Three-Gear Transmission for Electric Vehicles
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Solution Overview
Problem
Current drive systems for electric vehicles, particularly two-gear transmissions, suffer from narrow rotational speed ranges and efficiency issues due to the use of sliding sleeves, leading to traction force interruptions that impair comfort in automated drivetrains.
Innovation Solution
A three-gear transmission design utilizing planetary gearsets and shifting elements to achieve a large transmission spread with small gear intervals, optimized for space efficiency and high efficiency, allowing for smooth gear shifts without traction force interruptions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If sliding sleeves are used in two-gear transmissions, then the electric machine can be made smaller with cost advantage, but traction force interruption occurs during shift impairing comfort
Solution Approach 1:
A friction clutch is introduced as an intermediary element between the sliding sleeve and the power flow. The friction clutch gradually transfers torque during the shifting process, mediating between the disengaging sliding sleeve and the engaging gear, thereby preventing sudden traction force interruptions while maintaining the cost-effective sliding sleeve structure
Solution Approach 2:
The friction clutch changes the torque transfer parameter from abrupt (on/off) to continuous (gradual). By controlling the friction clutch's engagement degree, the torque transmission is smoothly adjusted during shifting, transforming the discrete switching action into a continuous parameter change that eliminates shocks and improves comfort
2Device complexity
If one-gear transmissions are used, then the structure is simple, but the electric drive must cover complete rotational speed range reducing overall efficiency
Solution Approach 1:
The single gear ratio is segmented into multiple gear ratios (first gear with ratio iI and second gear with ratio iII). This segmentation allows the electric drive to operate in different transmission stages, keeping the rotational speed within the electric machine's high-efficiency range while maintaining relatively simple transmission structure through planetary gearsets
3Weight of moving object
If two-gear transmissions are used, then the electric machine size is reduced, but the rotational speed range is narrow
Solution Approach 1:
Two planetary gearsets are nested within each other, with the first planetary gearset having sun gear, planetary gearwheels, and ring gear, and the second planetary gearset similarly structured. This nested configuration enables multiple gear ratios to be achieved within a compact space, expanding the rotational speed range while keeping the electric machine size reduced
Data Source
AI summary
A transmission having a drive input shaft (AN), a drive output shaft (AB), a housing (G), at least two planetary gearsets (PR1, PR2), and at least three shifting elements (A, B, C) whose selective engagement produces various transmission ratios between the drive input shaft (AN) and the drive output shaft (AB), so that at least three gears can be obtained. To obtain a gear in each case, two shifting elements are engaged and a further shifting element is disengaged.