EP0184626B1

EP0184626B1 - Control method for a fuel injection engine

Info

Publication number: EP0184626B1
Application number: EP85112425A
Authority: EP
Inventors: Teruji Sekozawa; Makoto Shioya; Motohisa Funabashi; Mikihiko Onari; Masami Shida
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1984-11-26
Filing date: 1985-10-01
Publication date: 1990-01-10
Anticipated expiration: 2005-10-01
Also published as: KR860004235A; KR930012226B1; DE3575331D1; JPS61126337A; EP0184626A2; EP0184626A3; JP2550014B2

Description

Background of the invention

The present invention relates to a control method and apparatus for fuel injection engines of the type used in vehicles such as automobiles and more particularly to a fuel injection control method so designed that the film mass deposited on the wall of the intake manifold is estimated and the desired fuel injection quantity is determined on the basis of the estimated film mass.
The fuel injected from the fuel injection valve is partly deposited on the intake manifold wall or the fuel deposited as the film mass is vaporized and fed into each cylinder thus failing to wholly supply the injected fuel into the cylinder and in particular the quantity of fuel supplied to the engine deviates considerably from the fuel quantity required from moment during the engine acceleration or deceleration.
EP-A-0 069 219 discloses a method and apparatus for controlling the fuel injection into an engine, wherein the desired combustion chamber fuel (DFC) is calculated on the basis of a basic fuel amount (BF), a temperature etc. correction coefficient (TCC) and an excess air correction coefficient (EXC) derived from an O2 sensor.
An interrupt routine is initiated in synchronism with the crankshaft rotation at each fuel injection time to calculate an actual fuel command (AFC) for determining the time the injection valve is opened, by the following steps: The actual amount of fuel (SQF) squirted in through the fuel injection valve for the respective injection pulse is obtained by subtracting from the desired fuel amount (DFC) a fuel sucking-off amount (SOA), i.e. the amount of fuel entrained from fuel adhering to the inner manifold surfaces, and dividing the result by a figure (1-AWC) representing the proportion of the injected fuel that does not get adhered to the manifold wall. Further, the amount of fuel (WF) adhering to the manifold surface is renewed by adding to the previously calculated amount a figure (AWA) representing the amount that gets adhered to the wall, and subtracting therefrom the above figure (SOA) representing the sucking-off amount. The actual valve opening duration (AFC) is finally calculated on the basis of the above figure (SQF), increased by a dead time (DT) of the valve.
It is an object of the present invention to provide a method and apparatus for controlling the fuel injection into an engine more accurately.
The invention meets this object by the method and apparatus characterised in claims 1,3, respectively.
The invention distinguishes from the prior art in that the amount of fuel to be injected is subjected to the correction derived from an 0₂ sensor and that this corrected value is utilized in updating the film mass quantity adhering to the manifold wall and in determining the fuel injection pulse width. The film mass correction control miss is thus also fed back. In contrast, the prior art just introduces the correction value (EXC) in determining the desired amount of fuel (DFC) to be supplied to the engine.
Furthermore, while the prior art performs the various calculations to determine the valve opening time for the fuel injection (AFC) by a subroutine initiated only for each fuel injection time, the method and apparatus of the present invention perform the various calculations on a time basis and use the most recent value to control the engine, thereby again achieving higher accuracy and providing a uniform load on the computer.
Formulas relating to the dynamics of fuel injection in the intake system of as internal combustion engine, taking into account wall wetting without 0₂-sensor feedback, have been published in SAE-paper 810495.

Brief description of the drawings

Figure 1A is a schematic diagram showing the construction of a fuel injection control apparatus to which the present invention is applied.
Figure 1 B is a flow chart showing the fuel injection control procedure of the computer 1.
Figure 2 is a diagram showing the behavior of the inducted air and fuel in the intake manifold.
Figure 3 is a block diagram of the fuel injection control system.
Figure 4 is a flow chart of the ordinary computing processing and interrupt processing.
Figures 5A to 5C are time charts illustrating the time relationship between the strokes and the cycle periods.

