Friction Damping Decoupler for Alternator Torsional Vibration
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Solution Overview
Problem
Decouplers for belt-driven accessories like alternators are not durable enough for harsh engines, as they are prone to reduced fatigue life due to torsional vibrations, particularly at frequencies near the natural frequency of the decoupler, leading to increased stress on isolation springs.
Innovation Solution
A decoupler design with a hub, pulley, and isolation spring that provides adjustable damping torque to attenuate torsional vibrations, specifically targeting first-order vibrations that can trigger the alternator's voltage regulator to switch at frequencies near the decoupler's natural frequency, thereby reducing the stress on the isolation spring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a decoupler is used to isolate torsional vibrations in belt-driven accessories, then the accessory can operate at constant speed, but the isolation spring suffers from reduced fatigue life due to high torsional vibrations near the natural frequency
Solution Approach 1:
The patent changes the damping parameter by introducing a friction-based damping mechanism between the pulley and hub. This friction damping dissipates torsional vibration energy, particularly reducing vibrations near the natural frequency that would otherwise cause excessive stress on the isolation spring and reduce its fatigue life.
Solution Approach 2:
The patent converts the harmful friction between moving parts into a beneficial damping mechanism. The friction that would normally be considered a source of loss and wear is intentionally utilized to dissipate torsional vibration energy, protecting the isolation spring from fatigue damage.
2Duration of action of stationary object
If damping torque is increased to reduce torsional vibrations, then isolation spring fatigue life is extended, but the decoupler complexity increases
Solution Approach 1:
The friction-based damping mechanism serves multiple functions: it provides damping torque to reduce torsional vibrations, utilizes existing relative motion between decoupler components, and does not require separate dedicated damping components. This multi-functionality achieves vibration reduction without significantly increasing overall device complexity.
3Reliability
If the decoupler is designed to handle harsh engine conditions, then reliability improves, but the device complexity increases
Solution Approach 1:
The decoupler components themselves generate the damping torque through friction during their normal relative motion. The system uses its own operational characteristics (relative rotation between pulley and hub) to create the protective damping effect, eliminating the need for separate active control systems or complex additional components.
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 decoupler design extends the fatigue life of the isolation spring by reducing torsional vibrations at critical frequencies, minimizing the alternator's voltage regulator-induced stress and maintaining the decoupler's operational effectiveness.
Implementation Method 1
a friction surface biasing member positioned for exerting a biasing force to biasing the first and second friction surfaces against each other, thereby generating at least a selected damping torque during relative rotational movement between the pulley and the hub
Implementation Method 2
an isolation spring positioned to transfer rotational force from the pulley to the hub and to accommodate torsional vibration between the pulley and the hub
Data Source
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AI summary
The present invention relates to an endless drive arrangement for an engine (10), comprising: a crankshaft pulley; an alternator pulley (24, 124) mounted to an input shaft (15) of an alternator (18), wherein the alternator (18) operates at at least a first switching frequency and a second switching frequency; an endless drive member (14) that is positioned to transfer power from the crankshaft pulley to the alternator pulley (24, 124) such that first order vibrations are produced at the crankshaft (12); and a decoupler (20) including a hub (22, 122) that is adapted to be coupled to the alternator shaft (15) such that the alternator shaft (15) co-rotates with the hub (22, 122) about a rotational axis, a pulley (24, 124) rotatably coupled to the hub (22, 122), the pulley (24, 124) having an outer periphery that is positioned to engage the endless power transmitting element (14), an isolation spring (28, 128) positioned to transfer rotational force from the pulley (24, 124) to the hub (22, 122) and to accommodate torsional vibration between the pulley (24, 124) and the hub (22, 122), a first friction surface (60, 160) operatively connected with the pulley (24, 124), a second friction surface (62, 162) operatively connected with the hub (22, 122), a biasing member (68) positioned to exert a bias force between the first and second friction surfaces (60, 160; 62, 162), and a retainer (96) engaging the biasing member to maintain the bias force,wherein the second switching frequency is near a natural resonance frequency of the decoupler (20) and the bias force between the first and second friction surfaces (60, 160; 62, 162) generates a damping torque during relative rotational movement between the pulley (24, 124) and the hub (22, 122) which attenuates said first order vibrations so as to reduce a tendency of the alternator to operate at the second switching frequency, thereby reducing a tendency of the alternator (18) of transmitting vibration to the decoupler at frequencies near the natural frequency. Further it is provided a decoupler and a method for operating an engine accessory drive.