JPS62253935A - Fuel control device - Google Patents

Abstract

PURPOSE:To prevent wrong fault judgement to output lowering of an inlet air amount sensor by detecting fault of the inlet air amount sensor by its output, and stopping detection of the fault until the output of the inlet air amount sensor becomes the predetermined level. CONSTITUTION:An ECU 10 determined fuel injection amount based on respective signals from an AFS (inlet air amount sensor) 2, a crank angle sensor 11, starting switch 13, engine cooling water temperature switch 13 and a throttle sensor 4, and controls the pulse width of fuel injection pulse of an injection 9 by synchronizing with the signal from the crank angle sensor 11. And when all the burnoff conditions are established, the ECU 10 generates burnoff control signal 14. In this case, the fault is detected by the output level of the AFS 2. And after the burnoff control is finished, operation of the fault detecting unit is stopped until the output of the AFS sensor 2 reaches the predetermined level.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fuel control system for an internal combustion engine, and particularly to an improvement in the high-temperature burn-off operation of surface deposits of a hot-wire type intake air amount sensor.

[Conventional technology]

Characteristics of hot wire intake air flow sensors change due to substances adhering to the surface of the hot wire, resulting in errors in the amount of fuel supplied to the engine, leading to problems such as deterioration of exhaust gas and deterioration of driving performance. In order to deal with this problem, conventional methods have been used to heat the hot wire to a temperature higher than the normal operating temperature when the engine is stopped, and burn off the deposits on the surface of the hot wire.1. The burn-off method is disclosed in Japanese Patent Laid-Open No. 76182/1982. In order to effectively perform the purge-off operation, the heating temperature of the hot wire must be 1
Experiments have shown that the temperature should be around 000°C. However, heating the hot wire to too many degrees Celsius can ignite the gasoline mixture, which is inconvenient for the intake air amount sensor disposed in the intake passage of the Solin engine. Therefore, in order to avoid ignition of the gasoline mixture, when performing burn-off, the temperature and rotation speed of one engine must meet predetermined conditions, and gasoline that has been excessively supplied into the intake pipe during the warm-up process can be sufficiently scavenged. Execution is permitted only if the Further, after the engine is stopped, the time required for the air-fuel mixture to travel upstream from the fuel supply section and reach the intake air amount sensor is determined through experiments, and burn-off is performed within this time.

[Problem that the invention seeks to solve]

However, if the engine is restarted during or immediately after the burn-off described above, the output of the intake air amount sensor will be approximately 0 during the period (approximately 0.5 seconds) until the hot wire returns to the normal operating temperature.
Since the intake air amount sensor is in a normal state, it will be mistakenly determined to be a failure when determining the output level of the intake air amount centimeter to determine the failure. Furthermore, since the output of the intake air amount sensor is in an abnormal state, there is a problem in that if fuel is supplied based on this output, the air-fuel ratio becomes abnormal.

This invention has been made to solve the above problems, and aims to provide a fuel control device that does not make an erroneous failure judgment regarding a decrease in the output of an intake air amount sensor immediately after engine turn-off. .

[Means for solving problems]

The fuel control device according to the present invention stops the operation of the failure detection unit for a period after the burn-off control unit that performs burn-off of the hot-wire intake air amount sensor finishes operating, until the output of the intake air amount sensor reaches a predetermined level. It was designed to do so.

[Effect]

In this invention, if the engine is started during burn-off, the burn-off is stopped and the operation of the failure detection unit is stopped for a period of time until the output of the intake air amount sensor exceeds the failure judgment level of the failure detection unit. Do not output the failure judgment results.

〔Example〕

An embodiment of this invention will be described below. Figure 1 shows a hot wire intake air flow sensor (hereinafter referred to as A) that detects the intake air flow of the engine.
It's called FS. ) is a diagram showing the configuration of a general fuel control device using
AFS2 is arranged within the intake passage. 3 is a throttle valve that controls the intake air amount of the ENON, 4 is a throttle sensor that operates in conjunction with the throttle valve 3 and extracts its opening as a voltage signal, 5 is a Sarno tank, and 6 is an intake manifold. be. 7 butterfly Intake valve driven by a cam not shown, 8 cylinder (cylinder)
For the sake of simplicity, only one cylinder of the Ennon is shown, but it actually consists of multiple cylinders. 9 is a fuel control valve (hereinafter referred to as an injector) attached to each cylinder 8; 10 is a fuel control valve that controls the fuel injection amount of the injector 9 to a predetermined air amount with respect to the amount of air taken into each cylinder 8; This is an electronic control unit (hereinafter referred to as ECU) that controls the fuel (A/F) ratio. ECUlo is AF
S2% crank angle sen'? L L, starting switch 12,
Ennon cooling water temperature sensor? 13 and throttle sensor 4, and injects fuel from injector 9 in synchronization with the signal from crank angle sensor 11. Control the loop width. Additionally, gcUIO generates a burn-off control signal 14 when all burn-off conditions are met. The configuration and operation related to burn-off control of the AFS 2 are similar to known ones, so detailed explanations will be omitted.

