Method for indicating function of a pressure sensor and an indication device pertaining to the method Technical field of the invention

The present invention concerns a method and an indicating device according to the preambles of the independent claims.

Background of the invention

The exhaust gas management systems in modern vehicles often comprise one or more catalytic converters, such as a selective catalytic reduction catalytic converter (SCR catalytic converter), diesel oxidation catalytic converter (DOC) or diesel particle filter (DPF), all of which contribute to reducing the emissions of environmentally harmful substances. To be able to control these devices properly, a plurality of sensors is arranged along the exhaust gas line to measure various parameters that are needed for such control. For example, temperature sensors, ΝΟχ sensors that measure the content of nitrous oxides (ΝΟχ), and pressure sensors are so arranged.

The temperature of the exhaust gases varies depending on the level of operation of the combustion engine, and can be as high as on the order of 750°C in certain operating cases. This places heavy demands on the sensors and transmitters that are arranged so as to measure various parameters for the exhaust gas flow.

A pressure sensor is often arranged in connection with the measurement of pressures in, for example, exhaust gas pipes. According to one variant, said sensor is disposed in one end of a tube that debouches at its other end in the exhaust gas pipe. One reason why the pressure sensor is arranged in such a sensor tube is that the pressure sensor should not be exposed to temperatures higher than ca. 150°C, while the temperature in the exhaust gas pipe can, as noted, be as high as 750°C. The sensor tube can measure on the order of several centimeters to a few decimeters in length, and have an inside diameter of under 10 mm, for example between 6 and 8 mm. Another reason for such a placement is that it makes it easier to access the pressure sensor, for example in connection with service. The pressure sensor often consists of a membrane made of, for example, metal, ceramic or silica in which certain electronics can be arranged in connection with the membrane so as to measure the strain, which is a direct measure of the pressure to which the membrane is being subjected. For example, piezoelectric components can be used. A ceramic membrane is often used in applications for goods vehicles.

Soot, fuel residue and moisture often accumulate in the pipe during operation, resulting in a risk of clogging.

Such clogging is a slow process that takes months to years in modern pipes.

The following patent documents represent the state of the art within the field.

WO-2010/068146 concerns a diagnostic method for a pressure regulator for an exhaust gas system to determine whether an erroneous pressure value is the result of clogging of the pressure sensor or of other causes.

GB-2400444 describes how changes in the output signal from the pressure sensor membrane can be detected, wherein the changes depend on particles that are deposited on the membrane.

The object of the present invention is to achieve an improved indication of the function of a pressure sensor in order to avoid operational disruptions and unplanned workshop visits attributable to failures of the pressure sensor to function satisfactorily, including those attributable to wholly or partly clogged sensor tubes or to coatings on the pressure sensor.

Summary of the invention

The above object is achieved by the invention defined in the independent claims.

Preferred embodiments are defined in the dependent claims.

The present invention is based on the inventor's insight that, in connection with clogging of a sensor tube, the flow through the tube decreases gradually, which leads to a gradual decrease in the frequency span that the pressure sensor detects, in that the highest frequencies are lost, or expressed in the time plane in that the step response of the membrane acquires an increasingly longer rise time/fall time.

By detecting, according to the invention, the frequency loss or times related thereto, an early warning can be obtained to indicate that the pipe is about to clog. For example, an error code can be set that will result in replacement/cleaning of the tube during the next workshop visit. This entails in turn that unexpected operational disturbances and unplanned workshop visits because of, for example, clogging of the sensor tube can be avoided.

Information about the function of the pressure sensor can be obtained by studying the step response of the pressure sensor.

The present invention is generally applicable for indicating the function of a pressure sensor, wherein the pressure sensor is adapted so as to measure the pressure of a medium that can be a gas, for example an exhaust gas from a combustion engine, or a liquid, for example oil, urea, diesel or cooling liquid.

The present invention is primarily applicable for pressure sensors arranged in the end of a sensor tube, whereupon the information about the sensor indicates in part the extent to which the tube is clogged, but can also indicate whether any coatings have formed on the membrane. According to one embodiment, the pressure sensor is arranged directly in the exhaust gas pipe wall, and an indication as to whether coatings have formed can then be obtained through the application of the invention.

Brief description of the drawing

Figure 1 is a block diagram that schematically illustrates one embodiment of the present invention.

Figure 2 is a block diagram that schematically illustrates another embodiment of the present invention.

Figure 3 is a block diagram that schematically illustrates the embodiment shown in Figure t .

Figure 4 is a block diagram that schematically illustrates the embodiment shown in Figure 2. Figure 5 comprises graphs that illustrate the present invention. Detailed description of preferred embodiments of the invention

The present invention will now be described in detail with reference to the accompanying figures. The invention will be described with reference to a pressure sensor mounted in an exhaust gas line, exemplified here by an exhaust gas pipe, but the invention is also suitable for pressure measurements of other media and in other mounting sites on the vehicle, e.g. in connection with the engine, the exhaust gas management system or elsewhere on the vehicle, for example for measuring the pressure of the intake system gas or the lubrication system oil.

