CVT Speed Ratio Control for NVH Reduction
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Solution Overview
Problem
Continuously variable transmissions (CVTs) experience excessive engine speed rise and noise, vibration, and harshness (NVH) issues due to rapid changes in speed ratios when a driver requests more power, leading to undesirable 'Rubber-band Feel' phenomena.
Innovation Solution
A method to control the rate of change of speed ratios in CVTs by sensing vehicle and engine speeds, determining a desired engine speed based on accelerator pedal position, and implementing a three-step process: a quick rise, hold, and smooth rise to manage engine speed set-points, reducing the rate of change to minimize NVH.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the CVT changes speed ratios at a very fast rate when the driver requests more power, then the power delivery response is improved, but the engine speed rises excessively and NVH levels increase
Solution Approach 1:
The patent segments the speed ratio change process into multiple discrete stages: a first rate of change for initial response, a second (slower) rate of change for intermediate adjustment, and a third rate for final stabilization. This segmentation allows the system to achieve fast initial response while preventing excessive engine speed rise and NVH by controlling the rate of change at each stage.
Solution Approach 2:
The patent dynamically adjusts the rate of change of speed ratios based on real-time operating conditions. The control system monitors engine speed, vehicle speed, and accelerator pedal position, then adaptively selects among multiple rates of change (first rate, second rate, third rate) to optimize both response speed and NVH performance under varying driving conditions.
2Speed
If the CVT changes speed ratios rapidly, then the acceleration response is improved, but the 'Rubber-band Feel' phenomenon occurs due to sudden vehicle acceleration
Solution Approach 1:
The patent divides the acceleration process into segmented phases with different rates of speed ratio change. The first rate provides quick initial response, while subsequent rates (second and third rates) provide progressive, controlled acceleration. This segmentation eliminates the sudden 'Rubber-band Feel' by distributing the acceleration demand across multiple controlled stages rather than delivering it all at once.
Solution Approach 2:
The patent implements periodic adjustment of the speed ratio change rate, alternating between faster and slower rates of change based on the vehicle's acceleration state. This periodic modulation of the rate of change creates a more natural, progressive acceleration feel while maintaining responsive power delivery.
Data Source
AI summary
A method for controlling a rate of change of speed ratios in a continuously variable transmission (CVT) includes sensing a vehicle speed, sensing an engine speed, and sensing a change in a position of an accelerator pedal. The method includes determining a desired engine speed based on the change in the position of the accelerator pedal, the vehicle speed, and the engine speed. The method includes increasing a target engine speed at a first rate to a predetermined value, wherein the target engine speed corresponds to a speed ratio. The method includes measuring a difference between the target engine speed that is held at the predetermined value and an actual engine speed, and increasing the target engine speed to the desired engine speed at a second rate when the difference substantially equals a predetermined threshold, wherein the second rate is less than the first rate.