Freewheel Mode Transition in Motor Vehicle Clutch Systems
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Solution Overview
Problem
Existing methods for automatically switching a motor vehicle from 'normal' to 'freewheel' mode cause sudden deceleration and jerking sensations for passengers due to sudden clutch engagement and disengagement, which can be disruptive, especially when the transition is involuntary.
Innovation Solution
A transition step is introduced where the driven and drive shafts rotate at the same speed without transmitting torque, with the clutch remaining engaged, disengaged, or in a slip position, triggered by specific conditions such as reduced acceleration and engine torque, allowing for a smoother transition to 'freewheel' mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the clutch device is suddenly disengaged to switch to freewheel mode, then fuel consumption is reduced, but passengers experience sudden deceleration and discomfort
Solution Approach 1:
The system performs preliminary actions by monitoring driving conditions (accelerator position, vehicle speed, gear position) before switching to freewheel mode, and by pre-synchronizing engine speed with wheel rotation speed during the transition phase, thereby preparing the system to avoid sudden deceleration and discomfort for passengers
Solution Approach 2:
The clutch device transitions through dynamic states including an intermediate slip position rather than abrupt engagement/disengagement. The system dynamically adjusts clutch engagement based on the difference between engine speed and wheel rotation speed, allowing smooth transition that reduces harmful deceleration sensations while maintaining fuel efficiency
2Ease of operation
If the clutch device is suddenly re-engaged to return to normal mode, then vehicle control is restored, but passengers experience jerking motion
Solution Approach 1:
Before re-engaging the clutch device to return to normal mode, the system performs preliminary synchronization of engine speed with wheel rotation speed. This preliminary action ensures that when the clutch engages, there is minimal speed difference, thereby avoiding jerking sensations while restoring vehicle control
Solution Approach 2:
The system uses dynamic control of the clutch device, allowing it to pass through an intermediate slip position during re-engagement. This dynamic approach gradually transfers torque from the engine to the driven shaft, smoothing out the transition and eliminating jerking motions that would occur with abrupt engagement
3Loss of energy
If engine speed is reduced to idle speed during freewheel mode, then fuel savings are maximized, but the transition causes abrupt speed change
Solution Approach 1:
The system dynamically controls engine speed during the transition to freewheel mode, allowing gradual reduction to idle speed rather than abrupt change. The engine speed is adjusted in coordination with wheel rotation speed and clutch engagement state, maintaining smooth transition while maximizing fuel savings during coasting
Data Source
Figure 1~4
AI summary
The invention concerns a method for automatically controlling a motor vehicle (10) for switching from a "normal" mode to a "freewheel" mode, the vehicle (10) comprising an engine (12) capable of providing engine torque to drive wheels (14) via an automatically controlled clutch device (18) that comprises a drive shaft (15) and a driven shaft (16). A transition step (E1) is interposed chronologically between the "normal" mode and the "freewheel mode" during which the engine (12) is automatically controlled in such a way that the driven shaft (16) and the drive shaft (15) turn at the same speed without transmitting torque to the drive wheels (14).