WO2005085619A1 - Method for the diagnosis of a pressure sensor - Google Patents

Abstract

The invention relates to a method for the diagnosis of a pressure sensor (30) which detects the pressure of a component (31) arranged in an exhaust region (20) of an internal combustion engine (10), and a device for carrying out said method. According to the invention, a freezing signal (G) is generated when a minimum temperature (Turin) which depends on the air temperature (TL) falls short of a pre-determined threshold value (Lim). A first error signal (F1) is generated when a diagnosis error signal (DF) generated by a pressure sensor diagnosis (33) occurs, but there is no freezing signal (G). The invention enables a differentiation to be made between a defect of the pressure sensor (30) and the freezing of the component (31) which prevents a correct pressure measurement from being carried out. In this way, unnecessary service stops are avoided.

Description

Method of diagnosing a pressure sensor

State of the art

The invention is based on a method for diagnosing a pressure sensor that detects a pressure of a component arranged in an exhaust gas area of an internal combustion engine, and a

Device for carrying out the method according to the type of the independent claims.

From DE 19906287 AI a method and a device for controlling an internal combustion engine with an exhaust gas aftertreatment system are known, which contains a particle filter that retains the particles contained in the exhaust gas. For proper

When operating the particle filter, the state of loading with particles must be known, which can be detected indirectly via the pressure drop across the particle filter.

DE 101 39 142 AI describes a measuring device for determining a concentration of a urea-water solution, which acts as a reagent for a catalyst in the

Exhaust gas stream of an internal combustion engine is introduced. Ammonia is obtained from the urea-water solution, which reduces nitrogen oxides in the catalyst. A determination of the concentration of the urea-water solution is provided, whereby a precise metering of the reagent into the exhaust gas stream can be realized. To determine the concentration, an indirect measuring method is provided, in which the vapor pressure of the urea-water solution stored in a tank is measured with a pressure sensor. The vapor pressure arises from the ammonia generated due to hydrolysis of the urea plus the vapor pressure of the solvent water. If the vapor pressure is known, a Evaluation unit determine the correspondingly reduced urea quantity or urea concentration of the urea-water solution due to the outgassing.

A temperature sensor is also provided to record the temperature of the urea-water solution. With the signal from the temperature sensor, the dependence of the pressure on the temperature can be taken into account. The urea-water solution has a freezing point that is around - 11 degrees Celsius. If the known metering device is exposed to environmental conditions, freezing of the urea-water solution cannot be ruled out.

DE 101 12 138 AI describes a method and a device for diagnosing a

Pressure sensor has become known, the pressure in the range

Exhaust gas aftertreatment device detected. The exhaust gas aftertreatment device is a particle filter, the loading condition of which can be determined taking into account the pressure drop occurring at the particle filter. The diagnosis evaluates vibrations in the sensor signal that are caused by a change in the exhaust gas volume flow.

The pressure sensors used in each case record the pressure of a component arranged in the exhaust gas area of internal combustion engines. The pressure sensors are connected, for example via a hose, to the volume in which the pressure is to be recorded. In particular in the exhaust gas area of an internal combustion engine, contamination problems and / or difficulties with icing due to air humidity in the component can occur. A pressure sensor diagnosis will also provide an error signal in these cases, although the pressure sensor is not defective.

The invention is based on the object of specifying a method for diagnosing a pressure sensor which detects a pressure of a component arranged in an exhaust gas region of an internal combustion engine, and an apparatus for carrying out the method which take account of icing.

The object is achieved in each case by the features specified in the independent claims.

Advantages of the invention According to the invention, it is provided that a minimum temperature is formed as a function of the air temperature and that the minimum temperature is then compared with a predetermined threshold value. If the minimum temperature is below a predetermined threshold value, a freeze signal is provided. In contrast, a freeze error signal is only provided if the freeze signal and a pressure sensor error signal provided by a pressure sensor diagnosis are present at the same time.

