JP2551972B2 - Intake air amount measuring device for internal combustion engine - Google Patents

Description

The present invention relates to an intake air amount measuring device for an internal combustion engine.

[Prior Art] Conventionally, an intake air amount measuring device using a thermal air meter for measuring the intake air amount of an internal combustion engine is disclosed in, for example, Japanese Patent Laid-Open Nos. 55-50121 and 62-55517. It is disclosed. In this device, there is a temperature characteristic in its output characteristic, and this output characteristic is caused by the temperature dependence of the heat radiation coefficient from the intake air amount detecting resistor. In order to compensate for this temperature characteristic, for example, as shown in FIG. 6 of Japanese Patent Laid-Open No. 62-55517, a temperature measuring element 2 which is installed in the intake pipe 1 and whose resistance value changes according to the air temperature, and an intake air A bridge circuit is formed by the intake air amount measuring resistor 3 installed in the tube 1 and the fixed resistors 4, 5 and 6 having no temperature dependence, and the temperature characteristic is corrected by the bridge circuit. Was becoming.

[Problems to be Solved by the Invention] However, the temperature characteristic of the heat radiation coefficient does not become a constant characteristic with respect to the intake air amount depending on the shape, material, and configuration of the intake air amount measuring resistor 3, but has a flow rate dependency. In some cases, the conventional control method in which constant correction is performed regardless of the magnitude of the flow rate has a problem that ideal temperature characteristics cannot be compensated over the entire range of the measured air amount.

That is, as shown in FIG. 7, the intake air amount measuring resistor 3 is arranged on the support substrate 7 and attached to the support member 9 via the heat insulating member 8. There are two heat radiation paths from the intake air amount measuring resistor 3, that is, heat transfer to the air to be measured and conduction heat transfer to the support member 9 via the support substrate 7 and the heat insulating member 8. If the control temperature of the intake air amount measuring resistor 3 is TH, the temperature of the air to be measured is Ta, the temperature difference between both TH and Ta is ΔTH, and the mass flow velocity of air is u · ρ (however,
u is the flow velocity of air, ρ is the density of air), heat transfer heat quantity Q1 to air and heat transfer heat quantity Q2 through each member 7,8,9 are Q2 = α (Ta) ・ K2 ・ ΔTH where K1 and K2 are constants determined by the shape, material, and structure of the intake air amount measuring resistor, β (Ta) is the physical value of the air to be measured, and α (Ta) is Material constituting the conduction heat transfer path 7,8,9
Thermal conductivity of.

And the total heat dissipation QTOTAL is Becomes

here, Express.

Then, FIG. 8 shows the change of the total heat dissipation coefficient H (Ta) depending on the amount of air, and FIG. Figure 10 shows a general example of the change of α (Ta) · K2 with temperature. As shown in FIG. Is a function of the mass flow rate u · ρ, and increases monotonically with the increase of the mass flow rate u · ρ, and α (Ta) · K2 is the mass flow rate u · ρ.
Is a constant value for. Therefore, the ratio to the total heat dissipation coefficient H (Ta) of both changes depending on the magnitude of the mass flow rate u · ρ. Also, the respective temperature characteristics of both are β as shown in FIG. Has a positive temperature characteristic that increases with increasing temperature.
As shown in the figure, α (Ta) · K2 has a negative temperature characteristic that decreases with increasing temperature. As a result, the temperature characteristics of the total heat dissipation coefficient H (Ta) are shown in FIGS.
As shown in (c), it depends on the air flow rate, and different air flow rates G1, G2, and G3 (G1 <G2 <G3) require different correction on the circuit side.

However, since the conventional device shown in FIG. 6 can only make a certain correction regardless of the air flow rate, as shown in FIG.
For example, if the air temperature is set to 20 ° C as a reference, at -20 ° C and 80 ° C, which deviate from the reference temperature of 20 ° C, optimum correction can be performed at a specific flow rate (G2) and output error can be eliminated. However, the correction was not optimal at other flow rates (G1, G3), so an error occurred and the ideal temperature characteristics could not be corrected over the entire air amount range.

An object of the present invention is to provide an intake air amount measuring device for an internal combustion engine, which is capable of performing optimum temperature compensation over the entire air amount range.

[Means for Solving the Problem] In order to achieve the above object, the present invention is installed in an air flow to be measured, and a temperature measuring element whose resistance value changes according to the air temperature and an air flow to be measured are installed. The intake air amount measuring resistor and a fixed resistor having no temperature dependence form a bridge circuit, and the intake air amount of the internal combustion engine is measured while correcting the temperature characteristic of the bridge circuit. In the intake air amount measuring device, a plurality of sets of the fixed resistors having different resistance values are provided, and a selection means for selecting one of the plurality of sets of fixed resistors according to the intake air amount is provided. The subject is an intake air amount measuring device.

