CLIAMS:We Claim:
1 A method of calculating efficiency of a diesel particulate filter (DPF), the method comprising:
measuring a first resonant frequency of said DPF, said first resonant frequency corresponding to a frequency of said DPF when exhaust gases are entering into said DPF, wherein said first resonant frequency is used to calculate a mass flow rate of said exhaust gases entering into said DPF;
measuring a second resonant frequency of said DPF, said second resonant frequency corresponding to a frequency of said DPF when exhaust gases are flowing out of said DPF, wherein said second resonant frequency is used to calculate a mass flow rate of said exhaust gases flowing out of said DPF; and
determining difference between said mass flow rate entering into said DPF and said mass flow rate flowing out of said DPF, wherein said difference is used for calculating efficiency of said DPF.
2 The method as claimed in claim 1, wherein said first resonant frequency is measured using a first resonator located at an inlet of the DPF.
3 The method as claimed in claim 1, wherein said second resonant frequency is measured using a second resonator located at an outlet of the DPF.
4 The method as claimed in claim 1, wherein said first resonator and said second resonator is a langasite resonator.
5 The method as claimed in claim 1, wherein said efficiency of said DPF is calculated at regular intervals.
6 A method of determining regeneration state of a DPF, the method comprising:
measuring a first resonant frequency of said DPF, said first resonant frequency corresponding to a frequency of said DPF when exhaust gases are entering into said DPF, wherein said first resonant frequency is used to calculate a mass flow rate of said exhaust gases entering into said DPF;
measuring a second resonant frequency of said DPF, said second resonant frequency corresponding to a frequency of said DPF when exhaust gases are flowing out of said DPF, wherein said second resonant frequency is used to calculate a mass flow rate of said exhaust gases flowing out of said DPF;
determining difference between said mass flow rate of said exhaust gases entering into said DPF and said mass flow rate of said exhaust gases flowing out of said DPF, wherein said difference is used for calculating efficiency of said DPF; and
comparing said calculated efficiency with a threshold value to determine said regeneration state of said DPF.
7 A control unit for calculating efficiency of a diesel particulate filter (DPF), said control unit adapted to:
receive a first resonant frequency of said DPF from a first resonator, wherein said first resonant frequency is further used for calculating a mass flow rate of exhaust gases entering into said DPF;
receive a second resonant frequency of said DPF from a second resonator, wherein said second resonant frequency is further used for calculating a mass flow rate of exhaust gases flowing out of said DPF;
calculate difference between said mass flow rate of said exhaust gases entering into said DPF and said mass flow rate of said exhaust gases flowing out of said DPF, wherein said difference is used for calculating efficiency of said DPF.
8 A control unit for determining regeneration state of a DPF, said control unit adapted to:
receive a first resonant frequency of said DPF from a first resonator, wherein said first resonant frequency is further used for calculating a mass flow rate of exhaust gases entering into said DPF;
receive a second resonant frequency of said DPF from a second resonator, wherein said second resonant frequency is further used for calculating a mass flow rate of exhaust gases flowing out of said DPF;
calculate difference between said mass flow rate of said exhaust gases entering into said DPF and said mass flow rate of said exhaust gases flowing out of said DPF, wherein said difference is used for calculating efficiency of said DPF; and
compare said calculated efficiency with a threshold value to determine said regeneration state of said DPF. ,TagSPECI:The following specification particularly describes the invention and the manner in which it is to be performed.

Field of the invention
This invention relates to a method of calculating efficiency of a diesel particulate filter (DPF).

Background of the invention
A diesel particulate filter (DPF) is an exhaust treatment device that filters particulate matter emitted by the diesel engine. When the exhaust gases flows through the DPF, the DPF traps the particulate matter and further disposes the particulate matter trapped using a process called regeneration.

The DPF should be monitored regularly to ensure if particulate matter is efficiently filtered by the DPF before the exhaust gases are emitted to the atmosphere. When the DPF is completely clogged with the particulate matter, the filtration of the particulate matter by the DPF fails and particulate matter is emitted into the atmosphere thereby, failing to meet emission norms. When the DPF is completely clogged with the particulate matter, regeneration process should be undertaken so that the trapped particulate matter within the DPF is burnt. Hence, the DPF should be monitored regularly to determine if the DPF is filtering the particulate matter efficiently.

