CVT Acceleration Control Using Initial and Loading Ratios
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Solution Overview
Problem
Current continuous variable transmission (CVT) powertrains experience delays and inefficiencies in responding to acceleration demands, as they often operate at peak power, which is not the most energy-efficient region and results in harsh and unpredictable responses.
Innovation Solution
A method that applies an initial transmission ratio to provide immediate acceleration while increasing engine load, using a loading transmission ratio determined by vehicle acceleration to maintain acceleration by progressively increasing engine load or power output, with the ability to adjust ratios based on engine load and acceleration demand using look-up tables.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the engine speed is forced to peak power prior to changing the transmission ratio, then the acceleration demand is met, but there is an inherent delay between acceleration request and vehicle acceleration
Solution Approach 1:
The control system applies the initial transmission ratio immediately upon receiving the acceleration demand, before the engine speed has time to respond. This preliminary action of changing the transmission ratio first creates an instant acceleration response, eliminating the delay that would occur if engine speed were forced to peak power first.
2Speed
If peak power is used to meet acceleration demand, then the acceleration is achieved, but the engine operates inefficiently at peak power regardless of the actual power requirement
Solution Approach 1:
The control system dynamically adjusts the transmission ratio in two stages: first applying the initial transmission ratio for instant response, then transitioning to the loading transmission ratio that progressively increases engine load. This dynamic adjustment allows the engine to operate at efficient load levels while still achieving the required acceleration, rather than statically operating at peak power.
Solution Approach 2:
The system changes the transmission ratio parameter from the initial value to the loading value based on vehicle acceleration feedback. This parameter change enables the engine operating point to shift from a state that provides instant acceleration to a state that maintains acceleration efficiently, optimizing the balance between acceleration capability and energy efficiency.
3Loss of time
If the transmission ratio is changed immediately upon acceleration demand, then instant acceleration response is provided, but the engine load must be increased to maintain acceleration
Solution Approach 1:
The control system continuously monitors vehicle acceleration and progressively adjusts the transmission ratio from the initial value to the loading value. This continuous adjustment ensures that the engine load is increased smoothly and continuously to maintain acceleration, rather than applying a sudden large load change that would cause harsh operation.
4Speed
If the loading transmission ratio is applied to increase engine load, then acceleration is maintained, but the control system complexity increases
Solution Approach 1:
The control system uses vehicle acceleration as feedback to determine when to transition from the initial transmission ratio to the loading transmission ratio. This feedback mechanism automatically manages the complex control logic, where the acceleration sensor or calculator provides continuous information that triggers the appropriate control action, simplifying the overall system architecture.
Data Source
AI summary
A method for controlling the acceleration of a vehicle includes: receiving a demand for acceleration from an operator input device; applying an initial transmission ratio to provide a vehicle acceleration whilst maintaining a current engine speed; and applying a loading transmission ratio to increase the output from the engine, wherein the loading transmission ratio is determined using the vehicle acceleration.