CVT Engine Braking Control via Dynamic Speed Profiles
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Solution Overview
Problem
Continuously variable transmissions (CVTs) experience increased driveline noise and vibration during engine braking, which is undesirable, especially on negative grades, as they limit engine speed to maintain torque transfer, leading to an unpleasant driving experience.
Innovation Solution
Implementing a vehicle operating method that adjusts engine speed via a controller using multiple engine speed to vehicle speed profiles, allowing for controlled engine braking while minimizing noise and vibration, by constraining engine speed and adjusting engine pumping work based on road grade and vehicle conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the CVT controls engine speed to remain less than a maximum engine speed during engine braking, then driveline noise and vibration are reduced, but engine braking effectiveness is compromised
Solution Approach 1:
The patent applies dynamics by making the engine speed threshold dynamic rather than fixed. The maximum engine speed threshold is adjusted based on vehicle operating conditions including vehicle speed, acceleration demand, and driveline state. This allows the system to adaptively balance noise reduction with engine braking effectiveness across different driving scenarios.
Solution Approach 2:
The patent changes the parameter of engine speed threshold from a static value to a variable parameter that changes based on operating conditions. By modifying the threshold according to vehicle speed, acceleration requests, and driveline state, the system optimizes the balance between noise reduction and braking effectiveness.
2Power
If the CVT allows engine speed to increase above the maximum threshold to provide additional engine braking, then braking effectiveness is improved, but driveline noise and vibration increase
Solution Approach 1:
The system dynamically adjusts the engine speed threshold based on real-time conditions. When vehicle speed is high and acceleration demand is low, the threshold can be raised to allow more engine braking while keeping noise acceptable. When vehicle speed is low or acceleration is needed, the threshold is lowered to prioritize comfort.
Solution Approach 2:
The patent implements feedback control by continuously monitoring vehicle speed, acceleration demand, and driveline state to adjust the engine speed threshold. This closed-loop approach ensures the system responds appropriately to changing conditions, optimizing the balance between braking effectiveness and noise control.
3Ease of operation
If multiple engine speed to vehicle speed profiles are used to control engine braking, then drivability is improved by scaling noise with road grade, but system complexity increases
Solution Approach 1:
The patent segments the control strategy into multiple discrete profiles, each optimized for specific driving conditions such as different road grades. This segmentation allows the system to select appropriate control characteristics for each situation, improving drivability while keeping each individual profile relatively simple.
Solution Approach 2:
The system dynamically selects between different control profiles based on detected operating conditions. Rather than using a single complex control law, the system switches between pre-defined profiles that are simpler in nature, reducing the complexity of real-time calculations while maintaining adaptability.
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 provides desirable levels of driveline noise and vibration during engine braking, scaling noise with road grade severity and improving drivability by limiting profile switching, thus enhancing the driving experience.
Implementation Method 1
A vehicle may include a CVT to improve vehicle fuel economy and reduce vehicle weight. In some examples, the CVT may couple an engine to wheels via a belt or chain, and the belt or chain is positioned between a variable driving pulley and a variable driven pulley. A radius of the variable driving pulley may be increased or decreased to change the CVT input to output ratio.
Implementation Method 2
On the other hand, if the driver is not requesting torque or very little torque and the vehicle is traveling on a road having a negative grade, the belt or chain may transfer a portion of the vehicle's kinetic energy to the engine. Engine friction and pumping work may oppose torque transferred from the vehicle's wheels to the engine so that vehicle acceleration may be reduced.
Implementation Method 3
Engine friction and pumping work (e.g., compression and expansion of gases within the engine) may oppose torque transferred from the vehicle's wheels to the engine so that vehicle acceleration may be reduced.
Implementation Method 4
The CVT may take form a planetary gear set and a generator. Torque of the generator may be adjusted so that engine speed may be controlled independently of wheel speed.
Data Source
AI summary
Systems and methods for operating a vehicle that includes a continuously variable transmission are described. The systems and methods adjust engine speed according to one of a plurality of engine speed to vehicle speed profiles so that driveline noise, vibration, and harshness may be reduced. The different engine speed to vehicle speed profiles provide different levels of engine braking.