EPS automotive industry steering system summary: The automotive industry is booming, and more and more people are driving cars. Operating the steering wheel has become particularly familiar and important. Its stability and reliability directly affect the driver's driving experience, and the power steering system plays a key role. In this article, let's talk about how today's mainstream electronic power steering systems ensure stability and reliability.

1. Development history of automotive power steering system

The automotive power steering system has developed from the earliest traditional mechanical steering system with laborious operation, to the mechanical hydraulic power steering system, to the current general electronic hydraulic power steering system, which has already made a qualitative leap in the development of the power steering system. Nowadays, as energy saving, environmental protection and smart safety have become the themes of the development of the times, Electronic Power Steering (EPS) was born. On the basis of the electronic hydraulic power steering system, the hydraulic power assist system is removed, which makes the automobile power steering system more environmentally friendly, more energy-saving, more user-friendly, safer and more reliable.

2. How to ensure stable and reliable EPS operation

In order to ensure the stable and reliable operation of the EPS electronic control system, all actions from the front end to the back end of the entire core control unit should be monitored accordingly, and the ICs used should meet the safety requirements of the ISO 26262 standard to cope with the harsh environment inside the car. This paper introduces the scheme using integrated CAN/LIN transceivers. The power SBC chip of functional safety level ASIL D is responsible for interconnection and power monitoring management. It cooperates with the main control MCU SPC5744P of functional safety level ASIL D. The main control integrates FCCU errors independent of the MCU. The detection control unit, combined with the monitoring of the FCCU by the SBC, improves the robustness, stability and reliability of the system.

Figure 1 Functional safety level fault and failure rate indicators

Figure 2 Introduction of EPS control scheme

Main control MCU: In addition to meeting the safety level of ASIL D, SPC5744P also has more peripheral resources than the ARM framework, as well as a maximum of 384K RAM space and 2.5M Flash space, under the lock-step dual-core frequency of 200MHz , provides higher system flexibility and easily responds to various automotive electronic control application requirements. The verification core of the lockstep dual core executes the same instructions as the main core to verify whether the running instructions are correct. If a mismatch occurs, an FCCU fault is triggered for error handling. And the FCCU module supports up to 74 error sources, responds differently to different error sources, and improves the stability and reliability of the entire system control.

System Basis Chip: Using the FS6500 family of chips, it provides stable and reliable current and voltage for the normal operation of the system, and also integrates CAN/LIN transceivers to simplify the design and reduce the size of the system PCB. While mastering all the behaviors of the FCCU monitoring system, the SBC provides functions such as advanced watchdog, voltage level detection, and FCCU monitoring that monitor the master.

Pre-drive: GD3000 three-phase pre-drive, integrates three half-bridge pre-drives and a charge pump, the gate drive capacity can reach 2.5 A, and the drive output capability can be flexibly configured, while meeting the AEC-Q100 standard.

Figure 3 GD3000 block diagram

Magnetic rotary position sensor: AS5147 supports DAEC dynamic angle error compensation, 11-bit binary incremental pulse count, programmable zero position, supports 14-bit resolution, and meets AEC-Q100 grade 0 standard.

Field-Effect Transistor: Automotive-grade MOSFET, using charge-balancing technology, with low on-resistance and low gate charge performance. To minimize conduction losses, provide excellent switching performance, and can withstand extreme dv/dt rates.

EEPROM: In the EPS system, for important data, it is equipped with vehicle-grade EEPROM storage to store important data and backup.