Part 2 - Electrification of the car engine and its impact on automotive sensors
In the first part of this two-part article, we concentrated on how automotive sensors are being impacted by the increasing stringency and standardization of emissions testing—for example, in Europe CO2 targets of 130 grams of carbon dioxide (g CO2 / km).
Post-2020, however, European legislation has proposals in place that specify 95g CO2 / km, and a vision to reach 70g CO2 / km by 2025. Although hybrid electric vehicles (HEV) and battery electric vehicles (BEV) are emerging, the wider adoption of electrification is viewed as still being the main approach to meet these CO2 commitments, and most OEMs have active programs to add emissions-efficient propulsion systems to their fleets.
However, electrification varies by degrees—from today’s engines widely equipped with start-stop systems (called micro-hybrids), to mild- and full-hybrid variants, to plug-in hybrids, and, finally, to BEVs.
Of these options, the BEV is the most disruptive for sensing. In a BEV, many basic engine and exhaust sensors will vanish—potentially as many as 20 for diesels in the European market, according to IHS Markit analysis. Meanwhile, transmission systems can be simplified in an HEV, replacing automatic or double-clutch versions—the latter alone has many as 14 different speed, position, temperature, and pressure sensors. In comparison, an electric vehicle needs only 1 or 2 position and speed sensors.
As an example, the BMW i3 with range extender offers a combination of full EV and a 600cc motorcycle engine. Here the simple engine acts as a generator to charge the battery—not as a propulsion unit—so sensor content can be low because the loading on the engine is essentially constant. As a result, all the exhaust sensors described in Part 1—such as those to measure temperature, pressure, and oxygen—are no longer necessary.
Is hybridization a good thing for sensors?
A hybrid electric vehicle or HEV combines an engine for driving as well as an electric motor for propulsion. In the BMW i8, its plug-in hybrid features a turbocharged three-cylinder engine alongside an electric motor with a total of 349 HP (260 kW). When not operating in fully electric mode, the engine runs the car and needs full engine and exhaust aftertreatment equipment (along with control sensing) to handle various loading conditions.
Is exhaust sensor content reduced in an HEV compared to an internal combustion engine-driven vehicle? Because the duty cycle in HEVs may require that the engine be inactive for some periods, the operating temperature may also be lower than is sub-optimal, especially before the engine has fully warmed. Allowing for such a situation indicates that exhaust aftertreatment—and, indeed, sensing—is probably even more important to the clean operation of the vehicle in real driving conditions, owing to the increased variation in operating temperatures. In addition, HEV designs allow turbocharged downsized engines, which have been shown to produce higher quantities of NOx than some larger diesel engines. These factors equate to a net plus in terms of sensing for HEVs.
IHS Markit data show that HEVs, especially the gasoline engine type, will dominate the market in the coming years—excellent news for the sensor industry. The vehicle’s architecture will continue to deploy engines, with new sensors expected to be added for the electric motor and for the management of high-voltage batteries and other subsystems. Among those that benefit will be the suppliers of voltage, current, and temperature devices, as well as those for rotation and linear position sensing.
In comparison, BEVs won’t have as much of an impact on the total volume of sensors as the HEV, since BEVs make up only a small portion of the global automotive market by 2023, and probably just 10% by 2030.
Sensing in the electric vehicle
Overall, then, sensing in the new automotive powertrain economy is set to be positive given that electrification will entail a higher number of sensors. This is true especially around the battery, a part of the EV powertrain that amounts to 70% of its total cost. Sensing and measurement needs for the common subsystems of a plug-in HEV are shown in the figure below.
In an electric vehicle, whether HEV or BEV, all subsystems require sensors for voltage measurement, temperature, and current. A vehicle conforming to the diagram below, which represents the most complex architecture in an electric car, will incorporate approximately 15-20 current sensors and some 20-30 NTC thermistor temperature sensors (if automatic transmission is also considered).
