JPH0192551A - Air-fuel ratio control device for engine - Google Patents

Abstract

PURPOSE:To prevent damage of an engine in which D-jetro control and L-jetro control for controlling the amount of fuel in accordance with an intake-air amount and an intake-air pressure are used in combination, by cutting off fuel in a high load operating range when a pressure sensor is abnormal. CONSTITUTION:In an air-fuel ratio control device 6, there is provided a computer 62 for computing a fuel supply amount for controlling the air-fuel ratio of an engine at a desired air-fuel ratio in accordance with output signals from an intake-air amount sensor, a throttle valve opening degree sensor 3, a pressure sensor 4 and a rotational speed sensor 5. Further, there are provided an abnormality judging circuit 61 for judging whether the output signal from the pressure sensor 4 is normal or abnormal, and a switch for changing over a fuel supply signal to an injector 7. When it is judged that the output signal from the pressure sensor 4 is abnormal, and operating range exceeding a dynamic detection range of the intake-air amount sensor 2 is determined in accordance with the output of the throttle valve opening degree sensor 3, and fuel is cut off in this range.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention normally performs L-JETRO control, performs D-JETRO control at high loads, and controls fuel in the high-load operation region when the pressure sensor output signal is abnormal. The present invention relates to an air-fuel ratio control device for an engine that cant.

[Conventional technology]

The L-JETRO system, which detects the amount of intake air in the engine and determines the amount of fuel to be supplied to the engine based on this, is more direct than the D-JETRO system, which detects the intake pipe pressure and determines the amount of fuel based on this. Point where intake air amount is detected and EG
It is widely used for air-fuel ratio control because it is not affected by the amount of R (exhaust gas recirculation).

The detection dynamic range of currently used intake air flow rate sensors is usually about 1 for use in air-fuel ratio control.
The limit is 00 times.

On the other hand, the efficiency of engines has improved due to reductions in friction loss, and the minimum amount of intake air needed to operate the engine has tended to decrease.

On the other hand, there is a tendency for the output to improve and the maximum intake air amount to increase as a result of higher performance such as the installation of a turbo inktorer and the use of DOHC. As a result, the intake air amount range has been expanded, and currently used intake air amount sensors are no longer able to detect the intake air amount over the entire operating range.

Therefore, as a way to solve this problem, in low-load regular operation zones that require accurate air-fuel ratio control, air-fuel ratio control is performed using the L-JETRO method, which prevents intake air flow from exceeding the intake air amount detection and from being affected by the EGR amount. In high-load operating zones where the engine is not affected by air flow, a combined L-Jetro and D-Jetro control system is used, in which the air-fuel ratio is controlled by the D-Jetro method.

Here, with reference to FIG. 10, the transition of the target air-fuel ratio when the pressure sensor is abnormal in a conventional device will be discussed. Time t
Assuming that the operating conditions at , are rotational speed N9, intake air amount QI, and throttle opening θ1, if the output signal of the pressure sensor is abnormal, the D-JETRO control judgment is not performed, but a fuel cut judgment is made, and the target air-fuel ratio A/ Get F 1.

Next, consider a case where the driver depresses the accelerator at time t2 and the throttle opening sensor output changes from θ1 to θ2, entering the D-JETRO control region.

Conventional devices perform full-range L-JETRO control when the pressure sensor is abnormal, so even if the intake air amount sensor exceeds its measurement dynamic range, the target air-fuel ratio cannot be calculated based on the intake air amount sensor output. I will do it. Although the air amount sensor output in this operating region cannot be specified, as shown in Figure 4 (target air-fuel ratio map during JETRO control, which will be described later), the engine rotation speed is N at time t2. If we consider the case where the intake air amount sensor output decreases to θ3 with the same condition, the target air-fuel ratio A/
F4 is obtained, and the target air-fuel ratio changes as shown in FIG.

[Problem that the invention seeks to solve]

If the signal from the pressure sensor is abnormal, it is naturally impossible to control the air-fuel ratio using the D-JETRO system, which controls the air-fuel ratio based on the pressure sensor output.
The JETRO control area is controlled using the L JETRO method.

