Variable-Displacement Hydraulic Motor Eccentric Cam Control
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Solution Overview
Problem
Existing variable-displacement hydraulic motors face challenges in precisely and quickly controlling the position of an eccentric cam due to continuous variations in forces applied by propulsion members, leading to inefficient motor displacement and significant fluid leakages through non-leak-tight rotary seals.
Innovation Solution
A control system comprising a direct-control electrovalve with variable-duration pulses and adjustable throttle elements, combined with a feedback loop and processing unit, allows for precise control of the eccentric cam's position by comparing existing and desired motor displacement, pressure, or speed parameters, ensuring sufficient pressure and reducing fluid leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a proportional valve is operated in a constantly open condition to enable rapid changes in motor displacement, then the speed of displacement change is improved, but the pressure output is reduced to the point of being insufficient to counteract forces on the eccentric cam, causing uncontrolled displacement variations
Solution Approach 1:
The patent applies periodic action by using a double-acting cylinder with alternately activated chambers. The control system opens one chamber while closing the other in periodic cycles, allowing the eccentric cam to be moved in discrete steps. This periodic activation maintains high pressure in the active chamber (since the valve is mostly closed) while still achieving displacement changes, resolving the contradiction between speed and pressure.
2Adaptability or versatility
If the eccentric cam position is constantly corrected to adapt to propulsion member thrust movements, then the adaptability to load conditions is improved, but the eccentric cam position can never be precisely achieved due to constant oscillations
Solution Approach 1:
The patent implements feedback control by using sensors to detect the actual position of the eccentric cam and comparing it with the desired position. The control system processes this feedback information and adjusts the valve activation accordingly, stopping the correction process when the desired position is reached. This prevents constant oscillations while maintaining adaptability to load conditions through precise positioning control.
3Reliability
If the hydraulic circuit is kept under continuous pressure to maintain control feedback, then the reliability of control is improved, but fluid leakage through rotary seals increases significantly
Solution Approach 1:
The patent applies periodic action by maintaining hydraulic pressure only during the brief periods when the valve is activated to move the eccentric cam. Between activation cycles, the hydraulic circuit is depressurized. This periodic pressurization maintains control reliability when needed while dramatically reducing fluid leakage through rotary seals during non-operational periods.
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 enables fast and precise control of motor displacement while minimizing fluid leakage by maintaining hydraulic circuit pressure only during eccentricity transients, achieving simultaneous high speed and precision in motor displacement adjustments.
Implementation Method 1
a double-acting cylinder (350) movable along the axis of the driving shaft and designed to move the eccentric cam (306), changeable in position by means of a direct-control electrovalve (110) having an input for pressurized fluid (500a) and two outputs respectively connected to an associated chamber (350a) of the double-acting cylinder by means of a hydraulic control circuit arranged between the electrovalve and the double-acting cylinder
Implementation Method 2
a direct-control electrovalve (110) which has an input for pressurized fluid (500a) and two outputs respectively connected to an associated chamber (350a) of the double-acting cylinder
Data Source
Figure 1~1c
Figure 2~3
Figure 4a~4c
AI summary
Apparatus for controlling the position of an eccentric cam (306) of a shaft of a variable-displacement hydraulic motor (300), which comprises: - a control and command unit (200), which is feedback-connected between points for detecting one or more existing operating parameters (320a,320b,320c) of the motor (300) and points for entering set parameters (250a,250b,250c) for the one or more existing operating parameters of the motor and which is designed to control operation of a unit (100) for actuating the eccentric cam (306) connected to the shaft of the motor (300), the actuating unit being inserted in the hydraulic circuit (120) of means (350) for moving said eccentric cam (306), wherein said actuating unit (100) comprises a direct-control electrovalve (110) driven by variable-duration pulses emitted by the control and command unit (200) depending on the difference between an existing value (320,320b320c) detected and a desired stored (262) value (250a,250b,250c) of one of said parameters.