JPH05321719A - Fuel cut device of internal combustion engine - Google Patents

Abstract

PURPOSE:To restart fuel to supply by an engine speed as low as possible without generating engine stalling and rotating down after fuel cut. CONSTITUTION:An instantaneous value (N) of engine speed is detected by a detector 33, a smooth value (Nf) is found out from the instantaneous value (N) by a smoothing calculator 35, a deviation (DN) between the smooth value (Nf) and the instantaneous value (N) is found out by a deviation calculator 36, and the deviation (DN) is added to a based fuel return rotating number (Nbase) which is set in a setter 34 by a corrector 37 in the case where the deviation (DN) is a positive number. It is thus possible to vary a fuel return rotating number (Ninj) continuously according to the degree of deceleration so as to restart fuel to supply by engine speed of a minimum limit which is enough to supplement shortage of torque caused by primary delay phenomenon of pressure in an intake pipe by pressure accumulating efficiency of an intake system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cut device for an internal combustion engine (hereinafter also referred to as an engine), and in particular, for restarting fuel supply at an appropriate low engine speed in consideration of the pressure accumulation effect of the intake system. Regarding the improvement of.

[0002]

2. Description of the Related Art It is extremely effective to cut off fuel supply to an engine during deceleration operation of a vehicle from the viewpoint of improving running fuel efficiency and suppressing unburned gas emission. For this reason, it is desirable to continue the fuel cut to the lowest possible engine speed during deceleration operation, and then restart the fuel supply, but at the time of sudden deceleration, for example, during lane sig (driving) or coast (when the throttle is fully closed). When the engine and transmission are separated during rapid deceleration, the engine stall or rotation drop is more likely to occur due to the pressure accumulation effect of the intake system compared to during normal deceleration. The fuel supply is restarted when the engine speed falls below a fixed value that is sufficiently higher than the above.

On the other hand, in Japanese Patent Publication No. 60-48623 or Japanese Patent Publication No. 63-210215, two fixed values, high and low, are set as the engine speed (hereinafter referred to as the fuel return speed) for restarting the fuel supply. If the deceleration is small, the magnitude of the deceleration of the engine speed is determined from the differential value of the analog voltage signal that represents the engine speed or the time difference of the cycle of the crank angle pulse signal. A technique is disclosed in which the fuel supply is restarted when the speed reaches the return speed, and when the deceleration degree is large, the fuel supply is restarted when the speed reaches the higher speed of the fuel return. According to this, the range of fuel cut is widened during normal deceleration, it is possible to suppress the emission of unburned gas and improve the running fuel consumption, and it is possible to prevent engine stall and rotation drop during rapid deceleration.

[0004]

However, in the technique of selecting two high and low fuel return rotational speeds depending on the magnitude of the differential value of the engine rotational speed, etc., of course, various deceleration rates are not supported, so that the fuel cut range There is a limit to expansion. For example, since the types and the number of load devices for the engine are increasing in recent vehicles, the load devices are turned on / off.
Although various load torques are generated and various deceleration degrees are different depending on the off state, it is not possible to restart the fuel supply at the minimum engine speed within the optimum range, that is, in the range where the rotation drop does not occur.

In this case, it is conceivable that the deceleration degree is finely divided by using the differential value of the engine speed or the cycle difference of the crank angle pulse, and the fuel return rotational speed suitable for each is selected. Alternatively, even with the cycle difference, the degree of decrease in engine rotation after resuming fuel supply differs between the case of deceleration from a relatively high speed and the case of deceleration from a relatively low speed, which cannot be said to be a sufficient countermeasure. This is because the drop in engine speed depends on the engine torque when the fuel supply is restarted, and this engine torque depends on the intake pipe internal pressure, but the intake pipe internal pressure when the fuel supply is restarted is due to the pressure accumulation effect of the intake system. Since it shows a first-order lag response,
This is because it does not simply correspond to the differential value of the engine speed or the cycle difference of the crank angle pulse.

Therefore, the present invention provides a fuel cut device for an internal combustion engine which can resume fuel supply at an appropriately low engine speed in accordance with various decelerations in consideration of the pressure accumulation effect of the intake system. With the goal.