[Operation] The selecting means selects one of a plurality of sets of fixed resistors having different resistance values according to the intake air amount, and the temperature is corrected by the correction characteristic of the fixed resistor.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, a combustion chamber of an engine serving as an internal combustion engine sucks air through an intake pipe 11. An intake air amount measuring resistor 12 and a temperature measuring element 13 are arranged in the intake pipe 11. The intake air amount measuring resistor 12 and the temperature measuring element 13 are constituted by a resistance element having a temperature-resistance characteristic set by a resistance value corresponding to temperature, and a platinum wire or the like is used. Intake air amount measuring resistor
Heating power is supplied to a connection point between 12 and the temperature measuring element 13 via a transistor Tr.

The intake air amount measuring resistor 12 is grounded via a fixed resistor 14. On the other hand, the temperature measuring element 13 is grounded via a first switching circuit 15 as switching means and fixed resistors 16 and 17 as fixed resistors connected in series. Further, the temperature measuring element 13 is connected to fixed resistors 18 and 19 as fixed resistors which are also connected in series via the first switching circuit 15 and is grounded via the resistors 18 and 19. . These two sets of fixed resistors 16 and 17 and fixed resistors 18 and 19 are
The intake air amount measuring resistor 12 has different resistance values determined by the shape, material and the like. By the switching operation of the first switching circuit 15, the fixed resistors 16 and 17 are connected to the temperature measuring element 13, or the fixed resistors 18 and 19 are connected.
Can be switched to the connected state.

In this embodiment, a bridge circuit is composed of the intake air amount measuring resistor 12, the temperature measuring element 13, the fixed resistor 14, the fixed resistors 16 and 17, or the fixed resistors 18 and 19.

A connection point a between the fixed resistance 16 and the fixed resistance 17 and a connection point b between the fixed resistance 18 and the fixed resistance 19 are respectively connected via a second switching circuit 20 as switching means to a comparator.
21 is connected to one input terminal. Then, by the switching operation of the second switching circuit 20, the connection point a and the comparator are
21 is connected, or connection point b and comparator 21
It is possible to switch to the state where and are connected. The second switching circuit 20 and the first switching circuit 15
Means that both switching circuits 20 and 15 are switched by a switching signal generated by an engine control unit (not shown) depending on the amount of air.

The connection point c between the intake air amount measuring resistor 12 and the fixed resistor 14 is connected to the other input terminal of the comparator 21, and the potential of the connection point a or b and the connection point c is the comparator 21. Be compared. That is, the potentials at the connection point a or b and the connection point c when the transistor Tr is on and heating power is supplied are compared, and the temperature of the intake air amount measuring resistor 12 is specified with respect to the air temperature. A signal is output from the comparator 21 when the temperature difference rises to the set state.

The output terminal of the comparator 21 is connected to the reset terminal of the flip-flop circuit 22, and the circuit 22 is set by a start pulse signal which is periodically output. The output signal of the flip-flop circuit 22 is supplied as an intake air flow rate measurement signal to an engine control unit (not shown) via the buffer 23. The output signal of the buffer 23 is output to the base terminal of the transistor Tr, and turns on the transistor Tr when the flip-flop circuit 22 is in the set state.

Further, the heating power supplied to the intake air amount measuring resistor 12 is a specific voltage corresponding to the voltage value set by the reference power source 24 by the constant voltage circuit configured by the reference power source 24 and the operational amplifier 25. It is supposed to be kept in a state. Further, the cycle of the start pulse signal is set so that the time width of the output signal of the buffer 23 does not exceed half of the cycle of the start pulse signal in the upper limit state of the measured air flow rate. That is, heating power is supplied to the bridge circuit after the intake air amount measuring resistor 12 is completely cooled.

Next, the operation of the intake air amount measuring device for an internal combustion engine configured as described above will be described.

First, depending on the amount of air, an engine control unit (not shown) outputs a switching signal for switching the first and second switching circuits 15 and 20, and the fixed resistors 16 and 1
7 or using fixed resistors 18 and 19, connection point a or b
And the potential at the connection point c is compared by the comparator 21.

With either of these selected, the start pulse signal is sent to the flip-flop circuit 22 in synchronization with the rotation of the engine.
Is output to the flip-flop circuit 22, the set circuit outputs a signal from the flip-flop circuit 22 to turn on the transistor Tr. Then, heating power is supplied to the bridge circuit to heat the intake air amount measuring resistor 12, and the temperature thereof rises corresponding to the flow rate of the air flowing through the intake pipe 11. Then, when the temperature of the intake air amount measuring resistor 12 rises to a temperature range specified with respect to the intake air temperature observed by the temperature measuring element 13, a signal is output from the comparator 21 to the reset terminal of the flip-flop circuit 22, The circuit 22 is reset.

The time taken from when the signal output while the flip-flop circuit 22 is being set based on the start pulse signal to when it is ended by the signal from the comparator 21 is counted as the number of clock signals.
The amount of intake air flowing through 11 can be measured.