At this time, if the intake air amount sensor output deviates significantly from the actual intake air amount, the air-fuel ratio will exceed the flammable limit and the engine output will only decrease, but the intake air amount sensor output differs from the actual intake air amount. , the air-fuel ratio becomes lean within the flammability limit relative to the desired air-fuel ratio.

If high-load operation continues in this state, the exhaust gas temperature will rise abnormally, leading to problems such as the risk of engine destruction in the worst case scenario.

This invention was made to solve the above-mentioned problems, and when the output signal of the pressure sensor becomes abnormal, the air-fuel ratio can be determined in the entire operating range of the engine, and the air-fuel ratio can be fixed. This is an engine improvement that can prevent damage to the exhaust pipe, catalyst, etc., or destruction of the engine itself due to a rise in exhaust gas temperature due to premature lean, especially during high loads, and can make the user aware of the need for repair. The purpose is to obtain an air-fuel ratio control device.

[Means for solving problems]

The air-fuel ratio control device for an engine according to the present invention is provided with means for stopping fuel supply based on a signal from the pressure sensor when the output signal from the pressure sensor is abnormal.

[For production]

In this invention, when the output signal of the pressure sensor is abnormal and the engine enters a high-load operation region where D-JETRO control should be performed, the pressure sensor actively stops the fuel supply to the engine and The output is reduced and the engine is always operated in the L Jetro region.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, 1 is a four-stroke internal combustion engine normally used in automobiles, 2 is an intake air amount sensor that detects the intake air amount of the engine, and 3 is a throttle valve position that adjusts the intake air amount to the engine. A throttle opening sensor 4 is located in the intake pipe downstream of the throttle opening sensor 3 and detects the intake pipe pressure; 5 is a rotational speed sensor that detects the rotational speed of the engine 1; 6 is the intake air amount. An air-fuel ratio control device that receives information from a sensor 2, a throttle opening sensor 3, a pressure sensor 4, and a rotation speed sensor 5, determines the operating state of the engine, and determines the fuel supply amount for controlling the air-fuel ratio to a desired air-fuel ratio. , 7 are injectors that receive a fuel supply signal from the air-fuel ratio control device 6 and supply (Jt) fuel corresponding to this fuel supply signal to the engine 1.

Inside the air-fuel ratio control device 6, 61 is an abnormality determination circuit that determines whether the signal from the pressure sensor 4 is normal or abnormal, and 62 is an intake air amount sensor 2, a throttle opening sensor 3, a pressure sensor 4,
A computing unit 63 determines the operating state of the engine based on sensor information from the rotation speed sensor 5 and calculates the amount of fuel to be supplied to the engine in order to control the engine to a desired air-fuel ratio. This is a switch that changes whether or not to output a fuel supply signal to.

Next, the operation will be explained with reference to FIG. 2 and subsequent figures.

FIG. 2 and FIG. 6 are diagrams showing the operating zones of the engine, and in both figures, ■ is the L-JETRO control zone, O is the D-JETRO control zone, and ◎ is the fuel cut zone.

FIGS. 3 and 7 respectively show the pressure kettle for determining the D-JETRO control zone and the throttle opening degree map for determining the fuel cut zone, which are set for each rotational speed.

FIG. 4 and FIG. 5 are diagrams showing target air-fuel ratios for L-JETRO and D-JETRO, respectively. Also, Figures 3 to 5,
FIG. 7 shows map data stored in the calibrating calculator 62, and the engine operating mode and target air-fuel ratio are selected based on this stored data. The internal operation of the arithmetic unit 62 will be explained below.

First, the operation when the output signal of the pressure sensor 4 is normal will be explained. The engine operating state at time t is the engine rotation speed N1
, the intake pipe pressure P+, and the amount of intake air per revolution θ.

According to FIG. 2, at engine speed N1, intake pipe pressure P
1 is less than the D Jetro judgment pressure, it is determined to be in the L Jetro region, and from Fig. 4, A which is the intersection of θ1 and N1
A target air/fuel ratio of /F 1 is selected.

