JPS58120121A - Air flow meter for internal combustion engines - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air flow meter for an internal combustion engine of an automobile, and in particular,
This relates to a hot wire type air flow meter.

Many proposals have been made for intake metering methods for automobile internal combustion engines, and many techniques are well known. Methods currently in practical use include the movable vane method, which detects the air flow rate by receiving the dynamic pressure of the inhaled airflow with a movable vane and obtaining an electric signal commensurate with the vane's inclination angle, and the method using the Karman vortex frequency. There are the Karman vortex method, which detects the air flow rate, the swirl method, which uses a swirler that rotates in proportion to the air flow rate to detect the amount of intake air, and the hot wire method, which uses changes in the resistance of a hot wire.

These methods can accurately detect the air flow rate when the internal combustion engine is in steady operation and cruising, but when the number of cylinders is 4 or less and the internal combustion engine is rotating at low speed, the intake air flow rate can be accurately detected. Since this is a pulsating flow, there are many problems as a true air flow rate detection method.

FIG. 1 is a diagram showing changes in the intake flow rate of a four-cylinder engine, and the horizontal axis shows the crank angle. The shaded area below the zero air flow line indicates a backflow of air, which pulsates in the low rotational output range of a four-cylinder engine. Furthermore, the behavior of the intake air flow differs between when the intake and exhaust valves of the engine overlap and when only the intake valves are open.

That is, when the intake and exhaust valves are operating in an overlapping manner, the positive pressure from the exhaust valve side as the piston rises causes air to flow back toward the intake valve side, resulting in a so-called air blowback phenomenon. Furthermore, if only the intake valve is open, the air containing the blown back air is sucked in again. This phenomenon takes different forms depending on the shape of the engine's combustion chamber, the shape of the intake and exhaust pipes, the shape of the air cleaner, etc., but is especially true when the engine is running at low speeds (600 to 3000 rpm) and when the suction negative pressure is 100 feet Hg or less. It often appears in the low rotation output range. Note that the shaded part of the pulsating waveform in Figure 1 is the backflow that occurs when the intake and exhaust valves overlap, and the waveform part above the zero line is the forward flow when only the intake valve is open. It shows.

When such a backflow phenomenon occurs, the true amount of intake air cannot be detected using any of the various types of air amount detection devices described above. In particular, in conventional hot wire air flowmeters that were developed with the focus on low cost and high response (c) there is no means to distinguish and detect backflow in pulsating airflow, and the signal shown in Figure 2 is obtained. become.

Fig. 2 is a diagram showing the output signal of a hot-wire air flow meter, where the diagonally shaded part Q1 going down to the right is a reverse flow signal, and the part Q2 being diagonally shaded to the left is a forward flow signal. Both are detected in the same way and only one direction of output can be taken out. Therefore, the flow rate θ in the reverse direction and the flow rate θ in the forward direction
2 will be detected as the intake air amount, resulting in a flow rate detection error equivalent to twice the flow rate Q in the reverse flow direction.

Hot wire air flowmeters have advantages such as excellent responsiveness and the ability to measure the mass flow rate of air, so they do not require pressure correction, but they have problems with mechanical strength and have a diameter of 70 mm.
If a platinum wire of ~100 μm is stretched within the intake path of a vaporizer, the hot wire will vibrate and the durability will likely be compromised. In particular, they are susceptible to mechanical damage due to backfires that occur when the engine is malfunctioning, and in extreme cases, the platinum wire may break. There are problems such as the dust contained in the air adhering to the platinum wire and changing the output signal of the hot wire air flow meter. Note that this type of intake air amount measuring device is described, for example, in the following known example.

Japanese Patent Publication No. 49-48893 No. 47-19227 5AEI) aperA800468 USP43824966 In order to solve the above problems, a platinum wire is wound around a hollow ceramic support, and the entire surface is covered with a covering material to increase mechanical strength. Improved hot wire probes have been made and placed in bypass passages that bypass the venturi section of the intake passage.

FIG. 3 is a sectional view of a throttle body having a bypass passage in which a conventional hot wire probe is installed.

A venturi portion 3 is formed in the intake passage 2 of the throttle body 1, and a throttle valve 4 is installed downstream of the venturi portion 3. Further, a bypass passage 5 is provided in the throttle body 1 to bypass the venturi part 3, and its inlet 6 is formed upward in the upper enlarged inner diameter part of the throttle body 1, and its outlet 8 is formed in the annular gap in the venturi part 3. It is formed as In the bypass passage 5 having such a shape, a pair of hot wire probes 7a and 7b are installed at different levels.