Thereafter, depending on the amount of air from an engine control unit (not shown), a switching signal for switching the first and second switching circuits 15 and 20 is output, and at the same time, a start pulse signal is output. Further, the set time of the flip-flop circuit 22 is counted by the system clock signal or the like, and the amount of intake air flowing through the intake pipe 11 is measured as digital data.

The correction when using these two sets of series resistors 16, 17 and 18, 19 is shown in FIG. If the brush circuit using series resistors 16 and 17 is used and 18 and 19 are used, it means that the corrections for both are adjusted differently, with a bridge in the low air volume area and a bridge in the high air volume area. To use. Therefore, as shown in FIG. 3, temperature characteristics with less output error can be obtained over the entire air amount range.

As described above, in this embodiment, two sets of fixed resistors having different resistance values, that is, the fixed resistors 16 and 17 in series and the fixed resistors 18 and 19 in series are provided, and any one of the fixed resistors of the plurality of sets is provided. This is selected by the first and second selection circuits 15 and 20 according to the intake air amount. Therefore, since the temperature correction is performed by the correction characteristic by the selected fixed resistance, the temperature characteristic can be compensated with higher accuracy over the entire air amount range, and the optimum correction can be performed.

The present invention is not limited to the above embodiment,
For example, in the above-described embodiment, the resistance of the bridge circuit is switched by the switching signal from the engine control unit for use. However, as shown in FIG. 4, the integrator 26 for integrating the output signal in the intake air amount measuring device is used. , A comparison voltage generator 27 for setting the switching level and comparing means 26, 27 for comparing the two
And a switching signal generator 29 for generating a switching signal in response to the output from the comparison means 28, and the determination and operation of switching may be performed in the intake air amount measuring device. That is, the switching operation may be performed by an electric signal representing the air flow rate.

Further, in each of the above-mentioned embodiments, the embodiment concerning the digital control system is shown, but as shown in FIG. 5, it is also applicable to the analog control system. That is, the flow rate of the analog value may be measured by obtaining the potential of the connection point c.

Further, although two sets of fixed resistors 16 and 17 and fixed resistors 18 and 19 are provided in the above embodiment, three or more sets may be provided.

Further, in the above description, as an example in which the total heat dissipation coefficient H (Ta) changes depending on the air flow rate, heat transfer to air and each member
Although attention has been focused on heat conduction through 7,8,9, for example, even in the case where the total heat dissipation coefficient is determined as the sum of heat transfer to the air and radiant heat transfer, air of the temperature characteristics of the total heat dissipation coefficient is also determined by the present invention. It is possible to accurately compensate for the change due to the flow rate.

[Effects of the Invention] As described in detail above, according to the present invention, an excellent effect that optimum temperature correction can be performed over the entire air amount range is exhibited.

[Brief description of drawings]

FIG. 1 is a diagram showing an electrical configuration of an intake air amount measuring apparatus for an internal combustion engine embodying the present invention, FIG. 2 is a diagram showing a relationship between temperature and a correction amount, and FIG. 3 is an air flow rate and an output error. FIG. 4 is a diagram showing the electrical configuration of an intake air amount measuring device for an internal combustion engine of another example, and FIG. 5 is an electrical configuration of an intake air amount measuring device for an internal combustion engine of another example. FIG. 6 is a diagram showing a configuration, FIG. 6 is a diagram showing an electrical configuration of a conventional intake air amount measuring device for an internal combustion engine, and FIG. 7 is a vicinity of a mounting position of an intake air amount measuring resistor for explaining a heat flow. FIG. 8 is a diagram showing the relationship between the air flow rate and the heat dissipation coefficient, FIG. 9 is a diagram showing the relationship between the temperature and the rate of change of the heat dissipation coefficient, and FIG. Showing the relationship between FIG. 11 (a), (b),
(C) is a diagram showing the relationship between the temperature and the rate of change of the heat dissipation coefficient, and FIG. 12 is a diagram showing the relationship between the air flow rate and the output error in the conventional intake air amount measuring apparatus for an internal combustion engine. Reference numeral 11 is an intake pipe, 12 is an intake air amount measuring resistor, 13 is a temperature measuring element, 15 is a first switching circuit as switching means, 16 is a fixed resistor as a fixed resistor, and 17 is a fixed resistor. A fixed resistor, a fixed resistor 18 as a fixed resistor, a fixed resistor 19 as a fixed resistor, and a second switching circuit 20 as a switching means.

Claims (1)

(57) [Claims] 1. A temperature measuring element installed in an air flow to be measured, the resistance value of which changes depending on the air temperature, an intake air amount measuring resistor installed in the air flow to be measured, and temperature dependence. In a device for measuring the intake air amount of an internal combustion engine, in which a bridge circuit is formed by a fixed resistor that does not have a An intake air amount measuring device for an internal combustion engine, comprising: a plurality of sets of fixed resistors; and a selection means for selecting any one of the plurality of sets of fixed resistors according to an intake air amount.