EP0222019B1

EP0222019B1 - Fuel controller for engine

Info

Publication number: EP0222019B1
Application number: EP19860902028
Authority: EP
Inventors: Seiji Mitsubishi Denki Kabushiki Wataya
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1985-05-07
Filing date: 1986-03-27
Publication date: 1989-05-17
Also published as: EP0222019A1; JPS61255238A; DE3663380D1; WO1986006792A1

Abstract

When the fuel injection of an engine is controlled by an air flow sensor based on a heat radiation principle, an air fuel ratio sensor (10) capable of detecting the air fuel ratio of rich range from exhaust gas components is provided, and even if abnormal increase in the output signal of the air flow sensor occurs due to the blow-off of intake air at full load time, a feedback control is executed so that the air fuel ratio does not become rich higher than the predetermined value by the signal from the air fuel ratio sensor.

Description

Technical field

This invention relates to a fuel controller for an engine improved for the accuracy of an air fuel ratio at a high load time when fuel is injected from a gasoline engine employing an air flow sensor based on a heat radiation principle (e.g., a hot-wire type air flow sensor).

Background art

A fuel controller for an engine of an automobile generally controls an optimum amount of fuel supplied to the engine on the basis of an intake air quantity from an air flow sensor and the rotating speed of the engine from a rotary detector. The construction of a conventional fuel controller of an engine is shown in Fig. 6. In Fig. 6, 1 designates an engine, and 2 designates a suction manifold. An electromagnetic fuel injection valve 3 is provided in the suction manifold 2, and the fuel injection valve 3 is controlled by a controller 8.
The suction manifold 2 is coupled with a surge tank 4, which is connected to a suction conduit 5. A throttle valve 6 is disposed in the suction conduit 5. A hot-wire type air flow sensor 7 is provided in the conduit 5. The output of the sensor 7 is fed to the controller 8.
The rotating speed of the engine 1 is detected by a rotary detector 9, which applies the detected output to the controller 8. The controller 8 controls the fuel injection valve 3 by the output of the detector 9 and the output of the sensor 7.
The controller 8 is constructed as shown in Fig. 7, the output of the sensor 7 is converted by a digital converter 81 into a digital signal, and fed to a microprocessor 83.
The output of the detector 9 is supplied through an interface circuit 82 to the microprocessor 83. The microprocessor 83 calculates a predetermined fuel amount on the basis of the output from the sensor 7 and the information from the detector 9, amplifies it via an amplifier 86 and controls the valve 3.
A random access memory (RAM) 84 and a read only memory (ROM) 85 are connected to the microprocessor 83. The RAM 84 is used for calculating, and the ROM 85 stores the calculating sequence and the control data.
The operation will be described. In the state that the engine 1 is operated except the vicinity of wide open throttle (WOT), the output of the sensor 7 becomes a waveform which includes a normal ripple as shown in Fig. 8(a). When the area of the waveform is calculated, a true intake air amount can be produced. Thus, when the microprocessor 83 controls the drive pulse width of the valve 3 on the basis of the value produced by dividing the intake air amount by the rotating speed of the engine, desired air fuel ratio can be controlled.
However, the output waveform of the sensor 7 becomes as shown in Fig. 8(b) in the specific rotating speed range (generally 1000 to 3000 ppm) near the WOT due to the blow-off from the engine 1, and the portion indicated by the hatched lines is excessively added to the true air flow rate.
This is because the hot-wire type air flow sensor 7 based on the heat radiation principle detects as intake amount and outputs in irrespective of the air flowing direction.
The detecting error due to the blow-off depends upon the rotating speed as shown in Fig. 9, and is generated ordinarily in the vicinity that the suction conduit vacuum becomes near -50 mmHg and arrives at 50% at the maximum in the WOT range.
If the fuel amount is calculated and injected with the value including such large error, air fuel ratio becomes largely rich and cannot be utilized in a practical use. Therefore, as shown in Fig. 10, with the maximum air flow rate determined in response to the engine as the upper limit value (the value designated by a broken line) with respect to the range a that the error occurs due to the blow-off is heretofore stored in the ROM 85 in the controller 8, the detected value of the sensor 7 exceeding this value is ignored as shown in Fig. 8(b), it is clipped at the upper limit, thereby suppressing the excessively rich.air fuel ratio.
Since the upper limit value must be set to the intake air flow rate characteristic of the engine to be used at the ambient temperature in the sea level, it should become the upper limit value of mass flow rate at the ambient temperature at the sea level.
However, if the engine is operated, for example, with high load at a high level with low atmospheric density, such a disadvantage arises in which the output level of the sensor 7 does not arrive in the mean value at the predetermined upper limit value as shown in Fig. 8(c), the mean value of the output level including the blow-off is used to calculate the fuel as it is, and the air fuel ratio becomes excessively rich with respect to high altitude.
As described above, if the throttle valve is fully opened when the intake air flow rate of 4- cylinder engine is heretofore detected by the hot-wire type air flow sensor, the intake air reversely flow due to the blow-off to the sensor, and the sensor cannot detect the true intake air amount but produces an error due to an increase in the output from the true value.
Since this error arrives at approx. 50% at the maximum, if this value is used as it is to calculate the fuel amount, the air fuel rate becomes largely rich, and the engine becomes impossible to operate.
Thus, the upper limit of the output of the air flow sensor is heretofore stored in advance in the memory in the controller in response to the intake air flow rate characteristic of the engine, and even if the output of the sensor abnormally increases, a large error is eliminated in the air flow rate.
However, according to this method, since the upper limit is decided in response to the engine near the ambient temperature at a sea level, this method has such a drawback that the error in the airfuel ratio increases in the high altitude traveling or in high and low temperature atmosphere.
When the air intake amount is detected by the hot-wire type air flow sensor, a reduction in the error in the measurement of the airflow rate due to the reverse flow due to the blow-off from the engine is disclosed in Japanese Patent Laid-Open No. 56-108909 official gazette. In this configuration, the blow-off airflow rate Q, and the intake air flow rate Q₂ are predicted, and true air intake amount Q=Q₂=Q_l is calculated from these values. However, even if this method is utilized to control the fuel, it has such a disadvantage that the control of air fuel ratio at high altitude traveling or high and low temperature atmosphere cannot be accurately performed.

