The system discussion within Bosch
From: Lecture by Hermann Scholl, 40 years of Jetronic, 2007
At the beginning of 1970, Bosch was still feeling pretty good about the D-Jetronic. They even thought about getting rid of mechanical fuel injection completely. But the Diesel Division, which was responsible for the mechanical fuel injection, wasn’t ready to give up just yet.
They’d already started developing the purely mechanical K-Jetronic in 1967, citing cost advantages over the D-Jetronic as the main reason. There were also functional advantages, especially the direct measurement of the air sucked in by the engine via an airflow sensor plate, whose deflection was directly linked mechanically to the fuel quantity control system. The main problem was the extremely high manufacturing accuracy required for the slide fuel valve, with the volume variance of around 1 to 50 typical of continuous systems, while simultaneously ensuring a sufficiently uniform distribution between the cylinders.
Fighting back
The K-Jetronic system would have meant the end of D-Jetronic and thus the demise of electronic fuel injection at Bosch. That’s when the Electrical Division fought back. After a week-long retreat in the Swiss mountains, a small group of six employees developed the L-Jetronic system in just a few weeks. The system was a direct hit. Here is a system image from later years, already including the lambda probe.
A key feature was the use of three system-specific integrated circuits developed in-house; it was the world's first application of such technology. And the principle of air volume measurement was adopted from the K-Jetronic, using a rectangular damper connected to a potentiometer.
The potentiometer was a particularly ingenious design. It had a logarithmic characteristic curve. This could be adjusted over its entire course via a seven-stage external voltage divider. This was the only way to control the variance of the air volume of around 1 in 50 using measurement technology.
The air flap was later replaced, first by a hot wire and then by a hot-film air mass flow meter.
A great technical success
L-Jetronic was a resounding technical success and was introduced almost simultaneously with K-Jetronic in 1973. Commercially, however, the L-Jetronic system failed to take off, as most car manufacturers had already decided to switch to K-Jetronic in 1971 or 1972 due to the perceived lack of quality of the D-Jetronic system in the field. This allowed the K-Jetronic system to achieve significant economies of scale in terms of production volumes. In 1976, Bosch produced around 630,000 injection systems, more than three quarters of which were K-Jetronic, mainly due to its lower manufacturing costs.
In the meantime, electronic petrol injection had been transferred from the Electrical Division to the Diesel Division. The Diesel Division asked management to discontinue electronic injection altogether. However, I was able to prevent this by convincing the then Bosch chairman, Mr Merkle, that it would be disastrous for Bosch to abandon this emerging technology.
But time worked in favor of electronics. In the mid-1970s, higher technical requirements and new technological possibilities created additional opportunities for electronic injection. Stricter emission limits also required electronic adjustment of the ignition timing. This was only economically feasible using digital technology.
Bosch's advance development department had been working on a digital engine control system based on microcontrollers since the early 1970s. In the mid-1970s, it seemed promising to develop a digital engine control system for fuel injection, lambda control and ignition advance. The management decided - or at least allowed it - that Motronic would be developed in the Electrics Division, which was responsible for ignition. It was used for the first time at BMW. BMW, like VW, had retained electronic injection in some models in addition to the K-Jetronic; BMW had stuck with the D- and L-Jetronic for its luxury class vehicles.
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KE-Jetronic (1983): Hydraulic control unit -
KE-Jetronic (1983): Engine control unit
Motronic was superior to KE-Jetronic
The 1979 start-up was successful. The functional content of the Motronic was, comparatively speaking, still very modest, in line with the state of digital technology at the time. We needed seven large circuits: a microcontroller, one input and one output chip and four memories of 1 K each.
The K-Jetronic gradually reached its functional limits, especially in conjunction with the regulated catalytic converter. An electronic upgrade to the KE-Jetronic was therefore necessary. More and more electronics were installed. And the manufacturing costs were ultimately considerably higher than those of the Motronic. The Motronic was superior to the KE-Jetronic in terms of system technology.
The internal dispute at Bosch between KE-Jetronic and Motronic continued bitterly for several years. The electrical (K1) and diesel and gasoline (K5) divisions fought over every customer project, sometimes with competitive prices that were not covered by cost accounting. Both divisions got somewhat out of control, especially as they belonged to different management departments. This cost Bosch a lot of money, mainly through a sustained reduction in price levels. But the aggressive pricing ultimately led to more gasoline injections in Europe. It was a typical, albeit in this case unintentional, volume strategy that ultimately worked.