by Aditya Sharma, Research Analyst

Intelligent Systems

Statistics reveal that the vehicular traffic these days is reaching enormous heights. Drivers and co-passengers, in the present scenario can be exposed to high levels of pollution. The potential situations for high pollution concentration include being caught up in the traffic in congested areas and tunnels, driving through building encapsulated areas or the emissions from heavy vehicles. Vehicles not equipped with modern pollution control technologies could also be sources of unexpectedly high pollution levels. Under such adverse conditions the peak concentrations can be expected to be 100 to 1000 times higher than the normal levels. The failure of the driver manually adapting the cabin environment in such adverse situations could create a lack of oxygen and fresh air, ending up in fatigue! The intelligent Heating, Ventilation and Air Conditioning (HVAC) systems for automotive applications, gain their importance in the modern vehicles by automatically adapting the climate despite the adversities. These systems derive their intelligence from the advanced sensor technology and have become more of an essential part of vehicle comfort and convenience.

A control procedure can only be implemented if the parameters can be measured. At this juncture a sensor can be defined as a component that performs measurements and transforms the measured parameters into a suitable form to be further used by the Electronic Climate Control (ECC) units to carry out effective procedures.

Automotive HVAC control units rely on the vital signals from the sensors for the measurement of factors. Figure 1 shows the various kinds of sensors used in automotive systems.

Sensing the Environment

Sensors supply the information about the changing environment to the HVAC control unit. The location and the quality of the measurements that are made play a significant role in climate control of automobiles. Sensors for measuring each of the physical quantities mentioned are commercially available, and there are a good number of industrial players involved in the production of sensors for automotive applications.

To have a better understanding of the operation of a sensor in automotive systems, consider a situation where the vehicle enters into a polluted region. The air quality sensors located near the air inlets, detect the changes in the air composition entering the vehicle compartment and control the pollution from increasing in the passenger cabin by sending appropriate signal to the HVAC control unit. The HVAC unit responds to this by closing the ventilation flaps. Gas analyzers detect rising concentrations of toxic gases arising from the engine compartment or externally and prevent them from entering the passenger cabin by once again closing the ventilation flaps and activating recirculation. Humidity sensors continuously monitor the amount of water vapor in the air and regulate the blow out air temperature, thereby preventing fogging of windshields. The internal and external temperatures are continuously measured to maintain the thermal levels as requested by the passengers. Solar radiation can end up in increasing the temperature levels, and hence is accounted for by the radiation or the solar sensors to provide compensatory measures.

The desire of the automobile buyers for increased driving comforts and the declining costs of air conditioning equipment have transformed the use of air-conditioning systems as more of an essential feature rather than an optional accessory. This is evident from the fact that in the year 2001, 99.1 percent of the vehicles manufactured for the North American markets were factory fitted with air-conditioning systems.

Recent advances in sensor technology have been responsible for the applications of electronic intelligence in the automotive HVAC installations. This is evident from the statistics that in the year 1999, 25 percent of the HVAC installations had electronic control, which increased to a figure of 50-80 percent by the year 2003. The demand for sensors in automotive HVAC systems stood at 25.6 million units in the year 1999. Increasing at a compound annual rate of 21.3 percent their demand is expected to reach a high of 67.1 million by the end of 2004. These figures are applicable to the four major car-producing regions (North America, Europe, Japan and South Korea).

U.S. automobile manufacturers face a new emission standard for vehicle models manufactured after 2000. This new emission standard called the Supplemental Federal Test Procedure (SFTP) measure the tailpipe emissions with air conditioning systems operating. Results showed that emissions of oxides of Nitrogen and Carbon monoxide increased more than double during the SFTP cycle. Following are the percentages of vehicles subjected to SFTP,

Air-conditioning systems, being the single largest auxiliary load on the vehicle, reduce fuel economy and are highly unacceptable for high fuel efficiency vehicles. The U.S. emission standards are providing the impetus for the HVAC industry to evaluate new climate control concepts. Considering the recommendations of the National Renewable Energy Laboratory, the solutions for size reduction of the climate control systems lie in re-evaluating the glazing systems and in developing advanced techniques for delivering heating and cooling to the occupants.

The sensor industry is driven by the need for fast response, and more sensitive sensors for monitoring the thermal comforts in the new designs of HVAC systems. Recirculation of cabin air, in an attempt to reduce the outside air take-up also calls for the need of highly sensitive, fast response, low cost and maintenance gas analyzers and humidity sensors.

Thin film and miniaturization technologies developed by the semiconductor industry are increasingly being used to make Micro Electro Mechanical Systems (MEMS) that make the measurement of the physical work more precise. Sensor technology survives on the production of high precision, high sensitivity, reliable, small size and mass, and low cost products. MEMS have revolutionized the market for sensors by providing small, fast responding measurement devices at low costs. Their wide acceptance is highlighted by the fact that today on an average 25 to 75 MEMS sensors are used in automotive applications for gathering vital information. MEMS like the pressure sensors, humidity sensors, and infrared sensors find their applications in automotive climate control systems.

The field of optoelectronics is also making its way through the automotive HVAC systems. For example one of the leading manufacturers of sensors for automotive HVAC systems has come up with a solution of reducing the number of sensors and as an effect the extent of wiring, by providing Infrared (IR) sensors that monitor the incident IR radiations from the driver and the passengers to make an average of the surface temperatures and humidity of the occupants. This feature enables multi-zone climate control.

A recent study on the mortality rates by Germany’s Federal Environmental Agency reveals that carcinogenic effect of diesel fumes is the cause for approximately 14,000 deaths in a year. Stringent emission laws have forced U.S. automobile manufacturers to develop sophisticated systems to reduce emission levels of vehicles. Emphasis is laid on keeping the temperatures inside the vehicle constant as per the driver’s requirements, but not much attention is being paid in maintaining the quality of the air. Advancing sensor technology is giving a competitive advantage to the automobile manufacturers of not only providing luxury vehicles with systems that provide comfortable cabin temperatures, but also those that are free of harmful gases and unpleasant odor.

Awareness about the harmful and in some cases life-threatening effects of a polluted automotive environment has been attracting the customers to the health and safety benefits of automatic HVAC systems. The increasing demand for sensors clearly depicts the popularity of the intelligence, which sensors can offer in controlling the automotive climate. As a solution to legislative restraints faced by the automotive HVAC industry, as well as an increase in temperatures on account of global warming, sensors will always have to provide more accurate and reliable information for effective control procedures.