EP1199459B1 - Method for the starting up of an internal combustion engine - Google Patents

Description

State of the art

The invention is based on a method for starting an internal combustion engine, in particular of a motor vehicle, according to the preamble of claim 1.

Such a method, such an internal combustion engine, such a control device and such a computer program are for example from the DE 198 27 609 A1 known. There, the fuel is injected via injection valves during the intake phase or during the compression phase directly into the combustion chamber and burned there. For injection, the fuel is pressurized in an upstream fuel reservoir. This represents that pressure which acts on the fuel and with which the fuel is thus injected via the injection valves into the combustion chambers.

When starting the internal combustion engine an increased amount of fuel must be injected into the combustion chamber, especially in non-operationally warm engine. This has the consequence that the pressure in the fuel tank can significantly reduce. This pressure drop is still reinforced by the fact that when starting the engine, the pressure in the fuel tank may not be sufficiently available and can not be built and maintained so fast.

For the operation of the internal combustion engine in stratified operation, a certain pressure acting on the fuel is required. This results from the fact that in the compression phase, during which the fuel is injected into the combustion chamber during stratified operation, the compression pressure in the combustion chamber rises sharply. If now the compression pressure during the injection is greater than the pressure acting on the fuel, this has the undesirable consequence that the fuel to be injected is blown back into the pressure accumulator.

Due to the pressure drop described when starting the internal combustion engine, such a back-blowing can occur particularly quickly during the starting process.

Purpose and advantages of the invention

The object of the invention is to provide a method for starting an internal combustion engine, with the back-blowing of fuel in the accumulator is safely avoided.

This object is achieved according to the invention in a method of the type mentioned by the features of the characterizing part of claim 1. In an internal combustion engine, a control unit and a computer program of the type mentioned, the object is achieved according to the invention.

It is thus calculated specifically the pressure acting on the fuel pressure, which is still present at the end or after an injection. This calculation will be for each one Injection done individually. Depending on this determined pressure, it is then decided whether the risk of back-blowing of fuel exists, and therefore whether the shift operation must be excluded or can be permitted.

In this way it is ensured for each injection that can then be switched to shift operation only when the pressure acting on the fuel is large enough. If this is not the case, a switch to shift operation is excluded or an existing shift operation is switched off.

An undesirable back-blowing of fuel in the fuel storage is thus reliably prevented.

In the invention, from the pressure acting on the fuel before or at the beginning of the injection, a fuel mass present in the fuel accumulator prior to injection is determined. This is done on the basis of an equation that takes into account the compressibility of the fuel.

In the invention, a fuel mass present in the fuel accumulator after injection in the fuel accumulator is determined from the fuel mass present in the fuel accumulator prior to the injection and from the fuel mass to be injected. This is done by means of a difference.

Thereafter, the pressure acting on the fuel at the end or after injection is determined from the fuel mass present in the fuel accumulator after the injection. This is again done using the aforementioned equation.

At the end or after injection on fuel acting pressure is compared with a threshold pressure. The threshold pressure corresponds approximately to the pressure that is required for the shift operation to be carried out.

Thereafter, the stratified operation is excluded when the pressure acting on the fuel at the end or after the injection is smaller than the threshold pressure.

Of particular importance is the realization of the method according to the invention in the form of a computer program which is provided for a control unit of an internal combustion engine, in particular of a motor vehicle. In this case, the computer program is executable in particular on a microprocessor and suitable for carrying out the method according to the invention. In this case, therefore, the invention is realized by the computer program, so that this computer program in the same way represents the invention as the method to whose execution the computer program is suitable. The computer program can be stored on an electrical storage medium, for example on a flash memory or a read-only memory.

Other features, applications and advantages of the invention will become apparent from the following description of embodiments of the invention, which are illustrated in the figures of the drawing. All described or illustrated features, alone or in any combination form the subject matter of the invention, regardless of their summary in the claims or their dependency and regardless of their formulation or representation in the description or in the drawing.

Embodiments of the invention

FIG. 1

shows a schematic block diagram of an embodiment of an internal combustion engine according to the invention, and

FIG. 2

shows a schematic flow diagram of a method according to the invention for starting the internal combustion engine of FIG. 1 ,

In the FIG. 1 an internal combustion engine 1 of a motor vehicle is shown, in which a piston 2 in a cylinder 3 back and forth. The cylinder 3 is provided with a combustion chamber 4, which is limited inter alia by the piston 2, an inlet valve 5 and an outlet valve 6. With the intake valve 5 is an intake pipe 7 and with the exhaust valve 6, an exhaust pipe 8 is coupled.

