The Effect of Heavy Loads on Light Duty Vehicle Axle Operating Temperature

With the continued growth of the sport utility vehicle (SUV) market in North America in recent years more emphasis has been placed on fluid performance in these vehicles. In addition to fuel economy the key performance area sought by original equipment manufacturers (OEMs) in general has been temperature reduction in the axle. This is being driven by warranty claims that show that one of the causes of axle failure in these type vehicles is related to overheating. The overheating is, in turn, caused by high load situations, e.g., pulling a large trailer at or near the maximum rated load limit for the vehicle, especially when the vehicle or its main subcomponents are relatively new. The excessive temperature generally leads to premature failure of seals, bearings and gears. The choice of lubricant can have a significant effect on the peak and stabilized operating temperature under these extreme conditions.

Several laboratory methods evolved with time and experience to assess lubricant performance. One laboratory method was created to reproduce a scenario leading to the stated warranty issues encountered by some equipment manufacturers today. This involved using a new axle and subjecting it to a simulated severe road condition after a short break-in period and measuring the peak temperature as a function of fluid type. This was later validated with actual vehicle evaluations conducted in a desert region of the USA in high ambient temperature conditions. Good correlation was observed between the laboratory and vehicle methods. Further refinement of the laboratory method now is in progress based on vehicle data obtained during these evaluations. Both methods showed that fluid choice can have a significant effect on peak and stabilized temperatures.