Patent Application
20150153242
The present application claims priority to and the benefit of German patent application no. 10 2013 221 978.4, which was filed in Germany on Oct. 29, 2013, the disclosure of which is incorporated herein by reference.
The present invention relates to a method for monitoring a pressure sensor of a fuel metering system of an internal combustion engine, particularly of a motor vehicle. Furthermore, the present invention relates to a computer program which carries out all the steps of the method according to the present invention, when it is running on an arithmetic unit or a control device, as well as a computer program product having program code, which is stored on a machine-readable carrier, for carrying out the method according to the present invention, when the program is run on an arithmetic unit or a control device.
German document DE 10 2004 049 812 A1 discusses a fuel metering system, to which the present document also relates, in particular, a fuel injection system of a common rail (CR) system, as well as a method for its operation. The fuel injection system has a high pressure pump, to which fuel is supplied via a metering unit, and which pumps the fuel supplied with high pressure into a fuel accumulator (that is, presently, the so-called “rail”). Using injection valves or injectors, fuel from the rail is injected into combustion chambers of the internal combustion engine. The metering unit situated before the high pressure pump regulates the fuel supply to the high pressure pump and thus to the rail. In addition, a pressure regulating valve is situated on the rail, which controls the fuel outflow from the rail that is under high pressure into a low pressure system. Furthermore, a pressure sensor, i.e. a rail pressure sensor in this case, is assigned to the rail, with which the fuel pressure (“rail pressure”) is measured in the rail.
In a CR system, a rail pressure sensor mentioned is used both for regulating the rail pressure and for determining the fuel quantity to be injected into the respective injector. As is known, the evaluation of the sensor signal takes place using a rail pressure sensor characteristic curve, in which values of the rail pressure are plotted against the electric voltage. A malfunction of the rail pressure sensor and a drift behavior in the operation and over the service life of the rail pressure sensor work out negatively on the accuracy of the rail pressure to be set, and accordingly also disadvantageously on the accuracy of the injected fuel quantity.
Based on the direct influence on the injection quantity, a rail pressure sensor is ranked as relevant for an on-board diagnosis (OBD), and therefore has to be monitored accordingly in the operation of a motor vehicle. Thus, in countries like the USA, the provision of such a functional test of a rail pressure sensor is even specified by law.
Two different diagnostic methods are known, from the related art, for a rail pressure sensor, namely an offset test and a so-called APCV function (=adaptive pressure control valve). In the offset test it is checked whether the sensor characteristic curve mentioned has an offset error. In this context, the rail pressure signal is compared in specified operating states with values to be expected, and, as a function of the comparison, a faulty rail pressure signal is detected. However, such an offset test is only able to be carried out in operating states of the internal combustion engine or the CR system, in which the fuel in the rail is completely pressure-reduced, i.e. only when the internal combustion engine is shut down or switched off. This test has the additional disadvantage that a functional test is only able to be carried out in a very restricted operating range of the rail pressure sensor, namely, near the zero point of the rail pressure sensor characteristic curve mentioned, and only at points in time at which the rail pressure has already been dissipated completely, e.g. before the start of the internal combustion engine, or in the coasting down that takes place after shutting down the engine.
The sensor characteristic curve is able to be adapted using the APCV function mentioned. For this purpose, when (quasi) stationary operating conditions and an activated pressure regulating valve are present, the actual current present at the pressure regulating valve that is required for setting the desired rail pressure is measured and compared to an expected setpoint current. The relationship of the two currents is then stored as the adaptation value. In order to achieve a high accuracy of the adaptation, this method has to be carried out at rail pressures that are as high as possible, which are, as a rule, only reached at very high load conditions of the internal combustion engine. In addition, in the case of a two-controller approach having a pressure regulating valve, which is usual in CR systems, the APCV function is only able to be carried out if the CR system is in regulating mode, which is usually only active shortly after the start of the internal combustion engine, for the purpose of heating fuel. Since the complete tolerance chain of the CR system and the rail pressure regulation is to be additionally calculated into the monitoring limits of the APCV function for the least favorable case, this leads to great inaccuracy or rather, relatively large tolerances with respect to the monitoring result.
In addition, there comes about a further, relatively large tolerance in the actuation of the pressure regulating valve per se, namely, because of the rail pressure sensor characteristic curve mentioned on which it is based. For, the characteristic curve is set up by setting a corresponding rail pressure at the full flow of fuel through the high pressure pump mentioned, via a certain supply of current to the pressure regulating valve.
