KR20160011585A - Method for adapting fuel pressure in low pressure region of fuel direct injection system - Google Patents

Abstract

The present invention relates to a method for adjusting the fuel pressure (p) in a low pressure region of a fuel direct injection system of an automobile. The method includes setting a high-pressure temperature (T _141); and the high-pressure temperature low-pressure region within the fuel pressure (T ₁₄₁₎ to the reference fuel is in the liquid phase value in (p) for detecting in the high-pressure pump of a fuel direct injection system, Reducing the fuel pressure p in the low pressure region until a reduction in the transfer capacity of the high pressure pump of the fuel direct injection system is detected through reduction of the pressure in the distribution pipe of the fuel direct injection system, Raising the fuel pressure p by an applicable first offset O ₁ and raising the fuel pressure p in the low pressure region by a second offset O ₂ to an adjusted fuel pressure p _adap as, at this time the second offset (O ₂₎ is a step which, based on the fuel is selected according to the temperature-dependent change of the target pressure (p _soll) is present in the liquid phase.

Description

FIELD OF THE INVENTION The present invention relates to a method for adjusting a fuel pressure in a low-pressure region of a direct fuel injection system,

The present invention relates to a method for adjusting the fuel pressure in a low pressure region of a fuel direct injection system. The invention also relates to a computer program adapted to carry out the respective steps of the method according to the invention and to a machine-readable storage medium in which the computer program according to the invention is stored. Finally, the present invention relates to an electronic control device provided for adjusting the fuel pressure in the low-pressure region of a fuel direct injection system of an automobile by the method according to the present invention.

Fuel direct injection fuel is directly injected into the combustion chamber of the internal combustion engine through the high pressure injection valve by the pressure up to 20 MPa. This pressure is generated by a high-pressure pump driven by a drive cam on the camshaft of the internal combustion engine. The fuel supply is made through the low pressure system of the fuel system. Safe fuel transfer is possible only when the high-pressure pump can suck the liquid fuel. By directly installing a high-pressure pump in the internal combustion engine, the high-pressure pump can be very hot. The fuel in the high pressure pump is present only as a liquid until the fuel reaches a pressure higher than the vapor pressure of the fuel just used in the low pressure system. The pressure loss that may occur in the intake valve should be considered separately. Because fuel can have a wide variety of vapor pressures depending on the season and ethanol ratio, the low pressure setting is fitted to the vapor pressure curve of the most critical fuel actually expected.

The low pressure is generated by an electronic fuel pump in the tank. The electronic fuel pump is typically measured by a low pressure by setting a target value that can be implemented with a variable low-pressure setting, demand-controlled fuel supply - a part of the fuel supply system for the (co de mand ntrolled s upply DECOS). The target value is set to a case where it can be considered most unfavorably, and is applied as a low-pressure target characteristic curve according to the temperature. However, this necessitates an unnecessarily high drive output of the electronic fuel pump, resulting in carbon dioxide emission of unnecessarily high vehicle.

Of course, a DECOS system without a low-pressure sensor is also used. In order to derive the low pressure required in this reasoning, the driving of the electric fuel pump and the low pressure together therewith decrease stepwise until the high pressure pump no longer sufficiently transfers during engine operation and the high pressure begins to deviate from its target value . Then, the high-pressure pump reaches a point where it is operated with steam to an unacceptable degree. In this case, the drive value of the electronic fuel pump must be increased by an arbitrary offset. As a result, the low pressure rises to a sufficiently high value again. Of course, not only is the amount of fuel not known in this concept, but above all, the transport capacity of the electronic fuel pump is also under various operating conditions. Therefore, in this concept, it must be operated mainly in the vapor state and adjusted later. 30,000 to 40,000 learning cycles can be expected over the life of the fuel supply system. However, frequent steam operation of the high pressure pump can damage the high pressure pump because in most locations in the high pressure pump there is a lack of hydraulic damping by the liquid fuel or lubrication by the liquid fuel is no longer guaranteed Because. This is particularly dangerous if high pressure maintenance is still possible but the current low pressure in the high pressure pump already leads to localized vapor formation.

