JPH01271633A - Device for controlling air-fuel ratio of engine - Google Patents

Abstract

PURPOSE:To find out the deterioration of air-fuel ratio sensors earlier by comparing the output changes of two or more air-fuel ratio sensors provided on each cylinder group and judging the relative deterioration between the sensors. CONSTITUTION:An air-fuel ratio sensor is provided on the exhaust system of each of cylinder groups which are divided into at least two or more groups of a multicylinder engine, e.g., the right-left bank cylinder groups of a V-engine to carry out the feedback control of the air-fuel ratio of a mixture fed into each group by feedback means based on the output thereof. Also, by comparing the output changes of the two or more air-fuel ratio sensors provided on each cylinder group with a judging means to judge the relative deterioration between the sensors from the compared result. Thereby, the deterioration of air-fuel ratio sensors can be found out earlier.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention is directed to an engine having at least two or more air-fuel ratio control systems, in which deterioration of any one of the air-fuel ratio sensors can be detected at an early stage. The present invention relates to an air-fuel ratio control device.

(Prior Art) Air-fuel ratio sensors are prone to deterioration. Conventional sensor deterioration determination methods include, for example, a method of passing a predetermined current through the sensor and measuring the output voltage at that time, a method of detecting when the sensor output no longer falls below a predetermined slice level, and a feedback method. There are methods for detecting that the control cycle has become extremely long.

Conventionally, especially in V-type engines, the exhaust system was divided into two banks (left and right), and an oxygen sensor was installed in the exhaust system of each bank, and the output of each of these two sensors was Based on this, there is a technique (Japanese Unexamined Patent Publication No. 60-190630) that performs feedback control of the air-fuel ratio independently for both banks.

This is why two sensors have to be installed, especially in V-type engines. The exhaust pipes have to be grouped together at a location far from the exhaust manifold.On the other hand, in order to perform accurate feedback control using the oxygen sensor, it is preferable to locate the oxygen sensor close to the exhaust manifold. This is because there will always be problems if oxygen sensors are provided separately for the left and right banks.

(Problems to be Solved by the Invention) The conventional sensor deterioration determination methods described above either cannot detect deterioration until the sensor has completely deteriorated or require a special independent deterioration diagnosis device. Because there are
Early detection of deterioration is impossible and leads to increased costs.

Further, if two oxygen sensors are provided as in the above-mentioned Japanese Patent Application Publication No. 2003-120000, the probability of failure is doubled. Furthermore, even if only one of the cylinders fails, a torque difference will occur between the cylinder groups, causing vehicle body vibration.

Therefore, it is important to detect the deterioration of the air-fuel ratio sensor as early as possible at a low cost.The present invention was made against this background, and is intended for use in engines that have two or more air-fuel ratio feedback control systems. Focusing on the fact that it is possible to mutually monitor the output of air-fuel ratio sensors,
The aim is to detect sensor deterioration early.

(Means and operations for solving the problems) The configuration of the present invention for achieving the above-mentioned problems is as shown in FIG. an air-fuel ratio sensor that is disposed in each exhaust system and outputs a signal related to the air-fuel ratio, and for each cylinder group, based on the output of the sensor of that group,
By comparing output changes of two or more air-fuel ratio sensors arranged for each cylinder group with a feedback control means that feedback-controls the air-fuel ratio of the air-fuel mixture supplied to the cylinders of the group to a target value, The present invention is characterized by comprising a determining means for determining relative deterioration between the sensors.

(Example) An example in which the present invention is applied to a six-cylinder V-type engine will be described below with reference to the accompanying drawings.

<Overview of Example System> As shown in FIG. 2, the engine 10 includes an air filter 12 that filters intake air.
The air filtered by 2 passes through the intake pipe 14, passes through the intake valves 16a and 16b, and enters the cylinders 1 arranged in a figure 7 shape.
8a, 18b. In addition, in this FIG. 2, other four cylinders are arranged on the opposite side of the drawing, but are not shown. Also, each of the six cylinders, the first cylinder ~
If it is the 6th cylinder, the 1st cylinder is 18a and the 2nd cylinder is 18a.
8b, the cylinder 18a and the two cylinders on the opposite side form a left bank cylinder, and the cylinder 18b and the two cylinders on the opposite side form a right bank cylinder.