The procedure according to the invention makes it possible to distinguish between an actually defective pressure sensor and icing in the component in which the pressure sensor detects the pressure. Icing can lead to the pressure sensor being cut off from the volume to be examined in the component and therefore providing an incorrect display. The pressure sensor diagnosis determines the error that has occurred, although the pressure sensor is not defective. The additional consideration of possible icing enables a separation between an error that is caused by an actually defective pressure sensor or only by icing.

The invention enables a reduction in the occurrence of erroneous indications of a defect in the pressure sensor and thereby reduces unnecessary service expenditure.

Advantageous further developments and refinements of the procedure according to the invention result from the dependent claims.

A particularly simple determination of the minimum temperature as a function of the air temperature is possible by setting the minimum temperature at least approximately equal to the air temperature. The freeze signal is provided every time the air temperature drops below the specified threshold.

A particularly advantageous embodiment results from the fact that the minimum temperature is calculated as a function of the air temperature. According to one embodiment, it is provided that the minimum temperature is set at least approximately equal to the air temperature if the air temperature is less than or equal to the minimum temperature and that the minimum temperature is increased if the air temperature is higher than the minimum temperature. This procedure takes into account the thermal inertia of the possibly frozen material. For example, there may be icing even though the air temperature is already is above freezing. An experimentally determinable increase in the minimum temperature, which is essentially based on the usual temperature increases in the air temperature, initially takes into account a delayed thawing process at a higher air temperature. Furthermore, frequent averaging through the predetermined threshold value is avoided with the resultant averaging.

One embodiment provides that the minimum temperature is kept constant for a predetermined delay time or for a predetermined number of events from the point in time at which the air temperature becomes greater than the minimum temperature. With this measure it is achieved that after the time at which the

Air temperature becomes higher than the minimum temperature, a sufficient distance between the increasing air temperature and the minimum temperature can occur in order to avoid frequent exceeding or falling below the predetermined threshold value.

One embodiment provides that a display is provided when the pressure sensor error signal is provided and when there is no freeze signal. In this case, the display reports a defect in the pressure sensor that has actually occurred.

An advantageous embodiment provides that the freeze error signal is stored in an error memory, and that a check is then further provided to see whether both the

Freeze signal as well as the pressure sensor error signal no longer occur, and that an indication is provided when this state has occurred a predetermined number. With this measure it is avoided that an indication is given immediately with each freeze error signal provided. By specifying the specified number, the error status is only displayed after the specified number. A service is then required, but due to the freezing error signal available, the error can be searched specifically in the area of the pressure sensor, which may not be defective ,

Further advantageous developments and refinements of the procedure according to the invention result from further dependent claims and from the following

Description.

drawing FIG. 1 shows a technical environment in which a method according to the invention runs, and FIG. 2 shows signal profiles as a function of time.

FIG. 1 shows an internal combustion engine 10, in the suction area of which an air sensor 11 and in the exhaust gas area 20, a spray device 21 and an exhaust gas aftertreatment device 22 are arranged. A pressure sensor 30 detects the pressure in a component 31 which is arranged in the exhaust gas region 20. The pressure sensor 30 outputs a pressure signal 32 to a pressure sensor diagnosis 33, which is also supplied with an air signal msL provided by the air sensor 11.

A temperature sensor 40 detects the air temperature TL, which is fed to a minimum temperature calculation 41, a first comparator 42 and a second comparator 43. The first comparator 42 checks whether the air temperature TL is less than or equal to a minimum temperature Tmin, which the minimum temperature calculation 41 provides. Depending on the comparison result, the first comparator 42 gives the minimum temperature

Calculation 41 a yes signal j or a no signal n ab.

