Abstract:
An alternator comprises a housing including a first portion, and a second portion having a plurality of electrical connectors and having an aperture; a stator supported in the first portion of the housing; a rotor supported for rotation relative to the stator and configured to have a force current applied thereto; and a resistor coupled to the rotor and configured to reduce the current through the rotor, the resistor being removable and replaceable. Other apparatus and methods are provided.

Description:
RELATED PATENT DATA 
   This is a divisional application of U.S. patent application Ser. No. 11,067,041, filed Feb. 24, 2005, which in turn claims priority to U.S. Provisional Patent Application No. 60/547,485, filed Feb. 25, 2004, all of which are incorporated herein by reference. 

   TECHNICAL FIELD 
   The present invention relates to alternators. 
   BACKGROUND OF THE INVENTION 
   Alternator design is known in the art. It is a fundamental principle of physics that when a magnet rotates in a wire loop, a current is induced. A magnet has a south pole and a north pole. Assume that the north pole is just passing a top part of the wire loop and the south pole is just passing the bottom part of the loop. When the magnet has rotated through 180 degrees, the south pole will be passing the top part of the loop while the north pole will be passing the bottom part of the loop. This causes the direction of induced current to be reversed. In this way, alternating current is induced in each turn of wire in a stator of an alternator. 
   In an alternator, a rotor is spun inside a stator. The stator includes multiple windings of wire. A single turn would not induce enough voltage nor carry enough current for typical applications of an alternator. Therefore, a practical alternator has a stator with many turns of wire. 
   The rotor defines an electromagnet that provides a magnetic field that is spun inside the windings of wire to generate current. A relatively small field current used to define the electromagnet is supplied to the rotor by two small brushes that each ride on separate and continuous slip rings. Field current passes through the brushes into the slip rings into the rotor. 
   There are typically three separate windings of wire in the stator arranged so that the AC (alternating current) that is generated by each winding is slightly out of phase compared to the other windings. This smoothes the electrical output of the alternator. 
   A rectifier circuit including diodes is used to convert the AC to DC (direct current). The diodes are arranged so that current from each of the three stator wires is only allowed to pass in one direction, and the three outputs are connected together. A voltage regulator is typically provided to the DC output to keep the output voltage relatively steady. The voltage regulator can be a mechanical or solid state device. 
   For externally regulated alternators, there are typically four connections on the alternator: the output terminal (often labeled BAT), the ground terminal (often labeled GRD) or ground may be “implied” though the metal mountings of the alternator, the field connection (often labeled F), and separate connections to each of the three poles on the stator (R). 
   Internally regulated models also have four connections, but the voltage regulator is inside the alternator and constructed of solid-state components. For internally regulated alternators, the connections are: an output terminal (typically labeled BAT), a ground terminal (typically labeled GRD) or ground may be “implied” though the metal mountings of the alternator, and two connections typically labeled 1 and 2. One of these connections is a relatively small wire that is connected to a battery and the other is connected to a charge indicator light. 
   Brushes that ride against the slip rings of the rotor of an alternator are components that are likely the number one failure mode of an alternator since the brushes wear out over time due to friction. Such brushes are conventionally internal, and are housed inside the housing of an alternator. For conventional alternators, in order to changes brushes, the alternator must be removed from service and substantially disassembled. The brush blocks then have to be removed from inside of a rear shell housing component after the rear shell has been removed from the rest of the alternator. 
   Certain alternators are known in the art that have removable, externally accessible, brush blocks. However, in these designs, the brushes extend out past the end of the main housing. In these designs, the rear bearings of the alternator are axially inside of the slip rings and the brushes. 
   Certification of components for aircraft use is a lengthy process. Components used in alternators for aircraft have subtle differences when compared with alternators used in automobiles in view of the different environments in which they are used and more serious consequences of failures in aircraft environments. For example, different brush materials are used for alternators used in aircraft than the material used in automotive alternators. 
   An aircraft alternator designed to deliver a certain level of amperage cannot simply be used on an airplane designed for a lower amperage alternator. For example, an 80 Amp alternator cannot be used on a 40 Amp airplane even though a regulator will regulate the current down to 40 Amps. The problem is that aircraft wiring is typically geared around the maximum rating of the alternator. 
   For example, forty years ago, when some of these planes were built, 40 Amp alternators were the biggest alternators available. Therefore, the gauge of the wiring going from the alternator was geared around that rating. If higher amperage current, such as 80 Amps, was passed through, the wiring could burn up. Provided that the regulator is working correctly, this would not happen. However, regulators sometimes fail and fields sometimes short. Safety standards for aircraft dictate that an aircraft alternator cannot be capable of putting out more than the designated current. This means that different alternator designs are used in different aircraft, causing manufacturers to manufacture multiple different types of alternators and causing vendors and repair facilities to stock multiple different types of alternators. 
