Method for plausibilizing a rail pressure sensor value

Abstract

A method for plausibilizing a rail pressure sensor value of a rail pressure sensor of an internal combustion engine having a common rail system that has a fuel high-pressure piston delivery pump includes acquisition of the beginning of conveying by the piston delivery pump, calculation of the rail pressure from the compression work performed by the piston, and plausibilization of the rail pressure outputted by the rail pressure sensor on the basis of the calculated rail pressure.

Claims

1. A method for plausibilizing a rail pressure sensor value that is output by a rail pressure sensor of an internal combustion engine, the internal combustion engine being part of a common rail system that includes a fuel high-pressure piston delivery pump and a common rail, the method comprising: obtaining, by processing circuitry, an indication of when conveyance of fuel by the piston delivery pump into the common rail begins; calculating, by the processing circuitry, a pressure in the common rail based on the obtained indication; and plausibilizing, by the processing circuitry, the rail pressure sensor value that is output by the rail pressure sensor by comparing the rail pressure sensor value to the calculated rail pressure.

2. The method as recited in claim 1, wherein the beginning of conveying is obtained by temporally scanning a rotational speed signal of a crankshaft of a piston of the fuel high-pressure piston delivery pump.

3. The method as recited in claim 2, wherein the beginning of conveying is obtained by determining, based on the scanning of the rotational speed signal, when the rotational speed signal shows a kink.

4. The method as recited in claim 2, wherein the rotational speed signal is acquired using a high-resolution rotational speed sensor.

5. The method as recited in claim 4, wherein the high-resolution rotational speed sensor acquires a local tooth speed in an angular range of a pump cam.

6. The method as recited in claim 1, wherein the method is carried out during overrun operation of a vehicle with constant load.

7. A non-transitory machine-readable storage medium storing a computer program that is executable by a control device of an internal combustion engine, and that, when executed by the control device, causes the control device to perform a method for plausibilizing a rail pressure sensor value that is output by a rail pressure sensor of the internal combustion engine, the internal combustion engine being part of a common rail system that includes a fuel high-pressure piston delivery pump and a common rail, the method comprising: obtaining an indication of when conveyance of fuel by the piston delivery pump into the common rail begins; calculating a pressure in the common rail based on the obtained indication; and plausibilizing the rail pressure sensor value that is output by the rail pressure sensor by comparing the rail pressure sensor value to the calculated rail pressure.

8. The method as recited in claim 1, further comprising determining a compression work performed by a piston of the piston delivery pump based on the obtained indication, wherein the calculation is performed based on the determined compression work.

9. The method as recited in claim 1, further comprising determining a length of a stroke of a piston of the piston delivery pump based on the obtained indication, wherein the calculation is performed based on the determined length of the stroke.

10. A method for plausibilizing a rail pressure sensor value that is output by a rail pressure sensor of a common rail system that includes the rail pressure sensor, an internal combustion engine, a fuel high-pressure piston delivery pump, and a common rail, the method comprising: obtaining, by processing circuitry, an indication of at least one of (a) a measurement of a compression of volume performed by a piston of the fuel high-pressure piston delivery pump from a beginning of a compression phase until when the fuel high-pressure piston delivery pump begins to convey fuel into the common rail, (b) a compression work performed from the beginning of the compression phase until when the fuel high-pressure piston delivery pump begins to convey fuel into the common rail, (c) a length of a translational stroke of the piston from the beginning of the compression phase until when the fuel high-pressure piston delivery pump begins to convey fuel into the common rail, and (d) a rotational movement of a camshaft of the fuel high-pressure piston delivery pump from the beginning of the compression phase until when the fuel high-pressure piston delivery pump begins to convey fuel into the common rail; calculating, by the processing circuitry, a pressure in the common rail based on the obtained indication; comparing, by the processing circuitry, the rail pressure sensor value that is output by the rail pressure sensor to the calculated rail pressure; and determining a plausibility of the rail pressure sensor value that is output by the rail pressure sensor based on a result of the comparison.

