Hybrid Engine Starting Torque Allocation Strategy
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Solution Overview
Problem
Hybrid vehicles face inefficiencies in engine starting due to the need to reserve significant torque for cranking, which reduces available power for propulsion and introduces torque disturbances, especially when using a dedicated starter or integrated starter-generator, impacting vehicle efficiency and drivability.
Innovation Solution
A system with a processor-controlled engine starting strategy that selectively uses a first electric machine for propulsion by releasing reserved torque when a second electric machine, such as a starter motor or integrated starter-generator, is chosen for subsequent engine starts, allowing dynamic torque allocation based on vehicle speed and operational conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the electric machine is coupled to the engine to start the engine, then the engine can be started under various operating conditions, but significant torque capacity (80-150 Nm) must be reserved for cranking the engine, reducing available torque for vehicle propulsion by up to 40%
Solution Approach 1:
The system divides the engine starting function into two separate electric machines: a first electric machine (starter motor or ISG) dedicated to engine cranking, and a second electric machine (traction motor) for vehicle propulsion. This segmentation allows the first electric machine to be optimized for starting capability while the second electric machine provides full torque for propulsion without reservation, resolving the contradiction between reliable engine starting and available propulsion torque.
2Reliability
If the engine is coupled to driveline components during starting, then the engine can be started, but torque disturbances are introduced that reduce vehicle efficiency and drivability
Solution Approach 1:
The system extracts the engine starting function from the main driveline by using a dedicated first electric machine that can crank the engine independently without coupling it to driveline components. This extraction eliminates torque disturbances in the driveline during engine starting, maintaining vehicle efficiency and drivability while ensuring reliable engine starting through the dedicated starter machine.
3Reliability
If a dedicated starter motor or ISG is used for engine starting, then engine starting is reliable, but vehicle cost increases
Solution Approach 1:
The system employs a first electric machine that serves dual functions: acting as a dedicated starter motor or ISG for reliable engine cranking, and simultaneously functioning as a propulsion motor during EV mode operation. This multi-functionality allows the system to achieve reliable engine starting capability while reducing overall vehicle cost by eliminating the need for completely separate starter and propulsion systems.
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 enables robust and efficient engine starts by dynamically releasing reserved torque for propulsion, improving overall vehicle energy efficiency and minimizing drivetrain disturbances.
Implementation Method 1
a first electric machine selectively coupled to the engine by a first clutch... capable of propelling the vehicle during electric vehicle (EV) mode operation
Implementation Method 2
a second electric machine coupled to the engine... The second electric machine may be a starter motor or an integrated starter-generator
Implementation Method 3
a first clutch... a second clutch... engagement of the first clutch and disengagement of the second clutch
Data Source
AI summary
A system and method for controlling engine starting in a hybrid vehicle having first and second electric machines include starting the engine in response to an engine start request using the first electric machine and releasing second electric machine reserved engine starting torque for use in propelling the vehicle. The first electric machine may be controlled to start the engine in response to the first engine start after key-on and when the vehicle speed is below a corresponding threshold, with the second electric machine used when vehicle speed is above the threshold. The first electric machine may be an integrated starter-generator.