The minimum temperature calculation 41 contains an integrator 44 controlled by the no signal n and an assignment 45 which is acted upon by the yes signal j. The integrator 44 increases the minimum temperature Tmin according to a predetermined relationship. The

Assignment 45 sets the minimum temperature Tmin equal to the air temperature TL. The minimum temperature calculation 41 also contains a delay time specification 46, which holds the minimum temperature Tmin specified by the assignment 45 for the time tv defined by the delay time specification 46

The minimum temperature Tmin or the air temperature TL is compared in the second comparator 43 with a predetermined threshold Lim. Depending on the comparison result, the second comparator 43 provides the freezing signal G, which is fed to a first error memory Spl as well as to a first and second signal combination 50, 51. The two signal links 50, 51 link the freezing signal G with one of the

Pressure sensor diagnosis 33 provided pressure sensor error signal DF, which is also fed to a second error memory Sp2. The first signal combination 50 outputs a first error signal F1 to a counter Z, which outputs a second error signal F2 to a third error memory Sp3. The second signal combination 51 outputs a third error signal F3 to a third error memory Sp4.

The first error memory Spl gives a display A a first display signal AI, the second

Fault memory Sp2 a second display signal A2, the third fault memory Sp3 a third display signal A3 and the fourth fault memory Sp4 a fourth display signal A4.

FIG. 2 shows a profile of the air temperature TL and the minimum temperature Tmin as a function of the time t. The air temperature TL coincides with the at a first time t1

Minimum temperature Tmin. For the delay time tv specified by the delay time specification 46, the minimum temperature Tmin remains constant at the value that was present at the first time t1. Starting with the second point in time t2, which ends the delay time tv, the minimum temperature Tmin increases until it exceeds a predetermined threshold value Lim at a third point in time t3. At a fourth point in time t4

Air temperature TL less than or equal to the minimum temperature Tmin. The minimum temperature Tmin follows the air temperature TL up to a fifth point in time t5. After the fifth time t5, the air temperature TL rises, while the minimum temperature Tmin is kept constant again for the delay time tv. The delay time tv ends at a sixth time 16.

The method according to the invention works as follows:

The pressure sensor 30 detects the pressure prevailing in the component 31. The component 31 is, for example, a hose that connects the pressure sensor 30 to another, not shown in more detail

Connects component whose pressure is to be measured. The component 31 is arranged in the exhaust gas region 20 of the internal combustion engine 10.

The pressure sensor 30 detects, for example, the pressure in a urea metering system, of which only that arranged in the exhaust gas duct of the internal combustion engine 10 in FIG. 1

Spray device 21 is shown, which sprays a reagent into the exhaust gas stream of the internal combustion engine In another exemplary embodiment, the pressure sensor 30 detects the pressure occurring at the exhaust gas aftertreatment device 22. A particulate filter is provided, for example, as the exhaust gas aftertreatment device 22, the differential pressure occurring at the particulate filter being a measure of the loading condition.

In another exemplary embodiment, the pressure sensor 30 directly detects the pressure in the exhaust gas duct of the internal combustion engine 10.

In the exhaust gas area 20 of the internal combustion engine 10, rough environmental conditions can be expected. In the exhaust area 20 high

Temperature changes and pollution problems occur. For example, water vapor can precipitate in the exhaust gas region 20 and then freeze. Depending on the application, 20 reagents, such as a urea-water solution, can occur in the exhaust gas area, which also freezes above a certain temperature limit. It cannot be excluded that water or reagent freezes in the component 31, so that the pressure sensor 30 can no longer detect the pressure prevailing in the component 31.

The pressure sensor diagnosis 33 checks the pressure signal 32 for compliance with predetermined limit values, for example. Furthermore, the pressure sensor diagnosis 33 can check whether _: the pressure signal 32 has a predefined difference quotient and / or a predefined differential quotient. It can further be provided that the signal swing of the pressure signal 32 is checked. The pressure sensor diagnosis can also check the plausibility of the pressure signal 32 in that a relationship between a predetermined or occurring change in the exhaust gas volume flow and a corresponding change in the

Pressure signal 32 is produced.

If the pressure sensor diagnosis 33 detects a faulty pressure signal 32, the pressure signal diagnosis 33 provides the pressure sensor fault signal DF, which can be stored in the second fault memory Sp2. At this point in time, it cannot be ruled out that the pressure sensor 30 is working correctly, but cannot detect the correct pressure due to icing of the component 31. The temperature sensor 40, which detects the air temperature TL, is arranged, for example, in a control unit (not shown in more detail) or, for example, in the suction area of the internal combustion engine 10. Depending on the arrangement of the temperature sensor 40, the air temperature TL provided by the temperature sensor 40 is at least a measure of the temperature of the ambient air.

