DE102016220123B4 - Method and device for plausibilizing the functionality of a high-pressure sensor of a fuel injection system of a motor vehicle - Google Patents

Abstract

Method for plausibilizing the functionality of a high-pressure sensor of a fuel injection system of a motor vehicle, the functionality of the high-pressure sensor (7) is plausibilized using an evaluation of the system-specific behavior of the fuel pressure in the fuel injection system, characterized in that the operability of the high pressure sensor (7) using an evaluation of Pressure drop gradient is plausibility, and to determine the pressure reduction gradient complete opening of a high-pressure accumulator (6) of the fuel injection system connected pressure reduction valve (10), wherein fuel from the high-pressure accumulator (6) via a throttle (9) and the pressure reduction valve (10) in a Fuel return line (11) flows.

Description

The invention relates to a method and a device for plausibility of the functional capability of a high-pressure sensor of a fuel injection system of a motor vehicle.

In gasoline and diesel high pressure injection systems, a high pressure sensor is used to control the injection pressure to determine the current actual pressure value and to readjust one or more actuators, such as valves, to a current desired pressure value based on this actual pressure value.

If the actual pressure value determined by means of the high-pressure sensor is faulty, for example because of a component error or a component drift, then the fuel injection system is readjusted to a faulty fuel system pressure because of this incorrect actual pressure value. This has the consequence that the pressure in the fuel injection system deviates permanently from its actual operating point-dependent target pressure specification. Due to this deviation, erroneous parameters for the fuel injection are calculated. This in turn leads to poorer combustion and increased pollutant emissions as well as increased fuel consumption and a deterioration of drivability.

In order to avoid the above-mentioned disadvantages, in the presence of an intolerable deviation of the actual pressure value measured by means of the high-pressure sensor from the actually existing pressure value, the malfunction of the high-pressure sensor must be recognized. Furthermore, a sufficiently precise monitoring of the plausibility of the actual pressure values measured by the high-pressure sensor is required by on-board diagnostic legislation (OBD).

It is known to perform a check of the operability of the high pressure sensor in a pressureless state. The functionality of the high-pressure sensor in the vehicle in the start or stop phase compared to the ambient pressure is verified or made plausible. A disadvantage of this procedure is that any deviations of the measured values provided by the high-pressure sensor from the actually existing pressure values can not be determined over the entire operating range of the fuel pressure system, for example when a gradient error occurs. As already mentioned above, this has a negative effect on the operation of the motor vehicle.

Furthermore, it has already been proposed to use a second high pressure sensor to verify the operability of a high pressure sensor of a fuel injection system. However, this procedure was not considered in the vehicle series production for cost reasons.

It has also been proposed to compare the plausibility of the functionality of a high pressure sensor measured by the high pressure sensor actual pressure value with an expected value based on the control of an actuator, such as a flow control valve or a pressure control valve to compare. However, this approach is limited in terms of the error detection accuracy, since at a certain control value, the actually executed value, for example, a set valve position, deviates from the actual desired valve position due to component tolerances. If the controlled valve is, for example, a pressure regulating valve, then this is due to the fact that the actuation of the valve is force-based. In this case, a bore in the valve is held with a corresponding force by the imposition of a certain drive current. However, this force is very different due to component tolerances in the force-spring system. This means that no defined fuel drain through the valve is set. Consequently, this method is not suitable for a plausibility check of the functionality of a high-pressure sensor.

In the DE 100 20 629 A1 a method for operating a fuel supply system for an internal combustion engine, in particular a motor vehicle is described. In the fuel supply system, fuel can be pumped from a pump into a pressure accumulator. The pressure in the pressure accumulator can be measured and the pressure in the accumulator can be changed by the control of a pressure control valve. By a controller, the pressure control valve can be fully opened, and it can be compared by the controller, the measured pressure in the pressure accumulator with an expected pressure. The expected pressure can be determined as a function of parameters of an intact pressure control valve or as a function of current operating variables of the internal combustion engine.

