WO2018015091A1

WO2018015091A1 - Method for determining a fuel mass flow and for controlling the injection

Info

Publication number: WO2018015091A1
Application number: PCT/EP2017/065158
Authority: WO
Inventors: Joerg Nafe; Tobias FALKENAU
Original assignee: Robert Bosch Gmbh
Priority date: 2016-07-21
Filing date: 2017-06-21
Publication date: 2018-01-25
Also published as: CN109715922B; CN109715922A; DE102016213383A1

Abstract

Method (100) for determining the mass flow Q of fuel (2) through an open injector (1, la-lf), comprising the determination of the pressure p (110) and of the temperature T (120) of the fuel (2) at at least one measuring location (31) in the feed line (3, 3a-3f) to the injector (la-lf) and the evaluation (150) of the mass flow Q as proportional to the pressure p and inversely proportional to the root of the temperature T, wherein the pressure p is corrected (140) to the pressure p' by the pressure drop Δρ which occurs when the injector opens in the feed line (3, 3a-3f) between the measuring location (31) and the injector (la-lf), wherein the mass flow Q, the length L, L₁-L_6, the diameter D, DR, D_1-D_6, the Darcy friction factor λ, and/or the pressure loss coefficient ζ, the feed line (3, 3a-3f) between the measuring location (31) and the injector (1a-1f) are taken into account during the determination (130) of Δρ. Method (200) for controlling the injection of fuel (2) in an engine (10) having a plurality of injectors (1a-1f) and a feed line (3, 3a-3f) leading to the injectors (la-lf) which comprises a common distributor rail (32) for the fuel (2), wherein the opening period of each injector (la-lf) is determined (210) from the setpoint injection mass M of fuel (2) and the mass flow Q of the injector (1a-1f) in the open state, wherein the mass flow Q is determined (100) individually for each of the injectors (1a-1f) in the open state according to the invention. Control unit (300) and computer program product.

Description

Description title

Method for determining a fuel mass flow and for controlling the injection

The present invention relates to methods for determining a

Fuel mass flow and for controlling the injection in injection systems for vehicles. The invention also relates to an associated control device and computer program product.

State of the art

Injection systems for internal combustion engines generally have one or more injectors for fuel metering. The efficiency of combustion, and thus the smoothness and the energy and environmental balance of the engine, depend crucially on the fact that for each working cycle of a cylinder a precisely defined amount of fuel is injected.

The injectors are typically supplied via a common rail and actuated by an electronic control unit with suitable software. In this case, the mass flow Q of fuel per

Time unit in the open state of the injector on the basis of the pressure p and the temperature T of the fuel determined. The mass M to be injected is divided by this mass flow Q. This results in the period of time for which the injector is to be opened in order to inject the desired mass M.

The pressure p and the temperature T of the fuel are typically measured at a measuring location in the busbar, since it is usually not possible, pressure and temperature sensors directly at the input and output of the Place injectors. The accuracy of the metering is thus influenced by the fact that pressure p and temperature T directly at the injector differ from the values measured in the distributor rail. From DE 10 2005 036 192 AI is a correction for systematic

Deviations of the pressure p known. US Pat. No. 4,636,620 A discloses determining the actual temperature via the temperature coefficient of the injector coil and correspondingly correcting the triggering of the injector. The US 7,047,942 B2 pursues a different approach and discloses to make the supply lines from the busbar to all injectors of the same length, at least

To minimize deviations of the fuel masses injected by the individual injectors with each other.

Disclosure of the invention

In the context of the invention, a method for determining the

Mass flow Q on, in particular gaseous, fuel developed by an open injector. According to this method, the pressure p and the temperature T of the fuel are determined at at least one measuring location in the supply line to the injector. The mass flow Q is evaluated as proportional to the pressure p and inversely proportional to the root of the temperature T.

According to the invention, the pressure p is corrected by the pressure drop .DELTA.ρ, which arises when opening the injector in the supply line between the measuring location and the injector, to the pressure p '. In this case, when determining Δρ, the mass flow Q, the length L, the diameter D, the pipe friction coefficient λ, and / or the

Pressure loss coefficient ζ, which takes into account the supply line between the measuring location and the injector. Optionally, the volume of the busbar that supplies the injector can also be taken into account.

In particular, the combination of length L and diameter D of the supply line with the pipe friction coefficient λ, and / or with a pressure loss coefficient ζ, can be taken into account. The ultimate effects of the pipe friction coefficient λ and the pressure loss coefficient ζ on the pressure drop Δρ depend on length L and Diameter D, and of any pipe bends and branches, the supply line from.

