CVT Variator Speed Control for Launch Torque Continuity
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Solution Overview
Problem
Continuously variable transmissions (CVTs) experience 'torque holes' or output torque deficits during the launch phase due to the high rate of change of the variator, particularly in lower ranges, leading to inefficiencies in accelerating the transmission.
Innovation Solution
A method to reduce output torque deficits by determining the rate of change of the transmission ratio and predicting the required motor speed ratio rate of change, adjusting the variator output speed to achieve this rate, and using a transmission controller to send control signals to the variator or prime mover to compensate for torque imbalances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the variator accelerates through lower ranges quickly, then the acceleration rate is improved, but torque deficits are created
Solution Approach 1:
The system performs preliminary action by pre-calculating the required pump displacement rate of change before the variator actually transitions through ratios. The controller determines the optimal displacement trajectory in advance, ensuring that torque delivery remains smooth even as acceleration rate increases. This predictive approach allows the system to prepare the hydraulic system for upcoming ratio changes, preventing torque holes before they occur.
Solution Approach 2:
The system implements feedback by continuously monitoring the actual variator ratio, pump displacement, and transmission output torque, then comparing these against the predicted values. The controller adjusts the pump displacement rate in real-time based on the difference between actual and desired states, ensuring torque continuity is maintained while allowing high acceleration rates. This closed-loop control enables the system to respond dynamically to changing conditions.
2Productivity
If the variator pump displacement transitions quickly from stationary to high stroke rate, then the launch response is improved, but torque holes are created
Solution Approach 1:
The system applies dynamics by making the pump displacement rate adaptive rather than fixed. The controller dynamically adjusts the displacement trajectory based on real-time conditions including current ratio, desired acceleration, and load demands. This allows the system to optimize the transition from stationary to high stroke rate, maintaining smooth torque delivery while achieving rapid launch response. The dynamic adjustment prevents the rigid, step-change displacement patterns that create torque holes.
Solution Approach 2:
The system changes parameters by adjusting multiple variables simultaneously - pump displacement, displacement rate of change, and prime mover torque - to achieve smooth torque delivery during launch. Rather than changing only one parameter (displacement), the controller coordinates changes across the entire transmission system, optimizing the interaction between hydraulic and mechanical components to eliminate torque holes while maintaining rapid response.
3Adaptability or versatility
If multiple ranges are included in the CVT, then the acceleration capability is improved, but the rate of change through lower ranges increases causing torque deficits
Solution Approach 1:
The system segments the overall ratio transition into smaller, controlled increments across multiple ranges. Rather than allowing the variator to sweep through all ratios continuously and rapidly, the controller manages transitions through each range boundary separately, adjusting pump displacement rates appropriately for each segment. This segmentation allows the system to maintain high overall acceleration capability while preventing excessive rate of change within individual lower ranges, thereby avoiding torque deficits.
Data Source
AI summary
According to the present invention, there is provided a method of reducing output torque deficits during the launch of a vehicle having a continuously variable transmission, wherein the variator has an input connected to a prime mover and an output. The method comprises the steps of determining a rate of change of ratio in the transmission, and predicting a required motor speed ratio rate of change value of the variator on the basis of: (i) the determined rate of change of ratio in the transmission, and (ii) the configuration of the transmission. The speed of the variator output is adjusted so as to achieve the required motor speed ratio rate of change value.