Figure 1 is a block diagram that schematically illustrates one embodiment of the present invention. The figure shows an indicating device 2 intended to indicate the function of a pressure sensor 4 arranged so as to measure the pressure of the exhaust gases 6 in an exhaust gas pipe 8 from a combustion engine. The combustion engine can be arranged in a vehicle, such as a goods vehicle, bus or car, but also on a vessel or in industry.

As noted above, the pressure sensor 4 often consists of a membrane of, for example, metal, ceramic or silica wherein certain electronics can be arranged in connection with the membrane in order to measure the strain, which is a direct measure of the pressure to which the membrane is being subjected. For example, piezoelectric components can be used. A ceramic membrane is often used in connection with applications on goods vehicles.

The indicating device 2 is adapted so as to receive a pressure signal 10 from the pressure sensor 4 and a time signal 12 indicating the time point t _s for a pressure change in the exhaust gas flow. This can be one step, but can also assume other well-defined shapes or combinations of shapes, such as, for example, a ramp or a staircase.

The time point for the pressure change is known. This can consist of a change in any of the actuating devices of the engine, the exhaust gas management system or the vehicle. This change is seen as, for example, a change in the engine rpm, the time point for a request for exhaust braking, or the engagement of the turbo system. The change in the exhaust gas flow can be an increase or a decrease in the exhaust gas flow.

In order to be able to use the pressure change in the exhaust gas flow in connection with the indication of the function of the pressure sensor, it is necessary for the change to exceed a predetermined threshold value. This can, for example, be a specified portion of the current pressure exhibited by the exhaust gas flow, e.g. as 10%. It can also be represented by an absolute pressure change, e.g. 10 kPa. Because the sensor tube has a certain length, there will be a certain time delay before the pressure wave reaches the pressure sensor. This time delay plays no role, or only an extremely minor one, in connection with applications of the present invention.

The indicating device 2 is further adapted so as to determine the pressure signal 10 after the pressure change during a predetermined measurement period. The predetermined measurement period is long enough for the pressure sensor to be able to detect the pressure change, for example maximally on the order of magnitude of 1 minute.

The indicating device then determines a parameter Y for the pressure signal 10 and compares the determined parameter Y to one or a plurality of threshold values Y _T , and is adapted so as to generate an indication signal 14 in dependence upon said comparison, whereupon the indication signal 14 indicates the function of the pressure sensor 4.

The indication signal can, for example, consist of an indicator lamp in connection with the instrument panel, or can result in an interface accessible at the workshop being updated with the latest diagnostic information regarding the function of the pressure sensor, such as setting an error code.

According to one embodiment, the parameter Y for the pressure signal 10 can be a measured time from the time point t _s or, according to another embodiment, a frequency of the pressure signal after the time point t _s . The parameter Y is thus, according to one embodiment, a measured time t _m from the time point t _s . The threshold value Υχ is then a time point at which the pressure after t _s is a predetermined portion of the pressure change. The indication signal is adapted so as to indicate a degraded function if said measured time t _m exceeds said threshold value Y _f .

This embodiment will be explained in detail with reference to the graphs shown in Figure 5.

In Figure 5, the x-axis designates the time T, and the y-axis the pressure P.

The solid curve is the pressure in the exhaust gas pipe, which initially sits at a higher level Pi before subsequently, at time point t _s decreasing to a lower level P ₂ . This decrease is the pressure change discussed above. The pressure change can just as well be an increase in the pressure. It can, as in Figure 5, be a step, but it can also, as noted above, assume other well-defined shapes or combinations of shapes, such as a ramp or a staircase.

The figure also shows four examples Si, S ₂ , S ₃ and S ₄ , of step responses (broken lines in the figure), i.e. the pressures that are sensed by the pressure sensor 10 for a pressure sensor, which examples show a gradual degradation of the function of the pressure sensor. A measure of the function of the pressure sensor can be obtained by measuring the time it takes until the pressure sensor emits the output signal, which can, for example, be 63% of the total pressure change (see level Po.63 in the figure) and comparing this time to a predetermined threshold value (see the vertical broken marking Υτι).

The curve S i shows a pressure signal from a pressure sensor that essentially tracks the pressure change with no time delay, i.e. the pressure sensor is functioning perfectly.

The curve S ₂ shows a time delay t ₂ before the pressure sensor 10 detects the pressure decrease. Because t ₂ is shorter than Υτι, the function of the pressure sensor is acceptable. The curve S ₃ shows a time delay t ₃ before the pressure sensor detects the pressure decrease. In this case the time delay t ₃ is longer than Y _T i, and the indication signal 14 will then indicate that the pressure sensor 10 is not functioning acceptably.