The DE 197 57 655 A1 shows a method and a device for monitoring the operation of a pressure sensor, which receives the pressure in a pressure actuator controlled via a pressure accumulator. A model calculation of the expected pressure value in the accumulator at a certain time is performed on the basis of the pressure made by the pressure actuator and the rate of change in the mass balance of a medium contained in the pressure accumulator at a certain time expected pressure value compared to the pressure value recorded by the pressure sensor.

From the DE 100 20 627 A1 a method for operating a fuel supply system for an internal combustion engine, in particular of a motor vehicle is known. In the fuel supply system, fuel can be pumped from a pump into a pressure accumulator. The pressure in the pressure accumulator can be measured and the pressure in the pressure accumulator can be controlled such that an expected pressure would have to result in the pressure accumulator. By a control device, the pressure control valve is controllable to a predetermined value. By the controller, an expected pressure in the pressure accumulator can be determined. And it can be closed by the controller from the expected pressure and from the measured pressure on the operability of the pressure control valve. The expected pressure and the measured pressure are compared with each other and the pressure control valve is detected as defective if the measured pressure deviates significantly from the expected value.

The DE 10 2006 000 117 A1 shows a fuel injection system that monitors an error in the operation of a pressure reducing valve. The fuel injection system is equipped with a common rail pressure reducing valve in which fuel is accumulated to a selected pressure. The system is for estimating a maximum fuel pressure drop caused by a discharge of fuel, which is a maximum pressure drop within the common rail, which occurs after opening the pressure reducing valve in a state where a flow rate of the fuel passing through the Pressure reducing valve is to be at an upper limit of a standardized functional area of the pressure reducing valve. When an actual rail pressure drop, which is a pressure drop within the common rail, which is achieved by an operation of the pressure reducing valve in the pressure reducing mode exceeds an error decision pressure drop, which is the sum of the maximum pressure drop caused by the discharge of fuel, and a pressure drop caused by another factor estimated from a factor other than the opening of the pressure reducing valve, the controller determines that the pressure reducing valve has an error when closing.

The object of the invention is to provide a method and a device for plausibility of the functional capability of a high-pressure sensor of a fuel injection system of a motor vehicle, in which the disadvantages described above do not occur.

This object is achieved by a method with the in claim 1 solved characteristics. Advantageous embodiments and further developments of the invention are defined in the dependent claims 2 to 10 specified. The claim 11 has a device for plausibility of the functioning of a high pressure sensor of a fuel injection system of a motor vehicle to the object.

The advantages of the invention are in particular that the plausibility of the functioning of a high pressure sensor of a fuel injection system using a system-specific behavior of the pressure value takes place. In this case, a pressure reduction gradient is set by the complete opening of a valve present in the fuel injection system with a defined throttle to a pressure regulation. This valve is preferably a pressure reduction valve which has only one closed and one opened state. The pressure reduction in this approach is not dependent on control variables or a spring characteristic or a magnetic force characteristic, but solely on the physical behavior of the fuel flowing through the defined throttle. If the valve is fully open, then a defined volume flow flows through the valve through the valve back to the fuel tank. The amount of fuel flowing through the valve is pressure and viscosity-dependent and known on the basis of the known data of the fuel.

After all, the method according to the invention is distinguished, in particular, by the fact that it operates independently of control tolerances or component tolerances and, for this reason, permits precise detection of deviations of the actual pressure values measured by the high-pressure sensor from the actual pressure values present.

• 1 eine Skizze einer Vorrichtung zur Plausibilisierung der Funktionsfähigkeit eines Hochdrucksensors eines Kraftstoffeinspritzsystems,
• 2 eine Schnittdarstellung des in der 1 gezeigten Druckabbauventils im geschlossenen Zustand,
• 3 eine Schnittdarstellung des in der 1 gezeigten Druckabbauventils im geöffneten Zustand und
• 4 ein Diagramm zur Veranschaulichung eines Verfahrens zur Plausibilisierung der Funktionsfähigkeit eines Hochdrucksensors eines Kraftstoffeinspritzsystems.

Further advantageous features of the invention will become apparent from the following exemplary explanation with reference to FIGS. It shows:

• 1 a sketch of a device for plausibility of the functioning of a high-pressure sensor of a fuel injection system,
• 2 a sectional view of the in the 1 shown pressure reduction valve in the closed state,
• 3 a sectional view of the in the 1 shown pressure reduction valve in the open state and
• 4 a diagram illustrating a method for plausibility of the functioning of a high-pressure sensor of a fuel injection system.

