Hybrid Vehicle Limp-Home Control Using Counter EMF Speed Synchronization
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Solution Overview
Problem
Hybrid vehicles experience vibration (jerk) and reduced operability when the high voltage system fails, leading to an interruption in power supply to the inverter, as conventional limp-home strategies involve starting the engine through high-speed motor engagement, causing mismatched speeds between the stationary engine and rotating motor.
Innovation Solution
A limp-home control method and system that utilizes counter electromotive force from a first motor generator to drive a second motor generator, starting the engine and synchronizing speeds to minimize the difference between engine and motor speeds, thereby locking the engine clutch and reducing vehicle vibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the engine is started by attempting lock-up through the motor kept rotating at a high speed, then the engine can be started in limp-home mode, but vibration (jerk) occurs in the vehicle as the stationary engine is joined to the motor rotating at a high speed
Solution Approach 1:
The patent applies preliminary action by pre-accelerating the engine to a speed close to the motor speed before lock-up occurs. The controller increases engine speed using the motor generator as a starter motor, then synchronizes the speeds before engaging the engine clutch, thereby preventing vibration during the transition to limp-home mode
Solution Approach 2:
The patent changes the speed parameter of the engine from stationary to synchronized with motor speed before lock-up. The controller dynamically adjusts engine speed to match motor speed, ensuring smooth transition and minimizing vibration when the engine clutch engages
2Reliability
If the high voltage system fails and power supply to the inverter is interrupted, then the vehicle must switch to limp-home mode, but the HSG cannot be normally driven due to lack of high voltage
Solution Approach 1:
The patent applies self-service by using the motor generator to serve dual purposes: as a motor during EV mode and as a starter generator during limp-home mode. The motor generator directly drives the engine without requiring external high voltage power, enabling the system to start itself in failure conditions
Solution Approach 2:
The patent implements multi-functionality by designing the motor generator to perform multiple functions: propulsion in EV mode, charging the high voltage battery, and engine starting in limp-home mode. This universal component replaces the traditional separate starter motor, enabling operation across different system states
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 minimizes vehicle vibration and enhances operability by ensuring smooth power transmission when the high voltage system fails, by using counter electromotive force to synchronize engine and motor speeds during limp-home mode.
Implementation Method 1
driving, by a controller, a second motor generator for driving an engine using counter electromotive force of a first motor generator
Implementation Method 2
starting, by the controller, the engine according to driving of the second motor generator
Implementation Method 3
locking up, by the controller, an engine clutch and transmitting power of the engine to a drive shaft of the vehicle
Data Source
AI summary
A limp-home control method and a system for hybrid vehicles which can minimize vehicle vibration (jerk) and improve operability by driving an engine with counter electromotive force and locking up an engine clutch with a difference between an engine speed and a motor speed minimized when a high voltage to an inverter is interrupted due to a failure of a high voltage system of the hybrid vehicle.