This compact modular sensor design measures current as well as detects temperature. Both values are highly relevant as inputs for battery management. BID, on the other hand, is a lightweight alternative to heavy underfloor “armouring” against damage.
Keeping in mind that the battery is the most expensive component in an electric car, CSM was developed to not only protect the battery from overflow, but also to help maintain battery parameters by limiting the effects of aging.
Integrated into the battery disconnect unit or the battery itself, the CSM will provide two key pieces of information for battery safety as well as reliable driving range monitoring.
To support strict functional protection requirements, the CSM is available as a two-channel sensor, which measures current independently by integrating shunt technology and Hall technology into a compact, single unit.
In conjunction with a lightweight structure, the BID detects underfloor impacts and alerts the driver if a garage stop is necessary as a result. This relieves the driver of the challenging decision whether the battery could be damaged by impact at high speed or ground contact at low speed. BID solutions can save up to 50 percent of weight compared to current metal underfloor protection.
reliable charge monitoring
Lithium-ion batteries store a large amount of energy to provide an attractive driving range. Especially during charging, a high current flows through the battery. Due to unavoidable physical effects, charging (and discharging) a battery will overheat it – especially with high-power fast charging or sportive driving. To protect a car battery from overstressing, the current has to be regulated to limit the temperature gradient.
“The lithium-ion battery has an optimal temperature period in which it is very safe and runs very slowly,” says Horst Gering, program manager in the Passive Safety and Sensorics segment. “However, there is a tradeoff between charging the battery faster and healthier and limiting the duration of charging. This is best done based on accurate data.”
In addition, the CSM helps to calculate the exact remaining limit by monitoring the current consumption.
The CSM measured current can be calibrated to 2,000 amps, with better than ± 1 percent accuracy on the shunt channel and ± 3% accuracy on the Hall channel, as well as in the temperature range between -40 °C to 125 °C. Both current measurement technologies provide complete galvanic separation. This input is then provided to the battery management system via the CAN interface. In addition to optimizing the efficiency of charging while protecting the battery, the CSM will also assist in the detection of mechanical faults, which could lead to fire if not detected.
CSM fully supports ASIL D at the system level. Production of the CSM will begin within 2022 for a global automaker’s state-of-the-art electric vehicle. The first product is part of a modular sensing platform that is scalable for additional features such as voltage measurement and number of measurement channels.
underfloor protection
Typically, an electric car’s lithium-ion battery is integrated in an underfloor position where its weight contributes to a low center of gravity and where it is well protected by the vehicle structure – with two possible exceptions. : On high-speed objects, such as lashing straps, can be twisted and damage the underfloor. At low speeds, ground contact can also be damaged during parking maneuvers. Therefore, electric vehicles are equipped with a large and often heavy cover to protect the battery compartment from underneath. However, if there is an impact, it will be up to the driver to decide whether the car needs to be checked in the garage.
“This is not a satisfactory situation as there is poor visibility under the car, plus a trained eye is needed to assess the actual damage”, says Johannes Klemm, managing director of Continental Safety Engineering International in Algenau. To help with the situation and make lightweight underfloor protection viable, Continental has developed a pressure-sensor-based battery impact detection solution.
This system detects and classifies underfloor impact events to alert the driver if battery integrity may be breached. This way the car owner can take precautions before the punctured battery can burn out later. “In addition, the BID identifies an area of damage, so battery management can empty cells in that area to prevent any risk of fire,” Klemm says.
BID covers two specific impact risks: one is low-speed ground contact, for example, during parking maneuvers when the vehicle slowly rolls over a curb and hits the ground. During this type of incident, the BID signal can also be used to trigger a fast-acting active suspension system to temporarily increase underfloor clearance to reduce damage. The other use case is the high-speed intrusion that can occur due to the movement of heavy objects such as rocks or lashing bars on the road. Given the speed and impact, these types of objects can cause damage to the underfloor and potentially even penetrate the battery structure.
Compared to current solutions, sensor-based underfloor protection can save up to 50 percent of the weight of current battery shielding solutions per vehicle. The pressure sensors used in BID are derived from the satellite proven Pedestrian Safety System (PPS pSAT), which is in serial production and has been implemented in millions of vehicles for more than ten years.
Any impact is detected via the resulting pressure signal in an air-filled silicon tube that is integrated into the serpentine under the battery compartment. The time difference between the arrival of the signal on the two pressure satellites at both ends of the tube makes it possible to calculate the sphere of influence. The severity of the impact can be classified by means of a signal threshold that serves to trigger a cascade alarm to the driver.