Enhancing Safety and Simplifying Operation

A mainstay in modern vehicles, electric power steering (EPS) systems improve overall vehicle handling while providing opportunities for more advanced safety features compared to their hydraulic power steering counterparts.

EPS systems utilize a small electric motor and sensors to gauge how much torque, or effort, the driver is applying to the wheel at the time, then adjusts the power level accordingly. Benefits include:

• Slight fuel economy compared to hydraulic power steering
• Reduced maintenance compared to hydraulic fluid replacement 
• Enables a variety of modern features we rely on — from lane assist to parking 

As vehicles continue to get smarter and more helpful for drivers — even to the point where they drive themselves — EPS technology is a crucial factor. 

How does EPS work?

A small motor is installed on the steering rack or steering column, with several strategically placed sensors to detect the torque being applied by the driver. Together, these components increase or decrease power to help the driver steer based on the inputs of the driver’s torque, speed, and other data from the sensors. At lower speeds, the steering wheel can be turned effortlessly. At higher speeds, it requires a little more resistance to give the feel of control. 

The diagram below shows a brushless DC (BLDC) motor being utilized in the EPS system. BLDCs are relatively compact and cost-effective while delivering the benefits of long-lasting performance, easy installation, and reduced EMI noise.

Design considerations:

• Energy efficiency - lower energy usage enhances fuel economy and requires less power from the vehicle’s battery, which improves the range for EVs.
• High-temperature capability - components must be able to withstand the worst-case scenario in thermal surges.
• High current handling - the system should perform reliably under the worst possible conditions and current surges.
• Low on-resistance - minimizing heat generated during operation extends the life of the component, and low RDS(on) plays a crucial role while enhancing system responsiveness.
• Fast switching speed - switching should be fast enough to ensure smooth operation amid ever-changing conditions. 
• Low reverse recovery time - low Trr is needed to enable faster switching at high frequencies and improve efficiency.
• EMI protection - proper suppression and filtration are needed to reduce noise and electromagnetic interference.
• Applicable industry standards - to ensure maximum safety and reliability, adherence to AEC-Q101 and other standards is required for certain components.

EPS Block Diagram

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