Translation of the 1973 ATZ article on the K-Jetronic, Bosch continuous injection system

In this document

Introduction and genesis of the system

The text is the French translation of an article published in the German journal ATZ (No. 11, 1973), noted as following a "brief report" already published in ATZ 6/1973 p. 76. The development of the described system began in 1967, motivated by the search for a replacement "as simple as possible" for the series pump, by taking advantage of nascent electronic injection to avoid any mechanical drive p. 76.

The article recalls previous Bosch experience with continuous injection, notably the system of the Mercedes-Benz 220 SE, "practically a continuous system" p. 76, and mentions the constant-depression carburettor as a prefiguration of the principle p. 77. The air flow ratio to be mastered is given as 1:30 for a linearized measurement, against 1:900 for a Venturi principle "forbidden for the required precision" p. 77.

The design conditions set in advance include: one injection valve per cylinder placed near the intake valve, a high opening pressure, the interchangeability of nozzles without influence on the dosage p. 78. The system is first named "KA" (continuous, without drive), before becoming K-Jetronic after the envisaged introduction of a probe for a catalyst p. 79.

Basic principle and constituent elements

The system combines a float-type air flow meter (retaining disc in a conical funnel) and a fuel distributor with rectangular control slots, joined by a common lever forming the "mixture regulator" p. 79-80. The fundamental equations are detailed:

• air flow meter equation: Q_L = μ_L·A_R·√(2/ρ_L·ΔP_L) p. 81, simplified to Q_L = K₁·y·tgα·√(P_St/ρ_L) p. 82;
• distributor equation: Q_K = μ_K·A_St·√(2/ρ_K·Δp_hy) p. 84, simplified to Q_K = K₂·x p. 85;
• global K-Jetronic equation: Q_L = K₃·Q_K/tgα·√(P_St/ρ_L) p. 86.

Some numerical values given:

Then described are the fuel circuit (roller pump, accumulator, filter, pressure regulator, p. 86-87), the warm-up correction by auxiliary air register and electrically heated bimetal p. 88-89, the starting installation with electromagnetic valve p. 89, and the electrical pump control circuit p. 89-90.

The bibliography cites eight Bosch/MTZ/ATZ technical references from the years 1957 to 1973 p. 90, and the article closes with the detailed legend of the ten announced figures p. 90-92, the continuation being referred to a future issue ("to be continued", p. 90).

Context

The K-Jetronic developed by Bosch remained in automotive history as the most widespread mechanical continuous injection system of the 1970s-1980s, equipping many European manufacturers before the arrival of generalized electronic injection. The journal ATZ (Automobiltechnische Zeitschrift) is, like the MTZ, one of the main German technical publications of the automotive industry.

This period corresponds, at Citroën as elsewhere, to the intensification of research on petrol injection, motivated both by the search for dosage precision and by the new anti-pollution standards emerging in the United States and then in Europe.

Archivist's view

This document is a complete and very detailed technical translation — equations, numerical values, diagrams — of a reference article on the K-Jetronic, produced for the internal documentation of Paul Magès. It testifies to the technological monitoring work carried out on systems competing with or complementary to traditional carburetion p. 76-92.

The numerous handwritten annotations (insertions of technical words, λ symbol, corrections) suggest an attentive reading and an active appropriation of the content, probably with a view to drawing lessons for Magès's own research on fuel supply p. 77-90.

This document is part of a larger file on carburetion and injection, to be compared with the original German text of this article and the clippings from the Revue Automobile on the K-Jetronic.