JPS6233974Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention is a fuel injection control device for a supercharged engine;
In particular, it relates to an engine protection device when boost pressure becomes abnormally large.

The configuration of a conventional fuel injection control device for a turbocharged engine and its problems will be explained with reference to FIG.

In Fig. 5, 1 is the engine body, 2 is a fuel injection valve installed at the intake port of the engine, 3 is a throttle valve,
4 is an idle switch that detects the fully closed position of the throttle valve 3; 5 is an air flow meter that detects the intake air amount Q of the engine; 6 is an engine counter that faces a toothed disk 7 attached to the engine crankshaft; This is a crank angle sensor that detects the rotation speed N.

8 is a control unit that calculates a fuel injection pulse width T _i proportional to Q/N from the intake air amount Q detected by the air flow meter 5 and the engine speed N detected by the crank angle sensor 6; The fuel injection valve 2 is operated for a time corresponding to T _i for each revolution to control the amount of fuel supplied to the engine to an optimum value. This control unit 8 also uses the output signals of the idle switch 4 and crank angle sensor 6 to determine whether the throttle valve 3 is fully closed (the idle switch is ON) and the engine speed is N.
is greater than the set value N ₁ , the fuel supply is cut off,
During deceleration, fuel supply is restarted when the engine speed N becomes smaller than the set value N ₂ (N ₂ < N ₁ ) or when the throttle valve 3 is in a position other than fully closed (the idle switch is OFF). It has a fuel cut function.

9 in Figure 1 is a supercharger, and in engines equipped with such a supercharger, if the supercharging pressure increases too much, the load on the engine becomes excessive and the engine may be destroyed. The conventional fuel injection control device for a supercharged engine is not equipped with a protection device for the engine against such an abnormal increase in supercharging pressure.

In view of the above points, it is an object of the present invention to provide a fuel injection control device for a supercharged engine that can appropriately protect the engine from overload caused by an abnormal increase in supercharging pressure.

The structure of the present invention will be explained with reference to FIG. 1 (diagram corresponding to claims). a is an intake air amount detection means, b is an engine rotation speed detection means, and c is an intake air amount Q and engine rotation speed detected by each of the above means. The ratio of N (T _p =K×
Q/N), d is the second calculation means that calculates the fuel injection pulse width (T _i =AT _p +B) corresponding to the calculated value of the first calculation means c, and e
is the first determination means for determining whether the calculated value T _p of the first calculation means c exceeds the set value T _pp , and f is the first determination means
time measuring means for measuring the time during which the calculated value T _p of the first calculating means c exceeds the set value T _pp in response to the output of the determining means e; g is the set value T of the time measuring means f; A second determining means h receives the output of the second determining means g and supplies fuel for a predetermined time from the time when the indicated value T of the time measuring means f exceeds the set value T _{p .} control means for outputting a control signal to cut off the control signal; i is a fuel injection pulse output means for outputting a fuel injection pulse having a pulse width calculated by the second calculation means d, except for the time when the control signal is outputted; Yes, the calculated value T of the first calculation means c
When _p exceeds the set value T _pp , an abnormal increase in the boost pressure is detected, and this state continues for more than the set time T _p , the control means h sends the fuel injection pulse output means i
This system issues a control signal to cut off the fuel supply to the fuel tank.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 shows an example of the configuration of the control unit 8, which is the main part of the present invention. In the figure, 10 is an intake air amount reading circuit that reads the intake air amount Q from the output signal of the air flow meter 5, which is the intake air amount detection means, and 11 is the output signal of the crank angle sensor 6, which is the engine speed detection means. An engine speed reading circuit 12 reads the engine speed N from the intake air amount Q, the engine speed N, and a constant k to calculate the basic pulse width T _p by the formula T _p =k×Q/N. Arithmetic circuit (first computing means)
It is. 13 is a memory for storing correction values A and B (selected according to engine operating conditions requiring correction) for calculating the fuel injection pulse width T _i ;
The arithmetic circuit (second arithmetic means) 14 uses these correction values A and B to perform a correction calculation of T _p T _i =AT _p +B, and stores the calculated fuel injection pulse width T _i in the fuel injection pulse width register 15 Transfer to. On the other hand, the basic pulse width T _p is compared with a set value T _pp stored in the memory 16 by a comparator 17 which is a first determination means. When the boost pressure becomes abnormally high, the intake air amount Q becomes abnormally large relative to the engine speed N, and therefore T _p also becomes abnormally large. Therefore, an abnormality in the boost pressure can be detected by determining that T _p is larger than the set value T _pp .

When T _p >T _pp , a timer 18, which is a time measuring means, measures the time based on the output from the comparator 17. When timer 18 reaches T _p T _pp , it is reset by a signal obtained by inverting the output of comparator 17 with inverter 19 .

The time T measured by the timer 18 is compared with the set value T _p stored in the memory 20 by the comparator 21 which is the second judgment means, and only when the time T exceeds T _p is the control unit A trigger signal is output from the comparator 21 to the stable multivibrator 22 .
When the trigger signal is input, the contents of the fuel injection pulse width register 15 are forcibly reset to 0 for a certain period of time _t1 by the control signal output from the monostable multivibrator 22. Therefore,
During this time, the fuel injection valve 2 does not operate and the fuel supply is cut off. Operation circuit 14 except when fuel is cut off
The value T _i set in the fuel pulse width register 15 is sent to the fuel injection valve drive circuit 23, and a pulse signal for driving the fuel injection valve 2 is generated. The fuel injection pulse width register 15 and the fuel injection valve drive circuit 23 correspond to fuel injection pulse output means.

The basic pulse width _Tp may temporarily show an abnormally large value due to a delayed response of the engine or an overshoot of the air flow meter 5 during a transient state during acceleration, but since the indicated value T of the timer 18 does not exceed the set value _Tp of the memory 20 at this time, unnecessary fuel cutoff is not _performed .
If the fuel cutoff is immediately released when the set value T _Pp is reached or below, the fuel cutoff and release will be repeated in a short period of time, which may result in the fuel injection being interrupted midway or the fuel injection being reduced from two times per cycle to one time.
The mixture sucked into the engine becomes leaner on average, making it more likely to cause knocking when driving at high speeds.
In this embodiment, a monostable multivibrator 22 is used so that the fuel supply is not resumed even if _TpTpp is reached until a certain set _{time T1} has elapsed after the fuel cutoff. In this way, the mixture drawn into the engine is divided into a normal mixture ratio state and a state where there is no fuel at all, and it is prevented as much as possible from being drawn in an intermediate lean mixture ratio state.

FIG. 3 shows an example of the operation of each part using a time chart.

FIG. 4 shows a flowchart when the control unit 8 is provided with the above functions using a microcomputer. In FIG. 4, F-1 to F-14 indicate the steps of the program. If explained in comparison with FIG. 2, F-1 corresponds to the intake air amount reading circuit 10 and the engine speed reading circuit 11; -2 corresponds to the arithmetic circuit 12. In FIG. 4, TM1 is a register corresponding to the timer 18, and TM2 is a register corresponding to the monostable multivibrator 22. If the content of TM2 is 0, F-3 to F-4
Proceed to. F-4 corresponds to the comparator 17, and T _p > T _p
If not _p , the contents of TM1 are set to 0 in F-5. Idle switch is ON for F-6 and F-7
and the engine speed N is greater than the set value _N1 , this is a step for causing fuel cutoff.
When normal, it moves to F-8. F-8 is the arithmetic circuit 14
corresponds to

When T _p >T _pp , 1 is added to the contents of TM1 at F-9. F-10 corresponds to comparator 21,
When the contents of TM1 exceed the set value T _p , F-11
The value of T ₁ is set in TM2, and then T _i =
0, that is, the fuel injection pulse width T _i is reset to 0.

Returning to F-3, if the content of TM2 is not 0, 1 is subtracted from the content of TM2 in F-12, and TM2
T i =0 is maintained until T _i =0. The T _i values from F-8 and F-13 will be output at F-14.

Therefore, this embodiment also provides the same functionality as the embodiment shown in FIG.

As explained above, according to the present invention, when the ratio of the intake air amount to the engine speed exceeds a set value in a supercharged engine and this condition continues for a certain set time, the fuel supply is cut off. Therefore, damage to the engine due to overload when boost pressure increases abnormally can be prevented, and basic pulse width T _p temporarily becomes an abnormally large value in a transient state during acceleration. This eliminates malfunctions that sometimes result in unnecessary fuel shutoffs.

[Brief explanation of the drawing]

Figure 1 is a claim correspondence diagram showing the configuration of the present invention;
Fig. 2 is a circuit configuration diagram of the main part showing an embodiment of the present invention, Fig. 3 is a time chart showing an example of its operation,
FIG. 4 is a flowchart showing another embodiment of the present invention, and FIG. 5 is a schematic configuration diagram of a supercharged fuel injection engine. DESCRIPTION OF SYMBOLS 1... Engine body, 2... Fuel injection valve, 5... Air flow meter, 6... Crank angle sensor, 8... Control unit, 9... Supercharger, 12... First calculation means. Arithmetic circuit, 14...Arithmetic circuit as second computing means, 17...Comparator as first determining means, 18...Timer as time measuring means, 21...
...Comparator as second determination means, 22... Monostable multivibrator as control means, 15, 23
...A fuel injection pulse width register and a fuel injection valve drive circuit which are fuel injection pulse output means.

Claims (1)

[Scope of utility model registration request] an intake air amount detection means, an engine rotation speed detection means, a first calculation means for calculating a ratio between the intake air amount detected by each of the above means and the engine rotation speed;
and second calculation means for calculating a fuel injection pulse width corresponding to the calculation value of the calculation means, wherein the calculation value of the first calculation means corresponds to the set value. a first determining means for determining whether the set value has been exceeded; a time measuring means for receiving the output of the first determining means and measuring the time during which the calculated value of the first calculating means exceeds the set value; a second determining means for determining whether the indicated value of the time measuring means exceeds the set value; A control means for outputting a control signal to cut off fuel supply for a certain period of time, and a fuel injection pulse output for outputting a fuel injection pulse having a pulse width calculated by the second calculation means except for the time when the control signal is outputted. 1. A fuel injection control device for a supercharged engine, comprising: means.