JPS5828559A - Method of controlling air fuel ratio of spark-ignited engine - Google Patents

Abstract

PURPOSE:To prevent the useless consumption of fuel in an engine equipped with an ignition time controller which reduces the degree of advancement of ignition time when knocking is detected, by controlling the air fuel ratio to be lower than the theoretical one when the degree of advancement of ignition time is reduced. CONSTITUTION:In an engine equipped with a supercharger, a controller 50 receives the outputs of an air flow meter 19, an intake air temperature sensor 41, a water temperature sensor 42, an oxygen sensor 44, a cylinder detector 45 and a rotation angle sensor 46 to regulate a fuel injection valve 20 and an igniter 47. The controller 50 produces an ignition time signal to reduce the degree of advancement of ignition time when knocking has occurred. In that case, the controller 50 judges whether or not the modified degree thetar of advancement is larger than zero. When the modified degree thetar of advancement is smaller than zero, the injected fuel quantity compensation coefficient Tc is set at 1. When the modified degree thetar of advancement is larger than zero, a calculation Tc=1+thetar.k (k denotes a constant) is performed to determine the injected fuel quantity compensation coefficient Tc depending on the quantity of the reduction in the degree of advancement to compensate the quantity of injected fuel.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-fuel ratio control method for a spark ignition engine.
Further, the detailed report relates to a method for controlling the air-fuel ratio of a spark-ignition engine equipped with an ignition timing control device that detects knocking using a knocking sensor and reduces the advance angle of the ignition timing when knocking occurs.

In a spark ignition engine equipped with an ignition timing control device that detects knocking using a knock sensor and reduces the advance angle of the ignition timing when the knock sensor occurs, when knocking occurs, the advance angle of the ignition timing decreases.

As the ignition timing advance angle decreases, the concentration of exhaust gas discharged from the engine increases.

By the way, in a spark ignition engine equipped with a turbocharger, the temperature of the exhaust gas is set at a predetermined value (
It is necessary to operate in such a way that the temperature does not rise above the level of danger. For this reason, conventional spark-ignition engines equipped with a turbocharger are operated with a rich air-fuel mixture with an air-fuel ratio lower than the stoichiometric air-fuel ratio in operating ranges where the exhaust gas concentration may exceed the above-mentioned dangerous temperature. has been done.

The smaller the air-fuel ratio of the air-fuel mixture supplied to the engine is than the stoichiometric air-fuel ratio, the lower the exhaust gas and concentration will be. The smaller the air-fuel ratio of the air-fuel mixture, the better; however, when the air-fuel ratio of the air-fuel mixture supplied to the engine is low, fuel efficiency deteriorates. In a spark ignition engine with a turbocharger,
Due to thermal protection of the turbocharger, even when the advance angle of the ignition timing decreases and the exhaust gas concentration increases when a knocking sensor occurs, the exhaust gas m degree roars beyond a predetermined value determined by the heat resistance of the turbocharger. It is necessary to make the air-fuel ratio considerably smaller to prevent this from happening, and the air-fuel ratio of the mixture is uniformly set so that the concentration of exhaust gas does not rise above the predetermined value when the ignition timing advance angle is decreasing. In this case, when knocking is not occurring and the ignition timing advance angle is not decreasing, a mixture with an air-fuel ratio lower than necessary is supplied to the engine, resulting in a large amount of wasteful fuel consumption.

The present invention controls the air-fuel ratio of the air-fuel mixture supplied to the engine according to the advance angle of the ignition timing, and supplies the air-fuel mixture to the engine so as to prevent exhaust gas humidity from becoming higher than a predetermined value and to avoid unnecessary fuel consumption. An object of the present invention is to provide an air-fuel ratio control method for controlling the air-fuel ratio of an air-fuel mixture.

