CVT Sub-Transmission Gear Shift Control for Vehicle Restart
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Solution Overview
Problem
Conventional control devices for continuously variable transmission in vehicles cause shift shocks when downshifting, leading to a sense of incongruity for the driver, especially when the accelerator pedal is not being used, which deteriorates driving performance.
Innovation Solution
A control device with a sub-transmission mechanism that maintains the gear position in the second gear position when the vehicle is stopped and then shifts to the first gear position while stopped, using a Ravigneaux-type planetary gear mechanism and frictional engagement elements to manage hydraulic pressures and torque capacities, preventing shift shocks and ensuring drive power at restart.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gear position is shifted down from the second gear position to the first gear position before vehicle stop, then drive power at restart is ensured, but shift shock occurs and driving performance deteriorates
Solution Approach 1:
The gear position is shifted down from the second gear position to the first gear position while the vehicle is stopped, before restart occurs. This preliminary action ensures drive power is available at restart without causing shift shock during vehicle operation, as the shift occurs when the vehicle is stationary and the driver does not perceive it.
2Power
If the gear position is shifted down during deceleration without accelerator pedal use, then drive power is ensured, but driver comfort deteriorates due to sense of incongruity
Solution Approach 1:
The gear position change is performed in advance while the vehicle is stopped, before the driver would perceive any incongruity. By completing the shift operation during the stopped state, the system ensures drive power is ready for restart without disrupting the driver's perception during deceleration.
Solution Approach 2:
The control device copies the behavior pattern of manual transmission vehicles where the driver would naturally downshift before stopping, but automates it to occur during the stopped state rather than during deceleration, thereby maintaining the benefit of having low gear engaged for restart while avoiding the negative perception of unexpected shifts during operation.
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
This approach prevents shift shocks during downshifting, improves driving performance by maintaining the gear position during deceleration without accelerator pedal use, and ensures drive power at vehicle restart.
Implementation Method 1
adapted to switch between the first gear position and the second gear position by selectively engaging or releasing a plurality of frictional engagement elements
Data Source
AI summary
A control device continuously variable transmission for vehicle according to the present invention includes a continuously variable transmission mechanism capable of continuously changing a speed ratio, a sub-transmission mechanism provided in series with the continuously variable transmission mechanism, including a first gear position and a second gear position having a smaller speed ratio than the first gear position as forward gear positions and adapted to switch between the first gear position and the second gear position by selectively engaging or releasing a plurality of frictional engagement elements, and a transmission control unit wherein a vehicle is stopped with the gear position of the sub-transmission mechanism kept in the second gear position when being stopped in a state where the gear position of the sub-transmission mechanism is in the second gear position.