CVT Ratio Selection During Braking Using Predictive Velocity
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Solution Overview
Problem
Current methods for selecting speed ratios in continuously variable transmissions (CVT) during vehicle deceleration by braking are insufficient in achieving the minimum under-drive speed ratio during abrupt stops, leading to inefficient and rough vehicle launches from a complete stop.
Innovation Solution
A method that determines the distance of brake pedal travel, calculates the Available Speed Ratio Change, Current and Predictive Ratio Change Capabilities, and uses these to calculate the Time to Reach the Minimum Under-drive Ratio, predicting the vehicle's velocity to actuate the CVT to the desired speed ratio, ensuring smooth operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the TCM uses a look-up table based on brake pedal position to determine the speed ratio during deceleration by braking, then the control method is simple and easy to implement, but the TCM cannot determine and shift the CVT to its minimum under-drive speed ratio (0.38) before the vehicle comes to a complete stop in abrupt stop situations
Solution Approach 1:
The patent applies preliminary action by calculating a predictive speed ratio before the vehicle actually stops, based on current deceleration rate and time-to-collision estimates. This allows the CVT to be pre-positioned at the optimal minimum under-drive ratio (0.38) before the stop is complete, ensuring smooth launch readiness without waiting for the stop to finish. The control module proactively adjusts the ratio rather than reactively responding to already-completed deceleration.
Solution Approach 2:
The patent implements dynamics by transitioning from a static look-up table approach to a dynamic calculation method that continuously adapts the target speed ratio based on real-time vehicle deceleration rate, brake pedal position, and predicted stop timing. The system dynamically adjusts the predictive speed ratio as conditions change, allowing optimal performance across varying deceleration scenarios rather than relying on fixed pre-defined values.
2Stability of the object's composition
If the CVT remains at a higher speed ratio than the minimum under-drive ratio during abrupt stops, then the control system maintains stability, but the vehicle launch from a complete stop becomes inefficient and rough
Solution Approach 1:
The system performs preliminary action by calculating and commanding the minimum under-drive ratio (0.38) in advance, before the vehicle actually comes to a complete stop. This predictive approach ensures the CVT is already positioned at the optimal launch ratio when the stop is completed, eliminating rough launches and improving productivity without compromising control stability through aggressive ratio changes.
3Device complexity
If the TCM uses a static look-up table for speed ratio selection during braking, then the device complexity is low, but the system cannot adapt to varying deceleration rates and brake pedal positions in real-time
Solution Approach 1:
The patent applies dynamics by replacing the static look-up table with a dynamic calculation algorithm that continuously computes the predictive speed ratio based on real-time inputs including deceleration rate, brake pedal position, and vehicle speed. This dynamic approach enables the system to adapt to varying deceleration conditions while maintaining reasonable complexity through efficient mathematical calculations rather than complex hardware or multiple lookup tables.
Solution Approach 2:
The system implements parameter changes by using multiple varying parameters (deceleration rate, brake pedal position, vehicle speed, time-to-collision) to dynamically determine the optimal speed ratio. Instead of relying on a single static parameter, the system changes and weights multiple parameters in real-time calculations, enabling versatile adaptation to different braking scenarios while keeping the control logic manageable through standardized computational approaches.
Data Source
AI summary
A method and system for selecting a speed ratio for a continuously variable transmission (CVT) of a vehicle during braking. The method and system includes determining a Current Actual Speed Ratio of the CVT when the distance of a brake pedal travel exceeds a predetermined distance, determining, by a transmission control module (TCM), an amount of Available Speed Ratio Change (Δr), a Current Ratio Change Capability (Current-{dot over (r)}), and a Predictive Ratio Change Capability (Predictive-{dot over (r)}). The method further includes the TCM calculating a Time to Reach the Minimum Under-drive Ratio (tUD), calculating a Predicted Velocity of the Vehicle (vPr) using (tUD), determining a Desired Speed Ratio of the CVT using the Predicted Velocity of the Vehicle (vPr), and actuating the CVT to the Desired Speed Ratio.