11. The method of claim 10, further comprising: scanning a rotational speed signal indicating a rotational speed of a crankshaft; identifying a kink in the signal; and determining when the fuel high-pressure piston delivery pump begins to convey fuel into the common rail based on the identified kink, wherein the determined beginning is used for the obtaining step.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of the present invention are shown in the figures and are explained in more detail below.

(2) FIG. 1 shows a schematic representation of a fuel supply system of an internal combustion engine having a common rail system.

(3) FIG. 2 schematically shows a fuel high-pressure piston delivery pump for the explanation of the method according to the present invention.

(4) FIG. 3 shows the pressure over the volume during a stroke process of the delivery pump shown in FIG. 2.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

(5) FIG. 1 shows, in a schematic representation, a fuel supply system 10 that is used in an internal combustion engine. The figure shows a fuel container 12, a pre-conveyor pump 14, a high-pressure pump 16, a low-pressure limiting valve 18, a fuel storage device 20 that is connected to various injectors 22, and a pressure regulating valve 24 via which fuel storage device 20 is connected to fuel container 12. Pressure regulating valve 24 can be controlled by a coil 26, and as a rule is constructed in such a way that, when it receives a control signal, it maintains a particular pressure in fuel storage device 20 and drains unneeded fuel into fuel container 12.

(6) The lines between the output of high-pressure pump 16 and the input of pressure regulator valve 24 are designated the high-pressure region. In this region, the fuel is under high pressure. A sensor 30 is used to acquire the pressure in the high-pressure region. The lines between fuel container 12 and high-pressure pump 16 are designated the low-pressure region.

(7) Various actuating elements, such as for example high-pressure pump 16, injectors 22, and pressure regulating valve 24, are acted on by a control unit 40. Here, control device 40 processes various signals of different sensors 42 that characterize the operating state of the internal combustion engine, such as a rotational speed sensor. In control unit 40, there is provided a computing unit 44 for carrying out the method presented.

(8) During operation, the fuel is conveyed, by pre-conveyor pump 14, from fuel container 12 to high-pressure pump 16. If the pressure in the low-pressure region increases to excessively high values, then low-pressure valve 18 opens and releases the connection between the output of pre-conveyor pump 14 and fuel container 12. High-pressure pump 16 conveys the fuel from the low-pressure region into the high-pressure region, and builds up a high pressure in fuel storage device 20. In externally ignited internal combustion engines, typical values are between 30 and 100 bar. In self-igniting internal combustion engines, i.e., diesel engines, values between 1000 and 2000 bar are reached.

(9) Sensor 30 acquires the pressure in fuel storage device 20, also called the rail, or in the overall high-pressure region. The controllable high-pressure pump 16 and the pressure regulating valve are used to regulate the pressure.

(10) Vehicles that have such common rail systems are equipped with OBD systems. Such on-board diagnostic systems (OBD2) record disturbances and errors during operation of the internal combustion engine and of the vehicle. The recorded disturbances are stored in a storage device and can be read out later. In OBD2 legislation, it is a legal requirement that the measurement values of sensor 30, also referred to as the rail pressure sensor and referred to as such hereinafter, be plausibilized in the entire operating pressure range. This can be accomplished with the aid of a further pressure sensor in the high-pressure region. However, such a second pressure sensor may be undesirable due to the additional technical outlay, susceptibility to failure, and not least due to the additional costs that result. The example method described below avoids such an additional pressure sensor, and links the sensors in the internal combustion engine, having functions of control unit 40, also called the control device, or software functions of computing unit 44, with one another in such a way that it can be unambiguously determined whether the actual rail pressure value and the rail pressure measurement value outputted by rail pressure sensor 30 agree with one another. In this way, a plausibilization is possible of the measurement value of rail pressure sensor 30.

