Driveline fluids are responsible for transferring power through several automotive components and systems. With so much variety in the make and model of transmissions and gearboxes, how do you formulate the best fluid for the application? Afton seeks to answer the most common questions surrounding driveline fluids and provide best-in-class additive technology to meet today and tomorrow's performance needs.
What is a Driveline Lubricant?
A Driveline Lubricant is a specialized solution of base oil and performance additives to help optimize and protect power transmission in automobiles and heavy-duty equipment. Depending on the engine or transmission type, a driveline lubricant can be engineered to tailor fit the application for optimal performance and protection. There are a few driveline lubricant fluid types that we will highlight in this article:
Transmission Fluids
Axle & Gear Lubricants
Off-Road Lubricants
What is a Transmission Fluid?
The transmission in an automobile is a device connected to the back of the engine that sends power to the wheels. It is an integral part of the automobile responsible for transferring power generated from the engine into forward movement. A transmission fluid protects components within the transmission to ensure that the RPM speed stays within the desired operational range.
What Goes Into a Driveline Lubricant?
Driveline lubricant formulation can vary greatly by the specific end application, but all of the fluids can be broken down by three major components. The three components are the base oil, performance additive package, and a viscosity index improver (VII).
Component
Type
Typical Composition
(Vol %)
Base Oil
Group I, II, III or IV
80 — 90%
Viscosity Index Improver
VII (OCP, PMA)
5 – 15%
Additive Package
Dispersants
Extreme Pressure, Anti-wear
Seal Swell Agents
Friction Modifiers
Foam Inhibitors
Corrosion & Oxidation Inhibitors
5 – 10%
Driveline Composition - Base Oil
There are four common base oil types used in the formulation of driveline fluids. Each base oil type has its own performance properties, benefits, and weaknesses to consider. The table below helps simplify the base stock options.
Base Oil Group
Group I
Group II
Group III
Group IV
Sulfur Content (Vol %)
80 - 119
80 - 119
≥ 120
140
Viscosity Index
≥ 0.03
≤ 0.03
≤ 0.03
0
Aromatics Content (Vol %)
15 - 35
< 10
< 5
0
Characteristics
- -
- -
- -
- -
Low Temperature
OK
Better
Even Better
Best
Oxidative Stability
OK
Better
Even Better
Best
Seal Compatability
Best
Better
OK
Poor
Driveline Composition - Viscosity Index Improver (VII)
Viscosity index improvers (VII’s) are critical in ensuring consistent lubricant performance across a broad temperature range. A VII is designed to dissolve directly into the base oil, and expand at higher temperatures to maintain a target viscosity. Formulating with a VII prevents “thinning-out" and losing the desired protective properties of the oil. VIIs also contract at lower temperatures to maintain flowability for cold start environments. Afton Chemical provides several options for VII selection in their HiTEC® Performance Additive product line.
Driveline Composition - Additive Packages
There are many different types of performance additive technologies that can be used in a variety of driveline lubricants. The following table breaks down the most common additive types and the benefits exhibited in final fluid performance.
Additive Type
Performance Benefit in Lubricant
Detergents
Absorbs and dissolves deposit formation into the fluid to provide cleaner and longer-lasting lubricant performance.
Antioxidant
Keeps the fluid from oxidizing and degrading into potentially harmful and damaging by-products.
Pour Point Depressant (PPD)
Prevents wax crystal formation and inter-molecular bonding at low temperatures that prevents fluid flow & lubrication.
Friction Modifier (FM)
Reduces overall friction and helps minimize noise, vibration, and harshness (chatter, squeak) experienced that can lead to micro-pitting damage.
Extreme Pressure / Antiwear (EP/AW)
Prevents metal-on-metal abrasion, wear & damage under extreme pressures and high speeds during engine operation.
Corrosion Inhibitor (CI)
Prevents metal surfaces from rust & oxidation that can cause flaking and metal contamination to disperse into the lubricant damaging equipment during operation.
What Causes a Driveline to Fail?
There are many potential mechanical root causes for a driveline failure, however there are 3 main causes of failure that can be attributed to the fluid itself.
Contamination - Contamination in the fluid can lead to premature wear patterns, leakage and ultimately seizure and complete failure.
Incorrect Lubricant Selection - If the lubricant selected does not meet the recommendations of the manufacturer, it may fail to protect the driveline at its operational conditions. This can result in metal wear, grinding, fluid leakage, and ultimately componentry failure.
Not Following Drain Intervals – If the lubricant is not changed out periodically based on the owner’s manual, the lubricant can degrade over time. This unchanged fluid is subject to potential sludging and deposit formation that can detrimental to the lubricant’s ability to protect metal surfaces and the overall efficiency of the vehicle.
What are the Challenges Faced by Driveline Lubricants?
Driveline lubricants are subject to many difficult tasks in an ever-changing environment. There are a few specific challenges that stand out as most important to keep in mind over the next several years:
Fuel Economy - The industry standard is to maximize fuel economy and efficiency of new vehicles. This puts additional burden on automotive lubricants to continue to protect mechanical components with a decreasing fluid viscosity target.
Shear Stable Requirements - Multi-grade automotive lubricants include varying amounts of Viscosity Index Improver (VII) that is subject to high mechanical stress and repeated shear. Overtime this high amount of stress can result in an overall reduction of the fluid viscosity, resulting in a thin, inefficient lubricant. Performance additives will need to provide higher shear stability and withstand heavy-duty mechanical stresses.
Cold Start Requirements – Thermal stability is critical in ensuring engine components are not damaged when transitioning from extreme cold to operating temperatures. As fluid volumes decrease in new engine designs, it is important that these lubricants withstand the environmental conditions and maintain a protective lubrication boundary.
Industry Specifications – There are many industry and OEM standard specifications that ensure lubricant performance protects newer equipment designs. Common Specifications include DEXRON, MERCON, Type-F and more. If you have industry specifications required for your fluid, Afton & ChemPoint are here to help ensure your formula meets or exceeds those minimum performance benchmarks.
