What Is Hypoid Gearbox And Hypoid Gear Oil?

What is a Hypoid Gearbox?

Hypoid gearboxes represent a specialized form of spiral bevel gearboxes, distinguished primarily by the orientation of their axes. Unlike conventional spiral bevel gears, where the axes intersect, hypoid gears feature axes that are both offset and non-parallel.

This unique offset gives hypoid gears their characteristic hyperbolic geometry, in contrast to the conical shape typically associated with spiral bevel gears. One practical result of this design is that the spiral angle of the pinion is intentionally greater than that of the mating gear. This difference allows the pinion itself to be larger than what is possible in traditional bevel gear setups.

The advantage here is twofold: a larger pinion diameter means more surface area for contact, which in turn boosts the strength of the gear teeth. As a result, hypoid gearboxes are able to transmit higher torque and accommodate significantly higher gear ratios—sometimes reaching as much as 200:1.

Another benefit of the non-intersecting shafts is that it becomes possible to place bearings on both sides of the gear, adding an extra layer of rigidity to the entire assembly.

Of course, the distinct spiral angles between the pinion and the larger gear (often referred to as the crown) introduce a degree of sliding motion along the teeth. Fortunately, this sliding action is generally smooth—both across the tooth surface and along its length—which helps hypoid gears run quietly and efficiently.

That said, the increased pressure at the point of contact does require special consideration when it comes to lubrication; specifically, the use of Extreme Pressure (EP) gear oil is necessary to ensure reliable, long-term performance.

What is hypoid gear oil?

Hypoid gear oil is a specialized lubricant formulated specifically for use with hypoid gear systems. These gears are commonly found in gearboxes and differentials, where their unique design creates significant sliding contact between surfaces. Because of this, the oil must include extreme pressure (EP) additives, which play a crucial role in protecting the gears from wear that can occur during operation.

Hypoid gear oil sae 80W/90

GEAR OIL HYPOID SAE 80W/90 is formulated to meet the demands of situations where gears are exposed to intense pressure—think of applications like hypoid gears or cardan joints, where the mechanical stress can be particularly high.

This lubricant relies on high-quality paraffinic base oils, complemented by a carefully selected blend of advanced additives. Together, these components reinforce the oil’s protective film, making it exceptionally resistant to tearing. As a result, the risk of metal surfaces coming into direct contact is effectively minimized.

Difference Between GL-4 and GL-5 gear oils

When it comes to selecting a gearbox or gear oil, you might find yourself unsure about the meaning behind terms like GL-4 and GL-5, and how these classifications differ. This decision isn’t just a matter of preference—choosing the correct type is crucial, as each classification comes with specific properties, and using the wrong one can lead to significant damage to your vehicle.

Transmission and gear oils are grouped into four main classifications, each indicating a distinct performance standard for driven axles and manual gearboxes. These categories are particularly relevant across transportation industries in regions such as North America, Africa, and Asia. The currently recognized classifications include:

• GL-1
• GL-4
• GL-5
• MT-1

Essentially, as the Extreme Pressure (EP) capacity increases, so does the GL rating. One point that’s often overlooked is the distinction between the SAE Motor Oil Viscosity Chart (J300) and the SAE Gear Oil Chart (J306). These are separate standards, and it’s important not to confuse the two.

Keep in mind, viscosity doesn’t correspond to the API Gear Oil Classification. Instead, you’ll want to select viscosity based on the vehicle manufacturer’s guidelines, particularly considering the temperature ranges you expect to encounter while driving.

Is hypoid gear oil the same as GL5?

The primary distinction between GL-4 and GL-5 gear oils lies in their concentration of extreme pressure (EP) additives, specifically those containing sulfur and phosphorus compounds. These additives are incorporated to safeguard gear surfaces from microscopic welding, which can occur under the intense localized heat generated during operation—temperatures in these scenarios can easily surpass 800℃.

GL-5 oils, in particular, contain approximately twice the level of EP additives compared to GL-4. This higher concentration makes GL-5 the preferred choice in applications that demand resistance to extreme pressure, such as front and rear axle differentials.

On the flip side, there is a trade-off to consider. Sulfur and phosphorus additives, while excellent at protecting steel gears, tend to be quite harsh on metals like bronze and copper. This chemical reactivity poses a significant risk to the synchronizer rings found in many transmissions. For this reason, it is generally advised not to use GL-5 oil in gearboxes unless the manufacturer explicitly states that it is safe to do so.

To conclude:

• GL-4 is suitable for hypoid gear service when they are under severe service but are without shock loading.
• GL-5 is suitable for hypoid gear service under severe service and shock loads and not for use in a gearbox.

Where are Hypoid Gearbox use?

Hypoid gears are most commonly employed in situations where rotational speeds exceed 1,000 RPM; in fact, for applications above 8,000 RPM, it is generally advisable to use ground gears for optimal performance. Still, their usefulness is not limited to high-speed systems. In scenarios where machinery operates at lower speeds but demands exceptionally smooth or quiet operation, hypoid gears can be an excellent choice.

In multi-stage gear assemblies, hypoid gears frequently find their place at the output stage. Here, the operating conditions typically involve lower speeds and higher torques, which align well with the strengths of hypoid designs.

Perhaps the most familiar use for hypoid gears is within the automotive sector—particularly in rear axle assemblies of larger vehicles such as trucks. The design of these gears typically features a left-hand spiral on the pinion and a right-hand spiral on the crown, creating what is referred to as an “offset below center.”

This specific configuration allows the driveshaft to sit lower in the vehicle chassis, which in turn lowers the overall center of gravity. In practical terms, this adjustment not only contributes to improved vehicle stability but can also help minimize intrusion into the interior space, depending on the particular vehicle design.

Advantages of hypoid gearboxes

• Use when installation space is limited
• High torques
• Quiet
• Compact design
• Can be combined with other types of gearbox
• A hollow shaft is possible on the input shaft

Disadvantages of hypoid gearboxes

• Complex design
• Lower efficiency level than the planetary gearbox
• Not suitable for fast speeds

FAQs