The upstream side of the intake pipe 14 has a flow rate (
An air flow meter 20 for measuring the temperature (Q,) and an intake air temperature sensor 22 for measuring the temperature (T, ) of the intake air are attached.

The middle part of this intake pipe 14 is connected to each left and right bank.
The passage is divided into two passages, and each divided passage is provided with a throttle valve 24a, 24b. An opening sensor 27 is attached to one throttle valve 24a to detect its opening (TVO). In addition, the intake pipes 1 on the upstream and downstream sides of the throttle valves 24a and 24b
A bypass pipe 26 is connected to the intake pipe 14 in a state where the portion 4 is bypassed. An idle speed control valve 28 is attached to a midway portion of the bypass pipe 26. When there is A/C operation, power steering operation, heater operation, etc., the on/off operation of this SC valve 28 is controlled according to the load according to the signal ISO, and the air flow m of the bypass pipe 26 passing through the ISC valve 28 is controlled. <bypass air amount) will be controlled.

Further, the downstream side of the intake pipe 14 is branched and connected to cylinders 18a, 18b, etc. belonging to the left and right banks, and each branched connection pipe has a fuel injection valve 34a, 34b that supplies fuel into the corresponding cylinder. is installed. For each of the fuel injection valves 34a and 34b, a fuel injection pulse (τ^, τS) width is defined by an engine control unit (hereinafter referred to as ECU) 36, which will be described later. The subscript "A" refers to the signal related to the left bank system, and "B"
indicates a signal related to the right bank system.

Inside the left and right cylinders 18a and 18b, a piston 32a is provided.
, 32b are slidably disposed.

By sliding and reciprocating within the cylinders 18a and 18b, each piston rotates the crankshaft to which it is connected. Although not shown, spark plugs are provided at the tops of the cylinders 18a and 18b to combust the fuel injected therein. Further, each cylinder 18a, 18b is provided with a cooling water passage 40a, 40b for cooling each cylinder, and the temperature of the cooling water passing through the cooling water passage is adjusted to the engine temperature (T, ) A water temperature sensor 42 is attached to detect the water temperature.

On the other hand, the fuel burned in each cylinder 18a, 18b is passed through the corresponding exhaust valve 44a, 44b as exhaust gas to the exhaust manifold 46a, 46b, and then to the exhaust pipe 48.
a, 48b. This exhaust pipe 48a, 4
Catalytic converters 50a and 50b for purifying exhaust gas are provided in the middle of 8b.

As in the case of the intake pipe, in order to suppress mutual interference of exhaust gas, the exhaust manifold 46a from the cylinder 18a of the left bank and the exhaust manifold 46c from the remaining two cylinders of the left bank (from the other one cylinder) (exhaust manifold not shown) are combined into one exhaust pipe 48a,
The exhaust manifold 46b of the right bank cylinder 18b and the exhaust pipe 46d from the remaining right bank cylinders (the exhaust manifold of the other cylinder is not shown) are combined into one exhaust pipe 48b. 02 sensors 52a, 52b are attached to the exhaust pipes 48a, 48b to measure the oxygen concentration (o2) remaining in the exhaust gas passing through the exhaust gas at a position as close as possible to the above-mentioned merging point. The oxygen concentration output signals from these sensors 52a and 52b are respectively
Let E^, Ea.

53a and 53b are catalytic converters 50a and 50b, respectively.
The air-fuel ratio control of the left bank (cylinder 18a, etc.) is performed based on the output EA from the oxygen sensor 52a, which is a temperature sensor (output is TAc, Tac), and the air-fuel ratio control is performed based on the output E from the oxygen sensor 52b. , the air-fuel ratio control of the right bank (cylinder 18b, etc.) is performed independently between each bank.

25 is a fuel tank. The fuel gas components evaporated within this tank are trapped in the canister 19. This trapped gas is controlled by the signal PC from the ECU 36.
By opening the solenoid valve 17, the pipe 15a
, 15b, and is supplied to the left and right banks. As will be described later, the ECU 36 can detect the start and end of vaporized fuel supply by monitoring this signal PC.

