JP2007056718A - Air-fuel ratio control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent false detection of an air-fuel ratio sensor during exhaust braking or fuel cut and to prevent element break and the like of the air-fuel sensor in normal operation. <P>SOLUTION: An air-fuel ratio control device comprises a means for determining if operation condition is in the normal operation, exhaust braking operation or fuel cut operation, a means for duty-controlling applied voltage to a heater element of the air-fuel ratio sensor to maintain element temperature of the air-fuel ratio sensor in an appropriate range based on engine rotation speed and engine load when the operation condition is in the normal operation, a means for duty-controlling the applied voltage to the heater element of the air-fuel ratio sensor to inhibit the element temperature of the air-fuel ratio sensor from lowering out of the appropriate range based on the engine rotation speed when the operation condition is in the exhaust braking operation, and a means for duty-controlling the applied voltage to the heater element of the air-fuel ratio sensor to inhibit the element temperature of the air-fuel ratio sensor from lowering out of the appropriate range based on the engine rotation speed when the operation condition is in the fuel cut operation. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an engine air-fuel ratio control apparatus.

  For example, in a gas engine that uses gaseous fuel such as CNG (compressed natural gas), an air-fuel ratio sensor that detects an excess air ratio in the exhaust of the engine is provided, and the detected value of the air-fuel ratio is a target based on this detection signal. A control (air-fuel ratio feedback control) means for increasing / decreasing the fuel supply amount so as to become a value is provided (Patent Document 1).

The air-fuel ratio sensor has a built-in heater element that raises the temperature of the sensor element because the sensor element facing the exhaust gas becomes inactive and a predetermined output may not be obtained. In the case of Patent Document 1, the voltage applied to the heater element is maintained at a predetermined reference voltage (for example, 10 V) during normal operation, and the exhaust brake operating conditions (operating conditions that lower the exhaust temperature including the fuel cut operating conditions) When is established, in order to suppress the temperature drop of the sensor element, the voltage is switched to a higher voltage (for example, 12 V) than during normal operation.
JP 09-329574

  The voltage applied to the heater element of the air-fuel ratio sensor is higher than that during normal operation during the operation of the exhaust brake or fuel cut, but the voltage value is only controlled to be constant (for example, 12 V), so that the exhaust gas There is a possibility that the temperature drop of the sensor element cannot be sufficiently suppressed depending on the flow rate (see FIG. 5). Even during normal operation, the voltage applied to the heater element is only controlled to a constant value (for example, 10 V). Depending on the target value of the air-fuel ratio, the element temperature of the air-fuel ratio sensor may increase excessively, causing element cracking, etc. It can be invited (see FIG. 4).

  An object of this invention is to provide an effective means for solving such a problem.

  According to a first aspect of the present invention, there is provided an air-fuel ratio control apparatus comprising an air-fuel ratio sensor for detecting an excess air ratio in engine exhaust and means for controlling a fuel supply amount so that the detected value coincides with a target air-fuel ratio. Means for determining whether the engine is in normal operation, exhaust brake operation or fuel cut operation, and when the operation condition is normal operation, the air-fuel ratio sensor is based on the detected value of the engine speed and the detected value of the engine load. Means for duty-controlling the voltage applied to the heater element of the air-fuel ratio sensor to maintain the element temperature of the air-fuel ratio sensor, and when the operating condition is the exhaust brake operation, the air-fuel ratio sensor based on the detected value of the engine speed In order to prevent the temperature of the element from dropping from the appropriate range, the duty control is performed so that the voltage applied to the heater element of the air-fuel ratio sensor is higher than in normal operation. When the operating condition is the fuel cut operation, the applied voltage to the heater element of the air-fuel ratio sensor is normally set to suppress the element temperature of the air-fuel ratio sensor from falling from the appropriate range based on the detected value of the engine speed. Means for performing duty control higher than that during operation.

