JPS61138844A - Air-fuel ratio controlling method in diesel engine - Google Patents

Abstract

PURPOSE:To control an air-fuel ratio to be constant, by making a relative current value in a lean sensor larger in proportion as exhaust pressure comes high. CONSTITUTION:An output current I and exhaust pressure sensor output PE of a lean sensor are made into digital conversion and written in a random access memory at a step 110. At a step 112, a compensation value K correspond ing to the exhaust pressure sensor output PE is calculated from a map, finding a compensation relative current value IR at a step 114. With this constitution, even if lean sensor output is varied, an air-fuel ratio is always controllable to the desired value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an air-fuel ratio control method for a diesel engine, and in particular, the present invention relates to an air-fuel ratio control method for a diesel engine. The present invention relates to an air-fuel ratio control method for a diesel engine that controls the fuel ratio.

[Conventional technology]

Conventionally, in order to always control smoke to a predetermined value and improve emissions and fuel efficiency, an oxygen concentration detector that detects the oxygen concentration in exhaust gas is installed in the exhaust passage, and the output of the oxygen concentration detector is An air-fuel ratio control device (Japanese Unexamined Patent Publication No. 56-2433) that performs feedback control on intake air amount, EGR amount, and fuel injection amount is known.

Further, as an oxygen concentration detector, a glue sensor (limiting current type oxygen partial pressure detector) having a structure shown in FIG. 2 is known.

This lean sensor includes an oxygen ion conductive solid electrolyte 1, which is sandwiched between permeable planar electrodes 2 and 3, which act as an anode and a cathode, respectively.

Leads sza and aa are connected to the electrodes 2.3, respectively.

The outer periphery of the platinum electrode S3 is coated with a porous ceramic layer 4 as a diffusion resistance layer, and a ceramic heater 5 having air holes 5a and heating the cell is inserted inside the platinum electrode 2. This heater 5 has a lead pJ5J5c.
is connected. A Kn insulating bush t6 is interposed between the heater 5 and the platinum electrode 2. Note that 71- is a casing in which a large number of holes 7a are bored. This processor is attached so as to penetrate through the exhaust pipe wall 8 and protrude into the exhaust pipe.

Then, lead wire 2BT3a and lead wire 5b, 5
By applying a predetermined voltage across c, an output current corresponding to the exhaust gas air-fuel ratio can be obtained. This output current is expressed by the following equation, and if the exhaust pressure is constant, it becomes K as shown in FIG.

However, P is a constant for the exhaust pressure, PO7 is the oxygen partial pressure in the exhaust gas, T series/cell element temperature, and k+X+'l.

[Problem that the invention seeks to solve]

Although the element temperature T can be kept constant by the heater 5 mentioned above, the exhaust pressure changes due to changes in engine speed, accelerator lever opening, and atmospheric pressure, and the supercharger also changes. When installed, there is a problem in that the exhaust pressure changes depending on the supercharging pressure, and the output current of the cell changes based on the above equation (1). Figure 4 shows the output current l for changes in exhaust pressure when the exhaust gas air-fuel ratio is constant.
This shows the change in As can be understood from the figure, as the exhaust pressure increases, the value of the output current increases, and the output current I
d indicates a value on the leaf side of the actual exhaust gas air-fuel ratio. Therefore, when feedback controlling the air-fuel ratio by controlling the fuel injection amount and EGR amount using this leakage/sensor, the output current of the processor changes in accordance with the change in exhaust pressure, and the air-fuel ratio is adjusted to the target air-fuel ratio. There was a problem that the air-fuel ratio could not be controlled, resulting in smoke and emissions.

The present invention was made to solve the above problems, and an object of the present invention is to provide an air-fuel ratio control method for a diesel engine that can control the air-fuel ratio to be constant even if the exhaust pressure changes.

[Means for solving problems]

In order to solve the above problems, the present invention provides
When controlling the air-fuel ratio of the air-fuel mixture to the required air-fuel ratio by detecting the exhaust gas air-fuel ratio and controlling the fuel injection amount and EGR amount based on this exhaust gas air-fuel ratio, the exhaust gas air-fuel ratio is The air-fuel ratio is controlled by estimating the smoke limit based on the smoke limit and controlling the fuel injection amount so as not to exceed the exhaust gas air-fuel ratio corresponding to the smoke limit. At this time, if the exhaust pressure changes to become higher, the preset comparison current value of the leaf 7 noser output is increased.

