied to the EHC  14  is calculated and then, at step S 16 , whether or not WEHC is within the predetermined allowable range is discerned. If it is within the allowable range, step S 102  is performed straight, but if not, the EHC  14  is discerned as failure and, after the failure processing at step S 117 , such as illumination of a failure indicator lamp for the EHC  14 , the step S 102  is performed. If tm&gt;Ytm 2  is discerned at step S 112 , REHC=IEHC/VEHC, a resistance value of the EHC  14 , is calculated at step S 118  and, at step S 119 , whether or not REHC is within the predetermined allowable range is discerned. If it is within the allowable range, step S 102  is performed, but if not, after the failure processing at step S 117 , the step S 2  is performed. The resistance value REHC can be calculated from a sampling data for a short period of time and thus the failure discernment can be carried out even if the current supplying time is shortened at the time of low temperatures. 
     Although, in the second embodiment, at the time of low temperature, the current supplying time is shortened and also the heater voltage VEHC is lowered, it can be conducted only with either current supplying time reduction or the decrease in the heater voltage VEHC. An alternative is to vary the current supplying time or the heater voltage VEHC in correspondence to the water temperature TW so that they decrease as the water temperature TW decreases. 
     As elucidated with the explanation above, since the power amount applied to the electrically heated catalyst at low temperatures is reduced, the invention can prevent the degradation of durability caused by the heat shock on the electrically heated catalyst. Moreover, shift of the data for failure discernment from the integrated power amount to the resistance value enables the failure discernment with current supply for a short period of time at low temperatures. In this connection, although the exhaust purifying efficiency of the catalyst unit decreases when the amount of power electrified on the electrically heated catalyst decreases, this causes no special problems since any serious air contamination such as photochemical smog will not occur at low temperatures. 
     The present disclosure relates to the subject matter contained in Japanese patent application Nos. Hei. 10-224466 filed on Aug. 7, 1998 and Hei. 10-224468 filed on Aug. 8, 1998 which are expressly incorporated herein by reference in its entirety. 
     While only certain embodiments of the invention have been specifically described herein, it will apparent that numerous modification may be made thereto without departing from the spirit and scope of the invention.