  According to a second aspect of the present invention, there is provided an air-fuel ratio control apparatus comprising: an air-fuel ratio sensor for detecting an excess air ratio in engine exhaust; and means for controlling a fuel supply amount so that the detected value coincides with a target air-fuel ratio. Means for determining the reference heater energization duty for maintaining the applied voltage to the heater element of the air-fuel ratio sensor at a predetermined reference level based on the detected value of the battery voltage from the map data set as a parameter, and the operation condition is normal operation Means for determining whether the vehicle is in operation, exhaust brake operation, or fuel cut operation, and when the operating conditions are determined to be normal, the engine speed should be maintained to maintain the element temperature of the air-fuel ratio sensor during normal operation within the appropriate range. Corresponding to the detected value of engine speed and the detected value of engine load from the map data set in the engine load parameter When the exhaust brake is operating, the means for obtaining the motor energization duty correction coefficient, and when the operating condition is being determined, the engine speed is used as a parameter to prevent the element temperature of the air-fuel ratio sensor during exhaust brake operation from falling from the appropriate range. Means for obtaining the heater energization duty correction coefficient corresponding to the detected value of the engine speed from the map data set larger than that during normal operation, and when the operating condition is determined as the fuel cut operation, the air-fuel ratio during the fuel cut operation Means for obtaining a heater energization duty correction coefficient corresponding to a detected value of the engine speed from map data set to be larger than that during normal operation using the engine speed as a parameter in order to prevent the sensor element temperature from falling from an appropriate range; "Final heater energization duty = reference heater energization duty x operating condition And a means for duty-controlling the voltage applied to the heater element of the air-fuel ratio sensor based on the calculated value.

  In the first invention or the second invention, when the operating condition is normal operation, the voltage applied to the heater element of the air-fuel ratio sensor is controlled based on the detected value of the engine speed and the detected value of the engine load. Is done. For this reason, the element temperature of the air-fuel ratio sensor can be maintained in an appropriate range in the entire operation region. For example, it is possible to suppress an excessive increase in the element temperature of the air-fuel ratio sensor by controlling the voltage applied to the heater element to be lower than in the low load area in the high load area. When the operating condition is exhaust brake or fuel cut, the amount of fuel supplied to the engine is very small or very small, and the exhaust temperature decreases, but the applied voltage to the heater element of the air-fuel ratio sensor is higher than that during normal operation. Therefore, the decrease in the element temperature of the air-fuel ratio sensor can be suppressed and maintained within an appropriate range. Even in this case, the voltage applied to the heater element of the air-fuel ratio sensor is not controlled to be constant, but is duty-controlled based on the detected value of the engine speed. It can be suppressed and can be efficiently maintained within the proper range. As a result, erroneous detection of the air-fuel ratio sensor, element cracking, and the like can be prevented.

  In FIG. 1, reference numeral 10 denotes an engine that uses CNG (compressed natural gas) as a fuel. A throttle valve 11 is interposed in an intake passage 16 of the engine 10, and a nozzle 13 of a fuel supply device 12 is disposed upstream thereof. . The throttle valve 11 adjusts the intake air amount (air mixture amount or air amount) to the engine 10, and is opened and closed by a driving means 11a (motor). Reference numeral 18 denotes an idle control valve that controls an idle flow rate (a mixture amount to the engine), and is interposed in a bypass passage 17 that bypasses the throttle valve 11. The throttle valve 11 is controlled to an opening corresponding to a detected value of an accelerator opening sensor (detecting an accelerator operation amount). The opening degree of the idle control valve 18 is controlled so as to keep the idle rotation constant when the throttle is fully closed.

  An exhaust brake shutter (not shown) is interposed in the exhaust passage 20 of the engine 10. The exhaust brake shutter closes (squeezes) the exhaust passage 20 when the exhaust brake is operated, and an air cylinder 21 is provided in its driving means. The air cylinder 21 is connected to an air tank, and when the solenoid valve 22 (exhaust brake valve) is switched to the supply side, the exhaust brake shutter is closed by the compressed air from the air tank, while the solenoid valve 22 is switched to the exhaust side. The return spring operates to open the exhaust brake shutter. The exhaust brake valve 22 is controlled to the air supply side during the period when the exhaust brake operating condition is satisfied.

  Reference numeral 19 denotes an ignition plug of the engine 10, which is controlled to an optimal ignition timing corresponding to the engine speed and the intake pressure when the operation condition is normal operation, while the operation condition is during exhaust braking or fuel cut. Control is performed to set a predetermined pause period.

