CVT Transmission Controller Gear Ratio Return Strategy
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Solution Overview
Problem
In hybrid vehicles, the short time between engine stop and belt stop on the driving pulley makes it difficult to reliably return the gear ratio to the low-ratio range, leading to issues with smooth starts and increased power consumption.
Innovation Solution
A transmission controller that detects the gear ratio and pulley revolutions, varying the gear-ratio control start time based on these conditions, and includes throttle opening detection to initiate gear ratio control when the engine is stopped, ensuring steady and reliable gear ratio returns to the low-ratio range, even after engine stop, thereby reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gear ratio control is initiated immediately after engine stop to return to low-ratio range, then the reliability of gear ratio return is improved, but the actuator power consumption increases due to abrupt belt engagement
Solution Approach 1:
The control system initiates gear ratio return control before the engine completely stops, when the driving pulley is still rotating. This preliminary action ensures the belt is already engaged with the pulley groove before the pulley stops, preventing belt floating and ensuring reliable gear ratio return without requiring high power for abrupt engagement.
Solution Approach 2:
The control system dynamically adjusts the gear ratio return timing based on the driving pulley's rotation state. By detecting whether the pulley is rotating or stopped, the system adapts the control strategy to maintain reliability while optimizing power consumption - using gradual adjustment when rotating and preventing abrupt engagement when stopped.
2Reliability
If the engine stop timing is extended to allow gear ratio return, then the gear ratio return reliability is improved, but the loss of time in the transmission system increases
Solution Approach 1:
The system performs gear ratio return control in advance, before the engine stop is completed. By detecting the engine stop instruction and initiating control while the driving pulley is still rotating, the system ensures the gear ratio returns to the low-ratio range before the belt stops, eliminating time loss while maintaining reliability.
3Speed
If the groove width of the driving pulley is reduced after engine start to improve acceleration, then the acceleration performance is improved, but the belt may float from the driving pulley causing smooth start issues
Solution Approach 1:
The control system reduces the groove width of the driving pulley before the engine starts rotating, when the belt is already engaged. This preliminary groove width reduction ensures the belt is securely held in the groove before rotation begins, enabling smooth acceleration without belt floating, while still achieving good acceleration performance.
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
Enables steady and reliable gear ratio returns to the low-ratio range, ensuring sufficient acceleration at restarts while reducing actuator power consumption by optimizing the duty ratio of the control signal based on gear ratio and rotation-speed change rates.
Implementation Method 1
a centrifugal start-up clutch is provided on the input side (driving side) of the continuously variable transmission system
Implementation Method 2
a free wheeling clutch capable of transmitting power in one direction only is provided between a driven pulley and the driving wheels
Data Source
AI summary
A transmission controller for a continuously variable transmission system steadily returns a gear ratio toward the low-ratio range during deceleration, even in a hybrid vehicle which stops an engine during deceleration. A control unit determines the return-start number of revolutions of a driving pulley and the duty ratio of an actuator and issues a control instruction to the actuator which changes the gear ratio by varying the groove width of the driving pulley. The control instruction is issued after an engine stop instruction from a drive control element and the return-start number of revolutions is set higher as the gear ratio is closer to the top-ratio range.