JPS632026B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting a knock in a multi-cylinder engine, particularly a spark-ignition multi-cylinder engine.

In spark ignition engines for automobiles and the like, it has been considered to operate the engine economically by controlling the ignition timing while detecting the occurrence of knocks using a knock sensor that detects the occurrence of knocks through vibration.

Spark ignition engines commonly used in automobiles are multi-cylinder engines with four to eight cylinders.
If only one knock sensor is installed in the multi-cylinder engine, even if a knock occurs in a cylinder located near the installation position of the knock sensor, it will be reliably detected in a cylinder located further away from the installation position of the knock sensor. The occurrence of knocks is not reliably detected, and especially in the case of an in-line six-cylinder engine, there may be cylinders in which the occurrence of knocks is hardly detected by a single knock sensor.

Therefore, the generation of intake swirl can be suppressed by increasing the compression ratio of only one specific cylinder near where the knock sensor is installed compared to other cylinders, or by changing the shape of the intake port. It has been considered to make the cylinder more likely to generate knocks than in other cylinders, and to ensure that even in a multi-cylinder engine, the occurrence of knocks can be reliably monitored using only one knock sensor. However, in a multi-cylinder engine configured in this way, the combustion of the air-fuel mixture in one particular cylinder and the combustion of the air-fuel mixture in other cylinders naturally become uneven. , it is inevitable that differences in the combustion state of the air-fuel mixture will occur between the cylinders. Therefore, as mentioned above, if a specific cylinder is configured where knocks are likely to occur due to changes in the compression ratio or intake port shape, etc., knocks may occur in high-load operating ranges where knocks are likely to occur, even if it is unavoidable. Even in low to medium load operating ranges where this does not occur, there may be a difference in the combustion state of the air-fuel mixture between a specific cylinder and other cylinders, resulting in increased engine vibration or harmful emissions in the exhaust gas. Secondary problems arise, such as an increase in the number of components.

Knock in a spark ignition engine is caused by spontaneous combustion of end gas, and its occurrence is affected not only by the compression ratio and ignition timing of the engine but also by the air-fuel ratio of the mixture, and the knock occurs near the stoichiometric air-fuel ratio. It is the most likely to occur, and is less likely to occur even if the air-fuel ratio is higher or lower than that.

By the way, in a normal vehicle engine,
In high-load operating ranges where knocks are likely to occur, the amount of fuel is increased to obtain the necessary engine output, and the air-fuel ratio is lower than the stoichiometric air-fuel ratio.
In other words, the engine is operated with a rich air-fuel mixture, which is the output air-fuel ratio.

The present invention only works in operating ranges where knocks are likely to occur.
That is, a knock detection method is provided in which a specific cylinder is set in a state where knocks are more likely to occur than other cylinders only during high-load operation, and the occurrence of knocks in that specific cylinder is exclusively detected. The primary purpose is to do so.

Another object of the present invention is to effectively utilize fuel increase control performed in a high-load operating range to control the air-fuel ratio of the air-fuel mixture so that one specific cylinder is It is an object of the present invention to provide a knock detection method which detects the occurrence of a knock in a particular cylinder as a state in which a knock is likely to occur.

According to the present invention, fuel is supplied to each cylinder by an individual fuel injection valve, and during low to medium load operation, all of the fuel injection valves are operated with the same valve opening time, During high-load operation, only one specific fuel injection valve is operated with a valve opening time different from that of the other fuel injection valves, and the specific one fuel is supplied to one specific cylinder. The air-fuel ratio of the air-fuel mixture to be used is closer to the stoichiometric air-fuel ratio than that of other cylinders, and the knock sensor installed in the vicinity of the specific cylinder mainly detects the knock in the specific cylinder. This is achieved by a method for detecting a knock in a multi-cylinder engine, which is characterized by detecting the occurrence of a knock.

