Patent Publication Number: US-7216031-B2

Title: Electronic control unit for vehicles

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is based on and incorporates herein by reference Japanese Patent Applications No. 2004-123359 filed on Apr. 19, 2004 and No. 2005-65781 filed on Mar. 9, 2005. 
   FIELD OF THE INVENTION 
   The present invention relates to an electronic control unit. More particularly, the present invention relates to an electronic control unit capable of executing a plurality of different controls including control of operation of a vehicle-mounted engine and control of diagnosis to be performed on a fuel vapor processing system after the engine stops. 
   BACKGROUND OF THE INVENTION 
   Vehicle-mounted systems include an engine system having a fuel vapor processing unit. In the engine system, fuel vapor generated in a fuel tank is tentatively collected in a canister without being released to the atmosphere. The collected vapor is purged into an intake passage, and it is combusted in an engine. However, when a fault such as cracking or creation of a hole occurs in, for example, a vapor line or a purge line in the engine system, it is likely that the air tightness of the interior of the processing unit may not be maintained and appropriate processing of fuel vapor is disabled. 
   Electronic control units are therefore requested to have a capability to diagnose presence or absence of the foregoing fault. However, the internal pressure of a fuel vapor processing system tends to vary during a period in which an engine is in operation or a vehicle is traveling. The foregoing fault cannot be fully diagnosed during that period. Therefore, U.S. Patent No. 2003/0135309 A1 (JP 2003-205798 A) proposes an engine system. In this engine system, after power supply to an electronic control unit is discontinued by the turning off of an ignition switch, the power supply to the electronic control unit is resumed using, a timer in order to perform diagnosis on a fuel vapor processing apparatus. 
   In the engine system, normal engine control is executed while an engine is in operation and control of diagnosis to be performed on a fuel vapor processing unit is executed after the engine is stopped. The controls are executed mutually independently. Nevertheless, the control structure designed to perform the foregoing diagnosis during execution of a vehicle is employed as it is. An increase in a load of arithmetic operations, which are required for the controls, imposed on the electronic control unit cannot be ignored. 
   Specifically, in order to effectively utilize a space in an electronic control unit, various programs stored in a single program memory, that is, a sole read only memory (ROM) are selectively executed based on the state of an engine or the state of a vehicle in which the engine is mounted. Thus, the engine control or the control of diagnosis on a fuel vapor processing system is executed. Moreover, programs to be executed in common for the controls are stored in a ROM and used in common. Therefore, the ROM itself is structured to hold, in addition to various programs for executing the two kinds of controls, that is, the normal engine control and the control of diagnosis on a fuel vapor processing system, a mode designation program for determining based on the state of the engine or vehicle whichever of the two controls should be executed for each of the programs. 
   For execution of the various programs stored in the ROM, the mode designation program is invoked at every time of execution of a program. Consequently, control is executed appropriately according to the state of an engine or a vehicle. However, in practice, the control structure causes a large memory area in the ROM and eventually causes an increase in the load of arithmetic operations on the electronic control unit. 
   SUMMARY OF THE INVENTION 
   The present invention has an object to provide an electronic control unit in which even when a plurality of different controls including normal engine control and control of diagnosis on a fuel vapor processing system is executed, a load of arithmetic operations can be reduced appropriately. 
   An electronic control unit for a vehicle-mounted system according to the present invention has a computer and a single program memory. The program memory stores a plurality of functionally finely classified programs, which includes programs to be used in common among the plurality of modes. The plurality of programs is associated, as a reference table, with the plurality of different control modes by separating programs required for the respective control modes. The computer sequentially executes only programs associated with the designated control mode, when any of the control modes is designated. 
   The plurality of modes may be an engine control mode performed when an engine is normal and an evaporation leak diagnosis mode performed when the engine is stopped. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings: 
       FIG. 1  illustratively shows in a block diagram a first embodiment of an electronic control unit in accordance with the present invention; 
       FIG. 2A  and  FIG. 2B  show examples of a data structure adapted to packet data to be transferred between the electronic control unit in accordance with the first embodiment and any other control unit; 
       FIG. 3A  and  FIG. 3B  illustratively show in a block diagram a diagnosis apparatus for performing diagnosis on a fuel vapor processing system which is controlled via the electronic control unit in accordance with the first embodiment; 
       FIG. 4  illustratively shows associations presented by a reference table which the electronic control unit in accordance with the first embodiment references when executing programs; 
       FIG. 5  shows a procedure of mode designation for designating either a control mode for executing normal engine control or a control mode for executing control of diagnosis on a fuel vapor processing system; 
       FIG. 6  shows mainly the contents of processing relevant to normal engine control which is performed by the electronic control unit in accordance with the first embodiment; 
       FIG. 7  shows mainly the contents of processing relevant to diagnosis on a fuel vapor processing system which is performed by the electronic control unit in accordance with the first embodiment; 
       FIG. 8  shows a sequence of processing relevant to diagnosis on a fuel vapor processing system which is performed by the electronic control unit in accordance with the first embodiment; 
       FIG. 9  shows a mode for performing the processing relevant to diagnosis; 
       FIG. 10  shows a mode for performing communication (report) of the electronic control unit in accordance with the first embodiment with any other control unit; 
       FIG. 11  shows a mode for performing communication of the electronic control unit in accordance with the first embodiment with any other control unit; 
       FIG. 12A  and  FIG. 12B  show examples of packet data to be transferred between the electronic control unit in accordance with the first embodiment and any other control unit; 
       FIG. 13  shows a sequence of mode designation which an electronic control unit in accordance with the second embodiment of the present invention performed so as to designate either of a control mode for executing normal engine control and a control mode for performing diagnosis on a fuel vapor processing system; 
       FIG. 14  shows a mode for performing no transmission so as to inhibit a variant of the electronic control unit in accordance with the first or second embodiment from communicating with any other control unit; and 
       FIG. 15  shows a mode for performing forced stop on a microprocessor or an IC incorporated in a variant of the electronic control unit in accordance with the first or second embodiment. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   First Embodiment 
   Referring to  FIG. 1 , an electronic control unit (EGI-ECU)  10  for electronically-controlled gasoline injection (EGI) is constructed with a main microcomputer (MC)  11 , a sub-microcomputer  12 , an input/output IC  13 , an electrically erasable programmable ROM (EEPROM)  14 , and a timer  15 . The main microcomputer (main controller)  11  and sub-microcomputer (sub-controller)  12  each include a central processing unit (CPU)  11   a ,  12   a , a read-only memory (ROM)  11   b ,  12   b , and a random access memory (RAM)  11   c ,  12   c . The ROM  11   b  and  12   b  are used mainly as program memories. A normal engine control program, a diagnosis program for performing diagnosis on a fuel vapor processing system, and a control program for controlling driving of the sub-microcomputer  12 , which are executed by the CPU  11   a , are stored in the ROM  11   b . A control program for controlling an electronically-controlled throttle valve (ETC) which is executed by the CPU  12   a  is stored in the ROM  12   b . Moreover, the RAMs  11   c  and  12   c  are data memories in which data being handled in order to perform arithmetic operations and the results of arithmetic operations are temporarily stored. 
