JPS6118661B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to an improvement in air-fuel ratio control in a fuel injection engine, in which the intake air amount of the engine is detected and the fuel injection amount is controlled based on the detected intake air amount. The present invention relates to a novel exhaust gas purification device that controls the air-fuel ratio by appropriately controlling the amount of exhaust gas recirculated based on the output signal of an exhaust sensor.

Conventionally, fuel injection engines are well known, which include an air flow meter installed upstream of the engine's intake passage and a fuel metering means that controls the fuel injection amount based on the output signal of the air flow meter.
Since the fuel injection amount can always be controlled based on the intake air amount, there is an advantage that the control of the air-fuel ratio can be made more precise.

However, a fuel injection type engine using an air flow meter has the disadvantage that the fuel injection valve itself is expensive, and the air flow meter is expensive, making the engine as a whole extremely expensive.

For this reason, conventionally, the amount of intake air is calculated by using a computer to calculate the intake air amount by combining two quantities that are easy to detect: engine speed, intake negative pressure, and throttle valve opening. A control method has been proposed in which the amount of fuel injection is controlled based on the amount of fuel injected.

In a fuel injection engine that employs such a control method, part of the exhaust gas is returned to the intake passage,
When an exhaust gas recirculation device is installed to suppress the maximum combustion temperature of the engine, exhaust gas recirculation (hereinafter referred to as
It's called EGR. ), part of the intake air is replaced by exhaust gas, and the air-fuel ratio changes towards the rich side, so it is necessary to compensate for this.

In order to compensate for the air-fuel ratio associated with this EGR, conventionally, the required EGR amount according to the operating state of the engine is calculated from various quantities such as the engine speed, using a control map stored in advance in a computer, for example. Based on this requested EGR amount, the opening degree of the EGR control valve installed in the EGR passage is controlled, and in anticipation of EGR being performed as requested by the EGR control valve, the fuel metering means is adjusted to the required EGR amount in advance. A control method was used that compensated for the air-fuel ratio by setting the corresponding fuel injection amount.

However, this control method is not suitable for actual EGR
Since it is not based on quantity, even if the opening of the EGR control valve is accurately map-controlled,
The amount of EGR required due to clogging of the EGR passage, etc.
If the amount changes, the air-fuel ratio that should have been compensated will fluctuate, resulting in the problem that correct air-fuel ratio control cannot be performed.

In order to eliminate such difficulties, actual EGR
Either directly detect the amount and correct the fuel injection amount according to this detected value, or perform feedback control based on this detected value so that the actual EGR amount always approximates the required EGR amount. but,
For this purpose, an expensive air flow meter or an EGR amount detection device for detecting the actual amount of EGR is required, and as described above, this results in problems such as an extremely high cost for the entire device.

In view of this problem, the applicant has proposed a fuel metering means that calculates the intake air amount based on a combination of two quantities among engine speed, intake negative pressure, and throttle valve opening and determines the fuel injection amount. However, the intake air amount, fuel injection amount, and actual
The air-fuel ratio determined by the EGR amount is detected by an exhaust sensor installed in the exhaust passage, and the EGR amount is always controlled appropriately based on the output of the exhaust sensor, that is, feedback control is performed to obtain an EGR amount that approximates the required EGR amount. We have already proposed an exhaust gas purification device for fuel-injected engines based on a new technical idea that maintains the air-fuel ratio at an optimal value through this process.

In other words, this proposed device uses an exhaust sensor that can accurately detect the richness and leanness of the air-fuel ratio, and uses the exhaust sensor to detect changes in the air-fuel ratio over time due to EGR. By inputting the output signal of the sensor as information to the computer and controlling the EGR control valve based on this information, the EGS amount is increased or decreased according to the deviation between the actual air-fuel ratio and the set air-fuel ratio. The basic feature is that the air-fuel ratio is controlled to the set air-fuel ratio by performing EGR.

