CVT Downshift Control for Smooth Coasting Return
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Solution Overview
Problem
When a vehicle transitions from coasting mode to normal traveling mode, the engine speed can become excessively low, leading to noise, vibration, and potential engine stall, causing discomfort for the driver due to the clutch engaging at an inappropriate speed ratio of the continuously variable transmission.
Innovation Solution
A vehicle control system that includes an electronic control unit to manage the clutch and engine operation by performing a downshift of the continuously variable transmission before re-engaging the clutch, ensuring the engine speed is within a suitable range by setting a target speed ratio based on vehicle speed and input shaft speed, and controlling the hydraulic pressure to reduce noise and vibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the clutch is engaged at the speed ratio established at the time when coasting was started, then the vehicle returns from coasting to normal traveling, but the engine speed becomes lower than the rotational speed range of normal traveling, causing noise and vibration
Solution Approach 1:
The control device performs downshift of the continuously variable transmission before engaging the clutch, preparing the transmission speed ratio in advance to ensure the engine speed will be within the appropriate range when the clutch is engaged, thereby preventing noise and vibration
Solution Approach 2:
The control device changes the speed ratio parameter of the continuously variable transmission by performing downshift, adjusting it from the coasting speed ratio to a lower speed ratio that will result in appropriate engine speed when the clutch is engaged
2Loss of time
If the clutch is engaged during coasting without downshifting, then the vehicle returns from coasting quickly, but the engine speed becomes excessively low causing engine stall
Solution Approach 1:
The control device performs downshift of the continuously variable transmission before engaging the clutch, preparing the transmission speed ratio in advance to ensure the engine speed will be within the appropriate range when the clutch is engaged, thereby preventing engine stall
Solution Approach 2:
The control device dynamically adjusts the speed ratio of the continuously variable transmission based on the vehicle's operating conditions, performing downshift when returning from coasting to maintain appropriate engine speed
Data Source
AI summary
A control system of a vehicle includes an engine, a continuously variable transmission, drive wheels, a clutch, and an electronic control unit. The electronic control unit is configured to release the clutch and stop the engine when a predetermined execution condition is satisfied during traveling, such that the vehicle performs coasting. The electronic control unit is configured to keep the continuously variable transmission at a speed ratio established at start of the coasting, during the coasting of the vehicle. The electronic control unit is configured to restart the engine that has been stopped and perform downshift of the continuously variable transmission, when a predetermined return condition is satisfied during the coasting. The electronic control unit is configured to engage the clutch after the downshift is started, such that the vehicle returns from the coasting.