Two-Speed Transaxle Seamless Shifting via Dry Brake Discs
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Solution Overview
Problem
Conventional two-speed transaxles for electric vehicles experience a drop in traction force during shifting, leading to reduced comfort due to the configuration with a sliding synchronizer sleeve, which is not acceptable for drivers.
Innovation Solution
A two-speed transaxle design featuring an epicyclic gear set with a base sun gear, second sun gear, planet gears, and a common planet carrier, along with dry brake discs and caliper disc brake systems, allowing for shifting without interruption of traction through a compact and efficient configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a sliding synchronizer sleeve is used for speed selection, then the transaxle structure is simplified and cost is reduced, but traction force drops during shifting causing comfort loss
Solution Approach 1:
The invention extracts and eliminates the sliding synchronizer sleeve from the transaxle structure, replacing it with a different speed selection mechanism that uses a first brake disc, second brake disc, and one-way clutch to achieve speed changes without the harmful sliding action that causes traction loss
Solution Approach 2:
The invention introduces intermediary elements (brake discs and one-way clutch) that mediate the speed selection process, allowing smooth transitions between speeds without direct mechanical sliding contact, thereby maintaining traction force continuity during shifting
2Device complexity
If a conventional two-speed transaxle with sliding synchronizer is used, then device complexity is reduced, but traction force interruption occurs during shifting
Solution Approach 1:
The invention replaces the mechanical sliding synchronizer system with a hybrid system combining friction brakes and a one-way clutch, substituting the sliding mechanical action with a braking and locking mechanism that maintains continuous power transmission without traction interruption
3Volume of moving object
If an epicyclic gear set without ring gear is used, then transaxle size is reduced, but heat dissipation becomes more challenging
Solution Approach 1:
The invention moves the brake discs from an internal configuration to an external arrangement outside the transaxle housing, utilizing external space for heat dissipation components, thereby maintaining compact internal geometry while improving thermal management through external heat radiation surfaces
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 enables seamless shifting with minimal power loss and high reliability, maintaining traction and comfort by eliminating the need for a ring gear and reducing heat-related issues, making it suitable for electric and hybrid vehicles.
Implementation Method 1
a first dry brake disc (54), a second dry brake disc (48)... a first caliper disc brake system... a second caliper disc brake system
Implementation Method 2
an inner race of a overrunning or one-way clutch (63) is connected to the first sun gear member (30)... an outer race (64) of the one-way clutch (63) is connected to a two-speed transaxle casing
Data Source
Figure 1
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AI summary
A two-speed transaxle for an electric vehicle has an input shaft receiving power from an electric motor, and two output shafts delivering power to drive the vehicle. At least one epicyclic gear set is used. Each epicylic gear set has only an outer gear member, each of which meshingly engage a plurality of planet gears supported on a common carrier. The two-speed transaxle produces its first forward speed ratio when a first caliper brake system and a second caliper brake system are disengaged and a one-way clutch connects the first sun gear to the transaxle casing. Second forward speed ratio results when the second hydraulic brake is engaged to fix the second sun gear. Reverse drive and regenerative operation result when the first hydraulic brake fixes the first sun gear and the direction of power flow is reversed.