EP1828580B1 - Method and device for supplying internal combustion engines with fuel - Google Patents

Description

The invention relates to a method and a device for supplying fuel to internal combustion engines with an injection system by means of a high-pressure pump, in particular for the supply of common-rail systems, in which a prefeed pump supplies the high-pressure pump with fuel.

It is known to increase the fuel injection pressure to improve the performance of internal combustion engines with cylinder injection system and the reduction of exhaust gas so that the fuel is atomized into fine droplets. The internal combustion engine fueling system is therefore designed to achieve the typical high pressure values of 4 to 10 MPa for current systems.

Known fuel supply systems, such as in the DE 41 26 640 A1 are divided into a low-pressure and a high-pressure system. The pre-conveyed from the fuel tank by means of a low-pressure fuel pump and set under a slight pre-pressure fuel is delivered to the high-pressure pump, which is designed as a radial piston pump. The fuel pressure is further raised to a predetermined pressure value. The system pressure is controlled in the high-pressure system, wherein the actual pressure is detected by means of a high-pressure sensor, compared in a motor control unit with a desired pressure and a control value for a pressure relief valve is determined. In a common high-pressure common rail, the required pressure is adjusted and the excess amount of fuel throttled via a return line to the tank. The high pressure is regulated to the high pressure setpoint regardless of the amount of fuel injected into the engine. The excess amount of fuel can also be selectively guided in an additional purge stream. However, this raises the problem of excessive fuel heating.

According to the DE 196 52 831 A1 For example, instead of being returned to the tank, the fuel may be returned to the high pressure pump where it may be immediately re-compressed, which improves the efficiency of the fuel supply system.

The desired pressure of the low-pressure system is usually also regulated and variably predefined as a function of the vapor pressure curve of the fuel to be assumed in the worst case and determined adaptation values.
The detected by means of a low pressure sensor actual pressure is compared with the target pressure and processed in an engine control unit to a controller response, at the same time an adjusted adaptation value for the target pressure is determined and set. By means of the controller response of the low-pressure control, target pressure, adaptation value and the current fuel mass flow, a characteristic map with values for the delivery capacity requirement of the low-pressure pump, which is usually designed as an electric fuel pump, is addressed in the engine control unit and a power value for the pump is determined and output.

In the hot and cold start usually the target pressure assumes its highest values. In the hot start a vapor bubble formation must be avoided because the high pressure pump can no longer produce high pressure steam formation and in the cold start of the injectors a large amount of fuel must be injected into the combustion chamber with not yet active high pressure pump.

With increasing admission pressure, however, the delivery rate of the low-pressure pump decreases, so that at certain operating points with high target pressure, the low-pressure pump is very heavily loaded and may encounter its delivery limits.

On the one hand to prevent vapor bubble formation in the internal combustion engine and on the other hand to ensure the supply of the internal combustion engine with fuel in all operating states, is in the DE 199 51 410 A1 proposed to set the lowest possible form, in which evaporation of the fuel is still avoided set. For this purpose, the current temperature of the fuel in the high-pressure pump is determined and, depending on the determined temperature, the low-pressure pump is controlled or regulated such that it generates the determined admission pressure.

In addition to the temperature, however, the quality of the fuel has a decisive influence on the formation of vapor bubbles, since different fuels evaporate at different temperatures. In order to ensure a safe operation of the internal combustion engine, the form is usually set to the worstcase case with a large tolerance control. An optimal setting of the form is therefore not or only by further measures, such as a additional refueling recognition possible.

Furthermore, the system properties of the pressure systems during the life of the internal combustion engine, which can not be compensated or only by further increased tolerances with the known regulations, which also leads to an increased pressure level in the fuel supply system and thus to an unnecessarily high power consumption of the low-pressure pump.

From the DE 101 58 950 A1 a method for operating an internal combustion engine is known, wherein fuel is compressed by a first fuel pump to a pre-pressure, which is applied to a low-pressure side of a second fuel pump. The desired desired pressure is determined by means of a stored temperature-pressure relationship from a current temperature of the fuel in the second fuel pump. The pre-pressure is lowered from an initial value based on a standard temperature / pressure relationship and the lowering of the pre-pressure is terminated when cavitation in the second fuel pump exceeds a permissible level, with a difference between the original pre-pressure and the reduced pre-pressure for adaptation the standard temperature / pressure relationship is used,

From the DE 103 00 929 A1 a fuel injection system is known, wherein the delivery pressure of a first pump in dependence on the fuel temperature and the evaporation behavior of the fuel is adjusted.

