Electric Vehicle Braking Split Ratio Control
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Solution Overview
Problem
In electric vehicles, the change in vehicle attitude due to differing braking force split ratios between the motor and hydraulic brake systems leads to deterioration in drivability, as the braking force distribution between the front and rear wheels changes significantly when the motor braking is replaced by hydraulic braking.
Innovation Solution
An electric vehicle configuration with a driving force split device and a braking force applying device, controlled by a controller that sets a target braking split ratio initially within an allowable range of the transmission split ratio during motor braking, maintaining consistent braking force distribution between the front and rear wheels, thereby stabilizing vehicle attitude.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the motor braking force is replaced with hydraulic brake device braking force, then the braking force can be sufficient for target braking force, but the vehicle attitude changes due to significant difference in braking force split ratio
Solution Approach 1:
The controller dynamically adjusts the target braking split ratio based on the transmission split ratio. When the transmission split ratio changes, the target braking split ratio is updated accordingly to maintain consistent braking force distribution between front and rear wheels, preventing vehicle attitude changes during braking transitions.
Solution Approach 2:
The controller continuously monitors the transmission split ratio and uses this information to adjust the target braking split ratio in real-time. This feedback mechanism ensures that the braking force distribution adapts to changing driving conditions and maintains vehicle stability during the transition from motor braking to hydraulic braking.
2Adaptability or versatility
If the transmission split ratio is adjusted to change front-to-rear driving force distribution, then the driving force can be optimized for different conditions, but the braking force split ratio becomes inconsistent with the transmission split ratio
Solution Approach 1:
The target braking split ratio is set to change in response to changes in the transmission split ratio. This parameter coupling ensures that when the driving force distribution is optimized for different conditions, the braking force split ratio adapts accordingly to maintain consistency and prevent vehicle attitude changes.
Solution Approach 2:
The controller integrates both driving and braking control functions, using the transmission split ratio as a reference for both driving force distribution and braking force distribution. This multi-functional approach ensures coordinated behavior between driving and braking systems across various operating conditions.
Data Source
AI summary
When braking of the electric vehicle is performed, the braking is controlled based on a target braking split ratio which is a target value of the ratio of the braking force that is applied to the rear wheels to a total braking force that is applied to the front and rear wheels. In this case, an initial value of the target braking split ratio is set to a value within an allowable range about a transmission split ratio when braking of the electric vehicle is started while the electric vehicle is being braked by the motor, the transmission split ratio being the ratio of a braking force that is transmitted from a drive shaft to the rear wheels via a driving force split device to a total braking force that is transmitted from the drive shaft to the front and rear wheels via the driving force split device.