Hydraulic Steering Control with Smooth Open-Closed Loop Transition

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Solution Overview

Problem

Existing hydraulic steering systems suffer from mechanical play, backlash, hydraulic dead band, and steering drift due to open loop control, which affect the relationship between steering input and vehicle behavior.

Innovation Solution

Incorporating a closed loop control mechanism with cross-over transition means that dynamically switch between open and closed loop control based on vehicle parameters and steering conditions, using cross-over model means to manage transitions smoothly and mitigate the impact of wheel angle sensor faults.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If open loop control is used, then the steering system is simple and reliable, but steering precision and responsiveness deteriorate due to mechanical play, backlash, and hydraulic dead band

Engineering Contradiction:

Improveopen loop control reliabilityVSAvoidsteering precision

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The system dynamically switches between open loop and closed loop control modes based on operating conditions. The cross-over transition means enable the control system to adapt its structure in real-time, using open loop control for normal operations and closed loop control when precision is critical or faults are detected, thus resolving the contradiction between simplicity/reliability and precision

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system changes the control parameter structure by introducing a cross-over model that adjusts the control strategy based on vehicle speed, steering angle, and sensor fault status. This parameter-based adaptation allows the system to maintain reliability while improving precision when needed

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If closed loop control is used, then steering precision and responsiveness improve, but system complexity increases and sudden changes may occur during transition

Engineering Contradiction:

Improvesteering precisionVSAvoidcontrol system complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The cross-over transition means act as an intermediary between open loop and closed loop control systems. This mediator smoothly blends the two control modes during transition, preventing sudden changes and reducing the perceived complexity by providing a unified control interface that handles both modes

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The control system uses dynamic switching with smooth transition characteristics. The cross-over model calculates optimal blending ratios between open and closed loop control signals based on current operating conditions, maintaining precision while managing complexity through adaptive behavior rather than fixed complex architecture

Inventive Principle:

Principle #15Dynamics

3Stability of the object's composition

If closed loop control is used, then steering drift is reduced, but the system becomes more sensitive to wheel angle sensor faults

Engineering Contradiction:

Improvesteering stabilityVSAvoidsensor fault sensitivity

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The system uses feedback from the wheel angle sensor in closed loop control to reduce steering drift and improve stability. The feedback mechanism continuously monitors wheel position and adjusts control signals to maintain desired steering accuracy, directly addressing the stability improvement goal

Inventive Principle:

Principle #23Feedback

4Stability of the object's composition

If cross-over transition means are added, then smooth transition between control modes is achieved, but device complexity increases

Engineering Contradiction:

Improvecontrol transition smoothnessVSAvoidtransition control complexity

Core Design Contradiction:

Stability of the object's compositionVSDevice complexity

Solution Approach 1:

The cross-over transition means merge the open loop and closed loop control paths into a unified control architecture. By combining both control modes under a single cross-over model that manages transitions, the system achieves smooth operation while consolidating complexity into a manageable centralized control structure

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentUS12479500B2Hydraulic steering system

Publication Date: 2025.11.25 DANFOSS POWER SOLUTIONS APS

AI summary

A hydraulic steering system (1) includes a steering command device (2) having a steering sensor (3), a steering motor (6), a wheel sensor (9), a pressure source (P), and control means (12) controlling a fluid supply from the pressure source (P) to the steering motor (6), wherein the control means (12) has an open loop control (19). Such a steering system should have a good relationship between steering input from the operator and steering behaviour of the vehicle to be steered. To this end the control means (12) include in addition to the open loop control (19) a closed loop control (20), wherein cross-over transition means (21) are provided which are connected to the open loop control (19) and to the closed loop control (20) and control a transition between the open loop control (19) and the closed loop control (20).