The present invention has been made in connection with such a new technical idea, and as a measure for engine drivability, it is necessary to eliminate or suppress the amount of EGS in a specific operating range of the engine, that is, in the engine cold engine. At low loads, including when the engine is idling, and at high loads when the engine requires high output, the air-fuel ratio set by the fuel metering means,
By setting the air-fuel ratio in advance to be rich compared to the air-fuel ratio in operating ranges other than the specified operating range, the air-fuel ratio can be adjusted to the optimum value (set air-fuel ratio) with no or very small amount of EGR. ), and when the actual air-fuel ratio monitored by the exhaust sensor deviates from the set air-fuel ratio, the deviation is immediately compensated for by a small amount of EGR, while the In driving ranges other than
The air-fuel ratio is set to be lean by the fuel metering means, and a large amount of EGR is used to compensate the air-fuel ratio so that it becomes the set air-fuel ratio, and at the same time, to effectively control NOx, which can be generated in large amounts in this operating range. The present invention aims to provide an exhaust gas purification device for a fuel injection type engine.

Hereinafter, the present invention will be described in more detail based on illustrated embodiments.

In Fig. 1, 1 is an engine, 2 is an air cleaner, 3 is an intake passage of the engine 1, 4 is a throttle valve interposed in the middle of the intake passage 3, and 5 is a fuel injection nozzle whose tip faces the intake passage 3. , 6 is an exhaust passage of the engine 1, 7 is a catalyst that purifies exhaust gas flowing down the exhaust passage 6 by a catalytic reaction,
Reference numeral 8 denotes an EGR passage for recirculating exhaust gas taken out from upstream of the catalyst 7 in the exhaust passage 6 to the intake passage 3, preferably downstream of the throttle valve 4. Reference numeral 9 denotes a diaphragm interposed in the EGR passage 8 to control the amount of EGR. EGR valve 10 is a negative pressure outlet 11 opened downstream of the throttle valve 4 in the intake passage 3.
A negative pressure introduction passage 12 is interposed in the middle of the negative pressure introduction passage 10 and communicates with the negative pressure introduction passage 10 to introduce the intake negative pressure downstream of the throttle valve 4 into the negative pressure chamber 9a of the EGR valve 9. A three-way valve that controls the opening degree of the EGR valve 9 by reciprocally opening and closing the upstream port 12a and the atmosphere port 12b communicating with the atmosphere introduction passage 13, and diluting the intake negative pressure introduced into the negative pressure chamber 9a with the atmosphere. It is a solenoid valve.

More specifically, the fuel injection amount of the fuel injection nozzle 5 is determined by its valve opening time and the duty ratio (a certain time interval t) as a control signal for the three-way solenoid valve 12.
between the upstream port 1 of the three-way solenoid valve 12
When the time during which 2a is closed is τ, it is expressed as (τ/t)×100(%). ) is controlled by a microcomputer 14.

The data given as input data to this microcomputer 14 is as follows.

Throttle valve opening degree...Given as an output signal of the throttle sensor 15 that detects the rotation angle of the rotation shaft of the throttle valve 4.

Intake negative pressure V... Intake passage 3 downstream of throttle valve 4
It is given as an output signal of an intake negative pressure sensor 16 provided facing the air.

Cooling water temperature T...Cooling water passage of engine 1 (not shown)
It is given as an output signal of a water temperature sensor 17 provided facing the water temperature.

Engine rotation speed N... is given as an output signal of a rotation speed sensor 18 interlocked with the output shaft (not shown) of the engine 1.

Air-fuel ratio signal A/F...With the output signal of the exhaust sensor 19 (O ₂ sensor) provided with the detection part facing the exhaust passage 6 as one input, the stoichiometric air-fuel ratio is determined as a preset air-fuel ratio, for example. is given as the output of the comparator circuit 20 which compares it with a threshold value corresponding to .

As shown in Figure 2, the microcomputer 1
4 is a central processing unit 22 (CPU), a memory 23,
Analog-to-digital converter 24 (A/D converter), analog multiplexer 25, input interface circuit 26, output interface circuit 2
7, which are connected to each other by a control bus 28, and have a well-known configuration in which an address/data bus 29 exchanges address signals and data signals.

Among the above input data, V, T, N, and A/F, the intake negative pressure V, cooling water temperature T, and engine speed N are input to the analog multiplexer 25, and are read out as necessary. After being digitally converted by the converter 24, it is sent to the central processing unit 22. The remaining input data, that is, the throttle valve opening and the air-fuel ratio signal A/F, are input to the input interface circuit 26, and are sent to the central processing unit 22 as necessary.
is loaded into.

