JPH05149186A - Intake air flow rate detecting device for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent a detected value, being excessive to a true intake air flow rate, from being outputted right after a power supply is closed to a temperature-sensitive flow meter. CONSTITUTION:A lapse time (t) starting from turning ON of an ignition switch and a power supply is closed to a temperature-sensitive type flow meter is measured at steps S1-S4. When, the lapse time (t) at a step 6, is within the error occurring time T (at a step S5) of the temperature-sensitive type flow meter set according to a source voltage VB, an intake air flow rate Q set based on a throttle valve opening alpha and an engine rotation speed N produces a final output at a step S7. When a time T exceeds the lapse time (t), the intake air flow rate Q normally based on the output of a temperature-sensitive type flow meter 1 in regaded as a finally detected result at stop 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an intake air flow rate detecting device for an internal combustion engine, and more particularly to a temperature sensitive flow meter for detecting an engine intake air flow rate based on a temperature sensitive resistance arranged in an intake passage of the internal combustion engine. The present invention relates to a technique for compensating for a detection error immediately after the power is turned on.

[0002]

2. Description of the Related Art An electronically controlled fuel injection system for an internal combustion engine is equipped with an air flow meter (air flow meter) for detecting the intake air flow rate Q of the engine, and the intake air flow rate Q detected by this air flow meter is It is known that the basic fuel injection amount Tp = K × Q / N (K is a constant) is calculated from the engine rotation speed N, and the air flow meter is disclosed in Japanese Utility Model Laid-Open No. 59-78926. In some cases, a temperature-sensitive flow meter as disclosed in US Pat.

In the temperature-sensitive flow meter, a so-called hot-wire type or hot-film type temperature-sensitive resistor is arranged in the intake passage, and an electric current is supplied to generate heat at a constant temperature (resistance value). The decrease is compensated by the increase in current,
The intake air flow rate is calculated from the current value. That is, FIG.
Taking the temperature-sensitive flow meter 1 in the example as an example, the temperature-sensitive resistance R
_{In addition to H} (hot wire or hot film), temperature compensation resistance R _K, reference resistance R _s, fixed resistances R _{1 and} R ₂ are provided,
The bridge circuit B is configured by these.

The temperature sensitive resistor R of the bridge circuit B
_H and the reference resistance R _s are connected in series, the potential at the voltage dividing point (the terminal voltage of the reference resistance R _s ) and the temperature compensation resistance R
_K and the potential of the voltage dividing point (the terminal voltage of the fixed resistor R ₂ ) on the side where the fixed resistors R _{1 and} R ₂ are connected in series are input to the differential amplifier OP, and the difference The supply current to the bridge circuit B is corrected via the transistor Tr according to the output of the dynamic amplifier OP.

That is, when the intake air flow rate of the engine increases, for example, when the bridge circuit B is in equilibrium,
The temperature-sensitive resistance R _H is further cooled by this air flow, its resistance value decreases, and the terminal voltage of the reference resistance R _s increases,
The bridge circuit B becomes unbalanced and the output of the differential amplifier OP increases. As a result, the supply current to the bridge circuit B controlled by the transistor Tr increases, the temperature-sensitive resistor R _H is heated, and its resistance value increases, whereby the balanced condition of the bridge circuit B is restored.

Here, when the temperature of the intake air decreases, for example, the temperature-sensitive resistor R _H is cooled and its resistance value decreases, but the temperature-compensating resistor R _{K in the} same atmosphere as the temperature-sensitive resistor R _H.
At the same time, the resistance value of the bridge circuit B is decreased and the resistance value of the bridge circuit B is decreased. Therefore, the change of the current value supplied to the bridge circuit B due to the temperature change of the intake air is suppressed. Therefore, the intake air flow rate of the engine and the current supplied to the bridge circuit B correspond independently of the intake air temperature, and the intake air flow rate can be measured by detecting the terminal voltage of the reference resistance R _s. it can.

[0007]

By the way, in the above-mentioned temperature sensitive flow meter using the temperature sensitive resistor, as described above, the supply current is controlled so as to keep the temperature of the temperature sensitive resistor constant. It takes a certain amount of time according to the heat capacity from turning on the power supply voltage to the temperature sensitive flow meter until the temperature sensitive resistance in the ambient temperature state reaches the normal control temperature (for example, about 400 ° C). In particular, in the case of a hot film type temperature sensitive flow meter, which generally has a larger heat capacity than the hot wire type, it takes a relatively long time to reach the normal control temperature. ..

