JPH0435008B2 - - Google Patents

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 measures characteristic changes due to deterioration of a hot wire using a deterioration index measured in a state where air is not moving. The present invention relates to an air flow measuring device that corrects air flow rate. 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 of a hot wire flowmeter using a hot wire as a measuring device is
It is described in Japanese Utility Model Application Publication No. 155427/1983.

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 a hot wire changes depending on the air flow rate passing through it. However, after being used for many years while attached to the intake passage of an engine, it deteriorates and its flow rate detection characteristics change. Furthermore, when dust that flows through the intake passage adheres or is removed, the heat dissipation area changes each time, and a similar phenomenon occurs. If such a state is left as it is, the measurement accuracy of the air flow rate by the hot wire will deteriorate, making it impossible to use it for adjusting the air-fuel ratio.

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 changes in characteristics due to 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, the degree of deterioration of the hot wire can be measured. An object of the present invention is to provide a hot wire type air flow measuring device whose characteristics can be corrected.

[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 start delay means that delays the start of the engine by the starter when the ignition switch is turned on. time difference calculation means for detecting and calculating the difference from a preset reference time;
The present invention is provided with an intake air amount correction means for correcting a change in characteristics of the hot wire based on the time difference.

[Effect]

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, the intake air does not flow through the intake passage, and in this state, the 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 detected 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, and the amount of fuel supplied is controlled to obtain a desired air-fuel ratio, thereby creating a mixture with an air-fuel ratio that is optimal for engine operation.

〔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. Engine control circuit 4
In order to control the engine speed, the engine 1 is equipped with a rotation speed sensor 6 for detecting its rotation speed, and the intake passage 2 immediately after the air cleaner 7 is equipped with a hot wire 8.
A temperature sensor 9 is provided to detect the temperature. Furthermore, the control circuit 4 is also configured to receive a signal indicating whether the ignition switch 10 is turned on or off.

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 the hot wire 8.
Correction control is also performed to correct changes in characteristics. That is, the control circuit 4 includes the start delay means 12, the time difference calculation means 13, and the intake air amount correction means 14 shown in FIG.

The start delay means 12 starts the engine 1 by the starter 11 when the ignition switch 10 is turned on.
This is to temporarily delay the startup of the starter switch, and to prevent the flow of intake air in the intake passage 2 during the very short period of time until the hot wire correction preparations are completed even after the starter switch is turned on. be. Note that this delay time is a short time, for example, several tens of milliseconds, which will be described later, so it is 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 required time when the hot wire is normal (predetermined in advance). (set as a reference time) to confirm 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, the hot wire 8
If dust adheres to or removes from the wire, or if the wire 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. Since this error can be ascertained by the difference in the temperature rise rate of the hot wire, the hot wire is placed in a state where it is not affected by air flow so that the temperature rise rate can be measured in advance.

The measurement is carried out 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 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 change in characteristics of the hot wire from the time difference, and obtains a correction coefficient Cw. This correction coefficient Cw is 1
-C×ΔT, 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, in the following,
Include and explain the steps to avoid the harm caused by the operation.

According to the above-described embodiment, the hot wire correction is performed as follows. When the ignition switch 10 is turned on (Step 1 of the flowchart in FIG. 4, hereinafter referred to as S1, etc.), the start delay means 12 immediately starts the starter
(S2). Then, no movement of air occurs in the intake passage 2,
The air at the location where the hot wire 8 is attached remains stationary. Since the car is burnt off immediately after it is stopped, if too much time has passed since the car was stopped, the hot wire may not have returned to an appropriate temperature to take data for correction. 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 (S4) and the timer starts counting time (S5). The hot wire 8 is set to a predetermined temperature of 100% from the initial temperature.
When the temperature sensor 9 detects that the temperature has increased (S6), the time Trw required for this is measured by the timer (S7), and the difference △T from the separately stored required time Tsw in the normal case is The time difference calculation means 13 calculates the deterioration index (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, the above-mentioned time difference ΔT is corrected only when its absolute value exceeds a preset allowable time width Ta. If it exceeds (S9), a correction coefficient Cw is calculated as 1-C×ΔT (S10), and it is stored. Then, the energization of the hot wire 8 and the inhibition of starting the engine 1 by the start delay means 12 are canceled (S11), and the engine 1 rotates. Air is taken 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.

In addition, in step 9, if the time difference ΔT is smaller than the absolute value Ta, 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 used as the true intake air amount. be treated. 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 adopted (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 has the following features:
Start-up delay means that delays startup when the ignition switch is turned on; Time difference calculation means that calculates a time difference by detecting the time it takes for the hot wire to change a predetermined temperature; and Air intake amount correction means that corrects the flow rate detection characteristics of the hot wire based on the time difference. This makes it possible to accurately measure the degree of change in the characteristics of the hot wire prior to starting the engine, and to correct the measured value based on this to accurately measure the amount of intake air in the intake passage. I can do it.

[Brief explanation of drawings]

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 the case where the hot wire is heated to a predetermined temperature. FIG. 4 is a flowchart explaining the operation of this device. 8...Hot wire, 10...Ignition switch, 11...Starter, 12...Start delay means, 13...Time difference calculation means, 14...Intake air amount correction means.

Claims (1)

[Scope of Claims] 1. In a hot wire type air flow measuring device that detects the amount of intake air using a hot wire, a start delay means delays starting of the engine by a starter when the ignition switch is turned on, and a state in which the engine is stopped. and 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.