A German patent number DE-102013214656 discloses one such technique to monitor the DPF by measuring pressure drops across the DPF at two different instant of times.

Brief description of the accompanying drawings
Figure 1 is a flowchart illustrating a method of calculating efficiency of a diesel particulate filter (DPF), in accordance with an embodiment; and
Figure 2 is a flowchart illustrating a method of determining regeneration state of a DPF, in accordance with an embodiment.

Detailed description
Figure 1 is a flowchart illustrating a method of calculating efficiency of a diesel particulate filter (DPF), in accordance with an embodiment.

In accordance with this disclosure, the method includes measuring a first resonant frequency of the DPF. The first resonant frequency corresponds to a frequency of the DPF when exhaust gases are entering into the DPF. The first resonant frequency is used to calculate a mass flow rate of the exhaust gases entering into the DPF. The method also includes measuring a second resonant frequency of the DPF. The second resonant frequency corresponds to a frequency of the DPF when exhaust gases are flowing out of the DPF. The second resonant frequency is used to calculate a mass flow rate of the exhaust gases flowing out of the DPF and determining difference between the mass flow rate entering into the DPF and the mass flow rate flowing out of the DPF as shown in step 115. The difference is used for calculating efficiency of said DPF.

At step 105, a first resonant frequency of the DPF is measured. The resonant frequency is measured using a first resonator located at the inlet of the DPF. In one case, the first resonator is a langasite resonator since the langasite resonator can withstand temperature range existing in an exhaust pipe of the vehicle. However, it should be noted that other resonators that can withstand temperature range of the exhaust gases existing in the exhaust pipe can also be used for determining the first resonant frequency of the DPF. The langasite resonator is connected at the inlet of the DPF using a bolted contact.

The first resonant frequency is measured when the exhaust gases are entering into the DPF. When the exhaust gases passes through the langasite resonator, a piezoelectric crystal present in the langasite resonator begins to vibrate with maximum amplitude during resonance. At resonance, the first resonant frequency, of the DPF, is detected by platinum electrodes present in the langasite resonator. Further, the platinum electrodes transmit the first resonant frequency to a control unit in the form of a voltage value.

The first resonant frequency is used for calculating the mass of the exhaust gases entering into the DPF. For obtaining the mass of the exhaust gases at high precision, the mass flow rate of the exhaust gases entering into the DPF is determined. The mass flow rate is determined by measuring the first resonant frequency repeatedly over time. Hence, mass of the exhaust gases corresponding to each of the multiple resonant frequencies is obtained. Further, the mass of the exhaust gases corresponding to each of the resonant frequency is integrated to determine the mass flow rate of the exhaust gases entering into the DPF.

At step 110, the second resonant frequency of the DPF is measured. The second resonant frequency is measured when the exhaust gases are flowing out of the DPF. The second resonant frequency is measured using a second resonator located at the outlet of the DPF using a bolted contact. The second resonator is also a langasite resonator. When the exhaust gases are flowing out of the DPF, the peizoelectric crystal present in the langasite resonator begins to vibrate during resonance with maximum amplitude. At resonance, the second resonant frequency of the DPF is detected by platinum electrodes present in the langasite resonator. The second resonant frequency is then transmitted to the control unit in the form of a voltage value. The second resonant frequency measured will not be equal to the first resonant frequency because of change in mass of the DPF that occurs due to the deposition of particulate matter in the DPF.

The second resonant frequency that is measured is used for determining mass of the exhaust gases flowing out of the DPF. For obtaining the mass of the exhaust gases at high precision, mass flow rate of the exhaust gases flowing out of the DPF is determined. The mass flow rate is determined by measuring second resonant frequency values repeatedly over a period of time when the exhaust gases are flowing out of the DPF. Further, mass of the exhaust gases that correspond to each of the multiple resonant frequencies are calculated. The masses of the exhaust gases are then integrated to determine the mass flow rate of the exhaust gases flowing out of the DPF.