The method according to the present invention for adjusting the fuel pressure in a low pressure region of a fuel direct injection system of an automobile, in particular a DECOS system,

- detecting the high pressure temperature in the high pressure pump of the fuel direct injection system,

- setting the fuel pressure in the low pressure region to a value at which the reference fuel is present in the liquid phase at the high pressure temperature,

Reducing the fuel pressure in the low pressure region until a reduction in the transfer capacity of the high pressure pump of the fuel direct injection system is detected through pressure reduction in the distribution line of the fuel direct injection system,

- raising the fuel pressure in the low pressure region by an applicable first offset,

- raising the fuel pressure in the low pressure region to a regulated fuel pressure by a second offset, wherein the second offset is selected in accordance with a temperature dependent change in the target pressure in which the reference fuel is in the liquid phase.

As the reference fuel, in particular, a fuel having the most unfavorable vapor pressure curve that can be actually expected is used.

With the method according to the invention, the fuel direct injection system can be operated with a low drive output of the electronic fuel pump, without the need for a large number of learning cycles in which the high pressure pump is operated with steam. Here, although variable, a sufficiently high low pressure is ensured for the safe operation of the fuel direct injection system.

The high pressure temperature is in particular the temperature of the fuel present in the high pressure pump or the temperature proportional to the temperature of the fuel present in the high pressure pump.

When a high temperature is calculated using the temperature model, it is preferable that the first offset is applied according to the tolerance of the temperature model. In this way, the method according to the present invention can take into account the plus / minus tolerance of the temperature model, so that the high-pressure pump can be prevented from unintentionally operating with steam.

The method according to the invention is preferably repeated for a plurality of different high pressure temperatures. The temperature dependence of the regulated fuel pressure is calculated from each regulated fuel pressure. This allows an optimal low pressure characteristic curve of the fuel direct injection system to be derived with little learning cycles.

It is particularly preferred that the pressure in the low pressure region is set to a value derived from the detected temperature dependence of the regulated fuel pressure according to the high pressure temperature until next time the fuel is injected into the vehicle. Thus, for example, if the learning period per tank charge is eight, the total number of cycles over the lifetime of the fuel direct injection system is reduced by approximately 3,000 to 5,000 cycles.

In an embodiment of the method according to the invention, a second offset is selected according to a first derivative of the temperature dependent change of the target pressure with temperature. This is due to the tangent to the low pressure curve of the reference fuel at the high pressure temperature, that is, the temperature dependent change of the target pressure with temperature is applied to yield the first derivative. The second offset is then derived from the difference between the temperature tolerance and the tangent slope.

In one alternative embodiment of the method according to the present invention, a second offset is selected according to the slope of the temperature dependent change of the target pressure between the two sample temperatures. At this time, the first sample temperature is higher than the high-pressure temperature, and the second sample temperature is lower than the high-pressure temperature. This procedure is provided particularly where temperature-dependent changes in the target pressure are stored for multiple sampling points.

A computer program according to the present invention is adapted to perform each step of the method according to the invention, particularly when the computer program is run on a computer or a control device. In this way, the method according to the present invention can be implemented by an existing computer or a control device without the necessity of performing a structural change. In order to execute a computer program according to the present invention in a computer or a control device, a machine-readable storage medium according to the present invention in which a computer program according to the present invention is stored is provided. By executing the computer program according to the present invention in a conventional electronic control apparatus, an electronic control apparatus according to the present invention, which is provided for adjusting the fuel pressure in the low-pressure region of the fuel direct injection system of an automobile by the method according to the present invention, is obtained .

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic diagram of a fuel direct injection system of a motor vehicle in which the fuel pressure in the low pressure region can be adjusted according to an embodiment of the method according to the invention.
2 is a pT graph showing the fuel pressure regulation in the low pressure region of the fuel direct injection system according to FIG. 1 using a method according to an embodiment of the present invention.