Disclosure of the invention

The present invention has been made to eliminate said prior art disadvantages and an object thereof is to provide a fuel controller for an engine which can obviate air fuel ratio error due to atmospheric pressure (in high altitude) and intake air temperature and obtain stable burning state under all operating conditions of the engine.
A fuel controller for an engine according to the present invention comprises an air flow sensor which detects the engine intake air quantity on the basis of a heat radiation principle; an air-fuel ratio sensor which detects, from the engine exhaust gas, whether the air-fuel ratio is rich or lean compared with a predetermined value; an electromagnetic fuel injection valve for injecting fuel; and a control unit which controls the opening time of the valve in dependence on the sensed air-fuel ratio and the intake air quantity; characterised in that at high engine load, the control unit controls the opening time of the valve in dependence on the sensed air-fuel ratio to maintain the said ratio at the predetermined value by feedback when the sensed air-fuel ratio is rich, and when the sensed air-fuel ratio is lean, the control unit controls the opening time of the valve in open-loop control in dependence on the sensed air flow quantity as a main parameter.
Since the present invention detects the air fuel ratio of rich side by an air fuel ratio sensor to suppress the air fuel ratio error due to the blow-off of the intake air when the engine is fully opened, stable burning state can be attained under all operating conditions of the engine.
EP-A-87801 describes a fuel control system including a plurality of sensors sensing various operation parameters of an engine, a digital computer controlling the quantity of fuel supplied to the engine depending on the outputs from the sensors, including a hot-wire airflow sensor, a pulse generating circuit generating a pulse signal for controlling the quantity of supplied fuel in response to the output from the digital computer, and fuel supplying means for supplying fuel on the basis of the pulse signal generated from the pulse generating circuit. This fuel control system operates by computing the quantity of air taken into the engine on the basis of the output from one of the sensors, integrating the quantity of intake air computed in the first step, determining the level for setting the period of generation of the pulse signal on the basis of the output from one of the sensors, and generating pulses of predetermined pulsewidth from the pulse generating circuit when a predetermined relation is attained between the level determined in the third step and the result of integration in the second step.
According to one feature of this fuel control system, the measured air-fuel ratio is used as a control factor, only when the engine is not operating at high load. Under high power, the engine is controlled on the basis of the instantaneous intake air quantity and the engine speed. This system is therefore not able to compensate for errors in air flow detection by a heat-radiation sensor at high power.

