JPS6197528A - Hot wire type air flow rate measuring apparatus - Google Patents

Abstract

PURPOSE:To enable the measurement of the degree of deterioration in a hot wire prior to the start of the engine accurately, by providing a startup delaying means, time lag computing means, an intake correction means and the like. CONSTITUTION:A control circuit 4 includes a startup delaying means 12, a time lag computing means 13 and an intake correction means 14. This means 12 temporarily delays the startup of the engine 1 with a starter 11 when an ignition switch 10 is turned ON. The means 13 detects the time when a hot wire 8 is changed for a specified time with air at rest in an intake path 2 to compute the difference from the required time when the wire 8 is normal. The means 14 corrects changes in the characteristic of the wire 8 from the time difference. Then, as the switch 10 is turned ON, the means 12 checks the startup of the engine 1 with the starter 11 immediately. Here, when the temperature of the temperature sensor 9 is low enough to perform the correcting operation, the wire 8 is electrically energized. If the hot wire deteriorates, a deterioration indicator is computed by the means 13 and correction is done with the means 14.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a hot wire air flow rate measuring device, and more specifically, the present invention relates to a hot wire type air flow rate measuring device, and more specifically, it is a method for measuring characteristic changes due to hot wire deterioration, etc., using deterioration indicators measured in a state where air is not moving. The present invention relates to an air flow rate measurement device that uses the air flow rate measurement device for correction. This is used in the field of technology in which a hot wire air flow rate measuring device is interposed in an intake passage to detect the amount of intake air.

[Prior art]

In order to obtain an air-fuel mixture with an optimal air-fuel ratio, an air flow rate measuring device that measures the amount of intake air is provided in the intake passage of the engine. An example in which a hot wire flowmeter using a hot wire is employed as the measuring device is described in Japanese Utility Model Application Publication No. 57-155427.

It is well known that the amount of intake air can be measured from the detected voltage by utilizing the fact that the resistance of the hot wire changes depending on the air flow rate passing through it. However, as it is installed in the engine intake passage and used for many years, it deteriorates and its flow rate detection characteristics change.Also, dust that flows through the intake passage becomes attached or removed. Then, the heat dissipation area changes each time, and the same thing happens.If this condition is left untreated, the accuracy of measuring air flow rate using the hot wire will decrease, making it impossible to use it to adjust the air-fuel ratio. Become something.

According to the above-mentioned publication, an example is described in which the dust adhering to the hot wire is burned off in order to avoid characteristic changes caused by the dust. Even if the hot wire is cleaned in this way, changes in characteristics due to deterioration cannot be avoided, and the problem of reduced accuracy in measuring the amount of intake air remains, and a solution to this problem is desired.

[Purpose of the invention]

The present invention was made in view of the above-mentioned problems, and its purpose is to ensure a period in which there is no movement of intake air in the intake passage, so that the degree of deterioration of the hot wire can be accurately measured, and based on this, it is possible to accurately measure the degree of deterioration of the hot wire. An object of the present invention is to provide a hot wire type air flow rate measuring device that can correct the characteristics of a wire.

[Structure of the invention]

The hot wire air flow measuring device of the present invention is characterized by a start delay means that delays the start of the engine by the starter when the ignition switch is turned on, and a method that detects the time required for the hot wire to change the temperature to a predetermined value while the engine is stopped. Accordingly, the present invention includes a time difference calculating means for calculating a difference from a preset reference time, and an intake air amount correcting means for correcting a change in characteristics of the hot wire from the time difference.

[For production]

In response to a signal indicating that the ignition switch is turned on, the start delay means delays the start of the engine by the starter for a certain period of time. During this time, intake air does not flow into the intake passage,
In this state, a hot wire interposed in the intake passage is energized to raise the temperature to a predetermined value. The time from the start of energization until the temperature rise is achieved is measured, and the difference between that value and a separately stored reference time is determined by a time difference calculation means. The time difference is an index of the degree of deterioration of the hot wire, and the intake air amount correction means calculates a correction coefficient from the time difference and stores it. Note that after the above-mentioned time has been measured, the startup suppression by the startup delay means is canceled and the engine is started.