  The fuel supply device 12 is provided with a pipe for supplying fuel (CNG) from a gas cylinder (not shown) to the nozzle. The low-pressure fuel cutoff valve 15 and the gas control valve 14 (injection valve) are connected to the pipe from the gas cylinder side. A high-pressure fuel shut-off valve (main stop valve) and a regulator are installed in this order. The high-pressure fuel cutoff valve and the low-pressure fuel cutoff valve 15 are controlled so as to open when the ignition switch (engine key switch) is turned on and close when the ignition switch is turned off. The regulator regulates (depressurizes) the high-pressure fuel to a predetermined low-pressure fuel, and the gas control valve 14 supplies the nozzle 13 with a supply amount (injection amount) so as to generate an air-fuel mixture having a substantially constant air-fuel ratio. Is controlled according to the operating state. The injection amount (injection pulse width) of the gas control valve 14 is based on the deviation between the basic injection amount corresponding to the engine speed and the intake pressure, and the detected value of the air-fuel ratio and the target value when the operating condition is normal operation. And a feedback correction amount. When the operating condition is exhaust brake or fuel cut, the low-pressure fuel cutoff valve 15 is closed and the gas control valve 14 is controlled to an injection amount 0 (injection pulse width 0%).

  A control unit 28 includes an accelerator opening sensor (not shown), a crank angle sensor 24 (functioning as an engine rotation sensor), an intake pressure sensor 25 (functioning as an engine load sensor), an air-fuel ratio sensor 23, and the like. Based on the detection signal, the throttle valve 11, the idle control valve 18, the spark plug 19, the low-pressure fuel cutoff valve 15, the gas control valve 14, and the exhaust brake valve 22 are controlled as described above.

  Regarding the exhaust brake control of the control unit 28, when the exhaust brake operating condition is satisfied, the ignition signal is turned off together with the fuel cut (the low pressure fuel cutoff valve 15 is closed and the gas control valve 14 is controlled to 0% of the injection pulse width). To do. When a predetermined time elapses, the exhaust brake shutter is closed and the ignition signal is turned on. Thereafter, the exhaust brake shutter is opened when abnormal combustion (backfire or the like) is determined while the air-fuel ratio sensor 23 monitors the air-fuel ratio.

  The air-fuel ratio sensor 23 has a built-in heater element that raises the temperature of the sensor element facing the exhaust gas, and means (air-fuel ratio heater control means) for duty-controlling the voltage applied to the heater element is set in the control unit 28. In FIG. 1, the voltage applied to the heater element of the air-fuel ratio sensor 23 is predetermined based on the detected value of the battery voltage sensor (not shown) from the map data set with the battery voltage as a parameter to compensate for the battery voltage drop. Means 30 (reference heater energization duty calculation means) for determining a reference heater energization duty for maintaining the reference level of the engine, and means 31 (operation for determining whether the operation condition is normal operation, exhaust brake operation or fuel cut operation) Condition determination means), when the determination of the operating condition is during normal operation, from the map data in which the engine speed and the engine load are set as parameters in order to maintain the element temperature of the air-fuel ratio sensor 23 during normal operation within an appropriate range Detection signal of crank angle sensor 24 (detection value of engine speed) and detection of intake pressure sensor 25 Means 32 (heater energization duty correction means during normal operation) for obtaining a heater energization duty correction coefficient corresponding to the signal (detected value of engine load), and when the operation condition is judged to be exhaust brake operation, In order to prevent the element temperature of the fuel ratio sensor 23 from falling from an appropriate range, the engine speed is used as a parameter to map signal that is set to be larger than that during normal operation, and the detection signal of the crank angle sensor 24 (detected value of engine speed) The means 33 for obtaining the corresponding heater energization duty correction coefficient (heater energization duty correction means at the time of exhaust brake). When the operation condition is determined to be during the fuel cut operation, the element temperature of the air-fuel ratio sensor 23 during the fuel cut operation is within an appropriate range. The engine speed is usually used as a parameter to prevent Means 34 (heater energization duty correction means at the time of fuel cut) for obtaining a heater energization duty correction coefficient corresponding to a detection signal (detection value of engine speed) of the crank angle sensor 24 from map data set larger than the time of rotation. Provided.

  35 is a means for selecting the heater energization duty correction means 32 to 34 corresponding to the output (determination signal) of the operation condition determination means 31, and 36 is "final heater energization duty = reference heater energization duty x heater corresponding to the operation condition" 37 is a means (heater energization duty control means) for duty-controlling the voltage applied to the heater element of the air-fuel ratio sensor 23 based on this calculated value.

  FIG. 2 is a diagram illustrating the air-fuel ratio heater control means. The heater energization duty selection means 35 is a contact corresponding to the heater energization duty correction means 32 during normal operation when the operation condition determination signal is “00”. When “00” is selected and the operation condition determination signal is “01”, the contact “01” corresponding to the heater energization duty correction means 33 at the time of exhaust braking is selected. When the operation condition determination signal is “02”, the fuel is cut. The contact “02” corresponding to the heater energization duty correction means 34 is selectively closed.

