JP6188364B2 - Air-fuel ratio control device - Google Patents

Description

  The present invention relates to an air-fuel ratio control device that controls a fuel injection amount in an internal combustion engine.

Generally, in the exhaust passage of an internal combustion engine, harmful substances HC contained in the exhaust gas discharged from an internal combustion engine, CO, three-way catalyst to harmless by oxidation / reduction of NO _x is mounted. In order to efficiently purify all of HC, CO, and NO _x , it is necessary to make the air-fuel ratio of the exhaust gas converge to a certain range near the stoichiometric air-fuel ratio called a window. For this purpose, a front O ₂ sensor and a rear O ₂ sensor are arranged upstream and downstream of the catalyst, respectively, and a double feedback loop using the output signals of these O ₂ sensors is constructed to feedback control the air-fuel ratio.

As shown in FIG. 5, the air-fuel ratio control device described in the following patent document has an output voltage of a front O ₂ sensor that detects the air-fuel ratio of the gas upstream of the catalyst as a target voltage value (represented by a chain line). In comparison, if it is higher than the target value, it is determined to be rich, and if it is lower than the target value, it is determined to be lean. When the output of the front O ₂ sensor is switched from lean to rich, the feedback correction coefficient FAF is decreased by the skip value RSM after the rich determination delay time TDR has elapsed. Thereafter, the correction coefficient FAF is decreased by a lean integral value KIM per predetermined time. As the correction coefficient FAF decreases, the fuel injection amount is reduced, and the air-fuel ratio of the air-fuel mixture moves toward lean.

When the output of the front O ₂ sensor is switched from rich to lean, the feedback correction coefficient FAF is increased by the skip value RSP after the lean determination delay time TDL has elapsed. Thereafter, the correction coefficient FAF is increased by the rich integral value KIP per predetermined time. As the correction coefficient FAF increases, the fuel injection amount is increased and the air-fuel ratio of the air-fuel mixture becomes richer.

The delay times TDR and TDL increase / decrease according to an index value FACF indicating the degree of the air / fuel ratio of the gas downstream of the catalyst. As shown in FIG. 3, the air-fuel ratio control device described in the following patent document has an output voltage of a rear O ₂ sensor that detects an air-fuel ratio of gas downstream of the catalyst as a target voltage value (represented by a chain line). In comparison, if it is higher than the target value, it is determined to be rich, and if it is lower than the target value, it is determined to be lean. While the output of the rear O ₂ sensor is rich, the index value FACF is decreased by a lean integrated value FACFKIM per predetermined time. As shown in FIG. 6, as the index value FACF increases, the rich determination delay time TDR (represented by a solid line) is extended, and the lean determination delay time TDL (represented by a broken line) is shortened. In this case, the time when the feedback correction coefficient FAF starts to decrease is delayed, and the time when the feedback correction coefficient FAF starts to increase increases. As a result, the fuel injection amount increases on average, and the control center of the air-fuel ratio is displaced to the rich side.

Conversely, while the output of the rear O ₂ sensor is lean, the index value FACF is increased by the rich integrated value FACFKIP per predetermined time. As the index value FACF decreases, the rich determination delay time TDR decreases and the lean determination delay time TDL increases. Then, the time when the feedback correction coefficient FAF starts to decrease from the increase is advanced, and the time when the feedback correction coefficient FAF starts to increase is delayed. As a result, the fuel injection amount decreases on average, and the control center of the air-fuel ratio is displaced to the lean side.

In the control method disclosed in the following patent document, when the rich determination delay time TDR or the lean determination delay time TDL becomes longer, the period of oscillation of the feedback correction coefficient FAF is extended. The extension of the oscillation cycle of the correction coefficient FAF means that the period during which the air-fuel ratio of the gas upstream of the catalyst is out of the window becomes longer, and causes a temporary increase in emission of harmful substances HC and CO or NO _x. Concerns remain.

