DE102016213383A1 - Method for determining a fuel mass flow and for controlling the injection - Google Patents

Abstract

Method (100) for determining the mass flow Q of fuel (2) through an opened injector (1, 1a-1f), comprising determining the pressure p (110) and the temperature T (120) of the fuel (2) at at least one Measuring location (31) in the supply line (3, 3a-3f) to the injector (1a-1f) 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 to the Pressure drop .DELTA.p, which arises when opening the injector in the supply line (3, 3a-3f) between the measuring point (31) and the injector (1a-1f) is corrected (140) to the pressure p ', wherein in the determination (130 ) of Δp the mass flow Q, the length L, L1-L6, 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 point (31 ) and the injector (1a-1f). Method (200) for controlling the injection of fuel (2) in a motor (10) having a plurality of injectors (1a-1f) and a supply line (3, 3a-3f) to the injectors (1a-1f) having a common rail (32) for the fuel (2), wherein the opening duration of each injector (1a-1f) is determined from the desired injection mass M of fuel (2) and the mass flow Q of the injector (1a-1f) in the open state (210 ), wherein for each of the injectors (1a-1f), the mass flow Q in the open state according to the invention is determined individually (100). Controller (300) and computer program product.

Description

The present invention relates to methods for determining a fuel mass flow and for controlling the injection in fuel 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 unit time in the opened state of the injector is determined on the basis of the pressure p and the temperature T of the fuel. 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 to place pressure and temperature sensors directly at the inlet and outlet of the 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 the DE 10 2005 036 192 A1 a correction for systematic deviations of the pressure p is known. The US 4 636 620 A discloses using the temperature coefficient of the injector coil to determine the actual temperature and to correct the control of the injector accordingly. The US Pat. No. 7,047,942 B2 takes a different approach and discloses to make the supply lines from the busbar to all injectors of the same length to minimize at least 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, in particular gaseous, fuel has been 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.p, which arises when the injector opens in the supply line between the measuring location and the injector, to the pressure p '. In the determination of Δp, the mass flow Q, the length L, the diameter D, the pipe friction coefficient λ, and / or the pressure loss coefficient ζ, the supply line between the measuring location and the injector are taken into account. 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 Δp depend on length L and diameter D, as well as on any pipe bends and branches, the supply line.

On the one hand, it was recognized that, especially with the use of gaseous fuels, the variables mentioned are the main influencing factors on which the pressure drop Δp 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 Δp.

On the other hand, it has been recognized that the fuel pressure, especially for gaseous fuels, is the dominant factor for determining the mass flow. If the injector is operated at a pressure ratio before and after the injector that is above the critical pressure ratio, the pressure p and the temperature T of the fuel upstream of the injector determine the pressure independent of the counterpressure after the injector Mass flow Q of fuel through the open 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. As a result, the fuel experiences different friction on the different paths to the individual injectors, so that finally different pressures p are present at the individual injectors. 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 be significantly improved in particular the smooth running of the engine, which depends on a correct choreography of the combustion between the individual cylinders. As a result, fuel consumption and engine emissions are also reduced. This is especially true when the amount of fuel injected by each injector is accurately delivered to one of a plurality of cylinders, for example, through multipoint port injection.

Furthermore, the production costs of the motor are also indirectly reduced. Deviations in the injection behavior among each other arise in a real engine not only from the described injector-specific pressure drop Δp, 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. If the specified specification can be exceeded by the correction of the injector-specific pressure drop Δp, on the other hand, the manufacturing tolerances of the injectors can be significantly expanded and at the same time the specifications are still met. As a result, an engine which fulfills the specifications can be obtained at low production costs since the production costs for injectors with more stringent manufacturing tolerances increase disproportionately.

In principle, the pressure drop Δp could also be minimized physically, e.g. due to the large diameter of the supply line and the busbar, the pressure differences are not noticeable in the final 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 p _S 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 evaluated as proportional to the outflow function Ψ formed from the pressure p _S and the fuel pressure p.

The pressure p _S in the intake manifold is the back pressure against which the fuel is injected through the injector. If the pressure ratio at the injector is smaller than the critical pressure ratio (subcritical flow), the intake manifold pressure is applied to the injected mass flow Q as a further influencing parameter via the outflow function Ψ.

In a further particularly advantageous embodiment of the invention, the pressure p _S is corrected by the pressure drop Δp _S , which arises in the intake manifold between the measuring location and the injector, to the pressure p _S '. When determining Δp _S , the air mass flow Q _S conveyed through the intake manifold and the length L _S , the diameter D _S , the pipe friction coefficient λ _S , and / or the pressure loss coefficient ζ _S , of the intake manifold between the measuring location and the injector are taken into account. Analogous to the correction of p to p ', in particular the combination of the length L _S and the diameter D _S with the pipe friction coefficient λ _S , and / or with the pressure loss coefficient ζ _S , can be taken into account.

