JPS6052302B2 - Fuel injection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fuel injection method, and in particular provides an electronically controlled fuel injection method in which a controller calculates the amount of fuel to be injected according to the amount of air taken into an internal combustion engine. It is something to do.

It is extremely convenient to operate the internal combustion engine while maintaining the concentration of the air-fuel mixture supplied to the internal combustion engine at a predetermined air-fuel ratio, for example, when attempting to purify exhaust gas using an Ξ main catalyst.

To this end, it is important to accurately measure the amount of air taken into the engine, calculate the corresponding fuel injection amount using the controller, and supply it to the engine. Special Public Service 1977-
No. 9661, No. 9662, No. 38409, etc.
An example of a device for measuring the above-mentioned intake air amount, the first
As shown in the figure, a hot wire flowmeter 14 having a hot wire 13 is installed upstream of a throttle valve 12 disposed in an intake pipe 11 of an engine 10, and a signal (voltage) V detected from the hot wire flow meter 14 is transmitted to an amplifier 15. and transmits the information to the control unit 16 via the
The rotation signal R from the distributor 17 is also input here, and the intake air flow rate per engine revolution is calculated from these two signals.

Then, based on the calculation result, the unit calculates an appropriate fuel flow rate to achieve a predetermined air-fuel ratio, and applies a pulse signal P corresponding to the fuel flow rate to the nozzle 18 to inject it. Measuring the intake air amount with the hot wire flowmeter 14 using the hot wire 13 as described above is advantageous because the device is small and inexpensive, the degree of freedom in attaching it to the intake pipe is large, and the deterioration over time is very small. It has many advantages, such as the fact that it can be easily corrected using the control unit.

However, under load conditions that frequently change within an extremely wide rotation range, such as in internal combustion engines, especially automobile engines,
When this hot wire flowmeter is used, it is not necessarily the case that only the above-mentioned advantages can be obtained.

This method has a fatal problem in that the intake flow rate cannot be accurately measured on the high-load side of the engine. That is, as shown by the solid line in FIG. 2, theoretically there is a proportional (linear) relationship between the load (boost pressure) and the intake flow rate. When measuring the inspiratory flow rate, it should be measured in a low load range (e.g. -100
mHg), the flow rate can be measured accurately according to the above theory, but when the load becomes large, it begins to sag (as shown by the dotted line in the figure) (or suddenly sag as shown by the dashed line in the figure). ), it becomes impossible to detect the flow rate according to the above theory.

Note that the intake flow rate in FIG. 2 is based on the fact that the output signal v from the flow meter 14 draws a sine curve-like curve as shown in FIG. 3 due to the intake pulsation of the engine.
This is the value obtained by taking out signals at several points between cycles and averaging them.

For example, in a 4-cylinder engine, the above curve will have a cycle of 180 crank angles due to ignition timing.
Signal V1 at each point equally divided into 5 minutes every 36 fires during this period.
~V, and the measured intake flow rate q1 at each of them.
~ Calculate Q5 from the formula q=a(V2-b)2, and further divide this sum into 5 minutes: (q1-Q2+Q3+4+Q5)÷
5 to calculate the average value d. The reason why the above-mentioned measured intake flow rate is inaccurate is that on the high load side where the opening degree of the throttle valve 12 is large, the buffering effect of the throttle valve against intake pulsation and blowback is lost, and the This is caused by the intake air flow being disturbed and being detected, and this problem cannot be easily resolved even if a rectifying chamber as shown at 19 in FIG. 1 is provided.

In this way, the amount of intake air cannot be measured accurately. Then,
In FIG. 2, two different loads L. 15L indicates the intake air amount of Koichi, and since the fuel injection amount is determined according to the intake air amount as described above, it becomes impossible to maintain the set air-fuel ratio. .

The inventors of the present application focused on this point and conducted various research experiments, and as a result, they discovered that the signal V output from the hot wire 13 has certain characteristics.

As shown in Figure 4, this is the difference between the maximum and minimum values of the signal V within one cycle for each engine speed: The amplitude w in Figure 3 becomes regular as the load increases. This means that the two different loads Ll and I- in Fig. 2 have a distinct difference in amplitude, and the The inspiratory flow rate can be measured indirectly.

Note that the graph in FIG. 4 shows only the amplitude of the signal with the center of the amplitude w set at zero. In other words, as mentioned above, there is a proportional relationship between the intake flow rate that can be measured from the amplitude and the load, and if the air-fuel ratio is to be kept constant, the engine rotation will change as shown in Figure 5. Number of N and load (boost pressure)
of. From the relationship, the fuel injection amount: that is, the width (time) T of the pulse P to be applied to the nozzle 18 is determined.
By preparing map data in which the width T of the pulse P can be determined from the amplitude W and the engine speed N as shown in Fig. 6 based on two conditions, ・This amplitude and the engine speed can be measured. This means that the fuel injection amount can be determined.

The present invention has been made with attention to this point, and when the engine is operating at low or medium load, the signal of the hot wire flowmeter is
The fuel injection amount is determined based on the intake flow rate obtained by picking up data from several points within the cycle and averaging them, and during high-load operation, the amplitude of the above signal within one cycle is determined. This method attempts to determine the fuel injection amount more indirectly than the engine speed.

The method of the present invention will be explained below with reference to the flowchart shown in FIG.

