Swashplate Angle Sensing via Magnetostrictive Sensor
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Solution Overview
Problem
The control loop of variable displacement hydraulic pumps is prone to instability due to clearances and signal interference from existing sensor technologies, particularly magnetostrictive sensors, which affect the precise control of the swashplate angle.
Innovation Solution
A contactless sensor arrangement using a linear magnetostrictive position sensor aligned parallel or coaxially with the control piston, featuring a magnet as a position marker, eliminates clearances and provides a wear-free design for stable pump control by detecting the position marker's movement and determining the actual swashplate angle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a proportional valve and control piston are used to sense the swashplate angle, then the pump control can be adjusted, but clearances in the control loop cause unstable operation
Solution Approach 1:
The patent replaces the mechanical clearance-based proportional valve and control piston system with a direct magnetic coupling sensor system. The magnetostrictive sensor detects the swashplate angle directly through the pump housing wall without mechanical contact, eliminating the control piston and proportional valve from the sensing path. This substitution of mechanical sensing with magnetic field-based sensing removes the source of clearance-induced instability while maintaining control adjustability.
Solution Approach 2:
The patent introduces a magnetic field as an intermediary to transmit the swashplate angle information from the moving swashplate to the stationary sensor. The magnetic field penetrates the pump housing wall non-contactually, allowing the sensor to detect angle variations without physical connection. This intermediary approach eliminates mechanical clearances and wear while preserving the ability to sense and control the swashplate position.
2Measurement precision
If a mechanical sensor system with clearances is used, then the swashplate angle can be sensed, but mechanical wear occurs reducing reliability
Solution Approach 1:
The patent replaces mechanical contact-based angle sensing with a magnetostrictive sensor that operates through magnetic field interaction. The sensor detects the position of a magnet attached to the swashplate through the pump housing wall without physical contact. This eliminates mechanical wear components while maintaining precise angle measurement capability, significantly improving sensor reliability and durability.
Solution Approach 2:
The pump housing wall serves as a non-magnetic intermediary that allows the magnetic field to pass through for sensing purposes. The magnetostrictive sensor on the stationary side detects the magnet's position on the moving swashplate through this intermediary barrier, achieving contactless measurement that prevents wear while preserving measurement precision.
3Reliability
If a contactless sensor arrangement is used, then wear is eliminated, but the sensor must be precisely aligned with the control piston movement
Solution Approach 1:
The pump housing wall acts as a fixed reference intermediary that establishes a predetermined geometric relationship between the stationary magnetostrictive sensor and the moving magnet on the control piston. This predetermined positioning, built into the housing structure during manufacturing, ensures proper alignment without requiring high-precision field adjustments. The intermediary structure translates the control piston's linear movement into corresponding magnet position changes that the sensor can accurately detect.
Solution Approach 2:
The patent transitions from a complex multi-dimensional mechanical linkage system to a simplified one-dimensional magnetic field sensing arrangement. The magnetostrictive sensor measures only the linear displacement of the magnet along the sensor's active axis, ignoring other spatial dimensions. This dimensional reduction simplifies alignment requirements, as the sensor only needs to be positioned along one primary measurement axis rather than precisely coordinating multiple mechanical degrees of freedom.
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 ensures more stable and predictable operation of variable displacement hydraulic pumps by eliminating clearances and reducing signal interference, resulting in a completely wear-free and stable control process.
Implementation Method 1
the sensor is a linear magneto strictive position sensor and the position marker is a magnet
Data Source
Figure 1
Figure 2~3
AI summary
A sensor arrangement for determining an actual swashplate angle of a swashplate (1) pivotally attached to a variable displacement hydraulic pump, comprises: a control piston (2) operable to control an angle of the swashplate (1) relative to the pump, a position marker (3) arranged on the control piston (2), and a sensor (4) arranged along the control piston (2) to detect a movement of the position marker (3). A method for determining the angular position of a swashplate (1), a controller for controlling the actuation of a control piston (2) of a variable displacement hydraulic pump, and a variable displacement hydraulic pump based on the use of such a sensor arrangement are also disclosed.