JP2010138791A - Air-fuel ratio control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To furthermore reduce HC and CO emissions by adjusting a correction amount to instantaneously shift a control center of air-fuel ratio feedback control to a lean side. <P>SOLUTION: This air-fuel ratio control device includes: a correction amount calculation section comparing output of a rear O<SB>2</SB>sensor with a determining value to determine whether the output of the sensor is rich or lean and calculating a correction amount FACF for displacing a center of air-fuel ratio control according to a determination result; a correction amount adjustment section comparing the output of the rear O<SB>2</SB>sensor with a threshold on a richer side than the determination value, and shifting the center of control to the lean side by subtracting the correction amount FACF by a subtracted value FACFOFM when the output of the sensor reaches the threshold; and an air-fuel ratio control section controlling feedback control over an air-fuel ratio based on the output of a front O<SB>2</SB>sensor and the correction amount FACF. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to air-fuel ratio control performed for the purpose of maintaining exhaust gas purification efficiency by a catalyst.

Generally, the exhaust passage such as an automobile, HC contained in the exhaust gas discharged from an internal combustion engine, a catalyst to detoxify by oxidation / reduction of CO and NO _x are mounted. In order to efficiently purify all of HC, CO, and NO _x , it is necessary to make the air-fuel ratio converge to a certain range near the theoretical air-fuel ratio called a window.

For this purpose, an O ₂ sensor is arranged upstream and downstream of the catalyst, and a double feedback loop using the output signals of both the front and rear sensors is constructed to control the air-fuel ratio (for example, the following patents) See literature). In the conventional air-fuel ratio control method, it is determined whether the output of the rear O ₂ sensor is rich or lean, and the correction amount FACF is calculated according to the determination result. The correction amount FACF serves to maintain the air-fuel ratio in the catalyst within the window by displacing the control center in the air-fuel ratio feedback control referring to the output of the front O ₂ sensor to the lean side or the rich side.

Recently, the OSC (oxygen storage capacity) of the catalyst tends to increase in response to the stricter exhaust gas regulations. If the OSC is large, even if the air-fuel ratio fluctuates upstream of the catalyst, the output signal of the rear O ₂ sensor does not change immediately. Therefore, when the output of the rear O ₂ sensor shows a transition from lean to rich, the oxygen in the catalyst is already insufficient, and the purification efficiency of HC and CO is reduced, and these emissions are increased. There was a thing.
Japanese Patent No. 2790896 Japanese Patent No. 2912478 JP 2007-187119 A

  The present invention, which has been made in view of the above problems, is intended to further reduce HC and CO emissions.

In the present invention, the front O ₂ sensor provided upstream of the exhaust gas purifying catalyst mounted in the exhaust passage of the internal combustion engine, the rear O ₂ sensor provided downstream of the catalyst, and the output of the rear O ₂ sensor A correction amount calculating unit that determines whether the sensor output is rich or lean by comparing with a predetermined determination value, and calculates a correction amount for displacing the control center of the air-fuel ratio according to the determination result; The direction in which the control center is displaced to the lean side when the output of the rear O ₂ sensor is compared with the threshold value on the rich side with respect to the determination value and the sensor output has reached the threshold value. An air-fuel ratio control device is provided that includes a correction amount adjustment unit that adjusts to and from the air-fuel ratio, and an air-fuel ratio control unit that performs feedback control of the air-fuel ratio based on the output of the front O ₂ sensor and the correction amount.

As is well known, the O ₂ sensor outputs a voltage signal corresponding to the oxygen concentration in the exhaust gas. The output characteristic of the O ₂ sensor shows a steep slope with a large output change rate with respect to the air-fuel ratio in the window range, and gradually approaches a low saturation value in a lean region where the air-fuel ratio is larger than that, and a rich region where the air-fuel ratio is small Now draw a non-linear Z-characteristic curve that is asymptotic to the high-order saturation value.

