Hydrostatic Transmission Offset Axes Minimize Dead Volume
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Solution Overview
Problem
Hydrostatic transmissions with bent axis-type axial piston units experience significant power loss due to decompression losses, which increase quadratically with pressure, especially at lower pivot angles, leading to substantial energy loss.
Innovation Solution
The rotational axes of the axial piston units are offset with respect to the pivot axis of the dual yoke or swashplate, ensuring that pistons remain near the bore end at dead center for all pivot angles, minimizing dead volume and reducing power loss, while compensating torques to maintain a compact and cost-effective servo system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the rotational axes of the axial piston units are aligned with the pivot axis of the dual yoke, then the control torques are relatively low and the servo system can be kept small, but significant power loss occurs due to decompression losses increasing quadratically with pressure
Solution Approach 1:
The rotational axes of the two axial piston units are deliberately offset asymmetrically with respect to the pivot axis of the dual yoke. This asymmetric arrangement creates different lever arms for the two units, allowing the high-pressure forces to act more effectively in minimizing dead volume while the torques from the two units compensate each other, reducing the net control torque required
Solution Approach 2:
The two axial piston units are positioned and offset in such a way that their torques counterbalance each other. The offset arrangement creates a torque compensation effect where the torque required to pivot one unit is offset by the torque from the other unit, allowing the use of smaller servo pistons while maintaining the ability to control the pivot angle
2Loss of energy
If the pistons are positioned to extend close to the bore end at maximum pivot angle, then decompression volume is minimized at that angle, but dead volume expands significantly at lower pivot angles causing high decompression losses
Solution Approach 1:
The problem is solved by introducing a new dimensional parameter: the offset of the rotational axes from the pivot axis. Instead of adjusting piston position within the bore along the single dimension of piston stroke, the invention offsets the entire rotational axis in a perpendicular dimension, creating a geometric relationship where the lever arm varies with pivot angle to maintain minimal dead volume across the full range of motion
Solution Approach 2:
The invention changes the geometric parameters of the system by offsetting the rotational axes from the pivot axis by a specific magnitude. This parameter change transforms the dead volume characteristics, ensuring that pistons remain in the direct vicinity of the bore end at dead centre for all pivot angles, thereby minimizing decompression losses across the entire operating range
3Loss of energy
If the rotational axes are offset from the pivot axis, then dead volume is minimized at all pivot angles, but torques exerted by the piston units increase requiring larger servo system components
Solution Approach 1:
Two axial piston units are merged into a single dual yoke assembly with coordinated rotational axes. The units work together in a coordinated manner where their torques combine and compensate, allowing the system to achieve the benefits of offset axes while maintaining manageable control torque levels through the synergistic interaction of the two units
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 configuration significantly reduces power loss by minimizing dead volume expansion from high to low pressure, allowing for a smaller servo system and lower operational costs with increased reliability.
Implementation Method 1
hydrostatic transmission having two bent axis-type axial piston units which are operated alternately as a pump and as a motor
Implementation Method 2
power loss which is caused substantially by decompression losses
Data Source
AI summary
The invention relates to a hydrostatic transmission having two bent axis- or swashplate-type axial piston units which are operated alternately as a pump and as a motor, with the two axial piston units being adjustable together with a pivotable dual yoke or by means of a pivotable dual swashplate. In order to minimize the dead volumes of the two axial piston units, the rotational axes of the two axial piston power units are offset with respect to the pivot axis of the dual yoke or of the swashplate by a magnitude such that, at all pivot angles, the power unit pistons, at dead center, are located in the direct vicinity of the bore end of the cylinder block.