The control unit 16 in FIG. 1 includes an interface 21, a memory 22, and a microprocessor 23.
etc., and the memory contains a data map as shown in FIG. 6, a certain set fuel injection amount: for example, a pulse width Ts corresponding to an intake flow rate of 9 s at a boost pressure of -10-Hg in FIG. A certain set amplitude: for example, the amplitude Ws at a boost pressure of -100 mkg in FIG. 4 is stored.

First, as the first step I, the output voltages V, ~V5 at 5 points every 36 points are picked up from among the signals outputted from the hot wire flowmeter 14 as shown in FIG. The processor 23 calculates the measured flow rate q1 to Q5 at each point (q=(V2-b)2 (second step), and further calculates the average flow rate d (h=115(q
1+Q2+Q3+Q,+Q5) (third step).

In the fourth step, the engine rotation speed N at that point is read from the rotation signal R from the distributor 17, and the engine 1
Calculate the measurement pulse width T per rotation (T=KX″q/N)
(5th step). In the sixth step, the pulse width T and the set pulse width Ts are compared (T≧Ts). If this result is NO and the pulse width T is the pulse width Ts
If it is smaller, this measurement pulse width T is applied to the nozzle 18 as it is because the output of the hot wire flowmeter shown in FIG. . On the other hand, if the result of the above comparison is Yes and the measured pulse width T is larger than the set pulse width Ts, then the hot wire flowmeter output in Fig. 2 is sagging (or rising rapidly). Due to the range of load operation, proceed to step 7.

Here, the maximum value Qmax and minimum value Qmin (in the example of FIG. 3, q1 and Q4) are determined from among the five measured flow rates q1 to Q5.
).

Then, calculate the measured amplitude W from the difference (W = Qmax - Q
min) (eighth step).

In a ninth step, it is compared whether this amplitude W is larger or smaller than the set amplitude Ws. If the result is NO and the measured amplitude W is smaller than the set amplitude Ws, the measured pulse width T obtained from the average value i is output as is. On the other hand, if the result of this comparison is Yes and the amplitude w is larger than the set amplitude Ws, the process proceeds to the 10th step x, and the measured amplitude w and the engine speed N are stored in the memory 22. The pulse width T is calculated from the data map shown in FIG.

That is, in Fig. 6, if the amplitude is w and the engine speed is N1, the pulse width can be read as T''1, and if it is N2, it can be calculated as T''. As,
In the method of the present invention, when the hot wire flowmeter 14 has stable output characteristics and is under low or medium load, the average value i of the output signal is
The pulse width T is determined based on the calculated intake flow rate, and the pulse width T is larger than the set pulse width Ts, and the measured width (W) is larger than the set width (Ws). If it is estimated that the operation is at a high load and the reliability of the above output characteristics is lost, the amplitude of this vibration can be reduced by skillfully taking advantage of the fact that the signal V vibrates due to the pulsation of the intake air. The characteristic that w increases regularly as the load increases is organically combined with the engine speed, and the pulse width is determined from the data map, so it can be used over the entire range from low load to high load as mentioned above. Therefore, this method does not have the problems of the known method of directly determining the intake flow rate from the average value i.

In addition, if you try to find the pulse width from the amplitude W over the above range, the amplitude in the low load range may be small and difficult to detect, making the measurement inaccurate. Since the pulse width is calculated directly based on the average value,
This problem doesn't exist either. Furthermore, since the pulse width is determined from the data map only when the two comparison results of the set pulse width Ts and the set pulse width (Ws) are satisfied at the same time,
Even if the signal V is temporarily disturbed for some reason, it is possible to prevent an immediate erroneous measurement. Furthermore, since there is no need to eliminate intake pulsation, there is also the effect that the intake system of the engine 10 can be simplified. In this specification, it has been explained that one cycle of the signal V is divided into five parts and the maximum value and minimum value are selected from among the signals V1 to V5 at that point. It is also possible to obtain the maximum value and minimum value by differentiating the signal V, and the present invention is not limited to this embodiment.

Furthermore, the hot wire type flowmeter referred to herein also includes one in which a film is used instead of the hot wire 13.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of an engine using a hot wire flowmeter, Figure 2 is a graph showing the relationship between load and intake flow rate, Figure 3 is a graph showing the change in signal with crank angle, Figure 4 is a graph showing the relationship between load and amplitude, Figure 6 is a graph showing the relationship between intake flow rate and amplitude, Figure 5 is a graph showing the relationship between pulse width and engine speed using load as a parameter. FIG. 7 is a flowchart illustrating the method of the present invention. 10... Engine, 11... Intake pipe, 12
... Throttle valve, 13 ... Heat wire, 14 ...
・・Hot wire flowmeter, 16・・Control unit, 17・・Distributor, 18・・・・
nozzle.

Claims (1)

[Claims] 1. The signal output from the hot-wire flowmeter installed in the engine's intake system is sent to the control unit to measure the intake flow rate, and based on this, the pulse width for regulating the fuel injection amount is determined in advance. , store in the memory of the control unit map data in which the relationship between the amplitude of the maximum value and minimum value of the measured intake flow rate based on the pulsation of the signal, the engine speed, and the pulse width is stored in the memory of the control unit; The above-mentioned pulse width calculated based on the average value of the measured inspiratory flow rate at multiple points within one cycle of the signal pulsation is larger than the preset setting pulse width, and If the measured amplitude detected from the maximum and minimum values of the measured intake flow rate is larger than the preset setting amplitude, the map data is calculated based on the measured amplitude and the engine speed at this point. A fuel injection method characterized in that a pulse width is determined, and in other cases, the pulse width is determined based on the average value.