[0008] Here, the bridge circuit is in an unbalanced state and a high current is supplied to raise the temperature of the temperature-sensitive resistor from the time when the temperature of the temperature-sensitive resistor is turned on until it reaches the vicinity of the normal control temperature. The high current at this time does not depend on the temperature drop of the temperature sensing resistor due to the increase of the intake air flow rate, but raises the temperature of the temperature sensing resistor from the ambient temperature state to around the normal control temperature. Since it is required for this, the intake air flow rate cannot actually be detected with high accuracy between the time the power is turned on and the temperature near the normal control temperature. Will be detected larger than that (see FIG. 4).

Therefore, if the starting state is entered before the temperature-sensitive resistance reaches the vicinity of the normal control temperature, the basic fuel injection amount is calculated based on the air flow rate larger than the true intake air flow rate. There was a fear that the air-fuel ratio of the engine intake air-fuel mixture would be made rich and the starting characteristics and exhaust characteristics would be adversely affected. Note that FIG. 4 shows the results of experiments in which the temperature-sensitive resistor is arranged in an air flow of a constant flow rate and the detection error decreases as the temperature of the temperature-sensitive resistor rises after the power is turned on.

The present invention has been made in view of the above problems, and the intake air flow rate of the engine is erroneously detected during the period from the power-on of the temperature-sensitive flow meter until the temperature-sensitive resistance reaches the vicinity of the normal control temperature. Accordingly, it is possible to suppress the adverse effect on the fuel control using the detected value of the intake air flow rate, and eventually to provide the intake air flow rate detection device for the internal combustion engine, which can improve the fuel controllability at the time of starting. To aim.

[0011]

Therefore, an intake air flow rate detecting device for an internal combustion engine according to the present invention is constructed as shown in FIG. In FIG. 1, a temperature-sensitive flow meter outputs a detected value of an engine intake air flow rate based on a resistance value change of a temperature-sensitive resistance arranged in an intake passage of an internal combustion engine according to an intake air flow rate.

The elapsed time measuring means measures the elapsed time since the power was turned on to the temperature sensitive flow meter. When the elapsed time measured by the elapsed time measuring means is within a predetermined time, the detection switching means replaces the detection result of the temperature-sensitive flow meter with a predetermined value equal to or less than the intake air flow rate corresponding to the engine start. The intake air flow rate is output as the detection result.

Here, it is preferable to provide detection switching time setting means for variably setting the predetermined time in the detection switching means in accordance with the power supply voltage of the temperature-sensitive flow meter. Further, an opening area detecting means for detecting the opening area of the engine intake system which is variably controlled and a rotation speed detecting means for detecting the rotation speed of the engine are provided, and a predetermined intake air flow rate in the detection switching means is set to the opening area. It is advisable to provide a switching output setting means for variably setting based on the detected values of the rotation speed and the rotation speed.

[0014]

According to this structure, within a predetermined time after the power supply to the temperature-sensitive flow meter is turned on, instead of outputting the detected value of the temperature-sensitive flow meter, the intake air flow rate is equal to or less than that when the engine is started. Since the predetermined intake air flow rate of is output,
It is possible to prevent an excessive intake air flow rate from being output as a detected value with respect to the true intake air flow rate, until the temperature-sensitive resistance reaches from the ambient temperature state to near the normal control temperature.

Further, since the time required for the temperature sensitive resistance to reach the vicinity of the normal control temperature from the cyclic temperature state changes according to the power supply voltage, the predetermined time is variably set according to the power supply voltage to detect it. The detection output can be switched according to the error generation period. Furthermore, if the predetermined intake air flow rate output instead of the detection value of the temperature sensitive flow meter is variably set based on the opening area of the intake system and the engine rotation speed,
It becomes possible to output a detection value close to the true intake air flow rate as compared with the case where a fixed value is adopted.

[0016]

EXAMPLES Examples of the present invention will be described below. FIG. 2 shows the hardware configuration of the embodiment, in which the power supply voltage (battery voltage) V _B is applied to the temperature-sensitive flow meter 1 via the ignition switch 2. The output voltage Us of the temperature-sensitive flow meter 1 is input to the microcomputer 4 via the A / D converter 3.