In FIG. 2, reference numeral 30 denotes a set voltage generation circuit for setting a threshold value V _th for the output signal of the exhaust sensor 19 for the comparator circuit 20.
As shown in FIG. 3, depending on whether the output signal of the exhaust sensor 19 is larger or smaller than the threshold value _Vth , it is determined whether the air-fuel ratio is richer or leaner than the stoichiometric air-fuel ratio (14.7). lean or not), and outputs the determination signal to the computer 14 as an air-fuel ratio signal A/F.

Next, the fuel injection nozzle 5 and the three-way solenoid valve 12 configured by the microcomputer 14 are
The control process of the control circuit will be explained based on the flowchart of FIG.

The microcomputer 1, which has been initialized in advance in step by a start signal,
4 repeats the following control process at a predetermined cycle time.

First, in a step, the output signal of the rotation speed sensor 18 is read, and in a step, the engine rotation speed N is read.
is stored at a predetermined address in the first memory area _M1 of the memory 23. Thereafter, each output signal is read in the order of intake negative pressure sensor 16 and water temperature sensor 17, and intake negative pressure V and cooling water temperature T are similarly memorized (step ~).

Next, in the step, from the memorized rotational speed N and intake negative pressure V, the memory as shown in FIG.
Using Map1, a reference pulse width _L0 , which is a reference for the injection pulse applied to the fuel injection nozzle 5, is calculated.

The above memory Map1 has a variation range of intake negative pressure of 8
Each grid point ai, j is given as the intersection of the row line that divides the rotation speed range into 8 equal parts and the column line that divides the rotation speed range into 8 equal parts.
, calculate in advance the fuel injection amount, that is, the injection pulse width L ₀ corresponding to the intake air amount determined from the intake negative pressure V and rotation speed N specified by the grid points ai and j, and calculate that value. It is something that has been memorized,
As shown in area A in Figure 5, in specific operating areas where EGR deteriorates drivability, namely when the engine is cold, at low loads including idling, and at high loads, the injection pulse width L ₀ is reduced to zero. The fuel ratio is reset in advance so that it is rich, and in other regions, that is, the engine medium load operating range B, the air-fuel ratio is lean set so that it is lean. That is, in a specific operating range A where EGR needs to be cut or suppressed to a very small amount, the air-fuel ratio set by the microcomputer 14 is preset to a value equal to or slightly larger than the stoichiometric air-fuel ratio. By doing so, even when the actual air-fuel ratio monitored by the exhaust sensor 19 deviates from the stoichiometric air-fuel ratio, the air-fuel ratio can be corrected to the stoichiometric air-fuel ratio even with a very small amount of EGR. There is.

In addition, in medium load region B, where it is necessary to sufficiently suppress NOx that can be generated in large quantities,
In order to ensure that the actual air-fuel ratio reaches the stoichiometric air-fuel ratio only when EGR is performed, a lean set is performed in advance to ensure a large and necessary amount of EGR.

Now, the point P specified by the intake negative pressure V and the rotation speed N read out by the central processing unit 22 is
As shown in FIG. 5, if the grid points ai,j do not match, a total of four grid points ai _-1 , J surrounding the point P
Based on each reference pulse width L ₀ of ai _-1 , j _-1 , ai, j _-1 , ai, j, the reference pulse width L ₀ corresponding to point P
(P) is calculated by interpolation calculation.

This calculated reference pulse width L ₀ (P) is stored in the first memory area M ₁ of the memory 23 at a predetermined address in a step. Next, in the step, the stored water temperature T is read out, and the correction coefficient K(T) at the water temperature T with respect to the reference pulse width L ₀ (P) is calculated using the memory Map 2 shown in FIG. 6, and in the step, The calculated correction coefficient K(T) is multiplied by the reference pulse width L ₀ (P) to obtain the injection pulse width L (=L ₀ (P)×K(T)) actually applied to the fuel injection nozzle 5. This injection pulse width L is set in the first memory area of the memory 23.
It is temporarily stored at a predetermined address in _M1 (step).

After completing the calculation of the injection pulse width L, the microcomputer 14 starts calculating the duty ratio D for the three-way solenoid valve 12.

For this purpose, first, in step 1, the signal from the throttle sensor 15 is read and the throttle valve opening degree is stored at a predetermined address in the first memory area M1 of the memory 23 (step ₁ ).

