The global market for sensors used in internal combustion engines (ICEs) is on the road of steady growth for the next few years, propelled by increasing utilization in engine management and exhaust aftertreatment, according to IHS. Sensor shipments for ICEs will top 1.34 billion units in 2019, up from about 1.08 billion in 2013. Overall, the projected six-year compound annual growth rate (CAGR) from 2013 to 2019 will equate to 3.6 percent. "Shipments of ICE sensors are growing slightly faster than car shipments," said Richard Dixon, Ph.D., principal analyst for MEMS and sensors at IHS. "The main reason is that new concepts in emissions mitigation in the engine and in exhaust aftertreatment systems require advanced sensors for their operation. Added to that, emission legislation in some major markets of the world, such as China, is beginning to catch up with that of mature markets like the US, Europe and Japan, at least in the larger cities."
IHS says that it has examined more than 20 sensors attached to the engine, fuel and exhaust systems of passenger vehicles. The list includes pressure sensors, devices to monitor flow and temperature, ceramic sensors for the nitrogen oxide (NOx) and oxygen gases, in addition to knock sensing, position and speed.
A long history of engine sensing
Among the 24 applications identified for sensors used in ICEs, several measurements have been essential to electronic fuel management systems for more than 20 years: the position of the throttle and crankshaft, the absolute air pressure of the intake manifold and the residual oxygen in the exhaust. And multiple sensor insertions are possible -- depending on the pipe configuration, a gasoline engine may feature four oxygen sensors, two of which serve an on-board diagnostics function to check for correct operation, although a diesel engine still has only one oxygen sensor, located before the diesel oxygen catalyst.
Back in 1993, five to seven sensors were required to meet the so-called Euro 1 set of requirements for European countries. In comparison, to meet upcoming Euro 6 standards beginning in September this year, at least 20 sensors are needed and possibly more, depending on the engine.
Most of the new sensors are related to exhaust aftertreatment because of new emissions laws, with NOx reduction being a focus alongside that of carbon dioxide. As a pollutant, NOx has long been a stronger focus for US legislation, which also dictates that the emission parameters are measured under realistic driving cycle conditions. But European legislators have also become tougher on this gas in recent years. IHS forecasts that the market for NOx sensors will grow at a CAGR of 9.3 percent during the next five years from 2014 to 2019.
It's getting hot in the engine
The largest category for sensing is temperature measurement, with multiple sensors used in exhaust systems. The technology utilized is typically platinum-based resistance temperature detector (RTD) sensors, which withstand temperatures of up to 1,000C (1,832F). On average, approximately two temperature sensors are used per vehicle. At lower temperatures, negative resistance sensors (NTCs) or semiconductor integrated circuits are also deployed. Examples include engine coolant monitoring to protect against overheating, intake air measurement or exhaust gas recirculation systems used to lower NOx output from the engine.
At other points in the powertrain, the fuel injection system and cylinder pressure are proving to be interesting new opportunities for pressure sensor suppliers. Although cylinder pressure sensing has been largely too expensive for car manufacturers to adopt, IHS expects significant growth in this area in coming years, led by Volkswagen and Daimler in diesel engines. Owing to the low penetration today, growth rates in the coming five years to 2019 are projected to be high at more than a 40 percent CAGR.
Exhaust is proving to be a big driver for sensing
The type of engine has an impact on exhaust systems. Lean-burn engines require more sensors than standard, stoichiometric engines because the exhaust aftertreatment is more complex. The high residual oxygen content in the exhaust of these engines makes it impossible for conventional three-way catalysts to reduce NOx pollutants.
Diesel and some direct injection gasoline engines fall into this category. These engines require feedback on NOx concentration in the exhaust stream as part of the emission control system. On the other hand, stoichiometric engines, some direct injected engines and all modern port injected engines, do not need a NOx sensor.
In addition, many vehicles today feature some kind of forced induction, turbo or supercharging, of the fuel-air mix. The increased use of turbochargers is the main factor enabling engines to be made smaller and less polluting.
As these boosters become more sophisticated, such as having a variable geometry, position sensing becomes important. So far, though, turbocharger speed sensing is mostly confined to the large commercial vehicle segment and is not yet widely found in passenger cars.
Also, for the first time, the European Euro 6 legislation specifies a particle number per kilometer as a key measure, with phased-in adoption. Direct injection gasoline engines produce more hazardous particles than standard gasoline multi-port injection engines. This means that gasoline particle filters on the exhaust will be adopted in the former, along with the means for self-monitoring, which will drive the use of particle mass and possibly pressure sensors.
Particle filters have been used on diesel engines to reduce NOx since legislation in Euro 4. In particular, diesel particle filters have pressure sensors to monitor the filter when it is clogged, indicating to the engine ECU when to regenerate the filter -- a process that also requires temperature sensing.
Sensor adoption also has a strong regional emphasis. As emissions standards are not yet harmonized worldwide, less stringent emission standards than those affecting US, Japanese or EU standards are in play, which leads to lower sensor content in emerging markets. A gasoline engine vehicle in Iran or Malaysia, for instance, will have a much lower sensor requirement than an engine in Japan. According to IHS, the difference can be as many as 10 sensors.
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