EP2205846B1 - Method for controlling a fuel injection system of an internal combustion engine - Google Patents

Abstract

In a method for controlling a fuel injection system (10) of an internal combustion engine, wherein the fuel injection system (10) comprises a manifold (24) and a high-pressure pump (20) and a fuel dosing unit (16) is associated with the high-pressure pump (20), wherein the fuel dosing unit (16) controls the amount of fuel delivered, an amount of fuel required for the operation of the internal combustion engine is determined as a function of a correction factor, which is based on a fuel pressure at the inlet of the high-pressure pump (20) and/or on a vapor pressure of the fuel to be delivered.

Description

State of the art

The present invention relates to a method of controlling a fuel injection system of an internal combustion engine, the fuel injection system comprising a manifold and an engine speed driven high pressure pump and associated with the high pressure pump is a fuel metering unit having an electromagnetically operable fuel control valve, the fuel metering unit controlling the amount of fuel delivered.

Such a fuel injection system is known from DE 198 53 103 A1 known. It comprises a high-pressure pump, the delivery rate of which can be adjusted by metering the amount of fuel reaching into a delivery chamber of the high-pressure pump. For this purpose, a Kraftstoffzumesseinheit is provided upstream of the pumping chamber, which comprises an electromagnetically actuated control valve. Depending on the position of a valve element of this electromagnetic control valve, an opening cross-section, through which the fuel must pass on the way to the delivery chamber, is more or less released. In this case, it is assumed that the delivery rate of the high pressure pump is proportional to the opening cross section.

From the DE 198 53 103 A1 It is also known that the opening cross section may have a slot-shaped, circular or triangular geometry.

From the DE 10 2005 025 114 A1 It is known that the proportional to the opening cross-section of the control valve flow rate of the high-pressure pump is influenced by additional pump-specific aspects. The DE 10 2004 062 613 A1 and the DE 199 51410 A1 each disclose adaptation methods for controlling a fuel supply system, which prevent evaporation of the Kaftstoffs or the formation of vapor bubbles in the high-pressure system. Furthermore, also have the Fuel pressure at the inlet of the high-pressure pump and the vapor pressure of the fuel to be supplied influence the flow rate of the high-pressure pump.

Disclosure of the invention

The object of the present invention is therefore to provide a method and a device which enable improved metering of an amount of fuel which is supplied to a high-pressure pump provided in a fuel injection system.

This problem is solved by a method for controlling a fuel injection system of an internal combustion engine. The fuel injection system includes a manifold and a high pressure pump. The high pressure pump is associated with a fuel metering unit. The fuel metering unit controls the amount of fuel delivered. An amount of fuel required to operate the internal combustion engine is determined in response to a correction factor based on a fuel pressure at the inlet of the high pressure pump and a vapor pressure of the fuel to be delivered.

The high pressure pump is preferably driven engine speed dependent, for example, by a drive connected to the crankshaft. The metering unit preferably comprises an electromagnetically operable control valve for supplying fuel.

The invention thus makes it possible to influence the delivered fuel quantity as a function of the fuel pressure at the inlet of the high-pressure pump and the vapor pressure of the fuel to be supplied, in order to ensure an improved metering of the quantity of fuel which is supplied to the high-pressure pump. As a result, the control quality of the pressure control in the distributor tube can be improved according to the invention and geometric and / or electrical tolerances of the high-pressure pump or the fuel metering unit can be compensated

The correction factor according to the invention is defined as the pressure difference between the fuel pressure at the inlet of the high-pressure pump and the vapor pressure of the fuel to be supplied Fuel determines. The high-pressure pump preferably has a delivery chamber with a check valve arranged on the input side, an opening pressure of the check valve being determined for determining the correction factor. This is subtracted from the pressure difference to determine a pressure correction value.

Thus, the pressure difference effective at the control valve, which affects the amount of fuel delivered, is determined and used as a correction factor for correcting the amount of fuel supplied to the high-pressure pump. As a result, a more precise precontrol of the high-pressure pump can be achieved by the fuel metering unit, whereby the influence of the fuel type and the corresponding admission pressure is reduced and an improved diagnosis is made possible.

Preferably, a desired fuel volume to be supplied to the high-pressure pump is determined, wherein the required fuel quantity is determined based on the desired fuel volume and the correction factor. In this case, the correction factor can be determined on the basis of a characteristic curve which defines suitable volume correction values for possible pressure correction values.

The use of a characteristic allows a quick and easy determination of the correction factor.

