JPH02136528A - Exhaust gas temperature controller depending on air-fuel ratio control on internal combustion engine - Google Patents

Abstract

PURPOSE:To control an air-fuel ratio without using an exhaust gas temperature detector as well as to keep off any thermal breakdown in an exhaust system by controlling the air-fuel ratio to the rich side according to the compared result between actual temperature around a combustion chamber and estimated temperature around the combustion chamber being set from engine load and speed. CONSTITUTION:In a control circuit inputting each output signal out of an air flow-meter 10, a knocking sensor 36, a head temperature sensor 39, a turning angle sensor 48, a cooling temperature sensor 38 or the like at time of vehicle running, a control signal is outputted, and an igniter 44 and a fuel injection valve 26 are controlled. In addition, an air-fuel ratio found on the basis of a driving state is controlled to the rich side according to exhaust gas temperature whereby this exhaust gas temperature is kept to be less than the specified value. Then, at time of this exhaust gas temperature control, actual temperature around a combustion chamber by the head temperature sensor 39 is compared with estimated temperature around the combustion chamber being set according to engine load and speed, and when a side of the actual temperature is higher than the estimated one, the air-fuel ratio should be controlled to the rich side.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention controls the air-fuel ratio determined by the engine load and engine rotational speed according to the temperature of the exhaust gas flowing through the exhaust system of an internal combustion engine. The present invention relates to an exhaust gas temperature control device using air-fuel ratio control for an internal combustion engine that maintains the temperature below a predetermined value.

[Prior art]

In general, internal combustion engines, especially internal combustion engines with a supercharger, are accompanied by an increase in intake air temperature due to compression supercharging by the supercharger, and in order to obtain an increase in supercharging pressure from the low speed range of the engine and to demonstrate the passage effect. It is necessary to minimize the area of the exhaust gas inlet nozzle into the turbine, which causes the exhaust pressure to rise in the high-speed range of the engine, making knocking more likely to occur with the normally used gasoline fuel. For this reason, the exhaust gas temperature rises rapidly, and exhaust system components such as a supercharger and a catalyst device installed in the exhaust system are exposed to high temperatures, and there is a risk of thermal breakdown.

Controlling the engine air-fuel ratio is the easiest and cheapest means to reduce the high exhaust gas temperature under high-speed, high-load conditions. As an example, Japanese Patent Laid-Open No. 56-81235 discloses that a temperature detector capable of detecting the temperature of the exhaust gas flowing into the turbine casing of the supercharger is installed in the exhaust system, and the temperature of the exhaust gas is lower than a predetermined value. It is disclosed that the fuel injection amount is determined so that the air-fuel ratio approaches the stoichiometric air-fuel ratio, and the fuel injection amount is determined so that the air-fuel ratio becomes rich when the exhaust gas temperature reaches a predetermined value or higher. There is. This can prevent heat damage to exhaust system components such as the supercharger and catalyst device, and can also improve fuel efficiency.

However, since the temperature detector itself that detects the temperature of exhaust gas is exposed to high temperatures, it is necessary to select a material with excellent heat resistance when manufacturing this temperature detector. Furthermore, 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 drawback that detection errors are likely to occur.

Therefore, instead of directly detecting the exhaust gas temperature, it is considered to estimate the exhaust gas temperature based on factors other than the exhaust temperature, such as engine speed, engine load, and throttle opening, and control the air-fuel ratio. (e.g.
JP-A-58-51241, JP-A-60-5364
No. 5, JP-A-62-87635, JP-A-62-87635
(Refer to Publication No.-203965). This eliminates the need to install a temperature detector in the exhaust system.

[Problem to be solved by the invention]

However, in a configuration in which the exhaust temperature is not directly detected as described above, if the exhaust gas temperature is estimated based on factors unrelated to temperature such as engine speed, engine load, and throttle opening, it will be The engine cannot respond to changes in temperature, etc. (including inside), and the current engine condition cannot be reliably grasped, resulting in errors in estimated values.Accurate air-fuel ratio control corresponding to exhaust gas temperature is required. I can't.

