Current, temperature, physical impact sensors to protect batteries of Evs
Date: 31/05/2022
Battery is the most important and expensive component of an electric car. The storage density of lithium ion batteries is in the range of 50-260 Wh/kg. With that amount of energy stored they need to be monitored and safeguarded to ensure longevity of batteries and also protecting them from catching fire. The batteries should be monitored for any over voltage, excess current, temperature and also physical damage.
The automotive component maker Continental has come out with two new sensors, one for measuring current and temperature and the other for physical impact sensing/detection.
The high-voltage Current Sensor Module (CSM) measures current and temperature at same time and the Battery Impact Detection (BID) system detects any physical impact to the battery compartment.
“Vehicle electrification brings new use cases and thus opens up more opportunities to our sensor activities, because an electric car has all the sensor needs a conventional car has – and more,” says Laurent Fabre, Head of Passive Safety and Sensorics Segment at Continental. “Protecting the battery and retaining its performance, for instance, are two additional tasks in electrified vehicles. The Current Sensor Module and Battery Impact Detection solutions serve both purposes.”
CSM can be integrated into the battery itself or into the external electrical/electronic system connecting to the battery. CSM not only protects battery from excessive currents, it ensures battery charging and discharging current is in the specified range to ensure battery lasts to its maximum age. To fulfill functional safety requirements, the CSM features both shunt type current sensing and hall-effect based magnetic current sensing in a compact single unit. This current/temperature sensor module fully supports ASIL D on system level.
There is a very close relationship between current and temperature in all kinds of batteries. Since Lithium-Ion batteries operate at large amount of energy, they charge and discharge at high currents and rise in temperature of the of batteries is inevitable, that is more so in case of high-power fast charging or sport driving. Using this sensor the current can be controlled to limit the temperature gradient. Using the data generated from this current sensor, optimum temperature span of lithium-ion battery and precise drive-range prediction can be achieved.
CSM can be used to measure currents up to 2000 Amperes with an accuracy of ±1 percent on the shunt channel and ±3% accuracy on the hall channel, with the sensor ability to work in the temperature range of -40° to 125° Celsius. CSM feature full galvanic separation and the measured current is fed via CAN interface to the battery management system. CSM is also said to detect mechanical malfunctions, which could lead to a fire if undetected.
ASIL D supporting CSM is expected to be in production volumes within year 2022, where the first product is part of a modular sensing platform which is scalable for additional features such as voltage measurement and number of measurement channels.
The BID Sensor can sense possible battery damage and warn the driver accordingly. The lightweight BID senses under floor physical impacts and sends alert-signals to the system, so that driver is informed for any immediate service and maintenance/repair required. This sensor saves the driver from doing personal checks of the impact.
To achieve lower centre of gravity, these heavy batteries are placed on the floor of the vehicle, where they are largely protected against any physical damage, except for some physical things swirled up and damage the underfloor and also any ground contacts at low speeds while parking and humpy uneven road drive.
Normally these days some of the latest electric vehicles are fitted with a large and often heavy armour cover underside battery. For any suspected damage the driver will have trouble in spotting damage due to difficulty in scaning underneath a car. To prevent such a situation Continental has developed this pressure-sensor based Battery Impact Detection which detects and classifies underfloor impact events to alert the driver if the battery' integrity is breached. This Prevents damaged battery from any fire/electric spark ignite at a later point. BID tells where exactly the damage has occurred, so that the maintenance staff can empty the battery cells in that particular area.
During low speed ground contact BID generated signal can be used to enable a fast-acting active suspension system to temporarily increase the underfloor clearance. When hard and heavy objects such as stones, rocks, metal pieces and any such objects hit the car bottom, BID sends alerts to system and driver. BID is 50% light in weight compared to other armoring type protection.
Continental says in its release "The pressure sensor satellites used in the BID derived from the proven Pedestrian Protection System (PPS Psat) which has been in serial production and applied in millions of vehicles for more than ten years. Any impact is detected via a resulting pressure signal in an air-filled silicone tube that is integrated in serpentines at the bottom of the battery compartment. The time difference between the signal’s arrival at the two pressure satellites at both ends of the tube makes it possible to calculate the area of the impact. The severity of the impact can be classified via signal thresholds that serve to trigger cascaded alarms to the driver."
Author: Srinivasa Reddy N
