Planetary Gear Transmission Synchronizer for Electric Vehicle Efficiency
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Solution Overview
Problem
Electric vehicles with single or fixed speed ratio transmissions face efficiency issues as the electric motor operates at low efficiency when the vehicle speed is low, and existing two-speed transmissions have complex configurations that are costly and large.
Innovation Solution
A planetary gear transmission with a synchronizer that provides two speed ratios by allowing the output shaft to be selectively coupled with either the sun gear or the planet carrier, using a splined hub, engagement rings, and a frictional taper mechanism, allowing for efficient operation in both low and high speed regions with a simple and compact design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single or fixed speed ratio transmission is used, then the transmission structure is simple, but the electric motor operates at low efficiency when vehicle speed is low
Solution Approach 1:
The transmission system dynamically switches between two operating modes using a synchronizer mechanism. The output shaft can be selectively coupled to either the sun gear or the planet carrier, enabling the system to adapt its speed ratio dynamically based on vehicle operating conditions, thereby maintaining electric motor efficiency across different speed ranges
2Loss of energy
If a two-speed automatic transmission is used to improve electric motor efficiency, then the electric motor can operate in high efficiency region, but the transmission configuration becomes complex and expensive
Solution Approach 1:
The invention merges the functions of two separate gear pairs and their associated switching mechanisms into a single planetary gear set with a synchronizer. The planetary gear structure inherently provides two distinct speed ratios through its geometry, and the synchronizer integrates the coupling/decoupling function for both ratios into one mechanism, significantly simplifying the overall transmission configuration while maintaining dual-speed functionality
Solution Approach 2:
The planetary gear set serves multiple functions simultaneously: it provides the first speed ratio when the sun gear is the input, provides the second speed ratio (direct drive) when the planet carrier is the input, and the synchronizer manages both coupling and decoupling operations. This multi-functionality eliminates the need for separate gear pairs and reduces the number of moving parts
3Loss of energy
If a two-speed transmission is used, then the electric motor efficiency is improved, but the transmission size and cost increase
Solution Approach 1:
The invention combines two gear pairs and their switching mechanisms into a single planetary gear set with a synchronizer, significantly reducing the transmission's physical size and weight while maintaining dual-speed functionality
Solution Approach 2:
The planetary gear structure naturally nests multiple gear elements (sun gear, planet gears, ring gear, planet carrier) in a compact concentric arrangement, allowing the transmission to achieve two speed ratios within a small footprint, thereby reducing both size and weight
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
The transmission enables the electric motor to operate at high efficiency in both low and high speed regions, reduces gear shifting jerk, and lowers costs by maintaining a simple structure, while integrating the electric motor and transmission into a single housing, enhancing driving comfort and reducing battery energy consumption.
Implementation Method 1
a frictional taper mechanism
Data Source
Figure 1
AI summary
A planetary gear transmission is disclosed, which comprises a planetary gear train having a sun gear, a fixed annular gear, at least one planet gear and a planet carrier; a synchronizer configured to be driven into a first coupling state in which it couples the sun gear with a prime mover, and a second coupling state in which it couples the planet carrier with the prime mover; and an actuator configured for selectively driving the synchronizer into one of its first and second coupling states. An electric vehicle comprising such a planetary gear transmission is also disclosed.