Hydraulic Motor China – Hydraulic Motor Housing Lubrication Planetary Gearbox Drainage
Lubricate the planetary gearbox drain with a hydraulic motor housing: Should it be done?
The use of planetary gearboxes in the hydraulic industry is very common. Some manufacturers, primarily mobile devices, use them in applications such as swing drives, drill bits and drive systems. A common way to lubricate a planetary gearbox is to use a “bearingless” hydraulic motor and use the housing to flow through it to lubricate the internal gears in the planetary gearbox.
In this blog, Hydraulic Motor China will discuss the advantages and disadvantages of doing so and recommend the best way to lubricate planetary gearboxes. In this special case, my customer is using a “bearingless” motor and using the motor housing to drain the lubricated planetary gearbox. My customers are now switching to the Eaton VIS40 motor with the internal chassis drain and the Auburn Gear 8 planetary gearbox because the gearbox is over-aged and worn out, eventually leading to premature failure of the gearbox.
Why do people lubricate planetary gearboxes with hydraulic motor housing lubricants?
There are several advantages to lubricating a planetary gearbox using a bearingless hydraulic motor housing drain.
1. It reduces the overall package size of the system
Thanks to the “bearing-free” design, the motor can be used in a shorter package, allowing the user to use it in areas with limited size. This is beneficial in many applications, especially wheel/crawler drives, where you do not have enough space to drive the system and/or you are trying to reduce the total weight of the machine.
The use of bearingless hydraulic motor designs is generally less expensive. Reducing the cost of the motor helps reduce the overall cost of the motor/planet assembly.
3. You don’t need two oils
Gear oils and hydraulic oils are two different types of oil. They have different viscosities and behave differently with temperature fluctuations. Running a “bearingless” design motor eliminates the need to use two different fluids because it allows the planet to operate on the same fluid as the hydraulic system. This is advantageous during equipment maintenance.
4. Why is this beneficial?
Since the hydraulic motor housing is always full of gearboxes and the gearbox always flows back to the tank, the system is well flushed, allowing the gearbox to receive new oil frequently. This contributes to the life of the planet as it removes metal shavings, dirt and contaminants, making it deteriorate faster. Flushing should allow the planet to last longer. Unfortunately, flushing the planet in this way can cause unforeseen problems.
Why shouldn’t the hydraulic motor housing be used to drain the lubricated planetary gearbox?
As mentioned above, the housing drain flush system is operated through the planetary gearbox, but many people are unaware that the flushed oil may be dirty oil.
The housing drain tube of the hydraulic motor is not only designed to protect the shaft seal from high pressure, but is also designed to flush dirt and contaminants in the motor. Punching the oil into the planetary gearbox can cause deterioration of the internal gear. The oil is now full of pollution, and the pollution caused by the physical wear of the internal gear accumulated over time can greatly shorten the life of the gearbox. This is what my customers are experiencing!
Another reason for not doing this is that the oil viscosity varies widely: gear oils are usually thicker (thicker) than hydraulic oils. Because the hydraulic oil is not so thick, it does not “hold” on the gear, which reduces the efficiency of the lubricant. This will shorten the life of the planetary gearbox over time.
Thicker oils also help reduce overheating. (See “Viscosity and Wear”). Adding the planet’s hot oil to the planet will cause the planetary gearbox to overheat! We know to avoid excess heat!
Finally, it can reduce the entire system piping/hose. If a “bearingless” motor is running into the planetary gearbox, a housing discharge line from the planetary gearbox to the tank/tank is required to allow excess fluid to leave the gearbox. However, running a hydraulic motor with internal emissions eliminates the need for a tank line for the motor. Once the planet full of gear oil will be blocked, there is no need to drain the tank back to the tank. This can reduce your piping/hose and save on manufacturing costs!
Short-term cuts have long-term costs
As you can see, there are many advantages and disadvantages to designing a system for housing flow-lubricated planetary gearboxes. In my opinion, the disadvantages far exceed the professionals, especially when you talk about a ~$1500 planetary gearbox!
I think the correct way to design this system is to use a standard hydraulic motor, which requires an external housing drain hose to return to the tank or a motor that does not require an external drain hose because it is internally emptied. You will benefit from this because you will use hydraulic oil in your hydraulic motor and gear oil in your planetary gearbox.
This will also make the planet run cooler and reduce gear degradation because it has the correct oil viscosity. This is a win-win situation that will allow each system to operate as designed, reduce wear and save time and money on expensive repairs.
I admit that there are some disadvantages to running this method:
Slightly increased size and pipe complexity
A slight increase in initial costs
Requires proper maintenance (routine maintenance) – the gearbox manufacturer will specify
Overall, I think this is a better way to reduce service costs and reliability of hydraulic motor and planetary gearbox operational applications. It is common to use a housing drain of a hydraulic motor to lubricate the gearbox and in many cases it works. However, there are many factors that affect this, including work cycle, operating speed, oil cleanliness (filtration) and temperature. Before designing your system, you must be sure to consider all of these factors and understand the consequences.