JP2006112302A - Fuel injection control device for engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To determine engine speed of recovery from fuel cut at an early stage. <P>SOLUTION: This device is provided with a fuel supply stop means 7 stopping fuel supply to an engine at a time of deceleration, a fuel recovery means 7 restarting fuel supply according to an operation condition after fuel supply stop, and a fuel recovery speed calculation means 7 calculating an estimation value of engine speed drop speed based on friction torque acting on the engine 1 and determining engine speed for restart of fuel supply according to the estimated value. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to engine fuel control, and more particularly, to a method for determining a return timing from a fuel cut during deceleration.

  Depending on the operating condition of the engine, for example, when the engine output is not required, such as coasting when the accelerator pedal is fully closed (coast), a fuel cut to stop fuel supply is performed for the purpose of improving fuel efficiency. Fuel control devices that perform are known. This fuel control device releases the fuel cut and restarts the fuel supply (fuel recovery) when the accelerator pedal is depressed from the inertia traveling to the acceleration traveling, but the idle rotation is continued even if the inertia traveling is continued. When a predetermined engine rotation speed set so as to be maintained is reached, fuel is returned to prevent the engine from stopping.

  In the fuel control device having the above-described function, there is known a fuel control device that changes the engine rotation speed at which fuel is restored in accordance with the gear position at the start of fuel cut.

  However, in the control of the fuel return rotation speed based on the gear position as described above, the fuel return is performed at the same engine rotation speed in any of the steady-road traveling, the uphill traveling, and the downhill traveling. For this reason, for example, if the fuel return rotational speed is set with reference to a constant ground travel, the travel resistance is large during uphill travel, and the possibility of engine stall is increased due to the large decrease in engine rotation speed. However, since the speed of decrease in engine rotation is small, the fuel is returned despite the fact that the fuel cut can be continued, and the fuel cut effect cannot be sufficiently obtained.

Therefore, in Patent Document 1, in addition to the gear position, the descent speed of the engine rotation and the road surface inclination are detected, and the uphill, the fixed ground, and the downhill are determined from the relationship between the gear position and the engine rotation speed, and accordingly A fuel control device that corrects the engine speed at which fuel is restored is disclosed.
JP-A-6-173740

  By the way, recently, by adopting CVT or the like, the so-called coast state engine rotational speed (coast rotational speed), which has been turned off, has become low. When deceleration is started by stepping on the brake from the coast state, The descent time may be as short as about 50 ms, for example.

  When the engine speed falls to the idle speed in such a short time, the control of actually detecting the engine speed and reducing the fuel return speed based on the detected value as in Patent Document 1, During the correction calculation, there is a possibility that the engine speed falls below the speed at which the fuel should be restored and the engine stalls. Therefore, in order to prevent such an engine stall, there is a method of setting the coast rotational speed and the rotational speed at which the fuel is restored to a higher value, but this does not provide the effect of improving the fuel efficiency.

  Therefore, an object of the present invention is to determine the fuel return timing in a short time and to perform fuel cut in a wide operation region.

  A fuel injection control device for an engine according to the present invention includes a fuel supply stop unit that stops fuel supply to the engine at the time of deceleration, a fuel return unit that restarts fuel supply according to an operating state after the fuel supply is stopped, and an engine And a fuel return rotational speed calculation means for calculating a predicted value of the engine rotational speed based on the friction torque and determining an engine rotational speed at which fuel supply is resumed according to the predicted value.

  According to the present invention, since the engine rotation speed is predicted from the friction torque applied to the engine, a predicted value of the engine rotation speed can be obtained before the engine speed actually decreases. Then, since the engine rotation speed at which the fuel is returned is determined based on the predicted value of the engine rotation drop speed, it is possible to determine the fuel return timing early after the start of deceleration. As a result, it is not necessary to provide a margin as a countermeasure against engine stall at the engine speed at which the fuel is restored, and fuel cut can be performed in a wide operation region.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic diagram of a system to which this embodiment is applied. DESCRIPTION OF SYMBOLS 1 is an engine, 3 is an intake passage which supplies intake air to the engine 1, 12 is an intake valve which opens and closes the opening part of the intake passage 3 opened to the engine 1, 14 is an exhaust passage for discharging exhaust gas, 13 is an engine 1 is an exhaust valve that opens and closes an opening of an exhaust passage 14 that opens to 1.

  In the engine 1 described above, intake air is introduced into the engine 1 by lowering the piston 2 while the intake valve 12 is open, and the intake valve 12 is closed when the piston 2 is near bottom dead center. As the air pressure rises, the intake air is compressed. When the piston 2 reaches the vicinity of the top dead center, spark ignition is performed by a spark plug 6 which will be described later, the intake air explodes, and the piston 2 is pushed down. When the piston 2 rises again, the exhaust valve 13 is opened, and the burned gas in the cylinder is discharged to the exhaust passage 14.

  A throttle valve 4 for adjusting the amount of intake air supplied to the engine 1 is interposed in the intake passage 3, and a fuel injection valve for injecting fuel into the intake passage 3 is provided downstream thereof. An ignition plug 6 sparks and ignites an air / fuel mixture supplied to the engine 1. The fuel injection valve 5 may be attached so as to face the cylinder of the engine 1 and fuel may be directly injected into the cylinder.

  The opening degree of the throttle valve 4, the injection amount of the fuel injection valve 5, and the ignition timing of the spark plug 6 are controlled by an engine control unit (hereinafter referred to as “ECM”) 7 according to the operating state and the like.

  The ECM 7 includes an automatic transmission controller (hereinafter referred to as ATCU) (not shown) in addition to detection signals from a rotation speed sensor 9 that detects the rotation speed of the engine 1 and an accelerator opening sensor 10 that detects the amount of accelerator depression by the driver. From the automatic transmission information such as gear ratio and torque converter speed ratio, and further information such as brake hydraulic pressure and road surface μ judgment is input from the ABS unit 8, and based on these signals and information, as fuel supply stop means and fuel return means Control of resumption of fuel injection after fuel cut and fuel cut (fuel return), which will be described later, and calculation of the engine speed at which fuel is returned are performed as fuel return speed calculation means.

  Here, the ABS unit 8 will be described with reference to FIG.

  As shown in FIG. 2, a wheel speed sensor 21 for detecting the rotational speed of the wheel and a brake hydraulic pressure sensor 22 for detecting the cylinder hydraulic pressure of the brake are provided in the vicinity of the wheel 20, respectively.

  Further, a G sensor 23 for detecting the acceleration of the vehicle is provided in the vicinity of the center of gravity of the vehicle body.

  The ABS unit 8 estimates the road surface μ, driving wheel load, and the like based on the detection signals of the wheel speed sensor 21, the brake hydraulic pressure sensor 22, and the G sensor 23, and sets the brake cylinder hydraulic pressure so that the wheel 20 does not lock during deceleration. Control.

  Next, control during deceleration executed in the present embodiment will be described.

  In the present embodiment, as in the prior art, so-called fuel cut is performed in which fuel injection is stopped when the accelerator is turned off during running (coast). Then, when the engine rotation speed is reduced to near the idle rotation speed, the fuel is returned and the idle rotation speed is maintained.

  By the way, if the fuel return timing is too late, the engine speed drops to such an extent that the engine rotation speed cannot be maintained until the engine 1 actually generates torque after the fuel return. On the other hand, if it is too early, the time for fuel cut is shortened and the effect of improving fuel efficiency cannot be obtained sufficiently.

  Conventionally, the engine rotational speed was measured during coasting, and the engine rotational speed for fuel recovery was determined based on the engine rotational speed. However, if the engine speed during coasting is low and the time to decrease to the minimum engine speed required to maintain idle speed after stepping on the brake and starting deceleration is short, the appropriate fuel recovery timing When the fuel return timing is determined, the actual engine speed may be lower than the engine speed at which the fuel is returned. Therefore, in this embodiment, the engine speed at which fuel is returned is determined in the ECM 7 according to the flowchart shown in FIG.

  Hereinafter, a description will be given according to the steps of FIG.

  In step S1, it is determined whether or not the vehicle is coasting and fuel is being cut.

  If the determination is no, the process ends. If the determination is yes, the process proceeds to step S2.

  In step S2, the detected value of the brake hydraulic pressure is read.

  In step S3, the brake braking force is calculated by the following equation (1).

B = PW × α (1)
B: Brake braking force PW: Brake hydraulic pressure α: Coefficient In step S4, the detection value of the G sensor 23 is read.

  In step S5, the vehicle body speed V1 is calculated from the deceleration G read in step S4.

  In step S6, the detection value (V2) of the wheel speed sensor 20 is read.

  In step S7, the road surface μ is calculated from the vehicle body speed V1 and the wheel speed V2 by the following equation (2).

μ = β / (V1-V2) (2)
β: Coefficient In step S8, the driving wheel load Fw is calculated by the following equation (3).

Fw = μ × WB (3)
W: Vehicle weight In step S9, the gear ratio and final reduction ratio of the automatic transmission read into the ATCU are read.

  In step S10, the friction torque transmitted from the automatic transmission to the crankshaft of the engine 1, that is, the friction torque Tf and brake braking force Thoki of the automatic transmission main body and oil pump other than the brake braking force are obtained and used. The engine rotation speed is calculated by the following equation (4).

ΔN / Δt = (Ti−Tf−Thoki) × K (4)
ΔN / Δt: Engine rotation drop speed Ti: Engine generated torque K: Coefficient The friction torque Tf other than the braking force is determined by the components used, and in this embodiment is a constant value obtained in advance through experiments or the like.

  Further, the brake braking force Thoki is determined by the following formula (5) from the driving wheel load Fw.

Thoki = Fw / (gear ratio / final reduction ratio) (5)
At the time of coasting, the friction torque transmitted to the crankshaft is determined on the basis of the magnitude of Thoki, that is, the driving wheel load Fw determined as shown in Expression (3) from the brake torque B and the road surface μ. Therefore, if the road surface μ is large, the driving wheel load Fw is large, so that the friction torque transmitted to the crankshaft is large, and if the road surface μ is small, the friction torque transmitted to the crankshaft is small. However, it can be seen before the engine speed actually drops.

  That is, by using Equation (4), the engine rotation speed can be estimated before the engine speed actually decreases.

  The coefficient K is determined by the moment of inertia of a rotating body in the driving force transmission path from the engine 1 to the wheel 20, for example, a drive shaft or a brake rotor.

  In step S11, at least the idling speed can be maintained, that is, the engine generated torque (necessary generated torque at the time of fuel return) at which the engine rotational speed decrease ΔN / Δt is zero or positive is obtained from the equation (4). Determine the amount of intake air and the mixing ratio required to generate, and the optimal ignition timing. Thus, by calculating the required torque at the time of fuel return according to the current deceleration state, it is possible to prevent the engine rotation from being blown up and engine stall at the time of fuel return.

  In step S12, the current engine speed is detected based on the detection signal of the rotation speed sensor 9.

  In step S13, it is determined whether or not to return the fuel. Specifically, it is determined whether the current engine speed is a fuel return speed described later.

  Here, a method of calculating the fuel return rotational speed will be described with reference to FIG. FIG. 4 is a graph in which the vertical axis represents the engine rotation speed Ne and the horizontal axis represents time.

  The slope of the graph is the engine rotation speed ΔN / Δt calculated in step S10. The idle rotation maintenance lower limit rotational speed is determined by design and is stored in the ECM 7 in advance.

  Assuming that the current engine rotation speed is Ne0, the engine rotation speed decreases by ΔN / Δt, and decreases to the idle rotation maintenance lower limit rotation speed after elapse of t2. However, since there is a response delay time td from when it is determined that the fuel return is performed in the ECM 7 until the actual fuel injection is performed, the determination of the fuel return is made after the engine speed reaches the idle rotation maintenance lower limit speed. Doing so will stall the engine.

  In view of this, the engine rotation speed at the time point that is delayed by the response delay time td from t2 is set as the fuel return rotation speed so that fuel injection is performed when the engine rotation speed decreases to the idle rotation maintenance lower limit speed.

  That is, based on the current engine rotation speed Ne0 and the engine rotation speed decrease speed ΔN / Δt, a time t2 during which the engine speed decreases to the idle rotation maintenance lower limit rotation speed is calculated, and then t1 is calculated by going back from t2 by the response delay time td. The engine rotation speed at t1 is calculated using the engine rotation effect speed ΔN / Δt and the current engine rotation speed, and this is set as the fuel return rotation speed.

  By setting the fuel return rotational speed by the method as described above, when the engine rotational speed decrease ΔN / Δt is large, a high fuel return rotational speed is set, and engine stall is reliably prevented. Can do. Further, as the engine speed decrease ΔN / Δt decreases, the fuel return rotational speed is set to a low rotational speed that is close to the idle rotation maintenance lower limit rotational speed, so that the operating range in which fuel can be cut is expanded, and fuel efficiency is improved. Can do.

  If it is determined in step S13 that the fuel return timing is reached, the process proceeds to step S14, and fuel injection is started under the conditions determined in step S10. If it is determined that it is not the fuel return timing, the process returns to step S12, and steps S12 and S13 are repeated until the fuel return timing is reached.

  As described above, in the present embodiment, the following effects can be obtained.

  During the fuel cut, the predicted value of the engine speed reduction is calculated based on the friction torque applied to the engine, and the engine speed at which the fuel returns is determined based on this predicted value. Therefore, before the engine speed actually decreases, It is possible to determine the engine speed at which the fuel returns to a low speed, and the fuel can be returned at the optimal timing while preventing engine stall even when decelerating from a low coast rotation or at a sudden deceleration. . As a result, fuel can be cut in a wide driving range, and fuel efficiency can be improved.

  Since the brake braking force B and the road surface μ are used as parameters for calculating the friction torque applied to the engine, the engine rotation descending speed can be accurately predicted.

  Since the torque generated by the engine 1 when the fuel supply is resumed is set based on the friction torque applied to the engine 1, it is possible to reliably prevent the engine rotation from rising and the engine stalling when the fuel is restored.

  The present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made within the scope of the technical idea described in the claims.

  The present invention is applicable to a vehicle that performs fuel cut during deceleration in an accelerator-off state.

It is a figure showing the system configuration | structure of this embodiment. It is a figure for demonstrating an ABS unit. It is a flowchart for demonstrating control of this embodiment. It is a figure for demonstrating the determination method of a fuel return engine rotational speed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 2 Piston 3 Intake passage 4 Throttle valve 5 Fuel injection valve 6 Spark plug 7 Engine control unit (ECM)
8 ABS unit 9 Rotation sensor 10 Accelerator opening sensor 11 AT control unit (ATCU)
12 Intake valve 13 Exhaust valve 14 Exhaust passage 15 Combustion chamber 20 Wheel 21 Wheel speed sensor 22 Brake oil pressure sensor 23 G sensor

Claims (3)

Fuel supply stop means for stopping fuel supply to the engine during deceleration;
Fuel return means for restarting the fuel supply according to the operating state after the fuel supply is stopped;
A fuel return rotation speed calculating means for calculating a predicted value of the engine rotation speed based on the friction torque applied to the engine and determining an engine rotation speed at which fuel supply is resumed according to the predicted value. An engine fuel injection control device.   The engine fuel injection control device according to claim 1, wherein the parameter for calculating the friction torque applied to the engine includes a brake braking force and a road surface resistance value.   The engine fuel injection control device according to claim 1, wherein the fuel return means sets a torque generated by the engine when the fuel supply is restarted based on a friction torque applied to the engine.

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