DE102007052096B4 - Method of identifying a fuel grade - Google Patents

Abstract

Method for detecting a type of fuel which is injected via an injection system, in particular a common rail injection system, into a combustion chamber of an internal combustion engine, wherein the injection system is a hydraulic system with a high-pressure region (3), the plurality of injectors (5) for injecting the fuel and the pressure in the high pressure region (3) is measured over time and in phases during which the high pressure pump does not deliver fuel, the balance equation of the hydraulic Systems dp dt = e V · (-Q INJ - Q CNT_LEAK - Q SWI_LEAK ) is used and integrated over a period considered, where p is the pressure in the high pressure range, E is the compressibility modulus of the fuel, V is the volume of the high pressure range, Q _{INJ is} the injected fuel _{flow rate} , Q _{CNT_LEAK is} the continuous leakage volume flow and Q _{SWI_LEAK is} the switching _{leakage volumetric flow} of the injectors and Q _INJ and Q _{SWI_LEAK} and possibly Q _{CNT_LEAK are} known or the latter is negligible in the period under consideration, and where characteristic curves of the type known for each fuel type are known.

Description

The Invention relates to a method for detecting a type of fuel, the above an injection system, in particular a common rail injection system is injected into a combustion chamber of an internal combustion engine.

Known Common rail injection systems include a volume flow control valve (VCV - Volume Control Valve), which regulates the amount of fuel that a high-pressure pump supplied is pumped and from this in a pressure accumulator (common rail) is a pressure control valve (PCV), the the pressure in the high pressure area, d. H. in the pressure accumulator with the associated feeders dependent adjusts, holds and degrades the load state of the internal combustion engine, and injectors with injectors, which are connected to the pressure accumulator and fuel into the combustion chamber inject the internal combustion engine. In another embodiment of injection systems, the pressure regulating valve is omitted, wherein then the pressure during the injection through the volume flow through the high-pressure pump is controlled or controlled. The hydraulic System, and in particular the injectors, leaks are inherent, with on the one hand it is a so-called switching leakage and on the other hand is a permanent leak. The switching leakage occurs during injection on and corresponds to a tax amount for indirect control the nozzle needle over a hydraulic power amplifier system is used. The permanent leak is a continuous leak and is due to leaks at the nozzle needle and valve piston guides due. The switching leakage quantities and continuous leakage amounts are typically returned to the fuel tank via a fuel return, in FIG if necessary, also the return the pressure control valve opens.

In the post-published document EP 1 873 378 A1 A method for detecting a type of fuel injected via a common rail injection system is described. The changing pressure is measured in the high pressure range. Furthermore, the pressure drop is used to identify the type of fuel by comparing the measured values by means of a trial-and-error method with predetermined maps that describe the leakage behavior, the density and the compressibility of the fuel.

Also the document DE 196 33 156 A1 discloses a method in which, based on the pressure variation over time, information about the fuel grade is obtained. Not only the pressure profile, but also the temperature is measured to determine the fuel grade.

In the published patent application DE 197 03 891 A1 On the other hand, it is disclosed that a pressure drop in the high-pressure region of a common-rail injection system is associated with a systemic leakage volume flow, which is divided into a discontinuous switching leakage volume flow and a continuous leakage volume flow. This relationship is recorded in the balance equation of the hydraulic system.

Of the The present invention is therefore based on the object despite the occurring leakage pressure, a method of identification or detection of the type of fuel reacted in the injection system, For example, to detect whether gasoline, diesel, winter or summer diesel is used to create based on a pressure measurement.

These Task is achieved by the features of claim 1 solved.

Corresponding The invention is the balance equation of the closed hydraulic Systems, d. H. the equation for used the pressure build-up or degradation in the system and indeed for the reduction the influencing variables in phases, while of which the high-pressure pump does not deliver fuel. The pressure change, d. H. the derivation of the pressure in the accumulator or in the high pressure area after the time by the volume flow of the injection, the equivalent is the injected fuel mass, the permanent leakage and the Schaltleckage and the compressibility modulus E of the fuel and the volume V of the pressure accumulator determined. By integrating the Balance sheet equation over a period considered and from known for each type of fuel Characteristic curves for the compressibility module E and the density ρ over the Pressure can be obtained by using these characteristics at a In the injection phase measured pressure found values for the compressibility module E and the density ρ in a trial and error procedure (Trial-and-error method) the pressure difference from the integrated Balance equation are determined and the pair of compressibility module E and density ρ, that's the best over reproduces the pressure difference measured over the considered period, be used to detect the fuel.

