Vehicle Yaw Rate Control via Differential Wheel Torque
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Solution Overview
Problem
Conventional motor vehicles with steerable axles that also function as drive axles face limited maneuverability due to restricted steering angles, particularly at low speeds, which hinders yaw rate and turning circle performance.
Innovation Solution
The method involves detecting the force applied to the steering wheel at its maximum angle and controlling individual electric machines to adjust wheel torques, mimicking tracked vehicle behavior by differentiating torque between inside and outside wheels, thereby increasing yaw rate without mechanical complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the steering angle is limited by the wheel suspension and steering system properties, then the steering device is simple and reliable, but the maneuverability and yaw rate are reduced
Solution Approach 1:
The patent replaces the mechanical steering system with an electrical control system. Instead of mechanically increasing the steering angle beyond the physical limits of the suspension and steering components, the invention uses electric machines (motors) to directly control the wheel torques and generate yaw rate. This substitution allows achieving enhanced maneuverability without modifying the mechanical steering structure, thus maintaining simplicity and reliability while improving performance.
Solution Approach 2:
The invention changes the control parameter from steering angle to wheel torque. By detecting the steering wheel torque and converting it into differential wheel torques applied by the electric machines, the system achieves yaw rate control without being constrained by the mechanical steering angle limits. This parameter transformation allows the vehicle to achieve higher yaw rates while keeping the steering system within its safe operational range.
2Ease of operation
If the steering wheel angle is increased beyond the maximum angle, then the yaw rate increases, but the steerable axle or wheels may be damaged
Solution Approach 1:
The patent substitutes the mechanical approach of increasing steering angle with an electrical approach using wheel torques. The electric machines generate the necessary yaw rate by applying differential torques to the wheels, eliminating the need to exceed the maximum steering wheel angle. This substitution protects the steering system from damage while achieving the desired yaw rate enhancement.
Solution Approach 2:
The system detects the steering wheel torque in advance and uses this information to control the electric machines before the driver would naturally over-turn the steering wheel. By anticipating the steering input and applying compensating wheel torques, the system prevents the steering mechanism from being subjected to damaging forces while still achieving the intended maneuvering effect.
3Ease of operation
If complex mechanical and electronic solutions are used to increase the adjustable yaw rate, then the maneuverability improves, but the device complexity increases
Solution Approach 1:
The patent makes the electric machines serve dual functions: they act as both drive devices for propelling the vehicle and as steering actuators for controlling wheel torques. This multi-functionality eliminates the need for separate mechanical steering mechanisms and complex electronic control systems, achieving enhanced yaw rate adjustability while keeping the overall device complexity low.
Solution Approach 2:
The invention merges the drive function and steering function into a single integrated system. The electric machines that provide propulsion are also used to generate differential wheel torques for steering and yaw rate control. This consolidation eliminates the need for separate mechanical steering components and reduces electronic complexity, achieving maneuverability enhancement without proportional increases in system complexity.
Data Source
Figure 1
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AI summary
The method involves determining steering angle of two of wheels (4, 5) of a front axle (2) by a steering wheel (18). The steering wheel is rotated up to a maximum steering wheel angle in a steering direction. Force applied on the steering wheel is detected during reaching of the maximum steering wheel angle. The wheels (4-7) are individually actuated by electric machines (8-11) for increasing yaw rate depending on the applied force. Torque applied on a steering device (17) is determined during reaching of maximum steering wheel angle. An independent claim is also included for a device for operating a motor vehicle.