In the region of the intake valve 5 and the exhaust valve 6, an injection valve 9 and a spark plug 10 protrude into the combustion chamber 4. Fuel can be injected into the combustion chamber 4 via the injection valve 9. With the spark plug 10, the fuel in the combustion chamber 4 can be ignited.

In the intake pipe 7 is a rotatable throttle valve 11th housed, via which the intake pipe 7 air can be supplied. The amount of air supplied is dependent on the angular position of the throttle valve 11. In the exhaust pipe 8, a catalyst 12 is housed, which serves to purify the exhaust gases resulting from the combustion of the fuel.

The injection valve 9 is connected via a pressure line with a fuel reservoir 13. In a corresponding manner, the injection valves of the other cylinders of the internal combustion engine 1 are connected to the fuel accumulator 13. The fuel storage 13 is supplied via a supply line with fuel. For this purpose, an electrical and / or mechanical Kraftstoffpunpe is provided which is adapted to build up the desired pressure in the fuel reservoir 13.

Furthermore, a pressure sensor 14 is arranged on the fuel accumulator 13, with which the pressure in the fuel accumulator 13 can be measured. This pressure is that pressure which is exerted on the fuel and with which therefore the fuel is injected via the injection valve 9 into the combustion chamber 3 of the internal combustion engine 1.

During operation of the internal combustion engine 1, fuel is conveyed into the fuel accumulator 13. This fuel is injected via the injection valves 9 of the individual cylinders 3 into the associated combustion chambers 4. With the help of the spark plugs 10 burns are generated in the combustion chambers 3, through which the piston 2 are set in a reciprocating motion. These movements are transmitted to a non-illustrated crankshaft and exert on this torque.

A controller 15 is of input signals 16 acted upon, represent the measured by sensors operating variables of the internal combustion engine 1. For example, the controller 15 is connected to the pressure sensor 14, an air mass sensor, a lambda sensor, a speed sensor, and the like. Furthermore, the control unit 15 is connected to an accelerator pedal sensor which generates a signal indicative of the position of an accelerator pedal operable by a driver and thus the requested torque. The control unit 15 generates output signals 17 with which the behavior of the internal combustion engine 1 can be influenced via actuators or actuators. For example, the control unit 15 is connected to the injection valve 9, the spark plug 10 and the throttle valve 11 and the like, and generates the signals required for driving them.

Among other things, the control unit 15 is provided to control the operating variables of the internal combustion engine 1 and / or to regulate. For example, the fuel mass injected by the injection valve 9 into the combustion chamber 4 is controlled and / or regulated by the control unit 15, in particular with regard to low fuel consumption and / or low pollutant development. For this purpose, the control unit 15 is provided with a microprocessor which has stored in a storage medium, in particular in a flash memory, a computer program which is adapted to perform said control and / or regulation.

The internal combustion engine 1 of FIG. 1 can be operated in a plurality of modes. Thus, it is possible to operate the internal combustion engine 1 in a homogeneous operation, a stratified operation, a homogeneous lean operation, a double injection operation and the like.

In homogeneous operation, the fuel is during the Injection phase of the injection valve 9 is injected directly into the combustion chamber 4 of the internal combustion engine 1. The fuel is thereby largely swirled until the ignition, so that a substantially homogeneous fuel / air mixture is formed in the combustion chamber 4. The torque to be generated is set essentially by the position of the throttle valve 11 by the control unit 15. In homogeneous operation, the operating variables of the internal combustion engine 1 are controlled and / or regulated such that lambda is equal to or at least approximately equal to one. Homogenous operation is used in particular at full load.

The homogeneous lean operation largely corresponds to the homogeneous operation, but the lambda is set to a value greater than one.

In stratified operation, the fuel is injected during the compression phase of the injection valve 9 directly into the combustion chamber 4 of the internal combustion engine 1. Thus, in the ignition by the spark plug 10 no homogeneous mixture in the combustion chamber 4 is present, but a fuel stratification. The throttle valve 11 may, except for requirements e.g. the exhaust gas recirculation and / or the tank ventilation, fully open and the internal combustion engine 1 are operated with it throttled. The torque to be generated is largely set in shift operation via the fuel mass. With the shift operation, the internal combustion engine 1 can be operated in particular at idle and at partial load.

