CVT Torque Control System for Smooth Downshifts
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Solution Overview
Problem
Conventional vehicle propulsion systems with continuously variable transmissions face challenges in achieving smooth downshifts and maintaining torque control, leading to potential power loss and reduced drivability due to communication delays and inadequate torque monitoring.
Innovation Solution
A control system that includes a positive torque request module and monitor within the transmission backbone, which calculates and limits torque requests based on engine acceleration and transmission ratios, ensuring that the torque provided to the engine backbone does not exceed predetermined thresholds, thereby avoiding the need for timers and enhancing responsiveness and smoothness during downshifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If torque requests are monitored and limited in the transmission backbone before forwarding to the engine backbone, then responsiveness and smoothness of downshifts are improved, but device complexity increases due to additional monitoring and limiting functionality
Solution Approach 1:
The patent implements preliminary action by monitoring and limiting torque requests in the transmission backbone before they are forwarded to the engine backbone. The positive torque request monitor proactively identifies and restricts excessive torque requests during downshift events, preventing power loss and improving responsiveness without requiring reactive corrections from the engine side.
2Loss of energy
If the positive torque request monitor limits torque requests to a maximum threshold, then power loss is prevented and torque delivery is optimized, but the driver's requested torque may be restricted
Solution Approach 1:
The patent applies the skipping principle by implementing a time-based filter that temporarily bypasses the torque limit during brief downshift events. The system allows torque requests to exceed the threshold for a limited duration (e.g., 200-500 milliseconds) during active downshifts, then re-enforces the limit afterward. This approach prevents power loss during normal operation while avoiding unnecessary restriction of driver torque requests during transient downshift conditions.
3Loss of time
If torque requests are monitored and limited proactively in the transmission backbone, then the need for timers and reactive monitoring in the engine backbone is eliminated, but communication and coordination requirements increase
Solution Approach 1:
The patent extracts the torque monitoring and limiting functionality from the engine backbone and relocates it to the transmission backbone. By moving the positive torque request monitor to the transmission control module, the system eliminates the need for timers and reactive monitoring mechanisms in the engine control module. This extraction simplifies the overall system architecture by consolidating torque management responsibilities in a single location.
Data Source
AI summary
A vehicle propulsion system includes a prime mover having a prime mover output shaft, a continuously variable transmission having a variator input shaft coupled to the prime mover output shaft and having a variator output shaft, a driver torque request module in communication with a driver input and for outputting a driver torque request, an engine backbone in communication with the prime mover, and a transmission backbone in communication with the continuously variable transmission and the engine backbone in the vehicle propulsion system. The transmission backbone includes a positive torque request module that generates a positive torque request, and a positive torque request monitor that limits a torque request from the transmission backbone to the engine backbone to a maximum of a predetermined threshold.