Next, the amount of fuel required to satisfy the target air-fuel ratio A/F 1 is calculated according to a predetermined method, and a corresponding signal is output to the injector 7.

Next, consider the case where the driver depresses the throttle and the intake pipe pressure moves from Pl to P2 at time t2. According to FIG.
It is determined that it is in the JETRO control region, and this time, from Fig. 5, N
A target air-fuel ratio of A/F 2, which is the intersection of , and P2, is selected, and the fuel supply amount to satisfy this target air-fuel ratio is calculated according to a predetermined method, and a corresponding signal is output to the injector 7. .

The operation of the pressure sensor when it is normal is the same as that of the conventional air-fuel ratio control device, and the transition of the target air-fuel ratio is as shown in FIG.

Next, the operation when the output signal of the pressure sensor 4 is abnormal will be explained in comparison with a conventional device. FIG. 9 is a diagram showing the transition of the target air-fuel ratio when the pressure sensor 4 according to the present invention is abnormal.

First, an abnormality in the output signal of the pressure sensor 4 is considered to be due to an abnormality in the pressure sensor 4 itself or an abnormality in the signal line from the pressure sensor 4 to the air-fuel ratio control device 6. Specifically, the abnormality in the output signal of the pressure sensor 4 is considered to be due to an abnormality in the signal line from the pressure sensor 4 to the air-fuel ratio control device 6. If the pressure signal has a value that is impossible for the intake pipe pressure of the engine 1, it is determined to be abnormal, and a pressure sensor output signal abnormality signal is output to the calculator 62.

Consider a case where the engine speed is NI, the throttle opening is θ, and the intake air amount is 01 at time t1. If the pressure sensor output signal is abnormal, the D-JETRO control determination is not performed, and a fuel cut determination is performed based on the output of the throttle opening sensor, which is the third sensor.

As shown in FIG. 7, the throttle opening θ1 at the engine speed N1 is less than the fuel cut determination throttle opening, so it is determined to be in the L-JETRO region, the target air-fuel ratio A/F 1 is selected according to FIG. The amount of fuel supplied to the engine 1 is determined using the same method as when the sensor output signal is normal.

Next, at time t2, when the engine speed remains at N and the throttle opening sensor output changes from θ8 to θ2, as shown in Figure 7, it is above the fuel cut judgment throttle, so it is determined that it is fuel cut mode, and the switch is switched on. 63 outputs a OFF signal to cut off the injector drive signal.

Furthermore, if the throttle opening remains at θ2 until time t3, the engine output will decrease due to fuel cut;
As the engine rotation speed decreases and in FIG. 7, the engine rotation speed falls to N2, it becomes the L-Jetro region again, and if the intake air amount at this time is θ2, then from FIG. 4, the target air-fuel ratio A/F The transition of the target air-fuel ratio beyond 3 is shown in FIG.

Next, a comparison between the conventional device and the device of this invention is shown in FIGS. 8 to 10.
This will be explained using figures. 8 to 10 are all at time 1. , which shows the transition of the target air-fuel ratio when the target air-fuel ratio is from A/F 1 to a high-load operating state by depressing the throttle, and the calculation of the target air-fuel ratio at each time is as explained above. It is as follows.

(i) to (iii) at the right end of each figure show the relationship between the air-fuel ratio and the engine operating state during high-load operation, and (
i) is an appropriate air-fuel ratio region, and if the engine is operated at an air-fuel ratio in this region, the engine will operate without problems, and within this region there is an optimum air-fuel ratio for each operating state under high load.

Further, (iii) is a non-flammable region, and if the air-fuel ratio is in this region, combustion within the engine will fail and the engine output will decrease.

Furthermore, (:i) is a dangerous air-fuel ratio region, which is a flammable region, and engine torque is generated, but since the amount of fuel is small, the cooling effect of the intake air by the fuel is small and the exhaust temperature also rises.

Especially in high load areas and areas with a large amount of intake air,
If this becomes a large amount of high-temperature exhaust gas and is output from the engine, there is a danger that the temperature will adversely affect various parts of the engine body and accessories.

