The project to get noise down to low levels in our hydraulic excavators started off in the spring of 2001. The goal was 10 dB less noise. That meant getting the level of noise that people can hear down to below one half. It could be called a reckless target. Hajime Nakajima, who has specialized in low noise level attainment all through his 30 years in the company, relates the background story with passion. "The fact that noise regulations had become stringent played a part, but I think really it was the willfulness of us engineers that set that high target. We wanted to win back the No. 1 low noise ranking more than anything." In the first half of the 1990s Kobe Steel had boasted its leading low-noise technology. The reason why they subsequently let rivals catch up was that there was little demand for low noise at the time, and because of cost-paring. The engineers' frustration from that period was a spur to their later efforts.
Kazuhiro Ueda, who led the design work for the low-noise project, looks back with these words: "The culprits in the noise are the engine and the cooling fan. To make them quiet all you have to do is seal them in so that the noise can't get out, but then the air won't pass through and that will cause overheating. What we came up with for that was the 'wind path' method".
This "wind path" method regards the air pathways that link the intake and exhaust ports to the engine as ducts. Because sound will be damped if it strikes against the duct walls, the ducts are appropriately bent to provide such damping while securing passage of air. Provided that unwanted gaps are blocked out, this can be expected to yield drastic reduction in noise.

Hajime Nakajima
Senior Manager,
Project Group
System & Component Development Department
Engineering & Manufacturing Division
Role in iNDr project:
Coordinator of component development

Kazuhiro Ueda worked on a series of experiments with the staff of the Kobe Steel Mechanical Engineering Research Laboratory. At the end of two years of trial and error he completed a remodeled machine incorporating the new system in the summer of 2003. Its noise was 9.4 dB lower than previous machines. Cheers went up from the staff and management at this outstanding achievement.

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Around that time, development of a filter that permitted radiator clogging to be cleaned up with ease was at an advanced stage. As both noise reduction and dust-proofing were subjects connected with air intake/exhaust, the two naturally got linked together. That was how the concept of iNDr came about.

But suddenly iNDr's progress encountered an obstacle. Its installation in the conventional models (the most standard models with the largest production volumes) was canceled. Instead, it was to be installed on a limited basis in the SR model, which is used in constricted worksites and prioritizes low noise levels. This policy turnaround gave rise to another problem. Explains Shigeaki Saito, who as models manager heads up the design work for the conventional models: "There were just too many factors rendering iNDr unsuitable for the conventional models. It was an agonizing decision but we finally took it. Inasmuch as hopes had been pinned on iNDr as the core feature of the next-version conventional models, it sent a shock running all through the company."

Shigeaki Saito
Group Manager,
Mini & Large Excavator Group
Hydraulic Excavator Engineering Department
Engineering & Manufacturing Division
Role in iNDr project:
In charge of conventional models

Masaaki Murakami is in charge of SR models and reveals his true feelings at the time: "I didn't think it was possible. Sure, the characteristic feature of the SR is that it's compact, but the engine and other basic parts are the same as in the conventional models. Adding a bended duct and filter to it would be quite a feat. Like forcing in a screw with the wrong kind of thread, was how I saw it." The hardest part in the matter was to find space for a counterweight to stabilize the body.
Shintaro Sakitani, in charge of exterior and interior of SR models, averts his eyes as he remembers: "The inside was crowded with parts. But that didn't mean we could let anything protrude to the outside. So what we did was we extended the length of the counterweight up to the maximum possible, and put the air intake and exhaust ports in there. This idea was a breakthrough, including the fact that it resulted in a design that emphasized the iNDr."

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In the fall of 2005 an error was found in the design of the prototype, which had finally been completed one year behind schedule. The noise level was a mere 2 dB quieter and it was back to the drawing board. Ultimately it was only in the following year that a machine worthy of an "extreme-low noise" appellation was completed – at the end of toil and hard struggle that had lasted six years. "The most moving thing was when we got words of praise for it from the people who used it at sites", remarks Murakami with a smile. His comment is met with grave nods from all his colleagues. They have already started on the race to the next target level.