CVT Speed Ratio Control During Sudden Vehicle Stops
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
During a sudden vehicle stop, continuously variable transmissions (CVT) face challenges in accurately measuring and controlling the speed ratio due to low rotational speeds, which can lead to inaccurate calculations and suboptimal performance.
Innovation Solution
A controller is programmed to calculate the current speed ratio using measured rotational speeds from sensors and compare it to calibrated threshold ratios, executing specific control actions based on which threshold is exceeded, including estimating or extrapolating the speed ratio when it drops below a threshold, to ensure optimal performance during and after the stop.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the CVT uses standard speed sensors to measure rotational speeds during sudden stops, then the device complexity is reduced, but the measurement precision deteriorates due to low rotational speeds falling below sensor resolution thresholds
Solution Approach 1:
The controller is pre-programmed with multiple calibrated threshold ratios and associated control actions. When a sudden stop is detected, the controller proactively compares the current speed ratio against these predetermined thresholds and executes the appropriate control action without waiting for sensor data to become unreliable. This preliminary preparation of control strategies ensures continuous accurate control even when rotational speeds drop below sensor resolution capabilities.
Solution Approach 2:
The patent introduces an intermediary estimation mechanism that bridges the gap when direct sensor measurement becomes unreliable. Instead of relying solely on speed sensor data at low speeds, the system uses the relationship between pulley pressures and calibrated threshold ratios to estimate the current speed ratio. This intermediary estimation method maintains measurement precision without requiring more complex high-resolution sensors.
2Ease of operation
If the controller continues to rely on sensor measurements during sudden stops, then the ease of operation is maintained, but the reliability deteriorates due to inaccurate speed ratio calculations at low speeds
Solution Approach 1:
The controller dynamically adapts its control strategy based on operating conditions. During sudden stops when rotational speeds drop below sensor resolution, the system automatically transitions from direct sensor-based measurement to threshold-based estimation. This dynamic adaptation maintains reliability without requiring complex manual intervention or system redesign, preserving ease of operation while ensuring accurate control throughout the full range of operating conditions.
3Productivity
If the CVT maintains a minimum speed ratio during sudden stops, then the productivity is improved by preparing for optimal launch conditions, but the loss of time increases due to the extended duration of the sudden stop event
Solution Approach 1:
The controller proactively manages the speed ratio during the sudden stop event to prepare optimal launch conditions in advance. By monitoring the current speed ratio against calibrated thresholds and executing appropriate control actions, the system ensures that the CVT reaches the minimum speed ratio and prepares for optimal launch conditions before the driver releases the brake pedal. This preliminary preparation eliminates launch delays while maintaining the necessary stop duration for safety.
Data Source
AI summary
A continuously variable transmission (CVT) includes input and output members, a primary variator pulley, and a secondary variator pulley. The respective variator pulleys are responsive to primary and secondary pressures. Speed sensors measure a respective rotational speed of each variator pulley. A controller executes a method by receiving the measured rotational speeds, calculating a current speed ratio of the CVT above a threshold CVT speed ratio using the rotational speeds, comparing the calculated current speed ratio to calibrated threshold ratios during a sudden stop event of the vehicle, and selectively executing a CVT control action after the calculated current speed ratio drops below the threshold CVT speed ratio during the sudden stop event. The control action depends on which of the threshold ratios is exceeded by the calculated current speed ratio after the calculated current speed ratio drops below the threshold CVT speed ratio, and on the measured rotational speeds.