RE: What is Dynamic Skip Fire? PH Explains

RE: What is Dynamic Skip Fire? PH Explains

Tuesday 21st August 2018

What is Dynamic Skip Fire? PH Explains

How continually activating and deactivating cylinders boosts economy without harming refinement



'Dynamic Skip Fire' is an advanced form of cylinder deactivation which offers improved refinement, flexibility and efficiency when compared to standard set-ups.

In conventional cylinder deactivation systems, the engine will alternate between fixed patterns of active cylinders in order to improve efficiency in light load conditions. These patterns will be decided by whichever combination of running cylinders results in the least vibration.

A Volkswagen four-cylinder engine equipped with 'Active Cylinder Technology', for example, will always shut down cylinders two and three. In certain situations, however, the efficiency of the engine could be boosted even further if it were to run on just the one cylinder - but doing so would induce prominent vibrations, reducing refinement.

DSF aims to permit such flexibility by firing the minimum number of cylinders per crankshaft revolution to maintain the desired torque output - and does so in an ever-shifting pattern that minimises engine vibration.

This form of dynamic 'variable displacement' was developed by Delphi Technologies and Tula Technology. Current users included General Motors, which has fitted it to the 5.3- and 6.2-litre versions of the 2019 model year Chevrolet Silverado. In GM's applications, the system is called 'Dynamic Fuel Management'.


What are the advantages of dynamic skip fire?

In standard cylinder deactivation systems, cylinders will be shut off when the engine load drops to low levels - such as when cruising at a steady speed. This improves the efficiency of the cylinders that remain active, reducing the overall fuel consumption of the engine.

These set-ups typically have to shut down cylinders in specific patterns, however, in order to avoid excessive vibration. In a V6, one bank will shut down; in a V8, the inner pair of cylinders on one bank will be deactivated along with the outer pair on the other bank.

This means that the potential efficiency savings are limited by the number of cylinders that must remain active in order to avoid compromising refinement excessively; transitions between the cylinder firing modes can also be noticeable, further reducing comfort.

These set-ups are not flexible in their operation, either. A driver may require only a fraction more power but that additional demand may necessitate the entire deactivation system being disabled. This inefficiently brings all the cylinders online to meet the power demands of that moment.

DSF aims to counter these issues by instead deciding whether or not to fire each individual cylinder when the opportunity arises - and, as the name suggests, it can 'skip' the firing of cylinders which might cause vibration or noise-related issues.

Because it can choose whether or not to fire each cylinder, instead of shutting down just a fixed selection of cylinders, the system is far more flexible. The management system will look at the torque required, then decide how many cylinders need to fire in that revolution to maintain that output. It will then further pick a combination of firing cylinders that will avoid resonance issues, helping quell any excess vibration or noise-related problems.

If more torque is required, then additional cylinders can be unobtrusively and quickly phased in to meet the new demands - without having to resort to simply bringing every cylinder back online, as a conventional system would.

In a four-cylinder engine running at 3,000rpm, according to the manufacturer, a DSF system can alter the cylinder combinations up to 6,000 times a minute. This process of continually firing the most efficient number of cylinders in the best order helps DSF to deliver effectively the optimum engine displacement, while maintaining a suitable degree of refinement, at any given moment.


How does dynamic skip fire work?

An advanced management system runs the DSF system. It continuously monitors the driver's inputs to work out how much torque is required at any given moment, then decides how many and which cylinders need to fire in order to meet the demands while avoiding noise and vibration issues.

DSF controls the flow of air into and out of each cylinder using oil-controlled roller finger followers or tappets - as found in other cylinder deactivation systems - which effectively function as an on/off switch for each valve.

When a cylinder is not needed, the deactivation mechanism disconnects the valves from the action of the camshaft, keeping the valves closed. The air trapped inside functions as a spring, helping smooth the engine's action and conserving some energy, then when the cylinder is needed the valves begin opening again and firing recommences.

The cylinders that remain operational function at higher power and efficiency levels which - in conjunction with reduced throttling losses - helps cut fuel consumption and emissions.

There are other advantages to this approach, too, including improved catalytic converter performance. During deceleration, all the cylinders can be shut down - reducing pumping losses and preventing cool air being pumped through the catalytic converter. This helps avoid reducing its temperature excessively, which harms the performance of the converter.

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Author
Discussion

JoshMay

Original Poster:

76 posts

107 months

Tuesday 21st August 2018
quotequote all
Very clever! Do they achieve double figures on the MPG for their mobile ozone hole?

ducnick

1,765 posts

242 months

Tuesday 21st August 2018
quotequote all
Dynamic skip fire sounds like what happens if you crash your Silverado on a bend.

Spuff_Monkey

43 posts

95 months

Tuesday 21st August 2018
quotequote all
Wonder if this will create a need to an increased cylinder count but small capacity. More cylinders equals more firing combinations?

996TT02

3,308 posts

139 months

Tuesday 21st August 2018
quotequote all
Thought it was about a wheelie bin on fire rolling down the road.