Taking the above facts into consideration, the present invention prevents thermal damage to the exhaust system by estimating accurate exhaust gas temperature and controlling the air-fuel ratio that is optimal for the current engine condition, without providing an exhaust system temperature detector. The object of the present invention is to obtain an exhaust temperature control device for an internal combustion engine by controlling the air-fuel ratio.

[Means to solve the problem]

The exhaust temperature control device by air-fuel ratio control for an internal combustion engine according to the present invention richly controls the air-fuel ratio determined by the engine load and engine rotational speed in accordance with the temperature of exhaust gas flowing through the exhaust system of the internal combustion engine. An exhaust temperature control device using air-fuel ratio control for an internal combustion engine that maintains the temperature of exhaust gas below a predetermined value by performing combustion at a side air-fuel ratio,
An engine body temperature sensor is attached to the engine body that forms the combustion chamber and detects the actual temperature around the combustion chamber, and the estimated temperature around the combustion chamber is set during steady operation of the engine based on the engine load and engine rotation speed. a setting means for comparing the actual temperature and the estimated temperature; and an air-fuel ratio control means for controlling the air-fuel ratio to the rich side air-fuel ratio if the actual temperature is higher as a result of the comparison by the comparison means; have.

[Effect]

The engine body temperature detector detects the actual temperature around the combustion chamber. Since the temperature change rate around the combustion chamber is dependent on the temperature change rate of the exhaust gas, the temperature of the exhaust gas can be predicted from this 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 rotation speed and engine load, and sets the estimated temperature. This estimated temperature and the actual temperature are compared by a comparing means, and if the actual temperature is higher, the air-fuel ratio is controlled to a rich side air-fuel ratio.

This lowers the temperature of the exhaust gas, prevents thermal damage, etc., and protects the exhaust system components.

Furthermore, when the estimated temperature is higher, the air-fuel ratio is not controlled to be richer than the rich-side air-fuel ratio. This means that during transient times, such as when the engine load suddenly increases from a steady operating 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 reach a high temperature. . Therefore, the control is not shifted to the rich side air-fuel ratio. Therefore, there is no need to cool the exhaust gas, and the air-fuel ratio can be controlled to be lean in order to improve fuel efficiency.

[Example °]

FIG. 1 schematically shows a six-cylinder spark ignition internal combustion engine with a supercharger according to this embodiment.

An air flow meter 10 is arranged downstream of an air cleaner (not shown). This air flow meter 10 detects intake air flow from changes in the openings of a compensation plate IOA rotatably arranged in a damping chamber, and a measuring plate IOB and a measuring plate 10B fixed to the compensation plate IOA. It is composed of a potentiometer IOC.

An intake air temperature sensor 12 is located near the downstream side of the air flow meter 10.
is located. The air flow meter 10 is connected to the intake passage 1
4. Surge tank 16 and intake manifold 18
Cylinder block 17 and cylinder head 19 via
The intake port 22 of the engine body 20 is connected to the intake port 22 of the engine body 20. A throttle valve 24 is arranged on the upstream side of the surge tank 16, and a potentiometer-type throttle sensor 24A that detects the opening degree of the throttle valve 24 is attached to the throttle valve 24. A fuel injection valve 26 is arranged so as to protrude from each cylinder. The intake port 22 communicates with a combustion chamber 28 formed within the engine body 20 via an intake valve 2OA. This combustion chamber 28 is communicated with an exhaust passage 34 via an exhaust valve 2OB, an exhaust port 30, and an exhaust manifold 32.

A non-king sensor 36 made of a piezoelectric element, a magnetostrictive element, etc. is attached to the cylinder block 17 of the engine body 20. Further, a cooling water temperature sensor 38 is attached to the engine body 20 so as to penetrate through the cylinder block and protrude into the water jacket. Furthermore, as shown in FIG. 2, a head temperature sensor 39 is attached to the cylinder head 19 of the engine body 20 to detect the temperature of the cylinder head 19.

A spark plug 40 is attached to each cylinder so as to protrude into the combustion chamber 28 of the engine body 20, and this spark plug 40 is connected to a distributor 42 and an eve knife 44.
It is connected via a control circuit 45 including a microcomputer. A cylinder discrimination sensor 46 and a rotation angle sensor 48 are attached to the distributor 42, each consisting of a signal rotor fixed to the distributor shaft and a pink-up fixed to the distributor housing. 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 disposed within the bypass passage 52. This 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 supercharger 56 is arranged such that the compressor 56A is located in the intake passage 14 and the turbine 56B connected to the compressor 56A is located in the exhaust passage 34.