The knowledge of the type of fuel and thus the compressibility modulus E and the density ρ brings numerous advantages. Thus, depending on the possible fuel types, the offset pressure control or the transition control (Q _TRA = V / E · dp / dt) can be adjusted. Furthermore, an adaptation of the parameters of the PID control, for example, the proportionality constant of the P controller to the possible fuel types can be made and thus each controller can be optimized. Finally, the fuel pressure prediction can be adjusted according to the possible fuel type. A correction of the injection duration and the start of injection may be made depending on the type of fuel, as well as other combustion control parameters. Finally, the determination of the fuel type may be used for engine monitoring, ie an alarm signal may be given if a wrong fuel is used, for example, when gasoline is being fueled in a diesel-fueled engine.

embodiments the method according to the invention are based on the attached Drawing closer explained. Show it:

1 a schematic representation of the hydraulic system of a common rail injection system,

2 a measurement of the pressure in the high-pressure region or in the rail over time,

3 Characteristics of the fuel density of summer diesel over the pressure for different temperatures,

4 Characteristics of the compressibility module on the pressure for summer diesel at different temperatures,

5 Characteristics of the fuel density for winter diesel over the pressure at different temperatures, and

6 Characteristics of the compressibility module over the pressure for winter diesel at different temperatures.

In 1 schematically the hydraulic system of a common rail injection system is shown, the one with a tank 1 connected flow control valve 2 (VCV), which is usually arranged in the low-pressure region of the system and supplies regulated fuel to a high-pressure pump, not shown. In this 1 are two tank containers 1 located. It can also only a single tank 1 be used, so that the supply line so also the return line in one and the same tank 1 lead. The quantity of fuel denoted by Q _VCV represents the delivery rate at the outlet of the high-pressure pump. The high-pressure pump supplies fuel to an accumulator designated as a common rail 3 , A pressure control valve 4 is at the high pressure pump or at the accumulator 3 attached the pressure in the accumulator 3 depends on the load condition of the engine. The volume flow through the pressure valve 4 is denoted by Q _PCV . The accumulator 3 is with injectors 5 connected, of which only two are shown (each combustion chamber at least one injector) and inject the fuel into the combustion chamber of the internal combustion engine. From the accumulator 3 with the volume V, an amount of fuel is supplied to the injectors, which is composed of the volume flow Q _INJ , the amount of fuel to be injected, and the leakage amount Q _LEAK . As already stated, the leakage quantity is composed of the continuous leakage Q _{CNT_LEAK} and the switching _{leak quantity} Q _{SWI_LEAK} , which flows out via the injectors during the injection. These leakages flow, as shown, back into the fuel tank, in which also the return fuel from the pressure control valve 4 flows.

In case the hydraulic system is not a pressure valve 4 has, of course, no volume flow Q _PCV present and take into account.

The injectors 5 are controlled by a motor control and regulating unit (not shown), which is also the signal of the pressure in the pressure accumulator 3 measuring pressure sensor (not shown) receives and evaluates. This engine control unit controls in a known manner, the flow control valve 2 and optionally the pressure regulating valve 4 The further parameters necessary for the control of the injection are supplied by corresponding sensors.

The balance equation for the pressure build-up in this closed hydraulic system can be described as follows. dp dt = e V · (Q VCV - Q PVC - Q INJ - Q CNT_LEAK - Q SWI_LEAK ) (1) where dp / dt is the derivative of the pressure p after the time, E the compressibility module and V the volume of the pressure accumulator 3 including the connection lines. The other sizes have already been described above. If no pressure valve 4 is used, Q is _PCV = 0.

In 2 is a diagram of a high-resolution measurement of the pressure in the accumulator 3 shown. High-resolution means in the present case that is measured at a high sampling rate, z. B. every millisecond a measured value is created. The high-pressure pump used in the injection system is z. B. a 3-piston pump, wherein the translation of the engine speed to the pump speed is 2/3. In this case, only one piston works in each segment, ie presses the fuel into the accumulator. In each segment, the pressure in the accumulator increases 3 because the corresponding piston of the pump is in the compression section. This is in the 2 for example, by the upward arrow 6 indicated. In this phase, the piston goes to top dead center (TDC). After the piston reaches top dead center and then retracts, there is no pump delivery into the accumulator, ie Q _VCV = 0. During this delivery pause, the injections take place, with in 2 the downward arrow 7 represents an injection phase. In an optimized operating condition is also the pressure control valve 4 closed, so that the equation (1) is reduced to dp dt = e V · (-Q INJ - Q CNT_LEAK - Q SWI_LEAK ) (2)

