Wrap Spring Clutch Decoupler for Time-Based Torque Slip
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Solution Overview
Problem
Existing accessory drive systems for vehicular engines face challenges in managing high, short-lived torque spikes that can cause stress on accessory shafts and components, as they lack effective decoupling mechanisms to prevent such torque from being transmitted.
Innovation Solution
A decoupler system comprising a shaft adapter, pulley, isolation spring, and wrap spring clutch, which automatically decouples the accessory shaft from the belt when torque exceeds a threshold, using an isolation spring that expands radially to engage a sleeve and constrain the wrap spring clutch, thereby limiting torque transfer and reducing stress on accessories.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a decoupler completely prevents torque transmission to protect accessories from high torque spikes, then accessory reliability improves, but the accessory cannot receive necessary torque during normal operation
Solution Approach 1:
The decoupler employs a wrap spring clutch that dynamically adjusts torque transmission based on operating conditions. During normal operation, the clutch engages to transmit torque from the input member to the output member. During high torque spikes exceeding a threshold, the clutch disengages to prevent damage, and during controlled slip events, it allows temporary slippage to dissipate energy while maintaining connection. This dynamic behavior resolves the contradiction by making torque transmission conditional rather than fixed.
Solution Approach 2:
The isolation spring's stiffness parameter is specifically designed to allow controlled slippage during high acceleration events. The spring compresses and expands radially, changing the effective torque transmission parameter dynamically. During normal operation, the spring maintains engagement; during torque spikes, it allows controlled disengagement and slippage. This parameter change enables the system to differentiate between normal and abnormal operating conditions, resolving the contradiction between protection and power transmission.
2Object-affected harmful factors
If the decoupler allows slippage during high acceleration events, then torque spikes are mitigated, but torque transmission efficiency decreases
Solution Approach 1:
The decoupler implements partial slippage rather than complete disengagement during high acceleration events. The wrap spring clutch allows controlled relative motion between input and output members, dissipating excess energy through friction and spring deformation while maintaining partial torque transmission. This partial action mitigates harmful torque spikes while minimizing energy loss, as the clutch remains engaged rather than fully disengaging, resolving the contradiction between protection and efficiency.
3Device complexity
If a simple clutch mechanism is used to limit torque, then device complexity is reduced, but it cannot provide time-based slip control for short-lived torque events
Solution Approach 1:
The isolation spring is pre-compressed during normal operation, storing elastic energy in advance. When a torque spike occurs, the pre-compressed spring immediately engages to allow controlled slippage, providing time-based protection without requiring complex control systems. The preliminary compression of the spring creates a time delay in torque transmission that naturally filters short-lived torque events, resolving the contradiction between simplicity and time-based control capability.
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 effectively mitigates high torque spikes by allowing slippage during short-lived acceleration events, reducing stress on accessory components and ensuring smooth operation by limiting torque transmission to manageable levels, thus enhancing the durability and efficiency of the accessory drive system.
Implementation Method 1
an isolation spring that expands radially to engage a sleeve and constrain the wrap spring clutch
Implementation Method 2
a wrap spring clutch that transmits torque from the pulley to the shaft adapter
Data Source
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AI summary
In one aspect, there is provided a decoupler for an accessory drive for an engine. The decoupler includes a decoupler input member and a decoupler output member. One of the decoupler input member and the decoupler output member has a clutch engagement surface. The decoupler further includes a wrap spring clutch and an isolation spring that act in series in a torque path between the decoupler input member and the decoupler output member. The wrap spring clutch has a radially inner surface and a radially outer surface. One of the radially inner and outer surfaces engages the clutch engagement surface in an interference fit with the clutch engagement surface. The decoupler further includes a volume of lubricant. During sufficiently high acceleration of the decoupler input member, there is slippage at the wrap spring clutch for a selected period of time after which the slippage stops.