   Moreover, a vehicle-mounted battery BT serving as a power source is electrically connected to the electronic control unit  10  with or without an electromagnetic relay RL, which is composed of a relay switch RS and a relay coil RC, between them. That is, backup power (VBB) that must be fed to the timer  15  is always supplied to the electronic control unit  10  without the electromagnetic relay RL between them. On the other hand, power (VB) that must be fed via the electromagnetic relay RL is supplied to the electronic control unit  10  when the relay switch RS is made after the relay coil RC becomes conducting in response to a conduction signal sent from an ignition switch (IGSW)  60  that is an engine start switch, the main microcomputer  11  or the timer  15 . 
   The electronic control unit  10  includes an OR circuit that detects the conduction signal, though the OR circuit is not shown. When the conduction signal sent from any of the ignition switch, main microcomputer and timer is detected, the relay coil RC becomes conducting or is kept conducting. The power VB is supplied to, for example, the main microcomputer  11 . Specifically, the power VB or VBB supplied to the electronic control unit  10 , that is, a supply voltage (normally, 14 V) developed at the vehicle-mounted battery BT is regulated into an operating voltage (for example, 5 V) by a power circuit (not shown) included in the electronic control unit  10 , and then supplied to the components of the electronic control unit  10 . 
   Moreover, external devices including an injector (INJ)  21 , an igniter (IGN)  22 , a warning lamp  23 , an O 2  sensor heater  24 , a radiator fan  25 , an electronically-controlled throttle valve (ETC)  26 , a boost pressure valve  27 , an immobilizer control unit (IMB-ECU)  28 , a switching valve  51 , a check valve  52 , and a vacuum pump  53  are connected to the electronic control unit  10  via a terminal TL. 
   Furthermore, various sensors including a temperature sensor  31 , a vehicle speed sensor  32 , an O 2  sensor (air-to-fuel ratio sensor)  33 , an accelerator sensor  34 , and a pressure sensor  54  are connected to the electronic control unit via the terminal TL. The temperature sensor  31  detects the temperature of coolant for cooling an engine. 
   Furthermore, the electronic control unit  10  is connected to an intra-vehicle LAN constructed with, for example, a controller area network (CAN) via the terminal TL. Over the intra-vehicle LAN, the electronic control unit  10  can cooperate with numerous other electronic control units including an automatic transmission (AT) control unit  41 , a traction (TRC) control unit  42 , an antilock brake system (ABS) control unit  43  by utilizing the multiplexing technique. Among the electronic control units including the electronic control unit  10 , data divided in units of a packet is transferred.  FIG. 2A  and  FIG. 2B  show examples of a data structure adapted to packet data to be transferred. 
   As shown in  FIG. 2A , the packet data includes eight data items DATA# 1  to DATA# 8  to which an ID (identification information) indicating a destination is appended as a header. In the examples, as shown in  FIG. 2B , among the eight data items, only three data items DATA# 1  to DATA# 3  are employed. The data DATA# 1  represents a data length, the data DATA# 2  represents a system ID equivalent to a processing item, and the data DATA# 3  represents a set value determined for the processing item. 
   Herein, the electronic control unit  10  shown in  FIG. 1 , that is, the electronic control unit  10  is an engine control unit (EGI-ECU) for controlling the operation of the vehicle-mounted engine. In the electronic control unit  10 , the main microcomputer  11  transfers data to or from the sub-microcomputer  12  so as to execute various vehicle controls including normal engine control. Moreover, the sub-microcomputer  12  executes, among controls of the operation of the vehicle-mounted engine, control of driving of an external device located around the engine, for example, the electronically-controlled throttle valve  26 . 
   Moreover, in the electronic control unit  10 , the input/output IC  13  transmits an output of the main microcomputer  11  or sub-microcomputer  12  via the terminal TL or receives an external signal via the terminal TL and transfers the signal to each of the microcomputers. A wave-shaping circuit, a multiplexer, an analog-to-digital converter are included in the input stage of the input/output IC  13 . Driver circuits for driving various actuators are included in the output stage of the input/output IC  13 . Moreover, the EEPROM  14  is realized with a nonvolatile memory for use in, for example, backing up data. 
   When power supply to the electronic control unit  10  is discontinued responsively to the turning off of the ignition switch  60  that is an engine start switch, various pieces of control information required for starting the engine next time are backed up in the EEPROM  14  immediately preceding the power supply stop, so that the control information may be used when the engine is started next time. After the power supply to the electronic control unit  10  is discontinued responsively to the driver&#39;s turning off of the ignition switch  60 , the timer  15  is used to automatically resume the power supply to the electronic control unit  10  in order to perform the aforesaid diagnosis on the fuel vapor processing system in a predetermined set time. 
