JPS6257201B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in the transient characteristics of automotive air flow measurement devices, particularly vortex flowmeters.

Karman vortex type and swirl type overflow meters have been put into practical use as air flow meters for automobiles, and both output frequency signals that are approximately proportional to the amount of intake air or flow velocity.

This frequency signal is highly accurate over a wide flow range.
It has the advantage of being very fast in following transient changes in flow velocity, but because it is a frequency output,
It is not possible to achieve a high-speed response that exceeds the period, and there is a drawback that the output response is poor, especially when the flow velocity changes from a low flow rate or when a sudden deceleration occurs from a high flow rate. Furthermore, even if you try to measure the period of the frequency signal to measure the air flow rate at a higher speed, there will be fluctuations in the period caused by fluctuations in the vortex, so it will not be stable unless averaging such as a moving average is performed. The disadvantage was that the output could not be expected and the response was further impaired. This drawback is
This is fatal for systems that control automobile fuel and exhaust gas based on the amount of intake air.

Figure 1 shows the delay when frequency output proportional to air flow rate is averaged. Compared to the analog air flow rate indication value shown in the figure, the digitized frequency information continues to output old information until the next pulse is input. This delay time always exists for one period of the pulse even when it is the minimum, and if n times are averaged, n times are required.

If the averaged frequency signal is used to control the amount of fuel in a car, it will become lean during acceleration and rich during deceleration, which is not desirable. On the other hand, if the frequency output is always processed using the minimum averaging time, frequency fluctuations in the steady state will become large, which is a problem.

This invention is intended to eliminate the above-mentioned drawbacks, and aims to eliminate the drawbacks of the frequency signal by outputting an electrical signal corresponding to the flow velocity at the same time as the frequency signal caused by the vortex. FIG. 2 is a basic configuration diagram of an embodiment of the present invention.

In FIG. 2, 1 is an intake air passage, 2 is a vortex generator, and 3 and 4 are a pair of hot wires provided downstream of the vortex generator 2. The hot wire 3 is connected to resistors 5, 6, 7 and the operational amplifier 11, and the hot wire 4 is connected to resistors 8, 9,
10 and an operational amplifier 12, each of which is controlled to a constant temperature. The control voltages of the hot wires 3 and 4 are assumed to be V ₁ and V ₂ , respectively. These control voltages V ₁ and V ₂ are connected to capacitors 13, 14, 22, resistors 15, 16,
17, 18, 20, 21 A difference signal amplification circuit comprising an operational amplifier 19 produces a difference amplification signal _V3 . The signal V ₃ becomes a frequency output V ₄ , that is, an output 1, by the waveform shaping circuit 23 . Moreover, the signals V ₁ and V ₂ are
The voltages are added by adding resistors 24, 25, and ₂₆ , resulting in a voltage output V5, that is, output 2.

FIG. 3 shows a voltage waveform diagram of each part in FIG. 2. Second
With the configuration shown in the figure, a regular Karman vortex street that is symmetrical to the left and right is generated in the wake of the vortex generator 2. The hot wires 3, 4 are cooled by the average flow velocity and at the same time regularly and alternately at a high frequency by the Karman vortex street. Therefore, the control voltages V ₁ and V ₂ for keeping the heating wires 3 and 4 at a constant temperature are components corresponding to the average flow velocity.
₁ , ₂ , and components △V ₁ and △V ₂ corresponding to changes in flow velocity due to Karman vortices.

The polarities of △V ₁ and △V ₂ are opposite, and (△V ₁ −
A signal V ₃ is obtained from △V ₂ )×K ₁ , and a frequency output V ₄ is obtained. The ratio between this frequency and the amount of intake air is approximately constant.

