Generator Power Control for Hybrid Vehicle Cold Start
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Hybrid electric vehicle powertrains face challenges in starting a cold engine quickly, quietly, and smoothly due to increased engine friction and reduced battery capacity, leading to potential engine stalls and battery over-discharge, especially when variable valve timing is involved.
Innovation Solution
The strategy involves controlling generator power rather than engine speed during engine cranking, selecting a target generator power below the battery's high voltage limit, and using a closed-loop control to maintain stable engine torque, thereby preventing power limit violations and reducing the duration of the starting cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If engine cranking is performed with high generator torque to overcome cold engine friction, then engine starting speed is improved, but battery power limits are exceeded causing over-discharge
Solution Approach 1:
The system dynamically adjusts generator torque based on real-time engine speed and battery state of charge. The generator torque is reduced when engine speed exceeds a threshold or battery charge drops below a threshold, creating a dynamic control strategy that adapts to changing conditions during engine cranking
Solution Approach 2:
The control system continuously monitors engine speed and battery state of charge, using this feedback to adjust generator torque in real-time. This closed-loop control ensures the system responds to actual operating conditions rather than using fixed torque values
2Object-affected harmful factors
If variable valve timing is activated during cold engine starting, then engine noise and vibration are reduced, but cranking speed requirement increases making starting more difficult
Solution Approach 1:
Variable valve timing is dynamically activated or deactivated based on engine speed and temperature conditions. The system transitions between valve timing modes to optimize the balance between noise reduction and starting capability across different operating conditions
3Device complexity
If engine speed is maintained at constant target value during cold start, then control simplicity is improved, but engine stalls occur due to resonance zone torque instability
Solution Approach 1:
The target engine speed is dynamically adjusted based on actual engine operating conditions rather than maintaining a constant setpoint. The system adapts the speed target to account for resonance zone effects and varying friction conditions during cold start
Solution Approach 2:
The control system changes the target engine speed parameter in response to detected conditions such as resonance zone entry or successful combustion events, allowing the engine to pass through unstable regions by temporarily accepting speed variations
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 ensures consistent and faster engine starting, reduces battery power usage, and simplifies calibration for improved exhaust gas emission quality by continuously assisting the engine through the starting process without exceeding battery limits.
Implementation Method 1
The generator, when it is acting as a motor, can deliver power to the planetary gearing. That power can be used to provide engine cranking during an engine start.
Implementation Method 2
When the generator is acting as a generator, it is driven by the planetary gearing to provide charging power for the battery.
Implementation Method 3
The generator, the motor and the planetary gear unit thus may operate as an electro-mechanical transmission with continuously variable ratio characteristics. The generator can act as a generator when it is driven by the portion of the engine power that is not delivered mechanically through the transaxle gearing. The balance of the engine power delivered through the planetary gearing to the generator charges the battery and the battery drives the traction motor
Data Source
AI summary
A system and method for controlling engine starting in a hybrid electric vehicle that includes a battery, an engine and a generator acting as a motor control generator power during engine starting so that generator torque complements or assists the engine to develop a stable running speed throughout an engine start event, particularly a cold engine start event, without violating battery power limits.