Cleanliness and lubrication are key for maintaining an efficient turbo

 

 

 

 

 

 

In order for turbos to work effectively in a vehicle, their bearing systems and shaft need to be kept lubricated to avoid overheating and failure.

Turbos are kept lubricated by engine oil that is fed from the sump to the turbo bearings using a Turbo Oil Feed Pipe.

These pipe assemblies operate at pressures of up to 20 bar and typically have two small diameter formed rigid tubes in either steel or stainless steel at either end, with a flexible section connecting them, usually in the form of a stainless steel braid coated PTFE line. It is this flexible section that allows for the pipes to be assembled within tight spaces and with radii which would not be achievable for fully rigid tubes.

The flexi line section is coupled to the steel tubes using a crimped joint. This joint is very strong and needs to be able to withstand a burst pressure of 10 kPa.

At the other end of each of the rigid steel tubes there is a brazed machined banjo fitting. Banjos are produced from either steel or stainless steel machined to very tight tolerances.

Banjos have a high level of surface finish to ensure that when installed there will be no risk of oil leaks which could result in a significant thermal event. Due to the high operating temperatures it is not possible to use rubber O rings for the sealing joint between the feed pipe and the turbo. Instead it is necessary to use compression washers made in copper which crush when bolted into position but are soft enough not to damage the sealing face of the banjo.

If the part is made in mild steel then it will require surface coating in order to meet the corrosion resistance specifications. The typical surface finish is zinc plating which will give corrosion protection up to approximately 500 hours in a salt spray test cabinet.

The assembly is retained in position by machined banjo bolts which are inserted through the banjo and screw into the turbo housing and the oil sump. The bolt has cross holes drilled into it to allow for the oil to flow through the assembly and keep the turbo bearings cooled.

In order to prevent damage to the workings of the turbo, it is required that the turbo feed assemblies have a very high level of cleanliness. A typical specification for cleanliness may be no metallic particles bigger than 250 microns when tested through a filter. To achieve this, the final assembly operations for the parts are carried out within a clean room environment, with operators required to wear specific anti-static PPE to maintain the required cleanliness levels.

Each part is flushed in a special purpose flushing rig, this bi-directional operation flushes a mineral oil through the tube assembly at pressure. The process induces air bubbles which help to agitate any metallic or non-metallic particles from the internal wall surface of the tubes.

The mineral oil used need to be compatible with the oil that is used within the engine, it is also used as it provides a level of anti-corrosion protection inside the tubes until they are assembled onto the engine.

Once flushed, the parts then undergo an air decay leak testing process, the required specification  to ensure that there are no potential leaks. Once this has been passed, plastic end caps are assembled onto the banjo bolts to protect the part in transit, and then a bespoke product label is printed by the system and scanned to confirm that the part is good before it is packed for shipping to the customer.

Once the oil has been fed into turbo to keep it cool, it is then drained back into the sump via the Turbo Drain pipe assembly. This is usually a larger diameter tube than the Turbo Feed pipe and operates at lower temperatures.

Turbo Drains are typically manufactured in mild steel with zinc plating as the surface coating. As they operate at lower temperatures the sealing method used between the tube and the turbo or sump, is a rubber O ring seal.

Sometimes, when the turbo temperature is too high for a standard O ring rubber, it may be necessary to use a special O ring seal, which is manufactured from a rubber compound that is able to withstand operating temperatures in excess of 350 degrees centigrade.