From the DE 102 00 795 A1 a fuel system of an internal combustion engine is known in which an estimated temperature is taken into account in the control and / or regulation of at least one component of the fuel system. To avoid cavitations of a high-pressure pump, the aim is to avoid cavitation by adapting the admission pressure as a function of measured fuel temperatures.

From the DE 100 01 882 A1 is a method for preventing cavitation in a high pressure pump by means of adaptation of the form as a function of measured fuel temperature known.

It is therefore an object of the present invention to provide a simple, accurate and secure setting of the generated by a low-pressure pump form to promote fuel for an internal combustion engine.

The object is achieved by a method according to claim 1 and a device according to claim 14.

The inventive method for supplying fuel to internal combustion engines, in which a low-pressure pump and a high-pressure pump promote the fuel for the internal combustion engine, the low-pressure pump provides a flow rate of fuel for the high-pressure pump and generates a voltage applied to the high-pressure pump form and the high-pressure pump, the flow rate with an injection pressure in an injection system of the internal combustion engine and in which the admission pressure is set to a determined by the vapor pressure curve of a fuel, variable target form, the injection pressure is controlled by a high pressure regulator and a corresponding to the desired form control value of the low pressure pump is corrected with an adaptation value characterized in that the adaptation value is determined in an adaptation mode of the fuel supply, wherein in the adaptation mode, the form pressure is changed until vapor bubbles before the high dr form the back pressure pump, the formation of vapor bubbles are detected by changing a regulator response of the high pressure regulator and in a detection of vapor bubbles current process parameters, preferably features of the low pressure pump and the temperature of the fuel, are determined, from which the adaptation value is derived. The target admission pressure set with the adaptation value is always higher than the vapor pressure of the fuel. In adaptation mode, the vapor bubbles are generated in such a way that the full function of the engine is given in each phase. To ensure this, the vapor bubble formation is preferably only very short or in the approach. According to the invention, the admission pressure in the adaptation mode is changed by an oscillation impression to the activation value of the low-pressure pump corresponding to the desired admission pressure, so that an oscillation is imparted to the delivery capacity of the low-pressure pump. During this pressure oscillation is the high-pressure controller monitoring active. If there is a vapor bubble formation in the oscillation valley upstream of the high-pressure pump, this is detected by the change in the controller response. If there is no change in the controller value, the desired admission pressure is lowered by a defined value and the adaptation mode continues until a detection of vapor bubbles has taken place. The nominal admission pressure is lowered in particular by lowering an applied adaptation start value. In order to ensure that the lowered adaptation start value does not permanently lower the desired admission pressure to vapor bubble formation, the reduced adaptation start value determined during vapor bubble formation is preferably set high by a defined value, and the adaptation value is derived from the lowered adaptation start value.

The applied vibration adjusts the admission pressure in the adaptation mode so that vapor bubbles can always form in the fuel only for a short time and thus a pressure drop in the high-pressure system is avoided.

The device according to the invention for supplying fuel to an internal combustion engine comprises at least one regulated high-pressure system and a controlled low-pressure system. The controlled high-pressure system has at least one injection system for injecting fuel into the internal combustion engine, a high-pressure pump for conveying fuel from the low-pressure system into the injection system and a high-pressure regulator for controlling an injection pressure in the injection system. The controlled low-pressure system has at least one low-pressure pump for pumping fuel from a tank into the high-pressure system, a control unit for setting a variable nominal pressure set by the vapor pressure curve of a fuel in the low-pressure system with an adaptation unit for generating an adaptation value in an adaptation mode for correcting the predetermined target Form on. The adaptation unit has at least one unit for triggering the adaptation mode, in which a form pressure in the low pressure system is varied, means for detecting the change of a controller response of the high pressure regulator in the adaptation mode in the formation of vapor bubbles in the low pressure system, means for detecting process parameters and a unit for deriving the adaptation value from the detected process parameters as well as means for changing the admission pressure in the adaptation mode by an oscillation impact to the control value of the low-pressure pump corresponding to the target admission pressure. By the latter measure, a vibration is impressed on the delivery of the low pressure pump.

