Accessory Drive Decoupler With Time-Based Slip for Torque Spikes
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Solution Overview
Problem
Existing accessory drive systems for vehicular engines face challenges in managing high, short-lived torque spikes, which can cause excessive stress on accessories due to the direct transmission of torque from the crankshaft to accessory shafts.
Innovation Solution
A decoupler mechanism with a wrap spring clutch and isolation spring in series, utilizing a lubricant to generate slippage at high acceleration thresholds, preventing excessive torque transmission by engaging the clutch without slippage after a selected period, thereby controlling torque transfer effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a direct torque transmission system is used from crankshaft to accessory shafts, then the structure is simple and reliable, but high torque spikes cause excessive stress on accessories
Solution Approach 1:
A decoupler mechanism is introduced as an intermediary device between the crankshaft and accessory shafts. This decoupler includes a clutch assembly with friction surfaces and a spring element that acts as a mediator to absorb and manage torque spikes, preventing them from reaching the accessories while maintaining normal torque transmission during steady operation.
Solution Approach 2:
The spring element in the clutch assembly is pre-loaded to provide cushioning before torque spikes occur. This beforehand cushioning allows the spring to compress and absorb excess torque energy during high-torque events, protecting the accessories from stress while automatically engaging to transmit normal operating torque.
2Reliability
If a decoupler mechanism is introduced to prevent torque spikes, then accessory protection is improved, but the device complexity increases
Solution Approach 1:
The clutch assembly is designed as a self-regulating mechanism that automatically engages and disengages based on torque conditions without external control. The spring element self-adjusts its compression based on the torque load, and the friction surfaces automatically slip or lock together based on the applied force, providing reliability without complex control systems.
Solution Approach 2:
The harmful high-torque spikes are extracted from the torque transmission path through the controlled slippage of the clutch friction surfaces. This extraction of excess torque energy protects the accessories while the decoupler structure remains relatively simple, using only basic mechanical elements.
3Object-affected harmful factors
If lubricant is used to generate slippage during high acceleration, then torque spike mitigation is improved, but the lubricant volume and interference fit precision requirements increase
Solution Approach 1:
The lubricant's viscosity and friction characteristics are utilized as a controllable parameter to enable slippage during high acceleration events. By selecting appropriate lubricant properties and controlling the interference fit dimensions, the system achieves reliable torque spike mitigation through predictable slippage behavior under high-load conditions.
Solution Approach 2:
The friction characteristics between the clutch surfaces are made dynamic through the use of lubricant, allowing the system to transition between locked (normal operation) and slipping (torque spike) states. This dynamic friction control enables the decoupler to adapt to varying torque conditions automatically.
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 initial high acceleration phases, reducing stress on accessories and ensuring smooth operation by engaging the clutch without slippage once the threshold is sustained, thus protecting the accessory drive components.
Implementation Method 1
a volume of lubricant that, in a first state of the decoupler, is positioned between said one of the radially inner and outer surfaces and the clutch engagement surface to lubricate the wrap spring clutch and the clutch engagement surface
Implementation Method 2
the volume of lubricant generates slippage between said one of the radially inner and outer surfaces and the clutch engagement surface
Implementation Method 3
One of the radially inner and outer surfaces engages the clutch engagement surface in an interference fit with the clutch engagement surface
Implementation Method 4
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
Data Source
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.