According to FIG. 8, if we trace the transition of the target air-fuel ratio when the pressure sensor is normal, it becomes the target air-fuel ratio A/F 2 according to D-JETRO in the high load region, and after time t2, the target air-fuel ratio is in the appropriate air-fuel ratio region (
It will be operated under i), and there will be no problem at all.

Next, if we trace the transition of the target air-fuel ratio when the pressure sensor is abnormal using Figs. (iii) becomes a non-flammable region, leading to a decrease in output,
Although the engine shifts to the low load zone again at time t3, it is not operated in the dangerous air-fuel ratio region shown in (ii).

Finally, in the conventional apparatus shown in FIG. 10, the engine is operated in the dangerous air-fuel ratio region (ii) of A/F 3 in the high-load operating region, resulting in an operating state that the engine should not be in.

〔Effect of the invention〕

As described above, according to the present invention, when the pressure sensor output signal is abnormal, the third sensor, which is the throttle opening sensor, determines the operating range in which the detection dynamic range of the intake air amount sensor is exceeded. Since the configuration is configured to actively cut fuel, the air-fuel ratio can be determined in all engine operating ranges, and the air-fuel ratio can be fixed,
Particularly, it is effective in preventing damage to the exhaust pipe, catalyst, etc. or destruction of the engine body due to a rise in exhaust gas temperature due to premature lean during high-load operation.

At the same time, by cutting fuel during high-load operation and causing engine torque fluctuations, the user is given an opportunity to detect some kind of abnormality and has the effect of making him aware of the need for repair.

[Brief explanation of the drawing]

Fig. 1 is an overall configuration diagram of an engine air-fuel ratio control device according to an embodiment of the present invention, Fig. 2 is a map showing the engine operating zone when the pressure sensor output signal is normal in the same embodiment, and Fig. 3 is the same as above. FIG. 4 is a target air-fuel ratio map during L-JETRO control to explain the above embodiment, and FIG. 5 is a D-JETRO control map to explain the above embodiment. Fig. 6 is a map showing the engine operating zone when the pressure sensor is abnormal to explain the above embodiment, Fig. 7 is a target air fuel ratio map during D-JETRO control to explain the above embodiment. , FIG. 8 is a map showing the transition of the target air-fuel ratio when the pressure sensor is normal, for explaining the above embodiment, and FIG. 9 is a map showing the transition of the target air-fuel ratio when the pressure sensor is abnormal, for explaining the above embodiment. The map shown in FIG. 10 is a map showing the transition of the target air-fuel ratio when a pressure sensor is abnormal, for explaining a conventional engine air-fuel ratio control device. DESCRIPTION OF SYMBOLS 1... Engine, 2... Intake amount sensor, 3... Throttle opening sensor, 4... Pressure sensor, 5... Rotation speed sensor, 6... Air-fuel ratio control device, 7...・Injector, 61... Pressure sensor abnormality determination circuit, 62...
- Arithmetic unit, 63... switch. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (2)

[Claims] (1) An intake air amount sensor that detects the intake air amount of the engine, and a pressure sensor that detects the pressure of the intake pipe of the engine, and based on the output of at least one of the intake air amount sensor and the pressure sensor. In the engine air-fuel ratio control device that determines the amount of fuel to be supplied to the engine, there is provided an abnormality detection means for detecting an abnormality in the output signal of the pressure sensor, and an abnormality detection means for detecting an abnormality in the output signal of the pressure sensor; switching from the output signal of the intake air amount sensor to the output signal of the pressure sensor, narrowing the fuel calculation area based on the output signal of the intake air amount sensor compared to switching from the output signal of the intake air amount sensor to the output signal of the pressure sensor, and An air-fuel ratio control device for an engine, further comprising a computing unit that stops fuel supply based on the output signal of the pressure sensor based on the output of the abnormality detection means when the narrowing occurs. (2) The air-fuel ratio control device for an engine according to claim 1, wherein the computing unit is configured to receive an output from an engine rotation speed sensor and an output from a throttle opening sensor.