Matthen

1,285 posts

150 months

Tuesday 21st August 2018
quotequote all
Spuff_Monkey said:
Wonder if this will create a need to an increased cylinder count but small capacity. More cylinders equals more firing combinations?
Doubt it. More cylinders generally means higher friction losses, resulting in an increased fuel consumption at WoT. Although, if the focus is refinement, I can see it working beautifully with a V6.

The Wookie

13,909 posts

227 months

Tuesday 21st August 2018
quotequote all
JoshMay said:
Very clever! Do they achieve double figures on the MPG for their mobile ozone hole?
You’d be surprised, we had a massive, ugly GMC Yukon as a rental on a business trip last year and it averaged 19mpg US, so over 20 imperial!

For a 3 tonne, bluff fronted beast with a 6 litre engine I thought that was pretty impressive

spookly

4,011 posts

94 months

Tuesday 21st August 2018
quotequote all
Matthen said:
Spuff_Monkey said:
Wonder if this will create a need to an increased cylinder count but small capacity. More cylinders equals more firing combinations?
Doubt it. More cylinders generally means higher friction losses, resulting in an increased fuel consumption at WoT. Although, if the focus is refinement, I can see it working beautifully with a V6.
Surely an I6 would be even better, as it is naturally smoother than a V6.

Dr Interceptor

7,743 posts

195 months

Tuesday 21st August 2018
quotequote all
Was expecting...


rodericb

6,657 posts

125 months

Tuesday 21st August 2018
quotequote all
What has prevented this from being done earlier? Computing power? No regulatory requirement?

yellowjack

17,065 posts

165 months

Tuesday 21st August 2018
quotequote all
I was expecting a news story about an arson attack at a council recycling centre...


getmecoat

jet_noise

5,630 posts

181 months

Tuesday 21st August 2018
quotequote all
Great undiscovered Fall track:
Dynamic Skip Fire-uh

Matthen

1,285 posts

150 months

Tuesday 21st August 2018
quotequote all
spookly said:
Matthen said:
Spuff_Monkey said:
Wonder if this will create a need to an increased cylinder count but small capacity. More cylinders equals more firing combinations?
Doubt it. More cylinders generally means higher friction losses, resulting in an increased fuel consumption at WoT. Although, if the focus is refinement, I can see it working beautifully with a V6.
Surely an I6 would be even better, as it is naturally smoother than a V6.
Well yes, was thinking of the practicalities of under-bonnet space though. Can't see an I6 getting shoehorned into the bonnet of a focus for example... However, a small block V6... way more chance.

ducnick

1,765 posts

242 months

Tuesday 21st August 2018
quotequote all
Unlikely to result in a drive for more refined engines for us :
1.We are now happy to accept diesel levels of vibration.
2. No reason to develop multi cylinder engines when the big drive is for electricification

The only real use case if for getting greater efficiency out of existing big engine applications with minimal investment at the top end + a bit of computing power. Suspect this will be a USA market only thing on truck / suv/ executive cars etc

luckystrike

536 posts

180 months

Tuesday 21st August 2018
quotequote all
Dr Interceptor said:
Was expecting...

Don’t be ridiculous.




They said dynamic:



biggrin

Lewis Kingston

240 posts

76 months

Tuesday 21st August 2018
quotequote all
luckystrike said:
They said dynamic:



biggrin
laugh

Don1

15,936 posts

207 months

Tuesday 21st August 2018
quotequote all
Lewis Kingston said:
luckystrike said:
They said dynamic:



biggrin
laugh
Exactly where I was going as well...

Sensibleboy

1,141 posts

124 months

Tuesday 21st August 2018
quotequote all
The Wookie said:
JoshMay said:
Very clever! Do they achieve double figures on the MPG for their mobile ozone hole?
You’d be surprised, we had a massive, ugly GMC Yukon as a rental on a business trip last year and it averaged 19mpg US, so over 20 imperial!

For a 3 tonne, bluff fronted beast with a 6 litre engine I thought that was pretty impressive
We drive a Chevrolet Suburban from miami to Orlando yesterday and it averaged 24 US mpg from the 5.3L V8. That spend a lot of time on cruise switching between V4 and V8 modes. The transition between the modes was very smooth but noticeable if you were aware of why it was doing it.

Smokehead

7,703 posts

227 months

Tuesday 21st August 2018
quotequote all
Lewis Kingston said:
luckystrike said:
They said dynamic:



biggrin
laugh
Has that Meriva crashed into the skip lorry?

fred bloggs

1,300 posts

199 months

Tuesday 21st August 2018
quotequote all
Diagnose an intermittent misfire.

fred bloggs

1,300 posts

199 months

Tuesday 21st August 2018
quotequote all
I hired a 6.3 supercharged camero for a long road trip to Europe, and this had cylinder deactivation. this year I took my holden with the 5.7 chev with a big cam, and I got better milage from the holden.

so there, its a load of bks.