At step 115, the difference between the mass flow rate of the exhaust gases entering into the DPF and the mass flow rate of the exhaust gases flowing out of the DPF is calculated. The value of difference calculated, indicates the mass of particulate matter deposited in the DPF.

The difference obtained is used for calculating the efficiency of the DPF. Efficiency of the DPF is calculated by computing ratio of the calculated difference and the mass flow rate of the exhaust gases calculated in step 105.

The efficiency of the DPF is compared with a threshold value. If efficiency of the DPF is lesser than or equal to the threshold value then it is considered that the DPF is unclogged. If the efficiency of the DPF is above the threshold then it is considered that the DPF is clogged with the particulate matter. The method of calculating the efficiency of the DPF is performed at regular intervals.

A control unit for calculating efficiency of the DPF is adapted to receive the first resonant frequency from a first resonator. Upon receiving the first resonant frequency, the control unit calculates mass flow of the exhaust gases entering into the DPF. The mass flow of the exhaust gases is calculated using the equation (1) as shown below:
F1= 1/(2p ) v(k/m1) equation (1)
F1= first resonant frequency
m1= mass of exhaust gases flowing into the DPF
k=vibration constant of the peizoelectric crystal
For obtaining the mass flow value of the exhaust gases entering into the DPF with higher precision, the mass flow rate of the exhaust gases is calculated. This is done by measuring the first resonant frequency repeatedly over a time period by the first langasite resonator. Hence multiple first resonant frequency values are received by the control unit from the first langasite resonator. The mass flow obtained with each of the first resonant frequency value is computed by the control unit. Further, the control unit integrates each of the mass flow values to determine the mass flow rate of the exhaust gases entering into the DPF.

The control unit also receives the second resonant frequency from the second resonator. Upon receiving the second resonant frequency, the control unit calculates mass flow of the exhaust gases flowing out of the DPF. The mass flow of the exhaust gases flowing out of the DPF is calculated using the equation (2) as shown below:
F2= 1/(2p ) v(k/m2) equation (2)
F2= second resonant frequency
M2= mass of exhaust gases flowing out of the DPF
k=vibration constant of the peizoelectric crystal

For obtaining the mass flow value of the exhaust gases entering out of the DPF with higher precision, the mass flow rate of the exhaust gases is calculated. The second resonant frequency is measured repeatedly over a time period by the second langasite resonator. Therefore multiple values of the second resonant frequency are received by the control unit from the second langasite resonator. The mass flow obtained with each of the second resonant frequency values is computed by the control unit and then the control unit integrates each of the mass flow values to determine the mass flow rate of the exhaust gases flowing out of the DPF.

Upon calculating the mass flow rate of the exhaust gases entering into the DPF and the mass flow rate of the exhaust gases flowing out of the DPF, the control unit calculates the difference between the mass flow rate of the exhaust gases entering into the DPF and the mass flow rate of the exhaust gases flowing out of the DPF. The difference calculated indicates the quantity of the particulate matter deposited in the DPF. If there is accumulation of the particulate matter in the DPF then the mass flow rate of the exhaust gases flowing out of the DPF will be lesser than the mass flow rate of the exhaust gases flowing into the DPF. If there is no accumulation of the particulate matter entering into the DPF then the mass flow rate of the exhaust gases entering into the DPF will be almost equal to the mass flow rate of the exhaust gases flowing out of the DPF.

The control unit further calculates efficiency of the DPF using the difference calculated. The control unit computes ratio of the calculated difference and the mass flow rate of the exhaust gases entering into the DPF for calculating the efficiency of the DPF. The efficiency value computed is compared to a threshold value.

The lower the efficiency value the cleaner is the DPF. Hence, if the efficiency value calculated is lesser than or equal to the threshold value then it is considered that the DPF is in working condition and does not require regeneration. If the efficiency value calculated is greater than the threshold value then it is considered that the DPF is completely clogged with the particulate matter and the DPF requires regeneration.