According to the invention, an opening cross section of the control valve is determined as a function of the correction factor, which is set to supply the required amount of fuel. Using the opening cross section of the control valve and a respective actual engine speed, a drive signal for the control valve is determined. The drive signal is determined on the basis of a characteristic curve that defines suitable drive signals as a function of possible opening cross sections and actual engine speeds.

Thus, the control valve is controlled in dependence on the correction factor, so that the fuel pressure at the inlet of the high pressure pump and / or the vapor pressure of the fuel to be supplied are taken into account in the control of the control valve and an improved metering of the delivered fuel quantity is guaranteed. In this case, the use of a characteristic allows a quick and easy determination of the drive signal.

The vapor pressure is determined in one embodiment of the invention from the actual temperature using at least one reference vapor pressure curve. Alternatively, the vapor pressure is determined from a post-start and / or warm-up factor and / or a factor of transition compensation. Furthermore, it is possible that the pre-pressure to determine the vapor pressure is reduced from an initial value until the delivery of the high pressure pump is zero and the vapor pressure of the difference of the pre-pressure and an opening pressure of a check valve of the high-pressure pump is determined.

The problem mentioned at the outset is also solved by a computer program with program code for carrying out all the steps of a method according to the invention when the program is executed in a computer.

The problem mentioned at the outset is also solved by an internal combustion engine having a fuel injection system comprising a manifold and a high pressure pump. The high pressure pump is associated with a fuel metering unit. The fuel metering unit controls the amount of fuel delivered. An amount of fuel required to operate the internal combustion engine is determinable in response to a correction factor based on a fuel pressure at the inlet of the high pressure pump and a vapor pressure of the fuel to be supplied.

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Showing:

Brief description of the drawings

Fig. 1

a schematic representation of a fuel injection system of an internal combustion engine with a high-pressure pump and a Kraftstoffzu- measuring unit;

Fig. 2

a partial section through a discontinued portion of the Kraftstoffzumesseinheit of Fig. 1 ;

Fig. 3

a schematic representation of a method for determining an opening cross-section for a control valve of the Kraftstoffzumessein- unit of Fig. 1 ;

Fig. 4

a schematic representation of a method for determining a drive signal for a control valve of the fuel metering of Fig. 1 ,

Embodiment of the invention

Fig. 1 shows a schematic representation of a fuel injection system 10 of an internal combustion engine. This comprises a fuel tank 12 from which a prefeed pump 14 delivers fuel to an inlet 15 of a fuel metering unit 16. Its outlet 18 leads to a high-pressure fuel pump 20. The low-pressure line running from the fuel tank 12 to the high-pressure pump 20 has the reference number 22 overall.

The high-pressure pump 20 preferably has a delivery chamber with a check valve arranged on the input side, compresses the fuel to a very high pressure and delivers it to a fuel collecting line 24 in which the fuel is stored under very high pressure and which also acts as a "distributor tube" or "Rail" is called. To this several injectors 26 are connected, which inject the fuel directly into them associated combustion chambers 28 of the engine not shown in detail below. The internal combustion engine serves, for example, for driving a motor vehicle.

The pressure in the fuel rail 24 is detected by a pressure sensor 30. Its signals are transmitted by the pressure sensor 30 to a control and regulating device 32, whose output is connected, inter alia, to the fuel metering unit 16. By means of the fuel metering unit 16 is in still darzustellender way the Flow rate of the high-pressure pump 20 is set. In this way, the actual pressure in the fuel rail 24, which is detected by the pressure sensor 30, a nominal pressure to be tracked.

How out Fig. 2 As can be seen, the fuel metering unit 16 is designed as a suction throttle. It comprises a housing 34, in which a valve piston 36 is received axially displaceable. The valve piston 36 protrudes into a valve chamber 38, in which a valve slide 40 is received axially displaceable. The valve spool 40 is pressed by a compression spring 42 against the valve piston 36. The inlet 15 of the fuel metering unit 16 is formed at the axial end of the valve chamber 38, whereas the outlet 18 is formed in a radial wall 44 of the valve chamber 38 in the form of a control port 46.

The position of the valve piston 36 is adjusted by an electromagnetic actuator 48. In de-energized state, the valve spring 42 pushes the valve spool 40 and the valve piston 36 in Fig. 2 completely down. This condition is in the left half of Fig. 2 shown. On the other hand, when the electromagnetic actuating device 48 is energized, the valve piston 36 presses the valve slide 40 against the force of the valve spring 42 Fig. 2 upward so that it covers the control opening 46 in the radial wall 44 partially or, in the end position, completely. This condition is in the right half of Fig. 2 shown. If the control opening 46 is completely free, a maximum amount of fuel passes from the prefeed pump 14 to the high-pressure pump 20 and from there into the rail 24. This operating state is referred to as full delivery. If the control port 46, however, partially covered by the valve spool 40, passes a smaller amount of fuel to the high-pressure pump 20 and into the rail 24. This operating state is referred to as "partial funding".

