JPH0359365B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a physical quantity measuring device for measuring a physical quantity such as an air flow rate taken in from an intake pipe of an internal combustion engine.

Conventionally, intake air is measured by converting the intake air flow rate into an electrical signal (voltage output) using a variable resistance value that is linked to a measuring plate that is placed in the intake pipe of an internal combustion engine and rotates according to the intake air flow rate. Flow measuring devices are widely known.

In addition, in digital engine control devices using microcomputers that have rapidly come into use in recent years, the voltage output value of the measured intake air flow rate is converted into a digital value using an A/D (analog/digital) converter. The digital value determines fuel injection amount, ignition timing, etc.

However, in the high engine speed and high air flow range of the engine, the measurement plate vibrates in small increments at high frequency due to resonance with the intake pulsation, and as a result, contact resistance may increase at the variable resistor portion. As the contact resistance increases, the measured voltage output value increases;
The air flow rate measuring device will determine that the air flow rate is lower than the air flow rate actually taken into the engine. Therefore, since the amount of fuel injected is less than the amount actually required, the air-fuel ratio deviates to a leaner one, resulting in an increase in exhaust temperature and catalyst temperature, which can lead to engine trouble. Ta.

The present invention was made in view of the above problems, and
The purpose is to determine physical quantities such as the air flow rate sucked into the engine without error.

Hereinafter, the present invention will be explained in detail by way of an example. In FIG. 1, 1 indicates a multi-cylinder, for example, a six-cylinder internal combustion engine. 2 is an air cleaner, 3 is a flow rate sensor that outputs an analog voltage according to the intake air flow rate, 5 is a throttle body equipped with a throttle valve 6, 7 is an intake manifold, and 8 is an ignition distributor, which controls internal combustion. It houses a crank angle sensor that detects the engine crank position and a rotation sensor that detects the rotational speed.

Reference numeral 9 indicates an electromagnetically actuated fuel injection valve that is attached near each cylinder port of the intake manifold 7 and injects fuel. Reference numeral 10 denotes an electronic control device for the internal combustion engine, which outputs a fuel injection pulse signal representing the opening time of the fuel injection valve 9 based on a signal from the flow rate sensor 3, a rotational speed signal from the distributor 8, and the like.

FIG. 2 is an internal block diagram of the electronic control device 10. In FIG. 2, numeral 21 indicates a microprocessor which forms the main part of the computer. 22 is
This is a memory that includes ROM and RAM, and stores control programs for the internal combustion engine. 23 is A/D
The A/D converter 23 receives an analog voltage from a flow sensor or the like, and generates a pulse having a width corresponding to the analog voltage. 25 is I/O
It is an input/output unit, and signals from various sensors (not shown) and the digital input circuit 26 are inputted thereto. An internal counter in I/O unit 25 counts pulses from A/D converter 23. The count value is sent to the microprocessor 21 and read as a digital value. The digital input circuit 26 receives a signal N from a rotation sensor in the distributor 8, a signal G from a crank angle sensor, and the like.

The microprocessor 21 determines the fuel injection amount Q/N based on the control program stored in the ROM, using the signal N from the rotation sensor and the air flow rate signal Q from the A/D converter 23 as main information. A digital signal is output to the output circuit 27 after calculation is performed and correction terms based on the water temperature signal, intake temperature signal, etc. from the A/D converter 23 are added.

FIG. 3 shows the configuration of the flow rate sensor 3. The flow rate of air taken into the engine is measured using the principle that the measuring plate 31 is pushed open by the pressure difference generated when air passes through. Slider 3 of variable resistor 30 mounted coaxially with plate 31
2 slides on the resistive film 33, air flow is detected as a voltage signal. Here, Vs means the voltage force equivalent to the intake air flow rate, and Vc means the constant voltage, so the higher the intake air amount, the more the voltage output
Vs becomes smaller.

FIG. 4 shows a detailed circuit of the flow rate sensor 3 and the A/D converter 23. In FIG. 4, a constant voltage Vc is applied to both ends of the resistive film 33 by the A/D converter 23, and the slider 32
The contact resistance Rs generated at the contact portion between the resistive film 33 and the slider 32 is equivalently shown in the part.

Further, a capacitor C' having a capacitance of 0.2 microfarad or more is connected in parallel between the slider 32 and the input terminal of the A/D converter 23. Note that GND is a grounding terminal.

The operation of the above configuration will be explained. In the flow rate sensor 3, a slider 32 slides on a resistive film 33 according to the intake air flow rate, changes the resistance value Rp according to the intake air flow rate, and generates a voltage Vs.
At that time, the measurement plate 31 of the flow rate sensor 3 vibrates due to resonance with the intake pulsation, and the resistance film 33 and slider 32
A contact resistance Rs occurs at the contact point. The voltage Vs corresponding to the intake air flow rate is determined by the pulse current Is sent out from the A/D converter 23 at regular intervals.
It is measured as Vs=Is×(Rp+Rs). However, in extremely high rotation and high air volume regions, the contact resistance Rs increases by ΔRs.

