InDetail: The Engine Oil System

FLOW

Keeping an engine that spins at up to 18,000rpm for nearly two hours lubricated and cooled is the job of the oil system. Rarely seen or talked about the pumps, tanks and plumbing are a critical part of an F1 cars packaging.

Engine oil circulation
Oil is pumped into the engine and is directed around the casings to the critical parts via numerous galleries inside the castings. Key parts receiving lubricating oil are the crankshaft, valve train and cylinder bores. For these parts the oil is cooling as well as the core job of lubricating. However oil is also sprayed under the piston crowns to help cool the piston, in this role lubrication is not a requirement. To do this there is an aluminium ring mounted at the base of the cylinder, the connecting rod passes through the ring and up to 8 fingers project upwards from the ring to spray oil in the recesses of the pistons underside.

FrontView

It’s important to note that this is the engine oil system, the gearbox receives its own formula of oil and is contained within a completely separate system, although teams have tried a combined oil systems previously.
Once the oil has completed is job of cooling/lubricating the engines moving parts, it needs to drain back to be de-aerated and cooled before being filtered and passes back into the engine.
Oil drains back into the sump where it will collect, so the oil is picked up by slots in the sump pan by scavenge pumps mounted along the right hand side of the engine. The scavenge pumps will be driven by an idler gear coming off the front of the crankshaft.

SideView
This set up is common to race cars and is known as a dry sump, as little remains in the sump at any one point. This allows the engine to lower, as a deep sump pan (in a wet sump set up) is not used to collect and store the oil. Additionally a dry sump reduces the amount of oil that is caught by the spinning crank shaft, this frees up more power as the crank is slowed by the drag of the oil. Thus the detail design of the sump is modelled in CFD to ensure the minimum of oil obstructs the crank, this may involve scrapers and baffles, but I have not seen these fitted to any F1 I have had a close look at, possible as the crankcase is wrapped so tightly around the reciprocating parts that their installation is impractical.
The sump is separated into four compartments one for each crank throw (each covering a left and right cylinder), so four scavenge pump stages are used to this purpose.

Scavenge

Other scavenge pump stages will also draw oil draining from the valve train in the cylinder heads. Typically team mount small oil scavenge pumps on the back of the engine driven by one of the cams. Some times oil will be scavenged from the compartment housing the timing gears.

Mercedes scavenge pump detail

Mercedes scavenge pump detail

Oil recirculation
Once collected by the scavenge pump, the oil is hot at around 90c and full of air bubbles, it is routed directly to the top of the oil tank mounted between the engine and monocoque. Its important to remove the air bubbles as the oil is less efficient at lubricating and cooling in this form, air bubbles will soon wreck bearings and ‘blow’ the engine.

Mercedes oil tank with fluid-level sensor visible at the top of the tank

Mercedes oil tank with fluid-level sensor visible at the top of the tank

Oil is pumped into the tank from the top both to remove the air bubbles and to allow the oil to start to cool; as heat rises the oil will be cooler at the bottom where the oil continues its journey. The oil pipe enters the tank at a tangent to the tank’s walls, this creates a swirl effect to start the de-aeration process. Additionally the tank will have a vent\over flow and its own temperature sensor. Its breather will vent into the airbox so that any oil spray does not find its way on the track and ends up being sucked into the inlets and burnt.
The oil tank will contain baffles to prevent oil surging away from the pick up point at its base, these baffles will help prevent surge in al directions, longitudinal, lateral and even vertical. Famously cresting the exit of Eau rouge at Spa will see the oil rise upwards in the tank and potentially starve the engine of oil. Teams design the tank to accommodate this; the system will ensure that enough oil remains at the bottom of the tank to feed the engine during this brief moment every lap. When being designed and tested, oil tanks will be fitted to gimball rigs to replicate the motion of the car around a lap. With both sensors and windows in the tank the team can assess how effective their baffle system is. Unlike the cars fuel tank, the oil tank will have a fluid level sensor; companies like Gill sensors provide a tall sensor that will measure the top of the oil level.  Gill report that the difficulties for an oil level sensor are the harsh conditions “temperatures often in excess of 100°C along with high vibration are the main challenges”, but “careful application engineering can achieve accuracy levels of <1.0%”.  This accuracy is possible as the “sensors have in built baffles to reduce the effects of slosh in the tanks”. (thanks to Gillsensors.co.uk @Gillsensors)

Oil telemetry data viewed from the pit garage

Oil telemetry data viewed from the pit garage

The oil will then pass out of the tank into the oil cooler. Teams only require one relatively small (compared to the water radiators) oil cooler for engine oil. This will be fitted to only one sidepod, thus the heat rejection requirements of one sidepod will differ from the other, and this is why teams run asymmetric cooling layouts. Oil needs to be warm to thin enough and also keep the engine warm (tight manufacturing tolerances mean that the engine needs to be at operating temperature in order to turn over, otherwise it is effectively seized at lower temperatures. But oil must not be allowed to overheat, as it both degrades the oil and the thinner oil risks damaging the engine due to lack of lubrication. Despite this oil temperatures run at over 100c, with temperatures when the car is idling in the garage (at 4k rpm) of 90c.

FLOW
From the oil cooler the oil piped to the oil pump where it is passed back in to the engine again. The oil pump itself is mounted to the side of the engine in front of the scavenge pumps; it uses a gear type pump process. Such is the rate of flow at around 4-5bar, the oil is cycled through the system rapidly; the entire system may only contain a 4-5 litres of oil.

MErcedes_oilpump

As the race progresses the oil level will go down as some is burnt away from the cylinder walls and due to degradation. All cars carry an auxiliary oil tank, this is often fitted low down on the side of the engine or inside the main oil tank and carries just a litre or two of oil. This oil will be called for during the race, the team will radio the driver, Lotus (Renault) often this called an oil bomb, and the cars hydraulic system forces the oil out of the auxiliary tank into the main oil tank. An ‘Oil’ button on the steering wheel achieves this function.