TECHNICAL FIELD

The present invention relates to a system and a method for determining the concentration of exhaust gases emitted by an automotive internal-combustion engine, preferably a petrol or diesel engine of a motor vehicle, or a motor cycle, or any other type of similar land vehicle, to which the ensuing treatment will make explicit reference, without this implying any loss of generality.

BACKGROUND ART

As is known, gas-analyser systems are configured for determining the concentration of pollutant gases emitted by motor vehicles, typically carbon dioxide CO ₂ and carbon monoxide CO, and/or hydrocarbon gases such as hexane, propane, etc., so as to be able to verify whether the concentrations detected are or not below corresponding limit thresholds established by law.

Some currently known systems for analysing engine exhaust gases function according to NDIR (non-dispersive infrared) technology and typically comprise: a gas-analysis chamber provided with an inlet terminal connected, through an active- carbon filter, to the exhaust duct of the engine in order to receive the exhaust gases to be analysed; a pump designed to take in the exhaust gases from the exhaust duct of the vehicle so as to introduce them into the analysis chamber; an infrared-emitter source designed to emit within the gas- analysis chamber a beam of radiation in the infrared frequency band; an infrared multidetector device configured for generating an electrical signal of an electrical quantity that indicates absorption of radiation by the exhaust gases in given frequency bands; and an electronic control circuit for determining the concentration of each pre-set exhaust gas on the basis of the electrical quantity of the signal associated to said pre-set gas detector, and of an electrical reference quantity associated to a condition of absence of gases in the analysis chamber.

The exhaust-gas-analyser systems described above are typically configured so as to carry out an initial automatic calibration, during which the electronic control circuit determines the electrical reference quantity, normally the voltage associated to a zero concentration of gases referred to hereinafter as "reference zero". The electrical reference quantity associated to the reference zero is then used precisely as reference in determining the concentration of the exhaust gases.

In the case in point, the automatic calibration is carried out by: taking in air from the external environment, filtering it through the active-carbon filter, and introducing it filtered into the analysis chamber; generating the beam of radiation into the chamber; and assigning to the electrical reference quantity the electrical quantity generated by the multidetector device.

Unfortunately, the determination of the electrical reference quantity, carried out through the initial automatic calibration described above, is affected, on the one hand, by intrinsic error caused by the presence of contaminating gases in the external environmental air used as "gas-free" reference air and, on the other, by the insufficient capacity of filtering of the gases by the active-carbon filter.

Laboratory tests conducted by the present applicant have in fact shown that the air taken in from the external environment is not pure, but contains concentrations of carbon dioxide and/or carbon monoxide that, in addition to not being negligible for the purposes of analysis of contaminating gases, vary on the basis of various factors, such as, for example, the place and the instant at which the analysis is carried out. The result of the aforesaid laboratory tests finds confirmation also in the statistical estimates present in numerous scientific publications, which show, for example, that the presence of carbon dioxide CO ₂ in the atmosphere tends to increase exponentially and that today its average percentage in the air is approximately 0.039%.

The present applicant has conducted an in-depth study having as object identification of a solution that will enable increase of the precision in determining the electrical reference quantity associated to the reference zero in the course of automatic calibration of the analyser system.

DISCLOSURE OF INVENTION

The aim of the present invention is hence to provide a solution that will enable the object indicated above to be achieved .

The above aim is achieved by the present invention in so far as it relates to a system and a method for determining the concentration of one or more exhaust gases emitted by an automotive internal-combustion engine, as defined in the annexed claims.

The present invention moreover regards a method for determining the concentration of one or more exhaust gases emitted by an automotive internal-combustion engine, as defined in Claim 5 and any one of the claims that depend thereupon .

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to the annexed drawings, which illustrate a non-limiting example of embodiment thereof, and in which:

Figure 1 is a schematic illustration of a system for analysing exhaust gases emitted by an automotive internal- combustion engine, provided according to the teachings of the present invention; and

- Figure 2 is a flowchart of the operations implemented by the exhaust-gas analyser system shown in Figure 1.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will now be described in detail with reference to the attached figures to enable a person skilled in the sector to implement and use it. Various modifications to the embodiments described will be immediately evident to skilled persons, and the generic principles described can be applied to other embodiments and applications without thereby departing from the sphere of protection of the present invention, as defined in the annexed claims. Consequently, the present invention must not be considered as being limited to the embodiments described and illustrated, but it must be granted the widest sphere of protection in conformance with the principles and characteristics described and claimed herein .