As internal combustion engines, which are supplied with the inventive method and apparatus according to the invention with fuel, both diesel engines and spark-ignited engines come into consideration.

With the help of the high-pressure regulator according to the invention in an adaptation mode, a statement about the outgassing behavior of the fuel and the state of the low-pressure pump is made. As soon as steam bubbles form in the adaptation mode in front of the high-pressure pump, the delivery rate of the high-pressure pump deteriorates. The high-pressure regulator always shows a clear regulator response to the worsening degree of delivery. This controller response is used to determine an adaptation value for the correction of the nominal form pressure to be set by the low-pressure pump.

The high-pressure regulator preferably regulates the injection pressure in the injection system by means of a quantity-controlled high-pressure pump. The injection system is preferably designed as a common-rall system (system with common line). The pressure generation and the fuel injection are separated or decoupled in the common rail system. The high-pressure pump continuously generates a specific high pressure, which is permanently available in the injection system as injection pressure. The high pressure is regulated and stored in the common line of the injection system and provided via short injection lines to the injectors for injecting the fuel into the cylinders of the engine. In this case, a high pressure in the two-digit Mpa range is usually generated in the line.

In an advantageous embodiment of the invention, in which the fuel supply is non-return, ie without fuel return is to promote the fuel from the high-pressure pump, which is designed in particular as a reciprocating piston pump, during the downward movement of the piston, a volume of fuel via an open quantity control valve, which is arranged between the high and the low pressure pump, promoted in the displacement of the pump. With an upward movement of the piston and closed quantity control valve, the fuel is compressed and conveyed into the injection system. The pressure detection is preferably carried out via a high pressure sensor arranged in the injection system. The setting of the target injection pressure by means of the high pressure control, in which the quantity control valve is used as an actuator.

To determine the adaptation value, the admission pressure is changed, in particular lowered by stepwise lowering of the delivery rate of the low-pressure pump, which is preferably designed as an electric fuel pump, until vapor bubbles are detected in the system. The vapor bubble formation is related to the specific vapor pressure, i. together with the specific pressure of the saturated vapor of the fuel. This is composed of the sum of the partial pressures of its individual components and is dependent on the temperature. If the pressure in the low-pressure system is lower than the specific vapor pressure of the fuel, vapor bubbles form. In the adoption mode, the fuel pressure limit of the fuel is targeted until the delivery rate of the high pressure pump deteriorates significantly and a defined deviation of the regulator response is achieved.

If the fuel introduced into the lift or compression space of the high-pressure pump consists of fractions of vapor bubbles, for example, an additional compression volume must be provided for pushing the vapor bubbles together in order to convey the same amount of fuel. The change in this controller response can preferably be used to detect vapor bubbles.

In an advantageous embodiment of the method, the admission pressure in the adaptation mode is reduced stepwise, with or without vibration imposition, until a predetermined maximum permissible change of the regulator response or a minimum permissible admission pressure is achieved. In this case, the nominal admission pressure from the vapor pressure curve of the fuel to be assumed in the worst case is preferably predetermined at the start of the adaptation mode. The vapor pressure curve shows the temperature dependence of the vapor pressure and is shown in the pressure-temperature diagram as a limit curve between the two phases liquid and gaseous. The vapor pressure curve depends on the fuel type. The worst case fuel is the highest volatility fuel, for example, freshly fueled winter fuel with a vapor pressure of 12 to 14 PSI.

When the predefined maximum permissible change in the controller response is reached, in an advantageous embodiment the current value of the delivery rate of the low-pressure pump and the current value of the temperature of the fuel are detected by suitable means and the adaptation value in the unit for deriving the adaptation value is determined from these values. The determination preferably takes place via characteristic maps with characteristic curves which specify the associated adaptation values for specific delivery rates and temperatures.

Upon reaching the predetermined maximum permissible change of the controller response, the current value of the lowered admission pressure is detected in a further advantageous embodiment, increased by a defined value and derived therefrom current adaptation value.