Then, when the output of the rear O ₂ sensor is examined in detail, in a situation where the air-fuel ratio rich state continues and the amount of HC and CO emissions increases due to insufficient oxygen in the catalyst, the rear O ₂ sensor It was confirmed that the output showed a high overshoot value. By utilizing this fact, in the present invention, when the output of the rear O ₂ sensor reaches a threshold value that is higher than the rich / lean judgment value, the correction amount is adjusted and the control center of the air-fuel ratio feedback control is immediately set. Shifted to the lean side. Accordingly, it is possible to suppress a decrease in the purification efficiency of HC and CO, and it is possible to avoid a temporary increase in HC and CO emissions particularly when the catalyst OSC is large.

  According to the present invention, HC and CO emissions can be further reduced.

  An embodiment of the present invention will be described with reference to the drawings. An internal combustion engine 100 schematically showing the configuration of one cylinder in FIG. 1 is mounted on, for example, an automobile. The intake system 1 of the internal combustion engine 100 is provided with a throttle valve 11 that opens and closes according to the amount of depression of an accelerator pedal (not shown), and an intake manifold 12 that integrally has a surge tank 13 downstream of the throttle valve 11. Is attached. A spark plug 8 is provided at the ceiling of the combustion chamber 21 formed at the top of the cylinder 2, and a fuel injection valve 3 is provided at the end of the intake manifold 12 on the intake port side.

An exhaust manifold 51 is attached to the exhaust system 5 of the internal combustion engine 100, and a three-way catalyst 52 for exhaust gas purification is attached. A front O ₂ sensor 53 is provided upstream of the catalyst 52 and a rear O ₂ sensor 54 is provided downstream. These O ₂ sensors 53 and 54 output a voltage signal corresponding to the oxygen concentration in the exhaust gas by reacting in contact with the exhaust gas.

  The intake system 1 and the exhaust system 5 are connected via an EGR (exhaust gas recirculation) device 6. The EGR device 6 includes an EGR passage 61 having a start end communicating with the exhaust manifold 51 and a terminal end communicating with the surge tank 13, and an external EGR valve 62 provided on the EGR passage 61.

An ECU (electronic control unit) 4 that controls operation of the internal combustion engine 100 is a microcomputer system having a central processing unit 41, a storage unit 42, an input interface 43, an output interface 44, and the like. The input interface 43 includes an intake negative pressure signal a output from a pressure sensor 71 that detects intake negative pressure, a rotation speed signal b output from a rotation speed sensor 72 that detects engine rotation speed, and a vehicle speed sensor that detects vehicle speed. 73, a vehicle speed signal c output from the idle switch 74, an IDL signal d output from the idle switch 74, a water temperature signal f output from the water temperature sensor 76 for detecting the cooling water temperature, and a knocking sensor 75 for detecting the knocking state based on a change in combustion pressure. From the timing sensor 93 at the end of the intake camshaft 91, the cylinder discrimination signal g from the timing sensor 93 at the end of the intake camshaft 91, and 240 ° CA from the timing sensor 94 at the end of the exhaust camshaft 92. (Crank angle) Exhaust cam signal h output at each rotation, output from front O ₂ sensor 53 The upstream air-fuel ratio signal i and the downstream air-fuel ratio signal j output from the rear O ₂ sensor 54 are input.

  From the output interface 44, a fuel injection signal n is output to the fuel injection valve 3, an ignition signal m is output to the spark plug 8, a valve opening signal o is output to the EGR valve 62, and the like.

  The central processing unit 41 interprets and executes a program stored in advance in the storage device 42, thereby executing combustion injection control, EGR control, and the like of the internal combustion engine 100. That is, various information a, b, c, d, e, f, g, h, i, and j necessary for operation control of the internal combustion engine 100 are acquired through the input interface 43, and control input is based on them. The fuel injection amount, the ignition timing, the opening degree of the EGR valve 62, and the like are calculated, and control signals m, n, and o corresponding to the control input are applied via the output interface 44.

