Power Steering Assist Control for Differential Lock Thermal Management
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Solution Overview
Problem
Electric power steering devices in four-wheel drive vehicles experience increased temperature and reduced assist function after differential locking, leading to heavy steering and potential system shutdown due to high assist force requirements, which are not adequately managed by existing technologies.
Innovation Solution
A power steering device with a diff lock sensor and control unit that reduces the maximum auxiliary force when the differential device is in a non-differential state, limiting the assist force to prevent overheating and allowing for smooth steering, and gradually returns to maximum assist when differential locking is released.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the electric power steering device supplies large current to generate substantial assist force during differential locking, then the steering force is maintained, but the temperature of the electric power steering device becomes high
Solution Approach 1:
The control unit dynamically adjusts the maximum assist force based on the differential locking state. When differential locking is detected, the control unit reduces the maximum assist force to a limited value, preventing excessive current supply and temperature rise. When differential locking is released, the control unit restores the maximum assist force to maintain steering performance.
2Reliability
If the electric power steering device stops operation when temperature reaches a prescribed value, then overheating is prevented, but the assist function cannot be restored until temperature falls, causing continual heavy handle operation
Solution Approach 1:
The control unit takes preliminary action by reducing the maximum assist force to a limited value when differential locking is detected, before the temperature reaches the shutdown threshold. This prevents the system from entering a state where it must stop completely, allowing the assist function to be maintained at an acceptable level without causing excessive temperature rise that would trigger a shutdown.
3Temperature
If the maximum auxiliary force is reduced to a limited value during differential locking, then temperature rise is suppressed, but the steering assist force is reduced
Solution Approach 1:
The control unit dynamically adjusts the maximum assist force based on the differential locking state. When differential locking is detected, the control unit reduces the maximum assist force to a limited value, preventing excessive current supply and temperature rise. When differential locking is released, the control unit restores the maximum assist force to maintain steering performance.
Data Source
AI summary
To suppress temperature rises of an electric power steering device provided at a vehicle equipped with a diff lock device and to restrict the operation of the electric power steering device at times other than during diff locking. An electric power steering device that is coupled to a steering shaft fitted with handlebars at an upper end and that generates auxiliary force that supplements the steering force, and a diff lock unit that selects a differential state and a non-differential state (diff lock) of a differential device are provided. An ECU reduces the maximum value of the auxiliary force generated by the electric power steering device to a prescribed limit value when the diff lock is detected by the diff lock sensor is also provided. The ECU releases limiting of the maximum value of the auxiliary force when release of the diff lock is detected by the diff lock sensor.