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

Control circuit 45 configured including a microcomputer
is a random access memory (R
AM) 58, read-only memory IJ (ROM) 60
, microprocessing unit (MPU) 62, first output capotro 4, second output capotro 6, first output capotro
The output port 8, the second output port 70, and a bus 72 such as a data bus or a control bus connecting these are provided. The first passenger capotro 4 is connected to an air flow make 10, an intake air temperature sensor 12, and a cooling water temperature sensor via an analog-digital (A/D) converter 74, a multiplexer 76, and buffers 78A, 78B, 78C, and 78D, respectively. 38 and a head temperature sensor 39. Also,
The first output capotro 4 is connected to provide control signals to the A/D converter 74 and the multiplexer 76 . The second input/output capotro 6 has a waveform shaping circuit 8.
0 to the cylinder discrimination sensor 46 and the rotation angle sensor 48, and is also connected to the knocking sensor 36 via the input circuit 82, and directly to the throttle sensor 24.
Connected to A.

The first output port door 8 is connected to the igniter 44 via a drive circuit 86, and the second output port door 0 is connected to the fuel injection valve 26 via a drive circuit 88. Note that 90 is a clock and 92 is a timer. Above ROM6
0, a map of the estimated value of the head temperature based on the engine speed N and the intake air IQ/N per unit speed shown in Fig. 5, and a map of the estimated value of the head temperature based on the engine speed N and the intake air IQ/N per unit speed shown in Fig. 6. A map of the air-fuel ratio A/F based on the intake air ff1Q/N is stored. Further, the ROM 60 stores in advance a control routine program to be described below.

The operation of this embodiment will be explained 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 in step 102, it is determined whether the read A/F is the stoichiometric air-fuel ratio (=14.5). , if the determination is positive, step 1
04, fuel injection is executed based on the read air-fuel ratio A/F, and this routine ends.

If the determination in step 102 is negative, it is determined that it is necessary to correct the air-fuel ratio A/F based on the head temperature, and the process proceeds to step 106. value). Then,
In step 108, the actual head temperature is detected by the head temperature sensor 39 (actually measured value), and then the process proceeds to step 110, where the difference ΔT between the map value and the actually measured value is calculated.

In the next step 112, it is determined whether the absolute value of this difference T is a significant difference of 10° C. or less. This significant difference varies depending on the characteristics of the engine, and in this example, it was set to 10°C, but it is not limited to this.

If an affirmative determination is made in step 112, it is determined that there is no need to correct the air-fuel ratio A/F based on the head temperature, and the process proceeds to step 104. If a negative determination is made in step 112, the process proceeds to step 114, and the air-fuel ratio A/F is determined depending on whether the actual measured value is higher or lower than the map value.
Determine whether F should be lean or rich. That is, generally, the amount of heat generated by combustion in the combustion chamber 28 is expressed as effective work + cooling loss + exhaust loss.

When the actual value is lower than the map value, the amount of heat taken away by the cooling water is large, so the exhaust temperature does not rise and there is no need to make the air-fuel ratio A/F rich. Conversely, when the actual value is higher than the map value, the temperature of the exhaust gas increases due to the amount of heat, so it is necessary to lower the exhaust gas temperature by making the air-fuel ratio A/F rich.

In this embodiment, when the ignition advance control is performed by the knocking sensor 36 or the like, non-king can be suppressed due to an increase in cooling loss, and the ignition can be advanced more, so that the reduction in effective work is small. Exhaust losses will be significantly reduced.

Therefore, if it is determined in step 114 that ΔT>Q, the process proceeds to step 116, where the calculated value of ΔT-10 is assigned to variable A, and then in step 118, the head temperature is set to 50°C.
Set A to variable B so that the corrected air-fuel ratio A/F is 1 in units.
Substitute the calculated value of 150. In the next step 120,
After replacing the air-fuel ratio A/F with the calculated value of A/F+B, the process moves to step 104 and fuel injection is executed.