On the other hand, if the exhaust pressure changes to become lower, the comparison current value of the Lee/Sensor/Ser output is reduced. Therefore, even if the exhaust pressure changes, the air-fuel ratio can be controlled to be constant. Also,
In areas other than full load, the air-fuel ratio is controlled to the target air-fuel ratio by controlling the amount of exhaust gas recirculated to the intake system, that is, EGRt, based on the exhaust gas air-fuel ratio. At this time, if the exhaust pressure changes to become higher as in the full load area,
The comparison current value of the leaf sensor output is increased, and if the exhaust pressure becomes low, the comparison current value is decreased.

〔Effect of the invention〕

As explained above, according to the present invention, the air-fuel ratio can always be controlled to the target value even if the saw/sensor output changes due to exhaust pressure.
The effect is that it is possible to prevent deterioration of exhaust gas/fuel efficiency.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 5 shows a fuel injection device and an EG to which the present invention is applied.
1 shows a schematic diagram of a diesel engine equipped with an R device. The air cleaner 10 is communicated with an intake boat of the diesel engine main body 20 via an intake pipe 12 and an innotheque manifold 14. An exhaust port of the diesel engine main body 20 is connected to an exhaust pipe 18 via an exhaust manifold 16. The diesel engine main body 20 is equipped with a well-known distribution type fuel injection valve 22 that pumps fuel to the fuel injection valves provided in each cylinder of the main body 20.
Further, an engine cooling water temperature control unit 24 is attached so as to protrude into the water jacket of the main body 20.

An EGR passage 26 is provided to communicate the exhaust pipe 18 and the intake pipe 12.
EGR pulp 28 that controls the amount of EGR flowing into the passage 26
is installed. This E G RtZ n・pu28
is controlled by actuator 30.

A glue 7 sensor 32 similar to that shown in FIG. 2 is attached to the exhaust pipe 18KVi so as to penetrate through the pipe wall and protrude into the exhaust pipe. An exhaust pressure sensor for detecting exhaust pressure is attached near the reno sensor 32. Further, a supercharger 36 is attached to this diesel engine, which is composed of a turret provided in the exhaust pipe 18 and a blower provided in the intake pipe 12.

Further, 38t:f is an accelerator lever opening sensor which is composed of a potentiometer connected to the accelerator lever of the distribution type fuel injection pump 22 and detects the opening degree of the accelerator lever, and 40 is a drive of the distribution type fuel injection pump 22. This is an engine speed control system consisting of a signal rotor coaxially fixed to a shaft and a pickup arranged to face the teeth of the signal rotor.

The cooling water temperature sensor 24, the lean sensor 34, the exhaust pressure sensor 32, the accelerator lever opening sensor 38, and the engine speed sensor 40ij are connected to the input ports of the microcontroller 42. Microcomputer 42#''
i. As is well known, U/dumb access memory (RAM)
, read-only memory (ROM), central processing unit wt (C
It is connected to the near solenoid and controls the position of the actuator 30 and the spill ring of the fuel injection pump 22 via the output port (PU) and input/output port of the microcomputer 42.

Next, a first embodiment in which the present invention is applied to the above diesel engine will be described. In this embodiment, as shown in FIG. 6, the exhaust pressure sensor output r and therefore the correction value K increases as the exhaust pressure increases, and as shown in FIG. As shown in Figure 8, a map of the comparison current IRo at times other than full load, which is determined according to the engine speed and fuel injection, and the control routine described below are stored in advance. The comparison current IRd mentioned above corresponds to the output current of the lean sensor, that is, the air-fuel ratio. This indicates the air-fuel ratio.The target air-fuel ratio is
It is determined by experiment to improve the quality of the product.

