Compact Alternator Nested in Wheel Member for Hand-Held Power Tools
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Solution Overview
Problem
Internal combustion engines in hand-held power tools face challenges in accommodating a powerful alternator that is resistant to mechanical and thermal loads while occupying minimal space, due to limited housing space and exposure to significant vibrations and thermal stress.
Innovation Solution
The alternator is integrated within the radial boundary of the wheel member and crankcase, with the stator penetrated by the crankshaft and the rotor fixed to the wheel member, providing mechanical protection and efficient space utilization. This configuration includes a claw pole alternator design with a stationary induction coil, annular magnet arrangement, and thin sheet metal stator yoke to manage magnetic flux and heat, allowing operation from 300/min to 15,000/min without overheating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the alternator is made powerful to deliver sufficient electric power, then the electric power output is improved, but the space occupied by the alternator increases
Solution Approach 1:
The alternator is nested within the radial boundary of the wheel member, with the stator positioned between the crankcase and the wheel member. The crankshaft penetrates the stator, and the rotor is integrated into the wheel member, creating a compact nested arrangement that maximizes power density within limited space.
Solution Approach 2:
The alternator is arranged in the radial direction within the wheel member rather than extending axially, utilizing the radial dimension for power generation components. This dimensional reorganization allows sufficient power output without increasing the axial length of the engine assembly.
2Volume of moving object
If the alternator is made compact to occupy minimal space, then the space utilization is improved, but the mechanical protection and thermal management become more difficult
Solution Approach 1:
The alternator components are merged with existing engine structures: the stator is integrated with the crankcase, the rotor is combined with the wheel member, and the crankshaft penetrates the stator. This merging provides inherent mechanical protection while maintaining compact dimensions.
Solution Approach 2:
The crankcase, which could be a source of mechanical stress, is designed to provide mechanical protection for the stator. The wheel member, subject to vibrations, is integrated with the rotor to convert vibrational energy into useful electrical generation while protecting the alternator components from damage.
3Volume of moving object
If the alternator is arranged within the radial boundary of the wheel member, then the space utilization is improved, but the mechanical complexity of integration increases
Solution Approach 1:
The wheel member serves multiple functions: it drives the tool through the clutch mechanism and simultaneously houses the rotor of the alternator. The crankcase provides both structural support and protection for the stator. This multi-functionality reduces the number of separate components and simplifies the overall integration.
Solution Approach 2:
The existing moving parts of the engine, particularly the wheel member and crankshaft, are utilized to drive the alternator without requiring separate drive mechanisms. The crankshaft rotation directly drives the rotor through the integrated wheel member, allowing the alternator to serve itself using the engine's existing motion.
4Power
If the alternator operates at high engine speed to deliver sufficient power, then the electric power output is improved, but the thermal load and heat development increase
Solution Approach 1:
The stator yoke is constructed from thin sheet metal pieces (approximately 0.5-1.5 mm thickness) that provide magnetic flux conduction while allowing heat to dissipate. The thin film structure reduces thermal mass and facilitates heat transfer to the surrounding environment, preventing excessive heat buildup at high operating speeds.
Solution Approach 2:
The thickness of the stator sheet metal is optimized to balance magnetic flux conduction and thermal management. By adjusting the thickness parameter within the range of 0.5-1.5 mm, the design achieves satisfactory power output at low speeds while preventing excessive heat development at high speeds.
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 solution enables a compact alternator that delivers sufficient electric power (2-200 watts) across varying engine speeds while withstanding mechanical and thermal stresses, serving as both an energy source and ignition angle transducer, and can function as a starter motor, thus enhancing the reliability and efficiency of hand-held power tools.
Implementation Method 1
An alternator is driven by the crankshaft and supplies an electric consumer
Implementation Method 2
The magnets of the annular magnet arrangement (magnet ring) are positioned expediently in recesses of the wheel member itself
Implementation Method 3
the stator sheet metal pieces are connected at the inner circumference of the coil support positive-lockingly or frictionally with one another and/or with the coil support for example, by a snap-on connection
Implementation Method 4
Electric sheet has the positive property that, as a result of its high electric resistance, detrimental eddy currents are reduced
Data Source
AI summary
An internal combustion engine has a combustion chamber having a spark plug arranged thereat. A crankcase supports a crankshaft. An intake for introducing fuel and combustion air into the combustion chamber is provided. An exhaust for exhausting combustion gases from the combustion chamber is provided. A piston is connected to the crankshaft and drives the crankshaft in rotation. A wheel member is connected to the crankshaft and rotates with the crankshaft. An alternator driven by the crankshaft supplies electric power to a consumer. The alternator is arranged within a radial boundary of the wheel member and external to the crankcase. The alternator has a stator and a rotor, wherein the crankshaft penetrates the stator and wherein the rotor is fixedly connected to the wheel member.