In a simple embodiment of the invention, the air temperature TL in the second comparator 43 can be compared directly with the predefined threshold value Lim.

In a preferred embodiment of the invention, the temperature supplied to the second comparator 43 is calculated. The calculation takes place in the minimum temperature calculation 41 as a function of the result of the first comparator 42, which checks whether the air temperature TL is less than or equal to the minimum temperature Tmin. In the case of the signal curves shown in FIG. 2, this is the case up to the first time t1. The first comparator 42 then outputs the yes signal j to the assignment 45. The assignment 45 then sets the

Minimum temperature Tmin fixed at least approximately to the air temperature TL.

At the first point in time t1, the first comparator 42 determines that the air temperature TL is greater than the minimum temperature Tmin. At the first time t1, the first comparator 42 therefore withdraws the yes signal j and outputs the no signal n to the integrator 44.

The minimum temperature Tmin provided by the minimum temperature calculation 41 is preferably kept constant for the delay time tv specified by the delay time specification 46. Instead of a specifically predefined delay line tv, a predefined number of events can be provided. Such events are, for example

Clock cycles or duty cycles in a computer.

From the second point in time t2, the integrator 44 takes over the determination of the minimum temperature Tmin. The integrator 44 causes the minimum temperature Tmin to rise according to a predetermined algorithm. In the simplest case, it is a linear one

Temperature rise, the slope can be determined depending on an expected change in the air temperature TL. The change per unit time is preferably less than the minimum possible temperature change in the air temperature TL. A non-linear temperature rise is conceivable, in which the rise increases with time. At the third point in time t3, the minimum temperature Tmin exceeds the predetermined threshold value Lim. The excess is detected in the second comparator 43.

The minimum temperature Tmin continues to increase until the fourth time t4. The fourth

At time t4, the first comparator 42 determines that the air temperature TL is again less than or equal to the minimum temperature Tmin. The second comparator 42 then takes back the no signal n and provides the yes signal j so that the minimum temperature is set equal to the air temperature TL on the basis of the assignment 45. Nothing changes in this state until the fifth time t5. At the fifth point in time t5, the first comparator 42 determines that the air temperature TL rises compared to the minimum temperature. The yes signal j is withdrawn and the no signal n is made available. However, the change can only take effect when the delay time tv specified by the delay time specification 46 has expired.

If the threshold temperature Lim is exceeded by the minimum temperature Tmin and is determined at the third time t3, the freezing signal G is withdrawn.

The threshold value Lim is at least approximately fixed to the freezing temperature of the material that can freeze in the component 31. The threshold Lim can be set, for example, to the freezing temperature of water. Another possibility is to fix a freezing temperature of a reagent present in the exhaust gas area 20, such as a urea-water solution, the freezing temperature of which is at least approximately -11 degrees Celsius.

The freeze signal G provided by the second comparator 43 can be stored in the first error memory Spl. The freeze signal G is linked in the first and second signal links 50, 51 with the pressure sensor error signal DF. The first signal link 50 provides the first error signal F1 when both the pressure sensor error signal DF and the freeze signal G are present. The occurrence of the two signals G, DF is symbolized by the respectively entered "1" in the first signal link 50. The error signal F1 that has occurred can be stored in the third error memory Sp3. The second signal combination 51 provides the third error signal F3 when the pressure sensor error signal DF is present and when the freezing signal G is not present at the same time. The occurrence of the pressure sensor error signal DF is symbolized in the second signal link 51 by a "1" and the freezer signal G which is not present is symbolized by a "0". A third error signal F3 that has occurred is stored in the fourth error memory Sp4.