FIG. 4 is a circuit diagram connected to the hot wire probe of FIG. 3. A Wheatstone bridge 10 is constituted by the air flow rate measuring resistor 7a, the temperature compensating resistor 7b, and the resistors 9a and 9b, and the potential difference at the midpoint thereof is detected by a differential amplifier circuit using an operational amplifier 11. This signal is input to the base of the transistor 12, and closed loop control is performed so that the potentials at the midpoint are always equal.

In FIG. 4, the resistance kR of the air flow velocity measuring resistor 7a
, , the resistance of the temperature compensation resistor 7b is Rt.

Assuming that the resistance of the resistor 9a is +R,1, and the resistor R1 of the resistor 9b, the following equation holds true.

Actually, R->Rt, and the flow rate measuring resistor 7
A is in a heated state, but the temperature compensating resistor 7b is in a slightly heated state from atmospheric temperature. Therefore, when the air temperature rises, Rt also rises and the resistance increases, thereby compensating for the influence of the rise in air temperature. In addition, if the air temperature is constant, R1 is constant, and the operational amplifier 11 operates so that R, is a constant value regardless of the air flow rate, and the Wheatstone bridge 1
Controls the current flowing to 0. That is, the air flow velocity signal flowing through the bypass passage 5 can be determined by the current at the midpoint of this Wheatstone bridge 10 or the potential at the emitter of the transistor 12.

Therefore, the amount of air flowing through the bypass passage 5 is determined.

The conventional air flow meter configured in this manner outputs a signal according to the flow velocity regardless of the direction of the air flow, as described above. Therefore, when the engine is operated at low speeds and under high load, when the intake air flows backward from the cylinder to the intake manifold during the overlap period of the intake and exhaust valves (7), if the blowback phenomenon occurs, the blowback air is also output as the amount of intake air. . Furthermore, in the operating range where the intake air pulsation is large, there is a tendency for the indicated value to be smaller than the true air flow rate for the following reasons.

That is, the output E of the hot wire probe 7 with respect to the air flow velocity U is generally expressed by the following equation.

E2=A+B pressure・・・・・・・・・・・・(2)
However, A and B are constants.

FIG. 5 is a diagram showing the relationship of equation (2), and its characteristics are nonlinear. That is, due to the intake pulsation, the air flow velocity of the hot wire probe 7 is U with respect to UTF.

If the solid line A represents the case where a temporal change is made as a sine wave between ~U8, in this case, the hot wire output (does not differ from E1 to E3) due to the response delay caused by the heat capacity of the hot wire probe 7. A solid line waveform B changes completely between E1' and E37.The amplitude of this B is smaller than that of A.

On the contrary, the air flow velocity waveform obtained from this waveform B is reduced as shown in A' and becomes the flow velocity rrsu1'~u,I
(8) The average value is u, I. Therefore, u, −
The hot wire air flowmeter will show a lower value by u,', and this tendency becomes larger as the change in flow velocity becomes larger and the pulsation amplitude becomes larger.

Figure 6 is a diagram showing the relationship between suction negative pressure and air flow rate of a hot wire air flow meter.As the throttle valve opening increases and the suction negative pressure decreases, suction pulsation begins to occur, as indicated by the arrow. Zone A shown is a region where intake pulsation occurs significantly. Also,
The B zone indicated by the arrow is a region where blowback is particularly noticeable in the intake pulsation region. Assuming that the straight line shown by the solid line is the true air flow rate line, the air flow rate determined from the output of the hot wire probe 7 has the characteristic of a series of circles, and in the A zone, the output signal of the hot wire probe 7 indicating the air flow rate decreases. This results in a large error. Furthermore, when entering the B zone, the value becomes larger than the true value due to the influence of blowback, resulting in a positive error.

As mentioned above, the conventionally used hot wire air flow meter
When entering the intake pulsation region and blowback region, the air measurement error becomes large, and even though the hot wire probe was completely removed from the hot wire stretching method (9) and the mechanical strength was increased, this drawback remained unresolved. .

An object of the present invention is to provide an air flow meter for an internal combustion engine that can eliminate measurement errors caused by intake pulsation and blowback, and can accurately measure and detect the air flow rate taken into the engine in all operating ranges. The characteristics of this feature are that the length of the bypass passage is expanded at least three times the distance between the inlet and outlet of the bypass passage, and the outlet of the bypass passage is opened toward the downstream of the main intake passage. The problem lies in the fact that it is configured to allow

FIG. 7 is an explanatory diagram of the hot wire air flowmeter of the present invention, and is shown schematically to facilitate theoretical calculations. An inlet 6 is provided on the upstream side of the venturi portion 3 of the main intake path 2, an outlet 8 is provided in the venturi portion 3, and a hot wire 13 is installed in a bypass passage 5 formed in the slot body 1. Now, if the pressure in the cross section passing through the inlet 6 shown by the dashed-dotted line a is p, and the pressure (10) in the cross-section passing through the outlet 8 shown by the dashed-dotted line is p, then the pressure difference generated during intake pulsation is p1-p2.
is expressed by the following equation.

