Six Sigma based modeling of the hydraulic oil heating under low load operation

Six Sigma based modeling of the hydraulic oil heating under low load operation
Darrius Drew
Industry 4.0
It takes approx. 5 minutes to read this article

A hydraulic oil cooler (or hydraulic oil intercooler) is part of an engine cooling system that uses water to cool the pressurized oil in an internal combustion engine. If a hydraulic oil cooler breaks down, it can cause the oil pressure to rise high enough to damage the engine. Therefore, it’s important to do periodic maintenance on this component so that it continues to work correctly and doesn’t become more costly to repair over time.


The heating phenomena of different types of air intercoolers, water intercoolers, and hydraulic oil coolers have been researched in detail. For determining their heat transfer efficiency, 2D and 3D CFD simulations and experimental analyses have been done for them. Experiments are set up to validate the results by measuring temperature changes on their surfaces during thermal cycling tests. The comparison shows that the accuracy of simulated temperatures is within ±2% compared with those measured experimentally for both water and air intercoolers, which proves that numerical simulation can be used as an alternative to expensive experiments. Through analyzing its heat transfer mechanism, it is found that a water intercooler has better cooling performance than an air one due to a higher effective surface area available for convection cooling. It also demonstrates a hydraulic oil cooler has better cooling performance than the other two kinds due to its unique structure and high effective surface area available for convection cooling. 

Models and Methods

In air intercooler systems, after the combustion of fossil fuels in a multi-cylinder internal combustion engine, high temperature and pressure exhaust gases are cooled before they exit to atmosphere. The cooling is usually achieved by dissipating heat in a very thin layer (i.e., radiation) between an upstream passageway and a downstream structure through which air flows at relatively low speeds. A typical system may consist of air intercoolers on each cylinder bank that cool down gases from each bank prior to their combined passage into a single large water intercooler immediately behind the vehicle’s radiator.

What is the problem?

Hydraulic systems operate at high temperatures and require pressure, but cooling loops need to be small. Air intercoolers are used because water can interfere with certain oils. There is not much data available on air intercoolers, so it’s difficult to create models for them, so they’re often ignored in favor of water intercoolers, which have more information available about them. However, air-based intercoolers are a viable option, and ignoring them leads to inefficient designs for some systems. To remedy that problem, more data needs to be collected on how effective air-based intercoolers really are. In some cases, they may even perform better than water-based ones.

Why we should solve it?

This phenomenon is called condensation overheating, which may lead to severe damage for a lot of machines, and even cause engine failure. By analyzing it in detail, we can learn how to build an efficient oil cooler or air intercooler and make smart use of them. In most cases, if you are using a water intercooler or air cooler as your heat sink for cooling fluid, for example, you should select one with a lower flow rate than another one with a higher flow rate but the same thermal efficiency; otherwise, condensation overheating will happen and results in an extra loss. Solving such issues systematically from a manufacturing process perspective helps improve your company’s overall management efficiency while at the same time increasing revenue through decreasing R&D costs. The six Sigma method provides us with a systematic way to solve these kinds of problems. It includes three steps: define, measure and control. You need to define what is going on (define), measure it accurately (measure), and then control it so that you can get some useful information out of those data. After that, there are several methods available: Control chart method (CCM), Design of experiment method (DOE), Pareto chart method (PCM), etc., which help you find out root causes quickly by comparing different factors and eliminating unnecessary ones step by step until you find out all factors influencing problem effectively.

Results and Discussion

In hydraulic systems, it is common to find different parts with different requirements, so it is necessary to design a piece of equipment able to satisfy all those needs. The hydraulic oil cooler provides a good example. Different hydraulic units are used in construction machines and agricultural machinery, each one with its own specific operating conditions. Since these units have different requirements for their lubrication systems, it is necessary to design a single device capable of serving them all without compromising efficiency or safety. This device must be efficient because it must achieve very high-pressure losses on small volumes and at high temperatures (the maximum temperature in these devices may exceed 150 °C). Additionally, these devices must also prevent the formation of deposits that might affect pumps’ operation or shorten their lifetime.


Hydraulic systems are used in all modern industry, machine, and plant constructions. Their existence is inevitable in any kind of industrial production and technical process. However, compared to other technological elements hydraulic systems are more sensitive to various factors affecting their design, construction, and maintenance. Among these factors, there are mainly external influences (climate conditions) or internal failure modes which could be linked to improper execution during system design or planning process. Thus it is necessary to pay attention to such aspects as thermal behavior and possible wear mechanisms for a given model.

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