JPH031497B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a fuel injection method for an internal combustion engine, and in particular, when the intake throttle valve is at the idle position, that is, fully closed, and the engine rotational speed is low enough to stop fuel injection. The present invention relates to a fuel injection method in which fuel injection is stopped when the rotational speed is higher than the engine rotational speed, and fuel injection is resumed when the intake throttle valve is in the idle position and the engine rotational speed is lower than or equal to the fuel injection return rotational speed.

[Prior art]

Conventionally, engine load (intake pipe pressure or engine 1
The basic fuel injection amount is determined by the intake air amount per revolution) and the engine rotational speed, and the basic fuel injection amount is corrected using various correction coefficients such as intake air temperature and engine cooling water temperature to determine the fuel injection amount. A synchronous fuel injection method is known in which a fuel injection valve is opened at every corner and an amount of fuel corresponding to the fuel injection amount is injected during the engine intake stroke. In this fuel injection method, from the viewpoint of improving fuel efficiency, synchronous fuel injection is stopped during deceleration, that is, when the intake throttle valve is in the idle position (fully closed) and the engine speed is equal to or higher than the fuel injection stop speed (for example, 2500 rpm). A so-called fuel cut is being carried out. Additionally, if the intake throttle valve is in the idle position and the engine speed falls below the fuel injection return speed (for example, 1600 rpm) during fuel cut, fuel injection will be restarted and synchronous fuel injection will be restored to prevent engine stall. I try to do that.

However, when the fuel is cut off, the fuel adhering to the inner wall of the intake manifold evaporates, so when the fuel injection returns, the injected fuel adheres to the inner wall of the intake manifold, reducing the amount of fuel supplied to the combustion chamber, and reducing the air-fuel ratio. When the engine becomes lean, resulting in a drop in output, and if the engine speed drops quickly, there is a problem in that engine speed undershoot or engine stall occurs. In order to solve this problem, it is conceivable to increase the amount of synchronous fuel injection once when the fuel injection returns from the fuel cut, but since synchronous fuel injection is executed during the intake stroke of each cylinder, the system will not be able to fully absorb the increased amount of fuel. If the engine speed drops rapidly without being sucked into the cylinders, the same problem as above will occur. These problems are particularly noticeable in so-called single-point injector type internal combustion engines, in which one fuel injection valve is provided upstream of an intake throttle valve and the air-fuel mixture is introduced into a combustion chamber through a relatively long intake passage.

[Purpose of the invention]

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a fuel injection method for an internal combustion engine that does not cause engine rotation undershoot or engine stall when returning fuel injection from a fuel cut. shall be.

[Structure of the invention]

In order to achieve the above object, the present invention stops fuel injection when the intake throttle valve is at the idle position during fuel injection and the engine speed is equal to or higher than the fuel injection stop speed, and the intake throttle valve is at the idle position. In a fuel injection method for an internal combustion engine of a vehicle equipped with an internal combustion engine that resumes fuel injection when the engine rotational speed becomes equal to or lower than the fuel injection return rotational speed which is lower than the fuel injection stop rotational speed, While changing the fuel injection return rotation speed, the engine rotation speed at the time when fuel injection was restored is stored, and the actual engine rotation speed is set to the stored engine rotation speed at the time of fuel restoration and the engine rotation speed at the time of fuel restoration. When the engine speed is lower than the engine speed by a predetermined value, and the actual engine speed drop within the predetermined time is greater than or equal to the predetermined value, the fuel injection amount at the time of fuel injection recovery is increased by the predetermined amount. I tried to let him do it.

〔Effect of the invention〕

Therefore, according to the present invention, the fuel injection is restored (restarted) when the engine speed decreases while the intake throttle valve remains in the idle position after the fuel injection is stopped,
After that, even if the fuel injection return rotation speed, which is the standard for determining whether or not to restore fuel, depends on the state of the vehicle (for example, whether the brake system is in operation or not, whether the vehicle speed is above a predetermined value, etc.) Even if the engine speed is changed, it will be possible to accurately judge the period during which an increase in fuel is required to prevent a large drop in engine speed, and this will enable stable control when the fuel is restored. A unique effect can be obtained.

[Embodiments of the invention]

Next, an internal combustion engine (engine) to which the present invention is applied
An example will be explained with reference to FIG. This engine is a single point injector type engine.