Brief description of the drawings

Fig. 1 is a view illustrating the entire construction of an embodiment of a fuel controllerfor an engine according to the present invention, Fig. 2 is a block diagram illustrating the internal construction of the controller in the fuel controller of the engine in Fig. 1, Fig.3 3 is a characteristic diagram of an airfuel ratio sensor in the fuel controller of the engine of the invention, Fig. 4 is a time chart for explaining the operation of the invention, Fig. 5 is a flow chart illustrating the flow of the operation of the fuel controller of the engine, Fig. 6 is a view illustrating the entire construction of the fuel controller of the conventional engine, Fig. 7 is a block diagram showing the internal construction of the controller in the fuel controller of the engine of Fig. 6, Fig. 8 is a characteristic diagram of an airflow sensor in the fuel controller of the engine of Fig. 6, Fig. 9 is a view showing the detecting error of the air flow sensor in the fuel controller of the engine of Fig. 6, Fig. 10 is an output characteristic diagram with respect to the rotating speed of the engine of the air flow sensor, and Fig.11 is a view showing an error with respect to an altitude due to the air flow sensor in the fuel controller of the conventional engine.

Best mode for carrying out the invention

One embodiment of a fuel controller for an engine according to the present invention will be described with reference to the drawings. Fig. 1 is a view showing the construction of an embodiment. In Fig. 1, the same reference numerals as in Fig. 6 designate the corresponding components, and description of the construction is omitted, and the portion different from Fig. 6 will be mainly described.
As apparent from the comparison of Fig. 1 with Fig. 6, an air fuel ratio sensor 10 is newly provided in the construction of Fig. 6, in Fig. 1, and the sensor 10 can linearly detect the air fuel ratio from the exhaust gas components of an engine 1. The other construction is the same as in Fig. 6.
The sensor 10 produces, as shown in Fig. 2, an output to an A/D converter 81 in a controller 8. Fig. 2 shows a block diagram of the sensor 10 corresponding to the conventional controller shown in Fig. 7, and the construction of Fig. 2 is different from Fig. 7 at the point that the output of the sensor 10 is newly delivered to the A/D converter 81, and the other construction is the same as in Fig. 7.
As a sensorfor linearly detecting the air fuel ratio a combination of a zirconia type oxygen battery (atmospheric air is supplied to one side, and exhaust gas affected by the influence of an oxygen pump is supplied to the other) exhibiting a switching characteristic at stoichiometric air fuel ratio and an oxygen pump is heretofore known, and NOx in the components of the exhaust gas and oxygen in CO are reduced to supply oxygen to the opposite atmospheric pressure side of the oxygen battery by applying a voltage to the oxygen pump to detect the air fuel ratio of rich side. The output voltage with respect to the air fuel ratio of the sensor 10 is as shown in Fig. 3.
In the construction as described, above, the operation when the engine 1 is operated with full load will be described in detail with reference to the time chart of Fig. 4 and the flow chart of Fig. 5. As shown in Fig. 4(a), when the opening of a throttle is increased, the output of the sensor 7 becomes excessive from the true value due to the blow-off of the intake air. Thus, the air-fuel ratio largely varies at the rich side as shown by a curve a in Fig. 4(b), and incomplete combustion occurs.
To overcome this, in accordance with the invention, when the actual air-fuel ratio detected by the exhaust gas sensor 10 reaches the predetermined value a (for example air-fuel ratio 12), Ihe pulse width of the fuel injection valve 3 is no longer controlled in dependence on the engine air intake quantity, but instead, is controlled by feedback to maintain the air-fuel ratio substantially equal to the predetermined value a. In particular, as shown in Fig. 4(b, c), the pulse width of the fuel injection valve, and the value of the air-fuel ratio, follow the curves b, so that the actual air-fuel ratio oscillates about the value a as a mean value. In this way, stable substantially complete combustion is obtained.