With reference to Figure 1, designated as a whole by 1 is an automotive exhaust-gas analyser system configured to determine the concentration of one or more exhaust gases emitted by an internal-combustion engine 2 of a vehicle 3, through an exhaust-gas duct 4.

Preferably, the vehicle 3 may correspond to a motor vehicle, or a motor cycle, or any other type of similar land vehicle.

The exhaust-gas analyser system 1 is provided with an infrared multidetector device 5, which comprises: an analysis chamber 6 structured for receiving and containing the exhaust gases to be analysed; an infrared emitter device 7, which is coupled to the analysis chamber 6 and is configured to emit a beam of radiation, which has wavelengths comprised in the infrared band, into the analysis chamber 6 so as to pass through the exhaust gases contained therein; and a series of infrared sensors or mult idetectors 8, which are coupled to the analysis chamber 6, preferably on the opposite side with respect to the infrared emitter device 7 to receive the radiation emitted, and are configured in such a way as to measure the concentration of one or more exhaust gases present within of the analysis chamber 6, on the basis of the variations of energy of the radiation in the bands of the absorption frequencies of the pre-set gases themselves.

Preferably, the infrared mult idetectors 8 could be configured to measure the concentration of one or more of the following exhaust gases: carbon dioxide CO ₂ , and/or carbon monoxide CO, and/or hydrocarbon gases such as, for example, hexane and propane or similar pollutant gases. In greater detail, infrared mult idetectors 8 are configured to output one or more electrical signals S _G As±r the electrical quantities (current or voltage) of which indicate the concentrations of the gases detected in the analysis chamber 6.

In particular, in the example illustrated in Figure 1, the electrical quantity of an electrical signal SQ _AS I generated by the infrared mult idetectors 8 indicates the concentration of carbon dioxide, the electrical quantity of an electrical signal S _GAS2 generated by the infrared mult idetectors 8 indicates the concentration of carbon monoxide, the electrical quantity of an electrical signal S _GAS 3 generated by the infrared mult idetectors 8 indicates the concentration of hexane, and the electrical quantity of an electrical signal SQ _AS4 generated by the infrared mult idetectors 8 indicates the concentration of propane.

With reference to Figure 1, the exhaust-gas analyser system 1 further comprises an intake pump 9 corresponding, for example, to a vacuum pump, which is connected to the analysis chamber 6 and is designed, upon command, to take in the exhaust gases contained in the latter so as to expel them preferably into the external environment .

According to a preferred embodiment shown in Figure 1, the analysis chamber 6 is structured to present an inlet terminal 10, which is designed to be connected to the exhaust-gas duct 4, through, preferably, an external connection pipe 11, which is for example flexible, for receiving the engine exhaust gases; and an outlet terminal 12 connected to an intake terminal 13 of the intake pump 9.

The exhaust-gas analyser system 1 further comprises an electrically controlled shut-off valve 14, for example a solenoid valve, which is arranged in a position corresponding to the inlet terminal 10 of the analysis chamber 6, for example along a duct which connects the inlet terminal 10 to the analysis chamber 6, and is configured to switch between an opening state and a closing state in which it opens and, respectively, closes the inlet terminal 10 so as to connect or, respectively, isolate the analysis chamber to/from the exhaust-gas duct 4.

With reference to Figure 1, the exhaust-gas analyser system 1 further comprises an electronic control unit 15, which is electrically connected to: the intake pump 9 and the infrared emitter device 7 in such a way as to control turning- on/turning-off thereof; the infrared multidetectors 8 so as to receive the electrical signals S QASI indicating the concentrations of the exhaust gases detected in the analysis chamber 6; and the shut-off valve 14 for controlling selectively the closing/opening state thereof.

In particular, the electronic control unit 15 is configured to perform an automatic procedure of calibration of an electrical reference quantity, for example a voltage V0, associated to a condition of absence of gases in the analysis chamber 6, and in use, controls intake of the exhaust gases into the analysis chamber 6, actuates the infrared mult idetector device 5 to generate the electrical signals S QASI, and determines the concentrations of one or more exhaust gases, on the basis of the electrical quantities, for example of the voltages Vmi, associated to the signals S _GRS ± received, and of the electrical reference quantity VO associated to the condition of absence of gases in the analysis chamber 6.