   On the other hand, among the aforesaid external devices, the injector  21  serves as an intake port or a fuel injection valve through which fuel is injected into the cylinder of the engine. The igniter  22  is an ignition device for igniting an air-fuel mixture in the cylinder of the engine. The warning lamp  23  is used to notify a driver or the like of an abnormality occurring in the external devices. Moreover, the O 2  sensor heater  24  is a heater for heating the O 2  sensor  33  so as to facilitate activation of the O 2  sensor  33  in the initial stage of starting of the engine. The radiator fan  25  is driven in order to improve the heat radiation efficiency of a radiator when, for example, a vehicle is at a halt or execution at a low speed. 
   The boost pressure valve  27  is included in a supercharger for the engine in order to regulate a boost pressure. Moreover, the immobilizer control unit  28  prevents robbery of a vehicle. Namely, every time the engine is started, the immobilizer control unit  28  checks a vehicle-inherent code, which is read from a transponder (not shown) incorporated in the ignition switch  60 , to determine whether the vehicle-inherent code agrees with an own security code. When the codes disagree with each other, the immobilizer control unit  28  instructs the electronic control unit  10  to cease fuel injection or ignition and thus disables the operation of the engine. Consequently, the start of the engine is enabled with a higher security level attained. 
   On the other hand, the switching valve  51 , check valve  52 , vacuum pump  53 , and pressure sensor  54  are included in a pump module  50  serving as part of a diagnosis apparatus for performing diagnosis on a fuel vapor processing system shown in  FIG. 3A  and  FIG. 3B , and manipulated or referenced at the time of performing diagnosis on the fuel vapor processing system. 
   Next, the diagnosis apparatus for performing diagnosis on the fuel vapor processing system controlled by the electronic control unit  10  will be described.  FIG. 3A  and  FIG. 3B  show two states into which the diagnosis apparatus for the fuel vapor processing system is brought at the time of performing diagnosis, or more particularly, diagnosing leakage of fuel vapor. In  FIG. 3A  and  FIG. 3B , the same reference numerals are assigned to components identical to those shown in  FIG. 1 . 
   The diagnosis apparatus includes a fuel tank TK in which fuel is preserved, a canister CN in which fuel vapor generated in the fuel tank TK is collected, and the pump module  50 . Herein, an intake passage P 1  leading to the engine, the canister CN and the fuel tank TK are interlinked with pipes P 2  and P 3 . A purge valve PV is provided in the pipe P 2 . When the purge valve PV is opened, the canister CN communicates with the intake passage P 1 , which leads to the engine, downstream of the throttle valve SV at which a vacuum pressure is developed. The pipe P 3  links the fuel tank TK and canister CN. 
   The diagnosis apparatus includes the pump module  50  that is controlled by the electronic control unit  10 . The pump module  50  and canister CN are linked by a pipe P 4 . Fuel vapor generated in the fuel tank TK is processed or diagnosis is performed on the fuel vapor processing system. 
   The pump module  50  includes a switching valve  51 . The switching valve  51  selectively allows the pipes P 4  and P 5  or the pipes P 4  and P 6  to communicate with each other. Specifically, when the switching valve  51  is non-conducting, the pipes P 4  and P 5  communicate with each other by way of a switching passage PA as shown in  FIG. 3A . On the other hand, when the switching valve  51  becomes conducting, the pipes P 4  and P 6  communicate with each other by way of a switching passage PB as shown in  FIG. 3B . 
   The pipe P 6  includes the check valve (non-return valve)  52  for preventing flow of air into the canister CN, the vacuum pump  53  that sucks air from the canister CN, and the pressure sensor  54  that detects the pressure in the pipe P 6  while being located upstream of the vacuum pump  53 . The check valve  52  is opened with the air sucked by the vacuum pump  53 . The pipe P 6  is joined to the pipe P 4  by way of a pipe fitting Rh. On the other hand, one end of the pipe P 5  is opened onto the air via a filter FL. The air sucked by the vacuum pump  53  is also released to the air by way of the pipe P 5  via the filter FL. 
   Referring to  FIG. 4  to  FIG. 12B , modes in which various vehicle controls are executed by the electronic control unit  10  will be described. More particularly, modes for executing control of the operation of the vehicle-mounted engine and control of diagnosis to be automatically performed on the fuel vapor processing system after the engine is stopped will be described below. 
   In the vehicle-mounted engine system, the electronic control unit  10  selectively execute the plurality of programs stored in the ROM  11   b  ( FIG. 1 ) according to which one of the control mode for executing control of the operation of the vehicle-mounted engine and the control mode for executing control of diagnosis of the fuel vapor processing system is designated. Thus, the electronic control unit  10  performs processing associated with the designated control mode. Specifically, the plurality of programs is functionally finely classified and associated in advance with the two control modes by selecting programs required for the respective control modes. The programs are compositely stored in the ROM  11   b . When either of the control modes is designated, the programs associated with the designated control mode are sequentially called to be executed. 
   Moreover, the control modes are associated with the plurality of programs by referencing a reference table (call information table) in which information on links of the control modes with programs required for the respective control modes is written as illustratively shown in  FIG. 4 . The table is also stored in, for example, the ROM  11   b . Herein, the control mode (first control mode) for executing control of the operation of the vehicle-mounted engine shall be discriminated from the control mode (second control mode) for executing control of diagnosis on the fuel vapor processing system by calling the first control mode a normal mode and the second control mode a leakage diagnosis mode. 
   As shown in  FIG. 4 , information on links with the programs stored in the ROM  11   b , for example, input control programs PA 1  to PA 5 , diagnosis programs PB 1  to PB 4 , communication control programs PC 1  to PC 3 , external device control programs PD 1  to PD 6 , and internal IC control programs PE 1  to PE 3  are written in the reference table. 
