Four-Wheel-Drive Vehicle Torque Coupling Synchronization Control
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Solution Overview
Problem
Conventional four-wheel-drive vehicles experience vibrations at the propeller shaft during mode switching from two-wheel-drive to four-wheel-drive, leading to discomfort and prolonged synchronization times due to excessive torque transmission.
Innovation Solution
A four-wheel-drive vehicle system featuring a dog clutch and torque coupling, controlled by an ECU, which adjusts torque transmission to synchronize propeller shaft rotation efficiently by setting initial high torque followed by lower torque values, and engages the dog clutch when rotational speed differences are minimized.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high torque is applied to rotate the propeller shaft during mode switching, then the synchronization speed is improved, but vibrations occur at the distal end portion of the propeller shaft causing discomfort and prolonged synchronization time
Solution Approach 1:
The patent applies dynamics by making the torque transmission capability variable through the torque coupling mechanism. The torque coupling allows the torque transmission amount to be dynamically adjusted during the switching process, enabling high initial torque for rapid acceleration followed by reduced torque to eliminate vibrations, thus resolving the contradiction between synchronization speed and vibration suppression.
Solution Approach 2:
The patent changes the torque parameter dynamically during the switching process. The control unit adjusts the torque transmission amount from a first torque value (higher) to a second torque value (lower) as the propeller shaft rotational speed increases, thereby achieving rapid synchronization initially and then suppressing vibrations by reducing torque, resolving the contradiction between speed and harmful vibrations.
2Productivity
If high torque is continuously applied to the propeller shaft, then the mode switching speed is improved, but the synchronization time is prolonged due to vibrations
Solution Approach 1:
The patent applies periodic action by changing the torque transmission amount in stages during the switching process. The control unit first applies a higher torque value to accelerate synchronization, then switches to a lower torque value to eliminate vibrations and complete the synchronization, thereby reducing the total synchronization time while maintaining high switching speed.
Solution Approach 2:
The torque coupling mechanism enables dynamic adjustment of torque transmission during the switching process. By making the torque transmission amount variable rather than constant, the system can optimize the switching process in two phases: rapid acceleration phase with high torque, and vibration elimination phase with reduced torque, thereby resolving the contradiction between switching speed and synchronization time.
3Speed
If the propeller shaft is rotated with high torque, then the four-wheel-drive mode engagement is accelerated, but driver and passenger comfort deteriorates due to transmitted vibrations
Solution Approach 1:
The control unit changes the torque parameter from a first torque value to a second torque value as the propeller shaft rotational speed increases. This parameter change allows the system to achieve rapid rotation speed initially while then reducing the torque to eliminate vibrations that would be transmitted to the driver and passenger, resolving the contradiction between rotation speed and comfort.
Solution Approach 2:
The patent converts the potentially harmful high torque that causes vibrations into a beneficial two-stage process. The high torque is applied only temporarily during the acceleration phase to achieve rapid synchronization, then reduced to eliminate vibrations. The harmful vibration-generating torque is thus converted into a controlled, time-limited acceleration mechanism that ultimately benefits performance without compromising comfort.
Data Source
AI summary
A four-wheel-drive vehicle includes a dog clutch provided between a propeller shaft and an engine, a torque coupling provided between a rear differential and rear wheels, and an ECU that controls the dog clutch and the torque coupling. When a drive mode is switched from a two-wheel-drive mode where the transmissions of torque by the dog clutch and the torque coupling are both interrupted, to a four-wheel-drive mode, the ECU sets the amount of torque that is transmitted by the torque coupling to a first torque value (T1) to increase the speed of rotation of the propeller shaft, and then sets the amount of torque that is transmitted by the torque coupling to a second torque value (T2) that is lower than the first torque value (T1), and engages the dog clutch when the rotations of first and second rotary members of the dog clutch are synchronized with each other.