CVT Transmission Ratio Control for Agricultural Vehicle Engine Stalling
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Solution Overview
Problem
In CVT-equipped agricultural vehicles, sudden increases in wheel load, such as when driving uphill, can lead to engine stalling due to excessive torque demands, as drivers tend to further depress the foot lever, increasing transmission ratio and engine load, which worsens engine speed drops.
Innovation Solution
Limiting the transmission ratio of CVT based on prevailing engine speed and its rate of change to prevent excessive torque demands, with the limit value increasing at lower engine speeds and remaining constant at higher speeds, thereby preventing engine stalling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the foot lever is depressed further to increase wheel speed during sudden wheel load increase, then the demanded transmission ratio increases, but the engine load increases excessively causing engine speed to drop further and potential stalling
Solution Approach 1:
The control unit dynamically adjusts the maximum permissible transmission ratio based on engine speed parameters. When engine speed drops below a threshold or its rate of change exceeds a limit, the system reduces the maximum transmission ratio to prevent excessive torque demands that would cause stalling, while still allowing wheel speed variation within safe operating parameters.
Solution Approach 2:
The control unit continuously monitors engine speed and its rate of change, using this feedback to adjust the maximum transmission ratio in real-time. This closed-loop control prevents the operator from inadvertently causing stalling by depressing the foot lever further during high-load conditions, as the system automatically limits the transmission ratio response.
2Speed
If the transmission ratio is increased to meet higher wheel speed demands, then wheel speed increases, but engine torque demand increases causing engine speed to decrease
Solution Approach 1:
The system implements dynamic parameter adjustment by modifying the maximum transmission ratio based on current engine operating conditions. When engine speed or torque capacity decreases, the control unit reduces the permissible transmission ratio, thereby limiting the wheel speed increase that can be demanded while preventing engine overload and maintaining stable power output.
Data Source
AI summary
A method is described for operating a vehicle fitted with a continuously variable transmission (CVT) and having a lever for varying the transmission ratio of the CVT to permit the vehicle operator to vary the vehicle wheel speed. In the invention, the transmission ratio of the CVT is limited to a value dependent upon at least one of the prevailing engine speed and the rate of change of the engine speed.