FIG. 3 shows the signals input to the ECU 36 and the signals input to the ECU 36.
This is a collection of signals output from. Although not shown in FIG. 1, as shown in FIG. 3, a signal GP, which is a signal from a transmission (not shown) and indicates the current gear position;
A signal I that is a signal from a switch provided in the throttle opening sensor 27 and indicates that it is in an idle state.
DLE, and a signal N indicating the engine speed from the distributor etc. are also input to the ECU 36.

<Control in Example> With reference to FIGS. 4A and 4B, the principle of the method for detecting sensor deterioration in this example will be explained using two methods.

The method shown in Figure 4A calculates the reversal time (T) of the voltage outputs (E^, EB) of the left and right air-fuel ratio sensors, respectively.
M A , T M a ) are determined and the deterioration of the sensor is determined by comparing them. For example, if TH is a predetermined threshold, if the absolute value of the difference in reversal time is 1'r M AT M a l > T Hr, it is determined that deterioration has occurred, and the one with the larger reversal time is It is determined that the sensor has deteriorated significantly.

The method shown in FIG. 4B is based on each sensor output (EA).

E,) for the peak-to-peak voltage difference (PPA.

PP, ), and the absolute value of the difference between these ppA and ppa is IPPA PP! If II>TH2, it is determined that deterioration has occurred, and the deterioration of the larger sensor is determined to be greater.

Next, details of the air-fuel ratio control of this embodiment will be explained according to the flowcharts shown in FIGS. 5A, 5B, 6A, and 6B. FIG. 5A and FIG. 5B are flowcharts showing the entire air-fuel ratio control. Also, Figure 6A,
Each of the diagrams in B is a sensor deterioration determination subroutine that is incorporated as a part of the air-fuel ratio control. It should be noted that the control shown in Fig. 6A is the fourth
In FIG. A, the control in FIG. 6B corresponds to that in FIG. 4B.

In the air-fuel ratio control of this embodiment, as will be described later, in the feedback control zone, the air-fuel ratio correction coefficient CAFII, Care by feedback control is integrated according to the outputs (EA, Ea) of the air-fuel ratio sensors (52a, 52b). Get based on control.

The final fuel injection amount for both banks (A+T:l is determined by the following formula. In the feedback control region, = τo (1+ CAre + Co) τB
:to (1+C5ra+Co), and if it is outside the feedback control region, τ,=τ. (1
+Co) teb=de. (1+Co), and 00 in the above equation is the intake air temperature Tab
Engine temperature, etc. is a coefficient for correction based on

In FIG. 5A, in step S2, the intake air amount Q1
1%Enter the engine speed N. In step S4,
Basic fuel injection amount based on engine speed N and intake air amount Q. Calculate.

In step S6, the signal IDLE and gear position signal GP are input. In step S8, the intake air temperature T, the engine temperature Tw, the catalytic converter temperature (TAC, TBC
), read the sensor output (EA, El). Step S
10, intake air temperature Ta% engine temperature, etc.

A correction coefficient 00 based on the calculation is calculated. In step S12, it is determined whether the current driving state is in the feedback region. This determination is made based on the engine rotation speed N and the like. If it is not in this area, the process proceeds to step 834 and subsequent steps.

If it is in the feedback zone, proceed to step 314 and subsequent steps.

Steps S14 to 318 are based on the current output EA of the air-fuel ratio sensor 52a in the left bank system.
(2) Determine the correction coefficient 0AFB for controlling (integral control). That is, if EA=1, then CArB=CAFII-ΔE.

And if E^≠1, then CAFIS = CAF6+△■^ It is. ΔIA is a constant for integral control.

Through steps S20 to S24, 08F11 is also determined for the right bank system.

In step S26, it is determined whether a condition (i.e., self-diagnosis period) is currently present under which it is possible to determine whether the air-fuel ratio sensor has deteriorated. As shown in FIG. 7, the self-diagnosis period refers to at least a period in which a certain period of time (to) has elapsed since the start of feedback control. This is because in order for the air-fuel ratio sensor to be activated, exhaust gas at a certain temperature needs to pass through the sensor for a predetermined period of time or longer. And further, step S
The self-diagnosis period in 26 refers to the intermittent timing (every tz) period 1+ after the above-mentioned certain period of time has elapsed.The reason why it is made intermittent is because there is no need to constantly perform such deterioration judgments. , in order to reduce the load on the ECU. Furthermore, the time width of the period t1 requires at least one period or more of feedback control in order to calculate the reversal time.