When the flow velocity of intake air passing through the intake passage is detected by the hot wire, the value is multiplied by the above-mentioned correction coefficient to correct the flow velocity. The amount of intake air is determined based on the flow velocity,
The amount of fuel supplied is controlled to obtain a desired air-fuel ratio, and a mixture with an air-fuel ratio optimal for engine operation is created.

〔Example〕

Hereinafter, the present invention will be explained in detail based on examples thereof.

FIG. 2 is a schematic diagram showing the intake system and its control of an engine in which the hot-wire air flow measuring device of the present invention is installed. A fuel injection nozzle 5 is provided which injects the amount of fuel adjusted by 4. In order to enable control in the engine control circuit 4, the engine 1
A rotation speed sensor 6 for detecting the rotation speed of the hot wire 8 and a temperature sensor 9 for detecting the temperature of the hot wire 8 are provided in the intake passage 2 immediately after the air cleaner 7. Moreover, a signal indicating whether the ignition switch 10 is turned on or off is also input to the control circuit 4.

The engine control circuit 4 not only controls the injection amount at the fuel injection nozzle 5 described above, but also controls the starter 11 that starts the engine and performs correction control to correct changes in the characteristics of the hot wire 8. There is. That is,
The control circuit 4 includes a start delay means 12, a time difference calculation means 13, and an intake air amount correction means 14 shown in FIG.

The start delay means 12 temporarily delays the start of the engine 1 by the starter 11 when the ignition switch 10 is turned on, and even after the starter switch is turned on, the start delay means 12 is used for a very short period of time until the hot wire correction preparation is completed. ,
This is to prevent the intake air from flowing in the intake passage 2. It should be noted that this delay time is a short time, for example, several tens of milliseconds, which will be described later, and is therefore not large enough to cause a perceptual difference in the driver's operation.

The time difference calculating means 13 detects the time required to change the temperature of the hot wire 8 by a predetermined value when the air is still in the intake passage 2, that is, when the engine is stopped, and determines the time required to change the temperature of the hot wire 8 to a predetermined value when the hot wire is normal. (previously set as a reference time) is calculated to check the degree of change in temperature rise characteristics due to deterioration of the hot wire, etc., before measuring the intake air flow rate. That is, hot wire 8
If dust adheres to or is removed from the wire, or if it becomes thin due to use, the change in resistance caused by the temperature change depending on the air flow rate passing through the hot wire will be different than if it were not. become. Therefore, an error occurs in the intake air amount measured from the detected voltage, etc., and the fuel injection amount falls outside the desired value, resulting in a decrease in air-fuel ratio control accuracy.

This error is determined by the difference in the temperature rise rate of the hot wire, so 1. The hot wire is left unaffected by air flow, allowing the rate of temperature rise to be measured in advance.

The measurement is performed by heating a hot wire with electricity and measuring the time required for a certain predetermined temperature rise. In principle, this measurement is performed every time the engine is started, so the temperature of the hot wire before heating is not necessarily the same. Therefore, the time required to raise the temperature by, for example, 100° C. from any room temperature is measured. This is compared with the time in the normal case shown in Figure 3, and the difference is the time △
T is taken as a deterioration index.

The intake air amount correcting means 14 corrects the characteristic change of the hot wire from the time difference, and obtains the correction coefficient Cw. This correction coefficient C- is calculated as 1-C×8, and by multiplying the value by the intake air amount measured by the hot wire, the true intake air amount can be determined. Note that C by which ΔT is multiplied is a constant.

By the way, in this embodiment, in order to burn off the dust adhering to the hot wire, when the ignition switch is turned off, a burn-off is automatically performed to heat the hot wire to a high temperature of about 1000°C. Therefore, the following description includes procedures for avoiding the harmful effects of such operations.
5.

