Manufactured to reduce the environmental impact, EVs have a significantly smaller carbon footprint than vehicles with internal combustion engines, even when considering the electricity required to charge up an EV’s battery.
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In a recent Ford/University of Michigan study, it was found that EVs have life-cycle emissions, which are 64% lower than those of internal combustion engine vehicles.
That which cannot be measured cannot be controlled. Hence, in the world of EVs, sensors must be employed to provide feedback on the environment and conditions of the battery, motor and vehicle controllers to minimize energy usage and maximize efficiency.
However, poor design choices may undermine an EV’s efficiency, resulting in less-than-optimum vehicle performance for driving and charging, which can negatively impact the owner’s experience.
Barriers to EV Efficiency
When it comes to efficiency, one of the most significant yet frequently overlooked flaws in the design of an EV has little to do with its physical appearance, motor size, or the number of battery cells. It is the absence of robust and reliable sensor technology.
Weak sensor design or quality can lead to reduced efficiency and range in addition to increased vehicle maintenance and expenses to both the manufacturer as well as owner.
Current electric vehicles normally have in excess of 100 individual sensors installed.
Sensors operate in concert with microcontrollers and embedded systems within the EV to monitor component pressures and temperatures, measure current and voltage, wheel and motor speed, along with camera systems, humidity, radar, and more.
One of the most important functions of sensors is to assist in maintaining the battery performance and manage the stress put on it by the demands of use.
Two critical components of EV that require sensor technology to help maintain efficiency are:
- Interior climate control/HVAC systems
- Battery, motor and electronics thermal management systems (The section of this article on the Thermal Management Systems Section of this Article is not about Efficiency - The structure of the article needs to be addressed)
Thermal Management Systems
Temperature management of lithium-ion batteries is a critical part of producing optimum performance and long life from an automotive battery pack. Temperatures not within the optimal range of 15-45 ℃ decrease battery life and degrade battery performance.
Electrochemistry is sluggish below these temperatures. The flow of ions through the battery cells is slower, potentially causing lithium to build up outside the node forming dendrites, which disrupts the flow of energy and wastes some of the lithium which would be better used to power the battery.
Available power is thus limited and can reduce range. High temperatures also degrade batteries by affecting the Solid Electrolyte Interphase (SEI). This layer is responsible for stabilizing the electrolyte enough to last and protect the anode from corrosion.
Excessive heat can affect the SEI protective layer, use up active lithium, and can inhibit the flow of ions. In extreme cases, excessive heat can trigger thermal runaway.
Without monitoring by sensors and regulation of thermal management, EVs are subject to:
- Reduced ability to hold a charge: Takes longer to charge fully.
- Reduced charging capacity: Impacts how much power an EV battery can hold and is of particular concern for colder climates.
- Reduce lifespan: Excessive temperatures degrade batteries more quickly; they will not last as long and require expensive replacement.
- Reduced range: Depletes charges more quickly, requires more frequent charging and reduces EV range.
The thermal management system for batteries is foundational to the performance of electric vehicle components and depends on the sensors’ reliability and stability.
To ensure the health of the components of batteries in electric vehicles, sensors must accurately detect coolant and battery temperatures at all times during charging and discharging.
Sensor design should consider the need for stability, accuracy, and robustness in use.
Both the electrical and mechanical elements of sensor design must consider the media to be measured, the location at which the measurement is taken, the power consumption of the sensor, and the nature of the signal to be communicated.
Some sensors generate an output that is purely analog - the temperature-dependent resistance measurement of a thermistor used in a temperature sensor, for example - while others give a digital stream of data in calibrated engineering units. In any case, the level of safety of a sensor must be assessed through the use of tools like DFMEAs and ISO26262.
Safety sensors should have self-diagnostics and, where necessary, redundancy such that a single point failure never puts the operator or system at risk.
A large source of criticism of the current generation of EVs is the limited driving range of Li-ion batteries and the depleting efficiency of the batteries over time.
Maximizing power output and minimizing degradation are crucial for extending the life of EV batteries, and accurate, reliable sensors contribute to the precision control needed to maintain long-term performance.
HVAC System
Besides the motor and inverter, the electric vehicle components managing the heating and cooling system (HVAC) will put substantial demand on an EV battery.
An EV is, in essence, a box made of metal and glass, and so work must be done to provide a comfortable experience for drivers and passengers. Modern EVs can maximize the driver’s comfort by anticipating their needs and preparing the cabin even before the driver has entered the vehicle.
The use of air conditioning and heating systems in early EVs lead to a substantial loss of range, sometimes up to 30% of the vehicle range lost in extremely cold or hot environments.
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The most recent EV system designs are more sophisticated and far more efficient. Heat pumps and targeted seat heating and cooling are now used in place of the earlier “single loop” heating and air conditioning systems.
These systems have significantly increased range; the Tesla heat pump with Octovalve is one such example, having provided more than 10% additional range to the vehicle’s performance in extreme climates.
This advancement requires increased precision in monitoring, using combined temperature/pressure sensors at key locations in the system to provide instantaneous feedback on the compression and expansion cycles, enabling the compressor to operate only as needed to either add or extract heat from the cabin.
Sensor technology provides immediate feedback to the HVAC system to regulate energy consumption from the battery. Multiple types of sensors help regulate the temperature in EVs:
- Refrigerant temperature sensor
- Refrigerant pressure sensor
- Discharge air temperature sensor
- Air flow valve position sensor
- Air filter differential pressure sensor
- Evaporate temperature sensor
- Automatic defog sensor
- Sun load sensor
- Seat and steering wheel temperature sensors
Ensuring EV Efficiency with Sensor Technology
Thermal systems and HVAC systems must operate efficiently to maintain the overall performance of EVs. The right sensors assist in keeping temperatures within optimal ranges and monitor key systems to prevent battery degradation.
Electric vehicles of all types meet expectations in the ongoing electrification conversion in transportation by continuously monitoring the temperature, load, and displacement of batteries and heating and cooling systems.
This information has been sourced, reviewed and adapted from materials provided by Amphenol Advanced Sensors.
For more information on this source, please visit Amphenol Advanced Sensors.