  The air-fuel ratio control will be described in detail. In the present embodiment, the ECU 4 operates the hardware resources according to a program, and exhibits functions as the air-fuel ratio control unit 401, the correction amount calculation unit 402, and the correction amount adjustment unit 403 shown in FIG.

  The air-fuel ratio control unit 401 controls the air-fuel ratio of the air-fuel mixture. Specifically, first, the basic injection amount TP is determined by calculating the intake air amount from the intake negative pressure signal a, the rotation speed signal b, and the like. Next, the basic injection amount TP is corrected with a feedback correction coefficient FAF determined according to the upstream air-fuel ratio signal i, and various correction coefficients K determined according to the state of the internal combustion engine 100 and invalid injection of the fuel injection valve 3. The final fuel injection time (energization time for the fuel injection valve 3) T is calculated in consideration of the time TAUV. The fuel injection time T is T = TP × FAF × K + TAUV. Accordingly, the signal n is input to the fuel injection valve 3 for the fuel injection time T, the fuel injection valve 3 is opened, and fuel is injected into the intake system 1.

The feedback control with reference to the upstream air-fuel ratio signal i by the air-fuel ratio control unit 401 is performed, for example, when the cooling water temperature is equal to or higher than a predetermined temperature, the fuel is not being cut, the power is not being increased, and a predetermined time has elapsed from the start of the internal combustion engine 100. This is performed when all the conditions such as the elapse of time and the front O ₂ sensor 53 being active and the pressure sensor 71 being normal are satisfied.

As shown in FIG. 3, the air-fuel ratio control unit 401 compares the output voltage i of the front O ₂ sensor 53 with a predetermined determination value, and determines that it is rich if it is higher than the determination value and lean if it is lower than the determination value. To do. When the sensor output i 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 i 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. 4 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 is extended and the lean determination delay time TDL 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 correction amount calculation unit 402 calculates the control center correction amount FACF. In the feedback control with reference to the downstream air-fuel ratio signal j by the correction amount calculation unit 402, for example, the cooling water temperature is equal to or higher than a predetermined temperature, and a predetermined time elapses from the start of the air-fuel ratio feedback control by the air-fuel ratio control unit 401. ₂ All the conditions such as the predetermined time has elapsed since the sensor 53 was activated, the fuel correction amount in the transition period is less than the predetermined value, the vehicle speed is 0 in the idling state, or in the predetermined operating range in the non-idling state, etc. Performed if established.

As shown in FIG. 5, the correction amount calculation unit 402 compares the output voltage j of the rear O ₂ sensor 54 with a predetermined determination value, and determines that it is rich if it is higher than the determination value and lean if it is lower than the determination value. To do. While the sensor output j is rich, the control center correction amount FACF is gradually decreased by the lean integral value FACFKIM per predetermined time. As already described, as the correction amount FACF decreases, the control center of the air-fuel ratio feedback control moves toward lean.

  Conversely, while the sensor output j 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 control center of the air-fuel ratio feedback control becomes richer.

After that, the correction amount adjusting unit 403 compares the output voltage j of the rear O ₂ sensor 54 with a threshold value higher than the determination value, and when the sensor output j has reached the threshold value, the control center correction amount. The control center of the air-fuel ratio feedback control is shifted to the lean side by adjusting the FACF.

As shown in FIG. 5, in a situation where the air-fuel ratio rich state continues and the amount of HC and CO emissions increases due to insufficient oxygen in the catalyst 52, the output j of the rear O ₂ sensor 54 overshoots. High value. The output voltage value exceeds the lean / rich determination value (0.7 V in the illustrated example). In such a situation, in the present embodiment, the control center correction amount FACF is subtracted by the subtraction value FACFOFM. The subtraction value FACFOFM increases or decreases in accordance with the output j of the rear O ₂ sensor 54. Specifically, as the output voltage j increases, the subtraction value FACFOFM increases, and therefore the control center correction amount FACF decreases. When the output voltage j is lower than the threshold value (0.8 V in the illustrated example), the subtraction value FACFOFM becomes zero.

