GB/T 45829-2025Functional safety requirements and testing methods for passenger car steering system (English PDF)

3.1 single element failure analysis; SEFA

A systematic analysis method for identifying the impact of single element failure.

3.2 system theoretic process analysis; STPA

A hazard analysis method based on system theoretic accident models and processes.

3.3 Safety metric

A quantified value of specific technical parameter given to meet safety objectives. [Source: GB 17675-2021, 3.2.7, modified]

5.1 Purpose

The purpose of this chapter is to define and describe the EPS system as a relevant item, so as to support the execution of subsequent stage activities.

5.2 Requirements

5.2.1 Define the relevant items for the EPS system in accordance with the requirements of 5.4 in GB/T 34590.3-2022. The functional requirements of the EPS system shall comply with GB 17675-2021.

Note 1. Examples of the functional, architectural, and non-functional requirements of the EPS system are shown in Appendix A.

Note 2. The functional interactions between the EPS system and other relevant items include.

-- Functions that the steering system requires from other relevant items and elements; for example, the EPS system requires the instrument system to provide the driver with system status and warning message;

-- Functions that other relevant items and elements require from the steering system; for example, the vehicle driving mode control system requires the EPS system to provide steering assist with different calibration characteristics.

5.2.2 The steering assist function of the EPS system shall meet the requirements of the vehicle's operating conditions and environmental constraints.

Note: In addition to considering normal vehicle operating conditions, the operating conditions of the EPS system may also include situations where the vehicle experiences an abnormal power outage while driving. For example, if the EPS system is powered by a backup power source, the steering assist provided can help ensure the safety of vehicle operation in emergency situations.

6.1 Purpose

The purpose of this chapter is to identify and classify hazardous events caused by abnormal performance of the EPS system, and define the safety objectives that the EPS system needs to meet, so as to avoid unreasonable risks.

6.2 Requirements

6.2.1 In accordance with the requirements of 6.4 in GB/T 34590.3-2022, hazard analysis and risk assessment shall be conducted on the EPS system.

6.2.2 Various abnormal functional behaviors of the EPS system shall be identified and analyzed in combination with the operation scenarios to form a list of hazardous events.

7.1 Purpose

The purpose of this chapter is to provide the safety requirements and mechanisms that the EPS system must meet in order to comply with safety objectives.

7.2 General requirements

Based on the definitions of relevant items and safety objectives of the EPS system specified in Chapters 5 and 6, and in accordance with the requirements of GB/T 34590.3-2022, functional safety concepts and technical safety concepts shall be derived to ensure that the relevant safety objectives are correctly and completely achieved.

7.3 Safety requirements for EPS system

7.3.1 Safety requirements for EPS system at the vehicle level

7.3.1.1 For unintended steering caused by unintended provision of steering assist or incorrect provision of excessive assist, the EPS system shall meet the safety metric for unintended lateral motion.

7.3.1.2 For excessive steering force caused by faults such as incorrect reverse assist, the EPS system shall meet the safety metric for unintended loss of lateral motion control.

7.3.1.3 For excessive steering force caused by insufficient or lost steering assist, the EPS system shall meet the safety metric for heavy steering when steering assist is lost.

7.3.2 Safety requirements for key components of the EPS system

7.3.2.1 The EPS system shall periodically detect abnormalities in the input signals related to steering assist requests to avoid misidentifying steering torque requests, which could lead to unintended lateral motion, loss of lateral motion control, or heavy steering.

7.3.2.2 The EPS system shall periodically detect faults such as short circuit (to ground or to power supply), open circuit, stuck signal, and deviation of the steering wheel torque sensor to avoid abnormal steering intention identification caused by faults, which could result in violation of the safety metric for unintended lateral movement, safety metric for loss of lateral motion control, or safety metric for heavy steering.

Example: By using redundant torque sensors, abnormalities in a single torque sensor can be detected.

Note: The determination of fault detection thresholds and detection cycles can be either derived from safety metrics and FTTI, or defined based on existing design experience, by verifying their rationality.

7.3.2.3 For EPS systems that adjust steering assist level according to vehicle speed, the integrity of vehicle speed signal transmission shall be periodically checked to avoid excessive, insufficient, or fluctuating steering assist due to abnormal vehicle speed signal communication, which could lead to violation of safety metric for unintended lateral motion, loss of lateral motion control, or heavy steering.

Example: By adding communication protection bits to the vehicle speed signal input to the bus, such as checksums and timestamps, abnormal communication of the vehicle speed signal can be detected.

7.3.2.4 The EPS system shall periodically detect abnormalities in the control unit to avoid incorrect steering torque calculations that could lead to violation of safety metric for unintended lateral motion, loss of lateral motion control, or heavy steering.

7.3.2.5 The steering torque of the EPS system generated by non-driver direct operation shall be controlled at a reasonable level and shall be able to ensure the driver's control of the steering, so as to avoid violating the safety metric for unintended lateral motion or loss of lateral motion control.

Example: The active self-centering function can provide steering torque independently of driver input.

Note: For sub-functions that can trigger steering torque simultaneously, consider constraining the generated overall torque. Appendix A provides examples of the main functions of EPS.

7.3.2.6 The EPS system shall periodically detect the drive link of the power assist motor and the short circuit and open circuit faults of the motor to avoid abnormal steering torque, which could lead to violation of safety metric for unintended lateral motion, loss of lateral motion control or heavy steering.

Example: The EPS system periodically detects short-circuit faults in the motor drive bridge (MOSFET) to avoid incorrect steering torque execution.

7.3.2.7 The EPS system shall periodically detect over-voltage, under-voltage, and open circuit abnormalities in the power supply link to avoid violation of safety metrics for unintended lateral motion, loss of lateral motion control, or heavy steering due to voltage abnormalities.

Example: The EPS system is fault-tolerant to over-voltage or under-voltage faults within a certain range. When the over-voltage or under-voltage exceeds the normal operating range, the EPS system shall shut down the motor drive link to avoid damage.

7.3.3 Safety requirements for EPS system failure degradation

7.3.3.1 When a fault occurs that may lead to a violation of safety objectives, the EPS system shall enter the safe state. […]