In addition, the dynamic range of the change in the air-fuel ratio control center by adjusting the increase / decrease in the delay times TDR and TDL is small (the vertical movement of the air-fuel ratio control center remains within a narrow range very close to the theoretical air-fuel ratio). Therefore, when the rear O ₂ sensor output shows clear rich or lean, that is, when the oxygen stored in the catalyst is depleted or the oxygen is filled up to the maximum oxygen storage capacity of the catalyst, the air-fuel ratio of the gas is reduced. It can be said that the response of the correction control for leaning or enrichment is slow. This is also again leads to an increase emission of HC and CO or NO _x.

JP2013-002430A

An object of the present invention is to maintain a high purification efficiency of harmful substances HC, CO, and NO _x by a catalyst and to further reduce the emission amount of these harmful substances.

In the present invention, the air-fuel ratio is feedback-controlled with reference to the outputs of the air-fuel ratio sensors provided upstream and downstream of the exhaust gas purifying catalyst mounted in the exhaust passage of the internal combustion engine. The target value to be compared with the output of the air-fuel ratio sensor is increased or decreased according to an index value representing the degree of air-fuel ratio based on the output of the air-fuel ratio sensor downstream of the catalyst, and the output of the air-fuel ratio sensor downstream of the catalyst And the target value, while the output is richer than the target value, the index value is decremented by a predetermined lean integral value per unit time, while the output is leaner than the target value performs only integral for gradually increasing the index value by a predetermined rich integration value per unit time, with respect to the amount of change in the index value, the ratio of the change amount of the target value to be compared with the output of the air-fuel ratio sensor upstream of the catalyst The air-fuel ratio control apparatus is configured to be smaller when the index value is within the range around the theoretical air-fuel ratio and larger when the index value is deviated from the range around the theoretical air-fuel ratio toward the lean side or the rich side. did.

According to the present invention, it is possible to maintain a high purification efficiency of the harmful substances HC, CO, and NO _x by the catalyst and to further reduce the emission amount of these harmful substances.

The figure which shows the hardware resource structure of the internal combustion engine and control apparatus in one Embodiment of this invention. FIG. 4 is a timing chart showing the correlation between the output of the front O ₂ sensor and the correction amount FAF by the air-fuel ratio control apparatus of the same embodiment. By the air-fuel ratio control apparatus of the embodiment, a timing diagram illustrating the correlation between the output and the index value FACF rear O ₂ sensor. By the air-fuel ratio control apparatus of the embodiment, the graph showing the relationship between the target value of the output index values FACF and the front O ₂ sensor. Timing diagram illustrating a conventional air-fuel ratio feedback control, the correlation between the output of the front O ₂ sensor and the correction amount FAF. The graph which shows the relationship between index value FACF and delay time TDR, TDL in the conventional air-fuel ratio feedback control.

  An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an outline of an internal combustion engine for a vehicle in the present embodiment. The internal combustion engine in the present embodiment is a spark ignition gasoline engine and includes a plurality of cylinders 1 (one of which is shown in FIG. 1). In the vicinity of the intake port of each cylinder 1, an injector 11 for injecting fuel is provided. A spark plug 12 is attached to the ceiling of the combustion chamber of each cylinder 1. The spark plug 12 receives spark voltage generated by the ignition coil and causes spark discharge between the center electrode and the ground electrode. The ignition coil is integrally incorporated in a coil case together with an igniter that is a semiconductor switching element.

  The intake passage 3 for supplying intake air takes in air from the outside and guides it to the intake port of each cylinder 1. On the intake passage 3, an air cleaner 31, an electronic throttle valve 32, a surge tank 33, and an intake manifold 34 are arranged in this order from the upstream.

  The exhaust passage 4 for discharging the exhaust guides the exhaust generated by burning the fuel in the cylinder 1 from the exhaust port of each cylinder 1 to the outside. An exhaust manifold 42 and an exhaust purification three-way catalyst 41 are disposed on the exhaust passage 4.