[0007]

SUMMARY OF THE INVENTION A fuel cut device for an internal combustion engine according to the present invention cuts the fuel supply during deceleration of the internal combustion engine and restarts the fuel supply when the fuel return rotational speed is reduced. In the cutting device, setting means for setting a basic fuel return rotation speed, detection means for detecting an instantaneous value of the rotation speed of the internal combustion engine, smoothing means for obtaining a smoothed value of the rotation speed from the instantaneous value, and a smooth value It is characterized by comprising means for obtaining the deviation of the instantaneous value with respect to the above, and means for correcting the basic fuel return rotational speed according to the deviation to obtain the fuel return rotational speed.

[0008]

When the fuel is cut off, the throttle valve of the engine is closed and a critical flow flows, but the relationship between the decrease in engine speed and the increase in intake pipe pressure is related to the relationship between the intake pipe volume and the cylinder volume ( It depends on the pressure accumulation effect) as follows. (1) In the case of an engine with a small intake pipe volume: There is almost no pressure accumulation effect in the intake system, and when the throttle valve closes and the rotation speed decreases, the intake pipe internal pressure rapidly increases in inverse proportion to it. Therefore, a large amount of engine torque is generated when the fuel supply is restarted, so that the rotation speed does not drop and converges to the idle rotation speed. (2) For engines with large intake pipe volume: MPI (Mu
In an engine with a surge tank such as a ti-Point Injection) system where the intake pipe volume is several times the cylinder volume, the pressure accumulation effect of the intake system is large, so the throttle valve closes and the engine speed increases. Even if it decreases, the increase in the intake pipe pressure is slow. Therefore, the engine torque at the time of restarting the fuel supply cannot generate a magnitude enough to maintain the idle rotation speed, a rotation drop occurs, and a fluctuation phenomenon (hunting) occurs in the rotation speed thereafter.

Therefore, when the fuel is cut during deceleration, when the torque shortage due to the pressure accumulation effect becomes more prominent, the rotation speed drop and stall can be suppressed by increasing the fuel return rotation speed. The range expands.

By the way, as described above, the rise in the pressure in the intake pipe is delayed due to the pressure accumulation effect, which is a first-order delay phenomenon. Therefore, the deviation between the instantaneous value of the engine speed during deceleration and its smoothed value corresponds to insufficient rise in the intake pipe pressure, that is, insufficient torque.

Therefore, according to the configuration of the present invention, the basic fuel return speed is set in advance, and the fuel return speed is corrected by the deviation between the instantaneous value of the engine speed and the smoothed value thereof to obtain the fuel return speed. Even if any load torque is applied with the increase of load devices, or even if it decelerates from high rotation,
Even after decelerating from a low speed, the fuel return speed changes continuously according to various deceleration rates, and the optimum speed for each, namely,
The fuel supply can be restarted at the minimum engine speed that does not cause a rotation drop.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 shows a schematic structure of a control system of an MPI type multi-cylinder gasoline engine to which a fuel cut device for an internal combustion engine according to the present invention is applied. First, a schematic description of the entire control system will be given. An electromagnetic fuel injection valve 3 is disposed adjacent to each intake port in each intake pipe (manifold) 2A connected to each cylinder of the engine 1. These intake pipes 2A
Is connected to one end of an intake pipe 2B via a surge tank 4, and an air cleaner 5 is attached to the other end of the intake pipe 2B to open to the atmosphere. A throttle valve 6 is provided in the middle of the intake pipe 2B, and a constant pressure of fuel is supplied to each fuel injection valve 3 from a fuel pump through a fuel passage 7.
Reference numeral 8 is a fuel pressure regulator. Each fuel injection valve 3 is electrically connected to the output side of an electronic control unit (ECU) 9, and is opened and closed by a drive signal from this electronic control unit 9 to inject a required amount of fuel into each cylinder. Supply, cut off fuel supply, restart fuel supply. An ignition plug 10 is provided in each cylinder, and each ignition plug 10 is connected to an electronic control unit 9 via a distributor 11 and an ignition coil 12. The electronic control unit 9 controls the ignition timing and its drive circuit. By shutting off the primary coil current (not shown), the air-fuel mixture in the combustion chamber of each cylinder is ignited.

The electronic control unit 9 is composed of a central processing unit (not shown), a storage unit, an input / output unit, etc., and in the storage unit, in addition to execution of cut and restart of fuel supply, fuel supply amount, ignition timing, idle rotation control. A control program for performing computations such as execution of, and various program variables are stored.

At the input side of the electronic control unit 9, an idle switch 1 for detecting the fully closed position of the throttle valve 6 is provided.
3. A crank angle sensor 14 that outputs a pulse signal (hereinafter, referred to as a TDC signal) every time when a predetermined crank angle position at or slightly before top dead center is detected, and a water temperature sensor for detecting an engine cooling water temperature WT. 15, a switch group 16 for detecting the operation of a load device such as a power steering device, an air conditioner device, and a headlamp, a throttle sensor 17 for detecting the valve opening of the throttle valve 6, and an opening of the intake pipe 2B to the atmosphere. An air flow sensor 18 that outputs a signal proportional to the intake air amount provided at the end, an intake air temperature sensor 19 that detects the intake air temperature Ta, and an atmospheric pressure Pa
An atmospheric pressure sensor 20 for detecting the above, a cylinder discrimination sensor 21 for detecting that a specific cylinder, for example, the first cylinder is at a predetermined crank angle position, etc. are connected for detecting the operating state.

A bypass passage 22 for bypassing the throttle valve 6 is provided in the intake pipe 2B,
A bypass valve (ISC valve) 23 is arranged in the bypass passage 22 for idle rotation control. The bypass valve 23 is driven by an actuator such as a step motor to change the valve opening, and the valve opening is controlled by a drive signal from the electronic control unit 9 and is supplied to the engine 1 through the bypass passage 22. Adjust the auxiliary air flow rate. In FIG. 1, reference numeral 24 denotes an exhaust manifold, and an exhaust manifold 2 is provided on the exhaust side of each cylinder of the engine 1.
4 is connected, and an exhaust pipe (not shown) is connected to the atmospheric side end thereof.

The electronic control unit 9 includes various sensors 13 to 13 described above.
Based on the detection signal of No. 21, in addition to the operating state of fuel cut and restart during deceleration, idle operating state, high load operating state,
Low load operating condition, O ₂ feedback control operating condition, etc.
The engine operating state is detected, the fuel injection amount corresponding to the detected operating state, that is, the valve opening time T _inj of the fuel injection valve 3 is calculated, and a drive signal corresponding to the calculated value T _inj is given to each fuel injection valve 3. Valve is opened to supply and cut the required amount of fuel to each cylinder. The electronic control unit 9 also controls the ignition timing according to the operating state of the engine.

Next, referring to FIG. 2, one example of the fuel cut device
An example will be described. In FIG. 2, 30 is for a fuel injection valve
Driver, 31 is a fuel cut / restart judgment device, 32 is a fuel
Material cut speed N_cutSetting device, 33 is the engine speed
Of the instantaneous value N of the fuel cell, 34 is the basic fuel return speed N_base
Is a smoothing value N of the engine speed._fCalculate
Smoothing calculator 36, and a deviation DN between the instantaneous value and the smoothed value.
(= N_f-N) deviation calculator, 37 is basic fuel
Return speed N_baseCompensator for, 38 is the basic ignition timing
θ_baseSetter 39, ignition timing correction amount calculator 40
Is the basic ignition timing θ _baseIs a compensator for each of these
The functional units 30 to 40 are central processing units of the electronic control unit 9,
Mainly by software such as storage devices and input / output devices
Has been realized.

The fuel cut device illustrated in FIG. 2 basically comprises a fuel injection valve driver 30 and a fuel cut / restart deciding device 31, and the driver 30 outputs a decision result signal 41 from the deciding device 31. During 1 ", a drive signal corresponding to the calculated valve opening time T _inj is given to each fuel injection valve _3-1 to 3-n to open the valve, but while the determination result signal 41 is" 0 ", the valve is opened. The drive signal is stopped and each of the fuel injection valves _3-1 to 3-n is closed regardless of the calculated value T _inj of the valve time. The conditioner 31 determines that the idle switch 13 has detected that the vehicle is in the decelerating state (switch-on), and after the engine speed N falls below the fuel cut speed N _cut , the engine speed N returns to the fuel return speed. The judgment result signal 41 until the number N _inj falls
Is set to "0", and the engine speed N is the fuel return speed N.
_{When it goes} down _inj , the judgment result signal 41 is returned to "1".

The fuel cut speed N _cut is preset in the setter 32, but in the present embodiment, it is not a fixed value, but is changed according to the engine cooling water temperature WT detected by the water temperature sensor 15. is there. Therefore, the setting device 32
In FIG. 3, the relationship between the cooling water temperature WT and the fuel cut speed N _cut as illustrated in FIG. 3 is stored as a map, and N _cut is output according to WT.

The engine speed N is an instantaneous value, and in the present embodiment, the detector 34 outputs a TDC signal for each specific angle by the crank angle sensor 14 at the crank angle.
Since the reciprocal of the pulse generation interval of the signal is proportional to the engine speed N, as shown in steps S1 and S2 of FIG. 4 (a), the ignition interrupt cycle, that is, the SGT cycle, is used by using the ignition interrupt of one stroke. The instantaneous value N of the engine speed is detected by dividing the constant by.

For the fuel return speed N _inj , the basic fuel return speed N _base set in the setter 34 is set to the functional units 35 to 3 respectively.
7 is calculated by correcting according to the deviation DN = N _f −N between the smoothed value N _f of the engine speed and the instantaneous value N. However, in the present embodiment, the basic fuel return speed N _base
Is not set to one fixed value, but is changed according to the engine cooling water temperature WT detected by the water temperature sensor 15. Therefore, the setting device 34 stores the relationship between the cooling water temperature WT and the fuel return rotational speed N _base as illustrated in FIG. 3 as a map and outputs the N _base according to WT.
The basic fuel return rotational speed N _base is set to a low rotational speed as low as possible so that the fuel supply can be restarted without a drop in the rotational speed in an ideal case where the pressure accumulation effect of the intake system is close to zero.

The smoothing calculator 35 is a filter of the following equation (1).
Instantaneous value N to smoothed value N _fIs calculated (Fig. 4
(See step S3 of (a)). N_f(N) = K_f・ N_f(N-1) + (1-K_f) · N ... Formula (1) where K_f: Smoothing coefficient N_f(N-1): Smoothed value N calculated last time_f(N): smoothed value calculated this time, but smoothing coefficient K_fSufficiently considers the pressure accumulation effect of the intake system
Therefore, the time constant, that is, the first-order lag of the intake pipe pressure
It is selected by the following equation (2) so as to be a constant. K_f= V_s/ (V_s+ V_c) Equation (2) where V_s: Intake system volume V_cDisplacement per cylinder

The deviation calculator 36 calculates the deviation DN by the following equation (3).
(Step S4 in FIG. 4A). DN = N _f −N Equation (3) FIG. 4A shows a flow of processing required for deviation calculation. This is an interrupt calculation using an ignition interrupt in one stroke, and is performed for each interrupt. The deviation DN is calculated.

The compensator 37 is based on the processing flow of FIG.
As shown in the main routine processing, fuel cut
The engine cooling water temperature WT from the setter 34 at the start of
Basic fuel return speed N corresponding to_baseCapture (step
S5), and determine whether the deviation DN at that time is positive or not.
(Step S6) If positive, the addition of the following equation (4) is performed.
Correction calculation to determine the fuel return speed N_inj
Is given (step S7). N_inj= N_base+ DN Equation (4) If the deviation DN is zero or negative, addition of DN is performed.
No, basic fuel return speed N _baseN as it is_injTo
(Step S8).

As can be seen from the above description, during deceleration operation of the engine, the fuel return rotational speed N _inj is optimum for compensating for the torque shortage due to the pressure accumulation effect in accordance with the primary delay and deceleration of the intake pipe pressure, that is, the engine. It continuously changes to the minimum number of rotations that does not cause a stall or a drop in rotation. An example of the effect of this will be described with reference to the experimental results shown in FIG. In this experiment, the basic fuel return rotation speed is 800 rpm,
The idle speed is set to 600 rpm, and the engine speed and fuel amount (T _inj ) when the speed is fully closed and decelerated from 2000 rpm when the transmission is in neutral with no load and power steering ON (load) are set. The solid line shows an example of the present invention, and the broken line shows a conventional example, that is, an example in which when the differential value is equal to or more than a predetermined value, the fuel return rotational speed is increased by a certain amount higher than the basic value. In the conventional example, the difference in behavior due to the difference in idle load is large, and a high rotation speed is necessary to avoid a drop in rotation,
When there is no load as shown in FIG. 5A, the fuel supply is restarted earlier than the optimum timing, which causes a slight disadvantage in terms of fuel consumption. On the other hand, in the present invention, it is possible to cope with the difference in the deceleration rate due to the slight difference in the load, and a stable behavior can be obtained.

In this embodiment, as shown in FIG. 2, the basic ignition timing θ _base setter 38, the correction amount calculator 39, and the corrector 40 are used to advance the ignition timing by the torque shortage due to the pressure accumulation effect. This is corrected to compensate for the torque shortage and stabilize the idle rotation. This ignition timing correction will be described with reference to FIGS. The setter 38 stores a map of a basic ignition timing θ _base that is set according to the engine speed N and the air amount A / N taken into the cylinder in one intake stroke. Output θ _base according to N. The correction amount calculator 39 calculates the smoothed value N _f of the engine speed described above.
To the deviation DN between the instantaneous value N and the idle stabilization gain KID
Is multiplied by to obtain the ignition timing correction amount (= KID · DN).
As shown in FIG. 6, the compensator 40 takes in the basic ignition timing θ _base from the setter 38 according to the engine speed N and the intake air amount A / N by the main routine processing (step S10), and determines whether or not it is in the idle state. Is determined (step S1
1) In the idle state, advance angle correction is performed by addition of the following equation (5), and ignition is performed at the corrected ignition timing θ _adv (step S12). _{θ adv = θ base + KID ·} DN ... If it is not the formula (5) idle state, without the addition of the correction amount KID · DN, and as it is the ignition timing θ _adv the basic ignition timing θ _{ba se.}

As described above, in addition to the correction of the continuous change of the fuel return rotational speed, the ignition timing is advanced by an amount proportional to the deviation DN, whereby the rotation drop can be further suppressed and stabilized. Further, since the deviation DN is shared by the parameters for the ignition timing advance angle correction and the fuel return rotation speed correction, the software load and the matching man-hours are reduced.
Great effect can be obtained.

[0029]

According to the present invention, the basic fuel return rotational speed is corrected in accordance with the deviation between the smoothed value and the instantaneous value of the engine rotational speed, so that the engine stall or the rotational speed drop does not occur and the intake system The fuel supply can be restarted at a low rotational speed sufficient to compensate for the torque shortage due to the pressure accumulation effect.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a control system of an internal combustion engine to which the device of the present invention is applied.

FIG. 2 is a block diagram showing an embodiment of the present invention.

FIG. 3 is a diagram showing an example of a relationship between a cooling water temperature and a basic fuel return rotation speed, a fuel cut rotation speed.

FIG. 4 is a diagram showing a flow of deviation calculation and fuel return speed correction.

FIG. 5 is a diagram showing an example of experimental results.

FIG. 6 is a diagram showing a flow of ignition timing correction.

[Explanation of symbols]

 1 Engine 2A Intake pipe (manifold) 2B Intake pipe 3,3-1 to 3-n Fuel injection valve 4 Surge tank 13 Idle switch 14 Crank angle sensor 15 Water temperature sensor 30 Fuel injection valve driver 31 Judgment device 32 Fuel cut speed Setter 33 detector for instantaneous value of engine speed 34 setter for basic fuel return speed 35 smoothing calculator 36 deviation calculator 37 corrector 38 basic ignition timing setter 39 correction amount calculator 40 corrector

Claims (1)

[Claims] 1. A fuel cut device for an internal combustion engine, which cuts off fuel supply when the internal combustion engine is decelerating and restarts fuel supply when the fuel return rotational speed falls to a setting for setting a basic fuel return rotational speed. Means, detecting means for detecting an instantaneous value of the rotational speed of the internal combustion engine, smoothing means for obtaining a smoothed value of the rotational speed from the instantaneous value, means for obtaining a deviation of the instantaneous value with respect to the smoothed value, and depending on the deviation, A fuel cut device for an internal combustion engine, comprising: a correction unit that corrects the basic fuel return speed to obtain the fuel return speed.