A! +(1-(-))ρ・u22・song interval (2]l However, L is the distance between a and b of the main intake path 2, and ρ is the air density. ξ is the friction loss coefficient A1 is the cross-sectional area of the main intake passage at the venturi part 3 A2 is the cross-sectional area of the bypass passage 5 u is the air flow velocity in the main intake passage in the cross section.

Furthermore, the air flow velocity W in the bypass passage caused by the pressure difference pt pg is expressed by the following equation.

However, t is the length of the bypass passage. In addition, the above (21)
, the first term on the right side of equation (3) indicates the inertia of the airflow (1
1) Ru.

Figure 8 shows the air flow velocity W in the bypass passage when the main intake flow velocity U at the outlet of the bypass passage is varied in a sinusoidal manner.
FIG. 2 is a diagram showing calculation results. In other words, the reason why the amplitude of W shown by the solid line is decreased compared to the amplitude of U shown by the broken line is because
This is due to the inertial lag effect. Also, cross section a in Fig. 7
, the Venturi effect between b, i.e. “1 1) 2
oell, 2, the average value W tends to be larger than u2. This is related to the t/L(r) value to the 11th order.

It shows such characteristics.

Figure 9 is a diagram showing the characteristics due to the bypass passage in Figure 7, where the horizontal axis is ! , , /IJ are shown, and the vertical axis is w / u.

shows the value of That is, by appropriately selecting L/Lf, it is possible to cancel the decrease in the hot wire output in the zone A in FIG. 6, where intake pulsation is significant, by increasing the average flow velocity in the bypass passage due to the inertial lag effect. Become. However, in this case, the effect is small in the blowback area of zone B, so it is expected that the characteristics will be as shown by the dashed line in Figure 6 (12).

FIG. 10 is a diagram showing the air flow velocity in the bypass passage during blowback, where the solid line U is the intake air flow velocity at cross section b in FIG. 7, and the broken line W is the air flow velocity in the bypass passage 5. In region X where backflow occurs during blowback, the main air flow velocity U, even in the case of backflow! , /L is increased, and the air flow velocity wit the bypass passage 5 is a normal flow. Therefore, if the dynamic pressure of the reverse flow of the main air is applied to the outlet 8 of the bypass passage 5 in the region X of the waveform W shown by the broken line and the forward flow is completely suppressed, the air flow velocity in the bypass passage 5 becomes zero. As the value approaches , the characteristics become as shown by the dashed line. If this is done, the dashed-dotted line in zone B in FIG. 6 will further approach the ideal value shown by the solid line, making it possible to reduce the air metering error.

FIG. 11 is a sectional view of a throttle body equipped with an air flow meter according to an embodiment of the present invention, in which the same parts as in FIG. 3 are given the same reference numerals. Although the throttle valve 4 is not provided in this case, there is no change in the function (13) as an airflow meter. 14 is a hot wire drive circuit connected to the hot wire probe 7 shown in FIG. 4, and 15 is an outlet pipe fitted to the outlet 8 of the bypass passage 5.

This outlet pipe 15 protrudes to the center of the main intake passage 2, has an outlet 8 on its lower surface, and extends the length t of the bypass passage. As a result, the distance tta between the inlet 6 and outlet 8 of the bypass passage 5 reaches three to four times the distance in the main intake passage 2 between both ends of the bypass passage 5.

Therefore, in addition to imparting the above-mentioned inertial delay effect to the bypass airflow, the outlet 8 of the bypass passage 5 is opened in the direction in which the dynamic pressure of the reverse flow acts, thereby suppressing the forward flow of the bypass airflow during blowback. It is possible to reduce measurement errors.

12, 13, and 14 are cross-sectional views of a throttle body equipped with an air flow meter that is a modification of FIG. 11. FIG. FIG. 12 shows an L-shaped inlet pipe 16 attached to the inlet side of the bypass passage 5, and FIG. 13 shows an outlet pipe 16 of the bypass passage 5 attached to the tip of an annular passage 17 extending halfway around the inside of the venturi section 3. Figure 14 shows the annular passage 1.
An inlet pipe 16 is attached to the inlet side of the bypass passage 5 formed on the outlet side (14). Figure 12 shows that the entire length of the bypass passage 5 is expanded by 4 to 6 times to promote the inertial lag effect, and to prevent a decrease in the air flow rate indication value determined from the hot wire output in zone A in Figure 6. This reduces weighing errors. Further, the blowback is the same as in the case of FIG. 11.

