Steering Authority Control for Differential Drive Vehicles
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Solution Overview
Problem
Vehicles with front wheel differential hydraulic drive systems face challenges in steering response at higher speeds, making manual operation difficult due to the sensitivity and response time of the front differential hydraulic drive system, particularly when primary steering authority is provided by differential rotational speeds of the front wheels.
Innovation Solution
A steering control system that reduces the steering sensitivity of the front differential hydraulic drive system by diverting a portion of the hydraulic fluid flow using a second front drive control valve, allowing the rear steering system to provide more steering authority, thereby improving vehicle stability at higher speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the front differential hydraulic drive system provides primary steering authority through differential rotational speeds, then steering response to operator input is achieved, but steering sensitivity becomes excessive and vehicle stability deteriorates at higher speeds
Solution Approach 1:
The system dynamically changes the steering ratio parameter based on vehicle operating conditions, particularly ground speed. At higher speeds, the steering ratio is reduced to decrease steering sensitivity and improve stability, while at lower speeds the normal steering ratio is maintained for adequate steering response
Solution Approach 2:
A steering authority control system acts as an intermediary between the operator's steering input and the front differential hydraulic drive system. This control system modulates the steering authority of the front wheels based on vehicle speed and operating conditions, preventing excessive steering sensitivity at high speeds while maintaining operational steering capability
2Adaptability or versatility
If the front wheels are mounted in a fixed forward facing orientation and steering is achieved through differential rotational speeds, then steering capability is provided, but steering sensitivity and response time become challenging at higher ground speeds
Solution Approach 1:
The steering system transitions from a static configuration to a dynamic one by enabling the rear wheels to rotate about their vertical axes. This dynamic rear wheel steering capability complements the differential drive steering, providing adaptive steering response that adjusts to varying ground speeds and operating conditions
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 reduced steering sensitivity of the front differential hydraulic drive system enhances vehicle stability and handling by increasing the contribution of the rear steering system, especially during manual operation at higher speeds.
Implementation Method 1
A pump is operable to circulate a hydraulic fluid
Implementation Method 2
A first front drive control valve is disposed in the hydraulic drive fluid circuit. The first front drive control valve is operable to output a defined fluid flow in response to the steering command input
Implementation Method 3
A second front drive control valve is disposed in the hydraulic drive fluid circuit, between the first front drive control valve and the front differential hydraulic drive system. The second front drive control valve is operable to selectively divert a portion of the defined fluid flow output from the first front drive control valve
Implementation Method 4
A front differential hydraulic drive system is operable to drive a front left wheel at a first rotational speed and a front right wheel at a second rotational speed. The second rotational speed is different than the first rotational speed to turn the vehicle
Implementation Method 5
A rear steering system has at least one rear wheel, e.g., a rear left wheel and a rear right wheel. Each rear wheel is rotatable about respective vertical axis a predetermined angle to turn the vehicle in response to the steering command input from the operator
Data Source
AI summary
A vehicle includes a rear steering system and a front differential hydraulic drive system. A first front drive control valve is operable to output a defined fluid flow in response to a steering command input. A second front drive control valve is operable to selectively divert a portion of the defined fluid flow output from the first front drive control valve. When the vehicle is operating in a pre-defined condition, a steering controller may control the second front drive control valve to divert a portion of the defined fluid flow from the first front drive control valve to define a reduced fluid flow, which is communicated to the front differential hydraulic drive system, to reduce a steering ratio of the front differential hydraulic drive system relative to the rear steering system, to desensitize steering provided by the front differential hydraulic drive system.