   Specifically, for example, the input control programs PA 1  to PA 5 , diagnosis programs PB 2  to PB 4 , communication control programs PC 1  to PC 3 , external device control programs PD 3  to PD 6 , and internal IC control programs PE 1  to PE 3  are distinguished and associated with the normal mode. Programs not needed in the control mode, for example, a program relevant to diagnosis (leakage diagnosis) on the fuel vapor processing system, that is, the diagnosis program PB 1 , and the external device control programs PD 1  and PD 2  are not executed. 
   On the other hand, the input control programs PA 1  to PA 3  and PA 5 , the diagnosis programs PB 1 , PB 3  and PB 4 , the communication control programs PC 1  and PC 3 , the external device control programs PD 1 , PD 2  and PD 6 , and the internal IC control program PE 2  are distinguished and associated with the leakage diagnosis mode. Consequently, programs not needed in the leakage diagnosis mode are not executed. Namely, the programs presented below are not executed in the leakage diagnosis mode:
     the input control program PA 4  for controlling an air-to-fuel ratio;   the diagnosis program PB 2  for performing diagnosis on a control system (system diagnosis);   the communication control program PC 2  for performing processing relevant to control of an immobilizer (IMB) that prevents robbery of the vehicle (especially, communication with the immobilizer control unit  28 );   the external device control program PD 4  for controlling fuel injection (especially, driving of the injector (INJ)  21 ) and controlling ignition (especially, driving of the igniter (IGN)  22 );   the internal IC control program PE 1  for performing processing relevant to control of an intake air quantity; and   the external device control program PD 3  for controlling driving of the O 2  sensor heater  24 .   

   Since the reference table is employed, the control modes can be readily associated with the plurality of programs. 
   Next, referring to  FIG. 5  to  FIG. 7 , execution of the controls will be described below.  FIG. 5  is a flowchart according to which the electronic control unit  10  designates either of the control modes and executes control in the designated control mode. The processing is performed in cooperation with the programs stored in, for example, the ROM  11   b.    
   In the series of steps, first, the electronic control unit  10  starts its processing at step S 1 . At step S 2 , it is determined how the electronic control unit  10  is started. Specifically, it is determined whether the electronic control unit  10  is started responsively to the turning on of the ignition switch (start switch)  60  or in response to a start command sent from the timer  15  after turning off of the ignition switch  60  (engine stop). When the electronic control unit  10  is determined to be started responsively to the turning on of the ignition switch  60 , normal control of the operation of the vehicle-mounted engine is considered to be executed. The control is executed in the normal control mode at step S 3 . In this case, at step S 4 , the ignition switch  60  is checked if it is turned on. When the ignition switch  60  is determined to be turned off, the electronic control unit  10  is stopped at step S 5 . 
   On the other hand, when the electronic control unit  10  is determined at step S 2  to be started for any reason other than that the ignition switch  60  is turned on, whether the electronic control unit  10  is started in response to the start command sent from the timer  15  is determined at step S 6 . When the electronic control unit  10  is determined to be started in response to the start command sent from the timer  15 , control of diagnosis on the fuel vapor processing system is considered to be executed. The control is then executed in the leakage diagnosis mode at step S 7 . Even in this case, at step S 8 , the ignition switch  60  is checked if it is turned on. When the ignition switch  60  is determined to be turned on, the processing returns to step S 2 . It is determined again why the electronic control unit  10  is started. When completion of diagnosis is determined at step S 9 , the electronic control unit  10  is automatically stopped. 
   On the other hand, when the electronic control unit  10  is determined at step S 6  not to be started in response to the start command sent from the timer  15 , the electronic control unit  10  is immediately stopped as a fail-safe operation. 
   In the electronic control unit  10 , when the ignition switch  60  is turned on in the leakage diagnosis mode, the leakage diagnosis mode is changed to the normal mode. In the normal mode, as long as the electronic control unit  10  is restarted, the normal mode is not changed to the leakage diagnosis mode. 
   A history of manipulations performed on the ignition switch  60  is checked as described above to determine why the electronic control unit  10  is started. Thus, either of the control modes is designated, that is, which of the normal mode and leakage diagnosis mode should be executed is determined. Namely, since the normal mode and leakage diagnosis mode should be executed during different periods that do not overlap, the programs associated with a designated control mode are smoothly sequentially executed. In this case, designation of either of the control modes, that is, the mode designation need be performed only once at the time of starting the electronic control unit  10 . Even from this viewpoint, a load of arithmetic operations imposed on the electronic control unit is largely reduced. 
   Moreover, whichever of the control mode (normal mode) for executing control of the operation of the vehicle-mounted engine or the control mode (leakage diagnosis mode) for performing diagnosis on the fuel vapor processing system is designated, the number of programs associated with the designated control mode is enormous. However, those programs can basically be utilized as they are. 
   Next, referring to both  FIG. 6  and  FIG. 7 , the normal engine control and the control of diagnosis on the fuel vapor processing system (leakage diagnosis) will be described below. 
     FIG. 6  is a flowchart showing the processing of step S 3  in  FIG. 5 , that is, processing relevant to the normal control of the operation of the vehicle-mounted engine. As shown in  FIG. 6 , during the processing relevant to the control of the operation of the vehicle-mounted engine, initialization is first performed at step S 310 . Thereafter, main processing (S 320 ) in the normal mode is executed. Specifically, the CPU  11   a  selectively executes various programs stored in the ROM  11   b  according to the reference table shown in  FIG. 4 , and thus actually executes the engine control and vehicle control. 
