Hybrid Vehicle Separating Element Speed Difference Management
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Solution Overview
Problem
Hybrid vehicles experience thermodynamic and rigidity problems at high speeds due to large differences in rotational speed between the shut-down internal combustion engine and the rotating electric machine, which can exceed the maximum permissible difference at the separating element.
Innovation Solution
The method involves opening the separating element below the maximum permissible rotational speed to allow purely electric driving or coasting, and above this speed, decoupling the separating element and electric machine using a clutch element in the transmission to prevent excessive rotational speed differences, allowing continued coasting and electric driving through a secondary electric machine if available.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the separating element is opened to allow purely electric driving or coasting, then electric driving capability is improved, but thermodynamic and rigidity problems occur at high speeds due to excessive rotational speed difference
Solution Approach 1:
A coupling element is introduced as an intermediary between the separating element and the first electric machine. This coupling element can be opened to decouple the separating element from the first electric machine when rotational speed differences become excessive, thereby protecting the separating element while maintaining electric driving capability through the second electric machine
2Reliability
If the separating element remains closed to prevent thermodynamic and rigidity problems, then separating element reliability is improved, but purely electric driving and coasting capability are lost
Solution Approach 1:
The system is segmented into two electric machines: the first electric machine connected via the separating element for low-speed operation, and the second electric machine for high-speed operation. This segmentation allows the separating element to remain closed during high-speed operation, preventing thermodynamic and rigidity problems while maintaining electric driving capability through the second electric machine
3Temperature
If the first electric machine is decoupled gradually at high speeds, then thermodynamic problems are reduced, but device complexity increases
Solution Approach 1:
The first electric machine is completely extracted from the power transmission path at high speeds by opening the coupling element, rather than attempting gradual decoupling. This simplifies the control system while still achieving the goal of reducing thermal problems, as the separating element remains closed and protected from excessive rotational speed differences
Data Source
AI summary
A method is provided for operating a hybrid drive train of a hybrid vehicle. The drive train has an internal combustion engine, a first electric machine, a transmission with an input shaft, a separating element and a first axle. The internal combustion engine can be connected to the first electric machine via the separating element. When the separating element is opened and the internal combustion engine is stationary, a difference in rotational speed occurs at the separating element between the internal combustion engine and the rotating first electric machine. The separating element is opened below and up to a maximum permissible difference in rotational speed at the separating element to drive the hybrid vehicle purely electrically by the first electric machine or to brake the vehicle or to coast. Above the maximum permissible difference in rotational speed the separating element and the first electric machine are separated from one another.