It was recognized on the one hand that especially with the use of gaseous fuels the mentioned variables are the main influencing factors of which the pressure drop

Δρ depends. Liquid fuels usually have a higher density than gaseous. Since the pressure loss in pipelines is proportional to the mass flow Q and the material properties, gaseous fuels show a higher pressure drop Δρ.

It was also recognized that the fuel pressure especially at

gaseous fuels are the dominant size for the determination of

Mass flow is. If the injector is operated at a pressure ratio before and after the injector which is above the critical pressure ratio, the pressure p and the temperature T of the fuel before the injector determine the mass flow Q of fuel through the opened injector independently of the backpressure after the injector. The pressure p is linear in the mass flow Q (power 1), the temperature T, however, only with the reciprocal of its root (power -0.5), so much weaker.

Since the multiple injectors of the engine extend spatially over a region of non-negligible magnitude, the geometries of the leads, each of which is measured from the location in the bus bar at which pressure p and temperature T are measured, will be different to the individual injectors. This causes the fuel in different ways to the individual

Injectors experiences different friction, so that at the individual injectors ultimately different pressures p abut. This in turn means that with the same drive duration of all injectors, the individual injectors

inject different fuel masses. The correction in this regard by determining the pressure drop .DELTA.p can therefore in particular the smoothness of the

Motors, which depends on a correct choreography of the combustion between the individual cylinders, be significantly improved. As a result, fuel consumption and engine emissions are also reduced. This is especially true when injected from each injector Amount of fuel is supplied to exactly one of a plurality of cylinders, for example by a multipoint intake manifold injection.

Furthermore, the production costs of the motor are also indirectly reduced. Deviations in the injection behavior among each other result in a real engine not only from the described injector-specific pressure drop Δρ, but also from production-related deviations of the injectors from one another. As a rule, an engine must fulfill a specified specification in terms of consumption and environmental properties. Can the

specified specification by the correction of injector-individual

Pressure drop Δρ can be exceeded, on the other hand the

Manufacturing tolerances of the injectors significantly expanded and at the same time the specifications are still met. An engine that fulfills the specifications, you get so in the result of low production costs, as the

Production costs for injectors with stricter manufacturing tolerances increase disproportionately.

In principle, the pressure drop Δρ could also be minimized physically, e.g. through such large diameter of the supply line and the

Distribution rail, that the pressure differences in percentage not notice in the end result. However, this would require additional space in the engine and at the same time significantly increase the production costs.

In a particularly advantageous embodiment of the invention, the pressure ps at at least one measuring location in a suction pipe, in which the fuel is passed from the injector determined. The mass flow Q is additionally proportional to the pressure ps and the fuel pressure p

Outflow function Ψ evaluated.

The pressure ps in the intake manifold is the back pressure against which the fuel is injected through the injector. Is the pressure ratio at the injector smaller than the critical pressure ratio (subcritical flow), goes beyond the

Outflow function Ψ the intake manifold pressure as a further influencing parameter on the injected mass flow Q a. In a further particularly advantageous embodiment of the invention, the pressure ps is corrected by the pressure drop Aps, which arises in the intake manifold between the measuring location and the injector, to the pressure ps'. When determining Aps, the air mass flow Qs conveyed through the suction pipe and the length Ls, the diameter Ds, the pipe friction coefficient λβ, and / or the

Pressure loss coefficient ζβ, of the intake manifold between the measuring location and the injector. Analogous to the correction of p to p ', in particular the

Combination of the length Ls and the diameter Ds with the pipe friction coefficient s, and / or with the pressure loss coefficient ζβ, are taken into account.

The pressure ps enters the mass flow Q approximately with linear power via the outflow function Ψ. A drop Aps of this pressure ps thus has the same effect on the accuracy of the injected mass flow Q as a drop Δρ of the pressure p.

In a further advantageous embodiment of the invention, the temperature T of the fuel is corrected by the temperature difference ΔΤ, which arises between the measuring location and the injector, to the temperature T '. In the determination of ΔΤ, the heat conduction at attachment points of the supply line and / or the injector, and / or the convection with the ambient air, and / or

Heat transfer by radiation e.g. of hot engine parts, considered.

The temperature difference .DELTA.Τ, which arises by convection with the ambient air, is typically proportional to the temperature difference between the supply line (or the injector) and the environment, the area relevant for the heat transfer and a heat transfer coefficient. Of the

Temperature difference .DELTA.Τ resulting from thermal conduction is typically proportional to the temperature difference bridged by the attachment site, to the heat transfer relevant area and length, to thermal contact resistance, and to a

Heat transfer coefficients. The temperature difference ΔΤ, which results from heat radiation, is proportional to the fourth power

Temperature difference between the surfaces of the pipelines and the

Distributor rails on the one hand and areas of hot engine parts on the other. Overall, the temperature difference ΔΤ can typically be up to 30 K.