   For example, when the diagnosis programs PB 2  to PB 4  ( FIG. 4 ) are executed, various kinds of diagnosis (system diagnosis, abnormal characteristic detection, break detection, etc.) are performed at step S 321 . Moreover, when the external device control programs PD 3  and PD 4  ( FIG. 4 ) are executed, fuel injection control, ignition control, and air quantity control are executed at steps S 322  to S 324 . When various communication controls (communication with the immobilizer, communication over the CAN, or any other serial communication) are executed at step S 325 , the communication control programs PC 1  to PC 3  ( FIG. 4 ) are executed. On the other hand, input processing of step S 326  is performed by execution of the input control programs PA 1  to PA 5  ( FIG. 4 ). Moreover, at step S 327 , the external device control programs PD 5  and PD 6  ( FIG. 4 ) are executed in order to execute control of various external devices. 
   At step S 328 , the internal IC control programs PE 1  to PE 3  ( FIG. 4 ) are executed in order to execute various controls required between ICs (integrated circuits) incorporated in the electronic control unit  10 , for example, the sub-microcomputer  12  and the input/output IC  13  or EEPROM  14 . 
   After these controls are executed, appropriate termination is executed at step S 330 . Thus, the series of steps is terminated. 
     FIG. 7  is a flowchart showing the processing of step S 7  shown in  FIG. 5 , that is, processing relevant to diagnosis (leakage diagnosis) on the fuel vapor processing system. As shown in  FIG. 7 , even during the processing relevant to diagnosis on the fuel vapor processing system, appropriate initialization is first performed at step S 710 . Thereafter, at step S 720 , the CPU  11   a  selectively executes the programs stored in the ROM  11   b  according to the reference table shown in  FIG. 4 , and thus executes control of the actual diagnosis. 
   For example, when the diagnosis programs PB 3  and PB 4  ( FIG. 4 ) are executed, various kinds of diagnosis (abnormal characteristic detection, break detection, etc.) are performed at step S 721 . At step S 722 , the diagnosis program PB 2  and external device control programs PD 1  and PD 2  ( FIG. 4 ) are executed in order to perform the fuel vapor leakage diagnosis. At step S 723 , the communication control programs PC 1  to PC 3  ( FIG. 4 ) are executed in order to execute various communication controls (CAN control and other serial communication control). When the input processing is executed at step S 724 , the input control programs PA 1  to PA 3  and PA 5  ( FIG. 4 ) are executed. At step S 725 , the external device control programs PD 5  and PD 6  ( FIG. 4 ) are executed in order to execute control of various external devices. At step S 726 , the internal IC control program PE 2  ( FIG. 4 ) is executed in order to execute controls required for the input/output IC  13  incorporated in the electronic control unit  10 . 
   The leakage diagnosis mode is automatically executed after the operation of the engine is stopped. Although the engine is stopped, when the fuel injection control, ignition control or air quantity control is executed, a signal that does not match the current situation may be transmitted or received to cause erroneous diagnosis and other drawbacks. For example, when the sub-microcomputer  12  dedicated to the control of opening of the electronically-controlled throttle valve  26  does not execute the control with the engine stopped, a load condition may vary at the time of starting the engine. 
   In the electronic control unit  10 , the control program for controlling driving of the sub-microcomputer  12  as well as the control programs for executing the fuel injection control, ignition control and air quantity control are not executed in the leakage diagnosis mode. Likewise, driving of the sub-microcomputer  12  and driving of the external devices relevant to the controls, for example, the injector  21  and igniter  22 , or the O 2  sensor heater  24  and radiator fan  25  will not be carried out. Consequently, the erroneous diagnosis and other various drawbacks can be prevented. 
   In order to initiate the leakage diagnosis, the boost pressure valve  27  is forcibly closed and other preparations are made. After the control of diagnosis (leakage diagnosis) on the fuel vapor processing system is executed, when abnormality is detected at step S 730 , this result is written in the EEPROM  14  and other appropriate termination is executed. Thereafter, power supply to the electronic control unit  10  is automatically ceased. 
     FIG. 8  shows a sequence of processing relevant to the diagnosis on the fuel vapor processing system, and  FIG. 9  shows a mode for performing the processing. The electronic control unit  10  controls the pump module  50  that serves as part of the diagnosis apparatus for performing the diagnosis on the fuel vapor processing system shown in  FIGS. 3A and 3B  and that includes the switching valve  51  and vacuum pump  53 . 
   Here, preconditions for the diagnosis processing are listed below:
     (a) the electronic control unit  10  is started based on the timer  15 ;   (b) a history of executions is preserved;   (c) a battery voltage falls within a guaranteed range;   (d) an engine speed (NE) falls below a predetermined value; and   (e) a pressure in the tank TK falls within a predetermined range (for example, from 70 kPa to 110 kPa).
 
When any of the preconditions is not met, the processing is suspended.
   

   In the processing relevant to the diagnosis to be performed on the fuel vapor processing system, first, during a period (A) in  FIG. 8 , the atmospheric pressure is measured as a base pressure at step S 10 . The pressure is shown with a characteristic line LA within the period (A) in  FIG. 9 . As for the state of the diagnosis apparatus at this time, the diagnosis apparatus is brought to the state shown in  FIG. 3A . Specifically, during the period A shown in  FIG. 9 , the purge valve PV is closed, the vacuum pump  53  is turned off (stopped), and the switching valve  51  is non-conducting. 
   During a period (B) in  FIG. 8 , at step S 11 , an amount of fuel vapor generated in the fuel tank TK is measured. Specifically, the switching valve  51  becomes conducting so that the diagnosis apparatus is brought to the state shown in  FIG. 3B . In this state, that is, in the state in which the pipe P 4  lying on the side of the fuel tank TK and the pipe P 6  communicate with each other, the pressure in the pipe P 6 , that is, the amount of generated fuel vapor is measured using the pressure sensor  54 . This pressure is shown with a characteristic line LB in  FIG. 9 . At step S 12 , when the value measured at step S 11  is determined to be too large (abnormal), the leakage diagnosis is suspended. 