The pressure p _S enters via the outflow function Ψ approximately with linear power in the mass flow Q a. A drop Δp _{S of} this pressure p _S thus has the same effect on the accuracy of the injected mass flow Q as a drop Δp of the pressure p.

In a further advantageous embodiment of the invention, the temperature T of the fuel is corrected by the temperature difference .DELTA.T, which arises between the measuring location and the injector, to the temperature T '. In the determination of ΔT, the heat conduction at attachment points of the supply line and / or the injector, and / or the convection with the ambient air, and / or the heat transfer by radiation, e.g. of hot engine parts, considered.

The temperature difference .DELTA.T, 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. The temperature difference .DELTA.T resulting from thermal conduction is typically proportional to the temperature difference bridged by the attachment site, the area and length relevant to heat transfer, the thermal contact resistance, and a heat transfer coefficient. The temperature difference .DELTA.T resulting from thermal radiation is in the fourth power proportional to the temperature difference between the surfaces of the piping and the distribution rails on the one hand and areas of hot engine parts on the other.

Overall, the temperature difference .DELTA.T 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.T 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. These measures, however, similar to the measures for leveling the pressure drop Δp, associated with costs and take up additional space.

In the determination of Δp, and / or in the determination of ΔT, an approximate value Q * for the mass flow Q is additionally taken into account. The accuracy of the determination of Δp can thereby be further increased. 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 Δp.

In a further advantageous embodiment of the invention, an approximate value Q _S * is additionally used in the determination of Δp _S for the air mass flow Q _S conveyed through the intake manifold. In this way, the determination of Δp _S becomes 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 are not dependent on the installation of additional sensors or other components in the injection system. Rather, an existing injection system can be provided with the functionality and the advantages according to the invention by a change of that functionality in the control unit of the injection system, which determines the energization duration of each injector. The invention therefore expressly also relates to a control unit for the injection of fuel into an engine. This control unit comprises means for metering the mass M of fuel injected by a plurality of injectors by charging each injector with a current I according to 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 I (t).

The method according to the invention is further distinguished by the fact that the integration of the corresponding functionality into 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. Such software therefore constitutes a salable product of its own. Thus, the invention also relates to a computer program product having machine-readable instructions which, when executed on a computer and / or on a controller for injecting fuel into an engine, the computer and / or the controller to a Upgrade control unit 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:

1 Construction of an engine with central intake manifold injection ( 1a ) and with multipoint port injection ( 1b );

2 Embodiment of the method 100 and the parent procedure 200 ;

3 Pressure drop on a single injector 1a - 1f during the injection process;

4 Fuel injection system 10a with additional consideration of incoming and outgoing heat flows W _K by convection, W _S by heat radiation and W _L by heat conduction;

5 Pressure difference between different injectors 1a - 1f in different installation positions;

6 Deviation of the temperature at the inputs of the injectors 1a - 1f from the place of measurement 31 measured temperature T for different operating points of the engine 10 ,

To 1a includes the engine 10 six cylinders 12a - 12f that have a common intake manifold 4 be supplied with a fuel-air mixture. The air supply to the intake manifold 4 is via a throttle 42 controlled. With a sensor 41 inside the suction pipe 4 the pressure p _{S is} measured.

A central distribution rail (fuel rail) 32 forms the supply line 3 to the six injectors 1a - 1f , Temperature T and pressure p are using sensors 31 within the fuel rail 32 measured. The injectors 1a - 1f be via a central control unit 300 and a tax bus 301 opened by energization. The one through the six injectors 1a - 1f subsidized fuel is in a central collector 11 collected and in the intake manifold 4 mixed with air. The fuel-air mixture is then added to the cylinders 12a - 12f fed.

To 1b are the injectors 1a - 1f right in front of the cylinders 12a - 12f arranged. This is each of the injectors 1a - 1f exactly one of the cylinders 12a - 12f assigned. In contrast to 1a will be differences in through the individual injectors 1a - 1f conveyed masses M of fuel 2 no longer in the central collector 11 and in the intake manifold 4 at least partially leveled. Instead, such differences directly affect the mixing ratio of the fuel 2 with air passing through the individual cylinders 12a - 12f is supplied. Thus, in multi-port intake manifold injection, it is more important than the central injector injection that the individual injectors 1a - 1f conveyed masses M of fuel 2 are consistent with each other.