Further, air-fuel ratio sensors 43 and 44 for detecting the air-fuel ratio of the exhaust gas flowing through the exhaust passage are installed upstream and / or downstream of the catalyst 41 in the exhaust passage 4. Each of the air-fuel ratio sensors 43 and 44 may be an O ₂ sensor having a non-linear output characteristic with respect to the air-fuel ratio of the exhaust gas, or a linear A / F sensor having an output characteristic proportional to the air-fuel ratio of the exhaust gas. There may be. In the present embodiment, an O ₂ sensor that outputs a voltage signal corresponding to the oxygen concentration in the exhaust gas is assumed for each of the upstream and downstream air-fuel ratio sensors 43 and 44 of the catalyst 41. The output characteristics of the O ₂ sensors 43 and 44 show a large and steep slope of the output change rate with respect to the air-fuel ratio in the window range, and asymptotically approach the low saturation value in the lean region where the air-fuel ratio is larger than that. In a small rich region, a so-called Z characteristic curve that draws an asymptotic approach to a high saturation value is drawn.

  An ECU (Electronic Control Unit) 0 that is an air-fuel ratio control apparatus of the present embodiment is a microcomputer system having a processor, a memory, an input interface, an output interface, and the like.

  The input interface includes a vehicle speed signal a output from a vehicle speed sensor that detects the actual vehicle speed of the vehicle, a crank angle signal b output from an engine rotation sensor that detects the rotation angle and engine speed of the crankshaft, and depression of an accelerator pedal. An accelerator opening signal c output from a sensor that detects the amount or the opening of the throttle valve 32 as an accelerator opening, and a temperature / pressure sensor that detects the intake air temperature and intake pressure in the intake passage 3 (especially the surge tank 33). Is output from an air-fuel ratio sensor 43 that detects the air-fuel ratio of the exhaust gas upstream of the catalyst 41. The air-fuel ratio signal f to be output and the air-fuel ratio output from the air-fuel ratio sensor 44 for detecting the air-fuel ratio of the exhaust gas downstream of the catalyst 41 The ratio signal g, a cam angle signal h or the like to be output from the cam angle sensor is input in a plurality of cam angle of the intake camshaft or an exhaust camshaft.

  From the output interface, an ignition signal i is output to the igniter of the spark plug 12, a fuel injection signal j is output to the injector 11, an opening operation signal k is output to the throttle valve 32, and the like.

  The processor of the ECU 0 interprets and executes a program stored in the memory in advance, calculates operation parameters, and controls the operation of the internal combustion engine. The ECU 0 acquires various information a, b, c, d, e, f, g, and h necessary for operation control of the internal combustion engine via the input interface, knows the engine speed, and is filled in the cylinder 1. Estimate the intake volume. Then, operating parameters such as required fuel injection amount, fuel injection timing (including the number of times of fuel injection for one combustion), fuel injection pressure, and ignition timing are determined. As the operation parameter determination method itself, a known method can be adopted. The ECU 0 applies various control signals i, j, and k corresponding to operation parameters and user operations via an output interface.

  Hereinafter, the air-fuel ratio feedback control will be described in detail. The ECU 0 of the present embodiment functions as a feedback controller and controls the air-fuel ratio of the air-fuel mixture that fills the cylinder 1. Specifically, first, the basic injection amount TP is determined by calculating the intake air amount from the intake pressure and intake air temperature, the engine speed, and the like. Next, the basic injection amount TP is corrected with a feedback correction coefficient FAF determined according to the air-fuel ratio on the upstream side of the catalyst 41. Further, various correction coefficients K determined according to the state of the internal combustion engine and the invalid injection time of the injector 36 The final fuel injection time (energization time for the injector 11) T is calculated in consideration of TAUV. The fuel injection time T is T = TP × FAF × K + TAUV. Then, the signal j is input to the injector 11 for the fuel injection time T, and the injector 11 is opened to inject fuel.

  The feedback control with reference to the air-fuel ratio signal f on the upstream side of the catalyst 41 is performed, for example, when the cooling water temperature of the internal combustion engine is equal to or higher than a predetermined temperature, the fuel is not being cut, the power increase is not being performed, This is performed when all of the conditions such as the air-fuel ratio sensor 43 upstream of the catalyst 41 is active and the intake pressure is normal are satisfied. The same applies to the idling operation.

