Front-Rear Drive Force Control for Dual-Unit Vehicle Drivetrains
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Solution Overview
Problem
Existing vehicle drive devices limit the range of driving force distribution between front and rear wheels, restricting the ability to adapt to various vehicle conditions and power storage device states, thus compromising traveling performance.
Innovation Solution
A vehicle drive device with a first drive unit for front wheels and a second drive unit for rear wheels, each equipped with rotary electric machines and differential gear mechanisms, allows for dynamic control of driving force distribution by switching between operation modes based on vehicle speed and power storage device charge level, enabling both wheels to be driven effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the driving force distribution between front and rear wheels is limited to basic configurations, then the device complexity is reduced, but the adaptability to different vehicle conditions and power storage states deteriorates
Solution Approach 1:
The drive system is divided into two independent drive units: a first drive unit for front wheels with an internal combustion engine and first rotary electric machine, and a second drive unit for rear wheels with a second rotary electric machine. This segmentation allows each unit to operate independently or in combination, providing flexible driving force distribution adapted to different vehicle conditions and power storage states without requiring a completely complex reconfiguration of the entire system.
Solution Approach 2:
The first rotary electric machine serves multiple functions: it can operate as a motor to drive the front wheels, as a generator to charge the power storage device, and its reaction force can be utilized for torque amplification of the internal combustion engine. The distribution differential gear mechanism also provides universal functionality by enabling various power transfer paths. This multi-functionality enhances adaptability without proportionally increasing device complexity.
2Adaptability or versatility
If the first drive unit operates in multiple modes with different power transfer paths, then the adaptability to various traveling situations is improved, but the device complexity increases
Solution Approach 1:
The first drive unit incorporates a distribution differential gear mechanism that dynamically switches between different operation modes based on vehicle conditions. The mechanism can transfer power from the internal combustion engine to the first output member, from the first rotary electric machine to the first output member, or utilize the reaction force for torque amplification. This dynamic adaptability allows the system to optimize performance for different traveling situations without requiring entirely separate mechanical systems for each mode.
Solution Approach 2:
The distribution differential gear mechanism acts as an intermediary that manages multiple power transfer paths between the internal combustion engine, first rotary electric machine, and first output member. By using this intermediate mechanism, the system can selectively engage different power sources and transfer paths without direct complex connections between all components, thereby reducing overall device complexity while maintaining operational flexibility.
3Force
If both drive units are sized to provide high driving force, then the traveling performance is improved, but the weight and size of the vehicle increases
Solution Approach 1:
The system merges the power output of the internal combustion engine and the first rotary electric machine through the distribution differential gear mechanism to provide high driving force at the front wheels. The second drive unit provides additional driving force to the rear wheels when needed. By combining these power sources strategically rather than relying on a single oversized drive unit, the system achieves high total driving force while avoiding the weight penalty of duplicating entire drive units.
Solution Approach 2:
The control device dynamically adjusts the operating parameters of the rotary electric machines based on vehicle conditions, power storage state, and driving requirements. By optimizing the output torque and speed parameters of each motor in real-time, the system maximizes the utilization of available driving force without requiring excessive oversizing of the motors, thereby reducing overall vehicle weight while maintaining adequate performance across different operating conditions.
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
The solution enables flexible driving force distribution between front and rear wheels, enhancing vehicle performance by ensuring appropriate power delivery regardless of charge level, while avoiding the need for larger drive unit sizes, and supporting high driving forces when required.
Implementation Method 1
a first rotary electric machine, and a distribution differential gear mechanism... a second rotary electric machine... the first rotary electric machine and the second rotary electric machine are electrically connected to a power storage device so as to transmit and receive electric power to and from the power storage device
Data Source
AI summary
A vehicle speed is lower than a first threshold, a control device controls both a first drive unit and a second drive unit to output a requested driving force by setting an operation mode of the first drive unit to a first mode when the requested driving force is smaller than a second threshold and the charge level of a power storage device is equal to or higher than a third threshold, and controls both the first drive unit and the second drive unit to output the requested driving force by setting the operation mode of the first drive unit to a second mode when the requested driving force is equal to or larger than the second threshold or the charge level of the power storage device is lower than the third threshold.