Current sensor family boost EV battery lifetime
Continental is expanding its sensor portfolio with two new sensors types for electric vehicles: the current sensor module and battery impact detection. Both new solutions focus on battery protection and/or preservation of battery characteristics. The compact modular current sensor module measures current and simultaneously detects temperature. Both values are of great importance as input variables for battery management. The company is also launching another innovative element for battery protection: battery impact detection is a lightweight alternative to heavy “underbody armor” against damage.
Considering that the traction battery is the most expensive component in an electric car, the current sensor module was developed not only to protect the battery from overcurrent, but also to preserve battery characteristics by limiting aging effects. Integrated either in the so-called Battery Disconnect Unit or in the battery itself, the module provides the two crucial pieces of information for the battery protection function and reliable range monitoring. To meet stringent functional safety requirements, the current sensor module is designed as a dual-channel sensor that independently measures current by integrating shunt and Hall technology in a compact, single unit.
Battery impact detection combined with a lightweight design detects underbody intrusions and warns the driver if this necessitates a workshop visit. This relieves the driver of the difficult decision of whether a high-speed impact or low-speed ground contact could have damaged the battery. Compared to current metal underbody protection, the system can save up to 50 percent in weight, the manufacturer promises.
Lithium-ion batteries store large amounts of energy. Thus, high currents flow into the battery, particularly during charging. Due to unavoidable physical effects, a battery heats up during charging (and discharging) – especially during fast charging with high power or sporty driving. To avoid overloading the car battery, the current must be regulated to limit the temperature gradient. “A lithium-ion battery has an optimal temperature range in which it is very safe and ages very slowly,” says Horst Gering, program manager in the Passive Safety and Sensorics segment. “However, charging the battery quickly is a trade-off between maintaining the safety and health of the battery and limiting the charging time. It’s best done based on accurate data.” In addition, by monitoring the battery’s current draw, the current sensor module helps calculate the exact remaining range.
The current measured by the current sensor module can be calibrated to up to 2,000 amps with an accuracy of less than ±1 percent on the shunt channel and ±3 percent on the Hall-channel, at temperatures ranging from -40°C to 125°C. These measured values are forwarded to the battery management system via CAN interface. The current sensor module not only optimizes charging efficiency and protects the battery, but also helps detect mechanical malfunctions that can lead to a fire without being noticed. It fully supports ASIL D at the system level. Production of the current sensor module is starting this year for an advanced electric vehicle from a global automaker.
Typically, an EVs tractionbattery is housed in the underbody, where its weight contributes to a low center of gravity. However, there are risks for potentially dangerous collisions with hard objects, such as during parking maneuvers. That’s why electric vehicles are equipped with a large and often heavy cover that protects the battery compartment from underneath. The new system detects and classifies underbody impacts or intrusions to warn the driver when the integrity of the battery may have been compromised. In this way, the car owner can take precautions before a faulty battery could later ignite. In addition, battery impact detection identifies the area of damage so that battery management can drain the cells in that area to avoid the risk of fire.
Compared to solutions commonly used today, sensor-based underbody protection can save up to 50 % of the weight of current battery shielding solutions per vehicle. The pressure sensor satellites used for battery impact detection are derived from the proven pedestrian protection system (PPS pSAT), which has been in production for more than ten years and is used in millions of vehicles. Each impact is detected via a resulting pressure signal in an air-filled silicone tube laid in a meandering pattern at the bottom of the battery compartment. The area of impact can be calculated from the time difference between the arrival of the signal at the two pressure satellites at either end of the hose. The severity of the impact can be classified by signal thresholds, which are used to trigger cascaded alarms for the driver.