Transmission and Axle lubrication

Since  the  lubrication of  transmissions  and axles  is  of  primary  importance  in  automotive vehicles, as gearing  is  concerned, this subject  will have first  consideration.  Mention of the lubrication of other gear sets in such vehicles   will then follow:

Also the major discussion will consider internal combustion engines as a source of power. Other  sources  of power  and methods other  than  gearing  for  driving  vehicles and the    consequent fluids  require  will also  receive  mention. Gearing  or  transmission  mechanisms  of automobiles, buses or  trucks  are  lubricated, in the  main , by  bath  or  splash  systems  with some   use of  forced  feed. The gear  cases are  generally  as small  as  possible  so that  consequently  the amount  of gear  oil  present  is  restricted. While  the fluids  present  in gear  boxes  may have  other uses, the primary  functions  are  to  prevent  wear  of gears  and to  act  as a  heat  transfer   medium. The  general  subject of wear  prevention  has been  discussed  previously  and  may  be  due  either  to  the  oil film  alone  or to  this fluid  supplemented by EP  films. The  oil  in gear  cases  of  vehicles takes  up heat  from  the  moving  gears  and transfers  it to the  inside  of the casing. Form here it is dissipated to the surrounding air. Such  radiation is not  always  what  is  desired  because  the gear  housing  becomes  coated  with  dust  or  dirt. Consequently, particularly  in  heavy  trucks  and  busses, the  temperature of the  lubricant may  reach  250  to 300  degree F  causing  excessive oil  deterioration.

 The  loads, speeds,  conditions of use and the  operators  of  vehicles  vary  so  widely  that  it is a wonder  that  automotive  gears  give such  long  and  trouble  free  operation as they  do in  most cases. The service  obtained  from such  gearing is  probably more of a  tribute  to the people who  formulated and  supplied   the  lubricants than  to the  designers  of  the  mechanisms. In fact Raymond, a few years  ago, stated: “ The  hypoid  axle  is easily  the hardest  working  and possibly  one  of the most  neglected   automotive  components”. Elsewhere  the  thought  was  advanced that gear  oil  manufacturers have been  asked to  perform  miracles, in order to lubricates  such  gears.

  

Transaxle Fluids

While a single lubricant for both transmissions and rear axles of certain automobiles is desirable, Hunsted et al.^28 ,when reviewing the situation with regard  to such fluids, concluded that as of January 1960 considerable  work  remained  to be done on transaxle fluids to achieve optimum results. Up to that  time  some  42 mineral  oil base and  synthetic base  fluids, with  various  additives, had  been  evaluated and only  three showed  any  promise  for  future  development. Since  it is  impractical  to  suggest even  tentative  formulations, all that  can be  done is to  indicate  the  requirements and  the handicaps.

A  transaxle  fluid  should  have  all  the  desirable  characteristics  of ATF and  in  addition  should  have  sufficient  EP value  to  lubricate  hypoid  gears. The above statement should be modified in that the desirable characteristics of ATF should also be maintained while in service. Thus, when  the  fluid is subjected to the  shear  effect of mating  gears, polymer type  additives may  lose  a large  part  of their  effectiveness  due  to  breakdown  of the  polymers to  lower  molecular weight  products. Therefore  base  fluids with  inherent  high  V.I. or  polymers of  initially  lower molecular  weight  are  dictated  in the  formulations.

EP agents  used  should  have no  adverse  effect  on any  of the  components of the  automatic transmission such  as  clutch  materials, various   metals, synthetic seals, etc. Of  course the most desirable  transaxle fluid  would  be  one  which  could  be  sealed  in a  case  and serve the  life  of the  car  but  first  a  fluid which  will perform  satisfactorily when  changed  periodically  will serve.

According to  Celanese  a  trimethylolpropane  ester  with  an EP additive  offers promise  for use  as a transaxle  fluid. Another suggestion for the purpose is methylchlorophenyl containing about 3 per cent chloride.