How Are Torque Sensors Used In Marine Propulsion Systems?
In marine propulsion systems, torque sensors are primarily installed between the main engine, shafting, and propeller. They perform online measurements of the propulsion shaft's torque, speed, and the calculated shaft power for performance monitoring, energy efficiency management, and fault diagnosis.
Installation Location and Form:
- A flange-type or ring-type torque sensor is mounted on the shaft between the diesel engine or electric motor output and the intermediate shaft/propulsion shaft. Strain gauges measure the shaft's torsional deformation.
- Alternatively, a torque ring/torque can be used, fitted onto the existing shaft without cutting the shaft. Strain gauges are attached to the shaft surface and protected by a rotor ring. The signal is then transmitted to the ship's control system wirelessly or inductively.
- The system typically measures torque and speed simultaneously, and is deployed on the main propulsion shaft or multiple shafts to monitor single-shaft or multi-shaft propulsion power.
Measurement Principle and Signal:
- Full-bridge strain gauges are placed on the propulsion shaft surface. The shaft experiences minute torsional deformation under propeller load, causing a change in resistance. This change is transmitted through a strain gauge bridge, outputting an electrical signal proportional to the torque.
- The on-shaft rotor electronic module amplifies, modulates, and digitizes the strain signal, then transmits it to a fixed receiver or I/O cabinet via a non-contact (electromagnetic/wireless) method.
- The host computer or PLC, combined with torque (T) and speed (n), calculates shaft power, enabling real-time display, recording, and alarm functions for torque-speed-power.
Main applications on ships:
- Propulsion performance and energy efficiency management: Real-time knowledge of the actual shaft power delivered from the main engine to the propeller can be used to optimize speed, pitch, load, and course, reducing fuel consumption and emissions.
- Operating condition monitoring and alarms: Monitors torque fluctuations, overloads, and abnormal torque peaks, triggering alarms or limiting power when limits are exceeded to protect the main engine, gearbox, and shaft system.
- Diagnosis and maintenance: Analyzing transient fluctuations in torque and speed can help diagnose propeller damage, cavitation, abnormal shaft torsional vibration, or gear meshing problems, providing a basis for condition-based maintenance.
Typical System Components:
- On-shaft section: Strain gauges, rotor rings, or flange-type torque sensor body, with built-in signal conditioning and transmission electronics modules. The structure must meet the requirements of large shaft diameter, high torque, and marine environment protection.
- Off-shaft section: Stator coils/receiving antenna, I/O cabinet or torque meter main unit, responsible for power supply, signal demodulation, linearization, and output (analog, serial, CAN, Ethernet, etc.), and interfacing with marine AMS/PMS/VDR systems.
- Host software: Used to display real-time torque, speed, power, and trend curves, with data logging, event alarms, report export, and other functions, supporting monitoring requirements compliant with classification society or military standards.
