Vehicle Drive State Control for Smooth 2WD to 4WD Transition
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Solution Overview
Problem
Existing vehicle drive state control systems struggle to smoothly transition from two-wheel drive to four-wheel drive without a rotation synchronizing apparatus, due to rotational speed discrepancies between axles, leading to potential slippage and inefficient power transmission.
Innovation Solution
A drive state control apparatus that includes first and second differentials, a multi-disc clutch mechanism, and a dog-type clutch mechanism, with rotational speed acquisition means and control means to synchronize axle speeds and adjust torque distribution, allowing seamless transition without a synchronizer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a dog-type changeover mechanism is used without a rotation synchronizing apparatus, then device complexity is reduced, but the connecting operation cannot be performed smoothly due to rotational speed differences between axles
Solution Approach 1:
The control device performs preliminary actions by switching the first changeover mechanism to establish power transmission to both output shafts before attempting to connect the second changeover mechanism. This preliminary power transmission equalizes the rotational speeds of the front and rear propeller shafts, creating the necessary conditions for smooth engagement of the dog-type clutch without requiring a rotation synchronizing apparatus.
Solution Approach 2:
The first changeover mechanism and the power transmission system act as intermediaries to equalize the rotational speeds of the two propeller shafts before the second changeover mechanism connects. By temporarily establishing power transmission through the first changeover mechanism, the system mediates the speed difference between axles, enabling smooth connection of the second changeover mechanism without direct synchronization.
2Adaptability or versatility
If the first changeover mechanism is switched from first state to second state, then four-wheel drive is established, but rotational speed difference between front and rear propeller shafts causes slippage and power transmission inefficiency
Solution Approach 1:
The system dynamically adjusts the engagement timing of the two changeover mechanisms based on real-time rotational speed conditions. The control device monitors the rotational speeds of both propeller shafts and only permits connection of the second changeover mechanism when the speed difference falls within a predetermined range, thereby dynamically optimizing power transmission efficiency during the transition from two-wheel to four-wheel drive.
Solution Approach 2:
The control device incorporates feedback by continuously monitoring the rotational speeds of the front and rear propeller shafts and using this information to determine the optimal timing for switching the second changeover mechanism. This feedback mechanism ensures that connection occurs only when rotational speed conditions are favorable, preventing slippage and maintaining high power transmission efficiency.
Data Source
AI summary
A drive state control apparatus is applied to a vehicle which has not only a transfer including a multi-disc clutch mechanism but also a changeover mechanism interposed in an axle and which can be switched between 2WD and 4WD. When a 2WD-to-4WD changeover condition is satisfied, the multi-disc clutch is immediately switched from a “decoupled state” to a “coupled state.” Meanwhile, a connecting operation of the changeover mechanism is started upon establishment of a state in which left and right rear wheels have no acceleration slippage, and a state in which rotational speeds of first and second axles on opposite sides of the changeover mechanism are approximately equal to each other. In addition, in the case where the left and right rear wheels have acceleration slippage after the 2WD-to-4WD changeover condition has been satisfied, an E/G output reduction control is executed. Thus, the connecting operation can be performed smoothly.