According to the present invention, this purpose is achieved by adjusting the ignition timing t as described above.
14'l) In the air-fuel ratio control method for a spark-ignition engine equipped with a @ position, when the ignition timing advance angle is reduced, the air-fuel ratio of the mixture supplied to the engine is set to a value smaller than the stoichiometric air-fuel ratio. This is achieved by an air-fuel ratio control method characterized by controlling the air-fuel ratio.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below by way of example embodiments with reference to the accompanying drawings.

FIG. 1 is a schematic configuration diagram showing one embodiment of a spark ignition engine suitable for implementing the air-fuel ratio control method according to the present invention. In the figure, 1 indicates an engine, and the engine 1 has a cylinder block 2 and a cylinder head 3, and the cylinder block 2 receives a piston 4 in a cylinder bore formed inside the cylinder block 2. A combustion chamber 5 is defined above the piston 4 in cooperation with the cylinder head.

An intake boat 6 and an exhaust port 7 are formed in the cylinder head 3, and these boats are adapted to be ammed by an intake pulp 8 and an exhaust valve 9, respectively. Also, a spark plug 10 is attached to the cylinder head 3,
The spark plug 10 is supplied with a current generated by an ignition coil 11 via a distributor 12, and generates a spark in the combustion chamber 5 by discharge. The intake boat 6 includes an intake manifold 13, a surge tank 14, a throttle body 15 equipped with a throttle valve 16, a compressor housing 31 of a turbocharger 30, an intake pipe 17, a connecting tube 18, an air flow meter 19, and an air cleaner (not shown) in this order. These are connected together and make up the engine's ventilation system. A fuel injection valve 20 is attached near the connection end of the intake manifold 13 to the intake boat 6. The fuel injection valve 20 is supplied with liquid fuel such as gasoline stored in a fuel tank (not shown) by a fuel pump through a fuel supply pipe.
The opening time of the valve is controlled by a signal generated by a control device 50, which will be described later, to quantitatively control the fuel injection amount.

An exhaust manifold 21 and a turbine housing 32 of a turbocharger 30 are connected to the exhaust port 7 .

The turbocharger 30 has its compressor housing 3
1 has a compressor wheel 33 connected by a shaft 34 to a turbine wheel 35 provided in the turbine housing 32;
The compressor wheel 33 rotates when the turbine wheel is rotationally driven by the pressure of the exhaust gas discharged from the engine 1, and the engine 1 is supercharged with intake air. Also, the turbine housing 3
2 is provided with a bypass passage 36 that bypasses a portion where the turbine wheel 35 is disposed, and this bypass passage 36 is selectively opened and closed by a bypass valve 37.

The bypass valve 37 is connected to a diaphragm device 39 via a link element 38 and is adapted to be driven by the latter. The diaphragm device 39 has the intake pipe pressure of the engine 1 introduced into its diaphragm chamber (not shown) through a conduit 40, so that the intake pipe pressure becomes the same as that of the engine 1.
When the value exceeds a predetermined value determined based on the durability, etc., the bypass valve 37 is opened to open the bypass passage 36.

The control device 50 may be a general microcomputer adapted to control the fuel injection amount and ignition timing, an example of which is best shown in FIG. This microcomputer 50 includes a central processing unit (CPU) 51, a read-only memory (ROM) 52, and a random access memory (RAM).
53, an input port device 54, and an output port I*55, which are interconnected by a bidirectional fumon bus 56.

The input port @@54 receives an air flow rate signal generated by the air flow meter 19, an intake temperature signal generated by the intake temperature sensor 41 attached to the air flow meter 19, and a water temperature sensor 42 attached to the cylinder block 2. Cooling water concentration signal and O! attached to the turbine housing 32. The excess air ratio signal (oxygen concentration signal) generated by the sensor 44, and the cylinder discrimination signal and crank rotation angle signal generated by the cylinder discrimination sensor 45 and rotation angle sensor 46 attached to the distributor 12 are inputted, respectively. The data is appropriately converted into signals and output to the CPU and RAM 53 according to instructions from the CPU 51. C
The PU 51 determines the fuel injection amount and ignition timing based on the data detected by each sensor according to a program stored in the RAM 52, and outputs a fuel injection signal based on the determined fuel injection signal from the boat device 55 to the fuel injection valve 20 and the ignition timing. Signals are output from the output boat device 55 to the igniters 47, respectively.

The igniter 47 is attached to the ignition coil 11 as shown in FIG.
The power supply circuit of the primary coil is cut off, and the advance angle of the ignition timing is controlled.

The manner in which the control method of the present invention is implemented will be described below with reference to the flowcharts shown in FIGS. 3 and 4.

Figure 3 shows the main routine including the step of determining the fuel injection amount, and Figure 4 shows the interrupt routine that determines the advance angle of the ignition timing.First, the ignition timing according to the routine shown in Figure 4 is shown. Explain the key points of control. This interrupt routine is performed at every predetermined crank angle, and in the first step, the engine speed calculated based on the crank rotation angle detected by the rotation speed sensor 46 and the intake air detected by the air flow meter 19 are calculated. The amount of knocking detected by the knocking sensor 43 and data on the knocking occurrence state detected by the knocking sensor 43 are read. In the next step, the basic advance angle θa is determined based on the engine speed and intake air amount.

In the next step, it is determined whether knocking occurred during the previous engine stroke. If knocking has occurred in the previous (c) engine stroke, in order to reduce the advance angle, the previous corrected advance angle θ, which was determined by the previous interrupt routine and stored in the RAM 53, is
A calculation is performed to add 1 to the value, and the new modified advance angle θ
" is calculated. On the other hand, if knocking has not occurred in the previous stroke, then it is determined whether or not knocking has occurred in the previous 10 strokes.
If knocking does not occur during the 0@ engine stroke, it is determined that there is room to increase the ignition timing advance angle, and a calculation is performed to subtract 1 from the previous corrected advance angle θ ``L-1''. Then, a new modified advance angle θ" is calculated. If the state in which no knocking occurs is less than 10 strokes, the previous modified advance angle θ" is calculated as 1-θ".

When the modified advance angle θ" is calculated as described above, in the next step, the previous modified advance angle θ"L-1 stored in the RAM 53 is rewritten to the new modified advance angle θ". .

In the next step, the following calculation is performed: (basic advance angle θa) - (corrected advance angle θr), the executed advance angle θ is calculated, and this is stored in the RAM 53.

If the modified advance angle θ is zero, the execution advance angle θ is equal to the basic advance angle θa, and if the modified advance angle θr is greater than 1, the execution advance angle θ decreases from the basic advance angle θa, that is, the advance angle On the other hand, if the modified advance angle θr is smaller than zero, the actual advance angle θ becomes larger than the basic advance angle θa, that is, the advance angle becomes larger.

The ignition timing signal is as above! ! It is determined according to the execution advance angle θ determined by the engine, the cylinder position and phase detected by the cylinder discrimination sensor 45, and the crank rotation angle detected by the rotation angle sensor 46, and is output to the igniter 47 at a predetermined time.

Next, the air-fuel ratio control procedure will be explained with reference to the flowchart shown in FIG. In this routine,
First, a basic fuel injection time TP is determined based on the engine speed and intake air amount.

In the next step, the intake air concentration detected by the intake air temperature sensor 41, the cooling water 11 degrees detected by the water volume sensor 42,
The fuel injection amount correction coefficient f(χ) is determined according to the excess air ratio of exhaust gas detected by the OW sensor 44. In the high-load operating range, feedback control of the air-fuel ratio is not performed using the Ox sensor signal in order to supply the engine with a mixture having an air-fuel ratio smaller than the stoichiometric air-fuel ratio, that is, a so-called output air-fuel ratio.

In the next step, the modified advance angle θ' determined by the above-mentioned interrupt routine and stored in the RAM 53 is
A determination is made as to whether or not is greater than zero. When θ is not 0, that is, when the advance angle is not decreased, the fuel injection amount correction factor To is set to 1. On the other hand, when θ is 0, that is, when the advance angle is decreased from the basic advance angle, T is set.
The calculation c-1+θ"×k (where k is a constant) is performed to calculate the fuel injection amount correction factor Tc according to the amount of decrease in the advance angle.

