Motor Bridge Driver Circuit Arbitration for Fault Tolerance
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Solution Overview
Problem
Existing motor bridge driver systems for electric power assisted steering are vulnerable to faults, particularly in the microprocessor, which can lead to incorrect control signals and loss of motor assistance due to impaired performance or internal faults, potentially causing the system to malfunction.
Innovation Solution
An integrated motor bridge driver circuit with two microprocessors, where an arbitration and diagnostic circuit ensures only one microprocessor, the master, controls the bridge at any time, and switches control if the master becomes faulty, using a watchdog function and monitoring supply voltage to maintain system reliability and prevent faults from affecting motor operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single microprocessor is used to control the motor bridge, then the device complexity is reduced, but the reliability deteriorates because a single component failure can lead to loss of motor assistance
Solution Approach 1:
The control system is segmented into two independent microprocessors (master and slave) that operate separately but control the same motor bridge. This segmentation allows the system to maintain functionality even if one microprocessor fails, as the other can take over control, thereby improving reliability without requiring a complete system redesign
Solution Approach 2:
The patent implements local quality by giving different roles to different microprocessors - the master microprocessor has full control authority while the slave microprocessor has limited control that is suppressed when the master is operational. This localized differentiation of control authority allows the system to maintain simplicity in normal operation while providing redundancy for fault tolerance
2Reliability
If two microprocessors are used to control the motor bridge, then the reliability is improved through redundancy, but the device complexity increases due to arbitration and diagnostic circuits
Solution Approach 1:
An arbitration circuit is introduced as an intermediary component that mediates between the master and slave microprocessors. This intermediary automatically determines which microprocessor should have control authority based on operational status, eliminating the need for complex software-based arbitration and reducing overall system complexity while maintaining fault tolerance
Solution Approach 2:
The diagnostic circuit continuously monitors the operational status of both microprocessors and provides feedback to the arbitration circuit. This feedback mechanism allows the system to automatically detect faults and switch control authority appropriately, improving reliability through continuous monitoring without requiring complex manual intervention systems
3Reliability
If the slave microprocessor is enabled to control the motor bridge, then the reliability is improved for fault coverage, but the harmful factors increase due to potential conflicting control signals
Solution Approach 1:
The control authority of the slave microprocessor is made dynamic rather than static. The slave microprocessor is enabled to control the motor bridge only when the master microprocessor is determined to be faulty by the diagnostic and arbitration circuits. This dynamic adjustment of control authority ensures that backup control capability is available when needed while preventing harmful control signal conflicts during normal operation
Data Source
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AI summary
A motor bridge driver integrated circuit comprises a first set of input ports arranged to receive control signals from a first microprocessor,a second set of input ports arranged to receive control signals from a second microprocessor,and at least one set of output ports arranged to output motor phase switching signals to the switches of a motor bridge. A diagnostic circuit receives and monitors the control signals received from the two microprocessors and from those signals determines which microprocessor is to be treated as a master and which is to be treated as a slave at any given time by the motor bridge driver. An arbitration circuit selectively enables only the master microprocessor to the take control of the motor bridge at any given time whilst preventing the slave microprocessor from taking control of the motor bridge.