The curve S ₄ shows an example in which the pressure sensor is not functioning at all as intended, in that no change in the pressure signal can be identified in connection with the pressure change in the exhaust gas flow. A plurality of threshold values Yn can naturally be used to be able to obtain more detailed information about the function of the pressure sensor, i.e. how far the degradation has progressed, and to be able to compare various measurement time points easily. For example, 2-5 threshold values can be suitable for achieving this.

It is also possible, within the framework of this embodiment, to measure the actual time it takes for the pressure sensor to detect a given pressure change, e.g. the time it takes to reach the level P ₀ . ₆ 3, and let that time constitute the information in the indication signal.

The pressure sensors that are currently in use normally have a maximum rated response frequency of roughly 100 Hz, which corresponds to a response time of 0.01 second. For example, the response frequency can be 10 Hz, corresponding to 0.1 second. Suitable values for the threshold value Yji preferably lie in the range of 0.1-10 seconds.

According to another embodiment, the parameter Y is the frequency of the pressure signal 10 after the time point t _s . The threshold value Υχ is then a frequency of the pressure signal after the time point t _s that represents a predetermined degradation of the function of the pressure sensor. The threshold value preferably lies within the range of 0.1-10 Hz, and is 1 Hz according to one embodiment. The pressure sensor is often arranged in the end of a so-called sensor tube 18, wherein the pressure sensor 4 is mounted in one end 20 opposite one end 22 that debouches in the exhaust gas pipe 8. The reason for disposing the pressure sensor in this way is both to protect the pressure sensor from the high temperatures, sometimes above 700°C, that the exhaust gases can exhibit, and to increase the accessibility of the pressure sensor. A sensor tube 18 can have a length of from several centimeters to several decimeters, and an inside diameter in the range of 2-20 mm.

Figure 3 schematically illustrates how the sensor tube 18 can be clogged by, for example, soot and oil residues 16. The indication signal 14 is thus adapted so as to indicate the degree of clogging 16 of the sensor tube 18. The present invention is also suitable for indicating the presence of coatings on a pressure sensor 4 even if it is not mounted in the end of a sensor tube. Figure 4 illustrates a case in which the pressure sensor is mounted directly in the wall of the exhaust gas pipe. The indication signal 14 is then adapted so as to indicate the presence of coatings 24 on the pressure sensor 4, and preferably the degree of coating on the pressure sensor as well.

According to an additional embodiment, the indicating device 2 is adapted so as to generate an initiating signal 26 to initiate a pressure change in the exhaust gas flow. This initiating signal 26 can be generated by means of a manual input by the driver, or generated automatically at a set measurement interval.

The present invention also includes a method for indicating the function of a pressure sensor arranged so as to measure the pressure of the exhaust gases in an exhaust gas pipe from a combustion engine. The method will now be described briefly with reference to the flow diagram in Figure 6. Reference is also made, where relevant, to the foregoing detailed description of the indicating device.

The method according to the invention comprises the steps of

A - imposing a pressure change in the medium, for example the exhaust gas flow;

B - determining the time point t _s for this pressure change;

C - determining at least one pressure signal after the imposed pressure change over a predetermined measurement period;

D - determining at least one parameter Y for the pressure signal;

E - comparing said determined parameter/parameters Y to one or a plurality of threshold values Yj, and

F - generating an indication signal in dependence upon said comparison, whereupon the indication signal is adapted so as to indicate the function of the pressure sensor.

According to one embodiment of the method, the parameter Y is a measured time t _m from the time point t _s . The threshold value Yj is then a time point, related to the time point t _s , at which the pressure after t _s is a predetermined portion of the imposed pressure change. The indication signal is adapted so as to indicate a degraded function if said measured time t _m exceeds said threshold value Y-p A detailed description of this embodiment has been provided above, including with reference to Figure 5.

According to another embodiment, the parameter Y is the frequency of the pressure signal after the time point t _s . The threshold value Υχ is then a frequency of the pressure signal after the time point t _s that represents a predetermined degradation of the function of the pressure sensor. The threshold value preferably lies within the range of 0.1- 10 Hz, and is 1 Hz according to one embodiment.

According to one embodiment, the indication signal is adapted so as to indicate the degree of clogging of a sensor tube where the pressure sensor is mounted in one end opposite the end that debouches in the exhaust gas pipe.

According to another embodiment, the indication signal is adapted so as to indicate the presence of coatings on the pressure sensor, and can be mounted directly in the wall of the exhaust gas pipe.

According to an additional embodiment, the indicating device is adapted so as to generate an initiating signal to initiate said pressure change in the exhaust gas flow. This change can be initiated manually by means of input from the vehicle driver, or initiated automatically at a set measurement interval.

The present invention is not limited to the preferred embodiments described above.

Various alternatives, modifications and equivalents can be used. The embodiments above are consequently not to be viewed as limiting the protective scope of the invention, which is defined in the accompanying claims.