In addition, a rotation sensor 5 as a rotation speed detecting means for detecting the engine rotation speed N, and a temperature-sensitive resistor _{RH of the} temperature-sensitive flow meter 1 are provided in an engine intake passage (not shown). A throttle sensor 6 as an opening area detecting means for detecting the opening α of the throttle valve is provided, and the detection signals from these sensors are input to the microcomputer 4 together with the output voltage Us of the temperature-sensitive flow meter 1. It is supposed to be done.

Here, the microcomputer 1 calculates the basic fuel injection amount Tp = K × Q / N (K is a constant) based on the detected values of the engine intake air flow rate Q and the engine rotation speed N, and The final fuel injection amount Ti is calculated by appropriately correcting the basic fuel injection amount Tp, and an injection pulse signal having a pulse width corresponding to this fuel injection amount Ti is generated at a predetermined timing synchronized with the engine rotation by an electromagnetic system (not shown). The fuel supply to the engine is electronically controlled by outputting to the fuel injection valve.

Since the structure and operation of the temperature-sensitive flow meter 1 have been described above, a detailed description of the temperature-sensitive flow meter 1 will be omitted here. Next, the microcomputer 4
Fig. 3 shows how the intake air flow rate Q is detected by
It will be described according to the flowchart of In this embodiment, it is assumed that the microcomputer 4 has the functions of the detection switching means, the elapsed time measuring means, the detection switching time setting means, and the switching output setting means, as shown in the flow chart of FIG. ..

In the flow chart of FIG. 3, first, in step 1 (denoted as S1 in the figure, the same applies hereinafter),
The on / off state of the ignition switch 2 is determined. When the ignition switch 2 is off, the routine proceeds to step 2, where the timer for measuring the elapsed time t from the power-on of the temperature-sensitive flow meter 1 is reset to zero, and when the ignition switch 2 is on, Go to step 3.

In step 3, it is judged whether or not the ignition switch 2 is turned on for the first time, and when the ignition switch 2 is turned on for the first time, in other words, the power source to the temperature-sensitive flow meter 1 is determined. When the power is on, the routine proceeds to step 4, where the counting of the timer (measurement of elapsed time from power-on) is started. In step 5, the switching control time T corresponding to the current power supply voltage V _B is set by referring to a map in which the switching control time T is set in advance using the power supply voltage V _B of the temperature sensitive flow meter 1 as a parameter.

In the next step 6, the elapsed time t from when the ignition switch 2 is turned on, which is measured by the timer, is t.
And the switching control time T are compared. When the elapsed time t has not reached the switching control time T, the process proceeds to step 7. In step 7, the map in which the data of the intake air flow rate Q corresponding to the throttle valve opening α and the engine speed N is stored beforehand is referred to, and the latest detected values of the throttle valve opening α and the engine speed N are corresponded. The intake air flow rate Q to be obtained is searched and obtained.

The throttle valve opening α is a value representative of the opening area of the engine intake system which is variably controlled by the throttle valve. In step 7, the opening area of the intake system and the engine speed are set as conditions. The intake air flow rate Q at the time of starting is indirectly obtained, and a value substantially corresponding to the true intake air flow rate Q is finally set. On the other hand, when it is determined in step 6 that the elapsed time t exceeds the switching control time T, the process proceeds to step 8 and the output voltage U of the temperature-sensitive flow meter 1
A process of converting s into the intake air flow rate Q based on a preset conversion characteristic is performed.

That is, when the elapsed time t has not reached the switching control time T, the throttle valve opening α and the engine speed N are used without using the output voltage Us of the temperature-sensitive flow meter 1.
The intake air flow rate Q predicted from the above is output as a final detected value, and after the elapsed time t exceeds the switching control time T, the intake air flow rate Q is calculated using the output voltage Us of the temperature-sensitive flow meter 1. The detection value is set, and the detection result of the intake air flow rate Q, which is switch-controlled as described above, is used for the calculation of the basic fuel injection amount Tp.