If it is determined in step 114 that ΔT≦0, the process proceeds to step 122, where the calculated value of 1ΔT-10 is substituted for variable A, and then in step 124, the corrected air-fuel ratio A/F is adjusted to 1 in units of 50°C for the head temperature. The calculated value of A150 is assigned to variable B so that In the next step 126, the air-fuel ratio A
After replacing /F with the calculated value of /F-B, step 1
04 to execute fuel injection. Note that the unit of the head temperature for increasing/decreasing the air-fuel ratio is not limited to the above-mentioned 50° C., but it is preferable to set an optimum value depending on the characteristics of the engine.

In this way, since the air-fuel ratio A/F is corrected based on the head temperature to prevent the exhaust gas temperature from increasing, there is no need for a highly durable sensor for directly detecting the exhaust gas temperature. Furthermore, since the exhaust gas temperature is estimated based on the head temperature, it can be made to correspond to the current engine condition, taking into account, for example, the cooling water temperature and outside temperature, and the error with the actual exhaust gas temperature can be reduced.

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

At time 0 in Fig. 7, the vehicle is running at an engine speed N of 3000 rpm, Q/N of 0.5 (see point A in Figs. 5 and 6), and an 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 is read as 12.5 from the map in FIG. 6 (see point B in FIG. 6). Further, although the head temperature (170° C.) is read from FIG. 5 (see point B in FIG. 5), this change actually increases gradually as shown by the solid line in FIG. Next, when the actual head temperature is detected by the head temperature sensor 39, as shown by the chain line in FIG. 7, there is a difference between the temperature estimated by the map (100°C at the time of initial measurement).
. According to this difference, the air-fuel ratio A/F (
=12.5), the air-fuel ratio A/F (=13.
7) and execute fuel injection. As a result, the air-fuel ratio can be controlled for a predetermined period of time after the throttle opening is fully opened, and the fuel efficiency can be improved accordingly.

In this embodiment, an engine with a supercharger is used as an example, but the same effect can be obtained with an engine without a supercharger. Further, in this embodiment, the engine load is taken as the intake air IQ, but 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, the base air-fuel ratio A/F is determined by the map, so it is richer than the stoichiometric air-fuel ratio, but the base air-fuel ratio A/F may be set to the stoichiometric air-fuel ratio.

〔Effect of the invention〕

As explained above, the exhaust temperature control device by controlling the air-fuel ratio of an internal combustion engine according to the present invention does not provide a temperature sensor in the exhaust system, and estimates the accurate exhaust gas temperature to determine the air-fuel ratio that is optimal for the current engine condition. Control has the excellent effect of preventing thermal damage to the exhaust system.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a supercharged six-cylinder spark ignition internal combustion engine according to this embodiment, FIG. 2 is a plan view of a cylinder head, FIG. 3 is a control block diagram, and FIG. 4 is an air-fuel ratio control flowchart. Figure 5 is a head temperature characteristic diagram based on engine speed and intake air amount, Figure 6 is an air-fuel ratio characteristic diagram based on engine speed and intake air amount, and Figure 7 is a time chart showing characteristics during engine transients. be. DESCRIPTION OF SYMBOLS 10... Air flow meter, 20... Engine body, 26... Fuel injection valve, 28... Combustion chamber, 34... Exhaust passage, 39... Head temperature sensor, 45... Control circuit .

Claims (1)

[Claims] (1) The air-fuel ratio determined by the engine load and engine speed is richly controlled according to the temperature of the exhaust gas flowing through the exhaust system of the internal combustion engine, and combustion is performed using this rich air-fuel ratio to maintain the temperature of the exhaust gas to a predetermined value. This is an exhaust temperature control device that controls the air-fuel ratio of an internal combustion engine, and includes an engine body temperature sensor that is attached to the engine body forming the combustion chamber and detects the actual temperature around the combustion chamber, and an engine body temperature detector that detects the actual temperature around the combustion chamber, and the engine load and engine rotation. a setting means for setting an estimated temperature around the combustion chamber during steady operation of the engine based on the speed; a comparison means for comparing the actual temperature and the estimated temperature; and a comparison result by the comparison means that the actual temperature is higher. and an air-fuel ratio control means for controlling the air-fuel ratio to the rich side air-fuel ratio.