The adaptation value is preferably stored and used for a calculation of the delivery power requirement of the low-pressure pump.
The determined adaptation value represents both the tolerance position of the low-pressure pump and the current outgassing activity of the fuel. Changes in the outgassing activity and the pump properties are thus taken into account and the low-pressure pump can work with setting the corrected with the determined adaptation value target form with optimal low power consumption.

The adaptation value is not constantly determined during the fuel supply, but rather in an adaptation mode, which is preferably triggered at regular intervals or by defined boundary conditions by a unit for triggering the adaptation mode, for example when the engine has been operated for a defined time or restarted after a longer downtime. Wherein the adaptation mode is preferably started only when stable operating or system conditions are present, in particular when the fuel mass flow and the temperature of the fuel before the high-pressure pump are stable. After the adaptation value has been determined, the adaptation mode is left again and the fuel supply runs in normal operation, wherein the corrected nominal admission pressure profile is set in the low-pressure system and the injection pressure in the high-pressure system is regulated. An appropriate frequency of the adaptation mode ensures that changes in the fuel quality and properties of the low-pressure pump are considered in good time.

Fig.1

eine schematische Darstellung des Kraftstoffversorgungssystems gemäß Beispiel A und B

Fig. 2

eine schematische Darstellung der erfindungsgemäßen Steuerung der Niederdruckpumpe mit einem Adaptionsmodus gem. Fig.4 (Beispiel A)

Fig.3

eine schematische Darstellung der erfindungsgemäßen Steuerung der Niederdruckpumpe mit einem Adaptionsmodus gem. Fig. 5 (Beispiel B)

Fig. 4

schematische Darstellung des Adaptionsmodus ohne Schwingungsaufprägung (Beispiel A)

Fig. 5

schematische Darstellung des Adaptionsmodus mit Schwingungsaufpragung (Beispiel B)

The invention will be explained in more detail with reference to exemplary embodiments. It shows

Fig.1

a schematic representation of the fuel supply system according to Example A and B.

Fig. 2

a schematic representation of the control of the low pressure pump according to the invention with an adaptation mode gem. Figure 4 (Example A)

Figure 3

a schematic representation of the control of the low pressure pump according to the invention with an adaptation mode gem. Fig. 5 (Example B)

Fig. 4

schematic representation of the adaptation mode without oscillation impulse (example A)

Fig. 5

Schematic representation of the adaptation mode with vibration superimposition (example B)

Example A: Adaptation mode without vibration impact

Fig.1 shows a schematic structure of an exemplary fuel supply system according to the invention with a controlled return-free high-pressure system 1 and a controlled low pressure system 2 for supplying a direct injection internal combustion engine 4 with fuel from a tank (not shown).

The low-pressure pump 7 is designed as an electric fuel pump and conveys the fuel from a tank to the high-pressure pump 5. The subsidized by the low-pressure pump 7 fuel is applied with a form at the high-pressure pump 5 .

The high pressure system 1 is a controlled system. The high-pressure pump 5 is designed as a volume-controlled lifting piston pump with a quantity control valve 19 and supplies the injection system 3 with fuel. The injection system 3 is designed as a common-rail system, so that the high-pressure pump 5 generates a permanent high injection pressure in the injection system 3 . The high-pressure regulator 6 regulates the injection pressure, wherein the actual injection pressure is detected via a high-pressure sensor 20 arranged in the injection system 3 and is processed in the high-pressure regulator 6 to form a control signal for the quantity control valve 19 .

To fill the lifting or compression chamber of the high-pressure pump 5 , the piston of the high-pressure pump moves downwards, wherein the quantity control valve 19 is opened and fuel is conveyed from the low-pressure system 2 into the high-pressure system 1 . The degree of delivery depends on the form and the quality of the fuel. During the upward movement of the piston of the high-pressure pump 5 , the fuel is compressed only when the quantity control valve 19 is closed. The amount of time that the quantity control valve 19 remains closed determines the amount of fuel delivered to the injection system 3 .