The present invention relates to a method and a device for plausibility of the functioning of a high-pressure sensor of a fuel injection system of a motor vehicle, wherein the operability of the high-pressure sensor is plausibilized using an evaluation of the system-specific behavior of the fuel pressure in the fuel injection system.

The 1 shows a sketch of a device for plausibility of the functioning of a high-pressure sensor of a fuel injection system.

The device shown has a fuel tank 1 , a low-pressure fuel line 2 , a high-pressure fuel pump 3 , a high-pressure fuel line 4 , a flow control valve 5 , a high-pressure accumulator 6 , a high pressure sensor 7 , Fuel injectors 8th , a throttle 9 , a pressure reduction valve 10 , a fuel return line 11 and a control unit 12 on.

In normal operation in the 1 shown device is fuel from the fuel tank 1 via the low-pressure fuel line 2 the high-pressure fuel pump 3 fed and brought there to a high pressure. The at the output of the high-pressure fuel pump 3 provided high pressure fuel is via the high-pressure fuel line 4 , within which the flow control valve 5 is arranged, the high-pressure accumulator 6 fed. From there, the high pressure fuel becomes fuel injectors 8th fed and injected by means of this in not shown combustion chambers of the internal combustion engine of the respective motor vehicle. To an outlet of the high-pressure accumulator 6 is over a throttle 9 a pressure reduction valve 10 connected, through which excess fuel to a fuel return line 11 spent and about this in the fuel tank 1 is returned.

The high-pressure fuel pump 3 , the flow control valve 5 , the fuel injectors 8th and the pressure reduction valve 10 be from a control unit 12 supplied with control signals st, which ensure proper operation of said components. The control unit 12 generates said control signals st in consideration of sensor signals se supplied thereto, a stored work program and stored data. The sensor signals mentioned include, among other things, the output signals of the high-pressure sensor 7 , by means of which in the high-pressure accumulator 6 prevailing fuel pressure is measured. The stored data include, among other maps and data corresponding to a pressure reduction gradient, which then arises when starting from a predetermined initial pressure of the fuel in the high-pressure accumulator for a predetermined time interval, a complete opening of the pressure reduction valve 10 is made, leaving the interior 6a the high-pressure accumulator 6 through the throttle 9 and the pressure reduction valve 10 Fuel into the fuel return line 11 spent and through this into the fuel tank 1 is returned.

These data corresponding to the pressure reduction gradient are known in advance since the dimensions of the throttle, the initial pressure, the fuel properties and the amount of fuel flowing through the depressurizing valve and also the duration of the opening of the depressurizing valve are known. This makes it possible to determine in advance the pressure reduction gradient corresponding data and in a memory of the control unit 12 to deposit. This data is data that represents a system-specific behavior of the fuel pressure in the high-pressure accumulator. These data are used in the present invention to validate the functionality of the high pressure sensor 7 perform as explained below with reference to the other figures.

The 2 and 3 show sectional views of the in the 1 illustrated pressure reduction valve 10 which about the throttle 9 to the interior 6a the high-pressure accumulator 6 connected. In this pressure reduction valve 10 it is a digital pressure reduction valve, which is switchable from an open position to a closed position and vice versa. In this pressure reduction valve, the closing body 10c that has a piston 10a with a spring 10b only occupy two positions, namely in the 2 shown closed position and in the 3 shown opening position. In the in the 2 shown closed position is the throttle 9 closed, so no fuel from the interior 6a the high-pressure accumulator 6 into the fuel return line 11 can get. In the in the 3 shown opening position of the closing body gives the output of the throttle 9 free, so that -as by the arrows 13 illustrated is fuel from the interior 6a the high-pressure accumulator 6 over the throttle 9 and the pressure reduction valve 10 into the fuel return line 11 drained and over this into the fuel tank 1 can be returned. The amount of fuel drained is by the opening time of the pressure reduction valve 10 established.

