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Neutral Safety Switch

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allowed to run free to the point where they will destroy themselves. SIX   WINDINGS,   SERIES-PARALLEL— Three pairs of series-wound field coils provide the  magnetic  field  for  a  heavy-duty  starter motor. This configuration uses six brushes. THREE  WINDINGS,  TWO  SERIES,  ONE SHUNT—The   use   of   one   filled   coil   that   is shunted  to  ground  with  a  series-wound  motor controls motor speed. Because the shunt coil is not affected by speed, it will draw a steady heavy current, effectively limiting speed. DRIVE  END FRAME.—The  drive  end  frame  is designed to protect the drive pinion from damage and to  support  the  armature  shaft.  The  drive  end  frame  of the starter contains a bushing to prevent wear between the armature shaft and drive end frame. Types of Starting Motors There are two types of starting motors that you will encounter  on  equipment.  These  are  the  direct  drive starter  and  the  double  reduction  starter.  All  starters require   the   use   of   gear   reduction   to   provide   the mechanical  advantage  required  to  turn  the  engine flywheel  and  crankshaft. DIRECT   DRIVE   STARTERS.—Direct drive starters make use of a pinion gear on the armature shaft of the starting motor. This gear meshes with teeth on the ring gear. There are between 10 to 16 teeth on the ring gear for every one on the pinion gear. Therefore, the  starting  motor  revolves  10  to  16  times  for  every revolution  of  the  ring  gear.  In  operation,  the  starting motor  armature  revolves  at  a  rate  of  2,000  to  3,000 revolutions  per  minute,  thus  turning  the  engine crankshaft  at  speeds  up  to  200  revolutions  per  minute. DOUBLE   REDUCTION   STARTER.—The double  reduction  starter  makes  use  of  gear  reduction within the starter and the reduction between the drive pinion and the ring gear. The gear reduction drive head is used on heavy-duty equipment. Figure 2-42 shows a typical gear reduction starter. The gear on the armature shaft does not mesh directly with the teeth on the ring gear, but with an intermediate gear   which   drives   the   driving   pinion.   This   action provides additional breakaway, or starting torque, and greater  cranking  power.  The  armature  of  a  starting motor  with  a  gear  reduction  drive  head  may  rotate  as many  as  40  revolutions  for  every  revolution  of  the engine  flywheel. Figure 2-42.—Gear reduction starter. NEUTRAL  SAFETY  SWITCH Vehicles  equipped  with  automatic  transmissions require the use of a neutral safety switch. The neutral safety  switch  prevents  the  engine  from  being  started unless   the   shift   selector   of   the   transmission   is   in NEUTRAL  or  PARK.  It  disables  the  starting  circuit when  the  transmission  is  in  gear.  This  safety  feature prevents  the  accidental  starting  of  a  vehicle  in  gear, which   can   result   in   personal   injury   and   vehicle damage. The neutral safety switch is wired into the circuit going to the starter solenoid. When the transmission is in forward or reverse gear, the switch is in the OPEN position  (disconnected).  This  action  prevents  current from   activating   the   solenoid   and   starter   when   the ignition switch is turned to the START position. When the  transmission  is  in  neutral  or  park,  the  switch  is closed  (connected),  allowing  current  to  flow  to  the starter when the ignition is turned. A  misadjusted  or  bad  neutral  safety  switch  can keep the engine from cranking. If the vehicle does not start, you should check the action of the neutral safety switch by moving the shift lever into various positions while trying to start the vehicle. If the starter begins to work, the switch needs to be readjusted. To  readjust  a  neutral  safety  switch,  loosen  the fasteners  that  hold  the  switch.  With  the  switch loosened,  place  the  shift  lever  into  park  (P).  Then, while   holding   the   ignition   switch   in   the   START position, slide the neutral switch on its mount until the engine cranks. Without moving the switch, tighten the fasteners.  The  engine  should  now  start  with  the  shift lever  in  park  or  neutral.  Check  for  proper  operation after the adjustment. If  by  adjusting  the  switch  to  normal  operation  is not resumed, it may be required to test the switch. All that is required to test the switch is a 12-volt test light. 2-29



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