Planetary Gear Transmission Layout for Low-Shift-Shock EV Drive Units
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Solution Overview
Problem
Existing automatic transmission units for electric vehicles with two forward speeds face increased shift shock due to high step ratios when switching between gear ratios, which can be mitigated by reducing the step ratio during shifting.
Innovation Solution
A unit with a power transmission mechanism incorporating a gear device comprising a first and second planetary gear mechanism, along with engagement elements that allow for switching connections and rotational states to achieve three gear positions, reducing the step ratio and power transmission loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the transmission gear ratio at the first speed is increased to enhance torque amplification effect, then the maximum torque of the motor can be reduced and a smaller motor can be selected, but the step ratio at the time of switching between the first speed and the second speed is increased, resulting in increased shift shock
Solution Approach 1:
The transmission system is segmented into two separate planetary gear mechanisms (first and second planetary gear mechanisms) that can be selectively engaged. This segmentation allows the system to achieve different transmission gear ratios (first speed with high torque amplification, second speed with lower step ratio) by engaging different planetary gear mechanisms, thereby resolving the contradiction between torque amplification and shift shock reduction
Solution Approach 2:
The transmission system dynamically switches between different planetary gear mechanisms based on operating conditions. The first planetary gear mechanism is engaged when high torque amplification is needed, while the second planetary gear mechanism is engaged when lower step ratio is required, allowing the system to adaptively optimize performance and minimize shift shock
2Speed
If the transmission gear ratio at the second speed is reduced to improve high-speed cruising performance, then the motor rotation speed decreases which is advantageous during high-speed cruising, but the step ratio at the time of switching between the first speed and the second speed is increased, resulting in increased shift shock
Solution Approach 1:
The transmission system uses segmented planetary gear mechanisms where the second planetary gear mechanism is specifically designed to provide appropriate gear ratios for high-speed cruising while maintaining a reasonable step ratio. This segmentation allows independent optimization of each speed range without compromising shift comfort
Solution Approach 2:
The system changes the transmission gear ratio parameter by switching between different planetary gear mechanisms. The first planetary gear mechanism provides high gear ratio for low-speed high-torque operation, while the second planetary gear mechanism provides lower gear ratio for high-speed cruising, with the step ratio between them optimized to minimize shift shock
Data Source
AI summary
Provided is a unit including: an input element; an output element; and a gear device including a first rotational part, a second rotational part, a third rotational part, and a fourth rotational part arranged in this order on an alignment chart. The input element is connectable to the first rotational part and connectable to the second rotational part, the output element is connected to the third rotational part, and the fourth rotational part is switchable between a rotating state and a non-rotating state. The gear device includes a first planetary gear mechanism and a second planetary gear mechanism, the first rotational part is implemented by coupling the third rotational element and the fourth rotational element, the second rotational part is implemented by the fifth rotational element, the third rotational part is implemented by coupling the second rotational element and the sixth rotational element, and the fourth rotational part is implemented by the first rotational element.