Hydraulic Return Circuit for Rear-Steering Cylinder Centering
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Solution Overview
Problem
Rear-axle steering systems in multi-axle vehicles face challenges in maintaining a safe failure state, particularly when driving in reverse or with non-adhesion-steered rear axles, as existing technologies fail to provide effective centering mechanisms.
Innovation Solution
A hydraulic circuit with a pressure accumulator and a valve arrangement that automatically centers the hydraulic cylinder to a safe failure position in the event of a fault or deactivation, using a combination of mechanical and hydraulic/pneumatic/electrical activation, ensuring the piston is locked in the straight-ahead position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a mechanically switchable valve arrangement with three switching positions is used to enable adhesion-guided return movement, then the steering system can achieve safe failure state in normal driving conditions, but the system fails to provide effective centering when driving in reverse or with non-adhesion-steered rear axles
Solution Approach 1:
The patent introduces a fourth switching position that can be activated in advance through hydraulic, pneumatic, or electrical deactivation of the valve arrangement. This preliminary action allows the system to prepare for safe failure states regardless of whether adhesion forces are present, enabling centering functionality to be triggered proactively rather than relying solely on passive adhesion-guided return
Solution Approach 2:
The patent employs an intermediary deactivation mechanism (hydraulic, pneumatic, or electrical) that mediates between the control system and the mechanical valve arrangement. This intermediary allows external control signals to override the mechanical sensing element, enabling active centering commands to be transmitted to the valve arrangement even when adhesion forces are absent or insufficient
2Extent of automation
If the valve arrangement is mechanically switched by a sensing element interacting with the piston rod, then the system responds automatically to piston position, but the valve arrangement experiences increased wear and reduced service life due to continuous load cycles
Solution Approach 1:
The patent replaces the continuous mechanical interaction between the sensing element and piston rod with an alternative deactivation mechanism. By using hydraulic, pneumatic, or electrical signals to deactivate the valve arrangement, the system reduces mechanical wear on the valve assembly while maintaining automatic response capability through the intermediary deactivation system
Solution Approach 2:
The patent implements periodic or event-driven deactivation of the valve arrangement rather than continuous mechanical switching. The valve arrangement is deactivated only when specific conditions are met (hydraulic pressure changes, pneumatic signals, or electrical commands), reducing the frequency of switching operations and thereby extending the service life of the valve assembly
3Reliability
If axles with caster angle are used to generate adhesive steering forces, then adhesion-controlled centering is achieved, but the system becomes inoperative when reversing as the axle deflects to maximum steering angle
Solution Approach 1:
The patent introduces a dynamically controllable valve arrangement that can be deactivated through hydraulic, pneumatic, or electrical means. This dynamic control allows the system to adapt its behavior based on operating conditions, enabling the valve to be actively positioned in a fourth switching position during reverse operations regardless of the axle's natural adhesion characteristics
Solution Approach 2:
The patent creates a universal centering mechanism that functions across multiple operating modes (forward and reverse driving, adhesion-steered and non-adhesion-steered axles). The multi-functional deactivation system (hydraulic, pneumatic, electrical) allows the same valve arrangement to serve both passive adhesion-guided centering and active controlled centering functions
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
The hydraulic circuit ensures safe and reliable steering in failure scenarios by hydraulically and mechanically locking the piston in the central position, reducing wear and extending the service life of the valve assembly through reduced load cycles.
Implementation Method 1
a pressure accumulator (30) which is charged in normal operation with a pressure applied to a pump connection (P1, P2) of the hydraulic circuit
Implementation Method 2
the valve arrangement (20) is designed to connect the second working chamber (11b) to the pressure accumulator (30) in the first switching state
Data Source
Figure 1
Figure 2a~2d
Figure 3
AI summary
This document describes a hydraulic circuit, used particularly for the steering system of a multi-axle vehicle, with a hydraulic cylinder that assumes a safe fail-safe position in the event of a fault or deactivation. To enable forced steering centering even when reversing or with axles lacking caster, a pressure accumulator is provided. During normal operation, this accumulator is charged with pressure applied to a pump port of the hydraulic circuit. A valve arrangement connects one working chamber of the hydraulic cylinder to the pressure accumulator and the other to a reservoir port, depending on the piston's displacement. This actively returns the piston to the safe fail-safe position and, in this position, blocks the connection between the working chambers and the pressure accumulator or reservoir port.