The measuring location at which the temperature of the fuel in the supply line or in the distributor rail is measured does not have to be identical to the measuring location at which the pressure of the fuel is measured. The temperature is ideally measured in the middle of the busbar.

The temperature difference .DELTA.Τ could in principle be leveled by physical means, for example by thermal insulation of the busbar against the environment and thermal decoupling of attachment points to the engine. However, these measures, similar to the measures for leveling the pressure drop Δρ, are costly and require additional costs

Space.

In the determination of Δρ, and / or in the determination of ΔΤ, an approximate value Q * for the mass flow Q is additionally taken into account. The accuracy of the determination of Δρ can be further increased thereby. For example, the approximate value Q * may be determined to be proportional to the pressure p and inversely proportional to the root of the temperature T without regard to Δρ.

In a further advantageous embodiment of the invention is in the

Determination of Aps additionally uses an approximate value Qs * for the air mass flow Qs conveyed through the intake manifold. This makes the determination of Aps more accurate.

From the foregoing, the invention also relates to a method of controlling the injection of fuel in an engine. The engine comprises one or more injectors. The supply line to the injectors comprises a common rail for the fuel. In this case, the time duration for which each injector is opened is determined from the mass M to be injected in each case and the mass flow Q of the injector in the open state. According to the invention, the mass flow Q in the open state is determined individually for each of the injectors according to a method according to the invention. In this way, the improved according to the invention accuracy with which the mass flow Q of the fuel can be determined by the open injector, converted into a more accurate, injector-specific compliance of the injected mass M of fuel. This will ultimately improve the smoothness, as well as the energy and environmental balance of the engine.

The methods according to the invention are characterized in that they do not depend on the installation of additional sensors or other components in the

Injection system are instructed. Rather, an existing

Injection system by a change of that functionality in the control unit of the injection system, which determines the Bestromungsdauer of each injector, be provided with the functionality and advantages according to the invention. The invention therefore expressly also relates to a control unit for the injection of fuel into an engine. This control device comprises means for metering the mass M of fuel injected by a plurality of injectors by applying a current I to each injector with a time program I (t). According to the invention, the control device is designed to carry out a method according to the invention when determining the time program l (t).

The method according to the invention is further distinguished by the fact that the integration of the corresponding functionality in the control unit is not dependent on a hardware modification of the control unit. Rather, the functionality can be retrofitted according to the invention by a pure extension of the software of the controller. A corresponding software is therefore an own salable product dar. Thus, the

Invention also relates to a computer program product with machine-readable instructions which, when on a computer and / or on a computer

Running control unit for the injection of fuel into a motor, upgrading the computer and / or the control unit to a control device according to the invention, and / or cause the computer and / or the control unit to carry out a method according to the invention. Further measures improving the invention will be described in more detail below together with the description of the preferred embodiments of the invention with reference to figures.

embodiments

It shows:

Figure 1 Structure of an engine with central intake manifold injection (Figure la) and with multipoint intake manifold injection (Figure lb);

Figure 2 embodiment of the method 100 and the parent method 200;

Figure 3 pressure drop at a single injector la-lf during the

Injection process;

Figure 4 fuel injection system 10a with additional consideration of incoming and outgoing heat flows WK by convection, Ws by heat radiation and Wi_ by heat conduction;

Figure 5 pressure difference between different injectors la-lf at different mounting positions;

FIG. 6 Deviation of the temperature at the inputs of the injectors 1a-1f from the temperature T measured at the measuring point 31 for different operating points of the motor 10.

According to Figure la, the engine 10 comprises six cylinders 12a-12f, which are supplied via a common intake manifold 4 with a fuel-air mixture. The air supply to the intake manifold 4 is controlled by a throttle valve 42. With a sensor 41 within the intake manifold 4, the pressure ps is measured. A central rail (fuel rail) 32 forms the supply line 3 to the six injectors la-lf. Temperature T and pressure p are measured with sensors 31 within the fuel rail 32. The injectors la-lf are opened by a central control unit 300 and a control bus 301 by energization. The fuel pumped by the six injectors la-lf is in a central

Collector 11 collected and mixed in the intake manifold 4 with air. The fuel-air mixture is then supplied to the cylinders 12a-12f.