Here, the switching control time T depends on the detection error characteristic between the temperature sensing resistor _RH and the normal control temperature state after the power is turned on to the temperature sensing flow meter 1. Te has been set in advance, since the temperature rise characteristic of the temperature-sensitive resistor R _H by the power supply voltage V _B changes, in this embodiment, so as to variably set the switching control time T according to the power supply voltage V _B I am doing it. However, for simplicity, the switching control time T may be a fixed time. Since the detection error characteristic is caused by the difference between the temperature of the temperature sensitive resistor R _H and the normal control temperature, the ambient temperature when the power is turned on is used as a parameter, and the ignition switch 2 is repeatedly turned on / off. The switching control time T may be variably set by using the elapsed time from the turning off of the ignition switch 2 as a parameter to cope with the case where the switching is turned off.

In the temperature-sensitive flow meter 1, the temperature is higher than the output voltage corresponding to the true intake air flow rate Q while the temperature of the temperature-sensitive resistance R _H rises up to around the normal control temperature after the power is turned on. Since a voltage is output, a larger detection error occurs as the elapsed time from power-on is shorter and the temperature of the temperature sensitive resistor R _H is lower (see FIG. 4). Therefore, for example, when the switching control time T is set, the detection error in the temperature-sensitive flow meter 1 is at an allowable level (detection error ± 4%).
4 (time t ₂ in FIG. 4, for example, about 0.3 to 1 second) until the temperature-sensitive resistor _RH is warmed from the ambient temperature to a predetermined normal control temperature. During this period, the detection value having a large detection error is avoided from being output as it is, and the intake air flow rate Q at the time of starting, which is closer to the true intake air flow rate Q predicted from the opening α and the rotation speed N, is obtained. Can be output as a detection value.

Therefore, even if the starting (cranking) is started during the time from turning on the power until the temperature-sensitive resistor R _H is warmed to near the normal control temperature, the opening α (opening area) and the rotation speed N are Since it is possible to output the amount of air flow at the time of starting that is obtained from the above, it is possible to calculate the basic fuel injection amount Tp that approximately matches the true cylinder intake air amount, and the air-fuel ratio at the time of starting is optimized. As a result, startability and exhaust gas characteristics at the time of starting are improved.

As described above, since the detection error becomes larger as soon as the temperature-sensitive flowmeter 1 is turned on, the time t ₁ in FIG. 4, that is, the balance of the bridge circuit is extremely disturbed and the maximum output is obtained. The intake air flow rate Q detection value is set based on the opening α and the rotation speed N only during the undetectable period (maximum detection error period) in which the voltage is output, and the detection error converges from time t _1. In the period up to time t ₂ (for example, about 8 seconds), although there is a detection error, the error level decreases, so the output of the temperature-sensitive flow meter 1 may be used as it is. In this case, the switching control time T in the flowchart of FIG. 3 may be matched so as to correspond to the time t ₁ in FIG.

Further, in this embodiment, the opening α and the rotation speed N
The intake air flow rate Q predicted based on the above is output instead of the detection output by the temperature-sensitive flow meter 1.
Intake air flow rate Q expected to be obtained when the engine is started
The following predetermined intake air flow rate (for example, 0 to several tens kg / h) is set in advance, and the predetermined intake air flow rate (fixed value) is output as a detection value within a predetermined time after the power is turned on. Is also good.

That is, immediately after the power is turned on when the temperature-sensitive flow meter 1 detects the intake air flow rate Q excessively, at least a detected value larger than the true intake air flow rate Q is finally output. If avoided, the accuracy will deteriorate as compared with the case where the intake air flow rate Q is indirectly determined from the opening area and the engine rotation speed, but at least the detection error of the intake air flow rate at the time of start-up causes the air-fuel ratio to become rich, It is possible to prevent the deterioration of the exhaust gas characteristics (increase in the emission amount of unburned components). In other words, the variable setting of the intake air flow rate Q based on the opening area and the engine rotation speed can output a value that follows the true intake air flow rate Q at the start, whereas Although the output cannot cope with the change in the true intake air flow rate Q at the time of starting, it is simple and easy to avoid that a detection value that is at least larger than the true intake air flow rate is output and unburned components are discharged. Is the way.

When a fixed value is output instead of the output of the temperature-sensitive flow meter 1 as described above, the period until the detection error of the temperature-sensitive flow meter 1 is converged may be used as the fixed value output period. Although it is good, it is preferable that the detection error of the temperature-sensitive flow meter 1 is up to a period (time t ₁ ) immediately after power-on, and if it is limited to the time t ₁ , the intake air is reduced during this period. Even if the flow rate Q is forced to be output when it is zero,
Since the time t ₁ is short, even if the start is started during this time, the startability is not adversely affected.

However, even during the period from the time t ₁ to the time t _{2 in} FIG. 4 in which the start of the engine is normally started, the fixed intake air flow rate below the intake air flow rate corresponding to the engine start is finally output. Is not able to follow the fluctuation of the true intake air flow rate Q at all, and there is a possibility that the startability is deteriorated. Therefore, as described above, during the period from time t ₁ to time t ₂ , It is desired to detect the intake air flow rate Q based on the rotation speed N or to use the output of the temperature-sensitive flow meter 1 as a final detection result although it includes a detection error.

Further, since the throttle valve is often in the fully closed state at the time of starting, the intake air flow rate Q at the time of starting is predicted by using only the rotation speed N as a parameter, and this is replaced with the output of the temperature-sensitive flow meter 1. You may make it output it.
The temperature-sensitive resistance R _H may be either a so-called hot wire type or a hot film type, but the time until the detection error converges due to a large heat capacity (time t in FIG. 4).
_The longer the value of ₂ ), the greater the effect of performing the control shown in this embodiment.

[0034]

As described above, according to the present invention, immediately after the power is turned on, the temperature-sensitive flowmeter has a large detection error.
By avoiding the detection value of the temperature-sensing flow meter, by outputting a predetermined intake air flow rate that is less than or equal to the intake air flow rate corresponding to engine startup, it is possible to avoid outputting an excessively large detection value for the true intake air flow rate. Therefore, when the fuel control is performed based on the detected value of the intake air flow rate, the startability and the exhaust gas characteristic at the start can be improved.

Further, if the predetermined time without using the output of the temperature-sensitive flow meter is variably set according to the power supply voltage of the temperature-sensitive flow meter, it is possible to set a period suitable for the detection error characteristic of the temperature-sensitive flow meter. ,
It becomes possible to switch the output. Furthermore, if the predetermined intake air flow rate output instead of the detection value of the temperature-sensitive flow meter is set based on the opening area of the intake system and the engine rotation speed, the detection value of the temperature-sensitive flow meter will be substantially Even in a period in which the intake air flow rate cannot be used for a long time, the detected value of the intake air flow rate can be obtained by substantially corresponding to the fluctuation of the true intake air flow rate.

[Brief description of drawings]

FIG. 1 is a block diagram showing a basic configuration of the present invention.

FIG. 2 is a system schematic diagram showing a hardware configuration of an embodiment of the present invention.

FIG. 3 is a flowchart showing how the flow rate is detected in the embodiment.

FIG. 4 is a diagram showing a detection error characteristic of a temperature-sensitive flow meter.

[Explanation of symbols]

 1 Temperature-sensitive flow meter 2 Ignition switch 4 Microcomputer 5 Rotation speed sensor 6 Throttle sensor

Claims (3)

[Claims] 1. A temperature-sensitive flow meter for outputting a detected value of an engine intake air flow rate based on a resistance value change of a temperature-sensitive resistance arranged in an intake passage of an internal combustion engine according to an intake air flow rate; The elapsed time measuring means for measuring the elapsed time after the power supply to the flow meter is turned on, and when the elapsed time measured by the elapsed time measuring means is within a predetermined time, the detection result by the temperature sensitive flow meter is displayed. Instead, an intake air flow rate detection device for an internal combustion engine, comprising: a detection switching unit that outputs a predetermined intake air flow rate equal to or less than the intake air flow rate corresponding to engine startup as a detection result. 2. An internal combustion engine according to claim 1, further comprising detection switching time setting means for variably setting the predetermined time in the detection switching means in accordance with a power supply voltage of the temperature-sensitive flow meter. Intake air flow rate detector. 3. An opening area detection means for detecting an opening area of an engine intake system which is variably controlled, a rotation speed detection means for detecting a rotation speed of an engine, and a predetermined intake air flow rate in the detection switching means, 3. The intake air flow rate detection device for an internal combustion engine according to claim 1, further comprising: a switching output setting unit that variably sets based on detected values of an area and a rotation speed.