Subsea Hydraulic Power Unit Cooling Circuit
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Solution Overview
Problem
Existing hydraulic power units for Remotely Operated Underwater Vehicles (ROVs) face limitations in size, weight, and power output, which restrict their performance and maneuverability, particularly due to inefficient cooling mechanisms that lead to hotspot formation and reduced energy density.
Innovation Solution
A hydraulic power unit with a cooling circuit independent of the hydraulic power circuit, featuring an electric motor with a rotor and stator, a distribution pump, and a heat exchange unit external to the housing, where cooled fluid is circulated through distribution conduits to effectively cool the motor components, enhancing power output and reducing size and weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a standard air-filled motor casing is used, then the motor can operate at atmospheric pressure, but the casing requires sophisticated shaft seals and pressure proof design, increasing device complexity
Solution Approach 1:
The patent changes the parameter of the motor casing from air-filled to oil-filled, which is incompressible and can withstand pressure differentials. This allows the casing to be simple and robust without requiring sophisticated shaft seals or pressure proof design, while still enabling operation at atmospheric pressure and deeper depths
2Device complexity
If oil-filled pressure compensation is used, then shaft seal complexity is reduced, but the motor cannot effectively dissipate heat, leading to hotspot formation and reduced power output
Solution Approach 1:
The patent segments the motor casing into multiple cooling zones with separate cooling channels that direct coolant flow to specific high-heat areas such as the stator, rotor, and shaft regions. This targeted cooling approach effectively dissipates heat from critical components, preventing hotspot formation and enabling sustained high power output
Solution Approach 2:
The patent introduces a coolant as an intermediary substance that circulates through cooling channels in the motor casing, transferring heat from the motor components to the surrounding environment. This intermediary cooling system enables effective heat dissipation while maintaining the oil-filled pressure compensation benefits
3Power
If motor size is increased to provide higher power output, then power rating increases, but ROV weight and volume increase, reducing manoeuvrability and increasing buoyancy requirements
Solution Approach 1:
The patent changes the thermal management parameters by implementing an active cooling system with controlled coolant flow rates and temperature differentials. This allows the motor to operate at higher power densities by maintaining lower operating temperatures, thereby providing higher power output from a smaller, lighter motor unit
4Temperature
If conventional cooling systems are used, then motor cooling is provided, but hotspot formation occurs and cooling efficiency is reduced, limiting power output
Solution Approach 1:
The patent segments the cooling system into multiple independent cooling channels, each targeting specific heat-generating components such as the stator windings, rotor, and shaft. This segmented approach ensures uniform heat distribution and prevents hotspot formation, enabling sustained high power output without thermal limitations
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 allows for a power rating twice that of standard motors, with significant weight and size reductions, achieving an energy density of 0.45 kW/kg to 0.35 kW/kg, improving ROV payload capacity and maneuverability while minimizing hotspot formation and increasing efficiency.
Implementation Method 1
a heat exchange unit provided externally to the housing adapted for losing heat to surrounding seawater
Implementation Method 2
the distribution circuit is arranged for direction of cooled fluid from the distribution conduit onto one or more of the rotor, the stator and the stator coils
Data Source
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AI summary
A hydraulic power unit for subsea use comprises a housing (16) containing a fluid, an electric motor (10) mounted in the housing, a distribution pump (17), a heat exchange unit (20) provided externally to the housing and at least one distribution conduit (32) in fluid communication with the heat exchange unit and the housing.