Gasoline-engine management Gasoline Fuel-Injection System K-Jetronic Technical Instruction
Published by: Robert Bosch GmbH, 2000 Postfach 30 02 20, D-70442 Stuttgart. Automotive Equipment Business Sector, Department for Automotive Services, Technical Publications (KH/PDI2). Editor-in-Chief: Dipl.-Ing. (FH) Horst Bauer. Editorial staff: Dipl.-Ing. Karl-Heinz Dietsche, Dipl.-Ing. (BA) Jrgen Crepin. Presentation: Dipl.-Ing. (FH) Ulrich Adler, Joachim Kaiser, Berthold Gauder, Leinfelden-Echterdingen. Translation: Peter Girling. Technical graphics: Bauer & Partner, Stuttgart. Unless otherwise stated, the above are all employees of Robert Bosch GmbH, Stuttgart. Reproduction, copying, or translation of this publication, including excerpts therefrom, is only to ensue with our previous written consent and with source credit. Illustrations, descriptions, schematic diagrams, and other data only serve for explanatory purposes and for presentation of the text. They cannot be used as the basis for design, installation, or scope of delivery. We assume no liability for conformity of the contents with national or local legal regulations. We are exempt from liability. We reserve the right to make changes at any time. Printed in Germany. Imprim en Allemagne. 4th Edition, February 2000. English translation of the German edition dated: September 1998.
K-Jetronic Since its introduction, the K-Jetronic Combustion in the gasoline engine gasoline-injection system has pro- The spark-ignition or ved itself in millions of vehicles. Otto-cycle engine 2 This development was a direct result Gasoline-engine management of the advantages which are inherent Technical requirements 4 in the injection of gasoline with Cylinder charge 5 regard to demands for economy of Mixture formation 7 operation, high output power, and Gasoline-injection systems last but not least improvements to Overview 10 the quality of the exhaust gases K-Jetronic emitted by the vehicle. Whereas the System overview 13 call for higher engine output was the Fuel supply 14 foremost consideration at the start of Fuel metering 18 the development work on gasoline Adapting to operating conditions 24 injection, today the target is to Supplementary functions 30 achieve higher fuel economy and Exhaust-gas treatment 32 lower toxic emissions. Electrical circuitry 36 Between the years 1973 and 1995, Workshop testing techniques 38 the highly reliable, mechanical multi- point injection system K-Jetronic was installed as Original Equipment in series-production vehicles. Today, it has been superseded by gasoline injection systems which thanks to electronics have been vastly im- proved and expanded in their func- tions. Since this point, the K-Jetronic has now become particularly impor- tant with regard to maintenance and repair. This manual will describe the K-Jetronics function and its particu- lar features.
Combustion in the gasoline engine Combustion in the gasoline engine combustion process pressurizes the The spark-ignition cylinder, propelling the piston back down, or Otto-cycle engine exerting force against the crankshaft and performing work. After each combustion stroke the spent gases are expelled from Operating concept the cylinder in preparation for ingestion of The spark-ignition or Otto-cycle1) a fresh charge of air/fuel mixture. The powerplant is an internal-combustion (IC) primary design concept used to govern engine that relies on an externally- this gas transfer in powerplants for generated ignition spark to transform the automotive applications is the four-stroke chemical energy contained in fuel into principle, with two crankshaft revolutions kinetic energy. being required for each complete cycle. Todays standard spark-ignition engines employ manifold injection for mixture formation outside the combustion The four-stroke principle chamber. The mixture formation system The four-stroke engine employs flow- produces an air/fuel mixture (based on control valves to govern gas transfer gasoline or a gaseous fuel), which is (charge control). These valves open and then drawn into the engine by the suction close the intake and exhaust tracts generated as the pistons descend. The leading to and from the cylinder: future will see increasing application of systems that inject the fuel directly into the 1st stroke: Induction, combustion chamber as an alternate 2nd stroke: Compression and ignition, concept. As the piston rises, it compresses 3rd stroke: Combustion and work, the mixture in preparation for the timed 4th stroke: Exhaust. ignition process, in which externally- generated energy initiates combustion via Induction stroke the spark plug. The heat released in the Intake valve: open, Fig. 1 Exhaust valve: closed, Reciprocating piston-engine design concept Piston travel: downward, OT = TDC (Top Dead Center); UT = BDC (Bottom Combustion: none. Dead Center), Vh Swept volume, VC Compressed volume, s Piston stroke. The pistons downward motion increases VC OT the cylinders effective volume to draw fresh air/fuel mixture through the passage s exposed by the open intake valve. Vh UT Compression stroke Intake valve: closed, Exhaust valve: closed, OT Piston travel: upward, Combustion: initial ignition phase. UMM0001E 1) After Nikolaus August Otto (1832 1891), who UT unveiled the first four-stroke gas-compression engine 2 at the Paris World Exhibition in 1876.
