CVT Shift Control Preventing Wheel Spin
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Solution Overview
Problem
Conventional shift control methods for vehicles without antilock brake systems (ABS) fail to prevent wheel spin and subsequent drivability issues on low-friction surfaces, leading to premature shifting to high-speed transmission ratios during wheel lock conditions, which can result in engine overload and poor vehicle control.
Innovation Solution
A shift control apparatus for continuously variable transmissions (CVT) that monitors driving-wheel acceleration and prohibits shifts to high-speed transmission ratios when acceleration exceeds a predetermined threshold, while allowing shifts to low-speed ratios to ensure vehicle start capability and prevent restart failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the transmission ratio is quickly changed to a high-speed side ratio in response to wheel spin detection, then the transmission ratio responds quickly to wheel spin conditions, but the vehicle cannot restart after stopping due to insufficient driving force
Solution Approach 1:
The patent applies dynamics by making the transmission ratio adjustment adaptive to vehicle operating conditions. The control system dynamically adjusts the transmission ratio based on detected wheel spin conditions, vehicle speed, and accelerator pedal position, transitioning from quick high-speed side ratio changes to controlled low-speed side ratio adjustments when restart capability is needed.
Solution Approach 2:
The patent changes the transmission ratio parameter based on detected conditions. When wheel spin is detected during vehicle operation, the system changes the transmission ratio to the low-speed side ratio to maintain driving force for potential restart operations, rather than quickly shifting to high-speed side ratio.
2Speed
If the target transmission ratio is quickly set at a low-speed side ratio according to quick decrease of driving-wheel speed, then the transmission ratio responds quickly to speed changes, but the vehicle stops before the transmission ratio is sufficiently returned to low-speed side ratio
Solution Approach 1:
The patent applies preliminary action by proactively setting the transmission ratio to the low-speed side ratio when wheel spin is detected, before the vehicle comes to a complete stop. This ensures that when the driver releases the accelerator pedal and the vehicle stops, the transmission ratio is already in the appropriate low-speed side ratio position, eliminating the delay that would otherwise occur after stopping.
3Reliability
If the transmission ratio is limited from changing to high-speed side ratio when wheel spin is detected, then the vehicle starting capability is ensured, but the drivability is degraded during high-speed running due to unintended shift prohibition
Solution Approach 1:
The patent applies local quality by making the transmission ratio control strategy location-specific to the operating condition. When wheel spin is detected during low-speed operation, the transmission ratio is limited to the low-speed side ratio to ensure starting capability. However, when wheel spin occurs during high-speed running, this limitation is not applied, allowing normal drivability and shift operations.
Solution Approach 2:
The control system dynamically adjusts the transmission ratio based on detected conditions. When wheel spin is detected during vehicle operation, the system changes the transmission ratio to the low-speed side ratio to maintain driving force for potential restart operations, rather than quickly shifting to high-speed side ratio.
Data Source
AI summary
A shift control apparatus of a CVT installed in a non-ABS equipped vehicle is arranged to estimate a condition of a transmission ratio of the CVT, to prohibit a shift operation of varying the transmission ratio to a high-speed-side transmission ratio relative to a first predetermined transmission ratio when the driving-wheel acceleration is greater than or equal to a predetermined acceleration, and to cancel the prohibition of the shift operation when the transmission ratio is in a high speed side relative to a second transmission ratio under a condition that the driving-wheel acceleration becomes greater than or equal to the predetermined acceleration.