Gearbox With Minus Plus Planetary Gearsets
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Solution Overview
Problem
Conventional gearboxes in electric vehicles with integrated differentials do not form a sum torque, limiting their ability to achieve higher gear ratios and efficient torque distribution to multiple axles, which is essential for improved transmission and drivetrain performance.
Innovation Solution
A gearbox design featuring a minus planetary gearset and a plus planetary gearset with stepped planets, where at least one of the gearsets is connected to a fixed component, allowing for a higher transmission ratio and efficient torque distribution to two output shafts, preventing the formation of a sum torque and enabling compact, high-efficiency operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional gearbox design with integrated differential is used, then the structure is simpler, but the transmission ratio is limited and cannot achieve higher gear ratios
Solution Approach 1:
The gearbox is divided into two separate planetary gearsets (first and second planetary gearsets) instead of using a single integrated differential design. Each planetary gearset can be independently configured with different tooth ratios, allowing the overall transmission ratio to be the product of both stages, thereby achieving much higher gear ratios while maintaining structural clarity and ease of manufacture
Solution Approach 2:
The first planetary gearset is nested within or alongside the second planetary gearset, with the ring gear of the first planetary gearset serving as the sun gear for the second planetary gearset. This nested configuration allows both gearsets to occupy compact space while their transmission ratios multiply, achieving high overall gear ratios without proportionally increasing the gearbox size
2Ease of manufacture
If two conventional minus planetary gearsets are used, then the design is straightforward, but the transmission ratio cannot be sufficiently increased
Solution Approach 1:
The patent employs one minus planetary gearset and one plus planetary gearset instead of two identical minus planetary gearsets. This asymmetric configuration allows the tooth ratios of the two gearsets to be optimized independently, with the minus planetary gearset providing a certain ratio range and the plus planetary gearset providing another ratio range, whose product achieves much higher overall transmission ratios while remaining manufacturable
Solution Approach 2:
By changing the type of planetary gearset from conventional minus to plus planetary gearset in the second stage, the patent expands the achievable transmission ratio range. The plus planetary gearset configuration allows for different tooth ratio characteristics compared to the minus planetary gearset, enabling the combination to achieve higher overall ratios without compromising ease of manufacture
3Productivity
If larger planet gears are used to achieve higher gear ratios, then the transmission ratio increases, but the gearbox size and complexity increase
Solution Approach 1:
By nesting the first planetary gearset within or alongside the second planetary gearset, the patent achieves high overall gear ratios through the multiplication of two moderate-stage ratios rather than requiring a single stage with a very large ratio. This nested configuration allows both gearsets to share space efficiently, preventing the gearbox size from increasing proportionally with the overall gear ratio
Solution Approach 2:
The patent segments the overall high gear ratio requirement into two separate planetary gearstage ratios. Instead of using one planetary gearset with a very large gear ratio that would require large planet gears and increase size, the total ratio is achieved as the product of two smaller, more compact planetary gearsets, each with moderate-sized components
4Device complexity
If a single planetary gearset is used, then the structure is compact, but the torque distribution to multiple axles is limited
Solution Approach 1:
The patent uses two separate planetary gearsets, each capable of independent torque distribution to different output shafts. The first planetary gearset distributes torque to a first output shaft and the second planetary gearset distributes torque to a second output shaft, enabling flexible torque distribution to multiple axles (such as in all-wheel drive or four-wheel drive vehicles) while keeping each individual gearset relatively compact and simple
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 design achieves a higher transmission ratio, reduces complexity and meshing forces, mitigates fretting issues, and provides a low locking value, resulting in a compact, efficient, and cost-effective gearbox suitable for electric and hybrid vehicles.
Implementation Method 1
a first planetary gearset (P1) and a second planetary gearset (P2) connected to the first planetary gearset (P1)... a torque introduced at the input shaft (10) is converted and distributed in a defined ratio to the two output shafts (11, 12)
Data Source
AI summary
A gearbox includes: an input shaft; a first output shaft; a second output shaft; a first planetary gearset; and a second planetary gearset connected to the first planetary gearset. The input shaft, the first and second output shafts, and the first and second planetary gearsets are configured such that a torque introduced via the input shaft is converted and distributed in a defined ratio to the first and second output shafts, so as to prevent formation of a sum torque. The first planetary gearset is configured as a minus planetary gearset, and the second planetary gearset is configured as a plus planetary gearset.