CVT Tractor Drivability Control via Adaptive Pedal Mapping
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Solution Overview
Problem
Agricultural and industrial vehicles with continuously variable transmissions (CVTs) face challenges in providing improved drivability and responsiveness to operator inputs, particularly in varying speed and acceleration conditions between off-road and on-road use, due to differences in speed range and pedal resolution.
Innovation Solution
A high drivability control system that calculates and adjusts target engine speed and transmission ratio changes based on operator inputs, using a combination of Electronic Control Modules to manage engine speed and transmission ratio, ensuring predictable and responsive speed control and acceleration, even with geared transmissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the vehicle operates in low speed range with high tractive output (off-road conditions), then the pedal resolution provides fine control, but a significant pedal variation is required to achieve small speed changes
Solution Approach 1:
The system dynamically adjusts the relationship between pedal position and transmission ratio based on operating conditions. In low-speed off-road mode, the CVT controller modifies the mapping between pedal input and transmission ratio changes to provide appropriate speed variation, transforming a static control system into an adaptive one that responds to different operational contexts
Solution Approach 2:
The system changes the control parameters by varying the transmission ratio response to pedal input based on the selected drive mode. In off-road mode, the controller adjusts the sensitivity and range of transmission ratio changes relative to pedal position, effectively changing the control parameter mapping to match the operational requirements
2Speed
If the vehicle operates in high speed range (on-road conditions), then the pedal resolution provides coarse control, but a small pedal variation causes significant speed changes
Solution Approach 1:
The system dynamically adjusts the relationship between pedal position and transmission ratio based on operating conditions. In high-speed on-road mode, the CVT controller modifies the mapping between pedal input and transmission ratio changes to provide appropriate speed variation, transforming a static control system into an adaptive one that responds to different operational contexts
Solution Approach 2:
The system changes the control parameters by varying the transmission ratio response to pedal input based on the selected drive mode. In on-road mode, the controller adjusts the sensitivity and range of transmission ratio changes relative to pedal position, effectively changing the control parameter mapping to match the operational requirements
3Extent of automation
If the CVT controller modifies both ERPM and CVT output ratio to achieve desired vehicle speed, then the vehicle speed control is automated, but the system complexity increases
Solution Approach 1:
The patent combines the ERPM control and CVT ratio control into a unified automated system. The CVT controller integrates both control functions, sending coordinated ERPM requests to the ECM and simultaneously adjusting the CVT output ratio, merging what could be separate control systems into one cohesive automated velocity control mechanism
Solution Approach 2:
The CVT controller is designed to perform multiple functions: it controls the CVT output ratio, manages ERPM through communication with the ECM, and coordinates both to achieve desired vehicle velocity. This multi-functional controller reduces the need for separate dedicated control systems for each parameter
4Measurement precision
If the transmission ratio is adjusted to achieve desired vehicle speed, then the speed control is precise, but the acceleration responsiveness decreases
Solution Approach 1:
The system performs preliminary action by proactively adjusting the ERPM in response to operator input before the transmission ratio changes take full effect. The CVT controller sends ERPM request signals to the ECM that anticipate the needed power delivery, preparing the engine to deliver the required torque before the transmission ratio adjustment is complete, thereby improving acceleration responsiveness while maintaining precision
Data Source
AI summary
A method for providing a high drivability control system for an agricultural or industrial vehicle having an engine and a continuously variable transmission (CVT) includes setting a maximum speed target (MST), and setting a vehicle speed percentage (VSP) according to input using a desired speed input. A target engine speed, a target rate of change of the engine speed, a target CVT ratio, and a target rate of change of the target CVT ratio is then calculated from the VSP, the MST, and the present engine speed. The target engine speed may be further calculated from the present vehicle speed and/or the present CVT ratio.