The sequence of the method according to embodiments of the present invention is described below in the example of fuel pressure adjustment in the low pressure region of the DECOS system. This DECOS system has the fuel direct injection system 1 shown in Fig. The fuel 111 is stored in the fuel tank 11. The fuel line from the fuel tank 11 is guided into the electronic fuel pump 131 through the fuel filter 12. This electronic fuel pump transfers the fuel 111 from the fuel tank 11 into the low pressure region 13 of the direct fuel injection system 1. [ A first pressure sensor 132 is provided to measure the fuel pressure p in the low pressure region 13. The high pressure pump 141 compresses the fuel 111 and transfers the fuel into the high pressure region 14 of the direct fuel injection system 1. [ In the high pressure region 14, the compressed fuel 111 is guided from the high-pressure pump 141 into the distribution pipe 142, also referred to as a rail. In the high-pressure region 14, a second pressure sensor 143 is disposed to detect the existing pressure therein. Four injectors 144a, 144b, 144c, and 144d inject fuel 111 from the distribution pipe 142 into the internal combustion engine (not shown). An electronic control unit (2) controls components of the fuel direct injection system (1).

The method according to the first embodiment of the present invention is started to adjust the fuel pressure p in the low pressure region 13 after the fuel tank 11 replenishes the new fuel 111. [ To this end, the temperature T ₁₄₁ of the fuel 111 in the high-pressure pump ₁₄₁ is first calculated using the temperature model. The control device 2 is supplied with the target pressure p _soll of the fuel pressure p in the low pressure region 13 in accordance with the high pressure temperature T ₁₄₁ in the high pressure pump 141 with respect to the reference fuel RSG E10 Pressure low-pressure characteristic curve is stored. The fuel pressure p in the low-pressure region 13 by the electronic fuel pump 131 is first set to the target pressure p _soll for the high-pressure temperature T ₁₄₁ detected using the temperature model. Due to this, the fuel pressure p in the low-pressure region 13 takes the first value p ₁ , as shown in Fig. The fuel pressure p in the low-pressure region is then reduced by the second pressure sensor 143 to a second value at which a reduction in the transfer capacity of the high-pressure pump 141 and a small pressure drop in the distribution pipe 142 are detected (p ₂₎ until a decrease in the fuel pressure (p), it is reduced by the reduction in capacity of the electronic fuel pump (131). This indicates that the second pressure p ₂ of the currently injected fuel 111 is below the vapor pressure curve p _gas of the fuel 111 at the high pressure temperature T ₁₄₁ . The fuel pressure p in the low pressure region 13 is now raised to the third pressure p ₃ by the first offset O ₁ by first increasing the capacity of the electronic fuel pump 131. The first offset (O ₁ ) is selected according to the tolerance of the temperature model used. Then the capacity of the electronic fuel pump 131 is further increased to increase the fuel pressure p in the low pressure region 13 by the second offset O ₂ to the fourth pressure p ₄ . In order to calculate the second offset (O ₂ ), the first derivative (dp _soll / dT) of the low pressure curve p _soll of the reference fuel at the high pressure temperature (T ₁₄₁ ) determined using the temperature model is first calculated. This is the tangent contact with the first derivative of the vapor pressure curve of the reference fuel from the _{(dp soll / dT) (p} soll) is derived, which extends to a third pressure (p ₃₎ as displacement is added to the temperature (T _+). The deviation between the high pressure temperature (T ₁₄₁ ) and the further temperature (T ₊ ) corresponds to the tolerance of the temperature model used. A second offset (O ₂ ) is calculated from the slope of the tangent line over this temperature range. The fourth pressure p ₄ represents one value on the adjusted low pressure curve p _adap of the presently injected fuel 111. The method according to the present invention is repeated for a plurality of different high pressure temperatures (T ₁₄₁ ), whereby a plurality of fourth pressure values (p ₄ ) are calculated and the total of the adjusted low pressure (p _adap ) The low pressure curve can be fitted. The fuel pressure p in the low pressure region 13 is now fed by the electronic fuel pump 131 to the low pressure curve 13 according to this learned low pressure curve to continue to operate the fuel direct injection system 1 with the currently injected fuel 111. [ Is always set to the value (p _adap ).

