Pusher Axle Steering Geometry for Mobile Crane Emergency Radius
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Solution Overview
Problem
Existing mobile crane steering systems face challenges in maintaining a small emergency steering radius, which affects the vehicle's ability to navigate tight corners safely, especially in the event of a steering fault.
Innovation Solution
The introduction of a pusher axle, a passively-steered rear axle positioned in front of the steering pole plane, improves steering by being guided between the front and centered rear axles, reducing the emergency steering radius and enhancing safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If all rear axles are equipped with centering cylinders to set them to straight running position in case of fault, then the emergency steering radius can be controlled, but the device complexity increases and the centering cylinders become significantly larger than steering cylinders
Solution Approach 1:
The patent extracts the passive steering function from the active steering system by introducing a separate passively-steered rear axle that does not require centering cylinders. This axle is positioned behind the steering pole plane and automatically follows the steering arc of the front axles through geometric constraints, eliminating the need for additional centering cylinder hardware while maintaining emergency steering radius control.
Solution Approach 2:
The passively-steered rear axle acts as an intermediary element between the actively-steered front axles and the rear of the vehicle. It translates the steering motion of the front axles into appropriate wheel angles for the rear axles through the geometric relationship defined by the steering pole plane, without requiring direct hydraulic control or centering mechanisms.
2Reliability
If passively-steered rear axles are installed at the rearmost position to reduce emergency steering radius, then the steering radius is reduced, but the axles cannot be effectively guided in tight curves and may cause understeering
Solution Approach 1:
The patent segments the rear axle steering function into two distinct components: actively-steered rear axles positioned before the steering pole plane that can be controlled for tight curves, and passively-steered rear axles positioned behind the steering pole plane that automatically follow the steering arc. This segmentation allows each component to optimize its function without compromising the other.
Solution Approach 2:
Instead of positioning passively-steered axles at the conventional rearmost location, the patent inverts the approach by placing them behind the steering pole plane rather than in front of it. This inversion allows the passive axles to be geometrically constrained by the steering pole, enabling them to automatically follow the steering arc and preventing understeering in tight curves.
3Speed
If the emergency steering circle is made small to allow high-speed navigation through tight corners, then speed can be maintained, but the steering system becomes more sensitive to faults and requires more precise control
Solution Approach 1:
The passively-steered rear axles positioned behind the steering pole plane automatically adapt to steering faults by following the steering arc of the front axles through geometric constraints. This self-adjusting mechanism eliminates the need for active control or centering cylinders, providing reliable emergency steering behavior without requiring precise control systems or risking instability from overly sensitive steering.
Data Source
AI summary
The disclosure relates to a steering system for a mobile work machine, in particular for a mobile crane, which comprises at least one mechanically steerable front axle, at least one passively-steered rear axle, as well as at least one rear axle that is steerable by means of at least one steering cylinder. The front and rear axles are arranged one behind the other along a longitudinal axis of the steering system and comprise wheels, the axes of rotation of which, virtually extended, in the case of cornering, on the side of the curve center, intersect a common steering pole plane positioned perpendicularly on the longitudinal axis. According to the disclosure, at least one passively-steered rear axle is arranged between a front axle and the steering pole plane. The disclosure furthermore relates to a mobile work machine comprising such a steering system.