Field of the Invention
The invention relates to an electronic control unit for a motor vehicle which has a driving engine, a clutch, a transmission, at least one driven wheel, an engine rpm transducer, and at least one speed transducer, in particular for ascertaining a vehicle speed or a power take off rpm of the transmission, which may be equipped with a transducer wheel having a given first number of teeth or a given second number of teeth.
One such control unit is known from German Published, Non-Prosecuted Application DE-OS 23 38 122, corresponding to U.S. Pat. No. 4,044,634.
With different kinds of equipment (mass-production or special equipment) of certain vehicle models, the electronic control units differ only in the memorized values of different numbers of teeth of transducer wheels in the speed transducers being used. The number of teeth, or a signal associated with that number, which is used in either case must be stored in memory in the control unit, because it is necessary in order ascertain the vehicle speed, wheel speeds or wheel rpm, which are parameters that are needed as input variables, for instance in anti-lock brake systems, traction control systems, and for limiting the speed of the transmission output shaft (cardan shaft), etc..
In the ensuing description, the term "speed" is intended to mean only the circumferential wheel speed in kilometers per hour for a vehicle wheel, although that term could also mean the rpm of the transmission output shaft (cardan shaft) or the drive shaft of the wheels in revolutions per minute.
Different numbers of teeth of the speed transducer require control units with different part numbers, making them expensive to keep in inventory because multiple versions must be kept on hand. Through the use of the gear ratios of the gear (including the differential), calculating the circumferential wheel speed from the engine rpm would be simple. However, since transmissions with different gear ratios are also used when the same vehicle model has different engine variants, the result would then be even more different parts numbers, making inventory even more expensive.