Power Tool Compound Planetary Transmission for Compact High-Torque Output

Solution Overview

Problem

Existing impact tools face challenges in achieving high torque and power output efficiently within a compact form factor, often requiring multiple stages of planetary gear reduction, which increases tool size and complexity.

Innovation Solution

A compact impact tool design featuring a single-stage compound planetary transmission with a gear reduction ratio of at least 14:1, utilizing a sun gear, planet gears with different pitch diameters, and a fixed ring gear to transmit rotational motion with intermittent impacts, enabling high torque and power output.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If multiple stages of planetary gear reduction are used to achieve high torque output, then the torque and power output are improved, but the tool size and structural complexity increase

Engineering Contradiction:

Improvetorque outputVSAvoidtransmission complexity

Core Design Contradiction:

PowerVSDevice complexity

Solution Approach 1:

The patent combines two planetary gear stages into a single integrated stage where the sun gear of the first stage serves as the sun gear of the second stage, and planet gears from both stages share common gear elements. This merging achieves high torque multiplication (14:1 reduction ratio) while reducing the number of separate transmission components and simplifying the overall structure.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent implements a nested configuration where the first planetary gear stage is positioned inside the second planetary gear stage, with the sun gear of the first stage located at the center of the sun gear of the second stage. This nesting allows compact arrangement of multiple gear reduction functions within a single transmission housing, reducing overall tool length while maintaining high torque output.

Inventive Principle:

Principle #7Nested doll (Nesting)

2Power

If multiple stages of planetary gear reduction are used to achieve high torque output, then the torque and power output are improved, but the tool length increases

Engineering Contradiction:

Improvetorque outputVSAvoidtool length

Core Design Contradiction:

PowerVSLength of moving object

Solution Approach 1:

The patent implements a nested configuration where the first planetary gear stage is positioned inside the second planetary gear stage, with the sun gear of the first stage located at the center of the sun gear of the second stage. This nesting allows compact arrangement of multiple gear reduction functions within a single transmission housing, reducing overall tool length while maintaining high torque output.

Inventive Principle:

Principle #7Nested doll (Nesting)

Solution Approach 2:

The patent arranges the planetary gear stages in a concentric, radial configuration rather than a linear sequence, utilizing the radial dimension to achieve compact packaging. The planet gears of both stages are distributed around the central sun gear, allowing the transmission to fit within a compact cylindrical space that minimizes tool length.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Volume of moving object

If a high gear reduction ratio is achieved in a compact space, then the tool size is reduced, but the transmission design complexity increases

Engineering Contradiction:

Improvetool sizeVSAvoidtransmission design

Core Design Contradiction:

Volume of moving objectVSDevice complexity

Solution Approach 1:

The patent combines two planetary gear stages into a single integrated stage where the sun gear of the first stage serves as the sun gear of the second stage, and planet gears from both stages share common gear elements. This merging achieves high torque multiplication (14:1 reduction ratio) while reducing the number of separate transmission components and simplifying the overall structure.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent designs the transmission so that certain gear elements serve multiple functions: the sun gear acts as both the central gear for the first planetary stage and the central gear for the second planetary stage, while the planet gears of both stages mesh with shared ring gear elements. This multi-functionality reduces the total number of components needed to achieve the compact high-ratio reduction.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 maximum fastening torque of at least 1200 ft-lbs with a compact form factor, reducing tool length and weight, and enhances efficiency by minimizing power consumption from the battery.

Implementation Method 1

a spring biasing the hammer axially forward toward the anvil

Methodology Applied

Scientific EffectElasticity: Elasticity

Implementation Method 2

a transmission configured to transmit rotational motion from the motor output shaft to the cam shaft, the transmission having a gear reduction ratio of at least 14:1

Methodology Applied

Scientific EffectMechanical Advantage: Mechanical Advantage

Data Source

PatentUS20250249557A1Power tool

Publication Date: 2025.08.07 BLACK & DECKER CORP

AI summary

A power tool includes a housing, a motor, an output spindle, a rotary impact assembly configured to transmit rotational motion with intermittent rotational impacts from a cam shaft to the output spindle, and a transmission.