The dry sump lubrication system is a design that intends to lubricate the engine's internal parts to provide optimal performance of the engine itself. It is currently the best system for high performance engines and is widely used in Formula One, Le Mans, IRL and other well known racing series.
Lubrication systems for a four-stroke, reciprocating piston engine can be categorised in just two groups: the wet sump design and the dry sump system. Both systems rely on an oil reservoir from which oil is drawn with a pump and spread around the engine for lubrication and cooling purposes. All oil is then allowed to flow back to the reservoir from where the cycle restarts.
Wet sump lubrication is the most widely used system as it is more cost efficient and perfectly adequate for normal passenger vehicles. In this design, the oil of the engine is stored in a sump located under the crankshaft as an integral part of the engine block. The oil pans' capacity can range from 3 to 7 litre, depending on the engine's size and purpose. From this pan, the oil is pumped up a pick-up tube and supplied to the engine under pressure. A wet sump design has several advantages, including its low cost, low weight and its simplicity. Because the sump is an internal part of the engine, there is no need for tubes to circulate the oil from the reservoir to the engine, reducing chances of leaks.
Despite its advantages, a wet sump system is unsuitable for racing purposes.Formula One cars for example experience lateral G-forces of up to 3G in mid corner. Such centrifugal accelleration would pull all oil to one side of the sump, possibly leaving the engine without oil for a short period. The latter phenomenon is also known as oil starvation. When performance and reliability matter, such a situation is unacceptable. To resolve this issue, the dry sump system was designed and is now in use in all major racing series.
The dry sump system literally keeps the sump of the engine dry and allows for it to be produced small, giving a further advantage to lower the engine's centre of gravity and reduce its empty weight. The design differs from a wet sump in its external oil tank. Again, the oil is pumped into the engine at elevated pressure and then flows down to the engine's sump. While it was previously held there, the oil is now sucked away from the engine by one or more scavenger pumps, run by belts or gears from the crankshaft, usually at around half the crank speed.
In most designs, the oil reservoir is tall and narrow and specially designed with internal baffles. The pump itself consists of at least two stages with as many as 5 or 6. With two stages, one is for scavenging while the second is a pressure stage. The three-stage dry sump pump has one pressure section and two scavenge sections, while the four-stage pump has one pressure and three scavenge sections. The pressure section of each feeds oil to the block, while the scavenge sections pull oil from special pickups in the dry sump oil pan. The latter system is connected similar to the three stage while the extra line of the scavenge section is routed to pull oil from the lifter valley. This prevents excess oil to slosh in the top of the engine, reducing windages and increasing horsepower. In some cases, a fifth stage is added to provide extra suction in the crankcase area.
Application in Formula One
As mentioned, all current F1 engines include a dry sump system, quite simply because it is impossible to create a similar high revving engines with a wet sump system. Due to the engine freeze, all engines also have a similar layout as the fuel tank is located ahead of the engine, just behind the driver. The oil pump that rotates the oil through the engine is - as required by the regulations - driven by the crankshaft through gears.
One of the providers of the required high performing lubricants is Shell, the supplier of Ferrari. Shell Technology Manager for Ferrari, Dr. Lisa Lilley explains: “Engine lubricant is critical. The very lifeblood of the engine, its job is to protect the moving parts from mechanical wear, reduce friction and power loss and cool the engine as it endures extreme track conditions. It takes a good engine lubricant to achieve just the right balance of these characteristics, while ensuring the car’s performance is optimised, no energy is wasted and maximum power is delivered to the engine.”
The first job of Shell Helix is to protect all the moving parts that rub together from mechanical wear. The oil is fed to the bearings of the camshafts to lubricate, minimising friction and wear, thereby enhancing the engine’s reliability. The enormous forces required to open the valves quickly enough at 19,000 rev/min must also be transmitted through a lubricant effectively and without failure.
The engine is exposed to extreme conditions and high temperatures as it turns. The ‘multi-tasking’ lubricant is designed to take away the heat, controlling the engine temperature and preventing the heat from having a detrimental affect. The ability of an engine oil to cool as well as lubricate is often overlooked. Pistons can exceed temperatures of 300°C; engine oil is sprayed on the underside of the pistons to keep them cool - without this extra protection they would undoubtedly fail in a race.
“When you consider that the oil flow around the engine is faster than the speed of the Ferrari Formula One car, this gives you an idea of the extreme conditions in a Formula One engine,” says Dr. Lilley. “At Shell we have a team dedicated to tailoring Shell Helix engine oil for the Ferrari so that we can ensure reliability and protection but we can also guarantee the car is receiving the most horsepower possible.”
|Oil is pumped from the “dry sump” oil tank on the front of the engine into the “distribution network” within the cylinder block and heads, which ensures it gets directly to all critical engine components
|Lubricant is fed to the bearings of the camshafts to minimise friction and wear and also to lubricate the critical cam-to-follower interfaces, where the enormous forces required to open the valves quickly enough at 19,000 rev/min must be transmitted through a layer of lubricant efficiently and without failure
|The lubricant is fed down the middle of the crankshaft, coming out inside the bearings to keep them working. The lubricant flung off these bearings then creates a film on the cylinder walls, on which the pistons and rings run smoothly to ensure minimum power losses and mechanical wear
|The lubricant squirts onto the underside of the pistons from small nozzles on the distribution network, to take away heat
|The used lubricant is sucked away from the bottom of the crankcase by the scavenge pumps, to be cooled in radiators and returned to the oil tank, refreshed and ready to start its circuit of the engine again
|The “camera” exits the engine, showing a fully lubricated engine