The low-pressure system 2 is a controlled system. The target admission pressure of the controlled low-pressure system 2 is variably predetermined by the vapor pressure curve 9 of the fuel to be assumed in the worst case, for example winter fuel with 12 to 14 PSI and an adaptation value determined by the control unit 8 in an adaptation mode. The adaptation value represents both the current tolerance position of the low-pressure pump 7, and the current fuel quality.

The control of the low pressure system 2 is in Fig.2 shown. With the sum of the resulting from the vapor pressure curve 9 pressure value and the adaptation value and the current fuel flow rate, a pilot control map 16 is addressed. The pilot control map 16 contains values for the delivery requirement of the low-pressure pump 7 as a function of pressure and fuel flow rate. The value for the delivery request is corrected via the voltage, the start overshoot and the fuel cut correction 18 and output to the power output stage of the low-pressure pump 7 .

The adaptation value is in a, in Fig. 4 schematically illustrated adaptation mode determined by the adaptation unit 10 . The determination is not continuous, but is actively learned in individual discrete events. A Lemereignis takes place when previously defined boundary conditions are met and recognizes in the unit for triggering 11 of the adaptation mode 12 Lembedarf. Lembedarf is detected when the engine 4 is restarted after a shutdown and the tank level has undergone a significant change or when the engine 4 was operated for a defined time. The defined boundary conditions also include stable operating conditions of the fuel supply system, which are recognized, for example, by steady-state process parameters such as temperature of the fuel and fuel mass flow at a defined level.

If the unit for triggering 11 detects a learning event, it is switched over to adoption mode 12 by means of a switch 17 and started. This lowers the subsidy requirement ( Figure 4 , Curve y2) of the low-pressure pump 7 from stepwise, whereby the form ( Figure 4 Curve y1) in the low-pressure system drops until vapor bubbles form in front of the high-pressure pump 5 . As a criterion of the detection of vapor bubble formation, a specific change of the controller response ( Figure 4 Curve y4) of the high-pressure regulator 6 is used. If the fuel delivered into the high-pressure pump 5 consists of fractions of vapor bubbles, the quantity control valve 19 must remain closed longer in order to convey the same amount of fuel into the injection system 3 . There must be an additional compression volume for pushing the Steam bubbles are provided, whereby the controller response increases by a certain pressure value. The change is registered with means for detecting the change in the governor response 13 , and when the governor response is increased by a defined pressure value of, for example, 0.3 Mpa, the detection of the fuel temperature at that time ( Figure 4 Curve y3) in front of the high-pressure pump 5 and the power output request applied to the power output stage of the low-pressure pump 7 is triggered. These parameters are determined by appropriate means for detecting process parameters 14, in particular means for detecting the temperature 14.2 and means for detecting Leistungsuhgsmerkmalen 14.1 of the low-pressure pump 7 and stored in the unit for deriving 15 . The stored values of the current delivery request and temperature of the fuel are read into a map of the unit for deriving 15 , with the map from the stored values, a current adaptation value is derived. This map may have been previously determined empirically, for example. Alternatively, an empirically determined formula can be used instead of the characteristic field:

The active adaptation mode 12 is then left again. The switch to normal operation is made with the switch 17, wherein the earliest time of switching to normal operation is the time of detection of vapor bubbles and the latest time of conversion, should be the time of determination of the adaptation value, the degree of delivery of the high pressure pump 5 does not deteriorate significantly.

In normal operation, the control of the admission pressure of the low-pressure system 2 then takes place with a corrected nominal admission pressure which results from the sum of the pressure value resulting from the vapor pressure curve 9 as a function of the temperature of the fuel upstream of the high-pressure pump and the currently determined adaptation value.

Example B: Adaptation mode with vibration imprint

The fuel supply system in Example B, analogous to Example A also consists of a regulated return-free high-pressure system 1 and a controlled low-pressure system 2, as in Fig. 1 shown. The mode of operation differs due to the execution of the adaptation mode with a vibration impact on the delivery power requirement of the low-pressure pump 7.

The high-pressure system 1 is, as already stated in Example A, a regulated system.

