CVT Clutch Slip Learning for Pulley Protection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Continuously variable transmissions (CVTs) face challenges in managing torque spikes, which can cause pulley slipping and damage, and the maximum clamping pressure used to prevent slipping negatively affects fuel economy.
Innovation Solution
A control system and method that adjust pressure to allow the clutch to slip first during transient events, determining a desired running pressure lower than pulley clamping pressure but higher than the clutch critical pressure, using clutch slip tests to collect data and calculate a gain and offset for determining the clutch critical pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If maximum clamping pressure is applied to the pulleys to prevent slipping during torque spikes, then pulley reliability is improved, but fuel economy deteriorates
Solution Approach 1:
The clutch is introduced as an intermediary component between the torque source and the pulley system. During torque spikes, the clutch slips (absorbing the shock) while the pulleys maintain lower clamping pressure, preventing pulley damage without requiring maximum pressure on all components. This mediator approach protects the pulley system while avoiding the fuel economy penalty of continuous maximum clamping.
Solution Approach 2:
The control system detects torque spikes in advance and preemptively adjusts clutch pressure before pulley slipping occurs. By detecting the torque disturbance early and responding with clutch pressure modulation, the system prevents pulley slip without needing to apply maximum clamping pressure to the pulleys, thus maintaining fuel efficiency while protecting the pulley system.
2Use of energy by moving object
If lower clamping pressure is used to improve fuel economy, then fuel efficiency is improved, but pulley slip risk increases
Solution Approach 1:
The clutch serves as a protective intermediary that slips first during torque disturbances, preventing the need for high clamping pressure on the pulleys. This allows the system to operate with lower pulley clamping pressure (improving fuel efficiency) while the clutch absorbs the protective function of preventing slip in the pulley system.
Solution Approach 2:
The clutch is designed to tolerate and undergo controlled slipping during transient torque events, acting as a sacrificial protective element. By allowing the clutch to slip rather than protecting the more valuable pulley system with maximum pressure, the system achieves fuel efficiency while maintaining overall reliability through the clutch's protective sacrifice.
3Reliability
If the clutch is designed to prevent slip at all times, then transmission reliability is improved, but the system loses the ability to act as a protective fuse
Solution Approach 1:
The clutch pressure is dynamically adjusted based on real-time operating conditions and detected torque disturbances. Rather than maintaining constant maximum pressure to prevent all slip, the system modulates clutch pressure adaptively, allowing controlled slipping during transient events when it provides protective fuse functionality, while maintaining reliability during normal operation.
Solution Approach 2:
The system changes the clutch pressure parameter dynamically in response to detected torque spikes and operating conditions. By adjusting the pressure parameter adaptively rather than maintaining a fixed high value, the clutch can switch between its protective fuse role (slipping during transients) and its reliable power transmission role (engaged during normal operation).
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
Prevents pulley slipping while maintaining fuel efficiency by allowing the clutch to act as a 'fuse' during torque spikes, ensuring the CVT operates effectively without excessive clamping pressure.
Implementation Method 1
A clutch is provided that is selectively engageable to couple the input shaft to the variator assembly
Implementation Method 2
A hydraulic system is configured to supply pressure to the variator assembly and the clutch
Data Source
AI summary
A continuously variable transmission, a control system, and a method are provided. The control system and method are configured to learn a desired running pressure to be applied to a clutch that is lower than a pulley clamping pressure and higher than a pressure at which the clutch would slip (a clutch critical pressure), so that the clutch can act as a fuse to avoid pulley slip. A plurality of clutch slip tests are performed, each of which include decreasing pressure supplied to the clutch until a clutch slip occurs. Clutch slip data points are collected at the point of slip and used to determine a gain and an offset, where the gain is a clutch pressure versus clutch torque capacity gain, and the offset is a clutch pressure offset, which is used to determine the clutch critical pressure.