As an alternative to the method of determining the second offset O ₂ in the manner described above, in a second embodiment of the method according to the invention, a temperature T _{+ which} is higher than the high-pressure temperature T ₁₄₁ and a high- calculating a second offset tangentially instead used in between the application of the low-pressure curve (the sample temperature to the p _soll) of the reference fuel in), and the sample temperature, in the first embodiment _- T ₁₄₁₎ lower still another temperature (T Is determined. As the sample temperatures, the temperatures of the tolerance of the temperature model (T ₊ and T _- ) can be used. Alternatively, different temperatures that lie above and below the high-pressure temperature T < ₁₄₁ > can also be used.

Claims (10)

A method for adjusting a fuel pressure (p) in a low pressure region (13) of a fuel direct injection system (1) of an automobile,
- detecting the high pressure temperature (T ₁₄₁ ) in the high pressure pump (141) of the fuel direct injection system (1)
- setting the fuel pressure p in the low pressure region (13) to a value at which the reference fuel is present in the liquid phase at the high pressure temperature (T ₁₄₁ )
Until the reduction of the transfer capacity of the high pressure pump 141 of the fuel direct injection system 1 is detected through the pressure reduction in the distribution pipe 142 of the fuel direct injection system 1, (p)
- raising the fuel pressure p in the low pressure region 13 by the first applicable offset O ₁ ,
- a step of the second rise by an offset (O ₂₎ to the low pressure region 13, the fuel pressure (p) of the fuel pressure adjusting (p _adap), wherein the second offset (O ₂₎ is based on the fuel is liquid _Wherein the selected target pressure is selected in accordance with a temperature-dependent change in the target pressure (p _soll ) present in the low pressure region of the fuel direct injection system. The high-pressure pump according to claim 1, characterized in that the high-pressure temperature (T ₁₄₁ ) is a temperature of the fuel (111) present in the high-pressure pump (141) or a temperature proportional to the temperature of the fuel Wherein the fuel pressure in the low pressure region of the fuel direct injection system is adjusted. Method according to claim 1 or 2, characterized in that the high pressure temperature (T ₁₄₁ ) is detected using a temperature model and the first offset (O ₁ ) is applied according to the tolerance of the temperature model. Fuel pressure in a low pressure region of a four-cylinder system. According to claim 1 or 2, wherein the method is repeated for a plurality of different high-pressure temperature (T _141), the temperature dependence of the adjustment on the basis of the adjusted each of the fuel pressure (p _adap) the fuel pressure (p _adap) Fuel ratio in the low-pressure region of the fuel direct-injection system. The method of claim 4, wherein the output of the low-pressure zone until the fueling of fuel 111 to the car next time (13) the pressure (p) is the adjusted fuel pressure (p _adap) according to the high-pressure temperature (T ₁₄₁₎ Fuel ratio in the low-pressure region of the fuel direct-injection system. 3. A method according to claim 1 or 2, wherein the second offset (O ₂₎ is a high-pressure temperature (T ₁₄₁₎ the temperature (T) target pressure first derivative of the temperature-dependent change in the (p _soll) (dp according to at _soll / dT) in the low-pressure region of the fuel direct-injection system. 3. A method according to claim 1 or 2, wherein the two with the slope of the temperature-dependent change in the sample a target pressure (p _soll) between the temperature is selected and the second offset (O _2), wherein the first sample temperature (T ₊₎ Is higher than the high-pressure temperature (T ₁₄₁ ) and the second sample temperature (T _- ) is lower than the high-pressure temperature (T ₁₄₁ ). A computer program, which is equipped to carry out the respective steps of the method according to claim 1 or 2 and is stored in a machine-readable storage medium. 9. A computer readable storage medium having stored thereon a computer program according to claim 8. An electronic control device (2) adapted to adjust a fuel pressure (p) in a low-pressure region (13) of a direct fuel distribution system (1) of an automobile by the method according to claims 1 or 2.

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