In the actual control sequence, as shown in Fig. 5, in step 100, the intake air quantity Qa and the rotating speed Ne of the engine are read out as essential parameters. In next step 101, the drive pulse _T, of the fuel injection valve 3 is calculated from the input information, and in next step 102, it is judged whether the output of the sensor 10 is larger than a predetermined air-fuel ratio (e.g., 12) or not. If larger (lean side) the final drive pulse width _T is determined as τ_µ (in step 104).
If the detected air-fuel ratio is smaller than the predetermined value a (rich), a flag is set as shown in Fig. 4(e), (in step 105). When the flag is set, an integration complementary term C_FB is calculated as a value corresponding to the required air-fuel ratio a, as shown in Fig. 4(d), (in step 106). The coefficient is applied to the previously calculated injector drive pulse width value to determine a modified pulse width Tc equal to t_BxC_FB, in steps 108 to 110. Specifically, if the modified pulse width value _Tc is determined to be smaller than the initial pulse width value _TB, the control unit provides as its output an injector drive pulse having the width T_c.
In this way, the drive pulse width of the fuel injection valve is prevented from becoming excessive due to the influence of the blow-back air on the sensor 7.
When the air-fuel ratio becomes larger than the value a (lean side), the integrating complementary term (C_FB) increases as shown in Fig. 4(d) and shifted to the rich side in steps 102 to 107.
This operation is repeated, and the actual air- fuel ratio is controlled to be fed back with the air- fuel ratio as a center. This operation is continued while the drive pulse width _Tc of the valve 3 due to the feedback control is smaller than the drive pulse width _TB of the valve 3 calculated from the intake air quantity Qa and the engine rotation speed Ne, and when _Tc becomes larger than _TB, the flag is reset in step 111, and the valve 3 is controlled with the pulse width _Te.
In the foregoing description, the air-fuel ratio on the rich side has been controlled by feedback by using an air-fuel sensor 10 capable of linearly detecting the air-fuel ratio. However, an air-fuel ratio sensor 10 which inverts the output in a switching manner at the predetermined air-fuel ratio (e.g., 12) may be used to provide similar advantages.

Industrial applicability

The present invention is mainly utilized for a fuel controller of an engine for an automobile, but is not limited to automobiles. For example, the present invention may be applied to the fuel control of a ship and aircraft engine which employ fuel such as gasoline.

Claims

1. A fuel injection controller for an engine, comprising:

an air flow sensor (7) which detects the engine intake air quantity on the basis of a heat radiation principle;

an air-fuel ratio sensor (10) which detects, from the engine exhaust gas, whether the air-fuel ratio is rich or lean compared with a predetermined value;

an electromagnetic fuel injection valve (3) for injecting fuel;

and a control unit (8) which controls the opening time of the valve (3) in dependence on the sensed air-fuel ratio and the intake air quantity;
characterised in that at high engine load, the control unit controls the opening time of the valve (3) in dependence on the sensed air-fuel ratio to maintain the said ratio at the predetermined value by feedback when the sensed air-fuel ratio is rich, and when the sensed air-fuel ratio is lean, the control unit controls the opening time of the valve in open-loop control in dependence on the sensed air flow quantity as a main parameter.

2. A fuel controller according to Claim 1 wherein said control unit employs the rotating speed signal (9) of the engine as the sub parameter for controlling the valve opening time of said fuel injection valve.

3. A fuel controller according to Claim 2 wherein said control unit comprises a microprocessor for inputting the outputs of said air flow sensor, said air-fuel ratio sensor and said engine rotation detector, and a memory for storing data necessary for calculating by said microprocessor.