(11) FIG. 2 schematically shows a high-pressure pump 16 realized as a piston delivery pump. The so-called element piston 100 is driven by a camshaft 300, on which there are situated for this purpose a corresponding cam 320 and a roller 330. The rotational movement of camshaft 300 is converted into a translational movement of piston 100 in a conventional manner. On the upper side of a cylinder 110 in which piston 100 runs back and forth there is situated a valve 150 that enables the supply of fuel from the low-pressure circuit, i.e., the corresponding low-pressure line 160. Likewise, in the upper region of cylinder 110 there is situated a high-pressure line 210 as well as a high-pressure valve 200 that, when a specified pressure is exceeded, creates a connection to rail 20. The downward movement of piston 100 results, via intake valve 150, in a suctioning of fuel from the low-pressure circuit, and the upward movement results in a compression of the previously suctioned fuel. The fuel compressed during the compression phase is conveyed into rail 20 via high-pressure line 210 and high-pressure valve 200.

(12) During the compression, for example from volume V.sub.1 to volume V.sub.2 (see FIG. 3), compression work W.sub.12 is performed. Path ds here corresponds to the compression stroke of element piston 100. The compression is an approximately adiabatic process. As is shown in FIG. 3, the surface under the adiabatic curve from V.sub.1 to V.sub.2 corresponds to compression work W.sub.12 that has to be performed by element piston 100. As soon as the pressure in element piston 100 p.sub.Kolben is greater than the pressure in the rail p.sub.Rail, there takes place a release of tension. The compressed fuel is then conveyed from the element chamber into rail 20. This causes the pressure in the element chamber to decrease, while the pressure in rail 20 increases. The compression work up to the opening of high-pressure valve 200 (p.sub.Kolben=p.sub.Rail) is here proportional to rail pressure p.sub.Rail. The greater the rail pressure is, the more compression work has to be performed by element piston 100. The compression work itself is in turn proportional to the stroke ds of element piston 100. This in turn is a function of the angle of the camshaft since the beginning of the compression (.sub.Nocken.sub._.sub.Beginn), which in turn has a fixed transmission ratio to the crankshaft.

(13) The time of opening of high-pressure valve 200, i.e., when p.sub.Kolben=p.sub.Rail, is therefore the endpoint of the increase of the compression work. In FIG. 3, this corresponds to point P.sub.2 at V.sub.2 on the adiabatic curve.

(14) The time of opening of high-pressure valve 200 can now be detected via a discontinuity, for example a kink, in the rotational speed signal, which is acquired anyway, of the crankshaft. For this purpose, on the crankshaft (not shown) there is situated a conventional rotational speed sensor, for example a toothed rotary sensor, and a sensor that acquires the tooth position. Because the compression work ultimately has to be applied by the crankshaft, the kink can be determined by the rotational speed sensor on the basis of a high-resolution scanning that acquires the local tooth speed in the angular region of the pump cam.

(15) As a result, it is possible to determine the stroke ds of element piston 100 as a function of .sub.Nocken.sub._.sub.Beginn to .sub.Nocken.sub._.sub.Frderung, where angular position .sub.Nocken.sub._.sub.Frderung is the camshaft position that corresponds to the opening of high-pressure valve 200.

(16) The pressure in the element chamber, i.e., in cylinder 110, can be determined from the known compression stroke ds and the concomitant change in volume, using the following equation:

(17) $\frac{V}{V}=-.Math.p,$
where designates the compressibility of the fuel. Alternatively, the compression characteristic of the fuel can also be stored in a characteristic field, so that influences of the fuel temperature can also be taken into account.

(18) The current rail pressure p.sub.Rail corresponds in the result to the element pressure, i.e., to the pressure in the piston at the time of opening of high-pressure valve 200. It is proportional to the change in volume V=V.sub.2V.sub.1.

(19) In order to exclude disturbing influences such as injections on the kink of the local tooth speed at the time of opening of the high-pressure valve, the recognition can be carried out during overrun at constant load.

(20) An advantage of the example method described above is that it covers the complete operating range from 0 bar up to p.sub.max. The example method is suitable both for systems having a pressure regulating valve and for systems not having such a valve.

(21) The example method described above can be implemented as a computer program and can run in computing unit 44 of control unit 40. No additional hardware, in particular no additional sensors, is required for the execution of the method; rather, the crankshaft signal is evaluated and only the dimension of the piston pump has to be known; because of this the method can thus be retrofitted at anytime. For this purpose, it is preferably stored on a data carrier that can be read in by computing unit 44 of the control unit or of control device 40.