CVT Step-Upshift Control via Deceleration Profile Synchronization
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Solution Overview
Problem
Existing continuously variable transmissions (CVTs) face challenges in smoothly executing step-upshifts, which can lead to abrupt changes in rotational speeds and engine torque, affecting drivability and fuel efficiency.
Innovation Solution
A method and control routine for determining a preferred CVT input deceleration profile based on desired variator speed ratio, present speed ratio, and shift time, synchronized with a command to reduce engine torque, to manage the change rate of the variator speed ratio and ensure a smooth step-upshift in the CVT.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a step-upshift is executed in the CVT, then the variator speed ratio increases to improve fuel consumption, but abrupt changes in rotational speed and engine torque occur which deteriorate drivability
Solution Approach 1:
The control system executes preliminary actions before the step-upshift by determining a desired variator speed ratio in advance and calculating a preferred CVT input deceleration profile that synchronizes with engine torque reduction commands. This preliminary planning ensures that speed ratio changes are coordinated with engine torque adjustments, preventing abrupt changes that would harm drivability while achieving the fuel consumption benefits of the upshift.
Solution Approach 2:
The system dynamically adjusts the variator speed ratio change rate based on real-time conditions. By controlling the change rate according to the preferred CVT input deceleration profile and synchronizing with engine torque commands, the system creates a dynamic transition that balances fuel efficiency improvement with smooth drivability, avoiding fixed or abrupt ratio changes.
2Loss of time
If the variator speed ratio changes rapidly, then the shift time is reduced to improve responsiveness, but vehicle deceleration glitches occur which worsen ride quality
Solution Approach 1:
The control system applies preliminary anti-action by synchronizing the CVT input deceleration profile with engine torque reduction commands before executing the speed ratio change. This coordinated approach counteracts potential deceleration glitches by ensuring that engine torque reduction occurs in sync with the variator speed ratio change, preventing the harmful effects of mismatched torque and speed transitions while maintaining efficient shift timing.
Solution Approach 2:
The system uses feedback by continuously monitoring the actual variator speed ratio and comparing it with the desired ratio, then adjusting the change rate according to the preferred deceleration profile. This closed-loop control ensures that the speed ratio transitions smoothly within the optimal time frame while preventing deceleration glitches through real-time synchronization with engine torque commands.
3Use of energy by moving object
If engine torque is reduced during step-upshift, then fuel efficiency is improved, but abrupt torque changes occur which worsen drivability
Solution Approach 1:
The control system determines the desired engine torque reduction command in advance and synchronizes it with the CVT input deceleration profile before executing the step-upshift. This preliminary coordination ensures that torque changes are smooth and timed appropriately, improving fuel efficiency while maintaining torque stability and avoiding abrupt transitions that would harm drivability.
Solution Approach 2:
The system manages engine torque by dynamically adjusting the torque reduction parameter in synchronization with the variator speed ratio change. By controlling the rate and timing of torque parameter changes according to the preferred deceleration profile, the system achieves fuel efficiency improvements while maintaining stable and smooth torque transitions that preserve drivability.
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 minimizes vehicle deceleration glitches and optimizes fuel consumption by controlling the CVT to achieve a desired speed ratio while managing engine torque, enhancing drivability and shifting performance.
Implementation Method 1
Frictional engagement between the sheaves of each pulley and the chain couples the chain to each of the pulleys to transfer torque from one pulley to the other
Implementation Method 2
The roller mechanism is placed within the cavity and is configured to vary the torque transmission ratio as the roller mechanism moves across the toroidal surface
Data Source
AI summary
A powertrain system including an internal combustion engine rotatably coupled to a variator of a continuously variable transmission (CVT) is described. A method for controlling the CVT includes determining a desired variator speed ratio in response to a change in an operator input and executing a step-upshift in the CVT based upon the desired variator speed ratio. The step-upshift includes determining a preferred CVT input deceleration profile based upon the desired variator speed ratio, a present variator speed ratio, and a preferred shift time and synchronizing the preferred CVT input deceleration profile with a command to reduce engine torque. A change rate for the variator speed ratio is based upon the preferred CVT input deceleration profile, and the CVT is controlled in response to the change rate for the variator speed ratio and the desired variator speed ratio.