The present invention is based on the idea of monitoring and checking the functioning of a pressure sensor of a fuel metering system, that is under consideration in this case, by lowering the current supply of a pressure regulating valve, that is first closed, until the pressure regulating valve opens and pressure is dissipated. This is based on the technical effect that, because of the opening of the pressure regulating valve, a measurable and evaluatable current signal is generated. The current signal is particularly generated by the electric current that is induced back by the opening of the pressure regulating valve.
The outflow of fuel conditioned upon what may be a brief opening of the pressure regulating valve has the effect of a (brief) lowering of the hydraulic pressure in the rail, or rather the high-pressure accumulator. With the aid of the exact opening time of the pressure regulating valve, known from the measured current signal, this pressure reduction is able to be compared to pressure values supplied by the pressure sensor, and the functional capability of the pressure sensor is thereby able to be checked and checked for plausibility.
The checking may take place only qualitatively or also quantitatively. Thus, in the case of a quantitative evaluation of the curve over time of the measured current signal, the quality of the checking result or the quality of the plausibility check is able to be improved in that, in addition to evaluating the time of opening of the pressure regulating valve, the duration of the opening of the pressure regulating valve is also evaluated, for instance, by an accurately timed increase in supplying current to the pressure regulating valve, in order to close it again as quickly as possible after its detected opening state, so as to return to the normal operating mode of the pressure regulating valve.
Therefore, the method according to the present invention enables an indirect monitoring or plausibility checking of a pressure sensor under consideration in this case, namely indirectly via the opening behavior of a pressure regulating valve, and is thereby, in particular, independent of the respective operating type of a present pressure regulation.
By contrast to a characteristic curve named at the outset, the method according to the present invention uses the opening behavior of the pressure regulating valve, which may also be characterized by a characteristic curve. For, each pressure regulating valve has manufacturing tolerances conditioned upon production methods and/or variances caused by the operational life. These require the application of certain offsets in the actuating current that has to be applied to a pressure regulating valve, so that it closes reliably. In order to be able to maintain a closing pressure of 2000 bar, for instance, the pressure regulating valve requires a pressure of 2000 bar+x bar in closing offset, the latter being recalculated to a current. Depending on the manufacturer and the type of the pressure regulating valve, this closing offset is lower than the characteristic curve already named. In this context, the opening tolerance is considerably smaller than the characteristic curve tolerance in the active control and/or regulating operation of the pressure regulating valve.
Using the method according to the present invention, one is additionally able to ascertain the opening time of a previously closed pressure regulating valve in the whole working range of the pressure regulating valve and the whole pressure range of the fuel metering system, i.e. in a CR system of minimum rail pressure to maximum rail pressure, a direct dependence coming about between the pressure currently present at the pressure valve and the closing pressure of the pressure regulating valve currently present. Thereby the functional capability of a pressure sensor under consideration in this case, i.e. a rail pressure sensor in the case of a CR system, may be checked for plausibility at a higher accuracy than is possible using the known methods, such as the APCV function named at the outset.
The present invention may be used in a pressure-operated fuel metering system of a motor vehicle, especially in a high-pressure operated CR injection system. It should be understood, though, that the method may also be used outside the usual motor vehicle technology, for instance, in special commercial vehicles, in watercraft, or in chemical industrial processing engineering, with the same advantages described herein.
Additional advantages and developments of the present invention result from the specification and the appended figures.
It will be appreciated that the features mentioned above and the features yet to be described below may be used not only in the combination given in each case but also in other combinations or individually, without departing from the scope of the present invention.
a and 2b show, in the case of a pressure regulating valve under condideration in this case, measured electrical current curves to illustrate the current induced back in response to an opening process of the pressure regulating valve.
The entire fuel injection system 10 is controlled and/or regulated by a control unit not shown in greater detail. For this, the control unit has a computer having an electrical storage medium, in particular, a flash memory. A computer program is stored on the memory medium, which is able to be run on the computer. This computer program is suitable for influencing fuel injection system 10 and thereby carrying out the desired control and/or regulation.
In addition to fuel injection system 10, in
Pressure sensor 14 generates a signal corresponding to the actual pressure ID in rail 13, and is sent to a comparator 21. There, the actual pressure ID is compared to a setpoint pressure SD. The differential pressure DD is passed on to three controllers, namely to a P controller 22 (proportional controller), a D controller 23 (differential controller) and an I controller 24 (integral controller). The outputs of these three controllers are added by an adder 25 to form a control value DS for a desired fuel flow. This desired fuel flow is then supposed to be supplied by metering unit 12 to pump 11, and thus to rail 13.
