Steer-by-Wire Control Device for Reducing Hydraulic Time Lag
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Solution Overview
Problem
The existing steer-by-wire electric hydraulic power steering systems experience delays in following the change in steering angle due to temperature-related decreases in hydraulic pressure discharge, leading to deteriorated operation feeling, especially when using a gear pump instead of a piston pump.
Innovation Solution
The system incorporates a control device that adjusts the rotation speeds of the electric motor and pump by referencing target voltage maps to compensate for time lags between steering and turning angles, increasing rotation speeds when volumetric efficiency decreases and reducing them when it recovers, thereby maintaining hydraulic pressure and reducing delays without adding special components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a gear pump is used to replace a piston pump, then manufacturing costs are reduced, but the discharge amount per rotation decreases with increasing liquid temperature, causing time lag and deteriorated operation feeling
Solution Approach 1:
The control device dynamically adjusts the rotation speed of the gear pump based on real-time monitoring of the time lag between steering angle and turning angle. When temperature increases cause discharge amount to decrease and time lag to increase, the system automatically increases rotation speed to compensate, maintaining responsive operation despite using the cost-effective gear pump
Solution Approach 2:
The system changes the operating parameter (rotation speed) of the pump in response to changing conditions (liquid temperature, time lag). By adjusting rotation speed as a variable parameter, the system compensates for the gear pump's temperature-sensitive discharge characteristics and maintains consistent hydraulic pressure delivery
2Loss of time
If the rotation speed of the pump is increased to maintain hydraulic pressure, then the time lag is reduced, but the energy consumption increases
Solution Approach 1:
Rather than maintaining a constantly high rotation speed, the system dynamically adjusts pump speed based on actual performance needs. The control device monitors time lag and only increases rotation speed when temperature-related discharge reduction causes unacceptable delay, thereby reducing energy consumption during normal operating conditions while maintaining responsiveness when needed
Solution Approach 2:
The system optimizes the rotation speed parameter by changing it only when necessary to compensate for temperature effects. This conditional parameter adjustment balances the trade-off between maintaining acceptable time lag performance and minimizing energy consumption during pump operation
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively suppresses delays in turning angle changes relative to steering angle changes, maintaining operational efficiency even with gear pumps, which reduces manufacturing costs and improves the system's responsiveness.
Implementation Method 1
an electric motor for rotating the pump in forward and reverse directions to operate the hydraulic actuator
Implementation Method 2
a pump for supplying hydraulic pressure to the hydraulic actuator
Data Source
Figure 1
Figure 2
Figure 3(a)~3(c)
AI summary
The purpose of the present invention is to suppress delays in changes in a turning angle with respect to changes in a steering angle, regardless of the type of pump being adopted in an electric hydraulic pressure type steer-by-wire steering system. The steer-by-wire steering system is provided with a hydraulic actuator (6) for changing the turning angle of an object to be steered; a pump (5) for supplying hydraulic pressure to the actuator; an electric motor (4) for rotating the pump in forward and reverse directions; and a control device (3) for controlling the turning angle to be corresponded to a steering angle by operating the motor. The control device is provided with: a motor driving unit for controlling the electric motor to decrease deviations between the steering angle and the turning angle; and a control correction unit for performing changes so as to reduce the time lag between changes in the steering angle and changes in the turning angle, said time lag being derived according to the deviations.