In one embodiment it can be provided that both the freeze signal G stored in the first error memory Spl and the pressure sensor error signal DF stored in the second error memory Sp2 are shown on the display A. The first error memory Spl transmits the first display signal AI and the second error memory Sp2 the second display signal A2 to the display A. The operator can use the information that can be read from the first and second error memories S 1, Sp 2 or is shown on the display A to indicate that the pressure sensor diagnosis 33 has responded and that there may be or may be icing in the component 31. Before the pressure sensor

30 is exchanged, the component 31 can be subjected to icing. If the pressure sensor error signal DF has occurred, but if there is no icing at the same time, it can be assumed that the pressure sensor 30 is actually defective.

In one embodiment, it can be provided that a first or second occurred

Error signal Fl, F2 is displayed. The first or second error signal F1, F2 indicates that both the pressure sensor error signal DF and the freezing signal G have occurred simultaneously. An operator then immediately has the information that the component 31 should first be checked for icing before the pressure sensor 30 is replaced.

A further development of this embodiment provides that not every first error signal F1 that has occurred is displayed A. The counter Z counts the number of first error signals F1 that have occurred. The number of events can be determined by specifying the maximum counter reading of the counter Z. When the maximum count of the counter Z is reached, the counter Z provides the third display signal A3, which brings the error A to the display A. With this further education measure, unnecessary service stays can be avoided. An essential embodiment provides that the third error signal F3 stored in the third error memory Sp4 is brought to the display A with the fourth display signal A4. The third error signal F3 indicates an error which is highly likely to indicate an error in the pressure sensor 30 since there is no freezing signal G at the same time. If only the third error signal F3 is brought to display A, the error display on display A is changed to

Reduced case in which an actually occurred error can be assumed. With this configuration, the number of service stays is further reduced

In the exemplary embodiment shown, the threshold value Lim is fixed, with which the minimum temperature Tmin is compared. In an alternative embodiment it is provided that the threshold value Lim is tracked as a function of the air temperature TL and, if necessary, is compared directly with the air temperature TL.

The device according to the invention includes a computer on which the functions described are implemented as software.

Claims

claims 1. Method for diagnosing a pressure sensor (30) which detects a pressure in a component (31) arranged in an exhaust gas area (20) of an internal combustion engine (10), in which a pressure sensor diagnosis (33) provides a pressure sensor error signal (DF) , characterized in that a minimum temperature (Tmin), which is formed as a function of the air temperature (TL), is compared with a predetermined threshold value (Lim) and that a freezing signal (G) is provided when the minimum temperature (Tmin) is below the threshold (Lim). 2. The method according spoke 1, characterized in that a first error signal (Fl) is provided when the freeze signal (G) and the pressure sensor error signal (DF) are present at the same time. 3. The method according to claim two, characterized in that a second error signal (F2) is provided when the freeze signal (G) and the drain sensor error signal (DF) are present for a predetermined number of times. 4. The method according spoke 1, characterized in that a third error signal (F3) is provided when the freeze signal (G) is not present and when the drain sensor error signal (DF) is present. 5. The method claim 4, characterized in that the third error signal (F3) is shown on a display (A). 6. The method according spoke 1, characterized in that the minimum temperature (Tmin) corresponds at least approximately to the air temperature (TL). 7. The method according spoke 1, characterized in that the minimum temperature (Tmin) is calculated as a function of the air temperature (TL). 8. The method according spoke 7, characterized in that the minimum temperature (Tmin) is set at least approximately equal to the air temperature (TL) when the air temperature (TL) is less than or equal to the minimum temperature (Tmin) and that the minimum temperature (Tmin) increases when the air temperature (TL) is higher than the minimum temperature (Tmin). 9. The method according spoke 8, characterized in that the minimum temperature (Tmin) for a predetermined delay time (tv) or for a predetermined number of events is kept constant from the time (tl, t5) at which the air temperature (TL) is greater is called the minimum temperature (Tmin). 10. The method according to claim 1, characterized in that the threshold value (Lim) is matched to the freezing temperature of water or to the freezing temperature of a urea-water solution. 11. Device for performing the method according to one of the preceding claims.