Description of the preferred embodiments

An embodiment of a control method for a fuel injection engine according to the invention will now be described with reference to Figures 1A to 2. Figure 1A illustrates a schematic diagram of a fuel injection control apparatus. In the Figure, the mass of air flow Q_a in the intake manifold of an engine is detected by a hot-wire air flow meter 2 and applied to a computer 1. The computer 1 receives the throttle position 8th from a throttle position sensor 3, the intake manifold pressure P from a manifold pressure sensor 4, the cooling water temperature T_w from a water temperature sensor 5, the engine speed N from a crank angle sensor 6 and a binary signal indicative of a lean or rich mixture from an O2 sensor 7. The computer 1 directs the desired fuel injection quantity G_f to an injector 8.
As shown in Figure 1 B, at a step 1, the computer 1 calculates the rate of deposition of the fuel injection quantity on the intake manifold wall and the rate of vaporization of the film mass deposited on the intake manifold wall from the following equations (1) and (2), respectively, according to the inputted data. If the deposition rate is represented by X and the vaporization rate by 1/_T, the deposition rate X is simply given for example as a function of the throttle position 8th as follows
On the other hand, the vaporization rate 1/_T is given as a function of the water temperature T_was follows
Here, it is assumed so that 1/τ=0.026 when T_w≧23°C.
Then, at a step 102, in accordance with the resulting deposition rate X and vaporization rate 1/_T, the current film mass quantity is calculated from the film mass quantity obtained during the preceding cycle and the actually injected fuel quantity as follows
where AT is the computing cycle period, M, is the film mass quantity, G, is the fuel injection quantity and G_f· y is the actually injected fuel quantity in terms of the fuel quantity per unit time.
Then, at a step 103, the fuel injection quantity per unit time is determined in accordance with the deposition rate and the film mass quantity in the following manner. The fuel injection quantity of the engine must correspond to the intake air flow and therefore the desired value of the fuel quantity to be supplied to each cylinder is given as follows.
where Q_a is the intake air flow, (A/F) is the desired air-fuel ratio and G_fe* is the desired value of the quantity of fuel injected into the engine cylinder. Figure 2 shows the behavior within the intake manifold of the fuel quantity entering the engine cylinder. As shown in the Figure, if G_f represents the injected fuel quantity, X· G_f represents the quantity of the fuel deposited on an intake manifold wall 21 and (1-X)G_f represents the quantity of the fuel supplied to the cylinder without deposition. Also, M/T represents the quantity of fuel supplied to the cylinder by the vaporization of the previously deposited fuel quantity (film mass quantity) on the intake manifold wall 21. As a result, if the quantity of fuel supplied to the cylinders is represented by G_fe, then the following equation holds
If the value of G_fe is equal to the fuel quantity G_fe* to be supplied to the cylinder, the desired air-fuel ratio will be attained. Thus, assuming that the equations (4) and (5) are equal,
Then, it is only necessary to determine the fuel injection quantity G, such that the above equation holds. Thus, the following equation holds
The equation (7) is obtained as follows. The fuel quantity Q_a/(A/F) to be supplied to the cylinder-to attain the desired air-fuel ratio is obtained in accordance with the intake air flow Q_a and the fuel quantity 1/_TM_f to be carried over to the cylinder is obtained in accordance with the vaporization rate 1/_T and the film mass quantity M_f. The fuel quantity 1/_TM_f is subtracted from the fuel quantity QJ(A/F) and the difference is divided by the non-deposition rate (1-X) of the injection fuel to be supplied to the cylinder without deposition thereby determining the desired fuel quantity per unit time.
Since the value of G, obtained at the step 103 is the fuel injection quantity per unit time, it is then converted to a fuel injection pulse width per stroke of the engine at a step 104, as follows
where N is the engine speed, k_l is a coefficient determined by the characteristics of the injector, y is the feedback correction factor derived from the 0₂ sensor signal and T_s is a dead fuel injection time.
The fuel injection pulse width per stroke T, is renewed at intervals of the computing cycle and therefore the actual fuel injection takes place for the duration of the fuel injection pulse width T_l existing at the time of arrival of an interrupt signal generated for every stroke. Therefore, as the fuel injection quantity data required for the computer to calculate the quantity of film mass during the next cycle, the actual fuel injection pulse width in terms of the following quantity corresponding to the fuel quantity per unit time is fed back
The expression (9) is used during the next computing cycle as shown by the equation (3).
Figure 3 illustrates a block diagram of the fuel injection control system in the computer 1 of Figure 1A. In the Figure, a fuel injection quantity per unit time G_f is calculated by computing means 12 in accordance with the film mass estimated by computing means 13 for estimating the film mass quantity M_f deposited on the intake manifold wall and the mass of air flow. In response to the signal generated from the 0₂ sensor 7, computing means 14 calculates an air-fuel ratio feedback correction factor y=f(O₂) aiming at a stoichiometric air fuel ratio. Computing means 11 calculates the quantity of fuel injected per stroke as shown by equation:
