Front Wheel Drive Bicycle Power Assist System

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Solution Overview

Problem

Conventional electric bicycles face inefficiencies due to heavy, high-torque motors that disrupt bike balance and require large battery units for long-distance operation, leading to increased weight and power consumption.

Innovation Solution

A Power Assist System (PAS) utilizing a lightweight brushless electric motor with a synchronous timing belt-pulley configuration, providing a 16:1 gear reduction to multiply torque and reduce rider effort, featuring a one-way bearing for freewheeling and a lithium battery pack for efficient power assistance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Force

If a high torque motor is used to provide auxiliary driving force, then the motor can overcome resistance and enable hill climbing, but the motor weight increases significantly, disrupting bike balance and reducing mechanical efficiency

Engineering Contradiction:

Improveauxiliary driving forceVSAvoidmotor weight

Core Design Contradiction:

ForceVSWeight of moving object

Solution Approach 1:

A belt-driven pulley system with gear reduction acts as an intermediary mechanism between the small motor and the rear wheel. The system uses a small diameter drive pulley connected to the motor shaft and a large diameter driven pulley attached to the wheel, creating a mechanical advantage that multiplies the motor's torque output while keeping the motor itself lightweight

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The system changes the torque parameter through mechanical advantage provided by the pulley ratio. By using a small drive pulley and large driven pulley configuration, the system transforms the low-torque, high-speed motor output into high-torque, low-speed wheel rotation, achieving the required auxiliary driving force without needing a heavy high-torque motor

Inventive Principle:

Principle #35Parameter changes

2Use of energy by moving object

If large and multiple battery units are used to provide sufficient power for long distance operation, then the power capacity increases, but the overall weight of the bicycle increases, leading to greater power consumption

Engineering Contradiction:

Improvepower capacityVSAvoidbattery weight

Core Design Contradiction:

Use of energy by moving objectVSWeight of moving object

Solution Approach 1:

The system replaces the need for large, heavy battery units by using a mechanically efficient belt-driven pulley system. The gear reduction mechanism allows a small, lightweight battery to power a small motor that, through mechanical advantage, can still provide sufficient auxiliary driving force for long distance operation and hill climbing

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Weight of moving object

If a small lightweight motor is used to reduce weight, then the motor weight decreases and bike balance is maintained, but the motor cannot provide sufficient torque for hill climbing and off-roading

Engineering Contradiction:

Improvemotor weightVSAvoidtorque output

Core Design Contradiction:

Weight of moving objectVSForce

Solution Approach 1:

The belt-driven pulley system serves as a torque-multiplying intermediary. The small drive pulley connected to the lightweight motor shaft drives a large driven pulley on the rear wheel, creating mechanical advantage that multiplies the motor's torque output by the ratio of the pulley diameters, enabling hill climbing capability with a small motor

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The system changes the torque parameter through the pulley gear ratio. By using a small drive pulley and large driven pulley configuration, the system transforms the small motor's low-torque output into high-torque wheel rotation, achieving sufficient force for off-roading and hill climbing without increasing motor weight

Inventive Principle:

Principle #35Parameter changes

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 PAS enhances traction and reduces rider effort, allowing for longer distances with minimal weight addition, maintaining bike balance and efficiency, suitable for various terrains and commuting, while enabling hill climbing and off-roading capabilities.

Implementation Method 1

a one way bearing fitted to the center of the second drive pulley, where the second drive pulley is mechanically connected to a motor shaft; when the motor is not powered, the one way bearing is not engaged to the motor shaft, allowing the wheel to spin freely ('freewheeling') when moving in the forward-direction

Methodology Applied

Scientific EffectOne way bearing: Ratchet

Implementation Method 2

a synchronous timing belt-pulley configuration of a relatively small diameter. The motor shaft is attached to a small drive (timing) pulley via a one way bearing fitted at the hub of the pulley. When the motor is powered, the one way bearing engages the motor shaft and spins the drive pulley at a relatively high RPM to transfer power by means of a timing belt onto a much larger diameter pulley that is attached to the spokes of the front wheel

Methodology Applied

Scientific EffectGear reduction: Gear

Implementation Method 3

The larger diameter pulley spins at a relatively slower RPM due to the gear reduction configuration. In one aspect, the aspect ratio of the smaller diameter drive pulley compared to the larger diameter wheel pulley is approximately 16:1. And because of the gear reduction, the torque is multiplied from a small motor and easily moves a much heavier load

Methodology Applied

Scientific EffectMechanical advantage: Mechanical Advantage