JP6153344B2 - 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 feedback loop using the output signals of these O ₂ sensors is constructed to feedback control the air-fuel ratio (for example, the following patents) See literature).

JP 2010-138791 A

There is a time lag from when the fuel injection amount is corrected to change the air-fuel ratio of the gas until when the output signal of the rear O ₂ sensor changes.

When the fuel injection amount is reduced based on the output of the rear O ₂ sensor indicating that the air-fuel ratio is rich, excess oxygen gas flows into the catalyst until the output of the rear O ₂ sensor switches to the air-fuel ratio lean. to continue. In other words, oxygen was occluded in the catalyst to the vicinity of the limit of the oxygen occlusion capacity of the catalyst, and NO _x was sometimes discharged immediately after the output of the rear O ₂ sensor showed lean air-fuel ratio. In such a situation, there is also a concern that the output signal of the rear O ₂ sensor vibrates violently and causes control hunting.

The present invention has been made by paying attention to the above-mentioned problem for the first time, and has an intended purpose of maintaining a high NO _x purification efficiency by the catalyst and further reducing the NO _x emission amount.

In the present invention, the air-fuel ratio of the gas flowing into the catalyst is feedback controlled with reference to the output of the air-fuel ratio sensor provided downstream of the exhaust gas purification catalyst mounted in the exhaust passage of the internal combustion engine. When the output signal of the air-fuel ratio sensor detects that the air-fuel ratio sensor has changed by a predetermined amount or more toward the air-fuel ratio lean side, the target value to be compared with the output of the air-fuel ratio sensor is set to the air-fuel ratio by a predetermined amount. The target to be compared with the output of the air-fuel ratio sensor until it is no longer detected that the output signal of the air-fuel ratio sensor has changed by a predetermined amount per predetermined time toward the air-fuel ratio lean side. An air-fuel ratio control apparatus that feedback-controls the air-fuel ratio of the gas flowing into the catalyst using the target value while correcting the value was configured.

According to the present invention, the NO _x purification efficiency of the catalyst can be kept high, and the NO _x emission amount can be further reduced.

The figure which shows the hardware resource structure of the internal combustion engine and control apparatus in one Embodiment of this invention. Timing diagram illustrating the pattern of the air-fuel ratio feedback control with reference to the output of the front O ₂ sensor. The graph which illustrates the relationship between control center correction amount FACF and delay time TDR, TDL. Timing diagram illustrating the pattern of the air-fuel ratio feedback control with reference to the output of the rear O ₂ sensor. The timing diagram which shows the pattern of correction of the target value of air-fuel ratio feedback control. Timing diagram illustrating a method for detecting a prelude to the vibration of the output of the rear O ₂ sensor. The timing diagram which shows the pattern of the conventional air fuel ratio feedback control without the correction of target value.

  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 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.

  Alternatively, when the sensor output f 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 or decrease according to the control center correction amount FACF. FIG. 3 illustrates the relationship between the correction amount FACF and the delay times TDR and TDL. As the correction amount 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 feedback control is displaced to the rich side.

  On the other hand, the smaller the correction amount FACF, the shorter the rich determination delay time TDR and the lean determination delay time TDL. 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 feedback control is displaced to the lean side.

The ECU 0 also calculates the control center correction amount FACF during the air-fuel ratio feedback control. In principle, the FACF is determined according to the air-fuel ratio on the downstream side of the catalyst 41. 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 front O ₂ sensor 43 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. 4, 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. Then, while the sensor output g is rich, the control center correction amount FACF is decreased by a lean integral value FACFKIM per predetermined time. As described above, the air-fuel ratio control center moves toward lean as the correction amount FACF decreases.

  On the contrary, while the sensor output g is lean, the control center correction amount FACF is increased by the rich integral value FACFKIP per predetermined time. As the correction amount FACF increases, the air-fuel ratio control center moves toward rich.

Rear O ₂ output g of the sensor 44 is reduced ECU0 fuel injection amount on the basis that indicates the rich air-fuel ratio, from the start to reduce the or control-center correction amount FACF, the output g of the rear O ₂ sensor 44 is empty There is a time lag until the fuel ratio becomes lean. This time lag is due to the oxygen storage capacity of the catalyst 41 (the fluctuation of the air-fuel ratio of the gas upstream of the catalyst 41 is absorbed in the catalyst 41 and is not directly transmitted downstream of the catalyst 41), and the response delay of the feedback control loop itself Due to

  During the above time lag, the oxygen-excess gas continues to flow into the catalyst 41. As a result, oxygen is stored in the catalyst 41 up to the vicinity of the limit of its oxygen storage capacity. When the catalyst 41 is already filled with oxygen, the catalyst 41 cannot absorb the fluctuation of the air-fuel ratio of the gas deviating from the stoichiometric air-fuel ratio.

Thus, as illustrated in FIG. 7, the time immediately after the time t ₀ the output g of the rear O ₂ sensor 44 is switched from the higher richer than the target value to a lower leaner than the target value, the rear O ₂ sensor 44 Output signal g and the correction amount FACF based on the output signal g vibrate vigorously. At the same time, NO _{x that} has not been reduced in the catalyst 41 is discharged from the catalyst 41.

Therefore, in this embodiment, before the output signal g of the rear O ₂ sensor 44 vibrates, the fuel injection amount is compared with the output g of the rear O ₂ sensor 44 so that the fuel injection amount can be switched from the decreasing tendency to the increasing tendency. The target value should be corrected online.

As shown in FIG. 7, immediately before the output signal g of the rear O ₂ sensor 44 oscillates, changes appear in the output signal g and the correction amount FACF that clearly decrease toward the air-fuel ratio lean side. . This change is a sign of oscillation of the output signal g, in other words, a sign of NO _x being discharged.