The air cleaner 2 is connected to the throttle body 6 via an inlet pipe 4. One fuel injection valve 8 is provided on the upstream side of the throttle body 6.
An intake throttle valve 10 is arranged downstream of the fuel injection valve 8 to adjust the amount of air-fuel mixture taken into the combustion chamber of the engine in conjunction with an accelerator pedal. The intake throttle valve 10 includes an intake throttle valve 10.
A throttle switch 12 is installed which is turned on when the intake throttle valve 10 is at the idle position and turned off when the intake throttle valve 10 is opened from the idle position. Furthermore, a pressure sensor 14 is attached downstream of the intake throttle valve 10 to detect the pressure in the intake pipe.

The throttle body 6 is connected to an intake manifold 16 having branch pipes connected to each cylinder of the engine, and the intake manifold 16 is equipped with an intake temperature sensor 18 that measures the intake air temperature from the temperature of the air-fuel mixture passing through the intake manifold. installed. The upstream bottom portion 16a of the intake manifold 16 is provided with a riser portion 20 through which engine cooling water is circulated to heat the air-fuel mixture.

22 is a well-known engine body, and the piston 2
The combustion chamber 2 is formed by the bottom surface of the cylinder 26 and the inner wall of the cylinder 26.
8 is formed, and the air-fuel mixture sucked in through the intake valve 30 is ignited by the spark plug 32.
A water jacket 3 is placed around the cylinder 26.
4 is formed, and the engine cooling water temperature is circulated through this water jacket 34 to cool the cylinder 26 and the like. An engine coolant temperature sensor 38 is attached to the cylinder block 26 to detect the temperature of the engine coolant in the water jacket 34.

An exhaust manifold 42 is connected to an exhaust port (not shown) of the cylinder head 40.
The residual oxygen concentration in the exhaust gas is detected downstream of the exhaust manifold 42. An O ₂ sensor 44 is attached. Furthermore, the exhaust manifold 42 is connected to an exhaust pipe 48 via a catalytic converter 46 filled with a three-way catalyst.

The spark plug 32 is connected to a control circuit 54 via a distributor 50 and an igniter 52. Attached to the distributor 50 are an engine rotation angle sensor 56 and a cylinder discrimination sensor 58, which each include a signal rotor fixed to the distributor shaft and a pickup fixed to the distributor housing. In the case of a 6-cylinder engine, this cylinder discrimination sensor 58 detects one sensor at a reference position (for example, top dead center of a specific cylinder) every time the distributor shaft makes one revolution, that is, every two revolutions of the engine (720°C). The engine rotation angle sensor 56 outputs one pulse every 30°C, for example. Note that 51 is a brake switch that is turned on during braking, and 53 is a vehicle speed sensor.

As shown in FIG. 2, the control circuit 54 includes a central processing unit (CPU) 60 that includes an arithmetic logic unit and registers, a read-on memory (ROM) 62 that stores control programs, etc., and a random access memory (RAM) 64. , Butu plum (BU)
-RAM) 66, input/output port (I/O) 68,
It is configured to include an analog-digital converter (ADC) 70 and a bus 72 such as a data bus or a control bus that connects these. I/O
68 includes a cylinder discrimination signal from the cylinder discrimination sensor 58, an engine rotation speed signal from the engine rotation angle sensor 56, a brake signal from the brake switch 51, a vehicle speed signal from the vehicle speed sensor 53, and an idle signal from the throttle switch 12. is input, and a fuel injection signal for controlling the fuel injection valve 8 and an ignition signal for controlling the igniter 52 are outputted via a drive circuit (not shown). The ADC 70 also receives an intake pipe pressure signal from the pressure sensor 14, an intake temperature signal from the intake temperature sensor 18, a water temperature signal from the water temperature sensor 38, and an O ₂
The air-fuel ratio signal from the sensor 44 is input, and the CPU
These signals are sequentially converted into digital signals in accordance with the 60 instructions. The above-mentioned ROM 62 stores in advance a control program shown in the following processing routine, a fuel injection stop rotation speed, a fuel injection return rotation speed, and the like. This fuel injection return rotation speed is set to a high rotation speed (e.g. 2600 rpm) when the coolant temperature is low (e.g. -25°C) because there is a high possibility of engine stalling when the engine coolant temperature is low.
The rotation speed is set to decrease as the cooling water temperature increases (for example, 1200 rpm at 80°C). Further, the fuel injection stop rotation speed is set to a rotation speed higher by a predetermined value (for example, 600 rpm) than the fuel injection return rotation speed determined as described above. Furthermore, since the negative acceleration applied to the vehicle is large while the brake system is in operation, the impact felt by the occupant when the fuel injection is restored is small. Therefore, in order to lengthen the fuel injection stop period without giving the occupants an unpleasant shock feeling, the fuel injection return rotation speed during braking is set to, for example, 1000 rpm, the normal fuel injection return rotation speed is set to, for example, 1600 rpm, and these fuel injection The return rotation speed may be changed. That is, the return rotation speed during braking may be lower than the normal return rotation speed.

Next, prior to applying the present invention to the above-mentioned engine, a prerequisite technology will be explained. FIGS. 3 and 4 show processing routines of the underlying technology according to the present invention. The underlying technology uses a rotation speed that changes depending on the engine coolant temperature as the fuel injection return rotation speed.

FIG. 3 shows an interrupt routine that is executed every predetermined time (for example, 32 msec).
Subtract the last captured engine speed NEi− ₁ from the engine speed change amount ΔNEi within a predetermined time.
is determined, and in step 103, the average value of the previously determined change amount ΔNEi- ₁ and the currently determined change amount ΔNEi is set as the change amount ΔNE. In the next step 104,
By determining whether the amount of change ΔNE is less than or equal to a predetermined negative value (for example, -22 rpm), it is determined whether the amount of decrease in engine speed within a predetermined time is greater than or equal to a predetermined value. When the amount of change .DELTA.NE exceeds a predetermined negative value, it is determined that the amount of decrease in engine speed is small, and the process proceeds to step 110 after setting the value of the A register of the arithmetic logic unit to 0 in step 109.

On the other hand, if the amount of change ΔNE is less than a predetermined negative value, it is determined that the amount of decrease in engine speed is large, and in step 105 it is determined whether the idle switch is on or not, that is, whether the intake throttle valve is at the idle position. At the same time, in step 106, it is determined whether the current engine rotation speed NEi is equal to or less than the fuel injection return rotation speed NR determined from the ROM data according to the engine cooling water temperature. Then, when the idle switch is on and the engine speed NEi is less than or equal to the fuel injection return speed NR, that is, when the fuel injection return condition is satisfied, the value of the A register is set to 1 in step 107, and the fuel injection return condition is satisfied. If not, the value of the A register is set to 0 in step 109.

In the next step 108, the engine speed NEi is changed from the fuel injection return speed NR by a predetermined amount (for example,
250 rpm), and if it is not within this range, change the value of the A register to 0 in step 109, and if it is within the above range, change the value of the A register to 0. The program proceeds to step 110 without changing the value of , and sets or resets the fuel injection return permission flag F using the value of the A register.

FIG. 4 shows the fuel injection time calculation routine. First, in step 111, it is determined whether or not the fuel injection return permission flag F has been set. If the flag F has been reset, in step 112, the amount of fuel is increased for the increased amount of fuel. The time B is set to 0, and if the flag F is set, the fuel increase time B for increasing the amount of fuel is set to a predetermined value (for example, 3 msec) in step 113, and the process proceeds to step 114. Step 114
Now, calculate the basic fuel injection time for the basic fuel injection amount from the intake pipe pressure and engine speed, correct the basic fuel injection time using various correction coefficients to find the fuel injection time TAU, and calculate the fuel injection time TAU. Increase amount time B is added to TAU, and in the next routine, the fuel injection valve is opened for a time corresponding to this added time to perform increased amount synchronous fuel injection.

As a result of the above, when the fuel injection return condition is satisfied when the amount of decrease in engine speed is equal to or greater than a predetermined value, increased fuel injection is executed a predetermined number of times until the engine speed drops by a predetermined value from the fuel injection return rotation speed.

Next, the processing routine of the embodiment according to the present invention will be explained using FIGS. 5 and 6. In this embodiment, the fuel injection return rotation speed is switched depending on whether the brake system is in operation or not, and whether the vehicle speed is above a predetermined value, etc., and the engine rotation speed when transitioning from fuel cut to fuel injection recovery is maintained. This maintained engine rotational speed is defined as the fuel injection return rotational speed NC. In addition, when switching the return rotation speed based on the vehicle speed, the return rotation speed when the vehicle speed is low is set lower than usual. FIG. 5 shows the main routine of this embodiment. In step 100, it is determined whether or not fuel is being cut. Only during fuel cut, in step 101, the engine rotation speed NE obtained from the engine rotation speed signal is set in a predetermined area of the RAM. is stored as the fuel injection return rotation speed NC. In step 101, the engine speed during fuel cut is always stored, so even if the fuel injection return speed changes due to the operating state of the brake system after fuel injection is restored, the engine speed during fuel cut is always stored. The engine speed is always held as the fuel injection return speed NC.

FIG. 6 is a flowchart according to this embodiment. This flowchart shows a routine similar to the routine shown in FIG. For this reason, the same parts are given the same reference numerals and the explanation thereof will be omitted, and only the different parts will be explained. In step 116, step 101
Using the fuel injection return rotation speed NC held in , it is determined whether the engine rotation speed NEi falls within a range from the fuel injection return rotation speed NC to a predetermined value (for example, 250 rpm). Then, based on the determination in step 116, the fuel injection return permission flag F is set or reset in the same manner as in the example shown in FIG. 3 above, and the routine proceeds to the routine shown in FIG. 4 to calculate the fuel injection time.

Here, if the same control as in the example in Fig. 3 is performed by adopting the fuel injection return rotation speed that is switched depending on whether the braking device is in operation or not, the fuel injection is returned during braking, and the braking is started immediately after that. When the fuel injection return rotation speed NR changes from, for example, 1000 rpm to 1600 rpm, increase synchronous fuel injection is performed until the fuel injection return rotation speed NR drops from 1600 rpm to 250 rpm. A problem arises in that the amount of fuel is not increased. However, in this embodiment, since the engine speed at the time of transition from fuel cut to fuel injection return is maintained and set as the fuel injection return speed NC, even if the fuel injection return speed NR is changed thereafter, the engine speed is changed from the engine speed NC. An effect can be obtained in that the amount of fuel is increased within the range that actually requires an increase until the amount decreases by a predetermined value.

[Application Example of the Invention] In the above, an example in which the present invention is applied to a single-point injector type engine has been described, but the present invention is not limited to this. It is also possible to apply the present invention to an independent injection type engine that injects fuel during the intake stroke of each cylinder.
In this independent injection type engine, especially if the time during the fuel cut is long, the fuel adhering to the inner wall of the intake manifold evaporates during the fuel cut like in a single point injector type engine, resulting in the same problem as described above. Furthermore, although the above description has been made regarding an engine in which the basic fuel injection amount is determined based on the intake pipe pressure and the engine speed, the present invention is applicable to an engine in which the basic fuel injection amount is determined based on the intake air amount per engine rotation and the engine speed. can also be applied.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing an example of an engine to which the present invention is applied, Fig. 2 is a block diagram showing an example of the control circuit of Fig. 1, and Fig. 3 shows an interrupt routine at predetermined time intervals in the underlying technology. Flowchart, FIG. 4 is a flowchart showing the fuel injection time calculation routine of the above-mentioned base technology, FIG. 5 is a flowchart showing the main routine in the embodiment of the present invention, and FIG. 6 is the third diagram of the embodiment of the present invention. 2 is a flowchart showing a routine similar to . 8...Fuel injection valve, 10...Intake throttle valve, 12
... Throttle switch, 54 ... Control circuit, 5
6...Engine rotation angle sensor.

Claims (1)

[Claims] 1 During fuel injection, when the intake throttle valve is at the idle position and the engine speed is equal to or higher than the fuel injection stop speed, fuel injection is stopped, and when the intake throttle valve is at the idle position and the engine speed is at the fuel injection stop speed, the fuel injection is stopped. In a fuel injection method for an internal combustion engine of a vehicle equipped with an internal combustion engine that resumes fuel injection when the fuel injection return rotation speed becomes lower than a fuel injection return rotation speed lower than a fuel injection return rotation speed, the fuel injection return rotation speed is varied according to the driving state of the vehicle, and The engine speed at the time when the fuel injection is restored is stored, and the actual engine speed is a predetermined value lower than the stored engine speed when the fuel is restored and the engine speed when the fuel is restored. fuel for an internal combustion engine, characterized in that the amount of fuel injected at the time of return to fuel injection is increased by a predetermined amount if the actual engine speed decreases within a predetermined time is equal to or greater than a predetermined value. Injection method.