If it is in the self-diagnosis period, the process advances to step S30 and a self-diagnosis subroutine is executed. In step S32,
Output the result of this subroutine. As a result of this deterioration diagnosis, in the subroutine of step S30, a flag FAD indicating that the left bank system sensor has deteriorated;
Flag p indicating that the right bank sensor has deteriorated
It is stored in aD. Then, the output of the result of step S32 is, for example, displayed on a display (not shown), or in feedback control, the feedback control of the degraded bank is not performed.

First, the details of step S30 will be explained with reference to FIG. 6A in the case of deterioration determination according to the method of FIG. 4A.

In step S50, it is determined whether the sensor output EA of the left bank crosses the slice voltage E0 in a gradually increasing direction. If it does not cross, in step S56, a counter t^ which is a coefficient of one reversal time width is incremented.

t^==tA+1 This counter ta was cleared in step S54 when the sensor output EA crossed Eo last time, so next time when the sensor output EA crossed Eo last time, this counter ta In ^, the inversion time width is accumulated. Therefore, in step S51, it is determined how many times the sensor output EA is at the slice level E within the self-diagnosis timing period tl.
A counter na that accumulates whether o has been crossed is updated.

Then, in step S52, this one inversion time width is accumulated in the register TM^. That is, this register TMA has accumulated nA times of inversion time width data.

The control in steps S58 to S64 is to measure the cumulative value TM in the right bank system.

Step S66 determines whether the self-diagnosis period t1 has elapsed. If it has not yet elapsed, return to the original state and continue feedback control. In this way, the reversal time is measured several times within the period ti, and the result is T M
A, TM e is accumulated.

In step 366, if time period t1 has elapsed, step 868. In step S70, the average reversal time is determined. That is, Step S72. In step S74, if the difference in average reversal time is TM A - T M e > T Hl, it is determined that deterioration has occurred in the right bank sensor 52b, and
The result is stored in flag Fso. Step S76,
In step 378, if the difference in reversal time is TMs - TM A > THr, it is determined that deterioration has occurred in the left bank system sensor 52b, and
The result is stored in flag FAII. Step SSO
, in step S82, for the next self-diagnosis period, n
AITMA, etc. are cleared.The reason why the reversal time is calculated n^ times in the above control is to reduce measurement errors.

In this way, sensor deterioration can be determined based on the difference in reversal time between both sensors. This is because if the sensor deteriorates, it will no longer be able to respond sensitively to changes in the air-fuel ratio in the exhaust gas.
This is because, as a result, the feedback control period gradually becomes longer.

Next, the details of step S30 will be explained with reference to FIG. 6B regarding the deterioration determination according to the method of FIG. 4B. Note that the control shown in FIG. 6A above recognizes the reversal of the sensor output, and
- times of reversal times were measured na times (or na times). - On the other hand, the method of determining the maximum contact width of the sensor output according to FIG. Maximum output value (E□□,
EBIJAX) and minimum value (E AMINI E BMI
N).

First, step S90. In step S92, the maximum value register E AMAX of the left bank system and the current sensor output E
Compare with A, and if EA is large, update E mouth ^×. Similarly, step S94. In step S96,
Update EAMIN.

In steps 398 to 5104, in the right bank system, E BMAXI E! Update IMIN.

In step 5105, it is determined whether the self-diagnosis period tl has elapsed. If the elapsed time has not yet elapsed, the process returns, but if the elapsed time has elapsed, the process proceeds to step 3106 and subsequent steps. Step 5106.
In step 5108, the peak-to-peak values (PPA, PPa) of the left bank system and the right bank system are calculated.

In steps 5ilo to 5116, the sensor deterioration is calculated using the PPa obtained above for each bank.

Judgment is made from the difference in P P a. In steps 311B and 5120, for the next self-diagnosis period, E
Clear AMAXI E AIIIIN etc.

In this way, the peak-to-peak value of the sensor output for each bank is determined, and sensor deterioration can be determined from the difference. This is because when the sensor deteriorates, its output value decreases.