The low-pressure system 2 is a controlled system and in Figure 3 shown schematically. The target pre-pressure of the controlled low-pressure system 2 is variably set by the vapor pressure curve 9 by detecting the temperature of the fuel upstream of the high-pressure pump 5 with means for detecting the temperature 14.2 and to a fuel to be assumed by the vapor pressure curve 9 of the worst case fuel, for example winter fuel With 12 to 14 PSI, given map is read, derived from a pressure value and an adaptation value is added. The adaptation start value and / or the adaptation value determined in an adaptation mode is predetermined by the adaptation unit 10 . The adaptation value determined in the adaptation mode represents both the current tolerance position of the low-pressure pump 7 and the current fuel quality.

With the corrected target form a pilot control map 16 is addressed. The pilot control map 16 contains values for the delivery capacity requirement of the low-pressure pump 7 as a function of the pressure. The value for the delivery request is corrected via the voltage, the start overshoot and the fuel cut correction 18 and output to the power output stage of the low-pressure pump 7 .

The adaptation value is in a, in Fig. 5 schematically illustrated adaptation mode determined by the adaptation unit 10 . The determination is not continuous, but is, as stated in Example A, actively learned in individual discrete events.

If the unit for triggering 11 recognizes a learning event, the adoption mode 12 is started, wherein the applied adaptation starting value remains unchanged in a first step and the conveying power requirement ( Figure 5 Curve y2) of the low-pressure pump 7, a vibration is impressed, wherein the admission pressure in the low pressure system is varied accordingly. If no vapor bubbles are detected, the predetermined adaptation start value ( Fig. 5 Curve y1) is gradually lowered until vapor bubbles form in front of the high-pressure pump 5 . As a criterion of the detection of vapor bubble formation, a specific change of the controller response ( Figure 5 Curve y3) of the high-pressure regulator 6 is used. This change is registered with means for detecting the change of the controller response 13 , whereby, when the controller response is increased by a defined volume value, the lowered adaptation start value present at this time is detected. This process parameter is used in the unit for Derived 15 and increased by a safety value and thus derived the adaptation value.

The active adaptation mode 12 is then left again. In normal operation, the control of the admission pressure of the low-pressure system 2 then takes place with a corrected nominal admission pressure, which results from the sum of the pressure value resulting from the vapor pressure curve 9 and the currently determined adaptation value.

Claims (22)

1. Method for supplying fuel to an internal combustion engine, in which method

   - a low-pressure pump and a high-pressure pump deliver a fuel for the internal combustion engine,

   - the low-pressure pump provides a delivery quantity of fuel for the high-pressure pump and generates a pilot pressure which prevails at the high-pressure pump, and

   - the high-pressure pump provides the delivery quantity at an injection pressure in an injection system of the internal combustion engine, and in which method

   - the pilot pressure is set to a variable setpoint pilot pressure which is defined by the vapour pressure curve of a fuel,

   - the injection pressure is regulated by way of a high-pressure regulator, and

   - an actuating value of the low-pressure pump, which actuating value corresponds to the setpoint pilot pressure, is corrected with an adaptation value,

   - the adaptation value is determined in an adaptation mode,

   - in the adaptation mode,

   - the pilot pressure being changed until vapour bubbles form upstream of the high-pressure pump,

   - a formation of vapour bubbles being detected by the change in a regulator response of the high-pressure regulator, and

   - in the case of a detection of vapour bubbles, actual method parameters being determined, from which the adaptation value is derived,

   - a setpoint pilot pressure being set which is higher than the vapour pressure of the fuel,

