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The arrival of new PureTech petrol engines in the Citroën
range is further proof of the Brand’s commitment to ‘Créative
Technologie’. The new family of three-cylinder engines has equivalent
or superior power compared with the previous generation powerplants,
combined with significantly lower fuel consumption and greenhouse gas
emissions, down by roughly 25%.
Available on several Brand ranges - C3, DS3 and C-Elysée
(for International markets) - the new engine family is produced at the
Trémery site in France.
The design brief for the new-generation PureTech engines
called for a clean break in powertrain development. The objective was
to make substantial cuts in emissions and fuel consumption, and also to
reduce the weight of the engines and to make them more compact. The
specifications also stipulated a specific power of 50 kW per litre.
Two different capacity versions have been developed; a 1.0
litre and a 1.2 litre with power ranging from 68hp to 82hp (50 to 60
kW). Depending on the model and the tyres fitted, combined cycle fuel
consumption for the new family is between 65.7mpg and 61.4mpg (4.3 and
4.6 l/100 km) and CO2 emissions range from 99 to 107g/km.
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PERFORMANCE PERFECTLY IN LINE
WITH CUSTOMER NEEDS
One PureTech engine is already available in the UK - on sale now in C3
and DS3 models - combining economy plus top-level performance. The VTi
82 engine has a capacity of 1,199cc. Maximum power of 60 kW comes at
5,750 rpm for a 6 kW increase on the 1.4 litre unit it replaces. Other
impressive advances have also been made with this version. Top speed is
up 7mph (11km/h), and fuel economy is also improved - by up to 15.7mpg
(1.5 l/100km) or 25% compared to the previous generation engine - to
62.8 mpg (4.5 l/100km). CO2 emissions are up to 35g/km lower at 104
g/km.
The VTi 68 engine, which will be available in the C3 range
next year, has a capacity of 999cc. Maximum power of 50 kW at 6,000 rpm
is up by 6 kW compared to the 1.1 litre engine it will replace.
Progress has been made across the board, with the top speed increasing
by 5mph (8km/h). Combined-cycle fuel consumption is down 17.8mpg (1.6
l/100km) to 65.7mpg (4.3 l/100km), while CO2 emissions are a full
38g/km lower at 99g/km.
TECHNICAL CHARACTERISTICS
FEATURING THE FINEST TECHNOLOGY
The PureTech engine family features the latest technologies to meet
customer expectations as closely as possible, including:
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A timing system with two overhead camshafts and four
valves per cylinder, controlled directly by two mechanical push rods
for enhanced fill-up and efficiency
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Continuous variable hydraulic timing for the intake and
exhaust camshafts, for better performance at low and medium engine
speeds and optimised fuel consumption
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On the VTi 82 version, a counter-rotating balancer shaft,
for reduced vibration and quieter operation
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Electronic management to optimise battery charge, with
freewheel alternator operation used to a maximum when it requires no
energy expenditure.
A NEW APPROACH TO MEET AMBITIOUS
OBJECTIVES
To achieve these results, PureTech development called for a
number of changes, chief among which were:
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Downsizing (reduction in capacity)
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The choice of three cylinders rather than four
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Reduced weight and more compact design
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Reduced internal friction
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Optimised combustion.
Some 52 patents were filed in the development of the new engine family,
23 concerning engine architecture, 20 engine control and 9 special
manufacturing processes and tools.
Downsizing for improved efficiency
Besides reducing weight and friction, downsizing technology
serves to significantly reduce fuel consumption and CO2 emissions.
Already used on a number of other Brand engines, diesel and petrol
included, downsizing is particularly relevant for the new engine range,
which is now the entry-level offer.
To deliver at least the same performance as the previous generation,
engine efficiency had to be improved to offset the reduction in the
number of cylinders.
Three rather than four
cylinders for multiple gains
A three-cylinder engine has a number of advantages over a
four-cylinder powerplant, including reduced energy loss through
friction, fewer moving parts, lower weight and more compact dimensions,
all of which cut fuel consumption.
Lighter and more compact
By reducing the number of cylinders, as well as redesigning
several components, the weight loss compared with the previous engines
is 25kg for the VTi 68 and 21kg for the VTi 82, or over 20% for
assembled engines without accessories (alternators, starters, etc.).
Using a special casting technique called investment casting, the
cylinder heads, in lightweight alloy, feature a number of functions
that limit weight and dimensions. The exhaust manifold is integrated
directly in the cylinder head, which reduces the number of parts and
overall weight. The cooling system outlet module and the upper engine
support, both integrated, also figure among the parts that come
directly out of casting at the Charleville foundry.
The cylinder casing, again in lightweight alloy, combined with work
right from the start of the project by the design, casting and
machining teams, as well as the use of digital technology in mechanics,
thermomechanics and acoustics, also led to weight reduction and the
integration of a number of functions. Made from pressure-cast
aluminium, the cylinder casing features linings that are inserted
during casting at the Mulhouse foundry.
The engine is also much more compact than the previous
generation, having lost 100mm in width and 70mm in height, accessories
included.
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Significant reduction in friction
and the number of moving parts
The decisions made during the design phase of the PureTech
engine family led to developments on a number of major parts aimed at
reducing friction, which accounts for roughly 20% of the power consumed
by an engine.
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The main parts and components concerned were the
crankshaft - and specifically its sizing - and the off-centered piston
jackets
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The piston pins, segments and push rods in the timing
system feature a low-friction coating (in diamond-like carbon) to keep
friction down to a minimum
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The regulated, variable-capacity oil pump continually
provides optimal lubrication pressure
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The timing belt, wet and housed in a casing, has the same
lifespan as the car itself. This technology also helps to reduce engine
noise
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All these improvements make the PureTech engine the new
benchmark on ultra-low friction, which has been reduced by 30% overall.
Optimised combustion for maximum reduction of fuel consumption and
emissions
The combustion system, a crucial component in fuel consumption
and emissions, takes full advantage of the engine technologies. The
bore/stroke ratio was chosen to optimise the compromise between the
intrinsic efficiency of the combustion system and engine friction loss.
The internal aerodynamics (intake ports, shape of piston heads and
combustion chamber with an 11-to-1 compression ratio) were optimised to
enable the combustion system to work with high rates of Internal Gas
Recirculation, which reduces fuel consumption and pollutant gas
emissions.
To get the engine up to temperature faster, the engine uses Split
Cooling technology. When the car starts up, with the engine cold, the
cooling circuits in the cylinder block and head are separated to
optimise the warm-up process. This system has two advantages. One, it
reduces CO2 emissions, which are higher when the engine is cold. And
two, it helps to warm up the cabin faster.
For maximum efficiency, the three-way catalytic converter is located
right at the engine outlet and equipped with two lambda sensors.
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