As the piston travels upward it reduces The ignition spark at the spark plug Otto cycle the cylinders effective volume to ignites the compressed air/fuel mixture, compress the air/fuel mixture. Just before thus initiating combustion and the the piston reaches top dead center (TDC) attendant temperature rise. the spark plug ignites the concentrated This raises pressure levels within the air/fuel mixture to initiate combustion. cylinder to propel the piston downward. Stroke volume Vh The piston, in turn, exerts force against and compression volume VC the crankshaft to perform work; this provide the basis for calculating the process is the source of the engines compression ratio power. = (Vh+VC)/VC. Power rises as a function of engine speed Compression ratios range from 7...13, and torque (P = M). depending upon specific engine design. A transmission incorporating various Raising an IC engines compression ratio conversion ratios is required to adapt the increases its thermal efficiency, allowing combustion engines power and torque more efficient use of the fuel. As an curves to the demands of automotive example, increasing the compression ratio operation under real-world conditions. from 6:1 to 8:1 enhances thermal efficiency by a factor of 12 %. The latitude Exhaust stroke for increasing compression ratio is Intake valve: closed, restricted by knock. This term refers to Exhaust valve: open, uncontrolled mixture inflammation charac- Piston travel: upward, terized by radical pressure peaks. Combustion: none. Combustion knock leads to engine damage. Suitable fuels and favorable As the piston travels upward it forces the combustion-chamber configurations can spent gases (exhaust) out through the be applied to shift the knock threshold into passage exposed by the open exhaust higher compression ranges. valve. The entire cycle then recommences with a new intake stroke. The intake and Power stroke exhaust valves are open simultaneously Intake valve: closed, during part of the cycle. This overlap Exhaust valve: closed, exploits gas-flow and resonance patterns Piston travel: upward, to promote cylinder charging and Combustion: combustion/post-combus- scavenging. tion phase. Fig. 2 Operating cycle of the 4-stroke spark-ignition engine Stroke 1: Induction Stroke 2: Compression Stroke 3: Combustion Stroke 4: Exhaust UMM0011E 3
Gasoline- engine management Gasoline- engine management Technical requirements Primary engine- management functions The engine-management systems first Spark-ignition (SI) and foremost task is to regulate the engine torque engines torque generation by controlling all of those functions and factors in the The power P furnished by the spark- various engine-management subsystems ignition engine is determined by the that determine how much torque is available net flywheel torque and the generated. engine speed. The net flywheel torque consists of the Cylinder-charge control force generated in the combustion In Bosch engine-management systems process minus frictional losses (internal featuring electronic throttle control (ETC), friction within the engine), the gas- the cylinder-charge control subsystem exchange losses and the torque required determines the required induction-air to drive the engine ancillaries (Figure 1). mass and adjusts the throttle-valve The combustion force is generated opening accordingly. The driver exercises during the power stroke and is defined by direct control over throttle-valve opening the following factors: on conventional injection systems via the The mass of the air available for physical link with the accelerator pedal. combustion once the intake valves have closed, Mixture formation The mass of the simultaneously The mixture formation subsystem cal- available fuel, and culates the instantaneous mass fuel The point at which the ignition spark requirement as the basis for determining initiates combustion of the air/fuel the correct injection duration and optimal mixture. injection timing. Fig. 1 Driveline torque factors 1 Ancillary equipment 1 1 2 3 4 (alternator, a/c compressor, etc.), 2 Engine, 3 Clutch, 4 Transmission. Air mass (fresh induction charge) Combustion Engine Flywheel Drive Fuel mass output torque output torque torque Tra...