According to Figure lb, the injectors la-lf are arranged immediately in front of the cylinders 12a-12f. Thus, each of the injectors la-lf is assigned to exactly one of the cylinders 12a-12f. In contrast to FIG. 1a, differences in the masses M of fuel 2 conveyed by the individual injectors 1a-1f are no longer at least partially leveled in the central collector 11 and in the intake manifold 4. Instead, such differences strike directly on the

Mixing ratio of the fuel 2 with air, which is supplied to the individual cylinders 12a-12f. Thus, in multipoint intake manifold injection, more than in the case of central intake manifold injection, it is important that the masses M of fuel 2 conveyed by the individual injectors la-lf are consistent with one another.

The number of cylinders 12a-12f and injectors 1a-1f shown in FIGS. 1a and 1b is merely exemplary. The method already works with only one injector la-lf and only one cylinder 12a-12f. Also, the method does not rely on the number of cylinders 12a-12f being equal to the number of injectors la-lf.

FIG. 2 shows an embodiment of the method 200 for controlling the injection of the fuel 2. In the higher-level step 210, the time program l (t) of the injected mass M of fuel 2 and the mass flow Q through the respective injector la-lf

Current supply for this injector la-lf determined. The mass flow Q is determined in each case with the method 100 according to the invention.

As part of the method 100, the pressure p of the fuel 2 is first measured at step 110 at the measuring location 31. At the same time, the temperature T of Fuel 2 is also measured in step 120, wherein the measuring point 31 may be the same as for the pressure, but also another. In step 130, the pressure drop Δρ between the measuring point 31 and the injector la-lf is determined, and in parallel the temperature difference ΔΤ between the measuring point 31 and the injector la-lf is determined in step 144. In each case, an approximate value Q * is also used for the mass flow through the injector la-lf in the opened state.

The pressure p is corrected in step 140 by the pressure drop Δρ to the pressure p '. The temperature T is corrected in step 145 by the temperature difference ΔΤ to the temperature T '. In step 150, the proportional dependence of the mass flow Q on the pressure p 'and on the reciprocal of the root of T' is evaluated.

The pressure ps in the intake manifold 4 is measured at the measuring location 41 in step 160. In step 170, the pressure difference Aps between the measuring location 41 and the injector la-lf is determined, wherein in addition an approximate value Qs * is used for the air mass flow Qs. In step 180, the pressure ps is corrected by the pressure difference Aps to the pressure ps'. In step 190, the

Dependence of the sought mass flow Q of the outflow function Ψ formed from the pressures p 'and Ps' evaluated.

In step 195, the dependence of the mass flow Q of p 'and T' is multiplied by the dependence of the mass flow Q of Ψ. Thus the final result for the mass flow Q is obtained.

The injector-specific approach is therefore taken:

with the substance size κ as isentropic coefficient.

FIG. 3 shows, by way of example, the course of the actual pressure pi at an injector 1a, the course of the pressure p measured at the measuring point 31, and the course of the current Ii through the injector 1a above the angle of rotation α1

Crankshaft, which dictates the timing in the engine 10. The start of the injection is with SOI (Start Of Injection) and the end of the injection with EOI (End Of Injection) designated. In addition, the corrected according to the invention pressure p 'is located. This correction is on average over the period of

Injection (between SOI and EOI) the difference between the

actual pressure pi and the measured at the measuring point 31 pressure p

approximately.

Figure 4 shows schematically a fuel injection system 10a with a

Fuel rail 32, which is fed by a supply line 3 and supplies six injectors la-lf via leads 3a-3f with diameters Di to De. The injectors la-lf are traversed by currents Ii to, for the sake of clarity, only the current Ii is located. At the measuring point 31, the temperature T and the pressure p of the fuel 2 are measured. Immediately before the injectors la-lf the fuel 2 has a temperature Ti, Je and a pressure pi, ..., p6. When determining the respective pressure drop Δρ and the respective

Temperature difference ΔΤ are each the diameter DR of the

Fuel rails 32, the diameter Di to De of the leads 3a-3f and taken into account from the measured location 31 distances Li to l_6 to the injectors la-lf. For the determination of the temperature difference .DELTA.Τ is further considered that from the fuel rail 32, a heat flow WK by convection into the environment at the ambient temperature Tu, a heat flow Ws by heat radiation between hot engine parts and the fuel system and another heat flow Wi_ by heat conduction into the attachment point and the downstream engine 10 on the engine temperature TM off or flows.

