Two-Stage Planetary Gearbox With Direct Carrier Support
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Solution Overview
Problem
Existing electric tailgate gearboxes have low torque transmission and high costs due to low transmission ratios, requiring large space and high material costs, and often use plastic sun gears which are not sufficient for higher torque requirements.
Innovation Solution
A redesigned planetary gear transmission box with a transmission ratio greater than 25, incorporating a metal second sun gear and direct support of the second planetary carrier on the gearbox body, eliminating the need for an output bearing and reducing rotation speed to minimize wear and costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the transmission ratio is increased to above 25, then the locked rotor torque increases to above 5.5 Nm, but the output rotation speed decreases
Solution Approach 1:
The patent changes the transmission ratio parameter from below 25 to above 25, which directly increases the locked rotor torque to above 5.5 Nm. This parameter change is the core solution that resolves the torque deficiency in existing gearboxes.
2Reliability
If a bearing is added to support the second planetary carrier, then the output rotation support is improved, but the device complexity and cost increase
Solution Approach 1:
The patent extracts and removes the bearing component from the output end support structure. By designing the second planetary carrier to be directly supported on the box body without a bearing, the patent reduces device complexity and cost while still providing adequate support for the reduced output rotation speed.
Solution Approach 2:
The patent replaces the expensive bearing with a simpler, cheaper direct support structure on the box body. This substitution is valid because the reduced output rotation speed from the higher transmission ratio makes the demanding bearing support unnecessary.
3Ease of manufacture
If plastic material is used for the sun gear, then the manufacturing cost is reduced, but the torque transmission capability is insufficient for higher torque requirements
Solution Approach 1:
The patent uses metal material for the second sun gear to ensure sufficient torque transmission capability for the higher torque requirements (above 5.5 Nm). The metal material provides the necessary strength and durability that plastic cannot achieve at this torque level.
4Force
If two gearboxes are arranged to achieve high transmission ratio, then the torque transmission is improved, but the occupied space increases
Solution Approach 1:
The patent merges two planetary gear stages into a single compact gearbox unit with a transmission ratio above 25. By integrating the first and second planetary gear transmission stages sharing common components (such as the first planetary carrier being supported on the box body), the patent achieves high torque transmission in a single gearbox rather than requiring two separate gearboxes.
Data Source
AI summary
Disclosed is a planetary gear transmission box, comprising a housing portion, a first planetary gear transmission stage, and a second planetary gear transmission stage, wherein the first planetary gear transmission stage comprises a first sun gear (3), a first planetary carrier (5), and a first ring gear; the second planetary gear transmission stage comprises a second sun gear, a second planetary carrier (7), and a second ring gear (6); the first sun gear (3) is connected to an external input element; the first planetary carrier (5) is connected to the second sun gear; the second planetary carrier (7) is connected to an output element; the transmission ratio of the gear transmission box is greater than 25; and the second planetary carrier (7) is directly supported on the housing portion. The locked rotor torque of the gear box is increased, such that the output rotational speed is reduced, and thus a bearing member at the output end can be omitted.