The ECU 0 of this embodiment repeatedly calculates a reduction amount (change amount toward the air-fuel ratio lean) ΔG per predetermined time ΔT of the output signal g of the rear O ₂ sensor 44, and the reduction amount ΔG is equal to or greater than a predetermined amount. When this happens, it is determined that a sign of oscillation of the output signal g has appeared. When such a precursor is detected, the target value to be compared with the output g of the rear O ₂ sensor 44 in the air-fuel ratio feedback control is corrected to the air-fuel ratio rich side by a predetermined amount ΔR as shown in FIG. Do (raise).

In the subsequent air-fuel ratio feedback control, the corrected target value is used. Further, the target value may be that the decrease amount ΔG per predetermined time ΔT of the output signal g of the rear O ₂ sensor 44 exceeds the predetermined amount until no sign of vibration of the output signal g and the correction amount FACF is detected. Corrections are made until it is gone.

As a result, as illustrated in FIG. 5, the occurrence of vibrations in the output signal g of the rear O ₂ sensor 44 and the correction amount FACF is suppressed, and the NO _x emission amount is reduced.

As shown in FIGS. 5 and 6, whether or not the decrease amount ΔG of the output signal g of the rear O ₂ sensor 44 per predetermined time ΔT is equal to or larger than the predetermined amount is determined by a plurality of successive time points t ₁ , t ₂ is preferable. At that time, the target value is corrected for the first time only when the change amount ΔG is equal to or larger than the predetermined amount at each of the time points t ₁ and t ₂ . This is intended to avoid a possibility that accidental noise mixed in the output signal g is mistaken as a precursor of vibration of the output signal g.

  In this embodiment, the output g of the air-fuel ratio sensor 44 provided downstream of the exhaust gas purification catalyst 41 mounted in the exhaust passage 4 of the internal combustion engine is referred to, and the air-fuel ratio of the gas flowing into the catalyst 41 is fed back. When it is detected that the output signal g of the air-fuel ratio sensor 44 has changed by a predetermined amount or more per predetermined time ΔT toward the air-fuel ratio lean side, the output g of the air-fuel ratio sensor 44 is The air-fuel ratio control device 0 is configured to correct the target value to be compared to the air-fuel ratio rich side.

According to this embodiment, it can be avoided that the air-fuel ratio of the gas flowing into the catalyst 41 continues to be excessively lean. Further, it is possible to prevent the catalyst 41 from storing oxygen to the limit of the oxygen storage capacity, and to keep the NO _x reduction efficiency by the catalyst 41 high, thereby further reducing the NO _x emission amount. .

The present invention is not limited to the embodiment described in detail above. As shown in FIGS. 5 and 7, when the output signal g of the rear O ₂ sensor 44 varies, the correction amount FACF also varies accordingly. Accordingly, the amount of decrease of the correction amount FACF per predetermined time ΔT (the amount of change toward the air-fuel ratio lean) is repeatedly calculated, and the output signal of the rear O ₂ sensor 44 is obtained when the amount of decrease is equal to or greater than the predetermined amount. It may be determined that g has changed by a predetermined amount or more per predetermined time ΔT toward the lean side of the air-fuel ratio (that is, a sign of oscillation of the output signal g and the correction amount FACF has appeared).

In the above embodiment, when the target value to be compared with the output g of the rear O ₂ sensor 44 is corrected, the correction amount ΔR is instantaneously increased to the target value, that is, the target value is changed stepwise at time t _2. However, the target value may be gradually increased by the correction amount ΔR after time t ₂ . When the target value is changed stepwise to (target value + ΔR) at time t ₂ , if the increment ΔR is large, the correction amount to the rich side of the air-fuel ratio temporarily becomes excessive, and the exhaust gas purification performance by the catalyst 41 is increased. While temporarily may be reduced, if the target value is gradually increased to t ₂ time after (target value + [Delta] R), to prevent deterioration of exhaust gas purification performance by the catalytic 41 to suppress excessive correction Can do.

The fact that the target value to be compared with the output g of the rear O ₂ sensor 44 is frequently corrected means that the output signal g of the rear O ₂ sensor 44 and the correction amount FACF are likely to vibrate. As a result, it is suggested that the catalyst 41 deteriorates with time and its oxygen storage capacity is reduced. Therefore, when the target value exceeds a predetermined threshold value after repeated corrections, the ECU 0, which is the control device, diagnoses that the catalyst 41 has deteriorated and provides information (diagnostic code) indicating that to the ECU 0. It is conceivable that the information is stored in the memory or output in a manner appealing to the driver's sight or hearing (lighting the check lamp, displaying on the display, outputting sound, etc.).

  Other specific configurations 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 ... injector 4 ... downstream air-fuel ratio sensor in the exhaust passage 41 ... catalyst 44 ... catalyst (O ₂ sensor)
g: Output signal of the air-fuel ratio sensor downstream of the catalyst

Claims (1)

With reference to the output of an air-fuel ratio sensor provided downstream of the exhaust gas purification catalyst mounted in the exhaust passage of the internal combustion engine, feedback control of the air-fuel ratio of the gas flowing into the catalyst,
When it is detected that the output signal of the air-fuel ratio sensor has changed more than a predetermined amount per predetermined time toward the air-fuel ratio lean side, the target value to be compared with the output of the air-fuel ratio sensor is rich by the predetermined amount. To the side ,
Thereafter, the target value to be compared with the output of the air-fuel ratio sensor is corrected until it is no longer detected that the output signal of the air-fuel ratio sensor has changed more than a predetermined amount per predetermined time toward the air-fuel ratio lean side. An air-fuel ratio control apparatus that feedback-controls the air-fuel ratio of the gas flowing into the catalyst using the target value .

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