FIG. 5 shows by way of example the course of the actual pressures pi, P2 and pe immediately before the injectors 1a, 1b and 1f above the angle of rotation α of FIG

Crankshaft, which dictates the timing in the engine 10. The different ones

Installation positions of the injectors la-lf lead to significant differences between the pressures pi to pe- With the method according to the invention, these differences are corrected and their influence on the determination of the

Mass flow Q pushed back by opened injectors la-lf. FIG. 6 shows the temperature T at the central measuring point 31 for different operating points of the motor 10, symbolized by horizontal lines XI to X8 for the 8 different operating points. At the same time, the course of the temperature at the inputs of the six injectors 1 a to 1 f is plotted for the same operating points (curves Y 1 to Y 8 for the 8 different operating points B 1).

BP8). The operating points Bpl to Bp8 differ in the number of revolutions and / or in the load P of the engine 10. The difference between the temperature T measured at the measuring point 31 and the actual temperature at the inlet of the injectors 1a-1f can be up to 30 K.

Claims

claims

A method (100) for determining the mass flow Q an, in particular gaseous fuel (2) through an opened injector (1, la-lf), comprising the determination of the pressure p (110) and the temperature T (120) of the fuel (2) at least one measuring location (31) in the feed line (3, 3a-3f) to the injector (la-lf) and the evaluation (150) of the mass flow Q as proportional to the pressure p and inversely proportional to the root of the temperature T, characterized in that the pressure p is corrected by the pressure drop Δρ, which arises when opening the injector in the supply line (3, 3a-3f) between the measuring point (31) and the injector (la-lf) to the pressure p '( 140), wherein in the determination (130) of Δρ the mass flow Q, the length L, l_i-l_6, the diameter D, DR, D1-D6, the pipe friction coefficient λ, and / or the pressure loss coefficient ζ, the supply line (3, 3a-3f) between the measuring location (31) and the injector (la-lf) are taken into account.

2. Method (100) according to claim 1, characterized in that the

Pressure ps at at least one measuring location (41) in a suction pipe (4), in which the fuel (2) from the injector (la-lf) is passed is determined (160) and that the mass flow Q in addition to proportional from the Pressure ps and the fuel pressure p formed outflow function Ψ is evaluated (190).

3. Method (100) according to claim 2, characterized in that the

Pressure ps to the pressure drop Aps, in the suction pipe (4) between the measuring point (41) and the injector (la-lf) is corrected to the pressure ps' (180), wherein in determining (170) of Aps by the suction pipe (4) promoted

Air mass flow Qs, the length Ls, the diameter Ds, the pipe friction coefficient λβ, and / or the pressure loss coefficient ζβ, the suction pipe (4) between the measuring point (41) and the injector (la-lf) are taken into account.

4. The method (100) according to any one of claims 1 to 3, characterized

characterized in that the temperature T of the fuel (2) around the

Temperature difference .DELTA.Τ between the measuring location (31) and the injector (31) is corrected (145), wherein in the determination (144) of ΔΤ the heat conduction at attachment points of the supply line (3, 3a-3f) and / or the injector (la-lf), the heat transfer by radiation, and / or the convection with the ambient air, is taken into account.

5. The method (100) according to any one of claims 1 to 4, characterized

characterized in that in the determination (130) of Δρ, and / or in the determination (144) of ΔΤ, in addition an approximate value Q * for the mass flow Q is taken into account.

6. The method (100) according to claim 5, characterized in that the

Approximate value Q * is determined to be proportional to the pressure p and inversely proportional to the root of the temperature T without regard to Δρ.

7. Method (100) according to claim 3 and optionally one of claims 4 to 6, characterized in that in the determination (170) of Aps additionally an approximate value Qs * for the through the suction pipe (4) funded air mass flow Qs is used.

8. Method (200) for controlling the injection of fuel (2) in an engine (10), wherein the engine (10) comprises one or more injectors (la-lf) and the supply line (3, 3a-3f) to the Injectors (la-lf) a common

Comprising the fuel injector rail (32), the period of time for which each injector (la-lf) is opened being determined from the mass M of fuel (2) to be injected and the mass flow Q of the injector (la-lf) is determined in the open state (210), characterized in that for each of the injectors (la-lf) individually the mass flow Q in the open state by a method (100) according to one of claims 1 to 7 is determined.

9. control unit (300) for the injection of fuel (2) in an engine (10), comprising means (301) for metering of a plurality of injectors (la-lf) respectively injected mass M of fuel by applying each Injector (la-lf) with a current I according to a time program l (t), characterized in that the control device (300) is adapted to perform in the determination of the time program l (t) a method according to one of claims 1 to 8 ,

10. Computer program product containing machine-readable

Instructions that when on a computer and / or on a computer

Control unit (300) for the injection of fuel (2) into a motor (10) are executed, the computer and / or the control unit (300) to a control unit (300) according to claim 9 valorise, and / or cause a

Method according to one of Claims 1 to 8.