After five years of development work, they were brought onto the market with the aim of strengthening and expanding the company‘s business outside the field of automotive electrics. A mere 1,000 were produced in 1931, but by 1934 that figure was already 100,000 and rising. The diesel injection pumps were supplied exclusively for truck engines.

A systematic approach to diesel

The diesel injection system did not just consist of an injection pump. Injection nozzles were also needed to ensure a fine spray of fuel, glow plugs for improved cold start, filters for cleaning the fuel, and last not least governor devices to ensure a constant engine speed when stationary and under constant load. Bosch the automotive parts supplier had already established itself as a system provider in 1913, when it introduced Bosch automotive lighting. In the case of diesel injection, too, the management recognized that it made sense for the company to produce key additional components itself.

Constant engine speed

One of the technical problems of the diesel engine is that it is not “self-governing” like the gasoline engine. Without additional control, it does not run at a stable engine speed, but either remains stationary or accelerates to the point of self-destruction, or has no braking effect on the vehicle when the driver takes his foot off the gas pedal. Bosch countered this problem with two solutions – the centrifugal governor that is dependent on the engine speed, and the pneumatic governor, the function of which is determined by the pressure in the intake manifold of the engine. Both control the amount of fuel injected into the engine and in this way govern the speed of the engine.

Centrifugal force and pneumatics

The centrifugal governor was originally only suitable for use in tugboats and motor boats, because it only had two functions – maintaining idling mode and limiting the maximum engine speed. It ensured that the two engine speeds required to operate these types of engines – idling level and working engine speed – were governed and that the maximum permissible engine speed was not exceeded. Under the name “variable speed governors”, centrifugal governors were later modified for use in road vehicles, particularly in trucks, where it was necessary to maintain a constant engine speed in every operating mode between stationary and full throttle. The second design principle was the pneumatic governor, which kept the throttle valve at a particular aperture setting in accordance with the speeddependent intake manifold pressure, thereby ensuring that an even engine speed was maintained when constant force was applied to the gas pedal. Eventually, however, the centrifugal governor won through. Although it was more expensive, its faster response times made it superior to the pneumatic governor.

Electronic governor

From 1986 onwards, Bosch offered a completely new system for governing the speed of diesel engines, one that has now become the standard for all modern diesel injection systems. Electronic Diesel Control (EDC) allows the governing variables (accelerator-pedal position/load, operating temperature, etc.) to be more comprehensively and accurately recorded than with mechanical measuring instruments, and to be converted more rapidly into control commands to perform corrections. The system works in three stages: recording the operating conditions by means of sensors, processing this information in the electronic control unit, and implementing the necessary control commands in the actuator mechanism. This type of control has now become essential, because it is the only type that can be networked with other electronic governing systems, such as TCS, which prevents wheel spin when starting and accelerating, or electronic transmission control.