   SUMMARY OF THE INVENTION 
   Embodiments of the invention provide an alternator with a removable brush block. Other embodiments provide an alternator with a replaceable resistor in series with the field. 
   One aspect of the invention provides a method of changing the maximum current output of an alternator, in view of aircraft safety standards requiring that alternators for aircraft not be able to put out more than a predetermined amperage, notwithstanding the ability to regulate current with a regulator outside of the alternator. Other methods and apparatus are also provided. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the invention are described below with reference to the following accompanying drawings. 
       FIG. 1  is a perspective view of an alternator in accordance with various embodiments of the invention. 
       FIG. 2  is a cut away perspective view of the alternator of  FIG. 1 . 
       FIG. 3  is an exploded perspective view of a housing portion, brush holder, and holder plate, of the alternator of  FIGS. 1 and 2 . 
       FIG. 4  is a view of the brush holder of  FIG. 3 , assembled to the holder plate of  FIG. 3 , and together removed from the alternator of  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   This disclosure of the invention is submitted in furtherance of the constitutional purposes of the U.S. Patent Laws “to promote the progress of science and useful arts” (Article 1, Section 8). 
   As mentioned above, brushes that ride against the slip rings of the rotor are perhaps the number one failure mode in alternators. They wear out. Therefore, besides making them as strong and as long lasting as possible, they are made to be easily interchanged. 
   With standard alternators, and with all or substantially all aviation alternators, in order to change out brushes, substantially the whole alternator has to be disassembled to replace the brushes. 
     FIG. 1  shows an alternator  10  embodying various aspects of the invention. In the embodiment of  FIG. 1 , the alternator  10  is an aircraft alternator. The alternator  10  includes a housing  12 . In the illustrated embodiment, the housing  12  includes a front case portion  14  ( FIG. 2 ), and a rear case portion  16  having a plurality of electrical connectors  60 ,  70 ,  72 ,  74 ,  76 , and  78  for inputs and outputs. Connector  60  is a field input. Connector  70  is a power output. Alternator  10  has a mounting end  33  and a free end  35  (see  FIG. 2 ). The housing further includes an aperture or material removed portion  20  ( FIG. 3 ). 
   The alternator  10  includes a stator  22  ( FIG. 2 ) supported in the housing  12 . More particularly, in the illustrated embodiment, the stator  22  is at least partially supported by the front case portion  14  of the housing and the rear case portion  16  can be removed from the front case portion  14  without removing the stator  22 . The alternator  10  further includes a rotor  24  ( FIG. 2 ), including slip rings  26  and  28 , and including a rotor shaft  30  configured to rotate about an axis  32 . The shaft has opposite ends  34  and  36 . 
   The alternator  10  further includes front and rear bearings  38  and  40  respectively supporting the ends  34  and  36  of the rotor shaft  30  in the housing  12  for rotation relative to the stator  22 . 
   The alternator  10  further includes a removable assembly  42  ( FIG. 2 ) including a support member or holder plate  44  and a brush holder  46  ( FIG. 3 ). The brush holder  46  includes brush blocks  48  and  50  ( FIG. 2 ) configured to slidingly support brushes  52  and  54  ( FIG. 4 ). The term brush block, as used herein, refers to any structure configured to support a brush. In the illustrated embodiment, the brush blocks  48  and  50  are each defined by a cartridge or chamber that slidingly receives a brush and a spring. More particularly, in the illustrated embodiment, the brushes  52  and  54  are biased by springs in the cartridges  48  and  50  into engagement with the slip rings  26  and  28 . The brushes  52  and  54  are electrically configured to pass a force current through the rotor  24  via the slip rings  26  and  28 . In the illustrated embodiment, the brushes  52  and  54  are each made of a special carbon used for aircraft applications. For example, for aircraft applications, aircraft grade brush material is used for high altitude applications. 
   The brush holder  46  ( FIGS. 3 and 4 ) is removably supported by the support member  44 . The removable assembly  42  is selectively fixed relative to the rear case portion  16  of the housing against movement relative to the front case portion  14  of the housing when in a “in use” position. When in the “in use” position, the brushes  52  and  54  engage the slip rings  26  and  28  and the support member  44  at least partially closes the aperture or material removed portion  20  ( FIG. 3 ). 
   The support member  44  has an inside surface  56  ( FIG. 2 ) configured to face inside the housing  12 , when the removable assembly  42  is in the “in use” position, and an outside surface  58  configured to face away from the alternator  10 , when the removable assembly  42  is in the “in use” position. The brush blocks  48  and  50  are mounted to, covered by or positioned by the inside surface  56 . In the illustrated embodiment, the brush holder  46  is mounted to and movable with the support member  44 . The outside surface  58  supports a force terminal  60  which is electrically coupled to one of the brushes  52 ,  54 . In the illustrated embodiment, the force terminal  60  is defined by an electrically conductive post extending away from the support member  44 . 
