Electric Vehicle Hill-Hold Control Motor Cooling
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Solution Overview
Problem
Existing hill-hold control systems for electric vehicles risk overheating the motor due to continuous current flow, which can lead to degraded performance and damage, while also potentially degrading the feeling of driving due to abrupt braking force changes when starting on a slope.
Innovation Solution
A control apparatus that initiates a first hill-hold control using motor driving force as a stopping force and transitions to a second hill-hold control using braking force when a set time, based on cumulative hill-hold control executions, to manage motor temperature and improve starting sensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hill-hold control is continuously executed using motor driving force, then the vehicle can be reliably held on a slope, but the motor temperature increases leading to overheating and potential damage
Solution Approach 1:
The control device switches between first hill-hold control (using motor driving force) and second hill-hold control (using service brake) in periodic cycles. The ECU alternates between activating the motor for hill-hold control and deactivating it to allow cooling, thereby maintaining reliable slope holding while preventing continuous motor overheating through periodic operation intervals
Solution Approach 2:
The control device changes the operational parameters of the motor by switching between two distinct control modes: first hill-hold control where the motor outputs driving force to maintain position, and second hill-hold control where the motor is deactivated and service brakes are used. This parameter change between active and inactive states manages motor temperature while maintaining hill-hold functionality
2Temperature
If the control device switches between motor-driven hill-hold and brake-driven hill-hold, then motor overheating is prevented, but the switching may cause abrupt braking force changes degrading driving sensation
Solution Approach 1:
The control device performs preliminary actions by pre-charging the service brake system during the first hill-hold control phase and gradually preparing the braking mechanism before switching to the second hill-hold control. This preliminary preparation ensures that when the transition occurs, the braking force is already partially established, reducing the abruptness of the force change and improving driving sensation
Solution Approach 2:
The control device applies beforehand cushioning by gradually increasing service brake engagement during the transition from first to second hill-hold control. The ECU modulates the brake force buildup rate to cushion the transition, preventing sudden jerks or abrupt braking sensations that would degrade driving comfort while still achieving effective motor cooling
3Temperature
If the set time for switching control modes is extended, then motor cooling is more effective, but the vehicle may slide backward on steep slopes before the switch occurs
Solution Approach 1:
The control device applies dynamics by making the switch timing between first and second hill-hold control adaptive rather than fixed. The ECU dynamically adjusts the switch timing based on real-time monitoring of motor temperature, slope angle, and vehicle position, allowing extended cooling periods when safe and automatically switching earlier when stability risks are detected, thereby balancing motor cooling effectiveness with position stability
Data Source
AI summary
A control apparatus of an electric vehicle including a motor capable of outputting a vehicle driving force that is a driving force acting on the electric vehicle, and a brake device configured to generate a vehicle braking force that is a braking force acting on the electric vehicle in accordance with a brake operation performed by a driver, includes: a controller. The controller is configured to start a first hill-hold control for maintaining the electric vehicle in a stopped state by using the vehicle driving force generated by the motor as a stopping force for stopping the electric vehicle when the brake operation is interrupted.