According to the knock detection method according to the present invention as described above, a mixture of the same air-fuel ratio is supplied to all cylinders during low to medium load operation in which no knock occurs and knock detection is not required. Therefore, there is no difference in the combustion state of the air-fuel mixture, and operation is performed in a stable state.During high-load operation, where knocks may occur and knock detection is actually required, specific cylinders are As the air-fuel mixture is supplied to the air-fuel ratio closer to the stoichiometric air-fuel ratio than other cylinders, this particular cylinder is more likely to cause a knock than other cylinders. From the detection of knocks, the tendency for knocks to occur can be found before all cylinders produce knocks.

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

FIG. 1 is a schematic diagram showing one embodiment of a spark ignition multi-cylinder engine in which the method of the present invention is implemented. In the figure, 1 indicates the engine,
This engine 1 has a plurality of cylinders, in this embodiment, four cylinders 2 to 5 in a row. Each cylinder of the engine 1 is configured to take in air from an air cleaner (not shown) through an air flow meter 6, a throttle valve 7, and an intake manifold 8. Fuel injection valves 9 to 12 are provided in branch pipe portions of an intake manifold 8 that are individually connected to each cylinder, corresponding to each cylinder. The opening times of the fuel injection valves 9 to 12 are controlled by an electronic control device, which will be described later, so that a predetermined amount of gasoline fuel is injected into each cylinder during each intake stroke of each cylinder. A mixture of air taken in from the air cleaner and gasoline fuel injected from the fuel injection valve is combusted in each cylinder and is discharged from the exhaust manifold 13 to the outside of the engine as exhaust gas.

Reference numeral 14 denotes an electronic control device that provides fuel injection signals with predetermined pulse widths to the fuel injection valves, and this electronic control device 14 includes a waveform shaping circuit 15, a frequency dividing circuit 16, a basic fuel amount calculation circuit 17, and a fuel increase circuit 1.
8, a voltage correction circuit 19, an output amplification circuit 20, and the like. This electronic control device may be well known, and if necessary, please refer to Japanese Patent Application Laid-Open No. 49-67016 for details of this device.

The waveform shaping circuit 15 includes a distributor 21.
A signal is given that represents the engine speed at which the engine rotates. The frequency dividing circuit 16 divides the frequency of the signal output by the waveform shaping circuit 15 by half to generate an engine rotation speed signal. The basic fuel calculation circuit 17 is designed to generate a basic fuel amount signal in accordance with the engine rotational speed signal and the intake air amount signal generated by the air flow meter 6. The fuel increase circuit 18 is adapted to modify the basic fuel amount signal given by the basic fuel amount calculation circuit 17 in order to increase the amount of fuel during warm-up, acceleration, and high load conditions. The voltage correction circuit 19 is configured to correct the fuel injection signal according to the voltage of the battery power source 22 in order to avoid fluctuations in the fuel injection signal due to voltage fluctuations of the battery power source 22. The output amplification circuit 20 amplifies the signal from the voltage correction circuit 19 and outputs it to the fuel injection valves 9 to 12, respectively.

Each of the fuel injection valves 9 to 12 and the battery power supply 22
Resistance elements 23 to 26 are connected in parallel to each other for each fuel injection valve in the middle of the electric circuit connected to the fuel injection valve. Further, another resistance element 27 is connected in series with the resistance element 26 in the middle of the electric circuit connected to the fuel injection valve 12 of the cylinder 5, and a pressure switch 28 is connected in parallel with the resistance element 27.
is connected.

Pressure switch 28 includes a diaphragm 29 defining a diaphragm chamber 30 on one side thereof. When a negative pressure of a predetermined value or more is introduced into the diaphragm chamber 30, the diaphragm 29 is displaced to the left in the figure against the spring force of the compression coil spring 31, and connects the contacts 32 and 33. On the other hand, when a negative pressure equal to or higher than a predetermined value is not introduced into the diaphragm chamber 30, the spring force of the compression coil spring 31 pushes the contacts 32 and 33 to the right in the figure. It's starting to pull away. The diaphragm chamber 30 is connected to the intake manifold 8 via a conduit 34, and is adapted to receive intake pipe negative pressure.

A vibration detection type knock sensor 35 is attached to the engine 1 at a position close to the cylinder 5. A signal generated by the knock sensor 35 is input to an ignition timing control circuit 36. The ignition timing control circuit 36 determines the advance angle of the ignition timing in response to a signal generated by the knock sensor 35. The ignition timing control circuit 36 is an igniter 37
It is connected to the primary side of the ignition coil device 38 via. Further, the secondary side of the ignition coil device 38 is connected to a spark plug (not shown in the diagram) of each cylinder by a rotor (not shown in the diagram) provided in the distributor 21. .

In the figure, numeral 39 is an ignition switch.

When the engine 1 is operated at a low to medium load, the intake pipe negative pressure in the intake manifold 8 is higher than the set value of the pressure switch 28, and therefore the contacts 32 and 33 of the pressure switch 28 are connected.
Resistive element 27 is short-circuited by this pressure switch 28 and has no substantial resistance effect. Therefore, in such an operating range, the fuel injection valves 9 to 12 of each cylinder each have one resistance element 2.
As a result, the opening time of each fuel injection valve becomes the same, and air-fuel mixture of the same air-fuel ratio is supplied to the four cylinders 2 to 5. Become so.

When the engine 1 is operated under a high load that requires fuel increase, the fuel increase is performed and the intake pipe negative pressure in the intake manifold 8 is reduced by the pressure switch 2.
8, the contacts 32 and 33 of the pressure switch 28 become separated. At this time, the fuel injector 12 is connected to the battery power supply 22 through a series circuit including a resistor 26 and another resistor 27, so that the voltage applied to the fuel injector 12 is applied to the other fuel injectors 9 to 11. Based on the voltage applied to the fuel injection valve 12, the opening characteristic of the fuel injection valve 12 changes compared to the others, and the effective fuel injection time of the fuel injection valve 12 is shortened compared to the others. . As a result, the amount of fuel added to the cylinder 5 is smaller than that of the other cylinders, and therefore the cylinder 5 is supplied with an air-fuel mixture having an air-fuel ratio closer to the stoichiometric air-fuel ratio than the other cylinders. As a result, cylinder 5 is more likely to cause knocks than other cylinders. A knock occurring in the cylinder 5 is detected by a knock sensor 35 installed near the cylinder 5.

FIG. 2 is a schematic configuration diagram showing another embodiment of an engine in which the method of the present invention is implemented. Furthermore, the second
In the figures, parts corresponding to those in FIG. 1 are designated by the same reference numerals as in FIG. 1. In this embodiment, the engine 1 has a turbocharger, and the compressor 40 of the turbocharger is provided in the middle of the intake passage of the engine 1. When a turbocharger is provided, the pressure in the intake manifold 8 becomes either negative pressure or positive pressure, and as the load on the engine 1 increases, the pressure becomes positive, and it generally increases as the load increases. . When a positive pressure equal to or higher than a predetermined value is introduced into the diaphragm chamber 30, the pressure switch 28 is displaced to the right in the figure against the spring force of the compression coil spring 31, and the contacts 32 and 33 are closed. On the other hand, when a positive pressure equal to or higher than a predetermined value is not introduced into the diaphragm chamber 30, the spring force of the compression coil spring 31 pushes the contacts 32 and 33 to the left in the figure. It's getting old.

In this embodiment as well, the resistance element 27 performs a substantial resistance action only during high-load operation when an increase in fuel quantity is to be carried out, so that the opening characteristic of the fuel injection valve 12 is different from that of other valves only at this time. As a result, cylinder 5 is supplied with an air-fuel mixture having an air-fuel ratio closer to the stoichiometric air-fuel ratio than other cylinders, and this cylinder 5 is more likely to cause a knock than other cylinders.

FIG. 3 is a schematic configuration diagram showing yet another embodiment of an engine in which the method of the present invention is implemented. still,
In FIG. 3, parts corresponding to those in FIG. 2 are designated by the same reference numerals as in FIG. In this embodiment, the turbocharger compressor 40 is located downstream of the throttle valve 7 in terms of the flow of intake air. Pressure switch 28
defines a first diaphragm chamber 30a on one side of the diaphragm 29 and a second diaphragm chamber 30b on the other side, and the first diaphragm chamber 30a is connected to the compressor 40 through a conduit 34a. The second diaphragm chamber 30b, on the other hand, is connected to the outlet of the compressor 40 via a conduit 34b. When the pressure in the second diaphragm chamber 30b is higher than the pressure in the first diaphragm chamber 30a by a predetermined value or more, the diaphragm 29 moves to the right in the figure to separate the contacts 32 and 33. When the pressure in the second diaphragm chamber 30b is not higher than the pressure in the first diaphragm chamber 30a by more than a predetermined value, it is pushed to the left in the figure by the action of the compression coil spring 31, connecting the contacts 32 and 33. I'm starting to do that.

During low to medium load operation, the rotational speed of the turbocharger compressor 40 is relatively low, and accordingly the pressure difference between its inlet and outlet is smaller than the set value of the pressure switch 28. Therefore, during low to medium load operation, contacts 32 and 33 of pressure switch 28 are connected, and resistance element 27 is short-circuited by pressure switch 28 and has no substantial resistance effect. On the other hand, during high load operation, the pressure difference between the inlet and outlet of the compressor 40 exceeds the set value of the pressure switch 28, and thus the contacts 32 and 33 of the pressure switch 28 are pulled apart.

Therefore, in this embodiment as well, the resistance element 27 performs a substantial resistance action during high-load operation in which an increase in fuel quantity is required, and accordingly, the opening characteristic of the fuel injection valve 12 becomes different from that of other valves. As a result, cylinder 5 is supplied with an air-fuel mixture having an air-fuel ratio closer to the stoichiometric air-fuel ratio than other cylinders. As a result, the cylinder 5 is more likely to generate knocks than other cylinders, and the knocks are detected by the knock sensor 35 installed near the cylinder 5.

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

[Brief explanation of the drawing]

1 to 3 are schematic configuration diagrams showing embodiments of a spark ignition multi-cylinder engine in which the method of the present invention is implemented. 1 - Engine, 2 - 5 - Cylinder, 6 - Air flow meter, 7 - Throttle valve, 8 - Intake manifold, 9 - 12 - Fuel injection valve, 13 - Exhaust manifold, 14 - Electronic control device, 15 - Waveform shaping circuit , 16 - frequency division circuit, 17 - basic fuel amount calculation circuit, 18 - fuel increase circuit, 19 - voltage correction circuit,
20-output amplifier circuit, 21-distributor, 22-battery power supply, 23-27-resistance element, 28-pressure switch, 29-diaphragm,
30 - diaphragm chamber, 31 - compression coil spring,
32, 33 - contact, 34 - conduit, 35 - knock sensor, 36 - ignition timing control circuit, 37 - igniter, 38 - ignition coil device, 39 - ignition switch, 40 - compressor.

Claims (1)

[Claims] 1. Fuel is supplied to each cylinder by an individual fuel injection valve, and during low to medium load operation, all of the fuel injection valves are operated with the same valve opening time, and during high load operation, one specific fuel injection valve is operated with the same valve opening time. Only the fuel injection valve is operated with a valve opening time different from that of the other fuel injection valves, so that the air-fuel ratio of the air-fuel mixture to be supplied to the specific one cylinder to which the specific one fuel is supplied is set to another value. The air-fuel ratio is closer to the stoichiometric air-fuel ratio than that of the cylinder, and the knock sensor provided at a position close to the specific cylinder mainly detects the occurrence of knock in the specific cylinder. A method for detecting knocks in multi-cylinder engines.