   In some embodiments, the support member  44  has a surface  62  configured to mate with the material removed portion or aperture  20  to close the aperture  20  when the removable assembly  42  is in the use position. Alternatively, the support member  44  overlaps or covers the aperture  20  either completely or partially. 
   The slip rings  26  and  28  are located ( FIG. 2 ) between the bearings  38  and  40  with respect to the axis  32  defined by the rotor shaft  30 . More particularly, in the illustrated embodiment, the brushes  52  and  54  ( FIG. 4 ) are internal of the housing  12  and the slip rings  26  and  28  are internal of the housing  12 . Still more particularly, in the illustrated embodiment, the rear bearings  40  are axially outside of the slip rings  26  and  28 , and the slip rings  26  and  28  are on the inside of the housing  12 , yet removable brush blocks  48  and  50  are provided. There are advantages to this design. The farther apart the front bearings  38  are located from the rear bearings  40 , the more stable the rotation will be. Also, this design gives better protection to the slip rings  26  and  28 . 
   The removable assembly  42  is removable from the rear case portion  16  of the housing  12  from outside the housing  12  (e.g., with a hand tool such as a screwdriver), without the need to remove the rear case portion  16  of the housing  12  from the front case portion of the housing  14 . 
   In the embodiment of  FIG. 1 , to remove the removable assembly  42  and the brush blocks  48  and  50 , a user removes fasteners  64  ( FIG. 3 ) that hold the removable assembly  42  in the housing  12 , from outside the housing  12 , removes the removable assembly  42 , replaces the assembly  42  with a new assembly  42  (or replaces the brushes  52  and  54  within the assembly), and refastens the new or upgraded assembly to the housing  12 . A removable pin  68  ( FIG. 4 ) holds the brushes  52  and  54  in the brush blocks  48 , against the bias of springs in the brush blocks  48  and  50 , until the removable assembly  42  is replaced. After the removable assembly  42  is replaced, the pin  68  is removed from the removable assembly  42 , allowing the brushes  52  and  54  to extend from the brush blocks  48 ,  50  into engagement with the respective slip rings  26 ,  28 . In the illustrated embodiment, the fasteners  64  are screws; however, other appropriate fasteners could be used. 
   The field current passes through the brush  52  or  54  into the slip ring  26  or  28 , and into the rotor  24 . That applies power to the rotor  24 , creating the magnetic field of the rotor  24  that causes the generation of energy in the stator  22 . 
   Typically, alternators are designed such that field current is transmitted generally directly to the rotor. In the illustrated embodiment, the alternator  10  is capable of a predetermined current output. For example, in the illustrated embodiment, the alternator  10  is an aircraft alternator capable of outputting up to about 80 Amps. However, there are aircraft that have different maximum current ratings. For example, some aircraft need 40 Amp alternators, some need 60 Amp alternators, and some need 70 Amp alternators. 
   Therefore, in some but not all embodiments, the removable assembly  42  further supports a resistor  66  ( FIG. 4 ) configured to reduce current provided to the rotor  24 . More particularly, in the illustrated embodiment, the resistor  66  is easily removable and replaceable. Still more particularly, in the illustrated embodiment, the resistor  66  is removable from the housing  12  with the brush blocks  48  and  50 . 
   The resistor  66  is placed in-line with the field current. For example, in some embodiments, the resistor  66  is electrically coupled between the force terminal  60  and one of the brushes  52  and  54 . More particularly, the resistor  66  is removably attached to the inside surface  56  of the support member  44  using a pair of screws  80  and  82 . Field current travels from externally of the alternator  10  through the post or terminal  60 , through this resistor  66 , and then to a brush  52  or  54 . 
   Depending upon the resistance value of the resistor  66  that is used, a different model alternator  10  is created for use on an aircraft that uses a certain ampere alternator. In the illustrated embodiment, the brush blocks  48 ,  50  are replaceable with brush blocks supporting resistors  66  that are appropriate to define a 40, 60, or 70 Amp alternator. Alternatively, the resistor  66  could be removed and replaced with a conductor or bypassed with a jumper to define an 80 Amp alternator. In fact, the same alternator  10  could be adapted to any ampere rating (lower than its maximum output) by replacing the resistor  66 . The resistor  66  is on the input or field end of the circuit. By reducing the amount of current going into the alternator  10 , the amount of magnetism produced is reduced by the resistor  66 . 
   This design saves expense in manufacturing and in stocking of alternators. 
   In some embodiments, the alternator case or housing used is a Delco™ 10DN case. Alternative housing styles could also be employed. 
   In compliance with the statute, the invention has been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the invention is not limited to the specific features shown and described, since the means herein disclosed comprise preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents.