Towed EV Battery Charge Control Using Regenerative Braking
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Solution Overview
Problem
Electrified vehicles cannot be safely towed with the ignition off, as electric pumps for lubrication and thermal conditioning are inactive, leading to potential damage and operational issues, and there is no efficient way to maintain battery charge during towing.
Innovation Solution
A towed vehicle mode that operates electric pumps for lubrication and cooling, uses regenerative braking for charging, and enables automatic braking, allowing the vehicle to maintain battery charge and operate without drawing power from the towing vehicle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the electrified vehicle is towed with the ignition off, then the towing operation is simpler, but the electric pumps are inactive causing lubrication and thermal conditioning failure
Solution Approach 1:
The towed vehicle's electric pumps are activated automatically when the towing vehicle's brakes are applied, allowing the towed vehicle to service itself by providing lubrication and thermal conditioning without external intervention or additional power connection
2Reliability
If regenerative braking is used to charge the traction battery during towing, then the battery charge is maintained, but the towing vehicle experiences additional load affecting drivability
Solution Approach 1:
The regenerative braking is activated partially - only when the towing vehicle's brake application exceeds a threshold level, allowing battery charging during deceleration events while avoiding continuous loading that would affect towing vehicle drivability
Solution Approach 2:
The system continuously monitors the towing vehicle's brake application level and adjusts regenerative braking activation accordingly, using feedback from brake sensors to determine when to enable or disable regenerative charging based on the threshold criterion
3Productivity
If the charging rate is increased to reach the target state of charge faster, then the battery charges more quickly, but the towing vehicle drivetrain and cooling systems are overtaxed
Solution Approach 1:
The regenerative braking provides partial charging action during available deceleration events rather than attempting full charging, accepting that the target state of charge may not be reached but avoiding overtaxing the towing vehicle systems
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Facilitates safe towing by maintaining battery charge and system operation, reducing effort and weight, and preventing shutdowns, while enhancing towing vehicle efficiency and safety.
Implementation Method 1
an electric machine configured to provide propulsive torque to vehicle wheels... vary charging rate of the high-voltage traction battery... varying power generated by the electric machine
Implementation Method 2
operation of one or more electric pumps to provide lubrication and/or cooling of vehicle components including one or more drivetrain components and the traction battery
Implementation Method 3
hydraulically actuated friction brakes based on brake activation of the towing vehicle or detection by vehicle speed, acceleration, and/or distance sensors/cameras
Data Source
AI summary
An electrified vehicle includes a human-machine interface to enable towed vehicle mode and specify a desired traction battery charge upon arrival at a destination. A controller is programmed to vary charging rate of the traction battery while the electrified vehicle is being towed over a user-specified distance to the destination to obtain the user-specified target charge for the traction battery upon reaching the destination. The target charge may be entered as a percentage state of charge (SOC), a distance to empty (DTE), or Watt hours, and converted to net energy input required for the traction battery. The controller distributes the charging load over the entire distance to reduce the affect on the drivability and efficiency of the towing vehicle by varying regenerative braking of the electric machine(s) while being towed to provide a net energy needed to obtain the target charge upon reaching the destination.