As shown in FIG. 2, the ECU 0 compares the output voltage f of the front O ₂ sensor 43, which is a sensor for detecting the air-fuel ratio of the gas upstream of the catalyst 41, with a target voltage value (represented by a chain line). If it is higher than the target value, it is determined to be rich, and if it is lower than the target value, it is determined to be lean. When the sensor output f is switched from lean to rich, the feedback correction coefficient FAF is decreased by the skip value RSM without waiting for the delay time to elapse. Thereafter, the correction coefficient FAF is decreased by a lean integral value KIM per predetermined time. As the correction coefficient FAF decreases, the fuel injection amount is reduced, and the air-fuel ratio of the air-fuel mixture moves toward lean.

  Alternatively, when the sensor output f is switched from rich to lean, the feedback correction coefficient FAF is increased by the skip value RSP without waiting for the delay time to elapse. Thereafter, the correction coefficient FAF is increased by the rich integral value KIP per predetermined time. As the correction coefficient FAF increases, the fuel injection amount is increased and the air-fuel ratio of the air-fuel mixture becomes richer.

In the present embodiment, the target value to be compared with the output voltage f of the front O ₂ sensor 43 is not always constant, and varies depending on the air-fuel ratio of the gas on the downstream side of the catalyst 41. The ECU 0 of the present embodiment refers to the output g of the rear O ₂ sensor 44 that is a sensor for detecting the air-fuel ratio of the gas downstream of the catalyst 41 during the air-fuel ratio feedback control, and the gas downstream of the catalyst 41 An index value FACF representing the degree of air-fuel ratio is calculated, and a target value of the output f of the front O ₂ sensor 43 is set based on the index value FACF.

In the feedback control with reference to the air-fuel ratio signal g on the downstream side of the catalyst 41, for example, the cooling water temperature is equal to or higher than a predetermined temperature, a predetermined time has elapsed from the start of the air-fuel ratio feedback control, and the rear O ₂ sensor 44 is activated. The fuel correction amount in the transition period is below a predetermined value, the vehicle speed is 0 or less than a predetermined value close to 0 in the idle state, or is in the predetermined operating range in the non-idle state, etc. Performed when all the conditions are met.

As shown in FIG. 3, the ECU 0 compares the output voltage g of the rear O ₂ sensor 44 that is a sensor for detecting the air-fuel ratio of the gas downstream of the catalyst 41 with a target voltage value (represented by a chain line). If it is higher than the target value, it is determined to be rich, and if it is lower than the target value, it is determined to be lean. While the sensor output g is rich, the index value FACF is gradually decreased by the lean integrated value FACFKIM per predetermined time.

  While the sensor output g is lean, the index value FACF is increased by the rich integrated value FACFKIP per predetermined time.

FIG. 4 shows the relationship between the index value FACF of the gas air-fuel ratio downstream of the catalyst 41 and the target value to be compared with the output voltage f of the front O ₂ sensor 43. Basically, as the index value FACF is larger, that is, as the air-fuel ratio of the gas downstream of the catalyst 41 tends to be leaner, the target value is raised to increase the fuel injection amount, and the gas flowing into the catalyst 41 To enrich the air-fuel ratio. Conversely, the smaller the index value FACF, that is, the richer the air-fuel ratio of the gas on the downstream side of the catalyst 41, the lower the target value to decrease the fuel injection amount, and the amount of gas flowing into the catalyst 41 decreases. Reduce the air-fuel ratio.

  In addition, as shown in FIG. 4, when the index value FACF is in the vicinity of the theoretical air-fuel ratio, in other words, within a predetermined range including the window (represented by halftone dots), the above-described change amount for the index value FACF The ratio of the change amount of the target value (the slope of the characteristic curve when the index value FACF is on the horizontal axis and the target value is on the vertical axis) is reduced. As a result, the fluctuation of the fuel injection amount correction amount FAF in the situation where the air-fuel ratio of the gas downstream of the catalyst 41 is close to the stoichiometric air-fuel ratio is suppressed, and the air-fuel ratio is stabilized.

