JP2591116B2 - Exhaust gas temperature control system by air-fuel ratio control of internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention controls an air-fuel ratio determined by an engine load and an engine rotation speed in accordance with the temperature of exhaust gas flowing through an exhaust system of an internal combustion engine, thereby reducing the temperature of exhaust gas. The present invention relates to an exhaust gas temperature control device for controlling the air-fuel ratio of an internal combustion engine, which keeps the exhaust gas temperature at or below a predetermined value.

(Prior art)

In general, in an internal combustion engine, especially an internal combustion engine with a supercharger, the intake air temperature rises due to compression supercharging by the supercharger, and in order to obtain a rise in supercharging pressure from a low speed range of the engine and to exert a passage effect. It is necessary to reduce the area of the exhaust gas turbine inlet nozzle as much as possible.
Knocking tends to occur with gasoline fuel that is normally used. For this reason, the temperature of the exhaust gas rapidly rises, and exhaust system components such as a supercharger and a catalyst device mounted on the exhaust system are exposed to high temperatures, which may cause thermal destruction.

The easiest and cheapest means for lowering the high exhaust gas temperature under high-speed, high-load conditions is control of the engine air-fuel ratio. As one example, JP-A-56-81235 discloses that an exhaust system is provided with a temperature detector capable of detecting the temperature of exhaust gas flowing into a turbine casing of a supercharger.
The fuel injection amount is determined so that the air-fuel ratio approaches the stoichiometric air-fuel ratio when the temperature of the exhaust gas is less than a predetermined value, and the fuel injection amount is determined such that the air-fuel ratio becomes rich when the temperature of the exhaust gas exceeds a predetermined value. Is disclosed. Thus, it is possible to prevent thermal destruction of exhaust system components such as a supercharger and a catalyst device, and to improve fuel efficiency.

However, since the temperature detector itself for detecting the temperature of the exhaust gas is exposed to a high temperature, a material having excellent heat resistance must be selected when manufacturing the temperature detector. Also,
Since the temperature of the flowing exhaust gas is detected, a temperature difference occurs depending on how the exhaust gas hits the temperature detector, and there is a disadvantage that a detection error easily occurs.

Therefore, instead of directly detecting the temperature of the exhaust gas,
It has been considered to control the air-fuel ratio by estimating the temperature of the exhaust gas based on factors other than the exhaust temperature, such as the engine speed, the engine load, and the throttle opening (for example, Japanese Patent Application Laid-Open No. 58-51241). JP-A-60-53645,
See JP-A-62-87635 and JP-A-62-203965. This eliminates the need for installing a temperature detector in the exhaust system.

[Problems to be solved by the invention]

However, in the configuration in which the exhaust gas temperature is not directly detected as described above, if the temperature of the exhaust gas is estimated from factors that are not related to the temperature, such as the engine speed, the engine load, and the throttle opening, the water temperature inside the engine and the outside air (engine room) (Including the inside) cannot respond to changes in temperature, etc., and the current engine state cannot be reliably grasped. Therefore, an error occurs in the estimated value, and accurate air-fuel ratio control corresponding to the exhaust gas temperature is performed. Can not do.

In consideration of the above facts, the present invention prevents the thermal destruction of the exhaust system by controlling the optimal air-fuel ratio for the current engine state by estimating the accurate exhaust gas temperature without providing an exhaust system temperature detector. It is an object of the present invention to provide an exhaust gas temperature control device for controlling the air-fuel ratio of an internal combustion engine that can perform the control.

[Means for solving the problem]

An exhaust temperature control apparatus for controlling the air-fuel ratio of an internal combustion engine according to the present invention controls the air-fuel ratio determined by the engine load and the engine speed in accordance with the temperature of the exhaust gas flowing through the exhaust system of the internal combustion engine. An exhaust gas temperature control device for controlling the air-fuel ratio of an internal combustion engine that keeps the temperature of exhaust gas at or below a predetermined value by burning at a predetermined air-fuel ratio. An engine body temperature detector to be detected, setting means for setting an estimated temperature around the combustion chamber during steady operation of the engine based on an engine load and an engine speed, and a comparing means for comparing the actual temperature with the estimated temperature And air-fuel ratio control means for controlling the air-fuel ratio to the rich air-fuel ratio when the actual temperature is higher as a result of the comparison by the comparison means.

[Action]

The actual temperature around the combustion chamber is detected by an engine body temperature detector. Since the temperature change rate around the combustion chamber is substantially equal to the temperature change rate of the exhaust gas, the temperature of the exhaust gas can be predicted from the actual temperature.

