What is Hypoid Gearbox?
Hypoid gearboxes are a type of spiral bevel gearbox, with the difference that hypoid gears have axes that are non-intersecting and not parallel. In other words, the axes of hypoid gears are offset from one another. The basic geometry of the hypoid gear is hyperbolic, rather than having the conical geometry of a spiral bevel gear.
In a hypoid gear, the spiral angle of the pinion is larger than the spiral angle of the gear, so that the pinion diameter can be larger than that of a bevel gear pinion. This offers more contact area and better tooth strength, which means that more torque can be transmitted and high gear ratios (up to 200: 1) can be used. Because hypoid gear shafts do not intersect, bearings can be used on either side of the gear to provide additional rigidity.
The difference in spiral angles between the pinion and the crown (larger gear) causes some sliding along the teeth, but the sliding is smooth, both in the direction of the tooth profile and lengthways. This gives hypoid gears very smooth running properties and quiet operation. However, due to the pressure between the teeth, special EP (Extreme Pressure) gear oil is also required to maintain effective lubrication.
What is hypoid gear oil?
A hypoid gear oil is a lubricant that is designed to operate effectively with hypoid gear designs. Most gearboxes and differentials use hypoid gear designs and the lubricant must contain EP (extreme pressure) additives to prevent wear between the sliding surfaces of a hypoid gear mesh.
Hypoid gear oil sae 80W/90
GEAR OIL HYPOID SAE 80W/90 is a high-pressure gear oil that can be used wherever very high levels of stress occur, such as in cardan joints, hypoid gears etc. The first-class paraffinic base oils and the coordinated, innovative additives give the lubricating film an extremely high level of tear resistance, thereby preventing direct contact with metal.
Difference Between GL-4 and GL-5 gear oils
When deciding on a gearbox or gear oil, you may be wondering what GL-4 and GL-5 mean and what are the differences between these two classifications. Choosing the right classification is extremely important as both have different properties and incorrect use can cause serious damage to your vehicle.
There are four different classifications for transmission/gear oil. These different classifications define a certain level of performance in driven axles and manual gearboxes. They are mainly important for the transport sector in North America, Africa, and Asia. The active classifications are:
The higher the Extreme Pressure (EP), the higher the GL category is. It is important to know that the SAE Motor Oil Viscosity Chart (J300) is different from the SAE Gear Oil Chart (J306). The viscosity has no relation with the API Gear Oil Classification and should be chosen based on the recommendations from the manufacturer based on the temperatures where you will drive.
Is hypoid gear oil the same as GL5?
The main difference between GL-4 and GL-5 gear oils is the amount of EP additives. Sulfur/Phosphorus-containing products are used as EP-additive. This additive has the purpose to prevent the occurrence of micro-welds on the gear flanks at the local high temperatures which prevail in EP circumstances (temperatures well in excess of 800℃!) GL-5 has roughly twice the amount of EP additives compared to GL-4, which is why it is often used in high-pressure circumstances such as in a front axle and rear axle differential.
However, sulfur/phosphorus additives have an unfavorable property: they can react aggressively to bronze and copper. This can be catastrophic for the synchronizer rings of a transmission. Therefore, it is not recommended to use GL-5 in a gearbox unless the manufacturer allows it.
- 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 generally used when the speed exceeds 1000 RPM (although ground gears above 8000 RPM are recommended). However, they are also useful for lower-speed applications that require extremely smooth running or quiet operation. In multi-stage gears, hypoid gears are often used for the output stage, where lower speeds and high torques are required.
The most common application for hypoid gears is in the automotive industry where they are used in rear axles, especially for large trucks. With a left spiral angle on the pinion and a right spiral angle on the crown, these applications have what is known as an “offset below center” which allows the driveshaft to be located deeper in the vehicle. This lowers the center of gravity of the vehicle and, in some cases, reduces the disruption of the interior of the vehicle.
Advantages of hypoid gearboxes
- Use when installation space is limited
- High torques
- 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