Figure 2 shows the internal configuration of the ECUIO, 10L is an interface circuit for the crank angle sensor 11 and the dinotal input of the start switch 12, 102 is an interface circuit for the analog inputs of the AFS 2 and water temperature sensor 13, and LO
It is a 3U multiplexer, and the analog input is sequentially converted into a digital value by an A/D converter 104. Also, 105 is ROMI 05 a, RAML O5b
and a CPU with built-in timers 105c and 105d), an interface circuit 101 and an A/D converter 1.
Based on the signal input from 04, the insector drive pulse width is calculated according to the program stored in the ROM 105a, and the timer 105c outputs a pulse with a predetermined time width. 106 is a circuit that amplifies this pulse and drives the injector 9. Since the above configuration related to fuel control is conventionally known, a more detailed explanation will be omitted. father.

105d is a timer that outputs a burn-off pulse;
This pulse is amplified by the drive circuit 107 and provided as the AFS2 heat burn-off signal 14.

The operation of the fuel control system having the above configuration will be briefly explained using the flowchart shown in FIG. Also, Figure 4 shows AFS
2 is a diagram showing the output level VQ of V! is the level corresponding to burn-off, % is the level immediately after burn-off, ■ is the normal operating level, v4 is the level at the time of failure, and vth is the level for failure determination.

In such a fuel control system, when the engine is started during burn-off, first, if burn-off is being executed in step S, the process proceeds to step S2 to stop burn-off, and then in step S3, the output VQ of AFS2 is read. It will be done. Then, in step S4, VQ reaches the failure judgment level vth.
It is determined whether or not it exceeds VQ, and if VQ<''/lh, this process is repeated.

Here, VQ is as shown in Figure 4, when the start switch is turned on, the hot wire temperature control is stopped until the hot wire heated to a high temperature drops to the normal temperature, so the output is V, -:O
After a predetermined time t has elapsed, it exceeds vth, and then returns to the normal operating level V. The failure detection unit outputs AFS 2 failure when VQ falls below vth, but immediately after burn-off, the failure does not spread, so it should not make a failure judgment corresponding to v2. ◎For this reason, judgment is prohibited for the predetermined time t. After that, it is brought into a normal operating state to enable determination of failure level v4.

Furthermore, since the AFS output level during the failure determination prohibition period does not correspond to the intake air amount, fuel control cannot be performed based on this. Therefore, during this period, the fuel control valve is either stopped or operated based on other parameters, regardless of the AFS output. If Vq>Vth, that is, t2 has elapsed in step S4, the process proceeds to step S5, where fuel control is performed based on the output of AFS2.

Also, when burn-off is not being executed, the process advances to step S6 to read the output of AFS2, and in step S7, VQ is set to vt.
Determine whether it exceeds h. Here, VQ > Vth
If so, proceed to step S5, perform fuel control, and set Vq
> If not Vth, a failure is output in step S8 and fuel control is not executed. Note that the results of AFS failure determination can also be displayed externally.

〔Effect of the invention〕

As described above, according to the present invention, failure determination of the intake air amount sensor is prohibited for a period until the intake air amount sensor output differs from a predetermined level after burn-off. Since there is no possibility of incorrect failure determination, and the control logic that prohibits failure determination can be achieved by only adding a small number of GLODARAMs, there is an effect that there is almost no increase in cost compared to the conventional method.

[Brief explanation of drawings]

1 and 2 are an overall configuration diagram and an electronic control unit configuration diagram of a fuel control device according to the present invention, respectively, FIG. 3 is a flowchart showing the operation of the fuel control device according to an embodiment of the present invention, and FIG. The figure shows AFS immediately after burn-off.
FIG. 3 is a characteristic diagram showing output. 2... Hot wire intake air amount sensor (AF'S), 9... Fuel control valve (injector), 10... iE child control unit) (ECU). In addition, the same reference numerals in each figure indicate the same or corresponding parts.

Claims (2)

[Claims] (1) Calculate the required fuel amount of the engine based on the output of the hot-wire intake air amount sensor installed in the intake passage of the internal combustion engine, and control the fuel control valve based on this calculated value to supply the desired amount of fuel to the engine. a burn-off control unit that heats the hot wire of the hot wire type intake air amount sensor to a temperature higher than the normal operating temperature to incinerate the surface deposits of the hot wire after the engine is stopped; and an output level of the intake air amount sensor. and a means for stopping the operation of the failure detection unit for a period of time after the burn-off control unit has finished operating, until the output of the intake air amount sensor reaches a predetermined level. A fuel control device featuring: (2) The fuel control according to claim 1, wherein during the period when the failure detection section is not operating, the fuel control valve is stopped operating or is driven independently of the output of the intake air amount sensor. Device.