  In contrast, when the index value FACF is outside the predetermined range around the theoretical air-fuel ratio, the ratio of the change amount of the target value to the change amount of the index value FACF is compared with the case where the correction amount FACF is within the range. To make it larger. As a result, in the situation where the air-fuel ratio of the gas downstream of the catalyst 41 deviates from the stoichiometric air-fuel ratio, the fluctuation of the fuel injection amount correction amount FAF is promoted, and the air-fuel ratio can be corrected quickly.

  In this embodiment, the air-fuel ratio is feedback-controlled with reference to the outputs of air-fuel ratio sensors 43 and 44 provided upstream and downstream of the exhaust gas purification catalyst 41 mounted in the exhaust passage 4 of the internal combustion engine. The target value to be compared with the output f of the air-fuel ratio sensor 43 upstream of the catalyst 41 is increased or decreased according to the index value FACF representing the degree of air-fuel ratio based on the output g of the air-fuel ratio sensor 44 downstream of the catalyst 41. The ratio of the change amount of the target value to the change amount of the index value FACF is smaller when the index value FACF is in the range around the theoretical air-fuel ratio, and the index value FACF is around the theoretical air-fuel ratio. Thus, the air-fuel ratio control device 0 is set so as to be set larger when it is deviated from the range to the lean side or the rich side.

According to the present embodiment, it is possible to maintain a high purification efficiency of the harmful substances HC, CO and NO _x by the catalyst 41 and to further reduce the discharge amount of these harmful substances.

  In particular, unlike the conventional control method of adjusting the delay times TDR and TDL, the period of the oscillation of the feedback correction coefficient FAF does not extend unnecessarily, and the air-fuel ratio of the gas upstream of the catalyst 41 is out of the window. Will not be long.

  In addition, since the target value of the output f of the air-fuel ratio sensor 43 upstream of the catalyst 41 is increased or decreased, the dynamic range can be increased. Therefore, when the output g of the air-fuel ratio sensor 44 downstream of the catalyst 41 shows an obvious rich or lean condition, it is possible to speed up the response of the correction control for leaning or enriching the gas air-fuel ratio. is there. It becomes easy to position the control center of the air-fuel ratio slightly lean.

  The present invention is not limited to the embodiment described in detail above. The specific configuration of each part can be variously modified without departing from the spirit of the present invention.

  The present invention can be applied to control of an internal combustion engine mounted on a vehicle or the like.

0 ... Air-fuel ratio control unit (ECU)
1 ... cylinder 11 ... air-fuel ratio sensor upstream of the injector 4 ... exhaust passage 41 ... catalyst 43 ... catalyst (O ₂ sensor)
44 ... air-fuel ratio sensor downstream of the catalyst (O ₂ sensor)
f: Output (voltage) of the air-fuel ratio sensor upstream of the catalyst
g: Output (voltage) of the air-fuel ratio sensor downstream of the catalyst

Claims (1)

Feedback control of the air-fuel ratio with reference to the outputs of air-fuel ratio sensors provided upstream and downstream of an exhaust gas purification catalyst mounted in the exhaust passage of the internal combustion engine,
The target value to be compared with the output of the air-fuel ratio sensor upstream of the catalyst is raised or lowered according to an index value representing the degree of air-fuel ratio based on the output of the air-fuel ratio sensor downstream of the catalyst,
The output of the air-fuel ratio sensor downstream of the catalyst is compared with the target value, and while the output is richer than the target value, the index value is decreased by a predetermined lean integral value per unit time, and the output is While it is leaner than the target value, it performs only integration that increases the index value by a predetermined rich integral value per unit time,
The ratio of the change amount of the target value to be compared with the output of the air-fuel ratio sensor upstream of the catalyst with respect to the change amount of the index value is smaller when the index value is within the range around the theoretical air-fuel ratio, An air-fuel ratio control apparatus in which the value is set larger when the value deviates from a range around the theoretical air-fuel ratio toward the lean side or the rich side.

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