Between the above modes of the internal combustion engine 1 can be switched back and forth or. Such switching is performed by the controller 15.

If the internal combustion engine 1 after a longer Standstill started, the fuel mass injected into the combustion chamber 4 is substantially increased, especially at low temperatures. In this way, not only an ignitable air / fuel mixture in the combustion chamber 4 is provided, but also those losses of fuel are compensated by the entry of fuel into the engine oil and / or by building a wall film of fuel in Combustion chamber 4 arise.

The required during startup large, injecting fuel mass has the consequence that the pressure in the fuel reservoir 13 is greatly reduced during the injection period. This is exacerbated by the fact that when starting the internal combustion engine 1, the electric and / or the mechanical fuel pump is not yet able to quickly enough to generate and maintain the required pressure in the fuel accumulator 13.

If the pressure in the fuel accumulator 13 decreases, there is the danger in stratified operation that during an injection of fuel into the combustion chamber 4 of the internal combustion engine 1 the compression pressure in this combustion chamber 4 becomes greater than the collapsed pressure in the fuel accumulator 13. This would then have the undesirable consequence that the fuel to be injected is blown back into the fuel reservoir 13.

In the FIG. 2 a method is shown with which by the control unit 15 of that pressure in the fuel accumulator 13 is determined, which is still present there after an injection. With the help of this pressure, it is then decided whether the internal combustion engine 1 can be operated in stratified mode or not. This procedure is especially for the starting process of Internal combustion engine 1 suitable, but can also be used during the other operation of the same.

In a step 20, the pressure in the fuel accumulator 13 is measured with the aid of the pressure sensor 14. This measurement is carried out as directly before or immediately at the beginning of the next injection of fuel into the combustion chamber. 4

mit p₁₃ = Druck im Kraftstoffspeicher 13
p₀ = Umgebungsdruck
E_Kr = Elastizitätsmodul des Kraftstoffs
ρ_Kr = Dichte des Kraftstoffs
V₁₃ = Volumen des Kraftstoffspeichers 13
m_Kr13 = Kraftstoffmasse im Kraftstoffspeicher 13
aus dem gemessenen Druck im Kraftstoffspeicher 13 auf die in demselben vorhandene Kraftstoffmasse m_Kr13 geschlossen. Hierzu wird der von dem Drucksensor 14 gemessene Druck als Druck p₁₃ eingesetzt, um dann die Gleichung nach der Kraftstoffmasse m_Kr13 aufzulösen. Der Umgebungsdruck, das Elastizitätsmodul des Kraftstoffs, die Dichte des Kraftstoffs und das Volumen des Kraftstoffspeichers 13 sind dabei bekannt oder können anderweitig gemessen oder berechnet werden.In a step 21, using the equation $${\mathrm{p}}_{}$$$${\mathrm{}}_{\mathrm{13}}\mathrm{=}{\mathrm{O}}_{\mathrm{0}}\mathrm{+}{\mathrm{e}}_{\mathrm{Kr}}\mathrm{\times }\left(\mathrm{1}\mathrm{-}{\mathrm{\rho }}_{\mathrm{Kr}}\mathrm{\times }\left({\mathrm{<figure-callout\; id="13"\; label="V"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">V</figure-callout>}}_{\mathrm{13}}\mathrm{/}{\mathrm{m}}_{\mathrm{Kr}\mathrm{13}}\right)\right)$$

with p ₁₃ = pressure in the fuel tank 13
p ₀ = ambient pressure
E _Kr = modulus of elasticity of the fuel
ρ _Kr = density of the fuel
V ₁₃ = volume of the fuel accumulator 13
m _Kr13 = fuel _mass in fuel storage 13
from the measured pressure in the fuel _accumulator 13 to the existing in the same fuel _mass m _Kr13 closed. For this purpose, the pressure measured by the pressure sensor 14 is used as pressure p ₁₃ , in order then to dissolve the equation according to the fuel _mass m _Kr13 . The ambient pressure, the modulus of elasticity of the fuel, the density of the fuel and the volume of the fuel accumulator 13 are known or can be otherwise measured or calculated.

In a step 22, as already explained, the fuel quantity m _{Kr to} be injected is calculated from the operating variables of the internal combustion engine 1 by the control unit 15. The operating variables may be the engine temperature, the ambient temperature and the like.

