Formula 1 valve trains

Question

There was a statement in a post regarding Formula 1 valve trains being pneumatic or magnetic. Are there valve trains driven magnetically or pneumatically that are on the market? When did they start using these kinds of valve trains? Does this mean they don't have camshafts and are controlled by a computer?

Answer 1

First, it's probably important to review what valves do and how they're supposed to work on a four stroke internal combustion engine.

What valves do

Essentially there are intake valves and exhaust valves with a minimum of one of each per piston, but F1 cars (and many modern road cars) use two of each. The following description will use "valve" singular, but it should be understood that in multi-valve engines, the valves operate in synchrony -- that is, whether the engine has one or two intake valves, they are in the same position at each instant in time.

The intake valve allows the fuel/air mixture into the cylinder as the piston moves down (away from the valve) and then closes so that the mixture can be compressed by the rising piston. It's then ignited by a spark and the resulting mini-explosion pushes the piston back down. That's the power stroke. Finally, the piston comes back up as the exhaust valve opens and the exhaust gas is pushed out of the cylinder.

How they work

As should be obvious from the above description, the valves must be exactly synchronized to the operation of the pistons moving up and down. If they were to get out of synchronization, the engine would have less power (if they're slightly off timing), or not run at all (if they're grossly off timing) or destroy the engine by causing the pistons to crash into the valves, bending or breaking the valves (in some designs). For many decades, and up to the current time, most engines use cams to push the valve down (opening it) and springs to close the valve again. It's inexpensive, reliable, efficient and a well-proven design, but there are limitations.

Let's go racing!

When engine speeds go up, the valves have to go faster. An F1 car is designed to rotate up to 15,000 RPM according to the current regulations; previous seasons' cars revved even higher. Typical road-going cars have "red line" at around half that. ("Red line" refers to an actual red line on the tachometer which is intended to indicate "if you go beyond this point, severe engine damage is likely!") When an engine is turning that fast, the spring becomes an issue. First, it needs to act very quickly. We can make it close the valve quicker by using a stiffer spring, but then we need to expend more energy compressing the spring each time the cam rotates to close the valve. Further, it was found that at certain engine speeds near the spring's resonant frequency, the valves don't close as quickly as they should, so some racing engines use two or three concentric springs with different resonant frequencies to overcome this.

Springtime in Paris

One approach that was used successfully by Renault originally (yes, I know they're not actually based in Paris, but I couldn't resist using the heading) and soon after by all F1 engine manufacturers was a pneumatic valve. Essentially, it's just a diaphragm filled with an inert gas such as nitrogen that acts like a spring, but faster. They also have the advantage of lower weight, which is always of interest to racing engineers. Keep in mind that while pneumatic valves could be used at lower RPMs, the problem they're meant to solve is at such high RPMs far above those that the family sedan could withstand, so that's why they're not (yet) used in road cars. There's also a system called "desmodromic" which essentially uses two cam lobes -- one to open the valve and another to close it. To my knowledge it hasn't ever been used in F1 (Forgive me Fangio, for I have sinned! The 1954 Mercedes-Benz W196 employed desmodromic valves.), and the primary user is Ducati in their motorcycles. This is already long enough, so I won't describe that one here.

Can we do still better?

The cam system I've been describing works well, but it's a compromise. The timing and duration of the periods that each valve is open is fixed by the shape of the camshaft lobes and the speed of the engine. At some point in the engine's RPM range, a particular cam shaft provides the optimal duration and timing, but only at that one point. For every other engine speed, it's going to be sub optimal in terms of efficiency or power or both. Ideally, we'd want better control of the valves to assure ideal settings at more than one specific RPM value.

How can we improve valve control?

There are a number of ways to address this. One simple way to do it is to have two cam lobes per valve and use an actuator that changes which one actually opens the valve. That's essentially exactly what Honda's VTEC system does. We can do even better by continuously varying the cam timing, which is what Toyota's VVT-i, BMW's VANOS and Porsche's Variocam systems do. They all have the ability to slightly vary the cam timing so that the engine is operating at peak power in a much broader range of engine speeds.

That's good, but we can imagine going still further. Even better would be to eliminate the cam entirely and use, for example, a solenoid under computer control. Obviously both the solenoid and the computer controlling it would have to precisely duplicate the timing that is currently being provided mechanically by the cams, but it has a significant potential advantage in both weight savings and in extremely flexible control allowing moment-by-moment dynamic adjustments of valve timing. However, this has proven very difficult to actually achieve reliably, so no production engines have yet been produced that use this kind of technology. Koenigsegg is rumored to be close, but few of us are going to be able to afford one of those.

Which variable valve system is used in F1?

The answer may surprise you: none of them. If you read through the 2016 Formula 1 Technical Regulations (and who doesn't?!) you'll see this:

5.9.2 Variable valve timing and variable valve lift profile systems are not permitted.

Drive proud!

So there you have it. While there is a lot of cool technology in F1 engines, including pneumatic valve "springs," you can smugly drive down the street in your primer-gray 1999 Honda Prelude with the missing fender and dented hood knowing that your engine actually incorporates technology that no current F1 car has -- variable valve timing.