The memorized throttle valve opening degree is determined by the throttle valve opening degree' memorized in the previous cycle (this is stored at a predetermined address in the second memory area _M2 of the memory 23), and the step. The magnitude is compared at , and when =', that is, the throttle valve opening is constant, the step is determined to be acceleration (>') or deceleration (
<'), the process moves to step 〓, respectively.

In this step, the first
The rotational speed N, intake negative pressure V, water temperature T, reference pulse width L ₀ , correction coefficient K, injection pulse width L, etc. stored in the memory area M ₁ are transferred to a second memory area M ₂ separately prepared in the memory 23. Move.

Next, in step, the output (air-fuel ratio signal A/F) of the comparison circuit 20, which receives the output signal of the exhaust sensor 19 as one input, is read, and in step, the air-fuel ratio signal A/F is stored in the first memory area _M1. In the step, it is compared with the previous air-fuel ratio signal A/F transferred to the second memory area _M2 to determine whether or not the air-fuel ratio has been reversed.If the air-fuel ratio has not been reversed, the step When this happens, the process moves to steps, and in each step it is determined whether or not it is rich.

Now, as shown in FIG. 7, the previous air-fuel ratio signal A/F (t 1 ) read at timing t ₁ and the current air-fuel ratio signal A/F (t ₁ ) read at timing t ₂ .
If both F(t ₂ ) are rich, then
In the step, the increment from the previous solenoid duty ratio D (t ₁ ) from time t ₁ to t ₂ (hereinafter referred to as
For example, the current solenoid duty ratio D(t ₂ ) is set to be 5% higher than the previous duty ratio D(t ₁ ) (D(t ₂ )=1.05D
( _t1 )).

Note that, as shown at timings t ₃ and t ₄ in FIG. 7, the previous and current air-fuel ratio signals A/F (t ₃ ),
If both A/F (t ₄ ) are lean, the current duty ratio D is
(t ₄ ) is reduced by 5% of the previous duty ratio D(t ₃ ) (D(t ₄ )=0.95D(t ₃ )).

On the other hand, as shown at timings t ₂ and t ₃ in FIG. 7, the previous air-fuel ratio signal A/F (t ₂ ) was rich;
At this time of reversal when _the air-fuel ratio signal A/F (t ₃ ) becomes lean _, in step For example, assuming that the current duty ratio is 15%, the current duty ratio D(t ₃ ) is set to be 15% less than the previous duty ratio D(t ₂ ) (D(t ₃ )=0.85D(t ₂ )).

Conversely, if the air-fuel ratio signal A/F(t) reverses from the lean side to the rich side, the step
The current duty ratio is set by increasing the proportional amount by 15%.

Furthermore, when the engine 1 is in an acceleration state or a deceleration state in step or, it is necessary to automatically reduce the EGR amount to ensure drivability. , map-controls the solenoid duty ratio D.

This memory Map3 is the memory Map shown in FIG.
1, it is a map in which the optimal unique solenoid duty ratio D is set in advance for each grid point bi, j specified by the intake negative pressure V and the rotation speed N. , the point Q (V, N) specified by the memorized intake negative pressure V and rotation speed N is a grid point.
When bi, j do not match, the solenoid is calculated by interpolation based on the solenoid duty ratio of a total of four grid points surrounding the point Q (V, N), as explained in Fig. 5. Calculate the duty ratio D.

As described above, the solenoid duty ratio D set in any one of steps 〓, 〓, 〓, or 〓 is set in the first memory area M1 in step _〓 .
is stored in memory.

Then, the injection pulse width L stored in the first memory area _M1 is read out in step 〓,
As shown in FIG. 2, a voltage is applied to the fuel injection nozzle 5 by the output interface circuit 27, and during the injection pulse width L, the fuel injection nozzle 5 injects fuel into the intake passage 3, thereby creating an empty air. Maintain fuel ratio at stoichiometric air/fuel ratio.

Next, in step 2, the calculated solenoid duty ratio is applied to the three-way solenoid valve 12 via the output interface circuit 27, and the duty ratio of the three-way solenoid valve 12 is controlled to a required value.