  In FIG. 5, the solid line indicates the case where the correction amount FACF is reduced, and the broken line indicates the case where the correction amount FACF is not reduced. Compared to the latter, the former emits less HC and CO.

FIG. 6 shows a procedure for calculating the control center correction amount FACF. The ECU 4 determines whether the output j of the rear O ₂ sensor 54 is rich or lean (step S1). If the output j is rich, the ECU 4 subtracts the correction amount FACF by the lean integral value FACFKIM (step S2). If there is, the correction amount FACF is added by the rich integral value FACFKIP (step S3). Further, if the output j of the rear O ₂ sensor 54 exceeds the threshold value (step S4), a subtraction value FACFOFM corresponding to the output value j is determined (step S5), and the correction amount FACF is subtracted from the subtraction value. Only FACFOFM is subtracted (step S6). The ECU 4 repeatedly executes the above steps S1 to S6.

According to this embodiment, the front O ₂ sensor 53 provided upstream of the catalyst 52 mounted in the exhaust passage 5 of the internal combustion engine 100, the rear O ₂ sensor 54 provided downstream of the catalyst 52, and the rear O ₂ The output j of the sensor 54 is compared with a predetermined determination value to determine whether the sensor output j is rich or lean, and the correction amount FACF for displacing the control center of the air-fuel ratio according to the determination result When the sensor output j has reached the threshold value, the correction amount calculation unit 402 for calculating the output j and the output j of the rear O ₂ sensor 54 are compared with a threshold value on the richer side than the determination value. A correction amount adjusting unit 403 that adjusts the amount FACF in a direction in which the control center is displaced toward the lean side, and an air-fuel ratio feedback control based on the output i of the front O ₂ sensor 53 and the correction amount FACF. Since the air-fuel ratio control device including the air-fuel ratio control unit 401 is configured, the problem of delay in the change of the output j of the rear O ₂ sensor 54 accompanying the increase in the OSC of the catalyst 52 can be effectively avoided. And contribute to the reduction of CO emissions. If the OSC of the catalyst 52 is increased, the robustness against the vertical movement of the air-fuel ratio of the air-fuel mixture is improved accordingly, and the exhaust gas purification efficiency can be kept high.

The present invention is not limited to the embodiment described in detail above. For example, in the above embodiment, when the output voltage j of the rear O ₂ sensor 54 becomes richer than a predetermined threshold, the control center correction amount FACF (and thus the delay times TDR and TDN) is adjusted. In addition, it is also conceivable to shift the feedback control center to the lean side by adjusting the rich integral KIP and / or the lean integral KIM. It is also conceivable to shift the feedback control center to the lean side by adjusting the skip value RSP and / or RSM.

  In addition, the specific configuration of each unit, the processing procedure, and the like can be variously modified without departing from the spirit of the present invention.

The figure which shows the hardware resource structure of the air fuel ratio control apparatus of one Embodiment of this invention. The block diagram of the air fuel ratio control apparatus of the embodiment. 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 flowchart which shows the procedure of the process which ECU performs.

Explanation of symbols

401 ... air-fuel ratio control unit 402 ... correction amount calculating unit 403 ... correction amount adjustment part 53 ... front O ₂ sensor 54 ... rear O ₂ sensor

Claims (1)

A front O ₂ sensor provided upstream of an exhaust gas purifying catalyst mounted in an exhaust passage of the internal combustion engine;
A rear O ₂ sensor provided downstream of the catalyst;
The output of the rear O ₂ sensor is compared with a predetermined determination value to determine whether the sensor output is rich or lean, and a correction amount for displacing the control center of the air-fuel ratio is determined according to the determination result. A correction amount calculation unit for calculating,
The output of the rear O ₂ sensor is compared with a threshold value on the richer side than the determination value, and when the sensor output reaches the threshold value, the correction amount is shifted in a direction in which the control center is displaced to the lean side. A correction amount adjustment unit to adjust,
An air-fuel ratio control device comprising an air-fuel ratio control unit that performs air-fuel ratio feedback control based on the output of the front O ₂ sensor and the correction amount.

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