Hybrid Gear-Shift Control for Low-µ Regenerative Braking Stability
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Solution Overview
Problem
Conventional hybrid vehicles face challenges in achieving both securement of regeneration amount and improvement in robustness, particularly in rear wheel-drive vehicles where oversteering occurs during deceleration due to regenerative braking torque.
Innovation Solution
The solution involves analyzing the relationship between gear-shifting control, motor regeneration, and oversteering during vehicle deceleration. By adjusting the shift-down point based on road surface conditions, the system delays gear-shifting when the road surface is low to avoid oversteering, while allowing earlier gear-shifting on high-road surfaces to maximize regeneration and fuel efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the motor performs a regeneration operation during deceleration, then fuel efficiency performance is improved, but the rear wheels are apt to fall into a slip state causing oversteering
Solution Approach 1:
The control apparatus dynamically adjusts the shift-down point parameter based on deceleration magnitude. When deceleration exceeds a threshold, the shift-down point is lowered to delay gear-shifting, which modulates the regenerative braking torque to prevent rear wheel slip while maintaining fuel efficiency benefits
Solution Approach 2:
The system continuously monitors deceleration magnitude and uses this feedback to adjust the shift-down point in real-time. This closed-loop control ensures that gear-shifting is delayed appropriately when high deceleration would cause oversteering, while allowing normal shifting when deceleration is mild
2Reliability
If gear-shifting control is delayed on low road surface conditions, then oversteering is suppressed, but regeneration amount is reduced
Solution Approach 1:
The control apparatus adjusts the shift-down point parameter based on road surface conditions. On low μ roads during high deceleration, the shift-down point is lowered to delay gear-shifting and prevent oversteering. On high μ roads, the shift-down point is raised to enable earlier gear-shifting and maximize regeneration
Data Source
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Figure 3A
AI summary
A vehicle gear-shifting control apparatus is equipped with an engine, a motor, an automatic transmission, a friction brake system, and a controller which executes, at least during deceleration of an automobile, regeneration control of imparting a regenerative braking torque to rear wheels by causing the motor to perform a regeneration operation and gear-shifting control of changing a shift stage of the automatic transmission in accordance with the rotation speed of an input shaft. The controller starts the gear-shifting control, triggered by the rotation speed of the input shaft dropping to a predetermined shift-down point, and during deceleration of the vehicle when it is determined that a road surface µ is lower than a predetermined threshold in the regeneration control, the controller sets the shift-down point lower than during deceleration of the vehicle when it is determined that the road surface µ is equal to or higher than the threshold.