In a step 23, that fuel _mass M _{Kr13 is} calculated which, after the injection of the fuel _mass m _{Kr, is} still present in the fuel _accumulator 13. This calculation is done according to the equation $${\mathrm{m}}_{\mathrm{Kr}\mathrm{13}\mathrm{after\; that}}\mathrm{=}{\mathrm{m}}_{\mathrm{Kr}\mathrm{13}}\mathrm{-}{\mathrm{m}}_{\mathrm{Kr}}$$

With the aid of equation (1), the pressure P _{13 is then determined} in the fuel _accumulator 13 in the combustion chamber 4 immediately at the end or immediately after the injection of the fuel _mass m _Kr in a step 24. In this case, the mass of fuel in the _accumulator 13 is no longer the fuel mass m _Kr13 present before the injection, but the fuel _mass m _Kr13danach available after the injection. The other variables, ie the ambient pressure, the modulus of elasticity, etc., are in turn either known or can be otherwise measured or calculated.

In a step 25, the pressure p _{13 is then compared} in the fuel _accumulator 13 at the end or after the injection with a threshold pressure p _threshold . The threshold pressure P _threshold corresponds approximately to the pressure that is required that the shift operation is performed, without causing the risk of Rückblasens of fuel in the fuel storage 13 is present.

If the pressure p _13danach greater than the threshold pressure P _threshold , it means that there is still enough pressure in the fuel tank 13 is available to operate the internal combustion engine 1 in the shift operation. In this case, therefore, in a step 26, the shift operation is permitted.

If the pressure p _13danach but smaller than that Threshold pressure P _threshold , it means that the pressure in the fuel reservoir 13 is no longer sufficient to operate the internal combustion engine 1 in a shift operation. In particular, in this case there is the risk that due to the larger compression pressure in the combustion chamber 4, the fuel to be injected is blown back into the fuel accumulator 13. This is prevented by the fact that in this case in a step 27, the shift operation is excluded.

In the method described above, the decision of steps 25, 26, 27 is based on a single injection. Alternatively, it is possible to extend this method to multiple injections. For this purpose, as in the FIG. 2 However, after step 24, steps 21 to 24 are repeated. This repetition then refers to the next injection. By means of four such repetitions, for example, four cycles of a particular cylinder can be calculated in advance. The result is then the pressure in the fuel storage after these four working cycles. The decision making of steps 25, 26, 27 can then be carried out with this pressure.

Claims (5)

1. Method for starting an internal combustion engine (1), in particular of a motor vehicle, in which a pressure is applied to the fuel which is located in a fuel accumulator (13), in which the fuel is injected directly into a combustion chamber (4) in a stratified mode during a compression phase or in a homogeneous mode during an intake phase, in which a fuel mass (m_Kr) which is to be injected is identified from operating variables of the internal combustion engine (1), in which the pressure acting on the fuel is measured by a pressure sensor (14), and in which the stratified mode is ruled out or permitted as a function of this pressure,
   characterized in that the pressure (p₁₃) acting on the fuel before or at the start of the injection is measured,
   in that a fuel mass (m_Kr13) which is present in the fuel accumulator (13) before the injection is identified from the pressure (p₁₃) acting on the fuel before or at the start of the injection,
   in that a fuel mass (m_Kr13danach) which is present in the fuel accumulator (13) after the injection is identified from the fuel mass (m_Kr13) which is present in the fuel accumulator (13) before the injection and from the fuel mass (m_Kr) which is to be injected,
   in that the pressure (p_13danach) acting on the fuel at the end of or after the injection is identified from the fuel mass (m_Kr13danach) which is present in the fuel accumulator (13) after the injection,
   in that the pressure (p_13danach) acting on the fuel at the end of or after the injection is compared with a threshold value pressure (p_Schwelle), and
   in that the stratified mode is ruled out if the pressure (p_13danach) acting on the fuel at the end of or after the injection is lower than the threshold value pressure (Pschwelle).
2. Computer program for a control unit (15) of an internal combustion engine (1), in particular of a motor vehicle, characterized in that the computer program is suitable for carrying out a method according to Claim 1.
3. Computer program according to Claim 2, characterized in that the computer program is stored on an electrical storage medium, in particular on a flash memory or a read-only memory.
4. Control unit (15) for an internal combustion engine (1), in particular of a motor vehicle, wherein the control unit (15) is configured to carry out the method according to Claim 1.
5. Internal combustion engine (1), in particular of a motor vehicle having a control unit (15) according to Claim 4.

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