Comprising the essential modules in EVs and HEVs are the car’s battery-monitoring function, the AC-DC converters for the plug-in charging function, and the DC-DC converters for HV-to-LV battery-voltage conversion. Each module, in turn, requires the monitoring of electrical parameters, such as current, often with 2-3 current sensors and at least one temperature sensor.
Caption: Typical sensing requirements for a plug-in hybrid, the most complicated electric architecture (IHS Markit).
Note: The diagram does not include regenerative braking systems.
Other types of measurements include position sensing of the main traction motor, today done with an expensive mechanical device called a resolver, supplied by companies such as Tamagawa Seiki; and the brushless DC (BLDC) electric motor control, which needs 2-3 current sensors. Typical are open-loop Hall sensors from companies like LEM, each made up of a core and a Hall sensor probe from companies like Micronas, Melexis, or ams. These motor-control-current devices are supplied to module makers like Bosch and deployed in EV motors used by BMW, Volkswagen, and the PSA Group including Peugeot, Opel, Citroen, and Vauxhall.
In the powertrain, one can also consider the transmission. An automatic or double-clutch system can comprise combinations of multiple fork-position measurements, input and output speed, and pressure sensing. But with a BEV, the number of gears needed for the transmission is radically reduced, and could be as few as 1-2 position sensors. This is one case in which electrification does not necessitate additional sensing requirements.
How healthy is my battery?
A key sensor module in HEVs and EVs is the battery monitoring sensor (BMS). The module is present in basic form on many 12-volt lead acid batteries used on today’s combustion engine vehicles. Analog Devices is dominant in the battery-monitoring integrated circuits (IC) space for this application, paired with shunt resistors from companies like Isabellenhütte and Vishay.
However, for a 48-volt system and a motor operating with 800 volts, the requirements on the battery are much more stringent than in a combustion engine. The main measurement is the battery’s state of health (for aging) and state of charge, whose performance translates directly into usable range.
Here voltage, temperature, and current are the main measurements. Voltage measurement is very critical for a BMS. Batteries are made up of packs of cells, each individual cell in a pack featuring a voltage measurement IC, in addition to a voltage IC for each pack; the number depends on battery architecture. In the case of a Mitsubishi iMiEV, this amounts to 8-cell voltage ICs per pack and 10 packs in total—altogether some 90 voltage measurement devices.
Other measurements of the battery may emerge in the future, such as pressure sensors for battery structural safety, and even optical measurements of the lithium-ion electrodes from directly inside the battery cells.
For BMS current measurement, shunt resistors, open-loop Hall sensors, and even expensive fluxgate devices are possible, a solution that can cost tens of euros. Temperature sensors for monitoring applications operating up to 150°C (302°F) are either silicon PTC or more commonly NTC thermistors, made by the likes of TDK or EPCOS. These are not the same kind of devices needed on exhausts, which operate at much higher temperatures.
Other implications for sensors
Electrification affects both the sensing content of the vehicle and the environment in which the electric car operates. Large electric motors generate sizable electromagnetic interference (EMI) fields, a phenomenon that affects magnetic sensors. The fields, which do not come from the motor but are caused by the large current-carrying cables associated with the system, disturb local magnetic fields around magnetic sensors.
So far this has not stalled the use of magnetic sensors, as many suppliers like ams, Infineon, and Allegro Microsystems mitigate EMI through differential sensing to remove the unwanted background signals. Another way would be to simply add shielding, or through placement of the sensor away from the main current carrying cables of the e-motor and battery.
Mitigating the EMI could be an argument, however, for the use of inductive sensors, which do not utilize magnets to make speed or position measurements. Companies that make inductive sensors include Hella, and more recently, ams and Texas instruments.
Conclusion: net positive for sensing
Overall, sensor content in EVs—and especially in HEVs—is anticipated to rise. For HEVs, given the coexistence of both the engine and the electric motor, net sensor and measurement content will also increase in the propulsion unit. And with the HEV propulsion system representing the most common propulsion system going forward because of HEV dominance in the electric-car market, sensor makers will have plenty to celebrate.
Note: More details can be found in my latest report, “Another good year for automotive MEMS sensors,” available to IHS Markit subscribers.