All Formula One cars, including the current generation with 1.6 litre turbocharged engines as well the previous V8s, feature dry-sump lubrication. The demands placed on the lubrication system in a Formula One car are extreme, with high temperatures and g-loadings making consistent oil supply a challenge. It is therefore worth looking at some of the methods used to ensure an optimal oil supply, while also ensuring maximum efficiency to minimise unnecessary losses.
Taking as an example the dry-sump system found on Honda’s V8-engined cars in use until the end of 2008, there are in fact two pumps on the engine, one feeding the oil and the other scavenging it from the sump. These pumps had torocoid rotors, with four inner and five outer teeth, which provided excellent volumetric efficiency.
A key design requirement for Honda was that each section of the engine should get the correct volume of oil, at the correct pressure, all the time. Ensuring that this happened was no easy matter, for example the valvetrain needed a high volume of oil at low engine speeds, but the demand did not rise with engine speed. Conversely, the oil supply to the main and big-end bearings, supplied though a centre feed in the crank, needed to rise in pressure as engine speed rose.
One major problem the team faced was a loss of feed pump performance as engine speeds increased (to more than 18,000 rpm eventually), due to suction cavitation in the pump. One potential solution would have been to reduce the pump speed and increase its size, but given the ever-present pressure to reduce mass and packaging size, this was not considered to be a viable option. Instead, Honda identified the root causes of the cavitation.
There were found to be two clear contributing factors. First, an insufficient volume of oil was being drawn into the rotor suction chamber during rotational transfer at high speeds. Second, the oil that was being drawn into the rotor chambers was leaking out because of centrifugal force. To cure the first issue, Honda replaced the thick, single rotors with thinner twin rotors, while the second was addressed by redesigning the suction port, so that as the suction chamber filled with oil, the port closed, preventing leakage.
The modifications were a resounding success. In 2005, Honda’s feed pump was rotating at 12,800 rpm but suffered a considerable decline in pressure at these speeds. With the modifications, which allowed for the basic pump design to be retained, flow rate increased by 30% for no reduction in speed.
Another interesting area of development for Honda was the pump rotor material itself. Initially, these rotors were constructed from sintered aluminium; however, in a bid to reduce rotating weight, and hence overall engine losses, Honda experimented with different materials.
The last generation of engines, used during the 2008 season, featured an inner rotor made from sintered magnesium, with an outer rotor of plastic. Due to the soft nature of these materials – particularly the plastic – the team had to develop a new profile for the rotors, which retained pumping efficiency but reduced surface pressure between the teeth. If the tooth geometry had been left the same as that used for the harder materials, the level of friction between the teeth would have increased, negating any gains from the rotors’ reduced mass.
This is only a small insight into the level of optimisation that goes into just one component in a Formula One powertrain, but it shows the lengths engineers will go to in order to find performance gains in such series and the interesting paths down which such investigations may lead them.
Written by Lawrence Butcher