According to a possible embodiment, the electronic control unit 15 is configured to determine the concentration of the exhaust gases contained in the analysis chamber 6 through a function of absorption of the radiation of the exhaust gases in the chamber F(V0/Vmi), where VO is the reference quantity generated by the infrared mult idetectors 5 in the course of automatic calibration, while Vmi is the voltage of the electrical signal S _GAS ± generated by the infrared mult idetectors 8 and is associated to the i-th gas.

Preferably, but not necessarily, the function of absorption of radiation implemented by the electronic control unit 15 for calculating the concentration of the gases can correspond, for example, to the known Beer-Lambert equation:

F(V0/Vmi)= -log (VO /Vmi)

Represented in Figure 2 are the operations implemented by the analyser system 1 during determination of the effective concentration of the engine exhaust gases, where it is assumed that the external connection pipe 11 is appropriately coupled to the exhaust-gas duct 4, for example fitted into the latter.

The electronic control unit 15 is configured to perform a first procedure in which it automatically calibrates the electrical reference quantity VO associated to the condition of absence of gases in the analysis chamber (Block 100), and then carries out a procedure of analysis so as to determine the concentration of the engine exhaust gases (Block 200) . In particular, in the calibration procedure, the electronic control unit 15: controls closing of the shut-off valve 14 (Block 110) so as to isolate the analysis chamber 6 from the exhaust-gas duct 4; and turns on the intake pump 9 (Block 120) in such a way as to suck the residual gases contained in the analysis chamber 6 until a condition of complete absence of gases in the analysis chamber 6 is reached, where the pressure inside the latter reaches approximately a minimum vacuum pressure (Block 130) . In other words, the electronic control unit 15 actuates the intake pump 9 for creating a negative pressure in the analysis chamber 6 so as to bring it to a minimum pre-set pressure corresponding approximately to a vacuum pressure associated substantially to a vacuum condition. In this step, the intake pump 9 advantageously clears the analysis chamber 6 of any trace of gas thus bringing about a complete cleaning thereof.

The minimum vacuum pressure can be comprised, for example, between about 0 and 5·10 ^~3 bar, preferably about 2.5·10 ^~3 bar.

The electronic control unit 15 is configured to carry out advantageously calibration of the electrical reference quantity V0 associated to the condition of absence of gases within the gas-analysis chamber 6 (Block 140) . In the case in point, the electronic control unit 15 switches on the infrared emitter device 7 to generate the beam of radiation in the analysis chamber 6, and receives from the infrared multidetectors 8 the electrical quantity associated to the condition of absence of gases. In detail, the electronic control unit 15 determines the electrical reference quantity V0 on the basis of the electrical quantity of the electrical signal generated by the infrared multidetectors 8 in the condition of absence of gases.

Complete cleaning of the gas-analysis chamber 6 enables in fact the analyser system 1 to associate in a conveniently accurate way the electrical reference quantity, for example the value of the voltage VO of the electrical signal generated by the infrared multidetectors 8 to a zero gas concentration (reference zero used by the system for the subsequent calculations of gas concentration) .

Once the calibration described above is through, the electronic control unit 15: governs opening of the shut-off valve 14 in such a way as to take in the exhaust gases emitted by the exhaust duct 4 within the analysis chamber 6 (Block 210); turns back on the infrared emitter device 7, if it is off, or keeps it on so as to emit radiation towards the exhaust gases in the analysis chamber 6 (Block 220); receives the electrical quantities Vmi associated to the electrical signals generated by the infrared multidetectors 8 on the basis of the energy absorption of corresponding gases in the pre-set frequency bands associated to the gases themselves; and determines the concentration of the exhaust gases on the basis of the electrical quantities Vmi themselves (Block 230) .

At this point, the electronic control unit 15 can preferably, but not necessarily, compare the concentrations of the exhaust gases determined with corresponding gas-concentration thresholds and generate, through a user interface 16, warning messages/signals on the basis of the result of the comparisons and/or communicate to the user the gas concentrations determined themselves.

The advantages of the exhaust-gas analyser system described above are evident. The complete evacuation of the residual gases from the analysis chamber carried out in the course of automatic calibration enables determination of a correct reference quantity in so far as it is associated to a real condition of absence of gases in the analysis chamber. The precision of calculation of the reference quantity, i.e., of the reference zero, consequently determines an increase in the precision of the effective measurements of concentration of the gases, in particular when a function associated to the absorption of radiation using the reference quantity itself is used in the calculation.

Finally, it is clear that modifications and variations may be made to the system described and illustrated above without thereby departing from the scope of the present invention defined by the annexed claims.