Hereinafter, a method for controlling the fuel injection system 10 of Fig. 1 according to an embodiment of the invention with reference to the 3 and 4 described in detail.

Fig. 3 shows a schematic representation of a method for determining an opening cross-section rozme_w for that of the valve piston 36, the electromagnetic Actuator 48, the valve spring 42 and the valve spool 40 formed, electromagnetically actuated control valve of the fuel metering unit 16 of Fig. 1 and 2 , According to a preferred embodiment of the invention, the method is implemented as a computer program and executed by the control and regulating device 32. Thus, the invention with existing components of the internal combustion engine can be realized easily and inexpensively.

In the following description of the method according to the invention is dispensed with a detailed explanation of known in the prior art method steps.

In a step 151, a fuel mass mkreff_w injected from the high pressure pump 20 into the manifold 24 is calculated. This is converted in a step 153 as a function of a temperature-dependent fuel density KLROHKRTF into a desired fuel volume vmkreff_w to be supplied to the high-pressure pump 20. The temperature-dependent fuel density KLROHKRTF can be determined according to the invention in a step 152 on the basis of a suitable characteristic curve based on a measured fuel temperature tfuelsq.

In a step 154, an amount of fuel required for operating the internal combustion engine is determined from the nominal fuel volume vmkreff_w to be supplied and a correction factor KLFOZMEDP. This required amount of fuel must be supplied to the high-pressure pump 20 and from the latter to the distributor pipe 24 in order to ensure there a fuel pressure and throughput required for the respective operating state of the internal combustion engine.

According to the invention, the opening cross section rozme_w of the control valve is determined in step 154. This is set to supply the required amount of fuel to the high-pressure pump 20. As below Fig. 4 described, based on the determined opening cross-section rozme_w a suitable drive signal for the control valve is determined.

The correction factor KLFOZMEDP can be determined in a step 148 on the basis of a characteristic field. This describes volume correction values depending on possible pressure correction values, which are suitable as a correction factor KLFOZMEDP for determining the required amount of fuel.

During operation of the internal combustion engine, the method according to the invention is preferably executed in the form of a loop by the control and regulating device 32. Accordingly, the correction factor KLFOZMEDP is determined at step 148 for an actual pressure correction value dpzme_w, respectively. This is determined in step 146 by subtracting the vapor pressure Pdampf of the fuel to be supplied and the opening pressure peiv of the check valve from the fuel pressure pekp at the inlet of the high-pressure pump 20. Here, the vapor pressure Pdampf of the fuel to be supplied and the opening pressure peiv the check valve may be summed in a step 144 beforehand.

Alternatively, a pressure difference between the fuel pressure pekp at the inlet of the high-pressure pump 20 and the vapor pressure Pdampf of the fuel to be supplied can also first be determined. In this case, the opening pressure peiv of the check valve is subtracted from the determined pressure difference to determine the pressure correction value.

According to a further embodiment of the invention, the actual pressure correction value dpzme_w can also be determined on the basis of an empirically determined relationship, such as e.g. a characteristic field. A suitable characteristic field can be determined as a function of the vapor pressure Pdampf and fuel pressure pekp, e.g. for low pressure systems with variable fuel pressure, or only depending on steam pressure Pdampf, e.g. for low pressure systems with constant fuel pressure pekp.

The vapor pressure Pdampf can be determined in various ways. This depends essentially on the temperature and only limited on the fuel used. Accordingly, in the simplest case, the vapor pressure Pdampf can be determined as a function of a respective actual temperature from a suitable, so-called reference vapor pressure curve. In order to take into account dependencies of the steam pressure Pdampf on the fuel used, depending on the fuel system, especially in so-called "flex fuel systems" also find several reference vapor pressure curves application, each possible fuel is associated with a corresponding curve.

Furthermore, the vapor pressure Pdampf may be determined using the adapted post-warming factor or using the adapted factor of the transient compensation. These correlate directly with the vapor pressure Pdampf of the fuel used, since they represent a measure of the evaporation tendency of the fuel.

Another way to determine the vapor pressure Pdampf is to reduce the pre-pressure Pvoradap until the promotion of the high-pressure pump 20 collapses. The set pressure then corresponds to the vapor pressure Pdampf increased by the opening pressure peiv of the check valve in the high-pressure pump 20, which thus results in Pdampf = Pvoradap-peiv. The opening pressure peiv can be regarded as constant with good approximation.

