CVT Gear Ratio Control for Engine Braking Feel
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Solution Overview
Problem
Continuously variable transmissions (CVT) lack a desirable engine braking 'feel' due to immediate gear ratio reduction when the accelerator pedal is disengaged, leading to minimal engine braking performance, which is not replicable in conventional automatic transmissions.
Innovation Solution
A method to selectively control gear ratio reduction in CVT by detecting a desired engine braking condition and applying a decay factor to maintain and gradually reduce the gear ratio, improving drivability and fuel efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the CVT immediately reduces gear ratio to the lowest available ratio when the accelerator pedal is disengaged, then the transmission responds quickly to driver input, but the engine braking performance is minimal and the driving feel is undesirable
Solution Approach 1:
The patent applies dynamics by making the gear ratio reduction process adaptive rather than static. The control system dynamically adjusts the rate of gear ratio reduction based on detected driving conditions, specifically implementing different reduction rates for uphill versus downhill scenarios. This dynamic adjustment allows the system to maintain desirable engine braking characteristics while still responding to driver input, resolving the contradiction between quick response and acceptable engine braking feel.
2Loss of time
If the gear ratio is immediately reduced to the lowest ratio in deceleration conditions, then the transmission achieves rapid downshifting, but fuel economy and drivability are compromised due to loss of engine braking
Solution Approach 1:
The patent applies parameter changes by modifying the gear ratio reduction rate parameter based on detected driving conditions. Instead of using a fixed immediate reduction to the lowest ratio, the system changes the reduction parameter dynamically - implementing slower reduction rates during downhill deceleration to maintain engine braking and improve fuel economy, while allowing faster reduction in uphill scenarios where engine braking is less critical.
3Stability of the object's composition
If the CVT provides continuous variable gear ratios without discrete selections, then the transmission achieves smooth operation, but the driving feel differs from conventional transmissions
Solution Approach 1:
The patent resolves this contradiction by dynamically controlling the rate of gear ratio change to simulate the discrete shifting feel of conventional transmissions. The control system adjusts the gear ratio reduction rate to create perceptible steps or phases in the downshifting process, making the continuous variable transmission behave more like a conventional transmission with discrete gear selections, thereby improving driving familiarity and acceptability.
Data Source
AI summary
This invention provides a method for controlling a gear ratio in an automatic transmission of a vehicle. The method includes detecting a desired engine braking condition associated with the vehicle. Once the engine braking condition is determined, a decay factor is determined for reducing the gear ratio of the transmission. The decay factor maintains the gear ratio for a delayed period of time before gradually reducing the gear ratio over time. After determining the decay factor, the gear ratio of the transmission is controlled in accordance with the decay factor.