The 4 FIG. 12 is a diagram illustrating a method of plausibility checking the operability of a high-pressure sensor of a fuel injection system, as shown in FIG 1 to 3 shown components can be performed. This method is in a no-load condition of the Fuel injection system performed, preferably in a coasting phase of the motor vehicle.

In this method, first using the high pressure pump 3 the fuel pressure in the high-pressure accumulator 6 to a predetermined starting value p0 brought. Indicates the fuel pressure in the high-pressure accumulator 6 the default value, then the high-pressure pump 3 deactivated or the flow valve 5 , which is also an integral part of the high-pressure pump 3 can be closed.

If this is done, then in the next step, the pressure reduction valve 10 fully open, so over the throttle 9 a known fuel flow through the pressure reduction valve 10 and the fuel return line 11 back to the fuel tank 1 flows. Point of time t1 at which the opening of the pressure reduction valve 10 starts, and the time t2 at which the pressure reduction valve 10 are fully open, are in the 4 illustrates

After complete opening of the pressure relief valve 10 takes place during the degradation of the fuel pressure in the high-pressure accumulator 6 over the throttle 9 a measurement of the high-pressure accumulator 6 prevailing fuel pressure by means of the high pressure sensor 7 , Using the means of the high pressure sensor 7 measured pressure values, which -as in the 4 is illustrated in the time interval τ , within which the pressure reduction takes place via the throttle, in a time interval .delta.t be detected, there is a difference formation of the measured pressure values ( p1 - p2 ) to determine a measured behavior of the fuel pressure which corresponds to a pressure reduction gradient determined from measured pressure values. This pressure reduction gradient determined from measured pressure values is correlated or compared with the system-specific pressure reduction gradient stored in advance.

If this comparison shows that the deviation of the pressure reduction gradient determined using the measured pressure values from the system-specific pressure reduction gradient is smaller than a predefined threshold value, then the functionality of the high-pressure sensor becomes 7 considered as given.

On the other hand, if the comparison shows that the deviation of the pressure reduction gradient determined using the measured pressure values from the system-specific pressure reduction gradient is greater than a predefined threshold value, then the functionality of the high-pressure sensor becomes 7 regarded as not given.

An advantageous development of the invention is not only to use the method described for plausibility of the functioning of a high-pressure sensor, but also in addition to use to detect an optionally present inertia of the high-pressure sensor. For this purpose, the period of time that elapses until that of the high-pressure sensor is also measured 7 output measured value has dropped to a low measured value predetermined by the system-specific pressure reduction gradient. If the measured value output by the high-pressure sensor does not reach the predetermined low measured value within a predetermined period of time, then the presence of a sluggish high-pressure sensor is detected.

After all, in a method according to the invention system-specific parameters are used as verifying quantities for a system pressure measurement. The method according to the invention operates independently of control tolerances of actuators, such as force-based pressure control valves.

The verification may be done by calculating the pressure drop taking into account the physical parameters such as the high pressure hydraulic volume, the modulus of elasticity of the fuel, the density of the fuel, the amount of exhaust flow through the throttle, and a comparison with corresponding signal values provided by the high pressure sensor.

An alternative possibility is to compare a measured pressure drop with pressure drop characteristics measured in advance for a corresponding system. If the measured characteristic lies within a predetermined tolerance range, then a sensor error, for example a sensor drift, can be excluded.

A method according to the invention can also be used to detect a sensor deviation and an optionally present sensor inertia during normal vehicle operation in the working pressure range and, if necessary, initiate a fault memory entry or necessary countermeasures, for example an emergency mode. This functionality makes a considerable contribution to the robustness of the fuel injection system, without the need for an additional component, for example a second high-pressure sensor.

• - In einem ersten Evaluierungs-Schritt wird unmittelbar nach dem Öffnungsbefehl bzw. bei Bedarf nach einer geeignet gewählten Ventil-Ansprechverzögerung bewertet, inwiefern der gemessene Druck in merklichem Maße zu fallen beginnt. Bleibt der Druck quasi konstant oder sinkt er nur weniger als eine definierte Mindestgrenze, so kann auf ein geschlossen hängendes Druckabbau-Ventil geschlossen werden.
• - In einem zweiten Evaluierungs-Schritt (nach fehlerfreiem Ergebnis des ersten Schrittes) wird im weiteren Verlauf anhand der vorangehend beschriebenen Bewertung des Druckabbaugradienten eine Sensorabweichung sowie eine gegebenenfalls vorliegende Sensorträgheit erkannt.