   On the other hand, when the measured value is determined to be normal at step S 11 , a reference pressure is measured at step S 13  during a period (C) in  FIG. 8 . Specifically, the diagnosis apparatus is restored to the state shown in  FIG. 3A , and the vacuum pump  53  is driven in this state. When a pressure detected sequentially using the pressure sensor  54  saturates, the pressure value is regarded as the reference pressure. This pressure is shown with a characteristic line LC in  FIG. 9 . At step S 14 , the measured value is checked to determine whether it is normal relative to the atmospheric pressure. When the pressure is detected as indicated with any of characteristic lines LC 1  to LC 4  within the period (C) in  FIG. 9 , a basic hole bored in the switching valve  51 , check valve  52 , vacuum pump  53  or pipe fitting Rh is estimated to be abnormal. 
   When the measured value is determined to be normal, a pressure is measured for leakage diagnosis at step S 15  performed during a period (D) in  FIG. 8 . Specifically, the diagnosis apparatus is brought to the state shown in  FIG. 3B , again. In this state, the pressure is detected using the pressure sensor  54 . At step S 16 , the measured value is checked to determine whether it is normal. When the measured pressure is determined at step S 15  to fall below the reference pressure measured previously at step S 13 , the measured value is determined at step S 171  to be normal (no leakage). This is shown with a characteristic line LD within the period (D) in  FIG. 9 . 
   On the other hand, when the measured value is determined to be abnormal, whether the abnormal value results from leakage is determined at step S 17 . For example, when a pressure that does not reach the reference pressure as indicated with the characteristic line LD 1  or LD 2  in  FIG. 9  (a variation of a pressure) is detected, occurrence of leakage is determined at step S 172 . On the other hand, when a rise of a pressure is, as indicated with a characteristic line LD 3  in  FIG. 9 , not detected during driving of the switching valve  51 , presence of an abnormality in the switching valve  51  (for example, the switching valve is held in the OFF state) is inferred. In this case, an abnormality other than leakage is determined at step S 173 . 
   When the leakage diagnosis is completed, remaining pressure is purged at step S 18  during a period (E) in  FIG. 8 . Specifically, after the vacuum pump  53  is stopped, a pressure is checked using the pressure sensor  54  to determine whether it is held unchanged. The purge valve PV is then opened. At this time, when the pressure is equal to the base pressure measured at step S 10 , the purge valve PV is determined to be normal. This pressure is shown with a characteristic line LE within a period (E) in  FIG. 9 . 
   On the other hand, after the vacuum pump  53  is stopped, when the pressure is, as indicated with a characteristic line LE 1  in  FIG. 9 , not held unchanged, the abnormality of the check valve  52  (for example, the check valve  52  is kept open) is estimated. For example, when the purge valve PV is opened, and pressure is not released, the abnormality of the purge valve PV (for example, the purge valve PV is held closed) is estimated. 
   After the atmospheric pressure is checked at step S 18 , finalization is executed at step S 19  performed during a period (F) in  FIG. 8 . Specifically, when an abnormality code is produced, the abnormality code is stored in the EEPROM  14 . That is, when occurrence of an abnormality is determined at step S 12  or step S 14  or when an abnormality is detected at step S 172  or step S 173 , an associated specific abnormality code is stored in the EEPROM  14 . 
   Even in the leakage diagnosis mode, in addition to erroneous diagnosis or a drawback attributable to the engine control program, erroneous diagnosis or a drawback may occur due to communication with any other control unit, which is connected to the electronic control unit  10  over a communication line so that it can communicate with the electronic control unit  10 . 
   In the electronic control unit  10 , the programs associated with the leakage diagnosis mode include a communication control program helping the electronic control unit  10  communicate information to other control units, which are connected to the electronic control unit  10  so that they can communicate with the electronic control unit  10 , for example, the automatic transmission control unit  41 , traction control unit  42 , and antilock braking system control unit  43 . At the start of leakage diagnosis, the communication control program is used to notify the control units of the fact that leakage diagnosis is in progress. Specifically, when control of diagnosis to be performed on the fuel vapor processing system is determined to be executed at step S 6  shown in  FIG. 5 , the control units are notified of the fact.  FIG. 10  and  FIG. 11  are timing charts showing modes for performing reporting according to two methods that can be adopted as a notification method. 
   As for the report, there are, for example, a method of periodically performing a report as shown in  FIG. 10  (timings T 11  to T 13 ), and a method of performing a report only once prior to start of leakage diagnosis (timing T 21 ). At this time, data communication is, as mentioned previously, achieved in units of a packet ( FIG. 2 ).  FIG. 12A  and  FIG. 12B  show examples of a data structure adapted to data to be transmitted to each of the control units. 
   For example, when the normal mode is changed to the leakage diagnosis mode in order to terminate diagnosis of the electronic control unit  10 , data shown in  FIG. 12A  is transmitted. In this example, 700 (signifying a destination (control unit)) is specified as an ID in a header.  02  (signifying a data length) is specified as data DATA# 1 ,  01  (signifying a processing item) is specified as data DATA# 2 , and  01  (set value for the processing item) is specified as data DATA# 3 . On the other hand, when the leakage diagnosis mode is changed to the normal mode in order to diagnose the electronic control unit  10 , data shown in  FIG. 12B  is transmitted. In this example,  700  (signifying a destination (control unit)) is specified as an ID in the header.  02  (signifying a data length) is specified as data DATA# 1 ,  01  (signifying a processing item) is specified as data DATA# 2 , and  01  (set value for the processing item) is specified as data DATA# 3 . 
   Through the foregoing communication, a value preventing an external device from operating abnormally or a value signifying that the electronic control unit  10  is stopped is transmitted. Consequently, erroneous detection or malfunction caused by an external device connected to the control unit can be avoided. 
   As described above, the electronic control unit  10  provides the following advantages. 
