Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-07-01
2001-05-15
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S253000
Reexamination Certificate
active
06232694
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to improvements in electric power systems for aircraft and, more particularly, to such systems which provide both starter and generator functions. The present invention has particular applicability to starter generators for helicopters.
Typically, in airborne electrical power generation systems, it is desirable to have a single system which provides both the starter and generator functions. The weight savings on an aircraft can be substantial when a dedicated starter is eliminated. For this reason, electrical power generating systems which are capable of providing engine start functions can provide both cost and weight savings.
The starter-generator commonly utilizes a machine that combines an induction motor with a synchronous generator. In this machine, a rotor-shaped stator is positioned inside a squirrel-cage induction rotor which has an array of magnets attached on the outer diameter thereof. The compound/dual machine operates as a starter by using the induction rotor to accelerate the permanent magnet rotor up to some low synchronous speed, where ac power can be applied to the outside stator of the synchronous-generator so as to lock-in the permanent magnet rotor synchronously with the rotating field created in the armature (stator) of the synchronous-generator.
Frequently, the weakest link in the design of a starter-generator is the brushes. The carbon brushes utilized in starter-generators wear rapidly when brush temperatures exceed 450 degrees F. During startup, the starter generator brush temperatures can exceed 800 to 1000 degrees F. or higher, thus significantly exceeding the 450 degree F. threshold for rapid wear. The life of the starter-generator is frequently governed by the life of the brushes. With the development of higher horsepower turbine engines the starter-generators utilized to start such engines have been experiencing rapid brush and armature commutator wear. Besides the cost of overhauling the starter generator after relatively short hours of use the rapid wearing of the brushes causes a build up of carbon dust inside the starter generator, in the engine compartment and outside on the cowling as well.
OBJECTS OF THE INVENTION
There is a particular need for improvements to a particular type of starter generator which is frequently used in helicopters. One common type of starter generator is a type sold by Aircraft Parts Corp. (APC) and also by Lucas and possibly by others. These starter generators are usually 150 amp generators and are characterized, because of the aircraft they are designed to be used on, as having a base that prevents the flow of air from exiting directly out the drive end of the starter generator. An example of this type of starter generator is shown in
FIGS. 1 and 2
. Because of their design, these generators have high maintenance and low hours between overhaul of the generator. These generators typically run hot and dirty, i.e., they generate high amounts of carbon dust due to the rapid wear of the brushes and this dust proliferates fouling the aircraft engine cowling and compartments. In addition, these generators also produce copper dust from wear to the armature commutator. This dust is a good conductor and can potentially create shorts in the starter-generator. Because of the rapid wear of the brushes due to the carbon itself and the high operating temperatures of the starter generators, the generators must be repaired and overhauled frequently at considerable cost and downtime.
Accordingly, it is an object of the present invention to provide improvements to starter generators that are designed such that air does not flow directly from the drive end of the starter generator.
It is an object of the present invention to provide an improved starter generator that requires low maintenance and has long brush life.
It is a another object of the invention to provide an improved starter generator housing that permits the starter generator to better withstand higher temperatures thereby improving brush life.
Another object of the present invention is to provide an improved brush spring design that reduces armature commutator and brush wear during operation of the starter generator.
A further object of the present invention is to provide a new brush composition and design that has provided longer brush life under diverse operating conditions.
REFERENCES:
patent: 3648086 (1972-03-01), Renner et al.
patent: 4142120 (1979-02-01), Hallerback
patent: 4142138 (1979-02-01), Taylor et al.
patent: 4204863 (1980-05-01), Schreiner
patent: 4580333 (1986-04-01), Griffis
patent: 5338618 (1994-08-01), Suzuki et al.
patent: 5876298 (1999-03-01), Kato et al.
O'Rourke Thomas A.
Perez Guillermo
Ramirez Nestor
Wyatt Gerber & O'Rourke
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