If equation (2) is integrated over time, the time being, for example, the one corresponding to arrow 1 for an injection process 7 is required, the equation (2) results in: Δp = E / V (-mf_inj_sum / ρ -V SWI_LEAK - Q CNT_LEAK Δt) (3)

In this case, mf_inj_sum denotes the mass of the fuel injected in the period, V _{SWI_LEAK} the volume of the switching _leakage occurring in the period, here the injection period, and Q _{CNT_LEAK} Δt the permanent leakage over the considered period, here the injection period.

In of equation (3) are the injection mass and the volume of the switching leakage for each Fuel type basically known, the permanent leakage can by an adaptation method in advance estimated become. However, this permanent leak is over the considered short Period very small, so that the last term of the equation (3) too neglected can be without significant errors. For directly driven Injectors (New Generation Injectors) eliminates the switching leakage.

Consequently are from the equation (3) only the compressibility E and the density ρ unknown, where the compressibility module E and the density ρ are basically pressure-dependent. However, because the pressure change in the considered period, z. B. the injection is relatively small is, can the compressibility module and the density is considered constant.

In the 3 to 6 are characteristics with respect to the compressibility module and the density of the pressure for summer diesel and winter diesel, with the third parameter, the temperature is plotted, so that for the Kompressi bilitätsmodul and the pressure characteristic curves are shown.

With the help of these characteristics is using the in the pressure accumulator 3 measured pressure value in each case the compressibility modulus E (p, T) and the density ρ (p, T) for the different fuel types, here summer and winter diesel, determined, and in a trial-and-error method can be calculated from the equation (3) Δp are calculated. The pair of compressibility E (p, T) and density ρ (p, T) representing the measured pressure difference (see 2 ) best represents the desired fuel type.

The table below shows the characteristic curves for different temperatures and given parameters 3 to 6 Pressure difference values Δp have been calculated to investigate the influence of the temperature of the fuel in the rail.

From this table it can be seen that in each case a different temperature differential pressure values for summer and winter diesel are achieved, so that a threshold or decision value can be specified. For example, fuel temperature of 10 ° may be given a value of 0.98, that is, if Δp is greater than 0.98, the fuel may be recognized as a summer diesel, and if the pressure differential is less than 0.98, winter diesel will be shut down. Thus, such decision values, which are dependent on the fuel temperature, can be stored in the control unit and used in the determination of the fuel type. It is important that the fuel temperature, which is also the temperature in the accumulator 3 corresponds to an order of magnitude which is within a tolerance of +/- 5 ° C.

Claims (2)

Method for detecting a type of fuel which is injected via an injection system, in particular a common-rail injection system, into a combustion chamber of an internal combustion engine, wherein the injection system is a hydraulic system with a high-pressure region (US Pat. 3 ), which has several injectors ( 5 supplied for injecting the fuel, and a flow control valve ( 2 ) for adjusting the fuel flow supplied to the high-pressure region via a high-pressure pump, and wherein the pressure in the high-pressure region ( 3 ) is measured over time and in phases during which the high pressure pump does not deliver fuel, the balance equation of the hydraulic system dp dt = e V · (-Q INJ - Q CNT_LEAK - Q SWI_LEAK ) is used and integrated over a period considered, where p is the pressure in the high pressure range, E is the compressibility modulus of the fuel, V is the volume of the high pressure range, Q _{INJ is} the injected fuel _{flow rate} , Q _{CNT_LEAK is} the continuous leakage volume flow and Q _{SWI_LEAK is} the switching _{leakage volumetric flow} of the injectors and Q _INJ and Q _{SWI_LEAK} and possibly Q _{CNT_LEAK are} known or negligible in the period in question, and from characteristics of the compressibility modulus and the density as a function of pressure known for each type of fuel, using the values for compressibility modulus found from these characteristics at a pressure measured in the injection phase and density in a trial-and-error method, the pressure difference is determined from the integrated balance equation, and wherein the pair of compressibility modulus and density best represents the pressure difference measured over the considered time range oduced, used to detect the type of fuel. Method according to claim 1, characterized in that that the temperature in the high pressure range is measured or calculated is, where the values for the compressibility module and the density under consideration the temperature can be found from the characteristic curves.