CVT Shift Control for Kickdown Acceleration Synchronism
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Solution Overview
Problem
Existing shift control systems for continuously-variable transmissions fail to maintain synchronism between engine speed and vehicle speed during reacceleration, particularly when the driver varies the accelerator pedal, leading to uncomfortable acceleration responses.
Innovation Solution
A shift control apparatus and method that includes an operating condition sensing section, a normal-time speed ratio determining section, a kickdown-acceleration request determining section, and an accelerator-operation-quantity variation-rate limiting section, which calculates a corrected accelerator operation quantity to control the speed ratio and ensure linear increase of output rotational speed with input rotational speed during kickdown acceleration requests.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the speed ratio is fixed at a constant value during kickdown acceleration to reduce time lag, then the acceleration responsiveness is improved, but the synchronism between engine speed and vehicle speed cannot be maintained when the driver varies the accelerator pedal
Solution Approach 1:
The patent applies dynamics by transitioning from a static fixed speed ratio to a dynamic speed ratio that adapts to changing accelerator operation. The kickdown-acceleration-time control section continuously adjusts the target speed ratio based on real-time accelerator operation quantity, enabling the system to respond dynamically to driver input while maintaining the benefits of reduced time lag.
Solution Approach 2:
The patent changes the parameter of speed ratio from a fixed constant value to a variable parameter that depends on accelerator operation quantity. By making the target speed ratio a function of accelerator operation during kickdown acceleration, the system can simultaneously achieve rapid response and maintain synchronism when the driver varies the accelerator pedal.
2Reliability
If the speed ratio is variably controlled by tracing a shift map to maintain synchronism, then the synchronism between engine speed and vehicle speed is preserved, but the acceleration responsiveness during kickdown operation deteriorates due to excessive down-shift amount
Solution Approach 1:
The patent changes the control parameter from map-based speed ratio to a direct function of accelerator operation quantity during kickdown. This parameter change allows the system to bypass the excessive down-shift characteristics of traditional shift maps and achieve both synchronism and rapid response.
Solution Approach 2:
The patent applies preliminary action by pre-defining the relationship between accelerator operation quantity and target speed ratio specifically for kickdown acceleration. This preliminary configuration ensures that when kickdown occurs, the system immediately applies the optimized control strategy without relying on general-purpose shift maps.
3Adaptability or versatility
If the accelerator operation quantity is allowed to vary freely during kickdown acceleration, then the driver's acceleration request is fully reflected, but the synchronism between engine speed and vehicle speed is lost
Solution Approach 1:
The patent applies feedback by continuously monitoring the accelerator operation quantity and using this information to adjust the target speed ratio in real-time. The kickdown-acceleration-time control section receives feedback from the accelerator operation sensing and dynamically adjusts the speed ratio control to maintain synchronism while responding to driver requests.
Solution Approach 2:
The patent changes the accelerator operation quantity parameter from a direct input to a corrected parameter that accounts for rate of change. By applying variation rate limitation when necessary, the system transforms the raw accelerator signal into a controlled parameter that maintains synchronism while still reflecting the driver's acceleration intent.
Data Source
AI summary
A shift control apparatus for a continuously-variable transmission includes an operating condition sensing section; a normal-time speed ratio determining section; a normal-time control section; a kickdown-acceleration request determining section; a kickdown-acceleration-time control section; and an accelerator-operation-quantity variation-rate limiting section. The kickdown-acceleration-time control section is configured to set a kickdown-acceleration-time target speed ratio in accordance with a vehicle speed and an accelerator operation quantity, to cause an output rotational speed of the transmission to increase substantially linearly with an increase of input rotational speed of the transmission, when the kickdown-acceleration request determining section determines that a kickdown acceleration request is present, and to control the speed ratio in accordance with the kickdown-acceleration-time target speed ratio. The accelerator-operation-quantity variation-rate limiting section is configured to calculate a corrected accelerator operation quantity by imposing a limitation on a variation rate of the accelerator operation quantity, when a predetermined variation of the sensed accelerator operation quantity occurs during the speed ratio control of the kickdown-acceleration-time control section, and to output the corrected accelerator operation quantity to the kickdown-acceleration-time control section in order to set the kickdown-acceleration-time target speed ratio.