Patent Application
20110166803
The present invention relates to a method for determining an overpressure in a fuel reservoir of an injection system of an internal combustion engine, to a corresponding computer program, and to a corresponding computer program product.
Common rail systems (CRS) are widely used at present for fuel injection in diesel engines. A common rail system is explained with reference to
Conventional (rail) pressure sensors furnish at the output a measurement signal that is proportional to the measured (rail) pressure. Conventional practice is to use pressure sensors that output a maximum measurement signal which correspond to a pressure value that is approx. 200 bar above the usual operating pressure of an injection system. It is thus not possible for the connected control unit to determine pressures above the maximum pressure value that can be outputted. The control unit has therefore not hitherto been capable of detecting overpressures, or harmful pressures, quickly enough. Additional elements such as, for example, pressure limiting valves are used for this reason in known injection systems in order to avoid harmful pressures in the fuel reservoir.
A variety of possibilities are known for regulating the pressure in the fuel reservoir or limiting it to harmless levels. For example, the high-pressure pump or the fuel reservoir can be equipped with a pressure regulating valve (DRV) that returns an excess delivered quantity back to the fuel container.
It is also understood, in order to reduce the costs of an injection system, to configure so-called adjuster systems, in which the pressure in the fuel reservoir is adjusted only by way of the metering, unit; this makes it possible to dispense with the cost-intensive pressure regulating valve. In order to limit the rail pressure in the event of a fault, however, for example if a defect exists in the metering unit or it remains in an open state (FMU stuck open), it usual to utilize injectors that open in the event a pressure threshold value (e.g. 2500 bar) is exceeded, and allow the pressure to be dissipated by leakage.
Injectors that do not have this kind of overpressure functionality, or in which leakage occurs only at pressures that are already harmful to the system, are also used, however. When such injectors are utilized it is therefore usual to equip the fuel reservoir with a pressure limiting valve (PLV) that, when a pressure threshold value is exceeded, opens and dissipates the pressure in the fuel reservoir. This action has the disadvantage, however, that the injection system must be equipped with an additional pressure limiting valve.
The exemplary embodiments and/or exemplary methods of the present invention therefore provides a method for determining an overpressure in a fuel reservoir of an injection system of an internal combustion engine, in particular of a common rail system; a corresponding computer program; and a corresponding computer program product, having the features of the independent claims, which do not exhibit these disadvantages. Advantageous refinements are the subject matter of the dependent claims and of the description below.
With the approach according to the exemplary embodiments and/or exemplary methods of the present invention, conventional pressure sensors are used to determine an overpressure in a fuel reservoir and as a consequence to initiate pressure reduction actions, with no need to provide additional, in particular cost-intensive, components. The exemplary embodiments and/or exemplary methods of the present invention offers the possibility of reliably operating an injection system, in particular a common rail system as depicted e.g. in
Advantageously, an overpressure in the fuel reservoir is identified only if the sensed pressure exceeds the predetermined pressure threshold value within a predetermined first time span after the derivative of the sensed pressure over time last exceeded the predetermined slope threshold value. The predetermined first time span can be zero, or arbitrarily short. For example, an overpressure is thus identified if the slope threshold value remains exceeded until the pressure threshold value is exceeded. A time interval can likewise be provided as being harmless for detection of an overpressure. An overpressure can therefore also be identified if the slope falls below the threshold value for a short time (corresponding to the first time span) before the pressure threshold value is exceeded.
Usefully, an overpressure in the fuel reservoir is identified only if the sensed pressure exceeds the predetermined pressure threshold value for longer than a predetermined second time span. An exceedance of the pressure threshold value that is brief (corresponding to the second time span), and thus harmless, can thus be accepted without identifying an overpressure.
It is advantageous if an overpressure in the fuel reservoir is identified only if the derivative of the sensed pressure over time exceeds the predetermined slope threshold value for longer than a predetermined third time span.
The first, second, and third time spans can be selected independently of one another, so that an advantageous combination of time spans can be made available for the particular injection system to be dealt with. An advantageous value for the second time span is, for example, 10 ms. The pressure threshold value must therefore be exceeded for at least 10 ms in order to identify an overpressure. Using the parameters described (time spans and threshold values), the method can be optimally matched to different injection systems.
It is particularly advantageous if a fuel pump that makes fuel available to a metering unit, and/or a high-pressure pump that pumps fuel into the fuel reservoir, are shut off when an overpressure is identified. The probability of harm to the injection system can thereby be decreased.
According to an exemplary embodiment of the present invention, fuel is discharged out of the fuel reservoir when an overpressure is identified. This can be accomplished, in a manner not affecting torque, through the injectors, as also discussed in DE 196 36 397 A1. The probability of harm to the injection system can thereby be further decreased.
