Coordinated Electric Machine and BISG Engine Start
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Solution Overview
Problem
In hybrid electric vehicles, very cold temperatures reduce the output of high voltage batteries, making it difficult for electric motors to crank the engine alone, and low voltage starters experience belt slip, hindering engine starting.
Innovation Solution
A coordinated actuation method where an electronic controller energizes both the electric machine and a belt-driven integrated starter-generator (BISG) to apply torque to the engine, with the electric machine spinning to a threshold speed before closing the disconnect clutch and the BISG providing additional torque, ensuring successful engine starting in cold conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the electric motor is used to crank the engine alone, then the structure is simple, but in very cold temperatures the battery output is significantly reduced and the torque produced is insufficient to crank the engine
Solution Approach 1:
The patent combines the electric motor and belt integrated starter-generator (BISG) into a coordinated dual-starting system. The controller synchronizes the operation of both motors to provide combined torque output, allowing the system to deliver sufficient cranking torque in cold temperatures while maintaining the simplicity of individual motor designs.
2Reliability
If the low voltage starter (BISG) is used to assist in starting the engine, then additional torque is provided, but in very cold temperatures the BISG experiences belt slip
Solution Approach 1:
The controller acts as an intermediary that coordinates the operation timing and torque distribution between the electric motor and BISG. By precisely controlling when each motor engages and disengages, the system optimizes torque delivery while minimizing conditions that cause belt slip in the BISG during cold temperature operation.
Solution Approach 2:
The electric motor is activated first to begin cranking the engine, and the BISG is engaged at the optimal moment when its torque contribution is most effective. This preliminary sequencing ensures the BISG operates in a regime where belt slip is minimized while still providing the necessary additional torque for reliable starting.
3Power
If both the electric machine and BISG are energized simultaneously, then sufficient torque is provided for cold starting, but the control complexity increases
Solution Approach 1:
The control system dynamically adjusts the operation of each motor based on real-time engine cranking speed and torque requirements. The controller continuously monitors system state and modulates the torque output of the electric motor and BISG accordingly, enabling coordinated operation that provides sufficient torque while managing control complexity through adaptive rather than static control strategies.
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 coordinated approach enhances engine start performance in low temperatures by providing sufficient torque, reducing the risk of belt slip and ensuring reliable engine cranking even when high voltage battery power is insufficient.
Implementation Method 1
The electric machine may start the engine by providing torque to crank the engine
Implementation Method 2
a belt drive connecting a crankshaft of the engine to the BIS(G)
Data Source
AI summary
A vehicle includes an engine and an electric machine coupled to a transmission element. The electric machine is also selectively coupled with the engine by a clutch. The vehicle includes a belt integrated starter-generator (BISG) operatively coupled to the engine. An electronic controller includes one or more inputs adapted to receive a temperature measurement and a request to start the engine. The electronic controller is programmed to energize the BISG and the electric machine in response to receiving an engine start request and a temperature measurement being less than a threshold temperature measurement. The electronic controller is further programmed to close the disconnect clutch to apply torque from the electric machine to the engine in response to the electric machine achieving a threshold electric machine speed.