In the next step, mTAU at the time of actual fuel injection is calculated according to the following formula.

TAU-TPx f(Z)XTc By determining the effective fuel injection time TALI as described above, when the ignition timing advance angle is not reduced, the engine has an engine-required air temperature that is approximately the stoichiometric air-fuel ratio or the output air-fuel ratio. When a mixture with the same fuel ratio is supplied and the ignition timing advance angle is reduced in the event of knocking, the effective fuel injection time TAU is extended and the amount of fuel injected in one engine stroke is increased. As a result, the engine is supplied with an air-fuel mixture having an air-fuel ratio smaller than the stoichiometric air-fuel ratio or even smaller than the output air-fuel ratio. When the advance angle is reduced in this way, a rich air-fuel mixture with an air-fuel ratio smaller than the stoichiometric air-fuel ratio is supplied to the engine in accordance with the amount of reduction, thereby increasing the concentration of exhaust gas emitted by the engine to a predetermined value or higher. This will be avoided.

In the above-described embodiment, the fuel injection amount correction factor Tc was calculated by the main routine, but this calculation may also be performed by an interrupt routine as shown in FIG. . Furthermore, the fuel injection amount correction factor To based on the advance angle of the ignition timing is determined regularly depending on whether the advance angle is decreased or not, as shown in the flowchart shown in FIG. may be done. Also, this fuel injection amount correction factor To is 1 when the advance angle is increased from the basic advance angle.
It may be determined that the fuel injection rate is reduced to the following value. If such fuel injection amount control is required, the fuel injection amount may be determined by a routine as shown in FIG.

Although the present invention has been described in detail with respect to specific embodiments above, it will be appreciated by those skilled in the art that the present invention is not limited thereto and that various embodiments can be made within the scope of the present invention. It should be obvious.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of a suitable spark ignition engine in which the air-fuel ratio control method according to the present invention is implemented, and FIG. 2 is a block diagram showing an example of control@cost for implementing the method of the present invention. 3 through 6 are flowcharts illustrating microcomputer routines for carrying out the method and related controls of the present invention. 1...Engine, 2...Cylinder block, 3...
・Cylinder head, 4... Piston, 5... Combustion chamber, 6... Intake boat, 7... Exhaust boat, 9...
exhaust pulp. 10-...Spark plug, 11...Ignition coil, 12-...
... Distributor, 13... Intake manifold, 14... Surge tank, 15... Throttle body, 16... Throttle valve, 17... Intake tube, 18... Connection tube, 19... Air 70-
Meter, 20...Fuel injection valve, 21...Exhaust manifold, 30...Turbocharger, 31...Compressor housing, 32...Turbine housing,
33... Compressor wheel, 34... Shaft, 35
...Turbine wheel, 36...Bypass passage, 3
7-...Bypass valve. 38... Link element, 39... Diaphragm device,
40... Conduit, 41... Intake temperature sensor, 42...
Water temperature sensor, 43...Knocking sensor, 44...
O! sensor. 45... Mood discrimination sensor, 46... Turn angle sensor,
47...Knocking, 50...Control device (microcomputer), 51...Central processing unit (CPU
). 52... Read only memory (ROM), 53...
Random access memory (RAM), 54... Input boat device, 55... Output boat device, 56... Fumon bus patent applicant Toyota Motor Corporation representative
Patent Attorney Takeshi AkishiFigure 2Figure 3

Claims (1)

[Claims] In an air-fuel ratio control method for a spark ignition engine equipped with an ignition timing control device that detects knocking using a knock sensor and reduces the ignition timing advance angle when knocking occurs, when the ignition timing advance angle is reduced, An air-fuel ratio control method whose special purpose is to control the air-fuel ratio of the air-fuel mixture supplied to the engine to a value smaller than the stoichiometric air-fuel ratio.