Hydrostatic Transmission Pressure Control for Mobile Machines
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Solution Overview
Problem
Conventional hydrostatic transmission systems experience sudden pressure increases in the series duct, leading to destabilization of wheels and hydraulic apparatus damage, especially on difficult terrains and during turns, due to the fixed pressure-setting pressure-limiting valve which can result in insufficient torque or excessive pressure.
Innovation Solution
The pressure-limiting valve is controlled as a function of the high pressure of the pump, allowing the maximum allowable pressure in the series duct to be dynamically adjusted based on the torque required, connecting the series duct to the low-pressure circuit when the pressure reaches a predetermined fraction of the high pressure, thereby limiting torque transmission to a mechanically acceptable value and preventing excessive pressure increases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a pressure-limiting valve is set to a high fixed pressure to avoid untimely opening, then sufficient torque is maintained, but sudden pressure increases and structural fatigue occur
Solution Approach 1:
The pressure-limiting valve transitions from a fixed pressure setting to a dynamic control mechanism that adjusts the pressure threshold based on steering angle. The valve opens at different pressure levels depending on whether the vehicle is turning or traveling straight, allowing the system to adapt pressure limitations to current operational conditions rather than using a static high-pressure setting
Solution Approach 2:
The control pressure threshold parameter of the pressure-limiting valve is changed dynamically based on steering angle input. When a turn is detected, the threshold is lowered to allow earlier pressure relief; when traveling straight, the threshold remains higher to maintain torque. This parameter adaptation resolves the contradiction between maintaining sufficient torque and preventing sudden pressure increases
2Reliability
If a pressure-limiting valve is set to a low pressure to prevent sudden pressure increases, then pressure stability is improved, but insufficient torque is generated
Solution Approach 1:
The system dynamically adjusts the pressure threshold based on operational context rather than using a fixed low setting. During straight-line travel, the valve maintains a higher pressure threshold to preserve torque, while during turns, it lowers the threshold to prevent pressure spikes. This dynamic behavior eliminates the need for a consistently low pressure setting
Solution Approach 2:
The system incorporates feedback from steering angle sensors to modulate the pressure-limiting valve's threshold. This feedback mechanism allows the valve to distinguish between normal torque demands during straight travel and conditions requiring pressure limitation during turns, thereby maintaining sufficient torque when needed while preventing excessive pressure increases
3Reliability
If a steering-angle-dependent pressure-limiting valve is used to eliminate pressure increases during turns, then pressure stability during turning is improved, but pressure increases during straight-line travel are not prevented
Solution Approach 1:
The pressure-limiting valve is designed to handle multiple operational scenarios through a single unified control mechanism. By incorporating both steering angle detection and variable threshold control, the valve provides universal protection against pressure increases during turns while also maintaining torque during straight-line travel, eliminating the need for separate control strategies for different driving 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
This solution effectively limits sudden pressure increases, ensuring stable torque delivery to wheels without depriving them of necessary drive torque, reducing the risk of wheel loss of grip and hydraulic apparatus fatigue, while maintaining drive torque during varying terrain conditions.
Implementation Method 1
said at least one pressure-limiting valve being suitable for connecting said series duct to the low-pressure circuit while being controlled as a function of the high pressure of the pump
Data Source
AI summary
Hydrostatic transmission apparatus for a vehicle having a front group of drive members and a rear group of drive members, a pump, a front motor and a rear motor contributing to driving respective ones of the front and rear groups of drive members; a first one of the motors and a second one of the motors connected to the first motor via a series duct also being connected to the main orifices of the pump, thereby constituting a closed transmission circuit; at least one pressure-limiting valve being interposed between the series duct and a low-pressure circuit, and being suitable for connecting the series duct to the low-pressure circuit while being controlled as a function of the high pressure of the pump. The pressure in the series duct is thus effectively limited to a pressure representative of the pressure necessary for driving the vehicle.