The in the 1a and 1b shown number of cylinders 12a - 12f and injectors 1a - 1f is just an example. The procedure already works with only one injector 1a - 1f and only one cylinder 12a - 12f , Also, the method does not depend on the number of cylinders 12a - 12f equal to the number of injectors 1a - 1f is.

2 shows an embodiment of the method 200 for controlling the injection of the fuel 2 , In the parent step 210 is from the injected mass M of fuel 2 and the mass flow Q through the respective injector 1a - 1f in the opened state, the time program I (t) of the energization for this injector 1a - 1f determined. The mass flow Q is in each case with the method 100 determined according to the invention.

As part of the procedure 100 will step in first 110 at the measuring location 31 the pressure p of the fuel 2 measured. At the same time, the temperature T of the fuel 2 in step 120 also measured, with the measuring location 31 the same as for the print, but also another. In step 130 is the pressure drop Δp between the site 31 and the injector 1a - 1f determined, and in parallel will be in step 144 of the Temperature difference ΔT between the measuring location 31 and the injector 1a - 1f determined. In each case, an approximate value Q * for the mass flow through the injector 1a - 1f used in the opened state.

The pressure p is in step 140 corrected by the pressure drop Δp to the pressure p '. The temperature T will be in step 145 corrected by the temperature difference ΔT 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 p _S in the intake manifold 4 will be in step 160 at the measuring location 41 measured. In step 170 the pressure difference Δp _S between the measuring location 41 and the injector 1a - 1f determined, wherein in addition an approximate value Q _S * for the air mass flow Q _S is used. In step 180 the pressure p _S is corrected by the pressure difference Δp _S to the pressure p _S '. In step 190 the dependence of the sought mass flow Q is evaluated by the outflow function Ψ formed from the pressures p 'and p _S '.

In step 195 the dependence of the mass flow Q of p 'and T' is multiplicatively combined with the dependence of the mass flow Q of Ψ. Thus the final result for the mass flow Q is obtained.

mit der Stoffgröße κ als Isentropenkoeffizient.The injector-specific approach is therefore taken:

with the substance size κ as isentropic coefficient.

3 shows by way of example the course of the actual pressure p ₁ at an injector 1a , the course of the place of measurement 31 measured pressure p and the course of the current I ₁ through the injector 1a above the angle of rotation α of the crankshaft, which is the timing in the engine 10 pretends. The start of the injection is designated with SOI (Start Of Injection) and the end of the injection with EOI (End Of Injection). In addition, the corrected according to the invention pressure p 'is located. This correction, on average over the period of injection (between SOI and EOI), equals the difference between the actual pressure p ₁ and that at the measurement site 31 measured pressure p approximately.

4 schematically shows a fuel injection system 10a with a fuel rail 32 that from a supply line 3 is fed and six injectors 1a - 1f via supply lines 3a - 3f supplied with diameters D ₁ to D ₆ . The injectors 1a - 1f are traversed by currents I ₁ to I ₆ , wherein for the sake of clarity, only the current I ₁ is located. At the measuring location 31 become the temperature T and the pressure p of the fuel 2 measured. Immediately before the injectors 1a - 1f has the fuel 2 in each case a temperature T ₁ ,..., T ₆ and a pressure p ₁ ,..., p ₆ . When determining the respective pressure drop .DELTA.p and the respective temperature difference .DELTA.T in each case the diameter D _{R of} the fuel rail 32 , the diameter D ₁ to D _{6 of} the supply lines 3a - 3f as well as the starting from the measuring location 31 measured distances L ₁ to L ₆ to the injectors 1a - 1f considered. For the determination of the temperature difference .DELTA.T is further considered that from the fuel rail 32 a heat flow W _K by convection into the environment at the ambient temperature T _U , a heat flow W _S by heat radiation between hot engine parts and the fuel system and another heat flow W _L by heat conduction into the attachment point and the downstream motor 10 at the engine temperature T _M drops or flows.

5 shows by way of example the course of the actual pressures p ₁ , p ₂ and p ₆ immediately before the injectors 1a . 1b and 1f above the angle of rotation α of the crankshaft, which is the timing in the engine 10 pretends. The different installation positions of the injectors 1a - 1f lead to significant differences between the pressures p ₁ to p ₆ . With the method according to the invention, these differences are corrected and their influence on the determination of the mass flow Q through opened injectors 1a - 1f pushed back.

