Multi-Speed Compound-Input Electrically Variable Transmission
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Solution Overview
Problem
Existing electrically variable transmissions (EVTs) face challenges such as higher transmission spin losses due to clutch drag and multiple planetary gear set friction, limited gearing range that restricts electric vehicle drive capabilities, and the need for larger electric motors and batteries to start the engine, leading to increased weight and cost, as well as limited reverse gear capabilities, especially in extreme climates.
Innovation Solution
A compound-input electrically variable transmission (CI-EVT) with a multi-speed input device that includes a transmission input shaft selectively coupled to a planetary gear set, featuring first and second clutch mechanisms to provide different input gear ratios, allowing for efficient engine operation, improved starting conditions, and integrated input brake functionality for enhanced reverse propulsion using both electric motors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the gearing range of the EVT is limited, then the transmission structure remains compact, but the electric vehicle drive capabilities are restricted
Solution Approach 1:
The patent introduces a multi-speed input device that adds a new dimension to the transmission's gear ratio capabilities. By providing multiple input shafts with different gear ratios (first input gear ratio, second input gear ratio) before the planetary gear set, the system expands its effective gearing range without proportionally increasing structural complexity. This enables broader EV drive capabilities including extended reverse propulsion and improved starting performance.
2Ease of operation
If separate clutch and brake mechanisms are added to provide input brake functionality, then the EVT can lock the input shaft to enable EV mode operation, but the cost and drag of the EVT increase
Solution Approach 1:
The input brake functionality is merged into the multi-speed input device structure itself. The planetary gear mechanism and clutch mechanisms serve dual purposes: providing gear ratio changes and enabling input shaft locking for EV mode operation. This integration eliminates the need for separate brake mechanisms, reducing both cost and system drag while maintaining full EV mode functionality.
3Reliability
If larger electric motors and batteries are used to provide adequate starting force for the engine, then the vehicle can start under worst starting conditions, but the weight and cost of the EVT increase
Solution Approach 1:
The multi-speed input device changes the mechanical advantage parameters available during engine starting. By providing multiple input gear ratios, the system can optimize the torque multiplication during starting conditions without requiring oversized electric motors. The altered gear ratio parameters enable smaller, lighter motors to deliver the necessary starting force, reducing overall EVT weight while maintaining reliable starting capability under all conditions.
Data Source
AI summary
A compound-input is provided for an electrically variable transmission for a motor vehicle. The compound-input electrically variable transmission has improved input gear ratios that allow the vehicle engine to be operated in its desired efficiency and/or performance range during both city and highway vehicle operation. Further, the multi-speed input electrically variable transmission provides an input brake without the need for a dedicated input brake clutch or braking mechanism and incorporates a reverse gear for reverse operation.