Cylinder deactivation: how it works

[mike]

Road cars have emissions regulations and basically if you pump in oxygen the catalyst won't work due to the lamda ratio of the exhaust gases. In a fully closed valve situation the chamber acts like a pneumatic spring and helps the power delivery smoothness of the engine. The disadvantage of having closed valves is that when you go down to half throttle and deactivates the cylinders the throttle has to move in order to control the flow, in a ignition cut situation the transition is quicker

[bhall]

How are any of these things possible given...

5.5 Engine torque demand :

5.5.1 The only means by which the driver may control the engine torque is via a single chassis mounted foot (accelerator) pedal.

5.5.2 Designs which allow specific points along the accelerator pedal travel range to be identified by the driver or assist him to hold a position are not permitted.

5.5.3 The maximum accelerator pedal travel position must correspond to an engine torque demand equal to or greater than the maximum engine torque at the measured engine speed.

The minimum accelerator pedal travel position must correspond to an engine torque demand equal to or lower than 0Nm.

5.5.4 The accelerator pedal shaping map in the ECU may only be linked to the type of the tyres fitted to the car : one map for use with dry-weather tyres and one map for use with intermediate or wet-weather tyres.

5.5.5 At any given engine speed the driver torque demand map must be monotonically increasing for an increase in accelerator pedal position.

5.5.6 At any given accelerator pedal position and above 5,000rpm, the driver torque demand map must not have a gradient of less than – (minus) 0.030Nm / rpm.

5.6 Engine control :

5.6.1 The maximum delay allowed, computed from the respective signals as recorded by the ADR or ECU, between the accelerator pedal position input signal and the corresponding output demand being achieved is 50ms.

5.6.2 Teams may be required to demonstrate the accuracy of the engine configurations used by the ECU.

5.6.3 The maximum throttle target map in the ECU may only be used to avoid throttle target oscillations when the change of torque is small for a change of throttle position. It must not be used to artificially reduce the maximum engine torque.

The selection of the maximum throttle target map will be fixed during qualifying and race.

5.6.4 Engine control must not be influenced by clutch position, movement or operation.

5.6.5 The idle speed control target may not exceed 5,000rpm.

5.6.6 Except when anti-stall or idle speed control are active, ignition base offsets may only be applied above 80% throttle and 15,000rpm and for the sole purpose of reducing cylinder pressure for reliability.

5.6.7 A number of engine protections are available in the ECU.

A minimum of nine seconds hold time should be configured for the engine protections enabled during qualifying and race. The configuration of the air tray fire detection and throttle failsafe are exceptionally unrestricted in order to allow each team to achieve the best level of safety.

5.7 Engine high rev limits :

Engine high rev limits may vary for differing conditions provided all are significantly above the peak of the engine torque curve. However, a lower rev limit may be used when :

• The gearbox is in neutral.
• Stall prevention is active.
• The driver clutch request is greater than 95% of the total available travel of the driver clutch actuation device, used only to protect the engine following a driver error.
• An engine protection is active.
• The bite point finder strategy is active.
• The safety car is deployed or during the formation lap.

Except for the above conditions, ignition, fuelling and throttle may not be used to artificially control the engine speed or alter the engine response in a rev range more than 1,000rpm below the final rev limit.

...that?

[MadMatt]

It's possible there could be more than one mode for cylinder deactivation. There could be one mode to lessen torque yet provide lots of exhaust gasses. But another mode may be for when the car is sitting and waiting, as in the scenario of the starting line, or waiting in line during qualifying. For those circumstances, cooling is an issue and deactivating cylinders can promote cooling and delay the inevitable melt-down long enough to get going again.

For the cars starting on the front row, they have to sit waiting for what to them is an eternity, and the longer you sit and wait, that's bad news to the engine guys. So if alternate cylinders go through the normal Otto cycle, then no spark, just cooling air pumped through the cylinders, that can keep the temperature from rising too quickly. Alternate and cycle through the cylinders, the cooling effect is functioning for all the cylinders.

I would add to this that cutting spark on cylinders is common in the rallyworld, especially on the gr.N Mitsubishis for example. It is called rotational idle, because the ECU cuts a spark in a rotational sequence on each cylinder. That is to be able to run antilag and coping with the gr.N regulations. Why ? Because the throttle body is open (and by open I mean OPEN) even at idle, so without cutting a spark, the car would not stay idle and start to rev. It depends on who built the car, and what ECU you are running, but that's the sound you can here in this video :

http://www.youtube.com/watch?v=u3sxtQwUMkE

And why a rotational sequence and not cutting the same cylinder ? To simply cool the engine as you said.

[Tommy Cookers]

For years on and off we have had F1 cars at about 4000 rpm idle for minutes at a time without overheating ?

Surely this has always been done by throttle opening and zero fuelling on 4+ cylinders (in rotation,avoids plug fouling)
(I regard the previous post as useful confirmation of what I thought we all knew)

Throttle open and minimal fuel is how a diesel ticks over for ever without a working radiator fan (I did this)

There's every reason to leave the valve motion unchanged in F1

What's not to like ??
Even if it is against some rule, nothing will be done unless there is a protest, no-one wants such a protest ?


Nothing to do with road cars (where deactivated cylinder temperatures need to be kept high to avoid wear, the problem in the earlier generation by GM, and there is an induction manifold )
(the catalyst is not an issue at tickover, it would act in oxidation only with tickover mixture anyway ?)

[mike]

(the catalyst is not an issue at tickover, it would act in oxidation only with tickover mixture anyway ?)

catalyst only works at lamda 1 so exhaust valves has to be closed in road cars

[riff_raff]

Ignoring the regulations for a moment, the most efficient form of cylinder deactivation would be to keep the valves closed. The deactivated cylinder would then simply function as an air spring. This is how displacement-on-demand automotive engines function.

As for which cylinders get deactivated, that becomes a bit tricky. You have to take into account things like torsional dynamics and intake/exhaust tuning.

[mike]

I would say that closing the valves does make the power smoother, but it is harder to switch between open and close compared to cutting the ignition. Cutting ignition also has another advantage in that it can chose to cut 1 cylinder per cycle or any number of cylinder per cycle and if you get the timing right the power delivering should be just as smooth, pumping air out of the exhaust also helps the scavenging affect of other cylinders.