FIG. 9 shows the main routine of this embodiment, in which the accelerator opening degree ACC1 is calculated from the engine revolution speed output obtained by digital conversion of the accelerator lever opening sensor output in step 100. Write engine speed NE to RAM. In step 102, based on the above accelerator opening 1i1 [Acc and engine speed NE,
The basic fuel injection amount τ0 is calculated from the basic fuel injection amount map determined by the accelerator opening degree and the engine speed. Then, in step 104, the position of the spill ring is controlled to inject an amount of fuel τ based on the basic fuel injection amount τ0, and the EGR
If the control conditions of the control device are satisfied, the duty ratio of the actuator is controlled in step 106 to generate a predetermined amount of EGR.
supply.

FIG. 1 shows an interrupt routine for calculating the fuel injection amount τ and the duty ratio.

This interrupt routine is executed for a predetermined period of time (for example, 50m5ec).
) is executed every time. First, in step 110, the output current 11 of the Lee/Se/S exhaust pressure sensor output PE and the accelerator lever opening output ACC are digitally converted and written to the RAM.
In step 112, a correction value K corresponding to the current exhaust pressure output PE is calculated from the map shown in FIG. Step 11
4. When the load is full, calculate the comparative current cost o from the map shown in FIG. 7, and when the load is not full, calculate the comparative current cost 0 from the map shown in FIG. 8, and calculate this comparative current I. A correction comparison current I is obtained by multiplying the correction value by . As a result, the correction comparison current I is increased as the exhaust pressure increases, and is increased at the same rate as the lean sensor output due to the increase in exhaust pressure.

When the load is full, the output current of the lean sensor is compared with the corrected comparison current I in step 118 to judge whether the currently detected air-fuel ratio exceeds the corrected smoke limit. do. If the output current of the lean sensor is equal to or greater than the corrected comparison current I, the air-fuel ratio feedback correction coefficient FAF is increased by a predetermined amount ΔF in step 122, and if the output current is less than the corrected comparison current IR, the air-fuel ratio The feedback correction coefficient FAF is reduced by a predetermined amount ΔF, and in step 124, the basic fuel injection amount 76 is multiplied by the air-fuel ratio feedback correction coefficient FAF to obtain the fuel injection amount τ. In addition, the feedback correction coefficient FAF
When increasing or decreasing , a proportional-integral operation is performed. Sensor output and feedback correction coefficient F at this time
Figure 10 shows changes in AF.

As a result of the above, the fuel injection amount is feedback-controlled based on the fuel injection output so as not to exceed the smoke limit estimated from the exhaust air-fuel ratio even if the exhaust pressure changes under full load.

On the other hand, when the load is other than full load, the output current of the lean sensor and the corrected comparison current I are compared in step 126, and if the output current of the lean sensor is equal to or higher than the corrected comparison current I, the duty is adjusted in step 130. The ratio correction coefficient FE is increased by a predetermined amount ΔE, and the output current of the lean sensor/su becomes the correction comparison current I,
If it is less than that, the correction coefficient FE is decreased by a predetermined amount ΔF in step 128. Then, in step 132, a correction coefficient FE is applied to the duty ratio Do corresponding to the target air-fuel ratio in FIG.
Find the corrected duty ratio by multiplying by

As a result of the above, when the load is not full, the EGR amount is feedback-controlled based on the output so that the air-fuel ratio becomes the target air-fuel ratio even if the exhaust pressure changes.

Next, the @2 embodiment of the present invention will be described. In this embodiment, the exhaust pressure is estimated according to the exhaust temperature and the engine speed by utilizing the phenomenon that the exhaust pressure increases as the exhaust temperature increases, and the exhaust pressure increases as the engine speed increases. The pressure is controlled similarly to the first embodiment.

For this reason, as shown in FIG. 11, an exhaust temperature sensor 44 is attached to the exhaust pipe 18 in place of the exhaust pressure sensor 32 shown in FIG. Furthermore, as shown in FIG. 12, R01/i of the microcomputer 42 stores in advance a map of the correction comparison current determined based on the engine speed NF and the exhaust temperature output T0. There is. Although this map requires a map of the corrected comparison current for full load and a map of corrected comparison current for other than full load, FIG. 12 shows only the map for other than full load.

