24 March 2013
Technical Focus: Throttles
Throttles are one of the most important components in an F1 engine, so read on to find out exactly what they are, how they have changed over the years and how Renault Sport F1 has optimised their operation.
Explain in simple terms what a throttle is.
A throttle has come to be associated with any part that controls the power of an engine - such as the accelerator pedal - but in actual fact it is a hydraulically operated mechanism used to increase or decrease inlet gases to the engine. In a V8 there are eight throttles on the top of the engine unit that control the amount of air that enters each of the engine cylinders from the airbox. When the throttles are open, air enters the engine unit. Fuel will be injected just before the inlet valve and hence the combustion chamber, and the spark plug will ignite the fuel and oxygen content in the air. The throttle therefore dictates the amount of fuel burned on each cycle to produce efficient power. When the throttle is closed, no air enters the engine and the combustion process is temporarily suspended. All the throttle valves are controlled via the accelerator pedal but the demand for power is sent via a signal to the ECU that then directly controls the exact position of the throttle valve through a number of maps.
What type of throttles are allowed in F1?
The technical rules governing throttles govern more the use of the engine torque and ignition maps, where the torque produced has to correspond to the position of the torque demand - ie. At full accelerator pedal travel, the throttles must be fully open and corresponding levels of torque produced, while at off throttle, the torque produced must be zero, or less than zero which translates into the throttle opening between 0 and 30%. The regulations concerning the physical throttles are actually much freer and a range of systems can be used. Generally, however, there are three types of throttle that have been used in F1 since the 1990s. The first is a guillotine valve, where the air inlet is sliced in two by a valve that extends and retracts like the mechanism of the same name. There is then the butterfly throttle, where the valve is hinged - at full throttle, the valve is vertical but when closed the valve swings into a horizontal position like a butterfly wing opening and closing. Then there are also the barrel valves where rounded barrels roll into the cylinder to stop the flow of air. Any one of these systems can be used, but generally engine manufacturers now go for the butterflies or the barrels in F1.
What sort of throttle system does the RS27 run?
The RS27 runs with the butterfly system. In the early days of the V10 and V8 throttle design, Renault Sport F1 experimented with the barrel system but elected to go with the butterflies. While the barrel system allows the engine to produce more power by allowing a greater flow of air to the engine at wide open throttle, the butterflies are more sensitive and allow a better air-fuel mixture preparation, therefore favouring driveability. The difference between the two systems is in the region of four to five horsepower and Renault believed greater gains could be found with the butterflies by delivering more stability and therefore tyre slip control and grip in the slower corners when the throttles are only partially open.
How has throttle operation changed, or been refined, since the introduction of the V8 in 2006?
The butterfly valve itself has been thinned. In the early 2000s, the valve was approximately three times thicker than it is today. With a change in materials used - from steel to titanium or aluminium to a composite plastic - the valve is now much thinner, which means only four horsepower is lost to the barrel system rather than 10 horsepower as was the case. The throttle linkage has also been simplified. In the first years of the V8 the throttles were linked by complicated separate mechanisms, which made the system heavy and difficult to maintain but very accurate. Now all the throttles are linked between cylinders by one single mechanism, which makes the whole system lighter and more integrated. The accuracy we've lost has been recovered through the possibility of running the engine with less than eight cylinders and hence the need for lower accuracy at low throttle opening.
Without the engine freeze, what would we be seeing now with regards to throttle design?
Actually, without any regulations you probably would not have throttles any more. In 2011 when teams were using maps to power off throttle blown floors, throttles were left (more or less) open the entire lap to maintain exhaust flow, and torque and ignition maps alone were used to control the torque produced. If the rules had not been clarified, then the air intake would have been left fully opened and torque would have been controlled completely by ignition. This would have made very efficient cars.
Any interesting stats and facts?
A throttle can go from completely closed to completely open in 10 to 15 milliseconds, the duration of light for a photo flash strobe. On a track such as Sepang, where wide open throttle time is equated to 60% of the lap, this translates to around 110 movements in the throttle, moving from completely open to closed and any position in between. With a lap time of around 1:36, the throttles will, on average, change position every 0.87secs, quicker than a human can blink.
Click on relevant pic to enlarge
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