Patent Publication Number: US-2007118272-A1

Title: Engine control apparatus

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an apparatus for controlling an engine, capable of detecting an abnormality in a power supply voltage supplied thereto.  
      2. Description of the Related Art  
      An apparatus for controlling an engine is supplied with power from a battery. The battery is charged by a generator mounted on a vehicle. The generator generates power when a field coil is excited with a field current and a power generation current is caused to flow through an armature coil rotating through rotation of the engine. Power generation control of the generator is performed by feedback control. That is, a control transistor is operated to be turned on and off to excite the field coil so that the voltage of the battery charged by the generator is held at a target voltage, and a target amount of power for making a voltage difference into zero is generated. The battery is charged through the power generation current, and the voltage of the battery is held at the target voltage.  
      When the output voltage of the generator has risen above an abnormally high voltage value, the field current is shut off to forcedly stop the power generation. Thus, the generator is protected from being destroyed through overcharge.  
      In order to detect an abnormality in a power supply voltage of the engine control apparatus, there is proposed a method using an ammeter (e.g., see JP 2001-69681 A).  
      However, the aforementioned protection against overcharge has the following problem. For instance, the engine control apparatus may operate by being supplied with power via a detour from a certain load terminal connected thereto when a power supply terminal of the engine control apparatus is disconnected. In this state, the power supply voltage supplied via the detour becomes lower than a normal power supply voltage due to a voltage drop. Accordingly, power generation control is performed based on this lowered power supply voltage, so the output voltage of the generator rises. While power generation can be forcedly stopped when the power supply voltage supplied via the detour is higher than an abnormally high voltage value, feedback control of the generator is performed when the output voltage of the generator is higher than the abnormally high voltage value but the power supply voltage supplied via the detour is equal to or lower than the abnormally high voltage value. Since power generation is then continued with the voltage higher than the abnormally high voltage value, the generator is destroyed through overcharge.  
      Further, since the ammeter is used as a detection unit, there is also a problem of high cost.  
     SUMMARY OF THE INVENTION  
      It is an object of the present invention to provide an engine control apparatus for detecting a voltage abnormality caused in a power supply of the engine control apparatus at low cost.  
      An engine control apparatus for controlling an engine, according to the present invention, includes: power supply voltage detecting means for detecting a power supply voltage of a battery mounted on a vehicle as a power supply, which supplies the engine control apparatus with power; and backup power supply voltage detecting means for detecting a backup power supply voltage of a backup power supply, which supplies the engine control apparatus with power from the battery via a different path. The engine control apparatus further includes: voltage difference calculating means for calculating a voltage difference between the power supply voltage and the backup power supply voltage; and power supply voltage abnormality determining means for determining that there is an abnormality in the power supply voltage when the voltage difference is not within a predetermined range.  
      An abnormality in the power supply voltage of the engine control apparatus according to the present invention is detected by comparing a power supply voltage of the engine control apparatus with a power supply voltage of a different power supply which is supplied with power from the battery via a different path. Thus, the engine control apparatus achieves the effects of eliminating the necessity to prepare an ammeter separately and detecting an abnormality in the power supply voltage at low cost. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      In the accompanying drawings:  
       FIG. 1  is a schematic diagram of an engine control apparatus according to a first embodiment of the present invention;  
       FIG. 2  is a functional block diagram of a microcomputer according to the first embodiment of the present invention;  
       FIG. 3  is a flowchart showing a power supply voltage abnormality detecting routine executed in the engine control apparatus according to the first embodiment of the present invention;  
       FIG. 4  is a flowchart showing a power generation control processing routine executed in the engine control apparatus according to the first embodiment of the present invention;  
       FIG. 5  is a functional block diagram of a microcomputer according to a second embodiment of the present invention;  
       FIG. 6  is a flowchart showing a power supply voltage abnormality detecting routine executed in an engine control apparatus according to the second embodiment of the present invention;  
       FIG. 7  is a functional block diagram of a microcomputer according to a third embodiment of the present invention;  
       FIG. 8  is a flowchart showing a power generation control processing routine executed in an engine control apparatus according to the third embodiment of the present invention;  
       FIG. 9  is a functional block diagram of a microcomputer according to a fourth embodiment of the present invention; and  
       FIG. 10  is a flowchart showing a power generation control processing routine executed in an engine control apparatus according to the fourth embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      The gist of an engine control apparatus according to the present invention consists in determining whether or not a voltage difference between a power supply voltage of a power supply line of the engine control apparatus supplied with power from a battery and a power supply voltage of a different power supply line supplied with power from the battery via a different path is equal to or larger than a predetermined value, and determining that the power supply voltage of the power supply line of the engine control apparatus is abnormal when the voltage difference is equal to or larger than the predetermined value. The following description will be given citing a backup power supply line and a load-side power supply line as examples of the different power supply line supplied with power from the battery via the different path. However, the present invention should not be limited to these examples.  
     First Embodiment  
       FIG. 1  is a schematic diagram of an engine control apparatus according to the first embodiment of the present invention.  FIG. 2  is a functional block diagram of a microcomputer according to the first embodiment of the present invention.  FIG. 3  is a flowchart showing a power supply voltage abnormality detecting routine executed in the engine control apparatus according to the first embodiment of the present invention.  FIG. 4  is a flowchart showing a power generation control processing routine executed in the engine control apparatus according to the first embodiment of the present invention.  
      An engine control apparatus  15  according to the first embodiment of the present invention drives a load  17  related to operation of an engine (not shown). The engine control apparatus  15  controls the charge/discharge of a battery  11 , which supplies the engine control apparatus  15  and the load  17  with power.  
      The battery  11  is connected to a power supply line  15   a  of the engine control apparatus  15  and a load-side power supply line  27  of the load  17  via an ignition switch  12 , a fuse  13 , and a relay switch  14   a  of a main relay  14 . The battery  11  is connected, as a backup power supply, to the power supply line  15   a  of the engine control apparatus  15  via a relay switch  19   a  of a subsidiary relay  19  as well. When the power supply voltage of the power supply line  15   a  has become lower than a permissible voltage, the subsidiary relay  19  is driven to connect a backup power supply line  26  to the power supply line  15   a . A drive coil  14   b  of the main relay  14  is connected to the engine control apparatus  15 .  
      When a signal generated in response to the closure of the ignition switch  12  is inputted to the engine control apparatus  15  and a current is caused to flow through the drive coil  14   b  of the main relay  14  based on the signal, the relay switch  14   a  of the main relay  14  is thereby closed. As a result, the power supply line  15   a  of the engine control apparatus  15  and the load  17  are supplied with power.  
      An output of the generator  18 , which can generate power through transmission of rotation of the engine, is inputted between the fuse  13  and the main relay  14 . A voltage of the power supply line  15   a  of the engine control apparatus  15  is compared with a predetermined threshold, so a current for exciting a field coil (not shown) of the generator  18  is caused to flow from the engine control apparatus  15 . Power generation by the generator  18  is thereby controlled. As a result, the terminal voltage of the battery  11  is held constant.  
      The engine control apparatus  15  includes a microcomputer  21  equipped with a CPU, a ROM for storing a processing program processed by the CPU, a RAM for temporarily storing a calculation result during calculation by the CPU, and an input/output port  22 . A transistor  16  for driving the load  17 , the field coil of the generator  18 , and a transistor  23  for driving the drive coil  14   b  of the main relay  14  are connected to the input/output port  22  of the microcomputer  21 . Diodes  24  for causing flyback energy to flow backward are connected to the transistors  16  and  23  respectively.  
      The power supply line  15   a  of the engine control apparatus  15  and the backup power supply line  26  are connected to the input/output port  22 . The input/output port  22  is equipped with an A/D converter  25  for performing A/D conversion of a power supply voltage of the power supply line  15   a  and a backup power supply voltage of the backup power supply line  26  as analog values into digital values. Although not shown in  FIG. 1 , various sensors for controlling the engine are connected to the input/output port  22 .  
      Next, functions of the microcomputer  21  will be described with reference to  FIG. 2 .  
      As shown in  FIG. 2 , the microcomputer  21  has a power supply voltage detecting unit  30  for detecting a power supply voltage of the power supply line  15   a  of the engine control apparatus  15  (hereinafter referred to simply as the power supply voltage), a backup power supply voltage detecting unit  31  for detecting a backup power supply voltage of the backup power supply line  26  (hereinafter referred to simply as the backup power supply voltage), a voltage difference calculating unit  32  for calculating a voltage difference between the power supply voltage and the backup power supply voltage, a power supply voltage abnormality determining unit  33  for making a determination on an abnormality in the power supply voltage of the power supply line  15   a  of the engine control apparatus  15  based on the voltage difference, and a generator control unit  34  for controlling the generator  18  based on a result of the determination on the abnormality.  
      Next, an operation of detecting an abnormality in the power supply voltage of the power supply line  15   a  of the engine control apparatus  15  according to the first embodiment of the present invention will be described with reference to  FIG. 3 .  
      A routine for detecting an abnormality in the power supply voltage as shown in  FIG. 3  is repeatedly executed at intervals of a predetermined cycle of, for example, 25 milliseconds after a vehicle has been started. An abnormality determining counter and an abnormality flag are initialized when the vehicle is started. In other words, the abnormality determining counter is set, and the abnormality flag is set to 0.  
      In step S 10 , when the power supply voltage abnormality detecting routine is started, the power supply voltage detecting unit  30  detects a power supply voltage from the A/D converter  25 , and the backup power supply voltage detecting unit  31  detects a backup power supply voltage.  
      In step S 11 , the voltage difference calculating unit  32  calculates a voltage difference between the backup power supply voltage and the power supply voltage.  
      In step S 12 , the power supply voltage abnormality determining unit  33  determines whether or not the absolute value of the voltage difference is larger than a predetermined voltage value, and makes a transition to step S 13  when the absolute value of the voltage difference is larger than the predetermined voltage value, or makes a transition to step S 16  when the absolute value of the voltage difference is equal to or smaller than the predetermined voltage value.  
      In step S 13 , the power supply voltage abnormality determining unit  33  determines that there is some abnormality in the power supply voltage of the engine control apparatus  15 , and increments the abnormality determining counter.  
      In step S 14 , the power supply voltage abnormality determining unit  33  determines whether or not the count value of the abnormality determining counter is equal to or larger than a predetermined count value, and makes a transition to step S 15  when it is determined that the count value is equal to or larger than the predetermined value, or terminates the power supply voltage abnormality detecting routine when it is determined that the count value is smaller than the predetermined count value.  
      In step S 15 , the power supply voltage abnormality determining unit  33  determines that there is an abnormality in the power supply voltage of the engine control apparatus  15 , and sets the abnormality flag to 1, thereby terminating the power supply voltage abnormality detecting routine.  
      In step S 16 , the power supply voltage abnormality determining unit  33  resets the abnormality determining counter to 0, and makes a transition to step S 17 .  
      In step S 17 , the power supply voltage abnormality determining unit  33  sets the abnormality flag to 0; thereby terminating the power supply voltage abnormality detecting routine.  
      As described above, an abnormality in the power supply voltage of the power supply line  15   a  of the engine control apparatus  15  is detected by comparing the power supply voltage with the backup power supply voltage of the backup power supply line  26 , which leads to the engine control apparatus  15  from the battery  11  via the different path. Therefore, there is no need to prepare an ammeter or the like separately. Consequently, an abnormality in the power supply voltage can be detected at low cost.  
      Next, a power generation control processing of the generator  18  will be described with reference to  FIG. 4 .  
      A power generation control processing routine shown in  FIG. 4  is repeatedly executed at intervals of a predetermined cycle of, for example, 5 milliseconds after the vehicle has been started.  
      In step S 20 , when the power generation control processing routine is started, the generator control unit  34  reads the abnormality flag set in the power supply voltage abnormality detecting routine, and makes a transition to step S 21 . More specifically, the generator control unit  34  accesses a predetermined address of the RAM of the engine control apparatus  15  into which the abnormality flag has been written.  
      In step S 21 , the generator control unit  34  checks whether the value set in the abnormality flag is 0 or 1, and makes a transition to step S 22  when the value is 0, or terminates the generator control processing routine when the value is 1.  
      In step S 22 , the generator control unit  34  determines that there is no abnormality in the power supply voltage, and performs normal power generation control, thereby terminating the power generation control processing routine.  
      As described above, power generation is stopped without performing power generation control when there is an abnormality in the power supply voltage of the engine control apparatus  15 . Therefore, the generator  18  can be prevented from being destroyed through overcharge resulting from the continuation of power generation.  
     Second Embodiment  
       FIG. 5  is a functional block diagram of a microcomputer according to the second embodiment of the present invention.  FIG. 6  is a flowchart showing a power supply voltage abnormality detecting routine executed in an engine control apparatus according to the second embodiment of the present invention.  
      The engine control apparatus according to the second embodiment of the present invention is different from the engine control apparatus according to the first embodiment of the present invention in that a power supply voltage for the load is used as a value to be compared with the power supply voltage instead of the backup power supply voltage. Since they are identical to each other in other respects, the description of identical parts will be omitted by assigning thereto the same symbols as in the first embodiment of the present invention.  
      A microcomputer  21 B according to the second embodiment of the present invention is different from the microcomputer  21  according to the first embodiment of the present invention in that the backup power supply voltage detecting unit  31  has been replaced with a load-side power supply voltage detecting unit  35 . Since they are identical to each other in other respects, the description of identical parts will be omitted by assigning thereto the same symbols as in the first embodiment of the present invention.  