On the other hand, the setting means estimates the temperature around the combustion chamber during steady operation of the engine based on the engine speed and the engine load, and sets the estimated temperature. The estimated temperature is compared with the actual temperature by the comparing means. If the actual temperature is higher, the air-fuel ratio is controlled to the rich air-fuel ratio. As a result, the temperature of the exhaust gas is lowered, and the exhaust system components can be protected by preventing thermal destruction and the like. If the estimated temperature is higher, the air-fuel ratio is not controlled to the rich side. This is because, for example, in a transient state such as when the engine load suddenly increases from the steady operation state, the amount of heat escapes to the engine body according to the temperature difference between the actual temperature and the estimated temperature, and the exhaust gas temperature does not become high . Therefore, the control shift to the rich air-heat ratio is not performed. Therefore, it is not necessary to cool the exhaust gas, and the air-fuel ratio can be controlled lean to improve fuel efficiency.

〔Example〕

FIG. 1 schematically shows a six-cylinder spark ignition internal combustion engine (engine) with a supercharger according to the present embodiment. An air flow meter 10 is disposed downstream of an air cleaner (not shown). The air flow meter 10 detects an intake air amount from a compensation plate 10A rotatably arranged in a damping chamber, a measuring plate 10B fixed to the compensation plate 10A, and a change in the opening of the measuring plate 10B. Potentiometer 10C
It is composed of An intake air temperature sensor 12 is arranged near the downstream side of the air flow meter 10. Air flow meter
Numeral 10 communicates with an intake port 22 of an engine body 20 including a cylinder block 17 and a cylinder head 19 via an intake passage 14, a surge tank 16, and an intake manifold 18. A throttle valve 24 is arranged on the upstream side of the surge tank 16, and the throttle valve 24 has a throttle valve.
A potentiometer-type throttle sensor 24A for detecting the opening degree of the cylinder 24 is attached, and a fuel injection valve 26 is arranged in the intake manifold 18 so as to protrude for each cylinder. The intake port 22 is connected to a combustion chamber 28 formed in the engine body 20 via an intake valve 20A. The combustion chamber 28 includes an exhaust valve 20B, an exhaust port 30,
It is connected to an exhaust passage 34 via an exhaust manifold 32.

A knocking sensor 36 composed of a piezoelectric element, a magnetostrictive element, or the like is attached to the cylinder block 17 of the engine body 20. A cooling water temperature sensor 38 is attached to the engine body 20 so as to penetrate the cylinder block and protrude into the water jacket. Further, as shown in FIG. 2, a head temperature sensor for detecting the temperature of the cylinder head 19 is provided on the cylinder head 19 of the engine body 20.
39 are installed.

An ignition plug 40 is attached to each cylinder so as to protrude into the combustion chamber 28 of the engine body 20.
Reference numeral 40 is connected to a control circuit 45 including a micro computer via a distributor 42 and an igniter 44. A cylinder discriminating sensor 46 and a rotation angle sensor 48 each composed of a signal rotor fixed to the distributor shaft and a pickup fixed to the distributor housing are attached to the distributor 42. The cylinder discrimination sensor 46 outputs a cylinder discrimination signal every 720 ° CA, and the rotation angle sensor 48 outputs a rotation angle signal every 30 ° CA.

A bypass passage 52 is connected to the exhaust passage 34, and a waste gate valve 54 is provided in the bypass passage 52.
Is arranged. The waste gate valve 54 is connected to the actuator 54A via a link mechanism, and is opened and closed via the link mechanism by air pressure supplied to the actuator 54A via the intake passage 14 and the pressure conduit 54B. The compressor 56A is provided in the intake passage 14.
And the turbocharger 56 is arranged such that the turbine 56B connected to the compressor 56A is located in the exhaust passage 34.

The air flow meter 10, the intake air temperature sensor 12, the throttle sensor 24A, the knocking sensor 36, the head temperature sensor 39,
Cylinder discrimination sensor 46, rotation angle sensor 48, and cooling water temperature sensor
38 is connected to a control circuit 45 so as to input a signal, and the igniter 44 and the fuel injection valve 26 are connected to the control circuit 45.
Are connected so as to be controlled by a control signal output from the controller.