In addition, the vapor pressure Pdampf can be determined by the fact that in the context of the tank ventilation, a value is determined which serves as a measure of the loading of the associated active carbon filter, with a high value indicating a very volatile fuel. From this value, taking into account a respective actual temperature, the vapor pressure Pdampf can be determined.

According to the invention, the admission pressure pekp can be measured with a suitable sensor or modeled based on activation parameters of the electric fuel pump 14. In this case, in the case of a constant-pressure system with a mechanical pressure regulator, its set opening pressure can be used taking into account the pressure drop across the fuel line 22.

Fig. 4 shows a schematic representation of a method for determining a drive signal for the control valve of the fuel metering unit 16 of Fig. 1 and 2 , According to a preferred embodiment of the invention, this method is also implemented as a computer program and executed by the control and regulating device 32.

In step 160, based on the gem. Fig. 3 determined opening cross section rozme_w and a respective actual engine speed nmot_w a suitable drive signal tavstzme_w determined for the control valve. This is preferably determined on the basis of a characteristic field which has different characteristic curves for different possible actual engine speeds nmot_v, wherein each characteristic curve defines suitable drive signals tavstzme_w as a function of possible opening cross-sections rozme_w.

Claims (12)

1. Method for controlling a fuel injection system (10) of an internal combustion engine, with the fuel injection system (10) comprising a distributor pipe (24) and a high-pressure pump (20), and with the high-pressure pump (20) being assigned a fuel metering unit (16), with the fuel metering unit (16) controlling the amount of fuel delivered, and with an amount of fuel required for the operation of the internal combustion engine being determined as a function of a corrective factor based on a fuel pressure at the inlet of the high-pressure pump (20) and a vapour pressure of the fuel to be supplied, characterized in that, to determine the corrective factor, a pressure difference between the fuel pressure at the inlet of the high-pressure pump (20) and the vapour pressure of the fuel to be supplied is determined.
2. Method according to Claim 1, with the high-pressure pump (20) having a delivery chamber with a check valve arranged at the inlet side, characterized in that, to determine the corrective factor, an opening pressure of the check valve is determined and is subtracted from the pressure difference in order to determine a pressure corrective value.
3. Method according to Claim 2, characterized in that a nominal fuel volume to be supplied to the high-pressure pump (20) is determined, with the required amount of fuel being determined on the basis of the nominal fuel volume and the corrective factor.
4. Method according to Claim 3, characterized in that the corrective factor is determined on the basis of a characteristic curve which defines volume corrective values suitable for possible pressure corrective values.
5. Method according to one of Claims 1 to 4, characterized in that an opening cross section of the regulating valve which must be set in order to supply the required amount of fuel is determined as a function of the corrective factor.
6. Method according to Claim 5, characterized in that an actuation signal for the regulating valve is determined using the opening cross section of the regulating valve and a respective actual engine speed.
7. Method according to Claim 6, characterized in that the actuation signal is determined on the basis of a characteristic curve which defines suitable actuation signals as a function of possible opening cross sections and actual engine speeds.
8. Method according to one of Claims 1 to 7, characterized in that the vapour pressure (Pdampf) is determined from the actual temperature using al. least one reference vapour pressure curve.
9. Method according to one of Claims 1 to 7, characterized in that the vapour pressure (Pdampf) is determined from a post-start and/or warm-up factor and/or a factor of a transition compensation.
10. Method according to one of Claims 1 to 7, characterized in that the admission pressure (Pvoradp) is reduced from an initial value until the delivery rate of the high-pressure pump is zero, and the vapour pressure (Pdampf) is determined from the difference between the admission pressure and an opening pressure (peiv) of a check valve of the high-pressure pump.
11. Computer program having program code for carrying out all the steps according to one of Claims 1 to 7 when the program is executed in a computer.
12. Internal combustion engine having a fuel injection system (10) which comprises a distributor pipe (24) and a high-pressure pump (20), with the high-pressure pump (20) being assigned a fuel metering unit (16) and with the fuel metering unit (16) controlling the amount of fuel delivered, and with an amount of fuel required for the operation of the internal combustion engine being determined as a function of a corrective factor based on a fuel pressure at the inlet of the high-pressure pump (20) and a vapour pressure of the fuel to be supplied, characterized in that, to determined Lhe corrective factor, a pressure difference between the fuel pressure at the inlet of the high-pressure pump (20) and the vapour pressure of the fuel to be supplied is determined.

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