A method according to the invention can also be used to evaluate the pressure profile after the activation command for opening the pressure reduction valve in two steps during normal vehicle operation in the working pressure range:

• In a first evaluation step, immediately after the opening command or, if necessary, after a suitably selected valve response delay, the extent to which the measured pressure begins to drop appreciably is evaluated. If the pressure remains quasi-constant or only drops less than a defined minimum limit, then it can be concluded that there is a closed-down pressure reduction valve.
• In a second evaluation step (after an error-free result of the first step), a sensor deviation as well as an optionally present sensor inertia are identified in the further course on the basis of the above-described evaluation of the pressure reduction gradient.

Then, if necessary, a fault memory entry or necessary countermeasures can be initiated, for example, an emergency mode.

In addition, the method according to the invention makes it possible to meet increasingly stringent OBD requirements with regard to a plausibility check of the functionality of the high-pressure sensor of a fuel injection system.

LIST OF REFERENCE NUMBERS

1

Fuel tank

2

Low-pressure fuel line

3

High-pressure fuel pump

4

High-pressure fuel line

5

Flow control valve

6

High-pressure accumulator

6a

Interior of the high-pressure accumulator

7

High pressure sensor

8th

fuel injector

9

throttle

10

Pressure reduction valve

10a

piston

10b

feather

10c

closing body

11

Fuel return line

12

control unit

13

arrow

p

print

p0

pressure value

p1

pressure value

p2

pressure value

t

Time

τ

time interval

.delta.t

time interval

t1

time

t2

time

Claims (11)

Method for plausibilizing the functionality of a high-pressure sensor of a fuel injection system of a motor vehicle, the functionality of the high-pressure sensor (7) is plausibilized using an evaluation of the system-specific behavior of the fuel pressure in the fuel injection system, characterized in that the operability of the high pressure sensor (7) using an evaluation of Pressure drop gradient is plausibility, and to determine the pressure reduction gradient complete opening of a high-pressure accumulator (6) of the fuel injection system connected pressure reduction valve (10), wherein fuel from the high-pressure accumulator (6) via a throttle (9) and the pressure reduction valve (10) in a Fuel return line (11) flows. Method according to Claim 1 , characterized in that it is performed in a no-load condition of the fuel injection system. Method according to Claim 2 , characterized in that it is carried out in a coasting phase of the motor vehicle. Method according to one of the preceding claims, characterized in that before the complete opening of the pressure reduction valve (10), the fuel pressure in the high-pressure accumulator (6) is brought to a predetermined starting value. Method according to one of the preceding claims, characterized in that the system-specific behavior of the fuel pressure is related to the behavior of the fuel pressure measured by means of the high-pressure sensor (7). Method according to Claim 5 , characterized in that for determining the behavior of the fuel pressure measured by means of the high-pressure sensor (7), a difference between a pressure value measured after the pressure reduction and a pressure value measured at the beginning of the pressure reduction is determined. Method according to Claim 6 , characterized in that the determined difference with the system-specific pressure reduction gradient is related. Method according to one of Claims 5 to 7 characterized in that, when the deviation of the behavior of the fuel pressure measured by the high-pressure sensor (7) from the system-specific behavior of the fuel pressure is smaller than a predefined threshold value, the functioning of the high-pressure sensor (7) is considered to be given. Method according to one of Claims 5 to 8th , characterized in that when the deviation of the by means of the high pressure sensor (7) measured behavior of the fuel pressure from the system-specific behavior of the fuel pressure is greater than the predetermined threshold, the functionality of the high pressure sensor (7) is considered not given. Method according to one of the preceding claims, characterized in that it is used in addition to a detection of the inertia of the high pressure sensor and / or to a detection of a closed-clamping pressure reduction valve. Device for plausibilizing the functionality of a high-pressure sensor (7) of a fuel injection system of a motor vehicle, characterized in that it comprises a control unit (12), which is designed to control a method according to one of the preceding claims.

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