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How losing cylinders is helping us gain in fuel economy

Image of Faye Sunderland
Author: | Updated: 10 Apr 2014 17:20

Tuesday 15 April, 2014. The Green Piece Column.

Cylinder deactivation technology – or variable displacement as it is also known – is not new; forms of it have been in use since the late 19th century and is almost as old as the car itself.

However in recent years it has been gaining our attention again as a valuable way to reduce CO2 emissions and boost the fuel economy of cars.

Easy loss

In recent times, Audi has been prominent in the use of such technology, which deactivates some engine cylinders when the vehicle is experiencing light load duties, such as cruising at a steady speed.

It has been a useful tool for the German brand, which is also been toying with the electrification of its range with plans to launch its first plug-in hybrid, A3 e-tron later this year.

Of course electrification comes at a price. The new e-tron is expected to be priced from £32,000 compared to a starting price of £18,280 for the regular A3.

Audi A3 Sportback CoD 600

For the mainstay of its range though, cylinder deactivation may provide a more affordable option. Its Cylinder-on-Demand technology is already available on Audi S, RS, A1 and A3 models helping to boost fuel economy so that its TFSI petrol engines are within in range of diesel equivalents.

In the A3 TFSI 140PS COD model for example, fuel economy is officially rated at 60.1mpg and emissions from 109g/km CO2, compared to 74.3mpg and 99g/km CO2 for the 1.6 TDI 105PS engine.

On both the A1 and A3 model ranges, the COD versions carry a premium of just £850 over their continuing 122PS 1.4 TFSI versions – a lot less of a premium than Audi A1 1.4 TFSI CoDopting for a hybrid drivetrain and yet delivering up to 6.8mpg more than the 122PS models.

That might not sound like much, but in the world of company cars that can significantly cut your tax bill. Comparing the COD models to 2.0 TDi equivalents, business users will find much lower purchase prices for virtually identical CO2 outputs. For a 40 per cent taxpayer, A1 COD model would offer a benefit-in-kind saving of up to £919 per annum, compared to the 2.0 diesel.

Audi isn’t the only brand making use of this technology. SEAT too has just announced that it will use what it calls Active Cylinder Technology (ACT) on its new SEAT Ibiza FR Edition. On this model the 140hp 1.4 TSI ACT engine enables SEAT to significantly reduce CO2 emissions by 30g/km compared to the old 150hp 1.4 engine and only marginally reduces the performance by 0.2 seconds in a 0-62mph dash.

How it works

So how does cylinder technology work these days? In Audi’s and SEAT’s tech, it is a simple tech which switches off two of the four cylinders when they are not needed.

But that won’t leave you feeling powerless once there is a need for some acceleration. In the case of SEAT’s tech it claims it takes just 40 milliseconds to switch the deactivated cylinders back on, when say, the driver accelerates suddenly, calling for additional power. Volkswagen, with its Polo GT, claims an ever faster switch on time of between 13 and 36 milliseconds for re-activation.

The technology is smart too and detects subtle changes in the driver’s behaviour to detect when it is necessary to re-activate the cylinders. The system monitors the accelerator pedal sensor and intelligent monitoring software can also detect irregular driving profiles; such as weaving along a country road for example to determine whether the cylinders can be shut down or not.

It helps reduce fuel consumption by increasing the pressure in the remaining, active cylinders, enabling them to burn more efficiently.

The video from Bosch, above, explains more about how the technology works.

There are lots of brands now offering technology similar to that of the Volkswagen Group and its Audi and SEAT brands, there is also Honda, Mercedes, GM and Lamborghini who have toyed with the technology in recent years.

It is not just about saving fuel economy; for luxury brands like Audi it is also a useful way of ensuring their cars can still deliver the performance their customers expect, without falling foul of increasingly strict EU rules governing average CO2 emissions.

So with that in mind, it seems agreed that less is now more; when it comes to cylinders at least.

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