Axle Torque Control for EV Rollback Prevention on Inclines
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Solution Overview
Problem
Electric vehicles equipped with axle assemblies experience rollback issues on inclines due to the limitations of simultaneous propulsion and brake torque application, particularly when the electric motor's brake torque is insufficient to prevent rolling, and the friction brake's effectiveness is short-lived, leading to potential overheating and inadequate rollback prevention.
Innovation Solution
A method and system that simultaneously provide propulsion torque and friction brake torque to the wheel when both braking and acceleration are requested for a predetermined period, allowing the propulsion torque to temporarily exceed the friction brake torque to preload the drivetrain and prevent rollback, while resetting the timer based on pedal inputs and vehicle speed conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If friction brake torque is applied to prevent rollback on inclines, then rollback prevention is improved, but the brake torque is insufficient and short-lived leading to overheating
Solution Approach 1:
The system applies propulsion torque in advance before the vehicle actually rolls backward. By detecting the driver's acceleration request and applying propulsion torque simultaneously with friction brake torque, the system pre-loads the drivetrain to prevent rollback before it occurs, rather than reacting after rollback has started
Solution Approach 2:
The system merges propulsion torque and friction brake torque into a unified torque application strategy. Both torques are applied simultaneously to the wheel, combining the motor's torque capability with the brake's holding capability to achieve both rollback prevention and sustained torque application without overheating
2Reliability
If propulsion torque is increased to prevent rollback, then rollback prevention is improved, but the electric motor's brake torque is insufficient
Solution Approach 1:
The system combines propulsion torque from the electric motor with friction brake torque to achieve the total torque needed for rollback prevention. The propulsion torque handles the sustained power requirement while the friction brake provides immediate holding torque, compensating for the electric motor's insufficient brake torque capability
3Reliability
If friction brake is applied continuously to prevent rollback, then rollback prevention is improved, but the friction brake overheats due to prolonged application
Solution Approach 1:
The system applies propulsion torque in advance when the driver requests acceleration, before rollback actually occurs. This preliminary torque application pre-loads the drivetrain and reduces the need for continuous friction brake application, allowing the brake to be released earlier and preventing overheating
Solution Approach 2:
The friction brake is applied periodically rather than continuously - it is engaged when rollback prevention is needed and released when propulsion torque is sufficient. This periodic application pattern allows the brake to cool down between uses, preventing thermal overload
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
This approach effectively reduces or prevents vehicle rollback, enhances drivability by allowing propulsion torque to exceed friction brake torque only when necessary, and avoids overheating by distributing torque effectively, thus improving the vehicle's stability on slopes without requiring additional slope-sensing mechanisms or expensive anti-lock braking systems.
Implementation Method 1
The electric motor is configured to provide propulsion torque to a wheel that is mounted to the axle assembly
Implementation Method 2
The friction brake is configured to provide friction brake torque to the wheel
Data Source
Figure 1
Figure 2
AI summary
A system and method of controlling a vehicle that has an axle assembly and a wheel. Propulsion torque and friction brake torque are simultaneously provided to the wheel with an electric motor and a friction brake, respectively, when braking and acceleration of the vehicle are both requested for a predetermined period of time.