where k_i is a coefficient which is used in the conversion to the fuel injection quantity per stroke and dependent on the injector characteristics and T_s is a dead injection time.
The computing means 13 computes the quantity of film mass in the intake manifold in accordance with equation (3):
Here, the right member M_fn represents the film mass quantity for the preceding cycle and the left member M_fn+1 is the newly estimated film mass quantity. Also, 1/_T represents the rate of vaporization of the film mass and X represents the rate of fuel deposition on the intake manifold wall to the injected fuel quantity (referred to as a deposition rate). Represented by AT is one cycle period of the computation by the blocks of Figure 3. Thus, the following in the right member represents the quantity of fuel delivered to the cylinder by the vaporization of the film mass during one cycle period
Also, of the quantity of fuel actually injected per unit time the quantity of fuel deposition during the cycle period is given by the second term of the right member in the equation (11) or the following expression
While a description will be made later of y · G_f in consideration of the time relationship between the time per stroke and the cycle period of computation, the fuel injection quantity per unit time y · G_f resulting from the integration of the feedback correction factor y represents the quantity of fuel injected per unit time which is renewed in response to the application of a stroke start signal from the crank angle sensor. While the deposition rate X and the vaporization rate 1/_T (_T is a vaporization time constant) are obtained by experiments in accordance with the throttle position θth, the water temperature T_w, the manifold pressure P, the mass air flow Q_a, etc., in this embodiment the deposition rate X is given as a function of the throttle position for purposes of simplicity, as in equation (1):
Also, the vaporization rate is given as a function of the water temperature as in equation (2)
Here, it is assumed that 1/_T=0.0566 when Tw≦23°C.
As described hereinabove, a feature of the construction of the control system resides, as will also be seen from Figure 3, in the fact that the feedback loop for feeding back the correction factor y in response to the 0₂ sensor signal and the loop of the fuel injection quantity y . G, for calculating the deposited quantity or the deposited part of the injected fuel overlap doubly.
Next, the timing of the injection per stroke and the timing of the computing cycle will be described. The computational operations shown in Figure 3 are performed at intervals of a given period T and the injection pulse width is renewed by injection timing adjusting means 16 of Figure 3 at a step 31 of Figure 4 for every period. The actual injection is initiated by an interrupt signal INT generated for every stroke. As a result, the fuel is actually injected for the duration of the most lately calculated injection pulse width T, as shown in Figures 5A to 5C. Figures 5A to 5C respectively show interrupt signals each generated for every stroke, injection pulse widths and calculated y . G, with the lapse of time. In accordance with the embodiment, when an interrupt signal is applied, the timely existing y . G, is stored in a y . G, memory. This operation is performed by injection synchronizing means 15 of Figure 3 and its timing corresponds to the application of the interrupt signal as shown at a step 32 of Figure 4. By performing these operations, the actually injected fuel quantity is fed back and used for the accurate estimation of the quantity of film mass.
In accordance with the present invention, the occurrence of lean spikes during the engine acceleration and the occurrence of rich spikes during the engine deceleration are eliminated as compared with the conventional method in which a basic fuel injection quantity is determined in accordance with the flow of intake air. This has the effect of improving the engine performance during the acceleration and ensuring effective removal of the harmful gases during the deceleration. Thus, it is possible to reduce the amount of the three-way catalyst by this method making it also effective economically. Further, while it has been necessary in the past to prepare various memory maps for providing acceleration and deceleration corrections on the basis of changes in the throttle position, etc., and search for the corresponding map values, in accordance with the present invention the desired acceleration and deceleration corrections can be provided by matching only the deposition rate of the fuel injection and the vaporization rate of the film mass in accordance with the acceleration and deceleration air-fuel ratios and thus the invention has the effect of providing more efficient manufacturing steps.
Further, in accordance with the invention, by virtue of the fact that the quantity of the film mass deposited on the intake manifold wall is estimated by newly estimating the film mass quantity by using the actually injected fuel quantity, it is possible to estimate an accurate film mass quantity closer to the actual film mass quantity. By using the method which determines the desired fuel injection quantity in consideration of such estimated film mass, the air-fuel ratio of the mixture supplied to the engine can be controlled at around the stoichiometric air-fuel ratio even during the engine acceleration and deceleration. Thus, the invention has the effect of improving the exhaust gas purification and the engine performance.

