Circle track cars need an ample supply of volts and amps to provide reliable power for ignition systems, engine cooling fans, and other electrical accessories. Conventional alternators are simply not up to the output requirements and extraordinary heat and vibration of racing conditions. It takes special technology to stand up to these demands, while holding weight to the absolute minimum.
The Robert Bosch Corp. offers a purpose-built racing alternator that includes sophisti-cated design features that help the unit produce less heat of its own, dissipate ambient heat more effectively, and withstand vibrations inherent in the 9,000+ rpm environment of a race car's enginecompartment-all while producing triple-digit amperage. This alternator was quickly accepted by a number of NASCAR Winston Cup teams.
"We started with a clean sheet of paper when we developed this unit," explains Wolfgang Hustedt, Bosch Motorsports manager. "This unit had to be designed from the start to be a racing-only product. We began with the rotor assembly and worked our way out.
"We knew we could achieve maximum alternator output with a rotor speed of about 8,000 rpm. But we also knew that we could achieve additional cooling at much higher rotor speeds. After all, the alternator is mounted directly behind the radiator, so it is sub-jected to the heated air produced by the radiator. We designed the rotor to operate at speeds approaching 20,000 rpm."
To make the rotor live at these speeds, there needed to be extraordinary levels of precision in manufacturing. The rotor shafts have a diameter machined to +/- 0.008 mm, which is equiva-lent to 0.0002363 inches. Surface finish is less than 4 micrometers.
All windings are done by hand, with a larger number of windings of a precision fine wire specially impregnated for better durability and safety. Research showed that two integral cooling fans-one at the front of the rotor and one at the rear-provided maximum cooling. The completed rotor assembly is then electronically balanced to +/- 0.005 grams. Front and rear ball bearings are special high-speed designs. The stator is similarly wound and protected. Research engineers determined that the conventional method of clamping the stator between the case halves provided the most rugged design.
In addition to all of the mechanical innovations, the Bosch design team elected to provide advanced electronics to meet the rigorous demands of racing. Therefore, the engineers started with the premise of one-wire technology to ensure simple installation and compatibility with a variety of electrical system designs. They added a specially dimen-sioned diode trio, consisting of application-engineered positive, negative, and exciter diodes.
The all-electronic voltage regulator incorporates special circuitry that accommodates the intermit-tent "on-off" nature of race car accessories like engine cooling fans and supplemental electric engine oil pumps. The advanced circuitry includes a special thermal shunt circuit to cut off alternator output when the unit's core temperature reaches a specified threshold. This allows the alternator to cool off while the car continues to operate on battery power, helping to avoid costly DNFs.
This Bosch alternator incorporates an exciter circuit in case a race team chooses to run a charging system warning light. When such a warning light is not used, a resistor is installed to prevent alternator damage. All electronic components are potted, and the rectifier and regulator are housed in a special phenolic cover for added protection and cooling.