Steer By Wire Technology

2019 Steer by Wire Technology Integration in Automotive

While electric power steering removes the hydraulic components but retains the traditional mechanical steering linkage, Steer-By-Wire does away with the steering linkage. These systems use electric motors to turn the wheels, sensors to determine how much steering force to apply, and devices that provide tactile feedback to the driver. These motors are more efficient, quieter, and require no maintenance.

The system uses software control, and it can be applied to other models if you modify some parameters. And this can save a lot of time for developing new models and reduce the costs.

Steer by Wire system will eventually replace the current traditional mechanical steering system, and it has gradually been accepted by the automotive industry. Refer articles by Chang Jiangxue, Li Manjiang & Bai Xuefeng, College of Engineering Technology, Jiangsu Institute of Commerce, Nanjing.

The chief customer concern with Steer-By-Wire is the lack of physical linkage. Because there are no mechanical linkages between the driver and the wheels, a controller is used to control the positioning of the motors used to steer the wheels. Products such as the InMotion APS (Advanced Power Steering) controller that meets the ISO standard 13849-1, category 3, level PL=d for functional safety, meets those safety needs.

Automakers are slowly developing autonomous driving technology. The new Q50 is the market’s first “steer-by-wire” model, meaning there’s no mechanical connection between the wheel in your hands and the wheels on the street. Just electric signals. CLICK https://www.wired.com/2014/06/infiniti-q50-steer-by-wire/amp to review.

INFINITI’s Direct Adaptive Steering® (DAS) removes the mechanical connection between the steering wheel and tires, allowing for instantaneous driver input that can be digitally processed and adjusted up to 1,000 times per second. The DAS is unaffected by the kickback and forced movement of conventional steering but still gradually requires more effort with increased speed and G-forces like a conventional system. CLICK https://www.infinitiusa.com/infiniti-now/technology/direct-adaptive-steering.html

Steer-by-wire systems offer the potential to enhance steering functionality by enabling features such as automatic lane keeping, park assist, variable steer ratio, and advanced vehicle dynamics control. Steer-by-wire systems replace the conventional mechanical linkages with electronic sensors, controllers and actuators.

Depending upon the design, a steer-by-wire system can offer several benefits compared to conventional mechanical steering systems. Elimination of the mechanical linkage between the steering wheel and the steering gear can provide an enhancement to design flexibility.

There are several significant challenges associated with the commercial application of steer-by-wire technology to automobiles. Safety and security objectives must be met. A steer-by-wire system contains electrical components that have lower reliability than the mechanical components found in conventional steering systems. Redundancy of electrical components may be an effective method to assist steer-by-wire systems in meeting safety objectives.

However, component redundancy may also have a negative impact on cost and reliability. Despite the continuous cost reduction of electronic sensors, controllers, and actuators, the steer-by-wire system cost remains a significant obstacle to application in passenger cars. Refer paper by Yong-Jun Lee and Young-Jae Ryoo from Dept. of Engineering and Robotics, Mokpo National University 1666 Youngsan-ro, Chyungye-Myun, Muan-Gun, Chonnam, Korea.

3rd Generation of Steering – Steer-by-Wire Technology

By Jim Yang, Ph.D.; FZB Technologies http://fzbtechnology.com.

FZB Technology Controller Design Targets:

• Scalable to higher power requirements (from 500W to 5KW).
• State-of-the-art electronic design: with latest generation of microcontrollers, and pre-drivers with advanced diagnostics functions.
• Compliant to safety standards (ISO-26262, ASIL-D): with redundancies in almost all subsystems.
• Expansible to all input voltage variants including 350V.
• Improved torque ripples and performance (where NVH shall be a big factor).
• Improved fail-safe features and “limp-home” mode

Benefits of FZB Tech Dual 3-phase PMSM Design:

1. True redundancies from the design that shall meeting the stringent safety requirements
2. Will have more room to minimize torque ripple
3. Improved efficiency
4. Improved limp-home feature.

FZB Technologies Redundancy Design:

1. Dual 3-phase inverters
2. Dual micros (either one micro plays the role monitoring or key results of two cores of a single microcontroller are compared)
3. Redundancy of power-supply: 48V and 12V
4. Redundancy in motor windings
5. Two position sensors

Generation of Steering Technologies:

1^st Generation: Conventional hydraulic steering systems which may come with/without steering assistance.

2^nd Generation: Hydraulic steering system which may come with Electrical Hydraulic Power Steering (EHPS) and a steering system which comes with Electric Power Steering (EPS).

3^rd Generation: Steer-by-wire – in which sensors detect the movements of the steering wheel and send information to a microprocessor. The computer then sends commands to actuators on the axles, which turn according to the driver’s directions.

Advantages of Steer by Wire:

1. Improved Driver Comfort: It is natural to implement variable steering ratios which shall improve driver comfort by reducing the ratio in parking lot and increasing to normal steering ratio when driving on high way.
2. Improved Safety: Safety can be improved by providing computer-controlled intervention of vehicle controls with systems such as electronic stability control (ESC), adaptive cruise control, and Lane Assist Systems.
3. Enhanced Reliability: The electromechanical components shall have better reliability and shall be more maintenance-free.
4. Increased vehicle design freedom: as the electromechanical components occupy less place compared to the mechanical counterparts, and the control modules can be placed wherever the design permits.
5. Reduces the vehicle’s weight: The technology eliminates any mechanical link between the steering wheel and the tires which are much heavier than electromechanical components.
6. Better Ergonomics: Improved ergonomics due to flexibility of location of controls.
7. Prepared for the future: The “steer-by-wire” is an autonomous-driving ready technology and well-prepared for the future.

Concerns About Relying on a Wire for Steering:

1. Mechanical backup: There’s an option of keeping a mechanical backup in case something goes wrong.
2. Dual CPUs system: Two microcontrollers that run independently can be utilized to check the integrity of each other.
3. Dedicated Communication Links: Faster and dedicated communication links (CAN, CAN Fd, LIN, and FlexRay) between the steering angle sensor and “steer-by-wire” ECU can be adopted to minimize time delays.

System Diagram:

• Communication: Besides the vehicle CAN bus, a dedicated communication link may be utilized between the Steering Angle Sensor (SAS) and the main ECU to handle the timing delay constraints and to meet reliability requirement.
• Road motor: We may choose to use one or two motors to drive the tires. If using two motors to drive two tires separately, it will better meet Ackermann angle requirements for the two tires.
• Road feeling: Feedback motor is used to generate desired road feeling.
• Safety requirements: Safety requirements (such as ISO-26262, ASIL-D) shall be met including adopting Dual CPUs.

For more information contact Dr Jim Yang at FZB Technologies or write to designhmi@gmail.com