The heater energization duty correction means 32 during normal operation outputs a search value corresponding to the detection signal of the crank angle sensor 24 and the detection signal of the intake pressure sensor 25 from the map data TBKAFHT as the heater energization duty correction coefficient vkafht. The heater energization duty correction means 33 at the time of exhaust brake outputs a search value corresponding to the detection signal of the crank angle sensor 24 from the map data TBKAFHT _- EXB as a heater energization duty correction coefficient vkafht. The heater energization duty correction means 34 at the time of fuel cut outputs a search value corresponding to the detection signal of the crank angle sensor 24 from the map data TBKAFHT _- CF as a heater energization duty correction coefficient vkafht. The reference heater energization duty calculation means 30 outputs the search value corresponding to the detection signal of the battery voltage sensor from the map data TBAFHT as the reference heater energization duty vafht.

  The final heater energization duty calculation means 36 calculates the final heater energization duty vafhtlod = vafht × vkafht from the reference heater energization duty vafht and the heater energization duty correction coefficient vkafht from the selection means 35. The voltage applied to the heater element of the air-fuel ratio sensor 23 is duty-controlled to the calculated value vafhtlod.

  Thus, when the operating condition is normal operation, the voltage applied to the heater element of the air-fuel ratio sensor 23 is duty-controlled according to the operating state (engine speed, engine load). For this reason, the element temperature of the air-fuel ratio sensor 23 can be maintained in an appropriate range in the entire operation region. For example, it is possible to suppress an excessive increase in the element temperature of the air-fuel ratio sensor 23 by controlling the voltage applied to the heater element to be lower than that in the low load area in the high load area. When the voltage applied to the heater element of the air-fuel ratio sensor 23 is controlled to be constant, a region where the element temperature is too low or a region where the element temperature is too high as shown in FIG. 4 tends to occur.

  When the operating condition is exhaust brake or fuel cut, the amount of fuel supplied to the engine is very small or very small, and the exhaust temperature decreases. However, the voltage applied to the heater element of the air-fuel ratio sensor 23 is Therefore, a decrease in the element temperature of the air-fuel ratio sensor 23 can be suppressed and maintained within an appropriate range. Even in this case, the voltage applied to the heater element of the air-fuel ratio sensor 23 is not controlled constant, but is duty-controlled based on the detected value of the engine speed. The voltage can be suppressed without excess and deficiency, and can be efficiently maintained within an appropriate range. When the voltage applied to the heater element of the air-fuel ratio sensor 23 is maintained at the same level as during normal operation, the element temperature falls from the appropriate range as shown in FIG. Therefore, the voltage applied to the heater element is higher than that during normal operation, but the decrease in element temperature increases with the engine speed, so the voltage applied to the heater element must be kept higher than during normal operation. In the case of control, there is a possibility that a decrease in the voltage applied to the heater element cannot be sufficiently suppressed.

  In this embodiment, the air-fuel ratio sensor 23 includes the operating condition determination means 35, the heater energization duty correction means 32 during normal operation, the heater energization duty correction means 33 during exhaust brake, and the heater energization duty correction means 34 during fuel cut. It is possible to prevent false detection and element cracking. In the exhaust brake control, the exhaust brake shutter is opened when abnormal combustion (backfire or the like) is determined while the air-fuel ratio sensor 23 monitors the air-fuel ratio after the ignition signal is turned ON. Since it is possible to prevent erroneous detection of the air-fuel ratio sensor 23, it is possible to maintain a normal and effective function of the exhaust brake.

  FIG. 3 is a flowchart for explaining the air-fuel ratio heater control means. In S1, the detection signal of the battery voltage sensor is read. In S2, a search value corresponding to the detected value of the battery voltage is obtained from the map data TBAFHT as the reference heater energization duty vafht. S5 to S12 are processed in parallel with S1 and S2. In S5, the detection signal of the crank angle sensor 24 is read. In S6, the detection signal of the intake pressure sensor 25 is read. In S7, it is determined whether the operating condition of the exhaust brake is satisfied or the operating condition of the fuel cut is satisfied as the operating condition, or other normal operation is being performed.

