Throttle body circumvention

[DannytheRadomski]

I've been reading the thread about the 2015 rule changes, and one of the more significant ones is the move of the throttle body in turbo cars.

After re-watching parts of the Inside Koenigsegg series today I was wondering if there is a snowball's chance in hell that a student team could design a pneumatic (or electro-hydraulic like the Renault F1 team) cam-less system like Cargine? I'm doubting it with the constant sealing problems, programming, and a whole milieu of other issues that inevitably get their way in there.

A (probably) simpler solution that might be more feasible (I'm only saying more feasible because it has been implemented in production cars) would be something along the lines of Fiat's MultiAir system of solenoid controlled oleo-hydraulic tappets. My guess is that this is still over the heads of most student teams, but it is an interesting idea to think about as throttle body placement becomes a topic.

With the new rules, throttle body placement may not even be an issue any more. I'm still pretty new to this. I'll be joining an FSAE team (probably) this fall, so that's when I'll really start learning how things actually work. Thanks for any and all responses.

[apalrd]

There are a lot of neat camless or partially camless (like Multiair) systems which could be tried in FSAE. There are a few issues though. Here are my thoughts:

-You already have full control of torque reduction through fuel-air ratio and spark advance. F/A can reduce torque (From MBT) with an efficiency gain (less pumping/higher manifold pressure to produce same output power) with limited authority (the lean limit is a concern), although you can skip to full fuel shutoff (or, for a multi cylinder engine, shut off one or more cyls) for drastic torque reduction. Spark advance can be retarded from MBT for torque reduction although EGT's increase, so your limit of authority is determined by the temperature limits of your exhaust components. Torque reduction through spark is also inefficient as the full fuel/air mass must be burned, but you don't extract the full energy from it. With a 4 cyl engine, you can likely control your torque sufficiently through only FA, FSO, and spark, although there would be many thermal concerns.

-Look up the basics of the 4-stroke combustion process. Familiarize yourself with a PV diagram for a 4-stroke spark ignition engine, the indicated loop, and the pumping loop. At all times, you want to control the size of the indicated loop while minimizing the pumping loop. The air mass in the cylinder determines the fuel mass which can be burned (since there is a limit to how lean combustion is stable), so you should focus on controlling the air mass. Since M = PV/RT and R is constant, P, V, and T are controllable. A throttle lowers the indicated loop by reducing the pressure for the constant volume, and which also lowers (more negative) the pumping loop due to the increased toqrue required to pull a vacuum in the manifold. Most variable valve systems reduce the effective volume for a fixed pressure, which results in much less pumping work for the same indicated work reduction.

-You can use valve timing to reduce in cylinder mass (EIVC or LIVC), which can be done (very primitively and easily) with a cam phaser. This isn't terribly difficult to implement mechanically (relative to everything else you've proposed), the software to properly calculate the airflows can get really tricky (changing the effective displacement and compression changes the air mass calculation, VE, MBT spark advance, knock limit spark, and that's pretty much everything an FSAE team calibrates). Kettering's Clean Snowmobile Challenge team has had success in the past using a static cam phase (moving the cam a tooth or two retarded) to increase efficiency at the expense of power, and many Atkinson/Miller cycle engines use a similar concept to this. Usually this isn't enough to completely remove the throttle, but it helps reduce dependence on it.

-The Multiair system is limited by the speed of the actuator, and the precision you can get at high engine speeds. Above roughly 3k rpm, the solenoid is too slow to multi-lift, and above roughly 7k rpm, the solenoid is too slow for the precision required by OEM's. You can push it, but you probably won't get up to the 12000rpm speeds of FSAE engines without a lot of solenoid development effort. The precision of most FSAE trigger wheel setups (e.g 12-1 VR) is also not nearly sufficient for this type of valve timing, and the math to calculate the airflows and spark for a system with that much variability is much more complex than the VVT system.

-BMW has a system which reduces valve lift by modifying the rocker ratio of a type 2 (roller finger follower) valvetrain. They call it Valvetronic. Since then, I have seen mention of a few other companies that now use adjustable ratio RFF's. This is not quite as efficient as modifying the IVC angle as the IVO angle also moves significantly which results in more pumping at the beginning of the intake stroke, but it is effective at controlling load.

-The power consumption of a fully camless system is pretty large. Multiair solenoids require around 30a at battery voltage to fire (I drive a multiair car and measured the coil resistance), without actually providing any energy to the valve. Most fully camless electromagnetic systems in development must run on 42v to keep the current low enough to be manageable. Multiair always uses EIVC to control load, which is very effective at reducing effective compression and displacement sufficiently to control load.


IMHO, the most important part of the proposed rule changes is the electronic throttle control proposal. This would allow the teams to develop much more complete optimization strategies, as ETC really allows the engineers and calibrators to decouple the engine requestors (idle, pedal, overspeed, traction control, transmission, 42v alternator for the camless solenoids, etc.) from the engine torque production (control of engine output through all means possible, including throttle airflow, fuel air, spark, valvetrain, etc.) and would be a large step in FSAE powertrain development.

[Mbirt]

I felt like Chris Matthews listening to an Obama speech as I read that. "I felt this thrill going up my leg." http://www.youtube.com/watch?v=no9fpKVXxCc


Kettering's Clean Snowmobile Challenge team has had success in the past using a static cam phase (moving the cam a tooth or two retarded) to increase efficiency at the expense of power
We were easily the most retarded team to ever win CSC.

[apalrd]

Okay, so after work I searched for a few more helpful things:

First, a quick Google search turned up this:
http://www.mechadyne-int.com/vva-reference/part-load-pumping-losses-si-engine
It's a broad overview of variable valvetrain systems for load control (and has some nice PV diagrams), from a company that makes some variable valvetrain hardware. Elsewhere they have animations of some of their hardware.

Valeo also has a SAE paper which highlights their electromagnetic valve lift system. SAE paper 2010-01-1197. The Valeo system is the system I've heard the most about, of it's type.

I searched and searched for a paper on the Fiat Multiair (INA UniAir actuator), and I didn't find one (that I had access to through my school). In any case, I can recite random facts about it from memory if you want.

[jlangholzj]

This is actually what my capstone project focused on my final year of uni. Its quite a complicated process and you've got lots of hardware that introduces a fair bit of complexity (and inherently) unreliability. Single cylinder may be able to pull it off but its easily a 3-year endeavor. We had to essentially make our own ECU, configure the servo-valves, and create a mechanical advantage to overcome exhaust pressures.

I'm not saying its not do-able but I hardly see a FSAE level team having the time and/or resources to make a reliable functioning form of a multiair system.

[apalrd]

I think it's within a FSAE team's capability to design a hydraulic type system.

The mechanical energy is still provided by a cam, so you wouldn't have any more trouble than if you designed a type 2 (RFF) valvetrain on your own (energy wise). The solenoids can be driven from DI injector drivers, which a few ECUs have (I know of several rapid prototype control modules which can have suitable power electronics).

The software is certainly not trivial, but without emissions regulations and with a lot of O2 and mass-airflow driven controls, you should be able to get it to run somewhat well, with calibrated IVO/IVC angles which you precalculate.

The advantage is a huge reduction in pumping losses, which may or may not be significant to teams. It's definitely very relevant to industry, idk about FSAE.