Gearbox & Hydraulics –

Partners For Life

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As the relationship between the gearbox and the hydraulic system becomes increasingly linked, Craig Scarborough shines a light on F1’s often-overlooked engineering partnership.

In the past two years, a lot of focus on the powertrain of an F1 car has been on the engine and energy recovery systems (ERS). Yet, sat behind both of these are two otherwise unsung elements to a cars’ overall efficiency: The gearbox and the hydraulic system.

What was once a clunky, unreliable part, the gearbox is now a seamless operating system, whose complexity often goes unrecognised. And the hydraulic system – which controls everything from the gearbox to the throttles and the steering – is another such F1 development whose importance deserves attention.

Historically, everything on an F1 car was mechanical. The gearbox was directly operated by the driver, and was considered one of the key items too complex for a small team to design and build themselves. Most teams bought in gearboxes from specialist suppliers, some of which even had their root in the humble VW Beetle.

Nowadays, however, nearly every team is responsible for their own gearbox, either making it in its entirety or having a primary role in designing it. Indeed, it’s fair to say things have moved on considerably since the days of the classic 4-speed H-gate gearboxes, which operated via a convoluted linkage from the gearbox to the lever in the cockpit.

These days, teams run 8 gears plus reverse in their gear cases. The gear lever has long since departed from the sport with the paddle gearshift selecting each gear sequentially. The modern gearbox really evolved through the nineties; its quick-shifting set up allowed by the reapplication of electro-hydraulic control systems, lifted from active suspension technology, itself cribbed from aircraft control systems.

Through the nineties, teams took greater ownership of the gearbox design. Not just the gear cluster itself, but also its casing, the hydraulic controls and the software required to keep the gearbox from exploding in a shower of metal gear teeth. Albeit this revolution still required the assistance of the same gearbox specialists, who continue – for the most part – to make the intricate gears and the shafts they spin upon.

With some 800hp being passed through the gearbox to the grippy rear tyres, loads and pressure on and within the gearbox are immense. To maintain the gearbox’s performance, the gears needs to mesh smoothly and be kept cool. A lack of lubrication will not only increase friction – thereby robbing the powertrain of power – but also generate heat. The carefully hardened steel gears cope very well with these running conditions but, if they run too hot, they lose their strength and this can lead to failures. Therefore, gearbox oil needs to act to both lubricate and cool, and so these oils are fed from a mechanical pump through the gear shafts, over the gears and over the selection mechanism and differential. To keep the oil (and therefore the gear cluster itself) cool, the gearbox oil emerges from the case to enter an oil cooler, which is fed by cooling air from the roll hoop area.

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Seamless

As the 21st century dawned, gearboxes and their hydraulic systems were still often unreliable and huge projects for a team to embark upon. Yet, already, another challenge was on its way.

For anyone who has driven a manual gearbox car enthusiastically, it’s obvious a quick gearshift allows quicker acceleration as the engine is driving the car forward more of the time, and not wasting time waiting for the next gear to be engaged. This knowledge wasn’t lost on the F1 fraternity. The hydraulically-operated gearboxes of the late nineties brought shift speeds down to milliseconds, using a motorcycle-style selector drum system to accurately select the next gear in turn. But, with this system, there was always an unavoidable period when the selector drum took the current gear out of engagement, in turn engaging the next gear. Of course, having two gears engaging at the same moment would spell catastrophe for the gearbox. With this glass ceiling, teams could not reduce lap times any further with the speed of the shift. Several teams looked at the problem and, although solutions were out there, they came at the cost of hideous complexity.

What was needed was a gearbox system that did not require watch-like complexity inside the gear case, yet one that still met the restrictive technical regulations. In the end, the solution was surprisingly easy.

The single selector drum which selected each of the gears was replaced with two selectors, which worked on alternate gears. With this set up, one gear could be engaged at the very moment the current gear was disengaged. In theory, two gears could be engaged simultaneously. This would allow the engine to keep driving the car forwards as there would be no break in the power delivery through the gearbox – in effect, a seamless delivery of power to the road. So why is it , then, that this did not lead to an exploding gearbox?

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Control

The secret to this current generation of seamless gearboxes was and still is the hydraulic control system, with its powerful hydraulic pump, accurate sensors and complex ECUs. So clever, is the current hydraulic control of the gearbox, that the ECU knows the radial position of the gears on their shafts and the engine’s firing order at the actual point the driver wants to select the next gear. And so, the shift is made at the point the gears are perfectly phased and the engine is in-between sparks. This minuscule and momentary gap allows the new gear to be engaged and, as the engine starts to drive the new gear, the load is taken off the old gear, allowing it to be pulled out of engagement. At no point does the ECU lift off the power delivery, and at no point do the wheels stop driving the car forwards. This technology wins several tenths of a second per lap. As such, once teams found out the secret, it soon became a must-have technology and it is now the case that every car has a seamless shift system controlling up to 8 gears.

Indeed, while the gearbox has been optimised and gained its dual selection mechanism, the real secret is the hydraulic control system. By having hydraulic actuators operated by electronic valves under ECU control, the hydraulic system can finely and proportionally operate nearly any sort of movement needed on the car. Currently, the hydraulic system operates a long list of systems on the car; gearshifts, clutch, reverse gear, differential, DRS, throttles, variable inlet, turbo wastegate, turbo pop-off valves, brake-by-wire and power steering. Back when refuelling was allowed, even the fuel flap was opened by use of a tiny hydraulic ram.

Mounted to the engine is a hydraulic pump, which pressurises the hydraulic fluid in the system and is held within an accumulator, ready for when a valve needs the pressure to control a system. A network of pipes carries the pressurised fluid around the car. When the driver needs a system operated, a small electronic valve opens to feed in the pressurised fluid to move the actuator. With a feedback loop from the sensors mounted to the actuator, the movement can be microscopic and highly accurate. Not only that but, as required, with the previously described gear selection, the hydraulic control can be very quick and very powerful.

Such control requires the fluid to be pumped at very high pressures: some 300 bar. This creates a lot of heat in the system – typically, the fluid runs at 120-140 – then there’s heat conducted into the system from the actuator’s proximity to hot areas of the car, such as the engine, gearbox and turbo. Containing heat within the system is further complicated by F1’s need to always be lightweight. As a result, the total volume of hydraulic fluid is just 800cc; thus, it is cycled through the system rapidly, leaving no scope for it to rest and cool. Therefore, a small oil cooler is built into the system, requiring the team to mount and feed cooling air through it.

Nowadays, all this high pressure control and rapid gearshifts operate with the utmost reliability. It’s now rare for a car to retire from hydraulic failure, while the gearboxes are required to last in their entirety for six races before being replaced with another unit. That’s some 2,000 miles of high-speed running without any team intervention or part-swapping. Such rock-solid performance and reliability is probably the main reason the gearbox and hydraulics remain unmentioned; yet it is an engineering feat which should perhaps be lauded.

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