Furthermore, a first pilot signal V1 is provided. which is added via a first adder 26 to control value DS, as well as a pilot control characteristic map 27, which on the output side supplies a second pilot control signal V2, which, via a second adder 28, is added to control value DS for the fuel flow. As input signal, current injection quantity q and current rotational speed n are supplied to pilot control characteristic map 27.
Control value DS for the desired fuel flow is supplied to a characteristic curve 29, which represents metering unit 12. With the aid of this characteristic curve 29, from a control value DS, that control value SS for a current is ascertained, with which metering unit 12 has to be actuated in order to produce the desired fuel flow. This control value SS represents a setpoint value for a post-connected current regulator 30. Metering unit 12 then has applied to it the current corresponding to control value SS by current regulator 30. The current actually flowing via metering unit 12 is measured by a sensor 31, and supplied as actual value IW to a comparator 32. There, actual value IW is deducted from control value SS. The difference is then applied to current regulator 30.
To check the functioning capability of a pressure sensor 14 shown in
The current mentioned, induced back in response to the opening process of the pressure regulating valve, is illustrated with the aid of the measuring curve shown in
a shows an electric current curve IDRV in units of milliAmpere (mA) as actual value 200 of the current as well as a specified setpoint value 225 of the current. In time window 223, that is emphasized by a dot-dashed line, there is a brief current increase 220 of actual value 200, which is used in the method described herein as the basis for determining the exact opening time of the pressure regulating valve.
In
b shows a cutout enlargement of area 223, shown in
The indirect checking or monitoring of the functioning of pressure sensor 14 mentioned takes place with the aid of the exemplary embodiment of a method sequence (or routine) shown in
In the exemplary embodiment shown in
In the following step 310, the supplying of current to pressure regulating valve 15 is lowered by an empirically specified differential value. Thereafter, it is checked 315, whether the current measurement mentioned (described in detail below) has recorded a (peak) current that was induced back. If this is not the case, the method returns to step 310, and the supply of current to the pressure regulating valve is correspondingly further lowered or reduced at the increment mentioned. If it turns out at test step 315, after such a further lowering of the supply of current, that a peak current induced back was measured, in subsequent step 320, a second actual pressure value ID#2, supplied, in turn, by pressure sensor 14, is recorded and also stored temporarily, if necessary.
The two values ID#1 and ID#2 are now compared in test step 325. If the test yields that the value of ID#2, for instance, within an empirically specifiable threshold value, is greater than the value of ID#1, which means that the condition in step 325 is satisfied, the method goes forward to step 330, and it is signaled to a diagnostic unit (e.g. OBD unit) or the like that pressure sensor 14 is fully functionally capable.
Otherwise the method goes to step 325, in which a malfunction of pressure sensor 14 is signaled.
Finally, in step 340 the supply of current to pressure regulating valve 15 is raised again to the original current value (i.e. before the beginning of the routine), in order to close the pressure regulating valve again for normal operation.
Alternatively or in addition to the plausibility check described, it may be provided that the peak current induced back, as was described above, is evaluated in greater detail, whereby the quality of the plausibility check is able to be improved.
The method described may advantageously be used or carried out in all possible operating states of a fuel metering system on which they are based (e.g. CR systems), in which the pressure regulating valve is closed, and consequently, over the entire pressure range available in the rail, since at each pressure, the operating current (or the control current) is able to be lowered for the pressure regulating valve, in the manner described, until an opening signal of the pressure regulating valve is measured and recorded. Thereafter, the operating current of the pressure regulating valve may quickly be raised again, whereby the rapid current drop, based on the quick detection of the opening, has no significant influence or negative effect on the currently present rail pressure or the injection behavior of the CR system.
The brief current change that is significant for the opening of the pressure regulating valve, which may be a rise in current, is able to be ascertained by the method described below with the aid of
The current measurement is particularly carried out synchronously at the two edges 405, 410 of PWM signal 400, and from the current values obtained, which correspond to a minimum current and a maximum current, an average value is formed. The average value that comes about is assumed to be the current value induced back.
It should be noted that the exemplary embodiment, shown in
Using the method described, a plausibility check of a pressure sensor of a fuel metering system, that is under discussion here, is able to be carried out with greater accuracy, and in addition, an operating range being accessible for the plausibility check which is not covered by the related art, such as the APCV function mentioned.
The method described may be implemented either in the form of a control program in an existing control unit for controlling an internal combustion engine, or in the form of a corresponding control unit.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2013 221 978.4 | Nov 2013 | DE | national |
