Electric Machine Braking Torque Control for EVs
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Solution Overview
Problem
Electric and hybrid vehicles face challenges in maintaining consistent braking behavior due to limitations in electric machine braking torque, especially when the battery is fully charged, leading to unexpected changes in braking force and increased costs with additional components like ohmic resistance for energy conversion.
Innovation Solution
A method that operates the electric machine in two modes: as a generator for regenerative braking and with reversed energy supply to generate opposing torque, allowing flexible adaptation of braking behavior based on vehicle state, and adjusts braking force in conjunction with friction brakes to maintain uniform pedal travel feedback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the electric machine is operated as a generator for regenerative braking, then energy recovery is optimized, but braking behavior becomes inconsistent when the battery is fully charged
Solution Approach 1:
The patent changes the operating parameter of the electric machine from generator mode to motor mode when the battery is fully charged. This parameter change allows the system to maintain braking functionality by switching from energy recovery (generator mode) to energy consumption (motor mode), thereby ensuring consistent braking behavior regardless of battery charge state.
2Reliability
If the braking torque of the electric machine is limited to maintain consistent braking behavior, then braking consistency is improved, but the full potential of recuperation cannot be utilized
Solution Approach 1:
The patent implements dynamic switching between generator mode and motor mode based on battery charge state. When the battery is not full, the electric machine operates in generator mode for maximum energy recovery. When the battery is full, it dynamically switches to motor mode to maintain braking consistency, thus optimizing both energy recovery and braking reliability under different operating conditions.
3Reliability
If additional ohmic resistance is installed to convert electrical energy into heat when the battery is full, then braking consistency is maintained, but installation space and costs increase
Solution Approach 1:
The patent makes the electric machine multi-functional by enabling it to operate in both generator mode (for energy recovery) and motor mode (for braking when battery is full). This eliminates the need for separate components like ohmic resistors, as the electric machine itself handles both energy recovery and braking functions across different operating conditions, reducing device complexity and installation space.
4Reliability
If blending-capable brake systems are used to control the friction brake independently, then uniform braking behavior is achieved, but system cost increases
Solution Approach 1:
The patent combines the braking functions of the electric machine with the friction brake system. By coordinating the electric machine's braking torque (in both generator and motor modes) with the friction brake, the system achieves uniform braking behavior without requiring complex independent control systems. The control unit integrates both braking sources, simplifying the overall system architecture while maintaining braking consistency.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach ensures consistent and familiar braking behavior for the driver, optimizes energy recovery, and eliminates the need for additional heat conversion components, reducing costs and installation space while maintaining safety and efficiency.
Implementation Method 1
the electric machine for braking the motor vehicle can be operated as a generator. This so-called recuperation makes it possible to convert part of the motor vehicle's kinetic energy into electrical energy when braking
Implementation Method 2
the at least one electrical machine is supplied with electrical energy from the energy store in such a way that the at least one electric machine generates a braking torque which is directed in the opposite direction to the drive torque
Implementation Method 3
additional friction brakes are installed with which the required braking torques can be applied
Data Source
Figure 1~2
Figure 3
AI summary
The invention relates to a method for braking a motor vehicle (10) which is driven by a drive torque of at least one electric machine (12) which is electrically connected to an electric energy storage means (14), wherein in a first operating mode the at least one electric machine (12) is operated as a generator for generating a generator braking torque, and in a second operating mode the at least one electric machine (12) is supplied with electrical energy from the energy storage means (14) in such a way that a braking torque which is opposed to the driving torque is generated by the at least one electric machine (12).