Therefore, Vs=Is×(Rp+Rs+ΔRs), and the voltage output increases by ΔVs=Is×ΔRs, and if this continues, the intake air amount Q will be measured to be smaller than the actual amount.

However, in the present invention, by providing a capacitor C and utilizing the charge/discharge characteristics of the capacitor, Vs
The potential of is smoothed. As a result of this smoothing, the potential of Vs becomes close to the true potential, and a voltage representing the intake air flow rate with less error is input to the microprocessor 21, allowing more accurate measurement of the intake air flow rate.

Furthermore, as shown in FIG. 5, the A/D conversion cycle of the air flow rate signal is changed in the high rotation range using the program of the electronic control device of the internal combustion engine, that is, the A/D converter 23 By changing the cycle of the pulse current Is, it becomes possible to use a capacitor with a larger capacity.
Therefore, the potential of Vs is further smoothed.

In FIG. 5, the microprocessor 21 outputs an A/D conversion command signal to the A/D converter ₂₃ every few milliseconds to execute the A/D conversion. Determine whether N is higher than the set rotation speed N _A , and if it is lower than the set rotation speed
If the answer is No, the A/D conversion period at step _S2 is set to the normal A/D conversion period. If it is higher than the set rotation speed N _A , the answer is Yes in step _S1 , and the A/D conversion cycle is changed to twice the normal time in step _S3 .

In step _S4 , the value of the A/D conversion cycle is checked, and if it is determined that an A/D converter should be used in the current cycle, the result is Yes, and an A/D conversion command signal is output in step _S5 . , the A/D converter 23 executes A/D conversion.

If it is determined in step _S4 that A/D conversion should not be performed, the answer is No and step _S5 is skipped.

FIG. 6 shows the effect of the present invention when the contact resistance increases, and a shows the movement of the voltage output Vs corresponding to the intake air flow rate in the conventional device. b puts capacitor C in the circuit,
The Vs potential is smoothed, and c is the one in which the period of the pulse current Is sent out by the A/D converter 23 is changed by the control program (in the figure, it is doubled) to measure the voltage output of Vs. ), and Vs when a large capacitor is installed in the circuit.
This shows the movement of potential.

In FIG. 6, level 1 is the potential of Vs corresponding to the actual intake air flow rate, and level is the voltage output of Vs detected by the microprocessor 1 by passing the pulse radio wave Is from the A/D converter 23. Show value. As will be understood, traditionally, true
The Vs potential (level 2) detected by the electronic control unit, which has a large potential difference from the Vs potential (level 1), can be obtained by smoothing the Vs potential by inserting a capacitor C and by changing the A/D conversion cycle. By changing the period of the pulse current Is, it becomes close to the true Vs potential (level 1), making it possible to accurately measure the amount of absorbed air.

In the flowchart of FIG. 5, the A/D conversion is set by determining the number of revolutions, but the period of A/D conversion may be changed by determining the amount of air instead of the number of revolutions.

As described above, according to the present invention, it is possible to reduce the increase in detection potential due to the contact resistance of the variable resistor, which increases especially at high speeds, by smoothing it with a capacitor. is the A/D conversion period, that is, the A/D
By lengthening the period of the pulse current flowing out from the converter, it becomes possible to use a large capacity capacitor, which allows for smoother smoothing, and allows for accurate measurement of a given physical quantity such as the amount of intake air in an internal heat engine. A/D
There is an excellent effect that can be converted and imported into a computer, which is impossible to achieve with the invention described in the above reference.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram showing an embodiment of the present invention;
Fig. 2 is a block diagram showing the electronic control unit, Fig. 3 is a block diagram showing the flow rate sensor, Fig. 4 is an electric circuit diagram showing the connection between the flow rate sensor and the A/D converter, and Fig. 5 is the microprocessor. FIG. 6 is a flowchart showing the main parts of the operation, and FIG. 6 is a waveform diagram for explaining the operation. 3...Flow rate sensor, 21...Microprocessor, 23...A/D converter, 30...Variable resistor, 31...Measuring plate, C...Capacitor.

Claims (1)

[Scope of Claims] 1. A variable resistance sensor having a variable resistor that detects a predetermined physical quantity such as the intake air amount of an internal combustion engine and outputs an analog voltage; A physical quantity of an internal combustion engine comprising an A/D converter that conducts current and A/D converts an analog voltage from the variable resistor generated by the pulsed current, and a computer that receives a digital signal from the A/D converter. In the measuring device, a capacitor for smoothing the analog voltage related to the physical quantity is provided between the variable resistor and the A/D converter, and the computer controls the A/D converter when the engine speed increases above a predetermined value. A physical quantity measuring device for an internal combustion engine, including means for changing the A/D conversion period of a converter to a longer period. 2. The physical quantity measuring device for an internal combustion engine according to claim 1, wherein the capacitor has a capacity of 0.2 microFarad or more.