Differential Rear Wheel Steering for Motor Graders
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Solution Overview
Problem
Machines with a broad wheelbase, such as motor graders, face challenges in making tight turns due to traction loss and uneven wear on tires, and difficulty in maintaining a constant load on tools like blades, especially in articulated or skid-steering configurations.
Innovation Solution
A steering system that includes pairs of rotatably mounted rear wheels on either side of the machine, with at least one spaced front wheel, and a plurality of drive units that control the rear wheels to rotate them at different speeds in response to a steering input signal, allowing for precise directional control by varying the rotational speeds of the rear wheels on each side.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If skid steering is used to steer the machine, then the machine can change direction, but traction is lost and wheel slip occurs resulting in excessive tire wear
Solution Approach 1:
The rear wheel drive system is segmented into independent left and right side drive units, allowing each side to operate independently. This enables differential speed control where the left and right rear wheels can rotate at different speeds, providing steering capability while maintaining traction through controlled differential rotation rather than uncontrolled skidding
Solution Approach 2:
The system changes the operational parameters by controlling the rotational speed of each rear wheel independently. By adjusting the speed parameter of left and right rear wheels differently during steering maneuvers, the machine achieves directional change while maintaining optimal traction and preventing excessive tire wear
2Ease of operation
If the front wheels are turned to steer the machine, then the machine can change direction, but the front wheels lean and skid causing excessive and uneven tire wear
Solution Approach 1:
Instead of steering through the front wheels as in conventional designs, this invention inverts the steering mechanism by using the rear wheels for directional control. The rear wheels are driven at differential speeds to steer the machine, while the front wheels remain passive and follow the direction determined by rear wheel speed differences, eliminating lean and skid issues
Solution Approach 2:
The system copies the successful steering approach from articulated vehicles (where rear wheel speed differential steers the machine) and applies it to this wide-wheelbase machine configuration, avoiding the problems associated with front wheel steering in machines with broad wheelbases
3Stability of the object's composition
If the machine has a broad wheelbase for stability, then the machine is more stable, but it becomes difficult to make tight corners
Solution Approach 1:
The system introduces dynamic control of rear wheel speeds to enable tight turning radii. By continuously adjusting the speed differential between left and right rear wheels during cornering maneuvers, the machine can achieve tight turns while maintaining stability through active speed control rather than static geometric constraints
Solution Approach 2:
The control system dynamically changes the rotational speed parameter of the rear wheels based on steering requirements. During tight cornering, the system increases the speed differential between left and right rear wheels, allowing the machine to navigate tight corners while the broad wheelbase continues to provide stability
4Ease of operation
If articulation cylinders are used to rotate the front frame, then the front frame can be steered, but the system becomes mechanically complex
Solution Approach 1:
The invention extracts and eliminates the articulation cylinder mechanism from the steering system. Instead of using mechanical articulation cylinders to physically rotate the front frame, the system uses differential speed control of the rear wheels to achieve steering, simplifying the mechanical structure while maintaining steering capability
Solution Approach 2:
The system replaces the mechanical articulation cylinder system with a controlled differential drive system. Instead of using mechanical linkages and hydraulic cylinders to articulate the front frame, the invention uses independent motor control of the rear wheels to achieve steering through speed differential, reducing mechanical complexity
Data Source
AI summary
A steering system for steering a machine having opposing first and second sides with first and second pairs of rotatably mounted rear wheels disposed along the respective sides and at least one rotatably mounted, spaced front wheel. The system includes at least one first drive unit and at least one second drive unit for rotating the rear wheels of the respective pairs, and a steering input device that provides a signal to a controller that produces drive unit request signals to control the drive units to rotate the associated rear wheels along one side at rotational speeds greater than those along the other side to facilitate turning.