6 shows the temperature T at the central measuring location 31 for different operating points of the engine 10 , symbolized by horizontal lines X1 to X8 for the 8th different working points. At the same time, the course of the temperature at the inputs of the six injectors is the same for the operating points 1a to 1f plotted (curves Y1 to Y8 for the 8 different operating points Bp1-Bp8). The operating points Bp1 to Bp8 differ in the number of revolutions and / or in the load P of the motor 10 , The difference between the one at the site 31 measured temperature T and the actual temperature at the entrance of the injectors 1a - 1f can be up to 30K.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102005036192 A1 [0005]
• US 4636620 A [0005]
• US 7047942 B2 [0005]

Claims (10)

Procedure ( 100 ) for determining the mass flow Q an, in particular gaseous, fuel ( 2 ) through an opened injector ( 1 . 1a - 1f ), 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 supply line ( 3 . 3a - 3f ) to the injector ( 1a - 1f ) as well as the evaluation ( 150 ) of the mass flow Q as being proportional to the pressure p and inversely proportional to the root of the temperature T, characterized in that the pressure p is the pressure drop Δp which occurs when the injector is opened in the supply line ( 3 . 3a - 3f ) between the measuring location ( 31 ) and the injector ( 1a - 1f ), is corrected for printing p '( 140 ), whereby in the investigation ( 130 ) of Δp the mass flow Q, the length L, L ₁ -L ₆ , the diameter D, D _R , D ₁ -D ₆ , 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 ( 1a - 1f ). Procedure ( 100 ) according to claim 1, characterized in that the pressure p _S at at least one measuring location ( 41 ) in a suction tube ( 4 ) into which the fuel ( 2 ) from the injector ( 1a - 1f ) is determined ( 160 ) and that the mass flow Q is additionally evaluated as proportional to the outflow function Ψ formed from the pressure p _S and the fuel pressure p ( 190 ). Procedure ( 100 ) according to claim 2, characterized in that the pressure p _S to the pressure drop Δp _S , in the intake manifold ( 4 ) between the measuring location ( 41 ) and the injector ( 1a - 1f ), is corrected for printing p _S '( 180 ), whereby in the investigation ( 170 ) of Δp _S passing through the suction pipe ( 4 ) conveyed air mass flow Q _S , the length L _S , the diameter D _S , the pipe friction coefficient λ _S , and / or the pressure loss coefficient ζ _S , the intake manifold ( 4 ) between the measuring location ( 41 ) and the injector ( 1a - 1f ). Procedure ( 100 ) according to one of claims 1 to 3, characterized in that the temperature T of the fuel ( 2 ) by the temperature difference ΔT between the measuring location ( 31 ) and the injector ( 31 ), is corrected to the temperature T '( 145 ), whereby in the investigation ( 144 ) of ΔT the heat conduction at attachment points of the supply line ( 3 . 3a - 3f ) and / or the injector ( 1a - 1f ), the heat transfer by radiation, and / or the convection with the ambient air, is taken into account. Procedure ( 100 ) according to one of claims 1 to 4, characterized in that in the determination ( 130 ) of Δp, and / or in the determination ( 144 ) of ΔT, in addition an approximate value Q * for the mass flow Q is taken into account. Procedure ( 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 Δp. Procedure ( 100 ) according to claim 3 and optionally one of claims 4 to 6, characterized in that in the determination ( 170 ) of Δp _S additionally an approximate value Q _S * for the through the suction pipe ( 4 ) conveyed air mass flow Q _S is used. Procedure ( 200 ) for controlling the injection of fuel ( 2 ) in an engine ( 10 ), the engine ( 10 ) one or more injectors ( 1a - 1f ) and the supply line ( 3 . 3a - 3f ) to the injectors ( 1a - 1f ) a common busbar ( 32 ) for the fuel ( 2 ), wherein the period of time for which each injector ( 1a - 1f ) is opened, from the respectively injected mass M of fuel ( 2 ) and the mass flow Q of the injector ( 1a - 1f ) is determined in the opened state ( 210 ), characterized in that for each of the injectors ( 1a - 1f ) individually the mass flow Q in the opened state according to a method ( 100 ) is determined according to one of claims 1 to 7. Control unit ( 300 ) for the injection of fuel ( 2 ) in an engine ( 10 ), comprising means ( 301 ) for the metering of several injectors ( 1a - 1f ) each injected mass M of fuel by pressurizing each injector ( 1a - 1f ) with a current I according to a time program I (t), characterized in that the control unit ( 300 ) is designed to perform in the determination of the time program I (t) a method according to one of claims 1 to 8. Computer program product containing machine-readable instructions which, when stored on a computer and / or on a control unit ( 300 ) for the injection of fuel ( 2 ) in an engine ( 10 ) the computer and / or the control unit ( 300 ) to a controller ( 300 ) according to claim 9, and / or cause to carry out a method according to any one of claims 1 to 8.

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