According to the embodiment of the above-described configuration, it operates as follows:
Hotwire correction is performed. When the ignition switch 10 is turned on (step 1 in the flowchart of FIG. 4, hereinafter referred to as 81, etc.), the startup delay means 12 immediately inhibits the starter 11 from starting the engine 1 (S2). Then, no movement of air occurs in the intake road 2, and the air at the location where the hot wire 8 is attached remains stationary. Since the vehicle is burnt off immediately after it is stopped, the hot wire may not have returned to an appropriate temperature to take data for correction unless too much time has passed since the car was stopped. Therefore, a temperature sensor 9 attached to the hot wire 8 detects the temperature of the hot wire. When the temperature has fallen sufficiently to perform a correction operation (S3), the hot wire 8 is energized (S3).
4), the timer starts counting time (S5-). The temperature sensor 9 detects that the hot wire 8 has risen by a predetermined 100°C from the initial temperature (S
6) and the time Trw required for it are measured by a timer (S7), and the required time T in a normal case is stored separately.
The difference ΔT from sw is used as a deterioration index by the time difference calculation means 13.
is calculated (S8).

Incidentally, although it is possible to always perform correction according to this time difference ΔT, there may be a measurement error, so it is not preferable to perform more control than necessary. Therefore, for the above-mentioned time difference, the absolute value of T is set in advance as the allowable time width T.
Correction is made only when the value exceeds a.

If it exceeds (S9), the correction coefficient C is 1-C×
ΔT is calculated (SIO) and it is stored. Then, the suppression of starting the engine 1 by the energization to the hot wire 8 and the starting delay means 12 is released (Sll), and the engine 1
rotates. Air is drawn into the intake passage 2, and the hot wire 8 measures the amount of intake air and multiplies it by the above-mentioned correction coefficient Cw to determine the true amount of intake air. When this intake air amount is divided by the rotation speed detected by the rotation speed sensor 6, the intake air amount per revolution is determined, and the fuel amount suitable for the intake air amount is selected to obtain the desired air-fuel ratio. , fuel injection nozzle 5
is injected from.

Note that in step 9, the absolute value of T to the time difference is Ta
If it is smaller, no correction is required, so 1 is selected as the correction coefficient Cw (S12), and the intake air amount measured by the hot wire 8 is treated as the true intake air amount. Incidentally, if the temperature of the hot wire after burn-off described above has not yet reached an appropriate temperature for collecting correction data, the previously stored correction coefficient is employed (S13), and the intake air amount is corrected.

〔Effect of the invention〕

As can be seen from the description of the embodiments above, the present invention includes a start delay means for delaying start-up when the ignition switch is turned on, a time difference calculation means for calculating a time difference by detecting the time it takes for the hot wire to change a predetermined temperature, and Since it is equipped with an intake air amount correction means for correcting the flow rate detection characteristics of the hot wire, it is possible to accurately measure the degree of change in the characteristics of the hot wire before starting the engine.
Based on this, the measured value is corrected, and the amount of intake air in the intake passage can be accurately measured.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the configuration of the hot wire air flow measuring device of the present invention, Fig. 2 is an overall schematic system diagram of an engine to which this device is installed, and Fig. 3 shows a hot wire heated to a predetermined temperature. FIG. 4 is a flowchart explaining the operation of the present device. 8--Hot wire, 10-Ignition switch, 11-Starter, 12-Start delay means, 13-Time difference calculation means, 14. - Intake volume correction means.

Claims (1)

[Claims] A hot wire air flow rate measuring device that detects the amount of intake air using a hot wire, comprising a start delay means for delaying the start of the engine by a starter when the ignition switch is turned on, A time difference calculation means for detecting the time for changing the temperature of the hot wire to a predetermined value and calculating a difference from a preset reference time; and an intake air amount correction means for correcting a characteristic change of the hot wire from the time difference. A hot wire air flow measuring device characterized by the following.