4WD Low-Range Shift Synchronization While Vehicle Is Moving
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current 4WD systems do not allow vehicles to shift into or out of 4WD low range while moving at speeds greater than very slow speeds, resulting in rough shifts and limited maximum vehicle speed for gear changes, which is perceivable to the driver and restricts operational flexibility.
Innovation Solution
A control strategy that synchronizes the speed of the transmission output shaft with the power transfer unit and rear differential unit by using sensors to determine and match the desired speeds, allowing smooth shifts into 4WD low range while the vehicle is in motion by selectively engaging and disengaging the clutch to manage torque flow and control the transmission output shaft speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the vehicle shifts into or out of 4WD low range while moving at speeds greater than very slow speeds, then the operational flexibility and driving experience are improved, but the gear shift becomes rough and the maximum vehicle speed for gear changes is limited
Solution Approach 1:
The control system performs preliminary speed synchronization before the actual gear shift occurs. The transmission output shaft speed is adjusted to match the target speed required for the 4WD low range shift, ensuring that when the shift happens, the speeds are already synchronized, resulting in a smooth transition even at higher vehicle speeds
Solution Approach 2:
The system dynamically adjusts the transmission output shaft speed during the shifting process. By actively controlling the transmission output shaft to accelerate or decelerate to match the target speed, the system adapts the speed profile in real-time to ensure smooth engagement of the 4WD low range gears regardless of the vehicle's initial speed
2Ease of operation
If the transmission output shaft speed is synchronized to match the speed of the power transfer unit and rear differential unit, then smooth gear shifts are achieved, but the control complexity and time required for speed matching increase
Solution Approach 1:
The control system continuously monitors the actual transmission output shaft speed and compares it to the target speed required for synchronization. Based on this feedback, the controller adjusts the transmission output shaft speed to eliminate any speed difference, ensuring smooth gear engagement. This closed-loop control automates the synchronization process, managing the complexity through systematic feedback mechanisms
3Speed
If the clutch is selectively engaged to manage torque flow during the shift, then synchronized shifting at higher speeds is enabled, but the shift time and complexity of torque management increase
Solution Approach 1:
The clutch is engaged in advance of the actual gear shift to begin torque management before the shift occurs. This preliminary engagement allows the system to gradually transfer and manage torque flow, preparing the drivetrain for the upcoming speed synchronization and gear engagement, enabling smoother shifts at higher speeds without extending the total shift time significantly
Data Source
AI summary
A method of controlling a four wheel drive (4WD) low range shift in a vehicle is provided. The vehicle has a powertrain including a transmission that drives a transmission output shaft to provide drive torque to a driveline including a power transfer unit (PTU) that delivers torque to front drive wheels and a rear differential unit (RDU) that delivers torque to rear drive wheels. The PTU and RDU are selectively rotatably coupled to each other through a propeller (prop) shaft. The PTU and the RDU are commanded into a neutral position. A clutch at the RDU is commanded to selectively engage to a degree that communicates a desired amount of torque from the prop shaft to the RDU. A determination is made that an output speed of the transmission output shaft is synchronized to match a speed of the RDU and the RDU is commanded to shift into 4WD low.