Claims

1. A method for controlling the fuel injection into an engine, wherein the following steps are performed in each one of successive computing cycles:

(a) determining a current fuel injection quantity G_t" per engine stroke according to the formula

wherein

G_fen=desired fuel quantity to be supplied to the engine (10),

1/τ · M_fn=fuel quantity vaporizing from a film mass quantity M_fn deposited on the intake manifold wall (21),

X=portion of the injected fuel quantity G_fn which deposits on said wall (21),

(b) calculating a fuel injection quantity feedback correction factory aiming at a stoichiometric air-fuel ratio A/F based on a signal generated by an O₂ sensor (7),

(c) determining a fuel injection pulse width T, according to the formula

wherein

k_i=coefficient dependent on the characteristics of the injector (8),

Y·= G _fn actual fuel injection quantity G_fn corrected by said factor y,

N=engine speed,

T_s=fuel injection dead time,

(d) determining the film mass quantity M_fn+1, for the subsequent computing cycle according to the formula

wherein

AT=computing cycle period.

2. The method of claim 1, wherein the fuel quantity actually injected into said engine (10) is that current fuel injection quantity G_fn which has been determined in the last computing cycle preceding the injection time point.

3. An apparatus for controlling the fuel injection into an engine, comprising

(a) means (12) for determining a current fuel injection quantity G_fn per engine stroke according to the formula

wherein

G_fen=desired fuel quantity to be supplied to the engine (10),

X=portion of the injected fuel quantity G_fn which deposits on said wall (21),

(b) means (14) for calculating a fuel injection quantity feedback correction factor y aiming at a stoichiometric airfuel ratio A/F based on a signal generated by an O2 sensor (7),

(c) means (11) for determining a fuel injection pulse width T, according to the formula

wherein

k_i=coefficient dependent on the characteristics of the injector (8),

Y·G _fn=actual fuel injection quantity G_fn corrected by said factor y,

N=engine speed,

T_s=fuel injection dead time,

(d) means (13) for determining the film mass quantity M_fn+1 for the subsequent computing cycle according to the formula

wherein

ΔT=computing cycle period,

wherein said means (a) to (d) are adapted to perform their functions sequentially and repeatedly in each one of successive computing cycles.

4. The apparatus of claim 3, including means (16) for converting said current fuel injection quantity G_fn into a width value of a fuel injection pulse applied to said injector (8).