   characterized in that the pilot pressure is changed in the adaptation mode by impressing an oscillation onto the actuating value of the low-pressure pump, which actuating value corresponds to the setpoint pilot pressure.
2. Method according to Claim 1, characterized in that the pilot pressure is lowered step by step in the adaptation mode.
3. Method according to one of the preceding claims, characterized in that the adaptation mode is carried out at predefined intervals in the case of stable operating conditions.
4. Method according to one of the preceding claims, characterized in that the adaptation mode is carried out after a re-start of the engine in the case of stable operating conditions.
5. Method according to one of the preceding claims, characterized in that the setpoint pilot pressure is predefined from the vapour pressure curve of the fuel which is to be assumed in the worst case.
6. Method according to one of the preceding claims, characterized in that the pilot pressure is lowered in the adaptation mode until a predefined maximum permissible change in the regulator response is achieved.
7. Method according to one of the preceding claims, characterized in that the pilot pressure is lowered by lowering of an adaptation starting value, and the lowered adaptation starting value is determined as an actual method parameter, from which the adaptation value is derived.
8. Method according to one of the preceding claims, characterized in that performance characteristics of the low-pressure pump are determined as actual method parameters, from which the adaptation value is derived.
9. Method according to one of the preceding claims, characterized in that the temperature of the fuel is determined as an actual method parameter, from which the adaptation value is derived.
10. Method according to Claims 8 and 9, characterized in that, when the predefined maximum permissible change in the regulator response is reached, the actual value of the delivery rate of the low-pressure pump and the actual value of the temperature of the fuel are detected, and the adaptation value is derived from these values.
11. Method according to one of preceding Claims 8 to 10, characterized in that the adaptation value is derived from at least one characteristic diagram which assigns adaptation values to method parameters.
12. Method according to one of the preceding claims, characterized in that the adaptation mode is quit after determination of the adaptation value.
13. Method according to one of the preceding claims, characterized in that the formation of vapour bubbles is detected by way of a compression volume, to be additionally applied and resulting as a regulator response, of the high-pressure pump in order to deliver an identical quantity of fuel.
14. Apparatus for supplying fuel to an internal combustion engine, at least comprising

    - a regulated high-pressure system (1) having at least

    - an injection system (3) for injecting fuel into the internal combustion engine (4),

    - a high-pressure pump (5) for delivering fuel from a low-pressure system (2) into the injection system (3), and

    - a high-pressure regulator (6) for regulating an injection pressure in the injection system (3),

    and

    - a controlled low-pressure system (2) having at least

    - a low-pressure pump (7) for delivering fuel from a tank into the high-pressure system (1), and

    - a control unit (8) for setting a variable setpoint pilot pressure in the low-pressure system (2), which variable setpoint pilot pressure is predefined by the vapour pressure curve (9) of a fuel, with an adaptation unit (10) for generating an adaptation value in an adaptation mode (12) for correcting the predefined setpoint pilot pressure, the adaptation unit (10) having at least

    - a unit for triggering (11) the adaptation mode (12), in which a pilot pressure in the low-pressure system is changed,

    - means for detecting the change in a regulator response (13) of the high-pressure regulator (6) in the adaptation mode (12) in the case of the formation of vapour bubbles in the low-pressure system,

    - means for detecting method parameters (14),

    - a unit for deriving (15) the adaptation value from the detected method parameters,

    characterized in that means are provided which bring about a change in the pilot pressure in the adaptation mode by impressing an oscillation onto the actuating value of the low-pressure pump, which actuating value corresponds to the setpoint pilot pressure.
15. Apparatus according to Claim 14, characterized in that, in order to regulate the injection pressure, the high-pressure regulator (6) is connected to a quantity control valve (19), which is arranged between the low-pressure pump (7) and the high-pressure pump (5), and to a high-pressure sensor (20) which is arranged in the injection system (3).
16. Apparatus according to either of Claims 14 and 15, characterized in that the high-pressure pump (5) is a reciprocating piston pump.
17. Apparatus according to one of preceding Claims 14 to 16, characterized in that the means for detecting the change in the regulator response (13) are means for detecting a compression volume, to be additionally applied, of the high-pressure pump in order to deliver an identical quantity of fuel in the case of the formation of vapour bubbles.
18. Apparatus according to one of preceding Claims 14 to 17, characterized in that the low-pressure pump (7) is an electric fuel pump.
19. Apparatus according to one of preceding Claims 14 to 18, characterized in that the means for detecting method parameters (14) comprise means for detecting performance characteristics (14-1) of the low-pressure pump.
20. Apparatus according to one of preceding Claims 14 to 19, characterized in that the means for detecting method parameters (14) comprise means for detecting the temperature (14.2) of the fuel.
21. Apparatus according to one of preceding Claims 14 to 20, characterized in that the unit for deriving (15) the adaptation value has at least one characteristic diagram which assigns adaptation values to method parameters.
22. Apparatus according to one of Claims 14 to 21, characterized in that the injection system (3) is a common rail system.

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