In the case of FIG. 13, the outlet 8 opens downstream to take in the dynamic pressure of the reverse flow, which is the same as in the cases of FIGS. 11 and 12. 14 is the same as FIG. 12 in that an inlet pipe 17 is provided to increase tf, but in order to apply the dynamic pressure of the reverse flow to the outlet 8, an annular slit is formed along the annular passage 17. An attempt was made to obtain a similar effect by opening the outlet 8 downward.

By forming such a bypass passage 5 of the throttle body 1, there are two problems: a decrease in the air flow rate indication value that conventionally occurred in zone A in FIG. 6, and an increase in the indication value that occurred in zone B. (15) Weighing errors can be significantly reduced.

FIG. 15 is a diagram showing the relationship between the suction negative pressure and the air flow rate of the hot-wire air flowmeter of FIG. 12, and corresponds to the conventional diagram of FIG. 6. With respect to the theoretical air flow rate line shown by the solid line, almost no air measurement error occurs even in the characteristic f'iA and B zones of this embodiment as shown by the circles. In this case L=
30M, 7=120 pieces and t/L=4. Furthermore, almost similar results were obtained for other examples. The experimental results are shown for the case where the engine rotation speed is 11000 rl), but the engine speed is 1000 to 6000 rl).
The effect can be obtained even in the range of rl)m, and a remarkable effect can be obtained even when the number of cylinders is 4 or less.

The hot wire air flowmeter of this embodiment increases the engine intake negative pressure by increasing the length of the bypass passage and providing a downward opening at the outlet of the bypass passage to take in the headwind pressure at the time of blowback into the bypass passage. Even in operating conditions where the intake air flow rate is small and the intake air flow rate is high and there is a lot of pulsation, and even in conditions where there is a lot of blowback and backflow, it is possible to significantly reduce the error in measuring the amount of air (16).

The air flow meter for internal combustion engines of the present invention makes it possible to eliminate # quantity errors due to intake pulsation and blowback by slight improvement of the bypass passage, and enables accurate measurement in all operating ranges for proper operation. This has the effect of being able to.

[Brief explanation of the drawing]

Figure 1 is a diagram showing changes in intake flow rate of a 4-cylinder engine.
Figure 2 is a diagram showing the output signal of the hot wire air flow meter, Figure 3
The figure is a cross-sectional view of a throttle body with a bypass passage in which a conventional hot wire probe is installed, Figure 4 is a circuit diagram connected to the hot wire probe in Figure 3, and Figure 5 is a line showing the relationship between air flow velocity and hot wire output. Figure 6 is a diagram showing the relationship between suction negative pressure and air flow rate of a hot wire air flow meter, Figure 7 is an explanatory diagram of the hot wire air flow meter of the present invention, and Figure 8 is an outlet of the bypass passage. A diagram showing the calculation results of the air flow velocity W in the bypass passage when the main intake flow velocity uzffi is changed by a sine wave,
FIG. 9 is a diagram showing the characteristics of the bypass passage in FIG. 7;
Fig. 10 is a diagram showing the air flow velocity in the bypass (17) passage during blowback, Fig. 11 is a sectional view of a throttle body equipped with an air flow meter which is an embodiment of the present invention, and Figs. Fig. 14 is a sectional view of a throttle body equipped with an air flow meter that is a modification of Fig. 11, and Fig. 15 is a diagram showing the relationship between suction negative pressure and air flow rate of the hot wire air flow meter of Fig. 12. It is. 1... Throttle body, 2... Main intake path, 3...
・Henturi part, 5... Bypass passage, 6... Inlet, 7... Hot wire probe, 8... Outlet, 9... Resistor, 10... Wheatstone bridge, 11... Operational amplifier, 12...Transistor, 13...Hot wire,
14...Hot wire drive circuit, (18) Fig. 1 Fig. 3 Fig. 4 Fig. 106 Fig. O Fig. 7 Fig. δ Fig. /θ Fig. 2 Fig. Boiling / 4 Fig. 75

Claims (1)

[Claims] 1. A bypass passage provided in the throttle body to communicate the venturi part of the main intake passage with its upstream part;
It has a hot wire probe installed in this bypass passage,
In the air flow meter for an internal combustion engine that measures the air flow velocity in the bypass passage to determine the amount of air intake into the internal combustion engine, the length of the bypass passage is determined by at least the length of the bypass passage relative to the distance between the inlet and the outlet of the bypass passage. An air flow meter for an internal combustion engine, characterized in that the bypass passage is expanded three times or more, and the outlet of the bypass passage is opened downstream of the main intake passage.