It is useful to provide a fault count value that is incremented, which may be by one, when an overpressure is identified. For example, a metering unit is not defective at the first occurrence of an overpressure. A fault count threshold value, for example, can be provided, such that when it is exceeded, a defect is identified. The possibility further exists of providing for component replacement after a defined number of fault events.
The exemplary embodiments and/or exemplary methods of the present invention further relates to a control unit for a motor vehicle that is designed to execute a method according to the present invention.
The exemplary embodiments and/or exemplary methods of the present invention further relates to a computer program having a program code arrangement which are suitable for executing a method according to the present invention when the computer program is executed on a computer or on a corresponding calculation unit, in particular on a control unit according to the present invention.
The computer program product provided according to the present invention encompasses a program code arrangement, stored on a computer-readable data medium, which are suitable for executing a method according to the present invention when the computer program is executed on a computer or on a corresponding calculation unit, in particular on a control unit according to the present invention. Suitable data media are, in particular, diskettes, hard drives, flash memories, EEPROMs, CD-ROMs, DVDs, and many more. Downloading of a program via computer networks (Internet, intranet, etc.) is also possible.
Further advantages and embodiments of the exemplary embodiments and/or exemplary methods of the present invention may be gathered from the description and the attached drawings.
It is understood that the features recited above and those yet to be explained below can be used not only in the respective combination indicated, but also in other combinations or in isolation, without leaving the context of the exemplary embodiments and/or exemplary methods of the present invention.
The exemplary embodiments and/or exemplary methods of the present invention is schematically depicted in the drawings on the basis of an exemplifying embodiment, and will be described in detail below with reference to the drawings.
A pressure harmful to the system has not yet been reached, however, when this rail pressure is reached. The pressure limiting valves recited in the introduction to the specification are designed, for example, for pressures of approx. 2500 bar. The method according to the present invention now makes it possible to distinguish between harmful and harmless pressures, as described below.
In the embodiment depicted, an overpressure, i.e. in particular a harmful pressure, is identified when the time-dependent signal curve 210 firstly exceeds a predetermined slope value. This predetermined slope value is depicted schematically in diagram 200 as straight line 210. It is additionally necessary for signal curve 210, after exceeding slope value 210 (immediately or with a time delay, depending on the embodiment), to exceed a threshold signal value 220.
A short circuit or other defect in the sensor usually furnishes a signal value that is well below the maximum signal value that can be outputted under operating conditions. In the illustration shown, an output value in the event of a sensor defect could be, for example 5V.
Rail pressure curve 320, on the other hand, corresponds to a pressure curve in which, utilizing the method according to the present invention, the overpressure is detected and electrical fuel pump 120 is then advantageously shut off. It is evident that rail pressure curve 320, after a maximum at approx. 3600 bar, decreases again and approaches a value of approx. 3000 bar. The probability of harm to the injection system can thereby already be decreased. Low-pressure curve 340 is associated with rail pressure curve 320.
To improve pressure dissipation when an overpressure is identified, the pressure in the fuel reservoir can be additionally dissipated, using the method according to the present invention, through injectors 160. A corresponding pressure curve is illustrated in
Rail pressure curve 410 initially has a value of approx. 1850 bar. At a time t1 located at approximately 0.81 s, a fault occurs in the metering unit of the injection system so that the metering unit remains in an open state. The rail pressure consequently rises sharply until, at a time to, it exceeds a threshold value 420. In addition, the slope of the rail pressure curve between times t1 and t0 is above a predetermined slope threshold value. The method used in
To prevent uncombusted fuel, in particular diesel, from being conveyed back to the combustion chamber and combusted after having been ejected therefrom, an exhaust gas recirculation (EGR) value that is present should be closed. To inhibit combustion of the ejected fuel, it is useful to reduce the quantity of oxygen in the exhaust gas. For this, the throttle should be closed to the greatest extent possible. Care should be taken in this context that, depending on the operating point of the engine, an appreciable vacuum can occur in the air system. If the throttle valve is completely closed, the result can be destruction of the air intake section and therefore uncontrolled air intake; this must therefore be avoided.
The method according to the present invention allows a harmful overpressure in an injection system of an internal combustion engine to be detected quickly and, consequently, also may be quickly dissipated.
It is understood that the Figures depicted illustrate only a exemplary embodiment of the present invention. Any other embodiment in addition thereto is also conceivable without departing from the scope of this invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102008001444.3 | Apr 2008 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2008/067912 | 12/18/2008 | WO | 00 | 12/30/2010 |
