DE3124493A1 - Fuel metering system for an internal combustion engine - Google Patents

Abstract

A fuel metering system for an internal combustion engine is proposed, which has a throttle air flow sensor without bypass duct and in which the characteristic curve of the air flow sensor indicates a rate of air flow increased by a constant value. The correction thereby necessitated is achieved in that a pulse varying only as a function of the engine speed is subtracted from the output signal of a timer element which processes engine speed and air flow signal. In this way a reliably functioning fuel metering system is achieved, even at very low engine speeds in the idling range with the very low rates of air flow then prevailing in the air intake pipe. <IMAGE>

Description

ε. 7106

21 Λ. 1981 Mü / Le

ERT BOSCH GMBH, 7OOO STUTTGART 1

State of the art fuel metering system for an internal combustion engine

The invention is based on clay a fuel injection system according to the genre of the main claim. It has long been the state of the art for intermittent injection systems to make the individual injection pulses dependent on the speed and air flow in the intake manifold. Included the air throughput is determined by the deflection of one in the air intake pipe Attached storage flap detected. This known baffle flap air flow meter has a bypass line through which an air volume that can be set to a constant value is passed. This will reduce the spread of the air flow meter itself, as well as those of some engine parameters, which means a correction of the measurement result is equivalent to.

In common internal combustion engine types, the known ones work Fuel metering systems satisfactory. Problems However, they are shown when, for reasons of fuel economy, the engines are extremely low-revving when idling should run because then the air flow in the intake pipe is very small and, depending on the accuracy of fit of the damper in the air flow meter, the flap then no longer deflects learns. A deflection of 0, however, signals the control

if the fuel metering system has a load = 0, theoretically follow the fuel supply interrupted would have to be.

Advantages of the invention

With the fuel metering system according to the invention with the Features of the main claim can be dispensed with the conventionally existing bypass, so that the air flow meter the total amount of air supplied to the internal combustion engine is detected. This can also the calculation of the amount of fuel to be supplied can be carried out correctly down to the lowest speed ranges, so that there is a risk of the alster dying Internal combustion engine is Terringert.

drawing

An embodiment of the invention is shown in the drawing and is described and explained in more detail below. FIG. 1 shows a rough block diagram of the fuel metering system according to the invention and FIG associated pulse diagram.

Description of the embodiment I.

The exemplary embodiment shows the most important components of the control unit of an intermittently working injection system. In Figure 1 is 10 with a speed sensor and with 11 denotes an air flow sensor. 12 marks a timer, in which, depending on the speed and load, pulses with a duration of tp1 are generated. The timer 12 is available for this purpose via a frequency divider stage 13 with the speed sensor 10 in connection as well as with the air volume sensor 11. A Correction stage 1U has an adjustment input 15 as well a trigger input 16 which is coupled to the frequency divider stage 13. The output signals of both the

- r- H

Timing element 12 as well as the correction stage 1U -be an AND gate IT supplied, the output of which with a subsequent multiplier 18 is in connection. The output signal ti of this multiplier 18 arrives then finally via an output stage 19 to at least one valve 20.

Significantly in the subject of Figure 1 is now, that the timer 12 provides a -verlängerten injection pulse, and this pulse-correcting extended depending on the output signal of the correction stage 1 h -is reduced again. This becomes clear from the pulse diagrams according to FIG. 2. There, FIG. 2 a shows the output signal of the timing element 12, FIG. 2 b the output signal of the correction stage 1U and finally FIG. 2 c the signal at the output of the AND gate 17 ·

In contrast to existing injection systems, with blocks 10 to 13 and 17 to 20, the correction stage 1U is added here parallel to the timing element 12. In the implementation, the correction stage lh presents no difficulties for the person skilled in the art. It can consist of a monostable multivibrator with an inverting output for outputting the signal according to FIG.

The mathematical basis on which the above-described Setup works is as follows.

As a rule, the following applies to the duration of the injection pulses

tp = c1 'Q / n (1)

where el is a constant, η the speed and Q the amount of air per unit of time.

The following applies to the output signal of the air volume sensor

Us. ^ 1 / Q / on

UB ^K '

NACHQER Bo; .γ] γ ι

According to the invention, a certain deflection of the flap of the air volume sensor is assigned an air volume increased by a constant value. This corresponds to the formulaic expression (Us) _ 1

(UB) Corr 1 c2. (3)

(.Us / UBf

c2 corresponds to a constant air volume here.

The output signal of the timer 12 thus has a Pulse duration accordingly

tp ₁ = d * - 1 / n ' 1 (h)

(Us / UB) Corr · ■ on.

It is now essential that the effect of the assumed increased air throughput is reversed and this is done via the printout

tp ₂ = c3 '1 / n (5)

j due to the assumed constant additional Air content only depends on the speed of the internal combustion engine. Overall, this results in The total signal formed from the two individual signals is the mathematical expression

tp ₃ = tp ₁ - tp ₂ = ej_. 1 _ cj_ (6)

η i_Us_) η (UB) Corr

It is also worth mentioning that, according to formula (3), the "^ signal to be processed

^ UjD ) Κ.ΟΓΓ

changes to a lesser extent than without the correction term. this brings advantages for signal processing in terms of accuracy and input smooth cycle range.

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Claims (3)

ρ 7 \ Π &
27.H.1981 Mü / Le ROBERT BOSCH GMBH, TOOO STUTTGART 1 At. s ρ call he 1J fuel metering system for an internal combustion engine with a timing element for generating injection signals depending on the speed and the air throughput in the intake manifold, characterized in that the timing element (12) emits pulses with an increased duration, a correction stage (lh) generates correction pulses and in a subsequent logical one Gate (1T) the difference between the two signals is formed. 2. Fuel metering system according to claim 1, characterized in that that an air flow sensor (11) a corrected characteristic (Us) = 1 (UB) Corr 1 ₊ c2 TÜsTÜB) and the total injection time after c1. 1 c3 tp
is formed. 3 "η (Us) η (UB) Corr