   (1) Among a plurality of programs stored compositely in the ROM  11   b , that is, a plurality of functionally finely classified programs including programs used in common in both the normal mode and leakage diagnosis mode, programs required separately for the respective control modes are distinguished and associated with the control modes in advance. When either of the control modes is designated, the programs associated with the designated control mode are sequentially executed. Consequently, a mode designation program that is used conventionally need not be applied to the plurality of functionally finely classified programs. Accordingly, the program memory (ROM  11   b ) can save its storage capacity. 
   Moreover, once either of the control modes is designated, pieces of processing required for the designated control mode are sequentially executed. A load of arithmetic operations imposed on the electronic control unit  10  is largely reduced. Moreover, the plurality of functionally finely classified programs can be basically utilized as they are. This leads to reduction in a cost of development. Furthermore, since the load of arithmetic operations is reduced, power consumption is minimized. Consequently, energy saving is accomplished. 
   (2) Associating the plurality of different control modes, that is, the normal mode and leakage diagnosis mode with the plurality of programs can be easily achieved by referencing the reference table in which information on links of the control modes with programs required for the respective control modes is written ( FIG. 4 ). 
   (3) Either of the control modes is designated by checking a history of manipulations performed on the ignition switch (start switch)  60  so as to determine why the electronic control unit  10  is started, for example, by checking whether the electronic control unit  10  is started responsively to the turning on of the ignition switch  60  or whether the electronic control unit  10  is automatically started based on the timer. Consequently, the sequential execution of programs associated with the designated control mode is achieved very smoothly. Moreover, the mode designation need be performed only once at the time of starting the electronic control unit  10 . Thus, the load of arithmetic operations on the electronic control unit  10  is greatly reduced. 
   (4) Among the plurality of functionally finely classified programs, the control program for controlling driving of the sub-microcomputer (sub-controller)  12  that executes part of control of the operation of the vehicle-mounted engine, or more particularly, executes control of the electronically-controlled throttle valve is associated with the normal mode alone. Consequently, in the leakage diagnosis mode that is executed effect when the engine is stopped, control will not be executed by the sub-microcomputer  12 . For example, it can be avoided that a condition of a load to be imposed at the time of starting the engine varies. 
   (5) The communication control program for communicating information to any other control unit over the communication line is associated with the leakage diagnosis mode. While processing associated with the leakage diagnosis mode is being performed, the communication control program is used to notify the other control unit of the fact that the processing associated with the leakage diagnosis mode is in progress. Consequently, when diagnosis is performed on the fuel vapor processing system with the engine stopped, erroneous detection or malfunction caused by other control unit (automatic transmission control unit  41 ) connected to the electronic control unit over the communication line can be avoided. 
   (6) Programs that are employed when the operation of the vehicle-mounted engine is controlled and that should preferably not be executed during diagnosis on the fuel vapor processing system (input control program PA 4 , diagnosis program PB 2 , communication control program PC 2 , external device control program PD 4 , internal IC control program PE 1 , and external device control program PD 3 ) are associated with the normal mode alone. Moreover, programs for performing the diagnosis on the fuel vapor processing system (diagnosis program PB 1  and external device control programs PD 1  and PD 2 ) are associated with the leakage diagnosis mode alone. 
   Consequently, a load of arithmetic operations on the electronic control unit  10  is reduced, and required control is appropriately executed according to the state of a vehicle. Specifically, for example, as far as diagnosis to be performed on a control system is concerned, since driving of unnecessary external devices is ceased, erroneous diagnosis is prevented. As for diagnosis to be performed on the fuel vapor processing system, since communication with the immobilizer control unit  28  that is required only at the time of starting the engine is ceased, occurrence of a drawback attributable to unestablished communication can be avoided. 
   Second Embodiment 
   An electronic control unit  10  according to the second embodiment is constructed similarly to the first embodiment shown in  FIG. 1 . However it is different in a sequence of processing performed when a control mode (either of the normal mode and leakage diagnosis mode) is designated. This processing is shown in  FIG. 13  and executed in cooperation with programs stored in, for example, the ROM  11   b  ( FIG. 1 ). 
   As shown in  FIG. 13 , in the series of steps, first, at step S 20 , an operation mode is designated. Specifically, whether the current mode is a normal mode or leakage diagnosis mode, or whether the current mode is an abnormal mode other than the normal and leakage diagnosis modes is determined based on data latched at the input/output (I/O) port of the main microcomputer  11  or data held in a register included in the main microcomputer  11 . Even in this case, the normal mode is a control mode for executing control of the operation of the vehicle-mounted engine, and the leakage diagnosis mode is a control mode for automatically performing diagnosis on the fuel vapor processing system after the operation of the engine is ceased. 
   After the current mode is determined as the normal mode or leakage diagnosis mode, the operation mode (normal mode or leakage diagnosis mode) is stored in an appropriate storage device (for example, the RAM  11   c ) at step S 21  or step S 22 . Moreover, initialization is performed appropriately according to the current mode. On the other hand, when the current mode is determined as the abnormal mode at step S 20 , the series of steps is terminated. 
   When the current mode is determined as either of the normal mode and leakage diagnosis mode at step S 21  or step S 22 , synchronization with one of a clock signal or a crankshaft angle (engine rotation angle) signal is performed in various manners. Specifically, the synchronization includes time synchronization in which synchronization is attained at intervals of, for example, 1 ms, 4 ms, 8 ms, 16 ms, 32 ms, 64 ms, 128 ms, or 256 ms, and angle synchronization in which synchronization is attained at intervals of, for example, 30° CA (crankshaft angle), 180° CA, or 360° CA. 
   Whichever of the cycles is adopted for the synchronizations, an operation mode is first designated. The designation of the operation mode is different from the one of step S 20 . The operation mode (or data representing the operation mode) stored in the storage device at step S 21  or step S 22  is checked in order to designate the operation mode. Namely, in practice, the designation of the operation mode (control mode) is not performed but the data stored in the storage device (result of designation) is merely checked. Therefore, the processing is terminated normally within one or two machine cycles. 