Control circuit 45 including microcomputer
Is a random access memory (RA) as shown in FIG.
M) 58, read-only memory (ROM) 60, microprocessing unit (MPU) 62, first input / output port 64,
A second input / output port 66, a first output port 68, a second output port 70, and a bus 72 such as a data bus and a control bus for connecting these are provided. First input / output port
Numeral 64 is connected to the air flow meter 10, the cooling water temperature sensor 38, the intake air temperature sensor 12, and the head temperature sensor 39 via an analog-to-digital (A / D) converter 74, a multiplexer 76 and buffers 78A, 78B, 78C, 78D, respectively. ing. Further, the first input / output port 64 is connected to supply a control signal to the A / D converter 74 and the multiplexer 76. The second input / output port 66 is connected to the cylinder discriminating sensor 46 and the rotation angle sensor 48 via a waveform shaping circuit 80, and is connected to the knocking sensor 36 via an input circuit 82. Further, the throttle sensor 24A is directly connected to the second input / output port 66.

The first output port 68 is connected to the igniter 44 via a drive circuit 86, and the second output port 70 is connected to the fuel injection valve 26 via a drive circuit 88. Incidentally, 90 is a clock, and 92 is a timer. The ROM 60 stores the engine speed N and the intake air amount Q / unit speed shown in FIG.
The map of the estimated value of the head temperature based on N and the engine speed N and the intake air amount Q / N per unit speed shown in FIG.
And the map of the air-fuel ratio A / F based on the above.
Further, a program for a control routine described below is stored in the ROM 60 in advance.

The operation of this embodiment will be described below with reference to the flowchart of FIG.

First, in step 100, the air-fuel ratio A / F is read from the map shown in FIG. 6, and then the process proceeds to step 102, where it is determined whether the read A / F is the stoichiometric air-fuel ratio (= 14.5). If it is determined, the process proceeds to step 104, where fuel injection is executed based on the read air-fuel ratio A / F, and this routine ends.

If a negative determination is made in step 102, it is determined that the air-fuel ratio A / F needs to be corrected based on the head temperature, and the routine proceeds to step 106, where the estimated head temperature (map) is first determined from the map in FIG. Value). Next, in step 108, after the actual head temperature is detected by the head temperature sensor 39 (actually measured value), the process proceeds to step 110 to calculate the difference ΔT between the map value and the actually measured value.

At the next step 112, the absolute value of the difference ΔT is
It is determined whether the temperature is 0 ° C. or less. This significant difference differs depending on the characteristics of the engine, and is set to 10 ° C. in the present embodiment, but is not limited thereto.

If an affirmative determination is made in step 112, it is determined that correction of the air-fuel ratio A / F based on the head temperature is not necessary, and step 104
Move to. If a negative determination is made in step 112, the process proceeds to step 114 to determine whether the air-fuel ratio A / F is lean or rich depending on whether the measured value is higher or lower than the map value. to decide. That is, in general,
The amount of heat generated by combustion in the combustion chamber 28 is the effective work +
Expressed as cooling loss + exhaust loss. When the measured value is lower than the map value, the amount of heat taken by cooling is large,
The exhaust temperature does not rise, and there is no need to make the air-fuel ratio A / F rich. Conversely, when the measured value is higher than the map value, the temperature of the exhaust gas is increased by the amount of heat, so it is necessary to lower the exhaust temperature with the air-fuel ratio A / F as the richness.

In the present embodiment, when the ignition advance control is performed by the knocking sensor 36 or the like, the knocking is suppressed by the increase in the cooling loss, and the advance can be further advanced. Thus, the exhaust loss is greatly reduced.

Therefore, if it is determined at step 114 that ΔT> 0, the routine proceeds to step 116, where the calculated value of ΔT−10 is substituted for the variable A, and then at step 118, the corrected air-fuel ratio A / The operation value of A / 50 is substituted for the variable B so that F becomes 1. In the next step 120, the air-fuel ratio A / F is set to A / F
After replacing with the calculated value of + B, the routine proceeds to step 104, where fuel injection is executed.

If it is determined at step 114 that .DELTA.T.ltoreq.0, the routine proceeds to step 122, where the calculated value of | .DELTA.T | -10 is substituted for the variable A. Then, at step 124, the corrected air-fuel ratio A / F at a head temperature of 50.degree. Is set to 1 so that the calculated value of A / 50 is substituted for the variable B. In the next step 126, after replacing the air-fuel ratio A / F with the calculated value of A / FB, the process proceeds to step 104 to execute the fuel injection. The unit of the head temperature for increasing or decreasing the air-fuel ratio is not limited to the above 50 ° C., and it is preferable to set an optimum value according to the characteristics of the engine.

