4WD Shift Torque Override During Automated Driving
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Solution Overview
Problem
Vehicles lacking controller functionality to reduce engine torque during automated-driving modes are prohibited from shifting from two-wheel drive to four-wheel drive, as existing systems rely on driver input to manage throttle inputs.
Innovation Solution
A controller is programmed to override the current engine-torque command and reduce engine torque below a torque limit when shifting from two-wheel drive to four-wheel drive, and then command engagement of the clutch to facilitate the transition, allowing for seamless shifting during automated-driving modes like cruise control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the vehicle operates in automated-driving mode with existing torque control systems, then the automated-driving function is maintained, but shifting from two-wheel drive to four-wheel drive is prohibited
Solution Approach 1:
The controller dynamically adjusts engine torque based on clutch engagement requirements. During automated-driving mode, when a four-wheel drive request is received, the controller temporarily overrides the automated torque command to reduce torque below the clutch torque limit, enabling clutch engagement. After clutch engagement, the controller resumes the automated torque command. This dynamic torque adjustment allows the system to maintain automated-driving functionality while enabling drivetrain configuration changes.
2Productivity
If the controller maintains current engine-torque command during clutch engagement, then automated-driving performance is optimized, but clutch damage occurs due to excessive torque
Solution Approach 1:
The controller performs preliminary torque reduction before clutch engagement by overriding the automated torque command. When the controller detects a four-wheel drive request during automated-driving mode, it proactively reduces engine torque below the clutch torque limit before the clutch engages. This preliminary action prevents excessive torque from damaging the clutch during engagement, while minimizing disruption to automated-driving performance since torque is restored after engagement.
3Adaptability or versatility
If the controller overrides engine torque to enable clutch engagement, then four-wheel drive shifting is enabled, but automated-driving mode is disrupted
Solution Approach 1:
The controller implements periodic torque management by temporarily suspending the automated torque command only during the brief clutch engagement period. The override is applied in a periodic manner: detect four-wheel drive request, override torque command to enable engagement, detect clutch engagement, then resume automated torque command. This periodic intervention enables drivetrain configuration changes while minimizing disruption to automated-driving mode, as the override is applied only when necessary and for the shortest duration possible.
Data Source
AI summary
A vehicle includes a primary axle, a secondary axle, and a powertrain. The powertrain has an engine coupled to the primary axle and selectively coupled to the secondary axle. The vehicle also includes a clutch associated with the secondary axle. A controller is programmed to, responsive to (i) a request to shift from two-wheel drive to four-wheel drive and (ii) a current engine-torque command exceeding a torque limit associated with the clutch, override the current engine-torque command to reduce a torque of the engine below the torque limit, and, responsive to the torque of the engine being less the torque limit, command engagement of the clutch.