Next, ₁ and ₂ are expressed as ₁ = ₂ = (a+bU
〓)〓 becomes the average flow velocity: a function of U. signal
By adding V ₁ and signal V ₂ , the opposite polarity △V ₁
and △V ₂ are canceled and V ₅ = K ₁ (V ₁ + V ₂ ) =
K _{2 1} =K _{2 2} (K ₁ and K ₂ are constants), and a signal V ₅ which is a function of the flow velocity U is obtained. This signal V ₅
Since it is an analog voltage signal, it has good responsiveness and always outputs information corresponding to the flow velocity U.

By effectively using signals V ₄ and V ₅ in parallel, a high-precision, high-speed response air flow meter for automobiles can be realized.

In FIG. 2, reference numeral 21 indicates various parameter information representing the operating state of the engine, such as engine rotational speed information, negative pressure, intake air temperature, atmospheric pressure, and water temperature. You can enter this information as necessary. 22 is an air flow signal processing circuit.

Consider a case where the amount of intake air increases rapidly in the air flow meter configured as described above. Since the analog signal of V ₅ corresponds to the amount of intake air,
By differentiating _V5 , an acceleration signal corresponding to the increase in intake air amount can be obtained. By changing the averaging time of the frequency signal of _V4 according to this acceleration signal, the averaging time can be shortened and the response delay can be reduced only during acceleration. If the change in the _V5 analog signal is small during steady operation, a long averaging time can be secured. The same applies when there is a sudden decrease. In this case, information on the intake air temperature is sufficient as the necessary engine operating parameter.

In the above embodiment, the case where the averaging time (or the number of moving averages) of the frequency signal of V ₄ is changed by the differential signal of V ₅ was explained, but the averaging time may be fixed for as long as necessary. Needless to say, the same effect can be expected even if the increase coefficient is determined and multiplied according to the magnitude of the differential signal of _V5 .

In the above embodiment, a case has been described in which the Karman vortex street is detected by a pair of hot wires, but it goes without saying that similar effects can be expected in the case of a swirl type vortex street. Furthermore, although the vortex detection means has been described as a heat wire, it goes without saying that similar effects can be expected even if a thermistor or other heat-sensitive element is used.

Furthermore, even if the vortex frequency signal is no longer usable due to a break in one of the pair of heating wires, the average flow velocity signal can be used as a backup signal.

As explained above, according to the present invention, since the air flow signal is obtained based on the average value of the frequency signal and corresponds to the rate of change of the analog signal, the air flow signal is highly accurate and has excellent responsiveness. There is an effect that can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the drawbacks when frequency output signals are averaged, FIG. 2 is a basic configuration diagram of an embodiment of the present invention, and FIG. 3 is a diagram of voltage signal waveforms at various parts in FIG. In the figure, 1 is the intake air passage, 2 is the vortex generator, 3, 4
is a hot ray. V ₄ is a frequency output signal approximately proportional to the intake air amount, V ₅ is an analog output signal corresponding to the intake air amount, 21 is an engine operating parameter input, and 22 is an air flow signal processing circuit.

Claims (1)

[Claims] 1. It has a pair of heat sensitive parts installed downstream of a vortex generator that is installed in the intake air passage of an internal combustion engine and generates a vortex downstream, and obtains first and second electrical signals by these pair of heat sensitive parts. a heat sensitive means, a means for outputting a frequency signal corresponding to the generation period of the vortex based on the difference between the first and second electric signals of the heat sensitive means, a means for outputting a frequency signal corresponding to the generation period of the vortex, based on the sum of the first and second electric signals; Means for outputting an analog signal corresponding to the average flow rate, and an average value of the periods of the frequency signals of a predetermined number of samples or an average value of the periods of the frequency signals occurring within a predetermined sampling time, calculated based on the frequency signals. signal processing means for outputting an air flow rate signal that is a predetermined function corresponding to;
the number of samplings of the signal processing means based on the analog signal, the sampling time;
Alternatively, an engine control device includes an air flow signal processing circuit having a control means for controlling at least one of the above calculation contents, and improves responsiveness to sudden changes in air flow.