<Modified example of deterioration determination> Example (4th example) in which deterioration determination is performed by checking the above reversal time.
In FIG. A and FIG. 6A), reversal is detected by checking whether the output EA (or Ea) crosses the slice level E0. However, if the sensor deteriorates, the output E^ (
Alternatively, since Ea) is usually accentuated, the above method results in a large error in detecting the reversal time. Therefore, the 8th
As shown in the figure, the time required to cross the voltage E0 is the reversal time TM
A (or TMe) and the output E^ (or Ea
) is above the voltage E1 is TMA. (1M6°),
If the time below El is T M Al (T M a□), more accurate determination can be made by comparing T M A, T M 60 □ and □ , TMA 'rMa or .

Further, in step S50, the sensor output crosses the slice level in the direction of gradual increase, but the reversal may be recognized by the cross in the direction of gradual decrease.

Further, in the case of the embodiment shown in FIG. 6B, the peak-to-peak value may be determined for each cycle of the sensor output.

In the embodiment described above, catalytic converters 50a and 50b were disposed in both the left and right banks, respectively.

However, as is clear from the explanation of the operation of the above-mentioned embodiment, the present invention has two
Since it is applicable as long as the air-fuel ratio is controlled independently based on the outputs of the two air-fuel ratio sensors, this is a modified example in which the exhaust pipes 48a and 48b are combined into one. It is also applicable even if there is only one catalytic converter.

Furthermore, when there are three or more cylinder groups, it is preferable to make a determination as to which group's sensor is degraded according to the principle of majority voting.

It goes without saying that this invention is not limited to the configurations of the embodiments and modified examples described above, and can be modified in various ways without departing from the gist of the invention.

(Effects of the Invention) As detailed above, according to the air-fuel ratio control device for an engine according to the present invention, feedback control of the air-fuel ratio is performed independently between different banks each having an air-fuel ratio sensor. Furthermore, since it is extremely unlikely that all the sensors have deteriorated, the relative degree of deterioration between the sensors can be determined by comparing changes in the outputs of the sensors. Furthermore, since the current sensor outputs are simply compared, there is no need to add new equipment, and cost increases can be prevented.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the configuration of the present invention; Fig. 2 is a diagram showing the configuration of an embodiment when the present invention is applied to a V-type engine; Fig. 3 is a diagram showing signals input and output to the ECU; Figure 4A,
FIG. 4B is a diagram showing the operating principle of this embodiment, FIGS. 5A and 5B are flowcharts showing the entire air-fuel ratio control according to this embodiment, and FIGS. 6A and 6B are diagrams showing the deterioration determination. Flowchart of procedures related to control, FIG. 7 is a diagram explaining a self-diagnosis period, and FIG. 8 is a diagram explaining a modification. In the figure, 10--Engine, lla, 1lb--Intake manifold, 12--Air filter, 13--Dashpot, 14--Intake pipe, 15a, 15b--
・Evaporative fuel supply pipe, 16a, 16b...Intake valve, 17
---Evaporative fuel supply control solenoid valve, 18a, 1
8b...Cylinder, 19...Canister, 20...
・Air flow meter, 22... Intake temperature sensor, 24a,
24b... Throttle valve, 25... Fuel tank, 2
6... ISO supply pipe, 27... Throttle opening sensor, 28... Idle speed control valve (I
SO valve), 32a, 32b...piston, 34a, 3
4b...Fuel injection valve, 36...Engine control unit (ECU), 40a, 40b-cooling water passage, 42...Water temperature sensor, 44a, 44b...Exhaust valve, 46a, 46b , 46 c, 46
d...exhaust manifold, 48a, 48b...exhaust pipe, 50a, 50b=catalytic converter, 53a, 53
b. "Temperature sensor, 52a, 52b" - Air-fuel ratio sensor.

Claims (1)

[Claims] (1) An air-fuel ratio sensor that is arranged in the exhaust system of each cylinder group divided into at least two groups of a multi-cylinder engine and outputs a signal related to the air-fuel ratio; feedback control means for feedback controlling the air-fuel ratio of the air-fuel mixture supplied to the cylinders of the group to a target value based on the output of the sensor of the group; and two or more air-fuel ratio sensors arranged for each cylinder group. 1. An air-fuel ratio control device for an engine, comprising: determination means for determining relative deterioration between sensors by comparing output changes of the sensors.