Figure 2 is a flowchart illustrating a method of determining regeneration state of a DPF, in accordance with an embodiment. The method includes measuring a first resonant frequency of the DPF. The first resonant frequency corresponds to a frequency of the DPF when exhaust gases are entering into the DPF. The first resonant frequency is used to calculate a mass flow rate of the exhaust gases entering into the DPF. The method also includes measuring a second resonant frequency of the DPF. The second resonant frequency corresponds to a frequency of the DPF when exhaust gases are flowing out of the DPF. The second resonant frequency is used to calculate a mass flow rate of the exhaust gases flowing out of the DPF, determining difference between the mass flow rate entering into the DPF and the mass flow rate flowing out of the DPF, the difference is used for calculating efficiency of said DPF and comparing the calculated efficiency with a threshold value to determine the regeneration state of the DPF.

During regeneration of the DPF or just after regeneration of the DPF, it is required to determine the regeneration state of the DPF. The regeneration state of the DPF indicates if the regeneration process is complete or if the regeneration is incomplete. In case the regeneration of the DPF is incomplete then the regeneration process can be continued until the DPF is unclogged from the particulate matter. Hence, Figure 2 defines a method of determining the regeneration state of the DPF.

At step 205, the first resonant frequency of the DPF is measured using a first resonator located at an inlet of the DPF. The first resonant frequency is measured when the exhaust gases are entering into the DPF. The first resonant frequency measured, is used to calculate the mass flow rate of the exhaust gases entering into said DPF. The mass flow rate of the exhaust gases entering into the DPF is calculated using similar steps as explained in step 105.

At step 210, the second resonant frequency of the DPF is measured using a second resonator located at an outlet of the DPF. The second resonant frequency is measured when the exhaust gases are flowing out of the DPF. The second resonant frequency measured, is used to calculate the mass flow rate of the exhaust gases flowing out of the DPF. The mass flow rate of the exhaust gases flowing out of the DPF is calculated using similar steps as explained in step 210.

At step 215, the difference between the mass flow rate of the exhaust gases entering into the DPF and the mass flow rate of the exhaust gases flowing out of the DPF is calculated. The difference is used for calculating the efficiency of the DPF. Efficiency of the DPF is calculated by computing the ratio of the difference calculated and the mass flow rate of the exhaust gases entering into the DPF.

At step 220, the efficiency of the DPF computed in step 215 is compared to a threshold value. If the efficiency is lesser than or equal to the threshold value then it is considered that the regeneration state of the DPF is complete and the DPF is working fine without any clogged particulate matter in the DPF. If the efficiency is greater than the threshold value, then it is considered that the regeneration state of the DPF is incomplete and the DPF is clogged with the particulate matter. In such a case, the regeneration process can be continued until the DPF is unclogged by particulate matter.

The control unit adapted to determine the regeneration state of the DPF is adapted to receive the first resonant frequency of the DPF from the first resonator. Further, the control unit calculates the mass flow rate of the exhaust gases entering into the DPF as explained in the above paragraphs.

The control unit then receives the second resonant frequency of the DPF from the second resonator. The control unit then calculates the mass flow rate of the exhaust gases flowing out of the DPF similar to the procedure as explained in the above paragraphs.

Further, the control unit calculates difference between the mass flow rate of the exhaust gases entering into the DPF and the mass flow rate of the exhaust gases flowing out of the DPF. The difference calculates is used for calculating the efficiency of the DPF. The control unit computes the ratio of the difference and the mass flow rate of the exhaust gases entering into the DPF for calculating the efficiency of the DPF.

The control unit then compares the efficiency of the DPF with a value using a comparator. The lower the efficiency value the more efficient is the DPF. Hence if the efficiency is lesser than or equal to the threshold value then it is considered that the regeneration is complete and the DPF is clean. If the efficiency is greater than the threshold value then it is considered that the regeneration is incomplete and the DPF is still clogged with the particulate matter. In this case, the regeneration process can be continued until the DPF is clean and all the particulate matter deposited in the DPF is eliminated.

It must be understood that the embodiments explained above are only illustrative and do not limit the scope of the disclosure. Many modifications in the embodiments with regard to the type of resonator used are envisaged and form a part of this invention. The scope of the invention is only limited by the claims.