Does anyone know much about this technology and whether Honda,Toyota or someone in F1 is or will be utilizing pneumatic activated valves?
The differences between a road car and a Grand Prix challenger are numerous. Some are blatantly obvious, others are hidden deep within the car to be glimpsed by only the chosen few. An example of the latter is Grand Prix engine valve springs.
What usually limits the maximum revs of a Formula 1 engine is the how quickly the valves can be opened and closed. Traditionally, valves are opened with the lobes on the camshaft and closed by a spring. For years this was no more than a piece of coiled wire like a bed spring only smaller and stiffer. Using this simple technology, engine designers had pushed maximum revs on 10 and 12-cylinder engines to more than 13,000rpm.
The problem is that at these revs the inertia of the valves becomes critical and if the spring cannot return the valve to its seat quickly enough, the rising piston will smash into it with disastrous results. A more effective way of closing valves was needed and first Renault in 1986, then later Cosworth came up with a solution. Rather than a coil spring, they developed a way of using compressed air. On the end of the valve is the cam follower that doubles as a small piston. This runs in a cylinder mounted on the cylinder head. Air is trapped in the cylinder and as the cam opens the valve, the air is compressed. When the valve is released, the air in the cylinder acts like a spring expanding to close the valve again. In the real world, a full cylinder of air at atmospheric pressure does not have enough force to close the valve again so the cylinders are pressurised to around 100psi. Obviously no seal is perfect and the teams expect some leakage so the cars carry a reservoir of nitrogen compressed to more 2500psi. This is regulated and fed to each of the valve spring cylinders via a ring main and keeps them all topped up to the required pressure. Nitrogen is used because of its stability, however, with the changing temperatures of an engine, pressures would also vary wildly. To combat this each cylinder also has its own bleed valve to release excess pressures. This has the added advantage of bleeding off any oil that collects in the cylinders.
The principle is remarkably simple to the point where one wonders why it has not been thought of before. It produces a lighter valve assembly and does not run out of travel as easily unlike a coil spring that can become coil-bound. The tricky part, though, is the design of the seal, a part that is crucial to the effective operation of the valves. Leakage must be minimal as too much gas loss will eventually bleed the system resulting in valves hitting pistons and the kind of spectacular retirements we see on TV. Certainly BMW has found this feature a challenge and the Williams Grand Prix cars have sometimes had their reservoirs topped up during race pit stops. Watch out for the man with an air-line.
The seals must also give a degree of friction to damp the valves movement. When the cam punches the valve open, its inertia can cause it to keep going so a little friction to help slow it down is essential. This used to be achieved with double valve springs mounted one inside the other. Made to precise tolerances, they would rub together giving that crucial source of friction. It now comes from the seal rubbing on the walls of the cylinder. With this technology, Formula 1 engines now rev to some 18,000rpm with consequent increases in the all-important power. In comparison, progress in conventional valve spring technology only allows Champ Car engines to spin to 15,000rpm. In an effort to keep costs down, the US series has banned pneumatic valve springs.
So, once mastered, the benefits of this technology are substantial which is why engine builders guard it closely. Back in the days of the International Touring Car Championship (ITC) Cosworth included pneumatic valve springs on the engines it developed for Opel. With the demise of the series, these high tech engines attracted the attentions of hill-climbers wanting to power their F1-style single seaters. In the end, they were allowed to buy examples of the unit, but stripped of their high tech valve train and had to develop a conventional alternative
That's really where it's going, and I can't wait.Cale said:The next step will be electro-mechanical valves. These are being worked on by Lotus Engineering. They will allow infinitely variable valve timing without mechanical connection to cam or crank shaft. Valve timing will be controlled by a computer.