In S8, it is determined whether the operation condition of the exhaust brake is satisfied in S8. When the determination in S8 is yes, in S9, a search value corresponding to the detected value of the engine speed is obtained from the map data TBKAFHT _- EXB as the heater energization duty correction coefficient vkafht. If the determination in S8 is no, in S10, it is determined whether or not the operation condition determination satisfies the fuel cut operation condition. When the determination in S10 is yes, in S11, a search value corresponding to the detected value of the engine speed is obtained as the heater energization duty correction coefficient vkafht from the map data TBKAFHT _- FC. When the determination in S10 is no, it is determined that the operation condition is determined to be during normal operation. In S12, the search value corresponding to the detected value of the engine speed and the detected value of the engine load is corrected from the map data TBKAFHT in the heater energization duty correction. Obtained as coefficient vkafht.

  In S3, vafhtlod = vafht × vkafht is calculated from the reference heater energization duty in S2 and the heater energization duty correction coefficient vkafht in S9, S11, or S12. In S4, duty control is performed on the voltage applied to the heater element of the air-fuel ratio sensor 23 based on the calculated value vafhtlod.

1 is a system configuration diagram illustrating an embodiment of the present invention. It is a diagram explaining an air fuel ratio heater control means similarly. It is a flowchart explaining an air fuel ratio heater control means similarly. It is a characteristic view which illustrates element temperature at the time of normal operation of an air fuel ratio sensor. It is a characteristic view which illustrates the element temperature at the time of the exhaust brake of an air fuel ratio sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Throttle valve 12 Fuel supply apparatus 14 Gas control valve 15 Low-pressure fuel cutoff valve 19 Spark plug 22 Exhaust brake valve 23 Air-fuel ratio sensor 24 Crank angle sensor 25 Intake pressure sensor 28 Control unit 30 Reference heater energization duty calculation means 31 Operating condition judgment means 32 Heater energization duty correction means during normal operation 33 Exhaust brake heater energization duty correction means 34 Heater energization duty correction means during fuel cut 35 Selection means 36 Calculation means 37 Final heater energization duty control means

Claims (2)

  An air-fuel ratio control apparatus comprising an air-fuel ratio sensor for detecting an excess air ratio in exhaust of an engine and means for controlling a fuel supply amount so that the detected value coincides with a target air-fuel ratio. Means for determining whether the brake is operating or the fuel cut is operating. When the operating condition is normal operation, the air-fuel ratio is maintained to maintain the element temperature of the air-fuel ratio sensor within an appropriate range based on the engine speed and the engine load. Means for duty-controlling the voltage applied to the heater element of the sensor, and when the operating condition is exhaust brake operation, the air-fuel ratio is controlled to prevent the element temperature of the air-fuel ratio sensor from falling from the appropriate range based on the engine speed. Means for duty-controlling the voltage applied to the heater element of the sensor, and when the operating condition is fuel cut operation, it is based on the engine speed. There, the air-fuel ratio control apparatus characterized by comprising means for duty control of the voltage applied to the heater element of the air-fuel ratio sensor to suppress the element temperature of the air-fuel ratio sensor is lowered from a proper range.   An air-fuel ratio sensor comprising: an air-fuel ratio sensor for detecting an excess air ratio in engine exhaust; and means for controlling a fuel supply amount so that the detected value coincides with a target air-fuel ratio. Means for setting the reference heater energization duty to control the voltage applied to the heater element to a predetermined reference level, means for determining whether the operating conditions are normal operation, exhaust brake operation or fuel cut operation, operation When the determination of the condition is during normal operation, the detected value of the engine speed and the engine are determined from a map in which the engine speed and the engine load are set as parameters in order to maintain the element temperature of the air-fuel ratio sensor during normal operation within an appropriate range. Means for obtaining the heater energization duty correction coefficient corresponding to the detected load value, and judgment of the operating condition is the exhaust brake During operation, the heater energization duty corresponding to the detected value of the engine speed from a map in which the engine speed is set as a parameter to suppress the element temperature of the air-fuel ratio sensor during exhaust brake operation from falling from the appropriate range When the means for setting the correction coefficient and the determination of the operating condition is during the fuel cut operation, the engine speed is set as a parameter in order to prevent the element temperature of the air-fuel ratio sensor during the fuel cut operation from falling from an appropriate range. Means for obtaining a heater energization duty correction coefficient corresponding to the detected value of the engine speed from the map, means for calculating a heater energization duty correction coefficient corresponding to the final heater energization duty = reference heater energization duty × operating conditions, Means for duty-controlling the voltage applied to the heater element of the air-fuel ratio sensor. An air-fuel ratio control apparatus.

Images