Mechanical engineering meets software: The STIHL MS 500i gasoline-driven chainsaw

Powerful symbiosis: STIHL MS 500i

Mechanical engineering is STIHL’s core specialty, and the foundation on which the company was grown. However, digitalization is bringing in new disciplines too – electronics and software engineering are becoming increasingly significant. The STIHL MS500i epitomizes the innovation that is facilitated by perfectly integrating old and new knowledge: The world’s first petrol chainsaw with electronic injection.

The MS 500i represents a completely new type of saw, and a whole new way of working together at STIHL.

Clemens Klatt, Function coordinator

THE FIRST IDEA

The year is 1957. Konrad Adenauer is starting his third term as Chancellor, the German economic miracle is in full swing, more and more households feature a television set of their own, Borussia Dortmund are winning the title of German football champion for the second time in a row. And this is the time when an idea makes the first mark that will shape STIHL. Student Hans Peter Stihl is preparing for his graduation. He is tinkering with a BLK engine and wants to equip it with injection. “Of course what I did was not ready for series production, more an investigation of the principle,” remembers the oldest son of company founder Andreas Stihl. A smile flickers across his face – after all, he nonetheless demonstrated it to all the doubters at the time and amazed even experienced professors.

RETHINKING TRIED-AND-TESTED APPROACHES

Although this prototype has not survived the past 60 years, the idea of bringing a hand-held power tool with injection to the market persisted. The STIHL MS 500i is now the first chainsaw with electronic injection. In the early 2000s, it began with special tests at the Karlsruhe Institute of Technology. These resulted in the STIHL TS500i series project, the first cut-off machine with electronic injection. The MS 500i project was built on this foundation. Project Manager Arno Kinnen (left) and Function Coordinator Clemens Klatt are two heads of a large team which exemplifies a new approach, embracing the fusion of classical mechanical engineering with advanced electronics and software.

High requirements for the new saw

A milestone in performance and lightweight construction while maintaining the distinct STIHL values of longevity and quality: Achieving this meant that more than just the injection had to be specially adapted for the tool. High engine speeds were required, as well as lightweight construction with a robust design, high performance, good acceleration and other features characteristic of STIHL performance – and it had to deliver that even at temperatures as low as minus 40°C. “We built the saw on paper from scratch to get the most out of it,” recalls Arno Kinnen.

STIHL enters new territory

The team had to break entirely new ground in many respects: For instance in the new and further development of injection components and functions, and also, on the classic mechanical engineering side, lightweight construction. Of course, injection offers many advantages in the latter area in particular. Whereas conventional control units draw their energy from rotating magnets in the fan wheel, the injection control unit is supplied by a generator and as such can be freely positioned in the machine. The resulting scope facilitates a significantly smaller fan wheel and therefore a more compact power unit.

A DUET OF DISCIPLINES

STIHL is familiar with the construction and redesigning of carburetor saws. “The additional expertise we have generated in recent years, for example in the fields of measurement technology and software development, is enormous,” reports Clemens Klatt, referring particularly to the coordination processes in software engineering. “We are highly integrative in this area, and cross-department interaction is crucial.” What can now be achieved within a few days of software development used to take several weeks. If the hardware is in place, it is possible to generate major development progress within a very short time by adapting the software.

The result of the perfect duet of disciplines is a unique, intuitive product with unrivaled performance and the best power-to-weight ratio of all professional chainsaws of proven STIHL quality. And yet it is also a battery-free machine built with a “less is more” approach. One result is fewer cable connections and the absence of a carburetor. Focusing on the essential hardware components and intelligent software functions makes the machine robust and low-maintenance. For the first time in a chainsaw, the control unit also has a fault memory, which supports maintenance at the specialist dealer providing service. “We have pushed the limits of what is possible with this machine in almost all respects,” says Clemens Klatt.

The MS 500i in detail

A real powerhouse, a professional machine. But the STIHL MS 500i is even more than that: It is the first chainsaw with electronic injection, the result of many years of experience in classical mechanical engineering and the latest developments in software and electronics.

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Overview of components and functions

Purger and injection pump: Makes the starting process much easier. Purge, pull – and done. The injection pump keeps the fuel pressure constant and guarantees that sufficient fuel is available to the injection valve at an optimum pressure at all times during operation.

Stop button and temperature sensor: The stop button is just as easily accessible as the purger. The machine can be switched off by pushing the button and then restarted immediately without any further action. The integrated sensor measures the ambient temperature.

Throttle valve: The MS 500i no longer has a carburetor. The user can set the speed and power of the machine by changing the position of the throttle valve.

Shroud lock: The shroud is centrally attached with a quarter-turn catch. This means just one turn is needed to open the machine for cleaning.

Generator: Generates all the power to run the saw. It also continuously informs the control unit about the crankshaft position and the engine speed.

Sensor unit: Measures the temperature and pressure in the crankcase and transmits the information to the control unit.

Injection valve: Injects the ideal fuel quantity with each revolution, as determined by the control unit – up to 230 times per second.

Control unit: As the hub of STIHL Injection, it constantly analyses information from the generator and sensors to control fuel injection and ignition: The control unit uses the data from the sensors to determine the machine load status and the user’s preferred power level. The required fuel quantity and injection duration as well as the appropriate ignition timing are calculated on this basis. The injection valve is then actuated with pinpoint accuracy and ignition is initiated.