Rear Axle Drivetrain Neutral Shift for Fault Deceleration Control
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Solution Overview
Problem
Existing drivetrains for motor vehicles face challenges in meeting safety standards for functional safety (FuSa) as mandated by regulations like ISO 26262, particularly in ensuring efficient drive power transmission while preventing excessive deceleration due to faults in electric drive engines or vehicle transmissions.
Innovation Solution
A drivetrain design featuring a switchable vehicle transmission with at least one gear stage, connected control units (E-motor control unit and transmission control unit) via redundant control lines, allowing for automatic switching to a neutral position in case of faults detected by redundant monitoring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If redundant monitoring and control lines are added to ensure functional safety, then safety standards compliance is improved, but device complexity increases
Solution Approach 1:
The patent combines the monitoring functions of the E-motor control unit and transmission control unit into a mutually redundant system where both units monitor each other through dual control lines. This merging of monitoring responsibilities into a shared redundant system achieves functional safety compliance while avoiding the need for completely separate safety systems.
Solution Approach 2:
The E-motor control unit and transmission control unit serve multiple functions: they control their respective components, monitor each other for faults, and can independently switch the drivetrain to a safe state. This multi-functionality reduces the need for dedicated safety components, managing complexity while maintaining high reliability.
2Reliability
If automatic switching to neutral position is implemented upon fault detection, then operational safety is improved, but response time and control complexity increase
Solution Approach 1:
The drivetrain is designed with a pre-defined safe state (neutral position) that both control units can independently activate upon fault detection. This preliminary preparation of a safe state allows for immediate switching without complex decision-making during the fault event, reducing response time while maintaining safety.
Solution Approach 2:
The redundant control lines provide continuous feedback between the E-motor control unit and transmission control unit, allowing each unit to monitor the other's status and respond to faults. This feedback mechanism enables rapid fault detection and automatic switching to the neutral position, improving operational safety while maintaining quick response times.
Data Source
AI summary
A drivetrain has at least one electric drive machine configured for driving a motor vehicle, a drivable rear motor vehicle axle for transmitting drive forces of the electric drive machine to a roadway surface, and a vehicle transmission which has at least one transmission ratio stage and which is configured for transmitting drive forces in the direction of the drivable rear motor vehicle axle. The transmission ratio stage can, in at least one operating mode of the drivetrain, be engaged by a transmission control unit. The vehicle transmission can, from the transmission ratio stage, be shifted by the transmission control unit into a neutral position in which a transmission output shaft is freely rotatable relative to a transmission input shaft. For control of the electric drive machine, an electric motor control unit is provided, wherein the electric drive machine is, by way of the electric motor control unit, operable at least in a motor operating mode and in a neutral mode, in which the electric drive machine is rotatable in a manner free from torque. The electric motor control unit and the transmission control unit are connected to one another by at least two control lines configured for transmitting control commands between the control units. A control command can be transmitted by the electric motor control unit via at least one of the two control lines to the transmission control unit, such that the transmission control unit sets the vehicle transmission into the neutral position.