      The load-side power supply voltage detecting unit  35  detects a load-side power supply voltage of the load-side power supply line  27  for supplying the load  17  with load-side power from the battery  11 .  
      Next, an operation of detecting an abnormality in the power supply voltage of the power supply line of the engine control apparatus according to the first embodiment of the present invention will be described with reference to  FIG. 6 .  
      A routine for detecting an abnormality in the power supply voltage as shown in  FIG. 6  is repeatedly executed at intervals of a predetermined cycle of, for example, 25 milliseconds after a vehicle has been started. An abnormality determining counter and an abnormality flag are initialized when the vehicle is started. In other words, the abnormality determining counter is set, and the abnormality flag is set to 0.  
      In step S 30 , when the power supply voltage abnormality detecting routine is started, the power supply voltage detecting unit  30  detects a power supply voltage from the A/D converter  25 , and the backup power supply voltage detecting unit  31  detects a backup power supply voltage.  
      In step S 31 , the voltage difference calculating unit  32  calculates a voltage difference between the backup power supply voltage and the power supply voltage.  
      In step S 32 , the power supply voltage abnormality determining unit  33  determines whether or not the absolute value of the voltage difference is larger than a predetermined voltage value, and makes a transition to step S 33  when the absolute value of the voltage difference is larger than the predetermined voltage value, or makes a transition to step S 36  when the absolute value of the voltage difference is equal to or smaller than the predetermined voltage value.  
      In step S 33 , the power supply voltage abnormality determining unit  33  determines that there is some abnormality in the power supply voltage of the engine control apparatus, and increments the abnormality determining counter.  
      In step S 34 , the power supply voltage abnormality determining unit  33  determines whether or not the count value of the abnormality determining counter is equal to or larger than a predetermined count value, and makes a transition to step S 35  when it is determined that the count value is equal to or larger than the predetermined value, or terminates the power supply voltage abnormality detecting routine when it is determined that the count value is smaller than the predetermined count value.  
      In step S 35 , the power supply voltage abnormality determining unit  33  determines that there is an abnormality in the power supply voltage of the engine control apparatus  15 , and sets the abnormality flag to 1, thereby terminating the power supply voltage abnormality detecting routine.  
      In step S 36 , the power supply voltage abnormality determining unit  33  resets the abnormality determining counter to 0, and makes a transition to step S 17 .  
      In step S 37 , the power supply voltage abnormality determining unit  33  sets the abnormality flag to 0, thereby terminating the power supply voltage abnormality detecting routine.  
      As described above, an abnormality in the power supply voltage of the power supply line  15   a  of the engine control apparatus  15  is detected by comparing the power supply voltage with the backup power supply voltage of the backup power supply line  26 , which leads to the engine control apparatus  15  from the battery  11  via the different path. Therefore, there is no need to prepare an ammeter or the like separately. Consequently, an abnormality in the power supply voltage can be detected at low cost.  
     Third Embodiment  
       FIG. 7  is a functional block diagram of a microcomputer according to the third embodiment of the present invention.  FIG. 6  is a flowchart showing a power supply voltage abnormality detecting routine executed in an engine control apparatus according to the second embodiment of the present invention.  
      The engine control apparatus according to the first embodiment of the present invention is different from the engine control apparatus according to the first embodiment of the present invention in that a power supply voltage for the load is used as a value to be compared with the power supply voltage instead of the backup power supply voltage. Since they are identical to each other in other respects, the description of identical parts will be omitted by assigning thereto the same symbols as in the first embodiment of the present invention.  
      A microcomputer  21 C according to the third embodiment of the present invention is different from the microcomputer  21  according to the first embodiment of the present invention in that the backup power supply voltage detecting unit  31  has been replaced with a load-side power supply voltage detecting unit  35 . Since they are identical to each other in other respects, the description of identical parts will be omitted by assigning thereto the same symbols as in the first embodiment of the present invention.  
      The generator control unit  34 C according to the third embodiment of the present invention feedback-controls the power generation amount of the generator  18  based on the power supply voltage when normal power generation control is performed, or feedback-controls the power generation amount of the generator  18  based on the backup power supply voltage when it is determined that there is an abnormality in the power supply voltage.  
      Next, a power generation control processing of the generator  18  according to the third embodiment of the present invention will be described with reference to  FIG. 8 .  
      A power generation control processing routine shown in  FIG. 8  is repeatedly executed at intervals of a predetermined cycle of, for example, 5 milliseconds after the vehicle has been started.  
      In step  40 , when the power generation control processing routine is started, the generator control unit  34 C reads the abnormality flag set in the power supply voltage abnormality detecting routine and makes a transition to step S 41 . More specifically, the generator control unit  34 C accesses a predetermined address of the RAM of the engine control apparatus  15 C into which the abnormality flag has been written.  
      In step S 41 , the generator control unit  34 C checks whether the value set in the abnormality flag is 0 or 1, makes a transition to step S 42  when the value is 0, or makes a transition to step S 43  when the value is 1.  
      In step S 42 , the generator control unit  34 C determines that there is no abnormality in the power supply voltage, calculates a voltage difference by subtracting a target voltage from the power supply voltage, and makes a transition to step S 44 .  
      In step S 43 , the generator control unit  34 C determines that there is an abnormality in the power supply voltage, calculates a voltage difference by subtracting a target voltage from the backup power supply voltage, and makes a transition to step S 44 .  
      In step S 44 , the generator control unit  34 C calculates a target power generation amount by multiplying the voltage difference by an F/B gain, and makes a transition to step S 45 .  
      In step S 45 , the generator control unit  34 C performs power generation control based on the target power generation amount, thereby terminating the power generation control processing routine.  
      As described above, power generation is continued while performing feedback control using the backup power supply voltage such that the voltage of the battery  11  becomes equal to the target voltage. It is therefore possible to ensure a sufficient amount of power for traveling to an auto-repair garage or the like without the aid of another vehicle from a spot where it is determined that there is an abnormality in the power supply voltage.  
      Since the voltage of the battery  11  is monitored using the backup power supply voltage, it is possible to prevent overcharge of the battery  11  which may occur when power generation is continued.  
     Fourth Embodiment  
       FIG. 9  is a functional block diagram of a microcomputer according to the second embodiment of the present invention.  FIG. 10  is a flowchart showing a power supply voltage abnormality detecting routine executed in an engine control apparatus according to the fourth embodiment of the present invention.  
      The engine control apparatus according to the fourth embodiment of the present invention is different from the engine control apparatus according to the second embodiment of the present invention in that a power supply voltage for the load is used as a value to be compared with the power supply voltage instead of the backup power supply voltage. Since they are identical to each other in other respects, the description of identical parts will be omitted by assigning thereto the same symbols as in the first embodiment of the present invention.  
      The generator control unit  34 D according to the fourth embodiment of the present invention feedback-controls the power generation amount of the generator  18  based on the power supply voltage when normal power generation control is performed, or feedback-controls the power generation amount of the generator  18  based on the backup power supply voltage when it is determined that there is an abnormality in the power supply voltage.  
      Next, a power generation control processing of the generator  18  according to the fourth embodiment of the present invention will be described with reference to  FIG. 10 .  
      A power generation control processing routine shown in  FIG. 8  is repeatedly executed at intervals of a predetermined cycle of, for example, 5 milliseconds after the vehicle has been started.  
      In step  50 , when the power generation control processing routine is started, the generator control unit  34 C reads the abnormality flag set in the power supply voltage abnormality detecting routine and makes a transition to step S 51 . More specifically, the generator control unit  34 D accesses a predetermined address of the RAM of the engine control apparatus  15 C into which the abnormality flag has been written.  
      In step S 51 , the generator control unit  34 C checks whether the value set in the abnormality flag is 0 or 1, makes a transition to step S 53  when the value is 0, or makes a transition to step S 53  when the value is 1.  
      In step S 52 , the generator control unit  34 D determines that there is no abnormality in the power supply voltage, calculates a voltage difference by subtracting a target voltage from the power supply voltage, and makes a transition to step S 44 .  
      In step S 53 , the generator control unit  34 D determines that there is an abnormality in the power supply voltage, calculates a voltage difference by subtracting a target voltage from the backup power supply voltage, and makes a transition to step S 44 .  
      In step S 54 , the generator controt unit  34 D calculates a target power generation amount by multiplying the voltage difference by an F/B gain, and makes a transition to step S 45 .  
      In step S 55 , the generator control unit  34 C performs power generation control based on the target power generation amount, thereby terminating the power generation control processing routine.  
      As described above, power generation is continued while performing feedback control using the load-side power supply voltage detecting unit such that the voltage of the battery  11  becomes equal to the target voltage. It is therefore possible to ensure a sufficient amount of power for traveling to an auto-repair garage or the like without the aid of another vehicle from a spot where it is determined that there is an abnormality in the power supply voltage.  
      Since the voltage of the battery  11  is monitored using the load-side power supply voltage detecting unit, it is possible to prevent overcharge of the battery  11  which may occur when power generation is continued.  
      Although the first to fourth embodiments of the present invention have been described using the examples, the present invention is not limited thereto at all. It goes without saying that the present invention can be realized as various embodiments as long as they do not depart from the spirit of the present invention.