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Sensor architecture allows real-time auto emissions monitoring

25 Apr 2012  | Ravindra Arora, Manmohan Rana, and Sunil Deep Maheshwari, Freescale Semiconductor

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Vehicle-emissions are currently strictly monitored and emission-norms being revised regularly to ensure a "greener" and pollution-free environment. Globally, various organizations are striving to make their processes as eco-friendly as possible, with the automotive industry leading this endeavor. However, present vehicle pollution-checking is still dependent on old mechanisms of manual-regular-checking of the auto-exhaust. The exhausts are sensed and analyzed by a machine and a pollution certificate is issued. This article highlights inherent limitations of this traditional approach and proposes a real-time exhaust monitoring solution to enforce better pollution control for a greener future.

The challenges of emission pollution control
Automobiles used worldwide produce vast amounts of harmful exhausts including carbon dioxide, carbon monoxide, nitrogen oxides (NOX), and un-burned hydrocarbons. All these add to greenhouse gases and are significant contributors to global warming. Adoption of cleaner fuels like compressed natural gas and commercial development of hydrogen-based automobiles is one of the priorities for many agencies. However, before such a long-term, fool-proof solution is reached, probably the easiest and the cheapest solution is to keep the pollution emissions of current automobiles in check.

In every country, the emission norms are regulated by their respective pollution control regulatory body. Vehicles are checked for their emissions and if exhaust is within the specified limit, a certificate with an expiry date is issued for the vehicle. However, this system has its own loopholes—-the system only checks for the emissions on the date of the test, not in between the two test dates. The data is not under load conditions, which might change according to the age and condition of the vehicle. Besides, many factors like engine-tuning and adulteration of fuel might increase the pollution temporarily and may move it to an unacceptable level.

This article proposes a mechanism which signal via wireless communication the real-time pollution level data of the vehicle to the owner/driver and, if required, also to monitoring and controlling authorities. In such cases, there might not be any need for regular pollution checks and issuance of vehicle fitness certificates. Authorities can take appropriate action against repetitively defaulting vehicle/owners. This would ensure better upkeep of the vehicles and as a result, and good upkeep of the environment. The rest of this article deals with the technical implementation of the above mentioned system/regime.

Proposed solution architecture
The basic blocks required for the real-time monitoring mechanism include: profiling of exhaust gases; conversion of data into digital form; storing and processing data; display of results, and data transmission. Each of these blocks works together to generate the desired results. The micro-level architecture of the proposed solution is shown below. Discussion of the operation of the above mentioned blocks follows.

Profiling the exhaust gases

An array of sensors is used to sense the amount of exhaust components. These sensors give real-time information of the exhaust components such as carbon monoxide, nitrous oxide, etc. The sensors give either digital or analog output. If the sensors with digital outputs are used, then they can be interfaced with some timer module of the MCU (microcontroller) to quantify the output. In case the sensors are of the analog output type, then the next mentioned block (converter) would be used to make the output usable by the MCU.

Another alternative is to use the data from the engine control and management unit (ECMU). This information serves as a replacement for the network of sensors. However, this method may suffer from relative inaccuracy because sensors directly sense the exhaust, and thus are able to give more accurate results as compared to the ECMU data. Then again, that statement is based upon the assumption that the array gives accurate results, and that the array would be sitting right at the exhaust, sensing the real-time information.

Converting analog data to digital format
To enable the sensors' data to be processed by the MCUs, one needs to convert this data into digital format. ADCs (analog-to-digital converters) can be used to convert the sensors' output into digital format, making it easier to store and process.

Given the type of application, one would not require constant or very frequent exhaust-profile data gathering. Therefore, one can easily multiplex various sensors' outputs on one or two ADCs so that each of them could be sampled one-by-one, saving on the BOM (bill of material).

Intervals when the MCU is not active or when its ADCs are free to sample the sensors' output can likewise be tapped. This way, data is available as is and when the core is free to process the data, higher MCU throughput can be achieved. For such systems, the overall accuracy of the solution is heavily dependent upon the sensors accuracy and the performance of the ADCs.

Storage and processing unit
The storage and processing unit are important for systems which would cater to this proposed solution on an as-and-when-free basis. This approach requires one to have a high speed processor, which can support MAC (multiply and accumulate)/DSP instructions to manipulate the data pool required for this solution. The solution also includes data coming in from the power-train MCU giving the engine loading information.

Another point to note is that the pollution control and monitoring application is an additional feature being extracted out of almost the same hardware. Therefore, this application will share its memory space with already existing applications. As a result, there will be an additional demand for memory to be able to meet all the requirements.

Adding such functions to the 'as-and-when-free' model of the application, requires one to be stringent with the memory access speed and more liberal with the on-chip memory. A situation may also arise where the on-chip memory is not sufficient for the needs of the overall system. Depending on the memory requirement and data size to be stored by the pollution control and monitoring unit, additional memory or external memory interface with fast access speed is required.

Without fast memory access, calculations and report-generation may be very slow. However, techniques like data pre-fetch from such an external memory might be able to overcome such limitations to a reasonable extent.

Display controllers
Display controllers are required to transmit data to the automobile dashboard/cluster so that the driver could take appropriate action. For example, if pollution increased due to overloading, the same can be calculated using the data from the power-train MCU and displayed as a flag on the cluster (see below). This visual sharing of information can be achieved in two ways—- either by on-chip display drivers or interfacing this MCU with an external display controller. The latter is achieved using communication peripherals like I2C, SPI, SCI, Flexbus, Ethernet, and USB.

Inspection of Car's Emission Using Infrared Spectrum Technique, M Kong,Z Luo, Y Lu and W j Fan

About the authors
Ravindra Arora has worked at Freescale Semiconductor as senior design engineer for about six years. He has worked on automotive cluster and safety architecture MCUs. He earned his M.Tech (Instrumentation) from N.I.T Kurukshetra and B.Tech from R.E.C Kurukshetra in India.

Manmohan Rana has worked at Freescale as senior design engineer for about five years. He has worked on memory circuit design, analog and mixed signal design and simulation for various SoC architectures. He earned his BE (Electronics and Communications) from the Delhi College of Engineering, Delhi University in India.

Sunil Deep Maheshwari has worked at Freescale as senior design engineer for about five years. He has worked on architectures ranging from motor control, power train, and metering to auto safety. He earned his BE (Electronics and Communications) from Netaji Subhas Institute of Technology, Delhi University in India.

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