Powerful Symbiosis

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Mechanical engineering is the flagship dis­cipline of the STIHL Group. The company’s growth was based on it. Digitalization, how­ever, means that electronics and software engineering are becoming increasingly important. The STIHL innovations that result when a perfect connection of old and new knowledge is made possible can be seen in the STIHL MS 500i – the world’s first gasoline-powered chain saw with electronic fuel injection.

THE INITIAL IDEA

The year is 1957. Konrad Adenauer is starting his third term as Chancellor, and Germany’s economic miracle, or “Wirtschaftswunder,” is in full bloom. Televisions are appearing in more and more households. Borussia Dortmund is German soccer champion for the second season in a row. And at this time a new idea started forming at STIHL. Hans Peter Stihl, still a university student, was preparing his final thesis. He was tinkering around with a BLK engine, wanting to give it fuel injection. “Of course, my work then was not ready for production – it was more of a general investigation,” recalls the oldest son of company founder Andreas Stihl. At the same time, a smile comes across his face – as he remembers how back then he had shown it to all the doubters and even amazed professors.

“The machine we see today is unbeatable.”
ARNO KINNEN
Easy and reliable starting in all operating conditions and automatic elevation adjustment when first starting the saw are the distinguishing features of the MS 500i.

TRIED AND TESTED INNOVATIVE THINKING

Although this prototype has not survived the 60 years since it was created, the idea of launching a hand-held fuel injection power tool has endured. The newly introduced STIHL MS 500i is the first chain saw with electronic fuel injection. Everything began at the start of the 2000s with special tests at the Karlsruhe Institute of Technology, which resulted in the STIHL TS 500i project – the world’s first cut-off machine equipped with electronic fuel injection. Based on the success of this project, the development of the MS 500i was started. Project Leader Arno Kinnen and Functional Coordinator Clemens Klatt lead a large team that focuses on a new way of working, fusing classical mechanical engineering and modern electronics and software.


The expectations placed on the new saw were high – to reach a milestone in high performance and lightweight construction while retaining STIHL’s core values of durability and quality. It wasn’t only the injection system that needed to be specially adapted to accomplish these lofty goals. High RPMs were required, as well as lightweight, robust design, strong acceleration and other markers of STIHL performance – even at temperatures down to minus 40 degrees Celsius. “We designed the saw on paper from the ground up to get the most out of it,” recalls Kinnen. In many respects, the team was in uncharted territory. The saw incorporates new components and new functionality associated with fuel injection, while also relying on classical mechanical engineering principles to achieve a lightweight design. Especially in this area, a fuel injection system offers many advantages. Conventional control units get their energy from rotating magnets in the fan wheel. In contrast, the fuel injection control unit is powered by a generator and can thus be positioned freely in the machine. The resulting freedom leads to a much smaller fan and thus a more compact engine.

The saw has been put through its paces in the forest. It is suitable for felling and processing timber, including the harvesting of hardwoods.

DUET OF DISCIPLINES

STIHL is well versed in the design and development of carbureted saws. “The additional know-how we have generated in recent years, for example in the fields of measurement technology and software development, is enormous,” says Klatt, referring to the special coordination with software engineering. “We are highly integrated in this area, and the interaction of the departments is crucial.” What now takes a few days in software development, used to take several weeks. If the hardware is running, it is possible today to advance development within a very short time by adapting the software.

“The MS 500i is a brand-new type of saw. And it represents a whole new kind of collaboration at STIHL.”
Clemens Klatt, FUNCTIONAL COORDINATOR
Even the composition of the core project team shows how many disciplines are united by the MS 500i: (from left) Arno Kinnen, Project Leader, Michael Unterkircher, Coordinator of Software, Electronics and Mechatronics, Marcel Förster, Design Coordinator, Ulrich Kapinsky, Testing Coordinator, and Clemens Klatt, Functional Coordinator.


The result of this collaborative integration of disciplines is a uniquely intuitive product with unprecedented performance and the best power-to-­weight ratio of any professional chain saw, delivered with proven STIHL quality. And yet it is also a battery-less power tool with a “less is more” motto. As a result, it has fewer cable connections and no carburetor. The focus on essential hardware components and intelligent software makes the machine robust and low-maintenance. Also, for the first time ever in a chain saw, there is an error registry in the control unit, which helps the servicing dealer with diagnostics and other maintenance. “In almost all respects, we have pushed the limits of what’s possible with this machine,” says Klatt.

MS 500i in Detail

A true powerhouse, a machine for professionals. And yet the STIHL MS 500i is even more. It is the first chain saw with an electronic fuel in­jection, the result of years of ex­perience in classic mechanical engineering and the latest STIHL developments in software and electronics.

Click on one of the Hotspots to get more information.
Purger and injection pump
Stop button and temperature sensor
Throttle
Locking shroud
Generator
Sensor unit
Injection valve
Control unit
Purger and injection pump

Eases the start-up process considerably. Purge, pull – done. The injection pump keeps the fuel pressure constant and ensures that the fuel injector will have the right amount of fuel and run at optimum pressure at any given time during use.

Stop button and temperature sensor

At the push of a button, the machine can be switched off and can be restarted immediately without any further action. The integrated sensor measures the ambient temperature.

Throttle

The MS 500i has no carburetor. The operator has complete control of the speed and power of the machine with the throttle.

Locking shroud

The shroud is locked in place with a quarter-turn closure. With just one turn, the machine can be opened for cleaning.

Generator

Generates the electricity needed for operation of the saw. In addition, it continuously updates the control unit with the crankshaft position and engine speed.

Sensor unit

Measures the temperature and pressure in the crank case and transmits the information to the control unit.

Injection valve

With each revolution, it injects the ideal amount of fuel – up to 230 times per second.

Control unit

The centerpiece of the STIHL injection system continuously analyzes the information from the generator and sensors as it controls fuel injection and ignition: The control unit determines the load on the machine and the power demand of the user. From this, the required fuel quantity, injection duration and appropriate ignition timing are calculated. Based on this data, the injection valve is controlled with precision and ignition is initiated.

Purger and injection pump

Eases the start-up process considerably. Purge, pull – done. The injection pump keeps the fuel pressure constant and ensures that the fuel injector will have the right amount of fuel and run at optimum pressure at any given time during use.

Stop button and temperature sensor

At the push of a button, the machine can be switched off and can be restarted immediately without any further action. The integrated sensor measures the ambient temperature.

Throttle

The MS 500i has no carburetor. The operator has complete control of the speed and power of the machine with the throttle.

Locking shroud

The shroud is locked in place with a quarter-turn closure. With just one turn, the machine can be opened for cleaning.

Generator

Generates the electricity needed for operation of the saw. In addition, it continuously updates the control unit with the crankshaft position and engine speed.

Imjectiom valve

With each revolution, it injects the ideal amount of fuel – up to 230 times per second.

Control unit

The centerpiece of the STIHL injection system continuously analyzes the information from the generator and sensors as it controls fuel injection and ignition: The control unit determines the load on the machine and the power demand of the user. From this, the required fuel quantity, injection duration and appropriate ignition timing are calculated. Based on this data, the injection valve is controlled with precision and ignition is initiated.

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