Next, the interrupt routine of this embodiment will be explained based on FIG. This routine/Vi, step 13 replaces steps 112 and 114 in the routine of FIG.
6. Therefore, the same parts Kfl will be given the same reference numerals and the explanation will be omitted. In step 136, the first
Based on the map etc. shown in Fig. 2, the corrected comparison current for full load and the corrected comparison current for other than full load are calculated, and in steps 116 to 132, the fuel injection amount τ and correction are calculated in the same manner as in the first embodiment. Calculate the duty ratio.

Next, a third embodiment of the present invention will be described. In this example, the first
A map of correction comparison currents determined based on the engine/engine/rotational speed and the required fuel injection amount shown in FIG. 4 is stored in the ROM in advance. This map is a comparison current value with pressure correction during supercharging, which is made to correspond to a target air-fuel ratio that compensates for exhaust pressure changes, and is controlled in the same way as in the first embodiment.

FIG. 15 shows the interrupt routine of this embodiment. In step 150, the digital value of the output current of the relay/controller is written into the RAM. In the next step 152,
The lean sensor output current 111t is calculated from the map shown in FIG. 14 by interpolation.

Then, in steps 118 and 126, the saw/cessor output current value and the lean sensor output current value Rt are compared, and at full load, the fuel injection amount is controlled to control ViEGR3 except for full load.

As a result of the above, even if the boost pressure increases and the exhaust pressure increases, the air-fuel ratio is controlled to reach the target air-fuel ratio.

In addition, although an example using an exhaust pressure sensor was explained above, as the intake pipe pressure increases, the exhaust pressure also increases. Therefore, an intake pipe pressure cassette is installed in place of the exhaust pressure sensor, and the exhaust pressure is controlled by the intake pipe pressure. The pressure may also be estimated. In addition, if feedback control is performed at full load, there is a risk that torque fluctuations will occur in the high rotation range due to fluctuations in the fuel injection amount, so it is better to neutralize the feedback control in the engine high rotation range (for example, 4000 rT) or higher. .

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing the interrupt routine of the first embodiment of the present invention, FIG. 2 is a sectional view showing a conventional lean processor, and FIG.
Figure 4 is a diagram showing the output current of the battery, Figure 4 is a diagram showing the change in output of the battery with respect to exhaust pressure, and Figure 5 is a schematic diagram of the diesel engine to which the first embodiment is applied. Figure, 6th
The figure is a diagram showing the change in the correction value of the first embodiment, Figure 7 is a # diagram of the comparison current of full load, Figure 8 is a diagram showing the map of comparison current other than full load, and Figure 9 is a diagram showing the comparison current map of other than full load. A flowchart showing the main routine of the embodiment, Fig. 10 a diagram showing changes in beam/processor output and FAF, and Fig. 11 a flow chart showing the beam/processor output of the second embodiment.
Fig. 12 is a diagram showing a comparison current map of the second embodiment, Fig. 13 is a flowchart showing the interrupt routine of the second embodiment, and Fig. 14 shows the engine of the third embodiment. FIG. 15 is a flowchart showing the interrupt routine of the third embodiment. 22...Fuel injection pop, 28...EGR valve,
32...Leanse/su, 34...Exhaust pressure se/su.

Claims (1)

[Claims] (1) Using a lean sensor that detects the exhaust gas air-fuel ratio in a region where the residual oxygen concentration in the exhaust gas is higher than the concentration corresponding to the stoichiometric air-fuel ratio, the smoke limit is estimated based on the exhaust gas air-fuel ratio in the full load range, and the smoke limit is The air-fuel ratio is controlled by controlling the fuel injection amount so as not to exceed the exhaust gas air-fuel ratio corresponding to the exhaust gas air-fuel ratio, and in areas other than full load, the amount of exhaust gas recirculated to the intake system is controlled based on the exhaust gas air-fuel ratio. In an air-fuel ratio control method for a diesel engine, which controls the air-fuel ratio so that it reaches a target air-fuel ratio, the comparison current value of the lean sensor increases as the exhaust pressure increases, and the exhaust pressure 1. An air-fuel ratio control method for a diesel engine, characterized in that the comparison current value is corrected to become smaller as the current becomes lower.