As described above, since the air-fuel ratio A / F is corrected based on the head temperature so as not to increase the exhaust gas temperature, a highly durable sensor for directly detecting the exhaust gas temperature becomes unnecessary. Further, since the exhaust gas temperature is estimated based on the head temperature, it can be made to correspond to the current engine state in which the cooling water temperature, the outside air temperature, and the like are taken into consideration, and the error from the actual exhaust gas temperature can be reduced.

Next, a specific example in which the throttle opening is fully opened from the steady state based on the above control will be described with reference to FIG.

In the state at time 0 in FIG. 7, the vehicle rotates at the engine speed N
Is running at 3000 rpm and Q / N is 0.5 (Figs. 5 and 6).
The air-fuel ratio A / F is controlled by the stoichiometric air-fuel ratio (14.5), and the head temperature is 90 ° C.

When the throttle is fully opened from this state, the A / F of 12.5 is read from the map in FIG. 6 (see point B in FIG. 6). Also, the head temperature (170 ° C.) is read from FIG. 5 (see point B in FIG. 5), but this change actually increases gradually as shown by the solid line in FIG. At this point, as before, if the air-fuel ratio A / F is set to the rich side,
Since the exhaust gas temperature decreases, the change in the head temperature actually increases gradually as shown by the solid line in FIG.

On the other hand, when the actual head temperature is detected by the head temperature sensor 39 and compared with the head temperature read from FIG. 5, the actual head temperature is lower due to the effect of the cooling loss (the initial measurement). 100 ° C at the time), the air-fuel ratio A leaner than the air-fuel ratio A / F (= 12.5) controlled only by the map
/ F (= 13.7) is set, and fuel injection is executed.

That is, when applied to the flowchart of FIG.
ΔT is 170 ° C.-100 ° C. (= 70 ° C.), and the affirmative determination is made in step 114. After that, 70 ℃ -10 ℃ (= 60 ℃), 60 ℃
After passing through / 50 ° C (= 1.2) (steps 116 and 118), 12.5 + 1.
2 (= 13.7).

Thereafter, the air-fuel ratio A / F by the map is set to A / F (12.5) as the actual head temperature increases, and fuel injection is performed. In this case, as shown by the chain line in FIG. Head temperature changes. As a result, since the air-fuel ratio control by the map can be made leaner for a predetermined period of time after the slot opening is fully opened, the fuel efficiency is improved by this amount. However, similar effects can be obtained for an engine without a supercharger. In this embodiment, the engine load is the intake air amount Q. However, the engine load may be obtained by detecting the intake pipe pressure.

Further, in this embodiment, the head temperature sensor 39 is attached to the cylinder head 19, but it may be attached to the cylinder block 17, or a plurality of head temperature sensors 39 may be provided.

In this embodiment, since the base air-fuel ratio A / F is determined by the map, it is richer than the stoichiometric air-fuel ratio, but the base air-fuel ratio A / F may be the stoichiometric air-fuel ratio.

〔The invention's effect〕

As described above, the exhaust gas temperature control apparatus based on the air-fuel ratio control of the internal combustion engine according to the present invention does not include a temperature detector for the exhaust system, estimates an accurate exhaust gas temperature, and determines an optimal air-fuel ratio for the current engine state. The control has an excellent effect that thermal destruction of the exhaust system can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a 6-cylinder spark ignition internal combustion engine with a supercharger according to the present invention, FIG. 2 is a plan view of a cylinder head, and FIG.
Fig. 4 is a control block diagram, Fig. 4 is an air-fuel ratio control flow chart, Fig. 5 is a head temperature characteristic diagram based on engine speed and intake air amount, and Fig. 6 is an air-fuel ratio characteristic based on engine speed and intake air amount. FIG. 7 is a time chart showing characteristics during engine transition. 10 Airflow meter, 20 Engine body, 26 Fuel injection valve, 28 Combustion chamber, 34 Exhaust passage, 39 Head temperature sensor, 45 Control circuit.

Claims (1)

(57) [Claims] An air-fuel ratio determined by an engine load and an engine speed is controlled in a rich manner according to a temperature of an exhaust gas flowing through an exhaust system of an internal combustion engine. An exhaust temperature control device for controlling an air-fuel ratio of an internal combustion engine to be kept at or below a predetermined value, the engine temperature detector being attached to an engine body forming a combustion chamber and detecting an actual temperature around the combustion chamber; Setting means for setting an estimated temperature around the combustion chamber during steady operation of the engine based on the engine speed; comparing means for comparing the actual temperature with the estimated temperature; An air-fuel ratio control unit for controlling the air-fuel ratio to the rich-side air-fuel ratio when the air-fuel ratio is high.