EV Hill Hold Torque Timing Before Drive Derating
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Solution Overview
Problem
The challenge of maintaining a vehicle's position on a slope using an electric drive system leads to overheating and derating issues, reducing the torque output and risking unintended vehicle movement.
Innovation Solution
A vehicle control unit (VCU) calculates the required hold torque, estimates power loss and heat generation, and determines the time until derating based on thermal and mechanical properties, providing a time indicator to manage the hill hold feature safely.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If constant torque is applied at zero speed to maintain hill hold, then the vehicle position is maintained on the slope, but the electric machine and power electronics overheat
Solution Approach 1:
The control unit performs preliminary thermal analysis before activating hill hold to predict temperature rise and prevent overheating. The system calculates equivalent power loss and temperature increase based on hold torque requirements, cooling conditions, and initial temperature, then determines a safe remaining time for hill hold operation.
Solution Approach 2:
The system continuously monitors cooling conditions and temperature during hill hold operation. The control unit receives information about cooling performance and adjusts the remaining time indicator based on actual thermal behavior, creating a closed-loop feedback mechanism that prevents overheating while maintaining hill hold functionality.
2Temperature
If derating is allowed to occur naturally, then overheating is prevented, but the torque output is significantly reduced causing vehicle rolling
Solution Approach 1:
The system predicts the time until derating would occur and provides advance warning to the driver through a remaining time indicator. This allows the driver to take preventive action (press accelerator or apply park brake) before torque reduction happens, avoiding unintended vehicle movement while still allowing thermal management.
Solution Approach 2:
The control unit acts as an intermediary between the thermal management system and the driver. It translates complex thermal states into a simple remaining time indicator, enabling the driver to make informed decisions without directly controlling torque or temperature parameters.
3Temperature
If mechanical brakes are used for hill hold, then overheating of electric drive is avoided, but the solution is not applicable to electric vehicle propulsion system integration
Solution Approach 1:
The control unit integrates hill hold functionality directly into the electric propulsion system, allowing the electric motor to serve dual purposes: propulsion and hill hold. The system calculates hold torque based on vehicle mass, slope, and friction, then applies appropriate torque to maintain position without requiring separate mechanical brake systems.
Solution Approach 2:
The invention replaces mechanical brake-based hill hold with electric motor-based torque application. By substituting mechanical braking with electric torque control, the system achieves better integration with the propulsion system, improved energy efficiency, and eliminated the need for separate hill hold hardware.
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 prevents overheating and ensures safe hill hold operation by accurately predicting the duration of the hill hold feature, protecting the electric drive system and ensuring user safety.
Implementation Method 1
Applying constant torque at zero speed can cause overheating for the electric machine and the power electronics, since all the power fed to the propulsion system is transformed into heat
Implementation Method 2
information about a cooling of the electric drive
Implementation Method 3
information about a cooling of the electric drive
Data Source
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AI summary
The disclosure relates to a vehicle control unit (VCU) for indicating a remaining time for which a hill hold feature of an electric vehicle can be provided. The hill hold feature enables keeping a position of the vehicle at standstill on a slope with the aid of an electric drive of the vehicle. The VCU is configured to receive information for determining a hold torque of the electric drive for holding the vehicle at standstill on the slope, information about a cooling of the electric drive and information about an initial temperature of the electric drive when the hill hold feature is enabled. The VCU is configured to determine a time until a derating of the electric drive begins based on a predefined derating model and the above information. The VCU is configured to determine a time indicator indicating the remaining time for which the hill hold feature can be provided based on the time until derating of the electric drive begins.