   At a succeeding step, programs (for example, various control programs listed in  FIG. 4 ) associated in advance with the operation mode (normal mode or leakage diagnosis mode) are executed. Basically, similarly to the reference table shown in  FIG. 4 , programs required for the respective control modes (normal mode and leakage diagnosis mode) are distinguished and associated in advance with the respective control modes. However, the reference table is not employed, but different programs are associated with each of the cycles to be exhibited by the clock signal or crankshaft angle signal, and optimal control is executed in relation to each of the cycles of the signal (processing timing). 
   As mentioned above, normal engine control or control of diagnosis (leakage diagnosis) on the fuel vapor processing system is executed as shown in  FIG. 6  or  FIG. 7  through the synchronization. Thereafter, at step S 24 , the storage device is accessed in order to check the operation mode. Termination associated with the operation mode (normal mode or leakage diagnosis mode) is executed, whereby the series of steps is terminated. 
   In the second embodiment, similarly to the first embodiment, reporting operation shown in  FIG. 10  or  FIG. 11  is performed. 
   According to the second embodiment, in addition to the same advantages as the advantages (1) and (4)–(6) of the first embodiment or equivalents, the following additional advantages are provided. 
   (7) Designation of one of the plurality of different control modes, that is, the normal mode and leakage diagnosis mode is achieved at intervals of a predetermined time synchronously with one of the clock signal and crankshaft angle signal. Therefore, the same advantage as the advantage (2) or an equivalent is provided. Moreover, normally, many of various controls of a vehicle are executed synchronously with one of the clock signal and crankshaft angle (engine rotation angle) signal. Accordingly, required controls can be executed appropriately. 
   (8) Moreover, programs to be executed with either of the control modes designated are varied depending on any of cycles to be exhibited by the clock signal or crankshaft angle signal that is used to determine the timing of designating either of the control modes. Consequently, optimal controls can be executed relative to each cycle of the signal (processing timing). 
   (9) When designation of either of the control modes is repeated a plurality of times, the result of the first designation is stored in an appropriate storage device (step S 21  and step S 22  in  FIG. 13 ). The result of the first designation stored in the storage device is used to achieve the succeeding designations (step S 23  and step S 24  in  FIG. 13 ). Consequently, a load of arithmetic operations imposed on the electronic control unit is reduced. This feature will be effective when it is applied to a configuration in which the number of times by which any of control modes is designated is large, such as, the electronic control unit of the this embodiment (step S 23  and step S 24  in  FIG. 13 ). 
   OTHER EMBODIMENTS 
   The above embodiments may be modified as described below. 
   In the first embodiment, the reference table ( FIG. 4 ) is stored in a program memory (ROM  11   b ) in which programs employed in the normal mode or leakage diagnosis mode are stored. Alternatively, the reference table (call information table) may be stored in, for example, the EEPROM  14 . 
   The reference table is not limited to the one shown in  FIG. 4 . Any table will be used as long as information (program call information) on links of the control modes with programs required for the respective control modes is written in the table. 
   In the second embodiment, both synchronization with the clock signal (time synchronization) and synchronization with the crankshaft angle signal (angle synchronization) are adopted. Alternatively, either of the synchronizations may be adopted. 
   Instead of the communications illustrated in  FIG. 10  and  FIG. 11 , a communication control program for allowing the electronic control unit to communicate information to the other control units, which is included in the programs associated with the leakage diagnosis mode, may be used to inhibit communication with the other control units during processing associated with the leakage diagnosis mode. 
     FIG. 14  is a timing chart indicating a mode for performing no transmission (communication inhibition). Namely, in this example, the no transmission is executed at a timing T 31  immediately before leakage diagnosis is initiated. At a timing T 32  at which power supply to the electronic control unit  10  is resumed after the leakage diagnosis is terminated, communication with the other control units is resumed. When this communication is adopted, erroneous detection or malfunction caused by any other control unit (automatic transmission control unit  41  or the like) connected to the electronic control unit  10  over the communication line can be avoided in a preferable manner. 
   At the time of initiating leakage diagnosis, driving of a microprocessor or an IC that is not related to the leakage diagnosis out of microprocessors including the CPU  12   a  ( FIG. 1 ) and ICs (integrated circuits) including the input/output IC  13  ( FIG. 1 ) and the EEPROM  14  ( FIG. 1 ), which are incorporated in the electronic control unit  10 , may be forcibly stopped. Namely, as illustrated in the timing chart of  FIG. 15 , for example, a signal with which the internal microprocessor or internal IC that has no relation with the leakage diagnosis is inactivated is transmitted at a timing T 41  immediately before leakage diagnosis is initiated. Thus, driving of the internal microprocessor or internal IC may be forcibly stopped. Thereafter, the microprocessor or IC is restored to an operational state (activated) at a timing T 42  at which power supply to the electronic control unit  10  is resumed after completion of the leakage diagnosis. Consequently, occurrence of a drawback during the diagnosis performed on the fuel vapor processing system with the engine stopped, for example, unnecessary driving of the electronically controlled throttle valve  26  ( FIG. 1 ) can be appropriately avoided. 
   In the above embodiments, the timer  15  is used to start resuming power supply to the electronic control unit  10  for the purpose of performing the diagnosis on the fuel vapor processing system. However, for example, a decrease in the temperature of the engine (temperature of cooling water) occurring after a vehicle (engine) is stopped may be monitored in order to automatically start the electronic control unit  10 . Aside from a timer, other devices and means may be used for automatically starting the electronic control unit  10 . 
   In the above embodiments, the control mode (normal mode) for executing control of the operation of the vehicle-mounted engine and the control mode (leakage diagnosis mode) for automatically performing diagnosis on the fuel vapor processing system after the engine is stopped are referred to as a plurality of different control modes for the vehicle-mounted engine system. Alternatively, the present invention can be applied to a combination with any other control mode (diagnosis mode) that would prove effective when it is executed with a vehicle (engine) stopped.