In this case, when the actual air-fuel ratio detected by the exhaust sensor 19 is richer than the stoichiometric air-fuel ratio, the duty ratio of the three-way solenoid valve 12 is controlled by the computer to increase. The degree of dilution increases due to
As a result, the negative pressure introduced into the negative pressure chamber 9a of the EGR valve 9 shown in FIG. 1 decreases, and the spring force of the coil spring 9b compressed in the negative pressure chamber 9a gradually increases to support the valve body 9c. The diaphragm 9d is displaced downward, the valve body 9c is closed, the EGR amount is decreased, and the intake air amount is increased by the decrease in the EGR amount to shift the air-fuel ratio to lean and match the stoichiometric air-fuel ratio.

Conversely, when the air-fuel ratio detected by the exhaust sensor 19 is lean, the three-way solenoid valve 1
By decreasing the duty ratio of 2,
The EGR valve 9 is further opened, the EGR amount is increased, the air-fuel ratio is shifted to the rich side, and the air-fuel ratio is again matched to the stoichiometric air-fuel ratio.

In the above control method, in the present invention, EGR
In the specific operating range A of the engine where it is necessary to cut or reduce the amount of air to a very small amount, the air-fuel ratio of the fuel metering means set by the microcomputer 14 is reset in advance, so that the actual air-fuel ratio monitored by the exhaust sensor 19 is Even when the fuel ratio deviates from the stoichiometric air-fuel ratio, the air-fuel ratio can be immediately corrected to the stoichiometric air-fuel ratio using a very small amount of EGR. This makes it possible to perform air-fuel ratio compensation while suppressing NOx.Therefore, it is possible to accurately perform the necessary air-fuel ratio compensation and EGR control while ensuring operability in a specific operating range of the engine. I can do it.

As described above, the present invention provides a fuel injection type engine equipped with a fuel metering means that controls the fuel injection amount by a computer using two of the following: engine speed, intake negative pressure, and throttle valve opening. , when the engine is in a specific operating range, i.e. when the engine is cold, at low load, and at high load, the air-fuel ratio of the fuel metering means set by the computer is reset relative to other operating ranges; , an exhaust sensor is installed in the exhaust passage, the output signal of the exhaust sensor is used as an input signal to the computer, and a control system is installed that controls the EGR amount based on this signal, and the actual air-fuel ratio is optimally controlled by controlling the EGR amount. An object of the present invention is to provide an exhaust gas purification device.

According to the present invention, when controlling the air-fuel ratio through the amount of EGR, the air-fuel ratio is reset in a specific operating range, so air-fuel ratio compensation can be performed as necessary with a very small amount of EGR, The effect is that accurate air-fuel ratio control can be performed without impeding performance.

[Brief explanation of the drawing]

Fig. 1 is an engine system diagram showing an exhaust gas purification device for a fuel injection engine according to the present invention, Fig. 2 is a block diagram showing a schematic configuration of the microcomputer shown in Fig. 1, and Fig. 3 is an output of an exhaust sensor. A waveform diagram showing the signal, FIG. 4 is a flowchart showing the control process by the microcomputer, FIG. 5 is an explanatory diagram of the memory Map1 for setting the reference pulse width for the fuel injection nozzle, and FIG. 6 is the reference pulse. An explanatory diagram of memory Map 2 for determining the correction coefficient K based on the water temperature for the width, Figure 7 is the first
FIG. 8 is a graph showing changes in the duty ratio for the three-way solenoid valve in relation to the air-fuel ratio signal, and FIG. 8 is an explanatory diagram of the memory Map 3 for the solenoid duty ratio during acceleration and deceleration of the engine. DESCRIPTION OF SYMBOLS 1...Engine, 3...Intake passage, 4...Throttle valve, 5...Fuel injection nozzle, 6...Exhaust passage, 8
...EGR passage, 9...EGR valve, 10...load introduction passage, 12...three-way solenoid valve, 14...microcomputer, 15...throttle sensor, 16...
Intake negative pressure sensor, 17... Water temperature sensor, 18... Rotation speed sensor, 19... Exhaust sensor.

Claims (1)

[Claims] 1. The intake air amount is detected by a combination of two quantities among the engine rotation speed, intake negative pressure, and throttle valve opening, and the fuel injection amount is controlled based on the intake air amount. In a fuel injection type engine equipped with a fuel metering means such as An exhaust gas recirculation passage having a gas recirculation control valve interposed therebetween is communicated, and an exhaust sensor is installed in the exhaust passage, and the opening degree of the exhaust gas recirculation control valve is feedback-controlled based on the output of the exhaust sensor. An exhaust gas purification device for a fuel-injected engine, which is characterized by: