Fuel Injection Timing Control in Electronically Controlled Engine

1. Field of the Invention

This invention relates to an apparatus for controlling fuel injection starting timing in an electronically controlled engine.

2. Description of the Prior Art

In Japanese patent application No. 52270/80 (Japanese Patent Laid-open No. 148636/81) this applicant described an electronically controlled engine in which mixture in a combustion chamber is stratified to form vortex control in the combustion chamber while distributing rich fuel mixture to the upper portion of the combustion chamber, i.e., near the ignition plug, in firing for stabilizing combustion and improving efficiency of fuel consumption and purification of exhaust gas while keeping the mixture lean as a whole. This prior application disclosed that fuel injection stopping timing is figured out as a function of rotational speed N of an engine, and fuel injection starting timing .theta. is defined according to the calculated fuel injection finishing timing .tau..sub.end and the ratio of intake air flow Q to N, i.e., Q/N. However, in such a system for establishing N, the fuel injection starting timing so established did not satisfactorily provide stratification of the mixture.

The present invention provides an apparatus for controlling a fuel injection starting timing in an electronically controlled engine to achieve satisfactory stratification of the fuel mixture.

According to the present inventions an apparatus for controlling fuel injection starting timing in an electronically controlled engine in which intake air is introduced into a combustion chamber to establish vortex control in the combustion chamber is utilized. Fuel is injected to an intake path from a fuel injector operated by electric signals, a basic injection timing (InjO) is set and an intermediate time (.DELTA.Inj), previously set as a function f(N, .tau.i) of rotational speed N of the engine and fuel injection pulse time .tau.i in the fuel injector is calculated to define a fuel injection starting subtracting from InjO intermediate time .DELTA.Inj. As a result, rich mixture is introduced into the combustion chamber to be accurately distributed near a cylinder head, close to its associated spark plug.

The intermediate time .DELTA.Inj used for calculating the fuel injection starting timing .theta. may be a sum of a first function value .DELTA.Inj 1, set as a function of the rotational speed N of the engine, and a second function value .DELTA.Inj 2, set as a function of the fuel injection pulse time.

Also, the intermediate time .DELTA.Inj may be calculated on the basis of a two dimensional map showing the rotational speed N of the engine and fuel injection pulse time .tau.i in coordinates.

The basic fuel injection timing InjO is set according to types of engines and vehicles so that fuel injected from the fuel injector is introduced into the combustion chamber during the later half of the intake stroke.

Preferably, the formed engine vortex in the combustion chamber is constructed to form a helical intake port and introduce such intake air into the combustion chamber.

FIG. 1 is a schematic view of an electronically controlled engine according to the present invention.

FIG. 2 is a block diagram of the electronic control apparatus.

FIG. 3 is an explanatory drawing for describing the basic concept of the present invention.

FIG. 4 is a graph showing the relationship between rotational speed of engine and its function value.

FIG. 5 is a graph showing the relationship between fuel injection pulse time and its function value.

FIG. 6 is a drawing showing data on a two-dimensional map having the rotational speed of engine and fuel injection pulse time as coordinates.

FIG. 7 is a drawing showing fuel injection starting timing in each combustion chamber.

FIG. 8 is a flow chart of a program of a first embodiment according to the present invention.

FIG. 9 is a flow chart of a program of a second embodiment according to the present invention.

In an intake path 1 are provided, order upstream from an air cleaner 2, an air flow meter 3 for detecting intake air flow Q and a throttle valve 4 for controlling the sectional area of flow in the intake path 1 connected to an accelerator pedal. An engine body 5 has four combustion chambers 6a.about.6d having ignition plugs 8, respectively and is connected to intake pipes 7a.about.7d at the intake system side, and to an exhaust manifold 11 at the exhaust system side. A catalyst converter 9 is provided in an exhaust pipe 10. Intake ports 13a.about.13d to form vortex in the combustion chambers 6a.about.6d are provided in the form of helical ports (or deviated type ports) for deviating and introducing intake air to the combustion chamber. Such helical port or deviated type port are well known. An electronic control apparatus 16 receives input signals from the air flow meter 3 and a crank angle sensor 17 to send output signals to drive circuits 18a.about.18d. The crank angle sensor 17 sends a first type of signal generating pulses at every 30.degree. change of crank angle and a second type of signal generating pulses at every 720.degree. change of the crank angle. The second type of signal is utilized for detecting the reference crank angle of a reference cylinder. Fuel injectors 19a.about.19d are provided near their respective intake ports 13a.about.13d to be driven individually by the drive circuits 18a.about.18d.

FIG. 2 is a block diagram of the electronic control apparatus 16. CPU 23, ROM 24, RAMs 25 and 26, A/D (analog/digital converter) 27 and I/O (input/output interface) 28 are connected to each other through a bus 29. RAM 26 is supplied with power from a back-up power source (not shown) even while an engine switch is turned off. The analog output of the air flow meter 3 is sent to A/D 27 and the digital output of the crank angle sensor 17 is sent to I/O 28. The drive circuits 18a.about.18d receive pulse signals from I/O 28.

FIG. 3 describes the basic concept of the present invention, in which A shows a period when an intake valve in the combustion chamber is opened and B the intake stroke respectively. The basic injection timing InjO may be set for a crank angle near the lower dead point of the intake stroke. The fuel injection starting timing .theta. may be set by subtracting intermediate time .DELTA.Inj (=.DELTA.Inj 1+.DELTA.Inj 2) from Inj0. .DELTA.Inj 1 is defined as shown in FIG. 4. In FIG. 4, the abscissa represents the rotational speed N of engine and the ordinate .DELTA.Inj 1. Further, N is detected through the input pulse from the crank angle sensor 17. .DELTA.Inj 1 is a constant when N.ltoreq.N1, an increasing function of N when N1.ltoreq.N.ltoreq.N2 and a constant or decreasing function of N when N.ltoreq.N2. .DELTA.Inj 2 is defined as shown in FIG. 5. In FIG. 5, the abscissa represents the fuel injection pulse time .tau.i and the ordinate .DELTA.Inj 2. .DELTA.Inj 2 is a primary increasing function of .tau.i. .tau.i is a function of intake air flow Q. Intermediate time .DELTA.Inj can be directly calculated from a map showing the rotational speed N of engine and fuel injection time .tau.i represented by the coordinates. Such a map is shown in FIG. 6 in which the units of N, .tau.i and intermediate time .DELTA.Inj are respectively r.p.m., msec and crank angle. If corresponding data are not defined on the map, the intermediate time .DELTA.Inj is calculated by interpolation. Fuel injection from the respective fuel injector 19a.about.19d is carried out once every two revolutions of the engine. The fuel injection pulse time .tau.i is approximately a proportional function of Q/N, and since fuel injection from the respective fuel injectors 19a.about.19d is carried out N/2 times per unit time, fuel injection amount per the unit time is approximately proportional to Q. Again with respect to FIG. 3, the fuel injectors 19a.about.19d receive fuel injection pulses since the fuel injection starting timing .theta. only for the fuel injection pulse time .tau.i is represented by the following formula:

where .tau..nu. represents ineffective injection time which is constant irrespective of running conditions of an engine and .tau.e effective injection time. Hence, the fuel injectors 19a.about.19d are opened at crank angle C when time .tau..nu. elapses after .theta. so that the point of fuel injection continues for .tau.e after the crank angle C. Since there exists a predetermined distance between the fuel injection position and combustion chamber, fuel enters the combustion chambers 6a.about.6d at crank angle D spaced by crank angle t1 from crank angle C, i.e., during the later half of the intake stroke. All fuel enters the combustion chambers 6a.about.6d immediately before the intake valve is closed. The basic injection timing Inj0 is set according to the types of engines and vehicles so that fuel enters the combustion chambers 6a.about.6d during the later half of the intake stroke under all running conditions of the engine. As a result, leaner mixture is distributed to the lower portion of the combustion chambers 6a.about.6d, i.e., near the piston, and richer mixture is distributed to the upper position of the combustion chambers 6a.about.6d, i.e., near the cylinder head, to flow together with vortex into the combustion chambers 6a.about.6d. The vortex prevents the mixture from dispersing in the axial direction of the combustion chambers 6a.about.6d and the stratified condition of the mixture is maintained until the piston reaches near the upper dead point of the compression stroke. Consequently, since rich mixture is distributed near the discharging gap of an ignition plug, stable combustion is obtained even with lean mixture as a whole. Such combustion improves the efficiency of fuel consumption while reducing noxious components in exhaust gas. Further, .DELTA.Inj 2 may be a function of .tau.e, and .tau.e may be used for the map shown in FIG. 6 in place of .tau.i. .tau.e is a function of .tau.i as is understood from the above-mentioned formula.

FIG. 7 is a time chart showing the fuel injection starting timing of the respective combustion chambers 6a.about.6d. The abscissa represents crank angle, and ignition order is 6a, 6c, 6d and 6b. As shown in the drawing, the range of the fuel injection starting timing .theta. covers before and after the upper dead point of the intake stroke, i.e., from the later half of the exhaust stroke to the first half of the intake stroke.

FIG. 8 is a flow chart showing a program of a first embodiment according to the present invention, i.e., an interrupting routine implemented when a predetermined crank angle is reached. On step 35 are read the rotational speed N of engine and intake air flow Q. On step 36 is figured out Q/N. On step 37 is figured out the basic injection pulse time .tau.p from .tau.p=K Q/N, where K is a constant. On step 38 is figured out effective injection pulse time .tau.e by correcting .tau.p with temperatures of engine colling water, intake air, etc. On step 39 is substituted .tau.e+.tau..nu. for .tau.i. On step 40 is read the basic injection period Inj0. On step 41 is figured out .DELTA.Inj 1 from N. On step 42 is figured out .DELTA.Inj 2 from .tau.i. On step 43 is figured out the fuel injection starting timing .theta. from .theta.=Inj0-(.DELTA.Inj 1+.DELTA.Inj 2). On step 44 is stored .theta. in RAM 25. On step 45 is read crank angle CA at the present time. On step 46 is judged whether or not CA=.theta.. When CA=.theta., fuel injection pulse is generated on step 47 and when CA.noteq..theta., the program returns to the first step. Thus, fuel injection is started from .theta..

FIG. 9 is a flow chart showing a program of a second embodiment according to the present invention. Steps implementing the same processes as those in FIG. 8 are shown with the letter b attached to the steps of FIG. 8, the description of these steps is not repeated. Steps 41, 42 in FIG. 8 are omitted and, instead, step 50 is implemented. On step 50 is figured out .DELTA.Inj directly from .tau.i and N according to the map in FIG. 6.

Thus, according to the present invention, a proper fuel injection timing is provided so that fuel positively enters the combustion chamber to distribute rich mixture near the cylinder head (i.e., ignition plug) in the combustion chamber for stabilizing the combustion.