Manufacturing specialist’s work on a hydraulic tensioner reveals the benefits of system simulation for fast-paced innovation
System simulation plays important role in the innovation process
Part of the Total Group, Hutchinson is a large company of 27,000 employees, specialized in manufacturing rubber-made products. Hutchinson Transmission is a mid-size division of 800 employees that develops and manufactures mechanical systems, mainly for engine accessory drives.http://www.hutchinsontransmission.com
- Châlette-sur-Loing, France
Hutchinson Transmission is one of the many companies that rely today on system simulation in its innovation process. Part of the Total Group, Hutchinson is a large company of 27,000 employees, specializing in manufacturing rubber-made products. Hutchinson Transmission is a mid-size division of 800 employees that develops and manufactures mechanical systems, mainly for engine accessory drives. Belts, tensioners, pulleys and transmission systems are the components that Hutchinson employees engineer for the automotive and other mechanical industries markets.
Fabien Zarka, manager of the systems and mechanical products department at Hutchinson Transmission, is a skilled system simulation expert. In the course of his career, he has been deeply involved with system simulation using world-class tools such as Simcenter Amesim software. System simulation is the creation of multi-physics models that define a controlled, regulated system with a limited number of parameters. Those simplified models describe the essence of the system, mainly the inner power transfers, giving a view on its transient behavior. In other words, system simulation tries to understand the flow of energy or power within a regulated system over time. Since it only uses a reduced set of parameters, it can be started at any predesign or specification stage.
At Hutchinson Transmission, Zarka employs Simcenter Amesim to better understand the impact of various parameters on product designs.
In this case, Zarka takes the example of a modelization study performed on a hydraulic tensioner to note the advantages of system simulation in the innovation process.
The modern challenges of innovation
A hydraulic tensioner is a system that applies a force to an object to maintain it in tension. It ensures that, independent of motion, the connection between elements remains intact, without any element becoming overstressed. In an engine, a hydraulic tensioner is fitted to the transmission belt. On one hand, it applies a force on the belt during its complete lifetime to ensure a constant belt tension in the accessory drive. On the other hand, it damps forces to increase belt durability and power transmission by limiting phenomena such as belt slipping, belt flapping or tension variation. The tensioner has to perfectly fulfill those functions at all times, during the start, steady state, transient or stop operation phases of the accessory drive.
In itself, a hydraulic tensioner is a relatively simple system with well-defined functions of tension and damping: the harsher the tension, the lower the damping. Finding the right balance between tension and damping has always been the task of Hutchinson engineers. But the previously simple requirement has evolved to become a complex demand. A few years ago, Hutchinson Transmission would only offer one or two different tensioner models. Nowadays, customers request bespoke items. Damping, filtering characteristics and shape of the tensioner, for example, need to be adjusted to ensure maximum performance and durability of the accessory drive.
To select the characteristics of a new tensioner, Hutchinson Transmission engineers use mechatronic system simulation in their innovation process. It helps them quickly fine-tune parameters. For example, they can easily lower the damping level when the engine rotates at low RPM or increase it at high frequencies to counter the effect of disturbing harmonics. System simulation is essential to develop innovative products in shorter time, but also serves the purpose of solving quality problems in the production phase.
Studies reveal critical parameters
Hutchinson has performed simulation studies to understand the impact of design parameters on the damping performance of the hydraulic tensioner. As a first step, engineers have modeled an existing type of tensioner in Simcenter Amesim. This model has been correlated with test results of the same mass-production tensioner. The analysis has revealed a good match between model and product over the full frequency range.
Engineers have used the model to perform a sensitivity analysis. Each parameter under study is isolated and modified, so that its influence on the complete system can be exposed; for example, engineers have compared the dynamics of two different valve types: a ball valve and a spring valve. The ball valve appears to perform better since it increases the force levels and the power dissipation at higher frequencies. The effect of oil viscosity on the system’s performance has also been studied. Higher-viscosity oil increases force level at low frequencies, as well as valve reaction time. At high frequencies, the force level decreases. This reveals that oil viscosity highly influences the system’s performance and damping capacity.
The study highlights the important parameters that improve the tensioner’s damping performances over different amplitudes and frequencies. Surprisingly enough, the most critical parameters are not, as first expected, the physical damping characteristics, but rather fluid characteristics such as oil viscosity, oil compressibility or hydraulic inertia.
The true role of system simulation
Experts like Zarka stress the importance of a proper use of system simulation. “Engineers sometimes try to complicate a model that seems not accurate,” says Zarka. “They believe that the physics behind the model are not right. But the analysis often reveals that the true source of the problem is missing or incorrect parameters. A pure mathematical approach can be erroneous. Reviewing your formula will not help if your hydraulic oil parameters are incorrect. In Simcenter Amesim, we have the possibility to enter many parameters, such as the bulk modulus, the temperature, the pressure, the air compression rate in oil. The software delivers a very accurate model, provided we have entered the right set of parameters. For us, getting these parameters from the oil suppliers can be a real challenge. In the product supply chain, oil or rubber providers do not feel involved in the engineering process. Data such as oil viscosity, oil aeration or oil compressibility are too often unknown parameters.”
According to Zarka, simulation is not to be considered in an absolute way. It remains inseparable from testing. Prototype testing is still needed in the process to validate simulated models or as input for future designs. A simulation tool like Simcenter Amesim is excellent to acquire a relative idea of the system’s functionality. By showing the way to the final design, it helps reduce time and the costs of research and development (R&D) processes. “The multi-physics system modeling of the hydraulic tensioner has reduced the number of necessary prototypes by half, from 15 down to 6 or 7,” notes Zarka. “This process improvement also saves us about 6 months of development time.”
An inspiring future
Zarka is convinced that system simulation will gain more and more importance in the industry. Easy-to-use tools that can be employed not only by expert engineers but also by job starters and technicians are in demand. “Simcenter Amesim is really a very reliable and user-friendly tool,” says Zarka. “Simcenter Amesim can be used by people with less experience or expertise. I envision the software’s evolution toward even more userfriendliness. Ideally, any technician should be able to perform some standard analysis in the development process. Super components in Simcenter Amesim already offer great ergonomics for non-experts.” For the future, Zarka dreams of inverse simulation: “This would be an interesting evolution of the software. The engineer would design the system with all its desired characteristics and the software would compute the parameters required to achieve the anticipated result.”